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THE
ANATOMY OF THE HORSE
DISSECTION GUIDE
i
J. M'PADYEAN, M.B., CM., B.Sc,
MEMBER OF THE ROYAL COLLEGE OF VETERINARY SURGEONS,
LECTURER ON ANATOMY AT THE ROYAL (DICK's) VETERINARY COLLEGE, EDINBURGH.
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W. & A. K. JOHNSTON,
EDINBURGH AND LONDON.
AU rights reserved.}                              » »,
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W. AND A. K. JOHNSTON, PRINTERS, EDINBURGH AND LONDON.
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TO
WILLIAM TURNER, M.B., LL.D., F.R.S.,
PROFESSOR OF ANATOMY IX THE UNIVERSITY OF EDINBURGH.
AS A TRIBUTE TO HIS EMINENCE
AS AN ANATOMICAL TEACHER.
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.
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P E E F A C E.
----------o----------
The want of an illustrated topographical treatise on equine anatomy has,
in the experience of the author, been a great barrier to the efficient
teaching of that all-important branch of veterinary education. In this
work the object of the author has been to place in the hands of veterinary
students a dissection guide comparable, in some degree, to the text-books
at the service of the practical student of human anatomy. The order of
dissection laid down is that which the author has found to be most advan-
tageous, and he has attempted to describe with accuracy and moderate
fulness the different organs as they present themselves in that order.
This description is largely supplemented by the illustrations, which are
so complete that almost every organ in the body is delineated. The
majority of these illustations are original, being faithful portraits of the
author's own dissections. It is hoped that they will prove useful to the
student, in the first place, as a plan and a guide in his work, and,
secondly, as a means by which he may afterwards summon up a mental
picture of his own dissections.
While the book is specially designed for use in the dissecting-room,
the author ventures to hope that it may also be serviceable to the
\eterinary practitioner. Special care has been taken in portraying those
regions that possess a surgical interest, and the illustrations furnish a
ready means by which the surgeon may refresh his memory regarding
the objects to be met in the course of an operation.
The greater number of the original drawings were made in the dissecting-
room of the Eoyal (Dick's) Veterinary College, by Mr J. Bayne, artist;
a few were executed by Mr K. S. Eeid, artist; and the remainder by
Mr K. H. Potts, veterinary student. A few of the illustrations were
directly drawn on stone by Messrs W. & A. K. Johnston. To all of
these gentlemen the author is much indebted for the clearness and
fidelity with which they have delineated the various objects.
The source of each of the borrowed illustrations is duly acknowledged
elsewhere, but the author is constrained to make special mention of
those from the systematic text-book of Professor Chauveau, who
generously consented to the copying of as many of his figures as might
be thought useful for this work.
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PREFACE.
To insure accuracy, the author lias been careful to compare the nefcults
of his own dissections with the descriptions of other writers, and more
especially with the works of Percivall, Leyh, and Chauveau, to which he
begs to express his indebtedness.
To Professor Turner the author is under deep obligation for the
revision of the chapters on the brain, the eye, and the ear, and for much-
esteemed suggestions regarding other points.
Finally, the author's best thanks are due to his brothers Gavin and
Andrew, who have carefully revised the entire proof-sheets, and to
Mr. T. Barker, veterinary student, for assistance in making the index.
Royal (Dick's) Veterinary College, Edinburgh,
October, 1884.
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A few words are here necessary in explanation of the system of nomen-
clature used throughout this work. Although reluctant to add to the
confusion already prevailing in the nomenclature of veterinary anatomy,
the author has not conformed to any of the systems in general use.
The system here employed is based on the principle of naming each
object after the homologous object in human anatomy. So far, indeed,
as any of the systems in use can be said to follow a principle, it is that
just stated; but the violations of the principle are numerous, and, in
most cases, appear to have been dictated by the merest caprice. The
most vicious form of departure from the principle is that in which terms
adopted from human anatomy are employed to designate not the actual
homologues, but other parts having, it may be, some faint resemblance
in shape or otherwise to the objects bearing these names in the human
svibject. This method is indefensible, since it tends to produce the
greatest confusion, and, if generally adopted, would render a comparison
of the anatomy of any two animals an impossibility. Many such terms
have long been in use, but it is hoped that they are not ineradicable.
In cases where objects appear to be without homologues in human
anatomy, new names must, of course, be found. In only a few of these
instances, however, has the author employed terms of his own invention,
preferring, in general, to adopt some of those already in use.
The greatest diversity of names, it will be found, exists in the case of
muscles, and the following table of synonyms has been compiled for the
convenience of those already familiar with the terms employed in some
other works.
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TABLE OF SYNONYMS OF MUSCLES.
Leth.
Chauveau.
Percivail.
Posterior pubio-femoralis.
Middle pubio-femoralis.
(part of) Urethral muscle.
Small humero-olecranius.
Sterno-scapularis.
Small sterno-humeralis.
Idem.
Palato-staphylinus.
Coraco-radialis.
Sacro-ischio-tibialis ant.
Humero-radialis.
Idem and molaris.
Great scapulo-olecranius.
i External scapulo-olecranius.
Internal humero-olecranius.
Small kerato-hyoid.
j Idem.
Dorso-occipitalis.
Ischio-coccygeus.
Middle scapulo-humeralis.
Superior external palpebral.
Idem.
Sacro-coccygeus lateralis.
Great adductor of thigh.
Small adductor of thigh.
Bulbo-cavernosus.
Small extensor of fore-arm.
(part of) Deep pectoral.
(part of) Superficial pectoral.
Idem.
Palato-staphyleus.
Long flexor of the fore-arm.
Long vastus.
Short flexor of fore-arm.
Alveolo-labialis.
Chief extensor of the fore-arm.
Short extensor of the fore-arm.
Middle extensor of fore-arm.
Idem.
Idem.
Great complexus.
Ischio-coccygeus.
Idem.
Fronto-palpebral.
Idem.
Sacro-coccygeus lateralis.
! Adductor magnus.
Adductor parvus.
Accelerator urinse.
I Anconeus.
Anterior deep pectoral.
Anterior superficial pectoral.
I Aryteno-pharyngeus.
Azygos uvulse.
I Biceps.
1 Biceps femoris.
Brachialis anticus.
Buccinator.
j
; Caput magnum,
i Caput medium.
j Caput parvum.
Cerato-hyoid.
Cervico-auriculares.
Complexus.
Compressor coccygis.
Coraco-humeralis.
Corrugator supercilii.
Crico-pharyngeus.
Curvator coccygis.
Adductor longus.
Adductor brevis.
■ Idem.
Idem.
Pectoralis parvus.
\ (part of) Pectoralis transversus.
(Not described.)
Circumflexus palati.
Flexor brachii.
Biceps abductor femoris.
Humeralis externus.
Idem and caninus.
Idem.
Idem.
Idem.
Hyoideus parvus.
1 Retrahontes.
Complexus major.
Idem.
Idem.
Levator palpebral superioris.
Constrictor pharyngis posterior.
Idem.
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Table of Synonyms of Muscles—continued.
Chauveau.
Leyh.
Peecivall.
Deep flexor of digit (fore limb).
Deep flexor of digit (hind limb).
Deep gluteus.
Deltoid.
Depressor labii inferioris.
Depressor labii superioris.
Depressor coccygis.
Dilatator naris inferior.
Dilatator naris lateralis.
Dilatator naris superior.
Dilatator naris transversalis.
Erector clitoridis.
Erector coccygis.
Erector penis.
Extensor brevis.
Extensor metacarpi magnus.
Extensor metacarpi obliquus.
Extensor pedis (fore limb).
Extensor pedis (hind limb).
Extensor suffraginis.
External oblique of abdomen.
External pterygoid.
(See flexor pedis perforans.)
Gluteus internus.
Teres minor.
Idem.
Idem.
Idem.
Small ilio-trochanterius.
Great scapulo-trochanterius.
Maxillo-labialis inferior.
Incisive of upper lip.
Long and short sacro-coccygeus
inferior.
Small super-maxillo nasalis.
Great super-maxillo nasalis.
Short muscle of nose.
Idem.
Long abductor of arm.
Maxillo-labialis.
Intermediate anterior.
Sacro-coccygeus inferior.
(part of) Nasalis brevis labii superi- j (part of) Small super-maxillo na-
oris.                                                i salis.
Idem.                                                    j Great super-maxillo nasalis.
(part of) Nasalis brevis labii superi- I (part of) Small super-maxillo na-
oris.                                                         salis.
Dilator naris anterior.                        | Naso transversalis.
Transversus nasi.
Idem.
Sacro-coccygeus superior.
Idem.
Ischio-cavernosus.
(Un-named
.)
Pedal muscle.
Idem.
Anterior extensor of metacarpus.
Idem.
Oblique extensor of metacarpus.
Idem.
Anterior extensor of phalanges.
Idem.
Anterior extensor of phalanges.
Idem.
Idem.
Lateral extensor of phalanges.
Idem.
Idem.
Idem.
Idem.
Oblique flexor of phalanges.
Epitrochlo-
carpeus.
External flexor of metacarpus.
Epicondylo
-metacarpeus.
Internal flexor of metacarpus.
Epicondylo
-carpeus.
Oblique flexor of metacarpus.
Idem.
Idem.
Sacro-coccygeus superior.
Ischio-penial muscle.
(As Chauveau.)
Humero-metacarpeus anterior.
Kadi o-metacarpeus.
Humero-pre-phalangeus.
Femoro -pre-pbalangeus.
Radio -pre-phalangeus.
Costo-abdominalis exterior. .
(part of) Spheno-maxillaris.
Small tibio-phalangeus.
Humero-supercarpeus externus.
Humero-metacarpeus internus.
Humero-supercarpeus internus.
Tibio-j ire-metatarsus,
Flexor accessorius.
Flexor metacarpi externus.
Flexor metacarpi interims.
Flexor metacarpi medius.
Flexor metatarsi.
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Flexor pedis per- ("ulnar head.
forans (fore -s radial head.
limb)                    ( humeral head.
Flexor pedis perforans (bind limb).
Flexor pedis perforates (fore limb).
Flexor pedis perforates (hind limb).
Gastrocnemius.
Gemelli.
Genio-glossus.
Gracilis.
Great hyo-glossus.
Hyoideus transversus.
Iliacus.
Infraspinatus.
Internal intercostal.
Internal oblique of abdomen.
Internal pterygoid.
Interossei.
Intertransversales of neck.
Ischio-urethral.
Lateralis sterni.
Latissimus dorsi.
Levator anguli scapula?.
Levatores costarum.
Levator labii superioris alaaqui
nasi.
Levator labii superioris proprius.
Levator menti.
Levator palati.
Levator rjalpebrse superioris.
Longissimus dorsi.
Longus colli.
Lumbricales.
Masseter.
Ulnaris accessoritis.
Radialis accessorius.
Flexor pedis perforans.
Hexor pedis.
Idem.
Gastrocnemius internus.
Gastrocnemius externus.
Gemini.
Genio-hyo-glossus.
Idem.
Hyo-glossus brevis.
(Not described.)
Idem.
(part of) Postea-spinatus.
Idem and sterno-costales extern
Idem.
Idem.
Lumbrici anteriores.
(Not described.)
Triangularis penis.
Idem.
Idem.
Part of serratus magnus.
Idem.
Idem.
Nasalis longus labii superioris.
Idem.
Stylo-pharyngexis.
Levator palpebral superioris int
nus.
Idem and spinalis dorsi.
Idem.
Lumbrici posteriores.
Idem.
Eadio-phalangeus.
Great tibio-phalangeus.
Humero-phalangeus.
Femoro-phalangeus.
Bi-femoro-calcaneus.
Gemelli of pelvis.
Idem.
Pubio-tibialis.
Hyo-glossus.
Idem.
Great and middle ilio-femoralis.
Posterior spinous.
Idem.
Ilio-abdominalis.
(part of) Spheno-maxillaris.
Idem.
Idem.
Part of urethral muscle.
Transverse muscle of ribs.
Dorso-humeralis.
Traehelo-scapularis.
Idem.
Fronto-labialis.
Maxillo-labialis superior.
Incisive of lower lip and mento- j
labialis.
Stylo-staphylinus.
Superior internal palpebral.
Ilio-spinalis.
Dorso-atloideus.
Idem.
Zygomato-maxillaris.
Deep flexor of phalanges.
Deep flexor of phalanges.
Superficial flexor of phalanges.
Superficial flexor of phalanges.
Gemelli of leg.
Gemelli of pelvis.
Idem.
Short adductor of the leg.
Idem.
Idem.
Iliac psoas.
Subspinous.
Idem,
Idem.
Idem.
Idem.
Idem.
Compressor of Cowper's glands.
Transverse muscle of ribs.
Great dorsal.
Angularis scapulse.
Supercostales.
Supernaso-labialis.
Supermaxillo-labialis.
Intermediate posterior and mento-
labialis.
Peristaphyleus internus.
Idem.
Ilio-spinalis.
Idem.
Idem.
Idem.
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Table of Synonyms of Muscles—continued.
Pekoivall.
Chauveau.
Leyh.
1
Mastoido-auricularis.
(Not described.!
Tympano-auricularis.
1
Idem.
Mastoido-humeralis.
Levator humeri.
Idem.
Common muscle of the arm, neck,
and head.
Middle gluteus.
Gluteus maximus.
Idem.
Great and middle ilio-trochanterius.:
Middle hyo-glossus.
(Not described.)
(Not described.)
Kerato-glossus internus.
Mylo-hyoideus.
Idem.
Idem.
Idem and mylo-glossus.
Obliquus capitis inferior.
Idem.
Great oblique of head.
Axoido-atloideus.
Obliquus capitis superior.
Idem.
Small oblique of head.
Atloido-occipitalis lateralis.
Occipito-styloid.
Stylo-hyoideus.
Idem.
Stylo-hyoideus.
Orbicularis oris.
Idem.
Labialis.
Orbicularis of the lips.
Palato-glossus.
(Not described.)
Pharyngo-glossus.
Pharyngo-glossus.
Palato-pliaryngeus.
Idem (in part).
Pharyngo-staphyleus.
Staphylinus communis.
Parieto-auricularis externus.
Attolens maximus.
Temporo-auricularis externus.
Common muscle of ear.
Parieto-auricularis internus.
Attolens posticus.
Temporo-auricularis internus.
Parieto-auricularis.
Parotido-auricularis.
Abducens vet deprhnens aurem.
Idem.
Idem.
Pectineus.
Idem.
Idem.
Pubio-femoralis anterior.
Peroneus.
Idem.
Lateral extensor of phalanges.
Tibio-pre-phalangeus.
Popliteus.
Idem.
Idem.
Oblique femoro-tibialis.
Posterior deep pectoral.
Pectoralis magnus.
(part of) Deep pectoral.
Great sterno-humeralis.
Posterior superficial pectoral.
(part of) Pectoralis transversus.
(part of) Superficial pectoral.
Sterno-radialis.
Psoas magnus.
Idem.
Idem.
Lumbo-femoralis.
Psoas parvus.
Idem.
Idem.
Lumbo-ilialis.
Pterygo-pharyngeus.
(part of) Palato-pharyngeus.
Idem.
Idem.
Pyriformis.
Idem.
(part of) Obturator internus.
Sacro-trochanterius.
Quadratus femoris.
(Not described.)
Quadrate crural.
Small ischio-femoralis.
Quadratus lumborum.
Sacro-lumbalis.
Idem.
Idem.
Rectus abdominis.
Idem.
Idem.
Sterno-pubialis.
Rectus capitis anticus major.
Idem.
Idem.
Trachelo-occipitalis.
Rectus capitis anticus minor.
Idem.
Idem.
Atloido-occipitalis inferior.
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Atloido-styloideus.
Atloido-occipitalis longusand brevis.
Atloido-occipitalis superior.
Ilio-rotuleus anterior.
Small ilio-femoralis.
Lumbo-costalis.
Cervico-subscapularis and dorso
scapularis.
Ilio-rotuleus internus.
Costo-trachelius.
Idem.
Long scapulo-olecranius.
Idem.
Idem.
Great ischio-femoralis.
Transverse sjiinous.
Sacro-ischio-tibialis post.
Idem.
Costo-scapularis.
Idem.
(Not described.)
Kerato-pharyngeus inferior.
Peroneo-calcaneus.
Sterno-thyroid and sterno-hyoid.
I Kerato-glossus externus.
Great kerato-hyoid.
Idem.
Kerato-pharyngeus superior.
Scapulo-hyoid.
I Obliquus capitis anticus.
i Idem and complexus minor.
j Idem.
Rectus.
I Crureus.
(part of) Obliquus abdominis
internus.
Idem.
I Idem.
Idem.
Idem.
Anterior straight of thigh.
Anterior gracilis.
Rectus capitis lateralis.
Rectus capitis posticus major.
Rectus capitis posticus minor.
Rectus femoris.
Rectus parvus.
Retractor costse.
Rhomboideus.
Idem.
Long adductor of the leg.
Idem.
Small scapulo-humeralis.
Long extensor of the fore-arm.
Idem.
Idem.
Idem.
Transverse spinous.
Transverse spinous.
Idem.
Anterior small serratus.
Idem.
Posterior small serratus.
Idem.
Idem.
Idem.
Sterno-thyroid and sterno-hyoid.
Idem.
(part of) Digastricus
Idem.
Idem.
Idem.
Idem.
Idem.
(part of) Caput magnum.
Anterior conchse.
Posterior conchas.
Adductor magnus.
Idem.
Spinalis colli.
Adductor tibialis.
(part of) Superficialis costarum.
Idem and levator anguli scapulas.
(part of) Superficialis costarum.
(Not described.)
(Not described.)
Plantaris.
Idem.
Hyo-glossus longus.
Hyoideus magnus.
Idem.
Hyo-pharyngeus.
Idem.
See flexor pedis perforatus.
Gluteus externus.
Antea-spinatus.
Idem.
Idem.
Sartorius.
Scalenus.
Scapulo-humeralis gracilis.
Scapulo-ulnaris.
Scuto-auricularis externus.
Scuto-auricularis interims.
Semimembranosus.
Semispinalis of (back and loins).
Semispinalis (colli).
Semitendinosus.
Serratus anticus.
Serratus magnus.
Serratus posticus.
Small hyo-glossus.
Small stylo-pharyngeus.
Soleus.
Sterno-thyro-hyoideus.
Stylo-glossus.
Stylo-hyoideus.
Stylo-maxillaris.
Stylo-pharyngeus.
Subscapulo-hyoid.
Superficial flexor of digit (fore limb)
Superficial flexor of digit (hind limb)
Superficial gluteus.
Supraspinatus.
Temporalis.
Tensor palati.
Ilio-trochanterius externus.
Anterior spinous.
Temporo-maxillaris.
Peristaphylinus externus.
Idem.
Supraspinous.
Idem.
Peristaphyleus externus.
-ocr page 14-
Table of Synonyms of Muscles—continued.
Pekcivall.
Chauveau.
Leth.
Tensor vagina? femoris.
Idem.
Muscle of fascia lata
Ilio-rotuleus externus.
Teres major.
Idem.
Adductor of arm.
Great scapulo-humeralis.
Teres minor.
(part of) Infraspinatus.
Short abductor of arm.
Middle and small scapulo-trochi-
terius.
Trachelo-mastoid.
Idem.
Small complexus.
Dorso-mastoideus.
Transversalis abdominis.
Idem.
Idem.
Costo-abdominalis internus.
Transversalis costarum.
Idem.
Common intercostal.
Common intercostal.
Transversus perinsei.
(Not described.)
Idem.
Idem.
Trapezius.
Idem.
Idem.
Cervico-acromialis.
Triangularis sterni.
Sterno-costales interni.
Idem.
Sterno-costalis.
Vastus externus.
Idem.
Idem.
Femoro-tibialis externus.
Vastirs internus.
Idem.
Idem.
Fcmoro-tibialis internus.
Wilson's muscle.
(part of) Triangularis penis.
Sphincter uretlme.
Prostatic muscle.
Zygomatico-auriciilaris.
Attolens anterior.
Idem.
Temporo-auricularis and fronto-
auricularis.
Zygomaticus.
Idem.
Zygomatico-labialis.
Zygomatico-labialis.
-ocr page 15-
PLATES.
Plate.
1.  Pectoral Region ....
2.   Pectoral Eegion ....
3.   Brachial Plexus ....
4.   Shoulder—Outer Aspect .
B. Shoulder and Arm—Inner Aspect
0. Shoulder, Arm, and Fore-arm—Inner Aspect
7.   Fo. e limb—Outer Aspect .
8.   Shoulder, Arm, and Fore-arm—Outer Aspect
9.   Metacarpus and Digit—Inner Aspect
10.   The Foot.....
11.   Joints and Ligaments of Fore limb
12.  Thigh—Inner Aspect
13.   Thigh—Inner Aspect
14.   Thigh—Inner Aspect
15.   Hip and Thigh         ....
16- Hip and Thigh ....
17.   Leg—Inner Aspect
18.  Leg—Outer Aspect
19- Metatarsus and Digit—Outer Aspect
20.   Chest-wall and Back
21.   Chest-wall and Back
22.  Thoracic Cavity—Lett Side
23.   Heart and Great Vessels-—Left Side
24.   Heart and Great Vessels—Bight Side
25.   Thoracic Cavity—Eight Side
20. Thoracic Cavity—Eight Side
27.   Neck and Intermaxillary Space .
28.  Neck             .
29.   Side of Face             ....
30.   Cavity of the Mouth
31.   Cavity of the Mouth, Pharynx, etc.
32.   Tongue, Pharynx, etc.
•«. Brain—Inferior Aspect
34. Brain—Superior Aspect .
3o. Brain—Lateral and 4th Ventricles, etc. .
36.   Brain—Ganglia of the Base
37.   Male Periiueum ....
38.  Abdominal Wall ....
39.  Abdominal "Wall ....
40.  Abdominal Wall ....
41- Intestines and Anterior Mesenteric Artery
4-- Intestines and Mesenteric Arteries
43.   Cceliac Axis, etc. ....
44.  Abdominal Viscera, etc. .
4o. Sublumbar Eegion and Diaphragm
40. Male Pelvis
47.   Genito-urinary Organs of Male .
48.  Lumbo-sacral Plexus
-ocr page 16-
lb
-ocr page 17-
CONTENTS.
CHAPTER I.
DISSECTION OF THE ANTEKIOR I.IMB.
Pagk.
1
The Foot
35
8
The Shoulder-joint
The Elbow-joint
43
44
10
The Knee
The Fetlock-joint .
46
50
17
The Pastern-joint .
52
19
The Coffin-joint
52
27
chap:
PER II.
The Pectoral Region and the Axilla
The Outer Scapular Region .
Inner Aspect of the Shoulder and
Arm......
Outer Aspect of the Shoulder and
Arm......
The Fore-arm         ....
The Metacarpus and Digit
DISSECTION OF THE POSTERIOR I.IMB.
The Metatarsus and Digit . .77
The Stifle-joint .... 81
The Tarsus.....86
The Tarso-metatarsal articulation . 90
The Inner Aspect of the Thigh .      50
The Hip and Outer Aspect of the
Thigh......      63
The Leg......      70
CHAPTER III.
DISSECTION OF THE BACK AND THORAX.
122
123
129
132
134
130
Examination of the Lung
Dissection of the Heart
Structure of the Heart .
Articulations of the Ribs
Intervertebral Joints and
ments
The Spinal Cord .
The Chest-wall and Back . . 94
The Cavity of the Thorax . . 100
The Lungs.....103
The Pericardium .... 105
The Heart.....106
The Nerves and Vessels of the left
side of the Thorax . . .108
The Nerves and Vessels of the right
side of the Thorax . . .116
Liga
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CONTENTS.
XVU1
CHAPTER IV.
DISSECTION OF THE HEAD AND NECK,
Page.
143
151
158
159
164
168
170
172
176
184
Page.
195
200
202
The Under part of the Neck .
The Upper part of the Neck .
Ligaments and Articulations of the
Neck posterior to the Dentata
The External Ear .
The Parotideal Region .
The Region of the Poll .
The Intermaxillary Space
The Appendages of the Eye .
The Face         ....
The Pterygo-maxillary Region and
the Region of the Guttural Pouch
The Tongue ....
The Hard Palate .
The Soft Palate .
The Pharynx, the Hyoid Bone, and
the Base of the Skull ... 204
TheOrhit.....208
The Occipito - atlantal Articula-
tion ......214
The Atlanto-axial Articulation . 215
The Temporo-maxillary Articulation 215
The Cavity of the Nose . . .216
CHAPTER V.
DISSECTION OF THE LAHYNX.
Cartilages of the Larynx . . 224
Articulations, Ligaments, and Mem-
branes of the Larynx . . . 226
Muscles of the Laryrx
Nerves of the Larynx
Interior of the Larynx
228
230
230
CHAPTER VI.
DISSECTION OF THE BRAIN.
. 233
The Cerebellum
. 236
The Cerebrum
. 238
The Cranial Nerves
. 240
CHAPT,
ER VII.
DISSECTION OF
THE EYEBALL.
Membranes of the Brain
Arteries of the Brain
The Medulla Oblongata .
The Pons Varolii .
240
242
253
Dissection of the Eyeball............257
CHAPTER VIII.
DISSECTION OF THE EAE.
. 267 | The Internal Ear
269
The Middle Ear
CHAPTER IX.
DISSECTION OF THE PERINEUM IN THE MALE.
280
281
ThePerinaeum . . . .274
The Scrotum.....277
The Testicle and Epididymis . . 279
The Prepuce
The Penis
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CONTENTS.                                                                    XIX
CHAPTER X.
ION OF THE ABDOMEN.
3AGB.
Page.
285
Structure of the Liver .
. 330
294
Structure of the Spleen .
. 332
320
Structure of the Pancreas
. 333
328
Structure of the Kidney
. 333
The Abdominal Wall .
The Cavity of the Abdomen
The Sublumbar Kegion .
Structure of the Stomach
CHAPTER XL
DISSECTION OF THE PELVIS.
The Hip-joint and the Ligaments
of the Pelvis . . . .338
The Cavity of the Pelvis . . 340
Reproductive Organs in the Female. 351
The Tail
Joints and Ligaments
Sacrum and Coccyx .
360
of the
363
Pig.                                                                                                                                                             Page.
1.   Dissection of the Metacarpus and Digit, showing the Tendons and their
Synovial Sheaths             .           .            .           .            .           .            .           .33
2.   Muscles of the Tail, deep Muscles of the Hip, and Pelvic Ligaments .            . 68
3.  Flexor Metatarsi Muscle .            .            .            .            .            .            .            .76
4.  Femoro-tibial Ligaments .            .            .            .            .            .            .            .83
5.   Ligaments of the Tarsus .            .            .            .            .            .            .            .87
6.   Diagrams showing Disposition of the Pleura? ..... 101
7.  Floor of the Thorax            ........ 120
8.  Termination of the Air Passages in the Lung ..... 122
9.   Diagram of the two Cavities of the Right Side of the Heart .            .            . 125
10.  Diagram of the two Cavities oi the Left Side of the Heart .            .            . 128
11.   Root of the Common Aorta laid open ...... 129
12.  View of a partial Dissection of the Fibre3 of the Left Wall of the Ventricles in
a Sheep's Heart ......... 131
13.    Two costo-vertebral, and two intervertebral Joints, viewed from below           . 132
14.   Two costo-vertebral, and two intervertebral Joints, viewed from above            . 133
15.  View of the Membranes of the Spinal Cord         ..... 138
16.   Portion of Spinal Cord with the Roots of the Nerves .... 139
17.  Transverse Section of Spinal Cord of Calf             ..... 141
18.  Ligamentum Nucha? and Deep Muscles of the Neck .            .            .            . 156
19.  Auricular Muscles and Nerves of a Mule ...... 161
20.   Cartilages of the Nose .            .            .            .            .            .            .            .176
21.   Hard Palate             ......... 201
22.  Muscles of the Eyeball........209
23.  Muscles of the Eyeball........210
24.  Longitudinal Section of the Head, showing the Cavities of the Mouth, Nose
and Pharynx ......... 217
25.   Transverse Section through the Nasal Chambers             .... 218
26.  Larynx, side view ......... 228
27.  Larynx, side view ......... 229
28.   Larynx, back view ......... 230
29.   Interior of the Larynx, seen from behind             ..... 231
30.  Arteries of the Brain          ........ 236
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CONTENTS.
XX
Page.
31.   Corpus Callosum and inner face of cerebral Hemisphere.            .            .            . 248
32.  View of the Lower Half of Kight Adult Human Eye, divided horizontally
through the middle          .           .            .            .            .            .            .           . 258
33.   Choroid Membrane and Iris exposed by the removal of the Sclerotic and
Cornea .......... 261
34.   Diagram of the membranous Labyrinth ...... 269
35.   Transverse Section through the Tube of the Cochlea .... 271
36.   Vertical Section through the Wall of the Duodenum, showing the Glands of
Brunner .......... 309
37.   Diagrammatic View of a small portion of the Mucous Membrane of the Colon 310
38.   Vertical Section of the Coats of a Pig's Stomach             .... 329
39.   Stomach, Everted and Inflated .           .            .            .            .            .            .330
40.  Longitudinal Section of a Portal Canal, from the Pig .... 331
41.   Transverse Section through the Hepatic Lobules             .... 332
42.   Cut Surface of Horse's Spleen, Trabecular Framework .            .            .            . 333
43.  Vessels of the Kidneys and Uriniferous Tubules              .... 335
44.  Bladder and Intrapelvic portion of the Urethra opened from below .            . 348
45.   Section of the Cat's Ovary.......353
46.   Kight Ovary and Fallopian Tube ....... 354
47.   Generative Organs of the Mare, viewed from above .... 356
48.  Muscles of the Tail, Deep Muscles of the Hip, and Pelvic Ligaments .            . 361
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CHAPTER I.
DISSECTION OF THE ANTEKIOK LIMB.
THE PECTORAL BEGION AND THE AXILLA.
As the first step in the examination of the fore limb, the student should
dissect the structures which pass between the trunk and the ventral
aspect of the limb.
Position.—The subject should be placed on the middle line of its
back, and its limbs should be forcibly drawn upwards and outwards by
ropes running over pulleys fixed to the ceiling. If only one side is
being dissected, the subject may be inclined as in Plate 1. This will put
the muscles and other structures on the stretch, and thus facilitate their
dissection.
Surface-marking.—In the fore part of the pectoral region the student
will notice the well-marked prominence formed by the anterior super-
ficial pectoral muscle. Between this muscle and the lower edge of the
mastoido-humeralis there is' a groove in which will afterwards be
dissected the cephalic vein and a branch of the inferior cervical artery.
Extending inwards from the point of the elbow is a prominent fold of
skin over the hinder edge of the posterior superficial pectoral muscle.
Directions.—An incision through the skin, but not deeper, is to be
made along the middle line of the sternum, from the ensiform cartilage
as far forwards as the cariniform cartilage. From the middle of this
incision another is to be carried transversely outwards, and terminated
a little beyond the elbow-joint. Where this second incision stops,
another is to be made across the inner face of the fore-arm. Beginning
at the point where these incisions meet, the student should raise and
turn outwards the two flaps of skin, so as to denude the superficial
pectoral muscle. In doing this, it may be noticed that here, as in other
unexposed situations, the skin is comparatively thin. Beneath the skin is
the subcutaneous fascia, and search is to be made in it for the cutaneous
nerves of this region.
Cutaneous Nerves. A nerve of considerable size, derived from the
oth cervical nerve (Plate 1), crosses the groove between the mastoido-
nimeralis and the anterior superficial pectoral, and distributes branches
to the skin over the latter muscle and part of the posterior superficial
pectoral. Other small cutaneous twigs, which are branches of the inter-
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PLATE I
Subcutaneous thoracic nerve
Subcutaneous thoracic vein
Panniculus
Post, deep pectoral ;
Ant. subcutaneous vein
Cephalic vei:
Ant. superficial pectoral
Mastoido-humeralis
Post, superficial pectoral
Inf. cervical artery
Cutaneous nerves from 6th cervical-
Ant, deep pectoral-
Sternal band of panniculus
s
Drawn fcFrmlea by V VA K John«ton. Ednjburgn fc London
PECTORAL REGION
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2
THE ANATOMY OF THE HORSE.
costal nerves, appear near the middle line, and are directed transversely
outwards.
Directions.—The surface of the superficial pectoral muscles should
now be carefully cleaned by the removal of the subcutaneous fascia;
and this operation should be conducted by beginning at the anterior or
posterior border of the muscle and working parallel to the direction of
the muscular fibres. When this has been effected, a line will be seen
on the surface of the muscle; and by dissecting carefully down on this
line, the student will be able to separate the anterior from the posterior
part of the muscle. Search is to be made, in the groove already men-
tioned, for the cephalic vein, and the fat is to be carefully removed from
the vein and its accompanying arterial branch.
Superficial Pectoral Muscle (Pectoralis transversus of Percivall).—This
muscle is divided, though not very distinctly, into two portions, which
may be distinguished as the anterior superficial pectoral and the pos-
terior superficial pectoral.
The Anterior Superficial Pectoral (Plate 1) arises from the first
two or three inches of the inferior border of the sternum, its posterior
fibres overlapping the anterior part of the next muscle. It is inserted
into the external lip of the musculo-spiral groove.
The Posterior Superficial Pectoral (Plate 1) arises from the inferior
border of the sternum from within an inch of its anterior end as far
back as a point behind the 6th costal cartilage, and from a fibrous cord
which joins the muscle along the middle line to its fellow of the opposite
side. It is inserted into the superficial fascia which descends on the
inner face of the fore-arm; and a few of its anterior fibres, forming
a band about one inch in breadth, are inserted along with the preceding
muscle into the external lip of the musculo-spiral groove. At the
elbow-joint the muscle covers the posterior radial vessels and the median
nerve, but these are not to be exposed at present.
Action.—The superficial pectoral muscle is an adductor of the limb at
the shoulder, and the posterior division of the muscle is also a tensor of
the fascia of the fore-arm.
Directions.—Both divisions of the muscle are now to be cut across near
their origin, and dissected carefully from the subjacent deep pectoral;
and while this is being done, search is to be made for their nerves, which
come from the brachial plexus by passing between the two divisions of
the deep pectoral muscle. In reflecting the muscle, the dissector will
cut many small branches of the external or internal thoracic vessels.
The reflected muscles are now to be fastened outwards with- chain and
hooks, and the dissection of the deep pectoral is to be undertaken after
the cephalic vein has been examined.
The Cephalic Vein (Plate 1). This is the upward continuation
of one of the divisions of the internal subcutaneous vein of the fore-arm.
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PL A TE IT
Ant. superficial pectoral
Post, superficial pectoral
Post, deep pectoral
Ant. deep pectoi
iAnt. subcutaneous vein
Cephalic vein
*-llf. cervical art.
Brawn & Pnrnti ""jjr "W. &A K Johnston. Edinburgh It London
PECTORAL REGION
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3
DISSECTION OF THE ANTERIOR LIMB.
It ascends in the groove between the anterior superficial pectoral and
the mastoido-humeralis. In the inner third of this groove it lies on the
anterior deep pectoral, in company with a branch of the inferior cervical
artery. It empties itself into the jugular about two inches from the
lower end of that vessel.
Beep Pectoral Muscle.—This consists of two distinct divisions, which
may be distinguished as the anterior deep pectoral and the posterior
deep pectoral.
The Posterior Deep Pectoral {Pectoralis magnus of Percivall) (Plate
2) is a muscle of large size ; and its posterior part, being subcutaneous,
was visible before reflection of the superficial pectoral. It arises from the
abdominal tunic covering the external oblique and the straight muscles
of the abdomen ; from the tips of the cartilages of the 5th, 6th, 7th, and
8th ribs, and from the immediately subjacent lateral surface of the
sternum. It is inserted into the inner tuberosity of the humerus, into
the tendon of origin of the biceps, and into the fascia which retains that
muscle in the bicipital groove. By its deep face the muscle serves to
bound the axillary space ; while its upper border is closely united to the
panniculus, and bordered by the subcutaneous thoracic nerve and vessels.
The Anterior Deep Pectoral (Pectoralis parvus of Percivall) (Plate 2)
arises from the cartilages of the first four ribs, and from the immediately
subjacent lateral surface of the sternum; and, being carried upwards in
front of the supraspinatus nearly as far as the cervical angle of the
scapula, it is somewhat loosely inserted into the fascia covering the last-
named muscle. This insertion is concealed by the mastoido-humeralis,
and will be better seen in the dissection of the muscles on the outer
surface of the scapula (Plate 4). The deep face of the muscle forms
part of the inferior boundary of the axilla.
Action.—The two divisions of the deep pectoral have the same action,
■which is to pull the shoulder-joint, and thus the whole limb, backwards.
When the limbs are fixed, the muscle may to some extent act as
a muscle of inspiration.
Directions.—The deep pectoral muscles are now to be severed care-
fully about midway between their origin and insertion, and the cut
portions are to be turned outwards and inwards. Their nerves,
which come from the brachial plexus, will be found entering their
deep face; and care is to be taken of the external thoracic and
inferior cervical arteries. By the reflection of these muscles, the axilla
is exposed. Owing to the limited power of abduction at the shoulder-
Joint of the horse, the dissection of the space is attended with much
greater difficulty than in man. The best method of procedure is as
follows:—All the pectoral muscles having been cut across, the limb is
to be forcibly separated from the chest-wall; and, to permit this to
a sufficient extent, it may be necessary to cut the mastoido-humeralis in
-ocr page 26-
PLATE III
To levator and serratus
From 8th cervical
From 7th cervical
o levator ang. scap. and rhomboideus
To levator ang. scap.
Upper division > of scalenug
/ lower division t
7
From 6th cervical
From 5th cervical
To latissimus dorsi
Common trunk of circumflex
and nerve to teres major J
To subscapulars —
■To levator and serratus
-To serratus magnus
Suprascapular
To snbscapularis
—To ant. deep pectoral
/Common trunk of circumflex
land nerve to teres major
JTo latissimus dorsi
- Sub cutaneous thoracic
Post, root of median
Ulnar
Ext. thoracic art.
Axillary art.
Median
To biceps and coraco-humeralis
1st rib.
Cariniform cartilage
Suprascapular
To ant. deep pectoral
To biceps and coraco-humeralis
To superf. pectoral
kPn&lrfl V>- "W. iA K Johnston EdmTmr^h k Lor.ior.
BRACHIAL PLEXUS
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4
THE ANATOMY OF THE HORSE.
front of the shoulder. On looking into the space, the dissector will now
see it occupied by a large amount of loose, areolar connective-tissue,
which envelops its contents, and facilitates the play of the shoulder on
the wall of the thorax. This areolar tissue must be cleaned away from
the axillary vessels and the brachial plexus of nerves, but most of the
branches of these will be more conveniently followed after separation of
the limb from the trunk.
The Axilla corresponds to the arm-pit of the human subject, and is
the important space across which the large vessels and nerves for the
supply of the fore limb are transmitted.
Boundaries of the space.—In the natural movements of the limb, and
before dissection, the space can hardly be said to have any existence
except at its lower part; but in the dissected condition it may be
observed to have the following boundaries. On its outer side are the
subscapularis, teres major, and (in part) latissimus dorsi muscles. The
inner side of the space is formed by the anterior part of the chest-wall
covered by the serratus magnus, lateralis sterni, and intercostal muscles.
Inferiorly the space is enclosed by the deep pectoral muscles, and there
the space is most extensive. Superiorly the outer and inner boundaries
meet at the insertion of the serratus magnus into the scapula. The
anterior limit of the space may be taken as formed by the mastoido-
humeralis and the reflected portion of the anterior deep pectoral 5 while
posteriorly the space is closed by the pannicuhis carnosus and skin where
these are carried from the wall of the thorax over the outer aspect of
the shoulder.
The Axillary Artery (Plates 3 and 5) begins within the thorax. On the
left side it arises as one of the terminal branches of the anterior aorta; while
on the right it is a branch of the arteria innominata. It leaves the chest
and reaches the axilla by turning round the anterior border of the first
rib, below the inferior insertion of the scalenus. It crosses the axillary
space, inclining downwards and backwards; and at the anterior border
of the teres major tendon it is directly continued as the brachial artery.
In this course it gives off four vessels, viz., inferior cervical, external
thoracic, suprascapular, and subscapular; but only the first two are to
be followed at present.
The Inferior Cervical Artery (Plates 1 and 2) arises from the front
of the axillary where that vessel turns round the first rib. After a course
of about two inches it bifurcates, its superior branch passing between
the mastoido-humeralis and the subscapulo-hyoideus, while the inferior
division passes into the groove between the mastoido-humeralis and the
anterior superficial pectoral, where it has already been seen in company
with the cephalic vein.
The External Thoracic Artery (Plate 3) arises about the same point
as the preceding, but from the opposite side of the parent vessel; and
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PLATE IV
Splenitis
Levator ang. scapulae
Ant. deep pectoral
Trapezius (cervical part)
Trapezius (dorsal part)
atus anticus
Ant. deep pectoral
Mastoido-humeralis
Supraxpinatus'
Deltoid
Serratus niagnus
Caput magnum
Caput medium
Drnra fcfrimed ty w. SiA.K Johnswn Edinburgh fctondm
SHOULDEK—Outer Aspect
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DISSECTION OF THE ANTERIOR LIMB.                                     5
passing backwards in relation to the axillary surface of the deep pectorals,
it distributes branches to these, and also to the superficial pectorals. A
slender branch from it accompanies the subcutaneous thoracic vein to
the panniculus carnosus.
The Axillary Vein is the upward continuation of the brachial vein, and
is, at its lower part, posterior to the artery; but at the anterior border of
the first rib it is below the artery, and it here joins the jugulars and the
axillary vein of the opposite side, thus forming the anterior vena cava.
Directions.—The axillary vessels may now be cut as they turn round
the first rib, and the limb may be further abducted to facilitate the
dissection of the brachial plexus, which, in its first step, should be
Undertaken by the dissectors of the limb and of the neck conjointly.
The Brachial Plexus (Plate 3) is composed of the nerves for the
supply of the fore limb. It is formed by the inferior primary branches
°f the last three cervical (6th, 7th, and 8th) and first two dorsal nerves.
These, however, do not enter into it in equal proportions. The 6th
cervical sends only a very slender branch to it, while the 7th and
"th, after detaching a communicating filament to the sympathetic,
are wholly expended in it. The 1st dorsal is, with the exception of a
similar communicating filament and a slender intercostal branch, also
entirely expended in it, but the 2nd dorsal gives off, besides the
usual communicating branch, a considerable intercostal nerve before
joining the plexus.
These roots of the plexus converge towards each other, and come out
as a flat fasciculus between the upper and lower portions of the scalenus.
In descending to this point, the dorsal roots of the plexus turn round the
anterior border of the first rib, leaving on it a smooth impression near
:ts upper end. The several roots anastomose in an intricate fashion,
contributing to the formation of the various branches of the plexus, in
Proportions that the student will not be able to trace accurately in the
course of an ordinary dissection.
The manner in which the several roots of the plexus comport themselves is liable to
Khght variation, but the following is probably as common as any other :—
I- The root from the 6th cervical nerve is a slender branch detached from the division
which that nerve sends to aid in the formation of the phrenic. Passing obliquely back-
Wards on the scalenus muscle, it resolves itself into three divisions—or rather its fibres
are traceable in three groups, viz.,—1. To the suprascapular nerve; 2. to the anterior
root of the median; 3. to join branches from all the other roots of the plexus in forming
a broad, flat fasciculus from which arise the subscapular, circumflex, and musculo-spiral
nerves.
II. The root from the 7th cervical nerve gives a branch to the nerve for the serratus
Magnus, and then divides its fibres in three directions, viz.,—1. To the above-mentioned
asciculus giving off the subscapular, circumflex, and musculo-spiral nerves; 2. to the
suprascapular nerve; 3. to the phrenic, anterior root of the median, and nerve for the
anterior deep pectoral muscle.
HI- The root from the 8th cervical nerve gives a branch to the nerve for the serratus
magmis, and then sends its fibres in three directions, viz.,—1. To the before-mentioned
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PLATE V
Subscapular!*
Bupraaplnatufr
latissinius dorsi
Suprascapular
* erve to subscapular!
Aervo r ,
10 latissiimis dursi
Circumflexnei
SuPfascapular artery
«iUary artery-
•Teres major
Nerve to teres niaior
("Artery to
l]atis.-imus dorsi
Subcut. thoracic nerve
Subscapular artery
Musculo-spiral nerve
Deep humeral artery
Caput parvum
.Ulnar nerve
Ulnar artery
Scapulo-ulnaris
0st- deep pectoral
Ant- deep pectoral
Median nerve- '^^^^—
Brachial artery
Biceps
Mastoido-humeralis
Pout, radial artery
Superficial pectoral—
Cutaneous branch of ulnar nerve
8i?nnwd by "W &A K. J°1in«tan. Edinburgh fcLondoi
SHOULDER AND ARM—Inner Aspect
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G
THE ANATOMY OF THE HOUSE.
fiat fasciculus giving off the subscapular, etc.; 2. to join the cord from which arise the
posterior root of the median, the ulnar, and the subcutaneous thoracic nerve; 3. to the
anterior root of the median and the nerve for the anterior deep pectoral muscle.
IV. The roots from the 1st and 2nd dorsal nerves unite to form a common cord which
divides its fibres in two directions, viz.,—1. To join the above-mentioned cord giving off
the posterior root of the median, etc. ; 2. to join the broad fasciculus from which arise
the subscapular, etc.
The following is a list of the branches of the plexus :—
1.   The phrenic or diaphragmatic nerve (in part).
2.   The suprascapular nerve.
3.   Nerves to the pectoral muscles.
4.   The nerve to the subscapularis.
5.   Nerves to the serratus magnus and levator scapulae (cervical
portion of the serratus), the latter only in part.
6.   The circumflex nervo.
7.   Nerves to the teres major and latissimus dorsi.
8.   The musculo-spiral nerve.
9.   The median nerve (two roots).
10.   The ulnar nerve.
11.   The subcutaneous thoracic nerve.
The Phrenic Nehve. This nerve is formed by the union of two, or
sometimes three, branches. The inconstant branch comes from the
5th cervical; the other two come from the 6th and 7th respectively.
The root from the 6th nerve gives off a branch to the brachial plexus,
and then unites on the scalenus with the root from the 5th—when that
is present. The single cord resulting passes obliquely backwards and
downwards, and at the lower edge of the scalenus it joins with the root
from the 7th nerve. This last comes from the fore part of the brachial
plexus. The trunk of the nerve, as thus formed, passes backwards
between the axillary artery and its inferior cervical branch, and enters
the thorax. It is the motor nerve to the diaphragm.
The Nerves to the Levator Anguli Scapula and Ehomboideus.
In Plate 3 two nerves are seen at the upper edge of the scalenus.
They are not, strictly speaking, branches of the brachial plexus;
but come from the inferior primary branch of the 6th nerve, and
pierce the muscle either together or separately. They are distributed
to the levator anguli scapula;, and the posterior of the two is continued
in that muscle to reach the rhomboideus.
The Nerve to the Serratus Magnus is formed by the union of two
branches, which pierce the upper division of the scalenus before uniting.
These are branches of the 7th and 8th nerves respectively. By their
fusion there is formed a broad nerve, which passes backwards on the
surface of the serratus, distributing its filaments upwards and downwards.
Before fusion, the branch from the 7th gives off a nervo which is
distributed to both the levator and the serratus.
-ocr page 32-
PLATE VI
Subscapularis
Suprascapular art.
Suiiraspinatus
Musculo-spiral nerve
Circumdex nerve
Ulnar nerv_
Roots of median nerve
Axillary art,
Nerve to biceps^
and Coraco-humeralis
Coraco-hurueralis
Brachial art.
.Median nerve
M usculo-cutaneoui
Ulnar art.
>Tere8 major
Subscapular art.
Air.. t<> Latissimus dors]
Latissimus dorsi
Caput magnum
lieep humeral art.
Prehumeral art.
Caput pttrvum
Ant. radial art.
Art. to biceps
Post, radial art
Ulnaris accessoriutj
Ulnar head of 1 Flexor metacarpi
Radial head of j medius
Flexor perforans
Ulnar artery
■f----------Ulnar nerve
Flexor perforatus
Flexor meta carpi int
Int. plantar nerve
Large metacarpal art.
Branch of median to ext. plantar nerve
Branch of ulnar to ext. plantar nerve
Ext. plantar nerve
Small metacarpal art.
fcPrinwd tyV7 StA X ,lo>m»ton, Ednibut^h S: London
SHOULDER, ARM, AND FORE-ARM—Inner Aspect
-ocr page 33-
7
DISSECTION OF THE ANTERIOR LIMB.
The Subcutaneous Thoracic Nerve (Plates 1 and 3) derives its fibres
from the dorsal roots of the plexus and from the 8th cervical, but princi-
pally from the former. It accompanies the spur vein to near the flank,
being distributed with perforating intercostal branches on the deep face
of the panniculus carnosus. A branch from it unites with perforating
branches from the 2nd and 3rd intercostal nerves, and turns round behind
the limb, to be distributed to the panniculus over the shoulder and arm.
The Nerves to the Pectoral Muscles have already been referred to.
The nerve to the anterior deep pectoral leaves the fore part of the
plexus deriving its fibres from the 7th and 8th cervical nerves. The
nerve to the superficial pectoral muscle (both divisions) derives its fibres
from both roots of the median. In general, there are two nerves to the
posterior deep pectoral. The first—to the anterior part of the muscle,
comes off with the posterior root of the median, the other—to the
posterior part of the muscle, comes off in common with the subcutaneous
thoracic.
Directions.—The remaining nerves of the brachial plexus can be more
satisfactorily followed after separation of the limb from the trunk, and
the dissector should therefore now proceed as follows :—Pass a cord
round the nerves of the plexus as they emerge from between the two
divisions of the scalenus, and then cut the roots of the plexus as near
their points of origin as possible. Cut also the axillary artery and vein
at the first rib. This will allow the limb to be carried well out from
the trunk, so as to expose the serratus magnus and levator anguli
SQ&pulaa, which are now to be cleaned.
Serratus Magnus and Levator Anguli Scapula.—These muscles are,
ln the horse, not very distinctly marked off from each other, and have
therefore been frequently described as one muscle under the first
uame.
The Serratus Magnus (Plate 4) arises from the outer surfaces of the
eight (or nine) anterior ribs, its eight slips of origin forming a curved,
serrated line which gives to the muscle its name. The posterior four
of these slips inter-digitate with slips of origin of the external oblique
muscle of the abdomen (Plate 39), and are overspread by the abdominal
tunic. It is inserted into a triangular area on the ventral surface of the
8°apula near its dorsal angle, and, in common with the next muscle, into
another triangular area at the cervical angle.
Action.—It pulls the dorsal angle of the scapula downwards and
backwards on the chest-wall, causing the shoulder-joint at the same
time to move upwards and forwards; but when the limbs are fixed, it
°an become a muscle of inspiration, pulling the ribs upwards and for-
wards. In the standing posture of the animal at rest, the chest is, in
a manner, slung on the fore limbs by means of the right and left ser-
ratus muscles.
-ocr page 34-
PLATE VII
v..^-,
mm------Supraspinatus
Infraspinatus
-Teres minor
ircumflex vessels and nerves
Caput magnum
Deltoid
Caput medium
Anconeus-------
Ulnaris accessorius
Ulnar nerve and artery-
Flexor metacarpi ext.'
Biceps
Extensor metacarpi mag.
Deep flexors
Extensor suffraginis
Interosseous artery
Extensor metacarpi obliq.
Band from carpus to extensor \ ": d j j
sutfr. tendon
Subcarpal ligament
Flexor perforatus tendon
Plexor perforans tendon
Suspensory ligament
.Extensor pedis tendon
Extensor suffr. tendon
__Slip from suspensory ligament
to extensor pedis
Drawn ScrriTUed by "W &.A.X Jchn«t4n Edinburgh & -tmdo
FORE-LIMB—Outer Aspect
-ocr page 35-
THE ANATOMY OF THE HORSE.
The Levator Anguli Scapulae (Plate 4) arises from the trans-
verse processes of the last four cervical vertebra ; and its fibres converge
to be inserted into the triangular area on the ventral surface of the
scapula near its cervical angle, in common with the anterior fibres of
the preceding muscle, from which it is not distinct. The two muscles,
taken together, have a well-marked fan-like arrangement, having an
extensive convex border where they take origin, while they converge to
a comparatively narrow point at their insertion.
Action.—The levator anguli scapulas carries the articular angle of the
scapula backwards by pulling the cervical angle forwards; but when
the scapula is fixed, the right and left muscles, acting together, can
raise the cervical portion of the spinal column, or the single muscle can
incline it to one side.
The Subscapulo-hyoid. This muscle, which arises from the sub-
scapular fascia, is described with the dissection of the neck.
THE OUTER SCAPULAR REGION.
Position.—The muscles which pass between the shoulder and the
trunk, on the outer aspect of the former, must next be dissected; and,
to permit this, the subject must be placed in an entirely new position.
The standing posture of the animal is the best for this purpose ; and it
may be imitated by suspending the subject to a stout iron rod provided
with chains and hooks, and capable of being raised or lowered by means
of a system of pulleys or a small windlass.
Surface-marking.—About the centre of the region to be dissected the
student will feel the spine of the scapula, the most prominent part of
which is its tubercle. In a well-nourished, sound horse the spine should
not be very distinctly visible, but in an emaciated animal, or in one
whose scapular muscles are atrophied as an accompaniment of joint-
disease, it forms a very prominent ridge.
Directions.—An incision through the skin is to be made along the
spine of the scapula from the withers to the middle of the arm, where
a transverse incision is to be made from the anterior to the posterior
border of the limb. Another incision is to be carried along the middle
line of the back, and prolonged forwards along the neck by the dissector
of that region, and backwards to the lumbar region by the dissector of
the back. The dissectors of the three regions should here work
together, the skin being turned down as a single flap from the neck and
anterior half of the shoulder, and as another flap from the back and
posterior half of the shoulder. The skin, it will be observed, is thicker
than in the pectoral region, and it has the panniculus carnosus attached
to its inner surface. Care must be taken not to remove this panniculus
with the skin.
The Panniculus Carnosus is the muscle which enables the horse to
-ocr page 36-
PLATE VIII
Infraspinatus
Suprascapular nerve
Supraspinatus
I Branches from subscapular
(         artery
Tores minor
Circumflex nerve
Caput magnum
aput parvum
Deltoid
aput medium
Bicepa
—Brachialis anticns
—Musculo-spiral nerve
—Anconeus
Ulnarts accessorius
Musculocutaneous nerve )
(cutaneous division) J
Extensor metacarpi >
magnus               J
Ant. radial artery
Flexor metacarpi ext.
Extensor suffraginis
Ulnar nerve
Extensor metacarpi)
obliquns             f
Cutaneous branch
Branch to ext. planter nerve
Extensor pedi
Primed by W. &A X JuhTi»t/>n Edinlwar^h klimda
SHOULDER, ARM, AND FORE-ARM—Outkk Aspect {Chaurcau)
-ocr page 37-
9
DISSECTION OP THE ANTERIOR LIMB.
twitch its skin, and thus remove offending insects. It is most extensive
over the thorax and abdomen, but it is here carried over the muscles
covering the scapula and humerus. Before the muscle passes on to
the limb, it sends an aponeurotic layer inwards between the limb and
the chest-wall. At its upper border this layer is provided with a small
tendon, which becomes inserted into the inner tuberosity of the humerus,
and which will be seen when the limb is dissected from the trunk. A
nerve will be seen ramifying in the scapulo-humeral part of the panni-
culus. This turns round the posterior border of the limb; and, as
already seen, it is formed by the union of the subcutaneous thoracic
with some perforating intercostal nerves.
Directions.—The panniculus is now to be dissected away from the
limb; and in doing this in front, care is to be taken of the thin
cervical trapezius muscle, which might be mistaken for a portion of the
Panniculus.
The Trapezius in the horse has its muscular svibstance interrupted
Dy a tendinous portion, and is therefore sometimes described as two
separate muscles, distinguished as the cervical and the dorsal trapezius.
The Cervical Trapezius (Plate 4) arises from the funicular por-
tion of the ligamentum nuchse; and it is inserted into the tubercle on
the spine of the scapula, while its most anterior fibres are continuous
With an aponeurosis covering the scapular muscles. Both the deep and
the superficial face of the muscle have a thin, adherent, fibrous covering,
the direction of whose fibres is at right angles to that of the muscular fibres.
Action.—It draws the scapula forwards and upwards.
The Dorsal Trapezius (Plate 4) is continuous with the preced-
lng by the aponeurotic centre already mentioned. It arises from the
sUnimits of a few of the anterior dorsal spines, and is inserted into the
tubercle on the scapular spine.
■Action.—It pulls the scapula backwards and upwards.
Directions.—Both divisions of the trapezius are now to be severed
close to their origin, and reflected downwards; and while this is being
°-°ne, search is to be made for the branches of the 11th, or spinal
accessory, nerve, which enter their deep face. The muscles which were
covered, wholly or in part, by the trapezius, will now be exposed,
these are : the splenius, the levator anguli scapula;, the supraspinatus,
the infraspinatus, the anterior deep pectoral, the latissimus dorsi, and
the rhomboideus.
It will be remembered that in the dissection of the pectoral region
the anterior deep pectoral could not be followed to its termination.
the reflected portion of the muscle is here seen (Plate 4), but is partly
covered by the insertion of the mastoido-humeralis.
The Latissimus Dorsi (Plate 4). Though neither the origin nor
the insertion of the muscle is found here, attention should be given to
-ocr page 38-
PLATE IX
plexor i
Flexor metacarpi ined.
Branch of median to ext.
plantar nerve
-Art. to supracarpal arch.
Large metacarpal art.
Branch from ulnar to ext.
plantar nerve
Ext. plantar nerve
tetaoarpi int
post. radial art
Int- plantar nerve
Small
metacarpal art.
Ex
ensor metacarpi
oblique
lut. plantar nerve
Large metacarpal art.
Int. metacarpal vein
Flexor perforatus
Flexor perforans
Ant.
interosseous artery
Oblique branch from int.
to ext. plantar nerve
Suspensory ligament
Interosseous muscle
-Lumbricalis
Post, digital nerve
Digital art.
Digital vein
3H                    Extensor pedis
r°ni suspensory ligament
0 extensor pedis
Middle digital nerve
Ant. digital nerve
--Ligament from ergot
K Printed by W. &=A K. Johnston Edinburgh fc London
METACARPUS AND DIGIT—Innek Aspect
-ocr page 39-
10                                   THE ANATOMY OP THE HORSE.
it as it is being exposed by the dissector of the back. It arise; by an
aponeurotic tendon from the series of vertebral spines, beginning about
the 4th dorsal, and extending backwards to the last lumbar. This
tendon is succeeded by a thick muscular portion, which contracts and
passes in between the limb and the trunk, where it will afterwards be
followed to its insertion into the internal tubercle of the humerus. Its
anterior fibres will be noticed to play over the dorsal angle and cartilage
of prolongation of the scapula.
Action.—It is a flexor and an inward-rotator of the shoulder-joint.
The Rhomboideus (Plate 4), like the trapezius, comprises a cervical
and a dorsal portion. The cervical part is an elongated, narrow muscle,
which extends as far forward as the axis, and arises from the funicu-
lar part of the ligamentum nucha). Its fibres take a very oblique
direction downwards and backwards, and are inserted into the anterior
part of the cartilage of prolongation on its inner surface, being there
confounded with the insertion of the levator anguli scapulas. The
dorsal portion consists of fibres which arise from the anterior dorsal
spines, and pass in a nearly vertical direction to be inserted into
the inner surface of the cartilage of prolongation, behind the fibres of
the cervical division. It will be recollected that the nerve to these
muscles passes from the 6th cervical nerve, and reaches its destination
by traversing the levator anguli scapulas.
Action.—To pull the scapula upwards and forwards on the chest-wall.
The Mastoido-humeralis, or Levator Humeri (Plate 4). This
muscle, in the greatest part of its extent, is found in the head and
neck, where it takes its origin from the mastoid crest and the trans-
verse processes of the first four cervical vertebra;; but attention must
here be given to its insertion, which is into the external lip of the musculo-
spiral groove, after covering the shoulder-joint. It receives here some
branches from the circumflex nerve.
Action.—It is an extensor and inward-rotator of the shoulder-joint.
When the limb is fixed, it bends the neck laterally.
Directions.—The limb may now be detached from the trunk by
severing the attachment of the rhomboideus, serratus magnus, levator
anguli scapulas, mastoido-hameralis, and latissimus dorsi, the last being
cut where it plays over the angle of the scapula. Pieces of clean cloth
saturated with some preservative solution should be placed on the outer
aspect of the shoulder where the skin has been removed, while the
dissector proceeds to examine the structures over the inner surface of
the scapula and humerus.
inner aspect of the shoulder and arm.
Directions.—The dissector should now identify the terminal portions
of the muscles already dissected, and cut them off within an inch or
-ocr page 40-
Fig. Ill
Fig. I
Fig. IV
PLATE X
-ocr page 41-
11
DISSECTION OF THE ANTERIOR LIMB.
two of their insertion, except in the case of the latissimus dorsi, which
!s to be left at its present length until its nerve and artery have been
followed. The posterior superficial pectoral should be cut away on a
level with the olecranon, but care is to be taken not to disturb the
vessels and nerves which it covers. The aponeurosis which the
panniculus sends within the shoulder will now be observed, and, at its
upper border, a small glistening band passing to be inserted into the
internal tuberosity of the humerus.
The next step is to dissect out the axillary and brachial vessels, and
the remaining branches of the brachial plexus; and this is an operation
clemanding time and care. While an assistant holds the nerves on the
Wretch, the fat and areolar connective-tissue which surround them and
the vessels, are to be cleaned away piecemeal, always proceeding from
tne main trunks to the branches. In doing this, the dissector will meet
two groups of lymphatic glands.
Brachial Lymphatic Glands. The upper group consists of a cluster
Placed behind the brachial vessels, on a level with the middle of the
humerus. The lower group consists of one or two glands in relation to
the vessels, just above the elbow-joint.
The Axillary Artery (Plates 5 and 6). This vessel has already been
Seen passing in a curved direction from the anterior border of the 1st
riD, across the inner aspect of the shoulder-joint, where it rests above the
terminal insertion of the posterior deep pectoral, and on the tendon of
the subscapulars. It passes on to the teres major, and is continued as
the brachial artery. In this course it gives off four vessels, viz., the
"werior cervical, external thoracic, suprascapular, and subscapular,
the first two have already been dissected in the axilla.
The Suprascapular Artery (Plate 5) is a small, tortuous vessel
spi inging from the upper surface of the axillary artery about the middle
its extra-thoracic course. It passes upwards for a short distance,
aud then divides into branches, the longest of which passes over the
/ubscapularis to reach the anterior deep pectoral. A branch passes
1 between the subscapularis and the supraspinatus, while smaller
ranches are expended in the tendons about the shoulder.
the Subscapular Artery (Plates 5 and 6) is a comparatively large
esSel, and beyond its origin the parent trunk is much reduced in calibre.
arises at the interstice between the subscapularis and teres major
muscles; and, disappearing between these muscles, it ascends behind
ne glenoid border of the scapula, as far as its dorsal angle. It gives
a considerable number of vessels that cannot at this stage be
°ftipletely followed, but near its origin it will be seen to throw off a
.ranch which runs upwards and backwards on the latissimus dorsi
(Plate 5).
-The Brachial Artery (Plates 5 and 6) is the direct continuation of the
-ocr page 42-
PLATE XI
Fig. VI
Fig. V
Fig. IV
Fig. I
Fig. n
Fig. Ill
■ ■
JOINTS AND LIGAMENTS OF FORE LIMB
-ocr page 43-
12                                 THE ANATOMY OF THE HORSE.
axillary, which changes its name when it passes on to the teres major.
It descends in a nearly vertical direction to the lower extremity of the
humerus, where, above the inner condyle, it divides to form the anterior
and posterior radial arteries.* In its course it crosses the direction of
the humerus obliquely, and rests successively on the tendons of the teres
major and latissimus dorsi, the small head of the triceps, and the bone.
In front of it is first the coraco-humeralis, and then the biceps ; but
these are separated from it by the median nerve, which is in close
contact with the vessel. Behind the artery is the satellite vein,
posterior to which is the ulnar nerve. Its collateral branches arc : the
pre-lmmeral, the deep humeral, the ulnar, the nutrient artery of the
humerus (sometimes), and innominate muscular branches.
The Pre-humeral or Anterior Circumflex Artery (Plate 6) arises
at the tendon of the teres major, and passes in front of the humerus,
between the upper and lower insertions of the coraco-humeralis, to
terminate in the biceps or the mastoido-humeralis. Some of its fine
twigs may anastomose with divisions of the posterior circumflex.
The Deep Humeral Artery (Plates 5 and 6) arises at the lower border of
the latissimus dorsi tendon, and soon splits into three or four branches,
the larger of which perforate the large head of the triceps extensor
cubiti, while the smaller supply the small and medium heads of the
same muscle. A branch is continued round behind the humerus, in
company with the musculo-spiral nerve, to the front of the elbow-joint,
where it anastomoses with branches of the anterior radial. This
branch will not be followed at present.
Muscular Branches of the Brachial. The largest and most constant
of these is a vessel of considerable size which penetrates the lower part
of the biceps (Plate 6).
The Ulnar artery and the two terminal branches of the brachial will
be followed in the dissection of the fore-arm.
The Brachial Vein is a large vessel wdiich ascends behind the
artery, and receives branches that for the most part correspond to those
of the artery. It receives also the subcutaneous thoracic or spur vein.
Directions.—As the brachial vein generally contains a large quantity
of blood which exudes from the smaller cut branches, it will contribute
to the neatness and cleanness of the dissection if the dissector will
carefully remove the vein and all its branches before he proceeds to
follow the nerves.
The Brachial Plexus. The mode of formation of the plexus has
already been explained, and the student will recollect that he has
already followed branches from it to the levator anguli scapulas,
serratus magnus, and pectoral muscles, as well as the subcutaneous
* In Plate 6 the termination of the brachial artery has "been pulled slightly forwards iVi order to
show the origin of the anterior radial artery.
-ocr page 44-
T'LA TE XII
Sartorius —
Int. saphena vein
Saphena art._ "
Int. saphenous ne
Vastus interims
Ift-awn fc trotted ty"W tAK JoTiTi«tt.i Edm>UT^h fc-Londoi
THIGH—Innbb Aspect
-ocr page 45-
DISSECTION OF THE ANTERIOR LIMB.                                  13
thoracic nerve, and the filament furnished by the plexus to the phrenic
nerve. He can now easily identify and trace the following branches :—
The Nerve to the Latissimus Dorsi (Plate 5) derives its fibres
from the 8th cervical and the dorsal roots of the plexus.
The Nerve to the Teres Major (Plate 5)—one or more filaments,
generally deriving fibres, in common with the circumflex nerve, from
the 7th and 8th cervical roots (with possibly some fibres from the 6th).
The Nerve to the Subscapularis (Plate 5) derives its fibres from
aU the cervical roots of the plexus.
The Circumflex Nerve (Plates 5 and 6). Its fibres come from the 7th
and 8th cervical roots, and possibly also from the 6th. It turns round
behind the shoulder-joint in company with the posterior circumflex
Artery • and on the outside of the joint it supplies branches to the teres
ttunor, deltoid, mastoido-humeralis, and skin (Plate 7). It gives a twig
to the small scapulo-humeral muscle.
The Suprascapular Nerve (Plate 5), deriving its fibres from the
"th, 7th, and 8th cervical roots, passes into the interstice between the
subscapularis and the supraspinatus. It then turns round the anterior
border of the scapula; and gaining its dorsal surface, is expended in
the supraspinatus and subspinatus muscles (Plate 8).
The Musculo-spiral Nerve (or radial nerve) (Plates 5 and 6) is, at its
0rigin, the thickest of the nerves of the brachial plexus. Deriving its fibres
trorn the 7th and 8th cervical, and from the dorsal roots of the plexus, it
Passes downwards and backwards on the subscapularis and teres major
Muscles, and some little distance behind the axillary vessels, from
which it is separated by the ulnar nerve. On reaching the deep
numeral artery, it disappears in front of the large head of the triceps,
aild is continued round the humerus in the musculo-spiral groove,
v*here it rests on the brachialis anticus (humeralis externus), and, after-
Vards, at the posterior or outer border of that muscle. It reaches the
ront of the elbow-joint, being here deeply placed between the brachialis
' lvticus inwardly, and the origin of the great extensor of the metacarpus
Utwardly. Before the nerve disappears behind the humerus, it gives
lanches to the great and small heads of the triceps, and a long branch
hlch passes backward to divide under the scapulo-ulnaris for the
ttpply of that muscle. Behind the limb it supplies the medium head
of ti •
yie triceps and the anconeus, and furnishes a few cutaneous branches
"lch perforate the caput medium, or emerge at its lower part, to be
aistributed to the skin of the outer side of the fore-arm, below the
oo w. <p|ie termination 0f the nerve will afterwards be followed in
e fore-arm, where it supplies the extensor muscles and the flexor
^etacarpi externus.
■'■he Ulnar Nerve (Plates 5 and 6) derives its fibres from the dorsal
°ts of the brachial plexus. At first it lies close behind the main
-ocr page 46-
PLATE XIII
Gracilis
J Branches of obturator nerve
\\ and deep femoral art.
Femoral art.
Deep femoral artery
Common tendon of
psoas mag. and iliacus
Prepubic art.
Art. to quadriceps
Int. saphenous nerve
Ant. crural nerve
Poupart's ligament
rtorius
Branch of deep femoral art.
Rectus femoris
{Articular branoh
of femoral art.
Vastus intemus
Drawn fcTri-Med tiy V. fcA-K Jchn«wn. EdmbiirfK fcLondon
THIGH—Inner Aspect
-ocr page 47-
14
THE ANATOMY OF THE HORSE.
vessels; but as it passes downwards, it recedes from them, and passing
under cover of the scapulo-ulnaris, it reaches the space between the
olecranon and the inner condyle. Thence it descends to the back of the
fore-arm, where it will subsequently be dissected. At present it is seen
to give off only one branch, which disappears within the superficial
pectoral muscle, and afterwards becomes distributed to the skin of the
fore-arm (Plate 5).
The Median Nerve (Plates 5 and 6) is formed by the union of two roots.
The anterior of these comes from the 6th, 7th, and 8th cervical, while
the posterior is derived from the 8th cervical and the 1st dorsal. These
roots gives off some pectoral twigs, and then unite by forming a loop in
which the axillary artery rests. The nerve then descends in front of
the axillary artery and its brachial continuation, and will afterwards be
seen to accompany the posterior radial artery. The following branches
of the nerve may be found at present:—
The Nerve to the Biceps and Coraco-humeralis comes off close below the
union of the two roots of the median, or from the anterior root above
the point of union. It passes between the upper and lower insertions
of the coraco-humeralis, supplying that muscle and terminating in the
biceps.
Musculo-cutaneous branch.—This is given off from the median about
the middle of the humerus; and passing underneath the biceps, it
divides into a muscular branch for the brachialis anticus, and a cutane-
ous branch for the front of the fore-arm.
Directions.—The muscles of this region should now be examined in
the order of their description.
The Latissimus Dorsi (Plates 5 and 6). The insertion of this muscle
into the inner tubercle of the humerus is here seen. About an inch or
two from its termination the tendon gets a twist which alters the direc-
tion of its surfaces, and brings it to be inserted in front of the termina-
tion of the teres major on the same tubercle.
Action.—The muscle is a flexor and an inward-rotator of the shoulder-
joint.
The Teres Major (Plate 5). It arises from the dorsal angle of the
scapula, and from an aponeurosis between it and the subscapularis. It
is inserted into the internal tubercle of the humerus, its terminal tendon
resting in the twist formed by the tendon of the latissimus dorsi muscle.
Action.—It is a flexor and an inward-rotator of the shoulder.
The Soapulo-Ulnaris (Plate 5). This is a thin, flat muscle which
rests on the inner surface of the triceps, and is provided, in front and
above, with a thin, transparent tendon. It arises from the posterior
border of the scapula, and is inserted into the posterior border of the
olecranon, and into the fascia of the fore-arm. At its lower extremity
the muscle covers the ulnar vessels and nerves.
-ocr page 48-
PLATE XIV
eraoralarf.
on tendfltfof
)syas uaagr^Jitl iWacun
Branches of/>bturator nerve
Obturator art
Drawn ItPmiled by VI. 1A.1C John.wn. Edirftm.-gh fc Louden
THIGH—Inner Aspect
-ocr page 49-
15
DISSECTION OP THE ANTERIOR LIMB.
Action.—To extend the elbow-joint, and tense the fascia of the fore-
arm.
J-he Triceps Extensor Cubiti. This is an immense muscular mass
ich, Ayith the preceding, fills up the angle formed behind the
ulder-joint. ^ *las three divisions or heads, which may be distin-
guished as the caput magnum, the caput medium, and the caput
Parvurn.
the Caput Magnum, or large head (Plate 5), forms a great mass
nch is seen on both the outside and the inside of the limb. It arises
°ni th dorsal angle and glenoid (posterior) border of the scapula ;
' ^ it is inserted into the olecranon, there being a synovial bursa
tween the summit of that eminence and the tendon,
-'■he Caput Parvum, or small head (Plate 5), is, when compared with
e preceding, a very small muscle. It arises from the shaft of the
nierus below and behind the internal tubercle, and it is inserted into
the olecranon.
J-he Caput Medium, which is not now visible, will be dissected with
tJle outside of the shoulder.
Action of the triceps. It is an extensor of the elbow-joint, and acts
a lever of the first order, the joint, which represents the fulcrum,
eiug between the power and the weight. The large head is also a
flexor of the shoulder.
I he Subscapularis (Plates 5 and 6). This muscle is lodged in the fossa
the same name on the ventral surface of the scapula, and it arises from
e ^'hole extent of that fossa. It is inserted into the inner tuberosity
the humerus, a small synovial bursa being interposed between the
llQ-on an(j fckg \Mne_ The tendon is crossed by the origin of the
laco-humeralis, and another small bursa is here interposed, between
e tendons. Above its insertion it is closely related to the capsular
bament of the joint. The muscle is partly united in front with the
Praspinatus, and behind with the teres major.
Action.—It is an adductor of the shoulder.
-j-he Coraco-iiumeralis (or coraco-brachialis) (Plates 5 and 6). This,
. lcn is rather a small muscle, arises from a small tubercle on the inner
. e of the coracoid process of the scapula. It has two insertions, the first
0 the inner surface of the shaft of the humerus above the internal
erele, the second into a line which begins on a level with the
ernal tubercle, and runs down the anterior surface of the shaft near
5 inner border. Between these two insertions, the pre-humeral artery
and fV>
w*6 nerve to the biceps pass. The tendon of origin of the muscle
J ies out between the supraspinatus and subscapularis muscles, and
e posterior border of the muscle is related to the brachial artery.
4ction.— To adduct and flex the shoulder.
he Biceps (Plates 5 and 6). This muscle receives its name in the
-ocr page 50-
PLATE XV
f-i—Middle Gluteus
Ext. angle of Ilium
I-------Superficial gluteus
Tensor vaginae femori-s
— semitendi nosus
Biceps femoris
Urajwn ^Printed l>y"W. IcAX Johniton, Edinburgh feLondo:
HIP AND THIGH
-ocr page 51-
16                                   THE ANATOMY OF THE HORSE.
human subject from its having two heads of origin. It is also known as the
flexor brachii or coraco-radialis. It arises from the whole of the coracoid
process of the scapula with the exception of the tubercle on its inner
side, which is for the coraco-humeralis. Its strong tendon of origin
emerges from between the outer and inner tendons of the supraspinatus,
and passes over the shoulder-joint, a pad of fat separating its deep face
from the capsular ligament of the joint. The tendon, which is of fibro-
cartilaginous consistency, then plays over the bicipital groove of the
humerus, on which its deep face is moulded, and a synovial bursa
facilitates the movements of the tendon in the groove. The central
portion of the muscle, which is thick and fusiform, has numerous
tendinous intersections, and is traversed throughout by a fibrous cord.
It rests on the anterior face of the humerus, and at its lower end
terminates by a tendon which, passing over the anterior ligament of
the elbow-joint (to which it is adherent), is inserted into the bicipital
tuberosity of the radius: The tendon is partly covered by the internal
lateral ligament of the elbow. The muscle has a second insertion, in
the shape of a strong fibrous band, detached from the main tendon to
blend with the sheath of the extensor metacarpi magnus, and deep
fascia on the front of the fore-arm.
Action.—-To flex the elbow-joint, and make tense the fascia of the
fore-arm. In the first of these actions it is a good example of a lever of
the third order, where the power is applied between the fulcrum—
represented by the elbow-joint, and the weight—represented by the
distal portion of the limb. The fibrous cord which traverses the
muscle is a mechanical extensor of the shoulder-joint, as long as the
elbow is kept extended by the triceps extensor cubiti.
Directions.—The teres major from the shoulder upwards should now
be removed, in order to follow more thoroughly the course of the sub-
scapular artery with its branches, and to expose the small scapulo-
humeral muscle, which lies on the capsular ligament behind the joint;
but care should be taken, in dissecting the tendons in the neighbour-
hood of the joint, to preserve the capsular ligament intact.
The Subscapular Artery (Plate 6) springs from the axillary trunk
at the interstice between the subscapularis and teres major muscles,
and disappearing from view, runs upwards at the posterior border of the
scapula. It gives off as its most important branches :—
1.   A Muscular branch of considerable volume which passes backwards
and upwards on the deep face of the latissimus dorsi.
2.   The Posterior circumflex artery, which, turns round behind the
shoulder, passing through a triangular space bounded by the teres major,
caput magnum, and scapulo-humeralis gracilis. At the outer side of
the joint (Plate 7) it appears between the caput magnum, caput medium,
and teres minor, and is covered by the deltoid. It splits into branches
-ocr page 52-
PLATE XVI
Upper post, gluteal nerve
Lower post, gluteal nerve
Bap. ilio-siicnil ligament
Jsuliiatiuart.
(■'"teal arteries
t- gluteal nerves
Int. putlic art.
Great saoro-soiatic ligament
0,)tiii-,te""lnion terldon of the
""°r int. and piriformis
Drawn ft.Fruited by "W. &A.K Johnston, Edinburgh fcLondon
HIP AND THIGH
-ocr page 53-
17
DISSECTION OF THE ANTERIOR LIMB.
which are distributed to these muscles and the supraspinatus (Plate 7).
" ^ accompanied by the circumflex nerve.
•»• Other branches of the subscapular are as follows :—A few inches
above the origin of the posterior circumflex, a vessel is detached which
Passes backwards, and divides to supply the caput magnum. A number
smaller branches come off from the anterior aspect of the vessel, and
ai'e distributed on both surfaces of the scapula. One of these supplies
the nutrient artery of the scapula.
The Scapulo-humeralis Gbacilis is a very slender muscle. It arises
!orn tlu scapula above the rim of its glenoid cavity; and passing over
the capsular ligament of the shoulder, on which some of its fibres seem
to terminate, it insinuates itself between the fibres of the brachialis
a'iticus (humeralis externus), and is inserted into the posterior surface of
the shaft of the humerus. It is supplied by a small nerve from the
circumflex.
Action.—The muscle is too inconsiderable in size to exercise any
appreciable action on the joint over which it passes, and, probably, its
urwtion is to raise the capsular ligament and prevent its injury during
flexion of the joint,
OUTER ASPECT OF THE SHOULDER AND ARM.
Directions.—The limb is now to be turned over, and the muscles and
°ther structures on the outer side of the scapula and humerus are
t0 be dissected.
Scapular Fascia.—This is a strong, glistening, fibrous covering which
*s spread over the muscles on the dorsum of the scapula, affording by
ts inner surface an origin to many of their fibres. When traced
Awards, it is seen to be inserted into the scapula or its cartilage of pro-
rogation; while before, behind, and inferiorly, it becomes less fibrous,
lci is continuous with the fascia covering the muscles on the inner
surface of the scapula and the outer aspect of the arm. It furnishes
'epta to pass between the subjacent muscles, and it is adherent to the
. erele on the scapular spine. If an attempt be made to dissect
°ff these muscles, they will be exposed with a rough surface,
owing that they there take origin from the inner aspect of the
fascia.
J-he Deltoid Muscle (scapular portion) (Plates 4 and 7). This muscle
vas Dy Percivall erroneously termed the teres minor. It is not the
oniologue of either of the teres muscles of human anatomy, but is, most
clearly, the representative of that part of "the deltoid muscle which in
an takes origin from the scapula. A linear depression which traverses
e muscle corresponds to an imperfect division of it into an anterior
cl a posterior portion. It arises by its anterior portion from the
-ocr page 54-
PLATE XVII
Femoral artery
Great sciatic nerve
Ext. popliteal nerve
Int. popliteal nerve
•Ext. saphenous nerve
Femoro-popliteal art-
Popliteal art.
Middle straight patellar") ^
ligament J j
Inner straight patellar ligament
Int. lateral ligament of stifle
Flexor perforatum
Fopliteus
Flexor aucessorius
-Outer head of gastrocnemius
Inner head of gastrocnemius
Flexor perforans
+------Tendon of flexor perforatus
Post, tibial art.
Cutaneous nerve from post, tibial
k Pnnwd by w S..A K Jolm«wp. Edurt>wfh * I.ondoi
LEG—Inner Aspect
-ocr page 55-
18                                   THE ANATOMY OF THE HOUSE.
scapular fascia, and by its posterior portion from the dorsal angle of
the scapula. It is inserted into the deltoid (external) tubercle of the
humerus.
Action.—To abduct the humerus, and rotate it outwards. Acting
with the teres major, it is also a flexor of the shoulder.
Directions.—The last-mentioned muscle should be carefully cut at
the level of the shoulder, and reflected upwards and downwards. This
will expose the divisions of the circumflex vessels and nerve, branches
of which will be seen entering the muscle, and it will at the same time
bring into view the next muscle.
The Teres Minor (Plates 7 and 8). (This small muscle arises from the
posterior border of the scapula, from the rough lines at the lower part
of the infraspinous fossa, and from the small tubercle on the outer rim
of the glenoid cavity. Its tendon, which is crossed by a glistening
band of fascia, is inserted into the lower half of the ridge running
upwards from the deltoid tubercle to the external tuberosity.
Action.—The same as the preceding muscle.
The Infraspinatus (subspinatus, or postea-spinatns) (Plates 7 and 8)
occupies the greater part of the fossa of the same name. It arises from
the whole extent of the fossa, and from the inner surface of the scapular
fascia. It possesses two tendons of insertion, the outer of which passes
over the convexity of the external tuberosity, a synovial bursa being-
interposed, and is inserted into the upper half of the ridge connecting
that tuberosity to the deltoid tubercle. If this tendon be cut where it
plays over the convexity, the synovial bursa will be opened, and,
at the same time, the inner insertion of the muscle into the inside
of the convexity will be exposed. This inner tendon is more fleshy
than the outer, and is in contact with the capsular ligament of the
shoulder.
Action.—It abducts the humerus, and rotates it outwards.
The Supraspinatus (antea-spinatus) (Plates 7 and 8) fills the whole of
the fossa of the same name, and takes origin from it as well as from
the scapular fascia. It is bifid inferiorly, having an inner tendon
inserted into the internal tuberosity at its highest point, and an outer
tendon inserted into the corresponding point of the external tuberosity.
These two tendons are in contact with the capsular ligament of the
joint, and the tendon of origin of the biceps emerges from between them.
Action.—It is an extensor of the shoulder-joint.
Directions.—The outer aspect of the triceps extensor cubiti is here
seen; and when its surface has been cleaned, a line will be observed
running from the shoulder to the point of the elbow. Careful dissection
downwards into the mass, along this line, will separate the caput mag-
num (already described) from the caput medium, which lies below it.
While the surface of the muscle is being cleaned, some small cutaneous
-ocr page 56-
PLATE XVIII
Rectus femorli
Vastus externus
-Great sciatic nerve
Ext. popliteal nerve
'------Int. popliteal
—Origin of peroneal cutaneous nerve
Outer head of gastrocnemius
Accessory branch to ext. saphenous nerve
Ext. lateral ligament of patella
Anterior tibial nerve
Musculocutaneous nerve
Nerve to soleus
Soleus
Ext. straight patellar ligament
Middle straight patellar ligament
Ext. lateral ligament of stifle
Flexor metatarsi
Extensor pedis—
Peroneus—
-Flexor perforans
-Tendon of gastrocnemius
Ext. saphenous nerve
Tendon of flexor perforatus
Annular bands of hock
Extensor brevis
Drawl fcPnmea *y V J.A K Johnston Edinburgh fcLondan
LEG—Outer Aspect
-ocr page 57-
DISSECTION OF THE ANTERIOR LIMB.                                  19
erves from the musculo-spiral will be found to pierce the muscle, or
merge at its lower edge, and become distributed to the outer side of the
ore-arm. These should, as far as possible, be preserved.
J-he Caput Medium (Plates 7 and 8) arises, by a short aponeurotic ten-
on, from a curved line beginning on the deltoid tubercle and continued
P^ards to the external tuberosity. It is inserted into the olecranon.
Action.—Like the other divisions of the triceps, this muscle is an
extensor of the elbow-joint.
Erections.—By raising the lower edge of the last muscle and dissect-
mg upwards, the anconeus will be partly exposed; but to effect a com-
and natural separation of the two muscles, is a matter of some
difficulty.
the Anconeus (Plates 7 and 8) is a small muscle which lies above the
eci'anon fossa, and there covers the synovial membrane of the joint,
Pad of fat being interposed. It arises from the margin of the fossa,
01 is inserted into the olecranon on its outer and anterior aspect.
Action.—To assist in extending the elbow, and at the same time to
Se the synovial membrane and prevent its injury between the bones.
Erections.—If the caput medium be now severed at its origin, and
ued backwards, the musculo-spiral nerve and some branches of the
P humeral artery will, as already described, be found turning round
e humerus in the musculo-spiral groove, which is mainly filled by the
brachialis anticus muscle.
yie Brachialis Anticus muscle (Plate 8), also known as the humeralis
lcpins or externus, is lodged in the furrow of torsion on the shaft of the
Uierus, The muscle has its origin on the posterior aspect of the shaft
tag humerus i3eiow jts articular head. Its tendon, which cannot be
i °wed at present, passes in front of the elbow-joint, and is afterwards
ected under the internal lateral ligament of the joint, to be inserted
mto the radius and ulna.
Action.—-To flex the elbow-joint.
THE FORE-ARM.
Urface-inarking.—At the elbow-joint the olecranon process of the
a is distinctly seen; but the shafts of the bones of the fore-arm are
hed with muscles, except at the lower third of the inner border of
iadius, where the bone is subcutaneous. On the outer side of the
°i the elbow-joint a large muscular mass is formed by the extensor
acarpi magnus and the anterior extensor of the digit (extensor
ls)- In the livine- animal (in which it is preferable to study these
ace-markings) this is more distinctly visible, and the tendons of these
scfes and that of the lateral extensor (extensor suffraginis) may be
;^c% traced. On the inner side of the elbow-joint one may feel the
on of insertion of the biceps; and just behind the tendon the posterior
-ocr page 58-
PLATE XIX
Flexor perforatus_____A
Gastrocnemius------
Ant. tibial art.
Peroneus
Extensor pedis
Flexor metatarsi
JSxtensor brevis
Peroneus
Extensor pedis
Large metatarsal art.
Lowest annular bandcut and reflected
•H
Flexor perforatus-
Flexor perforans-
Satellite art. of plantar nerve-----1
Int. metacarpal vein-------j-
-Suspensory ligament
- Button' ot splint-bone
Lumbricalis
Slip from suspensory lig.
to extensor pedis
Digital art.
Digital vein
Perpendicular art.
Coronary plexus
I Pr-.Tited by*W IA K Jolmiuin. EJmVjr^h k londoc
METATARSUS AND DIGIT—Outer Aspect
-ocr page 59-
20
THE ANATOMY OF THE HOESB.
radial vessels and the median nerve may be felt as they lie on the bone
under cover of the posterior superficial pectoral, and they may be made
to roll under the finger. This should be practised, as the posterior
radial artery is a convenient vessel at which to feel the pulse. The
internal subcutaneous vein crosses the inner face of the fore-arm
obliquely upwards and forwards; and in the living animal, pressure at
the upper part will distend the vessel and bring it into view. At the
outer side of the carpus the prominence formed by the pisiforni bone
may be seen and felt. On the inner surface of the fore-arm, at its lower
third, the skin presents an oval-shaped, horny callosity, vulgarly termed
the chestnut. This is largest in coarse-bred animals.
Directions.—The skin is now to be carefully removed from the
fore-arm and carpus, and the cutaneous nerves and vessels are to be
sought.
Cutaneous Neeves. (1) At the front of the elbow-joint (Plate 8) the
cutaneous division of the musculo-cutaneous branch of the median appears
from beneath the biceps, and splits into two branches, one accompanying
the anterior, the other the internal, subcutaneous vein; (2) a little way
below the elbow, on its inner aspect, the cutaneous branch of the ulnar
(Plate 5) appears from beneath the insertion of the posterior superficial
pectoral, and divides for the supply of the skin of the back of the fore-arm
on both its outer and its inner side; (3) perforating the caput medium,
or emerging at its lower edge, are some twigs from the musculo-spiral
nerve, which are distributed to the skin of the outer side of the fore-arm
beneath the elbow; (4) on the outer side of the carpus (Plate 8) are the
ramifications of a cutaneous branch of the ulnar, which comes out be-
tween the tendons of the external and oblique flexors of the metacarpus.
Subcutaneous Veins.—1. The Median or Internal subcutaneous vein
begins at the inner side of the carpus, where it continues upwards the
internal metacarpal vein. It crosses the fore-arm obliquely upwards
and forwards, in company with a cutaneous nerve already described,
and divides into the cephalic and basilic veins. The Cephalic vein has
already been seen ascending in the groove between the mastoido-
humeralis and the anterior superficial pectoral to terminate in the
jugular. The Basilic vein pierces the posterior superficial pectoral
to concur in forming the bracnial vein.
2. The Anterior subcutaneous or radial vein is much smaller than the
preceding vessel. It begins at the front of the carpus, and, ascending
on the middle line of the fore-arm, it empties itself into the cephalic or
the median vein.
Directions.—The thin superficial fascia in which these nerves and
vessels are distributed should be removed to show the deep fascia.
Deep Fascia of the fore-arm.—This is spread in the form of a close-
fitting fibrous envelope around the fore-arm. Above it receives an
-ocr page 60-
PLATE XX
Serratus anticus
Kerratus posticus (three ant. slips removed)
Fl
I
W r
i>
Anext. intercostal
Drawn fc.Prrn.u4 tyV 3,. A V. Julmaxon Edrn'out^h feloaaun
CEEST-'WM.L \SUBJlCK.
-ocr page 61-
DISSECTION OF THE ANTERIOR LIMB.                                 21
isertion from the biceps, and another from the scapulo-ulnaris; below
_ continued over the carpus to form sheaths for the tendons; while
y its deep face it furnishes septa to pass between the muscles of the
fore-arm.
■directions.—The dissection of the back of the fore-arm is now to be
. rtaken. The before-mentioned fascia is to be incised along the
nes of separation of the muscles, and these are to be cleaned and
wtecl. The remaining portion of the posterior superficial pectoral
Miscle, which covers the posterior radial vessels and the median nerve
the inner side of the elbow, is to be removed; and care is to be
ven of the ulnar vessels and nerve, which are placed beneath the
Ueep fascia, on the middle line at the back of the limb.
ine Ulnar Artery (Plates 6 and 7) is a collateral branch of the brachial,
°m which it comes off at the lower border of the caput parvum. It
scends parallel to the lower border of that muscle, to the space between
0 °^ecranon and the inner condyle, where it is covered by the scapulo-
oaris. It here places itself in company with the ulnar nerve; and,
' 0SSlng beneath the ulnar origin of the middle flexor of the metacarpus,
descends to the carpus by following the tendon of the ulnar portion of
e deep flexor (ulnaris accessorius), being placed between the external
. oblique flexors of the metacarpus. At the upper limit of the carpus
concurs in the formation of the supracarpal arch, by joining a branch
ached from the large metacarpal artery. In this course it gives off
\l) the nutrient artery to the humerus (sometimes); (2) articular
nches to the elbow-joint; (3) muscular branches in the neighbour-
ed the joint, to the scapulo-ulnaris, caput parvum, and posterior
Perficial pectoral; (4) cutaneous branches to the skin on the inner
Slde of the fore-arm.
ne Ulnar Vein accompanies the artery and nerve, and at the elbow
CUrs in the formation of the brachial vein.
, e Ulnar Nerve (Plates 6 and 8) has already been partly described in
dissection of the arm. At the lower part of that region it crosses
ulnar artery, with which it places itself in company between the ole-
on and the inner condyle. It here gives off branches to the following
,a.' es :'—(1) the anterior head of the middle flexor of the metacarpus ;
\. . e ulnar head of the same muscle ; (3) the superficial flexor of the
«? (perforata); (4) the ulnar origin of the deep flexor (ulnaris
sorius). Iu tne fore-arm it descends in close company with the
s of the same name, and at the carpus it gives off the cutaneous
l Gl au"eady described (page 20). At the upper border of the pisiform
i and beneath the tendon of the middle flexor,* it joins a branch
n the median to form the external plantar nerve.
•^fiction - >iS an^ ^ *^e termination °f the nerve has been pulled slightly forwards to show its
,Vlth ihe branch from the median.
-ocr page 62-
I*£iAT£ XXI
Longissimus dorsi
Serhispinalis
Transversalis costarurn
Middle gluten
Two internal intercostals
An external intercostal
"Dra*rn &. Primed by V. ScA.K Johnston. Edinburgh fc. London
CHEST-WALL AND BACK
-ocr page 63-
22
THE ANATOMY OP THE HORSE.
The Posterior Eadial Artery (Plate 6) is one of the terminal
branches of the brachial. It is so much larger than the other terminal
branch (the anterior radial), that it might be described as the direct
continuation of the brachial, whose direction it prolongs. Beginning
above the inner condyle, it descends on the bone, and then lies over the
internal lateral ligament of the elbow-joint, and posterior to the tendon
of insertion of the biceps. It is here covered by the posterior superficial
pectoral, and is related to the median nerve, which lies close behind it,
and to its satellite veins. At this point it is favourably placed for taking
the pulse, and its situation and relations should be carefully noted.
After crossing the elbow, it inclines forwards and disappears with the
median nerve between the radius and the internal flexor of the meta-
carpus. In this position it descends to within a short distance of the
carpus, where it divides into two terminal branches of unequal size—
the large and small metacarpal arteries. It gives off the following
collateral branches :—
1.   Articular Branches to the elbow-joint.
2.   The Interosseous Artery of the fore-arm, which reaches the outside of
the limb by passing through the radio-ulnar arch. It then descends along
the outer side of the line of junction of the radius and ulna (Plate 7),
where it will be followed in the dissection of the front of the fore-arm.
3.   Muscular Branches to the flexors of the metacarpus and digit.
4.   Cutaneous Branches.
The Posterior Radial Veins. The artery is accompanied by three or
four satellite veins, which surround it and the nerve, and anastomose
freely with each other. They begin at the carpus, where they anasto-
mose with the metacarpal veins, and at the elbow-joint they unite with
the basilic and ulnar veins to form the brachial vein. They receive
branches corresponding more or less exactly to those of the artery.
The Median Nerve in the fore-arm (Plate 6). This nerve has already
been followed in the dissection of the arm, where it was seen descending
in front of the brachial artery. It preserves the same relationship to the
first few inches of the posterior radial arteiw, but at the elbow it crosses
the artery superficially to take up a posterior position. Below the joint
it again changes its position by mounting on the surface of the artery,
or it may even again place itself in front. At a variable point in the
fore-arm it terminates by dividing into two branches, one of which is
continued as the internal plantar nerve, while the other joins the ulnar
to form the external plantar. In the subject from which Plate 6 was
taken, the division took place considerably above the middle of the fore-
arm, but more frequently it occurs in the lower third. Immediately
below the elbow the nerve furnishes a branch to the internal flexor of
the metacarpus, and branches to the deep flexor of the digit (humeral
and radial heads).
-ocr page 64-
Phrenic nerve
Inf. laryngeal nerve
Post aorta
9th intercostal art.
10th nerve
A cardiac nerve,
Trachea
Thoracic duct
(Esophagus
A cardiac nerve,
Left axillary art.
Longus colli
Dorsal art,
Art. innominata
Ant. vena cava,
Sup. cervical art^
Vertebral art.
PLATE XXII
Doraal cord of sympathetic nerve
Great splanchnic nerve
Scalenus
1st rib
Jugular vein
Axillary art.
AciUary vein
Int. thoracic art.
\ (Left lung, collapsed and
) reflected
Pericardium
| Right Inng, seen through
I mediastinal pleura
Diaphragm
Dra*ni It Printed fcy1*. I.A K. Joamtun EdirrtreTgb fcLondw
THORACIC CAVITY—Left Side
-ocr page 65-
DISSECTION OF THE ANTERIOR LIMB.                                  23
Directions.—The muscles on the back of the fore-arm must now be
tearnt. These consist of the three flexors of the metacarpus, and the two
flexors of the digit.
The Flexor Metacarpi Internus (Plate 6). This muscle lies along
the inner edge of the posterior surface of the radius, where it conceals
tne posterior radial vessels and the median nerve. It arises from the
inner condyle of the humerus, just behind the point of origin of the
internal lateral ligament, where it is confounded with the origin of the
middle flexor. It terminates interiorly in a long, slender tendon, which,
after passing through a synovial sheath at the inner side of the carpus,
is inserted into the head of the inner small metacarpal bone.
Action.—It is a flexor at the carpal articulations—i.e., it flexes the
maims on the fore-arm.
The Flexor Metacarpi Medius (Plate 6). This muscle descends in
c°ntact with the posterior edge of the internal flexor. It has two heads
°i origin—an anterior and a posterior. It arises by its anterior head
Just behind the origin of the preceding muscle, and by its posterior
•lead from the upper part of the posterior edge of the olecranon. After
a course of three or four inches these two heads unite, and the single
interior tendon is inserted into the upper border of the pisiform bone.
1 ne ulnar nerve and vessels pass beneath the posterior or ulnar head of
the muscle.
Action.—The same as the preceding muscle.
The Fl exor Metacarpi Externus (Plates 7 and 8) is situated at the
outer side of the back of the fore -arm, having the lateral extensor of the
cugit (extensor suffraginis) in front of it, while behind it is separated from
ine last-described muscle by the ulnar division of the deep flexor of the
"git (ulnaris accessorius). It arises from the lowest point of the outer
!"ge bounding the olecranon fossa. At its lower end it has two inser-
*ow.s, viz., (1) into the upper border of the pisiform bone, whexe it is
c°nfounded with the insertion of the middle flexor; (2) by a cord-like
eudon which, after descending in a synovial sheath formed inwardly by
. e oblique groove on the outer surface of the pisiform bone, is inserted
nto the head of the external small metacarpal bone.
Action.—Like the preceding two muscles.
directions.—The three flexors of the metacarpus surround the flexors
the digit, and they should be cut about their middle and reflected to
bring these latter into view.
I he Superficial Flexor of the Digit (flexor pedis perforatus) (Plate
) arises, by a tendon common to it and the deep flexor, from the
wer extremity of the ridge bounding the olecranon fossa on the inside.
8 muscrdar belly contains much tendinous tissue, and cannot without
itticulty be separated from the deep flexor, on which it rests. At the
wer part of the radius its muscular portion is succeeded by a tendon,
-ocr page 66-
PLATE XXIII
Art. innominata
Sup. cervical art.
Ant. aorta
Trachea
Jugular vein
Common carotid art.
Vertehral art.
Vertebral vei
Thoracic duct.
Inf. cervical art.
Cephalic vein
Ext. thoracic art.
Axillary vein
Int. thoracic art.
Int. thoracic vein
Common aorta
Hth intercostal art.
Post aorta
(.Esophagus
Post, vena cava
Right ventricle
krmuei by7» VA K JuhnsUm EAinbur^h kIonian
H¥iKR,T A^D GTfc'&A.T YBSSEU&—V.W? Sttya
-ocr page 67-
24                                   THE ANATOMY OP THE HORSE.
which, after being reinforced by a fibrous band from the back of the
radius, passes through the carpal sheath behind the carpus, and is
ultimately inserted by a bifid tendon into the second phalanx. The
examination of this and the succeeding muscle, from the carpus down
wards, must be postponed till the dissection of the metacarpus and
digit is undertaken.
Action.—The muscle flexes successively the pastern, fetlock, and
carpal joints.
The Deep Flexor, of the Digit (flexor pedis perforans) (Plate 6).
This muscle is situated in contact with the posterior surface of the
radius, and consists of three divisions, which may be distinguished as
the humeral, the radial, and the ulnar portions. The humeral or main
division arises, in common with the preceding muscle, from the lower
extremity of the ridge bounding the olecranon fossa on the inside. The
radial portion, or radialis accessorius, is deeply placed, and arises from
the back of the radius. The ulnar division, or ulnaris accessorius. is
placed beneath the deep fascia of the fore-arm, where it lies between the
external and oblique flexors of the metacarpus, and is accompanied by
the ulnar nerve and vessels. It arises from the summit and posterior
border of the olecranon. These three divisions unite above the carpus,
and have a common tendon which passes through the carpal sheath,
and is ultimately inserted into the os pedis.
Action.—It flexes successively from below inwards the inter-phalan-
geal joints, the fetlock, and the carpus.
Directions.—The front of the fore-arm must now be dissected; and
here it will be convenient to turn attention in the first place to muscles;
but while these are being isolated, care is to be taken of the interosseous
vessels, which descend along the lateral extensor at the outer side of the
region, and of the tendon of the oblique extensor where it crosses over
the tendon of the extensor metacarpi magnus above the carpus.
The Extensor Metacarpi Magnus (Plates 7 and 8) corresponds to the
long and short radial extensors of the wrist in the human subject. It is
a powerful muscle, having at its upper end a massive muscular belly,
which tapers downwards, and terminates a few inches above the carpus
in a tendon. It arises from the anterior and upper part of the outer
ridge of the olecranon fossa (the outer condyloid ridge), where this ridge
bounds the musculo-spiral groove ; and by a second tendon, in common
with the extensor jiedis, from a depression which is placed external to
the coronoid fossa. Its inferior tendon lies in the largest and most
internal of the vertical grooves at the lower end of the radius ; and after
gliding over the front of the carpus in a synovial sheath, it is inserted
into a special tubercle on the upper end of the large metacarpal bone at
its inner side.
Action.—It extends the manus on the fore-arm.
-ocr page 68-
Common aorta
j Ant. aorta
Ant. vena cava
J Lorso-cervical vein
Art. Innominata
Dorso-cervieal art.
Vertebral vein.
PLATK A'XIV
(Esophageal art. (snp./
I Bronchial trunk dividing
j j Broncho-oasophageal art.
!>th Intercostal art.
.Trachea
-Common carotid art
Vertebral art.
.Jugular vein
Cephalic trunk
Axillary art.
Inf. cervical art.
Axillary vein
Ext. thoracic art.
Post aorta
Right bronchus
(Esophagus -
^^^^^^^^^^^^ Left bronchus
Pulmonary veins
Sinus venosus of right auricle
Post. «na cava
Int. thoracic vein
Int. thoracic art.
—Right auricular appendix
Right ventricle
Left coronary art.
Drawn JcPrinted by"W J*A.X Johnston, F.faiiburgn fcLondoj
HEART AND GREAT VESSELS—Right Side
-ocr page 69-
25
DISSECTION OF THE ANTERIOR LIMB.
J-he Extensor Metacarpi Obliquus (Plates 8 and 9). This is the re-
| es6»tative of the extensor muscles of the thumb in man. It arises from
e outer side of the radius; and its tendon, after passingoblig uely
__ ^ awards and inwards over that of the great extensor, is inserted into
e head of tile inner small metacarpal bone. It lies in an oblique
. 00Ve at the lower end of the radius, where the play of its tendon
acilitated by a small synovial bursa.
rJ:tlon-—Like the preceding muscle.
ihe Extensor Pedis, or anterior extensor of the digit (Plate 7),
presents the extensor communis digitorum of man. At its origin it
^mediately to the outer side of the extensor metacarpi magnus, but
he lower part of the fore-arm the extensor metacarpi obliquus emerges.
^ between the two muscles. It arises, by a tendon common to it
the extensor metacarpi magnus, from a depression external to the
°uoid fossa ; also from the external lateral ligament of the elbow, and
le external tuberosity at the upper end of the radius. It consists of
° parallel portions of unequal size, and these are succeeded by two
«ons which lie close together, but are distinct from each other.
ese tendons pass in common through a vertical groove at the lower
°t the radius, and over the front of the carpus, where they are pro-
eti with a synovial sheath. In the dissection of the metacarpus and
s11! the tendons will be pursued to their insertion, the outer and
auer * joining the tendon of the extensor suffraginis, while the inner
main tendon becomes inserted into the pyramidal process of the os
Pedis.                                                                 .
ction.—This muscle extends in succession the interphalangeal joints,
*etloek, and the carpus.
Qe Extensor Suffraginis, or lateral extensor of the digit (Plates 7
and S\ •                                                                    .                          .
, . /> ls a smaller muscle than the extensor pedis, to the outer side of
11 it lies. It is the homologue of the extensor of the little finger in
Ulan t
it arises from the external lateral ligament of the elbow, from the
. nal tuberosity at the upper end of the radius, from the line of
' Wn of the radius and ulna, and from the outer border of the radius.
. 6n passes first through a vertical groove on the external tuber-
- at the lower end of the radius, then through a synovial sheath at
. uter side of the carpus, and it will subsequently be followed to its
' SeJtion into the first phalanx.
c ion..—it jg au extensor 0f the fetlock and of the carpus.
Sections.—The nerves and bloodvessels on the front of the fore-arm
.f Uext be sought, and in order to fully expose them, some of the
Oomg muscles must be cut. The biceps is to be cut about its
* Th'
of the pre" sometimes termed the muscle of Phillips. Occasionally there occurs, to the inner side
before re, i'.1""' another and smaller fasciculus, with a slender tendon which joins the main tendon
' c "ng the carpus. Tlr.s is the muscle of Thiernesse.
-ocr page 70-
PLATE
Great splanchnic nerve
Post.aorta
ung, collapsed and reflected
Intercostal vessels
Diaphragm
Great vena azygos
Dorsal cord of sympath. nerve
ngus colli
cardiac branch of 10th nerve
0th nerve
.Trachea
orso-cervic&l vein
Dorso-cervical art.
-Vertebral vein
Ant. vena cava
Scalenus
1st rib
Phrenic nerve
Ant. mediastinum
ight auricle
Bight coronary art.
Bight ventricle
X Printed ty "W. &A.K. Jul ■                              - It Landoj
THORACIC CAVITY—Right Side
-ocr page 71-
26                                   THE ANATOMY OF THE HORSE.
middle in order to follow the anterior radial artery; and by dissecting
deeply down in front of the elbow, between the brachialis anticus and
the extensor metacarpi magnus, the artery will be found to meet the
musculo-spiral nerve. The extensor metacarpi magnus is to be cut
about its middle and carefully reflected in order to follow the artery,
which lies in relation to the deep face of the muscle; and the extensor
pedis is to be similarly reflected to trace the termination of the mus-
culo-spiral nerve.
The Anterior Kadial Artery (Plate 8) is the smaller terminal
branch of the brachial. It separates at an acute angle from the pos-
terior radial, and passes forwards beneath the biceps and then beneath
the brachialis anticus. It meets the musculo-spiral nerve in the inter-
space between the brachialis anticus and the extensor metacarpi magnus,
and afterwards descends on the anterior surface of the radius, where it
is covered by the last-mentioned muscle. It terminates at the carpus
by anastomosing inwardly with branches from the posterior radial, and
outwardly with the interosseous artery of the fore-ami. It supplies
articular branches to the elbow, and muscular branches to the muscles
on the front of the fore-arm.
The Interosseous Artery of the fore-arm (Plate 7) is a branch
given off by the median at the back of the fore-arm. It comes out-
wards through the radio-ulnar arch, and descends along the extensor
suffraginis, terminating in slender branches in front of the carpus.
It supplies articular branches to the elbow; the nutrient artery of the
radius; and muscular twigs to the extensor suffraginis, extensor pedis,
and extensor metacarpi obliquus.
The anterior radial and interosseous arteries are, generally, compara-
tively slender vessels, but they are liable to some variation in size and
distribution, and the one may partly supplant the other.
Veins. Satellite veins of the same names run in company with the
foregoing arteries.
The Musculo-spiral Nerve in the fore-arm (Plate 8). In the dissec-
tion of the axilla and arm, this nerve has already been seen as a large
trunk descending from the brachial plexus, and taking a spiral course be-
hind the humerus. It reaches the front of the elbow, where it meets the
radial artery in the interspace between the brachialis anticus inwardly,
and the origin of the extensor metacarpi magnus outwardly. It here
gives off branches to the extensor metacarpi magnus, extensor pedis,
extensor suffraginis, and flexor metacarpi externus; and, much
reduced in size, it descends between the shaft of the radius and the
extensor pedis, and terminates in the extensor metacarpi obliquus. The
nerve to the flexor metacarpi externus is furnished after the branches to
the extensor pedis, and passing outwards between the latter muscle and
the bone, it penetrates its muscle at the radio-ulnar arch.
-ocr page 72-
PLATE XXVI
Pulmonary art., right branch
10th nerve, emitting cardiac branches
Cardiac nerve from mid. cerv. ganglion
Inf. cerv. ganglion
Inf. laryngeal nerve
Mid. cerv. ganglion
Jrachea
Cervical cord of
sympathetic nerve
10th nerve
Common carotid art.
Jugular vein
Vertebral art.
Phrenic nerve
Sup. cervical art.
Axillary vessels
Ext. thoracic art.
Dorso-cervical art.
NArt. innominata
Ant. vena cava
Int. thoracic vessels
Ant. mediastinum
Bight coronary art.
Heart
Cut edges of pericardium
■ nied by W. kA K Johimbin E.lm.-.
Left bronchus
Intercostal vessels,
(Esophageal art.
Sup. oesophageal nerve.
Great splanchnic nervi
Dorsal cord of sympathetic nerve
Post, aorta
Great vena azygos
Diaphragm
Oesophagus
Inf. oesoph. nerve
Left lung
Post, vena cava
Pulmonary veins
Phrenic nerve
THORACIC CA.VITY—Right Side
-ocr page 73-
DISSECTION OF THE ANTERIOR LIMB.                                  27
Sections.—In this stage of the dissection the student will be better
to trace the musculo-cutaneous branch of the median nerve, and the
iq\ °n8 °^ *he biceps and brachialis anticus muscles (see pages 16 and
y)- When these have been examined, he may, as the next step, either
ssect the articulations of the shoulder and elbow (pages 41 and 43), or
nay saturate the parts already dissected with some preservative solu-
n> and postpone the examination of these joints till after the dissec-
>°n of the metacarpus and digit,
THE METACARPUS AND DIGIT.
e distal portion of the horse's fore limb, beyond the lower extremity
the radius, is technically termed the manus, as it corresponds to the
1 of man. The carpus, or,' as it is commonly but erroneously
fted, the knee, of the horse corresponds to the wrist of the human
Ject. The portion of the limb between the carpus and the fetlock,
Presenting the palmar portion of man's hand, is called the metacarpus ;
j e the rest of the limb, beyond the fetlock, is the digit, and is the
omologue of man's middle-finger.
' Urfuce-marhing.—By flexing the carpal and fetlock joints, the splint
es may be felt at the back of the metacarpus. Behind the bones in
same region lie the flexor tendons, the subcarpal ligament, and the
1 Peiisory ligament. These, whose edges may be more or less distinctly
m a well-bred animal, have the relation to each other shown in
„ ' e '■ Behind the fetlock-joint is a tuft of hair in which will be
p         a horny spur or ergot, which is largest in coarse-bred animals.
J Manipulation, the flexible lateral cartilages may be felt above the
°°f> in the region of the heels.
fi li V>ectlons-—The entire remaining portion of skin should now be care-
} removed from the limb. Should it be intended to study from the
e Preparation the parts contained within the hoof, this must, before
removal of the skin, be detached by for ce in the manner described
it i ^6          '^e various structures are now to be defined by dissection
ii . le 01*^ei' of the following description; and while the vessels and
IS are being cleaned, care must be taken of the small lumhricales
r_ ' es, which lie on the tendon of the deep flexor above the fetlock.
A\ P mav arterial arches cannot be fully exposed at this stage of the
re'. ou' hut it is convenient to describe them here, from their
°nshir> to the wssaIs nf the
tap to the vessels of the region. The same applies to the
l
jj Metacarpal artery and the plantar nerves behind the carpus,
'hich can be fully traced in the examination of the carpal sheath
(P;Jge 33).
ai,, e, Large Metacarpal Artery (Plate 9). This is the largest
2 in the part of the limb now exposed, and is, by means of its ter-
-ocr page 74-
PLATE XXVII
Parotido-au ocularis
Submaxillary gland
Parotid gland           SptonilM
Trapezius
M astoido-hu meralis
k
Sternal band of panniculus
Nv^higular vein
Common caftrtid »rt>: "
Subscapulo-hyoideus
Sterno-maxillaris
Submax. lymph, glands
Submaxillary art.
V, ]«buua y.Air.i.unA. ^ Loninn
V.Y.*.VVS. rOtJ.V> Y^YVA*.-^ tOCtt A.JVAOT SSXC*
-ocr page 75-
28
THE ANATOMY OF THE HOUSE.
minal branches, the main vessel of- supply to the digit. It has already
been seen at its origin, as the larger of the two terminal branches of the
posterior radial artery; and, indeed, from its volume and direction, it
might be described as the direct continuation of that vessel. From its
point of origin at the lower end of the radius, it descends in company
with the flexor tendons, by passing behind the carpus and beneath the
carpal arch. Emerging from beneath the last-named structure, it con-
tinues to descend on the inner side of the flexor tendons until a little
above the fetlock, where it sinks slightly inwards to bifurcate into the
digital arteries. From the carpus downwards the artery is related to
the internal metacarpal vein, which ascends in front of it, and to the
internal plantar nerve, which is in contact with it posteriorly. The
relative position of the three structures should be carefully noted in
reference to the higher operation of neurotomy. Only two of its
collateral branches are of sufficient size to merit description, and both
are somewhat irregular in their origin. The first of these comes
off near the origin of the parent vessel, and may come from the
posterior radial itself. It crosses behind the lower extremity of the
radius, and anastomoses with the termination of the ulnar artery to
form the supracarpal or superficial palmar arch. The second is an
un-named vessel which springs from the large metacarpal at or near its
point of bifurcation, and divides into branches that ascend to anastomose
with the interosseous metacarpal arteries.
The Supracarpal or Superficial Palmar Arch is formed behind the
lower extremity of the radius, by the junction of the above-mentioned
branch of the large metacarpal artery with the termination of the ulnar.
The convexity of the arch is turned downwards, and from it there arise
several branches. The largest and most regular of these descends
within the carpal arch, and joins the small metacarpal artery to form
the subcarpal or deep palmar arch, which will be dissected at a later
stage.
The Digital Arteries (Plates 9 and 10) are the terminal branches
of the large metacarpal artery. They separate at an acute angle, the
outer one passing above the fetlock, between the deep flexor and the
suspensory ligament. Each passes over the side of the fetlock-joint, and
descends at the edge of the flexor tendons as far as the inner face of
the basilar process, where it bifurcates to form the plantar and pre-
plantar arteries. Each artery is related in front to the vein of the
same name, and behind to the posterior branch of the plantar nerve.
The anterior branch of the same nerve crosses the vessel at the
fetlock; while other twigs cross over the artery and form the
middle branch, which will be found between the artery and vein, or
resting on the former. Crossing these vessels and nerves obliquely,
is a small glistening ligamentous cord (Plate 9) which stretches
-ocr page 76-
PLA TE XXVIfl
Occipital art
Int. carotid art
Ext. carotid art.
Pth new
Post, auricular art.
Ant. auricular art.
7th nerve
Trans, facial art.
Trapezius
Preseapular glands
Inf. cervical art.
Msatoido-hnmeratu
Jugular vein
Sterno-max illari.s
Division of ext. carotid intO(
superf. temp, and int. max J
Maxillo-musc. art. —i
Submaxillary aft.
12th nerve
~"T
Sternal band
of panniculus
NUrnothyro-hyoideus
!/OituQon carotid art.
Subscapnlo-'hjoideiis
Inf. laryngeal nerve*"**-
(Esophagus
Trachea
Drawn fcPriwed fcy "W ScA.K John»lfln. Edinburgh & Londoi
NECK
-ocr page 77-
DISSECTION OP THE ANTERIOR LIMB.                                  29
'awards and forwards from the horny spur behind the fetlock,
corning attached within the wing of the os pedis. A knowledge of
lese relationships is of importance for the performance of the lower
1 Nation of neurotomy. The collateral branches of the digital
arteries are :—
•   At different levels numerous small branches for the skin, tendons,
| * "dilations. Among these may be included the rameaux echelonnes
. ^ouley (Plate 10). These branches, some of them of considerable
A spring from the posterior aspect of the artery, and anastomose
ss tar back of the digit with corresponding branches from the oppo-
e 8lde, forming arches arranged like the steps of a ladder.
,, ' ^ne Perpendicular Artery, which comes off at a right angle about
middle of the first phalanx, and divides almost immediately into an
ending and a descending set of branches, both of which are distri-
e°- on the front of the first phalanx. Branches from each of those
anastomose with corresponding vessels from the opposite side.
•   -I he Artery of the Plantar Cushion.
•   v essels forming the Coronary Circle.
.„ e last two, as well as the terminal branches of the digital arteries,
Will 1
°e described in connection with the foot.
ne Small Metacarpal Artery (Plate 9). This, the smaller
"inial branch of the posterior radial artery, descends behind the
e and towards its inner side. It is superficially placed to the
., °Us band completing the carpal arch, while the large metacarpal
k beneath that structure. In company with it is the first part of the
ian vein. At the level of the head of the inner metacarpal bone it
ses to the outer side by passing between the suspensory ligament
, the subcarpal ligament, or check-band furnished from the
°i the carpus to the tendon of the deep flexor. It here anasto-
° 8 with a branch already described as descending from the supra-
' rf ai"ch. In this way the subcarpal arch is formed.
ne Subcarpal or Deep Palmar Arch gives off the following two
Pa^ of ai.teries :_
ihe Anterior or Dorsal Interosseous Metacarpal Arteries.—These
for\Sma11 vessels (Plate 9)>
one on each side of the limb, which turn
tv, a round the heads of the small metacarpal bones, and descend in
grooves between these bones and the large metacarpal. They
a t'16 skin an(l subjacent structures on the front of the metacarpus,
anastomose above the fetlock with divisions of the artery springing
the large metacarpal at its point of bifurcation.
•   -l he Posterior or Palmar Interosseous Metacarpal Arteries.—These
end on the edge of the suspensory ligament, each being internally
lit ^° *^e 8maU metacarpal bone of its own side. They anastomose
he preceding, and supply small branches to the suspensory ligament
-ocr page 78-
Parotido-auricularis
I
Maxillo-ruuseular vessels
Parotid gland
7th nerve
Masse ter
PLATE XXIX
Orbital art. from sup. dental
Levator labii sup. proprius
Angular branches of submax. vessels
Zygomaticus
Levator labii sup. alseque nasi
Buccinator
Dilat. naris lateralis
Depressor labii inf.
Orbicularis oris
Submaxillary vein
Submaxillar; art.
N**al branches of vubmax. vessels
Drawn fc Primed bj » UA.K Jonn«oon EdiriVnrtfi It London
SlDte OT ¥AOK
-ocr page 79-
30
THE ANATOMY OF THE HORSE.
and flexor tendons. One of them gives off the nutrient artery of the large
metacarpal bone. They arc of unequal size, the outer being the larger.
The Digital Veins (Plate 9). These are the satellites of the digital
arteries, in front of which they ascend. They drain away the blood
from the venous plexuses within the hoof, and, uniting with one
another above the fetlock, they form an arch between the deep flexor
and the suspensory ligament. From this arch spring the metacarpal veins.
The Metacarpal Veins are three in number:—
1.   The Internal Metacarpal Vein (Plate 9), which is the largest of
the three, ascends in front of the large metacarpal artery, on the inner
edge of the flexor tendons. At the inner side of the back of the
carpus it is continued as the median vein.
2.   The External Metacarpal Vein is similarly disposed on the outside
of the flexor tendons, in company with the external plantar nerve. At
the carpus it divides into several anastomosing branches, which are
continued as the ulnar and posterior radial veins.
3.   The Interosseous or Deep Metacarpal Vein is an irregular vessel
ascending between the suspensory ligament and the inner splint bone.
At the back of the carpus it breaks up into branches that anastomose
with the external and internal metacarpal veins.
The Plantar Nerves (metacarpal nerves of Percivall).—These are the
nerves which confer sensibility on the digit, and which, in their main
trunks, or in one of their terminal branches, are cut in the operation of
neurotomy. They must therefore be dissected with great care, and the
student must make himself thoroughly acquainted with their situation
and relations.
