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THE ANATOMY

OF THE

DOMESTIC ANIMALS

SEPTIMUS SISSON, S.B., V.S.

PROFESSOR OF COMPARATIVE ANATOMY IN THE OHIO STATE UNIVERSITY, COLUMBUS, OHIO

MEMBER OF THE AMERICAN ASSOCIATION OF ANATOMISTS

FELLOW OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE

WITH 725 ILLUSTRATIONS
MANY IN COLORS

SECOND EDITION, ENTIRELY RESET

PHILADELPHIA AND LONDON

W. B. SAUNDERS COMPANY

Reprinted June, 1911

Revised, Entirely Reset, Reprinted

AND ReCOPYRIGHTED SEPTEMBER, 1914

Reprinted September, 1917

Reprinted March, 1921

Reprinted October, 1927

Reprinted September, 1930

PRESS OF

W. B. SAUNDERS COMPANY

PHILADELPHIA

TO
MY WIFE

KATHERINE OLDHAM SISSON

IN GRATEFUL RECOGNITION OF CONSTANT INSPIRATION
AND ENCOURAGEMENT

PREFACE

This book supersedes the author's Text-book of Veterinary Anatomy. A
comparison of the two will show the new title to be justified by the extent and
character of the changes which have been made.

The number of illustrations has been increased from 588 to 725. More than
three hundred new and original figures have been prepared. Nearly all of these
are reproductions of photographs, most of which were taken by the author. The
preparation of the prints for reproduction has been executed by Mr. W. J. Norris
with unusual care and skill.

Continued observations of well-hardened material and frozen sections have led
to a considerable number of modifications of statement. It is scarcely necessary
to say that the recent literature, so far as available, has been utilized.

Many changes in nomenclature have been made. Most of the synonyms have
been dropped or relegated to foot-notes. Exceedingly few new names have been
introduced. Nearly all eponyms have been eliminated, on the ground that they
are not designative and are usually incorrect historically. The changes made in
this respect are in conformity with the report of the Committee on Revision of
Anatomical Nomenclature which was adopted by the American Veterinary Med-
ical Association two years ago. Progress in the direction of a simplified and uni-
form nomenclature is much impeded by the archaic terminology which persists to
a large extent in clinical literature and instruction.

The author is under special obligation to Professors EUenberger, Baum, and
Schmaltz, and to their publishers, for permission to use or to copy figures from
their excellent works. Their generosity in this matter has been of great value to
those who are unable to use the German literature. A few illustrations have been
taken from other sources and credit has been given in each case.

For helpful suggestions and for assistance in the reading of the proof-sheets
the author is much indebted to his colleague, Dr. F. A. Lambert.

Great credit is due the publishers for their determination to spare neither
pains nor expense in attaining a high degree of typographical excellence.

Septimus Sisson
The Ohio State University, Columbus, Ohio.

PREFACE TO THE FIRST EDITION

The lack of a modern and well-illustrated book on the structure of the princi-
pal domestic animals has been acutely felt for a long time by teachers, students,
and practitioners of veterinary medicine. The work here offered is the expression
of a desire to close this gap in our literature.

The study of frozen sections and of material which has been hardened by intra-
vascular injection of formalin has profoundly modified our views concerning the
natural shape of many of the viscera and has rendered possible much greater pre-
cision in topographic statements. The experience of the author during the last
ten years, in which almost all of the material used for dissection and for frozen
sections in the anatomical laboratory of this University has been hardened with
formalin, has demonstrated that many of the current descriptions of the organs in
animals contain the same sort of errors as those which prevailed in regard to similar
structures in man previous to the adoption of modern methods of preparation.

While the method of treatment of the subject is essentially systematic, topog-
raphy is not by any means neglected either in text or illustrations; it is hoped that
this will render the book of value to the student in his chnical courses and to
the practitioner. Embryological and histological data have been almost entirely
excluded, since it was desired to offer a text-book of convenient size for the student
and a work of ready reference for the practitioner. It is believed that the use of
black type for the names of important structures and of small print for certain
details or matter of secondary importance will prove useful in this respect.

Veterinary anatomical nomenclature is at present quite chaotic in EngUsh-
speaking countries. In this work an attempt is made to eliminate some terms
which do not appear to the author to fulfil any useful purpose, and others which are
clearly erroneous or otherwise undesirable. In many cases the terms agreed upon
by the Congresses at Baden and Stuttgart are adopted either in the original Latin
or in anglicized form; otherwise these terms are added in parenthesis. The
author favors the substantial adoption of this terminology, but considered it
desirable to offer a sort of transitional stage at present.

The original illustrations are chiefly reproductions of photographs, many of
which were taken by Mr. F. H. Haskett. The preparation of the pictures for
reproduction was carried out by Messrs. J. V. Alteneder and W. J. Norris. The
author takes pleasure in expressing his appreciation of the care and skill exercised
by these gentlemen in this often difficult task.

The author is under great obligation to Professors Ellenberger and Baum in
Dresden, to Professor Schmaltz in Berlin, and to their pubUshers for permission to
use or to copy figures from their most excellent works. Their generosity in this
matter has made it possible to supply this text with a larger number of high-class
illustrations than is to be found in any other. A few figures have been taken from
other sources, and proper credit has been given in each case.

For checking over certain data and for assistance in the correction of the proofs
the author is much indebted to his associate, Dr. F. B. Hadley.

The author desires to express his high appreciation of the determination and
constant effort of the publishers to do all in their power to render the book worthy
of favorable reception by the profession for whom it is intended.

Ohio State University, Columbus, Ohio Septimus Sisson.

CONTENTS

INTRODUCTION

OSTEOLOGY p^ob

The Skeleton 20

Structure of Bones 21

Development and Growth of Bone 23

Composition and Physical Properties of Bone 24

Descriptive Terms 25

The Vertebral Column 25

The Ribs and Costal Cartilages 27

Costal Cartilages 27

The Sterjium 28

The Thorax 28

The Skull 28

Bones of the Thoracic Limb 29

Bones of the Pelvic Limb 30

Skeleton of the Horse 32

Vertebral Column 33

Ribs 45

Sternum 48

Bones of the Skull 49

Cranium 49

Face 63

The Skull as a Whole 73

The Cranial Cavity 81

The Nasal Cavity 82

The Paranasal Sinuses 84

Bones of the Thoracic Limb 86

Bones of the Pelvic Limb 105

Skeleton of the Ox 125

Vertebral Column 125

Ribs 130

Sternum 131

Bones of the Skull 131

The Skull as a Whole 140

Bones of the Thoracic Limb 145

Bones of the Pelvic Limb 151

Skeleton of the Sheep 156

Vertebral Column 156

Ribs 156

Sternum 157

Skull 157

Bones of the Thoracic Limb 160

Bones of the Pelvic Limb 160

Skeleton of the Pig 161

Vertebral Column 161

Ribs 165

Sternum 166

Bones of the Skull 166

The Skull as a Whole 173

12 CONTENTS

PAGE

Bones of the Thoracic Limb 176

Bones of the Pelvic Limb 180

Skeleton of the Dog 184

Vertebral Column 184

Ribs 188

Sternum 188

Bones of the Skull 188

The Skull as a Whole 195

Bones of the Thoracic Limb 197

Bones of the Pelvic Limb 202

ARTHROLOGY
Synarthroses 207

DiARTHROSES 208

Amphiarthroses 210

Articulations of the Horse 211

Joints and Ligaments of the Vertebrae 211

Atlanto-occipital Articulation 214

Costo-vertebral Articulations 215

Costo-chondral Articulations 216

Chondro-sternal Ailiculations 216

Sternal Joints and Ligaments 217

Articulations of the Skull 217

Articulations of the Thoracic Limb 218

Articulations of the Pelvic Limb 229

Articulations of the Ox, Pig, and Dog 244

MYOLOGY

The Muscles and Accessory Structures 252

Fascl« and Muscles of the Horse 254

Fasciae and Muscles of the Head 255

Fascia? and Muscles of the Neck 266

Fascite and Muscles of the Back and Loins 276

Fasciae and Muscles of the Tail 279

Muscles of the Thorax 281

Abdominal Fasciae and Muscles 287

Muscles of the Thoracic Limb 293

Fasciae and Muscles of the Pelvic Limb 317

Muscles of the Ox 343

Muscles of the Pig 359

Muscles of the Dog 368

SPLANCHNOLOGY

Digestive System of the Horse 385

The Mouth 385

The Tongue 390

The Teeth 394

The SaHvary Glands 404

The Pharynx 405

The CEsophagus 409

The Abdominal Cavity 410

The Peritoneum 411

The Pelvic Cavity 412

The Stomach 415

The Small Intestine 419

The Large Intestine 422

The Pancreas 432

The Liver 434

CONTENTS 13

PAGE

The Spleen 439

The Peritoneum 441

Digestive System of the Ox 444

Digestive System of the Sheep 470

Digestive System of the Pig 477

Digestive System of the Dog 491

THE RESPIRATORY SYSTEM

Respiratory System of the Horse 508

The Nasal Cavity 508

The Larynx 514

The Trachea 523

The Bronchi 525

The Thoracic Cavity 525

The Pleuraj 526

The Lungs 530

The Thyroid Gland of the IIorse 535

The Thymus of the Horse 536

Respiratory System of the Ox 537

Respiratory System of the Pig 545

Respiratory System of the Dog 548

THE UROGENITAL SYSTEM

Urinary Organs of the Horse 554

The Kidneys 554

The Ureters 561

The Urinary Bladder 561

The Adrenal Bodies 563

LTrinary Organs of the Ox 564

Urinary Organs of the Pig 567

Urinary Organs of the Dog 569

THE MALE GENITAL ORGANS

Genital Organs of the Stallion 571

The Testicles 571

The Scrotum 574

The Ductus Deferens 575

The Spermatic Cord 575

The Tunica VaginaUs 576

Descent of the Testicles 577

The Vesiculse Seminales 578

The Prostate 578

The Uterus MascuUnus 579

The Bulbo-urethral Glands 579

The Penis 580

The Prepuce 582

Genital Organs of the Bull 586

Genital Organs of the Boar 591

Genital Organs of the Dog 593

THE FEMALE GENITAL ORGANS

Genital Organs of the Mare 596

The Ovaries 596

The Uterine or Fallopian Tubes 599

The Uterus 599

The Vagina 602

14 CONTENTS

PAGB

The Vulva 603

The Urethra 604

The Mammary Glands 604

Genital Organs of the Cow 605

Genital Organs of the Ewe 609

Genital Organs of the Sow 610

Genital Organs of the Bitch 612

ANGIOLOGY

General Considerations 614

The Organs of Circulation 614

Blood-vasct'lar System of the Horse 617

The Pericardium 617

The Heart 617

The Pulmonary Artery 629

The Systemic Ai-teries 629

The Coronary Arteries 630

Common Brachiocephalic Trunk 631

Arteries of the Thoracic Limb 650

Branches of the Thoracic Aorta 660

Branches of the Abdominal Aorta 661

Arteries of the Pelvic Limb 673

The Veins 681

The Pulmonary Veins 681

Cardiac Veins 681

The Anterior Vena Cava and its Tributaries 682

The Posterior Vena Cava and its Tributaries 692

The Lymphatic System 697

The Thoracic Duct 697

The Right Lymphatic Duct 698

The Lymph Glands and Vessels of the Head and Neck 698

The Lymph Glands and Vessels of the Thorax 700

The Lymph Glands and Vessels of the Abdomen and Pelvis 701

The Lymph Glands and Vessels of the Thoracic Limb 703

The Lymph Glands and Vessels of the Pelvic Limb 703

The P'cetal Circulation 704

Blood-vascular System op the Ox 705

The Pericardium and Heart 705

The Arteries 706

The Veins 719

Lymphatic System of the Ox and Sheep 722

Circulatory System of the Pig 734

The Pericardium and Heart 734

The Arteries 736

The Veins 740

Lymphatic System 740

Circulatory System of the Dog 742

The Pericardium and Heart 742

The Arteries 744

The Veins 754

Lymphatic System 756

NEUROLOGY.— THE NERVOUS SYSTEM

General Considerations 760

Nervous System of the Horse 764

The Spinal Cord 764

The Brain 768

CONTENTS 15

PAGE

The Cranial Nerves 793

The Spinal Nerves 810

Sympathetic Nervous System of the Horse 829

Nervous System of the Ox 834

Nervous System of the Pig 843

Nervous System of the Dog 847

^STHESIOLOGY

The Sense Organs and Common Integument of the Horse 857

The Eye 857

The Ear 870

The Common Integument 884

The Ergot and Chestnut 895

The OKactory and Gustatory Apparatus 895

The Sense Organs and Common Integument of the Ox 896

The Sense Organs and Common Integument of the Pig 900

The Sense Organs and Common Integument of the Dog 902

Index 907

THE ANATOMY OF THE DOMESTIC ANIMALS

INTRODUCTION

Anatomy is the branch of biological science which deals with the form and
structure of organisms, both animal and vegetal. It is therefore in close correlation
with physiology, which treats of the functions of the body.

Etymologically the word "anatomy" signifies the cutting apart or disassociat-
ing of parts of the body. In the earlier phases of its development anatomy was
necessarily a purely descriptive science, based on such observations as were possible
with the unaided eye and simple dissecting instruments — the scalpel, forceps, and
the like. At this time, therefore, the term adequately expressed the nature of the
subject. But as the scope of the science extended and the body of anatomical
knowledge grew, subdivisions became necessary and new terms were introduced to
designate special fields and methods of work. With the introduction of the mi-
croscope and its accessories it became possible to study the finer details of structure
and minute organisms hitherto unknown, and this field of inquiry rapidly developed
into the science of microscopic anatomy or histology as conventionally distinguished
from macroscopic or gross anatomy. In the same way the study of the changes
which organisms undergo during their development soon attained sufficient im-
portance to be regarded on practical grounds as a separate branch known as
embryology.^

Comparative anatomy is the description and comparison of the structure of
animals, and forms the basis for their classification. By this means — including
extinct forms in the scope of inquiry — it has been possible to show the genetic
relationship of various groups of animals and to elucidate the significance of many
facts of structure which are otherwise quite obscure. The deductions concerning
the general laws of form and structure derived from comparative anatomical
studies constitute the science of morphology or philosophical anatomy. The
morphologist, however, deals only with such anatomical data as are necessary to
form a basis for his generalizations. The anatomical knowledge required in the
practice of medicine and surgery is evidently of a different character and must
include many details which are of no particular interest to the morphologist.

Special anatomy is the description of the structure of a single type or species,
e. g., anthropotomy, hippotomy.

Veterinary anatomy is the branch which deals with the form and structure of
the principal domesticated animals. It is usually pursued with regard to pro-
fessional requirements, and is therefore largely descriptive in character. As a
matter of convenience, the horse is generally selected as the type to be studied in
detail and to form a basis for comparison of the more essential differential characters
in the other animals.

Two chief methods of study are employed — the systematic and the topo-
graphic. In the former the body is regarded as consisting of systems of organs or

1 Tliis term is usually limited in its application to the earlier phases of development during
which the tissues and organs are formed. The term ontogeny is used to designate the entire
development of the individual. The ancestral history or phylogeny of the species is constituted
by the evolutionary changes which it has undergone as disclosed by the geological record.
2 17

X8 INTRODUCTION

apparatus which are similar in origin and structure and are associated in the per-
formance of certain functions. The divisions of systematic anatomy are :

1. Osteology, the description of the Skeleton.

2. Arthrology, the description of the Joints.

3. Myology, the description of the Muscles and accessory structures.

4. Splanchnology, the description of the Viscera. This includes the following
subdivisions :

(1) Digestive System

(2) Respiratory System

(3) Urogenital System

(a) Urinary Organs
(h) Genital Organs

5. Angiology, the description of the Organs of Circulation

6. Neurology, the description of the Nervous System

7. ^sthesiology, the description of the Sense Organs and Common Integu-

ment

The term topographic anatomy designates the methods by which the relative
positions of the various parts of the body are accurately determined. It presup-
poses a fair working knowledge of systematic anatomy.

Descriptive Terms. — In order to indicate precisely the position and direction
of parts of the body, certain descriptive terms are employed, and must be under-
stood at the outset. In the explanation of these terms it is assumed here that
they apply to a quadruped such as the horse in the ordinary standing position.
The surface directed toward the plane of support (the ground) is termed ventral
(or inferior), and the opposite surface is dorsal (or superior) ; the relations of parts in
this direction are named accordingly. The longitudinal median plane divides the
body into similar halves. A structure or surface which is nearer than another to the
meclian plane is medial (or internal) to it, and an object or surface which is further
than another from the median plane is lateral (or external) to it. Planes parallel
to the median plane are sagittal. Transverse or segmental planes cut the long axis
of the body perpendicular to the median plane, or an organ or limb at right angles
to its long axis. A frontal plane is perpendicular to the median and transverse
planes. The term is also used with reference to parts of the limbs or various organs
in a similar sense. The head end of the body is termed anterior or cranial; and the
tail end posterior or caudal ; relations of structures with regard to the longitudinal
axis of the body are designated accordingly. With respect to parts of the head,
the corresponding terms are oral and aboral. Certain terms are used in a special
sense as applied to the limbs. Proximal and distal express relative distances of
parts from the long axis of the body. The anterior face of the thoracic limb from
the elbow downward is termed dorsal, and the opposite face volar. In the corre-
sponding part of the pelvic limb the terms are dorsal and plantar respectively. In
the same regions radial and ulnar (thoracic limb), tibial and fibular (pelvic limb),
may be used to designate that side of the extremity on which the corresponding
bone is situated; they are therefore equivalent respectively to medial and lateral
in the animals with which we are concerned. The terras superficial (superficialis)
and deep (profundus) are useful to indicate relative distances of i);irts from the
surface of the body.

It is evidently advantageous to employ terms which are as far as possible independent of
the position of the body in space and capable of general application, e. g., dorsal, ventral, proximal,
etc. It is also desirable that the terms internal and external be reserved to indicate relations of
depth in cavities or organs, and medial and lateral to designate relations to the median plane.
Such terms are coming into more extensive use in human and veterinary anatomy, but the older
nomenclature is very firmly established and cannot well be discarded at once and entirely. To
facilitate the transition, a table of the older and more recent terms is given below; the recent
terms are in the first column and the older equivalents in the second.

INTRODUCTION

A. Relating to Head, Neck, and Trunk:

Dorsalis Superior

Ventralis Inferior

MediaUs I?tf™^\

LateraUs External

Cranialis 1 Anterior

Oralis /

Caudalis 1 Posterior

Aboralis J

B. Relating to Limbs:

Proximalis Superior

Distalis Mf"?^

DorsaUs Anterior

Volaris \ , . Posterior

Plantaris f

Radialis ] Internal

Tibialis f

Ulnaris \ External

Fibularis f

OSTEOLOGY

THE SKELETON
The term skeleton is applied to the framework of hard structures which sup-
ports and protects the soft tissues of animals. In the descriptive anatomy of the
higher animals it is usually restricted to the bones and cartilages, although the
ligaments Avhich bind these together might well be included.

In zoology the term is used in a much more comprehensive sense, and includes all the harder
supporting and protecting structures. When the latter are situated externally, they form an
exoskeleton, derived from the ectoderm. Examples of this are the shells and cliitinous coverings
of many invertebrates, the scales of fishes, the shields of turtles, and the feathers, hair, and hoofs
of the higher vertebrates. The endoskeleton (with which we have to deal at present) is embedded
in the soft tissues. It is derived from the mesoderm, but includes the notochord or primitive
axial skeleton, which is of entodermal origin.

The skeleton may be divided primarily into three parts: (1) axial; (2) appen-
dicular; (3) splanchnic.

The axial skeleton comprises the vertebral column, ribs, sternum, and skull.

The appendicular skeleton includes the bones of the limbs.

The splanchnic or visceral skeleton consists of certain bones developed in the
substance of some of the viscera or soft organs, e. g., the os penis of the dog and the
OS cordis of the ox.

The number of the bones of the skeleton of an animal varies with age, owing
to the fusion during growth of skeletal elements which are separate in the fostus
or the young subject. Even in adults of the same species numerical variations
occur, e. g., the tarsus of the horse may consist of six or seven bones, and the carpus
of seven or eight; in all the domestic mammals the number of coccygeal vertebrae
varies considerably.

The bones are commonly divided into four classes according to their shape
and function.^

(1) Long bones (Ossa longa) are typically of elongated cylindrical form with
enlarged extremities. They occur in the limbs, where they act as supporting
columns and as levers. The cylindrical part, termed the shaft or body (Corpus),
is tubular, and incloses the medullary cavity, which contains the medulla or marrow.

(2) Flat bones (Ossa plana) are expanded in two directions. They furnish
sufficient area for the attachment of muscles and afford protection to the organs
which they cover.

(3) Short bones (Ossa brevia), such as those of the carpus and tarsus, present
somewhat similar dimensions in length, breadth, and thickness. Their chief func-
tion appears to be that of diffusing concussion. Sesamoid bones, which are de-
veloped in the capsules of some joints or in tendons, may be included in this group.
They diminish friction or change the direction of tendons.

(4) Irregular bones (Ossa irregularia) . This group would include bones of
irregular shape, such as the vertebrae and the bones of the cranial base; they are
median and unpaired. Their functions are various and not so clearly specialized
as those of the preceding classes.

^ This classification is not entirely satisfactory; some bones, e. g., the ribs, are not clearly
provided for, and others might be variously placed.

STRUCTURE OF BONES

STRUCTURE OF BONES i
Bones consist chiefly of bone tissue, but considered as organs they present
also an enveloping membrane, termed the periosteum, the marrow, vessels, and
nerves.

The architecture of bone can be studied best by means of longitudinal and
transverse sections of specimens which have been macerated so as to remove most
of the organic matter. These show that the bone
consists of an external shell of dense compact sub-
stance, within which is the more loosely arranged
spongy substance. In tyjDical long bones the shaft
is hollowed to form the medullary cavity (Cavum
medullare) .

The compact substance (Substantia compacta)
differs greatly in thickness in various situations, in
conformity with the stresses and strains to which
the bone is subjected. In the long bones it is
thickest in or near the middle part of the shaft and
thins out toward the extremities. On the latter the
layer is very thin, and is especially dense and smooth
on joint surfaces.

The spongy substance (Substantia spongiosa)
consists of delicate bony plates and spicules which
run in various directions and intercross. These are
definitely arranged with regard to mechanical re-
quirements, so that systems of pressure and tension
plates can be recognized, in conformity with the
lines of pressure and the pull of tendons and liga-
ments respectively. The intervals between the
plates are occupied by marrow, and are termed
marrow spaces (Cellulse meduUares). The spongy
substance forms the bulk of short bones and of the
extremities of long bones; in the latter it is not con-
fined to the ends, but extends a variable distance
along the shaft also. Some bones contain air-spaces
within the compact substance instead of spongy
bone and marrow, and hence are called pneimiatic
bones (Ossa pneumatica) . These cavities are termed
sinuses, and are lined with mucous membrane;
they communicate indirectly with the external air.
In certain situations the two compact layers of flat
bones are not separated by spongy bone, but fuse
with each other; in some cases of this kind the bone
is so thin as to be translucent, or may undergo
absorption, producing an actual deficiency.

The flat bones of the cranial vault and sides
are composed of an outer layer of orchnary compact
substance, the lamina externa, an inner layer of
very dense bone, the lamina interna or tabula vitrea, and between these a variable
amount of spongy bone, here termed diploe.

The periostetun is the membrane which invests the outer surface of bone,
except where it is covered with cartilage. It consists of an outer protective fibrous

1 Only the gross structure is discussed here. For the microscopic structure reference is to
be made to histological works.

Fig. 1. — Sagittal Section op Large
Metatarsal Bone of Horse
(Right).

S.c, Compact substance; S.s.,
spongy substance; Cm., medullary
cavity; F.n., nutrient foramen. Note
the greater thickness of the compact
substance of the anterior part of the
shaft.

OSTEOLOGY

layer, and an inner cellular osteogenic layer. During active gro^vth the osteogenic
layer is well developed, but later it becomes much reduced. The fibrous layer
varies much in thickness, being in general thickest in exposed situations. The
adhesion of the periosteum to the bone also differs greatly in various places; it
is usually very thin and easily detached where it is thickly covered with muscular
tissue which has little or no attachment. The degree of vascularity conforms to
the activit}^ of the periosteum.

The endosteum is a thin fibrous membrane which lines the medullary cavity
and the larger Haversian canals.

The marrow (Medulla ossium) occupies the interstices of the spongj^ bone and
the medullary cavity of the long bones. There are two varieties in the adult —
red and yellow. In the young subject there is only red marrow (Medulla ossium
mbra), but later this is replaced in the medullary cavity by yellow marrow (Medulla
ossium flava). The red marrow contains several types of characteristic cells and
is a blood-forming suV)stance, Avhile the yellow is practically ordinary adipose tissue.^

Vessels and Nerves. — It is customary to recognize two sets of arteries — the
periosteal and the medullary. The former ramify in the periosteum and give off

Fig. 2. — Cross-section of Proximal Third of Shaft
OF Right Humerus of Horse.

Fig.

Cross-section of Distal Third of Shaft op
Left Humerus of Horse.
Section passes through nutrient foramen and canal.

innumerable small branches which enter minute openings (Volkmann's canals) on
the surface and reach the Haversian canals of the compact substance. Other
branches enter the extremities of the long l^ones and supply the spongy bone and
marrow in them. In the case of the larger bones — and especially the long bones —
the large nutrient or medullary artery (Arteria nutricia) enters at the so-called nu-
trient foramen (Foramen nutricium), passes in a canal (Canalis nutricius) through
the compact substance, and ramifies in the marrow; its branches anastomose -with
the central branches of the periosteal set. The larger veins of the spongy bone do
not, as a rule, accompany the arteries, but emerge chiefly near the articular surfaces.
Within the bone thej^ are destitute of valves. The l5anph-vessels exist as peri-
vascular channels in the periosteum and the Haversian canals of the compact sub-
stance. They also form a fine subperiosteal network, froxn which the larger vessels
proceed, usually in company with veins. Lymph-spaces exist at the periphery of
the marrow.

The nerves appear to be distributed chiefly to the blood-vessels. Special nerve-

1 Since yellow marrow is formed by regressive changes in red marrow, including fatty infiltra-
tion and degeneration of the characteristic cells, we find transitional forms or stages in the process.
In aged or badly nourished subjects the marrow may undergo gelatinous degeneration, resulting
in the formation of gelatinous marrow.

DEVELOPMENT AND GROWTH OF BONE

endings (Vater-Pacini corpuscles) in the periosteum are to be regarded as sensory,
and probably are concerned in mediating the muscle sense (kinesthesia)

DEVELOPMENT AND GROWTH OF BONEi

The primitive embryonal skeleton consists of cartilage and fibrous tissue, in
which the bones develop. The process is termed ossification or osteogenesis, and
is effected essentially by bone-producing cells, called osteoblasts. It is customary,
therefore, to designate as membrane bones those which are developed in fibrous
tissue, and as cartilage bones those which are preformed in cartilage. The princi-
pal membrane bones are those of the roof and sides of the cranium and most of the
bones of the face. The cartilage bones comprise,
therefore, most of the skeleton. Correspondingly
we distinguish intramembranous and endochondral
ossification.

In intramembranous ossification the process
begins at a definite center of ossification (Punctum
ossificationis) , where the osteoblasts surround them-
selves with a deposit of bone. The process extends
from this center to the periphery of the future bone,
thus producing a network of bony trabeculae. The
trabeculae rapidly thicken and coalesce, forming a
bony plate which is separated from the adjacent
bones by persistent fibrous tissue. The superficial
part of the original tissue becomes periosteum, and
on the deep face of this successive layers of perios-
teal bone are formed by osteoblasts until the bone
attains its definitive thickness. Increase in circum-
ference takes place by ossification of the surround-
ing fibrous tissue, which continues to grow until
the bone has reached its definitive size.

In endochondral ossification the process is
fundamentally the same, but not quite so simple.
Osteoblasts emigrate from the deep face of the peri-
chondrium or primitive periosteum into the cartilage
and cause calcification of the matrix or ground-
substance of the latter. Vessels extend into the cal-
cifying area, the cartilage cells shrink and disappear,
forming primary marrow cavities which are occupied
by processes of the osteogenic tissue. There is thus
formed a sort of scaffolding of calcareous trabeculae
on which the bone is constructed by the osteoblasts.
At the same time perichondral bone is formed by

the osteoblasts of the primitive periosteum. The calcified cartilage is broken down
and absorbed through the agency of large cells called osteoclasts, and is replaced
by bone deposited by the osteoblasts. The osteoclasts also cause absorption of the
primitive bone, producing the marrow cavities; thus in the case of the long bones
the primitive central spongy bone is largely absorbed to form the medullary cavity
of the shaft, and persists chiefly in the extremities. Destruction of the central
part and formation of subperiosteal bone continue until the shaft of the bone has
completed its growth.

A typical long bone is developed from three primary centers of ossification,

1 Only a brief general statement of osteogenesis can be made here; details must be sought
in embryological literature.

Fig. 4. — Left Femur of Young Piq,
Lateral View, to Show Di-
VI8IOX OF A Long Bone into
Shaft (s) and Extremities.
Proximal extremity consists of
two parts, head (h) and trochanter
major (t.m.), which have separate
centers of ossification. Distal extrem-
ity consists of trochlea (0 and condyles
(c); e.L, epiphyseal cartilages; s.f.,
supracondyloid fossa.

24 OSTEOLOGY

one, which appears first, for the diaphysis or shaft and one for each epiphysis oi
extremity. Many bones have secondary centers from which processes or apophyses
develop.

The foregoing outhne accounts for the gro^Hh of bones except in regard to
length. Increase in length may be explained briefly as follows : Provision for con-
tinued ossification at either end of the diaphysis is made by a layer of actively
groAving cartilage — the epiphyseal cartilage — which intervenes between the diaph-
ysis and the epiphysis. It is evident that so long as this cartilage persists and
grows, new bone may continue to be formed at its expense, and increase of length
is possible. When the epiphyseal cartilage ceases to grow, it undergoes ossification,
the bone is consolidated, and no further increase in length is possible. This fusion
takes place at fairly definite periods in the various bones, and it is of value to know
the usual times at which it occurs in the larger bones of the limbs at least. In the
case of membrane bones, increase in circumference is provided for by the ossification
and new formation of the surrounding fibrous tissue.

After the bones have reached their full size, the periosteum becomes relatively reduced and
inactive so far as its osteogenic layer is concerned; the bone-forming function may be stimulated
by various causes, as is well seen in the heaUng of fractures and the occurrence of bony enlarge-
ments.

Profound changes occur in the skeleton after birth, and during the period of growth the bones
are much more plastic than might be supposed. In the new-])orn foal, for example, it is evident
that the rnetacarpal and metatarsal bones are relatively long and the scapula and humerus short;
also that in general the shafts of the long bones are slender in comparison with the extremities.
The various prominences are much less pronounced than in the adult, and most of the minor
surface markings are absent, so that the bones have a relatively smooth appearance. The period
of gro^v-th may be regarded as terminating with the union of the extremities and shafts of the long
bones and the fusion of the parts of other bones. During adult life the skeletal changes proceed
more slowly; they comprise accentuation of the larger prominences and depressions and the ap-
pearance of smaller ones. These secondary markings are chiefly correlated with the attachments
of muscles, tendons, and hgaments, or are produced by pressure exerted by various structures on
the bones. Later in hfe ossification invades more or less extensively the cartilages and the at-
tachments of tendons and ligaments. Senile changes in the bones, consisting of decrease of the
organic matter and rarefaction of the bone tissue, render them brittle and liable to fracture.

CHEMICAL COMPOSITION OF BONE
Dried bone consists of organic and inorganic matter in the ratio of 1 : 2 ap-
proximately. The animal matter gives toughness and elasticity, the mineral
matter hardness, to the bone tissue. Removal of the organic matter by heat does
not change the general form of a bone, but reduces the weight by about one-third,
and makes it very fragile. Conversely, decalcification, while not affecting the form
and size of the bone, renders it soft and pliable. The organic matter (ossein) when
boiled yields gelatin. The following table represents the composition in 100 parts
of ox bone of average quality :

Gelatin 33.30

Phosphate of Ume 57.35

Carbonate of lime 3.85

Phosphate of magnesia 2.05

Carbonate and chlorid of sodium 3.45

100.00
PHYSICAL PROPERTIES OF BONE
Fresh dead bone has a yellowish-white color; when macerated or boiled and
bleached, it is white. The specific gravity of fresh compact bone is a little over
1.93. It is very hard and resistant to pressure; a 5-millimeter cube of compact
bone of the ox will resist pressure up to 852 pounds, if the pressure be applied in
the line of the lamellae (Rauber). Its tensile strength is estimated to be nearly
twice that of oak.

THE VERTEBRAL COLUMN 25

DESCRIPTIVE TERMS

The surfaces of the bones present a great variety of eminences and depressions,
as well as perforations. The prominences and cavities may be articular, or non-
articular, furnishing attachment to muscles, tendons, ligaments, or fascia. A
number of descriptive terms are used to designate these features, and the following
are some of those in general use:

Process (Processus) is a general term for a prominence.

A tuberosity (Tuber, Tuberositas) is a large, rounded projection; a tubercle
(Tuberculum) is a smaller one.

The term trochanter is applied to a few prominences, e. g., the trochanters of
the femur.

A spine (Spina) or spinous process (Processus spinosus) is a pointed projection.

A crest (Crista) is a sharp ridge.

A line (Linea) is a very small ridge.

A head (Caput) is a rounded articular enlargement at the end of a bone; it
may be joined to the shaft by a constricted part, the neck (Collum).

A condyle (Condylus) is an articular eminence which is somewhat cylindrical;
a non-articular projection in connection with a condyle may be termed an epi-
condyle (Epicondylus).

A trochlea is a pulley-like articular mass.

A glenoid cavity (Cavitas glenoidalis) is a shallow articular depression, and a
cotyloid cavity or acetabulum is a deeper one.

The term facet is commonly applied to articular surfaces of small extent,
especially when they are not strongly concave or convex.

The terms fossa, fovea, groove or sulcus, and impression are applied to various
forms of depressions.

A foramen is a perforation for the transmission of vessels, nerves, etc.

A sinus is an air-cavity within a bone or bones; it is lined with mucous mem-
brane and communicates with the exterior.

Other terms, such as canal, fissure, notch, etc., require no explanation.^

THE VERTEBRAL COLUMN

The vertebral coliram (Columna vertebralis) is the fundamental part of the
skeleton. It consists of a chain of median, unpaired, irregular bones which
extends from the skull to the end of the tail. In the adult certain vertebrae have
become fused to form a single bony mass with which the pelvic girdle articulates.
Vertebrae so fused are termed fixed (or ''false") vertebrae (Vertebrae immobiles), as
distinguished from the movable (or 'Hrue") vertebrae (Vertebrae mobiles).

The column is subdivided for description into five regions, which are named
according to the part of the body in which the vertebrae are situated. Thus the
vertebrae are designated as cervical, thoracic, lumbar, sacral, coccygeal (Vertebrae
cervicales, thoracales, lumbales, sacrales, coccygeae). The number of vertebrae in
a given species is fairly constant in each region except the last, so that the verte-
bral formula may be expressed (for the horse, for example) as follows:

C7Ti8L6S5Cyi5.21.

The vertebrae in a given region have characters by which they may be dis-
tinguished from those of other regions, and individual vertebrae have special
characters which are more or less clearly recognizable. All typical vertebrae have

1 As might be expected from the history of anatomy, a good many of these terms are more or
less interchangeable; furthermore, a given skeletal feature may differ greatly in various species.

OSTEOLOGY

a common plan of structure, which must first be understood. The parts of which
a vertebra consists are the body, the arch, and the processes.

The body (Corpus vertebrae) is the more or less cylindrical mass on which the
other parts are constructed. The anterior and posterior extremities of the body
are attached to the adjacent vertebrse by intervertebral fibro-cartilages, and are
usually convex and concave respectively. The dorsal surface is flattened and enters
into the formation of the vertebral canal, while the ventral aspect is rounded later-
ally, and is in relation to various muscles and viscera. In the thoracic region the
body presents two pairs of facets (Foveae costales) at the extremities for articula-
tion with part of the heads of two pairs of ribs.

The arch (Arcus vertebrae) is constructed on the dorsal aspect of the body.
It consists originally of two lateral halves, each of which is considered to consist
of a pedicle and a lamina. The pedicle (Radix arcus vertebrge) forms the lateral
part of the arch, and is cut into in front and behind by the vertebral notches (In-
cisura vertebralis cranialis, caudalis). The notches of two adjacent vertebrae form
intervertebral foramina (Foramina intervertebralia) for the passage of the spinal

nerves and vessels; in some vertebrae, how-
ever, there are complete foramina instead
of notches. The laminae are plates which
complete the arch dorsally, uniting with each
other medially at the root of the spinous
process.

The body and the arch form a bony
ring which incloses the vertebral foramen
(Foramen vertebrale); the series of verte-
bral rings, together with the ligaments which
unite them, inclose the vertebral canal
(Canalis vertebralis), Avhich contains the
spinal cord and its coverings and vessels.

The articular processes, two anterior
and two posterior (Processus articulares
craniales, caudales), project from the bor-
ders of the arch. They present articular
surfaces adapted to those of adjacent verte-
brae, and the remaining surface is roughened
for muscular and ligamentous attachment.
The spinous process or spine (Processus
spinosus) is single, and projects dorsally from the middle of the arch. It varies
greatly in form, size, and direction in different vertebrae. It furnishes attachment
to muscles and ligaments.

The transverse processes (Processus transversi) are two in number and project
laterally from the sides of the arch or from the junction of the arch and body.
In the thoracic region each has a facet for articulation with the tubercle of a rib
(Fovea costalis transversalis) . They also give attachment to muscles and liga-
ments.

Some vertebrae have also a ventral spine or a haemal arch.
Mammillary processes (Processus mamillares) are found in most animals on
the last thoracic and anterior lumbar vertebrse, between the transverse and an-
terior articular processes or on the latter.

Accessory processes (Processus accessorii), when present, are situated between
the transverse and posterior articular processes.

Development. — The vertebrae are developed by ossification in the cartilage
Avhich surrounds the notochord and forms the sides of the neural canal. There are
three primary centers of ossification, one for the body and one for each side of the

Cosraijkcef

Fig. 5. — First Thoracic Vertebra of Horse.
To illustrate plan of structure of vertebrae.

THE COSTAL CARTILAGES 27

arch. Secondary centers appear later for the summit of the spinous process
(except in the cervical region), the extremities of the transverse processes, and the
thin epiphyseal plates at the extremities of the body.

Sometimes there are at first two centers for the body, which soon fuse. The process of ossifi-
cation extends from the lateral centers to form, not only the corresponding part of the arch, but
also the processes and a part of the body next to the root of the arch (Radix arcus) . In the horse
and ox the body and arch are fused at birth or unite very soon after, but the epiphyses do not
fuse till growth is complete. In the pig, sheep, and dog the body and arch are united at l)irth
by cartilage (neurocentral synchondrosis), but fuse in the first few months.

THE RIBS

The ribs (Costae) are elongated curved bones which form the skeleton of the
lateral thoracic walls. They are arranged serially in pairs which correspond in
number to the thoracic vertebrae. Each articulates dorsally with two vertebrae
and is continued ventrally by a costal cartilage. Those which articulate with the
sternum by means of their cartilages are termed sternal ribs (Costae sternales);
the remainder are asternal ribs (Costae asternales). Ribs at the end of the series
which have their ventral ends free in the abdominal wall are named floating ribs
(Costae fiuctuantes). The intervals between the ribs are termed intercostal spaces
(Spatia intercostalia) .

A typical rib^ consists of a shaft and two extremities. The shaft (Corpus
costae) is band-like and varies much in length, breadth, and curvature in different
ribs. In the case of some ribs the curvature is not uniform, but is accentuated at a
certain point, termed the angle of the rib (Angulus costae) ; this occurs at a variable
distance from the vertebral end, and is usually marked by a rough ridge. The
direction also varies; the first rib is usually almost vertical, while the remainder
slope backward in increasing degree. The lateral surface (Facies lateralis) is con-
vex, and the medial surface (Facies medialis) flattened from edge to edge; on the
latter, close to the posterior border, is the costal groove (Sulcus costae), which fades
out ventrally. It contains the intercostal vein. The anterior and posterior
borders (Margo cranialis, caudalis) are thin and sharp on some ribs, rounded on
others.

The vertebral extremity (Extremitas vertebralis) consists of the head, neck,
and tubercle. The head (Capitulum costae) is the actual end of the rib, and is
rounded and somewhat enlarged. It presents two facets (Facies articularis capituli
costae) for articulation with the bodies of two adjacent thoracic vertebrae; these
surfaces are separated by a groove in which the conjugal ligament is attached.
The neck (CoUum costae) joins the head to the shaft. It varies in length and
diameter. Its lateral surface is rough, its medial smooth. The tubercle (Tuber-
culum costae) projects backward at the junction of the neck and shaft. It has a
facet (Facies articularis tuberculi costae) for articulation with the transverse process
of the posterior vertebra of the two with which the head articulates. The tubercle
gradually approaches the head in the posterior ribs, and eventually fuses with it.

The sternal extremity (Extremitas sternalis) is commonly slightly enlarged,
and is roughened at the junction with the costal cartilage.

Development. — The ribs are ossified in cartilage from three centers — one each
for the shaft (and sternal end), head, and tubercle; the third center is absent in
some ribs at the terminal part of the series.

THE COSTAL CARTILAGES

These (Cartilagines costales) are bars of hyaline cartilage which continue the
ribs. Those of the sternal ribs articulate with the sternum, while those of the

1 The term is employed here, as is usual in descriptive anatomy, to designate only the bony
part of the rib (Os costale) ; morphologically it includes the cartilaginous part also.

28 OSTEOLOGY

asternal ribs overlap and are attached to each other to form the costal arch (Arcus
costalis). The cartilages of floating ribs are not attached to those adjacent.

THE STERNUM

The stemxun (or breast-bone) is a median segmental bone -which completes the
skeleton of the thorax ventrally, and articulates Avith the cartilages of the sternal
ribs laterally. It consists of six to eight bony segments (Sternebra^) connected by
intervening cartilage in the yoimg subject. Its form varies with that of the thorax
in general anil with the development of the clavicles in animals in which these bones
are present. Its anterior extremity, the manubrium stemi or presternum, is
specially affected by the latter factor, being broad and strong when the clavicles
are well ileveloped and articulate with it (as in man), relatively small and laterally
compressed Avhen they are absent (as in the horse) or rudimentary (as in the dog).
The cartilages of the first pair of ribs articulate with it. The body or mesostemimi
(Corpus sterni) presents laterally, at the junction of the segments, concave facets
(Incisura^ costales) for articulation Avith the cartilages of the sternal ribs. The
posterior extremity or metastemiun presents the xiphoid cartilage (Processus
xiphoideus) ; this is thin and wide, as in the horse and ox, or narroAv and short, as
in the dog.

Development. — The cartilaginous sternmn is formed by the fusion medially
of two lateral bars which unite the ventral ends of the first eight or nine costal
cartilages, and is primitively imsegmented. The manubrium ossifies from a single
center, but the centers for the other segments appear to be primitively paired.
The sternum never becomes completely ossified; details in regard to persisting
cartilage will be given in the special descriptions. The layer of compact tissue is
for the greater part very thin and the spongy substance is open-meshed and ver^'
vascular.

THE THORAX

The skeleton of the thorax comprises the thoracic vertebnp dorsally. the ribs
and costal cartilages laterally', and the sternmn ventrally. The thoracic cavity
(CaAinn thoracis) resembles in shape an irregular truncated cone; it is compressed
laterally, especially in front, and the dorsal wall or roof is much longer than the
ventral wall or floor. The anterior apertvire or inlet (Apertura thoracis cranialis) is
bc^unded by the first thoracic vertebra dorsally, the first pair of ribs and costal
cartilages laterally, and the manubrium sterni ventrally. The posterior aperture
(Apertura thoracis caudalis) is bounded by the last thoracic vertebra, the last
pair of ribs, the costal arches, and the anterior part of the xiphoid cartilage.

It may be noted here that the diaphragm (which forms the partition hetween the thoracic
and abdominal caA-ities) does not follow the costal arches in its posterior attachment, so that the
posterior ribs enter also into the formation of the abdominal wall.

THE SKULL

The term skull is usually imderstood to include all of the bones of the head.
The head consists of the cranium and the face, and it is therefore convenient to
diAnde the bones into cranial antl facial groups.

The cranial bones (Ossa cranii) inclose the brain AA-ith its membranes and
vessels and the essential organs of hearing. They concur with the facial bones in
forming the orbital and nasal caA'ities, in AA-hich the peripheral organs of sight ami
of smell are situated.

The facial bones (Ossa faciei) form the skeleton of the oral and nasal caA'ities,
and also support the pharA'nx, the larynx, and the root of the tongue.

THE BONES OF THE THORACIC LIMB 29

Most of the bones of the skull are flat bones, developed in membrane; those
of the cranial base may be classed as irregular, and are developed in cartilage. Only
two form permanent movable joints with other parts of the skull. The mandible
(or lower jaw-Vjone) forms diarthrodial joints with the temporal bones, and the
hyoid bone is attached to the latter Vjy bars of cartilage. The other bones form
immovable joints, most of which disappear with age.

In order to study the separate bones, skulls of young subjects are necessary, since later most
of the hnes of demarcation become effaced. The relations of each bone to its surroundings should
be specially noted, since the final object is to understand the skull as a whole. In the descriptions
which follow the skull is considered with its long axis horizontal, and that of the horse will serve
as a type.

THE BONES OF THE THORACIC LIMB

The thoracic limb (Extremitas thoracalis) consists of four chief segments, viz.,
the shoulder girdle, the arm, the forearm, and the manus.

The shoulder girdle (Cingulum extremitatis thoracalis) , when fully developed,
consists of three bones — the scapula (or shoulder-blade), the coracoid, and the
clavicle (or collar-bone). In the domesticated mammals only the scapula, a large,
flat bone, is well developed, and the small coracoid element has fused with it, while
the clavicle is either absent or is a small rudiment embedded in the brachiocephali-
cus muscle. There is therefore no articulation of the shoulder with the axial
skeleton.

The shoulder girdle is fully developed in birds and the lower mammals (monotremata) . In
the higher manmials the coracoid is reduced to the coracoid process of the scapula, and the develop-
ment of the clavicle is in conformity with the function of the hmb. Thus in typical quadrupeds,
such as the horse and ox, in which the foreUmbs are used only for support and locomotion, the
clavicle is absent. Other animals which use these hmbs for grasping, burrowing, chmbing, etc.
(e. g., man, apes, moles), have well-developed cla\'icles which connect the scapula with the stemiun.

The arm (Brachium) contains a single long bone, the humerus (or arm bone).

In the forearm (Antibrachium) are two bones, the radius and ulna. These
vary in relative size and mobility. In the horse and ox the two bones are fu.sed,
and the distal part of the limb is fixed in the position of pronation. The radius is
placed in front and supports the weight. The ulna is well developed only in its
proximal part, which forms a lever for the extensor muscles of the elbow. In the
pig the ulna is the larger and longer of the two bones, but is closely attached to
the back of the radius. In the dog the ulna is also well developed and a small
amount of movement is possible between the two bones.

The manus,! the homologue of the hand in man, consists of three subdivi-
sions, viz., the carpus, metacarpus, and digit or digits.

The carpus, popularly termed the "knee" in animals, and homologous with
the wrist of man, contains a group of short bones, the ossa carpi.^ These are typic-
ally eight in number and are arranged in two transverse rows — a proximal or anti-
brachial, and a distal or metacarpal. The bones of the proximal row, named from
the radial to the ulnar side {i. e., from within outward), are the radial, intermediate,
ulnar, and accessory carpal bones. The bones of the distal row are designated
numerically, in the same direction, as first, second, third, and fourth carpal bones.

This nomenclature, introduced by Gegenbaur, and now used largely by comparative anat-
omists, seems decidedly preferable to the ^'ariety of terms borrowed from human anatomy and
based on the form of the bones in man. The follo^vang table of synonyms in cornmon use is ap-
pended for comparison. The Latin terms and abbreviated notations are given in parentheses.

1 It is unfortunate that there is no popular name for this part of the limb. The term "fore-
foot" is sometimes appUed to it, but this leads to confusion, since the word "foot" has long been
used in a different sense.

2 The term "knee" as applied to this region is unfortunate, but the usage is very firmly
established and there is no other popular name.

30 OSTEOLOGY

The central carpal bone (Os carpi centrale) is omitted, since it is not a separate element in the
animals under consideration here.

Radial (Os carpi radiale, Cr) Scaphoid

Intermediate (Os carpi intermedium, Ci) Semilunar

Ulnar (Os carpi ulnare, Cu) Cuneiform

Accessory (Os carpi accessorium, Ca) Pisiform

First carpal (Os carpale primum, CI) Trapezium

Second carpal (Os carpale secundum, C2j Trapezoid

Third carpal (Os carpale tertium, C3) Os magnum

Fourth carpal (Os carpale quartum, C4) Unciform

The metacarpus contains typically five metacarpal bones (Ossa metacarpalia
I-V), one for each digit; they are long bones and are designated numerically from
the radial to the ulnar side (i. e., from within outward). This arrangement occurs
in the dog, although the first metacarpal is much smaller than the others, and the
second and fifth are somewhat reduced. Further reduction has taken place in the
other animals, resulting in the perissodactyl and artiodactyl forms. In the horse
the first and fifth metacarpals are absent, the third is the large supporting meta-
carpal bone and carries the single digit, while the second and fourth are much re-
duced. In artiodactyls (e. g., ox, sheep, pig) the third and fourth are the chief
metacarpals and carry the well developed digits; they are fused in the ox and sheep.
The others are variously reduced or absent, as noted in the special descriptions to
follow.

The fossil remains of the ancestors of the existing Equidse illustrate in a most complete man-
ner the reduction which has occurred in this respect. The earliest known ancestor of the horse,
Eohippus of the Lower Eocene, had four well developed metacarpal bones, each of which carried
a digit; the first metacarpal bone was small. Intermediate forms show the gradual evolution of
the race from this primitive animal, which was about the size of the domestic cat. There is reason
to believe that earlier forms had five digits.

The digits (Digiti manus) are homologous with the fingers of man, and are
typically five in number. They are designated numerically from the radial to
the ulnar side, in correspondence with the metacarpus. The full number is present
in the dog. In the ox and pig the third and fourth are well developed and support
the weight, while the second and fifth are reduced. The existing horse has a single
digit, the third of his pentadactyl ancestors. The skeleton of each fully developed
digit consists of three phalanges and certain sesamoid bones. The first phalanx
(Phalanx prima) articulates with the corresponding metacarpal bone above and
with the second phalanx (Phalanx secunda) below. The third phalanx (Phalanx
tertia) is inclosed in the hoof or claw, and is modified to conform to the latter. The
sesamoid bones (Ossa sesamoidea) are developed along the course of tendons or in
the joint capsules at points where there is increased pressure. Two proximal
sesamoids (Ossa sesamoidea phalangis primse) occur at the flexor side of the meta-
carpo-phalangeal joint and form a pulley for the flexor tendon. The distal sesa-
moid (Os sesamoideum phalangis tertise) is similarly placed between the deep
flexor tendon and the joint between the second and third phalanx; it is absent in
the dog, which has a small sesamoid on the extensor side of the metacarpo-phalan-
geal joint, and often at the proximal interphalangeal joint also.

Numerous cases are recorded of the occurrence of supernumerary digits (hyperdactylism)
in the horse and other animals. In some pigs, on the other hand, the two chief digits are fused,,
and the condition (syndactylism) appears to be inherited.

THE BONES OF THE PELVIC LIMB

The pelvic limb (Extremitas pelvina), like the thoracic, consists of four seg-
ments, viz., the pelvic girdle, thigh, leg, and the pes; the last is subdivided into
tarsus, metatarsus, and digits.

The pelvic girdle (Cingulum extremitatis pelvinse) consists of the os coxae (or

THE BONES OF THE PELVIC LIMB 31

hip bone), which joins its fellow of the opposite side ventrally at the symphysis
pelvis, and articulates very finnlj^ with the sacrum dorsally. The two coxal bones,
together with the sacrum and the first three or more coccygeal vertebrae, constitute
the bony pelvis. The os coxae consists originally of three flat bones, the ilium,
ischium, and pubis, which meet at the acetabulum, a large cotyloid cavity with
which the head of the femur articulates. These three parts are fused before growth
is complete, but are considered separately for convenience of description. The
iliimi (Os ilium) is situated in the lateral wall of the pelvis, the pubis (Os pubis) in
the anterior part, and the ischium (Os ischii) in the posterior part of the ventral
wall.

The thigh (Femur), like the arm, contains a single long bone, the femur (or
thigh bone) (Os femoris). This articulates with the acetabulum above and the
tibia and patella below.

The skeleton of the leg (Crus) comprises three bones (Ossa cruris), viz., the
tibia, fibula, and patella. The tibia is a large, prismatic long bone which supports
the weight, and articulates distally with the tibial tarsal bone. The fibula is
situated along the lateral border of the tibia, from which it is separated by the
interosseous space of the leg. It is much more slender than the tibia and does not
articulate with the femur. In the pig and dog it has a complete shaft and two
extremities, but in the horse and ox it is much reduced and otherwise modified.
The patella (or "knee-cap") is a short bone which articulates with the trochlea of
the distal end of the femur; it is to be regarded as a large sesamoid bone intercalated
in the tendon of the quadriceps femoris muscle.

The tarsus (or "hock") consists of a group of short bones, the ossa tarsi,
numbering five to seven in the different animals. The proximal or crural row con-
sists of two bones, the tibial and fibular tarsals ; the former is situated at the tibial
side, and has a trochlea for articulation with the distal end of the tibia; the latter,
situated at the fibular side, has a process, the tuber calcis, which projects upward
and backward and constitutes a lever for the muscles which extend the hock joint.
The distal or metatarsal row consists of four bones when seven tarsal elements are
present, as in the pig and dog. They are best designated numerically as first tarsal,
second tarsal, etc. The central tarsal is interposed between the rows.

The preceding terms are anglicized abbreviations of those introduced by Gegenbaur into
comparative anatomy. The Latin names and synonyms are given in the following table:

Tibial (Os tarsi tibiale, Tt.) Astragalus or Talus

Fibular (Os tarsi fibulare, Tf.) Calcaneus or Os calcis

Central (Os tarsi centrale, Tc.) Scaphoid or Navicular

First Tarsal (Os tarsale primum, Tl) First or internal cuneiform

Second Tarsal (Os tarsale secundum, T2) Second or middle cuneiform

Third Tarsal (Os tarsale tertium, T3) Third or external cuneiform

Fourth Tarsal (Os tarsale quartum, T4) Cuboid

The metatarsal and digital bones resemble in general those of the corresponding
regions of the thoracic limb; the differential features will be noted in the special
descriptions.

THE SKELETON OF THE HORSE

The skeleton of the horse consists of 205 bones, as shown in the following table:

Vertebral column 54

Ribs 36

Sternum 1

Skull (including auditory ossicles) 34

Thoracic limbs 40

Pelvic limbs 40

205

In this enumeration the average number of coccygeal vertebrae is taken to be 18, the tem-
poral and OS coxae are not divided into parts, the usual number of carpal and tarsal elements is
taken, and the sesamoids are included.

Fig. 6. — Skeleton of Horse, with Outune of Contour of Body.
I.H., Atlas; 7.H., seventh cervical vertebra; I.R., first thoracic vertebra; 17. R., seventeenth thoracic vertebra;
I.L., first lumbar vertebra; O.L., sixth lumbar vertebra; K, sacrum; I.S., first coccygeal vertebra; 16.S., sixteenth
coccygeal vertebra; ^.i?., sixth rib; e. A'., costal cartilage; 18. R., lust rih; 1, scapula; 1', cartilage of scapula; 2, spine
of scapula; 4, humerus; 4' lateral epicondyle of humerus; 5, lateral tuberosity of humerus; 6, deltoid tuberosity;
7, shaft of ulna; 8, olecranon; 9, radius; 10, carpus; 11, accessory carpal bone; 12, metacarpus; 13, digit; 14, sternum,
14", xiphoid cartilage; 15, ilium; 16, 16', angles of ilium; 17, ischium; 18, femur (shaft) ; 19, trochanter major; 20,
patella; 21, tibia (shaft); 21', lateral condyle of tibia; 2.3, fibula; 22, tarsus; 24, tuber calcis; 25, metatarsus;
26, digit; 27, trochanter minor of femur; 28, trochanter tertius of femur. (After EUenberger-Baum, Anat. fiir
Kiinstler.)

THE VERTEBRAL COLUMN

The Vertebral Column

The vertebral formula of the horse is C7Ti8L6S5Cyi5-2i.

Anterior artic-
ular process
of axis
Spinous proc-
ess of axis

Transverse
process of axis

Fig. 7. — Cervical Vertebrae of Horse; Dorsal View.
a, Articular processes; b, transverse processes; 1,
dorsal arch of atlas; 2, w-ing of atlas; 3, intervertebral
foramen of atlas; 4, alar foramen of atlas; 6, foramen
transversarium of atlas; 6, dens of axis; 7, intervertebral
foramen of axis; 8, foramen transversarium of axis; 9,
spinous processes.

Fig. 8. — Cervical Vertebr.e of Horse; Ventral
View.
a. Transverse processes; 1, ventral tubercle of atlas;

3, anterior articular cavities of atlas; S, fossa atlantis;

4, alar foramen; 6, foramen transversarium; 6, ventral

THE SKELETON OF THE HORSE

Head

Fig. 9. — Sixth Cervical Vertebra of Horse; Anterior View.

THE CERVICAL VERTEBRA

The cervical vertebrae (Vertebrae cervicales) are seven in number.
The first and second cervical vertebrae are highly modified in conformity with

the special functions of support
and movements of the head.
The sixth and seventh present
special characters, but do not
differ greatly from the tj'pe.
With the exception of the first,
they are quadrangular, mass-
ive, and longer than the ver-
tebrae of other regions; they
decrease in length from the
second to the last. The third,
fourth, and fifth have the fol-
lowing characters:

1. The body is long as
compared with those of other
vertebrae. The ventral surface
presents a median ventral
spine, which becomes more
prominent as it is traced back-
ward, and is tuberculate at its
posterior end ; it separates two
concave areas. The dorsal sur-
face has a flat central area which is narrow in the middle of the vertebrae, and ^\^de
at either end ; it gives attachment to the dorsal longitudinal ligament. On either
side of this area there is a groove which lodges the longitudinal spinal vein. These
lateral grooves are connected about the middle of the surface by a transverse furrow,
in which there are several for-
amina through which veins
emerge from the spongy sub-
stance of the body. The an-
terior extremity or head (Ca-
put vertebrae) has an oval
articular surface which faces
forward and downward; it is
strongly convex, and wider
above than below. The pos-
terior extremity is larger and
has a nearly circular cotyloid
cavity (Fossa vertebrae).

2. The arch is large and
strong. It is perforated on
either side by a foramen which
communicates with the for-
amen trans versarium. The
vertebral notches are large.

3. The articular processes
are large. Their articular sur-
faces are extensive, oval in outline, and slightl}^ concave; the anterior ones are
directed dorso-medially; the posterior, ventro-laterally. The remaining surface is
mainly roughened for ligamentous and muscular attachment. A crest connects

— Spinous process

Vertebral

foramen Articular

I process

PlBff^ — ' f

jii iri,

fW>-— -^ A

/ 1 m \

L|^jL^

^-' Trans-
H^ perse

process

^^^^^^^

Ventral spine
Seventh Cervical Vertebra of Horse;

Anterior View

THE ATLAS

the articular processes of the same side on the fourth and fifth; on the third it does
not reach the anterior process.

4. The transverse processes are large and plate-like. Each arises by two
roots, one from the arch and one from the body; between these is the foramen
transversariiun, through which the vertebral vessels and a nerve pass. The aggre-
gate of these foramina constitutes the canalis transversarius. The process divides
laterally into anterior and posterior branches, which are thickened and rough for
muscular attachment.

5. The spinous process has the form of a low crest (Crista spinosa), which
widens behind, and is connected by ridges with the posterior articular processes.

The sixth cervical vertebra has the following distinctive features: It is shorter
and wider than the fifth. The arch is large, especially posteriorly. The posterior
articular processes are shorter, thicker, and further apart; each is connected with
the corresponding anterior one by a thick ridge. The spinous process is less rudi-
mentary; it is half an inch or more (ca. 1.5 cm.) in height. The transverse proc-
esses have three branches; the third part is a thick, almost sagittal plate, which
forms with its fellow and the body a wide ventral groove; the other branches
correspond to those of the typical vertebrae, but are short and thicker.^ The fora-
men transversarium is large; below its posterior end there is a fossa. The
ventral spine is small and is less prominent posteriorly.

The seventh cervical vertebra is readily distinguished by the following charac-
ters : It is shorter and wider than the others. The body is flattened dorso-ventrally
and wide, especially behind; here it has a facet on each side for articulation with
part of the head of the first rib. The arch and its notches are large. The anterior
articular processes are wider and longer than the posterior pair. The spinous
process is an inch or more (ca. 3 cm.)
in height. The transverse process is
undivided, and has no foramen trans-
versarium.2 The ventral crest is re-
placed by a pair of tubercles.

The Atlas

This vertebra is decidedly atypi-
cal in form and structure. The body
and spinous process are absent. It
has the form of a strong ring, from
which two curved plates, the wings,
project laterally. The ring incloses a
very large vertebral foramen, and con-
sists of two lateral masses connected
by dorsal and ventral arches.

The lateral masses (Massse later-
ales) present two deep oval anterior
articular cavities (Foveas articulares

craniales) which receive the occipital condyles; they are separated by a wide notch
above and a narrow one below. The lateral margin is also notched, and a trian-
gular non-articular depression cuts into the medial part of each cavity. The pos-
terior articular surfaces (Facies articulares caudales) are somewhat saddle-shaped;
they are confluent on the ventral arch, but are widely separated dorsally, and do
not conform in shape to the corresponding surfaces of the axis.

1 The third branch of the transverse process and the fossa are sometimes absent or reduced
on one side.

2 In some specimens a large foramen transversarium is present on one side or (rarely) on
both sides.

Fig.

Atlas of Horse, Dorsal, View after Removal
OF Dorsal Arch.
1, Anterior articular cavities; 2, 2', posterior articular
surfaces; 3, articular surface of ventral arch for dens of
axis; 4, transverse ridge; 5, 5', alar foramina; 6, 6', foram-
ina transversaria.

'36 THE SKELETON OF THE HORSE

The dorsal arch (Arcus dorsalis) presents a median dorsal tubercle (Tuber-
culum dorsale) and is concave ventrally. It is perforated on either side near its
anterior margin by the intervertebral foramen (Foramen invertebrate). The an-
terior border is deeply notched, and the posterior is thin and concave.

The ventral arch (Arcus ventrahs) is thicker, narrower, and less curved than
the dorsal. On its lower surface is the ventral tubercle (Tuberculum ventrale),
into which the terminal tendon of the longus colli muscle is inserted. The upper
face has posteriorly a transversely concave articular surface, the fovea dentis, on
which the dens or odontoid process of the axis rests. In front of this is a transverse
rough excavation and a ridge for the attachment of the ligamentum dentis.

The wings or alae are modified transverse processes. They are extensive
curved plates which project ventro-laterally and backward from the lateral masses.
The dorsal surface is concave. Between the ventral aspect of the wing and the
lateral mass is a cavity, the fossa atlantis; in this there is a foramen which opens
into the vertebral canal. The border is thick and rough; its position can be recog-
nized in the living animal. Two foramina perforate each Aving. The anterior one,
the foramen alare, is connected with the intervertebral foramen by a short groove.
The posterior one is the foramen transversariimi.

Development. — The atlas ossifies from four centers, two for the ventral arch,
and one on either side for each lateral mass, wing, and half of the dorsal arch. At
birth the bone consists of three pieces — the ventral arch and two lateral parts,
which are separated by a layer of cartilage in the dorsal median line and by two
ventro-lateral layers. These parts are usually fused at about six months.

The Axis

The axis (Axis s. Epistropheus) is the longest of the vertebrae, and is character-
ized by the presence of the dens or odontoid process, which projects from the an-
terior part of the body.

The anterior extremity of the body presents centrally the dens or odontoid

Spinous process

Dens

Anterior articular process

Posterior articular process

Trajisverse process

Body

Fig. 12. — Axis of Horse, Left View.
1, Arch; 2, intervertebral foramen; 3, notch; 4. foramen transversarium.

process (Dens axis) ; this has a convex articular surface ventrally for articulation
with the ventral arch of the atlas, and two rough depressions for the attachment of
the ligamentum dentis dorsally. Flanking this on either side are the modified
anterioi articular processes, which have saddle-shaped articular surfaces confluent

THE THORACIC VERTEBRA

ventrally with that of the dens. The posterior extremity has the usual cavity.
The ventral spine resembles that of the typical vertebrae.

The arch presents in the young subject a notch on each side of its anterior
border; this is converted into a foramen by a ligament which ossifies later. The
posterior border has the usual notches.

The posterior articular processes are typical.

The transverse processes are small, single, and project backward. The
foramen transversariiun is small.

The spinous process is very large and strong. Its free border is rough, thickens
posteriorly, and is continued to the articular processes by two ridges. The lateral
surfaces are concave and rough for muscular attachment.

Development. — The axis has six or seven centers of ossification. In addition
to the usual five, one or two appear for the dens, which is regarded as the displaced
body of the atlas. A nucleus behind the dens, which remains distinct to three or
four years of age, is considered to be the head of the axis.

Spinous
process

THE THORACIC VERTEBRA
The thoracic vertebrae (Vertebrae thoracales) are usually eighteen in number in
the horse, but there are sometimes nineteen, rarely seventeen. As regional char-
acters we note the surfaces for articulation with the ribs and the length and form of
the spinous processes. Those in the
middle of the series are the most
typical and present the following fea-
tures:

1. The bodies are short and con-
stricted in the middle. The ends are
expanded and have articular surfaces
which are not strongly curved; the an-
terior surface is convex, the posterior
concave. On the upper part of each
side are anterior and posterior costal
facets (Fovea costalis cranialis, cau-
dalis), which, with those of adjacent
vertebrae and the intervening fibro-car-
tilages, form sockets for the heads of
the ribs.

2. The arches are small. Their
posterior notches are relatively large
and are often converted into foram-
ina.

3. The articular processes are
small. The anterior processes are in
fact represented only by two oval facets
on the anterior part of the arch which
face almost directly upward. The pos-
terior processes spring from the base of the spinous process; their facets face
almost directly downward.

4. The transverse processes are short, thick, and tuberous at the free end.
Each has a facet (Fovea transversaria) for articulation with the tubercle of the
rib which has the same serial number.

5. The spinous process is large, narrow, and slopes upward and backward.
The anterior border is thin, the posterior wider and furrowed. The summit is
expanded and rough.

Facet for tubercle
of rib

Facet for
head
of rib

Body

Fig. 13. — Seventh Thoracic Vertebra of Horse, An-
terior View.

THE SKELETON OF THE HORSE

The first thoracic vertebra has the following specific characters: The body is
wide and flattened dorso-ventrally. In front it has a head like the cervical verte-

Spinnus process
Articular processes

Arch

Facet for tubercle of first rib A^ ~-^__^ Transverse process

Facet for head of second rib ""'^fl^'^ Body
Fig. 14. — First Thoracic Vertebra of Horse, Posterior View.

brae, and behind a cavity somewhat deeper than any other thoracic vertebra. Two
large costal facets are found on either side, and a well-marked spine ventrallj".

Fir., l.'i. — T,\sT Three THORArir ^■ERTEBR.E of Horse, [.eft \'iew.

1, Body; 2, 2, facets for head of rib; S, facet for tubercle of rib; 4, J/ , articular processes; 5, intervertebral foramen;

6, mammillary process; 7, spinous process.

The arch is large and strong, and has large notches. The articular processes are
much larger than those of other thoracic vertebrae, and resemble a good deal those
of the seventh cervical. The transverse processes are short and thick, and each

THE LUMBAR VERTEBRA 39

has on its ventral aspect a large concave facet for articulation with the tubercle of
the first rib. The spinous process is curved backward and tapers to a point. Its
length is usually about three or four inches (ca. 8 to 10 cm.). This vertebra may be
mistaken at first glance for the last cervical, but is promptly identified by the three
costal facets on each side and the length of the spine.

The last thoracic vertebra is distinguished by the absence of the posterior pair
of costal facets, and the confluence of the anterior pair with those on the transverse
processes.

The serial position of others may be determined at least approximately by the
following data: (1) The bodies graduallj^ diminish in length and width to the
middle of the region and then increase slightly. Their costal facets become smaller
and less concave from first to last. The ventral crest is distinct on three or four
vertebrae at either end of the region. (2) The transverse processes diminish in
size and are placed lower down as they are traced backward. Their costal facets
become smaller and lower in position; on the last (and sometimes on its predecessor
also) it fuses with the costal facet of the body. The upper non-articular part of
the process gradually becomes more sharply defined, and in the last four or five
forms a distinct mammillary process. (3) The spinous processes increase in length
to the third and fourth, and then gradually diminish to the fifteenth, beyond which
they have about the same length. The backward inclination is most pronounced
in the second, the sixteenth is vertical, and the last two are directed a little forward.
The longest spines {i. e., those of the withers) are the thickest and have expanded
summits which remain more or less cartilaginous; the others are more plate-like,
and are surmounted by a thick lip. The second spine is more than twice as large
as the first. The summits of the fourth and fifth usually form the highest point
of the withers.

Development. — There are six or seven centers of ossification, three for the
body, two for the arch, and one for the spinous process; some of the latter have an
additional center for the summit.

THE LUMBAR VERTEBRJE

The lumbar vertebrae (Vertebrae lumbales) are usually six in number in the
horse. They are characterized by the size and form of their transverse processes.

The bodies of the first three are semi-elliptical on cross-section, and present a
distinct ventral crest. From the fourth backward they become wider and flatter
and the ventral crest subsides.

The arches of the first three are about equal in size and similar to that of the
last thoracic; behind this they increase in breadth and height. The posterior
notches are much deeper than the anterior ones.

The anterior articular processes are fused with the mammillary processes, and
present dorsally concave surfaces for articulation with the posterior pair of the
preceding vertebra. The posterior articular processes project distinctly from the
arch at the base of the spinous process, and have ventrally convex articular surfaces,
which fit into the concave surfaces of the anterior pair of the next vertebra.

The transverse processes are elongated plates, flattened dorso- ventrally, which
project outward and usually curve slightly downward; their length increases to
the third or fourth, and then diminishes to the last, which is the shortest. The
first one or two usually curve somewhat backward, the last two decidedly forward.
Those of the fifth have an oval concave facet on the medial part of the posterior
border for articulation with the sixth process; the latter has a corresponding con-
vex facet on the anterior border, and a larger concave surface on the posterior border
for articulation with the wing of the sacrum. Sometimes the fifth process has a
small surface for articulation with the fourth. The medial part of the sixth process

THE SKELETON OF THE HORSE

is tliick, the lateral part thinner, narrower, and curved forward. The medial part
of the fifth is also somewhat thickened. Medial to the articular surfaces the edges
of the transverse processes are cut into by notches, which form foramina by apposi-
tion with each other and the sacrum.

The spinous processes resemble those of the last two thoracic vertebrae.

Spinous process

Mammilhinj process
Articular process

\r f ■} ■ Transverse process

Ventral spine
Fig. 16. — Second Lumbar Vektebra of Horse; Posterior View.

They are usually about equal in height, but minor differences are common, and the
width diminishes in the last three.

Development. — This is similar to that of the thoracic vertebrae. The extremi-
ties of the transverse processes remain cartilaginous for some time after ossification
is otherwise complete.

The transverse processes of this region are considered equivalent to the proper transverse
process + the costal element, and hence the distinctive term processus lateralis (s. costarius)

Spinous process

Vertebral foramen
> Articular processes

Transverse process

Notch

Body

Articular surface for
wing of sacrum
-Last Lumbar Vertebra op Horse; Posterior View.

has been proposed. The occurrence of a rib in connection with the transverse process of the first
lumbar vertebra is common. Reduction of the number to five has been observed frequently, and
may or may not be compensated by an additional thoracic vertebra. Very few cases are recorded
of seven lumbar vertebra^ — especially with the normal thoracic number. An anomalous vertebra
with mixed thoracic and lumbar characters sometimes occurs at the junction of the two regions.

THE SACRUM

The sacrum (Os sacrum) is formed by the fusion of five vertebrae, and is con-
veniently described as a single bone. It is triangular in form and is wedged in
between the ilia, with which it articulates very firmly on each side. Its long axis
is gently curved and slightly oblique, so that the posterior end is a little higher
than the anterior. It presents two surfaces, two borders, a base, and an apex.

The dorsal surface (Facies dorsalis) presents centrally the five sacral spines
(Processus spinosi), which are directed upward and backward, and have (with the
exception of the first) tuberous summits which are sometimes bifid.

Wing

Transverse process

Fig. 18. — Sacrum of Horse; Dorso-lateral View.
I-V, Spinous processes; I-4, dorsal sacral foramina; 5, 0', articular processes; 6, surfaces of wings for articulation
with transverse processes of last lumbar vertebra; 7, body of first sacral vertebra. Arrows point into sacral
canal.

The first spine is relatively thin and narrow, and is not so high as the sacral angle of the
ilium. The second is the longest and highest, and the length and height diminish to the last.
The bases of the spines are often fused in old subjects.

On either side of the spines there is a groove, in which are the four dorsal sacral
foramina (Foramina sacralia dorsalia); the dorsal branches of the sacral nerves
emerge through them.

The pelvic surface (Facies pelvina) is concave in its length, wide in front,
narrow behind. The curvature is variable and is more pronounced in the mare
than in the stallion. It is marked by four more or less distinct transverse lines
(Lineae transversse) , which indicate the demarcation of the bodies of the vertebrae.
At the ends of these lines are the ventral sacral foramuia (Foramina sacralia ven-

THE SKELETON OF THE HORSE

tralia), which are larger than the dorsal series and diminish in size from first to
last; they transmit the ventral divisions of the sacral nerves.

The dorsal and ventral foramina communicate with the sacral canal and are
together equivalent to the usual intervertebral foramina.

The lateral borders are rough, thick in front, thin behind.

The base (Basis ossis sacri) is directed forward, and is relatively very wide.
It presents centrally the body of the first sacral segment, which is wide transversely,
flattened dorso-ventrally, and has a rounded surface which articulates with the
last lumbar vertebra through the medium of an intervertebral fibro-cartilage.
The ventral margin projects slightly, forming the promontory (Promontorium) . On

Fig. 19. — Sacrum of Horse; Ventral View.
J- F, Bodies of original five vertebrse, marked off by transverse lines; /-4, ventral sacral foramina; 5, articular
surface of body of first vertebra; 6, 6, notches; 7, 7, surfaces of wings for articulation with transverse processes of last
lumbar vertebra; S, S, wings; 9, auricular surface; 10, lateral border; 11, transverse process; 12, posterior orifice
of sacral canal; 13, last spinous process.

either side of the body there is a smooth notch, which, with one on the last lumbar
vertebra, forms a large foramen for the passage of the ventral branch of the last
lumbar nerve. Above the body is the entrance to the sacral canal, flanked by a
pair of articular processes, which project upward and forward from the arch, and
have concave surfaces medially for articulation with those of the last Imnbar
vertebra. Lateral to each of these is a smooth notch which is converted into a
foramen by apposition with the last lumbar vertebra. The lateral parts of the base,
the alae or wings (Alae sacrales), are strong prismatic masses with pointed ends.
Each has in front a large, oval, slightly convex surface for articulation with the
transverse process of the last lumbar vertebra. Posteriorly there is an elongated
oval area which faces dorso-laterally; this is the auricular surface (Facies auricu-

THE COCCYGEAL VERTEBRA 43

laris), which articulates with the ihum; it is slightly concave in its length, and
somewhat rough and irregular. The rest of the dorsal surface of the wing is rough-
ened for ligamentous attachment, while the ventral surface is smooth.

The apex (Apex ossis sacri) is the posterior aspect of the last sacral vertebra
and is quite small. It presents the elliptical flattened surface of the body, above
which is the triangular posterior opening of the sacral canal, surmounted by the
last sacral spine. There is a pair of narrow notches between the arch and body,
above which rudiments of articular processes may occur.

The name sacral canal (Canalis sacralis) is applied to that part of the vertebral
canal which traverses the sacrum. Its anterior part is large and has the form of
a triangle with the angles rounded off; its width is nearly tAvice its height. Traced
backward it is seen to diminish in size rapidly, and the posterior opening is small
and triangular.

The term lateral part (Pars lateralis) designates the portion lateral to the
foramina, which results from the fusion of the transverse processes.

Development. — The several sacral vertebrae ossify in the typical manner.
Separate centers for costal elements in the lateral parts have not yet been found in
the domesticated animals. Fusion begins in front, and is usually not complete
till adult age.i The lateral parts unite before the bodies. It is rather curious
that the epiphyseal plates of adjacent segments unite with each other before they
fuse with the main portion of the bodies.

THE COCCYGEAL VERTEBRA

The coccygeal vertebrae (Vertebrae coccygeae) vary considerably in number, but
eighteen may be taken as an average. From first to last they become reduced
in size and, with the exception of a few at the beginning of the series, consist of

] 'crtebral foramen Vertebral foramen

Arch
A rch

Transverse process

Spinous process Spinous process

Vertebra

Transverse proc-

Groove
Body Body

Fig. 20. — First CoccygEAL Vertebra of Horse; Fig. 21. — Second Coccygeal Vertebra of Horse;

View. Posterior View.

Leader to arch points to rudimentary articular

bodies only. The first three have bodies which are somewhat flattened dorso-
ventrally, constricted in the middle, and have at the ends convex, elliptical, artic-
ular surfaces. The ventral surface has a median groove (Sulcus vasculosus) for
the coccygeal artery. The arch is small and triangular; it is formed of two flat
plates which are prolonged to form a short spinous process with a thickened and
often double summit. The anterior notches are absent. Functional articular
processes are not present, but small rudiments of the anterior pair commonly occur.
The transverse processes are relatively large plates which project horizontally
outward. Further back the arch becomes incomplete dorsally, and soon disap-
pears; the transverse processes gradually fade out, and the vertebrae are reduced
to cylindrical rods of diminishing size. The last one has a pointed end.

^ It is not rare to find fusion of some of the bodies incomplete even in adult subjects.

THE SKELETON OF THE HORSE

Variations. — The number is said by good observers to vary between fourteen and twenty-
one. In old age the first is often fused with the sacrum, and sometimes with the second. The
arch of the third may be open.

THE VERTEBRAL COLUMN AS A WHOLE

In the mid-dorsal line is the series of spinous processes, which are low ridges
in the cervical region with the exception of the second and seventh, reach their
maximum height at the fourth and fifth thoracic vertebrae, and diminish to the
fifteenth or sixteenth thoracic. Behind this they are about equal in height as far
as the last lumbar and first sacral, which are somewhat lower. The second sacral
spine is about as high as the middle luml^ar; behind this they diminish rather
rapidly in height and fade out about the third coccygeal. Their inclination back-
ward is most decided at the second thoracic and diminishes from the sixth or seventh
to the sixteenth thoracic, which is vertical and is termed the anticlinal or dia-
phragmatic vertebra. Behind this they are inclined a little forward until the
sacrum is reached; here there is an abrupt change to the backward inclination, so
that a considerable interspinous angle is formed.

On either side of the spinous processes is a vertebral groove which contains the
deep muscles of the spine. The floor of the groove is formed by the arches and
articular processes. It is wide in the neck and narrows progressively in the back.

Viewed from the side, the column presents a series of curves. When the head
and neck are in the ordinary neutral position, the anterior part of the cervical spine
forms a gentle curve, concave ventrally. The posterior cervical and first thoracic
vertebrae form a more pronounced curve in the opposite direction. At the junction
of the cervical and thoracic regions there is a marked change of direction, forming a
ventral projection or angle. At the second thoracic vertebra a gentle curve, con-
cave ventrally, begins. This is continued to the lumbo-sacral junction, where
there is a change of direction, and hence a promontory. The sacrum has a variable,
but never very pronounced, ventral concave curvature, which is continued in a
much accentuated form in the coccygeal region. It should be noted that a line
through the summits of the spines does not correspond to these curves formed by
the bodies.

The vertebral canal corresponds in its curvature to that of the bodies. Its
caliber varies greatly at different points. The greatest diameter is in the atlas,
where it contains the dens of the axis in addition to the spinal cord, and provision
must be made for extensive movement. It is very much smaller in the axis. It
widens considerably at the junction of the cervical and thoracic regions to accom-
modate the cervical enlargement of the spinal cord. Beyond this it diminishes,
and is smaller in the middle of the back than at any preceding point ; this is corre-
lated with the small size of the spinal cord and the very limited movement of the
spine here. Beyond the middle of the lumbar region it again enlarges considerably
to contain the lumbar enlargement of the spinal cord. The caliber diminishes very
rapidly from the second sacral segment backward, and the canal ceases to be com-
plete at the fourth coccygeal vertebra.

The transverse and vertical diameters of the vertebral canal at various points are given
in the annexed table. The measurements were made on a horse of medium size; they represent
the maximum width and height in the middle of the vertebra and are expressed in centimeters.

Vertebra

TIO

5.2
4.2

2.6
2.5

2.6
2.1

3.5
2.5

2.3
1.7

2.4
l.S

4.0
2.5

4.0
2.1

1.8

Vertical

1.5

The articular processes are very large and wide apart in the neck, greatly

THE RIBS 45

reduced and much closer together in the back, larger and interlocking in the lumbar
region.

The transverse processes are large and outstanding in the neck, where they
form the lateral boundary of a ventral groove occupied by the longus colli muscle.
In the back they are short and stout, and are characterized by the facets for the
tubercles of the ribs. On the first thoracic vertebra this facet is large, deeply con-
cave, and situated almost directly outward from the cavity for the head of the rib;
traced backward it becomes smaller and flatter, and gradually comes to lie behind
the cavity for the head of the rib, with which it is fused on the last and often also on
the next to the last thoracic vertebra. The processes in the lumbar region have a
characteristic elongated plate-like form. In the sacral region they are fused to
form the wings and lateral parts of the sacrum. In the coccygeal region they are
at first of considerable size relatively, but undergo rapid reduction, and disappear
at the fifth or sixth vertebra.

The cavities for the heads of the ribs diminish progressively in size and depth
from first to last.

The mammillary processes are usually distinct on the fourteenth to the seven-
teenth thoracic vertebrae. In front of these they blend with the transverse, behind
with the anterior articular, processes.

The length of the vertebral column (including the intervertebral fibro-cartilages) in a horse
of medium size is about nine feet (ca. 2.7 meters). The relative lengths of the various regions ap-
pear to vary most in the neck and back. The following average lengths of the several regions
were obtained by measurement of several subjects: Cervical, 70 cm.; thoracic, 86 cm.; lumbar,
34 cm.; sacral, 20 cm.; coccygeal, 60 cm. The percentage values are approximately 26, 32, 12.5
7.5, 22.

The Ribs

There are usually eighteen pairs of ribs in the horse, but a nineteenth rib on
one side or both is not at all rare. Eight are sternal ribs, the remainder asternal.
Ribs from different parts of the series vary much in length, curvature, and other
characters. We will therefore consider as a type a rib from the middle of the series
first, and afterward note the chief serial differences; such a rib has the following
characters :

The shaft or body (Corpus costae) is elongated, relatively very narrow, and
strongly curved; the curvature is most pronounced in the dorsal third, and the
ventral part is twisted and inclined inward, so that when a rib is laid with its lateral
surface on the table, the sternal end is raised. The lateral surface is convex in
its length and also transversely; its anterior part is, however, grooved longitudin-
ally. A distinct angle, i. e., a point at which the curve of the rib changes rather
suddenly, as in man, can scarcely be said to exist in the horse. The term is some-
times applied, however, to a corresponding rough elevation which gives attachment
to the longissimus muscle. The medial surface is smooth, concave in its length,
and rounded from side to side; the costal groove (Sulcus costse), situated posteriorly,
is very distinct above and fades out about the middle; it contains the intercostal
vein. The anterior border is concave, the posterior convex.

The vertebral extremity (Extremitas vertebralis) consists of the head, neck,
and tubercle. The head (Capitulum costse) has an articular surface (Facies
articularis capituli costse) which is composed of two convex facets, anterior and
posterior, separated by a groove (Sulcus capituli) for the attachment of the con-
jugal ligament. It articulates with the cavity formed by facets on the bodies of
two adjacent thoracic vertebrae and the intervertebral fibro-cartilage. The neck
(Collum costse) is roughened above and in front. The tubercle (Tuberculum costse)
is placed above and behind the junction of neck and shaft; it has an oval surface

THE SKELETON OF THE HORSE

(Facies articularis tuberculi costae) for articulation with the transverse process of
the corresponding thoracic vertebra.

The sternal extremity (Extremitas sternalis) is slightly enlarged, and is united
with the costal cartilage.

The first rib is easily distinguished. It is shortest and the shaft widens greatly
toward the sternal end. At the lower part of the anterior border there is a smooth.

Tubercle

^ Costal groove

Head Neck Tubercle

Groove

Head

Anterior border

Anterior border -

Sternal extremity
Fig. 22. — Left Eighth Rib of Horse; Lat-

Costo-
chondral
junction

Sternal extremity of costal cartilage

Fig. 23. — Right Eighth Rib and Costal Cartilage of
Horse; Medial View.

impression where the brachial vein curves around it; above this there is commonly
a small tubercle (Tuberculum scaleni) which indicates the lower limit of the in-
sertion of the scalenus muscle. The costal groove is absent. The head is large and
has two facets of unecjual extent, which meet at an acute angle in front ; the smaller
one faces forward antl articulates with the last cervical vertebra; the larger one is
directed medially and articulates with the first thoracic vertebra. The neck is
thick and very short. The tubercle is larger than that of any other rib and has an

THE COSTAL CARTILAGES

Tubercle

extensive articular surface which is convex in its length. The sternal end is larger
than that of any other rib; it is thick and very wide, and is turned a little forward.

The last rib is the most slender and regularly curved. It is usually but little
longer than the second. The facet on the tubercle is confluent with that of the head.
(This feature, however, is common on the seventeenth also, and may occur on the
sixteenth.)

The serial position of the other ribs may be determined approximately by the fol-
lowing considerations : The length increases from the first to the tenth and eleventh
and then diminishes. The width increases somewhat to the sixth and then diminishes.
The anterior border is thin and sharp from the
second to the eighth, and behind this becomes thick
and rounded. The groove of the lateral surface is
distinct on the fourth to the eighth inclusive. The
curvature increases in degree rapidly from the second
to the seventh, remains a])Out the same to the six-
teenth, and then decreases very noticeably. In re-
gard to dorso-ventral direction, the first rib inclines
a little forward, the second is about vertical, while
behind this they slope l)ackward in increasing de-
gree, so that a transverse plane tangent to the ventral
ends of the last pair cuts the third lumbar vertebra.
The head and tubercle diminish in size from first to
last. Their relative positions change, in that the
tubercle of the first rib is almost directly lateral to
the head, while further back it gradually comes to
lie behind it. The neck is longest on the longest
ribs, and is absent on the last two or three. A
costo-transverse foramen (Foramen costo-transver-
sarium) is formed between the neck and the trans-
verse process.

Development. — The ribs ossify in cartilage from
three centers, one each for the shaft, head, and
tul)ercle; the third center is absent in some of the
posterior ribs.

Cartilage

-Left First Rib of Horse;
Medial View.

Variations. — A nineteenth rib on one side or both is not
at all rare. It is usually imperfectly developed and quite vari- j-j^ 24.
able. In many cases it is a mere strip of cartilage connected
by ligament with the first lumbar transverse process; in other
cases it is well developed, and may be fused with the process;

in others again it is connected with a vertebra which may be thoracic or lumbar or ambiguous
in character. It is commonly floating, but may be attached to the eighteenth costal cartilage.
Reduction in number is uncommon. In rare cases the first rib is imperfectly developed and does
not reach to the sternum. Partial fusion of adjacent ribs and other anomalies occur.

THE COSTAL CARTILAGES

The first costal cartilage is an inch or more (2.5 to 3 cm.) in length. The
dorsal end is very wide and thick. The sternal end is small. The two articulate
with each other as well as with the sternum. The cartilages of the other sternal
ribs increase progressively in length and become more rounded. The sternal end
is enlarged and has an elliptical convex facet for articulation with the sternum.
The cartilages of the asternal ribs are long, slender, and pointed. The ninth is
very firmly attached to the eighth; it and the next two are the longest and behind
this they diminish progressively in size. The cartilages of the asternal ribs overlap
and are attached to each other by elastic tissue, forming the costal arch (Arcus

THE SKELETON OF THE HORSE

costarum). Except in the case of the first, the cartilage does not continue the
direction of the rib, but forms with the latter an angle which is open in front, and
increases from second to last. More or less extensive ossification is to be regarded
as a normal occurrence, especially in the cartilages of the sternal ribs.

Costal
carlilages"^^^^

Cariniform
cartilage

Ribs

The Sternum

The sternum of the horse is shaped somewhat like a canoe; it is compressed

laterally, except in its posterior part, which is flattened dorso-ventrally. It is

inclined obliquely so that the posterior end
is about six to eight inches (15 to 20 cm.)
lower than the anterior.

The dorsal surface (Facies dorsalis) has
the form of a very narrow isosceles triangle
with the apex in front. It is concave longi-
tudinally, flattened transversely.

The lateral surfaces (Facies laterales)
are convex above, slightly concave below, and
diminish in extent behind. Each presents on
its upper part seven costal cavities (Foveas
costales), with which the sternal ends of the
second to the eighth costal cartilages inclu-
sive articulate. These cavities are situated
in series at the intersternebral junctions.
The first four are elliptical in outline with
the long diameter vertical, and are sepa-
rated by considerable regular intervals.
The others are progressively smaller, more
circular, and closer together. The area

below these cavities gives attachment to the pectoral muscles.

The dorso-lateral borders separate the dorsal and lateral surfaces. They give

attachment to the lateral branches of the sternal ligament.

The ventral border forms the prominent keel-like crest of the sternum (Crista

sterni) which may be felt in the living animal; it fades out behind.

Xiphoid cartilage

Fig. 25. — Sternum and Costal Cartilages of
Horse; Ventral View. (After Ellenberger-
Baum, Anat. f. Kiinstler.)

yi/rarinJfor"l

r a. I

Fig. 26. — Sternum of Horse; Lateral View.
The sternebrae are designated by Roman numerals and the costal facets by ordinary figu

The anterior extremity or manubrium sterni^ can be distinctly felt in the
central furrow of the breast. It consists largely of a lal;erally compressed cartil-
aginous prolongation, commonly called the cariniform cartilage. Its lateral sur-
faces are flat and furnish attachment to muscles of the breast and neck. The

^ The manubrium sterni of man is equivalent, strictly speaking, to the cariniform cartilage
-h the first osseous segment of the horse.

THE THORAX — THE OCCIPITAL BONE

ventral border is rounded, and is continued backward on the body of the bone.
The dorsal border is concave and has an articular cavity for the first pair of costal
cartilages.

The posterior extremity is formed by the xiphoid cartilage (Processus xiphoideus).
This is a thin plate, connected in front with the last bony segment by a relatively
thick, narrow neck, and expanding in nearly circular form behind and laterally.
Its dorsal surface is concave, and gives attachment to the diaphragm. The ventral
surface is convex and furnishes attachment to the transversus abdominis and the
linea alba. The free margin is very thin.

Development. — At birth the sternum of the horse consists of seven bony seg-
ments termed sternebrse, which are united by in-
tersternebral cartilages. The last two sternebra}
fuse in the second month, but the others do not
usually unite completely even in old age. The
sternebrse consist of very vascular spongy bone
covered by a very thin layer of compact sub-
stance. The adult sternum thus consists to a /v-^IP^ Jil^ ^- First
very considerable extent of persisting cartilage, w .,« ^^"'^fc.^vl thoracic

viz., the intersternebral cartilages, the ventral
keel, and the extremities; in old age these under-
go partial ossification.

THE THORAX

The bony thorax of the horse is remarkably
compressed laterally in its anterior part, but
widens greatly behind. The anterior aperture
(Apertura thoracis cranialis) is oval and very
narrow below; in a horse of medium size its
greatest width is about 4 inches (10 cm.), and its
height 7 to 8 inches (ca. 18-20 cm.). The ventral
wall or floor is about 16 inches (40 cm.) long, and
the dorsal wall or roof about 38 to 40 inches
(95-100 cm.) long. The height from the last seg-
ment of the sternum to the seventh or eighth
thoracic vertebra is about twice that of the anterior
aperture; this is due to the obliquity and diver-
gence of the roof and floor. The greatest width of
the posterior aperture is about 20 to 24 inches

(50-60 cm.). The intercostal spaces (Spatia intercostalia) increase in width from
the first to the seventh or eighth, and then diminish. Their average width is
about I'j/i to 13^ inches (3-3.5 cm.).

vertebra

First rib

Cariniform
cartilage of
sternum

Fig. 27. — Anterior Aperture of Tho-
rax OF Horse. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)

The Skull

(A) BONES OF THE CRANroM
The bones of the cranium (Ossa cranii) are the occipital, sphenoid, ethmoid,
interparietal, parietal, frontal, and temporal. The first three are single, the others
paired.

The Occipital Bone

The occipital bone (Os occipitale) is situated at the posterior part of the era-
oium, of which it forms the posterior wall and part of the ventral wall or base.^
1 The long axis of the skull is considered to be horizontal in these descriptions.

THE SKELETON OF THE HORSE

Its lower part is perforated centrally by a large, almost circular opening, the
foramen magnum (Foramen occipitale magnum), at which the cranial cavity and
vertebral canal join. The foramen is bounded laterally and dorsally by the lateral
parts of the bone, and ventrally by the basilar part. Above the lateral parts —
but not entering into the formation of the foramen magnum — is the squamous' part.

The lateral parts (Partes laterales)^ bear the occipital condyles (C'ondyli oc-
cipitales), which articulate with the atlas. The condyles are obliquely placed,
wide apart dorsally, and separated ventrally by a small interval (Incisura inter-
condyloidea). The articular surface is curvecl so sharply in the dorso- ventral

Occipital Parietal Squamous temporal

Fig. 2S. — Skull of Horse, Right View.
1, Occipital condyle; 2, paramastoid process; 3, mastoid process; 4> posterior process of squamous temporal bone;
6, external acoustic process; 6, zygomatic process of temporal bone; 7, postglenoid process; 8, glenoid cavity of squamous
temporal bone; 9, condyle of same; 10, supraorbital process of frontal bone; 11, temporal part of frontal bone; 12,
orbital part of frontal bone; /5, fossa sacci lacrimalis; 74, orbital surface of lacrimal bone; 75, lacrimal tubercle; 16,
zygomatic process of malar bone; 77, maxillary tuberosity; ZS, facial crest; 79, infraorbital foramen; ^0, naso-maxil-
lary notch; 21, body of premaxilla; 21', nasal process of same; 22, body of mandible; 23, mental foramen; 24, 25^
horizontal and vertical parts of ramus of mandible; 26, condyle of mandible; 27, coronoid process of mandible; 2S,
angle of mandible; 29, vascular impression; 30, interalveolar margin; 31, incisor teeth; 32, canine teeth; 33, hyoid
bone (great cornu) .

direction as to form a blunt ridge. The cranial surface is concave and smooth.
Lateral to the condyle is the paramastoid process (Processus paramastoideus),^ a
strong plate of bone which projects downward and backward; its lateral surface is
convex and roughened for muscular attachment ; its medial surface is concave from
end to end. Between the root of this process and the condyle is a smooth depres-
sion, the condyloid fossa (Fossa condyloidea ventralis) ; in this is the h3rpoglossal
foramen (Foramen hypoglossi), which transmits the nerve of like name.

The basilar part (Pars basilaris)^ is a strong, somewhat prismatic bar, which

1 Also known as the exoccipitals. ^ Also known as the styloid or jugular process.

' Also termed the basi-occipital or basilar process.

THE OCCIPITAL BONE

extends forward from the ventral margin of the foramen magnum. It is wide and
flattened behind, narrower and thicker in front. The ventral surface is rounded.
The cranial surface is concave and smooth ; its posterior part supports the medulla
oblongata, and its anterior part has a shallow cavity on which the pons rests. The
lateral borders are thin and sharp, and form the medial margin of the foramen
lacerum. The anterior end has, in the young subject, a semicircular, flat, pitted
surface which is attached to the body of the sphenoid bone by a layer of cartilage ;
in the adult there is complete fusion. On the ventral aspect of the junction are the
basilar tubercles (Tubercula basilaria) for the attachment of the ventral straight
muscles of the head.

The squamous part (Squama occipitalis)^ is the somewhat quadrilateral mass

Fig. 20. — Occipital Bone of Colt; Front View.
1, Depression of squamous part for cort'bclluin; 2, foramen magnum; 3, paramastoid process; 4, condyloid fossa;
a, squamous part; 6, lateral part; c, basilar part; rf, junction with interparietal bone; e, junction with parietal bone;
/, junction with petro-mastoid part of temporal bone.

situated dorsal to the lateral parts, from which it remains distinct till the second
year. The external surface is crossed by a very prominent ridge, the nuchal crest
(Crista nuchalis) ; the middle part of this is thick, transverse in direction, and forms
the highest point of the skull when the head is in the ordinary position; laterally it
becomes thinner and runs downward and forward to join the temporal crest.- The
crest divides the surface into two very unequal parts; the small dorsal area (Planum
parietale) presents a median ridge which is the posterior part of the external parietal
crest (Crista sagittahs externa) ; the large area ventral to the crest (Planum nu-
chale) has a central eminence, the external occipital protuberance, on which the funic-
ular part of the ligamentum nuchte is attached. The internal surface is concave

^ Also known as the supraoccipital.

^ The nuchal crest of this description is equivalent to the external occipital protuberance
and superior nuchal line of man; it has been commonly termed the occipital crest, but is not the
equivalent of that feature of the human skull. A curved line a httle lower down, which is con-
tinued on the paramastoid process, represents the inferior nuchal line of man.

52 THE SKELETON OF THE HORSE

and presents a deep central depression and two shallower lateral ones which adapt
it to the surface of the cerebellum.

The parietal border (INIargo parietalis) is united by suture with the parietal
and interparietal. The mastoid border (Margo mastoideus) joins the petro-
mastoid part of the temporal bone. The basilar part is connected by cartilage (in
the young subject) with the body of the sphenoid. The condyles articulate with
the atlas.

Development. — The occipital bone ossifies in cartilage from four centers, and
consists at birth of four pieces as described above. The lateral parts unite with the

11 10

Fig. 30. — Cranium of New-born Fo.\l; Posterior View.
A, B, C, Squamous, lateral, and basilar parts sf occipital bone; D, interparietal bone; E, parietal bone; F, squa-
mous temporal bone; 6', petro-mastoid part of temporal bone; 1, external occipital protuberance; 2, 2, depressfons in
which complexus tendons are attached; 3, sutural (preinterparietal?) bone; 4, supraorbital process; 5, zygomatic
process of temporal bone; 6, postglenoid process; 7, posterior process of squamous temporal bone; 8, mastoid process;
9, paramastoid process; 10, occipital condyle; 11, arrow in foramen magnum.

basilar part at three to four months, and with the squama in the second year, when
the bone is consolidated.

The parieto-occipital suture and the spheno-occipital synchondrosis are ob-
literated about the fifth year usually. The occipito-mastoid suture partially ossifies
in old subjects.

The Sphenoid Bone

The sphenoid bone (Os sphenoidale) is situated in the base of the cranium, its
central part lying in front of the basilar part of the occipital. It consists of the
body, two pairs of wings, and two pterygoid processes.

The body (Corpus) is situated medially; it is cylindrical, but flattened dorso-
ventrall}', and wider in front than behind. Its ventral surface (Facies externa) is
convex in the transverse direction, and its anterior part is concealed to a large extent
by the vomer and pterygoid bones. The cerebral surface (Facies cerebralis)
presents the following features: (1) In front there is a raised, flattened part (Jugum
sphenoidale) which is partially subdivided by a median elevation into two slightly
concave lateral areas; this part has a posterior, thin, free margin (Limbus sphe-

THE SPHENOID BONE

noidalis), which overhes the entrance to the optic foramina. The median ridge is
termed the ethmoidal spine, since it fits into a notch of the cribriform plate of the
ethmoid bone and joins the crista galh. (2) Just behind this and at a lower level
is a smooth transverse depression, the optic groove (Sulcus chiasmatis), on which
the optic chiasma rests. (3) From each end of this groove the optic foramen
(Foramen opticum) passes forward and outward to terminate in the posterior part
of the orbital fossa. ^ (4) Near the posterior end is a central depression, the hypo-
physeal or pituitary fossa (Fossa hypophyseos) , which lodges the hypophysis cerebri
or pituitary body. On each side of this is a shallow groove for the internal carotid
artery and the cavernous sinus. The anterior end is expanded, and joins the eth-
moid and palatine bones; it is excavated to form the sphenoidal sinuses. These
cavities extend back as far as the optic
groove, and are usually continuous in front
with the cavities in the vertical parts of the
palate bones;- they are separated by a com-
plete septum which is not always median.
The posterior end is flat and is joined to
the basilar part of the occipital ; at the line
of junction there is dorsally a slight trans-
verse elevation, the spheno-occipital crest
(Crista spheno-occipitalis).

The orbital wings (Alse orbitales) curve
dorso-laterally from the sides of the body of
the presphenoid. Their cerebral surface is
concave, and is marked by digital impres-
sions (Impressiones digitatse) for the gyri
of the cerebrum. The lateral surface is con-
vex and is largely concealed by the overlap-
ping temporal wing and the squamous tem-
poral and frontal bones ; a narrow part of it
(Facies orbitalis) is uncovered on the medial
wall of the orbital cavity at the sphenoidal
notch of the frontal bone. The dorsal bor-
der unites with the frontal bone at the
spheno-frontal suture. The anterior border
joins the ethmoid at the spheno-ethmoidal
suture ; at its lower part it concurs with the
ethmoid and frontal in the formation of the
ethmoidal foramen (Foramen ethmoidale).^
The posterior border is overlapped by the
temporal wing and the squamous temporal.
The root of the wing is perforated by the
optic foramen (Foramen opticum) . Immedi-
ately below and behind the latter (i. e., beneath the root) is the foramen orbitale.
Below this, and separated from it usually by a thin and often incomplete plate, is a
larger opening, the foramen rotundum, which is bounded externally by the root of
the pterygoid process.

The temporal wings (Alse temporales) extend outward and somewhat upward
from the body of the postsphenoid; they are smaller than the orbital wings and

Fig. 31. — Sphenoid Bone and Basilar Part of
Occipital Bone of New-born Foal; Dorsal
View.

C, Body of presphenoid; C, body of postsphe-
noid; B.O., basilar part of occipital bone; A.o., orbital
wing of sphenoid bone; A.t., temporal wing of sphe-
noid bone; 1, 1, optic foramina; 2, optic groove; 3,
hypophyseal fossa; 4, 5, grooves; 6, ethmoidal
notch; 7, ethmoidal spine; 8, junction with crib-
riform plate of ethmoid bone; 9, junction with
frontal bone; 10, junction with squamous temporal
bone; 11, margin of foramen lacerum anterius; 12,
spheno-occipital crest; 13, junction of basilar part
of occipital bone with lateral part.

1 This foramen might well be called a canal, since it is an inch or more in length.

2 The cavity so formed may be termed the sphenopalatine sinus. The sphenoidal sinus may
be a separate cavdty which communicates only with the ventral ethmoidal meatuses; this arrange-
ment exists in about a third of the cases according to Paulh.

' Also called the internal orbital foramen.

54 THE SKELETON OF THE HORSE

are irregularly quadrilateral in outline. The temporal surface (Facies temporalis)
enters into the formation of the infratemporal fossa, and bears the pterygoid process
on its anterior part; at the junction with the body there is a small groove which
leads forward to the pterygoid canal. The cerebral surface (Facies cerebralis)
presents, at the junction with the body, two longitudinal grooves (Sulci nervorum).
The lateral groove is the larger, and leads forward to the foramen rotundum; it
contains the maxillary nerve. The medial groove conducts to the foramen orbitale,
and contains the cavernous sinus of the dura mater. The outer groove is bounded
laterally by a thin overhanging crest, on which is a small groove for the fourth nerve.
The remainder of the surface is concave and supports the pyriform lobe of the brain.
The dorsal border joins the squamous temporal at the spheno-squamous suture.
The anterior border joins the orbital A\dng above; below this it is free and forms the
pterygoid crest (Crista pterygoidea) . The crest is continued on the pterygoid
process; on or under its upper part there is usually a small opening, the trochlear
foramen (Foramen trochleare). Just behind the crest is the foramen alare parvimi,^
through which the anterior deep temporal artery emerges from the alar canal of
the pterygoid process. The posterior border forms the anterior boundarj?- of the
foramen lacerum; it presents three notches, which are, from within outward, the
carotid, oval, and spinous (Incisura carotica, ovalis, spinosa). The angle of junc-
tion of the dorsal and posterior borders articulates with the parietal bone.

The pterygoid processes (Processus pterygoidei) arise from the temporal wings
and the body. They project downward and forward, and curve outward at the
lower part. The root is perforated by the alar canal (Canalis alaris),- which trans-
mits the internal maxillary artery. From this canal a branch leads upward and
forward to open at the foramen alare parvum. The lateral surface is concave, and
is marked by lines for muscular attachment. The medial surface is convex; it is
largely concealed by the overlapping palate and pterygoid bones.

The pterygoid canal (Canalis pterygoideus)^ continues the groove noted on the
ventral surface of the temporal wing at its junction with the body. It extends for-
ward and upward between the root of the pterygoid process, the presphenoid, and
the pterygoid bone, and opens in the posterior part of the pterygo-palatine fossa.
It transmits the nerve of the pterygoid canal.

Development. — The sphenoid is ossified in cartilage, and consists in early life
of two distinct parts, the presphenoid and postsphenoid. The former develops
from two centers, one in each wing; the latter has three centers, one for the body
and one for each wing. The pterygoid processes ossify from the centers of the
temporal wings.

In the new-born foal the unossified dorsal part of the orbital wing fits into a hiatus of the
frontal bone; in some cases it comes to the surface through a defect in the frontal bone at the place
where the horn process is situated in animals which have frontal horns.

The Ethmoid Bone

The ethmoid bone (Os ethmoidale) lies in front of the body and orbital wings
of the sphenoid. It projects forward between the orbital parts of the frontal bones
and enters into the formation of the cranial, nasal, and paranasal cavities.^ It
consists of four parts — the cribriform plate, two lateral masses, and the perpen-
dicular plate.

The cribriform plate (Lamina cribrosa) is a sieve-like partition between the

^ Also termed the temporal foramen.

^ This is also called the subsphenoidal canal or pterygoid foramen.

^ Also known as the Vidian canal.

^ On account of its deep situation and the fact that it cannot be separated from its surround-
ings, the ethmoid must be studied by means of appropriate sagittal and transverse sections of the
ekuU.

THE ETHMOID BONE

cranial and nasal cavities. Its margin joins the orbital wings of the sphenoid
laterally, the body of the sphenoid ventrally, and the cranial plate of the frontal
bones dorsally. Its cerebral surface is divided into two parts by a median ridge,
the crista galli, which may be regarded as the intracranial projection of the perpen-
dicular plate. Each half forms a deep oval cavity, the ethmoidal fossa, which
lodges the olfactory bulb. The plate is perforated by numerous small foramina for
the passage of the olfactory nerve filaments, and on either side is the much larger
ethmoidal foramen. The nasal surface is convex, and has the lateral masses
attached to it.

Each lateral mass or labyrinth (Labyrinthus ethmoidalis) is conical in shape and
its base is attached to the cril)riform plate. It projects forward into the posterior

Vomer

Fig. .32. — Cross-section of Cranium of Horse. The Section Passes Through the Middle of the Orbits and

IS Viewed from In Front.
1, Lateral mass of ethmoid bone; 2, perpendicular plate of same; 3, common nasal meatus; 4, sphenopalatine
sinu=i; .■>, perpendicular part of palatine bone; 6, zygomatic process of temporal bone; 7, zygomatic arch; 8, orbital
part of frontal bone.

part of the nasal cavity. The medial surface is separated by a narrow space from the
perpendicular plate. The lateral surface is convex and faces chiefly into the frontal
and maxillary sinuses, but is attached behind to the inner wall of the orbital cavity;
it is covered by a very thin layer of bone, the lamina lateraUs. The mass consists
of a large number of delicate, scroll-like plates of bone, termed ethmo-turbinates.^
These are attached to the lamina lateralis, and are separated by narrow intervals
termed ethmoidal meatuses, which communicate with the nasal cavity. In the
fresh state the ethmo-turbinates are covered with mucous membrane.

The lateral mass is a very complex structure, the arrangement of which may be understood
by examination of cross-sections. Each mass consists of six turbinates which extend almost to the

' The term "ethmoid cell," borrowed from human anatomy, should not be retained, since
it connotes an entirely erroneous conception of these structures in macrosmatic animals, such as
those under consideration.

THE SKELETON OF THE HORSE

perpendicular plate and are termed endoturbinates. These diminish in size from above down-
ward; the largest is attached to the nasal bone, and is hence usually called the dorsal or nasal
turbinate; the second is much smaller, and is very commonly termed the great ethmoid cell.
The cavaty enclosed by this communicates laterally with the maxillary sinus, but not directly
with the nasal cavity. Between the endoturbinates are twenty-one small ectoturbinates, and
all are beset ^\-ith secondary and tertiary coiled lamellae.

The perpendicular plate (Lamina perpendicularis) is median, and forms the
posterior part of the septum nasi. Its lateral surfaces are nearly plane, but are
marked below by some grooves and ridges; they are covered by the nasal mucous
membrane. The anterior border is irregular and is continuous with the septal
cartilage. The posterior border projects into the cranial cavity as a ridge, the

Posterior end Siipraorbital
of frontal sinus process

{sawn off)

Frontal bone {temporal pari)
Orbital icing of sphenoid

Foramen orbitale
— Foramen rotundum
Alar canal

Body of sphenoid Pterygoid process

Fig 33. — Cross-section of Cranium of Horse. The Section is Cut Just in Front of the Temporal Condyle

AND Is Viewed from Behind.

1, Internal plate of frontal bone; 2, crista galli; 3, cribriform plate; 4, ethmoidal foramen; 5, ethmoidal spine of

sphenoid bone; 6, optic foramina.

crista galli. The dorsal border joins the frontal l^ones at their line of junction.
The ventral border is received into the groove of the vomer.

Development. — The ethmoid develops in cartilage from five centers, two for
each lateral mass, and one for the perpendicular plate; from the latter ossification
extends into the cribriform plate. At birth the perpendicular and cribriform plates
are cartilaginous. By the time ossification is complete the ethmoid has united
with surrounding bones to such an extent that it cannot be separated intact for
study.

The Interparietal Bone

This bone (Os interparietale) is centrally placed between the squamous part
of the occipital and the parietal bones. It is usually described as a single bone,
although it ossifies from two chief lateral centers, and is often distinctly paired in
skulls of young foals.

THE PARIETAL BONES

The external, parietal surface (Facies parietalis) is quadrilateral and is flat and
smooth in the very young foal; later it presents the parietal crest.

The internal, cerebral surface (Facies cerebralis) presents the internal occipital
protuberance, a three-sided process which projects downward and forward into the
cranial cavity between the cerebral hemispheres and the cerebellum; it has three
concave surfaces, and three sharp borders which form part of the tentorium osseum.
Behind the base of the protuberance there is a transverse groove for the sinus com-
municans of the dura mater.

The posterior border is thick; it joins the squamous part of the occipital
bone. The lateral and anterior borders are
united with the parietal bones. Squaytwus part of

Development.— The interparietal ossi- occipital bone

fies in membrane from two chief lateral cen-
ters.^ It fuses first with the parietals, some-
what later with the occipital, but the period
at which this union takes place is quite
variable.

The Parietal Bones

The two parietal bones (Ossa parie-
talia) form the greater part of the roof of
the cranium; they unite in the median line,
forming the parietal suture. Each is quadri-
lateral in outline and has two surfaces and
four borders.

The external, parietal surface (Facies
parietalis) is convex, and is marked by a
more or less prominent curved line, the ex-
ternal parietal crest; this is median in its
posterior part, and is continuous with the
crest of like name on the interparietal and
occipital; in front it curves outward and is
continuous with the frontal crest. The sur-
face lateral to the crest (Planum temporale)
enters into the formation of the temporal
fossa, and is roughened for the attachment
of the temporal muscle.

The internal, cerebral surface (Facies
cerebralis) is concave. It presents numerous
digital impressions (Impressiones digitatae)

which correspond to the gyri, and ridges (Juga cerebralia) which correspond to the
sulci, of the cerebrum. There are also furrows (Sulci vasculosi) for the meningeal
arteries. Along the medial border there is a sagittal groove (Sulcus sagittalis) for
the superior longitudinal sinus.

The anterior border joins the frontal bone at the parieto-frontal suture (Sutura
parieto-f rontalis) .

The posterior border meets the occipital bone at the parieto-occipital suture.
Below this junction it curves inward and concurs with the temporal bone in the
formation of the temporal canal (Meatus temporalis) . A transverse groove (Sulcus
transversus) connects this canal with the sagittal sulcus.

The medial border is thick and serrated. It joins its fellow in great part at the
parietal suture, but (in the young subject) meets the interparietal at its posterior

^ According to Martin, there are originally four centers, two anterior and two posterior
(smaller) ones, which fuse in a variable manner.

Fig. 34. — Interparietal and Squamous Part or
Occipital Bone of New-born Foal; Ven-
tral View.

1, Junction of interparietal with squamous
part of occipital bone; 2, interparietal suture; 3,
internal occipital protuberance; 4, transverse groove
for sinus; 5, depression for vermis cerebelli; 6, de-
pression for hemisphere of cerebellum; 7, junction
of squamous part with lateral part of occipital
bone; 8, junction of occipital with petro-mastoid;
9, 9, junction of interparietal with parietal.

THE SKELETON OF THE HORSE

part. The line of junction of the two parietal bones is marked internally by the
internal parietal crest (Crista parietalis interna).

The lateral border is })eveled and is overlapped by the squamous temporal

Fig. .35.— Right Parietal Bone of New-born Foal; Dorso-lateral View.

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamoua

temporal; .5, junction with frontal,

bone, forming the squamous suture (Sutura squamosa). The angle of junction of
the lateral and posterior liorders articulates with the posterior angle of the temporal
wing of the sphenoid.

Development. — Each parietal bone ossifies in membrane from a single center.

Fig. 36. — Right Parietal Bone of New-born Foal, Cerebral Surface.

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamous

temporal; 5, junction with frontal; 6, edge which concurs with temporal bone in formation of temporal canal.

In the young foal the central part of the bone is more convex than in the adult and
forms a prominence similar to the pronounce 1 tuber parietale of the young child;
the external parietal crest is not present, and the external surface is smooth. The

THE FRONTAL BONES

parietal suture is usually closed at four years, the parieto-occipital at five years, and
the squamous at twelve to fifteen years.

The Frontal Bones

The frontal bones (Ossa frontalia) are situated on the limits of the cranium
and face, between the parietals behind and the nasal bones in front. Each is
irregularly quadrilateral, and consists of naso-frontal, orbital, and temporal parts.

The naso-frontal part (Pars naso-frontalis) forms the basis of the forehead.
Its external or frontal surface (Fades frontalis) is nearly flat, and is smooth and
subcutaneous ; it is separated from the temporal part by the external frontal crest
(Crista frontalis externa). At the junction with the orbital part the supraorbital
or zygomatic process (Proc. zygomaticus) curves outward and downward to join
the zygomatic arch. The process partially separates the orbit from the temporal
fossa; its root is perforated by the supraorbital foramen (Foramen supraorbitale),
or presents instead a notch on its anterior l)order; its upper surface is convex, while
the orbital surface is concave and smooth, forming a shallow fossa for the lacrimal

Fir,. 37. — Left Frontal Bone of New-born Fo.\l; Ventro-medi.\l View.
.4, Cerebral surface; B, B, vorbital part; C, temporal part; D, nasal surface; 1, surface of junction with opposite
bone; 2, frontal sinus; 3, ridge to which cribriform plate of ethmoid bone is attached; 5, fissure into which orbital wing
of .sphenoid bone fits; 6, sphenoidal notch; 7, supraorbital process; 8, junction with nasal bone; 9, junction with pari-
etal bone; 10, junction with squamous temporal bone.

gland (Fossa glandulae lacrimalis). The internal surface enters into the formation
of the cranial and nasal cavities. The two plates of the bone separate and diverge
in front, and thus inclose a large air-space which is part of the frontal sinus. The
internal plate curves downward and forward and joins the cribriform plate of the
ethmoid. Beyond this it inclines upward and joins the external plate at the naso-
frontal suture. The cerebral surface presents digital impressions for the cerebral
gyri. The nasal surface is longitudinally grooved. The external plate extends
forward and joins the nasal and lacrimal bones.

The orbital part (Pars orbitalis) forms the major part of the medial wall of the
orbital cavity. It is separated from the naso-frontal part by a prominent ridge
which is part of the orbital margin. Its orbital surface (Facies orbitalis) is concave
and smooth, and presents superiorly a small depression (Fovea trochlearis), which
is bridged by a small bar of cartilage, around which the superior oblique muscle of
the eye is reflected. The lower border concurs with the orbital wing of the sphenoid
in the formation of the ethmoidal foramen. The nasal surface faces into the
frontal sinus and is to a small extent united with the lateral mass of the ethmoid.

The temporal part (Pars temporalis) is separated from the orbital part by the

60 THE SKELETON OF THE HORSE

deep sphenoidal notch (Incisura sphenoidalis), which is closed by the orbital wing
of the sphenoid. Its lateral svurface forms part of the inner wall of the temporal
fossa. The medial surface is largely covered by the orbital wing of the sphenoid
in the young subject, but later forms part of the wall of the frontal sinus.

The principal connections of the frontal bone are as follows: (1) The medial
border joins its fellow at the frontal suture. (2) The anterior border meets the
nasal and lacrimal at the naso-frontal and fronto-lacrimal sutures. (3) Laterally
it forms the spheno-frontal suture with the orljital wing of the sphenoid, and also
joins the palatine bone and maxilla at the fronto-palatine and fronto-maxillary
sutures. (4) Posteriorly it meets the parietal at the parieto-frontal suture, and
articulates below this with the squamous temporal at the squamous suture.
(5) The extremity of the supraorbital process unites with the zygomatic process
of the temporal bone.

Development. — Each ossifies in membrane from one center which appears in
the root of the supraorbital process. In the new-born foal there is a slit between
the cranial plate and the orbital and temporal plates which receives the unossified
dorsal part of the orbital wing of the sphenoid.

The Temporal Bones

The temporal bone (Os temporale) forms the greater part of the lateral wall
of the cranium. It is situated between the occipital behind, the parietal dorsally,
the frontal in front, and the sphenoid ventrally. It consists in the horse of two
distinct parts, squamous and petrous.

1. The squamous temporal bone (Squama temporalis) is a shell-like plate
which has two surfaces and four borders.

The cerebral surface (Facies cerebralis) is concave and is largely overlapped
by the surrounding bones, but its central part is free and presents digital impres-
sions and vascular grooves.

The temporal surface (Facies temporalis) is convex, and enters into the forma-
tion of the temporal fossa. From its ventral part there springs the zygomatic
process (Processus zygomaticus) , which forms the lateral boundary of the tem-
poral fossa. The process is at first directed outward, and is wide and flattened
dorso-ventrally. It then turns forward, becomes narrower, and is twisted so that
its surfaces are medial and lateral. Its anterior end is pointed and joins the zygo-
matic process of the malar bone, wdth which it forms the zygomatic arch (Arcus
zygomaticus) . The narrow anterior part has a convex lateral surface and a concave
medial one. Its dorsal border has a rough area for articulation with the supra-
orbital process of the frontal. Its ventral border is wide and rough. The wide
posterior part presents on its ventral face a surface for articulation with the condyle
of the mandible. This surface consists of a transversely elongated condyle (Condy-
lus temporalis) , behind which is the glenoid cavity. The fossa is limited behind by
the postglenoid process (Processus postglenoidalis), the anterior surface of which
is articular. Behind this process there is a fossa, in which is the postglenoid fora-
men (F. postglenoidale), the external opening of the temporal canal. The dorsal
surface is concave and forms the lateral boundary of the temporal fossa. The
dorsal border is sinuous and is continuous behind with the temporal crest.

The posterior process (Processus aboralis) springs from the posterior part of
the squama. Its lateral surface bears the temporal crest, which forms here the
lateral limit of the temporal fossa. The medial surface forms the outer boundary
of the temporal canal, and is elsewhere applied to the petrous portion. It divides
into two branches, upper and lower; the upper branch unites with the occipital
bone, while the lower one curves downward behind the external acoustic process
and overlaps the mastoid process.

The dorsal border of the squamous temporal articulates with the parietal,

THE TEMPORAL BONES

forming the squamous suture. The ventral border joins the temporal wing of the
sphenoid at the spheno-squamous suture. The anterior border unites with the
frontal bone at the squamo-frontal suture, and the posterior with the occipital
and petrous temporal bones.

2. The petrous temporal bone (Os petrosum) is placed between the occipital

Fig. 38. — Right Squamous Temporal Bone of New-born Foal; Lateral View.
1, Zygomatic process; 2, glenoid cavity; 3, condyle; 4, postglenoid process; 5, notch; 6, posterior process; 7,
temporal crest; 8, junction with parietal; 9, junction with frontal; 10, junction with supraorbital process; 11, junction
with zygomatic process of malar; 12, junction with sphenoid; 13, junction with petro-mastoid- 14, junction with oc-
cipital.

behind and the parietal in front, and is largely overlapped by the squamous tem-
poral. It has the form of a four-sided pyramid, the base of which is ventral.

The lateral surface is mainly concealed by the squamous temporal, but two
features are visible. A short tube of bone, the external acoustic process (Processus
acusticus externus) , protrudes from the lowest part through the notch of the squa-
mous temporal. The process is directed outward, upward, and a little forward.

Fig. 39. — Right Squamous Temporal Bone op New-born Foal; Medial View.
F.C., Cerebral surface; 1, zygomatic process; 2, junction with parietal; 3, junction with temporal wing of sphenoid;
4, posterior process (overlaps petro-mastoid).

It gives attachment to the annular cartilage of the ear. Its lumen, the external
acoustic meatus (Meatus acusticus externus), conducts to the cavity of the middle
ear (tympanum) in the dry skull, but is separated from it by the tympanic mem-
brane in the natural state. The mastoid process (Processus mastoideus) projects
ventrally in the interval between the posterior process of the squamous temporal

THE SKELETON OF THE HORSE

and the root of the paramastoid process of the occipital bone. It is crossed by a
groove which leads to the mastoid foramen (Foramen mastoideum), from which a
canal extends forward to the temporal canal.

The medial surface faces into the cerebellar fossa of the cranium. It is con-
cave and smooth. l)ut irregular. In its ventral part is the entrance to a short canal,
the internal acoustic meatus (Meatus acusticus internus), which transmits the
seventh and eighth cranial nerves.

The entrance to the meatus is termed tlie porus acusticus internus. The fundus of the
meatus is divided by a crest into two fossae. In the superior one is the origin of the facial canal,
which curves through the bone and opens externally at the stylo-mastoid foramen; it transmits
the facial (seventh cranial) nerve. The inferior fossa presents small foramina for the passage of
fibers of the acoustic (eighth cranial) nerve.

Behind the meatus and near the posterior margin of the surface is the slit-like
external opening of the aquseductus vestibuli (Apertura externa aquseductus ves-

FlG.

40. — Left Petrous Temporal
Lateral View.

OF Horse:

1, External acoustic meatus; 2, mastoid process; 3,
hyoid process; 4, muscular process; 5, petrosal crest; 6,
groove which concurs in formation of temporal canal;
7, groove for posterior meningeal artery.

Fig. 41. — Left Petrots Temporal Bone of Horse;
postero-medial view.
1, Mastoid process; 2, notch which concurs with
occipital bone in formation of mastoid foramen; 3, apex;
4, opening of aquseductus vestibuli; 5, medial surface;
6, petrosal crest; 7, internal acoustic meatus; 8, mus-
cular process; 9, bullaossea; 10, stylo-mastoid foramen;
A.c, opening of aquseductus cochleae.

tibuli), covered by a scale of bone. Below this there is a narrow fissure, the
orifice of the aquseductus cochleae (Apertura externa aquseductus cochlese).

The anterior surface looks upward and forward. The greater part articulates
with the parietal bone, but a small medial part faces into the cerebral fossa of the
cranium. A sharp border, the petrosal crest (Crista petrosa), separates this sur-
face from the medial one.

The posterior surface is slightly concave and is attached to the lateral part of
the occipital bone.

The base forms the lateral boundary of the foramen lacerum. It is very
irregular and presents a number of important features. The hyoid process (Pro-
cessus hyoideus) is a short rod which projects doAvnward and forward below the
base of the external acoustic process, inclosed in a bony tube; it is connected by a
bar of cartilage with the hyoid bone. The stylo-mastoid foramen (F. stylo-
mastoideum) is situated between the hyoid process and the mastoid process; it is

BONES OF THE FACE— THE MAXILLAE 63

the external opening of the facial canal, through which the facial nerve emerges. The
bulla ossea is a considerable eminence situated centrally; it is thin walled and
incloses a cavity which is part of the tympanum. The muscular process (Processus
muscularis)^ is a sharp spine which projects downward and forward from the an-
terior part of the base; it gives origin to the tensor and levator palati muscles.
Lateral to the root of the preceding is the small petrotympanic fissure (Fissura
petrotympanica) for the passage of the chorda tympani nerve. The osseous
auditory or Eustachian tube (Tuba auditiva ossea) is a semicanal at the medial
side of the root of the muscular process; it leads to the tympanum. At the medial
side of the preceding is the slit-like orifice of the petrosal canal, which communi-
cates Avith the facial canal.

The apex projects upward and backward between the squamous temporal and
the occipital bone.

Development. — The squamous temporal develops in membrane. The pe-
trous temporal may be regarded as consisting of petro-mastoid and tympanic parts.
The latter includes the external acoustic process, the bulla ossea, and the muscu-
lar process; it is developed in membrane. The petro-mastoid is developed in the
cartilaginous ear capsule. Its petrous part consists of very dense bone which con-
tains the labyrinth or internal ear and forms the medial wall of the tympanum.

The auditory ossicles and the interior of the petrous temporal bone are described in the
section on the organ of hearing.

The temporal canal (Meatus temporalis)- is a continuation of the transverse
groove which extends laterally from the base of the tentorium osseum. It is
directed downward, forward, and somewhat outward, and opens externally in front
of the root of the acoustic process. It is bounded by the squamous temporal
laterally, the petrous behind, and the parietal in front and medially. Several
foramina open from it into the temporal fossa. It contains a large vein (Vena
cerebralis dorsalis), the continuation of the transverse sinus of the dura mater.

The foramen lacerum (basis cranii) is a large, irregular opening in the cranial
base, bounded medially by* the basilar part of the occipital bone, laterally by the
petrous temporal, and in front by the temporal wing of the sphenoid. It consists
of a large anterior part (Foramen lacerum anterius), and a narrow posterior part
(Foramen lacerum posterius) . It transmits the internal carotid artery, the middle
meningeal artery, the mandibular, ninth, tenth, and eleventh cranial nerves, and
the ventral cerebral vein.

In the fresh state the foramen is occupied by a dense fibrous membrane which is perforated
by apertures for the various structures transmitted. Thus there are three openings in front for
the internal carotid artery, the mandibular nerve, and the middle meningeal artery; these are
named (from within outward) the foramen caroticum, ovale, spinosum.

(B) BONES OF THE FACE
The bones of the face (Ossa faciei) are the maxilla, premaxilla, palatine,
pterygoid, nasal, lacrimal, malar, dorsal turbinate, ventral turbinate, vomer, mandi-
ble, and hyoid. The last three are single, the others paired.

The MAXILL.E
The maxillae are the principal bones of the upper jaw and carry the upper
cheek teeth. They are situated on the lateral aspect of the face, and articulate
Avith almost all of the facial bones and the frontal and temporal also. For descrip-
tion each may be divided into a body and two processes.

1 This has been termed the styloid process. It is not the homologue of the styloid proc-
ess of man.

* This is also known as the parieto-temporal canal.

THE SKELETON OF THE HORSE

The body (Corpus maxillae) presents two surfaces, two borders, and two ex-
tremities. The lateral surface (Facies lateralis) is somewhat concave in front and
convex behind.^ On its posterior part there is a horizontal ridge, the facial crest
(Crista facialis) ; in a skull of medium size its anterior end is about an inch and a
half (3 to 4 cm.) above the third or fourth cheek tooth, and it is continued behind
on the malar bone. About two inches (5 cm.) above and a little in front of the
anterior end of the crest is the infraorbital foramen (Foramen infraorbitale) ; this
is the external opening of the infraorbital canal.

The medial or nasal surface (Facies nasalis) is concave dorso-ventrally; it
forms the greater part of the lateral wall of the nasal cavity. Its upper part is
crossed obliquely forward and downward by the shallow lacrimal groove (Sulcus
lacrimalis), which contains the naso-lacrimal duct; in the adult the posterior part
of the groove is converted into a canal, which is continuous Avith that on the inner
surface of the lacrimal bone. Below the groove is the ventral turbinate crest
(Crista turbinata ventralis), to which the ventral turbinate Ijone is attached.
Lower down and parallel with the turbinate crest is the palatine process, which

Fig. 42. — Right Maxilia of New-born Foal; Medial View.
1, Lacrimal groove; 2, ventral turbinate crest; 3, palatine process; 4, maxillary sinus; 5, 5, area of articulation
with palatine bone; 0, groove which concurs with one on the palatine bone to form the palatine canal; 7, zygomatic
process; 8, maxillary tuberosity; 9, junction with nasal bone; 10, junction with nasal process of premaxilla.

projects horizontally like a shelf. Behind this the surface is rough for articulation
with the palatine bone; this area is crossed b,y a groove which concurs with one on
the palatine bone in the formation of the palatine canal (Canalis palatinus). The
posterior part of the bone is excavated to form part of the maxillary sinus.

The dorsal border is irregular and scaly. Its anterior part is grooved and
its posterior part beveled for articulation with the nasal process of the premaxilla
and the nasal and lacrimal bones.

The ventral or alveolar border (Processus alveolaris) is in its greater part thick,
and presents six large cavities, the dental alveoli, for the cheek teeth. The alveoli
are separated by transverse interalveolar septa. There is often a small alveolus
for the first premolar ("wolf tooth") close to the first large one. At the bottom
of the alveoli there are small openings (Foramina alveolaria) for the passage of
vessels and nerves. Further forward the border is narrow and forms part of the
interalveolar or interdental space (Margo interalveolaris). Behind the last alve-
olus is a rough area, the alveolar tuberosity (Tuber alveolare).

The anterior extremity is pointed. It joins the premaxilla, and forms with it
the alveolus for the canine tooth.

- In the young horse the anterior part of the surface is convex over the embedded parts of the
teeth. As the hitter are extruded the surface flattens and becomes concave in old subjects.
The form of the underlying teeth may be indicated by ridges (Juga alveolaria), and sometimes in
young horses there may be defects in the bone over the teeth.

THE PREMAXILL^ 65

The posterior extremity forms a rounded prominence, the maxillary tuberosity
(Tuber maxillare). Medial to the tuberosity is a deep recess (Recessus maxillaris),
in which are three foramina. The upper one, the maxillary foramen (Foramen
maxillare) , leads into the infraorbital canal. The lower one, the posterior palatine
foramen (Foramen palatinum aborale), is the entrance to the palatine canal. The
sphenopalatine foramen (Foramen sphenopalatinum) perforates the medial wall
of the recess and opens into the nasal cavity.

The zygomatic process (Processus zygomaticus) projects backward, dorso-
lateral to the tuberosity; it is overlapped by the corresponding part of the malar
and also articulates with the zygomatic process of the temporal. A small curved
plate (Processus temporalis) extends medially from it and joins the frontal and
palatine bones, forming part of the floor of the orbit.

The palatine process (Processus palatinus) is a horizontal plate which projects
from the lower part of the medial surface of the body. It forms the greater
part of the basis of the hard palate. Its nasal surface is smooth and is con-
cave transversely; on its anterior part, close to the medial border, there is a
shallow groove in which the vomero-nasal organ (of Jacobson) is situated. The
palatine surface is slightly concave from side to side, and presents along its lateral
part the palatine groove (Sulcus palatinus); this is continuous at the anterior
palatine foramen (Foramen palatinum orale) with the palatine canal, and con-
tains the palatine vessels and nerve. The medial border unites with its fellow to
form the median palatine suture; its nasal aspect bears the nasal crest (Crista
nasalis), which forms, with that of the opposite process, a groove for the vomer.
The posterior border unites with the horizontal part of the palatine bone at the
transverse palatine suture. Variable accessory palatine foramina perforate the
process.

The infraorbital canal (Canalis infraorbitalis)i extends almost horizontally
from the maxillary foramen to the infraorbital foramen. It is placed at the upper
edge of the inner plate of the maxilla, and traverses the maxillary sinus. Near the
infraorbital foramen it gives off a small canal (Canalis alveolaris incisivus) which
lies above the roots of the premolars and extends also into the premaxilla, carrying
vessels and nerves to the teeth there.

Development. — The maxilla ossifies in membrane ventral and lateral to the
cartilaginous nasal capsule. It has one chief center and a supplementary one in
the region of the deciduous canine tooth (Martin).

The Premaxilla

The premaxillae (Ossa incisiva) form the anterior part of the upper jaw and
carry the incisor teeth. Each consists of a body, a nasal process, and a palatine
process.

The body (Corpus) is the thick anterior part which carries the incisor teeth.
Its labial surface (Facies labialis) is convex and smooth, and is related to the upper
lip. The palatine surface (Facies palatina) is concave and often presents a foramen
a little behind its middle.- The medial surface (Facialis medialis) is rough, and
joins the opposite bone; it is marked by a curved groove, which forms, with that on
the opposed surface, the foramen incisivum. The alveolar border (Limbus alveo-
laris) separates the palatine and labial surfaces ; it is curved and thick, and presents
three deep alveoli for the incisor teeth; behind the third alveolus it is free, forming
part of the interalveolar space.

The nasal process (Processus nasalis) projects backward and upward from the
body, forming here the lateral wall of the nasal cavity. The two surfaces, facial

^ This is also known as the superior dental canal.

"^ This foramen is somewhat variable in position, but is commonly opposite the corner in-
cisor. Smaller inconstant foramina are often present.
5

THE SKELETON OF THE HORSE

and nasal, are smooth and rounded. The dorsal border is free, thick, and smooth;
it concurs with the free margin of the nasal bone in forming the naso-maxillary
notch (Incisura nasomaxillaris). The ventral border is dentated and joins the
maxilla; at its anterior end it forms with the latter the alveolus for the permanent

canine tooth. ^ The posterior ex-
tremity fits into the interval be-
tween the nasal bone and the
maxilla.

The palatine process (Pro-
cessus palatinus) is a thin plate
which forms the anterior part of
the basis of the hard palate. Its
nasal surface (Facies nasalis) has
a longitudinal ridge which forms
with that of the other side a groove
for the septal cartilage; lateral to
the ridge there is a groove for the
vomero-nasal organ. The palatine
surface (Facies palatina) is flat.
The medial border is serrated and
meets its fellow at the median pala-
tine suture. The lateral border is
separated from the maxilla and the
nasal process by the palatine fis-
sure (Fissura palatina). The pos-
terior extremity fits into the inter-
val between the vomer and the
palatine process of the maxilla.

Development. — The premax-
illa ossifies from a single center.
Fusion of the two bones is com-
plete at the end of the third or
the beginning of the fourth year.

The Palatine Bones

The palatine bones (Ossa pala-
tina) are situated on either side of
the choanse or posterior nares, and
form the posterior margin of the
hard palate. Each is twisted so as
to form a horizontal and a perpen-
dicular part.

The horizontal part (Pars hori-
zontalis) is a narrow^ plate which
forms the posterior part of the
hard palate. It presents smooth
nasal and palatine surfaces (Facies
nasalis, palatina). The medial border meets its fellow at the median palatine
suture, on the nasal aspect of which is the nasal crest. The anterior border joins
the palatine process of the maxilla at the transverse palatine suture, and forms with
it the anterior palatine foramen (Foramen palatinum anterius). The posterior
border is concave and free ; it gives attachment to the aponeurosis of the soft palate.

Fia. 43. — Upper .Jaw of Horse About Four and a Half
Years Old; Ventral View.
1, 1, Choanse or posterior nares; 2, vomer; 3, horizontal
part of palatine bone; 4, anterior palatine foramen; 5, palatine
groove; 6, transverse palatine suture; 7, median palatine suture;
8, palatine process of maxilla; 9, palatine process of premaxilla;
10, foramen incisivum; 11, malar bone; 12, maxilla; 13, anterior
end of facial crest; 14, interalveolar space; /. 1-3, incisor teeth;
C, canine tooth; P.l, first premolar or "wolf" tooth. The
opening lateral to 9 is the palatine fissure.

The alveolus for the temporary canine is commonly formed in the maxilla alone.

THE PTERYGOID BONES THE NASAL BONES 67

The perpendicular part (Pars perpendicularis) is more extensive and forms
most of the lateral wall of the choanse or posterior nares. The nasal surface (Facies
nasalis) is in the greater part of its extent concave and smooth, but presents a
narrow rough area to which the pterygoid bone is attached. Below this the bone
curves outward, forming the pterygoid process. The maxillary surface (Facies
maxillaris) presents three areas for consideration. The largest articulates with the
maxilla; it is rough and is crossed by a groove which concurs with one on the max-
illa in the formation of the palatine canal. Behind this is a smooth part which
assists in forming the pterygo-palatine fossa (Fossa pterygopalatina). The rough
area below this is overlapped by the pterygoid process of the sphenoid bone. The
dorsal border is perforated by the sphenopalatine foramen. Behind the foramen
the two plates of the bone separate to inclose part of the sphenopalatine sinus.
The inner plate curves medially to articulate with the vomer. The outer plate
joins the maxilla and frontal and the orbital wing of the sphenoid; it may join the
lacrimal bone also.

Development. — The palatine bone ossifies in membrane from a single center.

The Pterygoid Bones

The pterygoid bones (Ossa pterygoidea) are narrow, thin, bent plates, situated
on either side of the posterior nares. Each has two surfaces and two extremities.
The medial surface is smooth, and forms part of the wall of the posterior nares.
The lateral surface articulates with the palatine, vomer, and sphenoid, concurring
with the last in the formation of the pterygoid canal. The ventral extremity is
free, turned slightly outward, and forms the hamulus pterygoideus ; this is grooved
externally and forms a pulley around which the tendon of the tensor palati muscle
is reflected.

Development. — The pterygoid ossifies in membrane from a single center.

The Nasal Bones

The nasal bones (Ossa nasalia) are situated in front of the frontal bones and
form the greater part of the roof of the nasal cavity. They have an elongated
triangular outline, wide behind, pointed in front. Each presents two surfaces, two
borders, and two extremities.

The facial surface is smooth and is convex transversely; the profile contour is
usually slightly wavy, with a depression about its middle and a variably prominent
area in front.

The nasal surface is smooth and concave from side to side. About in its
middle it presents the dorsal turbinate crest (Crista turbinata dorsalis), which is
parallel with the medial border, and has the dorsal turbinate bone attached to it.
Most of this surface faces into the nasal cavity, but its posterior part, lateral to
the turbinate crest, enters into the formation of the frontal sinus; the latter area is
marked off by an oblique ridge which corresponds to the septum between the an-
terior and posterior parts of the dorsal turbinate bone.

The medial border is straight, and meets the opposite bone at the nasal suture.

The lateral border is irregular. Its anterior third is free and concurs with
the nasal process of the premaxilla in forming the naso-maxillary notch (Incisura
naso-maxillaris) . Behind this it joins the end of the nasal process, the maxilla,
and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures.

The greater part of the edge is beveled and fits into a groove on the upper border of the
nasal process, the maxilla, and the lacrimal bone.

The posterior extremity or base is beveled and overlaps the frontal bone,
forming the naso-frontal suture.

The anterior extremity or apex is pointed and thin.

68 THE SKELETON OF THE HORSE

Development. — Each nasal bone ossifies in membrane from a single center.
The nasal suture does not close completely even in old age. In some cases the two
plates separate to inclose a small air-space (nasal sinus) in the posterior part.

The Lacrimal Bones

The lacrimal bones (Ossa lacrimalia) are situated at the anterior part of the
orbit, and extend forward on the face to the posterior border of the maxilla. Each
presents three surfaces and a circumference.

The lateral face is clearly divided into orbital and facial parts by the orbital
margin. The orbital surface (Facies orbitalis) is triangular in outline, smooth and
concave ; it forms part of the medial and front wall of the orbit. Near the orbital
margin it presents a funnel-like fossa (Fossa sacci lacrimalis), which is the entrance
to the lacrimal canal; the fossa is occupied by the lacrimal sac, which is the dilated
origin of the naso-lacrimal duct. Behind this is a depression in which the inferior
oblique muscle of the eye takes origin. The facial surface (Facies facialis) is more
extensive, and has the form of an irregular pentagon. It is slightly convex and
smooth in the foal, flattened in the adult. It usually bears the small lacrimal
tubercle, which is situated nearly an inch (ca. 2 cm.) from the orbital margin.
The orbital margin (Margo orbitalis) is concave, rough above, smooth below.

The nasal surface (Facies nasalis) faces into the frontal and maxillary sinuses.
It is concave and very irregular, and is crossed almost horizontally by the osseous
lacrimal canal (Canalis lacrimalis osseus).

The circumference articulates dorsally with the frontal and nasal bones,
ventrally with the malar and maxilla, in front with the maxilla, and behind with
the frontal. The various sutures so formed are designated by combinations of the
names of the bones.

Development. — Each ossifies in membrane from a single center.

The Malar Bones

The malar or zygomatic bones (Ossa zygomatica) are placed between the lac-
rimal above and the maxilla below and in front. Each is irregularly triangular in
outline and presents three surfaces, three borders, and a process.

The facial surface (Facies facialis) is smooth, slightly convex, wide in front,
and narrow behind. At its lower part it presents the facial crest, which is continu-
ous in front with the similar ridge on the maxilla and behind with the zygomatic
process of the temporal; the crest is rough below, where the masseter muscle is
attached to it.

The orbital surface is much smaller than the facial surface, from which it is
separated by the concave orbital margin (Margo orbitalis). It is concave and
smooth, and forms part of the lower and front wall of the orbit.

The nasal surface is concave and faces into the maxillary sinus. In the young
foal a consideraljle part of it articulates with the maxilla.

The dorsal border articulates with the lacrimal chiefly, but to a small extent
behind with the maxilla also.

The ventral and anterior borders articulate with the maxilla.

The posterior extremity is formed by the zygomatic process, which is beveled
above and is overlapped by the zygomatic process of the temporal bone.

Development. — Each ossifies in membrane from one or two centers.

The Turbinate Bones
These (Ossa turbinata) are delicate, scroll-like bones, four in number, which
are attached to the lateral walls of the nasal cavity. They project into the cavity
and greatly diminish its extent. Each is composed of a very thin lamina, cribri-

THE TURBINATE BONES

form in many places, and covered on both sides witli mucous membrane in the fresh
state. They are arranged in two pairs, dorsal and ventral.

The dorsal turbinate bone (Os turbinatum dorsale)^ is somewhat cylindrical in
form, but is flattened from side to side and tapers at each end. It is attached to
the turbinate crest of the nasal bone and the nasal plate of the frontal bone. The
anterior part is rolled like a scroll one and a half times, thus inclosing a cavity which
communicates with the middle meatus nasi. The arrangement is best seen on a
cross-section (Fig. 55). The posterior part is not rolled, but its ventral border is
attached to the lateral nasal wall, thus helping to inclose a large space which is part
of the frontal sinus. This cavity is separated from that of the scroll-like part by a
transverse septum. The medial surface is flattened, and is separated from the sep-
tum nasi by a narrow interval, the common meatus (Meatus nasi communis).
Another narrow passage, the dorsal meatus (Meatus nasi dorsalis), separates the
dorsal surface from the roof of the nasal cavity. The space between the ventral
surface and the ventral turbinate is the middle meatus (Meatus nasi medius). The

A^asal Frontal

sinus sinus

Nasal
bone

at nasal

13 Sphenoidal
sinus

Hamulus of
pterygoid bone

Fig. 44. — Part of Sagittal Section of Skull op Horse.
1, Perpendicular plate of ethmoid bone; 2, great ethmo-turbinate; 3, dorsal turbinate; 4, ventral turbinate; 5,
vomer; 6, middle nasal meatus; 7, ventral nasal meatus; 8, perpendicular part of palatine bone; 9, palatine process of
maxilla; 10, body of premaxilla; 11, nasal process of premaxilla; 12, palatine process of premaxilla; 13, pterygoid proc-
ess of palatine bone. Dotted lines indicate septa.

anterior extremity is prolonged toward the nostril by two small bars of cartilage.
The posterior extremity is small, and joins the cribriform plate and lateral mass of
the ethmoid.

The ventral turbinate bone (Os turbinatum ventrale)^ is shorter and smaller
than the upper one. It is attached to the ventral turbinate crest, and consists',
like the upper one, of an anterior coiled and a posterior uncoiled portion.

To express briefly the mode of coiling of the two bones of the same side we may say that
they are rolled toward the septum and each other.

The ventral and posterior borders of the posterior part are attached to the
maxilla, thus helping to inclose a cavity which is part of the maxillary sinus. The
lower surface is separated from the floor of the nasal cavity by the ventral meatus
(Meatus nasi ventralis), which is much larger than the other nasal passages. The
anterior extremity is prolonged toward the nostril by a curved bar of cartilage.

Development. — Each ossifies in cartilage from a single center.

1 This bone is also termed the naso-turbinal ; it is really a greatly developed first ethmor
turbinate.

^ This is also called the maxillo-turbinal.

70 THE SKELETON OF THE HORSE

The Vomer

The vomer is a median bone, which assists in forming the ventral part of the
septum nasi. It is composed of a thin lamina which is bent (except in its posterior
part) so as to form a narrow groove (Sulcus vomeris) , in which the lower part of the
perpendicular plate of the ethmoid bone and the septal cartilage are received. The
lateral surfaces, right and left, are highest near the posterior end and diminish
gradually to the anterior end; they are slightly convex dorso-ventrally, and are
covered by the nasal mucous membrane during life. The ventral border is thin
and free in its posterior third, and divides the choanae or posterior nares medi-
ally; in the remainder of its extent it is wider and is attached to the nasal crest.
The anterior extremity lies above the ends of the palatine processes of the premax-
illae. The posterior extremity consists of two wings (Alae vomeris) which extend
outward below the body of the presphenoid; posteriorly they form a notch (In-
cisura vomeris), and laterally join the palatine and pterygoid bones.

Development. — The vomer is primitively double, and ossifies from a center on
cither side in the membrane covering the cartilaginous septum nasi; the two
laminse then fuse below and form a groove.

The Mandible

The mandible (Mandibula),^ or lower jaw bone, is the largest bone of the
face. The two halves of which it consists at birth unite during the second or third
month, and it is usually described as a single bone. It carries the lower teeth, and
articulates l^y its condyles with the squamous temporal on either side. It consists
of a body and two rami.^

The body (Corpus mandibulse) is the thick anterior part which bears the incisor
teeth. It presents two surfaces and a border. The lingual surface (Facies lin-
gualis) is smooth and slightly concave; during life it is covered by mucous mem-
brane, and the tip of the tongue overlies it. The mental surface (Facies mentalis)
is convex and is related to the lower lip. It is marked by a median furrow which
indicates the position of the primitive symphysis mandibulse. The curved alveolar
border (Limbus alveolaris) presents six alveoli for the incisor teeth, and a little
further back two alveoli for the canine teeth in the male; in the mare the latter are
usually absent or small.

The rami (Rami mandibulse) extend backward from the body and diverge to
inclose the mandibular (or submaxillary) space (Spatium mandibulare). Each
ramus is bent so as to consist of a horizontal part (Pars molaris) which bears the
lower cheek teeth, and a vertical part (Ramus mandibulse [S. N. A.]) which is ex-
panded and furnishes attachment to powerful muscles; the term angle is applied
to the most prominent part of the curve. The ramus presents two surfaces, two
borders, and two extremities. The lateral surface is smooth and slightly convex
from edge to edge on the horizontal part; at the junction with the body it presents
the mental foramen (Foramen mentale), which is the external opening of the man-
dibular canal. On the vertical part it is somewhat concave and presents a number
of rough lines for the attachment of the masseter muscle. The medial surface of
the horizontal part is smooth, and presents a shallow longitudinal depression in its
middle; above this there is often a faint mylo-hyoid line (Linea mylohyoidea) for
the attachment of the muscle of like name. At the lower part of the junction with
the body there is a small fossa for the attachment of the genio-hyoid and genio-

^ This bone is also commonly called the inferior maxilla.

^ In the Stuttgart Anatomical Nomenclatm-e (S. N. A.) the body (Corpus) is the part which
bears the teeth, and is divided into a pars incisiva and a pars molaris. The ramus is the rest of
the bone. This mode of description is copied from the Basel Nomina Anatomica. It does not
seem to the author to be well adapted to comparative purposes.

THE MANDIBLE 71

glossus muscles. On the vertical part the surface is concave, and is marked in its
lower and posterior part by rough lines for the attachment of the medial pterygoid
n^.uscle. In front of its middle is the mandibular foramen (Foramen mandibulare)/
which is the posterior orifice of the mandibular canal (Canalis mandibulae).- The
canal curves downward and passes forward below the cheek teeth, opening exter-
nally at the mental foramen; it is continued into the body of the bone as a small
canal (CanaUs alveolaris incisivus), which carries the vessels and nerves to the
incisor teeth. The dorsal or alveolar border (Limbus alveolaris) forms anteriorly
part of the interalveolar space; here it is thin. Behind this it is thick and is ex-
cavated by six alveoli for the lower cheek teeth. Behind the last alveolus it curves
sharply upward and is narrow and rough. In the young foal there is commonly a
small alveolus for the vestige of the first premolar ("wolf tooth") close to the first
large one. The ventral border of the horizontal part is nearly straight; it is thick
and rounded in the young horse, becoming narrower and sharp in old subjects. At

Fig. 45. — Left Half of Mandible of Hor.se; Medial View.
1, Body of mandible (median section); 2, 2', horizontal and vertical parts of ramus; 3, interalveolar border; 4,
depression for attachment of genio-hyoideus muscle; o, mandibular foramen; 6, vascular impression; 7, angle; 8,
condyle; 9, coronoid process; 10, mandibular notch; 11, incisor teeth; 12, canine tooth; 13, cheek teeth.

its posterior part there is a smooth impression (Incisura vasorum) where the facial
vessels and parotid duct turn round the bone. Behind this point the border curves
sharply upward, forming the angle of the mandible (Angulus mandibulse) ; this part
is thick and has two roughened lips, separated by a considerable intermediate space;
near the condyle it becomes narrower. The anterior extremity joins the body.
The articular extremity comprises the coronoid process in front and the condyle
behind, the two being separated by the mandibular notch (Incisura mandibulae),
through which the nerve to the masseter muscle passes. The coronoid process
(Processus coronoideus) is thin transversely and curved slightly medially and
backward. It projects upward in the temporal fossa and furnishes insertion to
the temporal muscle. The condyle of the mandible (Condylus mandibulae) lies at
a much lower level than the end of the coronoid process. It is elongated trans-
versely and articulates with the squamous temporal through the medium of an

^ This is also commonly called the inferior maxillary foramen.
^ This is also termed the inferior dental canal.

THE SKELETON OF THE HORSE

articular disc. The part below the condyle is usually termed the neck of the
mandible (CoUum mandibulse) ; on its antero-medial part is a depression, the fovea
pterygoidea, in which the lateral pterygoid muscle is attached. The middle of the
vertical part of the ramus consists to a large extent of a single plate of compact
substance which may be so thin in places as to be translucent.

Development. — The mandible develops from two chief centers in the connec-
tive tissue which overlies the paired Meckel's cartilages. At birth it consists of
two symmetrical halves which meet at the median symphysis mandibulae. Fusion
usually occurs in the second or third month.

Age Changes. — These are associated largely with the growth, and later with the reduction,
of the teeth. In the young horse, in which the teeth are long and are in great part embedded
in the bone, the body is thick and strongly curved, and the horizontal part of the ramus is also
thick. Later, as the teeth are extruded from the bone, the body becomes flattened and narrower,
and the horizontal part of the ramus is thinner, especially in its lower part. In the old subject
the angle, the vascular impression in front of it, and the lines for the attachment of tendinous
layers of the masseter and pterygoid muscles are more pronounced.

The Hygid Bone

The hyoid bone (Os hyoideum) is situated chiefly between the vertical parts
of the rami of the mandible, but its upper part extends somewhat further back.
It is attached to the petrous temporal bones by rods of cartilage, and supports the

root of the tongue, the pharynx, and the
larynx. It consists of a body, a lingual
process, and three pairs of cornua.

The body or basihyoid (Corpus ossis
hyoidei) is a short transverse bar, com-
pressed dorso-ventrally. The dorsal sur-
face is concave and smooth in its middle,
and presents at each end a convex facet
or tubercle for articulation with the small
cornu. The ventral surface is flattened
and is slightly roughened for muscular
attachment. The anterior border carries
medially the lingual process. The pos-
terior border is concave and smooth in its
middle, and carries on either side the thy-
roid cornu. The body, the lingual proc-
ess, and the thyroid cornua are fused
and may be compared to a spur or a fork
with a very short handle.

The lingual process (Processus lingu-

alis) projects forward medially from the

body, and is embetlded in the root of the

tongue during life. It is compressed laterally and has a blunt-pointed free end.

The lateral surfaces are slightly concave. The dorsal border is thin and irregular,

and the ventral border is thick and rough.

The thyroid cornua or thyrohyoids (Cornua thyreoidea)i extend backward and
upward from the lateral parts of the body. They are compressed laterally (except
at their junction with the body), and the posterior end has a short cartilaginous
prolongation which is connected with the anterior cornu of the thyroid cartilage
of the larynx.

The small cornua or keratohyoids (Cornua minora) are short rods which are
directed upward and forward from either end of the body. Each is somewhat
constricted in its middle part and has slightly enlarged ends. The ventral end has
' These correspond to the great cornua of man.

Fia. 46. — Hyoid Bone or Horse, Viewed from the
Side and Somewhat from in Front.
o. Body; 6, lingual process; c, thyroid cornu; c',
cartilage of c; d, small cornu; e, middle cornu; /.great
cornu; /', muscular angle of great cornu; g, cartilage
of great cornu. (EUenberger-Baum, Anat. d. Haus-
tiere.)

THE SKULL AS A WHOLE 73

a small concave facet which articulates with the body. The dorsal end articulates
with the great cornu, or with the middle cornu when present.

The great comua or stylohyoids are much the largest parts of the bone. They
are directed dorsallj" and backward, and are connected above with the base of the
petrous temporal bones. Each is a thin plate, seven or eight inches (ca. 18 to 20
cm.) long, which is slightly curved in its length, so that the lateral surface is con-
cave and the medial surface is convex; both are smooth. The borders are thin.
The dorsal extremity is large and forms two angles; the articular angle is connected
by a rod of cartilage with the hyoid process of the petrous temporal bone; the
muscular angle is somewhat thickened and rough for muscular attachment. The
ventral extremity is small, and articulates with the small or the middle cornu.

The middle comua or epihyoids are small, wedge-shaped pieces or nodules
interposed between the small and great cornua. They are usually transitory, and
unite with the great cornua in the adult.

Development. — The hyoid ossifies in the cartilages of the second and third
visceral arches. Each part has a separate center, except the lingual process, which
ossifies by extension from the body. In the foal there is a separate nucleus at each
end of the body which intervenes between the latter and the thyroid cornu; it
articulates with the small cornu. The anterior part of the lingual process may be
a separate piece.

THE SKULL AS A WHOLE

The skull of the horse has, as a whole, the form of a long, four-sided pyramid,
the base of which is posterior. It is convenient, however, to exclude the mandible
and hyoid from present consideration. The division between the cranium (Cra-
nium cerebrale) and the face (Cranium viscerale) may be indicated approxi-
mately by a transverse plane through the anterior margins of the orbits.

The dorsal or frontal surface (Norma frontalis) is formed by the squamous
part of the occipital, interparietal, parietal, frontal, nasal, and premaxil-
lary bones. It may be divided into parietal, frontal, nasal, and premaxillary
regions. The parietal region extends from the nuchal crest to the parieto-frontal
suture. It is marked medially by the external parietal crest, which bifurcates in
front, the branches becoming continuous with the frontal crests. The latter curve
outward on either side to the root of the supraorbital process. The frontal region
is the widest part of the surface, and is smooth and almost flat. It is bounded in
front by the naso-frontal suture. On either side of it is the root of the supraorbital
process, pierced by the supraorbital foramen. The nasal region is convex from
side to side, wide behind, narrow in front. Its profile is in some cases nearly
straight; in others it is undulating, with a variably marked depression about its
middle and at the anterior end. The premaxillary region presents the osseous
nasal aperture (Apertura nasalis ossea) and the foramen incisivum.

The lateral surface (Norma lateralis) (Fig. 28) may be divided into cranial,
orbital, and preorl)ital or maxillary regions.

The cranial region presents the temporal fossa, the zygomatic arch, and the
outer part of the petrous temporal bone. The temporal fossa is bound medially
by the parietal and frontal crests, laterally by the temporal crest and the zygomatic
arch, and behind by the nuchal crest. Its upper and middle parts are rough for
the attachment of the temporal muscle. In its lower posterior part are several
foramina which communicate with the temporal canal. The fossa is continuous
in front with the orbital cavity. The zygomatic arch is formed by the zygomatic
processes of the temporal, malar, and maxilla. Its ventral face presents the con-
dyle and glenoid cavity for articulation with the lower jaw, through the medium
of the articular disc. Behind the glenoid cavity is the postglenoid process. The

THE SKELETON OF THE HORSE

external acoustic process projects outward through a deep notch in the ventral
margin of the squamous temporal below the temporal crest. A little further back
is the mastoid process, crossed in its upper part by a groove for the posterior
meningeal artery.

The orbital region comprises the orbit and the pterygo-palatine fossa. The

Nuchal crest

Occipital
Interparietal -

Parietal ^// /

Squamous temporal

Frontal

Parietal crest

Temporal fossa
Temporal crest

Coronoid process
Zygomatic arch

Supraorbital process
S upraorbital foramen

Orbit
Facial crest

I >ifra orbital foramen

Nasal process of premaxilla

Body of premaxilla

Foramen, incisivum

Fig. 47. — Skull of Horse; Dorsal View.
1, Parieto-ocoipital suture; 2, squamous suture; 3, parietal suture; 4, parieto-frontal suture; 5, frontal suture;
•6, naso-frontal suture; 7, naso-lacrimal suture; 8, lacrimo-malar suture; 9, lacrimo-maxillary suture; 10, maxillo-
■malar suture; 11, naso-maxillary suture; 12, nasal suture.

orbit is a cavity which incloses the eyeball, with the muscles, vessels, and nerves
associated with it. It is not separated in the skeleton from the temporal fossa.
The axis of the orbit (Axis orbitse), taken from the optic foramen to the middle of
the inlet, is directed forward, outward, and slightly upward. The medial wall
(Paries medialis) is complete and extensive. It is concave and smooth, and is
formed by the frontal and lacrimal and the orbital wing of the sphenoid. In its

THE SKULL AS A WHOLE

extreme anterior part is the fossa for the lacrimal sac. Behind this there is a small
depression in which the inferior oblique muscle of the eye arises; here the plate
which separates the orbit from the maxillary sinus is very thin. The dorsal wall
(Paries dorsalis) is formed by the frontal and to a small extent by the lacrimal bone.
It presents the supraorbital foramen, which perforates the root of the supraorbital
process. The ventral wall (Paries ventralis) is very incomplete, and is formed by
the malar, the zygomatic process of the temporal, and to a small extent by the max-
illa. The lateral wall (Paries lateralis) is the supraorbital process. At the extreme
posterior part is the orbital group of foramina. Four are situated in front of the
pterygoid crest. Of these, the uppermost is the ethmoidal foramen, which trans-

FlG. 48. — Cranial and Orbital Regions of Skull of Horse; Lateral View. The Zygomatic Arch and Supra-
orbital Process Have Been Sawn Off.
5. 0., Squamous part of occipital; P, parietal; S, squamous temporal; B.o., basilar part of occipital; B.s., body of
sphenoid; A. «., temporal wing of sphenoid; A. o., orbital wing of sphenoid; P<. p., pterygoid process of sphenoid; P.p.,
perpendicular part of palate bone; F, F', facial and orbital parts of frontal bone; L, L' , orbital and facial parts of lacri-
mal bone; M, facial part of malar bone; M.x., maxilla; a, parieto-occipital suture; b, squamous suture; c, d, spheno-
squamous suture; e, fronto-palatine suture; /, fronto-lacrimal suture. 1, Occipital condyle; 2, condyloid fossa; 3,
paramastoid process; 4, nuchal crest; 5, external occipital protuberance; 6, external acoustic meatus; 7, mastoid
process; 8, hyoid process; 9, stylomastoid foramen; 10, muscular process; 11, foramen lacerum; 12, postglenoid
process; 13, glenoid cavity; 14, temporal condyle; 15, pterygoid groove; 16, alar canal of pterygoid process indicated
by arrow; 17, alar foramen; 18, ethmoidal foramen; 19, optic foramen; 20, foramen orbitale; 21, maxillary fora-
men; 22, sphenopalatine foramen; 23, posterior palatine foramen; 24, supraorbital foramen (opened) ; 25, fossa for
lacrimal sac; 26, depression for origin of obliquus oculi inferior; 27, facial crest; 28, maxillary tuberosity; 29, alveolar
tuberosity ; 30, hamulus of pterygoid bone.

mits the ethmoidal vessels and nerve. The optic foramen is situated a little lower
and further back; it transmits the optic nerve. Immediately below the optic is
the foramen orbitale, which transmits the ophthalmic, third, sixth, and sometimes
the fourth nerve; commonly there is a very small trochlear foramen in the crest
for the last-named nerve. The foramen rotundum is below the foramen orbitale,
from which it is separated by a thin plate; it transmits the maxillary nerve. The
alar canal opens in common with the foramen rotundum, and the anterior opening
of the pterygoid canal is also found here. The foramen alare parvum is just be-
hind the pterygoid crest and on a level with the foramen orbitale. It is the upper
opening of a canal which leads from the alar canal, and through it the anterior deep

THE SKELETON OF THE HORSE

temporal artery emerges. The inlet of the orbital cavity (Aditus orbitae) is cir-
cumscribed by a complete bony ring, which is nearly circular. Its infraorbital
margin (Margo infraorbitalis) is smooth and rounded; the supraorbital margin
(Margo supraorbitalis) is rough and irregularly notched. During life the cavity is
completed by the periorbita, a conical fibrous membrane, the apex of which is at-
tached around the optic foramen. Ventral to the orbital cavity is the pterygo-
palatine fossa. Its wall is formed by the pterygoid process, the perpendicular
part of the palate bone, and the tuber maxillare. Its deep anterior recess contains
three foramina. The upper one, the maxillary foramen, is the entrance to the in-

Nuchal ere at

Dorsal border of

for. magnum

Foramen magnum

Hypoglossal foramen

For. lacenim posterms

Stylomastoid foramen

Hyoid process

Muscular process
For. lacerum anterius
Basilar tubercles

Alar canal

Pterygoid process
of sphenoid
Pterygoid hone

Vomer {alee)
Pterygoid process of

palatine bone
Palatine bone {per-
pendicular part)
Alveolar tuberosity

Posterior nares
Last molar tooth

External occipital pro-
tuberance

Occipital condyle

Paramastoid process

Condyloid fossa

Mastoid process

Bulla ossea

process

Glenoid cavity

Temporal condyle
Zygomatic process
Infratemporal fossa
Zygomatic process of
malar

Pterygo-palatine fossa
Maxillary recess
Maxillary tuberosity
Facial crest
Hatnulus of pterygoid
Vomer

Palatine bone {hori-
zontal part)
Ant. palatine foramen

Palatine groove

Palatine process of
maxilla

Fig. 49. — Line Drawing of Posterior Half of Base of Skull of Horse, Without Mandible. (Key to Fig. 50.)
A, Basilar part of occipital; B, body of sphenoid; C, temporal wing of sphenoid; D, squamous temporal bone;

£, petrous temporal bone; F, orbital part of frontal bone, i, Incisura carotica; ;
4, external orifice of temporal canal; 5, osseous auditory or Eustachian tube; 6
acoustic process; S, hyoid process ; S, pterygoid groove ; iO, supraorbital process.

ovalis; 3, incisuraspinosa;
petro-tympanic fissure; 7, external

fraorbital canal, which transmits the infraorbital nerve and vessels. The spheno-
palatine foramen perforates the medial wall of the recess and transmits vessels and
nerves of like name to the nasal cavity. The lower foramen, the posterior palatine,
transmits the palatine artery and nerve to the palatine canal. The upper part of
the fossa is smooth, and is crossed by the internal maxillary artery and the maxillary
nerve. The lower part is chiefly roughened for the attachment of the lateral
pterygoid muscle, but is crossed in front by a smooth groove in which the palatine
vein lies. In its extreme posterior part is the small opening of the pterygoid
canal.

The preorbital or maxillary region is formed chiefly by the maxilla, but also by

THE SKULL AS A WHOLE

the premaxilla, and the facial parts of the lacrimal and malar bones. Its contour
is approximately triangular, the base being posterior. It offers two principal
features. The facial crest extends forward from the ventral margin of the orbit,
and ends abruptly at a point about an inch and a quarter (ca. 3 to 3.5 cm.) above the

Fig. 50. — Ventral Surface op Skull of Hohse, Posterior Half Without Mandible.
The skull is inclined slightly. (Notation on key Fig. 49.)

third or fourth cheek tooth ;i its ventral aspect is rough for the attachment of the
masseter muscle. The infraorbital foramen is situated in a transverse plane about
an inch (ca. 2 to 3 cm.) in front of the end of the crest and about two inches (5 cm.)

1 This relation varies with age. In the new-born foal the posterior part of the second tooth,
in the young horse the posterior part of the third tooth, in the older subject the fourth, lies below
the end of the crest.

78 THE SKELETON OF THE HORSE

above it. The foramen opens forward, and through it the infraorbital artery and
nerve emerge. The surface over the premolar teeth varies greatly with age, in
conformity "s^dth the size of the embedded parts of the teeth. In the young horse
the surface here is strongly convex, the outer plate of bone is thin and even defective
sometimes in places, and the form of the teeth is indicated by eminences (Juga
alveolaria). In the old animal the surface is concave on account of the extrusion
of the teeth from the bone. The downward curve of the premaxilla is pronounced
in the young subject, very slight in the aged.

In some skulls there is a distinct depression a short distance in front of the orbit; here the
levator labii superioris proprius arises.

The ventral or basal surface (Norma basalis), exclusive of the mandible,
consists of cranial, choanal, and palatine regions.

The cranial region (Basis cranii externa) extends forward to the vomer and
pter3'goid processes (Fig. 50). x\t its posterior end is the foramen magnum, flanked
by the occipital condyles. Lateral to these is the condyloid fossa, in which is the
hypoglossal foramen, which transmits the hypoglossal nerve and the condyloid
vein. Further outward are the paramastoid processes (Processus jugulares)
of the occipital bone. Extending forward centrally is a prismatic bar, formed
by the basilar part of the occipital and the body of the sphenoid bone; at the
junction of these parts are tubercles for the attachment of the ventral straight
muscles of the head. On either side of the basilar part of the occipital bone is the
foramen lacerum (basis cranii), bounded laterally by the base of the petrous tem-
poral bone. In front of these the region becomes very wide on account of the lateral
extension of the zygomatic processes, which present ventrally the condyle and
glenoid cavity for articulation with the mandible. Beyond this the process turns
forward and joins the zygomatic process of the malar, completing the zygomatic
arch and the surface for the attachment of the masseter muscle. On either side of
the body of the sphenoid is the infratemporal fossa, formed by the temporal wing
and the root of the pterygoid process of the sphenoid bone. It is bounded in front
by the pterygoid crest, which separates it from the orbit and the pterygo-palatine
fossa. In it is the alar canal, which transmits the internal maxillary artery. A
little lower is the entrance to the pterygoid canal.

The choanal region presents the pharyngeal orifice of the nasal cavity. This
is elliptical and is divided in its depth medially b}^ the vomer into two choanae or
posterior nares. It is bounded in front and laterally by the palate and pterygoid
bones, behind by the vomer. It is flanked by the hamular process of the pterygoid
bone. The plane of the opening is nearly horizontal, and the length is about
twice the width.

The palatine region comprises a little more than half of the entire length
of the base of the skull (Fig. 43). The hard palate (Palatum durum) is concave
from side to side, and in its length also in the anterior part. It is formed by the
palatine processes of the premaxillae and maxillse, and the horizontal parts of the
palatine bones. It is circumscribed in front and laterally by the alveolar parts of
the maxilla and premaxilla. The interalveolar space (]\Iargo interalveolaris) is that
part of the arch in which alveoli are not present. Behind the last alveolus is the
alveolar tuberosity, and medial to this is a groove for the palatine vein. In the
middle line is the median palatine suture (Sutura palatina mediana). In the line
of the suture, a little behind the central incisors, is the foramen incisivum, through
which the palato-labial artery passes. On either side, parallel with the alveolar
part of the maxilla, is the palatine groove (Sulcus palatinus), which contains the
palatine vessels and nerve. It is continuous at the anterior palatine foramen with
the palatine canal, which is situated between the maxilla and the palatine bone.
The palatine fissure is the narrow interval along the lateral margin of the palatine

THE SKULL AS A WHOLE

process of the premaxilla; it is closed in the fresh state by a process of the cartilage
of the septum nasi. Scattered along each side of the palate are several accessory
foramina. The transverse palatine suture (Sutura palatina transversa) is about
half an inch from the posterior border. The latter is opposite to the fifth cheek
tooth in the adult, and is concave and free.

The nuchal or occipital surface (Norma occipitalis) is formed by the occipital

Zygomatic arch
Glenoid cavity

Condyle of
mandible

Neck of mandible

Angle of mandible

Fig. 51. — Skull of Horse; PosTp:nioR View

The Hyoii) F,(

is Been Removed.

1, External occipital protuberance; 2, curved line; 3, foramen magnum; 4, occipital condyle; 5, paramastoid
process; 6, basilar part of occipital; 7, mastoid foramen; 8, mastoid process; 9, postglenoid process; 10, muscular
process of petrous temporal; 11, alar canal; 12, pterygoid process of sphenoid; 13, body of sphenoid; 14, vomer; 15,
15', perpendicular and horizontal parts of palatine bone; 16, 16, posterior nares or choanae; 17, hamulus of pterygoid
bone; 18, maxillary tuberosity; 19, palatine process of maxilla; 20, palatine process of premaxilla; 21, palatine fissure;
22, accessory palatine foramina; 23, bodj' of mandible; 24, mandibular foramen.

bone. It is trapezoidal in outline, wider below than above, concave dorso-ventrally,
convex transversely. It is separated from the dorsal surface by the nuchal crest.
Below the crest are two rough areas for that attachment of the complexus muscles.
A little lower is a central eminence, the external occipital protuberance, on which the
ligamentum nuchse is attached. At the lowest part centrally is the foramen mag-
nmn. This is bounded laterally by the occipital condyle, lateral to which is the
paramastoid process.

THE SKELETON OF THE HORSE

.a g

i g'^

" ft «

o ^" I

-2 O m
a. .S «

THE CRANIAL CAVITY

The apex of the skull is formed by the bodies of the premaxillae and mandible,
carrying the incisor teeth.

THE CRANIAL CAVITY

This cavity (Cavum cranii) incloses the brain, with its membranes and vessels.
It is relatively small and is ovoid in shape.

The dorsal wall or roof (Calvaria) (Fig. 52) is formed by the supraoccipital,
interparietal, parietal, and frontal bones. In the middle line is the internal parietal
crest, which joins the crista galli in front, and furnishes attachment to the falx
cerebri. Posteriorly the crest is continued by the sharp anterior margin of the

Occipital bone
{squamous part)

Parietal bone

Frontal bone

Paramasioid Occipital hone Sphenoid bone
process {basilar part) {body)

^^gg^^.

Fig. 54. — Sagittal Section of Cranium or Horse.
1, Lateral wall of foramen magnum; 2, hypoglossal foramen; 3, foramen lacerum posterius; 4, 5, 6, carotid, oval,
and spinous notches; 7, floccular fossa; 8, internal acoustic meatus; 9, petrosal crest; 10, hypophyseal or pituitary
pons (Fossa pontis) depression below 12 is the hjijophyseal fossa; 11, groove for maxillary nerve; 12, groove for cav-
ernous sinus; 13, optic foramen; 14, 14, sphenoidal sinus; 15, crista galli; 16, perpendicular plate of ethmoid bone;
17, vomer; 18, septum between frontal sinuses; 19, orbital wing of sphenoid; 20, temporal wing of sphenoid; 21, in-
ternal occipital protuberance; 22, canalis transversus; 23, depression for vermis cerebelli.

tentorium osseum, which projects downward and forward into the cavity, and gives
attachment to the tentorium cerebelli by its sharp lateral edges. Behind this the
roof is grooved centrally for the middle lobe or vermis of the cerebellum. Trans-
verse grooves pass from the base of the tentorium osseum to the temporal canals.
The anterior part of the roof is hollowed by the frontaj sinus. The occipital part
is very thick and strong.

The lateral wall (Fig. 54) is formed chiefly by the temporal and frontal bones
and the orbital wing of the sphenoid. It is crossed obliquely by the petrosal crest,
which concurs with the margin of the parietal bone and the internal occipital pro-
tuberance in dividing the cavity into cerebral and cerebellar compartments. Behind

32 THE SKELETON OF THE HORSE

the crest is a depression for the hemisphere of the cerebellum. Behind this are the
internal acoustic meatus and the openings of the aquseductus vestibuli and aquse-
ductus cochlese.

The roof and lateral walls are marked by digital impressions and vascular
grooves.

The ventral wall or floor (Basis cranii interna) (Fig. 53) may l)e regarded as
forming three fossae. The anterior fossa (Fossa cranii oralis) supports the frontal
and olfactory parts of the cerebrum. It is formed chiefly by the presphenoid, and
lies at a higher level than the middle fossa. In front the fossa is divided medially
by the crista galli, lateral to which are the deep ethmoidal fossae for the olfactory
bulbs. The ethmoidal foramen perforates the cranial wall at the outer side of these
fossae. Further back the central part of the surface is slightly elevated, and is
flanked by shallow depressions which support the olfactory tracts. Posteriorly
is a bony shelf which covers the entrance to the optic foramina; the edge of this
shelf and the posterior borders of the orbital wings of the sphenoid may be taken as
the line of demarcation between the anterior and middle fossae. The middle fossa
(Fossa cranii media) is the widest part of the cavity. It extends backward to the
spheno-occipital and petrosal crests, thus corresponding to the postsphenoid. In its
middle is the hypophyseal fossa in which the hypophysis cerebri lies. On either side
are two grooves: the medial one transmits the cavernous sinus and the ophthalmic,
third, and sixth nerves to the foramen orbitale; the lateral one leads to the foramen
rotundum, and lodges the maxillary nerve. Lateral to the grooves is a depression
for the piriform lobe of the cerebrum. The posterior fossa (Fossa cranii posterior)
corresponds to the basilar part of the occipital bone. It contains the medulla
oblongata, pons, and cerebellum. In front is a median depression (Fossa pontis)
for the pons. The surface behind this (Fossa meduUae oblongatae) is concave trans-
versely and slopes gently downward to the foramen magnum; it supports the
medulla oblongata. On either side are the foramen lacenmi and the h3rpoglossal
foramen.

The anterior or nasal wall (Fig. 33) is formed by the cribriform plate of the
ethmoid, which separates the cranium from the nasal cavity. It is perforated by
numerous foramina for the passage of the olfactory nerve-bundles.

THE NASAL CAVITY

The nasal cavity (Cavum nasi) is a longitudinal passage which extends through
the upper part of the face. It is divided into right and left halves by a median
septum nasi. The lateral walls are formed by the maxilla, premaxilla, the per-
pendicular part of the palatine, and the turbinate and ethmoid bones in part. This
wall is crossed obliquely by the lacrimal canal and groove for the naso-lacrimal
duct, and its posterior part is perforated by the sphenopalatine foramen. The
dorsal wall or roof is formed by the frontal and nasal bones, which form a median
prominence at their junction. It is concave from side to side, and nearly straight
longitudinally, except in the posterior part, where it curves downward. The ven-
tral wall or floor is formed by the palatine processes of the premaxillae and max-
illae, and the horizontal parts of the palate bones. It is wider but considerably
shorter than the roof. It is concave transversely, and nearly horizontal from
before backward, except in the posterior third, where there is a slight declivity.
The anterior part presents a median groove for the cartilage of the septum, and a
furrow for the vomero-nasal organ (of Jacobson) on either side. Posteriorly there
is a median elevation, the nasal crest, to which the vomer is attached. Lateral to
the palatine process of the premaxilla is the palatine fissure.

The septum nasi osseum is formed by the perpendicular plate of the ethmoid

THE NASAL CAVITY

behind, and the vomer below. In the fresh state it is completed by che cartilage
of the septum nasi (Cartilago septi nasi).

Fig. 55. — Cross-section of Nasal Region op Skull
OF Horse; the Section Passes Through the
Anterior End of the Facial Crest, and Be-
tween the Third and Fourth Cheek Teeth.
a, Dorsal, 6, ventral, turbinate bone; c, d, cavities
of a and 6; e, common meatus; /, g, h, dorsal, middle,
ventral meatus; i, k, passages to cavities of turbinate
bones; I, naso-lacrimal duct; m, infraorbital canal; n,
anterior end of maxillary sinus; o, septal cartilage.
(After EUenberger, in Leisering's Atlas.)

Fig. 56. — Cross-section of Nasal Region of Skull
OF Horse; the Section is Cut About Half-
way between the Orbit and the Anterior
End op the Facial Crest, and Passes be-
tween the Fifth and Sixth Cheek Teeth.
o. Dorsal, b, ventral, turbinate bone; c, d, cavities
of a and b; e, common meatus; /, dorsal, g, middle, h,
ventral meatus; i, placed over ridge in maxillary sinus;
k, communication between outer and inner (turbinate)
part of maxillary sinus; I, naso-maxillary opening; m,
naso-lacrimal canal; n, infraorbital canal. (After
EUenberger, in Leisering's Atlas.)

The turbinate bones divide each half of the nasal cavity into three meatus
nasi.

The dorsal meatus (Meatus nasi dorsalis) is a narrow passage between the
roof and the dorsal turbinate bone. It ends at the cribriform plate of the ethmoid.

Fig. 57. — Skull of Young Horse; Lateral View, with Sinuses Opened Up.
A', A, Anterior and posterior compartments of maxillary sinus; B, B' , frontal and turbinate parts of frontal siiiu.i,
C, orbit; 1, septum between compartments of maxillary sinus; 2, 2, infraorbital canal; 3, turbinate part of maxillary
Binus; 4, 5, 6, last three cheek teeth (covered by thin plate of bone) ; 7, anterior limit of maxillary sinus in older subject;
8, infraorbital foramen; 9, anterior end of facial crest; 10, course of naso-lacrimal duct; 11, fossa for lacrimal sac; 12,
dorsal turbinate bone; 13, fronto-maxillary opening.

The middle meatus (Meatus nasi medius) is the space between the two turbinate
bones. In its posterior part is the very narrow opening into the maxillary sinus.
The ventral meatus (Meatus nasi ventralis) is the channel along the floor which is

THE SKELETON OF THE HORSE

overhung by the ventral turbinate bone; it is much the largest and is the direct
path between the nostrils and posterior nares.

The osseous nasal aperture (Apertura nasi
ossea) is bounded by the nasal bones and the
premaxillse.

The posterior extremity or fundus is separ-
ated from the cranial cavity by the cribriform
plate of the ethmoid, and is largely occupied by
the lateral masses of that bone.

THE PARANASAL SINUSES

Connected directly or indirectly with the
nasal cavity, of which they are diverticula, are
four pairs of air-sinuses (Sinus paranasales),
viz., maxillary, frontal, sphenopalatine, and
ethmoidal.

The maxillary sinus (Sinus maxillaris) is the
largest. Its lateral wall is formed by the maxilla,
the lacrimal, and the malar. It is bounded medi-
ally by the maxilla, the ventral turbinate, and the
lateral mass of the ethmoid bone. It extends
backward to a transverse plane in front of the
root of the supraorbital process, and its anterior
limit is indicated approximately by a line drawn
from the anterior end of the facial crest to the
infraorbital foramen. Its dorsal boundary cor-
responds to a line drawn backward from the in-
fraorbital foramen parallel to the facial crest.
The ventral wall or floor is formed by the alve-
olar part of the maxilla; it is very irregular and
is crossed by bony plates running in various
directions. The last three cheek teeth project
up into the cavity to an extent which varies
with age; they are covered by a thin plate of
bone. The cavity is divided into anterior and
posterior parts by an oblique septum (Septum
sinus maxillaris) . The lateral margin of the sep-
tum is commonly about two inches (ca. 5 cm.)
from the anterior end of the facial crest; from
here it is directed inward, backward, and up-
ward. The upper part of the septum (formed
by the posterior end of the ventral turbinate
bone) is very delicate and usually cribriform.

Fig. 58. — Skull of Young Horse; Dorsal
View, with Sinuses Opened Up.
1, 2, Ends of frontal sinus; 3, fronto-
maxillary opening: 4, dorsal turbinate bone;
5, lateral mass of ethmoid bone; 6, 6', two
compartments of maxillary sinus; 7, septum
between 6 and G'; 8, orbit; 9, anterior end
of facial crest; A, frontal bone; B, nasal
bone; C, lacrimal bone; D, maxilla. Note
difference in position and form of septum in
maxillary sinus as compared with preceding
figure.

The position and shape of the septum are very
variable. It is often further forward — in some cases
even as far forward as the anterior end of the facial crest. Exceptionally it is much nearer the
orbit than is stated above. In the recent state, i. e., when covered by the mucous membrane on
both surfaces, it is nearly always complete, but in very exceptional cases there is an opening of
variable size in the upper part.

The anterior compartment, often called the inferior maxillary sinus, is partially
divided by the infraorl)ital canal into a lateral maxillary part and a medial smaller
turbinate part. The latter communicates with the middle meatus by a very narrow
slit situated at its highest part. The posterior compartment, often called the

THE PARANASAL SINUSES

superior maxillary sinus, is also crossed by the infraorbital canal, over which it
opens freely into the sphenopalatine sinus. It communicates dorsally with the
frontal sinus through the large oval fronto-maxillary opening, situated at the level
of the osseous lacrimal canal and the corresponding part of the medial wall of the
orbit; the orifice is commonly about one and a half to two inches (ca. 4 to 5 cm.)
long and an inch or more (2 to 3 cm.) wide. Just in front of this, and covered by a
thin plate, is the narrow naso-maxillary fissure (Aditus naso-maxillaris), by which
the sinus opens into the posterior part of the middle meatus.

The foregoing statements refer to the arrangement in the average adult aniinal. In the
foal the cavity (with the exception of its turbinate part) is largely occupied by the developing
teeth. In horses five to six years of age the maxillary part of the sinus is filled up to a large degree
by the embedded parts of the teeth. As the teeth are extruded to compensate the wear, more
and more of the cavity becomes free, until in old age only the short roots project up in the floor,
covered by a layer of bone. Other facts in this connection will be given in the description of the
teeth. In exceptional cases the posterior part of the ventral turbinate is smaller than usual and
leaves a considerable interval, through which the maxillary sinus communicates with the nasal
cavity. The fronto-maxillary opening is very variable in size.

Squamous
Squamous Parietal temporal
part of occip- bone bone Frontal

ital bone

bone

Lacrimal Max-

Nasal bone

Premaxilla

Lateral

part of

occipital

bone

Basilar part of
occipital bone

Mandible Incisor teeth

(first and second)

Fig. 59. — Skull of Foal About Two Months Old.
This figure illustrates differential features of skull of young foal as compared with that of adult animal shown in
Fig. 28. 1, Occipital condyle; 2, paramastoid process; 3, mastoid process; 4, external acoustic meatus; 5, zygomatic
process of temporal bone; 6, supraorbital process of frontal bone; 7, zygomatic process of malar bone; 8, facial crest;
9, infraorbital foramen; 10, mental foramen; 11, angle of 'mandible; 12, condyle of mandible; 13, coronoid process
of mandible.

The frontal or frbnto-turbinate sinus (Sinus frontalis) consists of frontal and
turbinate parts. The frontal part is bounded chiefly by the two plates of the
frontal bone, but its floor is formed in part by the lateral mass of the ethmoid. It
extends forward to a plane through the anterior margins of the orbits, backward to
one through the temporal condyles, and outward into the root of the supraorbital
process. It is separated from the sinus of the opposite side by a complete septum
(Septum sinuum frontalium). It is partially subdivided by a number of bony
plates. The turbinate part is situated in the posterior part of the dorsal turbinate
bone, roofed in by the nasal and lacrimal bones. It extends forward to a transverse
plane about half-way between the anterior margin of the orbit and the end of the
facial crest. It is in free communication behind with the frontal part over the
lateral mass of the ethmoid. It is separated from the nasal cavity by the thin

80 THE SKELETON OF THE HORSE

turbinate plate. The frontal and maxillary sinuses communicate through the
large opening described above.

The sphenopalatine sinus (Sinus sphenopalatinus) consists of two parts which
communicate under the lateral mass of the ethmoid. The sphenoidal (posterior)
part is excavated in the body of the presphenoid. The palatine (anterior) part is
between the two plates of the perpendicular part of the palatine bone, under the
lateral mass of the ethmoid; it communicates freely with the maxillary sinus. The
septum between the right and left sinuses is not usually median in the sphenoidal
part.

In about one-third of the cases (according to PauUi) the sphenoidal and palatine parts are
separated by a transverse septum, and the sphenoidal part then communicates only with the ven-
tral ethmoidal meatuses.

The term ethmoidal sinus is often applied to the cavity of the largest ethmo-
turbinate. It communicates with the maxillary sinus through an opening in the
lateral lamina.

The Bones of the Thoracic Limb
the scapula

The scapula is a flat bone which is situated on the anterior part of the lateral
wall of the thorax; its long axis extends obliquely from the fourth thoracic spine
to the sternal end of the first rib. It is curved slightly and slopes outward in
adaptation to the form of the thoracic wall. It is triangular in outline, and has
two surfaces, three borders, and three angles.

The lateral surface (Facies lateralis) is divided into two fossae by the spine of
the scapula (Spina scapulae), which extends from the vertebral border to the neck
of the bone, where it subsides. The free edge of the spine is thick, rough, and in
great part subcutaneous. A little above its middle there is a variable prominence,
the tuber spinas, to which the trapezius muscle is attached. The supraspinous
fossa (Fossa supraspinata) is situated in front of the spine, and the infraspinous
fossa (Fossa infraspinata) behind it. The former is much the smaller of the two;
it is smooth and is occupied by the supraspinatus muscle. The infraspinous fossa
lodges the infraspinatus muscle; it is wide and smooth in its upper part, narrower
below, where it is marked by several rough lines for muscular attachment; near
the neck is the nutrient foramen, and a little lower is a vascular groove.

The costal surface (Facies costalis) is hollowed in its length by the subscapular
fossa (Fossa subscapularis) ; this occupies nearly the whole of the lower part of the
surface, but is pointed above and separates two rough triangular areas (Facies
serrata), to which the serratus ventralis is attached. In the lower third there is a
vascular groove with several branches.

The anterior border (Margo cranialis) is convex and rough above, concave and
smooth below.

The posterior border (Margo caudalis) is slightly concave. It is thick and
rough in its upper third, thin in its middle, and thickens again below.

The vertebral border (Margo vertebralis) carries the scapular cartilage (Car-
tilago scapulae). In the young subject this edge of the bone is thick, and is pitted
by impressions into which the cartilage fits. The cartilage is the unossified part
of the foetal scapula. Its lower edge fits the depressions and elevations of the bone.
It thins out toward the free edge, which is convex and lies alongside of the vertebral
spines. In front it continues the line of the bone, but behind it forms a rounded
projection. The lower part of the cartilage undergoes more or less ossification, so
that the vertebral border of the bone in old subjects is thin, irregular, and porous.

The anterior or cervical angle (Angulus cranialis) is at the junction of the

THE SCAPULA

■APULA OF Horse; Lateral Surface,
1, Spine; 2, tuber spinse; 3, cartilage; 4, anterior
angh'; 5, posterior angle; 6, supraspinous fossa; 7, in-
fraspinous fossa; 8, anterior border; 9, posterior bor-
der; 10, muscular lines; 11, nutrient foramen; 12,
vascular groove ; 13, neck; 14, tuber scapulse; 15, glen-
oid cavity.

Fig. 61. — Right Scapula of Horse; Costal Surface.
1, Anterior angle; 2, posterior angle; 3, anterior border;
4, posterior border; 5, neck; 6, vascular groove; 7, glenoid
cavity; 8, coracoid process; 9, tuber scapulas.

anterior and vertebral borders and lies opposite to the second thoracic spine. It is
relatively thin and is about a right angle.

The posterior or dorsal angle (Angulus caudalis) is thick and rough; it is
opposite to the vertebral end of the seventh rib, and
its position can be determined readily in the living
animal.

The glenoid or articular angle (Angulus glenoid-
alis) is joined to the body of the bone by the neck
of the scapula (Collum scapulae). It is enlarged,
especially in the sagittal direction. It bears the
glenoid cavity (Cavitas glenoidalis) for articulation
with the head of the humerus. The cavity is oval
in outline, and its margin is cut into in front by the
glenoid notch (Incisura glenoidalis), and is rounded
off laterally; just above its postero-lateral part is a
tubercle to which a tendon of the teres minor is at-
tached. The tuber scapulae^ is the large rough
prominence in front, to w^hich the tendon of origin

» Formerly termed the bicipital tuberosity.

Glenoid
cavity

Fig. 62. — Distal Extremity of Left
Scapula of Horse; End View.

88 THE SKELETON OF THE HORSE

of the biceps brachii is attached; projecting from its medial side is the small coracoid
process (Processus coracoideus), from which the coraco-brachiahs muscle arises.

Development. — The scapula has four centers of ossification, viz., one each for
the body of the bone, the tuber scapulae and coracoid process, the anterior part of
the glenoid cavity, and the tuber spinae. The last ossifies after birth and fuses with
the spine about the third year. The tuber scapulae and coracoid process fuse with
the body of the bone about the end of the first year.

In old subjects the spongy substance disappears at the middle part of the fossse, so that the
bone consists here of a thin layer of compact substance. Considerable ossification of the cartilage
is usual, the borders become much rougher, the muscular lines are more pronounced, and a medul-
lary cavity may appear in the neck. Aluch variation occurs in dimensions and slope. The aver-
age ratio between the length and breadth (scapular index) is about 1 : 0..5, but in many cases the
base is relatively wider. The inclination on a horizontal plane varies from .50 to 6.5 degrees. Ex-
ceptionally the coracoid process reaches a length of an inch or more (2}^ to 3 cm.), and the chief
nutrient foramen may be on the posterior border or in the subscapular fossa.

THE HUMERUS

The humerus is a long bone which extends from the shoulder above, where it
articulates with the scapula, to the elbow below and behind, where it articulates
with the radius and ulna. It is directed obliquely downward and backward, form-
ing an angle of about 55 degrees with a horizontal plane. It consists of a shaft
and two extremities.

The shaft (Corpus humeri) is irregularly cylindrical and has a twisted appear-
ance. It may be regarded as having four surfaces. The lateral surface (Facies
lateralis) is smooth and is spirally curved, forming the musculo-spiral groove
(Sulcus musculi brachialis), which contains the brachialis muscle; the groove is
continuous with the posterior surface above and winds around toward the front
below. The medial surface (Facies medialis) is nearly straight in its length,
rounded from side to side, and blends with the anterior and posterior surfaces.
Just above its middle is the teres tuberosity (Tuberositas teres), to which the
tendon of the latissimus dorsi and teres major muscles is attached. The nutrient
foramen is in the distal third of this surface. The anterior surface (Facies crani-
alis) is triangular, wide and smooth above, narrow and roughened below. It is
separated from the lateral surface by a distinct border, the crest of the humerus
(Crista humeri), which bears above its middle the deltoid tuberosity (Tuberositas
deltoidea). From the latter a rough line curves upward and backward to the
lateral surface of the neck, and gives origin to the lateral head of the triceps muscle.
Below the tuberosity the border inclines forward, becomes less salient, and ends at
the coronoid fossa. The posterior surface (Facies caudalis) is rounded from side
to side and smooth.

The proximal extremity (Extremitas proximalis) consists of the head, neck,
two tuberosities, and the intertuberal groove. The head (Caput humeri) presents
an almost circular convex articular surface, which is about twice as extensive as the
glenoid cavity of the scapula, with which it articulates. In front of the head is a
fossa, in which are several foramina. The neck (Collum humeri) is well defined
behind, but is practically absent elsewhere.^ The lateral tuberosity (Tuberositas
lateralis)- is placed antero-laterally, and consists of two parts: the anterior part
forms the lateral boundary of the intertuberal or bicipital groove and gives attach-
ment to the lateral branch of the supraspinatus muscle; the posterior part gives
attachment to the short insertion of the infraspinatus, while its outer surface is
coated with cartilage, over which the chief tendon of the same muscle passes to be

^ The proper "anatomical neck" (Collum anatomicum) is, however, indicated by the shallow
depression which separates the head from the tuberosities, and gives attachment to the joint capsule.

"^ The term "tubercle" as used in human anatomy does not apply well to the domestic ani-
mals.

THE HUMERUS

inserted into a triangular rough area below the anterior part. The medial tuber-
osity (Tuberositas medialis) is less salient, and consists of anterior and posterior
parts; the anterior part forms the medial boundary of the intertuberal groove,
and furnishes insertion to the medial branch of the supraspinatus above, and the
posterior deep pectoral muscle below; the posterior part gives attachment to the
subscapularis muscle. The intertuberal or bicipital groove (Sulcus intertuberalis)'^
is situated in front; it is bounded by the anterior parts of the tuberosities, and is
subdivided by an intermediate ridge. The groove is covered in the fresh state by

Intertuberal
{or bicipital) Lateral
groove tuberosity

crest

Coronoid

Medial
condyle

Lateral
condyle

Head

Neck

Lateral
tuberosity

Medial
epicondyle

Olecra-
Lateral non fossa
epicondyle

Fig. 63. — Left Humerus of Horse; Lateral View.
1, Rough area to which tendon of infraspinatus is
attached; 2, crest; 3, depression for attachment of
lateral Ugament.

Medial
tuber-

Medial
condyle

Fig. 64. — Right Humerus of Horse; Front View,

1, Rough area for attachment of extensor carpi

radialis and extensor digitalis communis; 2, synovial

cartilage, and lodges the tendon of origin of the biceps brachii muscle. Just below
the intermediate ridge is a small fossa in which several foramina open.

The distal extremity has an oblique surface for articulation with the radius
and ulna, which consists of two condyles of very unequal size, separated by a ridge.
The medial condyle (Condylus medialis) is much the larger, and is crossed by a
sagittal groove, on the anterior part of which there is usually a synovial fossa. Pos-
teriorly the groove extends upward considerably above the rest of the articular
surface and reaches the olecranon fossa, and this part articulates with the semilunar

^The name "intertuberal" is designative of the position of the groove, while the term
"bicipital" has reference to its occupation by the tendon of the biceps brachii. The term "sulcus
intertubercular's" is also in common use.

THE SKELETON OF THE HORSE

notch of the ulna. The lateral condyle (Condylus lateralis) is much smaller and
is placed somewhat lower and further back, giving the extremity an oblique ap-
pearance; it is marked b}^ a wide shallow groove. The coronoid fossa (Fossa coro-
noidea) is situated in front, above the groove on the medial condjde; it furnishes
origin to part of the extensor carpi, and lateral to it is a rough depression from
which the common digital extensor arises. Behind and above the condyles are two
thick ridges, the epicondyles. The medial epicondyle (Epicondylus medialis)
is the more salient; it furnishes origin to flexor muscles of the carpus and digit,
and bears a tul^ercle for the attachment of the medial ligament of the elbow joint.
The lateral epicondyle (Epicondylus lateralis) bears laterally the condyloid crest
(Crista condyloidea), which forms here the outer boundary of the musculo-spiral
groove, and gives origin to the extensor carpi radialis. Below this is a rough excava-
tion in which the lateral ligament is attached. The distal border of the epicondyle
gives attachment to the ulnaris lateralis. Between the epicondyles is the deep
olecranon fossa (Fossa olecrani), into which the processus anconseus projects.

Fig. Go. — Proximal Extremity of Left Humerus of
Horse; End View.
1, Intertuberal (or bicipital) groove; 2, 3, anterior
parts of lateral and medial tuberosities; 4, fossa; 5, 6,
posterior parts of lateral and medial tuberosities; 7,
head.

Fig. 60. — Dist.vl Extremity of Left Humerus of
Horse; End View.
1, Medial condyle; 2, lateral condyle; 3, part of
medial epicondyle to which medial ligament is attached;

4, depression in which lateral ligament is attached;

5, 6, areas of attachment of flexor and extensor muscles
of carpus and digit; 7, olecranon fossa.

Development. — The humerus ossifies from six centers, viz., three primary
centers for the shaft and extremities, and three secondary centers for the lateral
tuberosity, the deltoid tuberosity, and the medial condyle respectively. The
proximal end fuses with the shaft at about three and one-half years, the distal at
about one and a half years of age.

THE RADIUS

The radius is much the larger of the two bones of the forearm in the horse.
It extends in a vertical direction from the elbow, where it articulates with the hum-
erus, to the carpus. It is gently curved, the convexity being dorsal. It consists
of a shaft and two extremities.

The shaft (Corpus radii) is curved in its length, somewhat flattened from before
backward, and widened at its ends. It presents for description two surfaces and
two borders. The dorsal surface (Facies dorsalis) is smooth, slightly convex in
its length, and rounded from side to side. The volar surface (Facies volaris)

THE RADIUS

is correspondingly concave in its length and is flattened in the transverse direction.
At its proximal part there is a smooth shallow groove, which concurs with the ulna
in the formation of the interosseous space of the forearm (Spatium interosseum
antibrachii) ; the nutrient foramen is in the lower part of this groove Below this
there is in the young subject a narrow, rough, triangular area to which the ulna is

Olecranon

Processus anconeus

Semilunar notch
Humeral articular
surface v
Coronoid — i«i:,r— '"
process
Radial tu-
berosity

Olecranon

Ridge
2

Fig. 07. — Left R.\dius and VhN\ of Hor.se; L.\teral
View.
1, Tuberosity for attachment of lateral ligament of
elbow joint, and common and lateral extensor muscles;
2, tuberosity for attachment of lateral ligament of
carpal joint; 3, groove for common extensor tendon;
4, groove for lateral extensor tendon.

Processus

anconceus
Semilunar notch

Glenoid cavity

Radial
'- 'dM tuberosity

-Left Radius and Ulna of Horse; Medial
View.
1, Tuberosity for attachment of short part of
medial ligament of elbow; 2, prominence for long part
of same; 3, groove for end of brachialis muscle; 4,
tuberosity for attachment of medial ligament of carpal
joint; 5, oblique groove for tendon of extensor carpi
obUquus.

attached by an interosseous ligament; in the adult the two bones are fused here.
A variable rough elevation distal to the middle and close to the medial border gives
attachment to the radial check ligament. The medial border (Margo medialis)
is slightly concave in its length and is largely subcutaneous; at its proximal end
there is a smooth area on which the tendon of insertion of the brachialis muscle lies,
and a small rough area just below gives attachment to that muscle and the long

92 THE SKELETON OF THE HORSE

medial ligament of the elbow-joint. The lateral border (Margo lateralis) is more
strongly curved, but presents no special features.

The proximal extremity or head ((Extremitas proximalis s. capitulum radii)
is flattened from before backward and wide transversely. It presents the humeral
articular surface (Facies articularis humeralis) which corresponds to that of the
distal end of the humerus; it is crossed by a sagittal ridge, which has a synovial
fossa on its posterior part, and ends in front at a prominent lip, the coronoid proc-
ess (Processus coronoideus). Just below the posterior border, and separated by
a depression, there are two concave facets (Facies articularis ulnaris) for articula-
tion with the ulna, and between these and the interosseous space is a quadrilateral
rough area at which the two bones are united by an interosseous ligament. At
the medial side of the dorsal surface is the radial or bicipital tuberosity (Tuberositas
radii), into which the biceps tendon is inserted. The medial tuberosity (Tuber-
ositas proximalis meclialis) is continuous with the preceding eminence, and fur-
nishes attachment to the short part of the medial ligament. The lateral tuberosity
(Tuberositas proximalis lateralis) is more salient; it gives attachment to the lateral
ligament and to the common and lateral extensor muscles of the digit.

The distal extremity is also compressed from before backward. It presents
the carpal articular surface (Facies articularis carpea), which consists of three parts.
The medial facet is the largest, is quadrilateral, concavo-convex from before back-
ward, and articulates with the radial carpal bone; the intermediate one is some-
what similar in form but smaller, and articulates with the intermediate carpal bone;
the lateral facet is smaller, is convex, and articulates below with the ulnar carpal
and behind with the accessory carpal. The dorsal surface presents three grooves,
separated by ridges. The middle one is vertical and gives passage to the tendon
of the extensor carpi radialis; the lateral one is similar and contains the tendon of
the common digital extensor; the medial one is small and oblique and lodges the
tendon of the extensor carpi obliquus. The volar aspect is crossed by a rough
ridge, below which are three depressions. On either side is a tuberosity (Tuber-
culum ligament!) to which the collateral ligament is attached. The lateral one is
marked by a small vertical groove for the passage of the lateral extensor tendon.

Development.^ — The radius ossifies from four centers, viz., one each for the
shaft, the two extremities, and the lateral part of the distal end; the last is morpho-
logically the distal end of the ulna which has fused with the radius, and the line of
fusion is often indicated by a distinct groove on the carpal articular surface. The
proximal extremity unites with the shaft at about one and a half years, the distal
end at about three and a half years usually.

THE ULNA

The ulna of the horse is a reduced long bone situated behind the radius, with
which it is partially fused in the adult.

The shaft (Corpus ulnae) is three-sided and tapers to a point distally. The
dorsal surface (Facies dorsalis) is applied to the volar surface of the radius, and be-
low the interosseous space the two bones are fused in the adult. The surface which
enters into the formation of the space is smooth and usually presents a small nu-
trient foramen, directed upward. Above the space it is rough and is attached to
the radius by an interosseous ligament which is usually permanent. The medial
surface (Facies medialis) is smooth and slightly concave. The lateral surface
(Facies lateralis) is flattened. The medial and lateral borders (Margo medialis,
lateralis) are thin and sharp, except at the interosseous space. The volar border
(Margo volaris) is slightly concave in its length and is rounded. The distal end is
pointed and is usually a little below the middle of the radius. It is commonly

THE CARPUS

continued by a fibrous cord to the distal tuberosity of the radius, but this band may
be replaced in part or entirely by bone.

The proximal extremity (Extremitas proximalis) is the major part of the bone.
It projects upward and somewhat backward behind the distal end of the humerus,
and forms a lever arm for the extensor muscles of the elbow. The medial surface
is concave and smooth. The lateral surface is convex and is roughened al)ove.
The dorsal border bears on its middle a pointed projection, the processus anconaeus
or "beak," which overhangs the semilunar notch

(Incisura semilunaris).^ The latter is triangular ' "

in outline, concave from above downward, convex
transversely, and articulates w4th the humerus; in
its lower part there is an extensive synovial fossa.

Just below the notch are two convex facets which *'

articulate with those on the volar aspect of the
proximal end of the radius. The volar border is
nearly straight, and is thick and rounded. The
free end or summit is a rough tuberosity, the ole-
cranon, which gives attachment to the triceps
brachii and other muscles.

The primitive distal extremity has, as pre-
viously stated, fused with the radius.

Development. — The ulna ossifies from three
centers, of which one is for the main part of the . .. — ^
bone, one for the olecranon, and one for the distal
end. The cartilaginous embryonic ulna extends
the entire length of the forearm. The distal part
of the shaft is usually reduced to a small fibrous
band or may disappear entirely; in some cases a ^v
variable remnant of it ossifies. The distal ex- "»' .

-;i5,!''

Fig. 69. — Distal End of Left Radius and Ulna of Horse; End
View.
1, 2, 3, 4, Facets which articulate with radial, intermediate, ulnar,
and accessory carpal bones respectively; 5, groove for tendon of exten-
sor carpi radialis; 6, groove for tendon of common digital extensor; 7,
tuberosity for attachment of medial ligament of carpal joint.

Fig. 70. — Sagittal Section of Uppbb

Part of Radius and Ulna of Horse.

Cm, Medullary cavity of ulna.

tremity fuses before birth with the radius. The olecranon unites with the rest
of the bone at about three and a half years. A medullary cavity appears to occur
constantly in the adult — contrary to the statements of some authors.

THE CARPUS
The carpus of the horse consists of seven or eight carpal bones (Ossa carpi)

arranged in two rows, proximal or antibrachial and distal or metacarpal,
1 Formerly called the sigmoid cavity.

The

94 THE SKELETON OF THE HORSE

(abbreviated) names and relative positions of the bones of the left carpus are in-
dicated below:

Proximal Row:
Radial Intermediate Ulnar Accessory

Distal Row:
First Second Third Fourth

The Radial Carpal Bone

The radial carpal bone (Os carpi radiale)4s the largest bone of the proximal row;
it is somewhat compressed transversely, and is clearly six-sided. The proximal
surface is convex in front, concave behind, and articulates with the medial facet
on the distal end of the radius. The distal surface is also convex in front and con-
cave behind; it articulates with the second and third carpal bones. The lateral
surface bears upper and lower facets on its anterior part for articulation with the
intermediate; between and behind these it is excavated and rough. The dorsal
surface is rough and slightly convex. The medial surface and the volar surface
are rough and tuberculate.

The Intermediate Carpal Bone

The intermediate carpal bone (Os carpi intermedium)- is somewhat wedge-
shaped, wider in front than behind. The proximal surface is saddle-shaped, and
articulates with the middle facet on the distal end of the radius. The distal sur-
face is smaller, convex in front, concave behind, and articulates with the third and
fourth carpal bones. The medial surface has upper and lower facets for articula-
tion ^v^th the radial carpal, and between these it is excavated and rough.
The lateral surface is similar to the preceding and articulates with the ulnar car-
pal. The dorsal surface is rough and slightly convex. The volar siuiace bears a
tuberosity on its lower part.

The Ulnar Carpal Bone

The ulnar carpal bone (Os carpi ulnare)^ is the smallest and most irregular
bone of the proximal row. The proximal surface is concave and fits the lower part
of the lateral facet on the distal end of the radius. The distal surface is oblique
and undulating for articulation with the fourth carpal bone. The medial surface
has upper and lower facets for articulation with the intermediate. The dorsal and
lateral surfaces are continuous, convex, and rough. The volar surface is oblique,
and bears a concave facet for articulation with the accessory carpal bone; below
this is a tubercle.

The Accessory Carpal Bone

The accessory carpal bone (Os carpi accessorium)* is situated behind the ulnar
carpal bone and the lateral part of the distal end of the radius. It is discoid and pre-
sents for description two surfaces and a circumference. The medial surface is con-
cave and forms the lateral wall of the carpal groove. The lateral surface is con-
vex and rough; a smooth groove for a tendon crosses its anterior part obliquely
downward and slightly forward. The dorsal border bears two facets; the proximal
one is concave and articulates with the back of the lateral facet on the distal end of
the radius; the distal one is convex and articulates with the ulnar carpal bone.
The remainder of the circumference is rounded and rough.

1 Also known as the scaphoid. ^ ^\^q known as the semilunar or lunar.

^ Also known as the cuneiform.

* Also known as the pisiform and erroneously as the trapezium.

THE FIRST CARPAL BONE THE SECOND CARPAL BONE

The accessory does not directly bear weight, and may be regarded as a sesamoid bone
interposed in the course of the tendons of the middle and lateral flexors of the carpus, which it
enables to act at a mechanical advantage. The posterior border furnishes attachment to the
transverse carpal ligament, which completes the carpal canal for the flexors of the digit.

The First Carpal Bone
The first carpal bone (Os carpale primum)i is a small inconstant bone, com-
monly about the size and shape of a pea, which is situated in the distal part of the
medial ligament of the carpus, behind the second carpal bone.

This bone appears to be absent on both sides in about half of the cases; in a good many
subjects it is present on one side only. In size it varies from a minute nodule to a discoid or cylin-
drical mass 12-15 mm. in length. In exceptional cases it articulates with both the second carpal
and the second metacarpal bone; in other cases with the former only, but in the majority of speci-
mens no articular facet is present.

Fig. 7L — Left Corpus of Horse, with Parts of Adjacent Bones; L.^teral View.
a, Intermediate carpal; Cu, ulnar carpal; Ca, accessory carpal; C3, third carpal; C4, fourth carpal; McIII,
McIV, metacarpal bones; 1, groove for common extensor tendon; 2, groove for lateral extensor tendon; 3, groove
for long tendon of ulnaris lateralis; 4, metacarpal tuberosity; o, original distal end of ulna, which is fused with the
radius and regarded as part of the latter.

The Second Carpal Bone

The second carpal bone (Os carpale secundum)- is the smallest constant bone

of the distal row, and is irregularly hemispherical in shape. The proximal surface

is a convex facet, which is continued upon the volar surface and articulates with the

radial carpal. The lateral surface faces obliquely outward and forward, and bears

1 Also known as the trapezium, and often erroneously called the pisiform.
^ Also known as the trapezoid.

THE SKELETON OF THE HORSE

three facets for articulation with the third carpal bone. The dorsal and
medial surfaces are continuous and bear a tuberosity to which the collateral liga-
ment is attached. The distal surface is articular and consists of a large flattened
facet for the second or inner metacarpal bone, and a small one for the third or large
metacarpal bone. Some specimens have a small facet on the lower part of the volar
surface which articulates with the first carpal bone.

The Third Carpal Bone

The third carpal bone (Os carpale tertium)^ is much the largest bone of the

distal row, forming more than
two-thirds of the width of the
latter. It is flattened from
above downward, and is twice as
wide in front as behind. The
proximal surface consists of two
facets separated by an antero-pos-
terior ridge; the medial facet is
concave and articulates with the
radial carpal; the lateral facet —
for the intermediate carpal — is
concave in front and convex be-
hind, where it encroaches on the
volar surface. The distal surface
is slightly undulating, and articu-
lates almost entirely with the third
or large metacarpal bone, but it
usually bears a small oblique facet
at its medial side for the second
metacarpal, and there is commonly
a non-articular depression later-
ally. The medial surface faces
backward and inward, and bears
three facets for articulation with
the second carpal, between which
it is excavated and rough. The
lateral surface has two facets for
articulation with the fourth car-
pal, and is depressed and rough
in its middle. The dorsal sur-
face is convex and is crossed
by a rough transverse ridge. The
volar surface is relatively small,
and is rounded; its upper part

MdU

Pig. 72. — Left Carpus of Horse, with Parts of Adjacent
Bones; Medial View.
Cr, Radial carpal; Ca, accessory carpal; Ct, first carpal;
C2, second carpal; McII, McIII, metacarpal bones; 1, tuber-
osity of radius for attachment of medial ligament of carpus;
2, groove for tendon of extensor carpi obliquus; 3, third car-
pal; 4, metacarpal tuberosity.

is encroached upon by the proximal articular surface, below which it is rough.

The Fourth Carpal Bone

The fourth carpal bone (Os carpale quartum)- is somewhat wedge-shaped, and
is readily distinguished from the second by its greater size and its volar tubercle.
The proximal surface articulates with the intermediate and ulnar; it is convex and
curves outward, backward, and downward, encroaching on the lateral and volar sur-
faces. The distal surface bears two medial facets for the third or large metacarpal

1 Also known as the os magnum or capitatufti.

2 Also known as the unciform or hamatum.

THE FOURTH CARPAL BONE

and a lateral one for the fourth or lateral metacarpal bone. The medial surface
has two or three facets for articulation with the third carpal, between which it is
excavated and rough. The dorsal surface is convex and rough. The lateral sur-

McIII

Fig. 73. — Left Carpus of Horse, with Pauts )f Adjacent Bones; Volar View.
The accessory and first carpal bones have been moved out of their natural position and their articular connections
indicated by arrows. Cr, Radial carpal; 3, intermediate carpal; Cu, ulnar carpal; Co, accessory carpal; CI, first
carpal; C2, second carpal; 4, third carpal; C4, fourth carpal; 1, groove for lateral extensor tendon; 2, tuberosity
of radius for medial ligament of carpal joint; 5, volar tubercle of fourth carpal; 6, rough area on large metacarpal
bone for attachment of suspensory ligament.

Intermediate

Third

Radidl

Fig. 74. — Proximal Row of Left Carpus of Horse;

Proximal View.

1-4, Articular facets corresponding with those on Fig. 69;

5, groove for tendon of ulnaris lateralis.

Fourth

Second

First

Fig. 7.5.— Distal Row of Left Carpus of Horse:
Proximal View.
1, Articulation of first carpal with second; 2, 2,
facets for radial; 3, 3', facets for intermediate 4,
facet for ulnar.

THE SKELETON OF THE HORSE

face is small, being encroached upon b}- the proximal articular surface.
surface bears a tubercle on its distal part.^

The volar

The Carpus as a Whole
The bones of the carpus, exclusive of the accessory, form an irregular quadran-
gular mass, the width of which is about twice the height or the dorso-volar diameter.
The dorsal surface is convex from side to side, depressed along the line of junction
of the two rows, and prominent below. The volar surface is in general slightly
convex, but very irregular. It forms with the accessory
carpal the carpal groove (Sulcus carpi) , which in the recent
state is rendered smooth by the volar ligament; it is con-
verted into the carpal canal (Canalis carpi) for the flexor
tendons by the transverse carpal ligament, which stretches
across from the accessory bone to the medial side. The
proximal surface is widest medially and is elevated in front,
concave behind ; it is entirely articular and adapted to the
car])al articular surface of the radius. The distal surface
is also articular and is irregularly faceted in adaptation to
the surfaces of the metacarpal bones; each of the distal
bones usually articulates with two metacarpal bones, but
sometimes the third rests on the third metacarpal only.
The medial and lateral surfaces are both irregular and
rough, the former being the wider. With the exception of
the accessory, ulnar, and second, each bone articulates
with two bones of the other row.

Development. — Each ossifies from a single center.

McIV

McIII

Fig. 76. — Right Metacarpal
Bones op Horse; Vol.\r
View.

1, Nutrient foramen of
large (third) metacarpal bone;
2, 3, 4, proximal extremities; 5,
surface for attachment of sus-
pensory ligament; 6, sagittal
ridge of distal end of large meta-
carpal bone; 7, 7', distal ends of
small (second and fourth) meta-
carpal bones.

Fig.

McII
iRPAL Bones of Horse; End

-Proximal Extremities of Left Metac.
View.
2, 2', Facets for second carpal bone; 3, 3', facets for third carpal bone; 4, 4', facets
for fourth carpal bone; 5, metacarpal tuberosity.

THE METACARPUS

Three metacarpal bones (Ossa metacarpalia) are
present in the horse. Of these, only one, the third or
large metacarpal bone, is fully developed and carries a
digit; the other two, the second and fourth, are much
reduced, and are commonly called the small metacarpal or "splint" bones.

The Third or Large Metacarpal Bone
This (Os metacarpal tertium) is a very strong long bone, which is situated ver-
tically between the carpus and the first phalanx. It consists of a shaft and two ex-
tremities.

^ This bone is probably equivalent to the fourth and fifth carpals of forms in which five
carpal elements are present in the distal row.

THE SMALL METACARPAL BONES 99

The shaft (Corpus) is semicylindrical, and presents two surfaces and two
borders. The dorsal surface is smooth, convex from side to side, and nearly
straight in its length. The volar surface is somewhat convex from side to side and,
with the small bones, forms a wide groove which lodges the suspensory ligament.
On either side of its proximal two-thirds it is roughened for the attachment of the
small metacarpal bones. The nutrient foramen occurs at the junction of the
proximal and middle thirds. The distal part is wider and flattened. The borders
are rounded.

The proximal extremity (Extremitas proximalis s. basis) bears an undulating
articular surface adapted to the distal row of carpal bones. The greater part sup-
ports the third carpal bone; the oblique lateral part, separated from the preceding
by a ridge, articulates with the fourth, and a small facet for the second is usually
found at the medio-volar angle. On either side is a notch separating two small
facets which articulate with the proximal ends of the small metacarpal bones.
Toward the medial side of the dorsal surface is the metacarpal tuberosity, into
which the extensor carpi radialis is inserted. The volar surface is roughened for
the attachment of the suspensory ligament.

The distal extremity (Extremitas distalis s. capitulum) presents an articular
surface for the first phalanx and the proximal sesamoid bones, which is composed of
two condyles, separated by a sagittal ridge; the medial condyle is slightly the larger.
On either side is a small fossa, surmounted by a tubercle, for the attachment of the
collateral ligaments of the fetlock joint.

The large metacarpal is one of the strongest bones in the skeleton. The compact substance
is specially thick in front and medially. The medullary cavity extends further toward the ends
than in most of the long bones of the horse and there is little spongy substance.

The Small Metacarpal Bones

These, numerically the second and fourth metacarpal bones (Ossa metacarpalia
secundum et quartum) , are situated on either side of the volar surface of the large
metacarpal bone, and form the sides of the metacarpal groove. Each consists of a
shaft and two extremities.

The shaft (Corpus) is three-sided and tapers to the distal end. It is variably
curved, convex toward the middle line of the limb. The attached surface is flat-
tened and is rough, except in its lower part; it is attached to the large metacarpal
bone by an interosseous ligament, except near the distal end. The dorsal or ab-
axial surface is smooth and rounded from side to side above, grooved below. The
volar or axial surface is smooth and concave from edge to edge, except below,
where it forms a rounded edge.

The proximal extremity (Extremitas proximalis s. basis) is relatively large. In
the case of the medial bone it usually bears two facets above which support the sec-
ond and third carpal bones, while the lateral bone has here a single facet for articu-
lation with the fourth carpal bone. Each has also two facets for articulation with
the large metacarpal, and is elsewhere roughened for the attachment of ligaments
and muscles. The medial bone may present a small facet behind for the first carpal
bone.

The distal extremity (Extremitas distalis s. capitulum) is usually a small nod-
ule, which projects to a variable extent in different subjects, and is easily felt in the
living animal. It is situated two-thirds to three-fourths of the way down the region.

The small metacarpal bones vary much in length, thickness, and curvature. In the ma-
jority of cases the medial bone is the longer; in other subjects the lateral one is the longer or there
is no material difference. Sometimes the curvature is very pronounced, so that the distal end
causes a decided projection. The distal end is very variable in size and may be a mere point; in
other cases, especially in large draft horses, it may present a prolongation wliich is regarded as the
vestige of the digital skeleton.

Development. — The large metacarpal bone ossifies from three centers. The

100

THE SKELETON OF THE HORSE

proximal extremity unites with the shaft before birth, the distal extremity toward
the middle of the second year. The small metacarpal bones ossify from two cen-
ters, one of which is for the proximal extremity. Their distal ends are cartilaginous
at birth. Fusion of the middle part of the shaft with the large metacarpal bone is
common. ■''■■:'

THE PHALANGES
The First Phalanx
The first phalanx (Phalanx prima) ^ is a long bone, and is situated between the
large metacarpal bone and the second phalanx. It is directed obliquely downward
and forward, forming an angle of 50 to 55 degrees with the horizontal plane in well-
formed limbs. It consists of a shaft and two extremities.

Distal end of small meta-
carpal bone

Proximal sesamoid hone

Distal end of first phalanx
Proximal end of second phalanx

Distal sesamoid bone

Distal end of large metacarpal bone
Proximal end of first phalanx

Dorsal groove —

Angle _ ., '- '

DiMal border of third phalanx
Fig. 78. — Skeleton of Digit and Distal Part of Metacarpus of Horse; Lateral View.
1-7, Eminences and depression for attachment of ligaments. Cartilage of third phalanx is removed.

The shaft (Corpus) is wider and much thicker above than below, and presents
two surfaces and two borders. The dorsal surface is convex from side to side and
smooth. The volar surface is flattened, and bears a triangular rough area, bounded
by ridges which begin at the proximal tuberosities and converge distally; this area
furnishes attachment to the distal sesamoidean ligaments. The borders, medial
and lateral, are rounded and have a rough area or a tubercle on their middle parts.

The proximal extremity (Extremitas proximalis s. basis) is relatively large.
It bears an articular surface adapted to the distal end of the large metacarpal bone,
^ This bone is also called the large pastern bone or os suffraginis.

THE FIRST PHALANX

101

consisting of two glenoid cavities separated by a sagittal groove; the medial cavity-
is a little larger than the lateral one. On each side is a buttress-like tuberosity for
ligamentous attachment. The dorsal surface has a slight elevation for the attach-
ment of the extensor tendons.

The distal extremity (Extremitas distalis) is smaller, especially in its dorso-
volar diameter. It presents a trochlea for articulation with the second phalanx,
consisting of a shallow sagittal groove separating two condyles; the medial con-

I Titer mediate groove

Proximal articular surface

Tuberosity

Eminence for extensor tendons

Dorsal surface -

Eminence for collateral ligament -
Distal articular surface '

Proximal articular surface -

Dorsal surface —
Eminence for collateral ligatncnt
Distal articular surface

Articular surface

Angle ..

Depression for collateral
ligament

Dorsal groove
Coronary border '''f"'\^
Articular surface -'*■'«.'

Extensor process ■-'

Dorsal surface

First phalanx

Second phalanx

Distal sesamoid

Third phalanx

Distal border ■ ' ''

Fig. 79. — Phalanges and Distal Sesamoid of Horse; Dorsal Aspect.

dyle is a little the larger, and the two are separated posteriorly by a notch. On
either side, just above the margin of the articular surface, is a depression sur-
mounted b}^ a tubercle, to both of which the collateral ligament is attached. Be-
hind the tubercle is a distinct mark to which the superficial flexor tendon is
attached.

Development. — The first phalanx ossifies from three centers. The distal end
unites with the shaft before birth, the proximal end at about one year of age.

The first phalanx contains a small medullary cavity in the middle of the shaft. It may be

JQ2 THE SKELETON OF THE HORSE

remarked that the bone is twisted sUghtly; when placed volar surface down on the table, it touches
the latter by three points only, the proximal tuberosities and the medial condyle.

The Second Phalanx
The second phalanx (Phalanx secunda)i is situated between the first and
third phalanges, its direction corresponding to that of the first phalanx. It is
flattened from before l)ackward, and its width is greater than its height. It may
be described as possessing four surfaces.

The proximal surface presents two glenoid cavities separated by a low ridge,

and articulates with the first phalanx.
The middle of the dorsal border is ele-
vated and roughened in front for the
attachment of the common extensor
tendon. The volar border is thick and
overhanging; in the fresh state its mid-
dle part is covered with cartilage, over
which the deep flexor tendon passes.
On either side there is an eminence, to
which the collateral ligament and the
superficial flexor tendon are attached.
The distal surface is trochlear,
and articulates with the third phalanx
and distal sesamoid bone. It resem-
bles somewhat the trochlea of the first
phalanx, but is more extensive and en-
croaches more on the dorsal and volar
surfaces.

The dorsal surface is convex from
side to side and smooth in its middle;
on each side of its distal part is a rough
depression, surmounted by a tuber-
osity, to both of which ligaments are
attached.

The volar surface is smooth and
fiattened. The borders which separate
the dorsal and volar surfaces are con-
cave from above downward, rounded
from before backward.

Development. — The second pha-
laiLx ossifies like the first, but the proxi-
mal end unites with the shaft two or
three months earlier.

Tuberosity

Ridges for

attachment

of middle

distal sesd-

moid ligament

Imprint for

tendon of

superfici(d

flexor

Condyle

Transverse
prominence

-Digital Bones of Fore Limb of Horse; Volar
Aspect.

The Third Phalanx
The third phalanx (Phalanx ter-
tia)^ is entirely inclosed by the hoof,
It presents for examination three sur-

to which it conforms in a general way.
faces, three borders, and two angles.

The articular surface (Facies articularis) faces upward and backward, and is
chiefly adapted to the distal surface of the second phalanx, but a narrow, flattened
area along the volar border articulates with the distal sesamoid. The proximal or
coronary border bears a central eminence, the extensor process (Processus exten-

1 This bone is also called the small pastern bone or os coronse.

2 This bone is also called the os pedis or coffin bone.

THE THIRD PHALANX

103

sorius), to which the common extensor tendon is attached. On either side is a de-
pression for the attachment of the collateral ligament.

The dorsal or wall surface (Facies dorsalis) slopes downward and forward.
The angle of inclination on the ground plane is about 45 to 50 degrees in front.

Cartilage

h Dorsal Angle

grooir

) Arlicular surface

Extensor process

Depression for collateral ligament
Dorsal surface

l)istal border

Fig. si. — Third Phalanx of Horse; Lateral View.
a, b. Anterior and posterior extremities of cartilage.

Laterally the height diminishes, and the slope becomes steeper, especially on the
medial side. From side to side the curvature is almost semicircular. The surface
is rough and porous, resembling pumice stone somewhat. It is perforated by nu-
merous foramina of various sizes; a series of larger ones is situated on or near the
distal border. On either side the dorsal groove (Sulcus dorsalis)'^ passes forward
from the angle and ends at one of the
larger foramina. In the fresh state this
surface is covered by the corium of the
wall of the hoof. The distal border is
thin, sharp, and irregularly notched;
there is commonly a wider notch in
front.

The volar surface (Facies volaris)
is arched, and divided into two unequal
parts by a curved rough line, the semi-
lunar crest (Crista semilunaris) . The
larger area in front of the crest is cres-
cent-shaped, concave, and compara-
tively smooth; it corresponds to the
sole of the hoof, and may be termed
the sole surface. The part behind the
crest is much smaller, and is semilunar;
it is related to the deep flexor tendon,
and is hence called the flexor surface
(Facies flexoria) . It presents a central
prominent rough area, on either side of
which is the volar foramen (Foramen

volare), to which the volar groove (Sulcus volaris) conducts from the angle.^
The foramina lead into the semilimar canal (Canalis semilunaris) within the
bone, from which small canals lead to some of the foramina of the dorsal sur-

FiG. 82. — Section of Third Phalanx of Horse.

Section is cut approximately parallel with volar sur-
face and opens up the semilunar canal (C.s.). Volar for-
amina indicated by arrows.

Formerly termed the pyramidal process.
Formerly termed the plantar groove and foramen.

Formerly termed the preplantar groove.

104

THE SKELETON OF THE HORSE

face. The deep flexor tendon is inserted into the semilunar crest and the central

rough area behind it.

The volar grooves and foramina transmit the terminations of the digital arteries into the
semilunar canal, where they meet and form a terminal arch, from which branches pass through
canals in the bone and emerge through the foramina on the dorsal surface.

The angles or wings (Anguli) are prismatic masses which project l^ackward on
either side; the medial one is usually the shorter. Each is divided into upper and
lower parts by a notch, or is perforated by a foramen which leads to the dorsal
groove.^ The proximal border carries the cartilage.

The cartilages of the third phalanx (Cartilagines phalangis tertise)- are rhom-
boid curved plates which surmount the angles on either side. They are relatively
large and extend above the margin of the hoof sufficiently to be distinctly palpable.
The abaxial surface is convex, the axial, concave. The proximal border is sinuous

and thin ; the distal is thicker and is in
part attached to the wing. The anterior
end is attached by ligament to the side
of the second phalanx. The posterior
end curves toward its fellow at the heel,
and is perforated by numerous for-
amina for the passage of veins.

It wll be noted that the size and form
of the angles vary much in difTerent specimens.
In the new-born foal the angle is a small,
pointed projection. Later the process of ossi-
fication invades the lower part of the car-
tilage to a varying extent. In some cases the
greater part of the cartilage is ossified — a con-
dition commonly termed " sidebone. " In the
young subject the cartilage is hyaline, but later
it changes to the fibrous type.

Development. — The ossification of
the third phalanx is peculiar. While
the proximal articular part is still car-
tilaginous, a perichondrial cap of bone
is formed in relation to the hoof. Later
the process extends into the upper part.
Structure. — The interior of this
bone is channeled by numerous canals
for vessels, most of which radiate from
the semilunar canal to the dorsal sur-
face; these are not canals for nutrient
vessels of the bone, but transmit
arteries to the corium of the hoof. Thick layers of compact substance are found
at the articular and flexor surfaces and the extensor process, i. e., at the points of
greatest pressure and traction.

The Sesamoid Bones

The two proximal sesamoids (Ossa sesamoidea phalangis primse) are situated
behind the distal end of the large metacarpal bone, and are closely attached to the
first phalanx by strong ligaments. Each has the form of a three-sided pyramid.
The articular surface (Facies articularis) conforms to the corresponding part of the

^ The upper and lower divisions of the angle are sometimes termed the basilar and retrossal
processes respectively.

^ These are usually called the lateral cartilages, but this designation could not be retained.
They have the same relation to the third phalanx that the cartilage of the scapula has to the latter
bone, and are here named in similar fashion.

Fig. 8.3. I n vi > ,..i - of
New-born 1'o\l; Dor-
sal View.

Cartilages of third phalanx
removed.

Fig. 84. — Phalanges and
Distal Sesamoid of
New-born Foal; Vo-
lar View.

Cartilages of third phalanx
removed.

OS COX^ THE ILIUM 105

distal end of the large metacarpal bone. The flexor surface (Facies flexoria) is
flattened and oblique; in the fresh state it is covered by a layer of cartilage which
also fills the interval between the opposed borders of the two bones, and forms a
smooth groove for the deep flexor tendon. The abaxial surface is concave, and
gives attachment to part of the suspensory ligament; it is separated from the
flexor surface by a rough everted border. The base is distal, and furnishes attach-
ment to the distal sesamoidean ligaments. The apex is proximal and is rounded.

The distal sesamoid or navicular bone (Os sesamoideum phalangis tertise) is
shuttle-shaped, and is situated behind the junction of the second and third pha-
langes. Its long axis is transverse, and it possesses two surfaces, two borders, and
two extremities. The articular surface (Facies articularis) faces upward and
forward; it consists of a central eminence, flanked by concave areas, and articulates
with the distal end of the second phalanx. The flexor or tendon surface (Facies
flexoria) is directed downward and backward. It resembles the articular surface
in form, but is more extensive and not so smooth. In the fresh state it is coated
with cartilage and the deep flexor tendon plays over it. The proximal border
(Margo proximalis) is wide and grooved in its middle, narrower and rounded on
either side. The distal border (Margo distalis) bears in front a narrow facet for
articulation with the third phalanx. Behind this is a groove, which contains a
number of relatively large foramina, and is bounded behind by a prominent edge.
The extremities are blunt-pointed.

Development. — Each ossifies from a single center.

The Bones of the Pelvic Limb

The pelvic girdle (Cingulum extremitatis pelvinae) consists of the os coxae,
which unites ventrally with the opposite bone at the symphysis pelvis, and artic-
ulates with the sacrum dorsally.

OS COX^

The OS coxae or hip bone^ is the largest of the flat bones. It consists primarily

of three parts, the ilium, ischium, and pubis, which meet to form the acetabulum,

a large cotyloid cavity for articulation with the head of the femur. These parts

are fused at about one year of age, but it is convenient to describe them separately.^

The Ilium

The ilium (Os ilium) is the largest of the three parts. It is irregularly triangu-
lar and presents two surfaces, three borders, and three angles.

The wide part of the bone is the wing (Ala ossis ilium). Its gluteal surface
(Facies glutaa) faces dorso-laterally and backward. It is wide and concave in
front, narrower and convex behind. The wide part is crossed by the curved
gluteal line (Linea glutaea), which extends from the middle of the medial border
toward the tuber coxae. This surface gives attachment to the middle and deep
gluteal muscles.

The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex,
and consists of two distinct parts. The medial triangular part (Pars articularis)
is roughened for ligamentous attachment, and bears an irregular facet, the auricu-
lar surface (Facies auricularis) , for articulation with the sacrum. The lateral quad-
rilateral part (Pars iliaca) is in general smooth. It is crossed by the ilio-pectineal
line (Linea iliopectinea), which begins below the auricular surface and is continued

1 Formerly called the os innominatum.

2 The proper terms, strictly speaking, for these bones are os ilium, os ischii, and os pubis, but
the names given above are sanctioned by common usage.

106

THE SKELETON OF THE HORSE

on the shaft of the bone to join the anterior border of the pubis. The hne is inter-
rupted by furrows for the iliaco-femoral vessels, and below these it bears the psoas
tubercle (Tuberculum psoadicum), which gives attachment to the psoas minor mus-
cle. The iliacus muscle is attached to the surface lateral to the ilio-pectineal line.

The anterior border or crest (Crista iliaca) is concave, thick, and rough.

The medial border (Margo medialis) is deeply concave. Its middle part forms
the greater sciatic notch (Incisura ischiadica major) and it is continuous behind
with the ischiatic spine.

The lateral border (Margo lateralis) is concave and in great part rough. Its
a,nterior part is crossed l)y grooves for the ilio-lumbar vessels, which are continued

Sacral spines

Tuber sacralf Crest of ilium

Apex of sacrum

Tuber
coxce

Ac( tabular branch of pubis

Ventral ischiatic
spine

Fig. 85. — Right Os Cox-e axd Sacrum op Horse; Right Lateral View.
1, Gluteal line; 2, impression of ilio-lumbar artery; 3, impression of iliaco-femoral artery; 4, depressions for at-
tachments of tendons of origin ofj rectus femoris; 5, crest to which lateral tendon of rectus femoris and capsularis are
attached; G, 6', articular surface of acetabulum (facies lunata) ; 7, acetabular fossa; 8, obturator foramen; 9, line for
attachment of gemellus muscle; 10, lateral border of sacrum; 11, dorsal sacral foramina.

Symphyseal branch
of pubis

on the pelvic surface. The nutrient foramen is usually situated on or near the
posterior part of this border.

The medial angle is termed the tuber sacrale; it curves upward and a little
backward opposite to the first sacral spine, and forms here the highest point of the
skeleton. It is somewhat thickened and rough.

The lateral angle, tuber coxae, forms the basis of the point of the hip. It is a
large quadrangular mass, narrow in its middle, and enlarged at either end, where
it bears a pair of tuberosities. It is roughened for muscular attachment.

The acetabular angle (Angulus acetabularis) meets the other two bones at the
acetabulum, of which it forms about two-fifths. Its prominent dorsal border forms

THE ISCHIUM

107

part of the ischiatic spine (Spina ischiadica), which is roughened laterally, smooth
medially. Two depressions above and in front of the acetabulum give attachment
to the tendons of origin of the rectus femoris muscle. This angle is connected with
the wing or wide part of the bone by a constricted part, termed the shaft (Corpus
ossis ilium). The latter is of three-sided, prismatic form. Its lateral surface is
convex and rough, and gives attachment to the deep gluteus muscle. Its pelvic
surface is smooth and is grooved for the obturator vessels and nerve. Its ventral
surface is crossed by vascular grooves, below which there is a rough area, which is
bounded medially by the psoas tubercle.

Tuber sacrale

Ischiatic spine

Tuber ischii

Ischial arch

Fig. 86. — Ossa Cox.\rum of Horse; Dorsal View.
A, Wing; A', shaft of ilium; B, acetabular, B', symphyseal branch of pubis; C, body, C, acetabular branch (or
shaft), C", symphyseal branch, of ischium; 1, gluteal line; 2, grooves for obturator nerve and vessels; 3, symphysis
pelvis; 4, greater sciatic notch; 5, ilio-pectineal eminence; 6, pubic tubercle. Dotted hnes indicate primitive separa-
tion of three bones.

The Ischium

The ischium (Os ischii) forms the posterior part of the ventral wall or floor of
the bony pelvis. It slopes a little downward and inward, but is practically hori-
zontal in the longitudinal direction. The body of the ischium (Corpus ossis
ischii) is irregularly quadrilateral, and may be described as having two surfaces,
four borders, and four angles.

The pelvic surface (Facies pelvina) is smooth and slightly concave from side
to side.

The ventral surface (Facies ventralis) is nearly flat, and is in great part rough-
ened for the attachment of the adductor muscles.

The anterior border forms the posterior margin of the obturator foramen.

108

THE SKELETON OF THE HORSE

The posterior border is thick and rough. It slopes medially and forward
to meet the border of the other side, forming with it the ischial arch (Arcus
ischiadicus).

The medial border meets the opposite bone at the symphysis ischii.

The lateral border is thick and rounded, but concave in its length; it forms
the lesser sciatic notch (Incisura ischiadica minor), the lower boundary of the lesser
sciatic foramen.

The antero-medial angle or symphyseal branch (Ramus symphyseos)

C'nsl of ilium

Grooves for ilio-
lumbar vessels
Grooves for
iliaco-femoral

Depression for

medial tendon

of rectus

femoris

Obturator foramen

Fig. 87. — O.ssa Coxarum of Mare; Ventral View.
A, Wing, A', shaft of ilium; B, acetabular branch, B', symphyseal branch, of pubis; C, body, C, acetabular
branch (shaft), C", symphyseal branch, of ischium; 1, auricular surface; 2, ilio-pectineal line; 2', psoas tubercle; 3,
arcuate hne; 4, articular part, 5, iliac part, of pelvic surface of ihum; 6, ilio-pectineal eminence; 7, pubic tubercle; 8,
acetabular fossa; 9, articular surface of acetabulum (facies lunata) ; 10, symphysis pelvis; 11, pubic groove. Dotted
Unes indicate primitive division of os coxae.

meets the pubis, with which it forms the medial boundary of the obturator
foramen.

The antero-lateral angle or acetabular branch (Ramus acetabularis) joins the
other two bones at the acetabulum, of which it forms more than half. Dorsally
it bears part of the ischiatic spine (Spina ischiadica), and medially it is grooved for
the obturator vessels. The term shaft is often applied to the constricted part of
the acetabular branch.

The postero-medial angle joins its fellow at the symp?iysis.

The posterolateral angle is a thick, three-sided mass, the tuber ischii (Tuber
ischiadicum) ; its lower border is the ventral ischiatic spine, to which the biceps
femoris and semitendinosus muscles are attached.

THE PUBIS — THE OBTURATOR FORAMEN 109

The Pubis

The pubis (Os pubis) is the smallest of the three parts of the os coxae. It
forms the anterior part of the pelvic floor, and may be described as having two
surfaces, three borders, and three angles.

The pelvic surface (Facies pelvina) is convex in the young subject and the
stallion, concave and smooth in the mare and usually in the gelding also.^

The ventral surface (Facies ventralis) is convex, and in great part rough for
muscular attachment. Near the anterior border it is crossed by the pubic groove
(Sulcus pubis), the medial part of which is occupied by a large vein, the lateral part
by the accessory ligament; the groove leads to the acetabular notch.

The anterior border is thin in its medial part (except in the young subject and
the stallion), forming the pecten ossis pubis. Laterally it bears the rough ilio-
pectineal eminence (Eminentia iliopectinea), beyond which it is continuous with
the ilio-pectineal line. Near the symphysis is a variable prominence, the tuber-
culum pubicum.

The medial border joins the opposite bone at the symphysis pubis.

The posterior border forms the anterior margin of the obturator foramen, and
is marked laterally by the obturator groove.

The medial angle meets its fellow at the anterior end of the symphysis. This
part is very thick in the young subject and the stalHon, but in the mare, and usually
in the gelding also, it becomes thin with advancing age.

The acetabular angle joins the ilium and ischium at the acetabulum.

The posterior angle joins the ischium, with which it forms the inner boundary
of the obturator foramen.

The pubis may conveniently be regarded as consisting of a body (Corpus ossis
pubis) and two l^ranches; the latter are termed the acetabular branch (Ramus
acetabularis) and the -symphyseal branch (Ramus symphyseos) .

The Acetabulum

The acetabulum is a cotyloid cavity which lodges the head of the femur. It
faces ventro-laterally, and consists of an articular and a non-articular part. The
articular part (Facies lunata) is crescentic, and is cut into internally by a rough
non-articular depression, the acetabular fossa (Fossa acetabuli). The medial
part of the rim is correspondingly cut into by the acetabular notch (Incisura
acetabuli), which is converted into a foramen by the transverse ligament in the
fresh state, and transmits the accessory and round ligaments to the head of the
femur.

The Obturator Foramen

The obturator foramen (Foramen obturatum) is situated between the pubis
and ischium. It is oval in outline, the longer axis being directed forward and
outward. Its margin is grooved antero-laterally for the obturator nerve and ves-
sels.

Development. — Each division of the os coxse ossifies from one chief center.
The center for the ilium first appears near the acetabulum, followed quickly by one
for the ischium, and a little later l\y the pubic center. Secondary centers appear
for the crest and tuber coxse of the ilium, the tuber and posterior border of the
ischium, and the acetabular part of the pubis. The symphyseal branches of the
pubis and ischium are usually united with each other before birth, but the three

1 The pelvic surface of the pubis is quite variable. In the mare and in geldings which have
been castrated eariy the two pubic bones form a central depression of variable depth and curvature.
This depression is bounded posterioriy by two obhque convergent hues or ridges, to which the
obturator internus muscle is attached. Not rarely small eminences may be present along the
symphysis.

110

THE SKELETON OF THE HORSE

bones are not fused until the second year. The epiphyseal parts fuse with the
main mass at four and a half to five years of age.

The acetabular part of the pubis ossifies from a separate center. It is most distinct in the
embryo at three months, and is often called the os acetabuli. Martin says that the ilium has a
center for the acetabular part, one for the shaft and wing, and a third for the crest. He also
states that there is a special center for the acetabular part of the ischium, and a transitory nucleus
in the symphyseal part of the pubis.

THE PELVIS
The bony pelvis is composed of the ossa coxarum, the sacrum, and the first
three coccj^geal vertebrae. The dorsal wall or roof is formed by the sacrum and
first three coccygeal vertebrae, and the ventral wall or floor by the pubic and ischial

Crest of ilium

Sacral Tuber
spines sacrale

Tuber coxa

Depressioji in which
tendon of rectus
femoris is attached

I Ho- pectineal eminence

Acetabidmn

Tuber ischii

Ischium
Pubic tubercle

Fig. 88. — Pelvic Bones op Mare, Viewed from in Front and Somewhat from Below.
1, Body of first sacral segment; 2, surface on wing of sacrum for articulation with like surface on transverse process
of last lumbar vertebra ; 3, wing of sacrum; 4, sacro-iliac articulation ; 5, sacral canal; 6, promontory; 7, apex of sac-
rum; 8, ilio-pectineal line; 9, ischiaticspine; 10, grooves for ilio-lumbar vessels; 11, grooves for iliaco-femoral vessels.

bones. The lateral walls are formed by the ilia and the acetabular part of the
ischia. The defect in the skeleton here is supplied in the fresh state by the sacro-
sciatic ligaments and semimembranosus muscles.

The anterior aperture or inlet of the pelvis (Apertura pelvis cranialis) is bounded
by the terminal line (Linea terminalis) or brim, which is composed of the base of
the sacrum dorsalh% the ilio-pectineal lines laterally, and the pecten pubis ventrally.
It is almost circular in the mare, semi-elliptical in the stallion, and faces obliquely
downward and forward. It has two principal diameters. Of these, the con-
jugate or sacro-pubic diameter (Conjugata anatomica) is measured from the sacral
promontory to the anterior end of the symphysis. The transverse diameter

THE PELVIS

111

(Diameter transversa) is measured at the greatest width, i. e., just above the psoas,
tubercle.

The posterior aperture or outlet of the pelvis (Apertura pelvis caudalis) i&
much smaller and is very incomplete in the skeleton. It is bounded dorsally by the

Fig. 90. — Pelvic Bones op Mare; Front View.
C, Conjugate, D.t., transverse, diameter of pelvic inlet.

third coccygeal vertebra and ventrally by the ischial arch; in the fresh state it is
completed laterally by the sacro-sciatic ligament and the semimembranosus muscle.

The axis of the pelvis is an imaginary line drawn through the centers of the
inlet, cavity, and outlet.

Sexual Differences. — Marked differences exist in the size and form of the pel-
vis in the two sexes. The average conjugate diameter is about 93^ inches (ca. 23 to

112 THE SKELETON OF THE HORSE

24 cm.) in the mare, 73^ inches (ca. 18.75 cm.) in the stallion. The transverse
diameter of the inlet is about the same as the conjugate in the mare, but is about
8 inches (ca. 20 cm.) in the stallion. The obliquity of the inlet or inclination of the
pelvis (Inclinatio pelvis) is greater in the female ; the difference is indicated by the
fact that a vertical plane from the pecten cuts the fourth sacral segment in the fe-
male, the second in the male. The outlet is also larger in the mare, the ischial arch
being about one-third wider than in the stallion. The cavity is much more roomy
in the female; the transverse diameter between the middles of the superior ischiatic
spines is about 8 inches (20 cm.) in the mare, 6 inches (15 cm.) in the stallion. The
pubic part of the floor in the female is concave and lies considerably lower than the
ischiatic part, which is wide and almost flat. In the stallion the pubis is very thick
medially, and this part of the floor is convex, while the ischial part is relatively nar-
row, and is concave from side to side. The obturator foramina are correspondingly
larger in the female. The ilium is shorter, especially with regard to its shaft, and
the greater sciatic notch is deeper and narrower in the male. The pelvis of the geld-
ing, when castration has been performed early, resembles that of the mare; other-
wise the male characters appear to be retained to a large degree.

THE FEMUR

The femur or thigh bone (Os femoris) is the largest and most massive of the
long bones. It extends obliquely downward and forward, articulating with the
acetabulum above and the tibia and patella below. It presents for examination a
shaft and two extremities.

The shaft (Corpus femoris) is in general cylindrical, but flattened behind, and
larger above than below. The anterior, medial, and lateral surfaces are continuous
and strongly convex from side to side; there is often a central vertical rough line
on the proximal part, but otherwise these surfaces are smooth. They are covered
by the quadriceps femoris muscle. The posterior surface is wide, flat, and smooth
in its proximal fourth. Distal to this part there is a rough elevation laterally for
the attachment of the femoral tendon of the biceps femoris, and a rough line medi-
ally to which the quadratus femoris is attached. The middle third is narrower,
and is rough for the attachment of the adductor muscle. Just distal to this area
an oblique groove crosses the surface, indicating the position of the femoral vessels.
The medial border l^ears on its proximal part the trochanter minor, a thick rough
ridge, to which the iho-psoas muscle is attached. From this a rough line curves
up to the front of the neck and indicates the posterior limit of the attachment of
the vastus medialis muscle. A narrow rough area about the middle of the border
gives attachment to the pectineus muscle, and the nutrient foramen is usually
found just in front of this mark. The medial supracondyloid crest (Crista supra-
condyloidea medialis) is situated below the groove for the femoral vessels, and gives
origin to the medial head of the gastrocnemius. The lateral border is prominent
in its upper part, and bears at the junction of its proximal and middle thirds the
trochanter tertius ;^ this process is curved forward, and has a thick edge to which
the tendon of the superficial gluteus muscle is attached. At the distal part is the
supracondyloid fossa (Fossa supracondyloidea),^ in which the superficial digital
flexor arises; it is bounded laterally by a thick, rough margin, the lateral supra-
condyloid crest (Crista supracondyloidea lateralis), to which the lateral head of the
gastrocnemius muscle is attached.

The proximal extremity (Extremitas proximalis) is large and consists of the
head, neck, and trochanter major. The head (Caput femoris) is placed at the
medial side and is directed inward, upward, and somewhat forward. It is ap-
proximately hemispherical and articulates with the acetabulum. It is cut intc

1 Also termed the external trochanter. ^ ^|gQ termed the fossa plantaris.

THE FEMUR

113

medially by a deep notch, the fovea capitis, in which the accessory and round liga-
ments are attached. The articular surface is surrounded by a distinct margin.
The neck (Collum femoris) is most distinct in front and medially. The trochanter
major is situated laterally; it presents three features. The anterior part or con-
vexity is situated opposite to the head and rises little above the level of the latter;
it gives attachment to the deep gluteus muscle, and in the fresh state its lateral
surface is coated with cartilage, over which a tendon of the middle gluteus passes,
to be inserted into, the crest, which is placed below and behind the convexity.
The posterior part or summit is separated from the anterior part by a notch; it is
situated behind the plane of the head and rises to a much greater height. It

Lateral

epi-

cundyle

Medial

epi-

condyle

Medial
condyle

Trochlea
Fig. 91. — Right Femur of Horse; Froxt View.

Lateral
condyle

I nterco itdyloid fossa
-Right Femur of Horse; Posterior View.

furnishes insertion to part of the middle gluteus muscle. Its posterior border is
continued downward as the trochanteric ridge (Crista trochanterica), which forms
the lateral wall of the trochanteric fossa (Fossa trochanterica). A number of
foramina are found in the concave area medial to the convexity.

The distal extremity (Extremitas distalis) is large in both directions and com-
prises the trochlea in front and two condyles behind. The trochlea consists of two
ridges separated by a groove, and forms an extensive surface (Facies patellaris) for
articulation with the patella. It is very unsymmetrical ; the medial ridge is much
wider, more prominent, and extends up higher than the lateral one, and the two
converge below. The condyles, medial and lateral (Condylus medialis, lateralis),

114

THE SKELETON OF THE HORSE

are separated by the deep intercondyloid fossa (Fossa intercondyloidea), and
articulate with the condyles of the tibia and the menisci of the stifle joint. A ridge
connects each condyle with the lower part of the corresponding ridge of the trochlea.
The intercondyloid fossa lodges the spine of the tibia and the cruciate ligaments of
the stifle joint, which are attached here.

The condyles are obliquely placed with their long axes directed downward, forward, and
inward. The articular surface of the lateral condyle is more strongly convex from side to side
than that of the medial one, and the ridge which connects it with the trochlea is much narrower.

The medial epicondyle (Epicondylus medialis) is a rounded prominence on
the medial surface of the distal extremity, to which the collateral ligament and the
adductor muscle are attached. The corresponding lateral epicondyle (Epicondylus

Fig. 93. — Proximal Extremity of Right Femur of

Horse; End View.

1, Head; 2, fovea capitis; 3, neck; 4, 5, anterior and

posterior parts of trochanter major.

Intercondyloid fossa

Fig. 94. — Distal Extremity of Right Femur of
Horse; End View.
1, 1', Medial and lateral ridges of trochlea; 2, 2',
medial and lateral condyles; 3, 3', medial and lateral
epicondyles; 4, extensor fossa; 5, depression for origin
of popliteus.

lateralis) is less distinct; it presents a mark where the lateral ligament is attached,
below and behind which there is a depression (Fossa musculi poplitei) in which the
popliteus muscle arises. Between the lateral condyle and trochlea is the extensor
fossa (Fossa extensoria), in which the common tendon of origin of the extensor
digitalis longus and peroneus tertius is attached.

Development. — The shaft and the distal end each ossify from one center, but
the proximal end has two centers, one of which is for the head and the other for the
trochanter major. The edge of the trochanter tertius also has a separate center.
The proximal end fuses with the shaft at three to three and a half years, the distal
at about three and a half years.

THE TIBIA

The tibia is a long bone which extends obliquely downward and backward
from the stifle to the hock. It articulates above with the femur, below with the
tarsus, and laterally with the fibula. It possesses a shaft and two extremities.

The shaft (Corpus tibiae), large and three-sided above, becomes smaller and
flattened in the sagittal direction below, but widens at the distal end. It presents
for notice three surfaces and three borders. The medial surface (Facies medialis)
is Inroad above, where it presents rough prominences for the attachment of the

THE TIBIA

115

medial ligament and the sartorius and gracilis muscles; below this it is narrower,
convex from edge to edge and subcutaneous. The lateral surface (Facies lateralis)
is smooth and somewhat spiral. It is wide and concave in its proximal fourth,

1— ■

95. — Right Tibia axd Fibula of Horse

ERAL View.
1, Tuberosity; 2, sulcus muscularis; 3, crest

4,
impres-

spine; 5, lateral condyle; 6, head of fibul
sion of anterior tibial vessels; 8, shaft of fibula; 9, lat-
eral border of tibia; 10, lateral malleolus; 11, groove
for lateral extensor tendon.

Fig. 96. — Right Tibia and Fibula of Horse; Poste-
rior View.
1, Medial condyle; 2, lateral condyle; .3, spine; 4,
fossa for anterior cruciate ligament; .5, popliteal notch;
6, tubercle for posterior cruciate ligament; 7, head of
fibula; 8, vascular impression; 9, interosseous space;
10, shaft of fibula; 11, muscular lines; 12, tubercle; 13,
nutrient foramen; 14, medial malleolus; 1.5, groove for
tendon of flexor digitalis longus; 16, lateral malleolus.

l)elow which it becomes narrower and convex, and winds gradually to the front of
the bone; near the distal end it widens a little, becomes fiat, and faces forward.
The posterior surface (Facies caudalis) is flattened, and is divided into two parts
by the rough popliteal line (Linea poplitea), which runs obliquely from the proxi-

116

THE SKELETON OF THE HORSE

7 —

mal part of the lateral border to the middle of the medial border. The triangular
area above the line is occupied by the popliteus muscle, while the area below is
marked by rough lines (Linese musculares) to which the deep flexor muscle of the

digit is attached; the lines fade out distally,
^ where the surface is smooth and flat. The

,t nutrient foramen is situated on or near the

2 -.^ ' popliteal line. The anterior border is very

prominent in its proximal third, forming the
crest of the tibia (Crista tibiae) ; distally it is
reduced to a rough line, which ends at a small
elevation near the distal end of the bone. The
medial surface of the crest presents a rough
prominence for the attachment of the ten-
don of the semitendinosus. The medial border
(Margo medialis) is rounded in its proximal
half, to which the popliteus muscle is attached,
and a tubercle is found on this part. The dis-
tal part is a rough line on well-marked bones.
The lateral border (Crista interossea) is con-
cave in its proximal part and concurs with the
fibula in the formation of the interosseous space
of the leg (Spatium interosseum cruris); a
smooth impression indicates the course of the
anterior tibial vessels through the space to the
front of the leg. About the middle of the bone
the border divides and incloses a narrow trian-
gular surface.

The proximal extremity (Extremitas proxi-
malis) is large and three-sided. It bears two
articular eminences, the medial and lateral con-
dyles (Condylus medialis, lateralis) . Each pre-
sents a somewhat saddle-shaped surface for ar-
ticulation with the corresponding condyle of the
femur and meniscus. The spine or intercondy-
loid eminence (Eminentia intercondyloidea) is
the central prominence, upon the sides of which
the articular surfaces are continued ; it consists
of a high medial part and a lower lateral part
(Tuberculum intercondyloideum mediale, lat-
erale). On, l^efore, and l^ehind the spine are
the intercondyloid fossae, in which the anterior
cruciate ligament and the menisci are attached.
The condyles are separated behind by the deep
popliteal notch (Incisura poplitea), on the
medial side of which there is a tubercle for
the attachment of the posterior cruciate liga-
ment. The lateral condyle has an overhang-
ing outer margin (Margo infraglenoidalis), be-
low which there is a facet (Facies articularis
fibularis) for articulation -v^dth the fibula. The
large anterior eminence is the tuberosity of the
tibia (Tuberositas tibiae). It is marked in front by a groove (Sulcus ligamenti),
the lower part of which gives attachment to the middle patellar ligament, and
the groove is flanked b}^ rough areas for the attachment of the medial and lateral

Fig. 97. — Right Tibia and Fibula of Hor.se;
Anterior View.
1, Spine; 2, tuberosity; 3, groove for
toiddle patellar ligament; 4, medial condyle;
5, sulcus muscularis; 6, lateral condyle; 7,
head of fibula; 8, interosseous space; 9, lateral
surface of tibia; 10, shaft of fibula; 11, imprint
for attachment of gracilis; 12, crest; 13, promi-
nence for attachment of semitendinosus; 14,
medial surface of tibia; 15, medial malleolus;
16, lateral malleolus.

THE FIBULA

117

patellar ligaments. A semicircular smooth notch, the sulcus muscularis, separates
the tuberosity from the lateral condyle, and gives passage to the common tendon
of origin of the extensor digitalis longus and the peroneus tertius.

The distal extremity (Extremitas distalis) is much smaller than the proximal
one ; it is quadrangular in form and larger medially than laterally. It presents an
articular surface (Cochlea tilDise), which is adapted to the trochlea of the tibial
tarsal bone, and consists of two grooves separated by a ridge. The ridge and
grooves are directed ol^liquely forward and laterally, and are bounded on either
side by the malleoli, to which the collateral ligaments of the hock joint are at-
tached. A shallow synovial fossa is usually present on the middle of the articular
ridge. The lateral groove is wider and shallower than the medial one; it is fre-
quently marked by a line or groove which indicates the former demarcation between
the tibia and fibula. The medial malleolus (Malleolus medialis) is the more prom-
inent of the two, and forms the anterior Ijoundary of a groove for the tendon of the
flexor digitalis longus. The lateral malleolus (Malleolus lateralis) is broader, and
is marked by a vertical groove for the passage of the lateral extensor tendon.

Development. — The tibia has the usual three chief centers of ossification and
supplementary ones for the tuberosity and the lateral malleolus. The latter is
really the distal end of the fibula; it is a separate piece at birth, and the line of
union is commonly quite evident in the adult in the articular groove. The proxi-
mal end unites with the shaft at about three and a half years, and the distal end at
about two years of age.

Fig. 98. — Proximal Extremity or Right Tibia of
Horse; End View.
1, Medial condyle; 2, lateral condyle; 3, groove
on 2 for popliteus tendon ; 4, popliteal notch ; 5, tuber-
osity; 6, groove for middle patellar ligament; 7, tuber-
cles of spine; 8, sulcus mu.scularis; l.c.a., l.c.p., depres-
sions for attachment of anterior and posterior cruciate
ligaments; I, m, m, depressions for attachment of

Fio. 99. — Distal Extremity of Right Tibia (and
Fibula) of Horse; End View.
1, 1', Articular grooves; 2, intormeliate ridge and
synovial fossa; 3, line of fusion of primitive distal end
of fibula with tibia; 4, medial malleolus; 5, 5', lateral
malleolus; 6, anterior border.

THE FIBULA

The fibula of the horse is a much reduced long bone, situated along the lateral
border of the tibia.

The shaft (Corpus fibula?) is a slender rod which forms the lateral boundary of
the interosseous space of the leg; it usually terminates below in a pointed end about
one-half to two-thirds of the way down the lateral border of the tibia.

The proximal extremity or head (Capitulum fibula)) is relatively large, and is
flattened transversely. Its medial surface presents a narrow area (Facies articu-
laris capituli) along the upper border for articulation with the lateral condyle of
tibia. The lateral surface is rough and gives attachment to the lateral ligament
of the stifle joint. It has rounded anterior and posterior borders.

118

THE SKELETON OF THE HORSE

The distal extremity is fused with the til)ia, constituting the lateral malleolus.

Development. — Tliis resembles that of the ulna. The embryonic cartilaginous
fibula extends the entire length of the leg, but does not articulate with the femur.
The distal part of the shaft is usually reduced to a filjrous band. Three centers of
ossification appear, one each for the shaft and the extremities. The distal end
unites early with the tibia, forming the lateral malleolus.

It is interesting to note that in some cases the entire shaft of the fibula develops, a reversion
to the condition in the Miocene ancestors of the horse.

THE PATELLA

The patella is a large sesamoid bone which articulates with the trochlea of the
femur. It presents for description two surfaces, two borders, a base, and an apex.

The anterior, free surface (Facies libera) is quadrilateral, convex, and rough
for muscular and ligamentous attachment.

The articular surface (Facies articularis) is also quadrilateral, ]:)ut much less
extensive. It presents a vertical rounded ridge, which corresponds to the groove

Base

Aj)ex
Fig. 100. — Right Patella of Horse; Anterior View.
1, Attachment area of middle patellar ligament;
2, attachment area of lateral patellar ligament and
biceps femoris.

Accessory cartilage Apex

Fig. 101. — Right Patella of Horse; Posterior View.
1, Medial part, 2, lateral part, of articular surface.

on the trochlea of the femur, and separates two concave areas. Of the latter, the
medial one is much the larger, and is not very well adapted to the corresponding
ridge of the trochlea; in the fresh state, however, it is completed and rendered more
congruent b}^ the curved accessory fibro-cartilage.

The borders, medial and lateral, converge to the apex below, and each forms an
angle at the base. The medial border is concave. The lateral border is rounded
and its angle is less prominent. The medial angle and the adjacent part of the
posterior margin of the base give attachment to the fibro-cartilage of the patella
(Fibrocartilago patellae) .

The base (Basis patellae) faces upward and backward, and is convex trans-
versely, concave from before backward.

The apex (Apex patellae) forms a blunt point directed distally.

Development. — The patella develops as a sesamoid bone from a single center
in a cartilaginous deposit in the te'ndon of the quadriceps femoris muscle.

THE TARSUS

The tarsus or hock of the horse usually comprises six short bones (Ossa tarsi),
but exceptionally seven are present.

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120

THE SKELETON OF THE HORSE

The Tibial Tarsal Bone
The tibial tarsal bone (Os tarsi tibiale) ^ is the medial bone of the proximal row.
It is extremely irregular in form, but may be considered as offering six surfaces for
description.