The Internal Plantar Nerve (Plate 7). This is one of the ter-
minal branches of the median nerve. Beginning at a variable point
above the carpus, it passes within the carpal arch, in close company with
the large metacarpal artery, both resting on the side of the deep flexor
tendon. Here the norve crosses beneath the artery, to place itself
behind it. Throughout the metacarpal region the same relationship
is preserved, the nerve lying immediately behind the artery, in front
of which is the internal metacarpal vein. Just above the fetlock the
artery sinks in somewhat more deeply than the vein and nerve, and
thereby allows these to approach each other. In the higher operation
of neurotomy the nerve is cut a little way above the fetlock, and before
it divides. About the middle of the metacarpus it gives off a consider-
able branch which winds obliquely downwards and outwards behind the
flexor tendons, to join the external plantar nerve an inch or more above
the button of the splint bone. At the level of the sesamoid bones the
trunk of the nerve divides into three digital branches, which are
distinguished as anterior, middle, and posterior. These are of very
unequal size, the posterior being much the largest, and also the most
-ocr page 80-
PLATE XXX
Inf. dental vein
Inf. dental art.
Inf. dental nerve
it. pterygoid
Mylo-hyoid nerve
uecal vein
,Great hyo-glossus
tylo-glossus
Lingual nerve
Infra-orbital nerves
.Levator labii sup. proprius
Sublingual gland
ylo-byoideus
Parotid gland
Subscapulo-hyoid
Int. pterygoid'
Genio-hyoideuj
Dr^n kfraiwd \>y W i. A K .lohi>«toii EdmVurpi fc Lon.lw
CANITY OY THE MOTJTH.
-ocr page 81-
DISSECTION OF THE ANTERIOR LIMB.                                  31
1 ortant, as it is tho nervo which is cut in the lower operation of
eurotomy when performed for navicular arthritis. The middle is the
uestartd most irregular, and all three branches are in close relation-
shlP with the digital vessels.
Tl i
18 Anterior branch descends in front of the vein, distributes cutane-
wanches to the front of the digit, and terminates in the coronary
cushion.
he Middle branch, which is small and irregular, descends between
artery and vein. It is generally, as in Plate 9, formed by the
n Of several smaller branches which cross forwards over the artery
re uniting- and it terminates in the sensitive laminae and coronary
cushion.
. i -Posterior branch lies close behind the arteiy, except at the fetlock,
"e the nerve is almost superposed to the artery. It accompanies the
&* al artery into the hoof, and passes with the preplantar branch of
W- Vessel to De distributed to the os pedis and the sensitive lamina).
m the hoof it gives off several branches, which for the most part
' °mPauy the arteries.
_ he External Plantar Nerve (Plate 9). This is formed by the
, a or the termination of the ulnar nerve with one of the terminal
of            °^ *ne median. These two branches unite at the upper border
to i . Plsiform bone, beneath the middle flexor of the metacarpus.
tP                carpus the nerve inclines downwards and outwards, in the
re of the annular ligament that completes the carpal sheath. In
on «. caipal region it occupies, on the outside of the limb, a position
0          nexor tendons analagous to that of the internal plantar nerve
onl ° llls^e- Unlike the latter nerve, however, it is accompanied by
j a single vessel—the external metacarpal vein, which lies in front of
tli n. ln°k or niore above the button of the splint bone it is joined by
ique branch from the internal nerve. In the higher operation
1a, \ 10tonry it is cut at the same point as the inner nerve. At the
sj .. W1e sesamoid bones it divides into three digital branches, exactly
Tv.        those of the internal nerve already described,
tern P antar nerves give filaments to the lumbricales and interossei
sj and to the suspensory ligament,
foil • ow&—The student must now pursue the dissection of the
yjz 8 muscles which have already been dissected in the fore-arm,
limV,        extensor pedis and extensor suffraginis on the front of the
tw'         ^he superficial and deep flexors behind. In addition to these,
to
j, . ne lumbricales and interossei muscles, which entirely belong
°ver, e»10n; and, as they are of small size, and might easily be
Tl ° t tlleir ^is8eoti°n must be first undertaken.
hum,0 i rBRI0ALEs Muscles (Plate 9) receive their name in the
1 net, from their resemblance to a common earthworm. In the
-ocr page 82-
PLATE XXXI
Great coron of hyoid
Buixnl nerve,         Inf. dental nerve
Mylo- hyoid nerve
Guttural pouch
• and temporal
Nerve to int.l
'X Pterygoid/'
Tensor palati
Pterygo-pharyngeus
Lingual nerve
Great hyo-glossus
Stylo-glossus
^            /            Genio-glossus
^wp. ^v        -~^,si»-                 7*--. Wharton's duct
Subzygomatic nerve
Int. maxillary art...
7th nerTev
Superf. temp. artv
Ext. carotid art..
Occipito-styloid.
Stylo-hyoid.
Digastricus, upper belly_
Stylo-maxillaris ..
Submaxillary glands
Crico-pbaryngeus
Thyroid body
Thyro-pharyngeus
Subscapulo-hyoideus
Thyro-hyoideus
Pliaryngeal art.
Submaxillary artJ
Submental art.
CAVITY OF THE MOUTH, PHARYNX, Etc.
Brawn JtPrYtued l>y"W kA K.John«wn, Edmonrgh fc London
-ocr page 83-
32
THE ANATOMY OF THE HORSE.
horse they are of small but very variable size. Frequently they contain
but little muscular tissue, but now and again a subject is met iu which
they are very distinct. They are two in number, one being placed on
each side of the deep flexor tendon, above the fetlock. The fibres of
the small muscular belly arise from the side of the deep flexor, and
terminate in a small tendon which is lost in the tissue beneath the
horny spur of the fetlock.
The Interossei Muscles (Plate 9). These are the representatives
of the muscles which, in the human hand, fill up the interspaces of the
metacarpal bones, and give lateral movement to the fingers. In the
horse they are two in number, and are extremely rudimentary. Each
is to be sought to the inner side of the small metacarpal bone of its
own side, between that bone and the edge of the suspensory ligament.
Each has at its upper end a small muscular belly taking origin from
the neighbourhood of the head of the small metacarpal bone. It is
succeeded by a long, slender, nerve-like tendon, which at the fetlock
blends with the band sent from the suspensory ligament to the extensor
pedis tendon, or with the connective-tissue on the side of the joint.
The interossei and lumbricales muscles are of great interest to the
comparative anatomist, but, from their small si/e, they can have no
appreciable effect on the movements of the digit.
The Tendon of the Extensor Suffraginis (Plate 7) is to be followed
from the point below the carpus to which it has already been dissected.
The flat tendon, after crossing the carpus, descends to the outer side
of the anterior surface of the large metacarpal bone. As it passes over
the fetlock-joint, it becomes somewhat broader, and its play over the
anterior ligament of the joint is facilitated by means of a small synovial
bursa. Immediately below the joint it is inserted into the fore part of
the upper end of the first phalanx. In the region of the metacarpus
the tendon receives on each side a reinforcing band. The outer band
comes from the external side of the carpus; the inner is detached from
the extensor pedis tendon.
Action.—The museie is primarily an extensor of the digit on the meta-
carpus. When contraction is carried beyond this, it extends the meta-
carpus on the fore-arm.
The Tendon of the Extensor Pedis (Plate 7). This tendon, after
throwing off the slip to the extensor suffraginis, descends over the front
of the metacarpus and digit, and lies on the middle line. Its play over
the anterior ligament of the fetlock is facilitated by a small synovial
bursa; while, over the front of the interphalangeal joints, the synovial
membrane is directly supported by the deep face of the tendon, there being
no anterior ligament for these joints. At the middle of the first phalanx
the tendon is joined on each side by a strong band which descends
obliquely over the side of the fetlock from the suspensory ligament-
-ocr page 84-
PLATE XXXII
Ant. auric.art.
Upper end of great conn
Oceipito-styloi<
Occipital art.
Guttural pouch
Transv. facial art.
Post, auric.art.
Int. maxill. art.
Inf. dental art.
Eustachian tube
Levator palati
TenBor palati
Hyo-pharyngeus
Stylo-pharyngeus
Pterygo-pharyngeus
Palato-pharyngeus
Cerato-hyoid
Great hyo-glossus, turned upwards
Sup. laryngeal nerve
Int. carotid art.
10th nerve„
11th nerve
Cervical cord of)
sympathetic nerve •
Palatoglossus
Stylo-gloss\is
Genio-glossug
Genio-hyoidens
Mylo-hyoideus
Mid. hyo-glossus
Inter- cornual joint
Glossal process
Lingual art.
ubmental art.
ubmaxillary art.
Common carotid art.
Ext. carotid art.
Thyroid body
12th nerve
Crico-pharyngeuK
Thyro-pharyngevis
ThTto-hyoideOn
llra-Km It Printed Vy W. tA K Johmton IdinVuT^h fc Louden
TONGUE, PHARYNX, Etc.
-ocr page 85-
DISSECTION OF THE ANTERIOR LIMB.
33
Tl
pedis end°n ^ finally inserted int0 the pyramidal process of the os
Action,.-
Phalanx
-The first action of the muscle is to extend the third
*« second on the first.
d, and then
+ . — —1 the first. When con-
^ a°tion is continued, it produces
uccessively extension of the fet-
lock
and of the carpus.
, ~*reetions.~The tendons on the
ack of the metacarpus and digit
^ Ust next be dissected; and as
arid1*61"11"™17 Step' the oarPal<___
for metaoarP°-phalangeal sheaths
»ied in connection with these
ei«Ions should be examined.
tul 1 °ARPAL Sheath (Fig. l)is the
fle nlar passage through which the
xors of the digit are transmitted
Und the carpus. It is formed
trout by the back of the carpus
covered I 4.1
j.            uy the posterior common
jjf^ent of that joint. Behind it r,
th nded in its outer third by
t\ve P*Slform b°ne, and in its innerR ''"
reD°" h by a stroug fibrous baud S'6
1 resenting the anterior annular
b™^ °f the human wrist This
<* stretches like an arch from
°f «* carpus
ne to the inner side
It is continuous
back Wlth tne deeP fescia on the
may f  the fore-arm, of. which it
DrlJ-          considered a thickened
1 ortion •          lii
thii '    an "elow it becomes
lllei',   and is continued
as the
'asCla
011 the back
car
------ of the meta-
„' 1Us (palmar fascia of man).
Fig. 1
Uo «*pal sheath is
provided with
•1)l
:SSECTION OP
the Metacarpus and Digit, showing the Tendons and their Synovial
Sheaths (Chauveau)
' Syno
S?,?V,ial m«mbranf nf°«the e*t™s°r metacarpi magnus; 2. Superior eul-de-sew, or pouch, of the
Cff^ovia membf        ^rpal sheath ; 2', 2'. Inferior part of the same ; 3. Pouch of the radio-
"ynoviaf"nV'"'?-°arl»l ligament;
jovial mem jbrane of the letl°
sy the reir.ov.,ir'l?!,of tlle metacarpo-phalangeal sheath ; !
p.!bc'»Tal Hai°t the reinforcing sheath of the perforans t........_____„___„„ ,™_,. 0
"• *le-xor perforaaV- F PV S,™301' Vfis ' S' S' SuPerior sesamoidean (suspensory) ligament; F.
-ocr page 86-
PLATE XXXM
Great longitudinal fissure between
hemispheres of cerebrum
Olfactory bulb
-v.            Olfactory Peduncle
Int. olf. tract
Optic (2nd) nerve
Optic chiasm*
Pituitary bod;'
Ext. olf. t"1'1
lnfundibulum
Tuber cinereum.
jrd nerve
4th nerve
J2 int. root \
■j&rt. root>
Mof5threrV«
6th nerve
7th nerve
Cms cerebri
Great oblique
fissure ^B^
Pons Varolii
Trapezium
lateral lobe
of cerebellum
12th nerve
Medulla oblongata
I in natation of pyramids
Inf. pyramid
&PriT.^a V? V LJk X Jol B««                           :.Llondon
BRAIN—Inferior Aspect
-ocr page 87-
34
THE ANATOMY OF THE HORSE.
a synovial membrane, which lines it, and is reflected over the flexor
tendons to facilitate their gliding. If the fibrous band just described be
cut, and a probe be passed upwards and downwards within the sheath,
an idea of the extent of the synovial sac will be gained. It will be
found to extend upwards for two or three inches above the carpus,
and downwards as far as the middle of the metacarpus.
Directions.—The fibrous band should be entirely removed in order to
permit the examination of the tendons, and of the nerves and bloodvessels
which accompany these within the sheath.
The Metacarpo-phalangeal or Great Sesamoid Sheath (Fig. 1). This
is a second synovial apparatus developed in connection with the flexor
tendons. If a vertical incision be made through the superficial flexor just
above the fetlock, and a probe passed into the incision, it will enter the
synovial cavity, and may be pushed upwards for two or three inches
above the fetlock, and downwards as far as the middle of the second
phalanx. The synovial membrane lubricates the pulley-like surface
formed by the sesamoid bones and the inter-sesamoid ligament, and is
reflected on to the tendons. It is supported laterally by a fibrous
expansion which, adhering to the superficial flexor behind, is inserted
in front by three slips on each side, the highest insertion being into the
sesamoid, and the other two into the first phalanx. At its lower extremity
this synovial membrane meets that of the navicular sheath, and in front
of the same point it is separated from the synovial capsule of the coffin-
joint by a kind of partition of yellow fibrous tissue connecting the front
of the perforans tendon to the back of the os corona) (Plate 10, fig. 2).
The Superficial Flexor tendon (Plates 5, 9, 10, and 11). The
tendon succeeds the fleshy portion of the muscle at the lower part of the
fore-arm, and it is there reinforced by a fibrous band which springs from
the back of the radius and is sometimes termed the superior carpal ligament,
in contradistinction to the band which reinforces the tendon of the deep
flexor below the carpus. The tendon passes through the carpal sheath
in company with and behind the deep flexor, and then descends behind
the metacarpus. Having arrived at the fetlock, there is formed in it
a remarkable ring, through which the tendon of the deep flexor plays.
It is in consequence of this arrangement that the superficial muscle is
termed perforates, and the deep one perforans. As already seen, the
tendons are here enveloped by the synovial membrane of the meta-
carpo-phalangeal sheath. At its extremity the tendon is bifid, and
each slip is inserted into the upper extremity of the second phalanx on
its lateral aspect.
Action.—The muscle flexes successively the pastern, fetlock, and
carpal joints.
The Deep Flexor tendon (Plates 5, 9, 10, and 11) is, through-
out its course, closely related to the preceding, in front of which it lies.
-ocr page 88-
PLATE XXXJV
(Jreat longitudinal fissure between
hemispheres of cerebrum
Crucial fissure.
Crucial fissure
•total fi*"
Lateral lobe of
I cerebellum
Middle lobe of
I cerebellum
Medulla oblongata
v Printed oy ^ 1A K Jolmium Edinburgh fc London
Bit AIN—Superior Aspect
-ocr page 89-
DISSECTION OP THE ANTERIOR LIMB.                                    35
* C1 escellding through the carpal sheath, it is joined by a very strong
Us band—the inferior carpal ligament, which is the down ward continua- j
, °* the posterior common ligament of the carpus. This fuses with I
tendon about the middle of the metacarpus, and it is of consider-j
t< lmportance, being frequently involved in what is commonly termed
Plain of the back tendons." In that condition it may be very distinctly
r,, y Manipulating in front of the flexor tendons, just below the carpus,
tendon, as thus reinforced, descends between the suspensory liga-
,. m front, and the perforates tendon behind; and at the fetlock it
b es over the sesamoid palley, and passes through the ring of the
1 einoial flexor. It then passes between the terminal branches of the
-mentioned muscle, glides over the smooth surface on the back of
second phalanx, plays over the navicular bone, and finally becomes
• "> ted into the semilunar crest of the os pedis. The terminal portion
ne muscle, as well as the navicular sheath developed in connection
!t, will be examined with the parts contained within the hoof.
etion.—The muscle flexes successively the interphalangeal joints, the
IetI°ck, and the carpus.
THE FOOT.
Di
the
Sections.—By the term foot, as here applied, is meant the hoof and
parts contained within it. If it is intended to study this in a limb
wnole of which is to be successively dissected, the student must
ed in the following manner. When the dissection of the fore-arm
°een completed, and before the removal of the skin from the nieta-
I us and digit, the hoof must be forcibly removed by the aid of a
^ng-smith's hammer, toe-knife, and pincers. To facilitate this, the
may be heated in a fire, the skin of the digit being swathed in a
th i *° Prevent charring. This is the speediest method of removing
°oi, but it has the double disadvantage of destroying in great
tl + u ^e ^00^ i*self> ar,d also tne injection of the vessels, provided
, as been executed. The following is a preferable method of pro-
,• ■ -^Procure a foot severed a few inches above the fetlock, and
inject tb
j . , ne arteries and veins from the metacarpal vessels. When the
.         °n has solidified, roll the foot in a piece of wet cloth, and bury it
rermenting heap of stable manure. Decomposition will speedily
> and after a week the preparation should be examined at intervals
for 'i °r ee days, the metacarpal bone being fixed in a vice while
eg. e attempts are made to pull off the hoof. When this has been
sat ' ne foot and removed hoof should be immersed for a day in a
s. • .         solution of carbolic acid in water, to which a little methylated
v . may be added. This will speedily remove all odour of decom-
Th °n' and dissection maytnen be proceeded with.
bar. !,           (Plate 10. ngs- 4 and 6). This is made up of the wall, the
m> Resole, and the frog.
-ocr page 90-
PLATE XXXV
Olfactory bulb
Septum lucidum
Corpus callosum
ly of fornix
orpus striatum
Choroid plexus
Taenia hippocampi
ippocampus
Nates
Testes
Ant. ped. of cerebellum
Mid. ped. of cerebellum
Post. ped. of cerebellum
8th nerve
4th ventricle
Medulla oblongata
Cerebellum
IfcPnntM W W. JcA K Johnston Edinburgh IcLondon
BRAIN—LATERAL AND 4TH VENTRICLES, Etc.
-ocr page 91-
THE ANATOMY OF THE HORSE.
3G
The Wall is that part of the hoof which is exposed when the foot
rests in its natural position on a flat surface. It is divided, though
not by any well-defined boundaries, into toe, quarters, and heels. The toe
includes an area on each side of the middle line of the wall in front;
and it passes on each side into the quarter, which comprises the lateral
region of the wall. Posteriorly the wall changes its direction, and
disappears from view, forming an angular part, which is termed the heel.
In reality, the wall does not stop at the heel, and it is this concealed
continuation that is termed the bar. In a well-formed hoof the wall in
the region of the toe slopes at an angle of about 50°.
The External Surface of the wall is, in a state of nature, covered by a
kind of epithelial varnish termed the periople, which is thickest at the
top of the wall, just under the hair. This, which is a natural varnish
provided to check evaporation and consequent cracking of the subjacent
horn, is generally rasped away by the shoeing-smith. The internal sur-
face of the wall is traversed in a vertical direction by the series of horny
lamince. These number about five or six hundred; and before, separa-
tion of the hoof they were interleaved with the sensitive lamina; to be
presently described. The superior border of the wall shows a kind of
gutter, termed the cutigeral groove, which is the mould left by the
coronary cushion. The floor of this groove has a closely punctated
appearance, each minute perforation being the upper end of one of the
horn tubes of the wall, and lodging, in the natural state, one of the
papilla: of the coronary cushion. The inferior border embraces the
sole, and in the unshod animal comes into contact with the ground.
The wall is thicker at the toe than at the quarters or heels; and in
each of these areas, it is thicker on the outside than in the correspond-
ing area on the inside.
The Bars. These are the reflected terminations of the wall behind the
heels; and if the foot be turned up, the continuity will be distinctly seen-
The Outer Surface of the bar, which is here seen, slopes towards the
frog, and bounds outwardly the lateral lacuna of that body. It shows
an inferior border, which runs towards the centre of the sole, but stops
a little behind the point of the frog. The bars are also seen in the
interior of the hoof, where ^hey show an internal surface bearing horn}'
lamina: like those of the wall. The superior border of the bars is
included between the frog and the sole, and blended with them.
The Sole presents an inferior face, which is vaulted, and this inde-
pendently of any paring to which the foot may have been subjected, as
the horn of which it is composed exfoliates so as to give it this con-
figuration naturally. The superior face is somewhat convex, and has
a&punctated appearance similar to that already seen in the cutigeral
<>Toove. The minute holes lodge the papilla of the so-called sensitive
sole which is the horn secreting structure of this region. Anteriorly
-ocr page 92-
PLATE XXXVI
Corpus striatum
"edunole of pineal body,
Body of fornix
Ant. pillar of fornix
Ant. )
Mid. V commissure
Post, j
P ineal body
Nates
Testis
£nV 1 peduncles of the
_&£) cerebeUum
8th nerv.
Floor of 4th ventricle
—Medulla oblongata
-. A K Johnston. Edbibur^h feLondoj
BRAIN—GANGLIA OF THE BASE
-ocr page 93-
DISSECTION OF THE ANTERIOR LIMB.                                    37
e sole presents a convex border, which unites it intimately to the
., r b°rder of the wall, a line of whitish horn marking the junction of
e two structures. Posteriorly it has a deep V shaped indentation,
0 the central point of which the frog penetrates, while behind that on
each side it is related to the bar.
_ «e sole of the hind hoof is distinguished from that of the fore by
Ulg more vaulted, and by being more pointed (less circular) at the toe,
s latter difference affecting also the form of the wall in the same
»ion. The outer edge of the sole is more convex than the inner,
rlcn enables one to readily distinguish between a right and a left hoof.
bs Frog. This is a distinctly elastic mass of horn which, in a state
mature, projects sufficiently to come into contact with the ground,
thus give the animal a secure foothold. Its inferior surface shows
■ eriorly a shallow cleft, or depression, termed the median lacuna,
lateral lacuna? lie at the sides of the frog, the outer boundary of
lacuna being formed by the bar. The superior surface shows,
ically over the median lacuna, a projection termed the frog-stay.
ach side of the frog-stay this surface is depressed, and the whole is
ued on the plantar cushion. This surface is punctated, and the
TV,         °^ *ne Pumtar cushion are received into the minute apertures
Posterior extremity, or base, of the frog consists of two rounded emi-
1         " the bulbs, or glomes—separated from each other by the median
a- The anterior extremity, or point, is wedged into the centre of the
tV,               lateral borders bring the frog into relation with the bars and
„~ ° e> and there is an intimate union with each of these at the point
ot contact.
"& nute Structure of the hoof. The entire hoof is an a»»regation of
e ., a epithelial cells, which here represent the horny layer of the
ex 1I111S" When a thin section across the wall, sole, or frog is
of +m *fte uom substance is seen to be arranged in the form
Co *. • ' cemented together by an mtertubular substance, and
aii ' & within their lumen a quantity of intratubular material.
ui Tc          —tubular, intertubular, and intratubular—are composed of
of h epithelial cells, differing in the three situations in the direction
c . eells, their state of aggregation, or the presence or absence of
par u1Iled P^ent- The tubes of the .vail are straight, and extend
toon *' to the surface, from the coronarv to the inferior edge of the
" ai] Tii                          '                                   "                                    °
ft' ine tubes of the sole have the same disposition, but those of the
ailb1aie lightly flexuous. The upper end of each tube is occupied by
the n*=ate<* vascular papilla, which belongs, in the case of the wall, to
the • 011ai'v cushion ; in the periople, to the perioplic ring; and in
Kl. . e ana- frog, to the sensitive structures of the same names. In the
(wli' 8          tae 1joucl °f connection between these papillated surfaces
iepresent the eorium of the skin) and the corresponding part of
-ocr page 94-
PLATE XXXVII
;.\
Testicle
hf--------Septum scroti
Tunica vag. reflexa
Cremasteric fascia-
/ Dartos
Infundibuliform fascia
Spermatic fascia
Corpus cavernusum
Semimembranosus
\
Erector penis
Int. pudic art.
Sphincter ani ext.
\
\
V
I>ra.HTi ^Printed "by"W. StAl Johnston. Edinburgh fcLondon
MALE PERINEUM
-ocr page 95-
38                                   THE ANATOMY OF THE HORSE.
the hoof, is a stratum of soft protoplasmic epithelial cells by whose
growth and multiplication the hoof-horn is formed. This stratum of
cells represents the deepest cells of the rete mucosum in the skin, and
it is by its ready decomposition that the bond of connection between
the sensitive and insensitive structures is destroyed, permitting the
extremity of the digit to be extracted from its horny investment.
Directions.—The student should next turn his attention to the ex-
tremity of the digit as exposed by the removal of the hoof, and he will
find it to present a configuration not unlike the exterior of the hoof itself
(Plate 10, figs. 1 and 5). And in the first place, let him examine that
part which he will easily recognise as having been separated from the
inner surface of the wall. This is traversed by a series of leaves which,
in contradistinction to those already seen on the inner surface of the
wall, are termed the sensitive lamina?, and sometimes the podophyllous
tissue.
The Sensitive Laminae. Each lamina is fixed by one of its borders to
the periosteum of the os pedis, and extends in a vertical direction from
near the coronary cushion to the sharp edge of the bone, where it
terminates in five or six long papilla). In the natural state the sensitive
and the horny laminae are interleaved, and the former hero represent
the corium, or true skin. The lamina), it will be noticed, become pro-
gressively shorter as they are traced backwards ; and at the end of the
series on each side, and adjacent to the plantar cushion, there is a number
of small leaves that were interleaved with the horny lamina) of the bars.
The Coronary Cushion. This is a projecting, cornice-like structure,
placed above the laminse and below the limits of the skin of the digit.
It fits into the cutigeral groove at the upper border of the wall, and its
surface is closely set with long papilla) which were received into the
apertures found in that groove. These papilla) give the coronary
cushion a velvety pile, which may be rendered very evident by immers-
ing the foot in water. If the coronary cushion be traced backwards, it
will be seen to pass into the plantar cushion. Above the cushion is a
narrow groove separating it from the periopolic ring. Below the cushion
there is a narrow smooth space which runs between the cushion and the
sensitive lamina). The coronary cushion is a modified portion of the
corium, and through the agency of the cells which cover the surface of
its papilla), the wall of the hoof is formed.
The Perioplic King. This ring is composed of papilla) like those of
the coronary cushion, but smaller in size ; and it is by its agency that
the perioplc which covers the exterior of the wall is formed.
The Plantar Cushion. This is a fibro-elastic pad interposed between
the horny frog and the terminal part of the perforans tendon. It
possesses two faces, two borders, a base, and an apex. The lower face
looks backwards as well as downwards when the foot rests on a flat
-ocr page 96-
PLATE XXXVIII
Panniculus oarnosus
Abdominal tunic
.Subcutaneous thoracic (spur) vein
%
5
/
V
Subcutaneous abdominal art
Superficial inguinal glands
y
T'ti. n fc PnnLed by "W fc.A K.JoTra*t'R. Ertuiburgl. I
AKDCMTNA1., WALL.
-ocr page 97-
V
PLATE X.
'ig. I.—The Digit with the Hoof removed, flexed and viewed from behind.
F m, ns*tive sole ; B. Sensitive laminae that were interleaved with the horny laminfe of the bar ;
S;ln # Pyramidal body, or sensitive frog ; L. Lateral lacuna of the same ; M. Median lacuna of the
foi-if ' Fibrous sheath uniting the two branches of the perforatus ; R. Branches of the per-
pei'f l"1)assino to be inserted into the os coronae ; T. Tendon of the perforatus ; T. Tendon of the
Plant'nS ln *tS Pass:iSe between the branches of the perforatus ; V. Reinforcing sheath of the
** aponeurosis ; X. Attachment of the same to the side of the os suffraginis.
Fig. II.—Vertical mesial Section of the Digit.
F. p, ,, S Pedis; B. Coronary cushion; C. Coffin-joint; D. Navicular bone; B. Os coronse;
Boron          J0^ ; H. Branch of the perforatus at its insertion into the lateral aspect of the os
Perfn ■■■ ' Insei'tion of the plantar aponeurosis into the semilunar crest; K. Os suffraginis ; L. The
Perf . US *,ent^on » M. Ligament of yellow fibrous tissue which unites the anterior face of the
ses;i ' s to the posterior face of the os coronae, and separates the inferior cul-de-sac of the great
syUov' \ B"eafck from that of the synovial membrane of the coffin-joint; N. Protrusion of the
0, a, .' membrane of the corono-pedal joint between the navicular bone and the os pedis;
gteft* ■ aesamoid sheath ; P. Synovial membrane of the coffin-joint in contact superiorly with the
°f the' arriol(l sheath, from which it is separated by the yellow transverse ligament M. ; T. Tendon
Perforans ; y. Fetlock-joint.
Fig. III.—Arteries of the Digit.
(rameo ^1*a^ artery; C. Perpendicular artery at its Origin; H. One of the posterior branches
°f tli i ",e^onn^s)i for the perforans tendon ; J. Another of the same ; K. Origin of the artery
^ariie ■ ' ar cushion ; M. Origin of anterior branch of coronary circle ; M.' Posterior branch of the
Pedis f ' Origin of preplantar artery ; S. Plantar artery in the plantar groove and in the os
the H*. .I1Ulne with the opposite artery the semilunar anastomosis ; V. V. Descending branches from
^ttitnnar anastomosis.
Fig. IV.—The Hoof—plantar aspect.
B. ,\ " ^S*0* of the toe ; S. Sole ; L- Frog; A. Line indicating the junction of wall and sole ;
of t*j *™ of inflexion of the wall, showing the continuity of the wall and the bar ; E. Inferior edge
g■"* bar ;F. Lateral 1 acuna of the frog; G. Bulbs of the frog ; Q. Median lacuna of the frog;
egwns of the quarters ; O. Eegions of the heels.
£■ V.—Extremity of the Digit with the Hoof removed—viewed from the side.
• Plantar cushion with its villosities ; D. Groove between the plantar cushion and the
Per
Podo i, n* ' ^' Per'°luic iin? < P- Inferior border of the plantar cushion ; G. Sensitive lamina,
P yllous tissue ; H. Villosities which terminate the laminae.
or
**B- VI—Anteroposterior mesial Section of the Hoof—showing its interior.
l'«rio d""08 °' llorny laminse ; O. Section of the wall; P. Section of the sole ; S. Upper edge of the
1' e above the eutigeral groove ; T. Section of the frog ; X. Cutigeral groove.
-ocr page 98-
PLATE XXXIX
External oblique muscle
-^^                      Serratus magiras
Poupart's ligament
Spermatic cord
Ext. abdominal ring
\ J
(4 Lr*~ a
Aiffbcutaneous abdominal art.
^MSlx. pudic art.
^f^M>t. dorsal art. of penis
Umbilicus
Drwn kPnntei by W &A.K JoTm^ton. Edinburgh fc T.unJoi
ABDOMINAL WALL
-ocr page 99-
40
DISSECTION OF THE ANTERIOR LIMB.
surface; and it is moulded on the upper face of the homy frog, to which
it has a close resemblance in form. The central portion of the cushion
is therefore sometimes termed the sensitive frog, and it is also known as
the pyramidal body. It shows in front a single ridge, which posteriori)7
becomes divided into two by a deep median cleft for the reception of
the frog-stay. This surface has a villous aspect, the papilla? being
imbedded in the foramina seen on the upper surface of the horny frog.
The horny frog is formed by the agency of the cells covering these
papilla;. The upper face looks forwards as well as upwards, and is
applied to the reinforcing sheath of the deep flexor tendon. The
borders, which are right and left, bring the plantar cushion into relation
with the inner surface of the lateral cartilages. The apex lies in front
of the semilunar crest of the os pedis, with whose periosteum the tissue
of the cushion is intimately blended. The base of the cushion consists
of two thick rounded masses termed the bulbs of the plantar cushion.
These are continuous in front with the ridges of the pyramidal body,
and they present the same velvety aspect; while, on each side, the
villous tissue joins the extremities of the coronary cushion.
The Sensitive Sole. The student should next examine that part of
the foot which, before separation of the hoof, came into contact with
the upper surface of the horny sole, and which for that reason is termed
the sensitive sole. It is of a roughly crescentic form, being penetrated
by the pyramidal body behind; and it is co-extensive with the plantar
surface of the os pedis. Its connective-tissue basis is firmly adherent to
the periosteum of the bone, while its free surface bears long papilla)
which penetrate the horn tubes of the sole. The horny sole is formed
by the agency of the cells which clothe the papillae of the sensitive sole.
Directions.—On manipulating the bulbs of the plantar cushion, the
student will feel the .lateral cartilages of the foot; and one of these is
to be exposed and defined by removing one half of the plantar cushion.
The Lateral Cartilages. These are in the main composed of
hyaline cartilage, though often erroneously termed the fibro-cartilar/es of
the foot. As is common with fibro-cartilage in many other regions, it
shows a transitional structure at its periphery, where its matrix becomes
more or less fibrous. Each plate of cartilage possesses two faces, and
four borders separated by four angles. The external face is convex and
covered by a plexus of veins, some of which penetrate the plate and
connect the plexus with another lying beneath it. The internal face is
concave. Behind it is united to the plantar cushion, while anteriorly
it protects the corono-pedal articulation; and a cul-de-sac of the synovial
membrane of the joint lies in direct contact with the cartilage, a fact
which it is important to remember in connection with operations for
"quittor." The superior border is thin and flexible, and may be felt in
the living animal. The digital vessels cross this border in passing into
-ocr page 100-
PLATE XL
Poupart's ligament
Spermatic cord
Ext. pudic artery
Post, abdominal artery (under tendon)
Obliquus abdominis int.
An intercostal nerve
Transversalis abdominis
°riTK*d bj w tA K luhn.wn Y.<\.'
ABDOMINAL WALL
►
----------------
-ocr page 101-
THE ANATOMY OP THE HORSE.                                   41
oot. The inferior border is supported by the wing of the os pedis in
ll, while posteriorly it blends with the plantar cushion. The anterior
(er slopes downwards and backwards, and is blended with the antero-
■*i ligament of the corono-pedal joint. The posterior border is parallel
anterior, and is covered by the plantar cushion. The four borders
a^ *°ur anglesi of which the postero-superior one and the one diago-
y opposite are obtuse, while the other two are acute.
i^        disease termed "Side-bones," the lateral cartilages lose their
_, Vj in consequence of their conversion into bone.
. -fhe Bloodvessels of the Foot (Plate 10, fig. 3). These should be studied
n injected limb from which the hoof has been removed by the method
decomposition described at page S5. The arteries of the foot are
lved from the digital artery, which has already been dissected in its
' cent towards the foot, where, within the wing of the os pedis, it
^ cles into the plantar and preplantar arteries. Some of the collateral
c ches of the digital artery have already been described at page 29; but
e remain for examination the artery of the plantar cushion and the
rnT**y circle, as well as the plantar and preplantar terminal branches.
e Artery of the Plantar Cushion arises from the digital, just as
' "Vessel passes within the upper border of the lateral cartilage, and
• ses obliquely downwards and backwards to its destination. Besides
if 1 Jing the plantar cushion, it gives off a branch which turns forwards
Ucur in the formation of the circumflex artery of the coronary
ri-n
_» e Coronary Circle. Where each digital artery lies under cover
WV' i! eral cartilage, it gives off an anterior and a posterior branch
s          mosculate on the middle line before and behind with the corre-
T] ■ m^ branches of the opposite side, and thus form an arterial circle.
, circle closely embraces the os corona;; and among the largest
ai 'l j furnished by it, are two which emanate from its anterior half,
in ,,esccu^> 011e at each border of the extensor tendon, to aid in form-
rp, e cu'cumflex artery of the coronary cushion,
a si G CDMFLEx Artery of the Coronary Cushion (Chauveau). This is
Avi . er vascular arch placed immediately above the coronary cushion, to
Hie r ltS ^rancnes arc distributed. It is fed in front by the two above-
th- l °Ue vcssels from the coronary circle, and behind, on each side, by
ore-mentioned branch from the artery of the plantar cushion.
0f ,, replantar Artery is the smaller of the twTo terminal branches
°s n i. ^ital- I* passes forwards through the notch in the wing of the
that 18' aUC*tllen a^ouo tne preplantar groove on the laminal surface of
ne, where its branches are expended in the sensitive laminee.
for          lANTab Artery passes along the plantar groove to enter the
Co * 1 ° tnc same name. Within the os pedis it inosculates with the
ponding vessel of the opposite side, forming the plantar arch, or
-ocr page 102-
PLATE XLI
Pelvic flexure
Colon (3rd part)
Colon (2nd part)
Direct colic art,
—Retrograde colic art.
iaphragmatic flexure
Suprasternal flexure
Colon (4th part)
Post, aorta
-1st art. to single colon
/Ant. div. of ant.
(mesenteric art.
j Arteries to small
intestine
Duodenum
Small intestines
Ilio-caecal ait.
Ileum
Art. of the arch
Bight division of ant.Aj
mesenteric art.
Cseeuni
Sup. csecal art.
A m
Great
mesentery
Pnnttd by"W. StA.K. John«wn. EdinVur^h fe Lon3o]
INTESTINES AND ANTERIOR MESENTERIC ARTERY (Chauveau)
-ocr page 103-
42
DISSECTION OF THE ANTERIOR LIMB.
semilunar anastomosis. From this intra-osseous arch a great numler of
branches proceed. An ascending {anterior laminal) set of these leave
the os pedis by the numerous small foramina which cribble its laminal
surface. A descending {inferior communicating) set escape from the
bone by the series of larger foramina which open on the sharp edge
separating its laminal and plantar surfaces. These inferior communi-
cating arteries anastomose right and left with each other, and thus form
the circumflex artery of the toe. From the concavity of this artery
branches pass backwards, and supply the tissue of the sole.
The Veins of the Foot.—Intra-osseous vessels. Within the os pedis
the arterial branches are accompanied by satellite veins. There is
thus a semilunar venous anastomosis, to which small veins converge
from the laminal surface of the bone. The blood from this sinus is
drained away by a larger vessel which passes out by the plantar fora-
men in company with the plantar artery, and joins the posterior part of
the coronary plexus. Extra-osseous vessels. The foot is richly provided
with a superficial system of vessels, which are arranged in the form of a
close-meshed network having little or no communication with the deep
set. This venous envelope of the foot is divided into a solar, a laminal
(podophyllous), and a coronary plexus. Where the solar and laminal
plexuses meet, a composite venous vessel runs in company with the
circumflex artery of the toe. These two plexuses communicate freely
with each other, and with the coronary plexus. This last consists of a
central part, which underlies the coronary cushion, and of two lateral
parts, which on each side ramify on both surfaces of the lateral cartilage.
By the convergence of branches belonging to this cartilaginous division
of the coronary plexus, the digital veins are formed; and these drain
away the blood from both the intra-osseous and extra-osseous systems
of vessels.
Directions.—The terminal portion of the deep flexor tendon, and the
synovial apparatus developed in connection with it, should now be
examined.
The Deep Flexor tendon (Plates 10 and 11), when it reaches the
upper border of the navicular bone, widens out to form what is called the
plantar aponeurosis. This plantar aponeurosis plays over the navicular
bone by means of the navicular sheath, and is covered posteriorly by a
fibrous layer which ultimately blends with it. It becomes inserted into
the semilunar crest of the os pedis, and into the bone behind that crest.
The above-mentioned fibrous layer was first described by Bouley, and
designated by him the reinforcing sheath of the perforans. This expansion
is attached on each side by a slip to the lower half of the first phalanx,
and it serves to maintain the plantar aponeurosis against the navicular
bone.
The Navicular or Small Sesamoid Sheath (Plate 10, fig. 2). This is »
-ocr page 104-
PLATE XLII
Double colon
etrograde colic art.
Direct colic art.
tight fasciculus of ant. mesenteric
Ant. fasciculus of ant. mesenteric
:ft fasciculus of ant. mesenteric
Ant. mesenteric art.
Renal art.
Small intestine
.Colic mesentery
Single colon
Post, mesenteric
artery
Ext. iliac art.
Int. iliac art.
Urinary bladder
P«l
vic flexure-
Printed byV 1.AK Johmtfln EdinVurgh ItLondoi
INTESTINES AND MESENTERIC ARTERIES (Chauveav)
-ocr page 105-
43
THE ANATOMY OP THE HORSE.
' jHovial apparatus developed in connection with the perforans tendon
ere it plays over the navicular bone. It lines the deep face of the
"Clou, and is reflected on to the navicular bone and interosseous liga-
ent. It aiso extends above the navicular bone, where it is in contact
' the synovial membrane of the coffin-joint and that of the metacarpo-
phalangeal sheath.
THE SHOULDER-,) OINT.
"-ais joint is formed between the glenoid fossa of the scapula and the
ot the humerus. It is enclosed by a single capsular ligament
internally by the synovial membrane. The absence of lateral or
ler retaining ligaments in connection with the joint, is compensated
by the numerous tendons which pass from one bone to the other in
, B re^ation to the capsular ligament. These muscles are as follows :—
supraspinatus, infraspinatus, teres minor, biceps, and small scapulo-
oieralig. The last passes over the joint behind, where some of its
es Seem to be inserted into the ligament. In front of the joint the
°n of the biceps is separated from the ligament by a pad of fat.
°\ements.—The joint belongs to the class of enarthrodial or ball-
-socket joints, and the amount of its mobility should be proved by
^UliPulation before the removal of the muscles. If the scapula be kept
> it will be found that the humerus can be carried backwards so as
Wnnish the angle formed by the meeting of the bones. This is a
enient of flexion. Or the humerus can be carried forward in the
Tl ■ p e as in the preceding movement, but increasing the angle.
is
lon either outwards or inwards. When, in the living animal, it
llned inwards, the limb is thrown towards the middle plane of the
y, and is gajd to be adducted. The opposite movement, by which
mb is carried outwards from the middle plane, is termed abduction.
tner movements are permitted in the joint, viz., rotation and
„ i , Auction. In rotation the humerus, without change of place as a
"hole +                                                       •
,        > turns round its own axis. In circumduction the shaft of the
,'Us moves so as to describe the surface of a cone.
a*v_i. 6Se different terms having been here defined at length, their
PPlica+i •
n„ i ' u m the case of the other joints of the body will be readily
Understood)
fr , shoulder-joint of the horse is thus possessed of considerable
the k         m°vement; but still, the range of its mobility, owing to
rrm ■' Sence °f a clavicle, and to the different disposition of the pectoral
> IS much more restricted than in the human arm.
rem %on*-—-The muscles which surround the joint must now be
Th. -i °are '3euiS taken not to cut the capsular ligament.
psular Ligament loosely surrounds the articular ends of the
-ocr page 106-
PLATE XLIII
ight sac of stomach
Left lobe of liver
Pleuro-cesophageal art.
nt. gastric art.
ost. gastric art.
eft sac of stomach
Splenic artery
Left gastro-omental artery
.Gastro-splenic omentum
Spleen
Pyloric art.
Middle lobe of liver
Eight gastro omental art
Right lobe of liver
Duodenal art.
Duodenum
Kidney
Portal vein
Suprarenal capsule
Hepatic art.
Renal artery
Post, vena cava
Urete:
Suprarenal capsule
Kidney
Renal artery
Ant. mesenteric art.
Post, aoi'ta
Circumflex iliac art.
Ext. iliac art.
Int. iliac art.
Prvnt/.d by"W JcAK Johnston Edinburgh & London
CCELIAC AXIS, Etc. (Chauveau)
-ocr page 107-
ii                                  DISSECTION OF THE ANTERIOR LIMB.
bones, and may be conceived as having the form of a double-mouthed
sack, one mouth being attached around the rim of the glenoid cavity,
and the other at the periphery of the head of the humerus. The wall
of this sack is comparatively thin, but in front it is strengthened by
accessory fibres that pass in a divergent manner from the coracoid pro-
cess to the outer and inner tuberosities. These correspond to the
coraco-humcral ligament of man.
Directions.—If, in the removal of the muscles, the ligament has been
preserved perfectly intact, it will be noticed that though a considerable
force be exerted to pull the articular surfaces from each other, they still
remain in contact. If, however, an incision be made in the ligament, the
air will be heard to rush into the joint, while the bones separate to the
extent of half an inch or more. In the shoulder then, as in other joints,
atmospheric pressure is to be included among the agents keeping the
articular surfaces in contact. The capsular ligament is to be slit up so
as to expose the smooth and glistening aspect of the synovial membrane,
and the articular surfaces of the bones covered by articular cartilage.
The Synovial Membrane lines the inner surface of the capsular
ligament. It secretes the synovia, or joint oil, some of which will be
seen escaping from the joint.
THE ELBOW-JOINT (PLATE 11, fig. 1).
This joint is formed by the lower extremity of the humerus and the
upper extremities of the bones of the fore-arm. It possesses two lateral
ligaments, and an anterior ligament which supports the synovial
membrane in front; but behind, there being no ligament, the synovial
sac is directly supported by muscles.
Movements.—This is a ginglymoid joint, the only movements being'
flexion and extension. Inflexion, while the humerus remains fixed, the
bones of the fore-arm are carried forwards until the movement is arrested
by the coronoid process passing into the fossa of the same name. In
this movement the bones of the fore-arm do not move in the plane in
which the humerus lies, but deyiate a little outwards. The opposite
movement is extension, in which the radius and ulna are carried back-
wards until they are arrested by the tension of the lateral ligaments,
and by the passage of the beak of the olecranon into the fossa of the
same name.
Directions.—The anterior and lateral ligaments are to be exposed
and defined by removing the muscles from the front of the joint, but on
the posterior aspect of the joint the muscles should not be removed at
present.
The External Lateral Ligament is a cord-like band which is fixed
superiorly to a depression on the outer side of the lower extremity of
the humerus, and to the ridge which forms the lower boundary of the
-ocr page 108-
PLATE XLIV
Ensiform cartilage
Diaphragm
Falciform lig. of liver
Middle lobe of liver
Left lobe of liver
Right lobe
of liver
Stomach
Ant. gastric art.
Post, gastric art.
.— Spleen
___Splenic vessels
_Suprarenal body
-Ant. mesent. art.
Renal vessels
Left kidney
Poet, aorta
—Ureter
Post, mesent. art.
Circunif. iliac art.
Int. iliac art.
Ext. iliac art.
Artery of cord
— Spermatic art.
—Cremaster m.
Int. abdom. ring
'as deferens
Bight kidney
Post, vena cav;
From last dorsal
Transv. abdom
Aortic plexus
From 1st lumbar nerve
Psoas magnus--------
From 2nd lumbar nerve
From 3rd lumbar nerve-
Int. oblique
Inguinal nerves
yv-v ^
To pelvic plexus
Lateral and inf. ligamon
of bladder
Prepubicart. Rectum
Bladder
Drawn &. Pni.ttd bv V tA K Johnston Edvnonrfh It La
ABDOMINAL VISCERA, Etc.
-ocr page 109-
THE ANATOMY OF THE HORSE.                                          45
isculo-sph-al groove ; while interiorly it passes to be inserted into the
■" ernal tuberosity at the upper end of the radius.
the Internal Lateral Ligament forms a longer but more slender
Cord than the preceding, and passes from a small eminence on the
er side of the lower extremity of the humerus to be inserted into the
art of the radius below the bicipital tuberosity. Some of the anterior
les join the tendon of the biceps or the anterior ligament, while some
ne posterior join the areiform fibres connecting the radius and ulna.
J-he Anterior Ligament is of a membranous form. Its upper border
nxeu to the humerus, its lower border to the radius, while its lateral
orders blend with the lateral ligaments.
Sections.—The anterior and lateral ligaments should now be cut
^nsversely about their middle in order to expose the interior of the joint.
J-he Synovial Membrane will be seen to line the inner face of the
. _J evior and lateral ligaments, but at the back part of the joint there
l0 ligament and the membrane is supported by the muscles. If the
8er be passed backwards and upwards, it will enter a process of the
°vial capsule which extends upwards into the olecranon fossa, where
PM of fat intervenes between it and the anconeus muscle. Just
,, Q(* the external lateral ligament the membrane lines the origin of
,, Hexor metacarpi externus. On the inner side of the joint, behind
Eternal lateral ligament, the membrane lines the tendons of origin
Of fVl                                       O               '                                                                                                  O
. ne middle and internal flexors of the metacarpus, and of the super-
and deep flexors of the digit. This disposition of the synovial
I' ttle will be rendered more evident by cutting the above-mentioned
ies a few inches below the joint, and then turning their tendons of
0n|a upwards.
Sections.—The humerus being now completely severed from the
8 and ulna, the mode of union of these latter bones should be
t-xaniined.
e ^adio-itlnar Articulation.—In the adult animal the bones of
of 1°le"arrn are fused together below the radio-ulnar arch, by ossification
e interosseous fibres which in the young animal are interposed
b + °en *^le kw° bones. Above the arch, however, the fibres interposed
en the bones do not ossify except in a very old animal, but persist
"■ 'interosseous ligament. The union of the two bones is further
amed by areiform fibres passing on each side from the one bone to
u         ei'> and blendiug with the lateral ligaments of the elbow. At the
otl ^ai'^ °^ *neu" opposed surfaces, the two bones respond to each
g . y two small synovial facets, which, however, have no special
ui membrane, but are lubricated by processes from the synovial
'aP^le of the elbow-joint.
gx ement&.—These are inappreciable, the limb of the horse being
m a condition of pronation.
-ocr page 110-
PLATE XLV
Ensiform cartilage
Asternal artery
Foramen dextrum
Phrenic sinus
iCEsophagus in
'foramen sinistrun
-Post, aorta in hiatus
Curiae axis
Left crus of diaphragm
Ant. mesenteric art.
—Renal ait.
Psoas parvus
- A lumbar art.
Spermatic art.
Quadratns lumborum.
- Post, mesenteric art.
An intertransverse muscle
N—Circumflex iliac art.
V——— Ext. iliac art.
Int. iliac art.
Last lumbar art.
—Ant. crural nerve
Iliacus
Psoas magnus
Prepubic art.
Femoral art.
-1—Deep femoral art.
Art. to quadriceps
Int. saphenous nerve
'«ght eras of diaphragm
From last dorsal nerve^J^
Retractor costae___
Post, vena cava -
From 1st lumbar nerve-
Frorn 2nd lumbar nerve
Piom parvus-----
Psoas magnus--------
From 'Srd lumbar nerve-
Inguinal nerve-----
Urinary bladder
BortoriuA-
'•'ddlu lig. of Bladder
«ep inguinal glands
Drawn kPrrnud by "W, kA KJoTin«Lon Edinburgh JcLondoi
SUBLUMBAR REGION AND DIAPHRAGM
-ocr page 111-
46                                  DISSECTION OF THE ANTERIOR LIMB.
THE KNEE, OR CARPUS (PLATE 11, fig'S. 2 and 3).
This is not a simple, but a composite, joint, and entering into its
formation there are the carpal bones, the lower extremity of the radius,
and the upper extremities of the bones of the metacarpus. The carpal
bones are arranged in two rows, or tiers, and the bones of each row are
firmly bound together and converted into a single piece by ligaments
passing between the adjacent bones. A transverse joint is then formed
between the upper and the lower tier. This may be called the inter-
carpal joint, and it is secured by special ligaments passing between the
two rows. Another transverse joint is formed between the lower row
and the heads of the metacarpal bones; and this, which has also got
special ligaments, is termed the carpo-metaearpal articulation. A third
transverse joint is formed between the lower end of the radius and the
upper row. This, which is the radio-carpal joint, is also provided with
special ligaments. Lastly, there are four ligaments which do not belong
specially to any of these articulations, but secure the stability of the
entire composite joint, and are therefore termed common.
Movements.—The movements which take place at the carpus are
flexion and extension, and each of the transverse joints above-mentioned
is a ginglymus. When these movements are executed, however, the
three joints do not participate in them in an equal degree. The largest
share of the movement occurs at the radio-carpal articulation, and the
smallest between the carpus and the metacarpus ; while, as regards the
amount of movement, the inter-carpal transverse joint occupies an inter-
mediate position. When the limb is flexed at the carpus, it will be
noticed that the metacarpus and digit deviate a little outwards from the
plane of the fore-arm. When the limb is fully extended the lateral
ligaments are tightly stretched, and resist any attempts to produce
abduction or adduction ; but these movements can be produced when the
limb is fully flexed, in which position the lateral ligaments are relaxed.
Lateral movement, however, is not executed at this joint in any appreci-
able degree in the living animal. The gliding movement permitted
between adjacent bones in each row is of importance, as tending to
distribute pressure, and obviate the bad effects which would have been
likely to result from concussion had each row7 been a single rigid mass.
Directions.—The tendons which pass in relation to the joint before
and behind should be removed, and the ligaments should be studied
in the order of the following description.
There are four ligaments common to the whole joint, viz., two lateral,
an anterior, and a posterior.
The External Lateral Ligament is a cord-like band composed of &
deep and a superficial set of fibres, which slightly cross each other. 1*
is fixed superiorly to the external tuberosity at the lower end of the
-ocr page 112-
Post, mesenteric! art.
Int. pudic art
Obturator artery
Urinary bladder
Ureter
Rectum
Iliaco-femoral art
Gluteal art.
Lateral sacral art.
PLATE XLVI
Yesiuula semi ualis
(Suspensory ligament of rectum
Retracoyr penis ,
3phini'te>,ani
^-Vesico-prostatic art.
Prostrate gland'
Cowper's glaoA
rt. cf "the corpus iavcrn.osurn
Post, aorta
Ext. iliac art.
I nibilicill art
Erector penii i jijii
j!
Suspensory lig. of the penis
Post, dorsal art. of penis
Ant. dorsal art. of penis
Epididymis
Testicle
Primed by W ,VA K Johnston Edjnb-urgh te London
MALE PELVIS (Chauveau)
-ocr page 113-
(i)
PLATE XL
Fig- I.—Ligaments of the Elbow, seen from behind (Leyh).
A. Ext i +
'liuir-w          Ul B8«mont; B. Int. lateral ligament; C. C. C. Areiform ligaments; D. Radio-
Fig. II.—Ligaments of the Carpus, front view (Ckauv&m).
llietacar i ■ ^gamen*s of upper row ; 2. An ant. ligament of lower row ; 3. 3. Ant. carpo-
Pal 1]gaments ; 4. Int. lateral ligament; 5. Ext. lateral ligament.
s- III.—Ligaments of the Carpus, viewed from the outer side (Chauveau).
llletacar" -          ligaments of upper row; 2. An ant. ligament of the lower row; 3. 3. Ant. carpo-
^Sfttttent laments; 4. An intercarpal ligament; 5. Ext. lateral ligament; 6. A radio-carpal
Fig. iv _T
• LIGAMENTS OF THE FETLOCK, PASTERN, AND COFFIN-JOINTS ; SIDE VIEW (Chauveail).
slil>s of « °lal fascic"luts of the ext. lateral ligament of the fetlock ; 2. 3. Sesamoid and phalangeal
Machine- *i ^ ^isciCIllus of the same ligament; 4. 5.6. Upper, middle, and lower fibrous slips
^* Anter° ^ ^ ou^ll horo -cartilage to the os suffraginis ; 7. Lateral ligament of the pastern-joint;
eia* ligament of the coffin-joint; 9. Posterolateral ligament of the same joint.
*%■ V.-
Back
of the Digit dissected to show the Tendons and Ligaments (Bouley).
A A
*atei'al Koj ateial ligament of the coffin-joint; B. Insertion of extensor pedis tendon ; D. Postero-
^° the Tvto           °^ *^e comn"Joint; E. Divergent fibres of the same ligament passing to be attached
Ug&lUeni f           6 0a Pe<^is an(l inner surface of the lateral cartilage ; F. Slip sent from suspensory
Pei'forHtus° ^XtpnS01 tendon » r- -Branch of bifurcation of th-j suspensory ligament; R. Bi'anch of
the reinfoi-' ■ ' er^orans emerging from between the branches of the perforatus ; Y. Attachment of
S'Sheath of the perforans tendon to the side of the os suifraginis.
**6- VI _j»
' -°ACK of the Digit dissected to show the Tendons and Ligaments (Bouley).
Cai'tilage 0f t, inferior sesamoidean ligament; B. Highest slip attaching the glenoidal fibro-
SeSamoidea 1* l)astei'n-joint to the first phalanax ; O. Branch of perforatus ; P. Middle inferior
s*18ath of f] . ^aillent y S. Insertion of plantar aponeurosis into semilunar crest; T. Reinforcing
* plantar aponeurosis ; X. Perforans tendon.
A ;                Fig- VII.-Back of the Fetlock-joint (Modified from Bouley).
C- Middle b ?loid ^gament; B. B. Lateral bands of the middle inferior sesamoidean ligament;
^anioiiip., ',. c ie same ligament, its upper attachment cut away to show D. the deep inferior
an hgarnent.
-ocr page 114-
PLATE XLVII
Post aorta
Renal artery
Supra-renal capsule
Right kidney
Left kidney
Umbilical art.
Testicle
----Cowper's gland
r-------Crus penis
Retractor puni.s
Prmtrd bjTT. LA.K Jalmau
GENITO-URINARY ORGANS OF MALE (Chadveav)
-ocr page 115-
48
THE ANATOMY OF THE HORSE.
radius; and passing over the outside of the carpus, it furnishes slips to
the cuneiform and unciform bones, and terminates on the head of the
external small metacarpal bone. The ligament is perforated by a thecal
canal in which the tendon of the extensor suffraginis plays.
The Internal Lateral Ligament is fixed superiorly to the internal
tuberosity of the radius, and inferiorly to the heads of the large ana
inner small metacarpal bones, furnishing slips, as it passes over the
carpus, to the scaphoid, magnum, and trapezoid bones.
The Anterior Common Ligament has a flattened, four-sided form. It
is fixed superiorly to the radius, and inferiorly to the large metacarpal
bone, while its lateral borders are united to the lateral ligaments. Its
deep face is partly adherent to the carpal bones or their anterior
ligaments, and partly it is lined by synovial membrane. The tendons
of the extensor pedis and the extensors of the metacarpus play over its
superficial face, where they are provided with synovial bursse. The
ligament is somewhat loose when the joint is extended, and is put ou
the stretch during flexion.
The Posterior Common Ligament is a much stronger ligament than
the preceding. It is fixed above to the radius, and below to the large
metacarpal bone. Its internal border mixes its fibres with the internal
lateral ligament, while its outer border is blended in the same way with
the most external of the intercarpal ligaments. Its anterior or deep
face is very intimately united to the carpal bones, and its posterior face
is smooth and lined by the synovial membrane of the carpal sheath.
The snhcarpal ligament, or fibrous band which reinforces the perforaus
tendon below the carpus, takes origin from the posterior common ligfc"
merit, or may be described as the downward continuation of that
ligament.
Directions.—The anterior and lateral ligaments just described are to
be carefully dissected away, and in removing the first of these, care is
to be taken of the anterior bands connecting the bones in each row.
Eadio-carpal Ligaments.—There are three of these. The strongest
of them is a thick cord that stretches obliquely downwards and inwards
behind the carpus, and connects the radius and scaphoid. It will be
seen, without removing the posterior common ligament, which covers it,
by strongly flexing the joint and looking into it from the front. The
second is a very slender ligament which is fixed to the radius beneath
the preceding, and passes downwards to be attached to the pisiform and
the interosseous ligament uniting the cuneiform and semilunar bones.
The third is situated at the outside of the carpus, where it connects
the radius and the upper border of the pisiform bone, and is partly
covered by the lateral ligament.
The Inter-carpal Ligaments are also three in number. Two of
them are situated behind the joint, under cover of the posterior common
-ocr page 116-
PLATE XLVIII
Int. iliac art.
Lateral sacral art.
From 6th lumbar
From 1st sacral
From 2nd sacral
From 3rd sacral
Ischiatic art.
Lateral coccygeal art.
From 4th sacral
Middle coccygeal art.
From 3rd lumbar
From 4th lumbar
Iliaco-mugcular nerve
From 5th lumbar-
Int. pudic art.
Ant. crural nerve
Obturator nerve
Ilio-lumbar art.
Gluteal art.
Great sciatic nerve
Obturator art.
Iliaco-femoral art.
pper post, gluteal nerve
Lower post, gluteal nerve
Pudic nerve
Hsemorrhoidal nerve
. ■ y W. &-.A H Johnston. Edinburgh fcLondon
LUMBOSACRAL PLEXUS
-ocr page 117-
DISSECTION OF THE ANTERIOR LIMB.                                   49
! »arnent, and will he seen without further dissection on flexing the
nt and looking into it from the front. One of these connects the
scaphoid to the magnum and trapezoid, the other joins the cuneiform
. Magnum. The third is a strong ligament situated at the outer
e °f the joint, where it is blended with the lateral ligament in front,
with the posterior common ligament behind. Its fibres are fixed
Periorly to the pisiform bone, and inforiorly to the unciform and head
ne external small metacarpal bone.
1 bp Carpo-metacarpal Ligaments are four in number—two anterior
two interosseous. One of the anterior ligaments is composed of
separate slips which connect the os magnum and large metacarpal
The other passes from the unciform to the head of the external
. U metacarpal bone, under cover of the lateral ligament. The two
rosseous pass, one on each side, from the point of articulation of the
»e and small metacarpal bones, to join the interosseous ligaments
°nnecting the bones of the lower row.
of /rec^0,w-—Attention may at this stage be given to the disposition
e synovial membranes of the carpus, which are three in number.
jovial Membranes.—1. The radio-carpal synovial membrane not
j facilitates the movements between the radius and the bones of the
• Y r°w, but also descends between the latter bones as far as their
rosseous ligaments. 2. The inter-carpal synovial membrane, in the
e way, belongs to the intercarpal transverse joint; but it is also
"ttated above, between the bones of the upper row as far as their
osseous ligaments, and descends in the same way below, between
o aclJacent bones of the lower row. It communicates with the next.
b
" + le carP°-met(icarpal synovial membrane facilitates the movements
b + 6eU ^le l°wer row and the heads of the metacarpal bones, ascends
,        e" the adjacent bones of the lower row as far as their interosseous
s» ents, and dips down to supply the articulations between the large
an^mall metacarpals.
eedons.—The radio-carpal, inter-carpal, and posterior common
is^l l6n*s should now be cut transversely. The upper row will thus be
nn, as a single piece for the examination of its special ligaments.
■ , e Ligaments of the Upper How are three anterior, and three
sseous j and they are extremely simple. The anterior ligaments
j , tteile(j bands connecting the adjacent bones in front, while the
''seous bands are very short and connect the contiguous surfaces
0f*e bones.
0          -Laments of the Lower Row are two anterior, and two inter-
e . / and they are disposed like those of the upper row. In
th 1U^ *hese, the lower tier of bones must not be separated from
si          acarpusj as that would involve the destruction, in part, of the
Pensory ligament of the fetlock.
-ocr page 118-
50
THE ANATOMY OF THE HORSE.
The Inter-metacarpal Articulations. The head of the large meta-
carpal bone responds to one of the small metacarpals on each side by a
small synovial joint lubricated by a process from the carpo-metacarpal
synovial membrane. Below that point the union of the bones is main-
tained by short interosseous fibres, which, in adult animals, arc very
frequently ossified. The lower extremities of the splint bones, however,
for a short distance above the little knob that terminates them, remain
freely movable, as may be felt by manipulation in the living animal.
In addition to the interosseous fibres, the ligaments of the carpus which
get inserted in common into the heads of both large and small metacarpal
bones, contribute to the union of these bones.
THE FETLOCK-JOINT (PLATE 11, FIGS. 4-7).
This, which is technically termed the metacarpophalangeal articula-
tion, is a ginglymoid joint; and its articular surfaces are furnished by
the lower extremity of the large metacarpal bone, the upper extremity
of the first phalanx, and the two sesamoid bones. It corresponds to the
joint at the knuckles in the human hand.
Movements.—Flexion and extension are, in the natural state, the only
movements executed at the joint; but by manipulation, slight lateral
movements may be produced when the joint is fully flexed. In com-
plete extension the digit is carried beyond the point at which it lies in a
straight line with the metacarpus (over-extension), until the movement is
arrested by tension of the suspensory ligament.
Directions.—The tendons which pass in relation to the joint before
and behind having been carefully removed, the ligaments should be
dissected and studied in the order of their description.
The Superior Sesamoidean or Suspensory Ligament.—The main por-
tion of this ligament is lodged in the channel formed by the three meta-
carpal bones, where it is related by its posterior face to the perforans
tendon and its reinforcing band (subcarpal ligament). It has a double
origin behind the carpus, viz., (1) by a superficial layer from the lower
row of carpal bones, and (2) by a deeper layer from the upper end of
the large metacarpal bone. (In the hind limb it has a similar origin froni
the .tarsus and metatarsus). These two portions blend, and descend be-
hind the metacarpus as a flattened band which bifurcates a few inches
above the sesamoid bones. Each branch passes to the sesamoid bone of
its own side, where a considerable proportion of its fibres become inserted;
while the rest is continued in the form of a band which crosses obliquely
downwards and forwards over the side of the fetlock to join the extensor
tendon on the front of the digit, and be continued with it to the os pedis-
The ligament is composed of white fibrous tissue with a constant admix-
ture of striped muscular tissue. The presence of muscular tissue here,
points to the conclusion (strengthened by other considerations) that the
-ocr page 119-
DISSECTION OF THE ANTERIOR LIMB.                                  51
Pensory ligament is a muscle which, in the evolution of the horse,
undergone retrogressive changes, and lost its original function.*
ne Inferior Sesamoidean Ligaments. These are three in number,
may be distinguished as superficial, middle, and deep. The super-
nt ligament is fixed below to the glenoidal fibro-cartilage developed
lnd the superior articular surface of the second phalanx. It ascends
c flattened band behind the os suffraginis, where it is placed between
middle ligament and the tendon of the deep flexor; and, widening a
e. it is inserted into the base of the sesamoids and the intersesamoid
&ament. By cutting the ligament about its middle, and reflecting it
P vards and downwards, the middle ligament will be brought into view.
e m^ddle ligament consists of a median and two lateral bands. Each
xed to the back of the os suffraginis, and ascends to be inserted into
base of the sesamoids. This should be cut and reflected like the
ceding ligament, in order to expose the next. The deep ligament
sists of a few short fibres disposed like the letter X, and fixed, on the
nand, to the upper part of the posterior surface of the os suffraginis,
' °n the other, into the base of the sesamoid bones. This ligament
i Ports the synovial membrane of the joint.
ne Lateral Ligaments of the fetlock-joint. Each comprises (1) a
P incial fasciculus connecting the lower extremity of the large
acarpal bone to the upper extremity of the first phalanx; and (2) a
P fasciculus attached, on the one hand, to the large metacarpal
atn the preceding, and, on the other, to the sesamoid and upper
extremity of the first phalanx.
Anterior Ligament has a membranous, four-sided form. It
ls the joint in front, and supports the synovial membrane by its
I race; while the extensor pedis tendon passes over its superficial
P °t, a synovial bursa being interposed. It is fixed above to the
lai'ge r
lateral
metacarpal, below to the first phalanx, and on each side to the
"garnent.
lections.—On one side of the joint the lateral ligament and the
P ent from the suspensory ligament to the extensor tendon must be
^°ved to expose the next ligament.
le Lateral Sesamoidean Ligaments. These are not to be con-
with the lateral ligaments of the joint, by which they are
}T covered. Each fixes the sesamoid of its own side to the upper
™xity of the first phalanx.
e Intersesamoid Ligamemt is the name given to the fibro-cartila-
tissue which unites the two sesamoids, and with them forms
«" ey-hke surface for the passage of the deep flexor tendon.
„ Synovial Membrane is supported in front by the anterior
'iganient ' «? Pressor D. J. Cunningham (Reports of the Challenger Expedition, Vol. V.), the
object lie l\ a^tel'ed flexor brevis of the middle digit, the corresponding muscle in the human
g t le 1st plantar interosseous muscle.
-ocr page 120-
52                                   THE ANATOMY OF THE HORSE.
ligament, and on each side by the lateral ligament. Behind the joint
it is supported below the sesamoids by the deep inferior sesamoideau
ligament, but above these bones it is unsupported;. and when the
synovial sac is distended, it bulges upwards between the branches of
the suspensory ligament (Fig. 1, page 33).
THE PASTERN-JOINT (PLATE 11).
This joint, which is technically termed the first interphalangeal
articulation, is formed between the distal end of the os suffraginis and
the proximal end of the os corona). It is a ginglymus, or hinge joint,
and corresponds to the second joint of the human finger.
Movements.—As with the joint last described, the only natural
movements are flexion and extension.
Directions.—The tendon of the extensor pedis, which passes over
the front of the joint, should be cut and reflected downwards. This
will show that the tendon completes the joint in front, where it plays
the part of an anterior ligament, and supports the synovial membrane.
The lateral ligaments are next to be defined, and after these, the
supplementary cartilaginous apparatus placed benind the joint.
The Lateral Ligaments. Each of these stretches from the lower
extremity of the first phalanx on its lateral aspect, to be inserted into
the side of the os coronas, and beyond that point some of its fibres are
continued downwards and backwards as the postero-lateral ligament of
the second interphalangeal joint.
The Glenoidal Fibro-Cartilage. This is a piece of fibro-cartilago
fixed at the posterior edge of the upper articular surface of the os
corona;. It serves to increase that surface, and its anterior face is
moulded on the lower articular surface of the first phalanx, while its
posterior face is smooth for the passage of the perforans tendon. Three
fibrous slips pass from it on each side, and are attached to the first
phalanx. The superficial inferior sesamoidean ligament is inserted into
it, and the terminal insertion of the perforatus tendon is blended with
it on each side.
Synovial Membrane. This is supported in front by the extensor
tendon, and on each side by the lateral ligament. Posteriorly it lines
the glenoidal fibro-cartilage, and is prolonged upwards as a pouch behind
the lower extremity of the first phalanx (Plate 10, fig. 2).
the coffin-joint (plate 11).
This, the second interphalangeal joint, has three bones entering into its
formation, viz., the os coronffi, the os pedis, and the navicular bone. I*
is a ginglymus, and corresponds to the first joint of the human finger.
Movements.—Flexion and extension.
-ocr page 121-
DISSECTION OF THE ANTERIOR LIMB.                                  53
Possesses an interosseous ligament, and two pairs of lateral ligaments,
e Interosseous Ligament is composed of short fibres passing from
e inferior border of the navicular bone to the os pedis behind its artic-
ular surface.
he Antero-Lateral Ligaments. Each of these passes from the side
he os ooronse to be inserted into the excavation at the side of the
Pyramidal process of the os pedis.
e Postero-Lateral Ligaments. These seem to be the downward con-
lations of the lateral ligaments of the pastern-joint. Passing from the
w the os coronse, each is inserted into the upper border of the nav-
of n V ne> and sends slips to the wing of the os pedis and inner surface
*he lateral cartilage.
' 'jovial Membrane. This is supported in front by the extensor
°n' an(^ laterally by the lateral ligaments. A protrusion of it passes on
side between the antero-lateral and postero-lateral ligaments, and
, m relation to the deep face of the lateral cartilage. A third protru-
of         ses upwards posteriorly, between the navicular bone and the back
the os coronse (Plate 10, fig. 2).
Abular view of the muscles of the fore limb in their
action on the different joints.
Shoulder.
( Superficial pectoral.
Adductors < Subscapularis.
(. Coraco-humeralis.
(Deltoid.
I Coraco-humeralis.
Pi
exors
I Latissimus dorsi.
Teres major.
Teres minor.
Scapulo-humeralis gracilis (?)
\Large head of triceps.
■^tensors j SuI>raspinatus.
t Mastoido-humeralis.
Deltoid
Teres minor
Infraspinatus
Rotators
outwards
C Mastoido-humeralis.
. Latissimus dorsi.
Rotators
inwards
Actors |
urs S
X
5eltoit1-.
Teres minor.
{Teres major.
Elbow.
( Triceps extensor cubiti.
Extensors \ Anconeus.
(, Scapulo-ulnaris.
Cahpus.
I Infraspinatus.
Fl
j Flexor brachi.
t Brachialis anticus.
exors
(EJexor metacarpi externus.
f Extensor metacarpi magnus.
J Extensor metacarpi obliquus.
J Extensor pedis.
V Extensor suffraginis.
flexors
Flexors
Plexors
I
; pi
exor metacarpi medius.
exor rnetacarpi interims.
Extensors
(Fjexor perforans.
flexor perforatus.
1 Flexor perforans.
tilexor perforatus.
f Flexor perforans.
( flexor perforatus.
Fetlock.
Extensor pedis.
Extensors
[ Extensor suffraginis.
Pastekn.
I Extensor —Extensor pedis.
Coffin-joint.
Flexor—Flexor perforans.         1 Extensor—Extensor pedis.
-ocr page 122-
Name op Muscle.
Origin.
Insertion.
Source of Nerve.
Anterior superficial pectoral
Posterior superficial pectoral
Anterior deep pectoral
Posterior deep pectoral
Serratus magnus
Levator anguli scapulae
Trapezius (cervical)
Trapezius (dorsal) .
Rhomboideus (cervical)
Rhomboideus (dorsal)
Latissimus dorsi
Mastoido-humeralis
Teres major
Subscapularis .
Humerus, outer lip of musculo-spiral groove .
Humerus (with the preceding) ; and super- {
flcial fascia of fore-arm ...         j
Fascia covering supraspinatus
Humerus, inner tuberosity; biceps tendon
and its retaining fascia ....
j Scapula, two triangular areas on ventral )
(         surface ......         j
Scapula, triangular area on ventral surface,
at cervical angle .....
( Scapula, tubercle of spine ; and aponeurosis ^
\         over outer scapular muscles . .         j
Scapuh, tubercle of spine ....
j Scapular cartilage of prolongation, inner 1
\         surface ......         j
Soapular cartilage (behind the preceding)
Humerus, inner tubercle         ....
Humerus, outer lip of musculo-spiral groove .
Humerus, inner tubercle         ....
Humerus, inner tuberosity
Sternum, first 2 or 3 inches of inferior border
1 Sternum, inferior border; and median fibrous
\         cord         .......
| Costal cartilages, 1st four; and sternum, .)
|         lateral surface ....         j
f Abdominal tunic; side of sternum; and tips of
\         costal cartilages, 5th, 6th, 7th, and 8th.
Ribs, 1st eight or nine .....
( Cervical vertebras, last four, transverse pro-
( cesses .......
Ligamentum nucha?, funicular portion .
f Anterior dorsal spines (or supraspinous liga- )
\         ment) ......         j
Ligamentum nuchas, funicular portion .
j Anterior dorsal spines (or supraspinous liga- \
\         ment)......j
f Vertebral spines, 4th dorsal to last lumbar )
\ (or supraspinous ligament) . . j
( Mastoid process and crest; and cervical ver- {
^         tebrre, 1st four, transverse processes j
i Scapula, dorsal angle ; and intermuscular (
(         septum (between it and subscapularis) J
Scapula, fossa of same name ....
From brachial plexus.
From brachial plexus.
From brachial plexus.
From brachial plexus
(2 branches).
From brachial plexus.
From Oth and 7th
cervical nerves.
Spinal accessory.
Spinal accessory.
Oth cervical.
Oth cervical.
From brachial plexus,
( Cervical nerves and
( circumflex.
Brachial plexus.
Brachial plexus.
-ocr page 123-
/ Ulna, olecranon process; and fascia of fore-arm I Muscnlo-spiral.             j
Vina, olecranon process.....I Musculo-spiral.              I
Scapula, posterior border ....
Scapula, dorsal angle and posterior border )
Humerus, shaft.....(
Humerus, shaft . . . . .         /
Humerus, margin of olecranon fossa . /
j Scapula, above and behind rim of glenoid \
{ cavity......(j
Scapula, coracoid process
Scapula, coracoid process ....
Scapula, dorsal angle; and scapular fascia .
( Scapula, posterior border, lower part of infra-
( spinous fossa, and tubercle on glenoid rim
j Scapula, infraspinous fossa ; and scapular
( fascia .......
f Scapula, supraspinous iussa ; and scapular
\ fascia .......
Humerus, shaft ......
Humerus, inner condyle         ....
j Humerus, inner condyle; and ulna, ole- (
(         cranon process (two heads) . .         j
Humerus, outer condyloid ridge
Humerus, inner condyloid ridge
Ulna, olecranon process ....
Humerus, inner condyloid ridge
Radius shaft ......
( Humerus, outer condyloid ridge, and de- ^
\         pression external to coronoid fossa         j
Radius, shaft.......
^Humerus, depression external to coronoid
s fossa; external lateral ligament of
V elbow ; and radius, upper extremity
iLateral ligament of elbow; radius, upper"!
< extremity; and line of junction of v
(. radius and tilna .... J
Perforans tendon......
Splint bone, head......
j Scapulo-ulnaris
Triceps extensor■/£*£*££*
cubltl- (caput rued
Anconeus
Scapulo-lmmeralis gracilis
Coraco-lmmeralis
Biceps
Deltoid .
Teres minor
Infraspinatus .
Supraspinatus
Brachialis anticus
Flexor metacarpi internus
Flexor metacarpi medius
Flexor metacarpi externus
Flexor perf oratus .
{ulnar head
humeral head
radial head.
Extensor metacarpi magnus
Extensor metacarpi obliqu is
Extensor pedis
Extensor suffraginis
Lumbricales (2)
Interossei (2) .
Circumflex.
Median.
Median (or its anterior
root).
Circumflex.
Circumflex.
Suprascapular.
Suprascapular.
( Musculocutaneous
( (of median).
Median.
Ulnar.
Musculo-spiral.
Ulnar.
Ulnar.
Median.
Median.
Musculo-spiral.
Musculo-spiral.
Musculo-spiral.
Musculo-spiral.
Plantar.
Plantar.
Humerus, shaft......
Humerus, shaft (two insertions)
Radius, bicipital tuberosity; and fascia of
fore-arm.......
Humerus, deltoid (outer) tubercle .
Humerus, ridge between outer tubercle and |
tuberosity......)
Humerus, outer tuberosity and ridge below (
it (two insertions)                                         )
Humerus, outer and inner tuberosities (two 1
insertions).....J
Radius and ulna, inner side ....
Inner splint bone, head.....
Pisiform, upper edge .....
j Pisiform, upper edge ; and inner splint bone;
|         head (two tendons)         ....
Os corona? (bifid tendon)         ....
Os pedis, semilunar crest and surface behind it
Large metacarpal bone, upper extremity
Inner splint bone, head ....
Os pedis, pyramidal process ; and to join
tendon of extensor suffraginis (two
tendons)......
Os suffraginis, upper extremity
Tissue beneath ergot of fetlock
j Suspensory ligament, band sent to extensor
t pedis tendon.....
-ocr page 124-
CHAPTER II.
DISSECTION OF THE POSTERIOR LIMB.
In the male subject, the dissection of the perinseum must be completed
before the dissector of the hind limb can begin his operations.
THE INNER ASPECT OP THE THIGH.
Position.—The animal should be placed on the middle line of its back,
and its hind limbs should be drawn forcibly upwards and outwards by
ropes running over pulleys fixed to the ceiling. This is the position
most convenient for allowing the dissection of both hind limbs to be
23ursued at the same time. If only one limb is being dissected, the rope
may be unfastened from that limb, and the body allowed to incline to
the same side, as in Plate 12.
Surface-marking.—The internal saphena vein ascends on the inner
aspect of the thigh; and a few inches below the upper limit of the region,
it dips in between the sartorius and gracilis muscles. Pressure at this
point in the living animal will produce distension of the vessel, and
render its course much more evident. Venesection is sometimes per-
formed on this vessel. Above the point where the before-mentioned
vessel disappears from view, the deep inguinal lymphatic glands are
situated in the interstice between the sartorius and gracilis muscles.
They here cover the femoral artery, and may be very distinctly felt in a
case of lymphangitis, or "weed."
Directions.—An incision through the skin is to be carried down the
middle line of the thigh, and terminated a few inches below the level of
the stifle-joint. Here another incision is to be made across the inner
aspect of the limb, from its anterior to its posterior border. These
incisions, together with those already made in the dissection of the
perinseum, will enable the dissector to reflect the skin as an anterior and
a posterior flap. The student should then dissect the internal saphcna
vein with its accompanying artery and nerve, and the cutaneous nerves
at the forepart of the region, which are derived from the lumbar nerves.
Thereafter the surface of the sartorius and gracilis is to be cleaned, and
these muscles are to be examined.
The Internal Saphena Vein (Plate 12). This is a large vessel
-ocr page 125-
DISSECTION OF THE POSTEEIOR LIMB.                                  57
on the inner side of the leg by the junction of an anterior and a
rior root, these being the upward continuations of the inner and
metatarsal veins. In the thigh it inclines upwards and forwards
j le 8ui'face of the gracilis, until it disappears between that muscle
Tv, sartorius, to empty itself into the femoral vein.
he Saphena Artery (Plate 12). This artery lies in front of the
, " It is a long and slender vessel given off by the femoral artery
o,. .,. middle of the femur. It conies out between the sartorius and
, lsi or it rnay pierce the edge of one of these muscles. It then
,               m front of the saphena vein, and finally divides into two
Ti 1<3S' Wnich accompany the roots of that vessel.
e Internal Saphenous Nerve (Plate 12) is a branch of the anterior
ural f
At k m wn'ch it is given off a little above the brim of the pelvis.
fe 6 crural arch (Poupart's ligament) it descends in front of the
It tl artery, to which and the sartorius muscle it supplies branches.
th 1 des into two cutaneous branches, which emerge from between
an 1 'rnas and the gracilis, in company with the saphenous artery
vem. The anterior half of the nerve gives off branches for the
J ot the thigh in front of the vein, and is continued downwards
Th 1G ^orePai't of the inner side of the leg, as far as the hock.
ter'         eri°r half sends branches backwards for the supply of the pos-
Part of the thigh, and it then descends behind the anterior half.
at tv> ANEous Branches from the lumbar nerves. These will be found
ace          rePart of the thigh, the largest (from the 3rd lumbar) being
TV, arue<^ by the posterior division of the circumflex iliac artery.
at ,, "Eecrural Lymphatic Glands. These are superficially placed
m ? UlUer side of the front of the thigh, on the track of the above-
°ned branch of the circumflex iliac artery.
ov         A' "^ *ne forepart of the region now exposed, the muscles are
to the read
Dy a strong membranous fascia, which is attached superiorly
Who • on °f the external oblique muscle of the abdomen, at the line
h0rri , ls reflected to form Poupart's ligament. Round the anterior
but vV,           thigh this fascia is continuous with the strong fascia lata ;
Part f ^ ced backwards, it becomes less fibrous, and over the posterior
the f. • re8'i011 it is thin and areolar. When it has been examined,
rpi         ls to be cleaned away from the subjacent muscles.
in        r^EEP In guinal Lymphatic Glands (Plate 45) are ten or twelve
in +}          ' and form a chain connected by areolar tissue, and situated
nil 1 PPer part of the interstice between the gracilis and sartorius
The^S aiUl °Ver the femoral vessels-
at Dr rtokius (Plate 12). This is a somewhat slender muscle which
deseeti 1 • Can ^e dissected only in a part of its course. It is seen
the ab 1 * Deileath Poupart's ligament, from its point of origin within
mal cavity. It there takes origin from the iliac fascia (Plate 45).
-ocr page 126-
58                                   THE ANATOMY OF THE HORSE.
In the thigh it lies in front of the gracilis. About the middle of their
line of apposition the saphena vessels and nerves emerge, but below that
point the muscles are adherent to each other. It is inserted into the
internal straight ligament of the patella.
Action.—To adduct and flex the hip-joint. To a slight extent it may
also rotate the limb inwards at the stifle.
The Gracilis (Plate 12). This muscle does not possess the slender
character from which it is named in human anatomy. It is a large,
somewhat four-sided mass, forming the greater part of what is termed
the flat of the thigh. A linear depression seen on the surface of the
muscle when it is cleaned, is often mistaken by students for the line of
separation between it and the sartorius. It arises from the lower face
of the pubis and ischium close to the symphysis, and it is here united
to its fellow of the opposite side. Inferiorly it has a broad flat tendon;
united in front to that of the sartorius. It is inserted with the sartorius
into the internal straight ligament of the patella, and into a line on the
tibia between its anterior and internal tuberosities. The posterior edge
of its tendon is continuous with the deep fascia of the leg. A large
branch from the external pudic veins traverses the muscle near its
origin, and opens into the femoral vein.
Action.—To adduct the hip, and rotate the limb inwards.
Directions.—The two preceding muscles are to bo carefully cut across
about their middle, and turned upwards and downwards. On reflecting
the proximal half of the gracilis, branches of the obturator nerve and
deep femoral artery will be seen penetrating its deep face; and, in the
same way, twigs from the saphena nerve wdll be found entering the
sartorius. The deep inguinal glands are to bo removed, and the
femoral vessels and anterior crural nerve are to be dissected.
The Femoral Artery (Plate 13) is the main arterial trunk for the
supply of the hind limb. It is the direct continuation of the external
iliac, the brim of the pelvis being selected as the arbitrary line oi
division between the two vessels ; and, in like manner, it is directly con-
tinued by the popliteal artery, the vessel changing its name when l*
passes between the two heads of the gastrocnemius muscle. The lower
third of the vessel, however, will not bo exposed till the next stage °'
the dissection. The part of the vessel now seen begins at the pehTic
brim, where it is seen issuing from beneath Poupart's ligament. *■
there rests on the common termination of the iliacus and psoas magnuSj
having the sartorius in front and the pectineus behind. In the thigh l*
descends obliquely downwards and backwards, resting first on the con*'
mon termination of the iliacus and psoas magnus, and then on the
vastus internus. It has the sartorius in front; while posteriorly it lS
related first to the pectineus, and then to the adductor parvus. In this
course it corresponds to the interstice between the gracilis and sartorius
-ocr page 127-
DISSECTION OF THE POSTERIOR LIMB.                                  59
Muscles
closely
and is covered by the deep inguinal lymphatic glands. It is
related to the femoral vein, which lies beneath and slightly pos-
—-*G_ik. except at the brim of ffie pelvis, where the vein is imme-
J posterior to the artery. In the present stage of the dissection
jj, Lssel disappears between the upper and lower insertions of the
coll °r ma8'nus! where it will subsequently be followed. The following
eral branches of the femoral are here seen :—
0fp ' le Profunda or Deep Femoral Artery. This branch is given
u . er Poupart's ligament at the pelvic brim. At its origin it
j. ' - i°nns a short common trunk with the prcpubic artery. It
foil ^wnwards and backwards under the pectiueus, and will be
en in the next stage of the dissection.
ar-T' Muscular Branches. The largest of these is a vessel of consider-
'ize for the supply of the quadriceps extensor cruris muscle. It
„          °": at about the same level as the profunda, which it generally
Hi) 1 S U1 Vamme j an(l passing over the psoas magnus and iliacus, and
int            sartorius, it penetrates between the rectus femoris and vastus
a , . ' lri company with the anterior crural nerve. Other innominate
°t smaller size enter the vastus internus, pectineus, gracilis,
Cronus, and adductors.
' ^'ie Saphena Artery already described (page 57).
ins '          Nutrient Artery of the Femur is given off at the tendon of
85ei*«>n of the pectineus.
;,.. " u Articular branch, of slender volume, descends between the vastus
mterr-
T)11U8-aUCl adductor magnus to the stifle-joint.
re . Femoral Vein ascends in close company with the artery, and
d            wanches which correspond more or less exactly to those just
c°ntimi
The Ant
erior Crural Nerve (Plate 13) is derived from the lumbo-
Da • "          us' It descends between the psoas magnus and parvus ; and
wj _ * over the common termination of the iliacus and psoas magnus,
is covered by the sartorius, it splits into a bundle of branches
5©tJier penetrate between the vastus internus and rectus femoris
c * ' " the mass of the quadriceps extensor cruris. While under
escr
Si
, . '%ms-—The pectineus, adductor parvus, adductor magnus, and
m , embranosus muscles are now to be cleaned and isolated. These
Son j ■ Succee<^ each other from before to behind in the order named,
tion 1 ' difficulty may be experienced in finding the line of separa-
of 8 Ween the two adductors, but a reference to Plate 13 will prove
Pale • > assistance- Moreover, the fibres of the small adductor are of a
0ur than those of the adductor mairnus.
-ocr page 128-
GO
THE ANATOMY OF THE HOHSE.
The Pectineus (Plate 13). This muscle has a distinctly conical forto-
It lies posterior to the femoral vessels, and the profunda artery disap-
pears beneath it. It arises from the brim and inferior surface of the
pubis, and it is there penetrated by the pubio-femoral ligament, fro'11
which some of its fibres take origin. Its tapering point is inserted into
the shaft of the femur in the neighbourhood of the nutrient foramen.
Action.—It adducts the limb, and flexes the hip.
The Adductor Parvus (Adductor brevis of Percivall) (Plate 13) is Sit*1'
ated between the pectineus and the great adductor. It arises from the
inferior surface of the pubis, and is inserted into the posterior surface ot
the femur about its middle.
Action.-—It is an adductor and outward-rotator at the hip-joint.
The Adductor Magnus (Adductor longus of Percivall) (Plate 13)
arises from the inferior surface of the ischium, and from the tendon °*
origin of the gracilis. It has two insertions, between which the femoral
artery passes. 1. Its deeper fibres are inserted into the posterior surface
of the femur, on a quadrilateral area above the smooth groove in which
the femoral artery rest's. 2. Its more superficial and longer fibres are
inserted into the forepart of the supracondyloid crest.
Action.—It is an adductor at the hip.
The Semimembranosus (Adductor magnus of Percivall) (Plate 13). Tins
is a muscle of large size. It arises from the lower surface of the ischium;
including its tuberosity, and by a small slip from the fascia investing'
the muscles of the tail. It is inserted into the inner condyle of the
femur, behind the tubercle for the attachment of the internal lateral
ligament of the stifle.
Action.—Commonly, it is an adductor and extensor of the hip; but
when the femur is fixed, it acts as a lever of the first order, and assists
in rearing.
Directions.—The foregoing muscles must now be cut and partially
removed as follows :—
The semimembranosus is to be cut transversely, an inch or two above
its insertion. The muscle is then to be raised upwards from the scffU-
tendinosus, on which it rests; and in doing this, branches of nerves
from the great sciatic will be found entering it in front. The central
portion of the muscle may then be removed, leaving a few inches at its
origin. The other muscles must be served in the same way, leaving
only short portions at the origin and insertion, except in the case of the
adductor jjarvus and upper half of the adductor magnus, whose
common insertion into the back of the femur is to be entirely removed'
Care is to be taken of the femoral artery where it rests on the bone, and
in performing the dissection it will be well to refer to Plate 14 as a
guide. In reflecting the upper portion of the great adductor, a branch
of the obturator nerve will be found entering its deep face, after having
-ocr page 129-
DISSECTION OF THE POSTERIOR LIMB.                                  61
ci through the obturator externus muscle. Other branches of the
nerve will be found supplying the small adductor and the pecti-
le Femoral Artery (Plate 14). The remaining portion of this
»          is now exposed as it winds round behind the shaft of the
' having its impress on the bone. It is seen passing in between
iads of the gastrocnemius muscle, at which point it takes the
ot popliteal. In this part of its course it gives off only one vessel
^te—the femoro-popliteal.
• Emoro-popliteal Artery. The point of origin of this branch
s the lower limit of the femoral artery. It passes backwards in a
' ntal direction, and penetrates the semitendinosus. Near its origin
b
ft> » ott a considerable branch which ascends behind the femur, sup-
I => *ne biceps, and anastomosing with the profunda. Other branches
W from it to the gastrocnemius,
tr LITEAL Lymphatic Glands. A few glands will be found on the
hi.          ^le femoro-popliteal artery between the semitendinosus and
°eps fenioris muscles.
e Profunda or Deep Femoral Artery. In the preceding
stage of +1
o ui the dissection this branch of the femoral was seen at its
rif?m t*.
ed                passes downwards and backwards, between the adjacent
. * ' °* the iliacus and obturator externus, and under cover of the
leus and adductor parvus. Above the insertion of the quadratus
to 1S l* orosses behind the femur, where its terminal branches descend
. PPv the biceps. It also furnishes collateral branches to the
ylneus. gracilis, and adductors,
th               ^ne foregoing arteries are accompanied by satellite veins of
J*0* names.
rib C <^XJADKATlJS Femoris (Plates 14 and 16). This is a somewhat slender
in fi. aPe<^ nauscle. It arises from the lower surface of the ischium
0            °f the tuberosity, and it becomes inserted into an oblique line
back of the femur, at the level of the third trochanter.
TV,               ^8 an extensor and outward-rotator at the hip.
fas • B URAT0R Externus (Plate 14). This muscle, which is coarsely
a r ated, covers the obturator foramen, and conceals the obturator
t          aU vessels as they emerge from the pelvis. It is traversed by
°'r + an°nes of the obturator nerve, the posterior of which is for the
of fl ' c*orJ while the anterior splits into branches for the supply
8u „ Iaa" adductor, pectiueus, and gracilis. It arises from the lower
fos '                 pubis and ischium, and is inserted into the trochanteric
j^. •' +t is an extensor and outward-rotator at the hip.
sho li ' l°m' ^he nerves which emerge from the obturator externus
'e traced through the substance of that muscle to their origin
-ocr page 130-
62                                   THE ANATOMY OF THE HOESE.
from the obturator nerve. The muscle itself may then be removed to
expose the obturator vessels and nerve.
The Obturator Artery (Plates 14 and 46). This vessel begins at the
pelvic inlet as one of the terminal branches of the internal iliac. I*
leaves the pelvis by the obturator foramen, in company with a vein and
nerve of the same name. At its point of emergence it is covered by
the obturator externus, and it passes backwards between that muscle
and the bone, and then curves downwards to terminate in the biceps
and semitendinosus. It gives off the artery of the corpus cavernomm.
The Obturator Vein passes into the pelvis by the obturator foramen*
and aids in forming the internal iliac vein.
The Obturator Nerve is a branch of the lumbo-sacral plexus.
Emerging by the obturator foramen, it divides for the supply of the
obturator externus, adductor parvus, adductor magnus, pectineus, and
gracilis muscles.
Directions.—In this stage of the dissection the great sciatic nerve is
seen in its course downwards through the thigh. Its examination is
more conveniently undertaken in the dissection of the hip and outer
aspect of the thigh, but attention may also be given to it here.
The Great Sciatic Nerve, which is a branch of the lumbo-saCr8*
plexus, after passing through the hip (see Plate 16), descends in the
thigh, behind the femur, where it is deeply enclosed between the
biceps and semitendinosus outwardly, and the semimembranosus and
great adductor inwardly. Under the name of the internal popliteal, $
passes in between the two heads of the gastrocnemius. The following
branches whose points of origin are not now visible, being situated i°
the hip, may be identified by reference to Plate 14:—(1) Branches to the
biceps, semitendinosus, and semimembranosus; (2) the external pop'
liteal; (3) the external saphenous. The last two will be again seen in
the dissections of the hip, thigh, and leg.
Directions.—The vastus interims, situated at the front of the thigh
should now be examined. It is a division of the great muscular mass
termed in man the quadriceps extensor cruris, whose other divisions—the
rectus femoris and vastus externus—will be dissected with the outer
aspect of the thigh. The dissection in this position of the limb will he
completed by an examination of the common insertion of the iliacus
and psoas magnus.
The Vastus Internus (and Crureus *) (Plates 13 and 14) is a thick
fleshy muscle whose fibres take origin from the internal surface and inner
half of the anterior surface of the femur, meeting along the front of the
femur the vastus internus, and with it forming a groove in which the
rectus femoris rests. Its fibres are inserted into the inner ligament of
* This is the name given to the fourth division of the quadriceps in human anatomy. The &tei
that represent it in the horse are in no way separable from the inner vastus. Under the same na"ia
Percivall describes (inaccurately) the rectus parvus.
-ocr page 131-
DISSECTION OF THE POSTERIOR LIMB.                                  63
Patella, or into that bone along with the other divisions of the
quadriCeps_
ction,—It is an extensor of the stifle-joint.
soas Magnus and Iliacus (Plate 14). Only the terminal portion of
t>i ° se muscles is here seen. They are more fully displayed in
issection of the sublumbar region, where the psoas magnus arises
the last two ribs, and the vertebrae from the 16th dorsal to the 5th
mbar (Plates 44 and 45). The iliacus arises from the iliac surface and
ial angle of the ilium, and from the sacro-iliac ligament. It presents
P groove for the terminal portion of the psoas magnus. The two
. Pass downwards beneath Poupart's ligament, and have a com-
i-nsertion into the small {internal) trochanter of the femur.
c ton.-—These muscles flex the hip-joint, and rotate it outwards.
THE HIP AND OUTER ASPECT OP THE THIGH.
, ^i%on.—The animal should be suspended in imitation of the natural
' „ mS posture, by the means mentioned at page 8.
j . r->act-rnarking.—A prominent feature of the region is the bony pro-
tp,         formed by the external angle of the ilium (angle of the haunch).
At v. er *scnu may a^so De felt by pressing deeply at the point of the hip.
of /7 6 Shest part of the croup the internal angle of the ilium (angle
e croup) may be felt, and in the middle line the tips of the sacral
S are subcutaneous. In a lean animal a number of grooves are seen
mg the divisions of the biceps and the line of opposition of that
' e with the semitendinosus (Plate 15).
rn'ri V3ns-—An incision through the skin is to be carried along the
. e hue from the root of the tail as far forwards as the lumbar
tv ,i a' Wnere a transverse incision is to be carried outwards and down-
Q ., ' as fer as the level of the angle of the haunch. Beginning at the
e hne above, the dissector is to reflect the skin from the limb, as
^ as tne middle of the leg. The first few inches of the skin will
i e to be raised by the use of the scalpel, and then an attempt may
th           ^° *ear '* downwards off the limb—a method which will show
taneous nerves distinctly without further dissection.
a ANE0XJS Nerves. 1. Appearing a few inches from the middle line,
th • nie s^ender branches derived from the sacral nerves. 2. Two or
Da         ranches of considerable size, derived from the lumbar nerves,
3 a a vai'ds and downwards over the forepart of the gluteal region,
fro CW lllcnes below the point of the hip a cutaneous branch derived
a ,          °i the posterior gluteal nerves appears from between the biceps
I a0^emitendinosus, and separates into a number of radiating filaments.
0 , a ievel with the stifle-joint the 2)eroneal-cutaneous branch of the
, a Popliteal nerve comes out through the biceps, and is distributed
^e outer side of the leg.
-ocr page 132-
64
THE ANATOMY OF THE HORSE.
Directions.—The dissector should, in the next place, direct his attei1"
tion to the strong fascia covering the muscles in this region, after which
the fascia must be removed, and the muscles cleaned and separated.
Gluteal Fascia and Fascia Lata. The gluteal fascia forms a bluish-
white covering over the muscles of the hip, and by its deep face affof"8
origin to many fibres of the superficial and middle gluteal muscles. **
is fixed above to the summits of the sacral spines and to the extern**
angle of the ilium, and between these points it is continuous forwards
with the tendon of the latissimus dorsi. It is prolonged downwards o^eI
the muscles of the thigh, where it takes the name of the fascia la$*
This fascia lata receives in front the insertion of the tensor vaghliB
femoris muscle, and it should not be removed until that muscle has beeo
examined. It forms a sheath for the muscles of the thigh, and is pr0"
longed downwards over the leg. From its inner face a septum is sent in
between the vastus internus and the biceps, to join the tendon of the
superficial gluteal muscle, and be inserted into the femur.
The Tensor Vagina Femoris (Plate 15). This muscle is situated
at the forepart of the thigh, in front of the superficial gluteal musclei
from which it is somewhat difficult to separate it, It arises from the
external angle of the ilium, and it is inserted into the fascia lata.
Action.—It flexes the hip-joint. It also keeps the fascia lata teuse>
and mechanically aids in keeping the stifle-joint extended.
Directions.—The gluteal fascia and the fascia lata are now to be
removed. It is a matter of some difficulty to remove the former, as its
deep face has the muscular fibres taking origin from it, and these are
therefore exposed with a rough surface when it is removed.
The Superficial Gluteus {Gluteus externus of Percivall, part of the gl'u'
teus maximus of human anatomy) (Plate 15). The outline of this muscle
is not distinctly recognisable until the gluteal fascia has been removed.
It is then seen to have some resemblance to the letter V, having in it9
upper border an indentation that divides it into an anterior and *
posterior branch. The anterior branch arises from the external ang'l6
of the ilium; the posterior from the gluteal fascia. Both converge
to a common tendon, which is inserted into the third trochanter of the
femur (trochanter minor externus). From the posterior branch of the
muscle an aponeurotic layer passes backwards' beneath the biceps, t°
be inserted into the sacro-sciatic ligament and the tuber ischii.
Action.—It is an abductor at the hip-joint.
The Biceps Femoris (Plate 15). This is one of the largest muscles
in the body. It arises from the sacral spines, the fascia enveloping the
muscles of the tail, the sacro-sciatic ligament, the tuber ischii, and the
gluteal fascia. Interiorly it has three divisions, one of which is inserted
into the anterior surface of the patella, a small synovial bursa being
interposed between the tendon and the bone, another into the tibi8*
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DISSECTION OP THE POSTEEIOR LIMB.                                  65
st> and the third into the fascia of the leg. Besides these, the
le has an insertion into the circular mark behind the third
nanter of the femur, by means of a fibrous band detached from the
16eP surface of the muscle.
etion.—The anterior half of the muscle, in virtue of its attachment
e patella, is an extensor of the stifle, and an abductor at the hip.
_ posterior half of the muscle, with its insertions into the tibia and
,, a °f the leg, is a flexor and an outward-rotator at the stifle. When
stifle-joint is kept extended, the lower end of the muscle becomes its
Point, and it then extends the pelvis on the femur, and aids in
Th q
"e Semitendinosus (Plate 15). This muscle is placed at the
erior border of the hip and thigh, where it occupies a position
een the last-described muscle and the semimembranosus. The
e ls bifid superiorly, where it arises by one division from the
^ d* spines and sacro-sciatic ligament, and by another and shorter
cii from the tuber ischii. Inferiorly it has a flat tendon, which is
erf jnto -the tibial crest, and whose posterior border blends with
fle fascia of the leg.
c«ow—To flex the stifle and rotate the leg inwards. When the
stifle is fl i •                           •
» nxed, it can aid in rearing.
e biceps femoris and semitendinosus muscles represent, apparently,
e Muscles of the same name in man, plus portions of the gluteus
th mU8' ■Per°ivall describes the semitendinosus as representing also
J yemimembranosug
of man.
li rectlons-—The biceps must be carefully severed at its origin, and
I           downwards. This will expose the aponeurotic layer that passes
a] a '* from the superficial gluteus. A branch from the posterior
ai nerves should be found entering the last-named muscle by turn-
s orwards round the middle gluteus. Both branches of the super-
giuteus should then be thrown downwards in order to fully
*lge the next muscle.
e Middle Gluteus (Gluteus maximus of Percivall) (Plate 15) is a
re ' e °* great size and strength. It was partly exposed before the
th           °^ *ne superficial muscle. The fibres of the muscle arise from
poneurosis of the common mass of the loins (longissimus dorsi),
sa •          luteal surface of the ilium, from the two ilio-saoral and the
an 1 ~SCla**c ugaments, and from the gluteal fascia. It has three distinct
tr .l ° an* insertions: 1. By a tendon, into the summit of the great
' nter. 2. By another tendon, which plays over the convexity of the
sarne fern •>*                                           .
th         uctlauter by means of a synovial bursa, and becomes inserted into
^ . . 3. By a triangular fleshy slip, into the back of the trochan-
" '""' *0 extend and abduct the hip. In the former of these
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GG
THE ANATOMY OP THE HORSE.
actions, when the limb is free to move, the femur, and with it the
whole limb, is carried backwards ; but when the femur is fixed, it raises
the trunk, as in rearing.
Directions.—The last-described muscle must be removed in order to
expose the deep gluteus and the other structures which it covers. A
deep incision should be made through the muscle along the crest of the
ilium, and the muscle is to be turned down by severing its fibres ^
their origin. Care must be taken, in doing this, to avoid cutting the
subjacent deep gluteus, whose fibres may be recognised, as soon as they
are reached, by their insertion within the great trochanter. A reference
to Plate 16 may here be useful. The semitendinosus is to bo turned
down in the same manner, by severing its superior attachments ; and
this muscle and the biceps may be removed to the extent shown in the
Plate. In performing this dissection, the gluteal nerves and vessels and
the ischiatic vessels are unavoidably severed, but a look-out should
be kept for these, and they should be cut about the points shown in
the figure.
The Gluteal Artery (Plate 16) is a branch given off from the
internal iliac within the pelvis. After a very short course it splits into
several branches, which, emerging by the great sacro-sciatic opening,
are distributed to the gluteal muscles.
The Isohiatic Artery (Plate 16) is one of the terminal branches
of the lateral sacral artery, which, again, is a collateral, branch of the
internal iliac. It perforates the sacro-sciatic ligament near the edge ot
the sacrum, and is distributed in the biceps and semitendinosus.
Veins of the same names accompany the foregoing arteries.
The Internal Pudic Artery. The dissection of this artery belong8
to another region, but the vessel is generally visible here in a part of
its course. A few inches of it are represented in Plate 16, as showing
faintly through the texture of the sacro-sciatic ligament. It is described
at page 342.
The Gluteal Nerves (Plate 16). These nerves, which are derived
from the lumbo-sacral plexus, issue from the great sacro-sciatic opening
in company with the gluteal vessels and the great sciatic nerve. They
consist of an anterior and a posterior set.
The Anterior gluteal nerves are three or four in number. One of then1
passes downwards and forwards between the middle and internal
"■luteal muscles, to reach the tensor vaginae femoris and anterior division
of the superficial gluteus. Another branch passes downwards over the
deep gluteus, to which it is distributed. One or two other branches
supply the middle gluteus.
The Posterior gluteal nerves are two in number—an upper and a
lower. The upper nerve passes backwards on the sacro-sciatic liga"
ment; and after giving branches to the posterior division of the
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DISSECTION OF THE POSTERIOR LIMB.
67
Perheial gluteus, and to the posterior fleshy slip of the middle
W a US' '* en^ers the biceps femoris. The lower nerve, passing down-
and backwards, divides into an outer and an inner branch ; the
lormgj. + •
ou ' mng over the tuber isohii on its outer side, becomes cutane-
th              back of the thigh about four or five inches below the tuber;
th ■' ' a^er giving twigs to the semitendinosus, joins a branch from
ternal pudic nerve to be distributed to the perineal structures.
ori« Great Sciatic Nerve (Plate 16). This is, at its point of
e> , the largest nerve in the body. It is furnished by the lumbo-
sacral -nl
rib ^lexus, and appears at the great sacro-sciatic opening as a broad
r,j ' tn its downward course in the hip it is covered by the middle
°li + S' ailC' rests in succession on the sacro-sciatic ligament, the
jn). 3 mternus, the gemelli and common tendon of the obturator
incl jUS auc^ Pyrif°rlrlis, and the quadratus femoris. In the thigh it is
s„ .         between the biceps and semitendinosus outwardly, and the
embranosus and great adductor inwardly. The trunk of the nerve
48 COVI+'
th lrmed as the internal popliteal nerve between the two heads of
In,, ^astrocnemius, where it will be followed in the dissection of the
It
gives off in succession the following branches :—1. A nerve for
fern • °^ *ne obturator internus, pyriformis, gemelli, and quadratus
,, s" This slender branch is given off about midway between the
0r. ., c nc' small sciatic openings, and it descends at the posterior border
th Parer|t trunk, or between that and the ligament. The nerves to
and          ratus and gemelli may arise from the sciatic independently,
anrl v ancn to the first of these muscles passes under the gemelli
2 To. Cominon tendon of the pyriformis and obturator internus.
- external popliteal nerve is a large branch that separates from the
cle S01atic about the level of the small sacro-sciatic opening; and,
and ,8 in front of the parent nerve, it passes between the biceps
j , e °uter head of the gastrocnemius, where it will be followed at a
stage. The peroneal cutaneous branch of this nerve has already
stifl een Perf°rating the lower part of the biceps, at the level of the
j ' • A branch that divides to supply the semimembranosus and
ter P0r^ons of the biceps and semitendinosus (Plate 14). 4. The ex-
saphenous nerve, which will be followed in the dissection of the leg.
bovi           &—The great sciatic nerve should now be cut at the upper
Th r *^e gluteus internus, and turned downwards with its branches,
obf ^ teus internus, and the common tendon of the pyriformis and
cle             internus, together with the gemelli, should be carefully
jm'ritaed and defined; and to facilitate this, the limb should be rotated
Th'' aS far as P08Sible, by pulling the point of the hock outwards.
k ul put these muscles on the stretch,
abo ° P Gluteus> or gluteus internus (Plate 16, and fig. 2), is placed
the hip-join^ in immediate contact with the capsular ligament.
-ocr page 136-
68                                   THE ANATOMY OF THE HOBSE.
It is a comparatively small muscle, with coarse fasciculi having a slightly
spiral direction. It arises from the rough lines on the gluteal surface oi
the shaft of the ilium just above the cotyloid cavity, and from the supra-
cotyloid ridge (superior ischiatic spine). It is inserted to the inner side
of the convexity of the great trochanter.
Action.—It is an abductor and inward-rotator at the hip-joint.
The Obtubatoe Intebnus and the Pyeifoemis (Plate 16, and fig. 2)
are two muscles arising within the pelvis, the former taking origin from
the bone around the obturator foramen, and the latter from the pelvic
surface of the ilium. They have a common tendon, which emerges
from the pelvis by the lesser sacro-sciatic opening, where it plays over
a smooth portion on the external border of the ischium. The tendon
is inserted into the trochanteric fossa.
Action.—To produce outward rotation at the hip.
The Gemelli. In Plate 16 a bundle of muscular fibres is seen at
each edge of the above-mentioned common tendon. If this common
Fig. 2.
Muscles of the Tail, deep Muscles of the Hip, and Pelvic Ligaments (fcftauveau).
1. Erector coccygis; 2. Curvator coccygis; 3. Depressor coccygis; 4. Compressor coccygi/'»
5. Deep gluteus; 6. Eectus parvus ; 7. Common tendon of obturator internus and pyriforniis;
8. Gemelli; 9. Accessory fasciculus of the same ; 10. Quadratus f emoris ; 11. Sacro-sciatic 'ligament;
12. Great sacro-sciatic foramen ; 13. Superior ilio-sacral ligament; 14. Inferior ilio-sacral ligament.
tendon be cut where it appears at the lesser sciatic opening, and raised
outwards, what previously seemed two distinct muscular bundles will
now be seen to be the edges of a single flattened muscle, which arises
from the ischium below and at the edges of the smooth surface for the
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DISSECTION OF THE POSTERIOR LIMB.                                 69
ge of the common tendon, and becomes inserted in common with
tha* tendon.*
to».—The same as the two preceding muscles.
''ections.—The tensor vaginae femoris and the gluteus interims
lit* U0W ^e cu* awavi care being taken not to injure the capsular
ent, on which the latter muscle rests. The rectus femoris, vastus
Uu-S, and rectus parvus are then to be dissected. The last-
0f oned muscle will be found by dissecting deeply into the upper part
th -v erstice between the other two muscles, and at the same point
'-aco-femoral artery will be found.
j , e ^Liaco-femoral Artert is one of the terminal branches of the
ah f 1 ^'ao (P^ite 48). It comes out between the iliacus and the
th            ^le ibum, an(I penetrates between the rectus femoris and
l7a8tus externus.
0n e Pectus Femoris (Plate 18) arises by two heads—one from each
cot ° Pressi°ns on the shaft of the ilium, above and in front of the
an I        cavity. The central portion of the muscle is thick and fleshy,
Sts in a groove formed bv the twovasti, with which it is confounded
^ its 1                                          . J v
f.n, „ iower extremity. It is inserted into the anterior face of the
Patella,
ton—To flex the hip-joint and extend the stifle.
fe e Vastus Externus (Plate 18) arises from the outer surface of the
Its fli' ail(^ from *ne outer half of the anterior surface of the same bone.
res become inserted along with the rectus femoris into the patella.
j?ion—To extend the stifle.
thp ^,e°tus Parvus (fig. 2) is very slender when compared with
a
lscles between which it is placed, being about the thickness of
vh' u ^ nil8'er- It arises from the ilium, external to the pit from
°a the
fivw.,           outer head of the rectus femoris takes origin. Passing in
ilont 0f j.i                                                                         °                   D
jj. . . wie capsular ligament of the hip-joint, to which it adheres,
lnto the
1 s ^self between the two vasti muscles, and is inserted
anterior surface of the femur.
n—The muscle is of too slender a size to exert any appreci-
, Xor action on the hip-joint, and probably its function is to raise
abl
pao- 'PSu^ar ligament during flexion of the joint. (See footnote,
D' ■
from t0M&'—The dissector is now in a position to detach the limb
and 6 truuk> and this should be done by cutting through the bone
qe            structures, below the level of the internal trochanter. It is
j°int ' ^ *° make the section at this point, in order to leave the hip-
for e .              common insertion of the iliacus and psoas magnus intact
mation by the dissector of the abdomen and pelvis. The limb
n°t hesitate t "S ?n,18cle c™sists of two separate slips, and from this disposition it is named. I do
UsUally ties ., glve ^ tne same designation here, although I have never found it double as it is
-ocr page 138-
70
THE ANATOMY OP THE HORSE.
having been removed, it should be placed on a table, and the cut
muscles connected with it may be completely cut away after they
have been identified. In doing this, a better opportunity will "e
afforded to observe accurately the insertion of each muscle. In remOv'
ing the lower portion of the biceps, particular care must be taken
not to cut the external popliteal and external saphenous nerves,
which are included between it and the outer head of the gastrocnemius
(Plate 18).
THE LEG.
Surface-marking.—The bones of the leg are clothed by muscle8
except at the inner side of the limb, where the tibia is subcutaneous-
This unprotected area of bone corresponds to the shin in man. The
superficial muscles of the region (see Plates 17 and 18) form prom1'
nences more or less distinct, especially in the neighbourhood of the hock,
where the various tendons stand out distinctly during the movement*5
of the living animal.
Position.—In the further dissection of the limb, it may be placed on 8
clean table, and laid on either side as may be convenient; or a cord TO&l
be passed round the femur, and the limb suspended at such a height as
just to permit the hoof to come into contact with the table. This latter
method has the advantage of keeping the part clean; and whi^
dissection is being carried on, the leg may be steadied in any position by
an assistant.
Directions.—An incision through the skin is to be carried down the
middle line of the limb on its inner side, and terminated a few inches
below the hock, where a circular incision may be carried round the
limb. The whole of the skin above the circular incision is then to he
removed, and the cutaneous nerves and vessels of the region are to be
examined.
The Internal Saphena Vein. On the inner side of the leg, above
the hock, two venous branches will be seen to converge and unite to
form the internal saphena vein, which is continued up the leg to v&
thigh, where it has already been dissected. The vessels by whose uni01'
the main vein is formed, are the upward continuations of the interna1
and external metatarsal veins. Slender branches of the saphena artery
accompany these veins.
The External Saphena Vein. This vessel begins at the hock, where
it communicates with the internal saphena vein, and with the posted01
tibial vein. It ascends at the outer side of the gastrocnemius tendon,
and, passing between that muscle and the biceps, it empties itself int
the femoro-popliteal vein.
Cutaneous Nerves. 1. The ramifications of the internal sapheno^
nerve cover the inside of the leg, and descend over the inside of th
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DISSECTION OF THE POSTERIOR LIMB.                                  71
2. The external saphenous nerve (Plate 18) is a branch of the
at sciatic. It descends over the outer head of the gastrocnemius,
!e it is covered by the biceps, and is reinforced by a branch from
e eternal popliteal (or fr om the peroneal cutaneous division of that
Jerve)- It then continues to descend, lying in company with the vein of
same name, in front of the outer edge of the gastrocnemius tendon ;
Passing over the hock, it is distributed to the skin on the outer
°i the metatarsus. 3. The cutaneous termination of the musculo-
uneous division of the external popliteal nerve (Plate 18) pierces the
I fascia on the outer side of the limb at the lower third of the leg;
' passing over the hock, it is distributed to the skin on the front of
the metatarsus.
eep Fascia of the Leg. This forms a close-fitting, fibrous
iope to the muscles of the region. Its inner face furnishes septa
„ pass in between the muscles; and over the inner surface and crest
e tibia, it is adherent to the bone. Above it is continuous with the
a lata and tendons of the gracilis and semitendinosus on the inside,
i with the tendon of the biceps on the outside. As it passes over the
!t becomes thinner, and is continuous with the fascia of the meta-
tarsa.l region.
Sections—The muscles on the back of the leg may now be dissected,
vessel and nerves shown in Plates 17 and 18 being at the same
e carefully preserved. By a reference to Plate 18, the student
note the position of the small soleus muscle, so as to avoid its
6 ThVal with the fascia-
,e Gastrocnemius (Plates 17 and 18). At its origin this muscle
te          °^ *wo distinct fleshy heads, which terminate in a single inferior
fo U' ^e outer head arises from the outer lip of the supracondyloid
0 . the femur, the inner head from the supracondyloid crest. The
ha 1        tendon is joined by that of the soleus, and is inserted into the
th + ^ °^ *ne summit of the os calcis. When the hock is strongly flexed,
0j. ndon for an inch or two above its insertion rests on the forepart
th SUrtlmit, and a small synovial bursa is here interposed between
ben           n and the bone. The tendon of the perforatus is at first
w> ; *hat of the gastrocnemius; but, passing to the inner side, it
sum •          superficial to the latter, which it completely covers at the
for              ^e os caI°is- I11 thus changing positions, the two tendons
Th'                twist, and indent each other like the strands of a rope.
ext ,.e on of the gastrocnemius corresponds to the firm tendon
mg upwards from the human heel, and known as the tench A chillis.
tfwn..-—To extend the hock-joint,
.           Soleus (Plate 18). In British veterinary text-books this muscle
text eousIy termed plantaris. It is a small muscle of delicate
' ail(I it is often partially or entirely removed in cleaning the
-ocr page 140-
72
THE AN ATOM Y OF THE HORSE.
gastrocnemius. It arises from the head of the fibula, and its tendon
joins that of the preceding muscle, which it assists in extending the hock.
Directions.—The inner head of the gastrocnemius is to be severed at
its origin, and turned downwards in the manner shown in Plato 17.
The Superficial Plexor of the digit (flexor perforatus) (Plates 17 and
18) is remarkable in that, throughout nearly the whole of its extent, w
exists as a strong tendinous cord with a sparing admixture of muscular
fibres at its upper fifth only. It arises from the bottom of the supra-
condyloid fossa; and, winding round the gastrocnemius tendon in
the manner already described, it gains the summit of the os
calcis, over the extreme posterior portion of which it plays b}'
means of a synovial bursa. At the os calcis it detaches on eacli side a
slip to be inserted into the bone. It is continued downwards in the meta-
tarsal and digital regions in the same manner as the perforatus of the
fore limb, becoming finally inserted by a bifid termination into the
second phalanx. In front of the tendons of the superficial flexor and
gastrocnemius there will be noticed a strong fibrous band, which is
united to these muscles above, and inserted into the os calcis below,
while laterally it is continuous with the deep fascia of the leg.
Action.—It flexes successively the pastern and fetlock joints ; and, by
its insertion into the os calcis, it is also an extensor of the hock-joint-
It also plays an important part in mechanically maintaining the hock
in a state of extension so long as the hip and stifle joints are kept
extended by muscular contraction.
The flexor perforatus of the horse is represented in man by two
distinct muscles—the plcmtaris and the flexor brevis digitorum.
Directions.—The deep laj-er of muscles at the back of the leg consists
of the popliteus, the flexor perforans, and the flexor acoessorius ; and
these should now be examined as far as possible without disturbance of
the vessels and nerves. The superficial muscles must therefore, in the
meantime, be allowed to remain in position.
The Popliteus (Plato 17). This muscle is placed immediately behind
the stifle-joint, whose posterior ligament it covers. It arises by a tendon
from the lower and most anterior of the two pits situated on the outer
side of the external condyle of the femur. (The other pit is for the
attachment of the externri lateral ligament of the stifle, the ligament
concealing the origin of the tendon.) The tendon is partly invested by
the synovial membrane of the joint, and plays round the external sem1"
lunar cartilage, and over the articular surface of the tibia. The fibres
of the muscle have an oblique direction downwards and inwards, and are
inserted into the comparatively smooth triangular area at the upper part
of the posterior surface of the tibia, and into the inner edge of the bone
at the same level. The terminal portion of the popliteal artery lS
concealed by the muscle.
-ocr page 141-
73
DISSECTION OF THE POSTERIOR LIMB.
Action.—It flexes the stifle, and to a slight extent rotates it inwards.
TL Deep Flexor of the digit (flexor perforans) (Plates 17 and 18).
ls muscle is indistinctly divided into an outer and an inner division,
e former being- the larger of the two. It arises from the ridged area
oil tl -
cne posterior surface of the tibia, from the external tuberosity at the
Pper end of the same bone, from the fibula, and from the interosseous
ernbrane uniting the two bones. At the lower third of the tibia the
Ocular divisions are succeeded by tendons, which soon unite ; and the
8'ie tendon thus formed glides through the tarsal sheath at the inner
°i the os calcis, and then descends at the back of the metatarsus
digit, to be inserted into the solar surface of the os pedis, in a man-
exactly similar to the flexor perforans of the fore limb. Like that
Scle, it receives, at the upper part of the metatarsus, a reinforcing
neck band—the subtarsal ligament, which is the downward continua-
°f the posterior tarso-metatarsal ligament of the hock. This band
ot so strong as the subcarpal ligament of the fore extremity.
. (-tion.—It flexes successively from below upwards the interphalangeal
r s and the fetlock, and finally extends the hock.
. e Tarsal Sheath, through which the tendon passes at the inner
oi the back of the hock, is formed outwardly by the grooved surface
tie os calcis, in front by the posterior ligament of the tibio-tarsal
ulation and by the posterior tarso-metatarsal ligament, and it is
pleted inwardly by a fibrous arch that converts the groove into a
'Plete canal. An extensive synovial membrane here invests the
°n and lines ,the passage, extending upwards for a few inches at
; lower extremity of the tibia, and downwards below the middle of
nietatarsus. A dropsical condition of this synovial sac gives rise
le condition termed ': thorough-pin."