The proximal and dorsal surfaces are continuous, and form a trochlea (Troch-
lea tali) for articulation with the distal end of the tibia. The trochlea consists
_ of two oblique ridges with a deep groove

between them; these curve spirally for-
ward, downward, and outward, forming
an angle of 12 to 15 degrees with a sagittal
plane. There is usually a shallow synovial
fossa in the groove. The distal surface is
convex from before backward, and most
of it articulates with the central tarsal;
laterally it has an oblique facet for the
fourth tarsal, and a non-articular groove
cuts into the surface to its middle. The
plantar surface (Facies plantaris) is ob-
lique and extremely irregular; it presents
four facets for articulation with the fibular
tarsal bone; the facets are separated by

Trochlea

Fig. 105. — Right Tarsus and Proximal Part of
Metatarsus of Horse; Lateral View.
Tt, Tibial tarsal (trochlea); Tf, fibular tarsal
(body); Tc, central tarsal; T3, third tarsal; T4,
fourth tarsal; 1, depression for attachment of lateral
ligament; 2, processus cochlearis; 3, prominence for
attachment of lateral ligament; 4, groove for great
metatarsal artery; 5, tuber calcis; Mt. Ill, IV, meta-
tarsal bones. Arrow points to vascular canal.

Fig. 106. — Right Tibial Tarsal Bone of Horse; Plan-
tar A'lEW.
1-4, Facets for articulation with fibular tarsal; 5, fossa;
6, distal tuberosity; 7, proximal tuberosity.

rough excavated areas, and the largest
fossa (Sulcus tali) forms with a corres-
ponding one on the fibular tarsal a cavity
termed the sinus tarsi. The media4 surface bears on its distal part a large tuber-
osity and on its proximal part a small one for the attachment of the medial liga-
ment of the hock joint. The lateral surface is smaller than the medial, and is
marked by a wide rough fossa in which the lateral ligament is attached.

The Fibular Tarsal Bone
The fibular tarsal bone (Os tarsi fibulare)^ is the largest bone of the hock. It
is elongated, flattened from side to side, and forms a lever for the muscles which

Also termed the astragalus or talus.

2 Also termed the calcaneum or os calcis.

THE CENTRAL TARSAL BONE

121

extend the hock joint. It consists of a body and a medial process, the sustentacu-
lum tali.

The body (Corpus) is enlarged at its proximal end to form the tuber calcis or
"point of the hock"; the posterior part of this eminence gives attachment to the
tendon of the gastrocnemius, while in front and on each side it furnishes insertion
to tendons of the superficial digital flexor, biceps, and semitendinosus muscles.
The distal extremity bears a concave facet for articulation with the fourth tarsal
bone. The medial surface of the body has on its lower part a strong process, the
sustentaculum tali, which projects inward. The process has a large, oval, slightly
concave facet in front for articulation with the tibial tarsal, and sometimes a small
articular surface below for the central bone. Its plantar surface forms with the
smooth medial surface of the body a groove for the deep flexor tendon (Sulcus tarsi) .
Its medial surface has a prominence on the distal part for the attachment of the
medial ligament. The lateral surface of the body is flattened, except below, where
there is a rough prominence for the attachment of the lateral
ligament. The dorsal border is concave in its length, smooth
and rounded in its upper part. About its middle is a blunt-
pointed projection (Processus cochlearis) which bears facets
on its medial and lower surfaces for articulation with the
tibial tarsal bone, and is roughened laterally for ligamen-
tous attachment. Below this are two facets for the tibial
tarsal, and an extensive rough fossa which concurs in
the formation of the sinus tarsi. The plantar border is
straight and broad, and widens a little at each end; it is
rough, and gives attachment to the long plantar ligament.

Tuber
calcis

Fig. 107. — Right Fibular Fig. 108.— Right Central Tarsal Bone op Horse; Proximal Surface.

Tarsal Bone of Horse; i_ Articular surface for tibial tarsal; 2, facet for fibular tarsal; 3, non-articular

Dorsal View. depression.

1-4, Facets for articulation with
tibial tarsal bone; 5, fossa.

The Central Tarsal Bone
The central tarsal bone (Os tarsi centrale)^ is irregularly quadrilateral, and is
situated between the tibial tarsal and the third tarsal. It is flattened from above
downward, and may be described as having two surfaces and four borders. The
proximal surface is concave from before backward, and almost all of it articulates
with the tibial tarsal; a non-articular depression cuts into its lateral part, and
sometimes there is a facet for the fibular tarsal bone on the posterior angle. The
distal surface is convex, and is crossed by a non-articular groove, which separates
facets for articulation with the third and the first and second (fused) tarsals. The
dorsal border and the medial border are continuous, convex, and rough. The
plantar border bears two prominences, separated by a notch. The lateral border
is oblique, and bears anterior and posterior facets for articulation with the fourth
tarsal, between which it is excavated and rough.

1 Also termed the scaphoid or navicular bone.

122

THE SKELETON OF THE HORSE

First and Second Tarsal Bones
The first and second tarsal bones (Os tarsale primum et secundum) ^ are usually-
fused in the horse, forming a ])one of very irregular shape, situated in the medio-
plantar part of the distal row, below the central and behind the third tarsal. It is
the smallest of the tarsal bones, and may he described as having four surfaces and
two extremities. The medial surface faces backward and inward, and is convex.
Its anterior part is ridged, and gives attachment to the medial ligament, and its
posterior part l^ears an imprint where the medial tendon of the tibialis anterior is
inserted. The lateral surface is marked by a deep notch which indicates the divi-
sion between the first and second tarsal elements; it bears on its anterior part a
facet for the third tarsal. The proximal surface is concave and has two facets for
articulation with the central tarsal; it is separated from the medial surface by a
prominent border. The distal surface is broad in front, where it articulates with

Fig. 109. — Right First and Sec-
ond (Fused) Tarsal Bones
OF Horse; Lateral Surface.
Tl, T2, First and second tarsal
bones; 1, 1', articular surface for
central tarsal; 2, facet for third tar-
sal; 3, facet for medial small meta-
tarsal bone. Separation between
two bones (when present) is indi-
cated so far as visible by dotted
line between 1 and 1'.

Fig. 110.— Right Third Tarsal
Bone of Horse; Proximal
Surface.

1, 2, Facets for central tarsal;
3, 4, facets for fourth tarsal; 5, non-
articular depression ; 6, dorsal ridge.

Fig. 111. — Right Fourth Tarsal
Bone of Horse; Medial Sur-
face.

1, 1', Facets for central tarsal;
2, 2', facets for third tarsal; 3, facet
for tibial tarsal; 4, 4', facets for
fibular tarsal; 5, facet for large
metatarsal bone; 6, groove which
concurs with central and third tar-
sals in formation of vascular canal
of tarsus.

the large and medial small metatarsal bones. The dorsal extremity bears a ridge
or tubercle. The plantar extremity is a blunt point.

In some cases the first and second tarsal Ijones remain separate — a remarkable reversion to
the condition in the early ancestors of the horse. In such specimens the first tarsal is a discoid
bone, articulating above with the central, below with the small metacarpal bone. The second
tarsal is quadrangular, equivalent to the thick anterior part of the bone as described above, and
overlapped in part by the first tarsal.

The Third Tarsal Bone

The third tarsal bone (Os tarsale tertium)- resembles the central, but is smaller
and triangular in outline. It is situated between the central above and the large
metatarsal l)one below. It possesses two surfaces and three borders.

The proximal surface is concave, and is crossed by a non-articular depression
which divides it into two unequal facets; it articulates with the central tarsal.
The distal surface is slightly convex, and rests on the large metatarsal bone; it
has an extensive central rough excavation. The dorsal border is convex and bears
a rounded ridge on its medial part. The medial border is deeply notched and has
a small facet for the second tarsal on its anterior part. The lateral border is also
divided by a notch into two parts, and bears two diagonally opposite facets for

Also termed the cuneiform parvum.

Also termed the cuneiform magnum s. tertium.

THE METATARSUS

123

articulation with the fourth tarsal. In some cases there is a facet for the medial
small metatarsal bone.

The Fourth Tarsal Bone
The fourth tarsal bone (Os tarsale quartum)i jg the lateral bone of the distal
row, and is eriual in height to the central and third together. It is cuboid m shape
and presents six sm-f aces. ,. , , n • a

The proximal surface is convex from side to side, and articulates chietly
with the fibular tarsal, but to a small extent with the tibial tarsal also.
The distal surface rests on the large and lateral
small metatarsal ])ones. The medial surface bears
four facets for articulation with the central and
third tarsal bones. It is crossed from before back-
ward by a smooth groove, which l)y apposition with
the adjacent bones forms the canal of the tarsus (Can-
alis tarsi) for the passage of the perforating tarsal
vessels. The dorsal, lateral, and plantar surfaces are
continuous and rough. A tuberosity behind gives
attachment to the plantar ligament.

Development.— The fibular tarsal bone has two
centers of ossification, one for the main mass and the
other for the tuber calcis; the latter fuses with the rest
of the bone at about three years of age. The first and
second tarsals have separate centers, but fusion usu-
ally occurs before birth. Each of the other bones
ossifies from a single center.

THE METATARSUS
The metatarsal bones (Ossa metatarsalia) , three
in number, have the same general arrangement as

Fig. 112. — Right Metatarsal Boxes
OF Horse; Plantar View.
1, Rough area for attachment of
suspensory ligament; 2, nutrient fora-
men. Compare with Fig. 76.

Mt.n Ml. HI ML IV

Fig. 113.— Proximal Extremities of Right Metatarsal Bones of
Horse; End View.
1, Facet for first tarsal; 2, 2', facets for second tarsal; 3, 3', facets for
third tarsal; 4, 4', 4", facets for fourth tarsal; 5, non-articular depr--
Compare with Fig. 77.

the metacarpal bones, but present some important differences. Their direction is
slightly oblique, downward, and a little forward. , , ,. . ■ , ^„. ^„p

The third or large metatarsal bone (Os metatarsal tertium) is about one-
sixth longer than the corresponding metacarpal; in an animal of medium size the
1 Also termed the cuboid.

124

THE SKELETON OF THE HORSE

difference is about two inches. The shaft is more cyhndrical, and is almost cir-
cular on cross-section, except in its distal part. At the proximal part of its lateral
surface there is a groove, which is directed obliquely downward and backward, and
is continued by the furrow formed by the apposition of the fourth or lateral meta-
tarsal bone; it indicates the course of the great metatarsal artery. A shallow im-
pression in a similar place on the medial side marks the position of the corresponding

vein. The nutrient foramen is rela-
tively higher than on the metacar-
pal bone. The proximal extremity
is much wider from before back-
ward than that of the metacarpal
bone. Its articular surface is
slightly concave, and is marked
by a large central non-articular de-
pression, continued outward by a
deep notch. The greater part of
the surface articulates with the
third tarsal, but there is a lateral
facet for the fourth, and usually a
small facet postero-medially for the
second tarsal bone. Posteriorly there are two pairs of facets for articulation with
the small metatarsal bones. The front is crossed by a rough ridge for insertion,
which becomes larger and turns downward on the lateral side behind the vascular
groove. The distal extremity closely resembles that of the corresponding meta-
carpal bone.

In some cases the distal part of the shaft is bent backward somewhat. The distal articular
surface extends a httle higher behind than in the case of the metacarpal bone. The large meta-
tarsal bone is even more strongly constructed than the metacarpal. The shell of compact sub-
stance is very thick in the middle of the shaft, especially in front and medially.

Fig. 114
Figs. 114, 115.

Fig. 115.

OSS-SECTIONS OF LeFT METACARPAL ANI

Metatarsal Bones.
Sections are cut a little above middle of bones.

Fig. 110. — Third Phalanx of Thoracic Limb of Horse. Fig. 117. — Third Phalanx of Pelvic Limb of Horse.

The small metatarsal bones (Ossa metatarsalia secundum et quartum) are a
little longer than the corresponding metacarpals. The lateral (fourth) metatarsal
bone is relatively massive, especially in its upper part. The head is large and out-
standing, and bears one or two facets above for the fourth tarsal, and two in front
and medially for articulation with the large metatarsal ; elsewhere it is roughened
for attachment. The medial (second) metatarsal bone is much more slender than
the lateral one, especially in its proximal part. The head bears two facets above for
the first and second tarsals, and sometimes one for the third tarsal.

SKELETON OF THE OX

125

THE PHALANGES AND SESAMOID BONES

The axis of the phalanges of the hind Hmb forms with the ground plane an
angle which is about five degrees greater than that of the fore limb, and the chief
differences in the form and size of the bones are as follows :

The first phalanx is a little shorter, wider above, and narrower below.

The second phalanx is narrower and slightly longer.

The third phalanx is narrower, the angle of inclination of the dorsal surface is a
little (ca. 5 degrees) greater, the plantar surface is more concave, and the angles
are less prominent and closer together. The term plantar is to be substituted for
volar in the designation of corresponding features.

The proximal sesamoids are a little smaller, except in thickness. The distal
sesamoid is narrower and shorter.

SKELETON OF THE OX

VERTEBRAL COLUMN

The usual vertebral formula is C7Ti3L6S5Cyi8-2o-

The cervical vertebrae are much shorter than those of the horse and are smaller
in their other dimensions. The articular processes are smaller than in the horse,
and a plate of bone connects each two of the same side. The transverse processes
of the third, fourth, and fifth are double; the upper part projects backward, and
is short and stout; the lower part is directed
downward and forward, and is longer and
more plate-like. The lower part of the sixth
transverse process is a large, thick, quadri-
lateral and almost sagittal plate, directed
ventrally. The seventh transverse process is
single, short, and thick, and presents no fora-
men transversarium; it is in series with the
upper part of the preceding processes. The
spinous processes are well developed, and in-
crease in height from before backward. They
are directed upward and forward, with the ex-
ception of the last, which is nearly vertical
and is about four or five inches (ca. 10 to 12
cm.) in height. The summit of that of the
third vertebra is usually bifid. The ventral
spines are prominent and thick in their pos-
terior part ; they are absent on the last two.

The atlas has a large rough tuberosity
on its dorsal arch. The ventral arch is very
thick. The wings are less curved than in the

horse, and the foramen transversarium is absent. The anterior articular cavities for
the occipital condyles are partially divided into dorsal and ventral parts by a non-
articular area, and are separated by a narrow interval below. The posterior artic-
ular surfaces are flattened behind and are continued into the vertebral canal, form-
ing an extensive area for the dens of the axis.

The axis is short. The spine projects a little in front, and increases in height
and thickness behind; its posterior border descends abruptly. The dens is wide,
and its dorsal surface is deeply concave from side to side. The intervertebral

Fig. 118. — Third Cervical Vertebra of Ox;
Lateral View.
1, Spinous process; 2, 2', anterior and pos-
terior articular processes; .3, 3', ends of body;
4, 4', transverse process; 5, foramen transver-
sarium; 6, ventral spine.

126

SKELETON OF THE OX

VERTEBRAL COLUMN

127

foramen is circular and not so close to the anterior border of the arch as in
the horse. The posterior notches are not so deep. The transverse processes are
stouter, but the foramen transversarium is small and sometimes absent.

The thoracic vertebrae, thirteen in number, are larger than those of the horse.

Fig. 120. — Sixth Cervical Vertebra of Ox; Pos-
terior View.
1, Posterior cavity of body; 2, vertebral foramen;
3, arch; 4, 4', posterior articular processes; 5, 5, an-
terior articular processes; 6, 6', lateral branches of trans-
verse processes; 7, 7', ventral branches of transverse
processes; 8, foramen transversarium; 9, spinous proc-

/ 9 > # \

Fig. 122. — Atlas of Ox; Dorsal View.
1, Dorsal tubercle; 2, intervertebral foramen; 3, alar
foramen; 4, wing; 5, 5, posterior articular surfaces ; 6, ven-
tral arch (surface for dens of asis).

Fig. 121. — Seventh Cervical Vertebra of Ox; Pos-
terior View.
1, Posterior cavity of body; 2, 2', facets for head
of first rib; 3, vertebral foramen; 4, 4', arch; 5, 5', ar-
ticular processes; 6, 6', transverse processes; 7, spinous

Fig. 123.— Axis of Ox; Lateral View.

1, Body; 2, ventral spine; 3, anterior articular
process; 4, posterior articular process; 5, dens; 6,
arch; 7, intervertebral foramen; 8, transverse proc-
ess; 9, foramen transversarium and canalis trans-
versarius (dotted line) ; 10, spinous process.

128

SKELETON OF THE OX

The body is longer and is distinctly constricted in the middle. It bears a thin-
edged ventral crest. The arch — in addition to the usual notches, which are
shallow — is perforated in the posterior part by a foramen. The transverse proc-

FiG. 124. — Fourth Lumbar Vertebra of Ox; Posterior View.
1, Cavity of posterior end of body; 2, notch of arch; 3, 4, articular processes; 5, spinous process; 6, transverse process.

ess is thick and strong, and bears a rounded mammillary process (except at the
posterior end of the series) ; the last two, although prominent, do not always articu-

late with the ribs. The spinous process is long.

Median crest

The first is much higher than in
the horse, the next two are usu-
ally the most prominent, and be-
hind this there is a very gradual
diminution in height. The back-
ward slope, slight at first, in-
creases to the tenth; the last is
vertical and lumbar in charac-
ter. The summit is usually
pointed on the first, and the
thickening on those further back
is less than in the horse. The
width diminishes from the fifth
to the eleventh usually. Both
borders of the spines are in gen-
eral thin and sharp, but the last
three or four sometimes have
thick posterior margins.

The lumbar vertebrae, six in
number, are much longer than in
the horse. The body is much
constricted in the middle, ex-
panded at either end, and bears
a rudimentary ventral crest.
The fourth and fifth are usuall}^
the longest. The intervertebral
foramina are often double in
the anterior part of the series,
and are very large further back.
The articular processes are
large, and their facets are more
strongly curved than in the
horse. The transverse proc-
esses all curve forward. They are separated by considerable intervals, and form
no articulations with each other or with the sacrum. Their borders are thin and

Fig. 125. — Sacrum of Ox; Dorsal View.
1-4, Dorsal sacral foramina; 5, sacral canal; 6, 6, articular processes;
apex.

auricular surface;

VERTEBRAL COLUMN

129

irregular, and often bear projections of variable size and form. The first is the
shortest and the length increases to the fifth, the last being considerably shorter.
The spinous processes are relatively low and wide, the last being the smallest;
their summits are moderately thickened.

The sacrum is longer than that of the horse. It consists originally of five
segments, but fusion is more complete and involves the spinous processes, which
are united to form a median sacral crest (Crista sacralis media), with a convex
thick and rough margin. A lateral sacral crest is formed by the fusion of the ar-
ticular processes. The pelvic surface is concave in both directions, and is marked
by a central groove (Sulcus vasculosus), which indicates the course of the middle
sacral artery. The ventral sacral foramina are large. The wings curve downward
and forward; they are quad-
rangular, short, compressed
from before backward, and
high dorso-ventrally. They
have an extensive anterior
surface, which is concave
from side to side and non-
articular. The posterior sur-
face is rough, and at its lower
part there is a triangular area
for articulation with the
ilium. The body of the first
segment is very wide, and the
entrance to the sacral canal
correspondingly wide and
low. The anterior articular
processes are large and
widely separated; they are
concave and semicylindrical
in curvature medially . The
lateral borders are thin,
sharp, and irregular. The
bone does not become nar-
rower posteriorly, so that the
apex is usually a little wider
than the part just behind the
wings; the posterior end of
the median crest forms a
pointed projection over the
opening of the sacral canal.

The coccygeal vertebrae
are longer and better devel-
oped than in the horse. The first five or six have complete arches and spinous
processes. The transverse processes are relatively large in the anterior part of
the series, in which there are also anterior articular processes (which do not articu-
late), and a pair of ventral spines which form a groove (Sulcus vasculosus) for the
middle coccygeal artery.

Vertebral Curves. — The cervical curve is very slight and is concave dorsally.
The thoracic and lumbar regions form a gentle curve, concave ventrally. The
promontory is more pronounced than in the horse, especially in subjects in which
the sacrum is inclined upward behind. Another prominence occurs at the junction
of the sacrum and first coccygeal vertebrae.

Length.— The following table gives the lengths (inclusive of the inter-

FiG. 126. — Sacrum of Ox; Ventral View.
I-V, Segments; 1-4, ventral sacral foramina; 5, anterior end of body
of first sacral vertebra; 6, vascular groove; 7, posterior end of body of
last sacral vertebra.

130

SKELETON OF THE OX

vertebral fibro-cartilages) of the vertebral regions of a shorthorn cow of
medium size:

Cervical 50 cm.

Thoracic SO cm.

Lumbar 40 cm.

Sacral 25 cm.

Coccygeal 75 cm.

270 cm.

Variations. — Sometimes fourteen thoracic vertebrae and fourteen pairs of ribs are present;

reduction to twelve with the normal number
j^ , rryhcrcle °^ lumbar vertebrae is very rare. According to

^ Franck there are sometimes seven lumbar verte-

brae with the normal number in the thoracic

^^^^ region. The number of coccygeal vertebrae may

Head ^-J^^BIlt^SI^^ vary from sixteen to twenty-one.

THE RIBS

Anterior border-

Thirteen pairs of ribs are present
normally, of which eight are sternal and
five asternal. They are in general longer,
wider, flatter, less curved, and less regular
in form than in the horse. The eighth,
ninth, and tenth are the longest and
widest. The width of most of the ribs
increases considerably in the middle, and

Tubercle

Head

Neck

Anterior border

Sternal end
Fig. 127. — Right Eighth Rib of Ox; Medial View.

Sternal end

Cartilage

Fig. 12S.— First Rib of Ox; Medial Vi

the breadth of the intercostal spaces is correspondingly diminished ; this is not the
case in the posterior part of the series, where the intercostal spaces are very wide.

THE STERNUM THE THORAX THE SKULL 131

The neck is long, and forms (except in the posterior part of the series) a smaller
angle with the shaft than in the horse. The articular surface of the tubercle is
concave transversely, except on the last two or three, where the facet is small and
flat or absent. The ventral ends of the second to the tenth or eleventh inclusive
form diarthrodial joints with the costal cartilages. The first costal cartilages are
very short; they articulate by their medial surfaces with the sternum, but not with
each other.

The presence of a fourteenth rib is not very rare. It is usually floating and may correspond
to an additional thoracic vertebra or to the first lumbar. Reduction of the thirteenth is more
common. The eighth cartilage often does not reach the sternum, but articulates with the seventh.

THE STERNUM
The sternum consists of seven sternebrse, most of which are developed from
two lateral centers. It is wider, flatter, and relatively longer than in the horse,
and the ventral crest or "keel" is absent. The manubrium is somewhat wedge-
shaped and laterally compressed. Its base forms a diarthrodial joint with the
body of the bone, and laterally it bears extensive facets for articulation with the
first pair of costal cartilages. The body widens from before backward, but behind
the last pair of costal facets it becomes much narrower. The ventral surface is
prominent on the second and third segments, concave further back. The lateral
borders are notched for the passage of vessels. The cariniform cartilage is absent.
The xiphoid cartilage is like that of the horse but is smaller.

THE THORAX

The bony thorax is shorter than in the horse. The inlet is higher. The roof
is short, and the floor is wider and relatively longer. The transverse diameter is
wider in the posterior part. The summits of the spinous processes are almost in a
straight line from the second thoracic vertebra to the middle of the lumbar region.

The Skull

Bones of the Cranium
The occipital bone forms the lower part only of the posterior surface of the
skull, and is separated from the highest part (the frontal eminence) by the parietal
and interparietal bones. The supraoccipital, interparietals, and parietals fuse
before birth or soon after, and the mass so formed is separated from the lateral
parts of the occipital bone by a transverse suture in the skull of the calf. Above
this suture is a central tuberosity, the external occipital protuberance, to which
the ligamentum nuchse is attached, and the surface on either side is depressed and
rough for muscular attachment. There is commonly a median occipital crest
which extends ventrally from the protuberance. Below the suture the bone is
much wider than that of the horse. The foramen magnum is wide, so that the
condyles are further apart, except below. The paramastoid processes are short and
wide and are bent inward. Usually at least two foramina are found in the condy-
loid fossa; the ventral one is the hypoglossal, the other (often double) conducts a
vein from the condyloid canal.^ The latter passes upward from a foramen on the
medial side of the condyle and opens into the temporal canal. The mastoid for-

^ The number of foramina here is variable. In exceptional cases the foramen which opens
into the condyloid canal is very small or absent; much oftener there are two, and sometimes three.
In some cases there are two hypoglossal foramina. Thus as many as five foramina may be present
here.

132

SKELETON OF THE OX

amen is situated on each side, at the junction of the occipital and temporal bones;
it communicates with the temporal and condyloid canals at their junction. The
cerebral surface of the supraoccipital presents a central depression, and above this
is a variable but never very pronounced eminence, the internal occipital protuber-
ance. A groove on either side leads to the temporal canal. The basilar part is short
and wide ; its cerebral surface is deeply concave, and the internal spheno-occipital crest
is prominent. Two large tubercles ventrally mark the junction with the sphenoid.

Processus corniis

Nasal bone

Mental foramen

Mandible

Angle of mandible

Fig. 129. — Skull of Ox; Lateral View.
separated for the sake of clearness. ^, Parietal bone; B, squamous temporal bone; C, occipital bone;

occipital

The jaws ;
D, perpendicular part of palatine bone; E, maxilla; F, malar bone; G, lacrimal bone; H, prema::illa;
condyle; 2, paramastoid process; 3, meatus acusticus externus; 4, bulla ossea; 5, zygomatic process of temporal bone;
6, 6', zygomatic and temporal processes of malar bone; 7, supraorbital process; 8, orbital part of lacrimal bone; 9,
lacrimal bulla; 10, fossa sacci lacrimalis; 11, facial tuberosity; 12, infraorbital foramen; 13, condyle of mandible; 14,
coronoid process of mandible.

The foramen lacerum is short and very narrow. In the adult animal the bone is
excavated to contain an air-cavity which is regarded as a part of the frontal sinus.

The sphenoid bone is short. The cerebral surface of the body presents a deep
sella turcica, in front of which it rises abruptly. The high anterior part bears a
central ridge, the ethmoidal spine, which joins the crista galli of the ethmoid.
Two foramina occur on either side. Of these, the large anterior one is equivalent
to the foramen rotundum, orbitale, and trochleare of the horse; it may be termed

BONES OF THE CRANIUM

133

Fig. 130. — Cross-section of Cranium of Ox.

The section cuts the posterior part of the temporal condyle and is viewed from behind, a, Body of sphenoid; b,

bulla ossea; c, temporal condyle; 1, dorsum sellae; 2, foramen ovale; .3, hypophy.seal or pituitary fossa; 4, foramen

orbito-rotundum; .5, optic foramina; 6, crista galli; 7, cribriform plate of ethmoid; 8, orbital wing of sphenoid; 9,

temporal wing of sphenoid; 10, internal plate of frontal bone; 11, frontal sinus; 12, temporal process of malar bone.

Fig. 131. — Cross-section of Cranium of Ox.
The section cuts the posterior part of the temporal condyle and is viewed from in front, a. Basilar part of occipital
bone; 6, bulla ossea; c, paramastoid process; d, meatus acusticus externus; e, temporal fossa; 1, tympanic cavity; 2,
internal opening of condyloid canal; 3, internal opening of temporal canal; 4, depression for vermis cerebelli; 5, internal
occipital protuberance; 6, internal plate of parietal bone; 7, internal plate of frontal bone; 8, frontal sinus; 9, petrous
temporal bone; 10, postglenoid process; 11, hyoid process.

134

SKELETON OF THE OX

the foramen orbito-rotundum. The posterior one is the foramen ovale, which

transmits the mandibular nerve. The orbital wing is thick and is overlapped by
the frontal in such manner as to appear externally to divide into two branches;
the anterior part joins the ethmoid at the sphenopalatine foramen, and contains a
small sinus which communicates with an ethmoidal meatus The temporal wing is
small, but forms a prominent thick pterj'goid crest. The pterygoid process is
wide, and there is no alar canal. The sphenoidal sinus is absent in the calf and
small in the adult ; it communicates by one or two small openings with an ethmoidal
meatus, and so with the nasal cavity.

Fig. 132. — Cranial and Orbital Regions op Skull of Ox.
The horn core, supraorbital process, and greater part of zygomatic arch have been sawn off: A, Frontal bone;
A', A", temporal and orbital parts of same; B, parietal bone; C, squamous temporal bone; D, D', orbital and facial
parts of lacrimal bone; E, malar bone; F, maxilla; G, perpendicular part of palatine bone; 1, occipital condyle; 2,
paramastoid process; 3, temporal crest; 4, temporal condyle; 5, postglenoid process; 6, external opening of temporal
canal; 7, meatus acusticus externus; S, bulla ossea; 9, sty lo-mastoid foramen; 10, muscular process of temporal bone;
11, tip of basilar tubercle; 12, foramen ovale; 13, foramen orbito-rotundum; 14, optic foramen; lo, ethmoidal foramen;
16, orbital opening of supraorbital canal; 17, pterygoid crest; 18, ridge of orbital wing of sphenoid; 19, pterygoid proc-
ess of sphenoid; 20, hamulus of pterygoid bone; 21, lacrimal bulla; 22, fossa sacci lacrimalis; 23, root of supraorbital
process; 24, processus cornus (section) ; 25, frontal eminence.

The ethmoid bone has an extensive perpendicular plate. The lateral mass
consists of five endoturbinates and eighteen ectoturbinates (Paulli). The largest
ethmoturbinate is so extensive as to be termed a third or middle turbinate bone ; it
projects forward between the dorsal and ventral turbinates. The lamina lateralis
appears to a small extent externally in the pterygo-palatine fossa, forming part
of the dorsal margin of the sphenopalatine foramen.

The interparietals are primitively paired, but unite before birth. As already
mentioned, fusion occurs before or shortly after birth with the parietals and supra-
occipital. The bone has no intracranial projection.

The parietal bones do not enter into the formation of the roof of the cranium.

BONES OF THE CRANIUM

135

They constitute the upper part of the posterior wall, bend sharply forward along
the lateral wall, and enter into the formation of the temporal fossa. The line of
inflection is marked by the prominent parietal crest, which is continuous with the
temporal crest below and the frontal crest anteriorly. The parietals are excavated
to form part of the frontal sinuses in the adult animal.

Frontal Parietal
eminence bone

Ti mporal
fossa

Supraorbital foramen
Supraorbital groove

Nasal bone

Palatine fissure

Facial tuberosity

Nasal process of premaxilla

Palatine process of premaxilla

Daily of premaxilla

Fig. 133. — Skull of Jersey Cow; Dorsal View.

The condition in the young subject is as follows: The two parietals are united with each other
and also with the interparietal and supraoccipital. The resulting mass is somewhat horseshoe-
shaped. Its occipital part (Planum occipitale) forms the greater part of the posterior wall of
the cranium and bears about its center the tuberosity for the attachment of the Ugamentum
nucha}. From either side of this a line curves outward and divides the surface mto an upper
smooth area and a lower area which is rough for muscular attachment. The upper border joms
the frontal bone and concurs in the formation of the frontal eminence. The temporal parts
(Plana temporaha) are much smaller and are concave externally; they join the frontal above and
the squamous temporal below. A median occipital crest extends ventrally from the external
occipital protuberance.

The frontal bones are very extensive, forming about one-half of the entire

136

SKELETON OF THE OX

length of the skull, and all of the roof of the cranium. The posterior borders
form -with the parietals a large central frontal eminence (Torus frontalis), the
highest point of the skull. At the junction of the posterior and the lateral border
is the processus comus or "horn core," for the support of the horn. These proc-

FiG. 134. — Skull OF Ox, without Mandible; Ventral View.
1, Foramen magnum; 2, occipital condyle; 3, paramastoid process; 4, condyloid foramen; 5, foramen lacerum;
6, basilar part of occipital bone; 7, 7', basilar tubercles; 8, bulla ossea; 9, foramen ovale (concealed by muscular proc-
ess) ; 10, meatus acusticus externus; 11, zygomatic process of temporal bone, 12, condyle of same; 13, external opening
of temporal canal ; 14, processus cornus; 15, muscular process of temporal bone; 16, pterygoid crest; 17, orbital open-
ing of supraorbital canal; 18, choanae or posterior nares; 19, hamulus of pterj'goid bone; 20, crest formed by pterygoid
processes of sphenoid and palatine bones; 21, horizontal part of palatine bone; 22, anterior palatine foramen; 23,
lacrimal bulla; 24, maxillary tuberosity; 25, palatine process of maxilla; 26, zygomatic process of malar bone; 27.
facial tuberosity: 28, body of premaxilla; 29, palatine process of same; 30, palatine fissure; 31, incisive fissure; 32,
premolars; 33, molars.

esses are of elongated conical form, and vary greatly in size, length, curvature,
and direction. The external surface is rough and porous, marked by numerous
grooves and foramina; in the fresh state it is covered by the corium of the horn.
The base has a constriction, the neck. The interior is excavated to form a number
of irregular spaces, partially divided by bony septa, and communicating with the

BONES OF THE FACE 137

frontal sinus. In the polled breeds these processes are absent, the skull is narrower
here, and the frontal eminence more pronounced (Fig. 139). The supraorbital proc-
ess is situated about half-way between the anterior and posterior margins; it is
short and joins the frontal process of the malar bone. The supraorbital foramen
(often double) is situated about an inch medially from the root of the process; it
is the external orifice of the supraorbital canal (Canalis supraorbitalis), which passes
downward and forward to the orbit. The foramen is in the course of the supra-
orbital groove (Sulcus supraorbitalis), which marks the course of the frontal vein.
The anterior ends of the naso-frontal parts form a notch which receives the nasal
bones, and sutural (or Wormian) bones are often found at this junction (naso-
frontal suture). The orbital part is extensive; it is perforated behind by the or-
bital opening of the supraorbital canal, and below by the ethmoidal foramen. It
does not articulate with the palatine bone, from which it is separated by the or-
bital wing of the sphenoid. The temporal part is also more extensive than in the
horse. The frontal sinus is very extensive, being continued into the parietals and
occipital, and the horn processes when present.

The squamous and petrous parts of the temporal bone fuse early — in fact
union is nearly complete at birth. The squamous part is relatively small. Its
lateral surface is divided into two parts by the prominent temporal crest, which is
continuous with the parietal crest above and turns forward below, ending at a
tubercle above the external acoustic meatus. The part behind the crest faces
backward, and is partly free, partly united with the occipital. The area in front
of the crest is concave and enters into the formation of the temporal fossa; it is
perforated by foramina which communicate with the temporal canal. The zygo-
matic process is much shorter and weaker than in the horse, and articulates with the
malar only. The condyle is convex in both directions. The postglenoid process
is less prominent, and behind it is the chief external opening of the temporal canal.
The cerebral surface is almost completely overlapped by the parietal and sphenoid.
The petrous part is small, but the tympanic part is extensive. The external
acoustic meatus is smaller than in the horse and is directed laterally. From it a
plate projects downward and helps to inclose the deep depression in which the hyoid
process is placed. Behind this plate is the stylo-mastoid foramen. The muscular
process is large and often bifid at its free end. The bulla ossea is large and later-
ally compressed. It is separated from th^ occipital bone by a narrow opening
which is equivalent to part of the foramen lacerum of the horse. The temporal
canal is formed entirely in the temporal bone. The facial canal, on the other
hand, is bounded partly by the occipital bone.

Bones of the Face
The maxilla is shorter but broader and relatively higher than in the horse.
Its lateral surface bears the rough facial tuberosity (Tuber faciale), placed above the
third and fourth cheek teeth; a rough line which extends backward from it to the
upper part of the malar bone may be regarded as the facial crest. The infraorbital
foramen — often double — is situated above the first cheek tooth. The tuber maxil-
lare is small, laterally compressed, and usually bears a small pointed process (Pro-
cessus pterygoideus) . The zygomatic process is very small. The interalveolar
border is concave, and there is no alveolus for a canine tooth. The palatine
process is wider, but somewhat shorter than in the horse. It incloses a large
air-space, which is continuous behind with a like cavity in the horizontal part of
the palate bone, forming the palatine sinus (Sinus palatinus). This communi-
cates laterally (over the infraorbital canal) with the maxillary sinus; in the
macerated skull it communicates with the nasal cavity by a large oval opening,
which is closed by mucous membrane in the fresh state. A median septum sepa-

138

SKELETON OF THE OX

rates the two palatine sinuses. The alveoH for the cheek teeth increase in size
from before backward. The maxillary sinus proper is small and is undivided.
The maxillary foramen is a narrow fissure, deeply placed at the medial side of the
lacrimal bulla. The maxilla takes no part in the formation of the palatine canal.
Sutural (or Wormian) Iwnes are often present at its junction with the lacrimal and
malar bones.

The body of the premaxilla is thin and flattened, and has no alveoli, since
the canine and upper incisor teeth are absent. A deep notch takes the place of
the foramen incisivum. The nasal process is short, convex laterally, and does not
reach to the nasal bone ; the space between the two processes is greater than in the
horse. The palatine process is narrow and is grooved on its nasal surface for the
septal cartilage and the vomer. The palatine fissure is very wide.

The palatine bone is very extensive. The horizontal part forms one-fourth or

Nasal bone

Fig. 135. — Sagittal Section of Skull of Ox, without Mandible.
A, A', Squamous and basilar parts of occipital bone; B, B', postsphenoid, presphenoid; C, lateral mass of ethmoid
bone; Z), internal plate of frontal bone; jE, parietal bone; F, petrous temporal bone; G, pterygoid bone; //.perpendicu-
lar part of palatine bone; I, outline of vomer (dotted line) ; J, palatine process of maxilla; K, nasal process of premaxilla;
L, dorsal turbinate bone; M, ventral turbinate bone; A'^, middle turbinate bone (great ethmo-turbinate) ; 1, occipital
condyle; 2, paramastoid process; 3, bulla ossea; 4, basilar tubercle; 5, muscular process; 6, hypoglossal foramen; 7,
openings of condyloid canal; 8, direction of condyloid canal (dotted line); 9, internal opening of temporal canal; 10,
meatus acusticus internus; 11, foramen lacerum; 12, sella turcica; 13, optic foramen; 14, sphenoidal sinus; 15, orbital
wing of sphenoid bone; 16, frontal sinus; 16', anterior limit of frontal sinus (dotted line) ; 17, dorsal nasal meatus; 18,
middle nasal meatus; 18', dorsal branch of middle meatus; 19, ethmoidal meatuses; 20, maxilla; 21, sphenopalatine
foramen; 22, opening into maxillary sinus; 23, opening into palatine sinus, and arrow indicating communication of
latter with maxillary sinus; 24, palatine sinus; 25, cross indicates anterior end of palatine sinus; 26, palatine fissure.

more of the hard palate. The anterior palatine foramen opens near the junction
with the maxilla, about half an inch from the median palatine suture and crest.
Accessory palatine foramina (Foramina palatina accessoria) are also present. The
palatine groove is usually not very distinct. The palatine canal is formed entirely
in this part, and there is no articulation with the vomer. A rounded ridge occurs
on the nasal side of the median suture. The interior is hollow, forming part of the
palatine sinus. The perpendicular part is an extensive, quadrilateral, thin plate,
which forms the posterior part of the lateral wall of the nasal cavity and in part
bounds the choanse or posterior nares. Its nasal surface is nearly flat, and is smooth
and free, except behind, where it is overlapped by the pterygoid bone. The lateral
surface is attached to a small extent to the pterygoid process behind, and is free else-
where. The sphenopalatine foramen is a long, elliptical opening, formed by a deep
notch in the upper edge of the palate bone and completed by the ethmoid and sphe-

BONES OF THE FACE 139

noid. The edge behind this foramen articulates with the orbital wing of the sphe-
noid, not the frontal, as in the horse.

The pterygoid bone is wider than in the horse, and forms the greater part of the
lateral boundary of the posterior nares. Its lateral surface is almost entirely united
to the palatine bone and the pterygoid process, but a small part is free in the pterygo-
palatine fossa. The hamulus is distinctly hook-like, thin, and sharp.

The nasal bone is little more than half the length of that of the horse. It is
straight in its length, but strongly curved from side to side. It does not fuse later-
ally with the adjacent bones, even in old age. The posterior extremity is pointed
and fits into the notch between the frontal bones. The anterior end is broader,
and is divided into two parts by a deep notch. In old animals there is a small
extension of the frontal sinus into this bone.

The lacrimal bone is very large. The extensive facial part is concave in its
length, and bears no lacrimal tubercle. The orbital margin is marked by several
notches. The orbital part bears ventrally the remarkable lacrimal bulla; this is a
large and very thin-walled protuberance, which bulges backward into the lower
part of the orbit, and contains an extension of the maxillary sinus. The fossa for
the lacrimal sac is small, and is just behind the orbital margin.

The malar bone is relatively long. The facial surface is extensive; it bears a
curved crest (Crista facialis) just below the orbital margin which is continued on
the maxilla, and below this it is concave dorso-ventrally. The zygomatic process
divides into two branches; of these, the frontal branch (Processus frontalis) turns
upward and backward and joins the supraorbital process of the frontal bone;
the temporal branch (Processus temporalis) continues backward, and is over-
lapped by the zygomatic process of the temporal bone, completing the zygomatic
arch.

The dorsal turbinate bone is less cribriform and fragile than in the horse, and
is widest in its middle, small at either end. It is attached to the turbinate crest
of the nasal bone, and curves downward, outward, and then upward to be applied
outwardly to the frontal and lacrimal bones. It thus incloses a cavity which com-
municates with the middle meatus nasi. (In the macerated skull it opens into the
frontal sinus, but this communication is closed by mucous membrane in the fresh
state.)

The ventral turbinate bone is shorter but much broader than in the horse. It
is attached to the maxilla by a basal lamella about an inch (ca. 2 to 3 cm.) wide,
which slopes ventro-medially. At the inner edge of this it splits into two plates
which are rolled in opposite directions, and inclose two separate cavities, sub-
divided by several septa. The dorsal one opens into the middle meatus, the
ventral one into the ventral meatus nasi.

The vomer forms a wider and deeper groove than in the horse. Its anterior
end rests in a groove formed by the ends of the palatine processes of the premaxillae.
The anterior third of its thin ventral edge fits into the nasal crest of the maxilla;
behind this it is free and is separated by a considerable interval from the nasal floor.

The two halves of the mandible do not fuse completely even in advanced age, so
that a symphysis mandibulae is present. The symphyseal surfaces are extremely
rough and are marked by reciprocal projections and cavities. The body is shorter,
wider, and flatter than in the horse, and has eight round and relatively shallow
alveoli for the lower incisors. The interalveolar border is long, curved, thin, and
sharp. There are no alveoli for the canine teeth, which are absent. The anterior
part of the ramus is narrow. The mental foramen is further forward than in the
horse, and is in the posterior end of a fossa. The rami diverge more, so that the
mandibular space is wilder than in the horse. They are also more strongly curved,
and the angle is more pronounced. The molar part is not so high, especially in its
anterior part. Its ventral border is convex in its length. Its alveolar border bears

140

SKELETON OF THE OX

six alveoli for the lower cheek teeth; the first is quite small, and they increase in
size from before backward. The vertical part is much smaller than in the horse
and its posterior border is relatively thin below, concave and wider above. The
mandibular foramen is about in the middle of its medial surface, and a groove for

Coronoid process

Condyle

Angle

Symphyseal surface

Fig. 136. — Right Half of Mandible of Ox; Medial View.
1, Mandibular foramen; 2, groove for lingual nerve.

the lingual nerve curves downward and forward from it. The condyle projects
medially further than in the horse, and is concave from side to side. The coronoid
process is extensive and curves backward.

The hyoid bone has a short tuberous lingual process. The middle cornua

are almost as large as the small cornua.
The great cornua are narrow, except
at the ends. The upper end divides
into two branches, which correspond
to the two angles of that of the horse.
The thyroid cornua do not fuse with
the body except in old age.

SKULL OF THE OX AS A WHOLE

The skull of the ox is more clearly
pyramidal than that of the horse, and
is shorter and relatively wider. The
cranium is quadrangular and larger
externally than in the horse ; its large
size is due mainly to the great extent
of the frontal sinuses and does not
affect the cranial cavity, which is
smaller than in the horse.

The frontal surface (Fig. 133) is

formed bj^ the frontals, nasals, and

premaxillae. The frontal part is

quadrilateral and very extensive, the greatest width being at the orbits. It

presents a central depression on its anterior part, and on either side are the

supraorbital grooves and foramina. Behind is the median frontal eminence,

Fig. 137. — Hyoid Bone of Ox.
o, Body; b, lingual process; c, thyroid cornu and cartil
age, c'; d, small cornu; e, middle cornu; /, great cornu; g
muscular angle. (Ellenberger-Baum, Anat. d. Haustiere.)

SKULL OF THE OX AS A WHOLE 141

and at the lateral angles the "horn cores" project in horned cattle. The
nasal part is very short. The osseous nasal aperture is wide. The premaxillae
do not bend downward as in the horse; they are relatively thin and weak,
and are separated by an interval which has a wide anterior part in place of
the foramen incisivum.

The lateral surface (Fig. 129) is more triangular than in the horse. The temporal
fossa is confined to this surface. It is deep and narrow, and its boundaries are more
complete. It is limited dorsally by a crest which extends from the postero-lateral
angle of the frontal bone to the supraorbital process, and is analogous to the pari-
etal crest of the horse. It is bounded behind by the temporal crest. It is clearly
marked off from the orbit by a rounded ridge and the pterygoid crest. The zygo-
matic arch is short, weak, and flattened, and is formed by the temporal and malar
only. Its condyle is convex and is wide from before backward. The glenoid cavity
and postglenoid process are small. The orbit is encroached upon below by the
lacrimal bulla, and presents the orifice of the supraorbital canal behind. The or-
bital margin is completed behind by the frontal process of the malar; its lower part
is prominent and rough, not smooth and rounded as in the horse. The pterygo-
palatine fossa is much larger, deeper, and more clearly defined. It has a long nar-
row recess between the vertical plate of the palate bone medially and the maxilla
and lacrimal bulla laterally; thus the sphenopalatine and maxillary foramina are
deeply placed. The preorbital region is short but relatively high. A tuberosity
and curved line correspond to the facial crest of the horse. The infraorbital fora-
men is situated above the first cheek tooth and is often double.

The basal surface (Fig. 132) is short and wide, especially in its cranial part. The
occipital condyles are limited in front by transverse ridges. The basilar tubercles at
the junction of the occipital and sphenoid are large. The condyloid fossse contain two
foramina, the hypoglossal below and in front, and the condyloid above and behind;
other inconstant ones occur. The paramastoid processes are short and convergent.
The foramen lacerum is slit-like. The bulla ossea is a large, laterally compressed
prominence. The muscular processes are usually long and narrow triangular plates,
with one or two sharp points. The external acoustic process is directed almost
straight outward. A curved plate extends ventrally from it and joins the bulla
ossea medially, completing the deep cavity which receives the articular angle of
the hyoid bone. The chief external opening of the temporal canal is in front of
this plate, and an accessory one lies behind it. The infratemporal fossa is small,
and presents the foramen ovale. The posterior nares are very narrow, and the
vomer does not reach to the level of their ventral margin. The hard palate is wide,
and forms about three-fifths of the entire length of the skull. A small central part
only of its posterior border enters into the formation of the posterior nares; the
lateral parts are notched and just above them are the posterior palatine foramina.
The anterior palatine foramina are an inch or more from the posterior margin,
and about the same distance apart. The palatine grooves are distinct for a short
distance only. Just beyond the cheek teeth the palate narrows and becomes con-
cave; beyond this it widens and flattens.

The nuchal surface is extensive and somewhat pentagonal in outline in the
adult. About its center is the external occipital protuberance for the attachment
of the ligamentum nuchae. From this a median occipital crest extends toward the
foramen magnum, and laterally two lines (Linese nuchse superiores) curve outward,
marking the upper limit of the area which is roughened for muscular attachment.
The surface above the lines is relatively smooth, and is covered only by the skin
and the thin auricular muscles in the living animal. It is separated from the
frontal surface by a thick border, which forms centrally the frontal eminence, and
bears at its extremities the processus cornus — except in the polled breeds. The con-
dyles are further apart, and the articular surfaces are more clearly divided into

142

SKELETON OF THE OX

upper and lower parts than in the horse. The mastoid foramen is at the junction
of the occipital and temporal bones; it is frequently very small.

Fig. 138. — Cranium of Jersey Cow, Nuchal View. The Fig. 139. — Cranium op Polled Angus Cow, Nuchal
Gre.^ter Part of the Processus Cornus has been View.

Sawn Off.
1, Foramen magnum; 2, occipital condyle; 3, parama.stoid process; 4, bulla ossea; 5, meatus acusticus externus;
6, mastoid foramen; 7, external occipital protuberance; 8, median occipital crest; 9, linea nuchse superior; 10, frontal
eminence.

Dorsal meatus

Middle meatus

Nasal bone

Dorsal part of ventral turbinate
Basal lamella

Ventral part of ventral
turbinate

Fig. 140. — Cross-section of Nasal Region of Skull of Ox. Section Passes Through Facial Tuberosity and

Third Cheek Tooth.
1, Cartilage of septum nasi; 2, vomer; 3, ventral meatus; 4, anterior extremity of maxillary sinus; 5, palatine
sinus; 6, infraorbital canal and nerve; 7, palatine process of maxilla. Dotted lines indicate mucous membrane A'hich
closes gap in bony floor of nasal cavity.

The cranial cavity is shorter and its long axis is more oblique than in the horse,
but it is relativel}^ high and wide. The anterior fossa lies at a much higher level

SKULL OF THE OX AS A WHOLE

143

than the rest of the floor. The ethmoidal fossse are smaller, and the hypophyseal
fossa or sella turcica is much deeper than in the horse. A deep groove leads from
the petrous temporal forward over the foramen ovale to the foramen rotundum.
Behind the sella there is often a distinct prominence (Dorsum sellae) . The internal
parietal crest is prominent anteriorl}^, but subsides further back. A faintly marked
elevation represents the internal occipital protuberance. The petrous temporal
bone projects into the cavity laterally. The ridges and digital impressions are very
pronounced. The temporal canal is formed entirely in the temporal bone, and
opens internally at the apex of the petrous, where it is joined by the condyloid
canal. The foramen lacerum is divided into two parts (For. lacerum orale et ab-
orale) .

The nasal cavity is incompletely divided l)y the septum, which does not reach

Dorsal meatus

Nasal bone

Dorsal turhinaU
Middle meatus

Lacrimal bone

Aaso-lacrimcd canal
Maxilla

Fig. 141.— Cross-section of N.\sal Region of Skull of Ox. Section is Cut between Fourth .a.nd Fifth Cheek

Tooth.
1, Cartilage of septum na.si; 2, vomer; 3, ventral meatus; 4, 4', maxillary sinuses; 5, 5', palatine sinuses; 6, infra-
orbital canal and nerve; 7, horizontal part of palatine bone; 8, communication between maxillarj^ and palatine sinuses.
Dotted lines indicate mucous membrane which closes gap in bony floor of nasal cavity.

the floor posteriorly. The floor is relatively long, and is more concave from side to
side than in the horse. In the dry skull it has a large oval opening (Hiatus maxillaris)
into the palatine sinus, which is closed during life by mucous membrane. The
middle meatus is divided behind into upper and lower branches by the great eth-
moturbinate. The choanal or posterior nares are narrow and obhque.

The frontal sinus is very large. It involves almost all of the frontal bone and
a large part of the posterior wall of the cranium. It also extends for a variable dis-
tance into the horn processes when these are present. A complete median septum
separates the right and left sinuses. The anterior limit is indicated by a transverse
plane through the middle of the orbits. It extends laterally to the crest, which
limits the temporal fossa above, and into the root of the supraorbital process. At
the highest part of the cranial cavity and at the external occipital protuberance

144

SKELETON OF THE OX

tlie two plates of the bone come together. The cavity is very irregular and is sub-
divided into numerous spaces by ridges and partial septa. This multilocular
character is most marked in the anterior part, and here several small spaces appear
to be cut off from the main cavity. The supraorbital canal passes through the
sinus. Several small openings lead from the sinus to the ethmoidal meatuses,
and thus indirectly to the upper division of the middle meatus nasi. The communi-
cations with the cavity of the dorsal turbinate and with the lacrimal part of the

Fig. 142. — Skull op Ox; Dorsal View.
The outer plate of bone has been removed to show the sinuses, a, Frontal sinus; a', cranial plate of frontal bone;
a", anterior part of frontal sinus, which is separated from remainder by a septum (b) ; c, c', communications between
frontal sinus and nasal cavity; d, supraorbital foramen; e, supraorbital canal; /, cavity of dorsal turbinate bone,
and fir, its opening into the nasal cavity; h. lacrimal sinus; i, its communication with the maxillary sinus; k, maxillary
sinus; Z, orbit; i, frontal bone; /', processus cornus; ^, nasal bone; 3, premaxilla (nasal process) ; 4. maxilla; 5, lacri-
mal bone; 6, malar bone; 7, dotted line indicating course of nasolacrimal duct. (After Ellenberger, in Leisering's
Atlas.)

maxillary sinus which are seen in the macerated skull are closed in the fresh state
by mucous membrane.

The maxillary sinus is excavated chiefly in the maxilla, lacrimal, and malar,
and is not divided by a septum as in the horse. It extends forward as far as the
facial tuberosity, or a little further in old animals. Its dorsal limit is indicated
approximately by a line drawn from the infraorbital foramen to the upper margin
of the orbit. It is continued into the lacrimal bulla to a point nearly opposite to

BONES OF THE THORACIC LIMB 145

the bifurcation of the zygomatic process of the malar. It also extends upward and
backward through a large opening into a cavity formed by the lacrimal, frontal,
ethmoid, and turbinal bones, at the medial side of the orbit. ^ The floor of the cavity
is irregular and the roots of the last three or four cheek teeth project up into it,
covered by a plate of bone. The sinus communicates with the palatine sinus freely
over the infraorbital canal through an oval opening about two to three inches (ca.
5 to 7.5 cm.) long. Above this it communicates by a shorter and much narrower
opening with the middle meatus nasi.

The palatine sinus is excavated in the hard palate, and is separated from that
of the opposite side by a median septum. It extends from the posterior border of
the palate to a plane an inch or more (2.5 to 3 cm.) in front of the first cheek tooth.
As mentioned above, there is a large communication with the maxillary sinus over
the infraorbital canal, so that the cavity is sometimes regarded as a part of that sinus.
The large defect in the bony roof of the sinus is closed by two layers of mucous

Fig. 143. — Skull op Ox; Lateral View without Mandible.
The maxillary, lacrimal, and turbinate sinuses have been opened, and part of the orbital margin removed, a. Cavity
of dorsal turbinate bone; 6, lacrimal sinus; c, maxillary sinus; d, communication between maxillary and palatine
sinuses; e, opening between maxillary and lacrimal sinuses; /, thin osseous bulla; g, lacrimal bulla; h, orbit; 1-6, cheek
teeth; 7, nasal bone; 8, premaxilla (nasal process); 9, maxilla; 9', infraorbital foramen; 10, frontal bone; 11, lacri-
mal bone; 12, malar bone; 13, fissure between nasal bone and maxilla; 74, temporal bone (squamous) ; 75, external
acoustic meatus; 75, paramastoid process; 77, occipital condyle; 7,?, palate bone (perpendicular part); 7 S, pterygoid
bone (hamulus); ^0, tympanic part of temporal; ^0', muscular process of petrous temporal. (After EUenberger, in
Leisering's Atlas.)

membrane in the fresh state. The palatine canal passes obliquely through the
posterior part of the sinus.

The sphenoidal sinus is almost entirely in the sphenoid bone and does not
communicate with the palatine sinus. It has one or two openings into the ventral
ethmoidal meatuses. There is no cavity in the perpendicular part of the palate
bone.

There are several small air-cavities between the lateral mass of the ethmoid
and the anterior part of the frontal sinus, which communicate separately with
ethmoidal meatuses.

BONES OF THE THORACIC LIMB

The scapula is more regularly triangular than in the horse, relatively wider at

the vertebral end and narrower at the distal end. The scapular index is about

1 : 0.6. The spine is more prominent and is placed further forward, so that the

supraspinous fossa is narrow and does not extend to the lower part of the bone.

1 This is termed the lacrimal sinus by some authors. It is similar in location and in the posi-
tion of its orifice to the turbinate part of the frontal sinus of the horse with the important differ-
ence that it does not communicate with the frontal sinus in the ox.
10

146

SKELETON OF THE OX

The spine is sinuous, bent backward in its middle, forward below. Its free border
is somewhat thickened in its middle, but bears no distinct tuber. Instead of sub-
siding below as in the horse, the spine becomes a little more prominent, and is pro-
longed by a pointed projection, the acromion, from which part of the deltoid muscle
arises. The subscapular fossa is shallow. The areas for the attachment of the
serratus muscle are not very distinct. The nutrient foramen is usually in the
lower third of the posterior border. The glenoid cavity is almost circular and
without any distinct notch. The tuberosity is small and close to the glenoid cavity.

Fig. 144. — Left Sc.\pul.\ of Ox; L.\teral View.

1, Anterior angle; 2, posterior angle; 3, supra.spinous fossa; 4, infraspinous fossa; 5, anterior border; 6, posterior

border; 7, spine; 8, acromion; 9, tuber scapulae; 10, glenoid cavity; 11, nutrient foramen.

The coracoid process is short and rounded. The cartilage resembles that of
the horse. The tuberosity unites with the rest of the bone at seven to ten months.
The humerus has a shallow musculo-spiral groove. The deltoid tuberosity
is less prominent than in the horse, and the curved line running from it to the neck
bears a well-marked tubercle on its upper part. The nutrient foramen is usually
in the distal third of the posterior surface. The lateral tuberosity is very large,
and rises an inch or more (ca. 3 cm.) above the level of the head. Its anterior part
curves medially over the intertuberal or bicipital groove, and below it laterally
there is a prominent circular rough area for the insertion of the tendon of the infra-
spinatus. The anterior part of the medial tuberosity has a small projection which

BONES OF THE THORACIC LIMB

147

curves over the groove. The groove is undivided. The distal articular surface
is decidedly oblique, and the grooves and ridge are very well marked. The coro-
noid and olecranon fossae are deep and wide. The condyloid crest is represented by
a rough raised area. The proximal end unites with the shaft at three and one-half
to four years, and the distal at about one and one-half years.

The radius is short and relatively broad. It is somewhat oblique, the distal
end being nearer the median plane than the proximal. The curvature is more
pronounced below than above. The shaft is prismatic in its middle part and has

Fig. 14.5. — Left Humerus of Ox;
Lateral View.
1, Head; 2, neck; 3, 3', lateral
tuberosity; 4, rough prominence for
attachment of infraspinatus tendon;
5, deltoid tuberosity; 6, coronoid
fossa; 7, lateral condyle; 8, lateral
epicondyle; 9, medial epicondyle;
10, olecranon fossa.

Fig. 146. — Left Humerus of Ox;
Anterior View.
1, Lateral tuberosity; 2, medial
tuberosity; 3, intertuberal groove;
4, rough prominence for attach-
ment of infraspinatus tendon; 5,
deltoid tuberosity; 6, teres tubercle;
7, musculo-spiral groove; 8, coro-
noid fossa; 9, medial condyle; 10,
lateral condyle.

Fig. 147. — Left Radius and Ulna
OF Ox; PosTERO-MEDiAL View.
1, Olecranon; 2, processus an-
conaeus; 3, semilunar notch; 4,
proximal extremity of radius; 5, 5',
proximal and distal interosseous
spaces; 6, shaft of radius; 7, shaft
of ulna; 8, vascular groove; 9, sty-
loid process of ulna.

dorsal, volar, and lateral faces. There is a marked increase in width and thickness
distally. The proximal articular surface presents a synovial fossa which extends
medially from the deep groove between the two glenoid cavities. The radial
tuberosity is represented by a slightly elevated rough area. The facets for the ulna
are larger than in the horse. The two bones commonly fuse above the proximal
interosseous space and always fuse below it, except near the distal end, where there
is a small distal interosseous space. A groove connects the two spaces laterally.
The distal extremity is large, and is thickest medially. Its articular surface is
oblique in two directions, i. e., from within upward and backward. The grooves

148

SKELETON OF THE OX

for the extensor tendons are shallow. The proximal end unites with the shaft at
one to one and one-half years, and the distal at three and one-half to four years.

The approximation of the lower ends of the forearms and the carpi gives the "knock-kneed"
appearance in cattle. The obliquity of the joint surfaces produces lateral deviation of the lower
part of the hmb in flexion. The facets for the radial and intermediate carpals are narrower than
in the horse and run obliquely dorso-laterally. The surface for the ulnar carpal is extensive and
saddle-shaped; its lateral part is furnished by the ulna.

The ulna is more fully developed than in the horse. The shaft is complete,
three-sided, and strongly curved. It is fused with the radius in the adult, except
at the two interosseous spaces mentioned above. Its proximal part contains a
medullary cavity which extends somewhat into the proximal end. The olecranon is

—u

i
3

Fig. 148. — Left Carpus and Adjacent Bones op Ox;
Front View.
if, Radius; XJ , ulna; C r., radial carpal; C. u.,
ulnar carpal; C. 2+3, fused second and third carpals;
C. 4, fourth carpal; 1,S, 3, grooves for extensor tendons;
4, metacarpal tuberosity; 6, vascular groove. Inter-
mediate carpal bone (between radial and ulnar) not
marked.

Mc. 3+4

Fig. 149. — Left Carpus and Adjacent Bones of
Ox; Lateral View.
R, Distal end of radius; U, styloid process of
ulna; I, distal interosseous space; C. i., intermediate
carpal; C. u., ulnar carpal; C. a., accessory carpal;
C. 2 + 3, fused second and third carpals; C. 4, fourth
carpal; Mc. 3+4. fused third and fourth (large)
metacarpal; Mc. 5, fifth (small) metacarpal; T, meta-
carpal tuberosity.

large and bears a rounded tuberosity. The distal end is fused with the radius; it
projects below the level of the latter, forming the styloid process of the ulna (Pro-
cessus styloideus ulna?), which furnishes part of the facet for the ulnar carpal.
The summit of the olecranon and the distal end unite with the shaft at three and
one-half to four years.

The carpus consists of six bones, four in the proximal row and two in the distal.
The proximal row is oblique in conformity with the carpal articular surface of the
radius. The radial and intermediate resemble in general those of the horse, but
are less regular in shape, and their long axes are directed obliquely backward and
medially. The radial is narrower than in the horse and curves upward behind. The
intermediate is constricted in its middle, and wider behind than in front. The
ulnar is large and very irregular. Its proximal surface is extensive and sinuous and
articulates with both radius and ulna; it has a large oval facet behind for articula-
tion with the accessory carpal. The accessory is short, thick, and rounded; it

BONES OF THE THORACIC LIMB

149

articulates with the ulnar carpal only. The first carpal is absent. The second and
third carpals are fused to form a large quadrilateral bone. The fourth carpal is a
smaller quadrilateral bone.

The metacarpus consists of a large metacarpal and a lateral small metacarpal
bone. The large metacarpal bone (Mc. 3+4) results from the fusion of the third
and fourth bones of the foetus, and bears evidences of its double origin even in the
adult state. The shaft is shorter than in the horse, and is relatively wider and
flatter. The dorsal surface is rounded, and is marked by a vertical vascular
groove connecting two canals which traverse the ends of the shaft from before
backward. The volar surface is flat and presents a similar but much fainter groove.
The borders are rough in the proximal third. The proximal end bears two slightly
concave facets for articulation with the bones of the lower row of the carpus; the
medial area is the larger, and they are separated by a
ridge in front and a notch behind. The lateral angle
has a facet behind for the small metacarpal bone. The
medial part of the extremity has anterior and posterior
tuberosities. The distal end is divided into two parts
by a sagittal notch. Each division bears an articular
surface similar to that in the horse, but much smaller.
The medullary cavity is divided into two parts by a ver-
tical septum which is usually incomplete in the adult.
The small metacarpal bone (Mc. 5) is a rounded rod
about an inch and a half (ca. 3.5 to 4 cm.) in length,
which lies against the proximal part of the lateral bor-
der of the large bone. Its proximal end articulates with
the latter, but not with the carpus. The distal end is
pointed.

Four cartilaginous metacarpals are present in the early foetal
state, viz., the second, third, fourth, and fifth. The second com-
monly either disappears or unites with the third; sometimes it
develops as a small rod of bone. The third and fourth gradually
unite, but can be cut apart at birth. Each has three centers of
ossification; the proximal epiphysis fuses with the shaft before
birth, the distal at two to two and one-half years.

Four digits are present in the ox. Of these, two —
the third and fourth — are fully developed and have
three phalanges and three sesamoids each. The second
and fifth are vestiges and are placed behind the fetlock;
each contains one or two small bones which do not ar-
ticulate with the rest of the skeleton.

The first phalanx is shorter and narrower than in
the horse and is three-sided. The interdigital surface is
flattened and its volar part bears a prominence for the

attachment of the interdigital ligaments. The proximal extremity is relatively
large, and is somewhat compressed from side to side. The articular surface is con-
cave from before backward and is cUvided by a sagittal groove into two areas, of
which the abaxial one is the larger and higher. Behind these are two facets for
articulation with the sesamoid bones. The volar surface bears two tuberosities
separated by a deep depression. The distal extremity is smaller than the proximal,
especially in the dorso-volar direction. Its articular surface is divided by a sagittal
groove into two convex facets, of which the abaxial one is decidedly the larger.
There are depressions on either side for ligamentous attachment. The bone con-
sists at birth of two pieces— the distal end and the fused shaft and proximal ex-
tremity. Union occurs at one and one-half to two years.

The second phalanx is about two-thirds of the length of the first and is dis-

FiG. 1.50. — Left Metacarpal

Bones of Ox; Front View.

The Small Bone has been

Moved Laterally.

1, Metacarpal tuberosity; 2,
vascular groove; 3, 3', foramina;
4, 4', condyles; 5, articular facet
of fifth (small) metacarpal bone.

150

SKELETON OF THE OX

tinctly three-sided. The proximal articular surface is divided by a sagittal ridge
into two glenoid cavities, of which the abaxial one is much the larger. There is a
central dorsal prominence and two tubercles are present on the volar face. The
cUstal extremity is smaller than the proximal. Its articular surface encroaches con-
siderably on the dorsal and volar surfaces, and is divided into two parts by a
sagittal groove. There is a deep depression for ligamentous attachment on the inter-
digital side. The bone contains a small medullary canal. The distal end unites
^^dth the rest of the bone about the middle of the second year.

The third phalanges resemble in a general way one-half of the bone of the horse.
Each has four surfaces. The dorsal surface is marked in its distal part by a shal-
low groove, along which there are several foramina of considerable size; the
posterior one of the series is the largest, and conducts to a canal in the interior of
the bone. Distal to the groove the surface is prominent, rough, and porous.

Fig. lol. — Boxes of Distal Part of Fore Limb of
Ox; Lateral View.
1, Distal end of metacarpal bone; 2, first phalanx;
3, proximal sesamoid bone; 4, second phalanx; 5, ex-
tensor process of third phalanx; 6, dorsal surface; 7,
angle; S, distal sesamoid bone.

Fio. 152. — Bones of Distal Part of Fore Limb of
Ox; Volar View.
1, Metacarpal bone; 2, proximal sesamoid bones;
3, first phalanx; 4, second phalanx; 5, distal sesamoid
bone; 6, third phalanx.

Near and on the extensor process are several relatively large foramina. The slope
of the surface is very steep posteriorly, but in front it forms an angle of 25 to 30 de-
grees with the ground plane. The articular surface is narrow from side to side, and
slopes downward and backward. It is also oblique transversely, the interdigital
side being the lower. It is adapted to the distal surface of the second phalanx, with
the exception of a facet behind for the distal sesamoid. The extensor process is
very rough. The volar surface is narrow and slightly concave, and presents two
or three foramina of considerable size. It is separated from the dorsal surface
by a border which is sharp in front, rounded behind. There is no semilunar crest,
since the deep flexor tendon is attached to the thick posterior border of the volar
surface. The interdigital surface is smooth and grooved below, rough and porous
above. At the proximal angle it is perforated by a large foramen, which is equiva-
lent to the volar foramen of the horse and leads to a cavity in the middle of the bone.
The surface is separated by a rounded border from the dorsal surface, and by a sharp

BONES OF THE PELVIC LIMB 151

edge from the volar surface. The angle is very short and blunt, and there is no
cartilage.

Four proximal sesamoids are present, two for each digit. They are much
smaller than in the horse. The bones of each pair articulate with the correspond-
ing part of the distal end of the large metacarpal bone by their dorsal surfaces,
with each other and with the first phalanx by small facets.

The two distal sesamoids are short and their ends are but little narrower than
the middle.

BONES OF THE PELVIC LIMB

The ilia are almost parallel to each other and are also less oblique with regard

to the horizontal plane than in the horse. They are relatively small. The gluteal

line is prominent and is nearly parallel to the lateral border; it joins the ischiatic

spine. A rounded ridge separates the two parts of the pelvic surface. The surface

Tuber sacrule

Greater
Lesfier sciatic Ischiatic sciatic

Tuber ischii notch spine notch

]^^s

Tuber
coxce

" Sliajt of ilium

Ischium

^- ' I I Acetabulum

Ji'tili/i Ohlurator Puliis
J'oramen

Fig. 153. — Right Os Cox« of Ox; Lateral View.
1, Gluteal line; 2, fossa acetabuli.

for articulation with the sacrum is triangular. The tuber sacralc is truncated, does
not extend as high as the vertebral spines, and is separated from the opposite angle
by a wider interval than in the horse. The tuber coxse is relatively large and prom-
inent; it is not so oblique as in the horse, and is wide in the middle, smaller at either
end. The shaft is short and compressed from side to side.

The ischium is large. Its long axis is directed obliquely upward and back-
ward, forming an angle of about 45 to 50 degrees with the horizontal plane. The
transverse axis is oblique downward and inward at a similar angle, so that this
part of the pelvic floor is deeply concave from side to side. The middle of the
ventral surface bears a rough ridge or imprint for muscular attachment. The
ischiatic spine is high and thin, and bears a series of almost vertical rough lines
laterally. The tuber ischii is large and three-sided, bearing dorsal, ventral, and
lateral tuberosities. The ischial arch is narrow and deep. The symphysis bears a
ventral ridge, which fades out near the ischial arch.

The acetabular branch of the pubis is narrow, and is directed laterally and a

152

SKELETON OF THE OX

little forward. The anterior border is marked by a transverse groove which ends
below the rough ilio-pectineal eminence. The symphyseal branch is wide and
■/hin.

The acetabulum is smaller than in the horse. The rim is rounded and is
usually marked by two notches. One of these is postero-medial and is narrow
and deep; it leads to the deep acetabular fossa and is often almost converted
into a foramen by a bar of bone. The other notch is antero-medial, small, and
sometimes replaced by a foramen or absent.

The obturator foramen is large and elliptical. Its medial border is thin and
sharp.

Fusion of the three bones occurs at seven to ten months.

The pelvic inlet is elliptical and is more oblique than in the horse. In a cow

Median
Wing of crest of Tuber
sacrum sacrum sacrale

Ilio-pectineal eminence

Sym-physis pubis

Acetabulum
Tuber ischii

Obturator foramen

Ventral ridge
Fig. 154. — Pelvic Bones of Cow, Viewed from in Front and Somewhat from Below.

of medium size the conjugate diameter is about nine and a half inches (ca. 23 to 24
cm.), and the transverse diameter about seven inches (ca. 18 cm.). The anterior
end of the symphysis lies in a transverse plane through the junction of the third and
fourth sacral segments. The dorsal wall or roof is concave in both directions. The
ventral wall or floor is deeply concave, particularly in the transverse direction.
The cavity is narrower and its axis is inclined strongly upward in the posterior part.
The distance between the acetabulum and the tuber coxae is only a little (ca. 3 to
4 cm.) more than the distance between the former and the tuber ischii.

The femur has a relatively small shaft, which is cylindrical in its middle, pris-
matic distally. The trochanter minor has the form of a rough tuberosity, and is
situated higher up than in the horse and encroaches on the posterior surface. The
trochanteric ridge (Crista intertrochanterica posterior) connects it with the tro-

BONES OF THE PELVIC LIMB

153

chanter major. The third trochanter is absent. The supracondyloid fossa is
shallow. The proximal extremity is very wide. The head is smaller than in the
horse, and the articular surface extends considerably on the upper surface of the
neck. The fovea capitis is a small depression on the middle of the head for the
attachment of the round ligament. The neck is well defined except above. The
trochanter major is very massive and is undivided; its lateral surface is very rough.

Fig. 1.55. — Right Femur of Ox; Poste-
rior View.
1, Head; 2, neck; 3, trochanter ma-
jor; 4, trochanteric fossa; 5, trochanter
minor; 6, nutrient foramen; 7, vascular
groove; 8, lateral supracondyloid crest;
9, supracondyloid fossa; 10, 10', medial
and lateral condyles; 11, 11', medial and
lateral epicondyles; 12, intercondyloid

Fig. 1.50.— liuaii- Ji.MLii of Ox;
Lateral View.
Numbers around bone: 1,
Head; 2, neck; 3, trochanter
major; 4, lateral border; 5, lateral
supracondyloid crest; 6, supra-
condyloid fossa; 7, lateral condyle;
8, trochlea. Numbers on bone: 1,
Eminence for attachment of gluteus
profundus; 2, lateral epicondyle;
3, depression for origin of popliteus
muscle; 4, extensor fossa.

Fig. 157. — Left Tibia and Prox-
imal Part of Fibula of Ox;
Posterior View.
Numbers around bones: 1, 1',
Medial and lateral condyles of
tibia; 2, nutrient foramen; 3,
lateral border; 4, distal extrem-
ity; 5, medial malleolus; 6, shaft
of fibula. Numbers on bone: 1, 1',
Tubercles of spine; 2, intercondy-
loid fossa; 3, muscular lines.
Arrow indicates groove for flexor
digitalis longus.

The trochanteric fossa is deep, but does not extend so far distally as in the horse.
The distal end presents no very striking differential features, but the ridges of the
trochlea are less oblique than in the horse, and converge very slightly below. The
proximal extremity unites with the shaft at about three and one-half years, the
distal at three and one-half to four years.

The tibia resembles that of the horse rather closely, but is somewhat shorter.

154

SKELETON OF THE OX

The shaft is distinctly curved, so that the medial side is convex. The posterior
surface is not divided into two areas, and the linese musculares are fewer and extend
up higher than in the horse. The articular grooves and ridge of the distal end are
almost sagittal in direction, and present an extensive but shallow synovial fossa.
The lateral groove is separated by a sharp ridge from an outer area which is for
articulation with the lateral malleolus. The anterior part of the medial malle-
olus is prolonged do'vvnward and has a pointed end. The groove behind it is broad
and well defined. Laterally there is a deep narrow groove which separates two
prominences. The proximal extremity fuses with the shaft at three and one-half
to four years, the distal at two to two and one-half years.

Tuber calcis

M.m.

M.l.

Mt. 5+4

Fig. 15S. — Right Tarsus and Adjacent Boxes of Ox; Fig. 1.59. — Right Tarsus and Adjacent Bones op
AIedial View. Ox; Dorso-l.\teral View.

M. m., Medial malleolus; .1/. I., lateral malleolus (distal end of fibula) ; T, tibia; T. t., tibial tarsal bone; T. /., fibulai
tarsal bone (sustentaculum); T. c+-J, fused central and fourth tarsal bones; T. i, first tarsal bone; T.2+S, fused
second and third tarsal bones; Mt. 2, small or second metatarsal bone; Mt. S+ 4. large metatarsal or fused third and
fourth metatarsal bones; 1, groove for tendon of flexor digitalis longus; S, groove for deep flexor tendon.

The fibula usually consists of the two extremities onlj\ The head is fused with
the lateral condyle of the tibia and is continued by a small, blunt-pointed prolonga-
tion below. The distal end remains separate and forms the lateral malleolus (some-
times called the os malleolare). It is quadrilateral in outline and compressed from
side to side. The proximal surface articulates with the distal end of the tibia, and
bears a small spine which fits into the groove on that bone. The distal surface
rests on the fibular tarsal, and the medial articulates with the lateral ridge of the
tibial tarsal bone. The lateral surface is rough and irregular.

The early cartilaginous fibula is complete, but later the shaft is reduced to the
small prolongation noted in speaking of the head and a fibrous cord which connects
it with the distal end (lateral malleolus). In some cases, however, the upper part
undergoes partial ossification, forming a slender rod which is usually united with
the lateral border of the tibia and is joined to the head by fibrous tissue.

BONES OF THE PELVIC LIMB

155

The patella is long, narrow, and very thick. The free surface is strongly con-
vex and very rough and irregular. The articular surface is convex from side to
side and nearly straight in the vertical direction. The large prominence on the
medial side for the attachment of the fibro-cartilage allows prompt determination
of the side to which the bone belongs. The apex is more pointed than in the horse.

The tarsus consists of five pieces; the central and fourth and the second and
third tarsal bones are fused.

The tibial tarsal bone is relatively long and narrow, and is somewhat flattened
from before backward. It bears a trochlea at either end. The groove and ridges
of the proximal trochlea are not spiral, but almost sagittal; the lateral ridge is the
wider, and articulates with both tibia and fibula. The distal trochlea consists
of two condyles divided by a groove, and articulates with the
combined central and fourth tarsals. The plantar surface bears
a large oval facet for articulation with the fibular tarsal; this
occupies most of the surface, and is convex and grooved from
above downward. The lateral surface presents two facets for
articulation with the fibular tarsal, and is excavated and rough
elsewhere. The medial surface bears a tuberosity at its upper
part, and is flattened below.

The fibular tarsal ])one is longer and more slender than in
the horse. The distal part of the body is compressed laterally,
and bears a projection in front which articulates with the lateral
malleolus. The tuber calcis is marked posteriorly by a wide
shallow groove, which is coated with cartilage in the fresh state.

The central and fourth tarsals are fused to form a large
bone (Os centrotarsale quartum, scapho-cuboid), which extends
across the entire width of the tarsus and articulates with all of
the other bones. The greater part of the proximal surface is
molded on the distal trochlea of the tibial tarsal, and its medial
part rises high above the rest posteriorly. Laterally there is a
narrow, undulating surface for articulation with the distal end
of the fibular tarsal bone. The plantar surface bears two tuber-
osities, of which the lateral one is rounded, the medial more
prominent and narrower.

The first tarsal bone is quadrilateral and small. It articu-
lates with the central above, the metatarsus below, and the
second tarsal in front.

The second and third tarsals are fused to form a rhomboid
piece. The proximal surface is concavo-convex, and articulates
with the central component. The distal surface is undulating
and rests on the metatarsus. The lateral surface bears a small
facet in front for the fourth tarsal component, and the plantar
surface a very small one for the first tarsal bone.

The large metatarsal bone is about one-seventh (ca. 3 cm.) longer than the
corresponding metacarpal. Its shaft is compressed transversely and is distinctly
four-sided. The groove on the dorsal surface is deep and wide. The plantar
surface is marked by variable grooves. The proximal foramen on this surface does
not perforate the shaft, but passes obliquely through the extremity, opening on the
posterior part of its proximal surface. The medio-plantar angle of the proximal
end bears a facet for articulation with the small metatarsal bone.

The small metatarsal bone is a quadrilateral disc a little less than an inch in
width and height. Its anterior face bears a facet for articulation with the large
metatarsal bone.

Fig. 160. — L a r g e
Metatarsal Bone
OF Ox; Dorsal
View.

1, Vascular groove;
2, foramen; 3, 3', con-
dyles.

156 SKELETON OF THE SHEEP

The large metatarsal bone is usually regarded as consisting of the fused third and fourth
metatarsal bones, and the small bone as the second metatarsal. The medullary cavity is subdivided
like that of the large metacarpal bone. Some anatomists, however, consider that the ridges at
the upper end of each border represent the second and fifth metatarsals (Rosenberg and Retterer).
On this basis the small bone would be the first metatarsal.

The phalanges and sesamoids resemble those of the thoracic limb so closely
as to render separate description unnecessary.

SKELETON OF THE SHEEP

VERTEBRAL COLUMN

The vertebral formula may be given as C7Ti3L6_7S4Cyi6-i8, but it should be
noted that, except in the cervical region, variation in number is common.

It is not very rare to find twelve thoracic and seven lumbar, or an ambiguous intermediate
vertebra. More commonly there are seven lumbar vertebriE without reduction in the thoracic
region. In some cases there are fourteen thoracic and five or six lumbar vertebrae, and Lesbre
records a case in which twelve thoracic and seven lumbar were present. In some cases the fourth
sacral vertebra remains separate, and in others the first coccygeal unites with the sacrum, although
the fusion here is rarely complete. Nathusius states that the number of coccygeal vertebrae
varies from tliree to twenty-four or more.

The cervical vertebrae are relatively longer than those of the ox. The atlas
differs chiefly in that the prominence on the dorsal arch is much less developed.
The anterior articular cavities are often separated by a central ridge. The wings
are produced to form blunt points behind. The spinous process of the axis is not
enlarged posteriorly; those of the succeeding vertebrae are less developed than in
the ox; they increase in length from the third to the last. The ventral spines are
rudimentar5\ The arches are separated dorsally by interarcuate spaces.

The thoracic vertebrae are usually thirteen in number, but fourteen may be
present, or, more rarely, only twelve. Their bodies are relatively wider and less
constricted than those of the ox, and their extremities are not so strongly curved,
especially toward the end of the series. The intervertebral foramina are larger, in
correlation with the absence of the foramina which usually occur in the arches of
these vertebrae in the ox.

The limibar vertebrae number six or seven, the former being a little more fre-
quent than the latter. It is not common to find the number reduced to five. In
some cases there is an ambiguous vertebra at the junction of the thoracic and lum-
bar regions. The bodies are more flattened dorso-ventrally than those of the ox;
their anterior ends are somewhat concave transversely, and the posterior ends are
almost flat. The anterior articular processes are strongly curved and overlap the
posterior ones. The transverse processes curve forward and have expanded ends.

The sacrum consists ordinarily of four segments, but the last vertebra may re-
main separate or undergo orfly partial fusion. There is no vascular groove on the
pelvic surface. The spines are not fused, ^vith the exception of the flrst and second,
which may be partially united. The transverse processes of the last segment are
distinct and outstanding.

The coccygeal vertebrae vary in number from three (in short-tailed sheep) to
twenty-four or more. The bodies have no hemal processes on the ventral surface.
The transverse processes are long and thin and project backward.

THE RIBS
The ribs usually number thirteen pairs, but the occurrence of fourteen pairs is
not at all unconmion. The thirteenth rib is floating and has a cartilage about an

THE STERNUM — THE SKULL 157

inch long. The fourteenth rib, when present, is also floating. As compared with
those of the ox, they are narrower and are more strongly curved in the anterior part
of the series. The lateral surface is in general smooth and rounded. The second
to the eleventh form diarthroses with their cartilages.

The thirteenth rib may be more or less rudimentary on one side or both, and may be fused
with the corresponding vertebra; the latter may, therefore, be ambiguous in character.

THE STERNUM
The sternum resembles in general that of the ox. The number of segments
may be reduced to six, and the primitive division of the next to the last sternebra
into two lateral halves may persist for a long time. The first segment is cylindrical,
with enlarged ends; the second and third are wide and flat; the last is long and nar-
row.

THE SKULL

The more important differences in the skull of the sheep as compared with
that of the ox are in regard to the cranium. Viewed from above, the cranium is
irregularly hexagonal in outline; it is widest in the frontal region, between the
posterior parts of the orbits, and narrows greatly both anteriorly and posteriorly.
In profile the roof of the cranium is strongly convex; the highest part of the curve
coincides with the greatest width, and the posterior part slopes at an angle of about
45 degrees with the basal plane.

The occipital bone forms all of the nuchal surface of the cranium, except a
small lateral area occupied by the mastoid part of the temporal bone. A narrow
part (about 1.5 cm. in width) enters into the formation of the roof of the cranium
also; it joins the parietal bones at a transverse suture. The parietal and nuchal
surfaces are separated by a rough transverse ridge, the central part of which is
united below with the external occipital protuberance, to which the ligamentum
nuchse is attached. The mastoid foramen is situated between the lateral border
and the petro-mastoid part of the temporal bone. The paramastoid process is
grooved laterally, has a concave anterior border, and tapers to a blunt point. The
basilar part is wide; the tubercles at its junction with the sphenoid are placed
laterally, and are broad and short.

The sphenoid bone resembles that of the ox. The posterior wall of the deep
hypophyseal or pituitary fossa is formed by a plate (Dorsum sellae) which is di-
rected forward and upward, and bears a projection (Processus clinoideus posterior)
at each side of its upper part. The sphenoidal sinus is commonly absent or rudi-
mentary.

The ethmoid bone resembles that of the ox.

The parietal bone fuses soon after birth with its fellow and with the inter-
parietal. From this union there result a central quadrilateral curved plate which
forms part of the roof of the cranium, and, separated from it by a curved line, a
narrower lateral part, which extends forward on either side as part of the medial
wall of the temporal fossa. The frontal sinus does not extend into the parietal bone.
There is no internal occipital protuberance.

The frontal bone is relatively less extensive than in the ox. The naso-frontal
part is strongly curved, but varies considerably in contour in different breeds. In
horned breeds the processus cornus projects from the lateral part of the external
surface a little (ca. 1.5 cm.) behind a transverse plane through the posterior margin
of the orbit. The process varies in size and shape, and does not contain an extension
of the frontal sinus. In other cases there is a rounded tuberosity or a slight rough-
ened elevation. The supraorbital foramen is further forward than in the ox, being
just behind a transverse plane through the middle of the orbit; it is a little nearer

158

SKELETON OF THE SHEEP

to the orbital margin than to the median line. The groove which leads forward
from it is often rather faint. The orbital part is deeply concave. The infraorbital
canal opens on the medial wall of the orbit as in the ox. The frontal sinus extends
backward to a transverse plane through the posterior part of the temporal con-
dyle, and forward to one through the anterior margin of the orbit.

The temporal bone consists of distinct squamous, tympanic, and petro-mastoid
parts. The squamous part in general resembles that of the ox, but has, like that of
the horse, a notch through which the external acoustic process protrudes. The root
of the zygomatic process is perforated by a foramen which opens ventrally behind
the postglenoid process, in front of the chief external opening of the temporal canal.
The latter extends upward and backward between the petro-mastoid and squamous
parts and the parietal l:)one, and opens into the cranial cavity in front of the apex
of the petrous. The tympanic part includes the external acoustic process, the bulla

Fig. 161. — Skull of Sheep; Lateral View.
A, Occipital bone; B, parietal bone; C, squamous temporal bone; D, frontal bone; S, nasal bone; F, lacrimal bone;
G, malar bone; H, maxilla; I, premaxilla; J, mandible; K, perpendicular part of palatine bone; L, hyoid bone; 1,
occipital condyle; 2, paramastoid process; 3, mastoid process; 4, meatus acusticus externus; 5, bulla ossea; 6, zygo-
matic process of temporal bone; 7, condyle of mandible; S, coronoid process; 9, supraorbital process; 10, processus
cornus; 11, 11', openings of supraorbital canal; 12, ethmoidal foramen; 13, optic foramen; 14, fossa sacci lacrimalis;
15, bulla lacrimalis; 16, external lacrimal fossa; 17, facial tuberosity; 18, infraorbital foramen; 19, mental foramen.

ossea, and the muscular process; the first resembles that feature in the horse, the
others those of the ox, but the cavity of the bulla is undivided. The cerebral sur-
face of the petrous part presents the floccular fossa on its upper part, and a round
eminence behind the internal acoustic meatus.

The bones of the face present, aside from the difference in size, few important
special features.

In regard to the maxilla it may be noted that the junction with the lacrimal and
malar is less oblique than in the ox, since the facial parts of these bones are quadri-
lateral and not produced to a point anteriorly. The facial tuberosity and the infra-
orbital foramen are a little further back, and lie about over the second and fourth
cheek tooth respectively. The palatine sinus extends from a point opposite to the
fir.st cheek tooth backward to the transverse palatine suture. The defect (in the
dry skull) in its nasal wall is quite small — in marked contrast to that of the ox —

THE SKULL

159

Occipital huno

Temporal crest
( 'oronoid process

Frontal bone

Orbit

Supraorbital
foramen

Malar bone
Lacrimal bone

since the basal lamella of the ventral turbinate bone curves ventro-medially, joins
the palatine bone, and is separated only by a narrow hiatus from the nasal plate of
the palatine process of the maxilla. The anterior palatine foramen is at the trans-
verse palatine suture. The anterior end of the palatine process tapers to a point.
The maxillary sinus resembles that of the ox, but is relatively small.

The premaxilla has a narrow and pointed body. The palatine process is ex-
tremely narrow in front and is grooved laterally. The palatine fissure is long and
narrows to a very acute angle behind.

The palatine bone resembles that of the ox, but there is no air-cavity in its
horizontal part. The spheno-
palatine foramen is large and Occipital hum Parietal bom
oval.

The pterygoid bone is
very broad above and narrow
below, where it ends in a sharp-
pointed hamulus.

The nasal bone tapers to
a point at its anterior end,
which is not notched.

The facial part of the
lacrimal bone has an elongated
quadrilateral outline; in front
of the orbit it forms, with the
adjacent part of the malar, the
external lacrimal fossa (Fossa
lacrimalis externa) which
lodges a cutaneous cul-de-sac
known as the infraorbital or
lacrimal pouch. The bone here
may be more or less cribriform.
The lacrimal bulla is relatively
small, is usually cribriform,
and has a pointed posterior
end; the maxillary sinus ex-
tends into it. The orbital
margin forms a distinct promi-
nence, and behind the latter is
the fossa for the lacrimal sac.

The facial part of the
malar bone is extensive and

quadrilateral. Its upper part concurs in the formation of the external lacrimal
fossa; this area is limited below by a curved crest which continues backward on
the zygomatic process. The latter divides into two branches, as in the ox.

The turbinates and the vomer resemble those of the ox.

The mandible differs from that of the ox chiefly in that the ventral border of
the ramus, from the body to the angle, is only slightly curved.

On account chiefly of the limited extent of the frontal sinuses, the cranial
cavity corresponds to the external form of the cranium more closely than is the case
in the ox. It is ovoid, and is much longer relatively, but has a much shorter dorso-
ventral diameter than that of the ox. The parietal bone forms a distinct ridge on
the lateral wall between the cerebral and cerebellar compartments, but, on the other
hand, the petrous temporal projects very little into the cavity.

The nasal cavity resembles that of the ox, but is relatively narrow (especially
anteriorly), and there is no large hiatus in the nasal plate of the maxilla.

Facial tuberosity
Maxilla

Nasal hone

Nasal process of pre-
maxilla

Palatine process of pre-
maxilla
Palatine fissure

of premaxilla

Incisor teeth

Fig. 162. — Skull of Sheep; Dorsal View.

160 SKELETON OF THE SHEEP

BONES OF THE THORAaC LIMB

The scapula differs chiefly from that of the ox in the following points : The ver-
tebral border is longer and the neck narrower. The spine is less sinuous. The
glenoid extremity is relatively long, since the tuber scapulae is connected with the
rim of the glenoid cavity. The subscapular fossa is more extensive.

The humerus is relatively longer and more slender than that of the ox. The
anterior part of the lateral tuberosity is blunt and less incurved, while the posterior
part is small. The deltoid tuljerosity is nearer to the proximal end and is less
prominent.

The bones of the forearm are relatively longer than those of the ox. The
radius is a little more curved than that of the ox, and its dorsal surface is more
regularly rounded. The shaft of the ulna is more slender, especially in its distal
half; its fusion with the radius occurs later and is usually much less extensive than
in the ox.

The carpal bones resemble those of the ox except in size. The accessory is
long and less tuberous.

The large metacarpal bone (Mc. 3 + 4) is long and slender. The lateral small
metacarpal bone (Mc. 5) is often absent or is represented by a ridge on the large
metacarpal.

The phalanges of the chief digits are relatively long and narrow. The third
phalanx in particular is much flattened on its abaxial side, so as to form a prominent
dorsal border. Of the proximal sesamoids, the abaxial ones are compressed from
side to side, and the axial ones from before backward. The flexor surface of the
distal sesamoids forms a shallow groove, not divided by a ridge. The accessory
digits usually have no phalanges.

BONES OF THE PELVIC LIMB

The OS coxae differs greatly from that of the ox. The long axis of the ilium
is almost in a line with that of the ischium. The gluteal line appears as a ridge
which is nearly parallel with the lateral border. The tuber coxa is only slightly
thickened, and the tuber sacrale is pointed. The crest is concave medially, convex
laterally. The shaft is relatively long and is flattened laterally. The superior
ischiatic spine is low and everted. The pubis resembles that of the ox, but its an-
terior border (pecten) is thin and sharp. The ischium slopes downward and back-
ward, and forms a much larger angle with its fellow than in the ox. The lesser
sciatic notch is very shallow. The tuber ischii is flattened and everted; it bears a
long, blunt-pointed lateral process, and a verj'' short and blunt dorsal prominence.
There is a very low ventral ridge on the symphysis. The latter is not usually com-
pletely ossified, even in old animals. The acetabulum is further back than in the
ox, and is relatively larger and deeper; it has a deep notch posteriorly. The
pelvic inlet is very oblique, so that a vertical plane from the anterior end of the
symphysis cuts the first coccygeal vertebra. The brim is elliptical; the conjugate
cUameter is about five inches (ca. 12 cm.), and the transverse about three and a
half to four inches (ca. 9.5 cm.). The floor of the pelvic cavity is wide and shallow
as compared with the ox, and the pelvic axis inclines downward posteriorly.

The shaft of the femur is slightly curved, the convexity being anterior. A dis-
tinct line separates the lateral and posterior surfaces. The supracondyloid fossa
is very shallow. The head has a shallow fovea and the neck is distinct. The tro-
chanter major is little higher than the head. The ridges of the trochlea are similar
and parallel, but slightly oblique.

The tibia is long and slender, but otherwise resembles that of the ox. The
fibula has no shaft, and its proximal end is represented by a small prominence be-

SKELETON OF THE PIG VERTEBRAL COLUMN

161

low the lateral margin of the lateral condyle of the tibia; the distal end forms the
lateral malleolus, as in the ox.

The patella is relatively longer and narrower than that of the ox.

The tarsal bones resemble those of the ox except in size.

The metatarsal and digital bones present special characters similar to those of
the corresponding part of the thoracic limb.

SKELETON OF THE PIG

VERTEBRAL COLUMN

The vertebral formula is C7Ti4_i5L6-7S4Cy2o-23.

The cervical vertebrae are short and wide. The bodies are elliptical in cross-
section, the long diameter being transverse. The anterior articular surfaces are
slightly convex from side to side and concave dorso-ventrally ; the posterior ones

Fig. 163. — Skeleton of Pig; Lateral View.
o. Cranium; b, maxilla; c, mandible; 1H.-7H., cervical vertebrae; IR.iv., first thoracic vertebra; 13 Rav., thir-
teenth thoiacic vertebra (uext to last); IL., first lumbar vertebra; 6L., sixth lumbar vertebra (next to last usually);
A'., sacrum; S., coccygeal vertebrse; IR., first rib; I4R., last rib; R.hi., costal cartilages; St., sternum; d, supraspin-
ous fossa; rf', infraspinous fossa; i, spine of scapula; ^, neck of scapula; e, humerus; 3, head of humerus; 4, tuberosities
of humerus; 5, deltoid tuberosity; 6, lateral epicondyle of humerus; /.radius; g, ulna; 7, olecranon; /j, carpus: 18-26,
carpal bones; i-i"", metacarpus; Z;-^"", proximal phalanges; Z-Z"", middle phalanges; m-m"", distal phalanges; n, o,
sesamoids; p, ilium; 5, tuber coxse; S, tuber sacrale; 1 , superior ischiatic spine; g, ischium; ??, tuber ischii; r, pubis;
12, acetabulum; s, femur; 13, trochanter major; 14, trochanter minor; lo, lateral epicondyle; t. patella; u. tibial-
is, crest of tibia; i 7, lateral condyle of tibia; w, fibula; m), tarsus; ^^-37, tarsal bones; ^6', tuber calcis. (After Ellen-
berger, in Leisering's Atlas).

are slightly concave. A ventral spine is not present. The arches are wide trans-
versely, but the laminae are narrow, so that a considerable interval (Spatium inter-
arcuale) separates adjacent arches dorsally. The pedicles are perforated by a
foramen in addition to the usual intervertebral foramina. The transverse processes
divide into two branches, both of which increase in size from the third to the sixth.
The dorsal branch projects outward and backward; it is short and is thickened at
its free end. The other branch is a quadrilateral plate cUrected ventrally; each
overlaps the succeeding one to a small extent, and the series forms the lateral
boundary of a deep and wide ventral groove. The spines increase in height from the
11

162

SKELETON OF THE PIG

third to the last; the anterior ones are incHned backward, the posterior ones for-
ward. The last cervical is recognized by the great length of its spine (ca. 10 cm.
in the adult), the absence of the ventral plate of the transverse process, and the flat-
ness of the body, which bears a pair of small facets on its posterior margin for the

. S"

■?:i

Fig. 164. — Fouhth Cervical
Vertebra of Pig; Lat-
eral View.

1, 1', Anterior and pos-
terior ends of body; 2, arch;
3, foramen of arch; 4, anterior
articular process; 5, spinous
process; 6, ventral branch of
transverse process.

— Sixth Cervical Vertebra

OF Pig; Anterior ^'IEW.

1, Body; 2, transverse process;

foramen transversarium ; 4, addi-

nal foramen of arch; 5, articular proc-

; 6, arch; 7, spinous process.

^■»

1^. 5'

^,^

4—^

^'^

1-^^^^

)

Fig. 166.— Seventh

Cervical

Vertebra op

Pig

Lateral

View.

1, 1', Anterior and posterior
ends of body; 2, facet for head of
first rib; 3, arch; 4, transverse
process; 5, 5', articular processes;
6, spinous process; 1 (number on
bono), foramina of arch.

Fig. 1()7. — Atlas of Pig; Dorsal View.
1, Dorsal tuberosity; 2, alar foramen; 3, wing;
4, intervertebral foramen; 5, dorsal arch; 6, ventral
tubercle; 7, surface for dens.

-Atlas of Pig; Anterior View.
1, Dorsal tuberosity; 2, wing; 3, alar foramen; 4, ante-
rior articular cavity; 5, ventral tubercle.

heads of the first ribs. It has foramina transversaria, and usually two foramina in
each side of the arch.

The dorsal tuberosity of the atlas is large. The ventral tubercle is long, com-
pressed laterally, and projects back under the axis. The wing is flattened and
bears a posterior tuberosity. The foramen transversarium passes through the

VERTEBRAL COLUMN

163

Fig. 169. — Axis of Pig; Lateral View.
1, Dens; 2, 2', anterior and posterior articular
processes; 3, posterior end of body; 4, transverse proc-
ess; 5, foramen transversarium ; 6, arch; 7, spinous
process. Arrow indicates intervertebral foramen.

Fig. 170. — Axis op Pig; Anterior View.
1, Dens; 2, 2', anterior and posterior articular
processes; 3, foramen transversarium; 4, arch; o, spi-
nous process.

posterior border of the wing to the fossa under the latter,
it is sometimes very small or absent. The
sides of the vertebral foramen bear two lat-
eral projections which partially divide it
into a ventral narrow part, which receives
the dens, and a dorsal larger part for the
spinal cord. In the fresh state the division
is completed by the transverse ligament,
which is attached to the projections.

The axis has a large spinous process,
which is directed upward and backward.
The dens is a thick cylindrical rod. The
transverse process is very small and the
foramen transversarium is often incom-
plete.

The thoracic vertebrae are commonly
fourteen or fifteen in number. Their
bodies are relatively long, constricted in
the middle, and without ventral spines.
Their extremities are elliptical, depressed
in the middle, and prominent at the peri-
phery. The arch is perforated by a fora-
men on each side and in most of the series
there is also a foramen in the posterior
part of the root of the transverse process
which communicates with the former or
with the posterior intervertebral foramen.
Sometimes there is a foramen in the an-
terior part of the process also. There are
mammillary processes except on the first
two ; in the posterior five or six vertebrae
they project from the anterior articular
processes. The facet for the tubercle of the
rib is absent or fused with that for the
head in the last five or six. The last trans-

(1 is not visi1)lc dorsally;

Fig. 171. — Second and Third Thoracic Vertebr.e
OF Pig; Lateral View.
Numbers around bones: 1, 1', Anterior and poster-
ior ends of bodies ; 2, cavities for heads of ribs ; 3, 3', artic-
ular process; 4, facet for head of rib; 5, spinous process.
Numbers on bones: 1, 1', Foramina of arches; 2, 2',
transverse procesaes; 3, 3', facets for tubercles of ribs.

Jg4 SKELETON OF THE PIG

verse process is lumbar in character, plate-like, and about an inch (2 cm.) long.
Small accessory processes occur in the posterior part of the region. The first
spinous process is broad, very high, and inclined a little forward. The others di-
minish very gradually in length to the tenth, beyond which they are about equal.
The seconcl to the ninth are inclined backward, the tenth is vertical (anticlinal), and
the rest incline forward. The width decreases decidedly from the fourth to the
tenth, beyond which there is a gradual increase. The summits are slightly enlarged
and lie almost in a straight line.

The lumbar vertebrae are six or seven in number. The bodies are longer than
in the thoracic region and bear a ventral crest. They become wider and flatter
in the posterior part of the series. The arches are deeply notched, and are separated
by an increasing space dorsally. The mammillary processes project outward and
backward. The transverse processes are bent downward and incline a little for-
ward. Their length increases to the fifth and is much diminished in the last. They
form no articulation with each other or with the sacrum. The posterior edge of the
root of the process is marked by a notch in the anterior part of the series, a fora-

FiG. 172. — Fourth Lttmbar Vertebra of Pig; Anterior View.
1, Body; 2, transverse process; 3, anterior articular process; 4, mammillary process; 5, posterior articular process;

6, spinous process.

men in the posterior part. The spines are broad and incline forward, with the ex-
ception of the last, which is narrow and vertical.

Lesbre states that six and seven lumbar vertebra? occur with almost equal frequency. The
number may be reduced to five, and the number of presacral vertebra; varies from twenty-six to
twenty-nine.

The sacrum consists usually of four vertebrae, which fuse later and less com-
pletely than in the other domesticated animals. It is less curved than in the ox.
The spines are little developed and commonly in part absent. The middle of the
dorsal surface is flattened and smooth, and presents openings into the sacral canal
between adjacent arches (Spatia interarcualia) . On either side are the dorsal
sacral foramina, and tubercles which indicate the fused articular processes. The
wings resemble those of the ox. The anterior articular processes are very large.
The pelvic surface resembles that of the ox, but is not so strongly curved, and the
transverse lines are very distinct.

The coccygeal vertebrae are specially characterized by the presence of func-
tional articular processes on the first four or five, beyond which these processes
become non-articular and smaller. The arches of the first five or six are complete.
The transverse processes are broad and plate-like in the anterior part of the series

THE RIBS

165

and diminish very gradually. Not rarely the first coccygeal vertebra unites with
the sacrum.

Vertebral Curves. — The cei-vical region is practically straight. The thoracic
and lumbar regions form a gentle curve, concave ventrally, the highest point of
which is at the junction of the two regions. The sacral promontory is not so pro-
nounced as in the ox, and the sacral curve is flatter.

Fig. 173. — Sacrum and First Coccygeal Vertebra op
^Pig; Dorsal View.
/-/]', Arches of sacral vertebrae; 1, 2, 3, dorsal sacral
foramina; 4, similar foramen between sacrum and first
coccygeal vertebra; A, body of first sacral vertebra; B,
articular process; C, wing; D, auricular surface; E, articu-
lar processes; F, first coccygeal vertebra.

Fig. 174. — Sacrum and First Coccygeal Vertebra of
Pig; Ventral View.
7-7 F, Sacral vertebrae (bodies) ; 1, 2, 3, ventral sacral
foramina; 4, similar foramen between sacrum and first
coccygeal vertebra; A, body of first sacral vertebra; B,
articular process; C, wing; D, auricular surface; E, first
coccygeal vertebra.

Length. — The regional lengths of the vertebral column of a large Berkshire sow were as fol-
lows: Cervical, 24 cm.; thoracic, 53.5 cm.; lumbar, 31 cm.; sacral, 17 cm.; coccygeal, 35 cm.

Variations. — The occurrence of fifteen thoracic vertebrse is quite common, and the existence
of sixteen or even seventeen has been recorded. Reduction to thirteen is very rare. Six and
seven lumbar vertebrse seem to occur with about equal frequency, and reduction to five is on rec-
ord. The number of coccygeal vertebrae varies from twenty to twenty-six according to the records
of several observers. Lesbre states that he has found twenty-three most frequently.

THE RIBS
The ribs number fourteen or fifteen pairs, of which seven are sternal and seven
or eight asternal usually. They are in general strongly curved in the improved
breeds, so that there is a fairly distinct angle, except toward the end of the series.

166

SKELETON OF THE PIG

The backward slope of the posterior ribs is slight. The first rib is prismatic, has a
large sternal end, and a very short cartilage. The width is greatest in the third
to the sixth, and the length in the sixth and seventh usually. The tubercle fuses
A\dth the head on the last five or six. The second
3 to the fifth form diarthrodial joints mth their car-

tilages, which are wide and plate-like.

The fifteenth rib, when present, may be fully developed
and its cartilage enter into the formation of the costal arch;
but in most cases it is floating, and in some cases it is only
about an inch (ca. 2-3 cm.) in length.

THE STERNUM
The sternum consists of six segments and re-
sembles that of the ox in general form. The first
segment (Manubrium) is long, flattened laterally^

Fig. 175. — Eighth Rib of Pig; Lat-
eral View.
1, Head; 2, neck; 3, tubercle; 4, ante-
rior border; 5, sternal extremity.

Fig. 176. — First Rib or Pig; Lateral View.
neck; 3, tubercle; 4, anterior border; o, vascular impression;
6, sternal extremity.

and bears a blunt-pointed cartilage on its anterior end; its posterior end forms a
diarthrodial joint with the body. The latter is flattened, wide in its middle, narrow
at either end. The widest segments are formed of two lateral parts, w^hich are
not completely fused in the adult. The last segment has a long, narrow part which
bears the xiphoid cartilage.

The thorax is long and is more barrel-shaped than in the horse or ox, since the
ribs are more strongly curved and differ less in relative length.

BONES OF THE SKULL
Cranium

The occipital bone has an extensive squamous part, which forms a very broad
and prominent nuchal crest. The latter is concave, and is thick and rough above,
where it forms the highest part of the skull; laterally it becomes thinner, turns

BONES OF THE SKULL — CRANIUM

167

downward, and is continuous with the temporal crest. Two divergent ridges pass
upward from the foramen magnum, and the surface between them is concave and
smooth. The greater part of the cerebral surface of the squamous part is united
with the parietal bones, but a ventral concave area faces into the cranial cavity.
The foramen magnum is almost triangular, and is narrow above, where it is flanked
by two small tuberosities. The paramastoid processes are extremely long and pro-
ject almost straight ventrally. The hypoglossal foramen is at the medial side of
the root of the process. The basilar part is short and wide; its ventral surface

Fig. 177. — Skull of Pig; Lateral View.
A, Occipital bone; B, squamous temporal bone; C, parietal bone; D, frontal bone; E, lacrimal bone; F, malar
bone; G, maxilla; H, premaxilla; I, nasal bone; J, os rostri; A', mandible; 1, occipital condyle; 2, paramastoid proc-
ess; 3, condyle of mantlible; 4, meatus acusticus externus; 5, temporal fossa; 6, parietal crest; 7, supraorbital process;
8, orbital part of frontal bone; 9, fossa for origin of ventral oblique muscle of eyeball; 10, orbital opening of supraorbital
canal; 11, lacrimal foramina; 12, supraorbital foramen and groove; 13, infraorbital foramen; 14, zygomatic process of
temporal bone; 15, temporal, and 15', zygomatic, process of malar bone; 16, incisor teeth; 17, canine teeth; 18, 18',
premolars; 19, 19', molars; 20, mental foramina; 21, mental prominence; 22, angle of mandible.

bears a thin median ridge and two lateral imprints or tubercles which converge at
the junction with the sphenoid bone.

The interparietal bone fuses before birth with the occipital. The internal
occipital protuberance is absent.

The parietal bone is overlapped by the occipital bone behind and concurs in the
formation of the nuchal crest. Its external surface is divided by the parietal crest
into two parts. The medial part (Planum parietale) faces upward and forward,
and is flattened and smooth. Its medial border is short and straight and unites
early with the opposite bone. Its anterior border is concave and joins the frontal

168

SKELETON OF THE PIG

bone. The lateral part (Planum temporale) faces outward and is more extensive;
it is concave, forms a large part of the temporal fossa, and is overlapped ventrally
by the squamous temporal. The parietal crest extends in a curve from the nuchal
crest forward and outward to the supraorbital process. The cerebral surface is con-
cave and is marked by digital impressions. The ventral border projects into the
cranial cavity and forms a crest w^hich separates the cerebral and cerebellar compart-

Squamous -part
of occipital hone

Occipital condyle
Paramastoid process (tip)

Basilar part of
occipital bone

Mastoid process

Temporal condyle

Maxillary recess

Zygomatic proces.
of malar hone

Maxilla

Molar teeth

Premolar teeth

Canine tooth

Prcmaxilla

Fig. 178. — Skull of Pig, Ventral View, without Mandible and Htoid.
1, Hypoglossal foramen; 2, foramen lacerum anterius; 3, foramen lacerum posterius; 4, bulla ossea; 5, body of
sphenoid; 6, pterygoid bone, and 6', hamulus of same; 7, vomer; 8, horizontal, and 8', perpendicular, part of palatine
bone; 9, pterygoid process of palatine bone; 10, pterygoid process of sphenoid bone; 11, supraorbital process; 12, or-
bital opening of supraorbital canal; 13, choanae or posterior nares; 14, 11', anterior palatine foramen and groove; 15,
palatine fissure.

ments laterally. The interior is excavated and forms part of the frontal sinus in
the adult. There is no temporal canal.

The frontal bone is long. The frontal surface slopes downward and forward,
the inclination varying in different subjects. The anterior part is concave and is
marked by the supraorbital foramen and the groove leading forward from the
foramen to the nasal bone. The supraorbital canal opens into the orbit at the

CRANIUM 169

upper part of the medial wall of the latter. The supraorbital process is short and
blunt-pointed, and is not connected with the zygomatic arch. The gap in the or-
bital margin is closed by the orbital ligament in the fresh state. The orbital part
is extensive and forms the greater part of the medial wall of the orbit. Its upper
part is perforated by the orbital orifice of the supraorbital canal, in front of which
is the distinct fovea trochlearis. The ethmoidal foramen is situated in the ventral
part near the junction with the orbital wing of the sphenoid. The temporal part
is very narrow and is separated from the orbital plate by a ridge which joins the

Parietal bone
Temporal fossa

Squamous temporal
bone

External acoustic
meatus

Zygom.atic process
of temporal bone
Supraorbital pro-
cess
Frontal bone

Supraorbital fora-
men
Zygomatic process
of malar bone
Lacrimal bone

Infraorbital foramen

Nasal process of premaxilla

Nasal bone

Canine tooth

Palatine fissure
Body of premaxilla

Nuchal crest
Temporal crest
Parietal crest

y,^ — ^ — Lacrimal foramen
Preorbital fossa

Fig. 179. — Skull of Pig; Dorsal View.

pterygoid crest below. The interior of the bone is excavated by the frontal sinus in
practically its entire extent in the adult. In the young subject the cavity is con-
fined to the anterior part and the rest of the bone is thick.

The temporal bone has a general resemblance to that of the ox. The zygo-
matic process is short and stout and is bent at a right angle. The dorsal border of
the process is thin; traced from before backward it curves sharply upward and
forms a high prominence in front of the external acoustic meatus; beyond this
it drops rather abruptly and is then continued upward to the nuchal crest. The
anterior part of the ventral border joins the zygomatic process of the malar, which

170 SKELETON OF THE PIG

is deeply notched. The condyle is concave in the transverse direction. The post-
glenoid process is absent, but the articular surface is bounded behind and medially
by a crest. There is no temporal canal. The external acoustic meatus is very
long and is directed dorso-laterally. The bulla ossea is large, compressed laterally,
and bears a pointed muscular process in front. A narrow space intervenes between
the bulla and the basilar part of the occipital bone, so that the foramen lacerum
resembles that of the horse. The small hyoid process is situated in a deep de-
pression in front of the root of the paramastoid process, and the stylo-mastoid
foramen is lateral to it. The petrous part presents no important differential fea-
tures. The squamous part (including the root of the zygomatic process) contains
an air-cavity, which is continuous with the sphenoidal sinus.

The sphenoid bone is short and resembles that of the ox in general. The body
is narrow. The hypophyseal or pituitary fossa is very deep, and is limited behind
by a prominent dorsum sellse; the dorsum bears lateral projections, the posterior
clinoid processes (Processus clinoidei aborales). The foramen ovale is absent,
being included in the foramen lacerum anterius. The other foramina are like those
of the ox. The pterygoid process is broad and twisted. Its base is not perforated
and its free edge is thin and sharp. It concurs with the pterygoid and palate bones
in the formation of the pterygoid fossa (Fossa pterygoidea), which opens backward
and is not present in the horse or ox. The sphenoidal sinus is very large and oc-
cupies the body, the temporal wings, and a great part of the pterj^goid processes
in the adult; it is continued into the temporal Ijone as mentioned above.

The ethmoid bone has a relatively long perpendicular plate, which is marked
by ridges corresponding to the ethmoidal meatuses. The cribriform plate is ex-
tensive and very oblique, so that it and the crista galli are almost in line with the
basi-cranial axis. A linear series of relatively large foramina is found on either
side of the crista. The lateral mass consists of five endoturbinates and eighteen
ectoturbinates (Paulli). The lamina lateralis concurs in the formation of the
pterygo-palatine fossa. The lamina transversalis separates the fundus of the
nasal cavity from the naso-pharyngeal meatus.

Face

The maxilla is extensive. Its facial surface forms a longitudinal groove,
which is continued upon the premaxilla in front and the facial parts of the lacrimal
and malar behind. The infraorbital foramen — sometimes double — is large a,nd
is situated above the third or fourth cheek tooth. The alveolus for the canine
tooth produces a ridge (Juga canina) at the anterior end which is very pronounced
in the boar. The facial crest extends forward from the root of the zygomatic proc-
ess and fades out behind the infraorbital foramen; in some specimens it is prom-
inent and thin-edged, in others it is rounded and projects little. The zygomatic
process is short but stout and buttress-like; it is overlapped laterally by the malar.
The maxillary tuberosity forms in the young subject a long bulla, which occupies
most of the pterygo-palatine fossa and contains the developing permanent molars;
after the eruption of the teeth the tuberosity flattens and joins the vertical part of
the palate bone. The palatine process is very long and is marked in its anterior
part by transverse grooves (Sulci palatini transversi) corresponding with those of
the mucous membrane of the palate. The anterior palatine foramen is near the
junction with the palate bone; from it the palatine groove can be traced distinctly
along the entire length of the process. The alveolar border presents a large alveolus
for the canine tooth at its anterior end; behind this are seven alveoli for the cheek
teeth, which increase in size from first to last. The maxillary foramen and infraor-
bital canal are very large. The maxillary sinus is small.

The body of the premaxilla is narrow and prismatic. It presents three alveoli
for the incisor teeth, which are separated by short intervals and diminish in size

FACE 171

from before backward. As in the ox, a narrow space separates the right and left
bones and takes the place of the foramen incisivum. The palatine process is long
and narrow. The nasal process is very extensive and is somewhat rhomboid in
outline. Its dorsal border forms a very long suture with the nasal bone, and the
ventral articulates to about the same extent with the maxilla. The palatine fissure
is relatively wide.

The horizontal part of the palatine bone forms a fourth to a fifth of the length of
the palate; its palatine surface is triangular, the apex being anterior; its nasal
surface is deeply grooved and smooth. A pterygoid process (Processus pyramidalis
of man) projects backward and downward, and its thick rounded end is received
between the pterygoid process of the sphenoid and the pterygoid bone. The
perpendicular part is largely overlapped laterally by the maxilla and concurs in

Fig. 180. — Sagittal Section op Skull op Pig, without Mandible.
A, A', Basilar and squamous parts of occipital bone; B, body, B', temporal wing, B", orbital wing, of sphenoid
bone; C, parietal bone; D, D', internal and external plates of frontal bone; E, E', cribriform and perpendicular plates
of ethmoid bone; F, pterygoid bone; G, G', perpendicular and horizontal parts of palatine bone; H. palatine process of
maxilla; /, vomer; J, nasal bone; K, body of premaxilla; L, dorsal turbinate bone; M, ventral turbinate bone;
I, II, III, fossse cranii; 1, hypoglossal foramen; 2, foramen lacerum posterius; 3, meatus acusticus internus; 4, fora-
men lacerum anterius; 5, hypophyseal or pituitary fossa; 6, foramen orbito-rotundum; 7, lateral crest between cerebral
and cerebellar parts of cranial cavity; 8, optic foramen; 9, ethmoidal foramen; 10, frontal sinus; 11, meatus naso-
pharyngeus; 12, 13, 14, dorsal, middle, and ventral nasal meatuses; 15, incisor teeth; 16, canine tooth; 17, premolar
teeth; 18, molar teeth; 19, paramastoid process; 20, bulla ossea.

forming part of the palatine canal. The two plates separate dorsally and inclose
an air-cavity which opens into an ethmoidal meatus. The inner plate curves
inward and unites with the vomer and ethmoid to form a horizontal plate, the
lamina transversalis, which divides the posterior part of the nasal cavity into a
dorsal olfactory part and a ventral respiratory part.

The pterygoid bone is nearly vertical in direction, and is narrow in its middle,
wide at each end. The lateral surface is free below and forms the medial wall of
the pterygoid fossa. The ventral end is notched and forms a distinct hamulus.

The nasal bone is very long and its width is almost uniform, except at the
anterior end, which is pointed and reaches almost as far forward as the premaxilla.
The facial surface is flattened from side to side. In profile it is nearly straight in
some subjects, variably concave in others. The lateral border is free to a small
extent in front only; otherwise it is firmly connected with the premaxilla and

172

SKELETON OF THE PIG

maxilla. In the adult the frontal sinus extends into the posterior part of
the bone.

The lacrimal bone is very sharply bent. Its facial surface presents a deep
depression, surmounted by a ridge or tubercle. On or close to the orbital margin
are two lacrimal foramina which lead to the lacrimal canals. The orbital surface
presents a fossa in which the inferior oblique muscle of the eyeball arises, and its
lower part bears a crest, which is crossed obliquely by a vascular furrow. The
dorsal border articulates with the frontal only. The bone concurs in the formation
of the maxillary sinus.

The malar bone is strongly compressed from side to side. Its facial surface

is small and presents a fossa which is con-
tinuous with the depressions of the maxilla
and lacrimal. The orbital surface is still
smaller and is smooth and deeply grooved.
The zygomatic process is very extensive,
especially in the vertical direction. Its
lateral surface is convex and free, and
bears a rough eminence in its middle. Its
medial surface is concave; it is over-
lapped in front by the maxilla, and in the
remainder of its extent is free and smooth.
The dorsal border is thick and rounded in
front, where it forms the lower part of the
orbital margin; behind this it forms an
extensive notch which receives the zygo-
matic process of the temporal. (It might
be regarded as dividing into frontal and
temporal branches.) The ventral border
is convex and becomes thinner behind.

The turbinate bones resemble those
of the ox. The dorsal turbinate is, how-
ever, relatively longer, less fragile, and
more firmly attached to the nasal bone.
There is no middle turbinate.

The vomer is very long. The anter-
ior extremity reaches to the body of the
premaxilla or very close to it. The ven-
tral border is received into a groove
formed by the nasal crest of the maxillge
and palatine bones and in front by the
palatine processes of the premaxillse. The
posterior border is concave, thin, and
sharp.

The OS rostri (or prenasal bone) is
situated in the snout between the nostrils.
It has the form of a short, three-sided prism. The dorsal surface is convex and is
notched at each end. The lateral surfaces are concave, smooth, and converge
below, forming a grooved ventral border. The posterior surface is triangular,
notched centrally, and rough laterally. The anterior surface is deeply pitted and
is surrounded by an irregular sharp border.

The mandible is very strong, and differs very much from that of the horse or
ox. The body narrows decidedly in front; the lingual surface is deeply concave;
the mental surface is strongly convex, slopes downward and backward, and forms
a distinct prominence (Tuber mentale) at the point of divergence of the rami.

Fig. 181. — MandibixE of Pig; Dorsal View.

A, Body; B, B', horizontal and vertical parts of
ramus; C, condyle; D, coronoid process; 1, 2, 3, in-
cisor teeth; 4, canine tooth; 5, 6, 7, premolar teeth
(first absent) ; 8, 9, 10, molar teeth.

THE SKULL AS A WHOLE 173

Above this prominence is a pair of foramina. The alveolar border presents six
alveoli for the incisor teeth, and a little further back two large cavities for the
canine teeth. There are two pairs of mental foramina of considerable size and a
variable number of smaller ones. The rami diverge more than in the horse or ox,
and the upper part is somewhat incurved. The horizontal part is very thick and
strong. Its lateral surface is strongly convex from above downward. The medial
surface is prominent over the roots of the molar teeth and overhangs the concave
lower part. The alveolar border is thin in front and widens behind; it does not
follow the axis of the ramus, but runs nearly straight and produces the marked over-
hang noted above. There are seven alveoli for the lower cheek teeth, which in-
crease in size from before backward. The first is small, not always present in the
adult, and is separated by short spaces from the second and the canine alveolus.
The vertical part is relatively wide above. The condyle is convex in both direc-
tions, wide in front, narrow and declivitous behind. The very small and thin-
edged coronoid process is not quite so high as the condyle, from which it is separated
by a very wide notch. The mandibular foramen is large. The two halves of the
bone unite soon after birth in the improved breeds.

The body of the hyoid bone is broad from before backward, short transversely,
and bears on its ventral aspect a very short pointed lingual process. The thyroid
cornua are wide and curved, concave and grooved dorsally; their ends are attached
to the thyroid cartilage of the larynx by rather long bars of cartilage. The small
cornua are short, wide, and flattened dorso-ventrally ; they are attached to short
bars which project from the junction of the body and thyroid cornua. The middle
cornu is a little longer than the small cornu, but is relatively slender; it is largely
cartilaginous in the young subject and does not ossify at either end. The great
cornu is a very slender rod, slightly enlarged at either end; the dorsal extremity is
attached to the hyoid process of the temporal by a rather long and wide bar of
cartilage.

THE SKULL AS A WHOLE

The length and the profile vary greatly in different subjects. Primitively
the skull is long — especially in its facial part — and the frontal profile is almost
straight. The condition is very pronounced in wild or serai-feral pigs, and exists
also — though in less degree — in the improved breeds during extreme youth. Most
of the latter are decidedly brachycephalic when fully developed; the face is
"dished" in a pronounced fashion. The frontal region slopes sharply upward,
and the nasal region is shortened, and in some specimens even distinctly concave
in profile. The supraorbital foramina are about midway between the orbital mar-
gin and the frontal suture. The supraorbital grooves extend forward from the
foramina to the nasal region and turn ventro-laterally toward the infraorbital
foramina over the ridges which separate the nasal and lateral regions.

The lateral surface is triangular when the mandible is included. The tem-
poral fossa is entirely lateral and its long axis is almost vertical. It is bounded
above by the nuchal crest, behind by the temporal crest, in front by the parietal
crest, and is marked off from the orbital cavity by the supraorbital process and a
curved crest which extends from it to the root of the pterygoid process. The
zygomatic arch is strong, high, and flattened from side to side. Its root is notched
dorsally and bears a projection ventrally. It curves sharply upward behind and
forms a pointed recurved projection above and in front of the external acoustic
meatus. The orbit is small. Its margin is deficient behind in the dry skull, thick
and rounded in front and below. The cavity is limited below by a ridge on the
frontal and lacrimal bones, and is separated by a crest from the temporal fossa.
The medial wall is perforated above by the orbital opening of the supraorbital
canal, and below by the optic and ethmoidal foramina; on its antero-inferior part

174

SKELETON OF THE PIG

is the fossa in which the inferior oblique muscle of the eye takes origin. Two lac-
rimal foramina are found on or close to the anterior margin. The pterygo-palatine
fossa is well defined ; its upper part forms a deep groove which leads from the fora-
men orbito-rotundum to the very large maxillary foramen. The preorbital region
is deeply grooved in its length and is clearly marked off by a ridge from the nasal
and frontal regions. The facial crest is short, usually thin-edged, and lies above the
fifth and sixth cheek teeth. A little (ca. 2 cm.) in front of it is the infraorbital fora-

Nuchal crest

Fig. 182. — Skull of Pig; Posterior View.
1, 2, 3, Squamous, lateral, and basilar parts of occipital bone; 4, foramen magnum; .5, occipital condyle; 6, para-
mastoid process; 7, squamous temporal bone; 8, meatus acusticus externus; 9, temporal condyle; 10, zygomatic
process of malar bone; 11, bulla ossea; 12, 12', perpendicular and horizontal parts of palatine hone; 13, 13', choanae or
posterior nares; 14, vomer; 15, pterygoid process of sphenoid bone; 16, pterygoid process of palatine bone; 17, con-
dyle of mandible; 18, mandibular foramen; 19, body of mandible.

men. There is a ritlged prominence over the canine alveolus. In some skulls the
anterior part of the upper jaw is inclined upward.

The most striking features of the basal surface are as follows: The basioc-
cipital is wide and flattened; it bears a median crest and two lateral tubercles.
The paramastoid process is extremely long, less flattened than in the horse and ox,
and nearly vertical. At the medial side of its root is the h3'poglossal foramen,
and in front of it are the stylo-mastoid foramen and a deep cavity in which the
hyoid process is concealed. The bulla ossea is long, compressed lateral!}', and bears
a sharp, short, muscular process. The posterior nares are small and are wider be-
low than above. On either side of them is the tuberosity of the palate bone, and

THE SKULL AS A WHOLE 175

above this is the pterygoid fossa. The palate constitutes about two-thirds of the
entire length of the skull, and is relatively narrow. It is widest between the canines
and premolars and narrow at each end. It is marked by a crest medially and by
the palatine foramen and groove laterally. The anterior part bears transverse
ridges. It is moderately arched from side to side. In some specimens it is nearly
straight or slightly concave in its length; in others it curves upward to a variable
degree in front. The posterior end always slopes upward more or less.

The nuchal surface is remarkable for its height and the breadth of the nuchal
crest. The central part above the foramen magnum is smooth and concave from
side to side, and is bounded laterally by ridges, which converge ventrally and end
on two tubercles at the upper margin of the foramen magnum. The surface is
separated from the temporal fossse by the temporal crests, which curve downward
and outward and blend with the external acoustic meatus. The mastoid process
has the form of a plate which overlaps the root of the paramastoid process and bears
a crest on its anterior part.

The cranial cavity is small, in spite of the great size of the cranium; the
discrepancy is due to the enormous development of the frontal sinuses in the adult.
It is relatively longer, but much lower than that of the ox. Its width is greatly
diminished between the orbits. The olfactory fossse are extensive and very ob-
lique. The floor resembles that of the ox, but the foramen ovale is absent, the
dorsum sellse is more developed, and the foramen lacerum is like that of the horse.
Two oblique lateral crests clearly mark the limit between the cerebral and cerebellar
compartments. The internal occipital protuberance and the temporal canal are
absent.

The nasal cavity is very long. Its posterior part is divided by the lamina
transversalis into olfactory and respiratory parts. The olfactory' part or fundus is
dorsal, and contains the ethmoturbinates and ethmoidal meatuses. The ventral
part is continuous with the ventral meatus and leads to the pharyngeal orifice;
hence it is called the naso-pharyngeal meatus. The bony roof is almost complete
in front on account of the great length of the nasal bones.

The frontal sinus is a vast excavation in the adult animal. It involves all of
the roof and almost all of the sides of the cranium, and extends forward into the
roof of the nasal cavity a variable distance — sometimes as far as a transverse plane
through the infraorbital foramina. The septum between the right and left sinuses
is usually deflected in an irregular manner in its middle part, but is practically
median at either end. Each sinus is sul^divided by numerous septa, some of which
are complete. Thus the sinus is divided into compartments, each of which com-
municates with an ethmoidal meatus.

In the young pig the sinus is small and is confined to the anterior part of the frontal bone.
Later it extends backward, outward, and to a less extent forward. In the old subject it penetrates
laterally into the supraorbital process and the root of the zygomatic process of the temporal bone,
and behind almost down to the foramen magnum and the occipital condyles. It then consists
of six to eight compartments usually.

The maxillary sinus is relatively small. Its anterior end is a little less than
an inch (ca. 2 cm.) behind the infraorbital foramen, and it extends upward into
the lacrimal and backward into the malar bone. The infraorl^ital canal passes
along its floor, and the roots of the molar teeth do not project up into it. It does
not communicate with the frontal and sphenoidal sinuses, but with the posterior
part of the middle meatus nasi by means of a considerable orifice.

The sphenoidal smus is very large. It involves the body, pterygoid processes,
and temporal wings of the sphenoid bone, and extends into the squamous temporal.
It communicates with the ventral ethmoidal meatus.

There is a small sinus in the perpendicular part of the palatine bone which
communicates with an ethmoidal meatus.

176

SKELETON OF THE PIG

BONES OF THE THORACIC LIMB
The scapula is very wide, the index being about 1 : 0.7. The spine is tri-
angular and is verj^ wide in its middle, which curves backward over the infra-
spinous fossa and bears a large tuberosity. Its lower part bears a small projection
(rudimentary acromion). The anterior border is strongly convex in profile, sinuous
when viewed from the front, and thick and rough in its middle. The posterior
border is wide, slightly concave, and bears a rough outer lip. The vertebral border
is convex, and the cartilage is not so extensive as in the horse and ox. The anteri-
or angle is thin and bent medially a little. The posterior angle is thick and is about

Fig. 183. — Left Scapula of Pig; Lateral View.
Anterior angle; 6, posterior angle; c, anterior border; d, posterior border; e, neck; /, glenoid cavity; g, tuber
scapulae; 1, spine; 2, tuber spinas ; 3, acromion; 4, supraspinous fossa; 5, inf raspinou3 f ossa ; 6, cartilage.

a right angle. The neck is well defined. The rim of the glenoid cavity is rounded
and not notched. The tuber scapulae is just above the antero-medial part of
the glenoid cavity and bears no distinct coracoid process; it unites with the rest of
the bone at about one year.

The humerus has an appearance in profile somewhat like an italic / minus the
cross-bar; this is due to the marked backward and forward inclination of the prox-
imal and distal ends respectively. The shaft is decidedly compressed from side to
side. The medial surface is extensive and flattened; it is separated from the
anterior surface by a distinct border, and bears no teres tubercle. The musculo-
spiral groove is shallow. The deltoid tuberosity is small, and there is a larger
rounded eminence midway between it and the lateral tuberosity. The nutrient

BONES OF THE THORACIC LIMB 177

foramen is on the posterior surface below its middle. The head is more strongly
curved and the neck better marked than in the horse or ox. The lateral tuber-
osity is very large and extends upon the front of the extremity. It is divitled into
two high prominences by a wide deep groove. There is a third eminence below
and laterally for the attachment of the supraspinatus muscle. The intertuberal or
bicipital groove is at the front of the medial side; it is undivided and is almost con-
verted into a canal. The lateral groove on the distal articular surface is so shallow
as to give the appearance of two condyles of similar size. The olecranon fossa is
very deep, and the plate of bone which separates it from the coronoid fossa is thin
and sometimes perforated. The proximal end unites with the shaft at three and a
half years, the distal at one year.

£7

Fig. 184. — Left Scapula of Pig; Medial View.

a. Anterior angle; h, posterior angle; c, anterior border; d, posterior border ; e, neck; /, vascular groove; g, glenoid

cavity; /i, tuber scapulae; 1, subscapular fossa; 2, serratus area; 3, cartilage.

The radius is short and narrow, but thick. The shaft increases in size distally.
The greater part of the volar surface is in apposition with the ulna; this part is
marked by a vascular furrow which runs distally from the proximal interosseous
space, and has the nutrient foramen at its proximal end. The radial tuberosity is
represented by a rough area. The distal end is relatively large. Its carpal sur-
face consists of concavo-convex facets for the radial and intermediate carpal bones.
There is a wide shallow groove on the middle of the front. The proximal end fuses
with the shaft at one year, the distal at three and a half years.

The ulna is massive. It is much longer and considerably heavier than the

radius. The shaft is curved. The dorsal surface is convex and most of it is rough

and attached to the radius by the interosseous ligament. There is a smooth area

on the upper third, which concurs with the radius in forming the proximal inter-

178

SKELETON OF THE PIG

Deltoid
tuberosity

Lateral
tuberosity

Medial
condyle

Lateral
condyle

Head

Lateral
epicondyle

Nutrient
foramen

Lateral con-
dyloid crest

Olecranon
fossa

Medial epi-
condyle

Intertuberal

Lateral

tuberosity
Head

Medial
condyle

Fia. 185. — Left Humerus of Pig; Lateral View.

Medial Lateral
epicondyle condyle
Fig. 186. — Left Humerus of Pig; Medial Vi

Olecranon

-r Olecranon
I

Shaft of -I \ '^: 1 ^V/«/^ of ulna

radiuH

Carpal surface
of radius
-Left Radius and Ulna of Pig; Lateral
View.

Distal end
of radius
-Left Radius and Ulna of Pig; Medial
View.

BONES OF THE THORACIC LIMB

179

osseous space, and is marked in its upper part by the nutrient foramen. From this
space a vascular furrow descends to the distal part of the shaft, where there is often
a distal interosseous space for the passage of vessels. The medial surface is exten-
sive, concave, and smooth. The lateral surface is slightly convex, and its proximal
part is marked by an oblique rough line or ridge. The proximal extremity is
large and is bent medially somewhat; its length is more than one-third of that of
the entire bone. The distal extremity is relatively small; it articulates with the
ulnar and accessory carpal bones, and is notched in front to accommodate the ridge

Fig. 189. — Skeleton of Distal Part of Left Thor-
acic Limb of Pig; Dorsal View.
R, Distal end of radius; U, distal end (styloid proc-
ess) of ulna; C. r., radial carpal; C. i., intermediate
carpal; C. u., ulnar carpal; C. 2, C. 3, C. 4, second,
third, and fourth carpal bones; Mc. 2-5, metacarpal
bones; Ph.l, Ph. 2, Ph. 3, first, second, and third pha-
langes.

Fig. 190. — Skeleton of Distal Part of Left
Thoracic Limb of Pig; Volar View.
R, Distal end of radius; U, distal end (styloid proc-
ess) of ulna; C. r., C. i., C.u., C. a., radial, intermedi-
ate, ulnar, and accessory carpal bones; C. 1-4, first to
fourth carpal bones; Mc. 2-5, metacarpal bones; Ph. 1,
Ph. 2, Ph. 3, first, second, and third phalanges; S, prox-
imal, and <S', distal sesamoid bones.

on the radius. The bone contains a considerable medullary canal, and is con-
solidated at three to three and a half years.

The carpus comprises eight bones, four in each row. The bones of the prox-
imal row resemble those of the ox, with the exception of the accessory, which is more
like that of the horse, but has no lateral groove. The first carpal is small, elon-
gated from before backward, rounded, and articulates in front with the second carpal.
The latter is high and narrow, and articulates with the second and third metacarpal
bones distally. The third carpal articulates with the radial and intermediate
above, the third metacarpal bone below. The fourth is the largest bone of the row;
it articulates with the intermediate and ulnar above, the fourth and fifth meta-
carpals below, and bears a tuberosity on its volar aspect.

180

SKELETON OF THE PIG

Four metacarpal bones are present. The first is absent, the third and fourth
are large and carry the chief chgits, while the second and fifth are much smaller and
bear the accessory digits. Their proximal ends articulate with each other and with
the carpus as indicated above. The distal ends fuse with the shafts at about two
years of age.

The third and fourth metacarpals are flattened from before backward, three-sided, and
placed close together. The distal end of each bears a trochlea for articulation with the first
phalanx and the sesamoids. The third is the wider of the two, and articulates with all of the distal
row of the carpus except the first. The fourth articulates with the fourth carpal chiefly, but has a
small facet for the third. The second and fifth metacarpals are placed further back than the chief
bones. The fifth is considerably the thicker of the two. The proximal ends are small and articu-
late with the corresponding carpal and metacarpal bones. The distal end is relatively large; its
articular surface is condyloid in front, trochlear behind.

Each chief digit comprises three phalanges and three sesamoids. The bones
of the chief digits resemble those of the ox in form, but there is no foramen on the
interdigital side of the extensor process and the proximal sesamoids are narrow and
ridged behind. The phalanges of the accessory digits (which do not reach the
ground ordinarily) are similar in form but much smaller. Fusion of the proximal
ends with the shafts takes place at about two years for the fir.st phalanges, at about
one year for the second phalanges.

Crest of ilium Gluteal line

V / ... ^

\ ^ 5*p^- Tuber sacrale

Ischiatic Lesser sciatic Tuber

sjiinv notch ischii

Tuber coxcr

Ilium (shaft)

Acetabulum Ischium

Fig. 191. — Left Os Cox.e of Pig; Lateral View.

Tuber sarmh

( 'n st of ilium

Lesser
Tuber sciatic Ischiatic

ischii notch spine

Tuber coxce

\ Ilio-pectineal
eminence
Pubis (acstah-
ular branch)
Fig. 192. — Left Os Cox.e of Pig; Medial View.

BONES OF THE PELVIC LIMB
The OS coxae is long and narrow. The ilium and ischium are almost in line
with each other and nearly sagittal in direction. The wing of the ilium bends out-
ward much less than in the horse or ox. The gluteal surface is divided into two fossa?

BONES OF THE PELVIC LIMB

181

by a ridge, which is continuous with the superior ischiatic spine behind. The
pelvic surface presents an extensive rough area behind, which is in apposition with
the wing of the sacrum. The smooth iliac area is narrow, and is bounded above
by a ridge. The crest is convex, and is thick, rough, and prominent in its middle,
which forms the highest point of the bone. The tuber sacrale is lower than the
crest, is directed backward, and articulates internally with the sacrum. The tuber
coxffi is lower still and is very little thickened. The ischia in the female are some-
what divergent and flattened behind. The tubera are everted and bear three prom-
inences. There is a crest or tuberosity on the ventral surface. The superior
ischiatic spine is like that of the cow, but is slightly incurved and the muscular

Trochant'T

major //< nd

Trochan-
taric Trochanter

Head fossa / major

Lateral Trochlea Medial

condyle condyle

Fig. 193. — Right Femur of Pig; Anterior View.

hd r- \

Medial condyL- condyloid Lateral condyle
fossa

Fig. 194. — Right Femur of Pig; Posterior View.

ridges on its lateral face are more pronounced. The symphyseal part of the pubis
is thick and the two bones are almost in a horizontal plane. The ilio-pectineal
eminence is prominent and the psoas tubercle is well marked.

The acetabulum is placed a little further back than in the ox. The rim is
thick and is cut into posteriorly by a narrow fissure, which leads into the deep fossa
acetabuli. The three pieces of the os coxse are fused by the end of the first year,
but the crest and the tuber ischii are partially separate till the sixth or seventh year.
The symphysis does not usually undergo complete ankylosis. Interischial bones
are present.

The inlet of the pelvis is elliptical and very oblique. In a sow of full size the
conjugate diameter measures five to six inches (12.5-15 cm.), and the transverse

182

SKELETON OF THE PIG

about three and a half to four inches (ca. 8.75 to 10 cm.). In the female the tloor
is relatively wide and flattened, especially at the outlet, where the tubera are
everted; it also has a decided ventral inclination behind. The pelvic axis is there-
fore correspondingly oblique. The ischial arch is wide. In the boar the pubis is
much thicker and the ischia are not everted posteriorly. The inlet is smaller; the
conjugate diameter is about four and a half to five inches (ca. 11-12.5 cm.), and the
transverse three to three and a half inches (ca. 7.5-8.75 cm.). The floor is concave
from side to side and slopes decidedly less than in the sow. The superior ischiatic
spines are more incurved, and the ischial arch is much narrower and deeper.

The femur has a relatively wide and massive shaft, on which four surfaces
might be recognized. The principal nutrient foramen is situated in the proximal

Spine of tibia Tuberositi/

Lateral condyle Js./.-.^ Medial

'condyle

Head of
fibula

Crest of tibia

Medial condyle Spine of tibia

I ateral condyle

Groove for
tendons

Lateral
malleolus

Fig. 195. — Right Tibia and Fibula of Pig; Ante-
rior View.
Arrow indicates muscular notch of proximal end of
tibia.

Distal end of tibia

Fig. 196. — Right Tibia and Fibula of Pig; Pos-
terior View.
o, Groove on medial malleolus for tendon of flexor dig-
italis longus.

third of the anterior surface. The posterior surface is wide, and is limited laterally
by a ridge which extends from the trochanter major to the large lateral supra-
condyloid crest. There is no supracondyloid fossa. The head is strongly curved,
and is marked toward the medial side by a rather large fovea for the attachment of
the round ligament. The neck is distinct. The trochanter major, although massive,
does not extend above the level of the head. The trochanteric ridge and fossa re-
semble those of the ox. The third trochanter is absent. The ridges of the trochlea
are similar and almost sagittal. The extremities unite with the shaft at about
three and a half years.

The shaft of the tibia is slightly curved, convex medially. The tuberosity
is grooved in front, and a narrow sulcus separates it from the lateral condyle.
The facet for the fibula is on the posterior border of the latter, and is bounded

BONES OF THE PELVIC LIMB

183

medially by an eminence. The proximal part of the crest is very prominent and
curves outward. The distal end resembles in general that of the ox, but is rela-
tively narrower transversely and thicker from before backward. The proximal
end unites with the shaft at about three and a half years, the distal at about two
years.

The fibula extends the entire length of the region, and is separated from the
tibia by a wide interosseous space. The shaft is flattened from side to side; the
proximal part is wide and deeply grooved laterally; the distal part is narrower

Tuber calcis

T. t

T,c.

ML 2

ML 5

Fig. 197. — Skeleton op Right Pes of Pig; Dorsal
View.
T. t., Tibial tarsal; T. /., fibular tarsal; T. c, cen-
tral tarsal; T. 3, third tarsal; T. 4, fourth tarsal; Mt.
2-5, metatarsal bones; Ph. 1, Ph. 2, Ph. S, first, second,
and third phalanges.

Fig. 198. — Skeleton of Right Pes of Pig; Plantar
View.
T.t., Tibial tarsal; T. /., fibular tarsal; T.c, cen-
tral tarsal; T.l, T.4, first and fourth tarsal bones;
Mt. 2-5, metatarsal bones; Ph. 1, Ph. 2, Ph. 3, first, sec-
ond, and third phalanges; .S, proximal sesamoid bones;
distal sesamoids shown but not marked; a, tarsal
sesamoid bone.

and thicker. The proximal end is flattened, grooved laterally, and articulates
medially with the lateral condyle of the tibia. The distal end forms the lateral
malleolus. It is grooved laterally, and articulates with the tibia and tibial tarsal
medially, with the fibular tarsal bone distally. The proximal end unites with the
shaft at about three and a half years, the distal at about two and a half years.

The patella is very much compressed transversely and presents three surfaces.

The tarsus comprises seven bones. The tibial and the fibular tarsals resemble
in general those of the ox. The axis of the tibial is, however, slightly oblique (ven-
tro-medial), and its distal end bears a double trochlea for articulation with the cen-

184 SKELETON OF THE DOG

tral and fourth tarsals. The tuber calcis is deeply grooved posteriorly. The
central tarsal is narrow transversely and thick. Its proximal surface is deeply
concave, and the plantar bears a large tubercle. The first tarsal is high and
narrow; it articulates with the central and second tarsals and the second metatarsal
bone. The second tarsal is small and somewhat prismatic; it articulates with
the central above, the third in front, the first behind, and the second and third
metatarsals below. The third tarsal is much larger, and is compressed from above
downward, wide in front, narrow behind. It articulates with the central tarsal
above, the third metatarsal below, the second tarsal medially, and the fourth tarsal
laterally. The fourth tarsal is large. Its lateral face is crossed by an oblique
groove for the tendon of the peroneus longus. The medial surface articulates
with the central and third tarsals. The proximal surface supports the tibial and
fibular tarsal bones, and the distal surface rests on the fourth and fifth metatarsals.
It ossifies from two centers. The summit of the tuber calcis fuses with the rest
of the bone at two to two and a half years.

The four metatarsal bones resemble the corresponding bones of the fore limb,
but are somewhat longer. The proximal ends of the third and fourth each have a
considerable plantar projection; the process on the third has a facet for articulation
with a discoid sesamoid bone. The second and fifth are placed more toward the
plantar aspect of the large bones than is the case in the fore limb.

The first and second phalanges are a little longer and narrower than those of
the fore limb.

SKELETON OF THE DOG

VERTEBRAL COLUMN

The vertebral formula is CTTisLrSsCy^o-os-

The cervical vertebrae are relatively longer than in the ox and the pig. The
bodies of the typical vertebrae diminish in length from first to last and are com-
pressed dorso-ventrally. The anterior extremity is moderately convex and the
posterior slightly concave; both are oblique. The median ridge and lateral grooves
on the dorsal surface of the body are very well marked. The second, third, and
fourth have distinct ventral spines. The spinous process of the third has the
form of a long low crest; in the remainder it is higher, blunt-pointed, and inclined
forward. The transverse processes of the third, fourth, and fifth project ventrally
and backward, and divide into two branches; of these, the anterior one is thin,
and the posterior is thick and tuberculate at its free end. The process of the
sixth has two parts; one of these is an extensive quadrilateral plate which is di-
rected ventro-laterally and is ridged on its medial surface; the other part is short and
blunt, and is directed outward and a little backward and upward. The seventh is
readily distinguished by its shortness, the length of its spine, and the single trans-
verse process. The posterior articular processes bear tubercles which are large on
the third, fourth, and fifth.

The ventral arch of the atlas is narrow from before backward, and bears a
small tubercle posteriorly. The dorsal surface of the' dorsal arch is strongly convex
and rough centrally. The wings are wide, flattened, and almost horizontal. The
dorsal surface is rough. There is an alar notch (Incisura alaris) on the anterior
border instead of the alar foramen. The foramen transversarium is present.

The body of the axis is flattened dorso-ventrally, especially in front. The
dens is rounded and relatively long, reaching almost to the occipital bone; it is
inclined upward a little. The articular surfaces which flank it are condyloid in
form and very oblique. The ventral surface is wide, and is divided by a median

VERTEBRAL COLUMN

185

*■ I

Fig. 199. — Skeleton or Dog; Lateral View.
a. Cranium; 6, face; c, mandible; 1H-7H, cervical vertebrse; 13B, last thoracic vertebra; 1L-7L, lumbar verte-
bra; K, sacrum; S, coccygeal vertebrae; 1R-13R, ribs; R.kn., costal cartilages; St., sternum; d, scapula; d' , supia-
spinous fossa; d", infraspinous fossa; i, spine of scapula; ^.acromion; 3, tuberosity of scapula; S', articular end of
scapula; e, humerus; 4, head of humerus; o, lateral tuberosity of humerus; 5', deltoid ridge; 6, 6', epicondyles of
humerus; 7, lateral condyloid crest ; 7', coronoid fossa; /.radius; ff, ulna; S, olecranon; 5, "beak" of ulna; /», carpus;
i, metacarpus; k, proximal phalanges; I, middle phalanges; m, distal phalanges; n, sesamoid; p, iUum; 10, wing of
ilium; ii, shaft of ilium; i^, crest of ilium; i5, tuber coxse; i^i tuber sacrale; i5, superior ischiatic spine; g, pubis;
r, ischium; iff, tuber ischii; 7 7, acetabulum; s, femur; i 5, head of femur; iS, trochanter major; ^0, trochanter minor;
^i, trochanter tertius; ^^, ^S, condyles; ^4, ;g5, epicondyles; ^ff, trochlea; /.patella; m, tibia; ^7, tuberosity of tibia;
;25, ^5, condyles of tibia; SO, medial malleolus; u, fibula; S/, lateral malleolus; S^, head of fibula; w), tarsus; x, meta-
tarsus; y, phalanges; 33, occipital bone; 34, paramastoid process; 35, parietal bone; 36, frontal bone; 37, lacrimal
bone; SS, malar bone ; SS, squamous temporal; ^0, maxilla; 4"', infraorbital foramen; 4?. premaxilla; 4^, nasal bone:
43, external acoustic meatus; 44 ■ canine tooth; 45, masseteric fossa; 4^i angular process of mandible. (After Ellra-
berger, in Leisering's Atlas.)

Fig. 200. — Third Cervical Vertebra of Dog; Left
Lateral View.
.t, S, Anterior and posterior ends of body; 3, 3,
articular processes; 4, spinous process; 5, 6, transverse
process; 7, foramen transversarium.

Fig. 201. — Fourth Cervical Vertebra of Dog;
Left Lateral View.
1, 1', Anterior and posterior ends of body; 2, 2',
articular processes; 3, transverse process; 4, spinous'
process.

186

SKELETON OF THE DOG

crest into two fossae. The transverse processes are single, pointed, directed back-
ward and outward, and perforated by relatively large foramina transversaria. The

spinous process is thin and of moderate
height, but very long; it is prolonged for-
ward so as to overhang the dorsal arch of
the atlas, and is terminated behind by a
tuberosity which is connected by two
crests with the posterior articular proc-
esses. The anterior notches are large
and are never converted into foramina.

Fig. 202. — Seventh Cervical Vertebra of Dog;
Posterior View.
1, Body; 2, costal facet; 3, transverse process;
4, notch; 5, 5', articular processes; 6, spinous process.

Fig. 203. — Atlas of Dog; Dorsal View.
1, Dorsal arch; 2, 2, posterior articular cavities; 3,
ventral tubercle; 4, 4' intervertebral foramina; 5, 5', wings;
6, 6', alar notches; 7, 7', foramina transversaria.

The bodies of the thirteen thoracic vertebrae are wide and compressed dorso-
ventrally, especially at each end of the region. Their con-
vex anterior surfaces are depressed in the middle. The
posterior facets for the heads of the ribs are absent on the
last three or four. The transverse processes resemble those
of the horse. They bear mammillary processes except at
the anterior end of the region. The facets for the tubercles
of the ribs are large and concave in the anterior part of the
series, and become smaller and slightly convex further back.

Fig. 204. — Axis or Dog; Left Lateral View.
1, Dens; 2, anterior articular process; 3, posterior end of body; 4, arch; 5, pos-
terior notch; 6, transverse process; 7, intervertebral foramen; 8, posterior articular
process; 9, spinous process.

Fig. 205. — Fourth Thoracic
Vertebra of Dog; Left
View.

1, Body; 2, 2', costal facets
of body; 3, posterior notch;
4, 4', articular processes; 5,
transverse process; 6, facet for
tubercle of rib; 7, mammillary
process; 8, spinous process.

VERTEBRAL COLUMN 187

The last three have accessory processes also. The first three or four spinous proc-
esses are about equal in length. Behind this they become gradually shorter to the
tenth, and then remain equal. The backward slope is most marked in the ninth
and tenth. The eleventh is practically vertical (anticlinal vertebra), and the last
two incline slightly forward.

The bodies of the seven lumbar vertebrae are decidedly flattened dorso-ventrally,
and increase in width from first to last. The length increases to the sixth. The
transverse processes are plate-like and are directed forward and downward. Their
length increases to the fifth and sixth. They form no joints with each other or
with the sacrum. Their extremities are enlarged, with the exception of the last.
The accessory processes project backward over the posterior notches of the first
five. The anterior articular processes are large, compressed laterally, and bear
mammillary processes. The spinous processes are broad below, narrower above,
and with the exception of the last, incline a little forward. Their height diminishes
behind the fourth.

The sacrum results from the early fusion of three vertebrae. It is short,

Fig. 206. — Fifth Lumbar Vertebra op Dog; Dorsal View. Fig. 207. — Sacrum of Dog; Ventral View.

1, Anterior end of body; 2, spinous process; 3, 3', artic- I, II, III, Bodies of vertebrse; 1, 2, ventral sac-

ular processes; 4, transverse process; 5, accessory process; ral foramina; 3, 4, lineae transversae; 5, anterior end
6, groove for spinal nerve. of body of first sacral vertebra; 6, 6', anterior artic-

ular processes; 7, 7', wings; 8, posterior end of body
of last sacral vertebra; 9, 9', posterior articular proc-
esses; 10, sacral canal; 11, spinous ^'process; 12,
12', transverse processes; 13, auricular surface.

wide, and quadrangular. The spines are fused to form a median crest, which is
notched, however, between the summits of the spines. On either side are two
tubercles, vestiges of the fused articular processes. The pelvic surface is deeply
concave and presents two pairs of foramina. The wings are prismatic and very
high. Their lateral surfaces are extensive, face almost directly outward, and bear
an auricular surface on the lower part. The anterior surface of the body of the
first vertebra is extensive, depressed in its middle, and bears a prominent lip below.
The anterior articular processes are large and have extensive, slightly concave
facets which face dorso-medially. The posterior articular processes are small.
The transverse processes of the last vertebra project backward and may articulate
or fuse with those of the first coccygeal. The sacral canal is strongly compressed
dorso-ventrally.

The coccygeal vertebrae are fully developed in the anterior part of the region.
The arch is complete in the first six usually. The first three or four have well de-
veloped articular processes at each end. Behind this the posterior processes
quickly disappear, and the anterior ones become non-articular and gradually re-

188 SKELETON OF THE DOG

duced in size. The transverse processes of the first five or six are relatively large;
behind this they quickly disappear. Hemal arches (or chevron bones) in the form
of a V or Y occur ventrall}^ at the intercentral junctions of the third, fourth, and
fifth usualh^ They transmit the middle coccygeal artery, which passes between
pairs of ventral tubercles further back.

Curves. — A gentle curve, convex ventrally, is formed by the cervical and the
anterior part of the thoracic region. The posterior thoracic and the lumbar
vertebrae form a second curve, concave ventrally. The sacral promontory is well
marked. The sacrum and the anterior part of the coccygeal region constitute
a third and more pronounced curve, concave ventrally. In long-tailed dogs the
sacro-coccygeal region is somewhat S-shaped.

Variations. — Numerical variations are not common except in the coccygeal region. Tlie
number of thoracic vertebrae may be twelve or fourteen, with or without compensatory change in
the lumbar region. Girard recorded a case with eight lumbar and the usual number of thoracic
vertebrae. Six lumbar with foiu-teen thoracic vertebrae have been met with. The first coccygeal
sometimes unites with the sacrum.

THE RIBS

Thirteen pairs of ribs are present, of which nine are sternal and four asternal.
They are strongly curved, narrow, and thick. Those in the middle of the series
are the longest. The first eight or nine increase in width in their lower part. I'he
last rib is usually floating. The costal cartilages are long and curve ventrally and
forward; the length and curvature of the first pair are striking special features.

THE STERNUM

This is long, laterally compressed, and consists of eight sternebrae, which fuse
only in exceptional cases and in extreme old age. The first segment is the longest-;
its anterior end is blunt-pointed and bears a short conical cartilage. It widens
at the point of articulation of the first pair of cartilages. The last segment is
also long, thinner than its predecessors, wide in front, and narrow behind, where it
bears a narrow xiphoid cartilage.

The thorax is distinctly barrel-like and is not decidedly compressed anteriorly
like that of the horse and ox. The inlet is oval and is relatively wide on account
of the marked curvature of the first pair of ribs and cartilages.

BONES OF THE SKULL i

Cranium
The occipital bone is similar in position to that of the horse. The nuchal crest
is prominent, angular, and directed backward. Just below the crest are two rough
imprints or tubercles for muscular attachment. The surface below these is convex
from side to side and concave dorso-ventrally. On each side, at the junction
with the squamous temporal, is the mastoid foramen which opens into the cranial
cavity. The condyles are somewhat flattened and are widely separated above;
at the medial side of each is a short condyloid canal, which opens into the temporal
canal. The paramastoid processes are very short. The basilar part is wide and
joins the bulla ossea on either side; its ventral surface is flattened and the tubercles
are at the junction with the bulla. The hypoglossal foramen is small and is close
to the foramen lacerum posterius ; the latter is bounded in front by the bulla ossea,
behind and medially by the occipital bone.

^In the following descriptions of the separate bones an intermediate type — e. g., a fox terrier,
— is selected, and the most striking differences in the brachycephalic and dolichocephalic breeds
will be considered in the section on the skull as a whole.

BONES OF THE SKULL — CRANIUM

189

The interparietal bone fuses with the occipital before birth. It bears the high
posterior part of the parietal crest, and is wedged in between the two parietal bones.
It forms the central part of the tentorium osseum, which is thin and curved, con-
cave ventrally. Its base concurs with the occipital and parietal bones in the for-
mation of a transverse canal which is continuous with the temporal canals.

The parietal bone is rhomboid in outline and is strongly curved. It is exten-
sive and forms the greater part of the roof of the cranial cavity. At the junction
of the right and left bones there is a prominent parietal crest which is continued
upon the frontal bones. The ventral border articulates with the temporal wing
of the sphenoid by its anterior part and with the squamous temporal in the remain-
der of its extent. The external surface enters into the formation of the temporal

-V*^

-14

Fig. 208. — Sktjll of Dog; Lateral View.
A, Occipital bone; 5, parietal bone; C, squamous temporal bone; D, frontal bone; E, lacrimal bone; F, malar
bone; G, perpendicular part of palatine bone; H, maxilla; /, premaxilla; J , nasal bone; K, mandible; 1, parietal
crest; 2, occipital condyle; 3, paramastoid process; 4, stylo-mastoid foramen; 5, bulla ossea; 6, meatus acusticus
externus; 7, external opening of temporal canal; 8, postglenoid process; 9, zygomatic process of temporal bone; 10,
zygomatic process of malar bone; 11, supraorbital process; 12, entrance to lacrimal canal; 13, infraorbital foramen;
14, mental foramina; 1.5, condyle of mandible; 16, coronoid process; 17, mandibular notch; 18, angular process; 19,
masseteric fossa; i. i', incisor teeth c, c', canine teeth.

fossa. The cerebral surface is marked by digital impressions, and by grooves for
the middle meningeal artery and its branches.

The external surface of the frontal bone is crossed by a frontal crest, which
extends in a curve from the parietal crest to the supraorbital process, and separates
the frontal and temporal parts. The frontal parts of the two bones form a central
depression and slope downward and forward. The supraorbital process is very
short, so that the supraorbital margin is incomplete as in the pig. The supraor-
bital foramen is absent. In front there is a narrow pointed nasal part which fits
in between the nasal bone and the maxilla. The orbital and temporal parts are
relatively extensive. Two ethmoidal foramina are commonly present. The
frontal sinus is confined to the frontal bone.

The parts of the temporal bone fuse early. The zygomatic process curves
widely outward and forward. Its anterior part is beveled ventrally and articulates

190

SKELETON OF THE DOG

extensively with the corresponding process of the malar. The articular surface
for the condyle of the mandible consists of a transverse groove which is continued
upon the front of the large postglenoid process. Behind the latter is the lower
opening of the temporal canal. There is no condyle. The mastoid part is small,
but bears a distinct mastoid process. The external acoustic meatus is wide and
verj^ short, so that one can see into the tympanum in the dry skull. The bulla ossea
is very large and is rounded and smooth; its medial side is united to the basilar
part of the occipital bone. Above this junction and roofed in by the union of the
petrous part and the basioccipital is the petro-basilar canal (Canalis petrobasilaris) ;
this transmits a vein from the floor of the cranium to the foramen lacerum posterius.
The latter opens into a narrow depression behind the bulla ossea. It transmits the

Interparietal bone

Parietal crest

Zygomatic process of

temporal hone

Coronoid process

Frontal crest
Supraorbital process

Zygomatic process of

malar bone

Lacrimal bone

Infraorbital foramen

Nasal process of premaxilla
Canine tooth
Incisor teeth

Parietal bone
Squamous temporal bone
Frontal bone

Body of premaxilla

Fig. 209. — Skull of Doa; Dorsal View.

ninth, tenth, and eleventh cranial nerves. The carotid canal branches off from
the petro-basilar, passes forward lateral to it through the medial part of the bulla
ossea, and opens in front at the carotid foramen; it transmits the internal carotid
artery. The Eustachian opening is immediately lateral to the carotid foramen.
The muscular and hyoid processes are extremely rudimentary. The petrous part
projects into the cranial cavity and forms a sharp prominent petrosal crest. The
medial surface presents a deep floccular fossa above the internal acoustic meatus.
The anterior surface is also free. The anterior angle is perforated by a canal for
the fifth cranial nerve (Canalis nervi trigemini).

The body of the sphenoid bone is flattened dorso-ventrally. The hypophyseal
fossa is shallow, but the dorsum sellse is well developed and bears posterior clinoid
processes. A pair of anterior clinoid processes (Processus clinoidei orales) pro-

FACE 191

ject back from tlie roots of the orbital wings. The latter are relatively small and
are crossed laterally by a crest, which is continued forward upon the palatine bone.
The temporal wings are extensive and articulate dorsally with the parietals. Per-
forating the roots of the wings are the following foramina, named from before back-
ward : The optic passes through the orbital wing. The foramen orbitale is a little
lower and is at the junction of the wings. The foramen rotundum opens into the
alar canal, which passes through the root of the short but wide pterygoid process.
The foramen ovale is near the posterior border of the temporal wing. There is no
sphenoidal sinus.

The ethmoid bone is highly developed. The cribriform plate is extensive,
and the olfactory fossae are very deep. The crista galli is little developed, and often
incomplete. The perpendicular plate is long. The lateral masses are greatly
developed and project into the frontal sinus. There are four large endoturbinates

Fig. 210. — Cranial and Orbital Regions of Skull of Dog. The Zygomatic Arch Has Bi^en Sawn Off.
.4, Occipital bone; B, interparietal bone; C, parietal bone; D, squamous temporal bone; E, E', temporal and
orbital parts of frontal bone; F, F', orbital and temporal wings of sphenoid bone; G, perpendicular part of palatine bone;
ff, pterygoid bone ; J, lacrimal bone; /.maxilla; 1, parietal crest; 2, nuchal crest; 3, occipital condyle; 4, paramastoid
process; 5, stylo-mastoid foramen; 6, bulla ossea; 7, meatus acusticus externus; 8, articular surface for condyle of
mandible; 9, section of root of zygomatic process of temporal bone; 10, alar canal; 11, foramen orbitale; 12, optic
foramen; 13, ethmoidal foramen; 14, posterior palatine foramen; 15, sphenopalatine foramen; 16, entrance to lacrimal
canal; 17, supraorbital process; 18, zygomatic process of malar bone (section); 19, maxillary foramen; 20, last molar
tooth.

and six ectoturbinates. The lamina lateralis is extensive and forms the medial wall
of the maxillary sinus. Its ventral border joins the palatine process of the maxilla
and the horizontal part of the palate bone. A shelf-like plate extends inward from
its lower part and concurs with the similarly incurved part of the palatine bone in
forming the lamina transversalis, which divides the olfactory fundus of the nasal
cavity from the naso-pharyngeal meatus.

Face
The maxilla is short, but very high posteriorly. The facial crest is absent.
The infraorbital foramen is over the alveolus for the third premolar. The frontal
process fits into a deep notch between the nasal and orbital parts of the frontal
bone, and the middle part of the posterior border lies along the orbital margin.
There are more or less pronounced ridges, juga alveolaria, over the canine and
molar teeth. The zygomatic process is short and thin ; it is completely overlapped
laterally by the malar, and is perforated by a number of foramina (Foramina

192

SKELETON OF THE DOG

alveolaria). A maxillary tuberosity is not present in the adult, but there is a
pointed projection, the pterygoid process, behind the last alveolus. The nasal
surface bears a short turbinate crest on its anterior part, behind which it is deeply
concave and forms the lateral wall of the maxillary sinus. The palatine process is
short, wide behind, and moderately arched from side to side. The anterior palatine

Foramen Foramen Occipital
hypoglossi magnum condyle

Foramen lacerum posterius ^^ ^
Stylo-mastoid foramen
Meatus acusticus externus

Parnmnstoid process

Bulla ossea
mporal canal

Molar teeth

Premolar teeth

Canine tooth

Zygomatic process of malar
bone

Palatine process of rnaxilla

Prcmaxilla

Incisor teeth

Fig. 211. — Skull of Dog; Vkntral View, Without Mandible.
A, Basilar part of occipital bone; B, body of sphenoid bone; C, vomer; D, D', perpendicular and horizontal parts
of palatine bone; E, pterygoid bone; 1, Eustachian opening; 2, external carotid foramen; 3, foramen ovale; 4, 5,
posterior and anterior openings of alar canal ; 6, foramen orbitale ; 7, postglenoid process; 8, articular groove of temporal
bone; 9, supraorbital process; 10, meatus naso-pharyngeus ; 11, anterior palatine foramen; 12, palatine groove; 13,
palatine fissure; 14, foramen incisivum.

foramen is situated at or close to the transverse palatine suture and about midway
between the median suture and the alveolar border. The palatine groove is dis-
tinct. The large alveolus for the canine tooth is completed by the premaxilla.
The small alveolus for the first premolar is separated from the preceding one by a
small interval. The next two consist of anterior and posterior parts for the roots
of the teeth. The fourth and fifth are much larger and are divided into three

FACE 193

parts. The last is small and consists of three divisions. The infraorbital canal is
short.

The body of the premaxilla is compressed dorso-ventrally, and contains three
alveoli for the incisor teeth, which increase in size from first to third; it also com-
pletes the medial wall of the large alveolus for the canine tooth. The foramen
incisivum is very small except in large skulls. The interalveolar border is wide
and very short. The nasal process is wide at its origin and tapers to a sharp point
behind; the anterior part curves upward, backward, and a little inward, and forms
the lateral margin of the osseous nasal aperture; the posterior part extends back-
ward a long distance between the nasal bone and the maxilla. The palatine process
turns upward and outward, forming with its fellow a wide groove for the septal
cartilage; the posterior end is pointed and fits into a notch between the palatine

Fig. 212. — Sagittal Section ok Skull of Dog, Without Mandible.
A, A', Basilar and squamou.s parts of occipital bone; B, B', presphenoid and postsphenoid; C, C, perpendicular
and cribriform plates of ethmoid bone; i>, parietal bone; £?, frontal bone; i'', pterygoid bone; G, G", vertical and hori-
zontal parts of palatine bone; //.vomer; /.premaxilla; J, nasal bone; /C, dorsal turbinate bone; L, ventral turbinate
bone; /, //, ///, anterior, posterior and middle fossae of cranium; 1, occipital condyle; 2, opening of condyloid canal;
3, canal for intertransverse sinus of dura mater; 4, internal occipital protuberance; 5, internal opening of temporal
canal; 6, mastoid foramen; 7, floccular fossa; 8, meatus acusticus internus; 9, canal for trigeminal nerve; 10, internal
carotid foramen; 11, 12, openings into petro-basilar canal; 13, foramen hypoglossi; 14, petrosal crest; 15, dorsum sellae;
16, hypophyseal or pituitary fossa; 17, optic foramen; 18, ethmoid foramen; 19, meatus naso-pharyngeus; 20,21,22,
dorsal, middle, and ventral meatus nasi; 23, incisor teeth; 24, canine tooth; 25, premolar teeth; 26, molar teeth; 27,
septum between frontal

processes of the maxillae, and supports the end of the vomer. The palatine fissare
is short but wide.

The horizontal part of the palatine bone is extensive, forming about one-third
of the hard palate. It presents a variable number of accessory palatine foramina.
There is usually a pointed posterior nasal spine (Spina nasalis aboralis) at the end
of the median suture. The palatine canal is sometimes formed entirely in this bone.
The perpendicular part is even more extensive. Its lateral surface is chiefly free
and forms most of the medial wall of the large pterygo-palatine fossa. The max-
illary foramen is situated in a deep recess between this bone and the zygomatic
process of the maxilla. Just above it there is commonly another foramen which
opens into the nasal cavity. The posterior palatine and sphenopalatine foramina
are situated further back and a little lower; the former is ventral to the latter. A
horizontal plate extends from the nasal surface, meets that of the opposite bone, and
completes the lamina transversalis spoken of in the description of the ethmoid bone.
There is no palatine sinus.

The pterygoid bones are very wide and short. They form a considerable part
13

194

SKELETON OF THE DOG

of the lateral boundaries of the posterior nares. The lower and posterior borders
are free and at their angle of junction there is a variable hamulus.

The nasal bones are (in most breeds) long and wider in front than behind.
The facial surface is variably concave in its length and is inclined toward the
median suture so as to form a central groove. The medial borders turn downward
and form an internal nasal crest which becomes very prominent behind. The pos-
terior parts fit into a notch formed by the frontal bones. The anterior ends form
an almost semicircular nasal notch.

The lacrimal bone is very small. The facial part extends very little or not
at all beyond the orbital margin. The orbital surface is small and triangular,
and presents the entrance to the lacrimal canal.

The large zygomatic process constitutes the bulk of the malar bone. It is
very long and is strongly curved. The dorsal border is convex, free in front, where
it forms part of the orbital margin, beveled behind for articulation with the similar
process of the temporal bone. Between these it bears an eminence, the processus
frontalis, to which the orbital ligament is attached. The body of the bone may be
considered to consist of a lacrimal process directed dorsally and fitting in between

Symphyseal
surface

Fig. 213. — Right Half of Mandible of Dog; Medial View.

the lacrimal and maxilla, and a maxillary process directed ventrally. The facial
surface is convex.

The dorsal turbinate bone is in its anterior part a simple plate, attached by
one edge to the nasal bone; it curves ventro-medially, and its free border is thick-
ened and everted. The posterior part is wider and resembles the ethmoturbinates,
with which it is connected.

The ventral turbinate bone is short and very complex. It is attached to the
nasal surface of the maxilla by a basal lamina, which divides into two secondary
lamellae. The latter detach numerous tertiary lamellae, which are coiled and have
thick free edges.

The vomer is not in contact with the posterior part of the floor of the nasal
cavity, and does not divide the posterior nares. The posterior end is narrow and
deeply notched. Near the posterior nares the two plates curve outward and join
the palatine bones and assist in forming the lamina transversalis.

The two halves of the mandible do not fuse completely even in old age, so that
there is a permanent symphysis mandibulae. The body presents six alveoli for the
incisor teeth and two for the canines. The incisor alveoli increase in size from first
to third. The canine alveoli extend deeply downward and backward. The rami
diverge less than in the pig. The ventral border of the horizontal part is convex
in its length and is thick and rounded. The alveolar border is slightly concave in

THE SKULL AS A WHOLE 195

its length and is a little everted, especialty in its middle; it presents seven alveoli
for the lower cheek teeth, which resemble those of the upper jaw except that the
fourth and sixth are much smaller and the fifth is like the fourth of the upper series.
The interalveolar space is very short or even absent. There are two or three men-
tal foramina on either side. The vertical part is relatively small. Its lateral sur-
face presents a deep masseteric fossa (Fossa masseterica) which encroaches on the
coronoid process and is limited by ridges in front and below. The medial surface
is convex and is marked by the usual mandibular foramen. At about the same
level as the latter is the rough angular process (Processus angularis), which pro-
jects backward from the posterior border, and is equivalent to the angle of the
other animals. The condyle is placed very low — not much higher than the apex
of the canine tooth when the bone is resting on a flat surface. It is long trans-
versely and the medial part of the articular surface is much the wider and extends
over the posterior surface. Its long axis is a little oblique, the medial end being
inclined somewhat downward and forward. The coronoid process is very exten-
sive and is bent slightly outward and backward.

The body of the hyoid bone is a slightly curved transverse rod; it is compressed
from before backward, and bears no lingual process. The thyroid cornua are per-
manently attached to the body by cartilage; they diverge widely, curve inward, and
are compressed laterally. The small cornua are short, prismatic, and strong. The
middle cornua are commonly a little longer than the great cornua; they are com-
pressed laterally, and are slightly enlarged at the ends, which are joined by cartilage
to the adjacent cornua. The great cornua are bent outward and are somewhat
twisted.

THE SKULL AS A WHOLE
The different breeds of dogs display great variations in the form and size of
the skull. Those which have a long narrow skull (e. g., greyhound, collie) are
designated dolichocephalic. Other dogs (e. g., bulldog, small spaniels, pugs) have
very broad, short skulls and are termed brachycephalic. Intermediate forms
(e. g., fox terrier, dachshund) are mesaticephalic.

The length is usually measured from the nuchal crest to the anterior end of the premaxil-
lary suture, and the breadth between the summits of the zygomatic arches. The cephaUc index
is the relation of the breadth to the length, assuming the latter equal 100; the formula is:

1 P?h ^ cephalic index. The index of extreme dolichocephalic breeds is about 50,

as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in the pug and
some toy terriers. Among the mesaticephalic types are the fox terrier, with an index of about
70, and the white Pomeranian, with one about 72 to 75. The cranio-facial index is the relation of
the distance between the nuchal crest and the fronto-nasal sutvu-e to that between the latter and
the nasal notch. It varies from 10 : 3 in extreme brachycephalic breeds to 10 : 7 in extreme
dolichocephalic subjects.

The frontal surface shows the wide outward curve of the zygomatic arches
and the great extent of the temporal fossae. The latter are separated bj^ the parietal
crest, which in the larger breeds is very strong and prominent, and is continued by
the diverging frontal crests to the supraorbital processes. The frontal and nasal
regions are centrally depressed, and are more or less concave in profile. The nasal
region is narrow and is terminated in front by a nasal notch. In the extreme
brachycephalic breeds the differences are very striking. The cranium is strongly
convex in both directions and is considerably longer than the face. The parietal
crest is more or less effaced posteriorly and is formed by the interparietal onl3\ The
parietofrontal crests are separated by an interval behind and diverge to the supra-
orbital processes, so that the temporal fossae are widely separated. The frontal
region is wide, strongly convex, and has a shallow central depression. The nasal
region is very short, relatively wide, and centrally depressed. In profile there is a

196

SKELETON OF THE DOG

marked depression at the fronto-nasal junction, producing what is termed by fan-
ciers the "stop" of the face.

On the lateral surface the great extent of the temporal fossa is seen. The
orbit communicates freely with the fossa, the posterior part of the orbital margin
being absent in the dry skull. The axis of the orbital cavity forms a much smaller
angle with the median plane than in the horse and ox. A distinct crest marks the
limit between the orbital cavity and the extensive pterygo-palatine fossa. The
preorbital region is somewhat triangular, concave in its length, and convex dorso-
ventrally ; the infraorbital foramen is on its lower part above the third cheek tooth.
In extreme brachycephalic breeds the orbit is relatively very large and the preor-
bital region extremely short but high. In the bulldog the lower jaw protrudes be-
yond the upper — a condition known as prog-
nathism. The opposite condition, l^rachygna-
thism, is seen in the dachshund.

Striking features on the basal surface of
the cranium are the width and flatness of the
basilar part of the occipital bone, the small size
of the paramastoid processes, the large size and

Fig. 214. — Skull or Dolichocephalic Dog;
Dorsal View.

Fig. 215. — Skull of Brachycephalic Dog; Dorsal View.

rounded shape of the bulla ossea, and the grooved form of the articular surfaces
for the mandible. The posterior nares are long and narrow and are not divided
b}' the vomer. The hard palate is usually about half the length of the skull. It
is commonly marked b}^ a median crest or rough line, and on each side are the
anterior and accessory palatine foramina and the palatine grooves. The width
is greatest between the fourth pair of cheek teeth, and here there is in most skulls
a pronounced depression on either side. The length, width, and contour vary
greatly in different breeds.

The angle of divergence of the rami of the mandible varies from 25 to 30 de-
grees; it is smallest in the greyhound, largest in extreme brachycephalic types,
e. g., bulldog, pug.

The nuchal surface is somewhat triangular, with the base ventral. The sum-
mit is formed l)y the nuchal crest, which projects very stronglv l)ackward in the
large breeds. Below it there are two very distinct rough imprints for muscular
attachment. In some skulls there is a thin median occipital crest, in others a
rounded elevation. Laterally are the temporal crests and the mastoid processes.

BONES OF THE THORACIC LIMB 197

The mastoid foramen is at the junction of the occipital and temporal bones, above
the root of the paramastoid process; it opens directly into the cranial cavity.
The foramen magnum varies greatly in form ; most often the transverse diameter is
the greater, but in some skulls it is equaled or exceeded by the vertical diameter.

The cranial cavity (Fig. 212) corresponds in form and size with the cranium,
especially in those breeds in which the various crests are more or less effaced and the
frontal sinuses are small. The basi-cranial axis is almost parallel with the palate,
and the floor is flattened. The anterior fossa is narrow and is only slightly higher
than the middle one. The ethmoidal fossae are very deep and the crista galli is
little developed. The hj^pophyseal fossa is variable in depth, and the dorsum sellse
is relatively high and bears clinoid processes laterally. The cerebral and cerebellar
compartments are well marked off laterally by the petrosal crests and dorsally by
the tentorium osseum. The base of the latter is traversed by a canal which con-
nects the two temporal canals. The anterior angle of the petrous temporal is
perforated by a canal for the fifth cranial nerve.

The nasal cavity (Fig. 212) conforms to the shape of the face. Its anterior
aperture is large and nearly circular in most dogs. The complex ventral turbinates
occupy the anterior part of the cavity to a large extent, except near the aperture.
Behind the ventral turbinate is the large opening of the maxillary sinus. Behind
this the cavity is divided by the lamina transversalis into a large upper olfactory
region or fundus nasi and a lower naso-pharyngeal meatus. The fundus is occupied
largely by the ethmoturbinates. The posterior nares are undivided and are in
general long and narrow, but vary with the shape of the skull.

The frontal sinus is of considerable size in the large breeds, but is confined to
the frontal bone. It is usually divided into a small anterior and a much larger
posterior compartment, each of which opens into the dorsal ethmoidal meatus.
The sinus is very small in extreme brachycephalic types.

The maxillary sinus is small, and is in such free communication with the nasal
cavity as to make it rather a recess than a true sinus. It is bounded medially by
the lamina lateralis of the ethmoid, and its lateral wall is crossed obliquely by the
naso-lacrimal canal. The roots of the molar teeth do not project up into it.

BONES OF THE THORACIC LIMB

The clavicle is a small, thin, irregularly triangular bony or cartilaginous plate.
It is embedded in the brachiocephalicus muscle in front of the shoulder-joint and
forms no articulation with the rest of the skeleton. (It is nearly an inch long in
a large cat and is a slender curved rod.)

The scapula is relatively long and narrow. The spine increases gradually
in height from above downward and divides the lateral surface into two nearly
equal fossae. Its free edge is thick and rough above, and at the lower part is thin
and bent backward. The acromion is short and blunt and is opposite the rim of
the glenoid cavity. The subscapular fossa is very shallow and is marked by rough
lines (Linese musculares). The rough area above it for the attachment of the ser-
ratus ventralis is large and quadrilateral in front, narrow and marginal behind.
The anterior border is thin, strongly convex, and sinuous. The posterior border
is straight and thick. The vertebral border is convex and thick and bears a band
of cartilage. The anterior angle is rounded. The posterior angle is thick and square.
The neck is well defined and bears a rough eminence posteriorly, from which the
long head of the triceps arises. The glenoid cavity is continued forward upon the
lower face of the tuber scapulae, which is blunt and bears no coracoid process. The
cervical angle is opposite the first thoracic spine; the dorsal angle lies above the ver-
tebral end of the fourth rib, and the glenoid angle at a point just in front of the
sternal end of the first rib in the ordinary standing position. The tuber scapulae

198

SKELETON OF THE DOG

unites with the rest of the bone at six to eight months. The shoulder has a great
range of movement on the chest wall.

The humerus is relatively very long, rather slender, and has a slight spiral
twist. The shaft is somewhat compressed laterally, especially in its proximal two-
thirds; this part is curved in varying degree, convex in front. The deltoid tuber-
osity has the form of a low ridge, and it is continued by a crest which runs up-
ward and backward and bears a tubercle on its proximal part. Another line runs
from it down the anterior aspect and forms .the medial boundary of the very shallow
musculo-spiral groove. The nutrient foramen is about in the middle of the posterior
surface. A slight elevation on the proximal third of the medial surface represents
the teres tubercle. The head is long and strongly curved from before backward.
The neck is better marked than in the horse. The undivided lateral tuberosity is
placed well forward and extends little above the level of the head. The medial tu-

Cartilage

Tuber
scapulce

Cartilage

Pos-
terior
angle

I Glenoid catnty
Acromion

Fig. 21G. — Left Scapula of Dog; Lateral Viei

Glenoid cavity
Fig. 217. — Right Scapula of Dog; Medial View.

berosity is small. The intertuberal or bicipital groove is undivided and is displaced
to the medial side by the extension forward of the lateral tuberosity. The distal
end bears an oblique trochlear articular surface for articulation with the radius and
ulna, the lateral part of which is the more extensive and is faintl}^ grooved. The epi-
condyles are prominent. The coronoid and olecranon fossae often communicate
through a large supratrochlear foramen. The proximal end unites with the shaft
at about one year, the distal at six to eight months.

The two bones of the forearm are relatively long and articulate with each other
at each end in such a manner as to allow of slight movement. A narrow inter-
osseous space separates their shafts. The radius is flattened from before back-
ward and increases in size distally. The shaft forms two curves, so that it is con-
vex dorsally and medially. The dorsal surface is convex in both directions and is
marked in its distal half by a groove for the oblique extensor of the carpus. The
volar surface presents the nutrient foramen in its proximal third, and bears a rough

BONES OF THE THORACIC LIMB

199

line (Crista interossea) laterally for the attachment of the interosseous ligament.
The proximal end (Capitulum radii) is relativel}^ small and is supported by a dis-
tinct neck (Collum radii). It bears a concave surface (Fovea capituli) for articu-
lation with the humerus, and a convex marginal area (Circumferentia articularis)
behind for the ulna. The radial tuberosity is small. There is a large lateral tuber-
osity and below this a rough eminence. The distal extremity is much wider.
It has an extensive concave carpal articular surface. Its medial border projects
downward, forming the styloid process of the radius. Laterally there is a concave
facet (Incisura ulnaris racUi) for articulation with the ulna. Dorsally are three
distinct grooves for the extensor tendons. The ulna is well developed, but dimin-

Lateral
tuber ositij

Medial

I tdert liberal

tuberosity ^'l'"''

Head

Neck
Deltoid tuberosity

Musculo-spiral
groove

Coronoid fossa

Lateral condyloid
crest

Olecranon fossa

Lateral epicondyle ^"^'"^ epicondyle
FiQ. 218. — Left Humerus of Dog; Lateral View.

tH-

Medial condyle

Fig. 219. — Left Humerus op Dog; Medial View.

1, Attachment of medial ligament of elbow joint; 2,

attachment of flexor muscles to medial epicondyle.

ishes in size distally. It crosses the volar surface of the radius medio-laterally.
The shaft is large and three-sided in its proximal two-thirds, smaller and more
rounded below. Its dorsal surface is in general rough. The nutrient foramen is
near the proximal end. A vascular groove descends from it and indicates the course
of the interosseous artery. The proximal end is relatively short. It is concave
and smooth mediall}', convex and rough laterally. The olecranon is grooved and
bears three prominences, of which the posterior one is large and rounded. The
semilunar notch is wide below and completes the surface for articulation with the
trochlea of the humerus. Below it is a concave surface (Incisura radialis), which
articulates with the back of the head of the radius, and below this is a fossa, which
receives a tuberosity of the radius. The distal end (Capitulum ulnae) is small and

200

SKELETON OF THE DOG

Olecranon

Processus anconceus

Semilunar notch
y^ Fovea capituli

Shaft of ulna

Shaft of
radius

is produced to a blunt point (Processus styloideus ulnae). It articulates with the
ulnar carpal distally, and has a convex facet on its dorso-medial aspect for the radius.
The proximal end of the radius unites with the shaft at six to eight months, the
distal at about one and a half years of age. The olecranon and the distal end of the
ulna fuse with the rest of the bone at about fifteen months.

The carpus comprises seven bones — -three in the proximal row and four in the
distal. The numerical reduction in the proximal row is apparently due to the
fusion of the radial and intermediate, constituting a large bone (radio-intermediate)

which articulates with almost all of the
distal surface of the radius and with the
bones of the distal row. It projects promi-
nently on the volar surface of the carpus.
The ulnar carpal is long; it articulates with
the radius and ulna above and the acces-
sory behind; below it rests on the fourth
carpal and is prolonged downward to ar-
ticulate with the fifth metacarpal also.
The accessory is cylindrical, constricted
in its middle and enlarged at each end; the
anterior extremity articulates with the
ulna and ulnar carpal bone. The first car-
pal is the smallest bone of the lower row;
it articulates ^vith the second carpal later-
ally and the first metacarpal distall3^ The
second carpal is wedge-shaped, the base be-
ing posterior; its proximal surface is con-
vex, and its distal is concave and rests on
the second metacarpal. The third carpal
is somewhat like the second ; its distal sur-
face is concave and articulates chieflj^ with
the third metacarpal. The fourth carpal
is the largest of the row; it articulates with
the fourth and fifth metacarpals. Two
small bones or cartilages may be found on
the volar surface at the junction of the two
rows, and a third small bone articulates
with the medial side of the radio-inter-
mediate.^

Five metacarpal bones are present.
The first is much the shortest; the third
and fourth are the longest, and are about
one-fifth longer than the second and fifth.
The fifth is the widest at the proximal end
and is slightly shorter than the second.
They are close together above, but diverge
somewhat distally; the first is separated
from the second by a considerable interosseous space. They are so arranged as to
form a convex dorsal surface and a concave volar surface, which corresponds to
the hollow of the palm of the hand in man. Each consists of a shaft and two ex-
tremities. The shaft is compressed from before backward. In the third and fourth
it is almost four-sided, in the second and fifth three-sided, in the first rounded.
The proximal ends (Bases) articulate with each other and with the corresponding

1 The third bone was termed the phacoid in the cat by Strauss-Durckeim, and is regarded
by some authors as the vestige of an additional digit, the prepollex.

Styloid process
of ulna

Carpal articular
surfaces

Fig. 220.-

-Left Radius and Ulna of Dog; Medial
View.
o, Rough area for attachment of biceps brachii
and brachialis muscles; b, groove for tendon of exten-
sor carpi obUquus.

BONES OF THE THORACIC LIMB

201

carpal bones. The carpal articular surface formed by them is concave from side
to side, convex from before backward. The distal ends (Capitula) have articular
surfaces of the nature of a head, but bear a sagittal ridge on the volar aspect, ex-
cept the first, which is grooved. Ossification is complete at five or six months of
age.

The five digits have three phalanges each, except the first, which has two.
The third and fourth digits are the
longest ; the first is very short and does
not come in contact with the ground
in walking. The first phalanges of the
chief digits have four-sided shafts,
which are slightly curved dorsally.
The proximal end of each has a con-
cave surface for articulation with the
metacarpal bone and is deeply notched
behind. The distal end has a trochlea
for articulation with the second pha-
lanx, and depressions on each side for
ligamentous attachment. The second
phalanges are about two-thirds of the
length of the first phalanges. The
proximal articular surface consists of
two cavities separated by a sagittal
ridge. The distal extremity is wider
and flatter than that of the first. The
third phalanges correspond in general
to the form of the claws. The base has
an articular surface adapted to the
second phalanx and is encircled by a
collar of bone (Crista unguicularis).
The volar surface bears a wing or tuber-
osity, and on each side of this is a fora-
men. The ungual part is a curved rod
with a blunt-pointed free end. It is
rough and porous. Its base forms with
the collar previously mentioned a deep
groove, into which the proximal border
of the claw is received. The two pha-
langes of the first digit resemble in ar-
rangement the first and third phalanges
of the other digits. Ossification is
complete at five or six months.

Nine volar sesamoids are usually
present. Two are found at each meta-
carpo-phalangeal joint of the chief
digits. They are high and narrow,
articulate with the distal end of the

metacarpal bone in front, and have a small facet on the base for the first phalanx.
On this joint of the first digit there is usually a single flattened sesamoid, but ex-
ceptionally two are present. The distal volar sesamoids remain cartilaginous. A
nodular dorsal sesamoid occurs in the capsule of the metacarpo-phalangeal joints,
and cartilaginous nodules are found in a similar position in connection with the
joints between the first and second phalanges.

Fig. 221. — Skeleton of Distal Part op Right Thoracic
Limb of Dog; Dorsal View.
The digits are spread. J, Distal end of interosseous
space; R, distal end of radius; C. r.+ i., radio-intermediate
carpal; C u., ulnar carpal; C. a., accessory carpal (very
small part \asible) ; C. 1,C. 2, C. S, C. 4, first to fourth car-
pal bones; Mc. I, metacarpal bone of first digit; P. 1 + 2,
fused first and second phalanges of same; P. 3, third phalanx
of same; Mc. V, fifth metacarpal bone; P. UP. 2, P. 3,
phalanges of fifth digit; S, dorsal sesamoid; C, C, volar

202

SKELETON OF THE DOG

BONES OF THE PELVIC LIMB

The ilium is nearly parallel with the median plane and its axis is only slightly
oblique with regard to the horizontal plane. The gluteal surface is concave. The
pelvic surface is almost flat. The auricular surface faces almost directly inward,
and in front of it there is an extensive rough area. The ilio-pectineal line is very
distinct and is uninterrupted. The crest is strongly convex, thick, and rough.
The tuber sacrale is represented by a thickened part which bears two eminences,
homologous with the posterior superior and posterior inferior iliac spines of man.
The tuber coxse also has two prominences, which are equivalent to the two anterior
spines present in man. The shaft is almost sagittal and is compressed laterally.
It is smooth and rounded dorsally, and it bears a ventro-lateral crest (Linea glu-
tae ventralis), which terminates at a tuberosity in front of the acetabulum.

The ischium has a twisted appearance, owing to the fact that its acetabular
part is nearly sagittal while the posterior part is almost horizontal. The two bones

Fig. 222.— Rk
1, Gluteal surface of ilium; 2, crest of i

HT Os Cox« OP Dog; Lateral View.

3, tuber sacrale; 4, tuber coxa; 5, shaft of ilium; 6, nutrient fora-

10, ilio-pectineal

uum;
Tnen; 7, greater sciatic notch; S, ventral gluteal line; 9, tubercle to which rectus femoris is attached;
eminence; 11, 11', acetabular and symphyseal branches of pubis; 12, articular surface of acetabulum; 12', fossa acetab-
uli; 13, obturator foramen; 14, ischiatic spine; 15, lesser sciatic notch; 16, 16', acetabular and symphyseal branches
of ischium: 17, tuber ischii.

also diverge behind and the tubera are flattened and everted. The superior ischiatic
spine is low and thick ; its posterior part is marked by transverse grooves and has a
prominent outer lip. The greater sciatic notch is elongated and very shallow. There
is no lesser sciatic notch. The ischial arch is relatively small and is semi-elliptical.

The symphyseal part of the pubis is thick and fuses late with the opposite bone.
There is no subpubic groove.

The acetabulum is about twice as far from the tuber coxae as from the tuber
ischii. The fossa acetabuli is deep, and is bounded medially by a flat plate of bone;
its floor is so thin as to be translucent. There is a small notch behind.

The obturator foramen resembles in outline an equilateral triangle with the
angles rounded off.

Union of the three parts of the os coxse has usually taken place at six months,
but the epiphyses of the ilium and ischium do not fuse with the main part of these
bones till about the end of the second year.

The inlet of the pelvis is very oblique. It is almost circular in the female,
but in the male it is elliptical and the conjugate diameter is the longer. The cavity
is narrowest between the acetabula, and very wide behind. The floor is concave
and relatively narrow in front, wide and flat behind.

BONES OF THE PELVIC LIMB

203

The femur is relatively much longer than in the horse or ox. The shaft is regu-
larly cylindrical, except near the extremities, where it is wider and compressed froiiz
before backward. It is strongly curved in its distal two-thirds, convex in front.
The posterior surface is flattened transversely, narrow in the middle, and widens
toward each end. It is bounded by two rough lines (Labium laterale, mediale)
which diverge toward the extremities. The third trochanter and the supracondyloid
fossa are absent. There are two supracondyloid crests, the medial one being small.
The nutrient foramen is in the proximal third of the posterior surface. The head
is a little more than a hemisphere and has a shallow fovea behind and lateral to its
center. The neck is well defined. The trochanter major does not extend as high

Crest of ilium Tir ■ /• •, •

V_ n mg of ilium

Tuber coxce

Shaft of ilium

Ilio-pedineal
eminence

Acetabular branch of
pubis

Symphyseal branch of
pubis
Symphyseal branch of _
ischium

Vascular impression

- Sacro-iliac articulation

Nutrient foramen
Ilio-pectineal line

Tubercle
Acetabulum

Obturator foramen

Acetabular branch of
ischium

Tuber ischii

Ischial arch
Fig. 223. — Pelvic Bones of Dog; Ventral View.
1, Body of first sacral vertebra; 2, wing of sacrum; 3, sacral canal; 4, median crest of sacrum; 5, pelvic surface of

as the head; a thick ridge runs from its anterior surface to the neck. The trochanter
minor has the form of a blunt tuberosity. The trochanteric fossa is round and
deep. The ridges of the trochlea are practically sagittal in direction and are al-
most similar. The intercondyloid fossa is wide. Just above each condyle pos-
teriorly there is a facet for articulation with the sesamoid bone which is developed
in the origin of the gastrocnemius muscle. Union of shaft and extremities takes
place at about one and a half years.

The tibia is about the same length as the femur. The shaft forms a double
curve; the proximal part is convex medially, the chstal part laterally. The prox-
imal third is prismatic, but is compressed laterally and is long from before backward.
The remainder is almost regularly cylindrical. The crest is short but very prom-

204

SKELETON OF THE DOG

inent. The nutrient foramen is usually in the proximal third of the lateral border.
The tuberosity is not grooved, but bears a distinct mark where the ligamentum
patellae is attached. There is a small facet for the fibula on the postero-lateral part
of the lateral condyle, and a small sesamoid bone in the tendon of origin of the
popliteus is in contact with the posterior angle of the latter. The distal end is quad-
rangular and relatively small. The articular grooves and ridge are almost sagittal.
There is a facet laterally for articulation with the fibula. There is a vertical groove
medially and a shallower one behind — both for tendons. The proximal end unites
with the shaft at about eighteen months, the distal at fourteen or fifteen months.

Head

Trochanteric
fossa

\,. . — ^[ed^al

Lateral _i £. ( jncondyle

epicondyle "" \_^, ,^*

Trochlea
Fig. 224. — Right Femur of Dog: Anterior View.

Lateral
condyle

I ntercondyloid

fossa

Fig. 225. — Right Femur of Dog; Posterior View.
1, 2, Sesamoid bones.

The fibula extends the entire length of the region. It is slender, somewhat
twisted, and enlarged at either end. The proximal part of the shaft is separated
from the tibia by a considerable interosseous space, but the distal part is flattened
and closely applied to the tibia. The proximal extremity is flattened and articu-
lates with the lateral condyle of the tibia. The distal end is somewhat thicker and
forms the lateral malleolus. It articulates medially with the tibia and the tibial
tarsal bone. Laterally it l)ears two tubercles.

The patella is long and narrow. The free surface is convex in both direc-
tions. The articular surface is convex from side to side and slightly concave from
above downward.

BONES OF THE PELVIC LIMB

205

The tarsus comprises seven bones. The tibial tarsal consists of a body, neck,
and head, like the bone in man. The body presents a proximal trochlea for articula-
tion with the tibia and fibula. The plantar surface has three facets for articulation
with the fibular tarsal bone. The head is directed a little inward and articulates
with the central. The fibular tarsal has a long anterior process or "beak," but
the sustentaculum is short. The tuber calcis presents a sagittal groove. The
central has a concave proximal surface adapted to the head of the tibial tarsal.
Its distal surface articulates with the first, second, and third tarsals. It bears two
plantar tubercles. The first tarsal is flattened and irregularly quadrangular; its
proximal surface articulates with the central and the distal with the first metatarsal.

Sulcus muscu-,
laris

Head of fibula

Tuberosity

Medial
condyle

Head of fibula

Shaft of tibia

Interosseous space

Fig. 226. — Right Tibia and FiBUL.'t of Dog; Ante-
rior View.

# ^ E- Lateral inalleolus

-Right Tibia and Fibula of Dog; Poste-
rior View.

The second tarsal is the smallest and is wedge-shaped; it articulates distally with
the second metatarsal bone. The third tarsal is also wedge-shaped, the base being
in front; it articulates with the third metatarsal distally. The fourth tarsal is
remarkably high, and resembles a quadrangular prism; its proximal surface
articulates with the fibular tarsal, its distal with the fourth and fifth metatarsal,
and the medial with the central and third tarsal bones. A groove for the tendon of
the peroneus longus crosses its lateral and plantar surface, and above it are one or
two tubercles. The tuber calcis fuses with the body of the bone at fourteen or
fifteen months.

Five metatarsal bones are present. The first is commonly very small and has
the form of a blunt cone, somewhat compressed laterally. It articulates with the

206

THE ARTICULATIONS OR JOINTS

first tarsal and furnishes insertion to the tibialis anterior muscle. In some cases
it fuses with the first tarsal; when the first digit is well developed, its metatarsal
may resemble the others (except in size) or be reduced in its proximal part to a
fibrous band. The other metatarsals are a little longer than the corresponding:
metacarpals. Their proximal ends are elongated from before backward and have
plantar projections, which in the case of the third and fourth usually have facets

Fig. 228. — Skeleton of Distal Part of Left Pelvic Limb of Dog; Dorsal View.
L, Lateral malleolus (distal end of fibula); T. t., tibial tarsal bone; T. /., fibular tarsal bone; T. c, central tarsal
bone; T. 2, T. 3, T. 4, second, third, and fourth tarsal bones; P. l-\- 2, fused first and second phalanges, and P. 3, third
phalanx, of first digit; Mc. 5, fifth metacarpal bone; P. 1, P. 2, P. 3, phalanges of fifth digit; S, dorsal sesamoid.

for articulation with two small rounded sesamoid bones. In other respects they
resemble the metacarpals.

The first digit is often absent. When present, its development varies and it
contains one or two phalanges. In other cases — especiall}' in very large dogs —
a sixth digit is present; it does not articulate with the metatarsus, but is attached
by fibrous tissue. The phalanges of the other digits resemble those of the tho-
racic limb.

Ossification of the metatarsal bones and phalanges is complete at five or six
months.

ARTHROLOGY

THE ARTICULATIONS OR JOINTS

An articulation or joint is formed by the union of two or more bones or carti-
lages by other tissue. Bone is the fundamental part of most joints; in some cases
a bone and a cartilage, or two cartilages, form a joint. The uniting medium is
chiefly fibrous tissue or cartilage, or a mixture of these. Union of parts of the
skeleton by muscles (Synsarcosis) , as in the attachment of the thoracic limb in
the horse, will not be considered in this section.

Joints may be classified — (a) anatomically, according to their mode of develop-
ment, the nature of the uniting medium, and the form of the joint surfaces; (6)
physiologically, with regard to the amount and kind of movement or the absence
of mobility in them; (c) by a combination of the foregoing considerations.

The classification of joints is still in a very unsatisfactory state, and unfortunately the same
term is used in various senses by different authors. The two main subdivisions proposed by Hep-
burn are: (1) Those in which the uniting medium is coextensive with the opposed joint surfaces,
and in which a direct union of those surfaces is thereby effected. (2) Those in which the uniting
medium has undergone interruption in its structural continuity, and in which a ca\'ity of greater
or less extent is thus formed in the interior of the joint. This distinction is of considerable im-
portance chnically.

Three chief subdivisions of joints are usually recognized — viz., sjniarthroses,
diarthroses, and amphiarthroses.

SYNARTHROSES
In this group the segments are united by fibrous tissue or cartilage, or a mix-
ture of the two in such a manner as practically to preclude movement; hence they
are often termed fixed or immovable joints. There is no joint cavity. Most of
these joints are temporary, the uniting medium being invaded by the process of
ossification, with a resulting ankylosis or synostosis. The chief classes in this
group of joints are as follows:

(1) Suture.— This term (Sutura) is applied to those joints in the skull in which
the adjacent bones are closely united by fibrous tissue — the sutural ligament. In
many cases the edges of the bones have irregular interlocking margins, forming the
sutura serrata, e. g., the frontal suture. In others the edges are beveled and
overlap, forming the sutura squamosa, e. g., the parieto-temporal suture. If the
edges are plane or shghtly roughened, the term sutura harmonia is applied to the
joint, e.g., the nasal suture.

(2) Syndesmosis. — In these the uniting medium is white fibrous or elastic
tissue or a mixture. As examples are the union of the shafts of the metacarpal bones
and the attachments to each other of costal cartilages.

(3) Synchondrosis.— In these the two bones are united by cartilage, e. g.,
the joint between the basilar part of the occipital bone and the sphenoid bone.
Very few of these joints are permanent.

(4) Symphysis. — This term is usually limited to a few median joints which
connect symmetrical parts of the skeleton, e. g., symphysis pelvis, symphysis
mandibulge. The uniting medium is cartilage and fibrous tissue. In some cases
a cleft-like rudimentary joint cavity occurs.

207

208

THE ARTICULATIONS

(5) Gomphosis. — This term is sometimes applied to the implantation of the
teeth in the alveoli.

The gomphosis is not, properly considered, a joint at all, since the teeth are not parts of the
skeleton.

DIARTHROSES

These joints are characterized by the presence of a joint cavity and by their
mobility. They are often called movable or true joints. A simple joint (Articu-
latio simplex) is one formed by two articular surfaces; a composite joint (Articulatio
composita), one formed by several articular surfaces. The following structures
enter into their formation:

1. The articular surfaces (Facies articulares) are in most cases smooth, and
vary much in form. The}^ are formed of specially dense bone, which differs his-
tologically from ordinary compact substance. In certain cases (vide Osteology)
the surface is interrupted by non-articular cavities known as synovial fossae.

2. The articular cartilages (Cartilagines articulares), usually hyaline in type,
form a covering over the articular surfaces of the bones. They vary in thick-
ness in different joints; they are thickest on those
which are subject to the most pressure and fric-
tion. They usually tend to accentuate the curva-
ture of the bone, ^. e., on a concave surface the
peripheral part is the thickest, while on a con-
vex surface the central part is the thickest. The
articular cartilages are non-vascular, very smooth,
and have a bluish tinge in the fresh state. They
diminish the effects of concussion and greatly reduce
friction.

3. The articular or joint capsule (Capsula articu-
laris) is, in its simplest form, a tube, the ends of which
are attached around the articulating surfaces. It
consists of two layers — an external one, composed of
fibrous tissue, and an internal one, the synovial layer
or membrane. The fibrous layer (Stratum fibrosum) ,
sometimes termed the capsular ligament, is attached
either close to the margins of the articular surfaces or
at a variable distance from them. Its thickness varies
greatly in different situations: in certain places it is extremely thick, and sometimes
cartilage or bone develops in it; in other places it is practically absent, the cap-
sule then consisting only of the synovial membrane. Tendons which pass over a
joint may partially take the place of the fibrous layer; in these cases the deep face
of the tendon is covered by the synovial layer. Parts of the capsule may undergo
thickening and so form ligaments, which are not separable, except artificially, from
the rest of the capsule. The synovial layer (Stratum synoviale) lines the joint
cavity except where this is bounded by the articular cartilages; it stops normally
at the margin of the latter. It is a thin membrane, and is richly supplied by close
networks of vessels and nerves. It frequently forms folds (Plicae synoviales) and
villi (Villi synoviales), which project into the cavity of the joint. The folds com-
monly contain pads of fat, and there are in many places masses of fat outside of the
capsule which fill up interstices and vary in form and position in various phases of
movement. The synovial membrane secretes a fluid, the synovia, which lubricates
the joint; it resembles white-of-egg, but has a yellowish tinge.^ In many places the

^ It is doubtful whether the synovia is a true secretion or a transudate containing products of
friction. The view given above is that which is more commonly accepted. It contains albumen,
mucin, and salts, and is alkaline. In it there are commonly cells derived from the synovial mem-
brane, portions of cells, cells which have undergone fatty degeneration, particles of articular
cartilage, etc.

Fig. 229. — Diagram op Section of

DiARTHROSIS.

f.l., Fibrous layer, s.L, synovial
layer of joint capsule. The articular
cartilages are white, bones dotted, and
the joint cavity black in the figure.

DIARTHROSES 209

membrane forms extra-articular pouches, which facilitate the play of muscles and
tendons.

The articular or joint cavity (Cavum articulare) is enclosed by the synovial
membrane and the articular cartilages. Normally, it is, strictly speaking, only a
potential cavity, which contains nothing but a small amount of synovia.

The student must guard against a false conception of the joint cavity which may result from
dissections and diagrams in which an actual cavity of considerable extent appears to exist. A
correct idea of the intimate apposition of the parts is best obtained from the study of frozen sec-
tions. On the other hand, it is instructive to examine joints which have been injected so as to
distend the capsule fully. It is then seen that the cavity is often of much greater potential extent
than one might suppose, and that the capsule is often very irregular in form, i. e., forms a variety of
sacculations.

The foregoing are constant and necessary features in all diarthroses. Other
structures which enter into the formation of these joints are ligaments, articular
discs or menisci, and marginal cartilages.

4. Ligaments. — These (Ligamenta) are strong bands or membranes, usually
composed of white fibrous tissue, which bind the bones together. They are pli-
able, but practically inelastic. In a few cases, however, e. g., the ligamentum
nuchae, they are composed of elastic tissue. They may be subdivided, according
to position, into periarticular and intraarticular. Periarticular ligaments are fre-
quently blended with or form part of the fibrous capsule; in other cases they are
quite distinct. Those which are situated on the sides of a joint are termed col-
lateral ligaments (Ligamenta collateralia) . Strictly speaking, intra-articular liga-
ments, though within the fibrous capsule, are not in the joint cavity; the synovial
membrane is reflected over them. The term seems justifiable, however, on prac-
tical grounds. Those which connect directly opposed surfaces of bones are termed
interosseous ligaments. In many places muscles, tendons, and thickenings of the
fascia3 function as ligaments and increase the security of the joint. Atmospheric
pressure and cohesion play a considerable part in keeping the joint surfaces in appo-
sition.

5. Articular discs or menisci (Disci s. menisci articulares) are plates of fibro-
cartilage or dense fibrous tissue placed between the articular cartilages, and divide
the joint cavity partially or completely into two compartments. They render cer-
tain surfaces congruent, allow greater range or variety of movement, and diminish
concussion.

6. A marginal cartilage (Labrum glenoidale) is a ring of fibro-cartilage which
encircles the rim of an articular cavity. It enlarges the cavity and tends to pre-
vent fracture of the margin.

Vessels and Nerves. — The arteries form anastomoses around the larger joints,
and give off branches to the extremities of the bones and to the joint capsule. The
synovial membrane has a close-meshed network of capillaries; the latter form loops
around the margins of the articular cartilages, but do not usually enter them.
The veins form plexuses. The synovial membrane is also well supplied with lymph-
vessels. Nerve-fibers are especially numerous in and around the synovial mem-
brane and there are special nerve-endings, e. g., Pacinian bodies and the articular
end-bulbs described by Krause.

Movements.— The movements of a joint are determined chiefly by the form
and extent of the joint surfaces and the arrangement of the ligaments. They are
usually classified as follows:

1. Gliding.— This refers to the sliding of one practically plane surface on
another, as in the joints between the articular processes of the cervical vertebrse.

2. Angular Movements. — In these cases there is movement around one or
more axes. Motion which diminishes the angle included by the segments forming
the joint is termed flexion, while that which tends to bring the segments into line
with each other is called extension. With reference to the joints of the distal parts

210 THE ARTICULATIONS

of the limbs, it seems advisable to employ the terms dorsal and volar or plantar
flexion, since these joints can be "overextended." Similarly the terms dorsal and
ventral flexion are applied to the corresponding movements of the spinal column.
The meaning of the term lateral flexion as applied to the vertebral column is evi-
dent. These movements are all rotations around axes which are approximately
either transverse or vertical. Depression, elevation, and transverse movement of
the lower jaw fall in this category.

3. Circumduction. — This designates movements in which the distal end of
the limb describes a circle or a segment of one. In man such movement is easily
performed, but in quadrupeds it is possible to a limited degree only, and is to be
regarded usually as an indication of disease.

4. Rotation. — As a matter of convenience, this term is reserved to indicate
rotation of one segment around the longitudinal axis of the other segment forming
the joint. It is seen typically in the atlanto-axial joint.

5. Adduction and abduction designate respectively movement of a limb to-
ward and away from the medial plane, or of a digit toward and away from the
axis of the limb.

Classification. — This is based on the form of the joint surfaces and the move-
ments which occur. The following chief classes may be recognized :

1. Arthrodia, or gliding joint. In these the surfaces are practically flat, ad-
mitting of gliding movement. Examples: carpo-metacarpal joints; joints be-
tween the articular processes of the cervical and thoracic vertebrse.

2. Ginglymus, or hinge-joint. In this class the joint surfaces consist usually
of two condyles, or of a segment of a cylinder or cone, which are received by cor-
responding cavities. In typical cases the movements are flexion and extension,
i. e., around a single transverse axis. Examples: atlanto-occipital and elbow
joints.

3. Trochoid, or pivot joint. In these the movement is limited to rotation of
one segment around the longitudinal axis of the other. Example: atlanto-axial
joint.

4. Enarthrosis, or ball-and-socket joint. These are formed by a surface of
approximately spherical curvature, received into a corresponding cavity. They
are multiaxial, and allow of the greatest variety of movement, e. g., flexion,
extension, rotation, abduction, adduction, circumduction. Examples: hip and
shoulder joints."^

AMPHIARTHROSES

These joints, as the name indicates, share some characters with both of the
preceding groups. In them the segments are directly united by a plate of fibro-
cartilage, and usually by ligaments also. The amount and kind of movement are
determined by the shape of the joint surfaces and the amount and pliability of the
uniting medium.^ These joints are all medial in position, and are best illustrated
by the joints between the bodies of the vertebrse. There is usually no joint cavity,
but in certain situations a rudimentary one exists.

1 This classification makes no claims to scientific accuracy, but is simply a statement of the
terms in general use. A grouping based on mechanical principles is desirable, but appears to be
almost impossible on account of the great variety and irregularity of form of the articular surfaces.

2 The movements in some of these joints are more extensive and varied than in some diar-
throses. To illustrate this we may compare the movements of the cervical or coccygeal vertebrae
with those possible in the carpo-metacarpal or the sacro-ihac joints.

THE ARTICULATIONS OF THE HORSE INTERCENTRAL ARTICULATIONS 211

THE ARTICULATIONS OF THE HORSE
Joints and Ligaments of the Vertebrae

The movable vertebrae form two sets of articulations, viz., those formed by the
bodies, and those formed by the articular processes of adjacent vertebra; the
former are termed intercentral, and the latter intemeural. Associated with these
are ligaments uniting the arches and processes; some of these are special, i. e., con-
fined to a single joint, while others are common, i. e., extend along the entire ver-
tebral column or a considerable part of it. The joints between the atlas and axis
and between the former and the skull require separate consideration.

Supraspi-
nous liga-
ment

Fig. 230. — Sagittal Section of Last Two Thoracic and First
Lumbar Vertebr.e, showing Ligaments and Spinal Cord
(Medulla). (After Schmaltz, Atlas d. Anat. d. Pferdes.)

INTERCENTRAL ARTICULATIONS
These are amphiarthroses, formed l)y tlie junction of the extremities of the
bodies of adjacent vertebrae. The articular surfaces in the cervical region consist
of a cavity on the posterior
end of the body of the anter-
ior vertebra, and a correspond-
ing convexity or head of the
succeeding vertebra. In the
other regions the surfaces are
much flattened. The uniting
media are :

1. The intervertebral
fibro-cartilages (Fibrocartila-
gincs intervertebrales). Each
of these is a disc which fits into
the space between the bodies
of two adjacent vertebrae, to
which it is intimately attached.
The discs are thinnest in the
middle of the thoracic region,
thicker in the cervical and lum-
bar regions, and thickest in the

coccygeal region. Each consists of a peripheral fibrous ring (Annulus fibrosus)
and a soft central pulpy nucleus (Nucleus pulposus) .

The fibrous ring consists of laminae of fibrous tissue and fibro-cartilage, which pass obliquely
between the two vertebrae and alternate in direction, forming an X-shaped arrangement. The
central part of the ring is largely cartilaginous, and gradually assumes the character of the pulpy
center. The latter is very elastic and is compressed, so that it bulges considerably from the sur-
face of sections; it consists of white and elastic fibers, connective-tissue cells, and pecuhar clear,
transparent cells of various sizes. It is a remnant of the notochord. There are joint cavities in
the cervical intercentral joints, and in those between the last cervical and the first thoracic, and
between the last lumbar and the sacrum.

2. The ventral longitudinal ligament (Lig. longitudinale ventrale)^ lies on the
ventral surface of the bodies of the vertebrae and the intervertebral fibro-car-
tilages, to which it is firmly attached. It begins to be distinct a little behind the
middle of the thoracic region, and is at first a narrow, thin band. Further back
it becomes gradually thicker and wider, and terminates on the pelvic surface of
the sacrum by spreading out and blending with the periosteum. It is strongest in
the lumbar region, where the tendons of the crura of the diaphragm fuse with it.

3. The dorsal longitudinal ligament (Lig. longitudinale dorsale)- lies on the
floor of the vertebral canal from the axis to the sacrum. It is narrow over the mid-

^ Also termed the inferior common ligament.
2 Also termed the superior common ligament.

212

THE ARTICULATIONS OF THE HORSE

dies of the vertebral bodies, and widens over the intervertebral fibro-cartilages, to
which it is very firmly attached.

This ligament is in relation with the spinal veins on either side, and in the middle of each
vertebra a transverse anastomotic vein passes under the hgament.

INTERNEURAL ARTICULATIONS

Each typical vertebra presents two pairs of articular processes, which form
diarthroses with the two adjacent vertebrae. The articular surfaces are extensive,
almost flat, and oval in the cervical region, small and flat in the thoracic region,

Atlas

Funicular part

on at withers

Last cervical
vertebra

First thoracic
vertebra

1, Scapula; /', cartilage of scapul:

Fig. 231. — Ligamentum Nuch.e of Horse.

,; 4, lamellar part of ligamentum nuehse; x,

Baum, Anat. fiir Kiinstler.)

wing of atlas. (After Ellenberger-

while in the lumbar region the anterior ones are concave and the posterior convex.
The joint capsule is strong and ample in the cervical region, in conformity with the
large size and greater mobility of these joints in the neck. In the thoracic and
lumbar regions the capsule is small and close. These joints are arthrodia in the
neck and back, trochoid in the lumbar region.

Associated with these joints are the ligamenta flava, which connect the arches
of adjacent vertebrae. They are membranous and consist largely of elastic tissue.

The supraspinous ligament (Lig. supraspinale) extends medially from the
occipital bone to the sacrum. Behind the withers it consists of a strong cord of
white fibrous tissue, attached to the summits of the vertebral spines. In the neck

SACRAL AND COCCYGEAL ARTICULATIONS 213

and withers it is remarkably modified to form the Hgamentum nuchse, which re-
quires more extended notice.

The ligamentum nuchae is a powerful elastic apparatus, the principal function
of which is to assist the extensor muscles of the head and neck. It extends from
the occipital bone to the withers, where it is directly continuous with the lumbo-
dorsal part of the supraspinous ligament. It consists of two parts — funicular and
lamellar. The funicular part (Pars occipitalis) arises from the external occipital
protuberance and is inserted into the summits of the vertebral spines at the withers.
Two bursas are usually found under it in the adult. The atlantal bursa lies be-
tween the ligament and the dorsal arch of the atlas. The supraspinous bursa is
usually over the third and fourth thoracic spines, but may be over the second or
extend to the fifth. ^ Another bursa may be present at the spine of the axis; this is
between the funicular part and the large digitation attached to the axis. In the
neck the funicular part consists for the greater part of two bands closely applied and
attached to each other. Near and at the withers it broadens greatly, forming an ex-
pansion about five to six inches (ca. 12 to 15 cm.) in width, the lateral margins of which
are thin and turn down over the trapezius and rhomboideus muscles. Behind the
higher spines it becomes narrower and thinner, and is continued by the white fibrous
lumbo-dorsal part.^ A mass of fat and elastic tissue lies upon the ligament as far
back as the withers. It varies greatly in amount in different subjects, and is most
developed in stallions of draft breeds, in which it forms the basis of the so-called
''crest." The lamellar part (Pars cervicalis) consists of two laminae separated
medially by a layer of loose connective tissue. Each lamina is formed of digitations
which arise from the second and third thoracic spines and from the funicular part,
are directed do^vnward and forward, and end on the spines of the cervical vertebrae,
except the first and last. The digitation which is attached to the spine of the axis
is very thick and strong. Behind this they diminish in size and strength; the last
one, which is attached to the sixth cervical vertebra, is quite thin and feeble, or may
be absent.

The interspinous ligaments (Ligg. interspinalia) extend between the spines
of contiguous vertebrae. In the cervical region they are narrow elastic bands, and
in the thoracic and lumbar regions they consist of white fibers directed obliquely
downward and backward.

The intertransverse ligaments (Ligg. intertransversaria) are membranes
which connect adjacent transverse processes in the lumbar region.

INTERTRANSVERSE ARTICULATIONS
These joints (peculiar to equidae) are diarthroses formed by the transverse
processes of the fifth and sixth lumbar vertebrae and between the latter and the alae
of the sacrum. A similar joint between the fourth and fifth lumbar processes is
frequently present. The articular surfaces have an elongated oval form, the
anterior one being concave and the posterior one convex. The capsule is tight,
and is reinforced ventrally.

SACRAL AND COCCYGEAL ARTICULATIONS

In the foal the bodies of the five sacral vertebrae form joints which resemble
somewhat those in the posterior part of the lumbar region. These joints are in-

1 In dissecting-room subjects these bursse and the adjacent structures are commonly the seat
of pathological changes. They appear to be the starting-point of "poll evil" and "fistulous
withers." SulDCutaneous bursa} may be found over the Ugament at the withers.

- No natural line of demarcation exists between the ligamentum nuchse and the lumbo-dorsal
part of the supraspinous ligament, since the change from the elastic to the white fibrous structure
is gradual.

214

THE ARTICULATIONS OF THE HORSE

vaded bj^ the process of ossification early, so that the consolidation of the sacrum
is usually complete, or nearly so, at three years.

The coccygeal vertebrae are united by relatively thick intervertebral fibro-cartil-
ages, which have the form of biconcave discs. Special ligaments are not present, but
there is a continuous sheath of fibrous tissue. The movement in this region is exten-
sive and varied. In old horses the first coccygeal vertebra is often fused with the
sacrum.

MOVEMENTS OF THE VERTEBRAL COLUMN

The movements of the spine, exclusive of those at the atlanto-axial joint, are
dorsal, ventral, and lateral flexion, and rotation. The range of movement at a
single joint is small, but the sum of the movements is
considerable. The movements are freest in the cervical
|i I . yik.>i^ili ^ and coccygeal regions. Rotation is extremely limited
in the thoracic and lumbar regions.

ATLANTO-AXML ARTICULATION

This is a trochoid or pivot joint of a rather peculiar
character. The articular surfaces are : (1) On the lateral
masses of the atlas, two somewhat saddle-shaped facets,
which are separated by a wide notch above and a narrow
one below; (2) on the axis, reciprocal saddle-shaped sur-
faces which extend upon the dens and are confluent on
its ventral aspect. It will be observed that the joint
surfaces are not at all accurately adapted to each other,
so that only limited areas are in contact at any time.

The joint capsule is attached around the margins
of the articular surfaces. It is loose and ample enough
laterally to allow extensive movement.

The dorsal atlanto-axial ligament (Lig. interar-
cuale) is membranous and reinforces the capsule dor-
sally.

The interspinous ligament (Lig. interspinale) con-
sists of two elastic bands which extend from the dorsal
arch of the atlas to the spine of the axis.

The ventral atlanto-axial ligament (Lig. dentis ex-
ternum) arises from the ventral tubercle of the atlas and
is attached by two branches on the ventral spine of the
axis.

The ligament of the dens or odontoid ligament (Lig.
dentis internum) is short, very strong, and somewhat fan-
shaped. It extends from the rough concave dorsal sur-
face of the dens, widens in front, and is attached to the
transverse rough area on the inner surface of the ventral
arch of the atlas.

Movements. — The atlas and the head rotate upon
the axis; the axis of rotation passes through the center
of the bodv of the axis.

Fig. 232. — Atlanto-occipital and
Atlanto - AXIAL Joints of
Horse; Dorsal View after
Removal of Dorsal Arch of
Atl.\s.

a. Joint capsule of left part of
atlanto-occipital joint; 6, lateral
ligament of same; c, c', ligament of
the dens; d, atlanto-axial joint cap-
sule; e, joint capsule of articulation
between axis and third cervical
vertebra; /, interspinous ligament;
1, occipital bone; 2, atlas; 3, axis;
4, third cervical vertebra; 5, dorsal
longitudinal ligament. (Ellenber-
ger-Baum, Anat. d. Haustiere.)

THE ATLANTO-OCCIPITAL ARTICULATION
This joint may be classed as a ginglymus. The articular surfaces of this
joint are: (1) On the atlas, two deep oval cavities; (2) the corresponding condyles
of the occipital bone.

ARTICULATIONS OP THE THORAX — COSTO-VERTEBRAL ARTICULATIONS

215

The joint surfaces are oblique, coming very close to the median Hue ventrally, but separated
by a considerable interval dorsally. A triangular rough area cuts into the medial part of each of
the atlantal articular surfaces.

There are two roomy joint capsules, which sometimes communicate ventrally,
especially in old subjects.

The dorsal atlanto-occipital membrane (Membrana atlanto-occipitalis dorsalis)
extends from the dorsal arch of the atlas to the dorsal margin of the foramen mag-
num. It is blended with the capsules and contains many elastic fibers.

The ventral atlanto-occipital membrane (Membrana atlanto-occipitalis ven-
tralis) extends from the ventral arch of the atlas to the ventral margin of the fora-
men magnum. It is narrower and thinner than the dorsal membrane, and also
fuses with the joint capsules.

The lateral atlantal ligaments (Ligg. lateralia atlantis) are two short bands
which are partially blended with the capsules. Each is attached to the border of
the wing of the atlas near the intervertebral foramen, and to the lateral surface of
the paramastoid process of the occipital bone.

Movements. — These are chiefly flexion and extension. A small amount of
lateral oblique movement is also possible.

Articulations of the Thorax
costo-vertebral articulations

Each typical rib forms two joints with the vertebral column, one by its head,
and one by its tubercle. Thej^ are termed respectively costo-central and costo-
transverse joints.

I, The costo-central articulation (Articulatio capituli) is a trochoid or rotatory
joint, formed by the junction of the
head of the rib with the bodies of
two adjacent vertebrae and the
intervertebral fibro-cartilage. The
two facets on the head of the rib
are separated by a non-articular
groove, and correspond to the two
concave facets (Fovese costales) on
the vertebral bodies. The joint
capsule is rather tight, and is cov-
ered by the accessory ligaments,
which are as follows: 1. The radiate
ligament (Lig. capituli costae radi-
atum) extends ventrally from the
neck of the rib to spread out on
the vertebral bodies and the in-
tervertebral fibro-cartilage. 2. The
conjugal ligament (Lig. conjugale)
— absent from the first joint — is
attached to the groove on the head
of the rib, passes transversely into
the vertebral canal, and divides
under the dorsal longitudinal liga-
ment into two branches: one of these is attached to the body of the anterior vertebra;
the other is continued across to the head of the opposite rib, and is also attached to
the intervertebral fibro-cartilage. The joint cavity is divided into two compart-
ments by the conjugal ligament. 3. The ligament of the neck of the rib (Lig. colli

'\^Radiate ligament
Conjugal ligamen,

233. — Costovertebral Articulation; Anterior View.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)

216 THE ARTICULATIONS OF THE HORSE

costse) is a strong band which crosses the joint dorsally. It is attached on the
vertebra above the costal facet and on the neck of the rib.

II. The costo-transverse articulation (Articulatio costo-transversaria) . This
is formed by the facet on the tubercle of the rib and on the transverse proc-
ess of the vertebra. They are gliding joints. The capsule is reinforced by the
dorsal costo-transverse ligament (Lig. costo-transversarium dorsale), a distinct
strong band which arises on the transverse process and ends on the non-articular
part of the tubercle. It is covered by the levator costae muscle, and begins to be
quite distinct at the fifth joint.

The cavity for the head of the first rib is formed by concave facets on the bodies of the last
cervical and first thoracic vertebrjE. The conjugal ligament is absent, but the hgament of the
neck is short and strong. The radiate ligament is very strong, and consists of two parts. In the
case of the last two or three ribs the costo-central and costo-transverse joints are confluent, and the
various structures are correspondingly modified.

Movements. — The chief movement is rotation around an axis which connects
the centers of the head and tubercle of the rib. The movement is very limited in
the anterior part of the series of joints, but very considerable in the posterior part.

In the case of the first rib the movement is evidently extremely limited. The facet for the
tubercle of the rib is deeply concave, and the axis of rotation is almost transverse, so that the
movement is chiefly sagittal in direction. Further back the facets on the transverse processes
become flat, and the axis of rotation gradually approaches a longitudinal direction. This, in
connection with the mobiUty of the ventral ends of the asternal ribs and their elasticity, allows a
great increase here in the range of movement which is largely transverse, the effect being to enlarge
(chiefly) the transverse diameter of the thorax.

COSTO-CHONDRAL ARTICULATIONS

The costo-chondral junctions are synarthroses. The rib has a concave surface
which receives the convex end of the cartilage. They are united by the continuity
of the strong periosteum and perichondrium.

CHONDRO-STERNAL ARTICULATIONS

These joints (Articulationes sternocostales) are diarthroses formed by the
junction of the cartilages of the sternal ribs with the sternum. The articular ends
of the cartilages (except the first) are somewhat enlarged, and present surfaces of
cylindrical curvature. The articular surfaces on the sternum for the first pair of
cartilages are placed close together on the dorsal border of the carinif orm cartilage ;
the other seven are placed laterally at the junctions of the segments. The capsules
are strong and tight; the first pair of joints has a common capsule, and the cartil-
ages articulate with each other medially. The ventral ends of the first pair of ribs
are firmly attached to each other by dense fibrous tissue, which is prolonged for-
ward along the upper margin of the carinif orm cartilage and is continuous behind with
the sternal ligament. Each of the other capsules is reinforced dorsally by the radiate
costo-stemal ligament (Ligamentum sterno-costale radiatum), composed of radi-
ating fibers which blend with the sternal ligament. Interarticular bands may be
present. The movement is rotation around a nearly vertical axis, except in the
case of the first pair of joints.

INTERCHONDRAL LIGAMENTS
The eighth and ninth costal cartilages are firmly united by fibrous tissue. The
chondro-xiphoid ligament attaches the ninth costal cartilage to the xiphoid carti-
lage. The remaining cartilages are rather loosely attached to each other by elastic
tissue.

THE ARTICULATIONS OF THE SKULL — SYNARTHROSES OF THE SKULL 217

STERNAL ARTICULATIONS
In the new-born foal the seven bony segments are united by persisting cartilage
(Synchondroses intersternales) . The last two segments coalesce within a few weeks
after birth. In old subjects there is more or less ossification of the intersternebral
cartilage, which may lead to fusion of adjacent segments, especially posteriorly.
The internal sternal ligament (Lig. sterni proprium internum) lies on the thoracic
surface of the sternum. It arises on the first segment, and divides opposite the
second chondro-sternal joint into three bands. The median band passes back-
ward and spreads out on the last segment and the xiphoid cartilage. The lateral
branches — thicker and wider — lie along the lateral borders above the chondro-
sternal joints, and end at the cartilage of the eighth rib; they are covered by the
transversus thoracis muscle.

The Articulations of the Skull
mandibular articulation

This joint (Articulatio mandibularis) is a diarthrosis formed between the ramus
of the mandible and the squamous temporal bone on either side.

The articular surfaces are dissimilar in form and size. That on the squamous
temporal bone is concavo-convex, and the long axis is directed outward and some-
what forward; it consists of a condyle in front and a glenoid cavity, which is con-
tinued upon the postglenoid process behind. The mandible presents a trans-
versely elongated condyle.

The articular disc (Discus articularis) is placed between the joint surfaces,
which it renders congruent. Its surfaces are molded upon the temporal and man-
dibular surfaces respectively, and its circumference is attached to the joint capsule;
thus it divides the joint cavity into upper and lower compartments, the former being
the more room5^

The joint capsule is strong and tight. It is reinforced by two ligaments. The
lateral ligament (Lig. laterale) extends obliquely across the anterior part of the
lateral surface of the capsule, from which it is not distinctly separable. The pos-
terior ligament (Lig. posterius) is an elastic band which is attached above to the
postglenoid process, and below to a line on the posterior face of the neck of the
mandible.

Movements. — The chief movements take place around a transverse axis pass-
ing through both joints. Associated with this hinge-like action is slight gliding
movement, as in opening and shutting the mouth. When the mouth is shut,
the condyle of the mandible lies under the glenoid cavity. When the mandible
is depressed, the condyle moves forward under the articular eminence of the tem-
poral bone, carrying the disc with it. In protrusion and retraction of the lower
jaw the gliding movement just described occurs without the hinge-like rotation
of the condyle. These movements are similar in both joints. In the transverse
movements (as usually performed in mastication) the action consists of rotation
of the condyles around a vertical axis, while the disc glides forward on one side and
backward on the other.

SYNARTHROSES OF THE SKULL
Most of the bones of the skull are united with the adjacent bones by sutures;
a few are united by cartilage. The difference in the uniting medium depends on
the fact that most of these bones are developed in membrane, but some are pre-
formed in cartilage. Most of these joints are temporary, and are obliterated at

218 THE ARTICULATIONS OF THE HORSE

various periods during development and groAvth. Their importance lies in the
fact that so long as they persist, continuous growth is possible. They are usually
designated according to the bones which enter into their formation, e. g., spheno-
squamous, naso-frontal, etc.

Detailed description of the sutures has not sufficient clinical value to justify much addition
to the statements made in the osteology in this connection. The obhteration or closure of the
sutures is, however, worthy of brief mention. The cranial sutm-es are. usually all closed at seven
years, but the apex only of the petrous temporal is fused with the occipital and squamous temporal.
Most of the facial sutures are {practically closed at ten years, although complete synostosis may in
some be delayed for years or may not occur at all; the nasal suture, for example, usually persists
even in advanced age, so far as its anterior part is concerned.

The principal synchondroses are: (1) That between the basilar part of the
occipital bone and the bod}' of the sphenoid (Synchondrosis spheno-occipitalis) ;
(2) that between the presphenoid and postsphenoid (Synchondrosis intersphenoid-
alis); (3) those between the parts of the occipital bone (Synchondroses intraoc-
cipitales). The first is ossified at four or five years, the second at three years, and
the occipital bone is consolidated at two years.

The symphysis mandibulae ossifies at one to six months.

THE HYOIDEAN ARTICULATIONS

The temporo-hyoid articulation is an amphiarthrosis, in which the articular
angle of the dorsal end of the great cornu of the hyoid bone is attached by a short
bar of cartilage to the hyoid process of the petrous temporal bone. The cartilage
(Arthrohyoid) is about half an inch (ca. 1-1.5 cm.) in length. The chief move-
ment is hinge-like, the axis of motion passing transversely through both joints.

The intercomual articulation is an amphiarthrosis formed by the junction of
the ventral extremity of the great cornu with the dorsal end of the small cornu of
the hyoid bone. They are united by a very short piece of cartilage, in which there
is usually a small nodule of bone in the young subject. This nodule, the epihyoid
or middle cornu, is usually fused with the great cornu in the adult. The chief
movement here is also hinge-like, the angle between the cornua being increased or
diminished.

The basi-comual articulation is a diarthrosis formed b^^ the junction of each
small cornu with the body of the hyoid bone. The small cornu has a concave facet
which articulates with the convex facet on either end of the dorsal surface of the
body. The capsule is ample enough to allow considerable movement, which is
chiefly hinge-like.

The m.ovements of the hyoid bone are concerned chiefly in the acts of mastica-
tion and swallowing. In the latter the ventral parts of the hyoid bone are moved
forward and upward, carrying the root of the tongue and the larynx with them,
and then return to their former position.

The Articulations of the Thoracic Limb

In the absence of the clavicle the thoracic limb forms no articulation with the
trunk, to which it is attached by muscles. The movement of the shoulder on the
chest-wall is chiefly rotation around a transverse axis passing through the scapula
behind the upper part of the spine.

THE SHOULDER JOINT

The shoulder or scapulo-humeral joint (Articulatio scapulo-humeralis) is
formed by the junction of the distal end of the scapula with the proximal end of
the humerus. The articular siufaces are: (1) On the scapula, the glenoid cavity;

THE ELBOW JOINT

219

(2) on the humerus, the head. Both surfaces are approximately spherical and
similar in curvature, but the humeral surface is about twice as extensive as that of
the scapula.

The joint capsule is ample enough to allow the bones to be drawn apart about
an inch (ca. 2-3 cm.) ; but this requires a very considerable amount of force unless
air is admitted into the joint cavity. The fibrous layer is not attached to the mar-
gin of the joint surfaces, but at a distance of one to two centimeters from it. It is
strengthened in front by two diverging elastic bands, which arise on the tuber
scapulae and end on the tuberosities of the humerus. A pad of fat is interposed
between the capsule and the tendon of the biceps.

Ligaments are absent from this joint, but the muscles and tendons around it
afford remarkable security, so that dislocation very seldom occurs. The large ex-
tent of the head of the humerus is also of importance in this regard.

The principal muscles which are attached around the joint and act as ligaments are:
laterally, the supraspinatus, infraspinatus, and teres minor; medially, the subscapularis ; in
front, the biceps and supraspinatus; behind, the triceps. Fibers of the brachialis are attached to
the lower edge of the posterior part of the joint capsule, and would evidently tense the latter. In
some cases the joint cavity communicates with the bicipital or intertuberal bursa.

Movements. — While it is a typical enarthrosis in structure, and capable of the
various movements of the ball-and-socket joint, the chief normal movements are
flexion and extension. In the position of rest the angle formed between the scapula
and humerus posteriorly is about 110° to 120°; in flexion it is reduced to about 80°,
and in extension it is increased to about 145°. Adduction and abduction are very
restricted, the former being limited chiefly by the infraspinatus, the latter by the
subscapularis and the low insertion of the superficial pectoral muscles. Rotation
is somewhat freer, but does not exceed 33° when
all the muscles are removed (Franck).

THE ELBOW JOINT

This, the cubital articulation (Articulatio
cubiti), is a ginglymus formed between the dis-
tal extremity of the humerus and the proximal
ends of the radius and ulna.

The articular surfaces are: (1) A trochlear
surface formed by the condyles of the humerus
and the ridge between them ; (2) the correspond-
ing glenoid cavities and groove on the proximal
extremity of the radius, together with the semi-
lunar notch of the ulna.

The articular surface of the condyles does not ex-
tend upon the back of the extremity, but the groove which
receives the semilunar notch of the ulna extends up into
the olecranon fossa. In the fore part of the gi'oove there
is a synovial fossa. The surface on the lateral condyle is
much smaller than that of the medial one, and is sub-
divided into two unequal parts by a shallow furrow. On
the lower part of the semilunar notch and the adjacent
part of the ridge on the radius are synovial fossis.

The joint capsule is extremely thin behind,
where it forms a pouch in the olecranon fossa
under the anconeus muscle and a pad of fat.

Fig. 231. — Left Elbow Joint of Horse;
Posterior View. The Capsule is Re-
moved. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)

In front it is strengthened by
oblique fibers (Ijig. ol)liquum or anterior ligament), and on each side it fuses
with the collateral ligaments. It also is adherent to the tendons of muscles
which arise from the distal end of the humerus or end on the proximal end of the
radius. The synovial membrane sends prolongations to the small radio-ulnar

220

THE ARTICULATIONS OF THE HORSE

THE RADIO-ULNAR ARTICULATION THE CARPAL JOINTS 221

joints and also pouches downward under the origins of the flexors of the digit and
the lateral flexor of the carpus. There are two collateral ligaments.

The medial ligament (Lig. collaterale radiale) is attached above to an
eminence on the medial epicondyle of the humerus, and divides into two parts:
the long, superficial part ends on the medial border of the radius, just below the
level of the interosseous space; the deep, short part is inserted into the medial tu-
berosity of the radius.

The lateral ligament (Lig. collaterale ulnare) is short and strong. It is at-
tached above to a depression on the lateral epicondyle of the humerus, and below
to the lateral tuberosity of the radius, just below the margin of the articular surface.

Movements. — This joint is a typical ginglymus, the only movements being
flexion and extension around an axis which passes through the proximal attachments
of the collateral ligaments. In the standing position the articular angle (in front) is
about 140° to 150°. The range of movement is about 55° to 60°. Complete ex-
tension is prevented chiefly by the tension of the collateral ligaments and the biceps
muscle. (The axis of movement is slightly oblique, so that in flexion the forearm
is carried somewhat outward.)

THE RADIO-ULNAR ARTICULATION

In the foal the shaft of the ulna is attached to the radius above and below the
interosseous space by the interosseous ligament of the forearm (Lig. interosseum
antibrachii). Below the space the two bones become fused before adult age is
reached. Above the space the ligament usually persists, but may undergo more
or less ossification in extreme old age. The transverse or arciform ligament (Lig.
transversum ulnare et radiale ulnae et radii) consists of fibers which pass above the
interosseous space from each border of the shaft of the ulna to the posterior sur-
face of the radius. The proximal radio-ulnar articulation (Articulatio radio-ulnaris
proximalis), formed by two small convex facets on the ulna and the corresponding
facets on the posterior surface of the proximal extremity of the radius, is inclosed
in the capsule of the elbow-joint and does not require separate consideration. The
distal extremity of the ulna fuses early with the radius, and is therefore regarded
usually as a part of the latter.

Movement. — This is inapprecia])le, the forearm being fixed in the position of
pronation.

THE CARPAL JOINTS

These joints taken together constitute the composite articulatio carpi, or what
is popularly termed the "knee-joint" in animals.^ This consists of three chief
joints, viz., (1) The radio-carpal or antibrachio-carpal joint (Articulatio radiocarpea)
formed by the distal end of the radius and the proximal row of the carpus; (2) the
intercarpal joint (Articulatio intercarpea), formed between the two rows of the car-
pus; (3) the carpo-metacarpal joint (Articulatio carpometacarpea), formed between
the distal row of the carpus and the proximal ends of the metacarpal bones. The
proximal and middle joints may be regarded as ginglymi, although they are not
typical or pure examples of hinge-joints. The distal joint is arthrodial. In addi-
tion there are arthrodial joints formed between adjacent bones of the same row
(Articulationes interossese). All these form a composite joint with numerous liga-
ments. The articular surfaces have been described in the Osteology.

The joint capsule may be regarded, so far as the fibrous part is concerned, as
being common to all three joints. It is attached close to the margin of the articu-

^ The term is a very unfortunate one, since it is a distinct misapplication of the name as it is
used in regard to man. It is, however, very firmly established, and appears likely to persist in-
definitely in the absence of a convenient popular equivalent.

222

THE ARTICULATIONS OF THE HORSE

- R

lar surface of the radius above and the metacarpus below; its deep face is also
attached to a considerable extent to the carpal bones and to the small ligaments.
Its anterior part, the dorsal carpal ligament, is loose, except during flexion, and
assists in forming the fibrous canals for the extensor tendons. Its posterior part,
the volar carpal ligament (Lig. carpi volare), is very thick and dense, and is closely
attached to the carpal bones. It levels up the irregularities of the skeleton here,
and forms the smooth anterior wall of the carpal canal. It is continued downward
to form the subcarpal or inferior check ligament, which blends with the tendon of
the deep flexor of the digit about the middle of the metacarpus, and may well be
regarded as the carpal (tendinous) head of that muscle.

The synovial membrane forms three sacs corresponding to the three joints.

The radio-carpal sac is the
most voluminous; it includes
the joints formed by the acces-
sory carpal bone, and also those
between the proximal carpal
bones as far as the interosseous
ligaments. The intercarpal sac
sends extensions upward and
downward between the bones
of the two rows as far as the
interosseous ligaments; it com-
municates between the third
and fourth carpal bones with
the carpo-metacarpal sac. The
latter is very limited in extent,
and is closely applied to the
bones; it incloses the carpo-
metacarpal joint, and lubri-
cates also the lower parts of
the joints between the distal
carpal bones and the inter-
metacarpal joints.

The lateral ligament (Lig.
carpi collaterale ulnare) is at-
tached above to the lateral
tuberosity of the distal end of
the radius. Its long superficial
part is attached below to the
proximal end of the lateral
small metacarpal chiefly, but
some fibers end on the large
metacarpal bone. A canal for the lateral extensor tendon separates a short deep
band which ends on the ulnar carpal bone. Other deep fibers connect the latter
with the fourth carpal bone, and the fourth carpal with the metacarpus.

The medial ligament (Lig. carpi collaterale radiale) resembles the preceding
in general, but is stronger and wider distally. It is attached above to the medial
tuberosity of the distal end of the radius and ends below on the proximal ends of
the large and medial small metacarpal bones. Deep fasciculi are detached to the
radial and second carpal bones. The first carpal bone, when present, is usuall^^
embedded in the posterior part of the distal end of the ligament. The posterior
part of the ligament is fused with the transverse ligament of the carpus (Lig. carpi
transversum), and concurs in the formation of a canal for the tendon of the flexor
carpi radialis.

Fig. 238.-

-Left Carpal Joints of Horse; Dors
Joint Capsule is Removed.

.L Vii

C. u.

Mc. IV

Mc. Ill

The

R, Lateral distal tuberosity of radius; M, medial ligament; L,
lateral ligament; C. r., radial carpal bone; C. u., ulnar carpal bone;
C. 3, third carpal bone; C. 4, fourth - carpal bone; Mc. Ill, Mc. IV,
metacarpal bones; 1, intermediate carpal bone; 2-6, dorsal ligaments.

INTERMETACARPAL JOINTS

223

A number of special short ligaments connect two or more adjacent bones; only the most
distinct of these will be described here.

The accessory carpal bone is connected with adjacent bones by three hgaments (Fig. 234).
The proximal one is a short band which extends from the accessory carpal in front of the groove on
its lateral face and is inserted into the distal end of the radius behind the groove for the lateral
extensor tendon. A middle band connects the accessory with tlie ulnar carpal. The distal liga-
ment consists of two strong bands which pass from the distal margin of the accessory to the fourth
carpal and the proximal end of the fourth
metacarpal bone; these bands transmit the
action of the muscles which are inserted into
the accessory carpal bone. The other bones
of the proximal row are connected by two
dorsal Ugaments, which are transverse m direc-
tion, and two interosseous Hgaments. An
oblique ligament passes from an eminence on
the volar surface of the radial carpal bone to
a small depression on the radius medial to the
facet for the accessory carpal bone.

Two ligaments connect the proximal and
distal rows posteriorly. The medial one joins
the radial to the second and third carpal, and
the lateral one attaches the ulnar to the third
and fourth carpals.

The bones of the distal row are con-
nected by two strong transverse dorsal
ligaments and two interosseous ligaments.

There are four carpo-metacarpal liga-
ments. Two obHque dorsal Hgaments (Ligg.
carpometacarpea dorsaHa) connect the third
carpal with the large metacarpal bone. Two
interosseous Hgaments pass downward from
the interosseous Hgaments of the distal row
to end in depressions of the opposed surfaces
of the proximal ends of the metacarpal bones.
Volar Hgaments (Ligg. carpometacarpea vo-
laria) connect the second and third carpal
bones with the metacarpus. Other short
special Ugaments have been described, but
some of them at least are artefacts.

Movements. — Taking the joint as
a whole, the chief movements are flex-
ion and extension. In the standing
position the joint is extended. When
the joint is flexed, shght transverse
movement and rotation can be pro-
duced by manipulation. The dorsal
part of the capsule is, of course, tense
during flexion, the volar part in exten-
sion.

The movement practically all occurs at
the radio-carpal and intercarpal joints, the
articular surfaces of which are widely separ-
ated in front during flexion, but remain in
contact behind. The distal row remains in
contact with the metacarpus. The inter-
mediate and ulnar carpals move together as

one piece, but the radial does not move so far as the intermediate, so that the dorsal and inter-
osseous Ugaments connecting these bones become tense and obUque in direction.

Fig. 239. — Left Carpal Joints op Horse; Volar View.
Accessory Carpal and Capsule have been Re-
moved.

R, Dist.al end of radius; M, medial ligament; L,
lateral ligament; 1, 2, ligaments connecting radial carpal
bone and radius; 3, ligament connecting intermediate
carpal with radius; 4, stump of ligament connecting inter-
mediate and accessory carpal ; 5, ligament connecting radial
and second carpal; 6, 6', ligaments connecting second
carpal and metacarpal bones; 7, 7', ligaments connecting
third carpal and metacarpal bone; 8, ligament connecting
ulnar and third and fourth carpal bones; 9, deep short part
of medial collateral ligament; 10, 11, 12, radial, inter-
mediate, and ulnar carpal bones; 13, 14, 1.5, second, third,
and fourth carpal bones; 16, 16', 17, metacarpal bones.
(Of the preceding volar ligaments, 1, 3, and 8 are distinct
from the capsule.)

INTERMETACARPAL JOINTS

The small joints formed between the proximal ends of the metacarpal bones
(Articulationes intermetacarpeae) are enclosed by the carpal joint capsule, as des-
cribed above. The opposed surfaces of the shafts of the bones are closely united by
an interosseous metacarpal ligament (Lig. interosseum metacarpi), which often
undergoes more or less extensive ossification.

224 THE ARTICULATIONS OF THE HORSE

THE FETLOCK JOINT

This, the metacarpo-phalangeal articulation (Articulatio metacarpo-phalangea),
is a ginglymus formed by the junction of the distal end of the large (third) meta-
carpal bone, the proximal end of the first phalanx, and the proximal sesamoid
bones.

Articular Surfaces. — The surface on the large metacarpal bone is approxi-
mately cylindrical in curvature, but is divided into two slightly unequal parts by a
sagittal ridge. This is received into a socket formed by the first phalanx below and
the two sesamoids together with the intersesamoid ligament behind. The latter
is a mass of fibro-cartilage in which the sesamoid bones are largely embedded. It
extends above the level of the sesamoids, and is grooved to receive the ridge on the
metacarpal bone; its volar surface forms a smooth groove for the deep flexor ten-
don.

The joint capsule is attached around the margin of the articular surfaces. It
is thick and ample in front; here a bursa is interposed between it and the extensor
tendons, but the tendons are also attached to the capsule. Posteriorly it forms a
thin-walled pouch which extends upward between the metacarpal bone and the
suspensory ligament about as high as the point of bifurcation of the latter.^ The
capsule is reinforced by two collateral ligaments.

The collateral ligaments, medial and lateral (Lig. collaterale ulnare, radiale),
are partially divided into two layers : the superficial layer arises from the eminence
on the side of the distal end of the large metacarpal bone, and passes straight to
the rough area below the margin of the articular surface of the first phalanx; the
deep layer, shorter and much stronger, arises in the depression on the side of the
distal end of the metacarpal bone, and passes obliquely downward and backward
to be inserted into the abaxial surface of the sesamoid and the proximal end of the
first phalanx.

The capsule is further strengthened by a layer of oblique fibers which pass over the collateral
ligament on either side and end on the extensor tendon and the proximal extremity of the first
phalanx. It may properly be regarded as fascia rather than ligament.

Movements. — These are of the nature of flexion and extension, the axis of
motion passing through the proximal attachments of the collateral ligaments. In
the ordinary standing position the joint is in a state of partial dorsal flexion, the
articular angle (in front) being about 140° to 150°. (In the hind limb it is about
5° greater.) Diminution of this angle (sometimes termed "overextension") is nor-
mally very limited on account of the resistance offered by the sesamoidean appa-
ratus, but it varies considerably in amount in different subjects. Volar flexion is
limited only by contact of the heels with the metacarpus. During volar flexion
a small amount of transverse movement is possible.

THE SESAMOIDEAN LIGAMENTS

Under this head will be described a number of important ligaments which are
connected with the sesamoid bones and form a sort of stay apparatus or brace.

The intersesamoidean ligament (Lig. intersesamoideum) not only fills the
space between and unites the sesamoid bones, but also extends above them, enter-
ing into the formation of the articular surface of the fetlock joint. Other facts
in regard to it have been given above.

The collateral sesamoidean ligaments, lateral and medial (Ligg. sesamoidea

^ This pouch is in part bound down by a layer of elastic tissue which arises by two branches
from the distal part of the volar surface of the shaft of the large metacarpal bone and ends on the
intersesamoid ligament. It was first described by Skoda who terms it the lig. metacarpo-inter-
sesamoideum.

THE SESAMOIDEAN LIGAMENTS

225

ulnare et radiale), arise on the abaxial surface of each sesamoid bone, pass forward,
and divide into two branches, one of which ends in the depression on the distal end
of the large metacarpal bone, the other on the eminence on the proximal end of the
first phalanx. They are partly covered by the branches of the suspensory or
superior sesamoidean ligament.

The suspensory ligament or interosseous tendon (Tendo interosseus)i lies in
great part in the metacarpal groove, where it has the form of a wide, thick
band. It is attached above to the proximal part of the posterior surface of the large

Extensor tendon

Proximal end of capsule of fetlock
joint

Bursa

Collateral ligament of fetlock joint
Fascia

Branch of suspensory ligament

Lateral volar ligament of pastern if^

joint

Suspensory ligament of navicidar
bone
Band from cartilage to extensor
tendon
Collateral ligament of coffin joint

Superficial flexor tendon
Deep flexor tendon
Suspensory ligament
Lateral interosseous tendon

Proximal end of digital sheath
Ring of superficial flexor tendon
I ntersesamoidean ligament
Posterior annular ligament (cut)

Collateral sesamoidean ligament
Superficial distal sesamoidean

ligaynent
Middle distal sesamoidean ligament

Attachments of proximal digital
annular ligament

Pouch of digital sheath

Distal digital annular ligament
Cartilage of third phalanx

Fig. 240. — Ligaments and Tendons of Distal Part of Limb of Horse.

Mc.in, Large metacarpal bone; Ph. I, first phalanx; Ph.H, second phalanx; Ph.IH, third phalanx; 1, deep flexor

tendon; 2, band from first phalanx to digital cushion. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

metacarpal bone and to the distal row of carpal bones. At the distal fourth of the
metacarpus it divides into two diverging branches. Each branch passes to the
abaxial face of the corresponding sesamoid, on which a considerable part is attached.
The remainder passes obliquely do^vnward and forward to the dorsal surface of the
first phalanx, where it joins the extensor tendon; there is a bursa between this ex-
tensor branch and the proximal end of the first phalanx. This ligament possesses

^ This is also known as the superior sesamoidean Hgament; it is described here in deference
to custom and on account of its Ugamentous function.
15

226

THE ARTICULATIONS OF THE HORSE

considerable elasticity, and is the highly modified interosseous medius muscle. It
consists mainly of tendinous tissue, but contains a variable amount of striped mus-
cular tissue, especially in its deep part and in young subjects. Its principal func-
tion is to support the fetlock, i. e., to prevent excessive dorsal flexion of the joint
when the weight is put on the limb. The branches which join the common exten-
sor tendon limit volar flexion of the interphalangeal joints in certain phases of move-
ment. ^

The distal sesamoidean ligaments are three in number. The superficial or

Large metacarpal bone

Lateral small metacarpal bone

Bifurcation of suspensory
ligament

Bifurcation of common digital artery
Medial digital artery

Oblique or middle distal sesamoid
ligament
Straight or superficial distal
sesamoid ligament

Distal annular ligament of digit (cut
and reflected)

Capsule of fetlock joint (proximal

pouch)
Sesarnoid groove

Volar annular ligament of fetlock
(cut and reflected)

Lateral sesamoid ligament
Stump of proximal digital annular

ligament
Extensor branch of suspensory

ligament
Volar ligaments of pastern joint

Insertion of superficial flexor

tendon
Fibrous plate
Deep flexor tendon

Lateral ligament of pastern joint
Distal end of digital sheath
Suspensory ligament of navicular

bone
Dorsal branch of digital artery
Volar branch of digital artery

Fig. 241. — Deep Dissection of Distal Part of Right Fore Limb of Horse, Showing Joints and Ligaments;

Posterior View.
1, Cartilage of third phalanx; 2, flexor surface of navicular bone; 3, diatal navicular ligament; 4, insertion of
deep flexor tendon. Small arrows point to openings made in capsules of pastern and coffin joints. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)

straight sesamoidean ligament (Lig. sesamoideum rectum) is a flat band and is
somewhat wider above than below. ^ It is attached above to the bases of the sesa-
moid bones and the intersesamoid ligament, below to the complementary fibro-
cartilage of the proximal end of the second phalanx. The middle sesamoidean
ligament is triangular, with thick, rounded margins (Ligg. sesamoidea obliqua) and
a thin central portion.^ Its base is attached to the sesamoid bones and intersesa-

* This is often called the Y-shaped ligament — a rather undesirable name, since it is not
bifurcate.

^ It is also called the V-shaped ligament.

THE SESAMOIDEAN LIGAMENTS

227

moid ligament, and its deep face to the triangular rough area on the volar surface
of the first phalanx. The deep or cruciate sesamoidean ligaments (Ligg. sesamoidea
cruciata) consist of two thin layers of fibers which arise on the base of the sesa-
moid bones, cross each other, and end on the opposite eminence on the proximal
end of the first phalanx.

The two short sesamoidean ligaments (Ligg. sesamoidea brevia) are best seen

Skin

Tendon of common extensor

Bursa

Capsule of fetlock joint
Cavity of fetlock joint

Cavity of pastern joint

Cavity of coffin joint

Middle sesamoidean ligament
Digital synovial sheath
Cavity of pastern joint
Superficial sesamoidean ligament
Deep flexor tendon
Distal end of digital sheath

Digital cushion

Corium of periopl
Periople

Coronary corium

Wall

Laminae

Sole Corium of sole
Fig. 242. — Sagittal Section of Digit and Distal Part of Metacarpus op Horse.
A, Metacarpal bone; B, first phalanx; C, second phalanx; D, third phalanx; E, distal sesamoid bone; 1, volar
pouch of capsule of fetlock joint; 2, intersesamoidean ligament; 3, 4, proximal end of digital synovial sheath; 5, ring
formed by superficial flexor tendon; 6, fibrous tissue underlying ergot; 7, ergot; 8, 9, 9', branches of digital vessels; 10,
distal ligament of distal sesamoid bone; 11, suspensory ligament of distal sesamoid bone; 12, 12', proximal and distal
ends of bursa podotrochlearis. By an oversight the superficial flexor tendon (behind 4) is not marked.

by opening the joint in front and pushing the sesamoid bones backward; they
are covered by the synovial membrane. Each is a short band which extends from
the anterior part of the base of the sesamoid bone outward or inward to the posterior
margin of the articular surface of the first phalanx.

The distal sesamoidean ligaments may be regarded as digital continuations
of the suspensory ligament, the sesamoid bones being intercalated in this remark-
able stay apparatus, by which the fetlock is supported and concussion diminished.

228 THE ARTICULATIONS OF THE HORSE

THE PASTERN JOINT

This, the proximal interphalangeal articulation (Articulatio interphalangea
proximalis s. phalangis secundffi), is a ginglymus formed by the junction of the
distal end of the first phalanx and the proximal end of the second phalanx.

The articular surfaces are: (1) On the first phalanx, two slightly unequal con-
vex areas ^Adth an intermediate shallow groove; (2) on the second phalanx, a cor-
responding surface, completed behind by a plate of fibro-cartilage.

The joint capsule is close-fitting in front and on the sides, where it blends with
the extensor tendon and the collateral ligaments respectively. Behind it pouches
upward a little and is reinforced by the straight sesamoidean ligament and the
branches of the superficial fiexor tendon.

There are two collateral and four volar ligaments.

The collateral ligaments, medial and lateral (Lig. collaterale rachale, ulnare),
are very short and strong bands which are attached above on the eminence and de-
pression on each side of the distal end of the first phalanx, and below on the em-
inence on each side of the proximal end of the second phalanx. The direction of
the ligaments is about vertical and, therefore, does not correspond to the digital
axis.

The volar ligaments (Ligg. volaria) consist of a central pair and lateral and
medial bands which are attached below to the posterior margin of the proximal end
of the second phalanx and its complementary fibro-cartilage. The lateral and
medial ligaments are attached above to the middle of the borders of the first phalanx,
the central pair lower down and on the margin of the triangular rough area.

These ligaments are very commonly thickened as a result of clironic inflammation, and then
are not well defined. The central ones blend below with the branches of the superficial flexor
tendon and with the straight sesamoidean Ugament.

Movements. — These are very limited, and consist of flexion and extension.
The axis of motion passes transversely through the distal end of the first phalanx.
In the standing position the joint is extended. A small amount of volar flexion is
possible, and in this position slight lateral and medial flexion and rotation can be
produced by manipulation. Dorsal flexion is prevented by the lateral, volar, and
straight sesamoidean ligaments.

THE COFFIN JOINT

This joint, technically termed the distal interphalangeal articulation (Articu-
latio interphalangea distalis s. phalangis tertise), is a ginglymus formed by the junc-
tion of the second and third phalanges and the distal sesamoid bone.

Articular Surfaces. — The surface on the distal end of the second phalanx is
convex in the sagittal direction, concave transversely. The articular surface of the
third phalanx slopes sharply upward and forward; its central part is prominent,
and is flanked by two glenoid cavities. It is completed behind by the articular
surface of the distal sesamoid or navicular bone.

Joint Capsule. — This is attached around the margins of the articular surfaces.
In front and on the sides it is tight, and is blended with the extensor tendon and the
collateral ligaments respectively. It forms a considerable pouch behind, which
extends upward to about the middle of the second phalanx, where it is separated by
a fibrous membrane from the digital synovial sheath. On each side small pouches
project (especially during volar flexion) against the cartilages of the third phalanx
just behind the collateral ligaments.^

Ligaments. — The collateral ligaments, medial and lateral (Lig. collaterale

' Tliis should be noted in regard to resection of the cartilage or other operations in this
vicinity.

THE ARTICULATIONS OF THE PELVIC LIMB

229

ulnare, radiale), are short, strong bands v/hich are attached above in the depressions
on either side of the lower part of the second phalanx, under cover of the cartilage
of the third phalanx. They widen below and end in the depressions on either
side of the extensor process and on the anterior end of the cartilages.

The collateral sesamoidean or suspensory navicular ligaments, medial and
lateral (Lig. sesamoideum coUaterale ulnare, radiale),i are strong, somewhat elastic
bands, which form a sort of suspensory apparatus for the third sesamoid. They are
attached superiorly in and above the depressions on each side of the distal end of
the first phalanx and are here partly blended with the collateral ligaments of the
pastern joint. They are directed obliquely downward and backward, and end
chiefly on the ends and proximal border of the distal sesamoid, but detach a
branch to the axial surface of each cartilage and angle of the third phalanx.

The phalango-sesamoidean or distal navicular ligament (Lig. phalangeo-sesa-
moideum) reinforces the capsule distally. It is a strong layer of fibers which
extend from the distal border of the distal sesamoid to the flexor surface of the third
phalanx.

Movemenis.— 'The chief movements are flexion ana extension. In the stand-
ing position the joint is extended. During volar flexion a very small amount of
lateral movement and rotation can be produced by manipulation. Dorsal flexion
is very limited.

Dorsal flexion appears to be checked mainly by the deep flexor tendon, since in cases of rup-
ture of the latter the toe turns up. The mobility of the posterior part of the socket for the second
phalanx (formed by the distal sesamoid) diminishes concussion when the weight comes on the foot

LIGAMENTS OF THE CARTILAGES OF THE THIRD PHALANX

In addition to the bands mentioned above, which attach the cartilages to the
extremities of the navicular bone, there are three ligaments on either side which
attach the cartilages to the phalanges.

An ill-defined elastic band passes from the middle part of the border of the first
phalanx to the upper part of the cartilage, detaching a branch to the digital cushion.

A short, strong band connects the anterior extremity of the cartilage with the
rough eminence on the second pha-
lanx in front of the attachment of the
collateral ligament of the coffin joint.

The lower border of the cartil-
age is covered in part by fibers which
attach it to the angle of the third
phalanx.

The Articulations of the
Pelvic Limb

the sacro-iliac articulation

This joint (Articulatio sacro-
iliaca) is a diarthrosis formed be-
tween the auricular surfaces of the
sacrum and ilium. These surfaces
are not smooth in the adult, but are

marked by reciprocal eminences and depressions, and are covered by a thin laj^er of
cartilage. The joint cavity is a mere cleft, and is often crossed by fibrous bands.

Sacro-iliac
articulation

243. — Left Sacro-iliac Articulation of Horse; An-
terior View. (Adapted from Schmaltz, Atlas d. Anat.
d. Pferdes.)

^ These are termed the postero-lateral ligaments by M'Fadyean.
suspensory ligaments of the navicular bone.

Functionally they are

230 THE ARTICULATIONS OF THE HORSE

The joint capsule is very close fitting, and is attached around the margins of
the articular surfaces. It is reinforced by the ventral sacro-iliac ligament (Lig.
sacro-iliacum ventrale), which surrounds the joint; this is exceedingly strong above,
where it occupies the angle between the ilium and the wdng of the sacrum; it con-
sists chiefly of nearly vertical fibers.

The movements are inappreciable in the adult — stability, not mobility, being
the chief desideratum.

LIGAMENTS OF THE PELVIC GIRDLE

The following ligaments (Ligg. cinguli extremitatis pelvinse) may be regarded
as accessory to the sacro-iliac joint, although not directly connected with it:

Fig. 244. — Pelvic Ligaments and Hip Joint.
1, Dorsal sacro-iliac ligament; S, lateral sacro-iliac ligament; 3, saero-sciatic ligament; 4. greater sciatic foramen;
S, lesser sciatic foramen; 6, line of attachment of intermuscular septum between biceps femoris and semitendinosus;
7, capsule of hip joint; 8, capsularis muscle; 9, lateral tendon of origin of rectus femoris; 10, tuber sacrale; 11, tuber
cox«; /;?, shaft of ilium; ^i?, superior ischiatic spine; /4. pubis; 7.J, tuber ischii; iff, trochanter major; / 7, semimem-
branosus; IS, fifth lumbar spine; 19, 20, first and second coccygeal vertebrae.