'         e Flexor Accessorius (Plate 17) is a somewhat slender muscle
acting obliquely downwards at the back of the leg, between the
ti l 6US ail<^ the perforans. It arises from the back of the external
j 0Slty at the head of the tibia. Its tendon, which begins at the
third of the leg, descends first in a groove on the deep flexor, and
through a synovial passage at the inner side of the tarsus, and
J Mends with the tendon of the deep flexor at the back of the
metf*irsus.
•4c*io%__To asgist the deep flex01.
„ , . ectl°ns.—The vessels and nerves of the region must now be noticed,
it will be convenient to begin with the latter.
Qi> . e t^TERNAL Popliteal Nerve (Plates 17 and 18) is the continuation
cm ■ 'Jn'at static. It passes in between the two heads of the gastro-
Perf S musc^e' follows for a short distance the posterior border of the
Co ,. s> and at the level of the lower border of the popliteus it is
under the name of the posterior tibial nerve. The nerve fur-
-ocr page 142-
74
THE ANATOMY OF THE HORSE.
nishes branches to all the muscles at the back of the leg, viz., both
heads of the gastrocnemius, the soleus, the perforatus, the popliteus,
the perforans, and the flexor accessorius. The branch to the soleus gains
its muscle by passing between the popliteus and the outer head of the
gastrocnemius.
The Posterior Tibial Nerve (Plate 17) continues the internal
popliteal. It is at first deeply placed beneath the inner head of the
gastrocnemius, where it crosses the perforatus. Becoming more super-
ficial by emerging from beneath the first-named muscle, it descends on
the inner side of the leg, in front of the tendo Achillis, being covered by
the deep fascia of the leg. At the tarsus it bifurcates to form the
external and internal plantar nerves. These accompany the perforans
tendon through the tarsal sheath, and are continued through the meta-
tarsal and digital regions like the corresponding nerves of the fore limb.
The only collateral branches of the posterior tibial nerve are slender
cutaneous filaments, one of which is shown in Plate 17, descending over
the inner side of the hock.
The External Popliteal Nerve and the External Saphenous Nerve
cross the external head of the gastrocnemius on its outer side (Plate 18)-
The latter nerve has already been described, an 1 the former should be
preserved to be followed in the dissection of the front of the leg.
Directions.—The outer head of the gastrocnemius and the perforatus
should now be detached close to their origin, and turned downwards-
This will expose the whole of the popliteus, which must be dissected
carefully from the posterior ligament of the stifle and from the tibia, in
order to follow the popliteal artery.
The Popliteal Artery (Plate 17) is the direct continuation of the
femoral. In veterinary anatomy the arbitrary line of distinction is
usually drawn at the point where the vessel passes in between the heads
of the gastrocnemius. It passes over the posterior ligament of the
stifle, where it is covered by the popliteus; and at the tibio-fibular arch
•it bifurcates to form the anterior and posterior tibial arteries. It gives
off—(1) articular branches to the stifle, and (2) muscular branches to
the superficial muscles at the back of the leg.
The Posterior Tibial Artery (Plate 17) is much the smaller of the
two terminal branches of the popliteal. In the first part of its course it
is deeply jflaced beneath the popliteus and the deep and accessory flexors.
As it descends, it becomes more superficial, and appears at the posterior
border of the flexor accessorius, whose tendon it follows in the same posi-
tion. A little above the hock it forms an S-shaped curve that brings it
into company with the terminal part of the posterior tibial nerve ; and
passing with that nerve into the tarsal sheath, it divides at the back of
the hock into the two plantar arteries. The collateral branches of the
posterior tibial are—(1) muscular branches to the deep muscles at the
-ocr page 143-
DISSECTION OP THE POSTERIOR LIMB.                                  75
k of the leg; (2) the nutrient artery of the tibia ; (3) a retrograde
(inch which, emanating from the second curve of the sigmoid flexure,
°ends in front of the tendo Achillis ; (4) articular branches to the tarsus.
eins. The foregoing arteries run in company with satellite veins
bearing the same names.
directions.—The front of the leg must now be dissected; and as
in.          step, the muscles of the region should be cleaned and isolated.
ese are—the extensor pedis, the flexor metatarsi, and the peroneus.
e nrst of these is superposed to the second on the front of the leg,
, to the outer side of both is the smaller peroneus. In dissecting
tendons of these muscles in the region of the hock, care should
aken of three transverse fibrous bands that retain the tendons in posi-
1011 (Plates 18 and 19). The first of these bands is fixed by its extremities
the lower end of the tibia, and beneath it pass the tendons of the ex-
Sor pedis and flexor metatarsi. The second is fixed outwardly to os
s j and, passing over the extensor pedis tendon, it is attached to the
0r metatarsi. The third retains the tendons of the extensor pedis
peroneus in position at the upper end of the large metatarsal bone,
J^tuch its extremities are attached.
he Extensor Pedis (Plate 18). This muscle arises, in common with
tendinous portion of the flexor metatarsi (fig. 3, page 76), from the pit
een the trochlea and external condyle of the femur. It has a thick,
°rm muscular belly, which at the lower third of the leg is succeeded
J ' strong tendon. This passes over the front of the hock, and under
hree annular bands just described. It then descends over the front
„ e metatarsus, where it receives the insertion of the short extensor
e digit, and is joined by the tendon of the peroneus. In the dissec-
°i the digit it will be pursued to its insertion into the pyramidal
mmenceoftheospedis.
1C.l0'l-~"It extends in succession from below upwards the interphalan-
^ joints and the fetlock, and finally flexes the hook.
e Peroneus (Plate 18). This is a much smaller muscle than the
„ aing, to whose outer side it lies. Its muscular fibres have a penni-
st'fl arrailSement, and arise from the external lateral ligament of the
tl a m the fibula, and from the aponeurotic septum between it and
eP nexor of the phalanges. Its tendon passes through the groove
tih' 6 erternal tuberosity (external malleolus) at the lower end of the
s '' .and then over the outer side of the hock, where it plays in a
ho I- ■ Cana* formed in the external lateral ligament. Below the
De V 1S d'rected obliquely forward, and joins the tendon of the extensor
about the middle of the metatarsus.
ion. The same as the preceding muscle,
refl          °m-—Cut the extensor pedis about the middle of the leg, and
uPwards and downwards to expose the next muscle.
-ocr page 144-
7G
THE ANATOMY OF THE HORSE.
The Flexor Metatarsi (fig. 3). This muscle consists of two parallel
portions—a superficial and a deep. The superficial division exists in
the form of a tendinous cord with little or no
muscular tissue, and arises, in common with the
extensor pedis, from the pit between the trochlea
and external condyle of the femur. This tendon
of origin passes through the notch between the
anterior and external tuberosities at the upper
end of the tibia, and is there enveloped by the
2 synovial membrane of the femoro-tibial joint. In
the leg the tendinous cord rests on the deep
division of the muscle, and passes under the
annular band at the lower extremity of the tibia, in
company with the tendon of the extensor pedis.
At the front of the hock it is perforated by the
tendon of the deep division, and then bifurcates,
one branching continuing downwards to bo inserted
into the upper extremity of the large metatarsal
bone, the other deviating outwards to be inserted
into the cuboid.
The deep division of the flexor metatarsi rests on
the tibia, and its muscular fibres arise from the
upper part of the outer surface of that bone. At
the lower end of the tibia it is succeeded by a
tendon which perforates that of the superficial
Fig. 3.
Flexou Metatarsi Muscl
(Ghauveem),
1. Superficial division of
the muscle; 2. Its origin
from the femur; 3. Its
cuboid brand); 4. Its
metatarsal branch ; 5.
Deep division of the
muscle; 6. Its tendon
passing through that of
the superficial division ;
7. Cuneiform branch of
this tendon ; 8. Metatarsal
branch of the same ; 9.
Extensor pedis; A. Pero-
neus ; B. Insertion of
middle straight patellar
ligament; 0. Femoral
trochlea.
division of the muscle, and divides, one branch
passing to be inserted into the head of the large
metatarsal bone, along with the large division of
the superficial cord, while the other branch is
carried inwards to be inserted into the cuneiform
parvum.
Action..—To flex the hock. In this action the
superficial tendinous cord plays merely a mechanical
part, flexing the hock when the stifle is flexed.
The External Popliteal Nerve (Plate 18)-
This nerve has already been seen in the hip and
thigh. It is a branch given off by the great sciatic;
and, descending in front of the parent nerve, it
passes between the biceps and the outer head of the gastrocnemius,
where, a little behind the external lateral ligament of the stifle, it
divides into the musculo-cutaneous and anterior tibial nerves.
The Musculo-Cutaneous Nerve descends along the line of contact
of the extensor pedis and peroneus, supplying filaments to the latter
muscle. At the lower third of the leg, as has already been seen, the
-ocr page 145-
77
DISSECTION OF THE POSTERIOR LIMB.
aneous division of the nerve pierces the deep fascia, and passes over
e hock to supply the skin on the outer side of the metatarsus.
J-he Anterior Tibial Nerve separates from the preceding at an
\ an8'le, and a few inches below the stifle it passes under cover of
e extensor pedis. It supplies twigs to the last-named muscle, the
-'or metatarsi, and the short extensor ; and descends at the outer side
ne tibial vessels, afterwards accompanying the large metatarsal artery
terminate in the skin on the outer side of the digit.
The Anterior Tibial Artery (Plate 19). This, it will be recoi-
led, is one of the terminal branches of the popliteal artery. Origi-
' lng behind the upper extremity of the tibia, it is here seen coming
wards through the tibio-fibulav arch. It descends on the tibia,
r cover of the flexor metatarsi, and accompanied by the nerve and
n of the same name. Gaining the front of the hock, it rests on the
erior tibio-tarsal ligament, covered by the flexor metatarsi and
ensor pedis at their line of contact. Here it deviates outwards under
endon of the last-mentioned muscle, and divides into two vessels
unequal size. The larger of these, which continues the direction
Of ■f'K
ne parent vessel, is the large metatarsal artery; the other is the
°rating metatarsal artery; and both will be dissected with the
ai'sus. The anterior tibial artery gives off numerous un-named
cuiar branches to the extensor pedis, flexor metatarsi, and peroneus ;
'^ articular branches to the hock.
re Anterior Tibial Vein, which may be double, keeps close com-
j with the artery. It is formed at the front of the hock by
. usion of several rootlets. The largest of these is the upward
QUation of the deep metatarsal vein, which comes forwards through
^ ascular canal between the tarsal bones. After passing backwards
. gh the tibio-fibular arch, the anterior joins the posterior tibial
6111 to form the popliteal.
THE METATARSUS AND DIGIT,
rni
Qr. e °-lstal portion of the horse's hind limb, beyond the lower extremity
tibia, is technically termed the pes, as it corresponds to the foot
i *"• The tarsus, or hock, represents the human ankle; the part
fo + Gn ^6 tarsus and fetlock corresponds to the body of the human
th '„a *s termed the metatarsus; while the rest of the limb, beyond
jock, is the digit, and is the homologue of man's third toe.
tei 1 e~marking.—Extending down the middle line in front is the
0i,. a °t the extensor pedis, which, a little below the tarsus, is joined
r . y "J the tendon of the peroneus. Behind the metatarsus, and
ao. . " ou the bone, is the suspensory ligament ; and behind that
^l are the deep and superficial flexors of the foot. The edges of
•n ., s ructures can be distinctly seen or felt in the living animal, and
clead subject they may be identified by a reference to Plate 19.
-ocr page 146-
78
THE ANATOMY OP THE HORSE.
At the upper part of the inner face of the metatarsus is a
flattened
horny callosity, or chestnut; and another horny excrescence, in the
form of a spur, or ergot, is concealed in the tuft of hair behind the
fetlock. By manipulation in the neighbourhood of the heels, the lateral
cartilages may be felt.
Directions.—Remove the entire remaining portion of skin from the
limb; and if it is intended to study on the same preparation the parts
contained within the hoof, this must, before the removal of the skin, be
detached by force in the manner described at page 35. The various
structures are now to be defined by dissection, in the order of the
following description; and while the vessels and nerves are being
cleaned, care must be taken of the small lumbricales muscles, which lie
on the tendon of the deep flexor, above the fetlock.
Cutaneous Nerves.—Descending over the inner side of the hock and
metatarsus are twigs of the internal saphenous and posterior tibial
nerves, and on the outer side of the same regions are branches of the
external saphenous and musculo-cutaneous nerves.
The Large Metatarsal Artery (Dorsalis pedis of man) (Plate 19)
is the larger branch resulting from the division of the anterior tibial
artery at the front of the tarsus. It inclines outwards and down-
wards under the extensor brevis and the peroneus, and places itself m
the groove formed on the outer side of the metatarsus by the junction ot
the large and outer small metatarsal bones. Along this groove w
descends in company with the slender continuation of the anterior
tibial nerve, until, a little above the button of the smaller bone, »
passes to the back of the metatarsus by penetrating between the W*
bones. Finally, it bifurcates above the fetlock, between the two
divisions of the suspensory ligament, to form the digital arteries. I*
gives off numerous un-named twigs to the skin, tendons, etc.
Descending in the metatarsal region, there are other four arteries
besides the vessel just described. They will be found, one at each side
of the flexor tendons, in company with the vein and nerve, and another
at each edge of the suspensory ligament, within the splint bone of the
same side. All of these are branches of an arterial arch formed across
the origin of the suspensory ligament from the back of the tarsus. The
arch corresponds to the subcarpal arch of the anterior limb, and is
formed as follows :—
The Perforating Metatarsal Artery, the smaller branch resulting
from the division of the anterior tibial artery, passes from the front to
the back of the tarsus by the canal between the cuboid, scaphoid, and
cuneiform bones. Here it unites with the outer and inner plantar
divisions of the posterior tibial, which descend in the tarsal sheath, one
on each side of the perforans tendon. Of the four vessels that spriu8'
from the arch thus formed, the two that descend with the plantai"
-ocr page 147-
DISSECTION OF THE POSTEEIOE LIMB.                                 79
1 Q\ 6S ^ ^e S'^e °^ ^ue flexor tendon are un-named and slender (Plate
+ .          other two are termed the plantar interosseous metatarsal
les. This may be regarded as the most typical arrangement of the
11SS uero> but it is not constant. Sometimes the inner plantar
ry is directly continued as the satellite vessel of the internal plantar
lclve m the
metatarsus, the outer plantar artery alone uniting with the
^orating metatarsal artery.
ne External Plantar Interosseous Artery is very slender. It
ends, as beforesaid, between the outer splint bone and the edge of
uspensory ligament; and above the fetlock it anastomoses with a
rrent twig from the large metatarsal artery.
ne Internal Plantar Interosseous Artery, a vessel of consider-
Slze, descends between the inner splint bone and the edge of the
1 ensory ligament. Above the lower extremity of that bone it inclines
1(te the middle of the limb to join the large metatarsal artery. It
,p s the nutrient artery of the large metatarsal bone.
6 "*->IGITAL Arteries (Plate 19). These arteries separate at an
of tk ail8^e' m passing backwards between the branches of bifurcation
• 6 SUsPens°ry ligament. For the remainder of their course they
d eatical with the homonymous vessels of the fore limb. For their
e^iption, turn to page 28.
Digital Veins (Plate 19). These are the satellites of the digital
» les> in front of which they ascend. They drain away the blood
an tv ven°us plexuses within the hoof; and, uniting with one
th ei* a^ove the fetlock, they form an arch between the deep flexor and
UsPensory ligament. From this arch spring the metatarsal veins.
e -Metatarsal Veins are three in number :—
the a Internal Metatarsal Vein ascends in front of the inner edge of
ep flexor tendon, in company with the internal plantar nerve and
.„, ei' artery. The vein is the most anterior of the three structures,
ne slender artery is between the vein and the nerve. At the
j* third of the metatarsus the vein deviates forwards, crossing the
sid 8Puut bone and the large metatarsal obliquely, to gain the inner
int              bock, above which it is continued as the anterior root of the
nal saphena vein. The course of the vein over the hock is generally
th '         ln *^le living animal, and when very prominent it constitutes
J^-called "blood-spavin."
0p ' e External Metatarsal Vein (Plate 19) ascends on the inner edge
th •         P flexor, having the same relationship to nerve and artery as
tin ernal vein. After communicating with the deep vein, it is coll-
ie through the tarsal sheath to become the posterior root of the
mtf*al saphena.
j^p         e **«5P Metatarsal Vein ascends between the suspensory liga-
1 u the large metatarsal bone : and passing from the back to the
a
-ocr page 148-
80
THE ANATOMY OF THE HOUSE.
front of the hook, by the vascular canal for the perforating metatarsal
artery, it is continued as the anterior tibial vein.
The Plantar Nerves. These nerves result from the bifurcation ot
the posterior tibial nerve when it gains the back of the tarsus. The)
accompany the perforans tendon in the tarsal sheath ; and diverging
from one another, they descend in the metatarsal region, one at eacn
side of the deep flexor tendon. Each is accompanied in the metatarsus
by the metatarsal vein of that side, and by a slender artery from the
vascular arch at the back of the tarsus. A little below the middle oI
the metatarsus the inner nerve detaches a considerable branch that
winds obliquely downwards and outwards behind the flexor tendons to
join the outer nerve above the level of the button of the splint bone
At the fetlock each nerve, coming into relation with the digital vessels;
resolves itself into three branches for the supply of the digit. These
are identical in their arrangement with the like branches of the plant»r
nerves in the fore limb, for the description of which, turn to page 30.
The student must now pursue the dissection of the following muscles
which have already been dissected in the leg, viz., the extensor pedis
and peroneus on the front of the limb, and the superficial and deep
flexors behind. In addition to these, there are the short extensor ot
the foot, the lumbricales, and the interossei, which entirely belong *°
this region; and since they are of small size, and might easily be over-
looked or injured, their dissection must be first undertaken.
The Lumbricales (Plate 19) and Interossei Muscles. These exact!)
resemble the muscles of the same name in the anterior member. Turn>
therefore, to the description of the latter given at page 31, substituting
the word foot for hand, toes for fingers, and metatarsal for metacarpal.
The Short Extensor of the foot {extensor brevis digitorum of man)
(Plate 19). Look for this small muscle at the front of the tarsus, in tne
angle of union of the extensor pedis and peroneus tendons. It aris(s
from the os calcis and astragalus, and is inserted into the united tendon
of the above-mentioned muscles, to whose action it is auxiliary.
The Extensor Pedis tendon (Plate 19) descends along the middle
line of the limb in front, to be inserted into the pyramidal eminence oi
the os pedis. Above the middle of the metatarsus it receives on i*s
outer side the tendon of the peroneus, and at the same point it is join0"
by the short extensor. A small synovial bursa is interposed between
the tendon and the anterior ligament of the fetlock, but at the front o»
the interphalangeal joints the ligament supports directly the articula1
synovial membranes. At the middle of the first phalanx the tend0"
is joined on each side by a strong band that descends from t*1
suspensory ligament.                                                                                     ,
Action.—It extends in succession from below upwards the interphai'
angeal joints and the fetlock, and finally it flexes the hock.
-ocr page 149-
DISSECTION OP THE POSTERIOR LIMB.                                  81
., e Peroneus (Plate 19). The tendon of this muscle emerges from the
°al canal in the external lateral ligament of the tarsus, and joins the
°U °^ *^e last-described muscle about the middle of the metatarsus.
ction.—The same as the preceding muscle.
he Superficial Flexor (flexor pedis perforatus) (Plate 19). The
°n °^ this muscle, after playing over the os calcis, descends on the
uie liile of the limb to the back of the fetlock, where it forms a
ai'kable ring for the passage of the tendon of the deep flexor. Be-
this point the tendon bifurcates, and each half is inserted into the
PI er extremity of the second phalanx, on its lateral aspect. In oon-
a°n with the tendon of this and the next muscle there is developed an
,.nsive synovial apparatus, termed the metatarso-phalangeal sheath,
j. "■ exactly resembles the metacarpophalangeal sheath of the fore
lmb, described at page 34.
ction.—It flexes successively the pastern and fetlock joints; and, by
isertion into the os calcis, it is also an extensor of the hock-joint.
So Mechanically maintains the hock in a state of extension as long
„, e mP and stifle joints are kept extended by their proper muscles.
th' DEEP Flexoe (nexor perforans) (Plate 19). The tendon of
bpf rnuscle, after its passage through the tarsal sheath, descends
f ..v^J^the suspensory ligament and the superficial flexor. At the
l , . * it passes through the ring ot tiie last-named muscle, descends
•           the digit, plays over the navicular bone, and finally becomes
e« into the solar surface of the os pedis (see page 42). At the
. r part of the metatarsus it receives the check band, or subtarsal
ent, which is analagous to the subcarpal ligament of the fore limb,
in 7 l S° s*rong- Like the analagous structure in the fore limb, it is
ioi           *n sPrain °f the back tendons. A little lower the deep flexor is
, -Jffl its outer side by the tendon of the flexor accessorius.
ion—it fleXeg successively from below upwards the interphalaneeal
JOl^*d the fetlock.
for e° '■—■F'01" the description of the foot, which is identical in the
sect )               limbs, turn to page 35. If the student has already dis-
the foot in a fore limb, he may proceed at once to the articulations.
THE STIFLE-JOINT (PLATES 17 AND 18).
Th'
lat' corresPonds to the knee-joint of man. It comprises—(1) the articu-
tio etween the patella and the femoral trochlea; and (2) the articula-
etween the condyles of the femur and the proximal end of the tibia,
to h ons-—The various structures in connection with the joint are
examined in the order of the following description ; and in order
the " • 8 t^lem' the muscles, fat, etc., are to be removed from around
serv         Caie kehi§ taken, in the first stage of the dissection, to pre-
le thin femoro-patellar capsule intact,
G
-ocr page 150-
82
THE ANATOMY OP THE HORSE.
FEMORO-PATELLAR ARTICULATION.
Movements.—This joint is commonly classified as an arthrodia. The
movements (see page 43) of the patella on the trochlea, however, are not
those of simple gliding, but of gliding with coaptation. In the latter
movement, while the patella moves as a whole upwards or downwards,
successive areas of its articular surface come into contact with the
trochlea. These movements take place at the same time as the move-
ments in the femoro-tibial articulation. In complete extension of that
joint the patella lies at the upper part of the trochlea, and the three
straight patellar ligaments are tense. When flexion takes place, these
ligaments become relaxed, and the patella descends over the trochlea
till it rests at its lower part.
The ligaments of the joint are—one capsular, two lateral, and three
straight.
The Capsular Ligament is loose and membranous, and it supports
the synovial membrane. It is attached, on the one hand, to the margin
of the patellar articular surface, and, on the other, at the periphery °*
the trochlea.
The Lateral Ligaments are two thin, riband-shaped bands, stretching;
one on each side of the joint, from the femur to the patella. They serve
to strengthen the capsular ligament, from which they are not distinct.
The Straight Patellar Ligaments. These correspond to the sing*6
ligamentum patellw of the human knee. They are three in number, and
are distinguished as external, middle, and internal. All three ligaments
are attached superiorly to the anterior surface of the patella, the inner
one having a fibro-cartilaginous thickening which extends the articular
surface of the patella, and glides on the inner ridge of the femora1
trochlea. The middle ligament lies on a deeper plane than the other
two, and rests inferiorly in the vertical groove on the anterior tuberosity
of the tibia. It is inserted into the lower part of this groove, and a
small synovial bursa is developed between the ligament and the bone
above the point of insertion. The external and internal ligaments are
inserted into the same tuberosity, one on each side of the attachment °t
the middle ligament. These three ligaments may be regarded as the
terminal tendon of the quadriceps extensor cruris, whose action thev
transmit tc the bones of the leg.
Synovial Membrane. This will be exposed by incising the capsul*1"
ligament. It lines the inner surface of that ligament, and extends
upwards beyond the trochlea, forming a protrusion under the qu»o-
riceps extensor cruris. Inferiorly it is in contact with the synovia*
membranes of the femoro-tibial joint, and sometimes it communicates
with them.
It is a point worthy of notice in connection with the interior of tn
joint, that the inner ridge of the femoral trochlea is much higher than
-ocr page 151-
83
DISSECTION OF THE POSTERIOR LIMB.
t
°uter; and when the patella is dislocated, it is carried outwards
er the external ridge.
THE FEMORO-TIBIAL ARTICULATION (FIG. 4).
* ements.—This is a ginglymus, or hinge joint, in which the move-
f\. are principally flexion and extension. In extension the bones of
eg are carried forwards, but cannot be brought into a straight line
Fig. 4.
, Exte:
A. Femoro-tibial Ligaments, back view.
j.' Outer serrn atera* l*&amenfc; 2. Internal lateral ligament; 3. Inner semilunar fibro-cartilage ;
gSaroents) 0f-iTlnar nbro-cartilage, with 5, and 6, the femoral and tibial attachments (coronary
• Head of fih i Posterior extremity; 7. Posterior crucial ligament; 8. Anterior crucial ligament ;
eRo-posterior Vertical Section of the Femoro-tibial Articulation to show
lt fj»                                                     the Crucial Ligaments.
5' an,l 6, ^^^or cruoiaIligament; 2. Anterior crucial ligament; 3. External lateral ligament; 4,
lj„ e feraur, the movement being arrested by tension of the lateral
flex' • an<^ °^tne anterior crucial ligament. The contrary movement,
A si' l nna"y arrested by tension of the posterior crucial ligament.
degree of lateral movement and rotation can be produced when
theJoiuti8]
°u e \,RAL Laments.—These are two strong fibrous cords, placed one
side of the joint. The external is fixed above to the higher of the
-ocr page 152-
84                                 THE ANATOMY OF THE HORSE.
two pits on the external condyle of the femur, where it covers the origua
of the popliteus from the lower pit. It descends over the external
tuberosity of the tibia, a synovial bursa being interposed, and is inserted
into the head of the fibula. The internal is longer, but more slender,
than the preceding. It is fixed above to a small tubercle on the innei'
condyle, plays over the inner edge of the tibial articular surface, and is
inserted into the internal tuberosity of the tibia.
The Posterior Ligament is of a flattened, membranous character, and
consists of a superficial and a deep layer, which are separable from each
other superiorly, but blended below. Superiorly the ligament is attached
to the posterior surface of the femur above the condyles; below it is
inserted into the corresponding surface of the tibia, just below the
margin of the articular surface; while laterally its margins blend with
the lateral ligaments. The superficial surface of the ligament is related
to the popliteal vessels, and to the gastrocnemius, flexor perforatus, and
popliteus muscles. Its deep face serves to support the synovial men1"
branes of the joint, and is partly adherent to the semilunar cartilages
and posterior crucial ligament. The ligament presents apertures f°r
the transmission of vessels to the interior of the joint.
Synovial Membranes. These are two in number, one for each oondyl6
of the femur and corresponding part of the articular surface of the tibia-
They are separated from each other by the crucial ligaments in the
interior of the joint; while behind, and at the sides, they line the
posterior and lateral ligaments. In front they are in contact with the
synovial capsule of the femoro-patellar articulation, and are supported
by a pad of fat, which separates them from the straight ligaments ot
the patella. A communication frequently exists in front between these
synovial capsules and that for the gliding of the patella. These
synovial membranes invest the semilunar cartilages; and the externa1
one covers, in addition, the tendon of origin of the popliteus, and the
common tendon of origin of the flexor metatarsi and extensor of the
digit.
Directions.—The posterior ligament should now be cut away; and
the patella being thrown down, the synovial membrane and fat should
be removed from the front of the joint. The joint should then he
strongly flexed, in order to expose, as far as possible, the crucial lig"a"
ments in the intercondyloid groove. The rims of the semilunar
cartilages and their coronary ligaments will at the same time he
exposed.
The Crucial Ligaments are two strong fibrous cords stretching between
the femur and the tibia, and lodged in the intercondyloid groove. They
cross one another somewhat like the limbs of the letter X, and hence
their name. They are distinguished as anterior and posterior. The
anterior, the most external of the two, is attached superiorly to the
-ocr page 153-
DISSECTION OP THE POSTEBIOB LIMB.                                 85
• , rcoildyloid groove, and to the external condyle of the femur where
Unds that groove. Its fibres have a slightly spiral arrangement,
., extend downwards and forwards to be inserted into the summit of
tibial spine. The posterior' ligament is longer than the anterior,
!s fixed superiorly to the intercondyloid groove and inner condyle,
tends downwards and backwards to be fixed to a special tubercle
ne back of the tibia below the rim of its articular surface. These
figaments bind the femoral and tibial articular surfaces closely
~ er; and at the same time restrict the movements of the joint, the
ally
same
0r %ament being put upon the stretch during extension, and fin-
arresting that movement, while the posterior ligament plays the
Part with regard to flexion.
e Inter-akticulab or Semilunae Fibeo-cartilages. These are two
entic or sickle-shaped pieces of fibro-cartilage, interposed between
ondyles of the femur and the articular surface of the tibia. The
x Margin of each is turned outwards, and is much thicker than the
concavn j
to '         8e> which embraces the tibial spine, and is so thin as to be
,         ucent. The lower surface of each is flattened to rest on the tibia,
Th           "Pper surface is hollowed to embrace the femoral condyle.
j are fixed in position as follows:—The anterior extremity of the
fibro-cartilage is fixed into an excavation in front of the tibial
, ' while its posterior end is similarly fixed behind the spine. The
\vh'l Car^at?e is fixed by its anterior extremity in front of the spine,
lts posterior extremity is bifid, having an upper slip inserted into
lo ession at the posterior part of the intercondyloid groove, and a
th lnt° *^e r™ °^ *^e tibial articular surface, partly under cover of
evt • . r*or interosseous ligament. These slips of insertion at the
lit           6S °^ the fibro-eartilages are sometimes termed the coronary
fib-            three of which belong to the outer, and two to the inner,
rj- . ' rtuage. Although these insertions serve to prevent the total
th l ertlent of the fibro-cartilages, some degree of movement is, never-
fle . "" ' Permitted to the latter; for it will be noticed, that during
Wh'i ■ y arei as it were, squeezed towards the front of the joint,
n extension they are carried backwards,
hate i *'■"—^ the internal lateral ligament be now cut, and the
the " C0T1dyle removed with the saw, a better view will be obtained of
tibi i° bgaments; after which, complete separation of the femur and
Cr . 0uW he effected by cutting the remaining lateral ligament, the
** tl a gaments> and the slip of insertion of the external fibro-cartilage
the a°k °f tlle intercondyloid groove. This will expose thoroughly
T^llunar fibro-cartilages.
pe . "Fibular Abticulation. In the horse the amount of movement
ap              between the bones of the leg is very restricted, and not
le on the general movements of the limb. Where the head of
-ocr page 154-
SG
THE ANATOMY OP THE HORSE.
the fibula is opposed to the rough diarthrodial facet on the external
tuberosity at the upper end of the tibia, short and strong perip^era
fibres pass between the two bones, and bind them closely together. A'1
interosseous membrane extends across the tibio-fibular arch, and is perfor'
ated by the anterior tibial vessels. Just above the aperture for the
transmission of these vessels the fibres of the ligament are disposed 'n
opposite directions, like the limbs of the letter X.
Where the osseous substance of the fibula ceases, a fibrous cord begins»
and this is carried downwards to the region of the external tuberosity
at the lower end of the tibia, where it mixes its fibres with the externa1
lateral ligament of the tibio-tarsal joint.
THE TARSUS (PIG. 5).
Several articulations are formed in the tarsus, or hock; and these
are of very unequal importance as regards the amount of movement
permitted. The most important of them is that corresponding to tbe
ankle-joint of man, which is formed between the astragalus and the
lower extremity of the tibia; and attention should first be given to the
movements that take place here. This is one of the most typi°a
ginglymoid joints in the body, the movemerts being limited to flex*011
and extension. It will be observed that in flexion the distal part of the
limb does not move in the plane of the leg, but deviates a little out'
wards, and that in extension the movement is arrested by tension <?*
the lateral ligaments before the distal portion of the limb is brought
into the same straight line as the leg.
In the other articulations found in connection with the tarsus th
movements are of a very restricted character, and are not concerned i11
the general movements of the limb. They, however, serve a no less
important purpose in the joint, distributing and equalising pressure)
and obviating the bad effects which concussion would have been likely
to produce in the tarsus, had it been one rigid structure.
Directions.—The ligaments of the tarsus are both numerous and con1'
plicated, and the best order of their dissection is that in which they are
hereafter described. Since one set of ligaments must be removed ip
order to expose the following set, the dissector should not proceed wit*1
undue rapidity.
Tibio-tarsal Ligaments.—These are four in number, viz., two lateral
an anterior, and a posterior.
The External Lateral Ligament consists of a superficial and a deep
fasciculus, which cross one another like the legs of the letter X. ^
superficial division, which is the larger of the two, is fixed superiorl)
to the posterior part of the external tuberosity at the lower en
of the tibia, while inferiorly its fibres are inserted into the astrag
alus, os calcis, cuboid, large metatarsal bone, and external smal
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87
DISSECTION OF THE POSTERIOR LIMB.
atarsal. It is perforated by the thecal canal for the passage of the
0Ueus tendon. The deep division of the ligament extends down-
, s and backwards from its point of attachment to the forepart of
external tuberosity of the tibia, and it becomes inserted by distinct
+"k 1U*° ^e astragalus and os calcis. In order to expose it thoroughly,
® superficial division should be cut at its point of attachment to the
\ _ tuberosity, and dissected downwards, the difference of direction
lng to distinguish the fibres of the two divisions.
^he Internal Lateral Ligament is, like the preceding, a composite liga-
nt, and consists of three divisions, which may be distinguished as
—z
Fig 5.
j R                                    A.—Ligaments of the Tarsus, front view.
(Wo'sjjPS'ficial fasciculus of the internal lateral ligament (cut) ; 2. Middle fasciculus of the same
?ient; q, j] ?ee? fasciculus of the same ; 4. Superficial fasciculus of the external lateral liga-
lnS J&etatarsn? scicullls °f the same ; 6. Astragalo-metatarsal ligament; 7. Canal for the perforat-
1£1ent • xo' p i artcry; S. Anterior cuboido-cunean ligament; 9. Anterior cuboido-scaphoid liga-
■ cuboid insertion of the flexor metatarsi.
B.—Ligaments of the Tarsus, back view.
lateral ligament; 2. Internal lateral ligament; 3. Tarso-metatarsal _ligament;
6- Subt°i"raiitv;lgln<:ras thickening of the posterior ligament. 5. Calcaneo-metatarsalEligament;
ai "gament, or check-band to perforans tendon ; 7. Suspensory ligament. MuJjjL
^Perficial, middle, and deep. The superficial division, the largest of
le three, is fixed, on the one hand, to the internal tuberosity at the
)Wer end of the tibia, and, on the other, to the astragalus, scaphoid,
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88
THE ANATOMY OP THE HORSE.
large and small cuneiforms, and large and internal small metatarsal
bones. The middle division is of intermediate size; and in order to
expose it, the superficial division must be cut, and dissected downwards.
Above it is attached to the internal tuberosity of the tibia; and, passing
downwards and backwards, it is inserted by distinct slips into the
astragalus and os calcis. The deep division is very slender, and
stretches between the tibia and the astragalus, under cover of the middle
fasciculus, whioh must be removed in order to expose it.
The Anterior Ligament is membranous and four-sided. It is
fixed
above to the tibia; and below to the astragalus, scaphoid, cuneifoi'm
magnum, and astragalo-metatarsal ligament; while on each side it
blends with the lateral ligament. The posterior surface of the ligament
is lined by the synovial membrane of the joint. The anterior surface
is related to the anterior tibial vessels, and to the flexor metatarsi
and extensor pedis tendons. Towards its inner side the ligament
is unsupported; and hence, when the synovial membrane becomes
dropsical, the distension shows at that point, constituting a "bog'
spavin."
The Posterior Ligament is of a similar form to the preceding. It is
fixed above to the tibia, below to the astragalus and os calcis, and at
the sides to the lateral ligaments. Its anterior surface supports the
synovial membrane of the joint; while the posterior is lined by the
synovial membrane of the tarsal sheath, and presents a fibro-oartil*"
ginous thickening where the perforans tendon plays over it. This tendon
affords support to the posterior ligament, which therefore does not
bulge so readily as the anterior ligament; but in a case of extreme
distension of the synovial membrane, the swelling shows itself at the
back of the joint.
The Synovial Membrane is supported by the anterior, posterior, and
lateral ligaments; and it communicates with the synovial membrane
that lubricates the articulations between the os calcis and the astragali
on the one hand, and the cuboid and scaphoid on the other. It also
sometimes supplies the two upper facets between the os calcis and
astragalus.
Directions.—The anterior and posterior ligaments should be incised
in order to expose the synovial membrane; and, thereafter, these and
the lateral ligaments should be cut away. This will effect the separa-
tion of the tibia; and the next group of ligaments may then be
examined.
The following ligaments can hardly be classified as belonging specially
to any one articulation or set of articulations. For the most part they
bind together the series of tarsal bones, and also serve to bind these to
the metatarsal bones.
The Astragalo-metatarsal Ligament.—This is a flat, radiating ligament*
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DISSECTION OP THE POSTERIOB LIMB.                                 89
ated on the inner side of the tarsus. Its fibres are attached above
le tubercle on the inner side of the astragalus; and, widening as it
ends, it becomes inserted into the scaphoid, cuneiform magnum,
?, large metatarsal bone.
ne Calcaneo-metatarsal or Calcaneocuboid Ligament.—This is a
, ng, cT>rd-like ligament, situated at the outer side of the back of the
' aild attached to the posterior border of the os calcis, the cuboid,
the head of the external small metatarsal bone.
ne Tarso-metatarsal Ligament will be seen covering the tarsal bones
ae back of the hock. It forms a thick mass of fibrous tissue
'"lately adherent to these bones and to the heads of the metatarsal
OoiltN T
,. , a- its inner border is blended with the lateral ligament of the
p "tarsal joint; and its outer with the calcaneo-metatarsal ligament.
„ v Jt is continued as the subtarsal ligament, which joins the per-
^ls tendon. The anterior face of the ligament, where not adherent
e bones, is lined by synovial membrane; and its posterior face is
"Mlarly Hnecl
by the synovial membrane of the tarsal sheath.
Sections.—At the front of the hock the point of a scalpel should be
Q-Uced into the articulation between the astragalus and the
P«oid • and by cutting round the hock through the three ligaments
described, an attempt should be made to separate the astragalus
th' S ua^s> as a single piece, from the rest of the tarsal bones. Before
, . an be effected, however, there must be cut an interosseous ligament,
Oi
]s composed of short and strong fibres passing between the os
th aU<^ astragalus on the one hand, and the cuboid and scaphoid on
„ ner- At the same time the synovial membrane belonging to the
Uations between these two sets of bones will be opened into. This
to1 COmrnunicates in front with that of the tibio-tarsal joint, and " is
of tl, ^^ 8UPeri°riy between the calcis and astragalus, to lubricate two
dp acets by which these bones come into contact. In addition, it
for- « between the cuboid and scaphoid bones, to form a prolongation
[ e anterior cuboido-scaphoid arthrodia."—Chauveau.
uartients uniting the Os Calcis and Astragalus.—There are four of
c          a superior, 'two lateral, and an interosseous. The first of these is
I osecl of fibres passing between the two bones above their surfaces
„ . act; the lateral ligaments pass between them on each side ; while
bet r erosseou3 ligament cannot be seen in its entirety, as it passes
D         n the rough impressions on the surfaces of apposition of the
j and must be cut before these can be separated.
me t ecttons-—Attention should next be turned to the following liga-
rp, S' Wn'ch bind together the other four tarsal bones.
bet --           r'^'0,' Cuboido-scaphoid Ligament is of small size, and passes
lYy n *be two bones from which it is named, above the entrance to
by which the perforating metatarsal artery passes through the
-ocr page 158-
90                                   THE ANATOMY OP THE HORSE.
hock. The same bones are joined by an interosseous ligament, which
forms the roof of that canal.
The Anterior Cuhoido-cunean Ligament connects the cuboid and cunei-
form magnum bones below the entrance to the above-mentioned vas-
cular canal; and an interosseous cuboido-cunean ligament forms the fl°01
of the canal.
The Scaphoido-cunean Interosseous Ligament joins the scaphoid and
two cuneiform bones.
The Intercunean Ligament passes between the two cuneiforms.
These and the other interosseous ligaments are concealed in t"e
interstices between the different bones which they bind together, afiw
cannot be fully seen until the bones are separated.
Synovial Membranes.-—"There is a proper synovial membrane for the
facets by which the scaphoid and cuneiform magnum bones corre-
spond; this synovial membrane belongs also to the two cuboido-
scaphoid, and posterior cuboido-cunean arthrodia;. The anterior
cuboido-scaphoid diarthrosis receives a prolongation from the synovia1
membrane between the os calcis and astragalus on the one hand,
and the cuboid and scaphoid on the other. The play of the
anterior cuboido-cunean, and inter-cunean facets is facilitated by two
prolongations of the tarso-metatarsal synovial membrane."—Chauveau-
THE TARSO-METATARSAL ARTICULATION.
An Interosseous Ligament binds the heads of the metatarsal bones *°
the tarsal bones with which these articulate, and the union is furthei
secured by many of the ligaments, already dissected, which, though
they belong to the hock, have points of insertion into the heads of the
metatarsal bones.
Synovial Membrane.—This not only supplies the tarso-metatarsal j oi'1*'
but also ascends between the two cuneiforms, and into the anterior facet
between the cuboid and cuneiform magnum. It also descends into the
articulations between the large and small metatarsal bones.
Directions.—For a description of the remaining joints of the hind lina
(except the hip), turn to the description of the corresponding articUJ®"
tions of the fore limb (page 50). The hip-joint is described with the
pelvis, at page 338.
-ocr page 159-
91
DISSECTION OF THE POSTERIOR LIMB.
ABULAE VIEW OF THE MUSCLES IN THEIR ACTION ON THE JOINTS
OF THE HIND LIMB.
Hip.
/Sartorius.
I Pectineus.
j Tensor vaginae femoris.
I Rectus femoris.
\Rectus rjarvus (?)
( Semimembranosus.
-' Elisors                  ; Quadratus femoris.
' j Middle gluteus.
V Obturator externus.
f Superficial gluteus.
■A-bdu<!+^.»                 ' Biceps femoris (anterior half).
\ Middle gluteus.
Deep gluteus.
{Sartorius.
Gracilis.
Adductor magnus.
Semimembranosus.
Pectineus.
Adductor parvus.
'Deep gluteus.
Adductor parvus.
^^^^^^^^^^ Quadratus femoris.
J?n+ .                           Psoas magnus.
u««ors outwards < Iliacus.
Obturator externus.
Obturator internus.
Pyriformis.
^^^^^^^^^^^^ Gemelli.
Stifle.
Jf]e                             ( Biceps femoris (posterior half).
rs • • . . -\ Semitendinosus.
{ Popliteus.
»,                                I Vastus internus.
^^^^^^^^^^^ J Vastus externus.
j Rectus femoris.
Jtotat                         I Biceps femoris (anterior half).
°r outwards — Biceps femoris (posterior half),
rotators inwards •! Semitendinosus.
( Popliteus.
Hock.
{Gastrocnemius.
( Extensor pedis.
■s Peroneus.
{ Flexor metatarsi.
Extensors
Fetlock.
( Flexor perforatus.
< Flexor perforans.
(Flexor accessorius.
Extensors
P
,-VSTEKN.
(Flexor perforatus.
s Flexor perforans.
\ Flexor accessorius.
Extensors
COFFIN-JOINT.
( Flexor perforans.
Extensors
Soleus.
Flexor perforatus.
Flexor perforans.
Flexor accessorius.
(Flexor perforatus.                                                  (Extensor pedis.
< Flexor perforans.                 Extensors . . . s Peroneus.
(, Extensor brevis.
Flex                           
8 • • . .
(Flexor perforatus.                                                  (Extensor pedis.
.)-en____i__,-------                  -C..4.--------            , J Peroneus.
(.Extensor brevis.
-                                         Extensor pedis.
f Flexor nerforans.                 t*~a--------            _ -^Peroneus.
Flev„                         
flexors. .             
Jexors,                   
I, Extensor brevis.
-ocr page 160-
CO
Source of Nerve.
Insertion.
Origin.
Name of Musole.
Inner straight ligament of patella .
Inner straight ligament of patella; and tibia, \
line between anterior and internal tuber-1
osities .......
Femur, shaft near nutrient foramen
Femur, posterior surface of shaft
Femur, posterior surface of shaft and supra-
condyloid crest (two insertions) .
Femur, trochanteric fossa
Femur, inner condyle ....
Femur, posterior surface of shaft
Femur, small (internal) trochanter .
Internal Saphenous.
Iliac fascia......
Pubis and iscbium, lower face
j Pubis, brim and inferior surface; and pubio- )
( femoral ligament .... j
Pubis, inferior surface.....
j Ischium, inferior surface; and tendon of
\ origin of gracilis          .....
Pubis and ischium, lower surface
( Ischium, inferior surface and tuber; and |
( fascia of coccygeal muscles         . . (
Ischium, lower surface .....
(Ribs, last two; and vertebras, 16th dorsal ~\
I to 5th lumbar.....(
( Ilium, iliac surface and external angle ; and (
\ sacro-iliac ligament ....         J
Femur, outer and anterior surfaces of shaft
Femur, inner and anterior surfaces of shaft
Ilium, abo%'e acetabulum (two heads)
Ilium, above acetabulum ....
Ilium, external angle ....
Ilium, external angle ; and gluteal fascia
(Ilium, gluteal surface; ilio-sacral and sacro- "j
s sciatic ligaments; gluteal fascia and fascia >
t of longissimus dorsi .... j
j Os innominatum, shaft of ilium and supra-
\ \ cotyloid ridge ......
Sartorius .
Gracilis
Pectineus .
Adductor parvus
Adductor magnus
Obturator externus .
Semimembranosus .
Quadratus femoris .
Psoas magnus .
Iliacus
Vastus externus
Vastus internus
Rectus femoris
Rectus parvus .
Tensor vagina? femoris
Superficial gluteus .
Middle gluteus
\ Deep gluteus .
Obturator.
Great sciatic.
Lumbar nerves.
Patella .......
Patella and its inner straight ligament .
Anterior crural.
Patella.......
Femur, anterior surface of shaft
Fascia lata ......
Femur, third trochanter ....
Femur summit, crest, and ridge of great \, Ql t j
trochanter......
Femur, inner side of convexity of great 1
trochanter......
-ocr page 161-
' Sacral spines; tuber ischii; sacro-sciatic liga
ment; gluteal and coccygeal fascia; .
Sacral spines; tuber ischii; and sacro-sciatic )
j I ligament....../
___rd trochanter; \
/ Biceps femoris
Semitendinosus
Obturator interims .
I Pyriformis
j Gemelli .
Gastrocnemius .
Soleus
Flexor perforatus
Flexor perforans
Flexor accessorius
Popliteus .
Peroneus .
Extensor pedis
(" Superficial )
Flexor metatarsi*! division J
(. Deep division
Extensor brevis
Lumbricales (2)
Interossei(2) .
and I
/ patella; tibia, crest; and fascia of l*>g         L
Tibia, crest....../ j
Femur, trochanteric fossa
great sciatic.
Great sciatic.
Internal popliteal.
Musculo-cutaneous.
Anterior tibial.
Plantar.
/ Pubis and ischium, pelvic surfaces .
I Ilium, pelvic surface
Ischium, outer edge
I
I Femur, outer lip of supracondyloid fossa,
( and supracondyloid crest (two heads) j
Fibula, head.......
Femur, bottom of supracondyloid fossa . j
{Tibia, external tuberosity and posterior sur- "j
face of shaft; fibulaj and interosseous >
membrane......j
Tibia, external tuberosity ....
Os calcis, summit.....
Tendon of gastrocnemius ....
Cs calcis (slip to either side); and os coronre |
(bifid tendon).....
Os pedis, semilunar crest and surface behind
it........
Tendon of perforans.....
Tibia, posterior surface and inner edge of J
shaft.......
Tendon of extensor pedis          ....
Os pedis, pyramidal eminence                          \
j Large metatarsal, upper extremity; and j
t cuboid (bifid tendon) ....{.
j Large metatarsal, upper extremity; and /
( cuneiform parvum (bifid tendon) . j
Tendon of extensor pedis                                  '
Tissue beneath ergot of fetlock . . "j
Suspensory ligament, band sent to extensor >
tendon.......J
H
Q
h3
5
a
o
US
a
m
►a
o
u:
►a
a
I
s
Femur, outer condyle ....
j External lateral ligament of stifle; fibula;
( and intermuscular septum .
Femur, between trochlea and outer condyle
Femur, in common with extensor pedis
Tibia, outer surface         ....
Perforans tendon.....
Splint bone, head.....
to
-ocr page 162-
CHAPTER III.
DISSECTION OF THE BACK AND THOKAX.
The dissection of the thorax should be begun at the same time as that
of the outer scapular region (see page 8).
THE CHEST-WALL AND BACK.
Directions.—The portion of skin remaining on the chest-wall and loins
should be removed, the operation being commenced at an incision
carried along the middle line, from the withers to the croup. The cut-
aneous nerves must then be sought, after which the other structures
are to be taken up in the order of their description.
Cutaneous Nerves. In the back these are derived from the dorsal
nerves. One set of branches appears close to the spinous processes J
and another a few inches outwards, along the course of the longissinuis
dorsi muscle. Both of these are derived from the superior primary
branches of the dorsal nerves. Over the sides of the chest the cutaneous
nerves are derived from the perforating branches of the intercostal
nerves, which are dissected with the abdominal muscles (see page 288)-
In the loins the cutaneous nerves are derived from the superior
primary branches of the lumbar nerves, and the most posterior of them
are continued backwards to the skin over the gluteal region.
The Panniculus Carnosus (Plate 38). This is an extensive muscle
adherent to the deep surface of the skin over a large part of the abdo-
men, thorax, and shoulder. It is fully described at page 287, which see-
Directions.—The panniculus should now be entirely removed, begin"
ning at its upper border.
The Latissimus Dorsi. This muscle is partly described at pagcS
9 and 14, in connection with the dissection of the fore limb. 1
arises by a broad aponeurotic tendon from the series of vertebral spines,
beginning about the 4th dorsal, and extending back to the last lumbar-
This tendon is not well defined at its inferior border, where i* lS
adherent to the ribs, and blends with the oblique muscles of the
abdomen. Posteriorly the tendon becomes continuous with the gluteal
fascia. The tendon is succeeded by a thick muscular portion, which
contracts and passes to the inner side of the fore limb, where it become8
inserted into the internal tubercle of the humerus.
Action.—It is a flexor and an inward-rotator of the shoulder-joint.
-ocr page 163-
DISSECTION OF THE BACK AND THORAX.                              95
he Serratus Magnus (Plate 4). This muscle will be seen here, as
by the dissector of the fore limb. The student should notice its
e of origin from the ribs (see page 7), and then carefully remove it.
Sections.—The latissimus dorsi must now be removed, beginning
., w> where its muscular portion was cut by the dissector of the fore
. • This operation must be conducted with care, in order to leave
°t the anterior and posterior serratus muscles, whose thin tendons
, Querent t° that of the latissimus. Indeed, over the last ribs, in an
subject, it will be found impossible to separate the latissimus from
underlying serratus, and the former may there be cut off.
■'■he Serratus Posticus (Plate 20). (This and the succeeding
cle are described together by Percivall, under the name superficialis
tn,arum- It corresponds to the serratus posticus inferior of man.)
muscle is provided with an aponeurotic tendon, by which it
es from the summits of the vertebral spines from the 11th dorsal to
<md lumbar. The inferior border of the tendon has a muscular
b6 with eight or nine distinct slips, which are inserted into the
erior borders and outer surfaces of the same number of ribs at the
end°f the series.
_ctl°n.—It is a muscle of expiration.
ne Serratus Anticus (Serratus posticus superior of man) (Plate 20).
* muscle is partly covered by the preceding, whose three anterior
PS should therefore be carefully removed, as has been done in Plate
It repeats the form of the posticus, having a thin, translucent
t, eur°tic tendon, which, in front, is confounded with the splenitis.
j e uPper border of this tendon it arises from the summits of the
0rsal spines from the 2nd or 3rd to the 13th. The inferior border of
, tendon is succeeded by the fleshy portion of the muscle, and this is
g,, e* into the anterior borders and outer surfaces of the ribs from the
y° the 13th inclusive.
c w».-—To assist in inspiration.
0 , w ections.—The two muscles just described must be removed in
a             expose the next layer; and this is to be done by incising the
. eurotio portion of each horizontally, an inch or two above its point
ca            u with the muscular portion. The portions above the incision
th              without difficulty be stripped upwards from the surface of
ongissimus dorsi. The lower portions must next be dissected
th' War *n or^er to expose the transversalis costarum. In doing
of +k Wl^ ^e f°UI1(l that a fibrous septum passes from the aponeurosis
th +6 Serra*us anticus near its lower border, and, penetrating between
De6 Wo muscles now exposed, becomes attached to the ribs. This must
fro U ' ^ tlle muscular slips of the serrati must be carefully raised
y tne transversalis costarum.
Essels and Nerves. A set of nerves will be found at the inner
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96
THE ANATOMY OF THE HORSE.
edge of the longissimus dorsi, and another perforating its substance
Both sets are derived from the superior primary branches of the dorsa
or lumbar nerves.
The arteries and veins are branches of the dorso-spinal divisions of tb°
intercostal or lumbar vessels.
The Transveesalis Costarum (Plate 21). (This muscle corresponds
to the ilio-costalis and musculus accessorius of man.) This is a composrf
muscle extending across the entire series of ribs, being five or six inches
removed from the spine posteriorly, but close to it in front. Its fibi'e
are directed forwards and slightly downwards, and it possesses t*°
series of tendons. One set, forming slips of origin, is concealed at the
upper edge of the muscle; the other, serving as slips of insertion, lS
visible at its lower edge. By the upper set of tendons it arises from the
transverse processes of the first two lumbar vertebra), and from the
anterior borders of the ribs. By the lower set of tendons it is inserted
into the hinder edges of the ribs anterior to the 14th, and to the trail8'
verse process of the last cervical vertebra.
Action.—To pull the ribs backwards, and thus assist in expiration-
Both muscles acting together may also assist in extending the spine >
or acting singly, they may incline it laterally.
The Longissimus Dorsi (Plate 21). This is the longest a»a
strongest muscle in the body, and it is also the most complex. *■*
extends along the spine, from the sacrum to the neck. In the loins J1
forms a great muscular and tendinous mass (the common mass of man) j
and anteriorly it is bifurcate, the trachelo-mastoid and complesuS
muscles getting origin between its two branches. Its fibres arise from
the sacral surface of the ilium between the crest and the sacro-iliac join*'
and from a strong, glistening fascia covering the surface of the muscle)
this fascia being fixed to the lumbar and dorsal spines, or to the supi"a'
spinous ligament. Its fibres are inserted into the lumbar transverse aD"
articular processes, the dorsal transverse processes, and the ribs as far
outwards as the edge of the transversalis costarum. About the 5th rib J*
divides; and the lower branch, continuing the outer series of attachment3'
is inserted into the ribs, and the transverse processes of the first four
dorsal and last four cervical vertebras; while the upper division, getting
many new fibres from the first four dorsal spines, becomes inser ted into
the spinous processes of the four cervical vertebras in front of the last.
Action.—Acting with the opposite muscle, it is the great extensor °*
the dorso-lumbar portion of the spine, being, in this respect, the chieJ
antagonist of the sublumbar and abdominal muscles. By its cost**
attachments it may also assist in expiration. By its cervical attach-
ments it raises the neck. Acting singly, it inclines the spine to tfle
side of the acting muscle.
Retractor Cost/E (Plate 45). This is a small triangular muS<»e
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DISSECTION OF THE BACK AND THORAX.                               97
nch lies under cover of the last slip of the serratus posticus. It is
1 and aponeurotic at its upper edge, where it arises from the first
or three lumbar transverse processes. The remainder of the muscle
eshy, and it is inserted by it's anterior edge into the posterior border
. ^e last rib. Its lower edge is parallel to the highest fibres of the
ernal oblique muscle of the abdomen, and it is generally described as
a Part of that muscle.
Action.—To assist in expiration.
Erections.—Two sets of muscles lie under cover of the longissimus
' '5l! viz., the semispinalis of the back and loins, and the levatores
arum, A. segment of the longissimus, from the 13th to the 17th
' should be excised after the fashion of Plate 21 j or if it be desired
xP°se the whole of each series, the longissimus dorsi must be
entirely removed.
he Levatores Costarum (Plate 21). These form a series of small
» eacn occupying the extreme upper part of an intercostal space,
at that point taking the place of the external intercostal muscle.
a arises from the transverse process of a dorsal vertebra; and
.' lng downwards and backwards, it expands, and becomes inserted
the outer surface of the rib posterior to the vertebra from which it
8 Origin, In the first two or three spaces the muscles are rudi-
ai6llt*ry or absent.
4c«WM,__To assist in inspiration.
.fte Semispinalis of the back and loins (Plate 21). This
is a com-
e muscle, covering the sides of the vertebral spines from t__
the neck, and consisting of numerous fasciculi directed obliquely
th ' ail°* forwards. Anteriorly these fasciculi are in series with
f . ^-spinalis colli, and posteriorly with the curvator coccygis. The
tnK        take origin from the lateral lip of the sacrum, from the articular
th /i °^ ^le iumbar vertebrae, and from the transverse processes of
e„ , 0rsal vertebrae. They become inserted into the vertebral spines,
0l ■ Sciculus being inserted into the 3rd or 4th vertebra anterior to the
jo ft1 which it takes origin. In the forepart of the dorsal region (Fig.
it '■ . &e 156) the insertion is into the sides of the spines, but elsewhere
o or near the summits of the processes.
«,„ . n' It is an extensor or a lateral flexor of the spine, according as
t> « and left muscles act together or singly,
cost' l C lons'~—Clean the outer surfaces of a few of the external inter-
st„„ muscles about the middle of the series, and at the side of the
uenne the lateralis sterni muscle.
broad ^ATekalis Sterni. This is a thin, flat muscle, a few inches
tilao- ' • ls^n9 from the outer surface of the 1st rib above its car-
chond' ■: I)a>:ises obliquely downwards and backwards over the 2nd
-costal joint, and over the 3rd and 4th costal cartilages, and
H
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98
THE ANATOMY OF THE HORSE.
is inserted into the side of the sternum. Frequently some of its fibres
terminate on the 3rd and 4th costal cartilages, or on the aponeurosis
over the internal intercostal between these cartilages.
Action.—Acting from its attachment to the 1st rib as its fixed point)
the muscle will exert a feeble inspiratory action.
The External Intercostal Muscles (Plate 21). Each muscle of this
set occupies an intercostal space, extending from near the spine as f;U
as the lower extremities of the ribs. The muscular fibres of each »re
fixed by their extremities to the margins of the ribs that bound the
intercostal space. They pass obliquely downwards and backwards;
and
may be considered as having their point of origin from the anterior rift
and their insertion into the posterior rib.
Directions.—In one or two of the spaces the external intercostal should
be removed (see Plate 21) in order to expose the internal muscle, which
will readily be distinguished by the different direction of its fibres.
The Internal Intercostal Muscles (Plate 21). These equal in
number the external set, one being lodged in each intercostal space-
They differ from the external set in that they are prolonged beyond
the lower extremities of the ribs to fill the interspaces of the costal
cartilages, while in the extreme upper part of the intercostal spaces the)'
are absent or much reduced in thickness. They differ, moreover, in *"*
direction of their fibres, which is oblique downwards and forwards; ^n^
each may be viewed as having its origin from the posterior rib an*
cartilage, and its insertion into the anterior rib and cartilage, of tne
space that it occupies. The inner surface of each is lined by pleura,
but at present no attempt need be made to expose this.
Action of the intercostal muscles.—The external set and the inter'
cartilaginous portions of the internal set are muscles of inspiration-
The interosseous portions of the internal set are muscles of expiration-
Directions.—In a few of the intercostal spaces the vessels and nerve*
should be exposed. They will be found at the hinder edge of the rift
and should be followed upwards and downwards.
Intercostal Arteries. There are seventeen intercostal arteries o»
each side, one for each space. The first is derived from the super*01
cervical artery ; the second, third, and fourth from the dorsal artery or us
subcostal branch; and the remaining thirteen from the posterior aort*'
Their points of origin will be seen in the dissection of the cavity °
the thorax. Each vessel on gaining the upper extremity of the inter"
costal space gives off a large dorso-spinal branch, and then descends
behind the rib, with the vein and nerve. The dorso-spinal artery sen*
a branch into the spinal canal by the vertebral foramen, and is t"6
expended in the muscles occupying the costo-vertebral groove at the Sifl
of the dorsal spines. In the intercostal space the intercostal artery
accompanied by a vein and nerve, the vein being in front, and the nerv
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99
DISSECTION OF TUB BACK AND THORAX.
*/ terior. In the upper third of the space the vessels descend between
outer and inner muscles, and rest in the groove at the posterior edge
ne rib. For the rest of their course they are under cover of the
r edge of the rib, and, generally, between the inner muscle and the
., ra > but, here and there, slips of the inner muscle may pass between
e Vessels and the pi eura. At the lower extremities of the intercostal
r es the arteries behave as follows :—The first six (or seven) anastomose
ascending branches from the internal thoracic artery ; the remainder
ar as the thirteenth anastomose with similar branches from the
c^rnal artery; and the last four run into the abdominal wall and are
pended in its muscles, anastomosing with the abdominal and circumflex
arteries. In their descent the intercostal arteries give off costal,
ral, muscular, and cutaneous branches.
., e tNTERcosi'AL Veins accompany the arteries. On the left side
nrst joins the superior cervical vein, the next ten or eleven join
left dorsal vein, and the last five or six the great vena azygos.
right side the first joins the superior cervical vein, the next
join the dorsal vein, and the remaining thirteen the great vena
dzygos.
i e -Dorsal Nerves. There are eighteen dorsal nerves, one emerging
j ,, e lr,tervertebral foramen behind each dorsal vertebra. Each divides
e *oramen to form a superior and an inferior primary branch. The
„. 10r primary branch supplies the muscles in the costo-vertebral
1 , e' and the superjacent skin. The inferior primary branch of the
br i,erVe' a^er detaching a very slender intercostal twig, joins the
pj J lai Plexus. The 2nd nerve gives a slender branch to the brachial
j, j and is continued as the intercostal nerve of the second space.
ar erior primary branches of the succeeding nerves, except the last,
bran irec^v cor,tinued as intercostal nerves. The inferior primary
Pao-           the last (18th) dorsal
nerve descends behind the last rib (see
^ 292 and 324).
ternr ntercostal Nerves.—These accompany the intercostal vessels, and
l'eacVi ' * Us :—^ne ^s* intercostal nerve is very slender and does not
the n 6 tom °f tne space ', the six nerves behind the 1st perforate
the +k ° muscles and become cutaneous at the side of the sternum;
Oosfcoi >rs \*en) are continued beyond the lower extremities of the inter-
spaces to be distributed in the abdominal wall.
and l rcostal nerves give branches to the muscles of the same name,
f°rat'         *^e m^^e °f tne intercostal space each gives off a large per-
ovnvi ■ ranch (lateral cutaneous of man) to supply the panniculus and
Th* Skin'
these TIMBAR Nerves and Vessels. The superior primary branches of
to th rV6S ^x m number) have a distribution in the loins analagous
orresponding branches of the dorsal nerves in the back. They
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100
THE ANATOMY OF THE HORSE.
supply muscular branches to the muscles over the lumber transverse
processes, and cutaneous twigs to the skin of the loins and croup-
Branches of the lumbar arteries and veins accompany these nerves.
Each artery sends a spinal branch through the intervertebral foramen-
THE CAVITY OP THE THORAX.
Directions.—In order to expose the thoracic cavity, the chest -wall3
must be in part removed ; and it is most convenient, in the first place,
to make the opening on the left side. The trunk should be allowed to
remain in the suspended position. If the diaphragm is intact, and if n°
opening quite through the chest-wall has been made in the previolls
dissection, then the first step should be to perforate one of the intercostal
spaces with the finger or a blunt instrument. This is to be done i11
order to allow the lungs to collapse; and a sharp instrument must not
be used, lest the surface of the lung might be injured. As soon as the
finger or instrument is withdrawn from the aperture, the air will "e
heard to rush in and fill the pleural cavity, which was previously
occupied by the distended lung. This is precisely what occurs when
the chest-wall is perforated in the living animal, in which, in health, the
e
outer surface of the lung is closely applied co the inner surface of th
wall, following it in all its movements. The lung is kept in this dis-
tended state by the atmospheric pressure, which operates on the 8»
passages in the interior of the lung, but not on its exterior, where the
pressure is borne by the chest-wall; and the lung is kept thus distended)
in opposition to a strong natural tendency to contract, which it possesses
in virtue of the large amount of elastic tissue in its structure, ^u
when the wall of the ehest is perforated, the pressure of the atmosphei'e
becomes exerted on the exterior as well as the interior of the lung, aI1
the unopposed elasticity of the lung texture then comes into play.
By means of the saw and bone-forceps, the ribs, except the first and
a few at the end of the series, are to be removed, the upper secti°u
being made a few inches below the head of each rib, and the lower a
little above the chondro-costal articulation.
Form and Boundaries of the Cavity (Plates 22 and 25).—If the co»'
tained organs were removed from the thorax, and a cast were taken of itri
interior, it would be tound to have an irregularly conical form, but the
symmetry of the cone is largely departed from. The base of the coO0,
is formed by the diaphragm, which, viewed from the thoracic side, l
markedly convex like the roof of a dome. The plane of attachment °
the diaphragm slopes downwards and forwards, so that the antei'0'
posterior measurement of the cavity is much less helowr than abo^e-
Moreover, as the diaphragm is dome-shaped, this measurement is leS
when taken from its centre than from its sides. It is in consequence °
this configuration of the diaphragm, that the liver, the stomach, a11
other abdominal organs lie under cover of the ribs. The vertex of tH°
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101
DISSECTION OF THE HACK AND THORAX
le lies in front, and is bounded by the body of the 1st dorsal vertebra
0Ve> and at the sides by the 1st ribs, which meet below. The
' ea> the oesophagus, the bloodvessels of the fore limb and head,
a many important nerves are transmitted through this opening. On
c Sverse section, the thorax is not circular, as a cone is, but gives a
' '"Shaped outline. It looks as if it had been squeezed laterally ; and
ignt be described as having a roof, formed by the dorsal vertebra
and +v •                                                v ?                 j
the ribs as far as their angles; a floor, much less extensive, formed
•> the sternum : and lateral wails, formed by the ribs and intercostal
^scles.
°ntents of the Cavity.—In point of size, the lungs are the most
P°rtant organs in the thorax, the heart coming next. Besides these.
4-4-
tle«r;i fn, • a11' 2' Pleural cavity or sac ; 3. Lung; 4. Mediastinal pleura (parietal); 5. Costal
P- (So \,{?tal) ; 6. Pulmonic pleura (visceral); i. (No. S) Abdominal cavity ; D. (No. 3) Diaphragm ;
etlTeloDin encardial sac; R. (No. 1) Root of lung ; V. (No. 8) Fold of right pleural membrane
' g Posterior vena cava.
4.r
th aVl^r lodges the main arterial and venous trunks, the thoracic duct,
will a° *^e oesophagus, and many important nerves, all of which
°e examined in due course.
ter G 1:>LEX]E^- Each half of the thorax possesses a serous membrane
in th tlle Plenra- Like other serous membranes, the pleura is arranged
le form cf a shut sac, and consists of a visceral and a parietal
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102                                 THE ANATOMY OF THE HORSE.
portion. The visceral pleura is that which invests the lung, and it jS
therefore termed the pulmonic pleura. Around the root of the lung it is
continuous with the parietal portion. The parietal pleura lines the
walls of the chest on the side to which it belongs. It covers the inner
surface of the ribs and intercostal muscles, forming the costal pleura; l*
is spread over the anterior surface of the diaphragm, constituting the
diaphragmatic pleura; and towards the middle line of the cavity m
together with the corresponding layer of the opposite side, forms a
vertical septum termed the mediastinum. This is the mediastinal
pleura. Behind the root of the lung a double fold of pleura, termed
the ligamentum latum pulmonis, is prolonged along the mediastinum to
the diaphragm. On the right side of the chest the pleura forms a special
fold that includes between its two layers the posterior vena cava and
the right phrenic nerve. All these differently named divisions of the
pleura are continuous the one with the other ; and they unite to form a
close sac termed the pleural cavity. This disposition of the pleura will b°
more readily understood by reference to the accompanying diagrams (page
101), the first of which represents the arrangement of the membrane at the
root of the lung, the second in front of, and the third behind, that point-
These diagrams, it is to be observed, however, are not true to nature;
for, whereas they show a distinct pleural cavity, in the living healthy
animal that cavity has only a potential existence, the pulmonic, being
everywhere in contact with the visceral, pleura. But when air lS
admitted to the cavity, or when inflammatory or other effusions are
poured out from the surface of the membrane, the parietal and the
visceral pleura become separated, and the cavity comes to have an actual
existence. The free surface of the healthy pleura is exquisitely smooth;
and is lubricated by a sparing amount of serous fluid, which gives it a
glistening aspect. Its function is to facilitate the movements of the
lung on the walls of the chest during respiration. When, in inflamma-
tion of the membrane (pleurisy), it loses its smoothness and becomes
dry, these movements, which normally give rise to no sensation, ai'e
attended with the most acute pain. In structure, the pleura, like othei
serous membranes, comprises a single layer of endothelial cells forming
the free surface of the membrane, and a sub-endothelial layer of fibrous
connective-tissue supporting the bloodvessels, nerves, and lymphatics.
The Mediastinum. This, as has already been said, is a septum
formed towards the mesial plane of the chest by the approximation ot
two layers of pleura, one from each sac. At some points the right and
left layers are in close contact, as, for example, in front of the heart IB
a lean subject; but at other points the layers are pushed apart by organs
included between them. The largest of these organs is the heart,
opposite which the right and left layers of the mediastinum are distant
four or five inches from one another. In the foetus of the horse, an"
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DISSECTION OF THE BACK AND THORAX.                            103
uoughout adult life in some animals, the mediastinum is a complete
Imperforate septum, there being no communication between the right
au^ left pleBxai sacs ; but in the adult horse the mediastinum immedi-
ateV behind the heart is cribriform or lacedike, and through the aper-
les which exist here, a pleural effusion formed on one side passes
readily through to the other.
ine heart, contained within its pericardial sac, is, as has already been
,, > tne largest organ in the mediastinum, and it is situated about
e centre of that septum. For convenience of description, this division
the mediastinum and the part vertically over it may be termed the
™e 'mediastinum; and the portions before and behind this, the
erior mediastinum and the posterior mediastinum respectively. Adopt-
b this arbitrary division of the mediastinum, the organs included in
Jt toay be tabulated thus :—
111 the Anterior Mediastinum.—The trachea ; the oesophagus ; the
ai'y and innominate arteries and their collateral branches; the
tenor vena cava and its tributaries ; the thoracic duct; the pneumo-
5« stvic, recurrent, phrenic, and cardiac nerves ; the tracheal lymphatic
1K's; and, in the foetus and young animal, the thymus gland.
"* the Middle Mediastinum.—The pericardium and the heart; the
mon aorta and its bifurcation into anterior and posterior aortse; the
Nations of the anterior vena cava and vena azygos ; the pulmonary
sels j the thoracic duct; the trachea and its bifurcation into the
uchi j the oesophagus ; the pneumogastric, phrenic, and left recurrent
Aes J and the bronchial lymphatic glands.
., *ne Posterior Mediastinum.—The posterior aorta, the vena azygos,
thoracic duct, the oesophagus, the oesophageal continuations of the
Nasogastric nerves, the left phrenic nerve, and the oesophageal
ly*l*atic glands.
TV*
e posterior vena cava, and the right phrenic nerve in the latter
Part f ■                                                         .
°* its course are not in the mediastinum, being included in a
al doubling belonging to the right pleural membrane.
THE LUNGS (PLATES 22 AND 25).
ue lungs are two in number, and they occupy the greater part of
cavity of the thorax. As now seen, however, they are collapsed,
the
occupy but a small moiety of the cavity, a condition which makes
" examination more easy. Each lung appears to lie somewhat loosely
* th« chest •
but if it be grasped, and an attempt be made to remove
TV          '* Wil1 be found to lae attached at a point on its inner surface,
an J8' Wlllcl1 is termed the root of the lung, is the point where the bronchi
Vessels enter it. Each lung presents for examination two surfaces,
fee borders, a base, and an apex.
e External (or costal) surface is much the larger of the two. It is
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104
THE ANATOMY OF THE HORSE.
smooth and convex, and in health it is closely applied to the chest-wait
The internal (or mediastinal) surface is moulded on the laediastinu*8
and the organs contained in it. Thus, it presents opposite the hear*
a depression for the lodgment of that organ; behind that point, and
near the upper limit of the surface, a longitudinal groove for the posten01
aorta; and beneath that again a second furrow parallel to the first but
not so deep, which is the impress left by the oesophagus. This last
impression is very faint on the right lung. This surface also presents
the root of the lung, which is situated close behind and above the
depression for the heart ; and the broad ligament of the lung (or liganie'1'
turn latum pulmonis) already mentioned. In front of the heart, whore
this surface is applied to the anterior mediastinum, it is narrow and flat-
The inner surface of the right lung presents posteriorly a small, senn~
detached lobule, not present on the left. The base (or diaphragmatic
surface) is concave and moulded on the diaphragm. This surface on the
right lung shows the base of the small, semi-detached lobule, and the
posterior vena cava disappearing into the fissure between that lobule
and the main mass of the lung. The apex of the lung is pointed, aud
lies at the entrance to the chest. The superior (or vertebral) border is
long, thick, and rounded, and it is lodged in the costo-vertebral groove
at the roof of the cavity. The inferior (or sternal) border is short aud
sharp; and opposite the heart it is widely notched, a circumstance
which allows the pericardium to be tapped at this point without dauger
of wounding the lung. The notch is smaller on the right side. The
posterior (or diaphragmatic) border circumscribes the base, and the greats*
part of it is included between the periphery of the diaphragm and the
chest-wall.
Directions.—The student should now attempt by the following method
to restore the lung as nearly as possible to its natural dimensions
and relations. The nozzle of a pair of bellows should be wrapped
firmly round with a strip of wet cloth until it is made of a conveui611
size to fit the trachea, which is to be cut across about the middle of the
neck for its reception. The nozzle is then to be tied tightly into the
trachea with a thick piece of string carried several times round, and the
lung is to be gradually inflated while an assistant guides it into position*
and guards it from being wounded by the cut ends of the ribs. Provided
the lung has not been injured, it can by this means be restored to its
natural position, and the student should then observe the area oi
pericardium which is left uncovered at the notch in the lower border-
The right side of the chest may next be opened, making the same
incisions as on the left. On raising the base of the right lung ft'001
the diaphragm, its supernumerary lobule will be seen, aud also the
posterior vena cava and right phrenic nerve invested by the special fo"*
of pleura. The right lung may then be inflated, and the extent oi
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DISSECTION OF THE BACK AND THORAX.                            105
rp, arc'luQi left uncovered by lung on this side should be observed.
Barter, the lung should be reflected towards the spine, and the
i'a should be stripped off its root. The vessels, nerves, and bronchus
«* be isolated by teasing and scraping, rather than by cutting.
e R°ot of the Lung, it will be observed, is placed behind the upper
oi the heart; and it is composed of the bronchus, bloodvessels,
rp, Pn"vessels, and nerves of the lung, with some connective-tissue.
bronchus enters each root in front and above ; the pulmonary veins
r behind ; and the pulmonary artery enters in front of the veins.
Essels. Two sets of vessels pass to and from the lung at the root,
•> the pulmonary artery and veins, and the bronchial artery and vein.
ie Pulmonary Artery is the enormous vessel carrying impure (venous)
*00<1 from the right ventricle to be purified in the capillaries on the
cells of the lung. It will be recognised by the thickness of its wall.
pulmonary veins bring the purified (arterial) blood back from the air-
s> and discharge it into the left auricle. They form at the root of
lung from two to four trunks, which are extremely short, especially
.,          left side. The pulmonary vessels are the functional vessels of
rp, =£
ue Bronchial Artery is a slender vessel entering the lung on the
chus. It carries nutritive or pure blood to the lung structure, and
' j therefore be termed the nutrient artery of the lung. The blood which
arries is led out of the lung by the bronchial vein, which joins the
oronary sinus of the heart.
He Nerves of the lung are derived from the vagus, as will be seen
c later stage. They form a plexus at its root, and pass along the
Dro^chi into its interior.
Sections.—Both lungs are to be left until the heart and the thoracic
ls and nerves have been examined. Proceed now to the examina-
, .,, °* the pericardium. It is best examined from the left side, and
will 1
De sufficiently exposed by hooking the left lung towards the spine.
THE PERICARDIUM (PLATES 22 AND 26).
Tti
. e Pericardium is the bag that contains the heart. It occupies a
j ^wn about the centre of the thorax, and between the right and left
■ . rs °* the mediastinum. The sac is fibrous in structure, and is lined
Uially by a serous membrane Like the organ which it encloses,
Pericardium has a conical form, the point of the ccne being fixed to
Vtv, P °f tllQ stenuun from about the third chondro-sternal joint to
*n au inch of the insertion of the diaphragm across the ensiform
th • G' ^bove the sac is pierced by the large vessels of the heart, and
Tteie lts fibrous texture blends with the outer coat of the vessels.
outer surface is overspread by the mediastinal pleura, which can
asuy be stripped off.
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106                                      THE ANATOMY OF THE HORSE.
Directions.—The pericardium should be pinched up, and slit from lts
apex to near the base of the heart.
The pericardium is considerably larger than the heart which it con-
tains, but this disposition is not very evident until it is opened, when
the sac can be pulled away from the heart, and a considerable cavity W
between them. The inner surface of the bag and the outer surface of the
heart are overspread by a serous covering—the serous membrane of W*
pericardium. The parietal division of this membrane is that which
lines the sac; the visceral division covers the heart and the roots of the
great vessels at its base, investing the aorta and pulmonary artery in a
common tube. The visceral portion is also known as the epicardniW-i
and around the base of the heart it is continuous with the parietal
division. The free surface of this, as of other serous membranes, is
exquisitely smooth, and is formed by a single layer of endothelial cells-
Its object is to facilitate the movements of the heart in its sac; and f"1'
this purpose, it is kept moist by a minute quantity of serous fluid. ^-s
with the pleura, the cavity of the serous sac is only a potential one; bs*
when inflammatory or other effusions are poured out by the membrane,
it becomes an actual cavity, and the parietal and visceral layers of the
membrane may be pushed widely apart. In old and emaciated subjects
this is not infrequently the case, the cavity containing a considerable
quantity of watery, dropsical fluid.
THE HEART (PLATES 23 AND 24).
Directions.—The pericardium may now be slit transversely, and the
heart should be tilted out by introducing the hand beneath its ape*-
This will permit the examination of the exterior of the hei irt without
destroying any of its connections; and afterwards, in order to observe
accurately its position, it should be restored within the pericardium.
Exterior of the Heart. The heart is a hollow muscular organ, and
acts the part of a force-pump in maintaining the circulation of the blood-
In its interior there are four cavities—two auricles and two ventricles,
the auricle of each side being placed above the ventricle. This sub'
division of the interior of the heart into cavities is indicated on it&
exterior by certain grooves. Thus, the auriculo-ventricular groove ru»s
around the heart like a belt, and marks off the auricles from the
ventricles. Although this groove is carried quite round the heart, it
is not very evident in front, being concealed there by the origins
of the
aorta and pulmonary artery. Two other grooves, one on the right side,
the other on the left, descend from the base of the heart, and become
continuous a little in front of the apex. These grooves correspond to
the edges of the septum which separates the cavities of the right sid
from those of the left. They are much more distinctly marked on the
ventricular portion of the heart, where they are termed the ventrku'a*
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107
DISSECTION OF THE BACK AND THORAX.
ves. The grooves of the heart lodge the coronary vessels, and a
quantity of fat which is present in all but the most emaciated subjects.
a lorm the heart resembles a cone compressed from side to side;
its exterior may be described as presenting two surfaces, two
aers, a base, and an apex. The surfaces of the heart are formed by
ventricles; and when these cavities are distended, both surfaces are
vex. The right side of the heart is formed principally by the right
tncle, but partly also by the left. The right ventricular groove
°ends on it, and crosses round the anterior border a little above the
iJ x. rpne iej^ s^e belongs chiefly to the left ventricle, but partly in
to the right. It shows the left ventricular furrow crossing
ai'ds the anterior border, where it joins the furrow of the opposite
• The anterior border of the heart is slightly convex, and has an
1Ue direction downwards and backwards when the heart is in position.
elongS nearly altogether to the right ventricle, the two ventricular
°ws, which denote the position of the septum between the two
ties, becoming continuous round this border a little above the apex.
posterior border is thicker and less flaccid than the anterior. It is
y straight, and is disposed almost vertically when the heart is in
' won., Xt belongs entirely to the left ventricle. The base of the
ueart V
, h Hes above, and is formed by the auricles. At this point the
»e vessels pass to and from the heart, and form the principal
'Us of its suspension. The left auricle forms the left posterior
°t the base, and consists of a sinus venosus into which the
i 0llary veins open, and an ear-shaped appendix—the auricula, the
* being most posterior. The right auricle forms the right anterior
th          ^le DaS3> and also consists of a sinus venosus and an auricula,
sel         er ^Tmg in front. The large systemic veins discharge them-
, s ^ mto the sinus venosus of the right auricle. The apex of the
is blunt and firm, and belongs to the left ventricle.
°sition and relations.—In order to study these, the heart should now
Tn           *° its natural position within the pericardium.
a „ e Position of the heart may be expressed with regard to the skeleton
4tli VS '~—■"■* ^es beneath the bodies of the dorsal vertebra? from the
a . . *"e 10th inclusive ; it responds to the four ribs behind the 2nd ;
■ . J « placed above the sternum from about the 3rd chondro-sternal
o within an inch of its posterior extremity.
a • a medium-sized animal the most anterior part of the heart (right
eh + 1S ^istant about four or five inches from the entrance to the
san '• Posterior border at its upper part is separated by about the
low. Ulterval from the tendinous centre of the diaphragm, but at its
theT"^1'1 ** is °nly al)0llt an inch in fr0Ilt °f the insertion of the rim °f
°f t!/apllra§m across the ensiform cartilage; and during great distension
e abdominal viscera, the diaphragm may be driven forwards so as
-ocr page 176-
108
THE ANATOMY OF THE HORSE.
to entirely obliterate the interval between it and the heart, a conditio11
which interferes not only with respiration but also with the movements
of the heart.
The base of the heart has its mid point a little to the right of the
mesial plane of the body, and is distant about six inches from the
spine, to which it is suspended by the great systemic vessels.
The apex of the heart lies over the posterior extremity of the stern Wu>
and slightly to the left of the mesial plane.
THE NERVES AND VESSELS OF THE LEFT SIDE OF THE THORAX (PLATE 22).
Position.—It will be most convenient to lower the trunk from «*
suspended position, and lay the thorax flat on a table, with the left side
upwards.
Directions.—Sever the insertion of the scalenus into the 1st rib, and
then remove that bone by sawing through its lower extremity an<l
disarticulating its costo-vertebral joints. In these operations take care
not to cut the vessels or nerves to the inner side of the rib. In oi'dei
to follow many of the nerves and vessels of the thorax, but little dis-
section is necessary, as they show distinctly through the transparent
pleura which covers them. The phrenic, pneumogastrie, and cardiac
nerves should be found in the anterior mediastinum, and traced back-
wards ; the sympathetic chain will be seen at the roof of the cavity*
extending under the costo-vertebral articulations.
The Left Phrenic or Diaphragmatic Nerve is formed at the root of the
neck by the union of three branches (Plate 3), the smallest of which is not
constantly present. The inconstant branch is from the inferior primal'}
branch of the 5th cervical nerve, the others are furnished by the corre-
sponding branches of the 6th and 7th cervical nerves. The nerve, as
thus formed, enters the chest between the first pair of ribs, passlOe
between the axillary artery and the origin of its inferior cervical branch-
Continuing backwards between the layers of the mediastinum, it crosses
the common trunk of the dorsal, superior cervical, and vertebral veinSj
and the pericardium at the level of the common aorta. Behind tne
heart it passes under the root of the lung, through the posterio1
mediastinum, and is distributed to the left half of the diaphragm
(muscular rim and pillar), of which it is the motor nerve.
The Left Pneumogastric, Vagus, or 10th Cranial Nerve. At tl>°
entrance to the chest this nerve lies on the trachea, at the upper edge
of the cephalic trunk, and a little below the sympathetic. It crosses
in beneath the arch of the left axillary, in company with a cardiac nerve-
It is continued backwards across the angle of separation between the
anterior and posterior aortas; and crossing the root of the latter vessel)
it reaches the root of the lung, where it divides. The upper division lS
continued backwards to fuse above the ossophagus with the corresponding
-ocr page 177-
DISSECTION OF THE BACK AND THORAX.                            109
°f the
from the right vagus, this fusion taking place about the middle
posterior mediastinum. The lower division unites in the same
j with a branch from the nerve of the opposite side, the fusion taking
"Ce on the left bronchus. The resulting nerves are termed the
Pe-nor and inferior (esophageal nerves, and they are continued back-
c ds, the one above, and the other below, the gullet, giving branches to
hd accompanying it through the foramen sinistrum of the dia-
phragm,*
h this part of its course the vagus detaches the following branches :—
•   A Branch of Communication with the middle cervical ganglion of the
, apathetic (or with the inferior ganglion when the middle is not
^eloped). It is given off within the 1st rib.
the
1 The left Inferior (recurrent) Laryngeal Nerve.—This is detached at
r°ot of the posterior aorta; and turning round behind the vessel at
1t point, it gains its inner side, to be included between the artery and
., eft bronchus, where it receives twigs from the cardiac nerves. It
. * Passes forwards along the lower face of the trachea, in company
"■ a cardiac nerve; and issuing from the chest, it is continued up the
fc to the larynx. As it is included between the aorta and left
hchus, it is related to the bronchial lymphatic glands. Within the
?~x the nerve gives branches that pass upwards and forwards to the
(( hea and oesophagus. The left recurrent is the nerve implicated in
Sarins "
•   Pulmonary Branches.—These form at the root of the lung a plexus
m which filaments are continued into the lung along the ramifications
0t *e air tube.
°RSal Roots of the Brachial Plexus. These are two branches of
*st and 2nd dorsal nerves respectively. They will be found at the
^Per Part of the 1st and 2nd intercostal spaces. After giving branches
he inferior cervical ganglion, they turn round the inner surface of
-1st rib, close to its upper extremity.
_ he Sympathetic Nerve. The cervical cord of the sympathetic,
lcn m the neck is fused with the vagus, separates from it at the entrance
e °hest, and terminates in a stellate greyish ganglion—the middle
0ervical ganglion.
he Middle Cervical Ganglion.—This will be found within the 1st rib,
ln front of it, at the line of contact of the trachea and oesophagus.
ick connecting branch continues it up to another enlargement—the
O1'ior cervical ganglion. The middle cervical ganglion has a branch
communication with the vagus, and gives off two or three cardiac
nerves.
* Tb
°ases A suPerior oesophageal nerve is generally, if not always, larger than the interior ; and in most
tt'e ri^i't"6 fonnd tllat tlle »PP<sr nerve is formed in greater proportion by the left vagus than by
descrj? W'<Ue tlle lower is formed about equally from each. Chauveau, on the other hand,
the )„«.. and flSlu'es the upper nerve as being formed mainly by the right vagus, and the lower by
lett vagus.
-ocr page 178-
110                             THE ANATOMY OF THE HORSE.
The Inferior Cervical Ganglion is placed a little above the preceding!
to which it is connected by a short thick nerve. It rests on the long'uS
colli, between the vertebral and superior cervical arteries. It is joined
by the vertebral nerve, and by short branches from the inferior primary
divisions of the 8th cervical and first two dorsal nerves. By its posterior
extremity it is continued into the dorsal cord of the sympathetic. **
gives off a cardiac filament.
Cardiac Nerves of the left side.—These nerves, like many others,
have a variable disposition, but the following is what I have found to
be the most common arrangement.
The middle cervical ganglion detaches two cardiac nerves: (1) One ot
these (which may be double at its origin), the smaller of the two, Is
distributed to the great arteries in the anterior mediastinum. (2) The
other immediately divides into two branches—a lower and an upper-
(a) The lower branch, joined by a filament from the vagus, passes
beneath the arch of the left axillary in company with the vagus, aa«
reaching the angle of bifurcation of the common aorta, it divides, one
branch continuing backwards on the posterior aorta to dip down
between the right and left divisions of the pulmonary artery and
gain the left auricle, while the other descends along the common
aorta, and uniting at the origin of the right coronary artery witB
a cardiac branch of the right side, is distributed to the roots of the
great arteries and to the ventricles, the largest branches following
the right coronary artery, (b) The upper division of the second nerve,
passing to the inner side of the left axillary, and along the lower face
of the trachea, unites with a right cardiac filament, crosses to the
right of the common aorta, and is reflected round that trunk to gain
the left coronary artery, its divisions following the main branches of
that vessel.
The inferior cervical ganglion detaches a slender cardiac nerve which,
after throwing off some twigs to the arteries in the anterior medias-
tinum, passes downwards and backwards to the left auricle.
[" The cardiac nerves of the horse (left side) ordinarily have the following disposition '•
There are found four nerves, two of which, very slender, proceed from the middle
cervical ganglion and lose themselves on the vessels arising from the convexity of t'ie
brachial trunk. The two others are the one superficial, the other deep. The superficial
nerve, the more voluminous, commences by a filament which springs from the middle
cervical ganglion, passes backward and downwards, contracts beneath the brachial trunk
an anastomosis en arcade with a branch detached from the inferior cervical ganglion, and
then places itself alongside of the following. The deep nerve is formed at first by three
elements : (1) of medullary fibres furnished by the spinal pairs ; (2) of a ramuscule
furnished by the cervical cord of the sympathetic; (3) of a slender filament which pr°'
ceeds from the left pneumogastric at the entrance to the chest. It places itself in the
direction of the heart, adheres to the superficial nerve, is inflected on the concavity of
the brachial artery, margins this vessel to the left and insinuates itself between the aorta
and the pulmonary artery. At this point these nerves are distributed to the heart and t°
the great vessels, a branch passes under the right auricle and plunges into the cardiac
-ocr page 179-
DISSECTION OF THE BACK AND THORAX.                            Ill
tig) t ' a f econ<l spreads itself over the origin of the pulmonary artery and over the
the entncle ; two other branches, grayish, plexiform, anastomose more or less between
coi             atlc^ *'le Plllm°n*ry artery, unite under the aortic root with a nerve which
pv, , rom *ue right side, then descend in the vertical furrow of the heart, and are
in the left ventricle; finally, some other ramuscules, parallel to the pneumo
c> are expended on the pulmonary artery and on the aorta."—Chauveau. "Traite
11 anatomi
comparee des animaux domestiques."]
ne left Dorsal Cord of the Sympathetic.—This will be seen through the
rpj sParent pleura, extending beneath the costo-vertebral articulations.
nrst portion of the cord is concealed at the outer edge of the kragus
Co l'
touscle, where it joins the inferior cervical ganglion. It crosses
„ ^tercostal vessels superficially; and in company with it, from the
mtercostal space backwards, is the great splanchnic nerve. Poster-
j. 5 it passes between the psoas parvus and the left cms of the
, Ptlragm, and is continued as the lumbar cord. The cord is studded
With
ganglia of a flattened form and greyish colour, there being a gang-
er each intercostal space. Each ganglion is placed at the posterior
_. ^ of the space to which it belongs, and partly on the posterior rib.
18 connected by an afferent filament to the intercostal nerve of the
le space, and from it proceed other branches, which are sometimes
1 ned efferent. The efferent branches from the first five or six ganglia
ay*p
rp Very small, and pass to the adjacent arteries, ligaments, or vertebrae.
e efferent branches from the succeeding ganglia unite to form the
&Pianchluc nerves.
-I he Great Splanchnic Nerve lies to the inner side of the gangliated
. ' as far as the 15th intercostal space. There it crosses to the outer
e> and is continued backwards to enter the abdomen by passing
ween the psoas parvus and the rim of the diaphragm. In the
°nien it joins the semilunar ganglion. The first efferent filament
ibuting to the formation of the nerve comes usually from the 6th
*'uguon, and the last from the 16th. The intermediate ganglia coll-
ate irregularly, some sending no branch, in which case the next
giion contributing sends a branch of more than the usual size,
he Small Splanchnic Nerve is either the efferent filament from the
h ganglion, or it is formed by the union of that and the filament
11 the 16th. It passes directly to the solar, the renal, or the supra-
reQal plexus.
he Pulmonary Aeteht. This is a short vessel of enormous calibre.
sPnngs from the conus arteriosus of the right ventricle : and passing
font of the common aorta, it gains its left side, crosses the root of
16 Posterior aorta, and divides behind it into a right and a left branch,
tJne for each lung. Each of these enters the root of the lung and
Vldes. As the trunk of the pulmonary artery rests on the root of the
?.tenw aorta, it is connected to it, in the adult, by a fibrous cord
lch is the remains of the ductus arteriosus—a vessel which in the
-ocr page 180-
112
THE ANATOMY OF THE HORSE.
foetus brings the two arteries into communication. The pulmoiia1)
artery conveys venous blood to the lungs to be purified.
The Common Aoeta. This is the primary trunk of the systew^
arteries. It is of great calibre, but not more than three inches in lengt* •
It springs from the left ventricle, and divides into two unequal vessels-""
the anterior and the posterior aorta. Where the vessel springs ft'01
the ventricle, it shows, when injected, three bulgings, each corresponding
to a sinus of Valsalva. From two of these sinuses spring the right aB
left coronary arteries of the heart. These, which are the first collate*8
branches of the arterial tree, are described with the heart.
The Posterior Aorta is by far the longer of the two terminal branches
of the common trunk, and it has also the greater calibre. It passes
backwards and upwards, describing a curve—the arch of the aorta, an
reaches the spine at the 10th dorsal vertebra. From that point it :
continued backwards along the vertebral bodies, being at first a little to
the left of the middle line; but it gradually inclines to the right, uiitu>
at the 14th dorsal vertebra, it lies almost entirely to the right of the
median plane of the body. It passes into the abdominal cavity
through
the hiatus aorticus—an opening between the pillars of the diaphragm
The arch of the vessel is crossed to the right by the oesophagus, and by
the termination of the trachea. The remaining portion of the artery
is related on its right to the thoracic duct and vena azygos, the due
being usually between the vein and artery, but sometimes to the left °
the latter. The thoracic branches of the posterior aorta are :—
1.   The Broncho-msophageal Artery.—This vessel will be more cow
veniently dissected with the right side of the chest. It is described at
page 118.
2.   Intercostal Arteries.—The last thirteen of these generally have thlS
origin. They spring from the upper aspect of the artery, and pass over the
vertebral bodies, crossing beneath the dorsal cord of the sympathetic t°
gain the upper end of an intercostal space. Here each gives off a larg6
dorso-spinal branch, and places itself at the posterior border of a rWi
along which it descends. The latter part of the intercostals and then"
dorso-spinal branches have already been followed in the dissection of the
chest-wall and back.
The Anterior Aorta. This vessel, after a course of not more than
three inches, divides into two vessels of unequal size. The left and sniall^'
of the two is the left axillary artery; the other is the arteria innoffl111'
ata. The direction of the anterior aorta is oblique upwards and v&"
wards, and it is in great part included within the pericardial sac. It ha&
no collateral branches of a size meriting description. Of its terminal
branches only the left axillary will be followed now The left axilla^
is the vessel for the supply of the neck, the fore limb, and the subjacen
part of the chest-wall on the left side; while the arteries innomiuata>
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DISSECTION OF THE BACK AND THORAX.                            113
besirl
ues supplying the corresponding parts on the opposite side, carries
')lo°d for the head.
ne Left Axillary Artery is smaller than the other division of the
rior aorta, and placed at a higher level. It passes forwards in the
rior mediastinum, describing a curve which has its convexity
°ted upwards and forwards. It leaves the chest by passing to the
r side of the 1st rib, and turns round the anterior border of the
; where it leaves a smooth impression below the lowest fibres of the
nus. From this point it is directed downwards and backwards
's the inner aspect of the shoulder, beyond which it is continued as
,/ Drachial or humeral artery. The vessel has thus a part within the
dx, and another in the axilla; but only the former presents itself
• ' -h1 the human subject the artery passes beneath the clavicle and
] ft. ^ the Subclavian. The arch formed by the thoracic part of the
. Hillary rests to its right on the trachea, and touches at its highest
point- «,
, cne (Esophagus, Beneath the arch the vagus and phrenic nerves,
of +i,°ne °^ *ne *e^ cai'diac nerves pass backwards. The common trunk
i „ e ^eft dorsal, superior cervical, and vertebral veins crosses it on the
of «ln PaS8mg down to the anterior vena cava. The collateral branches
e artery arising within the chest are four in number, three of them,
•' the dorsal, superior cervical, and vertebral arteries, arise from the
(.-, ^ °f the arch; the other, the internal thoracic or mammary artery,
origin from its lower aspect, at the hinder edge of the 1st rib.
an 1 6 RSAIj Artery' passes upwards and forwards across the oesophagus
int 0118us colli muscle, and disappears at the upper end of the 2nd
svJ         ^ 8pace. At the outer edge of the longus colli it gives off the
a , . ^ artery, a vessel which furnishes the 2nd, 3rd, and 4th intercostal
0j> les- The 2nd intercostal artery may arise directly from the trunk
e dorsal. External to the chest the dorsal artery is distributed to
Parts beneath the scapula, and to the upper part of the neck.
CfirT 6 EEI0E Cervical Artery' arises a little in advance of the pre-
UT)                crosses the oesophagus and longus colli, and perforates the
art 6 °^ *ne ^s* intercostal space. It supplies the 1st intercostal
|~v I and, external to the chest, it is distributed in the neck.
-ie Vertebral Artery has its origin a little in front of the preceding.
1st ■           1uely upwards and forwards, it crosses the inner side of the
.           near its upper extremity, and enters the root of the neck to pass
cession through the series of vertebral foramina,
pri™ Eternal Thoracic Artery arises at the inner side or hinder
fln„              ^st r'b. It descends along the inner face of the rib to the
u°or of tv, i
tne chest, where it will be followed at a later stage.
off f PERI0R Cervical and External Thoracic Arteries are given
ma ?m tne axillary at the anterior edge of the 1st rib, and their roots
e seen now, but they are distributed to parts without the thorax.
i
-ocr page 182-
114                                 THE ANATOMY OF THE HOHSE.
The Anterior Vena Cava. This large vessel will be seen below the
large arteries in the anterior mediastinum. It is formed at the entrance
to the chest by the union of the axillary and jugular veins of both
sides, and it terminates in the right auricle. It is better seen on the
right side of the thorax, and will be more fully described in that
connection. It receives the following branches on this side :—
1.   The Internal Thoracic, which accompanies, and exactly corresponds
to, the homonymous artery.
2.   A large venous trunk formed by the union of the vertebral, superWr
cervical, and dorsal veins. It crosses to the left of the axillary artery t°
reach the vena cava. Very exceptionally, as in Plate 23, the vertebral
vein may join the cava independently. The vertebral and super101
cervical veins exactly correspond to the arteries of the same names, but
the subcostal root of the dorsal vein is of greater extent than the corre-
sponding artery, for it drains the intercostal spaces from the 3rd to the
11th or 12th. The left dorsal vein is also called the small vena azygos-
These veins are superficially placed to the corresponding arteries as
they lie on the oesophagus and longus colli.
Intercostal Veins.—The last five or six of the left side join the ff>'e(ti
vena azygos, a vessel of the right side of the chest.
The Thoracic Duct. This is the largest lymphatic vessel in the
body, and has a calibre about twice that of a goose quill. It will he
most readily found in the angle of separation of the anterior an°-
posterior aortas, resting on the trachea, at the lower edge of the
oesophagus. It will be recognised as a very thin-walled vessel, empty
or with a small amount of coloured contents, so that it might be mis-
taken for a vein. There is not, however, any vein of so large a size u1
this situation. Open it, and pass a blunt probe along it towards the
entrance of the chest. Most commonly the duct has the following
course :—Entering the chest by the hiatus aorticus, to the right of the
posterior aorta, it extends forwards along the spine, having the aorta on
its left and the great vena azygos on its right. It descends from the
spine on the right side of the aortic arch, crosses the before-mentioned
angle, where it rests on the trachea. It then passes to the right side w
the left axillary artery, and dips down between that vessel and the
arteria innominata. It terminates at the anterior edge of the 1st rib;
in the angle of junction of the left jugular with its fellow or with the
left axillary vein, that is, at the beginning of the anterior vena cava.
At its termination it is slightly dilated, and furnished with a valve-'
The duct may be found to the left of the posterior aorta, or it may "e
double as far as the heart, there being a branch on each side of the
aorta. The thoracic duct discharges into the venous system the
lymph collected throughout the whole animal except the right f°re
limb, and the right side of the head, neck, chest-wall, and diaphragm1.
-ocr page 183-
DISSECTION OF THE BACK AND THORAX.                           115
8 by this channel, also, that the chyle absorbed from the intestine
rs the red-blood vessels. The before-mentioned exceptional areas
drained by the right lymphatic duct, a short vessel to be sought
envards on the right side.
tV,         Trachea. The thoracic portion of the windpipe is situated in
middle plane of the cavity. Entering between the first pair of ribs,
Passes backwards through the anterior mediastinum ; and over the
® of the heart it bifurcates to form the right and left bronchi. The
fe e of bifurcation is under the 6th dorsal vertebra. It is related above
ne cesophagus and right longus colli; and below to the cephalic
, S arteria innominata, anterior vena cava, and right auricle. On its
side are the arch of the axillary, the thoracic duct, and the arch of
Posterior aorta. On the right side it is crossed near its termination
by ^                                         °
lt great vena azygos, as will be seen at a later stage. It is also
th ' *° ^e va8'us) recurrent, sympathetic, and cardiac nerves; and to
Prepectoral, tracheal, and bronchial lymphatic glands.
le CEsophagus. At the entrance to the chest the gullet lies above
trachea, and a little to its left side; but as it passes backwards
ath the longus colli muscle, it mounts on to the middle of the
Upper f
i x lace of the trachea, and passes directly over its bifurcation,
u8 the arch of the aorta to its left. Beyond that it enters the
i ri°r mediastinum, between whose layers it passes, a few inches
.        the spine, to perforate the diaphragm by the foramen sinistrum.
th S entrance into the chest, and for some distance beyond that point,
Muscular wa^ °f the tube is red, but behind the heart it is pale.
tr i,6 rnciw'e of the oesophagus is described at page 150, that of the
a£nea at page U9
Hia liIPHATIC Glands of the thorax. The following groups of glands
y be seen at this stage :—
U ' Esophageal glands of small size, along the oesophagus, between the
°i the posterior mediastinum.
OS*' . chial glands, situated at the bifurcation of the trachea, and
y, lnS along the bronchi. The lymphatic vessels of the lung join
fa ' racheal or Cardiac glands, a double chain of glands on the lower
£„          *he trachea, in the anterior mediastinum, and placed on the
e of the lymphatic vessels from the heart.
«xtr v^serieS °f sma11 8'lands heneath the pleura, at the upper
5 D 0I" the intercostal spaces,
thorax
''Qier
^pectoral glands.—These belong to the neck rather than to the
some of tJiem may ^ave been left bytlie dissecto1'of tne
f
tile q61' regio11- Tney are situated at the entrance to the chest, beneath
great vessels.
! Thymus Gland. In the fectus this is a considerable organ,
-ocr page 184-
116
THE ANATOMY OF THE HORSE.
composed of lymphoid tissue, and included between the layers of the
anterior mediastinum. It steadily atrophies after birth, and in tne
adult only the shrivelled remains of it will be found.
the nerves and vessels of the eight side of the thorax
(plates 25 and 26).
Directions.—Reverse the position of the thorax, turning the rign
side upwards, and proceed as already directed for the display of the
structures on the left side (page 108).
The Right Phrenic Nerve. This nerve enters the chest by passing
beneath the right axillary artery, being included between that vessel
and the anterior vena cava. In the anterior mediastinum it lies on tne
side of the anterior vena cava. It crosses the pericardium as on the lei''
side, and behind the heart it passes across or below the posterior ven9
cava to reach the diaphragm, where it terminates. Behind the heart the
nerve and the vena cava are included between the layers of a speci'"
fold of pleura which passes upwards from the diaphragm and floor of tne
chest to envelop them.
The Right Vagus. Separating from the cervical cord of the
sympathetic, the right vagus enters the chest by passing under tne
arch of the right axillary in company with a cardiac nerve, having
the anterior vena cava below. It is then directed obliquely back-
wards and upwards across the trachea; and crossing to the iimer
side of the great vena azygos, it divides at the line of contact of the
gullet and windpipe. Each branch unites, as already described?
with the corresponding branch of the left vagus, thus forming tne
superior and inferior oesophageal nerves. The thoracic branches °
the right vagus are :—
1.   Brandies of Communication with the middle and inferior cervic*
ganglia of the sympathetic.
2.   The right Inferior (recurrent) Laryngeal.—This nerve differs fro11*
the left in its relations and point of origin. It is given off from tne
vagus at the origin of the dorso-cervical artery. Turning round behind
the root of this trunk, between it and the trachea, it passes forward
on the lower face of the windpipe, above the cephalic artery, and interua
to the middle cervical ganglion of the sympathetic. Reaching the r°°
of the neck, it crosses between the carotid artery and the trachea, a11
is continued up the neck below the artery. In the larynx it is distr1
buted in the same manner as the left. In the chest it communi°a
with the cardiac nerves and with the middle cervical ganglion of tn
sympathetic, and emits tracheal and oesophageal filaments as on the lei
side. The right recurrent nerve, it will be observed, is con
siderably
shorter^than the left, having its origin at the posterior edge of the Is
rib, while the left has its origin at the base of the heart. Moreover, tn
-ocr page 185-
117
DISSECTION OF THE BACK AND THORAX.
6 t is reflected round a comparatively small artery, while the left is
cted round the great aorta. The right recurrent nerve is not impli-
cated in "roaring."
•   Cardiac Branches, variable in number, pass downwards and back-
• . s ^° reach the lower face of the trachea, whence, after anastomosing
eatery with the sympathetic cardiac nerves, they pass on to the
"gat auricle.
•    "ulmonary Branches as on the left side.
orsal Boots of the Brachial Plexus. These do not differ from
u *°se of the left side (page 109).
ne Sympathetic Nerve.
he Middle Cervical Ganglion.—This resembles that of the left side.
ls placed on the trachea, internal to the insertion of the scalenus
Cle in-(.0 the \st rib. It receives the cervical cord of the sym-
. eac in front, and behind it is prolonged by a short cord connecting
the inferior cervical ganglion. It communicates with the vagus
recurrent nerves, and gives off the cardiac nerve accompanying the
gus beneath the axillary artery.
fle Inferior Cervical Ganglion is situated on the longus colli, at the
y r edge of the trachea, and between the vertebral and superior cervi-
; f Tories. It receives the vertebral nerve and branches from the
nor primaiy divisions of the 8th cervical and first two dorsal nerves,
ls continued into the dorsal cord of the sympathetic as on the left
•     It emits a cardiac nerve.
Qrdiac Nerves of the right side.—(1) The middle cervical ganglion
' ones a considerable cardiac nerve which accompanies the right
c bUs m passing back beneath the arch of the axillary artery. Reach-
e the lower face of the trachea, it unites with one of the cardiac
, es of the loft side, and is reflected behind the common aorta to be
ibuted to the left side of the heart, as already described. This
e emits a branch to unite with another cardiac nerve of the left
. lnat which follows the right coronary artery. (2) The inferior
W ganglion gives origin to a cardiac nerve, smaller than the
fling, which it joins after giving fibres to the right vagus and
rrent. (3\ The cardiac branches of the right vagus have already
beeQseen.
The fi f rignt side we reckon two principal cardiac nerves and four secondary filaments.
vical I carcliac nerve is a long branch which takes origin at the level of the middle cer-
by thf^811™' It is I0rmecl by fibres from tlle sympathetic and by a fasciculus furnished
taScforj         Pneumogastric, at the entrance to the chest; it receives probably also some
oetwelaiy fibros trough the intermediation of a branch of communication thrown
fllamerri the middle ganglion and the inferior ganglion. This nerve is reinforced by two
second .Wnlon Pr<>ceed from the inferior cervical ganglion, and sometimes from the
left sy midllle ganglion, of which one, the posterior, is reinforced in the same way by a
Apathetic filament which gains its destination in passing alongside of the recurrent
-ocr page 186-
118                                 THE ANATOMY OF THE HORSE.
nerve. "When it is fully constituted the first right nerve creeps over the base of *
heart, turns round the root of the aorta, and mixes its terminal filaments with those
the left cardiac nerves. The second right cardiac nerve is formed by the union of
behind
branches which take origin in succession from the corresponding pneumogastric
the dorsal artery, along the right side of the trachea. This nerve is in eommurno*"1
with the sympathetic of the dorsal region by three branches which approach the la
beneath the first, fourth, and sixth ribs.
When the second right nerve arrives above the termination of the anterior vena ca^ >
it divides into two branches : the one is thrown into the roof of the auricles ; the oth »
reinforced by a filament coming from the pneumogastric, is expended, by
numerous
filaments, on the surface of the left ventricle; some reaching as far as the right ventric '
The four secondary filaments are arranged like the steps of a ladder on the portion
the pneumogastric comprised between the entrance of the chest and the division of * °
bronchi. These filaments are expended in the great vessels and in the walls of the heart.
—Chauvcau. "Traite d'anatomie comparee des animaux domestiques."]
The Right Dorsal Corel of the Symjxtthetie does not differ materiaJv
from the left.
The Posterior Aorta is here seen in a large part of its course, but it b8
already been fully described in connection with the left side. It detach68
to this side thirteen intercostals, exactly similar to those of the left.
The Broncho-GEsophageal Artery. This artery arises from t'ie
convexity of the aortic arch, a little anterior to the bifurcation of thc
trachea. Generally, as in Plate 24, it arises not independently but as
a division of a short vessel which is at the same time the conim01*
trunk for the 1st and 2nd pairs of aortic intercostals. It is a sural
vessel, not larger than an intercostal. It is reflected downwards auc
backwards on the right side of the aorta, and divides into the bronchi
trunk and the oesophageal artery. The mmphageal artery, which is «*>
smaller of the two, is continued backwards above the gullet, through t'1
posterior mediastinum, extending sometimes to near the foramen sin11'
trum, and anastomosing with the pleuro-cesophageal branch of *D_
gastric artery. Sometimes there is an analogous vessel in the mediast
num below the oesophagus (inferior oesophageal), but when present this •
a very slender artery. The bronchial trunk dips down between tw
aorta and the gullet, and bifurcates to form the right and left bronchi11
arteries, each of which enters the root of the lung on the bronchus,
is the nutrient vessel to the lung. The above-mentioned inferior oesop'111'
geal may be a branch of one of the bronchial arteries.
The Arteria Innominata is the right division of the anterior aoi'*a'
the left axillary artery being the other division. In calibre it is gre&"6
than the left axillary, and it is placed on a lower level. It is related t
the trachea above; and to the anterior vena cava below and to the let '
After a course of about two inches, it divides to form the cephalic trim
and the right axillary artery, and immediately in front of its point
division it detaches the dorso-cervical artery.
The Dorso-cervical Artery. This is a short trunk which p<asse _
upwards on the trachea, and divides to form the dorsal and super10
-ocr page 187-
119
DISSECTION OF THE BACK AND THORAX.
vical arteries, which have precisely the same course and distribution
. nose of the left side. They have also the same connections, save that
"ey do not touch the oesophagus.
ifle Cephalic Artery. This vessel, which has a length of about two
nree inches, passes directly forwards at the lower face of the trachea,
ouurcatcs at the entrance to the chest, forming the common carotid
arteries (right and left).
^he Right Axillary Artery. This vessel in its intrathoracic course
"IS a continuous curve, or arch, with the arteria hmominata; this
n being) however, on a lower level, and less abrupt, than that of the
axillary. It gives off here the vertebral and internal thoracic arteries,
ihe Vertebral Artery and the Internal Thoracic Artery do not
differ f
l troni the homonymous vessels of the left side.
h         Amemor Vena Cava. This large vessel, already referred to, is
seen from the right side of the chest. It is formed at the entrance
ue chest by the union of the jugular and axillarv veins of both sides,
of «. mit!al portion is fixed by fibrous processes to the inner surfaces
ne first pair of ribs. It passes backwards through the anterior medias-
of ta' ^em8' there related to the great arteries, beneath and to the right
oicli it is placed. * It enters the roof of the right auricle. Besides the
" els already seen entering it on the left side (page 14), it receives—
1 he Internal Thoracic Vein.
ilie Vertebral Vein.
■ A trunk formed by the union of the dorsal and superior cervical
veins en.          ■                       ■ ,         , , >
Vinese veins may enter independently.)
beV           Great Vena Azygos (sometimes). This large vein begins
. "** the hiatus aorticus, where it receives the first pair of lumbar
veins tj •
0f ' "assmg through the hiatus, it extends along the dorsal portion
v e spine to the right of the posterior aorta, the thoracic duct being
j. J between the two vessels. At the 6th or 7th dorsal vertebra
„ ^ es the spine and curves downwards to the right of the aortic arch,
c SoPhagus, and the trachea; terminating either in the anterior vena
B i-j 01' *n ^e aur'°le immediately behind the opening of that vein.
int. 6S ^e ^rs* P!™' °^ lumbar veins, it receives the last thirteen
^°stal veins of the right side and the last five or six of the left.
thr e ^os™Rior Vena Cava. This great vein enters the thorax
f0 ^ the foramen dextrum of the diaphragm. It passes directly
aids to terminate in the right auricle, being included between the
Vl n^ass of the right lung and its internal lobule, and placed at the
bra Sr 6 °f a double serous fold belonging to the right pleural mem-
• 1 he right phrenic nerve is in company with it.
6 'wght Lymphatic Duct. This is a short lymphatic vessel (not
* Th
than natur^ ** in the naturaI position in Plate 25. In Plates 24 and 26 it is represented as smaller
■ and slightly lowered in position, in order to expose the arteries.
-ocr page 188-
120
THE ANATOMY OF THE HORSE.
more than two inches) which empties itself into the initial part of ttie
anterior vena cava, at the angle of junction of the jugular and axilla1?
Fig. 7.
Floor of the Thorax.
Nos. 1 to 8 indicate the corresponding ribs. Nos. 0 to 12, the cartilages of the corresponding Iltt_'
A. Cariniform cartilage ; B. Internal thoracic artery ; 0. Asternal artery ; I). Triangularis stern' >
E. An internal intercostal muscle ; F. Rim of diaphragm ; G. Ensiform cartilage.
-ocr page 189-
DISSECTION OF THE BACK AND THOBAX.                            121
di k ^e r^Sn* s^e- Its opening is provided with a valve. It
C arSes into the venous system the lymph collected in the right
s.,erior half of the animal, viz., the right fore limb, and the right
of the head, neck, chest-wall, and diaphragm.
Sections.—Cut out the trachea and lungs with the heart and great
tV,            Sever the lungs from the heart by cutting the great vessels at
root, and set both lungs and heart aside in carbolic or other preser-
e solution to serve in the examination of the structure of these
^ans. or, since they are likely to be much decomposed, it will be
^ er to discard them if fresh organs can be obtained. In the mean-
, separate the sternum and costal cartilages as shown in Fig. 7,
lissect the triangularis sterni muscle and the internal thoracic
at+ ' Portions of the longus colli and psoas muscles which are
1 ctied to the lower face of the dorsal vertebrae should be noticed.
fongus co\i[ jg described at page 156, and the psoas muscles at
I>a8e 325
1 , e Triangularis Sterni (Fig. 7). This muscle arises from the
. af margin of the thoracic surface of the sternum, beginning at a
e opposite the 2nd costal cartilage, and extending backwards to the
is -' °rTl1 cart,uage, from the edge of which the last few fibres arise. It
*^erted into the costal cartilages from the 2nd to the 8th inclusive,
nto an aponeurosis on the internal intercostal muscles. Its outer
and
Se
•   is strongly serrated. It covers the internal thoracic vessels, and is
"J pleura on its upper face.
ka ,^l0n-~~It pulls the cartilages to which it is attached inwards and
ards, and thus assists in expiration.
(jet ® Eternal Thoracic (Mammary) Artery (Fig. 7). This vessel,
fac'C fr°m tlle axlllary artery at the 1st rib, descends on the inner
Wh            * bone, and disappears beneath the triangularis sterni muscle.
the muscle is removed, the artery is seen to pass backwards at
aW ^6 °^ *^e sternum, crossing the chondro-sternal joints. Over or
abd            ^ °^ tnese joints it divides into the asternal and anterior
tr: lnai arteries. The asternal branch emerges from under cover of the
tho         lls sterni, and runs up the cartilage of the 9th rib, on the
tlle aCl° Slde °f the ori8'm of the diaphragm. About the upper end of
ahd °arti*a§e it passes through the edge of the diaphragm to its
cart-Jlamal side- The anterior abdominal, artery dips down between the
ente a§e °f the 9th ril3 and the ea"Se of the ensiform cartilage, and
tivJ* the ahdominal wall. The collateral branches of the internal
^oracic are :—
•     ranches to the mediastinum and pericardium.
j^q * Pectoral branches, perforating the intercostal space and anasto-
g with the external thoracic artery,
ntercostal branches, which ascend to anastomose with the inter-
-ocr page 190-
122
THE ANATOMY OF THE HORSE.
This series is continued by branches of the astern
d
costal arteries
artery.
The Internal Thoracic Vein runs in company with the artery, aI1'
internal to it. Beneath the triangularis sterol it is placed between tfi
artery and the fibrous cord that traverse the edge of the sternum.
of
Suprasternal Lymphatic Glands. These include (1) a group
glands on the thoracic side of the insertion of the diaphragm across t»
ensiform cartilage, and (2) some small scattered glands along the cowl's
of the internal thoracic vessels.
examination of the lung.
th
Physical Characters.—The exterior of the lung is exquisitely snioc
Through this thin, transparei'
covering, the surface is seei,
especially when the lung is o-I&
tended, to be divided by intel"
secting lines into small areas, eac
of which corresponds to a lob*11
of the lung. The lines a1'6
forme d by the interlobular con-
nective-tissue.
The colour of the lung varies
with the age of the animal.
the young subject it is pale pinK'
but in old animals it is of
grayish or slaty hue. In *"
foetus it is a bright pink.
in virtue of its pleural covering.
the
has
also
The lung is spongy to
touch, and its cut surface
the same appearance. It is
markedly elastic, this quali*.
the
being best illustrated by
rapidity with which the inflate0
lung collapses when the diste»
ing force is removed. It crep
tates on pressure with t'1
fingers, and it floats on wate*-
The foetal lung is non-crepitai1 '
Fig.
o.
Termination of the Air Passages in the Lung
(modified from Turner).
A, A. Terminal bronchiolaa ; B. Aninfundibulum,
showing the air-cells on its surface ; C. Pulmonary
artery; D. Pulmonary vein ; E. Pulmonary capil-
laries.
and sinks in water.
it divides again afl®
chia1
Structure.—When the bronchus enters the lung,
again until there results a remarkable tree-like arrangement of broncii
tubes. Of this tree, the bronchus entering the root of the lung iotv>s
the main stem; and as the division is traced onwards,
the
smaller,
nchi
until
tubes, representing the branches, become smaller and
-ocr page 191-
1 OS
DISSECTION OF THE BACK AND THORAX.
there is reached a tube of comparatively small calibre which belongs
exclusively t0 Qne lobllle> and is therefore termed a lobular or terminal
br°nchus. The left bronchus has a length of three or four inches before
dividing, but the right immediately gives off from its outer side a con-
querable branch (Plate 26). Within each lobule the terminal bronchus
^amifies,forming smaller tubes or bronchioles, the last and smallest of which
lea<i into recesses or dilatations. Each such dilatation is termed an
alveolar passage, and it is bounded by delicate sacculated walls,
ea°h sacculation being an infundibulum. The infundibula are thcm-
Selves sacculated, the minute recesses of their walls being termed
(<?--cells. The air-cell is thus the ultimate part of the air passages withm
he !ung, and a group of air-cells forms an infundibulum. The wall
°f an air-cell consists of a delicate membrane supporting the capillary
Ple*us of the pulmonary vessels, and lined towards the air passage by a
Sl»gle layer of squamous cells. The bronchial tubes comprise m their
Walls: (1) an outer fibro-elastic coat sustaining segmented rings ot
cartilage; (2) within the preceding, a complete coat of non-striped
Muscular fibres circularly arranged; (3) an inner fibre-elastic coat; (4)
* Mucous membrane with a ciliated epithelium on its free surface.
f;UQierous mucous glands lie in the outer fibrous coat, and discharge
^eir secretion into the bronchus. The bronchi in their ramifications
are accompanied by divisions of the pulmonary artery and veins these
tWo sets of vessels being connected by the capillary plexus on the air-
f6^- Along the bronchi run also the much smaller branches of the
3r°nchial vessels, as well as nerves and lymphatics.