The dorsal sacro-iliac ligament (Lig. sacro-iliacum dorsale breve) is a strong
band which is attached to the tuber sacrale and the summits of the sacral spines.

The lateral sacro-iliac ligament (Lig. sacro-iliacum dorsale longum) is a tri-
angular, thick sheet which is attachetl in front to the tuber sacrale and adjacent
part of the medial border of the ilium above the great sciatic notch, and below to
the lateral border of the sacrum. It blends above with the dorsal sacro-iliac liga-
ment, below with the sacro-sciatic ligament, and behind with the coccygeal fascia.

The sacro-sciatic ligament (Lig. sacroischiadicum s. sacrospinosum et tuber-
osum) is an extensive quadrilateral sheet which completes the lateral pelvic wall.

SYMPHYSIS PELVIS THE HIP JOINT 231

Its dorsal border is attached to the border of the sacrum and the transverse processes
of the first and second coccygeal vertebrae. Its ventral border is attached to the
superior ischiatic spine and tuber ischii. Between these it bridges over the lateral
border of the ischium and completes the lesser sciatic foramen (Foramen ischiadi-
cum minus). The anterior border is concave, and completes the greater sciatic
foramen (Foramen ischiadicum majus). The posterior border is fused with the
vertebral head of the semimembranosus muscle.

The lesser sciatic foramen is closed, except where the tendon of the obturator internus and
a vein pass tlirough it, by a thin fibrous sheet given off from the sacro-sciatic ligament.

The ilio-lumbar ligament (Lig. ilio-lumbale) is a triangular sheet which at-
taches the ends of the lumbar transverse processes to the ventral surface of the
ilium below the attachment of the longissimus muscle (Fig. 273) .

SYMPHYSIS PELVIS
The symphysis pelvis is formed Ijv the junction of the two ossa coxarum at
the ventral median- line. In the young subject the bones are united by a layer of
cartilage (Lamina fibrocartilaginea) ; in the adult the latter is gradually replaced
by bone, the process beginning in the pubic portion and extending backward,
but commonly the ischia are in part not fused. The union is strengthened by
white fibrous tissue dorsally and ventrally. A transverse band also covers the
anterior border of the pubis, and other fibers (Lig. arcuatum ischiadicum) extend
across at the ischial arch. No appreciable movement occurs even before synosto-
sis takes place.

OBTURATOR MEMBRANE

This (Membrana obturatoria) is a thin layer of fibrous tissue which covers the
obturator foramen, leaving, however, a passage (Canalis obturatorius) for the
obturator vessels and nerve.

THE HIP JOINT

This joint (Articulatio coxae) is an enarthrosis formed by the proximal end of
the femur and the acetabulum.

Articular Surfaces. — The head of the femur presents an almost hemispherical
articular surface, which is continued a short distance on the upper surface of the
neck. It is more extensive than the socket which receives it. It is cut into medi-
ally by a deep notch for the attachment of the round and accessory ligaments.
The acetabulum is a typical cotyloid cavity. Its articular surface is somewhat
crescentic, being deeply cut into medially by the acetabular notch and fossa.

The acetabulum is deepened by a ring of fibro-cartilage, the cotyloid ligament
(Labrum glenoidale), which is attached to the bony margin; that part of the liga-
ment which crosses the notch is called the transverse acetabular ligament (Lig.
transversum acetabuli) (Fig. 291).

The joint capsule is roomy. It is attached around the margin of the acetab-
ulum and the neck of the femur. It is thickest laterally.

The attachment on the femur is about 1 cm. from the margin of the articular surface, except
above, where 2 to 3 cm. of the neck is intracapsular. A thin, oblique band corresponding in direc-
tion with the capsularis muscle reinforces the antero-lateral part of the capsule; this appears to
be the feeble homologue of the very strong ilio-femoral ligament of man. The capsule is very
thin under the iho-psoas, and is adherent to the muscle. Its fibrous part is perforated medially
by the accessory and round ligaments and the articular

The round ligament (Lig. teres) is a short, strong band which is attached
in the subpubic groove close to the acetabular notch, passes outward, and ends
in the notch on the head of the femur (Fig. 581).

232 THE ARTICULATIONS OF THE HORSE

The accessory ligament (Lig. accessorium)i does not occur in the domestic
animals other than the equidse. It is a strong band detached from the prepubic
tendon of the abdominal muscles (Fig. 581). It is directed outward, backward,
and upward, passes through the acetabular notch dorsal to the transverse ligament,
and ends behind the round ligament in the notch on the head of the femur. The
origin of the pectineus muscle is perforated by the ligament, which furnishes at-
tachment to many fibers of the muscle.

The synovial membrane is reflected over the intracapsular parts of these lig-
aments and covers the fossa acetabuli. A pouch also extends from the acetabular
notch for a variable distance along the subpubic groove above the accessory liga-
ment.

Movements. — This joint is capable of all the movements of a ball-and-socket
joint, viz., flexion, extension, abduction, adduction, rotation, and circumduction.
The greatest range of movement is displayed in flexion and extension. When
standing at rest, the joint is partially flexed, the articular angle (in front) being
about 100° to 115°. The other movements occur to a very limited extent in normal
action. Abduction appears to be checked by tension of the round and accessory
ligaments. The accessory ligament is tensed most promptly by inward rotation of
the thigh.

THE STIFLE JOINT

This joint (Articulatio genu), which corresponds to the knee-joint of man,
is the largest and most elaborate of all the articulations. Taken as a whole, it
may be classed as a ginglymus, although it is not a typical example of the group.
In reality it consists of two joints — the femoro-patellar and the femoro-tibial.

The femoro-patellar articulation (Articulatio femoro-patellaris) is formed
between the trochlea of the femur and the articular surface of the patella.

Articular Surfaces. — The trochlea consists of two slightly oblique ridges,
with a wide and deep groove between them. The medial ridge is much the larger
of the two, especially at its proximal part, which is wide and rounded. The lateral
ridge is much narrower, and is more regularly curved; its proximal part lies about
an inch behind a frontal plane tangent to the medial one. The articular surface
of the patella is much smaller than that of the trochlea. It is completed medially
by a supplementary plate of fibro-cartilage (Fibrocartilago patellae), which curves
over the medial ridge of the trochlea. A narrow strip of cartilage is found along
the lateral border also. The articular cartilage on the trochlea completely covers
both surfaces of the medial ridge, but extends only a short distance on the lateral
surface of the outer ridge.

Joint Capsule. — This is thin and is very capacious. On the patella it is
attached around the margin of the articular surface, but on the femur the line of
attachment is at a varying distance from the articular surface. On the medial side
it is an inch or more from the articular cartilage; on the lateral side and above,
about half an inch. It pouches upward under the quadriceps femoris for a distance
of two or three inches, a pad of fat separating the capsule from the muscle. Be-
low the patella it is separated from the patellar ligaments by a thick pad of fat,
but inferiorly it is in contact with the femoro-tibial capsules. The joint cavity is
the most extensive in the body. It usually communicates with the medial sac of
the femoro-tibial joint cavity by a slit-like opening situated at the lowest part of
the medial ridge of the trochlea. A similar, usually smaller, communication with
the lateral sac of the femoro-tibial capsule is often found at the lowest part of the
lateral ridge.

The medial communication is rarely absent in adult horses, but is liable to be overlooked
on account of the fact that it is covered by a valvular fold of the synovial membrane. It is about

^ This is also commonly called the pubo-femoral ligament.

THE STIFLE JOINT

233

half an inch ^vnde, and bes under the narrow articular area wliich connects the trochlea and medial
condyle. Ihe lateral communication occui-s in 18 to 25 per cent, of cases, according to Baum; in
rare cases it is larger than the inner one. It is instructive to distend this capsule and thus obtain
an idea of its potential capacity and relations (Fig. 246).

Ligaments. — The femoro-patellar ligaments, lateral and medial (Lig. femoro-
patellare fibulare, tibiale), are two thin bands which reinforce the capsule on either

Patella

Accessory cartilage of —
patella

Medial ridge of trochlea
Medial patellar ligament

Medial epicondyh

Medial femoro-tibial
ligament

Medial meniscus
Medial condyle of tibia

Tuberosity of tibia

Biceps femoris

Lateral patellar ligament

Lateral femoro-tibial
ligament

Lateral meniscus
Lateral condyle of tibia

Interosseous space

Fibula

hderosseous ligament

Fig. 245. — Left Stifle Joint of Horse; Froxt View. The Capsules are Removed.
1, Middle patellar ligament; 2, stump of fascia lata; 3, stump of common tendon of extensor longus and peroneus

side. The lateral ligament is fairly distinct; it arises from the lateral epicondyle of
the femur just above the lateral femoro-tibial ligament, and ends on the lateral
border of the patella. The medial ligament is thinner and is not distinct from the
capsule; it arises above the medial epicondyle, and ends on the patellar fibro-car-
tilage.

The patellar ligaments (Ligg. patellae)^ are three very strong bands which at-

^ They are also termed the straight ligaments of the patella. This term seems objectionable
since they are all obUque in direction.

234

THE ARTICULATIONS OF THE HORSE

tach the patella to the tuberosity of the tibia. The lateral patellar ligament ex-
tends from the lateral part of the anterior surface of the patella to the lateral part
of the tubcrosit}^ of the tibia. It receives a strong tendon from the biceps femoris
muscle and also part of the fascia lata. The middle patellar ligament extends
from the front of the apex of the patella to the distal part of the groove on the
tuberosit}^ of the tibia; a bursa is interposed between the ligament and the upper
part of the groove, and a smaller one occurs between the upper part of the ligament
and the apex of the patella. The medial patellar ligament is attached above to the

Proximal end of
femoro- patellar

Lateral head of gastrocnemius

Lateral fetnoro-patellar ligament

Attachment of joint capsule
Lateral condyle of femur
Lateral fejnoro-tibial ligament-
Popliteus

Deep digital flexor

Base of patella

-Distal end of capsule
— -Middle patellar ligament
ll'^^ Medial patellar ligament

Lateral patellar ligament

{stump)

Tuberosity of tibia
Tibialis anterior

Long extensor

Lateral extensor

Fig. 246. — Right Stifle Joint of Horse; Latehal View.

The femoro-patellar capsule was filled with plaster-of-Paris and then removed after the cast was set. The femoro-

tibial capsule and most of the lateral patellar ligament are removed. M, Lateral meniscus.

patellar fibro-cartilage, and ends on the tuberosity of the tibia at the medial side of
the groove. It is joined by the common aponeurosis of the gracilis and sartorius,
and its proximal part furnishes insertion to fibers of the vastus medialis. These
so-called ligaments are, in reality, the tendons of insertion of the quadriceps
femoris and biceps fe-moris muscles, and transmit the action of the latter to the
tibia; they also function similarly for the other muscles attached to them as noted
above.

It will be noticed that the proximal attachments are further apart than the distal ones, so
that the ligaments converge below. The medial ligament is especially oblique. The middle
ligament is more deeply placed than the others, and therefore cannot usually be felt so distinctly
in the living animal. The lateral ligament is very largely the tendon of the anterior part of the

THE STIFLE JOINT

235

biceps femoris, but it also furnishes insertion to the tensor fasciae latse by means of the fascia
lata, which blends with it.

The femoro-tibial articulation (Articulatio femoro-tibialis) is formed between
the condyles of the femur, the proximal end of the tibia, and the interposed articular
menisci or semilunar cartilages.

Articular Surfaces. — The condyles of the femur are slightly oblique in direc-
tion. The articular surface of the lateral one is more strongly curved than that of
the medial one; the latter is confluent below with the medial ridge of the trochlea.

Base of patella

Medial condyle of
femur
Medial femoro-tibial
ligament
Medial meniscus

Medial condyle of
tibia

Accessory cartilage

'^Tf Medial ridge of trochlea

Medial patellar liga-

Middle patellar liga-
metd

Tuberosity of tibia

Fig. 247. — Left Stifle Joint of Horse; Medial View. The Capsules are Removed,

while the narrow ridge which connects the lateral condyle with the trochlea is
usually non-articular. The saddle-shaped surfaces of the condyles of the tibia are
not adapted to the femoral condyles, and are in contact with only a small part of
them.

The menisci, lateral and medial (Meniscus lateralis, medialis),i are two C-
shaped or crescentic plates of fibro-cartilage which produce congruence in the ar-
ticular surfaces. Each has a proximal concave surface adapted to the condyle of
the femur, and a distal surface which fits the corresponding condyle of the tibia.
1 These are also commonly termed the semilunar cartilages, although they are not so shaped.

236

THE ARTICULATIONS OF THE HORSE

The lateral meniscus does not cover the lateral and posterior part of the tibial con-
djde, over which the tendon of origin of the popliteus muscle plays. The peripheral
border is thick and convex, the central one very thin and concave. The fibrous
ends or ligaments are attached to the tibia in front of and behind the spine. The
lateral meniscus has a third attachment by means of an oblique band (Ligamentum
femorale menisci lateralis) which passes from the posterior end to the posterior
part of the intercondyloid fossa of the femur.

Base of patella

Medial ridge of
trochlea

Lateral patellar liga- :

ment

Middle patellar liga-
ment

Stump of biceps
femoris

La teralfem oro-pa tellar
ligament

Lateral condyle of
femur

Lateral femoro-tihial

ligament

Lateral meniscus

Lateral condyle of
tibia

Tvherosity of tibia

Fig. 248. — Left Stifle Joint of Honsio; Lateral Vie-v. The CAPSULEa are Remov

1, Stump of tendon of origin of extensor longus and peroneus tertius; 2, stump of fascia lata; 3, patellar attachment of
biceps femoris and lateral patellar ligament.

The ligaments of the medial meniscus (Ligamenta tibialia anterius et posterius menisci m.edi-
alis) are attached in front of and beliind the medial eminence of the spine. The anterior ligament
of the lateral meniscus (Ligamentum tibiale anterius menisci lateraUs) is attached in front of the
lateral eminence of the spine. The posterior one bifurcates; the lower branch (Ligamentum tibiale
posterius menisci lateralis) is inserted at the popliteal notch, the upper (Ligamentum femorale
menisci lateralis) in a small fossa in the extreme posterior part of the intercondyloid fossa.

The joint capsule is attached to the margin of the tibial articular surface,
but on the femur the line of attachment is for the greater part about half an inch
(ca. 1 cm.) from the articular margin. It is also attacterl to the convex borders of
the menisci and to the cruciate ligaments. It is thin in front, where it consists

THE STIFLE JOINT

237

practically of the synovial layer only. It is much stronger posteriorly: here it
is reinforced by what might be regarded as a posterior ligament. This is a
strong, flat band which arises from the femur just lateral to the origin of the medial
head of the gastrocnemius, and extends down to the posterior border of the medial
condyle of the tibia; it is wider below than above. There are two synovial sacs,
corresponding to the double nature of the articular surfaces; they do not usually
communicate, and each is partially divided into an upper and a lower compartment
by the meniscus. The medial sac pouches upward about half an inch over the con-

Lateral condyle of

Jem ur

Lateral femoro-

tibial ligament

Shimp of pop-

liteus tendon

Lateral meniscus

Lateral condyle of
tibia

Head of fibula

Interosseous space

Y* — Medial femoro-
'\\ tibial ligament

condyle of
femur

Medial meniscus

Medial condyle of
tibia

Fig. 249. — Left Stifle Joint of Horse; Posterior View. The Capsule is Removed.
1, Femoral ligament of lateral meniscus; 2, posterior ligament of lateral meniscus; 3, anterior cruciate ligament; 4,

posterior cruciate ligament.

clyle of the femur. The lateral sac invests the tendon of origin of the popliteus
muscle, and also pouches downward about three inches (ca. 7.5 cm.) beneath the
peroneus tertius and extensor longus muscles. As stated above, the lateral sac
sometimes communicates with the femoro-patellar joint cavity, and the medial
sac usually does so in the adult.

Ligaments. — There are four of these — two collateral and two cruciate.

The medial ligament (Lig. collaterale tibiale) is attached above to the prom-
inent medial epicondyle of the femur, and below to a rough area below the margin
of the medial condyle of the tibia.

238

THE ARTICULATIONS OF THE HORSE

The lateral ligament (Lig. collaterale fibulare) is somewhat thicker; it arises from
the upper depression on the lateral epicondj^e, and ends on the head of the fibula.

Middle patellar
ligament

Lateral patellar
ligament

Medial patellar
ligament

Medial condyle

Medial meniscus

Fig. 250. — Proximal End of Right Tibia with Menisci, Etc.
1, 2, Anterior and posterior cruciate ligaments; 3, posterior ligament of medial meniscus; 4, femoral ligament of
lateral meniscus; 5, 5', anterior ligaments of menisci; 6, groove for popliteus tendon; 7, spine of tibia; 8, 9, medial
and lateral femoro-tibial ligaments.

It covers the tendon of the origin of the popliteus muscle, a bursa being interposed

between the two; another bursa is present
between the lower part of the ligament and
the margin of the lateral condyle of the tibia.
The cruciate ligaments are two strong
rounded bands situated mainly in the inter-
condyloid fossa of the femur, between the two
synovial sacs. They cross each other some-
what in the form of an X, and are named ac-
cording to their tibial attachments. The
anterior cruciate ligament (Lig. cruciatum an-
terius) arises in the central fossa on the tibial
spine, extends upward and backward, and ends
on the lateral wall of the intercondyloid fossa.
The posterior cruciate ligament (Lig. crucia-
tum posterius) is medial to the preceding, and
is somewhat larger. It is attached to an emi-
nence at the popliteal notch of the tibia, is
directed upward and forward, and ends in the
anterior part of the intercondyloid fossa of
the femur.

It may be added that these ligaments do not lie in a sagittal plane, but are somewhat twisted
across each other; outward rotation of the leg untwists and slackens them.

Movements. — The principal movements of the stifle joint as a whole are

Fig. 251. — Proximal End of Right Tibia of
Horse, with Areas of Ligamentous At-
tachment.
1, 2, Medial and lateral patellar ligaments;

3, 4, anterior ligaments of menisci; 5, 7, anterior

and posterior cruciate ligaments; 6, posterior

ligament of medial meniscus.

TIBIO-FIBULAR ARTICULATION THE HOCK JOINT 239

flexion and extension. In the ordinary standing position the articular angle
(behind) is about 140° to 150°. Flexion is limited only by contact of the leg with
the thigh, if the hock is also flexed. Extension is incomplete, i. e., the femur and
tibia cannot be brought into the same straight line. Rotation is limited, and is
freest during semiflexion. The patella glides on the femoral trochlea upward in
extension, downward in flexion.

Extension is checked mainly by tension of the cruciate and collateral ligaments. In extreme
extension, which is accompanied by slight outward rotation of the leg, the patella can be pushed
upward and inward so that its fibro-cartilage hooks over the upper end of the medial ridge of the
trochlea, but it will not remain there unless held in position. When pressure is removed, the base
of the patella tips forward and the cartilage lies upon the most prominent part of the trochlear
ridge. During flexion, which is accompanied by slight inward rotation of the leg, the condyles
of the femur and the menisci gUde backward on the tibia; the movement of the lateral condyle
and meniscus is gi-eater than that of the medial one. In extreme flexion the patellar and posterior
cruciate ligaments are tense; the other ligaments are relaxed. The movement of the patella is
gliding with coaptation, i. e., different parts of the opposing articular surfaces come into contact
successively. Only a narrow transverse strip (ca. 1.5-2 cm. wide) of the patella is in contact
with the trochlea at a time.

TIBIO-FIBULAR ARTICULATION

This joint (Articulatio tibiofibularis) is formed by the head of the fibula ar-
ticulating with a crescentic facet just below the outer margin of the lateral condyle
of the tibia. The joint capsule is strong and close. The shaft of the fibula is at-
tached to the lateral border of the tibia b}^ the interosseous membrane of the leg
(Membrana interossea cruris); this is perforated about an inch from its proximal
end by an opening which transmits the anterior tibial vessels to the front of the tibia.
A fibrous cord usually extends from the distal end of the shaft of the fibula to the
lateral malleolus. The latter is the distal end of the fibula which has fused with the
tibia. No appreciable movement occurs in this joint.

THE HOCK JOINT

This is a composite joint made up of a number of articulations (Artie ulationes
tarsi). These are: (1) The tibio-tarsal articulation; (2) the intertarsal articula-
tions; (3) the tarso-metatarsal articulation.

The tibio-tarsal articulation (Articulatio talocruralis) is a typical ginglymus
formed by the trochlea of the tibial tarsal bone and the corresponding surface of the
distal end of the tibia. The ridges and grooves of these surfaces are directed ob-
liquel}^ forward and outward at an angle of about 12° to 15° with a sagittal plane.
The trochlear surface is about twice as extensive as that on the tibia, and its ridges
have a spiral curvature. The other articulations are arthrodia, which have joint
surfaces and ligaments of such a nature as to allow only a minimal amount of glid-
ing motion.

As in the case of the carpal joints, it is convenient to describe first the common
capsule and ligaments, which are the more important practically, and then to
consider very briefly the special ligaments.

The fibrous part of the joint capsule is attached around the margin of the
tibial articular surface above and the metatarsal surfaces below; it is also attached
in part to the surfaces of the bones which it covers, and blends with the collateral
ligaments. Its dorsal part (anterior ligament) is rather thin; in distention of the
capsule, as in "bog-spavin," its antero-medial part, which is not bound down by
the tendons passing over the joint, forms a fluctuating swelling over the medial
ridge of the trochlea. The plantar part (posterior and tarso-metatarsal ligaments)
is very thick below, and is intimately attached to the tarsal bones. It is in part
cartilaginous, and forms a smooth surface for the deep flexor tendon. The proximal
part pouches upward behind the distal end of the tibia for a distance of about two

240

THE ARTICULATIONS OF THE HORSE

inches (ca. 5 cm.) ; here it is thin. It is continued downward to form the sub-
tarsal or check ligament, which unites with the deep flexor tendon about the mid-
dle of the metatarsus.

There are four synovial sacs: 1. The tibio-tarsal sac lubricates the proximal
joint, and is much the largest and most important.^ 2. The proximal intertarsal
sac lines the joints formed by the tibial and fibular tarsal bones above, and the cen-
tral and fourth tarsals below; it communicates in front with the til)io-tarsal sac.
3. The distal intertarsal sac lubricates the joints formed between the central tarsal
and the bones below and on either side. 4. The tarso-metatarsal sac lubricates

Tuber calcis

Medial malleolus

Long medial ligament
Trochlea of tibial tarsal bone

Dorsal ligament

ML III

ML II

Fig. 252. — Right Hock Joixt of Horse; Medial View. The Capsule is Removed.

1, 2, Branches of short part of medial ligament; 3, tarso-metatarsal ligament; 4, proximal tuberosity of tibial tarsal

bone; 5, sustentaculum; 6, groove for deep flexor tendon; Mt. II, Ml. Ill, metatarsal bones.

the joints formed between the tarsal and metatarsal bones, those between the
proximal ends of the metatarsal bones, and those formed by the third tarsal with
the bones on either side.

Common Ligaments. — The lateral ligament (Lig. collaterale fibulare) consists
of two distinct bands which cross each other. The long lateral ligament (Lig.
collaterale laterale longum) is superficial ; it arises on the posterior part of the lateral
malleolus, is directed almost straight downward, and is attached to the fibular and
fourth tarsal bones and the large and lateral small metatarsal bones. It forms a
canal for the lateral extensor tendon. The short lateral ligament (Lig. collaterale

^ It is this part of the capsule which is chiefly involved in distention by excess of fluid in the
joint cavity (as in "bog-spavin").

THE HOCK JOINT

241

laterale breve) is deeper; it arises on the anterior part of the lateral malleolus, is
directed chiefly backward, and ends on the rough excavation on the lateral surface
of the tibial tarsal and the adjacent surface of the fibular tarsal bone.

The medial ligament (Lig. collateral tibiale) also consists of two parts which
cross each other. The long medial ligament (Lig. collateral mediale longum)
is superficial; it arises on the posterior part of the medial malleolus, becomes wider
below, and is attached on the distal tuberosity of the tibial tarsal, the large and
medial small metatarsal bones, and the surface of the lower tarsal bones which it

Tuber calcis

Plantar ligament

ML IV

Short lateral ligament
Long lateral ligament

Fig. 253. — Right Hock .Joint or Hor.se; Lateral View. The Capsule is Removed.
1, Ligament connecting lateral ridge of tibial tarsal with processus cochlearis of fibular tarsal bone; 2, groove for
lateral extensor tendon; T. t., lateral ridge of trochlea of tibial tarsal bone; T. c, central tarsal bone; T. 3, third tarsal
bone; Mt. Ill, Ml. IV, metatarsal bones.

covers. The short medial ligament (Lig. collaterale mediale breve) lies largely
under cover of the long one. It extends from the anterior part of the medial malleo-
lus, runs backward and somewhat downward, and divides into two branches; one
of these ends on the proximal tuberosity on the medial surface of the tibial tarsal
bone, the other on the sustentaculum tali.

The plantar ligament (Lig. tarsi plantare)i is a very strong, flat band which
covers the outer part of the plantar surface of the tarsus. It is attached to the
plantar surface of the fibular and fourth tarsal bones and the proximal end of the
lateral metatarsal bone.

The dorsal ligament (Lig. tarsi dorsale)^ is a triangular sheet which is attached

^ Also termed the calcaneo-metatarsal ligament. ^ Also known as the oblique ligament.
16

242

THE ARTICULATIONS OF THE HORSE

above to the distal tuberosity on the medial face of the tibial tarsal bone, and
spreads out below on the central and third tarsal bones, and the proximal ends of
the large and outer small metatarsal bones, to all of which it is attached.

Special Ligaments. — A considerable number of short bands which connect
adjacent bones of the tarsus and metatarsus are described by various authors;
some of these are quite distinct; others are difficult to isolate. Most of them are
not of sufficient importance to justify detailed description.

Tuber calcis

Lateral malleolus

Short lateral ligament

Trochlea, of tibial tarsal
bone

Short tncdial ligaments

Ml. IV

Fig. 254. — Right Hock Joint of Horse. Viewed from the Front and Slightly Laterally After Removal of

Joint Cap.sule and Long Collateral Ligaments.

T. t., Tibial tarsal bone (distal tuberosity); T. c, central tarsal bone; T. 3, ridge of third tarsal bone; T.f., fibular tarsal

bone (distal end); T. 4, fourth tarsal bone; Mt. Ill, Mt. IV, metatarsal bones. Arrow points to vascular canal.

(1) The tibial and fibular tarsal bones are united by four bands (astragalo-calcaneal liga-
ments). The medial ligament extends from the sustentaculum tali to the adjacent part of the
tibial tarsal, blending with the short collateral ligament. The lateral ligament extends from the
cochlear process of the fibular tarsal to the adjacent part of the lateral ridge of the trochlea.
The proximal ligament extends from the posterior margin of the trochlea to the fibular tarsal.
The interosseous ligament is deeply placed in the sinus tarsi between the two bones, and is at-
tached in the rough areas of the opposed surfaces.

(2) The smaller bones are attached to each other as follows: The central and third tarsal are
united by an interosseous and an oblique dorsal ligament (scaphoido-cunean ligaments). The
central and fourth tarsal are united by an interosseous and a lateral transverse ligament (cuboido-
ecaphoid ligament). The third and fourth tarsals are similarly connected (cuboido-cunean liga-
ments). The third tarsal is joined by an interosseous (intercunean) ligament to the (fused) first
and second tarsals; the latter are connected with the fourth tarsal by a plantar transverse liga-
ment.

(3) The smaller bones are connected with the proximal row as follows; The central is

THE HOCK JOINT

243

attached to the tibial by plantar and interosseous (astragalo-scaphoid) ligaments, and to the fibular
tarsal by a short oblique (calcaneo-scaphoid) band. The fourth is attached to the fibular tarsal
by interosseous and plantar (calcaneo-cuboid) hgaments. The (fused) first and second tarsals
are connected with the fibular tarsal by a plantar (calcaneo-cunean) ligament.

(4) The distal tarsal bones are connected with the metatarsus by tarso-metatarsal hgaments,
which are not distinct from the common Hgaments, except in the case of the interosseous ligament
between the third tarsal and metatarsal bones.

Movements. — These are flexion and extension, which take place at the tibio-
tarsal joint. The movements between the tarsal bones, and between the latter
and the metatarsus, are so limited as to be negligible so far as the action of the joint
as a whole is concerned. In the standing position the articular angle (in front)

Superficial flexor tendon

Gastrocnemius tendon

Tarsal tendon of
biceps femoris

Calcanean bursa

Gastrocnemius
bursa

Tuber calcis-

Upper po^ich of
joint capsule

Tibial tarsal bone

Interosseous ligunient

Plantar ligament

Fourth tarsal bone

Interosseous ligament
Large metatarsal bone

Suspensory ligament
Check ligament

Tibia

Tibialis anterior
Peroneus tertius

Tibio-tarsal joint cavity
Joint capsule
Central tarsal bone
Third tarsal bone

Distal annular ligament

Fig. 255. — Sagittal Section of Hock of Horse.
The section is cut so far laterally that the deep flexor tendon does not show.

is about 150° to 160°. Complete extension is prevented by tension of the collateral
ligaments. Flexion is checked only by contact of the metatarsus with the leg,
provided the stifle joint is also flexed. Owing to the fact that the axis of motion
is slightly oblique, the lower part of the limb deviates somewhat outward during
flexion. The long collateral hgaments are tense in extension, the short ones in
flexion, of the joint. The movements of the hock joint must correspond with those
of the stifle on account of the tendinous bands in front and behind (peroneus tertius
and flexor superficialis), which extend from the lower part of the femur to the tarsus
and metatarsus.

The remaining joints differ in no material respect from those of the thoracic
limb.

244

COMPARATIVE ARTHROLOGY

COMPARATIVE ARTHROLOGY ^
Joints and Ligaments of the Vertebrje

Ox. — The ligamentum nuchse is better developed than in the horse. The
funicular part is clearly divided into two lateral halves, which are round at their
occipital attachment, but from the axis backward become rapidly Avider and fiat.
This wide portion is almost sagittal, lies on either side of the vertebral spines, and
is covered by the trapezius and rhomboideus muscles. From the highest part of
the withers (third thoracic spine) it gradually diminishes in size and fades out in
the lumbar region. The lamellar part is thick, and consists of anterior and pos-
terior parts. T'he anterior part is double; its fibers proceed from the funicular
part to the second, third, and fourth cervical spines. The posterior part is single;
its fibers extend from the first thoracic spine to the fifth, sixth, and seventh cervical
spines.

The ventral longitudinal ligament is very strong in the lumbar region.

Fig. 256. — Ligamentttm Nttch/e of Ox.

o, Funicular part; 6, its wide portion; <?, rf, lamellar part; e, interspinous ligament; ?, spinous process of first thoracic

vertebra; 2, axis (Ellenberger-Baum, Anat. d. Haustiere.)

The intervertebral fibro-cartilages are thicker than in the horse.

The interspinous ligaments of the back and loins consist largely of elastic
tissue.

There are no intertransverse joints in the lumbar region.

Pig. — The ligamentum nuchae is represented by a fibrous raphe and thin
layers of elastic tissue which extend between the cervical spines.

The atlanto-occipital and atlanto-axial joints resemble those of the dog.

The interspinous ligaments of the neck are elastic.

Dog. — The ligamentum nuchse consists of a small fibrous band which extends
from the spine of the axis to the anterior thoracic spines; it may be regarded as a
mere fibrous raphe between the right and left muscles.

There are interspinous muscles instead of ligaments in the neck.

There are three ligaments in connection with the dens of the axis. The two
alar ligaments (Ligg. alaria) arise on either side of the dens, diverge, and end on

^ This section consists necessarily only of a brief statement of the most important differences
in the joints of the other animals.

ARTICULATIONS OF THE THORACIC LIMB 245

either side of the foramen magnum. The transverse ligament of the atlas (Lig.
transversum atlantis) stretches across the dorsal surface of the dens and binds it
down on the ventral arch of the atlas, a bursa being interposed. It is attached on
either side to the lateral mass of the atlas.

The two capsules of the atlanto-occipital joint communicate with each other,
and usually with the capsule of the atlanto-axial joint also.

Articulations of the Thorax

Ox. — The second to the eleventh costo-chondral joints inclusive are diarthroses
with close capsules, reinforced externall}-. (They are synchondroses in the sheep.)
The upper parts of the cartilages are attached to each other by cUstinct elastic liga-
ments (Ligg. intercostalia) .

The first pair of chondro-sternal joints are separate from each other; inter-
crossing fibers unite the costo-chondral junctions above the joints.

The first segment of the sternum forms ^\dth the body a diarthrodial interstemal
joint (Articulatio intersternalis) . The anterior joint surface is concave, the pos-
terior convex. The joint is surrounded by a close capsule, and the joint surfaces
are attached to each by a small inter-articular ligament. Limited lateral move-
ment is possible. (In the sheep the joint is a synchondrosis.) Both surfaces of the
sternum are covered by a layer of fibrous tissue (Membrana sterni).

Pig. — The second to the fifth or sixth costo-chondral joints are diarthroses.
The intersternal articulation and the sternal ligaments resemble those of the ox.

Dog. — The first chondro-sternal joints do not coalesce. The internal sternal
ligament divides into three bands.

TEMPORO-MANDIBULAR ARTICULATION

Ox. — The articular surfaces are of such a character as to permit more extensive
transverse movement than in the horse {vide Osteology). The posterior ligament
is absent.

Pig. — The considerable longitudinal diameter of the temporal articular sur-
faces and the very small size of the postglenoid process allow great freedom of
protraction and retraction of the lower jaw. Transverse movement is limited.
The posterior ligament is absent.

Dog. — The articular surfaces allow extremely little transverse or gliding move-
ment. They are cylindrical in curvature, and the interarticular disc is very thin.
The posterior ligament is absent.

The other articulations of the skull are sufficiently described in the Osteology.

Articulations of the Thoracic Limb
shoulder joint

Ox. — The articular angle is about 100°.

Pig and Dog. — The joint capsule communicates so freely with the bicipital
bursa that the latter may well be regarded as a pouch of the capsule. There is a
rudimentary marginal cartilage around the rim of the glenoid cavity. In the pig
the front of the capsule is reinforced by cruciate bands. In the dog there is usu-
ally a strong band extending from the acromion to the lateral part of the capsule;
another band (Ligamentum coraco-acromiale) often stretches between the scapular
tuberosity and the acromion.

246 COMPARATIVE ARTHROLOGY

ELBOW JOINT

Ox. — No important differences exist. The upper part of the intero.sseous
raclio-ulnar hgament is commonly ossified in the adult.

Pig. — There are no important differences. The radius and ulna are so firmly
united bj^ the interosseous ligament as to prevent any appreciable movement be-
tween them.

Dog. — The joint capsule is reuiforced in front by an oblique ligament which
arises on the front of the lateral condyle of the humerus above the joint surface,
and joins the terminal part of the biceps and brachialis below. There is a strong
reinforcement of the postero-medial part of the capsule, which extends obliquely
from the medial side of the olecranon fossa to the ulna, just above the processus an-
coneus. The lateral ligament is much stronger than the medial one. It is attached
above to the lateral epicondyle of the humerus, and below chiefly to the eminence
distal to the neck of the radius ; but part of it inclines backward and is attached to
the ulna. The middle part of the ligament is wide and forms a sort of cap over the
proxmial tuberosity of the radius. From this part a band, the annular ligament
of the radius (Lig. annulare radii), extends across the front of the proximal end of
the radius and ends on the ulna; although incorporated in the joint capsule it is
easily defined. The medial ligament is more slender. It arises from the medial
epicondyle of the hmnerus and passes deeply into the proximal part of the inter-
osseous space, ending chiefly on the posterior surface of the radius a little medial to
the attachment of the lateral ligament; there is also a small attachment to the
interosseous border of the ulna. This ligament is very oblique. An elastic band
(Ligamentum olecrani) extends from the lateral surface of the medial epicondyle
to the anterior border of the ulna.

There are two radio-ulnar joints. The proximal radio-ulnar joint (Articulatio
radioulnaris proximalis)is included in the capsule of the elbow, but is provided \\dth
an annular hgament, as described above. The distal radio-ulnar joint (Articulatio
radioulnaris distahs) is formed by a concave facet on the radius and a convex one on
the ulna, and is surrounded by a tight capsule. The interosseous membrane unites
the shafts of the two bones; its proximal part is specially strong and is attached to
prominences on both bones. The movements consist of limited rotation of the
radius (ca, 20°), carrying the paw with it. The ordinary position is termed prona-
tion; outward rotation is supination.^

THE CARPAL JOINTS

These have the same general arrangement as in the horse. Numerous minor
differences naturally exist, but must be excluded from this brief account, which
contains only important special features.

The lateral and medial movements are freer, especially in the dog, but flexion is
not so complete : the anatomical explanation of these facts lies in the nature of the
articular surfaces and certain hgamentous differences. The coUateral ligaments are
much weaker, the long lateral one being especially small in the ox. Two obhque,
somewhat elastic bands cross the front of the radio-carpal and intercarpal joints.
The proximal one is attached to the distal end of the radius and passes do^vnward
and outward to the ulnar carpal bone ; the other one connects the radial and fourth
carpal bones in a similar fashion.

In the ox the short collateral ligaments are well defined; a ligament connects
the accessory carpal with the distal end of the ulna, and strong volar bands connect

1 These movements are best seen in man, in whom the back of the hand may be turned for-
ward (pronation) or backward (supination). In the dog the rotation is much restricted and is
freest when the elbow is flexed.

INTERMETACARPAL JOINTS METACARPO-PHALANGEAL JOINTS

247

the distal bones with the metacarpus
ulnar carpal bone with the meta-
carpus.

The dorsal, volar, and interos-
seous carpal ligaments vary with the
number of carpal bones present in
the different species.

In the dog there are six dorsal
and six volar ligaments. The inter-
osseous ligaments are not inter-
ordinal. The accessory carpal bone
is attached l)y ligaments to the ulna,
the radio-intermediate, and the
third, fourth, and fifth metacarpal
bones. The distal carpal bones are
attached to the metacarpal bones by
dorsal and volar ligaments.

INTERMETACARPAL JOINTS

In the ox the small (fifth) meta-
carpal bone articulates with the large
metacarpal, but not with the carpus.
The joint cavity is connected with
that of the carpo-metacarpal sac.
The proximal end of the small meta-
carpal bone is attached by a ligament
to the fourth carpal, and another
band extends from its distal part
to the side of the large metacarpal.
There is also an interosseous liga-
ment, which is permanent and allows
a small amount of movement.

The chief metacarpal bones of
the pig, and the second to the fifth of
the dog, articulate with each other
at their proximal ends, and are con-
nected by interosseous ligaments,
which do not, however, unite them
closely, as in the horse. There are
feeble dorsal and volar ligaments
(Ligg. basium) which unite the
proximal ends of the metacarpal
bones in the dog.

A strong oblique ligament connects the

Fig. 257. — Distal Part of Limb of Ox, Showing Ligaments
AND Tendons. One Digit .\nd Corresponding Articu-
lar Part of Metacarpal Bone are Removed.
a, Suspensory ligament; a', branch of a to superficial flexor
tendon; a", a"', lateral and central branches of o; b, deep flexor
tendon; 6', branch of 6 to digit removed; c, c, superficial flexor
tendon; d, d', intersesamoid hgament (cut); e, interdigital col-
lateral hgament of fetlock joint; /, tendon of common extensor;
g, proximal interdigital hgament; h, digital annular hgament;
i, posterior annular hgament of fetlock; k, collateral hgament
of pastern joint; I, distal interdigital ligament; m, cruciate inter-
digital hgament (cut) ; m', m", attachments of m to second pha-
lanx and distal sesamoid bone; n, suspensory hgament of distal
sesamoid; o, dorsal elastic ligament; p, lateral volar ligament
of pastern joint; 1, metacarpus, sawn off at /'; S, first phalanx;
3, second phalanx; 4, third phalanx. (EUenberger-Baum, Anat.
d. Haustiere.)

METACARPO-PHALANGEAL JOINTS
Ox. — There are two joints, one
for each digit. The volar parts of
the two joint capsules communicate.
The two interdigital collateral liga-
ments (Ligg. collateralia interdigi-
talia) result from the bifurcation of a

band which arises in the furrow between the divisions of the distal end of the large
metacarpal bone; they spread out and end on the proximal ends of the first pha-

248 COMPARATIVE ARTHROLOGY

langes. The other collateral ligaments are arranged like those of the horse. A strong
interdigital ligament (Lig. interdigitale) , consisting of short intercrossing fibers,
unites the middles of the interdigital surfaces of the first phalanges of the chief digits.
It prevents undue divergence of the phalanges. It is not present in the sheep.

Cruciate ligaments (Ligg. phalango-sesamoidese) connect the proximal sesamoids
with the proximal end of the opposite first phalanx.

The intersesamoid ligament connects all four sesamoids, and extends upward
much less than in the horse.

The laterate and medial sesamoidean ligaments end chiefly on the first phalanges,
but also detach a small part to the large metacarpal bone.

The superficial or straight distal sesamoidean ligament is absent. The middle
distal sesamoidean ligaments of each digit are two short, strong bands which extend
from the distal margins of the proximal sesamoids to the proximal ends of the first
phalanges. The deep distal sesamoidean ligaments are strong and distinctly
cruciate.

The suspensory ligament or interosseus tendon contains more muscular
tissue than in the horse — indeed, in the young animal it consists almost entirely of
muscular tissue. At the distal third of the metacarpus it divides into three branches.
These give rise to five subdivisions, either by bifurcation of the lateral and medial
branches or trifurcation of the middle branch. The two lateral and two medial
bands end on the proximal sesamoid bones and the distal end of the large meta-
carpal bone, and cletach slips to the extensor tendons. The middle band passes
through the groove between the two divisions of the distal end of the metacarpus,
and divides into two branches which join the tendons of the proper extensors of the
digits; it sends fibers also to the interdigital collateral ligaments and to the central
sesamoids. About the middle of the metacarpus the suspensory ligament detaches
a band which unites lower down with the superficial flexor tendon, thus inclosing
the tendon of the deep flexor of the digit ; it also blends with the thick fascia of the
region. The latter gives off a band on either side to the accessory digits, and a ten-
dinous band descends from each accessory digit to the third phalanx and distal sesa-
moid bone, blending with the tendon of the corresponding proper extensor.

Pig. — There are four metacarpo-phalangeal joints, each of which has a capsule,
collateral, intersesamoidean, and cruciate sesamoidean ligaments. Since distinct
interosseous muscles are present, there are, of course, no suspensory ligaments.

Dog. — There are five metacarpo-phalangeal joints, each having its own capsule
and indistinct collateral ligaments. A small sesamoid bone occurs in the anterior
part of each capsule, over which the corresponding extensor tendon plays. The
intersesamoidean ligaments do not extend above the sesamoids. The cruciate
ligaments are present, as well as a fibrous layer which attaches the distal margins
of the sesamoids to the posterior surface of the proximal end of the first phalanx.

INTERPHALANGEAL JOINTS

Ox. — The two proximal joints have separate capsules, and broad, but rather
indistinct, collateral ligaments. Each joint has also central and collateral volar
ligaments. The central ligaments are largely fused to form a strong band which is
attached by two branches to the distal end of the first phalanx and to the depression
on the volar surface of the proximal end of the second phalanx. The collateral ones
extend from the borders of the first phalanx to the proximal end of the second
phalanx; those on the interdigital side are weak and indistinct.

The distal interphalangeal joints have, in addition to the capsules and collateral
ligaments, bands which reinforce them on either side. The interdigital pair arise
in the depressions on the distal ends of the first phalanges, receive fibers from the
second phalanges, and end on the interdigital surfaces of the third phalanges at the

INTERPHALANGEAL JOINTS

249

margin of the articular surface. The abaxial pair have a similar course, but are
thinner, and end on the corresponding third sesamoid. An elastic band crosses the
front of the second phalanx obliquely, from the distal end of the first phalanx to the
extensor process of the third phalanx.

The cruciate or distal interdigital ligaments (Ligg. cruciata interdigitalia) are
two strong bands which limit the separation of the digits. They are attached above
to the abaxial emmences on the proximal ends of the second phalanges (blending
with the collateral ligaments), cross the deep flexor tendon obliquely, and reach the

Fig. 2,58. — Ligaments axd Tendoxs of Digits of Pig;
VoLAB View.
a, Superficial flexor tendon; 6, deep flexor tendon; b',
branches of 6 to accessorj' digits; c, c', annular ligaments;
d-d'", ligaments of accessory digits; e, cruciate interdigital
ligaments; /, /', spiral band around the flexor tendons of
the accessory digits; g, abductor of accessory digit. (Ellen-
berger-Baum, Anat. d. Haustiere.)

Fig. 259. — Ligaments and Tendons of Digits of
Dog, Hind Limb; Volak View.
a, a', Superficial flexor tendon; b, tendon to
large pad; c, lumbricales muscles; d, interossei
muscles; e, f, annular ligaments at metatarso-
phalangeal joints; g, suspensory ligament of large
pad; /(, digital annular ligaments; i, deep flexor
tendon; k, distal sesamoid; I, suspensory ligament
of k; m, suspensory ligament of digital pad; n,
digital pads. (Ellenberger-Baum, Anat. d. Haus-
tiere.)

interdigital space, where they intercross and blend. Most of the fibers end on the
distal sesamoid of the opposite side, but some are attached to the interdigital as-
pect of the second phalanx and the distal sesamoid of the same side. In the sheep
there is, instead of the foregoing, a transverse ligament which is attached on either
side to the interdigital surfaces of the second and third phalanges and the distal sesa-
moid bone. It is related below to the skin, above to a pad of fat.

Pig. — The interphalangeal joints of the chief digits resemble in general those
of the ox. The distal interdigital ligament resembles, however, that of the sheep,
and is intimately adherent to the skin. There is, besides, a remarkable arrange-

250 COMPARATIVE ARTHROLOGY

ment of ligaments which connect the small digits with each other and with the
chief digits (Fig. 258).

This apparatus is somewhat complex, but its chief features are as follows : A proximal inter-
digital ligament is attached on either side to the third phalanges of the small digits, while centrally
it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal
joints of the chief digits. Two bands (central longitudinal interdigital Ugaments) arise on the
bases of the small digits, cross the flexor tendons obhquely downward and centrally, pass through
the proximal interdigital hgament, and blend below with the distal interdigital hgament. Two
collateral bands (collateral longitudinal interdigital ligaments) are attached in common with the
proximal interdigital Ugaments to the third phalanges of the small digits, and blend below with
the outer part of the distal interdigital hgament.

Dog. — Each joint has a capsule and two collateral ligaments. The distal
joints have also two elastic dorsal ligaments (Ligg. dorsaha), which extend from
the proximal end of the second phalanx to the ridge at the base of the third
phalanx. They produce dorsal flexion of the joint, and thus raise or retract the
claws when the flexor muscles relax. The distal sesamoids are represented by
complementary cartilages attached to the volar margins of the articular surfaces
of the third phalanges.

Three interdigital ligaments restrict the spreading apart of the digits (Fig. 259).
Two of these cross the volar surface of the proximal parts of the chief digits, i. e.,
one for the second and third, the other for the fourth and fifth ; they blend with the
annular ligaments on either side. The third ligament is attached on either side to
the foregoing ligaments and the annular ligaments of the third and fourth digits,
and curves downward centrally, ending in the large pad on the paw.

Articulations of the Pelvic Limb
sacro-iliac joint

This joint and the pelvic ligaments present no very striking differences in the
other animals except that the sacro-sciatic ligament in the dog is a narrow but
strong band which extends from the posterior part of the lateral margin of the
sacrum to the tuber ischii; it is the homologue of the ligamentum sacro-tuberosum
of man.

HIP JOINT

Ox. — The shallowness of the acetabulum is compensated by the greater size
of the marginal cartilage, which is specially large laterally. The head of the femur
has a smaller radius of curvature than that of the horse, and the articular surface
extends a considerable distance outward on the upper surface of the neck. The
round ligament is entirely intra-articular; it is small, and sometimes absent. The
accessory ligament is absent.

There are no important differences in the other animals.

STIFLE JOINT

Ox. — There is a considerable communication between the femoro-patellar
and medial femoro-tibial joint cavities; this is situated as in the horse, but is wider.
A small communication with the lateral femoro-tibial capsule sometimes occurs.
The two femoro-tibial capsules usually communicate. The middle patellar liga-
ment is not sunken, as there is no groove on the tuberosity of the tibia where it is
attached. The lateral patellar ligament fuses completely with the tendon of in-
sertion of the biceps femoris, and a large synovial bursa is interposed between them
and the lateral condyle of the femur.

Pig. — The femoro-patellar capsule is strongly reinforced on both sides by bands

TIBIO-FIBULAR JOINTS — HOCK JOINT 251

which blend with the collateral femoro-tibial ligaments. The cavity is continuous
below with that of the femoro-tibial joint. A sagittal synovial fold (rudimentum
septi) extends up a short distance from the anterior cruciate ligament. The supra-
patellar pouch extends an inch or more (ca. 2-3 cm.) above the trochlea; from this
a pouch extends up beneath the quadriceps femoris almost an inch and communi-
cates through a large round opening with the joint cavity. There is a strong
ligamentum patellae, which has a bursa under its distal part. The tendon of the
biceps femoris takes the place of the lateral patellar ligament. A small ligamentum
transversum connects the anterior faces of the menisci.

Dog. — The joint in general resembles that of the pig. The posterior part of
the capsule contains two sesamoid bones, which are imbedded in the origin of the
gastrocnemius.

TmiO-FIBULAR JOINTS

Ox. — The proximal end of the fibula fuses with the lateral condyle of the
tibia. The distal end remains separate, and forms an arthrosis with the distal end
of the tibia; the movement here is imperceptible, as the two bones are closely
united by strong peripheral fibers.

Pig. — The proxunal joint is provided with a capsule which is reinforced in
front and behind by fibrous tissue. The interosseous ligament attaches the shaft
of the fibula to the lateral border of the tibia. The distal joint is included in the
capsule of the hock joint, and is strengthened by dorsal and plantar ligaments
(Lig. malleoli lateralis dorsalis, plantaris), which extend almost transversely from
one bone to the other. There is also an interosseous ligament.

Dog. — The arrangement is essentially the same as in the pig, but there is no
interosseous ligament in the distal joint. Not uncommonly the distal part of the
shaft of the fibula and tibia are ankylosed.

HOCK JOINT

Ox. — There is very considerable mobility at the proximal intertarsal joint, the
capsule of which is correspondingly roomy. The short lateral ligament is attached
distally on the tibial tarsal only. A strong transverse ligament attaches the lateral
malleolus (distal end of the fibula) to the back of the tibial tarsal bone. The dorsal
ligament is narrow and thin.

Pig. — The arrangement in general resembles that of the ox. The medial liga-
ment consists of a thin superficial part which extends almost vertically from malleo-
lus to metatarsus, and a very strong deep part, which runs from the malleolus back-
ward and downward to the sustentaculum and tibial tarsal. The lateral ligament
also consists of two parts. The small superficial part exi;ends from the malleolus
down to the lateral face of the body of the fil^ular tarsal bone. The stronger deep
part arises from the anterior part of the malleolus, passes cheifly backward, ^videns,
and ends on a ridge on the lateral surface of the fibular tarsal. A strong band ex-
tends from the lateral face of the medial malleolus to a depression on the medial
surface of the proximal part of the tibial tarsal bone. An oblique dorsal band con-
nects the central and fourth tarsal bones.

Dog. — The long collateral ligaments are very small, and the short ones double.
The plantar ligament is weak, and ends on the fourth metacarpal bone. No dis-
tinct dorsal Hgament is present, unless we regard as such a ligament which extends
from the neck of the tibial tarsal to the fourth tarsal and third metatarsal bones.

The remaining joints resemble those of the thoracic limb.

MYOLOGY

Myology deals with the muscles and their accessory structures. The muscles
(Musculi) are highly specialized organs, which are characterized by their property
of contracting in a definite manner when stimulated. They are the active organs
of motion. The contractile part of the muscle is the muscular tissue. Three kinds
of muscular tissue are recognized, viz.: (1) Striated or striped; (2) non-striated,
unstriped or smooth; (3) cardiac, which may be regarded as a specialized variety
of striated muscle. Only the first of these will be considered in this section. The
striated muscles are for the most part connected directly or indirectly with the
skeleton, upon which they act, and are hence often designated as skeletal muscles
(Musculi skeleti), in distinction from non-striated muscle, which is often spoken
of as visceral. The striated muscles cover the greater part of the skeleton, and play
an important part in determining the form of the animal. They are red in color,
the shade varying in different muscles and under various conditions. Some are in-
timately associated with and attached to the skin, and are called cutaneous mus-
cles (Musculi cutanei) . The muscular part of each is composed of bundles of con-
tractile fibers surrounded by a thin sheath of connective tissue, the perimysium.

The description of the muscles may be arranged under the following heads: (1)
Name; (2) shape and position; (3) attachments; (4) action; (5) structure; (6)
relations; (7) blood and nerve supply.

(1) The name is determined by various considerations, e. g., the action, at-
tachments, shape, position, direction, etc. In most cases two or more of these are
combined to produce the name, e. g., flexor carpi radialis, longus colli, obliquus
externus abdominis.

A satisfactory comparative nomenclature is exceedingly difficult to work out, and much
confusion exists in this respect. This is due in great part to the lack of a uniform basis for the
formation of names and the difficulty in determining homologies in various species.

(2) The shape is in many cases sufficiently definite and regular to allow the
use of such terms as triangular, quadrilateral, fan-shaped, fusiform, etc. Some
muscles are characterized as long, broad, short, etc. Orbicular or ring-like muscles
circumscribe openings; since the contraction of such a muscle closes the orifice, it is
often termed a sphincter. The position and direction are usually stated with refer-
ence to the region occupied and to adjacent structures which may be presumed to be
already known.

(3) The attachments are in most cases to bone, but many muscles are attached
to cartilage, ligaments, fascia, or the skin. As a matter of convenience, the term
origin (Origo) is applied to the attachment which always or more commonly re-
mains stationary when the muscle contracts; the more movable attachment is
termed the insertion (Insertio). Such a distinction is often quite arbitrary, and
cannot always be made, as the action may be reversible or both attachments may be
freely movable. With respect to the muscles of the limbs, the proximal attaclmient
is regarded as the origin and the distal one as the insertion. In all cases the attach-
ment is made by fibrous tissue, the muscular tissue not coming into direct relation
with the point of attachment. But when the intermediate fibrous tissue is not evi-
dent to the naked eye, it is customary to speak of a ''fleshy attachment." The
term "tendinous attachment" is applied to those cases in which the intermediate
fibrous tissue — tendon or aponeurosis — is evident. A tendon (Tendo) is a band of

252

MYOLOGY 253

dense white fibrous tissue by means of which a muscle is attached; an aponeurosis
is a broad fibrous sheet which fulfils a similar function.

(4) The action belongs rather to physiological study, but the main points are
usually given in anatomical descriptions. In some cases the action is simple, in
others, complex. Muscles which concur in action are termed synergists; those
which have opposite actions are antagonists.

(5) The consideration of structure includes the direction of the muscular fibers,
the arrangement of the tendons, the synovial membranes, and any other accessory
structures. The terms fleshy and tendinous are sometimes used to indicate the
relative amounts of muscular and tencUnous tissue. In the case of the long muscles
of the limbs, the origin is termed the head (Caput), and when the muscle is fusi-
form, the large fleshy part is often called the belly (Venter) of the muscle. Some
muscles have two or more heads, and are hence designated as biceps, triceps, etc. A
digastric muscle is one having two bellies and an intermediate tendon. In most
muscles the muscle-fibers join the tendon at an acute angle, like the relation of the
barbs of a feather to its shaft ; hence the term pennate is applied to such an arrange-
ment. When the fibers are so arranged on one side of the tendon the muscle is
unipennate (M. unipennatus) ; while one in which this arrangement exists on both
sides is bipennate (M. bipennatus). The structure may be still more complex, re-
sulting in a multipennate muscle. The structure of many muscles is much more
complex than a superficial examination would lead one to suppose. Frequently

Fibrous sheath

Ji^esotendpn J^ibrous ^heafk.

fSyntwial sheath

A B

Fig. 260. — Diagrams of Cross-sections of Synovial Bursa (A) and Synovial Sheath (B); T, Tendon.
In both the synovial sac is represented for the sake of clearness as though somewhat distended.

they are intersected by tendinous layers or bands, known as tendinous intersec-
tions. Intersecting bands or tracts which appear on the surface — usually as zig-
zag lines — are termed tendinous inscriptions (Inscriptiones tendinese).

(6) The relations constitute a very important part of anatomical topography,
and a knowledge of them is fundamental to further study in this respect.

(7) The blood and nerve supply are, of course, important on clinical grounds.
The nerve supply is often of value in the determination of homologies. As might
be expected, the muscles have a large blood supply. They are also provided with
lymph-vessels. The nerves to the muscles are motor, sensory, and vasomotor in
function.

The accessory structures associated with the muscles are the synovial mem-
branes and the fascise.

The sjrnovial membranes are thin-walled sacs, similar to the synovial mem-
branes of the joints, and having a similar function. Two forms are recognized.
A S5niovial bursa (Bursa synoviafis) is a simple sac which is interposed at a point of
unusual pressure between a tendon or muscle and some underlying structure, com-
monly a prominence of the skeleton. A synovial sheath (Vagina synovialis ten-
dinis) differs from a bursa in the fact that the sac is folded around the tendon so that
two layers can be distinguished: the inner one is adherent to the tendon, while the
outer one lines the canal in which the tendon lies. The two layers are continuous
along a fold termed the mesotendon. The arrangement is showai in the annexed
diagrams. The synovial membranes of joints in some places form extra-articular

254 FASCIA AND MUSCLES OF THE HORSE

pouches which act as bursse. The sj-novial sheath is not to be confused with the
fibrous sheath of a tendon (Vagina fibrosa tendinis) .

The student will note in dissection that intermediate forms of these sacs occur. A synovial
sheath may belong to two or more tendons in common; in such cases the synovial membrane is
reflected from one tendon to the other, forming a secondary mesotendon. In the normal state
these sacs cannot be recognized on external examination of the subject. It is only when they are
distended that their presence is evident.

The fasciae are sheets of connective tissue, composed mainly of bundles of white
fibers, Avith a greater or less admixture of elastic fibers in some cases. At least two
layers may usually be distinguished. The superficial fascia (Fascia superficialis)
is subcutaneous, and is composed of loose connective tissue which usually contains
more or less fat. The deep fascia is composed of one or more layers of dense fibrous
tissue. Its deep face may be very slightly adherent to the underlying structures,
but in many places it is attached to the skeleton, Hgaments, and tendons. In many
places laminae are given off from the deep face of the fascia, pass between muscles,
and are attached to bones or ligaments; such layers are termed intermuscular septa
(Septa intermuscularia) . The groove in which a tendon lies is converted into a
canal by a band or fascial sheet known as a vaginal or annular ligament (Lig.
vaginale). Many fasciae furnish origin or insertion to muscles and thus act as
tendons; such are tendinous in structure, so as to render the distinction between
fascia and aponeurosis in these cases arbitrary. Bursse occur in certain situations
between the fascia and underlying structures, and are distinguished as subfascial
bursae. Those between the fascia and the skin are subcutaneous bursae.

FASCIA AND MUSCLES OF THE HORSE

The cutaneous muscle or panniculus camosus (Musculus cutaneus) is a thin
muscular layer developed in the superficial fascia. It is intimately adherent in
great part to the skin, but has very little attachment to the skeleton. It does not
cover the entire body, and may be conveniently divided into facial, cervical, omo-
brachial, and abdominal parts.

The facial part, m. cutaneus faciei, consists of a thin and usually incomplete
muscular layer, which extends over the mandibular space and the masseter muscle.
A distinct branch of it passes forward to the angle of the mouth and blends with the
orbicularis oris. This part, the m. cutaneus labiorum, retracts the angle of the
mouth, and has therefore been termed the retractor anguli oris.

The cervical part, m. cutaneus colli, is situated on the ventral region of the neck.
It arises from the cariniform cartilage and a median fibrous raphe. The fibers are
directed forward and diverge from the raphe to the sides of the neck in pennate
fashion. It is thick at its sternal origin, but thins out in front and laterally. On
the side of the neck it is attached to the cervical fascia, which acts as its aponeurosis.
It is related deeply to the sterno-cephalicus, the brachio-cephalicus (in part) and
the jugular vein. Some bundles extend upon the parotid gland, and in well-
developed subjects it is continuous with the facial part.

The omo-brachial part, m. cutaneus omo-brachialis, covers the lateral surface
of the shoulder and arm. Its fibers begin over the upper part of the scapula and
extend to the proximal part of the forearm. Most of its fibers are vertical, but
posteriorly they become oblique and are continued by the abdominal part.

The abdominal part, m. cutaneus tnmci, covers a large part of the body be-
hind the shoulder and arm. Its fibers are largely longitudinal. It is continuous
in front with the omo-brachial part, and a tendinous layer from it passes forward

THE FASCIA AND MUSCLES OF THE HEAD 255

with the posterior deep pectoral muscle to the medial tuberosity of the humerus.
Posteriorly it forms a fold, which, covered by the skin, forms the fold of the flank,
and ends on the fascia above the stifle. The dorsal limit of the muscle corresponds
approximately with a line drawn from the posterior angle of the scapula to the fold
of the flank. Ventrally the two muscles are about a handbreadth apart in the um-
bilical region. Further forward they diverge, so as to overlap the posterior deep
pectoral muscle only to a small extent. Here the cutaneous muscle is closely ad-
herent to the pectoral and contains the external thoracic vein. Posteriorly they
diverge to the fold of the flank.

The muscle is in general closely adherent to the skin and its contraction twitches
the skin, thus getting rid of insects or other irritants.

The Fascia and Muscles of the Head

The muscles of the head (Mm. capitis) may be divided into three groups, viz.:
(1) Superficial muscles, including the cutaneous muscle and those of the lips, cheeks,
nostrils, eyelids, and external ear; (2) the orbital muscles; (3) the mandibular
muscles; (4) the hyoid muscles.

The superficial fascia forms an almost continuous layer, but is very scanty
around the natural orifices. It contains a number of the thin superficial muscles,
so that care must be exercised in removing the skin. Over the frontal and nasal
bones the fascia blends with the periosteum.

The deep fascia is of special interest in three regions. The temporal fascia
(Fascia temporalis) covers the temporalis muscle, and is attached to the parietal
and frontal crests medially, and to the zygomatic arch laterally. The buccal fascia
(F. buccalis) covers the buccinator muscle and the free part of the outer surface of
the ramus of the mancUble. It is attached to the facial crest, and posteriorly it
forms a band (Raphe pterygomandibulare) which stretches from the hamulus of the
pterygoid bone to the mandible behind the last molar tooth. It is directly continu-
ous with the pharyngeal fascia (F. pharyngea), which is attached to the great and
thyroid cornua of the hyoid bone and the thyroid cartilage of the larynx ; it covers
the lateral walls of the pharynx, and blends dorsally with the mecUan raphe of the
constrictor muscles of the latter.

Cutaneus faciei. — This has been described (p. 254).

MUSCLES OF THE LIPS AND CHEEKS

1. Orbicularis oris. — This is the sphincter muscle of the mouth; it is con-
tinuous with the other muscles which converge to the lips. It lies between the
skin and the mucous membrane of the lips, and is intimately adherent to the
former. Most of the fibers run parallel to the free edges of the lips and have no
direct attachment to the skeleton.

Action.— It closes the lips.

Blood-supply — Palato-labial, facial, and mental arteries.

Nerve-supphj. — Facial nerve.

2. Levator nasolabialis.^ — This thin muscle lies directly under the skin, and
chiefly on the lateral surface of the nasal region.

Origin. — The frontal and nasal bones.

Insertion. — (1) The upper lip and the lateral wing of the nostril; (2) the com-
missure of the lips.

Action. — (1) To elevate the upper lip and the commissure; (2) to cUlate the
nostril.

^A.lso termed the levator labii superioris ala'que nasi.

256

FASCIA AND MUSCLES OF THE HORSE

Structure. — The muscle arises b}- a thin aponeurosis. The belly is also thin,
and divides into two branches, between which the lateral dilator of the nostril passes.
The dorsal branch reaches the nostril and upper lip, blending vdih. the lateral di-
lator; the ventral one is much smaller, and blends at the labial commissure ^^^th
the orbicularis and buccinator.

Relations. — Superficially, the skin, fascia, and lateral dilator (in part) ; deeply,

Fig. 261. — Muscles of Head of Horse; Lateral View. The M. ctttaneus is Removed.
o, Levator labii superioris proprius; 6, levator nasolabialis; c, brachiocephalicus; d, sterno-cephalicus ; d',
tendon of d; e, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; h, buccinator; i, depressor labii inferioris;
k, orbicularis oris; I, lateralis nasi, dorsal part; m, masseter; n, parotido-auricularis; o, zygomatico-auricularis; p,
interscutularis; p', fronto-scutularis, pars temporalis; q, cervico-auricularis profundus major; r, cervico-auricularis
superficialis; s, obliquus capitis anterior; <, splenius; r, occipito-mandibularis; i/, mastoid tendon of brachiocephalicus;
.2, posterior, 3, anterior, border of external ear; S, scutiform cartilage; 9, zygomatic arch; 70, orbital fat; 7S, temporo-
mandibular articulation; 27, facial crest; 30', angle of jaw; 37, external maxillary vein; 38, jugular vein; 39, facial
vein; .40, parotid duct; 4 A transverse facial vein; 4^, masseteric vein; 45, facial nerve; 44. parotid gland; 40, chin;
X, wing of atlas. By an oversight the superior buccal branch of the facial nerve is shown crossing over instead of under
the zygomaticus. (After EUenberger-Baum, Anat. fiir Kiinstler.)

the levator labii superioris proprius, lateral dilator (in part), buccinator, branches
of the facial vessels and nerve, and the infraorbital arterj' and nerve.

Blood-sup pi y. — Facial and palato-labial arteries.

Nerve-supphj. — Facial nerve.

3. Levator labii superioris proprius.^This lies on the dorso-lateral aspect of
the face, partly covered by the preceding muscle.

Origin. — The lacrimal, malar, and maxillary bones at their junction.

MUSCLES OF THE LIPS AND CHEEKS

257

Insertion. — The upper lip, by a common tendon with its fellow.

Action.— Kcimg with its fellow, to elevate the upper lip. This action, if
carried to the fullest extent, results in eversion of the lip. In unilateral action the
lip is drawn upward and to the side of
the muscle acting.

Structure.- — The muscle has a short,
thin tendon of origin. The belly is at
first flattened, but becomes narrower
and thicker, then tapers over the nasal
diverticulum, to terminate in a tendon.
The tendons of the two muscles unite
over the alar cartilages of the nostrils,
forming an expansion which spreads
out in the substance of the upper
lip.i

Relations. — Superficially, the skin,
the levator nasolabialis, and the angu-
lar vessels of the eye ; deeply, the later-
alis nasi, the transversus nasi, and the
infraorbital artery and nerve.

Blood-supply. — Facial artery.

Nerve-supply. — Facial nerve.

4. Zygomaticus. — This very thin
muscle lies immediately under the skin
of the cheek.

Origin. — The fascia covering the
masseter muscle below the facial
crest.

Insertion. — The commissure of the
lips, blending with the buccinator.

Action. — To retract and raise the
angle of the mouth.

Structure. — Fleshy, with a thin
aponeurotic origin.

Relatio7is. — Superficially, the skin;
deeply, the buccinator.

Blood-supply. — Facial artery.

Nerve-supply. — Facial nerve.

5. Incisivus superior. — This lies
under the mucous membrane of the
upper lip.

Origin. — The alveolar border of
the premaxilla from the second incisor
to the first cheek tooth.

Insertion. — The upper lip.

Action. — To depress the upper
lip.

6. Incisivus inferior. — This is ar-
ranged in the lower lip like the pre-
ceding muscle in the upper one.

Origin. — The alveolar border of the mandible from the second incisor to a
point near the first cheek tooth.

^ In rare cases a branch is given off from the ventral border of the muscle. It passes forward
and ends in the subcutaneous tissue at the posterior end of the diverticulum nasi.
17

Fig. 262. — Muscles of Head of Horse; Dorsal View.
The M. cutaneus is Removed.
a, Levator labii superioris proprius; a', common
tendon of a with opposite muscle; 6, levator nasolabialis;
/, dilatator naris lateralis; g, zygomaticus; I, lateralis
nasi; ?i, parotido-auricularis; o", scutulo-auricularis super-
ficialis superior; p, interscutularis ; p', fronto-scutularis,
pars temporalis; r, cervico-auricularis superficialis; u,
corrugator supercilii; x, transversus nasi; 2, posterior,
S, anterior, border of external ear; 8, scutiform cartilage;
9, zygomatic arch; 10, supraorbital depression; S3, medial
wing of nostril, containing lamina of alar cartilage; 39,
facial vein. (After EUenberger-Baum, Anat. fur Kiinstler.)

258 FASCIA AND MUSCLES OF THE HORSE

Insertion. — The skin of the lower hp and the prominence of the chin.
Action. — To raise the lower lip. The two incisivi bring the lips together,
concurring with the orbicularis oris in prehension of food.

7. Mentalis.^ — This is situated in the prominence of the chin. Its fibers arise
from each side of the body of the mandible and are inserted into the skin of the
chin. It is mingled with fat and strands of connective tissue, in which the roots
of the tactile hairs are embedded. It raises and corrugates the skin to which it is
attached.

8. Depressor labii inferioris. — This muscle lies on the lateral surface of the
ramus of the mandible, along the ventral border of the buccinator.

Origin. — The alveolar border of the mandible near the coronoid process and
the maxillary tuberosity, in common with the buccinator.

Insertion. — The lower lip.

Action. — To depress and retract the lower lip.

Structure. — The tendon of origin and the belly are fused with the buccinator
as far forward as the first cheek tooth. From this point forward the belly is dis-
tinct and rounded, terminating in a tendon which spreads out in the lower lip,
blending with the orbicularis and the muscle of the opposite side.

Relations. — Superficially, the skin, masseter, facial vessels, and parotid duct;
deeply, the mandible and inferior labial artery.

Blood-supply. — Facial artery.

Nerve-supply. — Facial nerve.

9. Buccinator. — This muscle lies in the lateral wall of the mouth, extending
from the angle of the mouth to the maxillary tuberosity.

Origin. — The lateral surface of the maxilla above the interalveolar space and
the molar teeth ; the alveolar border of the mandible at the interalveolar space and
also posteriorly where it turns upward to the coronoid process; the pterygo-mandib-
ular raphe.

Insertion. — The angle of the mouth, blending with the orbicularis oris.

Action. — To flatten the cheeks, thus pressing the food between the teeth;
also to retract the angle of the mouth.

Structure. — Two layers ma}^ be recognized. The superficial layer (Pars buc-
calis) extends from the angle of the mouth to the masseter. It is incompletely pen-
nate, having a longitudinal raphe on which most of the muscle-fibers converge.
The upper fibers are directed chiefly downward and backward, the lower ones up-
ward and backward. The deep layer (Pars molaris) consists mainly of longitudinal
fibers. It blends in part with the superficial layer of the orbicularis; it has a
small tendinous attachment to the coronoid process behind, and is united ventrally
with the depressor labii inferioris.

Relations. — Superficially, the skin and fascia, the zygomaticus, levator naso-
labialis, lateral dilator of the nostril, the superior buccal glands, the parotid duct,
the facial vessels, and branches of the facial nerve; deeply, the mucous membrane
of the mouth and the inferior buccal glands.

Blood-supply. — Facial and buccinator arteries.

Nerve-supply. — Facial nerve.

MUSCLES OF THE NOSTRILS

1. Levator nasolabialis. — This has been descriljed (p. 255).

2. Dilatator naris lateralis (M. caninus). — This thin, triangular muscle lies
on the lateral nasal region, and passes between the two branches of the levator
nasolabialis.

1 Also known as the levator menti.

MUSCLES OF THE NOSTRILS

259

Origin. — The maxilla, close to the anterior extremity of the facial crest.

Insertion. — The lateral wing of the nostril.

Action. — To dilate the nostril.

Structure. — The muscle has a flat tendon of origin, passes between the two
branches of the levator nasolabialis, and spreads out in the lateral wing of the
nostril. The lower fibers blend with the orbicularis oris.

Relations. — Superficially, the skin, fascia, and the labial branch of the levator
nasolabialis; deeply, the maxilla and the nasal branch of the levator nasolabialis.

Blood-supply. — Facial artery.

Nerve-supply. — Facial nerve.

3. Transversus nasi.^^ — This is an unpaired, quadrilateral muscle, which lies
bet^veen the nostrils. It consists of two layers.

Fig. 263. — Nasal and Superior Labial Muscles of Horse.
a, a', Transversus nasi; b, levator labii superioris proprius; 6', tendon of b; b", common tendon of two
levatores labii superioris proprii; c, c', c", d, ventral part of lateralis nasi; e, dorsal part of lateralis nasi; /, or-
bicularis oris; g, levator nasolabialis, a portion of which is removed; h, dilatator naris lateralis (the terminal part of
which is removed); i, cornu of alar cartilage; k, nostril; k', upper commissure of nostril; I, nasal diverticulum; m,
nasal bone. (After EUenberger-Baum, Top. Anat. d. Pferdes.)

Attachments. — Superficial layer, the superficial faces of the laminae of the alar
cartilages; deep layer, the convex edges of the cornua of the same.

Action. — To dilate the nostrils.

Structure. — It is composed of transverse fleshy fibers, which blend below with
the orbicularis.

Relations. — Superficially, the skin, fascia, and tendinous expansion of the
levator labii superioris proprius; deeply, the alar cartilages, the extremity of the
septum nasi, and the palato-labial artery.

Blood-supply. — Palato-labial artery.

Nerve-supply. — Facial nerve.

Lateralis nasi. — This is situated along the margins of the naso-maxillary notch,
and may be regarded as consisting of dorsal and ventral parts.

The dorsal part (Pars dorsalis m, lateralis nasi)- is a thin layer which lies along

^ Also called the dilatator naris transversus. ^ Also known as the dilatator naris superior.

260 FASCIA AND MUSCLES OF THE HORSE

the dorsal border of the naso-maxillary notch. Its fibers arise from the nasal bone
and pass outward and downward to the parietal cartilage and the adjacent part of
the soft lateral wall of the nasal cavity.

The ventral part (Pars ventralis m. lateralis nasi)^ is much thicker and lies
along the ventral border of the notch. It arises from the nasal process of the pre-
maxilla and the adjacent part of the maxilla, and its fibers curve inward to end on
the cartilaginous prolongations of the turbinate bones (chiefly the ventral one) and
on the lateral wall of the vestibule of the nasal cavity. A few bundles pass from
the cornu of the alar cartilage to the lateral wing of the nostril.

Action. — To dilate the vestibule of the nasal cavity, to rotate the turbinal car-
tilages outward, and to assist in dilating the nostril.

Relations. — Superficially, the skin, fascia, nasal diverticulum, the levator labii
superioris proprius, the levator nasolabialis, and the lateral nasal artery; deeply,
the nasal bone, the parietal cartilage, the maxilla, the premaxilla, the nasal mucous
membrane, and the anterior nasal branch of the infraorbital nerve.

Blood-supply. — Facial and palato-labial arteries.

Nerve-supply. — Facial nerve.

The preceding muscle does not dilate the so-called "false nostril" or nasal diverticulum, aa
is commonly stated. Both act on the lateral wall of the vestibule of the nasal cavity so as to draw
it outward, thus tending to constrict, rather than dilate, the nasal diverticulum. The thick part
of the ventral muscle which is attached to the cartilage of the turbinate bone has a similar effect.
When the nostril is fully dilated, the so-called "false nostril," i. e., the entrance to the nasal diver-
ticulum, is closed. The newer term seems preferable.

MUSCLES OF THE EYELIDS

1. Orbicularis oculi. — This is a flat, elliptical, sphincter muscle, situated in and
around the eyelids, the portion in the upper lid being much broader than that in
the lower. The chief attachment is to the skin of the lids, but some bundles are
attached to the palpebral ligament at the medial canthus and to the lacrimal bone.
Its action is to close the lids.

2. Corrugator supercilii.— This is a very thin, small muscle, which arises over
the root of the supraorbital process and spreads out in the upper eyelid, blending
with the orbicularis ocuh (Fig. 262). Its action is to assist in raising the upper lid
or, especially in pathological conditions, to wrinkle the skin.

3. Malaris. — This is a very thin muscle, which varies much in different sub-
jects. It extends from the fascia in front* of the orbit to the lower lid. Its action
is to depress the lower lid.

The foregoing muscles receive their blood-supply from the facial, transverse
facial, supraorbital, and infraorbital arteries; the nerve-supply is derived from the
facial nerve.

4. Levator palpebrae superioris. — This slender, flat muscle is almost entirely
within the orbit (Fig. 561). It arises on the pterygoid crest, passes forward above
the rectus oculi superior and below the lacrimal gland, and terminates in a thin ten-
don in the upper lid.

Action. — To elevate the upper lid.
Blood-supply. — Ophthalmic artery.
Nerve-supply. — Oculomotor nerve.

MANDIBULAR MUSCLES

The muscles of this group (Mm. mandibulae) are six in number in the horse.
They arise from the upper jaw and the cranium, and are all inserted into the man-
dible.

1 Also known as the dilata' or naris inferior.

MANDIBULAR MUSCLES 261

1. Masseter. — This muscle extends from the zygomatic arch and facial crest
over the broad part of the mandibular ramus. It is semi-elliptical in outline.

Origin. — By a strong tendon from the zygomatic arch and the facial crest.

Insertion. — The lateral surface of the broad part of the ramus of the mandible.

Action. — Its action is to bring the jaws together. Acting singly, it also carries
the lower jaw toward the side of the contracting muscle.

Structure. — The superficial face of the muscle in its upper part is covered by a
strong, glistening aponeurosis, and several tendinous intersections partially divide
the muscle into layers. The fibers of the superficial layer take origin from the
malar and maxilla only, and diverge somewhat to their insertion close to the thick
ventral border of the lower jaw. The fibers of the deep layer arise from the entire
area of origin, and pass straight to the border of the mandible; it will be noted that
a small part, near the temporo-mandibular joint, is not covered by the superficial
layer. The two layers are separable only above and behind; elsewhere they are
fused.

Relations. — Superficially, the skin and cutaneus, the parotid gland, the
transverse facial and masseteric vessels, and the facial nerve; deeply, the ramus of
the mandible, the buccinator and depressor labii inferioris muscles, the superior
buccal glands, the buccinator vessels and nerve, and the vena reflexa, which joins
the facial vein at the anterior edge of the muscle. The facial vessels and parotid
duct run along the anterior edge of the muscle; the duct, however, bends for-
ward about the middle of the border and leaves the muscle.

Blood-supply. — Transverse facial and masseteric arteries.

Nerve-supply. — Mandibular nerve.

2. Temporalis. — This muscle occupies the temporal fossa.

Origin. — The rough part of the temporal fossa and the crests which limit it.

Insertion. — The coronoid process of the mandible, which it envelops.

Action. — Chiefly to raise the lower jaw, acting with the masseter and medial
pterygoid muscles.

Structure. — The surface of the muscle is covered with a glistening aponeurosis,
and strong tendinous intersections are found in its substance. The medial edge of
the muscle is quite thin, but as the fibers converge toward the much smaller area
of insertion, the muscle becomes nearly an inch thick. It fuses partly with the
masseter.

Relations. — Superficially, the scutiform cartilage, the anterior muscles of the
external ear, and the auricular and orbital fat; deeply, the temporal fossa and the
deep temporal vessels and nerves.

Blood-supply. — Superficial and deep temporal, and posterior meningeal arteries.

Nerve-supply. — Mandibular nerve.

3. Pterygoideus medialis (s. internus).- — This muscle occupies a position on
the medial surface of the ramus of the mandible similar to that of the masseter
laterally.

Origin. — The crest formed by the pterygoid process of the sphenoid and the
palatine bone.

Insertion. — The concave medial surface of the broad part of the ramus of the
mandible and the medial lip of the ventral border.

Action. — Acting together, to raise the lower jaw; acting singly, to produce also
lateral movement of the jaw.

Structure. — The muscle is capable of division into two parts. The principal
part is superficial (medial), and its fibers are, for the most part, vertical in direc-
tion. It contains much tendinous tissue (septa). The smaller portion is lateral
to the foregoing, and its fibers are directed do^vnward and backward.

Relations. — Laterally, the ramus of the mandible, the lateral pterygoid muscle,
the inferior alveolar vessels and nerve, and the lingual and mjdo-hyoid nerves;

262

FASCIA AND MUSCLES OF THE HORSE

medially, the great cornu of the hyoid bone, the pharynx, the larynx, the tensor
palati, mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural pouch,
the external maxillary vessels, the ninth and twelfth nerves, the mandibular salivary
gland, the mandibular and parotid ducts, and the mandibular and pharyngeal lymph-
fflands.

Blood-supply. — Internal maxillary, masseteric, and inferior alveolar arteries.

Nerve-supply. — Mandibular nerve.

4. Pterygoideus lateralis (s. externus). — This muscle is considerably smaller
than the preceding one, and is situated lateral to its upper part.

Origin. — The lateral surface of the pterygoid process of the sphenoid bone.

Insertion. — The medial surface of the neck, the medial part of the anterior
border of the condyle of the mandible and the articular disc.

Actio7i. — Acting together, to draw the lower jaw forward; acting singly, to

Ethmo-
turhinates
Dorsal meatus
Dorsal turbinate
Middle meatus
Ventral iurhitiate
Ventral meatus

Septum of
frontal sinuses

Digastricus,
posterior
belly

Digastricus,
anterior belly

Intermediate tendon

Fig. 264. — Sagittal Section of Head op Horse, Showing Deep Pterygo-mandibular Region and Nasal and

Cra.nial Cavities.
1, Cerebral compartment of cranial cavity; £, cerebellar compartment of same; 3, tentorium osseum; 4i ten-
torium cerebelli; 5, sphenoidal sinus; 6, hamulus of pterygoid bone-tendon of tensor palati cut off short at anterior
border of hamulus; 7, mylo-glossus. The olfactory mucous membrane is shaded.

move the jaw also toward the side opposite to the muscle acting. The latter action
is due to the fact that the origin is nearer to the median plane than the insertion.

Structure. — The muscle is almost entirely fleshy, and the fibers are almost
longitudinal in direction. Some of them are inserted into the edge of the articular
disc.

Relations. — Laterally, the temporo-mandibular articulation and the temporalis
muscle; medially, the medial pterygoid and tensor palati muscles. The internal
maxillary artery crosses the ventral face of the muscle and dips in between it and
the tensor palati. The mandibular nerve lies on the ventral surface, and the buc-
cinator nerve perforates the origin of the muscle.

Blood-supply. — Internal maxillary and inferior alveolar arteries.

Nerve-supply. — Mandibular nerve.

5. Occipito-mandibularisi (M. jugulomandibularis).— This is a short, fusiform

^ This muscle is also known as the stylo-maxillaris, stylo-mandibularis, etc.

MANDIBULAR MUSCLES

263

muscle extending from the paramastoid process of the occipital bone to the posterior
border of the lower jaw; it is covered by the parotid gland.

Fig 265 -Mandibular and Laryngeal Regions of Horse, after Removal of Skin and Cutaneub.
c Brachiocephalicus: d. sterno-cephalicus; e. omo-hyoideus and sterno-hyoideus; h, buccinator; ^, depressor
labiiWerLris- m, masseter; «. occipito-mandibularis; u, mylo-hyoideus; ... posterior. 3. anterior, border of external
ear SO' angi; o jaw; 36 mandibular lymph-glands; ^7. external maxillary vein; 3^. facial continuation of ^7;
ro'parolid duct; L parotid gland; 4o, prominence of chin; x. wing of atlas. (After EUenberger-Baum. Anat. fur
Kiinstler.)

Origin.— The paramastoid process of the occipital bone, in common with the
posterior belly of the digastricus.

Insertion.— The posterior border of the ramus of the mandible.
Action.— To depress the lower jaw and open the mouth.

264 FASCIA AND MUSCLES OF THE HORSE

Structure. — The muscle contains a good deal of tendinous tissue. It blends
with the posterior belly of the digastricus.

/?e/'a^^ons.— Superficially, the parotid gland, the tendon of the sterno-cephalicus,
and the fibrous expansion which connects it with the tendon of the brachiocephali-
cus; deeply, the guttural pouch, the external carotid artery, the ninth and twelfth
nerves, the pharynx, and the mandibular salivary gland.

Blood-supply. — External carotid artery.

Nerve-supply. — Facial nerve.

6. Digastricus. — This muscle is composed of two fusiform, flattened bellies,
united by a round tendon.

Origin. — The paramastoid process of the occipital bone, in common with the
preceding muscle.

Insertion.- — The medial surface of the ventral border of the molar part of the
ramus of the mandible.

Action. — It assists in depressing the lower jaw and opening the mouth. If the
mandible be fixed and both bellies contract, the hyoid bone and the base of the
tongue are raised, as in the first phase of deglutition.

Structure. — The posterior belly has the appearance of a branch detached from
the medial surface of the occipito-mandibularis. It passes downward and forward,
and is succeeded by a small rounded tendon. The latter perforates the tendon of
insertion of the stylo-hyoideus, and is provided with a synovial sheath. The an-
terior belly is larger and terminates by thin, tendinous bundles.

Relations.- — The posterior belly has practically the same relations as the oc-
cipito-mandibularis. The intermediate tendon is in contact laterally with the me-
dial pterygoid muscle, the mandibular gland and duct, and the external maxillary
artery. The anterior belly lies in the mandibular space between the ramus of the
jaw and the mylo-hyoideus muscle; the sublingual vessels run along its dorsal
border.

Blood-supply.- — External carotid and sublingual arteries.

Nerve-supply. — Facial and mandibular nerves.

THE HYOID MUSCLES

This group consists of eight muscles (Mm. ossis hyoidei), one of which, the
hyoideus transversus, is unpaired.

1. Mylo-hyoideus.^ — This muscle, together with its fellow, forms a sort of
sling between the rami of the mandible, in which the tongue is supported.

Origin. — The medial surface of the alveolar border of the mandible.

Insertion.- — (1) A median fibrous raphe extending from the symphysis to the
hyoid bone; (2) the lingual process, body, and thyroid cornu of the hj'oid bone.

Action.- — It raises the floor of the mouth, the tongue, and the hyoid bone.

Structure. — Each muscle consists of a thin curved sheet, the fibers passing
ventrally from their origin and then curving toward the median raphe. It is
chiefly fleshy, and is thickest behind. There is a tendinous intersection between this
muscle and the omo-hyoideus, to which both muscles are attached. The anterior
superficial part of the muscle is termed the mylo-glossus.

Relations. — On the superficial surface of the muscles are the ramus, the metlial
pterygoid and digastricus muscles, and the mandibular lymph-glands. The deep
surface is in contact with the mucous membrane of the mouth, the stylo-glossus,
hyo-glossus, and genio-hyoideus muscles, the sublingual gland and vessels, the
mandibular duct, and the lingual and hypoglossal nerves. The sublingual vein
passes through the posterior part.

Blood-supply. — Sublingual artery.

^ Also known as the transversus mandibulae.

THE HYOID MUSCLES 265

Nerve-supply. — Mylo-hyoid branch of the mandibular nerve.

2. Stylo-hyoideus. — This is a slender, fusiform muscle, having a direction
nearly parallel to that of the great cornu of the hyoid bone (Fig. 559) .

Origin. — The muscular angle of the dorsal extremity of the great cornu of the
hyoid bone.

Insertion. — The anterior part of the thyroid cornu of the hyoid bone.

Action. — It draws the base of the tongue and the larynx upward and backward.

Structure.— It arises by a thin, short tendon, and has a fusiform belly. The
tendon of insertion is perforated for the passage of the intermediate tendon of the
cUgastricus, and at this point there is a small synovial sheath.

Relations. — Superficially, the medial pterygoid muscle and the parotid gland;
deeply, the guttural pouch, the pharynx, the external carotid and maxillary arteries,
and the hypoglossal nerve.

Blood-supply. — External carotid artery.

Nerve-supply. — Facial nerve (stylo-hyoid branch).

In rare cases an anomalous arrangement is present in which the stylo-hyoideus is not at-
tached to the thyroid cornu but is continuous with the intermediate tendon of the digastricus,
and no fibrous ring is formed. The posterior belly of the digastricus is inserted chiefly on the
thyroid cornu, but also sends a dehcate tenchnous shp to the intermediate tendon.

3. Occipito-hyoideus (M. jugulo-hyoideus). — This is a small triangular muscle,
which lies in the space between the paramastoid process and the great cornu of the
hyoid bone.

Origin. — The paramastoid process of the occipital bone.

Insertion. — The dorsal extremity and ventral edge of the great cornu of the
hyoid bone.

Action. — It carries the ventral extremity of the great cornu backward.

Structure. — The muscle is somewhat triangular, its fibers being longer as the
ventral border is approached. It blends with the posterior belly of the digastricus.

Relations. — Superficially, the parotid gland; deeply, the guttural pouch.

Blood-supply.- — Occipital artery.

Nerve-supply. — Facial nerve.

4. Genio-hyoideus. — This is a long, spindle-shaped muscle, which lies under
the tongue in contact with its fellow of the opposite side (Fig. 330) .

Origin. — A small depression on the medial surface of the ramus of the mandible,
close to the symphysis.

Insertion. — The extremity of the lingual process of the hyoid bone.

Action. — It draws the hyoid bone and tongue forward.

Structure. — The muscle arises by a short tendon, which is succeeded by the
belly, composed of long bundles of parallel fibers.

Relations. — Ventrally, the mylo-hyoideus; dorsally, the hyo-glossus, stylo-
glossus, genio-glossus, the sublingual gland, mandibular duct, and the lingual nerve.

Blood-supply. — Sublingual artery.

Nerve-supply. — Hypoglossal nerve.

5. Kerato-hyoideus. — This small triangular muscle lies in the space between
the thyroid and small cornu, under cover of the hyo-glossus (Fig. 331).

Origin. — The posterior edge of the small cornu and the adjacent part of the
ventral border of the great cornu.

Insertion. — The dorsal edge of the thyroid cornu.

Action.- — It raises the thyroid cornu and the larynx.

Relations. — The muscle is crossed laterally by the lingual artery.

Blood-supply. — Lingual artery.

Nerve-supply. — Glosso-pharyngeal nerve.

6. Hyoideus transversus. — This is a small, unpaired muscle, which extends
transversely between the two small cornua of the hyoid bone.

266 FASCIA AND MUSCLES OF THE HORSE

Attachments. — The small cornua close to the junction with the great cornua.
Action. — When relaxed, its dorsal surface is concave; when it contracts, it
elevates the root of the tongue.

Structure. — Fleshy, composed of parallel transverse bundles.
Blood-supply. — Lingual artery.
Nerve-supply. — Glosso-pharyngeal nerve.

7. Stemo-thyro-hyoideus, and

8. Omo-hyoideus. — These are described with the muscles on the ventral sur-
face of the neck (p. 268).

The Fascia and Muscles of the Neck

It is convenient to divide the muscles of the neck (Mm. colli) into ventral and
lateral groups, the two lateral groups being separated from each other by the liga-
mentum nuchse.

THE FASCIA OF THE NECK

The superficial fascia is in part two-layered, and contains the cervical cutaneous
muscle. The fasciae of the right and left sides are attached along the dorsal line
of the neck to the ligamentum nuchas, while along the ventral line they meet in a
fibrous raphe. A deep layer is detached which passes underneath the cutaneous
muscle, bridges over the jugular furrow, and crosses over the deep face of the brachio-
cephalicus and omo-hyoideus to join the superficial layer. It again separates to
pass under the cervical trapezius, and become attached to the ligamentum nuchse.
Along the ventral line a septum is detached which separates the sterno-cephalici.
Two other layers in front of the shoulder enclose the prescapular lymph-glands.

The deep fascia also forms two layers. The superficial layer is attached to
the wing of the atlas and the ventral edge of the longissimus capitis et atlantis and
scalenus. Passing downward it encloses the trachea, and, together with the deep
layer, furnishes sheaths for the vagus and sympathetic nerves and the carotid
artery. Passing upward it detaches septa between the extensor muscles of the spine.
Anteriorly it covers the thyroid gland, the guttural pouch, the adjacent vessels and
nerves, and the larynx, and is attached to the mastoid process of the temporal bone
and the thyroid cornel of the hyoid bone. Posteriorly it is attached to the first
rib and the cariniform cartilage of the sternum. The deep layer (prevertebral
fascia) covers the ventral surface of the longus colli, and encloses the trachea and
oesophagus. Anteriorly it forms, with the corresponding layer of the opposite
side, a septum between the guttural pouches; posteriorly it becomes continuous
with the endothoracic fascia. A fascia propria forms a tubular sheath around the
trachea, enclosing also the recurrent nerves.

VENTRAL CERVICAL MUSCLES

This group consists of twelve pairs of muscles which lie ventral and lateral to
the vertebrae.

1. Cutaneus colli. — This has been described (p. 254).

2. Brachiocephalicus. — This is described on p. 294.

3. Stemo-cephalicus.i — This is a long, narrow muscle which extends along the
ventral and lateral aspects of the trachea from the sternum to the angle of the jaw.
It forms the ventral boundary of the jugular furrow.

^ This muscle is probably the homologue of the sternal part of the sterno-cleido-mastoid
of man. On account of the differences in its insertion in the various animals, it seems desirable
to adopt the name sterno-cephalicus. It is also known as the sterno-mandibularis or sterno-
maxillaris.

VENTRAL CERVICAL MUSCLES

267

Origin . — The cariniform cartilage of the sternum.
Insertion. — The posterior border of the ramus of the mandible.
Action. — Acting together, to flex the head and neck; acting singly, to incUne
the head and neck to the side of the muscle contracting.

Structure. — The two muscles are fused at their origin, which is fleshy. Near

r '

Fig. 266. — Antero-lateral View of Muscles and Skeleton of Horse.
a, Trapezius; c, brachiocephalicus; d, sterno-cephalicus; /, long head of triceps; /', lateral head of triceps;
g, anterior superficial pectoral muscle; g', posterior superficial pectoral; h' , anterior deep pectoral; i), cutaneus colli;
z, supraspinatus; 29, omo-hyoideus; 30, steruo-th>TO-hyoideus; 31, jugular vein; 32, cephalic vein; 1, scapula;
7', cartilage of scapula; ;?, spine of scapula; 4. shaft of humerus; 4' lateral epicondyle; 5, lateral tuberosity of humerus;
e, deltoid tuberosity; 74, ventral border ("keel") of sternum; i^'. cariniform cartilage; 7. iJ., first rib. (After Ellen-
berger-Baum, Anat. fiir Kiinstler.)

the middle of the neck they separate, and, becoming narrower and thinner, each
muscle passes under the parotid gland and terminates by a flat tendon. The latter
is connected by a thin aponeurosis with that of the brachiocephalicus.

Relations. — Superficially, the cutaneous muscle; deeply, the sterno-thyro-
hyoideus and omo-hyoideus muscles. The dorsal edge of the muscle is related to
the jugular vein, which lies in the jugular furrow. The carotid artery, the vagus,

268 FASCIA AND MUSCLES OF THE HORSE

sjTnpathetic, and recurrent nerves also lie along the upper edge at the root of the
neck. The tendon passes under the external maxillary vein and the parotid gland,
having the mandibular gland and occipito-mandibularis muscle on its medial side.

Blood-supply. — Carotid artery.

Nerve-supply. — Ventral branch of the spinal accessor}' nerve.

4. Stemo-thyro-hyoideus (Sterno-thyreoideus et sterno-hyoideus). — This is a
long, slender, digastric muscle, applied to the ventral surface of the trachea and
its fellow of the opposite side.

Origin. — The cariniform cartilage of the sternum.

Insertion. — (1) A prominence on the posterior border of the lamina of the thy-
roid cartilage of the larynx at the ventral end of the oblique line; (2) the body
and lingual process of the hyoid bone.

Action. — To retract and depress the hyoid bone, the base of the tongue, and
the larynx, as in deglutition. It may also fix the hyoid bone when the depressors
of the tongue are acting, as in sucking.

Structure. — The origin of the muscle is fleshy, and as far as the middle of the
neck, it blends with its fellow. The common belly is then interrupted by a tendon,
or sometimes two tendons, from which arise three or four fleshj^ bands. The lat-
eral small bands (Sterno-thyroidei) diverge to reach their insertion into the thy-
roid cartilage by a delicate tendon; while the medial and larger bands (Sterno-
hyoidei), closely applied to each other and blending with the omo-hyoideus, pass
straight forward to reach the ventral surface of the hyoid bone.

Relations. — At the root of the neck the common belly is related ventrall}' to
the sterno-cephalicus, and the carotid arteries and recurrent nerves dorsally.
Further forward the trachea becomes the dorsal relation, and near the head the
omo-hyoideus, skin and fascia, the ventral one.

Blood-supply. — Carotid artery.

Nerve-supply. — Ventral branches of the first and second cervical nerves.

5. Omo-hyoideus.^ — This is a thin, ribbon-like muscle, almost entirely fleshy,
which crosses the trachea very obliquel}^

Origin. — The subscapular fascia close to the shoulder joint.

Insertion. — The body and adjacent part of the lingual process of the hyoid
bone, in common with the hyoid branch of the preceding muscle.

Action.- — To retract the hyoid bone and the root of the tongue.

Structure. — The muscle is composed of parallel fleshy fibers, except at its origin,
where it has a thin tendon.

Relations. — The posterior part of the muscle is related laterally to the supra-
spinatus, anterior deep pectoral, and brachiocephalicus and the prescapular lymph-
glands; and medially to the scalenus. It is intimately adherent to the brachio-
cephalicus. In the middle of the neck it is related superficially to the brachio-
cephalicus, sterno-cephalicus, and the jugular vein; deeply, to the rectus capitis
ventralis major, the carotid artery, the vagus, sympathetic, and recurrent nerves,
the trachea, and, on the left side, the oesophagus. In its anterior part the muscle
blends with the sterno-hyoideus, the two covering the sterno-thyroideus, the thy-
roid gland in part, and the ventral face of the larynx.

Blood-supply. — Carotid and inferior cervical arteries.

Nerve-supply. — Ventral l^ranch of the first cervical nerve.

6. Scalenus (M. scalenus primse costae).^ — This muscle is deeply situated on
the side of the posterior half of the neck. It is composed of two parts, between
which the cervical roots of the brachial plexus of nerves emerge.

Origin. — The anterior border and lateral surface of the first rib.
Insertion. — (1) The dorsal (smaller) part (M. scalenus dorsalis) is attached to
the transverse process cf the seventh cervical vertebra; (2) the ventral part (M.
1 Also termed the subscapulo-hyoideus.

VENTRAL CERVICAL MUSCLES 269

scalenus ventralis) is attached to the transverse processes of the sixth, fifth, and
fourth cervical vertebrae.

Action. — The neck is flexed or inclined laterally, according as the muscles act
together or singly. If the neck be the fixed point, the muscle may have a respira-
tory action by pulling forward or fixing the first rib.

Structure. — The dorsal part is composed of several small fleshy bundles. The
ventral portion, which is much larger, is almost entirely fleshy, and not so divided.

Relations. — Superficially, the anterior deep pectoral, brachiocephalicus, and
omo-hyoideus muscles, the phrenic nerve, and branches of the brachial plexus;
deeply, the vertebrae, the longus colli and intertransversales muscles, the oesoph-
agus (on the left side), the trachea (on the right side), the vertebral vessels,
the vagus, sympathetic, and recurrent nerves. The roots of the brachial plexus
form a flat anastomosis, which lies between the two parts of the muscle. The
brachial vessels cross the ventral edge close to the first rib.

Blood-supply. — Carotid, vertebral, and inferior cervical arteries.

Nerve- supply. — Ventral branches of the cervical nerves.

7. Cervicalis ascendens.^ — This muscle is the cervical continuation of the
longissimus costarum, and is sometimes regarded as a part of the scalenus, with
which it is partially united. It consists of three or four bundles which are attached
to the transverse processes of the last three or four cervical vertebrae and the first
rib.

Action. — To extend the neck or to flex it laterally.

Relations. — Superficially, the brachiocephalicus and anterior deep pectoral;
deeply, the scalenus and intertransversales.
Blood-supply. — Vertebral artery.
Nerve-supply. — Cervical nerves.

8. Rectus capitis ventralis major (M. longus capitis). — This is the largest
of the three special flexors of the head, and lies along the ventro-lateral surface
of the anterior cervical vertebrae and the base of the cranium.

Origin. — The transverse processes of the fifth, fourth, and third cervical ver-
tebrae.

Insertion. — The tubercles at the junction of the basilar part of the occipital
bone with the body of the sphenoid.

Action. — Acting together, to flex the head; acting singly, to incline it to the
same side also.

Structure. — ^The origin of the muscle is by fleshy digitations. The belly in-
creases in size by the union of these digitations, reaching its maximum at the axis.
It then diminishes, passes toward the median plane, and terminates on a rounded
tendon.

Relations. — Superficially, the brachiocephalicus and omo-hyoideus, the mandib-
ular gland, the carotid artery (which lies along the ventral border), the occipital
and internal carotid arteries, and the tenth, eleventh, and sympathetic nerves;
deeply, the vertebrae, the longus colli, intertransversales, and the rectus capitis
ventralis minor. The terminal part of the muscle lies in contact with its fellow
above the pharynx and between the guttural pouches.

Blood-supply. — Carotid, vertebral, and occipital arteries.

Nerve-supply. — Ventral branches of the cervical nerves.

9. Rectus capitis ventralis minor (M. rectus capitis ventralis). — This is a small
muscle which lies dorsal to and under cover of the preceding one.

Origin.- — The ventral arch of the atlas.

Insertion. — The basilar part of the occipital bone, close to the preceding muscle.

Action. — To flex the atlanto-occipital articulation.

Structure. — Fleshy .

1 This muscle is also known as the ilio-costalis cervicis.

270 FASCIA AND MUSCLES OF THE HORSE

Relations. — Ventrally, to the preceding muscle; dorsall}-, to the atlas, atlanto-
occipital articulation, and the basilar part of the occipital bone; laterally, to the
rectus capitis lateralis and the guttural pouch.

Blood-supply. — Occipital artery.

Nerve-supply. — Ventral branch of the first cervical nerve.

10. Rectus capitis lateralis. — This is a still smaller muscle, which lies for the
most part under the obliquus capitis anterior.

Origin. — The atlas, lateral to the preceding muscle.
Insertion. — The paramastoid process of the occipital bone.
Action. — The same as the preceding muscle.
Structure. — Fleshy.

Relations. — Superficially, the obliquus capitis anterior, the occipital vessels,
and the ventral branch of the first cervical nerve.
Blood-supply. — Occipital artery.
Nerve-supply. — Ventral branch of the first cervical nerve,

11. Longus colli. — This muscle covers the ventral surfaces of the vertebrae,
from the sixth thoracic to the atlas, and is united with its fellow. It consists of
two parts, thoracic and cervical.

Origin. — (1) Thoracic part, the bodies of the first six thoracic vertebrae; (2)
cervical part, the transverse processes of the cervical vertebrae.

Insertion. — (1) Thoracic part, the bodies and transverse processes of the last
two cervical vertebrae; (2) cervical part, the bocUes of the cervical vertebrae and
the ventral tubercle of the atlas.

Action. — To flex the neck.

Structure. — The muscle is composed of a succession of bundles. The largest
of these constitute the thoracic part of the muscle, which has a strong tendon in-
serted into the last two cervical vertebrae. A bursa is interposed between the ten-
don and the spine at the first costo-vertebral articulation. The cervical part con-
sists of a number of smaller bundles, each of which passes from its origin on the
transverse process of one vertebra forward and medially to its insertion into a ver-
tebra further forward. The most anterior bundle is inserted by a strong tendon into
the ventral tubercle of the atlas.

Relations. — The principal relations of the two muscles in the thorax are:
ventrally, the pleura, and, further forward, the trachea and oesophagus; dorsally,
the vertebrae and the costo-vertebral joints; laterally, the dorsal, deep cervical,
and vertebral vessels, the sympathetic nerve, and the thoracic roots of the brachial
plexus. In the neck important relations are: ventrally, the trachea and oesophagus,
the carotid artery, the vagus, sympathetic, and recurrent nerves; dorsally, the
vertebrae and, in the middle third of the neck, the intertransversales muscles; lat-
erally, the scalenus, the rectus capitis ventralis major, and the intertransversales
(in the anterior third). The terminal part of the muscle is separated from the
trachea by the oesophagus, which is here median in position.

Blood-supply. — Subcostal and vertebral arteries.

Nerve-supply. — Ventral branches of the spinal nerves.

12. Intertransversales colli (Mm. intertransversarii cervicis). — These are six
fasciculi which occupy the spaces between the lateral aspects of the vertebrae and
the transverse and articular processes. There is thus a bundle for each inter-
vertebral articulation except the first. Each bundle consists of a dorsal and ven-
tral part.

Attachments. — The dorsal bundles pass from transverse process to articular
process; the ventral bundles extend between adjacent transverse processes.
Action. — To flex the neck laterally.

Structure. — They contain strong tendinous intersections.
Relations. — Superficially, the brachiocephalicus, rectus capitis ventralis ma-

LATERAL CERVICAL MUSCLES 271

jor, obliquus capitis posterior, complexus, longissimus capitis et atlantis, splenius,
scalenus, and longissimus dorsi et costarum muscles; deeply, the vertebrae, the
longus colli muscle, and the vertebral vessels. The muscles are perforated by
branches of these vessels and by the primary branches of the cervical nerves.

Blood-supply. — Vertebral artery.

Nerve-supply. — The cervical nerves.

LATERAL CERVICAL MUSCLES
This group consists of twelve pairs of muscles arranged in layers.

First Layer

1. Trapezius cervicalis. — Described on p. 293.

Second Layer

2. Rhomboideus cervicalis. — Described on p. 293.

3. Serratus cervicis. — Described on p. 297.

Third Layer

4. Splenius. — This is an extensive, fiat, triangular muscle, partly covered by
the preceding three muscles.

Origin. — The second, third, and fourth thoracic spines by means of the dorso-
scapular ligament and the funicular part of the ligamentum nucha?.

Insertion. — The nuchal crest, the mastoid process, the wing of the atlas,
and the transverse processes of the third, fourth, and fifth cervical vertebrse.

Action. — Acting together, to elevate the head and neck; acting singly, to in-
cline the head and neck to the side of the muscle acting.

Structure. — The muscle arises in the withers from the anterior part of the
dorso-scapular ligament, which also affords attachment to the rhomboideus, ser-
ratus dorsalis, and complexus muscles. The fibers pass upward and forward
toward the head and the first cervical vertebra. The insertion on the occipital
bone and the mastoid process is by means of a thin aponeurosis common to the
brachiocephalicus and longissimus capitis. The atlantal insertion is by a strong,
flat tendon, in common with the longissimus atlantis and the brachiocephalicus.
The remaining insertions are fleshy digitations.

Relations. — Superficially, the skin and fascia, the trapezius, rhomboideus
cervicalis, serratus ventralis, and posterior auricular muscles' deeply the com-
plexus and longissimus dorsi muscles.

Blood-supply. — Deep cervical and dorsal arteries.

Nerve-supply. — Dorsal branches of the last six cervical nerves.

Fourth Layer

5. Longissimus capitis et atlantis.^ — This muscle consists of two parallel, fusi-
form portions. It lies between the deep face of the splenius and the ventral part
of the complexus.

Origin. — (1) The transverse processes of the first two thoracic vertebrse; (2)
the articular processes of the cer'Mcal vertebrse.

Insertion.- — (1) The mastoid process; (2) the wing of the atlas.

^di'on.— Acting together, to extend the head and neck; acting singly, to flex
the head and neck laterally or to rotate the atlas.

Structure. — The origin from the thoracic vertebrse is by aponeurotic slips
which blend with the complexus. The succeeding fleshy part, in passing along
lAIso termed the trachelo-mastoideus.

272

FASCIA AND MUSCLES OF THE HORSE

the neck, receives fasciculi from each of the cervical vertebra except the
first two. The dorsal division of the muscle (M. longissimus capitis) is
inserted into the mastoid process by a flat tendon which fuses with that of
the splenius; the ventral division (M. longissimus atlantis) is inserted into the

LATERAL CERVICAL MUSCLES 273

wing of the atlas by a ribbon-like tendon in common with the splenius and
brachiocephalicus.

Relations. — Superficially, the splenius muscle and dorsal branches of the
cervical nerves; deeply, the complexus, the spinalis colli, and the oblique muscles
of the head. The deep cervical vessels cross the deep face of the muscle obliquely
at the level of the sixth and seventh cervical vertebrae.

Blood-supply. — Vertebral and deep cervical arteries.

Nerve-supply. — Dorsal branches of the last six cervical nerves.

6. Complexus (M. semispinalis capitis). — This is a large triangular muscle
which lies chiefly on the ligamentum nuchse, under cover of the splenius.

Origin. — (1) The second, third, and fourth thoracic spines, in common with
the splenius and serratus dorsalis; (2) the transverse processes of the first six or
seven thoracic vertebrae ; (3) the articular processes of the cervical vertebrae.

Insertion. — A rough area on the occipital bone just ventral to the nuchal crest.

Action. — It is the chief extensor of the head and neck. Acting singly, the
muscle inclines the head to the same side.

Structure. — The origin of the muscle at the withers is aponeurotic. In the
neck the bundles arising from the articular processes run obliquely upward
and forward, giving the lower part of the muscle a distinct pennate character.
The dorsal part of the belly is crossed obliquely by four or five tendinous
intersections. The insertion is by a strong tendon.

Relations. — Superficially, the rhomboideus, serratus ventralis, splenius, and
longissimus capitis et atlantis; deeply, the ligamentum nuchae, the multifidus
cervicis, longissimus dorsi, and the oblique and dorsal straight muscles of the head,
the deep cervical vessels, and the dorsal cutaneous branches of the cervical nerves.

Blood-supply. — Deep cervical, vertebral, and occipital arteries.

Nerve-supply. — Dorsal branches of the last six cervical nerves.

7. Multifidus cervicis. — This muscle lies on the arches of the last five cervical
vertebrae. It consists of five or six segments.

Origin. — The articular processes of the last four or five cervical and the first
thoracic vertebrae.

Insertion. — The spinous and articular processes of the cervical vertebrae.

Action. — Acting together, to extend the neck; acting singly, to flex the neck on
the side of the muscle contracting and to rotate the neck to the opposite side.

Structure. — The muscle is composed of two sets of bundles. The superficial
bundles are directed obliquely forward and inward, each passing from an articular
process to the spine of the preceding vertebra. The deep bundles are shorter and
run straight from an articular process to that of the preceding vertebra.

Relations.- — Superficially, the complexus, longissimi, and obliquus capitis poster-
ior; deeply, the spinalis, the ligamentum nuchae, and the arches of the vertebrae.

Blood-supply. — Deep cervical and vertebral arteries.

Nerve-supply. — Dorsal branches of the last six cervical nerves.

8. Spinalis. — Described with the longissimus on p. 278.

9. Obliquus capitis posterior (s. caudalis) .— This is a strong, quadrilateral
muscle, which covers the dorso-lateral aspect of the atlas and axis.

Origin. — The side of the spine and the posterior articular process of the axis.

Insertion. — The dorsal surface of the wing of the atlas.

Action. — Chiefly to rotate j^fe atlas, and with it the head, to the same side;
also to assist in extending and fixing the atlanto-axial joint.

Structure. — The muscle is composed almost entirely of parallel fleshy fibers
directed obliquely forward and outward. It is covered by a special fascia.

Relations. — Superficially, the splenius, complexus, longissimus capitis, and
brachiocephalicus muscles; deeply, the arch and spine of the axis, the wing of
the atlas, the atlantoaxial joint, the rectus capitis dorsalis minor, the occipital and
18

274

FASCIA AND MUSCLES OF THE HORSE

vertebral vessels, and the first and second cervical nerves. The terminal part of
the vertebral arterj^ joins the posterior branch of the occipital artery under cover
of the muscle.

Blood-supply. — Occipital and vertebral arteries.

m no °^
3 3 9
m C ■*!

iiJI'lli

I ". s -^-

O 05 O —
^ I3J 73 H

LATERAL CERVICAL MUSCLES

275

Nerve-supply. — Dorsal branch of the second cervical nerve.

10. Obliquus capitis anterior (s. craniahs). — This short, thick, quadrilateral
muscle lies on the side of the atlantooccipital articulation.

Origin. — The anterior edge and ventral surface of the vnng of the atlas.

Insertion. — The paramastoid process and nuchal crest of the occipital bone
and the mastoid process.

Action. — Acting together, to extend the head on the atlas; acting singly, to
flex the head laterally.

Structure. — The muscle contains a good deal of tendinous tissue. The direction
of its fibers is forward, upward, and inward.

Fig. 269. — Deepest Layer of Muscles of Neck of House.
a, Obliquus capitis anterior; b, obliquus capitis posterior; c, rectus capitis lateralis; d, rectus capitis ventralia
minor; e, rectus capitis ventralis major; /, longus colli; s, s', scalenus; A, longissimus costarum; j, longissimus dorsi;
fc, spinalis et semispinalis; ?, multifidus dorsi ; m, multifidus cervicis; n, intertransversales; o, o', rectus capitis dorsalis
major; p, rectus capitis dorsalis minor; q, tendon of insertion of complexus; 1, lamellar part, 1', funicular part of liga-
mentum nuchae; 2, nuchal crest; 3, paramastoid process; 4. edge of wing of atlas; o, transverse, and 6, articular,
processes of cervical vertebrae; 7, nerves of brachial plexus (cut) ; S, first rib. (Ellenberger-Baum, Anat. d. Haustiere.)

Relations. — Superficially, the complexus, the aponeurosis of the splenius, longus
capitis, and brachiocephalicus, overlying which are the posterior auricular muscles,
artery, and nerve, and the parotid gland; deeply, the dorsal straight muscles,
the occipito-hyoideus, the atlanto-occipital articulation, the posterior meningeal
artery, and a branch of the occipital nerve.

Blood-supply.— Occipital artery.

Nerve-supply. — Dorsal branch of the first cervical nerve.

11. Rectus capitis dorsalis major. — This muscle extends from the axis to the
occipital bone, in contact with the ligamentum nuchse.

Origin. — The edge of the spinous process of the axis.

276 FASCIA AND MUSCLES OF THE HORSE

Insertion. — The occipital bone, below the complexus; the tendon of insertion
of the complexus.

Action. — To extend the head.

Structure. — The muscle is fleshy and may be divided into two parallel parts,
superficial and deep. The former blends somewhat with the terminal part of the
complexus. The deep part may be termed the rectus capitis dorsalis medius.
Bundles frequently arise from the fascia over the obliquus capitis posterior.

Relations. — Superficially, the obliquus capitis anterior, splenius, and com-
plexus; medially, the ligamentum nuchse; deeply, the atlas, the atlanto-occipital
articulation, and the rectus capitis dorsalis minor. The dorsal branch of the first
cervical nerve appears between this muscle and the obliquus capitis anterior.

Blood-supply. — Occipital artery.

Nerve-supply. — Dorsal branch of the first cervical nerve.

12. Rectus capitis dorsalis minor. — This small muscle lies under cover of the
preceding.

Origin. — The dorsal surface of the atlas.

Insertion. — The occipital bone beneath the preceding muscle and lateral to the
funicular part of the ligamentum nuchse.

Action. — To assist the preceding muscle.

Structure. — It is fleshy and varies a good deal in volume, being sometimes
small and difficult to recognize.^ On the other hand, it is sometimes double.

Relations. — Superficially, the preceding muscle and the obliquus capitis an-
terior; deeply, the atlas and the atlanto-occipital articulation.

Blood-supply. — Occipital artery.

Nerve-supply. — Dorsal branch of the first cervical nerve.

The Fascije and Muscles of the Back and Loins

(fascia et musculi dorsi et lumborum)

The superficial fascia presents no special features. The lumbo-dorsal fascia
(Fascia lumbo-dorsalis) closely invests the muscles, but is easily stripped off the
longissimus. It is attached medially to the supraspinous ligament and the spinous
processes of the vertebrae; it divides laterally into two layers. The superficial
layer is practically the aponeurosis of the latissimus dorsi. The deep layer gives
origin to the serratus dorsalis, the lumbar part of the obliquus abdominis externus,
the transversus abdominis, and the retractor costae. Its lateral edge curves under
the longissimus and is attached to the ribs and lumbar transverse processes. Pos-
teriorly it is continuous with the gluteal fascia. At the withers it forms an impor-
tant structure, the dorso-scapular ligament. This is a strong tendinous sheet,
attached to the third, fourth, and fifth thoracic spines. Its upper part is very
thick and gives origin by its superficial surface to the rhomboideus thoracalis, by
its anterior part to the splenius. The lower part is thin and elastic, and furnishes
numerous lamellae which intersect the scapular part of the serratus ventralis and
are attached to the scapula. Three lamellae are detached from the ligament.
The deepest of these passes between the longissimus and spinalis and is attached to
the transverse processes of the first seven thoracic vertebrae; it gives attachment
to the complexus. The middle one dips in between the longissimus dorsi and
longissimus costarum. The superficial one gives origin to the serratus dorsalis.
A strong fascial layer, the ilio-lumbar ligament, extends from the last rib to the
tuber coxae.

There are nine pairs of muscles in this region, arranged in four layers.

^ This seems due to pressure produced by pathological changes in the supra-atloid bursa,
which are frequently extensive in dissecting-room subjects.

the fascia and muscles of the back and loins 277

First Layer

1. Trapezius thora calls.

2. Latlsslmus dorsl.

Second Layer

3. Rhomboldeus thoracalls.

The foregoing are described with the other muscles which attach the thoracic
limb to the trunk (p. 293).

4. Serratus dorsalis anterior (s. cranialis). — This is a thin quadrilateral muscle,
named from its serrated ventral border. It lies under cover of the rhomboideus,
serratus ventralis, and latissimus dorsi.

Origin. — The lumbo-dorsal fascia and dorso-scapular ligament.

Insertion. — The lateral surfaces of the fifth or sixth to the eleventh or twelfth
ribs inclusive.

Action. — To draw the ribs on which it is inserted forward and outward, thus
assisting in inspiration.

Structure. — The muscle arises by means of a thin aponeurosis. The muscle-
fibers pass ventrally and backward to be attached to the ribs by seven or eight
digitations below the lateral edge of the longissimus costarum.

Relations. — Superficially, the rhomboideus, serratus ventralis, latissimus dorsi,
and serratus dorsalis posterior; deeply, the longissimus dorsi, longissimus costarum,
external intercostal muscles, and the ribs.

Blood-supply. — Intercostal arteries.

Nerve-supply. — Thoracic nerves.

5. Serratus dorsalis posterior (s. caudalis). — This muscle resembles the pre-
ceding one, which it partly covers.

Origin. — The lumbo-dorsal fascia.

Insertion. — The lateral surfaces of the last seven or eight ribs.

Action. — To draw the ribs backward, thus assisting in expiration.

Structure. — Similar to the preceding muscle. The fibers are directed ventrally
and forward and terminate in seven or eight digitations, one or two of which cover
the posterior teeth of the anterior muscle. The aponeurosis blends with that of
the latissimus dorsi.

Relations. — Superficially, the latissimus dorsi and external oblique; deeply,
the longissimus dorsi, longissimus costarum, external intercostals, serratus dorsalis
anterior, and the ribs.

Blood-supply. — Intercostal and lumbar arteries.

Nerve-supply. — Thoracic nerves.

Third Layer

6. Longissimus costarum.^ — This long, segmental muscle extends across the
series of ribs, in contact with the outer edge of the longissimus dorsi.

Origin. — (1) The deep layer of the lumbo-dorsal fascia as far back as the third
or fourth lumbar transverse process. (2) The anterior borders and lateral surface
of the last fifteen ribs.^

Insertion. — The posterior borders of the ribs and the transverse processes of
the last cervical vertebra.

Action. — Chiefly to depress and retract the ribs and so help in expiration.

1 This muscle is also known as the long costal, ilio-costaUs, or transversalis costarum. The
name given above was introduced by the International Commission for the Reform of Myological
Nomenclature and appears worthy of general adoption.

2 The lumbar part of this muscle is subject to variation. It may, in quite exceptional case^
extend as far as the ilium, and sometimes, on the other hand, it does not arise quite as far back as
given above. In some subjects the origin can be traced distinctly to the tips of lumbar transverse,
processes.

278

FASCIA AND MUSCLES OF THE HORSE

Acting together, they may assist in extending the spine, acting singly in inchning
it laterally.

Structure. — This muscle presents a distinct segmental arrangement. It is
composed of a series of bundles, the fibers of which are directed forward and a little
ventro-laterally. From these are detached two sets of tendons. The superficial
tendons spring from the lateral edge of the muscle. They are flat and are about
half an inch in width. Each crosses two or three intercostal spaces, to be inserted
on the posterior border of a rib. The deep tendons are detached from the dorsal
part of the deep face of the muscle. Each passes backward across one or two inter-
costal spaces to its origin on the anterior border or lateral surface of a rib. Small

bursae may be found between the ribs and
tendons.

Relations. — Superficially, the dorsal and
ventral serrati; deeply, the external inter-
costals and the ribs. The lumbar origin is
covered by the longissimus dorsi. The deep
cervical and dorsal vessels cross the surface of
the muscle at the first and second intercostal
spaces respectively, and branches of the in-
tercostal vessels and nerves emerge between
it and the longissimus dorsi; here a fascial
layer dips in between the two.

Blood-supply. — Intercostal arteries.
Nerve-supply. — Dorsal branches of the
thoracic nerves.

7. Longissimus dorsi.^ — This is the
largest and longest muscle in the body. It
extends from the sacrum and ilium to the
neck, filling up the space between the spinous
processes medially and the lumbar trans-
verse processes and the upper ends of the
ribs ventrally ; consequently it has the form
of a three-sided prism.

Origin. — (1) The tubera, crest, and ad-
jacent part of the ventral surface of the ilium ;
(2) the first three sacral spines ; (3) the lum-
bar and thoracic spines and the supraspinous
ligament.

Insertion. — (1) The lumbar transverse
and articular processes; (2) the thoracic
transverse processes; (3) the spinous and
transverse processes of the last four cer-
vical vertebrae; (4) the lateral surfaces of the ribs, except the first.

Action. — Acting with its fellow, it is the most powerful extensor of the back
and loins; by its cervical attachment it assists in extending the neck. By its costal
attachment it may also assist in expiration. Acting singly, it flexes the spine
laterally.

Structure. — This is quite complex. The posterior part of the muscle is greatly
developed and constitutes the common mass of the loins. This is covered by a
strong aponeurosis which blends with the supraspinous and sacro-iliac ligaments,
and is attached to the crest and sacral angle of the ilium and the first and second
sacral spines; it furnishes origin to the lumbar portion of the middle gluteus. In

' The muscle as here described includes the longissimus dorsi et cervicis and the spinalis and
semispinalis components, as the separation of these is largely artificial in the horse.

Fig. 270. — Right Portion op Cross-section op
Back op Horse. Section is Cut Through
Seventh Thoracic Vertebra.
a, Ligamentum nuchae; 6, trapezius mus-
cle; c, cartilage of scapula; d, latissimus dorsi; e,
cutaneus; /, rhomboideus thoracalis; g, ser-
ratus ventralis; h, serratus dorsalis; h', lumbo-
dorsal fascia, which divides below into three
layers; i, longissimus costarum; k, levator costae;
k', internal intercostal muscle; I, longissimus dorsi;
m, m', seventh thoracic vertebra; n, head of
eighth thoracic vertebra; o, head of eighth rib;
p, seventh rib; r, intercostal artery and nerve; s,
skin. The fascise are indicated by dotted lines.
(After Ellenberger, in Leisering's Atlas.)

THE FASCIA AND MUSCLES OF THE TAIL 279

its course further forward the muscle receives fasciculi from the lumbar and thoracic
spines, but diminishes somewhat in volume. About the twelfth thoracic vertebra
it divides into two parts. The dorsal division (m. spinalis et semispinalis), rein-
forced by bundles from the first four thoracic spines, passes forward under the com-
plexus to be inserted into the spines of the last four cervical vertebrae. The ventral
division passes forward and downward underneath the serratus ventralis to be in-
serted into the ribs and the transverse processes of the last four cervical vertebrae.
Three sets of fasciculi may be distinguished, viz. : (1) spinal, which are superficial
and medial; (2) transverse, attached to the transverse and articular processes,
which are medial and deep; (3) costal, which are lateral.

Relations. — Superficially, the middle gluteus, the lumbo-dorsal fascia, the
latissimus dorsi, serrati dorsales, serratus ventralis, and complexus; deeply, the
multifidus, intertransversales, external intercostals, levatores costarum, the liga-
mentum nuchse, and its fellow of the opposite side (in the neck).

Blood-supply. — Dorsal, deep cervical, intercostal, and lumbar arteries.

Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves.

8. Multifidus dorsi. — This is a long segmental muscle which lies along the sides
of the spinous processes of the vertebrae from the sacrum to the neck.

Origin. — (1) The lateral part of the sacrum; (2) the articular processes of
the lumbar vertebrae; (3) the transverse processes of the thoracic vertebrae.

Insertion. — The spinous processes of the first two sacral, the lumbar, thoracic,
and last cervical vertebrae.

Action. — Acting with its fellow, it is an extensor of the spine; acting singly,
it flexes it laterally.

Structure. — It is composed of a series of bundles which are directed obliquely
forward and upward. Each fasciculus passes over several vertebrae to its insertion.
In the posterior part of the series the bundles cross two or three vertebrae and are
inserted into the summits of the spines. Anteriorly the bundles have a more
horizontal direction, cross three to five vertebrae, and are inserted into the sides
of the spines considerably below their summits. A further complication consists
in the fusion of several bundles into a common insertion.

Relations. — Superficially, the longissimus dorsi; deeply, the vertebral spines.

Blood-supply. — Intercostal and lumbar arteries.

Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves.

9. Intertransversales lumborum. — These are very thin muscular and tendin-
ous strata, which occupy the spaces between the transverse processes of the lumbar
vertebrae except the fifth and sixth.

Action. — To assist in flexing the loins laterally or in rendering the region rigid.
Relations. — Superficially, the longissimus dorsi; deeply, the quadratus lum-
borum.

Blood-supply. — Lumbar arteries.
Nerve-supply. — Lumbar nerves.

The Fascia and Muscles of the Tail
(fascia et musculi caud^)

The muscles of the tail are inclosed in the strong coccygeal fascia, which is
continuous in front with the gluteal fascia and blends with the lateral sacro-iliac
ligament. At the root of the tail it is loosely attached to the subjacent muscles,
l^ut further back it is intimately adherent to them. From its deep face are de-
tached septa which pass between the muscles to become attached to the vertebrae.

1. Coccygeus.^ — This is a flat, triangular muscle which lies chiefly between the
sacro-sciatic ligament and the rectum.

^ Also termed the ischio-coccygeus or compressor coccygis.

280

FASCIA AND MUSCLES OF THE HORSE

Origin. — The pelvic surface of the sacro-sciatic ligament near the ischiatic spine.

Insertion. — The first four coccygeal vertebrae and the coccygeal fascia.

Action. — Acting together, to de-
press (flex) the tail, compressing it
over the perineum; acting singly,
to depress and incline it to the
same side.

Structure. — The origin of the
muscle is aponeurotic. Becoming
fleshy, its fibers pass upward and
backward and divide into two
layers. The lateral layer is at-
tached to the vertebrae, the medial
to the fascia; included between
the two lie the intertransversales.
When the tail is raised, the ventral
edges of the muscles produce a dis-
tinct ridge at either side of the anus.
Relations. — Laterally, the
sacro-sciatic ligament and the semi-
membranosus ; medially, the rectum
and the sacro-coccygeus ventralis
muscle. The internal pudic artery
crosses the origin of the muscle,
sacrococcygeus dorsalis medialis).^ — This

Fig. 271. — Cross-section of Tail of Horse.
1, 2, Branches of lateral coccygeal vessels and nerve; 3, mid-
dle coccygeal artery; 4, sacro-coccygeus dorsalis; 4', sacro-coccy-
geus lateralis; 5, 5', intertransversales; 6, sacro-coccygeus ven-
tralis; 7, recto-coccygeus; 8, coccygeal fascia; 9, fibro-cartilage
between fourth and fifth coccygeal vertebrae. The veins are black.

2. Sacro-coccygeus dorsalis (M.
muscle lies along the dorso-median aspect of the tail, in contact with its fellow

Origin. — The last three sac-
ral spines and some of the coccy-
geal spines.

Insertion . — The dorsal sur-
face of the coccygeal vertebrae.

Action. — Acting together, to
elevate (extend) the tail; acting
singly, to elevate and incline it
laterally.

Structure. — The muscle has
a strong rounded belly. It is in-
serted by means of short tendons
which fuse with those of the next
muscle.

Relations. — Superficially, the
coccygeal fascia; medially, its
fellow; laterally, the sacro-coccy-
geus lateralis; deeply, the verte-
brae.

3. Sacro-coccygeus lateralis
(M. sacro-coccygeus dorsalis later-
alis).^— This muscle hes immedi-
ately lateral to the preceding.

Origin. — The sides of the

1 Also termed the erector coccy-
gis.

■ Also known as the curvator
coccygis.

Fig. 272.-
a, Coccygeus; b
d, recto-coccygeus; e
tor penis; g, bulbo
pudic artery; k, anus; I, penis.
Anat. d. Pferdes.)

Muscles of Perineum of Horse.
retractor ani; c, c', sphincter ani externus;

■geus ventralis lateralis; /, retrac-
h, ischio-cavernosus; i, internal
(After EUenberger-Baum, Top.

THE MUSCLES OF THE THORAX 281

sacral spines, with the multifidus, and the transverse processes of the sacral and
coccygeal vertebrse.

Insertion. — The lateral surface of the coccygeal vertebrae, except the first four.

Action. — Acting with its fellow, to assist the preceding muscle in elevating the
tail; acting singly, to incline it to the same side.

Structure.— This, muscle appears to be a direct continuation of the multifidus
dorsi. The belly is fusiform and receives reinforcing fasciculi from the transverse
processes of the sacrum. This is succeeded by bundles of tendons, as many as four
lying alongside of each other.

Relations. — Superficially, the lateral sacro-iliac ligament and the coccygeal
fascia; dorsally, the sacro-coccygeus dorsalis; ventrally, the intertransversales;
deeply, the vertebrae and a branch of the lateral coccygeal artery and accompanying
vein and nerve.

4. Intertransversales caudae (Mm. intertransversarii caudse). — These con-
sist of muscular bundles which lie on the lateral aspect of the tail, between the
preceding muscle and the sacro-coccygeus ventralis. They begin on the lateral
edge of the sacrum and occupy the spaces between the transverse processes, to which
they are attached. They are, however, not arranged in a strict segmental manner.

Action. — Acting together, to fix the coccygeal vertebrae; acting singly, to assist
in lateral flexion.

5. Sacro-coccygeus ventralis (Mm. sacro-coccygei ventrales).^ — This muscle
lies on the ventral aspect of the sacrum and coccyx. It is composed of two parts,
described by Bourgelat and the German anatomists as separate muscles.

(a) The lateral part (M. coccygeus ventralis lateralis) is much the larger of
the two. It arises from the lateral part of the ventral surface of the sacrum, about
as far forward as the third foramen, and is inserted into the transverse processes
and ventral surface of the coccygeal vertebrae.

(6) The medial part (M. sacro-coccygeus ventralis medialis) arises from the
ventral surface of the sacrum medial to the preceding muscle and the first eight
coccygeal vertebrse, and is inserted into the ventral surfaces of the coccygeal ver-
tebrae.

Action. — Acting together, to depress (flex) the tail; acting singly, to incline
it laterally also.

Structure. — The lateral part has a somewhat compressed belly, and receives
bundles from the transverse processes of the coccygeal vertebrae. The medial part
is much smaller and shorter, reaching only about to the middle of the tail.

Relations.- — Ventrally, the pelvic and coccygeal fasciae; dorsally, the sacrum,
coccygeal vertebrae, and the intertransversales; laterally, the sacro-sciatic liga-
ment, the coccygeus, and the coccygeal fascia; medially, its fellow, the recto-
coccygeus, and the middle coccygeal vessels. Branches of the lateral coccygeal
vessels and nerves lie between the lateral division of the muscle and the intertrans-
versales.

Blood-supply. — Middle and lateral coccygeal arteries.

Nerve-supply. — Coccygeal nerves.

The Muscles of the Thorax
(muscuu thoracis)

These consists of seven muscles or sets of muscles, which are attached to the
thoracic vertebrae, to the ribs and their cartilages, and to the sternum. They are
muscles of respiration.

1. Levatores costarum. — These constitute a series of small muscles which oc-
cupy and overhe the dorsal ends of the intercostal spaces.
1 Also known as the depressor coccygis.

282

FASCIA AND MUSCLES OF THE HORSE

Origin. — The transverse processes of the thoracic vertebrse.

Insertion. — The lateral surfaces of the upper ends of the ribs posterior to the
A'ertebral origin.

Action.— To draw the ribs forward in inspiration.

Structure. — Arising by tendinous fibers, each muscle passes backward and out-
ward and expands at its insertion. Some fibers pass over one rib and are inserted

Seventh cervical vertebra-'
First thoracic vertebra-

Section of scapula

Intertransversales

Intercostal f

nervet< *i

Retractor co.

Intertransverse luja,

Ilio-lumbar ligament,.

Levatores costarum

External
intercostal
XT"- J muscles

Lateral border of lon-
gissimus dor si

Tuber coxce

Fig. 273. — Deep Dissection op Dorsal and Lumbar Regions of Horse; Dorsal View. (After Schmaltz, Atlas

d. Anat. d. Pferdes.)

on a succeecUng one. At the beginning and end of the series the muscle cannot be
distinguished from the external intercostal, of which it is in reality only a specially
developed part.

Relations. — Superficially, the longissimus dorsi; deeply, the ribs, internal in-
tercostal muscles, and the intercostal vessels and nerves.

Blood-supply. — Intercostal arteries.

THE MUSCLES OF THE THORAX 283

Nerve-supply. — Intercostal nerves.

2. External intercostals (Mm. intercostales externi). — Each of these occupies
an intercostal space, from the levatores to the sternal extremity of the rib. They
do not occupy the intercartilaginous spaces.

Origin. — The posterior borders of the ribs.

Insertion. — The anterior borders and lateral surfaces of the succeeding ribs.

Action. — To draw the ribs forward in inspiration.

Structure. — The fibers are directed downward and backward. There is a
considerable admixture of tendinous tissue. The thickness of the muscles grad-
ually diminishes toward the lower ends of the spaces.

Relations. — Superficially, the serratus ventralis, latissimus dorsi, serratus
dorsalis, longissimus dorsi, longissimus costarum, rectus thoracis, deep pectoral,
obliquus abdominis externus, and cutaneous muscles; deeply, the internal inter-
costals and (in the upper part of the spaces) the intercostal vessels and nerves.

Blood-supply. — Intercostal and internal thoracic arteries.

Nerve-supply . — I nter costal nerves .

3. Internal intercostals (Mm. intercostales interni). — These extend the en-
tire length of the intercostal spaces, including their interchondral portion.

Origin. — The anterior borders of the ribs and their cartilages.

Insertion. — The posterior borders of the preceding ribs and cartilages.

Action.- — To draw the ribs backward in expiration. It seems probable, how-
ever, that the intercartilaginous portion is inspiratory.'-

Structure. — The direction of the fibers is oblique downward and forward.
There is a smaller amount of tendinous tissue than in the external set, and the
thickness diminishes dorsally. In the upper part of the spaces fibers sometimes
cross a rib in a fashion similar to the subcostals of man. A thin fascia separates
the internal from the external intercostal muscle in each space.

Relations. — Superficially, the levatores costarum and the external intercostals;
deeply, the endothoracic fascia and pleura, the transversus thoracis, diaphragm,
transversus abdominis, and the internal thoracic and musculo-phrenic vessels.
In the upper part of the intercostal spaces the intercostal vessels and nerves lie
between the internal and external intercostal muscle, but below they lie chiefly on
the deep face of the internal muscle.

Blood-supply. — Intercostal and internal thoracic arteries.

Nerve-supply. — Intercostal nerves.

The muscles in connection with the costal cartilages are sometimes distinguished as Mm.
intercartilaginei ; their direction is similar to that of the internal intercostal, and they cover the
cartilages of the asternal ribs more or less. At the ventral ends of some of the intercostal spaces
there is a layer of longitudinal muscle.

4. Retractor costae. — This is a small triangular muscle which lies behind the
last rib, chiefly under cover of the serratus dorsalis.

Origra. — The transverse processes of the first three or four lumbar vertebrae
by means of the lumbar fascia.

Insertion. — The posterior border of the last rib.

Action. — To retract the last rib.

Structure. — The muscle arises by a thin aponeurosis. Its fibers are parallel
to those of the adjacent internal oblique.

Relations. — Superficially, the serratus dorsalis and external oblique; deeply,
the transversus abdominis.

Blood-supply. — Lumbar arteries.

Nerve-supply. — Lumbar nerves.

5. Rectus thoracis.^ — This is a thin muscle which lies under cover of the deep

^ The function of the intercostal muscles is still a subject of much discussion. The state-
ments made above seem to represent the view most commonly held in regard to their action.
2 Also known as the transversus costarum or lateralis sterni.

284

FASCIA AND MUSCLES OF THE HORSE

pectoral muscles. It is directed obliquely backward and downward, and crosses
the lower part of the first three intercostal spaces.

Origin. — The lateral surface of the first rib, below the scalenus.

Insertion. — The cartilage of the fourth rib. The aponeurosis usually joins the
rectus abdominis. It may reach the fifth rib or the sternum.

Cariniform cartilage

Sternal ligament

First rib
Internal thoracic vessels

Internal intercostal muscle

Fig. 274. — Dissection of Floor of Thorax op Horse.
The ribs have been sawn off near their sternal ends and the diaphragm and transversus abdominis cut off close to their

attachment.
1, Eighth rib; 2, 3, cartilages of ninth and tenth ribs; 4, xiphoid cartilage; 5, apex of pericardium.

Action. — It may assist in inspiration or concur with the rectus abdominis.
Relations. — Superficially, the deep pectoral muscles; deeply, the intercostal
muscles and the ribs.

Blood-supphj. — Internal and external thoracic arteries.
Nerve-supply. — Intercostal nerves.

THE MUSCLES OF THE THORAX 285

6. Transversus thoracis.— This is a flat muscle situated on the thoracic sur-
face of the sternum and the cartilages of the sternal ribs.

Origin.- — The sternal ligament, meeting the opposite muscle.

Insertion. — The cartilages of the ribs, from the second to the eighth inclusive,
and the adjacent part of some of the ribs.

Action. — It draws the ribs and costal cartilages inward and backward, thus
assisting in expiration.

Structure. — Each muscle has the form of a scalene triangle, of which the base
is the strongly serrated lateral border. The muscle contains a good deal of ten-
dinous tissue. The anterior bundles are directed forward and outward; the poste-
rior, backward and outward.

Relations. — Dorsally, the endothoracic fascia and pleura; ventrally, the
costal cartilages, the internal intercostal muscles, and the internal thoracic vessels.

Blood-supply. — Internal thoracic artery.

Nerve-supply. — The intercostal nerves.

7. Diaphragm. — This is a broad, unpaired muscle which forms a partition be-
tween the thoracic and abdominal cavities. ^ In outline it has some resemblance to
a palm-leaf fan. In form it is dome-shaped, compressed laterally. On a median
section it is seen to have a general direction downward and forward from the lumbar
vertebrae to the xiphoid cartilage. The thoracic surface is strongly convex, and
is covered by the pleura. The abdominal surface is deeply concave, and is covered
for the most part by the peritoneum. The muscle consists of a fleshy rim which
may be subdivided into costal and sternal parts; a lumbar part, composed of two
crura; and a tendinous center.

Attachments. — (1) Costal part (Pars costalis): The cartilages of the eighth,
ninth, and tenth ribs, and behind this to the ribs at an increasing distance from their
sternal ends.

(2) Sternal part (Pars sternalis) : The upper surface of the xiphoid cartilage.

(3) Lumbar part (Pars lumbalis): (a) The right crus (Crus dextrum) is at-
tached to the ventral longitudinal ligament, and by this means to the first four or
five lumbar vertebrae. (6) The left crus (Crus sinistrum) is attached in a similar
fashion to the first and second lumbar vertebrae.

Action. — It is the principal muscle of inspiration and increases the longitu-
dinal diameter of the chest. The contraction produces a general lessening of the
curvature of the diaphragm. In the expiratory phase the costal part and crura lie
almost entirely on the body walls, so that the bases of the lungs are in contact with
the tendinous center almost exclusively. In orcUnary inspiration the fleshy rim
recedes from the chest-wall, so that the bases of the lungs move backward to a line
about parallel with the costal arches, and about four or five inches (ca. 10-12 cm.)
therefrom.

It is stated that the inspiratory movement affects the tendinous center much less than the
fleshy part, and that the foramen venaj cava; scarcely moves at all, since the posterior vena cava
is firmly attached to it. It should be noted, however, that the direction of the thoracic part of
the vena cava in the expiratory phase is oblique upward and backward. Thus it would seem that
there is no anatomical reason why the diaphragm should not move as a whole in ordinary inspira-
tion at least; examination of formahn-hardened subjects in which the diaphragm appears to be
fixed in the inspiratory phase indicates that such is the case.

Structure. — The costal part consists of a series of digitations which meet, or
are separated by a very narrow interval from, the transversus abdominis; between
the two are the musculo-phrenic vessels. From the tenth rib backward the at-
tachments to the ribs are at an increasing distance above the costo-chondral junc-
tions. Thus at the last rib the upper limit of the attachment is four to five inches
(10-12 cm.) from the ventral end. Anteriorly the origin extends along the eighth

1 It should be noted, however, that in the embryo the diaphragm appears as a paired struc-
ture, extending from the lateral walls of the ccelom to fuse with the septum transversum.

286

FASCIA AND MUSCLES OF THE HORSE

and ninth costal cartilages to the xiphoid cartilage. From these points of origin
the fibers curve inward and forward to join the tendinous center.^ The right cms
is about twice as thick as the left one and is also longer. It arises by a strong tendon

Longissimus dorsi

Lumbar transverse
process

Costal arch
Musculo-phrenic
artery

Transvcrsus

abdominalis {cut

edge)
Xiphoid cartilage
(depressed)

Fig. 275. — Diaphr.^gm of Horse; Abdominal Surface.
i, Ventral longitudinal ligament; .2, ;2', tendons of crura; 3, lumbar sympathetic trunks; 4, external spermatic
nerve; o, 5, great splanchnic nerves; 6, cisterna chyli (opened); 7, 7, ce.sophageal continuations of vagus nerves;
8, lymph-gland; 9, coronary ligament of liver (cut); 10, right lateral ligament of Uver (cut); 11, left lateral ligament of
liver (cut); 12, falciform ligament of liver (cut); A.I., lumbo-costal arch; N.i., intercostal nerve; C.d., right crus;
C.S., left crus; A, aorta; Ca, coeliac artery; Oe., oesophagus; V.c, posterior vena cava; V.p., phrenic veins. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)

which blends with the ventral longitudinal ligament. The tendon is succeeded by
a rounded belly which leaves the vertebral column at the last thoracic vertebra.

1 It is interesting to note that when a nineteenth rib is present (even when it is well developed)
the diaphragm has no connection with it, but ends on the eighteenth rib at a point a Uttle more
ventral than usual.

THE ABDOMINAL FASCIiE AND MUSCLES 287

Passing downward and forward, its fibers spread out and join the tendinous center.
The left cms arises by a thin tendon from the ventral longitudinal ligament at the
first and second lumbar vertebrae. This is succeeded by a triangular belly which
joins the central tendon. Between the crura and the attachment to the last rib
the edge of the muscle crosses the ventral surface of the psoas muscles without at-
tachment, forming the so-called lumbo-costal arch (Arcus lumbocostalis) ; here the
thoracic and abdominal cavities are separated only by the serous membranes and
some areolar tissue. The tendinous center (Centrum tendineum) resembles the
periphery in outline, but is more elongated. It is partially divided into right and
left parts by the descent of the crura into it. It is composed largely of radiating
fibers, but many interlace in various directions; this is speciallj^ evident around the
foramen venae cavae, which is encircled by fibers. A strong tendinous layer extends
across below the hiatus oescphageus.

Schmaltz and others describe the lumbar part as consisting of four crura, two medial and two
lateral. On this basis the left crus of the preceding description becomes the crus lalerale sinistrum,
and the corresponding part of the right side is the crus laterale dextrtim. The central part is divided
by the hiatus oesophageus and the sht which extends from it dorsally into a crus mediale dextrum
and a crus mediale sinistrum. Both modes of division are in part artificial.

The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an
interval between the two crura and below the last thoracic vertebra. It contains
the aorta, vena azygos, and cisterna chyH. (2) The hiatus oesophageus^ perforates
the right crus near its junction with the tendinous center. It is situated a little to
the left of the median plane and about a hand breadth ventral to the thirteenth
and fourteenth thoracic vertebrae. It transmits the oesophagus, the vagus nerves,
and the oesophageal branch of the gastric artery. (3) The foramen venae cavae^
pierces the tendinous center about an inch (ca. 2-3 cm.) to the right of the median
plane, and about six to eight inches (ca. 15-20 cm.) below the eleventh and
twelfth thoracic vertebrae. The vena cava is firmly attached to the margin of the
opening.'^

Relations. — The thoracic surface is related to the endothoracic fascia, pleurae,
pericardium, the bases of the lungs, and the ribs in part. The abdominal surface
is in great part covered by the peritoneum, and is related chiefly to the liver, stom-
ach, intestine, spleen, pancreas, kidneys, and adrenals. The sympathetic trunk and
splanchnic nerve pass between the crus and the psoas muscles on each side. The
musculo-phrenic vessels perforate the edge of the muscle at the ninth costo-chondral
joint.

Blood-supply. — Phrenic and musculo-phrenic arteries.

Nerve-supply. — Phrenic nerves.

The Abdominal Fasci^e and Muscles
(fascle et musculi abdominis)

The superficial fascia of the abdomen is in part fused dorsally with the lumbo-
dorsal fascia; in front it is continuous with the superficial fascia of the shoulder and
arm, behind with that of the gluteal region. In the inguinal region it forms part
of the fascia of the penis or of the mammary glands. At the lower part of the flank
it forms a fold which is continuous mth the fascia of the thigh near the stifle joint.

1 Formerly termed the foramen sinistrum. ^ Formerly termed the foramen dextrum.

^ In order to get a clear idea of the relative positions of these foramina and of the form of
the diaphragm, the thoracic surface of the latter should be examined in properly preserved sub-
jects while the abdominal idscera remain in situ. It will be observed that the distances of the
hiatus oesophageus and foramen vense cavae from the vertebral column vary according to the ful-
ness of the abdominal viscera and the degree of contraction of the diaphragm. The statements
given above are averages.

288 FASCIA AND MUSCLES OF THE HORSE

In this fold are the prefemoral lymph-glands. Medially it blends with the linea
alba. It contains the abdominal cutaneous muscle (described on p. 254).

The deep fascia is represented chiefly by the abdominal tunic (Tunica flava
abdominis) . This is a sheet of elastic tissue which assists the muscles in supporting
the great weight of the abdominal viscera. It is practically coextensive with the
obliquus externus, which it covers. Ventrally it is thick, and is intimately ad-
herent to the aponeurosis of the muscle. Laterally it becomes thinner and is more
easily separated, although fibers from it dip in between the muscle-bundles. It is
continued for some distance upon the inter costals and serratus ventralis. Traced
forward, it passes as a thin layer beneath the posterior deep pectoral muscle. Pos-
teriorly it is attached to the tuber coxae. In the inguinal region it forms the deep
fascia of the prepuce or of the mammary glands.

The linea alba is a median fibrous raphe which extends from the xiphoid car-
tilage to the prepubic tendon. It is formed chiefly by the junction of the aponeu-
roses of the oblique and transverse muscles, but partly by longitudinal fibers. A
little behind its middle (about in a transverse plane tangent to the last pair of ribs)
is a cicatrix, the iimbilicus, which indicates the position of the umbilical opening
of the foetus.

1. Obliquus abdominis externus, — This is the most extensive of the abdominal
muscles. It is a broad sheet, irregularly triangular in shape, widest behind. Its
fibers are directed chiefly downward and backward.

Origin. — (1) The lateral surfaces of the last fourteen ribs, and the fascia over
the external intercostal muscles; (2) the lumbo-clorsal fascia.

Insertion. — (1) The linea alba and the prepubic tendon; (2) the tuber coxae and
shaft of the ilium; (3) the medial femoral fascia.

Action. — (1) To compress the abdominal viscera, as in defecation, micturition,
parturition, and expiration; (2) to flex the trunk (arch the back) ; (3) acting singly,
to flex the trunk laterally.

Structure. — The muscle is composed of a muscular part and an aponeurosis.
The muscular part lies on the lateral wall of the thorax and abdomen. It arises
by a series of digitations, the anterior four of which alternate with those of the ser-
ratus ventralis. The origin may be indicated by a slightly curved line (concave
dorsally) drawn from the lower part of the fifth rib to the tuber coxae. The fibers
are directed downward and backward and terminate on the aponeurosis, except in
the upper part of the flank, where they are less oblique in direction and end on the
tuber coxae. The line of junction is a curve (concave dorsally) extending from the
upper edge of the posterior deep pectoral muscle toward the point of the hip. The
aponeurosis is intimately attached to the abdominal tunic, and its fibers are largely
interwoven ventrally with those of the aponeurosis of the internal oblique. By
this fusion is formed the outer sheath of the rectus abdominis, which blends at the
linea alba with that of the opposite side. In the inguinal region the aponeurosis
divides into two chief layers; one of these curves dorsally and backward and is in-
serted into the tuber coxae and the prepubic tendon. Between these points the
aponeurosis is much strengthened and is called the inguinal ligament (Ligamentum
inguinale).^ This curves upward and somewhat forward, becomes thin, and blends
with the iliac fascia. It forms the posterior wall of the inguinal canal. About an
inch (ca. 2 to 3 cm.) in front of the pubis and about two inches (ca. 4 to 5 cm.)
from the mecUan plane the aponeurosis is pierced by a slit-like opening, the
subcutaneous or external inguinal ring (Annulus inguinalis subcutaneus).^ This is

1 Also commonly known as Poupart's ligament — based on a false historical allusion. It is
in no proper sense a ligament, but is the inguinal part of the aponeurosis of the obliquus externus;
it might therefore well be termed the lamina inguinalis.

- It is narrow and slit-like in the natural condition, but may appear oval in the dissecting-
room, especially if the hind limb is drawn back and abducted.

THE ABDOMINAL FASCIA AND MUSCLES

289

the external orifice of the inguinal canal. Its long axis is directed outward, for-
ward, and somewhat ventrally, and is four to five inches (ca. 10-12 cm.) in length.

•a <

o o

1 §
Is

OS
S ^ si

§•" a
§ s^

2 3 g
M J pp

The medial angle is rounded and is well defined by the junction of the aponeurosis
with the prepubic tendon, but the lateral angle is not so sharply defined. The bor-
ders or crura are constituted by arciform fibers of the aponeurosis (Crus mediale,
19

290 FASCIA AND MUSCLES OF THE HORSE

laterale). The femoral lamina of the aponeurosis (Lamina femoralis) passes on
to the medial surface of the thigh, where it blends with the femoral fascia. A
thin iliac lamina (Lamina iliaca) passes over the lateral margin of the iliacus and
is attached to the lateral border of the ilium.

Relations. — Superficially, the skin, the abdominal cutaneus, the abdominal
tunic, and the posterior deep pectoral muscle; deeply, the ribs and their cartilages,
the intercostal muscles, the obliquus abdominis internus, the contents of the inguinal
canal, and the sartorius and gracilis.

Blood-supply. — Intercostal and lumbar arteries.

Nerve-supply. — Intercostal and lumbar nerves.

2. Obliquus abdominis internus. — This muscle is situated under the preceding
one. Its fibers are directed do^\aiward, forward, and inward. It forms a triangular
curved sheet with the base behind.

Origin. — The tuber coxse and the adjacent part of the inguinal ligament.

Insertion. — (1) The cartilages of the last four or five ribs; (2) the linea alba
and the prepubic tendon.

Action. — Similar to that of the preceding muscle.

Structure. — Like the external oblique, it is composed of a fleshy portion and
an aponeurosis. The muscular part is fan-shaped, and is situated chiefly in the
flank. At its iliac origin it is covered by a glistening aponeurosis. Traced medially
and ventrally along the abdominal surface of the inguinal ligament, the muscular
origin is found to become much thinner, and also becomes looselj'' attached to the
ligament. This medial part of the muscle forms the anterior wall of the inguinal
canal. The abdominal orifice of the canal, the abdominal or internal inguinal
ring^ (Annulus inguinalis abdominalis), is found here. It is normally a narrow
slit, bounded in front by the edge of the internal oblique, and behind by the in-
guinal ligament. Near the last rib the muscle divides into two parts. The small
dorsal part is inserted by four or five thin tendinous strips to the medial surface of
the last four or five costal cartilages. The aponeurosis of the large ventral part
is to a great extent blended with that of the external oblique, being, indeed, consider-
ably interwoven Avith it ventrally. Where it covers the rectus abdominis it is at-
tached to the tendinous inscriptions of that muscle. It may be noted that the dor-
sal margin of the aponeurosis varies in different subjects in the fact that it may
cover the costal arch or lie ventral to it.

Relations. — Superficially, the obliquus externus; deeply, the rectus abdominis^
transversus abdominis, and the peritoneum.

Blood-supply. — Circumflex iUac, lumbar, and intercostal arteries.

Nerve-supply. — Ventral branches of the lumbar nerves.

3. Rectus abdominis. — This muscle is confined to the ventral part of the ab-
dominal wall ; it extends from the sternal region to the pubis.

Origin. — The cartilages of the fourth or fifth to the ninth ribs inclusive, and the
adjacent surface of the sternum.

Insertion. — The pubis, by means of the prepubic tendon.

Action. — Similar to that of the oblique muscles. It is especially adapted to
flex the lumbo-sacral joints and the lumbar and thoracic parts of the spine.

Structure. — The fibers of the muscle are directecl longitudinally. Nine to
eleven transverse bands of fibrous tissue extend in an irregular maimer across the

1 It must be admitted that the term "ring" is rather misleading as applied to the abdomi-
nal opening of the canal, since normally it is a mere dilatable slit. The ring-hke constriction
which exists here in the male is constituted by the peritoneum, which descends into the canal
to form the tunica vaginalis. This peritoneal ring is termed the vaginal ring (Annulus vagi-
nalis), and must not be confused with the subperitoneal ring, i. e., the abdominal or internal
inguinal ring. The internal inguinal ring is six or seven inches (ca. 16 cm.) in length. Its
direction corresponds approximately to a line from the lateral margin of the prepubic tendon to the
ventral part of the tuber coxa;.

THE ABDOMINAL FASCIA AND MUSCLES 291

muscle. These are termed inscriptiones tendineaB. They strengthen the muscle
and serve to prevent separation of its fibers. The width of the muscle is greatest
about its middle. The anterior part blends with the rectus thoracis.

Relations. — Superficially, the aponeuroses of the oblique muscles (which con-
stitute the external rectus sheath) and the posterior deep pectoral; deeply, the
transversus abdominis, intercostals, the cartilages of the ribs, and the sternum.
The posterior abdominal artery runs along the lateral edge of the muscle posteriorly,
and the anterior abdominal artery on or in its anterior part.

Blood-supply. — Anterior and posterior abdominal arteries.

Nerve-supply. — Intercostal and lumbar nerves.

4. Transversus abdominis. — This muscle, named from the general direction
of its fibers, is a triangular curved sheet. Its lateral part is muscular, its ventral
aponeurotic.

Origin. — (1) The medial surfaces of the distal ends or the cartilages of the
asternal ribs, meeting the costal attachment of the diaphragm; (2) the transverse
processes of the lumbar vertebrae, by means of the deep layer of the lumbo-dorsal
fascia.

Insertion. — The xiphoid cartilage and the linea alba.

Action. — Similar to that of the oblique muscles.

Structure. — The muscular part is a sheet of parallel bundles of fibers, directed
ventro-medially. It is thickest along the cartilages of the ribs, and from here it
thins out greatly toward the aponeurosis and the lumbar region. The fibers of the
aponeurosis directly continue those of the fleshy part. Posteriorly it becomes ex-
tremely thin and fades out without reaching the pelvis. It covers the deep face
of the rectus, so forming the internal rectus sheath.

Relations. — Superficially, the oblique and straight muscles, the retractor costae,
the cartilages of the asternal ribs, and the internal intercostal muscles; deeply, the
fascia transversalis and the peritoneum. The fascia transversalis is little de-
veloped in the horse, and is very thin in emaciated subjects, but in animals in good
condition it contains a good deal of fat. It blends with the iliac fascia and de-
scends into the inguinal canal. The musculo-phrenic artery runs along the inter-
val between the origin of the transversus and the costal part of the diaphragm.
The intercostal nerves pass down over the lateral surface of the muscle, to which
they give branches. Branches of the first three lumbar nerves are similarly cUs-
posed further back.

Blood-supply. — Intercostal, lumbar, and musculq|phrenic arteries.

Nerve-supply. — Intercostal and lumbar nerves.

5. Cremaster extemus. — This small muscle may be regarded as a detached
portion of the obliquus abdominis internus, with which it blends at its origin (Figs.
370, 575).

Origin. — The iliac fascia, near the origin of the sartorius.

Insertion. — The tunica vaginalis communis.

Action. — To raise the tunica vaginalis, and with it the testicle.

Structure.- — The muscle arises by a thin aponeurosis which is succeeded by a
flat muscular belly about two inches (ca. 5 cm.) in width in the stallion.^ It passes
down the inguinal canal on the postero-lateral surface of the tunica vaginalis, to
which it is very loosely attached. On reaching the point where the tunic is reflected
on to the tail of the epididymis, the muscle is inserted into the outer surface of the
tunic by short tendinous fibers.

Relations. — The muscle lies between the peritoneum and the fascia trans-
versalis in front and the iliac fascia and inguinal ligament behind. On reaching

1 As might be expected, the cremaster usually undergoes more or less atrophy and is paler
In the castrated subject. In the mare the muscle is very small, and ends in the connective tissue
in the inguinal canal.

292 FASCIA AND MUSCLES OF THE HORSE

the abdominal ring it descends the inguinal canal on the postero-lateral surface of
the tunica vaginalis communis.

Blood-supply. — External spermatic artery.

Nerve-supply. — External spermatic nerve.

The Inguinal Canal. — This term (Canalis inguinalis) is applied to an oblique
passage through the posterior part of the abdominal wall.^ It begins at the ab-
dominal inguinal ring, and extends obliquely ventro-medially, and somewhat for-
ward, to end at the subcutaneous inguinal ring. Its anterior wall is formed by the
fleshy posterior part of the internal oblique muscle, and the posterior wall by the
strong tendinous inguinal ligament. The average length of the canal, measured
along the spermatic cord, is about four inches (ca. 10 cm.). The abdominal or
internal inguinal ring (Annulus inguinalis abdominalis) is the internal opening of
the canal; it is bounded in front by the thin margin of the internal oblique muscle,
and behind by the inguinal ligament. It is directed from the edge of the prepubic
tendon approximately toward the tuber coxae. Its length is about six or seven
inches (ca. 15-17.5 cm.). The edge of the muscle is attached to the surface of the
ligament here by delicate connective tissue, except where structures intervene be-
tween the walls of the canal. The lateral limit of the ring is determined by the
muscle becoming firmly attached to the ligament, i. e., actually arising from the
latter. The subcutaneous or external inguinal ring (Annulus inguinalis subcutan-
eus) is a well-defined slit in the aponeurosis of the external oblique muscle, lateral
to the prepubic tendon. Its long axis is directed from the edge of the prepubic
tendon outward, forward, and slightly ventrally, and its length is about four or five
inches (ca. 10-12 cm.). The canal contains in the male the spermatic cord, the
tunica vaginalis, the external cremaster muscle, the external pudic artery (and in-
constantly a small sateUite vein), and the inguinal lymph vessels and nerves. In
the female it contains the mammary vessels and nerves; in the bitch it also lodges
the round ligament of the uterus, enclosed in a tubular process of peritoneum.

The two rings do not correspond in direction, but diverge laterally, so that the length of the
canal varies greatly when measured at different points. The medial angles of the two rings are
separated only by a distance equal to the thickness of the prepubic tendon (about a centimeter),
but the lateral angles are about seven inches (ca. 17.5 cm.) apart. The distance measured along
the spermatic cord is about four inches (ca. 10 cm.). The medial angle of the subcutaneous ring
is well defined and distinctly palpable at the side of the prepubic tendon; from here the direction
of the ring is traceable.

The Prepubic Tendon. — The prepubic tendon (Tendo prsepubicus) is essentially
the tendon of insertion of the two recti abdominis, but also furnishes attachment to
the obliqui, the graciles, and the pectinei. It is attached to the anterior borders of
the pubic bones, including the ilio-pectineal eminences. It has the form of a very
strong thick band, with concave lateral borders which form the medial boundaries
of the subcutaneous inguinal rings. Its direction is oblique upward and backward.^
Its structure is somewhat complex. Most of the fibers of the posterior part extend
from one ilio-pectineal eminence to the other. The fibers which belong to the recti
curve in to the median line. The aponeuroses of the internal oblique muscles are
inserted into its abdominal surface, and the inguinal ligaments are attached to and
continue across it in arciform fashion. The anterior part of the tendon of origin
of the gracilis is fused with it ventrally, and many of the fibers of the pectineus
arise from it. It gives off on either side a strong round band, the so-called accessory
ligament, which is inserted into the fovea of the head of the femur with the round

^ The term canal is somewhat misleading; it is rather a slit-like passage or space between
the two obUque muscles, since the inguinal ligament is that part of the aponeurosis of the exter-
nal obhque muscle which stretches between the tuber coxa; and the prepubic tendon.

- The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical
importance in regard to manipulation of the fcstus in obstetrical cases. The slope varies in
different subjects. In some cases the tendon forms about a right angle with the pubic bones.

THE MUSCLES OF THE THORACIC LIMB 293

ligament {vide hip joint). A band from the ventral surface extends backward and
blends with the tendon of origin of the gracilis on each side.

The Muscles of the Thoracic Limb

L the muscles of the shoulder girdle (Figs. 266. 267, 268, 276)
This group (Mm. cinguli extremitatis thoracalis) consists of those muscles
which connect the thoracic limb with the head, neck, and trunk. It may be re-
garded as consisting of two divisions — dorsal and ventral.^

A. Dorsal Dfvision

This division consists of two layers which overlie the proper muscles of the
neck and back.

First Layer

L Trapezius. — This is a flat, triangular muscle, the base of which extends
along the supraspinous ligament. It is divided by an aponeurotic portion into two
parts :

(a) Trapezius cervicalis. — Origin. — The funicular part of the ligamentum
nuchae, from the second cervical to the third thoracic vertebra.

Insertion. — The spine of the scapula and the fascia of the shoulder and arm.

(b) Trapezius thoracalis (s. dorsalis). — Origin. — The supraspinous ligament,
from the third to the tenth thoracic vertebra.

Insertion. — The tuber spinse of the scapula.

Action. — Acting as a whole, to elevate the shoulder; the cervical part draws
the scapula forward and upward and the thoracic part draws it backward and up-
ward.

Structure. — The muscle arises by a narrow, thin aponeurosis, from which the
fibers of the flat fleshy part converge to the spine of the scapula and the aponeurosis
which separates the two portions. The cervical fascia joins the ventral edge of the
cervical portion to the brachiocephalicus, or the two muscles may unite or overlap
here.

Relations. — Superficially, the skin and fascia; deeply, the rhomboideus,
latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus ventralis,
and anterior deep pectoral muscles, and the cartilage of the scapula.

Blood-supply. — Deep cervical and intercostal arteries.

Nerve-supply. — Spinal accessory nerve.

Second Layer

This consists of two muscles — the rhomboideus and latissimus dorsi.
2. Rhomboideus. — This consists of two parts:

(a) Rhomboideus cervicalis. — Origin. — The funicular part of the ligamentum
nuchse, from the second cervical to the second thoracic vertebra.

Insertion. — The medial surface of the cartilage of the scapula.

(b) Rhomboideus thoracalis (s. dorsalis). — Origin. — The spinous processes of
the second to the seventh thoracic vertebra by means of the dorso-scapular liga-
ment.

Insertion. — The medial surface of the cartilage of the scapula.
Action.- — To draw the scapula upward and forward. When the limb is fixed
the cervical part will elevate the neck.

^ The terms dorsal and ventral are here used in the topographic and not in the ixiorpho-
logical sense; all the muscles of the group are ventral in the latter sense.

294 FASCIA AND MUSCLES OF THE HORSE

Structure. — The cervical part is narrow, pointed at its anterior extremity, and
lies along the funicular part of the ligamentum nuchse, to which it is attached by
short tendon bundles. The fibers are directed for the most part longitudinally.
The thoracic part is quadrilateral in shape, and its fibers are nearly vertical. Its
deep face is intimately attached to the dorso-scapular ligament.

Relations. — Superficially, the skin and fascia (over a small area in front), the
trapezius, and the cartilage of the scapula; deeply, the dorso-scapular ligament,
the splenius, complexus, longissimus dorsi, and serratus dorsalis.

Blood-supply. — Dorsal and deep cervical arteries.

Nerve-supply. — Sixth and seventh cervical nerves.

3. Latissimus dorsi. — This is a ^vide muscle which has the form of a right-
angled triangle. It lies for the most part under the skin and cutaneous muscle,
on the lateral wall of the thorax, from the spine to the arm.

Origin. — The lumbo-dorsal fascia — and by this means from the lumbar and
thoracic spines as far forward as the highest point of the withers.

Insertion. — The teres tubercle of the humerus, in common with the teres
major.

Action. — To draw the humerus upward and backward and flex the shoulder-
joint. If the limb is advanced and fixed, it draws the trunk forward.

Structure. — The muscle arises by a wide aponeurosis, which fuses with that
of the serratus dorsalis and with the lumbo-dorsal fascia. The muscular part
is at first rather thin, but by the convergence of its fibers becomes thicker as it
approaches the arm. The anterior fibers pass almost vertically downward over
the dorsal angle of the scapula and its cartilage. The posterior fibers are directed
downward and forward. The thick belly formed by the convergence of these
passes under the triceps to end on the flat tendon of insertion, which is common
to this muscle and the teres major. The tendon of insertion furnishes origin to the
anterior part of the tensor fasciae antibrachii.

Relations. — Superficially, the superficial fascia, skin, cutaneus, trapezius,
and triceps; deeply, the cartilage of the scapula, the rhomboideus, the serrati, the
external intercostals, and the lumbo-dorsal fascia.

Blood-supply. — Subscapular, intercostal, and lumbar arteries.

Nerve-supply . — Thoraco-dorsal nerve .

B. Ventral Division

1. Brachiocephalicus.^ — This muscle extends along the side of the neck from
the head to the arm. It is incompletely divisible into two portions.

Origin. — (1) The mastoid process of the temporal bone and the nuchal crest;
(2) the wing of the atlas and the transverse processes of the second, third, and
fourth cervical vertebrae.

Insertion. — The deltoid tuberosity, the curved rough line which extends from
this almost to the distal extremity of the humerus, and the fascia of the shoulder
and arm.

Action. — When the head and neck are fixed, to draw the limb forward, ex-
tending the shoulder joint. When the limb is fixed, to extend the head and neck,
if the muscles act together; acting separately, to incline the head and neck to
the same side. By means of its attachment to the strong fascia which extends
from the deltoid tuberosity to the outer face of the elbow the muscle also acts as
an extensor of the elbow joint (e. g., in standing).

Structure. — As already mentioned, the muscle is capable of incomplete di-
vision into two parts, the line of division being indicated by the emergence of sup-
erficial branches of the ventral divisions of the cervical nerves. The mastoid part

^ This muscle is also called the mastoido-humeralis, humero-mastoideus, dero-brachialis and
levator humeri.

THE MUSCLES OF THE SHOULDER GIRDLE 295

(M. cleido-mastoideus) partly overlaps the other (M. cleido-transversarius), which
lies dorsal to it. The former is attached to the mastoid process and the occipital
bone by a broad tendon which fuses at its terminal part with that of the splenius
and longissimus capitis et atlantis; it is also attached to the tendon of insertion of
the sterno-cephalicus by aponeurosis. The dorsal part is attached to the transverse
processes by four fleshy digitations. The belly of the muscle is adherent superfi-
cially to the cervical fascia and the cutaneous muscle, and deeply to the omo-
hyoideus. In front of the shoulder its deep face may present a tendinous inter-
section of variable development.^ Here the muscle becomes wider, covers the
shoulder joint, passes between the brachialis and biceps, and is inserted by means
of a wide tendon which it shares with the superficial pectoral muscle.

Relations. — Superficially, the skin, cervical fascia, the parotid gland, the cuta-
neus, the brachialis, and branches of the cervical nerves; deeply, the splenius,
longissimus capitis et atlantis, rectus capitis ventralis major, omo-hyoideus, ser-
ratus ventralis, anterior deep pectoral and biceps muscles, the inferior cervical
artery, the prescapular lymph glands, and branches of the cervical nerves. The ven-
tral edge of the muscle forms the dorsal boundary of the jugular furrow. The
dorsal border may be in contact with the cervical trapezius, or be separated from
it by a variable interval.

Blood-supply. — Inferior cervical, carotid, and vertebral arteries.

Nerve-supply.- — Spinal accessory, cervical, and axillary nerves.

The pectoral fascia is a thin membrane covering the surface of the pectoral
muscles, to which it is, for the most part, closely attached. It detaches a layer
which passes between the superficial and deep pectorals. At the posterior edge of
the triceps another layer is given off, which passes on the lateral surface of this
muscle to blend with the scapular fascia; the deeper layer becomes continuous with
the subscapular and cervical fasciae.

The pectoral muscles form a large fleshy mass which occupies the space be-
tween the ventral part of the chest-wall and the shoulder and arm. They are
clearly divisible into a superficial and a deep layer. The superficial layer may be
subdivided into two parts by careful dissection; the deep layer is clearly made up
of two muscles.

2. Superficial pectoral muscle (M. pectoralis superficialis) .

(a) Anterior superficial pectoral muscle (pars descendens) .^ — This is a short,
thick, somewhat rounded muscle, which extends from the manubrium sterni to
the front of the arm. It forms a distinct prominence on the front of the breast,
which is easily recognized in the living animal.

Origin. — The cariniform cartilage of the sternum.

Insertion. — (1) The curved line of the humerus with the brachiocephalicus; (2)
the fascia of the arm.

Action. — To adduct and advance the limb.

Structure. — The belly of the muscle is convex on its superficial face, but deeply
it is flattened where it overlaps the posterior superficial pectoral. Here the two
muscles are usually closely attached to each other, and care must be exercised in
making the separation. The tendon of insertion blends with that of the brachio-
cephalicus and with the fascia of the arm. At the middle line of the breast a fur-
row occurs between the two muscles; laterally, another furrow, containing the
cephalic vein, lies between the muscle and the brachiocephalicus.

i^eZa^tows.— Superficially, the skin, fascia, and panniculus; deeply, the pos-

1 This is regarded as a vestige of the clavicle. On this basis the portion of the muscle from
the vestige to the arm represents the clavicular part of the deltoid and perhaps the clavicular part
of the pectoraUs major of man.

^ Also termed the pectoralis anticus or pars clavicularis.

296 FASCIA AND MUSCLES OF THE HORSE

terior division, the deep pectoral, and the biceps. The cephahc vein hes in the
groove between this muscle and the brachiocephalicus.

(b) Posterior superficial pectoral muscle (pars transversa). ^^ — This is a wide
muscular sheet which extends from the ventral edge of the sternum to the medial
surface of the elbow.

Origin. — (1) The ventral edge of the sternum as far back as the sixth car-
tilage; (2) a fibrous raphe common to the two muscles.

Insertion. — (1) The fascia on the proximal third of the forearm; (2) the
curved line of the humerus with the preceding muscle.

Action. — To adduct the limb and to tense the fascia of the forearm.

Structure. — It is thin and pale, and mixed with a good deal of fibrous tissue.
The right and left muscles fuse at a median fibrous raphe. The tendon of inser-
tion unites with the fascia on the medial side of the forearm for the most part;
only a small part in front, about an inch in width, is attached to the humerus.

Relations. — Superficially, the skin, fascia, and the preceding muscle; deeply,
the deep pectoral, the biceps, and the brachialis; at the elbow, the median vessels
and nerve, and the medial and middle flexors of the carpus.

3. Deep pectoral muscle (M. pectoralis profundus). — This muscle is much
thicker and more extensive in the horse than the superficial pectoral. It consists
of two distinct parts.

(a) Anterior deep pectoral muscle (pars scapularis).- — This is prismatic and
extends from the anterior part of the lateral surface of the sternum to the cervical
angle of the scapula.

Origin. — The anterior half of the lateral surface of the sternum and the car-
tilages of the first four ribs.

Insertion.- — The aponeurosis which covers the supraspinatus at its dorsal
end, and the scapular fascia.

Action. — To adduct and retract the limb; when the limb is advanced and
fixed, to draw the trunk forward.

Structure.- — The muscle is almost entirely fleshy. It describes a curve (con-
vex anteriorly), passing at first forward, then upward over the front of the shoulder,
a little to its medial side, and finally inclines somewhat backward along the anterior
border of the supraspinatus. It is loosely attached to the latter muscle, and
terminates in a pointed end which becomes more firmly attached near the cer-
vical angle of the scapula.

Relations. — Superficially, the skin and fascia, the cutaneus, superficial pec-
toral, trapezius, and brachiocephalicus muscles, the cephalic vein, and the in-
ferior cervical artery; deeply, the posterior deep pectoral, biceps, supraspinatus,
omo-hyoideus, and serratus ventralis muscles, the brachial vessels, and the branches
of the brachial plexus of nerves.

(b) Posterior deep pectoral muscle (pars humeralis s. ascendens).^ — This is
much the largest of the pectoral group in the horse. It is somewhat triangular or
fan-shaped.

Origin. — (1) The abdominal tunic; (2) the xiphoid cartilage and ventral
aspect of the sternum ; (3) the cartilages of the fourth to the ninth ribs.

Insertion. — (1) The posterior part of the medial tuberosity of the humerus; (2)
the anterior part of the lateral tuberosity of the humerus; (3) the tendon of origin
of the coraco-brachialis.

Action. — To adduct and retract the limb; if the limb is advanced and fixed,
to draw the trunk forward.

Structure. — This muscle is almost entirely fleshy. Its posterior part is wide

^ Also termed the pectoralis transversus or pars sternocostalis.
^ Also tenned the pectoralis parvus or pars praescapularis.
' Also known as the pectoralis magnus.

THE MUSCLES OF THE SHOULDER GIRDLE 297

and thin, but as the muscle is traced forward, it becomes narrower and much
thicker. It passes forward and slightly upward in a gentle curve to its insertion.
The humeral insertion is just below that of the medial division of the supraspinatus.
Part of the fibers are inserted by means of a tendinous band which binds down the
tendon of the biceps and is attached to the lateral lip of the intertuberal or bicipital
groove, and a small part is attached to the tendon of origin of the coraco-brachialis.

Relations. — Superficially, the skin, cutaneus, and superficial pectoral; deeply,
the abdominal tunic, the external oblique, the rectus abdominis et thoracis, the
brachial vessels, and branches of the brachial plexus of nerves. The external
thoracic vein lies along the lateral border.

Blood-supply. — Internal and external thoracic, inferior cervical, anterior
circumflex, and intercostal arteries.

N erve-siipply . — Pectoral nerves, from the brachial plexus.

3. Serratus ventralisi (Figs. 267, 268).— This is a large, fan-shaped muscle,
situated on the lateral surface of the neck and thorax. It derives its name from
the serrated ventral edge of its thoracic portion. It consists of cervical and tho-
racic parts.

(a) Serratus cervicis.

Origin. — The transverse processes of the last four or five cervical vertebrae.
Insertion. — The anterior triangular area on the costal surface of the scapula
(facies serrata) and the adjacent part of the cartilage.

(b) Serratus thoracis.

Origin. — The lateral surfaces of the first eight or nine ribs.

Insertion. — The posterior triangular area on the costal surface of the scapula
(facies serrata) and the adjacent part of the cartilage.

Action. — The two muscles form an elastic support, which suspends the trunk be-
tween the two scapulae." Contracting together, they raise the thorax; contracting
singly, the weight is shifted to the limb on the side of the muscle acting. The two
parts can act separately and are antagonistic in their effect on the scapula. The
cervical part draws the base of the scapula toward the neck, while the thoracic
part has the opposite action; these effects concur in the backward and forward
swing of the limb respectively. With the limb fixed, the cervical part extends
(raises) the neck or inclines it laterally. The thoracic part may act as a muscle of
forced inspiration.

Structure. — In the domesticated animals there is no such clear division of
the muscle as is found in man and the apes. On account of the difference in action,
however, it seems desirable to distinguish the two portions. The serratus cervicis is
thick aiKl almost entirely fleshy. The serratus thoracis has on its superficial face a
thick, tendinous layer which may sustain the weight of the trunk when the muscle
substance relaxes. The ventral edge presents distinct digitations, the last four of
which alternate with those of the obliquus externus abdominis, and are covered by
the abdominal tunic. The fourth and fifth digitations extend nearly to the sternal
ends of the ribs. The ninth digitation is small and may be absent. Exceptionally
additional digitations may be attached to the tenth or eleventh rib or to the fascia
over the intercostal muscles. The fibers converge to the insertion, which is thick
and is intersected by elastic lamellae derived from the dorso-scapular ligament.

Relations. — Superficially, the brachiocephalicus, trapezius, deep pectoral,
subscapularis, teres major, latissimus dorsi, cutaneus, the abdominal tunic, the
brachial vessels, and the long thoracic nerve; deeply, the splenius, complexus,

1 Formerly termed the serratus magnus.

2 It has been commonly stated that these muscles form a sort of sling in which the trunk is
suspended. This is not quite correct as the two muscles do not meet ventrally. The arrange-
ment is admirable, since the pull of the thorax on the muscles presses the scapula? against the body
wall.

298 FASCIA AND MUSCLES OF THE HORSE

serratus dorsalis, longissimi, the ribs and external intercostal muscles, and branches
of the deep cervical and dorsal arteries.

Blood-supply. — Deep cervical, dorsal, vertebral, and intercostal arteries.

Nerve-supply. — Fifth to eighth cervical nerves.

n. THE MUSCLES OF THE SHOULDER

The muscles of this group (Mm. omi) arise on the scapula and end on the arm;
the}' may be divided into two groups — one covering the lateral, the other the costal,
surface of the scapula.

The superficial fascia of the shoulder and arm contains the cutaneous muscle
of this region (vide p. 254), and may be considered to be continued on the medial
side of the limb by the subscapular fascia.

The deep fascia of the shoulder and arm (Fascia omobrachialis) is strong and
tendinous, and is intimately adherent to the muscles on the lateral surface of the
scapula, between which it detaches intermuscular septa, which are attached to the
spine and borders of the scapula. The brachial portion is, for the most part, only
loosely attached to the underlying muscles, for which it forms sheaths; it is attached
to the proximal and deltoid tuberosities of the humerus. A specially strong part
extends from the deltoid tuberosity to the lateral surface of the elbow; it furnishes
insertion to part of the brachiocephalicus and gives origin to fibers of the lateral
head of the triceps and of the extensor carpi radialis. The fascia blends distally
•with the tendon of insertion of the biceps, and is continued by the antibrachial
fascia.

A. Lateral Group (Figs. 267, 268)

1. Deltoideus. — This lies partly on the triceps in the angle between the scap-
ula and humerus, partly on the infraspinatus and teres minor.

Origin. — (1) The upper part of the posterior border of the scapula; (2) the
spine of the scapula, by means of the strong aponeurosis which covers the infra-
spinatus.

Insertion. — The deltoid tuberosity of the humerus.

Action. — To flex the shoulder joint and abduct the arm.

Structure. — The origin of the muscle is partly aponeurotic, partly fleshy.
The aponeurosis fuses with that which covers the infraspinatus; the posterior part
is attached to the scapula immediately in front of the origin of the long head of the
triceps. The belly of the muscle lies for the most part in a cavity formed in the
triceps. It is widest about its middle.

i?e?a^ions.— Superficially, the skin, fascia, cutaneus, and brachiocephalicus;
deeply, the infraspinatus, teres minor, triceps, and brachialis muscles, and branches
of the posterior circumflex artery and axillary nerve.

Blood-supply. — Subscapular artery (chiefly through the posterior circumflex).

Nerve-supply. — Axillary nerve.

2. Supraspinatus. — This muscle occupies the supraspinous fossa, which it
fills, and beyond which it extends, thus coming in contact ^vith the subscapularis.

Origin. — The supraspinous fossa, the spine, and the lower part of the car-
tilage of the scapula.

Insertion. — The anterior parts of the proximal tuberosities of the humerus.

Action. — To extend the shoulder joint. It also assists in preventing dislo-
cation.

Structure. — The surface of the muscle is covered by a strong aponeurosis,
from the deep face of which many fibers arise. The muscle is thin at its origin
from the cartilage, but becomes considerably thicker distally. At the neck of the
scapula it divides into two branches, between which the tendon of origin of the

THE MUSCLES OF THE SHOULDER 299

biceps emerges. These branches, fleshy superficially, tendinous deeply, are united
by a fibrous membrane already mentioned in connection with the deep pectoral
muscle; some fibers are attached to this membrane and the capsule of the shoulder
joint. A bursa is often present under the muscle at the tuber scapulae.

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and brachio-
cephalicus; deeply, the scapula and its cartilage, the subscapularis muscle, and the
suprascapular vessels and nerve; in front, the anterior deep pectoral muscle; be-
hind, the spine of the scapula and infraspinatus muscle.

Blood-supply. — Suprascapular and posterior circumflex arteries.

Nerve-supply. — Suprascapular nerve.

3. Infraspinatus. — This muscle occupies the greater part of the infraspinous
fossa and extends beyond it posteriorly.

Origin. — The infraspinous fossa and the scapular cartilage.

Insertion. — (1) The lateral tuberosity of the humerus, distal to the lateral
insertion of the supraspinatus ; (2) the posterior eminence of the lateral tuberosity.

Action. — To abduct the arm and rotate it outward.^ It also acts as a lateral
ligament.

Structure. — This muscle is also covered by a strong aponeurosis, from which
many fibers arise, and by means of which the deltoid is attached to the spine of
the scapula. A thick tendinous layer partially divides the muscle into two strata,
and, coming to the surface at the shoulder joint, constitutes the chief means of in-
sertion. This tendon, an inch or more (3 cm.) in width, passes over the posterior
eminence of the lateral tuberosity of the humerus; it is bound do^\^l by a fibrous
sheet, and a synovial bursa is interposed between the tendon and the bone. The
portion of the tendon which crosses the lateral tuberosity is in part cartilagi-
nous. When the long insertion is cut and reflected, the short insertion, partly
tenchnous, partly fleshy, is exposed.

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and deltoid;
deeply, the scapula and its cartilage, the shoulder joint and capsule, the long head
of the triceps, the teres minor, and branches of the posterior circumflex artery of the
scapula.

Blood-supply. — Subscapular artery.

Nerve-supply. — Suprascapular nerve.

4. Teres minor. — This is a much smaller muscle than the foregoing. It
lies chieflj^ on the triceps, under cover of the deltoid and infraspinatus.

Origin. — (1) The rough lines on the distal and posterior part of the infra-
spinous fossa; (2) a small part of the posterior border of the scapula, about its
middle; (3) a tubercle near the rim of the glenoid cavity.

Insertion. — The deltoid tuberosity and a small area just above it.

Action. — To flex the shoulder joint and to abduct the arm; also to assist in
outward rotation.

Structure. — The muscle is not rounded, but flat and triangular in the horse.
Its origin from the posterior border of the scapula is by means of a fascicular aponeu-
rosis which also gives origin to fibers of the infraspinatus and triceps. The short,
deep part of the muscle which lies on the joint capsule behind the lateral tuberosity
of the humerus is covered at its origin by the distal edge of the tendon of origin of
the long head of the triceps. A bursa is commonly found between the terminal
part of the muscle and the capsule of the shoulder joint, and is often continuous
with that of the infraspinatus.

Relations. — Superficially, the deltoid and infraspinatus muscles; deeply, the
scapula, the shoulder joint, and the triceps muscle.

Blood-supply. — Subscapular artery.

Nerve-supply. — Axillary nerve.

1 Giinther states that this muscle assists in extension or flexion according to the position
of the head of the humerus relative to the glenoid cavity.

300 FASCIiE AND MUSCLES OF THE HORSE

B. Medial Group

1. Subscapularis. — This muscle occupies the subscapular fossa, beyond which,
however, it extends both before and behind.

Origin. — The subscapular fossa.

Insertion. — The posterior eminence of the medial tuberosity of the humerus.

Action. — To adduct the humerus.

Structure. — The muscle is flat and triangular. The base is thin and inter-
digitates with the scapular attachments of the serratus ventralis. Distally the
belly thickens and becomes narrower. It is covered by an aponeurosis, and con-
tains a considerable amount of tendinous tissue. The tendon of insertion is crossed
by the tendon of origin of the coraco-brachialis; it is intimately adherent to the cap-
sule of the shoulder joint, and may be regarded as replacing the medial ligament of
the latter. A small bursa usually is present between the tendon and the tuberosity
of the humerus.

Relations. — Superficially, the scapula and shoulder joint, the supraspinatus,
triceps, and teres major muscles; deeply, the serratus ventralis muscle, the bra-
chial vessels, and the chief branches of the brachial plexus. The subscapular
vessels run along or near the posterior edge of the muscle.

Blood-supply. — Subscapular artery.

Nerve-supply. — Subscapular nerves.

2. Teres major. — This muscle is flat, widest about its middle, and lies chiefly
on the medial face of the triceps.

Origin. — The dorsal angle and the adjacent part of the posterior border of
the scapula.

Insertion. — The teres tubercle of the humerus, in common with the latissimus
dorsi.

Action. — To flex the shoulder joint and adduct the arm.

Structure. — It is for the most part fleshy, but the origin consists of an apo-
neurosis which blends with that of the tensor fasciae antibrachii. The insertion
is by a flat tendon which fuses with that of the latissimus dorsi.

Relations. — Laterally, the triceps; medially, the serratus ventralis. The sub-
scapular vessels lie in a groove between the anterior edge of this muscle and the
posterior border of the subscapularis; near the shoulder joint the posterior cir-
cumflex artery and the axillary nerve emerge between the two muscles. The
medial face of the muscle is crossed by the thoracic branches of the brachial plexus,
and by the artery which supplies the latissimus dorsi.

Blood-supply. — Subscapular artery.

Nerve-supply.- — Axillary nerve.

3. Coraco-brachialis.^ — This muscle lies on the medial surface of the shoulder
joint and the arm.

Origin. — The coracoid process of the scapula.

Insertion. — (1) A small area above the teres tubercle of the humerus; (2) the
middle third of the anterior surface of the humerus.

Action. — To adduct the arm and to flex the shoulder joint.

Structure. — The long tendon of origin emerges between the subscapularis and
the medial branch of the supraspinatus. It passes over the terminal part of the
subscapularis and is provided with a synovial sheath. The belly spreads out and
divides into two parts. The small, short part is inserted into the proximal third of
the medial surface of the shaft of the humerus ; the large, long part is inserted into
the middle third of the humerus, in front of the teres tubercle and the medial head of
the triceps.

^ Also termed the coraco-humeralis.

THE MUSCLES OF THE SHOULDER

301

Relations. — Laterally, the subscapularis, the brachialis, the tendon of insertion
of the latissimus dorsi, and the humerus; medially, the deep pectoral; in front,
the biceps brachii. The anterior circumflex artery and the nerve to the biceps
pass between the two parts, or between the muscle and the bone, and the brachial
vessels lie along the posterior border of the muscle.

Subscdpularis

Ankrior deep pectoral

Latissimus dorsi

Teres major

Tensor fascice antihrachii.

Deep fascia of forearm

"ipraspmatus

Posterior deep
pectoral

Cora co-brach ialis
Biceps brachii

Extensor carpi radialis

Brachialis

Long medial ligament of elbow

Fig. 277. — Muscles of Shoulder and Arm op Horse; Medial View.
1, Long head of triceps brachii; 2, medial head of triceps; 3, distal end of humerus.

Blood-supply. — Anterior circumflex artery.
Nerve-supply. — Musculo-cutaneous nerve.

4. Capsularis.^ — This is a very small muscle, which lies on the flexion surface
of the capsule of the shoulder joint.

1 Also known as the scapulo-humeralis posticus s. gracilis.

302 FASCIA AND MUSCLES OF THE HORSE

Origin. — The scapula, close to the rim of the glenoid cavity.

Insertion. — The posterior surface of the shaft of the humerus, a short distance
below the head.

Action. — It has been held that it tenses the capsule of the shoulder joint and
prevents its being pinched during flexion, but there does not appear to be any
attachment of the muscle to the joint capsule.

Structure. — It is fleshy and usually about the breadth of a finger. It may,
however, consist of only a few bundles of fibers ; sometimes it is double. It passes
through the brachialis muscle to reach its insertion.

Relations. — Laterally, the teres minor and triceps muscles; medially, the teres
major and subscapularis muscles, and the capsule of the joint.

Blood-supply. — Posterior circumflex artery.

Nerve-supply. — Axillary nerve.

m. THE MUSCLES OF THE ARM
This group consists of five muscles (Mm. brachii) which are grouped around the
humerus. They arise from the scapula and the humerus, and are inserted into the
forearm. They act on the elbow joint and the fascia of the forearm.

1. Biceps brachii.^ — This is a strong fusiform muscle, which lies on the anterior
surface of the humerus (Fig. 277).

Origin. — The tuber scapulae.

Insertion. — (1) The radial tuberosity; (2) the medial ligament of the elbow
joint; (3) the fascia of the forearm and the tendon of the extensor carpi radialis.

Action. — To flex the elbow joint; to fix the shoulder, elbow, and carpus in
standing; to assist the extensor carpi radialis, and to tense the fascia of the fore-
arm.

Structure. — The muscle is inclosed in a double sheath of fascia, which is attached
to the tuberosities and the deltoid ridge of the humerus. The tendon of origin
is molded on the intertuberal or bicipital groove; it is very strong and dense and
is partly cartilaginous. Its play over the groove is facilitated by the large inter-
tuberal or bicipital bursa (Bursa intertubercularis).^ The synovial membrane
covers not only the deep face of the tendon, but extends somewhat around the edges
to the superficial face. A well-marked tendinous intersection runs through the belly
of the muscle and divides distally into two portions. Of these, the short, thick
one is inserted into the radial tuberosity and detaches fibers to the medial collat-
eral ligament of the elbow joint. The long tendon (Lacertus fibrosus) is thinner,
blends with the fascia of the forearm, and ends by fusing with the tendon of the
extensor carpi radialis; thus the action is continued to the metacarpus.

Relations. — Laterally, the brachiocephalicus and brachialis muscles; medially,
the posterior deep pectoral and the superficial pectoral muscles; in front, the an-
terior deep pectoral muscle; behind, the humerus, the coraco-brachialis muscle,
the anterior circumflex and anterior radial vessels, and the musculo-cutaneous
nerve.

Blood-supply. — Branches of the brachial and anterior radial arteries.

Nerve-supply. — Musculo-cutaneous nerve.

2. Brachialis.^ — This muscle occupies the musculo-spiral groove of the humerus.
Origin.- — The proximal third of the posterior surface of the humerus.
Insertion. — The medial surface of the neck of the radius (under cover of the

long collateral ligament) and the transverse radio-ulnar ligament.
Action. — To flex the elbow joint.

^ Also known as the coraco-radialis or flexor brachii.

^ In some cases the bursa communicates with the cavity of the shoulder joint.

' Also known as the humeralis obliquus s. externus and as the brachialis anticus.

THE MUSCLES OF THE ARM 303

Structure. — The peculiar spiral course of this muscle gave rise to the name
often applied to it— humeralis obliquus. Beginning on the posterior surface of the
shaft, close to the head of the humerus, it winds over the lateral surface, crosses the
biceps very obliquely, and finally reaches the medial side of the forearm by passing
between the biceps and the extensor carpi. It is entirely fleshy, with the exception
of its relatively slejider tendon of insertion. Some fibers at the proximal end are
attached to the capsule of the shoulder joint, which may thereby be tensed during
flexion.

Relations. — Laterally, the skin and fascia, the teres minor, deltoid, triceps
(lateral head), and brachiocephalicus muscles. Deeply, the teres major, the bi-
ceps, and the humerus. The anterior radial artery crosses the deep face of the
muscle in its distal third, and the radial nerve accompanies the muscle in the distal
half of the musculo-spiral groove.

Blood-supply. — Brachial artery.

Nerve-supply. — Musculo-cutaneous nerve; frequently radial nerve also.

3. Tensor fasciae antibrachii (Fig. 277). ^ — This is a thin muscle which lies
chiefly on the medial surface of the triceps.

Origin. — The tendon of insertion of the latissimus dorsi and the posterior
border of the scapula.

Insertion. — (1) The deep fascia of the forearm; (2) the olecranon.

Action. — (1) To tense the fascia of the forearm and to extend the elbow joint.

Structure. — The origin consists of a very thin aponeurosis which blends with
those of the caput longum and the latissimus dorsi. In most cases there is a dis-
tinct division into anterior and posterior heads. The muscular portion is thin in
its anterior part, somewhat thicker behind, and is narrower than the aponeurotic
origin. It is succeeded by an aponeurotic insertion, which ends chiefly by blending
with the fascia of the forearm a little below the elbow. There is, however, a small
but constant tendinous attachment to the olecranon.

Relations. — Laterally, the cutaneus, triceps (long and medial heads), the medial
and middle flexors of the carpus, and the ulnar vessels and nerve; medially, the
latissimus dorsi, serratus ventralis, and posterior pectoral muscles.

Blood-supply. — Subscapular, ulnar, and deep brachial arteries.

Nerve-supply. — Radial nerve.

4. Triceps brachii (Figs. 267, 268, 277).— This, together with the preceding
muscle, constitutes the large muscular mass which fills the angle between the pos-
terior border of the scapula and the humerus. It is clearly divisible into three
heads.

(a) Long head (Caput longum tricipitis).' — This, the largest and longest of
the three heads, is a powerful, thick, triangular muscle, which extends from the
posterior border of the scapula to the olecranon.

Origin. — The posterior border of the scapula.

Insertion. — The lateral and posterior part of the summit of the olecranon.

Action. — (1) To extend the elbow joint; (2) to flex the shoulder joint.

Structure.— The muscle arises by a wide, strong aponeurosis from the posterior
border of the scapula. From this the bundles of the fleshy portion converge to
the short, strong tendon of insertion. A careful examination will show that the
muscle is penetrated by a tendinous intersection from which many fibers take origin
obliquely. The superficial face is covered by an aponeurosis which is specially
developed at its distal part. A small bursa occurs under the tendon of insertion.

1 M'Fadyean and Vaughan term this muscle the scapulo-ulnaris, while Arloing and Lesbre
term it "Ancone accessoire du grand dorsal." The above name seems to agree best with the
chief insertion and action, although it certainly arises largely from the tendon of insertion of the
latissimus dorsi.

* Also known as the anconaeus longus or caput magnum.

304 FASCI.E AND MUSCLES OF THE HORSE

Relations. — Laterally, the cutaneus, deltoid, infraspinatus, teres minor, and
the lateral head; medially, the tensor fasciae antibrachii, teres major, latissimus dorsi
and posterior deep pectoral muscles, and the subscapular vessels; in front, the
brachialis and the medial head, the deep brachial and posterior circumflex vessels,
and the axillary and radial nerves; behind, the skin and fascia.

J5/ood-SMpp??/.— Subscapular and deep brachial arteries.

Nerve-supply. — Radial nerve.

(b) Lateral head (Caput laterale tricipitis).' — This is a strong, quadrilateral
muscle, which lies on the lateral surface of the arm. Its proximal third is covered
by the deltoid and teres minor muscles, the remainder only by the thin cutaneous
muscle and the skin.

Origin. — (1) The deltoid tuberosity and the curved rough line which extends
from it to the neck of the humerus; (2) the strong fascia which extends from the
deltoid tuberosity to the lateral surface of the elbow joint.

Insertion. — (1) A small prominent area on the lateral surface of the olecranon;
(2) the tendon of the long head.

Action. — To extend the elbow joint.

Structure. — The origin consists of short tendinous fibers. The belly is thick,
and is composed of parallel bundles which are directed obliquely downward and
backward. They are inserted partly into the tendon of the long head and partly
into the olecranon below and in front of that tendon.

Relations. — Laterally, the deltoid, teres minor, and cutaneus muscles ; medially,
the long and medial heads and the brachialis muscle. Branches of the circumflex
vessels and axillary nerve emerge between the posterior edge of the muscle and the
long head. The deep face of the muscle is related to the branches of the deep bra-
chial artery and of the radial nerve.

Blood-supply. — Posterior circumflex and deep brachial arteries.

Nerve-supply. — Radial nerve.

(c) Medial head (Caput mediale tricipitis) (Fig. 277). ^ — This is much the small-
est of the three heads. It is situated on the medial surface of the arm, and extends
from the middle third of the humerus to the olecranon.

Origin. — The middle third of the medial surface of the shaft of the humerus,
behind and below the teres tubercle.

Insertion. — The medial and anterior part of the summit of the olecranon, be-
tween the insertion of the long head and the origin of the ulnar head of the deep
digital flexor.

Action. — To extend the elbow joint.

Structure. — The muscle is fleshy except at its insertion, where it has a flat ten-
don, under which a small bursa may be found.

Relations. — Laterally, the humerus, brachialis, anconeus, and the lateral head;
medially, the posterior deep pectoral, coraco-brachialis, teres major, latissimus dorsi,
and tensor fascise antibrachii muscles, the brachial and deep brachial vessels, and
the median and ulnar nerves; behind, the long head, branches of the deep brachial
vessels, and the radial nerve.

Blood-supply. — Deep brachial and ulnar arteries.

Nerve-supply. — Radial nerve.

5. Anconeus. — This is a small muscle which covers the olecranon fossa and
is covered by the triceps. It is somewhat difficult to separate from the lateral head.

Origin. — The distal third of the posterior surface of the humerus.

Insertion. — The lateral surface of the olecranon.

Action. — To extend the elbow joint, and to raise the capsule of the joint and
prevent its being pinched during extension.

* Also known as the anconi3eiis lateralis s. externus or caput medium.
2 Also known as the anconjeus mediahs s. internus or caput parvum.

FASCIA AND MUSCLES OF THE FOREARM AND MANUS

305

Structure. — It is almost entirely fleshy. The deep face is adherent to the joint
capsule.

Relations. — Superficially, the triceps muscle; deeply, the humerus and the
elbow joint.

Blood-supply. — Deep brachial artery.

Nerve-supply. — Radial nerve.

-Ul

•Deep flexor tendon

■•Distal end of small metacarpal bone
•'Suspensory ligament

Branch of superficial flexor tendon
Distal digital annular ligament
Upper border of cartilage
of third phalanx

IV. FASCIA AND MUSCLES OF THE FOREARM AND MANUS
(FASCIA ET MUSCULI ANTIBRACHII ET MANUS)

The forearm is covered on three sides by the muscles of this group, leaving
the medial surface of the radius for the most part subcutaneous. The extensors of
the carpus and digit lie on the
dorsal and lateral parts of the
region, while the flexors oc-
cupy the volar surface.

The fascia of the fore-
arm (Fascia antibrachii)
forms a very strong and com-
plete investment for all the
muscles of the region. The
superficial fascia is thin, and
blends at the carpus with the
deep fascia ; it furnishes inser-
tion to the posterior super-
ficial pectoral muscle. The
deep fascia is very strong and
tendinous in character. It
furnishes insertion at its
proximal and medial part to
the tensor fasciae antibrachii
muscle; at its proximal anter-
ior and lateral part to the
brachiocephalicus and biceps.
It is attached at the elbow to
the lateral tuberosities of the
humerus and radius, to the
ulna, and to the collateral
ligaments. On ' the medial
surface of the forearm it
blends with the periosteum
on the subcutaneous surface

of the radius. It is closely adherent to the surface of the extensor muscles, but is
rather loosely attached to the flexors; near the carpus it blends with the tendons
attached to the accessory carpal bone. From its deep face are detached intermus-
cular septa, which form sheaths for the muscles and are attached to the underlying
bones. The principal septa are: (a) One which passes between the common digital
extensor and the lateral extensor and ulnaris laterahs; (h) one between the com-
mon extensor and the extensor carpi radialis; (c) one between the medial and middle
flexors of the carpus.

The carpal fascia (Fascia carpi) is a direct continuation of that of the forearm.
It is attached chiefly to the tuberosities at the distal end of the radius, to the ac-
cessory carpal bone, and to the carpal collateral ligaments. In front it forms the
so-called dorsal annular ligament of the carpus (Lig. carpi dorsale), bridging over
20

Fia. 278. — Digit of Horse; Volar View.
14, Deep flexor tendon; 15, superficial flexor tendon; 16, volar an-
nular ligament of fetlock; 17, proximal digital annular or vaginal liga-
ment; 11, cartilage of third phalanx; 34, digital cushion. (After Ellen-
berger-Baum, Anat. fiir Kiinstler.)

306 FASCIA AND MUSCLES OF THE HORSE

the grooves and binding down the extensor tendons and their synovial sheaths. Be-
hind it is greatly thickened and forms the volar annular or transverse ligament of
the carpus (Lig. carpi transversum) . This stretches across from the accessory car-
pal bone to the medial collateral ligament and the proximal extremity of the medial
metacarpal bone. It thus completes the carpal canal (Canalis carpi), in which lie
the flexor tendons, the carpal synovial sheath, the common digital artery, and
the medial volar nerve.

The superficial fascia of the metacarpus and digit presents no special features,
but the deep fascia (Fascia metacarpea et digitalis) is complicated by the existence
of several annular ligaments. In the metacarpus it is hardly distinguishable from
the periosteum in front. On the proximal part of the volar surface it forms a strong
and close sheath for the flexor tendons, and is attached to the metacarpal bone
on each side. Lower down and between the annular ligaments it is thin. On the
flexion surface of the fetlock joint it is much thickened by fibers passing transversely
from one sesamoid bone to the other, forming the volar annular ligament of the fet-
lock, which binds down the flexor tendons in the sesamoid groove and converts the
latter into a canal. Distal to this is a second thick quadrilateral sheet, the prox-
imal digital annular ligament (Lig. vaginale), which covers and is adherent to the
tendon of the superficial flexor. It is attached on either side by two bands to the
ends of the borders of the first phalanx, thus firmly binding down the flexor tendons.
A little further down a crescentic fibro-elastic sheet, the distal digital annular liga-
ment, covers the terminal expansion of the deep flexor tendon. It is attached
on either side by a strong band to the side of the first phalanx about its middle; its
superficial face is largely covered by the digital cushion and its deep surface is in
great part adherent to the deep flexor tendon. It is also connected with the so-
called tendon or ligament of the ergot (Fig. 572). This is a thin and narrow
fibrous band, which begins in the fibrous basis of the ergot, as the mass of horn at the
fetlock is called. It descends to the side of the pastern joint, crossing over the
digital artery and nerve; here it widens out and blends with the fibro-elastic sheet
just described.

A. Extensor Division

1. Extensor carpi radialis (M. radialis dorsalis).^ — This is the largest muscle
of the extensor division, and lies on the dorsal surface of the radius.

Origin. — (1) The lateral condyloid crest of the humerus; (2) the coronoid
fossa; (3) the deep fascia of the arm and forearm and the intermuscular septum
between this muscle and the common extensor.

Insertion. — The metacarpal tuberosity.

Action. — To extend and fix the carpal joint and to flex the elbow joint.

Structure. — The tendon of origin blends with that of the common extensor
and is adherent to the capsule of the elbow joint. The belly of the muscle is rounded
and runs out to a point at the distal third of the forearm. The tendon, which runs
nearly the whole length of the fleshy portion, appears on the surface of the latter
about its middle; here the muscle shows a distinctly pennate arrangement. The
tendon passes through the middle groove at the distal extremity of the radius and
over the capsule of the carpal joint, bound down by the dorsal annular ligament and
invested with a synovial sheath. The latter begins three to four inches (ca. 8-
10 cm.) above the carpus and extends to the middle of the carpus. Distal to this
the tendon is attached to the joint capsule, but there is usually a small bursa at the
level of the third carpal bone. In the distal half of the forearm the deep fascia
blends with the tendon, and here the latter is joined by the long tendon of the biceps.

Relations. — Superficially, the skin, fascia, and the oblique extensor; deeply,
the capsule of the elbow joint, the short biceps tendon, the radius, the carpal joint

1 Also commonly termed the extensor metacarpi magnus.

EXTENSOR DIVISION 307

capsule, the anterior radial artery, and the radial nerve; laterally, the common ex-
tensor; medially, at the elbow, the brachialis and biceps.

Blood-supply. — Anterior radial artery.

Nerve-supply. — -Radial nerve.

2. Common digital extensor (M. extensor digitalis communis). ^ — This muscle
lies lateral to the foregoing, which it resembles in general form, although less bulky.

Origin. — (1) The front of the distal extremity of the humerus, in and lateral
to the coronoid fossa; (2) the lateral tuberosity on the proximal extremity of the
radius, the lateral ligament of the elbow, and the lateral border of the radius at the
junction of its proximal and middle thirds; (3) the lateral surface of the shaft of
the ulna; (4) the fascia of the forearm.

Insertion. — (1) The extensor process of the third phalanx; (2) the dorsal sur-
face of the proximal extremities of the first and second phalanges.

Action. — To extend the digital and carpal joints, and to flex the elbow joint.

Structure. — The muscle is a compound one, representing the common extensor,
together with vestiges of the proper extensors of the digits. Usually at least two
heads may be distinguished, although the division is always more or less artificial
so far as the muscular part is concerned. The humeral head (Caput humerale),
which constitutes the bulk of the muscle, arises from the front of the lateral epi-
condyle of the humerus in common with the extensor carpi; the tendon of origin
is adherent to the capsule of the elbow joint. Its belly is fusiform, and terminates
in a point near the distal third of the radius. The tendon appears on the surface
of the muscle about the middle of the belly, the arrangement being pennate. The
tendon passes downward through the outer of the two large grooves on the front of
the distal end of the radius, and over the capsule of the carpal joint. Passing down
over the front of the metacarpus, it gradually inclines medially, reaching the middle
line of the limb near the fetlock. A little below the middle of the first phalanx it
is joined by the branches of the suspensory ligament, and the tendon thus becomes
much wider. Two synovial membranes facilitate the play of the tendon. The
proximal one is a synovial sheath which begins about three inches (ca. 7-8 cm.)
above the carpus, and terminates at the proximal end of the metacarpus. At the
fetlock a bursa occurs between the tendon and the joint capsule, but otherwise
the two are adherent. The smaller head, arising chiefly from the radius and ulna,
is often divisible into two parts (Fig. 568). The larger of these is the radial head
(Caput radiale) ;- it arises from the lateral tuberosity and border of the radius, and
from the lateral ligament of the elbow joint. The flat belly is succeeded by a deli-
cate tendon, which accompanies the principal tendon over the carpus (included in
the same sheath), and then passes outward to fuse with the tendon of the lateral
extensor, or it may continue downward between the common and lateral extensor
tendons to the fetlock. Usually a slip is detached which is inserted on the prox-
imal extremity of the first phalanx, or ends in the fascia here. The smaller and
deeper division is the ulnar head (Caput ulnare) f it is usually somewhat difficult
to isolate. It arises from the ulna close to the interosseous space. It has a small
rounded belly and is provided with a deficate tendon which may fuse with the
principal tendon or may be inserted into the joint capsule and the fascia in front of
the fetlock joint.

Relations. — The chief relations of the belly of the muscle are : superficially, the
skin and fascia; deeply, the elbow joint, the radius and ulna, the extensor carpi
obliquus, and the anterior radial vessels and radial nerve; in front and medially,

^ Termed also the anterior extensor of the phalanges or extensor pedis.

2 This (formerly called the muscle of PhilUps) is considered to represent the part of the
common extensor for the fourth and fifth digits.

' Martin considers that this muscle (formerly termed the muscle of Thiernesse) represents
the extensor indicis proprius and the part of the common extensor for the second digit.

308

FASCIA AND MUSCLES OF THE HORSE

the extensor carpi radialis; behind, the lateral extensor and the interosseous
vessels.

Blood-supply. — Radial and interosseous arteries.

Nerve-supply. — Radial nerve.

Lesbre reports that he has found in one case a brachioradialis muscle in the horse. It
was a delicate fleshy bundle, superposed on the medial border of tlie common extensor, and ex-
tended from the lateral condyloid crest to the distal part of the medial border of the radius.

Extensor carpi obliquus

Metacarpal tuberosity -^ ' H
Tendon from common to lateral extensor '^'

Lateral small metacarpal hone

Branch of suspensory ligament to
extensor tendon

Olecranon
Ulnar head of deep flexor

Lateral extensor
Deep flexor {humeral head)

Tendon of ulnaris lateralis
Accessory carpal bone

Check ligament

Suspensory ligament
Flexor tendons

Flexor tendons
Cartilage of tJiird j)halanx

Fig. 279. — Muscles of Left Thoracic Limb of Horse from Elbow Downward; Lateral View.

O, Extensor carpi radialis; g, brachialis; g', anterior superficial pectoral; c, common digital extensor; e, ulnaris la -

eralis. (After EIlenberger-Baum, Anat. fiir Kiinstler.)

3. Lateral digital extensor (M. extensor digitalis lateralis s. digiti quinti pro-
prius).^— This muscle is much smaller than the preceding, behind which it is situated.
Origin.— The lateral tuberosity of the radius and the lateral ligament of the
^ Also known as the lateral extensor of the phalanges.

EXTENSOR DIVISION

309

elbow joint, the shaft of the uhia, the lateral border of the radius, and the inter-
muscular septum.

Insertion. — An eminence on the front of the proximal extremity of the first
phalanx.

Action. — To extend the digit and carpus.

Structure.— TliG: muscle is pennate, and is enclosed in a sheath formed by the
deep fascia, from which many fibers arise. The belly is thin and fusiform and
terminates at the distal third of the forearm. From here the tendon (at first
small and round) passes downward through the groove on the lateral tuberosity
of the distal end of the radius, then over the carpus, and, gradually inclining toward

Intermuscular septum

Common digital extensor

Extensor carpi obliquus

Intermuscular septum

Lateral digital extensor
Intermuscular septum

Deep digital flexor
{humeral head)

Ulnaris lateralis

Deep digital flexor
{ulnar head)

Extensor carpi radialis

Cutaneous branch of mv
culo-cutaneous nerve
Cephalic vein

Median nerve
Flexor carpi radialis

Flexor carpi ulnaris

Ulnar vessels and nerve

Superficial digital flexor

Fig. 280. — Cross-section of Left Forearm of Horse.

Section is cut a little above middle of region and the figure is a proximal view.

1, Median artery and satellite veins; 2, 3, branches of deep brachial and anterior radial vessels; 4, dorsal interosseous

vessels.

the front, but not reaching the middle line of the limb, it passes over the meta-
carpus and fetlock to its insertion. Two synovial membranes occur in connection
with the tendon. A synovial sheath envelops the tendon, beginning about three
inches (ca. 6-8 cm.) above the carpus, and reaching to the proximal end of the
metacarpus. At the fetlock a small bursa lies between the tendon and the joint
capsule, but otherwise the tendon is adherent to the capsule. The tendon becomes
flat and much larger below the carpus, having received the tendon of the radial
head of the common extensor and a strong band from the accessory carpal bone.

Relations. — Superficially, the skin and fascia; deeply, the lateral face of the
radius and ulna; in front, the common extensor, the oblique extensor, and the

310 FASCIiE AND MUSCLES OF THE HORSE

interosseous artery; behind, the lateral flexor of the carpus and the deep flexor of
the digit.

Blood-supply. — Interosseous artery.

Nerve-supply. — Radial nerve.

4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis
brevis).^ — This is a small muscle which curves obliquely over the distal half of the
radius and the carpus.

Origin. — The lateral border and adjacent part of the dorsal surface of the
radius (the attachment area begimiing at a point above the middle of the bone and
extending down to its distal fourth).

Insertion. — The head of the medial (second) metacarpal bone.

Action. — To extend the carpal joint.

Structure. — The muscle is pennate and has a flat belly which curves downward,
forward, and medially over the distal part of the radius. The tendon continues
the direction of the muscle, and passes over the tendon of the extensor carpi radialis ;
it then occupies the oblique groove at the distal end of the radius, and crosses the
medial face of the carpus. It is provided with a sjmovial sheath.

Relations. — Superficially, the skin and fascia, the lateral extensor, and the
common extensor; deeply, the radius, the extensor carpi radialis, the carpal joint
capsule, and the medial ligament of the carpus.

Blood-supply.- — Interosseous and anterior radial arteries.

Nerve-supply. — Radial nerve.

B. Flexor Division

1. Flexor carpi radialis (or medial flexor of the carpus).- — This muscle lies on
the medial surface of the forearm, behind the border of the radius.

Origin. — The medial epicondyle of the humerus, below and behind the col-
lateral ligament.

Insertion. — The proximal end of the medial (second) metacarpal bone.

Action. — To flex the carpal joint and to extend the elbow.

Structure. — The muscle has a short tendon of origin, which is succeeded by a
somewhat flattened, fusiform belly. The tendon of insertion begins near the distal
fourth of the radius and descends in a canal in the transverse carpal ligament. It
is provided with a synovial sheath which begins two or three inches (ca. 5-8 cm.)
above the carpus and extends almost to the insertion of the tendon.

Relations. — Superflcially, the skin and fascia, the posterior superficial pectoral,
and the tensor fasciae antibrachii; deeply, the elbow joint, the radius, the deep
flexor, the flexor carpi ulnaris, the median vessels, and the median nerve. At the
elbow the artery and nerve lie in front of the muscle, but below they dip beneath it.

Blood-supply. — Median artery.

Nerve-supply. — Median nerve.

On removing the deep fascia on the medial surface of the elbow the student may notice a
small muscle lying along the collateral ligament. This is the pronator teres, which is usually
not present or a mere vestige in the horse. It arises by a small, flat tendon from the medial epi-
condyle of the humerus, and is inserted into the medial ligament of the elbow. On account of its
small size and the fact that the forearm is fixed in the po.sition of pronation, the muscle can have
no appreciable function. It is usually represented by a tendinous band.

2. Flexor carpi ulnaris (or middle flexor of the carpus).^ — This muscle lies on the
medial and posterior aspect of the forearm, partly under, partly behind, the preced-
ing muscle. It arises by two heads — humeral and ulnar.

1 Also known as the extensor metacarpi obliquus.

2 Also known as the flexor carpi s. metacarpi internus or radialis volaris.

2 Also known as the flexor carpi (s. metacarpi) medius or ulnaris medialis.

FLEXOR DIVISION

311

Origin. — (1) The medial epicondyle of the humerus just behind the preceding
muscle; (2) the medial surface and posterior border of the olecranon.

Long head of triceps
Medial head of triceps

Olecranon
Ulnar head of deep flexor

Flexor carpi idnaris
Flexor carpi radialis

Accessory carpal bone
Medial ligament of carpus

Superficial flexor tendon

Deep flexor tendon
Suspensory ligament

Distal end of Mc. II
Annular ligament

Superficial flexor tendon
Deep flexor tendon

Biceps brachii

Extensor carpi radialis
Long tendon of biceps
Brachialis

Long medial ligament

Radius

Tendon of extensor carpi
obliquus

Metacarpal tuberosity

Mc. in

Fetlock joint

E.vtensor branch of suspensory
ligament

Common extensor tendon

Pastern joint

Cartilage of third phalanx

Fig. 2S1. — Muscles of Left Thoracic Limb of Horse from Elbow Downward; Medial View.
The fascia and the ulnar head of the flexor carpi ulnaris have been removed. 1, Distal end of humerus; 2, median

Insertion. — The proximal edge of the accessory carpal bone.
Action. — To flex the carpal joint and to extend the elbow.

312

FASCIiE AND MUSCLES OF THE HORSE

Structure. — The humeral head is much the larger, constituting, in fact, the
bulk of the muscle. It is flattened, curved, and tapers at both ends. The ulnar
head, much smaller and very thin, is covered by an aponeurosis from which many of
its fibers arise. It joins the large head a little above the middle of the forearm.

Ulnar head of deep flexor
Stump of flexor carpi radialis

Stump of flexor carpi idnaris

Superficial digital flexor
Deep digital flexor

Tendon of ulnar head

Radial head of superficial flexor
Insertion of flexor carpi idnaris
Accessory carpal bone

Deep flexor tendon
Superficial flexor tendon

Check ligament
Suspensory ligament

Biceps brachii

Brachialis

Long medial ligament

Extensor carpi radialis

Radius

Annular ligament

Deep flexor tendon
Cartilage of third phalanx

Tendon of flexor carpi radialis
Tendon of extensor carpi obliquus

Mc. Ill

Fetlock joint

Extensor branch of suspensory
ligament

Fig. 282. — Muscles of Left Thoracic Limb of Horse, fhom Elbow Downward; Medial View.
Parts of superficial muscles have been removed, carpal canal opened up, and flexor tendons drawn backward.

The tendon of insertion is short and strong; it blends with the posterior annular
ligament of the carpus.

Relations. — Superficially, the tensor fascise antibrachii, superficial pectoral, and
flexor carpi radialis, the skin and fascia, and cutaneous branches of the ulnar
nerve; deeply, the superficial and deep flexors of the digit. In the cUstal half of

FLEXOR DIVISION 313

the forearm the ulnar vessels and nerve lie between the lateral edge of this muscle
and the lateral flexor of the carpus.

Blood-supply. — Ulnar and median arteries.

Nerve-supply. — Ulnar and median nerves.

3. Ulnaris lateralis (or lateral flexor of the carpus).^ — This muscle lies on the
lateral face of the forearm, behind the lateral extensor of the digit.

Origin. — The lateral epicondyle of the humerus, behind and below the lateral
ligament.

Insertion. — (1) The lateral surface and proximal border of the accessory carpal
bone ; (2) the proximal extremity of the lateral (fourth) metacarpal bone.

Action.- — To flex the carpal joint and to extend the elbow.

Structure.- — The belly of the muscle is flattened and is intersected by a good
deal of tendinous tissue. There are two tendons of insertion. The short tendon
is inserted into the accessory carpal bone. The long tendon is detached just above
the carpus; it is smaller and rounded; it passes downward and a little forward
through a groove on the lateral surface of the accessory carpal bone, enveloped by
a synovial sheath, to reach its insertion on the lateral metacarpal bone. A synovial
pouch lies under the origin of the muscle at the elbow joint, with the cavity of
which it communicates.

Relations. — Superficially, the skin, fascia, and cutaneous branches of the ulnar
nerve; deeply, the elbow joint, the ulna, and the flexors of the digit; in front, the
lateral extensor of the digit; behind, the middle flexor of the carpus, the ulnar head
of the deep flexor, and the ulnar vessels and nerve.

Blood-supply. — Interosseous, ulnar, and median arteries.

Nerve-supply. — Radial nerve.

4. Superficial digital flexor- (M. flexor digitalis superficialis) . — This muscle is
situated in the middle of the flexor group, chiefly under cover of the middle flexor
of the carpus.

Origin. — (1) The medial epicondyle of the humerus; (2) a ridge on the pos-
terior surface of the radius, below its middle and near the medial border.

Insertion. — (1) The eminences on the proximal extremity of the second phalanx,
behind the collateral ligaments; (2) the distal extremity of the first phalanx, also
behind the collateral ligaments.

Action. — To flex the digit and carpus and to extend the elbow.

Structure. — The fleshy part of the muscle is the humeral head (Caput humerale) ;
it takes origin from the humerus. The radial head (Caput tendineum) consists of
a strong fibrous band, usually termed the radial or superior check Ugament, which
fuses with the tendon near the carpus. The belly of the muscle is intersected by
tendinous strands, and fuses more or less with that of the deep flexor, from which
it is therefore somewhat difficult to separate. Near the carpus it is succeeded by a
strong, thick tendon which passes down through the carpal canal and is enveloped
by a synovial sheath, in common with the deep flexor. This, the carpal sheath
(Vagina carpea), begins three or four inches (8-10 cm.) above the carpus, and ex-
tends downward nearly to the middle of the metacarpus. Below the carpus the
tendon becomes flattened and broader and at the fetlock it widens greatly. Near
the fetlock it forms a ring through which the tendon of the deep flexor passes (Fig.
286) . Here the two tendons are bound down in the sesamoid groove by the volar
annular ligament, which fuses more or less with the superficial flexor tendon. At
the distal end of the first phalanx the tendon divides into two branches which di-
verge to reach their points of insertion, and between these branches the tendon of

1 Also known as the flexor carpi (s. metacarpi) externus or extensor carpi ulnaris. Morpho-
logically it belongs to the extensor group.

2 Also commonly known as the flexor perforatus or superficial flexor of the phalanges.

314

FASCIA AND MUSCLES OF THE HORSE

the deep flexor emerges (Fig. 278). A second synovial membrane, the digital
synovial sheath (Vagina digitalis), begins at the distal fourth of the metacarpus,

183. — Synovial Sheaths and Burs^ of Distal
Part op Right Fore Limb of Horse; Medial
View.

Fig. 284. — Synovial Sheaths and Burs^ of Distal
Part of Right Fore Limb op Horse; Lateral
View.
The synovial sheaths (colored yellow) and the joint capsules (colored pink) are injected.

a. Sheath of extensor carpi obliquus; b, sheath
of flexor carpi radialis; c, carpal sheath; d, d', d", d'",
digital sheath; e, bursa under common extensor ten-
don; /, capsule of fetlock joint; 1, extensor carpi ra-
dialis; 2, tendon of extensor carpi obliquus; 3, flexor
carpi radialis; 4> flexor carpi ulnaris; 5, superficial
flexor tendon; 6, deep flexor tendon; 7, suspensory liga-
ment; 8, small metacarpal bone; 9, large metacarpal
bone; 10, volar annular ligament of fetlock; 11,
proximal digital annular ligament; 12, radius; 13,
radiocarpal joint; 14, fetlock joint; 1.5, cartilage of
third phalanx; 16, band from first phalanx to cartilage.
(After Ellenberger, in Leisering's Atlas.)

a, Sheath of extensor carpi radialis: b, sheath
of common extensor; c, sheath of lateral extensor; d,
sheath of outer tendon of ulnaris lateralis; e, e', carpal
sheath; /, /', /", digital sheath; g, bursa under com-
mon extensor tendon; h, bursa under lateral extensor
tendon; i, capsule of fetlock joint; 1, extensor carpi
radialis; 3, common digital extensor; 3, lateral digital
extensor; 4. ulnaris lateralis; 4'< 4", tendons of 4; 5,
superficial flexor tendon; 6, deep flexor tendon; 7,
suspensory ligament; 8, lateral metacarpal bone; 9,
large metacarpal bone; 10, volar annular ligament
of fetlock; 11, digital annular ligament; 12, fetlock
joint; 13, cartilage of third phalanx; 14, band from
first phalanx to cartilage. (After Ellenberger, in
Leisering's Atlas.)

two or three inches (ca. 5-8 cm.) above the fetlock, and extends to the middle of
the second phalanx.

Relations. — The belly of the muscle is related superficially to the ulnar head
of the deep flexor, the flexor carpi ulnaris, and, at its origin, to the ulnar vessels

FLEXOR DIVISION

315

and nerve; deeply, to the humeral head of the deep flexor. The tendon is re-
lated superficially to the skin and fascia; deeply, to the deep flexor tendon.

Blood-supply. — Median artery.

Nerve-supply. — Ulnar and median nerves.

5. Deep digital fiexori (M. flexor digitaUs profundus). — The fleshy part of
this muscle lies on the posterior surface of the radius, and is almost entirely under
cover of the preceding muscles. It is the largest muscle of the flexor group.

Origin. — (1) The medial epicondyle of the humerus; (2) the medial surface of
the olecranon; (3) the middle of the posterior surface of the radius and a small ad-
jacent area of the ulna.

Insertion. — The semilunar crest and the adjacent surface of the cartilage of
the third phalanx.

Action. — -To flex the digit and carpus and to extend the elbow.

Structure. — This muscle consists of three heads. The humeral head (Caput
humerale) constitutes the bulk of the muscle. It is marked by tendinous inter-
sections, and is separable into three secondary heads. A synovial pouch from the
elbow joint descends under its

Tendon of
lateral extensor

Tendon of
common extensor

origin about two inches. The
ulnar head (Caput ulnare) is
much smaller, and is at first
superficially situated between
the lateral and middle flexors
of the carpus. The radial head
(Caput radiale) is the smallest,
and is not always present; it
is situated on the distal two-
thirds of the posterior surface
of the radius, under the humer-
al head. Each of these heads
is provided with a tendon. The
principal tendon — that of the
humeral head — begins about
three or four inches (8-10
cm.) above the carpus and is
joined at the carpus by the
tendons of the other two heads.
The conjoined tendon passes
downward through the carpal

canal, being included in the carpal synovial sheath with the superficial flexor ten-
don, as previously described. The tendon is at first broad and three-sided, but
becomes narrower and rounded below. Continuing downward, it is joined about
the middle of the metacarpus by a strong fibrous band, the so-called inferior or
subcarpal check ligament (Caput carpale s. tendineum).^ This is a direct continua-
tion of the posterior ligament of the carpus. Below this the tendon passes through
the ring formed by the superficial flexor tendon, then in succession over the sesa-
moid groove, the chstal sesamoidean ligaments, and the flexor surface of the distal
sesamoid, to its insertion (Figs. 241 and 242). At the fetlock it widens consider-
ably, narrows again in the middle of the digital region, again widens at the pulley

Tendon of superficial flexor
Fig. 285.

Cross-sectiox of Distal Part of Lej
Horse, Just Above Sesamoids

Intersesamoi-
dean ligament

Digital vein
Digital artery
Digital nerve

Tendon of deep flexor

Metacarpus of

1 Also commonly knowTi as the flexor perforans or deep flexor of the phalanges.

- This might appropriately be termed the carpal head (caput carpale) or tendinous head
(caput tendineum). At its upper end it is broad, occup>ang the entire width of the space between
the small metacarpal bones; below it becomes narrower and thicker. It is related in front to
the suspensory ligament, and its posterior face, which is related to the deep flexor tendon, is
covered by the deep layer of the carpal sheath.

316

FASCIA AND MUSCLES OF THE HORSE

of the second phalanx, and forms a terminal fan-like expansion. At the pulleys
of the digit the tendon contains cartilage and is thickened. From the distal fourth
of the metacarpus to the distal end of the second phalanx it is inclosed in the dig-
ital synovial sheath described in connection with the superficial flexor. The bursa
podotrochlearis or navicular bursa is found between the tendon and the distal sesa-
moid or navicular bone. The terminal part of the tendon is bound down by the
distal digital annular ligament described with the fascia.

Relations. — The belly of the muscle is related posteriorly to the superficial

Extensor tendon

Proximal end of capside of fetlock
joint

Bursa

Collateral ligament of fetlock joint — ^ "^ '

Fascia

Branch of suspc7isory ligament-

Lateral volar ligament of pastem
joint

\ ^"l"

^hl\

Superficial flexor tendon
Deep flexor te?idon
Suspensory ligament
.Lateral interosseus tendon

' Proximal end of digital sheath
' Ring of superficial flexor tendon
• Intersesamoidean ligame7it
Posterior annular ligament {cut)

. .Collateral sesamoidean ligament
ij'/l Superficial distal sesamoidean
ligament
Middle distal sesamoidean ligament

> Attachments of proximal digital
' annular ligament

Pouch of digital sheath

llti^^rff^

^ ^Cartilage

Suspensory ligament of navicidar
bone

Ba?id from cartilage to extensor

tendon
Collateral ligament of coffin joint -{-

Fig. 286. — Ligaments and Tendons or Distal Part of Limb of Horse.

Mc. Ill, Large metacarpal bone; Ph. I, first phalanx; Ph. II, second phalanx; Ph. III. third phalanx; 1, deep flexor

tendon; 2, band from first phalanx to digital cushion. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

flexor and to the middle flexor of the carpus; medially, to the flexor carpi radialis,
the radial check ligament, and the median vessels and nerve; laterally, to the
ulnaris lateralis; anteriorly, to the radius and ulna and branches of the median
artery and nerve. Below the carpus the tendon is accompanied by the vessels and
nerves of the digit. It may also be noted that the muscle is not entirely covered
by the other flexors; it comes in contact with the skin and fascia on the postero-
lateral aspect of the proximal half of the forearm, and also on the lateral aspect of
the distal fourth.

Blood-supply. — Median and ulnar arteries.

FASCIA AND MUSCLES OF THE PELVIC LIMB — THE FASCIA 317

Nerve-supply. — Median and ulnar nerves.

The five muscles of the metacarpus and digit are either reduced to vestiges or
modified greatly in structure.

1, 2. Lvimbricales (medialis et lateralis). — These are two very slender fusiform
muscles which lie on either side of the flexor tendons above the fetlock. They arise
from the deep flexor tendon, and end in the fibrous tissue which lies under the nod-
ule of horn at the fetlock which is known as the ergot (Fig. 572). Their action is
inappreciable. The size of these muscles is subject to much variation. Often very
little muscular tissue can be foimd, but the small tendon is constantly present.

Blood-supply. — Volar metacarpal arteries.

Nerve-supply. — Median and ulnar nerves.

3, 4, 5. Interossei. — These are three in number in the horse, and are situated
chiefly in the metacarpal groove. Two, the medialis and lateralis, are very small
muscles, each of which arises from the corresponding small metacarpal bone near
its proximal extremity, and is provided with a delicate tendon which is usually lost
in the fascia at the fetlock (Fig. 240). They have no appreciable action. Their
blood- and nerve-supply is the same as that of the preceding muscles.

The interosseus medius is so much modified that it is usually termed the
suspensory or superior sesamoidean ligament. It contains little muscular tissue,
being transformed very largely into a strong tendinous band (Tendo interosseus),
bifurcate below, and having for its chief function the supporting of the fetlock. It
has been described, in deference to common usage, with the ligaments.

Fascle and Muscles of the Pelvic Limb
The FASCiiE

The iliac fascia (Fascia iliaca) covers the ventral surface of the iliacus and psoas
muscles, over which it is tightly stretched (Fig. 575). It is attached medially to
the tendon of the psoas minor; laterally it is attached to the tuber coxae and blends
with the deep layer of the lumbo-dorsal fascia. Its anterior part is thin. Pos-
teriorly it is continuous with the inguinal ligament and the pelvic fascia. It fur-
nishes surfaces of origin for the sartorius, cremaster externus, and transversus ab-
dominis muscles.

The pelvic fascia (Fascia pelvis) lines the cavity as the parietal layer and
at the pelvic outlet is reflected on the viscera to form the visceral layer. Laminae
are detached from it to strengthen the various peritoneal folds.

The superficial fascia of the gluteal region is thin and is closely adherent to
the deep fascia. A subcutaneous bursa may be found on the tuber coxae. The
gluteal fascia (Fascia glutea) covers the superficial muscles of the region, and de-
taches intermuscular septa, which pass between the muscles. It is attached to the
sacral spines, the dorsal sacro-iliac ligament, and the tubera of the ilium, and is con-
tinuous in front with the lumbo-dorsal fascia, behind with the coccygeal fascia.
Its deep face gives origin to fibers of the superficial and middle glutei, the biceps
femoris, and the semitendinosus, so that care is necessary in dissecting it off these
muscles. The chief intermuscular septa are: (1) One which passes between the
superficial gluteus and the biceps femoris; (2) one between the biceps and semi-
tendinosus, from which a lamella is detached which passes between the middle and
posterior parts of the biceps and is attached to the tuber ischii; (3) one between the
semitendinosus and semimembranosus, which is attached to the sacro-sciatic liga-
ment and tuber ischii; it furnishes origin for fibers of the long head of the semi-
membranosus.

The superficial fascia of the thigh presents no exceptional features, but the deep

318 FASCIA AND MUSCLES OF THE HORSE

fascia is very thick and strong on the front and lateral surface. This part, the
fascia lata (Fig. 267), is continuous mth the gluteal fascia; it is tendinous in char-
acter, and easily separable from the underlying muscles. It furnishes insertion to
the tensor fascise latse and to the biceps femoris (in part), by both of which it is
tensed. At the stifle it is attached to the patella and the lateral and medial patellar
ligaments. Medially it is continuous with the medial femoral fascia. It furnishes
the following intermuscular septa: (1) One which passes between the vastus lat-
eralis and biceps femoris to be attached to the third trochanter of the femur; (2)
two which pass between the three branches of the biceps femoris; (3) a fourth be-
tween the biceps femoris and semitendinosus. The medial femoral fascia (Fascia
femoralis medialis) covers the superficial muscles on the medial surface of the thigh.
At its upper part it is joined by the femoral lamina of the aponeurosis of the external
oblique muscle (Fig. 575). The posterior part is thin. It is continuous with the
fascia lata in front and the fascia cruris below. At the stifle it fuses with the ten-
dons of the sartorius and gracilis.

The fascia cruris, or fascia of the leg, consists of three layers. Two of these
invest the entire region and may, therefore, be termed the common fasciae. The
superficial layer is a continuation of that of the thigh, while the second layer may be
regarded chiefly as a continuation of the tendons of the superficial muscles of the
hip and thigh (biceps femoris, semitendinosus, tensor fascise latse, sartorius, and
gracilis). The two layers frequently fuse, and are attached chiefly to the medial
and lateral patellar ligaments and the crest and medial surface of the tibia. About
the middle of the leg the two layers unite behind the deep flexor of the digit and
form a strong band which passes dowTiward in front of the tendons of the gastroc-
nemius and superficial flexor, to be attached with the latter to the anterior and
medial part of the tuber calcis. This constitutes a tarsal tendon of insertion of the
biceps femoris and semitendinosus. A strong band, about two inches in width,
arises from the lateral supracondyloid crest, descends over the lateral head of the
gastrocnemius, and blends with the foregoing and the superficial flexor tendon.
The third layer forms sheaths for the muscles, furnishing origin in part to their
fibers. Two important intermuscular septa are detached, viz.: (1) One which
passes between the long and lateral digital extensors to be attached to the fibula
and the lateral border of the tibia; (2) one between the lateral digital extensor and
the deep digital flexor.

The tarsal fascia (Fascia tarsi) fuses with the ligaments and bony prominences
of the region. It is strong and tendinous in front, and joins the tendon of the long
extensor below the joint. On the sides it is thin and fuses with the ligaments.
Posteriorly it is very thick and strong, forming an annular ligament which stretches
from the medial ligament to the fibular tarsal bone and the plantar ligament. This
converts the groove at the back of the hock into a canal, in which are the deep flexor
tendon with its synovial sheath and the plantar vessels and nerves. In this vicinity
there are three annular ligaments (Ligamenta transversa). The proximal one binds
down the tendons of the long extensor, peroneus tertius, and tibialis anterior on
the distal end of the shaft of the tibia. The middle one stretches from the fibular
tarsal bone to the lateral tendon of the peroneus tertius, forming a loop around the
tendon of the long extensor. The distal band stretches across the proximal ex-
tremity of the large metatarsal bone and incloses the tendons (and sheaths) of the
two extensors of the digit.

The metatarsal and digital fasciae do not differ materially from those of the
corresponding regions of the thoracic limb.

THE MUSCLES THE SUBLUMBAR MUSCLES 319

The Muscles 1

I. THE SUBLUMBAR MUSCLES (Figs. 287, 575)
The muscles of this group are not confined to the sublumbar region, but ex-
tend beyond it both before and behind. Their chief function is to flex the hip
joint. Two, however, — the psoas minor and the quadratus lumborum,^ — have not
this action.

1. Psoas minor. — This is a fusiform, flattened, pennate muscle, which lies
along the ventro-lateral aspect of the bodies of the last three thoracic and the
lumbar vertebrae.

Origin. — The bodies of the last three thoracic and first four or five lumbar
vertebrae, and the vertebral ends of the sixteenth and seventeenth ribs.

Insertion. — The psoas tubercle on the shaft of the ilium.

Action. — To flex the pelvis on the loins, or to incline it laterally.

Structure. — The muscle arises by a series of digitations which pass backward
and outward to join the tendon at an acute angle. The latter lies along the lateral
border of the fleshy portion and is flattened. It appears on the surface of the mus-
cle at the third lumbar process and increases gradually in width until it reaches the
pelvic inlet, where it becomes narrower.

Relations. — The ventral surface of the thoracic part of the muscle is related
to the pleura, crura of the diaphragm, and sympathetic and splanchnic nerves.
In the abdomen the chief ventral relations are the peritoneum, the vena cava
(right side), the aorta and left kidney (left side), the sympathetic nerves, and the
ureters. Dorsally, the chief relations are the vertebrae, the psoas major, and lum-
bar nerves. The lumbar arteries pass through the medial edge. Near its insertion
the tendon is crossed medially by the external iliac artery, and laterally by the fem-
oral nerve.

Blood-supply. — Intercostal and lumbar arteries.

Nerve-supply. — Lumbar nerves.

2. Psoas major. — This is much larger than the preceding muscle, by which it
is partly covered. It is triangular, with the base anterior.

Origin. — The ventral surfaces of the transverse processes of the lumbar ver-
tebrae and the last two ribs.

Insertion. — The trochanter minor of the femur, by a common tendon with
the iliacus.

Action. — To flex the hip joint and to rotate the thigh outward.

Structure. — The origin of the muscle is fleshy, the belly being in general flat-
tened, thick in its middle, thin at its edges. The thoracic part is small, the abdom-
inal part much thicker and wider, extending laterally beyond the extremities of the
lumbar transverse processes. From the lumbo-sacral articulation it lies in a deep
groove formed in the iliacus (with which it is partly united), becomes smaller and
rounded, and passes downward and backward to terminate by a strong tendon
common to it and the iliacus. On account of the intimate union between the psoas
major and iliacus they are frequently considered a single muscle, to which the name
ilio-psoas is applied ; some anatomists include the psoas minor also under this term.

Relations. — Dorsally, the last two ribs and thoracic vertebrae, the lumbar
vertebrae, the internal intercostals, quadratus lumborum, longissimus dorsi, and
iliacus, and the lumbar vessels and nerves; ventrally, the pleura and peritoneum,
the iliac fascia, inguinal ligament, the diaphragm, psoas minor and sartorius,
and the circumflex iliac vessels.

^ On account of the very slight mobihty of the sacro-iUac articulation, the muscles of the
pelvic girdle are much reduced, and almost all of those which might be included in this group
extend to the femur or even to the leg. It seems undesirable, therefore, to attempt a morpho-
logical grouping.

320 FASCIA AND MUSCLES OF THE HORSE

Blood-supply. — Lumbar and circumflex iliac arteries.
Nerve-supply. — Lumbar and femoral nerves.

3. Iliacus. — This muscle covers the ventral surface of the ilium lateral to the
sacro-iliac articulation, and extends beyond the lateral border of the bone, under-
neath the middle gluteus.

Origin. — The ventral surface of the ilium lateral to the ilio-pectineal line, the
ventral sacro-iliac ligament, the ^\^ng of the sacrum, and the tendon of the psoas
minor.

Insertion. — The trochanter minor of the femur, by a common tendon with
the psoas major.

Action. — To flex the hip joint and to rotate the thigh outward.

Structure.- — The belly of the muscle is so deeply grooved for the psoas major
as to give the appearance of being completely divided into medial and lateral parts.
When the psoas is removed, it is seen, however, that the two heads are not entirely
separated. The lateral, larger head arises from the wing of the ilium chiefly; the
medial, smaller head arises chiefly from a small area on the shaft of the ilium, be-
tween the psoas tubercle and the depression for the medial tendon of the rectus
femoris, and from the tendon of the psoas minor. The two parts inclose the psoas
major in front of the hip joint.

Relations. — Dorsally, the ilium, sacrum, sacro-iliac articulation, the gluteus
medius, the ilio-lumbar and external circumflex vessels; ventrally, the iliac fascia,
inguinal ligament, the psoas major, sartorius, and abdominal muscles. At the
level of the hip joint the chief relations are: medially, the femoral vessels, the fem-
oral nerve, and the sartorius muscle ; laterally, the rectus femoris and tensor fasciae
latse; in front, the abdominal muscles; behind, the hip joint.

Blood-supply. — Lumbar, circumflex iliac, and deep femoral arteries.

Nerve-supply. — Lumbar and femoral nerves.

4. Quadratus lumborum. — This thin muscle lies on the lateral part of the ven-
tral surfaces of the lumbar transverse processes.

Origin. — The ventral surface of the upper part of the last two ribs and the
lumbar transverse processes.

Insertion. — The ventral surface of the wing of the sacrum and the ventral
sacro-iliac ligament.

Action. — Acting together, to fix the last two ribs and the lumbar vertebrae;
acting singly, to produce lateral flexion of the loins.

Structure. — The muscle is pennate, and is curved with the convexity lateral.
It is thin, largely mixed with tendinous fibers, and is, in general, little developed in
the horse in comparison with some of the other animals (e. g., dog, sheep).

Relations. — Ventrally, the psoas major and the last thoracic and first three
lumbar nerves; dorsally, the last two ribs, the lumbar transverse processes, and
the lateral branches of the lumbar arteries.

Blood-supply. — Lumbar arteries.

Nerve-supply. — Lumbar nerves.

5. Intertransversales lumborum.^ — (See p. 279.)

11. THE LATERAL MUSCLES OF THE HIP AND THIGH

Under this head the muscles of the lateral surface of the pelvis and thigh, and
those which form the posterior contour of the latter, will be described.

1. Tensor fasciae latae (Fig. 267). — This is the most anterior muscle of the
superficial layer. It is triangular in form, with its apex at the tuber coxae.

Origin. — The tuber coxae.

Insertion. — The fascia lata and thus indirectly to the patella, the lateral patel-
lar ligament, and the crest of the tibia.

THE LATERAL MUSCLES OF THE HIP AND THIGH 321

Action. — To tense the fascia lata, flex the hip joint, and extend the stifle joint.

Structure. — The muscle arises by a rather small head, about two inches (ca.
5 cm.) wide, on the antero-inferior eminence of the tuber coxae. Below this the
belly spreads out and terminates in the aponeurosis about midway between the
point of the hip and the stifle. Many fibers arise from an intermuscular septum
between this muscle and the superficial gluteus; this septum is attached to the lat-
eral border of the ilium. The aponeurosis fuses with the fascia lata, which may be
regarded practically as the tendon of insertion; it detaches a lamina which passes
with the tendon of insertion of the superficial gluteus to the lateral border of the
femur.

Relations. — Laterally, the skin and fascia; medially, the obliquus abdominis
externus, the iliacus, superficial gluteus, rectus femoris, and vastus lateralis, branches
of the circumflex iliac, ilio-lumbar, and iliaco-femoral arteries, and the anterior
gluteal nerve; anteriorly, the prefemoral lymph-glands. A considerable quantity
of connective tissue is found between the deep face of the muscle and the abdominal
wall.

Blood-supply. — Circumflex iliac, ilio-lumbar, and iliaco-femoral arteries.

Nerve-supply.- — Anterior gluteal nerve.

2. Gluteus superficialis (Fig. 267). — This muscle lies behind and partly
underneath the tensor fasciae latse. It is triangular and consists of an anterior and
a posterior head united by the gluteal fascia.

Origin. — (1) The tuber coxae and the adjacent part of the lateral border of
the ilium; (2) the gluteal fascia.

Insertion. — The third trochanter of the femur.

Action. — To abduct the limb, flex the hip joint, and tense the gluteal fascia.

Structure. — The anterior head of the muscle is not completely separable (ex-
cept artificially) from the tensor fasciae latse, since both muscles are attached to an
intermuscular septum. The attachment to the border of the ilium is by means of
an intermuscular septum, which passes beneath the thick lateral border of the
gluteus medius and furnishes origin to fibers of both muscles. The posterior head
arises from the deep face of the gluteal fascia, and so indirectly from the dorsal
sacro-iliac ligament. The two heads unite and terminate on a strong flat tendon,
which is inserted into the edge of the third trochanter of the femur, under cover of
the biceps femoris.

Relations. — Superficially, the skin, fascia, and biceps femoris; deeply, the
gluteus medius, iliacus, rectus femoris, and branches of the iliaco-femoral vessels;
in front, the tensor fasciae latae; behind, the biceps femoris.

Blood-supply. — Gluteal and iliaco-femoral arteries.

Nerve-supply. — Anterior gluteal nerve.

3. Gluteus medius (Figs. 268, 580).— This is a very large muscle which covers
the gluteal surface of the ilium and the greater part of the lateral wall of the pelvis,
and extends forward also on the lumbar part of the longissimus dorsi.

Origin. — (1) The aponeurosis of the longissimus dorsi, as far forward as the
first lumbar vertebra; (2) the gluteal surface and tubera of the ilium; (3) the dorsal
and lateral sacro-iliac and sacro-sciatic ligaments, and the gluteal fascia.

Insertion. — (1) The summit of the trochanter major of the femur; (2) the crest
below the trochanter; (3) the lateral aspect of the trochanteric ridge.

Action.— To extend the hip joint and abduct the limb. By its connection
with the longissimus a muscular mass is formed which is one of the chief factors in
rearing, kicking, and propulsion.

Structure. — The anterior extremity of the muscle is narrow and thin, and lies

in a depression on the surface of the longissimus, from the strong aponeurosis of

which the fibers take origin. The pelvic portion of the muscle is very voluminous,

and forms the bulk of the muscular mass which gives the haunch its rounded con-

322 FASCIA AND MUSCLES OF THE HORSE

tour. This part of the muscle is intersected by several tendinous sheets. One of
these is particularly distinct, and is attached to the gluteal line on the ilium. This
divides the muscle incompletely into superficial and deep strata. The superficial
part is inserted by a strong tendon into the summit of the great trochanter, and
by a pointed fleshy mass with a tendinous border into the lateral surface of the
trochanteric ridge. The deep part is termed the gluteus accessorius ; it is smaller,
and arises entirely from the ilium between the gluteal line and the tuber coxae (Fig.
580). It has a strong flat tendon which passes over the anterior part or convexity
of the trochanter to be inserted into the crest below it. The trochanter is covered
here A\dth cartilage, and the trochanteric bursa (Bursa trochanterica) is interposed
between the tendon and the cartilage.^

Relations. — Superficially, the skin, lumbo-dorsal and gluteal fasciae, the tensor
fasciae latse, gluteus superficialis, and biceps femoris; deeply, the longissimus, the
ilium, sacro-iliac and sacro-sciatic ligaments, the gluteus profundus, iliacus and
rectus femoris, the iliaco-femoral vessels, the gluteal and internal pudic vessels and
nerves, and the great sciatic nerve.

Blood-supply. — Gluteal, ilio-lumbar, lumbar, and iliaco-femoral arteries.

Nerve-supply.— Gluteal nerves.

4. Gluteus profundus.^^ — This much smaller quadrilateral muscle lies under
the posterior part of the preceding muscle, and extends over the hip joint, from the
superior ischiatic spine to the anterior part of the trochanter major (Fig. 580).

Origin. — The superior ischiatic spine and the adjacent part of the shaft of the
ilium.

Insertion. — The edge of the anterior part or convexity of the trochanter major
of the femur.

Action. — To abduct the thigh and to rotate it inward.

Structure. — The muscle is short and thick and contains numerous tendinous
intersections. The fibers are directed almost transversely outward over the capsule
of the hip joint and converge at the convexity of the trochanter.

Relations.- — Superficially, the gluteus medius and branches of the gluteal vessels
and nerves; deeply, the shaft of the ilium, the hip joint, and the rectus femoris
and capsularis.

Blood-supply.- — Gluteal artery.

Nerve-supply. — Anterior gluteal nerve.

5. Biceps femoris.^ — This large muscle lies behind and in part upon the super-
ficial and middle glutei. It extends in a curved direction from the sacral and
coccygeal spines to the lateral surface of the stifle and leg (Figs. 267, 292, 580).

Origin.-^{l) The dorsal and lateral sacro-iliac ligaments, the gluteal and
coccygeal fasciae, and the intermuscular septum between this muscle and the semi-
tendinosus; (2) the tuber ischii.

Insertion. — (1) A rough eminence on the posterior surface of the femur near
the trochanter tertius; (2) the free (anterior) surface of the patella and the lateral
patellar ligament; (3) the tibial crest; (4) the crural fascia and the tuber calcis.

Action. — The action is somewhat complex, because the muscle is composed
of three parts, has several points of insertion, and acts on all the joints of the
limb except those of the digit. The general action is to extend the limb, as in pro-
pelling the body, rearing or kicking, and to abduct it. The anterior part, by its
attachment to the posterior surface of the femur and to the patella, would extend

^ By most anatomists the portion inserted into the crest is termed the gluteus accessorius,
but Lesbre considers this to be the deep gluteus, homologous with the gluteus minimus of man.
The portion inserted into the trochanteric ridge apparently represents the piriformis of man.

^ Lesbre considers this to be the scansorius.

* Apparently the muscle represents the biceps, together with part of the gluteus super-
ficialis of man. Hence the names, gluteo-biceps and paramero-biceps have been suggested.

THE LATERAL MUSCLES OF THE HIP AND THIGH 323

the stifle and hip joints and abduct the hmb. The middle part, being inserted
chiefly on the tibial crest and the lateral patellar ligament, would extend the hip,
and may, with the semitendinosus, flex the stifle. The posterior part, by virtue
of its attachment to the tuber calcis, assists in extending the hock. It is to be noted,
however, that extension of the hock joint can occur only when the stifle is also ex-
tended, and vice versa.

Structure. — The muscle has two heads of origin. The long or vertebral head
arises chiefly from the dorsal and lateral sacro-iliac ligaments, the coccygeal fascia,
and the intermuscular septum. There is often a large bursa between this head and
the trochanter major. The short or ischiatic head arises by a strong tendon from
the ventral spine on the tuber ischii, which also furnishes origin to part of the semi-
tendinosus. They unite, and a short tendon, detached from the deep face of the
muscle, is inserted into the posterior surface of the femur near the third trochanter;
here a bursa is interposed between the tendon and the bone. The muscle then
divides into three parts, which terminate on a strong aponeurosis over the
junction of the thigh and leg. The anterior part is directed toward the patella,
the middle one toward the tibial crest, while the posterior one assists in the forma-
tion of the posterior contour of the limb. The aponeurosis blends with the deep
layer of the fascia cruris, as already described. A synovial bursa occurs under the
patellar insertion, and in some cases there is also one between the muscle and the
third trochanter.

Relations. — Superficially, the sldn and fascia; deeply, the sacro-iliac and sacro-
sciatic ligaments, the coccygeal fascia, the femur, the gluteus medius, obturator,
gemellus, quadratus femoris, adductor, semimembranosus, vastus lateralis, and
gastrocnemius muscles, branches of the lateral sacral, gluteal, obturator, femoral
and deep femoral vessels, the great sciatic, tibial, peroneal, and posterior gluteal
nerves; in front, the superficial and middle glutei; behind and medially, the semi-
tendinosus.

Blood-supply. — Gluteal, obturator, and posterior femoral arteries.

Nerve-supply. — Posterior gluteal and great sciatic nerves.

6. Semitendinosus. — This is a long muscle which extends from the first two
coccygeal vertebrae to the proximal third of the medial surface of the tibia. It lies
at first behind the biceps, then passes downward on the back of the thigh, between
that muscle and the semimembranosus (Figs. 268, 288, 580). It has two heads of
origin.

Origin. — (1) The transverse processes of the first and second coccygeal ver-
tebrae, the coccygeal fascia, and the intermuscular septum between this muscle and
the biceps femoris; (2) the ventral surface of the tuber ischii.

Insertion. — (1) The tibial crest; (2) the crural fascia and the tuber calcis.

Action. — To extend the hip and hock joints, acting wdth the biceps and semi-
membranosus in propulsion of the trunk, rearing, etc.; also to flex the stifle and ro-
tate the leg inward.^

Structure. — The long or vertebral head is small at its origin, but becomes larger
by the accession of fibers arising on the intermuscular septum. Below the tuber
ischii it unites mth the short head, which arises partly by fleshy fibers, partly by a
common tendon with the biceps. The muscle then passes downward on the back
of the thigh, and terminates on a wide tendon on the medial surface of the proximal
third of the leg. A distinct band passes forward to be inserted on the tibial crest
(a bursa lying between the tendon and the tibia), part fuses with the fascia of the
leg, while the remainder joins the biceps tendon and concurs in the formation of the
tendinous band, which, as before described, terminates on the tuber calcis (Fig.
583) . A bursa may occur under the long head where it passes over the tuber ischii.

1 It should be remembered, however, that the stifle can be flexed only when the hock is also
flexed and vice versa.

324

FASCIiE AND MUSCLES OF THE HORSE

Relations. — Laterally, the skin and fascia, the biceps, and the medial head
of the gastrocnemius; medially, the coccygeal fascia, the sacro-sciatic ligament,
the semimembranosus; anteriorly, the biceps femoris, branches of the femoral
artery, and the great sciatic nerve.

Blood-supply. — Posterior gluteal, obturator, and posterior femoral arteries.

Nerve supply. — Posterior gluteal and great sciatic nerves.

Origin of obhquus ab-
dominis internus
Inguinal ligament (part
removed)

Iliacus

Tensor facice latoe --

Rectus femoris

Vastus medialis ^B*

Sartorius

Gracilis

Patella

Medial patellar ligament _
Tendon of sartorius ^

Tendon of gracilL

Fascia cruris

Fig. 287. — Muscles of Pelvis and Thigh of Young Horse, Right Side; Medial View.
1, Psoas minor, and 1', its insertion; 2, psoas major; 3, 3', h3ads of obturator internus; 4, sacro-coccygeus ven-
tralis; 5, coccygeus; 6, retractor ani (cut) ; 7, sacro-sciatic ligament; 8, lesser sciatic foramen; 9, semimembranosus;
10, lumbo-sacral plexus; 11, obturator nerve and vessels (cut); 12, femoral vessels (origin); 13, pubis; 14, prepubic
tendon; 15, deep inguinal lymph glands; 16, opening for external pudic vein. Vertebrae are numbered by regions.

7. Semimembranosus^ (Figs. 276, 287, 288, 576).— This very large, three-
sided muscle lies on the medial surface of the preceding muscle and the gastroc-
nemius, and has two heads of origin.

Origin. — (1) The posterior border of the sacro-sciatic ligament; (2) the ventral
surface of the tuber ischii.

1 This muscle was incorrectly designated the adductor magnus by Percivall and Strange-
ways. Its name, however, is not at all descriptive of its structure in the domesticated animals.

THE MEDIAL MUSCLES OF THE THIGH 325

Insertion. — The medial epicondyle of the femur, behind the collateral ligament.

Action. — To extend the hip joint and to adduct the limb.

Structure.— The long head, small and pointed above, extends toward the root
of the tail, fusing with the sacro-sciatic ligament. Passing downward, it becomes
larger and covers in part the posterior aspect of the tuber ischii. A bursa may be
found here. Below this it joins the short head, which is larger. The large belly
so formed passes downward and forward, covered in great part by the gracilis, and
terminates on a short, flat tendon of insertion at the distal end of the femur.

Relations. — The upper part of the muscle concurs with the sacro-sciatic liga-
ment in forming the lateral boundary of the pelvic outlet. It is related posteriorly
and laterally to the skin and fascia and the semitendinosus ; medially, to the anus
and its muscles, the vulva in the female, and the internal pudic artery and nerve
(Figs. 577, 578). Below the pelvis the chief relations are: laterally, the semi-
tencUnosus, biceps, and gastrocnemius, branches of the obturator, femoral, and
posterior femoral arteries, and the great sciatic nerve and its chief branches;
medially, the crus penis and ischio-cavernosus muscle (in the male) and the
gracilis; in front, the adductor and the femoral vessels; behind, the skin and fascia.

Blood-supphj. — Obturator and femoral arteries.

Nerve-supply. — Great sciatic nerve.

m. THE MEDIAL MUSCLES OF THE THIGH

The muscles of this group are arranged in three layers.

First Layer

1. Sartorius (Figs. 287, 288, 576). — This long and rather narrow muscle is the
most anterior one of the first layer. It extends from the posterior part of the sub-
lumbar region to the lower and medial part of the stifle, and is directed downward
and somewhat backward.

Origin. — The iliac fascia and the tendon of the psoas minor.

Insertion. — The medial patellar ligament and the tuberosity of the tibia.

Action. — To flex the hip joint and adduct the limb.

Structure. — The muscle is thin at its origin, but becomes thicker, narrower,
and three sided distally. It terminates near the stifle joint on an aponeurosis which
blends with that of the gracilis and with the fascia of the leg.

Relations. — Medially, the inguinal ligament, the abdominal muscles, the skin
and fascia; laterally, the ilio-psoas, quadriceps femoris, and femoral nerve. It
forms the anterior boundary of the femoral canal, in which the femoral artery and
vein and the deep inguinal lymph glands are situated (Fig. 576).

Blood-supply.- — Femoral artery.

Nerve-supply. — Saphenous nerve.

A rare variation is the existence of a small accessory head which arises from the anterior
border of the pubis or from the prepubic tendon and joins the normal muscle near the middle of
the thigh.

2. Gracilis (Figs. 276, 287, 575). — This is a wide, quadrilateral muscle,
which is situated behind the sartorius, and covers the greater part of the medial
surface of the thigh.

Origin. — The middle third of the pelvic symphysis, the prepubic tendon and
accessory ligament, and the ventral surface of the pubis behind the prepubic ten-
don.

Insertion. — The medial patellar hgament, the medial surface of the tibia in
front of the medial femoro-tibial ligament, and the crural fascia.

Action. — To adduct the limb.

Structure. — The muscle arises by a strong tendon, chiefly in common with the

326 FASCIA AND MUSCLES OF THE HORSE

opposite muscle. Its direct attachment to the ventral surface of the pelvis is not
so extensive as a superficial inspection would suggest. The tendon of origin pre-
sents anteriorly a foramen for the passage of the external pudic vein. The belly-
is composed of parallel bundles, and is marked by a superficial furrow which, how-
ever, does not indicate a muscular division. It terminates on the medial surface
of the stifle on a thin wide tendon which blends in front with that of the sartorius,
below with the crural fascia.

Relations. — Superficially, the skin and fascia, the penis or mammary gland,
and the saphenous vessels and nerve; deeply, the pectineus, adductor, semimem-
branosus and semitendinosus, and, at the middle of the femur, the femoral vessels;
anteriorly, the sartorius. In the proximal third of the thigh the sartorius and gracili
are separated by a triangular interval (femoral triangle), in which lie the deep in-
guinal lymph glands and the femoral vessels.

Blood-supply. — Femoral and deep femoral arteries.

Nerve-supply. — Obturator nerve.

Second Layer

1. Pectineus (Figs. 276, 288, 576). — This muscle is fusiform and extends from
the anterior border of the pubis to the middle of the medial border of the femur.

Origin. — The prepubic tendon, the accessory ligament, and the anterior border
of the pubis.

Insertion. — The middle of the medial border of the femur, near the nutrient
foramen.

Action. — To adduct the limb and flex the hip joint.

Structure. — The belly is cylindrical and contains little fibrous tissue. Its
origin is perforated by the accessory ligament — from which many fibers arise —
and is thus divided into two unequal parts. The large upper part arises largely
from the prepubic tendon — only a small part gaining direct attachment to the
pubis. The small lower part does not reach the bone. The insertion is pointed
and tendinous.

Relations. — Medially, the gracilis; laterally, the femur, the vastus medialis,
the terminal part of the psoas major and iliacus, and the deep femoral artery; an-
teriorly, the sartorius, the femoral vessels, the saphenous nerve, and the deep in-
guinal lymph glands; posteriorly, the adductor and obturator externus, and the
obturator nerve (anterior division).

Blood-supply. — Femoral and deep femoral arteries.

Nerve-supply. — Obturator nerve.

The femoral canal is exposed in the dissection of the preceding muscles (Figs.
288, 290). It is bounded anteriorly by the sartorius, posteriorly by the pectineus,
and laterally by the ilio-psoas and vastus medialis. Its medial wall is formed by
the femoral fascia and the gracilis. Its upper or abdominal opening, the femoral
ring (Lacuna vasorum), lies behind the medial part of the internal inguinal ring and
is bounded anteriorly by the inguinal ligament, posteriorly by the anterior border
of the pubis, and laterally by the tendon of the psoas minor. The canal termi-
nates below at the insertion of the pectineus. It contains the deep inguinal lymph
glands, the femoral artery and vein, and the saphenous nerve.

2. Adductofi (Figs. 276, 288, 576).— This fleshy, prismatic muscle lies behind
the pectineus and vastus medialis. It extends downward and forward from the
ventral surface of the pelvis to the medial epicondyle of the femur.

Origin. — The ventral surface of the pubis and ischium and the tendon of ori-
gin of the gracilis.

1 It has been customary to describe two adductors — a parvus or brevis, and a longus or
magnus. This division is partly artificial, and has been abandoned in the new nomenclature —
a return to the views of Bourgelat and Girard.

THE MEDIAL MUSCLES OF THE THIGH

327

Insertion. — (1) The posterior surface of the femur from the level of the third
trochanter to the groove for the femoral vessels; (2) the medial epicondyle of the
femur and the medial ligament of the stifle joint.

Action. — To adduct the limb and extend the hip joint. It also rotates the fe-
mur inward.