Connective-tissue forms a framework for the lung. It surrounds
aud connects the bronchi and vessels as they run together in the lung
^stance; it connects and isolates the adjacent lobules; and beneath
the Pleura it forms a fibrous capsule for the lung. Lymphatic vessels
a^e abundantly distributed in it, and form three principal sets, viz., sub-
Pleiu'al, perivascular (around the pulmonary vessels), and peribronchial.
DISSECTION OF THE HEART.
^"e Vessels of the Heart.
Tlle Coronary Arteries (Plates 23 and 24) carry arterial blood to
ll0nrish the heart-wall. They are two in number, distinguished as right
*** left. Each arises from the common aorta, and has its mouth m
®°f the sinuses of Valsalva.                                                                   ,
The Sight Coronary Artery passes forwards to the right ol the p -
?°na*y artery at its root; and encircling the right auricular appendix,
f Piaces itself in the auriculo-ventricular furrow, in which rt passes to
the right side of the heart. On reaching the origin of the right ventn-
*J* furrow, it divides, one branch descending in that furrow, while the
0ther continues the course of the main trunk in the auriculo-ventricular
-ocr page 192-
124
THE ANATOMY OF THE HORSE.
groove. The terminal twigs of the vertical branch enter the he»i
a little above the apex; the horizontal branch reaches as far as tft
posterior border of the heart.
The Left Coronary Artery passes outwards and to the left, betwee
the pulmonary artery and the left auricular appendix. Beaching tn
auriculo-ventricular furrow at this point, it divides into a vertical and
horizontal branch. The former descends in the left ventricular fttrr°™ '
the latter turns backwards along the auriculo-ventricular furrow. 1
terminal portion of the vertical branch turns round the anterior h°r"
of the heart, and ends in twigs that enter the ventricular wall on
right of its apex; the horizontal branch terminates in the same vAJ
near the posterior border of the heart.
The corresponding branches of the right and left arteries, thus, appi'°aC
each other at their terminations, but they do not anastomose; nor
there any anastomosis between the arteries through their collated
branches. Still more, there is no anastomosis between the adjacent
collateral branches of the same coronary artery.*
The Coronary Veins,—These arise from the capillaries of the coronal J
arteries. The principal vessel of the right side ascends in the rig11
ventricular groove, and at the auriculo-ventricular furrow it joins to
main vein of the left side. The latter ascends at first in the left vent1
cular furrow, at the top of which it enters the auriculo-ventricul*
groove. Along this it is reflected backwards; and turning round tn
posterior border of the heart, it joins the right vein. The dilated vesse
resulting from this union is termed the coronary venous sinus, and
opens into the right auricle, beneath the mouth of the posterior vel>
cava.
For the most part, the veins arising in the wall of the right aUT10
do not join the large coronary veins, but open into the cavity indepel
dently, by minute mouths—the foramina Thebesii.
111^
The Nerves of the Heart have already been described (pages 110 •
117). In the heart of a lean subject long filaments are visible witho11
dissection, descending beneath the serous covering.
The Interior of the Heart.—The cavities of the heart should
studied in the order in which the blood passes through them, afl
therefore the right auricle falls to be examined first. The terBWB
tions of the anterior and posterior cava? and vena azygos (provide
that has an independent opening) should be identified ; and then a
incision should be made along the wall of the sinus venosus, fr0
the opening of the anterior to that of the posterior cava. Anotn
incision should be carried from this one to the point of the auricul' i
■ Percivall, Leyh, Chauveau, and all the other authors that I am acquainted with state tha
coronary arteries anastomose with one another. That they do not, I have repeatedly prove
injecting one of them, by which method none of the injection, however fine, can be driven int0
other artery.
-ocr page 193-
125
DISSECTION OF THE BACK AND THORAX.
aild the clots of blood having been cleared out, the cavity will be
l'eady for examination.
T"e Cavity of the Right Auricle. The interior of this and the
other cavities of the heart is smooth and glistening in virtue of an
eudothelial membrane termed the endocardium, which is here continuous
with the endothelial lining of the great veins. It will be observed that
t&e muscular wall of the auricle is thrown into parallel ridges, which
r°m their resemblance to the
eeth of a comb are termed
"1««cmK pectinati. The venous
rifices by which the blood is
Poured into the cavity are all
°und in the sinus venosus,
aild are as follows :—1. The
anterior yena cava empties
itself into the anterior part of
tlle roof of the sinus. 2. The
Posterior vena cava discharges
ltself at the lower and back
Pai"t of the outer wall of the
smus. 3 The cor0nary ven-
ois sinus conveys the blood
tr°tti the wall of the heart it-
^K and its mouth will be
011nd under that of the pos-
terior vena cava. 4. The vena
,zygos sometimes has an in-
ePendent opening into the                              FlG 9
a
. Ul'lcle, and it then discharges
|tself by the roof of the sinus,
Diagram of the two Cavities of the bight side
of the Heart (Ellis).
^ the mouth of the a- Anterior cava; b. Posterior cava; c. Right auriculo-
auterior r,               at-            ventricular opening; d. Fossa ovalis ; e. Opening of
u         ui Cava. At other times the coronary sinus;/. Foramina Thebesii, the openings
it
.                   .of veins; g. Aperture of the pulmonary artery; h.
0Pens into
the anterior Auricular appendix.
cVa- 5. The vence cordis
^niniw are small veins of the wall of the right auricle, which, instead
°5 discharging themselves by the coronary sinus, open directly on
^e wall by minute mouths named the foramina Thebesii. Of all
these orifices, that of the coronary sinus is the only one provided with
^7alve- I* is a thin fold of the lining membrane, termed the valve of
■* "rtesius.
The inner wall of the sinus venosus is formed by the auricular sep-
™**, which is the partition between the two auricles. On this the
following objects are to be noticed :—1. Between the orifices ol the
anterior and posterior cavse is a muscular prominence—the tubercle of
-ocr page 194-
126                                 THE ANATOMY OF THE HOUSE.
Loiver. 2. Above and in front of the opening of the posterior cava is
depression of the septum that looks like another venous orifice. This is
the fossa ovalis, and it marks the former position of the foramen ovale-"
an aperture which, in the foetus, established a communication between
the right and left auricles. The raised border which surrounds the
fossa is termed the annuhis ovalis. In the foetus of many animals
but not of the horse, a valve, termed the Eustachian valve, directs the
blood from the posterior cava through the foramen ovale. After birth
the foramen ovale in nearly every case becomes completely closed, bO»
sometimes an oblique slit remains, which, however, does not necessarn}
permit any blood to pass through the septum.
The blood which passes through the right auricle is venous in char-
acter. It has been circulating among the tissues, and it is poured in*0
the cavity at the venous orifices already enumerated. When the
auricle contracts, the blood is passed into the ventricle of the same side;
by a large aperture of communication between the two cavities—the
right auriculo-ventricular opening.
Directions.—The fore and middle fingers of the left hand should he
introduced through the auriculo-ventricular opening, so as to graspi
between the fingers and thumb, the wall of the right ventricle close to
the angle of junction between the right ventricular and the auriculo-ventri-
cular groove. The scalpel should then with the right hand be passed
through the wall of the ventricle at that point, and carried downwards
in front of the right ventricular furrow; and following that furrow
round the anterior border of the heart, the incision should be continued
up in front of the left ventricular furrow, as far as the root of the
pulmonary artery. This will enable nearly the entire wall of the right
ventricle to be raised as a triangular flap, and will give a good view °*
the cavity when looked into from below.
The Cavity of the Eight Ventricle. This cavity is widest above,
and tapers to its lowest point; and its shape is such that its transverse
section gives a crescentic outline, the wall of the ventricle being concave
towards the cavity, while the septum is convex in the same direction-
The inner surface of its wall is rendered irregular by muscular bands
and prominences—the columnce carnece, of which there are several
varieties: 1. Some of them have the form of bars or ridges sculptured
on the wall of the heart, to which they give a sponge-like appearance-
2. Others, the trabeculce carnece, are veritable bands or strings between
which and the wall of the ventricle the handle of a scalpel may be
passed. Of this variety two or three very tendinous strings, sometimes
more or less reticulate, stretch between the wall and the middle of the
septum; and since they are believed to prevent over-distension of the
ventricle, they have been named moderator hands. Other strings occur
in the angle of junction of wall and septum, and still others stretch
A
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DISSECTION OP THE BACK AND THOEAX.                            127
ween different parts of the wall. 3. A third variety are blunt,
Wle-shaped prominences called musculi papillaris, of which there are
Wionly three in this cavity, one being placed on the wall and two on
septum. Radiating from each of these is a set of fibrous strings—
c/iwdce tendinece, which are attached by their other ends to the seg-
, ts* of the valve guarding the auriculo-ventricular opening. The
9 >t ^ auriculo-ventricular opening is situated at the base of the cavity,
is a very large orifice. It is provided with a valve composed of
ee main cusps, or segments, and hence named tricuspid. Each of these
Ps is triangular in shape, being fixed by its base to the wall of the
> and having its edges free and directed towards those of the
jacent cusps. When the blood stream is rushing through the opening,
8egments of the valve hang down into the ventricle, and have one
ace directed towards the blood stream, and the other to the wall of
Ventricle. The first of these surfaces is smooth ; the other is rough,
and + •
10 it and the apex and edges of the cusp, the chorda) tendineae are
tChed. When, during contraction of the ventricle, the blood tends
regurgitate through the opening, the cusps are floated upwards, and,
,, lno each other, close the orifice. To the efficiency of this action,
chordae tendineai passing from the musculi papillares are essential;
' Deing attached to the edges and lower surfaces of the cusps, they
Teut the latter from being carried right up into the auricle. The three
lcipal cusps generally alternate around the opening with three of
°h smaller size. There are three musculi papillares, each with its
°t chorda? tendineee, and three large cusps; but it will be observed
' one set of the chorda; tendineas does not pass entirely to one cusp,
~ivid.es itself between two adjacent segments.
, Sections.—A better view of the tricuspid valve may now be obtained
J °utting through the auriculo-ventricular ring near the point where
nrst incision was begun in opening the ventricle, selecting the inter-
between two cusps. When some of the chordse tendinece have been
> this will enable the wall of the ventricle to be thrown outwards.
nen the ventricle contracts, the blood, prevented by the tricuspid
„ e from, passing back into the auricle, is forced upwards into the left-
aj,t rior portion of the ventricle, and leaves the cavity by the pulmonary
th ^' r^s portion of the cavity, which leads up to the artery, is termed
conus arteriosus. The orifice of the pidmonary artery is surrounded by
_ ve composed of three crescentic segments, and hence termed the
w 11 Wnar valve- The convex border of each segment is fixed to the
b wi *^e ai"';ery where it springs from the ventricle. The concave
t. .Cer is free, and shows at its midpoint a minute, fibro-cartilaginous
ckening—the nodulm or corpus Arantii. On each side of the corpus
siaall cresentic portion near the free edge of the segment, and dis-
nguished from the rest by its thinness, is termed the lunula. One
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128
THE ANATOMY OP THE HORSE.
surface of the valve is convex, and, during contraction of the ventricle
it is directed to the blood-stream; the other is concave, and directed t
the wall of the artery, which, opposite each segment, forms a pouch
the sinus of Valsalva. When the ventricle has ceased to contract, tn
elastic recoil of the artery forces the blood against the concave side o
the segments, and carries them inwards till they meet and completev
close the opening. The blood is thus propelled along the pulmonary
arteries to the lung, where, in the capillary plexus on the walls of *n
air-cells, it is purified. The purified fluid is then carried from the lung8
by the pulmonary veins, which pour it into the left auricle of the heart'
Directions.—The cavity of the left auricle is to be exposed by aI1
incision from the right to the left pulmonary veins, and by anotW1
from the first to the point of the appendix.
The Cavity of the Left Auricle is smaller than the right, but, like
it, consists of a sinus venosus and an ear"
shaped appendage—the auricula. The pul"
monary veins open on the roof of tril3
sinus venosus; and most commonly thej
have four openings—two from each lung;
but they may have as many *as eigntt
They are not provided with valves. The
ig) Q~*\         ^*Si         auricula and adjacent part of the sinu=
venosus show musculi pectinati similar t0
these of the right auricle. In the floor o»
the cavity is the left auricido-ventriculw
opening, by which, on contraction of the
auricle, the blood is passed into the le**
ventricle.
Directions.—The left ventricle should v°
opened by an incision similar to that used
on the right side. The point of the scalpel
should be passed through the wall of tne
ventricle near the upper end of the let
ventricular furrow, and the incision
Fig. 10
Diagram op the two Cavities of
THE LEFT SIDE OF THE H^ABT (Ellis).              , - -i
, T « ,             • • t,- J. ventricle
h. Left pulmonary veins; i. Right
should
ed down the left side of *ke
round the apex, and up t'1^,
pulmonary veins ; o. Remains of fora-
men ovale ; I. Left auriculo-ventric-
ular opening ; m. Auricular appendix ;
n. Aperture of the aorta.
right side to within a short distance °
the auriculo-ventricular groove, the °°
being made near the septum, to which tn
ventricular furrows will serve as a guide.
The Cavity of the Left Ventricle is longer than the right, and
almost conical in shape, the base being at the auriculo-ventricular
opening. On transverse section, it gives an oval or nearly circuia
outline, the septum, as well as the wall of the ventricle, being coiicaV
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129
DISSECTION OF THE BACK AND THORAX.
th v           cavity. It will be observed that its wall is about thrice
. Sickness of that of the right cavity, a circumstance which makes
sy to distinguish the right and left ventricles in the undissected
BolM i' ' whereas the former appears flabby, the latter is firm and
th ■° uo- The left ventricle possesses columnar carnece like those on
gnt side. The musculi papillares are two in number, and are of
ch ar^e S'ze' They are placed on the wall, and are provided with
« tendineoe stronger than those of the right cavity. The base of
sttialiaVity Sh°WS the Uft
auriculo-ventricidar opening, which is somewhat
a6, ^r *han the right. It is guarded by a valve with two large cusps,
. uence called the bicuspid valve. It is also very commonly
bHated the mitral valve, from a fancied resemblance to a bishop's
Avi . ' "he cusps are stronger than those of the tricuspid valve, with
they agree in shape and disposition. Two smaller segments
Fig. 11.
Root of the common Aorta laid opex.
' '}■ Sein
G01"onar"lilunar segments Of the aortic valve ; 2. Corpus Arantii ; 3, 3. Orifices of right and left
alt,
y arteries from two of the sinuses of Valsalva ; 4. Ventricular wall; 5. Arterial wall.
eruat
•e         ° with the main ones. In mode of action the mitral exactly
IS the tricuspid valve. When the ventricle contracts, the blood,
^Ventprl
Cavit          from
of the
;
reat systemic artery—the common aorta, which springs
h'Orr
°Hf) L^6 right-anterior part of the base of the ventricle. The aortic
are .f1S 8'uarded by a three-segmented semilunar valve. These segments
thev r°nger ttlan those at the mouth of the pulmonary artery, which
Veils           wise exactly resemble. Opposite to each a large sinus of
Sprjj, VCt ls developed on the wall of the artery, and from two of these
° e right and left coronary arteries of the heart.
STRUCTURE OP THE HEART.
Iu,
ittw ructure the heart consists of a muscular wall, an external serous
di
'Oient—the epicardium, and an internal serous lining—the endocar-
urn.
The valves are folds of the endocardium, strengthened with fibrous
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130
THE ANATOMY OF THE HORSE.
connective-tissue, to which are added some elastic fibres. The
muscular
tissue is of the striped variety (although not under the control of the wu />
and its fibres are grouped in bundles separated by fibrous connects
tissue. Connective-tissue occurs also in large amount in the neighbor
hood of the auriculo-ventricular and arterial openings, where i*
aggregated in the form of rings, or zones. These rings give to f
orifices that firmness which is necessary for the efficient working of »■
valves, and at the same time give origin to some of the muscular fibr0*
The tissue of which they are composed is mainly fibro-cartilagin°u '
In the heart of the ox, and rarely also in the horse, a bone—the °
cordis—is developed in the angle between the aortic ring and the t^v
auriculo-ventricular rings.
Directions.—The arrangement of the muscular tissue in the wall
the heart is exceedingly complex, and cannot be studied except B>
heart specially prepared. A heart from any of the domestic anim*1"'
but preferably from the horse, should be procured, and boiled for ab°u
an hour. This will favour the dissection of the fibres, by making tnepl
firm and softening the connective-tissue between them. The epicardim11'
fat, and vessels having been cleaned off the surface of the heart, w*
auricles should be first examined.
The auricles have the muscular fibres of their walls distinct fr°n
those of the ventricles. Moreover, the fibres are arranged in two layers
a deep set proper to each auricle, and a superficial set common to DO* '
some of the fibres of the latter stratum being carried into the auriou1'
• the
septum. In the deep stratum some of the fibres run obliquely m XJ
wall, while others are arranged as rings around the auricula and
different venous orifices, the latter playing an important part in Pr
venting regurgitation into the veins when the auricle contracts.
Directions.—Separation of the auricles from the ventricles should »e
be effected by cutting the auriculo-ventricular fibrous rings, which f01
the bond of connection between the auricular and ventricular ^"x
By combined cutting and teasing the following facts may be observed-
Over the whole exterior of the ventricles the fibres have an obli<
direction. Thus, on the left side the fibres pass obliquely downwards a11
backwards, and on the right side downwards and forwards. At the le
ventricular furrow many of the fibres dip into the septum; but on *
right side the fibres of the left ventricle pass across the furrow, and a
directly continued on the right ventricle. At the apex of the hea
the fibres turn inwards in a whorl-like manner and disappear from vie..J
If a thin stratum of these superficial fibres be now removed, they fl
be found to cover others having a less oblique course; and fur*11
dissection, will show that the fibres become less and less oblique uO
the centre of the wall is reached, where the fibres are approximate' ■>
horizontal. On peeling off these horizontal fibres, a deeper set win
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131
DISSECTION OF THE BACK AND THORAX.
•'Posed which are slightly inclined, but in a direction opposite to the
Policial fibres; and the obliquity of these increases until the inner
ce °f the wall is reached, where the fibres have a degree of obliquity
i" a* *° the most external fibres. So much the student will probably
aWe to make out without much difficulty, but according to Pettigrew
y                                                         Fig. 12.
SJhee -ARTIAL Dissection of the Fibres of the left Wall of the Ventricles in a
Ftdj„jP s . Heart, designed to show the different Degrees of Obliquity of the
Atth          (*"*»»)-
l^i hiore o^+if11^ aPex tne superficial layer of fibres is displayed : in the intervening space, more
nf left th'm ^Dres have been removed from above downwards, reaching to a greater depth on
°l the left y °? *he rigllt silie- "'• "'• The suPerncial lay«r of the right ventricle ; b'. 61. The same
^?ath, whVh *C*e ' a* ^ ^s 8uPernc^al layer has been removed so as to expose the fibres under-
rp£erent ov ^i6 se-en *° l)ave *ne same direction as the superficial ones over the left ventricle, but
Cerent • /V" ^Sht; at 3 some of these have been removed, but the direction is only slightly
aHa ; 5 \ ' -transverse or annular fibres occupying the middle of the thickness of the ventricular
t),C' 'he left lnternal fibres passing downwards towards the apex to emerge at the whorl; between
I reiuajn- venfricular groove, over which the fibres of the superficial layer are seen crossing ; in
■ The nui-J^ P&xt of the groove, some of the deeper fibres turn backwards towards the septum ;
Pulmonary artery : e. The aorta.
the fibr,
whi 6S are arrange(i in seven determinate layers—three external
dire +• are °^^clue» three internal, also oblique but in the opposite
ul °n> a'ad a central which is horizontal. Further, he describes the
0rjr-         ne most external layer as turning in at the auriculo-ventricular
lav l aU<* at *^e aPex °f tne heart to become continuous with the
Se eileath the endocardium. In like manner, he supposes that the
whil layer is contirmou8 with the sixth> and tlie third with tae fifth>
how         ^ourth or central layer has a zone-like arrangement. In truth,
aHoth ^ *^6 n^res °^ tne same stratum anastomose not only with one
er> but also with the fibres of adjacent strata, as is shown by the
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132
THE ANATOMY OF THE HORSE.
rough surface which is left when one set of fibres is removed from w*
underlying set.
Directions.—The joints and ligaments of the dorso-lumbar pa*
of the spinal column and of the ribs must now be dissecte
The ligaments of the lumbar region will be exposed by careful
removing from the surface of the bones the remains of muscles
and other textures already examined. The whole of the dorsa
region need not be dissected in order to expose the ligaments, but
will suffice to take a segment containing four or five vertebrae with the
costal articulations intact. The articulations of the costal cartilages *
the sternum are to be examined on the part of the thorax removed 1
the display of the triangularis sterni muscle.
ARTICULATIONS OF THE RIBS.
Each rib is articulated to the spinal column at two points, vl2''
by its head, and by its tubercle. The head is received into a dp"
like cavity formed by two adjacent vertebral bodies and the dis
that unites them. This is the costo-central joint. The tubercle articu'
lates with the flat facet on the transverse process belonging to th
posterior of the vertebrae to which the head is articulated. This is t"1
costo-transverse joint.
Oosto-central Joint. This possesses two ligaments—the costo
vertebral and interarticular, and two synovial sacs.
Fig. 13.
two costovertebral, and two intervertebral joints, viewed from below.
1. Attachment of costo-vertebral (stellate) ligament to intervertebral disc ; 2. and 3. Attachrfl^ e
of the same ligament to the anterior and posterior vertebral bodies ; 4. Posterior costo-traiis
ligament ; 5. Intervertebral disc, covered by 6. the inferior common ligament.
TtS
The Costo-vertebral or Stellate Ligament is placed beneath the joint,
fibres radiate from the rib just below its articular head, and beco111
attached to the body of the vertebra in front, to the body of *
vertebra behind, and to the intermediate disc.
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DISSECTION OF THE BACK AND THORAX.                                133
h a* erar^eu^ar Ligament is fixed to the groove dividing the articular
th ° *^e r^° mto *wo facets. It passes inwards across the floor of
Pmal canal, being united to the upper edge of the intervertebral
g ' an°- °n the middle line it becomes continuous with the corre-
It \ S ngament of the opposite rib. It is not present in the 1st rib.
ould be displayed by disarticulating the costo-transverse joints of
r              vertebra in the segment, and then removing the arch. On
hot Vm^ t^le suPeri°r common ligament, it will be found in the interval
Ween the two vertebral bodies.
jnovial Sacs.—There is one sac on each side of the interarticular
eat. There is only one sac for the first costo-ccntral joint.
0st°-transverse Joint. This is maintained by two ligaments—an
Sv U°r an<* a Posterior costo-transverse ligament, and it possesses a
Jovial sac.
Fig. 14.
°sto-vertebral, and two intervertebral Joints, viewed from above. The Laminae
T»,
of the Vertebra have been removed.
'% 3. Sun -ior costo-transverse ligament; 2. Anterior (interosseous) costo-transverse ligament
P<*ior common ligament.
Th
fibrine Posterior Costo-transverse Ligament is composed of a band of
es stretching across the joint behind, and fixed by its extremities to
0 and transverse process.
e Anterior (Interosseous) Costo-transverse Ligament stretches between
th antero-inferior aspect of the transverse process and the neck of
' It is partly concealed by the transverse process, and is best
When viewed from above and in front.
tra yn°vial &c.—This will be exposed by removing the posterior costo-
s a*1SVerse ligament. In the last two or three ribs there is no separate
cent^?1 Sa° f°r the costo-transverse joint; but the posterior costo-
a» sac is extended over it, the two articular surfaces being in
ese ril« continuous.
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134
THE ANATOMY OF THE HORSE.
Chondro-Costal Joint. The inferior extremity of the rib is slight
excavated, and receives the extremity of the costal cartilage. ™
periosteum passes from the rib to the cartilage, and serves to consolidate
the union.
tal
Chondro-Sternal Joint. This is the joint by which the
COS'
cartilage of each of the first eight ribs is articulated to the sternum-
Peripheral fibres envelop the joint and form a capsular liganie^ ■
Above and below the joint the capsule is somewhat thickened, forniiQ8
the superior and inferior costo-sternal ligaments.
Synovial Sac.—The joint possesses a synovial membrane. "^
cartilages of the first pair of ribs meet in a common joint on the middl
line, and there is a single synovial sac common to these chondro-sterna
articulations, and to the facet between the two cartilages.
Union op the Costal Cartilages to one another. The cartilag
of the first asternal rib (9th) is firmly bound to the preceding cart1'
lage by short fibrous bands. It is further bound to the lower face
of the xiphoid cartilage by a small band—the cliondro-xiphoid ligam^nt"
From the tip of each succeeding cartilage, a yellow elastic band is carrie
to the posterior edge of the cartilage in front of it.
Movements of the Eibs. Each rib with its cartilage moves around 8*
imaginary axis joining the head of the rib and the sternal end °
the cartilage. In inspiration the rib moves forwards and outward
round this axis, so as to bring the middle portion of the rib towards the
position occupied by the preceding rib at the end of expiration. T»i&
movement lengthens the line joining the mid point of each rib to w-
corresponding point on the opposite rib, and thus increases the capa01"
of the chest by increasing its transverse diameter. During expiratio1
the rib falls into its original position by moving in the opposite direction-
In these movements the head of the rib and the extremity of the costa
cartilage rotate slightly in their cavities, but without change of place-
The tubercle of the rib glides on the facet of the transverse procesSi
moving in a circle whose centre is the costo-central joint.
The Sternum. There are no joints in the sternum of the horse,I!
which the osseous segments are simply united by persisting portions
the original cartilaginous mass. In this connection, however, there m^
be noticed the two suprasternal fibrous cords which pass, one at eac
side of the thoracic surface of the sternum, internal to the mammar*
vessels.
INTER-VERTEBRAL JOINTS AND LIGAMENTS.
In the dorsal and lumbar regions adjacent vertebrae are connect13
(1) by an amphiarthrodial joint between their bodies, and (^) ^
synovial joints between their articular processes. These same joints 81
formed between the last lumbar vertebra and the sacrum; and,
addition, there is a synovial joint between the last lumbar transvei
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DISSECTION OP THE BACK ASD THORAX.                            135
cess and the base of the sacrum. Inter-transverse joints are also
Vel°ped between the 4th and 5th, and 5th and 6th lumbar transverse
., cesses. The ligaments may be classified into :—1. Those connecting
Processes and neural arches of adjacent bones. 2. Those connecting
'Ijacent vertebral bodies.
igaments of the Processes and Neural Arches :—
e Supraspinous Ligament is a strong longitudinal band, or cord,
ndmg along the tips of the spinous processes. It is continued back-
s on the sacral spines; and in the anterior part of the dorsal region
exture changes from white fibrous to yellow elastic tissue, andlis oon-
„ . forwards as the funicular portion of the ligamentum nucha;. It
only tends to maintain the union of the vertebra), but also affords a
t of origin to muscles of the back and loins.
tte Interspinous Ligaments occupy the interspaces of the spinous
, Cesses. In each space the ligament consists of a right and a left layer
. se fibres have a downward and backward direction. This oblique
ction of the fibres favours the separation of the spines during
G
apsuktr Ligaments of the Articular Processes.—These complete the
' nrodial joint formed between the articular processes of adjacent
ebree, and support the synovial sac of the joint. One of the
»'merits should be slit open to display the synovial membrane lining
18 inner surface.
Th r
th 6 9amenta subflava, or Ligaments of the Arches.—These pass between
, edges of adjacent neural arches. They are best seen by sawing
a ,1Zouta% through the pedicles of two vertebra;, close to the body,
ien pulling the arches apart while they are viewed from below.
apsular Ligaments of the Transverse Processes.—These surround the
7* developed between the transverse processes of the 4th and 5th,
of tk an(^ ®*n mmDar transverse processes, and between the last
ioi f6Se Processes and the base of the sacrum. On removing them, the
ho .           ^e f°un<l to possess a synovial membrane. In old subjects,
'er, these joints are generally obliterated by anchylosis.
^igajients of the Bodies :~
low C fer*or Common Ligament is a thin stratum of fibres covering the
tin 'r!8*6 °f t^ie vertebral bodies and the intervertebral discs. It is con-
li°'a kaekwards beneath the sacrum, but it is not traceable as a distinct
ft^ ment farther forwards than the 6th dorsal vertebra,
and S Superior Common Ligament lies on the floor of the spinal canal,
lib T*St b<3 exPosed by the removal of the neural arches. It is a
arti l         8tructure adherent to the vertebra] bodies, and to the inter-
diSo° ligamcnt of tlie ribs or to the upper edge of the intervertebral
W The edg'es of the ligament are scalloped, the ligament being
6St Wnere it passes over the intervertebral discs, and narrowest at
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136                                 THE ANATOMY OP THE HORSE.
the middle of the vertebral bodies. It is continued into the sacral an
coccygeal regions.
The Intervertebral Substance.—Between every two adjacent vertebJ*
bodies there is interposed a disc of fibro-cartilage. This will be ueS
seen on making a vertical mesial section of two centra. The dis° '
thinner in the back than in the loins or neck. The disc between the
last lumbar body and the sacrum is especially thick. In the dorsa
region they concur in forming the cavity for the head of a rib. 1ne
disc is not of uniform texture throughout. The peripheral part of eacn
is composed of alternating layers of fibrous tissue and fibro-cartilage
In each layer the fibres pass in an oblique direction between the two
bones, and in successive layers the fibres are alternately oblique ffl
opposite directions. The central portion of the disc is pulpy, soft, a11
elastic; and is interesting as being a persistent portion of the foet8*
chorda dorsalis. The peripheral part of the disc constitutes an extremely
resistant bond of union between the two vertebra?, while the centra1
pulpy portion permits rotation of the one bone on the other.
Movements of the dorso-lumbar part of the spinal column. These are
flexion, extension, lateral inclination, and rotation. Flexion and extension-
are opposite movements taking place in a vertical plane. In flexion tne
downward concavity of the column is increased, in extension it '
diminished. These movements are much more restricted here than B»
the neck, owing to the thinness of the intervertebral discs and the large
size of the spinous processes. They have a greater range in the lo1IlS
than in the back. Lateral bending is also much less free than in tne
neck, being impeded by the thinness of the intervertebral substance>
and by the ribs and lumbar transverse processes. Its greatest range ot
movement is in the anterior part of the lumbar region. Rotation is tne
twisting or turning of a vertebra round a longitudinal axis passing
through its body. It is not permitted in the lumbar region, owing *°
the form of the articular processes; and even in the back, it is scarce!/
appreciable.
THE SPINAL CORD.
Directions.—To expose the spinal cord of the horse in the whole oflt&
extent is a tedious and difficult operation. Moreover, where the dissec"
tion of the parts surrounding the vertebral column is apportioned
between the dissectors of the neck, thorax, abdomen, and j)elvis, it '
quite impossible, without unduly interfering with what is otherwise the
most convenient course of dissection, to expose at once the entire cord'
This, however, is not a matter of much importance, since, in all ***
main features of its structure, the spinal cord of the horse is idcntica
with that of any other mammal. The student is therefore advised to
study the cord of a dog or a cat, which may be exposed without din1"
-ocr page 205-
DISSECTION OF THE BACK AND THORAX.                            137
J- One of these animals having been secured (and preferably a dog),
"Quid be fastened to a table in the prone position, and a mesial inci-
through the skin and muscles, down to the vertebra, should be made
°m the occiput to the root of the tail. With the knife the muscles
to be reflected so as to expose the vertebrae as far as the junction of
arch with the body. The spinal canal is then to be opened by
t, 0Vlng the arches with a chisel and mallet, or with bone-forceps. In
dorsal region each arch must be disarticulated from its connection
1 the ribs. The spinal cord enclosed within its membranes will now
xPosed, and between the outer membrane and the bones are some
'ei"» and a quantity of fat.
Membranes, or Meninges, of the Spinal Cord.
■          Dura Matee. This is the most external of the membranes. It
e Protective envelope of the cord, and has the form of tubular mem-
' e °^ fiuroris connective-tissue, extending from the foramen magnum,
th            ls continuous with the corresponding envelope of the brain, to
posterior end of the spinal canal in the coccygeal region. It does
j lorm a tight-fitting covering to the cord, but invests it somewhat
j. v • Its outer surface, it is to be observed, is smooth, and does not
the vertebra, which have the ordinary periosteal covering. It is
li e°ted by some slender fibrous processes to the superior common
b uient. The capacity of the tube varies with the thickness of the
> being greater at the atlas, lower part of the neck, and lumbar
, s n than at the intermediate points. The spinal cord does not extend
jf° . the middle of the sacrum, but the dura mater is prolonged
Me
ches beyond that as an impervious, tapering process. On each
s>de
**« the:
ura mater is perforated by the roots of the spinal nerves, and
-hese it sends offsets as far as the intervertebral foramina.
Sections.—A small piece of the dura mater should be pinched up
With
it x. °,rceP8 ana" snipped through. Beginning at the slit thus formed,
a s , . ** he laid open backwards and forwards along the middle line.
ls is being done, the membrane should be pinched up, so as to
!!eilt mJury to the cord,
the A„.„._____ ■ ,,
ae Arachnoid is the second of the membranes of the cord. It is
tu • • m°le delicate than the dura mater, and in disposition and struc-
en l iS c°mparable to a serous membrane. Like such membranes, it
rn, ' es a cavity, or sac, and consists of a parietal and a visceral portion,
the 1 ^ 1S ^nown as the arachnoid cavity, or stib-dural space, receiving
div' .attei' ^esignation from its relation to the dura mater. The parietal
tj1 .Ion of the membrane is represented by a layer of endothelium lining
in* mner SUrface of the dura mater, to which it gives a smooth and glisten-
ed ,a^Pect' but from which it is not separable by dissection. The vis-
bra*         8ion "ivests the cord and pia mater as a thin transparent mem-
Ue> but it does so loosely, leaving a space between it and the outer
-ocr page 206-
138                                     THE ANATOMY OF THE HORSE.
surface'of the pia mater. This, which is the sub-arachnoid space, con
tains a variable amount of an alkaline fluid—the sub-arachnoid fluifl>
which acts as a water-bed to the cord. As the roots of the spinal nerve
extend outwards, they take with then1
a covering from the visceral arachnoid»
and where they pierce the dura m»ter>
this covering becomes continuous wit*1
the parietal layer.
The Pia Mater is the vascular mem-
brane of the cord. It consists of areolar
connective-tissue in which the vessel
subdivide before entering the cord. -1
invests the cord closely, and is intimate!}
connected to it; sending a considerable
process into the inferior median fissui'e>
and numerous other slender filament
which penetrate the substance of t^6
cord. On each side it is connected t
the inner surface of the dura mater "J
a series of pointed processes constitutive
the ligamentum denticulatum. Each °
these processes of pia mater passes out-
Fig. 15
wards from the side of the cord, and)
View of the Membranes of the Spinal carrying the arachnoid with it, become
oed ( is).                  attached to the dura mater, midway "e~
". Dnra mater cut open and reflected •
tween the points of perforation of th
and the inferior nerve-roots-
a*
6. Small part of the translucent arach-
noid, left; h. Pia mater closely investing
the spinal cord ; c. Ligamentum denticu-
latum on the side of the cord, shown by
Behind the point in the sacral region
which the spinal cord stops, the P1'
S'oTroot™0*8 °l the nerTes' mater is prolonged as an attenuated
thread—the filum terminate—which l
enclosed by, and blends with, the tapering end of the dura mater.
Directions.—Before the removal of the cord the student should obsei'v
its varying thickness at different points, and the disposition of the spma
nerves within the spinal canal.
c
ith
The spinal cord begins at the foramen magnum by continuity ^
the medulla oblongata, and it is here of considerable thickness. TraC
ing it backwards, it is seen to become thicker behind the middle °
the cervical region, forming the cervical enlargement, which extends a
far as the 2nd dorsal vertebra. It is from this enlargement that tn
nerves which supply the fore limb are given off. Beyond the ^n
dorsal vertebra the cord contracts slightly, so as to become about tn
middle of the back smaller even than in its initial portion. Preserving
this diminished thickness throughout the dorsal region, it again expand'
-ocr page 207-
139
DISSECTION OF THE BACK AND THOEAX.
111 the lumbar region, forming a second swelling—the lumbar enlarge-
%ew«, from which the nerves for the supply of the hind limb are de-
tached. Beyond the lumbar enlargement the cord rapidly becomes
reduced in volume, and tapers to a point about the 2nd sacral seg-
ment. This tapering extremity of the cord—the conus meduUaris—is
Prolonged backwards by the filum terminale, into which its nervous
strUcture is continued for a little distance.
The Spinal Nerves of the horse number forty-two or forty-three pairs,
and their number in the different regions of the vertebral column is
exPressed in the following formula:—
The 1st cervical nerve leaves the canal by the antero-internal foramen
of the atlas, the 2nd by the foramen in the front of the arch of
*he axis, and the others in succession pass out by the intervertebral
foramina.
*» the other regions the nerves are numbered according to the
^ertebrse behind which they emerge; thus, the 1st dorsal nerve emerges
by the intervertebral foramen behind the 1st dorsal vertebra, and so on
Mth the others.
In the cervical region the nerves pass nearly directly outwards from
the cord to their points of exit from the canal. In the dorsal region,
however, it will be observed that each nerve is slightly inclined back-
wards from the side of the cord to the foramen by which it emerges. In
the lumbar region this backward inclination of the nerves becomes
_______                         Pig, 16.
Portion of Spinal Cord with the Roots ok the Nerves (Quaiii).
i- int.
Ultp ■        UULSi ™« hOreS Ot WHICH pass HUO Liie gnugui
perior primary branch ; 9. Inferior primary branch.
augmented, and it continues to increase in the same way in each nerve
ot the sacral and coccygeal regions. The sacral nerves thus have their
V0°ts detached from the lumbar part of the cord, while the coccygeal
llerve8 are given off by the terminal part of the cord, which, as already
-ocr page 208-
140
THE ANATOMY OP THE HORSE.
stated, does not extend beyond the middle of the sacrum. These lftS
nerves have therefore a length of several inches within the spinal canal,
and as they pass back together, each to reach its aperture of exit, the)
have an arrangement which resembles the hairs of a horse's tail, and '=
therefore termed the ccwda equina.
Boots of the Nerves. Each spinal nerve has two roots connecting
it with the spinal cord—a superior and an inferior. The superl°r>
sensory, or ganglionic root consists of filaments which arise from aloBe
the supero-lateral fissure of the cord. These filaments perforate the
dura mater, and converge towards the intervertebral foramen, wher
they form a cord on which there is superposed a reddish oval
ganglion.
Immediately beyond the ganglion the cord mixes its fibres with the
inferior root.
The inferior, motor, or aganglionic root consists of fibres detached
from the cord along its infero-lateral fissure. These, which are fe*61
and smaller than those of the superior root, perforate the dura mate1
by openings distinct from those for the superior root; and, converging
towards the intervertebral foramen, they join the superior root immed1'
ately external to the point at which the ganglion is placed on it. Tne
fibres of the inferior root, thus, have no connection with the gangh011'
Where the superior and inferior roots meet in the intervertebral foramen,
they mix their fibres and form a short common cord, which almos
immediately divides into two—the superior and the inferior prvmOrs
branch; and each of these contains fibres from both roots. Botn
branches emerge by an intervertebral foramen, and, roughly speaking'
the series of superior primary branches supply the skin and muscle
above their points of emergence, while the inferior primary branches are
distributed to the skin and muscles below their points of emergence,
including the limbs. From the common trunk formed by the union °
the two roots, a filament re-enters the spinal canal to be distributed *°
the bones and vessels.
In the region of the neck the spinal accessory nerve (page 255) passe^.
along each side of the cord, between the superior and inferior roots °
the spinal nerves. It is formed by rootlets that spring out of the si<*
of the cord.
The Vessels of the Spinal Cord.
The Middle Spinal Artery begins beneath the cord, in the ring °
the atlas. It is here formed on the mesial plane by the fusion of rig11
and left branches, each of which is the posterior branch forroe<J
by the bifurcation of the cerebro-spiual artery. The middle spin*
artery passes backwards beneath the inferior median fissure of the cord.
Its branches are distributed to the cord and its membranes. As it passe
backwards giving off its branches, it is reinforced by other arte*16*
entering at the intervertebral foramina. Thus, at each intervertebia
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141
DISSECTION OF THE BACK AND THORAX.
arflen in t\l0 necfe a brajyjk 0f the vertebral artery enters the spinal
1 al- In the back similar branches enter from the dorso-spinal division
he intercostal arteries, in the loins the branches emanate from the
bar arteries, and in the sacral region from the lateral sacral artery.
,, rulei the branches entering by adjacent foramina anastomose, and
u give off branches to the cord and the vertebral bodies.
ne Veins op the Spinal Cord are tortuous, and form on its surface
P exus from which the blood passes into two large veins that lie one at
side of the superior common ligament. These receive also veins
ui the vertebral bodies, and they are drained by vessels that issue by
intervertebral foramina to join the vertebral, intercostal, lumbar, or
lateral sacral veins.
Sections.—For the examination of the structure of the spinal cord,
a i
an
A
w mches of it with the roots of the nerves intact should be procured,
*ept in spirit or some other hardening fluid for at least a week.
Portion from the spinal cord of any of the domestic animals will serve
e Purpose :
lerred.                                                .
tv, Uctuh:e of the Spinal Cord. The meninges having been removed,
student will note the following points regarding the surface of the
cord ■ T-t
.. •" it approaches the
yundricai in f
rf% flatteneMow. i
is
e and
traversed in
fe e longitudinal direction
I three fissures, and a
is sometimes de-
Sci'ibed Ti,            •          j
u- J-tie superior med-
■ J^sure is a narrow
^al extending into the
J along the middle line
o lts upper face. It is
wUpied by neur°glia- The
aynor median fissure is an
^c Ual cleft penetrating the
°rd al°ug the middle line
1 tfs lower
°CcuPied by
face. It
is
of
Fig. 17.
Transverse Section of Spinal Cord or Calf (Klein).
1. Superior median fissure ; 2. Central canal, in grey
(superior) commissure ; 3. Superior horn of grey mattei , i.
Inferior horn of grey matter; 5. Process of pa matei in
inferior median fissure; 6. White (inferior; commissure,
7. Inferior column of white matter ; 8. Inferior neiye loots
9. Lateral column of white matter; 10. Pia mater 11.
Superior column of white matter ; 12. Superior nene roots.
£.mater- The
cess
supero-
a^ fissure
is a faint
surf.
ace
,            depression extend-
al^ on the side of the cord,
_g the line of emergence
he superior roots of the spinal nerves. The infero-lateral fissure has
-ocr page 210-
142                                 THE ANATOMY OF THE HORSE.
no actual existence, but is sometimes described as extending along "*
line of emergence of the inferior roots.
These fissures will be better seen in a transverse section of the corn-
This should be made with a sharp scalpel, so as to leave a clean-cu
surface. On examining this surface, the superior median fissure will v
seen to extend inwards to near the centre of the cord, while the infen0'
median fissure, which is wider but not so deep, also extends towards
the centre of the cord. The superior and inferior median fissures do
not quite meet, being separated by a bridge of tissue connecting «B»
right and left halves of the cord. This bridge of tissue is made up °
the grey and white commissures of the cord. The grey commissure
stretches
across the bottom of the superior median fissure, and in its centre fchere
will be seen a dot-like mark, which is the section of the central canal ol
the spinal cord. This canal extends throughout the whole length of t'ie
spinal cord; and where the cord joins the brain, the canal is continue'
into the medulla oblongata, in which it opens into the 4th ventricle-
The white commissure forms a thinner stratum than the preceding
beneath which it stretches at the top of the inferior median fissure.
It will be observed that in each half of the cord there are two
kinds
of nerve tissue, distinguished by a difference in colour.
1.   There is the grey matter, which lies in the interior, and has a
crescentic form. The convex side of each crescent is turned inwards,
and the right and left crescents are connected by the grey commissar*
The extremities of the crescent are termed its horns. The superior ho"'11
is acute, and is prolonged to the supero-lateral fissure by a single
bundle of fibres belonging to a superior nerve-root. The inferior hor?1
is rounded, and lies some distance beneath the surface of the cord-
From it several bundles of fibres pass to form an inferior nerve-roo*-
The grey matter of the cord contains nerve cells, medullated and non'
medullated nerve fibres, and delicate nerve fibrilla;. The nerve cell"
are mostly of the multipolar variety, and are most numerous in t0e
inferior horn. The connective-tissue of the cord, both here and in the
white matter, is a delicate substance termed neuroglia.
2.   The white matter in each half of the cord surrounds the crescent
and it is divided into three columns by the crescent and the nei've
bundles passing from the horns. The superior column lies between the
superior median fissure and the upper half of the crescent. The infei'101
column is included between the inferior median fissure and the lower ban
of the crescent. The lateral column lies in the concavity of the crescent,
its limits being marked at the surface of the cord by the super0"
lateral fissure and the line of emergence of the inferior nerve-roots-
The white matter of the cord is composed, besides neuroglia, of medui'
lated nerve fibres having for the most part a longitudinal direction.
{For the muscles of this chapter, see the table at page 336.)
-ocr page 211-
CHAPTER IV.
DISSECTION OF THE HEAD AND NECK.
THE UNDER PART OP THE NECK.
8 the first stage in the examination of this region, the student should
18se°t the structures placed below the cervical vertebrae—in other words,
he under part of the neck.
Surface-marking.—A well-marked groove extends in the longitudinal
c Section on the side of this region, beginning at the upper part of the
'ec*> and terminating between the shoulder and the anterior part of the
Pe°toral region. It lodges the jugular vein, and is therefore termed the
ffitlar channel or furrow. In performing phlebotomy on this vein,
PIessure is made on the furrow with the fingers, in order to arrest the
ov'"nward current of blood, and thus distend and make prominent the
essel above the point of pressure. In the lower third of the furrow
tion that
lies in company with the carotid artery, and it is in this situa-
the latter vessel may be most conveniently exposed for ligature
°^ ^cision. The boundaries of the groove will be learnt after removal
0t the skin.
^ Potion.—-The dissection of this part of the neck should be completed
™«tte the dissector of the fore limb is engaged with the pectoral region,
e animal being placed on the middle line of its back, and the head
eing forcibly extended on the atlas in order to put on the stretch the
nicies and other structures to be dissected.
Directions.—An incision through the skin should be carried along the
iddle lin6j from the carjmform cartilage at the lower part of the neck
tfle centre of the intermaxillary space. From the latter point a
tUrVed incision should be carried outwards a little behind the angle of
e jaw, as far as the wing of the atlas. These, in conjunction with the
^cxsions made by the dissector of the pectoral region, will permit the
T i» to be reflected upwards as far as the middle of the side of the neck.
e cutaneous nerves and the cervical panniculus should then be
examined.
Cutaneous Nerves of the neck. Five stellate groups of nerves will
e seen perforating the mastoido-humeralis muscle. These are derived
°m the inferior primary branches of the cervical spinal nerves from the
-ocr page 212-
144
THE AN ATOM y OF THE H0HSE.
2nd to the 6th. The first of these appears behind the wing of the
atlas; and, besides twigs to the upper part of the neck, it sends in*0
the intermaxillary space a branch which may be traced to near the
symphysis, and auricular branches which will subsequently be followed
to the skin of the ear. Some branches from the lowest group turn down-
wards and backwards over the mastoido-humeralis in front of the shoulder,
and spread over the anterior part of the pectoral region (Plate 1). T'ie
branches of the other groups are disposed upwards, downwar ds, and later-
ally, to supply the skin of the neck.
Cervical Panniculus (Platymia myoides of man). This is the repre-
sentative in the neck of the muscle which is much more strong"?
developed in connection with the skin over the trunk and shoulder-
It may be said to take origin at the lower part of the neck, where its
fibres are fixed to the cariniform cartilage (Plate 27). At this point *■
is a band of considerable thickness; but as it passes up the neck,jt
widens and becomes thinner. At the upper part of the neck its fibres
do not form a complete layer, but are scattered in an aponeurosis which
prolongs the muscle into the intermaxillary sj>ace and over the face-
Along the middle line it is joined by means of a fibrous raphe to the
muscle of the opposite side. The outer edge of the muscle is continued
by an aponeurosis over the mastoido-humeralis, splenius, and trapez'uS
muscles. In the lower half of the neck the muscle is intimately
adherent to the inferior edge of the mastoido-humeralis, and a careful
dissection is necessary to separate them. It covers the jugular furrow,
and the sterno-maxillaris, sterno-thyro-hyoideus, and subscapulo-hyoideus
muscles. It is supplied by the cervical branch of the 7th cranial nerve,
which should be found entering it at the upper part of the jugul*1
furrow, and running on the deep face of the muscle or in its substance
where it covers the furrow.
Action.—The cervical panniculus, unlike the panniculus of the trunk)
is but slightly adherent to the skin, which, therefore, it can twitch only
slightly. Its principal action seems to be to brace the muscles over
which it is spread, and by its adhesion to the mastoido-humeralis jt
may aid in depressing the neck.
Directions.—Beginning at the middle line of the neck, the dissector
should carefully remove the foregoing muscle. This will expose the
jugular furrow lodging the jugular vein. After that vessel has been
examined, a little dissection will serve to separate the muscles lil
relation to the trachea.
The Jugular Vein (Plate 27) is the large vessel which drains aw»y
the blood from the head and the upper part of the neck. It is formed
by the junction of the superficial temporal and internal maxillary veins>
which unite at the deep face of the parotid gland, below and behind the
temporo-maxillary articulation. It passes outwards through the parotid,
-ocr page 213-
145
DISSECTION OP THE HEAD AND NECK.
then lies in a groove on the surface of the gland; but this part of
course is not to be examined at present. At the lower extremity of
it + ?aro*'d ^ is joined by a large branch—the submaxillary vein; and
e en passes into the jugular furrow, in which it descends to the
, ailce to the chest. The upper boundary of the furrow, it will now
served, is formed by the mastoido-humeralis, and the lower by the
, Uo'^axillaris. In the upper half of this groove the vein rests on the
capulo-hyoideus muscle, which there separates the vessel from the
tr V artery' Dut in tne lower half the vein rests on the side of the
o. ea' and is in direct contact with the carotid, which lies above and
rij • internal to it. The jugular of the left side differs from the
*e m being related, in the lower part of the groove, to the oesophagus
:           as *^e trachea. At the entrance to the chest the right and left
o/ ! ars unite with one another and with the axillary veins, thus forming
nitial portion of the anterior vena cava,
fvoi Jugular receives, in the part of its course now exposed, the
°^g branches:-
•   J-he Submaxillary or Facial vein, which joins the jugular at an
angle in which lies the inferior extremity of the parotid gland.
] ' "he Thyroid vein, bringing blood from the thyroid body and
•  Innominate cutaneous, muscular, oesophageal, and tracheal branches,
e disposition is not constant.
J-he Cephalic vein, which enters the jugular near its termination.
juguj Slngle jugular of the horse is generally said to be the representative of the external
This T1K°f.Inan > tne internal jugular, under that view, being undeveloped in the soliped.
rnari r belleve to be a mistake, and for the following reasons. The external jugular of
Vejjj - s ou the surface of the platysma (panniculus), and never beneath it as does the
ahd s >e. orse; moreover, it is a vessel of very variable volume, being frequently small,
mau ,0Inetimes absent. On the other hand, the cervical part of the internal jugular of
VeSsei . a ^nation exactly corresponding to that of the horse's vein, save that the latter
horSe jS £enei'ally superficially placed to the subscapulo-hyoid (omo-hyoid); and in the
')aily -Kn+v^6 Seen tne 3ugular> otherwise normal, pass under that muscle, keeping com-
" the carotid artery for the whole of its course.]
inn e Stebn°-maxillams (Plate 27). This muscle corresponds to the
forr r P°rtion of the sterno-mastoid of man. It arises from the carini-
an , Cartilage of the sternum, and is inserted by a flat tendon into the
lies \ °f the inferior maxilla. In the lower half of the neck the muscle
In ., .elow the trachea, and covers the sterno-thyro-hyoideus muscle.
mjd,18 Position the right and left muscles are in contact, but about the
f0 e of the neck they diverge, and cross obliquely upwards and
ten*!]*dS °Yer the trachea and the subscapulo-hyoideus muscle. Its
The mal tendon is included between the parotid and submaxillary glands,
fiirr UPPer 6dge of the muscle forms the lower boundary of the jugular
bec0°W' In Hs lower Part the muscle is thiok and rounded' but **
" mes m°re slender and flattened as it is traced upwards.
L
-ocr page 214-
146                                THE ANATOMY OF THE HORSE.
Action.—To depress (flex) the head or give it a lateral inclnw
according as the right and left muscles act singly or in concert.             ,
The Sterno-thyro-hyoideus (Plates 27 and 28). This is a long ' . .
slender muscle, extending along the lower face of the trachea, and clo& -
applied along the middle line to its fellow of the opposite side. B *a*.
origin from the cariniform cartilage of the sternum. About the DO**
of the neck its muscular substance is interrupted by a short tend»1(
portion, rendering the muscle digastric. Above this central tendon
muscle divides into two portions. The outer or thyroid band Paft
obliquely outwards and forwards between the trachea and the Sl
scapulo-hyoideus muscle, and becomes inserted into the edge oi
thyroid cartilage of the larynx. The inner or hyoid band is coiitm1 ^
directJy forwards in company with the corresponding branch ot
opposite muscle, and becomes inserted into the body of the hyoid b011
Action —To depress the hyoid bone and larynx.                                 .
The Subscapulo-hyoideus (Omo-hyoid of man) (Plates 27 and * ''
This is a thin, ribbon-shaped muscle having a breadth of three or to
inches. It takes origin at the inner side of the scapula, from the fr8
covering the subscapularis muscle. It then passes downwards and
wards between the scalenus and rectu" capitus anticus major nulSC
inwardly; and the supraspinatus, anterior deep pectoral, and mastOJ"
humeralis muscles outwardly. Appearing at the lower edge of
last-named muscle, to which it adheres closely, it passes between
jugular vein and carotid artery; and crossing over the upper part ot"".
trachea in a direction obliquely forwards and downwards, it applies n '
at the outer edge of the hyoid band of the sterno-thyro-hyoideus, a
becomes inserted along with that muscle into the body of the
bone. In the lower part of the neck the ascending branch of
inferior cervical artery and the prescapular group of lymphatic g''al
are included between this muscle and the mastoido-humeralis.
Action.—To depress the hyoid bone.                                                     i
Nerves. At the upper part of the neck a branch from the sp1 '
accessory nerve enters the sterno-maxillaris, asid branches from the
spinal nerve enter the sterno-thyro-hyoid and subscapulo-hyoid muse
These, however, will be better dissected at a later stage.
Directions.—The jugular vein should now be ligatured at the
and lower ends of the jugular furrow, and the intermediate portio11
the vessel should be cut away. The excised portion of the vein sh°
be laid open to expose its valves. The part of the subscapulo-hyolCl »
which passes over the trachea may be cut out after the manneI .,j
Plate 28, and the sterno-maxillaris may be similarly treated. This
expose for examination the trachea, the oesophagus, the carotid al* j
the pneumogastric and sympathetic nerves, and the recurrent nei"sre-
Valves of Veins. Three or four valves are placed in the jugulai' 1
-ocr page 215-
DISSECTION OF THE HEAD AND NECK.                              147
'^ch valv •
of t,         e Is composed of two or three semilunar folds of the inner coat
rxien-f- Yein' ^e folds having a close resemblance to the semilunar seg-
Part 8f°f the aortic valve (Fig- ll> PaSe 129)- Each flaP with the adjacent
to\         'le w^ll of the vein forms a small pouch with its mouth directed
tiles* S tll<3 neart- When the blood tends to regurgitate, it distends
tQe i Pou°hes until the segments meet across the vessel and thus arrest
vai ackward current. In most veins throughout the body similar
Ju ,, are found; but they are most numerous in the veins of the limbs.
Th * Sma^ veins each valve may be composed of only a single flap.
Vpj u°wing veins have few or no valves :—the pulmonary system of
p0 ' le veins of the portal system, the hepatic veins, the anterior and
10r vense cava}, and the veins of the brain.
■u,|.. e 1rachea, or wind-pipe (Plate 28), begins beneath the altanto-axial
Ujjj. ation) where it is continuous with the larynx. It descends in the
W Plane of the neck, beneath the spinal column; and passing
f0l. n the first two ribs, it gains the thorax, where it bifurcates to
tj.„ ,         bronchi. In the neck the muscles of the region envelop the
its 6a' ail(^ are relate(i to it as follows :—The longus colli is related to
the •+ asPect> the sterno-thyro-hyoideus extends along its lower face,
the ru°"maxillaris crosses its direction obliquely upwards and forwards,
aud D8caPulo-hyoideus crosses it obliquely downwards and forwards,
sCai        ne lower part of the neck it contacts on each side with the
jllo. , *S' It- is also related to the oesophagus, the carotid artery, the
TVi Vem, and the pneumogastric, sympathetic, and recurrent nerves.
of t> 6 HyRoid Body or Gland (Plate 29) is related to the upper part
has ra°hea on each side, resting on its first four rings. The gland
sUl3 ,. l0Unded form, and a reddish-brown colour; and it is richly
]ar          Avith blood, which it receives from the thyroid and thyro-
c0ll ^ branches of the carotid artery. Sometimes a narrow isthmus
The, ? tlle right and left glands across the lower face of the trachea.
*a6 gland l
Wjm           nas an investing capsule of fibrous connective-tissue, continuous
stan ' eternal trabecular framework. Under the microscope the sub-
by a ,•          organ is seen to contain numerous spherical spaces, each lined
Th ^ *ayer °f epithelium, and filled by a viscid colloid material.
caQaie ^ophagus, or gullet (Plate 28), is a segment of the alimentary
Pha - tt begins above the larynx, where it is continuous with the
few . *■ It descends on the upper face of the trachea, and in the first
relat n.° es °f its course it lies in the middle plane of the neck, being
deviat ° tllG lon8'us coui muscle above. It soon, however, begins to
S&tW.8 t0 tlle left side, so that below the middle of the neck it lies
this r i°n.the uPPer Part of the left side of the wind-pipe. Maintaining
being6 atlonslliP, the two tubes enter the thorax in company, the gullet
truHiofr°10nged through that cavity to pass by the foramen sinis-
the diaphragm into the abdomen, where it terminates in the
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148                                     THE ANATOMY OF THE HORSE.
stomach. The gullet is related to the muscles of the left side ahe'
•                                                                                   t iddlS
enumerated as contacting with the trachea, the sterno-thyro-hyoi"
.               . A tbc
excepted. It is also related to the carotid artery, the jugular vein, aim l
pneumogastric, sympathetic, and recurrent nerves of the left side.
cervical part of the oesophagus has the external appearance of a v0i
tary muscle, for which it is often mistaken at first sight by the stude
The examination of its structure, as well as that of the trachea, nal
be postponed until the accompanying vessels and nerves have *
examined.                                                                                                   ,
The Common Carotid Artery (Plate 28). This is the vessel ***
conveys the blood to the head and upper part of the neck. It l,e8
on the under aspect of the trachea, at the entrance to the thorax, v;il
it results from the bifurcation of a short vessel termed the cep
ck &
trunk—a branch of the arteria innominata. It ascends in the ne
company with the trachea, and terminates above the cricoid cartilag^
of
the larynx by dividing into the external carotid, the internal car0
and the occipital artery. It thus crosses the trachea very oblilu '
being at first on its under surface, then on its lateral aspect, and fin*
above it. It is in contact with the scalenus, longus colli, reC .
capitis anticus major, and subscap ilo-hyoideus muscles, the *'
mentioned intervening between the artery and the jugular vein in ,
upper half of the neck. In the lower half of the neck the artery ' ,
vein are in direct contact, the carotid being above and slightly inte*
to the jugular. The common cord of the pneumogastric and sympat" j
nerves is on the upper side of the artery, and the inferior laryHo
(recurrent) nerve is below it. At the entrance to the thorax the V
pectoral group of lymphatic glands is in contact with the artery- ,g
left carotid differs from the right in being- related for a consider
part of its course to the oesophagus, which separates it from the tra°*
The collateral branches of the carotid are as follow's :—
1,   Innominate and slender muscular, oesophageal, and tracheal bran0 ,
2.   The Thyroid artery, which arises a few inches behind the th
steri01
b
the
aspect. Sometimes this artery is distributed mainly or entirely t0
neighbouring muscles.                                                                              j
i +pi"i
3. The Thyro-laryngeal artery.—This is the largest of its collat. g.
branches. It arises a little in front of the preceding vessel, and pil& .g
to the inner side of the thyroid body, it divides in front of i* . e
thyroid and laryngeal branches. The former turn back to enter
gland in front, while the latter pass to the larynx and pharynx.           ^
The terminal branches of the carotid are not to be foll°we
present.                                                                                                  ^y
The Pneumogastric and Sympathetic Nerves in the neck (Plate ^ J)a
The pneumogastric, vagus, or 10th cranial nerve has its origin
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DISSECTION OE THE HEAD AND NECK.                              149
le medulla oblongata. It leaves the cranium by the posterior part of
foramen lacerum, and inclining downwards and backwards on the
* . llral pouch, it meets the cervical cord of the sympathetic, with
Ca it becomes in nearly all cases closely united. The common cord
Slutmg from tne fusion 0f the two nerves descends in company with
carotid artery, lying on the upper side of that vessel. At the lower
, °f the neck the two nerves, in passing into the thorax, again
bec°aie separate.
he cervical cord of the sympathetic begins at the superior cervical
^ nb'lion, which rests on the guttural pouch. After a short course it
es, as just described, with the vagus.
,, ° branches are given off from either the vagus or the sympathetic in
rn, wnere they form a common cord.
}g 1»e Inferior Laryngeal (Recurrent) Nerve (Plate 28). This
jj* llranch of the vagus, given off within the thorax. The right nerve
CeS.lts origin in front of the heart, and is reflected round the dorso-
po ^ artei7- The left nerve is longer than the right, having its
tft of detachment at the base of the heart, where it is reflected round
an, r°ot °f the posterior aorta. The nerves pass forwards on the trachea,
«e i eat6r tne neck by passing between the first pair of ribs. In the
Pest" 6aCh nervo ascends below the carotid artery, the right nerve
Part 8 °n the trachea> but that of the left side being> for the Sreater
be f °f its courso> ou tne oesophagus. The nerves will subsequently
reci°llowed in their distribution to the larynx. In the neck each
^lrent nerve throws off branches to the trachea and oesophagus.
GlUrlrections.~\t this stage the dissector of the fore limb will be
Bwf1 With the dissection of the axilla, and the dissector of the neck
of /j d °°-operate with him in the examination of the mode of formation
8o * brachial plexus of nerves, and, thereafter, of the levator anguli
Wat U1UScle- For the brachial plexus turn to page 3, and for the
or anguli soapulse to page 8.
plaoR^PECTORAL Lymphatic Glands. This is a large group of glands
the h beneath and at the side of the 8'reat vessels at the entranoe t0
the !rhest- They are placed on the course of the lymphatic vessels of
^ead, neck, and fore limb.
^(n^'efi0ns-~~A- segment about six inches in length may now be cut
are J1*"3 trachea, and a similar segment from the oesophagus. These
be dissected to display the structure of the two tubes.
oartr CTt7RE 0F THE Trachea. This comprises (1) a framework of
layer          United b? (2) fibro-elastk membrane ; (3) an incomplete
a L °f non-striped muscular tissue ; (4) a submucous layer; and (5)
^cous lining
are t ? artila9^ of the trachea number between fifty and sixty, and
WW hyaline varietv. Although usually denominated the rings of
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150
THE ANATOMY OF THE HORSE.
the trachea, they do not form complete circles, but have rather
resemblance to the letter C with its ends overlapping. In consequeii
of this configuration of the rings, the trachea is not circular on sectio >
but flattened in the vertical direction; and the overlapping of
extremities of the cartilages takes place on the middle of the UpP
aspect of the tube. The breadth of the rings is not quite uniform, "
averages about half an inch. Here and there, however, two adjac*
rings may be more or less fused by the obliteration of the unitize
fibro-elastic membrane. In the thoracic portion of the tube
extremities of the rings do not meet, and the deficiency is there m*
up by a number of thin cartilaginous pieces of irregular size and snap
and somewhat imbricated in their arrangement. The rings are thick
and strongest in their central portion, and thinnest at their extremity ■
The Fibro-elastic Membrane.—This connects the adjacent edges ot %
cartilages, and at the upper wall of the tube it connects their overlap?1 "
extremities. Its extensibility and elasticity permit the length of l
trachea to be accommodated to the movements of the neck, and to
properties will be made very evident by alternately extending 9
relaxing a segment of the tube containing five or six rings.
The Trachealis Muscle.—This is a layer of non-striped muscular tis
having its fibres directed transversely. It does not extend all r°l .
the tube, but is confined to its upper part, where the fibres lie interia»
to the extremities of the rings or the fibro-elastic membrane,
fibres form a continuous band, being not only placed under each A v
but also in the interval between adjacent rings.                                      ,
The Submucous Goat is composed of areolar connective-tissue »
numerous elastic fibres longitudinally disposed. It also contains i»a ,
small compound racemose glands, whose mucous secretion is dischair
by ducts opening on the free surface of the mucous membrane.
The Mucous Membrane, which forms a complete internal lining
the tube, possesses a stratified epithelium, the surface layer of cells t>e
ciliated.
Structure of the (Esophagus. This comprises (1) a muscular o° '
arranged in two layers ; (2) a submucous coat; and (3) a mucous W" .
The Muscular Coat consists of (a) an outer layer of fibres ^oVc
tudinally disposed, and (6) a deeper layer in which the fibres
arranged as transverse or oblique rings. In the cervical part of the 6° ^
and in the thoracic part about as far as the heart, the muscular n
+hc*
are for the most part of the striped variety, and the tube has w ,
the external appearance of a voluntary muscle. About the centre
the thorax, however, the character of the fibres gradually changeS ^
the pale, non-striped variety of muscular tissue, and behind that p
the tube is therefore pale like the stomach or the intestines.
The Submucous Coat is composed of areolar connective-tissue con
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151
DISSECTION OF THE HEAD AND NECK.
ln8 the alveoli of mimerous mucous glands, whose ducts penetrate the
n«icous membrane. It forms a very loose bond of connection between
he muscular and mucous layers; and when the oesophagus is cut
a°i-oss, the mucous coat appears almost as if it lay independently
1r~ui the muscular layer.
The Mucous Membrane has a thick stratified epithelium ; and, except
r^Og the act of deglutition, its free surface is thrown into longitudinal
j° ds whieh meet with one another and obliterate the lumen of the tube.
^colour it is whitish, owing to its low vascularity and the thickness
lts epithelial covering.
THE UPPER PART OF THE NECK.
Position.—The animal should be suspended in imitation of the natural
^nding posture, in the manner described at page 8, for the dissection
le °uter scapular region.
directions,—The whole of the neck behind the atlas should be
guided of skin. The cutaneous nerves of the region should then be
^oticed, and the spinal accessory nerve should be found crossing obliquely
Okwards and upwards on the surface of the splenius muscle.
^Taneous Nerves. For the most part, the cutaneous nerves of this
egion are derived from the stellate groups already seen perforating the
b astoido-humeralis. These are derived from the inferior primary
bi'.aUClles of the cervical spinal nerves from the 2nd to the 6th. Other
J1 Miches, which are derived from the superior primary branches of the
d*me nerves, emerge near the middle line of the neck above, and are
uouted to the integument beneath the mane.
ihe Spinal Accessory (11th Cranial) Nerve (Plate 27). This
n'e derives its fibres from the medulla oblongata and the cervical
Pait of the spinal cord. It leaves the cranium by the foramen lacerum
vsls cranii, passes backwards on the guttural pouch, turns upwards
o-v
ai 7 tlU' edge of the win8 of thc atlas' and passes obliclliely backwards
"lcl upwards beneath the mastoido-humeralis muscle. Appearing at
I
cl.e uPPer edge of the last-named muscle, it is continued in the same
potion on the gurface of the Splenius, and disappears beneath the
W'!Cal traPezhis, in which and the dorsal trapezius it terminates.
to the nock is elevated, the trunk of the nerve is thrown into
«er?r°U8 short sinuosities, apparently to obviate stretching of the
e when the neck is depressed.
tta !***»— The cervical portions of the trapezius and rhomboideus
for i GS 8hould now De examined in co-operation with the dissector of the
renllmh; and, thereafter, the mastoido-humeralis is to be dissected.
,jn e Trapezils. See page 9.
le Rhomboideus. See page 10.                                                     ...
ihe ^astoido-Humeralis, or Levator Humeri (Plates 27 and 28).
-ocr page 220-
152                                 THE ANATOMY OF THE HORSE.
This is a long and powerful muscle, extending between the head and t»
shoulder, on the side of the spinal column. It takes origin from *
mastoid process and crest, from the wing of the atlas, and from *fl
transverse processes of the 2nd, 3rd, and 4th cervical vertebra). J-'1
tendon of origin from the mastoid process and crest, which is not to "
exposed at present, is thin and aponeurotic; that from the wing of in
atlas is common to the splenius and trachelo-mastoideus muscles; "W
the succeeding slips of origin are fleshy. The muscle passes over t
shoulder-joint, and becomes inserted into the outer lip of the nniscu
spiral groove. As already seen, the lower edge of the muscle forms t
upper boundary of the jugular channel, and at the lower part of *
neck it is closely united to the sternal band of the panniculus.
Action,—It is an extensor and inward-rotator of the shoulder-j0111
When the limb is fixed, it bends the neck laterally.
This muscle represents the greater part of the sterno-mastoid of in'
(the rest being represented by the sterno-maxillaris), combined with t
clavicular part of the deltoid, this fusion resulting from the absence
a clavicle.                                                                                                   ..
Directions.—If the mastoido-humeralis has not already been cut,
should be divided in front of the shoulder, and turned upwards (1**
28) to show the prescapular glands and a branch of the infejl
cervical artery. The stellate groups of cutaneous nerves may thereat1
be traced through the mastoido-humeralis to their source.
The Prescapular Lymphatic Glands. These are arranged in ,,
form of a chain between the mastoido-humeralis and subscapulo-h)
muscles at the lower part of the neck.                                                   p ,
The Inferior Cervical Artery is a branch of the axillary, aris1
at the first rib. It divides into a descending (Plate 1) ana
ascending branch, the latter being here seen between the mastoi
humeralis and subscapulo-hyoid muscles, to which and the an°
mentioned glands it is distributed.                                                        _ f
Cervical Spinal Nerves. There arc eight pairs of these, the 1 st issui B
from the spinal canal by the antero-internal foramen of the atlas,
2nd by the foramen (converted notch) at the anterior edge of the a*
of the axis, and the others in succession by the intervertebral foram11 '
They have all a common disposition in that each divides at its pom1'
exit into superior and inferior primary branches. Only the inf8"
primary branches present themselves now for consideration, and of t'1 .
the 1st is more conveniently taken at a later stage. The remainmS
behave as follows :—                                                                                 ,
The 2nd, 3rd, 4th, 5th, and 6th communicate, each with the pre° /■
ins and succeedine branches of the scries, and divide into three setb
branches, viz., (1) communicating branches to the middle cervical gang
(sec vertebral nerve, page 157); (2) muscular branches to the mast01
-ocr page 221-
1 >1<?
DISSECTION OF THE HEAD AND NECK.                               luu
humeralis, longus colli, scalenus, and rectus capitis anticus major
^Hsoles, and to the diaphragm (see phrenic nerve, page 6); (3) cutaneous
Ranches which pierce the mastoido-humeralis and are distributed as
*e stellate groups already seen. Besides these, the 6th nerve sends
branches to the levator anguli scapulas and rhomboideus muscles, and
lts Phrenic branch sends a twig to the brachial plexus.
The branches of the 7th and 8th nerves are expended in the brachial
Paxils after each has detached a communicating filament to the middle
cervical ganglion, that from the 7th joining the vertebral nerve, while
hat from the 8th passes to the ganglion independently.
Directions.—The dissector of the fore limb will now be in a position
to separate the limb from the trunk, which will permit the dissection of
*ae remainder of the neck. The levator anguli scapula;, as left by the
^sector of the fore limb, must now be entirely removed in order to
e*P°se the posterior part of the splenius. The mastoido-humeralis may
a.So he out away as far forwards as the vertebra dentata. The inser-
tions of the splenius, trachelo-mastoideus, and complexus muscles into
*he head are not to be exposed at present, as that would involve the
^sti-uction of the muscles of the ear and other structures not yet
dlssccted.
The Splenius (Plate 27). This is a flat, fleshy muscle of a
*riangular form, having its fibres directed downwards and forwards. It
^akes origin from the 2nd, 3rd, and 4th dorsal spines, and from the
tuilicular portion of the ligamentum nucha). Its origin from the dorsal
8P"ie8 is aponeurotic, and confounded with that of the anterior serratus
and complexus muscles. It is inserted into the mastoid crest, the
Wln8 of the atlas, and the transverse processes of the succeeding four
cervical vertebra;. The mastoid insertion is flat and aponeurotic, and
!8 united to the mastoid tendon of the trachelo-mastoideus. I fie
'fei'tion into the atlas is tendinous and riband-like, and is common to
the trachelo-mastoideus and mastoido-humeralis. The other insertions
ai'e fleshy.
4«W.—The right and left muscles acting together elevate the
JJd and neck ; acting singly, they incline the head and neck to the
Sl e of the acting muscle.                                                                     , ,
directions.—The origin of the splenius should be carefully detacneu,
a^d the muscle should be raised and turned downwards so as to expose
^ subjacent structures. Nerves from the superior primary branches
0t the cervical nerves, and branches from the superior cervical, doisc
and vertebral arteries, will be found entering its deep face, i
J^elo-rnastoideus and complexus muscles, n<TW exposed, should oe
Jjected, the branches of nerves and vessels found in connection witb
e
Th
being as far as possible preserved.                                           owi1p1
TaAOT™T,n.Mla™™™ This muscle consists of two paiauei
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154
THE ANATOMY OP THE HORSE.
fleshy portions extending along the spine, under cover of the splewu&i
and resting on the complexus. The fibres of the muscle arise l'}
successive slips from the transverse processes of the first two dorsa
vertebrae; and, in common with the complexus, from the articw™
processes of the last six cervical vertebrae. The upper division of the
muscle is inserted, by a flat tendon common to the splenitis, into th
mastoid crest; the lower division terminates in a riband-like tendoB)
common to the splenitis and mastoido-humeralis, and inserted into thc
wing of the atlas.
Action.—Acting singly, to bend the neck laterally; acting with
the opposite muscle, to extend the occipito-atlantal articulation (elevate
the head).
The Complexus. This is one of the most powerful muscles of the
neck. It covers the lamellar portion of the ligamentum nucha', whi<*
separates the right and left muscles. It arises from the 2nd, 3rd, and
4th dorsal spines, in common with the splenius; from the transversC
processes of the first six or seven dorsal vertebras; and from the articulai
processes of the cervical vertebrae with the exception of the first. FrOfl*
these diffei'ent points of origin the fibres converge towards the poll, where
they terminate in a tendon inserted into the occipital bone.
Action.—Both muscles will extend the occipito-atlantal joint (elevate
the head); the muscle of one side will, while elevating the head, tin11
it slightly to the same side.
Nerves. As already stated, each cervical nerve resolves itself into a
superior and an inferior primary branch. The superior primary brancheS
of the last six may now be found distributing nerves to the splenhlS>
trachclo-mastoideus, complexus, and semispinalis colli muscles; ana J*
the complexus be raised from the ligamentum nucha, other braucheS
will be found to ascend between the muscle and the ligament to be
distributed to the integument near the middle line.
• . 1
The muscles and other structures which lie above the cei'Vica*
vertebra receive their chief blood supply from three vessels, viz., t',e
occipital, dorsal, and superior cervical arteries. The first of these g'ive
branches to the neighbourhood of the poll, but it is not to be soug ht at
present.
The Dorsal Artery will be found distributing branches to the uppel
part of the neck, in front of the withers. The artery has its orig111
within the thorax, where, on the left side, it is a branch of the axilla1)
artery, and, on the right side, of the arteria innominata. It leaves th
chest by the upper part of the second intercostal space; and inclin111"
backwards and upwards, it divides on the longissimus dorsi into
number of branches distributed to the withers, and the neck in front o
that region. These will be found ascending between the splenius an
complexus muscles.
-ocr page 223-
155
DISSECTION OF THE HEAD AND NECK.
The Superior Cervical Artery, like the preceding, arises within the
chest, and from the same source. It leaves the thorax by the upper
Part of the first intercostal space ; and placing itself on the inner
^rface of the complexus, it ascends between that muscle and the hga-
naentum nucha;, as far as the 2nd or 3rd cervical vertebra, where its
terminal branches anastomose with those of the occipito-muscular and
cl°rsal arteries.
Veins. The dorsal and superior cervical arteries are accompanied
bv veins of the same names, which, after entering the chest, discharge
themselves into the anterior vena cava.
directions.—The complexus, splenitis, and trachelo-mastoideus muscles
may now be removed as far as the hinder end of the axis. This will
expose the semispinalis colli muscle and the ligamentum nuchas.
The Semispinalis Colli Muscle (Fig. 18) rests on the lammffiol
the cervical vertebra), and consists of five bundles. The most postenoi
of these bundles may be described as taking origin from the antenoi
articnlar process of the 7th cervical vertebra, and passing forwards
aad inwards to be inserted into the superior spine of the 6th vertebra
The most anterior bundle passes in the same way between the dra
Vertebra and the axis, while the intermediate bundles have corresponding
attachments.                                                                                               ,
Action.— The right and left muscles, acting in concert, will extenr
(elevate) the cervical part of the spinal column. The muscle of one side,
acting singly will rotate and incline the spinal column to the opposite side.
The Intertransversales OoLLi Muscles (Fig. 18). These form a
Set of six muscular bundles with strong tendinous intersections, ana
c°ver the sides of the cervical vertebra. There is one bundle for eacn
intervertebral articulation except the first. Each muscular bundle
J***ta of an upper and a lower slip; and it may be described as armng
fro»i the articular process of one vertebra, and passing forwards to Dc
ln^rted into the transverse process of the vertebra in front. 1M
mi^cles conceal the intervertebral foramina and the vertebral vessels ,
aud they are perforated by branches of these vessels, and by the superior
and inferior primary branches of the spinal nerves of the neck.
Action.—To bend the neck laterally.                                               _, .
The Rectus Capitis Anticus Major (Plate 28 and Fig. 18). *
*«*&> begins by a tapering point on the side of the vertebral column
■* the 5th cervical vertebra ; and passing forwards and inwards it gams
tlle inferior face of the atlas, in passing to the base of the «™u.
«^es from the transverse processes of the 5th, 4th, and 3rd ™tcDr^
the slip of origin from the first of these crossing the point
^alenus. Its insertion, which is not to be exposed at present, is into
the tubercular processes at the junction of the basilar process with
body of the sphenoid.
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156
THE ANATOMY OF THE HORSE.
Action.—The right and left muscles, acting together, flex the head.
When only one muscle acts, it inclines the head to the same side.
The Scalenus (Plate 3 and Fig. 18). This muscle is situated on the
side of the lower half of the neck. It arises from the transverse processes
Fig. 18.
LlGAMENTUM NuCII^i AND DEEP MUSCLES OF THE NECK (Chawrat').
1. Lamellar portion of the ligamentum nuchas ; 2. Funicular portion of the same ; 8. Semispinal*^
of the hack and loins ; 4. Semispinalis colli; 5. Rectus capitis posticus major ; 6. Rectus capi**8
posticus minor ; 7. Obliquus capitis inferior ; S. Oblitruus capitis superior ; 9. Intertransversales
colli; 10. Rectus capitis anticus major ; 11. External intercostals ; 12. tipper and lower divisions ol
the scalenus.
of the last four cervical vertebra?, In front of the 1st rib it is perforated
by the roots of the brachial plexus, which there divide it into an upper
and a lower portion. The first of these is much the smaller of the two,
and it is inserted into the outer surface of the 1st rib near its upper end.
The lower portion is inserted into the anterior border and outer surface
of the same rib, the lowest fibres being immediately above the smooth
impression left on the anterior border of the bone by the axillary vessels-
Action.—To pull forwards or fix the 1st rib, and thus to aid H*
inspiration. When the rib becomes the fixed point, the muscles will
flex the neck or incline it to the side, according as the right and left
muscles act in concert or singly.
The Longus Colli (Plate 28). This muscle clothes the inferior face
of the spinal column from the 6th dorsal vertebra to the atlas, the
right and left muscles being closely united along the middle line, while
at its outer edge each muscle is partially blended with the intortrans-
-ocr page 225-
DISSECTION OF THE HEAD AND NECK.                              157
ei'se muscles. The dorsal portion of the muscle is seen in the
^section of the thorax (Plates 22 and 25), where its fibres take origin
°m the bodies of the first six dorsal vertebras, and pass forwards to
rQiinate m a tendon inserted into the 6th cervical vertebra. In the
ck the fibres of the muscle take origin from the transverse processes,
. ea°h bundle passes with a forward and inward direction, to be
*erted into the body of a vertebra anterior to that from which it arises.
0 most anterior fasciculi terminate in a tendon inserted into the
tuWcle of the atlas.
Action.—To bend the neck downwards.
Erections.—The vertebral vessels and the accompanying nerve should
w be exposed by the careful removal of the intertransversales muscles,
^ntion being at the same time directed to the superior and inferior
i' irnary branches of the spinal nerves. These nerves emerge in
lana°n from the intervertebral foramina, but separately pierce the
^scles,
Ihe Vertebral Artery is a branch of the axillary artery, given off
°m that vessel before it leaves the thorax. It enters the neck by
1 assing forwards to the inner side of the 1st rib a little below its upper
°~ It then ascends along the side of the spinal column, passing
st beneath the transverse process of the 7th vertebra, and then in
ccession through the vertebral foramina of the other bones as far as
e axis. Between the last-mentioned bone and the atlas it joins
ectly the retrograde branch of the occipital artery, but this is not to
, exPosed at present. It throws off in its course (1) muscular and
w spinal branches. The former are very numerous and consist of an
" va*d, a downward, and an outward set. Many of the upward set
ss over the vertebrae, and anastomose with branches from the superior
vical artery. The spinal branches are detached from the inner side
tne artery; and entering the spinal canal by the intervertebral
lamina, they join the middle spinal artery in supplying the spinal cord
^d its coverings.
. _ ne Vertebral Vein accompanies the artery, and within the chest
Jjf tue anterior vena cava.
he Vertebral Nerve runs in close company with the vessels. It
^formed by the union of filaments from the inferior primary branches
' the cervical nerves from the 2nd to the 7th. In the thorax it joins
inferior cervical ganglion of the sympathetic nerve. It is thus
composite nerve made up of the afferent filaments sent by the before-
loned spinal nerves to the sympathetic cord.
J-he Ligamentum Nucile (Fig. 18). This is the largest ligament in
™ e body. It i8 piaced on the middle plane of the neck, above the
^rtebrse, and it consists of a right and a left division, each of which,
gam' comprises a funicular and a lamellar portion. The entire liga-
-ocr page 226-
158
THE ANATOMY OF THE HORSE.
ment, like most of the other ligaments of the neck, is composed ot
yellow elastic tissue.
The funicular portion has the form of a flattened cord united by rts
inner edge to the corresponding structure of the, opposite side. Postei-
iorly, behind the summit of the 3rd dorsal spine, this cord is continuous
with the supraspinous ligament of the back. Anteriorly the cord ^
inserted into a special tubercle on the occipital bone. Between these
points of attachments the cord extends with a slight upward concavttj
when the ligament is relaxed, and above it there is developed, in vary-
ing amount, a quantity of fatty-elastic tissue supporting the integument
from which the mane grows.
1
The lamellar portion is triangular in form, occupying the interval
between the funicular portion and the vertebral column. Its fibres
have a downward and forward direction, being fixed above to the fin*
eular portion or to the spines of the 2nd and 3rd dorsal vertebra?, an<J
below to the spines of the last six cervical vertebra?. The fibres are
stronger and more closely aggregated in proportion as they are anterior)
the lamella forming a complete septum in its anterior two-thirds, but
having the form of a network in its posterior third. The right and let*
lamella? are applied together on the mcsipl plane, their inner faces being
united by areolar connective-tissue.
The ligamentum nuchas assists in suspending the head ; and whew
the head has been depressed, it aids the muscles in elevating it again-
But for its presence, a large additional amount of muscular tisstie
would have been necessary in the neck. In man, in whom the head is
supported by the spinal column, the ligament is very rudimentary, and
has lost its elastic texture.
Directions.—The spinal column should now be disarticulated between
the 3rd and 4th cervical vertebra?; and the head should be laid aside
on a clean table, while the student proceeds to the dissection of the
remaining ligaments of the neck. It will suffice to dissect carefully the
ligaments of one intervertebral articulation,—say that between the 4th
and 5th bones.
The intervertebral joints of the neck posterior to the vertebra dental*
are constructed after a common plan, which is also that of the dorsa*
and lumbar regions Each vertebra is articulated to the preceding and
the succeeding bone (1) by an amphiarthrodial union of the bodies, and
(2) by diarthrodial joints between the articular processes.
The atlanto-axial and the occipito-atlantal joints, which are purely
diarthrodial articulations, will be dissected at a later stage.
LIGAMENTS AND ARTICULATIONS OF THE NECK POSTERIOR TO
THE DENTATA.
' The ligaments may be classified into (1) those connecting the pr0'
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159
DISSECTION OF THE HEAD AND NECK.
cesses and neural arches, and (2) those connecting the adjacent vertebral
bodies.
-Ligaments of the Processes and Neural Arches :—
The Ligamentum Nucha;.—This has already been dissected.
The Interspmom Ligaments.—These are composed of yellow elastic
tissue. Each consists of two narrow parallel bands stretching between
Jacent superior spinous processes.
Capsular Ligaments of the articular processes.
Ligamenta subjiava.—For these two series of ligaments, see page 135,
*We the corresponding ligaments of the back and loins are described.
[a the neck these ligaments differ from those of the other regions in
emg composed of yellow elastic tissue.
Ligaments of the Bodies : —
The Superior Common Ligament lies on the floor of the spinal canal,
a«d terminates in front at the axis. See page 135.
The Intervertebral Substance.—See page 136.
Movements of the cervical part of the spinal column. These are
■fetOK, extension, lateral inclination, rotation, and circumduction, the last
eiug a combination of the first three. In flexion the vertebra are
carried downwards in a vertical plane, and extension is the opposite
foment. Botation is the twisting, or turning, of a vertebra round a
ongitudinal axis passing through its body. In consequence of the
* llckness of the intervertebral substance, and the feeble development of
he transverse and spinous processes, all these movements have here a
|>'eater range than in the back or loins ; and within the cervical region
le greatest range of movement is permitted in the posterior joints.
THE EXTERNAL EAR (PIG. 19).
.The organ of hearing consists of three divisions : the external, the
''niddle, and the internal ear. Only the first of these will now be
plained. The middle and the internal ear, which are cavities within
the Petrous temporal bone, are described at page 267. The external ear
°0I»Prises the external auditory process of the petrous temporal bone;
u'2e cartilages—conchal, scutiform, and annular; muscles which move
lese cartilages ; vessels ; and nerves.
directions.—An incision through the skin is to be begun a few inches
,.ehiad the summit of the occipital bone, and carried down the middle
lllle as far as the supraorbital process. It is here to be carried outwards
a
v.              'I^aoroiuu process, auu uiui uci^iw.^j.^, «»—o                 ij y
, '*• On reaching the articulation of the jaw, the incision should be
***** along the edge of the vertical ramus, and inwards to the middle
Ule- AH the skin mapped out by this incision is to be removed, the
011chal cartilage being also denuded of its outer covering. Hub win
^e not only the parts of the external ear, but also the parotideal
-ocr page 228-
160
THE ANATOMY OP THE HORSE.
region and the poll, and the dissection of these parts is to be made as
soon as the ear is finished. On one side the muscles and cartilages 0l
the ear may be dissected; and then the other side may be denuded oi
skin in the same manner as the first, in order to follow the vessels and
nerves.
Muscles of the Ear.—These are divided into extrinsic and intrinslC'
The former have their origin from extraneous parts, but the latter botn
arise from, and are inserted into, the cartilages of the ear. The cart11"
ages of the ear cannot be fully exposed until the muscles have beei
examined, but it may be premised that the conchal cartilage is the lai'gb
trumpet-like cartilage which mainly gives to the outer ear its form>
that the annular cartilage is a short tube, or ring, which is telescoped
on to the external auditory process, and is itself embraced by the con-
stricted base of the concha; and that the scutiform cartil: ige is a thin
plate which rides on the surface of the temporal muscle, in front of the
base of the concha.
Extrinsic Muscles.
The Pabotido-auhiculaeis, or Depeimens Aueem (Plate 29). This
muscle has the form of a broad riband. It arises from the outei
surface of the parotid gland; and pas ing vertically upwards, it lS
inserted into the outer part of the base of the concha, below the
opening.
Action.—To incline the ear downwards and outwards.
The Cervico-auriculares, or Retrahentes Aueem. There are
three of these, distinguished as the cervico-auricularis (or retraheus)
externus, medius, and internus. They all arise from the poll in th
neighbourhood of the insertion of the ligamentum nuchas, and they al'e
here superposed the one to the other. Suppose the ear to be place*
with the opening of the concha looking directly outwards, then the
externus is inserted into the middle of the inner face of the concha; th
medius into the outer side of the concha, beneath the opening, aI1
under cover of the parotido-auricularis muscle; and the internus to*
the base of the concha, on its posterior aspect, and under cover of th
parotid gland.
Action.—In moderate contraction, these muscles give the opening 0l
the concha an outward direction; and when forcibly contracted, they
direct the opening backwards as well as outwards, and incline the ear
towards the poll.
The Pabieto-aueicularis Externus, or Attolens Maximus. This lS
a wide, membranous muscle covering the temporalis muscle. It ari^6
from the parietal crest; and it is inserted by its upper fibres into tn
scutiform cartilage, and by its lower into the front of the concha
cartilage. Its upper fibres are, at their origin, continuous across th
middle line with the opposite muscle.
-ocr page 229-
161
DISSECTION OF THE HEAD AND NECK.
Action.—-To prick the ear, that is, to erect it and give its opening a
I0rward direction.
ne Zygomatico-auriculaeis, or Attolens Anticus. This muscle is
• nuous wit^ tne preceding by an intermediate aponeurosis, and
. °wn muscular substance is generally divided into two slips by
ermediate fascia. It arises from the zygomatic process of the squa-
Fig. 19.
1. pa .                     Auricular Muscles and Neeves of a Mule (Chauveau).
^wS^ricularis externus ; 2. Parieto-auricularis interims ; 8. Scutiform cartilage ; 4:. Scuto-
^^te^
°ns of the levatores lami superioris proprii ; 9. Dilatator nans teamveKSOM .*j*
>e? o« 1st cervical nerve ; B Anterior auricular nerve (of 7th); C. Supraorbital nerve ,
"ranch of the lachrymal nerve.
r
cartiit6mporal b(>ne; and it is inserted by an inner slip into the scutiform
c0llchye' and by an outer slip into the outer aspect of the base of the
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162                                     THE ANATOMY OF THE HOBSE.
Action.—To prick the ear, like the preceding muscle.
The Parieto-aueiculaeis Inteknus, or Attolens Posticus. 1°
muscle is to be exposed by the removal of the parieto-auricularis cxte
nus, beneath the upper part of which it lies. It arises from the up?
part of the parietal crest; and it is inserted into the inner side of »
concha, beneath the cervico-auricularis externus.
Action.—It is the opponent of the parotido-auricularis, bringing
ear into the erect position.
The Mastoido-auricularis. This muscle is to be exposed by cuttjPB
the preceding and the cervico-auricular muscles, and forcibly depressl1»
the ear outwards. This will expose, at the base of the ear, a consider&D
quantity of fat, which is constantly present, and facilitates the nio^
ments of the ear. On clearing away this fat, the muscle will be fc>vlU
at the inner side of the base of the ear. It forms a slender fascicul11
arising from the auditory process, and inserted into the base of the cone'1
Action.—To telescope the conchal on the annular cartilage.
Intrinsic Muscles.                                                                                   ,
Besides some scattered fibres on the outer and inner surfaces
the concha, this group includes, the following two distinct nwscie
passing between the conchal and scutiform cartilages.
The Scuto-auricularis Externus consists of two bundles of fibie
passing between the outer surface of the scutiform cartilage and tD"
inner side of the concha.
Action.-—To assist the parieto-auricularis externus in pricking the eft '
The Scuto-aueiculaeis Inteenus. In order to expose this niusC
the scutiform cartilage is to be raised from the surface of the temp01'
muscle, and turned upwards and outwards. The muscle is strong
than the preceding, and consists of two distinct crossed bundles, w0jC
arise from the inner surface of the scutiform cartilage, and Pa
round the inner side of the base of the concha to get inserted into
posterior aspect, above and internal to the insertion of the
retrain8
internus
Action.—It opposes the preceding muscle, and assists the retrahefl1*
in rotating the concha so as to turn the opening outwards and baC
wards.
Vessels.
The ear is supplied with blood by the anterior and posterior auvicU
arteries.
The Anteeioe Auricular Aeteey (Plate 28) is one of the two *"
minal branches of the superficial temporal artery, which vessel di*1
under the parotid gland, about an inch below the condyle of ,
lower jaw. It ascends behind the capsular ligament of the jaw ', a
after detaching muscular and cutaneous branches in front of the e»r>
enters the temporalis muscle.
-ocr page 231-
DISSECTION OF THE HEAD AND NECK.                              163
rn,
the 6 PosTERIOB Auricular Artery (Plate 28) is a collateral branch of
0f , emal carotid, detached while that vessel lies over the great cornu
occ' G lly°ld b°ne' and beneatn tne Par<>tid gland. It divides on the
ant 0"st^oid muscle into an anterior and a posterior branch. The
t^ 10r branch ascends in the parotid, and ramifies on the concha behind
ear           ior e(%e of its opening, after giving branches to the base of the
"Pa '' • ° *^e mteri°r of the concha. The posterior branch ascends in the
hent ^land, and crosses behind the base of the ear, beneath the retra-
ce! S musc^e- It then passes under the parieto-auricularis intemus,
scends on the inner surface of the concha as far as its tip.
a, . Di°od is drained away from the ear by the anterior and posterior
^cular veins.
aw. e ^-nteRior Auricular Vein is a larger vessel than the satellite
11 eery t, . .                                                °
tr £* n joins the subzygomatic vein to form the superficial temporal
Th n
tWo e Posterior Auricular Vein is formed at the base of the ear by
m^ 0ots which unite at the posterior edge of the parotido-auricularis
Hs s k ^ descends at first on the surface of the parotid, and then in
stance, where it joins the jugular vein.
Serves.
Th
p . e are derived from the 7th cranial nerve, from the 1st and 2nd
cerv;
ical
nerves, and from the lachrymal nerve of the trifacial.
a6r "osterior Auricular Nerve is detached from the 7th cranial
or in ,,S Jt issues from the stylo-mastoid foramen. It ascends beneath
th
le same
su°stance of the parotid gland, in company with the artery of
it s>a-        ttame; and passing immediately behind the mastoid process,
mUss i e back of the ear, and is distributed to the cervico-auriculares
The \rT
Pfecei-           E Auricular Nerve is detached at the same point as the
Pi"oce ^' ** ascends over the annular cartilage, behind the peaked
to thg tne eoicha, which it enters at its base. It is here distributed
TheTttei'ed
muscular fibres on the interior of the cartilage.
preoe,. NteRior Auricular Nerve is much larger than either of the
stylo-rnUg nerves- It is given off from the 7th midway between the
ia the aSt°ld f°ramen and the edge of the inferior maxilla. It ascends
lleath Jj*arot,ia-> turns over the zygomatic arch, passes downwards be-
SuPrao 1 6 Parieto"auricularis muscle, then internal to the root of the
^thju, ltal Process of the frontal bone, and terminates below the nasal
the Cor °f tne eyelids. It supplies the attolentes muscles as well as
^irial fi,U8ator supercilii and the orbicularis palpebrarum, and its ter-
Th
le CERVI
ts enter the levator labii superioris alaeque nasi.
tllroiiRh n,AL Branch of the 7th nerve. This nerve comes out
as the \ „ substance of the parotid gland, near or at the same point
Jugular vein, and under cover of the parotido-auricularis muscle.
-ocr page 232-
164                                THE ANATOMY OF THE HORSE.
It supplies that muscle, and is continued down the neck, as alre» j
seen (page 144).
Auricular Branches of the 1st Cervical Nerve. These, which a
derived from the superior primary branch of that nerve, appear in t .
poll between the obliquus capitis superior and the rectus capitis poS
cus muscles. Crossing the cervico-auriculares muscles, they are dis1
buted at the inner side of the base of the ear.                                         ,
Auricular Branches of the 2nd Cervical Nerve. These are denv
from the stellate group which the inferior primary branch of that ner
forms on the mastoido-humeralis, behind the wing of the atlas. ^ >
reach the ear by crossing over the parotid gland, and are distxibw
mainly to the skin of the concha on its posterior aspect (when
opening is directed outwards), but some branches reach its inner side-
Auricular Branch of the Lachrymal Nerve. . This nerve, wh1
emerges from the orbital sheath, crosses the direction of the ante'
auricular branch of the 7th on the zygomatic arch, and is distribu*'
to the skin in front of the ear.
Cartilages of the Ear.
The Conchal Cartilage. This anJ the other cartilages are c°
posed of yellow (elastic) fibro-cartilage. Although its name expresS
some likeness to a shell, it bears more resemblance to a trumpet. * ,
opening of the trumpet is somewhat elliptical, and can be direct^
forwards, outwards, or backwards. The margins of the opening nie
above and below in acute angles. Beneath the lower angle, or comn1
sure, the cartilage forms a complete tube, which is slightly i
nflated &
form. At its termination it becomes narrow, and slightly embraces
annular cartilage, over the outer side of which it sends a peaked P
cess, whose fibrous extremity is attached to the wall of the guttn '
pouch.                                                                                                     ,
The Annular Cartilage. This has the form of a ring surroundi t
the edge of the auditory process ; and it is itself embraced by the c
ohal cartilage, the three structures being related to one another like
tubes of a telescope. This connection between the cartilages is m*
tained by connecting elastic tissue, and by the lining membrane ot
ear in passing from the one structure to the other.
The Scutifohm Cartilage is superposed to the temporal musd6
front of the base of the concha, to which it is connected only "J
muscles already described. It is thin, flexible, and irregularly triaug'11'
in shape.
THE PAROTIDEAL REGION.
The Parotid Gland (Plates 27, 29, and 30). This is the largest of*
salivary glands. It derives its name from its proximity to the ear, be
the root of which it is placed. From that point it stretches dowiiw0.
-ocr page 233-
DISSECTION OF THE HEAD AND NECK.                               165
fill*
v mg UP the space between the wing of the atlas and the edge of the
flaf1Cal ramus of the inferior maxilla. The outer surface of the gland is
' arid is separated from the skin by the parotido-auricularis muscle,
"J the continuation of the cervical panniculus, which here takes
lorm of an aponeurosis with scattered muscular bundles. The
%Ular vein lies in a depression on the lower half of this surface, after
(jVmg become superficial by passing through the substance of the
J nd- Below and behind the ear the posterior auricular vein is visible
p.1 some distance before it passes into the gland to join the jugular.
„ a%, the outer surface is crossed obliquely upwards and forwards by
\V!G auriciilar branches of the 2nd cervical nerve, and obliquely down-
wards and backwards by the cervical filament of the 7th cranial nerve,
'Cn comes out through the gland at the same point as the jugular,
descends under cover of the parotido-auricularis and panniculus
ij, cies to be continued along the jugular channel of the neck.
ra 6 anterior edge of the gland is related to the border of the vertical
ad}/18' Wnicn ^ overlaps slightly. This edge is most intimately
■l en-t to the bone and to the masseter muscle, and at it the facial
cjies of the 7th and 5th cranial nerves, and the transverse facial and
* Ui°-muscular vessels pass on to the face by emerging between the
W an^ tne bone, or by perforating the edge of the former. The pos-
cov°r 6dge of the §'land is related t0 tne edSe of the winS of the atlaS
th . ^ tne mastoido-hvimeralis muscle, and the connection between
is m 1S merely by loose areolar tissue. The upper extremity of the gland
etched to embrace the root of the ear, and beneath or through it the
tie l ^ Uerves and arteries Pass to the ear. The inferior extremity of
be §!and is margined by the submaxillary vein, which joins the jugular
„laleatli the postero-mferior angle of the gland. The deep face of the
DV tK numerous and important relationships, which will be exposed
he removal of the gland; but its duct must first be examined.
86eoiENsoN's Duct. This is formed as a single duct by the union of
lo\\°ndary branches at the anterior edge of the gland, a little above its
t^61" extremity. It crosses over the tendon of the sterno-maxillaris
bP /if' and enters the intermaxillary space, where it will subsequently
Allowed.
expo!'eC<';OW'S"~"Tlle Parotid g'land should now be removed in order to
careSe the obJects beneath it. Its removal must be effected with great
benfi' !? as to lea^e, as far as possible, the vessels and nerves which lie
f
-sseTUlg the ^th nerve, and the transverse facial and maxillo-muscular
Veir, S',which emerge at the anterior edge of the gland, and the jugular
vesselW Ich Passes through its substance. In removing the gland, its
exter * ^ nerves must be cllt- Its arteries are derived from the
' nal carotid or its collateral branches; its veins empty themselves
-ocr page 234-
166                                 THE ANATOMY OF THE HOESE.
into the jugular or auricular veins; its nerves come from the 7th cran <■
nerve.
The deep face of the parotid gland is related to the follo^m?
structures:—The mastoid insertion of the mastoido-humeralis, the
minal tendon of the sterno-maxillaris, the stylo-maxillaris, the diga
tricus (upper belly), the occipito-styloid, the stylo-hyoid, the subma-
illary gland, the great cornu of the hyoid bone, the guttural pouch, *
external carotid artery (with its terminal, and some of its collated >
branches), the initial part of the jugular vein (formed by the junction
the superficial temporal and internal maxillary veins), and the '
nerve.
The Tendons of the Mastoido-Hdmbralis and Stern-o-
These muscles are described at pages 152 and 145 respectively- ^ ,
two tendons are connected by a fibrous expansion, which is inclu"
between the parotid and submaxillary glands. When they have be
examined, the fibrous expansion and the tendon of the sterno-rnaxiUal
may be removed.
The Stylo-Maxillaris. This muscle is not distinct from the diga
tricus (upper belly). It arises in common with that muscle from *
styloid process of the occipital bone, and it is inserted into the augle
the jaw.
Action.—To depress the lower jaw, and assist in opening the mouth-
The Digastricts (Plate 31). This muscle will be only imperfecta
exposed at present. It consists of an upper and a lower muscular bely'
with an intermediate tendon. The lower belly will be met in the
section of the intermaxillary space ; and the tendon, in the dissection l
the exposure of the mouth and pharynx. The upper belly arises &°
the styloid process of the occipital bone, in front of the origin of *
preceding muscle, with which it is confounded. It is succeeded by *
intermediate tendon, which plays through a perforation in the tendon
the stylo-hyoid, and is continued by the lower belly. The latter becom
inserted into the edge of the inferior maxilla, behind the symphysis.
Action.—To depress the lower jaw and open the mouth.
The Occipito-Styloid (Plates 31 and 32). This muscle arises fr°*
the front of the styloid process of the occipital bone ; and it is wW]
into the extremity of the styloid (great) cornu of the hyoid bone, beW"
its point of articulation with the skull. The deep face of the musde
lined by the mucous membrane of the guttural pouch; and in
operation for opening the pouch, the muscle is perforated.
Action.—To flex the temporo-hyoideal joint, and carry backwards
hyoid bone and the parts attached to it.
The Stylo-Hyoid (Plate 31). Only the origin of this muscle, from <*
heel-like part of the great cornu, will at present be seen. It should
identified, and preserved for examination at a later stage.
-ocr page 235-
167
DISSECTION OF THE HEAD AND NECK.
. Tlle submaxillary gland is to be preserved without disturbance until
* °an be exposed in its entirety. The guttural pouch will be described
m°re advantage at a later stage.
The Exteenal Cabotid Artery (Plate 28). Only the termination of
hat vessel is here seen. It is one of the terminal branches of the
co«iraon carotid, which divides above the cricoid cartilage, under cover
* the submaxillary gland. The first part of the artery—at present con-
C(jaled—reSts on the guttural pouch, and is covered by the stylo-max-
*   iiri% digastricus, and stylo-hyoid muscles. As now seen, it appears
etween the last of these muscles and the hinder edge of the great
°rnu; and crossing obliquely upwards and forwards on the surface of
.hat bone, it terminates by dividing into the superficial temporal and
^ternal maxillary arteries. The vessel detaches three collateral
reaches, viz., the submaxillary, maxillo-muscular, and posterior auricu-
ar arteries, of which the first is concealed by the digastricus and stylo-
hy°id muscles.
rhe Maxillo-Muscular Artery. This branch is given off at the
^Pper edge of the stylo-maxillaris muscle, immediately after the parent
fritI1k emerges between the stylo-hyoid muscle and the great cornu. It
prms With the continuation of the main trunk a very obtuse angle.
^assmg forwards and downwards, it divides into an outer and an inner
Jj^ch, which embrace between them the edge of the vertical ramus.
J*S outer branch appears on the face at the anterior edge of the parotid
? aH and enters the masseter muscle. The inner branch passes to the
rp^l Pterygoid muscle.
b Xlle Posterior Auricular Artery. This vessel has its origin a little
^ond the preceding, but from the opposite side of the carotid. Its
llbution to the car is given at page 163.
d. ihe Superficial Temporal Artery (Plate 28). Originating by the
v1Vlisi°n of the external carotid on the great cornu, this artery, after a
<Jery short course below and behind the condyle of the lower jaw,
lvides into the transverse facial and anterior auricular arteries.
cq rhe Transverse Facial Artery turns round the ramus below the
0l^yle, and will be followed in the dissection of the face.
th An™Rior Auricular Artery ascends to the front of the ear, on
/^.capsular ligament of the temporo-maxillary joint. Its distribution
S'ven at pao-e 162.
b Tlle Internal Maxillary Artery. This, much the larger terminal
ja7Ch °f the external carotid> Passes within thc COndyle °f             r
' ^ Where it will subsequently be followed.
vEiN8._The           ^ ve.n .g formed within tne substance ol tne
[arotld gland, close behind the articulation of the jaw, and superficial
the terminati0I1 of the external carotid, a few lobules of the gland
separating the artery and vein. The vessels which unite to form it are
-ocr page 236-
168
THE ANATOMY OF THE HOBSE.
the superficial temporal and internal maxillary veins. It passes °
through the substance of the parotid, and then lies in a groove °
its surface, where it receives maxillo-muscidar and posterior auricu'
branches.
The 7th Cranial Nerve (Portio dura) (Plate 28) emerges &o&
the aqueduct of Fallopius by the stylo-mastoid foramen of the petrol
temporal bone. It passes downwards and forwards at the inner face
the parotid or within its substance; and turning round the huerl
maxilla, it reaches the face with the transverse facial vessels. In *
course it is crossed superficially by the posterior auricular artery, a"
passes over the angle of division of the superficial temporal artery. •*
it turns round the inferior maxilla, it is joined by the sensory sn
zygomatic branch from the inferior maxillary division of the 5th cram
nerve. In this part of its course the 7th nerve detaches the follotfin»
branches :—
1.  The Anterior, Middle, and Posterior Auricular Nerves.—The first t*
are given off at the stylo-mastoid foramen, the last is detached
between the foramen and the edge of the ramus. The nerves ascend j
or beneath the parotid gland, and their distribution is given at page 1°'J'
2.   Nerves to the occipito-styloid, stylo-hyoid, digastricus (upPe
belly), and stylo-maxillaris muscles. These are given off at the stp°
mastoid foramen.
3.  The Cervical Branch, which is given off at nearly the same point Jk
the anterior auricular, but from the opposite side of the trunk-
passes through the parotid, and reaches the surface of the gland (se
page 163).
4.   Numerous small and irregular branches to the parotid gland an
guttural pouch.
The Subzygomatic Nerve (Auriculo-temporal of man) is a bran0
of the inferior maxillary division of the 5th nerve, given off at
the foramen lacerum basis cranii. It descends behind the capsw9
ligament of the jaw; and crossing over the termination of the supe
ficial temporal artery, it joins the 7th as it turns round the ramus.
sends a branch to accompany the transverse facial vessels (Plate 29).
THE REGION OF THE POLL.
c
Directions.—It will be convenient at this stage to dissect a group
muscles (with their nerves and vessels) placed above the occipito-atlant
and atlanto-axial joints (fig. 18, page 156). The cervico-auricular mil*1
of one side having been cleared away, the mastoid tendon of
mastoido-humeralis (page 152) will present itself. Beneath that, agal '
is the mastoid tendon common to the splenius and trachelo-mastoide1
(page 153); and still deeper, there is the occipital insertion of tn^
complexus. Each of these, having been identified, may be cut 6W'
-ocr page 237-
169
DISSECTION OF THE HEAD AND NECK.
^lld the following muscles are to be isolated, the nerves and vessels
eiQg thereafter dissected on the other side.
The Obliques Capitis Inferiob. This muscle, the most powerful of
ue group, covers the atlanto-axial joint on each side. It arises from the
SuPerior spine of the dentata; and it is inserted into the wing of the
atlas on its upper aspect.
Action.—To rotate the atlas (and head) around the odontoid process
0f the axis.
The Obliquus Capitis Superior. This muscle covers the occipito-
mental joint on each side. It arises from the free edge of the wing of
e atlas; and it becomes inserted into the mastoid crest and styloid
Process of the occipital bone.
Action.—To extend the head on the atlas.
The Rectus Capitis Posticus Major. This muscle is composed of
w° Parallel portions which, although not distinctly separated from one
pother, Were described as distinct muscles by Percivall. It arises from
the spinous process of the axis. Its most superficial fibres (complexes
**»or of Percivall) join the occipital insertion of the complexus; while
! s deeper portion {rectus capitis posticus major of Percivall) is inserted
**° the back of the occipital bone, beneath the insertion of the com-
Wexus.
Action.—The same as the preceding muscle.
The RE0TUS Capitis Posticus Minor. This is the smallest muscle of
. ae group. It lies beneath the preceding, and covers the occipito-atlantal
J.0lllt- It arises from the upper aspect of the ring of the atlas; and it is
%n^ntd into the back of the occipital bone, beneath the last-described
Muscle.
Action.—The sarae as the two preceding muscles.
-----" V^ililV V IVjillj XI .CUV* HI \KJ IA,WSWI/£JVVW "A *-^.v~"y -----------
e         % the antero-internal foramen of the atlas. At its point ot
^I'gence it resolves itself into superior and inferior primary branches,
he latter is immediately directed down through the antero-external
°ramen, and will be followed at a later stage. The superior primary
ranch appears between the obliquus capitis superior and the rectus
apitis posticus muscles, where it gives (1) muscular branches to these
1Us°les, and (2) auricular branches already followed to the skm of the
ear.                v '
The 2nd Cervical Nerve issues by the foramen at the anterior edge of
le arch of the axis, where it is covered by the obliquus capitis inferior^ It
,Uvides into superior and inferior primary branches, the latter of which
,8 already been referred to (page 144). The superior branch gives twigs
t0 ti» superior and inferior oblique muscles of the head, and is
°^«med like the succeeding members of the cervical series (page 104j.
rhe Occipital Artery. This vessel will be found ascending through
-ocr page 238-
170                                THE ANATOMY OF THE HORSE.
the antero-external foramen of the atlas, and dividing there into cerem
spinal and occipito-muscular branches. The former enters the spB»
canal by the antero-internal foramen; the latter div ides for the supP1?
of the muscles and other structures of the poll.
The Retrograde or Anastomotic branch of the occipital artery will
found issuing with a backward course from the posterior foramen of t"1
atlas, and inosculating with the termination of the vertebral artery.
The Mastoid branch of the occipital artery will be found benea* l
the obliquus capitis superior. It ascends behind the styloid process*
and crossing over the mastoid crest, immediately above the mastd
process, it passes under the edge of the squamous temporal bone, an
enters the parieto-temporal conduit, in which it anastomoses with t*1
spheno-spinous branch of the internal maxillary artery.
Veins.—Satellite veins accompany these arteries.
THE INTERMAXILLARY SPACE.
Directions.—Incise the skin along the middle line, from the men*9
symphysis upwards, and raise it on each side as far as the edges of w1
rami.
Cutaneous Nerves. The skin of the intermaxillary space is supple
by a nerve derived from the 2nd cervical nerve. It comes from the firs
stellate group of cutaneous nerves already seen on the surface of t*1
mastoido-humeralis; and crossing obliquely downwards into the spa"
(the long axis of the head is supposed to be vertical), it extends
near the symphysis of the lower jaw.
The Panniculus. This is here extremely thin. It hardly forms
continuous layer, but consists of muscular fasciculi scattered in an apo"
eurosis.                                                                                                        ,
The Submaxillary Lymphatic Glands (Plato 27). This group °
glands is placed on the inner side of the horizontal ramus, a little abo»*
the point where its edge is crossed by the submaxillary vessels an
Stenson's duct. It rests on the lower belly of the digastricus musd >
being related inwardly to the insertion of the subscapulo-hyoid musci '
and outwardly to the submaxillary artery. The right and left group
extend towards each other, and nearly meet below the extremity °
the glossal (spur) process of the hyoid bone. These glands are place
on the track of the lymphatic vessels coming from the mouth and nos i
and in morbid states of these parts, such as glanders, the glands beconi
inflamed and enlarged from the irritant matters conveyed in the lymph»tl0
vessels. They should be carefully excised to expose the submaxillar^
artery and the inferior belly of the digastricus muscle.
The Submaxillary or Facial Artery (Plate 27) appears at *B
upper part of the space, descending between the subscapulo-hyoid an
internal pterygoid muscles. At this point the inferior extremity
-ocr page 239-
171
DISSECTION OF THE HEAD AND NECK.
*° submaxillary salivary gland lies internal to it. In passing obliquely
backwards and downwards, it rests on the internal pterygoid muscle, and
!S Partly covered by the lymphatic glands, under cover of which it de-
aches its submental branch. It then comes into company with the vein
0t the same name, and with Stenson's duct; and the three vessels turn
J?Und the edge of the ramus to reach the face, the artery being below,
he vein in the middle, and the duct superior. Where the artery turns
l°Und the ramus, it is very favourably placed for taking the pulse, since
18 a vessel of considerable size, is in an easily accessible position, rests
lrectly on the bone, and is almost subcutaneous, only the thin panm-
us intervening between it and the skin.
The Submental Artery crosses downwards beneath the inferior belly of
he digastricus, then along the surface of the mylo-hyoideus, which it
Prorates a few inches above the symphysis. It will be followed to its
r^aation in the dissection of the mouth.
The Submaxillary Vein (Plate 27) is in contact with the artery where
e vessels turn round the ramus; but as it passes backwards, it recedes
'gatly from tne artery) and follows the posterior border of the sub-
maxillary gland_ It leaves the space above tr±e angle of the jaw, and is
0llt«rued along the lower edge of the parotid to join the jugular. At the
ymPhatic glands it receives the submental vein, a larger vessel than the
y of the same name.
bTENSoN>s Duct (Plate 27), after crossing the stemo-maxillaris tendon,
Passes into the space, at the posterior edge of the submaxillary salivary
HsT* lt Passes downwards on the internal pterygoid muscle, placing
self in contaot with tho submaxillary vein, in company with which and
s e artery it turns round the bone to reach the face. It is here the most
aUPei'i.or of the three vessels; and from its being superficially placed
** resting on the bone, it is liable to be opened when a blow is delivered
. *_ this region.
b :he Digastbicus. This muscle is named from its having two fleshy
st Ies> with an intermediate tendon. The upper belly arises from the
jJ.]A Process of the occipital bone, being confounded with the stylo-
axillark It ig succeeded by the intermediate tendon, which plays
be!rigl1 the tendon of the stylo-hyoid muscle ; but this and the upper
in t J aie at Present concealed within the jaw. The lower belly is placed
he-intermaxillary space, where it is partly covered by the lymphatic
J ands, and is related anteriorly to the mylo-hyoid muscle. It is inserted
dista flat fasciculated tendon into the edge of the horizontal ramus, a little
4auce above the symphysis.
rtion.—S£0 depress the lower jaw and open the mouth.
f0r Mylo-hyoid Muscles stretch across the intermaxillary space, and
; J1 a support for the tongue. Each muscle arises from a line on the
er surface of the horizontal ramus behind its alveolar border ; and its
-ocr page 240-
172                                 THE ANATOMY OF THE HOESE.
fibres pass transversely inwards, the most superior getting inserted int°
the body and glossal process of the hyoid bone, and the others into »
median fibrous raphe between the two muscles. The muscle is to
left intact at present, and its attachments will be better seen in tn
dissection of the mouth.
Action.—To raise the body of the tongue towards the roof of tne
mouth, and thus assist in mastication and deglutition.
Nerve to the mylo-hyoid and inferior belly of the digastric. 1'llS
is a branch of the inferior maxillary division of the 5th cranial nerve.
It descends between the internal pterygoid muscle and the vertical ramus >
and passing above the upper edge of the mylo-hyoid, it runs downward
on the surface of that muscle, in company with the submental artery-
In part of its course it is covered by the lower belly of the digastricus>
and it sends to that muscle a distinct branch, which enters it on >ts
outer side.
the appendages of the eye.
These are—the eyelids, the membrana nictitans, the earund"8
lachrymalis, the conjunctival membrane, and the lachrymal apparatus-
The lachrymal gland—the most important part of the last mention6
apparatus—will be dissected with the interior of the orbit; but tfr
other structures enumerated are to be examined now.
The Eyelids. The front of the eye is protected by two movable cur-
tains—the upper and lower eyelids ; and at the inner side of the eye the1
is placed another structure—the membrana nictitans, which plays tfl
part of a third eyelid. The upper lid is larger than the lower, and b&
a greater range of movement. Each eyelid presents two surfaces, t*
borders, and two extremities. The outer or facial surface is formed by
a continuation of the skin, and is covered by short hairs. Among thes
there occur in the lower lid some long tactile bristles. The inner or oculi1
surface is lined by the conjunctival membrane, and is moulded on to
front of the eye. If the upper lid be everted there will be found on n
inner surface, near the outer angle, a number of minute openings, int
which bristles should be passed. These are the openings of th«
excretory ducts of the lachrymal gland. On the same surface, but nea
the opposite angle, and close to the free edge of each lid, there is
round opening of larger size, but still minute. These are the pii^1
lachrymalia, the orifices of the lachrymal ducts, by which the lachryn1'
secretion is conveyed away from the eye. The free borders of the eyeh
circumscribe the palpebral fissure, which is a mere line when the eye
closed, but is ovoid or elliptical, with the long axis directed
oblique1)'
upwards and outwards, when the eye is open. The free edge of each J
is somewhat stiff, this stiffness being due to a slender rod of cartililo
which extends along it. The meibomian glands are lodged in depressio1
on the ocular surface of this cartilage, and may be seen through
-ocr page 241-
173
DISSECTION OF THE HEAD AND NECK.
c°njunctiva as close-set yellow lines having a direction at right angles to
"ie edge of the lid. They number about fifty or sixty in the upper lid,
ut they are fewer and less distinct in the lower. Each gland consists
a Wain tube with lateral sacculi opening into it on each side, and it
^charges its secretion by a dot-like orifice on the edge of the eyelid.
ne free edge of each lid carries a fringe of stiff hairs—the eyelashes,
rp n tend to prevent the entrance of foreign particles into the eyes.
ue attached edge of each lid is marked on the ocular side by the angle
deflection of the conjunctiva from the lid to the eyeball, but on the
'C1al side the eyelid passes into the surrounding skin without any
eniied line. At each extremity the eyelids join to form a commissure,
r canthus. The outer or temporal canthus is acute, but the inner or
8(W canthus is rounded, and lodges the caruncula lachrymalis.
, ne Cabuncula Lachrymalis is a small, rounded, and, generally,
^"Pigmented nodule placed within the nasal canthus, and about
MUidistant from the two puncta lachrymalia. It is covered by con-
fictrva, and is composed of connective-tissue with some mucous follicles
a the bulbs of a few short hairs, which project from it.
J- he Membbana Nictitans. This body is placed at the inner canthus,
*here, ordinarily, it projects to only a slight extent, but it is capable of
eiI1g thrust more than half way across the front of the eye. It has for
. s °asis a thin and flexible piece of elastic cartilage, which anteriorly is
ested by conjunctiva. Posteriorly this cartilage passes to the inner
lcle of the eyeball, where it becomes connected with the cushion of
Sermfluid fat which is found in the posterior part of the orbit. The
eiabrana nictitans has no muscle to move it directly; but when the
, , all is retracted within the orbit, it presses on the semifluid fat
b
3ehind
^^m
it, and this, tending to escape at the side of the eyeball, pushes
e tttembrana nictitans before it. In the eye of a subject just dead,
ls mechanism may readily be demonstrated by pressing the eyeball
ackwards into the orbit. About the centre of the outer face of the
^tilage, there will be found a cluster of reddish-yellow granules—the
arderian gland. The gland secretes an unctuous material which is
lseharged by a number of ducts that perforate the cartilage and open
011 its ocular surface.
e Lachrymal Apparatus comprises—the lachrymal gland with its
feretory ducts, the puncta lachrymalia, the lachrymal canals, the
^ryrnal sac, and the lachrymal duct,
0 , he Lachrymal Gland is placed within the orbit, beneath the supra-
„,al process of the frontal bone. The gland itself will be dissected at
a later stage.
of The excretory ducts of the gland discharge themselves by a number
minute .openings on the inner surface of the upper eyelid, close to the
mP<*al canthus. Sometimes a few of the ducts open on the lower lid
-ocr page 242-
\
174                                THE ANATOMY OF THE HORSE.
close to the same canthus. The watery secretion which issues fr°n
them is carried over the front of the eyeball by the movements of w1
eyelids, and at the nasal canthus it is drained away by the puncta
lachrymalia.
The Puncta Lachrymalia. Each punctum is placed on the innei
surface of the lid near its free edge, and distant about i of an inch ft'011
the caruncula. The lower punctum is generally larger and more easily
found than the upper. If a flexible bristle be passed into each punctunij
it may be directed along the lachrymal canal, into the lachrymal sac-
Taking the bristle as a guide, each canal may then be slit open *"*
scalpel or scissors.
The Lachrymal Canals will be found to converge towards the roof °
the lachrymal sac, into which they open by distinct orifices. The uppcl
canal is a little longer than the lower.
The Lachrymal Sac is a small reservoir lodged in the fossa of tflS
same name on the orbital surface of the lachrymal bone. It receives the
lachrymal secretion from the lachrymal canals, and it is directly
continued as the lachrymal duct.
The Lachrymal Duct {ductus ad nasum) conveys the lachrymal secre-
tion from the sac to the lower part of the nasal fossa. In the ni'S
part of its course it is lodged in an osseous canal, along which it passe
to reach the middle meatus of the nose, where it will subsequently °e
found. The lachrymal canals, sac, and duct have a fibrous wall with a
mucous lining, the epithelium being stratified and squamous in the canals>
but ciliated in the sac and greater part of the duct.
The Conjunctiva. This is a mucous membrane, consisting of a
palpebral part lining the inner aspect of the eyelids, and an ocW#*
portion which is reflected on the front of the eyeball. The
palpebra1
portion, including that covering the caruncula and membrana nictitanSi
consists of a stratified epithelium and a papillated layer of vascular
subepithelial connective-tissue containing small mucous glands. The
ocular portion where it covers the sclerotic resembles the preceding lJ1
structure, but is thinner, nonpapillated, and less vascular; where lt;
passes over the cornea, it consists of the epithelium only, which lS
generally enumerated as one of the constituent layers of the cornea
itself, being termed its anterior epithelium. Through the puncta
lachrymalia, the conjunctival epithelium is continuous with that lining
the lachrymal canals ; and at the free margin of the lids it is continuous
with the epidermis.
Structure of the Eyelids.—Each lid is composed of the following
parts :—a layer of skin outwardly, the palpebral conjunctiva inwardly>
a portion of the orbicularis palpebrarum muscle, the palpebral tendoUi
the tarsal cartilage, vessels, and nerves.
Besides these, there is found in the upper lid the tendon of a specia1
-ocr page 243-
175
DISSECTION OF THE HEAD AND NECK.
Sole—the levator palpebral superioris. Of these, the skin and con-
junctiva have already been sufficiently noticed.
The Orbicularis Palpebrarum (Fig. 19, page 161). This muscle will
exposed by removing the layer of skin from the eyelids, and from
ar°mid the orbital rim for the breadth of an inch. The fibres of the
UScle are closely adherent to the skin of the eyelids, and have a
c'ilar or elliptical disposition around the palpebral fissure. Below the
* Sal canthus a number of the fibres are inserted by a slender tendon
1 ° the lachrymal tubercle on the bone of the same name, but for the
°st part the fibres are without bony attachment. Above the orbit the
scle is confounded with some thin fibres—the corrugator supercilii—
v uch wrinkle the overlying skin.
Action.—The orbicularis muscle closes the eye by approximating the
ee edge of the eyelids, and in this action the upper lid has a much
~er range of movement than the lower.
*he Palpebral Tendon. This is a fibrous layer which will be
'posed by removing the orbicularis muscle. At the free edge of the
}ehd it is margined by the tarsal cartilage, while by its opposite border
lt 18 fixed to the rim of the orbit.
. -1-he Tarsal Cartilage. This is a slender rod of elastic cartilage
1 edded in the free edge of each eyelid. The meibomian glands lie in
8 °oves on its ocular surface. It prevents the margins of the lids from
r*§ drawn, or puckered, when the orbicular muscle contracts.
*he Levator Palpebr^ Superioris. This muscle is found in the
PPer eyelid only. The fleshy portion of the muscle is a slender flat
^ciculus which takes origin at the back of the orbit (Fig. 22, page 209)
' 0ve the optic foramen, where it will subsequently be exposed along
n the other contents of the cavity. Passing along the eyeball and
. aeath the lachrymal gland, it is succeeded by a thin flat tendon which
the Hd is placed beneath the palpebral tendon, and joins the tarsal
°artilage.
Action.—To open the eye by raising the upper lid. In this move-
eilt the muscle plays over the eyeball like a rope over a pulley. The
N ei' lid, it is to be observed, has no analogous muscle, because, in the
rst place, it is raised but slightly under the action of the orbicularis,
% secondly, because its own weight and elasticity are sufficient to
clepi-ess it.
vessels. The arteries of the eyelids are derived from the supra-
vital and lachrymal arteries, and from the orbital branch of the
SuPerior dental artery.
Tne Supra-Orbital Artery will be found emerging from the orbit
y the supra-orbital foramen. It is a branch of the ophthalmic
ai"tery.
fhe Lachrymal Artery is also a branch of the ophthalmic, and is
-ocr page 244-
176
THE ANATOMY OF THE HORSE.
distributed mainly to the gland of the same name, but it sends some
twigs to the upper eyelid.
The Orbital Branch of the Superior Dental Artery creeps over the
lower part of the rim of the orbit, and descends to anastomose with the
submaxillary artery. It gives some twigs to the lower eyelid.
Nerves. The sensory nerves of the eyelids are derived from the
supra-orbital and palpebro-nasal branches of the ophthalmic division o*
the 5th cranial nerve, and from the orbital branch of the superior
maxillary division of the 5th. The supra-orbital nerve emerges by the
foramen of the same name, and is distributed to the upper eyelid, and to
skin around its point of exit. The palpebro-nasal nerve sends a branch
to supply the lower lid and the structures at the inner canthus.
The orbital branch of the superior maxillary division of the 5th nerve
is distributed in the neighbourhood of the outer canthus. The motor
nerve to the orbicularis comes from the 7th, which crosses internal to
the nasal canthus. The motor nerve to the levator palpebral conies
from the 3rd, but cannot be reached at present.
THE FACE.
The Nostrils, or the Inferior or Anterior Nares. Some points in
connection with these may conveniently be noticed before the student
proceeds to dissect the
face. The nostril is the
entrance to the nasal
chamber or fossa—the first
segment of the respiratory
passages. It is a large>
somewhat oval opening
bounded laterally by the
ala', or wings, of the nostril'
The also meet above and
below, forming the com-
missures, the lower oi
which is wide and rounded,
while the upper is acute.
The outer ala is concave in
the whole of its extent;
but the inner ala, while
Fig. 20.
concave below, forms a
convex projection close t°
1, 1. Comma-like cartilages of the nostril ; 2. Septal eavtilaj
If
the upper commissure
now the inner wing be manipulated, it will be felt to contain a piece
of cartilage which begins above in the convex projection close to the
upper commissure, extends downwards and round the inferior commis-
-ocr page 245-
DISSECTION OP THE HEAD AND NECK.                              177
tilo ' an terminates in the lower part of the outer ala. This alar car-
b:
road
when dissected out, displays a close resemblance to a comma, the
Point ^ait ^eing placed in the upper part of the inner wing, and the
iltta 1, ° *°wer part of the outer wing. The cartilages are movably
of ti "y fibrous tissue to the lower extremity of the septal cartilage
"ost, 'l n°se' ano- they give the necessary firmness to the edges of the
the ' Preveuting these from falling together in the act of inspiration,
face rn . are coyered outwardly by skin continuous with that of the
C|irr' a Sk*n> which is thin and adherent to the subjacent textures, is
round the margins of the ala;, and for a short distance into the
SQj.r~ ° mmber. If the finger be introduced below the upper commis-
n°str'/ * be ^t to enter a peculiar diverticulum termed the false
it is i." his Wind pouch extends upwards for about four inches, and
continuation of the skin. If the wings of the nostril be
be s.        as widely as possible, the opening of the lachrymal duct will
W         a 1>ew inches within the lower commissure. The orifice is circu-
ity,, Peai'ing as if a small piece of skin had been punched out. Just
the               orifice the skin is continued by the mucous membrane of
by h • chamber, which is distinguished from the common integument
jj. ^ n°n-pigmented, vascular-looking, and destitute of hairs,
the lj eUlons-—The skin on the face should be entirely removed. Over
8^0, atl°- false nostril care is necessary to avoid going deeper than the
ftHel n ne S'de 8nould first be used for the muscles, and then the vessels
Th 6S should he dissected on the opposite side.
\vh;ci milscles now to be dissected include a series of thin muscles
\vhioli ^rminate in and move the lips and nostrils ; the buccinator,
mllScj 0rms the basis of the cheek ; and the masseter, a, powerful
A ref mastication, covering the vertical ramus of the lower jaw.
tftUsclerence to Plate 29 will enable the dissector to identify these
1 be p
tbe f ANnigulits Carnosus docs not form a continuous muscle on
Cuttoc '          consists of disconnected bundles developed in the sub-
it js °Us. fascia. It is best developed over the masseter muscle, where
strUct 0ntillu°us over the edge of the inferior maxilla with the same
few ^ e m tne parotideal and intermaxillary regions. On the cheek a
assist             reach the angle of the mouth, in whose retraction they
Bel0iv ti
tibres            nm of the orDit there is found a thin layer of Pale muscular
f;iciai r, .mterniediate fascia, which may be viewed as a part of the
"lal rauaTiCUlU8, It crinkles the overlying skin. This is the lachry-
The T °f "Frencl1 authors, and the inferior palpebral muscle of Leyh.
Uluscle bVAT0R LaB11 Supeeioeis Al^que Nasi (Plate 29). This
uasal b ftS * narrow> thin, and aponeurotic origin from the frontal and
°aes> below and internal to the orbit, ft passes over the levator
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178                                 THE ANATOMY OF THE HORSE.
labii superioris proprius ; and widening as it descends, it divides > ,
an anterior and a posterior branch, between which the lateral diM0
the nostril emerges. The anterior is the larger branch, and it Pa ,
beneath the last-mentioned muscle to end- in the outer wing 0I .
nostril and the adjacent part of the upper lip. The posterior bran°
inserted into the angle of the mouth.
Action.—To dilate the nostril and elevate the upper lip "^ . .
anterior branch; to raise the angle of the mouth by its postc
branch.
The Levator Labii Superioris Proprius (Plates 29 and 30, m10 .,
19). By its superior extremity, which is rounded and fleshy; .,
muscle takes origin below the orbit, from the malar and superior rfl<' ,
lary bones. Becoming narrower and thicker, it passes downwards
forwards beneath the last-described muscle, whose direction it cros
Appearing in front of this muscle, it lies on the false nostril; and heifc ^
muscular portion is succeeded by a narrow tendon, which passes invV' .
above the superior commissure of the nostril to gain the upper lip- ,
the lip it passes over the transverse dilator of the nose ; and appr°a. fl
ing the muscle of the opposite side, it becomes united to it across .
middle line by an intermediate fascia, and is inserted into the text*
the upper lip.                                                                                    ^ ^
Action.—Acting together, the right and left muscles elevate
upper lip vertically. When the muscle of either side acts singy'
lip is raised and inclined towards that side.                                            .{
The Dilatator Naris Lateralis. (Doubtfully the homologu
the caninus of man) (Plate 29). This muscle is triangular i11 ^
It is narrow and pointed at its upper extremity, where it arises
the superior maxilla. It passes between the two branches of the leV' (
labii superioris alseque nasi; and widening as it descends, it passes
the anterior branch of that muscle, and becomes inserted into the ol
- I'll
wing of the nostril. Its most posterior fibres blend with the orbi«u '
oris.                                                                                                         ^
Action.—To dilate the nostril by pulling the external wing out^8*" i
The Dilatator Naris Transversalis (Fig. 19). This is a four-si
fleshy muscle, whose fibres pass transversely across the middle lhie' .^
are inserted at either extremity into the broad part of the com018'' ..
cartilage of the nostril. It is partly covered by the termination 0»
levator labii superioris proprius.                                                              J
Action.—To dilate the nostrils by approximating the internal wiWs
opposite sides.                                                                                         jj
The Dilatator Naris Superior. This muscle comprises a fetf "',)C
fasciculi which arise from the projecting edge of the septum nasi » i
side of the nasal peak, and terminate in the wall of the false nosti'»>'
on the extremity of the ethmoidal (anterior) turbinated bone.
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DISSECTION OP THE HEAD AND NECK.                               179
^*'c%.—To dilate the false nostril.
^ e -Dilatator Naris Inferior. The fibres of this muscle arise from
th -16e G^e °*" t'le premaxillary an<l superior maxillary bones; and
Prd terminate m the wall of the false nostril, and on the cartilaginous
igation of the maxillary (posterior) turbinated bone.
c ion.—The same as the preceding muscle.
extr16 Zygomaticus (Plate 29) is a riband-shaped muscle, often
th le *nm- ^ extends vertically between its point of origin from
tid aC6 ol?tne masseter, behind the lower portion of the zygomatic
<= > and its insertion into the buccinator above the angle of the mouth.
tflon-~~To raise the angle of the mouth,
the t B0CCINATOR (Plate 29)- TWs muscle forms the main mass of
he- o ee*- It is not wholly exposed at present, its upper extremity
porK °°Vere<* ^y tIie masseter. It comprises a superficial and a deep
ca-ni °n' tlle former being separately described by Percivall as the
the ' ^le suPerncial portion shows a longitudinal raphe from which
In f • t"ar fibres pass forwards and backwards in apenniform manner.
alve 1 tllCSe nrjres become attached to the superior maxilla, from the
heh' ilS f°r tlle canme tooth to that for the first molar inclusive; and
the ' t0 *^e inferior maxilla opposite the interdental space between
l0llo,CatllUe and the first molar. The deep portion of the muscle is
ttiavii         narrower than the preceding. It arises from the superior
>ttrn •■ a m ^ront °f the three upper molar alveoli; from the scabrous
0f t, . 0n the same bone above the last alveolus; and from the edge
the          er*or maxilla above the last alveolus. Inferiorly the fibres of
, usole blend with the orbicularis oris at the angle of the mouth.
will k
sup v- 86en at a later sta8'e) after the removal of the masseter, the
i^f . or bllecal gland lies on the muscle at its anterior edge, while the
lll6 ,°r buccal gland lies under its posterior edge, and the mucous
Mi
ane °f the mouth lines its inner surface.
I'etr
on—when unopposed by the orbicularis oris, the muscle will
tion ■'         ate) the angle of the mouth; but otherwise, as in mastica-
te ' comPresses the cheek against the teeth and their alveoli, and
rUa ° *eep the food between the upper and the lower molars. In
the '           *^e °heeks are distended, as in blowing a wind instrument,
from t!!8Cle comPresses the volume of air and propels it as a stream
Th 6 mou1;n : hence the name, from the L. buccina, a trumpet.
alojj2' DePBB8SOB Labii Inferiors (Plate 29). This muscle is placed
its of- llinder edge of the buccinator, with which it is confounded at
ftlolju.^ fl"°m the alveolar ed8'e of the inferior maxilla above the last
4 . °th. It terminates in the texture of the lower lip.
Th 0?n ^° dePress (retract) the lower lip.
apert6 0bbi°ularis Oris (Plate 29). This muscle surrounds the
Ure of the mouth like a sphincter. It cannot be described as
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180                                THE ANATOMY OP THE HORSE.
having either origin or insertion, its fibres forming a continuous ellipse'
In both lips the fibres are intimately adherent to the skin, and they aI
partially blended with the labial insertions of some of the musdeS
already dissected.
Action.—To approximate the lips, as in the simple act of closing tiie
mouth or in prehension.
Directions.—Evert the upper lip, and wipe its exposed mucous lin111^
clean. Observe that it is studded with numerous short, tubercle-hK
papillre. Each of these is perforated by the duct of a labial mucou3
gland lying beneath the mucous membrane. Now dissect away *&
mucous membrane so as to expose these glands. At the same tluie>
there will be brought into view the following muscle :—
The Depressor Labii Superioris. Under this name, Perciv*1
describes a bundle of muscular fibres that in the human subject 1
reckoned a part of the buccinator. On each side the muscle arises fr°n
the premaxillary bone above the corner incisor and the interdeo*9
space as far as the canine tooth; and, on the other hand, its fi^re
terminate in the upper lip, blending with the orbicularis. Branches °
the infra-orbital and 7th nerves enter the lip between the outer edg
of this muscle and the lowest fibres of the buccinator.
Action.—To assist the orbicularis by depressing the upper lip.
The Palato-Labial Artery. While the upper lip is kept everte"'
dissect backwards on the middle line until this artery is found comina
forwards from the roof of the mouth by the incisor foramen. At'
point of exit it bifurcates, its branches passing right and left to anas*
mose with the superior labial artery.
Directions.—Evert the lower lip, and wipe its mucous surface cleaI'
Notice that it is smooth, with few or none of the tubercle-like pap1 ,
found on the upper lip. Dissect away the mucous membrane, which
intimately adherent to the orbicularis muscle. There arc few or n
labial mucous glands in the lower lip.
The Levator Menti. This is the name given by Percivall to
muscle of the lower lip resembling the depressor already dissected in **~
upper. Its fibres arise on each side from the inferior maxilla beiiea
the intermediate and corner incisors, and from the interdental space
far as the canine tooth. It runs downwards and backwards to tenftMia
in the so-called prominence of the chin, being there intermixed **
fibrous tissue, and confounded in front with the orbicularis oris. *
inferior labial artery enters the lip between the outer edge of the nius°
and the lower fibres of the buccinator.
Action.—To elevate the lower lip.                                                         ,
The Masseter (Plate 29). This muscle covers the vertical rannlS
the lower jaw. It has a flattened, semicircular form, and is thick a
powerful. In its anterior half the surface of the muscle is glisteni»=>
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181
DISSECTION OP THE HEAD AND NECK.
a»d tendinous, but posteriorly it is fleshy. Other strong tendinous
layers are included within the substance of the muscle, and give
attaclnnent to many of its fasciculi. The muscle arises from the
■ygotnatic ridge of the malar and superior maxillary bones, and it
>ecomes inserted into the outer surface of the vertical ramus.
■Action.—To elevate the lower jaw, and aid in mastication by bringing
le lower teeth forcibly into contact with the upper.
The Submaxillary or Facial Artery has already been dissected m
he intermaxillary space. It reaches the face by turning round the
edge of the inferior maxilla, in company with the vein of the same
naille and Stenson's duct (Plate 29). Here the artery is the most
Inferior of the three vessels, and the duct is the most superior. The
hree vessels cross the inferior maxilla at the lower edge of the masseter
mHscle, and preserve the before-mentioned relationship until they pass
J* to the buccinator. Here the vessels cross over the duct, being
^eniselves crossed superficially by the facial nerves; and passing
l6lleath the zygomatics, below the zygomatic spine, they reach the
*Urfaee of the superior maxilla, on which the artery divides into an
an9ular and a nasal branch. The angular branch detaches a twig to
'^stornose with the orbital branch of the superior dental artery, and is
^ distributed to the muscles and skin beneath the orbit. The nasal
)r«nch reaches the false nostril by passing beneath the levator labii
^Perioris aleeque nasi. The collateral branches which the submaxillary
^Je8_Off in this part of its course are the superior and inferior labial
j. 'ei'les; and unnamed cutaneous or muscular branches, of which
®e that pass to the masseter muscle are the largest.
ille Inferior Labial Artery is the largest branch. It is given off on
hh"SUrfaCe of tlle inferior maxilla. It passes beneath the depressor
' n inferioris, and descends to the lower lip, at the hinder edge of the
c°mator. At the mental foramen it anastomoses with the mental
thailcl1 of the inferior dental artery, and in the lip it anastomoses on
rn|aesial plane with the opposite vessel.
It ihe Superior Labial Artery is detached opposite the zygomatic ridge.
Passes beneath the levator labii superioris alseque nasi and the lateral
^ator of the ^^.^ and reaches the u?per Hr .u wh;on it auastomoses
h the palato-labial artery.
art Submaxillary Vein (Plate 29) runs in close company with the
Z Y' Where the vessels appear on the face, and throughout the
ZBater Part of their course, the vein is above the artery. It is formed
Qi * anmlar and a nasal branch, the first of which begins in the Iowa
yeH while the other originates beneath the skin of the false nostril,
It passes over the levator labii superioris alseque nasi to join the lust,
leceives branches corresponding to those of the artery, and, m adcli-
011' ««> alveolar and buccal veins join it at the edge of the masseter.
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182                             THE ANATOMY OP THE HORSE.
In thin-skinned, fine-bred animals the course of the vein and of lt:
angular and nasal branches is conspicuous during life.
Stenson's Duct (Plate 29), or the parotid duct, crosses the foce>
being at first between the edge of the masseter and the vein. It thel
passes forwards and upwards beneath the artery and vein, on the surface
of the buccinator ; and finally it perforates that muscle under cover <*
the zygomaticus, and opens on the inner surface of the cheek, oppoS1
the third upper molar tooth.
The Transverse Facial Artery (Plate 29) is a branch of tb
superficial temporal. Given off beneath the surface of the parow
gland, it turns round the edge of the ramus beneath the condyle, aU
at the anterior border of the gland it gives off a large masseteric branc
Having gained the face, it descends for a few inches on the surftc
of the masseter muscle, immediately below the zygomatic arch; andthei'
about midway between the temporo-maxillary joint and the orbit,
penetrates the masseter, and is distributed to it. Where the vessel ^
on the surface of the muscle, it is covered only by the thin &01
panniculus and the skin, and is conveniently placed for the taking
the pulse. Its masseteric branch at once plunges into the substance
the masseter, where it anastomoses with the maxillo-muscular arter)'
and with the posterior deep temporal by a small branch which traverse
the corono-condyloid notch.                                                                       ,
The Maxillo-Muscular Artery (Plate 29) is a collateral branch °
the external carotid. Beneath the parotid gland it bifurcates to ft"111
a pterygoid and a masseteric branch. The former passes within
ramus to reach the internal pterygoid muscle. The latter ernerg
between the ramus and the parotid gland, above the insertion of *
stylo-maxillaris, and penetrates the masseter.
Veins.—The transverse facial and maxillo-muscular veins acco
pany the arteries of the same name. The former joins the antei'1
auricular to form the superficial temporal vein, the latter empties its
into the jugular.
The 7th Nerve on the face (Plate 29). This nerve appears on tu
face a little below the articulation of the jaw, where it emerges n
beneath the parotid gland. Before its emergence it is joined by l
subzygomatic branch of the inferior maxillary division of the 5th.
nerve divides into a variable number of branches, which anastomose
the surface of the masseter and form a plexus, termed in man the 1
anserinus (from its resemblance to the foot of a goose). In this V ,
it is not possible to distinguish, among the motor fibres proper to
nerve itself, those sensory fibres derived from the subzygomatic »el
This plexus is covered by the skin and the thin facial panniculus, "
of which receive branches from it. Below the inferior edge of
masseter, branches of the plexus are continued over the submaxil' .
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183
DISSECTION OF THE HEAD AND NECK
Vessels to supply the muscles of the cheek, lips, and nostrils, as well as
tlle panniculus and skin. The largest of these branches is the most
'Ulterior, and it passes beneath the zygomatics muscle in company with
tllG superi01, labial vessels. It communicates with the infra-orbital
tterves emerging from the infra-orbital foramen, and passes with them
to the upper lip. Another branch of considerable size passes beneath
jhe retractor of the lower lip, and runs in company with the inferior
l*ial artery. It reaches the lower lip, in which it is distributed along
Nv'th the mental nerves.
The Subzygomatic Branch of the 5th nerve (Plate 31). The major
P0l'tion of this nerve joins the 7th, and is distributed with it on the
face 5 but before joining with that nerve, it detaches a branch which
Passes in company with the transverse facial vessels, and is traceable as
tar as the orbit.
The Infra-orbital Nerve (Plate 30). This, which is derived team
*he superior dental branch of the superior maxillary division of the
°tu> and is therefore sensory, emerges from the infra-orbital foramen,
,lnder cover of the ieTator labii superioris proprius muscle. Ine
dlvisions of the nerve descend beneath the levator labii superioris
al*1Ue na8i and the lateral dilator of the nostril, where they com-
milnicate with a branch of the 7th nerve, and are distributed in the
nostril and upper lip.                                                                               -, .
®irections.~The masseter muscle on one side is now to be remove. ,
and in doing this, the dissector should find the branch from the interior
^xillarv division of the 5th nerve which enters the muscle througu
Jhe corono-condyloid notch. The masseter having been removed, the
bUccmator muscle will now be fully exposed (see page 179), and tne
Sector is to examine the alveolar vein, the buccal glands, the buccal
llerve and vessels, and the interior of the cheek.
rhe Alveolar Vein. This vessel rests on the superior maxilla, along
the alveoli for the molar teeth. Inferiorly it joins the submaxillary
Veiu> and is here comparatively small. It speedily becomes ol large
S,ze> and it is continued round the upper extremity of the superio
Maxilla to reach the orbit, where it will afterwards be followed.
„ r*e Superior Buccal Gland. This consists of a string of lobules
"*** on the anterior edge of the buccinator. The string is tluokest
%»*> and thinnest below, where its lobules are placed at inter,.
^ ducts of the lobules perforate the buccinator, and will alter.
e seen opening on the cheek.                                                      , f the
r*e Buccal Artery will be found crossing the upper end
JPerior buccal knd_ It js di8tributed to the buccinator muscle ^
JJe other textures of the cheek. Its origin from the internal maxilhuy
"*«*> at the floor of the orbit, will subsequently be dissected
r»e Buccal Vein begins at the inferior edge of the masseter, where
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184                                 THE ANATOMY OP THE HOESE.
it joins the submaxillary vein. Above the cheek it is continued as t
internal maxillary vein.
Directions.—The buccinator muscle should be cut at its anter'0
edge, and turned backwards so as to expose the interior of the cheeK-
On the mucous membrane will be seen the following:—
1.  A linear series of small papillae opposite the upper molar teetfl-
Each papilla is perforated at its summit by a duct from one of *W
lobules of the superior buccal gland.
2.   A large rounded elevation opposite the third superior molar'
Stenson's duct opens on its summit.
3.   A linear series of small papilla? opposite the inferior molars. Eac
papilla is perforated by a duct from the inferior buccal gland.
The Inferior Buccal Gland will be exposed by incising the mucoi>-
membrane along the last-mentioned series of papilla?. It is conxpose
of a string of lobules included between the mucous membrane and tb
buccinator.
The Buccal Nerve will be found in close relation to the infer'01
buccal gland. It is the sensory nerve to the cheek, and is derived frolU
the inferior maxillary division of the 5th cranial nerve.
THE PTERYGO-MAXILLARY REGION AND THE REGION OF THE
GUTTURAL POUCH.
Directions.—The outer surface of the inferior maxilla having ^>e01
laid bare from the condyle to the symphysis by the removal of *llC
muscles, the dissector is to make two sections with the saw. The firs
is to be made obliquely from a point about an inch above the laS
molar tooth to the angle of the jaw; the second, close above *b
symphysis. In making the sections, the edge of the saw must be kep
parallel to the surface of the bone, in order to avoid injury to the S"
jaccnt structures. The jaw is next to be disarticulated by inserting
strong scalpel into the joint; and the scalpel is also to be passed rou*1
the coronoid process, which will be felt embedded in the temp01'
muscle, in the temporal fossa. The vertical ramus is now to be entii'6^
removed, at the same time leaving in position the parts beneath l
This is to be done by raising the bone at the angle, and cutting t'1
muscular fibres inserted into its deep face. The edge of the knife is
be kept cutting on the bone, which is at the same time to be foroif j
tilted upwards and forwards until the coronoid jirocess is torn out
the temporal muscle. The horizontal ramus is next to be folded do*
wards and outwards; and to permit this, it is only necessary to cut a11
raise slightly the mucous membrane below the molar teeth. When the
operations have been effected, the dissection will take the form of Pla
30. The vertical ramus is to be retained to show the insertion of tn
pterygoid and temporal muscles.
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DISSECTION OF THE HEAD AND NECK.                               1°5
The External Pterygoid Muscle (Plate 30) is conical in form, with
bo6 aPex below. Its fibres arise from the outer surface of the sphenoid
Qe above the entrance to the subsphenoidal canal, and from the entire
^ ® surface of the subsphenoidal process. They pass upwards and
ti Wards to be inserted into the inner aspect of the neck, or constric-
> below the condyle of the lower jaw.
10 hon—When the right and left muscles act simultaneously, the
mWer lncisors are made to protrude in front of the upper. When the
tjiUSoles °f one side act singly, the entire inferior maxilla is thrown to
tll6 °PPosite side ; and by the alternate contraction of the two muscles,
rp riturating action of the jaws and teeth is produced.
„ he Internal Pterygoid (Plate 30) is a much more powerful muscle
llean tlle preceding, from which it is separated by the inferior dental
r e aud vessels. It occupies a position on the inside of the vertical
bei US .analagous to that of the masseter on the outside, the ramus
boi*18 mcluded between the two muscles. Its fibres arise from the
hXiJ 0re8t formed by the subsphenoidal process and the palatine bone,
of th Pass backwards to be inserted into the depressed inner surface
he vertical ramus.
Ja\vd*°W'"~Tlle Prmcipal action of the muscle is to elevate the lower
alte ttec%, the two muscles acting together; but acting singly and
ate]yj they assist in producing lateral movement.
fibr 6 ^BMP0]tAL Muscle occupies the fossa of the same name. Its
Wlnf3 arise from tne Parietal, frontal, and squamous temporal bones
Orbit!ittey bound this fossa' and from the sphenoid bone above the
a(j- hiatus. They become irserted into the coronoid process and
ent part 0j tjle anter;or border of the vertical ramus,
the Cfe0,l'~~Cuiefly to elevate the lower jaw, acting in conjunction with
act; masseter and internal pterygoid. The temporals also oppose the
from11 by wllieb the external pterygoids protrude the lower incisors in
£. °f the upper.
l»nscrC^°W*'"~Emerging at the line of aPPosition of the tw0 Pteryg°id
the iJf are the inferior dental vessels and nerve, the mylo-hyoid nerve.
TliesT*11181 maxillai7 vein, and thc Ungual branch of the 5th nerve.
ijn6 are n°w to be examined.
lllaxilj Inperior Dental Artery (Plate 30) is a branch of the internal
It pa ary' detached before that vessel enters the subsphenoidal canal.
iunerSSeS 6rSt between the two pterygoid muscles, and then between the
iuferi mUscle and the bone, and enters the inferior dental canal of the
the tr°r maxilla- On examining the inner aspect of the vertical ramus,
cailal Uu°ated end of the vessel will be seen at the upper orifice of the
continued in the bone beneath the molar, canine, and
m*ntal 1t,ecth' supplying these, and detaching at the mental foramen a
branch.
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186
THE ANATOMY OF THE HOESE.
The Inferior Dental Vein (Plate 30) has a distribution simila1'
to
that of the artery which it accompanies, and it joins the intern9
maxillary vein.
The Inferior Dental Nerve (Plate 30) is a branch of the infer10
maxillary division of the 5th nerve. It accompanies the vessels in t'1
bone, supplying the teeth, and detaching sensory mental branches
the lower lip.
The Mylo-Hyoid Nerve (Plate 30) is a branch of the preceding •****!
It descends between the internal pterygoid muscle and the bone, an»
reaches the intermaxillary space. There it has already been dissecte
on the surface of the mylo-hyoid muscle, to which and the lower bell)'
the digastricus it is distributed.                                                                ,
The Lingual or Gustatory Nerve (Plate 30) is a large branch °
the inferior maxillary division of the 5th. Between the two pteryg01
muscles it is joined by the chorda tympani branch of the 7th ner* '
and it is continued between the internal pterygoid and the bono
reach the tongue. It will be followed in the dissection of that organ.
The Internal Maxillary Vein (Plate 30) lies in front of the p1
ceding nerve. It is the direct continuation of the buccal vein aire:1 }
dissected in the cheek. It will subsequently be followed to its tern1111'
tion, where it forms the jugular by union w ith the superficial tempo1'1
vein.
The Lingual Vein (Plate 30) drains blood away from the tong^
It runs in company with the gustatory nerve; and after recei'V11 e
branches from the soft palate and the pharynx, it joins the buccal ^
between the internal pterygoid muscle and the bone.
Pterygoid Vessels. The pterygoid muscles derive their blood ir°
branches of the internal maxillary or of the inferior dental art6 J
The inner muscle receives also the inner division of the maxillo-m
cular artery. The pterygoid veins join the internal maxillary vein.
Directions.—The external and internal pterygoid muscles must n
be removed. In cutting away the outer muscle, the thick buccal no
will be found passing through it near its origin, and giving branchef
the muscle. The nerve is to be preserved to show its origin. ^'
must also be taken of the internal maxillary vessels, and of the in101
maxillary nerves, which are included between the muscle and _
guttural pouch. The internal pterygoid is to be cut close to its otVS>
and taken away without severing the vessels and nerves just dissec
The pterygoid branch of the inferior maxillary division of the 5th no
will be found entering it, and an inch or two of the nerve should
preserved to show its origin. Extending along the deep aspect oi
origin of the muscle is the tensor palati muscle, and care must be tftj
not to injure it. The deep face of the internal pterygoid is relate
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187
DISSECTION OF THE HEAD AND NECK.
"ltermediate tendon of the digastricus, the larynx, and the submaxillary
glatli Besides these, it is related to Stenson's duct and the submaxillary
Vessels, which have already been dissected on its surface in the inter-
^llary space.
_ The Guttubal Pouches (Plates 31 and 32). There are two large
pities situated at the base of the skull, above the pharynx, and be-
*een the grent (styloid) cornua of the hyoid bone. Anteriorly they
ut°ud as far as the upper margin of the posterior nares, and posteriorly
''^ fai' as the atlantoaxial articulation. Inwardly the mucous lining of
(le two pouches forms a mesial partition. Outwardly each pouch has
^"tterous relations, the chief of which are as follows:—Behind the
=™*t coniu the pouch is covered by the submaxillary gland, and the
styj°;maxillaris, digastricus (upper belly), stylo-hyoid, and occipito-
yloid muscles, and is crossed by the external carotid, internal carotid,
JT1 occipital arteries, and by the 9th, 10th, 11th, 12th, and sympa-
letlc nerves. In front of the great cornu the pouch is covered by the
r*°tid gland and the internal pterygoid muscle, and is crossed by the
ei'llal maxillary vessels, the chorda tympani nerve, and the inferior
^axiUary division of the 5th nerve. The pouch is lined by mucous
tu]*branc continuous with that of the Eustachian tube, and by that
„ e it communicates with the pharynx and the middle ear. Normally
j, e Pouch contains air, which it receives from the pharynx through the
iafl Chian tube- when the mucous linin8' of the Pouch becomes
orifilmed' pus tends to accumulate in the cavity, since the Eustachian
pL Ce> by which the inflammatory products might escape into the
ura*yni, is, in the ordinary position of the head, situated towards the
£?r ?ai't of the pouch.
Yle Eustachian Tube (Plate 32). This is a fibro-cartilaginous tube
ree or four incnes m length, extending downwards from the petrous
P°ral bone to the pharynx. At its upper extremity the tube com-
tem
at
lucates with the cavity of the middle ear (in the temporal bone), and
s lower extrpi-nitv it. miens into the nharvnx bv a slit-like aper-
tUro
3T extremity it ope
j, "• * or nearly the whole
of its extent the tube is slit open along
°nter side, and is thus in free communication with the guttural
Pouch,
The tube is lined by mucous membrane, and through its agency
ear^ admitted from the pharynx to the guttural pouch and the middle
diJh° Inte*Nax Maxillaby Abteey (Plates 31 and 32) results from the
of l'1011 of the external carotid on the outer surface of the great cormi
Whi T hy°id bone- ^ is much larger than the superficial temporal,
°nte « the 0ther terminal branch of the external carotid. In passing to
the fi Subsphenoidal canal, it describes a double or sigmoid curve
arte"rSt C0,lvex downwards, the second upwards. In this course tlie
6ry » Placed within the articulation of the jaw and the external
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188
THE ANATOMY OF THE HORSE.
pterygoid muscle, and rests successively on the guttural pouch and the
tensor palati muscle. It is crossed superficially by the inferior dental
and lingual nerves, and deeply by the chorda tympani. It detaches the
following collateral branches :—
1.   The Inferior Dental Artery, a large branch arising from the convesit)
of the first curve. It has already been seen entering the inferior dental
canal.
2.   The Tympanic Artery, the smallest of the branches here given on,
is detached at nearly the same point as the preceding, but from the
opposite side of the parent vessel. It lies beside the chorda tympa111
nerve, and penetrates the petrous temporal bone to be distributed in the
tympanum, or middle ear.
3.   The Great Meningeal (spheno-spinous) Artery, a vessel of variable
volume detached from the upper side of the parent artery beneath the
inferior maxillary nerve, and entering the cranial cavity by the foramen
lacerum basis cranii.
f
4.   The Pterygoid Arteries, two or three, arising from the concavity 0J
the second curve.
5.   The Posterior Deep Temporal Artery, given off from the upper side
of the parent trunk about half an inch befou it enters the subsphei1"
oidal canal. It enters the temporal muscle by passing in front of the
condyle of the temporal articular surface, and it communicates with the
masseteric division of the transverse facial artery by a slender branch
which passes through the corono-condyloid notch.
The Internal Maxillary Vein passes between the two pterygoid
muscles ; and crossing below the articulation of the jaw, it joins the
superficial temporal vein to form the jugular. The junction takes plac"
in the substance of the parotid, a few lobules of the gland being inter'
posed between it and the termination of the external carotid artery.
The Inferior Maxillary Division of the 5th Nerve (Plate 31/-
This is a thick cord containing both sensoiy and motor filaments whicB
issues from the cranium by the forepart of the foramen lacerum baSw
cranii. It passes obliquely downwards and backwards on the wall of to ■
guttural pouch, in front of the temporo-hyoideal articulation, and divided
about an inch below its point of exit, into two branches of nearly equ*1
size—the inferior dental and lingual nerves. As it issues from t»
foramen, it gives off the following branches :—
1.   The Subzygomatic Nerve is detached from the posterior aspect o
the trunk. It turns round behind the articulation of the iaw, and h&
already been seen to join the 7th nerve, which it accompanies in J
distribution on the face. It sends a branch in company with the trans
verse facial vessels.
2.   The Nerve to the Internal Pterygoid arises from the antero-infei-1
aspect of the trunk.
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189
DISSECTION OF THE HEAD AND NECK.
"• The Nerve to the Masseter and Temporal Muscles. This is given off
rotn the front of the trunk. It detaches branches to the temporal
"Uscle, and is then continued through the corono-condyloid notch to
end in the masseter.
*• The Buccal Nerve is a larger branch than any of the foregoing.
^ arises at the same point as the preceding nerve, and passing through
fle external pterygoid muscle, to which and the temporal muscle it
uPplies branches, it is continued as a sensory nerve to the cheek.
The Inferior Dental Nerve is the larger of the two branches into
v luch the trunk of the inferior maxillary nerve divides. Under cover of
ae external pterygoid muscle, it crosses over the internal maxillary artery,
n company with the lingual nerve, which lies in front of it. It then
lasses in between the two pterygoid muscles, where it places itself in
°nt of the inferior dental vessels. It has already been seen issuing
°tti between the muscles to gain the inferior dental canal by passing
Ween the inner muscle and the bone.
I he Mylohyoid Nerve is detached from the posterior edge of the fore-
b°mg nerve at its point of formation. It crosses the inferior dental
es*els between the two pterygoid muscles, and then descends between
^ inner muscle and the bone. It has already been traced to the
gastric (lower belly) and mylo-hyoid muscles.
. -*-he Lingual or Gustatory Nerve is only slightly smaller than the
ei'ior dental. It lies immediately in front of that nerve as far as the
J Sterior edge of the external pterygoid muscle, where it passes forwards
etween the internal pterygoid and the bone to reach the tongue. It is
. SeHsory branch; and, while between the two muscles, it is joined by
fte chorda tympani.
-*-he Chorda Tympani Nerve. This is a branch detached from the
II    nerve in the aqueduct of Fallopius. It passes across the
J'ftipanum, or middle ear, and issues from the petrous temporal bone
•> the styloid foramen. It then descends on the guttural pouch; and
°ssing beneath the internal maxillary artery and the trunk of the
ei'ior dental nerve, it joins the lingual nerve between the two
infyg0id muscles.
■ J- he Otic Ganglion. This ganglion is at best minute, and sometimes
Sejit, or at least not well defined. To examine it well, it is neces-
. y to make a special preparation, exposing the inner aspect of the
, eilor maxillary nerve at its point of emergence from the cranium.
e ganglion is placed on the inner side of the before-mentioned nervc-
lnk near the origin of its buccal branch. Its afferent branches arc :
\ ; twigs from the buccal branch of the inferior maxillary nerve ; (2) the
, superficial petrosal nerve from the 7th • (3) twigs from the sympa-
tic branches that accompany the internal maxillary artery. It
Pphes efferent branches to: (1) the tensor palati muscle; (2)
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190                                 THE ANATOMY OF THE HORSE.
the tensor tympani; (3) the pterygoid muscles; (4) the Eustachian
tube.
The Submaxillary Gland (Plates 27 and 31) is, in point of size, t»e
second of the salivary glands. It is elongated, with blunt, rounded extrenH"
ties; and it is curved, the concavity being directed upwards and forward8-
Its outer surface is related to the tendon of the sterno-maxillaris muscle,
to the fibrous band connecting that tendon to the mastoid insertion ot
the mastoido-humeralis, and to the internal pterygoid. The stern0"
maxillaris tendon and the above-mentioned fibrous band separate it ft"0111
the overlying parotid. Its inner surface is related to the guttu*9
pouch, the larynx, and the thyro-hyoid muscle; and it conceals abo'v'-
the larynx the terminal part of the common carotid artery, and the
10th and 11th nerves. Its posterior border is, about its centre, «eaI
or in contact with the thyroid gland; and below that point it Js
margined by the submaxillary vein. Its anterior border is relate*
above to the stylo-maxillaris muscle, and for the rest, of its extent itlS
traversed by Wharton's duct—the excretory duct of the gland. The
superior extremity of the gland is loosely maintained beneath the wiSe
of the atlas; the inferior extremity is situated within the intermaxilla1')'
space, and is crossed outwardly by the submaxillary artery.
Wharton's Duct is formed by the union of small branches which
emanate from the gland structure along its anterior border. It descend^
along that border, and at the lower extremity of the gland it crosses to
the inner side of the submaxillary artery, and is continued beneath the
tongue, where it will subsequently be followed in its course towards the
barb.
The Digastricus (Plate 31). The upper belly of this muscle h88
already been seen to arise from the styloid process of the occipital bo»c>
where it is confounded with the stylo-maxillaris muscle. It is succeeded
by an intermediate tendon, which plays through a perforation in the
tendon of the stylo-hyoid muscle, in front of which it joins the lowei
belly. The lower belly has already been dissected in the inteimaxiUaJv
space, where it is inserted by tendinous slips into the posterior border of
the inferior maxilla, above the symphysis.
Action.—To depress the lower jaw.
The Stylo-hyoid (Plate 31). This muscle arises from the extreme
upper part of the hinder edge of the great cornu. Its inferior tendon lS
perforated for the passage of the digastricus, and is inserted into the base
of the thyroid cornu of the hyoid bone. The external carotid emei'g'cb
between the belly of the muscle and the great cornu.
Action.—It carries the base of the tongue and the larynx upwards and
backwards, by flexing the joint between the great and small cornua, auo-
the joint between the small cornu and the body.
Directions.—Pin the lower extremity of the submaxillary gland aii°-
-ocr page 259-
191
DISSECTION OF THE HEAD AND NECK.
Wharton's duct in position, and then remove the remainder of the gland
together with the stylo-hyoid, the digastricus, and the remains of the
stylo-niaxillaris. This will expose the posterior part of the guttural
Pouch, the pharynx, the larynx, the pharyngeal lymphatic glands, the
uPper part of the external carotid artery (and its terminal branches—the
external and internal carotids, and the occipital), the superior cervical
ganglion of the sympathetic (and the upper part of the cervical cord),
the first parts of the 9th, 10th, 11th, and 12th cranial nerves, and the
inferior primary branch of the 1st cervical nerve.
_ Pharyngeal Lymphatic Glands. These form an elongated cluster
S1tuated at the upper part of the side of the pharynx. They are placed
0li the course of all the lymphatic vessels of the head.
The Common Carotid Aktery (Plate 32) divides above the cricoid
cartilage of the larynx, and under cover of the submaxillary gland
°1- the stylo-maxillaris muscle, into three branches, viz., external
Cai'otid, internal carotid, and occipital arteries. The first of these con-
tinues the direction of the parent trunk, and is much larger than either
°t the others, which are of nearly equal size.
The Occipital Artery (Plate 32), The root of this vessel is external
to, and slightly in advance of, the root of the internal carotid. It passes
Upwards and slightly forwards over the anterior straight muscles of the
head, and enters the antero-external foramen of the atlas. In the
groove which connects this and the antero-internal foramen, the artery
'uvides into occipito-muscular, and cerebro-spinal branches. Before its
Passage through the foramen the vessel detaches three collateral
Ranches, viz., prevertebral, mastoid, and retrograde or anastomotic
arteries.
*■• The Prevertebral Artery.—This is the first and most slender of the
three branches. Passing upwards and forwards, it supplies muscular
Swigs to the anterior straight muscles of the head, and meningeal twigs
that pass into the cranium by the foramen lacerum basis cranii and the
condyloid foramen.
-'■ The Mastoid Artery, a considerable vessel, is detached about onc-
ftll'o. of an inch above the preceding. It crosses over the edge of the
lectus capitis lateralis, and ascends behind the styloid process of the
°CClPital bone, where it has already been exposed (page 170).
"• The Retrograde or Anastomotic Branch varies considerably in
°h-irae. Arising between the obliquns capitis superior and the rectus
capitis lateralis, beneath the wing of the atlas, it passes backwards
hrougli the posterior alar foramen, and anastomoses with the termina-
tlon of the vertebral artery.
-the Internal Carotid Artery (Plate 32) is a long vessel which is
ne main source of supply to the brain. It passes obliquely upwards
nd forwards, supported by the membrane of the guttural pouch, and
-ocr page 260-
192
THE ANATOMY OF THE HORSE.
enters the cranium by the foramen lacerum basis cranii. Its mode of
entrance and its distribution to the brain will be examined at a later
stage.
The External Carotid Artery (Plates 31 and 32). This vessel may,
for the purposes of description, be divided into two portions. The first
portion, comprising two-thirds of the artery, is included between the gut-
tural pouch inwardly, and the stylo-maxillaris, digastric, and stylo-hyoid
muscles outwardly. It emerges from beneath the last-named muscle,
and joins the second portion by passing between the muscle and the
posterior edge of the great cornu of the hyoid bone. It is crossed
inwardly by the 9th, and outwardly by the 12th nerve. The second
portion passes obliquely upwards and forwards on the great cornu, at
the upper part of which, and under cover of the parotid gland, it divides
into the superficial temporal and internal maxillary arteries. The
collateral branches of the vessel are: the submaxillary, maxillo-muscular,
and posterior auricular arteries. The last two spring from the second
portion of the artery, and have already been dissected.
The Submaxillary or Facial Artery is detached from the
external carotid beneath the digastric muscle. It is a vessel of large
calibre, being nearly equal to the parent vessel beyond its point of
detachment. It descends over the pharynx, being nearly parallel to the
posterior edge of the great cornu, and about an inch behind it, At first
under cover of the digastric and stylo-hyoid muscles, it then turns
round the anterior edge and outer surface of the stylo-hyoid where the
intermediate tendon of the digastric plays through it. Continuing its
course, it crosses Wharton's duct and the lower extremity of the sub-
maxillary gland to the outer side, and appears in the intermaxillary
space between the internal pterygoid and subscapulo-hyoid muscles-
Its further course in the intermaxillary space and on the face has already
been followed. Behind the great cornu the artery is in company with
the 12th nerve. From its origin to the extremity of the submaxillary
gland, it detaches three collateral branches, viz., the pharyngeal, lingual,
and submental arteries.
1.   The Pharyngeal Artery is a small branch given off at the anterior
edge of the stylo-hyoid or under cover of that muscle. It reaches the
pharynx by passing beneath the great cornu, crossing either outwardly
or inwardly the 9th nerve. It is distributed to the pharynx, giving also
a forward branch to the soft palate.
2.   The Lingual Artery, whose volume is about equal to that of the
distal part of the parent trunk, has its point of origin over the tip ot
the thyroid cornu. It descends on the cerato-hyoid muscle, and reaches
the tongue by passing beneath the great hyo-glossus muscle. It is the
main vessel of supply to the tongue, and will be followed in the dissec-
tion of that organ.
-ocr page 261-
193
DISSECTION OF THE HEAD AND NECK.
"• The Submental Artery is detached at the extremity of the sub-
maxillary gland, as the parent artery appears in the intermaxillary
Pace. It has already been seen in the dissection of that space.
■I he Occipital Vein. This vein descends from beneath the wing of
. e atlas, in company with the artery of the same name; and joins the
° Sular at the posterior edge of the parotid gland, a little above the
rmination of the submaxillary vein. It is formed by the union of
aiiches corresponding to those of the artery; and, besides these, it
ceives a branch which comes from the spinal canal by traversing the
. 8 °f the atlas, beneath the wing, and another from the subsphenoidal
lnus. This last will be exposed at a later stage.
ihe 9th Cranial Nerve, also called the Glosso-Pharyngeal (Plate
), issues from the cranium by the posterior part of the foramen lacerum
8ls cranii. It descends on the guttural pouch, behind the great cornu
the hyoid bone, and under cover of the digastric and stylo-hyoid
Uscles; and it here crosses to the inner side of the external carotid
. ei7- Reaching the pharynx, it continues to descend either close
und the posterior edge of the great cornu or under cover of it; and
re it is crossed by the pharyngeal artery, which may pass either over
Under it. It next passes within the articulation of the great and
nail cornua to reach the root of the tongue, where its terminal branches
*« be seen at a later stage. It gives off the following branches, the
st °f which will not now be seen :—
/• The Nerve of Jacobson, given off from Andersen's ganglion—a
mite ganglion placed on the nerve where it issues from the cranium,
cobson's nerve enters a minute foramen in the petrous temporal bone,
a is distributed to the tympanum.
*• -Branches of communication with the superior cervical ganglion of
lle sympathetic.
■ -4 Branch to the Carotid Plexus.
,, ' -4 Pharyngeal branch, which is given off at or near the point where
nerve crosses the external carotid. It is as large as the glossal
trauation of the trunk, and it passes on to the wall of the pharynx,
ma the stylo-pharyngeus muscle.
. * -^ Branch to the Stylo-pharyngeus muscle.—This may be detached
er before or after the preceding branch. It enters the outer side of
the muscle.
Tt
le 12TH Cranial Nerve, called also the Hypoglossal (Plate
)■> leaves the cranium by the condyloid foramen. It passes through
angle of separation of the 10th and 11th nerves, and descends on
e guttural pouch, crossing to the outer side of the external carotid at
near the origin of the submaxillary artery. It next crosses the
' i X m company with the submaxillary artery, and passes under the
e e formed by that vessel and its lingual branch. It is continued to
-ocr page 262-
194                                THE ANATOMY OF THE HORSE.
the muscles of the tongue. Where the nerve lies on the guttural pouchi
it is covered by the stylo-maxillaris, digastric, and stylo-hyoid muscles,
and below that point it is covered by the internal pterygoid muscle.
On the pharynx the hypoglossal is joined by a considerable twig ft'oni
the inferior primary branch of the 1st spinal nerve. On the guttura
pouch it constantly communicates with the superior cervical ganglion o
the sympathetic. It has no other branches until it reaches the tongue-
The 10th Cranial Nerve, also termed the Vagus or Pneumogastri0
(Plate 32), issues from the cranium by the extreme posterior part of the
foramen lacerum basis cranii. For about one inch and a half of J®
course it forms a common cord with the 11th nerve, which issues at tft
same point. The two nerves then separate (the 12th nerve passing
through the angle), and the vagus passes downwards and backwards 0*
the guttural pouch. It passes over the internal carotid artery, a11
under the occipital; and above the first part of the trachea it meets ttw
cervical cord of the sympathetic, the two nerves then uniting to form a
common cord, which applies itself to the upper side of the common
carotid artery, and descends with it in the neck. Between the foramen
lacerum and the point where the nerve joins the sympathetic, it detaches
the following branches :—
1.   Branches of Communication with the .-.superior cervical ganglion.
2.   A Pharyngeal Branch is detached near the point where the vagus
passes under the occipital artery. It passes to the inner side of the
external carotid artery, and reaches the pharynx. There it unites with
the sympathetic and the pharyngeal branch of the 9th, forming a plex«s
from which branches pass to the constrictors and mucous membrane oI
the pharynx, and to the first part of the oesophagus.
3.   The Superior Laryngeal Nerve is given off near the termination 0l
the common carotid artery; and crossing beneath the external carotid
or the termination of the common carotid, it passes over the pharynx t°
penetrate the thyroid cartilage at the anterior edge of the thyi'0"
pharyngeus muscle. Within the larynx, as will afterwards be learned, *"
is distributed to the mucous membrane ; and also gives branches to the
pharynx, oesophagus, and root of the tongue. Near its origin it detaches
an external laryngeal branch, which passes to the crico-thyroid and cric°"
pharyngeus muscles.
The trunk of the vagus is sometimes distinctly gangliform at the
point of detachment of its superior laryngeal branch. This is tnC
ganglion of the trunk of human anatomy.
The 11th Cranial Nerve, called also the Spinal Accessory NekvB,
(Plate 32), issues from the cranium by the posterior part of the foranie11
lacerum, in company with the vagus. For the space of about one ino'1
and a half it forms a common cord with that nerve. It then PiirtS
company with the vagus, and passes backwards at the edge of the rectus
-ocr page 263-
195
DISSECTION OP THE HEAD AND NECK.
capitis anticus major muscle, where it is crossed superficially by the
0c«pital artery. It then turns round the wing of the atlas at its most
Prominent point; and passes beneath the mastoido-humeralis muscle,
crossing the branches of the 2nd spinal nerve. Before it disappears
"eneath the mastoido-humeralis, it communicates with the superior
cervical ganglion, and gives a branch to the sterno-maxillaris muscle.
ts distribution in the neck has already been followed.
The Sympathetic Nervb (Plate 32). The initial part of the cervical
ord is here seen passing back from the superior cervical ganglion.
■^tter a course of a few inches it places itself beside the vagus, and forms
a common cord with it.
"he Superior Cervical Ganglion is placed on the guttural pouch,
°ove the internal carotid artery. It is about half an inch in length,
Usiform in shape, and of a reddish-grey colour. Below it tapers into
J he cervical cord, and above it tapers into the ascending offsets with the
eternal carotid artery. Connecting branches unite the ganglion with
the 1st spinal nerve, and with the last four cranial nerves. Communi-
ations with some of the other cranial nerves are also established through
the carotid offsets of the ganglion. The distributory branches from the
e&Dglion pass to the adjoining vessels and the pharynx. Of the former
Set; two branches accompany the internal carotid into the skull, and form
the carotid and cavernous plexuses. Other branches follow the external
earotid, and are continued on the branches of that artery.
The 1st Cervical Nerve. The inferior primary branch of this
1erve descends through the antero-external foramen of the atlas, and
' Ppears in company with the occipital vessels, between the rectus capitis
ateralis and the obliquus capitis superior. It passes towards the upper
xtremity of the trachea, and splits into branches that enter the
crminal parts of the subscapulo-hyoid, sterno-hyoid, and sterno-
hyoid muscles. Beneath the atlas it gives branches to the anterior
* 1(r lateral straight muscles of the head; and beyond that point it
«ashes a branch which supplies the thyro-hyoid muscle, and gives a
*Jg to join the hypoglossal nerve. It sends a communicating branch
the superior cervical ganglion of the sympathetic.
THE TONGUE.
Erections.—With the cavity of the mouth exposed as in Plate 30,
y portions of food found in the cavity should be removed, and the
Uc°us membrane made clean. By moving the tongue about, the
blowing points will be observed.
| he inferior portion of the tongue lies free on the floor of mouth, from
u°h it can readily be drawn out. This part is two-sided, being flat-
bed from before to behind, and rounded at its extremity like a spatula.
8 superior portion, on the other hand, cannot be displaced, and is
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196                                 THE ANATOMY OF THE HOUSE.
thick and of a three-sided form. The entire organ is invested by the
mucous membrane of the mouth, which, in passing on to the tongue,
forms certain folds, or doublings. Thus, if the free portion of the tongue
be raised from its position on the floor of the mouth, there will be seen
on the middle line a double fold of mucous membrane termed the frcenum
Ungues. At the extreme upper part of the mouth, again, the mucous mem-
brane, in passing between the root of the tongue and the soft palate,
forms on each side a fold termed the anterior pillar of the fauces.
The mucous membrane of the tongue has its surface raised into the
form of papilla! of which there are three varieties :—
1.   The Filiform Papilla; are the most numerous, and are found all
over the tongue. In shape they are conical, having a tapering summit
either simple or bearing secondary papillae. They are largest on the
upper half of the dorsum (anterior or upper surface), to which the)'
give a distinct pile.
2.   The Fungiform Papilla; are mushroom-shaped, being expanded at
the summit, which bears secondary papilla). They are scattered along
the dorsum and sides of the tongue, being most numerous in its middle
portion.
3.   The Cireumvallate Papillw are generally two in number, and are
placed on the dorsum, one on each side of the middle line, about five
inches from the epiglottis. Sometimes there is a third and smaller
papilla, placed on the middle line, about three-quarters of an inch above
the other two. Each is isolated by a circular trench, and is terminated
by a flat summit, which is level with the surrounding surface, and
bears numerous secondary papillae. They contain the peculiar gustatory
bodies, to which fibres of the glossopharyngeal nerve are distributed.
The Sublingual Ridge.—This is a longitudinal elevation of the mucous
membrane at the floor of the mouth, on each side of the fixed portion 0*
the tongue. It is caused by the underlying sublingual salivary gland,
whose ducts open on the summits of little tubercles which stud the
ridge.
The Barbs.—These are two flattened, leaf-like papillae situated on the
inferior part of the floor of the mouth, one on each side of the frsenum
linguae. Wharton's duct—the duct of the submaxillary gland—discharges
itself by a minute opening on the summit of the barb.
Structure of the Tongue. The tongue possesses a mucous covering;
a collection of mucous glands, a median fibrous cord, muscles, nerve°>
and connective-tissue.
Mucous Membrane of the Tongue.—This has already been partly notice"-
Like the rest of the lining membrane of the mouth, it has a stratifie
squamous epithelium. It is intimately adherent to the subjacent structures-
It is thickest on the dorsum of the tongue, where it is harsh and wrinkle"-
On the sides and posterior surface of the tongue it is thin and smooth-
-ocr page 265-
197
DISSECTION OP THE HEAD AND NECK.
The Lingual Fibrous Cord.—This is a fibrous cord extending along
the middle line of the dorsum of the tongue, immediately beneath the
mucous membrane. With a sharp scalpel incise the tongue along this
lne to the depth of half an inch or more, beginning the incision be-
nind the circumvallate papillee, and terminating it in the free portion of
the tongue. This will expose the cord in its entire length. It is a little
ess in thickness than a goose quill. It begins between the two large
circumvallate papillse, and it terminates towards the junction of the free
"- nd the fixed portion of the tongue, being about seven inches in length.
Lingual Glands.—These are aggregated as a thick layer under the
RHicous membrane at the upper part of the dorsum. The mucus which
hey secrete coats the bolus of food as it passes through the fauces. They
are of the racemose type, and their ducts open on little tubercles of the
ttiucous membrane.
■Directions.—The mucous membrane is to be raised from the sublingual
gland and the sides of the tongue. It is convenient to describe the
gland here, although it is not a part of the tongue.
The Sublingual Gland (Plate 30). This, the smallest of the
ahvary glands, is placed at the floor of the mouth, and at the side of,
ather than under, the tongue. It extends from the level of the 5th
Qlolar tooth to the symphysis. It is in contact outwardly with the
^ylo-hyoid muscle. Inwardly it is related to the stylo-glossus, genio-
glossus, and genio-hyoideus muscles, to Wharton's duct, and to the lingual
Serves. Its poster ior border is included between the mylo-hyoid and the
senio-hyoid muscles, and is related interiorly to the submental artery.
ts anterior border projects the mucous membrane at the side of the
°ngue, so as to form the sublingual ridge. The upper extremity is
elated to the lingual nerve and vein. It is a compound racemose gland,
' nd it discharges its secretion by from fifteen to twenty ducts—the ducts
J Rivinius—which perforate the little tubercles on the sublingual ridge.
directions.—The gland is to be carefully excised without injury to
vbarton's duct or the adjacent vessels and nerves. It will be observed
0 receive a nerve from the lingual branch of the 5th, while its vessels
1 re branches of the submental artery and vein.
Wharton's Duct (Plates 30 and 31) is the excretory canal of the sub-
axulary gland. Leaving the lower extremity of the gland, where it is
°ssed outwardly by the submaxillary artery, it passes between the
yio-hyoideug outwardly, and the great hyo-glossus and the stylo-glossus
scleg inwardly, its position here being immediately behind the body
the hyoid. A little in advance of the superior extremity of the
ningual gland, it passes to its inner side, and is continued downwards
Ween the gland and the genio-glossus muscle. Finally, it opens on
e summit of the flattened papilla, or barb, at the side of the frsenum
gll£e. As the duct passes to the inner side of the sublingual gland,
-ocr page 266-
198
THE AN ATOM V OF THE IIOBSE.
a branch of the lingual nerve turns round it. The duct will be readu)
recognised and distinguished from a blood-vessel by its slender ana
uniform calibre, and by its clear contents.
The Lingual or Gustatory Nerve is a branch of the 5th. It contains
here, however, not only its own proper fibres, but also fibres derived from
the 7th through the chorda tympani, which joins it in the first part
of its course. At the root of the tongue it passes between the mylo-
hyoideus and the stylo-glossus and great hyo-glossus muscles, until •
passes to the inner side of the sublingual gland. There it turns
forwards between the muscles, and is continued in a flexuou8
manner, giving off branches that are distributed to the mucous mem-
brane of the tongue in its lower two-thirds. At the base of the
tongue it detaches a few filaments to the mucous membrane there, to
Wharton's duct and the submaxillary gland, and a larger branch for tb«
sublingual gland and the adjacent mucous membrane.
The Hypoglossal (12th) Nerve (Plate 30) will be found at the base
of the tongue, in front of Wharton's duct, where it is included between
the mylo-hyoid and great hyo-glossus muscles. Passing to the innei
side of the sublingual gland, it comes into relation with the lingua1
nerve, and divides. The branches of the hypoglossal are motor to the
muscles of the tongue.
The Submental Artery. This vessel, a branch of the submaxillar)'"
has already been seen in the dissection of the intermaxillary space. 1*
leaves the space by passing forwards through the mylo-hyoid muscle
and extends along the posterior border of the sublingual gland, int0
which, and the muscles, it throws branches. It extends beyond the
lower extremity of the gland, and terminates in small branches to the
mucous membrane.
The Submental Vein. This is relatively larger than the artery)
which it accompanies.
The Lingual Vein (Plate 30). This vessel will be found at the
upper part of the tongue, in company with the gustatory nerve,
receives branches from the soft palate and pharynx, and joins the bucca
vein.
The lingual artery (which runs its course separate from the vein o
the same name) and the 9th nerve cannot be followed until some of tn
muscles have been dissected. Plate 31 will serve as a guide in tn
isolation of these muscles.
c
The Mylo-hyoid Muscle has already been seen in the dissection o
Tt
the intermaxillary space, and it is now seen on its opposite aspect
is described at page 171.
The Stylo-glossus. (Hyo-glossus longus of Percivall). (Plate 31). Th'&
is a long, riband-shaped muscle, arising by a thin aponeurotic tendo11
from the outer surface of the great cornu of the hvoid bone near «*
-ocr page 267-
DISSECTION OF THE HEAD AND NECK.                              199
ower extremity. It extends along the side of the tongue to near its
P> where its fibres are confounded on the middle line with those of the
opposite muscle.
■Action.—To retract the tongue, and at the same time to incline it
laterally if only one muscle acts.
"he Great Hyo-glossus (Hyo-glossus brevis of Percivall) (Plate 31).
0 expose this muscle fully, the stylo-glossus should be cut near its
l§m and reflected. The great hyo-glossus arises from the lateral
aspect of the glossal process, body, and thyroid cornu of the hyoid bone.
^8 fibres extend obliquely forwards and downwards across the side of
e fixed portion of the tongue, and turn inwards on reaching the
cl°rsum.
■Action.—To retract and depress the tongue.
-directions.—Incise the origin of the foregoing muscle, and raise it
°r wards after the manner of Plate 32. This will expose more fully the
"er muscles of the tongue, and also the lingual artery and the 9th
nerve.
^he Middle Hyo-glossus Muscle* (Plate 32) arises from the front of
e articulation between the great and the small cornu of the hyoid bone.
11 Passing downwards beneath the great hyo-glossus it crosses over the
Z11gual artery. Its fibres are confounded in front with those of the
P^lato-glossus.
■Action.—It is a feeble retractor of the tongue.
the Palato-glossus (Plate 32). This is a small, thin muscle arising
ror>i the edge of the soft palate. It passes downwards beneath the
»ieat hyo-glossus and over the lingual artery, and reaches the root of the
tor«ue.
■Action.—To narrow the fauces.
Erections.—The next two muscles lie internal to the small cornu. To
, ,P°Se them, the middle hyo-glossus should be cut, and the intercornual
JOlllt pulled outwards.
ifle Hyoideus Transversus is peculiar in that it is an impaired
. Sc'e without a median raphe. It extends transversely across the
idle line, being attached at its extremities to the small cornua in the
°le of their extent. When relaxed it passes between its points of
achment with a curve whose concavity is directed upwards aud
Awards.
cilon-—To raise the root of the tongue.
he Small Hyo-Glossus. This is a muscle of small size arising from
lower extremity of the small cornu and from the body of the hyoid
,, ' It passes forwards over the preceding muscle and terminates in
tne root of the tongue.
ffto*su US' ai'llarently> is the muscle first described by Brtihl, in 1S50, as the middle descending stylo-
-ocr page 268-
200                                THE ANATOMY OP THE HOUSE.
Action.—To aid in retracting the tongue.
The Genio-glosstjs, or Genio-hyo-glossus (Plates 31 and 32). TW*
muscle is fan-shaped. Its origin is from a depression on the innei
surface of the horizontal ramus of the lower jaw, near the symphysis'
From this point, and from a tendon at the posterior edge of the muscle,
its fibres radiate into the tip, centre, and base of the tongue, beneatu
those of the stylo-glossus and great hyo-glossus muscles.
Action.—The upper fibres protrude the tongue by pulling downward
its base, the lower fibres retract the free portion of the tongue, an
the intermediate fibres (or the entire muscle) depress the tongue as »
whole towards the floor of the mouth.
If the dissector will raise the posterior tendinous edge of the musci^i
he will find that he has now reached the middle plane of the tongue>
which is here occupied by a quantity of connective-tissue and i!l
between the right and left genio-glossus muscles.
The Genio-hyoideus (Plates 31 and 32). This is a muscle of t'ie
hyoid bone, rather than of the tongue. It is elongated and fusiform lfl
shape, and is placed beneath the tongue, near the middle line. It ans(S
from the inner surface of the horizontal ramus, close to the symphyslS>
and passing upwards along the inner .jdge of the mylo-hyoid, '
becomes inserted into the glossal or spur process of the hyoid bone.
Action.—To pull forwards the hyoid bone.
The Lingual Artery (Plate 32). This is a large branch of the suo-
maxillary artery, and has already been seen at its origin. It passe
under cover of the great hyo-glossus, crossing the small cornu of *"
hyoid bone. In passing to the root of the tongue, it crosses
obliquely
forwards and downwards beneath the middle hyo-glossus and the pal»t0
glossus. In the body of the tongue it lies beneath the great hyo-glossuS'
and in the free portion of the tongue it is internal to the stylo-glossu •
In its course it becomes reduced in size by detaching lateral braiicheS'
and it terminates at the tip of the tongue by turning inwards a-11
anastomosing on the middle line with the vessel of the opposite side-
Like the lingual nerve, the artery is flexuous in the inferior part of the
tongue, that it may be adapted, without stretching, to the varyWs
length of the organ.
The Glosso-pharyngeal (9th) Nerve (Plate 32). The linglUl1
continuation of this nerve will be found crossing the inner side of "*
articulation between the great and small cornua of the hyoid bone t°
reach the base of the tongue. Here it divides into branches for *"
mucous membrane on the superior third of the tongue.
the hard palate (fig. 21).
The surface of the hard palate is covered by a dense niuc°u
membrane having a stratified squamous epithelium. It is traversed B*
-ocr page 269-
201
DISSECTION OF THE HEAD AND NECK.
entire length by a median raphe, and is crossed from side to side by
m eighteen to twenty curved ridges. Tiie concavity of the ridges is
irected upwards (towards the root of the tongue). The ridges are
ipest and the interspaces are narrowest at the upper part of the
• A. layer of connective-tissue with numerous veins connects the
ucous membrane to the periosteum of the bones forming the basis of
the palate.
Fig. 21.
Has;
f01 f^LATE : i. Palato-labial artery of right side; 2. Inosculation of right and left arteries,
lap Ulng a single tibial artery which passes forwards through incisor foramen ; 3. Bar of carti-
Ke Under which palato-labial artery runs.
, ne Palato-labial Artery. This vessel passes along the side of the
Palate, restina- in a groove on the bone, close to the alveoli. An
wn should be made down to the artery in this position, and it should
Uowed backwards and forwards. It is accompanied by a satellite
and nerve. The vessel is the continuation of the internal maxillary
i • J^eginning at the maxillary hiatus, it reaches the upper extremity
-ocr page 270-
202
THE ANATOMY OF THE HORSE.
of the palate by traversing the palatine canal. It descends at the side
of the palate, and at the level of the corner incisor it curves B*"
wards towards the incisor foramen, where, on the middle line, it unites
with the vessel of the opposite side. The single labial vessel resulting
from this union passes forwards through the incisor foramen to reach the
upper lip. In passing in to join its fellow at the incisor foramen, the
palato-labial artery runs under a small flexible bar of cartilage, which is
fixed to the bone by its upper extremity, while its lower extremity >s
free. Where the artery curves inwards, it detaches a branch that
passes downwards to be distributed in the palate below the level of the
incisor foramen.
Palatine Veins. Over the whole extent of the hard palate there
exists a rich network of veins in the submucous connective-tissue. This
network is drained by a large vein which accompanies the palato-labial
artery as far as the lower orifice of the palatine canal. There it parts
company with the artery, and passes along the staphyline groove, with
the staphyline artery and nerve. It joins the alveolar vein. The
variable thickness of the palate depends principally on the amount ot
blood in these veins, this being greatest in the young animal.
The Palatine Nerve is a branch of the superior maxillary division ot
the 5th. It emerges from the palatine canal along with the artery>
around which its branches interlace. It is the sensory nerve to the
hard palate.
THE SOFT PALATE, Or VELUM PENDULUM PALATI.
This is an oblique valvular curtain placed on the limit of the oral aiifl
pharyngeal cavities. The oral surface of the curtain looks downward8
and backwards, and is covered by mucous membrane continuous with that
of the hard palate. The pharyngeal surface has the opposite direction?
and its mucous covering is continuous with that of the nasal chambers-
The anterior edge is fixed at the posterior margin of the hard palate-
The lateral edges are attached on the limits of the mouth and pharynx-
The posterior edge is free, and extends across the root of the tongue, 1°
front of the epiglottis. The mucous membrane in passing between the
soft palate and the root of the tongue is raised on each side in*0
a fold, and two similar but less prominent ridges of mucous membran
extend from the soft palate to the sides of the pharynx. These are
termed respectively the anterior and the posterior pillars of the so
palate. Between them is a space which marks the situation of the tons*
in most mammals, and into which numerous mucous glands open. in
soft palate of the horse is remarkable for its large size—a fact wbi°
explains the difficulty with which the horse can expire or eject rego*?'
itated matters through the mouth.
The Isthmus of the Fauces. This is the aperture of communication
-ocr page 271-
DISSECTION OF THE HEAD AND NECK.                              203
etween the mouth and the pharynx. It is bounded in front and laterally
J the free edge of the soft palate, and by its anterior pillars. Behind
is bounded by the extreme upper part of the dorsum of the tongue.
J1 the horse, owing to the length of the soft palate, this aperture is
°sed except during the passage of solids or liquids in deglutition.
Structure of the Soft Palate. This comprises two layers of mucous
embrane, and, included between these, a layer of mucous glands, a
r°us aponeurosis, muscles, vessels, and nerves.
Mucous Membrane.—The membrane covering the oral aspect of the
U1'tain j8 directly continuous with that of the hard palate, and through
e anterior pillars it is also continuous with the mucous membrane of
le tongue. It has a thick tesselated epithelium, and shows numerous
wall papilla? perforated by the ducts of the subjacent glands. The
ucous membrane of the pharyngeal surface of the curtain is continuous
Jth that of the nasal chambers, and will be exposed in the dissection of
tue pharynx.
"tapki/line * Mucous Glands.—These form a thick granular layer which
lu be exposed by removing the mucous membrane from the oral
riace of the soft palate. The ducts of the glands open on the oral
^ace of the curtain, and the bolus of food thus gets a mucous coating
1 s 't passes through the isthmus.
■fibrous Aponeurosis.—If the glandular layer be removed, this will be
xPosed in the anterior part of the curtain. It is fixed in front to the
niai"gin of the hard palate; and behind it is continuous with the palato-
1 1arja1geugj ^0 ^h^h ft serves as a tendon of origin.
Musdes of the Soft Palate.
J-he Palato-glossus Muscle (Plate 32). This muscle has been dis-
Se°ted with the tongue (page 199).
Ihe Palato - Pharyngeus (Plato 32). This muscle will be found
fteath the glandular layer in the posterior half of the curtain. At the
Idle line it is continuous with the opposite muscle, and in front it is
"tmuous with the fibrous aponeurosis. At the side of the soft palate
ls continued to the wall of the pharynx; and passing beneath the
" °~Pharyngeus muscle, it becomes inserted into the edge of the thyroid
wlage. In the latter part of its course it need not be exposed at
Present,
Action.—To tense the velum and carry its free edge upwards towards
^pharynx.
The Tensor Palati (Plates 31 and 32). This muscle and the next
"Will 1
. he found parallel to the Eustachian tube, and on its outer side. It
ses'ln common with the levator palati, from the styloid process of the
r°us temporal bone, and from the Eustachian tube. Its terminal
conve ■ ^ sPe:l^"nSi this adjective applies to structures pertaining to the uvula, but it may
is rin* . entiy "« used to distinguish parts belonging to the soft palate of the horse, in which the uvula
iuc developed.
-ocr page 272-
204
THE ANATOMY OP THE HORSE.
tendon is reflected inwards on the hamular or pulley-like process of the
pterygoid bone, a synovial bursa intervening, and expands on the pos"
terior surface of the fibrous aponeurosis of the palate.
Action.—To tense the anterior half of the palate.
The Levator Palati (Plate 32). This muscle is placed between the
preceding and the Eustachian tube. It arises with the tensor palat1
from the styloid process and the Eustachian tube. Reaching the uppel
wall of the pharynx, it passes beneath the pterygo-pharyngeus to galia
the pharyngeal surface of the palate, where it expands.
Action.—To raise the velum towards the roof of the pharynx, and
thus to shut off the communication between the pharynx and the nasal
chambers.
The Azygos Uvulae, which in man is situated in the uvula, ^'aS
named from the belief that it was a single muscle. It consists, how-
ever, of right and left halves applied together on the middle line of the
soft palate. In order to expose them, it will be necessary to remote
from the oral surface of the velum a portion of the palato-pharyngeus
muscles on each side of the middle line. The origin of the muscle
is from the fibrous aponeurosis of the palate, and it terminates at the
free edge of the curtain.
Action.—To raise the free edge of the velum.
The Staphyline Artery is a slender vessel arising from the internal
maxillary artery, above the maxillary hiatus. It reaches the velum by
passing in the staphyline groove, along with the nerve of the same naine
and the palatine vein.
The Pharyngeal Artery- (Plate 32), a branch of the submaxillary)
crosses the pharynx, and gives its terminal branches to the soft palate.
The Veins of the soft palate enter either the lingual vein or the
palatine vein, which lies in the staphyline groove.
Nerves.—The staphyline nerve will be found with the artery, in the
groove of the same name. It comes from the superior maxillary division
of the 5th nerve. It carries not only sensory fibres to the mucous>
membrane of the palate, but also motor fibres, which come from the 7tn
nerve through the spheno-palatine ganglion, and are distributed to tne
levator and probably also the azygos uvula).
The nerve to the tensor comes from the 5th, through the otic g&Bs
lion.
THE PHARYNX, THE HYOID BONE, AND THE BASE OF THE SKULL.
Directions.—Take Plate 32 as a guide, and remove the greater porti01
of the large cornu of the hyoid bone, making the upper section with to
bone-forceps just below the point at which the external carotid arteiy
crosses the hinder edge of the cornu, and the lower a little above to
articulation of the two cornua. Preserve the 9th nerve at the poster!0
-ocr page 273-
205
DISSECTION OP THE HEAD AND NECK.
eclge of the great cormi, and the pharyngeal artery passing beneath
it.
The Palato-pharyngeus has already been in part dissected with the
Muscles of the soft palate. See page 203.
The Pterygo-pharyngeus. This muscle arises from the pterygoid pro-
cess, from which point its fibres diverge to the upper and lateral aspect
the forepart of the pharynx. At its lower edge its fibres are parallel
l0> and with difficulty separated from, those of the palato-pharyngeus.
*«8 outer surface is constantly covered by a layer of fatty elastic tissue.
The Hyo-pharyngeus, origin—thyroid or heel process of the hyoid
bone.
The Thyro-pharyngeus, origin—thyroid cartilage.
The Crico-pharyngeus, origin—cricoid cartilage.
These three muscles succeed one another in the order named, the first-
mentioned being the most anterior. They pass upwards over the side of
be pharynx, and terminate on the middle line of its roof.
The Stylo-pharyngeus. This is a thin, strap-like muscle arising
r°ua the inner surface of the great cornu of the hyoid bone near its
uPpcr extremity. It descends to the pharynx, and expands on it at the
°uter edge of the pterygo-pharyngeus.
The Small Stylo-pharyngeus. This muscle is not constant, though
*requently present. It is a delicate, worm-like muscle arising from the
•uiier surface of the great cornu, about an inch above its lower extremity.
At Passes upwards on the pharynx at the anterior edge of the hyo-
Pharyngeu8.
The Aryteno-pharyngeus. This muscle will not be seen at present.
1 ls a small slip arising from the arytenoid cartilage, and passing to the-
Pharynx at its junction with the oesophagus.
Action of the Pharyngeal Muscles.—The stylo-pharyngeus dilates the
anterior part of the pharynx for the reception of the bolus. All the
ther muscles are constrictors, grasping in succession the bolus, and
ari'ying it on to the oesophagus.
-The Cerato-hyoid (Hyoideus parvus of Percivall) (Plate 33). This
usele is most conveniently dissected at this stage, and it is therefore
ere described although not belonging to the pharynx. It is a
la^l flat muscle occupying the angle between the small and the thyroid
rnu of the hyoid bone. It crises from the posterior edge of the
Hall cornu, and from the great cornu immediately above the inter-
ornual articulation. It is inserted into the upper edge of the thyroid
ruu- The lingual artery, in crossing down to the base of the tongue,
Passes over the muscle.
■Action.—To elevate the thyroid cornu and with it the larynx,
be Pharyngeal Artery. This is a small branch of the submaxillary
lch passes beneath the great cornu, Grossing either outwardly or
-ocr page 274-
206
THE ANATOMY OP THE HOUSE.
inwardly the 9th nerve. It gives branches to the pharynx, and is con-
tinued to the soft palate.
The 9th or Glosso-phaeyngeal Nerve descends on the gotttu*'
pouch, behind the great cornu; and crossing to the inner side of the
external carotid artery, it gives off its pharyngeal branch. This turns
round behind the stylo-pharyngeus muscle, and ramifies on the pharynx,
meeting there the pharyngeal branches of the 10th and sympathetic
nerves, and forming with them the pharyngeal plexus.
Nerve to the Stylo-pharyngeus.—This is a special branch of the glosso-
pharyngeal, given off either from the trunk of the nerve or from i*s
glossal continuation. It enters the muscle at the middle of its outer
face.
The Glossal Continuation of the 9th nerve passes over the hyo-ph*1'
ryngeus and palato-pharyngeus to reach the base of the tongue; and in
its course it detaches fibres which are probably motor to the palato-
pharyngeus, hyo-pharyngeus, cerato-hyoid, and hyoideus transversus.
For the pharyngeal branches of the 10th and sympathetic nerves see
pages 194 and 195.
Directions.—The pharynx is to be opened by an incision along >**
lateral aspect, when, by hooking back the edges of the incision, a vie*
-of its interior will be obtained.
The Pharyngeal Cavity (Fig. 24, page 217) is irregularly tubular 0*
form, and presents seven openings. These are :—
1.   The Isthmus of the Fauces, already described (page 202).
2.   The Superior Nares (2), situated vertically over the isthmus, fr°lB
which they are separated by the soft palate. They are wide, gaping
orifices, with rigid bony margins.
3.   The Lower Openings of the Eustachian Tubes (2), which are situate1
on the sides of the pharynx, behind and in line with the superior nareS'
The opening has the form of a vertical slit, the outer edge of whicn
contains the cartilaginous extremity of the tube.
4.   The Upper Aperture of the Larynx.—This is placed on the floor °
the pharynx, and has the form of a pitcher-mouth. During deglutiti011
the epiglottis folds over it like a lid, but at other times it is a large
patent orifice.
5.  The (Esophageal Orifice.—At the posterior end of the pharynx, lts
cavity is continued into the lumen of the gullet. Except during tn
passage of solids or fluids, however, this orifice is not open.
Mucous Membrane.—This lines the cavity completely, and is con-
tinuous through the before-mentioned orifices with the lining membra11
of the mouth, nasal chambers, Eustachian tubes and guttural pouch6 i
larynx, and oesophagus. It has a stratified squamous epithelium, excep
in its upper and anterior part, where it is ciliated. It has man.?
mucous glands.
-ocr page 275-
DISSECTION OF THE HEAD AND NECK.                              207
■Directions.—Remove the larynx by cutting across the remaining
great cornu of the hyoid bone, and the root of the tongue in front of the
8'lossal (spur) process. Cut away the remains of the pharyngeal
muscles; and after examining the articulations of the hyoid bone, set
the larynx (and the attached hyoid) aside for future examination. (The
laryilx is described at page 224).
Temporo-hyoideal Articulation. This joint will be found intact at
tne base of the skull. It is a typical amphiarthrodial joint, the toe-like
extremity of the great cornu being joined to the hyoid process of the
Petrous temporal bone by a short rod of cartilage (about half an inch in
eilgth). The interposed cartilage is sufficiently long and flexible to
Permit a considerable range of movement. By these joints the hyoid is
su«pended to the base of the skull, and swings backwards and forwards
11 movements comparable to flexion and extension. These movements
re concerned in the actions of mastication and deglutition.
The Intercorndal Articulation. This is another amphiarthrodial
Joint, the opposed extremities of the great and the small cornu being
«Uted by intermediate cartilage. In this cartilage there is frequently
0 be found a small pea-like micleus of bone which is the representative
a third cornu—the epihyal of comparative anatomy.
-The Basi-cornual Articulation. The lower extremity of the small
j°i'nu is articulated to the body of the hyoid in a small diarthrodial
Joint provided with a capsular ligament and a synovial membrane. The
mall cornu and the thyroid cornu form at this joint an angle, and the
°vernents are extension and flexion.
■Directions.—The dissector will now be able to trace the anterior root
the occipital vein to its origin from the subsphenoidal sinus, and
xereafter the anterior and lateral straight muscles of the head are to
be dissected.
J-he Subsphenoidal Sinus (or confluent). This is a venous sinus
*j °ed at the inner edge of the foramen lacerum basis cranii. It extends
inwards (the head being vertical) for half an inch below the carotid
tcn, the sphenoid bone being there depressed for the sinus. At this
.' Penalty it terminates blindly. Traced upwards, it lies along the
er edge of the foramen lacerum (the basilar process being depressed
eath it), and it is directly continued as one of the roots of the
Jpital vein. A little above its lower extremity the sinus is pene-
ea by the internal carotid. Slit open the sinus, and observe that
communicates by an oval foramen with the cavernous sinus of the
la mater. This oval foramen has its broad end circumscribed by the
otid notch of the sphenoid, and for the remainder of its extent it
ounded by the fibrous tissue that fills up the greater part of
foramen lacerum. Through the forepart of this oval foramen
carotid arterj^ passes from the subsphenoidal to the cavernous sinus,
-ocr page 276-
208
THE ANATOMY OF THE HORSE.
the artery here being remarkable in that it is actually within a
vein.
At the inferior end of the sinus the vidian nerve will be found descend-
ing in the vidian groove to enter the canal of the same name (page 214)-
The Rectus Capitis Anticus Major. This muscle was, for the most
part of its extent, exposed in the dissection of the neck, but its tendon
of insertion remains to be examined now (page 155).
The Rectus Capitis Anticus Minor. This small muscle arises from
the lower aspect of the ring of the atlas ; and passing over the occipit0"
atlantal joint, at the side of the preceding muscle, it becomes inserted
into the basilar process of the occipital and the body of the sphenoid at
their point of articulation.
Action.—To flex the occipito-atlantal joint (to nod the head).
The Rectus Capitis Lateralis. This is another small muscle placed
beneath the occipito-atlantal joint. It arises from the atlas, external to
the origin of the preceding muscle; and passes to be inserted into the
styloid process of the occipital bone.
Action.—The same as the preceding muscle.
the orbit.
Directions.—With the saw, cut through the supraorbital process
external to the foramen, and through the zygomatic arch at either
extremity. The palpebral ligament of the upper lid is to be detached
from the orbital rim, and the tri-radiate piece of bone marked out by
these sections is to be taken away.
The orbital cavity in the skeleton is not separated from the tenipon"
fossa, but in the living animal a fibrous membrane, continuous with the
periosteum of the bones circumscribing the cavity, completes the orbit
on its outer side, and separates it from the temporal fossa. The orbit
is thus lined and completed by a fibrous membrane of a conical fori»>
termed the octdar sheath. This membrane is composed of fibrous con-
nective-tissue with some unstriped muscular fibre.
Contents of the Orbital Cavity.—These arc : the eyeball with its
muscles, the lachrymal gland, the levator palpebrse, the membrane
nictitans, vessels, nerves, and a quantity of fat. For the proper dissec-
tion of the eyeball, fresh specimens are required, and it is therefore
separately described at page 257. The lachrymal gland and the
muscles may be dissected on one side, the other being reserved for the
display of the vessels and nerves.
The Lachrymal Gland is the organ which secretes the watery fllU
that moistens the front of the eye. It is lodged above the eye, beneat'1
the supraorbital process, which is slightly depressed where it covers the
gland. In structure it is of the racemose type, resembling the salivary
glands, but being looser in texture. Its secretion is discharged by B
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209
DISSECTION OF THE HEAD AND NECK.
number of ducts which open on the ocular surface of the upper eyelid,
°lose to the temporal canthus. The gland is to be removed.
the Levator PALPEBRiE Superioris is described at page 175.
Ane Membrana Nictitans and its connection with the adipose tissue
the cavity are described at page 173.
Fig. 22.
Muscles of the Eyeball.
5. j;i Superior oblique; 2. Fibrous loop for the same ; 3. Superior rectus ; i. Internal rectus ;
of y. ternal rectus; 6. Inferior rectus ; 7, 7, 7. Fasciculi of the retractor ; 8. Cut origin of the levator
le Upper eyelid ; 9. Nerve to inferior oblique.
Muscles of the Eyeball.—These are seven in number, viz., four recti,
e retractor, and two oblique. (A third oblique muscle was described
J the late Professor Strangeways, of the Dick Veterinary College, but
s Presence is, to say the least, not constant.)
Erections.—The muscles are to be defined by detaching the eyelids
j* conjunctiva from the front of the eye, and removing the levator
1 alpebrte and the loose fat which forms a packing material between the
Uscles, Special care must be taken not to injure the fibrous arch for
e tendon of the superior oblique at the inner side of the orbit.
A he Recti. There are four of these, distinguished as the superior
- M«, the inferior rectus, the external rectus, and the internal rectus.
„, ey are placed one above, one below, and one on either side of, the eye.
ney have all a flat riband-like form, and are terminated anteriorly by
aPoneurotic tendons. They all take origin around the optic foramen,
each becomes inserted into the forepart of the sclerotic.
J-he Retractor Oculi is placed within the recti, and around the
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210                                THE ANATOMY OF THE HORSE.
optic nerve. In form it is funnel-shaped, forming a kind of sheath
the optic nerve j but frequently it is divided into four distinct fascicu11'
Fig. 23.
Muscles of the Eyeball.
4. Internal rectus :
rect«s i
Superior
1. Inferior oblique ; 2. Inferior rec
6, 0. Retractor ; 7. Nerve tc inferior oblique.
of
one lying beneath each of the recti. Its origin is from the margin
the optic foramen, and it is inserted into the sclerotic.
The Superior Oblique, or Trochlearis, has a remarkable dispositi011.
It arises at the back of the orbit, and passes inwards to a fibrous aroft
or pulley, through which it plays at the inner wall of the orbit, bel0^
the root of the supraorbital process. Having passed through this arcl1)
the muscle is directed outwards above the eyeball; and it is continue
by a tendon which passes beneath the superior rectus to be inserted int
the sclerotic on its outer side, between the insertions of the super'0
and external recti.
The Inferior Oblique. This muscle has its origin from the lad11')
mal fossa at the floor of the orbit. It passes outwards below the e)
ball, and becomes inserted into the sclerotic between the insertions
0f the
inferior and external recti.
Action of the Muscles of the Eyeball.—The superior and the inferior i'e
tus rotate the eye around a horizontal transverse axis, the former roll111"
it upwards, the latter downwards. The external and the internal x'eC
tus rotate the eye around a vertical axis, the first rolling it outward
the second inwards. The oblique muscles rotate the eye around a
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DISSECTION OF THE HEAD AND NECK.                              211
antero-posterior horizontal axis, the superior muscle elevating the nasal
angle of the pupil, while the inferior muscle depresses it. The retractor
°culi pulls the eyeball directly backwards into its cavity, and is thus, by
pressure exerted on the orbital fat, instrumental in protruding the mem-
waaa nictitans, as explained at page 173.
Ihe Ophthalmic Artery is a branch of the internal maxillary, from
which it is detached within the subsphenoidal canal. Emerging from
that canal at the back of the orbit, it is directed inwards to enter the
eternal orbital foramen; and in this course it passes between the
' uPei'ior rectus and the retractor oculi, where the latter surrounds the
Ptic nerve. By the internal orbital foramen it reaches the forepart of
he cranial cavity. It is further described at page 238. In the
1 "tfol part of its course it gives off the following branches :—
*•• The Supraorbital Artery ascends on the inner wall of the orbit to
Pass through the foramen of the same name.
"• The Lachrymal Artery, distributed to the gland and the upper
e}*elid.
"• Muscular Branches.
*■ Ciliary Branches to the eyeball.
°- The Central Artery of the Retina, which places itself in the axis of
116 optic nerve, and enters the eyeball.
"he Orbital Branch of the superior dental artery. This is a long
nc* slender branch detached from the parent vessel before it enters the
„uPei'ior dental canal. It creeps over the floor of the orbit to reach the
Ce> where it anastomoses with the submaxillary artery (Plate 29).
Veins. The structures within the orbit are drained by vessels which
nite to form the ophthalmic vein. This, after uniting with the alveolar
einj passes into the cranial cavity by the foramen lacerum orbitale.
J-he Ophthalmic Nerve is one of the three primary divisions of the
h nerve. It is a sensory nerve, and divides into the following three
Ranches, which issue in company from the foramen lacerum orbitale :-—
h The Supraorbital Nerve, accompanying the artery of the same
name.
*• The Lachrymal Nerve, to the gland, and giving off a branch which
ayerses the ocular sheath to reach the skin over the temporal fossa.
rf- The Palpebro-nasal Nerve divides into a nasal branch which
' 'c°nipanies the ophthalmic artery through the internal orbital foramen,
d a palpebral branch to the lower eyelid and inner cantlms. The
J 'aPebro-nasal nerve also furnishes the sensory filaments to the ciliary
° u8'hon, through which it supplies sensory fibres to the eyeball.
*he Orbital Branch of the superior maxillary division of the 5th
rve issues with the parent nerve from the foramen rotundum. It
J? Ses at the outer side of the ocular sheath to gain the temporal can-
Us of the eyelids, where it is distributed. It is sensory.
-ocr page 280-
212
THE ANATOMY OF THE HORSE.
The 3rd Cranial Nerve, or Motor Ocijli, issues from the foramen
laoerum orbitale, and supplies the following muscles:—the superior
internal, and inferior recti; the corresponding fasciculi of the retract01
oculi; the inferior oblique; and the levator palpebrse superioris. 1*
also gives the motor root to the ciliary ganglion, and thus supplies the
ciliary muscle and the circular fibres of the iris.
The 4th Cranial Nerve (called also the trochlear or pathetic nerve)
issues by the pathetic foramen, and is wholly distributed to the
superior oblique muscle.
The 6th Cranial Nerve, or Abducens, issues by the foramen lacerum
orbitale, and is distributed to the external rectus and the subjacent
fasciculus of the retractor oculi.
The Ciliary Ganglion, called also the ophthalmic or lenticulai
ganglion. This minute ganglion should be sought near the origin of the
nerve to the inferior oblique muscle. Find that nerve entering the
muscle, and trace it back to its origin from the motor oculi. From its
minute size, the ganglion is likely to have been disturbed in the previous
dissection; and in order to display it satisfactorily, a special dissection
is necessary. The nerves which pass to and from the ganglion may
be arranged as follows :—
Afferent Branches.—(1) A motor root from the 3rd nerve, (2) a sensory
root from the palpebro-nasal nerve, (3) a sympathetic root from the
cavernous plexus, joining the ganglion independently or (more commonly/
with the sensory root.
Efferent Branches.—These are the ciliary nerves. They pierce the
sclerotic and are distributed to the eyeball, and will be again r
efcrred to
in the dissection of that organ.
The optic foramen, through which the optic nerve issues, is one of 'A
group of foramina termed the orbital hiatus, or the orbital group oI
foramina. When the head is vertical, there lies below this, at the
posterior and inner part of the orbit, another group of foramina—the
maxillary group or hiatus. The internal maxillary artery and the
superior maxillary division of the 5th nerve pass between these t*°
groups, and in that course detach several important branches. Then
dissection is conveniently undertaken after that of the muscles, vessel8)
and nerves of the eye.
The Internal Maxillary Artery issues from the lower orifice of t»e
subsphenoidal or pterygoid canal, and descends to the maxillary hiatuSi
where it is directly continued as the palato-labial artery. While with'11
the canal it detaches the ophthalmic and anterior deep temporal artery-
After its emergence it gives off the buccal, superior dental, staphyhne>
and spheno-palatine arteries.
The Ophthalmic Artery issues from the subsphenoidal canal along
with the parent artery. It has already been followed.
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DISSECTION OF THE HEAD AND NECK.                              213
The Anterior Deep Temporal Artery passes forwards out of the
^sphenoidal canal by an un-named foramen above the edge of the
fbital hiatus. It is expended in the temporal muscle and the overlying
skin.
The Buccal Artery is detached shortly after the parent vessel
'merges from the bone. It has already been followed in its distribution
to the cheek.
ihe Superior Dental Artery is a large branch which enters the
uperior dental canal. The vessel is continued above the roots of
fte molar, incisor, and canine teeth. Before passing into the canal, it
gives off an orbital branch which passes across the floor of the orbit to
each the face. Within the canal it emits an infraorbital branch which
8&ehes the face by the infraorbital foramen.
"he Staphyline Artery is a slender branch given off from the
Posterior aspect of the internal maxillary, close to the maxillary hiatus.
courses along the staphyline groove to reach the soft palate.
The Spheno-palatine (Nasal) Artery. This vessel is of considerable
Ze> and passes at once through the spheno-palatine foramen to be
lstributed in the nasal chamber.
The Palato-labial Artery is the continuation of the internal maxil-
' ry- It passes along the palatine canal to reach the hard palate.
veins. At this point the veins have a disposition slightly different
0111 the arteries. The alveolar vein—a large vessel lying on the
' uperior maxilla in front of the molar teeth—turns round the bone and
caches the maxillary hiatus. Here it receives superior dental, palatine,
<U(1 spheno-palatine branches. It then perforates the ocular sheath,
. hin which it joins the ophthalmic vein. The opthalmic vein passes
lto the cranial cavity by the foramen lacerum orbitale, and joins the
cavemous sinus.
I he superior dental and spheno-palatine veins emerge by the same
lamina as the corresponding arteries. The palatine vein, however,
°es not issue from the palatine canal, but turns round the bone in the
staphyline groove.
"he Superior Maxillary Division of the 5th Nerve. This sensory
vision of the trifacial emerges from the cranium by the foramen
ri
. undirm, as a large round cord. In company with the internal maxil-
y artery, it descends to the maxillary hiatus, where it enters the
Perior dental canal. Within the canal it gives dental branches to the
°ts of the molar, canine, and incisor teeth, and then issues on the face
at fh •
tne infraorbital foramen. In its passage between the orbital and the
axillary hiatus, it gives off the following branches :—
•   An Orbital Branch.—See page 211.
•   The Palatine Nerve accompanies the palato-labial artery into the
Palatine canal, and is distributed to the hard palate.
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214
THE ANATOMY OF THE HORSE.
3.   The Staphyline Nerve passes by the groove of the same name to the
soft palate.
4.   The Sphenopalatine Nerve enters the foramen of the same namej
and is distributed to the nasal mucous membrane.
The Sphenopalatine (Meckel's) Ganglion. This is a small, greyish
elongated and fusiform enlargement, generally adherent to the spheno-
palatine nerve. Slender branches radiate from it, and are divided in*0
afferent and efferent filaments.
Afferent Filaments.—1. The Vidian Nerve, which enters its posterior
extremity. This is a composite nerve formed by the union of the lai'ge
superficial petrosal branch of the 7th with a sympathetic filament-
Traced upwards, it enters a minute foramen—the lower orifice of the
vidian canal. At the upper orifice of the canal it enters the sub-
sphenoidal confluent, and passes into the cavernous sinus by the foramen
lacerum basis cranii. There it separates into its petrosal and sympa-
thetic branches.
2. Short branches passing from the spheno-palatine nerve to the
posterior part of the ganglion.
The vidian nerve is supposed to combine the motor and sympathetic
roots of the ganglion; the spheno-palatine branches represent its sensory
root.
Afferent Brandies.—Some of these pass to the ocular sheath, to the
ophthalmic vessels, and to the muscles and other accessory parts of the
eye. Others join the spheno-palatine, palatine, superior dental, and
staphyline nerves. The latter it is believed derives from this source the
motor filaments which it conveys to the levator palati muscle.
THE OCCIPITO-ATLANTAL ARTICULATION.
This joint possesses two synovial sacs and an enveloping capsule, wit"
accessory fasciculi above and at each side which are sometimes describe'*
as distinct ligaments—the cruciform and styloid.
The Occipito-Atlantal Ligament is membranous, and closes the
interval between the occiput and atlas. It is attached to the occiput a
the upper and lower edges of the foramen magnum, and to the outer sid
of the condyles. Its posterior edge is fixed to the anterior border of to
atlas. The most superior fibres pass obliquely, the right and left &>T8
intercrossing. This is the so-called cruciform ligament. On each side
thickened cord-like portion passes to be inserted into the styloid proces
of the occipital bone, and these constitute the styloid ligaments.
Synovial Sacs. Each of these belongs to an occipital condyle and i
receiving cavity on the front of the atlas. On the inner side each i
related to the dura mater and the occipital continuation of the odontoi
ligament, and elsewhere they are supported by the occipito-atlaut'
ligament.
-ocr page 283-
DISSECTION OF THE HEAD AND NECK.                              215
Movements.—It is at this joint that the nodding movements of the head
are executed.
THE ATLANTO-AXIAL ARTICULATION.
-This joint possesses four ligaments and a synovial capsule.
The Inferior Atlanto-axial Ligament is riband-shaped, and stretches
elow the joint, from the forepart of the inferior ridge of the axis to the
^bercle of the atlas.
_ The Superior Atlanto-axial Ligament is exactly like the inter spinous
lament of the succeeding joints of the neck. It consists of two parallel
a-nds of yellow elastic tissue connecting the bones above the joint.
The Atlanto-axial Interannular Ligament is membranous, and
c°nnects the neural arch of the atlas with that of the axis. It represents
he ligamentum subftavnm of succeeding joints.
The Odontoid Ligament is placed at the floor of the spinal canal in
his region. To expose it, it is necessary to remove the upper part of
he ring of the atlas. It is strong, flattened, and triangular. It is
"terow behind, where it is fixed to the depressed upper surface of the
OQ-ontoid process. It is widest in front, where it is fixed to the floor of
he atlas. A thin continuation of the ligament is carried forwards on
6flch side to be attached to the edge of the foramen magnum.
Synovial Sac. This is supported by the odontoid ligament above, by
he inferior atlanto-axial ligament below, and by the interannular
%ament laterally.
Movements. It is at this joint that the movements of the head from
*lde to side are executed. In these movements the axis remains fixed,
while the atlas rotates around the odontoid process, carrying with it the
head.
temporo-maxillary articulation.
This
is the joint formed between the articular surface of the squamous
eniporal and the condyle of the inferior maxilla. An interarticular
nhro-cartilage is interposed between the osseous surfaces, and the joint
Possesses a capsular ligament and two synovial sacs.
Capsular Ligament. This envelopes the joint, being attached around
he temporal articular surface above, and around the condyle of the
°wer jaw below. Its inner surface is adherent to the interarticular
Ca-rtilage. In front and inwardly the capsule is thin and membranous,
,ht behind and on the outer side it shows thickenings which are some-
hnes described as distinct posterior and external ligaments. The first of
^lese stretches from the post-glenoid process to the inferior maxilla
elow and behind the condyle. The second is attached above to the
°wer edge of the zygomatic arch, from which it extends downwards and
backwards to be fixed to the inferior maxilla below and external to the
condyle.
-ocr page 284-
216
THE ANATOMY OF THE HORSE.
The Interarticular Fibro-cartilage should be exposed by removing
the capsular ligament on the outer side. The cartilage extends com-
pletely across the joint, which it divides into an upper and a lower cavity-
Its upper surface is a cast of the temporal articular surface, while its
lower is moulded on the condyle of the jaw.
Synovial Sacs. The upper of these belongs to the articulation
between the fibro-cartilage and the temporal articular surface; the lo^ei
to the articulation between the fibro-cartilage and the condyle.
Movements. These are — depression, elevation, protraction, retraction,
and lateral movement of the inferior maxilla.
When the jaw is depressed, as in opening the mouth, the condyles oi
both jaws are carried forwards, taking with them the fibro-cartilages,
until they lie under the condyle of the temporal articular surface ; arlCl
at the same time, the maxillary condyles move in the depression on the
under surface of the interarticular fibro-cartilage, rotating around a
transverse axis. When the lower jaw is protracted, the movement
consists principally in antero-posterior gliding between the tempora
articular surface and the interarticular cartilage ; and when the same
movement is executed alternately on opposite sides, a lateral, grinding
action is produced.
THE CAVITY OP THE NOSE (FIGS. 24 AND 25).
Directions.—Make, with the saw, an antero-posterior vertical section
of the head, a little to one or other side of the mesial plane, taking the
mesial sutures on the front of the head as a guide.
The cavity of the nose is the first segment of the air-passages, and is
thus a part of the respiratory apparatus. It is also in part devoted to
the sense of smell, the olfactory nerve being distributed over a part of
its boundary walls. It is a large tubular passage tunnelled through the
skull in front of the mouth (the head being vertical). A mesial partition
■—the septum nasi—divides the passage longitudinally into the right
and left nasal fossa. Each nasal fossa may be described as having
anterior, posterior, and lateral walls, and a superior and an infen01'
extremity.
The Anterior Wall, sometimes termed the Hoof, is narrow and formed
by the frontal and nasal bones.
The Posterior Wall, sometimes termed the Floor, is considerably move
extensive than the roof. It is formed by the palatine, superior maxillary")
and premaxillary bones, but in much greater proportion by the second
of these.
The Outer Wall is formed by the nasal and superior maxillary bones,
and is occupied by the anterior and posterior turbinated bones, which
project into the cavity and separate the meatuses of the nose from one
another. Thus, the anterior meatus is the narrow interval between the
-ocr page 285-
217
DISSECTION OF THE HEAD AND NECK.
interior (ethmoidal) turbinated bone and the roof of the cavity (the
lasal bone) ; the middle meatus is another and larger interval between
"le two turbinated bones; while the posterior meatus, the largest of these
b u
Fig. 24.
Longitudinal Section qv the Head, showing the Cavities of the Mouth, Nose,
and Pharynx (Lei/h).
• Frontal sinus; 2. Lateral mass of ethmoid bone; 3. Anterior meatus of nasal chamber; 4.
^nterior turbinated bone"; 5. Middle meatus ; 6. Posterior turbinated bone ; 7. Posterior meatus ;
^{,1 lrcu.rn vallate papilla; of the tongue; 9. Section of soft palate ; 10. Opening of right Eustachian
lui e .°n side of pharynx; 11. Isthmus of the fauces; 12. tipper aperture or the larynx; 13. Coni-
zation between pharynx and oesophagus ; 14. Thyroid body ; 15. Trachea.
Nervals, is included between the posterior (maxillary) turbinated bone
an<* the floor of the cavity.
-The Inner Wall (the septum nasi) is partly bony, and partly cartila-
S^ous. ln its upper part it is formed by the bony perpendicular plate
the ethmoid, and at its posterior edge it is formed by the vomer bone ;
lvt for the greater part of its extent, the partition is composed of a plate
cartilage—the septal cartilage. This septal cartilage is continuous
ove with the perpendicular plate, which is merely an ossified portion
rt; behind it is received into the cleft of the vomer, and expands on
e Premaxillary suture; in front it expands on the inner aspect of the
rnasal suture; and inferiorly the alar cartilages are movably con-
noted to it,
-ocr page 286-
218
THE ANATOMY OP THE HOBSE.
The Inferior Extremities of the nasal fossse are termed the inferior nares
or, in common language, the nostrils. They have already been
described (page 176).
Fig. 25.
Transverse Section through the Nasal Chambers.
1. Anterior turbinated bone; 2. Posterior turbinated bone; 3. Anterior meatus; 4. Middle
meatus ; 5. Posterior meatus; 6. Septum nasi.
The Superior Extremities are separated from the cranial cavity by the
cribriform plate of the ethmoid bone, and are occupied by the lateral
masses of the same bone. Below and behind these are the superior
nares—the large patent orifices by which the nasal fossae communicate
with the pharynx, the right and left openings being separated by the
vomer bone.
The following openings into the nasal fossa should be found :—
1. The Opening of the Lachrymal Duct (ductus ad nasum).—Look fQl
this on the floor of the nasal fossa, a few inches within the nostril. 1*
is easily seen in the living animal, and has already been referred to H1
connection with the nostril (page 176). It is a small opening (about the
same diameter as a goose quill) with a circular outline, having an appe^1'"
ance as if a small circle of skin had been punched out. The opening, xt
is to be observed, is on the skin, and not the mucous membrane, taking
the presence of hair as distinguishing the former from the latter. The
duct passes upwards beneath the mucous lining of the middle meatus
until it enters the osseous tube that conducts it to join the lachrymal
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219
DISSECTION OF THE HEAD AND NECK.
sac at the floor of the orbit. The lower portion of the tube has a strati-
fied epithelial lining, but in its upper part the epithelium is ciliated.
2.   The Opening of Stenson's Canal.—Look for this opening on the
floor of the nasal fossa, over the incisor or naso-palatine cleft. Pass a
flexible probe into it. It will be found to pass obliquely into the
cartilaginous substance that closes this opening. It there joins another
canal—the organ of Jacobson, which passes upwards at the side of the
hinder edge of the septal cartilage, terminating blindly after a course of
tour or five inches. The organ of Jacobson has a wall of hyaline cartilage,
with, a mucous lining, and numerous mucous or serous glands. Its
epithelial lining is in part a stratified epithelium, and in part it resembles
the olfactory epithelium to be presently described ; and to the latter
Portion some fibres of the olfactory nerve are traceable.
3.   The Opening of Communication with the Sinuses of the Head.—This
|s placed towards the upper extremity of the middle meatus. Ordinarily
*t has the form of a curved slit not visible from the nasal fossa; but if a
flexible probe be insinuated between the two turbinated bones at this
point, it may be guided on into the frontal or the maxillary sinus.
The Nasal Mucous Membkane (Pituitary or Schneiderean Membrane).
As already seen in the examination of the nostrils, the skin is carried
round the edges of these, and for a short distance into the nasal fossa.
Along an abrupt line it loses its pigment and hair, and is continued by
the mucous membrane. This mucous membrane, it will be observed,
differs in its upper and its lower portions. Thus, in its lower three-
fourths the membrane has a rosy, vascular tint, while in its upper
toUrth it is distinguished to the naked eye by being of a pale, somewhat
yellowish colour. The first of these may be termed the respiratory
Portion of the membrane, as distinguished from the second, or olfactory
Portion. The former has a stratified, columnar, ciliated epithelium
Sllnilar to that of the air passages in general, and in its submucous
tissue are numerous small racemose serous or mucous glands. The
°uactory mucous membrane, on the other hand, has its free surface
tornied by a layer of columnar cells for the most part non-ciliated; and
between the bases of these are peculiar spindle-shaped olfactory cells.
*■ he olfactory cells are connected by their deep ends with the olfactory
flerre fibres, while their opposite extremities are insinuated between the
columnar cells, and terminate on the surface of the membrane in a
ew stiff, hair-like processes. In the submucous tissue are numerous
tubular glands—the glands of Bowman—which open on the free surface
ot the membrane. The nasal mucous membrane is continuous with that
°* Stenson's canal and the organ of Jacobson, the pharynx, and the
onuses of the head.
"he Olfactory (1st Cranial) Nerve. The delicate oval swelling
ermed the olfactory bulb, which is lodged in the fossa of the same name
-ocr page 288-
220
THE ANATOMY OP THE HORSE.
at the forepart of the cranial cavity, gives off from its surface the olfac-
tory nerve fibres. These pass in bundles through the foramina of the
cribriform plate and enter the nasal fossa, where they are distributed as
a network in the olfactory mucous membrane. As the fibres leave the
cranium, they carry with them prolongations from the membranes ot
the brain; and they are remarkable among cerebro-spinal nerves i°
being destitute of the white substance of Scwhann.
Spheno-palatine Nerve. This nerve, already seen at the back of the
orbit as a branch of the superior maxillary division of the 5th (page 2U),
enters the nasal fossa by the spheno-palatine foramen, and divides into
an outer and an inner branch for the nasal mucous membrane, ou
which it confers common sensibility.
The Nasal Branch of the Ophthalmic Nerve (page 238) is another
nerve of common sensation. Entering the upper extremity of the nasal
fossa, through a foramen in the cribriform plate, it ramifies in the
mucous membrane on both sides of the fossa.
Vessels. The mucous membrane of the nasal fossa is richly supplied
with blood by the spheno-palatine artery and the nasal branch of the
ophthalmic artery (pages 213 and 238), satellites of the two preceding
nerves. The veins form beneath the muccus membrane a rich plexus
which is drained principally by the spheno-palatine vein.
-ocr page 289-
Source of Nerve.
Origin'.
Insertion.
Name of Muscle.
j 11th (spinal acces-
( sory) nerve.
1st cervical nerve.
Sterno-maxillaris .
Stemo-thyro-hyoideus .
Subscapulo-hyoideus
Trapezius                  ^
Ehomboideus            >see p. 54
Mastoido-humeralis j
Splenius          ....
Traehelo-mastoideus
Complexus ....
Semispinalis colli .
Intertrausversales colli .
Rectus capitis anticus major .
Scalenus.....
Longus colli ....
Obliquus capitis inferior
Obliquus capitis superior
Rectus capitis posticus major .
Rectus capitis posticus minor .
Parotido-auricularis
Cervico-auricularis externus ^
Cervico-auricularis medius S
Cervico-auricularis internus j
Parieto-auricularis externus .
Sternum, cariniform cartilage
Sternum, cariniform cartilage
Subscapular fascia .
Inferior maxilla, angle ....
Thyroid cartilage ; and hyoid bone, body
Hyoid bone, body.....
( Dorsal vertebras, 2nd, 3rd, and 4th spines
( and funicular part of ligamentum nucha?
{Dorsal vertebrae, 1st and 2nd, transverse
\ processes; and cervical vertebrse, last
( six, articular processes .
/Dorsal vertebrse, 2nd, 3rd, and 4th spines, N\
J and transverse processes of first six or (
j seven; and cervical vertebras, last six f
V articular processes.....)
( Cervical vertebrse, 3rd to 7th, articular )
\ processes ...... J
f Vertebra?, first dorsal and last five cervical, )
( articular processes.....|
j Cervical vertebrae, 5th, 4th, and 3rd, trans- j^
| verse processes
Mastoid crest, wing of atlas, and transverse'
processes of 2nd to 5th cervical vertebra?
Mastoid crest, and wing of atlas .
Cervical and dorsal
nerves.
Occipital bone......
Cervical vertebrse, 2nd to 6th spines .
Vertebra?, last six cervical, transverse pro-
cesses .......
Occipital, basilar process; and sphenoid,
body.......
1st rib (two insertions) ....
Cervical vertebrse except last, bodies .
Atlas, wing.......
Occipital, mastoid crest and styloid process
Occipital......
Occipital......
J Cervical vertebrse,
last four, transverse i
processes
Cervical nerves.
first six bodies; and cer-'i
( Dorsal vertebra?
vical vertebra? except atlas, transverse >
^ processes
Axis, spine .
Atlas, wing
Axis, spine
Atlas, ring .
Parotid gland
Conchal cartilage, base
(Conchal cartilage, inner side
:
7th nerve.
Ligamentum nucha?
Parietal bone, crest
< Conchal cartilage, outer aspect of base
( Conchal cartilage, posterior aspect of base
Scutiform and conchal cartilages . . j
-ocr page 290-
Source of Nerve.
Name of Muscle.
Insertion.
Origin.
Zygomatico-auricularis .
Parieto-auricularis internus
Mastoido-auricularis
Scuto-auricularis externus
Scuto-auricularis internus
Stylo-maxillaris
Digastricus
Occipito-styloid
Stylo-hyoid
Orbicularis palpebrarum.
Levator labii superioris alae- )
que nasi ...         j
Levator labii superioris pro- \
prius         ...         |
Dilatator naris lateralis .
Dilatator naris transversalis
Dilatator naris superior .
Dilatator naris inferior .
Zygomaticus .
{Superficial por
tion
Deep portion
Depressor labii inferioris
Orbicularis oris
Depressor labii superioris
Levator menti
Masseter.
External pterygoid.
Internal pterygoid .
Temporalis
i Mylo-liyoid
Scutiform and conchal cartilages
Conchal cartilage .
Conchal cartilage .
Conchal cartilage .
Conchal cartilage .
Inferior maxilla, angle .
Inferior maxilla, above symphysis
Hyoid, styloid cornu
Hyoid, thyroid cornu
Surrounds palpebral fissure .
( Outer wing of nostril, upper lip, and
t angle of mouth (two divisions)
Upper lip.....
Outer wing of nostril
Same cartilage of opposite side
False nostril and ethmoidal turbinated bone
False nostril and maxillary turbinated bone
Buccinator muscle, above angle of mouth
Superior maxilla and inferior maxilla .
Squamous temporal, zygomatic crest
Parietal bone, crest
Auditory process ....
Scutiform cartilage, outer surface .
Scutiform cartilage, inner surface .
Occipital, styloid process
Occipital, styloid process
Occipital, styloid process
Hyoid, great (styloid) cornu .
Lachrymal bone, tubercle
Frontal and nasal bones .
Malar and superior maxillary bones
Superior maxilla ....
Cartilage of the nostril .
Septum nasi.....
Premaxillary and superior maxillary bone
Surface of masseter muscle
Median raphe (of the muscle)
Superior maxilla and inferior maxilla
Inferior maxilla ....
Surrounds the mouth
Premaxilla.....
Inferior maxilla ....
7th nerve.
Angle of mouth
Lower lip
Upper lip
Prominence of the chin
Inferior maxilla, inner
ramus
surface of vertical \
( Malar and superior maxillary bones,
zygo-
\         matic ridge ....
Sphenoid bone         ....
Sphenoid and palatine bones .
j Parietal, frontal, squamous temporal
\         sphenoid bones
\ Inferior maxilla, horizontal ramus .
Inferior maxilla, neck
Inferior maxilla, inner surface of vertical '
ramus
Inferior maxillary di-
vision of 5th nerve.
and an- I
ess; and i
j Inferior maxilla, coronoid process
\         tcrior border .
S Hyoid, body and glossal proc
and
\ median raphe .
-ocr page 291-
/ Stylo-glosaus .
j Great hyo-glossus .
j Middle hyo-glossns .
Small hyo-glossus .
Palato-glossus
Genio-glossus .
Cerato-hyoid .
Hyoideus transversus
Genio-hyoidens
Tensor palati .
Levator palati
Azygos uvulae .
Palato-pharyngeus .
Pterygo-pharyngeus
Hyo-pharyngeus
Thyro-pharyngeus .
Crico-pharyngeus .
Stylo-pharyngeiis .
Small stylo-pharyngeus
Aryteno-pharyngeus
Levator palpebral superioris
Rectus oeuli superior
Pectus oculi inferior
Pectus oculi externus
Pectus oculi internus
Retractor oculi
Obliquus oculi superior
Obliquus oculi inferior
Hyoid, great (styloid) cornu .
// Glossal process; body, and thyroid coi-nu of
j I hyoid ....
Hyoid, intercornual joint
12th nerve.
End in tongue
I
Hyoid, small cornu and body.
Soft palate ....
( Spheno-palatine gan-
( glion (7th nerve).
12th nerve.
9th nerve (?)
12th nerve.
Otic ganglion (5th
nerve).
Spheno-palatine gan-
glion (7th nerve).
Pharyngeal plexus.
Sup. laryngeal nerve.
9th nerve.
Pharyngeal plexus.
3rd nerve.
3rd nerve.
3rd nerve.
6th nerve.
3rd nerve.
3rd and 6th nerves.
4th nerve.
3rd nerve.
Inferior maxilla, near symphysis
Hyoid, great and small cornua
Hyoid, small cornu
Inferior maxilla, near symphysis
Hyoid, thyroid cornu
Same cornu of opposite side
Hyoid, glossal process
Soft palate
and
and
j Petrous temporal, styloid
process;
( Eustachian tube
j Petrous temporal, styloid
\         Eustachian tube
Aponeurosis of soft palate
Soft palate .
Pterygoid bone
Hyoid, thyroid cornu .
Thyroid cartilage .
Cricoid cartilage .
Hyoid, styloid (great) cornu
Hyoid, styloid (great) cornu
Arytenoid cartilage
Sphenoid, above optic foramen
Soft palate
Free edge of soft palate
End in wall of pharynx
Upper eyelid
Sclerotic coat
Sphenoid, near optic foramen
Lachrymal bone, fossa
-ocr page 292-
CHAPTER V.
DISSECTION OF THE LARYNX.
The larynx is a short tube forming the upper part of the windpip6.
It is, however, not merely a part of the respiratory apparatus, but is
also the organ of voice. It possesses a framework of cartilages, which
are movably articulated together, and connected by ligaments or
membranes. These cartilages are moved by muscles, some of which
pass between the different cartilages and constitute an intrinsic group!
while others pass between the cartilages and extraneous parts, and con-
stitute an extrinsic group.
Directions.—Provided the dissection has to be carried out on one
larynx, the study of the muscles must precede that of the cartilages-
When another larynx can be procured, it is more advantageous to
reverse this order, removing the muscles from the first larynx in order to
study the cartilages and their mode of union, and then using the other
for the examination of the muscles and remaining structures.
Even when the first method has to be followed, it is advisable, before
proceeding to dissect the muscles, to read the description of the cartilages,
which is therefore here put first.
CARTILAGES OF THE LARYNX.
These are five in number, viz., the cricoid, thyroid, and epiglottis, which
are single ; and the pair of arytenoid cartilages. In man there are two
additional pairs—two cornicula laryngis and two cuneiform cartilages-
In the horse the first of these are amalgamated with the tips of the
arytenoids, while the cuneiform cartilages are small, shot-like bodies
included in the aryteno-epiglottic fold of mucous membrane.