Structure. — It is almost entirely fleshy, and is composed of parallel bundles

Psoas minor
Sartorius (origin)

Iliopsoas

Tensor JascivE latce

Rectus fetnoris

Semimembranosus
Adductor

Vastus medialis

Patella

Middle patellar ligament ^^
Medial patellar ligament --'^^^
Tendon of sartorius

Tendon of gracilis

Tibial insertion of semitendinosus

Semitendinosus

Medial head of gastroc-
nemius
Tibial nerve

Fig. 288. — iMuscles of Pelvis and Thigh of Horse, Right Side; Medial View.
Figure represents deeper dissection of specimen shown in preceding figure.
1, Tendon of insertion of psoas minor; 2, lumbo-sacral plexus; 3, 3', heads of obturator internus; 4, sacro-coccy-
geus ventralis; 5, coccygeus; C, retractor ani (origin) ; 7, sacro-sciatic hgament; 8, lesser sciatic foramen; 9, femoral
nerve; 10, femoral vessels; 11, 11, pectineus; 12, accessory ligament; 13, external pudic vein; 14, pubis; 15, femoro-
patellar joint capsule; 16, distal end of femur; 17, medial meniscus; 18, medial ligament of stifle joint; 19, medial
femoro-patellar ligament.

united rather loosely. It is usually possible to separate from the principal mass a
small anterior short part/ which is inserted into the femur behind the pectineus.
The principal mass- is perforated just below the insertion of the pectineus by an
opening for the femoral vessels (hiatus adductorius), and is thus divided into two

^ This has been termed by various authors the adductor parvus or brevis.
2 Termed by various authors the adductor magnus or longus.

328 FASCIA AND MUSCLES OF THE HORSE

branches. The lateral branch is inserted into the back of the femur with the short
portion, while the medial branch is attached to the medial epicondyle and col-
lateral ligament. There is often a superficial slip which ends partly on the femoro-
patellar joint capsule and may reach the accessory cartilage or medial ligament of
the patella. Some fibers pass under the collateral ligament and end on the tendon
of the semimembranosus.

Relations. — Medially, the gracilis, and branches of the femoral artery and
of the obturator nerve; laterally, the femur, the obturator extern us, quadratus
femoris, biceps femoris, and the femoral, deep femoral, and obturator arteries; an-
teriorly, the pectineus, vastus medialis, and a large branch of the obturator nerve;
posteriorly, the semimembranosus and the great sciatic nerve.

Blood-supply. — Femoral, deep femoral, and obturator arteries.

Nerve-supply. — Obturator nerve.

3. Semimembranosus. — Described on p. 324.

Third Layer

1. Quadratus femoris.^ — This is a narrow, three-sided muscle, which lies under
cover of the upper part of the adductor (Fig. 581).

Origin. — The ventral surface of the ischium, just in front of the semimembrano-
sus.

Insertion. — An oblique line on the posterior surface of the femur, near the
lower part of the trochanter minor.

Action. — To extend the hip joint and to adduct the thigh.

Structure. — It is composed of parallel bundles of fibers directed do\\Tiward,
forward, and outward.

Relations. — Postero-medially, the adductor, semimembranosus, and the ob-
turator vessels; antero-laterally, the obturator externus and biceps femoris, the
deep femoral vessels, and the great sciatic nerve.

Blood-supply. — Deep femoral and obturator arteries.

Nerve-supply.- — Great sciatic nerve.

2. Obturator externus (Fig. 581). — This is a pyramidal muscle which extends
across the back of the hip joint from the ventral surface of the pelvis around the
obturator foramen to the trochanteric fossa.

Origin. — The ventral surface of the pubis and ischium, and the margin of the
obturator foramen.

Insertion. — The trochanteric fossa.

Action. — To adduct the thigh and to rotate it outward.

Structure. — It is almost entirely fleshy, the muscle-bundles being rather loosely
connected. The insertion is pointed, flattened, and partly tendinous. The origin
is perforated by the obturator vessels and nerve.

Relations. — Medially, the adductor and quadratus femoris and the deep
femoral vessels; laterally, the gemellus, the tendon of the obturator internus, the
biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus,
and the external pudic vein.

Blood-supply. — Deep femoral and obturator arteries.

Nerve-supply. — Obturator nerve.

3. Obturator internus (Fig. 288). — This arises within the pelvic cavity by two
heads, the tendon emerging through the lesser sciatic foramen.

Origin. — (1) The pelvic surface of the pubis and ischium around the obturator
foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum.
Insertion. — The trochanteric fossa.
Action. — To rotate the femur outward.

1 Also known as the ischio-femoralis.

ANTERIOR MUSCLES OF THE THIGH 329

Structure. — The ischio-pubic head Ues on the pelvic floor and covers the ob-
turator foramen. It is thin and fan-shaped. The iliac head extends along the
lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both
terminate on a flat tendon which passes outward through the lesser sciatic fora-
men to be inserted into the trochanteric fossa. The tendon furnishes insertion to
fibers of the gemeflus. A synovial bursa facilitates the play of the tendon over the
lateral border of the ischium.^

Relations. — The pelvic surface is covered by the pelvic fascia and in part by
the peritoneum. The obturator vessels and nerve lie between the two heads, and
the internal pudic vessels and nerve lie along the dorsal edge of the iliac head. The
tendon is crossed by the great sciatic nerve.

Blood-supply. — Obturator and internal pudic arteries.

Nerve-supply. — Great sciatic nerve.

4. Gemellus- (Fig. 580).— This is a thin, triangular muscle, which extends
from the lateral border of the ischium to the trochanteric fossa and ridge.

Origin. — The lateral border of the ischium near the ischiatic spine.

Insertion. — The trochanteric fossa and ridge.

Action. — To rotate the femur outward.

Structure. — The thin tendon of origin is attached to a line on the lateral border
of the ischium, which begins just below the posterior end of the superior ischiatic
spine. Many superficial fibers are inserted into the tendon of the obturator in-
ternus.

Relations. — Superficially, the biceps femoris, the tendon of the obturator in-
ternus, the gluteus medius, and the great sciatic nerve; deeply, the obturator ex-
ternus and the hip joint.

Blood-supply. — Obturator artery.

Nerve-supply. — Great sciatic nerve.

IV. ANTERIOR MUSCLES OF THE THIGH

This group consists of the sartorius, quadriceps femoris, and capsularis.

1. Sartorius. — This is described on p. 325.

2. Quadriceps femoris (Figs. 268, 289, 291). — This constitutes the large mus-
cular mass which covers the front and sides of the femur. It has four heads, one
of which, the rectus, arises from the ilium; the other three arise from the femur.
All are inserted into the patella.

(1) Rectus femoris. — This is fusiform and rounded. It arises by two tendons.

Origin. — Two depressions on the shaft of the ilium above and in front of the
acetabulum.

Insertion. — The base and anterior surface of the patella.

Action. — To extend the stifle joint and to flex the hip joint.

Structure. — It has two short strong tendons of origin; beneath the lateral one
is a bursa. The belly is rounded and rests in a groove formed by the other portions
of the quadriceps. Its sides are covered by a strong tendinous layer which fur-

1 The iliac head has been described as a separate muscle, and termed the piriformis. This
does not seem desirable, especially since it is probable that the homologue of the piriformis of
man is that portion of the middle gluteus which is inserted into the trochanteric ridge.

^ The name is based on the arrangement in man, in whom the muscle usually consists of two
fascicuh forming a groove between them for the tendon of the obturator internus. In the horse
it is usually undivided at its origin, but toward the insertion the upper part is separated from the
rest of the muscle or is readily isolated. The muscle is subject to much variation in size. When
well developed, the insertion extends from the proximal end of the trochanteric fossa to a point
just above the femoral attachment of the biceps femoris; in such cases the upper part, which
occupies the space behind the hip joint between the gluteus profundus and obturator externus,
is much thicker than the remainder, which covers the latter muscle. The gemellus may be re-
garded as the extrapelvic head of the obturator internus (Gegenbaur).

330

FASCIA AND MUSCLES OF THE HORSE

nishes insertion to fibers of the vasti. The tendon of insertion is formed by the
union of these tendinous layers on the lower part of the muscle. The lower portion
of the muscle is pennate, the fibers on either side converging on the tendon at an
acute angle.

Relations. — Medially, the iliacus, sartorius, and vastus medialis; laterally,
the tensor fasciae latae, glutei, and vastus lateralis; posteriorly, the hip joint and
the vastus intermedins; anteriorly, the fascia lata and the skin. The anterior
femoral artery and branches of the femoral nerve descend into the interspace be-

\' Shaft of ilium
y Medial tendon of origin
-^ of rectus femoris

Gluteus profundus

Vastus lateralis
Rectus femoris

Prepubic tendon (ir,
median section)
Obturator externus

Iliopsoas {insertion)
Adductor

Vastus medialis

Medial femoro-tibial ligament
Medial vieniscus

Lateral patellar ligament

Tuberosity of tibia

Fig. 289. — Muscles of Right Thigh of Horse, Deep Dissection. The Preparation is Viewed fro.m in Front

AND Somewhat Medially.

1, Accessory ligament of hip joint; 2, transverse ligament of same; 3, head of femur; 4, patella; 5, trochlea of femur;

6, 7, middle and medial patellar ligaments.

tween the upper part of the rectus and the vastus medialis; similarly, the iliaco-
femoral artery dips in between the rectus femoris and vastus lateralis.

Blood-supply. — Femoral and iliaco-femoral arteries.

Nerve-supply. — Femoral nerve.

(2) Vastus lateralis. — This lies on the lateral surface of the femur, extending
from the great trochanter to the patella. It is wide in its middle, smaller at each end.

Origin. — The lateral border and surface of the femur, from the trochanter
major to the supracondyloid fossa.

ANTERIOR MUSCLES OF THE THIGH

331

Insertion.— (1) The lateral part of the anterior surface of the patella; (2) the
tendon of the rectus femoris.

Action. — To extend the stifle joint. .

Structure.— The fibers are directed downward and forward, many being in-
serted into the tendinous sheet which covers the side of the rectus. A bursa is
usually present between the distal end and the patella.

i^e/a«ions.— Laterally, the fascia lata and skin, tensor fascia lata, superficial

Fold of flank
Tensor fasci(r latcB

Vastus lateralis

]■ T v^^^^^- oV Tl^^^^^^x ^ Vastus intermedium

Vastus mediahs * ^i— i ■■ ow »^^^^^^^ ^

Sartorius
Saphenous vein —-.^^jM
Saphenous nerve ''^
Femoral artery
Gracilis

Peroneal nerve
Tibial nerve

SemitendinosH

Fig. 290.— Cross-section of Middle of Right Thigh of Horse.

gluteus, and biceps femoris; medially, the femur and femoro-patellar joint capsule,
the rectus femoris, vastus intermedins, and the iliaco-femoral artery.

Blood-supply.— llisico-iemoral artery.

Nerve-supply.— Femoral nerve. j r „ :„ „ oir,.

(3) Vastus mediaUs.— This resembles the preceding muscle, and lies m a sim-
ilar position on the medial side of the femur. , ^ ^u r +„i +i.;rri

Onom.-The medial surface of the femur, from the neck to the distal third.

Insertion.-{l) The medial border of the patella and its cartilage, and the

332

FASCIA AND MUSCLES OF THE HORSE

proximal part of the medial patellar ligament. (2) The tendon of the rectus
femoris.

Action. — To extend the stifle joint.

Structure. — This is very similar to that of the vastus lateralis. It is, how-
ever, more difficult to separate from the intermedins, because many fibers of the
latter arise on the tendinous sheet which covers the contact surface- of the medial

Shaft of ilium

Gluteus profundus

Trochanter major
{anterior part)

Vastus lateralis
Vastus intermedium

Rectus femoris

Vastus lateralis

Biceps femoris

Patella

Lateral femoro-tibial
ligament
Lateral patellar ligament

Prepubic tendon
Obturator externum

Vastus medialis

Adductor

r Medial femoro-tibial ligament
Medial meniscus
Middle patellar ligament

Tuberosity of tibia

Fig. 291. — Mi s. i.ks <>f Right Thigh of Horse; Deep Dissection.
The preparation is viewed from tiie front and somewhat medially. Most of rectus femoris and vastus lateralis
has been removed. 1, Stump of origin of rectus femoris; 2, capsularis; 3, accessory ligament; 4, cotyloid ligament;
5, head of femur; 6, trochlea of femur.

vastus. Its insertion into the patella is chiefly by means of a broad, strong tendon.
From the deep face fleshy fibers are inserted also into the femoro-patellar joint cap-
sule.

Relations. — Medially, the skin and fascia, the iliacus, sartorius, pectineus, and
adductor, the femoral vessels, and saphenous nerve; laterally, the femur, femoro-
patellar joint capsule, rectus femoris, and vastus intermedins, the anterior femoral
artery, and branches of the femoral nerve.

THE MUSCLES OF THE LEG AND FOOT 333

Blood-supply. — Femoral and anterior femoral arteries.

Nerve-supply. — Femoral nerve.

(4) Vastus intermedius. — This muscle is deeply situated on the anterior face
of the femur, and is entirely covered by the preceding heads.

Origin.— {1) The anterior surface of the femur, from the proximal to the distal
fourth; (2) the tendinous covering of the vastus medialis.

Insertion. — (1) The base of the patella; (2) the femoro-patellar joint capsule.

Action. — (1) To extend the stifle joint; (2) to tense (raise) the femoro-patellar
capsule during extension of the joint.

Structure.- — The muscle is usually quite difficult to isolate from the other vasti,
so that many since Glinther have declared it an artefact.^ It is entirely fleshy, and
is small at its proximal end, but when traced downward increases in bulk by the
accession of fibers arising on the femur and the tendinous covering of the vastus
medialis. The terminal part is intimately adherent to the femoro-patellar joint
capsule, where the latter bulges above the level of the patella.

Relations. — Medially, the vastus medialis; laterally, the vastus lateralis;
anteriorly, the rectus ; posteriorly, the femur and femoro-patellar capsule.

Blood-supply. — Iliaco-femoral and anterior femoral arteries.

Nerve-supply. — Femoral nerve.

The patellar ligaments are to be regarded as tendons of the quadriceps which communicate
the action of the latter to the tibia, the patella being intercalated as a sesamoid bone.

3. Capsularis (Fig. 291). ^ — This is a small fusiform muscle (scarcely as large
as one's finger), which arises by a thin tendon on the ilium immediately above the
outer tendon of the rectus femoris. Its delicate tendon of insertion dips in between
the vastus intermedius and lateralis and is attached to the proximal third of the
anterior surface of the femur. It passes over the outer side of the hip joint, to the
capsule of which some fibers are attached. Sometimes the muscle has two dis-
tinct heads, in which case the additional head arises between the two tendons of
origin of the rectus femoris. Its action may be to raise the capsule during flexion
of the joint. It is related laterally to the gluteus profundus and vastus lateralis,
medially to the rectus femoris and vastus intermedius and the hip joint.

V. THE MUSCLES OF THE LEG AND FOOT
The muscles of this region cover almost all of the tibia except its medial face,
which is largely subcutaneous. As in the forearm, the muscles fall into two groups,
a dorso-lateral and a plantar. The muscles of the first group are extensors of the
digit and flexors of the hock, those of the second have the opposite action.

A. Dorso-lateral Group

1. Long digital extensor (M. extensor digitalis longus).^ — This muscle is sit-
uated superficially on the dorso-lateral aspect of the leg, and is provided with a long
tendon which passes dowTi over the front of the tarsus, metatarsus, and digit.

Origin.— The extensor fossa of the femur.

Insertion.— {1) The extensor process of the third phalanx; (2) the dorsal sur-
face of the proximal extremities of the first and second phalanges.

Action.- — To extend the digit and flex the hock. It also assists in fixing the
stifle joint.

^ While it is true that the separation of the intermedius is never entirely a natural one in the
horse, it varies in individual cases, and is usually clear on cross-sections. In some subjects it is
possible to separate another slip which may represent the articularis genu of man.

^ Also known as the rectus parvus.

3 Also termed the extensor pedis or the anterior extensor of the phalanges.

334

FASCIA AND MUSCLES OF THE HORSE

Structure. — The origin is by means of a strong tendon in common with the
peroneus tertius, on which also many fibers arise. The common tendon passes
downward in the groove between the lateral condyle and the tuberosity of the tibia,

Patella - —

Crest of tibia

Long digital extensor
Lateral digital extensor ■

Proximal annular ligament -
Lateral malleolus

Middle annular ligament

Distal annular ligament

Tendon of long extensor

Tendon of lateral extensor

Branch of suspensory ligament to
extensor tendon

~ Gastrocnemius, lateral head
Soleus
\,\ Tendon of gastrocnemius

- Tarsal tendon of biceps femoris

- Deep flexor

Superficial
flexor tendon

Superficial flexor
teridon

Deep flexor tendon

Suspensory
ligament

Fig. 292. — Muscles of Lower Part of Thigh, Leg, and Foot of Horse; Lateral View.

</, Faacia lata; g, g', g", biceps femoris; r, semitendinosus; .27', lateral condyle of tibia. The extensor brevis is visible

in the angle between the long and lateral extensor tendons, but by an oversight it is not marked. (After EUen-

berger-Baum, Anat. fiir Ktinstler.)

where a pouch from the femoro-tibial capsule descends three or four inches (ca.
7.5 to 10 cm.) beneath the tendon. The belly is fusiform and somewhat flattened.
The long tendon of insertion begins in the belly about its middle, and is clear of the

THE MUSCLES OF THE LEG AND FOOT 335

fleshy part near the tarsus. It passes downward over the front of the hock, bound
down by the three annular ligaments already described (see tarsal fascia), and en-
veloped by a sjmovial sheath which begins a little above the level of the lateral
malleolus, and extends nearly to the junction with the lateral extensor tendon.
This union occurs usually about a hand's breadth below the tarsus. In the angle
of union the extensor brevis also joins the principal tendon. Beyond this point
the arrangement is the same as in the fore limb.

Relations. — Superficially, the skin and fascia; deeply, the femoro-tibial joint,
peroneus tertius, and tibialis anterior; behind, the lateral extensor and the super-
ficial and deep peroneal nerves. In front of the tarsus the anterior tibial artery
crosses the deep face of the tendon (Fig. 585).

Blood-supply. — Anterior tibial artery.

Nerve-supply. — Peroneal nerve.

2. Lateral digital extensor (M. extensor digitalis lateralis).^ — This muscle lies
on the lateral surface of the leg, behind the preceding one.

Origin. — The lateral ligament of the stifle joint, the fibula, the lateral border
of the tibia, and the interosseous ligament.

Insertion.— The tendon of the long extensor, about a third of the way down
the metatarsus.

Action. — To assist the long extensor.

Structure. — The belly is fusiform, flattened, and pennate. The tendon runs
through the entire length of the belly and becomes free from it at the distal fourth
of the tibia. It descends through the groove on the lateral malleolus, bound down
by an annular ligament, and, inclining forward, blends (usually) with the tendon
of the long extensor. It is provided with a synovial sheath, which begins about
an inch (ca. 2 to 3 cm.) above the lateral malleolus and ends about one and one-
half inches (ca. 3 to 4 cm.) above the junction. Sometimes the fusion does not
occur; the tendon then descends alongside of that of the long extensor, and is in-
serted into the first phalanx like the corresponding muscle of the thoracic limb.

Relations.— Laierally, the skin and fascia and the superficial peroneal nerve;
medially, the tibia and fibula; anteriorly, the intermuscular septum, the long
extensor, and the tibialis anterior; posteriorly, the deep digital flexor and the soleus.

Blood-supply. — Anterior tibial artery.

Nerve-supply. — Peroneal nerve.

3. Peroneus tertius (Tendo f emoro-metatarseus) .^ — This consists in the horse
of a strong tendon which lies between the long extensor and the tibialis anterior.

Origin. — The extensor fossa (between the lateral condyle and the trochlea
of the femur), in common with the long extensor.

Insertion. — (1) The proximal extremity of the large (third) metatarsal bone
and the third tarsal bone ; (2) the fibular and fourth tarsal bones.

Action.- — Mechanically to flex the hock when the stifle joint is flexed.

Structure. — It is entirely tendinous. The proximal end and the underlying
prolongation of the synovial membrane of the femoro-tibial joint have been men-
tioned in the description of the long extensor. The superficial face gives origin
to fibers of the long extensor in the upper part of the leg, and the deep face is fused
with the tibialis anterior except at either end of the region. At the distal end of the
tibia the tendon is perforated for the emergence of the tendon of the tibialis anterior
and divides into two branches. The anterior branch is attached to the third tarsal
and third metatarsal bones, while the lateral one curves outward, bifurcates, and

^ Also known as the peroneus or the lateral extensor of the phalanges. Lesbre considers it
to be the homologue of the peroneus brevis of man and other pentadactyls.

2 It seems inadvisable to retain the old term, tendinous part of the flexor metatarsi, since it
is inapphcable to other domesticated animals in which the muscle is well developed (e. g., pig).
Schmaltz uses the term tendo femoro-tarseus, and Varaldi and Lesbre designate it the femoro-
metatarsal cord. The name peroneus anterior has also been proposed.

336

FASCIA AND MUSCLES OF THE HORSE

is inserted into the fibular and fourth tarsal bones. The lateral tendon gives off
a branch which forms a loop around the long extensor tendon (Fig. 293).

Relations. — Superficially, the long extensor; deeply, the tibialis anterior. The
anterior tibial vessels cross the deep face of the outer branch.

Lateral ridge of trochlea of femur
Lateral femoro-tibial ligament

Lateral meniscus
Lateral condyle of tibia "^

Long extensor (stump)

Peroneus tertius
Tibialis anterior
Lateral extensor

Tendinous loop
Extensor brevis

Tendon of lateral extensor
Tendon of long extensor

Medial ridge of trochlea of femur

Medial meniscus

Medial femoro-tibial ligament

Tendon of long extensor
Annular ligament
Peroneus tertius

Medial tendon of tibialis anterior

Anterior tendon of tibialis anterior
Anterior tendon of peroneus tertius

Annular ligament
Ml. Ill

Fig. 293. — Muscles of Right Leg of Horse; Front View.
The greater part of the long extensor has been removed. \, 2, 3, Stumps of patellar ligaments; 4, tuberosity of tibia.

4. Tibialis anterior.^ — This lies on the dorso-lateral face of the tibia; it is wide
and flattened above, pointed below.

Origin. — The lateral condyle and border of the tibia and a small area on the
lateral surface of the tuberosity.

^ This is also known as the muscular part of the flexor metatarsi.

THE MUSCLES OF THE LEG AND FOOT

337

Insertion. — (1) The ridge on the front of the proximal end of the large meta-
tarsal bone; (2) the first and second tarsal bones.

Action. — To flex the hock joint.

Structure. — The origin is fleshy, and forms a groove in which lie the common
tendon of the long extensor and peroneus tertius and a synovial pouch which de-
scends from the femoro-tibial joint. Many superficial fibers arise from the deep
fascia at the proximal part of the leg and thus from the tibial crest. Passing down-
ward on the tibia, the belly is united by tendinous and fleshy fibers with the per-
oneus tertius, and terminates close to the tarsus in a point on the tendon of inser-

FiG. 294. — Injected Synovial Sheaths and Burs.*;

OF Tarsal Region of Horse; Medial View.

a, Synovial sheath of peroneus tertius and tibialis
anterior; h, bursa under medial (cunean) tendon of
tibiahs anterior; c, synovial sheath of flexor longus;
d, tarsal sheath of deep flexor; e, e', bursa under
superficial flexor tendon; /, /', tibio-tarsal joint capsule;
1, long extensor; 2, tibialis anterior; 2', medial (cun-
ean) tendon of 2; 3, flexor longus; 4, deep digital
flexor; o, superficial flexor tendon; 6, gastrocnemius
tendon; 7, tibia; S, tarsus; 9, tuber calcis; 10, large
metatarsal bone; 11, medial small metatarsal bone;
12, 12', fascial bands. (After Ellenberger, in Leisering's
Atlas.)

Fig. 295. — Injected Synovial Sheaths and Burs«
OF Tarsal Region of Horse; Lateral View.
o, Synovial sheath of long digital extensor; 6,
synovial sheath of lateral digital extensor; c, c', bursa
under superficial flexor tendon; d, capsule of hock joint;
1. long extensor; 2, lateral extensor; 3, 3, 3, annular
ligaments; 4, deep digital flexor; 5, tendon of gastroc-
nemius; 6, superficial flexor tendon; 7, tibia; 8, tarsus;
9, tuber calcis; 10, metatarsus. (After Ellenberger,
in Leisering's Atlas.)

tion. The latter emerges between the branches of the peroneus tertius and bi-
furcates, the anterior branch being inserted into the large metatarsal bone, the
medial one into the first tarsal bone. The tendon is provided with a s3aiovial sheath
at its emergence, and a bursa is interposed between the medial branch and the
medial ligament of the hock.^

Relations. — Superficially, the long and lateral extensors, the peroneus tertius,
and the deep peroneal nerve; deeply, the tibia, the deep flexor, and the anterior
tibial vessels.

^ In surgical works the medial branch is termed the cunean tendon; it is sometimes resected
for the relief of bone spavin.
22

338

FASCIAE AND MUSCLES OF THE HORSE

Blood-supply.
Nerve-supply.

-Anterior tibial artery
-Peroneal nerve.

third of the femur to the point of the hock.

Sluifl of fcmu

Medial head of
gastroc7ierniits

Fascial hand

Latind head of
(jdst roc tic till us

B. Plantar Group
1. Gastrocnemius (Fi^s. 268, 292, 296).^This muscle extends from the distal

It arises by two heads.

Origin. — (1) Lateral head,
from the lateral supracondj^-
loid crest (margin of the supra-
condyloid fossa); (2) medial
head, from the medial supra-
condyloid crest.

Insertion. — The posterior
part of the tuber calcis.

Action. — To extend the
hock and to flex the stifle
joint; these two actions, how-
ever, cannot occur simulta-
neously.

Structure. — The two bel-
lies are thick, fusiform, and
somewhat flattened. They
are covered by a strong apo-
neurosis and contain tendinous
intersections. They terminate
toward the middle of the leg
on a common tendon, which at
first lies posterior to that of the
superficial flexor, but, by a
twist in both, comes to lie in
front of the latter. The deep
fascia blends with the tendon
throughout its length, and the
soleus muscle is inserted into
its anterior edge. A small
bursa (Bursa tendinis m. gas-
trocncmii) lies in front of the
insertion on the tuber calcis,
and a large bursa (calcanea
subtendinea) is interposed be-
tween the two tendons from
the twist downward to the
middle of the hock. The super-
ficial digital flexor lies between
the two heads and is adherent
to the lateral one (Fig. 584).
The term tendo calcaneus or
tendo Achillis is a convenient
designation for the aggregated
tendons in the distal part of the
leg which are attached to the
tuber calcis.
Rclations.—Antoviorly, the stifle joint, the superficial digital flexor, popliteus,
deep digital flexor, popliteal vessels, and tilnal nerve; medially (above), the semi-

Soleiis

Ural cxlcn-
sor

■.ror }i<dlucis

Tendon of (/os-
trocnctniua

Snpcrficiid
Jlcvor tendon

Tendon of deep flexor
Fig. 20G. — Musci.es op Right Leo of Horse: PosTEnioR View

Tendon of long
digital flexor

THE MUSCLES OF THE LEG AND FOOT 339

tenclinosus, semimembranosus, and adductor, (below) the fascia and skin; laterally
(above), the biceps femoris and peroneal nerve, (below) the fascia and skin. The
popliteal lymph lands lie on the upper part of the nmscle.

Blood-supply. — Popliteal artery,

Nerve-iiupph). — Tibial nerve.

2. Soleus (Fig. 29G). — This muscle is very small in the horse. It lies along
the lateral border of the gastrocnemius under the common deep fascia, on the prox-
imal half of the lateral surface of the leg.

Origin. — The head of the fibula.

Insertion. — The tendon of the gastrocnemius, about the middle of the leg.

Action. — To assist the gastrocnemius.

Structure. — It is a thin, fleshy band, usually about an inch (ca. 2 to 3 cm.) in
width, and terminates on a thin tendon which fuses with that of the gastrocnemius.^

Relations. — Superficially, the skin, fascia, and peroneal nerve; deeply, the
lateral extensor and deep flexor.

Blood-supply. — Posterior tibial artery.

Nerrc-supply. — Ti])ial nerve.

3. Superficial digital flexor (M. flexor digitalis pedis superficialis) (Figs. 292,
296, 297).- — The proximal part of this muscle lies between and under cover of
the two heads of the gastrocnemius. It consists almost entirely of a strong tendon,
the belly being very little developed.

Origin. — The supracondyloid fossa of the femur.

Insertion. — (1) The tuber calcis; (2) the eminences on each side of the prox-
imal extremity of the second phalanx, and the distal extremity of the first phalanx
behind the collateral ligaments of the pastern joint.

Action. — To flex the digit and extend the hock joint. On account of the ex-
ceedingly small amount of muscular tissue the action is to be regarded chiefly as a
mechanical effect which results from the action of other muscles on the stifle joint.

Structure. — The origin is by means of a strong round tendon which is incom-
pletely covered with fleshy fibers as far as the upper third of the leg. Here it is
intimately attached to the gastrocnemius, especially to the lateral head. At the
distal third of the tibia it winds around the medial surface of the gastrocnemius
tendon, and then occupies a position behind the latter. At the point of the hock
it witlens out, forming a sort of cap over the tuber calcis, and detaches on either side
a strong band which is inserted into the tuber calcis with the tarsal tendons of the
l)iceps and semitendinosus. It then passes downward over the plantar ligament,
l)ecomes narrower, and is arranged distally as in the thoracic limb. A large syno-
vial bursa (B. calcanea su])tcndinea) lies untler the t(»ndon from the distal fourth of
the tibia to the middle of the tarsus. A subcutaneous bursa (B. calcanea su])cu-
tanea) is sometimes present on the wide part of the tendon at the point of the hock.

Relations. — Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the
femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels;
medially, the tibial nerve.

Blood-supply. — Posterior femoral artery.

Nerve-supply. — Til^ial nerve.

4. Deep digital flexor (M. flexor digitalis pedis profundus) (Figs. 292, 298).^ —
The belly of this nuiscle lies on the posterior surface of the tibia, and is divisible
into three heads, which, however, finally unite on a common tendon of insertion.

Origin. — (1) The posterior edge of the lateral condyle of the tibia; (2) the
border of the lateral condyle of the tibia, just behind the facet for the fibula; (3)

^The soleus is sometimes included with the two heads of the gastrocnemius under the
name triceps suric.

2 This is also known as the flexor pedis perforatus or superficial flexor of the phalanges.
' This muscle is also commonly termed the flexor pedis perforans.

340

FASCIA AND MUSCLES OF THE HORSE

the middle third of the posterior surface and the upper part of the lateral border of
the tibia, the posterior border of the fibula, and the interosseous ligament.

Insertion. — The semilunar crest and the adjacent surface of the cartilage of
the third phalanx.

Action. — To flex the digit and to extend the hock joint.

Structure. — (1) The medial head is termed the long digital flexor (M. flexor
digitalis longus s. flexor accessorius) ; it is easily isolated (Figs. 298, 584). It has a
fusiform belly, which crosses the leg obliquely and lies in a groove formed by the

Peroneus tertius

Long digital
extensor

Superficial -peroneal

Tibialis ayiterior

Cutaneous branch of
enous nerve

Saphenous vessels
' nerve

Lateral head of gastroc-
nemius

Recurrent tarsal vein

Flexor digitalis longus
Vein

Tibial nerve
Superficial digital flexor

Medial head of gastroc-
nemius

Fig. 297. — Cross-ssction of Left Leg of Horse.
The section is cut about the junction of the proximal and middle thirds of the region. 1, .\nterior tibial vessels;
2, deep peroneal nerve; 3, fibula; 4, posterior tibial vessels; 5, recurrent tibial vessels. A cutaneous branch of the
saphenous nerve is shown medial to the popliteus, but is not marked.

other heads and the popliteus. This terminates near the lower third of the tibia
on a round tendon which descends in a canal in the medial ligament of the hock,
and joins the common tendon about a third of the way down the metatarsus. In
its course over the medial surface of the hock the tendon is provided with a S3mo-
vial sheath which extends from the distal fourth of the tibia to the junction with
the principal tendon. (2) The superficial head is the tibialis posterior (M. tibialis
posterior); it is only partially separable from the deep head. It has a flattened
belly, terminating near the distal third of the tibia on a flat tendon which soon fuses

THE MUSCLES OF THE LEG AND FOOT

341

with the principal tendon. (3) The deep head, the flexor haUucis (M. flexor
hallucis longus), is much the largest. It lies on the posterior surface of the tibia,
from the popliteal line outward and downward. The belly contains much tendi-
nous tissue, and terminates behind the distal end of the tibia on a strong round ten-

Shaft of femur -

Medial head of gastrocnemius -

Medial condyle of femur.

Medial femoro-tibial ligament-.^
Medial meniscus.
Medial condyle of tibia.

PopliteuS-
Flexor digitalis longus_

'Lateral head of gastrocnemius
'Superficial digital flexor

-Lateral condyle of femur
Lateral femoro-tibial ligament
Lateral condyle of tibia

■ Tibialis posterior
-Lateral digital extensor

Flexor hallucis

Pouch of joint capsule

Deep flexor tendon .
Tendon of flexor digitalis longus

Tendon of gastrocnemius

Superficial flexor tendon

Fig. 298.— Muscles of Right Leg or Horse, Deep Dissection; Posterior View.

don The latter receives the tendon of the tibialis posterior, descends in the tarsal
groove, bound do^vn by the strong plantar annular ligament (Ligamentum lacmi-
atum) and enveloped in a synovial sheath, receives the tendon of the medial head
below the hock, and, a little further down, the so-called check ligament (Caput
tendinemn). The tendon is partly cartilaginous where it plays over the hbular

342

FASCIA AND MUSCLES OF THE HORSE

tarsal bone. The tarsal sheath (Vagina tarsea) begins two to three inches (ea.
5 to 7.5 cm.) above the level of the medial malleolus, and extends about one-fourth
of the way dowTi the metatarsus. The check ligament resembles that of the fore
limb, except that it is longer and very much weaker; it may be absent.^ The re-
mainder of the tendon is arranged like that of the thoracic limb.

Tarsal sheath

Tibial tarsal bone

Medial tendon of
tibialis anterior

Joint canty
Dorsal ligament
Central tarsal bone
Third tarsal bone

Mt. in

Superficial flexor
tendon-

Joint capsule {tarso-
metatarsal ligament)

Fourth tarsal
Perforating tarsal vein
Check ligament
Suspensory ligament

Fig. 299. — Sagittal Section of Right Hock of Horse.
through the middle of the groove of the trochlea of the tibial tarsal bone

The section

of cavity of hock joint; 3, thick part of joint capsule over which deep flexor tendon play
tentaculum). A large vein crosses the upper part of the joint capsule (in front of 1).

1, 2, Proximal ends
4, fibular tarsal bone (sus-

Relations.- — Anteriorly, the tibia and fibula, the popliteus, lateral extensor,
tibialis anterior, and the tibial vessels; posteriorly, the gastrocnemius, superficial
flexor, and the tibial nerve; laterally, the fascia, skin, and the soleus; medially,
the fascia and skin.

1 This might well be called the tarsal (tendinous) head of the deep flexor.

MUSCLES OF THE METATARSUS AND DIGIT 343

Blood-supply. — Posterior tibial artery.

Nerve-supply. — Tibial nerve.

5. Popliteus (Fig. 298). — This thick, triangular muscle lies on the posterior
surface of the tibia above the popliteal line.

Origin. — A small depression on the lateral epicondjde of the femur, close to
the articular surface and under the lateral ligament.

Insertion. — A triangular area on the posterior surface of the tibia, proximal and
medial to the popliteal line; also the proximal half of the medial border and a
narrow adjacent part of the medial surface of the tibia.

Action. — To flex the femoro-tibial joint and to rotate the leg inward.

Structure. — The strong tendon of origin lies at first under the lateral ligament,
and curves backward and inward over the lateral condyle of the tibia in contact
with the lateral meniscus; it is invested by a reflection of the synovial membrane
of the joint (Fig. 584). The tendon is succeeded by a thick triangular belly, the
fibers of which are directed medially in the proximal part, but incline downward
below.

Relations. — Superficially, the fascia and skin, semitendinosus, gastrocnemius,
superficial flexor; deeply, the femoro-tibial joint, the tibia, the popliteal vessels
and their divisions. The saphenous vessels and nerve lie along the medial border
of the muscle, separated from it, however, by the deep fascia.

Blood-supply. — Popliteal and posterior tibial arteries.

Nerve-supply. — Tibial nerve.

MUSCLES OF THE METATARSUS AND DIGIT

Extensor digitalis brevis. — This small muscle lies in the angle of union of the
tendons of the long and lateral extensors of the digit. (Fig. 293.)

Origin. — The lateral tendon of the peroneus tertius, the middle annular liga-
ment, and the lateral ligament of the hock.

Insertion. — The tendon of the long extensor.

Action. — To assist the long extensor.

Structure. — It is principally fleshy, having a superficial origin from the annular
ligament, and a deep one (by a thin tendon) from the lateral tendon of the peroneus
tertius. The insertion is by a thin tendon.

Relations. — Superficially, the skin and fascia and the tendons of the long and
lateral extensors; deeply, the tarsal joint capsule, the great metatarsal artery, and
the deep peroneal nerve.

Blood-supply. — Great metatarsal artery.

Nerve-supply. — Deep peroneal nerve.

The interossei and lumbricales are arranged like those of the thoracic limb,
the only noticeable difference being the greater development of the lumbricales in
the pelvic limb.

THE MUSCLES OF THE OX
Muscles of the Face

The cutaneus is much more developed than in the horse, presenting as a special
feature the extensive frontalis muscle, which covers the frontal and nasal regions.

The orbicularis oris does not form a complete ring, the defect being in the
middle of the upper lip.

The levator nasolabialis is extensive, thin, and not very distinct from the

344

THE MUSCLES OF THE OX

frontalis; it divides into two layers, between which the levator labii superioris
proprius and the lateral dilator of the nostril pass. The superficial layer ends in
the nostril and upper lip, the deep layer on the accessory (lateral) nasal cartilages
and on the nasal process of the premaxilla.

The levator labii superioris proprius arises on and before the facial tuberosity
and terminates by several tendons in the muzzle. It passes between the two layers
of the preceding muscle, blending in part with the deep layer.

The zygomaticus is much stronger than in the horse. It arises on the masse-
teric fascia, and ends chiefly in the upper lip.

Fig. 300. — Muscles of Head of Ox; Lateral View.
o, Levator labii superioris proprius; b, levator nasolabialis; c, trapezius; c', brachiocephalicus; d, d', sterno-
cephalicus; e, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; y', malaris; h, buccinator; i, depressor labii
inferioris; k, orbicularis oris; to, masseter; n, parotido-auricularis ; o', zygomatico-auricularis and scutulo-auricularis
superficialis inferior; o", scutulo-auricularis superfioialis superior; o'", scutulo-auricularis superficialis accessorius;
p, p', soutularis; u, frontalis; w, mylo-hyoideus; 1, concha; 2, 3, posterior and anterior borders of 1; 8, scutiform
cartilage; 9, zygomatic arch; 2S', ramus of mandible; 37, external maxillary vein; 3S, jugular vein; 39, facial vein;
44, parotid gland; 50, 51', mandibular gland; dotted line at 50 indicates position of atlantal lymph gland, and the
parotid lymph gland lies partly under parotid gland, just in front of 44; 58, medial palpebral ligament; 69, laryngeal
prominence. (After Ellenberger-Baum, Anat. fiir Kunstler.)

The depressor labii superioris arises just in front of the facial tuberosity, and
divides usually into two branches, which terminate in a number of tendons that
form a network in the muzzle and upper lip.

The incisivus inferior is a small, rounded muscle, which arises on the body of
the mandible below the second and third incisors, and ends in the lower lip, blending
with the orbicularis.

The depressor labii inferioris is thin, and does not extend as far backward
as in the horse; only the anterior end is distinct from the buccinator.

MUSCLES OF THE FACE

345

The buccinator shows no marked variation, but its superficial layer is well
developed.

The dilatator naris lateralis arises in front of the facial tuberosity, passes for-
ward between the branches of the levator nasolabialis, and terminates in the lat-
eral wing of the nostril.

The dilatator naris apicalis is situated in the muzzle and joins its fellow at a
median raphe. It arises on the border and upper surface of the body of the pre-

FiG. 301. — Muscles op Head of Ox; Dorsal View.
a, a'. Levator labii superioris propriiis; h, levator nasolabialis; /, dilatator naris lateralis; g', malaris; o, zygo-
matico-auricularis and scutulo-auricularis superficialis inferior; o", scutulo-auricularis superficialis superior; o'",
scutulo-auricularis superficialis accessorius; p, scutularis; u, frontalis; z, orbicularis oculi; 1, concave surface of
concha; 3, 2, anterior and posterior borders of concha; 8, scutiform cartilage; 34, parietal cartilage; 39, facial vein;
49, muzzle; 58, medial palpebral ligament. (/Vfter EUenberger-Baum, Anat. filr Kunstler.)

maxilla, the fibers passing obliquely upward and outward to the medial wing of the
nostril.

The dorsal part of the lateralis nasi arises from the alar cartilage of the nostril
and ends in the medial wing of the nostril.

The ventral part of the lateralis nasi consists of two layers which arise on the
nasal process of the premaxilla and the lateral nasal cartilage and end in the lateral
^\^ng of the nostril.

The orbicularis oculi is well developed.

The corrugator supercilii is not present as a separate muscle, its place and
function being taken by the frontalis.

The malaris is broad, and spreads out below on the fascia over the buccinator
and masseter; it is divided into two parts.

346

THE MUSCLES OF THE OX

MANDIBULAR MUSCLES

The masseter is not so large as in the horse; a considerable part of it arises
on the facial tuberosity and is directed obliquely backward and downward, so that
it would draw the lower jaw forward as well as upward.

The temporalis conforms to the temporal fossa, and is therefore longer and
entirely lateral in position.

The pterygoideus medialis arises from the lateral surface of the perpendicular
part of the palatine bone and from the pterygoid process. Since the origin is nearer

Fig. 302. — Muscles of Head of Ox; Ventral View.
d, d', Sterno-cephalicus; e, omo-hyoideus; 5, zygomaticus; A, buccinator; i, depressor labii inferioris; ^•, orbicularis
oris; m, masseter; n, parotido-auricularis; o', zygomatico-auricularis; w, mylo-hyoideus; 1, concha, convex surface;
2, anterior border of concha; 30', angle of jaw; 39, facial vein; 44, parotid gland; 43, lower lip; 48, angle of mouth;
60, 50', mandibular gland; 69, larynx; X, wing of atlas. (After EUenberger-Baum, Anat. fur Kunstler.)

the median plane and the insertion further from it than in the horse, the muscle pro-
duces more marked lateral movement of the mandible.

The pterygoideus lateralis is flattened transversely, wide and thin in front,
narrower and thicker behind. It has an extensive origin in the pterj^go-palatine
fossa, where it is partly covered by the pterygoideus medialis.

The occipito-mandibularis is absent.

The digastricus has a tendinous origin on the paramastoid process of the
occipital bone; its bellies are short and thick. The intermediate tendon is round and
thick; it does not perforate the stylo-hyoideus. The anterior bellies are connected
beneath the root of the tongue by a layer of transverse muscle-fibers termed the
transversus mandibulse.

MUSCLES OF THE NECK — VENTRAL GROUP — LATERAL GROUP 347

HYOm MUSCLES

The mylo-hyoideus is thicker and more extensive than in the horse.

The stylo-hyoideus has a long, slender tendon of origin which is attached to the
muscular angle of the great cornu of the hyoid bone. The insertion is fleshy and
is not perforated by the digastricus.

The genio-hyoideus is much more developed than in the horse.

The kerato-hyoideus has an additional attachment on the middle cornu of the
hyoid bone.

The hyoideus transversus is bifid.

The stemo-thyro-hyoideus has no intermediate tendon and is thicker.

The omo-hyoideus arises as a thin band from the fascia over the third and
fourth cervical vertel^rse. It blends here with the rectus capitis ventralis major.

The occipito-hyoideus is thick. Its large lateral part entirely covers the para-
mastoid process (from which it arises) and is inserted into the muscular angle of
the great cornu. The smaller medial part arises from the ventral end of the para-
mastoid process and ends on the medial face of the great cornu below the dorsal
end.

Muscles of the Neck
a. ventral group

The cervical cutaneus is absent.

The stemo-cephalicus consists of two muscles. They arise from the manu-
brium sterni and first rib. The superficial muscle is the stemo-mandibularis ; it
is inserted on the anterior border of the masseter, the ramus of the mandible, and
the buccal fascia. The deep muscle is the stemo-mastoideus ; it crosses under the
preceding and ends on the mastoid processes, the mandible, and, in common with
the rectus capitis ventralis major, on the basilar part of the occipital bone.

There are two scaleni. The scalenus ventralis (s. primse costse) arises from
the transverse processes of the third to the seventh cervical vertebrae and ends on
the first rib. It is traversed by the roots of the brachial plexus, which divide it
into bundles. The emerging brachial artery separates a narrow part below from
the main mass. The scalenus dorsalis (s. supracostalis) arises usually on the
transverse processes of the fourth, fifth, and sixth cervical vertebrae. Its wide
posterior part lies on the ventral part of the serratus thoracis; it is attached to the
third rib and to the serratus thoracis.

The rectus capitis ventralis major arises on the third to the sixth cervical
transverse processes, and blends at its insertion with the sterno-mastoideus and
the cleido-mastoideus.

The rectus capitis ventralis minor is larger than in the horse.

The rectus capitis lateralis and longus colli resemble those of the horse.

The intertransversales are large. From the sixth cervical vertebra forward
they form a muscular mass (M. intertransversarius longus) which is inserted into
the wing of the atlas.

B. LATERAL GROUP
The splenius is thin. It arises directly from the first three or four thoracic
spines, and ends by a thin tendon on the occipital bone, the wing of the atlas,
and the transverse process of the axis, blending with the brachiocephalicus, longis-
simus capitis, and omo-transversarius. The remaining muscles present no very
marked differential features.

348

THE MUSCLES OF THE OX

MUSCLES OF THE THORAX — ABDOMINAL MUSCLES 349'

Muscles of the Thorax

The levatores costarum number ten or eleven pairs.

The external intercostal muscles are thick; they terminate at the costo-
chondral junctions. The internal intercostals are specially thick in relation to the
cartilages of the sternal ribs; here there exist bundles (comparable to the levatores
costarum) which are attached in front to the sternum, behind to a costal cartilage.
The interosseous part thins toward the upper end of the spaces.

The diaphragm presents several important differential features. Its slope is
much steeper and its width is greater than in the horse. The upper limit of the
costal attachment extends almost in a straight line from the last rib about a hand-
breadth above its middle to the junction of the eighth rib with its cartilage, and
along the latter to the sternum. The midline slopes from the twelfth thoracic
vertebra obliquely as far as the foramen vense cavae, beyond which it is almost
vertical. The right crus divides into two branches, which circumscribe the hiatus
oesophageus, unite below, and then spread out in the tendinous center. The left
crus is small. The hiatus a?sophageus is situated about four to five inches (10 to
12 cm.) below the eighth thoracic vertebra, a little to the left of the median plane.
The foramen vense cavae is a little more ventral and almost in the median plane. ^

In the sheep the costal attachment differs from that of the ox. The upper
limit of the attachment extends in a gentle curve (convex ventrally) from the
last rib about the junction of its middle and ventral thirds to the ventral end of
the ninth rib.

MUSCLES OF THE BACK AND LOINS

The serratus dorsalis anterior is very thin. It is inserted on the fifth to the
eighth ribs when fully developed, but it may be reduced to two or three digitations
or may be absent. The serratus dorsalis posterior is inserted on the last three or
four ribs.

The longissimus costarum has a distinct lumbar portion which is attached to
the lumbar transverse processes and the tuber coxae.

The longissimus dorsi resembles that of the horse, but it is more fleshy anter-
iorly, and the spinalis dorsi is clearly distinguishable from the common mass. In
the lumbar region the tendons meet across the summits of the spines.

Intertransversales are present in the back, and interspinales in the back and
loins.

Muscles of the Tail

These resemble in general those of the horse; the coccygeus is, however, much
more developed.

Abdominal Muscles

The obliquus abdominis extemus is somewhat thinner and has a less extensive
origin, which begins at the lower part of the fifth intercostal space and ends on
the last rib above its middle. The direction of the fibers in the flank is horizontal,
and they do not reach to the tuber coxae, nor as high as the lumbar transverse proc-
esses. (In this region the abdominal tunic has a strong attachment to the point

1 The sternal part is clearly separable from the costal part. The costal attachment is much
higher posteriorly than in the horse, thus diminishing the capacity of the thorax in comparison
with that animal. The last digitation is thus some seven or eight inches (ca. 18 to 20 cm.) above the
corresponding digitation of the transversus abdominis. There are small intermediate digitations-
at the last two intercostal spaces.

350

THE MUSCLES OF THE OX

of the hip and the lumbo-dorsal fascia.) The aponeurosis is intimately united with
the abdominal tunic, and does not detach a femoral lamina.

The obliquus abdominis intemus is more developed and has an additional
origin from the lumbo-dorsal fascia. The aponeurosis blends with that of the
external oblique near the linea alba, and detaches a layer which assists in the for-
mation of the internal sheath of the rectus.

The rectus abdominis arises on the lateral border of the sternum as far for-
ward as the third costal cartilage. The two muscles are separated, except near
the pelvis, by an interval varying from two to four inches (ca. 5 to 10 cm.), so that
this part of the abdominal wall is entirely fibrous. (The umbilicus is in a trans-
verse plane through the third lumbar vertebra.) There are five tendinous inscrip-
tions, at the third of which is a foramen for the passage of the subcutaneous ab-
dominal vein. The prepubic tendon has, in addition to lateral branches inserted

Fig. 304. — Deeper Muscles of Neck, Shoulder, and Thorax op Ox.
c', Cleido-oceipitalis muscle; d, sterno-cephalicus; /, /', long and lateral heads of triceps; g, superficial pectoral
muscle; h, h', deep pectoral muscle; i, i', serratus ventralis; k, latissimus dorsi; I, obliquus abdominis externus; »',
biceps brachii; w, splenius; x, rhomboideus; y, longissimus capitis et atlantis; z, supraspinatus ; z', infraspinatus;
z", tendon of insertion of z'; 1', cartilage of scapula; 2, tuberosity of spine of scapula; S, acromion; 5, lateral tuberosity
of humerus; 6, deltoid tuberosity; S, olecranon; £6, transverse processes of cervical vertebrae; 27, posterior auricular
muscles: X, wing of atlas. (After EUenberger-Baum, Anat. fiir Kunstler.)

into the ilio-pectineal eminences, a strong attachment to the median common ten-
don of the adductors of the thigh, so that the abdominal wall is strongly retracted
and almost vertical at its junction with the pubis.

The transversus abdominis presents no striking differential features. The
transversalis fascia is strong and distinct except over the diaphragm.

Muscles of the Thoracic Limb
i. muscles of the shoulder girdle

The trapezius is much thicker and broader than in the horse, and is undivided.
It arises on the ligamentum nuchae and supraspinous ligament, from the atlas to
the twelfth thoracic vertebra.

MUSCLES OF THE SHOULDER — MUSCLES OF THE ARM 351

The omo-transversarius arises on the wing of the atlas, and, inconstantly,
the transverse process of the axis, and is inserted into the scapular spine and fascia.

The rhomboideus is clearly divided into cervical and thoracic parts, the latter
extending further than in the horse.

The latissimus dorsi has a broad tendon of origin, which blends with the
lumbo-dorsal fascia; it is also attached to the eleventh and twelfth ribs and the
fascia over the external intercostal and oblique abdominal muscles. The anterior
fibers end on the tendon of the teres major, the middle part on an aponeurosis on
the medial surface of the caput longum, and the posterior part on a tendon which is
common to this muscle and the deep pectoral.

The brachiocephalicus has two distinct parts. The dorsal division, the cleido-
occipitalis, arises on the occipital bone and the ligamentum nuchas. The ventral
part, the cleido-mastoideus, is smaller and arises by a round tendon on the mastoid
process and the rectus capitis ventralis major, and by a thin tendon on the mandible.

The superficial pectoral muscle is thinner than in the horse and its two parts
are not so clearly separal^le.

The deep pectoral muscle arises as far forward as the second rib and is un-
divided. However, the scapular portion may be considered to be represented by a
small branch which arises from the anterior part of the sternum and the first rib
and passes upward to end on the deep face of the brachiocephalicus in front of the
shoulder joint. ^ A tendon detached from the dorsal edge blends with the latissimus
dorsi and coraco-brachialis.

The serratus ventralis is clearly divided into cervical and thoracic parts.
The former is large and extends from the third (or second) cervical vertebra to
the fifth rib, being overlapped behind by the thoracic part. It is inserted on a
large triangular area on the antero-superior part of the costal surface of the scapula.
The thoracic part is relatively thin and is covered by a very strong aponeurosis;
it is attached to the fourth to the ninth ribs by six digitations, and is inserted by a
flat tendon which insinuates itself between the middle and posterior parts of the
subscapularis to end on a rough line — equivalent to the posterior serratus area of
the horse — and also on the cartilage of the scapula in continuity with this line.

n. MUSCLES OF THE SHOULDER

The deltoid is clearly divided into acromial and scapular parts. The former
(Pars acromialis) arises on the acromion, the latter (Pars scapularis) on the posterior
border of the scapula and the aponeurotic covering of the infraspinatus. The
scapular part of the muscle is largely inserted into the fascia covering the triceps.

The supraspinatus, infraspinatus, and teres minor do not differ materially
from those of the horse.

The subscapularis consists of three parts with a common tendon of insertion.

The teres major and coraco-brachialis resemble those of the horse.

The capsularis is absent.

m. MUSCLES OF THE ARM

The biceps is smaller and less tendinous, and is situated more medially than
in the horse. The tendon of origin is flat, and is bound down in the intertuberal or
bicipital groove by a fibrous band. The tendon to the extensor carpi radialis is
less distinct than in the horse. (In the sheep the tendon of origin is round and is
invested by the synovial membrane of the shoulder joint. The tendon of inser-
tion bifurcates; one branch ends on the tuberosity of the radius, the other on the
ulna.)

1 According to Meckel and Lesbre, this is the homologue of the subclavius of man.

352

THE MUSCLES OF THE OX

The medial head of the triceps is more developed than in the horse, and ex-
tends up to the neck of the humerus.

The tensor fasciae antibrachii is a slender muscle which lies along the posterior

border of the triceps and is not
';j connected with the latissimus

I dorsi.

IV. MUSCLES OF THE FOREARM

AND MANUS

A. Extensor Division
The extensor carpi radialis

is like that of the horse. There
is sometimes a small muscle
lying along its medial border,
which may represent the exten-
sores pollicis.

There are three digital ex-
tensors: 1. The common digital
extensor (M. extensor digitalis
communis) arises by two heads
from the lateral epicondyle of
the humerus and from the ulna.
The heads fuse about the middle
of the forearm, and terminate
soon on a tendon which passes
over the carpus and metacarpus,
gradually inclining forward. At
the fetlock joint it divides into
two branches, each of which is
inserted into the extensor pro-
cess of the corresponding third
phalanx. 2. The medial digital
extensor (M. extensor digiti ter-
tii proprius) arises on the lateral
epicondyle, and is inserted by
two branches into the second
and third phalanges of the me-
dial digit. The tendon receives
two reinforcing slips from the
suspensory ligament. 3. The
lateral digital extensor (M.
extensor digitalis lateralis s.
digiti quarti proprius) is stronger
than that of the horse; it arises
from the lateral ligament of the
elbow joint, the lateral tuber-
osity of the radius, and the
ulna. The tendon terminates
like that of the preceding
muscle. "^
the horse.

^ It may be remarked that, in addition to the extension action, the common extensor approxi-
mates the digits, while the others tend to abduct them.

Fig. 305. — Muscles of Antibr.\-

CHIUM AND MaNUS OF Ox;

Lateral View.

o. Extensor carpi radialis; b,
extensor digiti tertii; c, extensor
digitalis communis; d, extensor
digiti quarti; e, ulnaris lateralis;
/, extensor carpi obliquus; /', ul-
nar head of flexor carpi ulnaris; g,
brachialis; h, interosseus mediug
or suspensory ligament; i, flexor
tendons; i', branch of h, to super-
ficial flexor tendon; 8, olecranon;
11, accessory carpal bone; 12',
metacarpal tuberosity. (After
EUenberger-Baum, Anat. fur
Kiinstler.)

Fig. 306. — Muscles of Anti-

BRACHIUM AND MaNUS OF

Ox; Medial View.

a. Extensor carpi radialis;
b, tendon of extensor digiti ter-
tii; /, tendon of extensor carpi
obliquus; s, brachiaUs; A, inter-
osseus medius or suspensory
ligament; i, flexor tendons; i',
branch of h; k, flexor carpi radi-
alis; /, flexor carpi ulnaris; m,
superficial digital flexor. (After
Ellenberger-Baum, Anat. fur
Kiinstler.)

The extensor carpi obliquus resembles that of

MUSCLES OF THE FOREARM AND MANUS

353

The extensor tendons are bound down at the carpus by an annular ligament,
and are furnished with synovial sheaths (Figs, 307, 308).

B. Flexor Division

The three flexors of the carpus are like those of the horse, but the long tendon
of the lateral flexor ends on the large metacarpal bone, not on the small one. The
tendon of the medial flexor naturally ends on the medial part of the large meta-
carpal bone.

The superficial digital flexor is somewhat blended at its origin with the middle
flexor of the carpus. It divides into two bellies, superficial and deep, terminating

Fig. 307. — Right Cahpus or Ox with Burs^ and Fig. 308. — Right Carpus of Ox with Burs^ and

Synovial Sheaths Injected; Lateral View. Synovial Sheaths Injected; Medial View.

1, Extensor carpi radialis, with synovial sheath (/') and bursa (/"); ^. extensor carpi obliquus, with synovial
sheath (2') and bursa {2"); 3, extensor digiti tertii proprius; 4< extensor digitalis communis; S', common synovial
sheath of 3 and 4; 5, extensor digiti quarti proprius, with synovial sheath (5') ; 6, 6', ulnaris lateralis, with bursa
(6"); 7, flexor carpi radialis, with synovial sheath; S, deep digital flexor, with synovial sheath {8'); 9, flexor carpi
ulnaris; 10, superficial digital flexor, with synovial sheath, 10'; a, radius; 6, carpus; c, metacarpus; d, cut edge of
annular ligament. (After Schmidtchen.)

on tendons at the distal part of the forearm. The superficial tendon passes over
the posterior annular ligament (Lig. carpi transversum), perforates the metacarpal
fascia, and joins the deep tendon about the middle of the metacarpus. The deep
belly is connected with the deep flexor by a strong fibrous band. Its tendon passes
under the annular ligament of the carpus in a groove on the deep flexor, from which
it receives fibers. The conjoined tendon soon bifurcates, each branch receiving a
reinforcing band from the suspensory ligament, and forming near the fetlock a
ring for the corresponding branch of the deep flexor tendon. Passing under two
digital annular ligaments, they are inserted into the volar surfaces of the second
phalanges by three slips,
23

354 THE MUSCLES OF THE OX

The deep digital flexor has the same heads as in the horse, the humeral head,
as before mentioned, being connected ^\^tll the deep part of the superficial flexor.
The tendon, which is not reinforced by a check ligament as in the horse, divides
near the distal end of the metacarpus into two branches which are inserted into the
volar surfaces of the third phalanges.

The synovial sheaths at the carpus present the following special features:
One is found in connection with the tendon of the superficial part of the superficial
flexor of the digits. There is a common sheath for the tendons of the common ex-
tensor and the medial extensor.

Bursse may occur under the tendons of the proper extensors of the digits at the
fetlock; they are constant only in old animals (Schmidtchen). The branches of
the tendon of the common extensor are provided with synovial sheaths from their
origin to the middle of the second phalanx. There are two digital synovial sheaths
for the flexor tendons; they may communicate at their upper part, and they ex-
tend from the distal third of the metacarpus nearly to the distal sesamoids. Bursse
occur between the latter and the branches of the deep flexor tendon.

A feeble pronator teres is present on the medial surface of the elbow along the
medial collateral ligament.

The fascia on the volar face of the metacarpus and digit is very thick. It is
continuous above with the ligamentum carpi transversum, and is attached on either
side to the metacarpal bone. At the fetlock it forms the fibrous basis for the small
claws, and below this it detaches two strong bands which diverge to be inserted into
the second and third phalanges, blending with the collateral ligaments.

The lumbricales are absent, unless we regard as such the muscular bundles
which arise on the deep flexor and are inserted into the superficial flexor tendon at
the carpus.

The interosseus medius, or suspensory ligament, is somewhat more muscular
than in the horse; indeed, in the young subject it may be almost entirely fleshy.
Its arrangement is somewhat complex. Single at its origin, it detaches about the
middle of the metacarpus a band which joins the tendon of the superficial flexor
and concurs near the fetlock in the formation of the ring for the deep flexor tendon. ^
A little lower down it divides into three and then into five branches. The abaxial
branches (two pairs) are attached to the corresponding sesamoids and tendons of
the proper extensors, while the middle branch passes through the sulcus at the distal
end of the metacarpus and bifurcates, each division fusing with the tendon of the
corresponding proper extensor.

The Muscles of the Pelvic Limb
l the sublumbar muscles

The psoas minor begins at the disc between the twelfth and thirteenth thoracic
vertebrae.

The psoas major has a fleshy origin on the posterior border of the last rib, and
a thin tendon attached to the twelfth rib; it is relatively narrower than in the horse
and does not entirely cover the quadratus lumborum.

The iliacus begins under the body of the sixth lumbar vertebra, and is more
closely united with the psoas major than in the horse.

The quadratus lumborum extends as far forward as the body of the tenth or
eleventh thoracic vertebra. It is wider than in the horse and extends beyond the
lateral border of the psoas major.

' Lesbre regards this band as the subcarpal check ligament, which on this basis is blended
with the suspensory hgament above.

LATERAL MUSCLES OF THE HIP AND THIGH

355

II. LATERAL MUSCLES OF THE HIP AND THIGH (Figs. 303, 309)

The tensor fasciae latae is large, and the fleshy part extends further down than
in the horse.

Tlie gluteus superficialis is not present as such; apparently its anterior part
has fused with the tensor fascise latae and its posterior part with the biceps femoris.

The gluteus medius is small, the lumbar part being insignificant and extend-
ing forward only to the fourth lumbar vertebra. Its deep portion (gluteus ac-
cessorius) is easily separable, and its strong tendon is inserted into the femur below
the trochanter major, under cover of the upper
part of the vastus lateralis.

The gluteus profundus is thin, but exten-
sive, arising as far forward as the tuber coxae,
and from the lower part of the sacro-sciatic liga-
ment. The fibers converge on a broad, strong
tendon which passes under the upper part of
the vastus lateralis, and is inserted into a tu-
bercle a short distance below the great tro-
chanter.

The biceps femoris is very wide at its
upper part, having apparently absorbed the
posterior part of the superficial gluteus. It
arises from the sacral spines, sacro-sciatic liga-
ment, and tuber ischii. It is divided by a
fi])ro-elastic septum in the thigh into two por-
tions, which end in front and below on a wide
aponeurosis; the latter is attached to the patella
and its lateral ligament and blends with the fas-
cia cruris and fascia lata. There is no femoral
attachment. A large bursa occurs between the
muscle and the great trochanter in the adult.
The part of the tendon which fuses with the
lateral patellar ligament presents a fibro-cartil-
aginous thickening, and an extensive bursa is
interposed between it and the lateral condyle
of the femur.

A layer derived from the fascia lata is intimately
adherent to the deep face of the muscle, and cases occur
in which this fascials ruptured by the trochanter major,
thus fixing the muscle behind the trochanter.

Fig. 309. — Gluteal, Femor.\l, and Crural
Regions of Ox, After Removal op
Superficial Muscles.
p. Gluteus medius; r, semitendinosus; u,
coccygeus; 28, vastus lateralis; 28', rectus fe-
moris; 29, semimembranosus; 30, gastrocnemi-
us; 31, sacro-sciatic ligament: 16, tuber coxae;
17, tuber ischii; 19, trochanter major; 20, patel-
la; 21', lateral condyle of tibia. (After Ellen-
berger-Baum, Anat. fiir Kiinstler.)

The semitendinosus and semimembrano-
sus arise on the ischium only. The latter is very large and has a branch attached
to the medial condyle of the tibia.

III. ANTERIOR MUSCLES OF THE THIGH

The quadriceps femoris reseml)les that of the horse; but the vasti (and es-
pecially the medial one) are not so thick, and the vastus intermedins is more clearly
separable, and consists of two parts. Bursae occur under the insertions of the
medial and lateral vasti, and often under the end of the rectus in the adult.

The articularis genu is a small muscle which lies under the distal part of the
vastus intermedins, and is partly inserted on the sui^rapatellar cul-de-sac of the
synovial membrane of the stifle joint.

The capsularis is absent.

356 THE MUSCLES OF THE OX

IV. MEDIAL MUSCLES OF THE THIGH

The sartorius arises by two heads, one from the tendon of the psoas minor
and the ihac fascia, the other from the shaft of the ihum. The femoral vessels
pass between them.

The gracilis is more extensively united with its fellow at its origin than in the
horse.

The pectineus is large, and arises by a single head from the pubis and prepubic
tendon. It divides into two branches, one of which is inserted as in the horse,
while the other extends to the medial epicondyle of the femur.

The adductor resembles that of the horse, but does not reach to the medial
condyle of the femur.

The quadratus femoris and obturator extemus resemble those of the horse.

The obturator intemus has no iliac head, and its tendon passes through the
obturator foramen.

The gemellus is large; some of its fibers of origin join the obturator internus
through the lesser sciatic foramen.

V. MUSCLES OF THE LEG AND FOOT

A. DORSO-LATERAL GrOUP

There are four digital extensors, two of which are fused with each other and
the peroneus tertius in the upper third of the leg.

1. The long digital extensor (M. extensor digitalis longus) arises in common
with the peroneus tertius and the medial extensor in the extensor fossa of the femur,
and separates from the other muscles near the middle of the leg. At the distal
end of the tibia it terminates on a tendon which passes down over the hock (bound
down by two annular ligaments) and ends like that of the thoracic limb.

2. The medial digital extensor (M. extensor digiti tertii proprius) arises in com-
mon with the preceding muscle and the peroneus tertius, and is covered by them
to the distal third of the tibia. Its tendon passes under the annular ligaments
between those of its cogeners and ends on the second phalanx of the medial digit.

3. The lateral digital extensor (M. extensor digitahs lateralis s. digiti quarti
proprius)^ arises on the lateral ligament of the stifle joint and the lateral condyle of
the tibia. Its tendon passes over the lateral surface of the hock, and terminates
on the dorsal surface of the second phalanx of the lateral digit.

The reinforcing bands from the suspensory ligament are arranged as in the
forelimb.

4. The short digital extensor (M. extensor digitalis brevis) resembles that of
the horse ; it is inserted on the tendon of the long extensor.

The peroneus longus (not present in the horse) is situated in front of the lateral
extensor. It arises on the lateral condyle of the tibia and the fibrous band which
represents the shaft of the fibula. Its tendon passes downward and backward
over the lateral surface of the hock, crosses over that of the lateral extensor and
under the lateral ligament, and ends on the first tarsal bone and the proximal end
of the large metatarsal bone. It is enveloped by a synovial sheath. It would ap-
parently act as an inward rotator at the hock joint.

The peroneus tertius is a well-developed muscle which arises on the common
tendon with the long and medial extensors. It has a large, fusiform belly, which
is superficially situated on the front of the leg. Close to the tarsus it ends on a
flat tendon, which is perforated by that of the tibialis anterior, and ends on the
proximal end of the large metatarsal and second and third (fused) tarsal bones.

^ Lesbre regards this muscle as the homologue of the peroneus brevis of man and other
pentadactyls.

MUSCLES OF THE LEG AND FOOT

357

The tibialis anterior is smaller, and arises by two heads. The larger head
springs from the lateral surface of the tuberosity and crest of the tibia; the lateral,
smaller one (M. extensor hallucis longus), arises from the upper part of the lateral

Fig. 310. — Muscles of Left Leg and Foot of Ox;
Antekiok View.
o, Peroneus tertius; a', tibialis anterior; 6, long
digital extensor; b', extensor digiti tertii; c, peroneus
longus; d, extensor digiti quarti; i, i, annular liga-
ments; k, lateral ligament of hock joint; I, branch of
suspensory ligament; 20, patella; SI', lateral condyle
of tibia; 28, tuberosity of tibia. (After Ellenberger-
Baum, Anat. fiir Kunstler.)

Fig. 311. — Muscles of Left Leg and Foot of Ox;
Later.^l View.
a, Peroneus tertius; a', tibialis anterior; 6, long
digital extensor; b' , tendon of 6; c, peroneus longus;
d, extensor digiti quarti; e, deep digital flexor; e', ten-
don of e; e", branch of interosseus medius or suspen-
sory ligament; /, gastrocnemius (the soleus lies just in
front of /) ; /', tendon of superficial digital flexor; h, in-
terosseus medius or suspensory ligament; i, i, annular
ligaments; 20, patella; 21', lateral condyle of tibia;
28, tuberosity of tibia. (After Ellenberger-Baum, Anat.
fur Kunstler.)

l)order of the tibia and the fibrous band which replaces the shaft of the fibula. The
tendon perforates that of the preceding muscle, passes to the medial face of the
hock, and ends on the metatarsal and second and third tarsal bones.

358

THE MUSCLES OF THE OX

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THE MUSCLES OF THE PIG — MUSCLES OF THE FACE 359

B. Plantar Group

The gastrocnemius and soleus resemble those of the horse.

The superficial flexor is more fleshy than in the horse. Its tendon termi-
nates as in the forelimb.

The deep flexor in general resembles that of the horse, but the tibialis poste-
rior (superficial head) is distinct and is larger than in the horse. The flexor digitahs
longus (medial head) is also larger, while the flexor hallucis longus (deep head) is
smaller. The common tendon ends like that on the forelimb.

The synovial sheaths and bursse of the muscles of the leg and foot are shown in
Figs. 312-315.

THE MUSCLES OF THE PIG
Muscles of the Face

The facial cutaneus is pale, thin, and difficult to separate from the skin.

The orbicularis oris is little developed.

The levator nasolabialis is thin and pale, and is undivided.

The levator labii superioris proprius may well be termed the levator rostri.
It has a large pennate belly, which arises in the preorbital fossa. The tendon ends
on the anterior part of the os rostri. A muscular slip connects it with the premaxilla.

The zygomaticus arises on the fascia over the masseter and ends at the angle
of the mouth.

The depressor labii inferioris separates from the buccinator only near the
angle of the mouth; it ends by a number of tendinous branches in the lower lip.

The dilatator naris lateralis is well developed. It arises under the levator
rostri and ends by a tendinous network around the nostril.

The transversus nasi is represented only by a few fibers which cross over the
OS rostri.

The depressor rostri arises on the facial crest. It has a long strong tendon
which passes below the nostril and turns dorso-medially to meet the tendon of the
opposite side and end in the skin of the snout. It depresses the snout and con-
tracts the nostril.

The malaris is absent, and the other palpebral muscles present no special
features.

MANDIBULAR MUSCLES

The masseter is thick.

The pterygoideus medialis is wide at its insertion.

The pterygoideus lateralis is large and distinct.

The digastricus has only one belly and has no connection with the hyoid bone.
It ends on the medial and lower surface of the mandible, in front of the groove for
the facial vessels.

HYOID MUSCLES

The mylo-hyoideus consists of two more or less distinct layers, the superficial
one being the transversus mandibulse.

The occipito-hyoideus and kerato-hyoideus are small.

The hyoideus transversus is absent.

The omo-hyoideus and stemo-hyoideus are referred to in connection with the
muscles of the neck.

THE MUSCLES OF THE PIG

Muscles of the Neck

The cutaneus consists of two layers which cross each other obhquely. The
fibers of the superficial layer are directed nearly vertically, those of the deep layer
toward the face, on which they are continued to form the facial portion.

The brachiocephalicus is described with the other muscles of the shoulder girdle.

The stemo-cephalicus arises on the sternum and is inserted by a long round
tendon on the mastoid process.

The thyroid part of the stemo-thyro-hyoideus has a peculiar arrangement.
It arises (separately from the opposite muscle) on the manubrium sterni. About
the middle of the neck it has an oblique tendinous intersection, beyond which it

Fig. 316. — Superficial Muscles or Pig, After Removal op M. Cut.vneus.
a. Levator nasolabialis; 6, levator labii superioris proprius; h', fleshy slip of h which comes from premaxilla; c,
dilatator naris lateralis; d, depressor rostri; e, orbicularis oris; /, depressor labii inferioris; s, zygomaticus; /i, masseter;
i i', i", brachiocephalicus (cleido-occipi talis, cleido-mastoideus, pars clavicularis deltoidei) ; k, stemo-cephalicus; I,
sterno-hyoideus; m, omo-transversarius; n, n', trapezius; o, anterior deep pectoral; p, latissimus dorsi; g, lumbo-
dorsal fascia ; r, obliquus abdominis externus; r', aponeurosis of r; s, serratus dorsalis; /, serratus ventralis; m, posterior
deep pectoral; v, supraspinatus; w, w', deltoideus; x, long head of triceps; y, lateral head of triceps; z, tensor fasciae
antibrachii; 1, brachialis; S, extensor carpi radialis; 3, extensor digiti quarti; 4, extensor digiti quinti; 5, extensor
carpi ulnaris; 6, ulnar head of deep flexor; 7, gluteus medius; 8, tensor fasciae latse; 9, 10, 10', biceps femoris; 11,
semitendinosus; 13, semimembranosus; 13, caudal muscles; H, panniculus adiposus in section. (After EUenberger,
in Leisering's Atlas.)

divides into two branches: one of these is inserted in the usual fashion, the other
ends on the laryngeal prominence. The hyoid part is well developed.

The omo-hyoideus is thin. It arises as in the horse, but has no connection
with the brachiocephalicus nor with the opposite muscle.

The omo-transversarius arises on the first or second cervical vertebra (under
cover of the brachiocephalicus), and is inserted into the lower part of the scapular
spine.

There are two scaleni. The scalenus ventralis (s. primse costse) resembles
that of the ox, is attached to the last four cervical vertebrse, and is perforated by
the nerves of the brachial plexus. The scalenus dorsalis (s. supracostalis) arises
on the transverse processes of the third to the sixth cervical vertebra, and ends
on the third rib.

The ventral muscles of the head present no special features.

The longus colli is separated from the opposite muscle, so that part of the
bodies of the cervical vertebrae is exposed as in man.

MUSCLES OF THE THORAX — MUSCLES OF THE BACK AND LOINS 361

The intertransversales resemble those of the ox.

The splenius is thick and extensive. It ends in three parts on the occipital,
the temporal, and the wing of the atlas (inconstant) .

The longissimus capitis et atlantis is small, and its atlantal part is blended
with the longissimus cervicis.

The complexus is large, and is clearly divided into two parts: the dorsal part
(Biventer cervicis) is marked by several tendinous intersections; the ventral part
is the complexus proper.

The obliquus capitis posterior is relatively thin.

The recti capitis dorsales are thick and more or less fused.

Muscles of the Thorax

The levatores costarum and rectus thoracis present no special features.

The external intercostal muscles are absent under the serratus dorsalis and the
digitations of the external oblique.

The internal intercostals are thick between the cartilages of the sternal ribs.

The retractor costae and the transversus thoracis resemble those of the horse ;
the latter extends back to the eighth cartilage and fuses with the transversus ab-
dominis.

The diaphragm has seven costal digitations on each side, the posterior ones
being attached to the ribs at some distance (ca. one-third to one-fourth of rib-
length) from the costo-chondral junction.^ The line of attachment reaches the
latter at the tenth rib, and passes along the eighth cartilage to the xiphoid process.
The tendinous center is more rounded than in the horse. The crura are well
developed. The right crus is very large, and is perforated by the extensive slit-
like hiatus oesophageus, which is median in position, and lies about two and one-
half to three inches (ca. 6 to 8 cm.) below the twelfth thoracic vertebra. The hiatus
aorticus is between the crura.

Abdominal Muscles

The abdominal tunic is little developed.

The obliquus abdominis extemus has an extensive fleshy portion and a cor-
respondingly narrow aponeurosis; the latter does not detach a femoral lamina,
but is reflected in toto to form the inguinal ligament.

The obliquus abdominis intemus resembles that of the ox; a small fusiform
muscle, which crosses the inguinal canal obliquely and is attached on the abdominal
surface of the inguinal ligament, is apparently a detached slip of the internal
oblique.

The rectus abdominis is extensive and thick. It has seven to ten inscriptions.
Its tendon of insertion fuses largely with the common tendon of the graciles, and
does not give off an accessory band to the head of the femur.

The fleshy part of the transversus abdominis is well developed. It blends
in front with the transversus thoracis.

The cremaster extemus is present in the female as well as in the male.

Muscles of the Back and Loins

The serratus dorsalis anterior is inserted into the fifth to the eighth ribs
inclusive, the serratus dorsalis posterior into the last four or five ribs. There are
usually no digitations attached to the ninth and tenth ribs.

1 It is interesting to note that the diaphragm has no attachment to the fifteenth rib, which is
often present and well developed.

362 THE MUSCLES OF THE PIG

The longissimus costarum extends to the wing of the atlas.

The spinalis et semispinalis can be separated without much difficulty from
the longissimus dorsi, the division from the common mass of the loins beginning
about the first lumbar vertebra.

The multifidus resembles that of the horse.

Interspinales are present, as well as distinct intertransversales of the Imck
and loins.

Muscles of the Tail

The dorsal and lateral sacro-coccygei arise as far forward as the last lumbar
vertebra. Gurlt explains the twist of the tail as being due to the spiral arrangement
of the insertions of the tendons.

Muscles of the Thoracic Limb
muscles of the shoulder girdle

The trapezius is very wide, its line of origin extending from the occipital bone
to the tenth thoracic vertebra. There is no clear division between its two parts,
which are both inserted into the scapular spine.

The omo-transversarius resembles that of the ox.

The rhomboideus consists of three parts. The cervical part (Rhomboideus
cervicalis) is greatly developed, its origin extending from the second cervical to the
sixth thoracic vertebra. The cephalic part (Rhomboideus capitis) arises with the
splenius on the occipital bone, and is inserted with the cervical part. The thoracic
part (Rhomboideus thoracalis) extends as far back as the ninth or tenth thoracic
vertebra.

The latissimus dorsi is attached to the four ribs preceding the last. It is
inserted into the medial tuberosity of the humerus.

The brachiocephalicus divides into two parts, the cleido-mastoideus and
cleido-occipitalis, which arise on the mastoid process and nuchal crest respectively,
and unite at the fibrous vestige of the clavicle.

The anterior superficial pectoral muscle is thin. The posterior superficial pec-
toral muscle is divided into two parts, one of which ends on the humerus, the other
on the fascia of the forearm. The anterior deep pectoral muscle resembles that of
the horse, but its origin does not extend behind the first two chondro-sternal joints.
The posterior deep pectoral muscle is very long.

The cervical part of the serratus ventralis is greatly developed, its origin ex-
tending from the wing of the atlas to the upper part of the fifth rib, and passing
under the thoracic part; the latter resembles that of the ox.

MUSCLES OF THE SHOULDER

The deltoid is undivided; it arises from the aponeurosis covering the infra-
spinatus, and it ends largely on the deltoid ridge, but partly on the fascia of the arm.

The supraspinatus is large ; it has a small attachment to the medial tuberosity
and ends chiefly on the lateral tuberosity of the humerus. There is a bursa between
the tendon and the anterior part of the lateral tuberosity.

The infraspinatus is wide ; it is inserted into a depression below the posterior
division of the lateral tuberosity. There is a bursa between the tendon and the
tuberosity.

The teres minor is large and rounded; it ends on a tubercle between the
lateral and deltoid tuberosities of the humerus.

MUSCLES OF THE ARM MUSCLES OF THE FOREARM AND MANUS 363

The subscapularis is very broad at its upper part. It extends posteriorly up
to the dorsal angle of the scapula, but anteriorly only about two-thirds of the way
up to the vertebral border.

The teres major presents nothing remarkable.

The coraco-brachialis is short, wide, and undivided. There is a bursa between
its broad tendon of origin and the tendon of insertion of the subscapularis.

The capsularis is variable; it may be half an inch wide or very small and
is frequently absent.

MUSCLES OF THE ARM

The biceps brachii is fusiform and not greatly developed. Its tendon of origin
is rounded and the underlying bursa communicates so freely with the shoulder joint
as to be regarded as an evagination of the synovial membrane of the latter. A small
band binds down the tendon in the bicipital groove. The tendon of insertion di-
vides into two branches. One branch passes back across the medial surface of the
neck of the radius to end on the proximal extremity of the ulna. The other is
attached to the radius under cover of the brachialis tendon.

The brachialis is large. Its tendon of insertion divides. The small branch is
inserted into the medial border of the radius distal to the biceps tendon. The large
branch crosses the medial border of the radius and ends on the medial surface of the
ulna distal to the biceps tendon; there is a bursa under this tendon.

The tensor fasciae antibrachii resembles that of the horse, but is very wide and
bends around the posterior border of the triceps.

The long head of the triceps is inserted into the summit of the olecranon by two
tendons, between which there is a synovial bursa. The lateral head is inserted into
a crest on the lateral surface of the olecranon by a thin tendon, under which there
is a bursa. The medial head arises from the proximal third of the medial surface
of the humerus; it is inserted into the medial surface of the olecranon by a short
tendon, under which there is a small bursa.

There are two anconei.

MUSCLES OF THE FOREARM AND MANUS

The extensor carpi radialis is a strong, fleshy muscle, the tendon of which is
inserted into the proximal end of the third metacarpal bone. It may be divided
into two parts (M. extensor carpi radialis longus, brevis).

The extensor carpi obUquus is well developed ; it arises from the distal two-thirds
of the lateral surface of the radius and ulna and ends on the second metacarpal bone.

The common digital extensor (M. extensor digitalis communis) arises on the
lateral epicondyle of the humerus and the lateral ligament of the elbow, and divides
into three parts. The tendon of the medial head ends chiefly on the third digit,
but commonly sends a small branch to the second. The tendon of the middle head
divides lower down into two branches for the third and fourth (chief) digits; above
this bifurcation it detaches a small branch to the second digit, which usually unites
with the tendon of the extensor digiti secundi. The tendon of the deep head di-
vides into two l)ranches, the medial one joining the tendon of the middle head, while
the lateral one ends on the fifth digit.

The extensor of the second digit (M. extensor digiti secundi proprius) is covered
by the preceding muscle, with which it is partially fused. It arises on the ulna.
Its delicate tendon usually unites with the tendon of the middle head of the common
extensor which goes to the second digit.

The lateral digital extensor (M. extensor digitalis lateralis) consists of two dis-
tinct parts: (1) The large dorsal muscle is the extensor digiti quarti proprius; it
has a long tendon which ends on the fourth digit, and often sends a slip to the fifth

364

THE MUSCLES OF THE PIG

digit. (2) The small volar muscle is the extensor digiti quinti proprius; it ends by
a long tendon on the lateral aspect of the fifth digit.

The supinator, when present, is a pale, thin muscular slip which arises on the

lateral border of the radius just above the interosseous space, extends medially and

downward across the dorsal surface of the bone to its medial

border, where it blends with the radial head of the deep

flexor.

The pronator teres is a delicate, fusiform muscle which
lies along the medial surface of the elbow and proximal part
of the forearm. It arises from the medial epicondyle and
collateral ligament of the elbow and is inserted by a thin
tendon to the medial border of the radius about its middle.
The flexor carpi radialis is well developed. It arises
on the medial epicondyle of the humerus, and is inserted
into the third metacarpal bone.

The flexor carpi ulnaris is narrow and has no ulnar
head. It runs obliquely down the back of the forearm in
the furrow between the superficial and deep flexors of the
digit. It arises from the medial epicondyle of the humerus
and ends on the accessory carpal bone.

The ulnaris lateralis (M. extensor carpi ulnaris) is
covered by a tendinous band, which is a thickened part
of the fascia of the forearm and extends from the lateral
epicondyle to the accessory carpal bone and lateral aspect
of the carpus. The belly of the muscle is round : its ten-
don of insertion perforates this band in the distal part of
the forearm and ends on the proximal end of the fifth
metacarpal bone.

The superficial digital flexor arises from the medial
epicondyle of the humerus and consists of two parts. The
tendon of the superficial head passes down behind the pos-
terior annular ligament of the carpus (bound down by a
special annular ligament), forms a ring at the fetlock for a
tendon of the deep flexor, and ends by two branches on the
second phalanx of the fourth digit. It receives a small
band from the accessory carpal bone. The tendon of the
deep head, after detaching a strong branch to the tendon
of the deep flexor, passes down with the latter (for which
it forms a ring), and ends on the third digit.

The deep digital flexor has three heads — humeral,
ulnar, and radial. The humeral head is very large and
forms the greater part of the contour of the volar face of
the forearm. It consists of two parts — a large superficial
part, and a much smaller deep part which arises with the
superficial flexor. Each ends at the distal part of the fore-
arm on a short tendon. These unite and receive the ten-
dons of the radial and ulnar heads and a branch from the
superficial flexor tendon. The ulnar head has a short,
thick, prismatic belly which arises from the medial surface of the proximal
part of the ulna. Its long, thin tendon passes down on the humeral head and
joins the tendon of the latter at the level of the accessory carpal bone. The
radial head is small. It arises from the upper part of the medial border of the
radius and from the deep fascia, and its tendon joins that of the humeral head at
the distal end of the forearm. The common tendon divides into four branches,

Fig. 317. — Muscles of Anti-

BRACHIUM AND MaNUS

OF Pig; Dorso- lateral

View.

a, a', Extensor carpi
radialis; b, extensor carpi
obliquus (s. abductor pollicis
longus) ; c, d, e, common dig-
ital extensor; c', c", tendons of
insertion of c; d', d", tendons
of d; e', e", tendons of e; f,
tendon of extensor digiti se-
cundi; ff, extensor digiti quarti ;
h, extensor digiti quinti; /(',
tendon of h; i, tendinous, and
k, fieshy, part of ulnaris later-
alis; k', tendon of k; I, ulnar
head of deep digital flexor; m,
superficial digital flexor; n,
brachialis. (After EUenberger,
in Leisering's Atlas.)

MUSCLES OF THE HIP AND THIGH 365

the larger central pair ending on the third phalanges of the principal digits, the
smaller abaxial pair on the accessory digits. The latter are bound down by a
peculiar spiral band. There is no subcarpal check ligament. The carpal sheath
envelops the tendon of the deep flexor and that of the deep part of the superficial
flexor. It extends from the distal third of the forearm to the distal third of the
metacarpus. At the proximal part of the metacarpus a small muscular band ex-
tends from the deep flexor tendon to the tendon of the deep part of the superficial
flexor. Another muscular bundle passes from the deep flexor tendon to the second
digit.

The liimbricales are represented by bundles which extend from the deep flexor
tendon to the tendon of the deep head of the superficial flexor.

The third and fourth interossei are present. Each sends two slips to the cor-
responding sesamoid bones and extensor tendon.

There are flexors, adductors, and abductors of the second and fifth digits.

Muscles of the Pelvic Limb
sublumbar muscles

The psoas minor is intimately united with the psoas major in front, and has a
long small tendon which ends on the psoas tubercle. It has no thoracic part.

The psoas major is large and rounded. It begins at the last rib.

The quadratus lumborum is well developed, and extends to the last three or
four thoracic vertebrae.

MUSCLES OF THE HIP AND THIGH

The tensor fasciae latae is broad, and its fleshy part reaches almost to the patella.

The gluteus superficialis has a sacral head only; it blends with the biceps
femoris.

The gluteus medius has a small lumbar part which does not extend so far
forward as in the horse. The deep part (Gluteus accessorius) is pretty clearly
marked.

The gluteus profundus is extensive, reaching nearly to the tuber coxae.

The biceps femoris has a narrow origin from the sacro-sciatic ligament and
tuber ischii. It ends below like that of the ox.

The semitendinosus has two heads like that of the horse.

The semimembranosus arises from the tuber ischii and has two insertions as
in the ox.

The sartorius has two heads of origin, between which the external iliac vessels
are situated. The medial one arises from the tendon of the psoas minor, the lat-
eral one from the iliac fascia.

The graciles are united at their origin even more than in the ox.

The pectineus is well developed and is flattened from before backward.

The adductor shows no division and is partially fused with the gracilis. It
ends on the femur just above the origin of the gastrocnemius.

The quadratus femoris is large.

The obturator extemus resembles that of the horse.

The obturator intemus is extensive and strong; its tendon emerges through
the obturator foramen.

The gemellus is fused in part ^vith the obturator intemus.

The quadriceps femoris is more clearly divided than in the horse, and its
action is transmitted by a single patellar ligament.

The capsularis is absent.

366

THE MUSCLES OF THE PIG

MUSCLES OF THE LEG AND FOOT
The peroneus tertius is a well-developed muscle which is in great part super-
ficially situated on the front of the leg. It covers the long digital extensor, with
which it is united except in the distal third of the leg. It arises from the extensor
fossa of the femur by a common tendon with that muscle,
a synovial pouch from the femoro-til)ial joint extending
down under the origin.

This sac is an inch and a half or more (ca. 3 to 4 cm.) in length
in large subjects and extends around the hiteral edge of the tendon
to its superficial face, so as to make a partial sheath and underlie
the origin of the peroneus longus also.

The muscle is continued at the distal end of the leg
by a strong tendon which passes over the flexion surface of
the hock, between the tendon of the long extensor (lateral)
and that of the tibialis anterior (medial), all three being
bound down by a strong annular ligament which extends
across from one malleolus to the other. It ends by two
or more branches on the first and second tarsal and third
metatarsal bones. Not rarely there is a thin tendon in-
serted into the fourth metatarsal bone. The tendon usu-
ally receives a small branch from that of the tibialis an-
terior at the annular ligament.

The tibialis anterior is smaller than the preceding. It
arises from the lateral surface of the tuberosity and lateral
condyle of the tibia. At the distal end of the leg the ten-
don passes under the annular ligament mentioned above
(where it detaches a small branch to the peroneus tertius),
and ends on the second tarsal and the proximal end of the
second metatarsal bone. The terminal part passes under a
superficial layer of the medial ligament of the hock, and is
provided with a bursa.

The peroneus longus descends in front of the fibula and
the lateral extensor. It arises chiefly from the lateral con-
dyle of the tibia. The tendon of insertion descends through
a groove on the lateral malleolus, crosses over the tendons
of the lateral extensor, then under the lateral ligament to
the plantar surface of the hock, to end on the first tarsal
bone. There is a bursa under the tendon where it lies in
the groove on the fourth tarsal. The muscle is a flexor of
the hock.

The long digital extensor arises in common with the
peroneus tertius, by which it is largely covered and with
which it is united to the distal third of the leg. Three ten-
dons appear at the proximal annular ligament and extend
downward and a little medially over the flexion surface of
the hock. Here they are bound down by an annular liga-
ment given off from the tendon of the peroneus tertius and attached laterally
to the distal end of the fibular tarsal bone. The tendons gradually diverge as
they descend the metatarsus. The central one divides at the distal end of the
metatarsus into two branches which end on the third phalanges of the chief
(third and fourth) digits. This tendon is joined before bifurcating by the tendon
of the extensor digitalis brevis. The medial tendon ends on the second and third
phalanges of the medial chief (third) digit. It receives a branch from the inter-

FiG. 318. — Muscles of Leg
.\ND Foot of Pig; Dorso-
L.\TER,\L View.
a. Tibialis anterior; a',
tendon of preceding; b, pero-
neus tertiu.s; b\ tendon of b;
c, long digital extensor; d, e, f,
/', /", tendons of c; g, peroneus
longus; g', tendon of g; h,
extensor digiti quarti; h',
tendon of h, which receives //'
from the interosseus medius;
i, extensor digiti quinti; k, deep
digital flexor; I, soleus; m,
gastrocnemius; n, extensor dig-
italis brevis. (After Ellenber-
ger, in Leisering's Atlas.)

MUSCLES OF THE LEG AND FOOT 367

osseus at the distal end of the first phalanx, and may detach a tendon to the second
digit. The lateral tendon is smaller. Its branches end on the third phalanges of
the accessory (second and fifth) digits and on the lateral chief (fourth digit) ; there
may be a branch to the third digit, and the branch for the fourth may go to the
corresponding branch of the central tendon. Other variations occur.

The synovial sheath for the tendons of the extensor longus and peroneus tertius at the hock
extends nearly half an inch (ca. 1 cm.) above the proximal annular ligament and an inch or more
(ca. 2 to 3 cm.) below the distal annular ligament in a large adult.

The lateral digital extensor lies on the lateral face of the leg, behind the per-
oneus longus. It arises from the lateral surface of the fibula, the lateral femoro-
tibial ligament, and the intermuscular septum between this muscle and the deep
digital flexor. It consists of two parts. The larger anterior muscle (extensor
digiti quarti) has a tendon which appears a little distal to the middle of the leg, de-
scends on the grooved lateral surface of the fibula, inclines forward, crossing under
the tendon of the peroneus longus, and ends on the extensor process of the third
phalanx of the lateral chief (fourth) digit. It receives an interosseus tendon at
the first phalanx. The tendon of the posterior muscle (extensor digiti quinti)
accompanies that of the anterior one to the tarsus and descends to the lateral ac-
cessory (fifth) digit.

The two tendons are bound down at the lateral malleolus by an annular ligament. The
anterior tendon may receive a branch of the long extensor tendon and send a tendon to the fifth
digit. The posterior tendon may send a reinforcing branch to the tendon of the long extensor for
the fifth digit. There may be a third small head which arises from the middle of the fibula and
sends a delicate tendon to join that of the posterior head.

The extensor hallucis longus is a small, fusiform muscle which is covered by the
extensor longus and peroneus longus. It arises from the proximal end of the fibula
and its delicate tendon descends at first under that of the peroneus tertius, inclines
medially at the hock, and ends on the medial accessory (second) digit.

The extensor digitalis brevis is a well-developed muscle which lies on the dor-
sal face of the distal part of the tarsus and on the chief metatarsal bones. It arises
from the neck of the tibial tarsal and the body of the fibular tarsal bone, and is
partially divided into three parts. The tendon of the superficial part joins that of
the long extensor for the chief digits. The deep part has two tendons which join
those of the long extensor for the accessory digits.

The gastrocnemius has short but wide and thick heads. The lateral one is
the larger and is united with the superficial digital flexor to the distal third of the
leg. The tendon forms a groove for the superficial flexor tendon above the hock
and is inserted chiefly into the prominences on each side of the notch of the tuber
calcis.

The soleus is thick and wide and blends with the lateral head of the gastroc-
nemius. It arises from the lateral epicondyle of the femur and the deep fascia
at the stifle. Its tendon joins that of the gastrocnemius.

The popliteus presents nothing remarkable.

The superficial digital flexor has a belly of considerable size. It arises with the
lateral head of the gastrocnemius, with which it is fused to the distal third of the
leg. The tendon is almost entirely enclosed by the twist of the gastrocnemius in
the lower part of the leg. At the tuber calcis it is thick and largely cartilaginous,
and is molded on the groove and ridges of the bone. It is attached by a strong
band to each side of the tuber calcis. A large bursa under the tendon extends up-
ward in the groove formed by the gastrocnemius almost to the muscular part and
downward to the middle of the fibular tarsal bone. The tendon divides distally
into two branches which go to the chief digits. It also detaches from its plantar
surface two bands which join the fascia of the accessory digits.

The deep digital flexor presents three distinct heads: (1) The tibialis pes-

368 THE MUSCLES OF THE DOG

terior is the smallest. It has a fusiform belly in the proximal half of the leg and
arises from the grooved plantar surface of the fibula. The tendon joins that of the
flexor hallucis at the distal end of the leg. (2) The flexor digitalis longus is much
larger and has a fusiform, pennate belly which extends obliquely across the prox-
imal two-thirds of the leg. It arises from the proximal end of the fibula, the pop-
liteal line, the middle third of the medial part of the plantar surface of the tibia, and
the intermuscular septum between this muscle and the flexor hallucis. The ten-
don (which has a synovial sheath) descends in a groove behind the medial malleolus,
bound down by an annular ligament, inclines laterally on the joint capsule, and
joins the tendon of the flexor hallucis. (3) The flexor hallucis has a large fusiform
belly which extends almost to the distal end of the leg. It arises from the greater
part of the plantar surface of the tibia, the medial surface and plantar border of
the fibula, and the interosseous membrane. The tendon descends in the tarsal
canal, receiving the tendons of the other heads, and ends like the corresponding
one of the forelimb. The tarsal synovial sheath begins at the distal end of the
muscular part and extends to the middle of the metatarsus.

The lumbricales are absent, but there are four interossei. Rudimentary
adductors of the second and fifth digits may be found.

THE MUSCLES OF THE DOG
Muscles of the Face

The cutaneus of the face is well developed. Most of it is a continuation of the
cervical cutaneus; the bundles extend forward over the lower part of the lateral
surface of the face to the angle of the mouth and the upper lip. Other bundles ex-
tend upward; some of these spread out on the cheek and lateral nasal region, and
a thin la3^er passes toward the lower eyelid, blending with the orbicularis oculi and
constituting a malaris muscle. Another stratum is attached to the scutiform carti-
lage and spreads out on the masseter.

The orbicularis oris is poorly developed. In the upper lip it is divided cen-
trally, and in the lower lip it is distinct only near the angles of the mouth.

The levator nasolabialis is wide and undivided. It has an extensive origin on
the frontal and nasal bones. The fibers run downward and forward to the lateral
wing of the nostril and the upper lip.

The levator labii superioris proprius arises behind the infraorbital foramen,
runs forward under the preceding muscle, and ends in numerous small tendons
which are in part inserted around the nostril, in part blend with those of the oppo-
site side.

The zygomaticus is narrow and very long; it arises on the scutiform cartilage,
and ends at the angle of the mouth.

The depressor labii inferioris is absent.

There are no special nasal muscles. The homologue of the lateral dilator is
triangular; it is small at its origin just ventral to the levator labii superioris pro-
prius, and ends almost entirely in the upper lip.

The buccinator is wide and very thin, and the two planes of fibers cross each
other.

The palpebral muscles present no very noteworthy special characters. Two
small muscles act on the upper eyelid. One of these, the corrugator supercilii,
arises from the fascia on the frontal bone and ends near the medial canthus. The
other arises from the zygomatic arch and ends near the lateral canthus.

MUSCLES OF THE FACE

369

Fig. 319. — Muscles op Head of Dog.
o, Scutularis; b, c, anterior auricular muscles; rf, helicis; e, antitragicus; /,/, zygomaticus, out of which a portion
is cut; g, stump of cutaneus attached to scutiform cartilage; h, parotido-auricularis; i, masseter; k, malaris; I,
levator nasolabialis; m, levator labii superioris proprius; ra, dilatator naris lateralis; o, p, buccinator (buccalis. molaris) ;
q, retractor angulioris (from cutaneus); r, occipito-mandibularis; s, mylo-hyoideus; /, base of concha; S, parotid
gland; 2', parotid duct; 3, mandibular gland; 4. mandibular lymph glands; S, buccal glands; 6, zygomatic arch;
7, maxilla; 8, dorsum nasi; 9, parotid lymph gland. (Ellenberger-Baum, Anat. d. Hundes.)

Fig. 320. — Superficial Muscles of Dog, After Removal of M. cutaneus.
Levator nasolabialis; 2, levator labii superioris proprius; 3, dilatator naris lateralis; 4, 4'i buccinator; 5,

tractor anguli oris; e, zygomaticus; 7, malaris; 5, masseter; 9, occipito-mandibularis, /O, scutularis; /i, other auric-
ular muscles; 12, parotido-auricularis; 13, mjlo-hyoideus; 14< sterno-hyoideus; IS, sterno-thyroideus; 16, spienius;
17, lumbo-dorsal fascia; 18, rectus abdominis; 19, obliquus abdominis externus; 19', aponeurosis of preceding; 20,
intercostal muscle; 21. sacro-coccygeus accessorius; 22, sacro-coccygeus dorsalis; 23, sacro-coccygeus ventralis; 24i
great trochanter; ^-5, jugular vein; a, 6, c, brachiocephalicus; d, clavicle; e, /, trapezius; a, serratus cervicis; A, omo-
transversarius; i, latissimus dorsi; k, posterior deep pectoral; I, supraspinatus; to, to', deltoid; re, infraspinatus; o,
triceps, long head; o', triceps, lateral head; p, brachialis; q, extensor carpi radialis; r, gluteus medius; s, gluteus
superficiaUs; <,«', tensor fasciae latae; u, sartorius; n, biceps femoris; i', fascia lata; t/), semitendinosus; z, semimem-
branosus; y, sartorius; z, gracilis; 26, pronator teres; 27, flexor carpi radialis; 28, flexor carpi ulnaris; 29, tibialis
anterior; 30, popliteus; 5/, 3/', deep digital flexor; 3^, superficial digital flexor; 33, gastrocnemius; 34, spine of scap-
ula; a, parotid gland, with a', its duct; fi, mandibular gland; S, mandibular lymph glands; rj, parotid lymph gland;
f, inferior buccal glands. (After EUenberger, in Leisering's Atlas.)
24

370

THE MUSCLES OF THE DOG

MUSCLES OF THE MANDIBLE
The masseter is thick and its superficial face is strongly convex. It arises
from the zygomatic arch, and extends beyond the branch of the jaw below and be-
hind. Three partly separate strata may be recognized in its structure.

The temporalis is very large and
strong, and contains much tendinous
tissue. It arises from the temporal
fossa and the orbital ligament and
ends on the coronoid process of the
mandible. It blends in part with
the masseter.

The pterygoideus lateralis is
not distinct from the medialis.

The digastricus is absent.

The occipito-mandibularis is a
strong, round, fleshy muscle, which
arises on the paramastoid process
and is inserted into the border and
medial surface of the ramus of the
mandible at the level of the last
molar teeth; it sometimes has a
tendinous intersection.

HYOID MUSCLES

The mylo-hyoideus is well de-
veloped.

The stylo-hyoideus is very slen-
der, and is inserted into the body of
the hyoid bone.

The hyoideus transversus and
omo-hyoideus are absent.

The stemo-thyro-hyoideus is
large and arises chiefly on the first
costal cartilage. It is clearly di-
vided into stemo-thyroideus and
stemo-hyoideus.

Fig. 321. — Ventral Muscles of Head, Neck, and Thorax
OF Dog.
a, Mylo-hyoideus; 6, occipito-mandibularis; c, sterno-
hyoideus; c', sterno-thyroideus ; d, sterno-cephalicus; e, brachio-
cephalicus; /, subscapularis; g, superficial pectoral; h, deep pec-
toral; i, rectus abdominis; k, obliquus abdominis externus; I,
long head of triceps; m, medial head of triceps; n, biceps
brachii; o, brachialis; 1, 1', 1", mandibular lymph glands; 2,
thyroid gland; 3, external jugular vein. (EUenberger-Baum,
Anat. d. Hundes.)

Muscles of the Thoracic Limb

The trapezius is thin, and is
divided into cervical and thoracic
portions by a narrow aponeurotic
part. Its line of origin extends from
about the middle of the dorsal bor-
der of the neck to the ninth or tenth thoracic spine, the right and left muscles
meeting (except at their posterior part) on a median fibrous raphe. It is inserted
into the entire length of the spine of the scapula.

The omo-transversarius arises by a tendon on the lower part of the spine of
the scapula (where it is often partially blended with the trapezius) , and is inserted
into the wing of the atlas.

MUSCLES OF THE THORACIC LIMB 371

The rhomboideus consists of three parts. The rhomboideus thoracalis is
small ; it arises from the fourth to the sixth or seventh thoracic spine, and is inserted
into the medial surface (chiefly) of the dorsal angle of the scapula. The rhom-
boideus cervicalis arises from the ligamentum nuchge as far forward as the second
or third cervical vertebra, and is inserted into the medial surface of the cervical
angle of the scapula. The rhomboideus capitis is a narrow band which is given off
laterally from the preceding; it is inserted into the nuchal crest.

The latissimus dorsi is extensive ; it has an attachment to the last two ribs and
also to the upper part of the spine of the scapula in addition to the origin from the
lumbo-dorsal fascia. Its lower edge blends near the shoulder with the cutaneus.

The brachiocephahcus contains in front of the shoulder a tendinous intersec-
tion and a fibrous mass in which the clavicle is embedded. Anterior to this it sepa-
rates into two diverging parts. The dorsal part is the cleido-cervicaUs, which
widens above and is attached to the median raphe of the neck and to the occipital bone.
The ventral part is the cleido-mastoideus ; it is narrow and is attached to the mas-
toid process. The common mass posterior to the clavicle and the fibrous inter-
section, which is attached to the humerus, is homologous with the clavicular part
of the deltoid of man.

The superficial pectoral muscle is small. It arises on the sternum from the
manubrium as far back as the third costal cartilage, and is inserted into the humerus
at the border between the medial and anterior surfaces. A superficial slip detached
from it is inserted into the fascia of the forearm. The deep pectoral has no scapular
part. It arises on the sternum and costal cartilages from the second costal to the
xiphoid cartilage, and from the aponeurosis of the obliquus abdominis externus.
It is inserted chiefly into the medial tuberosity of the humerus, but also Ijy small
slips into the lateral tuberosity and the fascia of the arm.

The serratus ventralis shows no clear division into cervical and thoracic parts.
It arises from the last five cervical vertebrae and the first eight ribs, and is inserted
into the upper part of the costal surface of the scapula.

The deltoid is clearly divided into scapular and acromial parts. The scapular
part is triangular and arises from almost the entire length of the spine of the scapula;
it is inserted largely into the fascia on the lateral surface of the arm. The acromial
part is short, thick, and fusiform; it arises from the lower edge of the acromion,
and ends on the deltoid tuberosity.

The supraspinatus is large ; it ends chiefly on the lateral tuberosity of the hu-
merus, but has a small attachment to the medial tuberosity also.

The infraspinatus is bipennate. The tendon of insertion passes in a groove on
the lateral tuberosity of the humerus, to end on a well-defined mark on the same; a
large bursa lies under the tendon.

The teres minor is short and fusiform ; it arises on a tubercle on the posterior
border of the scapula, just above the glenoid cavity, and is inserted into a tubercle
on the upper part of the deltoid ridge.

The subscapularis is wide and is multipennate in structure, being intersected
by fibrous septa which are attached to the rough lines on the costal surface of the
scapula. It is inserted into the medial tuberosity of the humerus.

The teres major is thick. It arises on the upper part of the posterior border
of the scapula and on the subscapularis, and is inserted into an eminence (tuber-
ositas teres) on the proximal third of the medial surface of the humerus by a com-
mon tendon with the latissimus dorsi.

The coraco-brachialis has a short and undivided belly. It arises from a small
depression on the medial surface of the tuber scapulae, and ends on the proximal
third of the humerus, just medial to the brachialis. The tendon of origin has a syno-
vial sheath.

The capsularis is absent.

372

THE MUSCLES OF THE DOG

The biceps brachii lies almost entirely on the medial surface of the humerus.
It is long and fusiform. The tendon of origin is round, and is bound down in the
intertuberal groove by an annular ligament. It is enveloped by an extension of
the synovial membrane of the shoulder joint. The tendon of insertion is bifid;

(

Teres major 1

Latissimus dorsi -.^^^^K\ ^ 'ir'/

Lot^g head of triceps _^ ^ '^

Tensor fascice antibrachii ... ||i'|,

-II r/ #/^

Medial head of triceps —MMLI^^^ / m//

Flexor carpi ulnar is -ll|'i \l \^

Flexor car pi radialis IIL-Vi \ '

Superficial digital flexor %- ^

Deep digital flexor «»,xM 1^ \\

~ Subscaj}ularis
- Supra spinatus

Coraco-brachialis
Accessory head of triceps

Biceps brachii

Humerus

Extensor carpi radialis
Pronator teres

Radius

Radial head of deep
digital flexor

[uscLEs OF Thoracic Limb of Dog; Medial View. CEllenberger-Baum, Anat. des Hundes.)

one branch is attached to a rough mark on the lateral surface of the ulna, just below
the semilunar notch; the other branch ends on a distinct mark on the postero-
medial aspect of the proximal part of the shaft of the radius, one to two inches be-
low the head.

MUSCLES OF THE THORACIC LIMB

373

The brachialis is very little curved. Its tendon of insertion passes over the
medial ligament of the elbow and under the ulnar tendon of the biceps and ends
just proximal to the latter. The tendon of the biceps forms a partial sheath for
that of the brachialis.

The tensor fasciae antibrachii is thin and narrow. It arises on the tendon and
lateral surface of the latissimus dorsi, and ends on the
olecranon and the fascia of the forearm.

The triceps has an additional deep head (Caput
accessorium), which arises just below the head of the
humerus. The medial head is very long; it arises from
a mark on the proximal fourth of the medial surface of
the humerus, just behind the insertion of the teres major
and latissimus dorsi. A bursa lies on the olecranon in
front of the common tendon of insertion.

The brachioradialis is a long, narrow, delicate mus-
cle, situated superficially on the dorsal surface of the
forearm. It arises with the extensor carpi on the crest
above the lateral epicondyle of the humerus, and is in-
serted into the distal part of the medial border of the
radius. It is often much reduced, and is sometimes ab-
sent. It rotates the forearm and paw outward.

The extensor carpi radialis arises on the lateral con-
dyloid crest and divides into two parts. The larger lat-
eral part, the extensor carpi radialis brevis, ends on the
proximal end of the third metacarpal bone. The medial
and more superficial part, the extensor carpi radialis
longus, ends on the second metacarpal bone. (A ten-
don to the fourth metacarpal ma}^ occur.)

The extensor carpi obliquus or abductor pollicis
longus arises from the lateral border and dorsal surface
of the ulna, the interosseous ligament, and the proximal
part of the lateral border of the radius. It is inserted
into the first metacarpal bone by a tendon which con-
tains a small sesamoid bone. It abducts the first digit.

There are three (or four) extensors of the digits.

1. The common digital extensor (M. extensor digi-
talis communis) arises on the lateral epicondyle of the
humerus and the lateral ligament of the elbow joint.
It has four bellies, each of which has a tendon of inser-
tion. These end on the third phalanges of the second,
third, fourth, and fifth digits.

2. The extensor of the first and second digits (M.
extensor pollicis longus et extensor indicis proprius) is
small, and is covered by the common and lateral ex-
tensors. It arises on the proximal half of the ulna. Its
tendon descends with that of the common extensor and
divides into two branches. The delicate medial branch
ends on the first digit, while the larger lateral one ends
with the tendon of the common extensor for the second
digit.

3. The lateral digital extensor (M. extensor digitalis lateralis) consists of two
muscles which are not rarely fused. They arise on the lateral epicondyle of the
humerus and the lateral ligament of the elbow joint. The larger superficial muscle
is the extensor of the third and fourth digits (M. extensor digiti tertii et quarti);

Fig. 323. — Muscles of Antibra-

CHIUM AND MaNUS OF DoG;

Lateral View.

a, Triceps brachii; 6, brachi-
alis: c, extensor carpi radialis; d,
common digital extensor; d', d",
d'", d"", tendons of preceding; e,
lateral digital extensor; e', /, ten-
dons of preceding; g, ulnarid
lateralis; h, ulnar head, h', hu-
meral head of flexor carpi ulnaris;
t, extensor carpi obliquus (s. ab-
ductor pollicis longus) ; k, inter-
ossei; I, branches from preceding
to extensor tendons; 1, olecranon;
2, radius; 3, lateral epicondyle of
humerus. (After EUenberger, in
Leisering's Atlas.)

374

THE MUSCLES OF THE DOG

its tendon divides at or near the carpus into two branches, which are inserted into
the third phalanges of the third and fourth digits, blending with the corresponding
tendons of the common extensor. The posterior muscle is the extensor of the fifth
digit (M. extensor digiti quinti) ; its tendon fuses with that of the common extensor
for the fifth digit.

The ulnaris lateralis or extensor carpi ulnaris is a large flat muscle which lies
on the lateral surface of the ulna. It arises on the lateral epicondyle of the humerus,
and is inserted into the proximal end of the fifth metacarpal and the accessory carpal
bone. It is chiefly an abductor of the paw.

The flexor carpi ulnaris consists of two quite distinct heads. The larger
humeral head arises on the medial epicondyle, while the smaller,
superficial ulnar head arises on the posterior border of the ulna.
The tendons of the two end on the accessory carpal bone and
have a bursa between them.

The flexor carpi radiaHs arises on the medial epicondyle of
the humerus and is inserted by a bifid tendon into the second
and third metacarpal bones.

The tendons of the foregoing eight muscles are provided
with synovial sheaths at the carpus.

The pronator teres is a fusiform muscle, which is situated
superficially on the proximal part of the medial border of the
radius. It arises on the medial epicondyle of the humerus, and
is inserted into the dorsal surface and medial border of the radius
almost half way to the carpus. It is related deeply to the radial
vessels, the median nerve, and the tendon of the biceps. Its
action is to flex the elbow and rotate the forearm inward (pro-
nation).

The superficial digital flexor is situated superficially on
the medio-volar surface of the forearm. It arises on the medial
epicondyle of the humerus and terminates near the carpus on a
tendon which passes dowTiward outside of the carpal canal and
receives below the carpus two reinforcing bands, one from the
accessory carpal, the other from the sesamoid bone at the medial
side of the carpus. It divides distally into four branches, which
are inserted into the second phalanges of the second, third,
fourth, and fifth digits.

The deep digital flexor has humeral, ulnar, and radial

heads; the radial head arises from the medial border of the

radius. They unite on a common tendon which passes down

through the carpal canal, gives off a branch to the first digit,

and divides into four branches. These perforate the tendons

of the superficial flexor and are inserted into the third phalanges

of the second to the fifth digits. The tendons are provided with

synovial sheaths from the middle of the metacarpus downward,

and are held in place by three digital annular ligaments.

The palmaris longus^ is a small muscle which arises from the deep digital

flexor below the middle of the forearm, and ends by two tendons which unite with

those of the superficial flexor for the third and fourth digits.

The supinator is a short, flat, fusiform muscle which arises from the front of
the lateral epicondyle of the humerus with the lateral ligament, and from the lateral
prominence of the head of the radius, and is inserted into the proximal fourth of the

1 The homology here is doubtful. Sussdorf regards the ulnar head of the deep digital flexor
as the homologue of the palmaris longus of man, while Alexais considers that the latter is repre-
sented by the superficial digital flexor.

Fig. 324. — Volar Mus-
cles OF Left Fore-
Paw OF Dog.
o, Abductor pol-
licis brevis et opponens
poUicis; b, flexor poUi-
cis brevis; c, adductor
poUicis; d, adductor
digiti secundi; e, ad-
ductor digiti quinti; /,
flexor digiti quinti
brevis; g, abductor
digiti quinti; h, in-
terossei; 1, accessory
carpal bone; S, first
digit; 3-6, sesamoids
of metacarpo-phalan-
geal joints. (Ellen-
berger-Baum, Anat. d.
Hundes.)

MUSCLES OF THE THORACIC LIMB 375

dorsal surface and the medial border of the radius. (A pouch of the capsule of the
elbow joint lies under the tendon of origin.) Its action is to rotate the forearm
outward (supination) .

The pronator quadratus consists of a thin layer of fibers which cross the volar
surface of the radius and the interosseous ligament of the forearm, except at the two
extremities of the latter. The fibers extend from the medial border of the radius
backward and outward to the interosseous border of the ulna. It rotates the fore-
arm inward (pronation).

The palmaris brevis (?) is a very small muscle, which arises on the tendon of
the superficial digital flexor at the carpus, and is inserted at the fifth metacarpo-
phalangeal joint into the sheath and annular ligament of the deep flexor.

The lumbricales are three very delicate muscles, which arise on the volar sur-
face of the tendons of the deep flexor, and are inserted into the first phalanges of the
third, fourth, and fifth digits.

The abductor poUicis brevis et opponens pollicis, a very small pale muscle,
arises on the fibrous band which connects the superficial flexor tendon with the
medial carpal sesamoid, and ends on the distal end of the first metacarpal bone and
the first phalanx of the first digit. It abducts the first digit. ^

The flexor pollicis brevis arises on the volar carpal ligament over the second
metacarpal bone, and ends on the volar sesamoid of the first digit.

The adductor pollicis, situated lateral to the preceding, is the largest of the
thumb muscles. It arises between the preceding and the second interosseous
muscle, and is inserted into the first phalanx of the first digit.

The adductor digiti secundi is situated between the second interosseous
muscle and the adductor digiti quinti. It arises on the volar carpal ligament, and
ends on the first phalanx of the second digit.

The adductor digiti quinti arises close to the preceding muscle, and passes
outward to end on the first phalanx of the fifth digit.

The flexor digiti quinti arises on the ligament connecting the accessory carpal
to the third and fourth metacarpal bones, crosses the corresponding interosseous
muscle, and ends on the fifth digit with the next muscle.

The abductor digiti quinti is larger than the two preceding muscles; it arises
on the accessory carpal bone, and ends on the lateral sesamoid of the fifth digit and
on the lateral ligament.

There are four interossei which lie on the volar surface of the metacarpus.
They are well developed and fleshy. They arise on the distal row of the carpus
and on the proximal ends of the metacarpals. Each divides distally into two
branches, which are inserted by small tendons on the corresponcfing sesamoid
bones, and detach slips to the extensortendons.

The chief facts with regard to the synovial membranes in connection with the muscles of the
forearm and manus are as follows: The tendons of the extensor carpi radiaUs frequently have a
synovial sheath at the distal part of the forearm, and there may be one or two bursse at the carpus.
The tendons of the extensor digitalis communis have a synovial sheath which extends from the distal
part of the forearm to the carpus or to the proximal part of the metacarpus. The tendons of the
extensor digitalis lateralis have in about half of the cases a synovial sheath at the distal part of the
forearm and at the carpus. The tendon of insertion of the extensor carpi obUquus has a synovial
sheath. The tendon of insertion of the ulnaris lateralis sometimes has a bursa between it and the
styloid process of the ulna. The tendon of insertion of the flexor carpi radialis has a synovial
sheath. There is a bursa between the two tendons of the flexor carpi ulnaris at their insertion;
it usually communicates with a subfascial bursa which lies on the accessory carpal bone. The
superficial digital flexor has a bursa under its origin; this communicates wath another bursa which
lies between the deep digital flexor and the flexor carpi ulnaris. The tendons of the digital flexors
for the second to the fifth digits have a common sheath for each digit which begins at the distal
part of the metacarpus. The tendon of the deep flexor for the first digit has a synovial sheath.

1 Movements of individual digits are specified with regard to the axis of the manus (paw),
and not to the median plane of the body.

376 THE MUSCLES OF THE DOG

Muscles of the Neck

The cervical cutaneus consists of two strata. One of these is composed of thin
bundles which curve across the ventral region of the neck and fade out laterally.
The other layer is thicker and rnore extensive. Its bundles begin at the dorsal
margin of the neck, are directed obliquely over the sides, and are for the most part
continued by the facial part as previously described.

The stemo-cephalicus is well developed. It arises on the manubrium sterni,
diverges from its fellow, and ends on the mastoid process, blending with the cleido-
cervicalis. It may be termed the sterno-mastoideus. It is crossed superficially
by the external jugular vein.

The scalenus ventralis (s. primse costae) arises on the last four cervical trans-
verse processes, and is inserted into the first rib.

The scalenus dorsalis (s. supracostalis) is large. It blends with the preceding
muscle in front, and divides into two parts posteriorly. The dorsal part is inserted
on the third and fourth ribs, the ventral part by a long, thin tendon on the seventh
or eighth rib.

The longus colli resembles that of the horse.

The rectus capitis ventralis major arises on the transverse processes of the
second to the sixth cervical vcrtebrse and ends as in the horse. The rectus capitis
ventralis minor and rectus capitis lateralis resemble those of the horse.

The intertransversales resemble those of the ox.

The splenius is strong and extensive. It arises on the first four or five thoracic
spines and the median raphe of the neck, and is inserted into the nuchal crest and
mastoid process.

The complexus is composed of dorsal and ventral parts — the biventer cervicis
and the complexus major. The biventer cervicis arises from the transverse proc-
esses of the fifth and sixth, and the spines of the second to the fifth (or sixth)
thoracic vertebrae, from the ligamentum nuchse, and the median raphe. It has
four oblique tendinous intersections. The complexus major arises on the trans-
verse processes of the first three or four thoracic vertebrae and the articular
processes of the last five cervical. Both end on a strong common tendon which is
inserted into the nuchal crest and the depression below it.

The longissimus capitis et atlantis consists of two unequal parts. The large
dorsal part, the longissimus capitis, arises from the transverse processes of the first
four thoracic and the articular process of the last three or four cervical vertebrae,
and ends with the splenius on the mastoid process of the temporal bone. The
small ventral part, the longissimus atlantis, arises from the articular processes of
the third, fourth, and fifth cervical vertebrae, and ends on the wing of the atlas.

The other muscles present no striking differential features, but it may be noted
that distinct interspinales are present. There are also small muscular bundles
which lie beneath the multifidus in the back. These extend from the transverse
process of one vertebra to the spine of the preceding one, and are appropriately
termed the submultifidus.

Muscles of the Thorax

There are twelve pairs of levatores costarum.

The external intercostal muscles do not occupy the spaces between the costal
cartilages.

The diaphragm is very strongly curved, and has a small tendinous center.
The hiatus oesophageus is between the crura and is ventral to the twelfth thoracic
vertebra. The costal part is attached to the lower (horizontal) part of the ninth

MUSCLES OF THE ABDOMEN

377

costal cartilage, to the tenth and eleventh cartilages a little (ca. 1 to 2 cm.) below
the junction with the rib, to the twelfth rib at its ventral end and to the last rib
below its middle. The cupola is very unsymmetrical ; on the left side it is opposite
the sixth rib, while on the right it is an intercostal space further back.

Muscles of the Back and Loins

The serratus dorsalis anterior arises from the median raphe of the neck and the
first six or seven thoracic spines, and is inserted into the second to the ninth ribs.
It is well developed. The serratus dorsalis posterior — much weaker — arises from
the lumbo-dorsal fascia, and is inserted into the last three or four ribs. Thus one
or two ribs intervene between the two.

The longissimus costarum is well developed, and extends from the ilium to the
sixth, fifth, or fourth cervical vertebra.

The longissimus dorsi resembles that of the other animals, but the spinalis et
semispinalis separates clearly from the longissimus proper at the sixth or seventh
thoracic vertebra. It is inserted into the articular and spinous processes of the
last six cervical vertebrae.

It has no depression in the ~\ ^

lumbar region for the glu-
teus medius.

The intertransversales
are fleshy, as in the ox.

The interspinales are
distinct and are most devel-
oped in the lumbar region.

Muscles of the Tail

These present the
same general arrangement
as in the horse. The sacro-
coccygei, however, arise on
the lumbar vertebrae also,
and the coccygeus on the
ischiatic spine. There is a
sacro-coccygeus accessor-
ius, which arises on the
medial border of the ilium,
the edge of the sacrum, and
the transverse processes of
the first coccygeal vertebra, and is inserted between the dorsal and lateral sacro-
coccygei. It is homologous with the intertransversales.

Fig. 325. — Muscles of Tail, Anus, and Genital Organs of Dog.
/, Ilium; ^, femur; 3, tuber ischii; 4, sacro-sciatic ligament; 5, aacral
region; 6, tail; 7, penis; 8, anus; 9, rectum; a, sacro-coccygeus dorsalis;
h, sacro-coccygeus accessorius; c, coccygeus; d, sacro-coccygeus ventralis; e,
retractor ani; /, /', sphincter ani externus; g, retractor penis; h, bulbo-
cavernosus; i, transversus perinei (?) ; k, m, ischio-urethrales; I, ischio-
cavernosus; n, tendon of obturator internus; o, gemellus, p, urethral
muscle. (After EUenberger, in Leisering's Atlas.)

Muscles of the Abdomen

The abdominal tunic is practically absent.

The obliquus abdominis externus has an extensive fleshy part. It arises from
the last eight or nine ribs and the lumbo-dorsal fascia.

The obliquus abdominis internus arises from the tuber coxae and the lumbo-
dorsal fascia. The fibers have an almost vertical direction, and there is a fleshy at-

378 THE MUSCLES OF THE DOG

tachment to the last rib. The anterior part of the aponeurosis divides into two
layers, which concur in the formation of the internal and external sheaths of the rec-
tus.

The rectus abdominis is attached by a long tendon on the first five or six costal
cartilages, and by fleshy fibers on the xiphoid cartilage. It usually has five ten-
dinous inscriptions. The two recti diverge very gradually in front, so that they are
about half an inch (ca. 1 cm.) apart in the xiphoid region.

The transversus abdominis presents no special features except that the poste-
rior part of its aponeurosis splits into two layers which include the rectus between
them.

Muscles of the Pelvic Limb

The psoas minor arises from the bodies of the last three or four thoracic and
first three or four lumbar vertebrae, and is inserted into the iliopectineal line. Its
anterior part blends with the quadratus lumborum.

The psoas major is relatively small and short; it arises from the last three or
four lumbar vertebrae.

The lateral head of the iliacus is small, while the medial head is large and fuses
with the psoas major to constitute an ilio-psoas.

The quadratus lumborum is well developed, and extends laterally beyond the
edge of the ilio-psoas. It arises from the last three or four thoracic vertebrae in
common with the psoas minor, and from the last rib and the lumbar transverse
processes, and ends on the pelvic surface of the wing of the ilium.

The tensor fasciae latae arises from the lateral border of the ilium and the
gluteus medius; it consists of two parts. The anterior part is long and rounded;
the posterior is shorter and fan-like.

The gluteus superficialis is small. It arises from the gluteal fascia, the lateral
part of the sacrum, first coccygeal vertebra, and sacro-sciatic ligament. It is in-
serted below and behind the trochanter major of the femur, on the lateral branch of
the linea aspera. In some cases there is a bursa between the tendon and the tro-
chanter major.

The gluteus medius has no lumbar portion. It is inserted into the trochanter
major by a strong tendon. There is a bursa under the tendon of insertion which
also extends under the gluteus profundus.

The gluteus profimdus is broad and fan-shaped. It arises on the superior
ischiatic spine and on the ilium as far forward as the gluteal line, and is inserted
into the trochanter major below the medius.^

The piriformis is not blended with the gluteus medius. It arises from the
border and ventral surface of the sacrum and from the sacro-sciatic ligament, and
ends on the trochanter major with or close to the gluteus medius.

The obturators, gemellus, and quadratus femoris resemble in arrangement
those of the horse, and present no notable special features. There is a large bursa
under the tendon of the obturator internus.

The biceps femoris has two heads of origin which soon fuse. The larger head
arises from the sacro-sciatic ligament and tuber ischii, the smaller one from the tuber
ischii. The aponeurosis of insertion ends on the patella, the patellar ligament,
the fascia lata, and the tibial crest. There is also a tendinous band, which comes
from the deep face of the muscle and terminates at the tarsus, as in the horse.
There is usually a bursa between the muscle and the trochanter major.

The abductor cruris posterior may be regarded as an accessory head of the
biceps femoris. It is a thin muscular band which arises from the sacro-sciatic

^ Lesbre maintains that this is the scansorius, and that the gluteus profundus is so intimately
united with the medius as to have been regarded by anatomists as part of the latter.

MUSCLES OF THE PELVIC LIMB

379

ligament, passes downward between the biceps and semimembranosus, and ends by
blending with the former.

The semitendinosus arises from the tuber ischii only. It ends on the crest and
medial surface of the tibia.

The semimembranosus is large and arises from the ischium only. It divides
into two parts : the anterior part ends on the tendon of the pectineus, on the femur
above the medial condyle, and on the medial sesamoid bone; the posterior part

Fig. 326. — Muscles of Pelvic Limb op Dog; Medial View.
a, Ilio-psoas; b, tendon of psoas minor; c, sacro-coccy-
geus ventralis lateralis; d, coccygeus; e, piriformis; /, obtur-
ator internus; g, origin of retractor ani; h, h', sartorius; i, rec-
tus femoris; k, vastus medialis; I, pectineus; m, adductor;
n, gracilis; o, semitendinosus; p, semimembranosus; q, gas-
trocnemius, medial head; q', tendon of gastrocnemius; r,
superficial digital flexor; r', tendon of r; s, tarsal tendon
of biceps femoris; t, popliteus; u, flexor hallucis longus; u',
long digital flexor; u", common tendon of u and u'; v, tendon
of tibialis posterior; w, tibialis anterior; x, tendon of long
digital extensor; 1, pelvic surface of ilium; S, section of sym-
physis pelvis; 3, tuber ischii; 4. medial condyle of femur;
5, ligamentum patellae; 6, 7, medial surface of tibia; 8, tarsus;
S', fibular tarsal bone; 9, metatarsus. (EUenberger-Baum,
Anat. d. Ilundes.)

ends on the medial condyle of the tibia, the tendon passing under the medial liga-
ment of the stifle joint.

It is not possible clearly to separate the quadriceps femoris into four heads.
The vastus lateralis is so much larger than the vastus medialis as to indicate that
the vastus intermedius is incorporated with the former. The rectus femoris has
only one tendon of origin. There is a bursa under the muscle at the distal third
of the femur. The single patellar ligament acts as the tendon of insertion of the
quadriceps.

380 THE MUSCLES OF THE DOG

The capsularis is usually present, but is small and pale.

The sartorius consists of two parts. The anterior part arises from the tuber
coxee and its flat tendon ends on the patella. The posterior part arises from the
lateral border of the ilium and ends on the medial surface of the tibia, its tendon
blending with that of the gracilis. The anterior part is superficial in front of the
tensor fascise latse and forms here the anterior contour of the thigh.

The graciles are not so much fused at their origin as in the other animals.
Its anterior part is thin. Its broad tendon is inserted into the tibial crest, and
blends ^\ath those of the sartorius and semitendinosus.

The pectineus is long and slender. It arises from the ilio-pectineal eminence
and ends on the medial branch of the linea aspera above the distal end of the femur.

The adductor femoris is a large muscle which arises on the ventral surface of
the pubis and ischium; it ends on the linea aspera of the femur and the medial
surface of the stifle. It is commonly separable into two parts.

The peroneus tertius is represented by a tendinous band which arises on the
medial surface of the tibia below the crest. It passes on the medial surface of the
tibialis anterior, blends with the annular ligament above the tarsus, and is attached
to the joint capsule and the proximal end of the third metatarsal bone.

Arloing and Lesbre say: "The third peroneus is a proper extensor of the fifth digit; it
is a very feeble, fleshy band, situated behind the peroneus bre^^s, which it partially covers. It
is attached to the upper part of the fibula, and is continued by a long, delicate tendon which
passes in the same malleolar groove with the muscle mentioned; it then crosses behind the tendon
of the peroneus longus and extends to the phalanges of the outer digit, where it joins one of the
branches of the common extensor."

The tibialis anterior is large and superficial. It arises on the lateral condyle
and crest of the tibia, and is inserted into the first metatarsal bone, or into the
first tarsal and second metatarsal.

There are four extensors of the digits.

1. The long digital extensor (M. extensor digitalis longus) is fusiform, and lies
largely under the preceding muscle. It arises from the extensor fossa of the femur.
The tendon is bound do"\vn by two annular ligaments: the proximal one, at the
distal end of the tibia, encloses also the tendon of the tibialis anterior; the distal
one is at the lower part of the tarsus. The tendon divides at the tarsus into
four branches, which end on the distal phalanges of the digits (second to fifth).

2. The lateral digital extensor {M. extensor digitalis pedis lateralis s. digiti
quinti) has a small, unipennate belly which is covered by the peroneus longus
and the deep digital flexor. It arises on the fibula below the head. The tendon
descends behind that of the peroneus longus, inclines forward under the lateral
ligament of the tarsus and the peroneus tendon, and joins the branch of the
tendon of the long extensor for the fifth digit.

3. The extensor hallucis longus is a very thin muscle which arises from the
fibula under the long extensor. Its delicate tendon accompanies that of the tibialis
anterior to the first metatarsal bone, or becomes lost in the fascia.

4. The extensor digitalis brevis has three divisions. It arises on the fibular
tarsal bone and the adjacent ligaments. The three tendons are inserted into
the second, third, and fourth digits, blending with the interossei. (Sometimes
there is a tendon for the rudimentary first digit, which may represent the extensor
hallucis brevis. There may be a fourth belly for the tendon to the second digit.)

The peroneus longus arises on the lateral condyle of the tibia, the head of
the fibula, and the lateral ligament. The belly does not extend to the middle of
the leg, and the long tendon passes down the leg parallel to the fibula. It is bound
down in the groove of the lateral malleolus by an annular ligament, crosses the
plantar surface of the tarsus transversely, and ends on the first metatarsal bone.

The peroneus brevis is unipennate and arises from the distal half or more

MUSCLES OF THE PELVIC LIMB

381

of the lateral face of the tibia and the fibula. Its tendon accompanies that of
the lateral extensor over the lateral malleolus, and ends on the proximal end of the
fifth metatarsal bone.

The soleus is absent. (It is present and large in the cat.)

The gastrocnemius arises from the rough lines above the condyles of the
femur. The origin of each head contains a sesamoid
bone about the size of a pea (Os sesamoideum m. gas-
trocnemii), which articulates with the corresponding
condyle of the femur. The tendon comports itself as
in the horse.

The superficial digital flexor has a large round
belly. It arises in common with the lateral head of
the gastrocnemius from the lateral rough line and sesa-
moid bone, and from the aponeurosis of the vastus
lateralis. The tendon winds around that of the gas-
trocnemius, passes over the tuber calcis (where it is
arranged as in the horse) , and divides below the tarsus
into two branches. Each of these divides into two
branches which end as in the forelimb. The lateral
and medial branches detach slips to the suspensory
ligaments of the large digital pad. Muscle-fibers
often occur in the tendon in the metatarsal region.

The deep digital flexor has two heads. The large
lateral head, the flexor hallucis longus, arises from the
posterior surface of the tibia and fibula, filling the in-
terosseous space. The small medial head, flexor digi-
talis pedis longus, also arises from the tibia and fibula;
its tendon passes through the groove on the medial
malleolus, inclines backward in its descent over the
tarsus, and joins that of the large head below the
tarsus. The common tendon detaches a branch to
the large digital pad and terminates as in the forelimb.

The tibialis posterior is a very small but distinct
muscle, which arises on the proximal part of the fibula.
The deUcate tendon accompanies that of the flexor
longus and ends on the medial ligament of the tarsus.

The tendon of origin of the popliteus contains a
small sesamoid bone.

The adductors of the second and fifth digits, the
lumbricales, and the interossei are arranged as in the
thoracic limb.

The quadratus plantae arises on the lateral surface
of the distal end of the fibular tarsal bone and on the
lateral tarsal ligament, passes downward and inward,
and terminates on a thin tendon which fuses with that
of the deep flexor.

The abductor digiti quinti is a very small muscle
which consists of two parts. One of these is a tendin-
ous slip which extends from the plantar surface of the
proximal part of the fibular tarsal bone to the head of
the fifth metatarsal bone; the other part arises from

the medial surface of the fibular tarsal bone (or from the tendinous part) and ends
on the first phalanx of the fifth digit.

In case the skeleton of the first digit is well developed, there are three muscles

Fig. 327. — Muscles op Leg and
Foot of Dog; Lateral View.
a. Quadriceps femoris; b, gas-
trocnemius, lateral head; c, super-
ficial digital flexor; d, deep digital
flexor; e, peroneus longus; /, ten-
don of lateral extensor; g, peroneus
brevis; h, long digital extensor; h',
h", h'", tendons of preceding; i,
tibialis anterior; k, extensor brevis;
I, slips from interossei (m); 1, lateral
condyle of femur; 2, patella; 3,
tibia; 4, tuber calcis; 5, 6, annular
ligaments. (After Ellenberger, in
Leisering's Atlas.)

382 THE MUSCLES OF THE DOG

which are homologous with those of the same digit in the forehmb. These are
the abductor hallucis, adductor hallucis, and flexor hallucis brevis.

The principal bursse and synovial sheaths of the muscles of the leg and foot are as follows:
The tibialis anterior has a bursa under its tendon at the tarsus. A pouch of the synovaal membrane
of the stifle joint underlies the tendon of origin of the extensor digitalis longus, and is partially
reflected upon the superficial face of the tendon; the tendons of insertion are provided with a
sjTiovial sheath wliich begins at the end of the muscular part and extends to the proximal part of
the metatarsus. The tendons of the lateral digital extensor and peroneus bre\ns have a common
syno\'ial sheath at the distal end of the leg and proximal part of the tarsus. The tendon of the
peroneus longus has a syno^'ial sheath wliich begins an inch or more above the lateral malleolus
(in a good-sized dog) and extends about to the middle of the tarsus; another sheath envelops the
tendon to the point where it bends round to the plantar surface of the hock; a bursa lies between
the tendon and the joint capsule and fourth tarsal bone, and communicates with the joint ca^'ity.
A bursa underlies the terminal part of the tendon of the peroneus brev-is. There is a bursa in
front of the distal part of the tendon of the gastrocnemius; it extends an inch or more (in large
dogs) above the tuber calcis. A bursa underUes the superficial flexor tendon at the tarsus; in large
dogs it extends about an inch above and below the tuber calcis. The tendon of the tibialis posterior
has a synovial sheath at the distal end of the leg. The tendon of the flexor digitalis longus has a
synovial sheath which begins a httlc above the medial malleolus and extends to the junction -with
the tendon of the flexor hallucis. The tarsal sheath of the flexor hallucis begins (in large dogs)
about an inch and a half above the level of the medial malleolus and extends to the distal end of
the tarsus; it communicates wth the tibio-tarsal joint cavity. The synovial apparatus in the
distal part of the hmb resembles that of the forelimb.

SPLANCHNOLOGY

This branch deals with the viscera of the digestive, respiratory, and uro-
genital systems.^ Each of these systems consists fundamentally of a tube or tract
which is lined with mucous membrane (Tunica mucosa) and communicates with
the exterior at one end or both. Thus the epithelium of the mucous membranes
is continuous with the epidermis at the various natural openings. In addition to
this fundamental part there are to be considered aggregations of secreting cells
known as glands, muscular tissue, fibrous membranes, serous membranes, vessels
and nerves.

Mucous Membranes. — These vary much in thickness, color, and other char-
acters. In many places they form folds (Plicae mucosae) which may be temporary
or permanent. In other places they form ridges (Rugse). With certain excep-
tions they are moistened by a viscid secretion, termed mucus, which is derived
from glands or goblet cells of the epithelium. The membrane consists of two dis-
tinct parts : the epithelium, which forms the free surface and is protective and secre-
tory; and the lamina propria, a layer of connective tissue which contains and sup-
ports the peripheral ramifications of the vessels and nerves. The mucous mem-
brane is connected with surrounding structures by areolar submucous tissue
(Tela submucosa). In many places there is a layer of unstriped muscle, the mus-
cularis mucosae, in the deepest part of the mucous membrane. In many situa-
tions the tunica propria presents numerous elevations, known as papillae. When
small (microscopic), the papillae do not modify the surface of the mucous membrane,
since the epithelium levels up the depressions between them, but when large (ma-
croscopic), they are conspicuous surface features, and are named according to their
shape as conical, foliate, etc.

Glands. — The term gland (Glandula) is usually understood to mean an aggre-
gation of epithelial cells, the secretion of which is extruded on the free surface of the
membrane, or is conveyed away in the blood or lymph stream.^ Glands are divided
according to their form into two chief classes, tubular and alveolar, each of which
may be simple or compound ; many, however, combine the characters of both tj'pes
and are termed tubulo-alveolar or alveolo-tubular. A simple tubular gland is a cylin-
drical depression lined by epithelium which is continuous with that of the surround-
ing mucous membrane, from which it developed originally as an outgrowth. The
deeper part of such a gland is termed the ftmdus, and here the epithelium is differ-
entiated and has taken on secretory function. The more superficial part which
conveys the secretion to the surface is called the duct; in it the epithelium resembles
more or less closely that of the surrounding surface. Many glands are microscopic,
while others are large organs. The larger ones are composed of subdivisions known
as lobules (Lobuli), which are held together by areolar interlobular tissue; each
lobule has its duct and by the union of these ducts there is formed an excretory
duct (Ductus excretorius), through which the secretion is conveyed. Some glands

1 The term viscus is applied in general to the organs which are contained in the body cavities.
It is usual to exclude the heart, except when considering the thoracic organs topographically.
Certain other organs which do not belong to these systems are usually considered with them as a
matter of convenience.

2 But unicellular glands are recognized in lower forms, and in higher forms the goblet-cells
of many mucous membranes have the same function. Other organs which are not epithelial in
structure are commonly classed as glands; such, for example, are the lymph glands and nodules,
the thymus, and the spleen. They are usually termed ductless or vascular glands, and are des-
cribed with the organs with which they are associated anatomically.

383

384 SPLANCHNOLOGY

consist of divisions of a larger order which are known as lobes (Lobi) ; these may be
separated by layers of connective tissue (Septa interlobares) or by fissures (In-
cisurse interlobares).

There is no correspondence between the size of a gland and the number of its excretory ducts.
Thus the largest gland in the body, the liver, has a single excretory duct, while some small glands
have many.

Muscular Tissue.— Most of the hollow organs are provided with a muscular
coat (Tunica muscularis) outside of the mucous membrane. This is in great part
composed of strata of unstriped muscle, but in certain places — and especially in the
vicinity of the natural apertures- — it consists of striped muscle. Some of the solid
organs contain muscular tissue in their capsule or stroma.

Fibrous Membranes. — Many viscera are enclosed by a fibrous coat (Tunica
fibrosa). In the case of glands such an enveloping membrane is usually called the
capsule. Other membranes of a like character are known as a tunica albuginea
or timica adventitia; the former consist mainly of dense white fibrous tissue, while
the latter usually contain many elastic fibers and are looser in texture.

Serous Membranes. — These are thin membranes which line the body-cavities
and cover more or less the external surface of the viscera contained therein.^ They
include the peritoneum in the abdomen, and the pleura and the deep layer of the
pericardium in the thorax. Their free surface is formed by a mesothelium of
flat cells; it is smooth and glistening and is moistened by a film of serum, thus re-
ducing friction to a minimum. The external surface is in most places connected
with the structure covered by areolar subserous tissue (Tela subserosa) which
often contains fat. The part which lines the wall of a cavity is termed the parietal
layer (Lamina parietalis), while the visceral layer (Lamina visceralis) is that which
forms the serous coat (Tunica serosa) of the viscera. Double layers which connect
viscera with the wall or with each other are in general called serous folds (Phcse
serosae) or serous ligaments (Ligamenta serosa) , but many special terms are in use
and will be referred to later.

1 The serous membranes form closed sacs, except in the female, in which case the uterine
tubes open into the peritoneal cavity and also communicate indirectly with the exterior.

THE DIGESTIVE SYSTEM

This apparatus (Apparatus digestorius) consists of the organs directly con-
cerned in the reception and digestion of the food, its passage through the body,
and the expulsion of the unabsorbed portion. These organs are conveniently
grouped under two heads, viz.: (1) the alimentary canal; (2) the accessory organs.

The alimentary canal (Tractus alimentarius) is a tube which extends from the
lips to the anus. It has a complete lining of mucous membrane, external to which
is an almost continuous muscular coat. The abdominal portion of the tube is
largely covered with a serous membrane — the visceral peritoneum. The canal
consists of the following consecutive segments: (1) The mouth; (2) the pharynx;
(3) the oesophagus; (4) the stomach; (5) the small intestine; (6) the large intestine.

The accessory organs are the teeth, tongue, salivary glands, liver, and pancreas.

DIGESTIVE SYSTEM OF THE HORSE

THE MOUTH

The mouth^ (Cavum oris) is the first part of the alimentary canal. It is
bounded laterally by the cheeks; dorsally, by the palate; ventrally, by the body of
the mandible and the mylo-hyoid muscles; behind, by the soft palate. In the
horse it is a long, cylindrical cavity, and when closed, it is almost entirely filled up
by the contained structures; a small space remains between the root of the tongue,
the soft palate, and the epiglottis; this may be termed the glosso-epiglottic space.
The entrance to the mouth (Rima oris) is closed by the Hps.

The cavity of the mouth is subdivided into two parts by the teeth and alveolar
processes. The space external to these and inclosed by the lips and cheeks is
termed the vestibule of the mouth (Vestibulum oris). In the resting state of the
parts the walls of this cavity are in contact, and the space is practically obliterated.
Its existence becomes very evident in facial paralysis, when the food tends to collect
in it laterally, pouching out the cheeks. The space within the teeth and alveolar
processes is termed the mouth cavity proper (Cavum oris proprium). When the
teeth are in contact, it communicates with the vestibule only by the interdental
spaces and the intervals behind the last molar teeth. Posteriorly it communicates
with the pharynx through the isthmus faucium.

The mucous membrane of the mouth (Tunica mucosa oris) is continuous at
the margin of the lips with the common integument, and behind with the mucous
lining of the pharynx. During life it is chiefly of a pink color, but may be more
or less pigmented.

The lips (Labia oris) are two musculo-membranous folds which surround the
orifice of the mouth. Their angles of union (Anguli oris s. commissurse labiorum)
are situated near the first cheek tooth and are rounded. Each lip presents two
surfaces and two borders. The external surface is covered by the skin, which pre-
sents long tactile hairs in addition to the ordinary fine hair. The upper lip has
a shallow median furrow (Philtrum), the lower a rounded prominence, the chin

^ The term "mouth" is commonly used to signify either the cavity (Cavum oris) or the
entrance to it (Rima oris).

25 385

386

DIGESTIVE SYSTEM OF THE HORSE

THE MOUTH 387

(Mentum). The internal surface is covered with mucous membrane which is com-
monly more or less pigmented. The small papilla? on the surface show on their
summits the openings of the ducts of the labial glands. Small folds of mucous
membrane which pass from the lip to the gum form the fraenula labii (superioris,
inferioris). The free border of the hp is dense and bears short, very stiff hairs.
The attached border is continuous with the surrounding structures.

Structure. — The hps are covered externally by the skin, and are lined by
mucous membrane; between these are muscular tissue, glands, vessels, and nerves.
The skin lies directly on the muscles, many fibers of which are inserted into it. The
muscles have been described (p. 255). The labial glands (Glandula? labiales)
form a compact mass at the commissures; they are numerous in the upper lip,
fewer in the lower. The mucous membrane is often pigmented, and is reflected
upon the bones of the jaws to form the gums.

Vessels and Nerves. — The arteries are derived from the superior and inferior
labial and palato-labial arteries. The veins go chiefly to the external maxillary
vein. The Ij^mph vessels go to the mandibular lymph glands. The sensory
nerves come from the trigeminus, and the motor nerves from the facial nerve.

The cheeks (Bucca) form the sides of the mouth, and are continuous in front
with the lips. They are attached to the alveolar borders of the bones of the jaws.

Structure. — This comprises: (1) The skin; (2) the muscular and glandular
layer; (3) the mucous membrane. The skin offers nothing in particular to notice.
The muscular tissue is formed mainly by the buccinator, but also by parts of the
cutaneus, zygomaticus, dilatator naris lateralis, levator nasolabialis, and depressor
labii inferioris. The buccal glands (Glandulse buccales) are arranged in two rows.
The superior buccal glands lie on the outer surface of the buccinator muscle, near
its upper border. The anterior part of the row consists of scattered lobules; the
posterior part, which lies under cover of the masseter muscle, is more developed and
compact. The inferior buccal glands, less voluminous than the upper, are situated
in the submucous tissue at the lower border of the buccinator muscle. The mucous
membrane is reflected above and below upon the gums, and is continuous })ehind
wdth that of the soft palate. It is reddish in color and frequently shows pigmented
areas. The parotid duct opens opposite the third upper cheek tooth on a papilla
(Papilla salivalis). Linear series of small papillae above and below indicate the
orifices of the small ducts of the buccal glands.

Vessels and Nerves. — The blood-supply is derived from the facial and bucci-
nator arteries, and the blood is carried away by veins of the same name. The lymph
vessels go to the mandibular lymph glands. The sensory nerves come from the
trigeminus and the motor nerves from the facial nerve.

The gums (Gingivae) are composed of a dense fibrous tissue which is intimately
united with the periosteum of the alveolar processes, and blends at the edges of
the alveoU with the alveolar periosteum; the latter fixes the teeth in their cavities.
They are covered by a smooth mucous membrane, destitute of glands, and of a
low degree of sensibility.

The hard palate (Palatum durum) is bounded in front and on the. sides by
the alveolar arches, and is continuous with the soft palate behind. Its osseous
basis is formed by the premaxilla, maxilla, and palatine bones. The mucous mem-
brane is smooth, and is attached to the bones by a submucosa which contains in
its anterior part an exceedingly rich venous plexus, constituting an erectile tissue.
A central raphe (Raphe palati) divides the surface into two equal portions. Each
of these presents about eighteen transverse curved ridges (Rugae palatini) which
have their concavity and their free edges directed backward. They are further
apart and more prominent anteriorly. The central prominence just behind the
first pair of incisors is the papilla incisiva ; it is margined by a fissure on each side.
There are no glands in the submucosa. The ductus incisivus (s. ductus nasopa-

DIGESTIVE SYSTEM OF THE HORSE

latinus) is a small tube of mucous membrane which extends very obliquely through
the palatine fissure. Its ventral or palatine end is blind and lies in the submucous
tissue of the palate. The dorsal or nasal end communicates with the nasal cavity
(in common with the vomero-nasal organ) by a slit-like opening in the anterior
part of the ventral nasal meatus.

Vessels and Nerves. — The blood-supply is derived chiefly from the palatine

arteries and the veins go to the vena re-
flexa. The nerves come from the tri-
geminus.

The soft palate (Palatum molle)
is a musculo-membranous curtain
which separates the cavity of the
mouth from that of the pharynx, except
during swallowing. It slopes down-
ward and backward from its junction
with the hard palate. The oral surface
faces ventrally and somewhat forward,
and is covered with a mucous mem-
brane continuous with that of the hard
palate. It presents a rounded, median
ridge, flanked usually by a sagittal fold
on either side. Numerous small ducts
of the palatine glands open on this sur-
face. On each side a short, thick fold
passes to the lateral border of the
tongue; this is the anterior pillar of
the soft palate (Arcus glossopalatinus).
The pharjmgeal surface faces dorsally
and a little backward and is covered by
a mucous membrane continuous with
that of the nasal cavity. The free bor-
der (Arcus palatinus) is concave and
thin ; it is in contact (except during deg-
lutition) with the epiglottis. It is con-
tinued by a fold of the mucous mem-
brane, which passes on each side along
the lower part of the lateral wall of the
pharynx and unites with the opposite
fold over the beginning of the oesopha-
gus; this fold is termed the posterior
pillar of the soft palate (Arcus pharyn-
gopalatinus). The space between the
diverging anterior and posterior pillars
(Sinus tonsillaris) is occupied by the
tonsil (Tonsilla palatina) . In the horse,
however, there is not a compact tonsil,
as in man, dog, etc., but a series of
masses of lymphoid tissue and mucous
glands which extend backward from
the root of the tongue on either side a distance of about four inches (ca. 10 cm.).
These cause elevations of the surface, on which there are depressions (crypts) in
which the gland ducts open. The soft palate is greatly developed in equidse, its
average length, measured medially, being about six inches (15 cm.). Its length and
contact with the epiglottis may account for the fact that in these animals mouth-

FiG. 329. — Hard Palate and Adjacent Part of Soft
Palate of Horse,
1, Raph6 of palate; 2, ridges of palate; 3, soft palate;
I. 1, I. 2, first and second incisor; Di. 3, deciduous third
incisor; P. 1-4, premolars; M. 1-3, molars.

THE MOUTH

389

breathing does not occur under normal conditions, and that in vomiting the ejected
matter escapes usually through the nasal cavity.^

Structure.— The soft palate consists of: (1) The oral mucous membrane,
continuous with that of the hard palate, which it resembles; it covers also a narrow
marginal area of the pharyngeal surface along the free border; (2) the palatine
glands (Glandular palatini), which form a layer about half an inch in thickness;
(3) the aponeurotic and muscular layer; (4) the pharjmgeal mucous membrane,
continuous with that of the nasal cavity, which it resembles.

Septum nasi Dorsal meatus

Naso-lacrimal duct

Infraorbital m rrc
and v( .ss( Is

Levator labii siipcri-
oris proprtus

Superior buccal
nerve
Facial artery

Superior bucc(d
glands

Parotid duct

Labial n
Inferior labial ai

Mylo-hyoidc

Dorsal turbinate
Common meatus

Middle meatus

]'r)itral lurbimite

Veidral meatus

T — i\[(Lrillary sinus
J {anterior end)

Palatine artery
Facial artery

Buccal mucous
membrane

Buccinator

Hypoglossal
nerve
Lingual artery

Buccinator nerve
Branches of lingual nerve

Mandibular duct
Sublingual gland

Digastricus Sublingual artery

Fig. 330. — Cross-section of He.\d op Horse .\t Anterior End of Facial Crest.

1, Cavity of dorsal turbinate; ^, cavity of ventral turbinate; 3, cavum oris; 4^ 4. genio-glos.si; o, -5, genio-hyoidei; 6,

hyo-glossus; 7, upper, 7', lower, fourth cheek tooth. Line to facial artery crosses zygomaticus.

The muscles proper to the soft palate are the palatinus, the levator palati,
and the tensor palati.

The palatinus (M. palatinus) consists of two small muscular bundles which
lie together at the median line. It is attached through the medium of the palatine
aponeurosis to the palatine bones, and terminates near the free edge of the soft
palate. Usually a bundle from it is continued a short distance into the posterior
pillar. Its action is to shorten the soft palate.

The levator palati (M. levator veli palatini) arises from the muscular process

1 The epiglottis may be either in fi-ont of or behind the soft palate; most often it is in front
(prevelar), as shown in Fig. 349.

390 DIGESTIVE SYSTEM OF THE HORSE

of the petrous temporal bone and from the lateral lamina of the Eustachian tube,
and passes at first forward, lateral to the latter; it then inclines ventral ly across
the deep face of the anterior pharjiigeal muscles and turns medially into the soft
palate, in which it spreads out above the glandular layer. It raises the soft palate,
thus closing the posterior nares during deglutition.

The tensor palati (M. tensor veli palatini) is larger than the levator, and is
fusiform and flattened. It arises from the muscular process of the petrous tem-
poral bone, the pterygoid bone, and the lateral lamina of the Eustachian tube,
and passes forward, lateral to the levator, across the medial surface of the origin of
the pterygoideus medialis. Its tendon is then reflected around the hamulus of the
pterygoid bone, where it is held in position by a fibrous band and lubricated by a
bursa, turns inward and expands in the aponeurosis of the soft palate. It tenses
the soft palate.

Vessels and Nerves. — The blood-supply of the soft palate is derived from the
internal and external maxillary arteries and the blood is carried away by the corres-
ponding veins. The lymph vessels go to the pharyngeal lymph glands. The nerves
come from the trigeminus, vagus, and glosso-pharyngeal nerves.

The floor of the mouth in its anterior part is free and is formed by the body of
the mandible, covered by mucous membrane. The remainder is occupied by the
attached portion of the tongue in the undisturbed state of the parts. The follow-
ing features are exposed by raising the tongue and drawing it to one side. About
opposite the canine tooth on each side is a papilla, the canmcula sublingualis,
through which the duct of the mandibular gland opens. Just behind these papillae
is a median fold of mucous membrane which passes to the ventral surface of the
tongue, constituting the frenum linguae. On either side is the sublingual fold
(Plica sublingualis) which extends from the frenum to the level of the fourth cheek
tooth. The fold indicates the position of the underlying sublingual gland, and
presents numerous small papillae, through which the ducts open. Behind the last
tooth a vertical fold of the mucous membrane passes from upper to lower jaw. This
is termed the plica pterygomandibularis ; it contains a ligament of like name.

The isthmus faucium is the orifice of communication between the mouth and
the pharynx. It is bounded above by the soft palate, below by the root of the
tongue, and laterally by the anterior pillars of the soft palate. It is relatively
small and not very dilatable in the horse, and is closed by the soft palate under
normal conditions, except during deglutition.

THE TONGUE

The tongue (Lingua) is situated on the floor of the mouth, between the rami of
the mandible, and is supported mainly in a sort of sling formed by the mylo-hyoid
muscles. Its posterior part, the root (Radix linguae), is attached to the hyoid bone,
soft palate, and pharynx. Only the upper surface of this part is free, and slopes
downward and backward. The middle part, the body (Corpus linguae), has three
free surfaces. The dorsal surface is slightly rounded. The lateral surfaces are
nearly flat for the most part, but anteriorly become rounded and narrower. The
ventral surface is attached to the mandible. The apex or tip (Apex linguae) is
free, spatula-shaped, and presents upper and lower surfaces and a rounded border.
The term dorsum linguae is applied to the dorsal surface; it is free throughout,
and in the resting state of the parts is in contact with the palate except at the glosso-
epiglottic space.

Structure. — The tongue consists of: (1) The mucous membrane; (2) the
glands; (3) the muscles; (4) vessels and nerves.

The mucous membrane (Tunica mucosa linguae) adheres intimately to the
subjacent tissue, except on the lower part of the lateral surfaces of the body and

THE TONGUE

391

Thyroid
gland

the ventral surface of the tip. It varies considerably in thickness. On the dorsum
it is very thick and dense ; underneath this part there is a dense fibrous cord, which
extends medially a distance of five or six inches forward from the vallate papillae.
On the sides and ventral surface of the tongue the membrane is much thinner and
smooth, and can more readily be dissected off the muscular tissue. ^ From the
lower surface of the free part of the tongue a fold of the mucous membrane passes
to the floor of the mouth, forming the frenum linguae. Posteriorly a fold passes
on each side from the edge of the dor-
sum to join the soft palate, forming the
anterior pillars of the latter. A thick
central glosso-epiglottic fold (Plica
glossoepiglottica) passes from the root
to the base of the epiglottis; this en-
closes the hyoepiglottic muscle. The
mucous membrane presents numerous
papillae, which are of four kinds — fiH-
form, fungiform, vallate, and foliate.
The filiform papillae (Papillae filiformes)
are fine, thread-like projections which
stud the dorsum and the sides of the
tip; they are absent on the root. On
the anterior part they are so small as
to be scarcely visible, but on the pos-
terior part they are much larger and
give the surface a distinct pile. The
f imgif orm papillae (Papillae f ungif ormes)
are larger and easily seen; they are
rounded at the free end, which is sup-
ported by a neck. They occur princi-
pally on the lateral part of the tongue,
but are also found scattered over the
dorsum. The vallate papillae (Papillae
vallatae) are usually two or three in
number. The two constant ones are a
quarter of an inch or more (ca. 6 to 7
mm.) in diameter, and are found on
the posterior part of the dorsum, one
on each side of the median plane, about
an inch (ca. 3 cm.) apart. The third,
when present, is behind these, is cen-
trally situated, and is always smaller.
Rarely a fourth may be found. They
are rounded, broader at their exposed
than at their attached surfaces, and are
sunk in a depression which is bounded
by an annular wall. Their free surface

is tuberculate, i. e., bears small, round secondary papillae. The foliate papillae
(Papillae foliatae) are situated just in front of the anterior pillars of the soft palate,
where they form a rounded eminence about an inch (ca. 2 to 3 cm.) in length,
marked by transverse fissures. The last three varieties are covered with micro-
scopic secondary papillae and are furnished with taste-buds. The mucous mem-
brane of the root of the tongue presents numerous folds and rounded elevations.

1 The mucous membrane is thick and closely adherent where food naturally comes in contact
with the tongue.

Trachea

Crico-arytenoid-

eus dorsalis

muscle

A rytenoideus

muscle
Arytenoid carti-
lages

Vocal cord

Adit us laryngis
Epiglottis

Tonsil

Radix lingucE

Anterior pillar of
soft palate (cut)

Dorsum linguae

Apex linguae

ToNGTJE, Larynx, and Part of Trachea of
Horse; Dorsal View.

392

DIGESTIVE SYSTEM OF THE HORSE

The latter are marked by crypts and consist essentially of a mass of Ij^mphoid
tissue; they are knowTi as lingual follicles (Folliculi linguales), and taken together
form what is sometimes called the lingual tonsil. The lingual glands (Glandulse
linguales) constitute a thick layer in the loose submucous tissue and also lie l^etween
the muscle bundles. Mucous glands are found also in part of the dorsum and sides
of the tongue.

The lingual muscles (Mm. linguae) may be divided into intrinsic and extrinsic.
The intrinsic musculature consists, not of distinct muscles, but rather of systems
of fibers which run longitudinally, vertically, and transversely, blending with the
extrinsic muscles, which are now to be described.^

'■^- ""^ Kendo-hyoidcus Hyo-pharyngeus

Genio-glossus Thyroid Trachea

Depressor labii ^^^'^'^

inferioris

Fig. 332. — Muscles or Tongue, Hyoid Bone, Pharynx, etc., of Horse.
T. p., Tensor palati; L. p., levator palati; Pt. p., pterygo-pharyngeus; P. p., palato-pharyngeus; S. p., stylo-
pharyngeus; Th. p., thyro-pharyngeus; C. p., crico-pharyngeus ; Th. h., thyro-hyoideus; Hyo. gl., hyo-glossus; G. p.,
guttural pouch; F. p., foliate papilla; A. v., facial artery and vein. Most of the left ramus of the mandible is removed.
The concealed parts of the hyoid bone are indicated by dotted lines.

1. Stylo-glossus. — This is a long, thin muscle, which lies along the lateral part
of the tongue. It arises by a thin tendon from the lateral surface of the great
cornu of the hyoid bone, near the articulation with the small cornu. It terminates
near the tip of the tongue by blending with its fellow of the opposite side and with
the intrinsic musculature. The action is to retract the tongue. Unilateral con-
traction would also draw the tongue toward the side of the muscle acting.

A small muscular band sometimes arises on the thyroid cornu of the hyoid bone and ends
on the tendon of origin of the stylo-glossu3. In some cases a similar band arises higher up, with
and on the hyo-glossus.

2. Hyo-glossus. — This is a wide, flat muscle, somewhat thicker than the pre-

1 This distinction is more or less conventional. It is evident that much of what may appear
on cross-sections of the tongue to be intrinsic muscle is in reality a part of the extrinsic musculature.
The arrangement is further complicated by the existence of bundles running in various directions,
intercrossing of bundles, and the breaking up of the systems by masses of fat.

THE TONGUE

393

ceding. It lies in the lateral part of the root and body of the tongue, partly under
cover of the preceding muscle. Its deep face is related to the genio-glossus. It

\ Thyroid
gland
Crico-thyroid
joint

Foramen for anterior
laryngeal nerve

Cenio-hyoideus (right)
Gejiio-glossus
Styh-glossus (stump)

Depressor labii inferioris (stump)

Fig. 333. — Muscles of Tongue, Pharynx, Larynx, etc.; Deep Dissection.
T. p.. Tensor palati; L. p., levator palati, concealed part indicated by dotted line; Pt. p., pterygo-pharyngeus;
P. p., palato-pharyngeus; St. p., stylo-pharyngeus; C. a., crieo-arytenoideus dorsalis; C. th., crico-thyroideus; Th. c.^
thyroid cartilage (lamina) ; T/i. /i., thyro-hyoideus; X. A., kerato-hyoideus; T/t. c, thyroid cornu; .S. c, small cornu;
L. p., lingual process; F. p., foliate papilla; Fu. p., fungiform papillae. Part of great cornu is removed and indicated
by dotted lines.

arises from the lateral aspect of the hyoid bone, from the lingual process to the oral
extremity of the great cornu, and from the thyroid cornu. The fibers pass obliquely

394 DIGESTIVE SYSTEM OF THE HORSE

forward and upward, and for the most part turn toward the median plane of the
dorsum of the tongue. Its action is to retract and depress the tongue.^

3. Genio-glossus. — This is a fan-shaped muscle, which lies parallel to the me-
dian plane of the tongue. It is separated from the muscle of the opposite side by a
layer of fat and areolar tissue. It arises from the medial surface of the ramus
of the mandible just behind the symphysis. From the tendon the fibers pass in
a radiating manner, some curving forward to the tip, others pass toward the dorsum,
and others toward the root of the tongue; some fibers pass from the posterior end
of the tendon to the body and small cornu of the hyoid bone. ' The muscle as a
whole is a depressor of the tongue, and especially of its middle portion; when both
muscles act, a median groove is formed on the dorsum. The posterior fibers pro-
trude the tongue, the middle fibers depress the tongue, and the anterior fibers
retract the tip of the tongue.

In some cases there is a small anomalous muscle which arises by a delicate tendon with the
genio-glossus and is attached behind with the genio-hyoideus.

Vessels and Nerves. — The arteries of the tongue are the lingual and sub-
lingual branches of the external maxillary artery. The veins go to the internal
and external maxillary veins. The lymph vessels go chiefly to the pharyngeal
lymph glands. The sensory nerves are the lingual and glosso-pharyngeal, and the
muscles are innervated by the hypoglossal nerve.

THE TEETH IN GENERAL
The teeth are hard white or yellowish-white structures implanted in the alveoli
of the bones of the jaws. Morphologically they are large calcified papillae. Func-
tionally they are organs of prehension and mastication, and may serve as weapons.
The domesticated mammals have two sets of teeth. The teeth of the first set
appear during early life and are known as deciduous or temporary teeth (Dentes
decidui),^ since they are replaced during the period of growth by the permanent
teeth (Dentes permanentes) . They are classified according to form and position
as follows:

1. The incisor teeth (Dentes incisivi) are situated in front and are implanted
in the premaxilla and mandible.

2. The canine teeth (Dentes canini) are situated a little further back, and
interrupt the interalveolar space.

3. The premolar and molar teeth (Dentes prsemolares et molares) form the
sides of the dental arch. The premolars form the anterior part of the series; they
appear in both sets. The molars appear only in the permanent dentition. The
term cheek teeth is used to include both premolars and molars.

The interval between the incisors and premolars is the interalveolar or inter-
dental space.

As the teeth of the two sides of the jaw are alike in niunber and character
(in normal cases), the complete dentition may be briefly indicated by a dental
formula such as the following :

2 ( I - C - P - M - I = 32.

(2 1 2 3\
I - C - P - M - )
2 12 3/

In this formula the letters indicate the kinds of teeth, and the figures above and
below the lines give the number of teeth of one side in the upper and lower jaw
respectively in man.

^ It may be possible to recognize in this muscle three parts, which would correspond to
the baseo-, kerato-, and chondro-glossus of man.

^ They are also popularly spoken of as "milk" teeth.

THE TEETH IN GENERAL 395

The individual teeth of each group are designated numerically, the starting-
point being the middle line ; thus the incisor on either side of the middle line is the
first incisor, and may be conveniently indicated by the notation I^ The deciduous
teeth may be designated in a similar manner, prefixing D (for deciduous) to the
letter indicating the kind of tooth. In addition to the above systematic method of
notation other terms have received the sanction of popular usage. Thus the first
incisors are commonly called middle incisors, ''pinchers," or "nippers"; the second,
intermediate; and the third, corner teeth. The canines, when highly developed,
may be termed tusks or fangs. The vestigial and inconstant first premolar of the
horse is popularly termed the "wolf tooth."

Each tooth presents for description a part coated with enamel, termed the
crown (Corona dentis), and a part covered with cement, termed the root (Radix
dentis). The line of union of these parts is the neck (Collum dentis).^ In many
teeth the neck is distinct and is embraced by the gum, e. g., the teeth of the dog
and the temporary incisors of the horse. In other teeth no constriction is present,
e. g., the permanent incisors of the horse. Between these extremes are the molars
of the horse, in which the neck is seen only in advanced age.

The surface of a tooth directed toward the lips is ternwd labial ; that toward
the cheek, buccal; and that toward the tongue, lingual (Facies labiahs, buccalis,
lingualis). The surface opposed to a neighboring tooth of the same dental arch
is termed the contact surface (Facies contactus). The masticatory surface (Facies
masticatoria) is that which comes in contact with a tooth or teeth of the opposite
jaw.-

Structure. — Teeth are composed of four tissues, which are considered here
from within outward. The pulp of the tooth (Pulpa dentis) is a soft, gelatinous
tissue, which occupies a space in the central part of the tooth termed the pulp
cavity (Cavum dentis). The pulp is well supplied with blood-vessels and nerves.
It occupies a relatively large space in young growing teeth, but later the dentine
deposited on its surface gradually encroaches on it until, in advanced age, the cavity
is much reduced or obliterated. The dentine (Substantia eburnea) forms the bulk
of most teeth, covering the surface of the pulp. It is hard, and is yellowish-white
in color. The enamel (Substantia adamantina) , the hardest tissue of the body,
constitutes a layer of varying thickness covering the dentine of the crown of the
tooth. It is easily distinguished by its clear, bluish-white appearance and its ex-
treme density. The cement (Substantia ossea) is the outermost tooth substance.
In simple teeth it forms usually a thin layer on the surface of the root only, but
in complex teeth it exists in considerable quantity, tending to fill in the spaces
between the enamel folds of the crown also. Its structure is practically the same
as that of bone without Haversian canals, and even these occur where the cement
forms a thick layer. The embedded part of the tooth is attached to the alveolus
by a vascular layer of connective tissue, the alveolar periosteum (Periosteum
alveolare); this is the periosteum of the alveolus and performs a like function
with regard to the embedded part of the tooth. The name pericementum has also
been applied to it.

lit will be noted that this definition of crown and root does not agree exactly with the
popular view that the crown is the free part and the root the embedded part. The objection to
the latter statement Ues in the fact that it is not capable of general appHcation. Thus the mor-
phological crown of the permanent molars in the horse is extremely long, and is, for the most
part, embedded in the bone in the young animal. The root proper begins to form at four or five
years of age, and continues its growth for about eight years. As the exposed part of the crown
wears down, the embedded part erupts, thus preventing deficiency of length. On the old basis
we should have to say that successive portions of the root become crown, while in point of fact it
is only in very extreme age that the true root comes into wear. This difficulty does not arise in
cases in which the eruption of the teeth is completed rapidly, e. g., man, dog. In such brachydont
forms the short crown is clearly marked off from the root or roots by a neck, which is embraced
by the gum. The opposite extreme is seen in the incisors of typical rodents, which grow con-
tinuously and have no roots.

2 This is popularly termed the grinding surface or "table" of the tooth.

396

DIGESTIVE SYSTEM OF THE HORSE

The blood-supply to the pulp is derived from the alveolar branches of the in-
ternal maxillary artery; the nerve-supply comes from branches of the trigeminus.

The Teeth of the Horse ^

The Permanent Teeth
The formula of the permanent teeth of the horse is:

(3 1 3 or 4 3 \
I _ C - P M - I
3 13 3/

40 or 42

Fig. 334. — Upper Teeth of Horse, About Four and One-half Fig. 335 — Lower Teeth of Horse,

Years Old.
2', /2, /', Incisors; C, canine; Pi, />», ps, P', premolars; M',M\
M', molars. The eruption of the third incisor is not complete and

Four Years of Age.
7', I-, First and second permanent

sors; Di's, third deciduous incisor. The
the tooth is unworn. cheek teeth are numbered according to

popular usage

1 Other figures illustrating the teeth are to be found in the description of the skull.

THE PERMANENT TEETH

397

In the mare the canines usually are very small and do not erupt, reducing the num-
ber to 36 or 38. ^

Incisor Teeth. — These are twelve in number. The six in each jaw are placed
close together, so that their labial edges form almost a semicircle in the young
horse. They have the peculiarity (not found in existing mammals other than the
equidse) of presenting, instead of the simple cap of enamel on the crown, a deep
invagination, the infundibulum, which becomes partly filled up with cement.
Hence as the tooth wears, the masticatory surface (or "table") has a central ring
of enamel surrounding this cavity in addition to the peripheral enamel. The
cavity becomes darkened by deposits from the food, and is commonly termed
the "cup" or "mark." Each tooth is curved so that the labial surface is convex

Fig. 3.36. — Upper Incisor Teeth op Horse. Fig. 337. — Lower Incisor Teeth of Horse.

The labial surfaces ot the teeth have been exposed by removal of the bone. Subject was five years old.

and the embedded parts converge. The average total length of an incisor at five
or six years of age is about two and a half to three inches (ca. 7 cm.). They taper
regularly from exposed crown to apex, without any constriction, and in such a
manner that in young horses the masticatory surface is broad transversely; toward
the middle the two diameters of a cross-section are about equal; near the apex
the antero-posterior diameter is considerably greater than the transverse.

This fact is of value in the determination of age by the teeth, since the mas-
ticatory surfaces at different ages represent a series of cross-sections. As the ex-
posed crown wears down, the embedded part (reserve crown) emerges from the

1 Ellenberger found, as the result of extensive observations (8000 subjects), that about
2 to 3 per cent, of mares have erupted canines in both jaws; that 6 to 7 per cent, have them in
the upper jaw; while 20 to 30 per cent, have them in the lower jaw. The numerical variation in
the above formula results from the fact that the first premolar ("wolf-tooth") is often absent and
further that it is doubtful to what set it belongs when present. It is commonly not included in
the enumeration.

398

DIGESTIVE SYSTEM OF THE HORSE

Infundibulu

Central enamel
Dentine
Peripheral
enamel

Cemetit

alveolus, so that the masticator}^ surfaces of the first and second lower incisors

are at first oval, with the long diameter transverse;
later — at about fourteen years usually for the first
lower incisors — they are triangular, with the base
at the labial edge. At the same time the infundib-
ulum or "cup" becomes smaller, approaches the
lingual border, and finally disappears; it remains
longer on the upper incisors, as it is deeper in
them. Another marked feature in old age is the
progressive approach to a horizontal direction as
seen in profile; at the same time the exposed
crowns of the teeth become parallel and finally
convergent.

Canine Teeth. — These are four in number in the
male ; in the mare they are usually absent or rudi-
mentary.^ They interrupt the interdental space,
dividing it into unequal parts. The upper canine

Peripheral enamel Cement
Dentine
Central enamel'
Cement-

FiG. 338. — Longitudinal Section op

Lower Incisor Tooth of Horse.

C, Pulp cavity. Cement is shown in the

infundibulum, but is not marked.

Fig. 339. — Cross-section of Lower Lx
/, Infundibulum

Tooth of Horse.

is situated at the junction of the premaxilla and the maxilla; the lower canine is
nearer the corner incisor. The canines are simple teeth, smaller than the incisors,

Fig. 340. — Lower Incisor and Canine Teeth of Fig. 34"

Horse, Five Years Old.
The lingual border of the third upper incisor is unworn.

— Upper Incisor and Canine Teeth op

Horse, Five Years Old.
/', /-, /', Incisor; C, canine.

and are curved with the concavity directed backward. The exposed crown in the

^ It is interesting to notice that vestigial canines are not at all uncommon in mares, espe-
cially in the lower jaw. They are very small, and do not usually erupt; their presence is indi-
cated in the latter case by a prominence of the gum. This is in conformity with the fact that
they were present in both sexes in Eocene and Miocene ancestors of existing equida;.

THE PERMANENT TEETH

399

young subject is compressed, convex and smooth laterally, concave with a median,
ridge medially; its edge is sharp in the unworn tooth. The embedded part (usu-
ally called the root) is round and the pulp cavity is large, persisting to advanced

age. In old subjects, when the compressed part of the crown has worn away, the

exposed part is rounded and blunt.

Cheek Teeth (Premolars and Molars). i— The constant number of these is
1 It is common in veterinary works to apply the term "molar" to all the cheek teeth, since,

in the horse particularly, the premolars are molariform, i. c, do not differ materially fron the true

molars in size or form. The term cheek teeth conveniently mcludes the premolars and molars.

400

DIGESTIVE SYSTEM OF THE HORSE

twenty-four — twelve in each jaw. Quite commonly, however, the number is in-
creased by the presence in the upper jaw of the so-called "wolf-tooth." This
tooth, the first premolar, is usuallj^ situated just in front of the first well-developed
tooth; it is a much-reduced vestige, not often more than one-half or three-fourths
of an inch (ca. 1 to 2 cm.) in length. (It is interesting as being the remnant of a
tooth which was well developed in the Eocene ancestors of the horse.) It may
erupt during the first six months, and is often shed about the same time as the
milk-tooth behind it, but may remain indefinitely. The occurrence of a similar
tooth in the lower jaw — which rarely erupts — increases the dental formula to 44,
which is considered the typical number for mammals.^ The cheek teeth are very
large, prismatic in form, and quadrilateral in cross-section, except the first and

last of the series, which are three-sided. The
Dentine Cement cro^\Ti is remarkably long, most of it being em-

bedded in the bone or projecting into the max-
illary sinus in the young horse. As the exposed
part wears away the embedded part erupts to
replace it, so that a functional crown of about
four-fifths of an inch (ca. 2 cm.) is maintained.^
The root begins to grow at about five years
of age, and is complete at twelve to fourteen,
although the deposition of cement may con-
tinue indefinitely.

The maxillary or upper cheek teeth are
embedded in the alveolar processes of the max-

Cement

Enamel

Cement

Root canal

Fig. 343. — Frontal Section of Upper

Cheek Tooth of Horse.

C, C, Pulp cavities. Infundibulum filled

with cement.

Fig. 344. — Cross-section of Upper Cheek Tooth of Horse.
Buccal (lateral) surface to left. /.Anterior, I', posterior infundib-
ulum, both almost filled up with cement.

ilia. The exposed parts of the crowns are normally in close contact, forming a
continuous row which is slightly curved, with the convexity toward the cheek.
The embedded parts diverge in the manner shoAvn in the annexed figures (Figs. 342,
347). Thus the long axis of the first is directed upward and a little forward, that
of the second is almost vertical, while in the remainder it is curved backward in
an increasing degree; the last tooth in particular is strongly curved in the adult.
The average length at six years of age is a little more than three inches (ca. 8 cm.).
The buccal surface presents a central ridge running lengthwise, and separating two
grooves; the first tooth has, in addition, a less prominent ridge in front of the
primary one. The lingual surface is marked by a wide, rounded ridge, the acces-
sory pillar or column, which separates two very shallow grooves. The masticatory

1 The question to which set these teeth belong is an open one.

'^ For teeth of this kind it is convenient to employ the terms functional crowTi and reserve

THE PERMANENT TEETH

401

surface presents two inf undibula, anterior and posterior. It slopes obliquely down-
ward and outward, so that the buccal edge is prominent and sharp. Its average
width, except at each end of the series, is about an inch (ca. 2.5 cm.). The first
and last teeth have three roots, the remainder four or three.

As may be seen in Fig. 342, the individual teeth of the series vary in length. In the speci-
men from wlaich the photograph was taken the lengths of the upper teeth in centimeters enumer-
ated from before backward were: 6.3, 7.7, 8.5, 8.0, 8.8, 8.2. The distance between the two rows
was 6.6 cm. at the anterior end and 8.6 cm. at the posterior end.

The position of the embedded crowns and roots of the last four varies at

different ages and in different subjects. Two factors in this variation may be

noted. All of these teeth are developed in the posterior part of the body of the

maxilla. As growth proceeds the teeth move forward, so that commonly only the

last three, but sometimes also the third, project into

the maxillary sinus. The second cause of variation

is the fact that the anterior limit of the maxillary

sinus may be at the extremity of the facial crest, or

about an inch beyond it. In the latter case the third

tooth projects into the sinus. ^

The mandibular or lower cheek teeth are im-
planted in the rami of the mandible, forming two
straight rows which diverge behind. The space be-
tween the rows is considerably less than that separat-
ing the upper teeth, especially in the middle of the
series. The length of the lower teeth is about the
same as that of the upper set. Their direction is

Cement

Dentine Cement
Enamel

Cement

Fig. 345. — Fro.n'tal Section op

Lower Cheek Tooth of Horse.

C, Pulp cavity. Infundibulum filled

with cement.

Fig 346. — Cross-section of Lower Cheek Tooth of Horse.
Buccal surface to left.

also similar, but the embedded portions diverge even more, with the exception
of the first and second. The long axis of the first is vertical; the remainder
project downward and backward in a gradually increasing obliquity. The buc-
cal surface has a longitudinal furrow; the last molar has a secondary shal-
lower furrow in addition. The lingual surface is uneven, but the grooves are
not regular; there are usually three on the first and last tooth. The mastic-
atory surface is oblique, sloping upward and inward in correspondence with the
opposing tooth; thus the lingual edge is prominent. Its average width (except
at each end of the series) is somewhat less than three-fourths of an inch (ca. 1.8 cm.).

' The student is advised to amplify these very general statements by the examination of
heads of subjects of varying ages. It may also be noted that the position of the septum between
the two divisions of the sinus varies much.
26

402

DIGESTIVE SYSTEM OF THE HORSE

The first five have two roots, while the sixth commonly has three. The width of the
lower molars is a little more than half that of the upper.

The structure is quite complex. Two infundibula run vertically through the

entire length of the crown; these become filled with cement. In the upper teeth
there are five main divisions of the pulp-cavity and five enamel folds, four of which
are arranged symmetrically, while the fifth is an outgrowth from the antero-medial
fold. In the lower teeth the infundibula are open along the lingual surface until

THE DECIDUOUS TEETH ERUPTION OF THE TEETH 403

closed by deposit of cement. The pulp-cavity has two main divisions (anterior
and posterior) and three or four secondary diverticula. The enamel folds corres-
pond, forming a pattern even more complicated than on the upper teeth. On
the exposed crown of the unworn tooth the enamel folds form rounded ridges
covered with a thin layer of cement. After the tooth comes into wear the enamel
on the masticatory surface stands out in the form of sharp, prominent ridges.^
Progressive cementation of the periphery of the tooth takes place, thus leveling up
the irregularities of surface to a considerable extent.

The lengths of the lower teeth shown in Fig. 342 were in centimeters: 5.7, 7.9, 9.0, 8. .5, S.2
7.B. The distance between the two rows was 4.7 cm. at the anterior end and 7 cm. at the posterior
end.

The Deciduous Teeth
The deciduous teeth are smaller and fewer than those of the permanent set.
The formula is :

/ 3 0 3\

2 I Di - Dc - Dp - I

V 3 0 3/

The deciduous incisors are much smaller than the permanent ones. They
have a distinct neck at the junction of the crown and root. The crown is short,
white in color, and its labial surface is smooth. The infundibulum is shallow.
The root is flattened; it undergoes absorption as the permanent tooth develops
l^ehind it.

The deciduous canines are quite vestigial. They occur in lioth sexes as slender
spiculse about a quarter of an inch in length, but do not erupt. The lower one
develops close to the corner incisor. They are not usually included in the formula,
as they are never functional.

The deciduous premolars differ from the permanent set chiefly in that they
have much shorter cro^vns than the latter. The roots form early, so that a distinct
neck occurs.

Vessels and Nerves. — The blood supply of the teeth is derived from the
infraorbital and alveolar branches of the internal maxillary artery. The lymph
vessels go to the mandilmlar and pharyngeal lymph glands. The nerves come
from the trigeminus.

Eruption of the Teeth
The subjoined table indicates the average periods of the erui^tion of the teeth:

Teeth Eruption

A. Deciduous:

1st incisor (Di 1) Birth or first week.

2nd " (Di 2) 4-6 weeks.

3rd " (Di 3) 6-9 months.

Canine (Dc )

1st premolar (Dp 2) | ^^^^^ ^^ ^^^^

2nd (Dp 3) \ . wPPk<5

3rd " (Dp 4) J ^""^ '^^^^^•

B. Permanent:

1st incisor (II) 2^ years.

2nd " (12) 31-2 years.

3rd " (13) AXi years.

Canine (C) 4-.5 years.

1st premolar (or wolf-tooth) (PI) 5-6 months.

2nd " (F2) 2H years.

3rd " (P3) 3 years.

4th " fF4) 4 years.

1st molar (Ml) 10-12 months.

2nd " (M2j 2 years.

,3rd " (M3) 3I2-4 years.

(The periods given for P 3 and 4 refer to the upper teeth; the lower ones may erupt
about six months earlier.)

^ It is estimated that the enamel ridges of an upper cheek tooth of a young adult horse, if
straightened out, would form a Une more than a foot long. The extent diminishes with age.

404 DIGESTIVE SYSTEM OF THE HORSE

THE SALIVARY GLANDS

This term is usually restricted to the three pairs of large glands situated on the
sides of the face and the adjacent part of the neck — the parotid, mandibular, and
sublingual. Their ducts open into the mouth.

The parotid gland (Glandula parotis) (Fig. 560) — so named from its proximity
to the ear — is the largest of the salivary glands in the horse. It is situated chiefly
in the space between the ramus of the mandible and the wing of the atlas. It is
somewhat triangular in shape, the apex partially embracing the base of the external
ear. Its length is about eight to ten inches (ca. 20 to 25 cm.), and its average thick-
ness nearly an inch (ca. 2 cm.). Its average weight is about seven ounces (ca.
200 to 225 g.). It presents for description two surfaces, two borders, a base, and
an apex. The lateral (or superficial) surface is covered by the parotid fascia and
the cutaneus and parotido-auricularis muscles. It is crossed obliquely by the j ugular
vein, which is largely embedded in the gland. It is also related to the great auricular
vein, the cervical branch of the facial nerve, and branches of the second cervical
nerve. The medial (or deep) surface is very uneven, and has numerous important
relations. Some of these are: the guttural pouch and the great cornu of the
hyoid bone ; the masseter, occipito-mandibularis, digastricus, and occipito-hyoideus
muscles; the tendons of the brachio-cephalicus and sterno-cephalicus (which
separate the parotid from the underlying mandibular gland) ; the external carotid
artery and some of its branches; the facial nerve; the pharyngeal lymph glands.
The anterior or facial border is closely attached to the ramus of the mandilDle and
the masseter muscle; it overlaps the latter to a varying extent.^ The posterior
or cervical border is concave, and is loosely attached to the underlj^ng muscles.
The base or ventral border is related to the external maxillary vein. The apex
is attached to the base of the external ear, which it partially embraces. The gland
has a yellowish-gray color and is distinctly lobulated. It is inclosed in a capsule
formed by the fascia. The parotid duct (Ductus parotideus)^ is formed at the
ventral part of the gland, near the facial edge, by the union of three or four radicles.
It leaves the gland about an inch (ca. 2 to 3 cm.) above the external maxillary
vein, crosses the tendon of the sterno-cephalicus, and gains the medial face of the
pterygoideus medialis. It then runs forward in the mandibular space below the
external maxillary vein and winds around the ventral border of the mandible be-
hind the vein, passes upward between the vein and the masseter muscle for about
two inches (ca. 5 cm.), turns forward underneath the facial vessels, and perforates
the cheek obliquely opposite the third upper cheek tooth. Before piercing the
cheek it is somewhat dilated, but its termination is small, and is surrounded by a
circular mucous fold (Papilla salivalis). The gland belongs to the compound
alveolar glands of the serous type.

Blood-supply. — Branches of the carotid and maxillary arteries.

Nerve-supply. — Trigeminal, facial, and sympathetic nerves.

The mandibular or submaxillary gland (Glandula mandibularis s. submax-
illaris)^ is much smaller than the parotid. It is long, narrow, and curved, the
dorsal edge being concave. It extends from the fossa atlantis to the body of the
hyoid bone, so that it is covered partly by the parotid gland, partly by the lower
jaw (Fig. 646). Its length is eight to ten inches (ca. 20 to 25 cm.), its width an inch
to an inch and a half (ca. 2.5 to 3 cm.), and its thickness al)out half an inch (ca.
1 cm.). It weighs about one and a half to two ounces (ca. 45 to 60 g.). It is often

^ In some cases there is a well-marked triangular facial process, which covers the temporo-
mandibular joint, the facial nerve, and the transverse facial vessels.
^ Formerly known as Stenson's or Steno's duct.
^ The term "submaxillary, " although firmly established by usage, is a misnomer.

THE PHARYNX 405

divisible into two parts. It presents for description two surfaces, two borders, and
two extremities. The lateral surface is covered by the parotid gland, the occipito-
mandibularis, digastricus, and pterygoideus medialis muscles. The tendon of the
^temo-cephalicus crosses this surface, and, together with the aponeurosis connect-
ing it with that of the brachiocephalicus, is a useful guide in separating the parotid
gland from it. The medial surface is related to the rectus capitis ventralis major,
the guttural pouch, the larynx, the division of the carotid artery, and the tenth,
eleventh, and sympathetic nerves. The dorsal border is concave and thin. It
is related to the guttural pouch and the duct of the gland. The ventral border
is convex and thicker. It is related to the external maxillary vein and often to
the thyroid gland. The posterior extremity is loosely attached in the fossa atlantis.
The anterior extremity lies at the side of the root of the tongue, and is crossed
laterally by the external maxillary artery. The mandibular or submaxillary duct
(Ductus mandibularis s. submaxillaris) ^ is formed by the union of small radicles
which emerge along the concave edge. It runs forward along this border, and, after
leaving the anterior extremity, crosses the intermediate tendon of the digastricus,
passes between the hyo-glossus and mylo-hyoideus, and gains the medial surface
of the sublingual gland. Its terminal part lies on the body of the mandible, under
the mucous membrane, which it pierces opposite the canine tooth. The orifice is
at the end of a flattened papilla, the caruncula sublingualis. The gland differs
in finer structure from the parotid in possessing serous, mucous, and mixed
alveoh.

Blood-supply. — Occipital, external carotid, and external maxillary arteries.

Nerve-supply. — Chorda tympani and sympathetic nerves.

The sublingual gland (Glandula sublingualis) (Figs. 330, 561) is situated be-
neath the mucous membrane of the mouth, between the body of the tongue and the
ramus of the mandible. It extends from the symphysis to the third or fourth
lower cheek tooth. Its length is about five or six inches (ca. 12 to 15 cm.) and its
weight about half an ounce (ca. 15 to 16 g.). It is flattened laterally, and has a
thin dorsal border which underlies the sublingual fold of the mucous membrane
of the floor of the mouth. The lateral surface is related to the mylo-hyoideus
muscle, and the medial surface to the genio-glossus and stylo-glossus, the mandib-
ular duct, and branches of the lingual nerve. The ventral border is related to
the geniohyoid muscle. The sublingual ducts (Ductus sublinguales), about thirty
in number, are small, short, and twisted; they open on small papillae on the sub-
lingual fold. The gland has mixed alveoli.

Blood-supply. — Sublingual artery.

Nerve-supply. — Trigeminal and sympathetic nerves.

THE PHARYNX

The pharynx is a musculo-membranous sac which belongs to the digestive and
respiratory tracts in common. It is somewhat funnel-shaped, the large anterior
part joining the mouth and nasal cavity, while the small end is continued by the
oesophagus. Its long axis is directed obliquely downward and backward, and has
a length of about six inches (ca. 15 cm.). The pharynx is attached by its muscles
to the palatine, pterygoid, and hyoid bones, and to the cricoid and thyroid cartilages
of the larynx.

Its principal relations are : dorsally, the base of the cranium and the guttural
pouches; ventrally, the larynx; laterally, the medial pteryoid muscle, the great
cornu of the hyoid bone, the external carotid and external maxillary arteries, the

1 Formerly known as Wharton's duct.

406

DIGESTIVE SYSTEM OF THE HORSE

glosso-pharyngeal, anterior laryngeal, and hypoglossal nerves, the mandibular
salivary gland, and the parapharyngeal Ijonph glands.

The cavity of the pharynx (Cavum pharyngis) presents seven openings.
Through the posterior nares or choanae it communicates dorsally with the nasal
cavity. The pharyngeal orifices of the two Eustachian tubes (Ostia pharyngea

Temporal muscle

Nerves III,
IV, VI, and
ophthalmic
Internal max-
illary artery
Transverse
facial nerve
Buccinator

nerve
Inferior al-
veolar nerve

Inferior al-
veolar artery

Great cornu of.
hyoid bone

Lingual branch.

of IX nerve
External max-
illary artery
Hypoglossal
nerve

Masseteric,
vessels

Thyroid cornu
of hyoid bone

Lymph gland

Coronoid proce

Ti a nsverse fa-
cial vessels
Ti a nsverse fa^

cial nerve
Lateral ptery-
goid muscle

internal maxil-
lary vein

Medial pteryoid
muscle

Ramus of man-
dible

Hyo-pharyngeus
muscle

Isthmus faucium,

■Tonsil

igastricus (in-
termed, tendon)

Anterior end of
mandibular gland

Sublingual vein

External maxil-
lary vein

Parotid duct

Fig. 348. — Cross-section of Head of Horse.
The section passes through the anterior part of the temporo-mandibular articulation, but is slightly oblique, passing
a few millimeters further forward on left side than on right. 1, Corpus callosum; 2, lateral ventricle of brain; 3,
caudate nucleus; 4, internal capsule; 5, lenticular nucleus; 6, optic chiasma; 7, middle cerebral artery; S, sphenoidal
sinuses; 9, cavernous sinus; 10, Eustachian tube, medial lamina; 11, 11, guttural pouches; 12, soft palate; IS, epi-
glottis; 7.^, hyo-epiglottic muscle; 75, thyro-hyoid muscle. The tensor palati (not marked) lies medial to the ptery-
goideus lateralis, and medial to the tensor is the levator palati, which blends above with the outer lamina of the Eustach-
ian tube.

tubse auditivse) are situated on the lateral wall behind the posterior nares and below
the level of the ventral nasal meatus. They are slit-like openings, directed ob-
liquely downward and backward, and are a little more than an inch (ca. 3 cm.)
in length. They are bounded medially by a fold which encloses the expanded
extremity of the cartilaginous Eustachian tube. The isthmus fauciimi is the oral
open ng; it is closed by the soft palate except during swallowing. The aditus

THE PHARYNX 407

laryngis occupies the greater part of the ventral wall or floor of the pharynx; it
is open except during deglutition. Behind this is the aditus oesophagi, the entrance
to the oesophagus.

The wall of the pharynx comprises, from without inward, the muscles, the
pharyngeal aponeurosis, and the mucous membrane.

The muscles of the pharynx (Mm. pharyngis) (Figs. 332, 333) are covered
by the pharyngeal fascia, which is attached to the base of the skull, the great cornu
of the hyoid bone, and the thyroid cartilage of the larynx. They are as follows:

1. The stylo-pharyngeus arises from the medial surface of the dorsal third
of the great cornu of the hyoid bone, passes ventro-medially, and enters the wall of
the pharynx by passing between the pterygo-pharyngeus and palato-pharyngeus.
Its fibers rjldiate, many bundles passing forward, others inward or backward be-
neath the hyo-pharyngeus. It raises and dilates the pharynx to receive the bolus
in swallowing.

2. The palato-pharyngeus arises chiefly by means of the aponeurosis of the
soft palate from the palatine and pterygoid bones ; some fibers are attached to the
anterior wide part of the Eustachian tube. Its fibers pass backward on the lateral
wall of the pharynx, and are inserted in part into the upper edge of the thyroid
cartilage, in part turn inward to end at the median fibrous raphe. Its action is to
shorten the pharynx, and to draw the larynx and cesophagus toward the root of the
tongue in swallowing.^

3. The pterygo-pharyngeus is flat and triangular. It lies on the anterior part
of the lateral wall of the i)harynx. It arises from the pterygoid bone above the
preceding muscle, — from which it is not distinctly separated, — crosses the levator
palati, and is inserted into the median raphe. Its action is similar to the preceding,

4. The hyo-pharyngeus may consist of two parts :

(a) The kerato-pharyngeus is a small and inconstant muscle which arises
from the medial surface of the great cornu of the hyoid bone near its ventral end.
It passes upward and backward on the lateral face of the palato-pharyngeus,
turns toward the raphe, and spreads out under the next muscle.

(6) The chondro-pharyngeus, broad and fleshy, arises from the thyroid cornu
of the hyoid bone and by a thin fasciculus from the lamina of the thyroid cartilage.
The bundles spread out and end at the median raphe. The posterior part dips
under the thyro-pharyngeus, while the anterior part overlies the pterygo- and
palato-pharyngeus.

5. The thyro-phar3mgeus arises from the lateral surface of the lamina of the
thyroid cartilage on and behind its oblique line. Its fibers pass forward and
medially to the median raphe.

6. The crico-pharyngeus arises from the lateral part of the arch of the cricoid
cartilage and ends at the raphe. The fibers are directed upward, forward, and
inward; they blend behind with the longitudinal fibers of the oesophagus.

The last three muscles are constrictors of the pharynx.

The phar5mgeal aponeurosis is attached to the base of the cranium. It is
well developed on the medial face of the palato-pharyngeus muscle and forms a
median raphe pharyngis dorsally, which is wide in its posterior part.

The mucous membrane of the pharynx is continuous with that of the several
cavities which open into it. It is thin and closely adherent to the base of the skull
in the vicinity of the posterior nares, where the muscular wall is absent. Behind
the Eustachian openings there is a median cul-de-sac, the pharyngeal recess (Re-
cessus pharyngeus) . The recess is somewhat variable, but is usually about an inch
in depth and will admit the end of the finger. In the ass and mule it is much deeper.
Here also the muscular wall is absent and the mucous membrane lies against the

1 Vermeulen states that the pharyngeal orifice of the Eustachian tube is opened by the
contraction of that part of the muscle which is attached to the tube.

408

DIGESTIVE SYSTEM OF THE HORSE

guttural pouches. From the Eustachian opening a fold of the mucous membrane
(Plica salpingo-pharyngea) passes toward but does not reach the aditus laryngis.
A horizontal fold, the posterior pillar of the soft palate (Arcus pharyngo-palatinus),
passes along the ventral part of the lateral wall and unites with its fellow over the
entrance to the oesophagus. The dorsal part of the cavity (Pars respiratoria)
is lined with a ciliated epithelium, while the ventral part (Pars digestoria) has a
stratified squamous epithelium. The communication between the two is oval

Fig. 349. — Posterior Part of a Sagittal Section op Head .4nd Part of Neck of Horse, Cut about 1 cm. to the
Left of the Median Plane.
1, Posterior nares; 2, pharyngeal orifice of Eustachian tube; 3, aditus laryngis; 4< aditus oesophagi; a, posterior
pillar of soft palate; S', junction of 3 with its fellow over entrance to oesophagus; 6, epiglottis; 7, body of thyroid
cartilage; <S, arytenoid cartilage; 5, S, cricoid cartilage; iO, true vocal cord; 7 /, false vocal cord; ;;2, lateral ventricle
of larynx; 13, crico-arytenoideus dorsalis; 14, oesophagus; 15, external carotid arterj'; 16, hypoglossal nerve; 17,
glosso-pharyngeal nerve; IS, great cornu of hyoid bone; 19, Eustachian tube; W, body of hyoid bone; 21, hyoideus
transversus; 32, ridges of hard palate; 22', soft palate; 23, septum between frontal sinuses; 24, olfactorj' mucous
membrane; 25, sphenoidal sinus; 26, basilar part of occipital bone; 26', supra-occipital; 27, body of sphenoid bone;
28, pituitary body; 29, chiasma opticum; 30, corpora quadrigemina; 31, thalamus; 32, arachnoid; 33, odontoid
ligament; 34, posterior auricular muscles.

and is bounded by the free edge of the soft palate and its posterior pillars; it is
termed the pharyngeal isthmus. On either side of the aditus laryngis is a narrow
deep depression, the piriform recess (Recessus piriformis).

The submucous tissue contains numerous mucous glands (Glandulae pharyn-
gese). In the young subject the lymph follicles are numerous and form a collection
dorsally and between the Eustachian openings, known as the pharyngeal tonsil
(Tonsilla pharyngea).

THE CESOPHAGUS 409

Vessels and Nerves. — The arteries are derived from the common carotid,
external carotid, and external maxillary arteries. The lymph vessels pass to the
pharyngeal and anterior cervical lymph glands. The nerves are derived from the
trigeminus, glosso-pharyngeus, and vagus.

THE CESOPHAGUS

The oesophagus is a musculo-membranous tube, about 50 to 60 inches (ca.
125 to 150 cm.) in length, which extends from the pharynx to the stomach. In
its course it shows several changes of direction. It begins in the median plane above
the anterior border of the cricoid cartilage of the larynx. At the fourth cervical
vertebra it has passed to the left side of the trachea, and continues this relation
as far as the third thoracic vertebra. Here it again gains the dorsal surface of the
trachea, and, passing backward, crosses the aortic arch, by which it is pushed over
to the right of the median plane. It continues in the mediastinum between the
lungs, backward and a little dorsally, inclining gradually to the left, and reaches
the hiatus oesophageus of the diaphragm. Passing through this it terminates at
once at the cardiac orifice of the stomach, a little to the left of the median plane,
and about four or five inches (ca. 10 to 12 cm.) ventral to the vertebral end of the
fourteenth rib.^

Viewed with reference to the horizontal plane, its course is downward and
backward till it enters the thorax and passes upward to gain the dorsal face of
the trachea. Then for a short distance (i. e., to the root of the lung) its direction is
almost horizontal; behind this it passes somewhat upward to its termination.
The cervical part (Pars cervicalis) of the tube is about four to six inches (10 to 15
cm.) longer than the thoracic part (Pars thoracalis), while the so-called abdominal
part (Pars abdominalis) is about an inch (2 to 3 cm.) long.-

The principal relations of the oesophagus at its origin are: to the cricoid
cartilage and dorsal crico-arytenoid muscles ventrally; to the guttural pouches
and the ventral straight muscles dorsally; and to the carotid arteries laterally.
In the middle of the neck the relations are: to the left longus colli muscle dorsally;
to the trachea medially; to the left carotid artery, vagus, sympathetic, and recurrent
nerves laterally. Near the thoracic inlet the oesophagus is usually in contact
with the left jugular vein for a short distance. At its entrance into the thorax
it has the trachea on its medial side; the first rib, the roots of the brachial plexus
of nerves, and the left posterior cervical ganglion laterally. After gaining the
dorsal surface of the trachea, it has the aorta on its left and the vena azygos and
right vagus nerve on its right side. In its course through the posterior medias-
tinum the oesophageal trunks of the vagus nerves he above and below it, and the
oesophageal artery is dorsal to it.

Structure. — The wall is composed of four coats: (1) A fibrous sheath termed
the tunica adventitia; (2) the muscular coat; (3) a submucous layer; (4) the
mucous membrane. The muscular coat is of the striped variety as far as the base
of the heart, where it rapidly changes to the unstriped type. In addition to this
change, the muscular coat becomes much thicker and firmer, while the lumen is
diminished. Except at each end of the tube the muscular coat consists chiefly of

^ The distance between the terminal part of the oesophagus and the vertebra varies. In
formalin-hardened subjects it is most commonly as given above, but in soft specimens or in those
which have been frozen without previous fixation it is usually nearer the spine.

2 Careful observations (especially on frozen subjects and those in which the organs have been
hardened in situ) show that there is no abdominal part of the oesophagus in the strict sense of the
term. The stomach here lies directly on the diaphragm, so that the last inch or so of the oesopha-
gus is placed obliquely in the hiatus oesophageus, and is covered on the right and ventrally by the
pleura, but not by peritoneum. In soft subjects the weight of the stomach, or traction on it, draws
part of^the oesophagus into the abdomen, inclosed in a collar of peritoneum.

410 DIGESTIVE SYSTEM OF THE HORSE

two layers of fibers arranged spirally or elliptically, which intercross dorsally and
A-entrally. At the origin two bundles nearly an inch (ca. 2 cm.) wide arise from
the wide posterior part of the pharyngeal raphe and from a tendon common to
the crico-pharyngeus and thyro-pharyngeus. These bundles, which blend and
decussate at their origin, diverge and pass to each side of the oesophagus. In the
angle between them a deeper layer of circular fibers is visible. Two small ventral
bundles emerge from the depression between the lamina of the cricoid cartilage
and the arytenoid cartilages. These curve around to the side of the oesophagus
and blend with the dorsal bundles before described. In the terminal part there
is an external longitudinal layer and an internal circular layer, the latter being
extremely thick. The mucous membrane is pale, and is covered with squamous
stratified epithehum. It is loosely attached to the muscular coat by an abundant
submucosa, and lies in longitudinal folds which obliterate the lumen except during
deglutition.^

Blood-supply." — Carotid, broncho-cesophageal, and gastric arteries.

Nerve-supply. — Vagus, glosso-pharyngeal, and sympathetic nerves.

THE ABDOMINAL CAVITY

The abdominal cavity (Cavum abdominis) is the largest of the body cavities.
It is separated from the thoracic cavity by the diaphragm and is continuous behind
with the pelvic cavity. The line of demarcation between the abdominal and
pelvic cavities is known as the terminal line, or brim of the pelvis; it is formed by
the base of the sacrum dorsally, the ileo-pectineal lines laterally, and the anterior
borders of the pubic bones ventrally.

The cavity is ovoid in form, but is somewhat compressed laterally. Its long
axis extends obhquely from the center of the pelvic inlet to the sternal part of the
diaphragm. Its dorso-ventral diameter is greatest at the first lumbar vertebra,
while its greatest transverse diameter is a little nearer the pelvis.

The dorsal wall or roof is formed by the lumbar vertebrse, the lumbar muscles,
and the lumbar part of the diaphragm.

The lateral walls are formed by the oblique and transverse abdominal muscles,
the abdominal tunic, the anterior parts of the ilia with the iliacus muscles, the
cartilages of the asternal ribs, and the parts of the posterior ribs which are below
the attachment of the diaphragm.

The ventral wall or floor consists of the two recti, the aponeuroses of the oblique
and transverse muscles, the abdominal tunic, and the xiphoid cartilage.

The anterior wall is formed by the diaphragm, which is deeply concave, thus
greatly increasing the size of the abdomen at the expense of the thorax.

It should be noted that the diaphragm also concurs practically in the formation of a con-
siderable part of the lateral walls, since its costal part even during ordinary inspiration lies directly
on the ribs over a width of four or five inches (ca. 10 to 12 cm.) ; in expiration this area of contact
includes about all of the costal part. This fact is of clinical importance, with reference to auscul-
tation and percussion and penetrating wounds. The cupola of the diaphragm extends as far
forward as a plane through the sixth rib to the right of the heart.

The muscular walls are lined by a layer of fascia, distinguished in different
parts as: (1) The diaphragmatic fascia; (2) the transversalis fascia; (3) the iliac
fascia; (4) the deep layer of the lumbo-dorsal fascia.

The subserous tissue (Tela subserosa) unites the fascia and peritoneum.

1 The potential lumen is difficult to determine at all accurately. When distended, its average
diameter (according to Rubeli) is a little more than 6 cm. The thickness of the wall varies (in-
versely as the lumen) from 0.4 to 1.2 cm. or more. The change in type of the muscular tissue is
gradual, and begins in the deep part; bundles of striped muscle are present even after the apparent
change to unstriped muscle, and may extend to the stomach. In the posterior part of the tube
many bundles intercross in an irregular plexiform manner.

THE PERITONEUM 411

It is areolar tissue, and is more or less loaded with fat according to the condition
of the subject, except over the diaphragm. It sends laminae into the various
peritoneal folds.

The peritoneum, the serous membrane which lines the cavity, will be described
later.

The abdominal walls are pierced in the adult by five apertures. These are
the three foramina of the diaphragm and the inguinal canals, which have been
described. In the foetus there is the umbilical opening also. This transmits the
urachus, a tube which connects the bladder with the allantois; the two umbilical
arteries, which carry ])lood from the foetus to the placenta; and the umbilical
vein, which returns blood from the placenta to the liver of the foetus. After birth
the orifice is closed by fibrous tissue, leaving a scar, the umbilicus, which is more
or less distinctly visible in the median ventral line in a transverse plane about
tangent to the ventral end of the last rib.

The cavity contains the greater part of the digestive and urinary organs, i^art
of the internal genital organs, numerous nerves, blood vessels, lymph vessels and
glands, ductless glands (spleen and adrenal bodies), and certain foetal remains.

For topographic purposes the abdomen is divided into nine regions by imagi-
nary planes.^ Two of these planes are sagittal and two are transverse. The
sagittal planes cut the middles of the inguinal ligaments; the transverse planes
pass through the last thoracic and fifth luml^ar vertebrae, or the ventral end of the
fifteenth rib and the tuber coxae respectively. The transverse planes divide the
abdomen into three zones, one behind the other, viz., epigastric, mesogastric,
and h)rpogastric : these are subdivided ]:)y the sagittal planes as indicated in the
subjoined table:

Left parachondriac Xiphoid Right parachondriac

Left lumbar Umbilical Right lumbar

Left ihac Prepubic Right iliac

Other useful regional terms are: sublumbar, diaphragmatic, inguinal. The
first two require no explanation. The inguinal regions (right and left) lie in front
of the inguinal ligament. The flank is that part of the lateral wall which is formed
only of goft structures. The triangular depression on its upper part is termed
the paralumbar fossa; this is bounded dorsally by the lateral border of the lon-
gissimus, ventrally by the upper border of the obliquus abdominis internus, and
in front by the last rib.

THE PERITONEUM =

The peritoneum is the thin serous membrane which lines the abdominal cavity
and the pelvic cavity (in part), and covers to a greater or less extent the viscera
contained therein. In the male it is a completely closed sac, but in the female
there are two small openings in it ; these are the abdominal orifices of the uterine
or Fallopian tubes, which at their other ends communicate with the uterus, and so
indirectly with the exterior. The peritoneal cavity (Cavum peritonsei) is only a
potential one, since its opposing walls are normally separated only by the thin
film of serous fluid (secreted by the membrane) which acts as a lubricant.^

The free surface of the membrane has a glistening appearance and is very
smooth. This is due to the fact that this surface is formed by a layer of flat mes-

^ This method of division, although long in use, is practically valueless for accurate descrip-
tion. It is mentioned here chiefly liecause agreement on a more useful topographic method has
not been arrived at.

^ Only a general account of the arrangement of the peritoneum is given in this section, since
a detailed description cannot be understood without a knowledge of the viscera concerned.

^ It is necessary not to confuse the peritoneal cavity with the abdominal cavity. The
organs are all extraperitoneal and the peritoneal cavity contains only the serous fluid.

412

DIGESTIVE SYSTEM OF THE HORSE

othelial cells, and is moistened by the peritoneal fluid. Friction is thus reduced
to a minimum during the movements of the viscera. The outer surface of the peri-
toneum is related to the subserous tissue, which attaches it to the abdominal wall
or the viscera.

In order to understand the general disposition of the peritoneum, we may-
imagine the abdominal cavity to be empty and lined by a simple layer of perito-
neum, termed the parietal layer (Lamina parietalis). We may further imagine
the organs as beginning to develop in the subserous tissue, enlarging, and migrat-
ing into the abdominal cavity to a varying extent. In doing so they carry the per-
itoneum before them, producing introversion of the simple sac, and forming folds
which connect them with the wall or with each other. The viscera thus receive
a complete or partial covering of peritoneum, termed the visceral layer (Lamina
visceraUs). The connecting folds are termed omenta, mesenteries, ligaments,
etc. They contain a varying quantity of connective tissue, fat, and lymph glands,

and furnish a path for the vessels and nerves of
the viscera. Some contain unstriped muscular
tissue. An omentum is a fold which passes from
the stomach to other viscera. There are three of
these, namely : (1) Thelesser omentum (Omentum
minus), ^ which passes from the lesser curvature of
the stomach to the liver; (2) the gastro-splenic
omentum (Ligamentum gastrohenale), which ex-
tends from the greater curvature of the stomach
to the spleen; (3) the greater omentum (Omen-
tum majus),- which passes from the greater curva-
ture of the stomach and from the spleen to the
terminal part of the great colon and the origin of
the small colon. It does not pass directly from
one organ to the other, but forms an extensive
loose sac (ligs. 377, 378). A mesentery (Mesen-
terium) is a fold which attaclies the intestine to
the dorsal wall of the abdomen. There are two
mesenteries in the horse: (1) The great mes-
entery connects the greater part of the small
intestine with the dorsal abdominal wall; (2)
the colic mesentery attaches the small colon to
the dorsal abdominal wall. Ligaments are folds
which pass between viscera other than parts of the
digestive tube, or connect them with the abdom-
inal wall. The term is also applied to folds which attach parts of the digestive tract
to the abdominal wall, but do not contain their blood-vessels and nerves. Some (e. g.,
the lateral and coronary ligaments of the liver) are strengthened by fibrous tissue;
others (e. g., the broad ligaments of the uterus) contain also unstriped muscular
tissue.

Fig. 350. — Diagrammatic Cross-section

OF Abdomen.

To show arrangement of peritoneum

when reduced to its simplest form. The

external black line indicates the body-wall.

1, Organ (e. g., kidney) in contact with wall;

2, organ (e. g., small intestine) at a dis-
tance from wall; 3, parietal peritoneum; 4,
4, visceral peritoneum; 5, mesentery; 6,
peritoneal cavity.

THE PELVIC CAVITY

The pelvis is the posterior part of the trunk. It incloses the pelvic cavity
(Cavum pelvis), which communicates in front with the abdominal cavity, the line
of demarcation being the terminal line or pelvic brim.

The dorsal wall or roof is formed by the sacrum and first three coccygeal
vertebrae. The lateral walls are formed by the parts of the iha behind the ilio-

' Also known as the gastro-hepatic omentum.
^ Also known as the gastro-colic omentum.

THE PELVIC CAVITY

413

pectineal lines and the sacro-sciatic ligaments. The ventral wall or floor is formed
by the pubic and ischial bones. The boundary of the outlet is formed by the third
coccygeal vertebra dorsally, the ischial arch ventrally, and the posterior edges
of the sacro-sciatic ligaments and the semi-
membranosus muscles laterally. The out-
let is closed by the perineal fascia ; this con-
sists of superficial and deep layers which
are attached around the margin of the outlet
and centrally to the organs at the outlet —
the anus and its muscles, the vulva (in the
female), and the root of the penis (in the
male).

The cavity contains the rectum, parts
of the internal genital and urinary organs,
some foetal remnants, muscles, vessels, and
nerves. It is lined by the fascia pelvis, and
in part by the peritoneum.

The pelvic peritoneum is continuous in
front with that of the abdomen. It lines the
cavity for a variable distance backward, and
is then reflected on to the viscera, and from

one organ to another. We may therefore distinguish an anterior, peritoneal, and a
posterior, retroperitoneal, part of the cavity. Along the mid-dorsal line it forms
a continuation of the colic mesentery, the mesorectum, which attaches the first or
peritoneal part of the rectum to the roof. In animals in fair condition a consider-

FiG. 351. — Diagram of Sagittal Section op
Male Pelvis to show Disposition op
Peritoneum.
a, Sacro-rectal pouch, continuous laterally with

b, recto-genital pouch; c, vesico-genital pouch; d,

vesico-pubic pouch. The lateral Une of reflection

of the peritoneum is dotted.

Fig. 352. — Schematic Cross-section to Show Ar- Fig. 353. — Schematic Cross-section to Show Ar-

rangement of Pelvic Peritoneum in the Male. rangement of Pelvic Peritoneum in the Female.

o, b. Recto-genital pouch; c, c, vesico-genital pouch; d, d, vesico-pubic pouch; 1, mesorectum; 2, 2, genital folds
in male, broad ligaments ot uterus in female; 3, 3, lateral ligaments of bladder; 4, middle hgament of bladder; v.d.,
ductus deferentes; u.m., uterus masculinus.

able quantity of subserous and retroperitoneal fat is found on the walls and in the
various interstices.

In the male the general disposition of the peritoneum here is as follows. If
traced along the dorsal wall, it is reflected from the sacrum on to the rectum,

414

DIGESTIVE SYSTEM OF THE HORSE

forming the visceral peritoneum for the first part of that tube.^ Laterally it is
reflected in a similar fashion. If the rectum be raised, it will be seen that the
peritoneum passes from its ventral surface and forms a transverse fold which lies
on the dorsal surface of the bladder (Fig. 370). This is the genital fold (Plica
genitalis). Its concave free part passes on either side into the inguinal canal.
The ventral layer of this fold is reflected on to the dorsal surface of the bladder.
Thus there is formed a pouch between the rectum and bladder — the recto-vesical
pouch (Excavatio recto- vesicalis), which is partially subdivided by the genital
fold into recto-genital and vesico-genital cavities. The fold contains the ductus
deferentes, part of the vesiculae seminales, and the uterus masculinus (a foetal
remnant). If the bladder is now raised, it is seen that the peritoneum passes

Left extremity

Antrum pyloricum

Fig. 354. — Stomach op Horse; Parietal Surface.

The organ was fixed in situ when well tilled. The lesser curvature has been opened up slightly and the peritoneum,

etc., in this vicinity removed. The larger branches of the anterior gastric artery and vein are visible.

from its ventral surface on to the pelvic floor, forming centrally the median um-
bilical fold or middle ligament of the bladder (Plica umbilicalis media). It also
passes from each side of the bladder to the lateral pelvic wall and forms thus
the lateral umbilical fold or ligament of the bladder (Plica umbilicalis lateralis) ;
this contains in its edge the so-called round ligament of the bladder (Ligamentum
teres vesicse) — the partially occluded umbilical artery, which is a large vessel
in the foetus.^

In the female the arrangement is modified by the presence of the uterus;

^ The point at which the reflection takes place is quite variable, and apparently depends
chiefly on the amount of feces in the rectum. When the bowel is very full the reflection may be
little behind the promontory; when it is empty, the reflection may l)e at the posterior end of the
sacrum.

^ In the foetus and new-born foal these three folds extend to the umbilicus in conformity with
the abdominal position of the bladder. When the latter becomes a pelvic organ, the lateral folds
conform to the change and end at the vertex of the bladder. The median fold may still be trace-
able to the umbilicus.

THE STOMACH

415

the genital fold is enlarged, so as to inclose the uterus and a small part of the vagina.
It forms two extensive folds, the broad ligaments of the uterus (Ligamenta lata
uteri), which attach that organ to the sides of the pelvic cavity and the lumbar
part of the abdominal wall (Pig. 530). It thus divides the recto-vesical pouch
completely into dorsal and ventral compartments — the recto-genital pouch (Ex-
cavatio recto-uterina) and the vesico-genital pouch (Excavatio vesico-uterina).
Further details will be given in the description of the pelvic viscera.

THE STOMACH

The stomach (Ventriculus) is the large dilatation of the alimentary canal
behind the diaphragm ; it intervenes between the oesophagus and the small intestine.
It is a sharply curved, U-shaped sac, the right part being, however, much shorter

Saccus cwcus
{left extremity)

Aim of attachment to dia-
phragm {non-peritoneal)

Fig. 355. — Stom.'^ch op Horse; Visceral Surface, with First Part of Duodenum.
Fixed in situ when full but not distended. The posterior gastric artery and its larger branches with two satellite veins

than the left one. The convexity is directed ventrally. When moderately dis-
tended, there may be a shght constriction which indicates the division into right
and left sacs. It is relatively small, and is situated in the dorsal part of the ab-
dominal cavity, behind the diaphragm and hver, mainly to the left of the median
plane.

It presents for description two surfaces, two curvatures, and two extremities.
The parietal surface (Facies parietalis) is convex and is directed forward, u]iward,
and toward the left ; it lies against the diaphragm and liver. The visceral surface
(Facies visceralis), also convex, faces in the opposite direction; it is related to the
terminal part of the large colon, the pancreas, the small colon, the small intes-

416

DIGESTIVE SYSTEM OF THE HORSE

tine, and the greater omentum. The borders between these surfaces are
termed the curvatures. The lesser curvature (Curvatura ventricuh minor)
is very^ short, extending from the termination of the oesophagus to the junc-
tion with the small intestine. When the stomach is in situ, its walls are here in
contact, and the cardia and pylorus close together.^ The greater curvature (Cur-
vatura ventriculi major) is very extensive. From the cardia it is first directed
dorsally and curves over the left extremity; it then descends, passes to the right,
crosses the median plane, and curves upward to end at the pylorus. Its left part
is related to the spleen, while its ventral portion rests on the left parts
of the great colon. The left extremity (Extremitas sinistra) has the form of a
rounded cul-de-sac termed the saccus caecus ; it lies ventral to the left crus of the
diaphragm, and so beneath the dorsal part of the sixteenth and seventeenth ribs.
It is related to the pancreas and the termination of the great colon behind and the
base of the spleen laterally. The right or pyloric extremity (Extremitas dextra)

is much smaller and is continuous w^ith
the duodenum, the junction being in-
dicated by a marked constriction. It
lies just to the right of the median
plane, and about two inches (ca. 5 cm.)
lower than the cardia; it is in contact
with the visceral surface of the liver.
About two or three inches (ca. 5 to 8
cm.) from the pylorus there is a con-
striction which marks off the antrum
pyloricum from the rest of the right
sac. The oesophageal orifice is termed
the cardia; it is situated at the left
end of the lesser curvature, but about
eight to ten inches (ca. 20 to 25 cm.)
from the left extremity.^ The oesopha-
gus joins the stomach very obliquely.
The opening is closed by the sphincter
cardiae and numerous folds of mucous
membrane. The pylorus is the open-
ing into the intestine. Its position is
indicated externally by a distinct con-
striction. Internally it presents a cir-
cular ridge caused by a ring of mus-
cular tissue — the sphincter pylori.

The stomach is held in position
mainly by the pressure of the sur-
The following peritoneal folds connect

Fig. 356. — ^Everted Stomach of Horse from which
THE Mucous Membrane has been Removed.
O, (Esophagus; D, duodenum; 6, circular layer;
c', internal oblique fibers; c", loop around cardia; c'",
transition of internal to external oblique fibers; d, fibers
connecting the two branches of the cardiac loop; p,
antral sphincter; p', pyloric sphincter. (EUenberger-
Baum, Anat. d. Haustiere.)

rounding viscera and by the oesophagus,
it with the adjacent parts:

1. The gastro-phrenic ligament (Lig. gastrophrenicum) connects the greater
curvature, from the cardia to the left extremity, with the crura of the diaphragm.
This leaves a narrow area uncovered with peritoneum, and here the stomach is
attached to the diaphragm by areolar tissue.

1 The more expressive term "incisiira angularis" has been suggested and is worthy of adop-
tion.

2 The position of the cardia varies of course vnth the excursion of the diaphragm. It is
usually an inch or more (ca. 3 cm.) to the left of the median plane and ventral to the vertebral end
of the fourteenth rib. When the diaphragm is contracted the cardia may be six inches (ca. 15 cm.)
below the level of the spine; when the diaphragm is relaxed, the interval may be reduced to about
two inches (ca. 5 cm.).

THE STOMACH 417

The use of the term ligament in regard to the arrangement here is somewhat misleading,
since the stomach is attached to the crus of the diaphragm by areolar tissue; the peritoneum
passes from the diaphragm to the stomach on each side of the area of adhesion. In soft material
there is the appearance of a Ugament composed of two layers of peritoneum, but this is an artefact.

2. The lesser omentum (Omentum minus) connects the lesser curvature and
the first part of the duodenum with the hver below the oesophageal notch and the
portal fissure.

The part of the omentum which extends from the liver to the stomach is designated the lig.
hepato-gastricum, and the remainder which goes to the duodenum as the lig. hepato-duodenale.

3. The gastro-splenic omentum (Lig. gastrolienale) passes from the left part
of the greater curvature to the hilus of the spleen; it is continuous ventrally with
the greater omentum.

4. The greater omenttmi (Omentum majus) connects the ventral part of the
greater curvature and the first curve of the duodenum with the terminal part of the
great colon and the initial part of the small colon. It does not pass directly between
these parts but forms a large sac, which will be described later.

5. The gastro-pancreatic fold (Plica gastropancreatica) extends from the left
sac above the cardia to the duodenum. It is attached dorsally to the liver and
vena cava, ventrally to the pancreas.

The stomach of the equidse is relatively small, its capacity varying from two
to four gallons (ca. 8 to 15 liters).

The size, form, and position of the stomach are subject to considerable variation. WTien
the stomach is nearly empty, the saccus csecus contains only gas and is strongly contracted; the
middle part (physiological fundus) contains the ingesta and preserves its rounded character,
while the pyloric part is contracted. In this state coils of small intestine usually lie ventral to the
stomach and may separate it entirely from the colon. In exceptional cases, when the organ is
empty and contracted, even the pyloric end is to the left of the median plane. When distended,
the middle part settles down some four or five inches, pushing back coils of the small intestine
which may lie between the greater curvature and the large colon, and also pusliing to one side the left
dorsal part of the great colon ; the spleen, small colon, and small intestine are pushed back by the
disteiltion of the left sac. When the stomach is moderately full, its most ventral part lies opposite
to the ninth intercostal space and tenth rib, about a handbreadth above the level of the left costal
arch.

Structure. — The wall is composed of four coats— serous, muscular, submucous,
and mucous. The serous coat (Tunica serosa) covers the greater part of the organ
and is closely adherent to the muscular coat except at the curvatures. It partially
bridges over the lesser curvature, and covers here elastic tissue which assists in
retaining the bent form of the stomach. The peritoneal folds have been described.
The muscular coat (Tunica muscularis) consists of three incomplete layers, an
external of longitudinal, a middle of circular, and an internal of oblique fibers. The
layer of longitudinal fibers (Stratum longitudinale) is very thin and exists only
along the curvatures and at the antrum. It is not present on the saccus csecus,
and about the middle of the greater curvature it is almost entirely replaced by
elastic fibers to the antrum pylori. At the lesser curvature it is continuous with the
longitudinal fibers of the oesophagus. On the antrum pylori it forms a well-de-
veloped complete layer which is separate from that of the curvatures. The layer
of circular fibers (Stratum circulare) exists only on the glandular part. At the
pyloric orifice it forms a thick ring — the pyloric sphincter (Sphincter pylori).
Another ring, the antral sphincter, is found at the left end of the antrum pylori.
The oblique fibers (Fibrse obliquse) are arranged in coarse bundles in two layers.
The external stratum covers the left sac and is largely a continuation of the longi-
tudinal fibers of the oesophagus. The internal stratum is found also on the left
sac; it is continuous with the circular fibers of the oesophagus and stomach and
exchanges fibers with the external oblique layer. It forms a remarkable loop
around the cardiac orifice, constituting a powerful cardiac sphincter (Sphincter
cardise). The submucous coat (Tela submucosa) is a layer of loose connective
27

418

DIGESTIVE SYSTEM OF THE HORSE

Saccus ccEcus
(left extremity)

(Ewphagcal region

Diverticulum duodeni

Fundus
gland
region

Pylorus
Pyloric gland region

-Frontal Section of Stomach and First Part of Duodenum op Horse.
C, Cardiac orifice. Photograph of specimen fixed in situ.

tissue which connects tlie muscular and mucous coats; in it the vessels and nerves
ramify before entering the mucosa. The mucous coat (Tunica mucosa) is clearly-
divided into two parts. That which
lines the greater part of the left sac re-
sembles the oesophageal mucous mem-
brane, and is termed the oesophageal
part (Pars oesophagea). It is white in
color, destitute of glands, and covered
with a thick, squamous, stratified epi-
thelium. At the cardiac orifice it pre-
sents numerous folds which occlude the
opening. '^ It terminates abruptly, form-
ing an irregular, sinuous, raised edge,
termed the margo plicatus (or cuticular
ridge). Below and to the right of this
line the mucous membrane has a totally
different character, being soft and vel-
vety to the touch, and covered by a mu-
coid secretion. It contains the gastric
glands (Glandulae gastricse), and is there-
fore termed the glandular part (Pars glandularis) . It is subdivided into three zones
according to the types of glands which it contains, but no distinct lines of demar-

1 This occlusion is usually so complete that distention of the stomach by air or fluid forced
in through the pylorus may be carried far enough to rupture the stomach without ligating the
oesophagus.

Fig. 358.

-Diagram of Zones of Mucous Membrane
OF Stomach of Hohsk.

THE SMALL INTESTINE 419

cation exist. A narrow zone next to the margo plicatus has a yellowish-gray color,
and contains short tubular cardiac glands (cardiac gland region) . Next to this is a
large area which has a mottled, reddish-brown color, and contains fundus glands
(fundus gland region) ; these glands have two distinct types of cells. This part of
the mucous membrane is thick and very vascular, and corresponds to the fundus
of the stomach in man and the dog. The remainder of the mucous membrane is
thinner, has a reddish-gray or yellowish-gray color, and contains pyloric glands,
which have a single type of cells corresponding to the chief cells of the fundus glands
(pyloric gland region) ; it corresponds to the pyloric portion of man and the dog.
The folding of the stomach wall at the lesser curvature produces a prominent
ridge which projects into the cavity of the stomach. The circular fold which
covers the pyloric sphincter is termed the pyloric valve (Valvula pylori).

The oesophageal part constitutes one third to two-fifths of the mucous membrane. The
cardiac gland region is extremely narrow (ca. 0.5 to 1 mm.) at the greater curvature, but becomes about
an inch wide toward the pyloric part. Since the majority of the glands here are not typical
cardiac glands, like those of the pig and other animals, but are intermediate in type between these
and pyloric glands, the term intermediate zone might well be used.

Vessels and Nerves. — The stomach receives blood from all the branches of
the cceliac artery. The gastric veins drain into the portal vein. The Ijmiph
vessels go chiefly to the gastric lymph glands, thence to the cisterna chyli. The
nerves are derived from the vagus and sympathetic nerves.

THE SMALL INTESTINE

The small intestine (Intestinum tenue) is the tube which connects the stomach
with the large intestine. It begins at the pylorus and terminates at the lesser
curvature of the csecum. Its average length is about seventy feet (ca. 22 meters),
and when distended its diameter varies from three to four inches (7.5 to 10 cm.).
Its capacity is about twelve gallons (40 to 50 liters).

It is clearly divisible into a fixed and a mesenteric part. The fixed part is
termed the duodenum, while the mesenteric part (Intestinum tenue mesenteriale)
is arbitrarily divided into parts termed the jejimum and ileum. ^

The duodenum is about three to four feet (ca. 1 m.) long. Its shape is
somewhat like a horseshoe, the convexity being directed toward the right. The
first part (Pars prima duodeni) is directed to the right and forms an po-shaped
curve. The convexity of the first part of the curve is dorsal, of the second, ventral.
It is in contact with the middle and right lobes of the liver, and presents two am-
pullae with a constriction between them. The duodenal angle (or head) of the
pancreas is attached to the concavity of the second curve, and here, five to six
inches (ca. 12 to 15 cm.) from the pylorus, the pancreatic duct and the bile duct
pierce the bowel Avail. The second part (Pars secunda duodeni) passes upward
and backward on the right dorsal part of the colon and ventral to the right lobe of
the liver, and, on reaching the right kidney and the base of the csecum, it curves
toward the median plane, opposite the last rib. The third part (Pars tertia duo-
deni) passes from right to left behind the attachment of the base of the csecum,
crosses the median plane behind the root of the great mesentery, and turns forward
to become continuous with the mesenteric part under the left kidney.- The sac-
culations of the first part have a diameter of three to four inches (ca. 7.5 to 10 cm.).
It is attached by a short peritoneal fold termed the mesoduodenum. This fixes

^ No natural line of demarcation exists, but there is a marked increase of the thickness of
the wall toward the terminal part. Other differences will be noted in the further description.

2 The duodenum commonly curves around the periphery of the right kidney, from which it
is separated by the base of the caecum, but in some cases it is in contact with the ventral surface
of the kidney. It may cross the median plane ventral to the second lumbar vertel)ra or further
back, depending apparently on the fulness of the csecum.

420

DIGESTIVE SYSTEM OF THE HORSE

the first part of the duodenum closely to the liver and the right dorsal part of the
colon; the remainder is somewhat less closely attached by it to the base of the
caecum and right kidney, the sublumbar muscles, and (more closely) to the terminal
part of the great colon and the first part of the small colon. ^

The mesenteric part, or jejuno-ileum, has been conventionally subdivided into
the jejunum and ileum, but no distinct point exists at which to make the demarca-
tion. With the exception of the origin and the last two or three feet, the mesen-
teric part of the intestine varies so much in position that only a general statement
can be made. It lies in numerous coils, mingled with those of the small colon,
chiefly in the dorsal part of the left half of the abdomen, from the visceral surface
of the stomach to the pelvis. It may insinuate itself between the left parts of the
colon and the abdominal wall ; also between the ventral parts of the colon, reaching

Fig. 359. — Topography of Viscera of Mare; Left View.
I.R., First thoracic vertebra; I.L., first lumbar vertebra; 2.K., second sacral spine; S., scapula; A., humerus;
St., sternum; B., ilium; O., femur; L., lung in complete expiration; L, dotted line indicating contour of lung in in-
spiration; //..pericardium; Z., costal part of diaphragm; Z'., tendinous center of diaphragm; i.A'^., left kidney; l.v.C,
lelt ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of colon; D., small intestine; M., small
colon; Af'., rectum; o, coccygeus muscle; 6, retractor ani; c, c, sphincter ani externus; rf, constrictor vulvae; e, sacro-
coccygeus ventralis; /, anterior gluteal artery; g, internal pudic artery; h, abdominal wall in section. (After Ellen-
berger, in Leisering'a Atlas, reduced.)

the floor of the abdomen. In some cases coils of it lie against the right flank when
the caecum contains little material. The terminal part of the intestine (ileum)
passes to the medial (left) surface of the caecum and joins the lesser curvature of
its base. The average diameter of the jejuno-ileum is about two and a half to three
inches (ca. 6 to 7 cm.). In the cadaver one often finds much of the tube presenting
irregular constricted and dilated parts which are not to be regarded as permanent
conditions. The last three or four feet (ca. 1 m.) are usually tightly contracted,
resembling somewhat the terminal part of the oesophagus. This part may be termed
the ileum.

The mesenteric part is connected with the dorsal abdominal wall by the great
mesentery. This is a wide, fan-shaped fold, consisting of two layers of peritoneum,

1 It will be noticed that the mesoduodenum is not continuous with the great mesentery, but
ends by a free edge. The mesentery begins on the opposite surface of the end of the duodenum,
so that the bowel is attached by two peritoneal folds at this point.

THE SMALL INTESTINE

421

between which the vessels and nerves reach the bowel ; it also contains the mesen-
teric lymph glands and some fat. The visceral border of the mesentery contains
the intestine, while the parietal border or root of the mesentery (Radix mesenterii)
is attached to a small area around the great mesenteric trunk under the first and
second lumbar vertebrae. The root is thick, as it contains a large number of vessels
and nerves placed close together. The mesentery is short at first, but soon reaches
a length of one and a half to two feet (ca. 50 cm.) — sufficient to allow coils of the
intestine to reach the abdominal floor, the pelvic cavity, or even to descend into
the scrotum through the inguinal canal. Near its termination the intestine leaves
the border of the mesentery, so that the latter has a free edge which passes to the
caecum. Thus there is formed the ileo-caecal fold (Plica ileocaecalis), which at-
taches the ileum to the lesser curvature of the caecum.

Structure. — The wall consists of four coats — serous, muscular, submucous, and
mucous. The serous coat is complete except at the mesenteric edge, where the
vessels and nerves reach the bowel. The muscular coat consists of an external
longitudinal and an internal circular layer, the latter being the thicker. In the
last few feet of the intestine the muscular coat is very thick, and being usually
firmly contracted in the dead subject, gives the impression that this part of the bowel
is of smaller caliber; such, however, is
not the case during life. The sub-
mucous coat is a layer of areolar tissue
in which the vessels and nerves ram-
ify. It contains also the duodenal
glands and the bases of the solitary
and aggregated lymph nodules. The
mucous membrane is soft and vel-
vety. It has a grayish or yellowish-
red color and is very vascular. About
five or six inches from the pylorus it
forms a pouch, the diverticulum duo-
deni, in which the pancreatic and he-
patic ducts open. On a small papilla
nearly opposite this is the termina-
tion of the accessory pancreatic duct.
At the ileo-caecal opening the mucous
membrane projects slightly into the

cavity of the caecum, forming the ileo-caecal valve. The free surface is thickly
beset with villi, small projections of the mucous membrane which can be seen well
by placing a piece of the membrane in water. They are relatively short and thick
in the horse. Each contains a central lymph-vessel (lacteal), and around this a
plexus of capillaries, lymphoid tissue, and unstriped muscle-fibers. They are im-
portant agents in absorption from the contents of the intestine. The epithelium
is columnar, with many gol^let cells. Underneath the basement membrane is a
layer of unstriped muscle-fibers, the muscularis mucosae. The glands of the small
intestine are of two kinds ; their secretion is termed the succus entericus.

1. The intestinal glands (Glandulae intestinales) are present throughout. They
are simple tubular glands which open between the villi.

2. The duodenal glands (Glandulae duodenales)i are present in the first
twenty feet or more (ca. 6 to 7 m.) of the bowel. They are branched tubulo-
alveolar glands, and are situated in the submucosa, so that their ducts perforate
the muscularis mucosae and the mucous membrane.

1 These were formerly known as Brunner's glands, but in the B. N. A. are termed glandulse
duodenales. On account of their extension beyond the duodenum and their submucous position,
Ellenberger has suggested the name glandulse submucosse.

Diverticulum
duodeni

Fig. 360. — Diagram of Section of Diverticulum duo-
deni OF Horse.
Solid line indicates mucous membrane; muscular and serous
layers are not shown.

422

DIGESTIVE SYSTEM OF THE HORSE

Lymphoid tissue occurs in the form of distinct nodules (NoduH Ijonphatici),
which are either scattered or in groups. In the former case they are termed solitary
nodules (NocUiU lymphatici soHtarii), in the latter aggregated nodules or Peyer's
patches (Noduli IjTnphatici aggregati). The solitary nodules are about the size of
a millet-seed or a small sago grain. The patches are situated chiefly along the
surface opposite to the mesenteric attachment and begin about three or four feet
from the pylorus. They number one to two hundred, and are usually one to two
inches (2 to 5 cm.) long and a quarter of an inch to one-half inch (ca. 2 to 14 mm.)
wide. Larger ones occur in the terminal part, where one patch may have a length
of seven to fifteen inches (ca. 17 to 38 cm.) and a width of half an inch to one inch
(ca. 5 to 25 mm.) in young horses (Ellenberger) . They vary much in number,
size, and distribution in different individuals, and undergo atrophy in old subjects.

Vessels and Nerves. — The arteries of the small intestine come from the
coeliac and anterior mesenteric arteries. The veins go to the portal vein. The
Ijmiph-vessels are numerous and go to the mesenteric lymph glands, thence to the

Fig. 361. — Large and Small AggrSg.^ted N

OR Peyer's Patche.s of Small Intestine of Horse.

cisterna chyli. The nerves are derived from the A'-agus and sympathetic through
the cceliac plexus.

THE LARGE INTESTINE
The large intestine (Intestinum crassum) extends from the termination of the
ileum to the anus. It is about twenty-five feet (ca. 7.5 to 8 m.) in length. It
differs from the small intestine in its greater size, in being sacculated for the most
part, possessing longitudinal bands, and having a more fixed position. It is divided
into caecum, great colon, small colon, and rectum.

The Cecum

The caecum (Intestinum caecum) is a great cul-de-sac intercalated between the

small intestine and the colon. It has a remarkable size, shape, and position in the

horse. Its average length is about four feet (ca. 1.25 m.), and its capacity about

seven to eight gallons (ca. 25 to 30 liters).^ It is conical in form, and is curved

1 The length given here is measured from end to end along the side and midway between the
curvatures.

THE C^CUM

423

somewhat like a comma. It is situated chiefly to the right of the median plane,
extending from the right iliac and sublumbar regions to the abdominal floor behind
the xiphoid cartilage. Both extremities are blind, and the two orifices are placed
close together on the concave curvature. It presents for description a base, a body,
and an apex. The base (Basis caeci s. Saccus csecus) extends forward on the right
side as far as the fourteenth or fifteenth rib, about a handbreadth below its middle,
and backward to the tuber coxae. ^ It is strongly curved, the greater curvature
being dorsal, the lesser ventral; connected with the latter are the termination of
the ileum and the origin of the colon. The rounded blind end is directed ventrally.
The body (Corpus caeci) extends downward and forward from the base and rests
largely on the ventral wall of the abdomen. Its lesser curvature is about parallel

Fig. 362. — Cecum of Horse; Left View.
-4. c, apex; I, ileum; 1, 2, longitudinal bands; 3, ileo-csecal fold,
lymph glands have been removed to expose the medial band (1).

with the costal arch and some five to six inches (10 to 15 cm.) ventral to it. The
apex (Apex caeci) lies on the abdominal floor, usually to the right of the median
plane, and about a hand's length behind the xiphoid cartilage.

The right or parietal surface of the caecum is related chiefly to the right ab-
dominal wall, the diaphragm, duodenum, and liver. The left or visceral surface lies
against the left and terminal parts of the colon, the root of the great mesentery,
and the small intestine.

The base is attached dorsally by connective tissue and peritoneum on the
ventral surface of the pancreas and right kidney, and a small area of the abdominal
wall behind these; it is attached medially to the terminal part of the great colon,
and ventrally to the origin of the great colon. The body is attached dorso-laterally

^ The forward extent of the base of the caecum is subject to some variation,
noted that the bhnd end is not the most anterior part.

It may be

424

DIGESTIVE SYSTEM OF THE HORSE

to the first part of the colon b}^ the caeco-colic fold. The apex is free, and conse-
quently may vary in position. — ■ — —

The csecmn has four longitudinal bands (Taeniae cseci), situated on the dorsal,
ventral, right, and left surfaces; these cause four rows of sacculations (Haustra).

The ventral band is almost entirely exposed or free (Taenia libera) ; it begins on the highest
part of the base, extends along the mecUal side of the greater curv'ature, and joins the medial band
near the apex. It is concealed only at its origin where the bowel is attached to the wall. The
dorsaJ band extends along the lesser cur\-ature from the termination of the ileum to the apex.
The medial band extends along the medial part of the lesser curvature of the base, inchnes
ventrally further fonvard, and ends by joining the ventral band. It is covered at its origin by the
adhesion to the right dorsal part of the great colon and beyond this by the csecal vessels and lymph
glands. Medial to the termination of the ileum it projects from the wall of the bowel as a falciform
band which can be felt distinctly although covered by vessels and fat. The lateral band is
continuous with that of the right ventral part of the colon. It is covered by vessels, lymph glands
and fat, but can be felt in its posterior part, where it forms a concave projecting edge. It inclines
ventrally in front and may extend to the apex or fade out without reaching it.

Fig. 303. — Orifices of C^cum of Horse.
1, Ileo-cacal orifice; 2, cseco-colic orifice; 3, intervening fold.

The ileo-caecal orifice (Ostium ileocsecale) is situated in the lesser curvature of
the base, about two or three inches (ca. 5 to 7.5 cm.) to the right of the median
plane, and in a transverse plane through the first or second lumbar vertebra. The
end of the ileum is partially telescoped into the caecum, so that the orifice is sur-
rounded by a fold of mucous membrane which encloses a thick circular muscular
layer, the sphincter ilei.

The caeco-colic orifice (Ostium caecocolicum) is lateral to the preceding one;
the interval between them is only about two inches (ca. 5 cm.), and they are separ-
ated by a large fold which projects into the interior of the caecum. The orifice is
small in relation to the size of the caecum and colon. It is slit-like, or has a narrow
oval outline, and is about two inches (ca. 5 cm.) long. It has a thick valvular fold
(Valvula csecocolica) at its ventral margin and is encircled by a muscular ring, the
sphincter caeci.^ Large crescentic or semilunar folds (Plicae caeci) project into the
cavity of the bowel, and between these are large pouches (Cellulae caeci).

^ The anatomical arrangement gives no support to the view which is sometimes expressed
that ingesta may pass directly from the ileum to the colon.

THE GREAT COLON

425

It is somewhat difficult to get a correct idea of the csecal orifices. The csecum is sharply-
curved here and a large fold projects into its interior, somewhat like a shelf, and separates the two
orifices. The ileo-cscal orifice faces chiefly dorsally, while the cseco-colic orifice faces forward
into the csecum.

The Great Colon
The great colon (Colon crassum) begins at the cseco-coUc orifice, and terminates
by joining the small colon behind the saccus csecus of the stomach. It is ten to
twelve feet (ca. 3 to 3.7 m.) long, and its average diameter (exclusive of its narrowest
part) is about eight to ten inches (ca. 20 to 25 cm.). Its capacity is more than
double that of the csecum. When removed from the abdomen, it consists of two
parallel parts, which are connected by peritoneum and partially by areolar and
muscular tissue also. In situ it is folded so that it consists of four parts, which are
designated according to their position or numerically. The three bent connecting
parts are termed the flexures. The first part, the right ventral colon (Colon ventrale
dextrum), begins at the lesser curvature of the base of the csecum, about opposite
the ventral part of the last rib or intercostal space. "^ It forms an initial curve, the

Origin of small colon

Diaphragmatic
flexure

Ileum
Fig. 364. — Diagram of Cecum and Large Colon op Horse.

convexity of which is directed upward and backward; this part is in contact with
the upper part of the right flank. It then passes downward and forward along the
right costal arch and then along the floor of the abdomen. ^ Over the xiphoid
cartilage it bends sharply to the left and backward, forming the sternal flexure
(Flexura sternalis s. diaphragmatica ventralis). The second part, the left ventral
colon (Colon ventrale sinistrum), passes backward on the abdominal floor, to the left
of the first part and the csecum and, on reaching the pelvic inlet, bends sharply
dorsally and forward, forming the pelvic flexure (Flexura pelvina) . This is continued
by the third part, the left dorsal colon (Colon dorsale sinistrum), which passes
forward dorsal or lateral to the left ventral part, and on reaching the stomach,
diaphragm, and left lobe of the liver, turns to the right, forming the diaphragmatic
flexure (Flexura diaphragmatica dorsalis). The fourth part, the right dorsal colon
(Colon dorsale dextrum), passes backward dorsal to the first part, and on reaching

1 The position of the origin of the great colon is variable, and one may easily get a wrong
impression on account of the peculiar arrangement of the bowel here. The colon usually presents
a saccular dilatation at the lesser curvature of the base of the cajcum, which may be mistaken for
its origin. The real origin is a constricted part or neck anterior to the sacculation. Thus the
colon passes at first backward and then curves sharply downward and forward. Schmaltz has
proposed the name "vestibulum coli" for this sacculation.

426

DIGESTIVE SYSTEM OF THE HORSE

Fig. 365. — Topography of Viscera of Horse; Right View.
IR., First thoracic vertebra; IL., first lumbar vertebra; 2K., second sacral spine; S., scapula; A., humerus;
S<., sternum; B., ilium; O., femur; L., right lung; 77., pericardium; Z., diaphragm (pars costalis); r.jj.C, right ven-
tral colon; V.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of colon; C, body, C, base, C"., apex, of caecum;
D., small intestine; F., pelvic flexure of colon; M., rectum; a., abdominal wall in section; b, duodenum; c, coccygeus
muscle; d, retractor ani; e, e, sphincter ani externus; /, anterior gluteal artery; g, internal pudic artery; h, xiphoid
cartilage. The origin of the colon would be above the blind end of the base of the caecum marked C". (After Ellen-
berger, in Leisering's Atlas.)

Fig. 366. — Topography of Viscera of Horse; Right Side, Deeper View.
I.R., First thoracic vertebra; I.L., first lumbar vertebra; 2.K., second sacral spine; .S., scapula; A., humerus;

B, ilium; O., femur; Sc/j., pubis; Si., ischium; St., sternum; L., right lobe of liver; r.N., right kidney; C, body,

C, base, C"., apex of caecum; r.v.C, right ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of
colon; r.d.C, right dorsal colon; F., pelvic flexure of colon; D., small intestine; H., urinary bladder; M., rectum;
a, left ventricle; a', right ventricle; 6, 6', right coronary artery; c, left atrium; c', right atrium; d, left coronary artery,
circumflex branch; e, vena azygos; /, anterior vena cava; g, posterior vena cava; h, sinus venosus; i, right phrenic
nerve; ^•, right vagus, with its dorsal (fc') and ventral (fc") divisions; Z, aorta; m, cEsophagus; 7i, trachea; o, diaphragm
(median section); p, right lateral ligament of liver; q, duodenum; r, dotted line indicating position in median section
of diaphragm in inspiratorj' phase; s, recto-coccygeus muscle; t, suspensory ligament of rectum; u, sphincter ani; v,
vesicula seminalis; m), prostate; x, bulbo-urethral gland; j/, urethra; s, abdominal wall; z', xiphoid cartilage. (After
EUenberger, in Leisering's Atlas, reduced.)

THE GREAT COLON

427

the medial surface of the base of the caecum it turns dorsally and to the left behind
the left sac of the stomach; here it becomes constricted, and joins the small colon
below the left kidney.

The sternal flexure extends forward to a point opposite to the ventral part of the seventh rib,
and the diaphragmatic flexure as far as the sixth intercostal space on the right of the median plane.

The caliber of the great colon

greatly at different points. At its origin

Fig. 367. — ^Abdominal Viscera of Horss; Ventral View.
The ventral wall and part of the lateral walls of the abdomen are removed. C, Csecum; r.v.C, right ventral
part of colon; v.Q., sternal flexure of colon; [l.v. C, left ventral part of colon; d.Q., diaphragmatic flexure of colon;
D., small intestine; M., small colon; a, ventral free band of caecum; 6, medial band of caecum; c, lateral band of ventral
part of colon d, ventral band of ventral part of colon; e, point of elbow; /, anterior end of sternal region; g, xiphoid
eartilage; h, teats. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)

it is only about two to three inches (ca. 5 to 7.5 cm.) in diameter.^ This soon
increases to about eight to ten inches (ca. 20 to 25 cm.) for the ventral parts.
Beyond the pelvic flexure the diameter is reduced to about three or four inches
(ca. 8 to 9 cm.). Toward the diaphragmatic flexure the caliber rapidly increases, and
reaches its maximum in the last part, where it forms a large sacculation, which may
1 Usually there is a sacculation of considerable size which succeeds the constricted origin.

428

DIGESTIVE SYSTEM OF THE HORSE

have a diameter of about twent}- inches (50 cm.). This is succeeded bj; a funnel-
shaped terminal contraction.

The right ventral part of the great colon is attached to the lesser curvature of
the caecum by two layers of peritoneum which form the caeco-colic fold (Plica
csecocolica). The right parts are united by peritoneum on either sde and also by
areolar tissue and muscular fibers, the surface of contact being about four or five
inches (ca. 10 to 12 cm.) -wade; the left parts are attached to each other in a similar
fashion near the anterior flexures, but further back the connection is a peritoneal
fold which gradually becomes wide enough to allow them to be drawn apart about

six inches (ca. 15 cm.) near the peMc
flexure. The terminal part of the colon
is attached by peritoneum and areolar
tissue to the ventral surface of the pan-
creas dorsally and to the base of the
caecum laterally. It is connected in-
directl}^ with the diaphragm and hver
by means of a fold derived from the
right lateral ligament of the liver.

The relations are complex, but the
more important facts are as follows:
The ventral parts have extensive con-
tact with the abdominal wall ventrally
and laterally. On the right side the
colon is almost entirely excluded from
contact with the flank by the caecum;
on the left side it has no contact with
the upper part of the flank, being ex-
cluded here by coils of the small colon
and small intestine. Dorsally the chief
relations are to the stomach, duodenum,
liver, pancreas, small colon, small intes-
tine, aorta, posterior vena cava, and
portal vein. Since there are no trans-
verse attachments of the right and left
parts, and the latter have no attach-
ment to the wall, they are subject to
considerable displacement.^ The pel-
vic flexure is variable in position, but
usually it is directed against the poster-
ior part of the right flank or lies in the
right inguinal region.-

The longitudinal bands (Taeniae

coli) vary in number on the different

parts. The ventral parts have four bands. The pelvic flexure has a band along

its lesser curvature. The left dorsal colon has at first only one band, which is

a continuation of the preceding one; further fonvard two other bands appear, and

1 Abnormal displacement, e. g., torsion of the left parts, is not rare, and is liable to produce
death if not promptly reduced.

^ The length of the left parts varies and this appears partly to account for the differences to
be found in the arrangement of their posterior parts and the pehac flexure. In subjects in which
these parts of the colon are relatively long, their posterior ends are usually bent to the right across
the pelvic inlet so that the peh-ic flexure lies to the right of the inlet. In few cases the 'eft parts
of the colon seem relatively short and the pelvic flexure lies at the pehic inlet. Other dispositions
are encountered.

G. 368. — Posterior Portion of I-eft Parts of Colox

OF Horse; Dorsal View.
Left dorsal part; 2, left ventral part; 3, pelvic flexure.

THE SMALL COLON THE RECTUM 429

the three are continued on the right dorsal part. The ventral parts have alternate
constrictions and sacculations (Haustra coli).

On the right ventral colon two bands are dorsal, and extend along the medial and lateral
sides of the attachment to the right dorsal colon. The medial one is covered by the colic vessels,
etc., and the lateral one is concealed entirely or almost entirely by the attachment to the right
dorsal part. A lateral band comes from the lesser curvature of the caecum and becomes ventral
at the sternal flexure; it is free. The ventral band is also free. On the left ventral colon also two
bands are dorsal. Of these, the medial one is covered by the vessels and lymph glands and in the
anterior part also by the adhesion to the left dorsal part. At the pelvic flexure it is continued
along the concave face of the bowel to the left dorsal part; it is important clinically as being the
only distinct band on the flexure and may be felt per rectum. The dorso-lateral band is largely
free, but is covered in front by the attachment to the left dorsal part. It fades out at the pelvic
flexure. The ventro-medial and ventro-lateral bands are free and fade out at the pelvic flexure.
The left dorsal colon has at first only one band, which is the continuation of the one along the lesser
curvature of the pelvic flexure; it extends along the ventral surface and is continued on the right
dorsal colon. Beyond the middle of the left dorsal colon two dorsal bands begin, diverge very
gradually, and are continued on the right dorsal colon; both are free and broaden at the diaphrag-
matic flexure. On the right dorsal colon the ventral band is concealed by the attachment to the
right ventral colon and by the vessels and lymph glands. The two dorsal bands are free except
at the parietal attachment of the bowel; the lateral one is very wide and somewhat indistinct;
the medial one is narrower and more distinct, and is continued along the mesenteric border of the
small colon.

The Small Colon

The small colon (Colon tenue) begins at the termination of the great colon,
behind the saccus csecus of the stomach and ventral to the left kidney, and is con-
tinued by the rectum at the pelvic inlet. ^ Its length is about ten to twelve feet
(ca. 3.5 m.), and its diameter three to four inches (ca. 7.5 to 10 cm.).

Its coils lie chiefly in the space between the stomach and the pelvic inlet,
dorsal to the left parts of the great colon. They are mingled with those of the
small intestine, from which they are easily distinguished by the bands and sac-
culation.

It is attached to the sublumbar region by the colic mesentery, and to the
termination of the duodenum by the narrow duodeno-colic fold of peritoneum
(Lig. duodeno-colicum) . The greater omentum is also attached to the initial
part of the bowel. The colic mesentery is narrow at its origin, but soon reaches
a width of about three feet (ca. 80 to 90 cm.). Its parietal border is attached along
a line extending from the ventral surface of the left kidney to the sacral promontory;
it is continuous in front with the root of the great mesentery, and behind with the
mesorectum.

There are two longitudinal bands and two rows of sacculations. One of the
bands is free, the other is concealed by the mesentery. When the bowel is hardened
i7i situ its lumen between the pouches is reduced to a narrow slit.

The Rectum

The rectum (Intestinum rectum) is the terminal part of the bowel; it extends
from the pelvic inlet to the anus.^ Its length is about one foot (ca. 30 cm.). Its
direction may be straight or oblique. The first or peritoneal part of the rectum is
like the small colon, and is attached by a continuation of the colic mesentery termed
the mesorectum. The second or retroperitoneal part forms a flask-shaped dilata-
tion termed the ampulla recti ; it is attached to the surrounding structures by con-
nective tissue and muscular bands.

The first part of the rectum commonly lies along the left wall of the pelvic
cavity, but may be about median or (more rarely) deflected to the right. It is
related to coils of the small colon and (inconstantly) to the left parts or pelvic

1 The position of the funnel-shaped termination of the great colon and the origin of the small
colon is fixed, and this fact is of clinical importance in regard to impaction, which is not rare here.
In horses of medium size this part of the bowel can be palpated per rectum when distended.

2 There is no natural line of demarcation between the small colon and rectimi: the plane
•of the pelvic inlet is selected as the division for convenience of description.

430

DIGESTIVE SYSTEM OF THE HORSE

flexure of the great colon; ventrallj^ to the bladder (when full) or to the uterus.
The second part of the rectum is related dorsally and laterall}^ to the pelvic wall.
Ventral ly the relations differ in the two sexes. In the male they are the bladder,
the terminal parts of the ductus deferentes, the vesiculse seminales, the prostate,
the bull)o-urethral glands and the urethra. In the female they are the uterus,
vagina, and vulva. ^

Structure of the Large Intestine
The serous coat covers the different parts in varying degree. It does not
cover (a) the opposed surfaces of the caecum and colon which are between the layers

Fig. 369. — Topogr.\phy of Vis^er.^^ of M.\.TtE; Left Deep View.
IR., First thoracic vertebra; IL., first lumbar vertebra; ^A'., second sacral spine; S., scapula; .4., humerus;
B., ilium; F., femur; Sch., pubis; .Si., ischium; L., liver (left lobe); Ma., stomach, the posterior contour of which is
indicated by dotted line x; Afi., spleen; Z.A'., left kidney, concealed part indicated by dotted line; j\/., small colon; D.,
small intestine, parts of which have been removed; l.d.C, left dorsal colon; l.v.C, left ventral colon; v.Q., sternal
flexure; d.Q., diaphragmatic flexure; O., left ovary; U., horn of uterus; L.I., broad ligament of uterus; M'., rectum; V.,
vagina; H., bladder; a, left ventricle; a', right ventricle; b, left coronary artery with descending (6') and circumflex
(6") branches; c, left auricle; d, pulmonary artery (cut) ; e, aorta; /, ligamentum arteriosum; 3, brachiocephalic trunk
(anterior aorta); A, trachea; i, oesophagus; A:, left phrenic nerve; Z, diaphragm in median section; m, uterine tube;
n, bursa ovarica; o, urethra; p, cut edge of broad ligament ; q, line of reflection of pelvic peritoneum; r, recto-coccygeus;
s, suspensory ligament of rectum; t, sphincter ani internus; u, sacro-coccygeus ventralis; v, abdominal wall in section;
w, xiphoid cartilage. (After Ellenberger, in Leisering's Atlas.)

of the cseco-colic fold and mesocolon; (h) the areas of parietal attachment of the
Cfficum and colon ; (c) the retroperitoneal part of the rectum.

The muscular coat consists of longitudinal and circular fibers. The bulk of
the former is in the bands of the caecum and colon. It is to be noted, however,
that the bands of the caecum and the ventral parts of the great colon are largely
composed of elastic tissue. The bands of the dorsal parts of the colon are largely
muscular, and those of the small colon are almost entirely muscular. Some of the
circular fibers pass from one part of the colon to another, where they are attached
to each other, forming the fibrte transversse coli. The muscular coat of the ampulla
of the rectum presents special features. The longitudinal layer of fibers is very

1 The anterior part of the rectum is variable in position and relations. The amount covered
by peritoneum dorsally and laterally is very variable, and appears to be in inverse proportion to
the fulness of the bowel.

STRUCTURE OF THE LARGE INTESTINE

431

thick and consists of large bundles which are rather loosely united. A large band,
the recto-coccygeus, is detached from it on either side, and passes upward and
backward to be inserted into the fourth and fifth coccygeal vertebrae.

The submucous tissue is abundant in the wall of the rectum, so that the mucous
membrane is loosely attached to the muscular coat, and forms numerous folds
when the bowel is empty.

The mucous membrane of the large intestine is thicker and darker in color
than that of the small intestine. It forms large crescentic or semilunar folds

Fig. 370. — Pelvic Inlet and Posterior Part op Abdominal Wall of Horse, Viewed from the Front.
The left inguinal canal is partially opened. The peritoneum is retained except over a part of the left cremaster
muscle. The sublumbar region is greatly foreshortened in this view, a, o', Kidneys; a", adrenal; 6., ureter; c, renal
artery; d, aorta; e, stump of cceliac artery; /, stump of anterior mesenteric artery; g, posterior mesenteric
artery; h, circumflex ihac artery; i, external iliac artery; k, internal iliac artery; I, spermatic artery in peritoneal
fold (phca vasculosa) , m; re, ductus deferens, enclosed in genital fold, o; p, urinary bladder; q, round ligament of blad-
der; r, middle ligament of bladder; s, rectum; t, margin of vaginal ring; u, posterior abdominal artery; v, external
pudic artery; w, rectus abdominis muscle; x, transversus and obliquus internus abdominis; y, y', cremaster externus;
z, posterior vena cava (cut). (After EUenberger-Baum, Top. Anat. d. Pferdes.)

(Plicae semilunares) , corresponding to the external constrictions. It has no villi
nor duodenal glands. The intestinal glands are large and numerous. Solitary
nodules are numerous, and there are aggregated lymph nodules at the apex of the
caecum and in the pelvic flexure and the adjacent portion of the left dorsal part of
the colon.

Vessels and Nerves. — The arteries come from the anterior and posterior
mesenteric and internal pudic arteries. The veins go to the portal and internal
pudic veins. The lymph vessels of the caecum and colon go to the caecal and colic
lymph glands, thence to the cisterna chyli. Those of the rectum go to the internal.

432 DIGESTIVE SYSTEM OF THE HORSE

iliac and lumbar glands. The nerves are derived from the mesenteric and pelvic
plexuses of the sympathetic.

The Anus

The anus is the terminal part of the alimentary canal. It is situated below the
root of the tail, where it forms a round projection, with a central depression when
contracted. It is covered externally by an integument which is thin, hairless, and
provided with numerous sebaceous and sweat glands. Its lumen, the anal canal
(Pars analis recti), is about two inches (ca. 5 cm.) long; except during defecation
it is closed by the contraction of the sphincter muscles and folds of the mucous
lining. The mucous membrane is pale, glandless, and covered with a thick, squa-
mous, stratified epithelium.

There are three muscles of the anus.

1. The sphincter ani intemus is the terminal thickening of the circular coat
of the bowel.

2. The sphincter ani extemus is a broad ring of striped muscle-fibers outside
the internal sphincter. Some fibers are attached to the coccygeal fascia above,
others to the perineal fascia below. Its action is to close the anus.

3. The retractor ani is a flat muscle which lies between the rectum and the
sacro-sciatic ligament; its fibers are directed backward and somewhat upward.
It arises from the superior ischiatic spine and the sacro-sciatic ligament, and ends
under the sphincter ani externus. Its action is to reduce the partial prolapse which
the anus undergoes during defecation.