In the natural position of the animal at rest, the long axis of the
larynx is oblique upwards and forwards. For convenience of description,-
however, we may assume it to be vertically placed, as indeed it is when
the head and neck are extended (elevated) to the fullest degree. In tins
position the cartilages are related to one another as follows :—The cricoid
is the lowest, and is connected to the first ring of the trachea. The thyoic
is placed above this, and bounds the tube of the larynx in front and at the
sides. The arytenoids surmount the cricoid behind, and the epiglottlb
is superposed to the thyroid in front of the upper aperture of the tube.
-ocr page 293-
225
DISSECTION OF THE LARYNX.
The Cricoid Cartilage has the form of a finger ring, from which
ft receives its name. The depth of the ring is greatest behind,
where it presents a portion comparable to the bezel, or part of a ring
ln which the stone is set. The inner surface of the ring is smooth,
and lined by the laryngeal mucous membrane. The outer surface of
tne bezel is divided by a vertical median ridge which increases the
Surface of origin of the posterior crico-arytenoid muscle. Towards the
Witer limit of this surface there will be seen on each side a little cavity
which is smooth for articulation with the thyroid cartilage. The inferior
border is notched in the middle line of the bezel, and is connected by
lament to the first ring of the trachea. The upper border has a wide
notch in front; and posteriorly, over the bezel, it shows a pair of
^ftiooth convex facets for articulation with the arytenoid cartilages. In
texture the cricoid is composed of hyaline cartilage.
The Thyroid Cartilage receives its name from covering the front and
'des of the larynx like a shield. It consists of a median thickened
Portion, or body ; and two lateral plates—the alse, or wings. The body
ls known in human anatomy as "Adam's apple"—the pomum Adartvi.
he epiglottis is superposed to it, the two cartilages being united by
astic fibres. On each side it is continuous with the wings. Each ala
s a rhomboidal plate of cartilage. The outer surface is slightly convex,
*ad the inner is correspondingly concave. The upper edge of the cartilage
ls attached to the thyroid cornu of the hyoid bone by the thyro-hyoid
Membrane. The lower edge slightly overhangs the cricoid, and receives
the insertion of the crico-thyroid muscle. The other two edges are
Greeted obliquely, one backwards and upwards, the other forwards and
downwards. The first of these receives the insertion of the palato-
Pharyngeus muscle ; the other, in receding from the corresponding edge
1 the opposite wing, leaves beneath the body a triangular gap which is
c°upied by the crico-thyroid membrane. Of the four angles of each
Pate, three demand mention. The supero-anterior angle is acute, and
Joins the ala to the body of the thyroid. The supero-posterior angle is
tuse, and carries a small bar of cartilage—the superior cornu of man—
u°h is articulated to the extremity of the thyroid cornu of the hyoid
one. Close to the base of this process the plate is perforated by a
ramen for the passage of the superior laryngeal nerve. The postero-
erior angle is acute like the first, to which it is diagonally opposite.
18 drawn out a little, forming a projection—the inferior cornu of
an which is terminated by a convex facet for articulation with the
Cold, The thyroid is composed of hyaline cartilage.
Arytenoid Cartilages. These stand at the upper aperture of
e larynx like the mouth of a pitcher, and from this resemblance they
' named. They are irregular in shape, but each bears some resemblance
a three-sided pyramid. The inner surface of the pyramid is covered
-ocr page 294-
226
THE ANATOMY OF THE HORSE.
by laryngeal mucous membrane ; the outer surface receives the insertion
of the thyro-arytenoid muscle; the posterior surface is covered by the
arytenoid muscle. The base of the cartilage possesses within its area »
smooth, depressed facet for articulation with the cricoid. Two
of the angles
of the base require particular notice, viz., the anterior angle, which is
pointed, and projects horizontally forwards to receive the insertion of the
vocal cord; and the postero-external angle, which is thick and rounded,
and receives the insertion of the crico-arytenoid muscles. The apex lS
directed upwards, and is prolonged by a slender piece of yellow fibro-
eartilage representing the comicula laryngis of man. This curves back-
wards and inwards; and with the corresponding process of the opposite
side forms, behind the upper aperture of the larynx, the pitoher-
like lip. Except in the apical prolongation, which is composed ot
yellow or elastic fibro-cartilage, the texture of the arytenoid is hyaline
cartilage.
The Epiglottis is shaped like an ovate, pointed leaf. Its anterioi'
surface is concave in the vertical direction, and convex from side to side-
Near the base it receives on the middle line the insertion of the hy°"
epiglottideus muscle. The posterior surface has the converse configui'a-
tion, and presents numerous pits in which are lodged mucous glands.
The borders of the cartilage are convex, and they are free above, but
below they are enveloped by the aryteno-epiglottic folds of mucous mem-
brane. The apex is pointed, and curved forwards in the uprig'1*
position of the cartilage. The base of the cartilage is expanded, and
rests on the body of the thyroid. From each side of it an irregular bar
of cartilage projects horizontally backwards. The epiglottis is composed
of yellow fibro-cartilage.
ARTICULATIONS, LIGAMENTS, AND MEMBRANES OF THE LARYNX.
Mode of Union with the Hyoid Bone. The larynx is suspended to the
base of the skull through the intervention of the hyoid bone, the tip ot
the thyroid cornu (heel process) of that bone being connected by liga"
mentous fibres (without a synovial membrane) to the so-called super101
cornu at the supero-posterior angle of the thyroid ala. The connection
between the hyoid bone and the larynx is further maintained by the
thyro-hyoid membrane, which is attached, on the one hand, to the body an
thyroid cornua of the hyoid, and, on the other, to the body and upPel
edge of each wing of the thyroid cartilage.
Mode of Union with the Trachea. The lower edge of the cricoi"
cartilage is connected to the first ring of the trachea by a fibro-elastic
membrane—the crico-tracheal ligament.
Union of the Cricoid and Thyroid Cartilages. The postero-iiiferi01
angle, or inferior cornu, of each thyroid ala is articulated to the concave
facet on the bezel of the cricoid in a diarthrodial joint, provided with a
-ocr page 295-
DISSECTION OF THE LARYNX.                                       227
small capsular ligament, and lined by a synovial sac. The two cartilages
are further united by the crico-thyroid membrane. This is a fibro-elastic
structure consisting of a central and two lateral portions. The central
Portion is triangular and fills up the space between the adjacent edges
°f the right and left thyroid alse. It is attached by its sides to these
eo-ges, while by its base it is inserted into the upper border of the
cricoid. Each lateral portion lies under cover of the laryngeal mucous
membrane, and is shaped somewhat like a quadrant, having an inferior
convex edge fixed to the margin of the cricoid in company with the central
Portion, an anterior edge confounded with the central portion, and an
upper straight edge which is thin and free on the side of the larynx.
J-his upper edge is the true vocal cord; and since its fibres are attached
111 front to the angle of union of the thyroid alse, and posteriorly to the
Projecting anterior angle of the base of the arytenoid, it is also termed
the thyro-arytenoid ligament. Vocal sounds are produced by the vibra-
tion of the vocal cords.
Movements.—The movements between the cricoid and thyroid cartil-
a§'es take place around an imaginary horizontal axis passing through the
right and left crico-thyroid joints, and in these movements either cartil-
a8e may be supposed to remain fixed while the other revolves around
tne axis. It should be observed that these movements vary the distance
between the angle of junction of the thyroid alse and the base of the
arytenoids, and thus vary the tension of the true vocal cords, which
stretch between these points.
Union of the Ckicoid and Arytenoid Cartilages. Each arytenoid
cartilage is articulated by the concave facet on its base to one of the
convex facets on the upper edge of the cricoid bezel. It is a diarthrodial
Joint, possessing a capsular ligament and a synovial sac.
Movements.—The arytenoid cartilage swings like a door, around a
Vertical axis passing through the crico-arytenoid joint. When the
artilage is swung outwards, the true vocal cord, wnich is attached to
ne anterior angle of its base, is separated from the cord of the opposite
8lcie, and the glottis is widened. The glottis is narrowed by the opposite
m°vement.
Union of the Thyroid and Epiglottis. These cartilages are united
V elastic fibi •es passing between them, and forming a kind of amphi-
ai*throsis.
Movements.—Except during the act of deglutition, the epiglottis stands
dect in front of the upper aperture of the larynx. During that act
ne cartilage is bent downwards and backwards so as to cover the
c Perture like a lid. This movement, however, is executed not exclusively
at the joint between the two cartilages, but partly by a bending of the
whole cartilage. At the close of the act of deglutition the epiglottis
ssumes the erect position, owing to its own elastic texture and the
-ocr page 296-
228
THE ANATOMY OF THE HORSE.
elastic fibres connecting it to the thyroid ; but in the horse this aCO°
is assisted by the hyo-epiglottideus muscle.
THE MUSCLES OP THE LARYNX.
Extrinsic Group.—This includes the sterno-thyroid, the thyro-by01 >
and the hyo-epiglottideus. The last of these is a single muscle ; t'1
other two are double.
The Sterno-thyroid Muscle (Fig. 26). See page 146.
The Thyro-hyoid Muscle (Figs. 26 and 27). This is a dark-coloured,
fleshy muscle taking origin from the thyroid cornu (heel process) of *n
hyoid bone, and inserted into an oblique line on the outer surface of *»
thyroid wing.
Action.—Acting alone, the thyro-hyoid muscles would elevate tn
larynx between the thyroid cornua of the hyoid bone ; but when tWJ
act in concert with the sterno-thyroid, the thyroid cartilage will
steadied, and will serve as the fixed point for the crico-thyroid and thy*0
arytenoid muscles.
The Hyo-epiglottideus Muscle (Fig. 27) takes origin from *^e
upper face of the body of tne
hyoid bone; and passing back
wards in the middle line, it '
inserted into the anterior siufac
of the epiglottis at its lower part-
Its fibres are mixed with a qual
tity of fatty-elastic tissue.
Action.—To assist the natural
elasticity of the epiglottis l!
restoring the cartilage to tn
erect position at the close of tn
act of deglutition.
Intrinsic Group.—This inch10-
Fig. 20.
Larynx, Side View.
1. Glossal Process of Hyoid; 2. Small Cornu;
3. Great Cornu ; 4. Arytenoid Cartilage ; 5. Thyro-
Hyoideus; 6. Insertion of Sterno-Thyroid ; 7. Crico-
Thyroideus ; 8. Crico-arytenoideus Posticus ; 9. 1st
Ring of Trachea ; 10. Thyroid Body.
four pairs of muscles, viz., u
crico-thyroid, the thyro-arytenoi ,
the posterior crico-arytenoid, au
the lateral crico-arytenoid; a»
a single muscle—the arytenoi
eus.
of the
from the side
The Crico-thyroid Muscle (Fig. _
6) a
cricoid cartilage; and its fibres, passing obliquely upwards and back'
wards, are inserted into the lower edge of the thyroid wing.
Action.—This muscle acts on the crico-thyroid joint, increasing t')0
tension of the vocal cord by increasing the distance between the f°re'
part of the thyroid and the base of the arytenoid cartilage. I'1 tD'
-ocr page 297-
DISSECTION OF THE LARYNX.                                              229
1011 either the cricoid or thyroid attachment may be the fixed point
of the fibres.
Directions.—The thyro-arytenoid and lateral crico-arytenoid muscles
e under cover of the thyroid wing, which must therefore be removed
** °ne side. This is to be done by removing the thyro-hyoid and crico-
nyroid muscles, disarticulating the crico-thyroid joint, and incising the
a a little behind the body of the thyroid, after the manner of Fig. 27.
The Thyro-arytenoid Muscle (Fig. 27) consists of two parallel
undies, between which the mucous membrane of the ventricle of the
arynx protrudes as a pouch. Its fibres arise from the inner surface of
ae thyroid wing near its junction with the body, and from the crico-
ayroid membrane. The lower fibres are inserted into the outer surface
the arytenoid cartilage, while its higher fibres join those of the
arytenoideus muscle.
. Action,.—The muscle is antagonistic to the crico-thyroid, dimin-
. hmg the tension of the vocal cord by acting on the crico-thyroid
joint.
The Posterior Crico-ary-
TEnoid Muscle (Figs. 26 and
2§). This is the most powerful
°i the intrinsic muscles. Its
Muscular tissue is dark red,
and mixed with tendinous
wssue. Its fibres take origin
tr°rn the outer surface of the
cricoid bezel, and are inserted
«reo the prominent tubercle
°n the external angle of the
arytenoid cartilage.
■Action.—To swing out-
^ards the arytenoid carti-
age, and thus to separate
*ne vocal cords and dilate
the glottis.
Fig. 27.
Larynx, Side View (thyroid ala removed).
1. Glossal Process of Hyoid; 2. Cut Base of Thyroid
Cornu ; 3. Small Cornu ; 4. Great Cornu ; 5. Epiglottis ;
6. Arytenoid Cartilage ; 7. Cut Wing of Thyroid Carti-
lage ; S. Facet on Cricoid for Articulation with Thyroid
Cartilage ; 9. Pouch of Mucous Membrane from Ven-
tricle of Larynx ; 10. and 11. Upper and Lower Bundles
of Thyro-Arytenoideus ; 12. Crico-Arytenoideus Lateralis;
13. Crico-Arytenoideus Posticus , 14. Thyro-Hyoideus;
15. Hyo-Epiglottidens; 16. Thyroid Body; IV. 1st Ring
of Trachea.
The Lateral
TEnoid Muscle
Crico-ary-
(Fig. 27).
Ihis muscle is placed below
6 thyro-arytenoid, under
Concealment of the thyroid
ftmg- Its fibres arise from the upper border of the side of the cricoid
Cartilage; and passing backwards and upwards, they become inserted
Hito the same tubercle on the base of the arytenoid as the posterior
muscle, and into the outer surface of the arytenoid in front of that
tubercle.
-ocr page 298-
230
THE ANATOMY OF THE HORSE.
Action.—The muscle acts on the crico-arytenoid joint in a manner
antagonistic to the preceding muscle, approximating the vocal cords ana
narrowing the glottis by swinging the arytenoid cartilage inwards.
The Abytenoideus Muscle (Fig. 28)-
This may be regarded either as a single
muscle, or as a double muscle whose right
and left fibres meet at a median raphe. Ks
fibres are inserted on each side into the pos-
terior surface of the arytenoid cartilage
and superiorly it is joined by the higher
fibres of the thyro-arytenoid muscle.
Action.—To approximate the right and
left arytenoid cartilages, and thus narrow
the glottis.
NERVES OF THE LARYNX.
Two nerves are distributed to the
larynx—the superior and inferior laryn-
geal nerves. The latter is also known
as the recurrent nerve, and both are
branches of the vagus, or 10th cranial
nerve.
The Superior Laryngeal Nerve has its
Fig. 28.
Larynx, Back View.
1. Epiglottis; 2. Arytenoid Carti-
lage ; 3. Thyroid Cartilage ; 4. Ary-
tenoideus ; 5. Crieo-Arytenoideus Pos-
ticus ; 6. Cricoid Cartilage; 7. 1st
Birig of Trachea; 8. Thyroid Body.
origin described at page 194. It gives
motor filaments to the crico-thyroid and
crico-pharyngeus muscles; and then pene-
trating the thyroid wing by the foramen
near its supero-posterior angle, the nerve
splits into sensory branches distributed to the mucous membrane of the
larynx, giving also twigs to the lining of the pharynx and oesophagus.
The Inferior Laryngeal (Recurrent) Nerve has its origin and
course described at page 149. It is the motor nerve to all the intrinsic
muscles except the crico-thyroid, and it also gives some sensory twigs to
the laryngeal mucous membrane.
INTEBIOB OF THE LARYNX.
Directions.—A vertical incision should be made along the middle lme
of the larynx behind, severing the arytenoideus muscle and the bezel oi
the cricoid cartilage. By separating the lips of this incision, a view of
the interior of the larynx from behind will be obtained, and this is to
be supplemented by looking into the tube from its upper and lower
apertures.
The Superior Aperture of the larynx is a large orifice placed at the
floor of the pharynx. It is bounded in front by the epiglottis, behind
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231
DISSECTION OF THE LABYNX.
by the pitcher-like lip of the arytenoid cartilages and the fold of mucous
membrane uniting them, and laterally by the aryteno-epiglottic fold of
mucous membrane. During degluti-
tion the epiglottis is folded over the
aperture, which it closes like a lid.
The Lower Aperture is circum-
scribed by the inferior edge of the
cricoid cartilage, and is directly con-
tinued by the lumen of the trachea.
The Glottis, or Eima Glottidis.
This is a third aperture, placed about
the middle of the tube of the larynx,
which it divides into an upper and a
lower compartment. In its anterior
two-thirds this opening lies between
the right and left vocal cords, and
hi its posterior third it lies between
the bases of the arytenoid cartilages.
The size of the aperture is varied by
the movements executed in the crico-
arytenoid joints, as already seen ; and
its form varies with its size. It can
he completely closed by the apposition
of its margins in the mesial plane.                       Fig. 20.
When it is only slightly opened, it is
Interior of the Larynx, seen from behind
a Slit-like antero-posterior aperture       l. Epiglottis; 2. Arytenoid cartilage; 2'
. _                                     l                           Z             , Its base where it bounds the glottis; 3. Out
Widest at the centre ; when moderately surface of cricoid cartilage; 4. Vocal cord;
. ,.          ., i ,i g Ventricle of the larynx ; 6. Snb-epiglottic
"pen, as in easy respiration, it lias tne
sinus.
form of an elongated isosceles triangle
with the base behind ; when dilated to the fullest extent, it is lozenge-
shaped.
The Ventricles, or Sinuses, of the larynx. Each of these is a recess,
°r cavity, placed on the side of the larynx. The entrance to it lies above
the vocal cord, whose free straight edge, covered by mucous membrane,
f°rms the lower margin. The upper margin is formed by a concave fold
of mucous membrane, containing in man a few fibres designated the
M«e vocal cord. The cavity of the ventricle descends to the outer side
of the true vocal cord, and a pouch of the mucous lining of the cavity
Passes out between the upper and lower divisions of the thyro-arytenoid
muscle.
The SuB-EriGLOTTic Sinus is a depression beneath the base of the
ePiglottis, and provided with a lunated fold of mucous membrane.
The Sub-arytenoid Sinus is a depression beneath the crico-arytenoid
joints.
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232                                 THE ANATOMY OF THE HOUSE.
Mucous Membrane op the Larynx. This, which is continuous with
the lining of the pharynx and trachea, is of a pale colour. It forms
the aryteno-cpiglottic folds, and lines the ventricle of the larynx. It 1S
provided with numerous mucous glands. Its free surface is covered by
an epithelium, which is ciliated except over the vocal cords and around
the superior aperture, in which positions it is stratified and squamous.
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CHAPTER VI.
DISSECTION OF THE BRAIN, OR ENCEPHALON.
•Directions.—The removal of the brain of the horse from its contain-
mg cavity is a somewhat difficult operation, in consequence of the
thickness of the cranial bones. Supposing the head of an animal
recently killed to have been procured for the special purpose, the first
steps are the disarticulation of the jaw on both sides, and the removal
°* the inferior maxilla. Next denude the cranial bones of the muscles
aild other soft structures, and with the saw remove on each side the
zygomatic arch, the supraorbital process of the frontal, and the styloid
Process of the occipital. Estimating the thickness of the last-named
"0ne at the poll, as much as possible of it may be sawn off without
a°tually encroaching on the cranial cavity. Armed with a chisel,
mallet, and strong bone-forceps, the student must now remove as
niuch of the cranial wall as will enable him to extract the brain ;
ai*d he may do this by removing either the roof or the floor of the
cavity. The first method is the speedier, but the latter has the
'^vantage of permitting the roots of the cranial nerves, the pituitary
°dy, and the cranial vessels to be better preserved. The dura mater is
to be left as far as possible intact, but its attachments along the inter-
rontal and interparietal sutures, and to the oblique ridge between
he cerebral and cerebellar divisions of the cranial cavity, must be cut
with the scalpel. When the forepart of the cavity is reached, the
lfindle of the scalpel is to be used to scoop the olfactory bulbs out of
tne fosste in which they lie.
The brain having been removed in its membranes, it should be laid
lth its base upwards on a broad strip of calico, and lowered into a
essel of methylated spirit or a ten per cent, solution of nitric acid in
ater. After a week's immersion, it will be ready for examination.
MEMBRANES, OB MENINGES, OP THE BRAIN.
ihe brain, like the spinal cord, is surrounded by three envelopes:
le ™ra mater, the arachnoid, and the pia mater.
1 he Dura Mater is the external of these envelopes. It is a strong
ions membrane, similar in structure to the spinal dura mater, with
lch it is continuous at the foramen magnum. It differs, however,
111 the same envelope of the spinal cord, in that it is closely adherent
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234
THE ANATOMY OF THE HORSE.
to the inner surface of the cranial bones, and forms for them an interna
periosteum. All over its outer surface it is connected by slender fibrous
processes' and vessels to the bones; but it is particularly adherent to
these along the lines of the sutures, and at the margins of foramina-
The meningeal vessels ramify on the outer surface of the membrane,
and leave their impressions on the inner surface of the cranial bones.
Sometimes the outer surface of the dura mater, on each side of the
middle line above, shows numbers of granular processes—the Paec/riof*'
ian bodies, which are developed from the subjacent arachnoid. Occa-
sionally they are large enough to cause the partial absorption of the
bones over them. The inner surface of the dura mater is smooth, v*
virtue of an endothelial layer representing the parietal layer of the
arachnoid. This inner surface is closely applied to the brain containe
within the other two membranes ; and along certain lines it detaches
processes which pass inwards, and form partial partitions between the
different divisions of the encephalon. These processes are : the 6**
cerebri and the tentorium cerebelli.
The Falx Cerebri is a vertical, mesial, sickle-shaped process which dips
in between the two hemispheres of the cerebrum. The convex tipper
edge of the process is attached to the cristagalli process, and to the intei-
frontal and interparietal sutures. The concave lower edge is thin ana
lace-like, and rests free on the corpus callosnm. The short posterior
edge, or base, is straight, and is attached to the intracranial projection
of the interparietal bone.
The Tentorium Cerebelli is a vaulted partition extending transversely
between the cerebrum and the cerebellum. In outline it is crescentic,
having a superior convex, and an inferior concave, border. The forme*
is attached on the middle line to the intracranial projection of the inter-
parietal bone, and on each side of that its attachment descends obliquely
forwards and downwards along the crest formed by the parietal alio
petrous temporal bones. The concave edge is free, and arches ovei
the crura cerebri. The anterior surface of the membrane is convex,
and the posterior ends of the cerebral hemispheres rest on it. The
posterior surface is concave, and is in contact with the cerebellum.
The Sinuses of the Dura Mater.—These are venous passages forme
by the splitting of the dura mater. They are as follows :—
The Superior Longitudinal Sinus is of considerable size, and lS
found in the falx cerebri at its attached or convex edge. Beginning a
the crista galli process, it becomes larger as it passes backwards, and i
terminates at the intracranial projection of the interparietal bone.
The Inferior Longitudinal Sinus is small and inconstant. >■
extends along the free or concave edge of the falx ; and after receiving
the veins of Galen, it is continued backwards in the tentorium cerebeltt
terminating at the same point as the preceding sinus.
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                     235
Where the two foregoing sinuses meet, they form the whirlpool of
Herophilus (torcular Herophili), from which the blood is drained away
"J the transverse sinuses.
"he Transverse Sinuses pass right and left at the periphery of the
tentorium cerebelli, and enter the parieto-temporal conduit. In that
canal each is continued as the parieto-temporal confluent, from which
Qe blood is drained away by the roots of the temporal veins.
I he Cavernous Sinuses. Each of these is placed in the dura mater
at the side of the sella turcica of the sphenoid bone. Anteriorly each
eeeives the ophthalmic vein, and posteriorly the right and left sinuses
ecome continuous behind the pituitary gland. The venous arch which
ney thus form discharges its blood through the foramen lacerum basis
cranii into the sub-sphenoidal confluent. The internal carotid artery
laverses the cavernous sinus, and forms while in it a sigmoid curve.
I he Petrosal Sinuses are small, and pass in the tentorium cerebelli
n each side, between the transverse and cavernous sinuses.
-I he Occipital Sinuses. These are placed in or external to the dura
®ater lining the cerebellar division of the cranial cavity. They are
°ntinuous through the foramen magnum with the spinal sinuses, and
heir contained blood is drained away by a large vein that passes through
ne condyloid foramen to join the occipital vein.
The Meningeal Arteries. These are derived from the meningeal
ranch of the ophthalmic artery, which enters the forepart of the cavity
the internal orbital foramen; and from the great meningeal or
^Pheno-spinous branch of the internal maxillary. The spheno-spinous
Artery enters by the foramen lacerum basis cranii, and, after detaching
eningeal branches, enters the parieto-temporal conduit to anastomose
rth the mastoid artery. Some meningeal twigs are also furnished by
^ prevertebral branch of the occipital artery (page 191).
The Meningeal Nerves. Filaments from the 4th, 5th, 9th, and
uth cranial nerves, and from the sympathetic, arc said to have been
traced to the dura mater.
ihe Arachnoid. This, like the same membrane of the spinal cord, is
delicate transparent membrane. In structure and disposition it is
c°mparable to a serous membrane. Its parietal layer is represented by
e endothelial lining of the dura mater; its visceral layer invests the
ain and pia mater; and the parietal and visceral portions together
close a space, which is the arachnoid cavity, or subdural space. The
e surface of the membrane bounding this space is smooth and moist
Ke a serous membrane. Between the visceral arachnoid and the pia
ater another space is left, which is termed the subarachnoid space. This
*Pace is most evident over the intervals between the cerebral convolu-
°&s, and over surface depressions at the base of the brain, for at these
P0lnts the arachnoid does not dip down to line the hollows, but bridges
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236                                 THE ANATOMY OF THE HORSE.
them over. The space is continuous with the same space in the spinal
meninges, and contains the limpid cerebrospinal fltiid.
The Pia Mater, This is the vascular membrane of the brain. »
consists of delicate areolar tissue and bloodvessels. It invests the
brain closely, following all its surface irregularities. Behind the cerebral
hemispheres it sends towards the interior of the cerebrum a wide process
—the velum interpositum; and where the cerebellum is superposed to the
medulla oblongata, it forms on each side a thickened granular cord—-the
choroid plasm of (he 4th ventricle. These will be exposed at a later stag6-
arteries of the brain (fig. 30).
Three vessels are concerned in supplying blood to the encephaloUi
viz., the basilai-, internal carotid, and ophthalmic arteries.
The Artekies oe the Brain.
1. Anterior branch of cerebrospinal artery ; 2. Basilar artery ; 3, 3. Irregular branches to medul'
and cerebellum; 4. Posterior cerebellar arteries; 5. Bifurcation of the basilar; 0. Anterior cer
bellar arteries ; 7. Posterior cerebral arteries (more numerous and smaller than usual) ; 8. Intern^
carotid; 9. Posterior communicating; branch ; 10. Anterior branch of internal carotid, which div)des
to form 11 and 12—the middle and anterior cerebral arteries ; 13. Single vessel formed by the unin J
of 11 and 12, disappearing into great longitudinal fissure ; A. Medulla oblongata ; B. Pons Va:" j |
C. Cerebellum; D. Cms cerebri; E. Corpus albicans; F. Optic commissure ; G. Olfactory buiD '
H. Cerebral hemisphere.
The Basilar Artery is formed on the middle line of the lower face of
the medulla oblongata, by the union of two vessels. These are the
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DISSECTION OF THE BRAIN, OB ENCEPHALON.                       237
anterior divisions of the right and left cerebro-spinal arteries, whose
posterior divisions unite in the same manner to form the middle spinal
artery. The basilar artery passes forwards in the median groove of the
medulla, and crosses the pons, in front of which it bifurcates to form
the posterior cerebral arteries. In its course the basilar artery detaches
°n each side, besides numerous vessels to the medulla and pons, the
posterior cerebellar arteries.
The Posterior Cerebellar Arteries are two in number, a right and left.
They are detached at different levels from the basilar, behind the pons;
and they turn round the medulla to reach the cerebellum.
The Posterior Cerebral Arteries diverge from each other in the inter-
peduncular space; and after being connected together by a short
transverse branch of considerable volume, and by numerous smaller
reticulate twigs, they are joined by the posterior communicating branch
°f the internal carotid. Each then turns outwards over the eras
cerebri to gain the choroid plexus and the posterior part of the cerebral
hemisphere. Behind the point at which the vessels are connected by
the short transverse branch, they give off the anterior cerebellar arteries.
Sometimes, as in Fig. 30, the posterior cerebral artery, instead of turning-
outwards as a single vessel, detaches from its outer side two or three
branches which wind round the crus.
The Anterior Cerebellar Arteries are variable in number and disposi-
tion, and may arise as branches of the basilar artery. Generally there
are two or three on each side, and they turn backwards and outwards
over the crus cerebri to gain the front of the cerebellum.
The Internal Carotid Artery. This vessel begins above the cricoid
cartilage of the larynx, as one of the terminal branches of the common
carotid. It passes upwards and forwards to the foramen laceram basis
C1'anii, being sustained in a fold of the guttural pouch, and accompanied
Dy some nervous branches from the superior cervical ganglion of the
sympathetic. Piercing the sub-sphenoidal sinus, it passes through the
toranien into the cavernous sinus, within which it forms a sigmoid curve,
ft then leaves the sinus, and gaining the deep face of the dura mater,
it divides at the margin of the sella turcica of the sphenoid bone into
an anterior and a posterior branch. The latter, termed the posterior
communicating artery, is reflected backwards to join the posterior cerebral
artery. The anterior branch passes forwards, and at the outer side of
the optic commissure divides into the middle and anterior cerebral
arteries.
The Middle Cerebral Artery passes outwards across the hemisphere, in
the fissure of Sylvius.
The Anterior Cerebral Artery unites in the mesial plane, above the
°Ptic commissure, with the corresponding vessel of the opposite side.
*he single vessel thus formed receives the meningeal branch of the
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238                                 THE ANATOMY OF THE HORSE.
ophthalmic artery, and turns round the anterior end of the corpus callo-
sum to gain the great longitudinal fissure. Here it separates into a
right and a left branch, each of which passes backwards along the tB»
face of the hemisphere.
By the anastomosis of the two anterior cerebral arteries in front, and
the junction of the posterior communicating artery on each side with
the posterior cerebral, which results from the bifurcation of the basilar
artery, a vascular circle is established around the pituitary body. This
is termed the Circle of Willis, and its object is to keep up a free blood
supply to the cerebrum, even should there be an obstruction in one of the
main vessels forming the circle. Moreover, the internal carotid arteries
of opposite sides are, before they divide, connected by a large transverse
branch which further contributes to the freedom of the circulation.
The Ophthalmic Arteby is a collateral branch of the internal maxil-
lary. It enters the cranial cavity from the orbit by the internal orbital
foramen, along with the nasal branch of the ophthalmic nerve, and
divides into meningeal and nasal branches.
The Meningeal Branches of opposite sides give off branches to the
dura mater, and then unite to form a single trunk which joins the
middle cerebral arteries.
The Nasal Branch passes through the cribriform plate to gain the
nasal chamber.
The Sympathetic Nerve. Two branches from the superior cervical
ganglion accompany the internal carotid artery, and anastomose around
it to form the carotid plexus. Within the cavernous sinus they form
another plexus—the cavernous plexus. From these plexuses filaments
pass to join the 3rd, 4th, 6th, and ophthalmic cranial nerves. A-
twig also joins the large superficial petrosal nerve from the 7th, to
form the vidian nerve; another passes to the lenticular ganglion, either
separately or with the ophthalmic nerve; and some filaments pass to
the Gasserian ganglion.
The Brain, or Encephalon, consists of four principal parts, viz., the
medulla oblongata, the pons Varolii, the cerebellum, and the cerebrum-
The medulla is the division which is in direct continuity behind with
the spinal cord. The pons projects as a thick transverse bar, or ridge, is
front of the medulla. The cerebellum is superposed to both medulla
and pons. The cerebrum lies in front of the other three segments, and
is larger than these taken together. The weight of the whole brain in
an average-sized horse is about twenty-three ounces.
the medulla oblongata, or bulb (plates 35 and 36).
The medulla oblongata is continuous at the foramen magnum with the
spinal cord, of which it appears to be the expanded anterior termination.
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DISSECTION" OF THE BRAIN, OB ENCEPHALON.                      239
it rests by its inferior face on the basilar process of the occipital bone;
and its superior face, which is concealed by the cerebellum, is depressed
and forms the floor of the 4th ventricle. Its anterior extremity is limited
by the pons Varolii, and is its widest part. The middle line of the
medulla above and below is traversed by lines which continue forwards
the superior and inferior median fissures of the cord.
The medulla is composed of both white and grey nerve matter. The
former occurs at the exposed surface of the medulla, and its nerve
fibres are for the most part longitudinal in direction, and are collected
mto tracts, or bundles. Thus, lying at each side of the inferior median
fissure of the organ, there is a tract termed the inferior pyramid. To the
outer side of this again, and isolated from it by a faint longitudinal
groove, is a tract occupying the position of the olivary fasciculus and
°Uvary body of human anatomy. More externally placed than the last,
and forming a thick cord at each side of the medulla, is the restiform
°°dy; while above the restiform body, and nearer the superior median
fissure, is a more slender column of fibres termed the superior pyramid.
the line 0f separation between the two last-mentioned tracts is very
taint, and in the horse there is seldom or never any surface line of demar-
cation between the restiform body and the olivary fasciculus.
Where the medulla joins the cord, the inferior pyramids become
"arrow, and the inferior median fissure shallow or nearly obliterated «
and at that point there is a visible crossing of fibres from one side to
the other, constituting the decussation of the pyramids. Towards the
Posterior part of the medulla its lateral aspect is crossed by superficial
curved fibres—the arciform fibres, and immediately behind the pons
' arolii there is a band of transverse fibres termed the trapezium. Within
the medulla some fibres pass across the median plane and connect its
right and left halves.
The grey matter of the medulla oblongata occurs in considerable
amount at the floor of the 4th ventricle, where it will subsequently
be exposed.
Course of the Longitudinal Fibres of the Medulla Oblongata.
the inferior pyramid is in part composed of fibres from the inferior
column of the same side of the cord, but principally of fibres crossing
l'°ttL the opposite side of the cord at the decussation. These decus-
sating fibres are furnished mainly by the lateral column, but partly
also from the superior column. The fibres of the inferior pyramid are
continued through the pons to the cerebrum.
The olivary fasciculus of fibres is derived from the inferior column
°t the cord on the same side, and it is continued through the pons to
*ae cerebrum.
The restiform body derives its fibres from all three columns of the
°ord on the same side, but in greatest proportions from the superior
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240
THE AX ATOMY OF THE HORSE.
column. It enters the cerebellum, of which it forms the posterior peduncle.
The superior pyramid derives its fibres from the innermost part of the
superior column of the cord on the same side, and its fibres are continued
through the pons to the cerebrum.
The medulla oblongata shows the superficial origin of the last seven
cranial nerves.
THE POXS VAROLII (PLATE 33).
The pons Varolii rests on the basilar process, in front of the medulla
oblongata. In front of it the crura cerebri appear. Its inferior
face is convex in both directions, and has a faint median furrow.
The superior face forms the anterior part of the floor of the 4th
ventricle. Its extremities are curved upwards to enter the cere-
bellum, of which they form the middle peduncles. The pons consists
of white and grey nerve matter. The nerve fibres of the white
matter are arranged in two sets—a transverse and a longitudinal-
The transverse fibres consist of the surface fibres of the pons, and
of deeper fibres separated from these by the longitudinal set. It lS
these transverse fibres that curve upwards at either extremity °'
the pons to enter the cerebellum as its middle peduncle, and they
accordingly play the part of a commissure to the right and left
halves of the cerebellum. The longitudinal fibres are the forward
continuation of the longitudinal fibres of the medulla oblongata,
minus the restiform bodies. In front of the pons these longitudinal
fibres are continued as the crura cerebri. The grey matter of the
pons occurs within its substance, and at the floor of the 4th ventricle-
To a group of pigmented nerve cells in the latter position, the tern1
locus cceruleus is applied.
The pons shows the superficial origin of the 5th cranial nerve, by two
distinct roots springing from its lateral aspect.
THE CEREBELLUM (PLATES 34 AXD 35).
The cerebellum is superposed to the medulla and pons, &nc
lies under the supra-occipital division of the occipital bone. The
tentorium cerebelli arches downwards in front of it, and isolates
it from the posterior extremities of the cerebral hemispheres. It lS
traversed in the aniero-posterior direction by two shallow grooves,
which divide it into a middle and two lateral lobes. The middw
lobe is the smallest, and is known as the vermiform lobe. When
followed forwards, the vermiform lobe is seen to be reflected roUBW
the anterior aspect of the cerebellum to gain its lower surface ;xt
the roof of the 4th ventricle ; and it terminates by a blunt end
about the middle of this surface. When followed posteriorly, the
vermiform lobe behaves in the same way, terminating at the roof ot
the 4th ventricle by a blunt end opposed to the first. These reflected
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                      241
Portions have a distinct resemblance to two caterpillars, and they may
De distinguished as the anterior and posterior vermiform processes. The
interior vermiform process is adherent to the valve of Vieussens. Each
lateral lobe is joined on its inferior aspect by three bundles of nerve
nbres, which are termed the peduncles. The posterior peduncle is the
termination of the restiform body, the middle peduncle is the reflected
extremity of the pons, and the anterior peduncle passes forwards beneath
the corpora quadrigemina.
Besides the grooves which divide the cerebellum into its lobes,
numerous smaller fissures occur over its surface, and divide the lobes
into folia, or leaflets. The arrangement of these leaflets will be made much
more evident by making an antero-posterior vertical section, at or near
the mesial plane of the organ. The peduncles are to be cut as they
enter the lower face of the lateral lobe, and the anterior vermiform
process is to be carefully separated from the valve of Vieussens with the
Scalpel. This will enable one half or a little more of the cerebellum to
De removed after the manner of Plate 35.
The cerebellum contains both grey and white matter. The white
niatter forms a large mass in the interior, and from this mass large plates
are given off towards the surface. From these primary plates proceed
niore numerous smaller secondaiy plates, and these again detach small
terminal plates which end in the surface folia. In consequence of this
disposition of the white matter, it presents on vertical section a strikingly
arborescent appearance, to which the term arbor vita: is applied. The
nerve fibres of the white matter are for the most part directly continuous
^'ith the peduncles; but some are proper to the organ, and connect
different points of the grey matter.
The grey matter of the cerebellum is spread over its surface, and also
t°rms two independent masses within the central mass of white matter.
J-hese latter have the form of a corrugated capsule, and each is placed a
rfctle to one side of the mesial plane, and is known as the corpus dentatum
t the cerebellum. The surface layer of grey matter invests the core
°t white matter within each leaflet, and also extends across the bottom
the fissures between adjacent leaflets. It consists of two strata : an
uter grey layer, and an inner rust-coloured layer.
■I he Fourth Ventricle (Plates 35 and 36). This is a space between
ne cerebellum above, and the medulla and pons below. Its boundaries
'le as follows:—Its floor is formed by the medulla and pons; its roof
y the valve of Vieussens, the under suface of the vermiform lobe, and
ne reflection of pia mater from, the medulla to the cerebellum; laterally
* ls bounded in its anterior third by the anterior peduncle of the cere-
ehiim, and in its posterior two-thirds by the restiform body. The
udest part of the space is at the point where the peduncles enter the
eerebellum, and it contracts towards both extremities. At the posterior
R
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242
THE ANATOMY OP THE HORSE.
extremity there is a minute hole, which is the entrance to the short tube
that continues the central canal of the cord into the posterior end
of the medulla. The pointed posterior end of the space is the
calamus scriptorius of human anatomy, so named from its resemblance to
a writing pen. The anterior end of the space lies under the valve 01
Vieussens, and leads into the aqueduct of Sylvius, which is a canal tunnelled
beneath the corpora quadrigemina, and opening anteriorly into the 3rd
ventricle. The floor of the cavity is traversed by a longitudinal niesia
furrow, and it shows the grey matter of the medulla and pons. *»*
cavity is lined by a ciliated epithelium, and it communicates by oEe
or more minute apertures in its floor with the sub-arachnoid space. tW
each side of the cavity, between the cerebellum and the restiform body>
there is a thickened piece of pia mater—the choroid plexus of the 4"1
ventricle.
The Valve of Vieussens is a delicate, translucent fold, placed at the
anterior part of the roof of the 4th ventricle. The lateral edges 01
the valve are fixed to the anterior cerebellar peduncles, its anterior edge
is attached behind the testes, and its posterior edge stretches across
the anterior vermiform process. The upper face of the valve is
adherent to the anterior vermiform process, and its lower face is free
and forms the anterior part of the roof of the 4th ventricle. The 4th
nerve arises in the valve, close behind the testes, the right and let*
nerves appearing continuous with one another across the middle line.
THE CEREBRUM.
Under the term cerebrum are included all the parts of the encepha-
Ion except the medulla, pons, and cerebellum. . It forms a mass large1
than these taken together, although the amount by which it ex-
ceeds them is much less in the horse than in man. The inferioi
aspect of the cerebral mass is termed its base, and the student should
begin by examining the objects to be seen there (Plate 33).
The Crura Cerebri are two thick, round, white cords, which appeal
in front of the pons. At this point they are close together; but as they
proceed forwards, they diverge and form the posterior boundaries of a
lozenge-shaped area—the interpeduncular space, which is completed J°
front by the optio tracts and commissure. Anteriorly each cru
disappears into the cerebral hemisphere, but its point of termination iS
concealed by the optic tract. The eras is composed of a superficial and
a deep layer of nerve fibres with an intermediate thin stratum of %veJ
matter. The superficial layer of fibres is known as the crusta, and the
deep is termed the tegmentum. The fibres of both layers are continued
posteriorly with the longitudinal fibres of the pons ; and they are trans-
mitted in front to the optic thalami, corpora striata, and grey niattei
of the hemisphere. The corpora quadrigemina, which are superposed
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DISSECTION OF THE BRAIN, OH ENCEPHALON.                      243
*0 the crura, also receive some fibres. The grey matter of the cms
contains nerve cells with dark pigment, and is therefore termed the
>ocm nit/er. The crura cerebri show the superficial origin of the 3rd
pair of nerves.
The Optic Teacts. These are two white cords of nerve fibres which
turn round the crura cerebri, and pass forwards and inwards to meet in
the middle line and form by their fusion the optic commissure or chiasma.
i his commissure rests on the sphenoid bone, in front of the pituitary
fossa ; and in front it gives off the diverging optic or 2nd nerves. The
optic tracts form the anterior boundary of the interpeduncular space.
The Pons Tarini is the grey matter in the posterior angle of the
interpeduncular space. It is also known as the locus perforatus posticus,
from its being penetrated by numerous vessels.
The Corpus Albicans is a pea-like, white nodule placed on the middle
hue, about the centre of the interpeduncular space. As will subse-
quently be learned, the body is formed by the reflection of the anterior
Pillars of the fornix.
The Tuber Cinereum is a layer of grey matter between the corpus
albicans and the optic commissure. It is perforated in its centre, and
connected to the upper surface of the pituitary gland by a hollow7 tube
°f grey matter—the infundibulum.
The Pituitary Body is a reddish-yellow, disc-shaped body, having a
diameter about equal to that of a sixpence. It is thickest in its centre
|Qd thinnest at its rim. Its lower face rests on the sella turcica of the
sPhenoid bone; and its upper face receives the insertion of the infundi-
Dulum, and covers the tuber cinereum, and, in part, the corpus albicans
aild optic commissure. Within its structure it comprises cells resembling
those of the blood-vascular or ductless glands, and others that resemble
nerve cells. In the foetus it is proportionally larger, and contains a
cavity which communicates with the 3rd ventricle through the infundi-
bulum.
-The pons Tarini, corpus albicans, and tuber cinereum form the floor
°t the 3rd ventricle, a cavity which the dissector will hereafter expose
°y working from the upper aspect of the cerebrum.
The Lamina Cinerea, or Lamina Terminalis, is a thin, delicate layer
°t grey matter which is placed above and in front of the optic commis-
' lu'e- It is the anterior boundary of the 3rd ventricle.
The Locus Perforatus Anticus is a spot of grey matter at each side
°* the optic commissure, penetrated by numerous vessels for the corpus
striatum, which lies above the spot.
The Fissure of Sylvius, is a faint and ill-defined groove which begins
at the locus perforatus anticus, and extends outwards across the hemi-
sphere.
"he Great Longitudinal Fissure. In front of the optic chiasma the
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244
THE ANATOMY OF THE HORSE.
cerebral mass is seen to be mesially divided by the great longitudinal
fissure. This fissure, as will be better seen when the brain is viewed
from above, is a great vertical mesial cleft extending the whole length oi
the cerebrum, which it partially divides into right and left halves, or
hemispheres.
The Olfactory Bulbs. The olfactory bulb is the white body situated
at the anterior end of the hemisphere. It occupies the olfactory fossa
at the forepart of the cranial cavity; and unless special care is taken m
the removal of the brain, the bulb is apt to be separated from the hem1"
sphere and left in that fossa. From the free surface of the bulb the
delicate filaments of the olfactory (1st cranial) nerve pass through the
cribriform plate of the ethmoid bone, and enter the nasal chamber. The
bulb is hollow, having a central cavity that is in communication with
the anterior cornu of the lateral ventricle.
The Olfactory Peduncle is a short, thick, white cord immediately
behind the bulb, and in direct continuity with it. The hemisphere is
slightly depressed over the peduncle, the depression being termed the
olfactory fissure. The peduncle divides posteriorly into the olfactory
tracts.
The Olfactory Tracts. These are two white diverging bands—an
inner and an outer—that continue the olfactory peduncle backwards.
The internal tract (inner olfactory root) is short, and passes backwards
and inwards to the edge of the great longitudinal fissure. The external'
tract (outer olfactory root) is a much longer band which curves out-
wards and backwards across the fissure of Sylvius, and then encircle
outwardly the uncinate and hippocampal convolutions, to reach the
tentorial aspect of the hemisphere, on which it is lost. At the fissure
of Sylvius the tract seems to lose some of its fibres in front of the unci-
nate convolution, and behind that point it becomes grey on its surface.
Behind the angle of divergence of the olfactory tracts is a smooth and
slightly convex area—the quadrilateral space of Paul Broca. The surface
layer of this space consists of grey matter constituting the middle o1
grey olfactory root; and, according to Broca, it covers white fibres that
connect the olfactory bulb to the cms cerebri and to the anterior cere-
bral commissure (anterior white commissure of 3rd ventricle).
If now the olfactory peduncle be raised from the olfactory fissure, jt
will be seen to be connected to the frontal lobe of the hemisphere vj
a lamina termed by Broca the superior olfactory root. This lamina lS
grey on its surface and white beneath, and if it be ruptured the cavity
of the bulb and the communication between that cavity and the antei'101
cornu of the lateral ventricle will be brought into view.
External to the outer olfactory tract, each hemisphere shows numerous
winding worm-like ridges, termed convolutions, and internal to the poS"
terior half of the same tract there is seen a thick ridge—the hipP0'
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                       245
camped convolution—which terminates behind the fissure of Sylvius
m a nipple-like eminence—the uncinate convolution (mastoid lobule, or
niammillary eminence). These will presently be more particularly
described.
Directions.—The student must now reverse the position of the brain,
laying it with its base downwards, while he proceeds to examine its
upper aspect.
The Great Longitudinal Fissure is now seen in its entirety. It
extends from the anterior to the posterior end of the cerebrum, and
appears to completely separate the right and left hemispheres. In the
natural state the fissure is occupied by the falx cerebri, Gently
separate the contiguous margins of the hemispheres, so as to widen out
the fissure. Except towards the hinder end of the fissure, this proceed-
lng requires no dissection, but at that point the hemispheres are united
°n the middle. It is, however, a mere adhesion through the medium of
Pia mater. Separate the hemispheres here by traction, or by cutting
carefully in the mesial plane. There will now be exposed (Fig. 31) a
white body—the corpus callosum—which connects the hemispheres at
the bottom of the great longitudinal fissure. At the same time there
will be brought into view the opposed inner surfaces of the hemispheres.
The Cerebral Convolutions. In his examination of the base of the
bi'ain, and more clearly now, the student will have observed that the
surface of the hemisphere is not smooth, but traversed by numerous
winding worm-like elevations. These are termed the cerebral convolu-
tions or gyri; and the intermediate grooves or fissures are technically
termed sulci.
At first sight it might be supposed, as indeed was believed until a
comparatively recent date, that the disposition of these convolutions is
quite irregular and hap-hazard. Observation has shown, however, that
such is far from being the case, and that the convolutions have a nearly,
'* not altogether constant, arrangement. In the human subject, indeed,
the surface of the hemisphere has been accurately mapped, and each
convolution named. In the brain of the horse the plan of these convo-
lutions appears to be as uniform as in man; and although, perhaps, the
convolutions are not absolutely identical in any two brains, or even in
ae two hemispheres of the same brain, still the irregularities are so
"gat as to permit one to describe with considerable minuteness what
night be termed a common plan. The mapping of the surface of the
eirtispheres derives its chief interest and utility from the discovery that
cnnite areas are associated with particular functions, in such a way that
uen these areas are destroyed or injured there follows total loss or dis-
U'bance of these functions, and that in some cases the exercise of par-
cular functions can be brought about by applying stimuli to particular
sPots of the cerebral cortex.
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246
THE ANATOMY OF THE HORSE.
In the brain of man the hemisphere is primarily subdivided into five lobes, viz., fronw,
parietal, occipital, temporo-sphenoidal, and central, the last being also known as the
Island of Reil, or the Insula. The lines of separation between these lobes are certain
well-marked fissures, distinguished from the sulci in general by their greater depth am
constancy. In each lobe, again, the secondary sulci form the lines of separation between
a definite number of convolutions.
In the third edition of Professor Chauveau's admirable work (TraiU d'Anatomic cow
paree des Animaux domestiques) an attempt is made to describe the cerebral convolu-
tions of the horse after the plan followed in human anatomy, and to establish an alroos
complete correspondence of these parts in the two brains. It appears to me, after very
careful consideration, that except in a few points, an identity between convolutions
in the two brains is not clearly indicated on anatomical grounds alone. That most o
the convolutions of the human brain have corresponding convolutions in the brain of tue
horse is more than probable; and experimental, pathological, or developmental evidence
may yet place this correspondence beyond doubt. In the meantime, however, and pr°'
visionally, I think it preferable to describe the cerebral convolutions of the horse accord-
ing to what appears the most natural plan.
The surface of each hemisphere (excluding from present consideration its inner aspect;
is divided into three lobes or areas, viz., an anterior lobe, a postero-superior lobe, and a
postero-inferior lobe. This subdivision is effected by certain fissures (Plate 34), 8»
follows :—
1.  The Crucial Fissure. This is a short fissure which begins near the middle of each
hemisphere where it margins the great longitudinal fissure. Passing outwards, it joins
the great oblique fissure. The crucial fissure separates the anterior from the postero-
superior lobe. In the right hemisphere of Plate 34 these lobes are connected across the
fissure by a small annectent or bridging convolution.
2.  The Great Oblique Fissure. This is the most pronounced fissure of the hem1"
sphere. Beginning near the middle of the upper surface of the hemisphere, where it *j
continuous with the crucial fissure, it is directed obliquely outwards, downwards, a'1'
backwards, to reach the tentorial aspect of the hemisphere (Plate 33). It separates the
postero-superior from the postero-inferior lobe.
3.  The Lateral Fissure. This fissure begins on the upper surface of the hemisphere,
at the point of junction of the crucial and great oblique fissures. It curves round th
side of the hemisphere, with a slightly forward inclination ; and it separates the anterior
from the postero-inferior lobe.
4.  The Fissure of Sylvius.* This begins at the base of the brain (Plate 33), at the
side of the optic commissure. It passes outwards as a faint and ill-defined depression &
front of the uncinate convolution; and crossing the outer olfactory tract, it divides in»"
four branches, which, however, arc mere sulci. One of these is directed backwards between
the outer olfactory tract and the postero-inferior lobe ; another passes forwards between
the inner olfactory tract and the anterior lobe; a third ascends into the postero-inferl01
lobe; and the fourth is directed forwards into the anterior lobe. In the first part of i'3
course the fourth branch separates the adjacent convolutions of the anterior and postero
inferior lobes, being itself separated by a bridging convolution between these lobes from
the lower extremity of the lateral fissure.
To the outer side of the outer olfactory tract, at the point from which these branche>
of the Sylvian fissure radiate, there is a minute nodular convolution that is partially °
entirely concealed from view until the adjacent convolutions are slightly separate* ■
This seems to foreshadow the convolutions of the insula of man.
The Anterior Lobe presents four convolutions :—
1.  The First Anterior Convolution (Plate 33, 1. A) is seen on the under surface of »j
lobe. It lodges the olfactory peduncle in the olfactory fissure ; and when the pedun"
is in position it shows an inner and an outer part, the former occupying the position
the gyrus rectus of human anatomy.                                                                                     1„
2.  The Second Anterior Convolution begins on the under surface of the lobe (PlatfjL^
* The first part of the fissure of Sylvius, as far as the outer olfactory tract, is sometimes ami n ^
correctly called the valley of Sylvius, and Broca restricts the term figure of Sylvius to the tnir
the above-described branches.
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DISSECTION OF THE BRAIN, OB ENCEPHAIiON.                      247
* A), external to the preceding. It runs forwards and upwards round the extremity of
the hemisphere, and abuts on the antero-marginal convolution (Plate 34).
3.  The Third Anterior Convolution begins at the under surface of the lobe (Plate 33,
"• A) to the outer side of and behind the preceding. It curves upwards and forwards
across the hemisphere, and reaches its upper aspect (Plate 34). Here it is reflected back-
wards and inwards; and turning upon itself, it descends to near the point from which it
started, being connected at its termination by a bridging convolution to the first convolu-
tion of the postero-inferior lobe.
4.   The Antero-marginal Convolution (Plate 34, A. M.) lies at the forepart of the great
longitudinal fissure, and is visible on both the upper and inner aspects of the lobe. Be-
ginning at the crucial fissure (being sometimes connected to the postero-marginal convolu-
tion of the postero-superior lobe), it passes forwards at the edge of the hemisphere, at the
anterior end of which the first and second anterior convolutions abut upon it.
The Postero-superior Lobe comprises three convolutions :—
1. The Postero-marginal Convolution (Plate 34, P. M.) extends along the margin of the
lobe, appearing on both its upper and inner surfaces, and lying in series with the antero-
niarginal convolution of the anterior lobe. Beginning at the crucial fissure, it passes
backwards at the edge of the hemisphere, and reaches its tentorial aspect.
_ 2. The First Oblique Convolution (Plate 34, 1. O) lies external to the preceding. Be-
ginning in front, near the margin of the hemisphere, it passes obliquely backwards and
outwards, and curves round the extremity of the lobe to reach its tentorial surface.
»• The Second Oblique Convolution (Plate 34, 2. 0) passes with an oblique direction
between the preceding convolution and the great oblique fissure, and reaches the tentorial
Efface of the lobe (Plate 33), from which it seems to be in part continued by the outer
olfactory tract.
The Postero-inferior Lobe. The sulci of this lobe are numerous and small, and it
13 difficult to divide it naturally into convolutions. For convenience of description, how-
ler, two convolutions may be recognised in it:—
1- The First Postero-inferior Convolution (Plates 33 and 34, 1. P. I.) is four-sided, and
c°ntains within itself several short sulci. It lies behind the third convolution of the
anterior lobe, to which it is connected by a bridging convolution.
«■ The Second Postero-inferior Convolution (Plates 33 and 34, 2. P. I.) lies at the
losterior part of the lobe, above the outer olfactory tract; and its posterior extremity
aPPears on the tentorial surface of the hemisphere. Like the preceding, it possesses
Numerous minor sulci within itself.
Directiona.—There still remains for examination the inner surface of each hemisphere.
eParate the hemispheres as widely as possible along the great longitudinal fissure. At
le upper edge of this fissure there will now be seen the inner aspect of the antero-marginal
1 "d postero-marginal convolutions already described, and between the lower edge of these
nu the corpus callosum there lies a thick convolution—the gyrus fornicatus.
The Gyrus Fornicatus (Fig. 31).—This is comparable to a lobe,* rather than to a
°nvo]ution. It is disposed in a great curve, or arch, from which it is named. It begins
the forepart of the under surface of the hemisphere, in front of the lamina cinerea,
na here it is narrow and pointed. It bends round the anterior extremity (genu) of the
rPus callosum, acquiring at its point of reflection a great increase in thickness. It
ssea backwards above the corpus callosum, and below the antero-marginal and postero-
arginal convolutions. From the former body it is separated by the fissure of the corpus
losuin, while the calloso-marginal fissure (great limbic fissure of Broca) separates it from
. le marginal convolutions above. In this part of its course the gyrus is distinctly divided
0 two tiers by a fissure that traverses it in its length. Posteriorly this fissure becomes
rv shallow, and the gyrus, losing its double character, turns round the posterior end
?! iim) of the corpus callosum and reaches the tentorial surface of the hemisphere.
this point it becomes slightly constricted; and after being connected with the convolu-
"aul Broca {Anatomic comparce des clrconvolutions cerebrates) considers that this part of the
Sphere represents not merely a lobe, but several lobes—that it is, in fact, the equivalent of all
t TeSt °f tJle cerer>ral cortex. He accordingly divides the surface of the hemisphere primarily into
great divisions—the great limbic lobe (gyrus fornicatus) and the convolulionary mass.
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248
THE ANATOMY OF THE HORSE.
tions of the postero-superior and postero-inferior lobes, it is directed forwards at the base
of the brain (Plate 33, Hipp, con.), between the cms cerebri and the outer olfactory
tract. Finally, it terminates in the nipple-like eminence already noticed (Unc. con. )•
The whole of this great convolution corresponds very closely to the gyrus fornicatus 01
human anatomy. Thus, the part which turns round the genu and rests on the upp61
surface of the corpus collosum is the callosal convolution; the part from the splenruB1
to the side of the cerebral crus is the hippocampal convolution; and the nipple-like
eminence is the uncinate convolution.
The hippocampal part of the gyrus fornicatus has a small process which projects
forwards under the splenium; and a3 the convolution curves forwards to emerge at the
side of the crus, it rests on the optic thalamus. By carefully raising the convolution from
the thalamus, there will be brought into view a fissure on the under aspect of the former.
This is the hippocampal fissure, and it projects the convolution into the lateral ventricle
as the hippocampus. Beyond this fissure the edge of the hippocampus is seen, mp.rginc'1
by a thin-edged white band—the taenia hippocampi. The hippocampus and its taenia
here form the upper boundary of the great transverse fissure of the brain, by which the
pia mater of the hemisphere projects towards the interior of the cerebrum as the velu'11
interpositum.
Corpus Callosum and Inner Face of the Cerebral Hemisphere.
1, 2. Right and left cerebral hemispheres; 3. Cerebellum; C. Corpus callosum ; G. F. Gy1'11^
fornicatus (its callosal portion); C. M. Calloso-marginal fissure; A. M. Antero-marginal convolu-
tion ; P. M. Postero-margmal convolution.
Directions.—With a large, thin-bladed, sharp knife a horizontal slice
should be removed from the top of one or both cerebral hemisphei'es>
down to the level of the corpus callosum.
The hemisphere will now be seen to contain both grey and wlute
matter. In the centre of the hemisphere the white matter forms a lai'ge
mass connected with that of the opposite side by the corpus callosun1'
At the surface the mass sends a white core into each convolution. The
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                      249
great sheet of grey matter on the surface of the hemisphere invests
"c white core in each convolution, and also extends across the bottom
of each fissure.
The Corpus Callosum (Plate 35 and Fig. 31) is a great commissure of
rve fibres connecting the right and left hemispheres. It termin-
ates behind in a thickened margin—the splenium; and in front it is
Abruptly bent downwards and backwards, the bend being named the
Jenu, and the reflected portion the rostrum. The rostrum becomes
larrower as it descends, and is connected to the optic commissure by the
amina cinerea. Along the middle line of its lower face the corpus
ahosum is connected posteriorly with the fornix, and anteriorly with
ne septum lucidum; and on each side it forms the roof of a cavity in
he hemisphere-Hie lateral ventricle. Nearly all the fibres of the
°orPus callosum have a transverse direction; but on each side of the
°ngitudinal middle line of its upper face there are a few longitudinal
Dres termed the striae longitudinales, or nerves of Lancisi.
■Directions.—If the corpus callosum be now cut through in the longi-
udinal direction, a little to one side of the middle line, and dissected
ll wards, the lateral ventricle will be exposed. The corpus callosum,
11 will now be seen, is thickest at its posterior extremity, and thinnest at
*fe middle.
"he Lateral Ventricles (Plate 35) are two in number, one in each
emisphere. They are separated from one another along the middle
lne by the fornix and septum lucidum, but beneath the former body they
mmunicate through the foramen of Monro. The central portion of
a°h cavity is termed the body, and its prolongations before and behind
e termed respectively the anterior and the descending cornu.
*Jn the floor oi the body of the cavity the following objects will
noticed :—In front, a large pear-shaped grey eminence—the corpus
1latum j behind, another body of about the same size but white on its
' itace—the hippocampus; between the corpus striatum and the
Ppocampus, a groove, in which there lies a red granular cord—the
°roid plexus. Where the hippocampus bounds this groove, it is
argined by a white band—the tcenia hippocampi; and if the choroid
exus be pulled gently backwards, another white band will be seen to
ai'gin the corpus striatum where it bounds the groove—this is the
Wnia semicircularis*
Th
A'ie anterior cornu is occupied by the base of the corpus striatum,
curves downwards and forwards into the anterior part of the
wjsphere, where it communicates with the cavity of the olfactory bulb,
he descending cornu contains the prolongations of the hippocampus
'ts taenia. It passes at first backwards and outwards, and then
visibl 6 0pfcic thalamus and taenia seniicircularis are generally enumerated among the objects
cornril l^ ^°dy of the lateral ventricle. In the "brain of the horse, however, the choroid plexus
J conceals from view the optic thalamus, and in most cases also the taenia seniicircularis.
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250
THE ANATOMY OF THE HORSE.
curves downwards, forwards, and inwards, terminating at the base of the
hemisphere in the uncinate convolution. The ventricles are lined by *
ciliated epithelium, which is continuous through the foramen of Moni'0
with the lining of the 3rd ventricle.
The Septum Lucidum is a thin, translucent partition between the two
lateral ventricles. It is broadest in front, where it is attached to the
rostrum, or reflected part of the corpus callosum. Its upper edge is
attached to the corpus callosum, and its lower edge to the fornix; and
posteriorly these edges meet at an acute angle. The septum consists
of white matter in its centre, with a layer of grey matter on each side.
In man it contains a small isolated cavity—the 5th ventricle.
The Fornix, or arch, is a mesially placed white band, consisting of a
central part, or body, and two pairs of processes, or pillars. The body
is flattened above and below, and broadest behind. Its upper face is
adherent posteriorly to the corpus callosum, but in front it dips down
and leaves beneath the forepart of the corpus callosum a space occupied
by the septum lucidum. The under surface of the body rests on the
velum interpositum, and at its anterior extremity arches over the
foramen of Monro. The anterior pillars of the fornix are two white
cords which descend in front of the foramen of Monro, being separated
by a slight interval. Eeaching the base of the brain, they turn on
themselves, forming thus the corpus albicans, and they then enter the
optic thalamus. The posterior pillars are broader and flatter, and not
so well defined. Each in part bestows its substance on the surface of the
hippocampus, and in part it descends along the anterior edge of that
body as the taenia hippocampi, or corpus fimbriatum.
The Corpus Striatum (Plates 35 and 36). This is the large grey
body already noticed in the body and anterior cornu of the lateral
ventricle. In shape it is pyriform, having its broad end directed
forwards and inwards, and its tapering end backwards and outwards to
the roof of the descending cornu. The body comprises two masses ot
grey matter, separated from each other by intermediate white fibres
which curve upwards and outwards from the cerebral eras. The uppe1'
mass of grey matter—termed the nucleus caudatus—is that which pro-
jects into the lateral ventricle. The lower mass—the nucleus lentiev>-
laris—lies above the quadrilateral space already seen at the base of the
hemisphere between the diverging olfactory tracts.
The Taenia Semicircularis (Plate 36) is a narrow white band tha*
extends between the corpus striatum and the optic thalamus. (Itri
relation to the thalamus will be better seen in the next stage of the dis-
section.)
The Hippocampus is the curved eminence already noticed in the body
and descending horn of the lateral ventricle. It rests on the opti°
thalamus, from which it is separated by the velum interpositum. The
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                       251
ventricular aspect of the body is white, but the surface that rests on the
optic thalamus is grey. The hippocampus is to be viewed as a convolu-
tion of the cerebrum, being, in fact, an inward projection of the hippo-
campal convolution already noticed (page 248).
Directions.—The corpus callosum and septum lucidum should be cut
away in order to see the upper surface of the fornix, which should then
be divided transversely in its middle. The anterior part should be
raised forwards and upwards to expose its anterior pillars and the
foramen of Monro. The posterior part should be removed along with
the hippocampus in order to bring into view the velum interpositum.
The dissection will then assume the form of Plate 36 ; but the optic
thalami and the pineal gland, there exposed, will be covered by the
velum.
The Velum Interpositum is a triangular fold of pia mater, continuous
by its base with the pia mater on the hinder end of the cerebrum. Its apex
lies at the foramen of Monro, and its lateral edges, fringed by the chor-
oid plexuses, project towards the lateral ventricle through what is termed
the great transverse fissure of the cerelyrum. This is an arched cleft extend-
ing over the optic thalami, from the extremity of the descending horn on
one side to the same point on the other. Above it is bounded centrally
by the fornix, and on each side by the hippocampus and its taenia.
The velum interpositum is, like the pia mater in general, a vascular
membrane; and the choroid plexus of each side is a thickened
and highly vascular portion of it. Along its centre the veins of Galen
extend backwards, and unite to turn round the posterior extremity of
the corpus callosum, and enter the inferior longitudinal sinus. The
velum should now be raised from its apex backwards, when it will be
seen to cover the optic thalami and the pineal gland, and care must be
taken lest the latter be removed with it.
The Optic Thalami. Each of these is a large grey-coloured body,
superposed to the crus cerebri behind the corpus striatum, and in front
of the corpora quadrigemina. Its upper surface is convex and covered
by the velum interpositum. When followed outwards this surface
changes its direction, looking backwards and downwards; and it there
forms part of the boundary of the descending horn of the lateral
ventricle. Inwardly the right and left thalami are opposed to
one another along the middle line, and they include between them
the 3rd ventricle. In front each thalamus is separated from the
corpus striatum by a groove, in which will now be seen more distinctly
the taenia semioircularis. Behind, another groove isolates the thalamus
from the nates.
The Pineal Gland is a small, reddish, conical body, named from its
resemblance to a pine cone. It stands by its base on the middle line
between the optic thalami and the nates. From its base two white
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252
THE ANATOMY OF THE HORSE.
bands—the peduncles of the pineal gland—extend forwards along the
groove between the two thalami; and at the foramen of Monro each
peduncle unites with the anterior pillar of the fornix to descend to the base
of the brain, and concur in forming the corpus albicans. In structure
the body presents some resemblance to lymphoid tissue, but it also
contains some branched corpuscles which are possibly nerve cells-
Imbedded in it is a quantity of gntty calcareous matter termed the
acervulus cerebri, or brain-sand.
The Third Ventricle is a narrow space whose sides are formed by
the optic thalami. Its floor corresponds to the parts already examined
in the interpeduncular space, viz., the pons Tarini, corpus albicans, and
tuber cinereum. Its roof is formed by the velum interpositum covered
by the fornix. In front it is bounded by the lamina cinerea, and it here
communicates with the lateral ventricles by the foramen of Monro.
Posteriorly the aqueduct of Sylvius enters it from the 4th ventricle.
The cavity is crossed by three commissures : 1. The Anterior Commis-
sure is a small white cord of nerve fibres stretching transversely between
the corpora striata at the anterior end of the cavity, and immediately i'1
front of the descending anterior pillars of the fornix. The fibres of the
commissure are traceable through the corpora striata into the white
matter of the hemispheres. 2. The Middle (soft) Commissure is com-
posed of delicate grey matter cementing the inner surfaces of the thalami,
and apt to be more or less ruptured in handling the brain. 3. The
Posterior Commissure is white, like the anterior; and its fibres connect
the two thalami at the base of the pineal body, and immediately in front
of the nates.
The 3rd ventricle has a ciliated lining continuous with that of the
4th through the aqueduct of Sylvius, and with that of the lateral
ventricles through the foramen of Monro. In the foetus the cavity com-
municates through the tuber cinereum and infundibulum with the
pituitary body.
The Foramen of Monro, or Foramen Commune Anterius, is the common
point of communication between the 3rd and lateral ventricles. It
might be described as a short vertical shaft ascending from the fore-
part of the 3rd ventricle, and opening under the fornix, which is thrown
over it like an arch. Beneath this arch the lateral ventricles communi-
cate with one another and with the 3rd ventricle.
The Corpora Quadrigemina are two pairs of bodies superposed to the
crura cerebri behind the optic thalami. The anterior pair of bodies, or
nates, are larger than the posterior pair, or testes, from which they are
separated by a groove. Between the right and left nates there is a well-
defined groove, but the groove between the testes is faint or not observ-
able. The nates are grey on their surface, but the testes are white.
The bodies were named nates and testes from a fancied resemblance
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                       253
to the hips and testicles of a man, but these terms are far from express-
ing the relative size of the two bodies.
The Aqueduct op Sylvius, or iter, is a tunnel which, commencing
posteriorly in the 4th ventricle, beneath the valve of Vieussens,
extends forwards beneath the corpora quadrigemina, and opens into the
hinder part of the 3rd ventricle. It possesses a ciliated lining con-
tinuous with that of the ventricles which it connects.
Optic Tracts and Corpora Geniculata.—The optic tracts have already
been seen at the base of the brain, where they form the anterior
boundaries of the interpeduncular space. When followed backwards,
each tract will be found to turn round the crus cerebri, and join the
optic thalamus. At the point of junction two eminences are placed, an
outer, or anterior, and an inner, or posterior. These are named respectively
the corpus geniculatum externum and internum. They are composed of
grey matter from which some fibres of the optic tract pass. Other
fibres of the tract come directly from the optic thalamus, and others
from the corpora quadrigemina.
the cranial or encephalic nerves (plate 33).
In the examination of the base of the brain, the roots of the cranial
nerves have already been noticed, but it will be advantageous to describe
them here as a series. The cranial nerves are distinguished by special
names, and also by numerical designations. It must be observed, how-
ever, at the outset that there are two different systems of enumeration
m use among anatomists, the first of which recognises twelve, and the
other nine, pairs of nerves. This diversity of nomenclature is apt to lead
to confusion, but fortunately this confusion does not extend to veterinary
anatomy, in which, both at home and abroad, the first and more natural
of these methods is exclusively employed. This system is also that
employed by human anatomists on the continent, but by British human
anatomists the number of cranial nerves is stated as nine pairs. The
following table exhibits in the central column the special names of
the nerves, and in the side columns their numerical designations under
the two systems :—
1st pail'      .        .    Olfactory nerves.....1st pair.
2nd   ,,        .        .    Optic nerves......2nd „
3rd   ,,        .        .    Oculo-motor nerves .... 3rd ,,
4th   „        .        .    Pathetic or Trochlear nerves . . 4th „
5th   ,,        .        .    Trifacial or Trigeminal nerves . . 5th „
6th   „        .        .    Abducent nerves.....6th ,,
7th   ,,        .        .    Facial nerves (Portio dura) . . . \
8th    ,,        .        .    Auditory nerves (Portio mollis) . . j "
9th   ,,        .        .    Glosso-pharyngeal nerves . . . x
10th   ,,        .        .    Pneumogastric or Vagus nerves . . j»gth
11th   ,,        .        .    Spinal Accessory nerves . . .j
12tli    ,,        .        .    Hypoglossal nerves .... 9th „
The Olfactory or 1st nerve. The fibres of this nerve leave the surface
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254
THE ANATOMY OP THE HORSE.
of the olfactory bulb, and pass through the foramina of the cribriform
plate to reach the summit of the nasal chamber. They are there distri-
buted in the olfactory division of the lining membrane of that chamber.
The Optic or 2nd nerve arises from the optic chiasma or commissure,
and reaches the back of the orbit by passing through the optic foramen.
Piercing the sclerotic and choroid tunics of the eyeball, its fibres radiate
outwards and form one of the layers of the retina. As already seen, the
optic chiasma is formed by the fusion of the optic tracts, each of which
derives its fibres from the optic thalamus, corpora geniculate, corpora
quadrigemina, and decussation of the pyramids. In the optic chiasma
some of the fibres of each tract cross and are continued in the optic
nerve of the opposite side. Some of the fibres of each optic tract, it is
stated, cross in the chiasma and return to the brain by the opposite
tract, while in the same way fibres pass from the one optic nerve to the
other optic nerve.
The Oculo-motor or 3rd nerve arises from the inner side of the eras
cerebri by a number of bundles, the fibres of which are traceable to
nerve cells in the corpora quadrigemina. The nerve leaves the cranium
by the foramen lacerum orbitale, and reaches the orbit.
The Pathetic, Trochlear, or 4th nerve appears to arise in the valve
of Yieussens (Plate 35). Some of its fibres are decussate with those of
the opposite nerve, and the others are traceable to nerve cells of the
locus cseruleus, or of the corpora quadrigemina. Emerging from the
valve, the nerve winds round the crus cerebri, and appears in front of
the pons. It leaves the cranium by the minute pathetic foramen, and
reaches the back of the orbit. It is the smallest of the cranial nerves.
The Trifacial, Trigeminal, or 5th nerve springs out of the side of
the pons by two roots. The outer and larger of these is termed the
sensory root; and its fibres are traceable to cells of the grey matter of
the medula, pons, and locus cseruleus, and possibly also to the cerebellum.
This root near its origin expands into a large ganglion—the Gasserian
ganglion, beyond which it divides into three branches, viz., the ophthal-
mic, superior maxillary, and inferior maxillary divisions. The inner or
motor root of the 5th nerve is traceable to grey matter of the pons. It
joins the inferior maxillary division of the sensory root. The superior
maxillary division leaves the cranium by the foramen rotundum, the
ophthalmic division by the foramen lacerum orbitale, and the inferior
maxillary division by the forepart of the foramen lacerum basis cranii.
The trifacial is the largest of the cranial nerves.
The Abducent or 6th nerve. This nerve springs from the anterior
part of the medulla, in line with the faint groove that limits outwardly
the inferior pyramid. Some of its fibres issue from the groove between
the pons and the medulla, while others penetrate the trapezium. The
fibres of the nerve are traceable to a group of nerve cells in the medulla.
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DISSECTION OF THE BRAIN, OR ENCEPHALON.                       255
The nerve reaches the orbit by passing through the foramen lacerum
orbitale.
The Facial or 7th nerve springs out of the medulla, close behind
the pons, its fibres seeming to continue outwards the trapezium. Its
rootlets are traceable to nuclei of grey matter in the medulla. The
nerve is joined by a delicate filament—the portio intermedia—which
appears between the roots of this and the next nerve. The 7th nerve
enters the internal auditory meatus in company with the 8th nerve.
Separating from that nerve, it passes along a canal in the petrous
temporal bone—the aqueduct of Fallopius—from which it emerges by
the stylo-mastoid foramen, under the parotid gland. Within the aque-
duct of Fallopius the nerve forms a knee-shaped bend, and at that point
it shows a minute ganglion—the geniculate ganglion—from which pro-
ceed the great and small superficial petrosal nerves (pages 189 and 214).
The Auditory or 8th nerve springs from the medulla, close behind
the pons, and immediately external to the root of the 7th. It is here
compounded of two roots—a superior and an inferior. The superior root
(Plate 35) passes over the restiform body to the grey matter at the floor
of the 4th ventricle. The inferior root springs out of the side of the
restiform body, its fibres arising from nerve cells of that body or of the
grey matter at the floor of the 4th ventricle, and possibly also from the
cerebellum. The 8th nerve enters the internal auditory meatus, and
penetrates to the internal ear.
The Glosso-pharyngeal or 9th nerve springs out of the side of the
medulla, a little behind the outer extremity of the trapezium. It is
here compounded of two or three bundles, the outermost being in line
with the roots of the next two nerves. The fibres emanate from nerve
cells of the grey matter at the floor of the 4th ventricle. The nerve
leaves the cranium by the posterior part of the foramen lacerum basis
cranii, and at that point it shows a minute ganglion—the petrous
ganglion, or the ganglion of Andersch, from which the nerve of Jacobson
arises (page 269).
The Pneumogastric, Vagus, or 10th nerve is formed by a number of
rootlets which spring from the side of the medulla, behind and in line
with the outermost fibres of the 9th nerve. Its fibres arise from nerve
cells of the medulla. The nerve passes out of the cranium by the
posterior part of the foramen lacerum basis cranii, and is joined by the
inner division of the 11th nerve. As the nerve passes through the
foramen it presents an enlargement—the upper ganglion, or ganglion of
Hie root. From this ganglion arises the auricular branch of the vagus,
which penetrates to the aqueduct of Fallopius, where it anastomoses
with the 7th nerve; afterwards emerging from the bone in company
with that nerve, to be distributed to the mucous membrane of the
external auditory process.
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256                                   THE ANATOMY OF THE HORSE.
The Spinal Accessory or 11th nerve comprises two sets of roots—a
spinal and a medullary. The spinal roots appear along the lateral
column of the cervical part of the spinal cord, in which they arise from
a group of nerve cells towards the middle of the grey crescent. By the
union of these roots there is formed a cord which travels upwards
between the superior and the inferior roots of the cervical spinal nerves,
becoming thicker as it ascends. This cord enters the cranial cavity by
the foramen magnum, and is then joined by the medullary roots. The
medullary roots spring out of the side of the medulla oblongata, behind
and in line with the roots of the 10th nerve, the fibres arising from
nerve cells at the floor of the 4th ventricle. These roots join the spinal
part of the nerve, which then leaves the cranium by the foramen lacerum
basis cranii, along with the 10th nerve. In the foramen of exit the
trunk of the nerve resolves itself into two portions—an internal and an
external. The internal portion joins the 10th nerve ; the external portion
is that which has already been seen in the dissection of the neck (page
151).
The Hypoglossal or 12th nerve is formed by the fusion of rootlets
that spring from the lower face of the medulla, along the line that indi-
cates the outer limit of the inferior pyramid. These roots are in series
with the inferior roots of the spinal nerves; and sometimes there is also
present a superior root, in series with the superior roots of the same
nerves, and provided with a minute ganglion. These roots arise from
nerve cells of the medulla. The roots of the nerve perforate the dura
mater, and unite in emerging from the cranium by the condyloid
foramen.
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CHAPTER VII.
DISSECTION OF THE EYEBALL.
Directions.—Let the student procure three or four eyes of the horse,
or, failing these, of the ox. They should be excised from the orbit
immediately after death, and as much as possible of the optic nerve should
be preserved in connection with the eye. While an assistant holds
the eye without squeezing it, the dissector should clean the optic nerve
and the outer surface of the sclerotic with forceps and a sharp scalpel.
One of the eyes so prepared should be completely frozen in a mixture of
ice and salt, and it should then be bisected vertically with a large knife
or fine saw. While still frozen, the section to which the optic nerve is
attached should be fastened by a strong pin to a layer of solid paraffin
at the bottom of a wide and shallow basin. It should be fastened with
the cut surface upwards, the pin being passed vertically from the centre
of that surface; and the vessel should then be filled with water. The
remaining segment should be laid on the freezing mixture, with its cut
surface upwards. By an examination of both segments, the student
should make out the following points :- -
The Globe or Ball of the eye approaches the spherical in form, as is
expressed by these designations. On closer inspection, however, it will
appear to be made up of two combined portions from spheres of different
sizes. The posterior portion, forming about five-sixths of the ball, is a
sphere of comparatively large size with a small segment cut off it in
front; and at this point there is applied to it the anterior portion, which,
being a segment of a smaller sphere, projects at the front of the ball
with a greater convexity than the posterior portion.
The eyeball consists of concentrically arranged coats, and of refracting
media enclosed within these coats. The coats are three in number, viz.,
(1)  an external protective tunic made up of the sclerotic and cornea,
(2)  a middle vascular and pigmentary tunic—the choroid, (3) an internal
nervous layer—the retina. The sclerotic is the white opaque part of
the outer tunic, of which it forms about the posterior five-sixths, being
co-extensive with the larger sphere already mentioned. The cornea
forms the remaining one-sixth of the outer tunic, being co-extensive with
the segment of the smaller sphere. It is distinguished from the
sclerotic by being colourless and transparent. The choroid coat will be
s
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258
THE ANATOMY OF THE HORSE.
recognised as the black layer lying subjacent to the sclerotic. It does
not line the cornea, but terminates behind the line of junction of that
coat with the sclerotic, by a thickened edge—th&j;iliary processes. At
a
i
Fig. 32.
View of the Lower Half of the Eight Adult Human Eye, divided horizontally
THROUGH THE MIDDLE. MAGNIFIED FOUR TIMES (A. Thomson).
1. The cornea ; 1'. Its conjunctival layer ; 2. The sclerotic; 2'. Sheath of the optic nerve passing
into the sclerotic; 3. 3'. The choroid ; 4. Ciliary muscle, its radiating portion ; 4'. Cut fibres of the
circular portion; 5. Ciliary fold or process; 6. Placed in the posterior division of the aqueous
chamber, in front of the suspensory ligament of the lens ; 7. The iris (outer or temporal side); 7'. The
smaller, inner, or nasal side ; S. Placed on the divided optic nerve, points to the arteria centralis
retinse ; 8'. Papilla optica at the passage of the optic nerve into the retina ; 8". Fovea centralis
retinae; r. The nervous layer of the retina ; r'. The bacillary layer; 9. Ora serrata, at the com-
mencement of the ciliary part of the retina ; 10. Canal of Petit ; 11. Anterior division of the
aqueous chamber, in front of the pupil; 12. The crystalline lens, within its capsule ; 13. The vitreous
humour ; a. a. a. Parts of a line in the axis of the eye ; b. b. b. b. A line in the transverse diameter.
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259
DISSECTION OF THE EYEBALL.
the line of junction of the sclerotic and cornea, the iris passes across the
interior of the eye. This, which may be viewed as a dependency of the
choroid, is a muscular curtain perforated by an aperture termed the
pupil. The retina will be recognised as a delicate glassy layer, lining
the greater part of the choroid.
The refracting media of the eye are three in number, viz., (1) the
aqueous humow—a watery fluid enclosed in a chamber behind the cornea ;
(2) the crystalline lens (and its capsule)—a transparent soft solid of a
biconvex form, and placed behind the iris; (3) the vitreous humour—a
transparent material with a consistence like thin jelly, and occupying as
much of the interior of the eye as is subjacent to the choroid.
Directions.—Another eye should be cleaned like the first, and
used for the more particular examination of the sclerotic and cornea.
The Sclebotio is a strong, opaque fibrous membrane which in great
measure maintains the form of the eyeball, and protects the more
delicate structures within it. Its anterior portion, which is covered by
the ocular conjunctiva, is visible in the undisseoted eye, and is commonly
known as the "white of the eye." Inform it is bell-shaped, and the
optic nerve pierces it behind like a handle. The point of perforation,
however, is not exactly at the centre of the summit of the bell, but a
little to its inner side. When the nerve is cut oft' close to the sclerotic,
the nerve-bundles appear as if passing through the apertures of a sieve,
and to this appearance the term lamina cribrosa is applied. The sheath
of the nerve passes on to the sclerotic around the point of perforation.
In front the rim of the bell becomes continuous with the cornea. The
outer surface of the membrane receives the insertion of the muscles of
the eyeball. The inner surface (which will afterwards be exposed) is of
a light brown colour, and is connected to the choroid by fine processes
of connective-tissue—the lamina fusca. The coat is thickest over the
posterior part of the eyeball, and is thinnest a little behind its junction
with the cornea.
Structure.—The sclerotic is composed of connective-tissue, there being
a great preponderance of white fibres, but intermixed with these are
some fine elastic fibres. The bundles of fibres, which are disposed both
meridionally and equatorially, have a felted arrangement, but the
surface fibres are mostly longitudinal. The texture of the sclerotic is
only slightly vascular, the capillaries forming a wide-meshed network.
It is most vascular just behind the cornea.
The Coenea is the anterior transparent portion of the outer coat of
the eyeball. It may be viewed as a part of the sclerotic specially
modified to permit the passage of light into the interior of the ej'e. Its
outline is elliptical approaching the circular, and its greatest diameter
is transverse. At its periphery it joins the sclerotic by continuity of
tissue; and as the edge of the cornea is slightly bevelled, and has the
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260
THE ANATOMT OF THE HORSE.
fibrous sclerotic carried for a little distance forward on its outer surface,
the cornea is generally said to be fitted into the sclerotic like a watch-
glass into its rim. The venous canal of Schlemm runs circularly around
the eyeball at the line of junction of the sclerotic and cornea. The
anterior surface of the cornea is exquisitely smooth, and is kept moist
by the lachrymal secretion. Its posterior surface forms the anterior
boundary of the chamber in which the aqueous humour is contained.
The cornea is of uniform thickness; and, as will afterwards be proved
in removing it, it is very difficult to cut, being of a dense, almost
horny consistence. When its normal convexity is disturbed, the cornea
becomes opaque.                                                                             •
Structure.—Save a few capillary loops at its margin, the cornea is
without vessels. Its structure comprises the following layers, which are
enumerated in order from the anterior to the posterior surface :—
1.   The Anterior Epithelium is a stratified, pavement epithelium,
continuous at the margin of the cornea with the conjunctival epithelium.
2.   The Anterior Elastic Lamina (Bowman's membrane). This is a
structureless, elastic layer. It is extremely thin in the eye of the
lower animals, but is better developed in the human eye.
3.   The Substantia Propria. This, which foims the main thickness of
the cornea, is composed of fibrous connective-tissue arranged in lamella)
parallel to the surfaces of the cornea. Between adjacent lamella! there
is left a network of spaces and branching canals, in which are found the
branched corneal corpuscles.
4.   The Posterior Elastic Lamina (Descemet's membrane) is a thick,
structureless, elastic layer.
5.   The Posterior Ejnthelium is a single layer of polygonal cells.
Directions.—A strong pin should now be passed through the optic
nerve, and used , to fasten the eye beneath the surface of water in a
wide and shallow' vessel, as already directed in the case of the frozen
section. While one hand steadies the eye beneath the water, an incision
is to be made with the other through the cornea, using for the purpose
a very sharp scalpel. As soon as the incision is made, some of the
aqueous humour will escape into the water, and may possibly be recog-
nised by a slight inky discoloration, which is due to a post-mortem
disintegration of the pigmented epithelium lining the cavity in which
the humour is contained. Still keeping the eye under water, one blade
of a pair of small scissors should be introduced within the incision, and
the cornea should be excised immediately in front of its junction with
the sclerotic. The iris will by this means be exposed, and the next step
must be to remove a portion of the sclerotic so as to expose the sub-
jacent choroid. Beginning at its anterior edge, it may be incised back-
wards towards the optic nerve, snipping it bit by bit with the point of
the scissors. Another incision may then be made parallel to the first,
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DISSECTION OP THE EYEBALL.                                      261
and about half an inch from it. The piece of sclerotic between the
incisions may then be raised and turned backwards by destroying the
slender processes, nerves, and vessels that connect it to the choroid. At
the anterior edge of the piece of choroid thus exposed, and immediately
behind the rim of the iris, there will be seen a whitish zone—the ciliary
body, or cmnulus albidus.
The Aqueous Humour occupies a chamber which is bounded in front
by the posterior surface of the cornea; and behind by the capsule and
suspensory ligament of the lens, and by the ends of the ciliary processes.
It is across this chamber that the iris extends, and the chamber is some-
times described as being divided by the iris into two compartments, viz.,
an anterior, in front of the iris; and a posterior, behind it. In the
living eye, however, the posterior surface of the iris contacts with the
lens-capsule, so as to leave only a narrow chink behind the attachment
of the curtain to which the term posterior chamber may be applied.
The aqueous humour is composed of water with a small proportion of
common salt in solution.
The Iris is a muscular pigmented curtain extended across the interior
of the eye, and having about its centre an aperture termed the pupil.
By variations in the size
of this aperture, the
amount of light trans-
mitted to the retina is
regulated. It varies
somewhat in colour, but
is most frequently of a
yellowish brown tint. Its
anterior surface, which
shows some lines con-
verging to the pupil, is
bathed by the aqueous
humour, as is also its
Posterior surface immedi-
ately internal to its
attachment. The greater
part of the posterior sur-
fsipp Iiawo-ooi. is in r.nn        CHOROID MEMBRANE AND IRIS EXPOSE1) BY THE REMOVAL
ice, now ever, IS in con-          of the Sclerotic and Cornea («mmi. after Zimi).
tact with the Capsule of a. One of the segments of the sclerotic thrown back; b. Ciliary
■t-l,^ i__           j v j             ., muscle; c. Iris; e. One of the ciliary nerves ; /". One of the vasa
tne lens, and glides On it TOrtico3a or choroidal veins.
during the movements of the curtain. The circumferential border is
attached within the junction of the sclerotic and cornea. The inner
border circumscribes the pupil, which varies in outline according to its
size. When much contracted, the pupil is a very elongated ellipse, the
long axis of which is in the line joining the nasal and temporal canthi of
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262
THE ANATOMY OF THE HORSE.
the eyelids; but when it is extremely dilated, the ellipse approaches the
circular in form. Appearing at the upper margin of the pupil, there are
generally two or three little sooty masses termed the corpora nigra.
These are little dependent balls of the uvea, or pigmentary layer covering
the back of the iris.
Structure.—This comprises a connective-tissue stroma, muscular tissue,
and an anterior and a posterior epithelium.
The Stroma is a framework of connective-tissue, the fibres having a
radial arrangement, and the corpuscles being branched and pigmented.
The pigment varies in shade from yellow to dark brown or almost black.
The Muscular Tissue is of the non-striated variety, and its fibres are
arranged in two sets, viz., (1) the sphincter of the pupil, a narrow band
around the pupil, and close to the posterior surface of the curtain; (2)
the dilator of the pupil, whose fibres begin at the attached edge of the
curtain, and extend radially inwards to end in the sphincter. The size
of the pupil is regulated by the state of contraction of these two muscles.
When the action of the sphincter preponderates, the aperture is con-
tracted ; when that of the dilator preponderates, the pupil is dilated.
The Anterior Epithelium is continuous at the attached edge of the
iris with the posterior epithelium of the cornea. It is a single layer of
pigmented cells.
The Posterior Epithelium, or Uvea, comprises several layers of cells
similarly pigmented; and, as before stated, the corpora nigra are small
dependent portions of it. In the eyes of albinos the iris is devoid of
pigment; and occasionally in the horse and dog the pigment is only
present in spots, and the animal is then said to be " wall-eyed."
Vessels.—The arteries of the iris are derived from the ciliary branches
of the ophthalmic. They form at the circumference of the iris a larger
circle, from which radial vessels pass inwards and form around the
pupil a smaller circle. The veins have a similar disposition, and termin-
ate in those of the choroid.
In the foetus the pupil is closed by a vascular transparent membrane
—the membrana pupillaris, which disappears before birth.
The Ciliaey Muscle. This is a zone of non-striated muscular tissue
which forms the outer layer of the ciliary body, and lies behind the
circumferent edge of the iris. It consists (]) of an outer radiating
set of fibres, which arise from the inner surface of the sclerotic close
behind its line of junction with the cornea, and pass backwards to
be inserted into the choroid and ciliary processes; and (2) of an inner
circular set, which surround the rim of the iris. When the radiating
fibres contract, they pull forward the choroid coat and ciliary pro-
cesses, and allow the lens to bulge forwards by slackening its tense
suspensory ligament. This is the mechanism by which the eye is
accommodated for near objects.
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DISSECTION OF THE EYEBALL.                                   263
The Choroid Coat. This is a bell-shaped, dark membrane which
lines the sclerotic. Its outer surface, when exposed by the removal of
the sclerotic, has a shaggy appearance due to the tunica fiisca which
unites the two coats. Between the two the ciliary vessels and nerves
pass forwards. The inner surface of the choroid is lined by the layer
of pigmented hexagonal cells belonging to the retina. Behind it is
pierced by the optic nerve; and in front it is continued as the ciliary
processes, which form, as it were, the rim of the bell.
Directions.—In the eye prepared to expose the iris and choroid, a
segment of the former and of the ciliary muscle should be carefully and
delicately removed with scissors, so as to lay bare a number of the
ciliary processes. This is to be done while the eye remains immersed
in water.
The Ciliary Processes. These form a fringe around the slightly
inverted rim of the choroid. They number upwards of a hundred, and
each projects on the inner side of the rim, as a small swelling separated
by depressions from the adjacent processes. The outer surface of each
is covered by the ciliary muscle ; the inner surface rests in a depression
on the suspensory ligament of the lens; behind each is continuous with
the texture of the choroid ; and in front it terminates in a rounded end
which bounds in part the so-called posterior chamber of the aqueous
humour, behind the peripheral part of the iris.
Structure.—The choroid possesses a stroma of connective-tissue with
ramifying corpuscles containing brown or black pigment—melanin.
This stroma is lined internally by a structureless layer—the lamina
vitrea, and it supports the vessels of xhe choroid. The arteries—which
are derived from the ciliary branches of the ophthalmic—and the veins
He together in the outer part of the stroma, while the capillaries lie in
its deeper part and form there the tunica Ruyschiana. The smaller
veins converge in whorls—the vasa vorticosa—to join four or five
principal trunks. The ciliary processes have the same structure as the
choroid. Each contains a rich plexus of tortuous vessels. The branched
cells at the anterior end of each process are without pigment. Over a
considerable area on the inner surface of the choroid the pigment is
absent; and there the choroid shines with a peculiar iridescent, metallic
appearance termed the tapetum lucidum. In the eyes of albinos the
choroid is entirely free from pigment.
The Ciliary Nerves are efferent branches of the lenticular ganglion.
They perforate the sclerotic in company with the ciliary arteries, and
run forwards between the sclerotic and cornea. They give branches to
the cornea and ciliary mu-scle, and terminate in the iris. They contain
sensory fibres, which are derived from the ophthalmic division of the
5th nerve; motor branches to the ciliary muscle and sphincter muscle
of the pupil, which come from the third nerve ; and motor fibres to the
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264                             THE ANATOMY OF THE HORSE.
dilator muscle of the pupil, which are derived from the sympathetic
system.
Directions.—In the immersed eye from which the cornea and part of
the sclerotic have been removed, the portion of choroid exposed is to be
torn away with two pairs of forceps from the subjacent retina. The
inner surface of the membrane will be seen, through the transparent
vitreous humour, in the submerged half of the eye that was frozen.
The Retina is the most delicate of the coats of the eyeball. It is
formed by the radiation of the optic nerve on the inner surface of the
choroid, and like that coat it is bell-shaped. Its external or choroidal
surface is covered by a layer of hexagonal pigment cells, which were at
one time referred to the texture of the choroid. Its inner surface is
moulded on the vitreous humour. This surface shows a little to the
inner side of the summit of the bell, or of the antero-posterior axis of
the eyeball, a disc-like elevation—the papilla optica, which is the point
at which the optic nerve begins to expand. In the centre of this spot
the arteria centralis retinas appears, and divides into branches which
radiate on the inner surface of the retina. The nei-vous structures of
the retina terminate at a wavy line—the ora serrata—behind the
ciliary processes; but the retina is continued beneath"these processes
in the form of an epithelial layer—the pars ciliaris retime, which forms
the edge of the bell.
In the human eye a yellow spot—the macula lutea—is placed a little
external to the papilla optica, and almost exactly in the antero-posterior
axis of the eyeball. This is not present in the eye of the horse or in any
mammal lower than the quadrumana.
The perfectly fresh retina is translucent and of a pale pink colour,
but it speedily becomes opaque. In consistence it is delicate and
jelly-like.
Structure.—Ten distinct layers are described as composing the thick-
ness of the retina. These enumerated from within to without are as
follows:—
The Membrana Limitans Interna.—This, although appearing as a
distinct line in a transverse section, is not a distinct stratum, but merely
the inner limiting line of a sustentacular framework—the radial fibres of
Mtiller—which pervades and supports the nervous elements in the
other layers of the retina.
2.   The Layer of Nerve fibres.—This layer results from the radiation
of the optic nerve, whose fibres at their isoint of entrance into the eye-
ball lay aside their medullary sheath.
3.   The Layer of Nerve Cells.—This is a single layer of multipolar
nerve cells.
4.   The Inner Molecular Layer is a thick stratum of fibres and inter-
mediate granular matter.
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265
DISSECTION OF THE EYEBALL.
5.   The Inner Nuclear Layer contains spindle-shaped or bipolar nerve
cells with distinct oval nuclei and only a small amount of protoplasm.
The inner and outer poles of the cells are continued through the 4th
and 6th layers respectively.
6.   The Outer Molecular Layer repeats the structure of the inner
molecular layer.
7.   The Outer Nuclear Layer contains spindle-shaped cells with con-
spicuous nuclei and a small amount of protoplasm, the poles of the cells
being prolonged as in the case of the similar elements in the inner
nuclear layer.
8.   The Membrana Limitans Externa.—This is the outer boundary of
the sustentacular framework of fibres already mentioned.
9.   The Layer of Hods and Cones, or the bacillary layer, is composed
of two different kinds of elements. The longer elements, the rods,
extend vertically between the 8th and 10th layers; the cones are much
shorter than the rods, and do not reach so far as the next layer.
10.   The Pigmented Epithelium.—This is a layer of polygonal pig-
mented cells, generally six-sided.
Directions.—The third eye should be transversely divided with a
sharp scalpel, about half an inch behind the junction of the sclerotic
and cornea. This should be done with the eye immersed in water.
The posterior half, after removal of the vitreous humour, should be used
for the better examination of the inner surface of the retina. The lens
should be removed for examination from the anterior half. In the eye
already used for the display of the retina, that coat should be in part
removed, so as to display the vitreous humour with the lens imbedded
in its anterior part. By a combined examination of all the preparations,
the following points regarding the lens and vitreous body may be made
out.
The Lens is situated behind the pupil, and is contained within a
capsule of its own.
The Capsule is a close-fitting, firm, transparent membrane, which is
four or five times thicker on the front than on the back of the lens.
The anterior surface of the capsule forms the posterior boundary of the
cavity in which the aqueous humour is contained, and the iris in its
movements glides on it. At its periphery the suspensory ligament of
the lens blends with it. The posterior surface is in contact with the
vitreous humour.
The lens is a transparent solid body of a biconvex shape, the convexity
of its posterior surface being considerably greater than that of the
anterior. It is maintained in a depression on the front of the vitreous
humour by a suspensory ligament. This ligament, which is also known
as the zonula of Zinn, arises behind and beneath the ciliary processes,
where it is connected with the hyaloid membrane of the vitreous
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266
THE ANATOMY OP THE HOBSE.
humour. It passes over the rim of the lens, and blends with the
anterior part of the lens-capsule. Behind the rim of the lens the
ciliary processes rest on the outer surface of the ligament; and when
these are removed, the ligament is there seen to have a fluted or plaited
appearance, each plait fitting into the depression between two processes.
At this same point the inner surface of the zonula forms the outer
boundary of a triangular chink which runs round the lens behind its
rim. This is the canal of Petit, which is bounded in front by the lens-
capsule, behind by the hyaloid membrane of the vitreous humour, and
outwardly by the zonula.
Structure.—When removed from its capsule, the lens is found to be
soft and pulpy in its outer portion, but its density increases in passing
from the surface to the centre. Both its surfaces show some faint
white lines radiating from the central point of the surface. The number
of these lines varies in the adult, but in the foetus they are three in
number, and each line on the posterior surface is in position midway
between two of the anterior lines.
A lens that has been hardened in spirit or by boiling may be broken
down into concentric laminae like the coats of an onion. Each of these
laminse is composed of long riband-shaped fibres. These lens-fibres when
examined microscopically are seen to have finely serrated edges by
which adjacent fibres are interlocked.
The foetal lens is nearly spherical, it is of a reddish colour, and not
quite transparent. In the young adult it is distinctly biconvex, firm,
colourless, and transparent. With advancing age it tends to become
flatter, denser, less transparent, and of a yellowish colour.
The Viteeous Humoue occupies four-fifths of the interior of the eye-
ball. It is globular in form, with a depression in front for the lodgment
of the lens. It is colourless, transparent, and of a consistency like thin
jelly. It is enveloped by a delicate capsule—the hyaloid membrane, which
is connected in front with the suspensory ligament of the lens, and ends
by joining the capsule behind the lens.
Structure.—The vitreous humour is composed of branched connective-
tissue corpuscles in a jelly-like matrix.
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CHAPTER VIII.
THE EAR.
The organ of hearing consists of three divisions—the external, the
middle, and the internal ear. The first of these comprises the osseous
external auditory process, and the trumpet-like organ which collects the
waves of sound and transmits them along that process to the middle
ear. It is described at page 159.
The middle and the internal ear are cavities excavated in the sub-
stance of the petrous temporal bone. From their situation and the
minuteness and intricacy of their parts, their dissection is extremely
difficult. The student is therefore recommended to study the anatomy
of these parts on the models and special dissections to which he is
likely to have access, and by the aid of the fuller description given in
systematic text-books. At the same time, an outline description will
be here given, which the student may illustrate to himself by procuring
two or three petrous temporal bones and dissecting them after they
have been decalcified in a hydrochloric or chromic acid solution.
THE MIDDLE EAR.
The Middle Eak—called also the Tympanum, or drum of the ear—
is a cavity of the petrous temporal bone. It contains air, and
across it there stretches a chain of minute bones, which transmit the
sound waves from the outer to the inner ear. The inner wall of the
chamber is formed by that portion of bone in which the divisions of the
internal ear are excavated, and it shows the following objects :—The
'promontory—a projection, or bulging, which corresponds to the first turn
of the cochlea. Above the promontory, the fenestra ovalis—an opening
which is closed by the base of the stapes (the innermost of the auditory
ossicles). Below the promontory, another opening—the fenestra rotunda,
which is closed by a thin membrane. A pin passed through the
fenestra ovalis, would enter the vestibular division of the internal ear;
if passed through the fenestra rotunda, it would penetrate the scala
tympani of the cochlea. The outer wall of the chamber is formed
mainly by the membrana tympani. This is a thin, translucent membrane
■Wiiich forms the septum between the tympanum and the outer ear.
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268
THE ANATOMY OF THE HORSE.
The rim of the membrane is fixed in a groove of the bone. The mem-
brane is slightly cupped towards the outer ear; while its inner surface
is convex, and has the handle of the malleus (the outermost ossicle)
attached to it. The surfaces of the membrane are inclined so that the
outer surface looks somewhat downwards, and the inner upwards. «*
structure the membrane comprises (1) a middle fibrous stratum, the
fibres being arranged both radially and circularly, with (2) an outer
and (3) an inner epithelial covering. The roof and the floor of the
tympanum present nothing of interest. The former is the more exten-
sive. The anterior exti'emity of the chamber shows a fissure by which
air is admitted from the Eustachian tube. Through this opening also
the mucous lining of the cavity is continuous with that of the Eustachian
tube. The posterior extremity, and part of the floor and outer wall
communicate with the cellular spaces of the mastoid protuberance.
The Auditory Ossicles.—There are three of these, viz., the malleus,
the incus, and the stapes.
The Malleus, named from its resemblance to a hammer, is the
largest bone. It possesses a head, a handle, and two processes. The
head is articulated by a synovial joint to the stapes. The handle is
fixed on the inner surface of the membrana tympani. The long process
is slender, and projects forwards to be fixed in a slit of the petrous
temporal. The short process is a mere projection of the root of the
handle, and is fixed to the membrana tympani.
The Incus is named from its supposed resemblance to an anvil, but it
has more likeness to a human bicuspid tooth. It presents a body and
two processes, or crura. The body has a saddle-shaped articular facet for
the malleus. The short process is directed backwards to be fixed to the
wall of the tympanum. The long process curves downwards and inwards
to terminate in a rounded point—the orbicular process, which articulates
with the head of the stapes.
The Stapes is stirrup-shaped. It is the smallest bone, and possesses
a head, a neck, a base, and two crura. The head is depressed for articula-
tion with the orbicular process, and is succeeded by the slightly
constricted neck. The base is a thin plate which closes the fenestra
ovalis. The crura are slender rods of bone connecting the base and the
neck.
Muscles of the Ossicles.—These are two—the tensor tympani and the
stapedius. (The so-called laxator tympani is now believed to be a
ligament.)
The Tensor Tympani arises from the petrous temporal bone near the
Eustachian orifice, and it is inserted by a slender tendon into the handle
of the malleus near its root.
Action. —To tense the membrana tympani.
The Stapedius arises within the pyramid—a small process of bone at
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269
THE EAR.
the back of the tympanum
into the neck of the stapes,
Issuing from the pyramid, it is inserted
Its tendon of insertion contains a small
nucleus of bone.
Action.—To regulate (diminish the excursions of) the movements of
the stapes.
Bloodvessels. The arteries of the tympanum are derived from the
tympanic artery, a branch of the internal maxillary artery.
Nerves. The chorda tyrrvpani branch of the 7th nerve enters the
cavity of the tympanum from the aqueduct of Fallopius; and passing
across the membrana tympani it leaves the cavity by the styloid fora-
men. The sensory nerves of the tympanum are derived from the
tympanic branch (J acobson's nerve) of the glossopharyngeal.
The Nerve to the Stapedius is a branch of the 7th.
The Nerve to the Tensor Tympani comes from the 5th, through the
otic ganglion.
THE INTERNAL EAR.
The Internal Ear, called also, from its complexity, the Labyrinth,
consists of a series of chambers, or passages, in the petrous temporal
bone, and of certain fluids and soft
textures contained within these
passages. The chambers, with the
wall of condensed bone tissue which
immediately surrounds them, con-
stitute the osseous labyrinth; the
contained soft structures form the
membranous labyrinth. The osseous
labyrinth consists of three divisions;
■—the vestibule, the cochlea, and the
Fig. 34.
Diagram of the Membranous Labyrinth.
DC. Ductus cochlearis ; dr. Ductus reuniens ;
S. Sacculus; U". Utriralus ; dv. Ductus vesti-
buli ; SC. Semicircular canals. (1'urner, after
Waldeyer).
semicircular canals, and each of these
contains a division of the mem-
branous labyrinth.
The Vestibule. This is the
central division of the labyrinth. It
lies between the inner w7all of the tympanum and the internal audi-
tory meatus. In front it communicates with the scala vestibuli of the
cochlea, and the semicircular canals open into it behind by five
openings. On its outer wall, which separates it from the tym-
panum, is the fenestra ovalis, closed by the base of the stapes. On
its inner wall in front there is a depression—the fovea hemispherica—
placed over the meatus auditorius internus, and pierced by minute
foramina for the passage of the filaments of the auditory nerve.
Behind the fovea hemispherica is a small slit which leads into the
aqueductus vestibuli. The roof of the vestibule shows another depres-
sion—the fovea liemi-elliptica.
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270
THE ANATOMY OF THE HORSE.
Contained immediately within the osseous vestibule there is a quantity
of limpid, serous fluid—the perilymph, which surrounds the parts of the
membranous labyrinth here found. These are two delicate sacs—the
saccule and the utricle.
• The Saccule is the anterior and smaller of the two sacs, and is lodged
in the fovea hemispherica. It contains a fluid termed the endolymph.
It communicates with the membranous canal of the cochlea by a
minute tube—the canalis reuniens, and with the utricle by a Y shaped
tube—the ductus vestibuli, the stem of which ends blindly in the aqueduct
of the vestibule.
The Utricle, placed above and behind the saccule, is lodged in the
fovea hemi-elliptica. Like the saccule, it contains endolymph. It com-
municates, as aforesaid, with the saccule; and the five openings of the
membranous semicircular canals open directly into it.
The interior of both saccule and utricle is elevated into a ridge—the
crista acoustica, in which are distributed the terminal filaments of the
vestibular division of the auditory nerve. On this crest are certain
peculiar cells, each having a peripheral hair-like process which projects
into the endolymph, and a central process which is probably continuous
with a filament of the auditory nerve. Here are also found the otoliths,
which are minute calcareous particles imbedded in a jelly-like material.
The Semicircular Canals are placed behind the vestibule. They are
three in number and are distinguished as supei-ior, posterior, and external.
The two first have a vertical direction, while the latter is nearly hori-
zontal. Each canal opens into the vestibule by a dilated extremity,
termed the ampulla. The non-ampullated end of the external canal
opens by an independent orifice into the vestibule, while the non-ampull-
ated ends of the other two canals have a common opening into the same
cavity. The three canals have thus five openings into the vestibule,
and three of these openings are ampullated.
The Membranous Semicircular Canals.—Contained immediately within
the osseous canals is a quantity of perilymph, which surrounds the
membranous canals. Each of these repeats the form of the osseous
canal in which it is lodged ; and they communicate with the utricle by
five openings, three of which are ampullated. The membranous canals
contain endolymph, and the ampullated end of each is raised inwardly
into a ridge, or acoustic crest, having hair cells, otoliths, and nerve
terminations similar to those of the saccule and utricle.
The Cochlea is named from its resemblance to a snail's shell. It has
the form of a slightly tapering tube wound spirally two and a half
times around a central axis—the modiolus. It is thus somewhat
conical in form, the base lying inwards near the internal auditory
meatus, from which point the axis of the cone is directed outwards, for-
wards, and downwards to the apex. Projecting half way into the tube
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271
THE EAR.
of the cochlea is a lamina, or shelf, of bone—termed the osseous spiral
lamina. The tube is thus imperfectly divided into two passages, termed
respectively the scala tympani and the scala vestihuli. The separation
between these two passages is rendered more complete, and a third
passage is marked off, by certain membranous structures. These are
the basilar membrane and Reissner's membrane. The basilar membrane
stretches from the free edge of the osseous spiral lamina to the outer
wall of the tube, where it joins a thickening of the lining of the tube,
termed the spiral ligament. Reissner's Membrane is much more delicate,
"nd stretches from the crista spiralis at the free edge of the osseous
spiral lamina, obliquely upwards and outwards to the wall of the tube.
Transverse Section through the Tube or the Cochlea.
Til. Modiolus; O. Outer wall of cochlea; SV. Scala vestibuli; ST. Scala tympani; DC. Ductus
cochlearis; mil. Membrane of Reissner ; bm. 3asilar membrane ; so. Crista spiralis ; si. Spiral liga-
ment ; sg. Spiral ganglion of auditory nerve ; oc. Organ of Corti {Turner).
The tube is thus divided into three passages, viz., the scala tympani,
the scala vestibuli, and the scala intermedia.
The Scala Tympani is the largest of the three passages, and is
separated from the other two by the osseous spiral lamina and the
basilar membrane. At the base of the cochlea it begins at the fenestra
rotunda, by which, in the dried bone, it communicates with the
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272
THE ANATOMY OF THE HORSE.
tympanum. At the apex of the cochlea it communicates with the scala
vestibuli by a small opening—the helicotrema.
The Scala Vestibuli is separated from the preceding by the osseous
spiral lamina, and from the scala intermedia by Reissner's membrane.
At the apex of the cochlea it communicates with the scala tympani by
the helicotrema, and at the base it opens freely into the osseous vestibule.
Like the vestibule, it therefore contains perilymph, and this passes also
by the helicotrema into the scala tympani.
The Scala Intermedia is the smallest but the most important of the
three passages. It is the true membranous cochlea, and is called also the
ductus cochlearis. It is separated from the scala vestibuli by the mem-
brane of Eeissner; and from the scala tympani mainly by the basilar
membrane, but partly by the osseous spiral lamina near its free edge.
At the base of the cochlea it communicates by the slender canalis
reuniens with the sacculus, and it thus contains endolymph.
The terminal filaments of the cochlear division of the auditory nerve
are distributed in the substance of the basilar membrane ; and on that
surface of the membrane which is directed towards the scala intermedia,
there occurs a peculiar arrangement of cells, termed the organ of Corti.
The Organ of Corti.—When the basilar membrane is examined in
transverse section, it is seen to support about the centre of the surface
directed towards the scala intermedia a double row of elongated rod-
like cells, termed Corti's rods. The rods of the two rows, where they
rest on the basilar membrane, are separated by a slight interval; but
they incline towards each other and meet at the opposite extremity, so
as to enclose a minute canal—the canal of Corti. On the outer side
of the external row of rods, the basilar membrane supports four or five
rows of shorter cells, the free extremity of each of which bears a tuft of
stiff, hair-like processes. In the same way the membrane supports a
single row of hair-bearing cells on the inner side of the inner rods of
Corti. On either side these hair-bearing cells are succeeded by cells
which become progressively shorter and pass into the general columnar
cell lining of the scala intermedia. A delicate cellular membrane—the
membrana reticularis—is spread over the outer hair-bearing cells.
Through apertures in this membrane, the tufts of hair-like processes
project, in a manner comparable to tufts of grass springing through the
interstices of a wire net. Still another membrane—the membrana tectoria
—springs from the edge of the osseous spiral lamina between the lines of
origin of the basilar and Eeissner's membranes, and passes outwards
over the organ of Corti.
The Auditory (8th) Cranial Nerve. This nerve enters the inter-
nal auditory meatus in company with the 7th, which passes into the
aqueduct of Fallopms. The 8th divides into two branches, one for the
cochlea, the other for the vestibule and semicircular canals. The
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273
THE EAR.
filaments of the latter branch penetrate the minute foramina seen at the
bottom of the internal auditory meatus, and are finally distributed in
the saccule, utricle, and ampvillated ends of the membranous semicircular
canals. The cochlear branch penetrates the modiolus, and in its passage
detaches twigs which pass outwards in the osseous spiral lamina to reach
the basilar membrane. Within the spiral lamina there are numerous
ganglion cells placed on the course of the nerve fibres.
-ocr page 342-
CHAPTER IX.
DISSECTION OF THE PERINEUM IN THE MALE.*
Under this section there will be described not only the perinteum
proper, but also the scrotum, testicle, prepuce, and penis. The dissec-
tion of all these must precede that of the hind limb and abdomen, and
it should therefore be begun without delay.
THE PERINEUM.
Position.—Place the animal on the middle line of its back, and draw
its hind legs upwards and outwards by ropes running over pulleys fixed
to the ceiling. The posterior extremity of the trunk should be level
with, or project slightly over, the end of the table on which the subject
rests. Empty the posterior part of the rectum, and stuff it with tow
saturated in some preservative solution. A stitch should then be put
through the edges of the anus.
Surface-marking.—The deep boundaries of the perinaeum are those of
the outlet of the pelvis (page 341), but its superficial boundaries are as
follows :—Above it is limited by the root of the tail, on each side it is
bounded by the semimembranosus muscle, and inferiorly it is continued
without any limit into the cleft between the thighs.
On the middle line below the root of the tail is the anus. This forms
an eminence more pronounced in the young, than in the old, animal.
The integumental covering of the eminence is thin, puckered, and hair-
less; and it is generally dark-pigmented. Passing between the rectum
and the root of the tail on each side, and most distinct when the latter
is forcibly elevated, there is a projection caused by the so-called suspen-
sory ligament of the rectum. Beneath the anus there can be seen or
felt a longitudinal prominence formed by the urethra; and on the middle
line of this, there is a median raphe which is prolonged between the
thighs.
Directions.—Make a mesial incision through the skin for a length of
six inches below the anus. Carry this incision round the sides of the
anus, and up to the root of the tail. Make another incision trans-
versely from one tuber ischii to the other. These incisions will enable
* The description of the perinseuni in the female is incorporated with that of the pelvis.
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275
DISSECTION OP THE PERINEUM IN THE MALE.
sufficient skin to be raised as four triangular flaps. Around the anus
there is a quantity of fat, whose amount varies with the condition of the
subject, but is greater in the young, than in the old, animal. In this
fat the perineal nerves are to be followed.
Perineal Cutaneous Nerves.—1. Hemorrhoidal Branch of 5th Sacral
Nerve. This nerve will be found emerging at the hinder edge of the
coccygeal origin of the semimembranosus, and curving downwards and
inwards at the root of the tail. It supplies the skin there, and gives
some twigs downwards to the skin of the anus.
2.   Ilcemorrhoidal Nerve. The trunk of the hsemorrhoidal nerve,
which cannot be reached at present (page 343), divides between the
sacro-sciatic ligament and the retractor ani. Its branches are as
follows :—1. A branch appears at the inner side of the coccygeal origin
of the semimembranosus, and is distributed at the side of the anus. 2.
External to the preceding a branch perforates the semimembranosus; and
descending over the tuber ischii, it is distributed at the side of the
penis. 3. About an inch or two below the anus a branch appears near
the middle line, and descends over the urethra.
3.   Pudic Nerve. Ascending on the side of the anus, beneath the
branches of the hsemorrhoidal nerve, are some twigs from the pudic
nerve. They terminate in the skin and the sphincter ani.
Perineal Fascia. The lower part of the perinseum is covered by two
layers of fascia, viz., a superficial and a deep. The superficial layer is
attached laterally to the fascia covering the muscles on the inside of the
thigh, towards the anus it loses its aponeurotic character and becomes
cellular, and inferiorly it blends with the dartos. The deep layer is
reflected upwards at each side of the penis, while above and below it
loses its distinctness and becomes cellular.
Directions.—These layers of fascia should be removed, and the parts
should be cleaned after the manner of Plate 37. Beneath the deep
layer a branch of the pudic nerve will be found descending on the acceler-
ator urinss muscle. The transversus perinsei, if present (it was absent
in the subject from which the Plate was taken), will be found concealing
the internal pudic artery, and may be removed on one side.
The Internal Pudic Artery. This vessel is a branch of the internal
iliac artery (Plates 46 and 47). It descends obliquely along the side of
the pelvis, on the inner side of the sacro-sciatic ligament or within its
texture. At the small sacro-sciatic foramen it passes backwards and
inwards to turn round the ischial arch. It penetrates the urethral bulb,
immediately resolving itself into a number of branches that supply the
erectile tissue of that body. Its position should be particularly noted
with reference to the operation of lithotomy, in which, by making a mesial
incision, the urethra may be opened without danger of wounding the
artery.
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276
THE ANATOMY OP THE HORSE.
In this part of its course the vessel gives off small branches -to the
anus and to the erector penis muscle.
The Internal Pudic Vein accompanies the artery.
The Sphincter Ani Externus. The fibres of this muscle are of the
striped variety, and they are circularly disposed around the anus.
Above the anus the fibres are fixed at the root of the tail, and below it
they unite to form a pointed slip inserted into the perineal fascia. The
muscle should be removed in order to expose the next.
The Sphincter Ani Internus. This is comprised between the outer
muscle and the mucous membrane. Its fibres are circularly disposed
like those of the external sphincter, from which they differ in being of
the non-striped variety. They are, in fact, nothing more than the last
of the circular muscular fibres of the rectum; and in the horse they are
not aggregated in the form of a ring, as they are in man.
Action of the sphincters.—To maintain the anus closed except during
the passage of excreta.
The Eetractor Ani (Levator ani of human anatomy). This muscle is
red like the external sphincter. It arises (but this cannot be seen at
present) from the superior ischiatic spine, and from the inner surface of
the sacro-sciatic ligament over the small racro-sciatic foramen. Its
fibres pass upwards and backwards, and terminate in tendinous slips
that are insinuated beneath the anterior edge of the external sphincter.
Action.—During the passage of fa3ces the anus is carried backwards
and everted, and the action of this muscle is to carry the anus forwards
and invert it after the act of defecation.
The Eetractor Penis. This muscle descends at the side of the rec-
tum, immediately in front of the external sphincter, and under cover of
the termination of the retractor ani, which must therefore be raised and
turned forwards. The fibres of the muscle are non-striped, and they
form a narrow riband which arises from the 1st and 2nd or 2nd and
3rd coccygeal bones. The right and left bands meet below the rectum,
for which they thus form a kind of sling. They are then prolonged
downwards on the middle line of the corpus spongiosum, on which they
are lost near the extremity of the penis.
Action.—To retract the penis within the prepuce when erection passes
off.
The Suspensory Ligament of the Eectum (Plate 46). This, although
denominated a ligament, is composed of non-striped muscular tissue. It
is derived from the longitudinal muscular fibres of the rectum, which it
leaves in front of the external sphincter; and passing upwards, it
becomes inserted into the 4th and 5th coccygeal vertebra?. It forms
at the root of the tail a prominence which has already been referred to.
The Transveesus Perin^ei. This muscle is not constantly present.
It arises from the tuber ischii, behind the origin of the erector penis;
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DISSECTION OP THE PERINEUM IN THE MALE.                      277
and it passes transversely inwards to terminate on the middle line over
the urethra, being confounded with its fellow of the opposite side, and
with the first fibres of the accelerator urinse.
Action.—To dilate the bulbous part of the urethra.
The Accelerator URiNiE. These muscles (right and left) cover the
sides and lower face of the urethra from the ischial arch to the free
extremity of the penis. Along the inferior median line of that tube the
right and left muscles are joined by an intermediate fibrous raphe.
From this raphe the fibres pass round the urethra on each side, with a
slightly forward inclination, and are lost on the upper aspect of
the tube, but without reaching the middle line. Beneath the anus the
first fibres of the muscle seem to arise from the retractor penis muscle,
but elsewhere the retractor is superficial to the intermediate raphe of
the right and left muscles.