The suspensory ligament of the anus (Lig. suspensorium ani) is a band of
unstriped muscle which arises from the first coccygeal vertebra, passes downward
under cover of the retractor ani, and unites with its fellow below the anus. In the
male it is largely continued by the retractor penis muscle; in the female it blends
with the constrictor vulvae. It may act as an accessory sphincter of the anus.

Vessels and Nerves. — The blood-supply comes from the internal pudic arteries,
and the veins go to the internal pudic vein. The lymph vessels go to the anal
lymph glands. The nerves come from the pudic nerve.

THE PANCREAS

The pancreas is situated transversely on the dorsal wall of the abdomen, the
greater part being to the right of the median plane. Its central part lies under the
sixteenth and seventeenth thoracic vertebrae. When fresh, it has a reddish cream
color, but if left in the unpreserved cadaver, it rapidly decomposes and becomes
dark. It resembles the salivary glands in appearance, but is softer, and its lobules
are more loosely united. Its average weight is about twelve ounces (ca. 350 g.).
When hardened in situ its shape is very irregular. It is triangular in outline, and
presents for description two surfaces, three borders, and three angles.^

The dorsal surface (Facies dorsalis) faces dorsally and forward. It is partially
covered by peritoneum. It is related chiefly to the ventral surface of the right
kidney and adrenal, the posterior vena cava, the portal vein, the coeliac artery and
its divisions, the gastro-phrenic ligament, and the saccus csecus of the stomach, the
right and caudate lobes of the liver, and the gastro-pancreatic fold. There are
grooves for the divisions of the coeliac artery and a large one for the splenic vein.

The ventral surface (Facies ventralis) faces ventrally and backward ; it is in
general concave. It presents two impressions, separated by an oblique ridge. The
smaller of these (Impressio csecalis) lies to the right, and is caused by the pressure
of the base of the caecum; the larger one (Impressio colica) indicates the area of

1 A descriptive method based on that in use in human anatomy cannot be applied with
clearness to the organ in the horse.

THE PANCKEAS

433

contact with the terminal part of the great colon and its junction with the small
colon. It has usually no peritoneal covering except over a small area at the anterior
angle.

The right border is nearly straight; it is related to the second part of the duo-
denum.

The left border is slightly concave, and is related to the first part of the duode-
num, the left sac of the stomach, and the splenic vessels.

The posterior border presents a deep notch (Incisura pancreatis) where the
root of the great mesentery is in contact with the gland. To the right the portal
vein lies in the notch, and passes through the gland very obliquely; there is a thin

Fig. 371. — P.4.ncreas of Horse with Chief Hki.atioxs; \'kxtral View.
The pancreatic duct and its two chief radicles are indicated by dotted lines, since they are in the substance of the gland.

bridge of gland tissue dorsal to the vein, thus forming the portal ring (Annulus
portae).

The anterior or duodenal angle (Angulus cranialis)^ is the most ventral part
of the gland; it is attached to the concavity of the second curve of the duodenum
and the adjacent part of the right lobe of the liver. The ducts leave at this ex-
tremity.

The left or splenic angle (Angulus sinister)- fits into the space between the
saccus csecus of the stomach in front, the left kidney behind, the base of the spleen
dorsally, and the termination of the great colon ventrally.

The right angle (Angulus dexter) is rounded, and lies on the ventral surface of
the right kidney and adrenal body.

^ This corresponds to the head of the pancreas of man.
2 This corresponds to the tail of the pancreas of man.
28

434 DIGESTIVE SYSTEM OF THE HORSE

The pancreas is attached dorsally by connective tissue to the kidneys and
adrenal bodies, the gastro-phrenic ligament, the suspensory iia;ament of the spleen,
the posterior vena cava, the portal fissure, and the gastro-pancreatic fold. The
ventral surface is mainly attached by areolar tissue to the base of the caecum and
the terminal part of the great colon.

There are almost invariably two ducts. The large one is termed the pan-
creatic duct (Ductus pancreaticus).^ It is formed by the union of two radicles
which come from the right and left extremities, and passes through the duodenal
angle to end at the duodenal diverticulum alongside of the bile-duct. The duct
is nearly half an inch (ca. 1 cm.) wide, and is very thin walled. It is situated in the
substance of the gland near its dorsal surface; none of it is free. The accessory
pancreatic duct (Ductus pancreaticus accessorius)^ arises either from the chief
duct or its left radicle, and ends on a papilla in the duodenum opposite the chief
duct.

Structure.^ — The pancreas belongs to the class of tubulo-alveolar glands, the
alveoli being long, like those of the duodenal glands; in other respects it resembles
the serous salivary glands very closely. It has no proper capsule and the lobules
are rather loosely united.

Vessels and Nerves. — The arteries of the pancreas come from the branches of
the cceliac and anterior mesenteric arteries. The veins go to the portal vein. The
nerves are derived from the cceliac and mesenteric plexuses of the sympathetic.

THE LIVER

The liver (Hepar) is the largest gland in the body. It is situated obliquely
on the abdominal surface of the diaphragm. Its highest point is at the level of
the right kidney, its lowest on the left side, usually about three or four inches
(ca. 8 to 10 cm.) from the abdominal floor, opposite the ventral end of the seventh
or eighth rib. The greater part of it lies to the right of the median plane.

It is red-brown in color and is rather friable. Its average weight is about ten
to twelve pounds (ca. 5 kg.), but in a large draft horse it weighs about twenty pounds.
When in the body, or if hardened in situ, it is strongty curved and accurately adapted
to the abdominal surface of the diaphragm. When removed in the soft state, it
flattens out into a cake-like form quite different from its natural configuration.
It presents for description two surfaces, and a circumference which may be divided
into four borders.

The parietal surface (Fades diaphragmatica) is strongly convex, and lies
against the diaphragm. It faces chiefly dorsally and forward. Its most anterior
part is opposite the ventral third of the sixth intercostal space or seventh rib. It
presents, just to the right of the median plane, a sagittal groove for the posterior
vena cava (Fossa venae cavae), which is partially embedded in the substance of the
gland.

The visceral surface (Facies visceralis) faces in general ventrally and backward;
it is concave and irregular, being molded on the organs which lie against it. It
presents the follo^ving features: (1) The portal fissure (Porta hepatis) is a depres-
sion above the middle of the surface and a httle to the right of the median plane;
through it the portal vein, hepatic artery, and hepatic plexus of nerves enter, and
the hepatic duct and lymph vessels leave the liver. The hepatic lymph glands are
also found here. The pancreas is attached at and to the right of the fissure, and
the lesser omentum around it. Above the fissure is the caudate lobe (Lobus cau-
datus), which is continued to the right by the pointed caudate process (Processus
caudatus). (2) The gastric impression (Impressio gastrica) is an extensive con-

1 Formerly termed the canal of Wirsung.

2 Formerly called the ductus pancreaticus minor or duct of Santorini.

THE LIVER

435

cave area which is the surface of contact with the stomach. (3) Leading from this
to the right of the portal fissure and dorsally is the duodenal impression (Impressio
duodenahs). (4) The colic impression (Impressio colica) is situated ventrally and
to the right of the gastric and duodenal impressions, from which it is separated by
a rido-e- it corresponds to the extensive contact of the diaphragmatic flexure and
right dorsal part of the colon. (5) A caecal impression (Impressio cseciilis) may
be found dorsal to the preceding; it corresponds to the anterior part oi the base ol
the cgecum.i Coils of the small intestine may also lie on this surface, and the apex
of the spleen mav reach to it when the stomach is empty.

The dorsal border (Margo dorsalis s. obtusus) is thick for the most part. It
presents from right to left: (1) The attachment of the right lateral ligament; (2)
a depression for the right kidney (Impressio renalis); (3) a notch, which is the

Right lateral ligament

h Posterior vena cava

Esophageal ^^^j lateral ligament

Coronary
ligament

Falciform ligament

■"'iiii^

Round
ligament

Fig. 372.-LIVER of Youmg Horse. Hardened in situ; Parietal Surface.

dorsal end of the fossa ven^ cav^; (4) thedeep oesophageal notch (Impressio oesoph-
agea), which is occupied partly by the end of the cesophagus ^^^ -7 ^ ^y the
thick margin of the hiatus cesophageus; (5) the attachment of the left lateral hga-

"^'""The ventral border (Margo ventralis) is thin, and is "^^^ked by two deep
interlobar fissures or incisures (Incisura. interlobares) , which partially divide the
^gan into three principal lobes-right, middle, and left. The right lobe is the
krgest except in old subjects, in which it is frequently much atrophied The
m d Ue lobe is the smallest. It is marked by several small fissures and by the
umbilicarfissure (Incisura umbihcalis); the latter contains the umbihcal vein m
the foetus, which is transformed into the round ligament after birth.

^ These impressions are not evident on the ^^^^ .-^f^or^.^'^^rL'^dlSe^
^^Z^al^"^. ^^T^JeScireSr^S Zlr^^^L of&n happens in
old horses, the right lobe of the liver is much atrophied.

436

DIGESTIVE SYSTEM OF THE HORSE

The right border (Margo dexter) is thin and long; it extends backward usually
to the sixteenth rib, a little below its middle.^

The left border (Margo sinister) is thin and convex. It begins at the left side
of the oesophageal notch, about a handbreadth ventral to the fourteenth thoracic
vertebra. It curves downward, outward, and somewhat forward to a point opposite

Renal impression

Caudate p7-ocess

Posterior vena cava

Attachment of (/astro- pancreatic fold
Portal vein

Specii:

Umbilical fissure

Fig. 373. — Liver of Horse; Visceral Surface.
from middle-aged subject, hardened in situ. The fissure between the left and middle lobes is shown but
not marked.

the ventral end of the ninth rib, and then runs forward about parallel with the
costal arch as far as the ventral end of the seventh rib. The ventral and lateral
borders together constitute the margo acutus.

The liver is held in position largely by the pressure of the other viscera and
by its close application and attachment to the diaphragm. It has six ligaments.

^ The right border varies much in subjects in the dissecting room, since in old subjects the
right lobe is often greatly atrophied. Atrophy of the left lobe is extremely rare.

THE LIVER 437

1 . The coronary ligament (Lig. coronarium hepatis) attaches it closely to the
diaphragm. It consists of two strong laminae. The right one is attached to the
right of the fossa venae cavse; the left one begins to the left of the vena cava and
passes dorsally and laterally, becoming continuous mth the left lateral ligament at
the left margin of the oesophageal notch; it detaches a middle fold which extends
to the oesophageal notch and is continuous with the lesser omentum. The two
laminae unite below the vena cava to form the next ligament.

2. The falciform ligament (Lig. falciforme hepatis) is a crescentic fold which
attaches the middle lobe to the sternal part of the diaphragm and to the abdominal
floor for a variable distance.

3. The round ligament (Lig. teres hepatis) is a fibrous cord in the concave

Renal impression

Posterior vena ca

Portal vein
Hepatic artery
Hepatic duct
(Esophageal notch

Middle lobe

Umbilical vein

Fig. 374. — Liver of New-born Foal, Hardened in situ; Visceral Surface.
The differences, when compared with the organ in the adult, are very striking.

edge of the falciform ligament which extends from the umbilical fissure to the
umbilicus; it is the vestige of the umbilical vein, which in the foetus carries the
blood from the placenta to the liver.'

4. The right lateral ligament (Lig. triangulare dextrum) attaches the dorsal
border of the right lobe closely to the costal part of the diaphragm.

5. The left lateral ligament (Lig. triangulare sinistrum) is a triangular fold
which attaches the dorsal edge of the left lobe to the tendinous center of the dia-
phragm,

6. The hepato-renal or caudate ligament (Lig. hepatorenale) attaches the
<3audate process to the right kidney and the base of the caecum.

The lesser omentum and the first part of the mesoduodenum are formed by the

^ It is to be noted that a remnant of the lumen of the vein is usually present, but has no
endothelial Uning.

438 DIGESTIVE SYSTEM OF THE HORSE

peritoneum leaving the visceral surface at the portal fissure and along a curved
line which extends from the fissure to the oesophageal notch. They pass to the
lesser curvature of the stomach and the first part of the duodenum.

As stated above, the liver is divided by fissures into three principal lobes —
right, middle, and left. The right lobe (Lobus dexter) is the largest in the young
subject and is irregularly quadrilateral in form. On its dorsal part is the caudate
lobe (Lobus caudatus), which ends in a pointed caudate process directed outward
and assists in forming the cavity for the right kidney. The central or middle lobe
(Lobus centralis) is normally much the smallest. The left lobe (Lobus sinister) is
oval in outline and thickest centrally. In old or middle-aged subjects it commonly
exceeds the right one in size, and in many cases constitutes the bulk of the gland.
In some cases the atrophy of the right lobe is so extreme that the middle lobe may
exceed it in size.^

The hepatic duct (Ductus hepaticus) is formed at the ventral part of the portal
fissure by the union of right and left chief lobar ducts. It is about two inches
(ca. 5 cm.) long and about half an inch (ca. 1 to 1.5 cm.) wide. It passes be-
tween the two layers of the mesoduodenum, and pierces the wall of the duodenum
five or six inches (ca. 12 to 15 cm.) from the pylorus, alongside of the pancreatic
duct. The ducts pass obliquely through the wall of the duodenum for about
half an inch (ca. 1 cm.) before opening into the diverticulum duodeni. The arrange-
ment forms a valve, which prevents regurgitation from the intestine. There is no
gall-bladder.

In the new-born foal the liver presents striking differences when compared with the gland of
the adult. It is relatively large and weighs 23^ to 3 pounds (ca. 1.25 kg.). It is thick and is strongly
curved, and a considerable part of the parietal surface is in contact with the floor of the abdomen.
The umbilical fissure is large and contains the umbilical vein. The latter is a very large vessel
which carries blood from the placenta and joins the portal vein in the substance of the liver; it is
in the edge of the falciform Ugament, which at this time extends to the umbiUcus. The visceral
surface is deeply concave and is in contact chiefly with the stomach and duodenum.

Structure. — The liver is covered by an external serous, and an internal fibrous,
coat. The serous coat (Tunica serosa) covers the gland except at the attachment
of the pancreas and at the portal fissure; it is reflected from it to form the ligaments
and the lesser omentum. The fibrous capsule (Capsula fibrosa) is in general thin;
it sends laminae into the ligaments, and also trabeculse into the gland. At the portal
fissure it is abundant and surrounds the vessels and ducts, which it accompanies
in the portal canals of the gland substance.

The gland substance is composed of the parenchyma and the interstitial
tissue. The parenchyma is made up of polygonal lobules (Lobuli hepatis), about
1.5 mm. in diameter, which are held together by a small amount of interlobular
connective tissue. On account of the very small amount of the latter, the
lobulation of the horse's liver is not usually at all distinct ; for the same reason the
organ is also quite friable. The lobules are composed of the polyhedral liver cells,
a delicate reticulum, the bile capillaries, a plexus of blood capillaries, and a central
vein.

Vessels and Nerves. — The portal vein enters at the portal fissure. It conveys
blood from the digestive tract and the spleen, which contains various products of
digestion and numerous white blood-cells. The hepatic artery also enters at the
portal fissure; it may be termed the nutrient vessel. All the blood is returned from
the liver to the posterior vena cava by the hepatic veins. The portal vein and the
hepatic artery both divide into interlobular branches, which run together in the

1 Flower and Ruge describe the mammalian liver as being primarily divided by the umbiUcal
fissure into two parts, the right and left lobes. Secondary fissures on either side may subdivide
each of these primary lobes. On this basis we may recognize in the liver of the horse right lateral,
right central, left central, and left lateral lobes. In the young foal these four lobes are distinctly
recognizable. The two central lobes would correspond to the central or middle lobe of the foregoing
description, and the right central lobe would be the equivalent of the quadrate lobe of man.

THE SPLEEN

439

portal canals of the interlobular tissue. The branches of the portal vein (Venae
interlobulares) give off intralobular branches which form plexuses of capillaries in
the lobules and give rise to a central vein (Vena centralis). The interlobular
branches of the hepatic artery (Rami arteriosi interlobulares) are of relatively
small size. They supply mainly (if not exclusively) the interlobular tissue, the
capsule, and the walls of the vessels and ducts. The hepatic veins' (Vena hepaticse)
empty into the posterior vena cava as it lies in the fossa of the gland. Their
ultimate radicles are the central lobular veins (Venae centrales), which emerge from
the bases of the lobules and join
the sublobular veins (Vena3 sub-
lobulares) ; the latter unite to form
the hepatic veins. The largest
hepatic veins, three or four in
number, join the posterior vena
cava just before it leaves the liver
to pass through the diaphragm.

The nerves come from the
hepatic plexus, which is composed
of branches from the vagus and
sympathetic nerves.

THE SPLEEN
The spleen (Lien) is the
largest of the heterogeneous group
of organs which are usually desig-
nated ductless glands.^ It is situ-
ated chiefly in the left parachon-
driac region, in close relation to the
left part of the great curvature of
the stomach, to which its long axis
corresponds. Its size and weight
vary greatly in different subjects,
and also in the same subject under
different conditions, depending
chiefly on the great variability of
the amount of blood contained in
it. The average weight is about 35
to 40 ounces (ca. 1 kg.), its length
about 20 inches (ca. 50 cm.), and
its greatest width about 8 to 10
inches (ca. 20 to 25 cm.). It is
usually bluish-red or somewhat purple in color,
yielding, but not friable.

The weight, which is extremely variable, appears to range ordinarily from about one to eight
pounds, although the latter figure even may be exceeded without any apparent evidence of disease.

1 The hepatic veins may be recognized on section from the fact that they remain open,
being connected closely with the parenchyma.

2 The ductless glands are organs which elaborate substances that pass directly into the
veins or lymphatics, instead of being conveyed away by ducts. This process is termed internal
secretion. The ductless glands include the lymph glands, which are described with the organs
of circulation; the thyroid and thymus bodies, described usually with the respiratory organs;
the adrenal or suprarenal bodies, described with the urinary organs; the pineal and pituitary
bodies, described with the brain; and the spleen, described w\th the digestive system as a matter
of convenience. The spleen is not, strictly speaking, a gland at all: it is not epithelial in origin
or structure, but is mesenchymatous.

Fig. 375. — Spleen of Horse; Parietal Surface.
a, Dorsal extremity or base; 6, c, anterior and posterior basal
angles; d, anterior border; e, ventral extremity or apex; 1, 2, 3,
impressions of last three ribs.

In the natural state it is soft and

440

DIGESTIVE SYSTEM OF THE HORSE

The author recently observed in a horse, which weighed about 1200 pounds, a spleen which weighed
lOM pounds, and measured 26 inches in length and 11 inches in width at the base. The ventral
end was situated opposite the lower part of the seventh intercostal space. In the new-born foal
the weight is about 10 to 12 ounces (ca. 300 gm.). There does not seem to be any constant relation
to the body-weight. For example, the spleen of a colt of medium size about ten months old
weighed three and a half pounds, while it often weighs less than two pounds in horses weighing
1000 to 1200 pounds. The chief variation in outUne consists of increase of width, especially of the
dorsal part.

It extends obliquely in a curved direction, corresponding to the left part of the
greater curvature of the stomach, from the left crus of the diaphragm to the ventral

third of the tenth or eleventh rib. It
presents for description two surfaces,
two borders, and two extremities.

The parietal or lateral surface (Fa-
des parietalis) is convex, and lies chiefly
against the diaphragm, but is in contact
with the dorsal parts of the last two ribs
and usually to a small extent with the
flank at the lumbo-costal angle.

The visceral or medial surface (Fa-
des visceralis) is in general concave. It
is divided into two unequal parts by a
longitudinal ridge; on this is a groove,
the hilus, in which the vessels and nerves
are situated. The area in front of the
ridge (Fades gastrica) is molded on the
greater curvature of the stomach; it
is about two inches (ca. 5 cm.) wide.
The area behind the ridge (Fades intes-
tinalis) is much more extensive; it is
related to the small colon, the left parts
of the great colon, the small intestine,
and the great omentum. It may be
marked by one or two fissures.

The anterior border (Margo crani-
alis) is concave and thin, being wedged
in between the diaphragm and the
greater curvature of the stomach.

The posterior border (]\Iargo cau-
dalis) is convex and thin.

The dorsal extremity or base (Ex-
tremitas dorsalis) is beveled, and fits into
the interval l)etween the left crus of
the diaphragm and sublumbar muscles
above, and the saccus caecus of the stomach and the left kidney below. When
hardened in situ, it shows an impression (Fades renalis) where it lies against the
kidney. The left extremity of the pancreas touches it also. The anterior basal
angle fits in between the saccus csecus of the stomach and the left kidney at the
seventeenth thoracic vertebra; the posterior basal angle usually lies against the
upper part of the left flank, just behind the last rib.^

The ventral extremity or apex (Extremitas ventralis) is small and varies in
position. It is commonly foimd opposite the tenth or eleventh rib, a handbreadth
or more above the costal arch, but may be further forward and higher.

1 It is uncommon to find the spleen extending more than two or three inches behind the last
rib; on the other hand, the posterior basal angle may lie just at the last rib.

Fig. .37C. — Spleen of Horse, Hardened
CERAL Surface.
o, Dorsal extremity or base; b, c, anterior and poste-
rior basal angles; d, anterior border; e, cut edge of sus-
pensory ligament ; /, g, splenic artery and vein in hilus.
The area marked intestinal impression is related to the
first coil of the small colon. The area enclosed by the
suspensorj- ligament is non-peritoneal.

THE PERITONEUM 441

The position of the ventral part depends largely upon two factors — the degree of fulness of
the stomach and the size of the spleen. When the stomach is empty or nearly so and the spleen
small (contracted), the latter is strongly curved, and its ventral end may be between the left lobe
of the liver and the left dorsal part of the great colon. When the stomach is full, it pushes the
spleen backward, affecting most the ventral part of the latter. Of course the spleen is affected
by the respiratory movements, as may be readily observed by examination per rectum of the
Uving subject.

The spleen is attached by two peritoneal folds, the suspensory ligament and
the gastro-splenic omentum. The suspensory ligament of the spleen (Lig. sus-
pensorium lienis) attaches the dorsal end to the left crus of the diaphragm and the
left kidney; it contains a quantity of elastic tissue. The dorsal layer of the liga-
ment, which passes to the diaphragm, is the ligamentum phrenico-lienale, and blends
with the gastro-phrenic ligament; the ventral part, which goes to the kidney, is
termed the ligamentum renolienale. The gastro-splenic omentum (Lig. gastro-
lienale) passes from the hilus to the left part of the greater curvature of the stomach.
It is narrow dorsally, where it joins the suspensory ligament; ventrally it becomes
much wider and is continuous with the great omentum.

Small globular or lenticular ma.sses of splenic tissue may be found in the gastro-splenic
omentum. They are termed accessory spleens (Lienes accessorii).

Structure. — The spleen has an almost complete serous coat (Tunica serosa).
Subjacent to this and intimately united with it is a capsule of fibrous tissue (Tunica
albuginea), which contains many elastic fibers and some unstriped muscular tissue.
Numerous trabeculae (Trabeculse lienis) are given off from the deep face of the
capsule and ramify in the substance of the organ to form a supporting network.
In the interstices of this framework is the spleen pulp (Pulpa lienis), a dark red, soft,
grumous material. This is supported by a delicate reticulum, and contains numer-
ous leukocytes, the large splenic cells, red blood-corpuscles, and pigment. The
pulp is richly supplied with blood. The branches of the splenic artery enter at
the hilus and pass along the trabeculse. The arteries which enter the pulp have a
sheath of lymphoid tissue, which collects on the vessel wall at certain points, form-
ing small splenic lymph nodules (Noduli lymphatici lienales).^ These are visible
to the naked eye as white spots, about as large as the head of a pin. The blood
passes into cavernous spaces lined by endothelium which is continuous with the
cells of the reticulum of the pulp. From these the veins arise. The splenic vein
runs in the hilus in company with the artery and nerves, and joins the posterior
gastric vein to form a large radicle of the portal vein.

Vessels and Nerves. — The arteries are derived from the splenic artery, which
is the largest branch of the coeliac artery. The splenic vein lies behind the artery
in the hilus; it goes to the portal vein. The lymph vessels go to the splenic lymph
glands. The nerves, derived from the coeliac plexus of the sympathetic, accom-
pany the vessels.

THE PERITONEUM

The general disposition of the peritoneum has been described, and other facts
in regard to it were mentioned incidentally in the description of the viscera. It is
now desirable to study it as a continuous whole- (Figs. 351, 352, 353, 377, 378).

We may consider the peritoneum as consisting of two sacs — a greater and a
lesser. The greater sac lines the greater part of the abdominal cavity, and covers
most of the viscera which have a peritoneal investment. The lesser sac is an
introversion or invagination of the greater sac, formed during the development of
the viscera. The two sacs communicate by a relatively narrow passage, termed

1 These are also known as Malpighian corpuscles.

2 The student is strongly recommended to study the peritoneum of a foal or other small
subject when the opportunity occurs, as in these the viscera are easily handled, and the course
of the peritoneum can be followed without difficulty.

442

DIGESTIVE SYSTEM OF THE HORSE

the epiploic foramen (Foramen epiploicum).^ This opening is situated on the
visceral surface of the hver dorsal to the portal fissure. It can be entered by passing
the finger along the caudate lobe of the liver toward its root. Its dorsal wall is
formed by the caudate lobe and the posterior vena cava. Its ventral wall consists
of the pancreas, the gastro-pancreatic fold, and the portal vein. The walls are
normally in contact, and the passage merely a potential one. It is usually about
four inches (ca. 10 cm.) in length. It is narrowest at the lateral extremity, where
it is about an inch (ca. 2.5 to 3 cm.) wide.^ If the finger is passed into the foramen
from right to left, it enters the cavity of the lesser sac. If now an opening is made
in the great omentum and the other hand introduced through it, the fingers of the
two hands can touch each other over the lesser curvature of the stomach. The
formation and boundaries of the lesser sac should now be examined by spreading
out the great omentum. It will be found that the latter now encloses a considerable
cavity behind the stomach; this is termed the omental cavity (Bursa omentalis).
Passing forward over the lesser curvature of the stomach, we enter another space,
the vestibule of the omental cavity (Vestibulum bursse omentalis). This space is

Fig. 377. — Diagram op General Arrangement of Peritoneum (of Mare) in Sagittal Tracing.
Sacro-rectal pouch, continuous with b, recto-genital pouch; c, vesico-genital pouch; d, pubo-vesical pouch; /, lesser
omentum; Int., small intestine. The arrow points to the epiploic foramen.

closed on the left by the gastro-phrenic ligament, ventrally and on the right by
the lesser omentum, and dorsally by the gastro-pancreatic fold, which is attached
to the dorsal border of the liver and to the posterior vena cava. Above the (Eso-
phageal notch there is a recess, into which the fingers can be passed around the
border of the liver and the vena cava till the coronary ligament is encountered.
Thus the vestibule is closed except — (1) on the right, where it communicates with
the cavity of the greater sac by the epiploic foramen; and (2) behind, where it
communicates with the cavity of the omentum.

The general arrangement of the greater omenttim has already been indicated.
We may now trace its line of attachment, which would correspond to the mouth of
the sac. Beginning at the ventral part of the greater curvature of the stomach, it
passes to the ventral face of the pylorus, then crosses obhquely the first part of
the duodenum to the point where the pancreas is adherent to it. Here it passes
to the anterior face of the terminal part of the great colon, runs along this trans-
versely (from right to left), and continues for some ten or twelve inches (ca. 25

^ Also known as the foramen of Winslow.

^ The passage is subject to a good deal of variation in caUber and is sometimes occluded.

THE PERITONEUM

443

to 30 cm.) on the small colon. It then forms an acute angle, passes medially and
forward along the small colon to the dorsal part of the hilus of the spleen, where it
blends with the suspensory ligament of the latter, and forms a recess (Recessus
lienalis) behind the saccus caecus of the stomach. It now passes along the hilus
of the spleen, and is continued to the greater curvature of the stomach by the
gastro-splenic omentum. It is convenient to regard the spleen as being interca-
lated in the left part of the greater omentum; on this basis the gastro-splenic
omentum would be that part of the greater omentum which connects the hilus of
the spleen with the greater curvature of the stomach. The greater omentum is.
relatively small in the horse, and is

usually not visible when the abdo- ^ Viaphracrm

men is opened. It is generally folded
up in the space between the visceral
surface of the stomach and the in-
testine.^

The lesser sac furnishes the perito-
neal covering for: (1) the visceral surface
of the stomach and a small area of the first
curve of the duodenum; (2) a large part of
the dorsal surface of the pancreas and por-
tal vein; (3) a small part of the visceral sur-
face of the Hver above the attachment of
the lesser omentum and the portal fissure ;
(4) the posterior vena cava, from the level
of the epiploic foramen to its passage
through the diaphragm (in so far as it is
not embedded); (5) the part of the parie-
tal surface of the liver between the right
and middle divisions of the coronary liga-
ment; (6) the corresponding part of the
diaphragm, and the right part of the right
crus of the same; (7) part of the anterior
siirface of the terminal part of the great
colon, and the origin of the small colon;
(8) the left extremity of the pancreas (in-
constant) ; (9) the spleen.

We may now trace the perito-
neum in a longitudinal direction, be-
girming in front. It is reflected from
the ventral abdominal wall and the
diaphragm upon the liver, forming
the ligaments and serous coat of the
gland. It leaves the visceral surface
of the liver as lesser omentum, and
the crura of the diaphragm as the

gastrophrenic ligament, reaches the saccus csecus and lesser curvature of the stomach
and the first curve of the duodenum, covers these organs, and is continued by the
greater omentum.

On the left it passes from the left crus of the diaphragm and the left kidney to
form the suspensory ligament of the spleen, clothes that organ, and leaves it to be
continued by the greater and gastro-splenic omenta.

On the right it passes from the right crus of the diaphragm and the dorsal
border of the liver to the concave border of the duodenum, forming the gastro-
pancreatic fold (second part of the mesoduodenum) , and covering part of the dorsal
surface of the pancreas. From the margin of the pancreas, the right kidney, and
a small area of the sublumbar region behind the latter, it passes on to the base of

1 In dissecting-room subjects (which are usually aged) the omentum often exhibits patho-
logical changes, such as adhesions, rents, tumors, formation of twisted strands, etc.

Fig. 378. — Diagram op Abdominal Peritoneum in Frontal
(OR Horizontal) Tracing.
D, Duodenum; 1, falciform ligament; 2, le.sser omentum;
3, gastro-splenic omentum; 4, greater omentum; 5, cavity of
omentum; 6, mesoduodenum; 7, general peritoneal cavity.
Arrow indicates epiploic foramen. By an oversight the pan-
creas, in front of the colon, is not marked.

444

DIGESTIVE SYSTEM OF THE OX

the csRcum and the terminal part of the great colon. From these it passes on the
right to the duodenum, forming the third part of the mesoduodenum. On the left
it covers part of the ventral surface and the lateral border of the left kidney, from
which it passes to the base of the spleen, forming the ventral layer of the suspen-
sory ligament of the latter. Behind the terminal part of the great colon it is reflected
from the abdominal wall around the great mesenteric artery to form the great
mesentery. Behind this it is reflected almost transversely from the roof of the
cavity and from the origin of the small colon on to the duodenum, forming the
terminal part of the mesoduodenum. The line of origin of the colic mesentery
begins on the medial part of the ventral surface of the left kidney, and extends to
the sacral promontory, where the mesorectum begins. At the termination of the
latter the peritoneum is reflected from the rectum on to the dorsal and lateral walls
of the pelvic cavity. Below the rectum it forms the genital fold, and passes on to
the dorsal surface of the bladder, covers its anterior part, and is reflected on to the
body-wall laterally and ventrally, forming the lateral and middle ligaments of the
bladder. In the female the broad ligaments of the uterus replace the genital fold,
mth which they are homologous.

In the new-born foal certain folds are specially large. The falciform ligament
of the liver extends to the umbilical opening, and contains in its free edge the large
umbilical vein. The bladder — at this time an abdominal organ — has a ventral
median fold (Plica umbilicalis media), which connects it and the urachus with the
alidominal floor. This is flanked on either side by a fold (Plica umbilicalis lateralis),
which also extends to the umbilicus, and contains the large umbilical artery.

DIGESTIVE SYSTEM OF THE OX

THE MOUTH

The cavity of the mouth is shorter and wider than that of the horse, and the
vestibule is more capacious (Figs. 381, 386).

The lips are thick, wide, and comparatively immobile. The middle part of

the upper lip and the surface between the nos-
trils is bare, and is termed the muzzle (Planum
nasolabiale). It is smooth, and (in health) is
kept cool and moist by a clear fluid secreted
by the naso-labial glands (Glandulse nasolabi-
ales); they form a subcutaneous layer about
half an inch (ca. 1.5 cm.) thick. It shows ir-
regular lines, mapping out small polygonal areas
on which the orifices of the gland ducts are visi-
ble. There is also a narrow bare strip along
the edge of the lower lip. The remainder of
the integument is provided with ordinary and
tactile hairs. The free edge and the adjacent
part of the lining membrane bear short, blunt,
horny papillae ; toward the angles the papillae
become longer and sharp-pointed. The labial
glands occur only near the angles, where they
form compact masses (Fig. 385) .

The cheeks are more capacious than in
the horse. The mucous membrane presents

Fig. 379. — Lips axd Muzzle of Ox.

1, Muzzle; 2, nostril; 3, 4, wings of nos-
tril; 5, 6, commissures of nostril; 7, 8, upper
and lower lip.

THE MOUTH

445

large pointed conical papillae (Papillae conicae), which are directed toward the
isthmus faucium and are covered with a horny epithelium. The largest of these
have a length of about half an inch (ca. 1 to 1.5 cm.) and are situated around
the angle of the mouth and parallel with the cheek teeth. The orifice of the parotid
duct is opposite the fifth upper cheek tooth. The buccal glands (Fig. 385) are very
well developed, and are arranged
in three parts. The dorsal part
extends from the angle of the
mouth to the maxillary tuberos-
ity; its lobules are of a light j'el-
low color. The ventral part con-
sists of a compact brownish mass
which reaches from the angle
of the mouth a short distance
under the masseter muscle. The
middle part consists of loosely
arranged yellow lobules. The
small ducts of these glands open
between the papillae of the cheek.

A linear series of large pa-
pillae exists on the floor of the
mouth on each side of the frenum
linguae. Near these are found
the openings of the small ducts
of the sublingual gland. The
caruncula sublingualis, the pa-
pilla on which the sub-maxil-
lary duct opens, is wide, hard,
and has a serrated edge (Fig.
383).

The hard palate is wide, and
is usually more or less pigmented.
The body of the premaxilla is
covered with a thick layer of
dense connective tissue, which
has a thick, horny epithelial cov-
ering— forming the so-called den-
tal plate or pad. The palatine
ridges extend from this back-
ward about two-thirds of the
length of the hard palate; they
number 15 to 19. They are
nearly straight, and, with the
exception of a few at the poste-
rior end of the series, are serrated on the free edge. A median raphe extends
between the ridges. The posterior third of the palate is smooth. Between
the dental plate and the first ridge is the triangular papilla incisiva; on either
side of this is a deep furrow, in which is the oral opening of the ductus incisivus.^
The duct is two inches or more (ca. 5 to 6 cm.) in length and opens on the floor
of the nasal cavity; it also communicates by a slit-like opening with the vomero-
nasal organ.

Fig. 380. — Hard Palate of Ox.
1, Dental pad or plate; 2, placed on papilla incisiva with lines
to orifices of ductus incisivi; 3, ridge of palate; 4, raph6 of palate;
5, smooth part of palate showing orifices of palatine glands; 6,
upper lip; 7, conical papillae of cheek.

This is also known as the naso-palatine canal.

446

DIGESTIVE SYSTEM OF THE OX

The soft palate is somewhat shorter than that of the horse, but is long enough
to close the isthmus faucium. The posterior pillars do not extend to the origin of
the oesophagus. The palatinus muscle is much better developed than in the horse.
The fibrous aponeurosis is for the most part replaced by muscular tissue.

Cavity

Dorsal

Septum

of dorsal

Frontal

turbinate

meatus

nasi

turbinate

vein

Middle meatus-

Naso-lacrimal
duct

Infraorbital

nerve

Inferior labial
vessels

Hypoglossal nerve

Masseter

Dorsal
buccal
glands
Facial
artery
Facial vein

Buccinator

Ventral buccal
glands

Sublingual gland

Digiistricus

Mandibular duct Lingwd nerve

Fig. 381. — Cross-section of Head of Ox.

The section passes through the medial canthi. L. a., Lingual arteries. The arrow indicates the communication be-
tween the maxillary and palatine sinuses.

The isthmus faucium is wide and dilatable. On either side, behind the an-
terior pillar of the soft palate, there is a deep depression, the tonsillar sinus (Sinus
tonsillaris) ; lateral to this is the compact, bean-shaped tonsil, which is about one
to one and a half inches (ca. 3 to 4 cm.) in length. The tonsil does not project into
the isthmus faucium, but outward instead: hence it does not occupy the tonsillar
sinus, and is not visible internally, as is the case in most animals.

THE TONGUE

447

THE TONGUE
The tongue of the ox is often variably pigmented. The root and body are
wider than that of the horse, but the free part is more pointed. The posterior part
of the dorsum forms a remarkable elliptical prominence, which is sharply defined
in front by a transverse depression. In front of this prominence there are large
and horny conical papillae (Papilla conica?), with sharp points directed backward;

Fig. 382. — Tongue and Fauces of Ox; Dorsal View.
The pharynx and soft palate are cut dorsally and reflected, a. Vallate papillae; 6, prominence of dorsum with
broad, flattened papillse; c, fungiform papillae; d, conical papillae of tip; 1, glosso-epiglottic space; 2, tonsillar sinus; 3,
cut surface of soft palate; 4, pharynx; 5, posterior pillar of soft palate; 6, epiglottis; 7, aditus laryngis.

they impart to the tongue its rasp-like roughness. The papillae on the prominence
are large, broad, and horny; some have a blunt, conical form, others are rounded or
flattened and are termed lenticular papillae (Papillae lenticulares) . Behind the
prominence, the papillse are long and soft, i. e., not horny. The fungiform papillse
are numerous and distinct; they are scattered over the dorsum and edges of the
free part. The vallate papillae number 8 to 17 on each side; they are smaller than
those of the horse, and form a long, narrow group on either side of the posterior
part of the prominence of the dorsum. The foliate papillse and the lingual fibrous
<Jord are absent. There are lingual follicles in the posterior part of the root and on

448 DIGESTIVE SYSTEM OF THE OX

each side of the glosso-epiglottic fold. The muscles are well developed, and re-
semble in general those of the horse; the hyo-glossus arises by additional portions
from the great and middle cornua of the hyoid bone. The tongue is highly pro-
tractile and is the chief organ of prehesion.

THE TEETH 1
The formula of the permanent teeth of the ox is:

(0 0 3 3\
I - C - P - IM - I = 3
4 0 3 3/

The incisors are absent from the upper jaw. There are eight incisors in the
lower jaw, arranged in a somewhat fan-like manner. They are simple teeth,
without infundibulum. The croAvn is white, short, and shovel-shaped. The root
is rounded, and is embedded in the jaw in such a manner as to allow a small amount
of movement. There is a distinct neck. In addition to the simple numerical
designation, the following terms are commonly applied to the individual teeth:

Fig. 383. — Ixcisor Teeth of Ox; Lixgual Aspect.
C. s., Caruncula sublingualis.

central, first intermediate, second intermediate, and corner incisors. It is probable
that the latter are much modified canines. The incisors of the adult ox do not
undergo continued eruption, as is the case in the horse; in old age, however, the
gum retracts so that the roots are partly exposed and may come into wear.- The
deciduous incisors differ from the permanent set chiefly in being much smaller.
The crowais are narrower and diverge more.

The canines are absent (unless the fourth incisors be considered to represent
them in the lower jaw).^

The cheek teeth (Figs. 134, 384) resemble those of the horse in number and
general arrangement. They are, however, smaller, and also differ in the fact that
they progressively increase in size from before backward. This feature is so marked
that the first tooth is quite small, and the space occupied by the first three (i. e.,
the premolars) is only about one-half of that required for the posterior three (i. e.,
the molars). The enamel folds stand out even more prominently in relief on the
masticatory surface than in the horse. The occurrence of wolf-teeth is rare.

^ Other figures which show the teeth are to be found in the description of the skull.

2 The reader will note here the difference between the structure and behavior of the bracny-
dont (short-crowned) incisors of the ox and the hypsodont (long-crowned) type of the horse.

' According to A. Hoffman, the anlagen of the upper canines are present in the foetus, but
soon disappear.

THE TEETH

449

450 DIGESTIVE SYSTEM OF THE OX

The formula of the deciduous teeth is :

- 1= 20

(0 0 3\
Di-Dc-Dp- )
4 0 3/

TABLE OF AVERAGE FERIOES OF EKUFTION OF THE TEETH IN THE OX

Teeth Eruption

A. Temporary:

First incisor (Di Ij 1

Second incisor (Di 2) 3j j^ 3 ^^ j.

Third incisor (Di 3) I

Fourth incisor (Di 4) J

First cheek tooth (Dp 1) Birth to 3 weeks.

IS'^SootU^s?:' ::::::::::::::::::::;:::} «-* ^ '- ^^y-

B. Permanent:

First incisor (II) 13^ to 2 years.

Second incisor (12) 2 to 23^ years.

Third incisor (13) 3 years.

Fourth incisor (14) 3J^ to 4 years.

First cheek tooth (PI) 2 to 2i/^ years.

Second cheek tooth (P 2j IJ/^ to 23^ years.

Third cheek tooth(P 3) 2J^ to 3 years.

Fourth cheek tooth (Ml) 5 to 6 months.

Fifth cheek tooth (M 2) 1 to 13^ years.

Sixth cheek tooth (M 3) 2 to 23^ years.

The eruption of the permanent teeth is sul)ject to great variation. The above
figures are the average of observations of improved breeds under favorable condi-
tions.

a. Parotid gland
buccinator nerve; h, buccinator vei
papillse of lip; 5, buccinator muscle

Fig. 385. — Salivary Glands of Ox.
mandibular gland; c, ventral, d, middle, and e, dorsal buccal glands; /, labial glands;

; 1, masseter (cut); 2, ramus of mandible;
(After EUenberger, in Leisering's Atlas.)

3, zygomaticus muscle; 4, conical

THE SALIVARY GLANDS THE (ESOPHAGUS 451

THE SALIVARY GLANDS

The parotid gland is smaller and denser in texture than that of the horse, and
is light red-brown in color; its average weight is about four ounces (ca. 115 g.).
It has somewhat the form of a very narrow long triangle, and lies chiefly on the
posterior part of the masseter muscle. The dorsal part is wide and thick; its
anterior border partly covers a large parotid lymph gland. The small ventral end
is bent forward and fits into the angle of union of the jugular and external maxillary
veins; it lies on the mandibular gland. The parotid duct leaves the ventral part
of the deep face; in its course it resembles that of the horse, but it pierces the cheek
opposite the fifth upper cheek tooth.

The mandibular gland is larger than the parotid, and is pale yellow in color;
its average weight is about five ounces (ca. 140 g.). It is covered to a small extent
by the parotid. Its general form resembles that of the horse, but its ventral end
is large and rounded, and is separated by a small interval only from the gland of
the other side (Fig. 302). This part can be distinctly felt in the living animal, and
is related laterally to a large lymph gland. The duct leaves the middle of the
concave border of the gland, crosses the stylohyoideus and the intermediate ten-
don of the digastricus, and is then disposed as in the horse.

The sublingual gland consists of two parts. The dorsal part (Glandula sub-
lingualis parvicanalaris) is long, thin, and pale yellow in color. It extends from the
anterior pillar of the soft palate about to the symphysis of the mandible. It has
numerous small tortuous ducts (Ductus sublinguales minores), which open between
the papillae under the side of the tongue. The ventral part (Glandula sublingualis
grandicanalaris) is shorter and thicker, and lies ventral to the anterior portion of
the dorsal part; it is salmon pink in color. It has a single duct (Ductus sublin-
gualis major), which either opens alongside of or joins the mandibular duct.

THE PHARYNX (Figs. 386, 476, 478)
The pharynx is short and wide. The vault (Fornix pharyngis) is divided into
two culs-de-sac by a median fold of mucous membrane (Septum nasi membrana-
ceum), which is a continuation of that of the septum nasi; on the lateral wall of
each is the relatively small opening of the Eustachian tube, which is covered by a
simple fold of mucous membrane. The posterior nares are small. The entrance
to the oesophagus is large.

On the dorsal wall of the pharynx there are two large suprapharyngeal lymph glands, which,
when enlarged, cause difficulty in swallowing and breathing (Fig. 386).

THE (ESOPHAGUS

This is much shorter, wider, and more dilatable than that of the horse. Its
average diameter (when moderately inflated) is about two inches (ca. 5 cm.), and
its length in an animal of medium size is about three to three and a half feet (ca.
90 to 105 cm.). The wall is relatively thin, and the muscular tissue is striped
throughout. The latter consists, in the greater part of the tube, of two strata of
spiral fibers, except near the stomach, where they are longitudinal and circular.
Fibers are continued into the wall of the stomach for some distance. The mucous
membrane forms a prominence at the ventral side of the pharyngeal end of the
tube which contains glands; elsewhere it is non-glandular. There is no terminal
dilatation, and no part in the abdominal cavity.

A very large mediastinal lymph gland lies above the posterior part of the oesophagus and
may, if enlarged, obstruct it (Fig. 389).

452

DIGESTIVE SYSTEM OF THE OX

THE ABDOMINAL CAVITY
The abdominal cavity of the ox is very capacious, both absolutely an 1 rela-
tively, as compared with that of the horse. This is due to several factors. The
lumbar part of the spine is about one-fourth longer than that of the horse. The
transverse diameter between the last ribs is greater. The costal attachment of the
diaphragm is almost vertical in direction from the ventral part of the ninth rib to

Frontal sinus

Cavity of great ethmoturbinate

Cavity of dorsal turbinate
Cavities of ventral turbinate

Vesti-
bule of
larynx
Thyroid
cartilage

Mylo-hyoideuG
muscle

Fig. 386. — Sagittal Section of Head of Cow, Cut a Little to the Right op the Median Plane.

1, Cerebral hemisphere; 2, corpus striatum; 3, hippocampus; 4< olfactory bulb; 5, corpora quadrigemina; 6,
optic nerve; 7, pons; <S, medulla oblongata; 9, spinal cord; ;0, pituitary body; i 7, sphenoidal sinus; i^, lateral n^ass
of ethmoid; 13 ventral straight muscles; 14, suprapharyngeal lymph gland; 1-5, longus colli; 16, soft pa'ate; IT,
vallate papillae; 18, tonsillar sinus; 19, conical papillae of cheek; £0, hyo-epiglotticus muscle; 31, epiglottis; S£, h/o-
glossus muscle; CI, C2, atlas, axis. Subject was hardened with mouth open.

the dorsal end of the thirteenth. Thus the abdomen is increased at the expense
of the thorax, and the last three or four ribs enter more largely into the formation
of the abdominal wall than in the horse. The flank is also much more extensive.
The ilia, on the other hand, do not extend forward beyond a transverse plane
through the middle of the last lumbar vertebra. The epigastric and mesogastric
regions would be separated by a plane through the ventral end of the tenth pair of

THE PELVIC CAVITY — THE STOMACH 453

ribs, or through the last thoracic vertebra. The chief differential features in the
arrangement of the peritoneum will be described with the viscera. The sub-
peritoneal tissue is more abundant than in the horse, and in general contains a
much larger amount of fat.

THE PELVIC CAVITY

The pelvic cavity is relatively long and narrow. The inlet is more oblique
than that of the horse; it is elliptical in outline, and the transverse diameter is
smaller than that of the horse. The pubic part of the floor is about horizontal,
but the ischiatic part slopes dorsally to a marked degree; this part is also deeply
concave transversely. The roof is concave in both directions. The peritoneum
extends backward as far as the first coccygeal vertebra, so that the retroperitoneal
part of the cavity is short.

THE STOMACH

General Arrangement. — The stomach of the ox is very large, and occupies
nearly three-fourths of the abdominal cavity. It fills the left half of the cavity
(with the exception of the small space occupied by the spleen) and extends con-
siderably over the median plane into the right half.

It is compound, and consists of four divisions, viz., rumen, reticulum, omasum,
and abomasum.'^ The division is clearly indicated externally by furrows or con-
strictions. The first three divisions are often regarded as proventriculi or oeso-
phageal sacculations, the fourth being the stomach proper (in the narrower sense
of the term). The oesophagus opens into the stomach on a sort of dome, the
atrium ventricuU, and is continued through the reticulum by the oesophageal
groove. From the ventral end of the latter a groove traverses the ventral wall of
the omasum, thus giving a direct path from the reticulum to the abomasum for
finely divided food or fluid. The abomasum joins the small intestine.

Capacity. — The capacity of the stomach varies greatly, depending on the age
and size of the animal. In cattle of medium size it holds 30 to 40 gallons, in large
animals 40 to 60, in small, 25 to 35. The relative sizes of the four parts vary with
age, in correlation with the nature of the food. In the new-born calf the rumen and
reticulum together are about half as large as the abomasum; in ten or twelve weeks
this ratio is reversed. During this period the omasum appears to be contracted
and functionless. At four months the rumen and reticulum together are about
four times as large as the omasum and abomasum together. At about one and one-
half years the omasum equals or approaches closely the abomasum in capacity.
The four divisions have now reached their definitive relative capacities, the rumen
constituting about 80 per cent., the reticulum 5 per cent., the omasum 7 or 8 per
cent., and the abomasum 8 or 7 per cent, of the total amount.

Exterior and Relations
The rumen occupies almost all of the left half of the abdominal cavity, and
extends considerably over the median plane ventrally and in its middle. It is
somewhat compressed from side to side and may be described as having two sur-
faces, two curvatures or borders, and two extremities. The parietal (or left)
surface (Facies parietalis ) is convex and is related to the diaphragm, left wall of
the abdomen, and spleen. It extends from the ventral part of the seventh inter-
costal space almost to the pelvis. The visceral (or right) surface (Facies visceralis)
is somewhat irregular, and is related chiefly to the omasum and abomasum, the

1 In popular language these are regarded as so many stomachs, and are often designated
numerically. Other names are in common use, e. g., paunch, honeycomb, manifold or manyplies,
and rennet or true stomach.

454

DIGESTIVE SYSTEM OF THE OX

intestine, the liver, pancreas, kidneys, the uterus in the female, and the posterior
aorta and vena cava. The dorsal curvature (Curvatura dorsalis) is convex, fol-
lowing the curve formed by the diaphragm and sublumbar muscles. It is firmly
attached to the left portion of the crura of the diaphragm and the sul)lumbar
muscles by peritoneum and connective tissue. The ventral curvature (Curvatura
ventralis) is also convex and lies on the floor of the abdomen. The surfaces are
marked by the right and left longitudinal grooves (Sulcus longitudinalis dexter,
sinister) , which indicate externally the division of the rumen into dorsal and ventral
sacs.^ The reticular (or anterior) extremity (Extremitas reticularis) is divided
ventrally by a transverse anterior groove (Sulcus ruminis cranialis) into two sacs.
The dorsal sac is the longer of the two, and curves ventrally over the round, bhnd

Fig. 387. — Stomach and Spleen of Ox; Left View.
1, Left longitudinal groove of rumen; 2, rumino-reticular groove (not so distinct dorsally as shown here); 3, an-
terior groove of rumen; 4, posterior groove of rumen; 5, 6, coronary grooves; 7, 8, anterior, 9, 10, posterior, blind
sacs of rumen.

end of the ventral sac. The former is continuous with the reticulum, the external
line of demarcation being the rumino-reticular groove (Sulcus rumino-reticularis).
The groove is deep ventrally and is distinct on part of the lateral surface, but dorsally
no natural separation exists, the rumen and reticulum together forming a dome-
like vestibule (Atrium ventriculi) on which the oesophagus terminates. The pelvic
(or posterior) extremity (Extremitas pelvina), extends nearly to the pubis; it is
related to the intestine and bladder, and to the uterus in the cow. It is divided
into dorsal and ventral blind sacs (Saccus csecus caudalis dorsalis, ventralis) by a
deep transverse posterior groove (Sulcus ruminis caudalis), which connects the
longitudinal grooves. The blind sacs are marked off from the remainder of the

1 It has been customary to term the sacs left and right respectively, but these do not repre-
sent the relations as they exist in situ and as they are presented on frozen sections. When the
stomach is removed in the soft state, it loses its shape and the dorsal and ventral sacs of the rumen
become left and right.

EXTERIOR AND RELATIONS

455

rumen by the dorsal and ventral coronary grooves (Sulcus coronarius dorsalis,

ventralis) .

The left longitudinal groove (Sulcus longitudinalis sinister) begins at the anterior transverse
groove, passes somewhat dorsally and backward and divides into two grooves. The ventral
one is the chief groove, and passes backward to terminate in the angle of union of the posterior
blind sacs. The dorsal (accessory) groove curves dorsally and then backward to terminate in
the dorsal coronary sulcus. On the right surface there are two longitudinal grooves. The dorsal
one is the chief sulcus (Sulcus longitudinalis dexter). It extends in a curved direction (the con-
vexity being dorsal), and is continuous with the left longitudinal groove by means of the grooves
between the dorsal and ventral blind sacs at each end. The ventral groove (Sulcus accessorius)
curves somewhat ventrally and backward and joins the chief sulcus between the posterior blind
sacs.

The reticulum is the most anterior and the smallest of the four divisions; it
is opposite to the ribs from the sixth to the seventh or eighth. It Hes against the

Fig. 388. — Stomach of Ox; Right View.

Oes., CEsophagus; 1, right longitudinal groove of rumen; 2, posterior groove of rumen; .3, 4, coronary grooves; 5, 6,

posterior blind sacs of rumen; 7, pylorus.

diaphragm and liver in such a position that the median plane divides it into two
nearly equal portions. It is somewhat piriform, but compressed from before
backward. The parietal or diaphragmatic surface (Facies diaphragmatica) faces
forward; it is convex and lies against the diaphragm and liver. ^ The visceral or
ruminal surface (Facies ruminalis) faces backward; it is flattened by the press-
ure of the other three compartments; it ends dorsally by joining the wall of
the rumen, the concave line of junction corresponding to a ridge in the interior
of the stomach which forms the lower margin of the large rumino-reticular orifice.
The lesser curvature faces to the right and dorsally, and is connected with the

1 It is important to notice that the reticulimi is separated from the pericardium by an inter-
val of only an inch or less (ca. 2 cm.j, since foreign bodies which are often swallowed by cattle
lodge in the reticulum, and not rarely (if sharp) perforate the reticulum and diaphragm. When
the reticulum is full, its visceral surface is opposite to the eighth rib.

456 DIGESTIVE SYSTEM OF THE OX

omasum. The greater curvature faces to the left and ventrally; it lies against the
diaphragm, opposite the sixth and seventh ribs. The ventral extremity forms a
rounded cul-de-sac, which is in contact with the sternal part of the diaphragm, the
liver, omasum, and abomasum; it may be termed the fimdus reticuli.

The omasum is ellipsoidal in form and somewhat compressed laterally. It is
very clearly marked off from the other divisions. It is situated almost entirely
to the right of the median plane, opposite the seventh to the eleventh ribs. The
parietal (right) surface (Facies dexter) lies against the diaphragm, liver, and lateral
wall of the abdomen. The contact with the latter extends over a small area only
(ventral part of eighth, ninth, and tenth ribs usually). The visceral (left) surface
(Facies sinistra) is in contact with the rumen and reticulum. The greater curvature
is directed dorsally and somewhat backward; it is convex, and is related to the
diaphragm, hver, and intestine. The ventral (lesser) curvature is concave, and
faces ventrally and somewhat forward; it is in contact with the abomasum chiefly,
the junction with the latter appearing as a constriction near the middle of the
curvature; at its anterior part there is a neck (Collum omasi) which is the con-
nection with the reticulum.^

The abomasum is an elongated, piriform sac, which lies for the most part on
the abdominal floor, to the right of the reticulum and the ventral sac of the
rumen. Its narrow posterior part is strongly curved, the concavity being dorsal.
The parietal (right) surface lies against the abdominal wall from a point opposite to
the seventh or eighth rib as far back as the eleventh or twelfth costal cartilage. The
visceral (left) surface is related chiefly to the ventral sac of the rumen. The lesser
curvature is dorsal, and is in contact with the omasum; the junction of the two sacs
is indicated by a constriction about four or five inches (ca. 10 to 12 cm.) from the
anterior extremity of the abomasum. The greater curvature is ventral, and rests
on the abdominal wall from the xiphoid cartilage to the ventral part of the last
(right) intercostal space; its direction is approximately parallel to the right costal
arch.2 The fundus or anterior extremity forms a rounded blind sac which lies
against the reticulum. The pyloric or posterior extremity is much smaller and bends
upward and forward to join the duodenum. The intermediate part is sometimes
termed the body. About six to eight inches (ca. 15 to 20 cm.) from the pylorus there
is a constriction which marks off the pyloric part from the body and fundus.

The rumen is attached by peritoneum and connective tissue to the crura of
the diaphragm and left psoas muscles, from the hiatus oesophagus backward to
the fourth or fifth lumbar vertebra.

A small area of the anterior part of the right face of the rumen is adherent to
the adjacent surface of the abomasum. The greater part of the ventral curvature
of the omasum is attached by connective tissue to the dorsal face of the abomasum.^

The lesser omentum attaches the right face of the omasum and the pyloric
part of the abomasum to the visceral surface of the liver.

Interior
The cavity of the rumen is partially divided into dorsal and ventral sacs by
the pillars (Pilge ruminis) ; these are folds of the wall, strengthened by additional
muscular fibers, and correspond with the grooves on the outside. The two ex-

1 The relative size of the omasum is subject to considerable variation. It may extend back
to a point opposite the ventral fourth of the twelfth rib. The ventral curvature is usually opposite
to the ninth, tenth, and eleventh costal cartilages, but in some subjects it faces chiefly forward and
is opposite to the ventral third of the eighth or ninth rib.

2 The greater curvature may be in contact in part with the costal arch, but is chiefly medial
and ventral to it. It usually bends dorsally near the last costal cartilage and runs upward and
forward to the eleventh intercostal space.

3 Adhesion of the reticulum to the diaphragm is frequently present, but is pathological; the
same is true in regard to adhesion to the liver.

INTERIOR 457

tensive chief pillars project like shelves into the anterior and posterior ends of the
cavity, forming the blind sacs at either extremity. The anterior pillar (Pila cranialis)
projects obliquely backward and upward from the ventral wall, and has a thick,
concave free edge which is opposite to the tenth and eleventh ribs. Its width from
the middle of the free edge to its attached border is about eight to ten inches (ca. 20
to 25 cm.). It is continued on either side by the relatively narrow longitudinal
pillars (Pila dexter, sinister), which connect it with the posterior pillar. The
posterior pillar (Pila caudalis) is more nearly horizontal than the anterior one, and
separates the large dorsal and ventral posterior blind sacs. Its concave free border
is about a hand's breadth in front of a transverse plane through the tuber coxge.
From it are detached three accessory pillars on either side ; of these, two pass around
the blind sacs to meet the corresponding pillars of the opposite side. They thus

Fig. 389. — Thoracic and Anterior Abdominal Viscera of Ox; Deep Dissection.
Most of the rumen has been removed and the left wall of the reticulum cut away. A., Left pulmonary artery;
B., left bronchus; F. V. V., pulmonary veins; 6. b., bronchial lymph glands; L. g., posterior mediastinal lymph gland;
D., termination of duodenum; F, rumino-reticular fold.

mark off the posterior blind sacs from the general cavity, and are termed the
coronary pillars (Pila coronaria dorsalis, ventralis). It will be noticed that the
ventral coronary pillar is complete, while the dorsal one is not. The other accessory
pillars join the right and left longitudinal pillars. The right longitudinal pillar is
in part double ; its ventral division fades out about the middle of the surface, vv^hile
the dorsal one joins the posterior pillar. The distance between the middles of the
anterior and posterior pillars is only about sixteen to eighteen inches (ca. 40 to 45
cm.) in a cow of medium size. In this space the dorsal and ventral sacs communi-
cate freely.

The anterior end of the dorsal sac of the rumen is separated ventrally from the
reticulum by an almost vertical fold formed by the apposition of the walls of the
two compartments. This rumino-reticular fold (Pila rumino-reticularis) is oppo-
site to the seventh or eighth rib.^ Its free dorsal edge is concave and forms the

1 The position of this fold naturally varies with the degree of fulness of the reticulum. When
the latter is full, it may extend back in part to the eighth intercostal space.

458

DIGESTIVE SYSTEM OF THE OX

ventral and lateral margin of the large, oval rumino-reticular orifice (Ostium
rumino-reticulare). The medial margin of the fold, if continued, would end about
at the cardia, but there is in this region no demarcation between rumen and reticu-
lum; hence it is termed the atrium ventriculi.

The lateral border of the rumino-reticular fold ends above the level of and behind the plane
of the cardia, the medial one just behind the oesophageal groove and about four to five inches
lower down. Undoubtedly food or water swallowed with even a small degree of force passes first
into the rumen. Foreign bodies (which are commonly swallowed by cattle) are, however, found
in the reticulum.

The cardia is opposite the seventh intercostal space or eighth rib, a little to the
left of the median plane, and about a handbreadth (ca. 10-12 cm.) ventral to the
vertebral column; it is not funnel-shaped.

The mucous membrane of the rumen is brown in color, except on the margins

Fig. 390. — Reticulum or Ox, rsoM Photograph.
The specimen was cut along the greater curvature and laid open by reflecting the anterior wall. C is the cardia.
The arrow points to the reticulo-omasal orifice. The spiral twist of the oesophageal groove was of necessity partly
undone by reflecting the wall ; its lips are drawn apart, showing some of the peculiar birdclaw-like papillae in the
ventral part.

of the pillars, where it is pale. It is for the most part thickly studded with large
papillse, many of which are nearly half an inch (ca. 1 cm.) long. The edges of the
chief pillars and a large part of the wall of the middle of the dorsal sac are, however,
not papillated. The papillary arrangement is most developed in the blind sacs.
The papillse vary much in size and form; the largest are foliate, many are narrow
or filiform, and others are conical or club-shaped. The mucous membrane on the
medial wall of the atrium is finely wrinkled and non-papillated, while dorsally and
laterally it is papillated. The papillary arrangement also extends over the edge
of the rumino-reticular fold an inch or two (ca. 2 to 5 cm.).

The oesophageal groove (Sulcus oesophagus) begins at the cardia and passes

INTERIOR 459

ventrally on the right wall of the atrium and reticulum to end at the reticulo-
omasal orifice.^ It is about seven or eight inches (ca. 18-20 cm.) in length. Its
axial direction is chiefly dorso-ventral, but it inclines forward to a variable extent
and somewhat medially in its ventral part; the ventral end, which is at the reticulo-
omasal orifice, is about an inch (ca. 2.5 cm.) in front of the plane of the cardia and
to the right of the median plane. The groove is twisted in a spiral fashion, so that
its thickened edges or lips project first backward, then to the left, and finally for-
ward. The twist involves chiefly the left lip, and the relative position of the lips
is reversed at the ventral end. The mucous membrane on the lips of the oesoph-
ageal groove is brown and wrinkled, like that of the atrium; in the bottom of the

A nterior

Fig. 391. — Omasttm op Ox, Sagittal Section; Right View.
1, 2,3,4, Laminae of various orders; 5, muscular pillar; 6, neck connecting with reticulum; 7, connection with

groove it is pale, like that of the oesophagus, marked by longitudinal folds, and pre-
sents pointed, horny papillae on its ventral part.

In the reticulum the mucous membrane is raised into folds about half an inch
high, which enclose four-, five-, or six-sided spaces or cells (Cellulse reticuli); this
peculiar arrangement suggested the scientific name and also the popular term
"honey-comb." These cells are subdivided by smaller folds, and the bottoms are
studded with pointed, horny papillae. The cells grow smaller and gradually dis-
appear near the oesophageal groove and the edge of the rumino-reticular fold; an
inch or two from the latter the mucous membrane has the papillary arrangement
of the rumen. At the reticulo-omasal orifice there are peculiar horny papillae,
which are curved and resemble the claws of a small bird; hence they are termed
ungulif orm (Papillae ungulif ormes) . The reticulo-omasal orifice (Ostium reticulo-
1 It might better be termed the sulcus reticuli.

460

DIGESTIVE SYSTEM OF THE OX

omasicum) is situated in the medial wall of the reticulum, about five or six inches
above the bottom of the latter. It is rounded, and is limited below and laterally
by the junction of the lips of the oesophageal groove.

The cavity of the omasum is occupied to a considerable extent by about a
hundred longitudinal folds, the laminae omasi, which spring from the dorsal wall
and the sides. The largest of these — a dozen or more in number — have a convex
attached edge, and a ventral, concave free edge, which reaches to within a short
distance of the ventral wall of the sac. If these are drawn apart or a cross-
section is made (Fig. 392), it will be seen that there is a second order of shorter
laminae, and a third and fourth still shorter; finally there is a series of very low
folds or lines. The food is pressed into thin layers in the narrow spaces between the
laminae (Recessus interlaminares) , and reduced to a fine state of division by being
ground do^vn by the numerous rounded, horny papillae which stud the surfaces of
the folds. The ventral wall of the omasum forms a groove, the sulcus omasi,

which connects the reticulo-
omasal opening with the
omaso-abomasal opening; it is
about three inches (ca. 7-8
cm.) long, and is directed back-
ward and downward. It is
free from laminae, but presents
usually slight folds and small
papillae; it may function as a
direct path from the reticulum
to the abomasum for fluid and
finely divided food. In the
neck of the omasum there are
thick folds, and a number of
the peculiar papillae already
mentioned as occurring in the
lower part of the oesophageal
groove. The omaso-abomasal
orifice (Ostium omaso-abo-
masicum) is oval, and is about
four inches (ca. 10 cm.) long.
It is bounded in front by a
thick muscular pillar, the fibers
of which spread out above in
the sides of the omasum. The
mucous membrane forms an
extensive fold on each side of the opening; these folds may act as valves (Valvulae
terminales), which probably prevent regurgitation of the contents of the abomasum.
The cavity of the abomasum is chvided by a constriction into two areas. The
first of these (fundus gland region) is lined with a soft glandular mucous membrane,
which forms a dozen or more extensive spiral folds (Plicae spirales). The second
part (pyloric region) is much narrower and resembles in appearance the corre-
sponding region of the horse's stomach. A small cardiac gland zone surrounds the
omaso-abomasal orifice. The pyloric orifice is small and round.

Structure. — The serous coat invests all of the free surface of the stomach.
The surface of the rumen which is attached to the dorsal abdominal wall is, of
course, uncovered, as well as the adjacent area to which the spleen is attached.
The furrows are bridged over by the peritoneum and superficial muscle-fibers,
and contain fat and (in most cases) branches of the gastric arteries.

The lesser omentum passes from the visceral surface of the liver to the right

■^^^

Fig. 392. — Cross-section of Omasum of Ox.
1-5, Lamina of various orders; 0, neck connecting with

INTERIOR 461

(parietal) face of the omasum and the pyloric part of the abomasum and the first
part of the duodenum. What might be regarded as a connection between the
omenta is a fold between the ventral curvature of the omasum and the dorsal
curvature of the abomasum.

The greater omentum conceals the greater part of the intestine on the right
side, with the exception of the duodenum, and covers the ventral sac of the rumen
almost entirely. It is not lace-like, as in the horse, and contains a large amount
of fat in animals in good condition. It may be described as consisting of two
parts, each of which is composed of two layers of peritoneum; the two serous layers
enclose a variable amount of fat. The superficial part extends from the left
groove of the rumen ventrally around the ventral sac and ascends on the right
side, covering the deep part. It ends along the retrograde part of the duodenum
and the greater curvature of the abomasum. The deep part is attached along the
visceral (right) surface of the rumen ventral to the right groove, and curves around
the intestinal mass to the right side, where it is covered by the superficial part. It

Fig. 393. — I>fTERioR of Abomasum of Ox.
F, Fundus gland region with large spiral folds; P, pyloric region; D, duodenum; 1, pylorus; 2, torus pyloricus.

ends chiefly by blending with the medial layer of the mesoduodenum, but anter-
iorly is attached on the first bend of the colon and the visceral surface of the liver
along the ventral border of the pancreas. The two parts are continuous at the
posterior groove of the rumen. They also join at the iliac flexure of the duodenum
and at the origin of the colon. The epiploic foramen is almost sagittal in direc-
tion.

The muscular coat of the rumen consists of two layers. The fibers of the
external layer are in general longitudinal; those of the thicker internal layer are
largely circular in direction. The latter forms the bulk of the chief pillars, where
it is about one-half to one inch (ca. 1 to 2 cm.) thick. Scattered bundles of striped
muscle-fibers radiate from the cardia in the wall of the atrium and extend also along
the oesophageal groove.

The arrangement is in fact by no means so simple as might be inferred from the above brief
statement, and much variation from the typical disposition is present. Along the furrows the
fibers of the external layer are disposed more or less obUquely or even vertically in part; a super-
ficial part of the layer bridges over the furrows (with the fat and vessels contained therein), while
the deeper fibers extend into the pillars. The fibers of the inner layer on approaching the furrows
change to an oblique or even horizontal direction. On entering the chief pillars this layer becomes

462

DIGESTIVE SYSTEM OF THE OX

much thicker and its fibers have the same direction as the pillars. Thus the muscular tissue of
the pillars is seen on cross-section to consist of two thick layers of longitudinal fibers, which are
separated (except at the free margin of the pillar) by a thin axial layer of fibers disposed at right
angles to the preceding.

The muscular coat of the reticulum consists of two chief layers which begin
and end at the oesophageal groove; they pass in a circular or oblique fashion around
the sac, the fibers of the two layers crossing each other at varying angles. The
walls of the cells contain a central muscular layer. The lips of the oesophageal
groove consist chiefly of a thick layer of longitudinal fibers, which are largely con-
tinuous at, or cross each other below, the reticulo-omasal orifice. The bottom of
the groove has two layers of oblique, unstriped muscle-fibers,
with a variable outer layer of striped muscle continuous with
that of the oesophagus.

The external muscular layer of the oesophagus is in part continued
down along the oesophageal groove (i. e., along the lesser curvature of
the reticulum), but in greater part spreads out on the wall of the rumen
and reticulum. The internal muscular layer of the oesophagus forms a
loop over the cardia and is largely continued in the hps of the oesopha-
geal groove; part of it is continuous with the muscular laj^er of the
bottom of the groove.

The muscular coat of the omasimi consists of a thin ex-
ternal longitudinal layer and a thick internal circular layer.
At the omasal groove there is an incomplete inner layer of
oblique fibers. The larger laminae contain three muscular
strata. The fibers of the central layer extend from the at-
FiG. 394. — MuscuLA- tached edge toward the free edge, but do not reach the latter ;

TURE OF (Esophageal
Groove and Adjacent
Part of Stomach of

Ox, SEEN FROM WITHIN

after Removal of

Mucous Membr.vne.

a, ffisophagus; b, in-
ner muscular layer of atri-
um; d, reticulo-omasal ori-
fice; e, e', muscle of lips of
groove; g, lower end of
muscle of larger lip, which
curves around the reticulo-
omasal orifice in part and
spreads out in the inner
muscular layer of the retic-
ulum in part; h, lower
end of muscle of smaller
lip, which in part curves
around the reticulo-omasal
orifice and is in part con-
tinuous with the inner mus-
cular layer of the omasal
groove and the omasum;
t, inner muscular layer of

reticulum. (Ellenberger- ^^°- 395- — Stomach of New-born Calf; Right View.

Baum, Anat. d. Haustiere.) The rumen is raised.

Oesophagui

here there is a marginal band of longitudinal fibers. The central layer is contin-
uous with the inner circular layer of the wall. On either side there is a layer of
longitudinal fibers, which are continuous at the attached border with the muscu-
laris mucosae.

The muscular coat of the abomasum consists of longitudinal and circular
layers; the latter forms a well-developed pyloric sphincter.

The mucous membrane of the first three divisions is destitute of glands, and
is covered with a thick, stratified, squamous epithelium; the superficial part of

THE INTESTINE

463

the latter is horny, and is shed in large patches in the rumen and omasum. The
tunica propria is papillated. The mucous membrane of the abomasum is glandular,
and corresponds to that of the right sac of the stomach of the horse. The fundus
glands (which are relatively short) occur in that part which presents the large folds,
while the long pyloric glands are found in the remainder, except about the omaso-
abomasal orifice, where cardiac glands occur. The mucosa of the fundus gland
region is very thin as compared with that of the

horse; toward the pylorus there is an increase in f'^?^\^

thickness. There is a round prominence (Torus ^ \ ■ '. ^

pyloricus) on the upper part of the pyloric valve.
Vessels and Nerves.— The blood supply is
derived from the coeliac artery, and the veins

go to the portal vein. The nerves come from B * i'^i^-"'
the vagus and sympathetic. Numerous ganglia
are present in the submucous and intermuscular
tissue, especially in the reticulum and oeso-
phageal groove. — «■—

THE INTESTINE

The intestine of the ox is about twenty
times the length of the body. It lies almost
entirely to the right of the median plane, chiefly
in contact with the right face of the rumen. It
is attached to the sublumbar region by a com-
mon mesentery.

The small intestine has an average length
of about 130 feet (ca. 40 m.) and a diameter of
about two inches (ca. 5 to 6 cm.). The duo-
denum is about three or four feet (ca. 1 m.) in
length. Beginning at the pylorus (usually at the
ventral end of the eleventh rib or intercostal
space), it passes dorsally and forward to the
visceral surface of the liver; here it forms, ven-
tral to the right kidney, an S-shaped curve (Ansa
sigmoidea) . Thence it runs backward almost to
the tuber coxae, where it turns on itself, passes
forward alongside of the terminal part of the
colon, and joins the mesenteric part (jejunum)
under the right kidney. It is attached to the
liver by the lesser omentum; the remainder of
the mesoduodenum is a narrow fold which is
largely derived from the right layer of the com-
mon mesentery, but at the iliac flexure it comes
directly from the sul^lumbar region. The bile
duct opens in the ventral part of the S-shaped curve
about a foot (ca. 30 cm.) further back.

The remainder of the small intestine is arranged in numerous very close coils,
which form a sort of festoon at the edge of the mesentery. It hes chiefly in the
space bounded medially by the right face of the ventral sac of the rumen, laterally
and ventrally by the abdominal wall, dorsally by the large intestine, and anteriorly
by the omasum and abomasum. It is not subject to much variation in position,
but a few coils may find their way behind the blind sacs of the rumen to the left
side. The terminal part leaves the edge of the mesentery and runs forward be-

FiG. 396. — Large and Small Aggregated
Follicles or Peyer's Patches op
Small Intestine of Ox (about M "."-t-
ural size).

The pancreatic duct opens

464

DIGESTIVE SYSTEM OF THE OX

tween the csecum and colon, to both of which it is adherent. The orifices of the
pancreatic duct and the bile duct are on papillse or thick folds, no diverticulum
being present. There are permanent transverse folds of the mucous membrane
(Plicae circulares). Duodenal glands occur in the first twelve to fifteen feet (4 to 4.5

Fig. 397, — Projection of Viscera of Bull on Body-wall; Right Side.
P., Pylorus; G.b., gall-bladder; R.K., right kidney; L.K., left kidney; P. (above duodenum), pancreas; Bl.,
urinary bladder; V.s., vesicula seminalis; B.g., bulbo-urethral (Cowper's) gland. Costal attachment and median
line of diaphragm are indicated by dotted lines.

Fig. 39S. — Projection of Viscera of Cow on Body-wall; Left Side.
Oes., Oesophagus; Ret., reticulum; b. s., anterior blind sac; b. s"., posterior blind sacs of rumen; 0, ovary. The
left kidney, concealed by the dorsal sac of the rumen, is indicated by dotted line. The median line of the diaphragm
is dotted.

m.), intestinal glands throughout. The aggregated follicles or Peyer's patches are
larger and more prominent and distinct than in the horse, and vary greatly in size
and number; in adult cattle there are eighteen to forty; in calves twenty to fifty-
eight have been counted. They usually have the form of narrow bands. There
is a patch close to the ileo-csRcal ^'alve.

THE LIVER 465

The large intestine is much smaller in caliber than that of the horse, has no
bands, and is not sacculated. Most of it is situated between the layers of the
common mesentery in the right dorsal part of the abdominal cavity. It is related
on the right to the lateral abdominal wall, from which, however, it is almost com-
pletely separated by the greater omentum. On the left it is chiefly related to the
rumen. The average length of the caecum is about thirty inches (ca. 75 cm.), and
the diameter is about five inches (ca. 12 cm.). It is directly continuous in front
with the colon, the conventional demarcation being the junction of the ileum with
the large intestine.^ From this junction, which is on the medial side and usually
near the ventral end of the last rib, the caecum extends backward and upward
along the right flank (from which it is separated by the greater omentum), and its
rounded blind end commonly lies at the right side of the pelvic inlet. The caecum
is attached along its medial side to the mesentery, except the posterior third, which
is free and variable in position. The terminal part of the ileum runs forward along
the medial surface of the caecum and is attached to the latter. The dorsal surface
is attached by areolar tissue and peritoneum to the colon. The colon is about
thirty-five feet (ca. 10 m.) in average length. Its diameter is at first the same as
that of the caecum, but diminishes to about two inches (ca. 5 cm.). The greater
part of it is arranged in double elliptical coils between the layers of the mesentery;
the coils are attached to each other by areolar tissue. It begins as the direct
continuation of the caecum, runs forward a short distance, and turns dorsally and
backward opposite to the ventral part of the last two ribs. It continues backward,
in relation to the right flank laterally and the caecum ventralh^, to the posterior
part of the sublumbar region. Here it turns forward and runs parallel -with the
retrograde part as far forward as the second lumbar vertebra, turns backward, and
is continued by the spiral part (Ansa spiralis). The coils of this are alternately
centripetal and centrifugal (Gyri centripetales et centrif ugales) ; they are best
seen from the left side. The bowel gradually diminishes in caliber, and the ter-
minal part (Ansa distalis) leaves the spiral mass, passes forward to the great mesen-
teric artery, and runs backward dorsal to the terminal part of the duodenum. It
inclines to the right in relation to the ventral surface of the right kidney, forms an
S-shaped curve near the pelvic inlet, and joins the rectum; this part is attached to
the sublumbar region by a narrow mesentery, and is also attached to the recurrent
part of the duodenum.

The rectum is somewhat shorter than that of the horse, and is usually covered
with peritoneum as far back as the first coccygeal vertebra. The retroperitoneal
part is surrounded by a quantity of fat. The anus is not prominent.

The serous coat is of course absent on the adherent surfaces of the spiral part
of the colon. There is a large amount of fat in the mesentery. The longitudinal
fibers of the muscular coat are evenly distributed, consequently there is no saccula-
tion of the bowel. There is a valvular mucous fold at the ileo-caecal orifice. A
Peyer's patch occurs in the beginning of the caecum and one in the first part of the
colon.

THE LIVER

The liver lies almost entirely to the right of the median plane. Its long axis
is directed obliquely dowTiward and forward, about parallel with the median plane,
and corresponds to the curvature of the right portion of the diaphragm. It is less
extensive, but thicker than that of the horse. Its average weight is about 10 to
12 pounds (ca. 4.5 to 5.5 kg.).

1 In formalin-hardened material there is sometimes a constriction in front of the termination
of the ileum. This might be regarded as the demarcation between the csecum and colon. The
opening of the ileum is directly forward, so that material from it enters the origin of the colon.
The posterior free part of the csecum is naturally variable in position; it may be bent ventrally,
so that the blind end faces forward.
30

466 DIGESTIVE SYSTEM OF THE OX

In small subjects the weight (according to Schmaltz) varies from 6J'2 to 10 pounds (ca.
3 to 4.5 kg.), in large subjects from 11 to 13 pounds (ca. 5 to 6 kg.). According to Schneider, the
average weight is about 13 pounds (ca. 6 kg.) — a little over 1 per cent, of the live weight and
about 2 per cent, of the dressed carcass.

When hardened in situ, it is seen to be adapted accurately to the structures
with which it is in contact.

The parietal surface is convex and is for the most part applied to the right
part of the diaphragm, but a small part of it is in direct contact with the last two
or three ribs and with the flank at the lumbo-costal angle. It faces dorsally, for-
ward, and to the right.

The curvature of the parietal surface is not quite regular. It is marked, except in its ventral
part, by a blunt oblique ridge which divides the surface into two areas. Of these, the lateral one

Caudate lobe

Faiciform ligament (cut)

Coronary ligament (cut)

Gall-bladder ^^^^^^^^mm^ ^as^^^^^^n^m

Posterior vena cava

Hepatic veins
(Esophageal notch

FiQ. 399. — Liver of Ox, Parietal Surface; Hardened in situ.

Is directed outward, is only slightly convex, and often shows impro^jsions of the last three ribs; it is
in contact in part directly with the right abdominal wall, in part with the costal part of the dia-
phragm which is in contact ordinarily with the lateral wall. The medial area presents a depression
produced by the right crus of the diaphragm, and otherwise is regularly convex and adapted to
the tendinous center and sternal part of the diaphragm. The falciform ligament is attached to
the surface from the oesophageal notch to the umbilical fissure. There is a triangular area of
considerable size on the dorso-medial part of the surface which is without a peritoneal covering,
since it is adherent to the diaphragm.

The visceral surface is concave and very irregular; it presents impressions of
the chief organs which are in contact with it— the omasum and reticulum. It is
also related to the pancreas and duodenum.

The following markings are quite distinct on the visceral surface of well-hardened speci-
mens: (1) The omasal impression (Impressio omasica) is a deep central cavity below the portal

THE LIVER

467

fissure. (2) The reticular impression (Impressio reticularis) is a smaller marginal depression below
the oesophageal notch antl the medial part of the preceding, from which it is separated by a rounded
ridge. (3) The abomasal impression (Impressio abomasica), present only in the young subject

Renal impression

Lesser omentum (cut)
(Esophageal notch

I' till nlical fissure

Fig. 400. — Liver of Heifer, Viscek.4.l Surface; Hardened in situ.
The abomasal impression ia shown to the right of the reticular impression, but by an oversight is not marked.

Area of attachment to
diaphragm (noii-pcriloitcal)

Caudate lobe

Coronary ligameiU
Posterior vena cava

Hepatic veins
(Esophageal iwtch
Fig. 40L — Liver of Ox, Left Marginal View; Hardened in st

usually, corresponds to the fundus of the abomasum. It lies along the ventral part of the surface
and is separated by ridges from the preceding impressions. It usually disappears as the omasum
and reticulum increase in size and displace the abomasum from contact with the liver. (4j Shallow

468 DIGESTIVE SYSTEM OF THE OX

grooves for the S-sliaped portion of the duodenum (Impressio duodenaUs) may be found dorsal
and lateral to the portal fissure. (5) The fossa of the gall-bladder (Fossa vesicae fellese) is distinct
when that organ is full. In the calf the omasal impression is small, and the abomasal one large in
correspondence with the relative sizes of these two sacs.

The portal fissure is a well-defined rounded depression, situated dorsal to the
omasal impression. It contains, besides the vessels and duct, several large hepatic
lymph glands. Dorsal and lateral to it a part of the pancreas is attached.

The dorsal border is short and thick; it usually extends backward a short
distance beyond the upper part of the last rib. It presents the large, thick, quad-
rilateral caudate lobe, and a deej^ depression for the right kidney and adrenal.

The ventral border is short and thin and has no interlobar incisures.

The right (or lateral) border is marked by the umbilical fissure, in which the
ligamentum teres is attached in the young subject.

The left border presents the oesophageal notch below its middle; the notch is
much shallower than in the horse. Above this it is practically median in position,
and lodges the posterior vena cava, which is partially embedded in the gland. Be-
low the notch the border extends an inch or two (ca. 2.5 to 5 cm.) to the left of the
median plane, opposite the ventral third of the sixth rib or intercostal space.

The right lateral ligament attaches the dorsal border to the anterior part of
the sublumbar region. The ligament of the caudate lobe passes to the ventral
surface of the right kidney. There is no left lateral ligament. The falciform liga-
ment is generally present, but the ligamentum teres is usually found only in young
subjects. The lesser omentum leaves the liver along a line extending from the
oesophageal notch to the portal fissure. The only distinct lobes in the adult are
the caudate and papillary. The latter is best seen in the soft specimen; it is a
tongue-like mass which partly overlaps the portal vein and fissure.-^

A gall-bladder (Vesica fellea) is present. This is a pear-shaped sac, four to
six inches (ca. 10 to 15 cm.) long, which lies partly in contact with the visceral
surface of the liver (to which it is attached), but largely against the abdominal wall
at the ventral part of the tenth or eleventh intercostal space. It may be regarded
as a diverticulum of the bile-duct, enlarged to form a reservoir for the bile. Its
neck is continued by the cystic duct (Ductus cysticus), which joins the hepatic
duct at an acute angle just outside of the portal fissure, to form with it the bile-
duct (Ductus choledochus) . The latter is short and enters the second bend of the
S-shaped curve of the duodenum, i. e., about two feet (ca. 60 cm.) from the pylorus.
The opening of the duct is at the end of a papilla or ridge-like fold. Several small
ducts (Ductus hepatocystici) open directly into the gall-bladder.

The wall of the gall-bladder consists of serous, muscular, and mucous coats. The muscular
tissue consists of unstriped fibers which run in various directions; externally many are longitudinal,
while internally (and especially at the neck) they are chiefly circular. The mucous membrane is
covered by a cylindrical epithelium and contains numerous groups of branched tubular glands.
The cystic and bile ducts have a similar structure.

In the new-born calf the liver is relatively much larger than in the adult. The visceral
surface presents, below the portal fissure, a rounded eminence, which is caused by the pres-
ence in the underlying gland substance of a large venous sinus into wliich the umbilical and portal
veins empty. A large vessel, the ductus venosus, leads from this sinus directly to the posterior
vena cava. The umbiUcal fissure is deep and partially divides the gland into two chief lobes.

THE PANCREAS

The pancreas of the ox is irregularly quadrilateral in form, and lies almost

entirely to the right of the median plane. Its weight is about the same as that of

the horse. Its dorsal surface is related to the liver, right kidney, crura of the

diaphragm, posterior vena cava, and cceliac and anterior mesenteric arteries; it is

^ The liver of the ox might be regarded as consisting of dorsal, ventral, caudate, and papillary
lobes. Pathological adhesions of the ventral part of the hver to the diaphragm and reticulum
are often present in dissecting-room subjects.

THE PANCREAS

469

covered to a large extent by peritoneum. It is attached to the hver at and lateral
to the portal fissure, and to the crura of the diaphragm. Between these adhesions
it is free and forms the ventral wall of the epiploic foramen. On the right side it
extends backward beyond the caudate lobe of the liver between the layers of the
mesoduodenum; here it is in contact with the upper part of the flank at the lumbo-
costal angle, and is related dorsally to the right kidney and by its ventro-lateral

Pancreatic duct ■

Caudate lobe
of liver

Duodenum

Gall-bladder
Round ligament
of liver

Fig. 402. — Pancreas and Related Strtctt hks of Ox.
1, Left extremity of pancreas; 2, posterior vena cava; 3, portal vein; 4, gastro-splenic vein; 5, probe in epiploic
foramen; 6, bile duct; 7, cystic duct; S, pancreatico-intestinal lymph gland; 9, cut edge of lesser omentum; 10,
omasal impression of liver. Intraglandular part of pancreatic duct and its chief radicles are shown by dotted lines.
Concealed parts of bile duct, cystic duct, and neck of gall-bladder are similarly indicated.

border to the retrograde part of the duodenum. The ventral or gastro-intestinal
surface is in contact with the dorsal curvature of the rumen and the intestine.
There is a deep notch (Incisura pancreatis) for the portal vein and hepatic artery,
and several lymph glands are present here. The left extremity is small and quad-
rilateral; it is related dorsally to the crus of the diaphragm, left adrenal, and the
cceliac and anterior mesenteric arteries, and is adherent ventrally to the rumen.

470

DIGESTIVE SYSTEM OF THE SHEEP

The right or posterior part is wide and thin and is often divided into two branches.
The duct leaves the posterior part of the ventro-lateral (or right) border and enters
the duodenum about twelve inches (ca. 30 cm.) further back than the bile-duct.

Dorsal extremity

Splenic vein
Splenic artery
Hilus

THE SPLEEN

The spleen has an elongated, elliptical outline, both extremities being thin,

rounded, and similar in size.

Its average weight is about two pounds (ca. 900 gm.), or about ^ & per cent, of

the body-weight. Its average length is about 20 inches (ca. 50 cm.), its width

about 6 inches (ca. 15 cm.), and in the
middle its thickness is about an inch (ca.
2 to 3 cm.).

The dorsal extremity lies under the
dorsal ends of the last two ribs, and may
extend back as far as the first luml^ar
transverse process. The ventral extrem-
ity is usually opposite the eighth or ninth
rib, about a handbreadth above its junc-
tion with the cartilage. The parietal sur-
face is convex, and is related to the dia-
phragm. The visceral surface is concave,
and is related chiefly to the left face of the
rumen, but also usually to a narrow ad-
jacent area of the reticulum. The dorsal
part is attached to the left crus of the dia-
phragm and the left surface of the rumen
by peritoneum and connective tissue ; the
ventral part is free. The hilus is situated
on the dorsal third of the visceral surface,
near the anterior border.

About one-half of the visceral surface of the
spleen is attached directly to the stomach and is
therefore not covered by peritoneum ; the line of re-
flection of the latter crosses the surface obliquely,
from the upper part of the posterior border to
the anterior border below its middle. Similarly
there is a narrow uncovered area on the upper
part of the parietal surface along the anterior
border. The hilus is not a groove, but a simple
depression. When hardened in situ, the organ is
seen to be somewhat twisted, so that the upper
part of the parietal surface faces dorsally and
forward, while below it is directed laterally. In
some cases the spleen is considerably longer than
IS stated aljove. and may extend to the ventral end of the eighth rib. Not uncommonly there are
pathological adhesions of the ventral part of the spleen to adjacent structures.

Ventral extremity

Fig. 403. — Spleen- of Ox; Visceral Surface.
1, Area of attachment to rumen (non-peritoneal);
line of peritoneal reflection.

posterior border;

DIGESTIVE SYSTEM OF THE SHEEP

The lips are thin and mobile; the upper one is marked by a very distinct
philtrum, and otherwise is not bare.

The anterior part of the hard palate is prominent and smooth, forming the
so-called dental pad or plate. On the posterior part of this area there are two

DIGESTIVE SYSTEM OF THE SHEEP

471

narrow depressions in the form of a V and separated by the central papilla incisiva,

at the deep anterior ends of which the incisive or naso-palatine ducts open. The

ridges of the palate, some fourteen in number, are irregular and their edges are

smooth; most of them alternate with those of the

opposite side, from which they are separated by the

median raphe palati. The posterior third or rather

more is not ridged and presents numerous orifices of

ducts of the palatine glands. The mucous membrane

is often more or less pigmented. The soft palate

resembles that of the ox.

The mucous membrane of the cheeks is covered
with large papillae, many of which are long and sharp-
pointed, while others are short and blunt. There is
also a series of conical papillae on the floor of the
mouth, under the lateral part of the tongue.

The tongue resembles that of the ox in form, but
the tip is comparatively smooth; the papillae here are
very numerous, but short and blunt. This difference
is in conformity with the dissimilarity in the mode of
prehension of the two species. The prominence of
the dorsum is commonly not so pronounced nor so
sharply marked off in front as in the ox. The root
is smooth. The mucous meml^rane of the dorsum is
often pigmented in spots.

The dental formula is the same as that of the
ox.^ The incisor teeth form a narrow and strongly
curved arch. The crowns are long and narrow; their
labial surfaces are strongly convex and end at a sharp
edge which is used in cropping the grass. The roots
are more firmly embedded than in the ox. The cheek p^^ 404.-Palate of sheep.

teeth resemble those of the ox, but have a thinner i_ Dental pad; 2, papiiia in-

layer of cement, which is often blackened by deposits cisiva; 3, 3, openings of incisive
from the food. The average periods of eruption of canals; <t, raph^ paiati; 5 phii-

. , , . . , , trum; G, conical papulae of cheek;

the teeth are mdicated m the sulijomed table: 7, tonsils; s, palatine arch.

Temporary

Permanent

Ii At birth or first week 1 to 1 ;^ 2 years

I2 First or second week 1 3^ to 2 years

I3 Second or third week 23^ to 3 years

I4 Third or fourth week 33 2 to 4 years

P2 [ 2 to 6 weeks 13^ to 2 years

P3J

Ml 3 months (lower), 5 months (upper)

M2 9 to 12 months

Ms 13^ to 2 years

The salivary glands resemble those of the ox in general. The parotid gland
is darker in color and more compact in texture than the mandibular. It is rounded
in outline, but has a pointed cervical angle at which the external jugular vein
emerges. The duct leaves the lower part of the anterior border of the gland and
runs forward over the masseter muscle, about an inch and a half (ca. 3.4 cm.)
above the ventral border of the ramus; it opens opposite the third or fourth
cheek tooth.

The tonsil is bean-shaped and about half an inch (ca. 12 mm.) in length. Jt
1 A lateral view of the teeth is given in the description of the skull.

472

DIGESTIVE SYSTEM OF THE SHEEP

does not project into the isthmus faucium. The mucous membrane of the latter
presents two deep and very narrow tonsillar sinuses on either side.

The fornix of the phar3mx presents a median plicated fold which is a continua-
tion of the septum nasi. The pharyngeal orifice of the Eustachian tube has the
form of a crescentic slit, placed about on a level with the ventral nasal meatus.
There are two large lymph glands and a number of hsemolymph glands above the
pharynx.

The oesophagus has a lumen of about an inch (ca. 2.5 cm.) when moderately
distended; otherwise it resembles that of the ox.

The stomach is like that of the ox in its general arrangement. Its average
capacity is about four gallons (ca. 15 liters). The cardia is opposite the eighth
intercostal space; it is just to the left of the median plane, and about two inches

Dorsal curvature of
rumen

Fig. 405. — Stomach of Shkep; Left View,
From photograph of specimen hardened in situ. The reticulum is

hat contracted.

(ca. 5 cm.) below the vertebral column. The dorsal sac of the rumen is a little longer
than the ventral sac and extends considerably (ca. 7.8 cm.) further forward than
the latter. The ventral sac is relatively larger and extends further to the right of
the median plane than in the ox; its posterior blind sac extends further (ca. 6-8 cm.)
back than that of the dorsal sac. The parietal attachment of the dorsal sac
extends back to the second lumbar vertebra. The left longitudinal groove ex-
tends upward and backward for a short distance only, and therefore does not
connect with the posterior groove. There are two longitudinal grooves on the
right side which join at each end, thus enclosing a long, narrow prominent area;
the dorsal one contains the right ruminal artery, and the ventral one corresponds to

DIGESTIVE SYSTEM OF THE SHEEP

473

the pillar. The left coronary grooves do not extend to the curvatures. There is
no dorsal coronary groove on the right side, but the ventral one is very distinct and
extends to the curvature. The arrangement of the pillars corresponds to these
external features. The papilla of the rumen are relatively large and somewhat
tongue-like; the largest are about a fourth of an inch (ca. 6 mm.) in length. The
dorsal part is papillated, not glabrous, as in the ox. The lateral part of the rumino-
reticular fold ends half an inch or more (ca. 1.5 cm.) behind the cardia. The
reticulum is relatively larger than in the ox. Its ventral part curves more back-
ward and less to the right than in the ox. The parietal surface extends forward as

Reticulo-
^ abomasal
groove

Fig. 406. — Stomach of Sheep; Right View.
From photograph of specimeii hardened in situ. Dotted line indicates position of spleen.

far as the sixth rib or intercostal space, and is related to the diaphragm and liver.
The fundus lies on the sternal part of the diaphragm and is in contact behind with
the abomasum. The oesophageal groove is disposed in general like that of the ox,
and is about four to five inches (ca. 8 to 10 cm.) long.

There are, however, several marked differences in the arrangement of the groove. Its ven-
tral part curves backward, so that the reticulo-omasal orifice is directed dorsally and lies in a trans-
verse plane about an inch (ca. 2-3 cm.) behind one passing through the cardia. These differ-
ences are correlated with the small size of the omasum and the large size of the reticulum.
Tubulo-alveolar glands have been found by Thanhofer and others; they occur chiefly in the
submucous tissue at the angle of junction of the hps and bottom of the groove.

The folds surrounding the cells of the reticulum are only 2-3 mm. in height,

474 DIGESTIVE SYSTEM OF THE SHEEP

and have serrated edges. The dorsal part of this sac has, in the vicinity of the
rumino-reticular orifice, a papillated mucous membrane just Ul^e that of the
rumen. The omasum is much smaller than the reticulum, its capacity being
only about one pint. It is oval and compressed laterally. It is situated almost
entirely to the right of the median plane, opposite to the ninth and tenth ribs,

Fig. 407. — Cross-section of Sheep, through Ninth Thoracic Vertebra; Anterior View.
1, Cardia; 2, oesophageal groove; S, rumino-reticular orifice; 4> rumino-reticular fold; 5, dorsal sac of rumen;
6, body of ninth thoracic vertebra; 7, vena hemiazygos; S, aorta; 9, posterior mediastinal lymph gland; 10, 10, crura
of diaphragm; 77, posterior vena cava; i^, portal vein; i?./., right lung; L.Z., left lung; S, spleen; L, liver; iJ, reticu-
lum (posterior wall) . Arrow points to reticulo-omasal orifice. The spleen is cut so obliquely as to appear much thicker
than it really is.

higher than in the ox, and has no contact with the abdominal wall. It is related
on the right to the liver and gall-bladder, on the left to the rumen, and ventrally
to the abomasum. The laminae are less numerous than in the ox; in the neck
which connects the omasum with the reticulum they have the form of low, thick
ridges, and bear long, pointed, horny papillae. The abomasum is relatively

DIGESTIVE SYSTEM OF THE SHEEP

475

larger and longer than in the ox. Its capacity is about twice that of the
reticulum and averages about two quarts (ca. 1.75 to 2 liters). The blind
anterior end Hes almost centrally in the xiphoid region, in relation to the liver and
reticulum. Its body extends backward a little ventral to and almost parallel
with the right costal arch. The pylorus is usually opposite the ventral end
of the eleventh or twelfth intercostal space. At the reticulo-omasal open-
ing and on the adjacent part of the laminae of the omasum are large, pointed,
horny papillse.

The general arrangement of the intestine is like that of the ox. The small

Fig. 408.— Abdominal Viscera of Sheep; Superficial Ventral Vii

intestine is about 80 feet (ca. 24 to 25 m.) long; its average diameter is about an
inch (ca. 2 to 3 cm.) , the caliber increasing in its terminal part, where a very extensive
Peyer's patch is found. Duodenal glands occur for a distance of two feet or more
(ca. 60-70 cm.) beyond the pylorus. The caecum is about 10 inches (ca. 25 cm.)
long, 2 inches (ca. 5 cm.) wide, and has a capacity of about a quart (ca. 1 liter);
only about two inches (ca. 5 cm.) of it is free. The colon is about 15 feet (ca. 4 to
5 m.) long. Its caliber is at first about the same as that of the caecum, but dimin-
ishes to about the width of the small intestine.

The liver weighs about 20 to 25 ounces (ca. 550 to 700 gm.). It lies entirely

476

DIGESTIVE SYSTEM OF THE SHEEP

to the right of the median plane. The parietal surface is related almost exclusively
to the right part of the diaphragm. The visceral surface presents extensive reticular
and abomasal impressions, and a small omasal impression medial to the portal
fissure. The umbilical fissure is deep and partially divides the gland into two
chief lobes, dorsal and ventral. The caudate lobe is prismatic and blunt-pointed.
The oesophageal notch is represented by a slight impression. The gall-bladder is
long and narrow. The bile-duct joins the pancreatic duct to form a common bile-
duct (Ductus choledochus communis), which opens into the duodenum about one
foot (ca. 30 cm.) from the pylorus.

The pancreas is arranged as in the ox. Its duct unites with the bile-
duct.

The spleen (Fig. 405) is approximately triangular, with the angles rounded off;

Renal impression

Caudate lobe

Posterior vena
cava

Portal vein

Hepatic artery

Omasal impres-
sion

Lesser omentum,

Reticular imprcs-

Bile-duct

Cystic duct

Fig. 409 —Liver of Sheep, Visceral Surface; Hardened in situ.

the wider end or base is dorsal. It weighs about three or four ounces (ca. 100 grams).
Its length is about five to six inches (ca. 12 to 15 cm.), and its greatest width three
to four inches (ca. 7.5-10 cm.). The long axis is oblique, and corresponds to a line
drawn from the vertebral end of the last rib to about the middle of the tenth inter-
costal space. The parietal surface is convex and is related to the diaphragm, to
which rather more than the anterior third is adherent; when hardened in situ, it
often shows impressions of the upper parts of the last three ribs. The visceral
surface is concave, and its anterior half is attached to the dorsal curvature of the
rumen. The borders are thin, the posterior one often being crenated. The dorsal
end or base is attached to the left crus of the diaphragm under the last two ribs;

DIGESTIVE SYSTEM OF THE PIG THE MOUTH

477

Fig. 410. — Liver of Sheep, Parietal Surface; Hardened in situ.
1, Posterior vena cava; 2, falciform ligament; 3, gall-bladder; 4, umbilical fissure.

it usually extends about an inch (ca. 3 cm.) behind the last rib. The hilus is on the
visceral surface, close to the anterior basal angle; it is a round depression, not a
groove. The ventral end is narrower and thinner than the base; it is usually
situated opposite the tenth intercostal space or eleventh rib, a little above its middle.

DIGESTIVE SYSTEM OF THE PIG
THE MOUTH

The rima oris is extensive, the angles of the mouth being situated far back.
The upper lip is thick and short, and is blended with the snout; the lower lip is
small and pointed. The labial glands are few and small.

The mucous membrane of the cheeks is smooth. The buccal glands are
compactly arranged in two rows opposite the cheek teeth. The parotid duct
opens opposite the fourth or fifth cheek tooth.

The hard palate is long and narrow; it is marked by a median furrow, on each
side of which are twenty or more ridges. On its anterior part there is a long narrow
prominence, the incisive papilla, at the posterior part of which the incisive or naso-
palatine ducts open. There is a round prominence in front of the first pair of
incisors.

The soft palate is wery thick; its length in an animal of medium size is about
two and a half inches (ca. 5 cm.). Its chrection almost continues that of the hard

478

DIGESTIVE SYSTEM OF THE PIG

palate, i. e., it is nearly horizontal. It extends to the middle of the oral surface
of the epiglottis. It has in many cases a small median prolongation termed the
uvula. The oral surface presents a median furrow, on either side of which is an
oval raised area, marked by numerous crypts; these elevations are the tonsils.
Tonsillar tissue also occurs in the lateral walls of the isthmus faucium and the root
of the tongue.

The tongue is long and narrow and the apex is thin. Two or three vallate

Fig. 411. — Hard Palate of Young Pig.

1, Papilla incisiva; 2, openings of ductus in-
cisivi; 3, raph6 of palate; a, incisor teeth; b, canine
tooth; c, premolar teeth; d, molar teeth.

Fig. 412. — Tongue of Pig.
1, Apex; 2, dorsum; 3, root; a, orifices of ducts of
lingual glands; b, papillae of root; c, vallate papilla (not
really so distinct as in figure); rf, fohate papilla; e, fungi-
form papillae; /, epiglottis (pulled back); g, median glosso-
epiglottic fold. (EUenberger-Baum, Anat. d. Haustiere.)

papillae are present. The fungiform papillse are small and are most numerous
laterally. The filiform papillae are soft and very small. On the root there are
soft, long, pointed papillae, directed backward. Foliate papillae are also present.

There is a well-marked median glosso-epiglottic fold, on either side of which is
a depression (Vallecula epiglottica) . The frenum linguae is double.

The dental f ormula^ of the pig is :

/ 3 1 4 3\
I I - C - P - M - )
V 3 1 4 3/

21 I-C-P-M-l = 44
V 3 1 4 3/

Several figures in the osteology also illustrate the teeth.

THE MOUTH

479

The formula for the temporary teeth is :

/ 3 1 4\

2 ( Di-Dc-Dp- I

V 3 1 4/

The upper incisors are small; they are separated from each other by spaces,
and from the canines liy a larger interval. The first incisors are the largest; they
are flattened and strongly curved, and the crowns are convergent; they have no

Fig. 413. — Skull of Pig about a Year and a Half Old, Sculptured to Show the Embedded Parts of the Teeth.
11-3, Incisors; C, canines; Pl-4, premolars; Ml-3, molars. The third molar has not erupted and its roots are not

yet formed.

Ce77ient Enamel Dentine

distinct neck. The convex labial surface has an extensive covering of enamel, but
the latter covers only a small marginal area on the lingual surface. The second are
much shorter and are only slightly curved ; they have a short flattened crown and
a rounded root. The third incisors are much smaller, are
flattened laterally, and have three small eminences on the
crown. The lower incisors are almost horizontal and are
convergent and close together. The first and second are
about equal in size, are rod-like, very slightly curved, and
deeply implanted in the jaw. The labial surface is slightly
convex, the lingual concave and marked near its extremity
by a ridge. The third incisor is much shorter and is some-
what flattened ; it has a short narrow crown and a distinct
neck.

The canine teeth or tusks of the male are greatly de-
veloped and project out of the mouth. The upper canine of the boar may be three
or four inches (ca. 8 to 10 cm.) long. The crown is conical and is curved some-
what backward and outward; the embedded part is curved and has a large pulrt

Fig. 414. — Cross-section of
Lower Canine TooTff
OF Pig.

c, Pulp cavity.

480

DIGESTIVE SYSTEM OF THE PIG

cavity. The lower canine may reach a length of eight inches or more (ca. 20 cm.) ;
the crown is prismatic and is curved backward and outward in front of the upper
one, so that the friction between the two keeps a sharp edge on the lower tooth.
In the sow they are much smaller. ^

The cheek teeth increase in size from before backward. They have (with
certain exceptions noted below) complex tuberculate crowns; the term bunodont
is applied to this condition, as distinguished from the lophodont and selenodont
structure in horses and cattle, in which there are prominent ridges of enamel.

Fig. 415. — Superfici.\l Glands of Head of Pig.
a, Parotid gland; a', a", cervical and mandibular angles of a; b, c, ventral and dorsal buccal glands; d, labial
glands; e, masseter muscle; /, /', lymph glands; g, dotted line indicating outline of mandibular gland, which is con-
cealed. (EUenberger-Baum, Anat. d. Haustiere.)

They are short-crowned teeth with a distinct neck and round, pointed roots. The
first tooth in each jaw is small, simple, and appears only once; in the lower jaw it is
near the canine; in the upper, near the second cheek tooth.^ The next two teeth
are larger, laterally compressed, and sectorial. The fourth tooth below is larger,
but otherwise like the preceding ones, while the upper one is much wider and is
tuberculate. The first premolar has two roots, the others three or four. The
molars have four roots, but the anterior pair may be largely fused.

1 The canines of the pig are "permanent pulp" teeth and therefore capable of continued
growth, and are without roots in the strict sense. The convex surface is covered with enamel, the
concave with cement.

2 It is often absent in the lower jaw.

THE MOUTH

481

Fig. 416. — Dissection op Mouth and Pharyngeal Region of Pig.
1, Hard palate; 2, tongue showing distinctly fungiform papilla; 3, foliate papilla; 4, lymph nodules of soft palate;
5, stylo-glossus muscle, out of which a portion has been cut; 6, hyo-glossus; 7, genio-glossus; 8, genio-hyoideus; 9,
mylo-hyoideus (reflected); 10, stylo-hyoideus; 11, great cornu of hyoid bone; 12, tensor palati; 13, levator palati;
i>^, pterygo- et palato-pharyngeus; /5, stylo-pharyngeus; i6, cervico-hyoideus; ^7, sterno- et omo-hyoideus; 18, a\i-
prapharyngeal lymph glands; a, bulla ossea; b, paramastoid process. (EUenberger-Baum, Anat. d. Haustiere.)

The average periods of eruption of the teeth are given in the subjoined table:

Tooth
Ii ..
I2 ..

L ..
C ..
Pi ..
P2..

P3..

P4..

M,..

M2..

Ms..

Eruption Change

2 to 4 weeks 12 months

/ upper 2 to 3 months

\ lower 1 H to 2 months 16 to 20 months

Before birth 8 to 10 months

Before birth 9 to 10 months

5 months

5 to 7 weeks 1

upper 4 to 8 days

lower 2 to 4 weeks J- 12 to 15 months

upper 4 to 8 days

\ lower 2 to 4 weeks

4 to 6 months
8 to 12 months
18 to 20 months

482 DIGESTIVE SYSTEM OF THE PIG

The parotid gland is large and distinct]}^ triangular. It extends very little on
to the masseter muscle, and its upper angle does not quite reach the base of the ear.
It is pale in color, and is embedded in fat in animals in good condition. On its deep
face are several large subparotid lymph glands, some of which are only partially
covered bj^ the parotid. The parotid duct arises on the deep face, has a course
similar to that of the ox, and perforates the cheek opposite the fourth or fifth upper
cheek tooth. Small accessory parotid glands (Glandulae parotidese accessorise) may
be found along the course of the duct.

The mandibular or submaxillary gland is small, reddish in color, and oval in
outline; it is covered by the parotid. Its superficial face is convex, and is marked by
rounded prominences. From its deep face a narrow process extends forward about
two or three inches (ca. 5 to 7.5 cm.) beneath the mylo-hyoideus muscle along with
the duct. The latter opens near the frenum linguae, but there is no papilla.

The sublingual gland has an arrangement similar to that of the ox. The pos-
terior part (Glandula sublingualis grand icanalaris) is reddish-yellow in color, and
is about two inches (ca. 5 cm.) long and half an inch wide; its posterior end is in
relation to the mandibular gland and its duct. The anterior part (Gl. sublingu-
alis parvicanalaris) is much larger, being two or three inches (ca. 5 to 7 cm.) long
and al)out twice the width and thickness of the posterior part. All or most of the
ducts from the posterior part unite to form the ductus sublingualis major, which
opens near the ductus mandibularis. Eight or ten ductus sublinguales minores
convey the secretion from the anterior part through the floor of the mouth.

Fig. 417. — Sagittal Section of Pharyngeal Region of Pig, Partlt Schematic.
7, Palatine bone; a^, sphenoid bone; ^', sphenoidal sinus; ^", occipital bone; 3, epiglottis; 4. arytenoid cartilage;
6, thyroid cartilage; 6, root of tongue; 7, mouth cavity; S, isthmus faucium; 9, hard palate; 10, septum nasi; //,
ventral muscles of head; a, soft palate; a', free edge of a; b, dorsal wall of pharynx; c, fornix of pharynx; d, cavity of
larynx; e, 3, naso-pharynx; /, oro-pharynx; A, posterior pillar of soft palate; i, dotted line indicating lateral boundary
between nasal cavity and pharynx; A, aditus laryngis; /, aditus cesophagi; ?n, Eustachian orifice; re, pharyngeal recess;
o, posterior naris. (.After Ellenberger, in Lieisering's Atlas.)

THE PHARYNX
The pharjmx presents in its posterior part a median cul-de-sac about an inch
and a half (ca. 3 to 4 cm.) long, which is situated between the ventral straight
muscles of the head and the origin of the oesophagus; this is termed the diverticu-
lum pharyngeum. Its ventral margin is formed by the junction of the posterior
pillars of the soft palate, which contain muscular tissue derived from the palatinus
and palato-pharyngeus. The fornix of the pharynx is divitled by a median fold of
mucous membrane which is a direct continuation of the septum nasi. On either
side of this is an infundibulum in which the Eustachian tube opens.

THE (ESOPHAGUS THE STOMACH 483

THE (ESOPHAGUS
The oesophagus is short and nearly straight. It has (according to Rubeh) a
potential caliber in the adult of nearly 3 inches (ca. 7 cm.) at either end, and about
1^ inches (ca. 4.2 cm.) in its middle part.^ The muscular coat is striated, except
near the cardia, where the deep part is unstriped. There are numerous tubulo-
alveolar glands in the anterior half of the tube; further back they occur in decreas-
ing numbers. Many lymph nodules and much lymphoid tissue are present.

THE STOMACH
The stomach is large; its average capacity is about l^^ to 2 gallons (ca.
5.7 to 8 liters). When full, its long axis is transverse and its greater curvature
extends backward on the floor of the abdomen a little further than a point midway

Durrti-
culuiiL

O'Jsophagus

Pylorus

Fig. 418. — Stomach of Pig; Parietal Surface. Fig. 419. — Stomach of Pig; Visceral Surface.

The organ contained a rather small amount of ingesta Organ was fixed in situ and is somewhat contracted,

and hence is somewhat contracted.

between the xiphoid cartilage and the umbilicus. The left part is large and rounded,
while the right part (Pars pylorica) is small, and bends sharply upward to join the
small intestine. The parietal surface faces chiefly forward, and is related to the
liver and diaphragm. The visceral surface faces chiefly backward, and is related
to the intestine, greater omentum, mesentery, and pancreas. The greater cur-
vature is related to the diaphragm, spleen, liver, and abdominal floor. The
pyloric end lies against the right lateral lobe of the liver, about opposite to the middle
of the next to the last intercostal space. The left extremity is opposite to the last
intercostal space or preceding rib, and is related to the dorsal end of the spleen and
the left extremity of the pancreas; it presents a flattened conical blind pouch, the
diverticulum ventricuU, the apex of which projects backward. The oesophagus
joins the stomach very obliquely, almost in the median plane, and about three or
four inches (ca. 8 to 10 cm.) ventral to the twelfth thoracic vertebra. The cardiac

^ It is usually stated that the cardiac end is funnel-shaped, but it is not so in formalin-hardened
cadavers nor in frozen sections. The hiatus oesophagus is a long slit in the right crus of the dia-
phragm, and the terminal part of the oesophagus, which lies in it, is flattened transversely.

484

DIGESTIVE SYSTEM OF THE PIG

opening is slit-like and is bounded above and to the left by a fold which contains a
thickening of the internal oblique layer of the muscular coat. The opening into
the diverticulum is situated above and a little to the left of the cardia; it is trans-

FiG. 421. — Everted Stomach of Pig, from which the
Mucous Membrane has been Removed.

Fig. 420. — Visceral Surface of Stomach of Pig,
from which the Serous Coat has been Re-
moved.

O, (Esophagus; D, duodenum; Di, diverticulum; a, a', a", a" , longitudinal fibers; b, circular fibers; c, external
oblique fibers; c', internal oblique fibers; c", cardiac loop; d, fibers which connect branches of cardiac loop; /, fold at
entrance to diverticulum; p,, pyloric sphincter; p', pyloric prominence. (Ellenberger-Baum, Anat. d. Haustiere.)

versely oval, and is bounded (except laterally) by a thick fold which contains
spirally arranged muscular fibers. The mucous membrane may be divided into
four regions (Fig. 422). Over a quadrilateral area around the cardia (about one

Fig. 422. — Diagram of Zones of Mucous Membrane of Stomach of Pig.

inch on the right and two or three inches on the left side of the orifice) it is oesopha-
geal in character, and presents a number of folds. A sharp line of demarcation
separates this from the rest of the mucous membrane, which is soft and glandular.
The cardiac gland region is pale gray in color and thin (ca. 0.5 to 1 mm.) ; it extends

THE STOMACH

485

about to the middle of the stomach. The fundus gland region is readily distin-
guished by its thickness (ca. 3 mm.) and its brownish-red, mottled appearance.^
The fourth or pyloric region is pale, thinner than the preceding, and presents a
number of irregular folds.^ At the pylorus a remarkable prominence (Torus pylo-
ricus) projects from the wall of the lesser curvature and diminishes considerably
the size of the orifice. It is about an inch and a half (ca. 3 to 4 cm.) long and

The greater omenturi

Fig. 423. — Abdominal Viscera of Pig; Ventral View.
has been removed. B, urinary bladder; G, gall-bladder; A', xiphoid cartilage. Arrows in-
dicate course of coils of colon. The spleen was contracted.

nearly half an inch (ca. 1 cm.) high. Sometimes it is a grooved ridge; in other
cases it has the form of a rounded eminence attached by a pedicle to the wall. It
consists largely of fat, but fibers from the circular muscular coat extend into it.
The arrangement of the muscular coat is shown in Figs. 420, 421.

1 It will be noted that the fundus gland region does not extend up to the lesser curvature;
here the cardiac gland region joins the pyloric.

2 Microscopic examination shows that these regions are not sharply marked off from each
other; instead, there are intermediate zones in which glands of both the adjacent regions are
present, and also glands of intermediate histological character.

486 DIGESTIVE SYSTEM OF THE PIG

THE INTESTINE

The intestine is about fifteen times the length of the body.
The small intestine is 50 to 65 feet (ca. 15 to 20 m.) long. The mesentery of
about the first two feet (ca. 60 cm.) is two to two and a half inches (ca. 5 to 6 cm.)

Fig. 424. — Diagram of Caecum and Colon of Pig.
Coils of colon have been pulled apart.

long; this part may be termed duodenum. The duodenum turns sharply medially
on the visceral surface of the liver to the right of the portal fissure. It then passes
backward, in relation to the medial part of the right kidney dorsally and the colon
ventrally, and about the middle of the sublumbar region turns across the median

Fig. 425. — Ileo-c^cal Opening of Pig,
1, Ileo-caecal opening; 2, 2, frenulum ilei.

Fig. 426. — Solitary Nodules op Large Intestine
of Pig. (EUenberger-Baum, Anat. d. Haustiere.)

plane and runs forward to be continued by the mesenteric part. The right end of
the pancreas is attached to the first part, and here the pancreatic duct opens into
the bowel. The remainder of the bowel (Jejuno-ileum) has a mesentery about six
to eight inches (ca. 15 to 20 cm.) long, which is thick and contains a quantity of fat,

THE INTESTINE

487

and numerous large lymph glands at its root; the root is attached in the sublumbar
region behind the stomach and blends here with the mesentery of the large intestine.
The mesenteric part is arranged in close coils and lies mainly above the colon and
caecum, from the stomach to the pelvis; many coils lie against the right flank and
on the posterior part of the floor of the abdomen. The opening of the bile duct is
about one or two inches (ca. 2.5 to 5 cm.) from the pylorus, and that of the pan-
creatic duct about six inches (ca. 15 cm.) beyond it. Aggregated lymph nodules
or Peyer's patches and solitary nodules are numerous and very distinct. The
patches are usually band-like and prominent; their number has been found to vary
from 16 to 38. They begin 8 to 20 inches (ca. 20-50 cm.) from the pylorus. The
last long one is continued a variable distance in the caecum. The solitary nodules

Fig. 427. — Cecum and Colon of Pig; Left Ventral View.
1, Apex of spiral coil of colon; 2, apex of caecum.

are distinct (except in the duodenum), but are only about a millimeter high. The
duodenal glands extend some 10 to 16 feet (ca. 3-5 m.) from the pylorus.

The large intestine is about 12 to 15 feet (ca. 4 to 4.5 meters) in length, and is
for the most part much wider than the small intestine; it is connected by a mesen-
tery with the dorsal abdominal wall between the kidneys. The caecum is cylin-
drical, about 8 to 12 inches (ca. 20 to 30 cm.) long, and 3 to 4 inches (ca. 8 to 10 cm.)
wide. It lies against the upper and anterior part of the left flank, and extends
ventrally, backward, and medially behind the coiled part of the colon, so that its
ventral blind end usually lies on the floor of the abdomen, near the median plane,
and at a variable point between the umbilicus and the pelvic inlet (Fig. 423). Its
dorsal end is directly continued by the colon, the line of demarcation being indi-
cated by the termination of the small intestine. The ileum joins the caecum

488 DIGESTIVE SYSTEM OF THE PIG

obliquely and projects considerably into the latter. A fold of mucous membrane
(Frenulum ilei) passes from each side of the ileo-csecal opening. The colon has at
first about the same caliber as the caecum, but becomes gradually smaller. It lies
chiefly to the left of the median plane, behind the stomach. Most of it is arranged
in three close, double spiral coils in the mesentery, in relation with the floor of the
abdomen ventralh^, the stomach and liver in front, the caecum and small intestine
behind, and the small intestine on the right. On emerging from this spiral laby-
rinth it passes at first forward in the sublumbar region to the right of the median
plane, and, on reaching the stomach and right end of the pancreas, turns to the left.
It then passes backward, on the ventral surface of the pancreas, and in relation to
the medial part of the left kidney, inclines medially, and is continued at the pelvic
inlet by the rectmn. This terminal part is closely attached by a short mesentery to
the sublumbar region. The rectum is usually surrounded by a quantity of fat.
The caecum has three longitudinal muscular bands and three rows of sacculations,
which are continued a short distance on the colon. The spiral colon has two bands
and two series of sacculations, which, however, gradually disappear in the centrif-
ugal part. The solitary nodules are numerous, and appear as round prominences,
2-3 mm. in diameter, often %vith a crater-like depression. The last Peyer's patch
of the small intestine is continued a variable distance in the caecum, and there are
often patches in the first part of the colon.

THE LIVER

The liver is relatively large, its average weight in the adult being about four
pounds (ca. 1.5-2 kg.). It is thick centrally, but the circumference is thin. It is
divided by three deep interlobar incisures into four principal lobes — bright lateral,
right central, left central, left lateral ; the last of these is usually considerably the
largest. On the upper part of the right lateral lobe, is the caudate lobe, which is
clearly marked off by a fissure and is often partially subdivided by a secondary
fissure. That part of the right central lobe which lies below the portal fissure and
to the left of the gall-bladder and cystic duct is homologous with the quadrate lobe
of man. Much the greater part is to the right of the median plane. The parietal
surface is extremely convex in conformity with the curvature of the diaphragm, to
which it is chiefly related.^ A small part of the surface is in contact with the
abdominal floor in the xiphoid region and ventral to the right costal arch. Its
most anterior part reaches to a transverse plane through the ventral part of the
sixth rib or intercostal space. The visceral surface is deeply concave; most of it
is related to the stomach, for which there is a correspondingly large and deep gastric
impression. There may be a duodenal impression on the upper part of the right
lateral lobe, but no renal impression exists, as the right kidney does not touch the
liver. The fossa for the gall-bladder (Fossa vesicae felleae) is mainly on the right
central lobe, but also in part on the adj acent surface of the left central lobe. The pos-
terior vena cava enters the dorsal border of the caudate lobe and soon becomes entirely
embedded in the gland substance, emerging only at its passage through the dia-
phragm. The oesophageal notch is large and is occupied mainly by the large right
crus of the diaphragm. The right lateral border extends backward to the upper
part of the last intercostal space. The left lateral border is opposite the ninth
intercostal space and eighth rib. The ventral border lies on the abdominal floor
a short distance (ca. 3-5 cm.) behind the xiphoid cartilage.

The coronary ligament resembles that of the horse. The falciform ligament is
very short or absent in the adult, and is attached to the diaphragm just below the

^ The description here given is based on the appearance of the organ as hardened in situ,
which differs radically from that of the soft organ. It also differs much in shape in young and
adult subjects.

THE LIVER

489

490

DIGESTIVE SYSTEM OF THE PIG

foramen vense cavae. The round ligament is present in the young subject. Neither
lateral nor caudate ligaments are present.

The gall-bladder is attached in the fossa vesicae felleae; its fundus does not

Fig. 430. — Projection of Visceba of Pig on Bodt-wall; Left Side.
D, Costal line of diaphragm; U, ureter; V.S., vesicula seminalis; B.g., bulbo-urethral gland; P, penis.

reach to the ventral border. The cystic duct joins the hepatic duct at an acute
angle immediately after the emergence of the latter from the portal fissure. The
bile duct (Ductus choledochus) opens at the papilla duodeni about one or two inches
(ca. 2.5 to 5 cm.) from the pylorus; an ampulla may be formed.

Fig. 431. — Projection of Viscera of Pig on Body-wall; Right Side.

D, Costal line of diaphragm; O, ovary. The pancreas and duodenum are not in contact with the flank, as would

naturally be inferred from this figure, but are situated more medially and are covered laterally by small intestine.

Owing to the large amount of interlobular tissue, the lobules are mapped out
sharply; they are polyhedral in form, and are 1 to 2.5 mm. in diameter. For the
same reason the gland is much less friable than that of the other animals, from which
it is easily distinguished.

DIGESTIVE SYSTEM OF THE DOG — THE MOUTH

491

THE PANCREAS
The pancreas extends across the dorsal wall of the abdominal cavity behind
the stomach. It is triradiate or triangular. The right extremitj^ is attachetl to the
first curve (Flexura portalis) of the duodenum, and here the duct passes to the
bowel. The left extremity is related to the left extremity of the stomach, the
dorsal end of the spleen, and the anterior pole of the
left kidney. The middle or posterior extremity or
lobe is practically median and is related to the portal
vein and the root of the mesentery. The pancreatic
duct passes from the right extremity directly through
the duodenal wall, opening about four or five inches
(ca. 10-12 cm.) from the pylorus. The interlobular
tissue usually contains a good deal of fat.

THE SPLEEN

The spleen is long and narrow. Its long axis is
nearly dorso-ventral in direction, and is curved to con-
form to the left part of the greater curvature of the
stomach. The dorsal end lies under the vertebral
ends of the last three ribs; it is related to the
stomach in front, the left kidney behind, and the
left extremity of the pancreas medially. The visceral
surface has a longitudinal ridge on which the hilus is
situated; this divides the surface into nearly equal
gastric and intestinal areas, which are in contact with
the stomach and colon respectively. The parietal
surface is convex and is related to the left lateral and
ventral wall of the abdomen. The ventral end is
smaller than the dorsal one; it lies on the abdom-
inal floor, usually in the umbilical region. The spleen
is attached so loosely to the stomach that it may be
regarded as being intercalated in the great omentum.
In large subjects it may reach a length of about 25
inches (ca. 60 cm.) and a width of 3 to 4 inches (ca. 8
to 10 cm.), and a weight of 10-15 ounces (ca. 350 gm.).

The position of the spleen varies according to the fulness
of the stomach and its own size. The dorsal end varies little.
But the ventral end has a wide range, as might be expected ; it
may be in contact with the left lobe of the liver or may be cen-
trally situated just in front of the umbilicus. As in other ani-
mals, the size of the spleen is extremely variable. Even in a

large adult it may be only a little more than a foot (ca. 35 cm.) long, two and a half inches wide,
and weigh six or seven ounces (ca. 200 gm.).

Fig. 432. — Spleen of Pig; Visceral
Surface.
1, Dorsal end; 2, ventral end; 3,
stumps of splenic vessels; 4, gastric
surface; 5, hilus with vessels.

DIGESTIVE SYSTEM OF THE DOG

THE MOUTH

The size and form of the mouth vary greatly in different breeds, the cavity

being in some long and narrow, in others short and wide. The rima oris is very

extensive, so that the labial commissure is opposite the third or fourth cheek tooth.

The lips are thin and mobile, and present numerous tactile hairs. The upper lip

492

DIGESTIVE SYSTEM OF THE DOG

has a small, central, bare area which forms part of the muzzle, and is marked by a
central groove, the philtrum, or (as in the bull-dog) a fissure, giving the appearance
of harelip. The lateral borders of the lower lip are flaccid and denticulated. The
mucous membrane is usually pigmented and forms distinct frena labiorum. The
labial glands are small and scanty.

The cheeks are loose and capacious, and their mucous lining is smooth and
more or less pigmented. The parotid duct opens usually opposite the third upper
cheek tooth. Near the last tooth are the openings of the four or five ducts from
the zygomatic gland. This gland may be regarded as the homologue of the dorsal

Fig. 433.-

-Palate of Dog.

noved by sawing through the i

of the mandible and cutting

The lower jaw and related structures have been
the soft structures horizontally.

1, Raph^ of palate; 2, ridges of palate; 3, papilla incisiva; 4, soft palate; 5, tonsil; 6, meatus naso-pharyngeus; 7,
dorsal wall of pharynx; 8, parotid gland; 9, mandibular gland; 10, pharyngeal lymph gland; 11, m. occipito-
mandibularis (cut); 12, m. masseter (cut); 13, cheek (cut); 14, ramus of mandible (section); 15, parotid lymph gland;
16, carotid artery; I, incisor teeth; C, canine tooth; P, premolar teeth; M, molar teeth.

buccal glands of the other animals; it will be described later. The ventral buccal
glands are opposite the cheek teeth and in series with the inferior labial glands.

The hard palate is widest between the fourth pair of cheek teeth. It has
eight to ten curved ridges on either side of the median raphe; the latter may be
indistinct or scarcely recognizable. Behind the first pair of incisor teeth is the
rounded or triangular papilla incisiva, at which the incisive or naso-palatine ducts
open. The mucous membrane is usually pigmented.

The soft palate (Figs. 433, 488) is thick, except at its margins. In the resting
state of the parts it comes in contact with the epiglottis. '^ Between its anterior and

1 It is usually stated that it is in contact with the oral surface of the epiglottis, but the epi-
glottis may be ventral to the soft palate (Fig. 488).

THE TEETH

493

posterior pillars on either side is a marked tonsillar
fusiform tonsil is situated; this is reddish in color,
about an inch long, and is largely or completely
concealed between two folds of mucous membrane.
The posterior pillar is double; the upper fold passes
to the dorsal wall of the pharynx, where it subsides;
the lower fold goes to the side of the epiglottis.

The tongue is wide and thin in front, thicker
posteriorly; it is very mobile. It is not pigmented,
but has a bright red color. The dorsum is marked
by a median groove (Sulcus medianus linguae), and
is thickly beset with short, pointed, filiform papillae,
the free ends of which are directed backward. On
the root there are long conical papillae which are
soft, and point backward; similar papillae occur
on the lateral walls of the isthmus faucium. The
fungiform papillae are small, and are scattered over
the dorsum and sides of the tongue, but are absent
on the posterior part of the dorsum and on the
root, where the conical papillae occur. There are
usually two or three vallate papillae on either side
on the posterior part of the dorsum, where the
conical papillae begin. Small foliate papillae are
also present just in front of the anterior pillars of
the soft palate ; they are oval and are crossed by
about half a dozen fine fissures. In the inferior
part of the tip of the tongue is the lyssa, a fusiform
cord, composed of fibrous tissue, muscular tissue,
and fat. In large dogs it is about two inches (ca.
4 to 5 cm.) long. The lingual muscles present no
remarkable special characters.

THE TEETH

The formula of the permanent teeth is:

sinus, in which an elongated,

/ 3 1 4 2\
( I-C-P-M- )
V 3 1 4 3/

All of the teeth have short crowns and dis-
tinct necks; they erupt rapidly. The crowns are
white, being destitute of cement.^

The incisors are placed almost vertically and
close together in the jaw bones. They do not cor-
respond to an opposing tooth, but rather to parts
of two teeth of the other jaw. They increase in
size from the first to the third. The crowns are
trituberculate, the central projection being the
largest. The labial surface is convex; the lingual
surface is slightly concave, and is marked off from
the neck by a V-shaped ridge, the cingulum. The
roots are narrow transversely. The lower incisors
are smaller than the upper ones. One or two supernumerary teeth may be present.

The canine teeth are large, conical, and curved. The upper canine is separated

1 Other figures which illustrate the teeth are to be found in the description of the skull.

Fig. 434. — Tongue, Pharynx, Larynx,
ETC., OP Dog; Dorsal View.

The pharynx and soft palate have
been cut medially and reflected, and the
oesophagus cut off.

1, Median groove of tongue; 2, long
conical papillae of root of tongue; 3, val-
late papillae; 4, tonsil (drawn out of ton-
sillar sinus; 5, floor of pharynx (promi-
nence here caused by cricoid cartilage
and m. crico-arytenoideus dorsalis) ; 7,
vestibule of larynx; 8, epiglottis; 9, ary-
tenoid cartilage; 10, trachea (membran-
ous part); 11, 11, lateral lobes of thyroid
gland; 12, 12', anterior and posterior thy-
roid vessels.

494

DIGESTIVE SYSTEM OF THE DOG

from the corner incisor by an interval into which the lower canine is received when
the jaws are closed.^ The lower canine is close to the corner incisor. The root is
about an inch (ca. 2 to 3 cm.) long and is flattened laterally.

The cheek teeth are typically y, but in brachycephalic breeds they are com-
monly reduced to f, and in extreme cases even to f . The reduction occurs at either
end or at both ends of the series.- The first tooth appears only once. The fourth
tooth of the upper row and the fifth of the lower row are much larger than the rest,
and are termed sectorial or camassial teeth. From these the teeth diminish in size
both forward and backward. The upper and lower teeth do not correspond, but
rather dovetail. The teeth behind the sectorial ones are tuberculate, i. e., have

-Skull of Adult St. Bernard Dog, Sculptured to Show the Embedded Parts of the Teeth.
11-3. Incisors; C, canines; Pi -4, premolars; Ml-3, molars.

rounded eminences on the masticatory surface. The others are all sectorial in
character, i. e., have sharp-edged, pointed projections, the middle one being the
most prominent. The premolars are laterally compressed, and are separated by
intervals from the canines and from each other, except in the brachycephalic
breeds. The upper molars have wide, somewhat quadrangular cro^vns, and three
roots. The crown of the upper fourth premolar (Dens sectorius) is divided into
two pointed lobes and has an antero-medial tubercle; it has three roots. The

1 In the bull-dog, which is very prognathic ("undershot"), the lower canmes are opposite
to or slightly in front of the plane of the upper incisors, and the upper canines are about opposite
to the first lower cheek teeth. In the epignathic ("overshot") dachshund the lower canines are
under or slightly behind the upper ones.

- Increase in number also occurs, the supernumerary teeth being at either end of the series.
The occurrence of a third upper molar is not rare.

THE SALIVARY GLANDS

495

crown of the first lower molar (Dens sectorius) is compressed laterally and has two
pointed, sharp-edged lobes, behind which are one or two tubercles; it has two roots.
The average periods of eruption are given below.

Tooth Eruption

I, 4 to 5 weeks. .

lo 4 to 5 weeks . .

I3 4 weeks

C 3 to 4 weeks . .

Pi 4 to 5 months.

P2 4 to 5 weeks . .

Ps 3 to 4 weeks. .

P4 3 to 4 weeks. .

M, 4 months

4 to 5 months

5 to 6 months

■jy.^ / upper 5 to 6 months

" \ lower 4 J/^ to 5 months

Ms 6 to 7 months

Jl-3, Incisors; C, canine; Pl-

FiG. 436. — Base of Skull of Cocker Spaniel.

premolars; Ml-2, molars. Note the crowding of the canines and premolars on
account of the shortness of the jaw.

THE SALIVARY GLANDS
The parotid gland is small and is irregularly triangular. Its dorsal end is wide
and is divided into two parts by a deep notch into which the base of the ear is
received. The ventral end is small and overlaps the mandibular gland. The
parotid duct leaves the gland at the lower part of the anterior border, crosses the
masseter muscle, and opens into the mouth opposite the third upper cheek tooth.

496

DIGESTIVE SYSTEM OF THE DOG

Small accessory parotid glands (Glandulae parotidese accessorise) are sometimes
found along the course of the duct.

The mandibular gland is usually larger than the parotid. In large dogs it
is about two inches (ca. 5 cm.) long and an inch or more (ca. 3 cm.) wide. It is
rounded in outline, pale yellow in color, and is enclosed in a fibrous capsule. Its
upper part is covered by the parotid, but it is otherwise superficial, and is palpable
in the angle of junction of the jugular and external maxillary veins. The
mandibular duct leaves the deep face of the gland, passes along the surface of
the occipito-mandibularis and stylo-glossus, and opens into the mouth on a very
indistinct papilla near the frenum linguae.

The sublingual gland is pink in color and is divided into two parts. The
posterior part (Glandula sublingualis grandicanalaris) lies on the occipito-man-

FiG. 437. — Dissection of Head of Dog, Showing Salivary Glands, etc.
o, Ocular muscles; 6, pterygoideus medialis (cut) ; c, stylo-glossus; d, occipito-mandibularis (cut) ; e, genio-glossus;
/, genio-hyoideus ; g, hyo-glossus; h, thyro-pharyngeus; i, crico-pharyngeus; k, thyro-hyoideus ; I, zygomatic process
of temporal (sawn off) ; i, parotid gland; ^, mandibular gland; 3, posterior part of sublingual gland; S', anterior part
of same; 4, mandibular duct; 5, ductus sublingualis major; 6, palatine glands; 7, zygomatic gland; S, ducts of 7; 9,
lacrimal gland. (Ducts colored red.) (After Ellenberger, in Leisering's Atlas.)

dibularis muscle in intimate relation with the mandibular gland, but is clearly separ-
able from it after removal of the common fibrous capsule. It has a pointed anterior
process. Its duct (Ductus sublingualis major) accompanies the mandibular duct,
and either opens beside it or joins it. The anterior part (Glandula sublingualis
parvicanalaris) is long and narrow; it lies between the mucous membrane of the
mouth and the mylo-hyoideus, dorsal to the stylo-glossus muscle. It has a number
(8 to 12) of small ducts (Ductus sublinguals minores), some of which open directly
into the mouth, while others join the large duct.

The zygomatic gland (Glandula zygomatica)i (Fig. 437) is situated in the
anterior part of the ptery go-palatine fossa. It is related superficially to the zygo-
matic arch and the masseter and temporal muscles. Its deep face is in contact
with the periorbita, the pterygoid muscle, the internal maxillary artery, and the

^ Also known as the orbital gland.

THE PHARYNX — THE CESOPHAGUS — THE STOMACH 497

maxillary nerve. It has four or five ducts which open near the last upper cheek
tooth; one of them (Ductus glandulse zygomaticse major) is almost as large as the
parotid duct; the others (Ductus glandulse zygomaticse minores) are small.

THE PHARYNX (Fig. 434)
The fornix is narrow. The pharyngeal orifices of the auditive or Eustachian
tubes are small and slit-like; the end of the tube causes a rounded projection of the
mucous membrane (Torus tubarius). The oesophageal aditus is relatively small
and is well defined by a transverse fold of the mucous membrane. The muscles
present no marked differential features, but the hyo-pharyngeus muscle is clearly
divided into a kerato-pharyngeus and a chondro-pharyngeus.

THE (ESOPHAGUS
The oesophagus is relatively wide and dilatable except at its origin, where there
is a constriction termed the isthmus oesophagi. This initial narrowness of the
lumen is caused by a prominence of the ventral part of the mucous membrane,
underlying which is a thick layer of mucous glands (Fig. 490). The cervical part
is at first median and is dorsal to the trachea, but in the posterior part of the neck
it lies to the left of the trachea. The thoracic part continues in this position and
ventral to the left longus colli to the base of the heart; here it inclines medially,
having the aortic arch on its left, and passes back over the bifurcation of the trachea.
Continuing backward between the lungs it usually inclines slightly to the left,
passes through the hiatus cesophageus, and joins the stomach just to the left of the
median plane and ventral to the eleventh or twelfth thoracic vertebra. The
muscular tissue is striated and consists mainly of two layers of spiral fibers which
cross each other; near the cardia, however, the fibers are longitudinal and circular.
There are tubulo-alveolar glands (Gl. oesophagae) in the submucosa throughout.

THE STOMACH

The stomach is relatively large. Its capacity in a dog weighing about 40
pounds is about six to seven pints.

Colin estimates the average capacity at about 3 liters (ca. 6^ pints), with a range between
0.6 and 8 liters (ca. l}4 to 173^ pints). Neumayer gives the capcaity as 100 to 250 c.c. per kilogram
of body-weight (ca. 2.7 ounces per pound). The average capacity of the human stomach is esti-
mated at 1.2 liters (23/2 pints) — not much more than a third of that of a dog of medium size.

When full, it is irregularly piriform. The left or cardiac part (Fundus et corpus
ventriculi) is large and rounded, while the right or pyloric part (Pars pylorica) is
small and cylindrical. When empty, or nearly so, the left sac is strongly contracted;
the pyloric part is much less affected by variations in the amount of ingesta.

The parietal surface of the full stomach is very extensive, strongly convex,
and faces partly forward, but largely ventrally and to the left. It is related to the
liver, the left part of the diaphragm, and the left and ventral abdominal wall as far
back as a transverse plane through the second or third lumbar vertebra. The
visceral surface is much less extensive and is considerably flattened ; it faces chiefly
dorsally and to the right, and is related to the intestine, pancreas, and left kidney.

The upper part of the lesser curvature is nearly straight and vertical, but the
lower part forms a deep, narrow angle (Incisura angularis), due to the fact that the
pyloric part is directed sharply forward and upward. The greater curvature is
nearly four times as long as the lesser curvature. In the full stomach it extends
considerably behind the left costal arch; ventrally it lies on the abdominal wall
about midway between the xiphoid cartilage and the pubis.
32

498

DIGESTIVE SYSTEM OF THE DOG

(Esophagus

Pylorus

The left extremity or fundus is large and rounded; it is the most dorsal part
of the organ, and lies under the vertebral ends of the eleventh and twelfth ribs.

The pyloric extremity is small
and is directed forward and dor-
sally; it lies usually opposite to
the ventral part of the ninth
or tenth intercostal space, and
about an inch (ca. 2-3 cm.) to
the right of the median plane.
It is related to the portal fissure
of the liver and to the pancreas.
The cardia is situated about two
to three inches (ca. 5 to 7 cm.)
from the left extremity, and is
oval; it lies just to the left of
the median plane, ventral to the
eleventh or twelfth thoracic ver-
tebra.

When empty, or nearly so,
the stomach is separated from
the ventral abdominal wall by
the liver and intestine, and the
greater curvature extends back
on the left side to the eleventh
or twelfth rib. In this state there is not rarely a marked constriction between the
right and left parts.

The preceding topographic statements are based on observations made on a considerable
number of formalin-hardened subjects, and are to be regarded as average findings in dogs of

18. — Stomach of Dog; Parietal Surface.
Organ fixed in situ when well filled.

Left extremity

Duodenum

Attachment of
greater omentum

Fig. 439. — Stomach of Dog; Visceral Surface.
Organ fixed in situ when it contained small amount of ingesta.

medium size. The cardiac an 1 pyloric ends vary least in position, but the former varies the
length of one vertebra and the latter as much as two intercostal spaces. This variation appears
to be due, not only to the amount of ingesta in the stomach, but also to the phase in which the
diaphragm is fixed.

THE STOMACH

499

The serous coat is almost complete. Along the curvatures it leaves the stom-
ach to form the omenta. The longitudinal muscular fibers are chiefly along the
curvatures and on the pyloric part; they are continuous with the external layer
of the oesophagus. The oblique fibers are arranged in two layers : the external layer
is largely a continuation of the longitudinal fibers of the oesophagus to the body
and fundus. The circular layer covers the whole stomach except the fundus, and
forms a pyloric sphincter and an antral sphincter. The internal oblique layer is
arranged as in the horse, and forms a similar loop-like, cardiac sphincter. Three
regions of the mucous membrane exist. Cardiac glands are found in a very narrow
pale zone around the cardiac opening, and also scattered along the lesser curva-

FiQ. 440.
1, Fundus gland region; 2, pyloric part;

-Stomach of Dog; Frontal Section

, lesser curvature; 4, cardia; 5, pylorus; 6, oesophagus; 7, duodenum.

ture. The fundus gland region has a thick, reddish-bro^^^l mucous membrane,
which lines about two-thirds of the organ. The pyloric mucous membrane is
thinner and pale; in the dead subject it is often stained by regurgitated bile.

The greater omentum is very extensive, and in well-nourished subjects it con-
tains much fat arranged in interlacing strands. Viewed ventrally it covers the
entire intestinal mass, extending from the greater curvature of the stomach to the
pelvic inlet. It is attached to the greater curvature of the stomach, the left part
of the colon, the left branch of the pancreas, and the hilus of the spleen.

The lesser omentum extends from the lesser curvature of the stomach to the
portal fissure; to reach the latter it passes in great part between the papillary and
left lateral lobes of the liver.

500

DIGESTIVE SYSTEM OF THE DOG

THE INTESTINE

The intestine is short — only about five times the length of the body.

The small intestine has an average length of about thirteen feet (ca. 4 meters).
It occupies most of the abdominal cavity behind the liver and stomach. The duo-
denum begins at the pylorus and passes backward and somewhat dorsally, at first

Fig. 441. — Abdominal Viscera of Dog.

Ventral view after removal of greater omentum. The stomach is full.

a, Cartilage of last rib; b, duodenum; x, xiphoid cartilage.

on the visceral surface of the liver, then in contact with the right flank. Near the
pelvis it turns medially and passes forward along the medial side of the left part of
the colon and the left kidney, bends ventrally, and joins the jejunum to the left of
the root of the mesentery. ^ The mesoduodenum is given off from the right side of the

1 The duodenum might be regarded as consisting of a right or retrograde part, an iliac flexure,
and a left or recurrent part; the terminal bend is the duodeno-jejunal flexure.

THE INTESTINE

501

common mesentery; it is a relatively wide fold. The left part of the duodenum is
connected with the mesocolon by a peritoneal fold; this fold has a free posterior
border which is clearly seen when the posterior flexure of the duodenum is drawn
away from the sublumbar region. The first part of the mesoduodenum contains
the right branch of the pancreas. Its root is blended with the mesocolon to form a
common mesentery. The remainder of the small intestine forms numerous coils,
and is attached by a wide mesentery to the sublumbar region. The terminal part
(ileum) passes forward in the sublumbar region along the medial surface of the
caecum and opens into the beginning of the colon at the ileo-colic orifice (Ostium

Fig. 442. — Deep Dissection of Abdominal Viscera of Dog (Female).
Bl., Bladder; B, body, C, C", cornua of uterus; O, O', ovaries; L. k., left kidney. The concealed part of the colon

is indicated by dotted li

The spleen is drawn backward and outward.

ileocolicum). The bile duct and smaller pancreatic duct open into the duodenum
about two or three inches (ca. 5 to 8 cm.) from the pylorus; the larger pancreatic
duct opens an inch or two (ca. 2.5 to 5 cm.) further back. The mucous membrane
has very long, thin villi. The duodenal glands occur only close to the pylorus.
Aggregated lymph nodules or Peyer's patches are numerous (about twenty in
young subjects), and begin in the duodenum. They are usually elliptical in out-
line, but the last one is band-like, reaches to the end of the ilemn, and is four to
sixteen inches (ca. 10 to 40 cm.) long in young dogs (Ellenberger) . There is an ileo-
colic valve. ^ The muscular coat is relatively thick.

1 The valve does not seem always to be efficient, since experience shows that rectal injections
can be made to pass beyond it. This may be partly due also to the fact that the terminal part of
the ileum runs horizontally forward, and its orifice faces forward into the beginning of the colon.

502

DIGESTIVE SYSTEM OF THE DOG

The large intestine is two to two and a half feet (ca. 60 to 75 cm.) long in
average. Its caliber is about the same as that of the small intestine, and it has
neither longitudinal bands nor sacculations.

The caecum averages about five or six inches (ca. 12.5-15 cm.) in length, and
is flexuous (Fig. 442). The flexures are maintained by the peritoneum, which
attaches it also to the ileum. It is situated usually about midway between the
right flank and the median plane, ventral to the duodenum and the right branch of
the pancreas.! Its anterior end opens into the origin of the colon, lateral to the
ileo-colic orifice. The other end is pointed and blind.

The colon is attached to the sublumbar region by a mesentery — the mesocolon.
It presents three parts, which correspond to the ascending, transverse, and descend-
ing colon of man. The first or right part (Colon
dextrum s. ascendens) is very short. It passes for-
ward along the medial surface of the first part of the
duodenum and the right branch of the pancreas till
it reaches the pyloric part of the stomach; here it
turns to the left and crosses the median plane,
forming the transverse part (Colon transversum).
The third or left part (Colon sinistrum s. descen-
dens) passes backward in the sublumbar region
along the medial border or ventral surface of the
left kidney; it then inclines toward the median
plane and is continued by the rectum. The cali-
ber of the colon is about the same throughout. It
has no bands nor sacculations. The mesen-
tery of the colon is termed the mesocolon; it is
given off from the left side of the common mesen-
tery. 2

The mucous membrane of the caecum con-
tains numerous solitary lymph nodules which are
circular, with a central depression; some are
present also in the first part of the colon.

The rectum is almost completely covered with
peritoneum, the line of peritoneal reflection being
under the second or third coccygeal vertebra. At
the junction of the rectum and anus the mucous
membrane has a stratified squamous epithelium,
and contains the anal glands. A small opening on
cither side leads into two lateral anal sacs (Sinus
paranales) ; these are usually about the size of a
hazel-nut, and contain a dirty gray, fatty substance,
which has a peculiar and very unpleasant odor.
The skin which lines these pouches contains coil-glands. Further back the skin
contains large sebaceous glands and peculiar circimianal glands.

The retractor ani muscle is extensive. It arises from the shaft of the ilium,
the pubis, and the symphysis pelvis, and passes upward and backward to end on the

Fig. 443. — Sectional View of Ileum

C^cuM, AND Colon of Dog.

1, Ileo-colic orifice; 2, caeco-colic orifice

3, apex of caecum.

1 In large dogs (e. g., St. Bernard or Great Dane) the csecum may reach a length of 45 cm.
(measured along its curves) and a diameter of 3 cm. Its position is somewhat variable. It may
be closer to the lateral wall, or more medial than is stated above. Its anterior end is usually
in a transverse plane through the ventral end of the last rib if the stomach is not very full.

2 The arrangement of the colon is variable. The transverse part may be quite long and
extend across from the angle of junction of the two branches of the pancreas to the dorsal end of
the spleen. On the other hand, a transverse part may be absent, the colon forming instead an
acute angle or flexure. When the stomach is empty and contracted, the transverse part of the
colon may be separated from the ventral wall by the omentum only.

THE LIVER

503

first coccygeal vertebrae and the sphincter ani externus. The retractors, together
with the coccygei, form a sort of pelvic diaphragm, analogous to that of man.

THE LIVER

The liver is relatively large, weighing usually about 3 per cent, of the body-
weight. It is divided into five chief lobes by fissures which converge at the portal
fissure. When the gland is ex-
amined in the soft condition post, l/ena cai/a

the lobes may be spread out so
as to be all visible (Fig. 444),
but when the organ is hard-
ened in situ the lobes overlap
to a considerable extent (Figs.
445, 446).

The left lateral lobe is the
largest, and is oval in outline.
The left central lobe is smaller
and is prismatic. The right
central lobe is second in size,
and presents a somewhat
tongue-shaped quadrate lobe,
marked off by the deep fossa
in which the gall-bladder lies.
The right lateral lobe is third

in size, and is oval in outline. On its visceral surface is the large caudate lobe;
this consists of two parts — on the right, the caudate process, on the left, the papil-
lary process, both often being subdivided by secondary fissures.

llnihiheni?

Fig. 444. — Liver of Dog.
Soft specimen sketched with lobes drawn apart.

Right lateral lobe

Left central lobe

Gall-bladder Quadrate lobe
Fig. 445. — Liver of Dog; Parietal Surface.
1, Hepatic veins opening into posterior vena cava; 2, coronary ligament; 3, falciform ligament.

504

DIGESTIVE SYSTEM OF THE DOG

When hardened in situ, the gland presents the following characters: The
parietal surface is strongly convex in conformity with the curvature of the dia-
phragm and the adjacent part of the ventral wall of the abdomen, Avith which it is
in contact.

The visceral surface is in general concave, but is irregular in adaptation to the
viscera in contact with it. The largest of these is the stomach, and the configuration
of the liver varies greatly in accordance with the degree of fulness of that viscus.
When the stomach is well filled, there is a ridge on the liver which corresponds to
the lesser curvature. To the left of this is a large concavity adapted to the body
and fundus of the stomach ; and on the right is a smaller impression of the pyloric
part of the stomach, the first part of the duodenum, and the anterior part of the

Left lateral
ligament

(Esophageal notch

Posterior tena cava

Right central lobe

Fig. 446. — Liver of Dog, Visceral Surface; Hardened in situ.
Left central lobe, gall-bladder, and great part of right central lobe not visible.

right branch of the pancreas. Dorsal to the cavity for the pyloric part of the
stomach is a deep depression, and at the bottom of this is the portal fissure. To
see the latter the papillary and caudate lobes must be drawn apart. The hepatic
artery enters the liver at the dorsal part of the fissure, the portal vein enters cen-
trally, and the hepatic duct emerges at the ventral part. The gall-bladder is
usually not visible till the right lateral and central lobes are drawn apart.

When the stomach is empty and contracted, the visceral surface of the liver is strikingly
different. There is then a shallow impression for the left part of the stomach on the left lolie
and a large convex area, related to the small intestine and a mass of omentum. The pyloric and
duodenal impressions are not much changed.

The dorsal l^order presents a deep renal impression on its right part. The
posterior vena cava passes ventrally and forward, at first in a deep groove on the
caudate lobe, then largely embedded in the parietal surface of the right lateral lobe;
it receives two or three large hepatic veins just before piercing the diaphragm.

THE PANCREAS

505

Dorsal end

The oesophageal notch is large, and is occupied on the right by the thick margin of
the hiatus oesophagus. The remainder of the circumference is thin, and is cut into
by deep fissures which separate the lobes. The ventral border lies on the abdominal
wall, a variable distance behind the xiphoid cartilage. The left border is also
variable, but usually extends back ventrally as far as the tenth intercostal space
or eleventh rib. The right border corresponds more or less closely in direction
with the costal arch ; the end of the caudate process is ventral to the right kidney,
opposite to, or a little behind, the last rib.

The gall-bladder lies in the fossa vesicae fellese, between the two parts of the

right central lobe; it does not reach to the
ventral border of the liver. The cystic duct
joins the hepatic duct at the ventral part of
the portal fissure, forming with it the bile
duct (Ductus choledochus) ; the latter passes
to the right and opens into the duodenum,
about two or three inches (ca. 5 to 8 cm.)
from the pylorus.

Of the ligaments, the coronary and right

Gastric
surface

Ventral end

Fig. 447. — Splee:^ op Dog; Parietal

Surface.

Ventral

Fig. 448. — Spleen of Dog; Visceral Surface.

Fig. 447 is from subject in -nhich the stomach was full, -r hile the organ shown in Fig. 448 was fixed in situ when the
stomach contained little food.

lateral are well developed, but the left lateral and falciform are small; a ligament
extends from the caudate process to the right kidney.

THE PANCREAS
The pancreas is V-shaped, consisting of two long narrow branches, which
meet at an acute angle behind the pylorus. The right branch extends backward
above the first part of the duodenum, below the caudate lobe of the liver and the
right kidney, and ends usually a short distance behind the latter; it is enclosed by the
mesoduodenum. The left branch passes to the left and backward between the

506

DIGESTIVE SYSTEM OF THE DOG

visceral surface of the stomach and the transverse colon, and ends at the anterior
pole of the left kidney. There are usually two pancreatic ducts. The smaller one
opens into the duodenum with the bile duct or close to it; the larger one opens into
the bowel an inch or two (ca. 3-5 cm.) further back.

THE SPLEEN
The spleen is bright red in color in the fresh state. It is somewhat falciform,
long, and narrow; the ventral part is the widest. Its weight in a dog of medium

Fig, 449. — Projection of Viscera of Dog (Male) on Body Wall; Left Side.

A, C, D, Apical, cardiac, and diaphragmatic lobes of lung; P, pericardium; Pr, prostate. Costal attachment and

median line of diaphragm are dotted.

Fig. 450. — Projection of Viscera of Dog (Female) on Body Wall; Right Side.
A, C, D, Apical, cardiac, and diaphragmatic lobes of right lung; P, pericardium; K, right kidney; Pan., right
branch of pancreas; O, ovary; L', cornu of uterus. Costal attachment and median line of diaphragm are dotted; also
posterior contour of stomach.

size is 13^-2 ounces (ca. 50 gm.). It is freely movable, and, with the exception
of its dorsal end, varies much in position and shape. The dorsal end is ventral to

THE SPLEEN 507

the vertebral end of the last rib and the first lumbar transverse process; it fits into
the interval between the left crus of the diaphragm, the left end of the stomach,
and the left kidney. When the stomach is full, the long axis of the spleen corre-
sponds to the direction of the last rib. Its parietal surface is convex and lies largely
against the left flank. The visceral surface is concave in its length, and is marked
by a longitudinal ridge, on which the vessels and nerves are situated, and to which
the greater omentum is attached. The spleen is so loosely attached by the omen-
tum as to be regarded as an appendage of the latter.

The dorsal end of the spleen does not vary in position, but the rest of the organ is very
variable. When the stomach is full, the part of the visceral surface of the spleen in front of the
hilus is usually in apposition with the left part of the greater curvature of the stomach (as in the
horse). It may have a similar position when the stomach is not full, and may be in contact with
the latter only to a small extent dorsally. It is not rare to find the spleen lying along the dorsal
part of the left flank, with its long axis almost longitudinal; this is liable to be the case when the
stomach is empty and contracted. In this condition the spleen shuts the left kidney entirely off
from contact with the flank.

THE RESPIRATORY SYSTEM

The respiratory apparatus (Apparatus respiratorius) comprises the nasal
cavity,^ the pharynx, the larynx, the trachea, the bronchi, and the lungs. The
lungs are the central organs in which the exchange of gases between the blood and
the air takes place; the other parts of the system are passages by which the air
passes to and from the lungs. The nasal cavity opens externally at the nostrils,
and communicates behind with the pharynx through the choanse or posterior nares;
it contains the peripheral part of the olfactory apparatus, which mediates the sense
of smell. The pharynx is a common passage for the air and food — a remnant of the
primitive embryonic arrangement; it has been described with the digestive tube.
The larynx is a complex valvular apparatus which regulates the volume of air pass-
ing through the tract; it is also the chief organ of voice. The trachea and the
bronchi formed by its bifurcation are permanently open conducting tubes. The
thorax, the pleural sacs which it contains, and the muscles which increase or di-
minish the size of the cavity are also parts of the system. The bones, joints, and
muscles of the thorax have already been described.

For topographic reasons two ductless glands, the thyroid and the thymus, are
usually described in this section, although they are in no sense a part of the respira-
tory system.

RESPIRATORY SYSTEM OF THE HORSE

THE NASAL CAVITY

The nasal cavity (Cavum nasi), the first segment of the respiratory tract, is a
long, somewhat cylindrical passage, enclosed by all the facial bones except the
mandible and hyoid. It is separated from the mouth ventrally by the palate.
It opens externally at the nostrils, and communicates posteriorly with the pharynx
through the posterior nares or choanse.

The nostrils (Nares) are somewhat oval in outline, and are placed obliquely,
so that they are closer together below than above. They are bounded by two alae or
wings (Alae nasi), which meet above and below, forming the conunissures. The
lateral ala is concave; the medial one is convex above, concave below. The
prominence of the medial ala is caused by the lamina of the alar cartilage; this
prominence, together with the alar fold which extends backward from it, partially
divides the nostril into a large lower part and a small upper part, which are pop-
ularly distinguished as the ''true" and "false" nostril.- The superior commissure
is narrow, the inferior one ^vide and rounded. If the finger is passed into the nostril
at the upper commissure, it enters a blind cutaneous pouch. This cul-de-sac, the
diverticulum nasi, extends backward to the angle of junction of the nasal bone and
the nasal process of the premaxilla. In order to enter the nasal cavity the finger
should be introduced at the inferior commissure and directed toward the septum
nasi. The naso-lacrimal orifice (Ostium nasolacrimale), the external opening of

^ A nose (Nasus extemus), such as exists in man, forming a projection distinctly marked
off from the rest of the face, does not exist in the domesticated animals.

2 These terms should be abandoned, as they tend unnecessarily to complicate the description
as well as to misconception with regard to function.

508

THE NASAL CAVITY

509

the naso-lacrimal duct, is seen when the nostril is dilated; it is situated on the floor
of the vestibule, aoout two inches (ca. 5 cm.) from the lower commissure, perforat-
ing the skin close to its junction with the mucous membrane. (It is not rare to find
one or two accessory orifices further back.)

Structure. — The skin around the nostrils presents long tactile hairs as well as
the ordinary ones. It is continued around the alee and lines the vestibule. The
skin of the diverticulum is thin
and usually black, and is cov-
ered with very fine hairs; it is
provided with numerous selia-
ceous glands. The medial wing
is supported by the alar cartil-
age (Cartilago alaris) , which is

Fig 451. — Cast of Left Nostril, Nasal
Diverticulum, and Nasal Vestibule
OF Horse; Dorsal View.
N, Nostril; D, diverticulum; 1, super-
ior commissure of nostril; 2, inferior com-
missure; 3, space occupied by alar fold; 4,
groove occupied by dorsal turbinate fold;
5, dorsal meatus.

Fig. 452. — Cross-section of Nasal Region of Horse.
The section is cut about two inches (5 cm.) behind the nostrils and a
little more than half an inch behind the labial commissure.
a. Dorsal meatus; 6, middle meatus; c, ventral meatus; d, diver-
ticulum nasi; e, dorsal turbinate fold; /, ventral turbinate fold; g,
prominence caused by venous plexus which extends back on lower part
of ventral turbinate; 1, nasal bone; 2, cartilage of septum nasi; 3, 4,
palatine and nasal processes of palatine bones; 5, maxilla; 6, tendon of
levator labii superioris proprius; 7, part of laterahs nasi muscle which
goes to cartilage of ventral turbinate; 8, 8', levator nasolabialis; 9, dila-
tor naris lateralis; 10, buccinator; 11, vomero-nasal organ; 12, naso-
lacrimal duct (wide part); 13, lateral nasal artery; 14, 14', branches of
superior labial artery; 15, palatine artery; 16, labial branches of infra-
orbital nerve; 17, external nasal nerve; 18, hard palate; 19, cheek; 20,
superior labial vein. The veins (black) are filled by a natural injec-
tion.

shaped somewhat like a com-
ma, the convex margin being
medial (Fig. 453) . The cartil-
ages are attached by fibrous
tissue to the extremity of the
septal cartilage. Each consists

of an upper, quadrilateral curved plate, the lamina, and a narrow comu which curves
ventro-laterally, supporting the medial wing and the inferior commissure, but not en-
tering into the formation of the lateral ^ving. The lamina causes the pro j ection of the
upper part of the medial wing, from which the thick alar fold (Plica alaris) passes
backward along the lateral wall of the nasal cavity to join the mucous fold which

510

RESPIRATORY SYSTEM OF THE HORSE

encloses the cartilaginous prolongation of the ventral turbinate bone.^ The extrem-
ity of the cornu usually causes a slight projection of the skin a short distance behind
and below the inferior commissure.

The muscles of the nostrils have been described (p. 258).

Vessels and Nerves. — The arteries are branches of the palato-labial, superior
labial, and lateral nasal arteries, and the blood is conveyed away by corresponding
veins. The lymph vessels go to the mandibular lymph glands. The nerves are
derived from the infraorbital nerve (sensory) and from the facial nerve (motor) .

The nasal cavity is divided into two symmetrical halves by the median septum
nasi (Figs. 452, 455, 456). The osseous septum (Septum nasi osseum) is formed
behind by the perpendicular plate of the ethmoid and ventrally by the vomer. A
few ridges on the former correspond to the ethmoidal meatuses. The major part

of it, however, is formed by the
cartilage of the septum nasi (Car-
tilago septi nasi). The surfaces
of the cartilage are marked by
faint grooves for the vessels and
nerves which course over it. The
dorsal border is attached along
the frontal and nasal sutures, and
extends beyond the apices of the
nasal bones about two inches (ca.
5 cm.). From this border a thin,
narrow plate, the parietal cartil-
age (Cartilago parietalis) curves
outward for a short distance on
either side. Near the nostrils
these plates are somewhat wider,
partially making good the defect
(naso-maxillary notch) in the
bony wall of the cavity in this
situation. The ventral border is
thick and rounded; it lies in the
groove of the vomer and the pala-
tine processes of the premaxillse;
its anterior part occupies the
space between the premaxillary
bones. A process from it extends
into the palatine fissure, which it
almost completely fills; the pala-
tine end of the process lies in the
submucous tissue of the hard palate, and the palatine artery turns medially between
the cartilage and the bone. The posterior border is continuous with the perpen-
dicular plate of the ethmoid bone.^ The alar cartilages are attached to the anterior
extremity l)y fibrous tissue in such a manner as to allow very free movement — in
fact an actual joint may be present. The ventral part of the cartilage is about
half an inch (ca. 1 cm.), the middle part about one-tenth of an inch (ca. 2.5 mm.),
and the dorsal part about a quarter to a third of an inch (ca. 6 to 8 mm.) in
thickness.

1 When the nostril is fully dilated it is circular in outline, and the so-called false nostril is
effaced by the lamina of the alar cartilage being brought in contact with the superior commissure.

2 The cartilage is to be regarded as an unossified part of the mesethmoid. It will be noted
that the line of demarcation between the bone and the cartilage is irregular and varies with age;
extensive ossification (or calcification) of the cartilage is commonly found m old animals. The
process often results in the formation of calcareous islands in the cartilage.

Lfuni/M
of alar
cartilage

Cornu
of alar
cartilage

Fig. 453. — Nasal Cartilages of Horse; Dorsal View.

1, Anterior extremity of cartilage of septum nasi; 2, foramen

incisivum.

THE NASAL CAVITY 511

The two turbinate bones project from the lateral wall, and divide the outer
part of the cavity into three meatuses— dorsal, middle, and ventral (Figs. 454,
455,456).

The dorsal nasal meatus (Meatus nasi dorsalis) is a narrow passage, bounded
dorsally by the roof of the cavity, and ventrally by the dorsal turbinate bone ; its
posterior end is closed by the junction of the inner plate of the frontal bone with the
cribriform plate and lateral mass of the ethmoid. It transmits air to the olfactory
region.

The middle nasal meatus (Meatus nasi medius) is between the two turbinate
bones. It is somewhat larger than the dorsal meatus, and does not extend back
so far; it ends near the great ethmoturbinate and the ethmoidal meatuses. In
its posterior part is the extremely narrow, slit-like interval by which the max-
illary sinus communicates with the nasal cavity — the naso-maxillary opening
(Aditus naso-maxillaris) . The opening, which is normally a mere fissure, is not
visible from the nasal side, being concealed by the overhanging dorsal turbinate.
A fine flexible probe, passed outward and somewhat backward between the turbinate

Dorsal „ ,

Veyitral turbinate r, , 7 T"\ Septum between

turbinate Middle Dorml turbinates frontal sinuses

Ventral \ 7neatus ^- -

meatus

Fig. 454. — Nasal Cavitt of Horse; Sagittal Section with Septum Removed.
/, Dorsal turbinate fold; 2, alar fold, containing cartilaginous prolongation of ventral turbinate; 3, arrow pointing-
to naso-maxillary opening, which is concealed by dorsal turbinate bone; 4, cranial cavity; 3, sphenoidal sinus; 6,
hamulus of pterygoid bone. The olfactory mucous membrane is shaded. Dotted lines indicate anterior limit of
uncoiled parts of turbinate bones, which inclose parts of frontal and maxillary :

bones, enters the maxillary sinus; if introduced a little further in the same direction,
it usually passes through the orifice of communication between the maxillary
sinus and the frontal sinus and enters the latter. A small part of the fissure usually
brings the anterior division of the maxillary sinus into communication with the
nasal cavity. The spaces enclosed by the coiled parts of the turbinates also open
into the middle meatus. This passage may be characterized as the sinus-meatus,
but it also conducts air to the olfactory region.

The ventral nasal meatus (Meatus nasi ventralis) is situated between the
ventral turbinate and the floor of the cavity. It is much larger than the other two,
and is the direct passage between the nostrils and the pharynx. The small, slit-
like orifice of the vomero-nasal organ and the incisive or naso-palatine duct is
situated in the floor of the anterior end of the meatus.

The common nasal meatus (Meatus nasi communis) is situated between the
septum and the turbinates, and is continuous laterally with the other meatuses.
It is very narrow dorsally, but widens ventrally.

The lateral masses of the ethmoid bone project forward into the posterior
part (fundus) of the nasal cavity. Between the ethmoturbinates, of which each

512 RESPIRATORY SYSTEM OF THE HORSE

mass IS composed, there are three principal and numerous small passages, the
ethmoidal meatuses (Meatus ethmoidales).

The choanae or posterior nares are two elliptical orifices by which the nasal
cavity and pharynx conununicate. They are in the same plane as the floor of the

Parotid External Mandibular

duct maxillary lymph glands

vessels
Fig. 455. — Cross-section of He.^d op Horse.
The section is cut midway between the medial canthus and the anterior end of the facial crest and is a front view.
1, Septum nasi; 2, 3, 4, dorsal, middle, and ventral meatus nasi; 5, common meatus nasi; 6, cavity of dorsa.'
turbinate bone (i. e., turbinate part of frontal sinus) ; 7, cavity of ventral turbinate bone (i. e., turbinate part of maxillajy
sinus); 8, maxillary sinus; 9, communication between 7 and 8 over infraorbital canal; 10, naso-lacrimal duct; 11,
infraorbital nerve and canal; 12, m. levator labii superioris proprius; 13, mouth cavity; 14, palatine artery; 15, fifth
upper cheek tooth (posterior part); 16, sixth lower cheek tooth (anterior part); 17, m. buccinator; IS, hard palate; 19,
vena reflexa; 20, superior buccal glands; 21, buccinator vessels and nerve; 22, alveolar vessels and nerve of mandible;
23, lingual artery; 24, mm. gj*nio-glossi ; 25, m. hyo-glossus (number placed between two radicles of lingual vein); 26,
m. stylo-glossus; 27, m. m^lo-hyoideus; 28, m. genio-hyoideus; 29, lingual nerve; 30, hypoglossal nerve; 31, sub-
lingual artery; 32, m. digastricus (anterior belly). The mandibular duct is shown in the fat lateral to the genio-hyoideua
but is not marked.

nasal cavity, and are separated from each other by the vomer. They are, taken
together, about two inches (ca. 5 cm.) wide and three to four inches (ca. 8 to 10
cm.) long.

The nasal mucous membrane (Membrana mucosa nasi) is thick, highly vas-
cular, and is, in general, firmly attached to the underlying periosteum and peri-

THE NASAL CAVITY

513

chondrium. It is continuous in front with the skin which hues the nostrils, and
behind with the mucous membrane of the pharynx. It is also continuous at the
naso-maxillary opening with the very thin and much less vascular mucous mem-
brane which lines the paranasal sinuses. In the anterior part of the cavity it forms
prominent thick folds on the lateral wall, which extend from the turbinate bones to
the nostril. There are usually two dorsal turbinate folds which unite anteriorly.

Dorsal meatus

Septum nasi Lacrimal sac

Transverse
facial vessels

Palatine artery

Vena reflexa
Palatine vein
Buccinator and
Dep. labii inf.
Buccinator
and

Lingual 7ierve
Lingual artery
Lingual vein

Mandibular
duct

Hypoglossal
nerve

Digastricus (ant. hdly)

External t, . i > ^
maxillary J '^rotul duct
vessels

Fig. 456. — Cross-section of Head of Horse. The Section Passes Through the Medial Canthi and is Viewed

FROM Behind.
J, Mylo-hyoideus; S, stylo-glossus ; 3, hyo-glossus; .<, genio-glossus; .5, lingual process of hyoid bone. An arrow
points to the naso-maxillary opening. The projecting edge just above the arrow point is the anterior margin of the
fronto-maxillary opening.

The upper one encloses a thin plate of cartilage which is continuous with the dorsal
turbinate bone. The ventral turbinate fold is curved, and encloses an '"N^ shaped
cartilaginous plate which prolongs the ventral turbinate bone; this fold is con-
tinuous with the alar fold of the nostril, and forms with it the upper margin of the
entrance from the nostril to the nasal cavity. Below this there is a rounded ridge
produced by the nasal process of the premaxilla. The mucous membrane of the
33

514 RESPIRATORY SYSTEM OF THE HORSE

greater part oi the cavity (Regio respiratoria) is red in color, and is covered with a
stratified cihated epithelium. It contains numerous tubulo-alveolar nasal glands
(Glandulae nasales). The submucosa contains rich venous plexuses which form
in certain situations a sort of cavernous tissue (Plexus cavernosus nasalis), composed
of several strata of freely anastomosing veins, between which there are unstriped
muscle-fibers. This arrangement is most marked in the turbinate folds, on the
lower part of the ventral turbinate bone, and the lower part of the septum. The
mucous membrane of the vestibule presents numerous small depressions (openings
of gland ducts), and is covered with stratified squamous epithelium. On the
posterior part of the lateral masses of the ethmoid and the adjacent part of the
dorsal turbinate and the septum (Regio olfactoria) the mucous membrane is brown-
ish-yellow in color and thicker; it contains the olfactory nerve-endings in a special
non-ciliated epithelium. In it are numerous olfactory glands (Glandulse olfactorise) ;
these are long, tubular, and often Ijranched.

The vomero-nasal organ (Organon vomeronasale)^ is situated on the floor of
the nasal cavity, on either side of the ventral border of the septum (Fig. 452).
It consists of a tubular cartilage (Cartilago vomeronasal! s) lined with mucous
membrane (Ductus vomeronasalis) , to which fibers of the olfactory nerve may be
traced. Its anterior part communicates with the nasal cavity by a slit-like orifice
in common with the incisive or naso-palatine duct. The posterior blind end is in a
transverse plane through the second or third cheek tooth. The average length of
the organ is about five inches (ca. 12 cm.).

The ductus incisivus (or naso-palatine duct) is a small mucous tube, an inch
or more (ca. 2.5-3 cm.) in length, which extends obliquely through the palatine
fissure. Its nasal end communicates with the nasal cavity through a slit-like
opening in common with the vomero-nasal organ. The palatine extremity ends
blindly in the submucous tissue of the hard palate.

The paranasal sinuses are described in the Osteology.

Vessels and Nerves. — The arteries are branches of the ethmoidal, spheno-
palatine, palatine, superior labial, and lateral nasal arteries. The blood is carried
away by corresponding veins. The lymph vessels go to the mandibular and
pharyngeal lymph glands. The nerves come from the olfactory and trigeminal

THE LARYNX

The larynx is a short tube which connects the pharynx and trachea. It is a
complex valvular apparatus, which regulates the volume of air in respiration,
prevents aspiration of foreign bodies, and is the chief organ of voice.

It is situated partly between the medial pterygoid muscles, partly in the neck
between the parotid glands.^ Its long axis is practically horizontal in the ordinary
position of the head and neck. It is related dorsally to the pharynx and the origin
of the oesophagus. Ventrally it is covered by the skin, fascia, and sterno-hyoid
and omo-hyoid muscles. Laterally it is related to the parotid and mandibular
glands and to the medial pterygoid, occipito-mandibularis, digastricus, stylo-hyoid,
and pharyngeal constrictor muscles. It is attached to the body and thyroid cornua
of the hyoid bone, and thus indirectly to the base of the cranium. Its cavity
communicates dorsally with the pharynx, posteriorly with the trachea. The
skeleton of the larynx consists of a framework of cartilages, which are connected by
joints and ligaments or membranes, and moved by extrinsic and intrinsic muscles.
It is lined with mucous membrane.

^ Commonly known as the organ of Jacobson.

2 In the ordinary position of the head and neck, and while the parts are at rest, about half
of the larynx lies between the branches of the mandible; when the head and neck are extended,
proportionately more of the larynx lies behind a plane through the posterior borders of the rami.

CARTILAGES OF THE LARYNX

515

Cartilages of the Larynx

There are three single cartilages and one pair; the single cartilages are the
cricoid, thyroid, and epiglottic; the arytenoid cartilages are paired.

The cricoid cartilage (Cartilago cricoidea) is shaped like a signet ring. The
dorsal part is a broad, thick, quadrilateral plate termed the lamina; the external
(dorsal) surface of this is marked by a median ridge (Crista mediana) separating two
shallow cavities, from which the dorsal crico-arytenoid muscles arise. On either
side of these depressions are two articular facets. The anterior facet (Facies articu-
laris arytaenoidea) is at the anterior border, is oval and convex, and articulates
with the arytenoid cartilage. The posterior facet (Facies articularis thyreoidea) is
situated on the front of a ridge, a short distance from the posterior border; it is
concave, and articulates with the posterior cornu of the thyroid cartilage. The
ventral and lateral parts of the ring are formed by a curved band, called the arch
(Arcus), which is narrowest ventrally. The lateral surfaces of the arch are grooved

Muscular process

pex

Crico-tracheal \ Oblique
membrane \ line

Crico-thyroid
membrane

Laryngeal prominence

Fig. 457. — Laryngeal Cartilages and Part of Trachea or Horse; Right View.
For "thyroid wing" read "thyroid lamina."

for the crico-thyroid muscle. The anterior l)order of the lamina is thick and
slightly concave; the posterior border is thin and irregular. The anterior border
of the arch is concave ventrally and gives attachment to the crico-thyroid membrane ;
laterally it is thicker and gives attachment to the crico-arytenoideus lateralis
muscle. The posterior border of the cartilage is attached to the first ring of the
trachea by the crico-tracheal membrane. The internal surface is smooth and is
covered with mucous membrane.

The thyroid cartilage (Cartilago thyreoidea) consists of a median thickened
portion, termed the body, and two lateral laminae. The body forms ventrally a
slight prominence (Prominentia laryngea), which can be felt, but is not visible in
the living subject; it is related dorsally to the base of the epiglottis, which is at-
tached to it by an elastic ligament. The laminae or wings spring from the body
on either side and form a large part of the lateral wall of the larynx. Each is a
rhomboid plate, presenting a slightly convex lateral surface, which is divided into
two areas by an oblique line (Linea obliqua), on which the thyro-hyoid and thyro-
pharyngeus muscles meet. The dorsal border is nearly straight; it gives attach-
ment to the pharyngeal fascia and the palato-pharyngeus muscle, and bears a cornu
at each end. The anterior cornu (Cornu orale) articulates with the cartilage of the

516

RESPIRATORY SYSTEM OF THE HORSE

thjToid cornu of the hyoid bone; below it is a notch (Fissura thyreoidea), which is
converted into a foramen (Foramen thyreoideum) by a fibrous band, and trans-
mits the anterior lar>Tigeal nerve to the interior of the larynx. The posterior cornu
(Cornu aborale) articulates with the cricoid cartilage. The ventral border joins
the body in front, and behind diverges
from its fellow to inclose a triangular 2Joc/;/

space, the thyroid notch (Incisura thy-
reoidea aboralis), which is occupied by
the crico-thyroid membrane. The anter-

Mediati ridge Lamina

Facet for
arytenoid

Posterior cornu
Surface for
cricoid

Fig. 458. — Cricoid Cartilage of Horse; Left Antero- Fig. 459. — Thyroid Cartilage of Horse; Ventral

LATERAL ViEW. ViEW.

ior border is slightly convex, and is attached to the hyoid bone by the thyro-hyoid
membrane. The posterior border overlaps the arch of the cricoid cartilage, and

Pharyngeal surface

Medial angle of base Apex

Cuneiform process

Fig. 460. — Epiglottic Cartilage of Horse; Right
Lateral View.

Vocal process

-Left Arytenoid Cartilage of Horse;
Medio-ventral View.

gives attachment to the crico-thyroid muscle. The medial surface is concave,
and is partly covered })y mucous membrane.

The epiglottic cartilage (Cartilago epiglottica), usually called the epiglottis for
the sake of brevity, is situated above the body of the thyroid cartilage and curves

JOINTS, LIGAMENTS, AND MEMBRANES OF THE LARYNX 517

toward the root of the tongue. It is shaped somewhat like a pointed ovate leaf,
and presents two surfaces, two borders, a base, and an apex. The oral (or anterior)
surface is concave in its length, convex transversely; the pharyngeal (or posterior)
surface has the reverse configuration. The borders are thin, irregular, and some-
what everted. The base is thick, and is attached to the dorsal surface of the body
of the thyroid cartilage by elastic tissue. From each side of it a cartilaginous bar
projects upward and backward; these are the cuneiform processes (Processus
cuneiformes) and correspond to the cuneiform cartilages of man. The apex is
pointed and curved ventrally. Nearly all of the epiglottic cartilage is covered with
mucous membrane. It usually projects into the isthmus faucium, but is often
on the pharyngeal side of the soft palate.

The arytenoid cartilages (Cartilagines arytenoideae) are situated on either side,
in front of the cricoid, and partly medial to the laminae of the thyroid cartilage.
They are somewhat pyramidal in form, and may be described as having three
surfaces, three borders, a base, and an apex. The medial surface is concavo-
convex, but very slightly curved, and is smooth and covered by mucous membrane.
The lateral surface is concave and is separated from the lamina of the thyroid
cartilage by the crico-arytenoideus lateralis and vocalis muscles, and the laryn-
geal saccule. The dorsal surface is also concave, and is covered by the aryte-
noideus muscle, which is attached to it. The dorsal and lateral surfaces are
separated (except in front) by a ridge which increases in size toward the lateral
angle of the base, where it forms a rounded prominence, the muscular process
(Processus muscularis). The anterior and posterior borders are convex; they
converge ventrally to a thin, wide angle, the vocal process (Processus vocalis).
The process is so named because it furnishes attachment to the vocal ligament.
The dorsal border forms a deep notch with the apex. The base is concave and
faces chiefly backward; it presents laterally an oval concave facet (Facies artic-
ularis) for articulation with the anterior border of the lamina of the cricoid carti-
lage. The medial angle of the base is attached to its fellow by the transverse
arytenoid ligament. The apex (Cartilago corniculata) curves upward and back-
ward, forming with its fellow the pitcher-shaped lip from which the cartilages derive
their name.

The cricoid and thyroid cartilages and the greater part of the arytenoid
cartilages are hyaline. The apices and vocal processes of the arytenoid and the
epiglottis (including the cuneiform processes) consist of elastic cartilage; they
show no tendency toward ossification at any age. The thyroid and cricoid carti-
lages regularly undergo considerable ossification; the process begins in the body of
the thyroid, and often involves the greater part of the cartilage.^

Joints, Ligaments, and Membranes of the Larynx
The crico-thyroid joints (Articulationes crico-thyreoidese) are diarthroses
formed by the apposition of the convex facets on the ends of the posterior cornua
of the thyroid cartilage with corresponding facets on the sides of the cricoid car-
tilage. The capsule is thin, but is strengthened by accessory bands dorsally,
laterally, and medially. The movements are chiefly rotation around a trans-
verse axis passing through the centers of the two joints.

The crico-arytenoid joints (Articulationes crico-arytsenoidea) are also diar-
throdial. They are formed by the apposition of the convex facets on the anterior
border of the cricoid cartilages with the concave facets on the bases of the arytenoid
cartilages. Each has a very thin, loose capsule, strengthened by accessory bundles

1 Calcareous deposits are present in the body of the thyroid cartilage even before adult age
is reached. Scheier (by use of X-rays) found complete calcification of the thyroid in two mares
eight and ten years of age; in the former the process also involved a large part of the lamina and
the adjacent part of the arch of the cricoid.

518 RESPIRATORY SYSTEM OF THE HORSE

dorsall}' and medially. The most important movement is rotation of the arytenoid
cartilage about a longitudinal axis so that the vocal process swings outward (ab-
duction) or inward (adduction), carrying the vocal cord with it. Another move-
ment here is rotation about a transverse axis, in which the apical part of the carti-
lage is raised or lowered. The arytenoid is also capable of slight inward or outward
gliding movement.

The th3rro-hyoid joints (Articulationes hyo-thyreoidese) are formed by the
anterior cornua of the thyroid cartilage and the cartilaginous extremities of the
thyroid cornua of the hyoid bone. They are diarthroses and the joint capsule is
reinforced by a relatively strong thyro-hyoid ligament. The thyroid cornu has
here a cartilaginous prolongation about a quarter of an inch (ca. 6 mm.) in length.
The chief movement is rotation around a transverse axis passing through the two
joints.

The crico-thyroid membrane (Membrana crico-thyreoidea) occupies the thy-
roid notch and extends backward to the arch of the cricoid cartilage. It is tri-
angular in form, and is attached by its base to the anterior border of the arch of
the cricoid cartilage, while its borders are attached to the margins of the thyroid
notch. It is strong, tightly stretched, and composed largely of elastic tissue. It
is reinforced ventrally by longitudinal fibers, dorsally by fibers which stretch across
the thyroid notch.

The thyro-hyoid membrane (Membrana hyo-thyreoidea) connects the body
and anterior borders of the thyroid cartilage with the body and thyroid cornua of
the hyoid bone.

The hyo-epiglottic ligament (Lig. hyo-epiglotticum) attaches the lower part
of the oral surface of the epiglottis to the body of the hyoid bone. It forms an
elastic sheath for the hyo-epiglottic muscle. Ventrally it blends with the thyro-
hyoid membrane, and dorsally it is not well defined.

The thyro-epiglottic ligament (Lig. thyreo-epiglotticum) is strong and thick;
it is composed chiefly of elastic tissue. It connects the base of the epiglottis with
the body and the adjacent medial surfaces of the laminae of the thyroid cartilage.
Other fibers attach the cuneiform processes somewhat loosely to the thyroid laminae.

The transverse arytenoid ligament (Lig. arytsenoideum transversum) is a
slender band which connects the medial angles of the bases of the arytenoid carti-
lages.

The vocal (or posterior thyro-arytenoid) ligament (Lig. vocale) underlies and
is intimately adherent to the mucous membrane of the true vocal cord. It is thin
and elastic and is attached ventrally to the body of the thyroid cartilage and the
crico-thyroid membrane close to its fellow of the opposite side, and ends dorsally
on the processus vocalis of the arytenoid cartilage.

The ventricular (or anterior thyro-arytenoid) ligament (Lig. ventriculare) is
included in the false vocal cord. It consists of loosely arranged bundles which
arise chiefly from the cuneiform process and end on the lateral surface of the pro-
cessus vocalis and adjacent part of the arytenoid cartilage.

The crico-tracheal membrane (Membrana crico-trachealis) connects the cri-
coid cartilage with the first ring of the trachea.

Muscles of the Larynx
A. Extrinsic Muscles
The stemo-thyro-hyoideus is described on p. 268.

The thyro-hyoideus (M. hyo-thyreoideus) is a flat, quadrilateral muscle, which
lies on the lateral surface of the thyroid lamina and the lateral part of the thyro-
hyoid membrane. It arises from the body and thyroid cornu of the hyoid bone
(almost meeting the opposite muscle), and ends on the oblique line on the lamina

MUSCLES OF THE LARYNX 519

of the thyroid cartilage. Its action is to draw the larynx toward the root of the
tongue. It is related laterally to the external maxillary vein and the anterior part
of the mandibular gland.

The hyo-epiglotticus (M. hyo-epiglotticus) is a feeble muscle which occupies a
median position above the central part of the thyro-hyoid membrane, enclosed by
an elastic sheath, the hyo-epiglottic ligament. It arises from the body of the hyoid
bone by two branches which unite and are inserted into the front of the base of the
epiglottis. Its action is to draw the epiglottis toward the root of the tongue.

B. Intrinsic Muscles

The crico-thyroideus (M. crico-thyreoideus) is a short muscle which fills the

groove on the lateral surface of the cricoid cartilage ; its fibers are directed dorsally

and somewhat forward. It arises from the ventral part of the lateral surface and

posterior edge of the cricoid cartilage, and is inserted into the posterior border and

Fig. 4G2. — Laryngeal Muscles of Horse, Seen from Left Side After Removal of Major Part op Lamina op

Thyroid Cartilage.
a, Kerato-hyoideus; b, thyro-hyoideus; c, crico-thyroideus; d, sterno-thyroideus; e, ventricularis; /, vocalis; g,
crico-arytenoideus lateralis; h, crico-arytenoideus dorsalis; i, arytenoideus transversus; 1, lingual process; 2, small
cornu, 3, thyroid cornu, of hyoid bone; 4< thyroid cartilage; 5, cricoid cartilage; 6, epiglottis; 7, apex of arytenoid
cartilage; 5, trachea; S, muscular process of arytenoid; ^0, lateral lobe of thyroid gland; iO', isthmus of thyroid gland;
11, laryngeal saccule. The saccule is larger than it is represented in this figure, and extends almost to the vocal
process. (Ellenberger-Baum, Anat. d. Haustiere.)

adjacent part of the lateral surface of the lamina of the thyroid cartilage. Its
action is to draw the thyroid cartilage and the ventral part of the cricoid cartilage
together. In this action the cricoid cartilage is probably rotated about a trans-
verse axis through the crico-thyroid joints, carrying the bases of the arytenoid
cartilages with it and thus tensing the vocal cords.

The crico-arytenoideus dorsalis (M. crico-arytsenoideus dorsalis)^ is a strong,
somewhat fan-shaped muscle, which, with its fellow, covers the dorsal surface of
the lamina of the cricoid cartilage. It is partially divisible into two layers. It
has a broad origin on half of the lamina of the cricoid cartilage, including the me-
dian ridge, and its fibers converge to be inserted into the processus muscularis of
the arytenoid cartilage. Its action is to dilate the rima glottidis by rotating the
arytenoid cartilage so as to carry the vocal process and cord outward (abduction).

The crico-arytenoideus lateralis (M. crico-arytsenoideus lateralis) lies on the
medial face of the thyroid lamina. It arises from the anterior border of the lateral
part of the arch of the cricoid cartilage. The fibers pass in a dorsal direction and
converge on the processus muscularis of the arytenoid cartilage. It closes the
rima glottidis by rotating the arytenoid cartilage inward (adduction).
1 Also known as the crico-arytenoideus posterior s. posticus.

520

RESPIRATORY SYSTEM OF THE HORSE

The arytenoideous transversus (M. arytsenoideus transversus) is an unpaired
muscle which stretches across the concave dorsal surface of the arytenoid cartilages.
Its fibers are attached on either side to the processus muscularis and the ridge which
extends forward from it. The right and left parts of the muscle meet at a fibrous
raphe, which is connected with the transverse arytenoid ligament. Fibers of the
ventricularis muscle overlap its anterior part. It narrows the rima by draw-
ing the arytenoid cartilages together (adduction).

The ventricularis^ lies in the lateral wall of the larynx, covered by the lamina of
the thyroid cartilage. It arises from the anterior part of the crico-thyroid membrane
and the ventral border of the thyroid lamina. Its fibers pass upward and backward

Salpingo-pharyngeal
fold

Epiglottis

Aryteno-epiglottic
fold

Root of tongue
Soft palate {cut)

FiQ. 463."

Wall of pharynx
Arytenoid cartilage (apex)

Posterior pillar of soft palate

Position of cricoid
cartilage under oesophagus

Thyroid gland
Trachea
(Esophagus

-Aditus Laryngi8 op Horse, Exposed bt Opening Pharynx and Beginning op Esophagus Along
Median Dorsal Line.
1, False vocal cord; S, lateral' ventricle; S, true vocal cords; 4< rima glottidis.

to end partly on the processus muscularis, partly on the arytenoideus transversus,
meeting its fellow.

The vocalis^ is also medial to the lamina of the thyroid cartilage, and is in part
separated from the preceding muscle by the laryngeal saccule. It has an extensive
origin on the crico-thyroid membrane. Its direction corresponds with that of the
true vocal cord. It is inserted into the lateral surface of the arytenoid cartilage
below the processus muscularis.

The two preceding muscles close the rima glottidis and slacken the vocal cords.
With the arytenoideus transversus and crico-arytenoideus lateralis they form a
sphincter which closes the entrance to the larynx.

1 These two muscles were formerly taken together as parts of the thyro-arytenoideus muscle.

CAVITY OF THE LARYNX

521

The ventricularis rotates the arytenoid so as to bring the apical part of the cartilage down-
ward and forward.

In some cases there is a small thyro-ar3rtenoideus extemus muscle which arises from the
medial face of the lamina of the thyroid cartilage near the dorsal border, passes upward and
backward, and blends with the arytenoideus trans versus.

Cavity of the Larynx

The cavity of the larynx (Cavum laryngis) is smaller than one would naturally
expect from its external appearance. On looking into it through the pharyngeal
end two folds are seen projecting from each lateral wall. These are termed the

Fig. 464. — Part of Sagittal Section of Head of Horse.
Section is cut just to left of median plane.
1, Epiglottis; 2, body of thyroid cartilage; 3, arytenoid cartilage; 4, 4', lamina and arch of cricoid cartilage; 5,
ary-epiglottic fold; 6, vocal cord (laoium vocale): 7, ventricular fold or false vocal cord (plica ventricularis); 8, lateral
ventricle of larynx; 8', dotted line indicating contour of laryngeal saccule; 9, middle ventricle of larynx; 10, m. crico-
arytenoideus dorsalis; 11, CEsophagus; 12, septum of areolar tissue between guttural pouches; 13, m. rectus capitis
ventralis; 14, body of sphenoid bone; 15, pharyngeal recess; 16, arrow points into nasal cavity; 17, pharyngeal open-
ing of auditive or Eustachian tube; 18, posterior pillars of soft palate united over aditus CEsophagi; 19, arrow points
into vestibule of larynx; 20, soft palate; 21, tonsil; 22, root of tongue; 23, m. hyo-epiglotticus; 24, hyoid bone; 25,
mandibular lymph glands; 26, mm. omo-hyoideus and sterno-hyoideus; A, vestibule of larynx; B, glottis; C, post-
glottic part of larynx; Z), trachea; E, pharynx, F, isthmus faucium.

vocal cords, and the narrow part of the cavity between them is the rima glottidis.
Thus it is convenient to recognize three divisions of the cavity.

The aditus laryngis, or pharyngeal aperture, is a large, oblique, oval opening,
which faces into the ventral part of the pharynx. It is bounded in front by the
epiglottis, behind by the arytenoid cartilages, and laterally by the aryteno-epi-
glottic folds of mucous membrane (Plicae aryepiglotticae) , which stretch between
the edges of the epiglottis and the arytenoid cartilages.

522

RESPIRATORY SYSTEM OF THE HORSE

The vestibule of the larynx (Vestibulum laryngis) is that part of the cavity
which extends from the aditus to the vocal cords. On its lateral walls are the false
vocal cords (Plicae ventriculares), each of which consists of a fold of mucous mem-
brane covering the ventricular ligament and the cuneiform process. Between the
false and true vocal cord there is a pocket-like depression termed the lateral ven-
tricle of the larynx (Ventriculus lateralis laryngis). This is the entrance to the
laryngeal saccule (Sacculus laryngis), a cul-de-sac of the mucous membrane which
is an inch or more (ca. 2.5 to 3 cm.) long and extends upward and backward on the
medial surface of the thyroid lamina. There is a small middle ventricle (Ventric-
ulus laryngis medianus) at the base of the epiglottis.

The term "larjmgeal saccule" seems decidedly preferable to the "appendix ventriculi lar-
yngis" of the B. N. A. The saccule is in relation with the ventricular and vocal muscles, and

Body of thyroid
cartilage

Crico-

arytenoideus
dor salts
muscle

Fig. 466. — Cast of Right Lateral Ventricle

AND Saccule of Horse; Medial View.

1, Ventricle; 2, saccule. Figure is a little less than

three-fourths of natural size.

Fig. 465. — Section of Larynx of Horse.
The section cut is parallel with the vocal cords.

Fig. 467. — Cast of Left Lateral Ventricle and

S-4.CCULE OF Larynx of Horse; Lateral View.

1, Ventricle; 2, saccule; 3, impression of ventricu-

laris muscle; 4, impression of vocalis muscle.

when the latter are atrophic (as in hemiplegia laryngis or "roaring"), the pouch is considerably
larger on the affected side, having occupied the space vacated by the muscles. The blind end of
the saccule lies just below the level of the muscular process of the arytenoid cartilage. It is loosely
attached to the contiguous structures. The average capacity of the saccule is about 5 to 6 c.c.

The middle, narrow part of the cavity is termed the glottis or rima glottidis.
It is bounded on either side ])y the true vocal cord and the medial surface of the ary-
tenoid cartilage. The true vocal cords (Labia vocales) are situated behind the
false cords and the lateral ventricles. They extend from the angle of junction of
the body and laminae of the thyroid cartilage to the vocal processes of the arytenoid
cartilages. They are prisniatic in cross-section, and their free edges look forward
and somewhat upward. The mucous membrane of the cord (Plica vocalis) is very
thin and smooth, and is intimately attached to the underlying vocal ligament. In

THE TRACHEA 523

ordinary breathing the rima is somewhat lanceolate in form (Fig. 465) ; when dilated,
it is diamond-shaped, the widest part being between the vocal processes. The
narrow part of the glottis between the vocal cords is termed the glottis vocalis (Pars
intermembranacea) , while the wider part between the arytenoid cartilages is the
glottis respiratoria (Pars intercartilaginea) .

In the revised nomenclature the terms "true" and "false" vocal cords have been replaced
by "labium vocale"and "plica ventricularis." The labium vocale consists of the plica vocalis,
lig. vocale, and m. vocalis; the last forms the bulk of the projection.

The posterior compartment of the laryngeal cavity is directly continuous with
the trachea. It is enclosed by the cricoid cartilage and the crico-thyroid membrane.
It is clearly marked off laterally by the vocal cord and the projection caused by the
posterior iDorder of the arytenoid cartilage. It is oval in form, the transverse
diameter being an inch and a half to two inches (ca. 4 to 5 cm.), and the dorso-
ventral diameter two to two and a half inches (ca. 5 to 6 cm.).

The mucous membrane of the larynx (Tunica mucosa laryngis) is reflected
around the margin of the aditus to become continuous with that of the pharynx,
and is continuous behind with that which lines the trachea. It is closely attached
to the epiglottis, except at the base, but elsewhere in the aditus and vestibule it is
loosely attached by submucous tissue which contains many elastic fibers. It is
thin and very closely adherent over the vocal cords and the medial surfaces of the
arytenoid cartilages. The epithelium is of the stratified squamous type from the
aditus to the glottis, beyond which it is columnar ciliated in character. There are
numerous mucous laryngeal glands (Glanclulse laryngese), except in the glottis and
the pharyngeal surface of the epiglottis, in which situations they are scanty. Lymph
nodules (Noduli lymphatic! laryngei) are also present, especially at the lateral
ventricle.

Vessels and Nerves. — The arteries are derived from the laryngeal and ascend-
ing pharyngeal arteries. The veins correspond to the arteries. The lymph-
vessels go to the anterior cervical and pharyngeal lymph glands. The nerves
come from the vagus. The recurrent or posterior laryngeal is the motor nerve to
the muscles with the exception of the crico-thyroideus. The anterior laryngeal
is the sensory nerve; it commonly supplies the nerve to the crico-thyroideus.

THE TRACHEA

The trachea extends from the larynx to the roots of the lungs, where it divides
into the right and left bronchi. It is kept permanently open by a series of fifty to
sixty incomplete cartilaginous rings embedded in its wall. It occupies a median
position, except near its termination, where it is pushed a little to the right by the
arch of the aorta. It is approximately cylindrical, but its cervical part is for the
most part depressed dorso-ventrally by contact with the longus colli muscle, so
that the dorsal surface is flattened. Its average length is about 30 to 32 inches (ca.
75 to 80 cm.). The average caliber is about two to two and one-half inches (ca. 5 to
6 cm.), but in the greater part of the neck the transverse diameter is greater and the
clorso-ventral smaller.^ It is enclosed by a fascia propria.

In its cervical part (Pars cervicalis) the trachea is related dorsally to the
oesophagus for a short distance, but chiefly to the longus colli muscles. It is related
laterally to the lateral lobes of the thyroid gland, the carotid artery, the jugular
vein, the vagus, sympathetic, and recurrent laryngeal nerves, and the tracheal

1 At its origin the trachea is almost circular in cross-section and the average diameter is
about two and a quarter inches (ca. 5.5 cm.). It soon becomes flattened dorso-ventrally, so that
the transverse diameter may be nearly three inches (ca. 7 cm.) and the dorso- ventral about two
inches (ca. 5 cm.). In the thorax the diameters become more nearly equal, and sometimes the
dorso-ventral diameter is the greater; this is the case where the aorta crosses the trachea.

524

RESPIRATORY SYSTEM OF THE HORSE

Ijonph ducts and cervical lymph glands. The oesophagus lies on its left face from
the third cervical vertebra backward. The sterno-cephalicus muscles cross it very
obliquely, passing from the ventral surface forward over its sides, and diverging to
reach the angles of the jaw. The omo-hyoidei also cross it very obliquely, passing
over the lateral surfaces of the tube, and converging ventrally in the laryngeal
region. The sterno-thyro-hyoideus lies on the ventral surface.^ The scaleni lie on
either side near the entrance to the thorax.

The thoracic part (Pars thoracalis) of the trachea (Figs. 553, 554) passes back-

Obliquiis

capitis

posterior

Intertrax.s

versali.

Longissirnii

capitis et atlanti

Rectus capitis

ventralis major

Brachiocephalic us

humeralis

Vagosympa-
thetic trunk
Carotid artery

Recurrent nerve
Jugular vein

Sterno-
cephalicus

Omo-hyoideus

Stemo-thyroideus Sterno-hyoideus

Fig. 468. — Cross-section of Ventral Part of Neck of Horse.
This section is cut at right angles to the long axis of the neck, passing through the junction of the second and third
cervical vertebrae. S.c, Spinal cord; S.v., spinal vein; V.v., V.a., vertebral vein and artery; T.p., transverse process
(tip); F, intervertebral fibro-cartilage; T, atlantal tendon common to brachiocephalicus, splenius, and longissimus
atlantis; M, digitation of brachiocephalicus inserted by T.

ward between the pleural sacs and divides into two bronchi over the left atrium of the
heart. It is related dorsally to ths longus colli tor a short distance, and beyond this to
the oesophagus. Its left face is crossed by the aortic arch, the left brachial artery, and
the thoracic duct. Its right face is crossed by the vena azygos, the dorso-cervical
and vertebral vessels, and the right vagus nerve. Ventrally it is related to the
anterior vena cava, the brachiocephalic and common carotid trunks, and the car-
diac and left recurrent nerves.

1 The arrangement of the muscles should be noted, since the space enclosed by the divergence
of the stemo-cephalici and the convergence of the omo-hyoidei is the area of election for the opera-
tion of tracheotomy.

THE BRONCHI THE THORACIC CAVITY 525

The bifurcation of the trachea (Bifurcatio trachese) is situated opposite to the
fifth rib or intercostal space, and about four or five inches (ca. 10 to 12 cm.) ventral
to the vertebral column.

The trachea is composed of — (1) the cartilaginous rings; (2) a fibro-elastic
membrane which encloses and connects the rings; (3) a muscular layer; (4) the
mucous membrane. The elastic membrane is intimately attached to the peri-
chondrium of the rings. In the intervals between the latter it constitutes the
tracheal annular ligaments (Ligamenta annularia trachealia). The rings of the
trachea (Cartilagines tracheales) are composed of hyaline cartilage. They are
incomplete dorsally, and when their free ends are drawn apart, resemble somewhat
the letter C. In the cervical part the free ends overlap, while in the thoracic part
they do not meet; here the deficiency is made up by thin plates of variable size
and form, embedded in a membrana transversa. Ventrally the rings are about
one-half inch (ca. 1.5 cm.) wide, while dorsally they are wider and thinner. The
first ring is attached to the cricoid cartilage by the crico-tracheal membrane, and is
often fused dorsally with the second ring. Various irregularities, such as partial
bifurcation or partial or complete fusion of adjacent rings, are common. The
arrangement in the terminal part is very irregular. The trachealis muscle (M.
trachealis) consists of unstriped fibers which stretch across the dorsal part of the
tube. It is separated from the ends of the rings and the membrana transversa by
a quantity of areolar tissue. When it contracts the caliber of the tube is diminished.
The mucous membrane is pale normally, and presents numerous fine longitudinal
folds, in which are bundles of elastic fibers. The epithelium is stratified columnar
ciliated. Numerous tracheal glands (Glandulae tracheales) are present; they are
tubulo-alveolar and mixed in type.

Vessels and Nerves. — The arteries are derived chiefly from the common
carotid arteries, and the veins go mainly to the jugular veins. The lymph-vessels
go to the cervical and mediastinal lymph glands. The nerves come from the vagus
and sympathetic.

THE BRONCHI

The two bronchi, right and left (Bronchus dexter, sinister), are formed by the
bifurcation of the trachea. Each passes backward and outward to the hilus of
the corresponding lung. The right bronchus is a little larger and less oblique in
direction than the left. They are related ventrally to the divisions of the puhnon-
ary artery, and dorsally to the branches of the bronchial artery and the bronchial
lymph glands. Their structure is similar to that of the trachea, but the cartilagi-
nous framework consists chiefly of plates instead of rings.

THE THORACIC CAVITY

The thoracic cavity (Cavum thoracis) is the second in point of size of the body
cavities. In form it is somewhat like a truncated cone, much compressed laterally
in its anterior part, and with the base cut off very obliquely. The dorsal wall
or roof is formed by the thoracic vertebrae and the ligaments and muscles connected
with them. The lateral walls are formed by the ribs and the intercostal muscles.
The ventral wall or floor is formed by the sternum, the cartilages of the sternal
ribs, and the muscles in connection therewith. It is about one-half as long as the
dorsal wall. The posterior wall, formed by the diaphragm, is very oblique and is
strongly convex. The anterior aperture or inlet (Apertura thoracis cranialis) is
relatively small, and of narrow, oval form. It is bounded dorsally by the first
thoracic vertebra and laterally by the first pair of ribs. It is occupied by the longus
colli muscles, the trachea, oesophagus, vessels, nerves, and lymph glands.

A longitudinal septum, termed the mediastinima thoracis (Septum medias-

526 RESPIRATORY SYSTEM OF THE HORSE

tinale), extends from the aorsal wall to the ventral and posterior walls, and divides
the cavity into two lateral chambers. Each of these chambers is lined by a serous
membrane called the pleura, and is termed a pleural cavity (Cavum pleurae) . The
mediastinum is, for the most part, not median in position, as might be inferred
from its name; this is chiefly due to the fact that the largest organ contained in it,
the heart., is placed more on the left side than on the right; consequently the right
pleural cavity and lung are larger than the left. Practically all of the organs in
the thorax are in the mediastinal space, with the exception of the lungs, the posterior
vena cava, and the right phrenic nerve. The part in which the heart and the peri-
cardium are situated, together with that dorsal to it, is usually called the middle
mediastinal space (Cavum mediastinale medium); the parts before and behind
this are termed respectively the anterior and posterior mediastinal spaces (Cavum
mediastinale craniale, caudale).

THE PLEURA

The pleurae are two serous membranes, right and left, which enclose on each
side a pleural cavity (Cavum pleurae) . They line the walls of the thorax, form the
lateral laminae of the mediastinum, and are reflected from the latter upon the lungs.
We therefore distinguish parietal, mediastinal, and pulmonary or visceral parts of
the pleurae.

The parietal pleura (Pleura parietalis) is attached to the thoracic wall bj^ the
endothoracic fascia. On the lateral thoracic wall it is adherent to the riljs and
intercostal muscles and is. termed the costal pleura (Pleura costalis) . Behind it is
closely attached to the diaphragm, forming the diaphragmatic pleura (Pleura
diaphragmatica) .

The mediastinal pleura (Pleura mediastinalis) covers the organs in the medi-
astinal space and is in part in apposition with the opposite sac. Where this layer
is adherent to the pericardium, it is distinguished as pericardiac pleura (Pleura
pericardiaca).^

From the mediastinum each pleura is reflected upon the corresponding lung,
which it covers, constituting the pulmonary or visceral pleura (Pleura pulmonalis).
The reflection occurs around and behind the hilus of the lung, and is in great part
direct, so that a portion of the mediastinal surface of each lung has no pleural
covering. Behind the hilus of the lung a considerable triangular area is not covered
by the pleura, the two lungs being attached to each other by a thin layer of con-
nective tissue in this situation.^ Posteriorly the reflection is not direct, so that
there is a fold formed by the reflection of the pleura from the mediastinum and the
diaphragm to the lung, behind the triangular area of adhesion just mentioned; it
is seen when the base of the lung is dra^vn outward. This is the pulmonary liga-
ment (Lig. pulmonale) ; it consists of two layers of pleura, between which there is
elastic tissue, especially abundant in its posterior part.

The right pleura forms a special sagittal fold about a nandbreaatn to the right
of the median plane, which encloses the posterior vena cava in its upper edge; it is
therefore called the fold of the vena cava (Plica venae cavae). It gives off a small
accessory fold for the right phrenic nerve. The fold arises from the thoracic floor
and from the diaphragm below the foramen venae cavae, and intervenes between the
intermediate lobe and the body of the right lung. It is delicate and lace-like.

The posterior mediastinum is very delicate ventral to the oesophagus, and

1 The student should bear in mind that these terms are employed simply as a matter of
convenience in description; all the parts of each pleural sac, though differently named, form a
continuous whole.

2 Here the mediastinal pleura does not extend continuously from the dorsal to the ventral
wall, but consists of dorsal and ventral parts.

THE PLEURA

527

Dorso-scapular ligament

Ligamentum nnchic

Trapezius
Rhomhuideus

Cartilage of scapula

Peciora lis profit nd u s
{p. scapular is)

Pectoralis superficialis
ip. transversa]

Longissimus dorsi
Multifidus
Serratus veniralis

Longissimus
cost arum
Levator costoe

Suhscapularis
Lnfraspinatus

Cutaneiis

Teres major

DeUoideus
Triceps
(c. longum)

Triceps
(c. later-ale)

Coraco-brachialis

Brachialis
Pectoralis prof,
{p. humeralis)
Extensor carpi
radialis
Biceps brachii

Fig. 469. — Section of Thorax of Horse.

The section is cut in an oblique direction corresponding with the spire of the scapula. It passes through the fourth
thoracic vertebra and a little more than an inch behind the shoulder joint. The pleural cavities, indicated by wide
black Unes, are exaggerated for the sake of clearness.

1, Pleural cavities (number is placed in mediastinum); 2, 2', lungs; 3, cesophagus; 4, trachea; 5, brachiocephalic
trunk; 6, anterior vena cava; 7, thoracic duct; 8, 8', vagi; 9, left recurrent nerve; 10, 10', phrenic nerves; 11, internal
thoracic vessels; 12, sympathetic trunk; 13, subcostal vessels; 14, external thoracic vessels; 15, brachial vein; 16_
brachial artery; 17, radial nerve; IS, ulnar nerve; 19, musculo-cutaneous nerve; 20, median nerve; 21, subscapular
vessels; a, m. longus colli; 6, m. rectus thoracis; c, m. transversus thoracis; d, m. intercostalis internus; S, sternum;
H, humerus. Ventral to the trachea there are shown, but not marked on account of lack of space, two cardiac nerves-
and a mediastinal lymph gland.

528

RESPIRATORY SYSTEM OF THE HORSE

Trapezius

Rhomboideus

Spinalis

MuUifidus

Cartilage of scapula

Longissimus dor si

Serratus dorsalis
Levator costce
et intercost. ext.
Longissimus costarum
I ntercostales

Serratus ventralis

Latissimus dorsi

Cidaneus

Triceps (c. longum)

Pecioralis prof,
(p. humeralis)

Tensor fascicB
uidihrachii

Pidoralis superficialis
{p. transversa)

Fig. 470. — Section of Thor.a.x of Horse.

The section is cut in an oblique direction corresponding with the spine of the scapula. It cuts the body of the
seventh thoracic vertebrae and the .seventh rib dorsally and the fourth rib and its cartilage ventrally. The pleural
and pericardiac cavities, represented by wide black lines, are exaggerated for the sake of clearness.

L, L', lungs; 1, aorta; 2, cesophagus; 3, thoracic duct; 4, vena azygos; 5, 5', bronchi; 6, bifurcation of pulmonary
artery; 7, 7', right and left atria; 8, right ventricle; 9, tricuspid valve; 10, origin of aorta; 11, right coronary arterj';
12, left coronary artery (circumflex branch) and satellite vein; 13, internal thoracic vessels; 14, external thoracic
vessels; S, sternum; U, ulna. The following structures are shown, but not marked on account of lack of space: The
right vagus is on the oesophagus and ventral to the vena azygos. The phrenic nerves are on the upper part of the peri-
cardium on each side. The sympathetic trunks are on each side of the body of the vertebra. The number 10 is placed
on the ventricular septum. Bronchial lymph-glands are shown ventral to the oesophagus and the left bronchus.

THE PLEURA

529

Trapezius

Rhomhoideus

Longissimus dor si
MuUifidus
Dorsal vessels

Cartilage of scapula

L<mgissimus

costarum

Latissimtis

dorsi

hdercostalis

exiernus

Phrenico-costal

171118

Cutaneus

External

thoracic vessels
Obliquus abdom-
inis externus
Musculo- phrenic

Anterior abdominal

I Rectus abdominis
Pectoralis profundus
{p. humeralis)

Transversus thoracis

Fig. 471. — Cross-section of Body of Horse.

The section is cut through the eighth thoracic vertebra and the anterior part of the xiphoid cartilage. It cuts the
vertebral end of the eighth rib and a little more than half of the seventh rib. The flexures of the great colon and a small
part of the liver, which lay in the concavity of the diaphragm, have been removed. The dotted Unes indicate the con-
tour of the bases of the lungs and the apex of the heart, which are concealed by the diaphragm. The pleural cavities,
indicated by wide black lines, are exaggerated for the sake of clearness.

1, 1', Lungs; 2, aorta; 3, oesophagus; 4, 4' stem bronchi; 5, 5', pulmonary arteries; 6, 6', large pulmonary veins;
7, posterior vena cava; 8, 8', phrenic nerves; 9, vena azygos; 10, falciform and round ligaments of liver; 11, position
of apex of heart; 12 (placed on cut surface of sternal part of diaphragm), xiphoid cartilage. The sympathetic trunks
(not marked) are shown on each side of the body of the vertebra. The oesophageal trunks of the vagi (not marked) are
shown in relation to the oesophagus. The thoracic duct is ventral to the vena azygos.

530 RESPIRATORY SYSTEM OF THE HORSE

usually appears fenestrated; when these apertures are present, tne two pleural
cavities communicate with each other. ^

The pleural sacs contain a clear serous fluid, the liquor pleurae ; in health there
is only a sufficient amount to moisten the surface, but it accumulates rapidly after
death.

It should be borne in mind that the pleural cavity is normally a capillary space between the
parietal and visceral parts of the pleura, and contams a film of serous fluid. In illustrations it is
necessary, for the sake of clearness, to exaggerate the space.

The pleura resembles the peritoneum in structure and appearance. It is
attached to the structures which it covers by subserous tissue, which is elastic and
in some situations contains fat. In the case of the parietal pleura the subserous
tissue is termed the endothoracic fascia. This lines the thoracic walls, but is
practically absent over the tendinous center of the diaphragm. A strong layer
descends from it in the mediastinum and blends with the fibrous part of the peri-
cardium. The subserous tissue of the pulmonary pleura is continuous with the
interlobular tissue of the lung.

The pleura receives an abundant blood supply which is derived chiefly from
the intercostal, internal thoracic, and bronchial arteries. Lymph vessels are very
numerous in the pleura and subserous tissue; they go chiefly to the intercostal and
mediastinal glands.

The parietal pleura is reflected along three lines which are known as the lines of pleural re-
flection; these may be termed vertebral, sternal, and diaphragmatic. The vertebral line of
pleural reflection is that along which the costal pleura turns ventrally to form the mediastinal
pleura; it extends along the longus colli and the bodies of the thoracic vertebrs to the vertebral
end of the last intercostal space, where it joms the line of diaphragmatic reflection. The
sternal line of pleural reflection is that along which the costal pleura is reflected dorsally
to become the mediastinal pleura. Anteriorly the two lines are close together along the middle of
the floor of the thorax, but further back they diverge to each side of the sternal attachment of the
pericardium. The reflection is at an acute angle and the narrow angular recess of the pleural cav-
ity here is termed the costo- mediastinal sinus (Sinus costomediastinalis). The diaphragmatic
line of pleural reflection is that along which the costal pleura passes from the lateral wall
to the diaphragm. This line is important clinically, since it is, from the standpoint of physical
diagnosis, the demarcation between the thoracic and abdominal cavities. It extends along the
eighth and ninth costal cartilages, crosses the sternal end of the nmth rib, and passes backward and
upward in a gentle curve and at a gradually increasing distance from the sternal ends of the ribs,
so that its most posterior part is about the middle of the anterior border of the last rib ; this is the
posterior limit of the pleural cavity. Here it turns medially and a little forward and ends at the
vertebral end of the last intercostal space. This reflection is also at an acute angle and the costal
and diaphragmatic pleura are in contact over an area of variable width along this line. The nar-
row angular recess of the pleural cavity here is termed the phrenico-costal sinus (Sinus phren-
icocostalis).

The apex of each pleural sac (Cupula pleurae) lies at the anterior aperture of the thorax.
On the right side it forms two culs-de-sac; one of these may extend forward more than an inch
(ca. 3 cm.) beyond the first rib in contact with the deep face of the scalenus; the other is ventral
to the anterior vena cava and may extend about an inch (ca. 2.5 cm.) beyond the first rib. The
apex of the left pleura usually does not extend beyond the plane of the first rib.

THE LUNGS
The lungs, right and left (Pulmo dexter, sinister), occupy much the greater
part of the thoracic cavity. They are accurately adapted to the walls of the
cavity and the other organs contained therein. The two lungs are not alike in
form or size, the right one being considerably larger than the left; the differ-
ence is chiefly in width, in conformity with the projection of the heart to the
left. The lung is soft, spongy, and highly elastic. It crepitates when pressed
between the finger and thumb, and floats in water. When the thoracic cavity of
the unpreserved subject is opened, the lung collapses immediately to about one-

' The apertures do not exist in the foetus, and are sometimes absent in the adult subject.
Some of them are doubtless produced in dissection by the necessary disturbance of the parts. The
character of the pleura here probably explains the clinical observation that in the horse fluid exu-
date resulting from unilateral pleurisy is usually present in both pleural sacs in like amount.

THE LUNGS

531

third of its original size, and loses its proper form; this is due to its highly elastic
character and the fact that the tension of the lung tissue caused by the air pressure
in its cavities has been relieved by the external air pressure.^ The color varies
according to the amount of blood contained in the lung. During life the lung has a
pink color, but in subjects which have been bled for dissection it is light gray or
faintly tinged with red. In unbled subjects it is dark red; the depth of color varies,
and is often locally accentuated by gravitation of blood to the most dependent parts
(hypostasis). The fcetal lung, since it contains no air and has a relatively small
blood-supply, differs from that of an animal which has breathed in the following
respects: (1) It is much smaller; (2) it is firmer and does not crepitate; (3) it sinks
in water; (4) it is pale gray in color. In form the lungs are like casts of the cavities
in which they are situated. When well hardened in situ, their surfaces present

j)ors al bo r d e t-

c-^

^pex

Fig. 472. — Right Lung of Horse; Costal Surface.
Specimen hardened in situ.

impressions and elevations corresponding exactly to the structures with which they
are in contact. Each lung presents two surfaces, two borders, a base, and an apex.

The costal surface (Facies costalis) is convex, and lies against the lateral
thoracic wall, to which it is accurately adapted.

The mediastinal surface (Facies mediastinalis) is much less extensive than the
costal surface. It is molded on the mediastinum and its contents. It presents a
large cavity adapted to the pericardium and heart; this is termed the cardiac
impression (Impressio cardiaca), and is larger and deeper on the left lung than on
the right. Above and behind this is the hilus of the lung (Hilus pulmonis), at which
the bronchus, vessels, and nerves enter the lung; the bronchial lymph glands are
also found here. Behind this the two lungs are adherent to each other over a
triangular area. Above this there is a groove for the oesophagus, which is deepest
on the left lung. A groove for the aorta (Sulcus aortse) curves upward and back-
ward over the hilus, and passes backward near the dorsal border of the lung; the

^No idea of the natural form and size of the lung can be obtained from a specimen in this
state, nor can an accurate conception be gained by examination of the soft inflated organ. The
lungs should be hardened in situ for this purpose, and if the process has been successful they con-
form in every detail to the structures with which they were in contact. ^

532

RESPIRATORY SYSTEM OF THE HORSE

curved part of the groove for the aortic arch is absent on the right lung, on which
there is a groove for the vena azygos. Anteriorly there are grooves for the trachea,
the brachiocephalic trunk, the anterior vena cava, and other vessels.

JDorsctl horder

Fig. 473. — Left Lung of Horse; Costal Surface.
Specimen hardened in situ.

Pulmonary

artery Brorochus
c.d. \ \ Groove for vena azygos

Ligament of lung (cut)

Puhnonary

Line of reflection of pie

Fig. 474. — Right Lung of Horse; Mediastinal and Diaphragmatic Surfaces.
Organ hardened in situ. c. d. Grooves for deep cervical and dorsal veins. Arrows indicate canal for posterior
vena cava between intermediate lobe and main part of lung. By an oversight the impression of the trachea is un-
marked; it is dorsal to the groove for the vena cava.

The dorsal border (Margo dorsalis) is long, thick, and rounded; it lies in the
groove alongside of the bodies of the thoracic vertebrjB.i

1 In some cases this border is cut into by a fissure which partly marks off the apex from the
body of the lung.

THE LUNGS

533

The ventral border (Margo ventralis) is thin and short ; it occupies tlie angular
space between the mediastinum and the ventral parts of the sternal ribs (Recessus
costo-mediastinalis) . It presents, opposite to the heart, the cardiac notch (Incisura
cardiaca) . On the left lung this notch is opposite to the ribs from the third to the
sixth, so that a considerable area of the pericardium here lies in direct contact with
the chest-wall. On the right lung the notch is much smaller, and extends from the
third rib to the fourth intercostal space.

The left cardiac notch is usually quadrilateral; its highest part is about four to five inches
(ca. 10-12 cm.) above the sternal ends of the fourth and fifth ribs. The right notch is usually
triangular; its apex is about three inches (ca. 7-8 cm.) above the level of the sternal end of the
ribs at the third intercostal space. In some cases a fissure partially marks off the apex from the
body of the lung.

The base of the lung (Basis pulmonis) is oval in outline; its surface (Facies

Ligament of lung {cut)

Bronchial artery
;' Bronchus
Pulmnnary i i Pulmonary Vascular
veins I I artery impression

Line of reflection
of pleura

Fig. 475. — Left Lung of Horse; Mediastixal and Diaphragmatic Surfaces.
Organ hardened in situ. Vascular impression for common dorso-cervico-vertebral vein.

diaphragmatica) is deeply concave in adaptation to the thoracic surface of the
diaphragm. Laterally and dorsally it is limited by a thin convex basal border
(Margo basalis) which fits into the narrow recess (Sinus phrenico-costalis) between
the diaphragm and the lateral chest-wall. The position of this border, of course,
varies during respiration. In the deepest inspiration it may reach the bottom of
this recess.

In dissecting-room subjects the distance between the border and the diaphrag-
matic line of reflection of the pleura increases from about two inches (ca. 5 cm.) at
the seventh rib to about six or seven inches (ca. 16-18 cm.) at the fifteenth, and
then decreases. The dorsal end of the base is usually at the vertebral end of the
sixteenth intercostal space or seventeenth rib.^

The apex of the lung (Apex pulmonis) is prismatic, narrow, and flattened
transversely. It is partially marked off from the rest of the lung by the cardiac
1 The ventral and basal borders may be taken together under the term margo acutus.

534 RESPIRATORY SYSTEM OF THE HORSE

notch. It curves downward, and is related deeply to the anterior mediastinum and
the anterior part of the pericardium.

The lungs of the horse are not divided into lobes by deep fissures, as is the case
in most mammals. The left lung may be regarded as consisting of a chief part,
the body of the lung (Corpus pulmonis), and the apex (Apex pulmonis). But
the right lung has in addition an intermediate lobe (Lobus intermedins),^ which is
separated from the body of the lung by a fissure which forms in its dorsal part a
canal for the posterior vena cava and the right phrenic nerve, enclosed in a special
fold of the right pleura. ^

The root of the lung (Radix pulmonis) is composed of the structures which
enter or leave the lung at the hilus on the mediastinal surface. These are: (1)
The bronchus ; (2) the pulmonary artery ; (3) the pulmonary veins ; (4) the bron-
chial artery; (5) the pulmonary nerves; (6) the Ijrmph vessels, which go to the
l)ronchial lymph glands. The bronchus is situated dorsally, with the bronchial
artery on its upper surface and the pulmonary artery immediately below it. The
pulmonary veins lie chiefly below and behind the artery.

The lobulation of the lungs is not very evident on account of the small amount
of interlobular tissue. The lobules appear on the surface or on sections as irregular
polygonal areas of different sizes. ^

Bronchial Branches. — Each bronchus at its entrance into the lung gives off a
branch to the apex of the lung (Bronchus apicalis) . It is then continued backward
as the main stem bronchus, parallel with the dorsal border of the lung, giving oft'
branches (Rami bronchiales) in monopodic fashion; these branch similarly and
reach all parts of the lung. The right bronchus gives off a special branch to the
intermediate lobe. The apical bronchus of the right lung is larger than that of
the left lung. A large ventral bronchial branch is given off from each stem
bronchus to the part of the lung which is homologous with the cardiac lobe of other
animals.

The structure of the larger bronchial tubes is, in general, similar to that of the
trachea. Their walls contain irregular plates of cartilage instead of rings. There
is a continuous layer of unstriped muscle, composed of circularly arranged bundles.
The mucous membrane presents numerous longitudinal folds; it contains many
elastic fibers, mucous glands, and lymph nodules, and is lined by ciliated columnar
epithelium. As the tubes diminish in size the coats become thinner and the car-
tilages smaller; in tubes about 1 mm. in diameter the cartilages and mucous glands
are absent.

By repeated branching the interlobular bronchi are formed, and from these
arise the lobular bronchioles. The latter enter a lobule and branch within it,
forming the respiratory bronchioles (Bronchioli respiratorii) ; these give off the
alveolar ducts (Ductuli alveolares), the walls of which are pouched out to form
hemispherical diverticula, the alveoli or air-cells.

A pulmonary lobule (Lobulus pulmonis), the unit of lung structure, is made up
of a lobular bronchiole with its branches, and their air-cells, blood- and lymph-
vessels, and nerves. Between the lobules is the interlobular tissue, which forms
the supporting framework of the lung.

Vessels and Nerves.^The branches of the pulmonary artery carry venous
blood to the lungs. They accompany the bronchi, and form rich capillary plexuses

1 This is also commonly called the mediastinal lobe.

2 Some authors consider each lung to be divided into anterior and posterior lobes by the
cardiac notch, so that the right lung would have three lobes and the left lung two lobes. Not
rarely a fissure or notch in the dorsal border partially marks off the apex from the body of the lung,
and in some cases there is a corresponding fissure in the ventral border.

^ In foetal lung the lobulation is much more distinct. Pigmentation of the lung is sometimes
seen in horses, and in such cases the pigment is deposited mainly in the interlobular tissue, thus
mapping out the lobules.

THE THYROID GLAND 535

on the walls of the alveoli. Here the blood is arterialized, and is returned to the
heart by the pulmonary veins. The bronchial arteries are relatively small vessels
which carry arterial blood for the nutrition of the lungs. The branches of these
arteries accompany the bronchial ramifications as far as the alveolar ducts, but
do not extend to the alveoli. The oesophageal branches of the broncho-oesophageal
and gastric arteries also supply pulmonary branches (in the horse) which reach the
lung by way of the ligament of the latter. These branches vary much in size, and
ramify chiefly in the subpleural tissue of the basal part of the lungs.^ The Ijonph
vessels are numerous, and are arranged in two sets. The superficial set forms
close networks in and under the pleura, while the deep set accompanies the bronchi
and pulmonary vessels. Most of them converge to the root of the lung and enter
the bronchial lymph glands, but some go to the mediastinal lymph glands. The
pulmonary nerves come from the vagus and sympathetic nerves. They enter at
the hilus and supply branches to the bronchial arteries and the air-tubes.

THE THYROID GLAND

The thyroid gland (Glandula thyreoidea) is situated on the anterior part of the
trachea, to which it is loosely attached. It is a very vascular ductless gland, and
is firm in texture and dark red-brown in color. It consists of two lateral lobes and
a very narrow connecting isthmus (Figs. 332, 649).

The lateral lobes (Lobus dexter, sinister) are situated on each side of the trachea
near to or in contact with the larynx. Their position is indicated approximately
by the angle of junction of the jugular and external maxillary veins. Each is oval
in outline and is about as large as a plum of medium size. The superficial surface
is convex and is covered by the cervical angle of the parotid gland and the sterno-
cephalicus and omo-hyoideus. The deep surface is adapted to the trachea. About
the lobe are the anterior cervical lymph glands. The anterior pole is large and
rounded, while the posterior is smaller and often tapers to a tail-hke process which
is continuous with the isthmus.

The isthmus (Isthmus gl. thyreoidese) extends across the ventral face of the
trachea, connecting the two lobes. It is usually extremely narrow in the adult
horse and is often reduced in great part to a small strand of fibrous tissue.

The lateral lobes are very variable in size and position, and are usually unsymmetrical. The
average length is about two inches (ca. 5 cm.). The greatest height averages a little more than an
inch (ca. 2.7 cm.), and the greatest width a little less than an inch (ca. 1.5-2 cm.). The average
weight is about half an ounce (ca. 15 gm.). The right lobe is commonly in contact with the crico-
pharyngeus or crico-thyroideus, but may be about a finger's breadth from the larynx. The left
lobe may be an inch or more (ca. 4 cm.) from the larynx, but in some cases is in contact with it.
The position varies considerably in the dorso-ventral direction also, irrespective of the ventral dis-
placement noted in enlargement of the gland. The most common forrn is oval, with a smaller
posterior pole which tapers to the isthmus. But the isthmus is sometimes connected with the
middle of the ventral border of one lobe or both, so that the two poles are about alike. Many ir-
regularities may be observed. Cases occur in which a variable posterior process is connected with
the body of the gland by a sort of neck. A complete glandular isthmus is not rare, although it is
usually very narrow and may easily escape notice; in quite exceptional cases it may be 6-8 mm.
in width. Its connection with the lateral lobes and crossing of the trachea are quite variable.
Most often it is connected with the posterior poles and passes almost directly between the two.
But it may run backward and cross much further back; in one case (personal observation) the
crossing was at the space between the ninth and tenth tracheal rings. In the foal the isthmus is
relatively large and entirely glandular. In the ass and mule there is almost always a well-developed
isthmus. Extending from it there is sometimes a narrow band of thyroid tissue which reaches to
the body of the hyoid bone; this is the lobus pyramidalis.

Structure.— The gland is enveloped by a thin fibro-elastic capsule, from which
trabeculse pass into the substance of the organ. The gland tissue is compact and

1 It must not be inferred from the necessarily brief accoimt here given that the two sets of
vessels are quite distinct. On the contrary, competent observers state that numerous small
branches of the bronchial arteries anastomose with pulmonary vessels.

536 RESPIRATORY SYSTEM OF THE HORSE

consists of lobules (Lobuli gl. thyreoidese), which are embedded in a stroma of
strands of fibrous tissue. The stroma contains numerous vessels. The lobules
consist of non-communicating alveoli or follicles of varying form and size. The
alveoli are lined by cubical or columnar epithelium, and contain a viscid colloid
substance.

Vessels and Nerves. — The arteries are relatively very large ; there are usually
two thyroid arteries, which arise from the carotid; their branches enter the gland
chiefly at or near the ends and the dorsal border. The veins are also large; they
go to the jugular vein; the largest one leaves the gland at its posterior pole. The
l3nnph vessels go to the cervical lymph glands. The nerves are derived from the
sympathetic system.

Nodules of thyroid tissue of variable size, sometimes as large as a pea, may be
found near the anterior extremity of the lateral lobes, on the course of the anterior
thyroid artery or on the trachea, even at a considerable distance from the thyroid
region. They are termed accessory thyroids (Glandulse thyreoideae accessorise) .

The parathyroids are small glandular bodies found in the thyroid region.
They are paler and not so dense as the thyroid tissue, but often cannot be differen-
tiated by their naked-eye appearance. In the horse there is usually only one on
each side in the connective tissue over the dorsal border or anterior extremity of the
lateral lobe of the thyroid. One may be embedded in the deep face of the lateral
lobe of the thyroid. They resemble in structure embryonic thyroid tissue.

THE THYMUS GLAND

The thjnnus is a ductless gland which has a close resemblance to the lymphoid
tissues. It is well developed only in late foetal life and for a few months after birth.
After this it undergoes rapid atrophy, fatty infiltration, and amyloid degeneration,
so that in the adult it is usually represented by a thin remnant in the ventral part
of the anterior mediastinum or has entirely disappeared. In the new-bom foal
it is of a grayish-pink color, and consists of right and left lobes (Lobus dexter,
sinister). The greater part of the gland is situated in the anterior mediastinum
ventral to the trachea and large vessels, but the two lobes are contmued into the
neck by a chain of lobules which lie on the trachea along the course of the carotid
artery, extending sometimes as far as the thyroid gland. ^

Structure. — The thymus is enclosed in a thin and loose fibro-elastic capsule,
and consists of secondary lobules (Lobuli thymi), of varying shape and size, held to-
gether by areolar tissue and fat, and comiected with a strand of comiective tissue
termed the tractus centralis. These lobules are subdivided into polyhedral primary
lobules, which are composed of lymphoid tissue, and present a dark, vascular cor-
tex, and a lighter medulla that contains small masses of concentrically arranged,
flattened cells; these are known as concentric corpuscles.

Vessels and Nerves. — The arteries are derived from the internal thoracic and
common carotid. The nerves come from the sympathetic and vagus.

1 The cervical part of the gland is very variable. The thoracic lobe of one side may have
no cervical continuation ; the other lobe may then give off a single prolongation which bifurcates.
The thoracic part in the new-born foal occupies most of the space which is later taken up by the
apices of the lungs. Its two lobes are in contact, and its deep surface is molded on the anterior
part of the pericardium and the large vessels. In exceptional cases a considerable remnant of the
thymus is present in adult or even old subjects; this is usually true only of the thoracic part, but
it may extend into the neck a short distance; but a large lymph gland must not be mistaken for
thymus.

RESPIRATORY SYSTEM OF THE OX — THE NASAL CAVITY

537

RESPIRATORY SYSTEM OF THE OX

THE NASAL CAVITY

The nostrils (Fig. 379), situated on either side of the muzzle, are relatively
small, and are much less dilatable than those of the horse. The alae are thick and
firm. The superior commissure is narrow. There is no diverticulum nasi. The
skin is smooth, bare, and moist, and there is no clear line of demarcation between
it and the nasal mucosa. The opening of the naso-lacrimal duct is not visible, as

Frontal eminence

Great ethmo-turbinate

Dorsal turbinate

Dorsal meatus
Middle meatus

Ventral
turbinate

Ventral
meatus

Genio- Mijlo-hy- Genio-
glossus oideus hyoideus

Fig. 476. — Sagittal Section of Head of Cow.

Thyroid cartilage

/, Cerebral hemisphere; ;2, lateral ventricle; -S, thalamus, 4. corpora quadrigemina; ^, optic chiasma; 6, pituitary
body; 7, pons; 8, medulla oblongata; 9, cerebellum; 10, spinal cord; 11, ventral straight muscles; 12, pharyngeal
lymph gland; / 3, arytenoid cartilage; ^4. epiglottis; 75, cricoid cartilage; i6', vocal cord; i 7, palatine sinus; 75, soft
palate; 19, Eustachian opening; CI, C2, C3, first, second, and third cervical vertebrae; B.o., basioccipital ; Sp., pre-
sphenoid.

it is on the lateral wall of the nostril, and is concealed by the cartilaginous pro-
longation of the ventral turbinate. There are two parietal cartilages on either
side, united by fibrous tissue. The dorsal cartilages are thin laminae which curve
ventro-laterally from the dorsal margin of the septal cartilage; they are prolonga-
tions of the nasal bones, and carry the alar cartilages on their anterior extremities.
The ventral pair are lateral continuations of the basal lamellse of the ventral tur-
binates. They lie along the nasal processes of the premaxillae; anteriorly they
become thicker, turn a little upward, and each blends with the cartilaginous pro-
longation of the upper coil of the ventral turbinate. The alar cartilages are of

538

RESPIRATORY SYSTEM OF THE OX

peculiar form. The lamina is oblong, and curves ventro-laterally from the anterior
extremity of the dorsal parietal cartilage, with which it is connected. The cornu
springs from the lateral part of the lamina and curves dorso-laterally into the outer
Aving of the nostril ; it carries on its extremity a small transverse bar, thus having
some resemblance to the fluke of an anchor.

The nasal cavity is short, wide anteriorly, narrow behind. It is not com-
pletely divided by the septum, which in its posterior third is separated from the
floor of the cavity by an interval that increases from before backward (Figs. 140,
141). The middle meatus is very narrow, and divides posteriorly into two branches;
the upper division leads to the ethmoidal meatuses, and communicates wdth the
frontal sinus and the cavity of the dorsal turbinate. Anterior to the division are
communications Avith the upper cavity of the ventral turbinate and the maxillary
sinus. The main facts in regard to the sinuses were stated in the Osteology.

THE LARYNX

The Iar3nix is more compact than in the horse, and presents numerous differ-
ential features. The cricoid cartilage is compressed laterally. The lamina is not
distinctly marked off from the arch; it slopes downward and backward and has a

Arytenoid Processus
cartilage muscularis

tl^'TJ.... Lateral lobe
of thyroid

cricoid cartilage

Epiglottis

Thyroid
cartilage

Laryngeal Arch of cricoid Isthmus of
-prominence cartilage thyroid

Fig. 477. — Cartilages op Larynx .'^.nd Part of Trachea of Ox; Left View.

Outline of thyroid gland indicated by dotted line.

1, Anterior cornu of thyroid cartilage; 2, thyroid foramen; 3, ligament converting notch into foramen; 4, posterior

cornu of thyroid cartilage; 5, capsule of thyro-arytenoid joint.

large median ridge. The thyroid cartilage is complete ventrally, i. e., the laminse
are united to form a long plate which is notched in front and behind ; the laryngeal
prominence is small and is situated posteriorly. The height and thickness of the
cartilage increase from before backward. The posterior cornua are curved and are
about an inch long; they form syndesmoses with the cricoid cartilage. The short
anterior cornua unite similarly with the hyoid bone ; near them there is a foramen
or a notch on each side for the passage of the anterior laryngeal nerve. The epi-
glottis is short, oval in outline, and its apex is rounded; its base rests on the thyro-
hyoid membrane, to which it is rather loosely attached. The cuneiform cartilages
are absent. The arytenoid cartilages present only slight differences. The muscular

THE LARYNX

539

process is well developed, and the vocal process is narrow and long. The vocal
cords are short and project very little from the wall, so that the rima glottidis is
wide; the vocal ligament is attached ventrally to the crico-thyroid membrane, it
has the form of a half tube, open behind. The lateral ventricle is represented by a
very shallow depression, and the saccule is absent. The thyro-arytenoideus muscle

Fig. 478. — Aditus Laryngis and Adjacent Structures of Ox.
The pharynx, soft palate, and origin of oesophagus have been cut along the dorsal median line and refiected.
1, Epiglottis; 2, aditus laryngis; 3, 3', apices of arytenoid cartilages; 4, posterior pillar of soft palate; 5, cut sur-
face of soft palate; 6, pharynx; 7, litnen oesophagi; 8, oesophagus; 9, trachea; 10, glosso-epiglottic space; 11, tonsil-
lar sinus; 12, root of tongue; 13, vallate papillae; 14, dorsum linguse.

is equivalent to the vocalis and ventricularis of the horse; it is fan -shaped, thick,
and narrow dorsally; it is attached ventrally to the base of the epiglottis, the angle
of the union of the thyroid laminae, and the crico-thyroid membrane. The hyo-
epiglotticus muscle is large and bifid; it arises from the small cornua and at their
articulation with the body of the hyoid bone, and thus may take the place of the
hyoideus transversus in its action on the small cornua.

540 RESPIRATORY SYSTEM OF THE OX

THE TRACHEA

The trachea is shorter than that of the horse, the average length being about
26 inches (ca. 65 cm.). Its cahber is relatively small, the width being about an
inch and a half (ca. 4 cm.) and the height about two inches (ca. 5 cm.). The rings
are smaller, and number about fifty. At the begimiing of the tube their free ends
are separated by a varying interval, so that the tube is flattened and membranous
dorsally; but further back the ends are in apposition, so that they fonn a ridge
dorsally. The trachea is adherent to the right lung from the second rib backward.
The bifurcation is opposite the fifth rib, about the junction of its middle and ventral
thirds.

In the sheep the average length of the trachea is about nine or ten inches (ca.
25 cm.) and its caliber a little less than an inch (ca. 2 cm.).

THE BRONCHI

There are three chief bronchi. The bronchus for the apical lobe of the right
lung (Bronchus apicalis) is detached from the trachea opposite to the third rib,
i. e., at a considerable distance anterior to the bifurcation.

THE THORACIC CAVITY AND PLEURA

The thoracic cavity is relatively small; it is especially short dorsally, and is
diminished laterally by the mode of attachment of the diaphragm to the ribs {vide
Myology). The endothoracic fascia is better developed than in the horse, and is
distinctly elastic. The pleura is also thick, and there are no perforations of the
mediastinum. The pleural sacs are even more unequal in extent than in the horse,
and the ventral part of the mediastinum is further to the left ; m front of the peri-
cardium it is for the most part in contact with the left wall of the chest.

The diaplxragmatic line of pleural reflection differs considerably from that of the horse in
conformity with the diiTerence in the costal attachment of the diaphragm. It begins over the
space between the seventh and eighth costal cartilages, crosses the ventral end of the eighth rib,
and extends in a very slight curve upward and backward, so that it crosses the twelfth rib a little
above its middle and reaches to the last rib a short distance from its vertebral end.

The pleura forms a cul-de-sac alongside of the body of the last thoracic vertebra. The right
pleural sac extends forward on the deep face of the scalenus a short distance beyond the first rib.

THE LUNGS

The difference in size between the two lungs is greater than in the horse, the
right lung weighing about half as much again as the left one. The average weight
of the lungs is about 73^ pounds (ca. 3 to 4 kg.) ; they form about y~to of the body
weight. They are divided into lobes by deep interlobar fissures (Incisurse inter-
lobares). The left lung is divided into three lobes, named from before backward
apical, cardiac, and diaphragmatic (Lobus apicalis, cardiacus, diaphragmaticus).
The right lung may be regarded as having either four or five lobes. The apical
lobe is much larger than that of the left lung, and occupies the space in front of
the pericarcUum, pushing the mediastinum against the left wall ; it is usually sub-
divided into anterior and posterior parts by a deep fissure. The other lobes are
the cardiac, diaphragmatic, and intermediate, the last resembling that of the horse.^

1 It has been customary to consider the cardiac lobe to consist of two parts, as showTi in Fig.
479. But the apical bronchus divides into two branches, the posterior of which goes to that
division of the lung which has been regarded as belonging to the cardiac lobe ; furthermore, these
parts of the lung are sometimes fused. It therefore appears desirable to include both as apical
lobe.

THE LUNGS

541

The apical lobe of the right lung receives a special bronchus from the trachea oppo-
site the third rib, and is adherent to the trachea from the second rib backward.
The two lungs are not adherent to each other behind the root as in the horse, but

horde>-

Hardened in situ. By

Fig. 479. — Right Lung of Ox; Costal Surface.
the inscription "cardiac lobe" extends forward upon what is a division of the apical

Linear
rejleclior,
<f fiJeufcL

Fig. 480. — Right Lung of Ox; Medial View.
Hardened in situ. 1, Left bronchus; 2, pulmonary veins; 3, pulmonary artery. Mediastinal lobe = intermediate lobe.

are in contact with the oesophagus; above and below the latter the pleura is re-
flected, as shown in Fig. 480.

The interlobar fissures begin at the ventral margin of the lung and pass toward the root.
Those of the left lung lie opposite to the fourth and sixth ribs. The diaphragmatic lobe is the

542

RESPIRATORY SYSTEM OF THE OX

largest, and has the form of a three-sided pyramid with its base resting on the diaphragm. The
cardiac lobe is prismatic and forms the posterior margin of the cardiac notch; its long axis corre-
sponds to the fifth rib. The apical lobe of the left hmg is small and pomted; its ventral margin

Dorsal border

DiapJtrag malic
lobe

Cardidc lube

Fig. 481. — Left Lung of Ox; Lateral ^'IEW.
Arrows indicate interlobar fissures.

Dorsal borda

Diuphrugmalic lobe
and surface

Apical lobe
Cardiac impression

Cardiac lube

Fig. 482. — Left Lung of Ox; Media
1, Stem bronchus; 1', bronchial branch for apical and cardiac lobes

i, groove for aorta; 5, groove for CBSophagus.

View.

^.pulmonary artery; 3, ^, 5, pulmonary veins;
Arrows indicate interlobar fissures.

lies on the pulmonary artery and the anterior aorta; below this the space in front of the heart
is occupied by the apical lobe of the right lung. In some cases additional fissures partially sub-
divide the apical lobe, and on the other hand the apical lobe of the right lung may be undivided.

THE LUNGS

543

Apical lobe

, Cardiac lobe

1 titermediaie lobe

Diaphragmatic lobe

Posterior mediastinal lymph gland

Fig. 48.'5.— TjUnos and Heart of Sheei'; Ventral View.
Specimen hardened in situ. Space between heart and king.s was occupied by pericanUum and fat.

r'S^^^ J^ort^e?-

(hoove for
wsophagus

"— Diaphragmatic surface

Apex I /

Cardiac notch

Fig. 484. — Right Lung of Sheep; Mediastinal Aspect.

Hardened in siiu. B, Bronchus; P.a., pulmonary artery: PjK, pulmonary vein; V.c, posterior vena cava; Ljj,

bronchial lymph gland. Mediastinal lobe = intermediate lobe.

544 RESPIRATORY SYSTEM OF THE OX

On the left side the cardiac notch leaves the greater part of the pericardium in contact with the
chest wall as far back as the fourth intercostal space. On the right side the lung commonly covers
the pericardium, so that the latter has no contact with the lateral wall of the thorax. But in some
cases (as in the annexed figures) there is a small cardiac notch at the ventral part of the third
intercostal space or fourth rib. In dissecting-room subjects the basal border usually begins at
the space between the fifth and sixth costal cartilages, crosses the ventral part of the sixth rib,
and is then about parallel with the diaphragmatic line of pleural reflection. It crosses the ninth
rib about its middle and ends at the vertebral end of the eleventh intercostal space.

The lobulation is very distinct on account of the extremely large amount of
interlobular tissue.

In the sheep the lungs resemble those of the ox in lobation, but differ from
them considerably in shape. They are relatively somewhat longer, and the basal
border differs in conformity with the diaphragmatic line of pleural reflection.
There is usually a small triangular cardiac notch on the right lung opposite to the
^'entral part of the fourth and fifth ribs; its greatest height is about two inches
(ca. 5 cm.). The left lung leaves the greater part of the pericardium uncovered as
far back as the fifth intercostal space. The lobulation of the lung is much less
distinct than in the ox. The pleural sacs form a cul-de-sac on each side of the first
lumbar vertebra.

In the sheep the diaphragmatic line of pleural reflection differs from that of the ox. It ex-
tends along the seventh and eighth costal cartilages, crosses the ninth cartilage close to the rib,
the ventral ends of the tenth and eleventh ribs, the twelfth rib about an inch (ca. 2-3 cm.) from
its ventral end, and the thirteenth rib about two inches (ca. 5 cm.) from its ventral end. It
reaches as far back as the anterior border of the first lumbar transverse process.

THE THYROID GLAND

The thyroid gland is softer in texture than in the horse and is pale in color in
the adult; in the calf it is dark red in color. The lateral lobes are irregularly
triangular in outline and are more extensive and flatter than in the horse. In
addition to their contact with the trachea they are related deeply to the oesophagus
and the crico-pharyngeus muscle to a varying extent. The superficial face is
related to the sterno-thyro-hyoideus, sterno-cephalicus, the carotid artery, internal
jugular vein, and the vagus and sympathetic nerves. The isthmus is constantly
present and glandular; it is band-like and is commonly a quarter to half an inch
(ca. 0.5-1 cm.) in width.

The lateral lobes average about three inches or more (ca. 8 cm.) in length and about half an
ounce (ca. 14-15 gm.) in weight. They are so soft and loose in texture that their true shape is
seen only in specimens hardened in situ. In soft material they appear oval in outline. The
isthmus may be connected with the ventral margin or the posterior end of the lateral lobes; it is
relatively large in the calf, and is very evident on account of its dark color.

In the sheep the thyroid gland is dark red in color. The lateral lobes have a
long elliptical outline and lie on each side of the first six or seA^en rings of the trachea;
they are two inches or more (ca. 5-6 cm.) in length antl half an inch or more (ca.
1.5 cm.) in height. They are connected by a flat glandular isthmus a quarter of
an inch or more (ca. 6-8 mm.) in width; the isthmus is connected Avith the lateral
lobe at or near the posterior end of the latter, and crosses the trachea about the fifth
ring.

Accessory thyroids may be found, and parathyroids also occur near the pos-
terior extremity or on the deep surface of the lateral lobes of the thyroid.

THE THYMUS GLAND
The thymus is pale and distinctly lobulated. It is much larger in the calf
than in the foal, weighing at five or six weeks about 15 to 25 ounces (ca. 425 to 600
grams). At the period of its greatest development it occupies the greater part of
the anterior mediastinal space, reaching back to the pericardium, pulmonary artery,
and aortic arch. Its left face (covered by the mediastinal pleura) is in contact

RESPIRATORY SYSTEM OF THE PIG — THE NASAL CAVITY

545

with the chest-wall and apical lobe of the left lung as far back as the third rib.
Its right face is largely molded on the great vessels in front of the heart. The
cervical part forms the bulk of the gland; it consists of right and left lobes which
extend along the trachea and oesophagus from the thoracic inlet to the thyroid
gland. The two lobes are large at the root of the neck, where they are in apposition

Fig. 485. — Thymus of Young Calf.

o, Thymus (cervical part) ; 6, trachea; c, isthmus of thyroid gland ; d, laryngeal prominence; /, apical loDe of right lung;

^, heart (left ventricle) ; 3, pulmonary artery; 4i aorta; 5, 5', cesophagus; 6', m. longus colli; 7, diaphragm.

and cover the trachea, oesophagus, carotid artery, and vago-sympathetic trunk.
Further forward they gradually diminish in size and diverge to the sides of the
trachea. They are related superficially to the sterno-cephalicus, sterno-thyro-
hyoideus, and external jugular vein. It undergoes atrophy slowly and remnants
of the thoracic part often remain even in advanced age.

RESPIRATORY SYSTEM OF THE PIG

THE NASAL CAVITY

The nostrils are small, and are situated on the flat anterior surface of the
rostrum or snout (Rostrum suis). The latter is a short cylindrical projection,
Avith which the upper lip is fused, and is circumscribed by a prominent circular
margin. The skin on the snout is thin and highly sensitive; it presents small
pores, and scattered over it are fine short hairs. In the snout between the nostrils
is the OS rostri, which is to be regarded as a special development of the extremity of
the septum nasi in adaptation to the habit of burrowing or rooting. A plate of
cartilage, representing the lamina of the alar cartilage of the horse, curves ventro-
laterally from the dorsal part of the os rostri, and a pointed bar of cartilage curves
upward from the lower part of the bone in the lateral wing of the nostril. The
notch between the nasal bone and the premaxilla is closed in by parietal cartilages
which resemble those of the ox.

The nasal cavity (Fig. 180) is long and narrow. It is divided behind by the
lamina transversalis into an upper olfactory part, which leads to the ethmoidal
meatuses, and a lower respiratory part, which is a direct continuation of the ventral
meatus. The posterior part of the septum is membranous. The turbinate bones
resemble in general those of the ox. The dorsal meatus is exceedingly small. The
middle meatus is a deep fissure between the two turbinates: it divides posteriorly
35

546 RESPIRATORY SYSTEM OF THE PIG

into two branches : one of these extends upward and backward between the lateral
mass of the ethmoid bone and the dorsal turbinate; the other widens and joins the
ventral meatus. The opening between the maxillary sinus and the middle meatus
lies in a transverse plane through the last cheek teeth. The middle meatus is
continuous with the space enclosed by the dorsal part of the ventral turbinate and
with the cavity of the dorsal turbinate. The dorsal division of the middle meatus
presents several openings into the frontal sinus. The ventral meatus is relatively
roomy; it communicates with the space enclosed by the lower coil of the ventral
turbinate. The opening of the naso-lacrimal duct is in the posterior part of the
ventral meatus. The incisive duct and the vomero-nasal organ resemble those of
the ox.

THE LARYNX

The larynx is remarkable for its great length and mobility. The cartilages
are more loosely attached to each other than in the other animals. The cricoid
cartilage is thick and compressed laterally; its lamina is long and narrow; its
arch is directed ol^liquely downward and backward. The thyroid cartilage is very
long; its laminae are united ventrally and form a median ridge. The anterior
cornua are absent, and no joints are formed with the hyoid bone. The posterior
cornua are broad, bent inward, and articulate with the cricoid cartilage. The
epiglottis is relatively very large, and is more closely attached to the hyoid bone
than to the rest of the larynx. The middle part of its base is turned forward, and
rests on the thyro-hyoid membrane; it is closely connected with the body of the
hyoid bone by the hyo-epiglottic ligament and the strong hyo-epiglottic muscle.^
The apex of the arytenoid cartilage is very large, and is divided into two parts at
its extremity; the medial part is fused with that of the opposite cartilage. There
is a small interarytenoid cartilage in the transverse ligament. The rima glottidis
is very narrow. The vocal cords are directed obliquely downward and backward;
and each is pierced by a long, slit-like opening, which leads into the large laryngeal
saccule. The vocal ligament is similarly divided into a larger anterior and a smaller
posterior part. There is a middle ventricle near the base of the epiglottis. The
thyro-arytenoid muscle is very strong and is undivided ; it is equivalent (as in the
ox) to the vocalis and ventricularis muscles of the horse. The arj^enoideus trans-
versus is very small. The crico-thyroid consists of two strata: the superficial
layer corresponds to the muscle of the other animals; the deep part consists of
transverse fibers.

TRACHEA AND BRONCHI
The trachea is about six to eight inches (ca. 15 20 cm.) long, and contains
thirty-two to thirty-five rings, which overlap dorsally. It is slightly depressed
dorsally, except the terminal part, which is circular in cross-section. A special
bronchus is detached for the apical lobe of the right lung, as in the ox. In the
right lung the stem-bronchus sends branches (one each) to the cardiac and inter-
mediate lobes and continues backward in the diaphragmatic lobe, in which it
ramifies. In the left lung the stem-bronchus gives off a bronchus which divides
into two branches for the anterior part of the lung (fused apical and cardiac lobes'),
and continues backward in the diaphragmatic lobe.

1 The arrangement here is one of the most striking features of the pig's larynx. The short
and thick middle hyo-epiglottic ligament and the anterior part of the thyro-hyoid membrane are
inelastic, while the posterior part of the membrane is thin and elastic and allows the epiglottis
to be separated by a consideral)le interval from the thyroid cartilage. Moreover, the borders of
the epiglottis are connected with the thyroid cornua of the hyoid bone by lateral hyo-epiglottic
ligaments.

THE THORAX AND PLEURA — THE LUNGS

547

THE THORAX AND PLEURAE
The ribs are in general strongly curved in most of the improved breeds, so that
the thorax is rounded. The pleural sacs extend forward to the first intercostal
space. The diaphragmatic line of pleural reflection begins at or a little above the
sternal end of the seventh rib, and extends in a gentle curve to about the middle of
the last rib, along the medial face of which it continues. (When a fifteenth rib is
present — a very common occurrence — it does not affect the arrangement of the
pleura or diaphragm).

Trachea (Esophagus

Apical lobe

Cardiac lobe

Diaphrag-
matic lobe

Fig. 486. — Lungs and Heart of Pig; Ventral View.
L. %., Intermediate lobe of right lung; F. d., diaphragmatic surface of lungs; 1, left brachial artery; 2, brachio-
cephalic artery ; 3, apex of heart; 4i pericardium (cut edge) ; 5, plica venae cava ; <?, posterior vena cava; 7, oesophagus;
8, ventral (Esophageal nerve trunk; 9, aorta.

THE LUNGS

The right lung has four lobes — apical, cardiac, diaphragmatic, and intermedi-
ate. In some cases the apical lobe is divided by a fissure into two parts; sometimes
it is fused with the cardiac lobe. The left lung may be regarded as having two or
three lobes. The diaphragmatic lobe is clearly marked off by a fissure. The part

548 RESPIRATORY SYSTEM OF THE DOG

anterior to the fissure represents the apical and cardiac lobes, which are, however,
separated only by the cardiac notch, not by an interlobar fissure, as is usual in the

Trachea Dorsal border

Diaphragmatic lobe

Apical lobe

notch

Cardiac lobe Intermediate lobe

Fig. 487. — Right Lung of Pig; Medial View.
1, Left bronchus (cut off) ; £, 2, pulmonary arteries; 3, 3, 3, pulmonary veins; 4, posterior vena cava; 5, groove for
anterior vena cava; 6, groove for vena azygos; 7, groove for aorta; 8 (placed on groove for oesophagus), lines of pleural
reflection. Arrows indicate interlobar fissures.

right lung. The lobulation is distinct, but the interlobular septa are thinner than
in the ox.

THE THYROID GLAND

The thjrroid gland is large and is situated usually at a considerable distance
from the larynx, but may be in contact with it. The lateral lobes are irregularl}'^
triangular in outline, and are two inches or more (ca. 5-6 cm.) in length in a large
adult. They are united to a considerable extent ventrally, so that an isthmus
cannot be distinguished. The gland is related deeply to the sides and ventral face
of the trachea, and is in contact dorsally with the oesophagus. The chief artery
enters at the posterior extremity.

THE THYMUS

The thymus in young subjects is very large, extending to the larynx or even to
the mandibular space.

RESPIRATORY SYSTEM OF THE DOG
THE NASAL CAVITY
The nostrils are situated on the muzzle, with which the upper lip blends. They
are shaped somewhat like a comma, with the broad part next to the septum and
the narrow part directed backward and outward. The skin around the nostrils
is bare, usually black, and in health moist and cool. The muzzle is marked by a
median furrow (philtrum), or a deep fissure in some breeds. The cartilaginous

THE NASAL CAVITY

549

framework is formed essentially by the septal cartilage and the parietal cartilages
which proceed from it. The septal cartilage projects beyond the premaxilla, and

Fig. 488. — Sagittal Section of Head and Part of Neck of Dog.

porsal meatus

%\ / Middle meatus

Fig. 489. — Key to Preceding Figure.

is much thickened at its extremity; it gives off from its margins the two parietal
cartilages, which curve laterally and toward each other. A grooved plate extends

550

RESPIRATORY SYSTEM OF THE DOG

outward from the septal cartilage in the floor of the nostril, and another lamina
supports the alar fold of the ventral turbinate bone; these may be termed accessory-
nasal cartilages (Cartilagines nasi accessorise).

The length of the nasal cavity varies greatly in different breeds, correspond-
ing, of course, to the length of the face. The cavity is roomy, but is very largely
occupied by the turbinates and the lateral masses of the ethmoid bone. The
middle meatus is short and narrow, and divides posteriorly into two branches: the
upper branch leads to the ethmoidal meatuses; the lower branch joins the ventral

meatus. The ventral meatus is very small in
its middle part, owing to the great develop-
ment here of the ventral turbinate. The
posterior part of the nasal cavity is divided
by the lamina transversalis into an upper olfac-
tory part and a lower respiratory part. The
sinuses have been described {vide Osteology).

THE LARYNX
The larynx is relatively short. The lamina
of the cricoid cartilage is wide; the arch is
grooved laterally. The laminae of the thyroid
cartilage are high, but short; they unite ven-
trally to form the body, on which there is an-
teriorly a marked prominence, and posteriorly
a deep notch. The oblique line on the lateral
surface of the lamina is prominent. There is
a rounded notch (Fissura thyreoidea) below the
short anterior cornu for the passage of the an-
terior laryngeal nerve. The posterior cornu is
strong, and has a rounded surface for articula-
tion with the cricoid cartilage. The arytenoid
cartilages are relatively small, and have between
them a small interarytenoid cartilage. The
epiglottis is quadrilateral; its lower part or
stalk (petiolus) is narrow, and fits into the
angle of the thyroid cartilage. The cuneiform
cartilages (Cartilagines cuneiformes) are large
and somewhat crescent shaped; they are not
fused with the epiglottis.

The false vocal cords extend from the
cuneiform cartilages to the thyroid. The true
vocal cords are large and prominent. The
large lateral ventricle is a long slit parallel with

the anterior margin of the true vocal cord. The lar3mgeal saccule is extensive and

lies lateral to both true and false vocal cords.

The crico-thyroid muscle is thick. The hyo-epiglotticus is well developed,

and is double at its hyoid attachment. The ventricularis or anterior part of the

thyro-arytenoideus arises on the cuneiform cartilage. Hence Lesbre has suggested

the name cuneo-arytenoideus for it.

Fig. 490. — Aditus Laryngis and Related

Structubbs or Dog.
The pharynx and CBsophagus have been cut

along the mid-dorsal line and reflected.

/, Epiglottis; 2, 2, corniculate cartilages;
S, 3, arytenoid cartilages; 4, glottis; o, wall of
pharynx; 6, oesophagus; 7, limen oesophagi; 8,
pcsterior pillar of soft palate; 9, median sulcus
of tongue; /O, vallate papillae; 11, conical pa-
pillae of root of tongue; IS, 12, tonsils (shown
by opening up tonsillar sinus).

THE TRACHEA AND BRONCHI

The trachea is practically circular in cross-section at its ends, but the inter-
vening part is very slightly flattened dorsally. It contains about forty to forty-

THE LUNGS

551

five U-shaped rings; the ends of the rings do not meet dorsally, so that here the
trachea has a membranous wall (Paries membranacea) , and is composed of a layer
of transverse smooth muscle-fibers outside of the rings, the fibrous membrane, and
the mucous membrane.

The stem-bronchi diverge at an obtuse angle, and each divides into two
branches before entering the lung, but the ramification differs in the two lungs.
In the right lung the anterior bronchus goes to the apical lobe, and the stem-
bronchus gives off a branch to the cardiac lobe and another to the intermediate lobe.
In the left lung the anterior bronchus divides into two branches for the apical and
ardiac lobes. The anterior branch of the left bronchus crosses under the pul-
monary artery.