Action.—The muscles of opposite sides always act together ; and when
they do so, they diminish the calibre of the urethra and expel its con-
tents. In this way they are instrumental in the ejaculation of semen.
In micturition the muscles ordinarily do not come into play until the
close of the act, when they empty the urethra from behind to before.
The necessity for this action exists because the expelling power of the
bladder is lost as soon as its own cavity is emptied.
The Erector Penis. This is a thick, dark-red muscle covering the
crus penis. Its fibres arise from the inferior ischiatic spine (of the
tuber), and they terminate on the crus.
Action.—To aid in erecting the penis by compressing the crus and
thus retarding the return of blood from the cavernous body of the
penis.
THE SCROTUM (PLATE 37).
Position.—Let the subject remain in the dorsal position, but unfasten
the rope from one of the hind limbs, and allow the trunk to incline to
the same side. The loose limb should be fastened backwards out of the
way.
Directions.—Grasp the neck of the scrotum close to the wrall of the
abdomen, so as to tighten the skin over the testicle, and then tie a piece
of soft cord round the constricted neck of the scrotum. This will facili-
tate the dissection of the different layers of the pouch.
The scrotum is the bag, or pouch, in which the testicles are sus-
pended. It is laminated, and comprises the following layers :—
1. The Scrotal Integument. This is continuous with the surround-
ing skin, of which it is a modified portion. It is thin, with short fine
hairs, and numerous sebaceous glands, whose secretion renders it moist.
It is traversed mesially by a raphe, continuous posteriorly with the
median raphe of the perinseum. The scrotal integument forms a single
bag for the two testicles.
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278
THE ANATOMY OF THE HORSE.
2.   The Dartos. If a portion of skin be removed from the scrotum, it
will expose a reddish-yellow layer, composed of connective-tissue with
many elastic fibres and a considerable quantity of involuntary muscular
tissue. This is the dartos, and, like the remaining tunics of the
testicle, it forms two distinct pouches, one for each testicle. In the mesial
plane, over the median raphe, the right and left pouches are applied
together and form the septum scroti; but superiorly they separate to
allow the penis to pass between them. Traced upwards, the dartos is
continuous around the external abdominal ring with the subcutaneous
fascia. Under the contraction of the muscular tissue of the dartos, the
scrotum becomes firm and wrinkled; during relaxation the scrotum is
smooth and pendulous.
3.   The Spermatic Fascia, continuous with the tendon of the external
oblique tendon.
4.   The Cremasteric Fascia, continuous with the internal oblique
muscle.
5.   The Infundibuliform Fascia, continuous with the transversalis
fascia.
6.   The Tunica Vaginalis Keflexa, a layer of serous membrane con-
tinuous with the peritoneum of the abdominal cavity.
In Plate 37 these layers are semi-diagrammatically represented as suc-
ceeding each other like the coats of an onion. The dissector will probably
be unable to discriminate layers 3, 4, and 5. The tunica vaginalis reflexa,
he wTill recognise as a semitransparent layer which, when cut through,
takes him into a smoothly lined pouch in which the testicle lies free.
This is the sac of the tunica vaginalis, a diverticulum of the peritoneal
cavity.
In the foetus the testicles make their first appearance in the sub-
lumbar region, close behind the kidneys. As development proceeds,
they descend through the abdominal wall into the scrotum; and hence
the correspondence between the coverings of the testicle and the layers
that compose the wall of the abdomen.
If the dissector will now lay hold of the testicle, and endeavour to
drag it out of the opening which he has made in its coverings, he will
bring into view the spermatic cord. The testicle, he will observe, is
covered by a glistening serous membrane, the tunica vaginalis propria,
which he can trace upwards on the cord. This spermatic cord contains
the vessels, nerves, and excretory duct (vas deferens) of the testicle,
which structures descend through the abdominal wall by an oblique
passage termed the inguinal canal. In the upper part of this canal,
which is not to be exposed at present, the tunica vaginalis propria of the
cord is continuous with the tunica vaginalis reflexa.
The Cremaster Muscle is continuous with the cremasteric fascia
already described. It is a bright red muscle, placed in the cord beneath
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•
DISSECTION OF THE PERINiEUM IN THE MALE.                      279
its serous covering. It passes upwards through the inguinal canal, in
which its connections will be observed at a later stage.
The Spermatic Vessels. The spermatic artery is an important vessel
from the haemorrhage to which it may give rise in castration. It is
placed in the anterior part of the cord, and in a well-injected subject its
remarkably convoluted disposition will be evident without dissection.
The spermatic veins accompany the artery. They are large and tor-
tuous.
The Vas Deferens is the excretory duct of the testicle, and is placed
at the posterior part of the spermatic cord, where it may be seen and
felt as a thick, firm tube.
Directions.—The student, having identified these different elements of
the cord, may practise the operation of castration by any one of the
common methods, taking care to sever the spermatic cord just above the
epididymis, at the upper border of the testicle. The cord is to be left
in the inguinal canal.
THE TESTICLE AND EPIDIDYMIS (PLATES 46 AND 47).
The Testicle is the gland that secretes the semen—the male fertil-
izing fluid. In form it is ovoid. Its faces, right and left, are smooth
and rounded; its inferior border is slightly convex and free; its upper
edge is nearly straight, and is related to the epididymis. Its anterior
extremity shows below the globus major of the epididymis a small cyst-
like body—the pedunculated hydatid of Morgagni.
The Epididymis is made up of the convolutions of the excretory tube
of the testicle. It presents anteriorly an enlargement termed the
globus major, and posteriorly a lesser enlargement termed the globus
minor, the intermediate part being called the body. At the globus
minor the tube loses its convoluted disposition, and is continued as the
vas deferens, which, as already seen, becomes one of the constituents of
the spermatic cord.
Structure. The testicle has for its most external investment the
tunica vaginalis propria,. This, as already explained, is a serous mem-
brane which passes on to the testicle from the cord, and is continuous
with the peritoneum at the upper opening of the inguinal canal. It is,
as it were, the visceral part of a serous membrane, the tunica vaginalis
reflexa—the inner lining of the bag in which the testicle lies free—
being the parietal portion of the same membrane. This covering is
thin and transparent, and closely adherent to the next covering—the
tunica albuginea. The tunica albuginea is a complete envelope of dense,
lamellated connective-tissue, containing some fibres of non-striped
muscular tissue. Towards the upper and anterior part of the testicle, a
strong process from the tunica albuginea passes into the interior of the
gland. This is termed the corpus Highmori, or mediastinum testis; and
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280
THE ANATOMY OF THE HOESE.
between it and the inner surface of the tunic, numerous trabecule pass,
forming a framework for the gland, and dividing it into a number of
conical compartments, or lobules, which lodge the seminal tubules. On
the inner surface of the tunica albuginea, and on its trabecular, the
bloodvessels are distributed, forming the tunica vasculosa.
Each seminal tubule begins either with a blind extremity, or by anas-
tomosing with an adjacent tubule. The tubes are highly convoluted
until they aj>proach the mediastinum, where they unite to form a series
of straight tubes—the tubuli recti, which enter the mediastinum and
form in it a network—the rete testis. From this network arise a number
of tubes termed the vasa efferentia, which perforate the tunica albuginea
above the anterior end of the testicle. On leaving the gland, these
become convoluted, forming little masses known as the coni vasculosis
and they then unite with one another until there results a single excre-
tory tube, whose convolutions make up the globus major, body, and
globus minor of the epididymis. The seminal tubules are composed of
a membrana propria and an epithelial lining. The epithelium is
arranged in several layers, and through the agency of the innermost
cells—spermatoblast cells—the spermatozoa of the semen are produced.
The tubuli recti and rete testis are lined by a single layer of columnar
epithelium. The tubes of the vasa efferentia and epididymis have a
wall that contains non-striped muscular fibres, and they possess a colum-
nar ciliated lining.
THE PEEPUCE.
The prepuce, vulgarly called the " sheath," is the involution of skin
which lodges the free portion of the penis when that organ is non-
erect. In this condition it consists of two layers—an external, similar
to the surrounding integument, with which it is continuous; and an
internal, which is intermediate in texture between skin and mucous
membrane. The latter layer is smooth, destitute of hair, and provided
with numerous preputial glands, which secrete a strong-smelling sebaceous
material. This material facilitates the protrusion of the penis during
erection; and, ordinarily, it accumulates in considerable amount within
the prepuce. These two layers are continuous with one another at the
orifice of the preputial cavity, and at the posterior end of the cavity the
inner layer is continuous with the investment of the penis. Towards
the orifice of the perputial cavity, two rudimentary tubercle-like teats
are sometimes found. Lay hold of the extremity of the penis, and pull
it forcibly forwards, at the same time pulling the prepuce backwards.
This will obliterate the prepuce, as in erection, in which condition the
inner layer of the prepuce becomes a part of the covering of the penis.
Directions.—While the penis is pulled forwards out of the prepuce,
carry a mesial incision through the skin from the perinaium to the
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DISSECTION OP THE PERINEUM IN THE MALE.                      281
entrance of the prepuce, and reflect the skin on each side for three or
four inches.
Suspensory Ligaments of the prepuce. When the outer cutaneous
layer of the prepuce is removed, there is exposed an elastic fibrous layer
which descends into it on each side from the abdominal tunic. These
are the suspensory ligaments of the prepuce.
Vessels and Nerves. The cutaneous nerves of the prepuce and scro-
tum are branches of the inguinal nerve or nerves. One or more of
these, derived from the 2nd and 3rd lumbar nerves, descend through
the inguinal canal. The arteries are branches of the subcutaneous
abdominal artery. This vessel, which is a branch of the external pudic
artery, passes forwards a few inches from the middle line. The trunk
of the artery is to be left undisturbed at present.
A rich plexus of veins exists in and around the scrotum. This
plexus is drained by a comparatively small vein that accompanies the
external pudic artery, and by a larger vessel which penetrates the
gracilis to empty itself into the femoral vein.
THE PENIS.
Directions.—While the penis is pulled forwards, reflect the integu-
montal covering from the upper face of its free portion, and follow back-
wards its dorsal vessels and nerves.
Dorsal Arteries of the penis (Plates 39 and 46). On each side there
are two of these, distinguished as anterior and posterior. 1. The anterior
dorsal artery of the penis is one of the terminal branches of the external
pudic artery. It results from the bifurcation of that vessel imme-
diately after its emergence from the inguinal canal, and after a course
of a few inches it divides into an anterior branch which passes forwards
on the free portion of the penis, and a posterior which passes backwards
on the fixed portion, meeting and anastomising with the posterior
dorsal artery. When the penis is non-erect, the anterior of these
branches has a flexuous disposition, which permits it to be elongated
without stretching when the organ becomes erect. 2. The posterior
dorsal artery of the penis is a branch of the cavernous artery (from the
obturator). It runs forwards on the dorsal aspect of the fixed portion
of the penis, and anastomoses with the posterior division of the anterior
dorsal artery. These arteries are mainly expended in branches to the
cavernous and spongy portions of the penis, and they also give off some
twigs to the prepuce.
Dorsal Nerves of the penis. These nerves, right and left, accom-
pany the dorsal vessels on the dorsum, or upper surface, of the penis.
Each is the continuation of the pudic nerve, which reaches the penis by
turning round the ischial arch. In proceeding forwards along the
penis, the nerves are disposed in a flexuous manner to allow them to be
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282
THE ANATOMY OF THE HORSE.
adapted without stretching to the varying length of the organ. They
emit numerous branches to the cavernous and spongy portions of the
penis, and terminate in the glans.
Suspensory Ligaments of the penis (Plate 46). These are two fibrous
bands, right and left, which are attached superiorly to the tendon of
origin of the gracilis, and below to the cavernous body of the penis.
Directions.—The penis may now be freed as far as its posterior
extremity, and its surface cleaned of vessels, nerves, and connective-
tissue. On one side the erector |>enis muscle should be removed, to lay
bare the crus and expose the artery of the corpus cavernosum.
The Artery of the Corpus Cavernosum (Plate 46). This is a branch
of the obturator artery, detached after the emergence of that artery
from the obturator foramen. It passes backwards on the lower face of
the ischium, and perforates the crus penis. It gives off as a collateral
branch the posterior dorsal artery of the penis.
The Penis (Plates 46 and 47) is the male organ of copulation. It
begins at the ischial arch, where it is attached by its crura to the ischial
tuberosities; and it terminates anteriorly in a free enlargement—the
glans. It may be said to consist of a posterior fixed portion, and an
anterior portion which is free and protrusible. The former portion
extends from the ischial arch to the scrotum; the latter, when the
organ is non-erect, is lodged in the prepuce, but during erection the
prepuce becomes obliterated, and this part of the penis then projects
freely in front of the scrotum.
The penis is compounded of three longitudinal and parallel columns,
viz., two corpora cavernosa and a single corpus spongiosum. From the
relationship of these to one another, the penis has been happily com-
pared to a double-barrelled gun, the barrels being represented by the
corpora cavernosa, and the ramrod by the corpus spongiosum.
The Corpora Cavernosa. Each corpus cavernosum begins at the
tuber ischii, to whose inferior ridge (inferior ischiatic spine) it is firmly
attached under cover of the erector penis muscle. These constitute the
roots, or crura, of the penis, and they converge towards each other and
form a single mass which makes up the main thickness of the penis as
far as the glans. The united corpora cavernosa have an upper flattened
surface, or dorsum, along which the dorsal vessels and nerves pass.
Their sides are smooth and slightly rounded, and inferiorly they form a
shallow median groove for the corpus spongiosum (Fig. 44). Anteriorly
they terminate bluntly in the glans.
The Corpus Spongiosum forms a much more slender column than the
corpora cavernosa. It is traversed in the whole of its length by the
extra-pelvic part of the urethra. This urethra, as will subsequently be
seen, begins at the neck of the bladder, and its first few inches are
intra-pelvic, being placed over the ischiatic symphysis. Turning round
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DISSECTION OF THE PEBIN^UM IN THE MALE.                      283
the ischial arch, the intra-pelvic urethra becomes directly continuous
with the extra-pelvic portion, and from the point of continuity onwards
the urethra is enveloped in a sheath of erectile tissue, which is the
corpus spongiosum. The corpus spongiosum forms at either of its
extremities an enlargement. The posterior enlargement, which is
situated at the ischial arch, is termed the bulb; the anterior enlarge-
ment is the glans penis. The glans forms the expanded free extremity of
the penis, and it surrounds the blunt anterior end of the united corpora
cavernosa. During erection the enlargement assumes a shape resem-
bling, somewhat, the rose of a watering-can, having a prominent ridge—
the corona glandis, behind which there is a slight constriction—the
cervix. The front of this rose-like swelling presents a fossa from which
the urethra projects for about half an inch as a free tube—the urethral
tube. Above the base of the urethral tube there is the opening of a
double cavity—the urethral sinus, which generally contains some of the
partially inspissated secretion of sebaceous glands that open into the
cavity. Inferiorly the corona glandis is interrupted on the middle line
by the suburethral notch.
The corpus spongiosum as far as the glans is surrounded by the
accelerator urinse muscle. Superiorly it fits into the groove on the
lower aspect of the corpora cavernosa, and along its under aspect pass
the retractor muscles of the penis.
Directions.—Immediately in front of the junction of its crura, the
penis should now be amputated, that the structure of its component
parts may be examined.
Structube of the corpora cavernosa. The corpora cavernosa possess
a strong envelope of white fibrous tissue, termed the tunica albuginea.
This tunica albuginea, besides forming a common envelope to the united
bodies, sends inwards an incomplete mesial septum between the two—
the septum pectiniforme. This septum when viewed laterally is seen to
be perforated by numerous vertical slits, which give its processes a
resemblance to the teeth of a comb; hence the name. Besides the sep-
tum pectiniforme, numerous small trabecular pass into the interior of the
corpora cavernosa, and by their anastomosis form a framework for these
bodies. The trabecular are composed of fibrous tissue with some bundles
of non-striped muscular tissue. Between the trabecular are innumer-
able intercommunicating spaces, placed between the capillaries and the
small veins. Driring erection the blood is poured into these spaces,
and thus is brought about the increase in the size of the organ. At
other times the blood passes in the ordinary manner from the capillaries
to the venous radicles. In the crura and peripheral part of the
cavernous bodies some of the small arteries terminate directly in
these venous spaces. The small arteries are imbedded in the
trabeculse, and when these are contracted, in the non-erect state, the
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284
THE ANATOMY OF THE HOESE.
arteries assume a coiled disposition, from which they receive the name
arterice helicinw.
Structube of the corpus spongiosum. The structure of the spongy
body resembles, somewhat, that just described. It possesses an
envelope of fibrous tissue with trabeculse and a plexus of large veins.
In its peripheral part, and in the bulb, it also contains true cavernous
spaces, like those of the cavernous bodies but smaller.
Structure of the spongy (or extra-pelvic) part of the urethra. This
should be laid open on its under aspect with scissors. The lumen of
the tube is not uniform. At the ischial arch (this will not be seen at
present) it presents a dilatation; and its calibre is again increased as it
enters the glans, forming what is termed in man the fossa navimlaris.
The interior of the tube is lined by mucous membrane having simple
columnar epithelium, except at its orifice, where it is stratified and
squamous. The ducts of numerous small racemose glands open on the
surface of the membrane. External to the mucous membrane the wall
of the urethra is made up of non-striped muscular tissue, arranged as an
inner circular and an outer longitudinal layer.
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CHAPTER X.
DISSECTION OF THE ABDOMEN.
Before this part can be begun in the male subject, the dissection of
the perinseum (Chapter IX.) must be completed.
THE ABDOMINAL WALL.
Position.—The subject should be placed on the middle line of its
back, or slightly inclined to one side, its limbs being drawn upwards and
outwards by ropes and pulleys.
The Mammary Glands, or the Udder. It is convenient to describe
here these glands, since their dissection must precede that of the
abdominal wall. They are organs peculiar to the female, occupying the
position of the scrotum in the male. As regards their function, they
may be viewed as an accessory part of the reproductive system, secreting
the milk upon which the young animal subsists for some time after
birth. It is only during the period of lactation that they become fully
developed, and therefore a subject suited for the satisfactory display
of their structure seldom presents itself in the dissecting-room.
The glands are two in number, and are placed side by side on the
middle line of the abdominal wall, in front of the pubes. They form
here a single mass, with a wide and shallow mesial furrow between
them. The term " udder " is used to include both glands. From the
most prominent part of each, the mamilla, teat, or nipple, projects.
This has the form of a short, flattened cone. Its free extremity is
perforated by two or three orifices belonging to the large milk ducts by
which the milk is extracted from the gland. The integumentary
covering of both glands and teats is thinner than the surrounding skin,
and it is generally black-pigmentcd. Moreover, the ordinary body hairs
are absent over it, their place being taken by a fine down, except over
the summit of the teat, where there are no hairs. It is richly provided
with sebaceous and sudoriparous glands, whose secretion renders it
moist.
When the cutaneous covering of the gland is reflected, there is
exposed a second envelope, composed of yellow elastic tissue. This
covering detaches a number of processes into the interior of the gland
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286
THE ANATOMY OF THE H0BSE.
between its main lobes, and on the mesial plane the elastic envelopes
of the two glands are applied together, and form a kind of intermediate
septum. A few strong slips of the same texture descend into the gland
from the abdominal tunic, and play the part of suspensory ligaments.
The secretory structure of the gland is arranged on the racemose
type. If a bristle be passed into one of the orifices seen at the extremity
of the teat, it will pass upwards by the large milk duct, and enter a
dilatation at the base of the teat, termed the galactopherous or lactiferous
sinus. The secretion of milk during the period of lactation is constant,
and the liquid accumulates in these reservoirs, to be drawn off by the
young animal. The milk ducts and the sinuses are lined by a mucous
membrane; and in the substance of the teat, between this mucous lining
and the external skin, there are some fibres of non-striped muscular
tissue, arranged both longitudinally and circularly. The circular fibres
prevent the escape of the milk from the sinus.
The milk enters each sinus from a number of tubes which, when
traced into the substance of the gland, divide and subdivide; and the
smallest ducts resulting from this subdivision lead up to the ultimate
acini of the gland structure. These acini are lined by a secretory
epithelium by whose agency the milk is formed.
The arteries and veins of the glands are branches of the external
pudic vessels. They undergo a great increase in size during lactation.
The nerves of the gland are branches of the inguinal nerves.
Directions.—Keflect the skin as shown in Plate 38. If the dissector
of the fore limb be engaged with the pectoral region, the skin from the
posterior part of that region will be turned back in a piece with that
over the front of the abdomen. If not, the dissector of the abdomen
must limit the skin which he is about to reflect, by an incision carried
outwards from the ensiform cartilage to the point of the elbow. He
will be guided in the same way towards the hind limb. Care must be
taken not to reflect the panniculus with the skin.
A slight degree of tympanitic distension of the intestines is favourable
for the dissection of the abdominal wall. When excessive, however, as
it often becomes, it interferes with the dissection, and is almost certain
to rupture the diaphragm, or the abdominal wall before its dissection
can be completed. This should be prevented by tapping the large
intestine with a canula and trochar, making the puncture at the most
prominent part.
Cutaneous Nebves. In reflecting the skin, a multitude of small
nerves will be seen on its inner surface. They are derived from the
intercostal nerves.
The Subcutaneous Abdominal Abteby (Plate 38). Look for this
vessel near the middle line, in the region of the prepuce or mammary
gland. It is one of the terminal divisions of the external pudic artery,
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287
DISSECTION OP THE ABDOMEN".
and is distributed to the scrotum and prepuce (skin of mammary gland
in mare), superficial inguinal glands, and skin, terminating a little in
front of the umbilicus.
The Subcutaneous Abdominal Vein runs in company with the artery.
The .Superficial Inguinal Lymphatic Glands (Plate 38). These
form a small group close to the subcutaneous abdominal artery, at the
side of the prepuce.
The Subcutaneous Thoracic (Spub) Vein (Plate 38) will be found
on the surface of the panniculus. The primary rootlets of the vein
collect blood from the skin in front of the mamma or prepuce, and pass
on to the surface of the panniculus, where they unite to form the trunk
of the vein. This is at first lodged in a groove on the superficial aspect
of the panniculus. It then perforates the lmiscle ; and gaining its deep
face, it passes forwards towards the axilla (Plate 1), where it joins the
brachial vein. The course of this vein is usually distinctly visible in the
living animal. From its position it is liable to be injured in deep
spurring, and hence one of its names.
The Panniculus Cabnosus (Plate 38). This is a thin extended sheet
of muscular tissue, which is adherent to the deep surface of the skin
over a large part of the abdomen and thorax, being continued also from
the latter region over the outer aspect of the shoulder. The most
posterior angle of the muscle is included in the fold of skin at the groin,
but it does not reach the hind limb. From this angle the superior edge
of the muscle (which will not at present be seen) slopes upwards with
two or three wide sinuosities to near the spine in the dorsal region,
while from the same point the posterior edge of the muscle slopes down-
wards and forwards to a second angle which is rounded and placed from
three to six inches external to the umbilicus. The inferior edge extends
from this latter angle forwards towards the elbow. Anteriorly the
muscle is continued over the scapular region, and sends also an apon-
eurotic tendon between the fore limb and the chest-wall to be attached
to the internal tuberosity of the humerus. The edges of the muscle are
prolonged by a thin fascia which is attached superiorly to the vertebral
spines, and below and behind is adherent to the abdominal tunic. The
outer surface of the muscle is with difficulty separated from the skin,
which indeed receives the insertion of its fibres. The muscular tissue
of the panniculus is, as compared with striped muscles in general, of a
pale colour.
Action.—It twitches the skin, and plays the part of a hand to the
animal in removing offending insects.
Directions.—Begin at the lower edge of the panniculus and raise it
upwards from the subjacent structures. This is easy over the abdo-
minal tunic, but anteriorly it is closely adherent to the edge of the
deep pectoral muscle. The panniculus is not to be removed, but raised
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288                             THE ANATOMY OP THE HORSE.
as far as is necessary to bring the origin of the external oblique muscle
of the abdomen into view. Notice on the inner surface of the muscle
ramifying nerves, and anteriorly the spur vein accompanied by a small
branch of the external thoracic artery.
Perforating Nerves. The nerves seen descending on the inner
surface of the panniculus are perforating branches derived from the
intercostal trunks, and from the last dorsal and first lumbar nerves.
These perforating nerves appear along a curved line a few inches belowT
the origin of the external oblique. They supply the panniculus, and give
cutaneous twigs through it to the overlying skin.
A perforating branch from the 2nd lumbar nerve appears close to the
bony prominence of the haunch, and descends to the skin on the front
of the thigh. A perforating branch from the 3rd lumbar nerve appears
below the same bony prominence, and two inches below the point of exit
of the preceding nerve. It is accompanied by a branch of the circum-
flex iliac artery, with which it descends to the thigh, internal to the last
described branch.
The Subcutaneous Thoracic Nerve (Plate 1). This will be found
running horizontally backwards on the inner surface of the panniculus,
behind the shoulder, and in company with the vessels of the same name.
It comes from the brachial plexus.
Perforating Vessels. Small un-named branches, mostly branches
of the intercostal vessels, appear at the same points as the nerves.
The Abdominal Tunic (Plate 38). This is a great expansion of
yellow elastic tissue which is spread over the inferior and lateral walls
of the abdomen. It is nearly co-extensive with the external oblique
muscle, to which it is adherent. It is thickest in its posterior part,
near the linea alba; and becomes gradually thinner as it is traced out-
wards over the muscular part of the external oblique, and forwards
beneath the posterior deep pectoral. Posteriorly it furnishes the sus-
pensory ligaments of the prepuce, or analogous slips to the mammary
gland. The tunic acts as an admirable elastic abdominal bandage,
assisting the muscles to support the heavy abdominal viscera, and
adapting the wall of the abdomen to the varying volume of its contents.
Directions.—The abdominal tunic must be entirely removed. This is
an operation requiring time and care, for the tunic is intimately adherent
to the tendon of the external oblique muscle, especially in its anterior
half. Transverse incisions should be made through it, taking care not
to cut the fibres of the subjacent tendon, which will be recognised by its
different colour and texture. Then seize the cut edges of the tunic with
the forceps, and tear it off in strips forwards and backwards. Proceed
in this way until the whole of it has been torn away.
Muscles of the Abdominal Wall. On each side there are four of these,
viz., the obliquus abdominis externus, the obliquus abdominis interims,
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289
DISSECTION OF THE ABDOMEN.
the rectus abdominis, and the transversalis abdominis. They arc stated
in the order of their occurrence, the first being the most external.
These muscles have not only to discharge the ordinary function of
a muscle, but they have also to close in the abdominal cavity; and for
this latter purpose, they are, with the exception of the rectus abdominis,
peculiarly modified in form. Thus, the two oblique muscles and the
transverse muscle have their tendons of insertion extended in the form
of great fibrous or aponeurotic sheets, and the fibres in each of these
tendons have a direction different from that of the others.
The Linea Alba is the white mesial raphe, or band, which extends from
the ensiform cartilage to the pubes. It is fibrous in structure, and is
formed by the meeting of the aponeurotic tendons of the right and left
muscles. A little behind its mid point is a puckered cicatrix—the
umbilicus.
The External Abdominal Eing (Plate 39). This is the lower orifice
of the inguinal canal. It has the form of a slit in the tendon of the
external oblique. The direction of the slit is oblique forwards and out-
wards. The lips, or pillars, of the slit are simply fibres of the external
oblique tendon. The inner angle or commissure is placed at the edge of
the prcpubic tendon. This prepubic tendon is a strong fibrous band by
which the abdominal muscles get a common insertion into the anterior
edge of the pubic bones, and from whose surface the pubio-femoral liga-
ment of the hip-joint arises. The external abdominal ring gives passage
in the male to the spermatic cord, the external pudio vessels, and the
inguinal nerves. In the female it transmits merely the corresponding-
vessels and nerves.
The Obliquus Abdominis Extebnus (Plate 39). This consists of
a muscular band at its antero-superior edge, and an aponeurotic tendon
over the inferior and lateral parts of the abdomen. It arises by its
muscular portion from tiie outer surface of the last fourteen ribs, and
behind the last rib from the tendon of the latissimus dorsi. Its anterior
slips of origin interdigitate with the serratus magnus. The muscular
fibres are directed obliquely downwards and backwards, and are suc-
ceeded by the aponeurotic tendon. The fibres of the tendon continue in
the same direction, and become inserted into the linea alba, the prepubic
tendon, and the external angle of the ilium • while between the two last-
mentioned points they are continued to form Poupart's ligament. Along
the line between these two points the fascia of the inside of the thigh is
inserted to the surface of the tendon, and it must be cut in order to
expose the ligament. It will then be observed that from the prepubic
tendon to the bony prominence of the haunch, the fibres of the external
oblique tendon, instead of becoming inserted into bone, curve upwards
and forwards and are lost to view. It is these reflected fibres that
constitute the ligament of Poupart (Plate 40), which may be described
u
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290
THE ANATOMY OP THE HORSE.
as having two extremities, two surfaces, and two edges. Its extremities
are attached to the pubis and angle of the haunch respectively. Its
anterior surface is concave, and directed towards the abdomen. This
surface gives origin outwardly to fibres of the internal oblique muscle,
and inwardly it forms the posterior wall of the inguinal canal. The
posterior surface is convex, and forms an arch over the femoral vessels,
the crural nerve, and the sartorius, iliacus, and psoas magnus muscles
(Plate 13). Neither of the edges of the ligament has a distinct [exist-
ence. The posterior or inferior edge is the line of continuity between
the ligament and the tendon of the external oblique. At its anterior or
superior edge the ligament becomes thin in texture, and disappears on
the fascia covering the sublumbar muscles. All of these points cannot
be made out at present, but they will become evident as the dissection
proceeds.
Action of the external oblique muscle.—When the right and left
muscles act in concert, they bend the trunk, and areh the back. If the
spine is fixed, they pull the ribs backwards and assist in expiration. If
both the spine and ribs are fixed, they compress the abdominal viscera,
and assist in urination, defsecation, and parturition. If only one muscle
acts, it bends the trunk or pelvis to the s°me side.
The Inguinal Canal is the oblique passage in the abdominal wall
through which the testicle descends in the young animal, and in which
the spermatic cord is lodged in the adult. The external abdominal ring,
which has already been examined, is the lower opening of the canal.
Its upper orifice, which will be seen at a later stage, is termed the
internal abdominal ring. The direction of the canal is oblique down-
wards and inwards, and it is slightly curved with the concavity forwards.
Introduce the finger into the canal and press on the posterior wall.
This, it will be seen, is formed by the reflected portion of the external
oblique tendon—in other words, by Poupart's ligament. Rotate the
hand, and press the finger on the anterior wall, at the same time separ-
ating the edges of the external abdominal ring. The anterior wall will
be seen and felt to be formed by muscular substance, viz., by the
muscular part of the internal oblique.
The canal gives passage in the male to the spermatic cord, the external
pudic vessels, and the inguinal nerves. In the female it is much
smaller, and transmits the corresponding vessels and nerves.
The Spermatic Coed. See page 278.
The External Pudic Artery (Plate 39) is one of the terminal
divisions of the prepubic. In the inguinal canal it descends posterior
and internal to the spermatic cord. After its emergence it divides into
the subcutaneous abdominal artery, and the anterior dorsal artery of
the penis. In the mare the latter branch is represented by the mammary
artery.
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291
DISSECTION OF THE ABDOMEN.
The External Pudio Vein is proportionally smaller than the artery,
which it accompanies.
The Inguinal Nerves are derived from the 2nd and 3rd lumbar nerves,
and are distributed to the prepuce, the scrotum, and the adjacent skin.
Directions.—Incise the external oblique tendon, from the external
angle of the ilium to the edge of the prepubic tendon. Eefiect Poupart's
ligament towards the thigh, and hook it up after the manner of Plate 40.
Then strip away the tendon of the external oblique from the subjacent
internal oblique. This will be found easy in the region of the flank,
where the tendon is related to the muscular part of the internal oblique ;
but over the inferior part of the abdomen, and especially in front, where
the tendons of the two muscles are applied to each other, the opera-
tion is difficult, and in some parts impossible. In this proceeding the
dissector has to guard against removing the thin tendon of the inner
muscle along with the outer, and this he will best do by observing that
the fibres of the inner tendon cross these of the outer at right angles,
being directed downwards and forwards. Observe that anteriorly the two
tendons are not simply in apposition, but actually interwoven—a disposi-
tion of tendons which is unique, and one which greatly increases the
strength of the abdominal floor. The muscular portion of the external
oblique should be raised as far as the lower extremities of the ribs. A
better view of the inguinal canal and its contents will now be obtained.
The Obliquus Abdominis Internus (Plate 40) consists of a fan-shaped
fleshy portion situated in the flank, and an aponeurotic tendon spread
over the abdominal floor. It arises from the external angle of the ilium,
and from the adjacent part of Poupart's ligament. It is inserted into
the prepubic tendon and the linea alba by the inferior edge of its tendon,
and by tendinous slips into the four or five last costal cartilages. In
front of the lower end of the fourth last intercostal space, the aponeurotic
tendon has a free edge which ordinarily lies under concealment of the
line of overlapping costal cartilages. When the abdomen is tym-
panitic, however, this edge is thrust outwards, and the transversalis
muscle is exposed as in Plate 40. The posterior edge of the fan-like
muscular portion lies in contact with Poupart's ligament; and the
inguinal canal, as already seen, passes between the two structures.
The highest fibres of its muscular part are parallel to the edge of a
small muscle—the retractor costce—inserted into the last rib, under
cover of the most posterior slip of the serratus posticus. This is
dcsciibed with the muscles of the back (page 96).
Action.—Similar to that of the external oblique.
Directions.—The internal oblique covers the transversalis and rectus
abdominis muscles. The outer edge of the last may be seen through
the thin tendon of the internal oblique, and through the same
tendon the posterior abdominal artery may be seen if well injected
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292                                 THE ANATOMY OF THE HORSE.
(Plate 40). The circumflex iliac artery is on the deep surface of its
muscular portion. In order to see these connections of the muscle to
the most advantage, incise the muscle along the line of junction of the
muscular fan and the tendon. Raise the muscular portion carefully,
and hook it back. Strip away entirely the aponeurotic tendon, using
the scalpel where the tendon is firmly adherent to the rectus abdominis.
The Circumflex Iliac Artery. This is a branch of the external
iliac artery, and will be better seen in the dissection of the sublumbar
region (Plate 44). It has an anterior division whose branches are
distributed to the internal oblique and transverse muscles in the flank,
and a posterior division which, after giving some twigs to the oblique
muscles, perforates them below the angle of the haunch, and descends to
the thigh.
The Posterior Abdominal Artery (Plate 40). This is a branch of
the prepubic artery, beginning at the inner side of the internal abdominal
ring. It places itself on the abdominal aspect of the internal oblique
muscle, crosses behind and internal to the ring, and runs forwards to
enter the rectus abdominis, in which, about midway between the sternum
and the pubis, it anastomoses with the anterior abdominal artery.
These arteries are accompanied by vein« of the same names.
The Eectus Abdominis (Plate 40). This muscle extends in the
form of a broad band from the sternum to the pubis, at the side of
the linea alba. To a large extent it separates the internal oblique and
transverse muscles, but beyond its outer border these muscles are
in contact in the flank and below the extremities of the ribs. The
muscle is widest about its centre, and it is crossed from side to side by
a number (about a dozen) of white lines—linece transversal, which are
caused by as many tendinous intersections of its muscular substance.
It arises from the lower face of the sternum, and from the five costal
cartilages behind the 4th. It is inserted into the anterior border of the
pubis by the prepubic tendon.
Action.—Similar to that of the oblique muscles.
Nerves (Plate 40). At the lower ends of the last ten intercostal
spaces, the intercostal nerves are prolonged beyond the rim of overlapping
cartilages to pass between the straight and transverse muscles, giving
fibres to both and also some perforating twigs to reach the skin. The
last dorsal nerve (behind the last rib) has a similar distribution. The
inferior primary branches of the 1st and 2nd lumbar nerves are similarly
prolonged after furnishing twigs to the oblique muscles in the flank.
Directions.—Cut the rectus abdominis transversely about the um-
bilicus, and reflect it forwards and backwards from the subjacent trans-
versalis. Look for the anterior abdominal artery on its deep face.
The Anterior Abdominal Artery is one of the terminal branches
of the internal thoracic artery. It appears at the side of the ensi-
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293
DISSECTION OP THE ABDOMEN.
form cartilage, where it turns round the 9th costal cartilage behind its
tip. It runs backwards along the middle of the superior face of the
rectus, giving off lateral branches, and terminating about midway
between the sternum and pubis in branches which anastomose with
those of the posterior abdominal artery. It is accompanied by a
satellite vein.
The Tbansversalis Abdominis (Plate 40). This muscle consists
of a fleshy band at its origin, and of an aponeurotic tendon over
the abdominal floor. In both of these the direction of the fibres is
transversely downwards and inwards towards the linea alba. It arisen
by its fleshy portion from the lower extremities or cartilages of the
asternal ribs (last ten), meeting here the origin of the diaphragm; and
from the transverse processes of the lumbar vertebraj. It is inserted
by the inner edge of the aponeurotic tendon into the ensiform cartilage
and the linea alba. The posterior edge of the tendon is thin and ill-
defined. The inner surface of the entire muscle is related to the
parietal peritoneum, there being interposed, however, a very thin layer
of connective-tissue representing the fascia transversalis of man. Slender
branches from the intercostal or asternal vessels run on the peritoneal
surface of the muscle.
Action.—Similar to that of the oblique muscles.
Directions.—The abdominal cavity will be exposed by the removal of
the transverse muscle and its peritoneal lining. If only one side of the
abdominal wall has been dissected, the other side may now be used for
the better display of things not satisfactorily made out in the first; and
particularly, a portion of the abdominal wall in front of Poupart's liga-
ment should be turned back in its entire thickness, so as to expose its
peritoneal aspect and the internal abdominal ring.
The Internal Abdominal Ring (Plate 44) is the abdominal opening
of the inguinal canal. As seen from the abdominal side, its posterior
or outer edge is prominent, and corresponds to the edge of the muscular
part of the internal oblique; while the opposite boundary of the ring is
flattened over the sublumbar muscles covered by the continuation of
Poupart's ligament.
The student can now see the direct continuity between the peritoneum
and the tunica vaginalis, the latter membrane passing directly into the
inguinal canal, and forming a well-defined edge on the posterior and
outer side of the entrance. It is by this opening that a portion of
intestine or mesentery sometimes passes into the inguinal canal, or
onwards into the scrotum, constituting an inguinal or scrotal hernia.
The Prepubic Artery (Plate 44). This vessel arises from the femoral
artery at the brim of the pubis, forming a short common trunk with the
deep femoral branch. It crosses to the edge of the internal oblique, and
divides into the external pudic and posterior abdominal arteries. The
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294
THE ANATOMY OP THE HORSE.
former enters the inguinal canal at a point internal to the internal
abdominal ring. The latter passes behind the ring, and crosses it on
the inner side. Both branches have already been followed, but the
relation of the posterior abdominal artery to the ring should now be
specially noted, as, in consequence of its position, an incision for the
relief of a strangulated hernia must be made outwards to avoid wound-
ing the vessel.
The Spehmatic Coed. The various structures which compose the
spermatic cord meet at the internal abdominal ring. The vas deferens
is seen turning inwards to enter the pelvis, and projecting the peri-
toneum to form a small band, or frffiiium, for itself. The vessels and
nerves of the cord are to be left undisturbed, so that they may be followed
to their source at a later stage.
The Ceemastee Muscle (Plate 44). The fibres of this muscle arc
now seen at their origin from the iliac fascia, where they are close to the
muscular fibres of the internal oblique. The}r pass into the inguinal
caual, where, separating but remaining connected by intermediate
areolar tissue, they constitute the cremasteric covering of the cord and
testicle. When the muscle contracts, it twitches the testicle upwards
by shortening the spermatic cord.
THE CAVITY OP THE ABDOMEN.
Boundaries of the Cavity.—The abdomen is the largest of the visceral
cavities of the body. It is placed behind the thorax, from which it is
separated by the diaphragm; posteriorly it is directly continuous with
the cavity of the pelvis; laterally and interiorly it is enclosed by muscu-
lar, tendinous, and elastic textures making up what is generally termed
the abdominal wall; and superiorly it is bounded by the lumbar portion
of the spine clothed by the sublumbar muscles.
Contents of the Cavity.—The cavity is occupied mainly by the gastro-
intestinal part of the alimentary tube, and its associated glands—the
liver and the pancreas. Besides these, it lodges the spleen and the
kidneys. In the female it contains the ovaries and the uterus (in part),
and in the male the vas deferens passes through it.
Divisions of the Cavity.—As a matter of convenience in describing the
position of its contained organs, the cavity is arbitrarily divided into the
following nine areas :—
left hypochondriac .           epigastric                   right hypochondriac
left lumbar                              umbilical                    right lumbar
left iliac                                  hypogastric                 right iliac
This subdivision is quite arbitrary, the boundaries between these areas
being certain imaginary planes. Thus, the three anterior regions are
separated from the three middle regions by a transverse vertical plane
passing through the lower end of the 15th rib, and the three middle
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DISSECTION OF THE ABDOMEN.                                      295
regions are separated from the three posterior regions by another trans-
verse vertical plane passing through the external angle of the ilium
(angle of the haunch). Again, each of these three regions—anterior,
middle, and posterior—is further subdivided into a central and two
lateral regions, this subdivision being effected by two vertical and
parallel longitudinal planes, each passing through the centre of Poupart's
ligament.
Directions.—The intestines of the horse, owing to their unwieldy size,
and generally also to the weight of their contents, are extremely incon-
venient to dissect. Prom the following description and the accompany-
ing plates, the student should first learn how the intestinal tube is
divided. He should then, with as little disturbance of the different
intestines as possible, observe how they are disposed within the abdo-
minal cavity.
The Intestines (Plates 41 and 42). The intestinal tube begins at the
pyloric orifice of the stomach, and it terminates on the surface of the
body, at the anus. It is primarily divided into small and large intestines,
and each of these is naturally or arbitrarily divided into segments.
The Small Intestine comprises the first portion of the tube, and in
a horse of medium size it measures about seventy-two feet in length. As
is expressed by its name, it is of smaller calibre than the large intestine.
Moreover, it is distinguished from nearly every part of the large intestine
by having a smooth and regular contour when distended. The first two
feet of the tube occupies a fixed position, and is termed the duodenum.
It received this name because in man its length is about equal to the
breadth of twelve fingers. The remainder of the small intestine has a
comparatively loose mode of suspension; and it is arbitrarily divided
into jejunum and ileum, the former succeeding the duodenum, and
measuring about thirty feet, the latter comprising the remainder of the
tube—about forty feet. These terms are borrowed from human anatomy,
where the term jejunum was applied in consequence of that portion of
the intestine being generally found empty in the dead body, while the
ileum was so designated on account of its convoluted disposition.
The Large Intestine is, for the most part, of vastly greater calibre than
the small; and, unlike the latter, it has when distended, not a smooth,
but a bosselated, surface. In a medium-sized animal it is about twenty-
five feet in length. It is subdivided—and in a much more natural
fashion than the small intestine—into ccecum, colon, and rectum, the
colon being further subdivided into double and single colon.
When the muscles which enclose the abdomen below and on each side
have been removed, it most commonly happens that only the large
intestines are exposed, and consequently their examination must precede
that of the small intestines.
The Caecum is the first of the large intestines. In an animal of
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296
THE ANATOMY OF THE HORSE.
medium size it measures about three feet in length, and when moderately
distended it has a capacity of about four gallons. At one of its extremi-
ties it is curved, forming what is termed the crook of the ccecum, while
the opposite extremity tapers to a blind point, from which the bowel is
named. The bowel has a puckered appearance, which is most evident
when it is distended. This is owing to the longitudinal muscular fibres
of its wall being not uniformly distributed as they are in the small intes-
tine, but collected into bands, which shorten the bowel by throwing it
into folds. The terminal portion of the ileum (small intestine) joins the
caecum on the concave side of the crook, and a few inches above the
point of communication is the orifice by which alimentary matters are
passed on to the colon. The crook of the csecum is fixed in the right
sublumbar region by means of loose cellular tissue, and it is in contact
with the right kidney and the pancreas. On its inner side it adheres by
cellular tissue to the termination of the double colon, and the duodenum
passes round it on the outer side. The remaining portion of the bowel
extends downwards and forwards through the right hypochondriac region,
terminating by its blind point in the epigastrium. The first portion of
the large colon, which lies to its inner side, extends in the same direction,
and the peritoneum in passing from the one bowel to the other forms a
fold which has been termed the meso-coscum. As the csecum is not
adherent to the abdominal parietes except in the neighbourhood of its
crook, it admits of some displacement; and the student must therefore
be prepared to find it deviating somewhat from the course just
described.
The Double or Large Colon. This bowel is termed double because
when taken out of the abdomen it is arranged in the form of two paral-
lel portions; but in order that it may be accommodated within the
cavity, it has again to be doubled, so that in its natural disposition it
presents four portions, which receive numerical designations. In an
animal of medium size its length is about ten feet, and its capacity
about sixteen gallons. It is puckered like the csecum, and from the
same cause.
The 1st division of the bowel begins at the crook of the caecum, by
an orifice of communication which is comparatively small. It extends
downwards and forwards through the right hypochondriac region, bulg-
ing laterally into the umbilical region ; and on reaching the epigastrium,
the bowel becomes bent on itself, forming what is termed, from its relation
to the ensiform cartilage of the sternum, the suprasternal flexure. The
angle of this flexure forms the point of separation between the 1st
and 2nd portions of the double colon.
The 2nd division, beginning at the suprasternal flexure, runs back-
wards on the left side of the abdomen, occupying the hypochondriac,
umbilical, and lumbar regions; and on approaching the entrance of the
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297
DISSECTION OF THE ABDOMEN.
pelvic cavity, the bowel forms in the iliac or hypogastric region a second
flexure—the pelvic flexure, the angle of which marks thcpoint of separa-
tion between the 2nd and 3rd portions. The 1st and 2nd portions of the
double colon have extensive contact with the abdominal wall, and they
conceal the other two divisions of the bowel, which lie above them (in the
natural standing posture).
The 3rd division, beginning at the pelvic flexure, extends forwards
along the left side of the abdomen, through the same areas as the 2nd
portion, being closely bound to it, and lying immediately above it. On
reaching the epigastric region, a third flexure is formed, in contact with
the diaphragm, liver, and stomach, and from these relations named the
diaphragmatic or gastro-hepatic flexure. This will be brought into view
by grasping and pulling backwards the suprasternal flexure, above which
it lies.
The 4th portion begins at the angle of the diaphragmatic flexure, and
passes backwards on the right side of the cavity, lying above the 1st
division, and closely bound to it. On reaching the inner side of the
crook of the caocum, to which it is adherent, it suddenly becomes much
reduced in calibre, and is continued as the small or floating colon.
The pelvic flexure of the colon should now be seized and carried for-
wards, so as to place the bowel in the position shown in Plate 41. It will
now be observed that the bowel is quite unattached except at its beginning
and termination, where it adheres to the pancreas and the crook of the
csecum. In this disposition the suprasternal and diaphragmatic flexures
are obliterated, and the 1st and 4th portions are seen to be closely
adherent to one another, and, in like manner, the 2nd and 3rd portions,
except just at the pelvic flexure, where, in the angle of the flexure, a small
space is bridged over by a racket-shaped piece of peritoneum. It will be
noticed also that the intestine varies greatly in calibre at different
points. Its greatest diameter is in its 4th portion, and its smallest
about the centre of the 3rd. This narrow portion of the intestine is
further distinguished from the rest by being not puckered, but plain,
when distended.
The Small or Floating Colon succeeds the double colon. It is much
narrower than that bowel, indeed it does not greatly exceed in calibre
the small intestine, from which, however, its coils are readily distin-
guished by their puckered appearance. In a medium-sized animal it is
about ten feet in length. It is disposed w7ithin the abdomen after the
manner of the small intestine, being suspended at the free edge of a de-
pendency of the peritoneum, termed the meso-colon or colic mesentery. It
has a convoluted disposition, and occupies the loft lumbar and iliac
regions. Its last coil passes into the pelvic cavity, and is continued as
the rectum.
The Rectum is the terminal portion of the intestine, and is about two
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298                             THE ANATOMY OF THE HORSE.
feet in length. It derives its name from its approximately straight course
through the pelvic cavity, in connection with which it will be more fully
described.
Directions.—The coils of the jejunum and ileum should be arranged
in the left flank after the manner of Plate 41. To get a view of the
duodenum, the caecum should be thrown across the abdomen, with its
point towards the left side. The duodenum will then be seen encircling
the crook of the cascum on its outer side. Should the large intestine
contain much ingesta, that should be evacuated through an incision across
the pelvic flexure of the double colon and another at the point of the
caecum. When the ingesta has been expelled, the bowels should be
moderately inflated, and the cut ends ligatured.
The Duodenum (Plate 44) is the first segment of the small intestine.
Its length is about two feet, but it cannot be very well seen in its
entirety at this stage of the dissection. It begins at the pyloric aper-
ture of the stomach, where it is related to the posterior surface of the
liver. It curves upwards and backwards across the lower face of the
right kidney, and then sweeping round the crook of the csecum to its
outer side, it crosses the spine behind the anterior mesenteric artery, and
is continued as the jejunum. It is maintained in position by a narrow
band of peritoneum, and in this fixity of position it is distinguished from
the rest of the small intestine.
The Jejunum and Ileum. These comprise the remaining portion of
the small intestine, of which about thirty feet is arbitrarily appor-
tioned to the former, and the remainder (about forty feet) to the latter.
They are arranged in the form of numerous coils, which occupy the
iliac, umbilical, and hypogastric regions. The coils are attached to
the free edge of a fold of peritoneum called the great mesentery; and
inasmuch as this mesentery is of considerable breadth, they may move
from place to place within the above-mentioned areas. When distended,
they have not a puckered, but a smooth, surface. The terminal port of
the ileum joins the crook of the cajcum, into which it projects for a little
distance, after the manner of a tap into a barrel; and at the point of
entrance there is a valvular arrangement—the ileo-cmcal valve, to pre-
vent regurgitation from the csecum into the ileum.
The Peritoneum is the lining membrane of the abdominal and pelvic
cavities. It belongs to the class of serous membranes, and, like all such
membranes, it consists of a parietal and a visceral division, these being-
portions of one great sac. The parietal part is that which lines the
abdominal walls, or parietes; the visceral part invests the solid and
hollow organs, or viscera, of the abdominal cavity. In virtue of this
membrane, all the free surfaces that present themselves when the
abdominal wall is removed, have a smooth and shining appearance.
The surface of the membrane is covered by a layer of endothelial cells,
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DISSECTION OP THE ABDOMEN.                                      299
and these rest upon a layer of vascular connective-tissue. The object
of the membrane is to facilitate the movements of the different ab-
dominal organs on each other and on the walls of the cavity, and
especially to facilitate the vermicular or peristaltic movements of the
intestines. For this purpose the surface of the membrane is kept moist
by a sparing amount of serous fluid, which gives to the membrane its
glistening aspect.
To trace the exact disposition of the peritoneum in the horse is very
difficult, in consequence of the unwieldy character of the intestines.
When the student has the opportunity he should examine the mem-
brane in a foal, in which the different organs can be manipulated with
ease.
The parietal and visceral peritoneum, as has already been stated,
form portions of one great sac, and the various abdominal viscera are
external to this sac. The sac of the peritoneum, it must be observed,
encloses not an actual, but merely a potential, cavity; the inner surface
of every portion of the sac being in contact with the same surface of
another portion. To facilitate the understanding of this, let the student
imagine the cavity of the abdomen (including the pelvis) as having its
natural form, but deprived of all its contents, and completely lined by
peritoneum, which, for simplicity's sake, he may suppose to be elastic.
The continuity of the membrane, and the fact that it formed a close
sac would then be apparent. Now let him imagine a simple tube of
intestine extending between this membrane and the spinal column, that
is, outside the serous sac. Conceive next this tube of intestine let
gradually down, until it extends through the cavity about its centre.
In this descent the intestine would first surround itself with peritoneum;
and then, as it sank farther, it would stretch the membrane so as to
form a kind of sling passing upwards to the point from which it started.
The membrane would now have lost its simplicity, for it would have a
parietal division continuing to line the abdominal walls, and a visceral
portion surrounding the tube of intestine. Moreover, these two portions
would be continuous with each other along the sling-like portion sus-
pending the tube. Lastly, imagine the tube of. intestine to grow and
branch, so as to completely fill up the abdominal cavity, and
obliterate the space between the parietal and visceral peritoneum. This,
of course, would not destroy the continuity of the serous sac, although it
would complicate it so that its continuity would be difficult to trace.
All the organs, then, that actually project into the abdominal cavity
get a more or less complete investment of visceral peritoneum ; and, in
the case of each organ, this visceral covering is traceable on to a neigh-
bouring organ, or on to the walls of the abdomen. Where organs are
contiguous to each other or to the abdominal parietes, the peritoneum
may pass directly from the one organ to another or to the abdominal
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300
THE ANATOMY OF THE HOUSE.
parietes; but, at other times, the connection between the parietal and
visceral peritoneum is traceable along bands or folds analogous to the
sling-like membrane that was formed in the imaginary case. These
folds constitute the various mesenteries, omenta, and peritoneal liga-
ments that will hereafter be described.
Although there is but a single peritoneal sac, this sac is so disposed
that it forms two compartments, termed respectively the greater and
lesser cavities of the peritoneum, the latter being also known as the
cavity of Window. The greater cavity is that which is exposed when
the inferior wall of the abdomen is removed, the lesser cavity is situated
behind the stomach, and is separated from the greater cavity mainly by
the omentum.
The Great or Gastro-colic Omentum.—Passing backwards among the
intestines, on the left side of the abdomen, there will have been noticed
a large lace-like membrane, which is the great omentum, epiploon, or web.
In order to examine its connection, the caecum and double colon should
be thrown backwards over the right flank, and the coils of the single
colon arranged over the left flank. The coils of small intestine should
at the same time be gathered backwards and to the right. The omen-
tum is composed of two layers of peritoneum, which include between
them vessels, and a varying quantity of fat. This fat is deposited
mainly along the course of the vessels, leaving, except in obese subjects,
intervening transparent areas that are free from fat; and it is from this
arrangement that the membrane possesses a lace-like appearance. The
two layers of the omentum may be distinguished as superficial and
deep.
When the superficial layer is traced backwards, it is seen to pass on
to the terminal part of the double colon (4th part) and initial part of
the single colon, covering the posterior aspect of these where they extend
across the roof of the abdominal cavity. Behind these it passes back-
wards along the roof of the abdominal cavity, from which it descends to
envelop the small intestine, forming the great mesentery, and the float-
ing colon, forming the colic mesentery. To the right, again, it passes
directly on to the csecum and the double colon; and after enveloping
these intestines, it returns to the abdominal wall, to pursue its back-
ward course to the pelvis. When followed forwards, the superficial
layer reaches the convex curvature of the stomach, and the initial dila-
tation of the duodenum; and it passes over the anterior surfaces of
these organs as visceral peritoneum. Passing off the duodenum and
stomach, it next forms the anterior layer of the gastro-hcpatic omen-
tum, and thus reaches the posterior surface of the liver at the portal
fissure. From that point it descends over the posterior surface of the
liver as visceral peritoneum, and turns round the inferior edge of the
gland to gain its diaphragmatic surface. It ascends on this surface ;
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301
DISSECTION OP THE ABDOMEN.
and where the liver and diaphragm are united, it passes from the former
to the latter, on which it descends to the inferior wall of the abdomen.
Along this it passes until it enters the pelvis, where it becomes con-
tinuous with the same layer already followed backwards along the roof
of the abdomen. In the male it is to be observed that the parietal
peritoneum of the abdominal floor passes into the inguinal canal, and
forms the tunica vaginalis of the testicle, the sac of which is a simple
diverticulum of the great peritoneal sac. Eeturning again to the
omentum, it will be noticed that its superficial layer, towards the left
side, in passing forwards to gain the convex curvature of the stomach,
encounters the spleen. Passing round that organ, it gives to it a
visceral covering, and then continues its course to the stomach. The
portion of omentum between the spleen and the left sac of the stomach
is termed the gastro-splenic omentum.
Now make a transverse opening about the centre of the great omen-
tum, and introduce the hand through the opening. The hand is now in
what is termed the cavity of Window, and the deep layer of the omen-
tum is exposed. When this layer is traced forwards, it is seen to reach
the convex curvature of the stomach, where, separating from the super-
ficial layer, it passes over the posterior surface of the stomach, and
initial dilatation of the duodenum. From these, again, it passes as the
posterior layer of the gastro-hepatic omentum, and reaches the liver at
the portal fissure. There it separates from the other layer of the gasti-o-
hepatic omentum, and ascends on the liver. It turns round the
superior edge of the gland, and passes from its anterior face to the dia-
phragm, on which it ascends to the spine. The deep layer of the omen-
tum is now to be followed in the backward direction. It is seen to
reach the terminal part of the double colon, and the initial part of the
single colon; and, separating there from the superficial layer, it passes
over the anterior aspect of these portions of intestine, and is reflected
forwards on the under surface of the pancreas. It turns round the
anterior edge of that gland, covers for a little distance its upper face,
and then passes on to the spine, where it meets the same layer advanc-
ing in the opposite direction. It is thus seen that the deep layer of the
omentum, when traced in the antero-posterior direction, forms a con-
tinuous layer, and at first sight it does not appear to be continuous
with the remainder of the peritoneum. As already stated, however, the
peritoneum forms a single sac, and the before-mentioned layer is con-
tinuous with the remainder of the serous membrane at a narrow opening
termed the foramen of Window. To find this opening, pass the dorsal
aspect of the left forefinger along the posterior surface of the lobulus
caudatus of the liver, close to the spine; and insinuate the point of the
finger onwards towards the left (of the subject). At the same time pass
the right hand up to the spine in the cavity of Winslow, and insinuate the
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302
THE ANATOMY OP THE HOUSE.
forefinger towards the right, above and behind the pylorus. The tips of
the forefingers of opposite hands can thus be made to meet, showing the
continuity of the larger sac of the peritoneum, in which the left hand is,
with the smaller sac, or cavity of Winslow, in which the right hand is.
Perhaps the simplest way to get an understanding of the relationship of
the two cavities, is to imagine the deep layer of the omentum to be
suppressed In that condition, the anterior aspect of the double and
single colon at their point of junction, the pancreas, the posterior
surface of the stomach and initial dilatation of the duodenum, the upper
parts of the liver and diaphragm, and the roof of the abdomen for a
short space behind the hiatus aorticus would be without a serous cover-
ing. It may be supposed that to supply this deficiency, a pouch of the
great sac of peritoneum has to be made. This pouch is made at the
foramen of Winslow, the peritoneum being there thrust outwards
towards the right, and expanded until it forms what has already been
traced as the deep layer of the omentum. The foramen will be observed
to have the following boundaries :—the base of the lobulus caudatus in
front, the 4th part of the double colon behind, the free edge of the
gastro-hepatic omentum below, and the posterior vena cava and right
pillar of the diaphragm above.
The Great Mesentery is the membrane that suspends the small intes-
tine. Like the omentum, it is composed of two layers of peritoneum.
These layers leave the spine at the root of the anterior mesenteric
artery, being there continuous with the parietal peritoneum; and they
descend, one on each side of the branches of that artery, until they
reach the intestine. At the concave edge of the bowel the two layers
separate; and after encircling the tube as visceral peritoneum, they
meet and become continuous at its convex or free border. Where the
mesentery suspends the first part of the jejunum, it is continuous with
the peritoneal fraenum of the duodenum; and at its opposite extremity,
where it envelops the termination of the ileum, it passes on to the caecum.
At the latter point it will be observed that the two layers of mesentery
do not become continuous around the convex border of the ileum, but
are prolonged beyond that, so that the terminal portion of the small
intestine is included in the mesentery some distance from its free edge.
The Colic Mesentery.—This is the membrane that suspends the single
or floating colon. It is composed of two layers of peritoneum, which
leave the roof of the abdomen along a line extending from the root of
the anterior mesenteric artery to the inlet of the pelvis. These two
layers include between them the posterior mesenteric artery and its
branches; and after enveloping the single colon, they become continuous
at its free edge. At its anterior extremity the colic mesentery is con-
tinuous with the great omentum and with the great mesentery, and at
the pelvic inlet it is continuous with the meso-rectum.
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303
DISSECTION OF THE ABDOMEN.
The Uterine Broad Ligaments.—These are the double peritoneal folds
that suspend the uterus, ovaries, and Fallopian tubes. Each ligament
leaves the roof of the abdomen in the lumbar region, and descends to
the concave edge of the cornu, and to the side of the upper face of the
body, of the uterus. At these points the layers of the ligament sepa-
rate, and pass on to the uterus as its visceral covering. The ligaments
are widely apart in front; but as they are traced backwards, they
become narrower and nearer to each other. The Fallopian tube is sus-
tained between the two layers of each ligament at its anterior edge, and
here the fimbriated extremity of the tube opens into the sac of the peri-
toneum. In the female, therefore, the peritoneum does not form a shut
sac. Stretching between the ovary and the uterine cornu is a cord of
non-striped muscular tissue--the ligament of the ovary—which forms
the free edge of a small secondary fold of peritoneum. This forms with
the adjacent part of the broad ligament a pocket-like cavity. On the
outer side of the broad ligament another secondary fold extends as far
as the internal abdominal ring, and contains a layer of non-striped
muscular tissue corresponding to the round ligament of the human
uterus. Besides some scattered fibres of non-striped muscle, the layers
of the broad ligament include between them the uterine and ovarian
vessels and nerves.
The other peritoneal ligaments will be described in connection with
the organs to which they belong.
Peritoneal Pockets. The peritoneum, in passing from one organ to
another, forms several remarkable pockets, one of which has been men-
tioned above in connection with the ligament of the ovary. The exact
position of the others will now be indicated. So far as I am aware,
these have not hitherto been described. Nevertheless, they possess
considerable interest, since, in the human subject, a coil of intestine has
been known to become incarcerated in a similar pocket of peritoneum.
1.   The entrance to the first of these pockets will be found imme-
diately in front of the base of the lobulus caudatus, which separates it
from the foramen of Winslow. It is bounded by the anterior end of the
right kidney, and by the lobulus caudatus and upper part of the right
lobe of the liver. It extends inwards to near the spine between the
diaphragm and the upper part of the right lobe of the liver.
2.   Another pocket will be found a little to the left of the root of the
anterior mesenteric artery, the entrance to it being on the anterior
surface of the mesentery suspending the first few inches of the jejunum.
The pocket is bounded in part by this piece of mesentery, and in part
by a peritoneal fold passing between the jejunum and the first part of
the single colon.                          ,
3.   Other two pockets will be found at the termination of the small
intestine. Turn the point of the coecum backwards and to the right,
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304
THE ANATOMY OF THE HORSE.
and pull upon the terminal part of the jejunum. On each side of the
point at which the latter perforates the csecal crook, there will be found
a recess, the posterior (in this position) being the deeper.
4.   Another considerable pocket will readily be found on the concave
side of the CEecal crook, being formed by the peritoneum in passing
between the caecum and the beginning of the double colon.
5.   Another but much smaller pocket will be found in the cavity of
Winslow, above and in front of the first few inches of the single colon.
Directions.—For the display of the mesenteric vessels and the sympa-
thetic nerve, the intestines should first be disposed after the manner of
Plate 41. When well injected, the arteries require but little dissection,
and they are closely accompanied by the veins and nerves. The arteries
of the caecum and colon should be taken where most conspicuous, and
traced in both directions. Each of these vessels must be carefully dis-
sected up to its point of origin, but only two or three of the arteries of
the small intestine need be fully dissected. The whole intestinal tube
with the exception of a short piece of the duodenum next the stomach,
is supplied by the anterior and posterior mesenteric arteries, which are
branches of the abdominal aorta. The first supplies the whole of the
small intestine except the piece of duodenum specified; and it also sup-
plies the caecum, the large colon, and a lew inches of the beginning of
the small colon. The remainder of the small colon, and the rectum are
supplied by the posterior mesenteric artery.
The Anterior Mesenteric Artery (Plate 41) comes off from the
inferior aspect of the aorta at the 1st lumbar vertebra. It is only about
an inch and a half in length, but it has a large calibre; and in old horses
it often shews aneurismal dilatation. It divides into three terminal
branches, which from their direction are distinguished as left, right,
and anterior. The left distributes its branches to the whole of the small
intestine except a few inches at the beginning of the duodenum and
about two feet at the end of the ileum; the right supplies the terminal
portion of the ileum, the entire caecum, and the double colon as far as
the pelvic flexure; and the anterior is distributed to the double colon
beyond the pelvic flexure, and to the first few inches of the single colon.
It is an assistance to the memory to study the different branches in the
order of their distribution to the intestine, taking first those that supply
the most anterior segment of the tube.
1. The Left Branch of the anterior mesenteric artery is no sooner
detached than it splits up into about fifteen or twenty arteries, which
pass between the layers of the mesentery to supply the small intestine.
Indeed, the left branch can scarcely be said to exist, for these arteries of
the small intestine seem to spring from a common point of the anterior
mesenteric trunk. As each artery approaches the intestine, it bifurcates,
each branch inosculating with the corresponding branch of an adjacent
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305
DISSECTION OF THE ABDOMEN.
artery to form an arch. From the convexity of these arches smaller
vessels pass to each side of the intestine, and anastomose round it. At
the anterior pai*t of the tube two sets of superposed arches are formed
before the ultimate vessels to the intestine are detached. The branch
which is most anterior in point of distribution anastomoses with the
duodenal branch of the coeliac axis, while the one which is most pos-
terior anastomoses with the ileo-csecal artery from the right branch of
the anterior mesenteric.
2.   The Right Branch of the anterior mesenteric artery divides into
four vessels, viz., the ileo-csecal, the superior csccal, the inferior csecal,
and the direct colic arteries.
a.   The Jleo-eceeal Artery (Plate 41, for ilio-ccecal read ileo-ccecal) sup-
plies the terminal portion of the ileum (about two feet in length), and
inosculates with the last of the arteries from the left branch.
b.   The Superior Ccecal Artery, in the present inverted position of the
intestines, passes beneath the termination of the ileum to run along one
of the longitudinal muscular bands of the caecum. It sometimes gives
off the ileo-csecal artery as a collateral branch, and at the point of the
csecum it anastomoses with the next vessel. It gives off branches right
and left to the walls of the caecum.
c.   The Inferior Ccecal Artery, in the present position of parts, passes
above the termination of the ileum to run along another of the muscular
bands of the ca;cum. Besides collateral branches to the main portion of
the bowel, it gives off the artery of the arch, which follows the concavity
of the caecal crook and terminates on the beginning of the double
colon.
d.   The Direct or Right Colic Artery.-—This is a large vessel, receiving
the first of these designations because the course of its blood stream is
the same as that of the alimentary matters in the bowel. It supplies,
by right and left collateral branches, the 1st and 2nd portions of the double
colon, and anastomoses at the pelvic flexure with the retrograde colic
artery.
3.  The Anterior Branch of the anterior mesenteric artery divides after
a very short course into two vessels of unequal size, viz., the retrograde
colic artery and the first artery of the small colon.
a.   The Retrograde or Left Colic Artery, much the larger of the two,
supplies successively the 4th and 3rd portions of the double colon, run-
ning parallel to the direct colic artery, but carrying its blood in a direc-
tion counter to the course of the alimentary matters in the intestine.
b.   The First Artery of the Small Colon supplies a short piece at the
beginning of that bowel. It is included between the layers of the colic
mesentery, and anostomoses with the first branch of the posterior
mesenteric artery.
Directions.—To display the posterior mesenteric artery, the small
x
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306
THE ANATOMY OF THE HORSE.
colon must be spread out over the left flank after the manner of
Plate 42.
The Posterior Mesenteric Artery is a much smaller vessel than the
anterior. It is a branch of the abdominal aorta, from which it is given
off at the 4th lumbar vertebra. It passes in a curved direction between
the layers of the colic mesentery and meso-rectum, and terminates near
the anus in vessels which supply the end of the intestinal tube.
From the convexity of its curve, which is directed downwards, about
twelve or fourteen branches pass to supply the small colon (except a few
inches at its beginning) and the rectum. The branches which supply
the first half of the small colon divide and form arches by anastomosis
in the mesentery, close to the bowel; but the more posterior branches
do not anastomose until they perforate the intestinal wall.
The Intestinal Veins.—The blood which is brought to the intestines by
the arteries just considered is carried away by vessels belonging to
the portal system. These veins for the most part run in close company
with the arteries, and receive the same names.
The Anterior Mesenteric Vein is a very large vessel having tribut-
aries which correspond almost exactly to the divisions of the artery of
the same name. It joins the splenic and posterior mesenteric veins to
constitute the vena porta.
The Posterior Mesenteric Vein has its roots in the hacmorrhoidal
veins around the termination of the rectum, which veins, on the other
hand, communicate with the internal pudic vein. After receiving blood
from the walls of the rectum and small colon, the posterior mesenteric
vein forms by union with the splenic a very short trunk which joins
the anterior mesenteric to form the vena porta;.
Lymphatic Vessels of the Intestine.—In an ordinary dissecting-room
subject the lymphatic vessels will not be visible unless the animal is
emaciated and has been killed shortly after a meal, in which case the
mesenteric vessels may be seen without dissection. They will be recog-
nised as vessels with very thin walls and milky contents, coursing
between the layers of the mesentery, from the intestine towards the
anterior mesenteric artery. The lympathic vessels of the small intestine
are called lacteals.
The Lymphatic Glands of the Intestine are very numerous. Those
of the small intestine are chiefly aggregated in the form of a cluster of
about thirty included between the layers of the mesentery, near the
anterior mesenteric artery; but a number are placed lower down in the
mesentery, along the course of the ileo-effical artery. The glands of the
cascum arc distributed in the form of two chains along the track of the
superior and inferior caecal arteries, and numerous glands are similarly
placed on the colon along the course of the direct and retrograde colic-
arteries. Those of the small colon and rectum are, for the most part,
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307
DISSECTION OF THE ABDOMEN.
placed on the wall of the bowel, at the edge of the mesentery; but a few
are included between the layers of the colic mesentery. The lacteals
from the small intestine and the lymphatic vessels from the large intes-
tine traverse these various groups of glands on their course towards the
reccptaculum chyli.
The Sympathetic Neeve. This nerve forms on the aorta, in front of
the anterior mesenteric artery, a great network termed the Solar plexus.
The solar plexus is at present concealed by the pancreas, but the student
has to notice the anterior and posterior mesenteric plexuses, which are
wholly or in part derived from it.
The Anterior Mesenteric Plexus comprises numerous nerves already
met in dissecting the branches of the anterior mesenteric artery. The
nerves interlace around the arteries, and pass with them to gain the
bowel, where they further interlace before penetrating its wall.
The Posterior Mesenteric Plexus.—The branches of this plexus run in
company with the divisions of the artery of the same name. Its nerves
are derived in part from the aortic plexus, which is a backward continua-
tion of the solar plexus, and in part from roots furnished by the lumbar
cord of the sympathetic. The ultimate branches are distributed in the
wall of the small colon and rectum.
Directions.—The intestinal mass is now to be removed in the folio wing-
manner. The ropes must be unfastened from the left limbs of the animal,
while those on the right limbs are to be lengthened until the subject
inclines considerably over to the left side. Two ligatures a few inches
apart are to be passed round the duodenum where it encircles the crook
of the caecum, and the bowel is then to be cut across between the liga-
tures, the object of which is to keep the contents from escaping. Where
the small colon joins the rectum, at the entrance to the pelvis, the bowel
is to be served in the same way, and the colic mesentery is to be cut
along its point of origin at the spine. Both large and small intestines
are then to be thrown as far as possible outwards over the left flank.
The next step must be to take the scalpel and carefully sever the con-
nective-tissue adhesions between the cajcal crook and colon on the one
hand, and the sublumbar region and pancreas on the other. In doing
this, the dissector must cut close to the wall of the bowel, and take
especial care not to take away any portion of the pancreas, which will be
recognised by its dark colour. The operation will be favoured by the
weight of the intestines, which tends to tear these connections. When
the ceecum and colon have been freed, it will be found that strong resist-
ance to the removal of the intestines is still offered by the mesentery, or
rather, by its included vessels. These must therefore be cut near the
spine, and the entire mass will then slip over the left side, the omentum
being cut or torn from its attachment to the colon. The intestines
should now be spread out on a table; and when the student has refreshed
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308
THE ANATOMY OP THE HOESE.
his memory regarding their form and connections with one another, he
must proceed to examine their structure. This should be done by taking
a short piece of the gut, slitting it up, and pinning it with its mucous
surface downwards on a block of wood.
Structure of the Small Intestine. The wall of the bowel is made
up of four layers, viz., serous, muscular, submucous, and mucous.
1.   The Serous Layer, the most external, is a part of the visceral
peritoneum. It reaches the bowel by the mesentery, whose two layers
separate at the concave border of the intestine, and pass round each side
to meet and become continuous on its convex or free border. It is
closely adherent to the subjacent muscular layer, which it completely
covers except at the line of separation of the two layers of the mesentery,
where the vessels enter. It must be stripped off to expose the next coat.
2.   The Muscular Coat is made up of two distinct sets of fibres:
1. Longitudinal fibres, which are most external, and form a thin layer
uniformly spread along the wall. 2. Circular fibres, thicker than the
preceding, and also spread over every part of the wall. These fibres are
of the pale, non-striated variety.
3.   The Submucous Coat is composed of loose areolar tissue uniting
the muscular and mucous layers. In the duodenum it contains the
glands of Brunner, which have the racemose type of structure, and are
about the size of a hemp seed. Their ducts pass through the mucous
membrane, and open on its free surface.
Directions.—A few feet of the jejunum and about the same length of
the ileum should be taken and slit up along the line of attachment of
the mesentery. After the pieces have been gently washed, they should
be spread on a flat surface with the peritoneal coat downwards.
4.  The Mucous Membrane forms an inner lining to the intestine. It is
a soft velvety-looking membrane which, when healthy and fresh, has a
pinkish-yellow colour. When a piece of intestine is floated in water, the
mucous membrane is seen to be studded with short, thread-like projec-
tions to which the velvety appearance of the membrane is due. These
are the intestinal villi Each of them may be regarded as an upheaval
of the mucous membrane, containing in its interior microscopic blood
and lymph vessels, some non-striped muscular fibres, and a framework
of lymphoid tissue. The villi are important agents in the absorption,
of nutrient particles from the contents of the bowel. They are found
throughout the whole of the small intestine, but are more numerous in
the jejunum than in the ileum. The free surface of the mucous mem-
brane, including the villi, is formed by a single layer of columnar epi-
thelium with goblet cells interspersed. Contained within the substance
of the membrane are numerous microscopic tubular glands—the glands
fo LieberMhn—whose mouths open on the free surface. The solitary
glands are small spherical bodies about the size of a mustard seed.
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309
DISSECTION OP THE ABDOMEN.
They are covered by the epithelium, and occur throughout the whole
intestine, but are more numerous in the ileum than in the jejunum.
They are composed of lymphoid tissue. The glands of Peyer, or, as
they are commonly called, Peyer's patches, are circular or oval patches
formed by the aggregation of solitary glands.
They are more numerous in the ileum than
in the jejunum, their total number being
about one hundred. They are distributed
along the convex or free border of the
intestine, and hence it was directed that
the bowel should be opened along the
attachment of the mesentery, so as to leave
the patches intact.
Directions.—The cfficum, with the first few
inches of the double colon and a like length
at the end of the small intestine, should be
separated from the rest of the intestinal
mass. After the serous and muscular coats
have been observed on the inflated caecum,
the bowel should be slit open on the convex
side of its crook, the incision being extended
to its point. The mucous surface is to be
gently washed; and in connection with its
study, the student is to examine the two
orifices found on the concave side of the
crook.
Structure of the Large Intestine.
Throughout nearly the whole of its length,
the wall of the large bowel is made up of
four coats, similar to those of the small
intestine.
1.  The Serous Coat is derived from the
Fig. 36.
Vertical Section through the
Wall of the Duodenum, show-
ing the Glands of Brunner
(Turner).
V. Intestinal villi ; L. Layer of
glands of Lieberkiilm ; B. ABrun-
ner's gland, d. its excretory duct;
S.M. Submucous coat; M. Muscular
coat.
peritoneum, but it forms here a less com-
plete investment than in the case of the
small intestine, considerable areas of the wall being without this cover-
ing. Thus, it is absent where the csecum and double colon adhere to
the pancreas and abdominal parietes in the sublumbar region; it is also
absent where these two intestines adhere to each other, and where the
parallel portions of the double colon come into contact; and lastly, as
will be seen in the dissection of the pelvis, the terminal part of the
rectum is without a peritoneal covering.
2. The Muscular Coat consists of two distinct layers—an external longi-
tudinal and an internal circular. Throughout nearly the whole extent
of the large intestine, the longitudinal fibres are not uniformly distri-
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310
THE ANATOMY OF THE HORSE.
buted over the wall, but are collected into distinct bands, the areas
between the bands being provided only with circular fibres. When these
bands contract, they shorten the intestine, and throw the wall of the
bowel between them into alternate ridges and furrows. The number of
these bands is different at different points. The csecum has four. The
colon in its 1st part has also four. Three of these disappear on the
2nd part, so that at the pelvic flexure there is only a single band, on
the concave side of the flexure. This single band is continued along
the 3rd part, and near the diaphragmatic flexure other two bands
originate. The 4th part has three bands. The single colon has two
bands, one on each curvature, and these are continued on the first half
of the rectum, but are lost on its terminal half, as will be seen in the
dissection of the pelvis. The inner layer of circular fibres is uniformly
distributed.
3.   The Submucous Coat is a layer of loose areolar tissue uniting the
muscular and mucous coats.
4.   The Mucous Goat lines the cavity of the bowel. Its surface is
covered by a single laj-er of columnar epithelium, and in its deeper part
it contains solitary glands and glands of Lieherkiihn, similar to those of
Fig. 37.
Diagrammatic View (magnified) of a small Portion of the Mucous Membrane ok the
Colon {Allen Thomson).
A small portion of the mucous membrane cut perpendicularly at the edges is shown in perspective ;
on the surface are seen the orifices of the crypts of Lieberkuhn or tubular glands, the most of them
lined by their columnar epi Uielium, a few divested of it and thus appearing larger ; along the sides
the tubular glands are seen more or less equally divided by the section ; these are resting on a wider
portion of the submucous tissue, from which the blood-vessels are represented ;ia passing into the
spaces between the glands.
the small intestine. No Peyer's patches are found in it; and it is with-
out villi. The foldings of the wall of the bowel produced by the longi-
tudinal muscular bands involve all the coats, and the interior therefore
shows the alternately ridged and furrowed appearance already seen on
the exterior.
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DISSECTION OP THE ABDOMEN.                                       311
Orifices of the Crook.—These are the apertures of communication with
the ileum, and with the large colon. At its termination the ileum pro-
jects slightly into the interior of the csecurn, and beneath the mucous
membrane surrounding the orifice, there is developed a ring of mus-
cular fibres. This fold of mucous membrane with its included muscular
fibres constitutes the ileo-ccecal valve. The opening of communication
with the colon is considerably larger than the preceding, above which
it is placed.
Directions.—The student must now return to the parts left within the
abdominal cavity, where, without further dissection, he will be able to
examine the stomach, spleen, pancreas, and liver. Should the stomach
be nearly empty, the ligature should be untied from the cut end of the
duodenum, and by means of bellows that intestine and the stomach
should be moderately inflated. To permit this, it will not be necessary
to ligature the oesophagus. At the present stage the above-mentioned
organs may be studied as regards their form, situation, and relations,
their structure being postponed for future consideration.
The Stomach (Plates 43 and 44) is the most dilated segment of the
alimentary tube. When moderately distended, it will be seen to have
the following configuration. It possesses an anterior and a posterior
surface, both being smoothly rounded. It has a concave or lesser cur-
vature, which is turned upwards and to the right; and a convex or
greater curvature, which is directed downwards and to the left. The
left extremity of the organ is much the larger, and is termed the
cardiac extremity, or the fundus. The smaller right end is termed
the pylorus. The stomach occupies the epigastric and left hypo-
chondriac regions, and it will be observed to have the following
connections. The anterior surface is related to both the liver and
the diaphragm, and in the natural position looks upwards as well as
forwards. The posterior face looks downwards as well as backwards,
and before the removal of the intestines was related to these, and
chiefly to the gastro-hepatic flexure of the double colon. The smaller
curvature is fixed to the liver by means of the gastro-hepatic omentum.
If, in the present inverted position of the animal, the greater curvature
be pulled backwards, so as to separate the anterior surface from the
liver and diaphragm, the oesophagus will be found entering the stomach
at its lesser curvature, about midway between the central point of
that curvature and the extremity of the fundus. The greater curvature
is related in its left half to the spleen, and throughout the rest of
its extent to the intestines, particularly to the suprasternal flexure of
the colon, now removed. The right extremity, or pylorus, is directly
continued into the duodenum, a slight constriction being the only
outward mark of their separation. The left or cardiac extremity
extends to the left beyond the insertion of the oesophagus, and is related
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312
THE ANATOMY OP THE HORSE.
to the pancreas and base of the spleen. The stomach is retained in
position by continuity with the oesophagus and duodenum, and by
certain folds of peritoneum, viz., the gastro-phrenic ligament, and the
gastro-hepatic, gastro-splenic, and gastro-colic omenta. The gastro-
'phrenic ligament extends from the diaphragm to the stomach, around
the oesophageal insertion. The gastro-hepatic omentum passes between
the lesser curvature and the posterior fissure of the liver. The gastro-
splenic omentum passes from the cardiac extremity to the spleen. The
gastro-colic or great omentum is continuous with the preceding, and
passes in the form of a loose fold from the greater curvature. It
extends backwards and downwards, and then curves upwards to the
roof of the abdominal cavity; and, as has already been explained
(page 300), it separates the greater and lesser cavities of the perito-
neum; and, inasmuch as in man it hangs downwards to float upon
the intestines, it has been termed the Epiploon, Even in emaciated
subjects, it contains between its layers a considerable quantity of
fat.
The Duodenum (Plates 43 and 44). A better opportunity to examine
this part of the intestine is now afforded. Commencing in the epigas-
trium, at the pyloric orifice of the stomach, it ascends across the posterior
face of the right lobe of the liver, in passing into the right hypochon-
drium. It then curves backwards in the right lumbar region, beneath
the right kidney; and sweeping round the crook of the cascum, it crosses
the spine and is continued as the jejunum. Its calibre is greatest just
beyond the pylorus, and at this point it presents, when inflated, a small
dilatation like a miniature stomach with its greater curvature superior.
Throughout the whole of its course it is retained in position by a narrow
band of peritoneum formed by the serous membrane as it passes to
envelop the bowel. The right extremity of the pancreas rests against the
duodenum, a few inches from the pylorus, and at that point the wall
of the bowel is perforated by the bile and pancreatic ducts.
The Spleen (Plates 43 and 44) is a bluish-purple solid organ placed
in close proximity to the left sac of the stomach. In the horse it has
a scythe-shaped outline. It presents an external face, which is slightly
convex; an internal face, which is slightly concave and narrower than
the outer; an anterior thick border; and a posterior border, which is
sharp. Its surfaces are widest above, where they terminate in the base
of the organ, and below they taper to the apex. The spleen is situated
in the left hypochondriac region, and has the following relations :—Its
outer surface is related to the diaphragm; its inner surface contacts with
the double colon; its anterior border is penetrated by the vessels and
nerves of the organ, and is related to the greater curvature of the
stomach; its posterior border is free, and is included between the intes-
tines and the diaphragm ; its base is related to the pancreas and left
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DISSECTION OF THB ABDOMEN.                                      313
kidney. The spleen is retained in the left hypochondrium by the gastro-
splenic omentum, and by a special splenic ligament. The gastro-splenic
omentum forms a loose connection between the left half of the greater
curvature of the stomach and the anterior border of the spleen. The
splenic ligament is a fold of peritoneum developed at the base of the
organ, and formed by the serous membrane in passing from around the
anterior end of the left kidney to envelop the spleen.
The Pancreas (Plate 44) is a body having a lobulated structure and a
very irregular shape. It is placed across the roof of the abdominal cavity,
its central portion underlying the last dorsal vertebra?. Its upper face
is applied to the aorta, the cceliac axis, the vena cava, the pillars of the
diaphragm, and the right kidney, and is partly covered by peritoneum.
Its lower face towards the right is adherent to the crook of the cajcum
and the termination of the double colon, wThile to the left it is covered
by peritoneum. Its anterior border is related to the stomach, the
duodenum, and the liver. Its posterior border is related about its centre
to the anterior mesenteric artery. Its right extremity, or head, is in
contact with the duodenum; while the left extremity, or tail, is related
to the base of the spleen. The entire thickness of the gland is perforated
by the portal vein, which passes from its lower to its upper surface
through wrhat is named the pancreatic ring. The gland possesses two
excretory ducts, both of which leave it at its right extremity. The main
duct is named the duct of Wirsung, and it perforates the wall of the
duodenum about six inches from the pylorus, and close by the point of
entrance of the bile duct. The accessory duct is much smaller, and pene-
trates the bowel at a point opposite the entrance of the duct of Wirsung.
The healthy fresh pancreas has a greyish-yellow colour; but when
decomposition sets in after death, this speedily changes to an almost
black hue.
The Liver (Plates 43 and 44) is the largest gland in the body. It
forms the bile and discharges it into the duodenum. In health it has a
reddish-brown colour and a moderately firm consistence. In form it is
not comparable to any common object, and its irregularity of shape makes
its description somewhat difficult. It should be observed, in the first
place, that interiorly the rim of the organ is deeply indented, or
notched, and two of the largest of these notches serve to partially
divide the gland into its three main lobes, viz., a right, a left, and
a middle, or lobulus quadratus. Of these the middle lobe is always
the smallest, and its inferior border shows two or three minor indenta-
tions. The left lobe is generally the largest, but sometimes it is less
than the right. The liver possesses a fourth lobe, in the form of
a small projection of liver substance about the size of two or three
of the human fingers, and situated at the upper part of the right lobe.
This is the homologue of the lobulus caudatus of the human subject.
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314
THE ANATOMY OF THE HORSE.
The exact form of the liver will be more distinctly seen when it has
been removed from the body; but while it remains in situ, the student
may endeavour to make out the following points:—Viewing the organ
as a whole, it may be described as having an anterior and a posterior
surface, and a circumference divisible into an upper and a lower border.
The anterior surface is closely applied to the diaphragm, and is convex.
The posterior vena cava, in descending from the spine to the foramen
dextrum, passes between this surface and the diaphragm; and its
course is marked on the liver by a vertical groove, which may be
termed the anterior fissure. The posterior surface, when the organ
is in situ, is concave; but when the liver is removed from the body,
this surface, like the anterior, is slightly convex. It presents the poi-tal
fissure (L. porta, a gate), by which the portal vein, hepatic artery, bile
duct, and hepatic nerves and lymphatics enter the liver. The upper
border shows about its centre a rounded notch for the reception of
the short abdominal portion of the oesophagus. The lower border shows
the sharper and deeper indentations dividing the liver into its three
principal lobes, and the lesser indentations that partially subdivide the
lobulus quadratus.
The liver is situated in the epigastric and right and left hypo-
chondriac regions. Its most important relations, besides those
already mentioned, are as follows:—The anterior surface is applied
to the diaphragm, the right lobe, which has the highest point
of contact, being related to the most superior part of the muscular
rim on the right side, the lobulus quadratus corresponding to the
phrenic centre, while the left lobe toiiches the lowest point reached
by the liver, and lies against the lower part of the muscular rim
on the left side and the adjacent part of the tendinous centre.
The posterior surface is related to the stomach, the duodenum, the
gastro-hepatic flexure of the double colon, the pancreas, and the
right kidney, the latter slightly indenting the upper part of the right
lobe.
If an attempt be made to pull the liver from its position, it will
be found that this is opposed by certain folds of peritoneum which
pass between it and the abdominal parietes. These are the ligaments
of the liver, and they are named as follows:—
The Right Lateral Ligament passes between the right lobe and the
adjacent part of the phrenic rim.
The Left Lateral Ligament attaches the left lobe to the phrenic
centre.
The Falciform or Suspensory Ligament attaches the lobulus quadratus
to the diaphragm and to the abdominal floor a little to the right of the
linea alba. Its posterior edge is concave and free, and contains the
shrivelled remains of the umbilical vein—the so-called round ligament.
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DISSECTION OP THE ABDOMEN.                                      315
The Ligament of the Caudate Lobe is a small peritoneal fold passing
between the anterior end of the right kidney and the lobulus caudatus.
The Coronary Ligament.—If all the preceding ligaments be cut, and
an attempt made to pull the liver out of position, it will be found that
the gland is still firmly attached to the diaphragm by its anterior face.
This adhesion takes place over an area that is traversed by the anterior
fissure lodging the vena cava, and the peritoneum in passing between
the gland and the phrenic centre on each side of this area constitutes
the coronary ligament.
Directions.—The cocliac trunk and its branches must now be prepared;
and, coincidently with this, the bile duct, portal vein, and solar plexus
must be dissected. The portal vein will be found passing through
the pancreas to the transverse fissure; and emerging from the fissure,
below the vein, is the bile duct, which passes to open into the duodenum
close by the principal pancreatic duct. The cocliac axis is concealed
by the pancreas, which must be carefully raised by dissection at its
anterior border, and pulled backwards. The same dissection will
expose the semilunar ganglia and the solar plexus, whose branches are
to be traced in company with the arteries. In dissecting the vessels,
the student will meet the lymphatic glands of the stomach, spleen, and
liver.
Lymphatics. The glands of the stomach form two groups, viz., (1)
a few large glands situated at the lesser curvature, and (2) a number of
smaller glands placed at the greater curvature. The glands of the
liver also form two groups, viz., (1) a number situated in the posterior
fissure, and (2) a group, between the portal vein and the pancreas.
The glands of the spleen are placed on the course of the splenic vessels.
The lymphatic vessels emanating from the stomach, liver, and spleen
traverse these groups of glands; and after anastomosing with each
other, they pass to the thoracic duct.
The Bile Duct. This is the main duct for the conveyance of the
bile from the liver to the intestine. It is formed at the portal fissure
of the liver, by the union of secondary branches from the three principal
lobes, and it passes between the layers of the gastro-hepatic omentum to
penetrate the wall of the duodenum, about six inches from the pylorus.
The excretory apparatus of the horse's liver has the peculiarity—shared
by a few other animals—of being without a gall-bladder.
The Cceliac Axis (Plates 43 and 44) is a collateral branch of the
abdominal aorta, arising from the inferior face of that vessel between
the pillars of the diaphragm. It is less than an inch in length, and it
divides into three branches: the gastric trunk, the hepatic artery, and
the splenic artery.
The Hepatic Artery is directed obliquely forwards, downwards, and
to the right, to gain the posterior fissure of the liver, which it penetrates
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316
THE ANATOMY OF THE HOKSE.
in company with the portal vein and the bile duct. At first imbedded
in the pancreas, it then passes over the duodenum, and reaches its des-
tination by passing between the layers of the gastro-hepatic omentum.
It crosses the posterior vena cava, from which it is separated by the
foramen of Winslow. It "gives off the following collateral branches :—
1.  Pancreatic Branches.
2.   The Right Gastro-omental Artery, which is, at its origin, of larger
volume than the continuation of the parent trunk, crosses behind
the duodenum; and placing itself in the texture of the great omentum,
it is carried round the greater curvature of the stomach to inosculate with
the left gastro-omental artery. It gives off the pyloric and duodenal
arteries, besides numerous omental and gastric branches. The pyloric
artery is detached from the right gastro-omontal artery near its origin,
and sometimes it is a branch of the hepatic artery. It supplies the
pylorus and the initial dilatation of the duodenum. The duodenal
artery is detached from the right gastro-omental artery before that vessel
crosses the duodenum; and following the lesser curvature of the
duodenum, in the narrow serous band that fixes the bowel, it meets,
and inosculates with, the first artery from the left branch of the anterior
mesenteric artery. The omental branches of the right gastro-omental
are small and unimportant. The gastric branches pass from the
concave side of the parent artery; and bifurcating at the greater
curvature, they are distributed to the right sac of the stomach on both
its surfaces, where they anastomose with branches of the pyloric and
gastric arteries.
The Gastric Trunk is the central of the three terminal branches of
the cceliac axis. After a course of a few inches downwards and forwards,
it bifurcates to form the anterior and posterior gastric arteries.
The Anterior Gastric Artery reaches the anterior surface of the
stomach by crossing the lesser curvature immediately to the right of
the oesophagus.
The Posterior Gastric Artery descends to the lesser curvature of the
stomach, where it divides into branches distributed on the posterior
aspect of the organ.
The Pleuro-oesophageal Artery is a vessel constantly present, but
variable as regards its origin. It may arise from the gastric trunk or
one of its branches, or from the splenic artery. Passing through the
foramen sinistrum along with the oesophagus, it enters the thoracic
cavity, and there anastomoses with the oesophageal arteries, supplying
the pulmonary pleura at the base of the lung.
The Splenic Artery is considerably larger than the gastric trunk or
the hepatic artery. Under cover of the pancreas, it passes outwards
between the left kidney and the cardiac extremity of the stomach.
Reaching the spleen, it descends along the anterior border of that
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317
DISSECTION OF THE ABDOMEN.
organ, beyond which it is continued as the left gastro-omental artery,
From its convex side it gives off many large splenic branches; and from its
concave side it emits gastric brandies, which pass in the gastro-splenic
omentum to reach the great curvature of the stomach, where they
bifurcate to be distributed to both surfaces of the left sac.
The Left Gastro-omental Artery is the continuation of the splenic
artery beyond the tip of the spleen. It passes in the texture of the
great omentum to meet, and inosculate with, the right gastro-omental
artery, advancing in the opposite direction. Besides omental branches, it
emits gastric branches, which bifurcate at the great curvature of the
stomach to be distributed to both its surfaces.
The Portal Vein (Plates 43 and 44) is the trunk which collects the
blood from the stomach, intestines, spleen, and pancreas, and conveys
it to the liver, where, as will afterwards be described in connection with
the liver structure, the vessel comports itself after the manner of an
artery. The vessel is formed behind the pancreas, by the junction of
the anterior mesenteric vein with a short trunk resulting from the union
of the posterior mesenteric and splenic veins. It gains the upper face of
the pancreas by passing through its substance, the perforation being-
termed the pancreatic ring; and descending in the gastro-hepatic
omentum to the posterior fissure of the liver, it penetrates the substance
of the gland in company with the bile duct and hepatic artery.
Anterior and Posterior Mesenteric Veins, satellites of the arteries of the
same names, have already been described; but there is no venous trunk
corresponding to the coeliac axis, the companion veins of the divisions of
that artery behaving as follows :— -
The Splenic Vein is the upward continuation of the left gastro-omental
vein. After receiving the posterior gastric vein, it becomes one of the
roots of the vena porta?, previously forming a short trunk by union with
the posterior mesenteric vein.
The Anterior Gastric Vein joins the vena portae in the posterior fissure
of the liver.
The Bight Gastro-omental Vein is continuous with the left vein of the
same name, in the texture of the great omentum, opposite the middle of
great curvature of the stomach. It receives gastric, omental, duodenal,
pyloric, and pancreatic branches, all of which run in company with the
arteries of the same names; and then, above the pancreas, it joins the
portal vein.
The (Esophageal Nerves. These nerves are the backward continu-
ations of the vagus, pneumogastric, or 10th cranial nerves. They reach
the abdominal cavity by passing through the foramen sinistrum of the
diaphragm, in company with the oesophagus and the pleuro-ossophageal
branch of the gastric artery. The inferior nerve forms at the lesser
curvature of the stomach a plexus wdiose filaments pass mainly to the
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318                                 THE ANATOMY OF THE HORSE.
right sac; while the superior, after giving branches to the left sac,
joins the solar plexus.
The Splanchnic Nerves. On each side there are two splanchnic
nerves—a great and a small. Both are formed by efferent branches of
the dorsal portion of the sympathetic gangliated cord, and they reach
the abdomen by passing between the diaphragm and the psoas parvus
muscle. The great splanchnic nerves terminate in the semilunar
ganglia; the small nerves pass directly to the solar plexus, or thej7 may
be continued to the renal or the suprarenal plexus.
The Semilunar Ganglia are the largest in the body. They are
placed one at each side of the lower face of the aorta, between the
cosliac and anterior mesenteric arteries. Each receives the great
splanchnic nerve of its own side, and the two ganglia communicate by
transverse branches across the lower face of the aorta. The efferent
branches which proceed from them form the solar plexus.
The Solar Plexus is an intricate network of nerves and ganglia. It is
joined on each side by the lesser splanchnic nerve, and by the terminal fila-
ments of the superior oesophageal nerve. From the plexus nerves pass to
the abominal viscera, and in doing so they run in company with arteries.
There is thus : a cosliac plexus, whose branches reach the liver, pancreas,
spleen, and stomach, by accompanying the divisions of the hepatic,
splenic, and gastric arteries; a renal and a suprarenal plexus, which pass
to the kidneys and suprarenal bodies ; an aortic plexus, continued back-
wards on the aorta to join the posterior mesenteric plexus; and an
anterior mesenteric plexus, already described.
Directions.—The form, situation, and relations of the kidneys, and the
course of the ureters should now be examined. Without displacing the
kidneys, the fat and peritoneum is to be stripped from their lower face,
their vessels being carefully cleaned at the same time. The ureter will
be found passing backwards from the notched inner border of each
kidney, and it is to be followed backwards to the entrance to the pelvis.
In close relation to each kidney is its suprarenal body, which, to prevent
displacement, may be transfixed in position with a long pin.
The Kidneys (Plates 44 and 47) are the two glandular bodies that
secrete the urine. Each kidney occupies a position at the side of the
vertebral column, on the inferior aspect of the loins, and at the roof of the
abdominal cavity. In all except the most emaciated subjects, the kidneys
are surrounded by a quantity of adipose tissue, which is so abundant in
fat animals as to completely isolate them from surrounding objects. The
most common shape of the mammalian kidney is so well known that it is
popularly used as a descriptive term, objects having a similar form being
described as "kidney-shaped." Each kidney possesses two surfaces, two
borders, and two extremities. The inferior surface is convex; the
superior, which is concealed at present, is almost fiat. The outer border
-ocr page 387-
DISSECTION OP THE ABDOMEN.                                    319
is convex; while the inner is concave, presenting a well-marked notch
termed the hilus. From this hilus the ureter issues, and in its neigh-
bourhood the renal vessels and nerves pass into or out of the kidney.
The extremities are anterior and posterior, and both are rounded. It
will at once be noticed, however (Plate 47), that although this description
applies to both kidneys, they are far from being identical in shape. The
right kidney has an outline somewhat like the "heart" of playing-cards,
while the left has a decided resemblance to a haricot bean. The right
has the longest transverse, but the shortest antero-posterior, diameter.
The right is nearly symmetrical on each side of a line drawn from the
hilus to the middle of the outer border; but if such a line be drawn on
the left, the part in front of the line will be considerably smaller than
the part behind it.
Furthermore, it will be noticed that the two kidneys differ in situation,
and in relations. The right kidney is the more anterior; and taking
their relation to the skeleton, the difference may be expressed thus: the
right extends from the middle of the third last intercostal space at its
upper end to a point beneath the 2nd lumbar transverse process; the
left extends from the second last intercostal space to the 3rd lumbar
transverse process.
The right kidney is related by its upper face to the psoas muscles and
to the rim of the diaphragm; by its lower face it contacts with the
pancreas and the crook of the caecum, and is partly covered by peri-
toneum ; its inner border is margined by the posterior vena cava, and is in
contact with the right suprarenal capsule in front of the hilus (some-
times behind); its outer border is in contact with the duodenum; its
anterior extremity is in contact with the right lobe of the liver (which is
slightly depressed for it) and with the lobulus caudatus, and to the latter
a small fold of peritoneum passes from the lower face of the kidney.
The left kidney has the same relations on its upper face as the right;
its lower face is covered by peritoneum, and is related to the small
intestines; its inner border is margined by the aorta, and is related to
the left suprarenal body in front of the hilus; its anterior border is
related to the left extremity of the pancreas; and the anterior half of
its outer or convex border is related to the base of the spleen.
Renal Arteries. Each kidney receives blood from a large vessel—
the renal artery—which is a branch of the aorta. Springing at a right
angle from the parent trunk, the artery passes towards the hilus, where
it divides into a number of branches that penetrate the kidney substance.
The left artery is short, and passes directly to the hilus; the right is
longer, and passes between the psoas parvus muscle and the vena cava
to reach its destination. It is also generally a little anterior to the left
in its point of detachment, both being a little behind the trunk of the
anterior mesenteric artery.
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320
THE ANATOMY OP THE HORSE.
The Eenal Veins are as large in proportion as the arteries. They
join the posterior vena cava, the right vein being the shorter and
passing directly from the hilus, while the left crosses the lower face of
the aorta behind the anterior mesenteric artery.
The Kenal Plexus of nerves interlace around the artery, and enter
the kidney with its branches.
The Suprarenal Capsules (Plates 44 and 47). These are two
small solid bodies found in close relation to the kidneys, the right being
between the vena cava and the inner border of the right kidney, and the
left between the aorta and left kidney. They have an irregular elon-
gated shape, and a slatey-brown colour. They are highly vascular,
receiving branches from the mesenteric or renal arteries, and having
veins that enter the posterior vena cava or the renal veins. They
have also a rich nervous supply, receiving the suprarenal plexus—an
offset from the solar plexus. Their substance consists of a cortical and
a medullary portion. Each possesses a fibrous capsule continuous with
an internal trabecular framework. The interspaces of these trabecules
contain nucleated polyhedral or branched cells, which in the medulla
and innermost layer of the cortex frequently enclose yellowish-brown
pigment. They are without ducts, and their function is not well known.
The Ureters. The ureter is the tube which conveys the urine from
the pelvis of the kidney to the urinary bladder. On the left side it has
the following course. Beginning at the hilus, it is directed backwards
and inwards across the lower face of the kidney to place itself at the
side of the aorta, over (under, in the natural position) the psoas
parvus muscle. Here it is crossed obliquely by the spermatic artery.
It next curves a little outwards, crossing over the circumflex iliac
artery and the artery of the cord, runs at the outer side of the
external iliac artery, and then crosses it very obliquely to enter the
pelvis. The right ureter has similar relations, except that it passes
at the side of the vena cava instead of the aorta.
Directions.—Pin each ureter in position immediately behind the
kidney, and then cut it across. Eemove carefully the liver, stomach,
duodenum, spleen, pancreas, and kidneys, by cutting the oesophagus
and the various ligaments, vessels, and cellular adhesions which retain
these organs in position. Put them in carbolic solution, or procure
fresh organs, to serve for the examination of their structure. In the
meantime proceed to dissect the sublumbar region.
THE SUBLUMBAR REGION.
Directions.—Under this heading there will be described the abdomi-
nal aorta and the vena cava, writh their branches ; the inferior primaiy
branch of the last dorsal nerve, and the corresponding branches of the
first four lumbar nerves; the aortic plexus and gangliated lumbar cord
-ocr page 389-
321
DISSECTION OF THE ABDOMEN".
of the sympathetic nerve ; and, lastly, a group of muscles, comprising
the iliacus, psoas magnus, psoas parvus, quadratus lumborum, and
lumbar intertransverse muscles. The great arterial and venous trunks
are mesially placed, and the aortic plexus is on the great artery. The
other structures enumerated ai'e the same on both sides of the body.
One side may be used for the nerves and the arterial and venous
branches, the other being reserved for the muscles. In the mare, after
the ovarian and uterine vessels have been examined, the broad ligaments
must be cut to allow of the ovaries and uterus being pushed into the
pelvic cavity, where they are to remain until they can be dissected along
with the other reproductive organs of the female.
Lymphatic Glands. In cleaning the nerves and vessels, the follow-
ing groups of lymphatic glands will be found:—1. Sacral glands,
between the right and left internal iliac arteries at the entrance to the
pelvis. 2. Internal Iliac glands, between and around the roots of the
external and internal iliac arteries on each side. 3. External Iliac
glands towards the point of bifurcation of the circumflex iliac artery.
4. Lumbar glands, on the lower face of the aorta around the roots of the
posterior mesenteric and spermatic arteries. These various groups of
glands are placed on the course of the lymphatic vessels of the hind
limb, pelvis, and spermatic cord; and the efferent vessels from the most
anterior group (lumbar) pass to enter the receptaculum chyli.
The Posterior Aorta (Plates 44 and 45). The abdominal portion of
this great artery appears close to the spine, between the two pillars of the
diaphragm, the opening being termed the hiatus aorticus. It passes back-
wards across the lumbar vertebral bodies, resting on the left pillar of the
diaphragm and the inferior common ligament. At the 5th lumbar vertebra
it terminates in f< ur branches, two diverging to each side. These are
the external and internal iliac arteries. On its right side the aorta is
related to the vena cava. On the left it is related to the psoas parvus,
the left lumbar sympathetic cord, and the left kidney and suprarenal
capsule ; and the left ureter is beside or in actual contact with it. Besides
the external and iliac arteries, which are described as its terminal
branches, it gives off the following :—
1.   Phrenic Branches (two or three) to the pillars of the diaphragm.
They are given off at the hiatus aorticus.
2.   Lumbar Arteries. There are six or seven of these on each side.
The last comes from the lateral sacral artery, the second last from the
internal iliac, and the others fron; the aorta. These last arise from
the upper aspect of the vessel, and divide into two branches—a superior
for the skin and muscles over the lumbar vertebrse, giving also a spinal
twig through the intervertebral foramen; and an inferior which passes out-
wards in the intertransverse spaces to the flank, where it anastomoses
with the circumflex iliac artery in supplying the abdominal muscles.
Y
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322
THE ANATOMY OF THE HORSE.
3.   The Middle Sacral Artery is an extremely slender vessel, and not
always present. Search for it in the angle between the internal iliacs.
Arising from the summit of that angle, it passes mesially backwards on
the sacrum. It is of interest as representing the large vessel which in
some animals continues the aorta to the coccygeal region.
4.   The Cceliac Axis is detached as soon as the aorta passes through
the hiatus aorticus.
5.   The Anterior Mesenteric—the largest of the branches—is detached
at the 1st lumbar vertebra.
6.   The Renal Arteries, right and left, arise from the sides of the
aorta at the articulation between the 1st and 2nd lumbar vertebra;.
7.   The Spermatic Arteries, right and left, come off a few inches
behind the renals, viz., between the 3rd and 4th lumbar vertebra?, and
one generally a little in advance of the other. As seen in the
dissection, each passes obliquely backwards and outwards over the
ureter and circumflex iliac artery to gain the internal abdominal ring,
where it joins the other constituents of the spermatic cord. In the
cord it has a remarkably tortuous disposition; and, although a long
vesssel, it detaches no branches of any size until it reaches the testicle.
In the mare it is represented by the c varian artery, which passes in a
tortuous manner between the layers of the uterine broad ligament to
reach the ovary. It gives off a uterine branch to the uterine horn.
8.   The Posterior Mesenteric Artery. This vessel is usually detached
at the 4th lumbar vertebra, a little behind the origin of the spermatics,
but this relationship may be reversed.
The External Iliac Artery is, speaking generally, the vessel of supply
to the hind limb. It is regarded as a terminal branch of the aorta, and
it has its root at the body of the 5th lumbar vertebra. It descends with
a curved course at the pelvic inlet, and at the anterior border of the pubis
it is directly continued as the femoral artery. It is placed immediately
beneath the peritoneum, and each is related on its outer side to the
psoas parvus, sartorius, and iliacus muscles, the tendon of the first of these
separating it from the great crural nerve. On the inner side it is related
successively to the common iliac and external iliac veins, the former
separating it from the internal iliac artery. Its branches are:—
1.   The Circumflex Iliac Artery. This is a large artery detached
from the outer side of the external iliac close to its origin. It passes
outwards across the psoas muscles ; and at the outer edge of the psoas
magnus it divides into an anterior and a posterior branch. The former
is distributed in the flank, beneath the internal oblique muscle; and the
latter perforates the oblique muscles near the bony angle of the haunch,
and descends to the thigh.
2.   The Artery of the Cord (Plate 44). This is a slender vessel
arising close to the preceding, or it may come from the aorta itself.
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323
DISSECTION OF THE ABDOMEN".
Parallel and internal to the spermatic artery, it passes to the internal
abdominal ring, and is distributed to the spermatic cord.
In the mare it is represented by the uterine artery. This, which is a
much larger vessel, passes between the layers of the broad ligament to
reach the uterus, being distributed to the body of that organ, and
anastomosing anteriorly with the uterine branch of the ovarian artery,
and posteriorly with the vaginal artery.
3. The PREruBic Arteby (Plates 45 and 46). This vessel arises at
the anterior border of the pubis, and marks the limit of the iliac and
femoral arteries. It forms, at its origin, a short common trunk with the
deep femoral artery. It is about two or three inches in length, and it
passes on the anterior face of Poupart's ligament to the posterior edge of
the internal oblique, where, at the inner side of the internal abdominal
ring, it divides into the posterior abdominal and external pudic arteries.
The Internal Iliac Artery. This vessel may be described as the
vessel for the supply of the pelvic walls and contents. It will be
described with the pelvis.
The Posterior Vena Cava (Plates 43, 44, and 45). This great venous
trunk is formed to the right of the termination of the aorta, by the union
of the two common iliac veins. It passes forwards along the right side
of the lumbar vertebral bodies, until it reaches the upper border of the
liver. Here it descends in the anterior fissure of the liver, being
included between that organ and the diaphragm. Passing through the
foramen dextrum, it enters the thorax. It is related on its left side to
the aorta; and on its right to the psoas parvus, ureter, kidney,
suprarenal capsule, and lumbar sympathetic cord of the same side. It
receives the following branches :—
1.   Lumbar Veivis, exactly corresponding to the arteries.
2.   Phrenic Veins, or sinuses (2). These begin in the muscular rim
of the diaphragm, and converge to the foramen dextrum, where they
join the vena cava. They are distinctly visible without dissection in
the tendinous centre of the diaphragm (Plate 45).
3.   Spermatic Veins (Ovarian in the mare). The right and left veins
often unite before joining the vena cava.
4.   Renal Veins, the left longer than the right.
5.   Hepatic Veins. These join the vena cava while it lies in the
anterior fissure of the liver. They discharge the blood of the portal
system of veins, after it has circulated in the liver.
Iliac Veins. There are external and internal iliac veins, with branches
corresponding in all respects to the divisions of the homonymous arteries.
The external and internal iliac veins of each side, however, unite and
form a short trunk termed the common iliac vein, which is placed in the
angle of separation between the external and internal iliac arteries. The
right and left common iliac veins unite to form the posterior vena cava.
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324
THE ANATOMY OF THE HORSE.
The Receptaculum Chyli. Separate the aorta and vena cava at the
origin of the anterior mesenteric artery, and look above them for this.
It is the dilated commencement of the thoracic duct. It is formed by
the union of a variable number of large lymphatic vessels, and it is
continued forwards by the duct. This is a thin-walled vessel of small
calibre which passes into the thorax between the pillars of the diaphragm,
being generally to the right of the aorta.
Last Dorsal and First Two Lumbar Nerves (Plates 44 and 45).
The inferior primary branches of these nerves appear at the outer edge
of the psoas magnus, the last dorsal being close behind the last rib, and
the other two issuing in series behind it. These nerves have already been
followed in the dissection of the abdominal wall, where they are distri-
buted in the region of the flank to the abdominal muscles, panniculus,
and skin. These lumbar nerves also furnish cutaneous branches to the
inside and front of the thigh.
3rd Lumbar Nerve (Plates 44 and 45). The inferior primary branch
of this nerve will be found in front of the circumflex iliac artery,
emerging from between the psoas magnus and parvus muscles, after
having penetrated the substance of the latter. It accompanies the
posterior division of the circumflex iliac artery to the front of the thigh,
where it is expended in cutaneous branches. Before it emerges, it gives
branches to the psoas and quadratus muscles.
Inguinal Nerves. There is considerable variation in the mode of
formation of these, but that figured in Plates 44 and 45 is probably as
common as any other. A nerve is there seen passing obliquely backwards
over the circumflex iliac artery. It is formed by the union of two
branches which emerge at the inner side of the psoas parvus, these being
from the 2nd and 3rd lumbar nerves respectively. It divides into three
sets of branches, viz.:—
1.  Muscular, to the internal oblique.
2.   Cremasteric, to the cremastcr muscle.
3.   Inguinal, which descend in the inguinal canal to supply the
scrotum, prepuce (mammary gland in the female), and surrounding skin.
The Lumbo-sacral Plexus (Plate 48). This is the plexus of nerves
for the supply of the hind limb. Like the corresponding brachial plexus,
the inferior primary branches of five nerves compose it, viz., the 4th,
5th, and 6th lumbar, and the 1st and 2nd sacral nerves. There is a
loop of communication between the first of these and the 3rd lumbar,
which to that extent also enters into the formation of the plexus. The
majority of its branches fall to be dissected with the pelvis, and a
complete account will then be given of it (page 349). In the meantime
only the most anterior of its branches will be dissected.
1. Branches to tliepsoas magnus and iliacus. These are derived from the
4th lumbar root of the plexus, or from the loop between that and the 3rd.
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325
DISSECTION OF THE ABDOMEN.
2. The Anterior or great crural nerve (Plate 45). This is a large
nerve which derives its fibres from the 4th and 5th lumbar roots, and
from the loop between the 3rd and 4th. Emerging between the psoas
magnus and parvus, it descends at the outer side of the external iliac
artery, but separated from it by the tendon of the last-named muscle.
It rests on the iliacus and psoas muscles, and crosses their common
termination to end in a fasciculus of branches for the extensors of the leg.
In this course it is covered by the sartorius muscle. It gives off as a
branch the internal saphenous nerve, whose origin is about opposite the
ilio-pectineal eminence.
The Aortic Plexus of the Sympathetic Nerve (Plate 45). This is the
backward continuation of the solar plexus. Its branches interlace around
the aorta behind the kidneys, and unite with the posterior mesenteric
plexus. It receives some of the efferent filaments of the lumbar ganglia.
The Posterior Mesenteric Plexus is formed around the root of the
artery of the same name. It is united in front with the aortic plexus,
and receives efferent branches from the lumbar ganglia. Three sets of
branches pass from it:—
1.   Branches following the divisions of the posterior mesenteric artery.
2.   Branches accompanying the spermatic artery, and forming the
spermatic plexus.
3.   Pelvic branches to join the pelvic plexus.
The Sympathetic Gangliated Cord in the loins. This is the back-
ward continuation of the dorsal cord. Beginning between the psoas
parvus and the diaphragmatic crus, it extends backwards to the lumbo-
sacral articulation, where it is directly continued by the sacral division
of the cord. Each nerve will be found on the inner aspect of the psoas
parvus muscle of the same side, the left nerve being related inwardly to
the aorta; and the right for the greater part- of its course to the vena
cava, but for a short distance in front to the aorta. Six fusiform,
greyish ganglia stud the cord, and from these proceed the various
branches of the cord. These branches are :—
1.   Communicating branches with the inferior primary divisions of the
lumbar spinal nerves.
2.   Branches to the aortic and posterior mesenteric plexuses.
Iliac Fascia. This is the name given to the aponeurotic layer which
covers the inferior face of the psoas magnus and iliacus muscles. It is
densest and most adherent at the side of the pelvic inlet, and becomes
more cellvilar as it is traced forwards and backwards. It is adherent
inwardly to the psoas parvus tendon, and outwardly to the bony promi-
nence of the haunch. Poupart's ligament is adherent to its inferior face,
and it gives origin to the sartorius and cremaster muscles.
The Psoas Magnus (Plates 44 and 45). This muscle is broad and
flattened anteriorly, and thick and pointed behind, where it rests in
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326
THE ANATOMY OF THE HORSE.
a depression of the iliacus. It arises from the last two dorsal vertebras
and the under surfaces of the last two ribs at their upper part; also
from the lumbar vertebras except the last, covering their transverse
processes. It is inserted, in common with the iliacus, into the internal
trochanter of the femur.
Action.—It is a flexor and an outward-rotator at the hip-joint. When
the hind limbs are fixed, the two muscles will arch the loins, or the single
muscle will incline the trunk to the same side.
The Psoas Parvus (Plate 45). This is a smaller and more tendinous
muscle than the preceding, to whose inner side it is placed. It arises
from the bodies of the last three or four dorsal and all the lumbar
vertebrae. It is inserted into the ilio-pectineal eminence (of the ilium)
at the side of the pelvic inlet.
Action.—To flex the pelvis on the loins when both musles act; or to
incline it laterally when a single muscle acts. If the pelvis be fixed, it
will execute the same movements on the loins.
Directions.—Eaise the outer edge of the psoas magnus, and remove it
except its fibres of origin beneath the rim of the diaphragm and its
conical tendon of insertion, as in Plate 45.
The Iliacus (Plates 45 and 16). This is a powerful fleshy muscle
which, when the psoas magnus muscle is in position, appears to consist
of an outer and an inner portion. In reality, however, it is a single
mass, with a deep groove in it for the terminal tendon of the psoas
magnus. It arises from the entire iliac surface of the ilium, from its
external angle, and from the sacro-iliac ligament. It is inserted into the
inner trochanter of the femur, in common with the psoas magnus.
Action.—The same as the psoas magnus.
The Quadratus Lumborum (Plate 45). This muscle lies under cover
of the great psoas muscle. Its most external and strongest fasciculus
arises from the sacro-iliac ligament. It is inserted by this same fasciculus
into the tips of the lumbar transverse processes, and into the hinder
edge of the last rib. From the main fasciculus others pass inwards to
the lumbar transverse processes, and to the under surfaces of the three
last ribs, close to the sj)ine.
Action.—To assist in bending the loins to the side of the acting muscle.
Both muscles, by fixing the last ribs, will enable the diaphragm to act
to more advantage.
Lumbar Intertransverse Muscles (Plate 45). These are thin
muscular and tendinous strata connecting the edges of adjacent lumbar
transverse processes.
Action.—To assist in bending the loins to the side on which the
muscles act.
Directions.—An examination of the diaphragm will complete the
dissection of the abdomen. Define its pillars attaching it to the lumbar
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327
DISSECTION OF THE ABDOMEN.
vertebrae, and clean the edges of its foramina. At its periphery, under
the costal cartilages, follow the asternal vessels (Plate 45).
The Asternal Abtery. This is one of the divisions of the internal
thoracic artery (Fig. 7, page 120). It passes from the thorax to the
abdomen by perforating the rim of the diaphragm about the 9th chondro-
costal joint. As here seen, it passes backwards at the rim of the
diaphragm, in the interval between it and the origin of the transversalis
abdominis, and terminates at the lower extremity of the 13th intercostal
space. It has three sets of branches, viz., (1) ascending branches, which
anastomose with the intercostal arteries of the spaces crossed; (2) internal
branches to the diaphragm; (3) descending branches, which run on the
peritoneal surface of the transversalis abdominis muscle.
The Asternal Vein accompanies the artery.
The Diaphragm (Plate 45) is the muscle which serves as a partition
between the thoracic and abdominal cavities. In outline it has some
resemblance to the heart of playing-cards, the point being at the ensiform
cartilage, and the base at the spine. Its general direction is oblique
downwards and forwards. Its anterior or thoracic surface (Plate 22) is
convex, covered by pleura, and related to the bases of the lungs. Its
posterior surface is concave, covered for the greater part by peri-
toneum, and related to the liver, stomach, spleen, and intestines. It
consists of a muscular rim, two muscular pillars, or crura, and an
aponeurotic centre.
The Fleshy Rim is composed of soft muscular fibres, the lowest of which
are attached outwardly to the upper face of the ensiform cartilage about
one inch behind its junction with the sternum (Fig. 7, page 120). From
this mid point the line of attachment of the rim rises on each side, the
fibres taking origin from the cartilages of the last ten ribs, or from the
ribs themselves above the chondro-costal joints. On each side these
fibres meet, or are separated by only a narrow line from, the fibres of
the transversalis abdominis at their origin ; and along the line of separa-
tion the asternal artery runs. The muscular fibres are all directed from
these points of origin inwards, where, along a denticulated line, they
terminate in the tendinous centre.
The Pillars, or Crura.—These are right and left. The right is the
largest, and arises by a strong tendon from the lumbar vertebra?, through
the medium of the inferior common ligament. Its muscular fibres
terminate in the tendinous centre, some of them diverging to the right,
but without joining the muscular rim, while others descend to near the
mid point. The left pillar has a similar origin from the left side of the
lumbar vertebra, and its fibres terminate in the tendinous centre, being
sometimes continuous outwardly with the muscular rim.
The Tendinous Centre is pearly white, and composed of glistening
fibres interlacing in various directions. By the descent of the pillars
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328
THE ANATOMY OF THE HOKSE.
into it, it is partially divided into right and left halves, or leaflets.
Ligamenta Arcuata.—On each side of the pillars the rim of the
diaphragm arches with a free edge over the apices of the psoas muscles,
forming the so-called arcuate ligament.
Foramina of the diaphragm.
The Foramen Sinistrum.—This is a slit between the fibres of the right
eras, formed slightly to the left of the mesial plane, and a little below
the spine. It transmits the oesophagus, the oesophageal continuations of
the vagus nerves, and the pleuro-oesophageal branch of the gastric artery.