THE LUNGS

The lungs differ in shape from those of the horse and ox in conformity with
the shape of the thorax, which is relatively very wide in the dog; the lateral thoracic
walls are strongly curved, and the costal surface of the lungs is correspondingly
convex.^

The right lung is much (ca. 25 per cent.) larger than the left. It is divided

Dorsal border

Cardiac notch

Fig. 491. — Right Lung of Dog; Medial View.
L. a., Apical lobe; L. c, cardiac lobe; L. (/., diaphragmatic lobe; L. i., intermediate lobe; /, stem-bronchus; S, S',
bronchi of apical lobe; 3, 3', divisions of pulmonary artery; 4-7, pulmonary veins; S, groove for anterior vena cava;
9, groove for vena azygos; 10, groove for CBSophagus; 11, groove for trunk of vertebral, cervical, and dorsal veins; IS,
groove for internal thoracic vessels.

into four lobes by deep fissures which extend to the root. The lobes are the apical,
cardiac, diaphragmatic, and intermediate. The apical lobe extends considerably
over the median plane in front of the pericardium. The intermediate lobe has the
form of an irregular, three-sided pyramid, with its base against the diaphragm and
its apex at the root; on its lateral face there is a deep groove which contains the
posterior vena cava and right phrenic nerve, enclosed in a special pleural fold. The
cardiac impression of the right lung is much deeper than that of the left. The

^The costal attachment of the diaphragm is lower than in the other animals, thus further
increasmg the capacity of the thorax (vide diaphragm).

552

RESPIRATORY SYSTEM OF THE DOG

Dorsal border

— L. d.

Apex-

Apical lobe

Cardiac lobe

Fig. 492. — Left Lung of Dog; Costal Surface.
L. d.. Diaphragmatic lobe. Arrows indicate interlobar fissures.

Intermediate Diaphragmatic lobe

lobe

Diaphragmatic lobe

Cardiac lobe
Cardiac lobe Apex of heart
Fig. 493. — Diaphragmatic Surface of Lungs and Heart of Dog.
1, Aorta; 2, ojsophagus; 3, oesophageal nerve trunk; 4, posterior vena cava.

THE THYROID GLAND — THE THYMUS 553

cardiac notch is triangular and allows the pericardium to come in contact with the
lateral wall at the fourth and fifth interchondral spaces.

The left lung is divided into three lobes — apical, cardiac, and diaphragmatic.
The cardiac impression is shallow, and a distinct cardiac notch is not present, but
the pericardium is in contact with the lateral wall along a narrow area at the ventral
part of the fifth and sixth interchondral spaces. The apical lobe has a small, blunt-
pointed apex which lies over the manubrium sterni. On account of the small
amount of interlobular tissue the lobulation is not distinct. Pigmentation of the
interlobular tissue is usual in dogs kept in town.

Accessory fissures may partially subdivide some of the lobes; this is most common in re-
gard to the apical lobe. When the lungs have been successfully hardened in situ, additional mark-
ings are seen on the mediastinal surface. On the right lung there are: (1) A groove for the an-
terior vena cava in front of the root; (2) a groove for the vena azygos which curves upward and
backward over the root; (3) a shallow groove for the aorta above the posterior part of the root;
(4) a groove for the a?sophagus behind the root; (5) a groove for the internal thoracic vessels curv-
ing downward and backward over the apex; (6) a groove for the right phrenic nerve in the upper
part of the cardiac impression; (7) grooves for the dorso-cervical and vertebral veins running from
the dorsal border to the groove for the vena cava. On the left lung there are: (1) A well-marked
groove for the aorta, which curves over the root and runs back just below the dorsal border; (2)
a shallow groove for the oesophagus behind the root; (3) grooves on the apical lobe for the left
brachial and brachiocephalic arteries; (4) grooves near the apex for the internal thoracic ves-
sels; (5) a groove for the left phrenic nerve is more or less evident; it passes downward and back-
ward over the middle of the apical lobe, then runs backward over the cardiac and diaphragmatic
lobes.

The diaphragmatic line of pleural reflection extends along the lower part of the ninth costal
cartilage, crosses the tenth cartilage a little (ca. 1-2 cm.) below the costo-chondral junction, and
the eleventh rib at the costo-chondral junction; it then curves up to the last rib, just above its
middle, and passes medially and backward to the second lumbar transverse process. In a good-
sized dog (e. g., bull-terrier) the apex of the pleural sac extends about an inch (ca. 2.5 cm.) anterior
to the plane of the first rib.

THE THYROID GLAND

The lateral lobes of the thyroid gland are long and narrow, and have a flat-
tened, ellipsoidal form; they are situated on the lateral surfaces of the trachea near
the larynx, extending along the first six or seven rings (Fig. 434). The extremities,
are small, the posterior one often being pointed. The isthmus is inconstant and
variable; in large dogs it has the form of a glandular band which may be nearly
half an inch (ca. 1 cm.) wide; in medium-sized dogs it is often absent, and in small
dogs it is usually absent. Accessory thyroids are frequently present; three or four
may be found on either side, as well as a median one near the hyoid bone.

The parathyroids, al)out the size of millet or hemp seed, are four in number
usually. Two are situated on the deep face of the thyroid lobes, in which they are
often embedded; the others are placed laterally near the anterior extremity of the
thyroid.

THE THYMUS

The thymus is relatively small, and is situated almost entirely in the thorax.
The left lobe is much larger than the right, and extends back on the pericardium as
far as the sixth rib at the time of its greatest size. According to Baum, the gland
increases in size during the first two weeks after birth, and atrophies rapidly in the
next two or three months. Traces of it are present at two or three years of age,
and may be found even in old subjects.

THE UROGENITAL SYSTEM

The urogenital apparatus (Apparatus urogeuitalis) includes two groups of
organs, the urinary and the genital. The urinary organs elaborate and remove the

chief excretory fluid, the urine. The geni-
tal organs serve for the formation, develop-
ment, and expulsion of the products of the
reproductive glands. In the higher verte-
brates the two apparatus are independent
except at the terminal part, which consti-
tutes a urogenital tract, and includes the
vulva in the female and the greater part of
the urethra in the male.

THE URINARY ORGANS

The urinary organs (Organa uropoiet-
ica) are the kidneys, ureters, bladder, and
urethra. The kidneys are the glands which
secrete the urine; they are red-bro\^^l in
color, and are situated against the dorsal
wall of the abdomen, being in most ani-
mals almost symmetrically placed on either
side of the spine. The ureters are tubes
which convey the urine to the urinary
bladder. The latter is an ovoid or piri-
form sac, which is situated on the pelvic
floor when empty or nearly so; it is a reser-
voir for the urine. The urine accumulates
in the bladder and is then expelled through
the urethra.

Fig. 494. — General Dorsal View of Urinary
Organs of Horse.
1, Right kidney; 1', left kidney; 2, 2', ad-
renal bodies; 3, 3', ureters; 4, urinary bladder; 4',
anterior end of bladder with cicatricial remnant of
urachus; 4", urethra; 3, aorta; 6, 6, renal arteries;
7, 7, external iliac arteries; 8, 8, internal ihac ar-
teries; 9, 9, umbilical arteries. (After Leisering'a
Atlas.)

THE URINARY ORGANS OF THE
HORSE

THE KIDNEYS
Each kidney presents two surfaces,
two borders, and two extremities or poles,
but they differ so much in form and position as to require a separate description
of each in these respects.

The right kidney (Ren dexter) in outline resembles the heart on a playing
card, or an equilateral triangle ^^^th the angles rounded off. It lies ventral to the
upper parts of the last two or three ribs and the first lumbar transverse process.
The dorsal surface (Facies dorsalis) is strongly convex; it is related chiefly to the
diaphragm, but also to a small extent posteriorly to the iliac fascia and psoas

554

THE KIDNEYS

555

muscles. In well-hardened specimens, especially those from thin subjects, impres-
sions of the last two ribs and the tip of the first lumbar transverse process are
usually visible.^ The ventral surface (Facies ventralis) is in general slightly con-
cave, and is related to the liver, pancreas, cfficum, and right adrenal; it either has
no peritoneal covering, or only a narrow peritoneal area laterally.^ The medial
border (Margo medialis) is convex and rounded; it is related to the right adrenal
and the posterior vena cava. It presents about its middle a deep notch, the renal
hilus (Hilus renalis) ; this is bounded by rounded margins, and leads into a space
termed the renal sinus (Sinus renalis). The vessels and nerves reach the kidney
at the hilus, and the sinus contains the renal pelvis or dilated origin of the ureter.
The lateral border (Margo lateralis) is rounded, and is thinner than the medial one.

C L.n

^ 7

^""^-^^z.Tzr^

Fig. 495. — Di.^gram of Pcsition and Dors.\l Relations op Kidneys of Horse.

Areas of direct relations are enclosed by continuous lines; parts of skeleton which overlie the kidneys are indicated by

dotted lines. L.I. — L.III, lumbar transverse processes.

It consists of two parts, anterior and posterior, which meet at a lateral angle; the
anterior part fits into the renal impression of the liver. The duodenum curves
around the lateral border. The anterior extremity (Extremitas cranialis), thick
and rounded, lies in the renal impression of the liver. The posterior extremity
(Extremitas caudalis) is thinner and narrower.

The left kidney (Ren sinister) is bean shaped. It is considerably longer and
narrower than the right one, and is situated nearer the median plane and further
back, so that the hilus of the left kidney is usually about opposite to the posterior
extremity of the right one. It is usually ventral to the last rib and the first two

1 The dorsal surface, being largely in contact with the diaphragm, slopes downward in front;
thus its anterior part is about three inches (ca. 6-8 cm.) ventral to the dorsal part of the seven-
teenth rib.

2 In exceptional cases a considerable area — as much as the outer and posterior third — of the
surface may have a peritoneal covering. In the new-born foal a large part is so covered; this is
apparently due to the small size of the ctECum and the small area of attachment of its base.

556

THE URINARY ORGANS OF THE HORSE

or three lumbar transverse processes. The dorsal surface is convex, and is related
to the left crus of the diaphragm, the iliac fascia and psoas muscles, and the dorsal end

Right adrenal

Left adrenal ,

Left ureter

Fig. 496. — Kidneys and Adrenals of Horse; Dorsal View.
Hardened in situ. Impression of seventeenth rib on right kidney is indicated by small cross. The left kidney W£
little further forward in this subject than is usual.

Ureters

Anterior mesenteric
artery {stump)

Renal arteries

Fig. 497. — Kidneys and Adrenals or Horse; Ventral View.
Hardened in situ. Left renal vein (not marked) is seen curving round posterior end of left adrenal.

of the spleen. The ventral surface is convex and irregular ; the greater part of it is
covered by the peritoneum. It is in relation with the origin of the small colon, the
terminal part of the duodenum, the left adrenal, and the left extremity of the

THE KIDNEYS

557

pancreas. The medial border is longer, straighter, and thicker than that of the
right kidney. It is related to the posterior aorta, the adrenal, and the ureter. The
lateral border is related chiefly to the base of the spleen. The anterior extremity
extends almost to the saccus caecus of the stomach; it is related to the left end of
the pancreas and the splenic vessels. The posterior extremity is usually larger
than the anterior one.

The form of the left kidney is variable. In some cases its outline is similar to that of the
right kidney, but its ventral surface is convex and is often marked by several furrows which diverge
from the hilus. In well-hardened specimens the three areas of the dorsal surface are often dis-
tinct. The psoas area (Impressio muscularis) is fiat, parallel with the medial border, and widens
behmd. The diaphragmatic area is small and convex; it is crescentic and is confined to the an-
terior end. The lateral splenic area is somewhat flattened and is often so extensive and distinct
as really to constitute a third surface as in Fig. 496.

Fixation. — The kidneys are held in position chiefly by the pressure of adjacent
organs and by the renal fascia. The latter is a special development of the sub-

Renal crest

Cortical substance

Medullary substance

Renal artery

Ureter

Fig. 498. — Frontal (Horizontal) Section of Kidnet of Horse.

The renal vein ia removed. A large accessory renal artery entered the posterior pole. Sections of arteries in limiting

layer between cortical and medullary substance are white in figure.

peritoneal tissue, which splits into two layers to enclose the kidney, together with
the perirenal fat, which is termed the capsula adiposa.^ On account of its relations
with the liver, pancreas, and base of the caecum, the right kidney is much more
strongly attached than the left one. It is, therefore, not surprising that the latter
varies somewhat in position; its posterior extremity may be ventral to the third or
fourth lumbar transverse process. The position of the right kidney, excluding its
movements during respiration, seems to be very constant.

Weight and Size. — The right kidney is usually one or two ounces heavier than
the left. The average weight of the right kidney is about 23 to 24 ounces (ca.
700 gm.); that of the left, about 22 to 23 ounces (ca. 670 gm.). The relation of
the weight of both kidneys to the body-weight is about 1 : 300-350. In the new-
born foal the kidney weighs about 6 ounces (ca. 170 gm.).

^ The amount of perirenal fat varies ; in animals in good condition it may entirely conceal the
kidneys; in such cases the impressions produced by contact of the kidney with contiguous struc-
tures may be indistinct.

558 THE URINARY ORGANS OF THE HORSE

Chauveau gives as an average 750 grams for the right kidney and 710 grams for the left.
Ellenberger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams;
and the left between 425 and 780; this is an average of 635 grams (about 22) 2 omices) for the
right kidney, and 602.5 grams (about 213^2 ounces) for the left. They give the relation of the
weight of both kidneys to the body-weight as 1 : 255-344. In a Percheron mare weighing about
2000 pounds the right kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a horse
of medium size the right kidney is about six inches (ca. 15 cm.) in length, about the same in width,
and about two inches (ca. 5 cm.) thick. The left kidney is about seven inches (ca. 18 cm.) long,
four to five inches (ca. 10 to 12 cm.) wide, and two to two and a half inches (ca. 5 to 6 cm.) thick.

Structure. — The surface of the kidney is covered by a thin but strong fibrous
capsule (Tunica fibrosa), which is in general easily stripped off the healthy kidney;
it is continued into the renal sinus, where it is attached. Sections through the
kidney show it to consist of an external cortical substance and an internal medullary
substance. The cortical substance (Substantia corticalis) is red brown in color
and has a granular appearance. It is dotted over with minute dark points; these
are the renal corpuscles (Corpuscula renis),^ each consisting of the dilated origin of
a uriniferous tubule (Capsula glomeruli), with an invaginated tuft of capillaries
(Glomerulus) enclosed by it. The medullary substance (Substantia meduUaris)

Renal crest Pelvis Renal Branches Ureter

vein of renal artery

Fig. 499. — Transverse Section or Right Kidney op Horse Passing Through the Hilus.
Posterior portion of organ hardened in situ. Note curvature of dorsal surface.

is more resistant and presents a distinct radial striation. Its central part is pale,
but its periphery, the intermediate zone, is of a deep red color; in the latter are
seen, at fairly regular intervals, sections of the relatively large arciform vessels,
which are taken to represent the demarcation between the primitive lobes.^ Be-
tween the vessels the medulla is prolonged somewhat toward the periphery, forming
the bases of the renal p)nraniids (Pyramides renales). These are not very pro-
nounced in the kidney of the horse, especially as the gland is not papillated. Be-
tween the bases of the pyramids processes of the cortex dip in toward the sinus,
forming the renal columns (Columnse renales).^ The inner central part of the
medulla forms a concave ridge which projects into the pelvis of the kidney. This
projection is termed the renal crest; it presents numerous small openings at which
renal tubules open into the pelvis of the kidney, and hence the surface here is known
as the area cribrosa.

^ Also known as Malpighian corpuscles.

^ The fcetal kidney is divided by furrows into a number of polygonal areas, each of which
is the base of a pyramidal lobe or renculus. These furrows usually disappear before or soon after
birth in the foal, although traces of them are sometimes seen in the adult.

^ In the kidney of the horse the renal columns dip in between the pyramids very superficially
as compared with the arrangement in the human kidney. Breuer states that the pyramids are
40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct.

THE KIDNEYS

559

Examination with a pocket lens shows that the cortex is imperfectly divided
into lobules (Lobuli corticales). Each lobule consists of an axial radiate part (Pars
radiata), surrounded by a convoluted part (Pars convoluta). The former appear
as ray-like prolongations from the bases of the pyramids (hence also termed medul-
lary rays) , and consist largely of narrow, straight or slightly flexuous tubules (limbs
of the loops of Henle). The convoluted part is granular in appearance, and con-
sists largely of the renal corpuscles and convoluted tubules.

The renal pelvis (Pelvis renalis) is the dilated origin of the excretory duct.
It lies in the sinus of the kidney, and it is funnel-shaped, but flattened dorso-ven-
trally. The renal crest^ (Crista renalis) projects into the outer part of the pelvis
in the form of a horizontal ridge with a concave free edge. The tubules of the
middle part of the medullary substance open on this crest into the pelvis. The
tubules from each end of the kidney do not open into the pelvis proper (Recessus
medius), but into two long, narrow diverticula (Recessus terminales), which pro-
ceed from it toward the poles of the kidney. The wall of the pelvis consists of
three layers. The external fibrous coat or adventitia is continuous with the sup-
porting tissue of the kidney. The muscular coat consists of longitudinal and

Tig. 500. — Cast of Right Renal Pelvis (a), Re-
cesses (c, c'), AND Origin of Ureter (b) of Horse.
(After Dumont.)

Fig. 501. — Cast of Left Renal Pelvis (a), Recesses
(c, c'), AND Origin of Ureter (6) of Horse.
(After Dumont.)

circular fibers. The mucous coat does not cover the renal crest nor is it continued
into the diverticula of the pelvis. It has a yellowish tinge, and forms numerous
folds. It contains compound tubular glands (Glandulae pelvis renalis), which
secrete the thick, viscid mucus always found in the pelvis.^

Renal Tubules. — The parenchyma or proper substance of the kidney is composed of the
small renal or uriniferous tubules (Tubuli renal es), which are very close together and have a
complicated course. Each tubule begins in a thin-walled, spherica,l dilatation or capsule (Cap-
sula glomeruli), which is invaginated to receive a tuft of looped capillaries termed a glomerulus;
these two structures constitute a renal corpuscle ; the corpuscles are visible as minute red or
dark spots in the convoluted part of the cortex. Succeeding this is a short narrow neck, beyond
which the tubule becomes wide and convoluted, forming the proximal convoluted tubule, and
enters the radiate portion of the cortex. It then gradually narrows and enters the intermediate
zone; becoming very narrow and nearly straight, it descends for a variable distance into the medul-
lary substance, turns sharply upon its(-lf, and returns to the cortex, forming thus the loop of Henle,
with its descending and asceiiding limbs. In the convoluted part of the cortex it widens and
becomes tortuous, constituting tlic distal convoluted tubule. The tubule then narrows, enters a
medullary ray, and opens with other tubules into a straight collecting tubule; this passes axially
through a pyramid, and unites with other collecting tubules to form the relatively large papillary
ducts, which open into the renal pelvis.

Stroma. — The interstitial tissue forms a reticulum throughout which supports the tubules

1 The crest is the result of fusion of the papillae or apices of the pyramids in the embryo and
is therefore also known as the papilla communis.

2 There are goblet cells in the epithelium of the pelvis which doubtless concur in the secretion
of mucus.

660

THE URINARY ORGANS OF THE HORSE

and blood-vessels. It is very scanty in the cortex, much more abundant in the medulla, in which
it increases in amoimt toward the pelvis.

Vessels and Nerves. — The kidneys receive a large amount of blood through the
renal arteries which come from the aorta.^ Branches of these enter at the hilus and
on the ventral surface of the gland, and reach the intermediate zone, where they
form anastomotic arches (Arterise arciformes). From these arciform arteries
branches pass into the cortex and medulla. The cortical branches (Arterise inter-
lobulares) have in general a radial course between the cortical lobules, and give off
short lateral branches, each of which ends as the afferent vessel (Vas afferens) of a
renal corpuscle. The blood is carried from the glomerulus by a smaller efferent

Arched collecting
tubule
Straight collect-
ing tubule
Distal convo-
luted tubule
Renal {Malpig-
hian) corpuscle
Proximal convo-
luted tubule
Loop of Henle

Collecting tubule

Arteria arci-
formis

Large collecting
tubule

^apillary duct

^ Artery of capsule

Interlobular
artery

Capillary net-
work. Vas
-' afferens
Arteriola recta
spuria

- Glomerulus

^"-^ Vena arciformis

Fig. 502. — Diagrammatic Scheme of Uriniferous Tubules and Blood-vesseus of Kidnet.
Drawn in part from the descriptions of Golubew (Bohm, Davidoff, and Ruber).

vessel, which breaks up immediately into capillaries which form networks around
the tubules. The medullary branches descend in the pyramids, forming in them
bundles of straight twigs (Arteriolse rectse). The renal veins are large and thin-
walled; they go to the posterior vena cava. In the superficial part of the cortex
the veins form star-like figures (Vense stellatae) by the convergence of several small
radicles to a common trunk. The l3nnph-vessels form two networks, capsular or
superficial, and parenchymatous or deep. On leaving the hilus they go to lymph
glands in this vicinity which are known as the renal lymph glands.

The nerves are derived from the renal plexus of the sympathetic, which en-
laces the renal artery.

^ The occurrence of accessory renal arteries is not at all rare. They may come from various
branches of the aorta (e. g., posterior mesenteric, spermatic, circumflex iliac) and enter the posterior
part of the gland.

THE URETERS — THE URINARY BLADDER 561

THE URETERS

The ureter is the narrow part of the excretory duct of the kidney. Each
begins at the renal pelvis and terminates at the bladder. It is about 3^ to 3^ inch
(ca. 6 to 8 mm.) in diameter, and its average length is about 28 inches (ca. 70 cm.).
The abdominal part (Pars abdominalis) of each ureter emerges ventrally from the
hilus of the kidney, and curves backward and medially toward the lateral face of the
posterior vena cava (right side) or the aorta (left side). They then pass almost
straight backward in the subperitoneal tissue on the surface of the psoas minor,
cross the external iliac vessels, and enter the pelvic cavity. The pelvic part (Pars
pelvina) passes backward and a little ventrally on the lateral wall of the pelvic
cavity, turns medially, and pierces the dorsal wall of the bladder near the neck.
In the male the pelvic part enters the genital fold and crosses the ductus deferens.
In the female the ureter is situated in most of its course in the dorsal part of the
broad ligament of the uterus.

The wall of the ureter is composed of three coats. The external fibrous coat
(Tunica adventitia) contains many elastic fibers. The muscular coat consists of
internal and external layers of longitudinal fibers, with a stratum of circular fibers
between them. The mucous membrane is covered with transitional epithelium;
glands (Glandulae mucosae ureteris) resembling those of the renal pelvis occur in the
first three or four inches of the ureter.

The blood-supply is derived from the renal and umbilical arteries. The nerves
come from the solar and pelvic plexuses; many minute ganglia are present.

THE URINARY BLADDER

The urinary bladder (Vesica urinaria) (Figs. 366, 369, 370) differs in form, size,
and position according to the amount of its contents. When empty and contracted,
it is a dense, piriform mass, about the size of a fist, and lies on the ventral wall of
the pelvic cavity at a variable distance behind the inlet. When moderately filled,
it is ovoid in form, and extends a variable distance along the ventral abdominal wall.
Its physiological capacity varies greatly, but may be estimated approximately at
about three or four quarts.

The anterior rounded blind end is termed the vertex ;^ on its middle is a mass
of cicatricial tissue (Centrum verticis), a vestige of the urachus, which in the foetus
forms a tubular connection between the bladder and the allantois. The middle
part or body (Corpus vesicae) is rounded, and is somewhat flattened dorso-ventrall}^
except when distended. It presents two surfaces, dorsal and ventral, the former
being the more strongly convex, especially in its posterior part in front of the en-
trance of the ureters.^ The posterior narrow extremity, the neck (Collum vesicae),
joins the urethra.

The relations of the bladder vary according to the degree of fulness of the
organ, and also differ in important respects in the two sexes. The ventral surface
(Facies ventralis) lies on the ventral wall of the pelvis, and extends forward on the
abdominal wall as the bladder fills. The dorsal surface (Facies dorsalis) in the male
is related to the rectum, the genital fold, the terminal parts of the ductus
deferentes, the vesiculae seminales, and the prostate; in the female it is in contact
instead with the body of the uterus and the vagina. The vertex of the full bladder
has variable relations with coils of the small intestine and small colon, and the pelvic
flexure of the large colon.

Fixation. — Displacement of the bladder is limited chiefly by three peritoneal

^ This is often termed the fundus by veterinarians, but is not the homologue of the fundus of
the human bladder.

2 This would correspond to the fundus vesicae of man.
36

562 THE URINARY ORGANS OF THE HORSE

folds, termed the middle and lateral ligaments (Figs. 352, 370). The middle liga-
ment (Plica umbilicalis media) is a median triangular fold, formed by the reflection
of the peritonemn from the ventral surface of the bladder on to the ventral wall of
the pelvis and abdomen. In the new-born animal it is extensive and reaches to the
umbilicus; in the adult it is usually much reduced in length relatively. It contains
elastic and muscular fibers in its posterior part. The lateral ligaments (Plica? um-
bilicales laterales) stretch from the lateral aspects of the bladder to the lateral pelvic
walls. Each contains in its free edge a round, firm band, the roimd ligament (Lig.
teres vesicae) ; this is the remnant of the large foetal umbilical artery, the lumen of
which in the adult is very small. The retroperitoneal part of the bladder is attached
to the surrounding parts by loose comiective tissue, in which there is a quantity of
fat. It is evident that the posterior part of the bladder has a definite fixed position,
while its anterior part is movable.

Structure. — The wall of the bladder consists of a partial peritoneal investment,
the muscular coat, and the mucous lining. The serous coat (Tunica serosa) covers
the greater part of the dorsal surface, from which it is reflected in the male to form
the genital fold; in the female it passes on to the vagina, forming the vesico-
genital pouch. Ventrally the peritoneum covers only the anterior half or less of
the bladder, and is reflected posteriorly on to the pelvic floor. The muscular coat
(Tunica muscularis) is relatively thin when the bladder is full. It is unstriped, pale,
and not clearly divided into layers, but has rather a plexiform arrangement. Longi-
tudinal fibers occur on the dorsal and ventral surfaces, but laterally they become
oblique and decussate with each other. A distinctly circular arrangement is found
at the neck, where the fibers form a sphincter vesicae. The mucous coat (Tunica
mucosa) is pale and thin. It is in general attached by a highly elastic submucosa
to the muscular coat, and forms numerous folds when the organ is empty and con-
tracted. It is modified dorsally in the vicinity of the neck over a triangular area,
termed the trigonum vesicae ; the angles of this space lie at the orifices of the two
ureters and the urethra, which are close together. Here the mucous membrane is
closely attached and does not form folds. From each ureteral orifice (Orificium
ureteris) a fold of mucous membrane (Plica ureterica) passes backward and inward,
uniting with its fellow to form a median crest (Crista urethralis) in the first part of
the urethra. The ureteral orifices are a little more than an inch (ca. 3 cm.) apart.
The terminal part of the ureter, after piercing the muscular coat of the bladder,
passes for a distance of about an inch (ca. 2 to 3 cm.) between the muscular and
mucous coats before piercing the latter; this arrangement constitutes a valve which
prevents absolutely the return of the urine from the bladder into the ureter. The
internal urethral orifice (Orificium urethrae internum) lies at the apex of the tri-
gonum, and is about an inch and a half (ca. 4 cm.) behind the ureteral orifices. The
mucous membrane is covered with transitional epithelium like that of the ureter
and renal pelvis. It contains lymph nodules.

Vessels and Nerves. — The arteries are derived chiefly from the internal pudic,
but branches also come from the obturator and umbilical arteries. The veins
terminate chiefly in the internal pudic veins. They form plexuses posteriorly.
The Isnnph-vessels form plexuses on both surfaces of the muscular coat. They
go to the internal iliac and lumbar glands. The nerves are derived from the pelvic
plexus (sympathetic and ventral branches of third and fourth sacral nerves). They
form a plexus in the submucosa which presents microscopic ganglia.

In the foetus and new-bom animal the bladder is situated chiefly in the abdomen. It is
long, narrow, and fusiform. Its abdommal end hes at the umbilicus, through which it is con-
tinued by the urachus to the extra-embryonic part of the allantois. The lateral hgaments also ex-
tend to the umbilicus and each contains in its edge the large umbilical artery. As the pelvis in-
creases in size and the large intestine grows, the bladder retracts into the pelvis and changes its
form.

The urethra will be described with the genital organs.

THE ADRENAL BODIES

563

THE ADRENAL BODIES

The adrenal bodies or glands (Glandulae adrenales)^ are two small, flattened
organs, which lie in contact with the anterior part of the medial border of the
kidneys (Figs. 496, 497). They are ductless. In the horse they are red-ljrown in
color, about three and a half to four inches (ca. 9 to 10 cm.) long, one to one and a
half inches (ca. 3 to 4 cm.) wide, and about half an inch or more (ca. 1.5 cm.) in
thickness. The weight varies from one to two ounces (ca. 28 to 56 gm.).

The right adrenal body is related medially to the posterior vena cava, to which
it is adherent. Its anterior part curves dorsally around the medial border of the
right kidney. Its posterior part is flattened and is related ventrally to the pancreas
and caecum, dorsally to the right renal vessels. The anterior extremity is con-
cealed in the renal impression of the liver; the posterior is related to the ureter.

The left adrenal body is a little shorter than the right one, and its extremities
are rounded; it is usually curved, so that its medial border partly embraces the
anterior mesenteric artery. Its dorsal surface is related
to the kidney, the renal artery, the aorta, and the left
coeliaco-mesenteric ganglion. The ventral surface is in
relation with the left extremity of the pancreas and the
root of the great mesentery. The posterior extremity

often curves inward behind the anterior mesenteric -? -Iff— ill M^ z

artery; it is related behind to the left renal vein.

When hardened in situ the adrenals present several features
not evident in the soft organs. The anterior part of the right
adrenal is twisted dorso-laterally over the medial margin of the
kidney, so that this part is prismatic and has three surfaces; of
these, the concave lateral one is applied to the kidney, the dorsal
one is related to the right crus of the diaphragm and the liver,
and the medial one is in contact with the posterior vena cava.
The anterior mesenteric artery is nearly always more or less en-
larged as a result of verminous arteritis, and the form and degree
of curvature of the left adrenal seem to vary m conformity with
the condition of the artery.

Structure. — The fibrous capsule adheres intimately
to the surface of the organ. It contains elastic fibers,
and in its deep part unstriped muscle-fibers. From it
trabeculse pass radially into the substance, blending
with the fine supporting reticulum. The parenchyma
consists of a cortical and a medullary part. The cor-
tical substance (Substantia corticalis) is red-brown in

color, and is clearly distinguishable from the yellow medullary substance (Substantia
medullaris). A large central vein (Vena centralis) is visible on cross-sections.

The cells of the cortex are arranged in chains of one or two rows. In the peripheral portion
the cells are of high cylindrical shape, and the chains form connecting loops; Gunther has pro-
posed the name zona arcuata for this part, instead of the usual term zona glomerularis. More
deeply the chains are distinctly palisade-like, and this region is called the zona fasciculata. Next
to the medulla is the zona reticularis, in which the chains form a network. The cells in these two
zones are polygonal and contain a brown pigment. The cells of the medulla are arranged in
irregular groups or form sheaths around the veins. They react to chromic salts by assuming a
yellow or yellow-brown color, and are termed chromaffin cells; they share this peculiarity with
certain cells of the sympathetic ganglia and paraganglia, with which they are probably related
genetically. The alkaloid adrenalin appears to be formed in the medullary cells.

Vessels and Nerves. — The adrenals receive a relatively large blood-supply
through the adrenal arteries, which arise from the renal arteries or from the aorta
directly. The veins terminate in the posterior vena cava and the left renal vein.

iFrom the standpoint of comparative anatomy the term "adrenal" is decidedly preferable
to "suprarenal."

Fig. 503. — Adrenal Body of
Horse; Horizontal Sec-
tion, Reduced.
1, Capsule; 2, 2', cortical

substance; 3, medullary substance;

4, blood-vessel in section. (From

Leisering's Atlas, reduced.)

564

URINARY ORGANS OF THE OX

The lymph-vessels go to the renal lymph glands. The numerous nerves are derived
from the sympathetic system through the solar and renal plexuses. The fibers
form a rich interlacement, especially in the medullary substance. Ganglion cells
are found chiefly in the medulla, but also occur in the deeper part of the cortex.

URINARY ORGANS OF THE OX

The kidneys are superficially divided into polygonal lobes by fissures of vari-
able depth. The lobes vary in size, and are commonly about twenty in number.
The fissures are filled with fat.

The right kidney has an elongated elliptical outline, and is flattened dorso-
ventrally. It commonly lies ventral to the last rib and the first two or three lumbar

Lateral border

Anterior extremity

Ureter Renal artery

Fig. 504.-
Organ hardened in siti

-Right Kidney of Ox; Ventral Face.

. Fat has been removed from fissures between lobes.

h^^

Renal artery

Fig. 505. — Frontal Section of Kidney of Ox.
L, Lobes of cortex; P, papillae; C, calyx major; c', calyces minores.

transverse processes, but its extremities may be ventral to the first and fourth
lumbar transverse processes. The dorsal surface is rounded, and is in contact
chiefly with the sublumbar muscles. The ventral surface is less convex, and is
related to the liver, pancreas, duodenum, and colon. The hilus is situated on the
anterior part of this surface, near the medial border. The medial border is
nearly straight, and lies parallel with the posterior vena cava. The lateral border
is convex. The anterior extremity occupies the renal impression of the liver, and
is capped by the adrenal body.

URINARY ORGANS OF THE OX 565

The left kidney occupies a remarkable position, and when hardened in situ
differs strongly in form from the right one. When the rumen is full, it pushes the
kidney backward and across the median plane, so that it is situated on the right
side, behind, and at a lower level than, the right kidney. It then lies usually
ventral to the third, fourth, and fifth lumbar vertebrae. When the rumen is not
full, the left kidney may lie partly to the left of the median plane. It has three
surfaces. The dorsal surface is convex, and presents on its antero-lateral part the
hilus, which opens laterally. The ventral surface is related to the intestine. The
third face is more or less flattened by contact with the rumen, and may be termed
the ruminal surface. The anterior extremity is small, the posterior large and
rounded.^

The kidneys are embedded in a large amount of perirenal fat termed the
capsula adiposa. The weight of a kidney of an adult animal is about 20 to 25 ounces
(ca. 600-700 gm.), the left one being usually an ounce or more the heavier. The
two form about ^ per cent, of the body-weight.

The right kidney measures about 8 or 9 inches (ca. 20-22.5 cm.) in length, 4 to 5 inches (ca.
10-12 cm.) in width, and 23^ to 3 inches (ca. 5-6 cm.) in thickness. The left kidney is one or
two inches (ca. 2 to 5 cm.) shorter, but its posterior part is much thicker than the right one.

Structure. — The hilus is equivalent to the hilus and sinus of the kidney of the

Fig. 506. — Cast of Origin of Ureter (a), Calyces Majores, and Calyces Minores (b) of Ox. (After Dumont.)

horse; in the right kidney it is an extensive elliptical cavity; in the left one it is a
deep fissure. The pelvis is absent. The ureter begins at the junction of two wide,
thin-walled tubes, the calyces majores; the anterior calyx is usually the larger.
Each calyx major gives off a number of branches, and these divide into several
funnel-shaped calyces minores, each of which embraces a renal papilla. The
space not occupied by the calyces and vessels is filled with fat.

On section through the kidney the renal pyramids are easily made out. The
blunt apex of each pyramid, the renal papilla (Papilla renalis), projects into a calyx
minor. On each papilla are small orifices (Foramina papillaria) by which the
papillary ducts (Ductus papillares) open into the calyx. The renal columns are
much more distinct than in the horse.

At the hilus the renal artery is dorsal, the vein in the middle, and the ureter
ventral; a quantity of fat surrounds these structures in the hilus.

iThe above statements refer to the adult subject, and are based on investigations made on
living subjects, and studies of frozen sections and material hardened in situ. In the new-bom
calf the kidneys are almost symmetrically placed, but as the rumen grows it pushes the left kidney
to the right and backward pari passu. It also usually causes a rotation of the kidney, so that the
primary dorsal surface comes to lie almost in a sagittal plane. Further, the gland is bent so that
the hilus is largely closed up and faces outward (to the right). In very fat subjects the three-
sided appearance of the kidney may be absent, and about one-third or more may remain to the left
of the median plane, even where the rumen is pretty well filled.

566

URINARY ORGANS OF THE OX

The kidneys of the sheep are bean-shaped and smooth, without any superficial
lol^ation. The soft organ is regularly elliptical in form, with convex dorsal and
ventral surfaces and rounded extremities; its length is about 3 inches (ca. 7.5 cm.),
its width about 2 inches (ca. 5 cm.), and its thickness a little more than 1 inch (ca.
3 cm.). They are embedded in fat normally. In position they resemble those of
the ox, except that the right one is usually a little further back, and lies under the
first three lumbar transverse processes.^ The average weight of each is about four
ounces. The hilus is in the middle of the medial border. There is a renal crest or
common papilla formed by the fusion of twelve to sixteen pyramids.

The ureters are, in general, like those of the horse, except in regard to the
first part of the left one, which has a peculiar course, in conformity with the remark-
able position of the kidney. It begins at the ventral part of the hilus (which faces

Fig. 507. — Right Kidney of Sheep; Ventral View.
V.V., Branches of renal vein.

Fig. .508. — Kidnet op Sheep; Horizontal Section.
1, Cortical substance; 2, medullary substance; 3,
renal crest; 4. renal pelvis; 5, ureter. (From Leisering's
Atlas, reduced.)

toward the right), curves over the lateral aspect of the kidney to its dorsal surface,
crosses the median plane, and runs backward on the left side.

The bladder is longer and narrower than that of the horse, and extends further
forward on the abdominal floor. The peritoneal coat extends backward further
than in the horse.

THE ADRENAL BODIES
The right adrenal lies against the medial part of the anterior pole of the right
kidney. When hardenetl in situ, it is pyramidal in form. Its medial surface is
flattened and is in contact with the right crus of the diaphragm. The lateral sur-
face is convex and lies in the renal impression of the liver. The ventral surface is
grooved for the posterior vena cava; on this surface a relatively large vein emerges
near the apex. The base is concave and rests obliquely against the anterior pole
of the kidney. The apex fits into the angle between the posterior vena cava and

1 When the rumen is full, the left kidney (which is attached by a short mesentery) usually
lies entirely to the right of the median plane, and is ventral to the third, fourth, and fifth luml^ar
transverse processes. The primitive dorsal siuiace has become ventro-medial, and is somewhat
flattened by contact with the rumen.

URINARY ORGANS OF THE PIG 567

the dorsal border of the Hver, The left adrenal Hes on the medial face of the
posterior vena cava, just behind the anterior mesenteric artery, and is therefore
practically median in position. It is flattened, and irregularly triangular or heart-
shaped in outline. Its left face is related to the dorsal sac of the rumen. Its right
face is related to the vena cava, and presents a large emergent vein. The posterior
border or base is deeply notched. The left adrenal does not migrate with the kid-
ney, but retains its primitive position; it lies usually two or three inches (ca. 5-8
cm.) in front of a transverse plane through the anterior pole of the left kidney.

The adrenals of the sheep are both bean-shaped. The right one lies along
the anterior part of the medial border of the kidney, at the angle of the junction of
the right renal vein and the posterior vena cava. It is a little over an inch (ca.

Posterior pole

Groove for vena cava

Anterior pole

Fig. 509. — Left Adrenal of Ox; Ventral View. Fig. 510. — Right Adrenal or Ox; Ventral View.

Hardened in situ. Hardened in situ.

3 cm.) long, and about half as wide. The left adrenal is usually longer, and is
flatter and somewhat bent. It lies across the left renal vein, to which it is at-
tached ; it is not in contact with the kidney, from which it may be separated by a
distance of nearly two inches (ca. 4 cm.).

URINARY ORGANS OF THE PIG

The kidneys are smooth and bean-shaped; they are more flattened dorso-
vent rally, more elongated, and smaller at the extremities than those of the dog.
The length is about twice the width. They are usually almost symmetrically placed
ventral to the transverse processes of the first four lumbar vertebrse, but the left
kidney is often a little further forward than the right one. The lateral border lies
against the flank parallel "with the edge of the longissimus muscle. The posterior
extremity is usually about midway between the last rib and the tuber coxae. The
anterior extremity of the right kidney has no contact with the liver.

Variations in position are not rare, and involve the left kidney oftener than the right; the
former has been found near the pelvic inlet. When a fifteenth rib is present the anterior end of
the kidney is usually ventral to it. The right kidney is usually separated from the liver by an
interval of an inch or more. Absence of the left kidney has been recorded.

568

URINARY ORGANS OF THE PIG

Fig. 511. — Kidneys of Pig in silu; Venthai. ^'I^;\v.
C.a., Hepatic artery; M.a., gastro-splenic artery.

Calyx major
Pelvis

Ureter

Cortical substance

Medullary substance

PapiUcB

Calyces minores

Fig. 512. — Frontal Section of Kidney of Pig.

URINARY ORGANS OF THE DOG 569

The weight of the kidney of an adult pig is about seven to nine ounces (200 to
250 grams). The ratio of their combined weight to that of the body is about
1 : 150-200. The length in an adult of good size is about five inches (ca. 12.5 cm.)
and the greatest width about two and a half inches (ca. 6-6.5 cm.).

Structure. — The hilus is about in the middle of the medial border. The pelvis
is funnel-shaped, and divides into two calyces majores, which pass in a curve for-
ward and backward respectively, and give off some eight to twelve short calyces
minores; each of the latter contains a papilla. Some papillae are narrow and coni-
cal, and correspond to a single pyramid; others are wide and flattened, and result
from the fusion of two or more pyramids; some project directly through the wall
of the renal pelvis without the formation of a calyx. The renal pyramids are dis-
tinct, but it is apparent that some are compound, i. e., formed by fusion of primi-
tively separate pyramids. The renal vessels enter the ventral part of the hilus,
and the ureter leaves it dorsally.

The adrenals are long and narrow. Each lies along the medial border of the
corresponding kidney from the hilus forward ; they are in contact medially with the
crus of the diaphragm and the posterior vena cava.

The only special features in regard to the ureter are that it is at first relatively
wide and gradually diminishes in caliber, and that it is slightly flexuous.

The bladder is relatively very large; when full, it lies chiefly in the abdominal
cavity. The dorsal surface is almost completely covered with peritoneum, but
the serous covering does not extend so far back ventrally.

URINARY ORGANS OF THE DOG

The kidneys (Fig. 624) are relatively large, forming about y^-q- to 2T0" of the
body-weight; the weight of the kidney of a medium-sized dog is about two ounces
(ca. 50 to 60 grams). They are both bean-shaped, thick dorso-ventrally, with a
rounded ventral surface and a less convex dorsal surface; the surfaces are smooth.

The right kidney is not subject to much variation in position; it is situated
usually opposite to the bodies of the first three lumbar vertebrae, but may be as far
forward as the last thoracic. Its anterior half or more lies in the deep renal im-
pression of the liver; its posterior part is related to the sublumbar muscles dorsally,
and the right branch of the pancreas and duodenum ventrally.

The left kidney is subject to some variation in position; this is due to the fact
that it is loosely attached by the peritoneum, and is affected by the degree of ful-
ness of the stomach. When the stomach is nearly empty, the kidney usually
corresponds to the bodies of the second, third, and fourth lumbar vertebrae, so that
its anterior pole is opposite to the hilus of the right kidney; exceptionally the
anterior pole may be opposite the posterior end of the first lumbar vertebra. When
the stomach is full, the left kidney is usually the length of one vertebra further back,
so that its anterior pole may be opposite the posterior pole of the right kidney.
The dorsal surface is related to the sublumbar muscles. The ventral surface is in
contact with the left part of the colon. The lateral border is related to the spleen
and the flank. The anterior extremity touches the stomach and the left extremity
of the pancreas.

The lateral border of the left kidney usually has considerable contact with the flank, and
hence it may be palpated more or less distinctly in the living animal, about half-way between the
last rib and the crest of the ilium. But in some cases the spleen assumes an almost longitudmal
direction, thus intervening between the kidney and the flank.

Structure. — The hilus is in the middle of the medial border and is relatively

570 URINARY ORGANS OF THE DOG

wide. Cortex, limiting zone, and medulla are clearly defined. On frontal sections
it is seen that the medullar}^ substance forms a horizontal renal crest like that of
the horse, but -with the important difference that curved ridges proceed dorsally
and ventrall}^ from the crest somewhat like buttresses. Sections above or below
the renal crest often cut these ridges in such a manner as to give the appearance
of conical papillse, and thus tend strongly to produce a false impression. The
pelvis is adapted to this arrangement of the medullary substance. It encloses a
central cavitj^ into which the renal crest projects, and is prolonged outward be-
tween the ridges, forming cavities for the latter, thus simulating the appearance
of calyces which do not exist.

The ixreters present no special features.

The bladder, when full, is abdominal in position, the neck lying at the anterior
border of the pubic bones. It is relatively large, and when distended, the vertex
may reach to the umbilicus. When empty and contracted, it is usually entirely in
the pelvic cavity. It has a practically complete peritoneal coat.

THE ADRENALS

The right adrenal lies between the anterior part of the medial border of the kid-
ney and the posterior vena cava. It is somewhat prismatic, and is pointed at
either end. The left adrenal lies along the posterior aorta, from the renal vein
forward, but is not in contact with the kidney. It is elongated and flattened dorso-
ventrally. (There is a furrow on the ventral surface for the phrenico-abdominal
vein which crosses it ; the part in front of this furrow is discoid, and may be taken
for the entire organ in a fat subject.) The cortex is pale yellow in color, the me-
dulla dark brown.

THE MALE GENITAL ORGANS

The male genital organs (Organa genitalia masculina) are: (1) The two
testicles, the essential reproductive glands, with their coverings and appendages;
(2) the ductus deferentes, the ducts of the testicles; (3) the vesiculae seminales;
(4) the prostate, a musculo-glandular organ; (5) the two bulbo-urethral (or Cow-
per's) glands; (6) the male urethra, a canal which transmits the generative and
urinary secretions; (7) the penis, the male copulatory organ. The vesiculae
seminales, the prostate, and the bulbo-urethral glands discharge their secretions
into the urethra, where they mix with the fluid secreted by the testicles; hence they
are often termed the accessorv sexual glands.

GENITAL ORGANS OF THE STALLION

THE TESTICLES

The testicles (Testes) are situated in the inguinal region, enclosed in a divertic-
ulum of the abdomen termed the scrotum. Their long axes are nearly longitu-
dinal.^ They are ovoid in form, but considerably compressed from side to side.
Each presents two surfaces, two borders, and two extremities. The medial and
lateral surfaces (Facies meclialis, lateralis) are convex and smooth; the former is
somewhat flattened by contact with the septum scroti. The free border (Margo
liber) is ventral and is convex. The attached or epididymal border (Margo epi-
didymidis) is dorsal; it is nearly straight, and is the one by which the gland is
suspended in the scrotum by the spermatic cord ; the epididymis is attached to this
border and overlies it laterally. The anterior and posterior extremities (Extremitas
capitata, caudalis) are rounded.

At the anterior extremity there is often a sessile or pedunculated sac which contains a clear
fluid; this is the appendix testis, from which a thread-hke process extends backward toward
the ductus deferens. It is regarded as a remnant of the Miillerian duct of the embryo.

A testicle of average size of an adult stallion is about four or five inches (ca.
10 to 12 cm.) long, two and a half to three inches (ca. 6 to 7 cm.) high, and two
inches (ca. 5 cm.) wide; it weighs about eight to ten ounces (ca. 225-300 grams).
They vary much in size in different subjects, and are commonly of unequal size,
the left one being more often the larger.

The epididjrmis is adherent to the attached border of the testicle, and overlaps
somewhat the lateral surface. Its anterior enlarged end is termed the head (Caput
epididymidis) ; and its posterior, slightly enlarged end is the tail (Cauda epididy-
midis); the intermediate narrow part is the body (Corpus epididymidis). The
head is closely connected with the testicle by the efferent ducts of the latter, by
connective tissue, and by the serous membrane. The body is less closely attached
by the serous covering, which forms laterally a pocket beneath the epididymis
termed the sinus epididymidis. The tail is continued by the ductus deferens; it is
attached to the posterior extremity of the testicle by a short ligament (Lig. epididy-
midis) , which is formed by a thick fold of the tunica vaginalis and contains smooth
muscle-fibers.

1 When the testicle is drawn up or has not completed its descent into the scrotum, its long
axis is almost vertical.

571

572

GENITAL ORGANS OF THE STALLION

Structure of the Testicle and Epididjonis. — The greater part of the surface
of the testicle is covered by a serous membrane, the timica vaginalis propria, which
is the visceral layer of the serous envelop of the cord and testicle ; this is reflected
from the attached border of the gland, leaving an uncovered area at which the
vessels and nerves in the spermatic cord reach the testicle.^ Beneath this serous
covering is the tunica albuginea, a strong capsule composed of dense white fibrous
tissue and unstriped muscle-fibers. When the tunic is cut, the gland substance,
which is soft and reddish gray in color, protrudes. From the attached border and
from the deep face of the tunica albuginea trabecule and septa of connective tissue

Fig. 513. — Inguinal Region of Staluon, with Testicles Exposed.
o, a', Testicles; b, scrotum, opened and reflected; c, tunica vaginalis communis, opened and reflected; d, reflection
of tunica vaginalis enclosing scrotal ligament; e, tunica vaginalis propria (mesorchium) ; /, ductus deferens; g, g', tail
of epididymis; h, body of same; i, head of same; k, sinus epididymidis; I, spermatic vessels showing through tunica
vaginahs propria; m, spermatic artery; n, prepuce; n', raph6; o, preputial orifice. (After EUenberger-Baum, Top.
Anat. d. Pferdes.)

and unstriped muscle (Septula testis) pass into the gland and subdivide the
parenchyma into lobules (Lobuli testis). The larger trabeculae radiate from the
attached border into the central part of the gland.

A distinct mediastinum testis, such as is present in man and many animals, does not exist in
the horse. The trabeculae and interlobular septa form a network which shows no special conden-
sation in any part of the gland. In correlation with this is the absence of a rete testis, formed by
the anastomosis of the seminiferous tubules in the mediastinum.

The spaces imperfectly marked off by the septa contain the parench3mia
testis, which consists of seminiferous tubules (Tubuli seminiferi), supported

^ In the normal state the surface of the testicle is quite smooth on account of the serous
covering. Frequently, and especially in old subjects, local inflammation has produced roughen-
ing of the surface and thread-like proliferations.

THE TESTICLES

573

by loose intralobular connective tissue. The tubules are at first very tortuous
(Tubuli contorti); then they unite with other tubules, forming larger straight
tubules (Tubuli recti). The latter unite with adjacent tubules and converge to-
ward the anterior part of the attached border of the gland. In this way there are
formed more than a dozen larger efferent ducts (Ductuli efferentes), which pierce
the albuginea at a small area (about a centimeter in diameter) at the anterior part
of the attached border and enter the head of the epididymis.

The epidid3miis is covered by the tunica vaginalis propria and a thin albuginea.
Its head consists of a dozen or more coiled tubules, which are grouped into lobules
(Lobuli epididymidis). The tubules of a lobule (four or five in number) unite to
form a single tube, and by the union of the latter with those of the other lobules
there is formed a single tube, the duct of the epidid3Tnis (Ductus epididymidis),

Fig. 514. — Right Testicle and Spermatic Cord op
Horse, Enclosed in Tunica Vaginaiis.
c, Tunica vaginalis communis; g, prominence
caused by tail of epididymis; p, cremaster externus
muscle. (After EUenberger-Baum, Top. Anat. d.
Pferdes.)

Fig. 515. — Right Testicle and Spermatic Cord of
Horse, Exposed.
a'. Lateral surface of testicle; c, tunica vagin-
alis, cut and reflected; d, reflection of tunica vaginalis;
e, mesorchium; g, tail, h, body, i, head, of epididymis;
k, sinus epididymidis; I, spermatic vessels showing
through tunica vaginalis propria; m, end of spermatic
artery. Dotted line indicates position of ductus
deferens on other side of mesorchium. (After EUen-
berger-Baum, Top. Anat. d. Pferdes.)

which, by its complex coils, forms the body and tail of the epididymis and termin-
ates in the ductus deferens. The tubules and the coils of the duct of the epididymis
are held together by connective tissue and unstriped muscle-fibers. The tubules
and duct are lined with ciliated epithelium, and the duct has a muscular coat which
consists of longitudinal and circular fibers.

Several foetal remnants in connection with the epididymis and adjacent part of the spermatic
cord have been described in man. The appendix epididymidis is a small, piriform body, 3-4
mm. long, which is attached to the head of the epididymis. The paradidymis consists of a number
of tubules which lie in the lower part of the spermatic cord close to the head of the epididymis.
Most of the tubules are blind and disappear in early life, but one or more may communicate with
the epididymis or rete testis; the latter may give rise to cysts. The ductuli aberrantes are
tubules that extend upward from the canal of the epididymis and end blindly. Similar structures
have been mentioned as occurring m the domestic animals, but authentic data in regard to them
are lacking.

Vessels and Nerves. — The testicle is richly supplied with blood by the sper-
matic artery, a branch of the posterior aorta. The artery descends in the anterior

574 GENITAL ORGANS OF THE STALLION

part of the spermatic cord, and is very tortuous near the testicle; on reaching the
attached border of the gland it passes backward in a flexuous manner, giving
branches to the testicle and epididymis, turns around the posterior extremity, and
runs forward on the free border to the anterior extremity. It is partially embedded
in the tunica albuginea, and detaches lateral branches which ascend and descend in
a tortuous fashion on each surface of the testicle; these give off small branches
which enter the gland on the trabeculae and septa. The veins on leaving the
testicle, form a network, the pampiniform plexus, around the artery in the sper-
matic cord. The spermatic vein, which issues from this plexus, usually joins the
posterior vena cava on the right side, the left renal vein on the left side. The
lymph-vessels follow in general the course of the veins and enter the lumbar lymph
glands. The nerves, derived from the renal and posterior mesenteric plexuses,
form the spermatic plexus around the vessels, to which they are chiefly distributed.

THE SCROTUM

The scrotum, in which the testicles and the adjacent parts of the spermatic
cords are situated, is somewhat globular in form, but is commonly asymmetrical,
since one testicle — more often the left — is the larger and more dependent. It
varies in form and appearance in the same subject, according to the condition of its
subcutaneous muscular tissue. The latter contracts on exposure to cold, so that
the scrotum is drawn up and becomes thicker and wrinkled; when relaxed under the
influence of heat or fatigue, or from debility, it becomes smooth and pendulous,
with a constriction or neck superiorly. It consists of layers which correspond
with those of the abdominal wall; considered from without inward, these are:

(1) The skin, which is thin, elastic, usually dark or black in color, and smooth
and oily to the touch. It presents scattered short fine hairs, and is abundantly
supplied with very large sebaceous and sweat glands. It is marked centrally by a
longitudinal raphe scroti ; this is continued forward on the prepuce and behind on
the perineum.

(2) The dartos (Tunica dartos) is reddish in color and is closely adherent to
the skin except superiorly. It consists of fibro-elastic tissue and unstriped muscle.
Along the raphe it forms a median partition, the septum scroti, which divides the
scrotum into two pouches. Dorsally the septum divides into two layers which
diverge on either side of the penis to join the abdominal tunic. At the bottom
of the scrotum fibers connect the dartos closely with the tunica vaginalis (and thus
indirectly with the tail of the epididymis), constituting the scrotal ligament.^
Elsewhere the dartos is loosely coimected with the underlying tunic by areolar
tissue which contains no fat.

(3) The scrotal fascia, which is apparently derived from the oblique abdom-
inal muscles.

It has been customary to describe three layers of fascia, in conformity with the accounts
given in text-books of human anatomy. These are: (1) The intercolumnar or spermatic fascia,
derived from the margin of the external inguinal ring; (2) the cremasteric fascia, derived from the
internal obhque muscle; (3) the infundibuliform fascia, derived from the fascia transversahs.
The first two cannot be distinguished by dissection and the third is (in the scrotum) fused with
the parietal peritoneum of the tunica vaginalis.

(4) The parietal layer of the tunica vaginalis. — This is a fibro-serous sac which
is continuous with the parietal peritoneum of the abdomen at the internal inguinal
ring. It is thin above, but is thick in its scrotal part, where it is strengthened by
fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It will be
described further under the caption tunica vaginalis.^

1 This is a remnant of the gubernaculum testis of the foetus.

2 The tunica vaginaUs is not a part of the scrotum in the strict or narrow sense of that term,
but is included here on practical grounds.

THE DUCTUS DEFERENS THE SPERMATIC CORD 575

Vessels and Nerves. — The blood supply' is derived from the external pudic
artery, and the veins go chiefly to the external pudic vein. The nerves are derived
from the ventral branches of the second and third lumbar nerves.

THE DUCTUS DEFERENS
This tube, also commonly termed the vas deferens, extends from the tail of the
epididymis to the pelvic part of the urethra. It ascends in the inguinal canal,
enclosed in a fold detached from the medial surface of the mesorchium, near the
posterior (attached) border of the latter. At the vaginal ring it separates from the
other constituents of the spermatic cord, and turns backward and inward into the
pelvic cavity (Fig. 370). For some distance it lies in the free edge of the genital
fold, by which it is attached to the inguinal part of the abdominal wall and the
ventral part of the lateral wall of the pelvis. In its further course (over the dorsal
surface of the bladder) it leaves the edge of the fold and inclines medially between
its layers, and comes in contact with the medial face of the vesicula seminalis. Over
the neck of the bladder the two ducts lie very close together, flanked laterally by the
necks of the vesiculae seminales, and having the uterus masculinus between them.
They then disappear under the isthmus of the prostate, and are continued through
the wall of the urethra to open in a small diverticulum on the colliculus seminahs
with the excretory duct of the vesicula seminalis. The common opening is the
ejaculatory orifice (Orificium ejaculatorium).

It has been customary to describe a short tube, the ejaculatory duct, as resulting from the
union of the ductus deferens and the duct of the corresponding vesicula seminahs. Such a duct,
about 18-20 mm. (ca. 'ji in.) long, exists in man as the morphological continuation of the ductus
deferens. In the domestic animals it is not present, since the ductus deferens and duct of the
vesicula seminahs open either in common or alongside of each other in a diverticulum or evagina-
tion of the mucous membrane on the side of the colhculus seminahs.

From its origin until it reaches the dorsal surface of the bladder the ductus
deferens has a uniform diameter of about a quarter of an inch (ca. 6 mm.). It then
forms a fusiform enlargement, the ampulla ductus deferentis (Fig. 517) ; this part
is about six to eight inches (ca. 15 to 20 cm.) long, and in its largest part nearly an
inch (ca. 2 cm.) in diameter in the stallion; in geldings the enlargement is usually
not very pronounced. Beyond the ampulla the duct abruptly diminishes in size.^

Structure. — The wall of the ductus deferens is thick and the lumen very small,
so that the tube has a firm and cord-like character. It is covered with peritoneum,
except in the last few inches of its course. The loose adventitia contains numerous
vessels and nerves. The thick muscular coat consists of longitudinal and circular
fibers. The mucous membrane has an epithelium of short columnar cells. In the
posterior part of the tube, and especially in the ampulla, there are numerous glands.

Vessels and Nerves. — The arteries are branches of the spermatic, umbilical,
and internal pudic arteries, and the nerves come from the pelvic plexus of the
sympathetic.

THE SPERMATIC CORD

The spermatic cord (Funiculus spermaticus) consists of the structures carried
down Ijy the testicle in its migration through the inguinal canal from the abdominal
cavity to the scrotum. It begins at the abdominal inguinal ring, where its constitu-
ent parts come together, extends obliquely downward through the inguinal canal,
passes over the side of the penis, and ends at the attached border of the testicle.
It consists of the following structures:

(1) The spermatic artery.

1 The term "ampulla" is not entirely satisfactory, smce it is likely to be interpreted to mean a
dilatation. There is no increase here in the lumen of the tube, and the increase in size is caused
by a thickening of the wall, due to the presence of numerous branched tubular glands. The term
"pars glandularis," suggested by Schmaltz, seems worthy of adoption.

576

GENITAL ORGANS OF THE STALLION

(2) The spermatic veins, which form the pampiniform plexus around tho
artery.

(3) The lymphatics, which accompany the veins.

(4) Syinpathetic nerves, which run with the artery.

(5) The ductus deferens.

(6) The internal cremaster muscle, which consists of bundles of unstriped
muscular tissue about the vessels.

(7) The visceral layer of the tunica vaginalis.

The first four of these constituents are gathered into a rounded mass which
forms the anterior part of the cord; they are united by connective tissue, inter-
spersed with which are bundles of the cremaster internus. The ductus deferens is
situated postero-'medially, enclosed in a special fold detached from the medial surface
of the tunic ; hence it is not visible laterally.

The term spermatic cord is to a certain extent misleading as applied to most animals, while
in man the structure is distinctly cord-like. In the horse, when the tunica vaginalis is slit open
and the "cord" stretched out, the latter is seen to have the form of a wide sheet, the mesorchium,
which has a thick, rounded anterior edge, the so-called "vascular part" of the cord. The posterior
edge of the mesorchium is continuous with the parietal layer of the tunic; its medial surface pre-
sents posteriorly the deferential fold (Plica ductus deferentis). Between the two layers of the
mesorchium are bundles of unstriped muscle (cremaster internus) and small vessels.

THE TUNICA VAGINALIS

The tunica vaginalis is a flask-like serous sac which extends through the in-
guinal canal to the bottom of the scrotum. Like the abdominal peritoneum, of

which it is an evagination, it con-

Spermatic vessels and nerves

("A

Parietal layer
of tunica
vaginalis

Mesorchium

Ductus
deferens

sists of two layers — parietal and vis-
ceral. The parietal layer or timica
vaginalis commimis lines the scrotum
below; its narrow, tubular part lies
in the inguinal canal, and is directly
continuous with the parietal perito-
neum of the abdomen at the abdom-
inal inguinal ring. The cavity of the
tunica vaginalis (Cavum vaginale) is
a diverticulum of the general perito-
neal cavity, with which it communi-
cates through the vaginal ring (An-
nulus vaginalis); it contains nor-
mally a small quantity of serous fluid.
The parietal layer is reflected from
the posterior wall of the inguinal
canal around the structures of the
cord, forming the mesorchiimi, a
fold analogous to the mesentery of
the intestine. The visceral layer

or tunica vaginalis propria covers the spermatic cord, testicle, and epididymis.
The external cremaster muscle (M. cremaster externus) lies on the lateral and

posterior part of the tunic, to the scrotal part of which it is attached.

Confusion has arisen from the use of the term abdominal or internal inguinal ring in two
senses. The term is used to designate the abdominal opening of the inguinal canal, but it is also
often applied to the opening of the cavity of the tunica vaginalis. It should not be used in the
latter sense. The peritoneal ring at which the cavity of the tunica vaginalis opens into the
general peritoneal sac is distinguished by the name vaginal ring. It is four or five inches (ca.
10 to 12 cm.) from the linea alba, and two or three inches (ca. 6 to 8 cm.) in front of the ilio-pec-
tineal eminence. In stallions it will usually admit the end of the finger readily, but it may be

Fig. 516. — Diagram of Cross-section of Spermatic Cord
AND Tunica Vaginalis; Latter Represented as Dis-
tended.

DESCENT OF THE TESTICLES 577

abnormally large and allow a loop of bowel to enter the cavity of the tunica vaginalis. It is large
in the young foal. In the gelding it is smaller and sometimes partially occluded. In man the
cavity is almost always obliterated early, except in its scrotal portion, thus abolishing the vaginal
ring and the inguinal part of the cavity.

DESCENT OF THE TESTICLES

During early foetal life the testicle is situated against the dorsal wall of the
abdominal cavity, in contact with the ventral surface of the corresponding kidney.
As growth proceeds it gradually migrates from this primitive position, and finally
passes down the inguinal canal into the scrotum. Previous to its descent through
the abdominal wall the testicle is attached to the sublumbar region by a fold of
peritoneum, termed the mesorchium. This fold contains the vessels and nerves
of the testicle in its anterior border. In its posterior edge is the elongated tail of
the epididymis, and two cords of fibrous tissue and unstriped muscle. One of these
cords is short and connects the tail of the epididymis with the testicle; later it
becomes shorter, and is termed the ligament of the epididymis. The other cord,
the gubemaculum testis, extends from the tail of the epididymis to the subperi-
toneal tissue in the vicinity of the future vaginal ring. The deferential fold (Plica
ductus deferentis) is given off from the medial face of the mesorchium, and joins the
genital fold posteriorly. The body of the epididymis at this time lies in the edge
of an oblique fold formed by the lateral layer of the mesorchium. After the middle
of foetal life a pouch of the peritoneum, the processus vaginalis, grows downward
through the inguinal canal, carrying with it cremaster fibers derived from the
internal oblique muscle and a layer from the transversalis fascia. It is accom-
panied by an inguinal extension of the gubernaculum testis. The latter blends
below with the subcutaneous tissue which later becomes the dartos. The tail of
the epididymis first enters the processus vaginalis, followed by the testicle with its
mesorchium, which descends within this diverticulum of the peritoneum until it
reaches the scrotum. The ductus deferens and its fold descend synchronously with
the epididymis and testicle. In the foal the descent of the testicles is often com-
plete at birth, but it frequently happens that one testicle or both may be retained
in the inguinal canal or in the abdomen for some months. In other cases the
testicle may return into the canal or abdomen, since in the young foal the vaginal
ring is large and the testicle small and soft, and not yet closely anchored by the
scrotal ligament. In rare cases the descent may be completed as late as the fourth
year.

The mechanical factors concerned in the migration of the testicle are matters on which
much uncertainty still exists. That the gubernaculum exerts sufficient traction to guide the
epididymis and testicle to the inguinal canal seems plausible. The abdominal inguinal ring may
constitute a locus minoris resistentiae in the abdominal wall, especially after the descent of the
processus vaginalis. Progressive shortening of the gubernaculum was formerly considered to be
the chief cause of the descent through the abdominal wall. Increase in the intra-abdominal
pressure is probably an important factor.

Indefinite retention of one testicle or both in the abdominal cavity or inguinal canal is not
rare in horses; this condition is termed cryptorchism. Abdominal retention is the more usual
form of cryptorchism in adult horses, inguinal retention being usually temporary. The retained
testicle is usually, but not always, small, thin, soft, and flabby, and is non-spermiogenic. The
processus vaginalis and the inguinal part of the gubernaculum are usually present, but may be
rudimentary. The ligament of the epididymis and the corresponding part of the mesorchium
are often so long that the tail of the epididymis may be several inches distant from the testicle.
The abdominal part of the gubemaculum may be eight to ten inches (ca. 20 to 25 cm.) long, and the
ligament of the epididymis much elongated (10 to 15 cm. in length, according to Vennerholm) ;
thus the testicle may have a wide range. The vaginal ring is sometimes closed.

In many mammals the testicles normally remain in the abdominal cavity; such animals are
termed testiconda, and include the elephant, some insectivora, hyrax, sloths, ant-eaters, armadillos,
and cetacea. In others the testicles descend periodically during the period of oestrum, and then
return into the abdomen, or they may be extruded and retracted voluntarily; this is true of most
rodents, many insectivora (moles, shrews, hedgehog), and bats.
37

578

GENITAL ORGANS OF THE STALLION

.Bladder

THE VESICULiE SEMINALES

The vesiculae seminales (Fig. 517) are two elongated and somewhat piriform
sacs, which He on each side of the posterior part of the dorsal surface of the blad-
der. They are partly enclosed in
^- , the genital fold, and are related to

the rectum dorsally. Their long axes
are parallel with the ductus def-
erentes and converge posteriorly.
^ Each consists of a rounded blind

end, the fundus; a middle, slightly
narrower part, the body ; and a pos-
terior constricted part, the neck or
duct.

In the stallion they are about
six to eight inches (ca. 15 to 20 cm.)
long, and their greatest diameter is
about two inches (ca. 5 cm.); in
the gelding they are usually much
smaller.^

The vesiculae are chiefly retro-
peritoneal, but the fundus extends
forward into the genital fold and
hence has a serous covering. The
excretory duct (Ductus excretorius)
dips under the prostate, and opens
in common with or alongside of the
ductus deferens in a pouch of the
mucous membrane on the side of
the coUiculus seminalis.

Structure. — The wall, exclusive
of the partial serous coat, consists
of a fibrous adventitia, a middle
muscular coat, and a mucous lining.
The muscular coat is thickest at the
fundus, and consists of two planes
of longitudinal fibers with a circular
layer between them. The mucous
membrane is thin, and is arranged
in numerous folds and projections
which form a network; the spaces
so enclosed present the openings of
tubulo-alveolar glands. The epithe-
lium is columnar. The blood-supply
is derived from the internal pudic
artery.

Ure^hral
muscU

Fig. 517. — I.xter.nal Genital Organs of Stallion; Dorsal
View.
On left side urethral muscle has been removed over bulbo-
urethral gland. Cornua of uterus masculinus are indicated in
genital fold. The posterior limit of the peritoneum is shown
but not marked. 1, Round ligament of bladder; 2, lateral liga-
ment of bladder; 3, bulbo-urethral gland.

THE PROSTATE
The prostate (Prostata) is a lobulated gland which hes on the neck of the
bladder and the beginning of the urethra, ventral to the rectum. It consists of

1 Sometimes one or both of the vesiculae are very large in the gelding. The writer has seen
four cases in the dissecting room, three of which were bilateral, the other unilateral. The vesicula
resembled the urinary bladder in appearance and contained about a quart of thick, amber-colored
secretion.

THE UTERUS MASCULINUS — THE BULBO-URETHRAL GLANDS 579

two lateral lobes and a connecting isthmus. The lateral lobes, right and left
(Lobus dexter et sinister), are somewhat prismatic in form, and are directed forward,
laterally, and somewhat upward. The deep surface of each lobe is concave and
partly embraces the corresponding vesicula seminalis. The dorsal surface is con-
cave and is in relation with the rectum The ventral surface is convex and lies
on the obturator internus muscle and fat. The apex is pointed and lies near the
posterior end of the superior ischiatic spine. The isthmus is a thin, transverse
band, about four-fifths of an inch (ca. 2 cm.) wide. It lies over the junction of the
bladder with the urethra, the uterus masculinus, the terminal parts of the ductus
deferentes, and the ducts of the vesiculae seminales. Dorsally it is partly covered
by fibers of the urethral muscle.

Structure. — The prostate is enclosed in a capsule of fibrous tissue, with an
admixture of unstriped muscle fibers. The gland substance is divided into sphe-
roitlal or ovoid lobules by trabeculse which consist to a large extent of unstriped
muscle. Each lobule is traversed by an axial duct, which gives off numerous
tubular branches and these ramify further in the lobule. The tubules are thickly
beset v/ith saccular diverticula, giving the gland a branched, tubulo-alveolar .struc-
ture. The ducts and tubules are lined with cubical or columnar epithelium. The
prostatic secretion (Succus prostaticus) is milky in appearance and has a character-
istic odor. There are fifteen to twenty prostatic ducts (Ductus prostatici) on either
side, which perforate the urethra and open lateral to the coUiculus seminalis (Fig.
521). The blood-supply is derived from the internal pudic artery.

The surface of the prostate is commonly tuberculate in old subjects, and amyloid bodies
and calcareous concretions may be found in it.

THE UTERUS MASCULINUS
The uterus masculinus or utriculus prostaticus is a foetal remnant of variable
size and form, which is situated centrally on the posterior part of the dorsal surface
of the bladder. When well developed, it consists of a median flattened tube, some
three or four inches (ca. 7.5 to 10 cm.) long, and about half an inch (ca. 1 to 1.5 cm.)
wide, the anterior part of which lies in the genital fold and gives ofT two slender
processes or cornua; the latter curve forward and outward in the fold a variable
distance, being sometimes traceable as far as the anterior end of the ampulla of the
ductus deferens. The posterior extremity of the tube passes under the isthmus of the
prostate, and opens into the urethra on the summit of the colliculus or joins a duct
of a vesicula seminalis or has a blind end. It has a muscular coat and a mucous
lining. In many cases it consists merely of a very small central tubule with a blind
anterior end, or a band, not sharply marked off from the adjacent tissue; in other
cases it cannot be recognized. It is a remnant of the ducts of Miiller and the
homologue of the uterus and vagina.

THE BULBO-URETHRAL GLANDS

The bulbo-urethral glands (Glandulae bulbourethrales)' are two in number,
and are situated on either side of the pelvic part of the urethra close to the ischial
arch (Fig. 577). They are covered by the urethral muscle, from which bundles
enter the larger trabeculse of the g'and. They are ovoid in form, somewhat de-
pressed dorso-ventrally, and their long axes are directed obliquely forward and
outward. In the stallion they may measure nearly two inches (ca. 4 cm.) in length,
and about an inch (ca. 2.5 cm.) in width. In the gelding they are about the size of
an average hazel-nut.

Structure. — They resemble the prostate in general structure, but the inter-
1 Also termed Cowper's glands.

580

GENITAL ORGANS OF THE STALLION

stitial tissue is much less abundant, and contains much less muscular tissue ; hence
the lobulation is not very distinct. The parenchyma consists of large collecting
tubules, into which numerous side branches open; these are lined with cubic
epithelium. In the larger septa there are striped muscle-fibers. Each gland has
six to eight excretory ducts (Ductus excretorii) which open into the urethra on a
series of small papillae behind the prostatic ducts and close to the median plane
(Fig. 521). The blood-supply comes from the internal pudic artery which overlies
the gland.

THE PENIS

The penis, the male organ of copulation, is composed essentially of erectile
tissue, and encloses the extrapelvic part of the urethra. It extends from the ischial
arch forward between the thighs to the umbilical region of the abdominal wall.
It is supported by the fascia penis and the skin, and its prescrotal portion is situated
in a cutaneous pouch, the prepuce or sheath. It is cylindrical in form, but much
compressed laterally in the greater part of its extent.

In the quiescent state it is about 20 inches (ca. 50 cm.) long; of this, about 6 to 8 inches
(ca. 15 to 20 cm.) is free in the prepuce. In erection it increases 50 per cent, or more in length.

Deep artery (from internal pudic)

Dorsal artery (from Corona glandis

external pudic) Collum glandis

Proc. dorsalis glandis v.

BODY

Retractor penis muscle

Fig. 518.— Pe

Horse; Lateral View.

It may be divided into a root, a body, and a terminal enlargement, the glans.

The root of the penis (Radix penis) is attached to the lateral parts of the ischial
arch by two crura, which converge and unite below the arch (Fig. 577). The
urethra passes over the ischial arch between the crura, and curves sharply forward
to become incorporated with the penis. The body of the penis (Corpus penis)
begins at the junction of the crura and constitutes the bulk of the organ. At its
origin it is attached to the symphysis ischii by two strong flat bands, the suspensory
ligaments of the penis (Ligamenta suspensoria penis), which blend with the tendon
of origin of the graciles muscles (Figs. 518, 576). This part of the penis is flattened
laterally for the most part, but becomes rounded and smaller anteriorly. It pre-
sents four surfaces. The dorsum penis is narrow and rounded ; on it are the dorsal
arteries and nerves of the penis and a rich venous plexus. The urethral surface
(Facies urethralis) is ventral; it is rounded, and along it runs the urethra, embedded
in the deep urethral groove of the corpus cavernosum. The lateral surfaces are
high and flattened, except anteriorly, where they are lower and rounded; they are
covered to a large extent by a plexus of veins.

The glans penis is the enlarged free end of the organ. Its anterior surface or
base is surrounded by a prominent, denticulated margin, the corona glandis. The

THE PENIS

581

surface is convex ; its lower part slopes backward, and presents a deep depression,
the fossa glandis, in which the urethra protrudes for about an inch (ca. 2.5 cm.) as a
free tube, the urethral process (Processus urethrse), covered by a thin integument.
The urethra is thus surrounded by a circular fossa, which opens superiorly into the
urethral sinus, a bilocular diverticulum lined by thin skin. This diverticulum is
filled sometimes with a caseous mass of sebaceous matter and epithelial debris.
Behind the corona glandis there is a constriction, the collum glandis. It is to be
noted, however, that this does not indicate the demarcation between the glans and
corpus penis, since the former extends backward above the corpus cavernosum a
distance of about four inches (ca. 10 cm.), forming the processus dorsalis glandis
(Fig. 518).

Structure. — The penis consists essentially of two erectile bodies, the corpus
cavernosum penis and the corpus cavernosum urethrse.

The corpus cavernosum penis forms the greater part of the bulk of the penis
except at its free extremity. It arises from each side of the ischial arch by a cms
penis, M^hich is embedded in the ischio-cavernosus muscle. Below the ischial arch
the crura unite to form the laterally compressed body of the corpus cavernosum;
this presents ventrally the urethral

Dorsum penis

Corpus
cavernosum
penis

Corpus
cavernosum
urethrce

Trabecules

Tunica

albuginea

Urethra

Bulbo-

cavernosus
muscle

Retractor penis muscle

Fig. 519. — Cross-section of Body of Penis of Hobsb.

groove (Sulcus urethralis), which con-
tains the urethra and corpus caverno-
sum urethrge. Anteriorly the corpus
cavernosum penis divides into three
processes — a long central one, which is
capped by the glans penis, and two
short blunt lateral ones. The corpus
cavernosum is enclosed by the tunica
albuginea, a thick capsule of fibrous
tissue which contains some elastic
fibers. Externally the fibers are chiefly
longitudinal ; internally they are mainly
circular and are looser in arrangement.
Numerous trabeculae pass inward from
the tunic and form a framework in the
interior of the corpus cavernosum. En-
closed by this framework is the erectile
tissue, which is readily distinguished
from the fibrous trabeculse by its red-
dish-gray color and softer texture. It is composed largely of strands of unstriped
muscle, between which there are cavernous spaces (Cavernse). These spaces may
be regarded as greatly enlarged capillaries; they contain blood, are lined with flat
endothelial cells resting upon a layer of delicate connective tissue, and are directly
continuous with the veins of the penis. Erection is produced by distention of
these spaces with blood; at other times the spaces are mere slits.

In man there are two distinct corpora cavernosa, separated by a median septum penis,
which is complete except in the middle part of the organ, where the septum is composed of vertical
trabeculse, between which are slit-like intervals; through the latter the blood-spaces of the two
corpora cavernosa commvmicate. In the horse no distinct septum exists except near the root, but
in the proximal and distal parts of the corpus cavernosum there are vertical trabeculse, which
form an arrangement like the septum pectiniforme of man.

The corpus cavernosum urethrae (or corpus spongiosum) forms a tube around
the urethra, and is continuous at its anterior end with the glans penis. It forms a
slight enlargement at the root of the penis, which is termed the bulb (Bulbus
urethrae). In the body of the penis it forms a thinner layer dorsally than on the
sides and ventrally. The structure of the corpus cavernosum urethrse is somewhat

582 GENITAL ORGANS OF THE STALLION

like that of the corpus cavernosiim penis, but the trabeculse are much finer; they
consist of fibrous tissue, much of which is elastic, and of bundles of unstriped muscle
which are chiefly longitudinal in direction. The spaces are numerous and large.

In the glans penis the trabeculse are highly elastic, and the spaces are large and
very distensible; the latter are specially wide in the posterior part of the processus
dorsalis, where they communicate with large veins on the dorsum penis. There is
a partial septum glandis. The skin covering the glans is thin, destitute of glands,
and richly supplied with nerves and special nerve-endings.

Vessels and Nerves. — The penis is supplied with blood by three arteries, viz.,
the internal jiudic, ol^turator, and external pudic. The terminal part of the internal
pudic artery enters the root as the artery of the Ijulb and breaks up in the bull) into
numerous branches. The obturator artery gives off the large arteria profunda
penis, which enters the crus penis and ramifies in the corpus cavernosum. The
external pudic artery gives off the dorsal arteries of the penis, branches from which
pass through the tunica albuginea. The veins form a rich plexus on the dorsum
and sides of the penis, which is drained by the external pudic and obturator veins ;
from the root the blood is carried by the internal pudic veins.^ The lymph vessels
run with the veins and go to the superficial inguinal glands. The nerves are derived
chiefly from the pudic nerves and the pelvic plexus of the sympathetic. The former
supply the dorsal nerves of the penis; special nerve-endings, the end-bulbs (of
Krause), occur in the skin of the glans penis. The sympathetic fibers supply the
unstriped muscle of the vessels and the erectile tissue.

MUSCLES OF THE PENIS (Figs. 272, 576, 577, 581)

1. The ischio-cavemosus- is a short but strong, paired muscle, which arises
from the tuber ischii and the adjacent part of the sacro-sciatic ligament, and is
inserted on the crus and adjacent part of the body of the penis. It is somewhat
fusiform, encloses the crus as in a sheath, and is situated in a deep depression in the
semimembranosus muscle. It pulls the penis against the pelvis, and assists in
producing and maintaining erection by compressing the dorsal veins of the penis.
Its blood-supply is derived from the obturator artery, and the nerve-supply from
the pudic nerve.

2. The retractor penis is an unstriped muscle which is a continuation of the sus-
pensory ligaments of the anus. The latter arise on the ventral surface of the first
and second coccygeal vertebrse and pass downward over the sides of the rectum to
meet below the anus. Here there is a decussation of fibers, thus forming a sort of
suspensory apparatus for the posterior part of the rectum and the anus. From the
decussation the muscle passes for a short distance between superficial and deep
layers of the bulbo-cavernosus, and then along the ventral surface of the penis, to
which it is loosely attached. Near the glans penis it splits up into bundles which
pass through the bulbo-cavernosus and are attached to the tunica albuginea. Be-
low the anus the muscle is attached to the sphincter ani externus. On the penis
the two muscles are intimately united to each other. Their action is to withdraw
the penis into the sheath after erection or protrusion.

THE PREPUCE
The prepuce (Praeputium), popularly called the "sheath," is a double in-
vagination of the skin which contains and covers the free or prescrotal portion of

1 It has been shown that the cavernous spaces of the glans penis receive blood exckisively
from veins which come from the penile layer of the prepuce. This may account for the fact that
the glans reaches its extreme size during erection later than the corpus cavernosum penis.

''■ Also termed the erector penis.

THE PREPUCE

583

the penis when not erect. It consists of two parts, external and internal. The
external part or sheath extends from the scrotum to within two or three inches of
the umbilicus, where the external layer is reflected ventrally and laterally, forming
the thick margin of the preputial orifice (Ostium praeputiale) ; dorsally it is directly
continuous with the integument of the abdominal wall. It is marked by a median
raphe praeputii, a continuation of the scrotal raphe. At the lower margin of the pre-
putial orifice there are often in the stallion two papillae, which are regarded as
rudimentary teats. The internal layer passes backward from the preputial orifice
a distance of about six to eight inches (ca. 15 to 20 cm.), lining the cavity of the ex-
ternal part of the prepuce, and is then reflected forward until it approaches the
orifice, where it is again reflected backward. It thus forms within the cavity of the
sheath a secondary tubular invagination, the prepuce proper, in which the anterior
part of the penis lies. This tubular cavity is closed behind by the reflection of the
internal layer on to the penis to form the penile layer of the prepuce. Its orifice is

-- **«»-—«■«— ^i)d,omihal i<jciH

Fig. 520. — Sagittal Section of Preptxe and Part of Pexis of House.

P, Internal part of prepuce or prepuce proper; P' , external part of prepuce or sheath; C.p., preputial cavity; F.g.,

fossa glandis; D, diverticulum of fossa glandis; P.m., processus urethrse.

surrounded by a thick margin, the preputial ring (Annulus prseputialis), which is
connected ventrally with the external part by the preputial frenum (Frenulum
praeputii).

The arrangement differs from that found in man in the fact that the imier part of the pre-
puce as described above is equivalent to the entire human prepuce. This part, the prepuce
proper, is well seen on sagittal sections, and can be demonstrated by pulling the penis, enclosed
in this prepuce, out of the cavity of the sheath; the arrangement of the free part of the penis and
prepuce is then like that in man. (In paraphimosis the penis is strangulated by the preputial
rmg.) The external part might be distinguished as the sheath or vagina penis.

Structure. — The outer skin of the external part resembles that of the scrotum.
The internal layers of skin, as far as the preputial ring, are almost hairless, variable
in color, and often irregularly pigmented ; they form irregular folds, and are supplied
with numerous large sebaceous glands and coil glands, which reach their greatest
size at the ring. Beyond this the glands are absent, and the skin resembles a non-
glandular mucous membrane. The secretion of the preputial glands (Glandulse
praeputiales) , together with desquamated epithelial cells, forms the fatty smegma
praeputii, which has a strong, unpleasant odor, and often accumulates in considerable

584

GENITAL ORGANS OF THE STALLION

amount. Beneath the skin there is a large amount of loose connective tissue,
except over the glans penis, where the skin is closely attached to the tunic of the
erectile tissue. The external part of the prepuce is strengthened by a layer of
elastic tissue, derived from the abdominal tunic, and termed the suspensory liga-
ment of the prepuce.

Vessels and Nerves. — The arteries are branches of the external pudic artery,
and the veins go chiefly to the external pudic vein. The lymph vessels go to the
superficial inguinal and lumbar lymph glands. The nerves are derived from the
pudic, ilio-hypogastric, and ilio-inguinal nerves.

THE MALE URETHRA
The male urethra (Urethra masculina) is the long mucous tube which extends
from the bladder to the glans penis. It passes backward on the floor of the pelvis.

Lateral lobe of prostate

Orifice of uterus masculinus

Ducts of lateral tirethral
glands

Collicidus seminalis

Ducts of bulbo-urethral
glands

Fig. 521. — Pelvic Urethra and Posterior Part op Bladder op Horse Sut Ventrally and Laid Open.
e.d., openings of ductus deferentes and ducts of vesiculse seminales.

turns around the ischial arch, forming a sharp bend, and passes forward as a part of
the penis, enclosed in the corpus cavernosum urethrse. It may, therefore, be divided
into two parts, pelvic and extrapelvic.

The pelvic part (Pars pelvina) is four or five inches (ca. 10 to 12 cm.) long.
At its origin it is not distinguishable from the neck of the bladder in size or structure;
in fact, no line of demarcation exists between the two. Behind the prostate the
tube dilates to a potential width of two inches or more (ca. 5 to 6 cm.). Near the

THE MALE URETHRA 585

ischial arch, between the bulbo-urethral glands, it contracts again, forming the
isthmus urethrae. It is related dorsally to the rectum and the prostate, ventrally
to the internal obturator muscles, and laterally to the bulbo-urethral glands. It
is enclosed, except at its origin, by the urethral muscle.^

The extrapelvic part (Pars externa) passes between the two crura of the penis
and runs along the groove on the ventral surface of the corpus cavernosum penis,
enclosed by the corpus cavernosum urethrae and the bulbo-cavernosus muscle. It
passes through the glans penis and projects forward about an inch in the fossa
glandis as a free tube, the processus urethrae; this part is covered by a delicate
integument, under which there is a thin layer of erectile tissue.

The lumen of the tube is largely obliterated in the inactive condition of the parts. WTien
moderately distended, its dimensions in a horse of medium size are as follows: At its origin the
diameter is about half an inch (1 to 1.5 cm.) . The pelvic dilatation at its widest part measures one
and a half to two inches (ca. 3.5 to 5 cm.) transversely, and about an inch (2 to 3 cm.) vertically;
it is elliptical in cross-section when fully distended. Ttie isthmus at the ischial arch is a little
smaller than the initial part. Beyond this the lumen is about one-half to three-fourths of an
inch (ca. 1.5 cm.) in diameter, and is fairly unifonn to the glans penis. Here there is a slight
fusiform dilatation (Fossa navicularis), beyond which the tube contracts.

The opening from the bladder into the urethra is termed the internal urethral
orifice (Orificium urethrse internum); it is closed except during urination. The
terminal opening is the external urethral orifice (Orificium urethrse externum) or
meatus urinarius. The colliculus seminalis is a rounded prominence, situated
medially on the dorsal wall, about two inches (ca. 5 cm.) behind the internal ure-
thral orifice. On either side of the colliculus there is a small diverticulum, in which
the ductus deferens and the duct of the vesicula seminalis open. The small orifice
of the uterus masculinus is placed centrally on the colliculus; it is inconstant. The
orifices of the prostatic ducts are on two groups of small papillae, placed lateral to
the ejaculatory openings. The ducts of the bulbo-urethral glands open on two
lateral series of small papillae, about an inch (ca. 2.5 cm.) further back and close to
the median line. The small orifices of the lateral urethral glands are situated
laterally in the wide pelvic portion.

Structure. — The mucous membrane contains a large amount of fine elastic
fibers, and in its pelvic part there are tubulo-alveolar urethral glands (Glandulae
urethrales) .2 The epithelium is at first like that of the bladder, then becomes
cylindrical, and in the terminal part is stratified squamous. In the dorsal wall the
membrane forms a median ridge, the urethral crest (Crista urethralis) ; this termi-
nates about two inches from the internal urethral orifice in the colliculus seminalis.

At the origin of the urethra there is a layer of circular unstriped muscle-fibers
outside of the mucous coat. Beyond this the latter is enclosed by a layer of erectile
tissue (Stratum cavernosum), which contains plexuses of veins supported by
trabeculae of elastic and unstriped muscular tissue ; in its peripheral part there are
numerous small arteries. There is a slight thickening of the erectile tissue at the
ischial arch, producing an enlargement known as the bulb of the urethra (Bulbus
urethrae). This is continued by the corpus cavernosum urethrse. Outside of the
erectile tissue there is a continuation of the intrinsic unstriped muscular coat,
consisting of external and internal longitudinal strata, with a layer of circular
fibers between them.

^It has been customary to divide the pelvic part of the urethra into prostatic and mem-
branous parts. These terms apply well in human anatomy, but have no special value in com-
parative anatomy. In the horse a prostatic part hardly exists, unless we assume that it and the
neck of the bladder together are only about an inch in length. There is no membranous part in
the sense in which that term is used in regard to man, since the tube has a continuous envelop of
erectile tissue.

^ Two sets of glands can be distinguished in the pelvic part of the urethra. Two rows of dor-
sal glands occur close to the median plane; their ducts open into those of the bulbo-urethral glands.
A series of lateral glands extends on either side from a point near the prostatic ducts to the end of
the pelvic urethra; their ducts open laterally, as mentioned above.

586 GENITAL ORGANS OF THE BULL

Except at its origin and termination the urethra is provided with a continuous
layer of striped muscle, placed outside of the erectile tissue. This is described as
consisting of two jxirts or muscles.

(1) The urethral muscle (M. urethralis)^ encloses the wide pelvic part of the
urethra, and covers the bulbo-urethral glands. It consists of longitudinal and
transverse fibers. It is a compressor of the pelvic part of the urethra and the bulbo-
urethral glands. By its forcible contraction it plaj^s an important role in the ejacula-
tion of the seminal fluid, and also in evacuating the last of the urine in micturition.

(2) The bulbo-cavemosus muscle (M. bulbocavernosus)^ is the continuation
of the urethral muscle on the extrapelvic part of the urethra; it extends from the
ischial arch to the glans penis. At the root of the penis it is the thickest, and
forms a complete layer of circular fibers which enclose the corpus cavernosum
urethrse. Beyond this it diminishes very gradually in thickness, and consists of
fibers which arise on a median ventral raphe and curve around the corpus cavernosum
urethrse to end on the tunica albuginea of the corpus cavernosum. Its action is to
empty the extrapelvic part of the urethra.

The ischio-urethral muscles (Fig. 577) are small bands which arise on the
ischial arch and crura of the penis and pass forward to become lost on the ventral
layer of the urethral muscle. They may assist in erection of the penis by exerting
pressure on the dorsal veins.

GENITAL ORGANS OF THE BULL

The scrotum is situated somewhat further forward than in the horse. It is
ovoid, but compressed from before backward, is long and pendulous, and has a well-
marked neck when not contracted. The skin here is usually flesh-colored, but in
some breeds it is more or less pigmented; it is sparsely covered with short hairs.
Just in front of it are four (sometimes only two) rudimentary teats.

The testicles are relatively larger than those of the horse, and have an elon-
gated, oval outline. The long axis is vertical, the attached border being posterior.
The medial surface is somewhat flattened. A testicle of an adult bull measures on
the average about four or five inches (10 to 12 cm.) in length, exclusive of the epi-
didymis; with the latter the length is about six inches (15 cm.). The width is
about two and a half to three inches (ca. 6 to 8 cm.), and the anterior-posterior
diameter about the same. The weight is about ten to twelve ounces (ca. 300 grams) .
The tunica albuginea is thin; it contains many elastic fibers, but no unstriped
muscle. The parenchyma is yellowish in color. The mediastinum testis is an
axial strand of connective tissue (about 5 mm. in thickness), which descends from
the upper part of the attached border deeply into the gland. From it the chief
trabeculse radiate, but distinct interlobular septa are not present. The seminif-
erous tubules form in the mediastinum a network, the rete testis. The efferent
ducts from the rete, a dozen in number, leave at the upper end of the mediastinum.

The epididymis is very closely attached to the testicle along the posterior
border of the latter. The head is long; it curves over the upper extremity and
about a third of the way down the anterior border of the testicle ; it is covered by
an extension of the tunica albuginea. The body is very narrow, and lies along the
lateral part of the posterior border of the testicle, to which it is attached bj^ a narrow
peritoneal fold. The tail is large and is closely attached at the lower extremity of
the testicle.

The spermatic cord antl the tunica vaginalis are much longer than in the horse;

1 Formerly termed Wilson's muscle. ^ Formerly called the accelerator iirinae.

GENITAL ORGANS OF THE BULL

587

the extra-inguinal part of the cord is about eight to ten inches (20 to 25 cm.) in
length. The cremaster externus is well developed, and almost completely encloses
the tunic to the neck of the scrotum; it is inserted about at the level of the upper
pole of the testicle. The vaginal ring is relatively very small, and is about four
inches (ca. 10 cm.) from the linea alba. The cremaster internus is feeble.

The spermatic cords emerge through the lateral angles of the subcutaneous inguinal rings, and
curve do\TOward and mward to the neck of the scrotum. The rings are about four inches (ca.
10 cm.) long, and are two and a half to three inches (6 to S cm.) apart. In animals in good condi-
tion there is a large mass of fat above the neck of the .scrotum, between the spermatic cords. The
mesorchium extends to the bottom of the tunica vaginalis, forming a narrow fold (ca. 1 cm. wide)
which attaches the epididymis to the posterior part of the tunic.

Vesicula seminalis
Body of prostate ^^'^'^■■^'^^

Tunica vaginalis

(opened)

External

urethral orifice

Testicle

Tail
Fig. 522. — General View of Genital Organs op Bulu

The inguinal canal presents several special features in the bull. The abdominal ring is very
long. Its anterior border, formed by the edge of the internal oblique, is decidedly concave and
is tendinous in its medial part. The long axis of the subcutaneous ring is directed outward, for-
ward, and downward. The spermatic cord lies in its lateral part, the external pudic vessels in its
middle. A muscular band about an inch wide, detached from the internal oblique muscle, cro.sses
the lateral side of the vaginal ring.

The ductus deferens is small in caliber and has a much thinner wall than that
of the horse. At first it pursues a flexuous course upward along the posterior
border of the testicle, then becomes straight and lies in the posterior part of the
spermatic cord. The genital fold is narrow, so that the ducts are closer together
in it than in the horse. On reaching the posterior part of the bladder they are in
apposition for a distance of about four inches (10 cm.), flanked and overlapped by
the vesiculse seminales. They form ampullae about four or five inches (10 to 12 cm.)
long and half an inch (1.2 to 1.5 cm.) wide, the mucous lining of which is pHcated.
They then pass under the body of the prostate and end, just medial to the ducts of
the vesiculse seminales, as slit-like openings on either side of the colliculus seminalis.

The vesiculae seminales are not bladder-like sacs, as in the horse, but are
compact glandular organs with a lobulated surface. In the adult they measure
about four or five inches (ca. 10 to 12 cm.) in length, two inches (5 cm.) in width in

588

GENITAL ORGANS OF THE BULL

their largest part, and an inch or more (ca. 3 cm.) in thickness. The dorsal surface
of each faces upward and medially and is partially covered with peritoneum. The
ventral surface faces in the opposite direction and is non-peritoneal. Each may be
regarded as consisting of a very thick-walled, sacculated tube, bent on itself in a
tortuous manner. This tube, if straightened out, would be about ten inches (25

Galea
glandis

Raphe
glandis

Raphe

prceputii
Prepuce

-Antkrior Extremity of Penis of Bull; Left
View. (After Bohm.)

Fig.

Bull;

523. — Internal Genital Organs

Dorsal View.

The right vesicula is sectioned frontally. The

dotted hne indicates the backward extension of the

peritoneum. 1, Ureter; 2, body of prostate; 3, vesicula

seminaUs; 4, urethral muscle; 5, bulbo-urethral gland.

Fig. 525. — Cross-section of Pelvic Urethra of Bull,
1, Prostate gland (pars disseminata); 3, urethra; S,
urethral muscle; 4, aponeurosis. The lumen of the urethra
is black and the shaded area around the urethral lumen ir
the stratum eavernosum.

em.) in length. They are commonly unsymmetrical in size and shape. Short
branches are often given off from the chief tube. The excretory duct opens at the
coUiculus seminalis, just lateral to the ductus deferens.

The structure of the vesicula is masked by a thick capsule of fibrous tissue and unstriped
muscle, which mamtains it in its bent condition and also sends trabeculse between the alveoU.
There is a central canal into which the secretion formed in the alveoli passes. The cavities (central
canal and alveoli) are lined with colunmar epithelium. On account of this structure the term
glandulse vesiculares is preferred by some anatomists.

GENITAL ORGANS OF THE BULL 589

The prostate is pale yellow in color, and consists of two parts, which are, how-
ever, continuous with each other. The body (Corpus prostatas) is a small mass
which stretches across the dorsal surface of the neck of the bladder and the origin
of the urethra. It measures about an inch and a half (ca. 3.5 to 4 cm.) transversely,
and about half an inch (ca. 1 to 1.5 cm.) in width and thickness. The pars dis-
seminata surrounds the pelvic part of the urethra; dorsally it forms a layer about
half an inch (ca. 10 to 12 mm.) thick, but ventrally it is quite thin (ca. 2 mm.).
It is concealed by the urethral muscle and its aponeurosis; hence it often escapes
notice, but is very evident on cross-section (Fig. 525). It has a branched tubular
structure, and the interlobular tissue contains a large amount of unstriped muscle.
The prostatic ducts open into the urethra in rows, two of which are between two
folds of the mucous membrane that proceed backward from the colliculus seminalis;
two other series occur on either side, lateral to the folds.

The uterus masculinus appears to be absent usually. Ellenberger states that
it opens between the ejaculatory orifices, while Martin says that it usually has two
orifices at the colliculus, but that it often unites with the ductus deferens.

The bulbo-urethral glands are somewhat smaller than in the stallion. They
are liable to escape notice, since they are covered by a thick layer of dense fibrous
tissue and also partially by the bulbo-cavernosus muscle. Each has a single duct
which opens into the urethra under cover of a fold of the mucous membrane.

The penis is cylindrical, and is longer and of very much smaller diameter than
in the horse. Just behind the scrotum it forms an S-shaped curve, the sigmoid
flexure; thus about one foot of the penis is folded up when it is fully retracted.
The flexure is effaced during erection. The glans penis is about three inches (ca.
8 cm.) in length. It is flattened dorso-ventrally, and its extremity is pointed and
twisted. The external urethral orifice is situated at the end of a groove formed
by this twist; it is only large enough to admit a probe of medium size. Even in
the non-erect state the penis is remarkably dense and firm. The tunica albuginea
is very thick, and encloses the urethra; it is composed of dense white fibrous tissue.
In the first part, as far as the first curve, there is a thick median septtun penis.
Beyond this there is a central axial band of dense fibrous tissue from which numerous
strong trabecules radiate. The erectile tissue is small in amount, except in the root,
so that the organ undergoes very little enlargement in erection, the chief effect
being increased rigidity. The walls of the cavernous spaces are fibro-elastic, not
muscular.

The length of the penis in the adult is about three feet (ca. 90 cm.). The crura are flattened
laterally; they contain a well-developed corpus cavernosum and numerous helicine arteries, some
of which open directly into the cavernous spaces. The suspensory ligaments are attached to the
ventral ridge on the symphysis pelvis. The body is somewhat flattened dorso-ventrally beyond
the first curve. The extremity of the glans is unsymmetrical, the urethral orifice being situated
ventro-laterafly. The glans contains only a thin superficial stratum of erectile tissue^ and hence
undergoes little enlargement in erection. In the body of the penis there is a longitudinal vein on
either side in the ventral part of the corpus cavernosum.

The bulbo-cavernosus muscle presents several remarkable features. It is for
the greater part an inch or more (ca. 3 cm.) in thickness, but its length is only
six to eight inches (15 to 20 cm.). It is covered by a strong aponeurosis, and is
divided by a median raphe into two lateral halves, except at its origin. It
diminishes in size from behind forward, and its anterior extremity is pointed.^

The ischio-cavemosus muscle resembles in general that of the horse, but is
flattened laterally. It is covered by a tight aponeurosis.

The retractor penis muscle resembles that of the horse in origin. Its two parts

iJn the sheep and sometimes in the ox there is a m. ischio-bulbosus which consists of fibers
that extend across the initial part of the bulbo-cavernosus. Fibers which extend from the ischial
arch over the bulbourethral gland form the m. ischio-glandularis. A urethro-cayernosus muscle
is sometimes present; it consists of fibers which arise on the urethra near the origin of the bulbo-
cavernosus and end on the latter and the ischio-cavemosus.

590

GENITAL ORGANS OF THE BULL

are about an inch (ca. 2 to 5 cm.) apart on the root of the penis, where they He
in a groove on either side of the bulbo-cavernosus. They then come close together
and pass on either side of the ventral curve of the sigmoid flexure. Further for-
ward they are on the ventral surface of the penis, and end about five or six inches
(ca. 12 to 15 cm.) behind the glans.

The prepuce is very long and narrow. Its orifice is about two inches (ca.
5 cm.) behind the umbilicus; it is only large enough to admit a finger readily, and
is surrounded by long hairs. The preputial cavity is about fifteen inches (35 to 40
cm.) long and a little over an inch (ca. 3 cm.) in diameter. The lining membrane
forms longitudinal folds; it is covered with squamous stratified epithelium, and
has coiled tubular glands. The penile layer is glandless, and is reddish in color.
It presents lymph nodules in its posterior part.

There are two pairs of preputial muscles which are derivatives of the cutaneus
muscle. The anterior preputial muscles or protractors of the prepuce (Mm.
prseputiales craniales) are two flat bands, two inches or more (5 to 6 cm.) in ^^ddth,
which arise close together in the xiphoid region, about eight inches (20 cm.) in

Processus urethroe

Galea glandis

Corona glandis
Collum glandis

Prepuce

Raphe
glandis

Processus urethrce
Galea glandis
Corona glandis

Tuherculum
Collum glandis

Prepuce
Raphe pra'putii

Fig. 526. — Anterior Part of Penis of Ram.
A, Right side; B. left side. (After Bohm.)

front of the preputial orifice. Traced backwartl they diverge, leaving the umbilicus
and an area about one and a half inches wide free, and then unite behind the pre-
putial orifice. They draw the prepuce forward. The posterior preputial muscles
or retractors of the prepuce (Mm. prseputiales caudales) arise in the inguinal region
and converge on the anterior part of the prepuce. They draw the prepuce back-
ward.^

The urethra in its pelvic part is about five inches (12 cm.) long, and is of
relatively small and uniform caliber. The urethral muscle encloses the tube
ventrally and laterally; it is very thick, crescentic in cross-section, and is covered
by an aponeurosis. Dorsally the aponeurosis is thick and the muscle absent.
Inside of these the pars disseminata of the prostate surrounds the urethra as far
back as the bulbo-urethral glands. The coUiculus semmaUs is a rounded promi-
nence about an inch (ca. 2.5 cm.) in length. On it there are two slit-like openings,
situated close together. These are the ejaculate ry orifices, at which the ductus
deferens and the excretory duct of the vesicula seminalis open. The urethral

^ These muscles are subject to a good deal of variation. The retractor may be absent. Many
fibers come m from the cutaneus on either side, dip under the protractor, and are inserted into
the skin just behind the preputial opening. The homologue of the protractor is present in the
cow.

GENITAL ORGANS OF THE BOAR 591

crest extends forward from the colliculus, and two mucous folds pass backward
from it and diverge. The mucous membrane behind the colHculus is red in color.
The extrapelvic part has an enlargement, the bulb, at its origin; it then gradually
diminishes in diameter, and is relatively very small at its termination. Other
features have been mentioned in preceding paragraphs.

The bulb of the urethra has a thick tunica albuginea, enclosing a highly developed erectile
tissue. The cavernous spaces are wide; their walls are relatively thin and consist of fibrous tis-
sue and unstriped muscle. On cross-section many arteries are visible laterally. Further forward
the urethra is surrounded by a well-developed corpus cavernosum, wjiich is thickest ventrally;
here an artery of considerable size occurs on each side.

In the ram the genital organs resemble in general those of the bull. But the
testicles are relatively much larger; a testicle of an adult ram may be four inches
(ca. 10 cm.) long and weigh about nine to ten ounces (ca. 250-300 gm.). They are
broader in proportion to their length. The prostate is entirely disseminate. The
bulbo-urethral glands are relatively very large. The peculiar character of the
terminal part of the penis is shown in the annexed figure. The urethra lies in a
groove on the ventral surface of the corpus cavernosum. Its terminal part pro-
jects commonly about an inch and a half (ca. 3-4 cm.) beyond the glans penis,
forming a twisted processus urethrse.

GENITAL ORGANS OF THE BOAR

The scrotum is situated a short distance from the anus, and is not so sharply
defined from the surrounding parts as in the other animals.

The testicles are very large and are regularly elliptical in contour. They are
placed so that the long axis is directed upward and backward, the free border being
superficial and the tail of the epididymis highest. They are comparatively soft in
texture. The tunica albuginea contains much elastic tissue, but no muscular fibers.
The mediastinum testis is an axial strand of fibro-elastic tissue, from which inter-
lobular septa radiate. Other septa are given off from the deep face of the tunica
albuginea. The interlobular tissue is abundant, and the lobulation correspond-
ingly distinct. The parenchyma is gray and often dark in fat animals. There is a
rete testis from which seven or eight efferent ducts proceed to the epididymis.
The epididymis is closely attached to the testicle; its tail is very large and forms a
blunt conical projection at the posterior end of the testicle.

The spermatic cord is necessarily very long (20 to 25 cm. in a boar of medium
size). The ductus deferens in its testicular part is flexuous, and is closely attached
by the tunica vaginalis; it forms no distinct ampulla. The cremaster extemus is
well developed, and extends to about the middle of the scrotal part of the tunic.

The vesiculae seminales are exceedingly large, and extend into the abdominal
cavity. They are three-sided pyramidal masses, are in apposition with each other
medially, and cover the posterior part of the bladder and the ureters, the ductus
deferentes, the body of the prostate, and the anterior part of the urethra and bulbo-
urethral glands. They are pale pink in color, distinctly lobate and glandular in
structure, and are enclosed in a thin fibrous capsule. Half a dozen or more large,
thin-walled ducts emerge from the medial surface of each and converge to a much
smaller excretory duct. The latter passes back lateral to the ductus deferens, and
terminates at a slit-like opening on the colliculus seminalis. The two ducts may
unite.

In the adult boar the vesiculse are about five to six inches (ca. 12 to 15 cm.) long, two to
three inches (ca. 5 to 8 cm.) wide, and one and a half to two inches (ca. 4 to 5 cm.) thick; they
weigh al)out 6 to 8 ounces each. They have a branched tubular structure and are distinctly di-

592

GENITAL ORGANS OF THE BOAR

vided into lobules. Many of the tubules are extremely wide (as much as 2 mm. in diameter), and
are lieset with bay-like extensions and short, wide branches. These axial spaces of the lobules are
succeeded by the efferent ducts. The cavities are lined by a single layer of columnar cells. The
secretion is thick and turbid, and has an acid reaction.

The prostate consists of two parts, as in the ox. The body is about an inch
(2.5 cm.) wide, and overHes the neck of the bladder and the urethra at their junc-
tion. It is concealed by the vesiculae seminales. The pars disseminata forms a
layer which surrounds the pelvic part of the urethra, and is covered by the urethral
muscle, except dorsally.

The uterus masculinus is small, and appears to be inconstant.
The bulbo-urethral glands are very large and dense. They are somewhat

cylindrical, and lie on either
side of and upon the posterior
two-thirds of the pelvic ure-
thra.^ In a large boar they
are about five inches (ca. 12
cm.) in length and an inch or
more (ca. 2.5 to 3 cm.) in
width. They are partially
covered with a layer of stri-
ated muscle (M. bulbo-glan-
dularis), and have a lobulated
surface. Each gland has a
large excretory duct which
leaves at the deep face of the
posterior part, perforates the
dorsal wall of the urethra at
the ischial arch, and opens in
a cul-de-sac covered by a fold
of mucous membrane.

It is to be noted that these
accessory glands are very small in
animals which have been castrated
early; the bulbo-urethral glands may
be only about an inch long in such
subjects.

The penis resembles in
general that of the ox. The
sigmoid flexure is, however,
prescrotal. The anterior part
has no glans, and is spirally
twisted, especially in erection.
The external urethral orifice is
slit-like and is situated ventro-
laterally, close to the pointed
extremity. The penis in the
adult boar measures about 18
to 20 inches (ca. 45 to 50 cm.) in length. Its muscles resemble those of the bull.
The bulbo-cavernosus is very strong but short. The retractor penis arises from
the third and fourth sacral segments; its two parts run backward and a little
ventrally on each side of the rectum to the perineum, where they reach the urethral
surface of the penis; they end on the ventral curve of the sigmoid flexure of the penis.

1 When hardened in situ, they are in great part three sided, with rounded edges. They are in
contact with each other to a considerable extent and cover the urethra dorsally and laterally. The
urethral muscle partly covers their lateral surfaces.

Fig. 527.— Genital Organs of Boar.
a, Testicle; b, epididymis; c, ductus deferens; d, spermatic artery;
e, vesicula seminalis; e', excretory ducts of vesiculae; /, body of prostate;
g, bulbo-urethral gland; h, urinary bladder; i, urethral muscle; k,
bulbo-cavernosus muscle; /, penis; I', sigmoid flexure of penis; I",
spiral anterior part of penis, exposed by slitting open prepuce; m, ori-
fice of preputial pouch; re, retractor penis muscle. The vesiculae sem-
inales are drawn outward to show the structures which, in the natural
position, are covered by them. (Ellenberger-Baum, Anat. d. Haustiere.)

MALE GENITAL ORGANS OF THE DOG 593

The prepuce has a narrow orifice, around which there are stiff hairs. The
cavity is very long, and is partially divided by a circular fold into a posterior narrow
part and a much wider anterior part. The lining membrane of the posterior part is
papillated, and is in close contact with the penis; it contains numerous lymph
nodules, the largest of which occur in the fundus. In the dorsal wall of the wide
part there is a circular opening which leads into a cul-de-sac, the preputial diver-
ticulum. This pouch is ovoid in form (when distended), and varies greatly in size
in different subjects. It extends for the most part backward over the narrow part
of the prepuce. Its cavity is partially divided by a narrow septum. It contains
usually decomposing urine and macerated epithelium, which have a characteristic
and very unpleasant odor. Concrements have been found in it.

Oehmke found that a cast of the pouch in a Yorkshire boar weighing about 500 pounds
measured 9 cm. in length, 12J^ cm. in breadth, and 6 cm. in height. The opening into the pre-
puce will admit two fingers in the adult, but is ordinarily closed by folds of the lining membrane.
The sac is much smaller in animals which were castrated young, and the opening is vertical and
further back ; in them it is often empty or contains only a Httle clear urine. The pouch is gland-
less, but contains many small lymph nodules; it is covered by a layer of striped muscle which is
mainly derived from the homologue of the protractor of the prepuce of ruminants.

The urethra has a very long pelvic part (ca. 15 to 20 cm. long in the adult);
it is covered (with the pars disseminata of the prostate) by a thick urethral muscle,
except dorsally, where there is a dense fibrous layer. Surrounding the mucous
membrane there is a rich venous plexus, which is regarded as a stratum cavernosum.
Outside of this the pars disseminata of the prostate is easily distinguished on cross-
section by its yellow color. The prostatic ducts are numerous and small. The
ductus deferentes and the excretory ducts of the vesiculae seminales have slit-like
openings close together in small diverticula on either side of the colliculus seminalis.
The latter has the form of a round prominence. A small uterus masculinus may
occur in the colliculus between the ducts, but it is often absent. There is a distinct
bulb at the root of the penis. It has a dense covering, which in part resembles
fibro-cartilage. The erectile tissue here is highly developed. The cavernous
spaces are large, and the trabeculse contain much unstriped muscle; between the
spaces there are numerous arteries. The penile part is of small caliber, and is
surrounded by erectile tissue which, however, does not extend to the extremity of
the penis.

MALE GENITAL ORGANS OF THE DOG

The scrotum is situated about half way between the inguinal region and the
anus. The skin covering it is pigmented and is covered sparsely with fine hairs.
The raphe is not very distinct.

The testicles are relatively small, and have a round-oval form. The long
axis is oblique, and is directed upward and backward. The mediastinum testis
is central and is well developed. The epididymis is large, and is closely attached
along the dorsal part of the lateral surface of the testicle.

The spermatic cord and the tunica vaginalis are long; they cross the side of
the penis verj^ obliquely. The upper end of the tunic is sometimes closed, so that
there is then no vaginal ring. The ductus deferentes have narrow ampullae.

The vesiculae seminales are absent.

The prostate is relatively large; it is yellowish in color, dense in structure,
and lies at or near the anterior border of the pubis. It is globular, and surrounds
the neck of the bladder and the urethra at their junction. A median furrow indi-
cates a division into two lateral lobes. The capsule and stroma contain a large
amount of unstriped muscle. The ducts are numerous. Lobules of prostatic
38

594

MALE GENITAL ORGANS OF THE DOG

tissue (pars disseminata) are also found in the wall of the urethra for a short distance
further back. The gland is subject to much variation in size, and is often enlarged,
especially in old subjects.

The position of the prostate varies. When the bladder is empty and contracted, the gland
is entirely in the pelvic cavity and may be an inch or more behind the anterior border of the
pubis. When the bladder is full, the prostate is often largely or entirely prepubic.

The uterus masculinus is a small compressed saccule in the colliculus seminalis.

The bulbo-urethral glands are absent.^

The penis presents several special features. In its posterior part there are two
distinct corpora cavernosa, separated by a median septum penis. In its anterior
part there is a bone, the os penis, which in large dogs reaches a length of four inches
(ca. 10 cm.) or more. It is regarded as a part of the corpus cavernosum which has

Fig. 528. — External Genital Organs of Male Dog; Ventro-
lateral View of Preparation.
1, Scrotum; ?', tunica vaginalis; 2, epididymis; S, vascular
part of spermatic cord ; 4, ductus deferens; 5, prepuce; 5,'pars longa
glandis; 6', corpus cavernosum penis; 7, bulbus glandis; 7', con-
tour of bulbus in erection; 8, ischio-cavernosus muscle; a, acetab-
ulum; 6, obturator foramen. (After Ellenberger, in Leisering's
Atlas.)

Fig. 529. — Internal Genital Organs of
Male Dog; Dorsal View.
1, Urinary bladder; 2, ureter; 3, ductus
deferens; 4, prostate; 5, urethral muscle; 6,
bulb of urethra; a, abdominal wall; b, ilium;
c, ischium. (After Ellenberger, in Leisering's
Atlas.)

ossified. Ventrally it is grooved for the urethra; dorsally it is convex, and an-
teriorly it becomes smaller and has a curved fibrous prolongation.^ The glans
penis is very long, extending over the entire length of the os penis; its anterior
part, the pars longa glandis, is cylindrical, with a pointed free end; behind this
there is a rounded enlargement, the bulbus glandis. Both are composed of erectile
tissue. The two dorsal veins arise from the bulbus glandis, pass backward on the
dorsum penis, and unite at the ischial arch. A small muscle (M. compressor venae
dorsalis penis) arises from the tuber ischii on either side; the two converge on the
dorsum penis near the bulbus glandis. They compress the dorsal veins, and may
also tend to elevate the penis and thus assist in copulation. The other muscles
offer no features worthj^ of special description.

1 They are present in the cat, and are the size of a pea.

2 In the young subject it has a prolongation composed of hyaline cartilage, which becomes
fibrous later.

MALE GENITAL ORGANS OF THE DOG 595

The cavernous spaces of the glans penis are venous in character. Von Frey has shown that
the spaces of the pars longa are continuous with veins which come from the penile layer of the pre-
puce, and have no arterial blood supply. The erectile tissue of the bulbus glandis receives its
blood by veins which come from the pars longa. This arrangement is considered to account for
the erection of the bulbus during copulation, and the slowness with which erection subsides.

The prepuce forms a complete sheath around the anterior part of the penis.
The outer layer is ordinary integument. The inner layers are thin, reddish in
color, and glandless. The penile layer is closely attached to the pars longa glandis,
more loosely to the bulbus glandis. There are many lymph nodules in these layers,
which are specially large and often prominent in the fundus of the preputial cavity.
The protractor muscles arise in the xiphoid region and decussate posteriorly around
the extremity of the prepuce.

The pelvic part of the urethra is relatively long. Its first part is enclosed in
the prostate.^ At the ischial arch the urethra has a well-developed bulb, formed
by an enlargement here of the corpus cavernosum urethrse. It is divided by a
median furrow and septum (Septum bulbi urethrse) into two lateral lobes or hemis-
pheres (Hemispheria bulbi urethrse), and is covered by the strong but short bulbo-
cavemosus muscle. The other erectile bodies have been described. The urethral
muscle is very strong; it encircles the urethra from the prostate backward and has
a median raphe dorsally. The ischio-urethral muscle arises from the tuber ischii
and ends on a fibrous ring at the symphysis ischii which encircles the dorsal veins
of the penis.

1 This is clinically important, since enlargement of the prostate may interfere with mic-
turition.

THE FEMALE GENITAL ORGANS

The female genital organs (Organa genitalia feminina) are: (1) The two
ovaries, the essential reproductive glands, in which the ova are produced; (2)
the uterine or Fallopian tubes, which convey the ova to the uterus; (3) the uterus,
in which the ovum develops; (4) the vagina, a dilatable passage through which the
foetus is expelled from the uterus; (5) the vulva, the terminal segment of the genital
tract, which serves also for the expulsion of the urine; (6) the mammary glands,
which are in reality glands of the skin, but are so closely associated functionally
with the generative organs proper that they are usually described with them.

GENITAL ORGANS OF THE MARE

THE OVARIES

The ovaries (Ovaria) of the mare are bean-shaped, and are much smaller
than the testicles. Their size varies much in different subjects, and they are

Fig. 530. — Lateral View of Genital Organs and Adjacent Structures of Mare.
It is to be noted that the removal of the other abdominal viscera has allowed the ovaries and uterus to sink down;
this has, however, the advantage of showing the broad ligaments of the uterus. 1, Left ovary; 2, uterine or Fallopian
tube; 3, left cornu uteri; 4, right cornu uteri; 5, corpus uteri; S', portio vaginalis uteri, and 5", os uteri, seen through
window cut in vagina; 6, broad ligament of uterus; 6", round ligament of uterus; 7, vagina; S, labia vulvae; 9, rima
vulvae; 9', dorsal commissure, and 9", ventral commissure, of vulva; 10, constrictor vulvae; 11, position of vestibular
bulb; 13, ventral wall of abdomen; 13, left kidney; 14, left ureter; IS, urinary bladder; 16, urethra; 17, rectum;
18, anus; 19, 19', unpaired and paired parts of sphincter ani externus; 20, retractor ani cut at disappearance under
sphincter ani externus; 21, suspensory ligament of anus; 22, longitudinal muscular layer of rectum; 22', recto-coocygeus;
23, constrictor vaginae; a, utero-ovarian artery, with ovarian (a') and uterine (a") branches; 6, uterine artery; c, um-
bilical artery; d, ischium; e, pubis; /, ihum. (After EUenberger, in Leisering's Atlas.)

normally larger in young than in old animals; one ovary is often larger than the
other. They are about three inches (ca. 7 to 8 cm.) long and an inch to an inch

596

THE OVARIES

597

and a half (ca. 3-4 cm.) thick. The weight is about two and a half to three
ounces (ca. 70-80 grams).

Each presents for description two surfaces, two borders, and two extremities.
The surfaces are termed medial and lateral (Facies medialis, lateralis); they are
both smooth and rounded. "^ The attached or mesovarial border (Margo mes-
ovaricus) is convex. It is enclosed in a part of the broad ligament termed the mes-
ovarium; the vessels and nerves reach the gland at this border. The free border
(Margo liber) is marked by a notch which leads into a narrow depression, the
ovulation fossa. The tubal or anterior extremity (Extremitas tubaria) is rounded,
and is related to the fimbriated end of the uterine
tube. The uterine or posterior extremity (Extremitas
uterina) is also round, and is connected with the horn
of the uterus by the ovarian ligament.

The ovaries are situated in the sublumbar region,
and are usually ventral to the fourth or fifth lumbar
vertebra. They are usually in contact with the lum-
bar wall of the abdomen. The average distance from
the ovaries to the vulvar orifice is about twenty to
twenty-two inches (ca. 50-55 cm.) in a mare of
medium size.

The position of the ovaries is very iBconstant, as might
be expected from their mode of attachment. Either ovary or
both may be deflected transversely in either direction to the
full limit allowed by the mesovarium. The so-called medial
and lateral surfaces are usually dorsal and ventral, or vice
versa, according to the direction of the deflection. The range
of variation in the longitudinal direction is greater than was
formerly thought to be the case. The right ovary is often
about six inches (ca. 15 cm.) behind the corresponding kid-
ney, but the distance between them may be nearly twice as
great or may be only about two inches (ca. 5 cm.). The left
ovary is usually a little (ca. 2-3 cm.) further back than the right
one, but is usually nearer the corresponding kidney, the average
distance between them being about four inches (ca. 10 cm.).
They may be about two inches (ca. 5 cm.) from the extremity
of the corresponding cornu of the uterus or in contact with it.
Except during pregnancy, they are almost always in contact
with the lumbar abdominal wall, and do not hang down among
the adjacent viscera.

Fig. 531. — Right Ovart of Mare,
WITH Adjacent Structures.
The extremity of the cornu is
opened. 1, Ovary; 1', corpus luteum;
2, uterine or Fallopian tube, with its
ostium abdominale (3'), fimbrise (2"),
and ostium uterinum (^'") ; 3, cornu
uteri with its mucous lining (3') ex-
posed; 4, ligament of ovary; 4\ meso-
salpinx. (After Ellenberger, in Leiser-
ing's Atlas, reduced.)

The ovary is attached to the sublumbar region
by the anterior part of the broad ligament of the
uterus; this part of the ligament, the mesovariiun,
is about three or four inches (ca. 8 to 10 cm.) wide,
measured from the ovary directly to the parietal at-
tachment. The uterine extremity of the ovary is
connected with the extremity of the cornu of the
uterus by the ligament of the ovary (Lig. ovarii pro-

prium) ; this is a band of unstriped muscle enclosed between the layers of the broad
ligament.

Structure. — The greater part of the surface of the ovary has a covering of
peritoneum. The peritoneal investment is absent at the attached border where
the vessels and nerves enter; this area is termed the hilus of the ovary (Hilus
ovarii), although there is no depression here. The ovulation fossa is covered by
a layer of short polygonal cells, a remnant of the primitive germinal epithelium.

^ These terms apply properly only when the adjacent viscera are removed and the ovaries
are actually "suspended" by the broad ligaments. When the ovary is in its natural position,
the surfaces are usually dorsal and ventral, the former corresponding to the "lateral" surface if the
free border is directed outward, to the "medial" if the free edge is medial.

598

GENITAL ORGANS OF THE MARE

The stroma of the ovary (Stroma ovarii) is a network of connective tissue. In the
meshes of the stroma there are (in young subjects) numerous ovisacs or folliculi
oophori, containing ova (Ovula) in various stages of development. The immature
ovum is surrounded by foUicle cells; those more advanced in development are
enclosed by several (5-8) layers of follicle cells, forming the stratum granulosum, and
by a condensation of the stroma termed the theca folliculi; ^\^thin the theca is a
quantity of fluid, the liquor folliculi. At one point the follicle cells are heaped up as
a sort of mound (Cumulus oophorus), in which the ovum is enclosed. Such sacs
are termed folliculi oophori vesiculosi;^ they enlarge as they mature, becoming
visible to the naked eye as vesicles Avith a diameter of a centimeter or more. When
fully developed, the follicles are superficially situated, and often project slightly
from the surface of the ovary. At intervals follicles rupture and their contents
escape. This process, which sets free the ovum, is termed ovulation ; it

takes place in the mare only
at the ovulation fossa, and
occurs during the periods of
oestrum.

The structure of the ovarj' of
the mare is peculiar and differs from
that of other animals in the fact
that it does not consist of a cortex
(zona parenchymatosa), in which
the follicles are situated, and a me-
dulla (zona vasculosa), which con-
tains the vessels and nerves. This
arrangement is present in the foetus,
but later the follicles become dis-
tributed throughout the interior of
the gland, and the vascular zone is
superficial.

After rupture of a follicle, its
cavity is partly occupied by a blood-
clot, constituting what may be
termed a corpus rubrum. By prolif-
eration and enlargement and fatty
changes, the follicle cells are trans-
formed into lutein cells, forming a
yellow mass knowni as a corpus lu-
teum. If impregnation takes place,
the accompanying increase in vas-
cularity of the organs may cause
the corpus luteum to reach a large
size; if impregnation does not oc-
cur, it is much smaller, and is
sooner replaced by scar tissue, form-
ing the corpus albicans s. fibrosiun.
In the new-boni foal the ovaries are large and oval in form. The free l^order is convex and
is covered by germinal epithelium, which extends over a large part of the surfaces also. This area
is distingiiishable by its dull gray appearance from the peritoneal siu-face, which has the usual
smooth glistening character. The hmit of the peritoneal epithelium is a distinct line, termed by
Waldeyer the margo limitans peritonsei. As growth proceeds the ovary gradually becomes bent
until it assumes its definitive curved shape. The germinal epithelium is then limited to the o\ni-
lation fossa. The ovary migrates somewhat during development from its primitive position,
which is the same as that of the testicle.

Fig. 5.32. — Schematic Represent.\tion of Changes in Ovary of
Mare from FfETAL to Adult State. (After Born.)
The changes affect chiefly the free border (upper in figure) and
the extent and form of the area covered by germinal epithelium (4).
1, Peritoneum (broad ligament); 2, ligament of ovary; 3, fimbria of
uterine tube; 4. germinal epithelium; o, vessels, which reach the
ovarj- at the attached border (6). The latter represents the hikus,
while the deep depression at the free border is the ovulation fossa.
(Ellenberger, in Leisering's Atlas.)

In old animals the ovaries commonly consist largely of fibrous tissue, in which
there are often cysts of various sizes. The ova, present in enormous number at
birth, have then been extruded, or destroyed by phagocytic action or degeneration.

Vessels and Nerves. — The arteries of the ovary are derived from the ovarian
artery. The artery is relatively large and is flexuous; it reaches the attached
border of the ovary by passing between the layers of the mesovarium. The veins
are large and numerous. They form a plexus somewhat like that of the spermatic

'■ Also known as Graafian follicles.

THE UTERINE TUBES THE UTERUS 599

cord. The lymph vessels pass to the lumbar glands. The nerves are derived from
the sympathetic system through the renal and aortic plexuses. They accompany
the arterial branches.

THE UTERINE TUBES

The uterine or Fallopian tubes (Tubse uterinse) act as excretory ducts of the
ovaries, since they convey the ova from the reproductive glands to the uterus.
They are not, however, in direct continuity with the glands, but rather partly in
contiguity with, and partly attached to, them.^ They are two flexuous tubes,
eight to twelve inches (ca. 30 to 20 cm.) long, which extend from the extremities
of the uterine cornua to the ovaries. The tube is very small at its uterine end
(ca. 2-3 mm. in diameter), but toward the ovary it widens considerably (4-8 mm.
in diameter), forming the ampulla tubae. Each is enclosed in a peritoneal fold,
derived from the lateral layer of the broad ligament, and termed the mesosalpinx.
This largely covers the lateral aspect of the ovary, and forms with it and the broad
ligament a pouch called the bursa ovarica. The uterine extremity (Extremitas
uterina) of the tube communicates with the cavity of the cornu by a minute orifice,
the ostium uterinum tubae. The ovarian extremity is expanded and somewhat
funnel shaped, and is therefore termed the infundibulum tubae uterinae. The
margin of the latter is slit into irregular processes, the fimbriae, some of which, the
fimbriae ovaricae, are attached in the ovulation fossa. About the middle of the
infundibulum is a small opening, the ostium abdominale tubae, by which the tube
communicates with the peritoneal cavity. The ovarian extremity of the tube
appears normally to be applied to the ovary, so that the extruded ova pass into it
and are conveyed to the uterus.^

Pedunculated cysts, the hydatides terminales,^ are often found on one or more of the
fimbriae. In the mesosalpinx are blind flexuous tubules, which constitute the paroophoron, a
remnant of the Wolffian body. They are most evident in the young adult, and tend to disappear
with increasing age. Not uncommonly they give rise to cysts.

Structure. — The tube is covered externally by a serous coat formed by the
mesosalpinx. The serous membrane is continued on the fimbriae, and meets the
mucous lining on them. The fibrous adventitia is [continuous with the fibrous
lamina of the broad ligament. The muscular coat consists chiefly of circular
fibers, outside of which there are longitudinal fibers derived from the broad liga-
ment; the thickness of the muscular coat diminishes toward the ovarian extremity.
The mucous coat is thin and is much plicated. The folds (Plicae tubariae) are
chiefly longitudinal, but in the wide part of the tube (Ampullse tubae) they are very
complex, so that on cross-sections the spaces between the folds may be mistaken for
branched tubular glands. The folds are continued on to the fimbriae. The epithe-
lium is a single layer of columnar ciliated cells, the cilia producing a current directed
toward the uterus. At the ovarian extremity this epithelium passes gradually into
the squamous type of the serous coat.

Vessels and Nerves. — The arteries are derived from the utero-ovarian artery.
The veins are satellites of the arteries. The lymph vessels pass with the ovarian
vessels to the lumbar glands. The nerves have a similar origin to those of the
ovary.

THE UTERUS

The uterus is a hollow muscular organ, which is continuous with the uterine
tubes anteriorly and opens into the vagina posteriorly. It is situated chiefly in the

^ The tubes may be regarded, both in origin and structure, as prolongations of the uterus.

^ The arrangement is the only exception to the general rule that the serous cavities are
closed. In this case the mucous membrane of the infundibulum is continuous with the adjacent
peritoneum, a persistence of the embryonic relations of the Miillerian duct.

^ Also kno^\-n as hydatids of Morgagni.

600

GENITAL ORGANS OF THE MARE

abdominal cavity, but extends a short distance into the pelvic cavity. It is at-
tached to the sublumbar region and the lateral walls of the pelvic cavity by two
folds of peritoneum termed the broad ligaments. It consists of two horns, the body,
and the neck.

The horns or comua of the uterus (Cornua uteri) are situated entireh^ in
the abdomen. They appear to vary considerably in position; commonly they
are pressed up against the sublumbar muscles by the intestine (caecum, left parts of

Fig. 533. — Genital Orgaxs of Mare; Dorsal View
The left horn and adjacent part of the body of the uterus and the vagina and vulva are opened up. /, Ovary; S,
uterine tube, with^', its ovarian end; 3, cavity of body of uterus; 4, cavity of left horn; 5, right horn, with 5', its com-
munication with the body; e, portio vaginalis uteri; 6', external orifice of uterus; 7, broad ligament of uterus; 5, liga-
ment of ovarj-; 9, vagina; 10, vulva; 10', orifices of ducts of glandulae vestibulares majores; 10", orifices of ducts of
glandute vestibulares minores; 11, transverse fold; 12, external urethral opening; 13, 13', labia vulvse; 14, glans
clitoridis; 14', junction of crura to form corpus chtoridis indicated by dotted lines; lo, urinary bladder; a, utero-
ovarian artery with ovarian (a') and uterine (o") branches; b, middle uterine artery. (After Ellenberger, in Leisering's
Atlas.)

large colon, small colon, and small intestine). They are cjdindrical when moder-
ately distended, and are about ten inches (ca. 25 cm.) in length. The anterior
extremity of each forms a blunt point which receives the uterine tube. Posteriorly
they increase somewhat in caliber, converge, and unite A\dth the body. The dorsal
border (Margo mesometricus) is slightly concave and is attached to the sublumbar
region by the broad ligament. The ventral border (Margo liber) is convex and free.

When a soft uterus is distended, its horns are strongly curved, but this does not represent
the natural form. When fixed in situ, the horns are either sUghtly curved or nearly straight.

THE UTERUS 601

The two horns are commonly unsymmetrical in length and diameter in mares which have borne
young.

The body of the uterus (Corpus uteri) is situated partly in the abdominal,
partly in the pelvic, cavity. It is cylindrical, but considerably flattened dorso-
ventrally, so that in cross-section it is elliptical. Its average length is seven or
eight inches (ca. 18-20 cm.), and its diameter, when moderately distended, about
four inches (10 cm.). Its dorsal surface (Facies dorsalis) is related to the rectum
and other parts of the intestine. Its ventral surface (Facies ventralis) is in contact
with the bladder, and has inconstant relations with various parts of the intestine.
The term fundus uteri is applied to the wide anterior part from which the cornua
diverge.

The position of the body of the uterus is variable, especially in regard to its anterior part.
It is often pressed up against the rectum, and may be deflected to either side — most frequently
to the left — by the pelvic flexure of the great colon or coils of the small colon.

The neck or cervix of the uterus (Cervix uteri) is the constricted posterior
part which joins the vagina. It is about two to three inches (5-7.5 cm.) in length,
and an inch and a half (3.5-4 cm.) in diameter. Part of it (Portio vaginalis uteri)
projects into the cavity of the vagina; it is therefore not visible externally, but
may be felt through the vaginal wall.

Attachments. — The body and horns are attached to the abdominal and pelvic
walls by two extensive peritoneal folds, the broad ligaments of the uterus (Liga-
menta lata uteri) . These extend on either side from the sublumbar region and the
lateral pelvic walls to the dorsal border of the cornua and the lateral margins of the
body of the uterus. They contain the vessels and nerves of the uterus and ovaries,
connective tissue, and a large amount of unstriped muscular fibers which are con-
tinuous with those of the uterus. The ureters are situated along their parietal
margins. The lateral layer of each gives off a fold, the round ligament of the uterus
(Ligamentum teres uteri), which blends with the parietal peritoneum over the
abdominal inguinal ring; its anterior extremity is situated above the extremity of
the cornu and forms a long round appendix. It contains muscular tissue, vessels,
and nerves, and is the homologue of the gubernaculum testis. The anterior part of
the neck is continuous with the vagina, and thus has a more fixed position than the
rest of the organ.

The cavity of the uterus (Cavum uteri) is largely obliterated in the non-
pregnant state by the contraction of the wall and by folds of the mucous lining.
At the extremity of each cornu it communicates with the uterine tube by a minute
opening on a small papilla. The cavity of the neck is termed the cervical canal
(Canalis cervicis); it is closed ordinarily by mucous folds and a plug of mucus.
It opens into the vagina by the orificiiun externum uteri,^ and into the body by the
orificium internum uteri.

Structure. — The wall of the uterus consists of three coats. The serous coat
(Perimetrium) is, for the most part, closely adherent to the muscular coat. It is
continuous with the broad ligaments. The muscular coat consists essentially of
two layers, a thin external stratum of longitudinal fibers, and a thick internal layer
of circular fibers. Between these is a very vascular layer (Stratum vasculare) of
connective tissue with circular and oblique muscular fibers in it. The circular coat
is very thick in the neck, where it forms a sphincter half an inch or more (ca. 1.5 cm.)
in thickness. The mucous membrane rests directly on the muscular coat, and is
brownish-red in color, except in the neck, where it is pale. It is covered by a single
layer of high columnar cells, and contains numerous long, branched tubular uterine
glands (Glandulse uterinae) ; these are absent in the cervix.

Vessels and Nerves. — The chief arteries are the uterine and the uterine
branch of the utero-ovarian, which have a flexuous course in the broad ligaments;
^ This is frequently desigiiated the os uteri.

602 GENITAL ORGANS OF THE MARE

there is also a branch from the internal pudic artery. The veins form pampini-
form plexuses and accompany the arteries. The lymph vessels are numerous and
go to the internal iliac and lumbar glands. The nerves are derived from the
sympathetic through the uterine and pelvic plexuses.

The foregoing statements refer to the non-gravid uterus. In the pregnant state it under-
goes important changes in size, position, and structure. The increase in size affects chiefly the
gravid horn (except in the case of twins) and the body. The horn attains a length of about
two and a half to three feet (ca. 80 to 90 cm.), and a corresponding diameter; in this process it
extends much beyond the ovary and the broad ligament. The gravid uterus is entirely abdominal
in position, and extends along the ventral wall, chiefly to the left of the median plane. It weighs
about nine pounds (ca. 4 kg.), according to Ellenberger. The broad ligaments increase greatly
in size and contain more muscular tissue. The vessels are greatly enlarged and form new branches.
The muscular coat, in spite of the increase in size and number of the fibers, is somewhat thinner,
except in the neck. The mucous membrane is thicker and more vascular.

THE VAGINA

The vagina is the passage which extends horizontally through the pelvic
cavity from the neck of the uterus to the vulva. It is tubular, is about six to eight
inches (ca. 15-20 cm.) in length, and, when slightly distended, about four or five
inches (ca. 10-12 cm.) in diameter. Its dilatability appears to be limited only by
the pelvic wall. There is no external line of demarcation between the vagina
and the uterus or the vulva.

It is related dorsally to the rectum, ventrally to the bladder and urethra, and
laterally to the pelvic wall. The recto-genital pouch of the peritoneum commonly
extends between the vagina and rectum for a distance of about two inches (5 cm.),
and ventrally the vesico-genital pouch passes backward somewhat further between
the vagina and bladder. Thus most of the vagina is retroperitoneal and is sur-
rounded by a quantity of loose coimective tissue, a venous plexus, and a variable
amount of fat.^

Structure. — With the exception of the short peritoneal part, as indicated above,
the proper wall of the vagina is composed of muscular and mucous coats. The
muscular coat is composed of a thin layer of longitudinal fibers, and a thicker layer
of circular fibers; it is covered externally by a fibrous adventitia, and there is a
large amount of intermuscular connective tissue. The mucous coat is highly
elastic, and is covered with a stratified — but not squamous^ — epithelium. It has
no glands.

Under usual conditions the cavity is practically obliterated b}^ apposition of
the walls, so that the lumen is a transverse slit; this condition is pronounced when
the rectum is full. The anterior end of the vagina is largely occupied by the intra-
vaginal part of the neck of the uterus, so that the cavity is here reduced to an an-
nular recess termed the fornix vaginae. The posterior part is directly continuous
with the vulva without anj^ line of demarcation except the transverse fold which
covers the external urethral orifice; in ver}^ young sul^jects this fold is continued
on either side, forming the hymen, which narrows the entrance to the vagina (In-
troit us vaginae) .-

Vessels and Nerves. — The arteries are branches of the internal pudic arteries.
The veins form a rich plexus which is drained by the internal pudic veins. The
lymph vessels go to the internal iliac lymph glands. The nerves are derived from
the sympathetic through the pelvic plexus; numerous ganglia are present in the
adventitia.

^The amount of the vagina which is covered by peritoneum varies, depending apparently
on the degree of fullness of the rectum and bladder. When these organs are empty, the peritoneum
may cover the vagina for a distance of three or four inches (ca. S-10 cm.); when they are full, the
vagina may be completely retroperitoneal or nearly so.

2 In formalin-hardened subjects there is frequently a pronounced ring-like constriction at the
junction of the vulva and vagina.

THE VULVA 603

THE VULVA

The vulva or urogenital sinus (Vestibulum vaginae) is the terminal part of the
genital tract. ^ It is continuous in front with the vagina, and opens externally at
the vulvar cleft below the anus. There is no external line of demarcation between
the vagina and vulva. The tube is four or five inches (ca. 10-12 cm.) in length,
measured from the external urethral orifice to the ventral commissure; dorsally
(from a point vertically opposite to the external urethral orifice) it is considerably
shorter. It is related dorsally to the rectum and anus, ventrally to the pelvic floor,
and laterally to the sacro-sciatic ligament, the semimembranosus muscle, and the
internal pudic artery. The external orifice, the vulvar cleft (Rima vulvae), has the
form of a vertical slit, four or five inches (ca. 10-12 cm.) high, and is margined
by two prominent rounded lips, the labia vulvae. The labia meet above at an acute
angle, forming the dorsal commissure (Commissura dorsalis), which is about two
inches (ca. 5 cm.) below the anus. They unite below to form the thick, rounded
ventral commissure (Commissura ventralis), which lies about two inches (ca. 5 cm.)
behind and below the ischial arch. When the labia are drawn apart, a rounded
body, about an inch (ca. 2.5 cm.) wide, is seen occupying a cavity in the ventral
commissure; this is the glans clitoridis, the homologue of the glans penis, and the
cavity in which it lies is the fossa clitoridis. The roof of the fossa is formed by a
thin fold, which overlies the glans clitoridis and is attached centrally to it. At
the anterior extremity of the ventral wall of the vulva, i. e., four or five inches (ca.
10-12 cm.) from the ventral commissure, is the external urethral orifice (Ori-
ficium urethrge externum).^ It readily admits the finger and is very dilatable. It
is covered by a fold of mucous membrane, the free edge of which is directed back-
ward (Fig. 533).

Structure. — The labia are covered by thin, pigmented, smooth skin, which is
richly supplied with sebaceous and sweat glands. This is continuous at a distance
of about half an inch (ca. 1-1.5 cm.) from the free edge with a thin, glandless
mucous membrane. Under the skin there is a layer of striped muscle, the con-
strictor vulvae; this fuses above with the sphincter ani, and embraces the clitoris
below, spreading out laterally at the ventral commissure. It constricts the vulvar
orifice and elevates the clitoris. The constrictor vestibuli muscle embraces the
vulva in front of the preceding; it is deficient dorsally and is joined on either side
by a band of unstriped muscle, the suspensory ligament of the anus. It constricts
the vulva. Within this there is an unstriped muscular coat, most of the bundles
of which are circular. Chiefly between this coat and the mucous membrane there
is in the lateral wall, just in front of the labia, a flattened, oval body, the bulbus
vestibuli (Fig. 578); this is an erectile structure, homologous with the corpus
cavernosum urethrae of the male. It is about two and a half to three inches (ca.
6-8 cm.) long, and an inch or more (ca. 3 cm.) wide. It is similar in structure to
the bulb of the corpus cavernosum urethrae of the male, and is supplied with blood
by a large branch of the internal pudic artery. The mucous membrane of the
vulva is reddish in color, and forms longitudinal and transverse folds. It presents
ventrally two linear series of small papillae which converge toward the ventral
commissure; these mark the orifices of the ducts of the glandulae vestibulares
minores. On either side of the dorsal wall is a group of eight to ten larger promi-
nences on which the ducts of the glandulae vestibulares majores open (Fig. 533).

Quite exceptionally there may be found on either side of the urethral orifice the openings of
the canals of Gartner (Ductus epoophori longitudinales) .

1 The term vulva is used here in the sense in which it is understood generally by English
and French veterinarians. In the German works it is applied only to the labia and other struc-
tures around the external orifice of the urogenital sinus, while the sinus itself is termed the vestibule
of the vagina (Vestibulum vagina*).

^ Also termed the meatus urinarius.

604 GENITAL ORGANS OF THE MARE

The clitoris is the homologue of the penis and consists of similar parts (minus
the urethra and its muscle). The corpus clitoridis is about two inches (ca. 5 cm.)
long, and its diameter about that of one's little finger. It is attached to the ischial
arch by two crura (Crura clitoridis). The glans clitoridis is the rounded and en-
larged free end of the organ which was noted above as occupying the fossa clitoridis
in the ventral commissure of the vulva. It is covered by a thin pigmented integu-
ment, similar to and continuous with that which lines the fossa; these constitute
the prepuce of the clitoris (Praeputium clitoridis) . The organ is composed of erectile
tissue similar to the corpus cavernosum penis. The ischio-cavemosus is the
homologue of the muscle of the same name of the male; it is a very feeble muscle.
The veins of the clitoris communicate by an intermediate plexus on either side with
the bulbus vestibuli.

THE FEMALE URETHRA

The female urethra (Urethra feminina) represents only that part of the canal
of the male which lies between the internal urethral orifice and the colliculus semi-
nalis. Its length is two to three inches (5-7.5 cm.), and its lumen is sufficient to
allow easily the introduction of the finger; it is, however, capable of remarkable
dilatation if sufficient care and patience are exercised in the process. It lies centrally
on the pelvic floor, and is related dorsally to the vagina, to which it is in part at-
tached. The external orifice is at the anterior end of the vulva, as described above.

Structure.— The intrinsic muscular coat consists of external longitudinal and
internal circular fibers; it is absent where the urethra is attached to the vagina.
The mucous membrane is thrown into longitudinal folds when the canal is closed;
it is highly elastic, and is covered with stratified epithelium. There is a rich sub-
mucous network of veins, forming a sort of corpus cavernosum.

The urethral muscle (M. compressor urethrae) embraces the urethra and is
continuous with the constrictor vestibuli. It is covered by a fibro-elastic membrane.

THE MAMMARY GLANDS

The mammary glands (Glandulse lactiferse) are modified cutaneous glands
which are so closely associated functionally with the genital organs as to be con-
sidered accessory to them.

In the mare they are two in number, and are placed on either side of the median
plane in the inguinal region. Each gland has the form of a very short, flattened
cone, much compressed transversely, and having a flat medial surface. It consists
of the glandular mass or body of the gland (Corpus mammae) and the papilla or
teat (Papilla mammae). The base is related to the abdominal wall, to which it is
attached by areolar tissue, which contains a venous plexus, the superficial inguinal
Ijnnph glands, and a variable amount of fat. The apex is constituted by the teat,
which is also flattened transversely and varies in length from one to two inches
(ca. 2.5 to 5 cm.). Between the bases of the teats is the intermammary groove.
On the apex of each teat there are usually two small orifices placed close together;
these are the openings of the lactiferous ducts.

Structure. — The skin covering the glands is thin, pigmented, chiefly hairless,
and supplied with numerous large sebaceous and sweat glands. Under this are two
layers of fascia, except on the teats. The superficial fascia presents no special
features. The deep fascia consists of elastic tissue ; centrally two laminae detached
from the abdominal tunic descend on either side of the median plane, forming a
septum between the two glands, and constituting their ligamentum suspensorium.^

The gland substance or parenchyma is pinkish gray in color, and of firmer

^ These laminae are separated almost completely by a layer of areolar tissue, so that it is pos-
sible to remove a diseased gland by careful dissection between the layers of the septum.

GENITAL ORGANS OF THE COW

605

consistence than the fat which is found around and within the giand. It is enclosed
by a fibro-elastic capsule which sends inward numerous trabeculse; these form the
interstitial tissue, and divide the gland into lobes and lobules. In the latter are
the secretory tubules and alveoli, which unite to form the larger ducts. Each lobe
has a duct, which opens at the base of the teat into a space called the lactiferous
sinus (Sinus lactiferus), and from this two (or three) lactiferous ducts (Ductus
lactiferi) pass through the extremity of the teat. These ducts are lined with a non-
glandular mucous membrane, which is covered with stratified squamous epithelium.
They are surrounded by unstriped muscular tissue, the bulk of the fibers being ar-
ranged in a circular manner to form a sphincter.

The size and form of the mammary glands are subject to much variation. In the young
subject, before pregnancy, they are small and contain little gland tissue. During the latter part
of gestation, and especially during lactation, they increase greatly in size, and the gland tissue is
highly developed. After lactation the secretory structures undergo marked involution, and the
gland is much reduced in size. The relative amomits of gland substance and interstitial tissue
vary greatly; in some cases a gland of considerable size contains little parenchyma and is con-
sequently functionally deficient.

Vessels and Nerves. — The arteries are derived from the external pudic artery,
which enters the gland at the posterior part of its base. The veins form a plexus
on either side of the base of the gland, which is drained by the external pudic vein
chiefly. The lymph vessels are numerous and pass to the superficial inguinal and
lumbar lymph glands. The nerves are derived from the inguinal nerves and the
posterior mesenteric plexus of the sympathetic system.

GENITAL ORGANS OF THE COW

The ovaries of the cow are much smaller than those of the mare ; they measure
usually about one and a half inches (ca. 3.5-4 cm.) in length, and an inch

Fig. 534. — Ovary of Cow.
1, Broad ligament of uterus; 2, ligament of
ovary; 3, fimbria ovarica; 4, attachment of broad
ligament; 5, surface of ovary covered with ger-
minal epithelium; 6, corpora lutea; ~, Graafian
follicle. (From Leisering's Atlas.)

Fig. 535. — Uterits of Cow, Contracted; Dorsal View.
a. Body of uterus; h, b', horn of uterus; c, ovary; d, d,
triangular folds connecting horns of uterus (Ligg. intercornu-
alia). (After Zieger.)

(ca. 2.5 cm.) in thickness in their largest part; the weight is half an ounce
or more (ca. 15-20 gm.).^ They are oval in form, pointed at the uterine

1 Hess gives the following average measurements of the ovaries of 95 cows: Length of right,
4.3 cm.; of left, 3.71 cm.; width of right, 2.8 cm.; of left, 2.36 cm. Zieger found that the right
one was larger than the left in 65 out of 75 cases.

606

GENITAL ORGANS OF THE COW

-1>^%^.-

end, and have no ovulation fossa. They are situated usually a little above

the middle of the lateral margin of the pelvic inlet in the non-pregnant subject, but

may be a little further forward. They are thus about 16 to 18 inches (ca. 40-45

cm.) from the vulvar opening in a cow of medium size. The greater part of the

surface of the gland is covered with germinal epithelium, the peritoneal epithelium

being limited to a narrow zone along the

attached border. Follicles of various sizes /'-

are often seen projecting from the surface,

as well as corpora lutea; a corpus luteum

verum has a pronounced yellow color, and

may reach a width of half an inch or more

(ca. 1-1.5 cm.).

The uterine or Fallopian tubes are long
(ca. 20-25 cm.) and less flexuous than in the
mare. The junction with the cornu of the
uterus is not so abrupt as in the mare, since
the extremities of the horns are pointed.
The uterine orifice of the tul^e is rather large
and funnel-shaped. The fimbrise are not so
extensive as in the mare.

The uterus lies almost entirely within
the abdominal cavity in the adult. The
body is only about an inch and a half (ca.
3-4 cm.) in length, although externally it

The photogra

aljout three-fourths natura
men of medium size.

Fig. 537. — Genital Organs of Cow; Dorsal.
View.
The right uterine cornu and the vagina and
vulva are opened up: 1, Labium vulvae; 2, ventral
commissure; 3, glans clitoridis; 4. glandula vestib-
ularis major, exposed by slit in mucous mem-
brane; 5, pouch in which the ducts of the pre-
ceding open; 6, suburethral diverticulum; 7, ex-
ternal urethral opening; 8, openings of canals of
Gartner; 9, orificium uteri externum; 10, corpus
uteri; 11, cornu uteri; 12, cotyledons; 13, uterine
tube; 14, ostium abdominale tubse; 15, ovary.
(From Leisering's Atlas, reduced.)

appears to be about five or six inches long.

This false impression is due to the fact that

the posterior parts of the cornua are united

by connective and muscular tissue and have

a common peritoneal covering. The cornua

are, therefore, really more extensive than

they appear externally and have an average

length of about fifteen inches (ca. 35-40 cm.) . They taper gradually toward the free

end, so that the junction with the uterine tubes is not abrupt, as in the mare. The

free part of the horn curves at first downward, forward, and outward, and then turns

backward and upward, forming a spiral coil. The cervix is about four inches (ca.

10 cm.) long; its wall is remarkably dense, and may be more than an inch (ca. 3 cm.)

GENITAL ORGANS OF THE COW 607

in thickness. Its lumen, the cervical canal, is spiral, and is ordinarilj^ tightly closed
and very difficult to dilate. The vaginal part of the uterus is fused ventrally with
the vagina, so that the fornix vaginae is dorsal, and not an annular space as in the
mare. The muscular coat of the uterus is thicker than in the mare. It consists
of an external .longitudinal layer and two circular strata. The inner circular layer
is about a fourth of an inch (ca. 6 mm.) thick in the cervix. The other layers are
continued in the vagina. The mucous membrane of the horns and body presents
as a characteristic feature the uterine cotyledons (Cotyledones uterinse).^ These
are oval prominences, about a hundred in number, which are either irregularly
scattered over the surface or arranged in rows of about a dozen.

In the non-gravid uterus they average about half an inch or more (ca. 15 mm.) in length,
and a Httle less in width and thickness. During pregnancy they become greatly enlarged and
pedunculated. The larger ones then measure about four or five inches (10 to 12 cm.) in length,
an inch and a half (3 to 4 cm.) in width, and an inch (2 to 2.5 cm.) in thickness. The deep face has
a hilus at which the vessels enter. The rest of the surface has a spongy appearance, due to numer-
ous crypts which receive the villi of the chorion.

The uterine glands are long and branched. The mucous membrane of the
cervix is pale, glandless, and forms numerous folds. The latter are arranged in
several series which obliterate the lumen.
At the external uterine orifice the folds
(PlicaB palmatae) form rounded prominences
arranged circularly, which project into the
cavity of the vagina. There are no glands
in the cervix, but a thick mucus is secreted
by goblet cells.

The broad ligaments are not attached
in the sublumbar region as in the mare, but

to the upper part of the flanks, about a Fig. 53S.— Di.a.grammatic Sagittal Section op

handbreadth below the level of the tuber P^Rt of Urogenital Tract of Cow,

mi. X • • J. Showing Suburethral Diverticulum.

coxse. 1 hey contam a conspicuous amount

of unstriped muscle. The round ligaments

are well developed, and can be traced distinctly to the vicinity of the abdominal

inguinal ring.

The vagina is somewhat longer and more roomy than that of the mare; its
wall is also thicker. Its length in the non-pregnant animal is about eight to ten
inches (ca. 20-25 cm.); but in the pregnant cow the length increases to twelve
inches (30 cm.) or more. The recto-genital pouch of peritoneum extends backward
about five inches (ca. 12 cm.) on the dorsal surface, while ventrally the serous coat
only extends backward about two inches (ca. 5 cm.). In the ventral wall of the
vagina, between the muscular and mucous coats, there are commonly present the
two canals of Gartner (Ductus epoophori longitudinales) . When well developed,
they may attain the diameter of a goose quill, and may be traced forward to the
anterior part of the vagina or even further. They open posteriorly near the ex-
ternal urethral orifice."

The vulva has thick, wrinkled labia, and both commissures are acute; the
ventral one is pointed, and has on it a number of long hairs; it lies about two inches
(5 cm.) behind, and about the same distance below the level of, the ischial arch.
The external urethral orifice is four or five inches (10 to 12 cm.) from the ventral
commissure. Beneath it is a blind pouch, the suburethral diverticulum, which is

^Also known as carimculse uterinse.

2 These tubes are remnants of the Wolffian ducts, and, like other fcEtal vestiges, are very
variable. Roder states that the right canal was absent in over 52 per cent., the left in only 22 per
cent., of the cows examined by him. In some cases they may be traced in the broad ligaments for
a variable distance toward the ovary. They are of clinical interest in that cysts frequently form
along their course.

608

GENITAL ORGANS OF THE COW

about an inch (ca. 3 cm.) long, and readily admits the end of a finger.^ The two
glandulae vestibulares majores- are situated in the lateral walls of the vulva, under
the constrictor vulvae. They are little over an inch (ca. 3 cm.) long and about half
an inch (ca. 1.5 cm.) in width. Each has two or three ducts which open into a
small pouch of the mucous membrane; this cul-de-sac opens on the floor of the
vulva, about an inch and a half (ca. 3-4 cm.) lateral to and behind the external

Fig. 539. — Cross-section of Mammary Glands of Cow.
■a, Body of gland; 6, lactiferous sinus; c, cavity of teat; d, lactiferous duct; e, intermammary groove; /, septum be-
tween glands; g, supramammary fat.

urethral orifice. The gland consists of lobules separated by relatively thick trabec-
ulse of connective tissue and unstriped muscle. The glandulae vestibulares
minores occur along the median ventral groove. Numerous lymph nodules are
present in the mucous membrane, especially in the ventral part; they may be
large enough to cause visible prominences.

The clitoris has very short crura, but the body is four or five inches (ca. 10-12

1 The form and position of this pouch should be carefully noted on account of the difficulty
it causes in catheterizing the bladder. If the catheter is passed along the ventral wall of the
vulva (as in the mare), it will always enter the pouch instead of the urethra.

2 Also known as the glands of Bartholin.

GENITAL ORGANS OF THE EWE 609

cm.) long and is flexuous. Only the pointed end of the glans is visible in the ventral
commissure of the vulva.

The urethra is about four inches (10 cm.) in length; it is narrower and much
less dilatable than that of the mare. It is fused dorsally with the wall of the
vagina, while laterally and ventrally it is covered by the constrictor vaginae muscle.

The mammary glands, normally two in number, are popularly termed the
udder. They are very much larger than in the mare, and the body of each is
somewhat ellipsoidal in form, but flattened transversely. The base of each gland
is slightly concave and slopes obliquely downward and forward in adaptation to
the abdominal wall, to which it is adherent; it is in relation posteriorly to the large
supramammary lymph-glands and a quantity of fat. The medial surface is flat,
and is separated from the other gland by a well-developed double septum. The
lateral surface is convex. Four well-developed teats are present; they average
about three inches (ca. 7-8 cm.) in length. It is customary to consider the udder
to consist of four "quarters"; there is no septum nor visible division between the
two quarters of the same side, but, on the other hand, injections of fluids of different
colors into the two teats of the gland demonstrate that the cavities drained by them
do not communicate.

The size and form of the glands vary greatly; in the highly specialized dairy breeds (e. g.,
Holsteins) they often attam enormous dimensions. The size of the udder is not a certain index
of its productivity, since some so-called "fleshy" udders contain a very large amount of inter-
stitial tissue and relatively httle parenchyma. Small accessory teats often occur posteriorly;
commonly these are rudimentary and imperforate (polythelia), but sometimes they drain a small
amount of gland substance (polymastia). Sanson described a case in which there were seven
teats, all giving milk.

Each teat has a single duct which widens superiorly and opens freely into a
roomy lactiferous sinus (Sinus lactiferus), popularly known as the milk cistern.
The lactiferous duct (Ductus lactiferus) or teat canal is lined by a glandless mucous
membrane which is covered with stratified squamous epithelium; the lower part
(ca. 1 cm.) of the canal is narrow, and is closed by a sphincter of unstriped muscle.
The mucous membrane of the sinus forms numerous folds which render the cavity
multilocular.

Vessels and Nerves. — The arteries are derived from the external pudic arteries.
The veins form a circle at the base of the udder, from which the blood is drained by
three trunks, viz., the very large subcutaneous abdominal, the external pudic, and
the perineal vein. The lymph vessels are numerous, and pass to the supramammary
glands chiefly. The nerves are derived from the inguinal nerves and the posterior
mesenteric plexus of the sympathetic.

GENITAL ORGANS OF THE EWE

The genital organs of the ewe resemble in general those of the cow, but a few
special features may be noted.

The ovaries are almond shaped and are half an inch or more (ca. 1.5 cm.) in
length.

There is no demarcation between the uterine tube and the horn of the uterus;
the tube is very flexuous near the infundil^ulum.

The uterus resembles that of the cow. The horns are four or five inches (ca.
10-12 cm.) long and taper in such a manner to their junction with the uterine tubes
that no clear distinction between the two exists. They are coiled in a close spiral,
and an inch or more of their posterior parts are united. The body is less than an
inch (ca. 2 cm.) long. The cotyledons are much smaller than those of the cow and
39

610 GENITAL ORGANS OF THE SOW

have a depression on the free surface. The neck is about an inch and a half (ca.
4 cm.) in length; its lumen is closed by reciprocal prominences and depressions of
the mucous membrane. The external uterine orifice is in the ventral part of the
vagina.

The vagina is three or four inches (ca. 8 cm.) long. Its ventral part contains
numerous lymph follicles.

The vulva is an inch or more (ca. 2.5-3 cm.) in length. There is a very small
diverticulum behind the urethral orifice. The glandulse vestibulares majores are
inconstant; when present, they may be about the size of a small bean. The labia
are thick and the ventral commissure is pointed and projects dowmward.

The clitoris is short, and the glans is concealed in the fossa clitoridis.

The mammary glands, two in number, are relatively large, and are approxi-
mately globular, but flattened on the septal side.

GENITAL ORGANS OF THE SOW

The ovaries are concealed in the bursa ovarii, owing to the large extent of the
mesosalpinx. They are more rounded than in the bitch, and have a distinct hilus.
They may be situated at or near the lateral margin of the pelvic inlet, as in the cow;
but their position is quite variable in animals which have borne young and they may
be only an inch or two behind the kidney. The surface commonly presents rounded
prominences, so that the gland usually has an irregular lobulated appearance;
the projections are large follicles and corpora latea. Mature follicles may have a
diameter of about a third of an inch (ca. 7-8 mm.), and corpora lutea may be found
which measure half an inch or more (ca. 12-15 mm.).

The uterine or Fallopian tubes are long (ca. 15-30 cm.), and less flexuous than
in the mare. The fimbriated extremity forms an ampulla and has a large abdominal
opening. The uterine end shades insensibly into the small extremity of the cornu
of the uterus.

The uterus presents several striking features. The body is only about two
inches (ca. 5 cm.) long. The horns are extremely long and flexuous, and are freely
movable, on account of the large extent of the broad ligaments. In the non-
pregnant animal they are arranged in numerous coils and appear somewhat like
thick-walled small intestine. They may be four or five feet (1.2-1.5 m.) in length.
The extremities of the horns taper to about the diameter of the uterine tubes. The
neck is remarkable for its length (ca. 10 cm.) and the fact that it is directly con-
tinued by the vagina without forming any intravaginal projection. When slit open,
peculiar rounded prominences are seen on its interior; some of these dovetail and
occlude the cervical canal. They are continuous behind with folds of the mucous
membrane of the vagina. The broad ligaments contain a large amount of unstriped
muscle; they also contain a large lymph gland near the ovary.^ In the upper part
of the ligament the muscular tissue forms a rounded band termed the round liga-
ment. In an adult sow of full size it is about six inches (ca. 15 cm.) long; its
anterior end forms a blunt projection and posteriorly it ends in the subserous
tissue at the internal inguinal ring. The medial layer of the broad ligament is
continuous with the lateral ligament of the bladder.

The vagina is about four or five inches (ca. 10-12 cm.) long in a sow of medium
size. It is small in caliber, and has a thick muscular coat which consists of circular

1 The changes m form and position of the uterus during pregnancy are similar to those men-
tioned later in the case of the bitch (p. 613).

GENITAL ORGANS OF THE SOW

611

fibers between two layers of longitudinal fibers. The mucous membrane is plicated,
and is intimately united with the muscular coat.

The vulva is about three inches (7.5 cm.) in length. The labia are thick and
are covered with a wrinkled integument. The dorsal commissure is rounded, but
the ventral one is produced to form a long pointed projection. The fossa clitoridis
is nearly an inch (ca. 2 cm.) anterior to the ventral commissure. Above it the
glans clitoridis forms a pointed projection, from which a mucous fold extends
laterally and backward on each side. There is a deep central depression about
half way between the fossa clitoridis and the external urethral orifice. The latter
is bounded on each side by a thick fold which extends backward for a variable

A^.^

' \

Fig. 540. — Genital Organs of Sow; Dorsal View. The Vulva, Vagina, and Cervix Uteri are Slit Open.
/, Labium vulvae; ^, glans clitoridis; S, vulva; 4< external urethral orifice; 5, vagina; .5', cervix uteri; 6, corpus
uteri; 7, cornua uteri, one of which is opened at 7' to show folds of mucous membrane; 8, uterine tube; 8', abdominal
opening of tube ; 9,9, ovaries; 10, ovarian bursa; 11, 11, broad ligaments of uterus; 13, urinary bladder. (From
Leisering's Atlas.)

distance. Lateral to this fold is a depression in which the ducts of vestibular glands
open.

On either side of the anterior part of the floor of the vulva there is a cul-de-sac and a deep
groove leading back from it; these are bounded medially by a longitudinal fold. Ductus epo-
ophori (canals of Gartner) may be found openiiig anterior to the external urethral orifice.

The clitoris is long and flexuous; its glans forms a pointed projection over the
fossa clitoridis.

The urethra is about three inches (ca. 7-8 cm.) long. Its posterior part is fused
with the vagina and produces a corresponding elevation of the floor of the latter.

The mammary glands are usually ten or twelve in number, and are arranged
in two rows, as in the bitch. Each teat has commonly two ducts.

612

GENITAL ORGANS OF THE BITCH

The ovaries (Fig. 442) are small, elongated-oval in outline, and flattened.
The average length is a little less than an inch (ca. 2 cm.). Each ovar}^ is commonly
situated a short distance (ca. 1-2 cm.) behind, or in contact with, the posterior pole
of the corresponding kidney, and thus lies opposite to the third or fourth lumbar
vertebra, or about half way between the last rib and the crest of the ilium. The

right one lies between the right part of the
duodenum and the lateral abdominal wall.
The left one is related laterally to the spleen.
Each is concealed in a peritoneal pouch, the
bursa ovarii, which has a slit-like opening
ventrally. The two layers which form this
pouch contain a quantity of fat and unstriped
muscle. They are continued to the cornu of
the uterus, constituting the mesosalpinx and
the ligament of the ovary. The surface of
the ovary presents prominences caused by
projecting follicles. Many follicles contain
several ova. There is no distinct hilus.

The uterine or Fallopian tubes are small
and average two or three inches (ca. 5-8
cm.) in length. Each passes at first forward
in the lateral part of the bursa ovarii, and
then runs backward in the medial part of
the pouch ; it is only slightly flexuous. The
pouch is thus a part of the mesosalpinx. The
fimbriated extremity lies chiefly in the bursa
ovarii, but part of it often protrudes through
the slit-like opening of the bursa ovarii; it
has a rather large abdominal opening. The
uterine orifice is very small.

The uterus has a very short body and
extremely long narrow horns. In a bitch of
medium size the body is about an inch (ca.
2-3 cm.) and the cornua five or six inches
(ca. 12-15 cm.) long. The horns are of
uniform diameter, are nearlj^ straight, and lie
entirely within the abdomen. They diverge
from the body in the form of a V toward each
kidney. Their posterior parts are united by
the peritoneum. The neck is very short and
has a thick muscular coat. Dorsally there
is no line of demarcation between uterus and
vagina, but the cervix uteri is much thicker
than the vagina. Ventrally the cervix forms
a cylindrical projection which lies in a depression of the vaginal wall. The mucous
membrane of the uterus has long uterine glands and also short tubular crypts.

The broad ligaments contain much fat and some unstriped muscle. They are
much wider in the middle than at either end. The posterior part is attached to the
anterior part of the vagina. The round ligaments are contained in the free edge of
folds given olT from the lateral face of the broad ligaments. They are bands of
unstriped muscle and fat. Each passes through the inguinal canal, enveloped by a
peritoneal pouch (processus vaginalis). A ligamentous fold extends forward from

Fig. 541. — Genital Organs of Bitch.
Vulva, vagina, and uterus (in part) are slit
open, a, Ovarian bursa; 6, same opened to show
the right ovary, c; d, d, horns of uterus; e, e', body
of uterus; /, neck of uterus; /', external uterine
orifice; ff, vagina; h, hymen; i, vulva; k, external
urethral orifice; I, urinary bladder; m, urethra;
n, 7t, labia vulvse; o, fossa clitoridis; p, central
projection of fold of mucous membrane which con-
ceals the clitoris. (After Ellenberger, in Leisering's
Atlas.)

GENITAL ORGANS OF THE BITCH 613

the bursa ovarii lateral to the kidney and is attached to the abdominal wall at the
middle of the last rib.

The horns of the gravid uterus present dilatations, the ampullae, which contain the
foetuses, and are separated by constrictions. The gravid uterus lies on the ventral abdominal wall,
and toward the end of gestation extends forward to the stomach and liver.

The vagina is relatively long. It is narrow anteriorly, and has no distinct
fornix. The muscular coat is thick and consists chiefly of circular fibers. The
mucous membrane forms longitudinal folds. The canals of Gartner are usually
absent.

The vulva has thick labia which form a pointed inferior commissure. The
mucous lining is smooth and red. It frequently presents small prominences caused
by lymph follicles. On either side of the urethral orifice there is a small depression.
The glandulse vestibulares majores are absent, but the smaller glands are often
present, and their ducts open ventrally on either side of a median ridge. The
vestibular bulbs are relatively large and are commonly united ventrally by a sort
of isthmus. The constrictor muscle is strong and divides into two layers which
enclose the vestibular bulb. The body of the clitoris is broad and flat, and is about
an inch and a half (ca. 3-4 cm.) long in a subject of medium size. It is not erectile
in structure, but is infiltrated with fat. It is enclosed by a fibrous albuginea and
contains large arteries and numerous nerves in its ventral part. The glans clitoridis
is composed of erectile tissue and is situated in a large fossa clitoridis. A fold of
mucous membrane extends backward over the glans and fossa; a central projection
of this fold may be mistaken for the glans clitoridis.

The mammary glands are usually ten in number, and are arranged in two series,
extending from the posterior part of the pectoral region to the inguinal region; they
are, therefore, designated according to location as pectoral, abdominal, and inguinal.
The teats are short, and present on their apices six to twelve small orifices of the
excretory ducts.

ANGIOLOGY

Angiology is the description of the organs of circulation of the blood and lymph
— the heart and vessels. The heart is the central hollow muscular organ which
functions as a suction and force pump; the differences in pressure caused by its
contraction and relaxation determine the circulation of the blood and lymph,
It is situated in the middle mediastinal space of the thorax and is enclosed in a fibro-
serous sac — the pericardium. The vessels are tubular and run through almost all
parts of the body. They are designated according to their contents as blood- and
lymph-vessels.

THE BLOOD-VASCULAR SYSTEM

The blood-vascular system consists of: (1) The arteries, which convey blood
from the heart to the tissues; (2) the capillaries, microscopic tubes in the tissues,
which permit of the necessary interchange between the blood and the tissues;
(3) the veins, which convey the blood back to the heart.

The blood-vessels are divided into the pulmonary and the systemic. The
pulmonary artery conveys the blood from the right ventricle of the heart to the
lungs, where it is arterialized, and is returned by the pulmonary veins to the left
atrium of the heart, and passes into the left ventricle. The systemic arteries
conve}^ the blood from the left ventricle all over the body, whence it is returned by
the venae cavae to the right atrium, and passes into the right ventricle.^

The term portal system is often applied to the portal vein and its tributaries
which come from the stomach, intestine, pancreas, and spleen. The vein enters
the liver, where it branches like an artery, so that the blood in this subsidiary
system passes through a second set of capillaries before being conveyed to the heart
by the hepatic veins and the posterior vena cava.

The arteries (Arteriae), as a rule, divide at an acute angle, giving off finer
and finer branches. In some cases branches come off at a right angle, and others
are recurrent, i. e., run in a direction opposite to that of the parent stem. The
intercommunication of branches of adjacent arteries is termed anastomosis. Most
commonly the connections are made by a network of numerous fine branches which
constitute a vascular plexus (Plexus vasculosus) . Relatively large communicating
branches (Rami communicantes) occur in certain places; they may be transverse
or in the form of arches. Wide-meshed networks of vessels are termed retia vas-
culosa. Terminal or end arteries are such as form isolated networks, i. e., do not
anastomose with adjacent arteries. A rete mirabile is a network intercalated in
the course of an artery. A collateral vessel (Vas collaterale) is one which pursues
a course near and similar to that of a larger vessel.

The veins (Venae) are in general arranged like the arteries, but are usually of
greater caliber. When a vein accompanies an artery, it is termed a vena comitans
or satellite vein and is usually homonymous; in many places two veins accompany
a single artery. The primitive venous trunks do not run with the arteries, and most
of the superficial veins (Venae cutaneae) pursue independent courses. They anas-
tomose even more freely than the arteries, and large communicating branches
are very common. Venous plexuses (Plexus venosi) occur in many places. Some
veins which are enclosed by dense membranes and run usually in bony grooves are

^ It should be noted, however, that the lungs also receive arterial blood through the systemic
bronchial arteries. This blood is returned in part by the bronchial veins to the right atrium (in-
directly), in part by the pulmonary veins to the left atrium.

614

ANGIOLOGY — THE LYMPHATIC SYSTEM 615

termed (venous) sinuses; their wall consists of endothelium only; examples of
this are the sinuses of the dura mater of the brain. A vein which connects one of
these sinuses with veins outside of the cranium is termed an emissarium.

A corpus cavemosum is an erectile structure which consists essentially of
intercommunicating blood-spaces enclosed by unstriped muscle and fibro-elastic
tissue. These spaces (Cavernse) are lined with endothelium and contain blood.
Some are to be regarded as greatly enlarged capillaries, since minute arteries open
into them and they are drained by veins; others are intercalated in the course of
veins. Distention of the cavernse with blood produces the enlargement and harden-
ing of the corpus cavernosum which is termed erection.

Structure of Arteries. — The wall consists of three coats. The external coat
or adventitia (Tunica externa) consists chiefly of fibrous connective tissue. In the
deeper part are some elastic fibers, and in some arteries there are also longitudinal
unstriped muscle-fibers. The middle coat (Tunica media) is composed of unstriped
muscle and elastic tissue in medium-sized arteries. In small vessels there is chiefly
muscular tissue, and in the largest trunks almost exclusively elastic tissue. The
internal coat or intima (Tunica intima) consists of a layer of endothelial cells, resting
on an elastic membrane. The sheath of the vessel (Vagina vasis) is a condensation
of the surrounding connective tissue, and is attached more or less closely to the
external coat.

Structure of Veins. — The walls of veins are similar in structure to those of
the arteries, but are very much thinner, so that veins collapse more or less com-
pletely when empty, while arteries do not. The middle coat is very thin and con-
sists to a large extent of ordinary fibrous tissue. The internal coat is also less
elastic than in the arteries. In many veins this coat forms semilunar valves, the
free edges of which are directed toward the heart. They are most numerous in the
veins of the skin and of the extremities (except the foot), while in most veins of the
body cavities and viscera they are absent or occur only where the veins open into
larger ones or where two veins join.

The walls of the vessels are supplied with blood by numerous small arteries,
called vasa vasorum. These arise from branches of the artery which they supply
or from adjacent arteries, ramify in the external coat, and enter the middle coat
also. The nerves of the vessels (Nervi vasorum) consist of both meduUated and
non-medullated fibers. They form plexuses around the vessels, from which fibers
pass mainly to the muscular tissue of the middle coat.

The Lymphatic System

The lymphatic system (Systema lymphaticum) is subsidiary to the venous
part of the circulatory system, from which it arises in the embryo. It consists of
the lymph vessels and glands.

The lymph vessels (Vasa lymphatica) contain a colorless fluid, the lymph,
which contains numerous lymphocytes. ^ They resemble the veins in structure
but have thinner walls and are provided with more numerous valves. The vessels
are sacculated opposite the segments of the valves and have a characteristic beaded
appearance when distended. The collecting lymph vessels do not usually form rich
plexuses, as veins often do, their branching is more limited and less tree-like than
that of the blood-vessels, and their caliber therefore increases less from the periphery
toward their termination. All of the lymph is ultimately carried into the venous
system by two trunks, the thoracic duct and the right lymphatic duct. Almost all

1 The term chyle is often applied to the lymph carried by the efferent vessels of the intestine
when it contains products of digestion, and these vessels may be designated accordingly as lacteals
or chyle

616 ANGIOLOGY

of the Ijaiiph passes through at least one group of lymph glands before entering the
blood-vascular system.

The lymph glands or nodes (Lymphoglandulse) are intercalated in the course
of the lymph vessels. They vary widely in size, some being microscopic, others
several inches in length. In form they may be globular, ovoid and flattened,
elongated, or irregular. In certain situations they are aggregated into groups,
and a knowledge of the position of these and the territory drained into them is im-
portant. It is convenient, when possible, to indicate their position with regard to
arteries on the course of which they are placed. In color they are usually gray or
yellowish-brown in the dead subject, pink or reddish-brown during life, but this
varies according to their position and functional state. The bronchial glands
are often blackened by infiltration with carbon. The mesenteric glands are creamy
or white while the chyle is passing through, but pink at other times. Vessels
which carry lymph to a gland are called afferent; the efferent vessels which convey
it away are larger and fewer. Each gland has a depression, the hilus, at which the
blood-vessels enter and the efferent lymph vessels emerge.

Lymph nodules or follicles (Noduli lymphatici) are minute masses of lymphoid
tissue which occur in certain mucous membranes. They may be solitary, as in the
solitary nodules or glands of the intestine, or aggregated into masses or patches, as
in the tonsils and the aggregate glands or so-called Peyer's patches.

The lymph nodule or follicle is the unit of structure of the lymph gland. It consists
essentially of an artery surrounded by a reticulum of connective tissue, the meshes of which
contain numerous lymphocytes. Surrounding this is a rich plexus of lymph vessels, forming the
so-called sinus, enclosed in some cases by a fibrous capsule. The gland consists of a mass of
follicles, enclosed in a fibrous capsule, from which trabeculae pass in and unite the follicles. Be-
neath the capsule is the peripheral sinus, which consists of a very rich plexus of lymph vessels;
to this the afferent vessels pass at various points of the surface. In the cortical substance the
cells are in rounded masses, the cortical nodules, while in the medullary substance they lie
around the arteries, forming the so-called medullary cords. The medulla is redder than the cor-
tex, since it is more vascular; it contains the central Ijrmph sinuses, which have a similar struc-
ture to the peripheral sinus.

The haemolymph glands differ from the lymph glands in color and structure.
They are of a deep red color or even black, which is due to the high vascularity of
the cortical substance. The peripheral sinuses especially are greatly developed
and contain numerous red blood-cells. There is no clear division into cortical and
medullary substance, and the trabecule contain smooth, muscle-cells. Some have
afferent and efferent lymph vessels and others do not. They resemble the spleen in
some respects, but their significance is not yet clear. They are numerous in the ox
and sheep, much fewer in the dog, and apparently are absent in the horse. They
occur along the course of the aorta, in the perineal fat, at the portal fissure, and with
the gastric and mesenteric lymph glands. In the ox they are also found under the
trapezius muscle, imder the skin of the upper part of the flank, and in other places
less constantly.

The tissue or lymph spaces are interstices of varying size between cells or in
the meshes of connective tissue. They contain a fluid derived from the blood-
plasma, which is usually called lymph. They are drained by the veins and lymph
vessels. The large serous sacs are often included in this category.

The exact relationship between the lymphatic capillaries and the tissue spaces is still a matter
of controversy. It is held by some that the lymph vessels are in direct communication with the
tissue spaces, while others maintain that the lymphatics are complete closed tubes. Communi-
cation between the spaces and vessels is in general very free. Mall has shown that granules in-
jected into the hepatic artery are returned by the lymphatics as well as by the veins, and intra-
muscular injections will enter the lymph vessels of the tendon in spite of the absence of lymphatics
in muscle.

BLOOD-VASCULAR SYSTEM OF THE HORSE THE HEART 617

BLOOD-VASCULAR SYSTEM OF THE HORSE
THE PERICARDIUM 1

The pericardium is the fibro-serous sac which surrounds the heart, and also
the great vessels in connection with it to a greater or less extent. Its form is in
general similar to that of the heart. The fibrous layer is relatively thm, but
strong and inelastic. It is attached dorsally to the large vessels at the base of the
heart, and is continued in part up to the longus colli muscle. It is firmly attached
ventrally to the middle of the posterior half of the thoracic surface of the sternum.
The serous layer is a closed sac, surrounded by the fibrous pericardium, and invag-
inated by the heart. It is smooth and glistening, and contains a small amount of
clear serous fluid, the liquor pericardii. Like other serous membranes, it may be
regarded as consisting of two parts, parietal and visceral. The parietal part lines
the fibrous layer, to which it is closely attached. The visceral layer covers the
heart and parts of the great vessels, and is therefore also termed the epicardium.
The serous pericardium is composed of a connective-tissue membrane, rich in
elastic fibers, and covered on its free surface by a layer of flat mesothelial cells.

The pericardium is covered by the pericardiac part of the mediastinal pleura
(Pleura pericardia), and is crossed laterally by the phrenic nerves. Its lateral
surfaces are related chiefly to the lungs, but the lower part is in partial contact with
the chest-wall. On the left side the area of contact is from the third rib to the
sixth rib and intercostal space. On the right side the contact is smaller and is
chiefly opposite the ventral part of the third and fourth intercostal spaces and inter-
vening rib. The anterior end of its base is opposite to the second intercostal space
or third rib, and the posterior border is opposite to the sixth rib and space. The
base is related to the great vessels, the trachea and its bifurcation, the bronchial
lymph glands, the oesophagus, and the vagus, left recurrent, and cardiac nerves.

The extent of contact of the pericardium with the lateral wall of the thorax is determined by
the cardiac notch of the lung. On the left side the anterior margin of the notch is at the third
rib and the posterior margin is at the sixth rib dorsally and sbith intercostal space ventrally. The
greatest height of the notch is at the fourth rib and intercostal space, where it is a handbreadth
or more (ca. 10-12 cm.) above the sternal end of the rib. The notch is quadrilateral, but much
narrower above than below. On the right side the notch is usually triangular and is much smaller.
Its anterior margin begins at the third intercostal space, about three inches (ca. 7-8 cm.) above the
sternal ends of the third and fourth ribs and runs obliquely to the sternal end of the third rib. The
posterior margin begins at the same point and extends to the ventral end of the fourth intercostal
space or of the anterior border of the fifth rib.

The two parts of the serous pericardium are, of course, continuous with each other at the
line of reflection on to the great vessels. The latter are covered in varying degree by the visceral
layer. The aorta and pulmonary artery are enclosed in a complete common sheath as far as the
bifurcation of the latter. The membrane passes inward between the pulmonary artery and the
left auricle, and is continued between the right auricle and the aorta, thus forming the transverse
sinus of the pericardium (Sinus transversus pericardii). The posterior vena cava is covered
on the right and ventrally for a distance of an inch or a little more (ca. 3 cm.). The pulmonary
veins have practically no serous covering. The epicardium is closely adherent to the muscular
tissue of the heart, but is attached to the vessels by areolar tissue and fat, and hence is easily dis-
sected off them.

THE HEART
The heart (Cor) occupies the greater part of the middle mediastinal space.
Its shape is that of an irregular and somewhat flattened cone. It is attached at
its base by the great vessels, but is otherwise entirely free in the pericardium. It
is decidedly asymmetrical in position, about two-fifths being to the right of the
median plane and three-fifths to the left. The long axis (from the middle of the
base to the apex) is directed ventrally and backward. The base of the heart (Basis
cordis) is directed dorsally and its highest part lies about at the junction of the

^ The pericardium is described before the heart, since it must be examined first in the labor-
atory.

BLOOD-VASCULAR SYSTEM OF THE HORSE

dorsal and middle thirds of the dorso-ventral diameter of the thorax. It is opposite
to the lateral wall of the thorax, from the second intercostal space or third rib to the
sixth rib or intercostal space. ^ The apex (Apex cordis) lies centrally above the last
segment of the sternum; it is half an inch or less (ca. 1 cm.) above the sternum and
about an inch (ca. 2-3 cm.) from the sternal part of the diaphragm. The anterior
border (Margo cranialis) is strongly convex and curves ventrally and backward;
the greater part is parallel with the sternum. The posterior border (Margo cau-
dalis) is much shorter, is nearly vertical, and is opposite to the sixth rib and inter-
costal space. The surfaces, right and left (Facies dextra, sinistra), are convex and

Lig. arteriosum Pulmonary veins

Brachiocephalic trunk

Left auricle

Coronary
groove

Left longitudinal groove
Fig. 542. — Heart op Horse; Left View.
The dotted line indicates the line of reflection of the serous pericardiui

not been removed.

Hardened in situ
1. The epicardium and subepicardial fat have

are marked by grooves which indicate the division of the heart into four chambers,
the two atria above and two ventricles below. The left surface (covered by the
pericardium) is related to the lower third of the chest-wall from the third to the
sixth rib. On the right side the cardiac notch of the lung is smaller, so that the
area of relation to the chest-wall extends from the third to the fourth intercostal
space.-

^ The size and form of the heart vary according to the degree of its contraction and relaxa-
tion (systole and diastole). In subjects which have been bled and preserved by intravascular
injection of formalin solution the right side is usually fixed in diastole while the left is more or less
strongly contracted. The base may extend back to" the seventh rib.

2 The arrangement in this regard has been stated at greater length in the descriptions of the
lungs and the pericardium.

THE HEART

619

The coronary groove (Sulcus coronarius)^ indicates the division between the atria
and the ventricles. It almost completely encircles the heart, but is interrupted at
the origin of the pulmonary artery. The longitudinal grooves,^ right and left,
correspond to the septum between the ventricles. The left longitudinal groove
(Sulcus longitudinalis sinister) is left-anterior in position. It begins at the coronary
groove, behind the origin of the pulmonary artery, and descends almost parallel to
the posterior border. The right longitudinal groove (Sulcus longitudinalis dexter)
is right-posterior in position. It begins at the coronary groove, below the termina-

Puhnonary veins

Pulmonary artery

Vena azygos

Carunary groove

Fig. 543. — Heart of Horse; Right View. Hardened in situ.

Line of reflection of serous pericardium dotted. Epicardium and subepicardial fat have not been removed from heart.

Left ventricle is considerably contracted.

tion of the posterior vena cava and passes toward the apex, but ends about an inch
and a half (ca. 3-4 cm.) above the latter. Thus the two grooves do not meet.
The grooves are occupied by the coronary vessels and a variable quantity of fat.

The left groove is opposite to the fourth rib, and the right one is opposite to the fifth inter-
costal space above and the sixth rib below.

Size and Weight. — The average weight of the heart is about nine pounds
(ca. 4 kg.) and is about 0.7 per cent, of the body-weight. There is, however,
great range of variation in apparently normal specimens.

^ Also termed the atrio-ventricular or auriculo-ventricular groove.
^ Also termed the interventricular grooves.

620

BLOOD-VASCULAR SYSTEM OF THE HORSE

As might be expected, race horses have hearts which are larger than the average, both abso-
lutely and relatively. In fat subjects the ratio to the body-weight may be about 0.4 per cent., and,
on the other hand, it is commonly 1 per cent, or more in light horses which are not fat.

The following average measurements were obtained in medium-sized hearts:

Sagittal diameter of base 25 cm.

Greatest width of base 18 to 20 cm.

Circumference at coronary groove 65 to 70 cm.

Distance between origin of pulmonary artery and apex 25 cm.

Distance between termination of posterior vena cava and apex IS to 20 cm.

Pulmonary vein&

Pulmonary
veins

Posterior vena cava
Left atrium

Fig. 544. — Base of Heart of Horse with Large Vessels: Dorsal View. Specimen Hardened in situ.

The Right Atrium

The right atrium (Atrium dextrum)^ forms the right-anterior part of the base
of the heart, and lies above the right ventricle. It consists of a sinus venarum,
into which the veins open, and an auricle- (Auricula dextra). The latter is a conical
diverticulum which curves around the right and anterior surfaces of the aorta, its
blind end appearing on the left side in front of the origin of the pulmonary artery; it
is the most anterior part of the heart.

There are five chief openings in the right atrium. The opening of the anterior
vena cava (Ostium venae cavse cranialis) is in the dorsal part, and is chiefly opposite
to the fourth rib. The opening of the posterior vena cava (Ostium vense cavae

^ Also termed the right auricle. 2 ^igQ termed the auricular appendix.

THE RIGHT ATRIUM

621

caudalis) is at the posterior part, opposite to the fifth intercostal space. Between
the two the wall pouches upward somewhat, and here the vena azygos opens. The
coronary sinus opens ventral to the posterior vena cava; the orifice is provided with
a small semilunar valve (V alvula sinus coronarii) . The small coronary vein has a
separate opening in some cases close to that of the coronary sinus. The right
atrio-ventricular orifice (Ostium atrio-ventriculare dextrum) is in the ventral part,

Orifice of vena azygos

Anterior vena cava

Posterior ___^

'^*^Wm^

vena cava

Orifice of

J^az^^

coronary -^^
sinus

l^^V^

Chordae
tendinece

,-- — ""^

^"l"^'

^^^

Fig. 545. — Right Side op Heart of Horse Opened up by Removal op Greater Part op Right Wall. Organ

Hardened in situ.
The right ventricle was in diastole, r, Intervenous crest; V, V, tricuspid valve; P. P, papillary muscles; m, m,
moderator bands. Arrow points into origin of pulmonary artery. The crista supraventricularis, which separates the
atrio-ventricular orifice from the conus arteriosus, is shown but not marked. The crista terminalis (unmarked) is
nearly directly dorsal to the preceding.

and leads into the right ventricle. In addition to the foregoing there are several
small orifices of the vense cordis parvse; these are concealed in the depressions
between the musculi pectinati.

The atrium is lined with a glistening membrane, the endocardium. Its walls
are smooth except on the right and in the auricle, where it is crossed in various
directions by muscular ridges, the musculi pectinati. Small bands extend across
some of the spaces enclosed by the musculi pectinati. The latter terminate above

622

BLOOD-VASCULAR SYSTEM OF THE HORSE

on a curved crest, the crista terminalis, which indicates the junction of the primi-
tive sinus reuniens of the embryo with the atrium proper, and corresponds with the
sulcus terminalis externalh'.^ The openings of the venae cavae are valveless. A
ridge, the intervenous crest (Crista intervenosa),^ projects downward and forward
from the dorsal wall just in front of the opening of the posterior vena cava; it
tends to direct the flow of blood from the anterior vena cava to the atrio-ventricular

Aurta

Left pulmonary artery
Right pulmonary artery

Pulmonary vein

Posterior vena cava

Fig. 546. — Left Side of Heart of Hokse, Opened up by Removal of Part of Wall.
A.S., Left atrium; Au. s., left auricle; V, V, V, bicuspid valve; V. s., left ventricle; M, M, moderator bands; P,
P, papillary muscles; 1, 2, great cardiac vein and circumflex branches of coronary arteries; 3, position of foramen ovale
of foetus; .^, ^, openings of pulmonary veins (chiefiy cut away) ; 5. atrio-ventricular orifice; 6, arrow points toward
aortic orifice.

opening. The fossa ovalis is a diverticulum in the septal wall, at the point of
entrance of the posterior vena cava, bounded laterally by a concave margin (Limbus
fossa? ovalis) . The fossa is the remnant of an opening in the septum, the foramen
ovale, through which the two atria communicate in the foetus.

^ The crista terminalis is showii, but not marked, in Fig. 545; it is almost opposite (anterior)
to the intervenous crest. The sulcus terminalis is commonly indistinct except near the vense
cavse.

^ Also termed the tubercle of Lower.

THE RIGHT VENTRICLE

623

Although called a fossa, it is usually a deep but narrow diverticulum in the horse. The
interatrial septum is very thin here, and in some cases the foramen ovale fails to close entirely.

The Right Ventricle

The right ventricle (Ventriculus dexter) constitutes the right-anterior part of
the ventricular mass. It foE;^ almost all of the anterior border of the heart, but
does not reach the apex, which is formed entirely by the left ventricle. It extends
from the third rib to the fourth intercostal space on the left side, to the fifth inter-
costal space on the right side. It is somewhat triangular in outline, and is crescentic
in cross-section. Its base is connected largely with the right atrium, with which it

Pulmonarij veins
Pulmonary artery //i 1 \\

Right coronary , \
artery

Tricuspid cnli, /
Chorda! tendincce

Great coronary
\ ^vein

«\y Left coronary
' _, artery {circum-
' Y ' flex branch)
-&"" Bicuspid valve

Chordce tendinecs

Musculus
"' papillaris

,-' Moderator band

,,' Lejt ventricle

Moderator bamt

Riijht V, Ntnde ■-

Right coronary artery -'"
Fig. 547. — Section of Heart of Horse.
Specimen hardened in situ and cut nearly at right angles to the ventricular septum. The left ventricle is contracted,
but not ad maximum. V.a., Segment of aortic valve.

communicates through the right atrio-ventricular orifice; but its left part projects
higher and forms the conus arteriosus, from which the pulmonary artery arises.
Its apex is two inches or more (ca. 5-6 cm.) above the apex of the heart. On
opening the cavity it is seen that the atrio-ventricular orifice and the cavity of the
conus arteriosus are separated b}^ a thick rounded ridge (Crista supraventricularis) .
The axis of the cavity, taken from this ridge to the apex, forms a spiral curve down-
ward and to the right. The septal wall is convex and faces obliquely forward and
to the right.

The right atrio-ventricular orifice (Ostium atrio-ventriculare dextrum) is oval
and is chiefly opposite to the fourth and fifth ribs and the intervening space. ^ The
plane of the opening is oblique, much lower in front than behind.

1 The extent of the atrio-ventricular orifices, of course, varies with the phase in which the heart
is fixed. In subjects which are preserved by intravascular injection of formalin solution the right
side of the heart is usually in diastole, while the left side is more or less contracted.

624

BLOOD-VASCULAR SYSTEM OF THE HORSE

The anterior part of the orifice is usually only about an inch or two (ca. 3-5 cm.) above the
level of the ventral end of the first rib, while the posterior part is four or five inches (ca. 10-12 cm),
higher than the sternal end of the fifth rib.

It is guarded b}^ the tricuspid valve (Valvula tricuspidalis) ; of the three large
cusps of this valve, one is between the atrio-ventricular opening and the conus
arteriosus, one is septal, and the third is on the right margin. Small intermediate
cusps intervene between the large ones. The peripheral edges of the cusps are at-
tached to the fibrous ring at the atrio-ventricular opening. The central edges are
irregular and hang down into the ventricle; they give attachment to chordae ten-
dinese. The auricular surfaces are smooth. The ventricular surfaces are rough and
furnish attachment to interlacing branches of the chordae tendineae. The valves
are folds of the endocardium, strengthened by fibrous tissue and at the periphery

Musculi pectinati

Aortic valve ^^/

Great coronary
vein
Left coronary

artery
Bicusjnd valve —

Chordae tendincce ^- — '

Papillary m usch' -

Musculi pectinati

"•'Right coronary
artery

Tricuspid valve
I pillar y muscle

Trahecul(e carneoe

. Fig. 548. — Section of Heart op Horse. Specimen Hardened in situ.
The section is cut nearly at right angles to the ventricular septum, and is viewed from the right and posteriorly.

by muscular fillers also. The chordae tendineae are attached below to the three
musculi papillares, which project from the ventricular wall; superiorly they
divide into branches which are inserted into the ventricular surfaces and the free
edges of the valves. Each cusp of the valve receives chordae tendineae from
two papillary muscles. Of the latter, two are on the septum and the third and
largest springs from the anterior wall.

The pulmonary orifice (Ostium pulmonale) is circular and is situated at the
summit of the conus arteriosus, opposite to the third rib and intercostal space.

The position of the orifice is somewhat variable. Its anterior margin may not be quite so
far forward as the posterior border of the third rib, and the posterior margin is often opposite to

THE LEFT ATRIUM THE LEFT VENTRICLE 625

the fourth rib. It is commonly about three or four inches (ca. 6-9 cm.) above the sternal ends
of the ribs.

It is guarded by the pulmonary valve, composed of three semilunar cusps
(Valvulse semilunares arterise pulmonalis); of these, one is medial, one lateral,
and the third posterior.^ The convex peripheral border of each cusp is attached
to the fibrous ring at the junction of the pulmonary artery and the conus arteriosus.
The central border is free and concave. Each cusp consists of a layer of endo-
cardium on its ventricular surface, a continuation of the inner coat of the artery on
its arterial surface, and an intermediate layer of fibrous tissue. The edge of the
conus arteriosus forms three arches with intermediate projecting angles or horns,
to all of which the cusps are attached; and the artery forms opposite each cusp a
pouch, the sinus of the pulmonary artery.^

The walls of the ventricle (except in the conus arteriosus) bear muscular ridges
and bands, termed trabeculae cameae. These are of three kinds, viz., (1) ridges or
columns in relief; (2) musculi papillares, somewhat conical flattened projections,
continuous at the base with the wall and giving off the chordae tendineae to the
tricuspid valve; (3) moderator bands (Musculi transversi cordis) which extend
from the septum to the opposite wall. The latter are partly muscular, partly
tendinous, and vary in different subjects. The strongest one is usually about
midway between the base and apex and extends from the septum to the base of
the lateral musculus papillaris (Fig. 547) . It is considered that they tend to prevent
overdistention.

The Left ATRroM
The left atrium (Atrium sinistrum)^ forms the posterior part of the base of the
heart. It lies behind the pulmonary artery and the aorta and above the left
ventricle. The auricle (Auricula sinistra) * extends outward and forward on the left
side, and its pointed, blind end is behind the origin of the pulmonary artery. The
pulmonary veins, usually seven or eight in number, open into the atrium behind
and on the right side. The cavity of the atrium is smooth, with the exception of
the auricle, in which the musculi pectinati are present. In some cases there is a
depression on the septal wall opposite the fossa ovalis, bounded above by a fold
which is the remnant of the valve of the foramen ovale of the foetus. The left
atrio-ventricular opening (Ostium atrio-ventriculare sinistrum) is situated below
and in front; it usually appears smaller than the right one on account of the con-
traction of the left ventricle in the dead subject. The apertures of small veins of
the heart are found in the spaces enclosed by the musculi pectinati.

The number and the arrangement of the pulmonary veins are variable. They may be
five to nine in number. The largest vein is posterior; it is formed by the union of veins from both
limgs. Usually three veins of considerable size, which lie above the posterior vena cava, enter
close together on the right, and three or four open close to the ridge which projects from the roof
at the base of the auricle.

The Left Ventricle
The left ventricle (Ventriculus sinister) forms the left posterior part of the
ventricular mass. It is more regularly conical than the right ventricle, and its
wall is much thicker except at the apex. It forms all of the posterior contour of
the ventricular part and the apex of the heart. Its base is largely continuous with
the left atrium, with which it communicates through the left atrio-ventricular
opening, but its anterior part opens into the aorta. The cavity usually appears
smaller than that of the right ventricle in the dead subject, on account of the greater
contraction of its wall. It is almost circular in cross-section.

^ In some cases there are four cusps, and very rarely only two.
^ These are also known as the sinuses of Valsalva.

^ Also termed the left auricle. ■* Also termed the auricular appendix.

626

BLOOD-VASCULAR SYSTEM OF THE HORSE

The left atrio-ventricular orifice (Ostium atrio-ventriciilare sinistrum) is
chiefly opposite to the fifth ril:) and intercostal space.

The orifice frequently extends back opposite to the sixth rib, and its anterior margin may
be opposite to the posterior border of the fifth rib. It is about four inches (ca. 10 cm.) above the
sternal end of the fifth rib. The plane of the opening is somewhat obhque, and is higher behind
than in front.

It is almost circular and is guarded by the bicuspid valve ( Valvula bicuspidalis) .^
The two cusps of this valve are larger and thicker than those of the right side of the

Fig. 549. — Cross-section op Venthicular Part of Heart op Horse.
The section is cut about 5 cm. from the coronary groove. The ventricles are moderately distended. V. d.. Right
ventricle; F. s., left ventricle; 6'. w., ventricular septum; 1, 1', papillary muscles of right ventricle; 2, large moderator
band of right ventricle; 3, 3, 3', papillary muscles of left ventricle; 4, 4', moderator bands of left ventricle; 5, descend-
ing branch of left coronary artery and great cardiac vein; 6, right coronary artery and small cardiac vein. The anterior
septal papillary muscle of the right ventricle is not visible, and the right one of the left ventricle is double.

heart. One is placed in front and separates the atrio-ventricular and aortic open-
ings. The other is placed behind and laterally and is usually divided into two or
three parts.

The aortic orifice (Ostium aorticum) is directed upward and slightly forward.
It is chiefly situated opposite to the fourth rib and intercostal space, but may extend
forward to the third space or backward to the fifth rib. It is about five inches (ca.
12-13 cm.) above the sternal end of the fourth rib.- It is guarded by the aortic
valve, composed of three semilunar cusps (Valvulse semilunares aortse); one cusp is

' Also termed the mitral valve.

^ It may be noted that the aortic opening is partly overlapped laterally, so to speak, by the
orifice of the pulmonary artery.

STRUCTURE OF THE HEART 627

anterior, the others right and left posterior. They are similar to those of the pul-
monary valve, but are much stronger. The free edge of each contains a central
nodule of fibrous tissue (Nodulus valvulse semilunaris).^

The chordae tendineae are fewer but larger than those of the right ventricle.
There are two large musculi papillares, one on each side; they are usually com-
pound. The moderator Ijands are variable. Commonly two larger ones (which are
often branched) extend from the musculi papillares to the septum. Smaller ones
may be found in various places, especially at the apex. The other trabeculse are
fewer and less prominent than in the right ventricle.

The interventricular septum (Septum ventriculorum) is the musculo-membran-
ous partition which separates the cavities of the two ventricles. It is placed ob-
liquely, so that one surface, which is convex, faces forward and to the right, and
bulges into the right ventricle; the other surface, which faces into the left ventricle,

Origin of right coronary artery

Cojius arteriosus

Pulmonary orifice

Right atrio-ven-
tricular orifice

Origin of left cor<mary^ -^Mj^ ^^-.^^^^T^HB^ ''^"'^'' '"^^''

Left atrio-ventricular
orifice

Fig. 550. — The Bases op the Ventricles op the Heart op the Horse.

The atria have been removed and the aorta and pulmonary artery cut off short. The right ventricle is dilated and the

left ventricle is contracted, p.v., Pulmonary valve; a.v., aortic valve.

is concave and looks backward and to the left. The greater part of the septum is
thick and muscular (Septum musculare) , but the upper part is thin and membranous
(Septum membranaceum). The latter intervenes between the left ventricle, on
the one hand, and the right ventricle and atrium, on the other.

Structure of the Heart

The heart-wall consists mainly of peculiar striped muscle, the myocardium,
which is covered externally by the visceral part of the serous pericardium or epi-
cardium, and is lined by the endocardium.

The epicardium is in general closely attached to the muscular wall, but is
loosely attached over the coronary vessels and the associated subepicardial fat.
1 These nodules are also termed the corpora Arantii.

628 BLOOD-VASCULAR SYSTEM OF THE HORSE

It consists of a layer of flat polygonal cells, resting on a membrane of white and
elastic fibers.

The myocardium consists of planes of fibers arranged in a somewhat compli-
cated manner. The muscular tissue of the atria is almost completely separated
from that of the ventricles by the fibrous rings around the atrio-ventricular orifices.

The connection between the musculature of the atria and that of the ventricles is established
by the atrio-ventricxilar bundle (Fasciculus atrio-ventricularis) . This begins as a network of
fibers about the opening of the coronary sinus and the adjacent atrial wall. The fibers con-
verge to a flat, irregular mass at the upper border of the ventricular septum. From this two chief
divisions proceed. One of these descends on the right side of the ventricular septum and passes
by the moderator band to the lateral papillary muscle. The other branch descends on the left
side of the septum and ramifies on the wall of the ventricle. The left branch is somewhat diffi-
cult to follow, since it is thin and reticulate and is covered in great part by a layer of ventricular
muscle fibers. The right branch is subendocardial. The bundle and its divisions are enclosed
in a fibrous sheath. The functional importance of the bundle in mediating the contraction
wave was shown by Erlanger, who found that clamping the bimdle caused heart-block.

In the atria the muscle bands fall naturally into two groups — superficial and
deep. The former are common to both atria, the latter special to each. The
superficial or common fibers for the most part begin and end at the atrio-ventricular
rings, but some enter the interatrial septum. The deep or special bundles also
form two sets. Looped fibers pass over the atria from ring to ring, while annular
or spiral fibers surround the ends of the veins which open into the atria, the auricles,
and the fossa ovalis.

The muscular wall of the ventricles is much stronger than that of the atria.
That of the left ventricle is in general about three times as thick as that of the right
one, but is thin at the apex. The superficial fibers are attached above to the atrio-
ventricular fibrous rings and pass in a spiral toward the apex. Here they bend
upon themselves and pass deeply upward to terminate in a papillary muscle of the
ventricle opposite to that in which they arose. The loops so formed at the apex
constitute a whorl, the vortex cordis. The deep fibers, although they appear to
be proper to each ventricle, have been shown by MacCallum to be in reality almost
all common to both. Their arrangement is scroll-like. They begin on one side,
curve around in the wall of that ventricle, then pass in the septum to the opposite
side, and curve around the other ventricle. There is a layer of deep fibers which is
confined to the basal part of the left ventricle; it is attached to the left atrio-
ventricular ring.

Four fibrous rings (Annuli fibrosi) surround the orifices at the bases of the
ventricles. The atrio-ventricular rings separate the musculature of the atria from
that of the ventricles. Those which surround the origins of the pulmonary artery
and aorta are festooned in conformity with the attached borders of the valves.
The aortic ring contains on the right side a plate of cartilage (Cartilago cordis),
which frequently becomes more or less calcified in old animals. Sometimes a
smaller plate is present on the left side.

The endocardium lines the cavities of the heart and is continuous with the
internal coat of the vessels which enter and leave the organ. Its free surface is
smooth and glistening and is formed by a layer of endothelial cells. The latter
rest on a thin layer of fibro-elastic tissue, which is connected with the myocardium
by a subendocardial elastic tissue containing vessels and nerves.

Vessels and Nerves. — The heart receives a large blood-supply through the two
coronary arteries which arise from the aorta opposite to the anterior and left cusps
of the aortic valve. Most of the blood is returned by the coronary veins, which
open into the right atrium by the coronary sinus.^ A few small veins open directly
into the right atrium, and others are said to open into the left atrium and the
ventricles. The lymph-vessels form a subepicardial network which communicates

^ These vessels will be described later in their systematic order.

THE ARTERIES — THE PULMONARY ARTERY — ^THE SYSTEMIC ARTERIES 629

through stomata with the cavity of the pericardium. There is a less distinct
subendocardial network. The vessels converge usually to two trunks, which ac-
company the blood-vessels in the grooves and enter the glands at the bifurcation
of the trachea. The nerves are derived from the vagus and sympathetic through
the cardiac plexus.

The Arteries
the pulmonary artery

The pulmonary artery (A. pulmonalis) springs from the conus arteriosus at the
left side of the base of the right ventricle. It curves upward, backward, and medi-
ally, and divides behind the arch of the aorta into right and left branches. It is
related in front to the right auricle, behind to the left auricle, and medially to the
aorta. It is enveloped with the latter in a common sheath of the visceral laj'er of
the serous pericardium. Near the bifurcation it is connected with the arch of the
aorta by a fibrous band about half an inch (ca. 1.2 cm.) in width; this is the liga-
mentum arteriosum (Fig. 542), a remnant of the large ductus arteriosus, which
conducts most of the blood from the pulmonary artery to the aorta in the foetus.^
The artery is bulbous at its origin, and forms three pouches, the sinuses of the
pulmonary artery, which correspond to the cusps of the pulmonary valve. Beyond
this it gradually diminishes in caliber.

In a horse of medium size the artery is about seven inches (ca. 17-18 cm.) long. At the
origin it is about two and a half inches (ca. 6-6.5 cm.) in width; at the bifurcation its caliber
is about one and a haK inches (ca. 3.5-4 cm.). The wall is relatively thin, especially at the
origin.

The right branch (Ramus dexter) of the pulmonary artery is longer and a little
wider than the left one. It passes over the forepart of the left atrium and
under the bifurcation of the trachea to the hilus of the right lung, and enters the
latter below the right bronchus. In the lung it passes to the ventro-lateral side of
the stem-bronchus and accompanies it to the base of the organ. The branches
correspond to the ramification of the bronchi. The left branch (Ramus sinister)
is very short. It passes backward and enters the lung below the left bronchus. Its
branches within the lung are arranged like that of the right one

THE SYSTEMIC ARTERIES

The aorta is the main systemic arterial trunk. It begins at the base of the left
ventricle and is almost median at its origin. Its first part, the ascending aorta
(Aorta ascendens), passes upward and forward between the pulmonary artery on
the left and right atrium on the right. It then curves sharply backward and dor-
sally, inclines somewhat to the left, forming the arch of the aorta (Arcus aortae),
and reaches the ventral surface of the spine at the eighth or ninth thoracic vertebra.
After passing backward along the ventral aspect of the bodies of the vertebrae and
between the lungs, it traverses the hiatus aorticus and enters the abdominal cavity,
where it lies ventral to the vertebral bodies and the psoas minor, just to the left of
the median plane. It divides under the fifth lumbar vertebra into the two internal
iliac arteries.

From the bifurcation a small vessel, the middle sacral artery (A. sacralis media), sometimes
passes backward on the pelvic surface of the sacrum. It becomes lost in the periosteum or joins
the coccygeal artery, or in exceptional cases is traceable to the sphincter ani extemus.

The caliber of the aorta is greatest at its origin, which is termed the bulbus

1 There is a depression in the interior of the artery which corresponds to the attachment of
the lig. arteriosum, and in some cases the latter has a very small lumen.

630

BLOOD-VASCULAR SYSTEM OF THE HORSE

aortae. Here is forms three pouch-like dilatations, the sinuses of the aorta. These
correspond to the cusps of the aortic valve, and the coronary arteries arise from the
left posterior and anterior sinuses. At the arch the diameter is about two inches
(ca. 5 cm.), and beyond this it diminishes rather rapidly in width.

It is convenient to divide the aorta into thoracic and abdominal parts. The
thoracic aorta (Aorta thoracica) (Figs. 553, 554) lies within the pericardium to the
point of attachment of the ligamentum arteriosum, and is enclosed with the pulmon-
ary artery in a prolongation of the epicardium. Beyond this it is between the two
pleural sacs. It is crossed on the right by the oesophagus and trachea, on the left
by the left vagus nerve. The left recurrent nerve winds around the concavity of the

Pulmonary veins

Right branch of
■pulmonary

Vena azygos

Great coronary vein

Small coronary vein

Bight coronary artery

Veins are black, arteries white.

Fig. 551. — Cardiac Vessels or Horse; Right Side.

The circumflex branch of the coronary artery is largely concealed by the great coronary
vein.

arch from the lateral to the medial side, and the vena azygos and thoracic duct lie
along the dorsal part of its right face. The trachea causes it to deviate to the left,
but beyond this it becomes median. The abdominal aorta (Aorta abdominalis)
(Fig. 575) is related dorsally to the lumbar vertebrae, the ventral longitudinal
ligament, and the left psoas minor muscle; in the hiatus aorticus it is related to the
cisterna chyli. On its right is the posterior vena cava, and on its left the left kidney
and ureter.

BRANCHES OF THE THORACIC AORTA
I. CORONARY ARTERIES
The two coronary arteries, right and left, are distributed almost entirely to
the heart, but send some small twigs to the origins of the great vessels.

The right coronary artery (A. coronaria dextra) arises from the anterior sinus
of the aorta. It passes forward between the conus arteriosus and the right auricle

COMMON BRACHIOCEPHALIC TRUNK

631

to the coronary groove, in which it curves around to the right and backward. It
then descends in the right longitudinal groove almost to the apex of the heart. It
usually gives off a circiimflex branch as it turns downward; this branch (Ramus
circumflexus) passes back in the coronary groove, and anastomoses with the cor-
responding branch of the left artery.

The left coronary artery (A. coronaria sinistra) arises from the left posterior
sinus of the aorta, emerges behind the origin of the pulmonary artery, and divides
into two branches. The descending branch (Ramus descendens) passes down the

Pulmonary veins

Right coronanj
artery

Left coronary artery,
descending branch

Great coronary vein

Left coronary artery,
circumiiex branch

The dotted lii

ARDiAC Vessels of Horse; Left Side.

indicate part of the left coronary artery which is concealed by the left auricle. The ligamentum
arteriosum is shown but not marked.

left longitudinal groove toward the apex. The circumflex branch (Ramus circum-
flexus) runs backward in the coronary groove, in which it winds around to the right
side.

2. COMMON BRACHIOCEPHALIC TRUNK

The common brachiocephalic trunk (Truncus l^rachiocephalicus communis)^
is a very large vessel which arises from the convexity of the arch of the aorta within
the pericardium. It is directed forward and upward. Its length in horses of
medium size is usually about two inches (ca. 5 cm.), but it is sometimes only half
an inch or less (ca. 1 cm.). It is crossed on the left by the left vagus and cardiac
nerves, and the left recurrent nerve runs between it and the trachea. It divides
opposite to the second intercostal space or third rib into the brachiocephalic and
left brachial arteries.

The brachiocephalic artery (A. brachiocephalica) is directed forward and some-
what dorsally in the anterior mediastinum, beneath the trachea. Opposite the
first rib it gives off the bicarotid trunk and is continued as the right brachial artery.
The latter (A. subclavia dexter) turns ventrally and bends around the anterior
^ Also known as the anterior aorta.

632

BLOOD-VASCULAR SYSTEM OF THE HORSE

border of the first rib and the insertion of the scalenus muscle above the brachial
vein. Its course and branches beyond this point will be described with the vessels
of the thoracic limb.

The left brachial artery (A. subclavia sinistra) is longer than the right one and
rises to a higher level. It forms an almost semicircular curve, the concavity being
ventral. It is related medially to the oesophagus, trachea, and thoracic duct;
and the left vagus, phrenic, and cardiac nerves cross under its origin.^ It emerges
from the thorax like the artery of the right side. There is thus a difference at first

Fig. 553. — Topography of Thorax of Horse, Left Side, after Removal of Lung, Pericardium, and Greater
Part of Mediastinal Pleura.
1, Right ventricle; 1', left ventricle; 2, right auricle; 2', left auricle; 3, pulmonary artery; 3', left branch of 3;
4, aorta; 5, brachiocephalic trunk; 6, left brachial vessels; 7, dorsal artery; 7', subcostal artery; 8, deep cervical
artery; 9, vertebral artery; 10, internal thoracic artery; 11, musculo-phrenic artery; 12, inferior cervical arterj'; 13, in-
tercostal artery; 14, bicarotid trunk; 15, common carotid arteries; 16, anterior vena cava; 17, thoracic duct; IS, left
vagus; 18', oesophageal continuations of vagi; 19, left recurrent nerve; 20, left phrenic nerve (part which crosses peri-
cardium indicated by dotted line) ; 21, cardiac nerve; 22, sympathetic trunk; 23, great splanchnic nerve; 24, oesophagus;
25, trachea; 26, left bronchus; 27, pulmonary veins; 28, apical lobe of right lung; 29, basal border of left lung indicated
by dotted hne; 30, diaphragm; 30', diaphragmatic Hne of pleural reflection; 31, 32, external and internal intercostal
muscles; 33, longus colh; 34, levator costse; 35, multifidus dorsi.

between the trunks of opposite sides, but beyond this their course and distribution
are similar.

The left brachial and brachiocephalic arteries give off within the thorax the
dorsal, deep cervical, vertebral, and internal thoracic arteries. At the first rib each
gives off the external thoracic and inferior cervical arteries.

1. The dorsal or costo-cervical artery (A. costo-cervicalis) of the left side
passes dorsally across the left face of the trachea and oesophagus toward the second
intercostal space. The right artery arises usually by a common trunk with the
deep cervical, crosses the right face of the trachea, and has no contact with the
oesophagus. Both detach small branches to the trachea, mediastinal lymph glands,
and pleura, and on reaching the longus colli divide into two branches. Of these, the

^ In some cases the artery is too low to touch the cesopbagus.

COMMON BRACHIOCEPHALIC TRUNK

633

subcostal artery (A. intercostalis suprema) is the smaller. It passes backward
along the lateral border of the longus colli with the sympathetic trunk. It gives
off the second, third, and fourth intercostal arteries, and ends at the fifth space,
where it anastomoses with the first aortic intercostal artery, or constitutes the fifth
intercostal artery, or dips into the longissimus muscle. It also gives off spinal
branches and twigs to the longus colli and the pleura. The other branch (A.
transversa colli) is the direct continuation of the trunk. It emerges through the

Fig. 554. — Topography of Thorax of Horse, Right Side, after Removal of Lung, Pericardium, and Greater
Part op Mediastinal Pleura.
1, Right ventricle; 1', left ventricle; 2, right atrium; 2', left atrium; 3, anterior vena cava; 4, posterior vena cava
5, vena azygos; 6, phrenic vein; 7, aorta; 8, right coronary artery; 9, bronchial artery; 9', oesophageal artery and vein
10, first aortic intercostal artery and vein; 11, right pulmonary artery; 12, pulmonary veins; 13, right brachial vessels
14, dorsal vessels; 14', subcostal vessels; 15, deep cervical vessels; 16, vertebral vessels; 17, inferior cervical artery
18, internal thoracic vessels: 18', musculo-phrenic artery; 19, bicarotid trunk; 20, common carotid arteries; 21, jugu-
lar vein; 22, thoracic duct; 23, right vagus; 23', oesophageal continuations of vagi; 24, right recurrent nerve; 25, right
phrenic nerve (part which crosses pericardium indicated by dotted line); 26, sympathetic trunk; 27, great splanchnic
nerve; 28, oesophagus; 29, trachea; 30, right bronchus; 31, left lung; 32, basal border of right lung indicated by dotted
line; 33, mediastinal pleura; 34, diaphragm; 35, diaphragmatic line of pleural reflection; 36, intercostal muscle; 37,
longus colli; 38, psoas; 39, interspinous ligament; 40, supraspinous ligament; 41, funicular part, 41', lamellar part, of
ligamentum nuchae.

dorsal end of the second intercostal space, passes across the longissimus costarum and
longissimus dorsi toward the withers, and divides into several diverging branches.
An anterior branch passes upward and forward between the splenius and complexus
and anastomoses with branches of the deep cervical artery; the others ascend on
the dorso-scapular ligament under cover of the serratus ventralis and rhomboideus
to the withers, supplying the muscles and skin of this region.

The left dorsal artery sometimes arises with the deep cervical by a common trunk; this
arrangement is usual on the right side, and there may be a common stem for the dorsal, deep cervi-
cal and vertebral arteries. Occasionally the artery arises from the brachiocephalic trunk. Some-
times it emerges through the third space. The subcostal may arise independently behind the
dorsal or from the deep cervical artery.

2. The deep or superior cervical artery (A. cervicalis profunda) arises in front
of the dorsal or by a common trunk with it. It crosses the oesophagus (left side),

634 BLOOD-VASCULAR SYSTEM OF THE HORSE

the trachea (right side), and the longus colli, and emerges from the thoracic cavity
by passing through the space behind the first costo-transverse articulation.^ In
the thorax it gives off a small mediastinal branch (A. mediastini cranialis) to the
mediastinum and the pericardium; also the first intercostal artery (A. intercostalis
prima), a very small vessel which passes down in the first intercostal space. After
leaving the thorax the artery passes upward and forward on the spinalis muscle
and the lamellar part of the ligamentum nuchas, covered by the complexus. Its
terminal branches anastomose with branches of the occipital and vertebral arteries
in the region of the axis. Numerous collateral branches are detached to the lateral
muscles of the neck, the ligamentum nuchse, and the skin, and anastomoses occur
with the dorsal artery also.

3. The vertebral artery (A. vertebralis) arises from the brachial on the left
side, the brachiocephalic on the right; it begins opposite the first intercostal space
and passes upward and forward. On the left side it crosses the oesophagus, on the
right, the trachea. Emerging from the thorax it passes between the longus colli
mediall}^ and the scalenus laterally, under the transverse process of the seventh
cervical vertebra, and continues along the neck through the series of foramina trans-
versaria, between which it is covered by the intertransversales colli. ^ Emerging

Branches of
occipital artery ^ Vertebral artery

Fig. 55.5. — Vertebral Artery of Horse. (After Sohmaltz, Atlas d. Anat. H. Pferdes.)

from the foramen of the axis, it crosses the capsule of the atlanto-axial joint, and
joins the recurrent branch of the occipital artery under cover of the obliquus
capitis posterior. At each intervertebral foramen a spinal branch (Ramus spinalis)
is given off which enters the vertebral canal and reinforces the ventral spinal artery.
It also gives off series of dorsal and ventral muscular branches (Rami musculares).
The dorsal branches are the larger; they supply the deep extensor muscles of the
head and neck, and anastomose with the deep cervical and occipital arteries. The
ventral branches supply chiefly the scalenus, longus colli, intertransversales, and
rectus capitis ventralis major. The artery is accompanied by the vertebral vein
and a sympathetic nerve trunk (Nervus transversarius).

4. The internal thoracic artery (A. thoracica interna) is a large vessel which
arises from the ventral side of the brachial opposite the first rib. It curves down-
ward and backward, being at first on the medial surface of the rib, and then crosses
the ventral part of the first intercostal space and passes under the transversus
thoracis muscle. It runs backward under cover of that muscle over the chondro-
sternal joints to the eighth costal cartilage, where it divides into musculo-phrenic
and anterior abdominal branches. At each intercostal space two collateral branches
are detached. The intercostal branches (Rami intercostales) ascend in the inter-
costal spaces and anastomose with homonymous descending arteries. The ventral

' The artery sometimes emerges through the second intercostal space.

- In some cases the last cervical transverse process has a foramen transversarium, through
which the artery passes.

THE COMMON CAROTID ARTERY 635

branches detach small twigs to the transversus thoracis, pleura, and pericardium,
and pass out between the costal cartilages as perforating branches (Rami perfor-
antes) to supply the pectoral muscles and skin, anastomosing with the external tho-
racic artery. A very small pericardiaco-phrenic artery (A. pericardiaco-phrenica)
ascends in the mediastinum on the left side, in the caval fold of pleura on the right
side; it supplies fine twigs to the pericardium and pleura and accompanies the
phrenic nerve to the diaphragm. In the young subject it gives small branches,
the thymic arteries (Aa. thymicse), to the thymus gland. The musculo-phrenic
or asternal artery (A. musculophrenica) passes along the groove between the eighth
and ninth costal cartilages and continues along the costal attachment of the trans-
versus abdominis (Fig. 275). It gives off intercostal branches which anastomose
with those descending from the thoracic aorta, and twigs to the diaphragm and
transversus abdominis. The anterior abdominal artery (A. epigastrica cranialis)
is the direct continuation of the internal thoracic. It passes between the ninth
costal cartilage and the xiphoid cartilage, runs backward on the abdominal surface
of the rectus abdominis, and then becomes embedded in the muscle (Fig. 590).
It supplies the ventral wall of the abdomen and anastomoses with the posterior
abdominal artery.

5. The external thoracic artery (A. thoracica externa) is given off from the
ventral aspect of the brachial, usually at the medial surface or anterior border of
the first rib. It turns around the first rib ventral to the brachial vein (when given
off within the thorax), and passes backward under cover of the deep pectoral muscle;
it is continued as a small vessel in the cutaneous muscle, where it accompanies the
external thoracic vein. It gives branches to the pectoral muscles and the axillary
lymph glands and terminates in the cutaneous muscle and the skin of the ventral
wall of the abdomen.

This artery varies in origin and size. Not rarely it arises from the internal thoracic or
from the brachial outside of the thorax. In other cases it arises by a common trunk with the
inferior cervical. It may be very small or even absent, in which case the perforating branches
of the internal thoracic compensate.

6. The inferior cervical artery (Truncus omo-cervicalis) arises usually from
the dorsal surface of the brachial artery opposite the first rib or where that vessel
winds around the rib. It is directed downward and a little forward across the
lateral surface of the terminal part of the jugular vein and the deep face of the
scalenus among the posterior cervical lymph glands, and divides into ascending and
descending branches. The ascending branch (A. cervicalis ascendens) passes
upward and forward along the lateral surface of the jugular vein, then turns sharply
backward and runs upward along the anterior border of the anterior deep pectoral
muscle, between the omo-hyoideus and brachiocephalicus and in relation to the
prescapular lymph glands; it gives branches to these muscles and the posterior
cervical and prescapular lymph glands. The descending branch (A. transversa
scapulae) passes ventro-laterally across the surface of the anterior deep pectoral and
then runs in the groove between the anterior superficial pectoral muscle and the
brachiocephalicus in company with the cephalic vein. It supplies branches to these
muscles and the skin of the breast.^

THE COMMON CAROTID ARTERY

The two common carotid arteries arise from the brachiocephalic artery by a
common trunk. This stem, the truncus bicaroticus, is detached from the medial
face of the brachiocephalic opposite the first rib and passes forward medially on the
ventral face of the trachea. It is related ventrally to the posterior cervical lymph
glands, the terminal parts of the jugular veins, and the anterior vena cava, and
1 In rare cases the two branches arise separately.

636

BLOOD-VASCULAR SYSTEM OF THE HORSE

laterally to the vagus and recurrent nerves. It is commonly two or three inches
(ca. 5-7 cm.) in length, but it may vary between one and eight inches (ca. 2.5-
20 cm.).i

The right common carotid artery (A. carotis communis dextra) passes obliquely
from the ventral face of the trachea to its right side and continues in this position,
but inclines toward the dorsal surface of the trachea near its termination. It

Fig. 556. — Vessels and Nerves of Neck of Horse.
a, Brachiocephalicus; b, sterno-cephalicus; c, omo-hyoideus; d, sterno-thyro-hyoideus; e, trachea; /, position of
cariniform cartilage; g, anterior superficial pectoral muscle; h, scalenus; i, intertransversales; k, insertion of serratus
cervicis; Z, remnant of trapezius; m, rhomboideus; n, splenius; o, complexus; p, g, longissimus capitis et atlantis; p',q',
tendons of same; r, longissimus; s, obliquus capitis posterior; t, wing of atlas; u, parotid gland; v, supraspinatus; w,
anterior deep pectoral ; x, spine of scapula; 2/, prescapular lymph glands; 1, external maxillary vein; ^, S, jugular vein;
4, carotid artery, exposed by drawing jugular vein aside; 5, 6, ascending and descending branches of inferior cervical
artery; 7, cephalic vein; S, branches of deep cervical artery; 9-14, ventral branches of second to seventh cervical nerves;
15, branches of dorsal divisions of cervical nerves. (EUenberger-Baum, Top. Anat. d. Pferdes.)

divides at the crico-pharyngeus muscle and under cover of the mandibular gland
into external carotid, internal carotid, and occipital arteries.- It is enclosed in a
fibrous sheath, and is accompanied dorsally by the vagus and sympathetic nerves,
ventrally by the recurrent nerve. In the posterior part of the neck it is in contact

1 In very rare cases there is no truncus bicaroticus. The two carotid arteries then arise
separately from the brachiocephaUc, the left one first, and the right one an inch or more further
forward.

^ A small nodule is present in the angle of division. This is the carotid body or glomus caro-
ticum.

THE COMMON CAROTID ARTERY

637

superficially with the jugular vein, but further forward the omo-hyoideus muscle
intervenes between the arter}^ and vein. Near its termination the artery becomes
more deeply placed and is related laterally
to the mandibular and parotid glands, medi-
ally to the oesophagus. In some cases it is in
contact ventrally with the lateral lobe of the
thyroid gland, especially when the latter is
more dorsally situated or larger than usual.
The left common carotid artery (A.
carotis communis sinistra) differs from the
right one in that it is related deeply to the
oesophagus also, which usually separates it
from the trachea in part of its course.

The left carotid is commonly in contact with
the trachea for a short distance (ca. 8-10 cm.) at the
root of the neck, but this contact may be even less
when the a?sophagus is more ventral than usual and
the bicarotid trunk long. On the other hand, the re-
lation to the trachea may be more extensive.

The collateral branches of the common
carotids are in the main small. They com-
monly comprise the following:

1. Muscular branches (Rami muscu-
lares) of variable size go to the ventral
muscles of the neck and the skin.

2. (Esophageal and tracheal branches
(Rami cesophagei et tracheales). Small
twigs go to the cervical lymph glands also.

3. The parotid artery (A. parotidea)
comes off near the termination and enters
the ventral part of the parotid gland. It
also sends twigs to the adjacent lymph
glands, and sometimes detaches a branch to
the mandibular gland. It is inconstant.

4. The anterior thyroid or thyro-larjoi-
geal artery (A. thyreoidea cranialis), the
largest collateral branch of the carotid,
arises from the latter two or three inches
before it divides. It curves over the anterior
ond of the thyroid gland, into which it sends
several branches. It gives off the lar3mgeal
artery (A. laryngea), which sends branches
to the external muscles of the larynx and the
constrictors of the pharynx, passes between
the cricoid and thyroid cartilages, and sup-
plies the internal muscles and the mucous
membrane of the larynx. A small pharyn-
geal branch (A. pharyngea ascendens) runs
upward and forward to the crico-pharyn-
geus, and supplies twigs to the posterior
part of the pharynx and the origin of the
oesophagus. Small innominate twigs are

given off to the trachea, the oesophagus, and the sterno-thyro-hyoideus and omo-
hyoideus muscles.

Fig. 557. — Cross-section of Neck op Hobse,
Passing through Fifth Cervical Ver-
tebra; Anterior View.

a, Branches of cervical nerves; a', nuchal fat;
b, intertransversalis muscle; c, longissimus mus-
cle; d, vertebral artery; e, vertebral vein; /, ner-
vus transversarius; g, spinal accessory nerve (dor-
sal division); h, recurrent nerve; i, vago-sympa-
thetic trunk; k, tracheal lymph duct; I, body of
fifth cervical vertebra; /', transverse process of
same; m, common carotid artery; n, jugular vein;

0, deep cervical artery; o', satellite vein of o;
p, spinal cord; q, dura mater; r, spinal vein; s,
ligamentum nuchse; t, rhomboideus muscle; u,
splenius; v, complexus; w, multifidus; x, serratus
cervicis; ;/, brachiocephalicus; ?, sterno-cephalicus;

1, rectus capitis ventralis major; $, omo-hyoideus;
3, cutaneus; 4j sterno-thyro-hyoideus; 5, longus
colli; 6, 7, longissimus capitis et atlantis; 8, trape-
zius; 9, spinalis; 10, oesophagus; 11, trachea, with
cartilaginous ring {11'), mucous membrane {11"),
and muscular layer {11'"). (After Ellenberger,
in Leisering's Atlas.)

638

BLOOD-YASCULAR SYSTEM OF THE HORSE

In some cases the thyroid and h^rJ^lgeal arteries arise from the carotid separately or by a
short common stem. A laryngeal branch is often detached from the carotid in front of the thyro-
larjmgeal and enters the larynx with the anterior la^3^lgeal nerve. The pharyngeal branch fre-
quently comes directlj' from the carotid.

Fig. 558. — Deep Dissection of Neck of Horse.
a, a, Endsof sterno-cephalicus; b, anterior part of omo-hyoideus; c, sterno-thyro-hyoideus; d, trachea; e, oesopha-
gus; /, cariniform cartilage; g, rectus cap. ventralis major; h, stump of longissimus atlantis; i, intertransversales; k,
multifidus; /, m, scalenus; n, serratus cervicis; o, o, stumps of splenius; p, longissimus cervicis; g, complexus (most of
which is removed) ; r, rhomboideus; s, trapezius; <, spinalis et semispinalis; m, lamellar part of lig. nuchse; d, brachio-
cephalicus; it', anterior deep pectoral; i, supraspinatus; 2/, anterior superficial pectoral ; z, tuber scapulse; i , 7 , articular
processes of cervical vertebrae; 2, 2, transverse processes of same; 3, atlas; 3', axis; 4> 4, jugular vein (remainder re-
moved) ; .5, common carotid artery, from which a piece is removed to show the accompanying nerves and the CESophagus;
6, vago-sympathetic trunk; 7, 7, tracheal and muscular branches of carotid artery; S, recurrent nerve; 10, left tracheal
lymph-duct; 11, 12, ascending and descending branches of inferior cervical artery {13) ; H, cephalic vein; 15-20, ven-
tral branches of second to seventh cervical nerves; 21, roots of phrenic nerve; 22, pectoral nerves; 22', nerve to ser-
ratus ventraUs; .23, musculo-cutaneous nerve; ^4i median nerve; ;25, ulnar nerve; ^6, radial nerve; .27, axillary nerve;
28, dorsal branches of cervical nerves; 28', accessory nerve (cut) ; 29, deep cervical artery; 30, muscular branch of ver-
tebral arterj" 31, posterior branch of occipital artery; 32, vertebral artery; 33, muscular branches of occipital artery;
34, obliquus capitis post.; 35, obi. cap. ant.; 36, twig from dorsal branch of third cervical nerve. (After EUenberger-
Baum, Top. Anat. des Pferdes.)

5. The posterior thyroid artery (A. thyreoidea caudalis) is a small and incon-
stant vessel which arises from the carotid at a variable distance behind the anterior
thyroid or from the latter or the parotid artery. It sends branches into the pos-
terior part of the thyroid gland, and detaches small tracheal and muscular twigs.
In some cases it is distributed chiefly or entirely to the adjacent muscles.

THE OCCIPITAL ARTERY

G39

THE OCCIPITAL ARTERY

The occipital artery (A. occipitalis) is usually the second in size of the terminals
of the carotid. It arises commonly just in front of the internal carotid, but in some
cases with that artery by a common trunk of variable length. It pursues a some-
what flexuous course to the fossa atlantis, where it divides into anterior and posterior
branches. It is related superficially to the mandibular gland and the brachio-
cephalicus, and deeply to the guttural pouch and the rectus capitis ventralis major.'-
The internal carotid artery, the
ventral cerebral vein, and the ac-
cessory, vagus, and sympathetic
nerves cross its deep face. It
gives off twigs to the mandibular
gland, the ventral straight mus-
cles of the head, the guttural
pouch and the adjacent lymph
glands, and two named collateral
branches.- The condyloid artery
(A. condyloidea) is a small vessel
which passes upward and forwartl
on the guttural pouch, and divides
into muscular and meningeal
branches. The latter enter the
cranium through the foramen
lacerum and hypoglossal foramen
and are distributed to the dura
mater. This artery is very vari-
able in its origin.^ The posterior
meningeal artery (A. meningea
aboralis)^ is a much larger vessel
which runs upward and forward
between the obliquus capitis an-
terior and the paramastoid proc-
ess, passes through the mas-
toid foramen into the temporal
canal, enters the cranial cav-
ity, and is distributed to the
dura mater. It gives collateral
branches to the atlanto-occipital
articulation and the adjacent
muscles.

The posterior or recurrent

1 The relation to the guttural
pouch is not constant. In some cases —
especially when the head and neck are
extended — the artery hes behind the
pouch. The backward extension of the
latter is variable.

- The branch to the mandibular
gland (A. gland ulaj mandibularis dor-
salis) may come from the external caro-
tid or the posterior meningeal artery.

' It is also known as the preverte-
bral ; it often comes from the posterior
meningeal artery.

* Also termed the mastoid artery.

Fig. 559. — Vessels and Nerves of Base op^^s^ of Horse.
/iJ, Cerebrospinal artery; /4, ventral spinal artery; ^o, basilar
artery; 16, posterior cerebellar artery; 17, anterior cerebellar ar-
tery; 18, internal auditory artery; 19, posterior cerebral artery;
'20, deep cerebral artery; 21, stump of internal carotid artery; 22,
anterior chorioid artery; 23, anterior meningeal artery; 24, middle
cerebral artery; 25, artery of corpus callosum; 26, anterior com-
municating artery; /, 1', 1", olfactory striae; 1'", olfactory
tract; 2-12, cranial nerves; a, olfactory bulb; 6, trigonum olfac-
torium; c, lamina perforata anterior; d, fossa lateralis; e, piri-
form lobe; /, cerebral peduncle; g, tractus transversus; h, corpus
mammillare; ?', tuber cinereum; k, lateral fissure (of Sylvius);
I, presylvian fissure; m, pons; o, pyramid; p, facial eminence;
q, corpus restiforme; r, cerebellum; s, middle peduncle of cerebel-
lum. (After EUenberger-Baum, Top. Anat. d. Pferdes.)

^40 BLOOD-VASCULAR SYSTEM OF THE HORSE

branch (Ramus recurrens)^ of the occipital passes up through the foramen trans-
versarium of the atlas and joins the vertebral artery. It gives branches to the
obliquus capitis posterior, which covers it.

The anterior or occipital branch (Ramus occipitalis)^ passes through the alar
foramen of the atlas and supplies the muscles and skin of the poll, anastomosing
with the deep cervical artery and its fellow of the opposite side. In the alar furrow
it gives off the cerebrospinal artery (A. cerebrospinalis), which enters the spinal
canal through the intervertebral foramen of the atlas, perforates the dura mater,
and divides into cerebral and spinal branches. The cerebral branch (Ramus
cerebralis) unites with that of the opposite side to form the basilar artery, and the
spinal branch (Ramus spinalis) similarly forms by union with its fellow the ventral
spinal artery.

The basilar artery (A. basilaris cerebri) passes forward in the median groove
on the ventral surface of the medulla oblongata and pons and divides into the two
posterior cerebral arteries. The collateral branches of the basilar are:

1. Medullary branches (Rami medullares), ten or twelve in number, dis-
tributed to the medulla oblongata.

2. Posterior cerebellar arteries (Aa. cerebelli aborales), which pass outward
around the medulla behind the pons to the cerebellum, to which they are distributed
after giving twigs to the medulla and pons.

3. The small auditory artery (A. auditiva interna) accompanies the eighth
nerve to the internal ear. It often arises from the posterior cerebellar.

4. Anterior cerebellar arteries (Aa. cerebelli orales). These are very variable
in number and origin. There are often two or three on either side, and they fre-
quently arise from the posterior cerebral. They pass outward in front of the pons
and supply the anterior part of the cerebellum.

The posterior cerebral arteries (Aa. cerebri aborales) diverge at an acute angle
and join the posterior communicating branches of the internal carotid arteries on
the ventral surface of the cerebral peduncles. They are connected by a transverse
branch and by a network of fine twigs which form often a rete mirabile.

The ventral spinal artery (A. spinalis ventralis) runs along the ventral median
fissure of the spinal cord, which it supplies. It is reinforced along its course by
branches from the vertebral, intercostal, lumbar, and lateral sacral arteries, which
■enter the vertebral canal through the intervertebral foramina.

THE INTERNAL CAROTID ARTERY (Figs. 559, 561, 562)

This artery (A. carotis interna) is usually somewhat smaller than the occipital.
It usually arises just behind that artery, crosses its deep face, and runs upward and
forward on the guttural pouch to the foramen lacerum.^ It is closely related to
the vagus nerve and the anterior cervical ganglion of the sympathetic nerve, fibers
from which accompany it. It is crossed laterally by the ninth and twelfth cranial
nerves and the pharyngeal branch of the vagus. It passes through the ventral
petrosal sinus and enters the cavernous sinus, within which it forms an S-shaped
curve. It is connected mth the opposite artery by a transverse branch, the inter-
carotid artery (A. intercarotica), which lies in the intercavernous sinus behind the
pituitary body. A branch (A. caroticobasilaris) often connects it with the basilar
artery. It then perforates the dura mater, gives ofi the posterior communicating
artery, and passes forward and divides at the side of the optic chiasma into anterior
and middle cerebral arteries.

The posterior communicating artery (A. communicans aboralis) turns back-

1 Also termed the retrograde or anastomotic branch.

2 Also termed the musculo-occipital.

^ Not rarely it arises with the occipital artery from a common trunk of variable length.

THE EXTERNAL CAROTID ARTERY 641

ward and joins the posterior cerebral branch of the basilar. It gives off the deep
cerebral artery (A. cerebri profunda), which winds around the cerebral peduncle
and is distributed chiefly to the mid-brain; it is often double. A smaller collateral
branch is the anterior chorioid artery (A. chorioidea oralis), which passes along the
optic tract and is distributed in the chorioid plexus of the lateral ventricle.

The anterior cerebral artery (A. cerebri oralis) unites with the corresponding
branch of the opposite artery above the optic chiasma. From this junction pro-
ceeds the artery of the corpus callosum (A. corporis callosi), which turns around the
genu of the corpus callosum, enters the great longitudinal fissure, divides into two
branches, and is distributed to the medial aspect of the cerebral hemispheres. The
anterior cerebral gives off the small internal ophthalmic artery (A. ophthalmica
interna), which passes forward at first lateral to the optic nerve; then, crossing over
the latter to its medial side, it joins a branch of the external ophthalmic. A small
anterior meningeal branch (A. meningea oralis) of the anterior cerebral is distributed
to the anterior part of the dura, and assists in forming a network in the ethmoidal
fossa (Rete ethmoidale), anastomosing with the ethmoidal branch of the external
ophthalmic artery and the artery of the corpus callosum.

The middle cerebral artery (A. cerebri media) passes outward in the fossa
lateralis in front of the piriform lobe, reaches the lateral fissure, and divides into
branches on the lateral surface of the hemisphere.

The circulus arteriosus (Fig. 559) ^ is formed at the interpeduncular space of
the base of the brain by the union of the anterior cerebral arteries in front, by the
diverging posterior cerebral arteries behind, and is completed laterally by the junc-
tion of the latter with the posterior communicating arteries and by the internal
carotid. It is irregularly polygonal in outline, and surrounds the optic chiasma
and pituitary body.-

THE EXTERNAL CAROTID ARTERY (Figs. 561, 562)

This artery (A. carotis externa), by its size and direction, constitutes the con-
tinuation of the common carotid. It passes forward on the lateral wall of the
pharynx at the lower border of the guttural pouch, covered by the mandibular
gland and the occipito-mandibularis, digastricus, and stylo-hyoideus muscles, and
in relation to the parapharyngeal lymph glands. It then emerges between the stylo-
hyoideus and the great cornu of the hyoid bone, ascends on the latter parallel with
the posterior border of the lower jaw, and terminates about two inches (ca. 5 cm.)
below the temporo-mandibular articulation by dividing into superficial temporal
and internal maxillary branches. It is crossed deeply near its origin by the anterior
laryngeal and pharyngeal branches of the vagus nerve. Just before its emergence
its superficial face is crossed by the hypoglossal nerve, and the glosso-pharyngeal
nerve passes over its medial surface at the ventral border of the great cornu. The
chief collateral branches are the masseteric, external maxillary, and posterior
auricular. It also furnishes variable branches to the mandibular and parotid
glands, the guttural pouch, and the pharyngeal lymph glands, as well as twigs to
some adjacent muscles.

1. The masseteric artery (A. masseterica)^ is given off from the external
carotid at its emergence from beneath the stylo-hyoideus. It passes downward
and slightly forward under cover of the parotid gland and over the tendon of in-
sertion of the sterno-cephalicus to the posterior border of the mandible and appears
on the masseter muscle, which it enters after a short course on its surface. It gives

1 Also termed the circle of Willis.

"^ The cerebral arteries are very variable in arrangement, and the foregoing account is a brief
statement of the more usual disposition of the larger vessels.
^ Also termed the maxillo-muscular.
41

542 BLOOD-VASCULAR SYSTEM OF THE HORSE

branches also to the medial pterygoid and occipito-mandibiilaris muscles and the
parotid gland.

2. The external maxillary artery (A. maxillaris externa)^ arises from the ex-
ternal carotid on the deep surface of the posterior belly of the digastricus (Fig. 561).
It runs downward and forward on the lateral wall of the pharynx across the deep face
of the stylo-hyoideus toward the great cornu of the hyoid bone, accompanied by
the glosso-pharyngeal nerve in front and the hypoglossal nerve behind. After
giving off the lingual artery at the posterior border of the great cornu, it inclines
more ventrally on the medial surface of the medial pterygoid muscle, crosses over
the hyo-glossus muscle, the hypoglossal nerve, the mandibular duct, and the inter-
mediate tendon of the digastricus, and turns forward in the mandibular space.
Here it lies on the lower part of the medial pterygoid muscle, and is related medially
to the mandibular lymph glands, above to the anterior belly of the digastricus, and
below to the homonymous vein. At the anterior border of the masseter it turns
around the ventral border of the jaw and ascends on the face in front of that
muscle. At the turn the artery is in front, the vein in the middle, and the parotid
duct posterior.^ The artery is conveniently placed at its inflection for taking the
pulse, since it is superficial and lies directly on the bone. Beyond this point it is
commonly termed the facial artery (A. facialis) . The artery and vein pass upward
along the anterior border of the masseter, under cover of the facial cutaneus and
the zygomaticus, and are crossed superficially by branches of the facial nerve and
deeply by the parotid duct. The artery terminates over the levator labii super-
ioris proprius by dividing into the dorsal nasal and the angular artery of the eye.
The chief branches of the external maxillary are as follows:

(1) The phar3mgeal artery (A. palatina ascendens) arises usually behind the
stylo-pharyngeus, passes between that muscle and the great cornu, and runs for-
ward on the lateral wall of the pharynx under the elastic pharyngeal fascia. It is
distributed to the pharynx, soft palate, and tonsil.

(2) The lingual artery (A. lingualis) is a large branch which diverges from the
parent trunk at an acute angle, runs along the ventral border of the great cornu
of the hyoid bone, and dips under the hyo-glossus muscle. It then passes across
the kerato-hyoideus, turns inward under the intercornual joint of the hyoid bone,
and runs forward in the tongue between the hyo-glossus and genio-glossus. This
part (A. profunda linguie) is flexuous and is accompanied by branches of the hypo-
glossal and lingual nerves. It is the chief artery of the tongue, and anastomoses
with the opposite artery and the sublingual.^

(3) The sublingual artery (A. sublingualis) is a smaller vessel which arises at
the anterior extremity of the mandibular gland (Fig. 561). It passes forward on the
anterior belly of the digastricus, between the ramus of the mandible and the mylo-
hyoideus, perforates the latter, runs along the lower border of the sublingual gland,
and ramifies in the mucous membrane of the anterior part of the floor of the mouth.
It detaches branches to the muscles and skin in the mandibular space, the mandib-
ular lymph glands, and the sublingual gland. It also gives off the small submental
artery (A. submentalis), which runs forward superficially toward the lower lip,
supplying twigs to the skin and the mylo-hyoideus.

In some cases the sublingual artery arises from the lingual and the submental from the
external maxillary. Sometimes the sublingual remains on the superficial face of the mylo-hyoideus
— thus resembling the submental of man — and the subhngual glan 1 is supplier! by a special
branch of the lingual.

' Also termed the submaxillary or facial artery. The term facial may be applied to the artery
after it reaches the lateral surface of the face.

- In exceptional cases the vein is in front of the artery.

3 In some cases the lingual trunk runs on the superficial face of the hyoglossus instead of
passing beneath it; in such specimens a small branch extends forward a variable distance under
the muscle.

THE EXTERNAL CAROTID ARTERY

643

A considerable branch may be given off in the mandibular space, which turns around the
lower border of the jaw and enters the middle of the lower part of the masseter muscle. In some
cases this artery is of large size and its pulsation can be felt. It is accompanied by a vein.

(4) The inferior labial artery (A. labialis inferior) arises from the external
maxillary a little before it reaches the depressor labii inferioris (Fig. 560). It
passes forward, dips under the depressor muscle, and continues to the lower lip.
It supplies branches to the muscles and skin in this region, to the inferior buccal
glands, the mucous membrane of the cheek, and the lower lip, anastomosing with
the mental artery and the corresponding vessels of the opposite side. It detaches

Fig. 560. — Superficial Dissection of Head op Horse. Most op the Cutaneus is Removed.
o, Lateralis nasi; 6, levator labii superioris proprius; c, levator naso-labialis; d, dilatator naris lateralis; e, buc-
cinator; /, zygomaticus, posterior part of which is removed; g, depressor labii inferioris; h, stump of retractor anguli
oris; i, masseter; k, k, scutularis; /, scutulo-auriculares superficiales; m, zygomatico-auricularis; n, parotido-auricu-
laris; o, occipito-mandibularis; p, sterno-cephalicus; p', tendon of p; g, omo-hyoideus; r, splenius; s, tendon of sple-
nius and longissimus capitis; t, corrugator supercilii; u, orbicularis oris; v, parotid gland; w, zygomatic arch; x, scuti-
form cartilage; y, upper commissure of nostril; /, facial nerve; ^, superior buccal nerve; 3, inferior buccal nerve; 4<
transverse facial nerve; 5, cervical branch of facial "nerve ; 6, posterior auricular branch of second cervical nerve; 7,
cutaneous cervical branch of same; 5, infratrochlear nerve; 5, frontal nerve; 70, lacrimal nerve; 70', end of auriculo-
palpebral nerve; 11, masseteric artery and vein; IS, transverse facial artery and vein; 13, facial artery; 14, inferior
labial artery; 15, superior labial artery; 16, lateral nasal artery; 17, dorsal nasal artery; 18, angular artery of the eye;
i5, posterior auricular artery; ;?0, ^7, jugular vein; ^^, external maxillary vein; 23, great auricular vein; 24, parotid
duct; 24', origin of same; 2.5, superior buccal glands; 26, facial vein. (After EUenberger-Baum, Top. Anat. d. Pferdes.)

a ]:)ranch (A. anguli oris) to the angle of the mouth, which anastomoses with the
superior labial.

(5) The superior labial artery (A. labialis superior) arises from the facial in
front of the facial crest (Fig. 560) . It passes forward under the dilatator naris lat-
eralis and levator nasolabialis to the upper lip, gives twigs to the upper part of the
cheek and the lateral nasal region, and ramifies in the upper lip, anastomosing with
the opposite artery and the palato-labial.

(6) The lateral nasal artery (A. lateralis nasi) arises usually a little above the
preceding one, and runs forward parallel with it and under the levator nasolabialis
to the nostril (Fig. 560). It supplies branches to the lateral nasal region and the
nostril.

644

BLOOD-VASCULAR SYSTEM OF THE HORSE

The vessel is often double. It may arise from the superior labial at the point of bifurcation
of the facial or with the dorsal nasal from the infraorbital artery (as in the ox). In some cases
it gives off a dorsal nasal branch.

(7) The dorsal nasal artery (A. dorsalis nasi) arises on the levator labii superi-
oris proprius and passes forward under the levator nasolabialis to the dorsum nasi
(Fig. 560).

(8) The angular artery of the eye (A. angularis oculi) runs toward the medial

Fig. 561. — Parotid, Masseteric, and Lingual Regions of Horse; Deep Dissection, Third Layer.
a, Mylo-hyoideus, anterior part, reflected; h, genio-hyoideus; c, genio-glossus; d, sublingual gland; e, ramus of man-
dible, greater part removed; e', stump of masseter; /, maxillary tuberosity; g, great cornu of hyoid bone; h, wing of atlas;
i, intermediate tendon of digastricus; i', anterior belly, i", posterior belly, of digastricus; k, posterior part of mylo-
hyoideus; I, hyo-glossus; to, pterygoideus medialis (cut); );, stylo-hyoideus; o, occipito-mandibularis; p, crico-
pharyngeus; g, obliquus capitis ant. ; r, tendon of longissimus atlantis; s, rectus cap. ventralis; t, brachioeephalicus
(cut) ; M, sterno-cephalicus (cut); v, sterno-thyroideus (cut) ; tf, sterno-hyoideus (cut); x, omo-hyoideus; y. obliquus
cap. post.; 2, splenius (cut) ; 1-4^, upper cheek teeth; 4'< last cheek tooth; 5, stump of facial nerve; 6, stump of bucci-
nator nerve; 7, lingual nerve; 7', superficial branch, 7", deep branch, of hngual nerve; 8, stumps of inferior alveolar
artery, vein and nerve; 9, mylo-hyoid nerve (cut) ; 10, glosso-pharyngeal nerve; 11, hypoglossal nerve; 12, anterior larjTi-
geal nerve; 13, ventral branch of first cervical nerve; 14, vagus and sympathetic; 15, dorsal branch of spinal accessory
nerve; 76, ventral branch of same; i 7, ventral cerebral vein; 75, mandibular duct; ^S, common carotid artery; 20,
parotid branch; SI, thyro-laryngeal artery; 22, pharyngeal artery; 23, laryngeal artery; 24, internal carotid artery;
25, occipital artery; 26, external carotid artery; 27, 31, external maxillary artery; 28, pharyngeal artery; 29, lingual
artery; 30, sublingual artery; 32, external carotid artery after emergence; 33, internal maxillary vein (origin); 34,
remnant of parotid gland; 35, thyroid gland; 36, jugular vein; 37, parapharyngeal lymph glands. (After Ellen-
berger-Baum, Top. Anat. d. Pferdes.)

canthus of the eye, where it anastomoses with the oYbital branch (Ramus malaris)
of the infraorbital artery (Fig. 560).

In addition to the preceding, unnamed branches are supplied to the mandibu-
lar salivary gland and lymph glands. There is commonly a branch of considerable
size which is given off as the external maxillary artery passes the anterior end of the
mandibular gland ; it runs upward and backward along the dorsal border of the
gland, which it supplies.

3. The posterior auricular artery (A. auricularis posterior) arises at an acute
angle from the external carotid just above the origin of the masseteric. It

THE EXTERNAL CAROTID ARTERY 645

upward under cover of the parotid gland, to which it gives branches, and divides
into several branches which supply the skin and muscles of the external ear (Fig.
560). The posterior branch passes to the posterior part of the base of the ear,
where it divides into two branches; of these, one (Ramus intermedins) passes up the
convex surface of the external ear to the apex, while the other (Ramus medialis)
winds around to the anterior (medial) border, and forms an arch with the inter-

FiG. 562. — Deep Dissection of Head of Horse.
The left ramus of the mandible and structures connected with it have been removed, a, a. Stumps of styloglossus;
6, genio-glossus; c, genio-hyoideus; d, omo-hyoideus; e, kerato-hyoideus; /, thyro-hyoideus; g, thyro-pharyngeus;
/i, crico-thyroideus; i, sterno-thyroideus; A;, thyroid gland; m, crico-pharyngeus; «, palatinus and palato-pharyngeus;
o, pterygoideus lateralis; p, tensor palati; g, levator palati; r, temporalis; s, rectus cap. ventralis major; t, obliquus
cap. ant.; u, guttural pouch; v, great cornu of hyoid bone, extremity of which is removed and indicated by dotted line;
w, position of small cornu, dotted line; i, thyroid cornu; 2/, tongue; z, anterior pillar of soft palate; ^ , superficial tem-
poral nerve; 2, chorda tympani; 9, stump of inferior alveolar nerve; 4, 4, lingual nerve, intermediate part removed; 5,
deep temporal nerve; 6, masseteric nerve; 7, buccinator nerve; 8, great palatine nerve; 9, infraorbital nerve; 10,
sphenopalatine and posterior nasal nerves; 11, spinal accessory nerve; 12, vagus; 13, pharyngeal branch of vagus;
14, anterior laryngeal nerve; lo, vago-sympathetic trunk; 16, sympathetic, with anterior cervical ganglion a little fur-
ther back; 17, glosso-pharyngeal nerve; 18, pharyngeal and 19, lingual, branches of glosso-pharyngeal ; 20, hypoglossal
nerve; ^/, left recurrent nerve; .2^, common carotid artery; ^3, parotid branch; ^-^, anterior thyroid or thyro-laryngeal
artery; ;?4'. l^^ryngeal artery; .25, occipital artery; .25, internal carotid artery; ^7, external carotid artery; 28, 30, ex-
ternal maxillary artery; ^9, pharyngeal artery; Si, Ungual artery; 32, external carotid artery; S3, stump of inferior
alveolar artery; 34, middle meningeal artery; 35, deep temporal artery; 36, buccinator artery; 37, palatine artery;
S8, end of internal maxillary artery; 39, right external maxillary artery; 40, satellite vein of 39; 41 j right parotid duct;
42, mandibular lymph glands; 43, parapharyngeal lymph glands; 44 > trachea; 40, wing of atlas; 46, dotted line indi-
cating outline of mandibular gland; 4'', lacrimal gland. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)

mediate branch. The lateral branch (Ramus lateralis) passes up the posterior
(lateral) border of the ear and forms an arch with the intermediate branch. The
deep branch (A. auricularis profunda) enters the interval between the external
acoustic process and mastoid process, and passes through an opening into the
interior of the external ear and ramifies in the skin which lines it. It gives off the
stylomastoid artery, which passes through the stylomastoid foramen into the tym-

646

BLOOD-VASCULAR SYSTEM OF THE HORSE

panum, forms an arch around the membrana tympani, and supplies the middle ear
and its muscles.

THE SUPERFICIAL TEMPORAL ARTERY

This artery (A. temporalis superficialis) is much the smaller of the two terminal
branches of the external carotid, and is usually less than an inch (ca. 2 cm.) in length.

It passes upward behind the posterior
border of the ramus of the mandible,
under cover of the parotid gland, and
divides below the level of the condyle
into the anterior auricular and trans-
verse facial arteries. It is crossed super-
ficially by the facial nerve.

The anterior auricular artery (A.
auricularis anterior) ascends behind the
temporo-mandibular articulation under
cover of the parotid gland and reaches
the temporalis muscle. It is crossed
deeply at its origin by the superficial
temporal nerve and is accompanied by
a satellite vein and the auriculo-palpe-
bral branch of the facial nerve. It is
distributed to the skin and the temporal
and anterior auricular muscles, and sends
a branch through the concha! cartilage
to the skin which lines it. Collateral
twigs are detached to the parotid gland,
and an anterior branch anastomoses with
the supraorbital artery. A branch some-
times passes into the temporal canal and
anastomoses with the posterior meningeal
artery.

The transverse facial artery (A.
transversa faciei) is larger than the pre-
ceding. It turns around the neck of
the mandible and emerges from beneath
the parotid gland (Fig. 560). It then
passes forward a short distance on the
masseter about half an inch below the
zygomatic arch, and enters the muscle,
in which it commonly divides into two
chief branches. It is accompanied by a
vein and a branch of the superficial tem-
poral nerve. It supplies the masseter and the skin of this region, and anastomoses
with the external maxillary and posterior deep temporal arteries.

Fig. 563. — Right Eye or Horse.

a, Remnants of periorbita; b, levator palpebrae
auperioris; c, obliquus oculi inferior; d, rectus oculi
inferior; e, rectus oculi lateralis; /, rectus oculi superior;
g, sclera; g', cornea; h, lacrimal gland; i, frontal nerve;
i', trochlear nerve; k, supraorbital artery; i, branches of
lacrimal nerve to gland; m, lacrimal artery; n, zygo-
matic nerve; o, branch of ophthalmic artery; p, branch of
oculomotor nerve to obliquus oculi inferior; q, maxil-
lary nerve; r, infraorbital nerve; s, posterior nasal
nerve; <, great palatine nerve; u, small palatine nerve;
J), internal maxillary artery; w, buccinator artery (cut) ;
I, infraorbital artery; x', malar artery; y, spheno-
palatine artery; z, great palatine artery; z', small
palatine (or staphyline) artery; /, anterior deep
temporal artery; S, stump of zygomatic arch (sawn
off) ; 3, stump of supraorbital process (sawn off) ; 4< fa-
cial crest; 5, temporal fossa; 6, foramen orbitale; 7,
foramen rotundum and anterior end of alar canal;
S, posterior opening of alar canal. (After EUenberger,
in Leisering's Atlas.)

THE INTERNAL MAXILLARY ARTERY (Figs. 562, 563, 564)

This artery (A. maxillaris interna) is much the larger of the two terminal

branches of the external carotid. It begins at the medial side of the posterior border

of the mandible, about two inches (ca. 5 cm.) below the articulation of the jaw,

and ends in the anterior part of the pterygo-palatine fossa. On account of its

THE INTERNAL MAXILLARY ARTERY 64 T

complex course and the large number of branches given off it is convenient to divide
it into three parts.

I. The first part is much the longest, forms an S-shaped curve, and is in great
part in contact with the guttural pouch. It passes upward and forward on the
medial surface of the mandible a distance of about an inch (ca. 2-3 cm.), and is
related here to the vein, which is ventral. It then turns inward on the ventral
surface of the lateral pterygoid muscle and the mandibular nerve, passes between
that muscle and the tensor palati, and runs forward to enter the alar canal.
This part gives off the following branches:

1. The inferior alveolar artery (A. alveolaris mandibulae s. inferior) ^ passes
downward and forward with the homonymous vein and nerve, being at first between

Fig. 564. — Left Eye of Horse, Deeper Dissection.
The outer plate of bone has been removed behind the pterygoid crest to expose the vessels and nerves, a, a, Rem-
nants of periorbita; 6, b, stumps of rectus oculi superior; c, obliquus oculi inferior; d, rectus oculi inferior; c, rectus
ocuU lateralis; e' , retractor oculi; /, rectus ocuh medialis; g, g, obliquus ocuU superior; h, eyeball; i, trochlear nerve;
k, ophthalmic nerve; k', nasal nerve; k", infratrochlear nerve; k'", ethmoidal nerve; I, optic nerve; m, frontal nerve;
71, lacrimal nerve; o, zygomatic nerve; p, nerve to obliquus inferior (from oculomotor); q, maxillary nerve; r, infra-
orbital nerve; s, sphenopalatine nerve; /, great palatine nerve; u, small palatine nerve; v, internal maxillary arteT":.-;
u\ buccinator artery (cut off); j, infraorbital artery; x', malar artery; y, spheno-palatine artery; z, great palatine
artery; 2', small palatine artery; 1, 2, stumps of zygomatic arch; 3, stump of supraorbital process; 4, facial crest;
S, temporal fossa; 6, external ophthalmic artery; 7, muscular branch of 6; 8, lacrimal artery (cut); 9, supraorbital
artery; 10, anterior deep temporal artery; ii, ethmoidal artery. (After EUenberger-Baum, Top. Anat. d. Pferdes.)

the lateral and medial pterygoid muscles, then between the latter and the ramus of
the mandible. It enters the mandibular foramen, passes downward and forward
in the mandibular canal, and terminates at the mental foramen by dividing into
mental and incisor branches. The mental branch (A. mentalis) emerges throuj h
the mental foramen and anastomoses in the lower lip with the opposite artery and
the inferior labial. The incisor branch (Ramus incisivus) continues forward in the
bone, supplies twigs to the canine and incisor teeth, and ana.stomoses with its fellow
of the opposite side. Collateral branches are detached to the pterygoid and mylo-
hyoid muscles, and within the bone to the teeth, alveolar periosteum, the gums,
and the spongy substance of the mandible.