The Foramen Dextrmn.—This is the aperture by which the posterior
vena cava passes from the abdomen to the thorax. It is formed near
the middle of the tendinous centre, but a little to the right of the mesial
plane. The margins of the opening are closely adherent to the wall of
the vein, and here the phrenic sinuses empty.
The Hiatus Aorticus.—This is the opening between the right and left
pillars, close to the spine. It gives passage to the posterior aorta, and
to the initial portions of the thoracic duct and great azygos veins.
Between the crus and the psoas parvus on each side the gangliated
cord of the sympathetic passes, and a little outward the great splanch-
nic nerve passes between the same muscle and the edge of the
diaphragm. The asternal vessels penetrate the edge of the diaphragm
at the 9th chondro-costal joint.
Action of the Diaphragm.—The diaphragm is the principal muscle of
inspiration. When it contracts, it moves backwards, and thus increases
the antero-posterior diameter of the thorax. In this action it pushes
back the abdominal viscera, and causes the abdominal wall to descend.
The movements of the diaphragm affect principally its periphery, any
great backward movement of the tendinous centre being prevented by
the posterior vena cava, which passes like a ligament between the centre
and the heart.
STRUCTURE OF THE STOMACH.
The wall of the stomach comprises four layers, viz., serous, muscular,
submucous, and mucous.
1.   The Serous Coat is a smooth, glistening covering derived from the
eritoneum. It is united to the subjacent muscular coat by areolar
tissue sometimes termed the subserous coat.
2.   The Muscular Coat.—This can be best displayed on a stomach
which has been boiled for a few minutes. If two such stomachs can be
procured, one of them should be everted and moderately inflated, and
then its mucous coat stripped off with fingers and forceps. From the
other, similarly inflated, the peritoneum should be stripped off. The
muscular fibres are disposed in three planes, viz., an outer longi-
tudinal, a middle circular, and an inner oblique layer. Of these the
-ocr page 397-
DISSECTION OF THE ABDOMEN.                                      329
circular layer is found all over the organ, but the other layers are
mainly confined to the left half. At the right extremity of the stomach
the circular fibres are aggregated to form
the sphincter-like pyloric ring. The fibres
are of the non-striped variety.
3.  The Submucous Goat is composed of
areolar connective-tissue, in which the
blood-vessels ramify before they pass into
t he next coat.
4.   The Mucous Coat.—It is desirable to
study this on the stomach of an animal
recently killed. If possible, take such a
stomach "with about a foot of the duo-
denum and a few inches of the oeso-
phagus attached, and fasten the duodenum
to a tap. Let water flow into the organ,
and it will be noticed that, even when
*ag^%
the stomach is much distended, none of
the water escapes by the orifice of the
Fig. 38.
Vertical Transverse Section ob-
tiie Coats of a Pig's Stomach.
30 Diameters (from Kolliker).
a. Gastric glands ; b. Muscular layer
of the mucous membrane ; c, Sub-
mucous or areolar coat; d. Circular
muscular layer ; e. Longitudinal mus-
cular layer ; /. Serous coat.
denum; and either evert the organ and inflate it, or incise it along its
convex curvature. It will at once be noticed that the mucous lining is
not the same throughout. The left or cardiac half of the cavity is lined
by a mucous membrane termed cuticular; the right or pyloric half has
a totally different lining, termed villous. The cuticular portion is pale,
harsh, without true gastric glands, but possessed of a few mucous follicles,
and covered on its free surface by a thick stratified squamous epithelium.
It is, in fact, an extension of the oesophageal mucous membrane, which
it resembles in all respects. Towards the middle of the stomach it is
separated from the villous half by an abrupt, raised, and slightly sinuous
line of demarcation—the cuticular ridge. The villous half is rosy, soft,
and velvety (but without villi), thickly beset with gastric glands, and
possessed of a single layer of columnar epithelium. The gastric glands
are of the tubular variety, and by the aid of a lens numbers of them
may be seen opening together into pits, or alveoli, of the mucous mem-
brane. The cuticular portion is but slightly vascular, but the villous
portion is richly supplied with blood-vessels. In the collapsed organ
the mucous membrane is thrown into folds, or rugm.
The (Esophageal Oeipice, it will now be seen, is very narrow, and
obstructed by the mucous membrane gathered into folds.
gitt
-ocr page 398-
330
THE ANATOMY OF THE HORSE.
The Pyloric Orifice is much larger, but capable of being completely
closed by the pyloric ring of muscular fibres.
Fig. 39.
Stomach, everted and inflated.
1. Left (cardiac) sac with its cuticular mucous lining; 2. Right (pyloric) sac with its villous
mucous lining ; 3. Cuticular ridge ; 4. Termination of oesophagus ; 5. Initial part of duodenum ;
6. Pyloric ring.
In the interior of the duodenum, about six inches from the pylorus,
the openings of the bile and pancreatic ducts will be found. The orifices
of the bile duct and duct of Wirsung are placed together on the con-
cave side of the bowel, and are surrounded in common by a ring-like
valvular fold of mucous membrane. The opening of the accessory pan-
creatic duct is placed opposite to these.
STRUCTURE OF THE LIVER.
Lay the organ with its diaphragmatic surface downwards. Find the
portal vein, hepatic artery, and bile duct, at the portal fissure, and trace
them for a little distance into the liver. Invert the organ, and observe
the course of the anterior vena cava in the anterior fissure, and the mouths
of the hepatic veins which there discharge themselves into the cava.
Tunics or Capsules of the liver. These are two in number: 1. A
peritoneal coat, giving the free surface of the organ its smooth and
glistening characters. 2. A tunica propria, or fibrous coat, placed beneath
the preceding. All over the surface of the liver it sends inwards delicate
processes that join the interlobular connective-tissue, and at the portal
-ocr page 399-
DISSECTION OF THE ABDOMEN.                                     331
fissure it furnishes a sheath that accompanies the portal vein, hepatic
artery, and bile duct into the liver. This sheath is the capsule of Glisson.
Lobules of the Liver.—When a fresh-cut surface of the liver is examined,
it shows a system of lines mapping it out into areas about the size of a
pin's head. These areas are sec-
tions of the lobules of the liver,
which are united together by
interlobular connective - tissue.
This interlobular connective-tissue
is much more abundantly de-
veloped in the pig, and, conse-
quently, in that animal the lobu-
lation of the liver substance is
much more evident. A lobule
may be viewed as having a frame-
work of blood-vessels, in which are
set the liver-cells. Between the
adjacent cells the rootlets of the
bile passages begin, and there are
possibly also branches of nerves
and lymphatic vessels.
The liver is supplied with blood
by
Fig. 40.
much the larger of the two is the longit
portal vein, the other is the hep
atic artery.
udinal Section of a Pobtal Canal,
TAINING A PORTAL VEIN, HEPATIC ABTEBY,
Hepatic Duct, from the Pig (after
rnan). About 5 diameters.
P. Branch of vena portas, situated in a portal
The rOBTAL V EIN Collects Its canal, formed amongst the hepatic lobules of the
liver ; p. p. Larger branches of portal vein, giving
off smaller ones (£. i.), named interlobular veins ;
there are also seen within the large portal vein
numerous orifices of interlobular veins arising
Hepatic artery; d. Biliary
blospl
the liver at the portal fissure, this f^ from **
vein comports itself like an artery,
in that it reduces itself by division and subdivision to branches that
become progressively smaller until they terminate in a set of capillaries.
In their course through the liver, the larger branches of the vein run
in tunnels of the liver substance—the portal canals—which contain
also branches of the hepatic artery and bile ducts, and are lined by
Glisson's capsule. The smaller branches of the portal vein are distri-
buted in the interlobular connective-tissue, where, at the circumference
of each lobule, they form an interlobular plexus. From this plexus
capillary vessels penetrate the lobule, and form within it the intra-
lobular -plexus. The capillaries of this last plexus converge towards
the axis of the lobule, and there empty themselves into what is termed
the central vein of the lobule. This is the initial vessel of the hepatic
system of veins, and at the base of the lobule it joins a larger vessel—
-ocr page 400-
332
THE ANATOMY OF THE HORSE.
the mblobular vein. By the union of these sublobular veins through-
out the liver, the larger hepatic venous trunks are formed ; and these,
as already seen, enter the pos-
terior vena cava in the anterior
fissure of the liver.
The Hepatic Artery is a
branch of the cocliac axis. It
enters the liver with the portal
vein, and ramifies with it. It
has three sets of branches : (1)
capsular branches, to the tunica
propria; (2) vaginal branches,
to Glisson's capsule and the
vessels within it; and (3) inter-
Fig. 41.
lobular branches, whose capil-
Tkassveese Sectios throuoh the Hepatic Lobules laries pass into the lobule
i,i,i. Interlobular vein^ding in the intralobular where the7 helP t0 foml &6
capillaries; c c. Central veins joined by the intra- intralobular plexus, and enter
lobular capillaries. At a, a. the capillaries of one                               r
lobule communicate with those adjacent to it.             the central vein. The capil-
laries of the vaginal and capsular branches terminate in veins that join
the portal vessels.
The Liver Cells.—These are granular nucleated masses of protoplasm,
often containing fat particles. They are arranged in columns between
the strands of the intralobular plexus of capillaries.
The Bile Passages begin within the lobule as a network of fine canals
■—the bile capillaries—tunnelled at the lines of apposition of the liver
cells. At the periphery of the lobule these become continuous with
interlobular bile ducts having a proper wall and a simple columnar
epithelial lining. The interlobular bile ducts unite to form the larger
ducts that accompany the blood-vessels in the portal canals, and these
finally form the main bile duct, which passes in the gastro-hepatic
omentum to perforate the wall of the duodenum.
STRUCTURE OF THE SPLEEN.
The spleen, like the liver, possesses two coats, viz., an outer serous or
peritoneal coat, and a deeper fibrous tunic, or tunica propria. The latter
is composed of white fibrous tissue with a considerable admixture of
elastic and non-striped muscular fibres. It detaches from its inner sur-
face a multitude of trabecular, which by their anastomosis form a fibrous
framework in the interior of the organ. The interspaces of this frame-
work are occupied by a grumous material—the splenic pulp. If the cut
surface of the spleen be washed beneath a tap, the pulp may be removed
and the fibrous trabecule rendered very evident.
The Splenic Artery, a division of the cocliac axis, is a very large
-ocr page 401-
DISSECTION OF THE ABDOMEN.                                       333
vessel. Its branches enter at the concave border of the spleen, and
carry with them sheaths derived from the fibrous tunic. These
branches reduce themselves by division,
and the smaller branches are remark-
able in having the outer coat formed of
lymphoid tissue Here and there this
lymphoid tissue forms distinct swellings
developed either uniformly around the
arteries, or more or less to one side.
These are the Malpighian bodies of the
spleen. The arteries terminate in tufts
of capillary vessels in the pulp. They
are believed to have incomplete walls,
allowing their contents to escape and
illlPillipi
form the pulp. The rootlets of the
splenic vein begin in the same manner,
having incomplete walls through which
lis
i^fllilli
their lumen is continuous with the spaces
lodging the pulp. Gradually their walls
become thicker and complete, and adja-
cent veins uniting on their course towards
Fig. 42.
Out Surface or House's Splees,
TRABECULAR FRAMEWORK.
the anterior border form the large splenic
vein, which is one of the main branches
of the portal vein.
The Splenic Pulp possesses a supporting network of retiform connective-
tissue ; and the meshes of this network are set with many lymphoid
cells like the colourless corpuscles of the blood, and with red blood
corpuscles, normal or in different stages of disintegration
STRUCTURE OF THE PANCREAS.
The pancreas is a compound tubular or racemose gland. It is com-
posed of lobules held together by a connective-tissue framework. When
the main ducts of the gland are traced backwards into the gland, they
are found to be formed by the union of smaller ducts, and so on until
the smallest ducts are reached. These begin in the alveoli, which are
lined by secretory epithelium.
STRUCTURE OF THE KIDNEY.
The kidney is invested by a fibrous capsule. In health this can with-
out difficulty be stripped off the kidney substance, to which it is con-
nected only by delicate processes and vessels. If a horizontal section be
made from the convex border to the hilus of the kidney, the organ will
be seen to possess a cavity towards the hilus, termed the pelvis, and to
-ocr page 402-
334
THE ANATOMY OF THE HORSE.
consist of two different kinds of tissue—the cortical and the medullary
substance of the kidney.
The renal pelvis is a curved cavity, its extremities being termed the
arms. On its outer side there is a horizontal ridge—the renal crest—
on which the uriniferous tubules open, and on its inner side it is con-
tinuous by a funnel-shaped opening with the lumen of the ureter.
The cortical substance forms a layer beneath the capsule ; the medulla
is disposed around the pelvis and is internal to the cortical substance.
The cortex is about twice as thick as the medulla, but the two layers
meet along a sinuous line, and slightly interpenetrate one another. It
will be noticed that the two layers contrast with one another in the
following respects:—The cortex is of a deep red colour, it is granular,
friable, and studded with numerous small shining points—the Malpighian
bodies. The medulla, on the other hand, is pale red, striated, and
fibrous-looking, less friable than the cortex, and without any Malpighian
bodies.
Uriniferous tubules.—The largest tubes, or papillary ducts, open on the
crest of the pelvis. If such a tube be traced, it will be found to pass
outwards through the medulla, having a straight course, and branching
dichotomously. The smaller tubes resulting from this division are
called the collecting tubes; and, still preserving their rectilinear course,
they enter the cortex in bundles termed the pyramids of Ferrein. At
the surface of these pyramidal bundles, the straight tubes curve out-
wards in the cortex, and become dilated and tortuous, forming the
intermediary or junctional tubules. Each of these is succeeded by a
narrow straight tubule, which descends from the cortex to the medulla,
where it forms a bend, or loop, and runs up again into the cortex.
There is thus formed the looped tube of Henle, which is shaped like the
letter U. Having re-entered the cortex, Henle's tube becomes dilated
and tortuous, constituting the convoluted tid>e, which becomes constricted
and then expands into a bladder-like dilatation—Bowman's capsule.
Bowman's capsule surrounds a clue-like tuft of capillary vessels called
the glomerulus, and the whole constitutes a Jfa/pighian body. It is
more natural, but less simple at first, to regard the tube as beginning
not at the crest of the pelvis, but at Bowman's capsule. The student
should mentally work it out in that direction for himself. The urini-
ferous tubules consist of a basement membrane with an epithelial lining.
In the convoluted and intermediary tubes the cells are irregularly
columnar, but their outlines are obscure; in the descending limb of
Henle's tube (nearest the capsule of Bowman) the cells are flattened;
and elsewhere the cells lining the tubes are cubical or columnar.
The Renal Vessels. The renal artery divides into a number of
branches which penetrate the kidney near the hilus. Reaching the
boundary line between the cortex and medulla, the arteries divide
-ocr page 403-
335
DISSECTION OF THE ABDOMEN.
and anastomose to form a series of arches from which both cortical and
medullary vessels arise.
The cortical or interlobular
Aj8
arteries are larger and more
numerous than those for the
medulla. They pass directly
outwards towards the surface of
the kidney, giving off lateral
branches—the vasa afferentia—to
Bowman's capsule, and terminal
branches to the fibrous coat of
the kidney. Each vas afferent
pierces Bowman's capsule, and
resolves itself into the glomer-
ulus, or capillary tuft. From
this again the blood is led out
of Bowman's capsule by the
vas efferens. The vasa efferentia
again resolve themselves into
vvy
capillaries, and these form a
network among the convoluted
tubes. From this intertubular
capillary network, small veins
arise and pass to join the inter-
lobular veins, running alongside
the arteries. These interlobular
veins begin at the surface of the
kidney by the convergence of
a number of minute veins from
the capsule —forming the stellate
veins. The interlobular veins
Fig. 43.
Vessels of the Kidneys, and uriniferous Tubules
(modified from Turner).
1. Papillary duct; 2. Collecting tube; 3. Inter-
mediary tube; 4. Looped tube of Henle ; 5. Con-
voluted tube ; G. Bowman's capsule ; A. Segment of
artery forming renal arch; B. Interlobular artery
C. Afferent vessel of glomerulus ; D. Efferent vessel
of the same ; E. Glomerulus ; F. Plexus formed by
vasa efferentia ; G. Arteriola; rectfe ; H. Interlobular
vein.
join venous arches disposed in
the boundary layer between cortex and medulla, and from these arise
the larger branches that finally unite to form the large renal vein at the
hilus.
The medulla is less vascular than the cortex. Springing from the
arterial arches in the boundary layer are branches that break up into
pencils of long straight arterioles—the arterioke rectce. These pass with
a rectilinear course between the straight tubules of the medulla, and
break up into a wide-meshed capillary network around and between these
tubules. Veins having a straight course like the arteries run in
company with them, and join the venous arches in the boundary layer.
Connective-tissue of the Kidney.—This exists very sparingly between
the tubes in the cortex, but more abundantly in the medulla.
-ocr page 404-
OS
OS
Name of Muscle.
Oeigin.
Insertion.
Source of Nerve.
( Ribs, posterior borders and outer surfaces of >
( eight or nine last ....
j Ribs, 5th to 13th, anterior borders and outer
(         surfaces ......
Ribs, 1st to 14th, posterior edges; and 7th
cervical vertebra, transverse process
/ Ribs ; lumbar vertebrae, transverse and ar- -
I         ticular processes; dorsal vertebrae,
/         transverse processes; and cervical ver-
J         tebrae, last four transverse processes,
v and four spines in front of last
Last rib, posterior edge.....
R'bs, outer surfaces . . . . .
Lumbar and dorsal vertebras, spines
Sternum, lateral surface
Ribs (except first) .....
Ribs and cartilages (except last)
( Costal cartilages, 2nd to 8th ; and aponeur-
(         osis over internal intercostal muscles
Linea alba; prepubic tendon; ilium, exter->
nal angle ; (and Poupart's ligament)
Prepubic tendon, linea alba, and four or five |
last costal cartilages
Pubis (by prepubic tendon) ... I
Rnsiform cartilage, and linea alba . . '
Serratus posticus .
Serratus anticus . .
Transversalis costarum .
Longissimus dorsi .
Retractor costae
Levatores costarum
Semispinalis of the back and
loins .....
Lateralis sterni
External intercostals
Internal intercostals
Triangularis sterni .
Obliquus abdominis externus .
Obliquus abdominis internus .
Rectus abdominis .
Transversalis abdominis .
Vertebral spines, 11th dorsal to 2nd lumbar
Vertebral spines, 2nd or 3rd to 13th
( Lumbar vertebrae, first two, transverse pro-
\ cesses; and ribs, anterior borders
Dorsal nerves.
(Ilium, sacral surface; lumbar and dorsal
(         spines (or supraspinous ligament) .
j Lumbar vertebrae, first two or three trans- I
\ verse processes . . . . .         j
Dorsal vertebra?, transverse processes .
( Sacrum, lateral lip; lumbar vertebrae, ar-
<         ticular tubercles; and dorsal vertebrae,
( transverse processes
1st rib, outer surface .....
Ribs (except last) ......
Ribs and cartilages (except first)
Sternum, edge of thoracic surface .
f Ribs, last fourteen, outer surfaces ; and ten-
\         don of latissimus dorsi ....
) Ilium, external angle; and Poupart's liga-
|         ment.......
j Sternum, lower face; and costal cartilages, )
| 5th to 9th . . . . j
j" Ribs, last ten, lower extremities or carti-i
■\ lages ; and lumbar vertebrae transverse y
(. processes.....j
Cervical, dorsal, and
lumbar nerves.
j Last dorsal and first
I lumbar nerve.
Dorsal nerves.
( Dorsal and lumbar
( nerves.
Intercostal nerves.
Last ten intercostal,
last dorsal, and first
two lumbar nerves.
-ocr page 405-
Psoas magnus
Iliacus
Psoas parvus
> see page 92,
( Vertebrae, bodies of lumbar and last three ]
( or four dorsal.....j
Sacro-iliac ligament.....
Lumbar vertebrae, transverse processes .
Ilium, ilio-pectineal eminence
( Lumbar vertebrae, transverse processes;
\ and ribs, last three
Lumbar vertebrae, transverse processes .
Quadratus lumborum
Intertransverse muscles
loins ....
Lumbar nerves.
of
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CHAPTER XL
DISSECTION OF THE PELVIS.
Under this heading there will be described not only the pelvic cavity
and its contents, but also the tail and the hip-joint
Directions.—The dissection of the abdomen having been completed,
the vertebral column should be sawn across or disarticulated about the
middle of the lumbar region. If the directions given on page 69 have
been attended to, the dissector of the pelvis should find the hip-joint
intact, with the femur sawn across below the small trochanter, as in
Fig. 48. The muscles or portions of muscles left around the hip-joint
should be carefully removed, and the ligaments of the joint are to be
dissected, noticing in the first place, ho.vever, its movements.
THE HIP-JOINT AND THE LIGAMENTS OF THE PELVIS.
The Hip-joint belongs to the class of enarthrodial or ball-and-socket
joints.
The bones that enter into its formation are the femur and the os
innominatum, the former furnishing a rounded hemispherical head, and
the latter a cup-like cavity—the acetabulum, or the cotyloid cavity.
Movements. If the stump of the femur be grasped, it w7ill be found
to have a great freedom of movement. Thus, it can be flexed, extended,
abducted, adducted, circumducted, and rotated. In flexion the femur is
carried forwards so as to diminish the angle formed by that bone and
the ilium. For the definition of the other terms see page 42. In the
horse the hip-joint admits of a greater range of movement than any
other joint of the limbs. The movement of abduction, however, is less
free than it is in the other domestic animals, being, as will presently
be seen, restricted by the pubio-femoral ligament.
The joint possesses four ligaments, viz., capsular, cotyloid, pubio-
femoral, and round ligaments.
The Capsular Ligament has the form of a double-mouthed sac,
attached, on the one hand, to the rim of the cotyloid cavity, and to the
cotyloid ligament, and, on the other hand, to the periphery of the
articular head of the femur. It is strengthened in front by an oblique
band representing the ilio-femoral ligament of man. Its inner face is
-ocr page 407-
DISSECTION OP THE PELVIS.                                         339
lined by the synovial membrane of the joint, while its outer face is
supported by the following muscles:—the deep gluteus above, the
obturator extemus below, the rectus femoris and the rectus parvus in
front, and the gemelli behind. The ligament should be incised to show
the synovial membrane, after which it may be removed entirely.
The Synovial Membrane forms a complete internal lining to the
capsular ligament, and also invests the pubio-femoral and round ligaments
in the interior of the joint.
The Cotyloid Ligament is a ring of fibro-cartilage fixed at the margin
of the cotyloid cavity, which it serves to deepen for the reception of the
femoral head. On the inner side of the joint, where the notch interrupts
the rim of the cotyloid cavity, the ligament bridges over the gap, and to
this portion of the ring the term transverse ligament is sometimes
applied. This portion of the ligament, thus, converts the notch into a
foramen, through which the pubio-femoral ligament enters the joint.
The Pubio-Femoral Ligament. This ligament derives its fibres
from the prepubic tendon of the abdominal muscles, the rio-ht and
left ligaments intercrossing their fibres in front of the pubes. It is
directed outwards and backwards, resting in a groove on the inferior
surface of the pubis, and perforating the origin of the pectineus muscle.
At the notch on the inner side of the cotyloid ligament it enters the
hip-joint by passing above (in the natural position) the so-called
transverse ligament, and it terminates in the depression on the head of
the femur. The ligament, being attached across the middle in front is put
upon the stretch when the limb is abducted, and therefore restricts
that movement.
The Bound Ligament (interarticular ligament, or ligamentum teres).
This short and strong ligament is fixed above to the non-articular
depression at the bottom of the cotyloid cavity, and below to the excava-
tion on the head of the femur, being confounded at the latter point with
the pubio-femoral ligament. It will be best displayed by cutting the
transverse ligament and abducting the femur.
Direction.—It is convenient to dissect at this stage the sacro-sciatic
ligament, as it is necessary to remove it in order to display the pelvic
contents. Along with it, there will be described two other ligaments__
the superior and inferior ilio-sacral ligaments.
The Sacro-sciatic Ligament (Plate 16, and Fig. 48). This is a large
membranous ligament which forms the greater part of the lateral
boundary of the pelvis. It is irregularly four-sided in form. Its upper
edge, which is pierced by the ischiatic artery, is fixed to the lateral lip
of the sacrum, and to the rudimentary transverse processes of the first
one or two coccygeal bones; its lower edge is attached to the superior
ischiatic spine and to the tuber ischii, and between these points it forms
the upper boundary of the small sacro-sciatic foramen; its anterior edge
-ocr page 408-
340
THE ANATOMY OP THE HORSE.
is short, and forms the posterior boundary of the great sacro-sciatic
foramen; its posterior edge, much more extensive than the anterior, is
thin, ill-defined, and united to the coccygeal origin of the semimem-
branosus. Its outer surface is crossed by the great sacro-sciatic nerve,
and is covered by the biceps femoris and semitendinosus muscles, which
in part arise from it. Its inner surface is lined anteriorly by peritoneum,
and is related posteriorly to the compressor coccygis and retractor ani
muscles, some of whose fibres take origin from it. The internal pudic
nerve and vessels cross this surface, or they may be partly embedded in
the texture of the ligament.
The Great Sacro-sciatic Foramen is an elliptical opening in the lateral
wall of the pelvis, its anterior boundary being formed by the ischiatic
edge of the ilium, and its posterior by the sacro-sciatic ligament. It
transmits the gluteal nerves and vessels, and the great sciatic nerve.
The Small Sacro-sciatic Foramen is an interval in the lower and
posterior part of the lateral wall of the pelvis. Its upper edge is formed
by the sacro-sciatic ligament; its lower by the smooth and rounded
external border of the ischium, between the tuber and the superior
ischiatic spine. By this opening the common tendon of the obturator
interims and pyriformis emerge from the pelvis, and the nerves to these
muscles pass in.
The Superior Ilio-sacral Ligament (Fig. 48) is cord-like, and passes
between the internal angle of the ilium (the angle of the croup) and the
summits of the sacral spines.
The Inferior Ilio-sacral Ligament (Fig. 48) is membranous and
triangular in form. Its anterior edge is fixed to the upper part of the
ischiatic border of the ilium; its lower edge is attached to the lateral
lip of the sacrum; its posterior or upper edge is ill-defined, being con-
tinuous with the fascia investing the muscles of the tail.
the cavity of the pelvis.
Directions.—Fix the pelvis on a table, with the inlet looking upwards.
Sponge out the cavity and distend the bladder with air or some preserv-
ative fluid, tying the urethra to prevent its escape.
The pelvis is not distinct from the abdominal cavity, but is merely a
backward continuation of it. It is, in fact, that portion of the general
cavity of the belly which is posterior to the bony circle formed by the
sacrum, pubes, and ilio-pectineal lines. The plane of separation between
the abdominal cavity proper and the pelvic cavity, is termed the inlet of
the pelvis; the posterior extremity of the pelvic cavity is termed its
outlet,
The inlet or brim of the pelvis is circumscribed by the promontory of
the sacrum above, by the anterior margin of the pubic bones below, and
by the ilio-pectineal line on each side. It looks downwards and forwards,
-ocr page 409-
341
DISSECTION OF THE PELVIS.
and it is considerably larger in the mare than the horse. In form it is
nearly circular.
The outlet of the pelvis is circumscribed by the first one or two
coccygeal bones above, by the posterior edges of the ischial bones below,
and by the posterior edge of the sacro-sciatic ligament on each side. In
outline it is ovoid, with the broad end below; and it looks backwards
and upwards, being nearly parallel to the inlet.
The Cavity of the Pelvis is the irregularly tubular passage between
the inlet and the outlet. Its transverse section approaches the circular
in front, but changes gradually to the oval as it is taken more posteriorly.
For convenience of description, however, it may be said to have a roof,
a floor, and two lateral walls. The roof is formed by the inferior surface
of the sacrum and first one or two coccygeal bones. The floor is formed
by the pubic and ischial bones. Each lateral wall is formed for a short
space in front by the pelvic surface of the shaft of the ilium, and for the
rest of its extent by the sacro-sciatic ligament.
Contents of the Cavity.—These vary with the sex. In both sexes it
contains the rectum, the urinary bladder, and the termination of the
ureters, and numerous important vessels and nerves. In the male it
lodges, besides these, the vasa deferentia (in part), the seminal vesicles,
the prostate, Cowper's glands, the ejaculatory ducts, and the prostatic
and membranous portions of the urethra. In the female it lodges
the posterior part of the uterus, the vagina, and the vulva.
The Peritoneum. The serous lining of the abdominal cavity is con-
tinued into the pelvis, whose walls and contents it in part covers. Thus,
if it be followed backwards along the roof of the cavity, it will be seen
to cover the lower face of the sacrum about as far as its 4th segment,
but at that point it is reflected on to the rectum. Again, if the peri-
toneum be traced over the pelvic brim at the pubes, it will be found to
cover the floor of the pelvis for a short distance, and then to become re-
flected on to the bladder. In the same way, along a curved line on the
side of the pelvis between these two points, the peritoneum leaves the
pelvic wall and passes on to the viscera. Since this reflection, however,
takes place anterior to the posterior extremity, or outlet, of the cavity,
it results that the pelvic viscera get at most only a partial covering of
peritoneum. Thus, the rectum for a length of from four to six inches in
front of the anus, the posterior extremity of the vesiculre seminales, and
(in the collapsed state) nearly the half of the upper face of the bladder,
and three-fourths of its lower face are without a serous covering.
In the mare, in the same manner, the posterior part of the vagina and
the whole of the vulva are without a serous covering.
The peritoneum in passing on to the viscera forms certain folds, or
ligaments. Thus, it forms below and on each side of the urinary bladder
a double fold, the inferior and lateral ligaments of the organ (Plate
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342
THE ANATOMY OF THE HORSE.
44). The inferior ligament is a mesial fold attaching the bladder to the
pubic symphysis, and to the middle line of the abdominal wall in front
of the pubic brim. The lateral ligaments pass between the sides of the
bladder and the lateral walls of the pelvis, and in the adult the free
(anterior) edge of each contains the cord-like remains of the umbilical
artery.
Again, the peritoneum, in descending from the roof of the cavity to
envelop the first part of the rectum, forms a suspensory fold—the meso-
rectum, which is continuous in front with the colic mesentery.
On each side the ureter and the vas deferens project narrow bands of
peritoneum, and the right and left vasa deferentia where they lie above
the bladder are connected by a triangular serous fold which contains
between its layers the prostatic vesicle.
In the mare there are formed in an analogous manner the uterine
ligaments described at page 303.
Directions.—The pelvis should now be either laid on its side, or sus-
pended in the natural position and at a convenient height. A side view
of its contents is to be exposed by the following steps :—With the saw
cut through the shaft of the ilium close above the cotyloid cavity. Make
another section through the same bone immediately external to the sacro-
iliac articulation. Remove the intermediate piece of bone, at the same
time separating the peritoneum from its inner aspect. Find the internal
pudic artery in the position shown in Plate 16. It will be either internal
to the sacro-sciatic ligament or in its texture. Trace it forwards and
backwards. It is accompanied by a satellite vein, and where the two
vessels pass above the small sacro-sciatic foramen they are crossed out-
wardly by the internal pudic nerve. This having been found should
be followed upwards. Without injury to the nerve and vessels, the
sacro-sciatic ligament may then be removed, taking care of the com-
pressor coccygis and retractor ani muscles, which lie internal to the pos-
terior part of the ligament.
The Internal Pudic Artery (Plates 46 and 47) is a branch of the
internal iliac, arising at the last lumbar vertebra. Entering the pelvis,
it descends obliquely downwards and backwards across the side of the
cavity, lying on the inner surface of the sacro-sciatic ligament or within
its texture (Plate 16). At the small sacro-sciatic foramen it passes with
an inward and backward direction, terminating in a manner that varies
with the sex.
In the male it turns round the ischial arch and reaches the perinseum,
where it penetrates the urethral bulb. Besides slender hemorrhoidal
and perineal branches, it gives off the vesico-prostatic artery.
The vesico-prostatic artery arises about the neck of the bladder, and
supplies the prostate, the vesicula seminalis, the posterior part of the
bladder, and the terminal part of the vas deferens.
-ocr page 411-
DISSECTION OF THE PELVIS.                                         343
In the female the internal pudic terminates in hemorrhoidal, vulvar,
and bulbous branches; and, instead of the vesico-prostatic, it gives off
the vaginal artery, which is expended in the bladder, vagina, and cervix
uteri, anastomosing with branches of the uterine artery.
The Umbilical or Hypogastric Artery. In the adult (Plate 46) this
is a comparatively small vessel arising from the internal pudic near its
root. It is pervious only in the first few inches of its course, giving off
a few twigs to the bladder, and being then continued as a solid cord at
the free edge of the lateral ligament of the bladder. In the foetus,
however, it is of great size, and carries the foetal blood to the placenta to
be purified.
The Internal Pudic Vein runs in company with the artery. It
receives branches corresponding to those of the artery, and terminates in
the internal iliac vein.
The Pudic Nerve is derived from the 3rd sacral. Descending on the
inner surface of the sacro-sciatic ligament, it crosses the internal pudic
vessels superficially at the small sacro-sciatic foramen. Here it turns
slightly inwards, and disappears beneath the ischio-urethral muscle.
Having gained the lower face of the urethra, it turns round the ischial
arch, and is continued as the dorsal nerve of the penis. Before leaving
the pelvis, it detaches a perinaio-anal branch, which gives twigs to the
muscles of the urethra and penis, and hemorrhoidal branches that pass
upwards on the rectum to reach the anus, some of them appearing to
terminate in the sphincter. These latter branches are crossed by de-
scending branches from the hemorrhoidal nerve.
The lower posterior gluteal nerve (Plate 16) gives fibres to both the
trunk of the pudic nerve and its perinaeo-anal branch, and in some cases
the latter derives the majority of its fibres from this source.
In the female the pudic nerve terminates in branches to the labia,
clitoris, and constrictor muscles of the vulva.
The Hemorrhoidal Nerve is derived mainly from the 4th sacral. It
descends on the inner face of the sacro-sciatic ligament, and (for a short
distance) the compressor coccygis muscle. It supplies a twig to that
muscle, and then penetrates it, or emerges between it and the retractor
ani. It then divides into branches for the retractor and sphincter
muscles of the anus, and for the skin of the perineum.
The Retractor Ani. This muscle is described with the perineum
(page 276), but it is here exposed in the whole of its extent.
The Compressor Coccygis (Fig. 48) arises from the inner surface of the
sacro-sciatic ligament, over the superior ischiatic spine. Passing back-
wards and upwards, it is inserted into the last sacral and first two coccy-
geal vertebrae. By its inner face it is related to the rectum, except close
to its insertion, where the edge of the depressor of the tail intervenes.
Action.—Acting with the opposite muscle, it forcibly depresses the
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344
THE ANATOMY OF THE HORSE.
tail, compressing it over the perinseum. Acting singly, it inclines the
tail to that side.
Directions.—The preceding two muscles should be entirely removed.
Above the rectum there will be found the terminal portion of the pos-
terior mesenteric artery; and on its side, the pelvic plexus of nerves.
The Posteeior Mesenteric Artery (Plate 46) is a branch of the
abdominal aorta. Its terminal portion enters the pelvic cavity between
the layers of the meso-rectum; and passing backwards above the bowel,
it terminates above the anus. In its backward course it detaches
numerous branches to the wall of the rectum.
The Posterior Mesenteric Vein runs in company with the artery.
Its initial portion is formed at the posterior part of the rectum, by the
union of hEemorrhoidal veins, which communicate with like branches of
the internal pudic vein. In the abdominal cavity it concurs in the
formation of the portal vein.
The Pelvic Plexus of the sympathetic nerve. This is an intricate
network of nerves, placed on the side of the rectum, and distributing
branches to the pelvic viscera. It receives in front the offsets from the
posterior mesenteric plexus, and above it is joined by branches from the
inferior sacral nerves. In both sexes it distributes branches to the
rectum and bladder; and, besides, it supplies branches to the prostate,
vesicula seminalis, and vas deferens in the male, and to the vagina and
uterus in the female.
The Eectum (Plate 46) is the terminal segment of the large intes-
tines. At the entrance to the pelvis it is directly continuous with the
small colon, and it terminates at the anus. Its initial portion resembles
the small colon in being puckered and of comparatively small calibre.
Its terminal portion, on the other hand, is dilated, and sac-like, forming
a large pouch in which the fseces collect.
In the male it is related inferiorly to the bladder, vesiculse seminales,
vasa deferentia, prostate gland, and pelvic part of the urethra. In the
female it is related on the same aspect to the vulva, vagina, and uterus.
Structure.—The wall of the rectum resembles that of the large intes-
tine in general (page 309), possessing serous, muscular, submucous, and
mucous layers. As already seen, its peritoneal investment is incom-
plete, its terminal portion being destitute of peritoneum, and connected
by loose areolar tissue to contiguous organs. In front of the anus the
longitudinal muscular fibres of the bowel form on each side a band that
passes upwards to be inserted into the coccygeal vertebra). This, which
is termed the suspensory ligament of the rectum, forms a prominence at
the root of the tail. At the anus the last of the circular muscular fibres
form what is termed the internal sphincter. Developed in connec-
tion with the termination of the rectum are two striped muscles—the
sphincter ani externus and the retractor ani. These are described at
-ocr page 413-
DISSECTION OP THE PELVIS.                                        345
page 276. In the male the retractor muscles of the penis (page 276) form
a kind of sling for the rectum in front of the anus; and similar cords
of involuntary muscular tissue unite below the rectum at the same point
in the female, and terminate in the vulva.
The Urinary Bladder (Plates 46 and 47) is the reservoir for the
accumulation of the urine. The secretory action of the kidneys is
constant; and the urine, passing along the ureter, accumulates in the
bladder, to be expelled at intervals. As now seen in its distended
condition, the bladder is not wholly contained within the pelvic cavity,
but projects a little beyond the pubic brim. When empty, however,
it lies entirely within the cavity, resting on the concave upper surface
of the pubic bones. In form the distended viscus is ovoid. The broad
end, which is free and directed forwards, is termed the fundus; the
narrow end has the opposite direction, and becomes continuous by a
constricted neck with the urethra; the sides of the bladder are related
to the pelvic walls; and the upper surface is related to the rectum, vasa
deferentia, and vesiculse seminales in the male, and to the vagina and
uterus in the female. It is maintained in position by the peritoneum,
which gives it only a partial covering, and by its continuity with the
urethra. As already noticed, the peritoneum in passing on to it forms
the folds called the middle and lateral ligaments of the organ.
The Ureters (Plates 46 and 47). Each tube having crossed the inlet
of the pelvis, passes across its lateral wall, sustained by a narrow band of
peritoneum. Finally, it is reflected inwards to perforate the upper wall
of the bladder, a little in advance of its neck.
Directions.—Should the subject be a mare, the dissector must now
turn to page 351 rf seq., where the urethra and reproductive organs of
the female are described.
The Urethpa in the male (Plate 47). This is a long tube, extending
from the neck of the bladder to the free extremity of the penis. The
first few inches of the tube are contained within the pelvis, between the
rectum and the ischiatic symphysis ; for the rest of its extent it is extra-
pelvic, and amalgamated with the penis except at its termination, where
it projects as a short tube from the glans penis. The intra-pelvic
division of the tube is divided into the prostatic and membranous
portions; the extra-pelvic division is called also the spongy portion.
The prostatic portion includes the first inch or two of the tube behind
the neck of the bladder, and it is embraced by the prostrate gland.
The membranous portion comprises the next two or three inches, extend-
ing as far as the ischial arch, where, at a very acute angle, it becomes
continuous with the spongy portion. It is at this angle that the point
of the catheter is likely to be arrested.
Muscles. The membranous part of the urethra has connected with
it two muscles. The first of these, termed Wilson's muscle, or the
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346
THE ANATOMY OF THE HORSE.
constrictor urethral, envelops the tube behind the prostrate gland, from
which, indeed, it is not well defined. Its muscular fibres, of a pale red
colour, comprise two sets, which extend across the urethra on its upper
and lower faces respectively, and embrace the tube like an elliptical
sphincter. The most posterior fibres of the muscle pass over Cowper's
glands. The other, termed the ischio-urethral muscle, consists on each
side of a band whose fibres arise from the ischial arch, and pass to the
urethra beneath Cowper's gland, blending with Wilson's muscle. Like
the preceding, it is composed of pale red muscular fibres.
Action.—These muscles are constrictors of the membranous urethra,
and aid in the ejection of urine and semen.
The spongy portion of the urethra, with its muscles—the transversus
perinsei and accelerator urinse—has been already described as a con-
stituent part of the penis (page 284).
The Prostate Gland (Plates 46 and 47) embraces the neck of the
bladder and the initial part of the urethra. It consists of a middle and
two lateral lobes; and in structure it is glandular, with a considerable
admixture of striped muscular tissue. Its glandular texture consists of
branching excretory tubes and acini, both having a columnar lining.
Its ducts, as will be seen at a later stage, perforate the urethral wall, to
which it is adherent.
Cowper's Glands (Plates 46 and 47). Each of these is placed at the
side of the membranous urethra, just in front of the ischial arch. They
are round, reddish-yellow, and (in the stallion) about the size of a hazel
nut. They have the racemose typo of structure, and their ducts
perforate the adjacent wall of the urethra.
The Vasa Deferentia (Plates 46 and 47). These are the excretory
ducts of the testicles. As already seen, each is one of the constituents
of the spermatic cord. Appearing at the internal abdominal ring, as a
tube about the thickness of a goose-quill, it is reflected backwards to
enter the pelvis. Crossing the direction of the ureter, it places itself on
the upper surface of the bladder, and expands to four or five times its
previous calibre, forming what is called the bulbous portion of the vas
deferens. It then passes backwards beneath the vesicula seminalis;
and contracting again, it terminates under the prostate, by uniting out-
wardly with the neck of the vesicula to form a short tube termed the
ejaculatory duct. Where the vasa deferentia lie above the bladder, they
are connected together by a peritoneal fold between whose layers there
is contained the vesicula prostatica, or uterus masculinus. This is a short
tube with a blind anterior end, and opening by its posterior extremity
into the urethra. It is the homologue of the uterus and vagina of the
female.
The VESicuLiE Seminales (Plates 46 and 47). These bodies are
placed between the rectum and the posterior part of the upper face of the
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347
DISSECTION OF THE PELVIS.
bladder. Each is a small ovoid sac, like a miniature bladder. The
anterior end of the sac is rounded and free; the posterior end contracts,
and unites with the vas deferens to form the ejaculatory duct. Only the
anterior half of the vesicula is covered by peritoneum, which in passing
between the two bodies forms a small triangular serous fold.
The Common Ejaculatory Ducts. Each of these is a short tube
formed under cover of the prostate, by the union, at a very acute angle,
of the neck of the vesicula seminalis with the vas deferens. Its opening
into the roof of the urethra will be presently exposed.
Directions.—Carefully raise the fundus of the bladder, and cut its
peritoneal and connective-tissue adhesions to the sides and floor of the
pelvis. Free, in the same way, the membranous urethra at the ischial
arch; and cut the crus penis and its erector muscle from the tuber
ischii. This will enable the dissector to remove from the pelvis the
organs just described, while maintaining their mutual relations. Lay
the bladder on a table with its upper or rectal aspect downwards, and
open it by a mesial incision on its lower face. Carry the incision
backwards into the urethra, so as to open the whole extent of its
prostatic and membranous portions. Care must be taken that the
incision in both bladder and urethra is on the inferior face.
Structure of the Bladder. This comprises four coats:—
1.   The Serous or Peritoneal Goat. This, as already seen, is an incom-
plete investment.
2.   The Muscular Goat is composed of bundles of non-striped fibres
arranged in all directions. Compared with its condition in many other
animals, this coat is very thin ; and its fasciculi in the distended
bladder seem hardly to form a continuous layer. At the neck of the
bladder some of the fibres have a circular disposition, forming the
sphincter vesic B.
3.   The Submucous Coat is composed of vascular areolar connective-
tissue, and it loosely unites the muscular and mucous coats.
4.   The Mucous Goat. This forms a complete internal lining for the
bladder, and in the empty viscus it is thrown into folds, or rugce.
Observe the slit-like orifices of the ureters, near one another and a little
anterior to the urethral orifice (Fig. 44). Pass a probe or bristle into
one of them, and notice that the ureter perforates the wall very
obliquely—an arrangement which has a valvular action in preventing
the regurgitation of urine from the distended bladder. Between the
uretral and urethral orifices in the human subject is a triangular
area—the trigone—over which the mucous membrane is smooth even in
the contracted bladder. In the horse, however, this area is wrinkled
like the rest of the surface. The epithelium of the mucous membrane
is stratified and transitional.
Structure op the Urethra. The spongy portion has been described
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348
THE ANATOMY OF THE HORSE.
with the penis. The prostatic and membranous portions have a
mucous lining, external to which is a muscular coat of non-striped fibres.
Observe the following points in connection with the interior of the
intra-pelvic part of the urethra (Fig. 44). On
the middle line of the roof of the tube, close
behind the communication with the bladder, there
is a mucous eminence—the colliculus seminalis, or
verumontanum. In the gelding this is often small,
and sometimes hardly recognisable, but in the
stallion it is sometimes a considerable eminence,
like the tip of the little finger. At each side of
this projection is the orifice of the ejaculatory
duct. These orifices in the stallion are sufficiently
large to permit of the tip of the little finger
being insinuated into them. This should be
remembered, as the point of catheter, if not
guided along the floor of the urethra, might
easily pass into one of them. At the summit of
the colliculus, and therefore on the middle line, is
a very minute opening—the orifice of the uterus
masculinus. Inser1 a fine bristle into it, and
guide it on into the tube. On the wall of the
urethra at each side of the colliculus, observe an
irregular series of minute orifices which belong to
the ducts of the prostate gland. Behind these
on each side, notice another series of small open-
Fig. 44.
Bladder and intrapelvic
portion of Urethra
opened from below
(Leyh).
1. Vas deferens ; 1'. Bulb-
ous part of the same ; 2. Peri-
toneal fold joining the vasa
deferentia ; 3. Bladder ; 4.
Vesicula seminalis ; 5. Ori-
fices of ureters ; 6. Prostate ;
7. Verumontanum with ori-
fices of ejaculatory ducts ; S.
Orifice of prostatic vesicle;
9. Cowper's gland; 10. Ori-
fices of ducts of prostate ; 11.
Orifices of ducts of Cowper's
gland; 12. Corpus caver-
nosum ; 13. Corpus spongi-
osum with urethra in its
centre.
ings with a linear arrangement. These are the
orifices of the ducts of Cowper's glands. Insert
bristles into a few of each set of openings, and
guide them on into the respective glands. Close
to the neck of the bladder the epithelium of the
urethra is of the same character as in the bladder,
but behind that point it is simple and columnar.
Structure op the Vesicul;e Semixales. The
walls of these are composed of fibrous, ftbro-
muscular, and mucous layers; and contain many
tubular glands, which discharge their secretion
into the cavity, where it mixes with the semen.
The bulbous portion of each vas deferens has the
same structure.
Directions.—The student must now return to the pelvis, at the roof of
which he is to dissect the lumbo-sacral plexus of nerves, and the
branches of the internal iliac artery (Plate 48). Thereafter he is to
examine the pyriformis and obturator internus muscles.
-ocr page 417-
349
DISSECTION OP THE PELVIS.
The Lumbosacral Plexus (Plate 48) is composed of the anastomos-
ing nerve trunks for the supply of the hind limb. It is formed by the
inferior primary branches of the last three lumbar (4th, 5th, and 6th)
and first two sacral nerves, and it receives also a fasciculus from the
corresponding branch of the 3rd lumbar nerve. Each of these roots
emerges from the intervertebral foramen behind the vertebra after
which it is named; thus, the root from the 6th lumbar nerve emerges
by the intervertebral foramen behind the 6th lumbar vertebra, the 1st
sacral root by the first inferior sacral foramen, and so on. The branches
of the plexus, taken in order from before to behind, are as follows :—
1.   Iliaco-muscular Branches, for the psoas and iliacus muscles.
Two of these are seen in Plate 48, one coming from the anterior root
of the plexus, and the other from the anterior crural nerve.
2.   The Anterior or Great Crural Nerve. In point of size, this
is the second nerve of the plexus. It derives its fibres from the first
two roots of the plexus (4th and 5th lumbar), and from the fasciculus
furnished by the 3rd lumbar nerve.
3.   The Obturator Nerve derives its fibres from the 4th and 5th
lumbar roots of the plexus. It descends in company with the obturator
vessels, resting on the pelvic surface of the ilium. Under cover of the
obturator internus muscle, it passes through the obturator foramen and
reaches the thigh.
The 5th lumbar root, having given a branch to aid in the formation
of the anterior crural, and another to the obturator nerve, is continued
obliquely backwards between the internal iliac artery and the spine, to
join a broad nervous fasciculus to which the remaining roots of the
plexus (6th lumbar and first two sacral) contribute the whole of their
fibres. The remaining branches of the plexus are divisions of this
fasciculus.
4.   The Anterior Gluteal Nerves. Three or four in number, these
leave the pelvis and reach the hip by passing through the forepart of
the great sciatic opening, with the gluteal vessels.
5.   The Great Sciatic Nerve, the largest in the body, passes out into
the hip through the great sciatic foramen, behind the preceding.
6.   The Posterior Gluteal Nerves, distinguished as superior and
inferior, pass out behind the great sciatic.
The 3rd Sacral Nerve. The inferior primary branch of this nerve
is continued as the internal pudic nerve, after giving a bundle of fibres
to aid in the formation of the hsemorrhoidal nerve.
The 4th Sacral Nerve receives the before-mentioned branch from
the 3rd nerve, and is continued as the hsemorrhoidal nerve.
The 5th Sacral Nerve gives a backward twig to the 1st coccygeal
nerve, and is then expended in the skin of the anus and root of the tail.
As in other regions of the spine, each of the inferior primary branches
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350                             THE ANATOMY OF THE HORSE.
just considered communicates with the contiguous ganglion of the sym-
pathetic cord, by one or more branches detached at the intervertebral
foramen; and the sacral nerves send each a filament to the pelvic plexus.
The Sympathetic Gangliated Cord in the sacral region. This is the
direct backward continuation of the lumbar cord. It is placed on the
inferior surface of the sacrum, internal to the inferior sacral foramina,
the lateral sacral artery intervening between it and the inferior primary
branches of the sacral nerves at their points of emergence. It possesses
a ganglion opposite each of the first three sacral foramina; and, as before
said, it communicates by filaments passing between these ganglia and
the corresponding spinal nerves. The emergent branches of these
ganglia are very slender, and pass to the cellular tissue beneath the
sacrum, or to the contiguous blood-vessels. The cord terminates at the
last ganglion, either abruptly, or by a filament passing on to the middle
coccygeal artery.
The Internal Iliac Artery (Plate 48). This is one of the terminal
branches of the posterior aorta. Beginning at the intervertebral disc
between the 5th and 6th lumbar vertebne, it passes downwards and
backwards across the articulation between the last lumbar transverse
process and the sacrum, and then across the sacro-iliac articulation; and
at the upper part of the ilio-pectineal line, a little above the eminence of
the same name, it divides into the iliaco-musoular and obturator arteries.
The vessel is covered by the peritoneum, and in the first inch or two of
its course it is separated from the external iliac artery by the common
iliac vein. The collateral branches of the internal iliac, taken in the
order of their point of detachment, are as follows:—
1.   The second last of the series of lumbar arteries arises from the in-
ternal iliac at its root. It behaves like the lumbar branches of the aorta.
Its upper division, much the larger of the two, passes upwards through
the intervertebral foramen between the 5th and 6th lumbar vertebrae.
2.   The Internal Pudic Artery. This is a considerable vessel having
its origin at the last lumbar vertebra Entering the pelvis, it descends
at the ischiatic edge of the ilium, and then passes backwards in the
texture of the saoro-sciatic ligament, or on its inner face.
3.   The Lateral Sacral Artery leaves the parent trunk at the sacro-
lumbar articulation, and passes backwards on the lower face of the
sacrum, beneath or at the inner side of the inferior sacral foramina.
A little behind the middle of the sacrum it divides into the ischiatic and
lateral coccygeal arteries. The former, much the larger of the two, passes
out through the edge of the sacro-sciatic ligament to reach the hip
(Plate 16); the latter continues the direction of the lateral sacral artery
to the tail. The inferior division of the 3rd sacral nerve appears in
the angle of separation between these two arteries. The collateral
branches of the lateral sacral artery are :—(1) Branches entering the
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351
DISSECTION OP THE PELVIS.
intervertebral foramen between the last lumbar vertebra and the sacrum
(last lumbar artery), and the first two or three inferior sacral foramina.
Each of these enters the spinal canal, furnishes there a spinal branch,
and then emerges by the corresponding superior foramen, and is dis-
tributed to the overlying muscles and skin. (2) The middle coccygeal
artery is an unpaired vessel, variable as to its origin, but generally,
as in Plate 48, furnished by the right lateral sacral artery. It passes
inwards to the middle line, and is continued backwards to the tail.
4.   The Ilio-lumbar Artery. This artery is in series with the lumbar
arteries, representing, as it were, the abdominal or inferior branch of the
last lumbar artery. Arising from the outer side of the parent trunk, it
passes outwards across the sacro-iliac joint, giving branches to the iliacus
and psoas magnus muscles. Its terminal twigs may reach the gluteus
maximus or the tensor vaginse femoris.
5.   The Gluteal Artery, a large vessel, arises at the edge of the
sacrum, and passes out into the hip by the great sacro-sciatic foramen,
dividing into a number of branches as it escapes (Plate 16).
The Iltaco-femoral Artery, one of the terminal branches of the
internal iliac, passes downwards and outwards between the shaft of the
ilium and the iliacus muscles, to reach the outer aspect of the thigh. It
supplies the nutrient artery of the ilium.
The Obturator Artery, the other terminal branch of the internal
iliac, passes downwards and backwards on the pelvic surface of the ilium,
at the anterior edge of the pyriformis muscle. Under cover of the
obturator internus muscle, it passes through the obturator foramen and
reaches the thigh. It is accompanied by a satellite vein, and by the
obturator nerve, which is placed anterior to the vessels. The tendon of
the psoas parvus muscle is inserted in the angle of separation between
this and the preceding artery.
The Internal Iliac Vein collects the blood from the satellite veins
of the foregoing arteries. It unites with the external iliac vein, forming
the common iliac vein.
The Obturator Internus and the Pyriformis. For a description of
these muscles turn to page 68.
reproductive organs in the female.
Comprised under this heading there are: the ovaries, the Fallopian
tubes, the uterus, the vagina, and the vulva. The ovaries, the Fallopian
tubes, and the uterus (in part) are abdominal organs, and their mode of
suspension in that cavity has already been noticed. Their more com-
plete examination can now be undertaken along with the dissection
of the purely pelvic parts of the same apparatus, and at the same time
it is convenient to examine the female urethra.
The Ovaries, as already seen, are situated in the lumbar region of the
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352
THE ANATOMY OP THE HOESE.
abdominal cavity (see page 303). Each ovary is about half the size of
the testicle—the corresponding organ of the male. In form it is ovoid,
with a distinct depression on its upper surface—the hilus. At the hilus
the nerves and vessels of the organ enter from the broad ligament of the
uterus, and in its neighbourhood the expanded end of the Fallopian tube
is attached by one of its fimbriae to the surface of the ovary. From the
posterior extremity of the ovary a cord of non-striped muscular tissue—
the ligament of the ovary—passes to the uterine cornu. The lateral
surfaces, the inferior border, and the anterior end of the ovary are
rounded and free.
Structure op the Ovary. This comprises (1) an epithelial covering
on the surface of the organ, (2) a fibrous framework, or stroma, and
(3) Graafian follicles.
1.   The Germinal Epithelium.—This is a single layer of short columnar
cells with granular contents. In veterinary text-books the surface of
the ovary is described as having a serous covering derived from the
broad ligaments. The cells of this surface covering, however, are in
marked contrast to the cells of the broad ligament, which have the
ordinary flattened and transparent endothelial characters. The term
germinal is applied to this layer because the ova, or germ-cells, are
separated from it in the festal ovary.
2.  TheStroma is composed of fibrous connective-tissue with some bundles
of non-striped muscular tissue. The blood vessels of the ovary ramify
in it, and it surrounds the Graafian follicles. Around the hilus it is
most vascular and open in texture, and this portion of the stroma is
sometimes termed the zona vasculosa or the medullary substance, in contra-
distinction to the peripheral cortical substance. A layer of condensed
stroma without any Graafian follicles lies beneath the surface epithelium,
and is sometimes termed the tunica albuginea of the ovary.
3.   The Graafian Follicles, or Ovisacs.—These are vesicular bodies for
the maturation and extrusion of the ova. A large-sized follicle possesses
the following parts :—
a.   The wall of the follicle, composed of an inner delicate tunica
propria, and an outer layer—the tunica fibrosa—derived from the
surrounding stroma.
b.   The Membrana Granulosa.—This forms an epithelial lining to the
wall of the follicle, and consists of several layers of cells. At one point
these epithelial cells are heaped up to form the cumulus or discus
proligerus, the cells of which surround the ovum.
c.   The Liquor Folliculi.—This is a fluid which fills up the remainder of
the cavity of the follicle.
The Ovum is a typical animal cell. It consists of an outer envelope—the
zona pellucida; protoplasmic cell-contents—the vitellus or yelk; a nucleus—
the germinal vesicle; and, within the nucleus, a nucleolus—thegerminalspot.
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DISSECTION OF THE PELVIS.                                         353
The Graafian follicles vary greatly in size. The smallest are imbedded
in the cortical part of the ovary. These are of microscopic size, and
differ from the larger follicles in having only a single layer of cells in
the membrana granulosa, and in having no liquor folliculi. Follicles of
intermediate size are placed more deeply in the ovary, and differ from the
largest chiefly in the small amount of liquor that they contain. These
differences of size represent different stages of development of the
follicles, the largest being the most mature. When mature, a follicle
occupies a considerable space in the substance of the ovary in the neigh-
bourhood of the hilus. Finally it bursts through the surface of the
Fig. 45.
Section or Cat's Ovary, magnified (from Schron).
1. Outer covering of the ovary ; 2. Fibrous stroma ; 3. Superficial layer of flbro-nuclear substance;
3'. Deeper parts of the same ; 4. Blood-vessels ; 5. Ovi-sacs forming a layer near the surface ; 6. One
or two of the ovi-sacs sinking deeper and beginning to enlarge ; 7. One of the ovi-sacs farther
developed, now enclosed by a prolongation of the fibrous stroma, and consisting of a small Graafian
follicle, within which is situated the ovum covered by the cells of the discus proligerus ; 8. A follicle
farther advanced; S'. Another which is irregularly compressed; 9. the greater part of the largest
follicle, in which the following parts are seen ; a. Cells of the tunica granulosa lining the follicle ;
6. The reflected portion named discus proligerus ; c. Vitellus or yelk part of the ovum, surrounded
by the zona pellucida ; d. germinal vessicle ; e. Germinal spot.
ovary, and the ovum, along with the liquor folliculi and part of the
membrana granulosa, escapes and is caught by the expanded extremity
of the Fallopian tube. The follicle then collapses, while it becomes in
part filled with blood from the vessels opened by the rupture of its wall.
The rupture then heals, and the follicle becomes converted into a
2 a
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354
THE ANATOMY OF THE HORSE.
yellowish body-—the corpus luteum. In the early stage of a corpus
luteum the cells of the membrana granulosa proliferate, while capil-
laries extend into it from the wall of the follicle. Later on the blood-
clot in the centre becomes decolorised, and the granulosa cells become
fatty; and finally the corpus luteum shrinks and disappears.
The Parovarium, or the Organ of Rosenmuller. This is a minute
body situated in the broad ligament, between the ovary and the
Fallopian tube. It consists of a number of short convoluted tubules
opening into a longitudinal tube, the latter representing the canal of
Godrtner in the cow. The parovarium is the homologue of the epididymis
of the male.
The Fallopian Tubes, or Oviducts. The Fallopian tube is the duct
for the conveyance of the ova from the ovary to the uterus. Ed its
Fie. 46.
Right Ovary and Fallopian Tube.
1. Fallopian tube ; 2. Abdominal opening (fimbriated extremity) of the same ; 3. A probe intro-
duced into the uterine opening of the tube ; 4. Ovary ; 5. Ligament of the ovary ; 6. Broad liga-
ment of the uterus ; 7. Tip of uterine cornu laid open.
course between these two organs the tube passes in a flexuous manner
at the anterior border of the broad ligament. The ovarian extremity
of the tube opens on the surface of an expansion whose rim is cut into
a few short fringe-like processes—the fimbria}. Inwardly the rim
of this expansion is fixed to the surface of the ovary near the hilus.
The upper surface of the expansion is covered by a mucous membrane
with delicate rugae that converge from its rim to its centre, where it
shows the orifice of the tube—the ostium abdominale. The under surface
-ocr page 423-
DISSECTION OP THE PELVIS.                                            355
of the expansion is smooth and covered by peritoneum. The uterine
extremity of the tube opens into the extremity of the uterine horn by a
minute orifice—the ostium uterinum.
Although the Fallopian tube bears to the ovary the relationship of an
excretory duct, in that it conveys away the ova, it differs from all other
excretory ducts in not having its lumen closely continuous with the
interior of the gland whose secretion it conveys. Moreover, this discon-
tinuity between the Fallopian tube and the ovary establishes an indirect
communication between the sac of the peritoneum and the surface of the
body, and brings about the single exception to the rule that serous
membranes form perfectly close sacs.
Structure of the Tube. The wall of the oviduct comprises the follow-
ing layers, enumerated from without inwards, viz., (1) an outer serous coat,
derived from the broad ligament; (2) a coat of non-striped muscular tissue,
arranged as an outer longitudinal and an inner circular set of fibres; (3)
a submucous coat of vascular connective-tissue ; (4) a mucous coat, having
a ciliated columnar epithelium.
The lumen of the tube is narrowest at its uterine extremity and widest
at the ovary.
The Uterus, or womb, is the organ that receives the ovum, retains it
during its development (provided it has been fertilised), and, finally,
expels it at the expiration of the full term of pregnancy. In situation
the organ is partly abdominal, and partly pelvic, and its mode of
suspension by the broad ligaments- has already been observed in
connection with the peritoneum (page 303).
The organ is single in its posterior portion, and bifid in front.
The anterior bifurcations of the organ are termed its cornua or horns.
At its anterior extremity each horn is pointed, and receives the uterine
opening of the Fallopian tube. From this point the calibre of the hom
gradually increases to its posterior end, where it opens into the body of
the organ. Each horn shows a concave upper border at which the broad
ligament reaches it, while its lower border is convex and free. The
cornua are entirely abdominal in position, and are related to the
intestines.
The posterior single portion of the uterus comprises the body, and the
neck, or cervix; but this division is not apparent on the exterior.
The body, placed in front, presents two faces, two borders, and two
extremities. The upper face is slightly flattened and related to the
rectum; the lower face, also flattened, is related to the intestines in
front, and to the bladder behind; the borders, right and left, show the
insertions of the broad ligaments; the anterior extremity, or fimdus, is
the widest part of the bod}', and it is joined at each angle by the cornu;
the posterior extremity is continuous with the cervix. The body of
the uterus is partly abdominal and partly pelvic in situation.
-ocr page 424-
356
THE ANATOMY OF THE HORSE.
The cervix is the extreme posterior part of uterus. It is directly
continuous with the body in front; and its posterior extremity, as will
is laid open, projects into the anterior
be seen when the organ
extremity of the vagina.
The Vagina is a tubular
organ which connects the uterus
and the vulva. It is lodged
entirely within the pelvis, being
related to the rectum above, to
the bladder and urethra below,
and to the ureters and pelvic
walls laterally. Its mode of
connection with the two cavities
that it connects will be ex-
amined later on. Its average
length is about nine or ten
inches.
The Vulva is the passage
that continues the vagina back-
wards, and opens on the surface
of the body beneath the anus.
The tube of the vulva is
about five inches in length. It
VIEWED FROM
is united by cellular tissue to
ABOVE.
the rectum above, and to the
1, 1. Ovaries; 2, 2. Fallopian tubes; 3. Fimbriated
extremity of the tube, outer face ; 4. The same, inner
face, showing the abdominal orifice ; 5. Ligament of
the ovary ; 6. Right cornu, intact; 7. Left cornu,
laid open ; 8. Body of the uterus ; 9. Broad ligament ;
10. Os uteri (externum); 11. Interior of the vagina;
12. Meatus urinarius, with its valve 13 ; 14. Mucous
fold, a vestige of the hymen ; 15. Interior of the
vulva ; 16. Clitoris ; 17, 17. Labia of the vulva; IS.
Inferior commissure of the vulva.
jjelvic floor below, while on
each side it is related to the
retractor ani muscle. Below
and laterally it is covered by a
layer of striped muscular tissue
-the anterior constrictor of the
vulva. The fibres of this muscle after embracing the tube of the vulva
are lost on the sides of the rectum.
The external opening of the vulva has the form of a vertical slit, and
it is bounded at the sides by the labia, which meet above and below to
form the commissures. The superior commissure is acute, and separated
from the anus by a narrow interval. The inferior commissure is rounded,
and immediately within it the clitoris is lodged. The labia are covered
externally by skin, which is thin, almost destitute of hairs, and generally
black-pigmented; inwardly they are lined by mucous membrane; and
at their sharp edges these cutaneous and mucous coverings meet. If the
cutaneous covering of the labia be removed, the 2^osterior constrictor of
the vulva will be exposed. This is a red muscle corresponding to the
compressor bulbi of human anatomy. Its fibres are elliptically disposed
-ocr page 425-
DISSECTION OF THE PELVIS.                                         357
around the extremity of the vulva, being confounded with the sphincter
ani above, while inferiorly some of the fibres are attached to the base
of the clitoris, and others are attached to the inner surface of
the skin below the inferior commissure. When the muscle contracts, it
constricts the orifice of the vulva. Its lower fibres may frequently be
observed to contract after micturition, depressing the inferior commissure
and exposing the clitoris, which is simultaneously erected.
The Clitoris. This small erectile body is the homologue of the male
penis minus the urethra. It is lodged within the inferior commissure of
the vulva, and presents a base, or attached extremity, a body, and a free
extremity. The base is bifid, and attached to the ischial arch by the
branches, or crura, each eras being covered by a rudimentary erector
clitoridis muscle—the homologue of the erector penis. The body of the
clitoris, which is from two to three inches in length, projects backwards
and upwards, and is composed of right and left halves like the corpora
cavernosa of the penis. The free extremity is formed by a rudimentary
r/lans, which is provided with a mucous cap analogous to the prepuce.
The clitoris is composed of erectile tissue resembling that of the
penis.
The Vestibular Bulb. This will be exposed by the removal of the
posterior constrictor muscle. It is an erectile body composed of right
and left halves, each of which is placed at the side of the vulvar cavity
(the vestibule), between the posterior constrictor and the mucous
membrane, Inferiorly the two halves of the organ are in communica-
tion with one another, and with the erectile tissue of the clitoris,
and superiorly each terminates at the side of the vulva by a rounded
end. The bulb is the homologue of the corpus spongiosum of the
penis.
Directions.—The pelvic viscera must now be removed to allow an
examination of the structure and interior of the organs just considered.
This is to be effected by cutting the meso-rectum and the peritoneal
ligaments of the bladder, carrying the knife above the anus and below
the inferior commissure of the vulva, and destroying the vascular
and connective-tissue attachments of the various organs to the pelvic
walls. The entire generative apparatus will thus be removed along
with the urinary bladder and the rectum. The latter organ should be
dissected from the vagina and vulva (for its structure see page 344),
and the other viscera examined seriatim. The canal of the vulva and
vagina is to be exposed by a mesial incision on the upper wall of these
organs.
The Canal of the Vulva. This, as already stated, is a tubular
passage about five inches in length. When removed from the body
and inflated, it assumes a large calibre, but ordinarily its walls are
in contact. Tracing the canal in an order inverse to that followed
-ocr page 426-
358
THE ANATOMY OF THE HOUSE.
in the previous description of parts, it may be said to begin on the
surface of the body at the vertical slit already described, and to
terminate in front by joining the tube of the vagina. In the
adult animal there is little to mark the line of separation between the
two passages, but in the young animal a membranous septum—the
hymen—stretches between the two. This is occasionally seen also in
the adult mare, and more frequently a few warty projections—the
carunculce myrtiformes—which are the shrunken remains of the hymen,
stud the line of junction; but very often the canal of the vulva passes
without interruption into that of the vagina. The vulva is lined by a
mucous membrane of a rosy, vascular tint. It possesses numerous
mucous follicles; and its free surface is formed by a stratified squamous
epithelium, which, towards the external opening, is often pigmented in
spots.
The Meatus Urinarius. The urethra opens on the middle line of
the floor of the vulva immediately behind its point of continuity with
the vagina. The opening is surmounted by a large mucous fold—
the valve of the meatus urinarius. This valve has its free edge
directed backwards, and it serves to direct the flow of urine towards
the exterior. Its presence must be remembered in passing the
female catheter, the point of which should be made to press on the floor
of the vulva as it is directed onwards. The meatus is of large size
when compared with the same orifice in the male, since it readily admits
two fingers.
Directions.—Reverse the natural position of parts, laying the uterus,
vagina, and vulva with their upper surfaces downwards, and open the
bladder by a mesial incision on its lower (in the natural position) face.
For an account of the structure of the bladder turn to page 347.
The Urethra of the female is very much shorter, but considerably
wider, than the corresponding tube of the male. Beginning as a funnel-
like prolongation of the neck of the bladder, it passes backwards on the
middle line of the lower face of the vagina, in whose wall it is partially
imbedded; and after a course of two or three inches it perforates the
lower wall of the vulva, and opens by the meatus already described.
The calibre of the tube is hi correspondence with the large size of the
meatus; and with slight stretching it will accommodate three fingers.
The wall of the urethra is composed of connective-tissue, and non-
striped muscular fibres circularly disposed; and it is lined internally
by a longitudinally folded mucous membrane with a stratified squamous
epithelium.
Structure and Interior op the Vagina. The tube of the vagina
is about nine or ten inches in length. Posteriorly it joins the vulva,
and anteriorly it embraces the cervix uteri. The connection between
the cavities of the vagina and uterus is, thus, not by simple continuity,
-ocr page 427-
DISSECTION OF THE PELVIS.                                        359
but the vaginal wall is carried forwards, so as to cause the os uteri to
project freely into the forepart of the vaginal canal.
The wall of the vagina comprises the following layers :—
1.   A Serous Goat.—This is only a partial covering, the posterior part
of the organ being without a peritoneal investment. In the hinder part
of the tube the place of the peritoneum is taken by connective-tissue
uniting it to surrounding parts. This connective-tissue is loose and
areolar towards the rectum ; but between the vagina and the bladder it
is closer, and forms a more intimate bond between the two organs.
2.   A Muscular Coat.—This is composed of non-striped muscular
tissue, continuous in front with the muscular coat of the uterus.
Posteriorly the muscular tissue is reddish in tint, and passes into the
anterior constrictor of the vulva. The fibres are arranged both longi-
tudinally and circularly.
3.   A Mucous Coat. This lines the tube inwardly, and it is longitudi-
nally folded. It possesses numerous mucous glands, and its epithelium
is stratified and squamous. It is of a pinkish, vascular tint, like the
mucous lining of the vulva.
Directions.—Lay open one of the horns of the uterus in its whole
extent, and carry the incision along the body and cervix to the os.
Structure and Interior op the Uterus. The interior of the uterus
comprises the cavities of the body and cervix, and those of the horns.
The Cavity of the Cervix begins posteriorly at the orifice of the tap-
like projection already noticed at the forepart of the vaginal canal.
This orifice is termed the os uteri externum, or, shortly, the os uteri.
Ordinarily the orifice is closed, and forms a circular depression from
which the folds of mucous membrane radiate outwards, and curve round
the circular lip of the os, to be carried to the vaginal wall.
In front the canal of the cervix passes gradually into the wider cavity
of the bod). (In the human subject the connection between the canal
of the cervix and the cavity of the body is abrupt, constituting the
os uteri internum.)
The Cavity of the Body is triangular in form, with the base in front.
At its posterior angle it passes into the canal of the cervix, and at each
antero-lateral angle it is joined by the cavity of a horn.
The Cavities of the Horns are conical and curved. Each is widest at
its base, where it joins the cavity of the body; and it tapers to its
anterior extremity, in the centre of which it presents a small tubercle
perforated by the uterine orifice of the Fallopian tube.
The wall of the uterus comprises serous, muscular, and mucous
layers :—
1.   The Serous Coat is peritoneum, continuous with the layers of the
broad ligaments. It completely envelops the organ.
2.   The Muscular Coat is composed of non-striped fibres arranged as
-ocr page 428-
360
THE ANATOMY OP THE HORSE.
an external longitudinal, and an inner circular set. To compensate for
the expansion of the uterine wall during pregnancy, and to provide a
force to expel the foetus at parturition, there is, during pregnancy, both
an increase in the size, and an addition to the number, of these
muscular fibres.
3. The Mucous Coat forms a complete lining to the uterus. It is
smooth, of a pale pink colour, and thrown into longitudinal wrinkles.
The epithelium is simple, columnar, and ciliated, except in the posterior
part of the cervix, where it is stratified and squamous, as in the vagina.
In the cornua and body the mucous membrane is set with numerous
utricular glands. The mouths of these glands open on the surface of
the membrane, while their blind ends lie against the muscular coat.
They lie obliquely in the membrane, and are branched at their deep
ends. They are lined by a single layer of columnar ciliated cells.
The mucous membrane of the cervix contains numerous mucous
follicles, and the peculiar ovula Nabothi, which appear to be mucous
glands distended into a vesicular form by their own clear secretion. In
pregnancy these cervical glands secrete the mucous plug that closes the
os uteri.
Directions.—The student must now return to the dissection of parts
remaining in the pelvis, beginning with the lumbo-sacral plexus (page
349).
THE TAIL (FIG. 48).
Directions.—Saw through the ilium that is still intact, making the
section across the bone at the great sciatic foramen. By cutting the
sacro-sciatic ligament on the same side, the sacro-coccygeal part of the
spine, with the sacro-iliac joints, will be isolated. Dissect away the
inferior ilio-sacral ligament, and remove the skin from the tail.
The skin of the tail differs from that of the body in general in the
greater length of its hairs. On its under surface, however, extending
backwards from its root, there is a triangular area without hairs.
Along the under surface of the tail, and especially in front, the skin is
thin; but on its upper aspect and sides it is thick, and intimately
adherent to the subjacent fascia.
The muscles of the tail are enveloped by a strong coccygeal fascia
which is continuous in front with the inferior ilio-sacral ligament. The
isolation of the muscles can be readily effected near the root of the tail,
but towards its tip they tend to blend with each other. In each half
of the tail there are three muscles, viz., one above, one below, and one
at the side. There are also three arteries—one on the middle line
below, and one between the inferior and lateral muscles on each side.
On each side there are two sets of nerves, one of which accompanies the
lateral artery, while the other is on the upper aspect of the bones,
-ocr page 429-
361
DISSECTION OP THE PELVIS.
between the lateral and superior muscles. [Besides the three muscles
now to be described, there is the compressor coccygis already dissected
(page 343).]
The Erector Coccygis (sacro-coccygeus superior). This muscle arises
from the sides and summits of the sacral spines, and it is inserted by
successive short tendons to the upper asjiect of the coccygeal vertebrae.
Action.—Acting with its fellow, to elevate the tail directly; acting-
alone, to elevate the tail and incline it laterally.
The Curvator Coccygis (sacro-coccygeus lateralis). This muscle
seems to continue backwards the semispinals of the loins. It arises
from the last two lumbar spines and from the spines of the sacrum,
and it is inserted into the lateral aspect of the coccygeal bones.
Action.—To bend the tail to the side of the acting muscle.
Fig. 48.
Muscles of the Tail, deep Muscles of the Hip, and Pelvic Ligaments (CAauveau).
1. Erector coccygis; 2. Curvator coccygis; 3. Depressor coccygis; 4. Compressor coccygis;
5. Deep gluteus; (5. Rectus parvus ; 7. Common tendon of obturator internus and pyriformis;
8. Gemelli; 9. Accessory fasciculus of the same ; 10. Quadratus femoris ; 11. Sacro-sciatic ligament;
12. Great sacro-sciatic foramen ; 13. Superior ilio-sacral ligament; 14. Inferior ilio-sacral ligament.
The Depressor Coccygis. Anteriorly this muscle consists of an
outer and an inner portion, which Leyh describes as separate muscles.
It arises from the lower face of the sacrum, beginning about the 3rd
foramen. The slips of the inner portion are inserted into the first six
coccygeal vertebras, while the outer portion extends to the extremity of
the tail, and is provided with strong tendons of insertion.
Action.—It inclines the tail laterally or depresses it, according as it
acts alone or with the opposite muscle.
-ocr page 430-
362
THE ANATOMY OF THE HORSE.
Between the preceding two muscles a number of semi-independeiit
fleshy fasciculi connect adjacent coccygeal bones. Leyh describes these
separately as the intertransversales caudce.
At the root of the tail, between the right and left depressors, the
retractor muscles of the penis take origin from the 1st and 2nd or
2nd and 3rd coccygeal bones; and behind these the so-called suspensory
ligaments of the rectum are inserted (Plate 46).
The Middle Coccygeal Artery (Plate 48). This is the largest
artery of the tail.* It is an unpaired vessel, and in the great majority
of cases it is a collateral branch detached from the inner side of the
lateral sacral artery towards the middle of the sacrum. Sometimes
it is detached in the same way from the left lateral sacral artery.
Passing backwards and inwards on the lower surface of the sacrum, it
places itself on the middle line, and extends in that position throughout
the tail, lying under the coccygeal vertebra, and between the right
and left depressor muscles. In its backward course it gradually reduces
itself by giving off lateral branches.
The Lateral Coccygeal Artery (Plate 48). Each artery (right or
left) is one of the terminal branches of the lateral sacral artery (the
ischiatic artery being the other branch). Having its origin towards the
middle of the sacrum, it passes backwards in the tail, crossing the sides
of the coccygeal bones, between the depressor and curvator muscles, the
former muscle separating it from the middle artery. It becomes smaller
by the detachment of numerous collateral twigs, the largest of which
pass upwards. Leyh designates this vessel the infero-lateral coccygeal
artery, describing as the supero-lateral coccygeal artery what is,
apparently, an unusually large branch of the first.
Veins. The foregoing arteries are accompanied by veins of the same
names.
Coccygeal Nerves. There are five or six pairs of coccygeal nerves,
and they are numbered according to the bones behind which they turn
outwards, the first issuing behind the first coccygeal vertebra, and so on
with the others. The first of them has a loop of communication with
the last sacral. As they turn outwards, they divide into an upper and
a lower branch corresponding to the superior and inferior primary
branches of the spinal nerves in other regions. The branches of each
of these sets are directed backwards, detaching slender filaments, and
then applying themselves to the next nerve of the same set. In this
way there are formed in each half of the tail two composite nerves, one of
which accompanies the lateral artery, while the other runs on the upper
aspect of the tail between the erector and curvator coccygis. These
cords are expended in branches to the muscles and skin of the tail.
* Leyh describes and figures this artery as being smaller than the lateral coccygeal,
but that, certainly, is not usually the case.
-ocr page 431-
363
DISSECTION OF THE PELVIS.
Sacral Nerves. On the upper aspect of the sacrum the superior
primary branches of the sacral nerves will be found at their points of
emergence from the spinal canal, the first four issuing by the superior
sacral foramina, and the last by the foramen between the sacrum and
the first bone of the coccyx. These nerves are much smaller than the
corresponding inferior primary branches ; and after giving twigs to the
muscles on the side of the spine, they pass upwards to the skin of the
croup. Slender branches of the lateral sacral artery issue from the
spinal canal in company with them.
JOINTS AND LIGAMENTS OP THE SACRUM AND COCCYX.
The sacral portion of the spine in the adult animal does not present
any joints between its constituent pieces, which are fused by anchylosis.
The lumbar supraspinous ligament is prolonged on the summits of the
sacral spines. This region, however, furnishes the important joint
between the vertebral column and the skeleton of the hind limb—the
sacro-iliac articulation.
The Sacro-iliac Articulation. The bony surfaces that concur to
form this are the auricular facet on the lateral aspect of the sacrum, and
the corresponding facet on the pelvic surface of the ilium. The move-
ments permitted in the joint are scarcely appreciable, as the student
may prove by grasping the sacrum and the part of the ilium left in
connection with it. Since this joint is the bond of connection between
the skeleton of the trunk and that of the hind limb, in which, in loco-
motion, the main propulsive efforts are originated, it is necessary that
but slight movement should be permitted, as otherwise these efforts
would not be transmitted with precision to the trunk. The stability of
the joint is effected mainly by one ligament—the sacro-iliac, and to a
less degree by the superior and inferior ilio-sacral ligaments and the
sacro-sciatic ligament already described (page 339).
The Sacro-iliac Ligament.—This ligament is composed of strong fibres
passing between the sacrum and ilium, in close relation to the joint.
It consists of an upper and a lower half, corresponding respectively to
the anterior and posterior sacro-iliac ligaments of human anatomy. The
former is much the stronger of the two; and the necessity for its strength
is apparent when one reflects that whatever weight is placed on the
back and loins of the horse, tends to drive the sacrum downwards from
its connection with the iliac bones, and that this tendency is rather
favoured than otherwise by the form of the articular surfaces, which
offer an arrangement comparable to an inverted arch.
The bones should be disarticulated to show the articular surfaces.
The joint is provided with a rudimentary synovial membrane.
Sacro-coccygeal and Inter-coccygeal Articulations. Ordinarily
these are movable joints, the articular surfaces being the opposed
-ocr page 432-
364                                THE ANATOMY OF THE HORSE.
extremities of the rudimentary vertebral bodies. These are connected
by small intervertebral discs, which are shaped like a biconcave lens,
since the bodies of the vertebra; are here convex on both extremities.
The bones are also invested by a fibrous sheath, which may be
supposed to represent the superior and inferior common ligaments of
the back and loins.
Movements.—The biconvex form of the vertebral centra, and the
suppression of the different processes in this region give a great range
and freedom of movement to the tail, which, provided with its appendage
of hairs, is admirably fitted to protect the hind quarters of the animal
from the attacks of insects. It is interesting to notice the absence of
the panniculus carnosus over the area within which the tail is serviceable
for this purpose. In animals above middle age it is not uncommon to
find the sacro-coccygeal, and even the first intcrcoccygeal joint,
anchylosed.
-ocr page 433-
INDEX.
-&------
Abdomen, 285.
Abdominal tunic, 288.
Accessory duct of pancreas, 313, 330.
Acervulus cerebri, 251.
Annular cartilage, 164.
Annulus ovalis, 126.
Appendages of eye, 172.
Aqueduct of Sylvius, 252.
Aqueductus vestibuli, 209.
Aqueous humour, 261.
Arachnoid, cranial, 235.
,,         spinal, 137.
Arciform fibres of medulla, 239.
Arteries—
Anastomotic, 170, 191.
Angular, 181.
Anterior abdominal, 292.
,, aorta, 112.
,, auricular, 102, 107.
,, circumflex, 12.
,, deep temporal, 213.
,, dorsal of penis, 281.
,, gastric, 310.
,, lamina!, 42.
,, mesenteric, 304, 322.
,, radial, 26.
tibial, 77.
Asternal, 327.
Axillary, 4,11, 113, 119.
Basilar, 236.
Brachial, 11.
Bronchial, 105.
Broncho-cesophageal, 118.
Buccal, 183, 213.
Cuscal, 305.
Centralis retina;, 211, 264.
Cephalic, 119.
Cerebellar, 237.
Cerebral, 237.
Cerebrospinal, 146, 170, 236.
Ciliary, 211.
Circle of Willis, 238.
Circumflex of coronary cushion, 41.
iliac, 292, 322.
of toe, 42.
Cceliac axis, 315, 322.
Colic, 305.
Arteries—continued.
Common aorta, 112.
carotid, 148, 191.
Coronary, 123.
circle, 29, 41.
Deep humeral, 12.
,, femoral, 59, 61.
Digital of fore limb, 28.
,, hind limb, 79.
Dorsal, 113, 154.
Dorso-cervical, 118.
Dorso-spinal, 96.
Duodenal, 316.
External carotid, 167, 192.
iliac, 322.
pudic, 290.
,, thoracic, 4, 113.
Femoral, 58, 61.
Femoro-popliteal, 61.
Gastric, 316.
Gluteal, 66, 351.
Great meningeal, 188.
Helicina;, 284.
Hepatic, 315, 332.
Hypogastric, 343.
Ileo-cascal, 305.
Iliaco-femoral, 69, 351.
Ilio-lumbar, 351.
Inferior cervical, 4, 113, 152.
,, communicating, 42.
„ dental, 185, 188.
„ labial, 181.
Infraorbital, 213.
Innominata, 118.
Intercostal, 98, 112.
Internal carotid, 191, 237.
„ iliac, 323, 350.
maxillary, 167,187, 212.
pudic, 66, 275, 342, 350.
,, thoracic, 113, 121.
Interosseous of fore-arm, 22, 26.
,,           metacarpal, 29.
-ocr page 434-
366
THE ANATOMY OF THE HOESE.
Arteries—continued.
Ischiatic, 6G, 350.
Lachrymal, 175, 211.
Large metacarpal, 28.
,, metatarsal, 78.
Lateral coccygeal, 350, 302.
,, sacral, 350.
Left gastro-omental, 317.
Lingual, 192, 200.
Lumbar, 99, 321.
Mammary, 290.
Mastoid, 170, 191.
Maxillo-muscular, 167, 182.
Meningeal, 188, 191, 238.
Mental, 185.
Middle coccygeal, 351, 362.
,, sacral, 322.
„ spinal, 140.
Nasal of ophthalmic, 220, 238.
,, submaxillary, 181.
Nutrient of femur, 59.
,,          humerus, 12, 21.
,,          ilium, 351.
,,          metacarpal bone, 30.
,,          metatarsal bone, 79.
,,          radius, 26.
,,          scapula, 17.
,,          tibia, 75.
Obturator, 62, 351.
Occipital, 169, 191.
Occipito-muscular, 170.
Oesophageal, 118.
Of corpus cavernosum, 282.
Of plantar cushion, 29, 41.
Of quadriceps, 59.
Of spermatic cord, 322.
Ophthalmic, 211, 212, 238.
Orbital, 176, 211.
Ovarian, 322.
Pancreatic, 316.
Palato-labial, 180, 201, 213.
Perforating metatarsal, 78.
Perpendicular, 29.
Pharyngeal, 192, 204, 205.
Phrenic, 321.
Plantar of digital, 41.
,, interosseous, 79.
„ of tibial, 74, 78.
Pleuro-cesophagea, 316.
Popliteal, 74.
Posterior abdominal, 292.
aorta, 112, 118, 321.
,, auricular, 163. 167.
,, circumflex, 16.
,, communicating, 237.
,, deep temporal, 188.
,, dorsal of penis, 281.
,, gastric, 316.
„ mesenteric, 306, 322, 344.
,, radial, 22.
tibial, 74.
Prehumeral, 12.
Preplantar, 41.
Prepubic, 293, 323.
Prevertebral, 191.
Arteries—continued.
Profunda, 59, 61.
Pterygoid, 186, 188.
Pulmonary, 105, 111, 127.
Pyloric, 316.
Benal, 319, 322, 334.
Retrograde of occipital, 170, 191.
Right gastro-omental, 316.
Saphenic, 57.
Small metacarpal, 29.
,, metatarsal, 78.
Spermatic, 279, 322.
Spheno-palatine, 188, 213, 220.
Spheno-spinous, 188.
Splenic, 316, 332.
Staphyline, 204, 213.
Subcarpal arch, 29.
Subcostal, 113.
Subcutaneous abdominal, 281, 286.
Submaxillary, 170, 181, 192.
Submental, 171, 193, 198.
Subscapular, 11, 16.
Superior cervical, 113, 154.
„ dental, 213.
„ labial, 181.
Superficial temporal, 167.
Supracarpal arch, 28.
Susrascapular, 11.
Supraorbital, 175, 211.
Thyroid, 148.
Thyro-laryngeal, 148.
Transverse facial, 167, 182.
Tympanic, 188, 269.
Ulnar, 21.
Umbilical, 343.
Uterine, 323.
Vaginal, 343.
Vertebral, 113, 157.
Vesico-prostatic, 342.
Articulations (see joints).
Arytenoid cartilages, 225.
Auricle, left, 128.
right, 125.
Auriculo-ventricular groove, 106.
,,               ,,           opening, left, 129.
right, 126.
Axilla, 4.
Barbs, 196.
Bars of hoof, 36.
Basilar membrane, 271.
Bicuspid valve, 129.
Bile duct, 315, 330, 332.
Bladder, 345, 347.
Bowman's capsule, 334.
,, glands, 219.
,, membrane, 200.
Brachial plexus, 5, 12.
Brain, 233.
Brunner's glands, 308.
Buccal gland, inferior, 184.
,, ,, superior, 183.
Bulb, 238.
-ocr page 435-
INDEX.
Csecum, 296.
Calamus scriptorius, 242.
Canalis reuniens, 270.
Canal of Corti, 272.
„ Petit, 26G.
Carpal sheath, 33.
Cartilages of ear, 164.
,,         foot, 40.
,,         larynx, 224.
,,         nostril, 176.
,,         trachea, 149.
,, tarsal, 175.
Caruncula lachrymalis, 173.
Caruncula; myrtiformes, 358.
Cavity of abdomen, 294.
,, nose, 216.
,, pelvis, 340.
,, pharynx, 20G.
thorax, 100.
„ Winslow, 300.
Central canal of spinal cord, 142.
Cerebellum, 240.
Cerebrum, 242.
Chorda; tendineae, 127, 129.
Choroid coat, 263.
,, plexus of 4th ventricle, 242.
,,              ,, lateral ventricle, 249.
Ciliary processes, 263.
Circle of Willis, 238.
Circumvallate papillae, 196.
Clitoris, 357.
Cochlea, 270.
Colic mesentery, 302.
Collecting tubules, 334.
Colliculus seminalis, 348.
Colon, large, 296.
„ small, 297.
Column* carnese, 126,129.
Columns of cord, 142.
Commissures of cord, 142.
,,             lateral ventricle, 252.
Common ejaculatory ducts, 347.
Conchal cartilage, 164.
Coni vasculosi, 231.
Conjunctiva, 174.
Conus arteriosus, 127.
,, medullaris, 139.
Convoluted tubules, 334.
Convolutions of cerebrum, 245.
Cornea, 259.
Cornicula laryngis, 226.
Corona glandis, 286.
Coronary cushion, 38.
Corpora cavernosa, 282.
,, geniculata, 252.
,, nigra, 262.
,. quadrigemina, 252.
Corpus albicans, 243.
,, Arantii, 127.
,, callosum, 248.
,, dentatum, 241.
„ Highmori, 279.
,, luteum, 354.
,, spongiosum, 282.
Cowper's glands, 346.
Cricoid cartilage, 225.
Crico-thyroid membrane, 226.
Crista acoustica, 270.
Crura of cerebrum, 242,
Crura of diaphragm, 327.
,, penis, 282.
Crusta, 242.
Cuticular ridge, 329.
Cutigeral groove, 36.
Dartos, 278.
Decussation of pyramids, 239.
Descemet's membrane, 260.
Diaphragm, 327.
Duct of Winning, 313, 330.
Ducts of Rivinius, 197.
Ductus ad nasum, 174, 177, 218.
,, cochlearis, 272.
,, vestibuli, 270.
Duodenum, 298, 312.
Dura mater, cranial, 233.
,, ,, spinal, 137.
Ear, external, 159.
,, internal, 269.
„ middle, 267.
Encephalon, 233.
Endocardium, 125.
Epicardium, 106.
Epididymis, 279.
Epiglottis, 226.
Epigastric region, 294.
Epiploon, 300, 312.
Eustachian tubes, 187, 206.
„         valve, 126.
External abdominal ring, 289.
Eyeball, 257.
Eyelids, 172.
Fallopian tubes, 354.
Falx cerebri, 234.
Fascia—
Coccygeal, 360.
Cremasteric, 278.
Gluteal, 64.
Iliac, 325.
Infundibuliform, 278.
Lata, 64.
Of fore-arm, 21.
Of thigh, 57.
Perineal, 275.
Scapular, 17.
Spermatic, 278.
Fenestra ovalis, 267.
,, rotunda, 267.
Filiform papilhe, 196.
Fimbriae of Fallopian tubes, 354.
Fissures of spinal cord, 141.
cerebrum, 243, 245, 246.
liver, 314.
Folia of cerebellum, 241.
Foot, 35.
Foramen dextrum, 328.
,, of Monro, 252.
of Window, 301.
,, ovale, 126.
,, sinistrum, 328.
-ocr page 436-
368
OF THE HOUSE.
THE ANATOMY
Inferior pyramid, 239.
Intestines, 295.
Internal abdominal ring, 293.
Interarticular cartilages of stifle-joint. 85.
„               ,,               jaw, 216.
Interpeduncular space, 242.
Intervertebral substance, 136, 159.
Iris, 261.
Isthmus of fauces, 202.
Jacobson's organ, 219.
Jejunum, 298.
Joints—
Atlanto-axial, 215.
Easi-cornual, 207.
Carpus, 46.
Chondro-costal, 134.
Chondro-sternal, 134.
Costo-central, 132.
Costo-transverse, 133.
Crico-thyroid, 226.
Crico-arytenoid, 226.
Elbow, 44.
Femoro-patellar, 82.
Femoro-tibial, 83.
Fetlock, 50.
Hip, 338.
Hock, 86.
Intercoccygeal, 363.
Intercornual, 207.
Intermetacarpal, 50.
Intervertebral, 134.
Knee, 46.
Occipito-atlantal, 214.
Pastern, 52.
Eadio-ulnar, 45.
Sacro-coccygeal, 363.
Sacro-iliac, 363.
Shoulder, 43.
Stifle, 81.
Tarsus, 86.
Temporo-hyoideal, 207.
Temporo-maxillary, 215.
Thyro-epiglottic, 227.
Tibio-fibular, 85.
Kidneys, 318, 333.
Labia vulva?, 356.
Labial glands, 180.
Labyrinth, 269.
Lachrymal canals, 174.
duct, 174, 177, 218
gland, 173, 208.
,, puncta, 174.
,,         sac, 174.
Lacteals, 306.
Foramina Thebesii, 125.
Fornix, 250.
Fossa ovalis, 126.
Fovea hemielliptica, 26!).
„ hemispherica, 269.
Frcenum lingufe, 196;
Frog, 37.
Fungiform papillae, 196.
Galactopherous sinuses, 286.
Ganglia—
Andersch's, 255.
Ciliary, 212.
Gasserian, 254.
Geniculate, 255.
Inferior cervical, 110, 117.
Middle ,, 109, 117.
Superior ,, 195.
Of roots of spinal nerves, 140.
,, root of vagus, 255.
„ trunk of ,, 194.
Otic, 189.
Petrous, 255.
Semilunar, 318.
Spheno-palatine, 214.
Gastric glands, 329.
Gastro-colic omentum, 300, 312.
Gastro-hepatic ,, 312.
Gastro-splenic ,, 301, 312.
Gland of Harder, 173.
Glands of Bowman, 219.
Glans penis, 283.
Glisson's capsule, 331.
Globus major, 279.
,, minor, 279.
Glomerulus, 334.
Graafian follicles, 352.
Great mesentery, 302.
„ omentum, 300, 312.
,, sesamoid sheath, 34.
,, transverse fissure of cerebrum, 257.
Guttural pouches, 187.
Gyrus fornicatus, 247.
Hard palate, 200.
Harderian gland, 173.
Heart, 106, 123.
Henle's tubes, 334.
Hiatus aorticus, 328.
Hippocampus, 250.
Hoof, 35.
Horny laminae, 36.
Hyaloid membrane, 266.
Hymen, 358.
Hypochondriac regions, 294.
Hypogastric regions, 294.
Ileo-csecal valve, 311.
Ileum, 298.
Iliac region, 294.
Incus, 268.
Inguinal canal, 290.
-ocr page 437-
INDEX.                                                              369
Ligaments—continued.
Interosseous tibio-fibular, 86.
Intersesamoid, 51.
Interspinous, 135, 159.
Intervertebral substance, 136, 159.
Lateral of bladder, 342.
,, elbow, 44, 45.
,,    femoro-patellar, 82.
,,    femoro-tibial, 83.
,, of fetlock, 51.
,, of knee, 46, 48.
,,         of liver, 314.
,, of pastern, 52.
,,    sesamoidean, 51.
,,    tibio-tarsal, 86.
Nuchas, 158.
Occipito-atlantal, 214.
Patellar, 82.
Posterior calcaneo-astragaloid, 89.
,, common of knee, 48.
,, femoro-tibial, 84.
,, temporo-maxillary, 215.
,, tibio-tarsal, 88.
Postero-lateral of coffin-joint, 53.
Pubio-femoral, 339.
Eadio-carpal, 48.
Round, 339.
Sacro-iliac, 363.
Sacro-sciatic, 339.
Scaphoido-cunean, 90.
Splenic, 313.
Stellate, 132.
Straight patellar, 82.
Styloid, 214.
Subcarpal, 35, 48.
Subflava, 135, 159.
Subtarsal, 81, 89.
Superior atlanto-axial, 215.
,, common, 135, 159.
,, ilio-sacral, 340.
,, sesamoidean, 50.
Supraspinous, 135.
Suspensory of liver, 314.
penis, 282.
,,           prepuce, 281.
,,           rectum, 276, 344.
Tarso-metatarsal, 89.
Thyro-arytenoid, 227.
Tibio-tarsal, 86.
Uterine broad, 303.
Linea alba, 289.
Lingual fibrous cord, 197.
,, glands, 197.
Liver, 313, 330.
Locus cajruleus, 240.
„ niger, 243.
,, perforatus anticus, 243.
,,           ,, posticus, 243.
Lumbar region, 294.
Lungs, 103, 122.
Lunula, 127.
2 B
Lamina cinerea, 243.
,, cribrosa, 259.
Large intestine, 295, 309.
Larynx, 224.
Lateral cartilages of foot, 40.
Lens, 265.
Lieberkiihn's glands, 308, 310.
Ligaments—
Anterior calcaneo-astragaloid, 89.
,, common of knee, 48.
,, cuboido-cunean, 90.
,, cuboido-scaphoid, 89.
,, of elbow, 45.
of fetlock, 51.
,, tibio-tarsal, 88.
Antero-lateral of coffin-joint, 53.
Arciform, 45.
Arcuate, 328.
Astragalo-metatarsal, 88.
Atlanto-axial, 215.
Broad of lung, 102.
,, uterus, 303.
Calcaneo-metatarsal, 89.
,, -astragaloid, 89.
Capsular, crico-arytenoid, 227.
,, crico-tliyroid, 227.
,, chondro-sternal, 134.
hip, 339.
,, femoro-patellar, 82.
,, intertransverse lumbar, 135.
,, intervertebral, 135, 159.
,, temporo-maxillary, 215.
Carpo-metacarpal, 49.
Chondro-xiphoid, 134.
Coronary of liver, 315.
Costo-transverse, 133.
Costo-vertebral, 132.
Cotyloid, 339.
Crucial of stifle, 84.
Cruciform, 214.
Denticulated, 138.
External temporo-maxillary, 215.
Falciform of liver, 315.
Gastro-phrenic, 312.
Hepatic, 314.
Inferior atlanto-axial, 215.
,, of bladder, 342.
,, common, 135.
,, ilio-sacral, 340.
„ sesamoidean, 51.
Interannular, 215.
Interarticular, 133.
Intercarpal, 48.
Intercunean, 90.
Interosseous calcaneo-astragaloid, 89.
,,          costo-transverse, 133.
,,          cuboido-cunean, 90.
,,          cuboido-scaphoid, 90.
,,          of coffin-joint, 53.
,,          radio-ulnar, 45.
,,         tarso-metatarsal, 90.
-ocr page 438-
370                                     THE ANATOMY OF THE HORSE.
Muscles —continued.
Caput medium, 18.
,, parvum, 15.
Cerato-hyoid, 205.
Cervico-auriculares, 160.
Ciliary, 262.
Complexus, 154.
Compressor coccygis, 343.
Constrictors of vulva, 356.
Coraco-humeralis, 15.
Corrugator supercilii, 175.
Cremaster, 278, 294.
Crico-arytenoideus lateralis, 229.
Crico-arytenoideus posticus, 229.
Crico-pharyngeus, 205.
Crico-thyroideus, 228.
Crureus, 62.
Curvator coccygis, 361.
Deep flexor of digit (fore limb),
24, 34, 42.
Deep flexor of digit (hind limb),
73, 81.
Deep gluteus, 67.
Deltoid, 17.
Depressor iabii inferioris, 179.
„ labii superioris, 180.
,,         coccygis, 361.
Diaphragm, 327.
Digastricus, 166, 171, 190.
Dilatator naris inferior, 179.
,, naris lateralis, 178.
,, naris superior, 178.
,, naris transversalis, 178.
„ pupillse, 262.
Erector clitoridis, 357.
,, coccygis, 361.
,, penis, 277.
Extensor metacarpi magnus, 24.
„               ,, obliquus, 25.
,, pedis (fore limb), 25, 32.
,,           ,, (hind limb), 75, 80.
,, suffraginis, 25, 32.
External intercostal, 98.
,, pterygoid, 185.
Flexor accessorius, 73.
,, metacarpi extermis, 23.
,,             ,, intern us, 23.
,,             ,,         inedius, 23.
,, metatarsi, 70.
,, pedis perforans (fore limb),
24,34.
Flexor pedis perforans (hind limb),
73, 81.
Flexor pedis perforatus (fore limb),
23, 34.
Flexor pedis perforatus (hind limb),
72, 81.
Gastrocnemius, 71.
Gemelli, 68.
Genio-glossus, 200.
Genio-hyoideus, 200.
Gracilis, 58.
Great hyo-glossus, 199.
Hyo-epiglottideus, 228.
Lymphatics—
Brachial, 11.
Bronchial, 115.
Cardiac, 115.
Iliac, 321.
Inguinal, deep, 57.
„ superficial, 287.
Intestinal, 306.
Lumbar, 321.
(Esophageal, 115.
Of liver, 315.
Of spleen, 315.
Of stomach, 315.
Pharyngeal, 191.
Popliteal, 61.
Precrural, 57.
Prepectoral, 115, 149.
Prescapular, 152.
Sacral, 321.
Submaxillary, 170.
Suprasternal, 122.
Thoracic, 115.
Tracheal, 115.
Malleus, 268.
Mammary glands, 285.
Malpighian bodies of kidney, 334.
,, spleen, 333.
Meatuses of nose, 216.
Meatus urinarius, 358.
Mediastinum of thorax, 102.
,,          testis, 279.
Medulla oblongata, 238.
Membrana nictitans, 173.
,,         pupillaris, 262.
,,         reticularis, 272.
,,          tectoria, 272.
,,         tympani, 267.
Membranes of brain, 233.
„            spinal cord, 137.
Mesentery, 302.
Meso-rectum, 342.
Mitral valve, 129.
Moderator bands, 126.
Modiolus, 270.
Movements of joints, 43.
Muscles—
Adductor magnus, 60.
„ parvus, 00.
Accelerator urinse, 277-
Anconeus, 18.
Anterior deep pectoral, 3.
,, superficial pectoral, 2.
Arytenoideus, 230.
Aryteno-pharyngeus, 205.
Azygos uvulae, 204.
Biceps, 15.
Biceps femoris, 04.
Brachialis anticus, 18.
Buccinator, 179.
Caput magnum, 15.
-ocr page 439-
371
INDEX.
Muscles—continued.
Rectus capitis anticus minor, 208.
,,          „ lateralis, 208.
,,          „ posticus major, 169.
,,          ,, posticus minor, 169.
,, femoris, 69.
,, parvus, G9.
Retractor ani, 276.
,, costas, 96.
„ oculi, 209.
,, penis, 276.
Rhomboideus, 10.
Sartorius, 57.
Scalenus, 156.
Scapulo-humeralis gracilis, 16.
Scapulo-ulnaris, 14.
Scuto-auricularis externus, 162.
,,           ,, internus, 162.
Semimembranosus, 60.
Semispinalis of back and loins, 97.
,,           colli, 155.
Semitendinosus, 65.
Serratus anticus, 95.
,, magnus, 7, 95.
,, posticus, 95.
Short extensor of foot, 80.
Small hyo-glossus, 199.
,, stylo-pharyngeus, 205.
Soleus, 71.
Sphincter ani, 276.
,, pupillie, 262.
Splenius, 153.
Stapedius, 268.
Sterno-maxillaris, 145, 166.
Sterno-thyro-hyoideus, 146.
Stylo-glossus, 198.
Stylo-hyoideus, 166, 190.
Stylo-maxillaris, 166.
Stylo-pharyngeus, 205.
Subscapularis, 15.
Subscapulo-hyoideus, 146.
Superficial flexor of digit (fore limb),
23, 34.
Superficial flexor of digit (hind limb),
72, 81.
Superficial gluteus, 64.
Superior oblique of eye, 210.
Supraspinatus, 17.
Temporalis, 185.
Tensor palati, 203.
,, tympani, 268.
,, vagime femoris, 64.
Teres major, 14.
,, minor, 17.
Thyro-arytenoid, 229.
Thyro-hyoid, 228.
Thyro-pharyngeus, 205.
Trachelo-mastoid, 153.
Transversalis abdominis, 293.
,,           costarum, 96.
Transversus perimei, 276.
Trapezius, 9.
Triangularis sterni, 120.
Triceps extensor cubiti, 15.
"Vastus externus, 69.
,, internus, 62.
Muscles—continued.
Hyoideus transversus, 199.
Hyo-pharyngeus, 205.
Iliacus, 63, 326.
Inferior oblique of eye, 210.
Infraspinatus, 17.
Internal intercostal, 98.
,, pterygoid, 185.
Interossei, 32, 80.
Intertransversales of loins, 326.
,,               ,,          neck, 155.
Ischio-urethral, 346.
Lateralis sterni, 97.
Latissimus dorsi, 9, 14, 94.
Levator anguli scapulae, 8.
Levatores costarum, 97.
Levator labii superioris alaeque nasi,
177.
Levator labii superioris proprius,
178.
Levator menti, 180.
palati, 204.
,, palpebral superioris, 175.
Longissimus dorsi, 96.
Longus colli, 156.
Lumbricales, 31, 80.
Masseter, 180.
Mastoido-auricularis, 162.
Mastoido-lmmeralis, 10, 152, 166.
Middle gluteus, 65.
,, hyo-glossus, 199.
Mylo-hyoideus, 171, 198.
Obliquus abdominis externus, 289.
,,              ,,          internus, 291.
,, capitis inferior, 169.
,,           ,, superior, 169.
Obturator externus, 61.
,,         internus, 67.
Occipito-styloid, 166.
Orbicularis oris, 179.
,,         palpebrarum, 175.
Palato-glossus, 199.
Palato-pharyngeus, 203.
Panniculus, 8, 94, 144, 170, 177,
287.
Parieto-auricularis externus, 160.
,,            ,,         internus, 162.
Parotido-auricularis, 160.
Pectineus, 60.
Peroneus, 75, 81.
Popliteus, 72.
Posterior deep pectoral, 3.
Posterior superficial pectoral, 2.
Psoas magnus, 63, 325.
„ parvus, 326.
Pterygo-pharyngeus, 205.
Pyriformis, 67.
Quadratus femoris, 61.
,,         lumborum, 326.
Recti oculi, 209.
Rectus abdominis, 292.
,, capitis anticus major, 155.
-ocr page 440-
372                              THE ANATOMY OF THE HORSE.
Muscles—continued.
Wilson's muscle, 346.
Zygomatico-auricularis, 161.
Zygomaticus, 179.
Musculi papillares, 127, 129.
,, pectinati, 125, 128.
Nares, inferior, 176, 218.
,, superior, 206, 218.
Nates, 252.
Navicular sheath, 42.
Nerves—
Abducent, 212, 254.
Anterior auricular, 163.
,, crural, 59, 325, 349.
,, tibial, 77.
Auditory, 255, 272.
Auricular of 1st cervical, 164.
2nd „ 164.
7th cranial, 163, 168.
10th „ 255.
,,         lachrymal, 164.
Brachial plexus, 5, 12, 109.
Buccal, 184, 189.
Cardiac, 110, 117, 124.
Cervical of 7th cranial, 144, 163, 168.
„ spinal, 152, 154, 169, 195.
Chorda tympani, 189, 269.
Ciliary, 212, 203.
Circumflex, 13.
Coccygeal, 362.
Cranial, 253.
Cremasteric, 324.
Cutaneous of chest-wall and back, 94.
,,          fore-arm, 20.
,,          hip and thigh, 63.
,,          intermaxillary space,170.
leg, 70.
,,          metatarsus, 78.
,,          neck, 143, 151.
,,          pectoral region, 1.
,,          perinseum, 275.
,,          prepuce, 281.
,,          thigh, 57.
Digital, 31.
Dorsal of penis, 281.
,, spinal, 96, 99
Eighth cranial, 255, 272.
Eleventh cranial, 140, 146, 151, 194,
255.
External laryngeal, 194.
„ popliteal, 62, 67, 74, 76.
,, saphenous, 62, 67, 74.
Facial, 168, 176, 182, 254.
Fifth cranial, 254.
First cranial, 219, 253.
Fourth cranial, 212, 254.
Glosso-pharyngeal, 193, 200, 206, 255.
Gluteal, 66, 349.
Great sciatic, 62, 67, 349.
Gustatory, 186, 198.
Nekves—continued.
Hemorrhoidal, 275, 343.
Hypoglossal, 193, 198, 256.
Iliaco-muscular, 349.
Inferior dental, 186, 189.
laryngeal, left, 109, 149, 230.
right, 116, 149, 230.
,, maxillary, 188, 254.
Infra-orbital, 183.
Inguinal, 281, 291, 324.
Intercostal, 99, 292.
Internal popliteal, 73.
,, saphenous, 57, 325.
Jacobson's, 193, 255.
Lachrymal, 211.
Large superficial petrosal, 214.
Lingual, 186, 189.
Lumbar, 96, 99, 292, 324.
Lumbo-sacral plexus, 324, 349.
Median, 14, 22.
Mental, 186.
Middle auricular, 103.
Musculocutaneous of median, 14.
,,          ,,          popliteal, 76.
Musculo-spiral, 13, 26.
Motor oculi, 176, 212, 254.
Mylo-hyoid, 172, 186, 189.
Nasal, 220.
Ninth cranial, 193, 200, 206, 255.
Obturator, 62, 349.
Oesophageal, 317.
Olfactory, 219, 253.
Ophthalmic, 211, 254.
Optic, 253.
Orbital of superior maxillary, 176, 211.
Palatine, 202, 213.
Palpebro-nasal, 176, 211.
Pathetic, 212, 254.
Perforating, 288.
Peroneal cutaneous, 67.
Pharyngeal, of 9th, 193, 206.
of 10th, 194.
,,            of sympathetic, 195.
Phrenic, 6, 108, 116.
Plantar, of fore limb, 30.
of hind limb, 80.
Pneumogastric, 108, 116, 194, 255.
Posterior auricular, 163.
tibial, 74.
Portio dura, 168, 176, 182, 254.
,, intermedia, 254.
,, mollis, 255, 272.
Pudic, 275, 343.
Pulmonary, 109.
Kecurrent laryngeal, 109,116,149, 230.
Sacral, 349.
Sacral, 363.
Second cranial, 253.
Seventh cranial, 168, 176, 182, 254.
Sixth cranial, 212, 254.
-ocr page 441-
INDEX.                                                              373
Pedunculated hydatid of morgagni, 279.
Penis, 281.
Pericardium, 105.
Perilymph, 270.
Perinseum, 274.
Periople, 36.
Perioplic ring, 38.
Peritoneum, 298.
,,           pockets of, 303.
Pes anserinus, 182.
Peyer's patches, 309.
Pharynx, 204.
Pia mater, cranial, 236.
,,          spinal, 138.
Pillars of soft palate, 202.
Pineal gland, 251.
Pituitary gland, 243.
,, membrane, 219.
Plantar cushion, 38.
Pleura, 101.
Plexuses of Nerves—
Anterior mesenteric, 307-
Aortic, 325.
Carotid, 238.
Cavernous, 238.
Cceliac, 318.
Pelvic, 344.
Posterior mesenteric, 307.
Renal, 320.
Solar, 318.
Spermatic, 325.
Suprarenal, 318.
Pomum Adami, 225.
Pons Tarini, 243.
„ Varolii, 240.
Portal fissure, 314.
Poupart's ligament, 289.
Prepuce, 280.
Prostate, 346.
Puncta lachrymalia, 174.
Pupil, 261.
Pylorus, 311.
Pyramidal body, 40.
Pyramids of Ferrein, 334.
medulla, 239.
Quadrilateral space, 244.
Receptaculum chyli, 324.
Rectum, 297, 344.
Reissner's membrane, 271.
Renal crest, 334.
Rete testis, 280.
Retina, 264.
Right lymphatic duct, 119.
Rivinius, ducts of, 197.
Root of lung, 105.
Roots of cranial nerves, 253.
,, spinal nerves, 140.
Rostrum, 248.
Saccule, 270.
Scala intermedia, 272.
,, tympani, 271.
,, vestibuli, 272.
Nerves—continued.
Small superficial petrosal, 189.
Sphenopalatine, 214, 220.
Spinal, 138.
accessory, 140, 146, 151, 194,
255.
Splanchnic, 111, 318.
Staphyline, 204, 214.
Subcutaneous thoracic, 7, 288.
Subzygomatic, 108, 183, 188.
Superior dental, 2i3.
laryngeal, 194, 230.
maxillary, 213, 254.
Supra-orbital, 176, 211.
Suprascapular, 13.
Sympathetic cord, cervical, 149, 195.
dorsal, 111, 118. .
,,            ,,         lumbar, 325.
,,           ,, sacral, 350.
Tenth cranial, 108, 116, 194, 255.
Third cranial, 176, 212, 254.
Trifacial or trigeminal, 254.
Trochlear, 212, 254.
Twelfth, 193, 198, 256
Ulnar, 13, 21.
Vagus, 108, 116, 194, 255.
Vertebral, 157.
Vidian, 214.
Nipple, 285.
Nodulus Arantii, 127.
Nostrils, 176.
(Esophagus, 115, 150.
Olfactory bulbs, 244.
cells, 219.
Olivary body, 239.
Omentum, gastro-hepatic, 312.
,,          gastro-splenic, 301, 312.
great, 300, 312.
Optic thalami, 251.
„ tracts, % 13, 252.
Orbicular process, 268.
Organ of Oorti, 272.
,, Jacobson, 219.
,, Rosenmuller, 354.
Osseous spiral lamina, 271.
Os uteri, 359.
Otic ganglion, 189.
Otoliths, 270.
Ovaries, 351.
Oviducts, 354.
Ovula Nabothi, 360.
Ovum, 352.
Pacchionian bodies, 234.
Palate, hard, 200.
,, soft, 202.
Palpebral tendon, 175.
Papilla? of tongue, 196.
Papilla optica, 264.
Pancreas, 313, 333.
Parotid gland, 164.
Parovarium 354.
Pelvis, 338.
Peduncles of cerebellum, 241.
,,          pineal gland, 251.
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374
THE ANATOMY OP THE HOESE.
Tubercle of Lower, 125.
Tubuli recti, 280.
Tunica albuginea, 279, 283.
,, Kuyschiana, 263.
,, vaginalis, 278, 279.
,, vasculosa, 280.
Tympanum, 267.
Udder, 285.
Umbilical region, 294.
Ureters, 320, 345.
Urethra, female, 358.
male, 282, 345, 347.
Urethral sinus, 283.
„ tube, 283.
Urinary bladder, 345, 347.
Uriniferous tubules, 334.
Uterus, 355, 359.
,, masculinus, 346.
Utricle, 270.
Utricular glands, 360.
Uvea, 262.
Vagina, 356, 358.
Valves—
Auriculo-ventricular, left, 129.
right, 127.
Bicuspid, 129.
Eustachian, 126.
Mitral, 129.
Of meatus urinarius, 358.
Of Thebesius, 125.
Of Vieussens, 242.
Semilunar aortic, 129.
,,         pulmonary, 127.
Tricuspid, 127.
Vasa deferentia, 279, 346.
,, efferentia, 280.
,, vorticosa, 263.
Veins—
Alveolar, 183, 213.
Angular, 181.
Anterior auricular, 163.
,, gastric, 317.
,, mesenteric, 306, 317.
,, subcutaneous of fore-arm, 20.
,, tibial, 77.
,, vena cava, 114, 119.
Asternal, 327.
Axillary, 5.
Azygos, great, 119.
,, small, 114.
Brachial, 12.
Bronchial, 105.
Buccal, 183.
Cephalic, 2, 145.
Circumflex iliac, 292.
Common iliac, 323.
Cordis minirme, 125.
Coronary of heart, 124.
Sehneiderean membrane, 243.
Sclerotic, 259.
Scrotum, 277.
Scutif orm cartilage, 164.
Semicircular canals, 270.
Semilunar cartilages of stifle, 85.
Seminal tubules, 280.
Sensitive frog, 38.
,, laminpe, 38.
,, sole, 40.
Septum lucidum, 249.
,, nasi, 217.
,, pectiniforme, 283.
,, scroti, 278.
Sheath, 280.
Sinuses of dura mater, 234.
head, 219.
,, larynx, 231.
valsalva, 128, 129.
Sinus, subsphenoidal, 207.
,, venosus, 107.
Small intestines, 295, 308.
,, sesamoid sheath, 42.
Soft palate, 202.
Sole of hoof, 36.
Solitary glands, 308.
Spermatic cord, 278, 294.
Spermatoblasts, 280.
Spinal cord, 136.
,, nerves, 139.
Spleen, 312, 332.
Splenium, 248.
Stapes, 268.
Staphyline glands, 203.
Stenson's duct, 165, 171, 182, 184.
,, canal, 219.
Stomach, 311, 328.
Strije longitudinales, 249.
Subarachnoid space, 138, 235.
Subdural space, 137, 235.
Sublingual gland, 197.
,,          ridge, 196.
Submaxillary gland, 190.
Subsphenoidal sinus, 207.
Suburethral notch, 283.
Suprarenal capsules, 320.
Tail, 361.
Taenia hippocampi, 250.
Tapetum lucidum, 263.
Teat, 285.
Tegmentum, 242.
Tentorium cerebelli, 234.
Testes, 252.
Testicle, 279.
Thoracic cavity, 100.
„ duct, 114.
Thymus gland, 115.
Thyroid body, 147.
,, cartilage, 225.
Tongue, 195.
Tonsil, 202.
Torcular Herophili, 235.
Trabecular carnese, 126.
of spleen, 332.
Trachea, 115, 149.
Trapezium, 239.
Tricuspid valve, 127.
Tuber cinereum, 243.
-ocr page 443-
375
INDEX.
VEINS—continued.
Coronary plexus, 42.
Digital, of fore limb, 30.
,, liind limb, 79.
Dorsal, 114, 119, 155.
Externarjiliac, 323.
„ pudic, 291.
Femoral, 59, 61.
Gastric, 317.
Gastro-omental, 317.
Great vena azygos, 119.
Hsemorrhoidal, 344.
Hepatic, 323, 332.
Inferior dental, 186.
Intercostal, 99, 119.
Internal iliac, 323, 351.
maxillary, 168, 186, 188.
pudic, 270, 343.
,, subcutaneous of fore-arm, 20.
,, saphena, 57, 70.
thoracic, 114, 119, 122.
Jugular, 144, 167.
Laminal plexus, 42.
Lateral coccygeal, 362.
Lingual, 186, 198.
Lumbar, 99, 119, 323.
Maxillo-muscular, 168, 182.
Median, 20.
Metacarpal, 30.
Metatarsal, 79.
Middle coccygeal, 362.
Obturator, 62.
Occipital, 170, 193.
Of Galen, 251.
Ophthalmic, 211, 213.
Palatine, 202, 213.
Phrenic, 323.
Popliteal, 75.
Portal, 317, 331.
Veins—continued.
Posterior abdominal, 292.
,,         auricular, 163, 168.
,, gastric, 317.
mesenteric, 306, 317, 344.
,, radial, 22.
,, tibial, 75.
,,         vena cava, 119, 323.
Pterygoid, 186.
Pulmonary, 105.
Kenal, 320.
Small vena azygos, 114.
Solar plexus of foot, 42.
Spermatic, 279, 323.
Spinal, 141.
Spheno-palatine, 213, 220.
Splenic, 317.
Spur, 287.
Staphyline, 204.
Subcutaneous abdominal, 287.
,,           thoracic, 287.
Vasa vorticosa, 263.
Velum interpositum, 251.
,, pendulum palati, 202.
Ventricle of brain, fourth, 241.
„            „          lateral, 249.
third, 252.
Ventricle of heart, left, 128.
right, 126.
Ventricles of larynx, 231.
Ventricular grooves, 106.
Vermiform lobe, 240.
Verumontanum, 348.
Vesiculse seminales, 346, 348.
Vesicula prostatica, 346.
Vestibular bulb, 357.
Vestibule of ear, 269.
Villi of intestine, 308.
Vitreous humour, 266.
Vocal cord, 227.
Vulva, 356, 357.
Wall of hoof, 36.
Wharton's duct, 190, 197.
Wirsung's duct, 313.
Zonula of Zinn, 265.