2. The pterygoid arteries, two or three in number, are distributed to the ptery-
goid and tensor and levator palati muscles.

1 Also known as the inferior dental artery.

648

BLOOD-VASCULAR SYSTEM OF THE HORSE

3. The tympanic artery is a very small vessel which passes along the Eusta-
shian tube to the petro-tympanic fissure and enters the middle ear.

4. The middle meningeal artery (A. meningea media) arises beneath the buc-
cinator nerve, where the internal maxillary turns forward. It passes backward
across the temporal wing of the sphenoid to the antero-lateral part (foramen spino-
sum) of the foramen lacerum. Entering the cranium, it divides into branches which
course in the grooves on the temporal and parietal bones and supply the dura
mater. It anastomoses with the posterior meningeal.

The size of this artery is variable, and is in inverse ratio to that of the posterior meningeal.

Fig. 565. — Sagittal Section of Head of Horse, Cut a Little to the Right of the Median Plane.
i.Skin; 3, nasal bone; 3, frontal bone ; 4i parietal bone; 4', tentorium osseum; 5, occipital bone; 6, sphenoid bone;
7, hard palate; 8, premaxilla; 9, mandible; 10, hyoid bone; 11, septum between frontal sinuses; 12, alar cartilage;
IS, transversus nasi; IJf., septum nasi with venous plexuses; 15, palato-labial artery; 16, 16', upper and lower
septal branches of i 5; i 7, septal branch of sphenopalatine artery and satellite vein; 18, septal branch of ethmoidal
artery; 19, sphenoidal sinus; 20, guttural pouch; 21, pharynx; 22, pharyngeal orifice of Eustachian tube; 23, posterior
naris; 24, soft palate; 25, palatinus muscle; 26, pharyngeal muscles; 27, cesophagus; 28, dotted line indicating posi-
tion of posterior pillar of soft palate; 29, lamina, 29', arch of cricoid cartilage; 30, arytenoideus transversus muscle;
31, epiglottis; 32, body of thyroid cartilage; 33, vocal process and cord; 34, arytenoid cartilage; 35, lateral ventricle
of larynx; 36, trachea; 37, ventral straight muscles of head; 38, longus colli; 39, atlas; 40, axis; 41, lig. nuchse; 42,
dorsal spinal muscles; 43, muscles of external ear; 4^, omo- and sterno-hyoideus; 4<5, tongue; 4^, mylo-hyoideus; 47,
genio-hyoideus; 45. genio-glossus; 4^, longitudinalis inferior; 50, longitud. superior; 51, hypo-epiglotticus; o^, chin
and mentalis muscle; 53, venous plexus of hard palate; 54, corpus callosum; 55, septum pellucidum; 56, fornix; 57,
thalamus; 58, pineal body; 59, corpora quadrigemina; 60, cerebral peduncle; 61, corpus mammillare; 62, pituitary
body; 63, chiasma opticum; 64, intercarotid artery; 65, medulla oblongata; 66, interventricular foramen; 67, infun-
dibulum; 6S, third ventricle; 6.9, cerebral aqueduct; 70, anterior medullary velum; 7^, fourth ventricle; 7^, posterior
medullary velum; 73, basilar artery; 74, spinal cord; 75, ethmoidal nerve; 76, septal branch of posterior nasal nerve;
76', branch of same to vomero-nasal organ; 77, olfactory nerve to vomero-nasal organ; 78, nasal branches of palatine
artery. (After Ellenberger, in Leisering's Atlas.)

5. The posterior deep temporal artery (A. temporalis profunda aboralis)
arises from the internal maxillary just before the latter enters the alar canal. It
passes upward and backward in the temporal fossa on the deep face of the temporalis
muscle, in which it ramifies. It sends a branch outward to the masseter, and
anastomoses with the superficial temporal and middle meningeal arteries.

In some cases the tympanic and middle meningeal arise from this artery.

II. The second part lies in the alar canal, and is about an inch (ca. 2-3 cm.) in
length. It gives off two branches — the anterior deep temporal and the external
ophthalmic.

1. The anterior deep temporal artery (A. temporalis profunda oralis) emerges
from the canal through the small alar or temporal foramen, and ascends in the

THE INTERNAL MAXILLARY ARTERY 649

anterior part of the temporal fossa on the deep face of the temporahs muscle, in
which it is chiefly distributed. It gives twigs to the orbital fat and the skin of the
frontal region.

2. The external ophthalmic artery (A. ophthalmica externa) emerges from the
anterior opening of the alar canal, and enters the apex of the periorbita. Within
this it forms a semicircular bend under the rectus oculi superior, and is continued
by the ethmoidal arter3^ Its branches are as follows:

(a) The supraorbital artery (A. supraorbitalis) is a small vessel which often
arises from the anterior deep temporal or the internal maxillary. It passes along
the inner wall of the orbit in company with the nerve of the same name to the supra-
orbital foramen, through which it emerges. It is distributed to the orbicularis
oculi, the corrugator supercilii, and the skin of the supraorbital region.

(6) The lacrimal artery (A. lacrimalis) runs upward and forward within the
periorbita along the lateral edge of the levator palpebrse superioris to the lacrimal
gland, in which it is chiefly distributed. It also sends twigs to the upper eyelid.

(c) Muscular branches (Rami musculares) supply the orbital muscles, the
periorbita, the thirtl eyelid, and the conjunctiva.

(rf) Ciliary branches (Aa. ciliares), two sets of very slender arteries, arise
from the ophthalmic direct and from the muscular branches. The anterior ciliary
arteries (Aa. ciliares anteriores) pierce the sclera in front of the equator and ramify
chiefly in the ciliary botly and the iris. The posterior ciliary arteries (Aa. ciliares
posteriores) pierce the posterior part of the sclera; most of them ramify in the
chorioid coat as the short ciliary arteries, but two of larger size, the long ciliary
arteries, run forward, one on each side, between the sclera and chorioid to the
periphery of the iris. Here they divide into branches which anastomose and form
a circle (Circulus iridis major). From this secondary branches are detached which
form a second circle around the pupil (Circulus iridis minor) .

(e) The central artery of the retina (A. centralis retinae) is a small vessel which
arises from the ophthalmic or from a posterior ciliary artery. It pierces the optic
nerve a short distance behind the sclera, and runs in its center to the lamina cribrosa,
where it breaks up in thirty to forty fine branches. These appear in the fundus of
the eye at the margin of the optic papilla and radiate in the posterior part of the
retina.

(/) The ethmoidal artery (A. ethmoidalis) is the continuation of the oph-
thalmic. It enters the cranial cavity through the ethmoidal foramen, passes
inward on the cribriform plate, and divides into meningeal and nasal branches.
The former ramify in the anterior part of the dura mater and anastomose with
branches of the artery of the corpus callosum. The nasal branch passes through the
cribriform plate, gives branches to the mucous membrane of the lateral mass of the
ethmoid and the adjacent part of the septum nasi, and runs forward on the dorsal
turbinate.

III. The third part passes forward in the pterygo-palatine fossa, accompanied
by branches of the maxillary nerve. On reaching the posterior palatine foramen it
is continued by the greater palatine artery. Its branches are as follows:

(1) The buccinator artery (A. buccinatoria) arises from the ventral aspect of
the internal maxillary shortly after its emergence (Fig. 562). It turns around the
maxillary tuberosity, accompanied by the buccinator nerve, and under the masseter
muscle, enters the cheek, and runs forward in it. It supplies branches to the
cheek, the superior buccal glands, and the masseter and pterygoid muscles. Near
its origin it gives off a branch to the orbital fat behind the periorbita.

(2) The infraorbital artery (A. infraorbitalis)^ arises from the upper aspect of
the internal maxillary a little in front of the preceding vessel. It passes upward
and forward to the maxillary foramen, runs in the infraorbital canal in company with

1 Also termed the superior dental artery.

650 BLOOD-VASCULAR SYSTEM OF THE HORSE

the nerve of the same name, and is continued forward within the jaw to the incisor
teeth. It gives branches to the teeth and gums, and detaches a branch through the
infraorbital foramen which anastomoses with the lateral nasal and superior labial.^
About midway between its origin and the maxillary foramen it gives off the malar
branch (Ramus malaris), which passes along the floor of the orbit to end in the lower
lid and anastomose with the angularis oculi. It gives twigs to the inferior oblique
muscle and the lacrimal sac.

(3) The lesser palatine artery (A. palatina minor) is a small vessel which
passes forward in the groove at the medial side of the maxillary tuberosity to the
soft palate. In the groove it is accompanied by the nerve of the same name and the
palatine vein.

(4) The sphenopalatine artery (A. sphenopalatina) arises in the anterior
part of the pterygo-palatine fossa, passes through the sphenopalatine foramen into
the nasal cavity, and divides into two branches. The medial branch is distributed
to the mucous membrane of the septum nasi; the lateral one goes to the ventral
turbinate, the ventral meatus, the posterior nares, and the maxillary and frontal
sinuses. It may arise from the infraorbital.

(5) The greater palatine artery (A. palatina major) is the direct continuation
of the internal maxillary. It passes through the palatine canal to the roof of the
mouth, accompanied by the palatine nerve, and runs forward in the palatine
groove, where it is joined by the vein. A little behind the plane of the corner
incisor teeth it curves medially over a bar of cartilage to the foramen incisivum,
where it unites with its fellow of the opposite side. The single artery thus formed
(A. palato-labialis) passes up through the foramen and divides under the transversus
nasi into two branches. These ramify in the upper lip and anastomose with the
lateral nasal and superior labial arteries. In its course in the palate the artery gives
off branches to the hard and soft palate and the gums, and others which pass through
the accessory palatine foramina to be distributed in the mucous membrane of the
lower part of the nasal cavity. Commonly two branches, right and left, are de-
tached from the convexity of the arch formed by the union of the two arteries;
these run forward in the anterior part of the hard palate.

Arteries of the Thoracic Limb
the brachial artery

The brachial artery, after crossing the ventral border of the scalenus at the
first rib, passes backward and downward across the origin of the coraco-brachialis
and the insertion of the subscapularis muscle at the medial side of the shoulder
joint.2 At the posterior border of the subscapularis it gives off the subscapular
artery, and turns distally on the medial surface of the arm. In its course in the
arm it inclines a little forward, crosses the humerus very obliquely, and is continued
by the median artery.

In its course over the chest-wall the artery is related medially to the ventral
border of the serratus thoracis and the rectus thoracis. Opposite the ventral end
of the first rib it is crossed medially by the median nerve and laterally by the mus-
culo-cutaneous nerve; the two nerves unite below the artery, which is thus sus-
pended in a sort of loop. In the arm it is related medially to the posterior deep
pectoral muscle and is covered by the deep brachial fascia. Laterally it lies on the
subscapularis, the brachialis, the insertion of the teres major and latissimus dorsi,

1 The infraorbital artery is usually small at its emergence upon the face, but in some cases it
is rather large and may partially replace the superior labial and lateral nasal arteries.

2 The term axillary is often applied to the artery from the first rib to the point of origin of
the subscapular artery, and the name brachial is given to the artery beyond this.

THE BRACHIAL ARTERY 651

and the medial head of the triceps. The coraco-brachialis muscle lies along the
front of the artery, which, however, overlaps the muscle distally. The vein crosses
the medial face of the artery and runs down behind it, accompanied part way by the
ulnar and radial nerves. The chief branches are as follows:

1. The suprascapular artery (A. thoraco-acromialis) is a small and somewhat
flexuous vessel, which arises near the anterior border of the subscapularis, runs
dorsally, and dips in between that muscle and the supraspinatus. It gives branches
to these muscles, the anterior deep pectoral, and the brachiocephalicus. A branch
passes in front of the coraco-brachialis to the shoulder joint and the proximal end
of the humerus. 1

2. The subscapular artery (A. subscapularis) is a very large vessel which arises
at the posterior border of the subscapularis muscle. It ascends in the interstice
between that muscle and the teres major, on the medial surface of the long head
of the triceps, turns around the posterior border of the scapula below the dorsal
angle, and ends in the infraspinatus and deltoid. Besides collateral muscular
branches (Rami musculares) to the subscapularis, teres major, triceps, and tensor
fasciae antibrachii, it gives off the following named branches:

(a) The thoraco-dorsal (A. thoracodorsalis) is a long artery which is usually
given off about an inch from the origin of the subscapular, crosses the medial face
of the teres major, and runs upward and backward on the latissimus dorsi. It gives
branches to these muscles, the abdominal cutaneus and the axillary lymph glands.

(h) The posterior circumflex artery of the humerus (A. circumflexa humeri
posterior) arises a little above the preceding vessel, and passes outward behind the
shoulder joint between the long and lateral heads of the triceps with the axillary
nerve. It gives branches to these muscles, the joint capsule, and the muscles and
skin of the lateral side of the shoulder, anastomosing with the anterior circumflex
artery.

(c) The circumflex artery of the scapula (A. circumflexa scapulae) arises about
two or three inches (ca. 5-7.5 cm.) above the shoulder joint, passes forward to
the posterior border of the scapula, and divides into two branches. The lateral one
runs forward on the lateral surface of the scapula below the spine, and gives branches
to the supraspinatus, infraspinatus, and teres minor. The medial branch passes
forward in a similar fashion on the costal surface of the scapula and supphes branches
to the subscapularis.

3. The anterior circtraiflex artery of the humerus (A. circumflexa humeri
anterior)" arises usually at the anterior border of the teres major. It passes forward
between the two parts of the coraco-brachialis or between the latter and the humerus.
It gives branches to the coraco-brachialis and deep pectoral and ends in the upper
part of the biceps and in the brachiocephalicus. It anastomoses with the posterior
circumflex artery.

Not rarely it is replaced largely by an artery which arises from the brachial at the distal end
of the coraco-brachialis, and ascends on the front of the humerus. In these cases a small branch
for the coraco-brachialis is usually given off at the usual pomt of origin of the anterior circumflex.

4. The deep brachial artery (A. profunda brachii) is a large but short trunk
which arises usually about the middle of the humerus. It passes backward to the
interval between the tendon of the teres major and latissimus dorsi, and the long and
medial heads of the triceps, where it divides into several branches which supply the
triceps, tensor fasciae antibrachii, anconeus, and brachialis. A branch runs in the
musculo-spiral groove with the radial nerve to the front of the elbow joint and
anastomoses with the anterior radial. A slender branch descends along the lateral

1 This vessel may be double, or be represented by one or more branches of the inferior cervical
iirtery.

" Also termed the prehumeral artery.

652

BLOOD-VASCULAR SYSTEM OF THE HORSE

A nterior deep
pectoral muscle
Suprascapular /
artery '

Posterior deep pecto-
ral niukcle
Tendon of cutaru us
Nerve to bic( ps
Anterior drcumjiix
arUry
Anterior superficial
pectoral muscle

Extensor carpi radialis

Radius
Accessory cephalic vein

Elbow joint
Flexor carpi
ulnaris
Fhxor carpi
radialis
Medial liga-
ment of elbow
joint

Fig. 56G. — Dissection of Shoulder and Arm of Horse; Medial Surface.
A, Brachial artery, the stump of which has been turned backward; B, subscapular artery; C, thoraco-dorsal
artery; D, deep brachial artery; E, ulnar artery; F, anterior radial artery; (7, median artery; //, stump of brachial vein;
J, external thoracic vein; J, brachial vein, part of w^hich has been removed to expose deep brachial artery; A', K, K,
median veins; L, cephalic vein; L', communicating vein; M, brachialis muscle; A'^, medial epicondyle of hu-
merus; O, prescapular lymph glands; P, indicating position of axillary lymph glands, should be dorsal to vein; Q, posi-
tion of cubital lymph glands; /, suprascapular nerve; S, subscapular nerves; 3, thoraco-dorsal nerve; 4, musculo-
cutaneous nerve; 4', cutaneous branch of musculo-cutaneous nerve; 5, median nerve; 6, axillary nerve; 7, ulnar nerve;
7', cutaneous branch of ulnar nerve; S, radial nervt; 9, thoracic nerves. The vein at the elbow which lies in front of the
median artery should be shown crossing over the median nerve and the median and ulnar arteries, as in the next figure.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)

THE BRACHIAL ARTERY

653

border of the extensor carpi and supplies cutaneous twigs. Anastomoses occur
with the ulnar and recurrent interosseous arteries.

The point of origin is inconstant and it is not uncommon to find two arteries instead of one.
Often a large branch for the posterior deep pectoral muscle is detached close to the origin or arises
from the brachial directly.

Brachial
Median nerve
Coraco-brachiahs

Biceps brachii

Cephalic vein

Vena communicans

Cutaneous branch of
musculo-cutaneous nerve

Extensor carpi radialis

Accessory cephalic vein

Cephalic vein

Radius

Flexor carpi radialis

Artery of rete carpi
dorsale

Medial ligament of
carpus

Tendon of extensor
carpi obliquus

Common digital vein

Branch to deep volar
arch

Dorsal metacarpal artery

Long head of triceps

Medial head of triceps.

Tensor fascim antibrachii

Ulnar head of flexor
carpi ulnaris
Humeral head of flexor
carpi ulnaris

Ulnar head of deep flexor
Flexor carpi radialis

Common interosseous
artery

Median artery

Ulnar vessels and nerve

Deep fascia

Lateral branch of median

nerve

Medial branch of median

nerve

Flexor carpi ulnaris

Lateral volar nerve

Lateral volar met. artery
and vein

Medial volar nerve

Common digital artery

Medial volar met. artery

Flexor tendons

Fig. 567. — Dissection or Right Forearm and Carpus of Horse; Medial View.
1, Ulnar vessels; 2, cutaneous branch of musculo-cutaneous nerve; 3, 3, satellite veins of median artery; 4, posi-
tion of cubital lymph glands; 5, anastomosis of ulnar and lateral volar metacarpal arteries; 6, brachialis muscle; 7,
superficial digital flexor; 8, deep digital flexor. Dotted lines indicate contour of flexor carpi radialis, most of which has
been removed. (After Schmaltz, Atlas der Anatomie des Pferdes.)

654 BLOOD-VASCULAR SYSTEM OF THE HORSE

5. Muscular branches (Rami musculares) are distributed to the teres major,
deep pectoral, coraco-brachialis, and biceps. The largest and least variable of
these supplies the distal part of the biceps.

6. The ulnar artery (A. collateralis ulnaris proximalis) arises at the distal
end of the coraco-brachialis and passes downward and backward along the ventral
edge of the medial head of the triceps under cover of the brachial vein and the
tensor fasciae antibrachii. It gives branches to these muscles, the posterior super-
ficial pectoral, the cubital lymph glands, cutaneus, and skin. At the elbow it lies
on the posterior part of the medial epicondyle, in relation in front to the ulnar
nerve, and largely covered by the satellite vein; it then turns downward under the
ulnar head of the flexor carpi ulnaris. It continues its descent with the vein and
nerve under the deep fascia of the forearm between the ulnar and humeral heads of
the deep flexor of the digit, and in the distal half of the region between the lateral
and middle flexors of the carpus. It unites just above the carpus (under cover of
the flexor carpi ulnaris) with a branch of the median artery, with which it forms the
supracarpal arch. It detaches small collaterals to the muscles along which it passes
and terminal twigs to the lateral surface of the carpus.

7. The nutrient artery of the humerus (A. nutritia humeri) is a short vessel
which enters the nutrient foramen of the humerus. It often arises from the ulnar.

8. The anterior radial artery (A. collateralis radialis distalis)i passes downward
and a little outward on the anterior face of the humerus under cover of the biceps
and brachialis to the front of the elbow joint, where it is in contact with the radial
nerve. It then descends on the anterior surface of the radius, under cover of the
common digital extensor, to the carpus, where it concurs in the formation of the rete
carpi dorsale, anastomosing with the median and dorsal interosseous arteries. It
supplies branches to the elbow joint, the biceps, brachialis, and the extensors of
the carpus and digit. A cutaneous branch emerges between the distal end of the
biceps and the brachialis.

THE MEDIAN ARTERY

The median or posterior radial artery (A. mediana)- is the direct continuation
of the brachial. It descends, inclining slightly backward, at first on the medial
surface of the humerus, and then over the capsule and medial ligament of the elbow
joint, under cover of the posterior superficial pectoral muscle.^ At the proximal
third of the forearm it dips under the flexor carpi radialis and passes down the medial
part of the posterior surface of the radius. In the distal part of the forearm it
inclines backward and is separated from the radius by the reinforcing band (Caput
tendineum) of the superficial flexor of the digit and is continued by the common
digital or large metacarpal artery.

It is accompanied by the median nerve, which lies in front of the artery at its
origin, then usually crosses over it obliquely at the elbow joint and becomes posterior.
At the distal end of the arm the artery is crossed by the large anastomotic vein
which connects the cephalic and brachial veins, and a radicle of the brachial vein lies
behind and partly upon the artery; lower down there are usually two satellite
veins, anterior and posterior. The chief collateral branches are as follows:

1. Articular branches are supplied to the elbow joint.

2. Muscular branches go to the flexors of the carpus and digit ; the largest of
these arise at the proximal third of the forearm.

3. The common interosseous artery (A. interossea communis) is a vessel of

^ This vessel is apparently the A. transversa cubiti of comparative anatomy.

2 Although the homology of some arteries in this region are still unsettled, it seems clear that
this vessel should be termed the median artery.

^ The pulse can be taken where the artery lies on the ligament, since the pectoral muscle is
thin here.

THE MEDIAN ARTERY

655

considerable size which arises at the level of the interosseous space, through which
it passes outward. Before entering the space it gives off a small branch, the volar

Deltoid

Brachiocephalicus

Lateral head of

triceps (cut)

Cutaneous hranch of

axillary nerve

Anterior radial arterij

Common digital extensor

Brachialis

Extensor carpi radialis

Extensor carpi obliquus

Tendon of extensor carf/i
radialis
Lateral lig. of carpus

Rete carpi dor sale

Tendon of common extensor

Branch to lateral extensor

Tensor fasdce antibrachii
Lung head of triceps

Brunch of radial nerve to
heads of triceps and anconeus
Deep brachial artery

Radial nerve

Long head of triceps

Medial head of triceps

Anconeus

Lateral head of triceps (cut off)

Olecranon

Ulnar head of deep flexor
Cutaneous branch of ulnar

nerve
Lateral lig. of elbow
Ulnar is lateralis (cut
and reflected)

Common interosseous artery

Ulna

Ulnar head of common

digital extensor
Deep digital flexor

Lateral digital extensor
Ulnar nerve and vein

- Ulnaris lateralis (stump)

Dorsal interosseous artery

Superficial branch of ulnar
nerve

Carpal sheath (opened)
Lateral tendon of ulnaris

lateralis
Accessory carpal bone

A ccessorio-metacarpal
ligaments

Band from accessory carpal
to lateral extensor tendon
Lateral extensor tendon

Fig. .568.— Dissection of Left Fore.a^rm of Hoksk; Lateral Surface.
The radial and ulnar heads of the anterior digital extensor are shown in front of the lateral extensor, but are not
marked. The muscular branches of the radial nerve are shown, but not designated indi^^dually. Dotted lines indi-
cate contour of parts of muscles which have been removed (lateral head of triceps, extensor carpi radialis, lateral flexor
of carpus). (After Schmaltz, Atlas d. Anat d. Pferdes.)

interosseous artery (A. interossea volaris), which descends to the radial head of the
deep flexor. In the space it supplies the nutrient arteries of the radius and ulna.

656

BLOOD-VASCULAR SYSTEM OF THE HORSE

Emerging from the space it gives off branches to the ulnaris lateralis, and the small
recurrent interosseous artery (A. interossea recurrens), which ascends on the lateral

Artery of rete carpi volare

Oblique ligament

Medial lig.
First carpal bone

Deep volar metacarpal arteries
Medial metacarpal bone

Radius

Accessorio-radial lig.
Accessorio-ulnar lig.

Lateral lig.
Check ligament

Accessorio-metacarpal lig.

Deep volar arch

Suspe7isory ligament
Lateral metacarpal bone

Fig. 569. — Deep Dissection of Right Carpus of Horse; Posterior View.
1, Radial carpal bone; 2, accessory carpal bone; 3, second carpal bone. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

Joint capsule

Tendon of lateral

extensor

Lateral ligament

Long tendon of.
ulnaris lateralis

Superficial branch
of ulnar nerve

Tf ndon of extensor
1(11 pi radialis

1 1 ndon of extensor
irpi obliquus

Midial ligament

1 1 ndon of flexor
( irpi radialis
Common digital vein
\[(dial volar meta-
((u pal artery

Common diqdal aitiry
Liiterul mttuvar pal vein

Lateral volar metacarpal artery
Fig. 570. — Cross-section of Proximal Part of Left Carpus of Horse.
Cr, Ci, Cu, Ca, radial, intermediate, ulnar, and accessory carpal bones; 1, superficial flexor tendon; 2, deep flexor
tendon; 3 (on volar carpal ligament), carpal canal; 4, oblique ligament from radius to radial carpal bone; 5, tendon of
common extensor; 6, medial volar nerve; 7, lateral volar nerve. Syno\'ial ca\'ities are black.

surface of the ulna and anastomoses with the deep brachial and ulnar arteries.
Under cover of the common digital extensor it connects with the anterior radial
artery and gives off the dorsal interosseous artery (Fig. 568). This vessel (A.

THE MEDIAN ARTERY

657

interossea dorsalis) descends between the common and lateral extensors of the digit
and concurs with the anterior radial in forming a network on the dorsal surface of
the carpus, the rete carpi dorsale. From the latter arise two small vessels, the
medial and lateral dorsal metacarpal arteries (A. metacarpea dorsalis medialis,
lateralis), which run distally in the grooves between the large and small metacarpal
bones and anastomose with the volar metacarpal arteries.

4. The artery of the rete carpi volare (A. retis carpi volaris) is a small vessel
which arises at the distal third of the forearm and descends on the radius to the
posterior surface of the carpus, where it concurs with branches of the volar meta-
carpal arteries in forming the rete carpi volare.

5. The lateral volar metacarpal artery (A. metacarpea volaris lateralis)^ is a
small vessel which arises just above the carpus under cover of the flexor carpi
ulnaris and anastomoses with the ulnar artery, forming the supracarpal arch.
From the latter a branch descends with the lateral branch of the median nerve,

Tendon of common extensor

Skin
Mc. Ill

Mc. II

Common digital vein
Common digital artery
Medial volar nerve
Superficial flexor tendon

Tendon of lateral extensor

_ _ Mc. IV

^ Suspensory ligament

j Lateral volar metacarpal

' vessel

Lateral volar nerve

Check ligament
Deep flexor tendon
Deep fascia

Fig. 571. — Cross-section of Right Metacarpus of Horse.

Section is cut a little above middle of region.

1, 1', Dorsal metacarpal arteries; 2, 2', deep volar metacarpal arteries; 3, deep volar metacarpal vein; 4, distal part of

carpal sheath.

inclines outward toward the posterior border of the accessory carpal bone, and
arrives at the head of the lateral metacarpal bone. Here it is connected with the
medial volar metacarpal artery, usually by two transverse branches, thus forming
the deep volar or subcarpal arch (Arcus volaris profundus proximalis). One of
these branches lies between the subcarpal check ligament and the suspensory
ligament ; the other (not always present) lies beneath the latter on the large meta-
carpal bone. A small branch descends to the fetlock with the lateral volar nerve.
Below the arch the artery pursues a flexuous course downward on the volar face of
the large metacarpal bone alongside of the lateral small metacarpal and under
cover of the suspensory ligament. At the distal third of the metacarpus it com-
monly unites with the corresponding vessel of the other side to form a short trunk
which passes backward through the angle of divergence of the branches of the sus-
pensory ligament and joins the lateral digital or the common digital artery. This
junction forms the distal volar arch (Arcus volaris distalis).

6. The medial volar metacarpal artery (A. metacarpea volaris medialis)^ is

1 Also termed the external metacarpal artery.

2 Also called the internal or small metacarpal artery.
42

658

BLOOD-VASCULAR SYSTEM OF THE HORSE

given off from the median at an acute angle, usually a little above the lateral
one or by a common trunk wath it. It passes clowii the medial side of the carpus
behind the tendon of the flexor carpi radialis and embedded in the posterior annular
ligament. Arriving at the proximal end of the medial metacarpal bone it becomes
more deeply placed and is connected with the lateral volar artery by one or two
transverse branches, as stated above. It then pursues a flexuous course downward

Medial ligament of carpus

Tendon of extensor carpi radialis
Tendon of extensor carpi obliquus

Medial ligament of fetlock joint
Common extensor tendon

Extensor branch of suspensory
ligament

Dorsal artery of first phalanx

Medial ligament of pastern joint

-■ Lateral metacarpal vein
Medial metacarpal vein

Postiriur annulnr ligament of
carpus

Superficial flexor tendon
Medial volar nerve

Communicating branch
Common digital artery
Medial metacarpal vein
Suspensory ligament
Lumbricalis muscle
Dorsal digital nerve
Volar digital nerve
Digital artery
Digital vein
Ligament of ergot
Deep flexor tendon.
Cartilage of third phalanx

Coronary plexus

Coronary corium
Laminar corium

Fig. 572. — Dissection of Right Carpus, Metacarpus, and Digit op Horse; Medial View. (After Schmaltz, Atlas

d. Anat. d. Pferues.)

alongside of the medial small metacarpal bone, like the corresponding lateral
artery, with which it commonly unites as described above. It is larger than the
lateral artery, and supplies the nutrient artery to the large metacarpal bone.

The foregoing account describes the most common arrangement of the dorsal and volar
metacarpal arteries. Variations in their origin and connections are common, but have no great
surgical importance. Collateral branches are omitted for the same reason. In some cases the
medial volar metacarpal is connected with the common digital artery a little below the carpus by
a branch passing obliquely across the medial border of the deep flexor tendon; this forms a super-
ficial volar arch.

THE COMMON DIGITAL ARTERY THE DIGITAL ARTERIES 659

THE COMMON DIGITAL ARTERY
The common digital artery (A. digitalis communis s. metacarpea volaris
superficialis)^ is the direct continuation of the median. It descends in the
carpal canal along the medial side of the flexor tendons in company with the
medial volar nerve. Continuing down the limb it preserves this relation to the
tendons to the distal third of the Lietacarpus, where it inclines toward the middle
line of the limb behind the suspensory ligament, and divides into the medial and
lateral digital arteries. In the metacarpus the artery is related to the vein in front
and the nerve behind, and is covered by the fascia and skin. It furnishes collateral
branches to the suspensory ligament, the flexor tendons, and the skin.

THE DIGITAL ARTERIES
The digital arteries, medial and lateral (A. digitalis volaris propria medialis,
lateralis), are formed by the bifurcation of the common digital at the distal third
of the metacarpus. They diverge, pass down over the abaxial surface of the cor-
responding sesamoid at the fetlock, and descend parallel with the borders of the deep
flexor tendon to the volar grooves and foramina of the third phalanx. Entering the
latter the two arteries unite in the semilunar canal and form the terminal arch
(Arcus terminalis), from which numerous branches pass through the bone to the
dorsal surface and ramify in the corium of the wall and sole of the hoof .^ A num-
ber of branches emerge through tlie foramina at the distal border, where they anas-
tomose with each other in arciform fashion.

These branches were named by Spooner the inferior communicating arteries, and the anas-
tomotic arch formed by them is termed the circumflex artery of the third phalanx (Chauveau)
or the artery of the distal border of the third phalanx (Leisering).

Each artery is accompanied by a vein and by the digital nerves. Above the
fetlock the artery is most deeply placed and is covered by the vein; the nerve is
beh nd the vein. At the fetlock the artery has become superficial and is related
to the vein in front and the posterior branch of the nerve behind. The anterior
branch of the nerve crosses over the artery obliquely to the side of the first phalanx.
The artery and nerves are crossed obliquely by a small band, the tendon or ligament
of the ergot {vide digital fascia).

In addition to branches to the joints, tendons and synovial sheath, ergot, and
skin, the digital arteries give off the following named branches:

1. The artery of the first phalanx (A. phalangis primse)^ is a short trunk which
arises at a right angle about the middle of the first phalanx, and divides into
dorsal and volar branches. The dorsal branch (Ramus dorsalis) passes between
the first phalanx and the extensor tendon and ramifies on the front of the digit,
anastomosing with its fellow. The volar branch (Ramus volaris) dips in between
the flexor tendons and the first phalanx and anastomoses with the opposite artery
between the superficial and middle distal sesamoidean ligaments.

2. The artery of the digital cushion (A. toricae phalangis tertise) arises at the
proximal border of the cartilage of the third phalanx and passes backward and
downward to ramify in the digital cushion and the corium of the heels and frog.

3. The dorsal artery of the second phalanx (Ramus dorsalis phalangis secundae)
arises a little above the level of the distal sesamoid bone, and passes forward under
cover of the cartilage of the third phalanx and the extensor tendon to the front of
the second phalanx, where it anastomoses with the opposite vessel. It gives

^ This vessel is also termed the large or palmar metacarpal artery.

2 The terminal part of the digital artery has been termed the plantar artery.

^ Also termed the perpendicular artery.

660 BLOOD-VASCULAR SYSTEM OF THE HORSE

branches to the skin, the tendon, the coffin joint, and the coronary corium of the
hoof.

4. The volar artery of the second phalanx (Ramus volaris phalangis secundse)
is smaller than the preceding, opposite to which it arises. It passes above the
proximal border of the distal sesamoid and unites with the opposite artery.

The arteries of the second phalanx form what is termed by Chauveau the coronary circle.
The dorsal (anterior) part of the circle gives off commonly an artery (A. coronal is phalangis tertite)
near either side of the extensor tendon, which divides into two branches. The central branch
unites with that of the opposite side, while the other joins a branch of lli(> artery of the digital
cushion. In this way is formed the circumflex artery of the coronary cushion, an anastomotic
arch which lies on the extensor tendon at tlie coronet. In some ca^es descending branches of the
arteries of the first phalanx concur in the formation of the arch.

5. The dorsal artery of the third phalanx (A. dorsalis phalangis tertise)^ arises
at the deep face of the angle of the third phalanx, passes through the notch or fora-
men there, and runs forward in the groove on the dorsal surface. It gives off
ascending and descending branches, which ramify in the corium of the wall of the
hoof, anastomosing above "with the circumflex artery of the coronary cushion and
distally with the circumflex artery of the third phalanx. Before passing through
the wing it detaches a retrograde branch to the digital cushion, and after emerging,
one which ramifies on the convex surface of the cartilage of the third phalanx.

BRANCHES OF THE THORACIC AORTA
In addition to the coronary arteries and the common brachiocephalic trunk
(which have been described), the thoracic part of the aorta gives off branches to the
thoracic walls and viscera and to the spinal cord and its membranes. The visceral
branches (Rami viscerales) are the bronchial and oesophageal, which arise by a
broncho-oesophageal trunk. The parietal branches (Rami parietales) are the
intercostal and phrenic arteries.

1. The broncho-cesophageal artery (Truncus broncho-cesophageus) is a short,
usually bulbous, trunk which arises at the sixth thoracic vertebra from the aorta or in
common with the first aortic intercostal arteries. It descends (under cover of the
vena azygos) over the right face of the aorta toward the bifurcation of the trachea
and divides into bronchial and oesophageal branches. The bronchial artery (A.
bronchialis) crosses the left face of the oesophagus to the bifurcation of the trachea,
where it divides into right and left branches. Each enters the hilus of the cor-
responding lung above the bronchus, which it accompanies in its ramification. It
supplies the lung tissue and also detaches twigs to the bronchial lymph glands and
the mediastinum. The oesophageal artery (A. oesophagea) (Fig. 554) is a small
vessel which passes backward dorsal to the oesophagus in the posterior mediastinum
and anastomoses with the oesophageal branch of the gastric artery. It detaches
twigs to the oesophagus and the mediastinal lymph glands and pleura, and gives off
two branches which pass between the layers of the ligaments of the lungs and ramify
in the subpleural tissue. Very commonly there is another artery which runs back-
ward ventral to the a'sophagus.-

2. The intercostal arteries (Aa. intercostales) (Figs. 553, 554) number eighteen
pairs. The first arises from the deep cervical artery, the next three from the
subcostal branch of the dorsal artery, and the remainder from the aorta. The
aortic intercostal arteries arise from the dorsal face of the aorta in pairs close to-
gether; the fifth and sixth usually spring from a common stem. Each passes across
the body of a vertebra to the corresponding intercostal space, detaches twigs to the
vertebrae and the pleura, and divides into dorsal and ventral branches. The dorsal

^ Also termed the preplantar artery.

2 In some cases there is no broncho-oesophageal trunk, the bronchial and oesophageal arising
separately. In other cases the second aortic intercostal arises in common with them also.

BRANCHES OF THE ABDOMINAL AORTA

661

branch (Ramus dorsalis) gives off a spinal branch (Ramus spinalis) which passes
through the intervertebral foramen, gives twigs to the membranes of the spinal
cord, perforates the dura, and reinforces the ventral spinal artery. A muscular
branch passes to the muscles and skin of the back. The ventral branch (Ramus
ventralis) is much the larger. It descends, at first almost in the middle of the
intercostal space between the intercostal muscles, then gains the posterior border
of the rib, and is subpleural. Each is accompanied by a vein and nerve, the artery
being in the middle and the vein in front. At the ventral part of the space it unites
with a ventral intercostal branch of the internal thoracic or the musculo-phrenic
artery. It supplies the intercostal muscles, the ribs and the pleura, and gives off
perforating branches which pass out to the serratus ventralis, the abdominal
muscles, and the skin.

3. The phrenic arteries (Aa. phrenicae) are two or three small vessels which
arise at the hiatus aorticus from the ventral aspect of the aorta, often by a common
trunk. They supply the crura of the diaphragm. In some cases they arise in
common with an intercostal artery.

BRANCHES OF THE ABDOMINAL AORTA

The collateral branches of the abdominal part of the aorta are distributed
chiefly to the walls and contents of the abdominal cavity, but some branches are

Fig. 673. — Plan of Branches of Cceliac Artery of Horse.
1, Coeliac artery; 2, gastric artery; 3, hepatic artery; 4, splenic artery; 5, posterior gastric artery; 6, anterior
gastric artery; 7, oesophageal branch; 8, gastro-duodenal artery; 9, pancreatico-duodenal artery; 10, right gastro-
epiploic artery; 11, pyloric artery; 12, left gastro-epiploic artery; 13, short gastric branches of splenic.

supplied to the spinal cord and its membranes, and others extend into the pelvis
and to the scrotum. The visceral branches are the cceliac, anterior mesenteric,

662 BLOOD-VASCULAR SYSTEM OF THE HORSE

renal, posterior mesenteric, and internal spermatic or utero-ovarian. The parietal
branches are the Imiibar arteries.

I, The coeliac artery (A. coeliaca) is an unpaired vessel, usually half an inch
or less (ca. 1 cm.) in length, which arises from the ventral aspect of the aorta at its
emergence from the hiatus aorticus. It divides on the dorsal surface of the pan-
creas into three branches — the gastric, hepatic, and splenic.

1. The gastric artery (A. gastrica sinistra) passes downward and forward in
the gastro-phrenic ligament, gives off oesophageal and pancreatic branches,
and divides above and behind the cardia into anterior and posterior branches.
The anterior branch (Ramus cranialis) crosses the lesser curvature just to the right
of the cardia and ramifies on the parietal surface of the stomach. The branches
pursue a fiexuous course toward the greater curvature and anastomose with the
short gastric arteries and the gastric branch of the hepatic artery. The pos-
terior branch (Ramus caudalis) is distributed in a similar fashion on the visceral
surface. The oesophageal branch (Ramus oesophageus) passes through the hia-
tus oesophageus into the thoracic cavity above the oesophagus and anastomoses
with the oesophageal branch of the broncho-oesophageal artery.

The gastric artery often arises by a common trunk with the splenic. The two terminal
branches may arise separately, or the anterior from the splenic and the posterior from the hepatic.
The oesophageal branch often arises from the splenic or the posterior gastric.

2. The hepatic artery (A. hepatica) is larger than the gastric. It passes for-
ward and to the right and ventrally on the dorsal surface of the pancreas, covered by
the gastro-pancreatic fold, crosses obliquely under the vena cava, and reaches the
medial border of the portal vein. It divides into three or four branches which enter
the portal fissure of the liver and ramify within the gland with the portal vein and
the hepatic duct. It gives off the following collateral branches: (1) Pancreatic
branches (Aa. pancreaticse) are given off as the artery crosses the pancreas, in
which it is partly embedded. (2) The pyloric artery (A. gastrica dextra) arises
above the first curve of the duodenum. It descends to the pylorus, sending branches
to the pylorus and the first part of the duodenum, and anastomoses with the gastric
and right gastro-epiploic arteries. It may arise from the gastro-duodenal. (3)
The gastro-duodenal artery (A. gastroduodenalis) passes to the second curve of the
duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal.
The right gastro-epiploic artery (A. gastroepiploica dextra) crosses over the posterior
surface of the duodenum and enters the greater omentum, in which it runs to the
left, parallel with the greater curvature of the stomach. It gives branches to the
latter and to the omentum and forms an anastomotic arch with the left gastro-
epiploic artery. The pancreatico-duodenal artery (A. pancreaticoduodenalis)
divides into pancreatic and duodenal branches. The former (Ramus pancreaticus)
supplies the middle part of the pancreas and is often replaced by a number of
variable twigs. The duodenal branch (Ramus duodenalis) passes to the right along
the lesser curvature of the duodenum and anastomoses with the first branch of the
anterior mesenteric artery.

Variations in the branching of the hepatic artery are not uncommon. The pancreatico-
duodenal may arise directly from the trunk, and there may be a common trunk for the pyloric and
right gastro-epiploic which runs along the dorsal surface of the first curve of the duodenum to the
pylorus; here it gives off the small pyloric branch and is continued across the parietal surface of
the pylorus as the right gastro-epiploic, no gastro-duodenal trunk being present.

3. The splenic artery (A. lienalis) is the largest branch of the coeliac. It passes
to the left (with the large satellite vein) on the left extremity of the pancreas and
across the saccus csecus of the stomach. Entering the suspensory ligament of the
spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued
as the left gastro-epiploic. It gives off the following branches: (1) Pancreatic
branches (Rami pancreatici), which supply the left extremity of the pancreas.

BRANCHES OF THE ABDOMINAL AORTA

6G3

(2) Splenic branches (Rami lienales), which plunge into the substance of the spleen.

3 Short gastric branches (Aa. gastric^ breves) which pass in the g^f ^^-^Pl^^^^

omentum to the greater curvature of the stomach, where they bifurcate and anas-

tomose^th the branches of the gastric arteries. (4) The left gastro-epiploic

Fig 574 —Plan of Chiep Branches of Anterior Mesenteric Artery of Horse.

2, stumps of arteries of small intestine; 3, lateral cscal artery; 4,

1, Stump of anterior mesenteric artery
_ 1 csecal artery; 5, ileal artery; 6, venti
small colon. By an oversight the left ventral colon is erroneous!

artery; 8, middle colic or first artery of
ily labeled right dorsal (upper left part of figure).

artery (A. gastroepiploica sinistra) is the continuation of the splenic artery It
nass^s to the right in the greater omentum, parallel with the greater curvature of the
stomach and 'anastomoses with the right gastro-epiploic. It gives off branches
to the greater curvature of the stomach and twigs to the omentum.

664

BLOOD-VASCULAR SYSTEM OF THE HORSE

E^ ^

BRANCHES OF THE ABDOMINAL AORTA 665

&.2 I »-. ^ s c £ o" t g II. The anterior or great mesenteric artery

S B ■% •„- § S .2. 1 ^ ,°1 =^ (A. mesenterica cranialis) arises from the ventral

^1 ^ ^"1 ^'^"^^-'^ ^^^6 of the aorta at the first lumbar vertebra. It

:§ §" "i S E ^ ? 1 1 o •" ^^ ^ large unpaired trunk, about an inch (ca. 2-3

"«' I i|« ■2'1'o-li cm.) in length, which passes ventrally between the

o ■^ a -t :: ^ s ^ I ^- "^ vena cava and the left adrenal into the root of

^" i :l ^ fi ^" ^ ^ I " -- ^^^ great mesentery, when it divides into three

'^- •- I 'I ^ - t - I I i branches — left, right, and anterior.^

l| ■§ -S§;5 l|ft:-|'^ 1. The left branch gives off at once about

8 .2 S 1^ § .s 'o g c a," I c fifteen to twenty arteries of the small intestine

iig-3 |c| l"aS"|| (Aa. intestinales) ."^ These come off close together

-||"3 "flig -slffii^ ^^^d P^^s i^ divergent fashion between the layers

I S § c| .g -^ g -^ ^ ^. -3 _! I of the great mesentery, each dividing into two

§ i" ^ 2 S i 1 1 1 -^ M t if ° branches which anastomose with adjacent branches

r.. -s .- .•= "^ o o I 1 .9 ^ I ° g ^Q form a series of arches. In the anterior part of

the series secondary arches are formed by the union
of branches given off from the primary set of
arches. From the convex side of these arches
terminal branches pass to the wall of the small
intestine, in which they ramify and form a vascu-
lar network. They are accompanied by satellite
i o ?. ^" s I I I I veins and by nerves and lymph vessels. The first

Ifeol s|^|fl°s|.S artery anastomoses with the pancreatico-duodenal,

^l|§ -^^-lli§^ ^^^ ^^^ l^s* "^^^^^ ^^^^ ^1^^^ branch of the great

si.,!-- fi 1 1 1 !• ^ I "H i mesenteric artery. Branches are supplied to the

i M ° .2 t o" I ° i ^ mesenteric lymph glands.

^" ir I 1 1 I 2. The right branch (A. ileo-caeco-colica)

"" I la- ^ ^ ^ might be regarded as the continuation of the

'^. I "x S* -S 1 1 "3 ^ .1 ;; '^ '^ !^ trunk. It runs downward and a little forward

and to the right, and gives off the ileal, the two
csecal, and the ventral colic arteries. (1) The
I t I ^- 1 5 ^ § M ileal or ileo-csecal artery (A. ilea) passes in retro-

ft^l!!§t'.BJ I grade fashion along the terminal part of the ileum

■^^ 1 1 1) :§• I III and unites with the last branch of the left division.

I)l||2s|l3 (2) The lateral caecal artery (Ramus csecalis later-

l^i > I a^^Z alls) passes between the caecum and the origin of

-g '!°, ^ S "^ "o 2 £ a the colon and runs on the lateral band of the caecum

I ^5) *" I " I I 2 S to the apex, where it anastomoses with the medial

ola^. 3 |ui>g"5°|'p' artery. Besides numerous collaterals to the caecum,

I. « -3 1 1- g I ^ S " i I Sh it gives off the artery of the arch, which passes

6 g I a iT ;s g i g I '^ I "S . along the lesser curvature of the base of the caecum

a .E

^;pg§a_cl5o>

^ ^ ^" '^- ^ ^" ^" I I
- o ^. ^ o j,- - -

-^ ._ ^ a

-tJ B O X X *^ •>,

.d ^ a o « X C
•- 2 _e o" ■- S °

and runs on the lateral face of the origin of the
great colon. (3) The medial caecal artery (Ramus

■Sli!". II l^^l caecalis medialis) passes along the medial band to
1 1 - "1 I ^ i" III ^ I "^ -o "the apex of the caecum, where it anastomoses with
^ I I -"^ 2 II- o s I '^^^ ^ S ii the lateral caecal artery. (4) The ventral colic

° I I "^ e "S .2 I ■§ C fi "^ " "^ 1 In the great majority of subjects this vessel and some

*^. ft 1 1 ^ c I - "° t -^ -2 ^ ^ of its branches are the seat of more or less extensive vermin-

r 95- ^ » I S ^ a S g, g I § -< ous aneurvsm, produced by the Sclerostomum vulgare.

■S '~' b- 1 -^ ^ « -2 "^ ^ .S *;^ .2 i In the author's experience an entirely normal specimen is

"'''"" quite unlikely to be encountered except in very young foals.

i "I 1 § '^" ° M o" "- "S ri 2 The left branch is a descriptive convention rather

§ .2

-2 =i ^ a J 'I 7. J ^- '^- '^ S I ^ than a reality, since the arteries of the small mtestine spring
"^ S fe"^^^ a 5; c'^ i'3'3:2« from the mesenteric trunk either directly or by short com-

o ^

mon stems with an adjacent vessel.

666 BLOOD-VASCULAR SYSTEM OF THE HORSE

artery (A. colica ventralis)^ runs along the dorso-medial bands of the opposed
surfaces of the ventral parts of the great colon to the pelvic flexure, where it unites
with the dorsal colic artery. It supplies the ventral parts of the great colon and
sends a branch to the base of the caecum.

3. The anterior branch divides after a very short course into the dorsal and
middle colic arteries. (1) The dorsal colic artery (A. colica dorsalis)^ is a large
vessel which passes along the dorsal parts of the great colon to the pelvic flexure,
where it joins the ventral colic artery. (2) The middle colic artery or first artery
of the small colon (A. colica media) is a much smaller vessel which passes to the
origin of the small colon, enters the colic mesentery, and forms an arch by joining
the first branch of the posterior mesenteric artery close to the lesser curvature of
the bowel. It sends an anastomotic branch to the dorsal colic artery.

III. The renal arteries (Aa. renales), right and left, are relatively large vessels
which arise from the aorta near the anterior mesenteric. The right artery is the
longer of the two. It crosses over the dorsal surface of the vena cava to the right
and somewhat forward. At the hilus it divides into several (five to eight) branches;
some of these enter the gland at the hilus, while others pass to the ventral surface
and enter there. The left artery is short and usually arises a little further back;
it passes directly outward to the kidney and is then disposed like the right one.
Small collateral branches are supplied to the ureters, the perirenal fat, the renal
lymph glands, and the adrenals. The latter also receive small adrenal arteries
directly from the aorta. The distribution within the kidney has been described.

Variations in the renal arteries are frequent. Two or more arteries may occur on one side or
both. Accessory arteries are more common on the left side and usually enter the posterior part
of the gland. They may arise from the aorta, the external iliac, or the circumflex iliac artery.

IV. The posterior or small mesenteric artery (A. mesenterica caudalis) is an
unpaired vessel which arises from the ventral face of the aorta at the fourth lumbar
vertebra, i. e., about five or six inches (ca. 12-15 cm.) behind the origin of the
anterior mesenteric artery. It is much smaller than the latter and supplies the
greater part of the small colon and rectum. It descends in the colic mesentery
and, after a short course, divides into two branches. The anterior branch (A. colica
sinistra) gives off three or four arteries which divide and form anastomotic arches
close to the bowel. The first arch is formed by union with the middle colic branch of
the anterior mesenteric. The posterior branch or anterior haemorrhoidal artery
(A. hsemorrhoidalis cranialis) passes backward in the upper part of the mesentery
and the mesorectum and terminates near the anus by anastomosing with the
internal pudic artery. Three or four of its anterior collateral branches form,
arches.

V. The internal spermatic arteries (Aa. spermaticse internse), right and left,
are long slender arteries which arise from the aorta near the posterior mesenteric
and supply the testicle and epididymis.^ Each passes backward in a narrow fold
of peritoneum (Plica vasculosa) to the internal inguinal ring and descends through
the inguinal canal to the scrotum. In its course in the anterior border of the
spermatic cord it forms numerous coils, surrounded by the pampiniform plexus
of veins, and associated closely with the spermatic nerves and lymphatics and
unstriped muscle-fibers. It passes between the epididymis and testicle, runs in
flexuous fashion along the attached border of the latter, turns around the posterior
pole, and runs forward on the free border to the anterior pole. The largest branches
arise from its ventral part, pass tortuously up either side of the gland, embedded
in the tunica albuginea, and give off fine branches to the gland substance. Small

1 Also termed the right or direct colic artery.

2 Also termed the left or retrograde colic artery.

' Variations in the origin of the internal spermatic artery are common. It may arise from
the posterior mesenteric, or from the renal, or the two may arise by a short common trunk.

BRANCHES OF THE ABDOMINAL AORTA

667

Internal iliac lymph gland.

Circumflex iliac vessels

External iliac lymph glands

Remnant of inguvial
ligament
Posterior branch of circum-
flex iliac artery
Lateral cutaneous nerve
of thigh
External spermatic nerve

Tensor fascice latoi

Femoral nerve and ante-
rior femoral vessels
Femoral artery
Prefemoral lymph glands

Deep inguinal lymph
gkijids

Fascia lata

Saphenous nerves
Saphenous vessels

Medial pntcllar ligament
Middle patellar ligament

Fig. 576.— Dissection of Pelvis, Thigh, and Proximal Part of Leg of Horsk; Medial View.
L, Lumbar vessels; T'.f., posterior vena cava; .4 , aorta (termination) ; C, sympathetic trunk; ;, internal iliae
artery; 2, lateral sacral artery; 3, middle coccygeal artery; 4, lateral coccygeal artery; 3, umbilical artery (cut off);
6, internal pudic artery; 6', vesico-prostatic artery; 7, obturator artery; 8, a. profunda penis (from left obturator);
5, posterior gluteal vessels; 70, external iliac artery; n, ii', deep femoral artery; /^, prepubic artery; i 5, branch of
deep femoral artery; 14, great sciatic nerve; IS, posterior gluteal nerve; 16 (above), pudic nerve; 16 (below, near
pelvic outlet), suburethral venous plexus; 7 7, sacro-coccygeus ventralis; ;S, coccygeus; 79, recto-coccygeus; ^0, re-
tractor ani; ^/, ^7 ', two heads of obturator internus; ^^, symphysis pelvis; ^3, prepubic tendon; ^4 suspensory liga-
ment of penis; 2d, retractor penis muscle; 26, bulbo-cavernosus muscle; 27, urethra (cross-section) ; ^5, crus penis
(cross-section); 29, suspensory ligaments of anus; 30, anal lymph glands; 31, tibial nerve. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)

668

BLOOD-VASCULAR SYSTEM OF THE HORSE

collateral branches are detached to the ureter, the epididymis, and the spermatic

cord.

V a. The utero-ovarian arteries in the female correspond to the precedmg ves-
sels, but are much larger and shorter. Each is placed in the anterior part of the
broad ligament of the uterus and divides into ovarian and uterine branches. The
ovarian artery (A. ovarica) pursues a flexuous course to the ovary, which it supplies.
The anterior uterine artery (A. uterina cranialis) passes to the concave border of the
cornu of the uterus, which it supplies, anastomosing with the middle uterine artery.

VI. The lumbar arteries (Aa. lumbales) are in series with the intercostal

Perineal artery
Perineal nerves
Internal pudic

artery
Dorsal nerve of

penis

Sacro-coccygeus ventral is
Recto-coccygeus
Sphincter ani externum
Retractor ani

Fig. 577. — Dissection of Perineum of Horse (Male).

/, Bulbo-urethral gland; 2, transversus perinei muscle (?); 3, ischio-urethral muscle; 4, retractor penis muscle; 5^

bulbo-cavernosus muscle. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

arteries and have a similar origin and distribution. There are usually six pairs of
lumbar arteries, of which five arise from the aorta and the sixth from the internal
iliac or the lateral sacral at the junction of the last lumbar vertebra and the sacrum.
Each passes across the body of a lumbar vertebra to the intertransverse space,
gives branches to the sublumbar muscles, and divides into dorsal and ventral
branches. The dorsal branch (Ramus dorsalis), the larger of the two, passes
upward to ramify in the extensor muscles of the spine and the skin of the loins;
it gives off a spinal branch (Ramus spinalis) which comports itself like the corre-
sponding branch of an aortic intercostal artery. The ventral branch (Ramus
ventralis) runs outward in the intertransverse space, passes between the transversus

THE INTERNAL ILIAC ARTERY

669

and obliquus internus abdominis, gives branches to these muscles, and ends in the
obliquus externus, the cutaneus, and the skin of the flank.

THE INTERNAL ILIAC ARTERY
The internal iliac or hypogastric arteries (Aa. hypogastrics) result from the
bifurcation of the aorta under the fifth or sixth lumbar vertebra. They diverge
at an angle of about 60 degrees, and each passes backward under the wing of the
sacrum, then inclines downward on the pelvic surface of the shaft of the ilium,
along the ventral border of the iliac head of the obturator internus, and divides a

Coccygeus muscle
Anal lymph glands
Branch of posterior gluteal
arteri)

Po'^tfnor hcemorrhoidal
nerve

VuUar branch of
pudic nerve
Internal pudic
artery

Branch of pu-
dic nerve to
clitoris

Obturator artery

Fig. 578. — Dissection op Perineum of Mare.
1, Sacro-coccygeus dorsalis; 2, sacro-coccygeus lateralis; 3, intertransversales; 4i sacro-coccygeus ventralis; 5,
recto-coccygeus; 6, sphincter ani externus; 6', branch connecting sphincter ani with constrictor vulvae; 7, vestibular
bulb; 5, tuber ischii; 9, sacro-sciatic Ugament. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

little (ca. 2 cm.) above the psoas tubercle into iliaco-femoral and obturator arteries.
The chief branches are as follows:

1. The last pair of lumbar arteries pass up through the foramina at the junc-
tion of the last lumbar vertebra and the sacrum and are distributed as already
described.

2. The internal pudic artery (A. pudenda interna) arises near the origin of the
internal iliac. It passes backward and somewhat downward, at first along the
ventral border of the iliac head of the obturator internus, then above the superior
ischiatic spine on the deep surface of the sacro-sciatic ligament, perforates the latter
and runs for a variable distance in its substance or on its lateral face. It then re-
enters the pelvic cavity, passes backward on the retractor ani to the ischial arch,
and divides into the perineal artery and the artery of the bulb in the male, perineal
and artery of the clitoris in the female. It is accompanied posteriorly by the
pudic nerve. Its chief branches are as follows:

670

BLOOD-VASCULAR SYSTEM OF THE HORSE

(1) The umbilical artery is given off from the internal pudic about an inch
(ca. 2-3 cm.) from the origin of that vessel. It is a very large artery in the
foetus, in which it curves downward and forward at the side of the bladder in the
edge of the lateral umbilical fold of peritoneum, passes through the umbilical open-
ing, becomes a component of the umbilical cord, and ramifies in the foetal placenta.
After birth it extends only to the vertex of the bladder and is much reduced. Its
lumen is almost obliterated and its wall is very thick, giving the vessel a cord-like
character, hence it is commonly termed the round ligament of the bladder. ^ It
gives off small vesical branches (Aa. vesicales craniales) to the bladder, and twigs
to the prostate and ductus deferens in the male. In the mare a small branch runs
forward along the ureter into the broad ligament of the uterus.

(2) The middle haemorrhoidal or vesico-prostatic artery (A. hsemorrhoidalis
media) in the male arises usually near the prostate and runs backward lateral to
the rectum. It supplies branches to the rectum, bladder, urethra, and accessory
genital glands. In the female the homologous vessel is much larger and gives off

the posterior uterine artery (A.
uterina caudalis). This runs for-
ward on the side of the vagina, to
which it gives branches, and rami-
fies on the body of the uterus, anas-
tomosing with the anterior and
middle uterine arteries. (In some
cases this artery arises from the
internal iliac or the umbilical.)

(3) The perineal artery (A.
perinei) is relatively small in the
male. It ascends at the side of the
anus, which it supplies, and gives
twigs to the bulbocavernosus mus-
cle and the skin of the perineum.
In the female it is large and is dis-
tributed to the anus and vulva, and
gives a large branch to the vestibu-
lar bulb.

(4) The artery of the bulb (A.
bulbi urethrse) may be regarded as
the direct continuation of the in-
ternal pudic in the male. It lies

at the side of the urethra above the ischial arch, dips under the bulbo-cavernosus
muscle, and ramifies in the corpus cavernosum urethrse. Before doing so it gives
off a small branch which turns around the ischial arch to reach the dorsum penis,
and anastomoses with the deep branch of the obturator.

(4 a) The artery of the clitoris (A. clitoridis) is the homologue in the female
of the preceding vessel, but is much smaller. It passes to the ventral surface of
the vulva with a branch of the pudic nerve, supplies the clitoris, and gives twigs to
the vulva.

3. The lateral sacral artery (A. sacralis lateralis) arises at the lumbo-sacral
articulation (Fig. 576). It passes backward under the wing of the sacrum, then
along the pelvic surface of the bone below the ventral sacral foramina and the
nerves emerging from them, and is continued by the lateral coccygeal artery. The
branches are as follows:

(1) Spinal branches (Rami spinales) enter the vertebral canal through the

1 The obliteration in the adult extends a variable distance from the vesical end toward the
origin, but usually involves completely only a small part.

Fig. 579. — Cross-sfxtion of Tail of Horse.
1, Dorso-lateral coccygeal vessels and nerve; £, ventro-lateral
coccygeal artery and nerve; 3, middle coccygeal artery; 4, sacro-
coccygeus dorsalis; 4', sacro-coccygeus lateralis; 5, 5', intertrana-
versales; 6, sacro-coccygeus ventralis; 7, recto-coccygeus; 8,
coccygeal fascia; 9, fibro-cartilage between fourth and fifth
coccygeal vertebrae. The veins are black.

THE INTERNAL ILIAC ARTERY

671

Superficial peroneal nerrc
Deep peroneal nerve

Deep femoral

Peroneal nerve

Tibial nerve
Posterior femoral

artery
A", cutaneus

surce^
Popliteal lymph

glands
Gastrocneynius
Recurrent tarsal

vessels

Tarsal or acces-
sory tendon of
biceps femoris

Deep flexor of
digit

Gastroc7iemius
tendon

Superficial flexor
tendon

Tuber calcis

Middle annular ligament ■
Lateral ligament

Distal annular ligament

Fig. 580. — Dissection of Pelvis, Thigh, and Leg of Horse; Lateral View.
1. Dorsal branches of last thoracic and first three lumbar nerves; ^, cutaneous branch of fourth lumbar nerve; 3,
ventral branches of last thoracic nerve; 4> branches of ilio-hypogastric nerve; 5, superficial branch of ilio-inguinal nerve;
6, great sciatic nerve; 7, S, nerves to biceps femoris (from posterior gluteal nerve); 9, nerve to semitendinosus (from
same); 10, posterior cutaneous nerve of thigh; 11, pudic nerve; 1£, anterior gluteal vessels and nerves; 13, posterior
gluteal vessels; 14, branches of obturator vessels; 15, proximal muscular branches of great sciatic nerve to biceps fem-
oris, semitendinosus, and semimembranosus; 16, nerve to tensor fascise latae (from anterior gluteal nerve); 17, gluteus
profundus; ;S, stump .of gluteus medius; 79, gemellus; ^0, stump of quadratus femoris; ;2/, stump of biceps femoris;
$2, sacro-coccygeus dorsalis; 23', sacro-coccygeus lateralis; 23, coccygeus; 24, sacro-coccygeus ventraUs; 2.5, line of
fusion of aponeuroses of internal and external obUque muscles of abdomen; 25', aponeurosis of external oblique muscle
(lamina iliaca); 26, branches of iliaco-femoral vessels; 27, ilio-lumbar vessels; 2S, ilio-lumbar ligament or deep layer
of lumbo-dorsal fascia; 29, tuber coxae; 30, tuber sacrale; 31, lateral sacro-iliac ligament; 32, sacro-sciatic ligament.
The ventral part of a nineteenth rib is shown in front of 3. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

672

BLOOD-VASCULAR SYSTEM OF THE HORSE

ventral sacral foramina. They give off branches to the spinal cord and its mem-
branes, which reinforce the ventral spinal artery-, and others which emerge through
the dorsal sacral foramina and supply the muscles and skin of the croup.

(2) The middle coccygeal artery (A. coccygea) is an unpaired vessel which
arises from the right or left lateral sacral or from a lateral coccygeal artery. It
passes backward on the pelvic surface of the sacrum to the median line and con-
tinues in that position along the tail between the ventral muscles, supplying
these and the skin.

(3) The posterior gluteal artery (A. glutea caudalis)^ emerges through the
upper part of the sacro-sciatic ligament and runs on the latter toward the tuber
ischii, under cover of the Ijiceps femoris (Fig. 580). It gives branches to that

Internal iliac arterij

External iliac artery
Circumflex iliac artery
Tuber c^xce \

Common
iliac veins

Femoral vessels

Remnant of

inguinal ligament

Sartonus

Femoral nirve

Deep femoral

vessels

Trochanter Urtius

Obturator

Biceps femoris
Semitendinosus
Sevnmevihranosus

Fig. 581. — Deep Dissection op Ventral Wall of Pelvis of Hokse (Male). ,^.

/, External pudic artery and small satellite vein; Z, anastomosis between external pudic vein and deep femoral
veins; 3, accessory ligament; 4, round ligament; 5, transverse ligament; 6, head of femur; 7, obturator externus
(stumps); 8. medial margin of obturator foramen; 9, origin of gracilis; 10, origin of adductor; 11, bulbocavernosus;
12, retractor penis; 13, suspensory ligament of penis. (After Schmaltz, Atlas d. Anat. d. Pferdes.;

muscle, the semitendinosus, semimembranosus, superficial gluteus, and coccygeus,
and anastomoses with the obturator, deep femoral, and posterior femoral arteries.
(4) The lateral coccygeal artery (A. caudalis lateralis ventralis) continues the
direction of the lateral sacral, but is much smaller than the preceding vessel. It
passes back between the ventral and intertransversales muscles of the tail and
divides into dorsal and ventral branches which supply twigs to the muscles and
skin.

4. The ilio-lumbar artery (A. iliolumbalis) arises at a right angle from the
internal iliac and runs outward behind the sacro-iliac joint, crossing the ventral
surface of the ilium under cover of the iliacus muscle. It gives branches to the ilio-
psoas and longissimus, turns around the lateral border of the ilium a little behind
the tuber coxae, and ends in the gluteus medius and tensor fasciae latae (Fig. 580).

5. The anterior gluteal artery (A. glutea cranialis) is the largest branch of the
internal iliac. It arises usually opposite to the preceding vessel, and passes outward

' Also termed the ischiatic artery.

ARTERIES OF THE PELVIC LIMB 673

through the greater sciatic foramen, dividing into several branches as it emerges;
these enter the gluteal muscles (Fig. 580).

6. The iliaco-femoral or lateral circumflex artery of the thigh (A. circumflexa
femoris lateralis) passes ventro-laterally across and beneath the shaft of the ilium,
under cover of the iliacus muscle, and dips in between the rectus femoris and vastus
lateralis. It is accompanied by two satellite veins. It gives collateral branches to
the iliopsoas, the glutei, and the tensor fasciae latse, supplies the nutrient artery of
the ilium, and terminates in the quadriceps femoris (Fig. 580) .

7. The obturator artery (A. obturatoria), the medial terminal branch of the
internal iliac, passes downward and backward on the pelvic surface of the shaft of
the ilium, along the ventral border of the iliac head of the obturator internus, ac-
companied by the satellite vein and nerve, which lie ventral to the artery (Fig. 576).
On reaching the obturator foramen it dips under the obturator internus and passes
obliquely through the lateral part of the foramen. In this part of its course it
gives off a vesical branch and twigs to the obturator internus and the hip-joint.
It emerges from the obturator foramen behind the obturator externus, passes be-
tween the quadratus femoris and the adductor, runs backward on the ventral face
of the ischium, and, in the male, enters the crus penis, forming the arteria profunda
penis. It anastomoses with the internal pudic, and usually with the external
pudic by a branch (A. clorsalis penis caudalis) which runs forward on the dorsum
penis. Collateral branches are detached to the obturator muscles, the adductors
of the thigh, the semimembranosus, biceps femoris, and semitendinosus, and anas-
tomoses are formed with the deep femoral and posterior femoral arteries. In the
female the terminal part is small and enters the root of the clitoris.

ARTERIES OF THE PELVIC LIMB
The main arterial trunk of each pelvic limb descends to the proximal part of
the posterior surface of the tibia, where it divides under cover of the popliteus
muscle into the anterior and posterior tibial arteries. The different parts of the
trunk receive names which correspond to the several regions through which it
passes. In the abdomen it is termed the external iliac artery, in the proximal two-
thirds of the thigh it is called the femoral artery, and distal to this it is termed the
popliteal artery.

The External Iliac Artery (Figs. 575, 576)
The external iliac artery (A. iliaca externa) arises from the aorta under the
fifth lumbar vertebra, and usually just in front of the origin of the internal iliac.
It descends at the side of the pelvic inlet along the tendon of the psoas minor,
crosses the insertion of that muscle, and reaches the level of the anterior border of
the pubis, beyond which it is continued by the femoral artery. It is covered by the
peritoneum and fascia, and is related behind to the corresponding vein. Its chief
branches are as follows:

1. The circimiflex iliac artery (A. circumflexa ilium profunda) arises from the
external iliac at its origin or from the aorta directly. It passes across the iliac
fascia toward the tuber coxae, and divides into two branches at or near the lateral
border of the psoas major. The artery lies between the fascia and the peritoneum
and is accompanied by two veins. It furnishes small branches to the psoas muscles
and the external iliac lymph glands. The anterior branch gives twigs to the iliacus
and psoas muscles, and passes downward and forward in the flank on the trans-
versus abdominis, along, or under cover of, the upper margin of the obliquus ab-
dominis internus. It gives branches to these muscles, the obliquus abdominis
externus, and the skin of the flank. The posterior branch perforates the abdominal
wall close to the tuber coxse, and runs downward on the medial face of the tensor
43

674

BLOOD-VASCULAR SYSTEM OF THE HORSE

fasciae latae to the fold of the flank, supplying branches to that muscle, the cutaneus,
the prefemoral hanph glands, and the skin.

2. The external spermatic or cremasteric artery (A. spermatica externa) is a
very small vessel which arises in a variable manner. It springs most often from the
external iliac near the origin of the latter, but may come from the circumflex iliac,
the aorta between the external and internal iliac, or the latter vessel. It accom-
panies the cremaster muscle to the inguinal canal, supplies twigs to that muscle,
the tunica vaginalis, and other constituents of the spermatic cord (Fig. 575).

2 a. The middle uterine artery (A. uterina media) of the female is regarded as
the homologue of the preceding vessel; it has a similar origin, but is a much larger
artery. It enters the broad ligament of the uterus, in which it pursues a flexuous
course to the posterior part of the horn of the uterus. Its branches are distributed
to the uterus and anastomose with those of the other uterine arteries.

The Femoral Artery (Figs. 575, 576)
The femoral artery is the main arterial trunk of the thigh. It begins at the
level of the anterior border of the pubis, from which it is separated by the femoral

Fig. 582. — Dissection of Inguinal Region and Medial Surface of Thigh of Horse.
1, External pudic artery; 2, anterior branches of /; 3, posterior branches of /; 4> transverse anastomosis between
external pudio veins; 4', venous plexus of dorsum penis; 5, femoral artery; 6, saphenous nerve; 7, anterior border of
external inguinal ring; S, obliquus abdominis internus; 9, posterior border of external inguinal ring; 10, tunica vag-
inalis; //, ductus deferens; /a', cremaster muscle; /3, prepuce; 74> glans penis; /5, external urethral orifice; 16, pos-
terior branches of circumflex iliac vessels; / 7, saphenous vessels; J S, fold of flank; /5, penis (cut) ; .-1, superficial ingui-
nal lymph glands; B, prefemoral lymph glands; C, deep inguinal lymph glands. The testicle (on the right side) has
been rotated somewhat to show the cremaster muscle. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

vein. It descends almost vertically in the femoral canal behind the sartorius
muscle, covered at first by the medial femoral fascia and lower down by the gracilis.
After passing over the insertion of the pectineus, it perforates the adductor muscle,
crosses in the vascular groove of the posterior surface of the femur, and is continued

THE FEMORAL ARTERY 675

between the two heads of the gastrocnemius as the popliteal artery. It is related
at its origin to the sartorius in front, the femoral vein behind (which separates it
from the pectineus), and the iliacus laterally. Lower down it is related super-
ficially to the deep inguinal lymph glands, and deeply to the vastus medialis, while
the saphenous nerve is in front of it, and the vein passes to its lateral face. The
chief branches are as follows:

1. The prepubic artery (Truncus pudendo-abdominalis) arises usually by a
common trunk \\dth the deep femoral, a little below the level of the pubis. It
passes forward across the edge of the inguinal ligament, inclining ventro-medially,
and then runs on the abdominal surface of the ligament to the medial part of the
internal inguinal ring, where it divides into the posterior abdominal and external
pudic arteries. (1) The posterior abdominal artery (A. abdominalis caudalis)
(Fig. 370) passes along the lateral border of the rectus abdominis and anastomoses
in the umbilical region with the anterior abdominal artery. It supplies branches
chiefly to the rectus and obliquus internus muscles. (2) The external pudic
artery (A. pudenda externa) descends on the inguinal ligament through the
medial part of the inguinal canal, and emerges at the medial angle of the ex-
ternal ring. In the male it divides into the subcutaneous abdominal artery
and the anterior dorsal artery of the penis. The former (A. abdominalis sub-
cutanea) runs forward on the abdominal tunic a short distance from the linea alba,
and gives branches to the superficial inguinal lymph glands, the sheath, and the
scrotum. The latter (A. dorsalis penis cranialis) passes to the dorsmn penis and
ends at the glans as the arteria glandis. It gives off collateral branches (Rami
profundi penis) to the corpus cavernosum, one of which usually passes backward
and anastomoses with a branch of the obturator arter3^ Branches are also supplied
to the superficial inguinal lymph glands, the prepuce, and the scrotum. In the
female the mammary artery (A. mammaria) takes the place of the anterior dorsal
artery of the penis ; it enters the base of the mammary gland, in which it ramifies.

2. The deep femoral artery (A. profunda femoris) (Fig. 581) arises either by a
common trunk with the prepubic or a little distal to it. The point of origin is
usually at the level of the anterior border of the pubis, but may be as much as an
inch lower. It passes backward and downward across the medial face of the
femoral vein, then below the pubis in the space between the hip joint and the pec-
tineus muscle. On reaching the obturator externus it inclines more ventrally and
laterally, passes out between the posterior surface of the femur and the quadratus
femoris, and ramifies in the biceps femoris and semitendinosus. It supplies large
collateral branches to the medial femoral muscles and twigs to the deep inguinal
lymph glands and the hip joint, and anastomoses with the obturator artery.^

3. The anterior femoral artery (A. femoris cranialis) (Fig. 575) arises a little
distal to the preceding vessel, from the opposite side of the femoral trunk. It
passes forward, outward, and a little downward across the deep face of the sartorius,
dips in between the rectus femoris and vastus medialis, and ramifies in these muscles
and the vastus intermedins. It is related laterally to the ilio-psoas and to the
femoral nerve.

In some cases this artery is replaced by a large branch of the iliaco-femoral or external cir-
cumflex, which passes between the iho-psoas and rectus femoris and enters the interstice between
the latter muscle and the vastus mediahs.

4. Innominate muscular branches (Rami musculares) of variable size and
arrangement are given off to the muscles of this vicinity.

5. The saphenous artery (A. saphena) (Figs. 576, 582) is a small vessel which
arises from the femoral about its middle, or from a muscular branch, and emerges
between the sartorius and gracilis or through the latter to the medial surface of the

1 In the new nomenclature the term A. circumflexa femoris medialis is applied to the part
which turns outward, while the part which runs backward is regarded as the continuing trunk.

676 BLOOD-VASCULAR SYSTEM OF THE HORSE

thigh. In company with the large saphenous vein and the saphenous nerve it
descends superficially on the anterior part of the gracilis, continues on the deep
fascia of the leg, and divides above the hock into two branches, which accompany
the radicles of the vein. It gives off cutaneous twigs and anastomoses with the
recurrent tibial artery.

In some cases this anastomosis does not occur. The artery may be larger and directly con-
tinuous with the medial tarsal artery.

6. The articular branch (A. genu suprema) is a slender artery which arises
from the femoral just before it passes through the adductor. It descends along the
posterior border of the vastus medialis to the medial surface of the stifle joint,
where it ramifies.

7. The nutrient artery of the femur (A. nutritia femoris) is given off at the
middle of the femur and enters the nutrient foramen.

8. The posterior femoral artery (A. femoris caudalis)i is a large vessel which
arises from the posterior face of the femoral just before or as the trunk passes be-
tween the two heads of the gastrocnemius (Fig. 584) . It is very short and divides
into two branches. The ascending branch passes upward and outward between
the adductor (in front) and the semimembranosus (behind), and ramifies in the
biceps femoris, vastus lateralis, adductor, and semitendinosus. The descending
branch passes downward and backward on the lateral head of the gastrocnemius,
then curves upward between the biceps femoris and semitendinosus (crossed
laterally by the tibial nerve) and divides into branches to these muscles. A branch
descends between the heads of the gastrocnemius, gives branches to that muscle
and the superficial digital flexor, and is continued by a slender artery which ac-
companies the tibial nerve and unites with the recurrent tibial artery. A small
branch often ascends alongside of the sciatic nerve, between the biceps and semi-
tendinosus and anastomoses with a descending branch of the obturator.

This branch is frequently absent, but the large vein which it accompanies when present, is
constant and connects the obturator and posterior femoral veins.

The Popliteal Artery
This artery (A. poplitea) is the direct continuation of the femoral. It lies
between the two heads of the gastrocnemius, at first on the posterior face of the
femur, then on the femoro-tibial joint capsule. It descends through the popliteal
notch under cover of the popliteus, inclines outward, and divides near the proximal
part of the interosseous space into anterior and posterior tibial arteries. The
satellite vein lies along its medial side at the stifle joint. Collateral branches are
supplied to the stifle joint and the gastrocnemius and popliteus.

One of the articular branches (A. genu media) runs directly forward, passes through the
posterior part of the capsule of the femoro-tibial joint, and supplies the cruciate ligaments, syno-
vial membrane, etc. Another branch (A. genu lateralis distalis) passes outward under the lateral
head of the gastrocnemius, and concurs with the articular branch of the femoral artery in forming
a plexus on the stifle.

POSTERIOR TIBIAL ARTERY

The posterior tibial artery (A. tibialis posterior) is much the smaller of the two
terminals of the popliteal. It lies at first between the tibia and the popliteus,
then between that muscle and the deep and medial heads of the deep digital flexor.
Lower down it descends along the tendon of the flexor longus, becomes superficial
in the distal third of the leg, and divides into lateral and medial tarsal branches. ^
The collateral branches include the nutrient artery of the tibia (A. nutritia tibiae)
and muscular branches (Rami musculares) to the muscles on the posterior surface
of the tibia.

1 Also termed the femoro-popliteal artery.

2 Instead of dividing thus, the posterior tibial may be continued by the lateral tarsal. The
medial tarsal may be a continuation of the saphenous artery.

POSTERIOR TIBIAL ARTERY

677

The lateral tarsal artery (A. tarsea lateralis) passes outward between the tibia
and the deep flexor of the digit, and is distributed to the outer surface of the hock.

Tibial insertion of
semitendinosus
Saphenous vein

Popliteu

Flexor dig long us

Posterior tibial vessels
Long extensor

Medial ligament of hock
Peroneus terlius

Medial tendon of

tibialis anterior

Outline of bursa of above

Medial or great
metatarsal vein

Tendon of semitendinosus

Gastrocnemius {medial
head)

Tendon of gastrocnemius

Tendon of superficial

flexor
Tarsal tendon of semi-
tendinosus
Tibial nerve

Recurrent tibial vessels

\ Deep flexor tendon

Medial tarsal artery

Tendon of flexor dig. longus
Lateral plantar vein
Medial plantar artery

Medial plantar nerve
Deep flexor tendon

Medial superficial plantar
metatarsal vessels

Fig. 583.— Dissection of Right Leg and Hock of Horse; Medial View. (After Schmaltz. Atlas d. Anat. d. Pferdes.)

It gives off the small recurrent tarsal artery (A. tarsea recurrens), which ascends
along the lateral margin of the gastrocnemius tendon with a satellite vein and nerve

678 BLOOD-VASCULAR SYSTEM OF THE HORSE

and anastomoses with a branch of the posterior femoral artery. In some cases an
arch is formed by junction with the peroneal artery on the lateral surface of the deep
flexor at the distal fourth of the leg.

The medial tarsal artery (A. tarsea medialis) usually forms a double curve in
front of the tuber calcis, then descends on the deep flexor tendon with the plantar
nerves, and divides into the two plantar arteries. From the second part of the
curve there arises a small branch, the recurrent tibial artery (A. tibialis recurrens).
This ascends along the medial border of the superficial digital flexor in company
with a satellite vein and the tibial nerve, and anastomoses with a descending branch
of the posterior femoral artery and with the saphenous arter3^^

6. The plantar arteries, medial and lateral (A. plantaris medialis, lateralis),
are the small terminals of the medial tarsal. They descend along the sides of the
tarsal sheath of the deep flexor tendon with the plantar nerves to the proximal part
of the metatarsus, where they unite with the perforating tarsal artery to form the
proximal plantar arch (Arcus plantaris proximalis). Four plantar metatarsal
arteries proceed from this arch. The two slender superficial plantar metatarsal
arteries (A. metatarsea plantaris superficialis medialis, lateralis) may be regarded
as the continuations of the plantar arteries; they descend on either side of the deep
flexor tendon with the plantar nerves, and unite with the corresponding digital
artery. The medial one is the smaller; it may give off or connect with the cor-
responding dorsal artery. The lateral, larger one usually unites with the lateral
digital artery. Both may unite at the distal part of the metatarsus to form a short
trunk which joins one of the digital arteries. They supply twigs to the flexor
tendons and the skin. The two deep plantar metatarsal arteries (A. metatarsea
plantaris profundus medialis, lateralis) descend on the plantar surface of the large
metatarsal bone alongside of the corresponding small metatarsal bone and unite
near the fetlock with the great metatarsal. The medial artery is the larger of the
two and usually appears to be the continuation of the perforating tarsal. It
supplies the nutrient artery of the large metatarsal bone. In other cases it is
the direct continuation of the medial plantar artery, the lateral artery only uniting
with the perforating tarsal. The connection of these vessels with the great meta-
tarsal artery forms the distal plantar arch (Arcus plantaris distalis) .

ANTERIOR TIBIAL ARTERY

The anterior tibial artery (A. tibialis anterior) is much the larger of the two
terminal branches of the popliteal. It passes forward through the proximal part of
the interosseous space and descends with two satellite veins on the lateral part of
the front of the tibia, under cover of the tibialis anterior. At the distal part of the
leg it deviates to the lateral border of the tendon of this muscle, passes on to the
capsule of the hock joint, gives off the large perforating tarsal artery, and is con-
tinued as the great metatarsal artery.- It gives off muscular branches to the dorso-
lateral group of muscles of the leg and articular branches to the hock. The per-
oneal artery (A. peronea) is a variable vessel which descends along the fibula under
cover of the lateral extensor; it gives off muscular branches and one which per-
forates the fascia and divides into ascending and descending cutaneous twigs.^

The perforating tarsal artery (A. tarsea perforans) arises under cover of the
lateral tendon of the peroneus tertius. It passes backward through the vascular
canal of the tarsus with a satellite vein and nerve and unites on the upper part of

1 The artery may be double in part or throughout. It may join the popliteal artery. The
S-shaped curve may be absent and the medial tarsal be the direct continuation of the recurrent
tibial artery.

2 The part of the arterial trunk which is on the dorsal surface of the tarsus may be distinguished
by the term A. dorsalis pedis.

^ In some cases the peroneal artery is larger than usual and forms an anastomotic arch with
the lateral tarsal in the distal part of the leg.

ANTERIOR TIBIAL ARTERY

679

the suspensory ligament with the plantar arteries (or only with the lateral plantar)
to form the proximal plantar arch (Arcus plantaris proximalis).

Vastus lateralis

Biceps femoris

Gastrocnemius, lateral head

Superficial digital flexor

Lateral articular vessels

Joint capsule

Lateral condyle of femur

Popliteus

Pouch of joint capsule,

opened

Lateral ligament of femoro-

tibial joint

Recurrent tibial vessels

Soleus
Tibialis posterioi

Lateral extensor tendon
Recurrent tarsal vein
Lateral plantar vein

Lateral tarsal viin
Lateral tarsal aitti 1/

Trochlea of tibial tarsal bunt
Lateral ligament of hod joint Ji-

Fibular tarsal bont

Femoral vessels
Posterior femoral artery
Popliteal artery
Adductor
Gastrocnemius, medial head
Tibial nerve

Flexor dig. longus
Flexor hallucis longus

Posterior tibial artery

Lateral tarsal artery
Medial tarsal artery
Proximal end of tarsal sheath
Deep flexor tendon
Long flexor tendon
Plantar nerves
Plantar arteries
Joint capsule, opened

Fig. 584. — Deep Dissection of Left Stifle, Leg, and Hock of Horse; Posterior View.
The hock is flexed at a right angle, and the tuber calcis is sawn off. The tibial nerve is drawn aside to show its
muscular branches. The capsules of the stifle and hock joints are partially removed. Branches of tibial nerve; 1, S,
to gastrocnemius; 3, 4, to superficial flexor; 5, to popliteus; 6, to flexor longus; 7, to deep flexor. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)

BLOOD-VASCULAR SYSTEM OF THE HORSE

In well-injected specimens it is seen that there is a fine arterial network (Rete
tarsi dorsale) on the dorsal surface of the hock, which is formed by twigs from the

Patella

Tendon of biceps femoris

Lateral patellar ligament
Gastrocnemius, lateral head

Lateral condyle of tibia

Lateral ligament of femoro-
tibial joint
Common peroneal nern

Superficial peroneal nerve

Lateral extensor

Long extensor

Peroneus tertius

Loop of lateral tendon
of peroneus tertius

Perforating tarsal artery

Stump of extensor

dig. brevis

Great metatarsal artery

Lateral extensor tendon

Long extensor tendon

Vastus medialis

Accessory cartilage of patella

Gracilis

Sartorius

Trochlea of femur

(medial ridge)

Medial patellar ligament

Middle patellar ligament

Medial condyle of tibia
Medial ligament of femoro-
tibial joint

Gastrocnemius, medial head

Crest of tibia

Tibial tendon of
semitendinosus

Tibialis anterior
Saphenous vein
Deep fascia (reflected)

Anterior tendon of pero-
neus tertius

Medial tendon of tibialis
anterior

Distal annular ligament
Great metatarsal vein
Deep peroneal nerve

Fig. 585. — Superficial Dissection- of Right Stifle, Leg, and Hock of Horse; Front View. (After Schmaltz,

Atlas d. Anat. d. Pferdes.)

anterior tibial and lateral tarsal arteries. From it proceed two very slender dorsal
metatsirsal arteries (A. metatarsea dorsalis medialis, lateralis). The medial one

THE VEINS PULMONARY VEINS— CARDIAC VEINS 681

descends in the furrow between the medial small and large metatarsal bones, and
anastomoses usually in the proximal part of the metatarsus with the medial super-
ficial plantar metatarsal, uniting sometimes with the medial deep plantar meta-
tarsal. The lateral vessel passes down under the periosteum on the dorsal face of
the large metatarsal bone and becomes lost or joins the great metatarsal artery.

In rare cases the anterior tibial artery passes undivided through the tarsus, gives off the
medial deep plantar metatarsal, and is continued as a very large medial superficial plantar meta-
tarsal along the deep flexor tendon, thus resembling the arrangement in the foreUmb.

In a few cases the perforating tarsal is a large vessel, directly continuing the anterior tibial,
and is continued by a large medial deep plantar metatarsal. The great metatarsal is then small.
Other variations are common.

THE GREAT METATARSAL ARTERY

This artery (A. metatarsea dorsalis lateralis) is the direct continuation of the
anterior tibial. It descends, inclining outward, under cover of the extensor brevis
and the tendon of the lateral extensor, at first on the joint capsule and then in the
oblique vascular groove on the proximal part of the large metatarsal bone. It then
descends superficially in the groove formed by the apposition of the large and lateral
small metatarsal bones, passes between the two, and divides on the distal part of
the plantar surface of the large metatarsal bone into the medial and lateral digital
arteries. It is not usually accompanied by a vein. It is joined near its termination
by two or more of the plantar arteries, and beyond this the term common digital
artery (A. digitalis communis) may be applied to it. In the digital region the
arterial arrangement is the same as in the thoracic limb; it is only necessary in
reading the description to substitute the word "plantar" for "volar."

THE VEINS 1
PULMONARY VEINS
The pulmonary veins (Vv. pulmonales), usually seven or eight in number,
return the aerated blood from the lungs and open into the left atrium of the heart.
They are destitute of valves. Their tributaries arise in the capillary plexuses in
the lobules of the lungs, and unite to form larger and larger trunks which accompany
the branches of the bronchi and pulmonary arteries. A very large vein is formed
by the union at an acute angle of a trunk from each lung, where the latter are ad-
herent to each other.

CARDIAC VEINS

The coronary sinus (Sinus coronarius) is a very short, bulbous trunk which
receives most of the blood from the wall of the heart. It is situated just below the
termination of the posterior vena cava, and is covered in part by a thin layer of
atrial muscle fibers. It opens into the right atrium just below the posterior vena
cava. It is formed by the union of two tributaries. The great cardiac or left
coronary vein (V. cordis magna) ascends in the left longitudinal groove and turns
backward in the coronary groove, in which it winds around the posterior border of
the heart to the right side and joins the coronary sinus. The middle cardiac or
right coronary vein (V. cordis media) ascends in the right longitudinal groove and
joins the coronary sinus, or opens separately into the atrium just in front of the

1 Most of the veins are depicted in the illustrations of the section on the arteries, to which
reference is to be made. Many satellite veins which are homonymous with the arteries which
they accompany, and present no important special features, are not described here.

682 BLOOD-VASCULAR SYSTEM OF THE HORSE

orifice of the great cardiac vein, so that a common trunk (coronary sinus) does not
then exist.

The small cardiac veins (Vv. cordis minores), three to five in number, are
small vessels which return some blood from the right ventricle and atrium; they
open into the latter near the coronary groove in spaces between the musculi pec-
tinati.

THE ANTERIOR VENA CAVA (Fig. 554)
The anterior vena cava (V. cava cranialis) returns to the heart the blood from
the head, neck, thoracic limbs, and the greater part of the thoracic wall. It is
formed at the ventral part of the thoracic inlet by the confluence of the two jugu-
lar and two brachial veins. It passes backward in the anterior mediastinum, at
first median and ventral to the common carotid trunk, then deviates to the right
of the common brachiocephalic trunk, and opens into the right atrium opposite
to the fourth rib. It is partly enclosed by the pericardium. The demarcation be-
tween vein and atrium is not very distinct. It contains no valves except at the
mouths of its radicles. Its length is about five to six inches (ca. 12-15 cm.) and
its caliber about two inches (ca. 5 cm.) in a subject of medium size. It is related,
dorsally to the trachea, the right vagus and cardiac nerves, and anterior medias-
tinal lymph glands. Its right face is crossed b}^ the right phrenic nerve, and on the
left it is related to the brachiocephalic trunk and artery. The thoracic duct opens
through the dorsal wall of the origin of the vena cava. It receives, in addition to
small pericardial and mediastinal veins, the following tributaries :

1. The internal thoracic vein (V. thoracica interna) is a satellite of the artery
of that name. It opens into the anterior vena cava at the first rib. The ventral
intercostal veins (Vv. intercostales ventrales) open into the internal thoracic and
musculo-phrenic veins.

2. The vertebral vein (V. vertebralis) corresponds to the homonymous artery.
On the right side it terminates either in front of the deep cervical vein or by a short
common trunk with it. On the left side it usually unites with the deep cervical
and dorsal veins to form a common trunk.

3. The deep cervical vein (V. cervicalis profunda) corresponds to the artery.
On the right side it passes downward and backward across the right face of the
trachea and opens into the vena cava; it may form a common trunk "svith the dorsal
or vertebral. On the left side there is usually a common trunk for all three. It
receives the first intercostal vein.

4. The dorsal vein (V. costocervicalis) corresponds to the artery. On the
right side it leaves the artery on entering the thorax, crosses the right face of the
trachea, and opens into the vena cava behind the deep cervical or by a common
trunk with it. On the left side it usually joins the deep cervical and vertebral to
form a short common trunk which crosses the left face of the intrathoracic part of
the brachial artery opposite the second rib and opens into the anterior vena cava.
It receives the third, fourth, and fifth intercostal veins by means of the subcostal
vein on the right side.

The Vena Azygos
The vena azygos (Fig. 554) is an unpaired vessel which arises at the level of
the first lumbar vertebra by radicles from the spinal and psoas muscles and the
crura of the diaphragm. It passes forward along the right side of the bodies of the
thoracic vertebrae, in contact usually with the thoracic duct, which separates the
vein from the aorta. At the seventh vertebra it leaves the spine, curves downward
and forward over the right side of the thoracic duct, trachea, and oesophagus, and
opens into the right atrium opposite the fourth intercostal space. Its tributaries

VEINS OF THE HEAD AND NECK — JUGULAR VEINS 683

1. The last fourteen dorsal intercostal veins (Vv. intercostales dorsales) of the
right side go directly to the vena azygos; but on the left side a variable number
(four to seven usually) at the end of the series go to the vena hemiazygos when that
vessel is present.

2. The vena hemiazygos arises from a branch of the left first lumbar vein and
twigs from the crura of the diaphragm. It passes forward through the hiatus
aorticus and continues along the left dorsal face of the aorta, and about the mid-
dle of the back joins the vena azygos. It receives the last four to seven dorsal
intercostal veins of the left side. It is inconstant and variable. In its absence
its tributaries join the vena azygos.

3. The oesophageal vein (V. oesophagea), satellite of the oesophageal artery,
joins the vena azygos as it inclines downward.

4. The bronchial vein (V. bronchialis) unites with the preceding to form a
short common trunk, or, according to Chauveau, empties into the great coronary
vein. The author is unable to find in the horse any distinct bronchial vein
emerging at the root of the lung.^

VEINS OF THE HEAD AND NECK
Jugular Veins

The jugular veins (Vv. jugulares), right and left (Fig. 556), arise behind the
ramus of the mandible, about two and a half inches (ca. 6-7 cm.) below the tem-
poro-mandibular articulation by the union of the superficial temporal and internal
maxillary veins. Each passes downward and backward, at first embedded more
or less in the parotid gland, and continues in the jugular furrow to the thoracic
inlet, where it unites with its fellow and the two brachial veins to form the anterior
vena cava. In the neck it is covered by the skin, fascia, and cutaneus muscle, and is
superficial to the carotid artery, from which it is separated in the anterior half of
the region by the omo-hyoideus muscle.^ It contains valves at the mouths of its
tributaries, and has several pairs of semilunar valves variably disposed along its
course. Its tributaries are as follows:

1. The internal maxillary vein (V. maxillaris interna) is larger than the external
maxillary. It may be considered to begin as the continuation backward of the
buccinator vein where that vessel crosses the alveolar border of the mandible,
about two inches (ca, 5 cm.) behind the last molar tooth. It runs backward on
the medial surface of the ramus ventral to the lateral pterygoid muscle, and covered
by the medial pterygoid muscle for a distance of about three inches (ca. 7-8 cm.),
then inclines a little downward and runs ventral to the artery for about an inch
(ca. 2-3 cm.). It crosses the lateral face of the artery at the posterior border of
the jaw, and is joined by the superficial temporal vein to form the jugular. Its
principal radicles are the following:

(1) The dorsal lingual vein (V. dorsalis linguae) is not a satellite on any artery,

1 In Chauveau-Arloing-Lesbre the statement is made that "the bronchial veins, which ramify
on the bronchi like the arteries of which they are satellites, open into the great coronary vein very
near its mouth, after having united to form a single vessel, which sometimes opens directly into
the atrium. " The arrangement is not illustrated. Ellenberger and Baum state that the bronchial
and a?sophageal vems open into the vena azygos separately or by a common trmik. Martin de-
scribes a short broncho-o^sophageal tnmk, but the vein which he figures as the bronchial does not
come from the Imigs, but is a small mediastinal vessel. The author finds such a vessel usually
entering the terminal part of the oesophageal vem, but no distinct bronchial vein in the horse.
The statement and figure in Bossi's recent work agree substantially with those of the German
authors.

2 There is usually only one jugular vein on each side in the horse, but in some cases there is an
internal or deep jugular vein which accompanies the carotid artery and ends at the confluence of
the external jugulars. M'Fadyean records a case in which the vein lay on the deep face of the
omo-hyoideus with the carotid artery. This would appear to be an instance of remarkable de-
velopment of the internal jugular in place of the usual external jugular vein.

6g4 BLOOD-VASCULAR SYSTEM OF THE HORSE

but is in company witli the lingual nerve. It receives tributaries from the tongue
and soft palate.

(2) The inferior alveolar or dental vein (V. alveolaris mandibulse) is a satellite
of the corresponding artery. It often unites with the preceding.

(3) The middle meningeal vein (V. meningea media) emerges through the
foramen lacerum anterius.

(4) Pterygoid veins (Rami pterygoidei).

(5) The posterior deep temporal vein (V. temporalis profunda aboralis) is a

Fig. 586. — Veins op Head op Horse.
Parts of the superficial muscles and the ramus of the mandible, and all of the masseter muscle except
its ventral margin, have been removed. Veins: 1, 3, Jugular; 2, thyroid; 3, internal maxillarj'; 4< cranio-
occipital trunk; 5, ventral cerebral; 6, occipital; 6', muscular branch of 6; 6", cerebrospinal branch of 6; 6"', vein
which emerges through foramen of lateral mass of atlas; 6"", vein which emerges through intervertebral foramen of
axis; 7, great auricular ; 7'-7"", radicles of 7; S, posterior auricular; S, masseterico-pterygoid; 70, superficial temporal;
11, deep auricular; 12, dorsal cerebral; 13, transverse facial and its anastomosis with internal maxillary; 13", pal-
pebral radicle of 13; 14, pterygoid; 15, mandibular alveolar; 16, dorsal lingual; 17, deep temporal; 18, buccinator;
19, anastomosis between buccinator and masseteric; 20, anastomosis between buccinator and common labial (21); 22,
;33, inferior and superior labial; ;g4. angular of mouth; ;g5, ;25', external maxillary; ^fi, facial; .27, lateral nasal; .25, dor-
sal nasal; ^9, angular of eye; SO, reflexa; 3^, trunk of infraorbital and sphenopalatine. Muscles, etc.: a, Orbicularis oris;
h, levator nasolabialis; c, dilatator naris lateralis; d, buccalis; e, zygomaticus; /, levator labii superioris proprius; g,
molaris and depressor labii inferioris; i, labial glands; k, m. temporalis; I, m. masseter; m, m. pterygoideus medialis;
n, m. parotido-auricularis; o, m. pterygoideus lateralis; p, m. sterno-cephalicus; q, m. rectus capitis ventralis major;
T, m. omo-hyoideus and sterno-hyoideus; s, parotid gland (dissected away from veins); t, dorsal buccal glands. (After
Mockel.)

large vessel which receives tributaries from the temporalis muscle and emissaries
from the temporal canal. It is connected with the dorsal cerebral vein and usually
with the meningeal veins by its frontal branch. The latter drains chiefly the
lacrimal gland and passes behind the supraorbital process.

2. The superficial temporal vein (V. temporalis superficialis) is the large
satellite of the corresponding artery. It is formed by the confluence of the anterior
auricular and transverse facial veins. The former is much larger than the cor-

JUGULAR VEINS 685

responding artery. Its radicles come from the posterior part of the temporalis
muscle and from the external ear. It receives the dorsal cerebral vein (V. cere-
bralis dorsalis), which is the emissary of the transverse sinus of the dura mater, and
emerges from the temporal canal behind the postglenoid process. The trans-
verse facial vein (V. transversa faciei) runs at first above the artery of like name,
then plunges deepl}^ into the masseter and unites in front with the facial vein. It
is connected with the vena reflexa and with the posterior deep temporal vein by a
branch which emerges from the temporal fossa through the mandibular notch.

3. The masseteric vein (V. masseterica) joins the jugular at the upper border
of the sterno-cephalicus tendon. It is a short but large trunk which is formed
by the confluence at the posterior border of the jaw of masseteric and pterygoid
veins. The former is commonly connected by an anastomotic branch with the
buccinator vein.

4. The great auricular vein (V. auricularis magna) is a satellite of the posterior
auricular artery above, but joins the jugular a variable distance below and behind
the point of origin of the artery.

5. The occipital vein (V. occipitalis) arises in the fossa atlantis by the union of
two radicles. It passes downward and backward on the rectus capitis ventralis
major and joins the jugular vein a variable distance in front of the termination of the
external maxillary vein. The anterior radicle is the ventral cerebral vein (V.
cerebralis ventralis). This is an emissary of the cavernous sinus of the dura mater;
it emerges through the foramen lacerum posterius and is connected with a venous
plexus in the infratemporal fossa, ^t receives the condyloid vein (V. conclyloidea),
which is an emissary of the basilar plexus and the petrosal sinus, and emerges
through the hypoglossal foramen.^ The posterior radicle is formed by the con-
fluence of musciilar and cerebro-spinal branches. The former (Ramus muscularis)
comes through the foramen transversarium of the atlas from the muscles of the
poll; it anastomoses with the vertebral and deep cervical veins. The latter (Ramus
cerebrospinalis) receives emissary veins from the meningeal plexus in the atlas,
which emerge through the intervertebral and alar foramina and the foramen of the
lateral mass of the atlas.

6. The external maxillary vein (V. maxillaris externa) arises by radicles which
correspond in general to the branches of the artery of like name. It passes down
■over the cheek along the anterior border of the masseter muscle behind the artery,
crossing over the parotid duct, which lies behind the vein lower down. Thus on
the ramus and as they turn around its ventral border the artery is in front, the vein
in the middle, and the duct posterior. In the mandibular space the vein is ventral
to the artery for some distance, then parts company with the artery, runs straight
backward along the ventral border of the parotid gland, and opens into the jugular
vein at the posterior angle of the gland.- The chief differences in the tributaries
of the vein as compared with the branches of the corresponding artery are as follows :

The labial veins (Vv. labiales), superior and inferior, are in the substance of the
orbicularis oris near the free edges of the lips. The upper one is the larger. They
anastomose with the opposite veins. They drain into a venous plexus which is
situated in the submucous tissue of the cheek and the buccinator muscle, and from
this plexus two veins emerge. The upper one passes back and joins the buccinator
vein. The lower one, the common labial vein (V. labialis communis), receives a
submental vein from the chin and joins the external maxillary vein.

Three veins connect with the external maxillary at the anterior border of the
masseter.

^ On account of the existence of this cranial affluent the term cranio-occipital has been pro-
posed for the venous trunk.

2 The venous angle formed by this junction indicates the position of the thyroid gland.

BLOOD-VASCULAR SYSTEM OF THE HORSE

The upper one is the transverse facial vein, which unites close to the end of
the facial crest.

A little lower is the large valveless vena reflexa, or alveolar vein. This passes
back under the upper part of the masseter on the maxilla, turns around the tuber
maxillare, perforates the periorbita, and joins the ophthalmic vein. It is relatively
small at each end, but presents one or two large fusiform dilatations. Its posterior

part is embedded in a mass of fat. It
receives the following tributaries : (a)
The great palatine vein (V. palatina
major), separates from the palatine
artery at the anterior palatine fora-
men, and passes in the groove between
the tuber maxillare and the palate
bone. The palatine veins form a very
rich plexus of valveless vessels in the
submucosa of the hard palate, which
consists of several layers anteriorly,
(6) The sphenopalatine vein (V.
sphenopalatina) is the satellite of the
artery; it forms a rich plexus of valve-
less vessels on the turbinate bones
and the septum nasi. The venous
plexuses are remarkably developed in
certain parts of the nasal mucosa.
On the septum a little below its
middle and on the turbinates the
veins are in several layers. The ol-
factory region does not share in this
arrangement, and the veins here are
small and join the ethmoidal vein.
(c) The infraorbital vein (V. infra-
orbitalis) is also a satellite of the ar-
terj^; it usually unites with the t pheno-
palatine to form a short common
trunk, (d) The ophthalmic vein (V.
ophthalmica) is a short trunk, which
is connected in front with the vena
reflexa and behind with the cavernous
sinus through the foramen orbitale.
It receives veins which correspond to
the arterial branches.

The buccinator vein (V. buccin-
atoria) extends backward from the ex-
ternal maxillary along the ventral bor-
der of the depressor labii inf erioris and
buccinator under cover of the mas-
seter, turns medially over the ramus
of the mandible about two inches (ca.
5 cm.) behind the last molar tooth, and is continued as the internal maxillary vein.
It has a large fusiform dilatation and is valveless. It receives a large vein from
the buccal plexus, and is usually connected with the masseteric vein.

The lingual vein (V. lingualis) is formed at the side of the lingual process of the
hyoid bone by the confluence of several veins which come from the substance of the
tongue. One or two considerable vessels run partly in the substance of the hyo-

iND Ad-

Fig. 587. — Dissection- of Mandibular Space
JACENT Part op Neck of Horse.
a. Ramus of mandible; b, sterno-cephalicus muscle;
c, c', omo-hyoidei and sterno-hyoidei (portion removed on
right side); d, hyoid bone; e, anterior belly of digastricus;
/, g, mylo-hyoideus; h, mandibular lymph glands (portion
removed on right side); i, parotid gland; k, mandibular
salivary gland; I, chin; m, occipito-mandibularis; 1, parotid
duct; 2, facial vein; 3, facial artery; 4, external maxil-
lary vein; 5, lingual vein; 6, sublingual artery; 7, ventral
branch of first cervical nerve; S, mylo-hyoid nerve. (After
Ellenberger, in Leisering's Atlas.)

THE SINUSES OF THE DURA MATER

687

glossus, and another in the genio-hyoideus. The vein is at first covered by the
mylo-hyoideus, perforates that muscle, runs back along the omo-hyoideus in rela-
tion to the mandibular lymph glands, and joins the external maxillary near the
posterior border of the jaw.

The sublingual vein (V. sublingualis) is smaller than the preceding. It re-
ceives veins from the skin and muscles of the mandibular space, the sublingual
gland, and the gums. It opens into the external maxillary vein near the lingual or
joins the latter.

7. The thyroid vein (V. thyreoidea) is a large vessel which joins the jugular
near the external maxillary vein. It receives anterior thyroid, laryngeal, and
pharjmgeal radicles, and sometimes a posterior thyroid vein.

8. Muscular, tracheal, oesophageal, and parotid veins.

9. The cephalic vein (V. cephalica) enters the jugular near its termination.
It will be described with the veins of the thoracic limb.

10. The inferior cervical vein (V. cervicalis ascendens) accompanies the as-
cending branch of the artery. It may open into the brachial vein.

The Sinuses of the Dura Mater
These (Sinus durae matris) are blood-spaces between the meningeal and peri-
osteal layers of the dura mater and are lined with endothelium. In many places

Fig. 588. — Median Section op Head of Horse, Upper Part with Septum Nasi Removed.
a. Lateral mass of ethmoid bone; 6, dorsal turbinate; c, ventral turbinate; d. d', turbinate folds; e, frontal sinus;
/, falx cerebri; g, tentorium cerebelli; h, medial surface of hemisphere; i, cerebellum; k, occipital bone; h', occipital
condyle; /t", paramastoid process; ?, external acoustic meatus; m, temporal condyle; «, temporal canal; /.branches
of ethmoidal artery; ;^, ^', branches of sphenopalatine artery; 3, 3', branches of sphenopalatine vein; 4, branches of
ethmoidal nerve; .5, .5', branches of sphenopalatine nerve; 6, artery of corpus callosum; 7, dorsal longitudinal sinus; 5,
straight sinus; 0, vena magna cerebri; 10, ventral longitudinal sinus; 11, 11', transverse sinuses; U, dorsal petrosal sinus;
13, occipital sinus; i4, dorsal cerebral vein; 15, corpus callosum; 16, fornix. (After Ellenberger, in Leisering's Atlas.)

the lumen is crossed by fibrous strands. They receive the cerebral veins (Vv.
cerebri), meningeal veins (Vv. meningese), diploic veins (Vv. diploicse), and com-
municate with veins outside of the cranium; their connections with the latter
are by means of emissary veins (Emissaria). They convey the blood directly or
indirectly to the jugular veins. Some are paired, others unpaired. They may be
divided into dorsal and basilar systems.

The dorsal system comprises the following:

The dorsal longitudinal or sagittal sinus (S. sagittalis dorsalis) is situated in
the convex border of the falx cerebri along the internal parietal crest. It begins
at the crista galli and ends near the tentorium osseum at the confluence of the
sinuses (Confluens sinuum) formed by the junction with the straight sinus. It
receives most of the ascending cerebral veins. Along each side are small pouches
(Lacunge laterales) into which the veins open. The lumen of the sinus is very
irregular; it is traversed by fibrous bands and is partially divided by a longitu-
dinal septum.

^88 BLOOD-VASCULAR SYSTEM OF THE HORSE

The ventral longitudinal or sagittal sinus (S. sagittalis ventralis) is much
smaller than the dorsal sinus. ^ It runs backward on the corpus callosum in the
concave edge of the falx cerebri, and joins the great cerebral vein to form the straight
sinus. It receives veins from the medial surface of the cerebral hemispheres and
from the corpus callosum.

The straight sinus (S. rectus) proceeds from the junction of the ventral longi-
tudinal sinus with the great cerebral vein behind the corpus callosum. It ascends
in the falx cerebri, inclining backward, and joins the dorsal longitudinal sinus at
the confluens sinuum.

The transverse sinuses (Ss. transversi), right and left, proceed laterally from
the confluens sinuum; they pass outward in the transverse grooves of the parietal
bones, enter the temporal canals, and are continued by the dorsal cerebral veins
to the superficial temporal veins. They receive the dorsal petrosal sinuses, veins
from the posterior part of the cerebrum and from the corpora quadrigemina, and
the posterior meningeal vein. The two sinuses are cormected by the sinus com-
municans, which extends across the cranial vault in a channel in the base of the
internal occipital protuberance.

The dorsal petrosal sinuses (Ss. petrosi dorsales) ascend in the tentorium
€erebelli and join the transverse sinuses near the internal opening of the temporal
canal. Each is the direct continuation of the vena rhinalis posterior and receives
the vena basilaris cerebri. There is sometimes an accessory petrosal sinus along-
side of the chief sinus, which is formed by the confluence of veins from the pons
and medulla oblongata.

The occipital sinuses (Ss. occipitales) are situated in the dura mater on each
side of the vermis cerebelli. They communicate in front with the sinus communi-
cans, and one of them is continued posteriorly by the dorsal spinal vein. Each
sinus is connected by a communicating branch with the transverse sinus and with
the ventral petrosal sinus. The right and left sinuses are connected by anasto-
motic branches, so that the arrangement is more or less plexiform. They re-
ceive veins from the cerebellum, medulla oblongata, and diploe.

The basilar system consists of the following:

The cavernous sinuses (Ss. cavernosi) lie in the medial grooves of the root of the
temporal wings of the sphenoid bone at either side of the pituitary fossa. The two
are connected by a wide transverse branch, the intercavernous sinus (Sinus inter-
cavernosus), behind and below the posterior part of the pituitary body.^ Each is
continuous in front with the ophthalmic vein and below with the ventral petrosal
sinuses; it communicates also by small anastomotic veins with the basilar plexus.
The third, sixth, and the ophthalmic and maxillary divisions of the fifth nerve lie
along the lateral wall of the sinus. The internal carotid artery traverses the sinus
and is connected with its fellow by a transverse branch which lies in the inter-
cavernous sinus. An oval opening in the floor communicates with the ventral
petrosal sinus and transmits the internal carotid artery.

The sinus is not subdivided by strands of fibrous tissue as in man, but a few delicate bands
attach the artery to its wall.

The ventral petrosal sinuses (Ss. petrosi ventrales)^ lie along the borders of
the basilar part of the occipital bone, enclosed in the thick dura which closes the
foramen lacerum. The anterior part extends about half an inch (ca. 12 mm.)
under the temporal wing of the sphenoid. Here communications exist with veins
in the pterygopalatine fossa. The posterior end is bulbous and lies in the condy-

^ It is also termed the vena corporis callosi major.

^ A small anterior intercavernous sinus may connect the two cavernous sinuses in front of the
pituitary gland. Mobilio states that he has seen the cavernous sinus having a blind anterior end,
the ophthalmic vein passing laterally to the ventral petrosal sinus.

^ These are termed the subsphenoidal confluents by Chauveau and M'Fadyean.

THE VEINS OF THE CRANIUM — VERTEBRAL AND SPINAL VEINS 689

loid fossa; it communicates with the condyloid vein issuing from the hypoglossal
foramen and is drained by the ventral cerebral vein; it also receives an emissary
vein from the temporal canal. The sinus communicates with the cavernous sinus
by an oval opening at the carotid notch which transmits the internal carotid artery;
the latter forms the first bend of its S-shaped curve in the petrosal and the second
in the cavernous sinus.

The basilar plexus (Plexus basilaris) is situated on the cerebral surface of the
basilar part of the occipital bone, and is directly continuous behind with the venous
plexus in the atlas. Its chief emissary is the condyloid vein, which brings it into
communication with the ventral petrosal sinus. It is connected with the cav-
ernous and intercavernous sinuses by small veins.

The Veins of the Cranium

The cerebral veins (Venae cerebri) do not in general accompany the cerebral
arteries. They have very thin walls, no muscular coat, and no valves. They are
arranged in two sets, superficial or cortical and deep or central. The superficial
veins are more numerous and larger than the arteries. They lie on the surface of
the brain in the pia mater and the subarachnoid space.

The ascending cerebral veins drain most of the convex surface and the medial
surface of the cerebral hemispheres. Most of them open into the dorsal longitudi-
nal sinus, but some enter the confluens sinuum or the transverse sinuses. Near the
termination they become bulbous, and open into the sinus obliquely and in such a
manner as to tend to prevent reflux of blood into them.^ The descending cerebral
veins which come chiefly from the ventral part of the convex surface of the cere-
]jrum open into the vena rhinalis posterior.

The basal cerebral veins converge to a large common trunk, the vena rhinalis
posterior ; this begins at the anterior end of the piriform lobe, runs backward in a
groove on the latter, enters the tentorium cerebelli, and opens into the dorsal
petrosal sinus.

The deep cerebral veins issue from the central or ganglionic parts of the brain
at the transverse fissure. The principal ones come from the chorioid plexuses, the
corpus striatum, and the septum pellucidum. These unite to form the internal
cerebral veins (Vv. cerebri internee), which run backward in the roof of the third
ventricle and unite to form the great cerebral vein (V. magna cerebri). This
passes upward and backward behind the splenium of the corpus callosum and is
continued as the straight sinus to join the longitudinal sinus.

The dorsal cerebellar veins ramify on the upper surface of the cerebellum.
They go chiefly to the occipital and dorsal petrosal sinuses. The ventral cerebellar
veins are larger and go chiefly to the basilar plexus. The veins of the medulla and
pons end chiefly in the basilar plexus and the occipital and dorsal (and accessory)
petrosal sinuses.

The meningeal veins (Vense meningese) arise in capillary plexuses in the su-
perficial and deep faces of the dura mater. Some end in the sinuses of the dura,
others accompany the meningeal arteries.

The diploic veins (Vense diploicse) are anastomosing channels in the spongy
substance of the cranial bones. Their walls are thin, consisting in many places
only of the endothelium, and they have no valves. Some open inward into venous
sinuses, others into extracranial veins.

Vertebral and Spinal Veins
Two venous trunks, the longitudinal vertebral sinuses (Sinus vertebrales
l(mgitudinales), extend along the floor of the vertebral canal, one on either side of

1 Most of these veins open into the sinus in the direction of the blood-stream in the sinus, but
some of the posterior ones open about at a right angle, or even contrary to the direction of the cur-
rent.

BLOOD-VASCULAR SYSTEM OP THE HORSE

the dorsal longitudinal ligament. They are continuous in front with the basilar
plexus. They lie in the grooves on the bodies of the vertebrae and are connected
by a series of transverse anastomoses which pass between the central part of the
bodies of the vertebrae and the dorsal longitudinal ligament or in channels in the
bone. They receive veins from the spinal cord, the meninges, and the bodies of the
vertebree (Venae basis vertebrae). Through the intervertebral foramina efferent
vessels connect with the occipital, vertebral, intercostal, lumbar, and lateral sacral
veins. The veins of the spinal cord are drained by dorsal and ventral longitudinal

trunks. The ventral vein, which is the smaller,
[y3g^-;Mraf||p!f^M}^ accompanies the ventral spinal artery.

If- If 1 *L.

VEINS OF THE THORACIC LIMB
The brachial vein (V. brachialis) (Fig. 566)
is the satellite of the extrathoracic part of the
brachial artery. It arises at the medial side of
the distal end of the shaft of the humerus and
ascends in the arm behind the artery under cover
of a layer of fascia and the posterior superficial
pectoral muscle. At the shoulder it is ventral to
the artery, crosses the anterior border of the first
rib, and concurs with its fellow and the two jugu-
lars in the formation of the anterior vena cava.
The roots of the vein are somewhat variable, but
most often four veins in addition to a large ob-
lique branch from the cephalic unite in its forma-
tion; two or three of these radicles are satellites of
the median artery. Its tributaries correspond in
general to the branches of the artery, but a few
differences are worthy of notice. The thoraco-
dorsal vein (V. thoracodorsalis) often joins the
external thoracic or the deep brachial vein. The
external thoracic vein (V. thoracica externa)^ is a
large vessel which arises in the ventral wall of the
abdomen, passes forward (embedded partly in the cutaneus muscle) along the lateral
border of the posterior deep pectoral muscle, and joins the brachial vein close to
the subscapular or in common with it. It may receive a vein which is the satellite
of the external thoracic artery.

The cephalic vein (V. cephalica) arises at the medial side of the carpus as the
continuation of the medial metacarpal vein. It ascends on the deep fascia
of the forearm at first in the furrow between the flexor carpi radialis and the
radius. Toward the middle of the forearm it inclines gradually forward on the
medial surface of the radius, accompanied by a branch of the musculo-cutaneous
nerve, and arrives at the insertion of the biceps. Here it detaches a large com-
municating branch (Ramus communicans), which passes upward and backward over
the medial insertion of the biceps and the median artery and median nerve,
and joins the brachial vein. The vein to this point is often termed the internal sub-
cutaneous vein of the forearm (V. cephalica antebrachii). It is continued (as the
V. cephalica humeri) in the furrow between the brachiocephalicus and the anterior
superficial pectoral muscle with a branch of the inferior cervical artery, crosses the
deep face of the cervical cutaneus, and opens into the terminal part of the jugular
or the brachial vein. It receives the accessory cephalic vein (V. cephalica accessoria) ,
which arises from the carpal network, runs upward on the deep fascia along the
1 Often termed the spur vein.

Fig. 589. — Vertebral Sinuses op Horse.
The vertebral canal has been opened
by sawing off the arches. The nerve-roots
are cut on one side and the spinal cord
turned over to right. 1, Ventral spinal
artery; 2, reinforcing branches from verte-
bral, intercostal, or lumbar arteries (ac-
cording to region); 3, longitudinal verte-
bral sinuses; a, ventral surface of spinal
cord; b, dura mater (cut); c, nerve-roots;
d, dorsal longitudinal ligament. (After
Ellenberger, in Leisering's Atlas.)

VEINS OF THE THORACIC LIMB

691

medial border of the extensor carpi, and joins the cephalic vein at the proximal
end of the forearm.

The deep veins of the forearm are variable. Commonly two median veins

Fig. 590. — Dissection of Pectoral Region and Anterior Part of Abdominal Wall of Horse.
1, Jugular vein; 2, loose connective tissue of axillary space; 3, ascending branch of inferior cer^'^caI artery; 4, de-
scending branch of same; 5, cephalic vein; 5, median nerve; 7, ulnar nerve ; 5, brachial artery; S, brachial vein; 10,
external thoracic vein; /;, anterior abdominal artery and vein; 12, branches of sixth cervical nerve; 13, cutaneous
branch of axillary nerve; 14, cutaneous branch of musculo-cutaneous nerve; 15, cervical cutaneus; 16, sterno-cephahcus ;
17, scalenus; 18, brachiocephalicus; 19, anterior superficial pectoral; 20, posterior superficial pectoral; 21, anterior
deep pectoral; 22, posterior deep pectoral; 23, abdominal cutaneus; 24, obliquus abdominis externus; 25, rectus
abdominis; 26, coraco-brachialis; 27, tensor fascise antibrachii; a, prescapular lymph glands; h, prepectoral lymph
glands; c, axillary lymph glands; d, cubital lymph glands; c. x., xiphoid cartilage. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)

(Vense medianae) accompany the artery of like name, one in front and one behind.
A third vein arises by radicles emerging from the proximal part of the deep flexor;

692 BLOOD-VASCULAR SYSTEM OF THE HORSE

it joins the posterior satellite of the median artery or forms one of the roots of the
brachial vein. The common interosseous vein joins the posterior satellite. The
anterior radial vein (V. collateralis radialis) is a satellite of the artery. The ulnar
vein is usually double at its proximal part, and communicates with the deep brachial
vein.

There are three chief metacarpal veins. The medial metacarpal or common
digital vein (V. metacarpea volaris superficialis medialis) arises from the volar
venous arch above the fetlock. It is the largest vein of the region and lies in
front of the common digital artery. It separates from the artery at the proximal
end of the metacarpus, passes upward on the medio-volar surface of the carpus,
under cover of the superficial layer of the volar annular ligament, and is con-
tinued as the cephalic vein. It communicates at its proximal part with the origin
of the median veins by a short but relatively large branch. The lateral metacaipal
vein (V. metacarpea volaris superficialis lateralis) arises from the venous arch above
the fetlock and passes upward behind the lateral border of the suspensory ligament
in front of the lateral volar nerve and accompanied by a small artery. At the
proximal end of the metacarpus it is connected with the deep metacarpal vein by
two transverse anastomoses which pass across the suspensory ligament. It then
ascends as a satellite of the lateral volar metacarpal artery and concurs in the
origin of the ulnar and median veins. The deep metacarpal vein (V. metacarpea
volaris profunda medialis) arises from the venous arch, passes forward between
the two branches of the suspensory ligament, and ascends on the posterior surface
of the large metacarpal bone. At the proximal end of the latter it communicates
with the other metacarpal veins, ascends with the medial volar metacarpal artery,
and concurs in forming the median veins.

The venous arch (Arcus venosus volaris), from which the metacarpal veins
arise, is situated above the sesamoids of the fetlock, between the suspensory liga-
ment and the deep flexor tendon. It is formed by the junction of the two digital
veins.

The digital veins, medial and lateral (V. digitalis medialis, lateralis), drain the
venous plexuses of the foot. They arise at the proximal edge of the cartilages of
the third phalanx and ascend in front of the corresponding arteries.

It is convenient to recognize the following venous plexuses of the foot, which,
however, communicate very freely :

1. The coronary plexus encircles the upper part of the foot. It covers the
terminal part of the extensor tendon, the cartilages of the third phalanx, and the
bulbs of the digital cushion.

2. The dorsal (or laminal) plexus covers the dorsal surface of the third phalanx
in the deep layer of the corium of the wall of the hoof. It forms the circumflex
vein of the third phalanx, or vein of the distal border of the third phalanx, which
corresponds to the artery of like name.

3. The volar plexus is in the deep layer of the corium of the sole of the hoof
and on the deep surface of the cartilages of the third phalanx. It communicates
around the distal border of the third phalanx with the dorsal plexus and through the
cartilages with the coronary plexus.

The deep vein of the third phalanx accompanies the terminal part of the
digital artery. It drains the intraosseous plexus contained in the third phalanx.

THE POSTERIOR VENA CAVA (Figs. 554. 575)

The posterior vena cava (V. cava caudalis) returns almost all of the blood from
the abdomen, pelvis, and pelvic limbs. It is formed by the confluence of the right
and left common iliac veins at the fifth lumbar vertebra, above the terminal part
of the aorta, and chiefly to the right of the median plane.

THE PORTAL VEIN 693

The mode of origin is variable. In some cases there is a common trunk formed by the
union of the two internal iliac veins so that the arrangement resembles the termination of the
aorta. In other cases the internal iliac vein does not exist. Exceptionally there is a small middle
sacral vein on the middle of the pelvic surface of the sacrum. It opens at the angle of divergence
of the common iliac veins.

It passes forward on the ventral face of the psoas minor to the right of the
abdominal aorta. At the last thoracic vertebra it separates from the aorta and
runs forward between the right crus of the diaphragm and the pancreas till it
reaches the liver. Here it inclines ventrally along the medial border of the right
lobe and on the parietal surface of the liver, largely embedded in the gland sub-
stance, and passes through the foramen venae cavae of the diaphragm. It then runs
forward and somewhat ventrally between the intermediate lobe and the main mass
of the right lung at the upper margin of a special fold of the right pleura, accom-
panied by the right phrenic nerve, and opens into the posterior part of the right
atrium opposite the fifth intercostal space. It receives the following tributaries:

1. The phrenic veins (Vv. phrenicse), two or three in number, return the blood
from the diaphragm. They are very large in comparison with the arteries, and
join the vena cava at the foramen venae cavae.

2. The lumbar veins (Vv. lumbales) correspond to the arteries. Five pairs
usually empty into the posterior vena cava. Sometimes the corresponding veins
of opposite sides unite to form a common trunk. The first communicate with the
vena azygos or hemiazygos, and the last usually enters the common iliac vein.

3. The internal spermatic veins (Vv. spermaticae internae) (Fig. 575) accompany
the arteries of like name. In the spermatic cord they form a very rich network, the
pampiniform plexus (Plexus pampiniformis) about the artery and nerves. Their
termination is variable. The right one commonly joins the vena cava near the
renal vein, often by a common trunk with the left one. Frequently the left vein
joins the left renal, and sometimes the right one ends similarly.

3 a. The utero-ovarian veins are much larger than the preceding and are
satellites of the arteries in the broad ligaments. The ovarian branch is plexiform
near the ovary. The uterine branches form a rich plexus in the wall of the uterus.
The trunk is very short and terminates like the corresponding vein of the male.

4. The renal veins (Vv. renales), satellites of the arteries, are of large caliber
and thin walled. The right vein passes medially and backward on the ventral face
of the kidney, between the artery in front and the ureter behind. It joins the vena
cava above the right adrenal. The left vein is somewhat longer. It passes medially
at first like the right one, then bends around the posterior end of the adrenal, crosses
the origin of the renal artery, and opens into the vena cava a little further back than
the right one. They receive veins from the adrenals, but some adrenal veins (Vv.
adrenales) open directly into the vena cava.

5. The hepatic veins (Vv. hepaticae) return the blood from the liver, and open
into the vena cava as it lies in the groove in the liver. Three or four large veins
open into the vena cava just before it leaves the liver, and numerous small ones
discharge into its embedded part.

Of the foregoing, the phrenic and lumbar veins are termed parietal radicles
(Radices parietales), and the remainder are visceral radicles (Radices viscerales).

THE PORTAL VEIN
The portal vein (V. porta?) is a large trunk which returns the blood carried to
the viscera by the gastric, splenic, and mesenteric arteries; its average diameter is
a little more than an inch (ca. 3 cm.). Its peripheral tributaries correspond closely
with the branches of the arteries, but the trunks do so in part only. The vein is
formed behind the pancreas and below the posterior vena cava by the confluence
of the anterior and posterior mesenteric and splenic veins. It passes forward,

694

BLOOD-VASCULAR SYSTEM OF THE HORSE

traverses the posterior part of the pancreas very obliquely, inclines ventrally and
a little to the right, and reaches the portal fissure of the liver. Here it divides into
three branches which enter the liver and ramify in the substance of the gland like
an artery, terminating in the lobular capillaries. From the lobules the blood passes
into the hepatic veins and through these to the posterior vena cava. Thus the
blood Avhich is distributed to the stomach, nearly the entire intestinal tract, the
pancreas, and the spleen, passes through two sets of capillaries prior to its return
to the heart, viz., the capillaries of these viscera and of the liver.

1. The anterior mesenteric vein (V. mesenterica cranialis) is the largest of
the portal radicles. It is situated to the right of the artery of like name, and its
tributaries correspond in general to the branches of the artery. The dorsal colic
vein usually unites with the ventral one at the pelvic flexure, thus forming a single
trunk (V. colica dextra) which runs between the right parts of the colon. There is,

Fig. 591. — Portal Vein of Horse.

a, Intrahepatic part, 6, extrahepatic part, of portal vein; c, anterior gastric vein; d, right gastro-epiploic vein;
e, pancreatico-duodenal vein; /, splenic vein; /', left gastro-epiploic vein; g, posterior gastric vein; ?i, posterior mesen-
teric vein; t, middle colic vein; i-, left colic vein; fc', anterior haemorrhoidal vein; m, jejunal trunk; m', jejunal veins;
o, right colic vein; o', ventral colic vein; o", dorsal colic vein; o'", small collateral vein connecting dorsal colic and
posterior mesenteric veins; p, ileal vein; g, csecal veins; J, liver; JJ, spleen; J7J, stomach; 7F, duodenum; T, jejunum;
VI, csecum; VII, ventral parts of great colon; VIII, pelvic flexure; IX, dorsal parts of great colon; X, small colon;
XI, rectum. (After Schmitz.)

however, a small vein on the right dorsal colon which is connected by numerous
branches with the right colic vein; it joins the posterior mesenteric vein or its
middle colic radicle. The veins of the small intestine (Vv. intestinales) unite to
form a short trunk.

2. The posterior mesenteric vein (V. mesenterica caudalis) is the smallest of
the radicles of the portal vein. It accompanies the artery in the colic mesentery,
and its rectal branches (Vv. haemorrhoidales craniales) anastomose with those of
the internal pudic vein. It receives the middle colic vein from the initial part of
the small colon and also the small vein of the right dorsal colon, as mentioned above,

3. The splenic vein (V. lienalis) is the very large satellite of the splenic artery.
It is formed by the union of two radicles at the base of the spleen. On leaving the
hilus of the spleen it passes medially between the anterior pole of the left kidney and
the saccus ciecus of the stomach and above the left end of the pancreas, receives

THE COMMON ILIAC VEINS — THE VEINS OF THE PELVIC LIMB 695

commonly the posterior gastric vein (V. gastrica caudalis), and unites with the
anterior mesenteric at the posterior border of the pancreas. Not uncommonly the
splenic and posterior mesenteric veins form a short common trunk.
The collateral tributaries of the portal vein are as follows:

(1) Pancreatic veins (Rami pancreatici).

(2) The gastro-duodenal vein (V. gastroduodenaHs), when present, corresponds
mainly to the extrahepatic branches of the hepatic artery; but in most cases it does
not exist, and the right gastro-epiploic vein (V. gastroepiploica dexi^ra) and pan-
creatico-duodenal vein (V. pancreaticoduodenalis) open directly into the portal
vein.

(3) The anterior gastric vein (V. gastrica cranialis) joins the portal vein at the
portal fissure.

THE COMMON ILIAC VEINS (Fig. 581)
These (V. iliacse communes) are two very large but short trunks, which result
from the union of the internal and external iliac veins of each side at the sacro-iliac
articulation. The left one is the longer, and crosses obliquely over the terminal
part of the aorta. The chief tributaries of each are as follows:

1. The last lumbar vein.

2. The circumflex iliac veins (Vv. circumflexae ilium profundae) are the two
satellites of the corresponding artery, on either side of which they are placed.
They may open directly into the posterior vena cava or into the external iliac vein.

3. The ilio-lumbar vein (V. iliolumbalis) may open into the common iliac,
the external iliac, or the internal iliac vein.

THE INTERNAL ILL^C VEINS
The internal iliac or hypogastric veins (Vv. iliacae internee s. hypogastricse),
right and left, are usually formed by the confluence of lateral sacral, gluteal, and
internal pudic veins. The obturator vein may open into them also. They are
short trunks, and are smaller than the external iliac veins. The tributaries corre-
spond in general to the branches of the three arteries of like names. The internal
pudic veins receive affluents from the anus and posterior part of the rectum ; from
the venous plexuses of the prepuce and penis in the male ; and from those of the
mammary gland, vulva, vagina, and vestibular bulb in the female. A large anas-
tomotic branch connects the internal pudic and obturator veins at the lesser sciatic
notch.

THE VEINS OF THE PELVIC LIMB
The external iliac vein (V. iliaca externa) (Figs. 576, 581) lies behind the cor-
responding artery at the brim of the pelvis. It is the upward continuation of the
femoral vein, and unites at the sacro-iliac joint with the internal iliac to form the
common iliac vein. Its tributaries are as follows:

1. The obturator vein (V. obturatoria) is a satellite of the artery, except in its
terminal part; it usually opens into the external iliac at the insertion of the psoas
minor. Its radicles anastomose with those of the internal and external pudic veins
(Figs. 576, 658).

2. The iliaco-femoral or lateral circumflex veins (Vv. circumflexae femoris
laterales) are the two satellites of the homonymous artery. They open a little
higher than the obturator.

The femoral vein (V. femoralis) (Figs. 575, 582) lies behind the artery in the
proximal part of the thigh, lateral to it lower down. Its chief tributaries are:

1. A large but short trunk is formed by the union of the deep femoral and
the external pudic vein. The deep femoral vein (V. profunda femoris) corresponds

696 BLOOD-VASCULAR SYSTEM OF THE HORSE

otherwise to the artery. The external pudic vein (V. pudenda externa) arises
chief!}' from a rich plexus of large veins situated above and along the sides of the
penis and prepuce in the male, the mammary glands in the female. It passes
through a foramen in the anterior part of the tendon of origin of the gracilis and
runs outward behind the pectineus to unite with the deep femoral vein. The right
and left veins are connected by a large transverse anastomotic branch which lies
in the subpubic groove, and each has a large connection with the obturator vein.
Each receives the posterior abdominal vein (V. abdominalis caudalis), which ac-
companies the artery of like name. The subcutaneous abdominal vein (V. ab-
dominalis subcutanea) arises in the skin and cutaneous muscle of the ventral
abdominal wall, anastomoses with the internal and external thoracic and deep
abdominal veins, and joins the external pudic or the posterior abdominal vein.
A small vein may accompany the external pudic artery in the inguinal canal.

2. The anterior femoral vein (V. femoris cranialis) accompanies the artery.

3. The saphenous vein (V. saphena) (Figs. 575, 576, 583) arises on the dorso-
medial surface of the tarsus as the upward continuation of the medial metatarsal
vein. Its course is distinctly visible. It ascends on the subcutaneous surface of
the tibia and the popliteus muscle, enclosed between layers of the deep fascia, in-
clines a little backward to the proximal part of the leg, then deviates slightly for-
ward, runs upward on the gracilis, passes between that muscle and the sartorius,
and joins the femoral or the external pudic vein.^ On the upper part of the capsule
of the hock joint it forms an arch with the anterior tibial vein. The vein has
numerous valves. The satellite artery is relatively small, and lies in front of the
vein as far as the junction with the recurrent tibial vein, which it accompanies on
the leg. It receives the recurrent tibial vein (V. recurrens tibialis) at the proximal
fourth of the leg. This vessel arises at the distal third of the leg, where it forms an
arch with the posterior tibial vein; here it is a satellite of the artery of like name.
It ascends in the furrow in front of the gastrocnemius tendon, inclines forward at
the proximal third of the leg, and joins the saphenous vein at an acute angle. It
gives off a branch which ascends with the artery and joins the posterior femoral or
the popliteal vein.^ A smaller vein from the anterior face of the metatarsus joins
the saphenous at the hock.

4. Muscular branches which correspond to the arteries.

5. The posterior femoral vein (V. femoris caudalis) is a satellite of the artery.
It receives the recurrent tarsal vein (V. tarsea recurrens), which arises at the lateral
side of the hock, ascends on the deep fascia of the lateral surface of the leg in front
of the tendo Achillis, passes between the biceps femoris and semitendinosus, and
joins the posterior femoral vein. It is connected with the recurrent tibial vein by
a large anastomotic branch which crosses in front of the tuber calcis. Usually a
branch from it ascends along the great sciatic nerve and anastomoses with the ob-
turator vein.

The popliteal vein (V. poplitea) lies along the medial side of the artery (Fig.
584). It is formed by the confluence of anterior and posterior tibial veins.

Two anterior tibial veins (Vv. tibiales anteriores) usually accompany the artery
of like name; the lateral vein is much the larger.^ In other cases there is a single

1 The place and mode of termination are quite variable. It may disappear from the surface
of the thigh at any point above the distal third. In some cases it passes through the anterior
part of the gracihs instead of dipping in between that muscle and the sartorius, and more rarely
it joins the external pudic vein at the origin of the gracilis.

2 The arrangement here is subject to variation. Some authors regard the ascending branch
of this description as the trunk, and the connection with the saphenous as an anastomotic branch.
The latter is usually, so far as size is concerned, the trunk.

' The large size of this vein, the thinness of its wall, and the fact that it is separated only by a
thin layer of muscle (lateral part of tibialis anterior) from the deep peroneal nerve should be noted
with reference to section of that nerve. The vein is sometimes markedly varicose in the proximal
part of the leg.

LYMPHATIC SYSTEM OF THE HORSE — THE THORACIC DUCT 697

large vein in the proximal part of the leg, two lower down. They arise from a
number of anastomosing radicles on the front of the capsule of the hock joint,
chiefly as the continuation of the perforating tarsal vein. A large branch from the
saphenous vein concurs in the formation of the somewhat plexiform arrangement
on the flexion surface of the hock.

The posterior tibial vein (V. tibialis posterior) is commonly double (Fig. 583).
It arises at the level of the tuber calcis, where it has a communication with the
recurrent tibial vein. It is a satellite of the artery.

The medial or great metatarsal vein (V. metatarsea dorsalis medialis (Figs.
583, 585) arises from the venous arch above the sesamoids at the fetlock, but is
practically the upward continuation of the medial digital vein. It ascends along
the medial border of the suspensory ligament, then in the groove on the proximal
part of the large metatarsal bone to the capsule of the hock joint, and is continued
by the saphenous vein. The small middle dorsal metatarsal vein (V. met. dorsalis
media) joins this vein or the saphenous at the hock.

The lateral metatarsal vein (V. metatarsea dorsalis lateralis) is the very small
satellite of the great metatarsal artery. It is inconstant, but may be double in the
proximal part of the metatarsus.

The medial plantar vein (V. metatarsea plantaris superficialis medialis) is very
small, and is not always present. It ascends along the medial border of the deep
flexor tendon in front of the corresponding nerve. It is connected below with the
medial digital vein, and above with the deep metatarsal or the lateral plantar vein.

The lateral plantar vein (V. metatarsea plantaris superficialis lateralis) arises
from the venous arch above the fetlock, but appears to be the upward continuation
of the lateral digital vein. It ascends along the lateral border of the deep flexor
tendon in front of the plantar nerve, and is connected with the deep metatarsal
vein at the proximal part of the metatarsus by a transverse branch. It then passes
upward along the deep flexor tendon in relation to the plantar nerves and the
medial tarsal artery, and is continued by the recurrent tibial vein.

The deep metatarsal vein (V. metatarsea plantaris profunda medialis) arises
from the plantar venous arch, above the fetlock, passes forward between the branches
of the suspensory ligament, and ascends on the posterior face of the large meta-
tarsal bone. At the proximal end of the metatarsus it is connected with the lateral
plantar vein by a transverse branch, thus forming the deep plantar arch (Arcus
plantaris profundus). It then passes, as the perforating tarsal vein (V, tarsea
perforans), through the vascular canal of the tarsus and forms the chief radicle of
the anterior tibial vein.

The distal plantar venous arch (Arcus venosus plantaris distalis) and the digital
veins are arranged like those of the thoracic limb.

Lymphatic System of the Horse

THE THORACIC DUCT (Figs. 553, 554)
The thoracic duct (Ductus thoracicus) is the chief collecting trunk of the lym-
phatic system. It begins as an elongated irregular dilatation, the cisterna chyli,
which is situated between the right side of the aorta and the right eras of the
diaphragm at the first and second lumbar vertebrae. The duct enters the
thorax through the hiatus aorticus and runs forward on the right of the median
plane, between the vena azygos and the aorta, covered by the pleura. At the sixth
or seventh thoracic vertebra it inclines somewhat ventrally, crosses obliquely over
the left face of the oesophagus, and passes forward on the left side of the trachea
to the inlet of the thorax. The extrathoracic terminal part passes downward and

^98 BLOOD-VASCULAR SYSTEM OF THE HORSE

forward a variable distance (3-4 cm.) on the deep face of the left scalenus muscle,
bends inward and backward under the bicarotid trunk, and opens into the dorsal
part of the origin of the anterior vena cava just behind the angle of junction of the
jugular veins. The terminal bend is ampuUate, and sometimes divides into two
very short branches which open close together.

Since the duct develops from a plexus of ducts in the embryo, considerable variation from
the more usual course occurs. There is often a left duct which arises at the cistema or at a var-
iable point from the right duct, rims across the left intercostal arteries parallel to the latter, and
unites with it over the base of the heart or further forward. The two are connected by cross-
branches. In some cases the left duct is the larger, and there may indeed be none on the right
side. Other variations are common.

The chief tributaries of the thoracic duct are as follows:

1. The two lumbar trunks (Trunci lumbales) are formed by the confluence
of the efferent ducts of the lumbar glands, and commonly unite with each other
and ^vith the posterior intestinal trunk before opening into the cistern.

2. The intestinal trunks (Trunci intestinales), two or three in number, receive
the efferents of the lymph glands of the intestine, stomach, liver, and spleen.^

In its course through the thorax the thoracic duct receives efferents from the
intercostal, mediastinal, and bronchial glands. At the thoracic inlet it is joined by
ducts from the prepectoral and right axillary glands, and by the left tracheal duct.
The duct is provided with several pairs of valves; the best developed are at its
termination.

THE RIGHT LYMPHATIC DUCT

This vessel (Ductus lymphaticus dexter) — when present — collects the l>Tnph
from the right side of the head, neck, and thorax, and from the right thoracic limb.
It is commonly absent, being represented by a number of short ducts which termin-
ate in the thoracic duct, the right jugulo-brachial junction, or the origin of the
anterior vena cava. When present in its typical form, it results from the con-
fluence of efferent ducts from the right axillary and posterior cervical lymph glands
with the right tracheal duct. It lies on the deep face of the scalenus muscle, above
the terminal part of the right jugular vein. It is more or less ampullate and usually
opens into the anterior vena cava to the right of the thoracic duct. It may be
connected with the latter by anastomoses or may join it.

The duct is very variable in form and in regard to its afferents. Often it is a very short,
irregular, and bulbous trunk; in some cases it is about an inch and a half (ca. 3-4 cm.) in length
and receives the tracheal duct at its terminal bend. The lymphatico-venous connections here
have not yet been satisfactorily worked out by modern methods.

THE LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK
1. The mandibular or submaxillary lymph glands (Lgg. mandibulares s. sub-
maxillares) (Figs. 265, 587) are arranged in two elongated groups in the mandibular
space along each side of the omo-hyoid muscles. The two groups are in apposition
in front of the insertion of these muscles, and diverge posteriorly in the form of a V,
extending backward about four or five inches (ca. 10-12 cm.). They are covered
by the skin and a thin layer of fascia and cutaneus muscle, and are therefore pal-
pable. Anteriorly they are firmly attached to the mylo-hyoidei, but otherwise they
are freely movable in the normal state. Each group is related laterally to the
external maxillary artery and the anterior belly of the digastricus, ventrally to the
external maxillary vein, and dorsally to the lingual and sublingual veins.

They receive afferent vessels from the lips, nostrils, nasal region, cheeks, the

1 The lymph vessels of these organs appear to vary considerably in their mode of termina-
tion, and the arrangement needs further study. Some lymph vessels from the stomach, liver, and
spleen open directly into the cistern.

THE LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK 699

anterior part of the tongue, the jaws, the floor of the mouth, and the greater part
of the hard palate and nasal cavity. The efferent vessels pass to the anterior
cervical and pharyngeal glands.

Most of the superficial lymph vessels of the face converge to twelve to fifteen trunks which
turn around the lower border of the jaw with and m front of the facial vessels. Those of the lips
form plexuses at the commissures. The nasal mucous membrane is richly supplied with lymph
vessels which accompany the veins; posteriorly they communicate with the subdural and sub-
araclmoid spaces and send efferents to the pharyngeal and anterior cervical glands.

2. The phar3nigeal lymph glands (Figs. 562, 706) usually comprise two
groups. One lies on the upper part of the lateral surface of the pharynx, along the
course of the external carotid artery. These glands are related laterally to the
occipito-mandibularis and cligastricus, and often to the mandibular gland also,
above to the guttural pouch; they may properly be termed the parapharyngeal
lymph glands (Lgg. parapharyngeales) . Other small glands are commonly found
on the guttural pouch along the course of the internal carotid artery; they are best
designated as the suprapharjnageal lymph glands (Lgg. suprapharyngeales).'^ They
lie below the artery and are covered by the aponeurosis of the brachiocephalicus
and the cervical end of the mandibular gland. In some cases a number of glands
occur in the angle of divergence of the external and internal carotid arteries.

They receive afferent vessels from the cranium, the posterior part of the tongue,
the soft palate, pharynx, guttural pouch, larynx, posterior part of the nasal cavity,
and efferents from the mandibular glands.

3. The anterior cervical lymph glands (Lgg. cervicales craniales) (Fig. 646) are
situated along the course of the common carotid artery, in the vicinity of the thyroid
gland, under cover of the cervical angle of the parotid gland. Some occur between
the thyroid and the mandibular salivary gland, others above and partly upon the
thyroid. They are related deeply to the posterior part of the larynx, the trachea,
the thyroid gland, and the oesophagus; below to the external maxillary vein and
the lateral border of the omo-hyoideus.^

These glands are variable. Often there are none in front of the thyroid and the group may
•extend back a considerable distance along the course of the carotid artery.

Their afferents are deep lymph vessels from the head, the pharynx, larynx,
guttural pouch, and thyroid gland, and efferents from the mandibular and pharyn-
geal glands. Their-^fferent vessels go to the middle and posterior cervical glands.

4. The middle cervical lymph glands (Lgg. cervicales medise) form an incon-
stant group situated a little in front of the middle of the neck on the trachea below
the caroticl artery. The group is usually small, and in some cases is replaced by a
number of glands occurring at intervals along the course of the carotid artery. In
other subjects the group consists of several glands of considerable size. They are
intercalated in the course of the tracheal lymph ducts.

5. The posterior cervical or prepectoral lymph glands (Lgg. cervicales caudales)
form a large group below the trachea at the entrance to the thorax (Fig. 590).
They occupy the interstices between the vessels and muscles and extend forward a
variable distance on the ventral aspect of the trachea. Posteriorly they are con-
tinuous with the anterior mediastinal glands. They are covered by the cutaneus
and sterno-cephalicus. Their afferent vessels come from the head, neck, thorax,
and thoracic limb. They receive efferent ducts of the anterior and middle cervical,
prescapular, and axillary glands. Their efferents go to the thoracic duct on the
left, to the right lymphatic duct on the right, or open directly into the vena cava.

6. The prescapular or superficial cervical lymph glands (Lgg. cervicales

1 Much confusion exists in the terminology used in regard to these glands and the next group.
'The terms here recommended appear to the author to be the best, all things considered. The
pharyngeal and anterior cervical glands are all subparotid in the horse.

2 Abscess here can be reached readily by an incision between the vein and the omo-hyoideus.

700 BLOOD-VASCULAR SYSTEM OF THE HORSE

superficiales) lie on the anterior border of the anterior deep pectoral muscle, in
relation to the omo-hyoideus medially and the brachiocephalicus laterally (Figs.
556, 566, 590). They are on the course of the ascending branch of the inferior
cervical artery, and may form an elongated series which is continuous ventrally
with the posterior cervical group. They receive afferents from the neck, breast,
shoulder, and arm. Their efferents pass to the posterior cervical glands.

The tracheal ducts, right and left (Ductus trachealis dexter, sinister), are col-
lecting trunks for the lymph of the head and neck. They lie on the trachea in
relation to the carotid arteries. The right one goes to the posterior cervical glands
or to the right lymphatic duct, the left one to the terminal part of the thoracic duct.

THE LYMPH GLANDS AND VESSELS OF THE THORAX

The thoracic lymph glands (Lgg. thoracales) are in general of small size, Imt
are numerous. They comprise the following:

1. The intercostal lymph glands (Lg. intercostales) are small and are situated
at the sides of the bodies of the thoracic vertebrae, in series corresponding to the
intercostal spaces; others are between the aorta and the vertebrae. They receive
afferents from the vertebral canal, the spinal muscles, the diaphragm, intercostal
muscles, and pleura. The efferent vessels go to the thoracic duct.^

2. The anterior mediastinal lymph glands (Lgg. mediastinales craniales)
are numerous. Some are situated on the course of the brachial arteries and
their branches; on the right side they are related deeply to the trachea, on the left
to the oesophagus also. They are variable in size and disposition and are continuous
in front with the posterior cervical glands. Other glands lie along the ventral face of
the trachea on the anterior vena cava and the right atrium of the heart; these are
continuous behind with the bronchial glands. A few glands usually occur along the
dorsal surface of the trachea, and there is often one at the angle of divergence of
the brachiocephalic trunk. The afferent vessels come chiefl}^ from the pleura,
the pericardium, the heart, the thymus or its remains, the trachea, the oesophagus,
and the bronchial lymph glands. Their efferent vessels pass to the posterior
cervical glands and the thoracic duct.

The glands along the ventral face of the trachea are frequently enlarged and commonly pig-
mented in dissecting-room subjects. The left recurrent nerve lies above them on the ventral
face of the trachea.

3. The bronchial lymph glands (Lgg. bronchiales) are grouped around the
terminal part of the trachea and the bronchi. One group lies on the dorsal surface
of the bifurcation of the trachea, and is continued a short distance backward under
the oesophagus. Others lie below the trachea and bronchi and also occupy
the angle between the aortic arch and the pulmonary artery, concealing the
left recurrent nerve and often covering the vagus in this part of its course.
Small glands occur along the chief bronchi in the substance of the lungs (Lg. pul-
monales). They receive the deep and most of the superficial lymph vessels of the
lungs, and the efferents from the posterior mediastinal glands. Their efferent
vessels go to the thoracic duct and the anterior mediastinal glands. The deep
lymph vessels of the lung arise in plexuses which surround the terminal bronchi
and accompany the bronchi to the root of the lung. The superficial vessels form
a rich network under the pleura; most of them pass to the bronchial glands, but
some go to the posterior mediastinal glands.

The bronchial glands are commonly pigmented (except in young subjects) and are often
enlarged and indurated.

4. The posterior mediastinal lymph glands (Lgg. mediastinales caudales) are
^ These glands appear to be more numerous in the young subject than they are later in life.

THE LYMPH GLANDS AND VESSELS OF THE ABDOMEN AND PELVIS 701

usually small and are scattered along the posterior mediastinum chiefly above the
oesophagus. They receive afferent vessels from the oesophagus, mediastinum,
diaphragm, pleura, and liver. The efferents go to the bronchial and anterior medi-
astinal lymph glands, partly to the thoracic duct directly.

Sometimes one or two small glands are situated in the acute angle between the
posterior vena cava and the diaphragm ; and the occurrence is recorded of a gland
between the apex of the pericardium and the sternal insertion of the diaphragm.

THE LYMPH GLANDS AND VESSELS OF THE ABDOMEN AND PELVIS
The abdominal and pelvic lymph glands (Lgg. abdominales et pelvinse) consist
of two main groups, parietal and visceral. The parietal glands lie in the subserous
or subcutaneous tissue; they receive the lymph vessels from the abdominal and
pelvic walls, from parts of the viscera, and from the proximal lymph glands of the
pelvic limbs. The visceral glands lie on the walls of the viscera or in the peritoneal
folds which connect the organs with the wall or with adjacent viscera. They receive
all or most of the lymph vessels from the organs with which they are connected.
The parietal glands comprise the following :

1. The lumbar lymph glands (Lgg. lumbales) lie along the course of the abdom-
inal aorta and posterior vena cava (Fig. 575). Some are placed along the ventral
surface and sides of the vessels, others above. A few small glands may be found
above the sublumbar muscles. The small nodes which are situated at the hilus
of the kidneys are often termed the renal lymph glands (Lgg. renales). They re-
ceive afferent vessels from the lumbar wall of the abdomen and the paired viscera
(kidneys, adrenals, genital organs), also the inguinal vessels and the efferents of the
iliac glands. Their efferents go to the thoracic duct, constituting the lumbar trunks
of origin of that vessel.

2. The internal iliac lymph glands (Lgg. iliacse internee) are grouped about the
terminal part of the aorta and the origins of the iliac arteries (Fig. 575). Their
afferent vessels come chiefly from the pelvis, pelvic viscera, and tail, and they re-
ceive efferent vessels of the external iliac and deep inguinal glands.

3. The external iliac lymph glands (Lgg. iliacse externae) form a group on either
side on the iliac fascia, at the bifurcation of the circumflex iliac artery (Fig. 575).
Their afferent vessels come from the flank and abdominal floor, the lateral surface
of the thigh, and the prefemoral glands. The efferent vessels go to the lumbar and
internal iliac glands.

4. The sacral lymph glands (Lgg. sacrales) are small nodes situated along the
borders of the sacrum and on its pelvic surface. They receive afferents from the
roof of the pelvis and from the tail, and their efferent vessels pass to the internal
ihac glands.

5. The superficial inguinal lymph glands (Lgg. inguinales superficiales) lie on
the abdominal tunic in front of the external inguinal ring (Fig. 582).^ They form
an elongated group along the course of the subcutaneous abdominal artery, on
either side of the penis in the male, above the mammary glands in the female;
in the latter they are often termed mammary. Their afferents come from the
medial surface of the thigh, the abdominal floor, the sheath, penis, and scrotum in
the male, and the mammary glands in the female. The efferent vessels ascend
through the inguinal canal and go to the deep inguinal, internal iliac, and lumbar
glands.

6. The ischiatic lymph glands (Lgg. ischiadicae) are small nodes on the upper
part of the sacro-sciatic ligament along the course of the posterior gluteal artery.
They receive lymph from the adjacent parts and from the popliteal glands, and send
efferents to the sacral and internal iliac glands.

1 In rare cases two or three of these glands are found behind the ring.

702 BLOOD-VASCULAR SYSTEM OF THE HORSE

The visceral glands include the f oHowing :

1. The gastric lymph glands (Lgg. gastricje) are situated along the course of
the gastric arteries. Several occur on the saccus csecus ventral to the left part of
the pancreas, and along the attachment of the gastro-phrenic ligament. A group
lies at the lesser curvature a short distance below the cardia. There is another
small group on the visceral surface where the posterior gastric artery divides into
its primary branches. There are usually two or three small nodes on the ventral
aspect of the pylorus. Other small glands are scattered along the course of the
gastro-epiploic and short gastric arteries, in the great and gastro-splenic omenta.
The efferent vessels pass largely to the coeliac radicle of the cisterna chyli, but along
the left part of the great curvature they go to the splenic glands.

2. The hepatic lymph glands (Lgg. hepaticae) lie along the portal vein and
hepatic artery and in the lesser omentum. Their efferent vessels go to the
coeliac radicle of the cisterna chyli.

Many of the lymph vessels from the parietal surface of the liver pass in the falciform and
lateral ligaments to the diaphragm and join the lymphatics of the latter. Some pass through the
diaphi'agm with the vena cava and go to the mediastmal glands.

The pancreatic lymph vessels follow the course of the blood-vessels which
supply the gland; most of them go to the splenic and hepatic glands.

3. The splenic lymph glands (Lgg. lienales) lie along the course of the splenic
blood-vessels in the hilus of the spleen and the gastro-splenic omentum. Their
afferent vessels come from the subcapsular network of the spleen, from the greater
curvature of the stomach, and from the left part of the pancreas. The efferents
pass to the glands of the saccus csecus of the stomach and to the cceHac radicle of the
cisterna chyli.

4. The mesenteric lymph glands (Lgg. mesentericse) are situated in the great
mesentery near its root. They are numerous and hence lie close together. They
receive a very large number of afferent vessels (400 to 500) from the small intestine.
They have several considerable efferents, which concur in the formation of the in-
testinal radicles of the cisterna chyli.

The lymph vessels of the intestine form three sets of capillary plexuses, viz., in the subserosa,
submucosa, and mucosa. The lymph follicles, solitary and aggregate, lie in the zone of the plexus
of the mucosa. The collecting vessels arise from the subserous plexus.

5. The caecal lymph glands (Lgg. csecales) are numerous and are distributed
along the course of the csecal blood-vessels. Their efferents enter into the formation
of an intestinal radicle of the cisterna chyli.

6. The colic lymph glands (Lgg. colicse) comprise those of the great colon and
those of the small colon. The glands of the great colon are extremely numerous
and are placed close together along the colic blood-vessels. Their efferent vessels
are large and numerous. They converge to two large trunks which concur with
those of the caecum and small intestine to form an intestinal radicle of the cisterna
chyli. The glands of the small colon are situated in part on the wall of the bowel
along the attachment of the mesentery, in part between the layers of the latter
along the course of the blood-vessels. The efferent vessels go to the lumbar glands
and to the posterior intestinal radicle of the thoracic duct.

The intestinal radicles of the cisterna chyli are formed by the confluence of efferents from
the intestinal lymph glands. The anterior trunk lies on the left side of the anterior mesenteric
artery, passes between that vessel and the ca?liac artery, turns sharply backward across the right
renal vessels, and opens into the cisterna. It is formed by the miion of the coeliac trunk with
efferents from the glands of the small intestine, ciECum, and colon. It is about four inches (ca.
10 cm.) in length and is ampullate. The posterior trunk receives vessels from the small intestine
and small colon. It usually opens into a trunk formed by the union of the right and left lum]:)ar
ducts. It is usually ampullate at its termination (Franck). The arrangement of these collecting
trunks is, however, very variable.

The rectal lymph glands (Lgg. rectales) form a chain along the dorsal surface

THE LYMPH GLANDS AND VESSELS OF THE PELVIC LIMB 703

of the bowel. They receive afferent vessels from the rectum and anus, and their
efferent vessels pass chiefly to the internal iliac glands.

7. The anal lymph glands (Lg. anales) form a small group of three or four on
either side of the sphincter ani externus (Figs. 578) . They receive afferents from the
anus, perineum, and tail. Their efferents go to the internal iliac glands.

THE LYMPH GLANDS AND VESSELS OF THE THORACIC LIMB

1. The axillary lymph glands (Lgg. axillares) (Fig. 590), some ten to twelve in
number, are grouped on the medial face of the distal part of the teres major and the
tendon of the latissimus dorsi at the angle of junction of the external thoracic and
subscapular veins with the brachial (Fig. 566) . Their afferents include most of the
lymph vessels of the limb, which come directly or as efferents from the cubital glands.
They receive also lymph vessels from the thoracic wall. The efferents accompany
the brachial blood-vessels and end in the posterior cervical glands and the thoracic
and right h^mphatic ducts.

2. The cubital lymph glands (Lg. cubitales), usually eight to ten in number,
form a discoid oval group at the medial side of the distal part of the shaft of the
humerus (Figs. 566, 590). They lie behind the biceps muscle on the brachial
vessels and median nerve, and are covered by the deep fascia and the posterior
superficial pectoral muscle. They receive as afferents most of the vessels from the
limb below this point. Their efferents pass chiefly to the axillary glands, but in
part to the prescapular glands also.

In quite exceptional cases a lymph gland may be found on the brachial vessels about the mid-
dle of the arm.

A number of superficial lymph vessels ascend with or near the subcutaneous
veins (cephalic and accessory cephalic), and join the prescapular and prepectoral
glands. Superficial vessels from the chest-wall and shoulder run across the latter
to the prescapular glands. The superficial lymphatics of the pectoral region form
a plexus which drains into the posterior cervical and prescapular glands by a number
of vessels which accompany the cephalic vein. The deep lymph vessels of the pec-
toral region run with the external thoracic vein to the axillary glands.

In one subject the author observed several small glands along the posterior
branch of the dorsal artery, under cover of the rhomboideus.

THE LYMPH GLANDS AND VESSELS OF THE PELVIC LIMB

1. The prefemoral or subiliac lymph glands (Lgg. prefemorales s. subiliacse) are
situated in the fold of the groin on the anterior border of the tensor fasciae latse,
about midway between the point of the hip and the patella (Figs. 575, 576, 582).
They lie on the course of the posterior branch of the circumflex iliac artery, and
number usually about a dozen. They receive superficial lymph vessels from the
hip, thigh, and flank. Their efi'erent vessels ascend with the posterior circumflex
iliac vein, enter the abdomen near the tuber coxse, and join the external iliac lymph
glands.

2. The deep inguinal lymph glands (Lg. inguinales profundse) form a large
group situated in the proximal part of the femoral canal, between the pectineus and
sartorius muscles (Figs. 576, 582). The group is elongated and is commonly four
or five inches (ca. 10-12 cm.) in length. They cover the femoral vessels and are
related superficially to the inguinal ligament. They receive nearly all of the lymph
vessels of the limb below them. Their efferent vessels ascend to the internal iliac
glands.

3. The popliteal lymph glands (Lg. popliteae), usually four to six in number,

704 BLOOD-VASCULAR SYSTEM OF THE HORSE

lie behind the origin of the gastrocnemius and between the biceps femoris and semi-
tendinosus at the division of the posterior femoral artery into its primary branches
(Fig. 580). They receive the deep lymph vessels of the distal part of the limb.
Their efferent vessels chiefly follow the course of the femoral vessels to the deep
inguinal glands, but one or two ascend in company with a vein along the great
sciatic nerve and may enter an ischiatic gland or accompany the internal pudic
vein and join the internal iliac glands.

Several superficial lymph vessels ascend with or near the medial metatarsal and saphenous
veins, enter the femoral canal, and end in the deep inguinal glands.

The Fcetal Circulation

The blood of the foetus is oxygenated, receives nutrient matter, and gives off
waste matter by close contiguity with the maternal blood in the placenta. The
chief differences in the blood-vascular system as compared with that which obtains
after birth are correlated with this interchange.

The umbilical arteries, right and left, are large vessels which arise from the
internal iliac arteries and pass downward and forward in the umbilical folds of peri-
toneum on either side of the bladder to the umbilicus. Here they are incorporated
w^ith the umbilical vein and the urachus in the umbilical cord, ramify in the allan-
tois, and end as the capillaries of the fa?tal placenta. They conduct the impure
blood to the placenta. After birth these vessels retract with the bladder to the
pelvic cavity; their lumen becomes greatly reduced and the wall thickened so
that they are cord-like and are usually termed the round ligaments of the bladder.

The umbilical vein receives the oxygenated blood from the placenta. Its
radicles converge to form in the horse a single large trunk which separates from the
other constituents of the umbilical cord on entering the abdomen and passes for-
ward along the abdominal floor in the free border of the falciform ligament of the
liver. It enters the latter at the umbilical fissure and joins the portal vein, so
that the blood conveyed by it passes through the capillaries of the liver before
entering the posterior vena cava. The vein contains no valves.

In the ox and dog some of the blood in the umbilical vein is conveyed directly
to the vena cava by the ductus venosus. This vessel is given off within the liver
from a venous sinus formed by the confluence of the portal and umbilical veins
and passes directly to the posterior vena cava.

The foramen ovale is an opening in the septum between the atria of the heart,
by which the latter communicate with each other. It is guarded by a valve (Val-
vula foraminis ovalis) which prevents the blood from passing from the left atrium
to the right. After birth the foramen soon closes, but this part of the septum
remains membranous, and there is a deep fossa ovalis in the right atrium which
indicates the position of the former opening. In some cases the foramen persists
to a variable extent in the adult without apparent disturbance of the circulation.

The pulmonary circulation is very limited in the foetus, and most of the blood
which enters the pulmonary artery passes through the ductus arteriosus to the
aorta. This vessel is larger than the divisions of the pulmonary artery which go to
the lungs, and joins the left side of the aortic arch. After birth the pulmonary
circulation undergoes promptly an enormous increase and the ductus is rapidly
transformed into a fibrous cord — the ligamentum arteriosum.

The only arterial blood in the foetus is that carried by the umbilical vein.
This blood is mixed in the liver with the venous blood of the portal vein, and after
passing through the capillaries of the liver is carried by the hepatic veins to the
posterior vena cava. The latter receives also the venous blood from the posterior
part of the trunk and the pelvic limbs. It is generally believed that the blood car-

THE BLOOD-VASCULAR SYSTEM OF THE OX 705

ried into the right atrium by the posterior vena cava passes largely, if not entirely,
through the foramen ovale into the left atrium, while the blood flowing into it
through the anterior vena cava passes into the right ventricle. On this basis the
blood received by the left atrium consists chiefly of mixed blood from the posterior
vena cava, since the small amount of blood conveyed by the pulmonary veins is
venous. This mixed blood passes into the left ventricle and is forced into the
systemic arteries. The venous blood from the anterior part of the body and the
thoracic limbs is conveyed by the anterior vena cava to the right atrium, passes
into the right ventricle, and is forced into the pulmonary artery, A small amount
is carried to the lungs, but the bulk of it passes by the ductus arteriosus into the
aorta behind the point of origin of the brachiocephalic trunk, and is carried to the
posterior part of the body, a large part passing by the umbilical arteries to the
placenta.

THE BLOOD-VASCULAR SYSTEM OF THE OX
The Pericardium and Heart

The pericardium is attached to the sternum opposite the facets for the sixth
costal cartilages by two fibrous bands, the sterno-pericardiac ligaments (Ligg.
sternopericardiaca) ; these ligaments, right and left, are embedded in the mass of fat
which separates the apex of the pericardium from the floor of the thorax. On the
left side the greater part of the pericardium is in contact with the chest wall as far
back as the fourth intercostal space. On the right side the pericardium is com-
monly covered by the lung, and has therefore no contact with the lateral chest wall.
But in some cases there is a small cardiac notch on the right lung opposite to the
ventral part of the third rib and intercostal space.

The heart of the adult ox has an average weight of about five and a half pounds
(ca. 2.5 kg.), or about 0.4 to 0.5 per cent, of the body-weight. Its length from base
to apex is relatively longer than that of the horse, and the base is smaller in both
its cliameters. The ventricular part is more regularly conical and more pointed.
A shallow intermediate groove (Sulcus intermedins) extends from the coronary
groove down the left side of the posterior border, but does not reach the apex. The
amount of fat in and near the grooves is much greater than in the horse. Even
more of the heart is situated to the left of the median plane than in the horse. The
base is opposite the chest wall from the third rib to the fifth intercostal space, both
inclusive. The apex is opposite to the fifth interchondral space; it is just to the
left of the median plane, and is about an inch (ca. 2.5 cm.) from the diaphragm.
The long axis is much less oblique than in the horse. The posterior border is
opposite to the fifth intercostal space; it is practically vertical and is slightly con-
cave.

The pulmonary orifice is opposite to the third rib in part and the third intercostal space,
about a handbreadth (ca. 10-12 cm.) above the sternal ends of the ribs. The aortic orifice is
chiefly opposite to the fourth rib. The right atrio-ventricular orifice is opposite to the third inter-
costal space and fourth rib and space. The left atrio-ventricular orifice is chiefly opposite to the
fourth mtercostal space and fifth rib.

The left longitudinal groove corresponds to the fourth rib. The right groove is chiefly pos-
terior; it begins below the termination of the posterior vena cava. The intermediate groove
begins below the posterior end of the left auricle, and in its descent inclines gradually to the left
side of the apex.

The vena hemiazygos usually unites with the terminal part of the great cardiac
vein, thus forming a trunk which opens into the right atrium below the posterior
vena cava.

Two bones, the ossa cordis, develop in the aortic fibrous ring. The right one
45

706

THE BLOOD-VASCULAR SYSTEM OF THE OX

is in apposition with the atrio-ventricular rings, and is irregularly triangular in
form. Its left face is concave and gives attachment to the right posterior cusp of
the aortic valve. The right surface is convex from before backward. The base
is dorsal. The posterior border bears two projections separated by a notch. It
is usualh" a little more than an inch (ca. 4 cm.) in length. The left bone is smaller
and is inconstant. Its concave right border gives attachment to the left posterior
cusp of the aortic valve. There is a large muscular moderator band in the right

Aurta

L iga m e nt um arteriosum

Left branch of -pulmonary artery
Pulmonary veins
I \\ Posterior vena cava

Anterior vena
cava

Brachiocephalit
trunk

Right auricle
Pulmonary artery

Right ventricle
Left coronary artery

Vena hemiazygos
I^ft auricle

Posterior branch of left
coronary artery in
intermediate groove
Left ventricle

Fig. 592. — Heart op Ox; Left View.
The ventricles are contracted.

ventricle, which extends from the base of the anterior septal papillary muscle to the
lateral wall at the base of the papillary muscle there. In the left ventricle there
are several branched moderator bands.

The Arteries!

The great arterial trunks in the thorax resemble those of the horse in general
disposition.

1 Only the most important differential features of the arrangement of the vessels as compared
with those of the horse will be considered.

THE COMMON CAROTID ARTERY 707

The left coronary artery is much larger than the right one; it gives off a branch
which descends in the intermediate groove, and terminates by running downward
in the right longitudinal groove. The right coronary artery, after emerging from
the interval between the right auricle and the pulmonary artery, divides into
branches which are distributed to the wall of the right ventricle.

The brachiocephalic trunk (anterior aorta) is usually four or five inches (ca.
10-12 cm.) in length.

The brachial arteries give off in the thorax the following branches :

1. A common trunk for the dorsal, deep cervical, and vertebral arteries.

(1) The subcostal artery commonly arises separately and runs forward along
the sides of the l^odies of the vertebra. It supplies the second to the fifth inter-
costal arteries.

(2) The dorsal artery is relatively small. It usually ascends in front of the
first costo-vertebral joint, and is distributed as in the horse. It gives off the first
intercostal artery.

(3) The deep cervical artery may arise from a common stem (Truncus vertebro-
cervicalis) with the vertebral, or may constitute a branch of that artery. It passes
up between transverse processes of the first thoracic and last cervical vertebra, or be-
tween the sixth and seventh cervical, and is distributed as in the horse.

(4) The vertebral artery passes along the neck as in the horse to the inter-
vertebral foramen between the second and third cervical vertebrae, gives off a
muscular branch, and enters the vertebral canal (Fig. 594). It runs forward on
the floor of the canal — connected with its fellow by two or three transverse anas-
tomoses— and divides in the atlas into two branches. The smaller medial division
(cerebrospinal artery) passes forward to the floor of the cranium and concurs with
the condyloid artery and branches of the internal maxillary in the formation of a
large rete mirabile. The large lateral branch emerges through the intervertebral
foramen of the atlas and ramifies in the muscles of the neck in that region, com-
pensating for the smallness of the branches of the occipital artery. It also sends a
branch to the rete mirabile. The collateral branches detached to the cervical mus-
cles are large and compensate for the small size of the deep cervical artery. The
spinal branches pass through the intervertebral foramina, divide into anterior and
posterior branches, and form two longitudinal trunks which are connected by cross-
branches so as to form irregular polygonal figures.

2. The internal thoracic artery presents no remarkable features.

3. The inferior cervical artery corresponds usually to the ascending branch of
that vessel in the horse.

4. The external thoracic artery is large and usually gives off a branch which is
•equivalent to the descending branch of the inferior cervical artery of the horse.

THE COMMON CAROTID ARTERY

The carotid arteries usually arise from a common trunk about two inches (ca.
5 cm.) in length, but in exceptional cases are given off separately from the brachio-
cephalic. Each pursues a course similar to that of the horse, and is accompanied
by the small internal jugular vein, but is separated from the external jugular vein
by the omo-hyoid and sterno-mastoid muscles. It divides at the digastricus into
occipital, external maxillary, and external carotid arteries. In addition to tracheal,
oesophageal, and muscular branches, it gives off the thyroid, laryngeal and inferior
parotid arteries. The thyroid artery (A. thyreoidea cranialis) bends around the
anterior end of the thyroid gland, in which it ramifies. The accessory thyroid
artery is usually absent. The laryngeal artery may arise with the thyroid.

1. The occipital artery is relatively small. It gives off the following:

708

THE BLOOD-VASCULAR SYSTEM OF THE OX

(1) The pharyngeal artery (A. palatina ascendens) goes to the phars^nx and
soft palate; it may arise from the external carotid.

(2) Muscular branches go chiefly to the ventral straight muscles of the head
and supply twigs to the atlanto-occipital joint.

(3) The condyloid artery passes into the cranium through the anterior foramen
in the condj^loid fossa, and joins the vertebral in the formation of the rete mirabile
about the pituitary gland. Before entering the cranium it gives off a branch to
the pharyngeal lymph glands and the middle meningeal artery; the latter passes

Fig. 593. — Schema of Chief Arteries of Head of Cow.
7, Common carotid artery; ^, thyro-laryngeal; 3, thyroid; 4> laryngeal; 5, pharyngeal ; 6, occipital; 7, condyloid;
8, middle meningeal; 9, pharyngeal; 10, external maxillary; 11, lingual; 12, sublingual; 13, superior labial; 14, in-
ternal maxillary; 15, masseteric; 16, inferior alveolar; 17, buccinator; IS, great palatine; 19, sphenopalatine; 20,
posterior auricular; 21, superficial temporal; 22, posterior meningeal; 23, anterior auricular; 24, artery to corium of
horn; :35, deep temporal; ^5, arteries to rete mirabile ; ^7, frontal; ^<S, malar; .g<S', dorsal nasal continuation of malar;
29, infraorbital; 29', lateral nasal continuation of 29.

through the foramen lacerum. Another branch enters the temporal canal and gives
twigs to the temporalis muscle and the mucous membrane of the frontal sinus. A
muscular branch emerges from the intervertebral foramen of the atlas. A diploic
branch goes into the occipital condyle and squama, and emits twigs to the occipital
muscles.

2. The external maxillary artery is smaller than that of the horse, but pursues
a similar course. ^ It gives off several branches to the parotid and mandibular
glands. The lingual artery is large, and often arises separately from the common

^ In the sheep the artery crosses the masseter muscle about its middle and is continued as
the superior labial artery.

THE COMMON CAROTID ARTERY

709

carotid; it gives off a branch to the mandibular gland, and the sublingual artery.
After turning around the j aw the facial gives off the two labial arteries. The inferior
labial artery is small; it runs forward along the ventral margin of the depressor
labii inferioris. The superior labial is large; it passes forward ventral to the
depressor labii superioris, and usually gives off a muscular branch which runs for-
ward almost parallel with the lateral nasal. The angular artery is very small or
absent, and the lateral and dorsal nasal arteries spring from branches of the in-
ternal maxillary.

3. The external carotid artery passes upward between the stylo-hyoideus
and the great cornu of the hyoid bone, turns forward across the lateral face of the
latter, and divides into superficial temporal and internal maxillary arteries. It
gives off the following collateral branches :

(1) The pharyngeal artery may be a branch of the external carotid, but often
arises from the occipital.

(2) The posterior auricular artery, which resembles that of the horse, sends a

Fig. 594. — ^Floor of Cranium and Anterior Part op Vertebral Canal op Ox.
1, Vertebral artery; 2, muscular branches of /; 3, branches of 1 to the rete mirabile; 4. 5, branches of internal max-
illary artery to rete; 6, branch of internal maxillary artery entering cranium through foramen ovale; 7, condyloid ar-
tery; 8, emergent artery from rete, distributed like internal carotid artery of horse; 9, 9', longitudinal vertebral sinuses;
a, cribriform plate; 6, optic formina; c, for. orbito-rotundum; d, foramen ovale; e, occipital condyle; /, g, h, first,
second, and third cervical vertebrse. (After Leisering's Atlas.)

stylo-mastoid branch into the tympanum. It may arise from the superficial
temporal.

(3) The superior parotid artery arises near the termination of the external
carotid and enters the upper part of the parotid gland.

(4) The masseteric artery resembles that of the horse, but is smaller; it may
arise from the internal maxillary artery.

The superficial temporal artery is large and presents the following special
features: (1) The transverse facial artery passes into the central part of the masse-
ter. (2) It gives off a branch which corresponds to the posterior meningeal artery
of the horse, enters the temporal canal, and ramifies in the dura mater, giving off
twigs to the external ear, the temporal muscle, and the frontal sinus. (3) It
usually gives off the anterior auricular artery. (4) A large branch passes around
the outer side of the base of the horn-core, supplies the corium of the horn, and
anastomoses across the back of the frontal eminence with the artery of the opposite
side. (5) Other branches go to the frontal muscles and skin and to the orbital
fat, the lacrimal glands, and the eyelids.

710 THE BLOOD-VASCULAR SYSTEM OF THE OX

The internal maxillary artery is entirely extraosseous, since the alar canal is
absent. It passes forward along the side of the pharynx and the lateral pterygoid
muscle and forms a double curve at the infratemporal fossa. It then runs forward
to the pterygo-palatine fossa and divides into two terminal trunks; one of these
divides into malar and infraorbital arteries, the other into sphenopalatine and
greater palatine. It gives off branches to the pterygoid muscles, and the principal
differential features in its branching are as follows :

(1) The buccinator artery arises from the first curve of the internal maxillary;
it is relatively large, supplies the superior buccal glands, and divides into two
branches. One of these enters the buccinator; the other, which is much larger,
ramifies in the deep part of the masseter.

(2) The anterior deep temporal artery usually arises by a common trunk with
the middle meningeal artery. The latter enters the cranial cavity through the
foramen ovale and concurs in the formation of the rete mirabile cerebrale.

(3) The ophthalmic artery forms a rete mirabile within the periorl)ita.^ Its
frontal branch enters the supraorbital canal and ramifies chiefly in the frontal sinus.

(4) Several branches which take the place of the internal carotid artery enter
the cranial cavity through the foramen orbito-rotundum. They concur with the
vertebral, middle meningeal, and condyloid arteries in the formation of an ex-
tensive rete mirabile cerebrale on the cranial floor around the sella turcica. From
each side of the rete an artery arises which is distributed in general like the internal
carotid and basilar arteries of the horse. ^

(5) The malar artery is large; it arises by a common trunk with the infra-
orbital and gives off the dorsal nasal and the angular artery of the eye.

(6) The infraorbital artery is large and emerges from the infraorbital foramen
to form the lateral nasal artery.

(7) The greater palatine artery usually arises by a common trunk with the
sphenopalatine. It passes through the palatine canal and along the palatine groove,
enters the nasal cavity through the incisive fissure, and does not go to the upper lip.
It forms a rete mirabile about the incisive canal and terminates in the mucous
membrane of the anterior part of the nasal cavity.

ARTERIES OF THE THORACIC LIMB
The brachial artery pursues the same course in the arm as that of the horse.
At the elbow it becomes the median.'^ The chief differential features in its branches
are as follows:

1. The subscapular artery is almost as large as the continuation of the brachial.
The posterior circumflex artery is large ; it sends branches backward and downward
into the triceps, taking the place in part of the deep brachial artery. The thoracico-
dorsal artery supplies branches to the pectoral muscles and the triceps as well as
the teres major and latissimus dorsi; it may arise directly from the brachial.

2. The smallness of the deep brachial artery is compensated, as noted al)ovc,
by the large size of the posterior circumflex.

3. The proximal collateral ulnar artery is often double, and does not extend to
the carpus. Its superficial descending branch goes to the superficial pectoral
muscle and the skin, and its ascending branch is distributed chiefly to the medial
head of the triceps and the anconeus.

(4) The (distal) collateral radial artery, which is given off at the elbow joint,

1 This may be distinguished as the rete mirabilf orbitale.

^ The arteries which concur in the formation of the rete may be termed the arteri» retis
mirabiUs cerebrahs.

^ The homologies of the vessels of the lower parts of the limbs are still uncertain. The ac-
count given here is mainly based on the views of Sussdorf and Baum.

ARTERIES OF THE THORACIC LIMB

711

sends branches to the biceps, brachiahs, and extensor muscles; it also supplies the
nutrient artery of the humerus. It does not descend to the carpus.

The median artery descends along the medial part of the posterior surface of
the radius and divides near the middle of the forearm into the radial and ulnar
arteries. It gives off at the proximal third of the forearm the common interosseous
artery, a large vessel which anastomoses with the deep brachial, passes through the
proximal interosseous space, and descends as the dorsal interosseous artery in the
groove between the radius and ulna, and concurs in the formation of the rete carpi

Fig. 595. — Arteries of Distal P.^rt of Right Fore
Limb of Ox; Dorsal View.
a. Interosseous artery; b, dorsal branch of radial
artery; c, rete carpi dorsale; d, dorsal metacarpal ar-
tery; e, dorsal common digital artery; /, /, dorsal proper
digital arteries.

Fig. 596. — Arteries of Distal Part of Right Poke
Limb of Ox; Volar View.
g. Ulnar artery; h, radial artery; i, volar branch
of common interosseous artery; k, I, m, deep volar
metacarpal arteries; A.v., volar arches; n, volar com-
mon digital artery; o, o', p, volar proper digital arteries.

dorsale. At the distal end of the forearm it sends a branch through the distal
interosseous space, which passes downward, assists in forming the rete carpi volare,
and is continued in the metacarpus as the lateral deep volar metacarpal artery.
This is a small vessel which passes down under the lateral border of the suspensory
ligament and assists in forming the deep volar arch near the fetlock. The recurrent
interosseous artery arises from the common interosseous and ascends to the lateral
surface of the elbow. A large muscular branch arises from the median at the
proximal end of the forearm; it is distributed chiefly to the flexor muscles.

712 THE BLOOD-VASCULAR SYSTEM OF THE OX

The radial artery is the smaller of the two terminal branches of the median. It
descends on the flexor carpi radialis, passes over the medio-volar surface of the
carpus, and is continued as the medial deep volar metacarpal artery. At the distal
end of the forearm and at the carpus it furnishes branches to the retia carpi. An-
other branch (A. met. perforans proximalis) runs outward between the suspensory
ligament and the large metacarpal bone, passes through the proximal foramen of
the bone, and unites with the dorsal metacarpal artery; before passing through the
foramen it detaches the middle deep volar metacarpal artery (A. met. volaris prof.
III.). This descends on the volar face of the metacarpal bone, receives an anasto-
motic branch from the medial deep artery, and concurs in the formation of the deep
volar arch above the fetlock. The medial deep volar metacarpal artery (A. met.
volaris prof. II.) descends along the medial part of the volar surface of the large
metacarpal bone and is continued as the medial volar proper digital artery. At the
distal part of the metacarpus it is connected by a transverse branch with the middle
deep volar metacarpal artery, and similarly with the volar common digital, forming
with the latter the superficial volar arch.

The ulnar artery, the larger of the two divisions of the median, descends under
cover of the fiexor carpi radialis without giving off any large branches in the fore-
arm. It passes through the carpal canal and continues along the medial side of the
deep flexor tendon as the volar common digital artery (A. met. volaris superficialis
III.). At the distal third of the metacarpus this vessel is joined by a branch from
the medial deep volar metacarpal artery, forming the superficial volar arch. Near
this another branch of the common digital (or of the medial digital) passes around
the lateral border of the flexor tendons to the posterior face of the metacarpal bone
and concurs with the deep volar metacarpal arteries in the formation of the deep
volar arch. A branch from the arch (A. met. perforans distalis) passes forward
through the distal foramen of the metacarpal bone and joins the dorsal metacarpal
artery which descends from the rete carpi dorsale in the dorsal metacarpal groove.

The volar common digital artery (A. metacarpea volaris superficialis III.)
passes into the interdigital space and divides into two volar proper digital arteries,
which descend along the interdigital surfaces of the chief digits and pass through
the foramina at the proximal part of the interdigital surfaces of the third phalanges,
enter the cavities in these bones, and ramify in a manner similar to the correspond-
ing vessels in the horse. The volar common digital detaches a branch (A. inter-
digitalis perforans) which passes forward through the upper part of the interdigital
space and anastomoses with the dorsal metacarpal artery.

The volar proper digital arteries (or the common digital) give off, in addition to other col-
laterals, branches which correspond to the arteries of the digital cushion of the horse. These
pass to the bulbs of the claws and anastomose with each other and with the medial and lateral
digital arteries, forming an arch from which numerous branches are distributed to the corium
of the hoofs.

The dorsal metacarpal artery (A. met. dorsalis III.) is a small vessel which
arises from the rete carpi dorsale, descends in the groove on the dorsal face of the
metacarpal bone, and is joined by the distal perforating metacarpal artery from
the deep volar arch to constitute the dorsal common digital artery. This vessel
(A. digitalis communis dorsalis III.) divides into two dorsal proper digital arteries.

The medial volar digital artery (A. digiti III. medialis) is the continuation of the
medial deep volar metacarpal artery. It descends on the medial side of the medial
digit and terminates at the bulb of the claw by anastomosing with the corresponding
volar proper digital artery. It gives off a branch to the rudimentary digit and
forms a transverse anastomosis behind the first phalanx with the volar common
digital or its medial division.

The lateral volar digital artery (A. digiti IV. lateralis) arises from the deep volar

BRANCHES OF THE ABDOMINAL AORTA 713

arch, passes down on the lateral side of the lateral digit, and is distributed like the
medial one.

BRANCHES OF THE THORACIC AORTA
The bronchial and oesophageal arteries often arise separately.
There are thirteen pairs of intercostal arteries. The first comes from the

dorsal, the next four from the subcostal, and the remainder from the aorta directly.
The two phrenic arteries are very variable in origin. They may come from

the aorta, the coeliac, left ruminal, or an intercostal or lumbar artery.

BRANCHES OF THE ABDOMINAL AORTA
The coeliac artery is about four to five inches (ca. 10-12 cm.) in length. It
passes ventrally and curves forward between the rumen and pancreas on the left
and the right crus of the diaphragm and the posterior vena cava on the right. It
gives off five chief branches.

1. The hepatic artery arises from the convex side of the curve of the coeliac
artery as it crosses the posterior vena cava. It passes downward, forward, and to
the right above the portal vein to the portal fissure, and gives off the following
branches :

(1) Pancreatic branches.

(2) Dorsal and ventral branches go to the corresponding lobes of the liver.
The ventral branch is the larger; it gives off the right gastric artery, which runs in
the lesser omentum to supply the origin of the duodenum and the pylorus, anas-
tomosing with the dorsal branch of the omaso-abomasal artery.

(3) The cystic artery supplies the gall-bladder.

(4) The gastro-duodenal artery divides into right gastro-epiploic and pan-
creatico-duodenal branches. The right gastro-epiploic artery anastomoses with
the left gastro-epiploic. The pancreatico-duodenal artery anastomoses with the
first intestinal branch of the anterior mesenteric artery.

2. The right ruminal artery (A. ruminalis dextra) is the largest branch, and
usually arises by a short common trunk with the splenic. It runs downward and
backward on the right face of the dorsal sac of the rumen to the posterior transverse
fissure, in which it turns around to the left and anastomoses with branches of the
left ruminal artery. It gives off a pancreatic branch, dorsal and ventral coronary
arteries, branches to the great omentum, and ramifies on both surfaces of the rumen.

3. The left ruminal artery (A. ruminalis sinistra) descends on the anterior part
of the right face of the rumen, enters the anterior furrow, in which it runs from
right to left, and continues backward in the left longitudinal groove, anastomosing
with branches of the right artery. It supplies chiefly the left face of the rumen,
but not its posterior part. It usually gives off near its origin the reticular artery

(A. reticularis) ; this rather small vessel passes forward on the dorsal curvature of
the rumen and turns downward in the rumino-reticular groove, in the bottom of
which it runs around ventrally to the right side. It gives off a branch which passes
to the left of the cardia and along the lesser curvature of the reticulum to the neck
of the omasum. The reticular branches anastomose with the omaso-abomasal and
left ruminal arteries.

4. The omaso-abomasal artery (A. gastrica sinistra) appears as the continua-
tion of the coeliac. It passes forward and downward to the greater curvature of
the omasum, and divides after a course of four or five inches into two branches.
The dorsal branch curves sharply backward on the dorsal surface of the omasum,
continues along the lesser curvature of the abomasum, and anastomoses with the
hepatic artery. It supplies branches to the omasum and to the lesser curvature

714

THE BLOOD-VASCULAR SYSTEM OF THE OX

Fig. 597. — Gastric Arteries of Ox; Right View (Partly Schematic).
i, Coeliac; ^, right ruminal; 3, splenic; 4 > reticular; 5, left ruminal; ff, omaso-abomasal; 7, dorsal branch of 6'
S, ventral branch oi 6 {= left gastro-epiploic) ; A, dorsal sac of rumen; B, ventral sac of rumen; C, C, posterior blind
sacs; D, oesophagus; i^, reticulum; F, omasum; G, abomasum; i/, duodenum; J, right longitudinal furrow of rumen.
By an oversight the reticular artery is shown as arising from the omaso-abomasal.

Fig. 598. — Gastric Arteries of Ox; Left View (Partly Schematic).
1, Left ruminal artery; 3, continuation of right ruminal artery; 3, reticular artery, which disappears into i
reticular groove ; A, dorsal sac of rumen; B, ventral sac of rumen; C, C, posterior blind sacs; D, cEsophagus; £, reticu-
lum; F, rumino-reticular groove; (1, left longitudinal furrow of rumen.

BRANCHES OF THE ABDOMINAL AORTA

715

and pyloric part of the abomasum. The ventral branch (A. gastro-epiploica
sinistra) runs forward and downward over the anterior extremity of the omasum,
passes backward in the great omentum close to the ventral curvature of the aboma-
sum, and anastomoses with the right gastro-epiploic. A considerable branch from it
curves around in front of the neck of the omasum to communicate with the reticular
artery. Another branch runs back across the left side of the omaso-abomasal
junction, and a third goes to the lesser curvature of the omasum.

5. The splenic artery usually arises by a common trunk with the right ruminal

•Small

Fig. 599. — Plan of Branches of Anterior Mesenteric Artery op Ox.
/, Anterior mesenteric artery; 2, middle colic artery; 3, ileo-cseco-colic artery; 4, ramus collateralis; 6, continua-
tion of anterior mesenteric artery, giving off branches to small intestine; 6, caecal artery; 7, colic branch of posterior
mesenteric artery; A, termination of duodenum.

artery. It passes forward antl to the left across the dorsal curvature of the rumen
and enters the hilus of the spleen.

The anterior mesenteric artery arises from the aorta just behind the cceliac,
and has about the same caliber as the latter. It descends, inclining a little to
the right, and crosses the colon as the latter emerges from the spiral to run backward.
After detaching twigs to the pancreas it gives off in succession the following branches:

1. The middle colic artery (A. colica media) passes to the colon as it emerges
from the spiral arrangement. This artery is comparable to the middle colic or
artery of the small colon of the horse; it runs backward along the terminal part of
the colon, which it supplies.

716

THE BLOOD-VASCULAR SYSTEM OF THE OX

2. The ileo-caeco-colic artery ramifies on the right face of the spiral part of the
colon. It gives off the ileo-caecal artery, which divides into ileal and csecal arteries.

3. The ramus collateralis runs in the mesentery in a curve along the ventral
border of the coils of the colon. (This vessel is absent in the sheep.)

4. The continuing trunk (Truncus intestinalis) of the anterior mesenteric
pursues a course in the mesentery corresponding to the series of mesenteric lymph
glands and is connected with the ramus collateralis.

The two preceding vessels are essentially the arteries of the small intestine,
which they supply with the exception of its initial and terminal parts. The ramus
collateralis gives off no considerable branches in its course along the ventral border
of the coils of the colon, but on curving upward along the latter it anastomoses with

Fig. 600. — Pelvic Arteries op Cow.
Part of the right wall of the uterus and vagina is removed and the cervix uteri is shown in sagittal section, o.
Aorta; 6, utero-ovarian artery; h', ovarian, and 6", uterine branch of h; c, external iliac artery; d, right internal iliac
artery; e, common trunk of umbilical artery (e') and middle uterine artery (/) ; g, ilio-lumbar artery; h, anterior gluteal
arteries; i, middle hsemorrhoidal artery; k, posterior uterine artery; I, perineal artery; m, posterior gluteal artery; n,
obturator arteries; o, artery of clitoris; p, posterior mesenteric artery; r, anterior hsemorrhoidal artery; s, middle
sacral artery; /, ovary; ^, apparent body of uterus, really apposed horns; 2', horn of uterus; 3, vagina; 4, neck of uterus;
4', external orifice of uterus (os uteri); 5, 5', broad ligaments, large part of right one removed; 6, urinary bladder; 7t
rectum; 8, sacrum; 9, symphysis pelvis. (After Zieger.)

the continuing trunk of the anterior mesenteric artery and detaches numerous
branches to the small intestine which form series of superposed anastomotic arches.
It supplies, roughly speaking, about one-third of the small intestine and terminates
by joining the ileal artery. The continuing trunk gives off numerous branches
which also form arches and supply about the first two-thirds of the small intestine,
exclusive of the small part supplied by branches of the cceliac artery. Both arteries
give branches to the lymph glands.^

The posterior mesenteric artery arises from the aorta near its termination. It
is small and supplies branches to the terminal part of the colon and to the rectum
(A. colica sinistra; A. haemorrhoidalis cranialis).

^ It is difficult to make the arrangement of these vessels clear in a brief textual description,
hut a reference to the schematic figure will explain the main facts.

ARTERIES OF THE PELVIC LIMB 717

The renal arteries arise from the aorta close together. The right one passes
outward and forward across the dorsal face of the posterior vena cava to the hilus
of the kidney. The left one runs backward, but necessarily varies in direction in
conformity with the position of the kidney (g. v.).

The spermatic arteries resemble those of the horse.

The utero-ovarian arteries are small.

The five pairs of lumbar arteries derived from the aorta are distributed much
as in the horse. The sixth usually comes from the internal iliac artery.

The middle sacral artery is a vessel about 5 mm. in diameter which continues
the aorta. It arises from the dorsal face of the aorta at the angle of divergence of
the internal iliacs, runs backward on the pelvic surface of the sacrum a little to the
left of the median line, and is continued as the middle coccygeal artery. It gives
off small collateral branches to the spinal cord and the muscles of the tail and the
lateral coccygeal arteries. The latter may have a common trunk of origin, and
each divides into dorsal and ventral branches. The middle coccygeal artery runs
through the ventral (haemal) arches of the coccygeal vertebrae. The coccygeal
arteries are connected at pretty regular intervals by segmental anastomoses.

The internal iliac arteries are much longer than in the horse. Each passes
backward on the sacro-sciatic ligament and divides about the middle of the pelvic
wall into posterior gluteal and internal pudic branches. The chief differences in
its distribution are: (1) A large trunk gives origin to the umbilical and middle
uterine arteries. The umbilical artery is usually largely obliterated, and its terminal
branches receive their blood through anastomoses with the internal pudic. It
gives off near its origin two small vessels, the ureteral artery (A. ureterica) and the
deferential artery (A. deferentialis), which accompany the ureter and the ductus
deferens respectively. The middle uterine artery (A. uterina media) is very large.
It is distributed chiefly to the cornu of the uterus, and compensates for the small
size of the utero-ovarian artery. (2) The ilio-lumbar artery is relatively small
and is distributed chiefly to the sublumbar muscles. It is sometimes replaced by
branches of the circumflex iliac and gluteal arteries. (3) The anterior gluteal
artery is commonly represented by several vessels. (4) The obturator artery is
represented by several small branches which supply the obturator and adductor
muscles. (5) The iliaco-femoral and lateral sacral arteries are absent. The
absence of the latter is compensated by the middle sacral and gluteal arteries. (6)
The posterior gluteal artery is large. It emerges through the lesser sciatic notch
and ramifies in the biceps femoris and adjacent muscles. (7) The internal pudic
artery (A. urethro-genitalis) is the direct continuation of the internal iliac. It
gives off branches to the rectum, bladder, urethra, and genital organs. In the
male it supplies the accessory genital glands and divides into dorsal and deep arteries
of the penis ; the a. dorsalis penis runs along the dorsum penis to the glans and gives
twigs to the prepuce; the a. profunda penis gives ofi a perineal branch and enters
the corpus cavernosum penis. In the female it gives off the large posterior uterine
artery, which supplies the posterior part of the uterus and gives branches to the
vagina and bladder. It ends as the a. clitoridis, which supplies the clitoris and
adjacent parts.

ARTERIES OF THE PELVIC LIMB

The external iliac artery has the same course as in the horse. The circumflex
iliac artery is large. A branch from it emerges between the abdominal and lumbar
muscles near the tuber coxae and ramifies like the terminals of the ilio-lumbar
artery of the horse.

The femoral and popliteal arteries pursue a similar course to those of the horse.
The chief differences in their branches are as follows:

1. The external pudic artery is distributed chiefly to the scrotum in the male.

718

THE BLOOD-VASCULAR SYSTEM OF THE OX

In the cow it is usually termed the mammary and is very large, especially during
lactation. Each divides at the base of the mammary gland into two branches
which are distributed to the anterior and posterior parts ("quarters") of the gland.
A small branch accompanies the subcutaneous abdominal vein to the xiphoid region.
2. The deep femoral artery gives off an obturator branch which passes up
through the obturator foramen to supply the obturator internus and compensates
otherwise for the absence of the obturator artery.

Fig. 601. — Arteries of Distal Part of Right Hind
Limb of Ox; Dorsal View.
a, Anterior tibial artery; b, proximal perforating
metatarsal artery; c, dorsal metatarsal artery; d, dorsal
common digital artery; e, e', dorsal proper digital ar-
teries.

Fig. 602. — Arteries of Distal Part of Right Hind
Limb of Ox; Plantar View.
c, Saphenous artery; /, /', internal and external
plantar arteries; g, g' , medial and lateral superficial
plantar metatarsal arteries; h, deep plantar metatarsal
artery; i, j, medial and lateral plantar digital arteries,
k, plantar common digital artery; I, /', medial and lat-
eral plantar digital arteries.

3. The anterior femoral artery is large. It often gives off the external cir-
cumflex artery of the thigh, which perforates the proximal end of the quadriceps,
gives branches to that muscle, the iliacus, glutei, anfl tensor fascise lata?.

4. The saphenous artery is large. It descends in front of the homonymous
vein over the medial surface of the leg, and divides near the hock into lateral
and medial tarsal arteries. The lateral tarsal artery is small and is distributed
on the outer part of the hock. The medial tarsal artery is the direct continuation

THE VEINS 719

of the saphenous. It descends along the medial border of the superficial flexor
tendon and divides into medial and lateral plantar arteries. The medial plantar
artery descends along the medial side of the deep flexor tendon with the medial
plantar nerve. It anastomoses at the proximal end of the metatarsus with the
perforating tarsal artery, assisting in the formation of the proximal plantar
arch, and continues distally as the a. met. plant, superfic. med. along the medial
border of the deep flexor tendon. Near the fetlock it concurs with the perforating
branch of the dorsal metatarsal artery and with a branch of the corresponding
lateral artery in the formation of the distal plantar arch. Below this it is continued
as the medial digital artery. The lateral plantar artery is small. ^ It descends
along the lateral border of the deep flexor tendon with the lateral plantar nerve,
concurs with the perforating tarsal and medial plantar arteries in the formation
of the proximal plantar arch, and gives branches to the rete tarsi dorsale. Continu-
ing downward along the deep flexor tendon as the a. met. plant, superfic. lat., it
assists in forming the distal plantar arch and becomes the lateral digital artery.

The posterior tibial artery is relatively small and is distributed chiefly to the
muscles on the posterior surface of the tibia. Lower down it is replaced by the
saphenous artery, as described above.

The anterior tibial artery has the same course as in the horse. It is continued
down the groove on the front of the metatarsal bone as the dorsal metatarsal artery.
At the tarsus branches are given off which concur with the lateral tarsal artery in
the formation of the rete tarsi dorsale. The perforating tarsal artery passes back
through the vascular canal and anastomoses with the plantar arteries, thus forming
the proximal plantar arch. From this the small deep plantar metatarsal artery
descends in the plantar groove of the large metatarsal bone to the distal plantar
arch. The dorsal metatarsal artery (A. met. dorsalis) is the chief artery of the
region and is accompanied by two veins. Near the distal end of the metatarsal
bone it gives off the perforating metatarsal artery, which passes back through the
distal metatarsal foramen and assists in forming the distal plantar arch.

The dorsal common digital artery is the direct continuation of the dorsal
metatarsal. It divides into two branches which unite in the interdigital space with
the corresponding branches of the plantar common digital to form the proper
digital arteries.

The plantar common digital artery descends from the distal plantar arch,
anastomoses in the interdigital space with the medial and lateral digitals, and
divides into two branches which join those of the dorsal common digital artery as
before mentioned.

The foregoing is a brief statement of the more common arrangement of the
vessels in the distal part of the limb, but minor variations are very common.

The Veins 2

The vena hemiazygos takes the place of the vena azygos. It lies along the
left side of the aorta and the bodies of the thoracic vertebrse, turns down across
the left face of the aorta and left pulmonary artery, runs back over the left auricle,
and usually joins the great cardiac vein, but may open into the right atrium. It
receives the dorsal intercostal veins.

Two jugular veins occur on either side. The internal jugular vein (V. jugu-
laris interna) is a relatively small vessel which accompanies the carotid artery. It

^ This vessel may arise instead from the rete tarsi dorsale.

2 Most of the differences in the veins of the ox are correlated with those of the arteries of
which they are satellites, and will not be described. The account here given consists chiefly of
those differential features which could not be deduced from a knowledge of the arteries.

720 THE BLOOD-VASCULAR SYSTEM OF THE OX

arises by occipital, laryngeal, and thyroid radicles, receives tracheal, oesophageal,
and muscular branches, and joins the external jugular near its termination. It is
sometimes absent, but in some cases it appears, on the other hand, to be large
enough to interfere with venesection practised on the external jugular. The
external jugular vein (V. jugularis externa) is very large and corresponds to the
jugular of the horse. It is separated from the carotid artery in the greater part
of its course by the sterno-cephalicus and omo-hyoideus muscles.

The ventral cerebral vein usually does not unite with the occipital ; the latter
is continued by the internal jugular vein.

The ventral longitudinal sinus is represented by a vein. There is an anterior intercavernous
sinus. The transverse sinus is connected with the basilar plexus by a vein which traverses the
condyloid canal. In the sheep there are two ventral occipital sinuses in place of the basilar plexus.

The orbital veins form a network between the periorbita and the muscles of
the eyeball. This plexus communicates with the cavernous sinus and with the
dorsal cerebral vein. It is also drained by the frontal vein, which runs in the
supraorbital canal and groove and joins the angular vein of the eye.

The dorsal nasal vein is usually double.

The superior labial vein usuall}^ joins the infraorbital.

The vena reflexa is absent, and the radicles which are received by it in the horse
go to the internal maxillary vein.

The sublingual vein is very large.

The veins of the thoracic limb differ chiefly in the distal part; the special
features are as follows :

The dorsal digital veins ascend on the front of the digits and are connected
with the other digital veins by transverse branches. They unite near the fetlock
to form the dorsal metacarpal vein. This runs upward on the dorsal face of the
metacarpus and carpus, inclines to the medial surface of the radius, and joins the
cephalic or the accessory cephalic vein.

The volar digital veins are larger than the dorsal veins. They lie on the inter-
digital surfaces of the digits and unite in the interdigital space to form a trunk which
is a satellite of the volar common digital artery. This trunk, the volar common,
digital vein, which is often double, is connected distally by transverse branches
with the lateral and medial digital veins to form the superficial volar arch; it is
continued upward as the satellite of the ulnar artery.

The medial and lateral digital veins lie in front of the corresponding arteries.
They are connected with the volar digital vein by a large branch which passes
between the flexor tendons and the first phalanx. At the distal end of the meta-
carpus each inclines forward and anastomoses with the volar common digital vein
to form the volar venous arch. The medial vein is continued as the medial volar
metacarpal vein along the medial border of the suspensory ligament, and becomes a
satellite of the radial artery in the forearm, while the lateral one is continued on the
volar face of the metacarpal bone by the lateral volar metacarpal vein. The latter
unites at the proximal part of the metacarpus with the middle volar metacarpal
vein, and the trunk thus formed joins the medial vein to form the deep plantar arch.
They unite below the carpus or join the volar common digital vein.

The digital veins arise from the venous plexuses of the corium of the hoof. They form by
anastomotic branches a venous circle at the coronary border of the hoof, which may be termed the
coronary circle. A vein which emerges from the foramen on the proximal part of the interdigital
surface of the third phalanx is the principal radicle of the dorsal digital vein.

The accessory cephalic vein is the upward continuation of the dorsal meta-
carpal vein and is much larger than in the horse.

The posterior vena cava is partially embedded in the medial border of the
liver. Its abdominal part has a thicker wall than in the horse. Its affluents

THE VEINS 721

correspond to the arteries of which they are satelhtes. The renal veins are large
and thick-walled; the}^ run obliquely forward and join the vena cava at an acute
angle. The left one is much the longer.

Two middle sacral veins usually accompany the artery.

The veins of the mammary glands deserve special notice. They converge to
a venous circle at the base of the udder, which is drained chiefly by two pairs of
veins. The subcutaneous abdominal vein (anterior mammary or "milk" vein)
is very large in animals of the dairy breeds, and its course along the ventral wall of
the abdomen is easily followed. It is usually flexuous. It emerges at the anterior
border of the udder abou^^jtwo or three inches (ca. 5-8^cm.) from the lineaalba^
rmisTorward"Xdeviating"a little" outward), dips under tKe cutaneus^ passes^rough_
a foramen in the^abdommai wail about a handbrjadth IromThe median plane7^nd~
"Joins the mternal thoracic_jyein73T^he two veinsare coflnected by a transverse_
^anSstOTnosis at the anterior border of the base oftFe udder, aiKTeach anastomoses

behind with a branchoTthFexterhglp!^^ The^externaTpudic vein (middle

"mammary veirl)~is^so of considerable size. It ascends in the inguinal canal as^a
satellite of the artery and joins the external iliac veinT 'Ihe right and left veins"
are connected at the posterior border of the base of the udder by a large transverse
branch. From the latter^ arises the perineal vein (posterior mammary vein),
which runs mediallv upward and backward to the jperineum, turns around the_
ischialarch, aiid joins"Hie internal pudicjvein. Two veins may present In the
male^ese veins are relatively small.

The deep veins of the thigh and leg resemble those of the horse, but there is
no recurrent til)ial vein.

The saphenous vein is much smaller than in the horse. It may be regarded
chiefly as the upward continuation of the medial tarsal vein, which arises from the
deep plantar arch.

The recurrent tarsal vein^ is large. It is the upward continuation of the dorsal
metatarsal vein and anastomoses with the anterior tibial and saphenous veins. It
arises on the lateral face of the hock, ascends at first in front of the tendo Achillis,
then crosses the latter laterally, passes up between the biceps femoris and semi-
tendinosus, and joins the posterior femoral vein.

There are three chief metatarsal veins. The large dorsal metatarsal vein
arises at the distal part of the metatarsus by the union of the dorsal digital vein
and a large branch from the venous arch above the sesamoids. It ascends super-
ficially between the long and lateral extensor tendons and may be regarded as being
continued in the leg by the recurrent tarsal vein; it also furnishes a large chief
radicle of the anterior tibial vein. The medial plantar metatarsal vein arises from
the venous arch above the fetlock, ascends between the medial border of the sus-
pensory ligament and the plantar surface of the metatarsal bone; it is connected
with the corresponding lateral vein at the proximal end of the metatarsus by a
transverse anastomosis, thus forming the deep plantar arch. From this the per-
forating tarsal vein passes through the vascular canal of the metatarsus and centro-
tarsal (as the perforating tarsal) and joins the anterior tibial vein. The lateral
plantar metatarsal vein pursues a similar course laterally, and is continued by the
lateral tarsal vein, which joins the recurrent tarsal vein above the hock. It passes
superficially over the lateral face of the hock and is continued by the recurrent tarsal
vein.

The digital veins differ from those of the forelimb chiefly in that the dorsal
common vein is large and the plantar absent or small.

The dorsal common digital vein arises at the distal part of the interdigital space by the union
of branches coming from the venous plexuses of each digit. It deviates outward at the fetlock and
joins the lateral digital vein to form the dorsal metatarsal vem. The medial digital vem ascends

1 Also termed the external saphenous vein.
46

722 LYMPHATIC SYSTEM OF THE OX AND SHEEP

along the medial surface of the medial chief digit, turns laterally above the fetlock joint, and is con-
nected with the corresponding lateral vein to form the plantar venous arch. From this the three
chief metatarsal veins ascend and to it come small veins from the rudimentary digits.

The portal vein is formed usuall}^ by the confluence of two radicles, gastric
and mesenteric. It receives the gastro-duodenal vein and veins of the pancreas.
The gastric vein is the largest affluent. It is formed by the junction of two trunks.
One of these, the right ruminal vein, receives the splenic vein. The other is a
short trunk which is formed by the confluence of the left rmninal and omaso-
abomasal veins; it receives the reticular vein. The anterior mesenteric vein is
formed by the confluence of three chief radicles which return the blood from the
entire intestine, with the exception of part of the duodenum and rectum; from
these the blood is conveyed by the gastro-duodenal and internal pudic veins. The
portal tributaries are in general satellites of the corresponding arteries.

LYMPHATIC SYSTEM OF THE OX AND SHEEP

The lymph glands of the ox are in general less numerous but larger than those
of the horse; in some situations a single large gland occurs instead of a group of
small ones, as found in the latter animal.

The thoracic duct arises from the cisterna chyli at the hiatus aorticus. In
some cases it remains single, as is most common in the horse, pursues a similar
course and opens into the origin of the anterior vena cava, or into the left common
jugular vein. But in many cases the duct divides into two branches which lie on
the right and left sides of the dorsal face of the aorta. The two ducts are united
by anastomotic branches and are embedded in fat. They usually unite about the
fifth thoracic vertebra. The terminal part is often ampullate, but the lymphatico-
venous opening is small. When single, the duct is 6-10 mm. in diameter. The
duct may receive efferent vessels from the intercostal, mediastinal, and bronchial
lymph glands.

Many other variations have been described. In the anterior mediastinum there may be
three or even four ducts (with connecting branches), which usually unite just before the lym-
phatico-venous opening, but may open separately.

The cisterna chyU lies in the hiatus aorticus, dorsal to the aorta and venti-al
to the last thoracic and first lumbar vertebrae. It receives the lumbar and intestinal
lymph trunks. It is very variable in form and is commonly about three-fourths
of an inch (1.5-2 cm.) wide.

The intestinal trunk (Truncus intestinalis) is formed at the ventral face of the
posterior vena cava, just behind the dorsal border of the liver. It results from the
union of the common efferent vessels of the gastric and intestinal lymph glands.

The trunk is a centimeter or less in diameter in the adult. It runs backward a short distance,
bends sharply dorsally between the aorta and vena cava, and unites (usually) with the lumbar
trunk to form the cisterna chyli.

The lumbar tnmk (Truncus lumbalis) is formed in the sublumbar region by
the confluence of efferent vessels from the iliac lymph glands. It concurs with the
intestinal trunk in the formation of the cisterna chyli. It receives efferent vessels
of the lumbar and renal lymph glands. The trunk is very variable in regard to
its mode of formation and two may be present.

The mandibular lymph glands are usually two in number, one on each side.
The gland is situated between the sterno-cephalicus muscle and the ventral part of
the mandibular salivary gland, and is usually related dorsally to the external maxil-
lary vein. The gland is oval and is commonly about an inch and a half (ca. 3-4 cm.)

LYMPHATIC SYSTEM OF THE OX AND SHEEP

f23

long and an inch (ca. 2-3 cm.) wide. In some cases a second, smaller gland is
present. Its position is variable; it may be behind or dorsal-medial to the large
gland, or may be on the deep face of the ventral end of the mandibular salivary gland.
Haemolymph glands often occur in this vicinity. The efferent vessels come from
the muzzle, lips, cheeks, hard palate, the anterior part of the turbinates and septum
nasi, the gums (in part) ; the sublingual and parotid glands; the tip of the tongue,
the muscles of the head, except those of the eye, ear, tongue, and hyoid bone; the
mandible, premaxilla, and nasal bone; the skin of the face in part. It also receives
the efferent vessels of the pterygoid lymph gland when present. The efferent
vessels, two to four in number, go to the atlantal gland.

The parotid lymph gland (Lg. parotidea) lies on the posterior part of the mas-
seter muscle and is partly covered by the dorsal end of the parotid salivary gland.
It is related deeply to the internal maxillary and superficial temporal vessels and
the superficial temporal nerve. It is about three inches (ca. 6-8 cm.) long and about
an inch (ca. 2-3 cm.) wide. In some cases there are instead two smaller glands.

Fig. 603. — Superfk
1, Mandibular; 2, parotid; 3, at Ian

LvMPH Glands of Cow Projected on Surface of Body.

4. parapharyngeal; S, anterior cervical: 6, middle cervical; 7, prescapular;

S, prefemoral. (With use of fig. in Ellenberger-Baum, Anat. f. Kiinstler.)

The afferent vessels come from the muzzle, lips, the gums (in part), the anterior
part of the turbinates and septum nasi; the parotid salivary gland; most of the
muscles of the head, including those of the eye and ear; the eyelids, lacrimal gland
and external ear; the frontal, malar, nasal and premaxillary bones and the mandible;
the skin of the head in great part. The efferent vessels, eight to twelve in number,
go to the atlantal gland.

The supraphar5aigeal Ijrmph glands (Lgg. suprapharyngese)^ are usually two
in number, right and left. They are situated about an inch apart, medial to the
great cornu of the hyoid bone, and between the phar\^lx and the ventral straight
muscles of the head (Fig. 386). They average about three inches (ca. 6-8 cm.)
in length. In some cases an additional gland is present. The afferent vessels come
from the tongue, the floor of the mouth, the hard palate, the soft palate, the gums
(in part), the pharynx, the sublingual and mandibular salivary glands; the posterior
^ Also commonly termed the retropharyngeal glands.

724 LYMPHATIC SYSTEM OF THE OX AND SHEEP

part of the nasal cavity, the maxillary and palatine sinuses, and the larynx; and the
rectus capitis ventralis major. The efferent vessels, four to eight in number, con-
cur in forming the tracheal h-mph duct.

A small parapharjoigeal l5rmph gland is usually present on the lateral wall of
the pharjTix, under cover of the mandibular salivary gland or at its posterior border.
It is ventral to the carotid artery and the atlantal gland. Its afferent and efferent
vessels are similar to those of the atlantal gland.

The atlantal l)rmph gland is situated ventral to the wing of the atlas, on the
cleido-mastoideus tendon, and partly under cover of the mandibular salivary gland.
It is related ventrally to the carotid artery. It is usually discoid and an inch and a
half to two inches (ca. 4-5 cm.) in length. One or more small l>Tnph nodes may
occur near the large constant one, and small hsemolymph glands are commonly
present here. The afferent vessels come from the tongue, the salivary glands, the
gums in part; the cervical part of the thymus; most of the hyoid and cervical
muscles. It also receives vessels from the parotid, mandibular, and suprapharjoi-
geal lymph glands. The efferent vessels, three to six in number, concur in forming
the tracheal lymph duct.

The pterygoid lymph gland (Lg. pterygoidea), which is present in the majority
of cases, is situated on the dorsal part of the lateral face of the pterygoid muscle,
close to the maxillary tuberosity. It is usually about half an inch (ca. 1-1.5 cm.)
in length and width, but may be much smaller and escape observation. Its affer-
ent vessels come from the hard palate and adjacent part of the gums. The efferent
vessels, to or three in number, go to the mandibular lymph gland.

The hyoid l5rmph glands (Lgg. hyoidese) occur in about 20 per cent, of cases. The anterior
hyoid gland (Lg. hyoidea oralis) lies on the thyroid cornu of the hyoid bone, at the insertion of the
stylohyoideus muscle. It is about half an inch (ca. 1-1.5 cm.) long. It receives afferent vessels
from the tongue. The efferent vessels, two or three in number, go to the atlantal gland, and may
go in part to the suprapharyngeal gland. The posterior hyoid gland (Lg. hyoidea aboralis) lies
on the dorsal end of the great cornu of the hyoid bone or in the angle between the bone and the
occipito-hyoideus muscle. It receives lymph vessels from the mandible which issue from the
mandibular foramen. The efferent vessels go to the atlantal gland.

The anterior cervical l3rmph glands (Lgg. cervicales craniales) are situated on
the anterior part of the trachea, along the course of the carotid artery. They are
variable in number and size. Four or five may be present. They vary in length
from about half an inch to two inches (ca. 1-2.5 cm.).

The-middle cervical Ijrmph glands (Lgg. cervicales media) lie on each side of
the trachea, in the middle third of the neck. They vary in position, number, and
size. The series may extend to the anterior group, or may reach back almost to
the posterior group. The number appears to vary from one to seven on either side.
Their length ranges from about one-fourth inch to an inch or more (ca. 0.5-3 cm.).
There are usually hsemolymph glands near them.

The posterior cervical lymph glands (Lgg. cervicales caudales) are situated
near the thoracic inlet. One of them lies dorsal to the manubrium sterni and the
cervical muscles attached to it. It is usually about half an inch (ca. 1-1.5 cm.)
long. Three or four others usually occur on either side. Of these, one is ventral
to the brachial vein at the first rib, one or two lie on the brachial vessels here, and
others are dorsal and ventral to the jugular vein. Hsemolymph glands usually are
present in the fat about this group.

The cervical lymph glands receive afferent vessels from the ventral muscles of
the neck, the oesophagus, the larynx, the trachea, the thyroid gland, and the cervical
part of the thymus. The anterior cervical glands receive efferent vessels of the
atlantal gland. The efferent vessels go in general to the tracheal lymph ducts, but
efferents from some of the posterior group may go to the terminal part of the thora-
cic duct or to the common jugular vein.

LYMPHATIC SYSTEM OF THE OX AND SHEEP 725

The costo-cervical l5niiph gland (Lg. costo-cervicalis)i is situated lateral to the
trachea and oesophagus and dorsal to the carotid artery and the vago-sympathetic
trunk. It lies usually just in front of the first rib, under cover of the scalenus
muscle, but it may be partly medial to the first rib. Its length varies from about
half an inch to an inch or more (1.5-3 cm.). Its afferent vessels come from the
muscles of the neck and shoulder, the costal pleura, the trachea, and the intercostal
and anterior mediastinal glands. The efferent vessels on the right side usually go
to the right tracheal duct or join the efferent vessel of the prescapular gland; on the
left they go most often to the end of the thoracic duct, but are very variable.

The tracheal lymph ducts (Ductus tracheales), right and left, are formed
essentially by the confluence of efferent vessels from the atlantal gland. They
usually receive efferent vessels from the cervical, costo-cervical, and prescapular
glands. The ducts pass along each side of the trachea and oesophagus; the right
one usually opens into the right common jugular vein; the left one joins the terminal
part of the thoracic duct or opens into the left common jugular vein.

These ducts are very variable in regard to formation, affluents, and termination. There
may be an accessory tracheal duct, which receives part of the lymph vessels that otherwise go to
the chief duct; this accessory duct runs a variable distance along the neck practically parallel
with the chief duct, and unites with the latter.

A short right lymphatic duct may be formed by the junction with the terminal
part of the right tracheal duct of efferent vessels from the right cervical, costo-cer-
vical, and prescapular lymph glands. It also usually receives an efferent vessel
from the anterior sternal lymph gland.

The prescapular or posterior superficial cervical Ijrmph gland (Lg. cervicalis
superficialis caudalis) is situated at the anterior border of the supraspinatus, a little
above the level of the shoulder joint; it is covered by the omo-transversarius and
brachiocephalicus muscle. It is elongated and may attain a length of four or five
inches (ca. 10-12 cm.) and a width of an inch or more (ca. 3 cm.). Its deep face
has a long and distinct hilus. It receives afferents from the skin of the neck,
shoulder, part of the ventral and lateral surfaces of the thorax, and the thoracic
limb; from the muscles of the shoulder-girdle, and from the external scapular
muscles; from the tendons of the muscles of the forearm and digit and the fascia
of the forearm; from the joints of the carpus and digit. The efferent vessel de-
scends over the scalenus muscle and opens on the right side into the end of the right
tracheal duct, on the left into the terminal part of the thoracic duct or the left
tracheal duct.

In one case Baum found two efferent vessels on the right side: one opened into the end of
the tracheal duct, the other went to a posterior cervical gland.

A chain of small nodes, five to ten in number, extends along the border of the supraspinatus,
dorsal to the prescapular gland, and covered by the trapezius and omo-transversarius. These
nodes, termed by Baum lymphoglandulse cervicales nuchales, are in most cases dark red in color,
and most of them are hsemolymph glands. But some are lymph glands, smce they receive afferent
vessels from adjacent muscles and send efferent vessels to the prescapular lymph gland or to
another gland of the group.

The intercostal lymph glands are situated in the dorsal ends of the intercostal
spaces, on the course of the intercostal vessels, and embedded in fat. Most of them
are small, but some may be nearly an inch (ca. 2 cm.) long. Not all of the spaces
contain glands, and quite exceptionally two may occur in one space. Associated
with them are hsemolymph glands. The afferent vessels come chiefly from the
intercostal and spinal muscles, the serrati, latissimus dorsi, trapezius, subscapularis,
longus colli, obliquus abdominis externus; from the costal pleura and the peri-
toneum; from the thoracic vertebrae and the ribs. The efferent vessels go to the
mediastinal lymph glands.

1 This gland has been included in the posterior cervical group, but forms a connecting link,
as it were, between the cervical and mediastinal glands. Baum has given it the above name and
has shown that it receives lymph vessels from the pleura.

726 LYMPHATIC SYSTEM OF THE OX AND SHEEP

The dorsal mediastinal lymph glands (Lgg. mediastinales dorsales) are situated
on each side of the thoracic aorta, in the fat which levels up the space between that
vessel and the bodies of the vertebrae. On the right side they lie chiefly dorsal to
the thoracic duct, and on the left side they are related to the vena hemiazygos.
They are irregular in arrangement and their length varies from about half an inch
to an inch and a half (ca. 1-3.5 cm.). They are in series with the anterior medias-
tinal glands.

Their afferent vessels come from the same parts as those of the intercostal
glands; also from the diaphragm, the mediastinum, the pericardium, the ribs, and
the intercostal lymph glands. The efferent vessels go chiefly to the thoracic duct
or join the common efferent duct of the posterior mediastinal glands.

The ventral mediastinal Ijmiph glands (Lgg. mediastinales ventrales) are
situated on the transversus thoracis muscle. Several (2-5) occur constantly in
the fat about the apex of the pericardium; they vary in length from about half an
inch to an inch or more (ca. 1-3 cm.). In some cases other glands are present
further forward. The afferent vessels come from the costal and mediastinal
pleura, the diaphragm, the pericardium, and the ribs. The efferent vessels usually
unite to form a trunk which goes to the anterior sternal lymph gland. Hsemolymph
glands may be present in this region.

The anterior mediastinal lymph glands (Lgg. mediastinales craniales) are
situated in part- at the thoracic inlet, in part along the oesophagus, trachea, anterior
vena cava, and brachiocephalic trunk. The former group comprises two to four
glands on either side, ventral to the trachea and oesophagus. Usually the largest
of these, which may be an inch or more (ca. 2-3 cm.) in length, lies along the origin
of the internal thoracic artery. The second group differs somewhat on the two sides.
On the right side there is usually a large gland, which may be two or three inches
(ca. 5-7 cm.) in length; it lies on the oesophagus and is crossed laterally by the
dorsal vein. Behind this there are commonly two or three glands on the oesophagus
or the longus colli, and in front two or three are placed similarly and on the trachea.
On the left side a variable number (2-7) are situated on the oesophagus, trachea,
brachiocephalic trunk, and anterior vena cava; glands may be between the vessels,
or between the vessels and the trachea, and escape superficial examination. Hsemo-
lymph glands are often present in the vicinity of these glands. The afferent vessels
come from the thoracic part of the oesophagus, trachea, and thymus; from the lungs,
pericardium, heart, costal and mediastinal pleura; from the intercostal glands of
the first four spaces and from the gland on the apical bronchus. In some cases these
glands receive also efferent vessels from the anterior sternal, left bronchial, and
other mediastinal glands. The efferent vessels for the most part go to the thoracic
duct, the right tracheal duct, and the costo-cervical glands.

The posterior mediastinal l3rmph glands (Lgg. mediastinales caudales) are
situated along the oesophagus, from the aortic arch backward. The largest of these
may be eight inches (ca. 20 cm.) or more in length; its anterior part is dorsal to the
oesophagus, while posteriorly it lies in the angle between the aorta and the diaphragm
(P'ig. 389). But in some subjects there are two glands in place of this large one; in
these cases the additional posterior one is usually the smaller. Several other glands
of smaller size lie in front of the large one, in the angle between the aorta and the
oesophagus. In front of these there are usually two or three on the right side on the
aorta and the oesophagus.^ The afferent vessels come from the oesophagus, the
lungs, the pericardium, the mediastinum, the diaphragm, the peritoneum, the liver,
and the spleen. The efferent vessels unite to form a common trunk which joins the
thoracic duct.

The diaphragmatic lymph glands (Lgg. diaphragmaticae) are small nodes which
may be present at the foramen venae cavse and the termination of the phrenic
^ These are termed by Baum the middle mediastinal lymph glands.

LYMPHATIC SYSTEM OF THE OX AND SHEEP 727

nerves. The one most often present is at the acute angle between the vena cava
and the chaphragm. The afferent vessels come from the diaphragm and medias-
tinum. The efferent vessels go to the posterior mediastinal glands.

The bronchial Ijnnph glands (Lgg. bronchiales) are situated on the termination
of the trachea and on the bronchi. Commonly three or four are present. One (Lg.
bifurcationis sinistra) constantly occurs on the left side in the angle between the aortic
arch and the left division of the pulmonary artery (Fig. 389) ; it is crossed laterally
by the vena hemiazygos. This gland is about an inch to an inch and a half (ca. 2.5-
3.5 cm.) in length and an inch (ca. 2.5 cm.) in width; it is often very irregular in
shape. A gland (Lg. bifurcationis dextra) is similarly situated on the right side in
the majority of cases. It is smaller than the left gland and appears to be absent
in about 25 per cent, of subjects; in some cases, on the other hand, two glands occur
here. In about half of the cases a small gland (Lg. bifurcationis dorsalis) is situated
above the bifurcation of the trachea. Another gland (Lg. eparterialis) occurs at the
origin of the bronchus of the apical lobe of the lung. Exceptionally a second small
gland is present here. The afferent vessels of these glands come chiefly from the
lungs and the pulmonary lymph glands, the thoracic part of the oesophagus, and the
heart. ^ The efferent vessels of the left gland are quite variable. They may join the
common efferent of the posterior mediastinal glands. Those of the right gland go
to a middle mediastinal gland, those of the dorsal gland go to the right gland, and
those of the apical gland go to anterior mediastinal glands.

The pulmonary lymph glands (Lgg. pulmonales) are inconstant and variable
nodes which may be found on the chief bronchi in the lungs. They appear to be
absent in one-third to one-half of the cases on one side or both. They vary in size
from a fifth to half an inch or more (ca. 0.5-1.5 cm.) in length. The afferent vessels
come from the lungs, and the efferent vessels go to the bronchial and posterior
mediastinal glands.

It is worthy of note that in some cases lymph vessels of the left lung go to glands on the right
(middle mediastinal glands), and lymph vessels of the right Imig go to the left bronchial gland.

The pericardiac l3miph glands (Lgg. pericardiacse) are small and variable nodes
which lie on the pericardium. The left gland is usually present and is situated at
the space between the aortic arch and the vena hemiazygos. In some cases it may
be unusually large — nearly three inches (ca. 7 cm.) in length — and extend back to
the left bronchial gland. Other small glands may be found in this vicinity or lower
down. The right gland is only exceptionally present. It is situated just ventral
to the termination of the posterior vena cava. The afferent vessels come from the
pericardium, and the efferents go to the dorsal mediastinal glands (or their efferents)
or to the left bronchial gland on the left side, to the apical bronchial gland or an
anterior mediastinal gland on the right side.

The sternal lymph glands (Lgg. sternales) are situated along the course of the
internal thoracic vessels. The largest, distinguished as the anterior sternal gland
(Lg. sternalis cranialis), is embedded in the fat in front of the transversus thoracis.
It is about half an inch to an inch (ca. 1.5-2.5 cm.) in length. The other glands are
covered by the transversus thoracis, and vary in size, number, and arrangement.
There is not one at every interchondral space, and, on the other hand, two may occur
at one space. The last of the series is often situated in the angle between the eighth
and ninth costal cartilages and the sterninn and may escape notice." The afferent
vessels come from the diaphragm, the intercostal, deep pectoral, serratus ventralis,
rectus thoracis, and abdominal nmscles; the costal and mediastinal pleura, the

1 Baum notes the curious fact that in many cases in which he injected the lyrnph vessels of
the diaphragmatic lobes the vessels went around the dorsal gland without entering it.

- Attention was recently drawn to this gland by Stroh, who designated it the xiphoid gland.
It is not always present.

728 LYMPHATIC SYSTEM OF THE OX AND SHEEP

pericardium, the peritoneum; the hver; the ribs, costal cartilages, and sternum;
the ventral mediastinal glands. The efferent vessels usually concur in forming
one or two trunks which run forward along the internal thoracic vessels to the
anterior gland. From the latter one or two efferents go to the anterior mediastinal
glands or directly to the end of the right tracheal duct or the thoracic duct (on the
left side).

The axillary l3niiph gland lies on the medial face of the distal part of the teres
major on the course of the vein from the latissimus dorsi. It is oval in outline and
is usually a little more than an inch (ca. 3 cm.) in length. Quite exceptionally two
glands may be present. The efferent vessels come from most of the muscles of the
shoulder and arm, the muscles of the forearm, the trapezius, latissimus dorsi, pec-
toralis profundus, and cutaneus; the fascia of the forearm; the shoulder, elbow, and
carpal joints; the scapula, humerus, radius, ulna, and carpus; the infraspinatus
gland. The efferent vessels (one to three) go to the posterior cervical glands.

The infraspinatus lymph gland (Lg. infraspinata) is a small node which is present in
somewhat less tliaii ;i fourth of tlic^ rases (Baum). It is situated at or near the posterior border of
the infraspinatus, about on a level with the proximal end of the caput longum. It receives lymph
vessels from the latissimus dorsi and sends an efferent vessel to the axillary gland.

The rhomboid lymph gland (Lg. rhomboidea) is small and only present in about 15 per
cent, of subjects (Baumj. It is situated under the rhomboideus cervicalis near its ventral border
and the cervical angle of the scapula. It receives afferents from the rhomboideus, supras-
pinatus, and serratus ventralis, and sends efferents to the costocervical gland.

The lumbar lymph glands (Lgg. lumbales) are situated along the abdominal
aorta and the posterior vena cava, and in some of the spaces between the transverse
processes.^ Some of the glands are dorsal to the vessels. Haemolymph glands also
occur in this region. The afferent vessels come from the spinal, sublumbar, ab-
dominal, and serratus dorsalis muscles; the lumbo-dorsal fascia; the kidneys,
adrenals, and the peritoneum; the lumbar vertebrse. The efferent vessels go to
the lumbar trunk and the cisterna chyli.

The renal l3miph glands (Lgg. renales) belong in reality to the preceding group,
from which they are only conventionally distinguished. They are situated on the
course of the renal vessels and vary in size and number. Their afferent vessels come
from the kidneys and adrenals, and the efferent vessels go mainly to the cisterna
chyli.

The cceliac lymph glands (Lgg. coeliacse) , two to five in number, are situated on
and near the cceliac and anterior mesenteric arteries, and in relation to the left
extremity of the pancreas, the dorsal curvature of the rumen, and the posterior
vena cava. One is a large discoid gland which lies on the cceliac artery and the
origin of the chief branches of that vessel (Fig. 389). It is heart-shaped, marked
by a deep notch, and is about two inches (ca. 5-6 cm.) long and an inch and a half
(ca. 3-4 cm.) wide. Their afferent vessels come from the spleen. The efferent
vessels go to the common efferent vessel of the gastric lymph glands, or to the
intestinal trunk, or to the cisterna chyh.

The internal iliac l5niiph glands are situated in relation to the terminal branches
of the aorta and the radicles of the posterior vena cava. They number commonly
six to eight and vary in length from half an inch to two inches (ca. 1-5 cm.). Their
afferent vessels come chiefly from muscles of the sublumbar region, pelvis, tail, and
thigh; from the genital organs; from the kidneys, bladder, and urethra. They also
receive vessels which are efferents of the external iliac, sacral, ischiatic, deep in-
guinal, prefemoral, and coxal glands. Their efferent vessels go chiefly to the lumbar
trunk.

' Baum distinguishes those about the vessels as lgg. lumbales aorticse, and terms those in
the intertransverse spaces lgg. lumbales propria;, and regards them as corresponding to the dorsal
mediastinal and intercostal glands respectively.

LYMPHATIC SYSTEM OF THE OX AND SHEEP 729

The deep inguinal lymph gland^ is situated ventral to the psoas minor, at the
angle of divergence of the circumflex iliac from the external iliac artery. It is
discoid and is commonly two to three inches (ca. 5-7.5 cm.) in length. A smaller
gland may be present near the large one or at the origin of the prepubic artery. The
afferent vessels come chiefly from the abdominal muscles; the pelvic limb; the
urinary organs, the vesiculae seminales, tunica vaginalis, cremaster muscle; and
the superficial inguinal, external iliac, sacral, prefemoral, and popliteal glands.
The efferent vessels go in part to the internal iliac glands, in part directly to the
lumbar trunk.

The external iliac lymph glands (Lgg. iliacae laterales) number one or two on
each side, and are situated at the bifurcation of the circumflex iliac artery. In the
majority of cases a single gland is found just in front of the origin of the anterior
branch of the artery, but another may lie in the angle between the two branches.
The more constant one is half an inch to an inch (ca. 1.25-2.5 cm.) in diameter.
They may be absent on one side or (quite exceptionally) on both sides. The
afferent vessels come from the abdominal muscles, the gluteus profundus, the tensor
fasciae latae, the fascia lata; the peritoneum of the adjacent region; the pelvic bones.
They also receive vessels from the prefemoral and coxal glands. The efferent ves-
sels go in part to the lumbar trunk, in part to the internal iliac or deep inguinal
glands.

The epigastric Ijrmph gland (Lg. epigastrica) is small and inconstant. It is situated
on the course of the posterior aladommal artery near the pubis. It receives afferent vessels from
the adjacent part of the peritoneum and abdominal muscles, and sends an efferent vessel to the
deep inguinal gland.

The paralumbar lymph glands (Lgg. paralumbales) are small and inconstant
nodes, variable in number, which may be found under the skin of the upper part
of the flank. Their afferent vessels come from the adjacent skin, and the efferents
go in part to the prefemoral gland, in part to the deep inguinal gland. Hsemolymph
glands occur in this region.

The superficial inguinal lymph glands (Lgg. inguinales superficiales) differ in
the two sexes. (1) In the bull they are situated below the prepubic tendon and in
the narrow interfemoral space. They lie in the mass of fat about the neck of the
scrotum and behind the spermatic cord, and are covered (in part) by the retractor
of the prepuce. It is usual to find one or two on each side of the penis, but in ex-
ceptional cases one or two more may be present. A central one above the penis
has been observed, and there may be one further back. The afferent vessels come
from the external genital organs (except the testicles); also from the skin of the
adjacent region, the medial and posterior surface of the thigh, and the medial sur-
face of the leg. The efferent vessels ascend through the inguinal canal to the deep
inguinal gland at the side of the pelvic inlet. (2) In the cow they are usually
termed the supramammary lymph glands (Lgg. supramammaricse) , since they are
situated above the posterior border of the base of the mammary glands.^ Usually
two are present on either side. The larger ones are in apposition medially and are
sometimes united. The smaller glands are above or in front of the large ones.
Exceptionally a third gland may be present or there may be only one on one side.
The large glands are usually two or four inches (ca. 6-10 cm.) long, the smaller
ones a fourth to one-half as large. The afferent vessels come from the udder, the
external genital organs, and part of the skin of the thigh and leg. The efferent
vessels converge to two or three large trunks which go to the deep inguinal glands
at the side of the pelvic inlet.

^ This gland, designated by Chauveau-Lesbre as external iliac, is here named in accorda,nce
with the observations of Baum, who found that it, together with the deep femoral gland, derives
its afferent vessels from substantially the same region as the deep inguinal glands of the horse.

2 When enlarged, they can easily be felt, and when much enlarged, may produce a prominence.

730 LYMPHATIC SYSTEM OF THP] OX AND SHEEP

The efferent vessels run forward on the base of the udder, then incUne outward and pass
through the aponeuroses of the obhque abdominal muscles at the lateral edge of the rectus ab-
flominis, a handbreadth or more in front of the pubis. On reaching the femoral ring they follow
the course of the external iliac vessels to the deep inguinal gland. When the deep femoral gland
on the upper part of the quadriceps femoris is present, some efferents go to it. Baum states that
efferents of one side may go to a supramammary or deep inguinal gland of the opposite side.

The sacral lymph glands (Lgg. sacrales) may be subdivided into two groups.^

(1) The medial sacral lymph glands (Lgg. sacrales mediales) are quite in-
constant. When present, there is a gland on either side on the deep surface of the
sacro-sciatic ligament, in the fat between the ligament and the rectum or the re-
tractor ani. Its afferent vessels come from the pelvic urethra and urethral muscle,
the root of the penis and its muscles, the prostate, the vagina and urethra, and the
coccygeal muscles. The efferent vessels usually go to the internal iliac glands.

(2) The lateral sacral lymph glands (Lgg. sacrales laterales) comprise one or
two inconstant nodes on the upper part of the outer surface of the sacro-sciatic
ligament. One occurs in the majority of cases at the greater sciatic foramen; the
other, which is further back, under the origin of the biceps femoris, is absent on one
side or both in more than half the cases. Their afferent vessels come from the
gluteus profundus, the lumbo-dorsal fascia, the pelvic bones, and the hip joint.
The efferent vessels go to the internal iliac and deep inguinal glands.

The ischiatic lymph glands (Lgg. ischiadicsB) are one or two in number. The
one which appears to be constant lies on the sacro-sciatic ligament, about an inch
(ca. 2-3 cm.) above the lesser sciatic notch, and under cover of the biceps femoris.
It is discoid and is an inch or more (ca. 2.5-3.5 cm.) in diameter. A second gland
occurs in the majority of cases at the medial side of the tuber ischii and the attach-
ment of the sacro-sciatic ligament, covered only by the skin and subcutaneous fat.^
The afferent vessels come from the rectum and anus; the vulva, the root of the
penis, the prostate, the bulbo-urethral glands, the urethra and urethral muscle;
the glutei, biceps femoris, semitendinosus, obturator internus, and gemellus, and
the lumbodorsal fascia; the skin of the hip and tail; the hip joint. They also
receive efferent vessels of the popliteal gland. The efferent vessels go to the internal
iliac glands.^

The gastric Ijonph glands (Lgg. gastricse) are numerous, as might be expected,
and are difficult to group satisfactorily. They comprise the following:

(1) The atrial lymph glands (Lgg. atriales) lie chiefly on the visceral surface
of the atrium, just behind the eardia; commonly three or four are present. Their
afferent vessels come from the atrium, from the adjacent part of the nun en and
reticulum, and from the spleen. They receive efferent vessels of the right and
anterior ruminal, reticular, omasal, and dorsal abomasal, glands. Their efferent
vessels commonly converge to a large trunk, the common efferent vessel (Vas
efferens commune) of the gastric lymph glands. This runs upward and backward
in relation to the coeliac artery and reaches the ventral face of the posterior vena
cava; here it unites with the common efferent vessels of the mesenteric glands to
form the intestinal trunk.

(2) The right ruminal Ijrmph glands (Lgg. ruminales dextrse) lie along the
course of the right ruminal artery. Commonly four or five are present, and they
are half an inch to an inch and a half (ca. 1-3.5 cm.) long. Their afferent vessels
come chiefly from the rumen. They also receive efferent vessels of the other
ruminal glands. The efferent vessels go from the anterior part of the series to the
reticular glands and the common gastric efferent.

^ Baum distinguishes three groups of sacral glands and terms the glands about the termina-
tion of the aorta and the origin of the vena cava as the lgg. sacrales hypogastricse. These have
been included in the internal iliac group of this description.

2 This gland is termed by Baum the Ig. tuberosa.

3 Many variations occur in the arrangement of those efferent vessels. An efferent may go
to a cceliac or mesenteric gland or to the intestinal trunk or cisterna chyli directly.

LYMPHATIC SYSTEM OF THE OX AND SHEEP 731

(3) The left ruminal lymph glands (Lgg. ruminales sinistrse) are inconstant.
One or two may be present in the left groove of the rumen. Their afferent vessels
come from the rumen, and the efferent vessels go to the anterior or the right ruminal
glands.

(4) The anterior ruminal glands (Lgg. ruminales craniales) are deeply situated
in the anterior groove of the rumen. They average four or five in number and about
half an inch (ca. 1.5 cm.) in length. They receive lymph vessels from the rumen
and from the left ruminal glands, and their efferent vessels go to the right ruminal
and atrial glands.

(5) The reticular lymph glands (Lgg. reticulares) are situated on the reticulum
above and below its junction with the omasum. They receive afferent vessels
chiefly from the reticulum and the adjacent parts of the omasum and abomasum.
Their efferent vessels go chiefly to the atrial lymph glands.

(6) The omasal l3nnph glands (Lgg. omasicse) lie on the omasum chiefly along
the course of the dorsal omasal vessels. Their afferent vessels come from the
omasum, and the efferent vessels go chiefly to the atrial lymph glands.

(7) The dorsal abomasal lymph glands (Lgg. abomasicse dorsales) form a series
along the lesser curvature of the abomasum. They receive afferent vessels from
the abomasum, duodenum, and ventral part of the omasum. The efferent vessels
go chiefly in the lesser omentum to the hepatic lymph glands, but some from the
anterior part of the series go to the omasal and reticular glands.

(8) The ventral abomasal l5miph glands (Lgg. abomasicse ventrales) comprise
a few nodes in the fat along the greater curvature of the pyloric part of the abo-
masum or in the omentum an inch or two distant from the abomasum.^ They
receive afferent vessels from the abomasum and the duodenum and their efferent
vessels go to the hepatic lymph glands.

The mesenteric lymph glands (Lgg. mesentericae) comprise a large number of
nodes which receive lymph from the intestine. The following groups may be
recognized, although the distinction is in part conventional.

(1) The duodenal Ijmiph glands (Lgg. duodenales) are small nodes in the
anterior part of the mesoduodenum. They receive afferent vessels from the duo-
denum and their efferent vessels go to the hepatic lymph glands.

(2) The jejuno-ileal lymph gland (Lgg. jejuno-ileales) lie in the part of the
mesentery to which the coils of the jejuno-ileum are attached. They vary in
number from ten to fifty, and in length from about a quarter of an inch to four feet
(ca. 0.5-120 cm.). As a rule, the long narrow glands are in the peripheral part of the
mesentery, while numerous small nodes are scattered throughout the mesentery
and extend centrally to the coils of the colon. Their afferent vessels come from the
mesenteric part of the small intestine. The efferent vessels converge to form a
large common efferent vessel. This receives efferent vessels of the csecal and colic
lymph glands, runs upward and forward on the right side of the spiral mass of the
colon, and reaches the ventral face of the posterior vena cava just behind the an-
terior mesenteric artery; here it unites with the common efferent vessel of the
gastric lymph glands to form the intestinal trunk.

(3) The caecal l5anph glands (Lgg. csecales) , usually not more than two or three
in number, are situated along the attached surface of the caecum. Their efferent
vessels come from the caecum and ileum. The efferent vessels go to colic or ileal
glands or to the common efferent ves.sel.

(4) The colic l3rmph glands (Lgg. colicae) are situated in part superficially on
the right side of the spiral mass of the colon, in part deeply between the coils. One
or two are constantly present on the initial part of the colon, near the termination
of the ileum. The afferent vessels come from the colon chiefly, but some of the

1 These glands are often difficult to find in the large mass of fat in which they are usually
embedded; they are not always present.

732 LYMPHATIC SYSTEM OF THE OX AND SHEEP

glands receive vessels from the ileum and csecum and their lymph glands. The
efferent vessels go to the common intestinal efferent or to other colic glands.

(5) The rectal l5rmph glands (Lgg. rectales) are situated along the dorsal and
lateral surfaces of the rectum. They receive afferent vessels from the rectum,
anus, and terminal part of the colon. Most of the efferent vessels go to other
glands of the group, but some unite to form one or two large trunks which end in the
internal iliac lymph glands. There are many small hsemolymph glands in relation
to the rectal lymph glands.

(6) The pancreatico-intestinal lymph glands (Lgg. pancreatico-intestinales)
lie on the ventral surface of the pancreas and along the right part of the latter in
relation to the duodenum. Some are at the pancreatic notch about the portal vein
and its affluents, and others are covered by the adhesion of the colon to the gland.
Their afferent vessels come from the pancreas, the duodenum, and the adjacent
part of the colon. The efferent vessels go to the common intestinal efferent.

Fig. 604. — Ixtestine of Ox, Spread Odt.
Ca, Caecum; C, colon; D, duodenum; II, ileum; J, jejunum; R, rectum; m, mesenteric lymph glands. (After

Edelmann.)

(7) The hepatic Ijrmph glands (Lgg. hepaticse) are situated in and ventral to
the portal fissure. Most of them are grouped about the portal vein, the hepatic
artery, and the bile duct, and are covered by the pancreas; but some are ventral
to the pancreas. Their average number is ten to fifteen, but twenty or more have
been counted. Their length varies from less than half an inch to three inches (ca.
1-7 cm.). They receive vessels from the liver, pancreas, and duodenum, and from
the abomasal lymph glands. Their efferent vessels converge to a large trunk
which passes along the portal vein and joins the common efferent vessel of the
intestinal glands or that of the gastric glands.

The prefemoral or subiliac lymph gland ^ is situated on the aponeurosis of the

obliquus abdominis externus, at the anterior border of the tensor fasciae latse and

about a handbreadth above the patella. It has an elongated elliptical outline

and is flattened. Its average length is three or four inches (ca. 8-10 cm.), and its

^ This is also termed the precrural or suprapatellar gland.

LYMPHATIC SYSTEM OF THE OX AND SHEEP 733

width about an inch (ca. 2.5 cm.) in the adult, but it may be considerably larger.
In some cases a second small gland is present above or below the large one. It
receives afferent vessels from the skin of the posterior part of the thorax, the ab-
domen, pelvis, thigh, and leg; also from the tensor fasciae latae and the prepuce.
The efferent vessels ascend on the deep face of the tensor fasciae latae and end
chiefly in the deep inguinal gland, but in some cases some go to the iliac glands.

The popliteal lymph gland (I.g. poplitea) is situated in a mass of fat on the
gastrocnemius muscle, behind the tibial and peroneal nerves and between the biceps
femoris and semitendinosus. Its average length is about an inch and a half (ca.
3-4 cm.) and its width about an inch (ca. 2-3 cm.). The gland receives afferent
vessels from the lateral and posterior part of the leg and from the distal part of the
limb; vessels from the biceps femoris and semitendinosus also go to it. The
efferent vessels go chiefly to the deep inguinal gland, but some end in the ischiatic
or internal iliac glands.

The coxal lymph gland (Lg. coxalis) is situated in front of the proximal part of
the quadriceps femoris, under cover of the tensor fasciae latae. It is present in the
majority of subjects on one side or both and may be an inch or more (ca. 2.5-3 cm.)
in length. It receives vessels from the quadriceps femoris, tensor fasciae latae,
fascia lata, and the prefemoral gland. The efferent vessels go to the iliac or the
deep inguinal glands.

One or two lymph glands are commonly present on the superficial face of the
tensor fasciae latae, an inch or two from the anterior border of the muscle and five
or six inches from the tuber coxae. They are often partially embedded in the muscle,
and are usually small, but may be almost an inch (ca. 2 cm.) long. Haemolymph
glands may be found here and in some cases appear to take the place of the l^rniph
gland. The afferent vessels come from the skin of the hip and the efferent vessels
go to the prefemoral or deep inguinal gland.

The Ijrmph glands of the sheep resemble in general those of the ox, but a few
special features may be noted. Homolymph glands are numerous, especially along
the course of the aorta; they are dark red or black and hence are easily seen, in
spite of their small size, in the fat in which they are chiefly embedded.

The mandibular lymph glands are usually two in number on each side, and are
situated behind the angle of the jaw on the course of the external maxillary vein.
The larger one is flattened and kidney shaped and may be nearly an inch (ca. 2 cm.)
long.

The parotid l3rmph gland lies on the posterior border of the masseter muscle,
about midway between the mandibular joint and the angle of the jaw. It is
related to and commonly partly covered by the anterior border of the parotid
salivary gland. It is flattened and has a deep notch posteriorly. It is usually a
little less than an inch (ca. 2 cm.) long.

The suprapharyngeal lymph glands, two in number, have an elongated oval
outline. They are situated on the dorsal wall of the pharynx, a quarter of an inch
or less (ca. 0.5 cm.) apart. They are related laterally to the dorsal end of the great
cornu of the hyoid bone, and dorsally to the ventral straight muscles of the head.
They are about an inch (ca. 2-3 cm.) long, and half as wide.

The atlantal l3rmph gland is related to the ventral part of the paramastoid
process and is dorsal to the carotid artery. It is discoid, oval in outhne, and about
half an inch (ca. 1.5 cm.) long. Commonly there is a small node behind the at-
lantal gland and one or more haemoljnnph glands occur here.

The sternal l3miph gland, which overlies the first segment of the sternum, is
about the size of a hazel nut.

The mesenteric lymph glands consist chiefly of long narrow elongated masses
instead of isolated small nodes.

The prefemoral Ijntnph gland is in front of the anterior border of the tensor

734

CIRCULATORY SYSTEM OF THE PIG

fasciae latae, about midAvay between the tuber coxae and the patella. It is kidney-
shaped and is a little more than an inch (ca. 3 cm.) long and nearly an inch (ca.
2 cm.) wide.

The superficial inguinal or mammary lymph glands are usually two in numl^er
on each side. The larger one is kidney-shaped; it may be an inch and a half (ca.
3.5 cm.) long and about half as wide. The smaller gland is oval and usually about
half an inch (ca. 1 cm.) in length.

CIRCULATORY SYSTEM OF THE PIG
THE HEART

The pericardium is attached to the sternum from a point opposite to the third
rib as far as the xiphoid cartilage, and also to the sternal part of the diaphragm.

Vena hemiazygos

Aorta

Left brachial artery

Pulmonary artery
Brachinci pJidlic
rtn-ij

:=■ Pulmonary veins

Posterior vena
cava,

Anterior vena
cava
Right auricle

Right ventricle

Fig. 605.— Heart of Pig; Left View.
1, Conus arteriosu.s; 2, great cardiac vein in left longitudinal groove; 3, cardiac vein in intermediate groove; 4, apex.

It has extensive contact with the chest wall from the second intercostal space to the
fifth rib.

THE HEART

735

The heart is small in proportion to the body-weight, especially in fat animals.
Its weight in a large adult is usually less than a pound. It is broad, short, and blunt.
When hardened in situ it is compressed dorso-ventrally. The ventral or sterno-
costal surface (Facies sternocostalis) is only moderately convex; it overlies the
sternum from the second sternebra to the anterior part of the last one. The left
longitudinal groove is on its left part, and is almost parallel with the left border.
The dorsal or diaphragmatic surface is more convex. The right longitudinal groove
runs obliquely across this surface; it begins below the end of the posterior vena
cava and extends to the left border. There is often an intermediate groove on the
left border; it may extend to the apex, but it is frequently small and is sometimes

Vena hemiazygos
Pulmonary artery
Left auricle

Right atrium

I'i'AMiy I

Left veiitricle

^^Ml Right ventricle

Fig. 606. — ^Heart of Pig, Diaphragmatic Surface.

1-5, Pulmonary veins; 6, left pulmonary artery; 7, 8, branches of right pulmonary artery; 9, vena azygos; 10,

fat in coronary groove; 11, vessels and fat in right longitudinal groove; 12, apex.

absent. The apex is blunt and is almost median; it overlies the anterior part of
the last sternebra, and is about a quarter of an inch (ca. 5-6 mm.) from the sternal
part of the diaphragm. When the ventricles are dilated, there is a notch at the apex
(Incisura apicis cordis) . The lower border of the left auricle is marked by several
notches and is situated at a lower level than the right one.

In the right atrium the large orifice of the vena hemiazygos is seen below that of the posterior
vena cava; the two are separated by a valvular fold with a concave free edge. The intervenous
crest is broad and rounded, not prominent, as in the horse. The musculi pectinati radiate from
a distinct crista terminalis and form a highly developed network in the auricle. The fossa
ovalis is extensive. There is a large moderator band in the right ventricle.

736 CIRCULATORY SYSTEM OF THE PIG

The Arteries

The pulmonary vessels present no remarkable features.

The aorta resembles that of the horse and ox in its course and relations, but the
arch is much more strongly curved. There is no common brachiocephalic trunk.

The brachiocephalic artery arises first from the aortic arch and passes forward
below the trachea to the first rib. Here it gives off the common carotid arteries,
separately or by a very short bicarotid trunk, and is continued around the first rib
as the right brachial artery.

The left brachial artery arises from the aortic arch just above the brachio-
cephalic. It curves forward and downward and turns around the anterior border
of the first rib.

The branches given off by the brachial arteries are as follows :

There is usually a common trunk for the dorsal, deep cervical, and vertebral
arteries. This trunk or the dorsal artery gives off the subcostal artery, which sup-
plies usually the third, fourth, and fifth intercostal arteries. The second inter-
costal artery arises separately. The dorsal artery emerges through the dorsal end
of the second intercostal space and divides into dorsal and cervical branches ; the
dorsal branch passes upward and backward and ramifies in the deep muscles of the
anterior part of the back ; the cervical branch passes deeply to the atlantal region,
where it anastomoses with the occipital artery. The deep cervical artery is a
much smaller vessel, which emerges through the first intercostal space; it gives off
the first intercostal artery, passes upward and forward deeply, and ramifies chiefly
in the complexus and muhifidus. The vertebral artery resembles that of the horse.

The inferior cervical artery is large ; its ascending branch gives off the posterior
thyroid artery and parotid branches.

The internal and external thoracic arteries give branches to the pectoral
mammary glands; the external artery may be absent.

The common carotid arteries arise from the brachiocephalic close together or
by a very short common trunk; they are accompanied by an internal jugular vein
of considerable size, and their collaterals are similar to those of the horse. They
terminate in occipital and internal and external carotid divisions.

The occipital artery resembles that of the horse.

The internal carotid artery usually arises by a common trunk with the occipital.
After giving off a large meningeal branch which enters the cranium through the
mastoid foramen, it passes through the foramen lacerum and forms with the oppo-
site artery a rete mirabile which resembles that of the ox, but is smaller; it is not
connected with the vertebral and condyloid arteries, but the meningeal branch just
mentioned and the middle meningeal artery concur in its formation.

The external carotid artery has the same course and termination as in the horse.
Its collateral branches present the following special features: (1) The lingual
artery is relatively large and supplies the pharyngeal artery, the sublingual artery,
muscular branches, and branches to the soft palate, mandibular gland, and larynx.
(2) The external maxillary artery is represented by a small vessel which ends in the
masseter muscle; it gives branches to the pterygoideus medialis, the parotid and
mandibular glands, and the mandibular lymph glands, the masseter and the cuta-
neus. It does not extend upon the lateral surface of the face. (3) The posterior
auricular artery is long and relatively large ; it ascends along the anterior border of
the paramastoid process and ramifies on the convex surface of the external ear. It
gives off the posterior meningeal artery, which enters the cranial cavity through the
mastoid foramen.

The internal maxillary artery pursues a flexuous course between the ramus of
the mandible and the pterygoid muscles to the maxillary recess and divides into
infraorbital and palatine branches. Its branches offer the following special features:

THE ARTERIES 737

(1) The inferior alveolar artery is large; branches from it emerge through four or
five mental foramina and take the place of the inferior labial. (2) The middle
meningeal artery enters the cranial cavity through the foramen ovale and concurs
in the formation of the rete mirabile. (3) The buccinator artery is large and partly
compensates for the lack of a facial artery. It ramifies in the cheek and its fine
terminal branches extend to the lips. (4) The large infraorbital artery extends to
the snout and replaces the superior labial largely and the lateral nasal in part. The
malar branch compensates largely for the absence of the lateral and dorsal nasal
arteries. (5) The palatine artery is small.

The superficial temporal artery ascends behind the temporo-mandibular
articulation and ramifies in the temporalis muscle; it is small and may be absent.
In the latter case the anterior auricular and transverse facial arteries arise separately
from the external carotid artery, which is directly continued by the internal maxil-
lary artery.

The intercostal arteries number usually fourteen or fifteen on either side; of
these ten to twelve arise from the aorta, usually by short common trunks. Fre-
quently an intercostal artery is given off from that of an adjacent space.

The bronchial and oesophageal arteries usually arise separately.

The ccehac artery is half an inch to an inch long. It supplies a branch to the
left crus of the diaphragm, and divides into two primary branches, gastro-hepatic
and splenic. The gastro-hepatic artery is the larger. It gives off pancreatic
branches, the anterior gastric artery, branches to the lesser curvature of the stomach,
pyloric, and gastro-duodenal arteries. The latter divides into pancreatico-duo-
denal and right gastro-epiploic. The anterior gastric usually supplies the oesopha-
geal artery. The continuing trunk (A. hepatica propria) gives off a cystic branch
and divides in the portal fissure into three or four branches which ramify in the
liver. The splenic artery gives off the posterior gastric (usually), a branch to the
stomach above the cardia (A. diverticuli), twigs to the pancreas, short gastric
arteries to the left part of the great curvature, and splenic branches, and is con-
tinued as the left gastro-epiploic artery.

The posterior gastric may arise from the gastro-hepatic or in the angle of divergence of the
two primary divisions of the coeliac. The oesophageal branch may come from the posterior gas-
tric or the splenic. Other variations occur.

The anterior mesenteric artery arises an inch or more behind the coeliac and
is long, like that of the ox. It gives twigs to the pancreas and is continued in the
mesentery as the artery of the small intestine or tnincus intestinalis. This gives off
about a dozen branches which form a series of arches along the mesenteric lymph
glands. From these is formed a rich network which gives off innumerable fine
branches placed close together. The ileo-caeco-colic artery gives off ileal and caecal
arteries, and enters the axis of the spiral coil of the colon. Here it pursues a spiral
course and gives off branches which form remarkable plexuses; from the latter
numerous fine branches go to the centripetal coils. A short trunk gives origin to
right and middle colic branches. The right colic artery is arranged hke the colic
branch of the ileo-cseco-colic artery, with which it anastomoses at the apex of the
coil; it supplies the centrifugal parts of the coil. The middle colic artery goes to
the colon as it emerges from the coil and anastomoses with the posterior mesenteric
artery.

A phrenico-abdominal artery arises on either side a little in front of the renal
arteries. It divides into branches which go to the costal part of the diaphragm
and the abdominal muscles.

The renal and spermatic arteries present no special characters.

The posterior mesenteric artery arises near the termination of the aorta. It
is small and is distributed like that of the ox.
47

738

CIRCULATORY SYSTEM OF THE PIG

Six pairs of lumbar arteries arise from the aorta. The seventh comes from
the middle sacral.

The terminal branches of the aorta resemble those of the ox.

The arteries of the shoulder, arm, and forearm resemble in general those of
the ox.

The brachial artery is continued over the medial surface of the elbow by the
median artery. The latter divides near the middle of the forearm into radial and
ulnar arteries.

The radial artery is the smaller of the two terminal branches of the median.
It descends along the medial border of the radius and divides at the proximal end

Fig. 607. — Arteries of Dir»TAL Part of Right Fore
Limb of Pig; Dorsal View.
a. Terminal part of volar interosseous artery; 6,
dorsal interosseous artery; c, rete carpi dorsale; d, dorsal
metacarpal arteries; e, dorsal common digital arteries;
/, dorsal proper digital arteries.

Fig. 608. — Arteries of Distal Part of Right Fore
Limb of Pig; Volar View.
g. Ulnar artery; h, superficial branch of radial
artery; ;, collateral ulnar artery/ j, volar interosseous ar-
tery; h, deep branch of radial artery; k, deep volar meta-
carpal arteries; /, superficial volar metacarpal arteries;
m, volar common digital artery; n, volar proper digital
arteries.

of the metacarpus into two branches. The superficial branch descends in the space
between the second and third metacarpal bones and unites with the ulnar artery
or with the lateral superficial volar metacarpal artery to form the superficial volar
arch. The deep branch joins the volar interosseous artery at the proximal end of
the metacarpus to form the deep volar arch. There is also a communicating branch
between the radial and ulnar arteries at the carpus.

The ulnar artery descends along the medial side of the deep digital flexor and
connects with the superficial branch of the radial artery to form the superficial
volar arch.

THE ARTERIES

739

The main facts as to the metacarpal and digital arteries are as follows: The
rete carpi dorsale is formed essentially by the terminals of the interosseous artery
of the forearm. It gives rise to three dorsal metacarpal arteries, which descend in
the corresponding interosseous spaces and unite with branches of the volar meta-
carpals to form three common digital arteries. Each of these divides into two
proper digital arteries, which descend along the interdigital surfaces of the digits.
From the superficial and deep volar arches described above there arise three super-
ficial and three deep volar metacarpal arteries. The deep arteries unite near the
distal end of the space between the principal metacarpal bones to form a stem
which unites with the middle (third) superficial artery. The superficial arteries

Fig. 609. — Arteries of Distal Part of Right Hind
Limb of Pig; Dorsal View.
a. Anterior tibial artery, continued on tarsus as the
dorsalis pedis; 6, perforating tarsal artery; c, dorsal
metatarsal arteries; d, common digital arteries; e,
proper digital arteries.

Fig. 610. — Arteries of Distal Part of Right Hixd
Limb of Pig; Plantar View.
/, Saphenous artery, continued as medial tarsal
artery; g, lateral tarsal artery; h, medial plantar artery,
h', lateral plantar artery; i, perforating tarsal artery;
J, deep plantar metatarsal arteries; k, common digital
artery; /, proper digital arteries.

unite to form an arch from which proper digital arteries are given off to the axial
aspect of the small digits, and a common digital which supplies two volar proper
digital arteries to each of the chief digits.

The arteries of the hip, thigh, and leg are arranged much as in the ox. A few
special features may be noted.

The ilio-ltmibar artery gives off a branch to the quadriceps femoris and lateral
muscles of the thigh, and ramifies in the abdominal muscles. It may also supply
the posterior abdominal artery, which otherwise arises from the deep femoral.

The deep femoral artery is given off above the level of the pubis. It is large
and compensates for the absence of the obturator artery. The posterior abdominal

740 CIRCULATORY SYSTEM OF THE PIG

and external pudic arteries may arise from it by a short common trunk or separately.
The external pudic gives branches to the prepuce and preputial bursa but not to
the penis. In the female it supplies the inguinal and abdominal mammary glands
and anastomoses with the external thoracic artery. The popliteal artery gives off
the peroneal.

The femoral artery gives off a short trunk which divides into anterior femoral
and lateral circumflex arteries, the latter being much the larger.

The saphenous artery is large. It descends as in the ox on the medial surface
of the leg and divides near the hock into lateral and medial tarsal arteries. The
latter is the real continuation of the saphenous; it divides into medial and lateral
plantar arteries, which concur with the perforating tarsal artery in forming the
proximal plantar arch.

The posterior tibial artery is small, being replaced distally by the saphenous.
It gives branches to the muscles on the posterior face of the tibia and supplies the
nutrient artery of that bone.

The anterior tibial artery is continued as the dorsalis pedis on the dorsal sur-
face of the tarsus. This gives off the perforating tarsal artery, which passes back
through the vascular canal of the tarsus and unites with the plantar arteries to
form the proximal plantar arch.

The metatarsal and digital arteries resemble in arrangement the corresponding
vessels of the limb.

The Veins

The veins resemble in general those of the ox. Thus there is a hemiazygos
vein and two jugular veins, the internal one being relatively larger than in the ox.
A few differential features may be noted.

The buccinator vein resembles that of the horse, and unites with the vena
refiexa to form a short common trunk which joins the external maxillary vein.

The external maxillary vein resembles in general that of the horse. The dorsal
nasal vein is large, receives the veins from the snout, runs backward in the groove
of the nasal bone, and joins the frontal vein; it is connected with its fellow by a
transverse branch, and anastomoses freely with the malar and facial veins.

The veins of the distal parts of the limbs naturally present differences which
are correlated with those of the arteries.

The Lymphatic System

The thoracic duct often divides near its termination into two branches which
unite to form an ampulla. The latter suddenly contracts and opens into the termi-
nal part of the left jugular vein. The lymph glands of animals in good condition
are almost all embedded in fat.

The mandibular lymph glands are situated in the space between the omo-
hyoid and medial pterygoid muscles, in relation to the lower part of the anterior
border of the mandibular salivary gland. There are commonly two on each side,
one large, the other small.

The parotid lymph glands (Fig. 415) are reddish-brown in color. There are
usually four of considerable size and several smaller ones on either side. One is
situated at the upper part of the posterior border of the masseter, partly covered
by the parotid salivary gland. A large subparotid gland lies below the base of the
ear on the terminal part of the brachiocephalicus muscle. Ventral to this are two
smaller glands, one above and one below the external maxillary vein.

The supraphar3mgeal lymph glands (Fig. 416) are situated on the dorsal wall
of the pharynx, dorsal to the external carotid artery and below and behind the
paramastoid process. There are usually two of considerable size on either side.

THE LYMPHATIC SYSTEM

741

They are related deeply to the rectus capitis ventralis major and are covered by the
cleido-mastoideus.

The middle cervical lymph glands form a group on the brachiocephalicus
on the course of the external jugular vein. Other small nodes are present in the
fat around the trachea.

The prescapular lymph glands are situated at the anterior border of the an-
terior deep pectoral muscle, under cover of the trapezius and omo-transversarius.

The posterior cervical or prepectoral lymph glands are reddish in color and
usually three in number. The largest is placed centrally under the trachea; the
others are situated on the brachial vessels as thev turn around the first rib.

Jig. 611. — Stomach and Part of Intestine of Pig, Spread Odt.

o, Pyloric part of stomach- 6, duodenum; c, jejunum; d, cacum; e, /, colon; g, pancreas; h, epiploic foramen;

I, portal vein; A:, hepatic lymph glands; i, gastric lymph glands; m, oesophagus. (After Edelmann.j

The axillary lymph glands are usually absent, but very small nodes may be
found near the insertion of the latissimus dorsi. Cubital glands are not present.

The thoracic lymph glands comprise the following:

(1) A sternal lymph gland of relatively large size lies on the first segment cf the
sternum. (2) The mediastinal l5miph glands include: a number of small reddish
nodes in the fat along the dorsal surface of the aorta; a gland on the left side of the
trachea in front of the aortic arch ; a gland on the aorta where it is crossed by the
vena hemiazygos; two or three glands in the posterior mediastinum along ohe
ventral surface of the aorta; several glands along the ventral surface of the trachea.
(3) The bronchial lymph glands include one on the bifurcation of the trachea and
another at the apical bronchus of the right lung.

742 CIRCULATORY SYSTEM OF THE DOG

The lumbar lymph glands are scattered along the abdominal aorta and the vena
cava. Those placed near the hilus of the kidney are often designated renal.

The internal iliac lymph glands are rounded and relatively large. They
comprise: (1) Three or four glands situated on and between the origin of the cir-
cumflex iliac and the external and internal iliac arteries; (2) a gland in the angle
of divergence of the internal iliac arteries; (3) several glands along the course of
the external iliac artery, the most ventral of which is usually the largest, and might
be regarded as a deep inguinal gland.

The external iliac lymph glands are small, three or four in number, and lie in
front of the circumflex iliac vessels.

The visceral lymph glands of the abdomen comprise the following:

1. The gastric lymph glands are situated on the lesser curvature of the stomach,
covered by the pancreas in situ. They are commonly five or six in number and are
in series with the hepatic glands.

2. Several hepatic lymph glands (Fig. 429) are present about the portal vein
at the portal fissure. The largest ones are about an inch (ca. 2-3 cm.) long.

3. A long splenic lymph gland lies on the splenic vessels near the dorsal end
of the spleen.

4. The mesenteric lymph glands are situated along the anastomotic arches
formed by the vessels of the small intestine.

5. Several caecal lymph glands are situated along the first part of the csecal
vessels.

6. Two series of colic lymph glands accompany the arteries of the spiral part of
the colon, and are exposed by separating the coils of the bowel. Small glands are
placed in the colic mesentery and above the rectum.

7. The anal lymph glands are situated on either side on the retractor ani.

A small ischiatic lymph gland is found on the sacro-sciatic ligament near the
lesser sciatic notch.

The prefemoral lymph gland is situated on the aponeurosis of the external
oblique muscle at the anterior border of the tensor fasciae latae, and a little above the
middle of the thigh. It has an elongated oval outline, and in the adult may be
about two inches (ca. 5 cm.) long, and nearly an inch (ca. 2 cm.) wide. It is em-
bedded in fat.

The superficial inguinal lymph glands form an extensive group, which may be
five inches or more (ca. 10-12 cm.) in length. The middle part of the group is at
the external inguinal ring, and the series extends back on the upper part of the
gracilis and forward and outward on the aponeurosis of the obliquus abdominis
externus. They number about a dozen; the largest are about an inch (ca. 2-3 cm.)
long, and the others about the size of a pea.

The popliteal lymph glands are small normally and may escape notice. They
are more superficially placed than in the other animals, and are in part in contact
with the skin.

A few small tarsal glands occur in front of the distal part of the tendo Achillis.
The occurrence of a gland in the subcutaneous fat about a handbreadth above the
tuber calcis has been noted by Hartenstein; it varies from the size of a pea to that
of a hazel nut.

CIRCULATORY SYSTEM OF THE DOG
Tpie Pericardium and Heart

The pericardium is attached to the sternal part of the diaphragm by a fibrous
band, the pericardiaco-phrenic ligament (Lig. pericardiaco-phrenicum). and is con-
nected with the sternum only by the mediastinal pleura.

THE PERICARDIUM AND HEART 743

The area of contact of the pericardium with the chest wall is chiefly ventral, and is best seen
with the subject on its back. In this position (after removal of the intercostal and rectus thoracis
muscles), the area is seen to be almost triangular. The anterior border of the triangle (formed by
the apical lobe of the right lung) is at the right fourth costal cartilage and extends across the median
plane, ending at the third interchondral space near the costo-chondral junction. The right border
extends from the sternal end of the fourth rib to the eighth chondro- sternal joint. The left border
begins at the left end of the anterior border, crosses the fourth cartilage nearly an inch from its
jimction with the rib and the fifth and sixth chondro-costal junctions.

The heart differs greatly in form and position from that of the larger animals.
In diastole it is ovoid and the apex is blunt and rounded. Its long axis is very-
oblique. Thus the base faces chiefly toward the thoracic inlet and is opposite to
the ventral part of the third rib. The apex is on the left side at the sixth inter-
chondral space or seventh costal cartilage, and in close relation to the sternal part
of the diaphragm. The sterno-costal surface corresponds largely to the floor of
the thorax from the fifth chondro-sternal joint backward. It is crossed obliquely

Aorta

^^ Lieji piu-

Pulmonary veins

Left brachial ■^//fn^mmt^^ m^^B^^^-^^S T^BH^^^^ Posterior vena cava

artery

Brachiocephalic "
artery
Anterior vena -
cava

Right auricle

Pulmonary artery ""^^UF ■^^ 7^^^!*^^"**^ '^ ^ \'^^^l^^^,^ Left ventricle

Conns arteriosus

Right ventricle .

Apex

Fig. 612. — Heart of Dog; Left View.
1, Pulmonary veins; 3, left auricle; 3, vessels and fat in coronary groove; 4, vessels and fat in left or ventral longitu-
dinal groove; 5, vessels and fat in intermediate groove.

by the left (or ventral) longitudinal groove, which begins behind the origin of the
pulmonary artery, and joins the right (or dorsal) groove at the right border, thus
forming a notch not far from the apex. The diaphragmatic surface is less ex-
tensive and less convex. On it is the right (or dorsal) longitudinal groove, which
begins at the coronary groove just behind the termination of the posterior vena
cava and joins the left (or ventral) groove to the right of the apex. There is fre-
quently an intermediate groove between these on the left ventricle, which extends
a variable distance toward the apex. The weight of the heart of a dog of medium
size is five to six ounces, and is about 1 per cent, of the body weight.

The relative weight is subject to wide variation. It is large in hunting dogs and such as are
trained for speed or worked. In fat dogs of sedentary habit it may be only about 0.5 per cent.

The fossa ovalis is very shallow and is bounded in front by the intervenous crest. The musculi
pectinati form a rich network in the right auricle. The tricuspid valve has two chief cusps and
three or four small ones. There are four musculi papillares in the right ventricle, all of which
spring from the septal wall. They diminish in size from before backward, the anterior ones being
long and cylindrical. Their bases are connected with the lateral wall by trabecular camese. Usu-

744

CIRCULATORY SYSTEM OF THE DOG

alh' sLx pulmonary veins open into the left atrium. The bicuspid valve consists of two large cusps
and four or five small ones. There are two musculi papillares in the left ventricle, both of which
arise from the lateral wall; they are much larger than those of the right ventricle.

The Arteries

The two coronary arteries usually spring separately from the origin of the aorta,
but may arise by a common trunk. Each divides into circumflex and descending
branches. The left artery is twice as large as the right one; it commonly gives off
a branch of considerable size which runs in the intermediate groove.

Fig. 61.3. — Vessels, Nerves, Etc., op Thorax of Dog; Right View.
i, First rib (stump) ; ^, sceruum; ^^ mauuDnum sterni; .2", xipnoid cartilage; 3, trachea; .^.oesophagus; 6-8,
ventral branches of tilth to eigntn cervical nerves; 9, ventral branch ot hrst thoracic nerve; 10, Iff , muscular and ten-
dinous parts of diaphragm; 11, 11', left ventricle and atrium of heart; 12, 12' , right ventricle and auricle of heart; IS,
coronary groove; H, right coronary artery; 15, middle cardiac vein; 16, pulmonary veins; 17, aorta; 18, thoracic
duct; i5, anterior vena cava; ;20, posterior vena cava; ;2i, dorsal intercostal vessels; ;2^, intercostal nerve; i^3, inferior
cervical (or omo-cervical) artery; ^4. external thoracic artery; 25, brachial vessels; 26, common jugular vein; 27, in-
ternal thoracic vessels; 28, sternal branches of internal thoracic vessels; 29, mediastinal arteries; 30, musculo-phrenic
artery; SI, anterior abdominal artery; S2, m. iongus colU; 3S, anterior mediastinal lymph glands; 3^, sternal lymph
glands; a, a', right brachial artery and vein; b, common carotid artery; c, deep cervical vessels; d, vertebral vessels;
e, dorsal vessels; /, subcostal vessels; ff, A, dorso-cervical trunks; i, vena azygos; ^, recurrent nerve; i, vago-sympathetic
nerve; I', I", dorsal and ventral branches of vagus; rn, phrenic nerve; n, roots of phrenic nerve; o, thoracic trunk of
sympathetic; o', nerve loop formed around brachial artery by branches which connect posterior cervical and first tho-
racic ganglia of sympathetic (Ansa subclavia) ; p, thoracic ganglia of sympathetic; q, rami communicantes; r, posterior
cervical ganglion; s, first thoracic ganglion; t, u, v, rami communicantes between s and seventh cervical, first thoracic,
and eighth cervical nerves; w, cardiac branch of first thoracic ganglion; J-, cardiac branches of posterior cervical gan-
glion: y, bronchial branches of vagus; z, depressor nerve. (After Bucher.)

The aorta runs at first almost straight forward and then turns backward,
forming a very sharply curved arch. It gives off at its origin the two coronary
arteries. From the convexity of the arch two large vessels arise. The first and
larger of these is the brachiocephalic artery; this runs forward at first on the
ventral surface of the oesophagus, then under the trachea. It gives off in succession
the left and right common carotid arteries, and turns around the first rib as the
right brachial artery. The left brachial artery passes forward on the left face of
the oesophagus, forming a slight arch (concave ventrally), and turns around the first
rib. The intrathoracic branches of the brachial arteries are as follows:

THE ARTERIES

745

(1) The vertebral artery arises opposite the first intercostal space from the
dorsal face of the parent trunk. It runs forward on the longus colli (crossing the
trachea on the right side), and passes along the neck in typical fashion to the third
cervical vertebra, where it divides into three branches. The largest of these supplies
the muscles in this region, compensating for the absence of branches of the deep
cervical artery. The second passes between the second and third cervical vertebrae
into the vertebral canal and unites with the opposite artery and a branch of the
occipital artery to form the basilar artery. The third branch is the small continua-

FiG. 614. — Vessels, Nerves, Etc., op Thorax or Dog; Left View.
1, First rib (stump) : 2, sternum; 2', manubrium sterni; 2'', xiphoid cartilage; 3, trachea; 3', bifurcation of trachea;
4, oesophagus; 6-8, ventral branches of fifth to eighth cervical nerves; 5, ventral branch of first thoracic nerve; 10, Iff,
muscular and tendinous parts of diaphragm; 11, 11', left ventricle and auricle of heart; 12, 12', right ventricle and auricle
of heart; 13, 13' , left coronary artery (descending branch) and great cardiac vein; H, branch of left coronary artery in
intermediate groove; ^5, pulmonary artery; / 6, pulmonary veins; 17, 18, auorta.; / 5, anterior vena cava; 20, 20', 20",
intercostal nerve, artery, and vein; 21, thoracic duct; 22, 22', internal thoracic vessels; 23, sternal branches of 22; 24,
mediastinal arteries; 25, musculo-phrenic artery; 26, anterior abdominal artery; 27, inferior cervical (or omo-cervical)
artery; 28, brachial vessels; 29, external thoracic artery; 30, left common jugular vein; 31, m. longus colli; 32, an-
terior mediastinal lymph glands; S3, sternal lymph glands; a, brachiocephalic artery; h, b', common carotid arteries;
c, c', brachial arteries; d, left brachial vein; e, e', dorso-cervical vessels; /, /', vertebral vessels; g, dorsal vessels; h,
subcostal vessels; i, deep cervical vessels; k, recurrent nerve; I, vago-sympathetic trunk; /', I", dorsal and ventral
branches of vagus; m, phrenic nerve; n, roots of phrenic nerve from fifth to seventh cervical nerves; o, thoracic trunk
of sympathetic; o', ansa subclavia formed by branches connecting posterior cervical and first thoracic ganglia; o",
great splanchnic nerve; p, thoracic ganglia of sympathetic; g, rami communicantes; r, posterior cervical ganglion; s,
first thoracic ganglion of sympathetic; t, v,v, rami communicantes connecting s with seventh and eighth cervical and
first thoracic nerves; w, cardiac branch of first thoracic nerve; x, cardiac nerves from posterior cervical ganglion ; y,
bronchial branches of vagus ; 2, depressor nerve, (.\fter Bucher.)

tion of the parent trunk; it passes to the wing of the atlas and anastomoses with
the occipital artery.

(2), (3) The dorsal and deep cervical arteries arise by a common trunk close
to the vertebral. The trunk crosses the lateral face of the latter, ascends on the
longus colli, and divides into two branches. The anterior branch, the deep cervical
artery, emerges medial to the upper end of the first rib and ramifies in the deep
muscles of the neck. The dorsal artery gives off the subcostal artery (which
supplies two or three intercostal arteries) and emerges through the dorsal end of
the first intercostal space and ramifies in the spinal muscles.

746

CIRCULATORY SYSTEM OF THE DOG

(4) The inferior cervical artery arises at the first rib, and gives off the ascending
cervical and transverse scapular arteries. The former runs on the deep face of the
brachiocephahcus, in which it ramifies. Tlie latter goes to the anterior border of
the subscapularis, and its largest branch (equivalent to the prescapular of the horse)
accompanies the suprascapular nerve.

(5) The internal thoracic artery is large and sends perforating branches to the
pectoral mammary glands.

The axillary part of the brachial artery gives off the thoraco-acromial and ex-
ternal thoracic arteries.

The thoraco-acromial artery supplies branches to the deltoid and pectoral
muscles.

The external thoracic artery passes backward under cover of the deep pectoral

Fig. 615. — Superficial Vessels of Head of Dog.
1, Facial artery; 3, inferior labial artery; 3, artery of angle of mouth; 4t superior labial artery; 6, lateral nasal
artery; 6, dorsal nasal artery; 7, superficial temporal artery; S, transverse facial artery; 9, anterior auricular artery;
iO, zygomatico-orbital artery; 7/, satellite vein of iO; /^, ant. auricular vein; i 5, superficial temporal vein; 74. internal
maxillary vein; lo, post, auricular vein; IG, 17, external jugular vein; IS, external maxillary vein; 19, 23, facial vein;
;?0, inf. labial vein; ^7, buccinator vein; ;92, vena reflexa ; ;?4, superior labial vem; £5, vena angularis oculi; 26,AoTsa.\
nasal vein; a, concha; b, parotid gland; c, mandibular gland; d, mandibular lymph glands; e, mylo-hyoideus; /,
digastricus; g, masseter; h, zygomaticus; i, scutularis; k, temporalis; I, orbicularis oculi; m, zygomatic arch; n, re-
tractor anguli oris; o, buccinator. (EUenberger-Baum, Anat. d. Hundes.)

muscle and ends in the abdominal cutaneous muscle. It sends branches to the
mammary glands.

The common carotid arteries, left and right, arise in that order from the
brachiocephalic. In the neck the right one lies on the trachea, the left on the
oesophagus. Collateral branches are the posterior th3n:oid (which may, however,
arise from the right or left ])rachial or the inferior cervical), pharyngeal, anterior
thjrroid, larjmgeal, muscular, tracheal, and glandular (to the mandibular gland).
Each carotid divides under the wing of the atlas into occipital and internal and ex-
ternal carotid branches.

The occipital artery is small; it ascends behind the hypoglossal nerve to the
paramastoid process, crossing laterally the internal carotid artery and vagus and
sympathetic nerves. It curves over the paramastoid process and pursues a flexuous

THE ARTERIES 747

course on the nuchal surface of the occipital bone parallel with the nuchal crest,
anastomoses with the opposite artery, and ramifies in the nuchal muscles. It
gives collateral branches to the ventral straight muscles and to the pharynx. It
also gives off the condyloid and posterior meningeal arteries. The latter passes
through the mastoid foramen and ramifies in the dura mater. The cerebrospinal
artery passes through the intervertebral foramen, and unites in the vertebral canal
with its fellow and a branch from the vertebral artery to form the basilar artery.
The recurrent branch anastomoses with the vertebral as in the horse.

The internal carotid artery, also small, arises just behind the occipito-mandib-
ularis muscle; it passes to the foramen lacerum posterius, enters the carotid canal,
and forms a bend before entering the cranial cavity through the carotid foramen.
It forms a plexus which is connected by branches with the middle meningeal and
external ophthalmic arteries. It then perforates the dura mater and enters into
the formation of the circulus arteriosus, which is formed in a manner similar to that
of the horse. The anterior cerebral artery gives off the internal ophthalmic artery
which accompanies the optic nerve to the eyeball. The middle cerebral artery is
large, and gives off the choroid artery.

The external carotid artery is the direct continuation of the common carotid.
It passes along the lateral wall of the pharynx, emerges from beneath the occipito-
mandibularis, and divides behind the postglenoid process into superficial temporal
and internal maxillary arteries. It gives off the following collateral branches:
The large flexuous lingual artery passes to the side of the root of the tongue, runs
forward under cover of the hyo-glossus, and continues to the tip of the tongue in
company with a satellite vein and the hypoglossal nerve. It ramifies in the
tongue and gives collateral branches to the pharynx and soft palate. The external
maxillary artery, smaller than the lingual, passes along the upper border of the occipi-
to-mandiljularis, gives off the sublingual, gains the anterior border of the masseter,
and divides into superior and inferior labial and the angularis oris. The last-named
vessel passes forward on the cheek between the labials to the angle of the mouth.
The sublingual artery passes along the upper border of the occipito-mandibularis,
then between the mylo-hyoideus and the ramus of the mandible. The great auric-
ular artery arises at the anterior border of the occipito-mandibularis, gives branches
to the parotid and mandibular salivary glands and the adjacent muscles, and ter-
minates in three auricular branches which ramifj^ on the convex face of the concha.
These branches anastomose with each other and the anterior auricular artery.

The superficial temporal artery, after giving off the anterior auricular artery
and a small transverse facial artery, turns forward under the temporal fascia toward
the eye, and divides into upper and lower branches which supply the frontal region
and the eyelids. It also supplies branches to the parotid gland and the masseter
and temporalis muscles.

The internal maxillary artery pursues a course similar to that of the horse,
and ends in the pterygo-palatine fossa by dividing into the infraorbital artery and a
common trunk for the greater jjalatine and sphenopalatine arteries. The mental
branches of the inferior alveolar artery are of considerable size and are distributed
in the lower lip and gums. Two or three deep temporal arteries are present; the
anterior one may arise from the buccinator artery. The middle meningeal artery
enters the cranium through the foramen ovale, ramifies in the dura mater, and sends
a branch to the carotid plexus. The external ophthalmic artery is comiected with
the internal carotid by a large ramus anastomoticus which passes through the
orbital foramen. The superficial branches of the infraorbital artery replace the
dorsal and lateral nasal arteries, and compensate for the small size of the superior
labial.

The brachial artery in its course in the arm presents no special features. At
the elbow it passes l^etween the biceps and the pronator teres, descends as the

748

CIRCULATORY SYSTEM OF THE DOG

median artery under the flexor carpi radialis about a third of the way down the
forearm, and divides into radial and ulnar arteries. Among its collateral branches
axe the following: (1) The large subscapular artery passes up between the sub-

FiG. 616. — Vessels and Nerves op Medial Surface
OF Shoulder and Arm of Dog.
a, b, Brachial artery; c, subscapular vessels; d,
thoraco-dorsal vessels; c, deep brachial vessels; /, prox-
iDial collateral ulnar vessels; g, brachial vein; h, h",
cephalic vein; h', mediano-radial vein; i, anterior tho-
racic nerves; k, musculo-cutaneoua nerve; I, median
nerve; m, ulnar nerve; n, radial nerve; o, thoraco-
dorsal nerve; 1, aubscapularis muscle; 2, supraspinatus
muscle; 3, teres major; 4, latissimus dorsi; 5, deep
pectoral muscle; 6, biceps brachii; 7, long head of tri-
ceps; 8, tensor fasciae antibrachii; 9, medial head of
triceps; 10, pronator teres. (EUenberger-Baum, Anat.
d. Hundes.^

Fig. 617. — Arteries op Forearm op Dog; Medial
View.
Arteries: a. Brachial; a', median; f, common interos-
seous; d, volar antibrachial; e, radial; e', e", dorsal
and volar branches of e; f, /', cutaneous branches of e;
g, ulnar. Muscles: 1, Biceps brachii; 2, extensor carpi
radialis; 3, pronator teres; 4. deep digital flexor; 5,
radius; 6, superficial digital flexor; 7, flexor carpi radi-
aUs; S, ulnaris lateralis; 9, humerus. ( Ellenberger-
Baum, Anat. d. Hundes.)

scapularis and teres major, turns around the posterior angle of the scapula, and
terminates in the supraspinatus, deltoid, trapezius, and brachiocephalicus. In
about half the cases it gives off the anterior circumflex, which often arises with the

THE ARTERIES 749

posterior circumflex. Its other branches resemble those of the horse. (2) The
anterior circumflex artery in about half the cases arises from the brachial. (3)
The deep brachial artery arises about a third of the way down the arm. (4) The
bicipital artery (for the biceps) is given off at the distal third of the arm. (5) The
proximal collateral ulnar artery arises almost opposite to the preceding vessel. It
ramifies chiefly in the distal part of the triceps, and sends a superficial branch to the
medial and posterior surfaces of the proximal part of the forearm. (6) The proxi-
mal collateral radial artery (not present in the horse) arises at the distal fourth of
the arm, crosses over the terminal part of the biceps, descends on the extensor
carpi radialis, and concurs with a branch of the volar interosseous artery in forming
the rete carpi dorsale. It often supplies the bicipital artery. (7) The distal col-
lateral radial artery is very small; it accompanies the deep branch of the radial
nerve on the dorsal surface of the forearm and supplies branches to the elbow joint
and the brachialis, supinator, and extensor muscles. (8) The common interosseous
artery is given off from the median a little below the elbow. It supplies
branches to the flexor muscles and gives off the dorsal interosseous artery,
which passes through the interosseous space, gives branches to the extensor muscles,
and by its terminal twigs concurs in the formation of the rete carpi dorsale. The
direct continuation of tne trunk is the volar interosseous artery, which descends
along the interosseous space undei cover of the pronator quadratus, gives off a
branch to the rete carpi dorsale and the fifth volar metacarpal artery, and termin-
ates by joining the volar branch of the radial artery to form the deep volar arch.
(9) The volar antibrachial artery (Ramus volaris antibrachii) arises below the
interosseous and descends at first under the flexor carpi radialis, then between the
heads of the deep flexor, and divides into ascending and descending branches which
ramify in the muscles mentioned.

The radial artery, the smaller terminal of the mechan, descends along the
medial border of the radius, and divides near the carpus into dorsal and volar
branches. The dorsal branch assists in forming the rete carpi dorsale. The larger
volar branch descends behind the medial border of the carpus and joins the end of
the volar interosseous in forming the deep volar arch. The arch extends across
the interossei at the proximal part of the metacarpus. From this arch three deep
volar metacarpal arteries descend in the second, third, and fourth intermetacarpal
spaces and concur with the corresponding superficial volar and the dorsal meta-
carpal arteries to form the common digital arteries.

The ulnar artery is much the larger of the two terminal branches of the median.
It descends with the median nerve along the medial border of the deep flexor of the
digit, and sends a connecting branch to the radial above the carpus. It then in-
clines somewhat laterally and passes between the superficial and deep flexor tendons.
Near the middle of the metacarpus it gives off the first volar metacarpal artery and
divides into the second, third, and fourth superficial volar metacarpal arteries.
The first volar artery unites with the corresponding dorsal artery to form the first
common digital artery, which supplies proper digital arteries for the opposed sur-
faces of the first and second digits. The superficial volar arteries descend in the
spaces between the other metacarpal bones, and unite near the metacarpo-phalangeal
joints with the corresponding deep volar and dorsal metacarpal arteries to form
three common digital arteries. Each of the latter divides after a short course into
two proper digital arteries, which run along the opposed surfaces of the second to
the fifth digits. The lateral digital artery of the fifth digit comes from the super-
ficial volar arch formed by the union of a branch of the volar interosseous with the
fourth superficial volar metacarpal artery.

The rete carpi dorsale gives off four dorsal metacarpal arteries which descend
in the intermetacarpal spaces and unite near the metacarpo-phalangeal joints with
the volar arteries to form the common digitals.

750

CIRCULATORY SYSTEM OF THE DOG

The thoracic aorta supplies the last nine or ten pairs of intercostal arteries,
but no anterior phrenic arteries. It gives off two or more oesophageal branches, in
addition to the broncho-cesophageal, which arises close to or with the sixth inter-
costal and ramifies in the usual manner.

The abdominal aorta, after giving off the external iliac arteries, continues
about half an inch to an inch (ca. 1-3 cm.) under the last lumbar vertebra, gives
off the internal iliac arteries, and is continued by the middle sacral artery (Fig.
624), This small vessel runs backward under the sacrum and coccygeal vertebrae
and gives off branches in segmental fashion. Six pairs of lumbar arteries are given
off from the aorta, the seventh coming from the internal iliac artery.

Fig. 618. — -Arteries of Distal Part of Right Fore
Limb of Dog, Dorsal View.
a, Branch of volar interosseous artery; 6, proximal
collateral radial artery (lateral branch) ; c, radial artery
(dorsal branch); d, rete carpi dorsale; e, deep dorsal
metacarpal arteries; /, superficial dorsal metacarpal
arteries; g, common digital arteries; h, proper digital
arteries.

Fig. (519. — Arteries of Distal Part of Right Fore
Limb of Dog; Volar View.
i', Radial artery; j, ulnar artery; k, volar inter-
osseous artery; I, deep volar arch; m, fifth volar meta-
carpal artery; n, deep volar metacarpal arteries; p, super-
ficial volar metacarpal arteries; o, q, common digital
arteries; r, proper digital arteries.

The coeliac artery gives off the hepatic artery and forms a short trunk from
which the gastric and splenic arteries arise. The hepatic artery, after giving off
several proper hepatic arteries, and the right gastric artery, which passes along the
lesser curvature of the stomach and anastomoses with the left gastric artery, is con-
tinued by the gastro-duodenal artery. This divides near the pylorus into right
gastro-epiploic and pancreatico-duodenal arteries; the former supplies branches
to the pyloric part of the stomach and passes along the greater curvature of that
viscus in the omentum and anastomoses with the left gastro-epiploic. The left
gastric artery passes to the lesser curvature of the stomach and ramifies chiefly on

THE ARTERIES

751

the left part of the stomach, giving off a branch which anastomoses with the right
gastric artery. The splenic artery gives off pancreatic branches, and reaches the
ventral part of the spleen. It gives off the left gastro-epiploic and a gastro-
splenic branch which passes to the dorsal end of the spleen, which it supplies,
besides giving off twigs to the left extremity of the stomach.

The anterior mesenteric artery arises close behind the coeliac. It gives off a
common trunk for two colic arteries and the ileo-caeco-colic. The right colic
artery is a small vessel which goes to the right part of the colon. The middle
colic artery, much the largest of the colic vessels, supplies the transverse colon
and part of the left colon. The ileo-caeco-colic gives off ileal, caecal, and colic
branches. Anastomoses are established between the colic arteries, and the ileal
branch anastomoses with the last jejunal artery. The trunk is continued as the

Fig. 620. — End Branches of Aorta and Radicles of Posterior Vena Cava of Dog.
a, Abdominal aorta; 6, posterior mesenteric artery; c, lumbar arteries; <-', circumflex iliac artery; e, external iliac
artery ;/, deep femoral artery ; s, posterior abdominal artery ; /i, external pudic artery; o, femoral artery; i, i, internal
iliac arteries; k, visceral branch of i; I, parietal branch of i; m, ilio-lumbar artery; n, anterior gluteal artery; o, lateral
coccygeal artery ; p, posterior gluteal artery; g, umbilical artery; r, middle haemorrhoidal artery; /3, posterior haemor-
rhoidal artery; s, perineal artery; t, art. profunda penis; n, art. bulbi urethra; v, art. dorsalis penis; w, middle sacral
artery; o', posterior vena cava; other veins are satellites of arteries and correspondingly named; 1, iho-psoas muscle;
;2, tendon of psoas minor; 3, abdominal muscles; 4. sartorius; 5, rectus femoris; 5', vastus medialis; ^;, pectineus; 6",
adductor; 7, gracilis; 8, symphysis pelvis; 9, ilium; 10, piriformis; 11, gluteus superficialis ; 12, obturator internus;
13, penis; 14, lumbar vertebree. (After Ellenberger, in Leisering's Atlas.)

artery of the small intestine, giving off fourteen to sixteen branches (Aa. jejunales),
which form a series of anastomotic arches in the mesentery near the bowel.

Two phrenico-abdominal arteries (Aa. phrenicae caudales) come off from the
aorta behind the anterior mesenteric, and divide into phrenic and abdominal
branches. Each phrenic artery diverges from its fellow in descending on the ab-
dominal surface of the corresponding crus of the diaphragm to the sternal part.
The medial branches anastomose with those of the opposite artery, the lateral
branches with intercostal arteries chiefly. The abdominal arteries pass outward
across the psoas muscles, give branches to the lumbar muscles, the renal fat and
adrenals, and ramify in the oblique abdominal muscles.

The renal and spermatic arteries offer no special features.

The utero-ovarian artery divides near the ovary into three or four branches

752

CIRCULATORY SYSTEM OF THE DOG

Pig. 621. — Arteries of Pelvic
Limb of Dog; Medial Vie^v
o, Abdominal aorta; b, fem-
oral; c, c', deep femoral; d, pos-
terior abdominal; e, external pudic; /, medial cir-
cumflex; g, anterior femoral (accompanied by an-
terior branch of, femoral nerve) ; h, lateral circum-
flex; 1, k, muscular branches; I, articular branch; m,
saphenous; n, o, plantar and dorsal branches of saphen-
ous; g, saphenous nerve; r, obturator nerve; 1, ilio-
psoas; 2, ilium; 3, gracilis; 4, semitendinosus; 5,
adductor magnus; 6, adductor longus; 7, quadri-
ceps femoris; 8, sartorius; 9, semimembranosus; 10,
gastrocnemius; i/. tibialis anterior; 7^, tibia. (Ellen-
berger-Baum, Anat. d. Hundes.)

which supply the ovary and uterine tube
and anterior part of the cornu of the
uterus, anastomosing with the uterine
artery.

The posterior mesenteric artery is
small. It divides into two branches which
supply the terminal part of the colon and
the anterior part of the rectum; the
former (A. colica sinistra) passes forward
along the left part of the colon and anas-
tomoses with the middle colic branch of
the anterior mesenteric artery; the latter
(A. hsemorrhoidalis cranialis) anastomoses
with the middle hsemorrhoidal branch of
the internal pudic artery.

The circumflex iliac artery usually
arises from the terminal part of the
aorta.

The external iliac artery usually gives
off no collateral branches.

The femoral artery has the usual
course in the femoral triangle and canal.
The deep femoral artery gives off the
posterior abdominal and external pudic
arteries by a very short common trunk
or separately. In the female the external
pudic divides into anterior and posterior
branches; the former runs forward, sup-
plies branches to the superficial inguinal
lymph glands, the mammary glands and
skin, and anastomoses with the mammary
branch of the internal thoracic artery ; the
posterior branch pursues a flexuous course
between the thighs to the vulva, where its
terminal branches anastomose with the
internal pudic artery. In the male the
artery crosses the medial side of the sper-
matic cord and runs forward to the
umbilical region; it supplies the inguinal
lymph glands, prepuce, and skin. The
anterior femoral artery may arise by a
short common trunk with the lateral cir-
cumflex. The former, accompanied by
the anterior branch of the femoral nerve,
dips in between the rectus femoris and
vastus medialis. The lateral circumflex
artery passes forward between the sar-
torius medially and the rectus femoris
and tensor fasciae latse laterally and sup-
plies branches to these muscles and the
glutei. In addition to muscular branches
of considerable size, an articular branch
(A. genu suprema) arises a little below
the middle of the thigh and runs down-

THE ARTERIES

753

ward and forward to the medial face of the stifle joint. The saphenous artery is
large. It arises from the medial surface of the femoral a little below the middle of the
thigh, descends superficially to the proximal part of the leg, and divides into two
branches. The smaller dorsal branch (Ramus dorsalis) passes obliquely downward
and forward across the medial surface of the tibia to the flexion surface of the hock and
gives off the second, third, and fourth superficial dorsal metatarsal arteries. These
descend along the grooves between the metatarsal bones and each divides into two
proper digital arteries. The plantar branch (Ramus plantaris), which is much the

Fig. 622. — Arteries of Distal Part of Right Hind
Limb of Dog; Dorsal View.
a. Lateral branch of anterior tibial artery; b, an-
terior tibial artery; c, saphenous artery (dorsal branch);
d, perforating metatarsal artery; e, dorsal metatarsal
arteries; /, deep dorsal metatarsal arteries; g, super-
ficial dorsa! metatarsal arteries; h, anastomoses between
dorsal and plantar arteries; i, common digital arteries;
i, proper digital arteries.

Fig. 623. — Arteries of Distal Part of Right Hind
Limb of Dog; Plantar View.
k, Saphenous arterj' (plantar branch); I, I', medial
and lateral plantar arteries; m, perforating metatarsal
artery; 7i, deep plantar metatarsal arteries; o, super-
ficial plantar metatarsal arteries; p, common digital
artery; q, proper digital arteries.

larger, descends on the medial face of the gastrocnemius and the long digital flexor.
It gives off the lateral tarsal artery to the lateral surface of the tarsus, and at the
plantar face of the tarsus detaches the medial and lateral plantar arteries ; these
descend on either side of the deep flexor tendon and unite with the perforating
metatarsal artery to form the proximal plantar arch. The artery continues
down the middle of the plantar surface of the metatarsus and divides near the
metacarpo-phalangeal joints into three superficial plantar metatarsal arteries
(II, III, IV). These vessels unite with three deep plantar metatarsal arteries, which
descend from the proximal plantar arch and with branches from ctie dorsal meia-
48

754 CIRCULATORY SYSTEM OF THE DOG

tarsal arteries. From these anastomoses four plantar digital arteries result; of
these, the central two have a common digital trunk.

The popliteal and posterior femoral arteries present nothing of special interest.

The posterior tibial artery is very small, being replaced largely by the saph-
enous. It supplies twigs to the flexor muscles at the proximal part of the leg.

The anterior tibial artery descends on the anterior face of the tibia and tarsus
and is continued as the perforating metatarsal artery, which passes through the
upper part of the space between the second and third metatarsal bones and concurs
with the plantar arteries in the formation of the proximal plantar arch. Besides
muscular and articular branches, the anterior tibial supplies the fifth dorsal meta-
tarsal artery for the lateral side of the fifth digit. At the proximal part of the meta-
tarsus it gives off three deep dorsal metatarsal arteries which descend in the in-
tervals between the metatarsal bones and concur with the superficial dorsal meta-
tarsal and the plantar arteries in the formation of the digital arteries. The latter
resemble in general arrangement the corresponding arteries of the thoracic limb.

The internal iliac artery (Fig. 620) runs backward and a little outward across
the ilio-psoas, and on reaching the ilium divides into parietal and visceral branches;
it gives off the seventh lumbar artery. The parietal branch is the larger. It runs
backward on the lateral wall of the pelvis, passes out through the lesser sciatic
notch, and breaks up into branches which supply the muscles of this region; this
terminal part may be regarded as the posterior gluteal artery. It gives off the
following branches: (1) The ilio-lumbar artery passes outward between the ilio-
psoas and the shaft of the ilium and ramifies in the gluteus medius, giving branches
to the ilio-psoas and tensor fasciae latse; it may arise from the internal iliac. (2)
The anterior gluteal artery passes out through the greater sciatic foramen and sup-
plies branches to the glutei. (3) Muscular branches go to the obturator internus,
coccygeus, and retractor ani. (4) The superficial lateral coccygeal artery (A. cau-
dalis lateralis superficialis) passes back at first on the lateral face of the coccygeus and
continues beneath the skin along the side of the tail. The visceral branch is equiva-
lent to the internal pudic artery ; it passes back below the parietal branch on the
lateral face of the rectum, retractor ani, and coccygeus. Its chief collateral branches
are: (1) The umbilical artery, which pursues a flexuous course and supplies twigs to
the bladder, ureter, and ductus deferens. In the bitch it gives off a large uterine
artery which ramifies chiefly in the body and neck of the uterus and the vagina
and anastomoses with the utero-ovarian. (2) The middle haemorrhoidal artery
arises near the ischial arch, passes upward and forward on the lateral surface of the
rectum, gains its dorsal surface, and anastomoses with the posterior mesenteric ; it
supplies the rectum and the anus, together with its muscles and glands. (3) A
small perineal artery is detached to the perineum. In the male the trunk turns
around the ischial arch as the artery of the penis (A. penis). This vessel, after
giving off the deep artery of the penis (A. profunda penis), which supplies the
artery of the bulb (A. bulbi urethrie) and enters the corpus cavernosum, is con-
tinued as the dorsal artery of the penis (A. dorsalis penis) along the dorsum penis.
In the female the terminal branches of the trunk go to the vulva, vestibular bulb,
and clitoris.

The Veins 1

The arrangement of the veins is, of course, correlated in general with the
arterial system, but a few special features are worthy of mention.

The coronary sinus is a large but short trunk formed by the confluence of the
cardiac veins; it opens into the right atrium below the posterior vena cava. The

1 Many of the veins are shown in the illustrations of the arteries.

THE VEINS 755

great cardiac vein ascends in the left longitudinal groove of the heart to the coronary
groove, in which it courses to the diaphragmatic surface. Here it is joined bj^ one
or two lesser cardiac veins, which are satellites of the right coronary artery, thus
forming the coronary sinus. There is commonly a vein in the intermediate groove
which joins the great cardiac vein.

The anterior vena cava (Figs. 613, 614) is formed by the junction of short right
and left brachiocephalic veins, and each of the latter results from the confluence
of jugular and brachial veins.

The vena azygos (Fig. 613) is continuous behind with the first lumbar vein; it
resembles that of the horse, and receives at the ninth or tenth thoracic vertebra a
vena hemiazygos.

Two jugular veins are present on each side. The external jugular vein is the
chief vein of the neck; it is formed by the union of external and internal maxillary
veins at the posterior border of the mandiliular gland. The two external jugulars
are commonly united by a transverse branch below the cricoid cartilage. Each
passes along the neck on the sterno-cephalicus, covered only by the skin and cu-
taneous muscle, dips under the cleido-cervicalis, and joins the internal jugular.
The internal jugular vein is the satellite of the connnon carotid artery. It results
usually from the junction of laryngeal and thyroid veins, but in some cases it is
formed by the confluence of the ventral cerebral and occipital veins.

The external maxillary vein arises on the lateral nasal region by the junction
of the dorsal nasal vein with the angularis oculi. Near the infraorbital foramen it
receives the lateral nasal vein, and a little lower the superior labial. In its course
along the anterior border of the masseter it receives the vena reflexa, which arises
in the pterygo-palatine fossa by the junction of infraorbital, sphenopalatine, and
palatine radicles, together with a branch from the cavernous sinus. At the ventral
border of the mandible it is joined by the inferior labial vein, which receives the
buccinator vein. The lingual vein is connected with its fellow by a superficial
transverse branch at the insertion of the sterno-hyoidei. The sublingual and
submental veins terminate in a variable manner, but often form a common trunk
which joins the lingual.

The internal maxillary vein arises from the pterygoid plexus, formed chiefly
by dorsal lingual, inferior alveolar, deep temporal, pterygoid, and meningeal tribu-
taries. It receives the dorsal cerebral, auricular, superficial temporal, transverse
facial, and masseteric veins, and often a trunk formed by the union of the ventral
cerebral and occipital veins.

The brachial and radial veins are satellites of the arteries.

The ulnar vein is usually double. It unites below the carpus with a branch of
the interosseous vein to form the superficial venous arch.

The cephalic vein accompanies the ulnar artery in the forearm and joins the
superficial venous arch below.

The accessory cephalic vein arises from the union of three dorsal metacarpal
veins. It joins the cephalic vein about the middle of the forearm.

There are three short volar metacarpal veins which open into the superficial
venous arch. They are formed above the metacarpo-phalangeal joints by the
junction of the volar digital veins, of which there are two for each of the chief
digits. The volar vein of the first digit joins the superficial venous arch.

Each of the chief digits has two dorsal digital veins, while the first digit has one.

The portal vein (Fig. 625) is formed by the union of a common intestinal or
mesenteric vein with the gastro-splenic vein. It receives the gastro-duodenal vein.
The intestinal trunk is formed in the mesentery by the confluence of veins from
the jejunum; it receives an ileo-caeco-colic vein.

The posterior vena cava, its collateral affluents, and common iliac radicles
present no special features of importance.

756 CIRCULATORY SYSTEM OF THE DOG

The internal iliac vein corresponds in regard to its tributaries with the branches
of the artery, except that it is not divided into parietal and visceral branches.

The external iliac, femoral, and popliteal veins with their collateral tributaries
are satellites of the arteries.

The anterior tibial vein is usually double, and the posterior tibial vein is very
small.

The saphenous vein is the upward continuation of the medial plantar meta-
tarsal vein. It communicates by a large branch with the dorsal metatarsal vein,
and ascends the leg as a satellite of the saphenous artery and its plantar branch.
The recurrent tarsal vein is larger. It is formed at the lower part of the leg by the
union of dorsal metatarsal and lateral plantar metatarsal veins, crosses the lateral
surface of the leg obliquely upward and backward, ascends behind the gastrocnemius,
and joins the femoral vein.

The metatarsal and digital veins resemble in general the corresponding vessels
of the forelimb.

The Lymphatic System

The cisterna chyli is relatively large and is fusiform; it is ventral to the last
thoracic and first lumbar vertebrae and is related ventro-medially to the aorta,
dorsally and laterally to the right crus of the diaphragm and the psoas minor. The
thoracic duct passes forward to the right of the aorta and ventral to the vena azygos
as far as the sixth thoracic vertebra; here it crosses to the left face of the oesophagus
and runs forward, turns ventrally at the thoracic inlet, and opens into the left
brachiocephalic or the common jugular vein. The duct may be single throughout,
but often divides anteriorly into two branches, which may then unite and form a
dilatation which receives the left tracheal duct and the vessels from the forelimb.
Other variations occur and the primitive plexiform arrangement persists in varying
degree. The tracheal lymph ducts accompany the internal jugular veins. The
right duct opens into the right brachiocephalic vein.

The mandibular lymph glands (Fig. 615) are commonly two or three in number
on each side, but as many as five have been observed. They are situated in the
angle between the masseter and the mandibular salivary gland, above and below
the external maxillary vein, and covered only by the skin and cutaneus muscle.

A small round parotid lymph gland is situated superficially between the upper
part of the posterior border of the masseter and the parotid salivary gland or partly
or completely under cover of the latter. Exceptionally two or three may be present.

The suprapharyngeal lymph glands, usually one on each side, lie dorsal to the
pharynx, under cover of the sterno-mastoideus and the mandibular salivary gland.
They are related deeply to the rectus capitis ventralis and the carotid artery, and
the anterior end is just behind the occipito-mandibularis (Fig. 433). Each is about
two inches (ca. 5 cm.) long in a good-sized dog. In a good many cases a second
gland is present.

Anterior cervical lymph glands appear to be absent in the majority of subjects,
but in other cases small nodes may be present in relation to the anterior end of the
thyroid gland. It should be noted, however, that parathyroids may l^e mistaken
for lymph nodes unless a microscopic examination is made. Middle cervical
Ijnnph glands are apparently not present, and the same is usually the case in regard
to the posterior cervical lymph glands ; but in some cases one or more of the latter
occur on the ventral face of the trachea near the thoracic inlet.

The prescapular or superficial cervical lymph glands lie on the serratus ven-
tralis, at the anterior border of the supraspinatus, embedded in a mass of fat. Usu-
ally two are present on each side, but there may be three or only one. They are
oval and are about an inch long in a dog of medium size when two are present.

TIIIO LYMPHATIC SYSTEM

757

The axillary lymph gland li(>s in a mass of fat on the mc(Hal face of the cHstal
part of the teres major. It is (Hseoid and is about an ineli (ca. 5 cm.) wide in a
lar^e dog. Exceptionally a se(;ond smaller
gland is present.

The cubital lymph gland is usually
absent. When ])resent, it is situated on
the medial face of tlu; long head of the
triceps or on the latissimus dorsi.

Intercostal lymph glands do not ap-
pear to b(> present.

Two sternal lymph glands (Fig. ()18)
are usually i)reseiit, one on each side.
They are situated on the course of tlu;
internal thoracic vessels, usually at tho,
second sternebra. A third node may bo
present in front of the more constant one,
and in some cases, on the other hand, the
gland is absent on one side. In large; dogs
the gland may be nearly an inch long.

The mediastinal lymph glands arc
variable in number and arrangement.
None have been found in the posterior
mediastinum, and the following statement
is to be underst(^od merely as an ac(H)vmt
of what is most often found. Two or three
glands usually o(;cur on the ventral face of
the trachea, oesophagus, and brachioceph-
alic artery to the left of i\w anterior vena
cava; thc^y are related v(>ntrally to the; thy-
mus, wh(m the latter is not too mu(!h re-
duced. Others may be found on the lat(u-al
face of the brachiocephalic artery. One
or two glands are usually present between
the tra(;hea and the anterior vena near
the thoracic inlet, and one or two are on
the right side of the; trachea, dorso-lateral
to the right l:)rachial artery. Another lies
on the trachea at the crossing of the vena
azygos over that tube.

The bronchial lymph glands are usu-
ally four in number. The largest one (Lg.
bifurcationis) is situated in the angh; of
divergence of the chief bronchi, to whic^h
it is adapted, so that it is som(!what V-
shay)ed. Another lies on the left })ron(;hus
at its bifurcation and in the angle betw(!(!n
the aortic arch and the; left pulmonary
artery. A third smaller one lies on the
right bronchus, lateral to the oesophagus;

it is not always present, A fourth is anterior to the root of the apical bronchus, in
relation in front to the vena azygos. These glands are {H)nunonly black, and tho
same is true of the gland on the right side of tlu; trachea in relation to the vena
azygos, indicating that all of these glands re(;eiv(! lymph from th(! lungs.

Minute pulmonary lymph glands occur in the lungs along the bronchial branches.

Fio. 024. — SnHLUMBAR AND Pblvic Lymph Glands
OF DoQ.
L 1', Ileiial lymph ulands; 2, lumbar lymph KlandH;
.3, '.i', l, 4', internal iliac lymph Kl^nds; 5, .5', mcrdial
sacral lymph glands; G, (>', lateral sacral lymph Klands;
7, 7', external iliac lymph glands; a, a', kidneys; b, b',
crura of diaphragm; c, c', psoas minor; d, d', ilio-
psoas; e, e', sacro-coccj^ous ventralis; /, /', coccy-
geus; I, posterior vena cava; //, abdominal aorta;
///, III', renal arteries; 77, IV', renal veins; V, V,
17, VI', circumflex iliac vessels; VII, VII', external
iliac arteries; VIII, VIII', internal iliac arteries; IX,
middle sacral artery; -Y, X' , parietal branches of in-
ternal iliac arteries; XI, XI', visceral branches of in-
ternal iliac arteries; XII, XII', common iliac veins;
XIII, Xlir, external iliac veins; XIV, XIV', in-
ternal iliac veins. (After Merzdorf).

758 CIRCULATORY SYSTEM OF THE DOG

The lumbar l3rmph glands are situated in the sublumbar region around and
l)etween the aorta and posterior vena cava. Most of them are very small and are
difficult to find in the fat in which they are usually embedded. Their nmnber is
verj' variable; as many as fifteen have been counted.

Usually two large internal iliac lymph glands are present. The right one lies
along the posterior part of the posterior vena cava and the common iliac vein; the
left one is similarly placed in relation to the aorta and left common iliac vein. Thej'
may be two inches or more (ca. 5-6 cm.) in length and nearly an inch (ca. 2 cm.)
wide in large dogs. In some cases there is a third small gland anterior to the large
one in relation to the origin of the circumflex iliac vessels. In most cases there is a
gland on each side of the middle sacral artery, between that vessel and the internal
iliac artery and its visceral branch. The gland may be absent on one side or there
maj' be instead two or three glands.

Fig. 625. — Lymph Gl.\nds of Abdominal Visceha of Dog.
l-d. Portal lymph glands; 7, 8, mesenteric lymph glands; 9-11, cseco-colic lymph glands; a, liver; 6, stomach;
c, spleen; d, duodenum (cut off and indicated by dotted line) ; c, jejunum; /.ileum; g, ca-cum; /i, i, i-, right, transverse,
and left parts of colon; /, portal vein; /J, gastro-duodenal vein ; ///, gastro-splenic vein; /!', splenic vein; T, common
gastric vein; VI, radicles of splenic vein; VII, ileo-cseco-colic vein; VIII, left colic vein; IX, middle colic vein; A',
right colic vein; XJ, caecal vein; A'/7, ileal vein; A'///, jejunal venous trunk. (After Alerzdorf.)

The external iliac lymph glands are situated on the ventral surface of the psoas
minor, between the diverging external and internal iliac veins. ^ They are inconstant
and variable. One may occur on each side or two on one side and none on the other.

The sacral lymph glands are situated along the roof of the pelvic cavity and
may easily escape notice on account of the fat in which they are embedded. Their
size, number, and arrangement are very variable. In the majority of subjects
there are two or three glands on the anterior part of the sacro-coccygeus ventralis
in relation to the middle coccygeal artery. In some cases one or two glands occur
at the interspace Ijetween the sacro-coccygeus ventralis and the coccygeus. In
other cases glands are present centrally or on one side only or appear to be absent.

The term portal lymph glands may be applied to those which occur along the
course of the portal vein and some of its affluents. The larger and more constant
of these are as follows: One lies to the left of the portal vein, on the origin of the

1 It seems not unlikely that these glands correspond regionally to the deep inguinal glands
of the horse.

THE LYMPHATIC SYSTEM 759

duodenum and the duodenal angle (or head) of the pancreas. In most cases two
glands occur on the right of the portal vein and further back along the mesenteric
vein. Glands of variable size and number occur in the gastro-splenic part of the
omentum along the splenic vein and its radicles.

The mesenteric lymph glands consist chiefly of two elongated nodes which
extend from the root of the mesentery of the jejuno-ileum along the course of the
artery of the small intestine and the corresponding vein.

The colic lymph glands comprise a variable number of nodes (5-8) in the meso-
colon. One is at the origin of the ileo-cseco-colic vein; a second one may be found
here. One or two may be found in the transverse mesocolon and others (2-5)
occur at the terminal part of the colon.

The renal lymph glands, one on each side of the aorta, are in relation to the
origin of the renal arteries; the right one is concealed by the vena cava.

The superficial inguinal l3miph glands are embedded in the fat about the ex-
ternal inguinal ring in relation to the external pudic vessels. In the male they are
related medially to the penis; in the female they are commonly termed supra-
mammary on account of their relation to the base of the inguinal mammary glands.
In the majority of cases two are present on each side, but there is often only one,
and sometimes three occur on one side.

The popliteal lymph gland is situated in a mass of fat on the gastrocnemius
at the level of the stifle joint. It is between the biceps femoris and semitendinosus,
but is more superficial than in the other animals, and hence is commonly palpable.
It is oval and in large dogs may be nearly two inches (ca. 4.5 cm.) long and more
than an inch (ca. 3 cm.) wide.

NEUROLOGY

THE NERVOUS SYSTEM

The nervous system (Systema nervorum) is a complex mechanism by which the
organism is brought into functional relation with its environment, and its various
parts are coordinated. For purposes of gross description it is divided primarily
into two parts, central and peripheral. The central nervous system (Systema ner-
vorum centrale) comprises — (a) the spinal cord (Medulla spinalis), and (b) the brain
(Encephalon). The peripheral nervous system (Systema nervorum periphericum)
includes — (a) the cranial and spinal nerves with their ganglia, and (6) the sympa-
thetic nervous system.

The division into central and peripheral parts is quite arbitrary, and is employed purely
as a matter of convenience of description. The fibers of which the nerves are composed either
arise or end within the central system, and therefore constitute an integral part of the latter.
The structural and functional unit of the nervous system is the neurone, which consists of the
cell-body, usually termed the nerve-cell, and all its processes. The processes arise as out-
growths from the cell-body and conduct impulses to or from the cell; they vary greatly in length,
some being less than a millimeter long, while others extend from a cell in the spinal cord to the
distal end of a limb. A nerve is composed of such processes, usually enclosed in a protecting
and insulating sheath, and united into bundles by areolar tissue. The neurones are embedded
in a peculiar supporting tissue termed neuroglia. This consists of a very intricate feltwork
of glia-fibers, many of which are connected with the small glia-cells or astrocytes. In addition
the nervous tissue is invested closely by a vascular layer of connective tissue, the pia mater, from
which ingrowths extend into the nervous substance proper.^

To the naked eye the central nervous system appears to be composed chiefly
of two kinds of substance, white and gray. The white matter (Substantia alba) is
dead white in color and is soft in the natural state. It consists largely of meduUated
nerve-fibers, packed closely together and arranged more or less clearly in large or
small bundles or tracts (funiculi, fasciculi). The gray matter (Substantia grisea)
is usually brownish-gray in color, often with a tinge of pink. It is softer than the
white substance and much more vascular. It is composed chiefly of cell-bodies
and non-medullated processes. In some situations it is modified to form the
gelatinous substance (Substantia gelatinosa), which is pale yellowish-gray and
jelly-like.

Ganglia are gray masses found on the dorsal roots of the spinal nerves and
on the course of many nerves. They are commonly ovoid in form, but some
are irregular in shape and branched. They vary greatly in size; some are micro-
scopic, while others are several inches long. They are enclosed in a fibrous capsule.
They are composed largely of the cell-bodies of neurones, but have connected with
and passing through them nerve-fibers (processes) which extend peripherally and
centrally. In origin and function the spinal ganglia belong properly to the central
system, but it is customary to include them with the peripheral part in gross ana-
tomical descriptions.

Nerves (Nervi) are conducting trunks composed of bundles of parallel nerve-
fibers. They are enveloped in a fibro-elastic sheath, the epineurium, which contains
the blood and lymph vessels. They are classified according to their central connec-
tions as cranial or cerebral, spinal, and sympathetic. The groups of cells of which
the nerve-fibers are processes are termed the nuclei of origin (Nuclei originis) or
terminal nuclei (Nuclei terminales) of the nerves, according as the latter conduct

1 Limitations of space and the purpose of this work preclude consideration of the finer
structure of the nervous system, for which ample literature is available.

760

THE MENINGES 761

impulses in a peripheral or central direction. ^ On the same basis the nerve-fibers
are designated efferent and afferent respectively. A bundle of fibers which passes
from one nerve-trunk to another is called an anastomotic branch (Ramus anasto-
moticus). In some situations the exchange of branches between adjacent nerves
is so free as to constitute a nerve-plexus (Plexus nervorum). The term ramus
commimicans is properly restricted to branches which connect the ventral divisions
of the spinal nerves with adjacent ganglia or nerves of the sympathetic system.
The terminal twigs of the nerves are designated, according to their distribution, as
muscular branches (Rami musculares), cutaneous nerves (Nervi cutanei), and
articular nerves (Nervi articulares) . The muscular branches are motor in function,
the cutaneous and articular sensory, but all contain vasomotor fibers which control
the caliber of the blood-vessels.

THE MENINGES
The central organs of the nervous system are enclosed in three meninges or
membranes. From without inward these are: (1) the dura mater, (2) the arach-
noidea, and (3) the pia mater.

The Dura Mater

The dura mater is a dense, resistant membrane of white fibrous tissue ; in the
fresh state it is bluish-white in color. On account of the difference in its arrange-
ment within the cranium from that in the spinal canal it is customary to describe
it as consisting of two parts, cerebral and spinal; these portions are continuous with
each other at the foramen magnum.

The cerebral dura mater (Dura mater encephali) is adherent to the interior
of the cranium, and may be regarded as forming an internal periosteum for the
bones here as well as being an envelope of the brain. Its outer surface is connected
with the bony wall of the cranial cavity by numerous fine fibrous strands and by
blood-vessels; hence it appears rough in many places when separated from the wall.
The degree of adhesion varies greatly at different points. It is most firmly attached
at the various projections, e. g., the internal parietal crest, the tentorium osseum,
the petrosal crest; also at the base and the foramen magnum. Before the sutures
are closed the dura is connected with the sutural ligaments and through them is
continuous with the external periosteum. The cranial nerves receive sheaths from
the dura, which is thus continuous without the cranium with the epineurium and
periosteum. Along the roof and sides (except as noted above) the adhesion is
relatively slight, and lymph spaces are said to exist between the dura and the bone.
The internal surface of the dura is smooth and glistening, since it is lined by endo-
thelium and is moistened by a fluid resembling lymph; it forms the outer boundary
of the subdural space. In accordance with its double function the dura is composed
of two layers, which are, however, intimately adherent to each other in most places
in the adult. The venous sinuses are channels between the two layers and are lined
by endothelium. They have been described with the other vessels. Two folds or
septa given off from the irmer surface of the dura project into the cranial cavity
between the gross subdivisions of the brain. These are: (1) the falx cerebri; (2)
the tentorium cerebelli.

The falx cerebri is a sickle-shaped median partition which is situated in the
longitudinal fissure between the cerebral hemispheres. It is attached dorsally
to the internal parietal crest, in front to the crista galli, and behind to the
tentorium osseum. Its dorsal border is convex and separates into two layers

^ These cell-groups are the real origin or termination of a nerve. The term "apparent
origin" is a convenient designation for the point at which a nerve is connected with the surface
of the brain.

762 THE NERVOUS SYSTEM

which enclose the dorsal longitudinal sinus. Its ventral border is concave and
lies over the corpus callosum. The falx is thick above, but much thinner below,
and is in some places cribriform. '^

The tentorium cerebelli is a crescentic transverse fold which occupies the
transverse fissure between the cerebellum and the cerebral hemispheres. It is
attached dorsally to the tentorium osseum and laterally to the petrosal crest. Its
ventral border is thin, concave, and free ; it forms the dorsal and lateral boundaries
of an opening (Incisura tentorii) in which the mid-brain is situated.

The diaphragm sellae is a thickening of the dura which roofs over the pitui-
tary fossa; it covers the pituitary body and the cavernous and intercavernous
sinuses. It is perforated centrally by an opening (Foramen diaphragmatis) for
the infundibulum.

The falx cerebelli, a sickle-shaped fold which projects into the median notch between the
cerebellar hemispheres in man, is not present in the domesticated animals. There is instead
merely a slight thickening of the dura.

The spinal dura mater (Dura mater spinalis) forms a tube around the spinal
cord from the foramen magnum to the second or third segment of the sacrum. It
is separated from the periosteum of the spinal canal by a considerable epidural
space (Cavum epidurale), which is occupied by fatty connective tissue and veins.
It is held in position chiefly by the sheaths which it furnishes to the roots of the
spinal nerves, and in its anterior part by two ligaments; the latter connect it with
the ventral atlanto-occipital membrane and with the dens of the axis. It is large
in proportion to its contents, but its diameter is not uniform. It is largest in the
atlas, small in the thoracic region, and becomes very small in its terminal part,
where it encloses the delicate filum terminale of the spinal cord.

The subdural space (Cavum subdurale) is the cavity between the inner surface
of the dura mater and the arachnoidea. It is a mere capillary space which contains
just sufficient fluid to moisten its surfaces; this fluid is usually regarded as lymph,
which is replenished by filtration through the walls of the blood-vessels. The
space is in communication with the lymph paths of the nerve sheaths.

The Arachnoidea

The arachnoidea is a very delicate and transparent membrane which is situated
between the dura and pia mater. Its outer surface forms the inner wall of the sub-
dural space and is covered by a layer of endothelium continuous with that of the
opposed surface of the dura mater. Between it and the pia mater is the subarach-
noid space (Cavum subarachnoideale) , which contains the cerebrospinal fluid. An
inner surface can scarcely be said to exist, since deeply the membrane becomes a
reticidum of fine fibers which traverse the subarachnoid space and are attached
to the pia mater. The arachnoidea furnishes sheaths to the cerebral nerves from
their superficial origins to a variable but usually short distance beyond the emer-
gence from the sac. In the case of the optic nerve this sheath extends to the eyeball.

The cerebral arachnoidea (Arachnoidea encephali), except in the case of the
great longitudinal and transverse fissures, does not dip into the sulci on the surface
of the brain. On the summits of the gyri it is so closely attached to the pia mater
that the two form practically a single membrane. Its outer part bridges over the
sulci, and here the subarachnoid space is partially divided up by the loose arach-
noid tissue into intercommunicating cavities. In certain situations the arach-
noidea is separated from the pia by spaces of consideral^le depth and extent. These
enlargements of the subarachnoid space are termed subarachnoid cisterns (Cisternse
subarachnoidales) . In them the subarachnoid tissue does not form a close network,

1 In the horse the posterior part of the falx cerebri does not extend to the corpus callosum, and
the cerebral hemispheres are here in contact and adherent to each other over a small area. In the
other animals the falx does not descend so far as in the horse.

PIA MATER 763

but consists of a relatively small number of long, thread-like strands which traverse
the cavity.

The chief cistemse are: (1) the cistema magna, which is at the angle formed between the
posterior face of the cerebellum and the dorsal surface of the medulla oblongata. It communi-
cates with the fourth ventricle through lateral openings in the latter, and behind with the wide
subarachnoid space of the spinal cord; (2) the cisterna pontis, on the ventral surface of the pons;
(3) the cisterna basolis, which lies at the base of the cerebrum and is divided by the optic chiasma
into two parts (cisterna chiasmatis, cisterna interpeduncularis) ; (4) the cisterna fossae lateralis,
situated at the lower part of the lateral fissure and continuous with the cisterna basalis.

Along the dorsal border of the falx cerebri the arachnoidea bears bulbous
excrescences, the arachnoid granulations.^ These are enclosed in thin evaginations
of the dura mater and project into the dorsal longitudinal sinus or the parasinoidal
sinuses along either side of it. In some cases they are sufficienth^ large to exert
pressure on the bone and produce in it depressions of variable depth.

The spinal arachnoidea (Arachnoidea spinalis) is continuous with that of the
brain at the foramen magnum. It forms a relatively wide tube around the spinal
cord, so that the latter (enclosed in the pia) is surrounded by a very considerable
quantity of cerebrospinal fluid. The spinal subarachnoid space is traversed by
fewer trabeculse than is the case in the cranium. It is partially subdivided by three
imperfect septa. One of these, the septum dorsale, is median and dorsal. The
other two, the ligamenta denticulata, are lateral and will be described with the pia
mater.

Pia Mater

The pia mater is a delicate and very vascular membrane, which invests closely
the surface of the brain and spinal cord and sends processes into their substance.
It also furnishes sheaths to the nerves, which blend outside of the dural sac with the
epineurium.

The cerebral pia mater (Pia mater encephali) follows accurately all the in-
equalities of the surface, dipping into all the fissures and sulci of the cerebrum, and
into the larger fissures of the cerebellum. Its external surface, which forms the
inner boundary of the subarachnoid space, is covered by a layer of endothelium.
From its deep face numerous trabeculse are given off which penetrate into the sub-
stance of the brain, forming a path for the blood-vessels, and concurring with the
neuroglia in forming the supporting tissue of the nervous substance proper. The
larger blood-vessels of the brain lie wdthin the subarachnoid space, but the smaller
vessels ramify in the pia, forming rich plexuses. The twigs which penetrate into
the gray matter are enclosed in pial sheaths. They are end-arteries, i.e., constitute
the entire supply of the district which they enter and do not anastomose with
adjacent vessels.

Important folds of the pia extend into two of the great fissures of the brain.
One of these passes in at the transverse fissure between the cerebellum and
the cerebral hemispheres, and is continued so as to overlie the third ventricle; it
forms the tela chorioidea of that cavity. Another fold passes in at the fissure
between the cerebellum and the medulla oblongata and forms the tela chorioidea
of the fourth ventricle. They constitute paths for the deeper vessels and their
edges contain vascular convolutions which are known as chorioid plexuses. They
will receive further consideration more appropriately later.

The spinal pia mater (Pia mater spinalis) is thicker and denser than that of
the brain. It has a strong outer layer of fibrous tissue, most of the fibers of which
are longitudinal. The inner layer is vascular and adheres closely to the surface
of the spinal cord, because numerous processes extend into the latter from it. It
sends a fold into the median ventral fissure and also helps to form the median
dorsal septum of the cord. Along the median ventral line it forms a band-like
1 They are also known as Pacchionian bodies.

764 NERVOUS SYSTEM OF THE HORSE

thickening, the linea splendens, along which the ventral spinal artery runs. On
each side the pia mater gives off a strong longitudinal band, the ligamentum den-
ticulatum, which is connected externally with the dura mater. The inner or pial
border extends in a line between the dorsal and ventral roots of the nerves. The
outer or dural border is denticulated and to a large extent free. The denticulations
are attached to the dura between the nerve-roots.

NERVOUS SYSTEM OF THE HORSE
The Spinal Cord

The spinal cord (Medulla spinalis) is the part of the central nervous system
which is situated in the vertebral canal. It extends from the foramen magnum to
about the middle of the sacrum. Its average length is about 76 to 78 inches (ca.
190-195 cm.), and its weight about 83^2 to 9 ounces (ca. 240-255 grams).

It is approximately cylindrical, but more or less flattened dorso-ventrally.
There is no natural line of demarcation between it and the medulla oblongata, but
for descriptive purposes the division is usually assumed to be at the plane of the
foramen magnum. Its posterior part tapers rapidly to a point, forming the conus
medullaris. This is prolonged for a short distance by the slender filum terminale.

Forty-two pairs of spinal nerves are connected with the sides of the spinal cord.
They are classified as eight cervical, eighteen thoracic, six lumbar, five sacral, and
five coccygeal. According to the attachments of these series of nerves the spinal
cord is divided into cervical, thoracic, lumbgir, and sacral parts.^

In the embryo these divisions correspond primitively to the regions of the
vertebral column, but later, through unequal growth of the cord and spine, the
correspondence between the two is not at all exact in the anterior regions and is
lost in the last two. The lumbar part of the cord in the horse ends at the junction
of the fifth and sixth lumbar vertebrae, so that the roots of the last lumbar nerve
must run backward the length of the last lumbar vertebra to reach the interverte-
bral foramen through which it emerges. The conus medullaris reaches only to the
anterior part of the sacral canal, so that the roots of the sacral and coccygeal nerves
extend backward in the spinal canal for a considerable distance, forming a leash
of bundles, in the center of which lie the conus medullaris and the filum terminale.
This arrangement is expressively designated the cauda equina.

Each pair of spinal nerves is attached by its root-fibers to a certain length of
the cord, and the latter is, therefore, regarded as consisting of as many segments
as there are pairs of nerves. It is to be noted, however, that there is no line of
demarcation between the segments other than the intervals between the root-fibers
of adjacent nerves.

The segments are of different lengths; the longest are the third to the sixth cervical, which
measure 11, 10, 10, and 8.5 cm. fespectively. The spinal nerves are in general designated accord-
ing to the vertebrae behind which they emerge from the vertebral canal. In the neck, however,
there are eight pairs of nerves and only seven vertebrae; here the first nerve emerges through the
intervertebral foramen of the atlas and the eighth between the last cervical and the first thoracic
vertebra?.

In the greater part of the thoracic region the spinal cord is fairly uniform in
size, but there are two conspicuous enlargements which involve the segments with
which the nerves of the limbs are connected. The cervical enlargement (Intumes-
centia cervicalis) begins gradually in the fifth cervical vertebra and subsides in

1 In a horse about 16J4 hands high these parts measured 65 cm. (ca. 26 in.), 86 cm. (ca. 34.4
in.), 27 cm. (ca. 10.8 in.), and 15 cm. (ca. 6 in.) respectively (Dexler).

THE SPINAL CORD

765

the second thoracic. Its maximum transverse diameter is about an inch (ca. 25
mm.) and its dorso-ventral nearly half an inch (ca. 12 mm.). The lumbar enlarge-
ment (Intumescentia lumbalis) is situated in the fourth and fifth lumbar vertebrae.

It is a little narrower than the cervi-
cal enlargement, and its dorso-ventral
diameter is also slightly smaller. Be-
hind this the cord tapers rapidly to
form the conus medullaris. The tip
of the latter is continued by a delicate
glistening strand, the filimi terminale,
which is composed largely of fibrous
tissue continued from the pia mater,
covered by arachnoid.

Fig. 626. — Ventral View of Medulla Oblongata
AND First and Second Segments of Spinal
Cord of Horse; the Membranes are Cut and
Reflected.

1, Lig. suspensorium arachnoideale ; 2, right cere-
brospinal artery; 3, 5, digitations of lig. denticulatum;
4, free border of lig. denticulatum; 6, middle spinal
artery; 7, basilar artery; S, pons; 9, arachnoidea;
10, dura mater; 11, 12, ventral root-bundles of first
and second segments of spinal cord; VI, N. abducens;
IX, X, glosso-pharyngeus and vagus; AT, accessory,
medullary part; XI', accessory, spinal part; a, line
between medulla oblongata and spinal cord. (Dexler,
in Ellenberger-Baum, Anat. d. Haustiere.)

Fig. 627. — Cauda Equina.
1, Dura and arachnoidea divided and reflected; S,
spinal cord; 3, nerve-roots. (From Leisering's Atlas, re-
duced.)

The surface of the spinal cord is
divided into two similar halves by a
dorsal median groove and a ventral
median fissure. On either side of the
former is the dorso-lateral groove (Sul-
cus dorsalis lateralis) , at which the fibers
of the dorsal nerve-roots enter the cord;
it is faint except at the enlargements, and is represented by two grooves in the first
cervical segment. The ventral root-fibers as they emerge from the cord do not
form a continuous series, but arise from a zone (Area radicularis ventralis) 3 to 5

766

NERVOUS SYSTEM OF THE HORSE

mm. in A\adth, a little lateral to the ventral median fissure, and no groove is found
here. In the greater part of the cervical region and the anterior part of the thoracic
region there is a shallow dorsal intermediate groove (Sulcus intermedius dorsalis) a
short distance lateral to the median groove. These grooves indicate the division
of the white matter of the cord into columns to be described later.

Examination of cross-sections of the spinal cord shows that it is a bilaterally
symmetrical structure, incompletely divided into right and left halves by a ventral
fissure and a dorsal septum. The ventral median fissure (Fissura mediana ven-
tralis) is narrow and penetrates nearly to the middle of the dorso-ventral diameter
of the cord. It is occupied by a fold of pia mater. The dorsal median septvmi
(Septum medianum dorsale) is a partition which descends from the dorsal median
groove to about the middle of the cord. It apparently consists of condensed neu-
roglia with an admixture of pial tissue. The two halves of the cord are connected

Fig. 62S.—
1, Dorsal column; 3,

^ROSS-SECTION OF SPINAL CoRD ill situ, ENLARGED AND IN PaRT SCHEMATIC.

iteral column; 3, ventral column; 4i dorsal horn; 5, ventral horn; 6, gray commissure; 7,

white commissure; <S, central canal; 5, dorsal septum; /O, ventral fissure; i/, dorsal nerve-root ; /^, ventral nerve-root.
13, spinal ganglion; 14, spinal nerve; 13, intervertebral foramen; 16, arch of vertebra; 17, epidural space; IS, dura
mater (represented a little too thick); 10, ligamentum denticulatum; 20, 30, longitudinal venous sinuses; 31, middle
spina! artery; 32, body of vertebra. The subdural and subarachnoid spaces (black) are traversed by delicate trabec-
ulae. The outer part of the arachnoid and the pia mater are not shown.

by commissures of gray and white matter. The gray commissure (Commissura
grisea) is a transverse band of gray matter at the ventral end of the dorsal septum.
It is divided into dorsal and ventral parts by the central canal of the cord. The
white commissure (Commissura alba) is a bridge of white matter which connects
the ventral columns of the cord over the dorsal end of the ventral median fissure,
and constitutes a conducting path from one side to the other.

The central canal of the spinal cord (Canalis centralis), the spinal vestige of the
lumen of the embryonal neural tube, is a minute passage which tunnels the gray
commissure. It opens at its anterior end into the posterior part of the fourth
ventricle of the brain, and its terminal part in the conus medullaris forms a slight
dilatation, the ventriculus terminalis. It is lined by epithelium and is surrounded
by a layer of modified neuroglia (Substantia grisea centralis).

The gray matter of the spinal cord as seen in cross-sections resembles roughly

THE SPINAL CORD 767

a capital H, the cross-bar of the letter being formed by the gray commissure.
Each lateral part is considered as consisting of dorsal and ventral gray columns
(Columna grisea dorsalis, ventralis), which appear in cross-section as the so-called
horns (Cornu dorsale, ventrale) . In the greater part of the cord the dorsal column
or horn is elongated and narrow and tapers to a point which extends almost to tho
surface of the cord at the attachment of the dorsal root-fibers of the spinal nerves.
Its apex or tip consists of gray matter which is lighter in color and less opaque
than that of the rest of the horn, and is termed the substantia gelatinosa. The
ventral column or horn is short, thick, and rounded, and is separated from the surface
of the cord by a thick layer of white matter, through which the fibers of the ventral
roots of the spinal nerves pass. From the middle of the cervical region to the
lumbar region there is a medial projection of gray matter on the ventral part of the
dorsal column; this is the nucleus dorsalis. ^ In the anterior part of the cord there
is an outward projection of the gray matter at the base of the ventral horn; this
is termed the lateral column or horn. The demarcation between the gray and
white matter is in many places indistinct; this is especially the case laterally,
where processes of gray matter extend into the white substance, producing what
is known as the formatio reticularis.

Cross-sections of the spinal cord present the following gross regional characters: (1) The
cervical cord near the medulla is compressed dorso-ventrally. Its width is about 18 mm. and
its greatest thickness about 8 mm. It has dorsally a deep median sulcus and a distinct dorso-
lateral sulcus. Lateral grooves are also present. The dorsal cornua are strongly everted. Each
has an expanded head, which comes very close to the surface of the cord, and has an extensive
cap of substantia gelatinosa. The neck is distinct. The ventral cornua are short and blunt and
diverge very little. The gray commissure is about in the middle of the section, and 2.5 mm.
in length. According to Dexler, the column between the median and lateral grooves dorsally
is the funiculus cuneatus, the funiculus gracilis being very small and not showing on the surface
in this region. In the middle of the cervical region the diameters are about 16 mm. and 10 mm.
respectively. The ventral surface is somewhat flattened. The dorsal cornua have pointed ends
and turn decidedly outward. The ventral cornua are short and thick and are directed very slightly
outward; their ends are about 4 mm. from the ventral surface. The gray commissure is just
above the middle of the section and is about 2 mm. long. The cervical enlargement measures
about 25 mm. transversely and 12 mm. vertically. The dorsal cornua are smaller than the ventral
and have a large cap of substantia gelatinosa. The ventral cornua are short and thick, curve
strongly outward, and are about 4 mm. from the ventral surface. Each bears a prominence on its
medial side near the base. The gray commissure is considerably above the middle of the section
and is about 4 mm. long. (2) In the middle of the thoracic region the cross-section is biconvex,
the ventral surface being the more strongly curved. The transverse diameter is about 15 mm.
and the dorso-ventral about 10 nmi. The gray columns are close together, the gray commissure
being only about 1 mm. in length, and lying considerably above the middle of the section. The
dorsal cornua are short and have slightly enlarged ends. The ventral comua have a uniform diame-
ter, turn very little outward, and end about 3 mm. from the ventral surface. (3) The lumbar enlarge-
ment is much flattened, especially dorsally. The transverse diameter is about 22 mm. and the
dorso-ventral 9 to 10 mm. The cornua are very large. The ventral cornua are thick and rounded
and turn sharply outward; they end about 2 mm. from the ventral surface. The dorsal cornua
are smaller and shorter and do not diverge so strongly. The gray commissure is about in the
middle of the section and is about 3 nmi. long. In the third lumbar vertebra the cord is about
3 mm. narrower and thicker, and both surfaces are about equally convex. The dorsal cornua are
smaller, considerably everted, and constricted in the middle. The ventral cornua are very short
and do not turn outward. (4) In the first sacral vertebra the cord is almost round and is 5 to 6 mm.
in diameter; the cornua are relatively very large and the commissure has the form of a high inter-
mediate mass.

The ventral horn contains large cells, the axones of which emerge as the fibers of the ventral
nerv^e-roots (Fila radicularia). The axones of many cells cross to the opposite side in the white
commissure and pass out in a ventral root of that side, or enter the white matter and pass forward
and backward, associating various segments of the cord. Some pass to the ventral horn of the
opposite side at the same or at different levels. Others pass to the periphery of the cord, join
the cerebellospinal fasciculus, and extend to the cerebellum. Scattered through the gray matter
are many smaller cells with axones which pursue a short course and serve to connect different
parts of the gray matter.

The white matter of the spinal cord is divided into three pairs of columns.
The dorsal columns (Funiculi dorsales) lie on either side of the dorsal median septum
and extend outward to the dorso-lateral groove and the dorsal gray column. The
1 Also known as Clarke's column.

768 NERVOUS SYSTEM OF THE HORSE

ventral columns (Funiculi ventrales) are situated on either side between the median
fissure and the ventral gray columns. They are connected above the fissure by
the white commissure. The lateral coliinins (Funiculi laterales) are lateral to the
gray columns on either side; their limits are indicated superficially by the dorso-
lateral groove and the emergence of the ventral root-fibers. The intermediate
groove (where present) indicates a subdivision of the dorsal column into two fasci-
culi or tracts; the medial of these is the fasciculus gracilis; the lateral one is the
fasciculus cuneatus.^

The amounts of gray and white matter vary greatly in different parts of the
cord both absolutely and relatively. In cross-section the absolute areas of both are
greatest in the enlargements. The relative area of gray matter is smallest in the
thoracic region (except at its anterior end), and increases from the lumbar enlarge-
ment backward.

Investigations have shown that in man the columns of white matter are subdivided into
fasciculi or tracts, which constitute definite conducting paths of greater or less length. Our
knowledge of the tracts in the domesticated animals is very limited, and it is quite unsafe to make
inferences from the arrangement in man. As evidence of this it may be noted that the ventral
cerebrospinal or direct pyramidal tract of man cannot be recognized as such.

The dorsal white columns consist essentially of two sets of axones. The afferent or sensory
axones which come from the cells of the spinal ganglia enter as the dorsal roots of the spinal nerves
and divide into two branches in the vicinity of the dorsal gray column. The anterior branches
form the direct sensory path to the brain and extend m the fasciculus cuneatus and fasciculus
gracilis or corresponding tracts to nuclei in the medulla oblongata. The posterior branches
extend backward for varying distances and give off numerous collaterals to cells of the gray column,
thus forming part of the mechanism for the mediation of reflex action. Some collaterals cross
in the white commissure to the opposite side. Many of these fibers are collected in the comma-
shaped tract between the fasciculus gracilis and cuneatus. The second set of axones arises from
the smaller cells of the gray column. They enter the white matter, divide into anterior and
posterior branches, forming the fasciculi proprii or ground bundles of the cord. Some branches
cross to the opposite side. The f miction of this set of axones is chiefly to associate various levels
of the cord.

The lateral columns contain some axones of the dorsal nerve-roots, which (in man) are
grouped in the marginal tract of Lissauer, situated just dorsal to the apex of the dorsal hom.
The cerebellospinal fasciculus (direct cerebellar tract of Flechsig) extends along the periphery
of the lateral column. It contains the axones of the cells of the nucleus dorsalis (Clarke's column),
which proceed to the medulla oblongata and enter the cerebellum by the restiform body. The
rubrospinal tract (of Monakow) appears to take the place of the lateral cerebrospinal fasciculus or
crossed pyramidal tract of m.an. It lies at the medial side of the cerebellospinal fasciculus. Its
fibers arise in the nucleus ruber of the mid-brain, cross the median plane (decussation of Forel),
and pass backward in the tegmentum and medulla oblongata to the lateral column of the cord.
It is a path for motor impulses coming from the cerebral cortex and the cerebellum . The lateral
fasciculus proprius or ground-bundle is deeply situated at the side of the gray columns. The
bulk of its fibers are axones of cells of the dorsal column which divide into anterior and posterior
branches. They are intersegmental paths which associate different levels of the gray matter of
the cord. The significance of the remaming fibers is not yet knowni.

The ventral white columns do not contain a ventral cerebrospinal or direct pyramidal tract,
as in man. There is a small tract (Fasciculus intracommissuralis ventralis) dorsal to the white
commissure, which separates it from the rest of the ventral column. It extends to the middle of
the thoracic region. It consists of intersegmental fibers, and contains in the anterior part of
the cervical cord in the sheep and goat both crossed and direct pyramidal fibers. The descending
cerebellospinal fasciculus extends from the cerebellum to the lumbar region. In the cervical
region it occupies a semilunai area which reaches almost to the surface ventro-laterally. Scattered
fibers belonging to it lie also in the medial part of the ventral column. Posteriorly it diminishes
in size and comes to occupy a position next to the ventral median fissure, corresponding to the
sulco-marginal fasciculus of man (Dexler).

The Brain

The brain or encephalon is the part of the central nervous system that is

situated in the cranial cavity. It is the enlarged and highly modified cephalic

part of the primitive neural tube. It conforms in great part in size and shape to

the cavity in which it lies. Its average weight without the dura mater is about

^ These are also known as the columns of Goll and of Burdach respectively.

THE BRAIN 769

23 ounces (ca. 650 gm.), and forms about y of 1 per cent, of the body-weight in a
subject of medium size.

It is desirable to examine the general external configuration of the brain before
studying its various parts in detail.^

When divested of its membranes and vessels (Fig. 629), its ventral surface or
base presents the median brain stem (Caudex encephali), which is continuous with
the spinal cord without any natural line of demarcation; it divides in front into
two branches, the cerebral peduncles, each of which disappears into the mass of
the corresponding cerebral hemisphere. The brain stem consists of three parts.
The medulla oblongata is the posterior part which extends forward as the direct
continuation of the spinal cord. The pons is a transversely elongated mass which
appears to turn up on either side into the cerebellum. The cerebral peduncles
(Pedunculi cerebri) extend forward from the pons and diverge to plunge into the
ventral part of the cerebral hemispheres. The area between them is the inter-
peduncular fossa. It is largely covered by the hjrpophysis cerebri or pituitary
body, a yellowish-brown, discoid structure, which is connected with the base of
the cerebrum by a delicate tube called the infundibulum.'' On drawing the pitu-
itary body gently aside, the infundibulum is seen to be attached to a slight gray
eminence, the tuber cinereum. Behind this is the mammillary body (Corpus
mamillare), a well-marked round prominence. The posterior part of the space
is perforated by numerous openings for the passage of small arteries, and hence
is termed the substantia perforata posterior. A large band of white matter, the
optic tract (Tractus opticus), crosses the anterior end of the cerebral peduncle ob-
liquely, and unites with the opposite tract to constitute the optic chiasm or commis-
sure (Chiasma opticum), and form the anterior boundary of the interpeduncular
fossa. Above and in front of the chiasm the hemispheres are separated by the
median longitudinal fissure. In contact with the anterior extremity of each
hemisphere is the olfactory bulb (Bulbus olfactorius), an oval enlargement which
occupies the ethmoidal fossa of the cranium. This appears as a gray swelling
on a wide flat band, the olfactory tract or peduncle (Tractus olfactorius), which
is continued behind by two divergent bands, the olfactory striae. The medial
stria (Stria medialis) disappears after a very short course on to the medial surface
of the hemisphere. The lateral stria (Stria lateralis) is larger and longer; it runs
backward, inclines at first outward and then curves medially and disappears on
the concealed or tentorial surface of the hemispheres. It is separated from the
lateral cerebral gyri by a distinct groove (Sulcus rhinalis). Along the medial side
of the stria are two eminences. The anterior of these is the trigonum oLfactoriimi,
a gray elevation situated in the angle of divergence of the medial and lateral strise.
Behind this is a depression, the fossa lateralis, which is continued across the lateral
stria and sharply limits the second and much larger eminence, the piriform lobe.

The superficial origins of most of the cranial nerves are visible on the base of
the brain.

The olfactory nerve-fibers join the convex surface of the olfactory bulb and give
it a shaggy appearance in specimens which have been removed intact — a difficult
proceeding.

The second or optic nerves converge to the optic chiasm.

The third or oculomotor nerve arises from the mechal part of the cerebral
peduncle.

1 The description given here is intended to present the chief facts in regard to the brain as
they may be studied in the dissecting-room. The vessels and membranes, which must be exam-
ined first, have been described.

2 Unless care is used in removing the brain, the infimdibulum is hkely to be torn and the
hypophysis left in the cranium. In this case there is a small opening which communicates with
the third ^'entricle.

770

NERVOUS SYSTEM OF THE HORSE

The fourth or trochlear nerve may be seen emerging between the pons and the
cerebral hemisphere, but its connection ^ith the brain is not visible.

The fifth or trigeminal nerve is connected with the lateral part of the pons.

Fig. 629.— Base of Bkai.n of House About Natural Size.
Hardened in situ

The sixth or abducent nerve arises just behind the pons and lateral to the
pyramid of the medulla.

• + I^^- ^^^^"*^ 0^ ^^^^^^ and the eighth or acoustic nerves arise close together
just behmd the pons on the extremity of the corpus trapezoideum.

THE BRAIN

The ninth or glosso-pharyngeal, the tenth or vagus, and the eleventh or spinal
accessory nerves are connected by a Hnear series of roots with the lateral aspect of
the ventral surface of the medulla. The spinal part of the accessory nerve comes
forward along the edge of the medulla to join its medullary root.

The twelfth or hypoglossal nerve arises from the posterior part of the medulla
along the lateral edge of the pyramid.

The parts that are visible when the brain is viewed from above are the cerebral
hemispheres, the cerebellum, and part of the medulla oblongata. The cerebral
hemispheres (Hemisphseria cerebri) form an ovoid mass, and are separated from
each other by the median longitudinal fissure (Fissura longitudinalis cerebri),

Lonrjil udinal fiss ure

Sulcus rhinalis v^
Oplic nerve ^
Optic chiasma-^^^
Tuber cinereum
Piriform lobe
Pituitary body -'
Oculomotor nerve

sensory root ^^

motor root —

Cerebellum-^

Tuberculum faciale —

Glosso-pharyngeal nerve

Vagus nerve

Accessory nerve {medullary root)

Accessory nerve {spinal root)

Hypoglossal nerve -

Fig. 630. — Line Drawing of
VI, Abducent nerve;

Trigeminal
nerve

— Olfactory bulb
^^^ Olfactory tract

__^-- Medial stria

— Lateral stria
— Trigonum olfactorium,

~ Fossa lateralis
-Cerebral peduncle
- Tractus ped. transversus
'—. Intel-peduncular fossa

— Pons
Co7-pus trapezoideum

Pyramid
Medulla oblongata

^-— Chorioid plexus of fourth
ventricle
-Median fissure and de-
cussation of pyramids
' Spinal cord

!ase of Brain of Horse. (Key to Fig. 629.)
'II, facial nerve; VIII, acoustic nerve.

in which the falx cerebri is situated. Their surfaces are marked by thick ridges,
the gyri cerebri, separated by sulci. The upturned ends of the olfactory bulbs
are seen in front of the frontal poles of the hemispheres. The occipital poles of
the hemispheres overlie the anterior part of the cerebellum, from which they are
separated by the transverse fissure (Fissura transversa cerebri) and the tentorium
cerebelli contained in it. The cerebellum is a much smaller rounded mass which con-
ceals the greater part of the medulla oblongata. Its surface is divided into a middle
lobe, the vermis cerebelli, and two lateral hemispheres (Hemisphseria cerebelli). It
is marked by numerous gyvi and narrow sulci which have in general a transverse direc-
tion. The posterior third of the medulla oblongata is not covered by the cerebellum.

The brain is developed from the expanded cephalic part of the neural tube of the enibryo.
The process comprises a series of thickenings, flexures, and unequal growth and expansion of

772

NERVOUS SYSTEM OF THE HORSE

various parts of the tube. In the higher animals the resuh- is that the tubular character of the
brain is not very evident, since the lumen comes to consist of four irregular cavities, the cerebral
ventricles, which are connected by narrow passages. The tube is first subdivided by two con-
strictions into three brain vesicles, termed respectively the hind-brain or rhombencephalon, the
mid-brain or mesencephalon, and the fore-brain or prosencephalon. The hind-brain gives rise to
three secondarj^ segments and the fore-brain to two. The annexed table indicates the origin of the
principal structures of the fully developed brain from the primitive vesicles. It has become
customary to describe the brain with reference to its embryological relations.

Longitvdinal
fissure

Transverse

Olfactory bulb

Frontal ■pole of hemisphere

Cerebrum

Occipital pole of
hemisphere

Cerebellum

Medulla oblongata

Fig. 631. — Brain of Horse; Dorsal View, About f Natural Size. Hardened in situ.
1, Entomarginal fissure; 2, marginal fissure; 3, ectomarginal fissure; 4t suprasylvian fissure.

TABLE INDICATING THE DERIVATION OF THE PRINCIPAL PARTS OF THE

Primary Segments.

Rhombencephalon (pos-
terior vesicle)

Mesencephalon (middle
vesicle)

Prosencephalon (ante-
rior vesicle)

BRAIN

Secondary Segments. Derivatives.

Myelencephalon Medulla oblongata. . .

Pons

Anterior cerebellar peduncles.
Anterior medullary velum . . .

Cavities.
Fourth ventricle

Metencephalon | Cerebellum

Isthmus rhombencephali

Mesencephalon { g°X^^, ^^^f^S'!^.^. :::::::} Cerebral aqueduct

Diencephalon

Optic thalami

Hypothalamic tegmenta.

Telencephalon.

Pineal body .

Pituitary body

Optic nerves and retinae. .
Cerebral hemispheres . . . .
Olfactory tracts and bulb.

Posterior part of third
ventricle

Anterior part of third
ventricle. Lateral

ventricles and olfac-
tory continuations.

THE RHOMBENCEPHALON 773

THE RHOMBENCEPHALON
The Medulla Oblongata

The meduUa oblongata (Figs. 629, 632, 635) lies on the basilar part of the
occipital bone. It is quadrilateral in outline, but much wider in front than behind,
and compressed dorso-ventrally. Its length, measured from the root of the first
cervical nerve to the pons, is about two inches (ca. 5 cm.).

Its ventral surface is convex in the transverse direction, and presents a ventral
median fissure (Fissura mediana ventralis), which is continuous behind with the
similar fissure of the spinal cord. The posterior part of the fissure is faintly marked,
but in front it becomes deeper and ends in a small depression (Foramen caecum)
behind the central part of a transverse band, the corpus trapezoideum. On either
side of the fissure is a rounded tract, the p3rrainid (Pyramis), which is bounded
laterally by a faint groove (Sulcus intermedins ventralis). The pyramids join
the pons in front ; behind they become narrower and disappear into the substance
of the medulla, in which their fibers intercross, forming the decussation of the
pyramids (Decussatio pyramidum).^ The superficial origin of the oculomotor
nerve (N. oculomotorius) is just lateral to the anterior end of the pyramid. The
corpus trapezoideimi is a transverse band which extends across the surface imme-
diately behind the pons. It is crossed by the pyramids, which cut off a small
central part. The lateral part extends out to the roots of the seventh and eighth
nerves on either side. Behind the lateral part of the corpus trapezoideum there
is a variably developed rounded eminence, the tuberculum faciale. The root-
fibers of the hypoglossal nerve form an oblique linear series lateral to the posterior
part of the pyramid.

The dorsal surface is largely concealed by the cerebellum and forms the greater
part of the floor of the fourth ventricle. The dorsal median fissure (Fissura
mediana dorsalis) , the direct continuation of the corresponding groove of the spinal
cord, extends forward to about the middle of the surface. Here the restiform
bodies, which constitute the lips of the fissure, diverge to form the lateral boun-
daries of a triangular depression; this is the posterior part of the rhomboid fossa or
floor of the fourth ventricle of the brain. The dorso-lateral groove winds outward
and forward to the lateral aspect of the medulla, where it presents the roots of the
glosso-pharyngeal, vagus, and accessory nerves. Lateral to it is a distinct oval
eminence on the anterior part of the lateral column, termed the tuberculum cin-
ereum. The central canal of the cord is continued in the posterior part of the
medulla, inclines dorsally, and opens in the posterior angle of the fourth ventricle.
Hence it is customary to distinguish a closed and an open part of the medulla.
The dorsal aspect of the latter, which is concealed at present, will be considered
later in the description of the fourth ventricle.

The lateral surface is narrow behind, wider and rounded in front. From it
the root-fibers of the ninth, tenth, "and eleventh cranial nerves arise in a linear
series, and alongside of it the spinal part of the eleventh nerve passes forward to
join the medullary root. Close inspection reveals the presence of strige which
curve ventrally and backward from the surface of the restiform body toward the
hypoglossal root-fibers; these are the external arcuate fibers (Fibrse arcuatae
externse) . The recess between the lateral aspect of the medulla and the cerebellum
is occupied by an irregular mass of villous projections of the pia mater, containing
tufts of vessels; this is the chorioid plexus of the fourth ventricle, and is the lateral
edge of the tela chorioidea of the ventricle. On raising the chorioid plexus, it is
seen that the tela chorioidea is attached to the dorsal aspect of the medulla, and
reinforces here the wall of the fourth ventricle; also that the restiform body ter-

1 The decussation varies superficially in different specimens. In some there is a distinct
superficial crossing of fibers so that the median fissure is practically effaced at this point.

774 NERVOUS SYSTEM OF THE HORSE

minates in front bj^ entering the base of tlie cerebellum, forming its posterior
peduncle.

In the medulla the fiber tracts of the spinal cord either terminate in the nuclei of the gray
matter or undergo changes in their relative position, and new tracts appear. The gray matter
is highly modified and forms masses which have no homologues in the cord. The central canal
of the closed part of the medulla is surrounded by a thicker layer of gray matter than is the case
in the spinal cord. As the medulla opens out this gray matter is naturally spread in the floor of
the fourth ventricle. The dorsal horns of gray matter become wide, siM-ca/l apart, and are broken
up to a great extent in the formatio reticularis. Two elongated masses of cells appear above the
centr.al gray matter; these are the nucleus gracilis anfl nucleus cuneatus, and in them the
fasciculi of like name gradually end. In front of these are the terminal nuclei of the afferent or
sensory cranial nerves and of the sensory portions of the mixed ner\-es. The ventral horns are
succeeded by the nuclei of origin ot the efferent or motor cranial ner\'es and the motor root-fibers
of the mixed nerves. Of the twelve pairs of cranial nerves, the last eight are cormected with
nuclei in the medulla and pons. The posterior olivary nucleus (Nucleus olivaris caudalis) is a
conspicuous gray mass which lies dorsal to the pyramid on each side. On cross-sections it appears

Transverse fissure

Cerebellum

Medulla
oblongata

Olfactory
tract

Cerebral
peduncle

Fig. 632. — Brain of Horse; Left View.
1, Lateral fissure; 2, suprasylvian fissure; 3, presylvian fissure; 4. ectomarginal fissure; 5, 5', sulcus rhinalis an-
terior et posterior; L. p., piriform lobe; B. p., middle peduncle of cerebellum (brachium pontis) ; P. c, choroid plexus
of fourth ventricle. Roman numerals indicate roots of cranial nerves.

as a wavy layer ot gray matter which is folded on itself so as to enclose a mass of white matter.
It is about 2 cm. long in the horse, but is smaller in circumference than in man and hence does
not cause any very distinct external enlargement (olivary eminence), as in the latter. It is con-
nected with the opposite side of the cerebellum by the cerebello-olivary fibers. At its medial side
are two small accessory olivary nuclei. The pyramidal tracts, which are small in ungulates, send
most of their fibers across to the opposite side in the posterior part of the medulla, forming the
pyramidal decussation. Some fibers, however, continue in the ventral column of the same side
of the cord, and others are eonnect(>d with the nuclei of the motor nerve-roots. From the nu-
cleus gracilis and nucleus cuneatus iiln-rs arise which are traceable fonvard to the thalamus.
These are the internal arcuate fibers (Fibra? arcuatte internae), which curve across the median
plane ventral to the central gray matter and form with those of the opposite side the decussation
of the fillet (Decussatio lemniscorum). Beyond the decussation the fibers form an important
longitudmal tract which extends forward in the mid-brain. This is the fillet or lemniscus, the
chief continuation of the sensory conducting path from the dorsal roots of the spinal nerves.
The external arcuate fibers (Fibrse arcuatse extemse), some of which were seen on the lateral
aspect of the medulla, have a similar origin. Part of them (Fibra; dorsales) pass directly to the
dorsal aspect of the restiform body of the same side; others (Fibrse ventrales) cross to the opposite
side, descend close to the ventral fissure, and then curve upward and forward to the restiform l:)ody.
The decussation of the arcuate fibers forms the distinct median raphe seen on cross-sections of the
medulla anterior to the pyramidal decussation. The restiform body, situated dorso-laterally,
contains, in addition to the arcuate fibers, the cerebello-olivary fasciculus before mentioned,

THE PONS

775

and the cerebellospinal fasciculus or direct cerebellar tract. The dorsal longitudinal fascic-
ulus corresponds to the ventral grountl-bundle of the spinal cord, displaced dorsally by the decus-
sation of the pyramids and fillet. In the posterior part of the medulla it is not marked off from
the fillet, along the dorsal edge of which it lies. From the level of the hypoglossal nucleus forward
it is distinct and can be traced as a conspicuous tract in the ventral margin of the gray matter of the
floor of the fourth ventricle and of the central gray matter of the mid-brain. Ventral to the resti-
form body and related laterally to the external arcuate fibers there is a considerable bundle of
longitudinal fibers, the spinal root (Tractus spinalis) of the fifth nerve; medial to it is the
terminal nucleus of the sensory root of the nerve.

^"^m^

Fig. 63.3. — Cross-section of Medulla Oblongata of Horse, Passing through Facial Nucleus.
Cr, Corpus restiforme ; Z), dorsal longitudinal fasciculus; Fa, ascending part of facial nerve; L, fillet; A''?', nucleus
of facial nerve; N8, triangular nucleus of of vestibular root of eighth nerve; NS', spinal root of eighth nerve; Py, pyra-
mid; /?a, raphe; ff7, radicular part of facial nerve; flS, vestibular root of eighth nerve; S;/, substantia gelatinosa; Ta,
posterior end of tuberculum acusticum; V, spinal root of trigeminus. (EUenberger-Baum, Anat. d. Haustiere.)

f, K

Fig. 6.34. — Cross-section of Medulla Oblongata of Horse; Section Passes through Middle of Corpus

Tr.^pezoideum.
Cr, Corpus restiforme; D, dorsal longitudinal bundle; Fa, ascending part of facial nerve; Fa', emergent or de-
scending part of facial nerve; L, fillet; M, central white matter of cerebellum; N6, abducens nucleus; A',?, triangular
nucleus; N8', nucleus of Deiters; N8", tuberculum acusticum; Oo, anterior olive; Pi/, pyramid; R6, root of abducens
nerve; R7, root of facial nerve; Re, cochlear nerve; Rv, vestibular nerve; Sg, substantia gelatinosa; T, corpus
trapezoideum; V, spinal root of trigeminus. (Ellenberger-Baum, Anat. d. Haustiere.)

The Pons
The pons is that part of the brain stem which Hes between the medulla and
the cerel^ral peduncles; it is marked off from these ventrally by anterior and

776 NERVOUS SYSTEM OF THE HORSE

posterior grooves. Viewed ventrally, it is elongated transversely, convex in
both directions, and presents a -wide shallow median groove (Sulcus basilaris),
which lodges the basilar artery. Laterally a large part of its mass curves dorsally
and backward into the base of the cerebellum, forming the middle cerebellar
peduncle (Brachium pontis). The superficial origin of the trigeminal (fifth) nerve
is at the lateral limit of the ventral surface. Transverse striations indicate the
course of superficial (ventral) fibers which connect the two sides of the cerebellum.
The dorsal surface is blended on either side with the overlying anterior peduncles
of the cerebellum; the central free portion forms the anterior part of the floor of
the fourth ventricle, and will be considered in the account of that cavity.

On cross-section the pons is seen to be composed of dorsal and ventral parts. The dorsal
part (Pars dorsaUs pontis) consists superficially of a layer of gray matter covered by the epen-
dyma of the fourth ventricle. Beneath this the median raphe of the medulla is continued into
the pons, di\dding it into similar halves. In the anterior part of the pons the fillet div-ides into
a medial and a lateral part, the medial and lateral fillets (Lemniscus mediahs, lateralis) ; the latter
arches outward to reach the outer side of the anterior cerebellar peduncle. The dorsal longitudinal
fasciculus becomes sharply defined into a round bundle which hes close to the raphe under the
gray matter of the floor of the fourth ventricle. In cross-section the formatio reticularis forms
a large area below the superficial gray matter and the longitudinal bundles. Dorso-lateraUy is
the large rounded section of the anterior cerebellar peduncle. Lower down is a large bundle, the
sensory root of the fifth nerve. In front of this is the motor nucleus of the same nerve, lateral
to which is its motor root. The basilar or ventral part of the pons (Pars basilaris pontis) is com-
posed of transverse and longitudinal fibers, and a large amount of gray matter which is broken up
into small masses (Nuclei pontis) by the intersection of the fibers. The transverse fibers are gath-
ered laterally into a compact mass which turns dorsally and backward and enters the central white
matter of the cerebellum, forming the middle cerebellar peduncle. Centrally the fibers are ar-
ranged in bundles which intercross. The transverse fibers are chiefly of two kinds. Some arise
from the Purkinje cells of the cerebellar cortex and pass either to the opposite side of the cere-
bellum or turn at the raphe and run forward and backward in the brain stem. Others are axones
of cells of the nuclei pontis, and pass to the hemispheres of the cerebellum. The corpus trape-
zoideum is mainly the central continuation of the cochlear division of the acoustic nerve. Above
it is the smaU anterior olivary nucleus (Nucleus ohvaris nasaUs). The longitudinal fibers of the
ventral part of the pons consist chiefly of the cerebrospinal or pyramidal fasciculi. These come
from the ventral part (basis) of the cerebral peduncles and are situated laterally, interspersed
among the deep transverse fibers in the anterior part of the pons. Toward the posterior part the
bundles inchne toward the median plane and become collected into a compact mass which appears
superficially at the posterior border. Many fibers come from the cerebral cortex and terminate
in the nuclei of the gray matter of the pons; they may be designated corticopontile fibers.

The Cerebelujm

The cerebellum is situated in the posterior fossa of the cranium, and is sep-
arated from the cerebral hemispheres by the transverse fissure and the tentorium
cerebelli which occupies it. It overlies the pons and the greater part of the medulla,
from which it is separated by the fourth ventricle. Its average weight is about two
ounces (ca. 60 gm.), or about 9 per cent, of the weight of the entire brain. Its
shape is approximately globular but very irregular. It is somewhat compressed
dorso-ventrally and its transverse diameter is the greatest.

The anterior surface faces dorsally and forward and is covered partially by
the tentorium cerebelli. The posterior surface is almost vertical. The ventral
siuiace or base lies over the fourth ventricle, and is connected by three pairs of
peduncles \vith the medulla, pons, and mid-brain.

It is customary to recognize three gross divisions of the cerebellum, viz., the
median vermis and two lateral hemispheres. The vermis cerebelli is curved in a
circular manner so that its two extremities are close together, or even in contact
on the ventral surface. The anterior extremity is termed the lingula; it lies
between the cerebellar peduncles and gives attachment to the anterior medullary
velum (Velum medullare orale), a thin lamina which forms the anterior part of the
roof of the fourth ventricle. The posterior extremity, the nodulus, gives attach-
ment to the posterior medullary velum (Velum medullare aborale), which covers the
posterior recess of the fourth ventricle. The hemispheres (Hemisphseria cerebelli)

THE CEREBELLUM 777

are separated from the vermis by two deep paramedian fissures. They lie in the
lateral depressions of the cerebellar compartment of the cranium.

In tracing the fissures from behind forward it will be noticed that they are nearly sagittal
as far as the anterior surface, where they diverge widely, so that the vermis forms all of the fore
part of the cerebellum.

The surface of the cerebellum is further cut up into numerous g3Ti (cerebelli)
by narrow and relatively deep sulci (cerebelli), many of which approach a trans-
verse direction. Certain of the sulci are more pronounced than the others, and by
means of them it is possible to define groups of gyri. Such groups are termed
lobes, and have received specific names, derived chiefly from the systematic de-
scriptions of the human cerebellum.

The lobes of the vermis are readily distinguished on median section. Enumerated from
the anterior to the posterior extremity they are: (1) lingula, (2) lob us centralis, (3) lob us ascendens,
(4) lobus culminis, (5) lobus chvi, (6) tuber vermis, (7) pyramis, (8) uvula, (9) nodulus. Each
hemisphere is cut into laterally by two sulci which mark off two sagittal discoid masses, termed by
Ziehen tabulations. The lateral tabulation consists of four or five lobules, the lowest of which
is regarded as the flocculus. The medial part of the hemisphere is divided into three or four lobes.
Martin proposes the term tractus for the sagittal masses; on tliis basis the vermis would become
the tractus medianus, and the others tractus laterales (primus, secundus, etc.). In the absence
of a satisfactory morphological basis it seems undesirable to deal with the lobation of the cere-
bellum in further detail.

The cerebellar peduncles (Pedunculi cerebelli), three on each side, join the
central white matter of the cerebellum at the base. The posterior peduncle is the
restiform body of the medulla, a large rounded tract derived from the lateral and
ventral columns of the cord. Near the middle of the medulla it inclines outward,
forms the lateral wall of the fourth ventricle, and ends by entering the central white
matter of the cerebellum. The middle peduncle is formed, as previously seen, by
the brachium pontis. The anterior peduncles (Brachia conjunctiva) pass forward
on either side on the dorsal surface of the pons, forming the lateral boundary of the
fore part of the fourth ventricle. They disappear under the corpora quadrigemina
into the substance of the mid-brain. At the point of disappearance the trochlear
(fourth) nerve emerges from the mid-brain. In some cases two or three bundles of
fibers (Fila lateralia pontis) arise in the angle between the middle and anterior
peduncle, curve obliquely forward and downward over the outer aspect of the
latter, and spread out on the ventral face of the cerebral peduncle just in front of
the pons.

On sagittal section the cerebellum is seen to consist of a layer of gray cortical
substance (Substantia corticalis) and the white meduUary substance. The white
matter consists of a large basal mass (Corpus meduUare), which is joined by the
peduncles and gives off primary laminae (Laminae medullares) to the lobules;
from these secondary and tertiary laminae arise, the latter entering the gyri. The
arrangement on sagittal section is tree-like, hence the term "arbor meduUaris,"
which is applied to it.^ The central gray matter consists of groups of cells which
form small nuclei embedded in the central white substance.

The principal connections estabUshed by the peduncular fibers of the cerebellum are as
follows: The posterior peduncle (Corpus restiforme) is composed of afferent and efferent fibers
which connect the cerebellum with the medulla and spinal cord. The cerebello-spinal fascicu-
lus or direct cerebellar tract, which arises from the cells of the nucleus dorsahs (Clarke's column)
of the cord, ends in the cortex of the vermis; many of its fibers cross to the opposite side. Nu-
merous arcuate fibers from the nucleus gracilis and nucleus cuneatus of the same and opposite
sides estabhsh connections with cells of the cerebellar cortex. Olivo-cerebellar fibers (chiefly
afferent) connect with the ohvary nucleus of the same and of the opposite side of the medulla
oblongata. The nucleo-cerebellar fasciculus comprises fibers derived from the nuclei of the
fifth, eighth, and tenth cranial nerves (Edinger). The descending cerebello-spinal fasciculus
consists of fibers wliich terminate in relation with cells of the ventral horns of the spinal cord.
The chief facts concerning the middle peduncle have been mentioned in the description of the
pons. The anterior peduncle is essentially an efferent tract, the fibers of which pass forward

^ Also known as the "arbor vitae."

778

NERVOUS SYSTEM OF THE HORSE

to the tegmentum of the cerebral peduncle, the hypothalamic region, and the thalamus. After
the peduncles disappear under the corpora quadrigemina, they converge and many of their fibers
intercross, forming the decussation of the anterior peduncles. A considerable number of fibers
end in tlic nucleus ruber. Thence impulses are transmitted in two directions: first, by thalamo-
cortical fibers to the cerebral cortex; second, by the rubro-spinal tract through the brain stem
and lateral columns of the cord to the ventral horn cells. The ventro-lateral cerebellospinal
fasciculus (Gowers' tract) is an ill-defined tract which connects the spinal cord with the cere-
bellum. Its fibers appear to be axones of cells of the dorsal columns of the cord; they pass
in the lateral column of the cord, become scattered in passing through the reticular formation
of the medulla and pons, and enter the cerebellum by way of the anterior medullary velum.

The Fourth Ventricle
The fourth ventricle (Ventriculus quartus) is the cavity of the rhombencepha-
lon; it communicates with the central canal of the spinal cord behind and through

Corpus callosum {section) Lateral vtnlrich

Plrxiis chorioideus

Cor/)us quddrigt'tninum

(in(('i-ius

Corpus qudflrigt-mirium

posterius

Septum pellucidum

Nucleus caudatus

I'halantus {anterior
tubercle)

Stria terminalis

Corpus geniculatum
Idterale

Corpus geniculatum mediate

Peduiiculus cerebri

Velum medullare anterius

Brachium conjunctivum
Brachium pontis

Corpus restiforme

Ca la m us scri plori us
Tuberculum cinereum

Fissura mediana

Fig. 635. — Dissection of Brain Stem and Basal Ganglia of Horse; Dorsal View.
/, Columns of fornix (section) ; 2, remnant of hippocampus; 3, taenia thalami; 4, pineal body; S, eminentia medialia;
e, sulcus inedianus; 7, sulcus limitans; V.IIL, third ventricle; V.IV., fourth ventricle. Stump.s of cranial nerves are
indicated by Roman numerals.

Tuberculu m acusticum
Tcenia ventriculi quarti

the cerebral aqueduct with the third ventricle in front. It is somewhat rhomboid
in outline, elongatetl from before backward, and narrowest behind. It is lined
completely by an epithelium (Ependyma) and contains a small amount of fluid.
Its floor, the fossa rhomboidea, is formed by the medulla oblongata and pons

THE FOURTH VENTRICLE 779

and is marked by three longitudinal furrows which converge behind. It is widest
and deepest a little in front of its middle. The posterior part narrows to a point at
the opening of the central canal of the spinal cord, and on account of its appearance
in man it has been termed the calamus scriptorius. The median sulcus (Sulcus
medianus) extends the entire length of the floor and is deepest toward the ends.
The limiting sulci (Sulci limitantes) begin on either side of the opening of the central
canal and extend forward as the lateral limits of the rhomboid fossa. Just beyond
the middle of the fossa they expand into a shallow depression, the anterior fovea
(Fovea oralis). On either side of the median sulcus and margined laterally by the
limiting sulcus is a slightly rounded column, the eminentia medialis. Opposite the
fovea this presents an elongated prominence, the coUiculus facialis, so named be-
cause it overlies the bend formed by the fibers of origin of the facial nerve. Lateral
to the limiting sulcus is a long fusiform elevation, the area acustica, from which a
band of fibers (Striae acusticae) winds over the anterior end of the restiform body to
the superficial origin of the cochlear nerve.

The lateral wall is formed by the restiform body and the anterior peduncle
of the cerebellum.

The roof (Tegmen ventriculi quarti) is formed in its middle part by the vermis

S T t
Fig. 636. — Brain Stem and Basal Ganglia or Horse; Right View.
F.a., External arcuate fibers; C.r., corpus restiforme; P, pyramid; T, corpus trapezoideum; B. p., middle pe-
duncle of cerebellum; P. f., cerebral peduncle; S, sulcus lateralis; TJ., tractus transversus; L, trigonum lemnisci; C.a.,
corpus quad, ant.; C.p., corpus quad, post.; B, commissure of C.p.; G, corpus geniculatum mediale; T.o., olfactory
peduncle; B.o., olfactory bulb.

of the cerebellum, covered by the epithelium before mentioned. There is com-
monly a dorsal recess (Fastigium) between the extremities of the vermis. The
anterior part of the roof is formed by a thin lamina of white substance, the anterior
medullary velum (Velum medullare anterius),^ which extends backward from the
corpora quadrigemina, and is attached on either side to the anterior peduncles of
the cerebellum. Its anterior part is relatively thick and contains the decussation
of the fibers of the trochlear nerves. Posteriorly it blends with the white matter
of the cerebellum. A thin lamina of white matter, the posterior medullary velum
(Velum medullare posterius), backed by pia mater, completes the roof posteriorly
After removal of the cerebellum the line of attachment (Taenia ventriculi quarti) to
the medulla is seen; it begins centrally over the opening of the central canal, runs
forward on the inner face of the restiform body, and turns outward behind the
brachium pontis. The thick part which stretches over the posterior angle of the
ventricle is termed the obex. The posterior part of the ventricle forms three
recesses, of which two are lateral and the third median and posterior. The lateral
recesses (Recessus lateralis) communicate with the subarachnoid space by lateral
apertures (Aperturse laterales). The layer of pia mater which actually forms the
roof here is named the tela chorioidea of the fourth ventricle. It is triangular in
outline and closely adherent to the velum. It forms three fringed masses which
1 Formerly termed the valve of Vieussens.

780 NERVOUS SYSTEM OF THE HORSE

contain vascular convolutions and are designated the median and lateral chorioid
plexuses of the fourth ventricle (Plexus chorioides ventriculi quarti). They appear
to lie ^\^thin the ventricle, but are really excluded from the cavity by the epithelial
lining, which they invaginate.

THE MESENCEPHALON

The mesencephalon or mid-brain connects the rhombencephalon with the
fore-brain. In the undissected brain it is covered dorsally by the cerebral hemi-
spheres. It consists of a dorsal part, the corpora quadrigemina, and a larger
ventral part, the cerebral peduncles, which are visible on the base of the brain.
It is traversed longitudinally by a narrow canal, the cerebral aqueduct, which con-
nects the fourth ventricle with the third (Fig. 639).

The corpora quadrigemina^ are four rounded eminences which lie under the
posterior part of the cerebral hemispheres. They consist of two pairs, separated
bj^ a transverse groove. The anterior pair (Colliculi nasales) are larger and much
higher than the posterior pair. They are gray in color, almost hemispherical, and
are separated by a narrow furrow which leads forward to the subpineal fovea.
A wide groove intervenes between them and the optic thalami. The posterior pair
(Colliculi caudales) are relatively small and are paler than the anterior pair. They
are marked by a wide median depression, and are limited behind bj' a transverse
furrow (Sulcus postquadrigeminus), at either side of which the trochlear (fourth)
nerve emerges. Laterally each is prolonged to the medial geniculate body by a
band of white matter termed the posterior peduncle (Brachium aborale).^

The cerebral pedimcles (Pedunculi cerebri)^ appear on the base of the brain
as two large, rope-like stalks which emerge from the pons close together and diverge
as they extend forward to enter the cerebrum. At the point of disappearance the
optic tract winds obliquely across the peduncle. About half an inch further back
a small tract (Tractus peduncularis transversus) curves across the peduncles, and
behind this, near the median line, is the superficial origin of the oculomotor nerve.
The triangular depression between the diverging peduncles is the interpedimcular
fossa (Fossa interpeduncularis) . It is covered to a large extent by the hypophysis
cerebri or pituitary body, a discoid brown mass which is connected with the base of
the brain by a hollow stalk, the infimdibulum. The posterior part of the fossa is
pierced by numerous minute openings which transmit blood-vessels, and is therefore
termed the substantia perforata posterior. The objects here belong to the dien-
cephalon, and wiW be described later. The lateral aspect of the peduncle is marked
by a groove (Sulcus lateralis mesencephali) which indicates the division into a
dorsal part, the tegmentimi, and a ventral part, the basis pedimculi; these are
separated by a layer of dark gray matter, the substantia nigra. The triangular
area (Trigonum lemnisci) above the lateral groove is faintly marked by fibers
passing dorsally and backward to the anterior cerebellar peduncle; these belong
to the fillet or lemniscus, an important tract that connects the thalamus and corpora
quadrigemina with, the sensory reception nuclei of the opposite side of the medulla.

The aqueduct of the cerebrtmi (Aquseductus cerebri)^ is the canal which extends-
through the mid-])rain from the third to the fourth ventricle. It is largest beneath
the posterior pair of corpora quadrigemina. It is surrounded by a layer of gray mat-
ter (Stratiun griseum centrale), in the ventral part of which are the nuclei of origin

1 In the new nomenclature the term lamina quadrigemina is applied to the dorsal mass of
the mid-brain, and the four eminences which it bears are the corpora quadrigemina.

2 In man a distinct superior brachium connects the superior pair with the lateral geniculate
body, but in the domesticated animals the imion with the optic thalamus is too direct to allow of
any definite arm being recognized.

' Also termed the crura cerebri.

* Also termed the aqueduct of Sylvius.

THE DIENCEPHALON 781

of the oculomotor and trochlear nerves, and laterally nuclei of the mesencephalic
roots of the trigeminal nerves.

THE DIENCEPHALON

The diencephalon or inter-brain comprises the thalamus and a number of
other structures grouped about the third ventricle, the cavity of this division of the
brain.^ To expose its dorsal aspect, the greater part of the cerebral hemispheres,
the corpus callosum, the fornix, the hippocampus, and the tela chorioidea of the
third ventricle must be removed (Fig. 635).

The thalamus is the principal body in this part of the brain. It is a large
ovoid mass placed obliquely across the dorsal face of each cerebral peduncle, so
that the long axes of the two thalami would meet in front about at a right angle.
Medially they are fused to a large extent, and around the area of adhesion they
are separated by a sagittal circular space, the third ventricle. The dorsal surface
is convex, and is separated from the overlying hippocampus by the tela chorioidea.
Laterally it is separated from the nucleus caudatus by an oblique groove in which
there is a band of white matter termed the stria terminalis. When the tela chori-
oidea of the lateral ventricle has been detached from this band it leaves a torn edge,
the taenia chorioidea. Medially it is bounded by a narrow white band, the stria
medullaris ; to this the tela chorioidea of the third ventricle is attached, and when
the latter is removed in dissection, there remains a thin irregular edge termed the
taenia thalami. The striae unite posteriorly and blend with the stalk of the pineal
body. Near this point they present a small enlargement caused by the nucleus
habenulae. Anteriorly there is a small eminence, the anterior tubercle of the
thalamus (Tuberculum orale thalami) . The posterior part of the thalamus has the
form of a rounded ridge which is continuous laterally with the optic tract.^ Behind
the point of origin of the tract, in the angle between the thalamus and the cerebral
peduncle, is the medial geniculate body (Corpus geniculatum mediale), a well-
defined oval prominence.

The lateral surface is separated from the lenticular nucleus by the internal capsule, an
important mass of white matter composed of fibers passing to and from the cerebral cortex.
These fibers go to form a large part of the ventral portion (basis) of the cerebral peduncle. From
the entire lateral surface of the thalamus fibers pass into the internal capsule and radiate to reach
the cerebral cortex; similarly fibers coming from the cortex converge in the internal capsule
to enter the thalamus. This arrangement is termed the thalamic radiation. Ventral to the
thalamus proper is the hypothalamic tegmental region. This is the continuation of the tegmental
part of the cerebral peduncle into the diencephalon. It contains the red nucleus (Nucleus ruber),
an important ganglion on the course of the motor tracts. It receives numerous fibers from the
cerebral cortex and the corpus striatum. From it fibers proceed to the thalamus and to the
spinal cord; the fibers to the cord, which constitute the rubro-spinal tract (Tractus rubro-spinalis),
cross to the opposite side and extend back in the tegmentum to the lateral columns of the cord.
Lateral to the red nucleus a conspicuous lenticular area of dark gi-ay matter is visible on cross-
sections of the hypothalamic region; this is the hypothalamic nucleus (Nucleus hypothalamicus
Luysi), which consists of pigmented nerve-cells scattered through a dense network of fine medul-
lated fibers, and is richly supplied with capillary blood-vessels. The two nuclei are connected
by a transverse commissure (Commissura hypothalamica) , which crosses the floor of the third
ventricle above the mammiUary body.

The pineal body or epiphysis cerebri (Corpus pineale) is a small ovoid or fusi-
form red-browm mass situated in a deep central depression between the thalami and
corpora quadrigemina. It is variable in size, but is commonly about 10 to 12
mm. long and 6 mm. wide. It is attached at the poster o-superior quadrant of
the third ventricle by a short stalk, in which is a small recess of that cavity. Its

1 On a strictly embryological basis the optic part of the hjrpothalamus, comprising the
anterior part of the third ventricle and the structures associated with it, belongs to the telen-
cephalon, but wiU be considered here as a matter of convenience.

2 This backward projection of the thalamus is equivalent to the pulvinar and lateral genicu-
late body of man, which are not superficially divided in the horse.

782

NERVOUS SYSTEM OF THE HORSE

base blends in front with the junction of the striae medullares of the thalamus.
Immediately under the posterior part of the stalk is a short transverse band of white
matter, the posterior commissure of the cerebrum (Commissura aboralis cerebri).

The pineal body is enclosed in a fibrous capsule from which numerous trabeculae pass inward,
dividing the organ into spaces occupied by round epithelial cells of the same origin as the epen-
dyma of the ventricle.

The mammillary body (Corpus mammillare) is a white, round elevation a little
larger than a pea which projects ventrally at the anterior end of the median furrow
of the interpeduncular fossa. While it is a single body in external form in the horse.

Sulcus rhinali
Ventral horn of
lateral ventricle

< )])tic tract

thalami

Fig. 637. — Cross-section of Brain of Horse, Natural Size.
Section passes through posterior part of third ventricle and is viewed from behind. 1, Longitudinal fissure; 2,
hippocampus; 2', fimbria; S, septum pellucidum; 4, lateral ventricle; 5, thalamus; 6, habenula; 7, third ventricle;
8, cerebral peduncle; 8', hypothalmus; ,9, mammillary body; 10, hypophysis or pituitary body; 11, piriform lobe;
12, ventral end of hippocampus; 13, amygdaloid nucleus. Between the upper parts of the taenise thalami is the chorioid
plexus of the third ventricle, and above this are the internal cerebral veins.

sections show that it is double in structure and contains a nucleus of gray matter
on either side (Fig. 637).

Three sets of fibers are connected with the mammillary body. The column of the
fornix curves down in the lateral wall of the third ventricle to the body and many of the fornix
fibers end in it. A bundle (Fasciculus thalamo-mammillaris) passes dorsally and backward
from it into the anterior part of the thalamus, and a tract (Fasciculus pedunculo-mammillaris)
extends back in the floor of the third ventricle to the tegmentum of the mid-brain.

The h5rpophysis cerebri or pituitary body was mentioned as covering part of the
interpeduncular fossa. It is oval in outline, flattened dorso-ventrally, and nearly an
inch (ca. 2 cm.) in width. It is attached by a delicate tubular stalk, the infundibu-
lum, to the tuber cinereum, a small gray prominence situated between the optic
chiasm in front and the mammillary body behind. A fibrous capsule, derived from
the dura mater, encloses and is intimately adherent to it.

The body consists of two parts which can be distinguished on sections by their color (Fig. 639).
The glandular lobe is brown in color and forms the external and greater part of the body. It is

THE TELENCEPHALON 783

glandulax in character a,nd there is good ground for the view that it is an organ of internal se-
cretion. Besides the cliief cells, which stain lightly, it contains large, deeply staining chromophile
cells. It arises as an outgrowth from the dorsal wall of the primitive mouth cavity. The cerebral
lobe is pale and is connected with the infundibulum so as to form a rather flask-shaped arrange-
ment. It is almost entirely enclosed by the glandular part. It arises as an outgrowth from the
primitive diencephalon, but loses most of its earher nervous character.

The optic chiasm and tracts form the anterior boundary of the interpeduncular
fossa (Figs. 629, 636). The optic chiasm (Chiasma opticum) is formed by the
convergence of the optic nerves and the crossing of the major part of the fibers of
the nerve of one side to the tract of the opposite side. From the chiasm each optic
tract (Tractus opticus) curves obhquely around the cerebral peduncle to the pos-
terior part of the thalamus and the medial geniculate body; some fibers reach the
anterior quadrigeminal body.

AH the fibers in the chiasm are not derived from the optic nerves. The posterior part
contains fibers which pass from one tract to the other and are connected with the medial genicu-
late bodies; this bundb is called the ventral commissure (Commissura ventralis). Above it is
the dorsal commissure (Commissura dorsahs), the fibers of which enter the hypothalamic body.^

The third ventricle (Ventriculus tertius) is the narrow annular space between
the thalami. It communicates by means of the cerebral aqueduct with the fourth
ventricle behind, and in front it is continuous with the lateral ventricle on each side
through the interventricular foramen. Its floor is formed by the structures of the
interpeduncular fossa, and to a small extent by the tegmentum of the cerebral
peduncles. The roof is formed in the strict sense only by the ependyma, above
which is a fold of pia mater, termed the tela chorioidea of the third ventricle.- The
roof is invaginated by the two delicate chorioid plexuses (Plexus chorioidei ventriculi
tertii) which appear to lie within the ventricle, although they are excluded from the
cavity by the epithelium. When the tela is removed, the delicate ependyma of the
roof is torn away with it, leaving the line of attachment to the stria medullaris to
constitute the taenia thalami. The anterior wall is formed by the lamina terminalis,
a thin layer of gray matter which extends from the optic chiasm dorsally to the
corpus callosum. A distinct rounded band of white matter extends across its
posterior face, bulging into the ventricle. This is the anterior commissure (Com-
missura oralis) of the cerebrum; its fibers extend to the olfactory bulb and to the
piriform lobe. A similar but more slender posterior commissure (Commissura
aboralis) crosses the posterior wall above the entrance to the cerebral aqueduct;
the connections of its fibers are not yet clearly known. The interventricular
foramen^ is situated on either side of the anterior part of the ventricle, and leads
outward and slightly dorsally between the column of the fornix and the anterior
tubercle of the thalamus (Fig. 639). The cavity presents three recesses or diver-
ticula, of which two are ventral and the third is posterior. The optic recess (Re-
cessus opticus) lies above the optic chiasm. Just behind it is the infundibular
recess (Recessus infundibuli), which extends through the infundibulum to the
pituitary body. The pineal recess (Recessus pinealis) is in the stalk of the pineal
body.

THE TELENCEPHALON
The telencephalon or end-brain comprises two principal parts, the cerebral
hemispheres and the optic part of the hypothalamus. The latter has been con-
sidered as a matter of convenience in the description of the diencephalon.

The Cerebral Hemispheres
The cerebral hemispheres (Hemisphseria) form the greater part of the fully
developed brain. Viewed from above (Fig. 631) they form an ovoid mass, of
1 These are commonly termed Gudden's and Meynert's commissures respectively.
^ Also commonly termed the velum interpositum. ^ Also termed the foramen of Monro.

784 NERVOUS SYSTEM OF THE HORSE

which the broader end is posterior, and the greatest transverse diameter is a Httle
behind the middle. The two hemispheres are separated by a deep median cleft,
the longitudinal fissure of the cerebrmn (Fissura longitudinalis cerebri), which is
occupied by a sickle-shaped fold of dura mater, the falx cerebri. In front the
separation is complete, and it appears to be behind also, but here the two hemi-
spheres are attached to each other over a small area by the pia mater. When the
hemispheres are gently drawn apart, it is seen that the fissure is interrupted in its
middle part at a depth of a little more than an inch (ca. 3 cm.) by a white commis-
sural mass, the corpus callosum ; this connects the hemispheres for about half of
their length. The transverse fissure (Fissura transversa cerebri) separates the
hemispheres from the cerebellum, and contains the tentorium cerebelli.

The convex or dorso-lateral surface (Facies convexa cerebri) conforms closely
to the cranial wall. The medial surface (Facies medialis cerebri) (Fig. 639) is flat
and sagittal and bounds the longitudinal fissure ; to a large extent it is in contact with
the falx cerebri, but behind the great cerebral vein the two hemispheres are in
contact and are attached to each other over a small area as noted above. In well-

FiG. 638. — Left Cerebral Hemisphere of Horse; Lateral View. The Olfactort Bulb is Cut Off.

1, Lateral fissure (of Sylvius) ; ;2, 5, 4. rniddle, posterior, and anterior branches of /,• .5, presylvian fissure; 6, 6', sulcus

rhinalis, anterior et posterior; 7, suprasylvian fissure; 8, ectomarginal fissure; 9, 9', ectosylvian fissure.

hardened specimens there is usually an impression for the vein in front of the area
of adhesion. The base or ventral surface (Basis cerebri) (Fig. 629) is irregular.
Its anterior two-thirds is adapted to the cerebral fossa of the cranial floor. Cross-
ing this area in front of the optic tract is a depression, the lateral fossa (Fossa
lateralis), which leads outward to the lateral fissure (Fissura lateralis),^ and lodges
the middle cerebral artery. In front of the fossa there is a considerable rounded
elevation knowai as the trigonum olfactorium. The trigonum and the medial part
of the fossa are pierced by numerous openings for the passage of small blood-vessels
and are equivalent to the suljstantia perforata anterior of man. Behind the lateral
part of the fossa is the rounded anterior end of the piriform lobe (Lobus piriformis) .
Traced backward, the lobe curves dorso-medially over the optic tract and the
thalamus to the tentorial aspect of the hemisphere; its continuation, the hippo-
campus, forms part of the floor of the lateral ventricle, and will be examined later.
The tentorial surface (Fig. 640) is flattened, faces medially and backward as well
as ventrally, and rests largely on the tentorium cerebelli; on its anterior part there
is a shallow depression adapted to the corpora quadrigemina and the pineal body.
^ Also commonly known as the fissm-e of Sylvius.

THE CEREBRAL HEMISPHERES 785

The frontal pole or anterior extremity (exclusive of the olfactory bulb) is
compressed laterally, and the occipital pole or posterior extremity forms a blunt
point.

The hemisphere comprises: (1) The pallium, which consists of an outer layer
of gray matter, the cortex (Substantia corticalis), covering a large mass of white
matter (Centrum semiovale) ; (2) the rhinencephalon or olfactory portion of the
brain; (3) the corpus callosum and fornix, the great commissural white masses;
(4) the lateral ventricle and certain important structures associated therewith.

The pallium is throwai into numerous folds, the gyri cerebri, which are sep-
arated by sulci or fissures of varying depth. The general pattern of the gyri and
sulci is similar in normal brains of the same species, but the details are very variable
and are never alike on the two hemispheres of the same brain. In the horse the
arrangement is complicated by the existence of numerous short accessory fissures
which cut into the gyri at right angles and tend to confuse the observer. The
principal fissures and sulci of the convex surface (Figs. 631, 632, 638) are as follows:^

1. The lateral fissure (Fissura lateralis Sylvii) ascends on the lateral surface
of the hemisphere as the continuation of the fossa lateralis in front of the piriform
lobe. After crossing the lateral olfactory stria it divides into three branches;
of these one passes dorsally, one runs obliquely forward and dorsally, and the third
is directed dorsally and backward. It contains the middle cerebral artery.

2. The suprasylvian fissure (F. suprasylvia)- is long and divides a large part
of the convex surface of the hemisphere into dorsal and lateral portions. It begins
on the dorso-medial border near its anterior end, and, inclining gradually do^vnward,
passes back to end on reaching the tentorial surface. It is usually continuous
medially with the transverse fissure and in front with the presylvian fissure.

3. The presylvian fissure (F. prsesylvia) is on the anterior part of the hemi-
sphere, passes forward and ventro-laterally almost to the frontal pole, and then
inclines backward to end at the groove which marks the dorsal limit of the rhinen-
cephalon (Sulcus rhinalis).

4. The marginal fissure (F. marginalis) extends along the dorso-medial border.
It begins a little in front of the middle of the border and turns around the occipital
pole to end on its tentorial aspect.

5. The entomarginal fissure (F. entomarginalis) lies medial to the dorso-
medial border. It does not extend quite as far forward as the marginal fissure,
from which it is separated by a narrow gyrus.

6. The ectomarginal fissure (F. ectomarginalis) lies about midway between the
marginal fissure and the posterior part of the suprasylvian fissure.

7. The sulcus rhinalis is a very distinct furrow on the ventral part of the
lateral surface which marks off the olfactory part of the brain (rhinencephalon) from
the rest of the hemisphere. It is undulating and is highest where it is crossed by
the lateral fissure.

Just above this point is a lobe which is homologous with the insula of man. When the
overhanging gyri which partly conceal it — forming the operculum — ^are removed, there are dis-
closed several short, deeply placed gjTi (Gyi'i breves).

1
On the medial surface (Fig. 639) the main fissures and sulci are as follows:
1. The calloso-marginal fissure (F. callosomarginalis) is extensive and well
defined. It is approximately parallel to the dorso-medial border of the hemisphere,
from which it is about half an inch distant. It begins in front a short distance
below and in front of the genu of the corpus callosum, and forms a C-shaped curve,
its posterior part extending on the tentorial surface to a point behind the depression

1 The homologies and terminology of many fissures of the brain in the domesticated animals
are still in a chaotic state. Only a few of the most important and constant ones are given here.

2 Termed by Lesbre the parietal fissure and by M'Fadyean the great oblique fissure.

786

NERVOUS SYSTEM OF THE HORSE

for the corpora quadrigemina. It separates the marginal gyri above from the gyrus
fornicatus, which extends down to the corpus callosum.

2. The transverse fissure (F. transversa) begins a Httle behind the middle of
the calloso-marginal fissure, passes obliquely dorsally and forward to the dorso-
medial border — into which it cuts deeply — and usually joins the suprasylvian
fissure.^

3. The subfimbic fissure (F. sublimbica) curves over the gyrus fornicatus a
short distance above the corpus callosum. Its middle part is commonly indistinct,
and it is often divided into anterior and posterior parts.

Trnnnverse Calloso-mar-
Gynin furiiiculus fissure ginal fissure

Marginal fissure

- Entomarginal fissure

A nterior com-
missure Lamina Chiasm a
terminalis opiicum

Posterior I
commissure ■

Anterior Fourth
Hypophysis Cerebral medul- ventricle
'cerebri aqueduct lary

velum.

Fig. 639. — Median Section of Brain of Horse.
The membranes and vessels are removed. C, Central white matter (corpus meduUare) of cerebellum; P.c, cere--
bral peduncle; C.q., corpora quadrigemina; P, pineal body; Th., thalamus; V.III., third ventricle; r, optic recess;
r', infundibular recess; Cm., mammillary body; s, subcallosal gyrus; A.p., area parolfactoria; G, genu of corpus
callosum; .S, splenium of same; F.i., interventricular foramen; B.o., olfactorj' bulb; C.p.. choroid plexus of lateral
ventricle. The cerebral lobe of the hypophysis cerebri or pituitary body is distinguished by its lighter color.

4. The callosal sulcus (Sulcus corporis callosi) separates the corpus callosum
from the gyrus fornicatus.

The hippocampus'- is a gyrus which curves from the deep face of the piriform
lobe around the thalamus and forms the posterior part of the floor of the lateral
ventricle. It can be displayed by cutting away the brain stem up to the optic
tract and the interventricular foramen. Viewed from below, the hippocampal
gyrus is seen to form a semicircular curve from the apex of the piriform lobe to
the angle of divergence of the crura of the fornix, i. e., to a point under the central
part of the corpus callosum. It is separated deeply by the hippocampal fissure
from the gyrus dentatus (Fig. 640). Along the concave margin of the latter is a

^ By some authors this is regarded as the homologue of the cruciate fissure of the dog, but it
seems likely tliat the latter is represented by a short and inconstant sulcus situated further forward.
^ Also termed the cornu Ammonis.

THE CEREBRAL HEMISPHERES

787

band of white matter, termed the fimbria, which is the prolongation of the greater
part of the crus of the fornix into this region. The ventricular surface of the
hippocampus (Fig. 642) is covered with a thin layer of white matter, the alveus,
which is also derived from the crus of the fornix, and is therefore continuous with
the fimbria. The two hippocampi are connected at their highest parts by trans-
verse fibers which constitute the hippocampal commissure.

The interval between the hippocampus and fimbria on the one hand, and the
brain stem on the other, is a lateral continuation of the transverse fissure of the
brain, and is occupied by a fold of pia mater, the tela chorioidea of the third ven-
tricle. This fold is triangular in outline and its apex reaches to the interventricular
foramen. Its base is continuous at the transverse fissure with the pia which covers
the surface of the brain. Its middle part lies over the epithelial roof of the third
ventricle, as has been seen (Fig. 637). The lateral borders will be seen on the floor

Subliinbic fissure [ant. part)

Inter ventricular foramen rr r

r, r ■ t Irons verse fissure

iTi/rus jormcatus ^, ,, • ■ ,

t • ,^ I Caltoso-marqinol

arginol fissure

Sublimhic fissure (post, port")

Entomarqinal fissure

Marginal fissure

Sulcus rhinab's anterior

Ectomarginal fissure

Hippocampal fissure

Sulcus rhinalis posterior

Fig. 040. — Medio-ventral Aspect of Right Cerebral Hemisphere op Horse.
The olfactory bulb is cut off. T.oL, Olfactory tract; A. p., area parolfactoria; Tr.o., trigonum olfactorium;
Tr.op., optic tract; Co., chiasma opticum; G.s., subcallosal gyrus; C.c, corpus callosum; S.p., septum pellucidum; F,
fornix; F', fimbria; G.c, callosal gyrus; T, cut surface of thalamus; G.d., gyrus dentatus; L.p., piriform lobe;
G.h., hippocampal gyrus.

of the lateral ventricles, where they form thick, rounded bands containing convolu-
tions of blood-vessels, known as the chorioid plexuses of the lateral ventricles (Fig.
642).

When the tela is pulled out, one may easily get the impression that the lateral ventricle
communicates with the exterior by means of the chorioid fissure. Such is not the case, since the
chorioid plexus is covered by the epithelial lining of the ventricle, which has been torn away.

The rhinencephalon or olfactory part of the brain comprises the olfactory
bulb, tract, and striae, the trigonum olfactorium, the area parolfactoria, and the
piriform lobe.^

The olfactory bulb (Bulbus olfactorius) is an oval enlargement which curves
upward in front of the frontal pole of the hemisphere. Its convex superficial face
fits into the ethmoidal fossa and receives numerous olfactory nerve-fibers through
the cribriform plate; hence it is very difficult to remove the bulb intact. It con-
tains a considerable cavity, the ventricle of the olfactory bulb (Ventriculus bulbi

1 From the morphological point of view other structures should be included, but in descriptive
anatomy it is usual to limit the application of the term to the parts enumerated above.

788 NERVOUS SYSTEM OF THE HORSE

olfactorii) which is connected with the lateral ventricle by a small canal in the
olfactory tract. The deep face is largely in contact with the frontal pole of the
hemisphere and is connected with the olfactory tract.

The gray matter of the bulb is external and is thickest on the convex anterior surface. The
posterior part consists to a large extent of fibers which are the axones of the mitral cells of the
deep layer of the gray substance and go to form the tract and stria.

The olfactory tract (Tractus olfactorius)i jg g^ ygj.y short but wide band of
white substance which arises in the olfactory bulb and extends back to be continued
by the olfactory striae. It contains a canal which connects the ventricle of the
bulb with the lateral ventricle.

The olfactory striae (Striae olfactorii)^ are two in number. The lateral stria
(Stria lateralis) is much the largest and most distinct. It passes backward, upward,
and outward, widens out and joins the piriform lobe. It is clearly defined dorsally
by the sulcus rhinalis and is marked off from the trigonum olfactorium by the
sulcus arcuatus. The medial stria (Stria medialis) is smaller, short, and not so

Fig. 641. — Lateral View op Cast of Cavities of Brain of Horse.
Bo, Cavity of olfactory bulb, which communicates through the canal / with a lateral ventricle; Ca, anterior horn,
Cm, body, Ci, ventral horn of lateral ventricle; M, interventricular foramen which connects lateral and third ventricles;
Ep, suprapineal recess, below which is the small infrapineal recess (not visible) ; Ro, optic recess; Rh, infundibular
and pituitary recess; S, aqueduct; Fl, ridge corresponding to sulcus hmitans; Rl, lateral recess, Rm, posterior
recess of fourth ventricle; Cc, beginning of central canal of spinal cord. (Dexler.)

well defined; it bends over to the parolfactory area on the medial face of the hemi-
sphere below the genu of the corpus callosum.^

The trigonum olfactorium is the prominent gray area situated in the angle of
divergence of the medial and lateral olfactory striae. It is bounded laterally by the
lateral olfactory stria, from which it is defined by the sulcus arcuatus. It is con-
tinuous with the area parolfactoria on the medial surface; behind the latter a band
descends from the rostrum of the corpus callosum and is continuous below Avith the
anterior perforated substance; it is termed the subcallosal gyrus (Gyrus sub-
callosus).

The piriform lobe (Lobus piriformis) is the well-marked prominence on the
base lateral to the optic tract and cerebral peduncle, from which it is separated by a
deep fissure. Its nipple-like apex lies behind the fossa lateralis and covers the
optic tract. The external surface is marked by one or two sulci (lobi piriformis).
The lobe contains a cavity, the ventral horn of the lateral ventricle.

1 Commonly termed the peduncle. 2 Commonly termed the tracts.

^ An intermediate or middle stria has been described; its presence cannot be demonstrated
m the horse.

THE CEREBRAL HEMISPHERES

789

The fibers of the olfactory striae go to the piriform lobe and hippocampus, the trigonum
olfactormm, the area parolfactoria, the subcallosal gyrus, and part of the gyrus fornicatus. The
central connections of the olfactory apparatus are complex and are not yet fully understood. The
anterior cerebral commissui-e contains fibers which pass from the oKactory bulb of one side by
way of the medial striae to the bulb of the opposite side; also fibers which cross in it from the
naedial striae of one side to the piriform lobe of the opposite side. Many fibers pass to the
hippocampus by way of the septum pellucidum, fornix, and fimbria. Other fibers pass in the
column of the fornix to the mammillary body and thence to the thalamus by the thalamo-mam-
millary bundle.

The corpus callosum is the great transverse commissure which connects the
two cerebral hemispheres through about half of their length. On median section

Olfactory bulb

^ - ' " Cortex cerebri

-i Corpus medullar e

Caudate nucleus

Chorioid plexus
Fornix
'~i - -Hippocampus

-Brain of Horse, with Lateral Ventricles Opened by Removal of Upper Part of Cerebral
Hemispheres and Most of the Corpus Callosum.

(Fig. 639) it is seen to be arched from before backward, white in color, and com-
posed substantially of transverse fibers. The middle part or truncus (Truncus
corporis callosi) slopes downward and forward and is thinner than the ends. The
anterior thickened end, the genu, bends ventrally and backward and thins out to
form the rostrum ; the latter is continuous with the lamina terminalis. The pos-
terior end, the splenium, also thick, lies at a considerably higher level than the
genu. The dorsal surface is convex in its length, concave transversely; it forms
the floor of the longitudinal fissure. It is covered by a thin layer of gray matter
(Induseum griseum), in which are strands of longitudinal fibers (Striae longitudi-
nales) ; the latter are arranged in medial and lateral bundles (Stria medialis, striae

790

NERVOUS SYSTEM OF THE HORSE

laterales).^ The ventral surface has the reverse configuration, and presents trans-
verse ridges and grooves. It forms the roof of the lateral ventricles, and the
septum pellucidum is attached to it medially. The fibers of the corpus cailosum
(with the exception of the longitudinal striae) run transversely and spread out
laterally in all directions in the central white matter of the hemispheres to the cor-
tex, forming the radiation of the corpus cailosum (Radiatio corporis callosi).

The fornix is a bilateral structure composed of white fibers which arch chiefly
over the thalamus and the third ventricle. It is described as consisting of a body,
two columns, and two crura. The body (Corpus fornicis) is formed by the fusion of
the two arches of which the fornix is composed. It is triangular and overlies the an-
terior parts of the thalami and the third ventricle. The dorsal surface gives

Opttc
chiasm

hdcrrcnlricidar Jorainen
\nU rior cu iii in lss u rt

Optic trad

Fio. 643. — Cross-section of Brain of Horse, About Natural Size.
Section passes through optic chiasm, and is viewed from in front. 1, Longitudinal fissure; 2, septum pellu-
cidum; 3, columns of fornix; 4, lateral ventricle; 5, chorioid plexus; 6, corpus moduUare (central white matter) of
hemisphere; 7, caudate nucleus; 5, lenticular nucleus; 9, internal capsule; iO, external capsule; n, insula.

attachment medially to the septum pellucidum, and on either side forms part of the
floor of the lateral ventricle. The lateral border is related to the chorioid plexus of
the lateral ventricle and forms the inner boundary of the interventricular foramen.
The columns (Columnae fornicis) (Fig. 643)2 are two slender round bundles which
emerge from the body in front of the interventricular foramen and diverge
slightly as they curve ventrally and backward to the mammillary body.

From the mammillary body the greater part of these fornix fibers are continued to the
thalamus by the thalamo-mammillary fasciculus (or bundle of Vicq d'Azyr). Others pass to
the cerebral peduncle. A portion of the fibers cross to the opposite thalamus and cerebral
peduncle.

The crura (Crura fornicis)^ are much larger bands which diverge widely from

^ It is generally believed that these constitute an olfactory path.

* Also known as the anterior pillars. ^ ^igQ termed the posterior pillars.

THE CEREBRAL HEMISPHERES 791

the posterior angles of the body. Each curves outward and backward over the
thalamus (from which it is separated by the tela chorioidea), and is chiefly continued
as the fimbria along the concave border of the hippocampus. The crura give off
fibers to form the alveus, a layer of white matter which covers the ventricular face
of the hippocampi, and between them are transverse fibers which constitute the
hippocampal commissure (Commissura hippocampi).

The septum pellucidum is the median partition between the two lateral ven-
tricles. Its convex dorsal border blends with the corpus callosum and its concave
ventral border joins the fornix. Its anterior part is received into the genu of the
corpus callosum. Traced backward, it diminishes in height and the two edges meet
at an acute angle at the splenium.

The septum consists of two layers (Laminae septi pellucidi) which are in contact with each
other. They consist of medullated nerve-fibers and 2;ray matter. The latter exists in considerable
amount m the thicker part of the septum adjacent to the columns of the fornix. Many of the
fibers of the septum pass up through the corpus callosum to the gyrus fornicatus. Others are
connected with the subcallosal gyrus and the paroKactory area.

Fig. 644. — Sagittal Section of Brain of Horse.
Section is cut about 1.5 cm. to the right of the median plane. M, Medulla oblongata; P, pons; P.c. (above M),
chorioid plexus of fourth ventricle; Cm., central white matter (corpus medullare) of cerebellum and of cerebrum;
P.c. (in front of P), cerebral peduncle; //, hippocampus; V, lateral ventricle; T, thalamus; N.c, caudate nucleus;
C.i., internal capsule; N.I., lenticular nucleus; B.o., olfactory bulb.

The lateral ventricle (Ventriculus lateralis cerebri) is the irregular cavity in the
interior of each cerebral hemisphere.^ Each communicates with the third ventricle
through the interventricular foramen (Foramen interventriculare),- and by a small
canal with the cavity of the olfactory bulb. It is usual to describe the ventricle
as consisting of three parts, viz., the central part or body, and anterior and ventral
horns. The central part (Pars centralis) extends back to the splenium of the corpus
callosum. It opens into the third ventricle through the interventricular foramen,
which is situated between the fornix and the anterior part of the thalamus. The
anterior horn (Cornu orale) is the part in front of the interventricular foramen;
it communicates ventrally with the olfactory cavity. The ventral horn (Cornu
ventrale) curves downward and forward into the piriform lobe. The roof of the
ventricle is formed by the corpus callosum, and the medial wall is the septum pellu-
cidum. After removal of the roof the floor is seen to be formed chiefly by two bodies.

1 It is hardly possible to get an accurate idea of the shape of the ventricle except by studying
a cast of it (Fig. 641). The size of the ventricles varies in different subjects, and it is conunon to
find more or less disparity between the two ventricles of the same brain.

- Formerly termed the foramen of Monro.

792 NERVOUS SYSTEM OF THE HORSE

The anterior one is the caudate nucleus (Nucleus caudatus), a somewhat pear-
shaped gray eminence, the long axis of which is directed obliquely upward, back-
ward, and outward. Its anterior large end is termed the head (Caput nuclei
caudati), and the posterior long tapering end the tail (Cauda nuclei caudati). The
posterior body, the hippocampus, is white on its ventricular surface, which is
strongly convex. It curves outward and backward and then turns ventrally and
forward to join the piriform lobe. The two bodies are separated by an oblique
groove which is occupied by the chorioid plexus of the lateral ventricle (Plexus
chorioideus ventriculi lateralis) . This is the thickened edge of a fold of pia mater,
the tela chorioidea of the third ventricle, which lies between the hippocampus and
the thalamus. It contains convolutions of small blood-vessels, and in old subjects
there are often calcareous concretions in it. The plexuses of the two sides are
continuous through the interventricular foramen. On drawing the chorioid plexus
backward, a narrow white band, the stria terminaUs,^ is seen along the margin of the
caudate nucleus, where it bounds the intermediate groove. The plexus partially
covers a mder white band which is blended with the white substance of the hippo-
campus; this is the cms of the fornix and its continuation, the fimbria.

The corpus striatimi- is the great basal ganglion of the hemisphere. It is sit-
uated in front of the thalamus and the cerebral peduncle, and its anterior rounded
end appears on the base of the hemisphere at the trigonum olfactorium. It is
composed of two masses of gray matter, the caudate and lenticular nuclei, separated
incompletely bj^ tracts of white matter which are known collectively as the internal
capsule. The caudate nucleus (Nucleus caudatus) is the dorso-medial and larger
of the two gray masses; it was seen in the examination of the lateral ventricle.
The lenticular nucleus (Nucleus lentif ormis) lies ventro-laterally, over the trigonum
olfactorium and the fossa lateralis. It is related externally to a layer of white
matter termed the external capsule (Capsula externa), which separates it from a
stratum of gray substance kno^vn as the claustrum. The two nuclei are fused in
front, and further back they are connected by strands of gray matter which inter-
sect the internal capsule.

The amygdaloid nucleus (Nucleus amygdalse) (Fig. 637) is an ovoid mass of
gray matter lateral to the ventral horn of the lateral ventricle and ventral to the
posterior part of the lenticular nucleus. Some fibers of the stria terminalis are
connected with it.

The internal capsule (Capsula interna) is a broad band of white matter situated
between the thalamus and caudate nucleus medially and the lenticular nucleus
laterally. A sagittal section through the brain (Fig. 644) shows that it is in great
part directly continuous with the basis or ventral part of the cerebral peduncle.
It contains most of the so-called projection fibers of the hemisphere, which con-
nect the cerebral cortex with nuclei of other and more posterior parts of the brain.
When the fibers of the internal capsule are traced forward it is evident that they
spread out in all directions to reach the cerebral cortex. This arrangement, in
which the fibers of the corpus callosum participate, is termed the corona radiata.

The internal capsule also contains fibers which connect the corpus striatum with the thala-
mus. These are termed the thalamo-striate and strio-thalamic fibers respectively, according to
the direction in which they conduct impulses.

The fibers of the stria terminaUs connect the amygdaloid nucleus with the septum pelluci-
dum and trigonum oKactorium. It is therefore probably part of the complex connections be-
tween the primary and secondary olfactory centers.

Blood-vessels of the Brain.— The arteries which supply the brain are derived
chiefly from the internal carotid and occipital arteries. The basilar artery, formed
by the union of the right and left cerebral branches of the occipital artery, enters

^ Formerly termed the tgenia semicircular is.

- The term arose from the striated appearance of the mass in sections cut in certain planes,
the gray matter being cut up into strands by tracts of white fibers.

THE CRANIAL NERVES THE OPTIC NERVE 793

the cranial cavity through the foramen magnum, and divides at the interpeduncular
fossa into the two posterior cerebral arteries. These concur with branches of the
internal carotid arteries in forming the remarkable arterial circle on the base of the
cerebrum. From these emanate basal arteries which supply in general the brain
stem and basal ganglia, and cortical arteries which in general run superficially
and supply the cortical substance and medullary white substance.

The veins enter the sinuses of the dura mater, and in the main are not satel-
lites of the arteries. The sinuses communicate with the ophthalmic, dorsal and
ventral cerebral, and spinal veins.

The Cranial Nerves

The cranial or cerebral nerves (Nn. cerebrales) comprise twelve pairs which
are designated from before backward numerically and by name. Their number,
names, and functional characters are given in the subjoined table:

I. Olfactory Sensory (Smell)

II. Optic Sensory (Sight)

III. Oculomotor Motor

IV. Trochlear Motor

V. Trigeminal Mixed

VI. Abducent Motor

VII. Facial Mixed

VIII. Acoustic Sensory (Hearing and Equihbration)

IX. Glosso-pharyngeal Mixed

X. Vagus Mixed

XI. Spinal accessory Motor

XII. Hypoglossal Motor

THE OLFACTORY NERVE
The olfactory nerve (N. olfactorius) is peculiar in that its fibers are not aggre-
gated to form a trunk, but are connected in small bundles with the olfactory Ijulb.
They are non-medullated, and are the central processes of the olfactory cells which
are situated in the olfactory region of the mucous membrane of the nasal cavity.
This region is distinguished by its brown color and comprises the posterior part of
the lateral mass of the ethmoid, a small adjacent area of the dorsal turbinate, and
the corresponding surface of the septum nasi. The nerve-bundles are enclosed in
sheaths derived from the membranes of the brain and pass through the foramina of
the cribriform plate to join the convex surface of the olfactory bulb. Some
fibers come from the vomero-nasal organ.

THE OPTIC NERVE

The optic nerve (N. opticus) is composed of fibers which are the central proc-
esses of the ganglion cells of the retina. The fibers converge within the eyeball to
the optic papilla, where they are collected into a round trunk, the optic nerve. The
nerve thus formed pierces the chorioid and sclera, emerges from the posterior part
of the eyeball, and passes backward and medially to the optic foramen. After
traversing the latter it decussates vnih its fellow of the opposite side to form the
optic chiasma. In the orbit the nerve is slightly flexuous and is embedded in the
fat behind the eyeball and surrounded by the retractor oculi muscle. Its intraos-
seous part is an inch or more (ca. 3 cm.) long. The sheath of the nerve is formed by
prolongations of the membranes of the brain, and includes continuations of the
subdural and subarachnoid spaces.

The greater part of the fibers of the optic nerve cross in the chiasma to the tract of the oppo-
site side. In the tract the fibers proceed to (1) the medial geniculate body, (2) the posterior

794

NERVOUS SYSTEM OF THE HORSE

part of the thalamus, and (3) the anterior quadrigeminal body (indirectly). The fibers which
go to the medial geniculate body appear to belong to Gudden's commissure and to be non-visual
in function. The visual fibers, which come from the lateral part of the retina of the same side
and the medial part of tlie retina of the opposite side, terminate about cells in the anterior quad-
rigeminal body and the part of the thalamus which corresponds to the pulvinar and lateral genicu-
late body of man. From the cells of the former fibers pass to the nuclei of the motor nerves of
the eyeball, and complete the reflex arc. Fibers proceed from the cells of the thalamus to the
visual area of the cortex in the occipital part of the hemisphere.

THE OCULOMOTOR NERVE

The oculomotor nerve (N. oculomotorius) arises by several radicles from the
basal surface of the cerebral peduncle, a little lateral to the interpeduncular furrow.

It turns sharply outward and for-
ward, crosses over the cavernous
sinus, and continues above the
maxillary nerve and in company
with the ophthalmic nerve to the
foramen orbitale. It emerges
through the foramen with the lat-
ter nerve and the abducens and
divides into two branches. The
dorsal branch is short and divides
into two twigs which supply the
rectus dorsalis and levator pal-
pebrae superioris. The ventral
branch (Figs. 563, 564) is larger
and much longer. It supplies the
motor fibers to the ciliary gan-
glion (which lies directly on this
branch in the horse) and short
branches to the rectus medialis
and rectus ventralis, and con-
tinues forward on the latter to
end in the ventral oblique mus-
cle.

The deep origin of the fibers of
the oculomotor nerve is in the oculo-
motor nucleus, situated in the gray mat-
ter of the floor of the cerebral aque-
duct in the region of the anterior cor-
pora quadrigemina.

Fig. 645. — Floor of Cr.\nial Cavity of Horse.
The roots of the cranial nerves are shown on the left side
and are designated by number: /, Anterior cranial fossa; //,
middle cranial fossa; III, posterior cranial fossa; a, ethmoidal
fossa; 6, ethmoidal foramen; c, foramen for nasal branch of
ophthalmic arterj'; d, orbital wing of sphenoid bone; e, optic
groove; /, hypophyseal fossa; g, spheno-occipital crest; h, h', con-
tour of hypophysis or pituitary body; h", slight elevation repre-
senting dorsum sellse; i, k, grooves for nerves and cavernous sinus;
I, depression for piriform lobe of cerebrum; m, groove for middle
meningeal artery; n, depression for pons; o, foramen lacerum an-
terius; p, foramen lacerum posterius; q, incisura carotica; q', inci-
sura ovalis; q", incisura spinosa; r, depression for medulla oblongata;
s, hypoglossal foramen; t, internal acoustic meatus; u, foramen
magnum; v, frontal sinus; u\ zygomatic process of temporal bone;
X, section of petrous temporal; y, section of occipital bone; z, crista
galli; 1, 1', 1", dotted lines indicating position of olfactorj' strise
and tract. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)

THE TROCHLEAR NERVE

The trochlear nerve (N. tro-
chlearis)^ is the smallest of the
cranial nerves. It arises from
the anterior cerebellar peduncle
just behind the corpora quadri-
gemina, curves outward and for-
ward, pierces the tentorium cere-
belli, and passes forward along
the lateral border of the maxillary
nerve (Figs. 635, 636). It emerges from the cranium through a small foramen
1 Formerly termed the nervus patheticus.

THE TRIGEMINAL NERVE 795

immediately above the foramen orbitale or through the latter and passes forward
along the medial wall of the orbit to end in the posterior part of the dorsal oblique
muscle of the eyeball (Fig. 564).

The fibers of the fourth nerve spring from a nucleus in the gray matter of the floor of the
cerebral aqueduct behind the oculomotor nucleus. The fibers run backward in the tegmentum,
then turn dorso-medially, and undergo total decussation with those of the opposite nerve in the
anterior part of the anterior medullary velum. In addition to this peculiarity it is the only nerve
which is connected with the dorsal aspect of the brain.

THE TRIGEMINAL NERVE

The trigeminal nerve (N. trigeminus) ^ is the largest of the cranial series. It
is connected with the lateral part of the pons by a large sensory root and a smaller
motor root (Fig. 629).

The sensory root (Portio major) extends forward through a notch on the lower
part of the petrosal crest and widens out to join the semilunar ganglion.

The semilunar ganglion (Ganglion semilunare)- is a crescent-shaped mass of
nerve-fibers and cells which overlies the antero-lateral part of the foramen lacerum
basis cranii, and is partly embedded in the dense fibrous tissue which occupies the
foramen except where vessels and nerves pass through. Its long axis, which is
about an inch (2.5 cm.) in length, is directed forward and medially and its convex
anterior face gives rise to the ophthalmic, the maxillary, and the sensory part of
the mandibular division of the nerve. The surface of the ganglion is irregularly
striated. It is connected by filam«ents with the adjacent carotid plexus of the sym-
pathetic, and sends delicate twigs to the dura mater.

The fibers of the sensory root arise from the ganglion as axones of the gangUon cells, and the
fibers of the nerves which extend peripherally from the ganglion are dendrites of the cells. The
sensory root-fibers enter the tegmentum of the pons and divide into anterior and posterior branches,
which terminate about the cells of the sensory nucleus of termination of the trigeminus. This
nucleus extends from the pons to the sixth cervical segment of the spinal cord (Dcxler). The
posterior branches of the fibers are collected into a compact bundle, the spinal tract or root of the
trigeminus, which lies lateral to the substantia gelatinosa in the medulla. The central connections
of the sensory part of the trigeminus are very extensive. The most important paths are: (1)
Axones of cells of the sensory nucleus and the substantia gelatinosa pass chiefly as arcuate fibers
across the raphe to the thalamus, whence impulses are transmitted by thalamo-cortical fibers
to the cerebral cortex. In ungulates a distinct tract extends from the anterior part of the sensory
nucleus to the thalamus of the same side (Wallenberg). It is probable that collaterals of the
arcuate fibers go to the motor nuclei of the fifth, seventh, ninth, and tenth cranial nerves. (2)
Axones of cells of the sensory nucleus enter the posterior cerebellar peduncle of the same side
and reach the cerebellar cortex. (3) Collaterals are distributed to the nuclei of origin of the
hypoglossal and of the motor part of the trigeminal and facial nerves.

The motor root (Portio minor) extends forward beneath the sensory root and
the semilunar ganglion and is incorporated with the mandibular division of the
nerve. Its fibers arise chiefly from the so-called masticatory nucleus, which is
situated in the pons near the inner face of the sensory nucleus; a few of these fillers
come from the nucleus of the opposite side and cross in the raphe. Other fibers,
which constitute the mesencephalic root, arise from cells in the outer part of the
central gray matter of the mid-brain.

It is evident from the foregoing statements that the trigeminus has essentially
the same arrangement as a typical spinal nerve. It divides into three branches.

I. The ophthalmic nerve (N. ophthalmicus) (Figs. 563, 564, 565) is purely
sensory and is the smallest of the three branches of the trigeminus. It arises from
the medial part of the front of the semilunar ganglion, passes forward along the outer
side of the cavernous sinus, and is blended with the maxillary nerve for some dis-
tance. It enters the foramen orbitale with the third and sixth nerves and divides
into three branches.

1. The lacrimal nerve (N. lacrimalis) runs forward on the rectus dorsalis and

1 Also known as the trifacial nerve. - Formerly termed the Gasserian ganglion.

796 NERVOUS SYSTEM OF THE HORSE

the levator palpebrse superioris and ramifies chiefly in the lacrimal gland and the
upper eyelid. A branch (Ramus zygomatico-temporalis) exchanges twigs with the
z3^gomatic branch of the maxillary nerve, perforates the periorbita, and emerges
from the orbital fossa behind the supraorbital process; it forms a plexus with
branches of the auriculo-palpebral and frontal nerves, and ramifies in the skin of
the temporal region.

2. The frontal nerve (N. frontalis), also termed the supraorbital, runs forward
almost parallel with the dorsal oblique muscle, at first within, then outside of, the
periorbita. It passes through the supraorbital foramen with the artery of like
name and ramifies in the skin of the forehead and upper eyelid, forming a plexus
with the lacrimal and auriculo-palpebral nerves. It divides into three branches.

3. The naso-ciliary nerve (N. nasociliaris), also termed the palpebro-nasal,
runs forward along the medial side of the optic nerve between parts of the retractor
muscle and divides into two branches. Of these, the ethmoidal nerve (N. ethmoid-
alis) is the continuation of the parent trunk. It accompanies the ethmoidal
artery through the foramen of like name into the cranial cavity and crosses the
lower part of the ethmoidal fossa. Leaving the cranium through an opening in the
cribi'iform plate close to the crista galli, it enters the nasal cavity and ramifies in
the nmcous membrane of the septum nasi and the dorsal turbinate. The infra-
trochlear nerve (N. infratrochlearis) runs forward to the medial canthus and rami-
fies in the skin in this region; it detaches twigs to the conjunctiva and caruncula
lacrimalis, and a long branch which supplies the third eyelid and the lacrimal ducts
and sac. The naso-ciliary nerve furnishes the sensory or long root (Radix longa)
of the ciliary ganglion.

The ciliary ganglion is placed on the ventral branch of the oculomotor nerve,
close to its origin from the latter. It is usually not larger than a millet-seed, and
is best found by following the nerve to the ventral oblique muscle back to its origin.
The ganglion receives — (a) sensory fibers from the naso-ciliary nerve; (6) motor
fibers from the oculomotor nerve; and (c) sympathetic fibers from the spheno-
palatine plexus. It detaches filaments which unite with twigs from the ophthalmic
and maxillary nerves and from the sphenopalatine ganglion to form the ciliary
plexus. From the latter emanate five to eight delicate short ciliary nerves (Nn.
ciliares breves), which pursue a somewhat flexuous course along the optic nerve,
pierce the sclera near the entrance of that nerve, and run forward between the
sclera and chorioidea to the circumference of the iris. Here the branches of ad-
jacent nerves anastomose to form a circular plexus (Plexus gangliosus ciliaris),
from which filaments go to the ciliary body, iris, and cornea.

The circular fibers of the iris and the ciliary muscle are innervated by fibers derived from the
oculomotor nerve, the radial fibers of the iris by the sympathetic.

II. The maxillary nerve (N. maxillaris)^ is purely sensory and is much larger
than the ophthalmic. It extends forward from the semilunar ganglion in the middle
cranial fossa in the large groove on the root of the temporal wing of the sphenoid.
It is related medially to the cavernous sinus and dorsaliy to the ophthalmic nerve,
with which it is blended for some distance. It emerges through the foramen
rotundum, passes forward in the ptery go-palatine fossa above the internal maxillary
artery and embedded in fat, and is continued in the infraorbital canal as the in-
fraorbital nerve (Fig. 564) . Its branches are as follows :

1. The zygomatic nerve (N. zygomaticus s. subcutaneus malse), also termed
the orbital branch, arises before the maxillary nerve reaches the pterygo-palatine
fossa (Figs. 563, 564, 646). It pierces the periorbita and divides into two or three
delicate branches which pass along the surface of the lateral straight muscle to

^ This is also termed the superior maxillary brancli.

THE TRIGEMINAL NERVE

797

the lateral canthus and ramify chiefly in the lower lid and the adjacent skin. Anas-
tomoses are formed with branches of the lacrimal nerve.

2. The sphenopalatine nerve (N. sphenopalatinus) is given off in the pterygo-
palatine fossa from the ventral border of the maxillary nerve (Fig. 564). It is
broad and flat and forms a plexus in which several small sphenopalatine ganglia

Fig. 646. — Dissection of Head op Horse.
The masseter and superficial muscles and the parotid gland are in great part removed, a, a. Levator labii superi-
oris proprius; 6, 6, levator nasolabialis; c, dilatator naris inferior; d, buccinator; e, common mass of buccinator and
depressor labii inferioris; /, depressor labii inferioris; g, masseter; h, orbicularis oculi; i, temporalis; k, occipito-
hyoideus; k', occipito-mandibularis; I, sterno-cephalicus; I', tendon of same; m, omo-hyoideus; n, crico-pharyngeus;
o, mastoid tendon of brachiocephahcus; p, splenius; q, inferior buccal and labial glands; r, superior buccal glands;
s, remnant of parotid gland; t, mandibular gland; u, anterior cervical lymph glands; v, probe passed into diverticulum
nasi; w, cornu of alar cartilage; x, medial palpebral hgament; y, wing of atlas; z, scutiform cartilage of ear; 1, lateral
nasal nerve; 2, anterior nasal nerve; 3, superior labial nerve; 4-, anterior part of superior buccal nerve; 5, buccinator
nerve; 6, 6', inferior alveolar nerve; 6", mental nerve — continuation of 6; 7, masseteric nerve; 8, facial nerve (cut) ;
fl, superficial temporal nerve; ^0, anastomosis between 9a.nd8; 11, internal auricular nerve; 7;?, posterior auricular
nerve; i 3, digastric nerve; i^i cervical branch of facial nerve (cut); 75, auriculo-palpebral nerve; iff, lacrimal nerve;
77, frontal nerve; i<S, infratrochlear nerve; iS, zygomatic nerve; ^0, spinal accessory nerve; £1, ventral branch of
spinal accessory nerve (to sterno-cephalicus); ££, ventral end branch of first cervical nerve; 33, thyro-laryngeal
artery; 24, internal maxillary artery; 23, masseteric artery; 26, great (posterior) auricular artery; 27, external branch
of ^6; ^S, deep auricular artery; ^5, anterior auricular artery; 50, transverse facial artery; 5/, facial artery; ^3, inferior
labial artery; 33, superior labial artery; 34, lateral nasal artery; 3o, dorsal nasal artery; 36, angular artery of eye; 37,
terminal branches of superior labial nerve ; S5, branch of buccinator artery; 3S, buccinator vein; 40, vena reflexa; 4^,
jugular vein; 4^, external maxillary vein; 44i ventral cerebral vein; 4-5. stump of great auricular vein; 4^, ramus of
mandible; 47, facial crest; 43, zygomatic arch; 4S, parotid duct. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)

are interposed. It divides into posterior nasal, and greater and lesser palatine
nerves. (1) The posterior nasal nerve (N. nasalis aboralis) passes through the
sphenopalatine foramen, in which it bears one or more minute ganglia, enters the
nasal cavity, and divides into medial and lateral branches (Figs. 565, 588). The
medial branch (N. septi narium) runs forward in the submucous tissue of the lower
part of the septum nasi, gives twigs to the mucous membrane here and to the
vomero-nasal organ, passes through the palatine fissure, and ramifies in the anterior

798 NERVOUS SYSTEM OF THE HORSE

part of the hard palate. The lateral branch (Ramus lateralis) ramifies in the
mucous membrane of the ventral turbinate and the middle and ventral meatus nasi.
(2) The greater or anterior palatine nerve (N. palatinus major s. oralis) (Figs.
563, 564) is the largest of the three branches. It runs forward in the palatine canal
and groove and ramifies in the hard palate and gums. It also supplies twigs to the
soft palate, and gives off branches which pass through the accessory palatine for-
amina to supply the mucous membrane of the ventral meatus.

The branches of the two nerves anastomose in the hard palate and form a plexus about the
branches of the palatine arteries.

(3) The lesser or posterior palatine nerve (N. palatinus minor s. aboralis),
also termed the staphyline, is much the smallest of the three branches (Figs. 563,
564) . It passes downward and forward with the palatine vein in the groove at the
medial side of the tuber maxillare and ramifies in the soft palate.

The sphenopalatine gangUa and plexus (Fig. 647) lie on the perpendicular part of the palatine
bone and the pterygoid process, under cover of the maxillary nerve. The afferent fibers of the
plexus and ganglia come chiefly from the branches of the sphenopalatine nerve and the nerve of
the pterygoid canal. Interspersed in these are several minute gangUa and one or more larger
ones. The nerve of the pterygoid canal (N. canaUs pterygoidei)i is formed by the union of sym-
pathetic fibers with the superficial petrosal branch of the facial nerve. It passes forward at first
between the Eustachian tube and the sphenoid bone, enters the canal between the pterygoid bone
and process, and joins the posterior part of the plexus. It is probable that it furnishes the motor
fibers to the levator palati and palatinus muscles. Efferent filaments go to the periorbita and the
ophthalmic vessels, and others accompany the branches of the maxillary nerve, around which they
have a plexiform arrangement.

3. The infraorbital nerve (N. infraorbitalis)- is the continuation of the maxillary
trunk. It traverses the infraorbital canal, emerges through the infraorbital fora-
men, and divides into nasal and superior labial branches. Along its course it gives
off maxillary alveolar or dental branches (Rami alveolares maxillae), which supply
the teeth, alveolar periosteum, and gums.

Small posterior alveolar branches (Rami alveolares maxilte aborales) are given off in the
pterygo-palatine fossa, pass through small foramina in the tuber maxillare, and supply the posterior
molar teeth and the maxillary sinus. The middle alveolar branches (Rami alveolares maxillae
medii) are given off in the infraorbital canal, and constitute the chief nerve-supply to the cheek
teeth and the maxillary sinus. The maxillary incisor branch (Ramus alveolaris maxillae incisivus)
runs forward in the incisor canal and supplies branches to the canine and incisor teeth. The fore-
going unite with each other to form the maxillary dental plexus (Plexus dentalis maxilla^) from
which the dental and gingival branches are given off.

The external nasal branches (Rami nasales externi), two or three in number,
accompany the levator labii superioris proprius and ramifj' in the dorsum nasi and
the nasal diverticulum.

The large anterior nasal branch (Ramus nasalis oralis) gives branches to the
upper lip and nostril, passes over the nasal process of the premaxilla under cover
of the lateralis nasi, and ramifies in the mucous membrane of the nasal vestibule.

The superior labial branch (Ramus labialis dorsalis) is the largest of the termi-
nals of the infraorbital nerve. It passes downward and forward under cover of the
levator nasolabialis and, after supplying the skin of the anterior part of the cheek,
forms a rich terminal ramification in the skin and mucous membrane of the upper
ip. It anastomoses with the superior buccal branch of the facial nerve.

III. The mandibular nerve (N. mandibularis)^ is formed by the union of two
roots; of these, the large sensory root comes from the semilunar ganglion, and the
small motor root is the pars minor of the trigeminus. It emerges from the cranium
through the oval notch of the foramen lacerum, and passes between the temporal
wing of the sphenoid bone and the muscular process of the petrous temporal. It
then runs forward, downward, and a little outward, between the ventral surface of

^ Also known as the Vidian nerve. 2 ^his is also called the superior dental nerve.

' This is also termed the inferior maxillary branch.

THE TRIGEMINAL NERVE

799

the pterygoideus medialis and the guttural pouch, and on reaching the lateral
surface of the pterygoideus lateralis, it divides into two terminal branches— the
inferior alveolar and lingual nerves. It gives off the following branches:

1. The masseteric nerve (N. massetericus) (Figs. 562, 646) passes outward
through the sigmoid notch of the mandible across the anterior surface of the tem-
poro-mandibular articulation and enters the deep face of the masseter muscle, in
which it ramifies.

2. The deep temporal nerves (Nn. temporales profundi) (Fig. 562), two or
three in number, arise from, or by a common trunk with, the masseteric. They
supply the temporalis muscle.

3. The buccinator nerve (N. buccinatorius) passes downward and forward
at first across the medial surface of the temporo-mandibular articulation, then
through the anterior part of the lateral pterygoid muscle, then between the bucci-

FiG. 647. — Deep Dissection op Base of Cranium, Viewed from the Right and Below.
The tympanic cavity is opened and the paramastoid process is sawn off. a, Occipital condyle; h, body of sphenoid;
c, external acoustic meatus (part removed) ; (i, malleus; e, incus; ;, stump of ophthalmic nerve; ^, stump of maxillary
nerve; 5, sphenopalatine plexus; 4, nerve of pterygoid canal; 4', deep petrosal nerve; 4", branch to tympanic plexus;
4'", superficial petrosal nerve; .5, superficial temporal nerve (cut off); 6, masseteric nerve (cut off); 7, mandibular
nerve (raised); S, lingual nerve (cut off); 9, pterygoid nerve (cut); 10, nerve to tensor tympani; 11, otic ganglion;
12, facial nerve; 13, stapedial nerve; 14, chorda tympani; 15, glosso-pharyngeal nerve (cut); 16, tympanic nerve; 17,
vagus (cut off); 18, auricular branch of vagus; 19, spinal accessory nerve (cut off); SO, hypoglossal nerve (cut off;
iil, sympathetic nerve (cut off) ; S3, internal carotid artery. (After EUenberger, in Leisering's Atlas.)

nator vein and the tuber maxillare (Fig. 646). It continues forward in the sub-
mucous tissue of the cheek along the ventral border of the depressor labii inferioris
and divides into branches which ramify in the mucous membrane and glands of the
lips in the vicinity of the commissure. It supplies small branches to the lateral
pterygoid and temporal muscles and detaches numerous collateral twigs to the
mucous membrane of the cheek and to the buccal glands. It also communicates
with the inferior buccal branch of the facial nerve.

4. The pterygoid nerve (N. pterygoideus) arises in common with the preceding,
passes downward and forward under cover of the parent trunk, and divides into
branches which enter the posterior part of the pterygoideus medialis at the division
between the two layers of the muscle (Fig. 647) .

The otic ganglion (G. oticum) is situated on the mandibular near the origin of
the buccinator nerve, and is related medially to the tensor palati and the Eustachian
tube. It receives motor fibers from the pterygoid nerve and sensory fibers by the

800 NERVOUS SYSTEM OF THE HORSE

small superficial petrosal nerve from the tympanic plexus, through which communi-
cations are made with the facial and glosso-pharyngeal nerves. Sympathetic
fibers are derived from the plexus on the internal maxillary artery. Efferent fila-
ments go to the tensor palati, tensor tympani, and pterygoid muscles and to the
Eustachian tube.

The ganglion is small and somewhat difficult to find, and in many cases it is replaced by
a number of minute ganglia interspersed in a fine plexus.

5. The superficial temporal nerve (N. temporalis superficialis) (Figs. 562,
646, 647) runs outward across the pterygoideus lateralis, passes between the parotid
gland and the neck of the ramus of the mandible, turns around the latter, and di-
vides into two branches. The transverse facial branch (Ramus transversus faciei)
accompanies the transverse facial vessels and ramifies in the skin of the cheek.
The larger ventral branch unites with the ventral buccal division of the facial nerve.
Before its division the nerve gives off twigs to the guttural pouch, the parotid
gland, the external ear, and the skin of the external acoustic meatus and the mem-

FiG. 648. — Part of Branch of Lower Jaw of Horse; Medial View.
The bone has been removed to show the vessels and nerves. 1, 1', Mandibular alveolar nerve; 3, 2, branches to
cheek teeth and gums; 2', branch to canine and incisor teeth; 3, S', alveolar artery; 4< satellite vein. (After Leiser-
ing'a Atlas.)

brana tympani. Branches from it concur with filaments from the cervical branch
of the facial nerve in the formation of the auricular plexus.

6. The mandibular alveolar nerve (N. alveolaris mandibulae) (Figs. 561, 562,
646)^ arises with the lingual by a common trunk which passes forward at first on
the lateral pterygoid muscle, then inclines ventrally between the medial pterygoid
and the ramus of the mandible. The lingual and alveolar separate at an acute
angle, and the latter enters the mandibular foramen and courses in the canal
within the ramus (Fig. 648). Emerging at the mental foramen, it terminates by
dividing into six to eight inferior labial and mental branches, which ramify in the
lower lip and chin. Before entering the bone, the nerve detaches the mylo-hyoid
nerve (N. mylohyoideus) , which runs downward and forward between the ramus
and the mylo-hyoid muscle; it supplies that muscle, the anterior belly of the
digastricus, and the skin of the anterior part of the mandibular space. The dental
and gingival branches detached from the nerve within the mandible are arranged
like the corresponding nerves of the upper jaw.

7. The lingual nerve (N. lingualis) arises by a common trunk with the mandib-
ular alveolar nerve (Figs. 561, 562). After separating from the latter it runs

^ Also termed the inferior dental nerve.

THE ABDUCENT NERVE — THE FACIAL NERVE 801

downward and forward, lying at first between the ramus of the mandible and the
medial pterygoid muscle, then on the medial face of the mylo-hyoid. On reaching
the root of the tongue it divides into superficial and deep branches. The super-
ficial branch (Ramus superficialis) runs forward on the stylo-glossus and accom-
panies the mandibular duct on the deep face of the sublingual gland. It supplies
the mucous membrane of the tongue and the floor of the mouth. At the root of the
tongue it gives off a recurrent branch to the isthmus faucium, which communicates
with the lingual branch of the glosso-pharyngeal nerve. The larger deep branch
(Ramus profundus) turns around the lower edge of the stylo-glossus and hyo-
glossus, passes upward and forward between the latter muscle and the genio-
glossus, and continues forward on the latter to the tip of the tongue. At the turn
it gives off one or more ascending branches which ramify on the deep face of the
hyo-glossus. It gives branches to the mucous membrane and the fungiform papillsB
of the tongue, and anastomoses with branches of the hypoglossal nerve and with
the superficial branch. Minute ganglia occur on the finer branches of the lingual
nerve. The chorda tympani branch of the facial joins the lingual nerve at the origin
of the latter and is incorporated with it in its distribution to the tongue.

THE ABDUCENT NERVE
The abducent nerve (N. abducens) emerges from the brain behind the pons
and just lateral to the pyramid (Fig. 629). It passes forward across the pons,
pierces the dura mater, and accompanies the third and ophthalmic nerves, below
which it emerges through the foramen orbitale. In the orbit it divides into two
branches which innervate the rectus lateralis and the retractor muscle of the eye-
ball. Within the cranium it receives filaments from the carotid plexus of the sym-
pathetic.

The fibers of the abducent nei-ve are axones of the large multipolar cells of the abducent
nucleus which is situated beneath the eminentia teres of the floor of the fourth ventricle. The
nucleus Ues within the loop formed by the fibers of origin of the facial nerve. It is connected
with (a) the anterior olive; (6) the oculomotor nucleus of the opposite side; (c) the motor area of
the cerebral cortex by means of the pyramidal tract of the opposite side.

THE FACIAL NERVE

The facial nerve (N. facialis) has its superficial origin at the lateral part of the
corpus trapezoideum, immediately behind the pons (Fig. 629). It passes outward
in front of the eighth nerve and enters the internal acoustic meatus. At the bottom
of the meatus the two nerves part company, the facial coursing in the facial canal
of the petrous temporal bone. The canal and nerve are at first directed outward
between the vestibule and the cochlea, then curve backward and ventrally in the
posterior wall of the tympanum to end at the stylo-mastoid foramen. The bend
formed by the nerve is called the knee (Geniculum n. faciahs), and bears at its
highest point the round geniculate ganglion (G. geniculi).

The nerve consists of two parts, motor and sensory. The motor part constitutes the bulk
of the nerve. Its deep origin is from the cells of the facial nucleus, which is situated in the meduUa
above the facial tubercle. On lea\'ing the nucleus the root-fibers pass dorso-medially, incHne for-
ward close to the median plane, and then bend sharply downward to the point of emergence. The
highest point of the bend is subjacent to the gray matter of the eminentia teres in the floor of the
fourth ventricle, and the abducent nucleus lies in the concavity of the cm-ve. The small sensory
part (N. intermedins) consists of axones of cells of the geniculate ganghon, which is interposed on
the facial nerve as it bends downward in the facial canal. The fibers of this part, after entering
the medulla, pass to the nucleus of termination which it shares with the ninth and tenth nerves.
The peripheral fibers from the geniculate ganglion constitute the chorda tympani.

After its emergence through the stylo-mastoid foramen (Fig. 646) the nerve
passes ventrally, forward, and outward on the guttural pouch under cover of the
51

802 NERVOUS SYSTEM OF THE HORSE

parotid gland, and passes between the origin of the superficial temporal and
internal maxillary arteries medially and the superficial temporal vein laterally. It
then crosses the posterior border of the ramus of the mandi]3le ventral to the trans-
verse facial artery and about an inch and a half (ca. 3.5-4 cm.) below the articu-
lation of the jaw. Emerging from beneath the parotid gland upon the masseter
muscle, it receives the ventral branch of the superficial temporal nerve, and divides
into dorsal and ventral buccal branches. The follo^ving collateral branches are
given off, the first five being detached \vdthin the facial canal, and the others
between the stylo-mast old foramen and the border of the jaw.

1. The great superficial petrosal nerve (N. petrosus superficialis major) arises
from the gcmculate ganglion.^ It passes through the petrosal canal, contributing
a filament to the tympanic plexus, receives the deep petrosal nerve from the carotid
plexus of the sjTiipathetic, emerges through the foramen lacerum, and is continued
as the nerve of the pterygoid canal to the sphenopalatine plexus and ganglia (Fig.
647).

2. A delicate branch (R. anastomoticus cum plexu tympanico) emerges from
the geniculate ganglion and unites with a filament issuing from the t\anpanic plexus
to fonn the small superficial petrosal nerve (N. petrosus superficialis minor) ; this
ends in the otic ganglion.

3. The stapedial nerve (N. stapedius) (Fig. 647) is a short filament detached
from the facial nerve as it turns down in the facial canal. It innervates the stape-
dius muscle.

4. The chorda tympani (Fig. 647) is a small nerve which arises a little below the
preceding and pursues a recurrent course in a small canal in the mastoid part of
the temporal bone (Canaliculus chordae tjanpani), to reach the tympanic cavity.
It traverses the latter, passing between the handle of the malleus and the long branch
of the incus. Emerging through the petrotympamc fissure, the nerve passes down-
ward and forward on the guttural pouch, crosses beneath the internal maxillary
artery, and joins the lingual nerve. It sends twigs to the mandibular and sublingual
glands, and through its incorporation with the lingual nerve furnishes fibers to the
mucous membrane of the anterior two-thirds of the tongue which are believed to
mediate the sense of taste.

5. Anastomotic filaments unite with the auricular branch of the vagus near
the stylomastoid foramen.

6. The posterior auricular nerve (N. auricularis aboralis) arises from the
facial at its emergence from the facial canal (Fig. 646). It runs upward and back-
ward with the posterior auricular artery under cover of the parotid gland, and sup-
plies the posterior and dorsal auricular muscles and the skin of the convex surface
of the external ear. It anastomoses with branches of the first and second cervical
nerves.

7. The internal auricular nerve (N. auricularis internus) springs from the
facial close to or in common with the preceding (Fig. 646). It ascends in the
parotid gland just behind the styloid process of the conchal cartilage, passes
through an opening in the cartilage, and ramifies in the skin of the concave surface
of the ear.

8. The digastric branch (R. digastricus) (Fig. 646) arises from the facial below
the auricular nerves and descends under cover of the parotid gland. Its branches
innervate the posterior belly of the digastricus, the stylo-hyoideus, and the occipito-
hyoideus. At its origin it gives off a small branch which forms a loop around the
great auricular artery or its posterior branch and rejoins the trunk.

9. The auriculo-palpebral nerve (N. auriculopalpebralis) (Fig. 646) arises
from the upper edge of the facial near the posterior border of the ramus. It ascends

1 Although this nerve springs directly from the ganglion, it contains motor as weU as sensory
fibers.

THE ACOUSTIC NERVE 803

in the parotid gland behind the superficial temporal artery, and terminates in
anterior auricular and temporal branches. The small anterior auricular branches
form with the frontal and lacrimal branches of the trigeminus the anterior auricular
plexus. They innervate the anterior auricular and parotido-auricularis muscles.
The temporal branch runs forward and inward over the temporal muscle to the
medial canthus of the eye, forms a plexus with the terminal branches of the ophthal-
mic nerve, and is distributed to the orbicularis oculi, corrugator supercilii, and
levator nasolabialis.

10. The cervical branch (R. colli) (Fig. 560) is small; it arises from the ventral
border of the facial opposite to the preceding nerve. It passes obliquely through the
parotid gland, emerging under cover of the parotido-auricularis, passes downward
and backward on or near the jugular vein, and anastomoses with the cutaneous
branches of the cervical nerves. It gives branches to the parotido-auricularis and
the cervical cutaneous muscle. In its course along the neck the nerve is reinforced
by twigs from the cutaneous branches of the second to the sixth cervical nerves.

11. Small branches are detached to the guttural pouch and the parotid gland.
The latter (Rami parotide!) concur with branches of the superficial temporal nerve
in forming the parotid plexus.

The facial nerve usually terminates after a short course on the surface of the
masseter by dividing into two buccal branches (Fig. 560).

1. The dorsal buccal nerve (N. buccalis dorsalis) passes forward on the upper
part of the masseter, dips under the zygomaticus, and reaches the ventral border of
the dilatator naris lateralis. It continues under cover of the last-named muscle
and the levator nasolabialis in company with the superior labial artery and ramifies
in the muscles of the upper lip and nostril. It gives collateral branches to the
buccinator and anastomoses with the infraorbital and ventral buccal nerve.

2. The ventral buccal nerve (N. buccalis ventralis) crosses the masseter
obliquely and continues forward along the depressor labii inferioris. It is connected
by variable anastomotic branches with the dorsal nerve. It gives collateral
branches to the cutaneus, buccinator, and depressor labii inferioris, and ramifies
in the muscles of the lower lip.

The buccal nerves are subject to much variation in regard to their course, anastomoses,
and relations to the sensory components derived from the superficial temporal nerve. Their
distribution is constant. The point at which the branch of the superficial temporal nerve joins
the facial is variable.

THE ACOUSTIC NERVE
The acoustic nerve (N. acusticus) is connected with the lateral aspect of the
medulla just behind and lateral to the facial (Fig. 629). It has two roots, vestib-
ular and cochlear (Radix vestibularis, cochlearis).

The acoustic nerve consists of two distinct parts which might well be regarded as separate
nerves. The cochlear part mediates the sense of hearing, while 1 he vestibular part is not auditory
in function, but is concerned in the sense of the position of the body and the mechanism of
equiUbration.

The nerve passes outward to the internal acoustic meatus, which it enters
behind the facial nerve. In the meatus it divides into two nerves, of which the
upper is the vestibular and the lower is the cochlear nerve.

1. The vestibular nerve (N. vestibuli) is distributed to the utriculus, the saccu-
lus, and to the ampullae of the semicircular ducts of the internal ear. In the
internal acoustic meatus the nerve is connected by filaments with the geniculate
ganglion of the facial nerve. At the bottom of the meatus it bears the vestibular
ganglion (G. vestibulare), from the cells of which the fibers of the nerve arise.

2. The cochlear nerve (N. cochleae) detaches a filament to the sacculus, passes

804 NERVOUS SYSTEM OF THE HORSE

through the lamina cribrosa to the labyrinth, and is distributed to the organ of
Corti in the cochlea.

The fibers of the vestibular nerve arise from the vestibular ganglion as central processes
(axones) of the bipolar cells of the ganglion. The peripheral processes (dendrites) of the cells
form arborizations about the deep ends of the hair-cells of the macula) and cristse acusticse of the
utriculus, sacculus, and semicircular ducts. The fibers enter the medulla, pass between the
restiform body and the spinal tract of the trigeminus, and spread out to end in the vestibular
nucleus in the floor of the fourth ventricle. Among the central connections of the vestibular
nerve are: (1) fibers which connect its nucleus with centers in the cerebellum (chiefly of the oppo-
site side); (2) the vestibulo-spinal tract, which conveys impulses to the motor cells of the ventral
colmnns of the spinal cord; (3) fibers which connect the nucleus with those of the abducent nerve
of the same side, the tliu'd and fom'th nerves, and the motor part of the trigeminus of both sides.

The fibers of the cochlear nerve are the central processes of the bipolar cells of the spiral
ganghon of the cochlea. The peripheral processes of these cells end in relation to the hair-cells
of the organ of Corti. Some of the nerve-fibers enter the ventral cochlear nucleus in the medulla
close to the superficial origin of the nerve; others end in the dorsal nucleus of the tuberculum
acusticum at the lateral angle of the floor of the fourth ventricle. From the ventral nucleus
fibers pass in the corpus trapezoideum to the anterior olivary nucleus of the same and of the
opposite side. Thence tracts pass to the nuclei of the motor nerves of the eye, and through the
lateral fillet to the posterior quadrigeminal body and the medial geniculate body. The axones
of the cells of the dorsal nucleus pass largely (as the strise acusticee) over the restiform body and
across the floor of the fourth ventricle toward the median plane. They then turn ventrally,
cross to the opposite side, and are continued by the lateral fillet. From the mid-brain a tract
proceeds to the cortex of the temporal part of the cerebral hemisphere.

THE GLOSSO-PHARYNGEAL NERVE

The glosso-phar5mgeal nerve (N. glossopharyngeus) is attached to the anterior
part of the lateral aspect of the medulla by several filaments (Fig. 629) . The root-
bundles enter the furrow ventral to the restiform body; they are separated by a
short interval from the origin of the facial nerve, but are not marked off behind from
the roots of the vagus. The bundles converge laterally to form a nerve which per-
forates the dura mater and emerges through the foramen lacerum posterius just
in front of the tenth nerve (Fig. 647). As it issues from the cranium the nerve
bears a considerable ovoid gray enlargement, the petrous ganglion (G. petrosum).^
It then curves downward and forward over the guttural pouch and behind the great
comu of the hyoid bone, crosses the deep face of the external carotid artery, and
divides into pharyngeal and lingual branches (Fig. 562). The collateral branches
are as follows:

1. The tympanic nerve (N. tympanicus) (Fig. 647) arises from the petrous
ganglion and passes upward between the petrous and tympanic parts of the temporal
bone to reach the cavity of the tympanum. Here it breaks up into branches to
form, along with branches from the carotid plexus of the sympathetic, the t3rmpanic
plexus. From the plexus branches pass to the mucous membrane of the tympanum
and the Eustachian tube. The continuation of the nerve issues from the plexus
and unites with a filament from the geniculate ganglion of the facial to form the
small superficial petrosal nerve; this runs forward and ends in the otic ganglion.

Filaments also connect the petrous ganglion with the jugular ganglion of the vagus nerve
and with the anterior cervical ganglion of the sympathetic.

2. A considerable branch runs backward on the guttural pouch, contributes
filaments to the pharyngeal plexus, and concurs with twigs from the vagus and the
sympathetic in forming the carotid plexus on the terminal part of the carotid
artery and on its chief branches. In this plexus is the small ganglion intercaroticum.

3. The very small nerve to the stylo-pharyngeus muscle (N. stylopharyngeus)
arises from the dorsal border of the nerve.

The pharyngeal branch (R. pharyngeus) (Fig. 562) is the smaller of the two
terminal branches. It runs forward across the deep face of the great cornu of the

1 This ganglion appears to be equivalent to the jugular or superior and petrous ganglia of man.

THE VAGUS NERVE 805

hyoid bone and concurs with the pharyngeal branches of the vagus and with sym-
pathetic filaments in forming the pharyngeal plexus; from this branches pass to
the muscles and mucous membrane of the pharynx.

The lingual branch (R. lingualis) is the continuation of the trunk (Fig. 562).
It runs along the posterior border of the great cornu of the hyoid bone in front of
the external maxillary artery, and dips under the hyo-glossus muscle. It gives
collateral branches to the soft palate, isthmus faucium, and tonsil, and ends in
the mucous membrane of the posterior part of the tongue, where it supplies gusta-
tory fibers to the vallate papillae. A considerable branch unites with a twig from
the lingual nerve.

The glosso-pharyngeal is a mixed nerve, containing both motor and sensory fibers. The
latter constitute the bulk of the nerve and include those which mediate tlie special sense of taste.
They are processes of the cells of the petrous ganglion. The central processes of the gangUon
cells enter the medulla, pass dorso-medially through the formatio reticularis, and end in the
nucleus of termination in the floor of the fourth ventricle. The motor fibers arise from dorsal and
ventral efferent nuclei in the medulla. The glosso-pharyngeal shares these nuclei with the vagus
and has practically the same central connections as that nerve {q. v.).

THE VAGUS NERVE
The vagus (N. vagus) ^ is the longest and most widely distributed of the
cranial nerves; it is also remarkable for the comiections which it forms with
adjacent nerves and with the sympathetic. It is attached to the lateral aspect of the
medulla by several filaments which are in series with those of the ninth nerve in
front and the eleventh nerve behind (Fig. 629). The bundles converge to form a
trunk which passes outward, pierces the dura mater, and emerges from the cranium
through the foramen lacerum posterius (Fig. 647) . In the foramen the nerve bears
on its lateral aspect the elongated flattened jugular ganglion (G. jugulare).

The ganglion communicates with — (a) the tympanic nerve, (b) The petrous ganglion of the
glosso-pharyngeal nerve, (c) the spinal accessory, and {d) the hj'iDoglossal. It also gives off the
auricular branch (R. auricularis), wliich runs forward below the petrous ganglion and passes tlii'ough
a small canal in the petrous temporal bone to gain the facial canal. Here it gives filaments to the
facial and emerges with that nerve through the stylo-mastoid foramen. It ascends beliind the
external acoustic meatus, dips under the deep auricular muscles, and passes through a foramen
in the conchal cartilage to ramify in the integument which lines the meatus and the adjacent
part of the ear. It may be noted that many fibers of the vagus pass over the medial face of the
gangUon without entering it.

A ganglion nodosum in the form of a compact mass is not present in the horse. It appears
to be represented by masses of ganglion cells in the nerve trunk which begin in front of the origin
of the pharyngeal branch and continue a considerable distance behind the origin of the anterior
laryngeal nerve.

Beyond the ganglion the vagus runs backward and downward with the spinal
accessory in a fold of the guttural pouch (Fig. 562). Then the two nerves separate,
allowing the hjqooglossal to pass between them, and the vagus descends with the
internal carotid artery and crosses the medial face of the origin of the occipital
artery. Here it is joined by the cervical trunk of the sympathetic, and the two
nerves continue along the dorsal aspect of the common carotid artery in a common
sheath (Fig. 558).- At the root of the neck the vagus separates from the sym-
pathetic, and from this point backward the relations of the right and left vagi differ
somewhat and must be described separately.

The right vagus nerve (Fig. 554) enters the thorax in the angle of divergence of
the right brachial artery and the truncus bicaroticus. It then passes backward and
slightly upward, crossing obliquely the lateral surface of the brachiocephalic artery
and the right face of the trachea. Reaching the dorsal surface of the latter near
the bifurcation, it divides into dorsal and ventral branches.

1 Also commonly termed the pneumogastric nerve.

2 There is formed thus a vago-sympathetic trunk.

806

NERVOUS SYSTEM OF THE HORSE

The left vagus nerve (Fig. 553) enters the thorax on the lateral or the ventral
face of the oesophagus, crosses obliquely under the left brachial artery, and passes
back on the lateral surface of that vessel in company with a large cardiac nerve.^
Separating from the latter, the vagus continues backward on the left face of the

Lig. nuchce
Splenius n^ y

Nuchal fat

Complexus tendon

Branch oj occipital artery ^>^^S*^
Complexus "v^^^l^^l^

^m^

/Rectus capitis
. y dorsalis minor
J^V Rectus capitis
^l^(;^ dorsalis major

Spinal

accessory

nerve

{dorsal

branch)

Brack
cephahcus
Vagus

Sympathetic
Carotid artery

Spinal accessory
nerve (dorsal
branch)
Rectus capitis
ventralis major

lar vein

TJiyro-laryngcal
artery

Anterior cervical
lymph glands

Sterno-cephalicus
Omo-hyoideus and slerno-hyoideus

Tliyroid gland

Sterno-ihyroideus

Fig. 649. — Cross-section of Neck of Horse, Passing through Posterior Part of Atlas.

The head and neck were extended. 1, Dorsal arch of atlas; 2, dens of axis; S, ligament of dens; 4. vertebral

sinuses; 5, dura mater; 6, spinal cord; 7, vertebral artery; 8, wing of atlas; '9, atlanto-axial joint cavity; 10,

oesophagus; 11, II, recurrent nerves; 12, 12, ventral branches of spinal accessory nerves. By an oversight the obliquua

cap. post, (above wing of atlas) is unmarked; also the parotid gland between the jugular and external maxillary vein-

aorta, inclines to the upper surface of the left bronchus, and divides into dorsal and
ventral branches.

The dorsal and ventral ])ranches unite with the corresponding branches of the
opposite nerve, thus forming dorsal and ventral oesophageal trunks (Truncus

' In some cases the left vagus pa.sses back below the junction of the jugular veins and the
termination of the left bracliial vein. It then runs backward and somewhat dorsally across the
left face of the anterior vena cava to reach its usual position.

THE VAGUS NERVE 807

oesophageus dorsalis, ventralis). These run backward in the posterior mediastinum,
dorsal and ventral to the oesophagus respectively, and enter the abdominal cavity-
through the hiatus oesophageus; they supply branches to the oesophagus and
anastomose with each other. The dorsal trunk receives the major part of its fibers
from the right vagus. After entering the abdomen it passes to the left of the
cardia, and divides into gastric and cceliac branches; the former gives branches to
the visceral surface of the stomach, forming the posterior gastric plexus; the latter
ends in the right coeliaco-mesenteric ganglion and the anterior interganglionic cord.
The smaller ventral trunk passes to the lesser curvature of the stomach and ramifies
on the parietal surface of the stomach; it forms here the anterior gastric plexus
from which branches are supplied also to the first part of the duodenum and to the
liver and pancreas.^

The collateral branches of the vagus are as follows:

1. The pharyngeal branch (R. pharjaigeus) is given off in relation to the
anterior cervical ganglion, turns around the internal carotid artery, and runs
ventrally and forward on the guttural pouch to the dorsal wall of the pharynx
(Fig. 562). Here its branches concur with the pharyngeal branch of the glosso-
pharyngeal nerve and with filaments from the spinal accessory and the sympathetic
in forming the pharyngeal plexus. This supplies the muscles of the pharynx and
of the soft palate (except the tensor palati), delicate filaments to the anterior
cervical ganglion of the sympathetic, and a larger branch which passes along the
side of the oesophagus and ramifies in its cervical part.

According to Ellenberger and Baum, the pharyngeal plexus receives filaments also from the
digastric, anterior laryngeal, hypoglossal, and first cervical nerves. The branches of the plexus
form secondary intermuscular and submucous plexuses, in which there are numerous minute
ganglia.

2. The anterior (or superior) laryngeal nerve (N. laryngeus cranialis) is larger
than the preceding and arises a little behind it (Fig. 562). It crosses the deep face
of the origin of the external carotid artery, runs downward and forward over the
lateral wall of the pharynx behind the hypoglossal nerve, and passes through the
foramen below the anterior cornu of the thyroid cartilage. Its terminal branches
ramify in the mucous membrane of the larynx, the floor of the pharynx, and the
entrance to the oesophagus; they anastomose with those of the recurrent. At
its origin the nerve gives off its small external branch (R. externus) ; this descends
to the crico-thyroid muscle, which it supplies, and sends filaments to the crico-
pharyngeus also. It often arises from the vagus just below the anterior laryngeal
and may come from the pharyngeal branch.

At the point of origin of the anterior laryngeal nerve there is a plexiform widening which is
regarded by some authors as the homologue of the ganglion nodosum of man; it often contains
minute ganglia. From it a filament arises wliich, after a short course, rejoins the vagus or enters
the sympathetic trunk. Stimulation of its central end causes a reduction of the blood-pressure,
and it is therefore termed the depressor nerve (N. depressor). On reaching the heart it passes
between the aorta and the pulmonary artery and is distributed to the myocardium.

3. The recurrent nerve (N. recurrens), also termed the inferior or posterior
laryngeal nerve, differs on the two sides in its point of origin and in the first part of
its course. The right nerve (Fig. 554) is given off opposite the second ril), turns
around the dorso-cervical artery from without inward, runs forward on the ventral
part of the lateral surface of the trachea, and ascends in the neck on the ventral
face of the common carotid artery. The left nerve (Fig. 553) arises from the vagus
where the latter begins to cross the aortic arch. It passes back over the ligamentum
arteriosum, winds around the concavity of the aortic arch from without inward,

1 It will be noted that the formation of the ventral oesophageal trunk usually occurs at the
root of the lungs, while the union of the dorsal branches of the two vagi generally occurs nearer the
hiatus oesophageus.

808 NERVOUS SYSTEM OF THE HORSE

runs forward on the ventral part of the left face of the trachea, and continues in the
neck in a position similar to the right nerve.

It is worthy of note that the left nerve passes beneath the bronchial lymph glands as it
winds around the aorta; also that in the next part of its course it hes between the left surface of
the trachea and the deep face of the aorta, and is then related to lymph glands which Ue along
the ventral tuspect of the trachea. The left reciu-rent is often incorporated in part of its coiu-se
in the anterior mediastinum with a deep cardiac nerve. Further, the left nerve hes at first ven-
tral to, and then upon, the oesophagus in the neck. The right reciu-rent is given off from, or in
common with, a considerable trunk which connects the vagus with the first thoracic ganghon
of the sjTnpathetic. The arrangement here is commonly more or less plexiform, and from it
one or two cardiac nerves arise.

The terminal part of each nerve (Fig. 649) lies on the dorsal surface of the
trachea, in relation to the oesophagus medially and the carotid artery dorsally.^ It
passes between the crico-arytenoideus dorsalis and the crico-pharjoigeus, and
enters the lar>Tix at the medial side of the lamina of the thyroid cartilage. Before
entering it gives branches to the crico-arytenoideus dorsalis and arytenoideus
transversus, and aftenvard supplies the internal muscles of the larynx. It also
communicates by delicate filaments with branches of the anterior laryngeal nerve.^
Collateral branches are given off to the cardiac plexus (Rami cardiaci), to the
trachea (Rr. tracheales), to the oesophagus (Rr. cesophagei), and to the posterior
cervical ganglion of the sjanpathetic.

4. Cardiac branches (Rr. cardiaci), usually two or three in number, are given
off from each vagus within the thorax (Figs. 553, 554). These concur with the
cardiac branches of the sympathetic and recurrent nerves to form the 'cardiac
plexus, which innervates the heart and great vessels.

5. Small tracheal and oesophageal branches (Rr. tracheales et cesophagei)
are given off from both vagi in the thorax. These concur with branches from the
recurrent nerves and the posterior cervical and anterior thoracic ganglia of the
sympathetic in forming the posterior tracheal and oesophageal plexuses, from
which Uvigs go to the trachea, oesophagus, heart, and large vessels.

6. Bronchial branches (Rr. bronchiales) are detached at the roots of the lungs
and unite ^vith sympathetic filaments in forming the pulmonary plexuses. From
the latter numerous branches proceed in a plexiform manner along the bronchi
and vessels into the substance of the lungs.

The vagus and glosso-pharyngeal nerves are so closely associated in origin and central
connections that they may be described together in this respect.

The sensory fibers arise from the petrous and jugular ganglia, and their central parts enter
the lateral aspect of the medulla and divide into anterior and posterior branches hke the fibers of
the dorsal roots of the spinal nerves. Most of the fibers end in arborizations about the cells of the
vago-glosso-pharyngeal nucleus of termination, which consists of two parts. Of these, the dorsal
sensory nucleus (Nucleus alse cinerese) is situated in the posterior part of the floor of the fourth
ventricle and in the adjacent part of the closed portion of the medulla near the median plane.
The other part is termed the nucleus of the solitary tract, and is so named because its cells are
grouped about the bundle (Tractus solitarius) formed by the posterior di\'isions of the afferent
nerve-fibers. It ends about the level of tlie pyramidal decussation. The secondary central con-
nections are similar to those of the .sensory part of the trigeminus.

The motor fibers (and those of the medullary part of the accessory) arise from the dorsal
motor nucleus and the ventral motor nucleus. The cells of the former lie in gi-oups along the
ventro-medial side of the dorsal sensory nucleus. The latter, also termed the nucleus ambiguus,
is situated more deeply in the lateral part of the formatio reticulai'is.

THE SPINAL ACCESSORY NERVE

The spinal accessory nerve (N. accessorius) is purely motor. It consists of
two parts which differ in origin and function.

^The nerve lies here about a finger's breadth above the thyroid gland. If, however, the
gland is enlarged it may come in contact with the nerve. The same is true in regard to the rela-
tion to the anterior cervical lymph glands.

■ The recurrent nerves innervate all the intrinsic muscles of the larynx except the crico-
thyroid.

THE SPINAL ACCESSORY NERVE

809

The meduUary part arises from the lateral aspect of the medulla by several
rootlets which are behind and in series with those of the vagus (Fig. 629). The
spinal part arises from the cervical part of the spinal cord by a series of fasciculi
which emerge between the dorsal and ventral roots. The bundles unite to form
a trunk which is very small at its origin at the fifth segment of the cord, but
mcreases in size when traced toward the brain, since it continually receives accessions
of fibers. It passes through the foramen magnum and joins the medullary part.

Fig. 650. — Neck of Horse, After Removal of Part of Cutaneus and Trapezius.
a, a', Brachiocephalicus; b, anterior superficial pectoral muscle; c, cervical cutaneus; d, sterno-cephalicus; e,
omo-hyoideus ; /, sterno-thyro-hyoideus; g, trachea; h, h', h", tendons of splenius, brachiocephalicus, and longissimus
atlantis; i, trapezius cervicalis; k, supraspinatus; I, anterior deep pectoral muscle; m, rhomboideus cervicalis
n, serratus cer\'icis; o, splenius, upper and lower borders of which are indicated by dotted lines; p, parotid gland
q, parotido-auricularis muscle; r, wing of atlas; s, spine of scapula; /, external maxillarj' vein; 2, S, jugular vein
4, carotid artery ; 5, descending branch of inferior cervical artery ; 6, cephalic vein ; 7-1 1 , ventral branches of second to
seventh cervical nerves; 13, cutaneous branch of second cervical nerve; 13, cervical branch of facial nerve; 14, terminal
branches of dorsal divisions of cervical nerves; 15, dorsal branch of spinal accessory nerve. (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)

The trunk thus formed sends its medullary fibers to the vagus and glosso-pharyngeal
nerves and emerges through the foramen lacerum posterius. It then runs backward
and downward ^vith the vagus in a fold of the guttural pouch, separates from that
nerve, crosses the deep face of the mandibular gland and the occipital artery, and
divides in the recessus atlantis into dorsal and ventral branches.

It is connected by anastomotic branches with the vagus and hypoglossal nerves and the
anterior cervical gangUon of the sympathetic, and contributes a branch to the pharyngeal plexus.

glO NERVOUS SYSTEM OF THE HORSE

The dorsal branch (R. dorsalis) (Figs. 558, 649, 650) receives a twig from the
second and third cervical nerves and turns around the atlantal tendon of the splenius
under cover of the brachiocephahcus. It then passes obhquely through the latter
muscle and continues backward on the cervical part of the serratus, inclines upward
across the anterior deep pectoral and the supraspinatus, and enters the deep face
of the trapezius, in which it ramifies.

The ventral branch (R. ventralis) (Fig. 561) is smaller and much shorter. It
passes do"s\Tiward and backward under cover of the cervical angle of the parotid
gland and enters the deep face of the sterno-cephalicus muscle at the junction of the
muscular substance -v^dth the tendon of insertion. It usually crosses over the
carotid artery just behind the lateral lobe of the thyroid gland.

The fibers of the spinal part of the accessory arise from the ventro-lateral cells of the ventral
gray column of the cord as far back as the fifth cervical segment. The fibers of the medullary
part come chiefly from the nucleus ambiguus in common with the motor fibers of the vagus.

THE HYPOGLOSSAL NERVE

The h5rpoglossal nerve (N. hypoglossus) is purely motor; it innervates the
muscles of the tongue and the genio-hyoideus (Fig. 562) . Its root-fibers arise from
the ventral face of the medulla in linear series about 3 to 4 mm. lateral to the poste-
rior half of the pyramid (Fig. 629) . The filaments converge to three or four bundles
which perforate the dura mater and unite to form the trunk. The latter emerges
through the hypoglossal foramen (Fig. 647) and runs downward and backward
between the guttural pouch and the capsule of the atlanto-occipital articulation
for a distance of a little less than an inch (ca. 2 cm.). It then passes between the
vagus and accessory nerves, turns downward and forward, crosses the lateral face
of the external carotid artery, and continues over the pharynx parallel with the
great cornu of the hyoid bone and behind the external maxillary artery. It then
crosses beneath the artery, runs forward on the lateral face of the hyo-glossus muscle,
and divides into its terminal branches (Rami linguales). The smaller branch
supplies the stylo-glossus, hyo-glossus, and lingualis. The larger branch passes
upward and forward between the hyo-glossus and genio-glossus, ramifies on the latter,
and supplies the remaining muscles and the genio-hyoideus. Anastomoses occur
with branches of the lingual nerve.

In the first part of its course the nerve communicates with the anterior cervical
ganglion and ^\^th the ventral branch of the first cervical nerve, and gives filaments
to the pharjaigeal branch of the vagus and the pharyngeal plexus.

The fibers of the nerve arise from the hypoglossal nucleus, an elongated gi'oup of large multi-
polar cells situated chiefly under the posterior part of the floor of the fourth ventricle, close to the
median plane. The two nuclei are connected by commissural fibers. The other central connec-
tions include: (a) communications by the medial longitudinal fasciculus with the nuclei of ter-
mination of other cranial nerves; (p) cortico-nuclear fibers which come from the cortex by way of
the internal capsule and the pyramids and go largely to the nucleus of the opposite side; (c) fibers
which join the dorsal longitudinal bundle of Schiitz, a tract which underlies the floor of the fourth
ventricle and is traceable forward below the cerebral aqueduct.

THE SPINAL NERVES

The spinal nerves (Nervi spinales) are arranged in pairs, of which there are
usually forty-two in the horse. They are designated according to their relations to
the vertebral column as cervical (8), thoracic (18), lumbar (6), sacral (5), and
coccygeal (5). Each nerve is connected with the spinal cord by two roots, dorsal
and ventral (Fig. 628).

The dorsal root (Radix dorsalis) is the larger of the two. Its fibers (Fila
radicularia) spread out in fan shape and join the cord in a linear series along the
dorso-lateral groove. The fibers converge laterally to form a compact bundle, on

THE SPINAL NERVES

811

which there is a gray nodular enlargement, the spinal ganglion (Ganglion spinale).
Beyond the ganglion the dorsal root joins the ventral root to constitute the nerve.
The ganglia are external to the dura mater, and are situated in the interverteljral
foramina, except in the case of the sacral and coccygeal nerves, the ganglia of which
lie within the vertebral canal. Those of the coccygeal nerves are intradural.

The ganglia vary greatly in size; that of the first cervical nerve is scarcely as large as a hemp-
seed, while that of the eighth cervical is about 2 cm. long and 1 cm. wide. On the large roots
connected with the cervical and lumbar enlargement of the cord there are multiple ganglia of
varying sizes mterposed in the com-se of the root-bundles. The fibers of the dorsal roots arise
from the cells of the spinal gangUa; connected with each ganglion cell there is a process which
bifurcates, giving rise to a fiber wlaich enters the spinal cord and another which passes into the nerve.

The ventral root (Radix ventralis) contains fewer fibers than the dorsal root,
except in the case of the first cervical nerve. It arises from the ventral surface of
the spinal cord (Fig. 626) by means of numerous small bundles of fibers which do
not form a linear series, but emerge from the cord over an area three to five
millimeters in width (ventral root zone). The fibers are processes of the
large cells of the ventral gray

columns of the spinal cord. Spinal branch of intercostal artery

There is no ganglion on the
ventral root.

Spinal ganglion
Dura mater
Lig. denticnlatum

Dorsal root bundles

Dorsal longitudinal ligament

Conjugal ligament

Fig. 651.

-Vertebral Canal Opened by Sawing off the Arches.

(After Schmaltz, Atlas d. Anat. d. Pferdes.)

In the cervical, thoracic, and
anterior lumbar regions the bundle^
of both roots pass through separite
openings in hnear series in the dura
mater before uniting into a root
proper. Further back the bundkb
of each root unite within the dui i
In the anterior part of the cervi( d
region and in the thoracic part of t he
cord there are intervals of varying
length between adjacent roots, but in
some places the fibers of adjac(Mit
roots overlap and an exchange ot
fibers may be observed. Many of t h(
roots are directed almost straight out-
ward or incUne slightly backward, but
the posterior lumbar, sacral, and coc-
cygeal roots and nerves run backward
to reach the foramina, tlirough which
they emerge. The distance thus to
be traversed increases from before
backward, so that these nerves form
a tapering sheaf around the conus

meduUaris and filum terminale in the last lumbar vertebra and the sacrum, wliich is known as the
Cauda equina.

The size of the spinal nerves varies greatly. The largest are connected with
the cervical and lumbar enlargements.

In, or immediately after its emergence from, the intervertebral foramen each
spinal nerve gives off a small meningeal branch (Ramus meningeus). This is
joined by a bundle of fibers from the ramus communicans and enters the vertebral
canal, in which it is distributed. Each nerve then divides into two primary-
branches, dorsal and ventral (Ramus dorsalis, ventralis). The dorsal branches
are smaller than the ventral, except in the cervical region. They are distributed
chiefly to the muscles and skin of the dorsal part of the body. The ventral branches
supply in general the muscles and skin of the ventral parts of the body, including
the limbs. Each nerve or its ventral branch is connected ^vith an adjacent ganglion
of the sympathetic system by at least one small short branch known as a ramus
communicans. Many nerves have two and some have three such rami. A nerve
may be connected with two ganglia, and a ganglion may be connected with two

812 NERVOUS SYSTEM OF THE HORSE

The dorsal root is sensory or afferent, i. e., it conveys impulses to the central system. Its
fibers are axones of the cells of the spinal gangUon. The ventral root is motor or efferent, and
conveys impulses toward the periphery. Its fibers are axones of the large cells in the ventral
gray columns of the spinal cord. The common trunk or nerve formed by the union of the two
roots contains both kinds of fibers, as do also their primary divisions. In addition to these fibers,
which are distributed to the skeletal muscles and the skin, the spinal nerves contain fibers derived
from the sjTnpathetic system through the rami communicantes; these go to the glands and
imstriped muscle and are designated secretory and vasomotor fibers.

THE CERVICAL NERVES

The cervical nerves (Nervi cervicales) (Figs. 556, 558, 650, 655) number eight
pairs. The first of these emerges through the intervertebral foramen of the atlas,
the second through that of the axis, and the eighth between the last cervical and
the first thoracic vertebrae.

The dorsal branches are distributed to the dorso-lateral muscles and skin of
the neck. They divide usually into lateral and medial branches. The medial
branches (Rami mediales) run in general across the multifidus and the lamellar part
of the ligamentum nuchas to the skin of the dorsal border of the neck; they supply
the deep lateral muscles and the skin. The lateral branches (Rami laterales) are
chiefly muscular in their distribution. The dorsal branches of the third to the
sixth nerves are connected by anastomotic branches to form the dorsal cervical
plexus.

The ventral branches are smaller than the dorsal ones — an exception to the
general rule. They increase in size from first to last. They supply in general the
muscles and skin over the lateral and ventral aspect of the vertebrae, but the last
three enter into the formation of the brachial plexus, and the two or three preceding
the last give ofT the roots of the phrenic nerve. An irregular ventral cervical plexus
is formed by anastomoses established between the ventral branches. The follo\\dng
special features may be noted:

The first cervical nerve emerges through the intervertebral foramen of the
atlas. Its dorsal branch (N. occipitalis) passes dorso-laterally between the obliqui
capitis and the recti capitis dorsales and supplies branches to these muscles, the
scutularis and posterior auricular muscles, and the skin of the poll. The ventral
branch descends through the alar foramen of the atlas, crosses over the ventral
straight muscles and the carotid artery under cover of the parotid gland, and divides
into two branches. The anterior branch enters the omo-hyoideus muscle. The
posterior branch passes downward and backward under cover of that muscle, unites
with a branch of the ventral division of the second cervical nerve, and continues its
course on the ventro-lateral surface of the trachea to enter the sterno-thyro-hyoideus
behind the intermediate tendon. In the recessus atlantis the ventral branch is
connected by one or more twigs with the anterior cervical ganglion of the sjtti-
pathetic, and a little lower with the hypoglossal nerve. It also sends branches to
the ventral straight muscles of the head and the thyro-hyoideus. Below the atlas
the ventral branch is crossed superficially by the spinal accessory nerve, the occi-
pital artery, and the ventral cerebral vein.

The second cervical nerve is larger than the first. It emerges from the verte-
bral canal through the intervertebral foramen of the anterior part of the arch of the
axis. Its dorsal branch ascends between the complexus and the ligamentum
nuchae and ramifies in the skin of the poll. The ventral branch gives off muscular
branches to the rectus capitis ventralis major, and anastomotic branches to the
spinal accessory and the ventral divisions of the first and third cervical nerves;
one of these crosses over the carotid artery and concurs in the formation of the nerve
to the sterno-thyro-hyoideus mentioned above. The ventral branch then becomes
superficial by passing between the two parts of the brachiocephalicus, and divides
into posterior auricular and cutaneous branches. The posterior auricular nerve

PHRENIC NERVE 813

passes upward and forward on the parotid gland parallel with the posterior border
of the parotido-auricularis to ramify on the convex face of the external ear. The
cutaneous nerve of the neck (N. cutaneus colli) crosses the brachiocephalicus muscle
and turns backward along the course of the jugular vein. On the lower part of
the parotid gland it is connected by a twig with the cervical cutaneous branch of
the facial nerve. It gives off twigs to the subcutaneous muscles and the skin of
the parotid and laryngeal regions, and a long branch which passes forward in the
mandibular space.

The third cervical nerve leaves the vertebral canal through the foramen be-
tween the second and third cervical vertebrae. Its dorsal branch emerges between
two bundles of the intertransversalis muscle, accompanied by a branch of the verte-
bral artery, turns dorsally on the multifidus, and divides into several branches which
radiate on the deep face of the complexus. It gives branches to these muscles and
to the skin, and a twig which joins the corresponding branch of the fourth nerve.
The ventral branch emerges through the intertransversalis below the bundle above
which the dorsal branch appears. It gives branches to the longissimus capitis et
atlantis, rectus capitis ventralis major, longus colli, splenius, and brachiocephalicus.
It also gives off a large cutaneous nerve which passes out between the two parts of
the brachiocephalicus and divides into several divergent branches.

The fourth and fifth cervical nerves are distributed in general like the third.
Their dorsal branches are united by anastomotic twigs with each other and with
those of the third and sixth nerves to form the dorsal cervical plexus. The ventral
branch of the fifth nerve often contributes a small twig to the phrenic nerve.

The sixth cervical nerve has a smaller dorsal branch than the fifth. Its
ventral branch is larger and goes in part to the brachial plexus; it supplies twigs
to the intertransversales, the longus colli, the brachiocephalicus, and the cervical
parts of the serratus and rhomboideus, furnishes a root of the phrenic nerve, and
gives off several considerable subcutaneous branches. One of the latter ramifies
on the thick part of the cervical cutaneus, to which it gives branches; another and
larger branch (N. supraclavicularis) sends twigs to the skin over the shoulder joint,
and descends to the skin over the superficial pectoral muscles (Fig. 590).

The seventh and eighth cervical nerves have small dorsal branches, which
ascend between the longissimus and multifidus, giving twigs to these muscles, the
spinalis and semispinalis, the rhomboideus, and the skin. Their ventral branches
are very large and go almost entirely to the brachial plexus; that of the seventh
nerve contributes the posterior root of the phrenic nerve.

Phrenic Nerve
The phrenic nerve (N. phrenicus) (Figs. 553, 554, 558), the motor nerve to the
diaphragm, is formed by the union of two or three roots which run obliquely down-
ward and backward over the superficial face of the scalenus muscle. The chief
roots come from the ventral branches of the sixth and seventh cervical nerves. The
root derived from the fifth nerve is small and inconstant. The root from the
seventh cervical comes by way of the brachial plexus. The nerve crosses the ventral
border of the scalenus a fingerbreadth in front of the first rib, passes through the
angle of divergence of the inferior cervical and brachial arteries, and enters the
thorax by passing between the latter vessel and the anterior vena cava. Beyond
this the course of the nerve is not the same on both sides. The right nerve courses
backward and somewhat downward over the right face of the anterior vena cava,
crosses the pericardium, and continues along the posterior vena cava to the dia-
phragm. In the latter part of its course it is enclosed in a special fold of the right
pleura and inclines gradually to the ventral face of the vein. The left nerve, in
part with the vagus, runs its entire course in the mediastinum. In the anterior
mediastinum it lies along the lateral face of the brachiocephalic artery ventral to

324 NERVOUS SYSTEM OF THE HORSE

the left vagus and a cardiac nCrve, and crosses over the dorso-cervical vein. It
then parts company with the vagus, passes over the upper part of the pericardium,
and runs backward in the posterior mediastinum to reach the tendinous center of
the diaphragm considerably to the left of the median plane. Each nerve is usually
connected near its origin with the first thoracic ganglion of the sympathetic by a
ramus communicans, and each terminates by dividing into several branches which
are distributed to the corresponding part of the diaphragm.

The Brachial Plexus
The brachial plexus (Plexus brachialis) (Fig. 558) results from anastomoses
established between the ventral branches of the last three cervical and first two
thoracic nerves. It appears as a thick, wide band between the two parts of the
scalenus muscle, and is covered by the anterior deep pectoral and subscapularis
muscles. Each of the three chief roots, i. e., those from the last two cervical and the
first thoracic nerve, is connected with the sympathetic by a ramus communicans.

The root derived from the sixth cervical nerve is very small, while the ventral branches of
the seventh and eighth cervical nerves go almost entirely to the plexus. The first thoracic nerve
furnishes the largest root; its whole ventral branch goes to the plexus with the exception of its
small first intercostal branch. The root from the second thoracic nerve is small, since most of its
ventral branch goes to form the second intercostal nerve.

The branches emanating from the plexus go for the most part to the thoracic
limb, but some are distributed on the chest- wall. The names of the branches, and
their arrangement so far as they can be conveniently examined before removal of
the forelimb, are as follows ■}

1. The large suprascapular nerve (N. suprascapularis) arises from the anterior
part of the plexus, passes ventro-laterally, and disappears between the supraspinatus
and subscapularis muscles.

2. The much smaller subscapular nerves (Nn. subscapulares), usually two
primary trunks, arise close behind the suprascapular, run backward a short dis-
tance, and divide into several branches which enter the distal third of the subscap-
ularis muscle.

3. The anterior thoracic or pectoral nerves (Nn. pectorales craniales), three or
four in number, arise from the anterior part of the plexus and from the loop formed
by the musculo-cutaneous and median nerves. One enters the anterior deep
pectoral muscle. Another passes between the divisions of the deep pectoral to
supply the superficial pectoral and brachiocephalicus, giving a twig usually to the
posterior deep muscle. The latter receives one or two other nerves.

4. The musculo-cutaneous nerve (N. musculocutaneus) arises from the ante-
rior part of the plexus and descends over the lateral face of the brachial artery,
below which it is connected by a large but short branch with the median nerve,
thus forming a loop in which the artery lies.^ One or two branches to the pectoral
muscles are given off from the nerve or the loop.

5. The median nerve (N. medianus) is usually the largest branch of the bra-
chial plexus. It descends over the insertion of the scalenus, crosses the medial
face of the brachial artery, and reaches the anterior border of that vessel. It is
easily recognized by its large size and the loop which it forms with the musculo-
cutaneous nerve.

6. The ulnar nerve (N. ulnaris) arises with the median by a short common

1 In order to examine the plexus and the origins of its chief branches conveniently and with
as little disturbance of relation as possible, the subject should be suspended in imitation of the
natural position and the foreUmb abducted as much as is necessary. In doing this some distm'b-
ance of the position and relations of the nerves and vessels takes place. The braclnal vessels are
drawn away from the chest-wall so that their lateral surface now faces forward, and the nerves
are similarly affected.

^ The loop may be absent or double.

SUPRASCAPULAR NERVE — MUSCULO-CUTANEOUS NERVE 815

trunk. It descends behind the brachial artery and is accompanied a short distance
by the radial nerve, from which it can be distinguished by its smaller size.

7. The radial nerve (N. radialis) arises from the posterior part of the plexus
and is sometimes the largest branch. It descends with the ulnar nerve over the
medial face of the origin of the subscapular artery and the lower part of the teres
major and dips into the interstice between that muscle and the long and
medial heads of the triceps.

8. The axillary nerve (N. axillaris) arises behind the musculo-cutaneous. It
passes downward and backward on the medial face of the subscapularis and dis-
appears between that muscle and the subscapular artery.

9. The long thoracic nerve (N. thoracalis longus) is wide and thin. It arises
from the anterior end of the plexus, gives off (usually) three branches to the ser-
ratus ventralis at the junction of its cervical and thoracic parts, and passes back-
ward across the surface of the serratus thoracis, to which it is distributed. The
branches which enter the muscle are given off both upward and downward in fairly
regular fashion.

10. The thoraco-dorsal nerve (N. thoracodorsalis) passes upward and back-
ward across the subscapularis muscle to ramify in the latissimus dorsi.

11. The external thoracic nerve (N. thoracalis lateralis) arises by a common
trunk with the ulnar. It passes backward and ventrally across the medial surface of
the humeral tendon of the cutaneus muscle, and continues backward in company with
the external thoracic vein. Its terminal branches ramify in the cutaneus and the
skin of the abdominal wall as far back as the flank. It gives collateral branches
to the deep pectoral muscle and others which anastomose with perforating branches
of intercostal nerves. A branch from it, accompanied by a large perforating inter-
costal branch, winds around the ventral border of the latissimus dorsi and ramifies
in the cutaneus on the lateral surface of the arm.

The term posterior thoracic or pectoral nerves (Nn. pectorales caudales) may be used to
include 9, 10, and 11.

Suprascapular Nerve
The suprascapular nerve (Fig. 566), short but large, is usually derived chiefly,
if not exclusively, from the sixth and seventh cervical components of the brachial
plexus. It passes between the supraspinatus and subscapularis muscles and turns
around the distal fourth of the anterior border of the scapula to reach the supra-
spinous fossa. It gives branches to the supraspinatus and continues backward
and upward into the infraspinous fossa, and terminates in several branches which
innervate the infraspinatus.

The direct relation of this nerve to the scapula renders it Uable to injury, the result 'of which
may be paralysis and atrophy of the muscles supplied by it. There is, however, a small tendinous
band which extends over the nerve as it turns around the edge of the scapula.

Musculo-cutaneous Nerve
The musculo-cutaneous nerve (Fig. 566) arises close behind the suprascapular,
and is derived chiefly from the part of the brachial plexus which is supplied by the
seventh and eighth cervical nerves. It descends across the lateral surface of the
brachial artery, below which a great part of the nerve unites with the median to
form the loop previously mentioned. It gives off a branch which enters the proxi-
mal part of the belly of the coraco-brachialis, passes downward and forward in
company with the anterior circumflex vessels between the two parts of that muscle
or between the muscle and the bone, and divides into branches which enter the biceps
brachii. It contributes one of the nerves to the pectoral muscles. In some cases
this nerve sends a branch to join the cutaneous branch of the median.

816

NERVOUS SYSTEM OF THE HORSE

Axillary Nerve
The axillary nerve (Figs. 566, 652) ^ derives its fibers chiefly from the eighth
cervical root of the brachial plexus. It runs downward and backward across
the distal part of the subscapularis, and, in company
with the posterior circumflex artery, dips in between that
muscle and the subscapular artery at the level of the
shoulder joint. Continuing outward in the interval between
the teres minor and the long and lateral heads of the triceps,
it reaches the deep face of the deltoid and divides into several
divergent branches. The muscular branches supply the teres
major, capsularis, teres minor, deltoid, and brachiocephali-
cus. The cutaneous branch (N. cutaneus brachii lateralis)
runs downward and a little forward across the lateral head
of the triceps and ramifies on the fascia on the front of the
forearm and on the superficial pectoral muscle.

Radial Nerve
The radial nerve^ (Figs. 566, 568, 652) is sometimes the
largest branch of the brachial plexus. Its fibers are derived
chiefly from the first thoracic root of the plexus. It passes
downward and backward over the medial surface of the origin
of the subscapular artery and the distal part of the teres
major. In this part of its course it is related in front to the
ulnar nerve, which separates it from the brachial vein.^ It
detaches a branch to the tensor fasciae antibrachii, passes out-
ward in the interval between the teres major and the long
and medial heads of the triceps, and gains the musculo-spiral
groove of the humerus. Accompanied by a branch of the
deep brachial arterj^, it runs obliquely downward and outward
in the groove, covered laterally by the lateral head of the tri-
ceps and the extensor carpi radialis, and reaches the flexion
surface of the elbow joint. In this part of its course it gives
off muscular branches to the three heads of the triceps and
to the anconeus, and a cutaneous nerve (N. cutaneus anti-
brachii dorsalis); branches of the latter emerge below or
through the lateral head of the triceps and ramify on the
dorso-lateral surface of the forearm. At the elbow the nerve
descends with the anterior radial vessels on the joint capsule,
between the brachialis and extensor carpi radialis, and sup-
plies branches to the extensor carpi and the common extensor
of the digit and (inconstantly) to the brachialis. Below the
elbow joint the nerve detaches a large branch which passes
back between the lateral extensor and the radius to the ulnaris
lateralis, and terminates by small branches which descend on
the radius to enter the radial and ulnar heads of the common
and lateral extensors of the digit, and the oblique extensor of
the carpus. Thus the radial nerve innervates the extensors
of the elbow, carpal, and digital joints, and supplies also
the lateral flexor of the carpus.^

' Also termed the circumflex nerve.

^ This is also known as the musculo-spiral nerve.

^ The relative positions of the vessels and nerves here are variable; not rarely the ulnar nerve
between the subscapular artery and vein.

■* Morphologically the last-named muscle belongs to the extensor group. In man and in
many ammals it is an extensor in function.

Fig. 652. — Cutaneous
Nerves op Right

FORELIMB OF HoRSE;

Lateral Face.

a, Cutaneous branch
of axillary nerve; b, cu-
taneous branches of radial
nerve; c, posterior cutane-
ous branch of ulnar nerve;
d, cutaneous branch of me-
dian nerve; e, superficial
branch of ulnar nerve; /,
lateral volar nerve; g, anas-
tomotic branch connecting
medial and lateral volar
nerves; 1, lateral head of
triceps: 3, extensor carpi
radiaUs; 3, common ex-
tensor; 4t ulnaris lateralis.
(After Ellenberger, in Leis-
ering's Atlas.)

ULNAR NERVE

817

Ulnar Nerve
The ulnar nerve (Figs. 566, 567, 568, 652) arises with the median from the
thoracic components of the brachial plexus. It descends between the brachial
artery and vein, accompanied for a short distance by the radial nerve. It then
crosses the vein and continues behind the latter along the anterior border of the
tensor fascia antibrachii and dips under that muscle near the elbow. Here it is
joined by the ulnar vessels and passes downward and backward over the medial
epicondyle of the humerus. In the forearm it crosses obliquely the deep face of the
ulnar head of the flexor carpi ulnaris and descends under the deep fascia with the

Extensor cu7 pi rudialis

Intermuscular septum

Conininn extetisor of digit

Intermuscular septum

Lateral extensor of digit
Intermuscular septum

Ulnaris lateralis "^'-
Deep digital flexor
{humeral head)

Superficial digital flexor
Deep digital flexor (ulnar head)

Ulnar vein Ulnar 7ierve

Uhuir artery

Fig. 653. — Cross-section of Forearm of Horse about Three Inches (ca. S cm.) below the Elbow Joint.
The deep fascia is designated by red line. A', A , V, Dorsal interosseous vessels and nerve.

Accessory cephalic vein

Vein

Cephalic vein
Medial ligament of elbow

- Median nerve
Median veins
Median artery

Flexor carpi radialis

Flexor carpi uhuiris

vessels, at first on the ulnar head of the deep flexor, and then l)etween the middle
and lateral flexors of the carpus. Near the level of the accessory carpal bone it
divides into two terminal branches, superficial and deep. It gives off two principal
collateral branches. The cutaneous branch (Ramus cutaneus volaris) is detached
just before the nerve passes under the tensor fasciae antibrachii; it runs downward
and backward on that muscle under cover of the posterior superficial pectoral,
becomes superficial below the elbow, and ramifies on the posterior surface and both
sides of the forearm. The muscular branches, which are given off at the elbow,
supply the superficial digital flexor, the ulnar head of the deep flexor, and the flexor
carpi ulnaris. Of the two terminals, the superficial branch (Ramus superficialis)
emerges between the tendons of insertion of the lateral and middle flexors of the
carpus and ramifies on the dorso-lateral aspect of the carpus and metacarpus. The
deep branch (Ramus profundus), after a very short course, unites under cover of
52

818

NERVOUS SYSTEM OF THE HORSE

the tendon of the ulnaris lateralis with the lateral branch of the median nerve to
form the lateral volar nerve.

Median Nerve
The median nerve (Figs. 566, 567, 572, 652, 653) derives its fibers chiefly from
the eighth cervical and first thoracic roots of the brachial plexus. It is usually the
largest branch, and it accompanies the chief arterial trunks to the distal part of the
limb. It descends over the medial face of the brachial artery, which it crosses
obliquely, and continues down the arm in front of the artery. Near its origin it is

Medial metacarpal vtin

Volar nerve

Digital arte i y

Dorsal digital branch
Volar digital branch

Coronary plexm

Distal end of lateral small meta-
carpal bone

Large metacarpal bone
Suspensory ligament

Superficial flexor tendon

Posterior annular ligament of
fetlock

Extensor branch of suspensory

ligament

Oblique or middle distal

sesamoidean ligament

Volar ligament of pastern joint

Proximal annular ligament of digit

Deep flexor tendon

Distal annular ligament of digit

Fig. 654. — Dissection of Distal Part of Right Fore Limb of Horse; Volar Surface.

1, Cartilage of third phalanx; S, 3, 4, ligaments from first phalanx to distal sesamoid, bulb of heel and cartilage of third

phalanx. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

joined by a large branch with the musculo-cutaneous nerve, thus forming a loop in
which the artery appears to be suspended. Near the elbow it usually crosses
obliquely over the median artery and lies behind it on the medial ligament.
Below the joint it again crosses the artery and lies behind the radius and the
lower part of the long medial ligament.

At the elbow the nerve is covered by the posterior superficial pectoral muscle and is crossed
by the large obUque connection between the cephalic and brachial veins. The variable and often
plexiform venous arrangement renders approach to the nerve here undesirable. It can be reached
best by an incision just behind the lower part of the long medial ligament; here the nerve
lies under the deep fascia in the furrow between the radius and the anterior border of the flexor
carpi radiahs, overlapped by the latter. Not uncommonly the nerve retains its position in front
of the artery at the elbow; in other cases it lies upon the artery, and rarely it crosses the deep face
of the artery.

MEDIAN NERVE 819

Passing beneath the medial flexor of the carpus, the nerve continues down-
ward in the forearm with the median vessels, and divides at a variable distance
above the carpus into two branches; these are the medial volar nerve, and the
lateral branch, which unites with the ulnar to form the corresponding lateral volar
nerve.

At the proximal part of the forearm the nerve runs almost straight downward along the
posterior border of the long medial ligament, while the artery here inclines somewhat backward.
Thus the nerve is superficial to the artery for a short distance, then lies in front of the latter to
about the middle of the region, where it incUnes a little backward and arrives at the interval
between the radial and ulnar flexors of the carpus. The division may occur about the middle of
the region or even higher, but commonly takes place in the distal third or fourth.

The collateral branches are as follows:

1. The musculo-cutaneous branch is in reality the continuation of the nerve of
that name. It is given off about the middle of the arm, passes beneath the lower
part of the biceps, and divides into muscular and cutaneous branches. The mus-
cular branch enters the brachialis. The cutaneous branch emerges between the
brachiocephalicus and the biceps and divides into two branches; these descend
on the fascia of the forearm with the cephalic vein and its accessory, and ramify
on the front and medial face of the forearm, carpus, and metacarpus.

2. Muscular branches to the radial flexor of the carpus and the humeral head
of the deep flexor of the digit are given off just as the nerve passes under the first
named muscle.

3. The small interosseous nerve passes through the interosseous space and
is distributed chiefly to the periosteum, but in some cases twigs may go to the
extensor muscles.

The volar or metacarpal nerves/ medial and lateral, are the continuations
of the median and ulnar nerves in the distal part of the limb.

The medial volar nerve (N. volaris medialis) arises as the medial terminal
branch of the median nerve at a variable distance above the carpus (Fig. 567).
It descends through the carpal canal along the medial border of the superficial
flexor tendon, and lies at first in front of the common digital artery. It then passes
behind the artery to the distal third of the metacarpus, where it lies behind the vein,
the artery here becoming deeper in position. In addition to cutaneous twigs, the
nerve gives off near the middle of the metacarpus a considerable anastomotic
branch which winds obliquely over the flexor tendons and joins the lateral nerve
below the middle of the metacarpus (Fig. 572). ^Near the fetlock the nerve divides
into two digital branches.

1. The dorsal (or anterior) digital branch (Ramus dorsalis) descends at first
between the digital artery and vein, then crosses over the vein and ramifies in the
skin and the corium of the hoof on the dorsal face of the digit.

2. The volar (or posterior) digital branch (Ramus volaris) is the direct con-
tinuation of the trunk. It descends behind the digital artery, which it accompanies
in its ramification. A middle digital branch is sometimes described as descending
behind the vein. In some cases this branch is distinct, but usually there are instead
several small twigs derived from the volar branch, which cross very obliquely
over the artery and anastomose in a variable manner with each other and with the
dorsal branch.

The lateral volar nerve (N. volaris lateralis) is formed by the union of the
lateral terminal branch of the median with the deep branch of the ulnar nerve
(Fig. 567). It descends with the lateral volar metacarpal artery in the texture of
the posterior annular ligament of the carpus. In the metacarpus it descends along
the lateral border of the deep flexor tendon behind the lateral metacarpal vein, and
is accompanied by a small artery from the volar subcarpal arch. Toward the

1 In veterinary works these are frequently termed plantar nerves, which is an unfortunate
misnomer.

820 NERVOUS SYSTEM OF THE HORSE

distal end of the metacarpus it is joined by the obhque branch from the medial
nerve, and beyond this is arranged Hke the latter. Below the carpus it detaches a
deep branch to the suspensory ligament and the interossei, and also supplies twigs
to the skin.^

THE THORACIC NERVES

The thoracic nerves (Nn. thoracales) number eighteen on either side in the
horse. Thej^^ are designated numericall}^ according to the vertebrae behind which
they emerge. Most of them are arranged in a very similar manner and therefore
do not require separate description. Each divides into a dorsal and a ventral
branch, the latter being the larger.

The dorsal branches (Rami dorsales) emerge behind the levatores costarum
and divide into medial and lateral branches. The medial branches ascend on the
multifidus and supply the dorsal spinal muscles. The lateral branches run outward
under the longissimus dorsi and emerge between that muscle and the longissimus
costarum; after giving twigs to these muscles they pass through the latissimus
dorsi and the lumbo-dorsal fascia and ramify as dorsal cutaneous nerves under the
skin of the back (Fig. 655) . In the region of the Avithers they give branches to the
serratus dorsalis and rhomboideus, and their cutaneous terminals pass through
these muscles and the dorso-scapular ligament to supply the skin over the liga-
mentum nuchse and the scapular cartilage.

The ventral branches or intercostal nerves (Nn . intercostales) are much larger
than the preceding, and are connected with the sympathetic by rami communi-
cantes. The first goes almost entirely to the brachial plexus, but sends a small
branch do\vnward in the first intercostal space, which is expended in the muscle
there without reaching the lower end of the space. The second ventral branch
furnishes a considerable root to the brachial plexus, but its intercostal continuation
is typical. The intercostal nerves (Fig. 273) descend in the intercostal spaces
wdth the vessels of like name, at first between the intercostal muscles, and lower down
chiefly between the pleura and the internal intercostal muscle. In the anterior
spaces the artery lies along the posterior border of the rib, with the nerve in front
of it; further back the nerve lies behind the border of the rib, with the arterj' in
front of it. They supply the intercostal muscles, give off lateral perforating branches,
and terminate in the following manner: The second to the sixth inclusive emerge
through the spaces between the costal cartilages and concur in supplying the pectoral
muscles. The second to the eighth give branches to the transversus thoracis.
The succeeding ones give branches to the diaphragm, pass between the transverse
and internal oblique abdominal muscles, give twigs to these, and end in the rectus
abdominis. There are three series of cutaneous nerves given off by the intercostal
nerves. The dorsal nerves emerge through the serratus ventralis and the external
intercostals about parallel with the digitations of the external oblique. The middle
ones perforate the origin of the latter muscle. The ventral ones appear through
the abdominal tunic. They supply branches to the abdominal muscles, the cu-
taneus, and the skin. Some of the anterior ones anastomose with the posterior
thoracic branches of the brachial plexus. The posterior three supply in part the
skin of the flank. The ventral branch of the last thoracic nerve runs outward
l)ehind the last rib across the dorsal surface of the psoas major and divides into
superficial and deep branches. The superficial branch passes over the superficial
face of the transversus abdominis, perforates the obliquus externus, and ramifies
under the skin of the flank (Fig. 657). The deep branch descends on the deep face
of the internal o])lique to the rectus abdominis, in which it ends.

^ Anastomoses are established between the digital branches, and the areas innervated by
them are not well defined, but really overlap each other. In certain diseased conditions, however,
in which the lesions are confined to the volar structures, reli<if from pain may be afforded by sec-
tion of tlie volar branches only.

822

NERVOUS SYSTEM OF THE HORSE

THE LUMBAR NERVES

There are six pairs of lumbar nerves (Nn. lumbales) in the horse, the last of
which emerge between the last lumbar vertebra and the sacrum. The anterior two
or three are about the same size as the thoracic nerves, but the others are much
larger.

Their dorsal branches are small in comparison with the ventral ones. They
are distributed to the muscles and skin of the loins and croup in a fashion similar
to those of the thoracic nerves.

The ventral branches are connected with the sympathetic by small rami
communicantes, and give branches to the sublumbar muscles. Those of the first
two nerves are arranged in a manner analogous to the corresponding branch of the
last thoracic nerve.

The ventral branch of the first lumbar nerve is termed the ilio-hypogastric
nerve (N. iliohypogastricus) . It passes outward between the quadratus lum-

Crura of diapludgm^^

Dia-phragm.

Last thoracic
nerve

Ilio-hypogastric
nerve
Ilio-inguinal nerve -
External spermatic
nerve
External cutaneous
nerve

Splanchnic nerve
L,~ Last inti rcostal arteries
First lumbar arteries

Attachments of psoas major
^ Body of vertebra

Eztcrrial spermatic nerve
' ■ Trunk of lumbar arteries

Sixth lumbar artery

Sympathetic
trunks

Insertion of quad-
ratus lumhorum

Anterior part of /,
lumbosacral plexus \:

Obturator nervi
Femoral nerve

Fig. 656. — Lumbar Nerves of Horse; Ventral View. (After Schmaltz, Atlas d. Anat. d. Pferdes.)

Ventral sacro-iliac
ligament

borum and the psoas major, and divides at the lateral border of the latter into a
superficial and deep branch. The superficial or cutaneous branch passes over the
dorsal edge of the internal oblique, descends between that muscle and the external
oblique, perforates the latter, and runs downward and backward and ramifies
under the skin of the posterior part of the flank and the lateral surface of the thigh.
It gives branches to the transversus and obliquus externus abdominis. The deep
(or muscular) branch is smaller; it runs downward and backward beneath the
peritoneum to the lateral border of the rectus abdominis, gives branches to the
internal oblique, and terminates in the rectus abdominis.

The ventral branch of the second limibar nerve is usually connected by an
anastomotic branch with that of the third nerve. It gives off a large branch to the
psoas major and is continued as the ilio-inguinal nerve (N. ilioinguinalis). This
divides like the ilio-hypogastric into superficial and deep branches. Its superfi-
cial branch perforates the external oblique muscle a little in front of the point of
the hip, runs downward on the front of the thigh and the lateral surface of the
stifle, and gives off cutaneous branches. The deep branch runs behind and parallel
with that of the ilio-hypogastricus and detaches branches to the abdominal muscles.

THE LUMBAR NERVES

823

It joins a branch of the external spermatic nerve, and the trunk so formed de-
scends the inguinal canal, to be distributed to the external genital organs and the
surrounding skin in the inguinal region.

The ventral branch of the third lumbar nerve is connected by a small anasto-
motic branch with the second nerve and furnishes a root of the lumbo-sacral plexus.
It gives off a branch to the psoas muscles, the external spermatic nerve, and
is continued as the lateral

cutaneous nerve. The ex- j^,_ j

temal spermatic nerve (N.
spermaticus externus) passes
backward in the substance of
the psoas minor and divides
into two branches. One of
these, the muscular branch,
emerges in front of the circum-
flex iliac vessels and goes to the
cremaster and internal oblique
muscles. The other, the in-
guinal branch, emerges behind
the vessels just mentioned. It
then runs lateral to and parallel
with the external iliac artery
and descends in the medial
part of the inguinal canal. It
emerges at the external ring
with the external pudic artery
and ramifies in the external
genital organs and the skin of
the inguinal region. The lat-
eral cutaneous nerve of the
thigh (N. cutaneus femoris
lateralis) runs backward in
the substance of the psoas
muscles and emerges at the
lateral border of the psoas
minor. It then passes outward
and backward on the iliac fas-
cia and accompanies the pos-
terior branch of the circumflex
iliac artery. With this vessel
it perforates the abdominal
wall by passing between the
external oblique and the iliacus
a short distance below the
point of the hip, descends on

the medial face of the tensor fasciae latse (near its anterior border), and ramifies
subcutaneously in the region of the stifle.

The origin and disposition of some of the foregoing nerves are variable. In some cases the
ilio-inguinal nerve ends in the psoas major, and appears then to be absent. The mode of formation
of the inguinal nerves is inconstant.

The ventral branches of the fourth, fifth, and sixth lumbar nerves concur in
the formation of the lumbo-sacral plexus.

Fig. 6.57. — Superficial Nerves of Pki/-
VIC Limb and Posterior Part of
Trunk of Horse.

a. Cutaneous branches of sixteenth
and seventeenth thoracic nerves; b, cuta-
neous branches of lumbar nerves; c, cu-
taneous branches of sacral nerves; d,
cutaneous branches of coccygeal nerves;
e, f, 9, cutaneous branches of last thoracic
and first and second lumbar nerves; g",
end of lateral cutaneous nerve of thigh;
h, posterior cutaneous nerve of thigh; i, i,
cutaneous branches of great sciatic nerve-,
k, posterior cutaneous nerve of the leg;
I, superficial peroneal nerve; m, terminal
part of deep peroneal nerve; n, lateral plantar nerve; 1, obUquus ab-
dominis externus; 3, tensor fascise latse; 3, gluteus superficialis; 4.
biceps femoris; S, semitendinosus; G, common extensor; 7, lateral ex-
tensor; 8, flexor tendons; 9, great metatarsal artery. (After Ellen-
berger, in Leisering's Atlas.)

g24 NERVOUS SYSTEM OF THE HORSE

LUMBO-SACRAL PLEXUS

This plexus (Fig. 576) results substantially from the union of the ventral
branches of the last three lumbar and the first two sacral nerves, but it derives a
small root from the third lumbar nerve also. The anterior part of the plexus lies
in front of the internal iliac artery, between the lumbar transverse processes and the
psoas minor. It supplies branches to the ilio-psoas (designated by Girard the
iliaco-muscular nerves). The posterior part lies partly upon and partly in the
texture of the sacro-sciatic ligament. From the plexus are derived the nerves of the
pelvic limb, which are now to be described.

Femobial Nerve

The femoral nerve (N. femoralis)^ is derived chiefly from the fourth and fifth
lumbar nerves, but commonly, if not always, receives a fasciculus from the third
nerve also (Fig. 656). It is the larger of the two nerves which are given off from
the anterior part of the lumbo-sacral plexus. It runs ventrally and backward, at
first between the psoas major and minor, then crosses the deep face of the tendon
of insertion of the latter, and descends under cover of the sartorius over the termi-
nal part of the ilio-psoas. It gives off the saphenous nerve, and divides into several
terminal branches which dip into the interstice between the rectus femoris and the
vastus medialis (Fig. 575), These branches are accompanied by the anterior
femoral vessels and innervate the quadriceps femoris. A collateral branch is given
off to the ilio-psoas.

The saphenous nerve (N. saphenus) (Figs. 575, 576, 582) is given off as the
femoral crosses the terminal part of the ilio-psoas. It gives off a branch which
enters the deep face of the sartorius, and descends with the femoral vessels in the
femoral canal. About the middle of the thigh it divides into several branches
which emerge from between the sartorius and gracilis, perforate the deep fascia, and
ramify on the medial surface and the front of the limb as far downward as the hock.
The longer posterior branches accompany the saphenous vessels, while the anterior
branches deviate forward toward the stifle and the anterior surface of the leg.

Obturator Nerve

The obturator nerve (N. obturatorius) is derived chiefly from the ventral
branches of the fourth and fifth lumbar nerves, but may receive fibers from the
third or the sixth (Fig. 656). It runs downward and backward, at first above
and then upon the external iliac vein, inclines inward across the obturator vein, and
passes through the anterior part of the obturator foramen (Fig. 576). It continues
downward through the obturator externus, and divides into several branches which
innervate the obturator externus, pectineus, adductor, and gracilis muscles (Fig.
581).

Anterior Gluteal Nerve

The anterior gluteal nerve (N. gluta?us cranialis) is derived chiefly from the
last lumbar and first sacral nerves, but commonly has a fifth lumbar root. It
divides into four or five branches which emerge through the greater sciatic
foramen Avith the divisions of the anterior gluteal artery and supply the glutei,
tensor fasciae lata^, and capsularis (Fig. 658). The nerve to the tensor fasciae latae
and the anterior part of the superficial gluteus passes between the deep part of the
gluteus medius and the gluteus profundus, and is accompanied on the iliacus by
branches of the lateral circumflex vessels.

Posterior Gluteal Nerve
The posterior gluteal nerve (N. glutaeus caudalis) is derived mainly from the
sacral roots of the lumbo-sacral plexus (Figs. 576, 658). It divides into two trunks
* Also termed the anterior crural nerve.

GREAT SCIATIC NERVE

825

which emerge above the great sciatic nerve. The dorsal nerve passes backward
on the upper part of the sacro-sciatic hgament and divides into branches which
enter the biceps femoris; it suppUes a branch to the posterior part of the middle
gluteus, and a nerve which turns around the posterior border of the latter and enters
the posterior head of the superficial gluteus. The ventral nerve runs downward
and backward on the sacro-sciatic ligament and divides into the posterior cutaneous
nerve of the thigh (N. cutaneus femoris caudalis) and muscular branches which
supply the semitendinosus. The former passes through the biceps femoris, emerges
between that muscle and the semitendinosus at or a little below the level of the tuber
ischii, and ramifies subcutaneously on the lateral and posterior surfaces of the hip
and thigh (Fig. 657). The deep part of the nerve is connected by filaments with
the pudic nerve.

Great Sciatic Nerve
The great sciatic nerve (N. ischiadicus) (Figs. 574, 580, 658), the largest in
the body, is derived chiefly from the sixth lumbar and first sacral roots of the lumbo-

Lateral 'ia( n>- f '^_" 4^ ^r'
iliac ligamt id \ ^^Jifif0^%^

Sacral spines

Sacro-scialic
ligament

Iliaco-fhmund or lateral circumflex vessels

Piiliic tuhercle

Lesser Gemel- Anastomosis
sciatic his between ob-
foramen turator and

internal pudic
veins

'^Obturator artery
^Obturator internus
^Obturator vein

()t

Fig. 658. — Vessels and Nerves on Pelvic Wall of Horse.

Nervus ischiadicus = great sciatic nerve; n. glut. inf. = posterior gluteal nerve; n. pudendus = pudic nerve. (After

Schmaltz, Atlas d. Anat. d. Pferdes.)

sacral plexus, but usually has a fifth lumbar root and may receive a fasciculus from
the second sacral nerve. It emerges through the greater sciatic foramen as a
broad flat band which is blended at first with the posterior gluteal nerve and
passes downward and backward on the lower part of the sacro-sciatic ligament and
on the origin of the deep gluteus muscle. It turns downward in the hollow between

826 NERVOUS SYSTEM OF THE HORSE

the trochanter major and the tuber ischii over the gemellus, the tendon of the
obturator internus, and the quadratus femoris. In its descent in the thigh it lies
between the biceps femoris laterally and the adductor, semimembranosus, and
semitendinosus medially, and is continued between the two heads of the gastroc-
nemius as the tibial nerve. Its chief branches are as follows:

1. In the pelvic part of its course the sciatic nerve supplies small muscular
branches to the obturator internus, gemellus, and quadratus femoris; the branch
to the obturator internus reaches the muscle by passing through the anterior end
of the lesser sciatic foramen.

These very small nerves arise from the upper border or deep face of the great sciatic, about
haK way between the two sciatic foramina. The nerve to the obturator internus lies along the
dorsal margin of the sciatic and divides into branches for both heads of the muscle. The nerves
to the gemellus and quadratus femoris commonly arise from the deep face of the sciatic by a com-
mon trunk which passes back between the latter and the sacro-sciatic ligament to the posterior
border of the gluteus profundus, where it divides.

2. As the sciatic nerve turns down behind the hip joint it gives off a large
muscular branch (Ramus muscularis proximalis), which divides to supply the
semimembranosus and the short heads of the biceps femoris and semitendinosus.

3. The posterior cutaneous nerve of the leg or external saphenous nerve (N.
cutaneus sura? caudalis) is detached from the sciatic about the middle of the thigh.
It receives a fasciculus from the peroneal nerve and descends with the recurrent
tarsal vein on the lateral face of the gastrocnemius to the distal third of the leg.
Here it perforates the deep fascia and ramifies under the skin on the lateral surface
of the tarsus and metatarsus (Fig. 657).

4. The peroneal nerve (N. peronaius) (Figs. 580, 585, 659)^ is a large trunk
which arises from the great sciatic nerve very shortly after the latter emerges from
the pelvic cavity. It descends with the parent trunk to the origin of the gastroc-
nemius; here the peroneal nerve deviates outward and forward across the lateral
face of the gastrocnemius under cover of the biceps femoris, and divides at the
origin of the lateral extensor muscle into superficial and deep branches. The
collateral branches include one to the biceps femoris, the reinforcing fasciculus
detached about the middle of the thigh to the posterior cutaneous nerve, and,
lower down, the lateral cutaneous nerve of the leg (Ramus cutaneus surae later-
alis).^ The latter emerges between the middle and posterior divisions of the
biceps femoris at the level of the stifle joint and ramifies under the skin. The
superficial peroneal nerve (N. peronseus superficialis)^ furnishes branches to the
lateral extensor, and descends in the furrow between that muscle and the long
extensor, perforates the deep fascia of the leg, and ramifies under the skin on the
front and the lateral face of the tarsus and metatarsus. The deep peroneal nerve
(N. peronseus profundus)^ is the direct continuation in point of size of the peroneal
trunk. It dips in between the lateral and long extensors of the digit, gives branches
to these muscles and the tibialis anterior, and descends in front of the intermuscular
septum which separates the two muscles first named. It continues do"v\Tiward
behind the tendon of the long extensor and divides on the front of the hock into
medial and lateral branches. The medial branch (Ramus medialis) passes down
under the skin on the anterior face of the metatarsus and supplies the cutaneous
fibers of this region. The lateral branch (Ramus lateralis) furnishes a twig to the
extensor brevis muscle and descends with the great metatarsal artery. It supplies
the skin on the lateral face of the metatarsus and the fetlock.

In the greater part of its course in the leg the deep peroneal nerve is separated from the
anterior tibial vessels by the tibialis anterior. It should be noted that the lateral one of the two

^ Also known as the external popliteal ner\'e.
^ Also termed the peroneal cutaneous nerve.
' Also termed the musculo-cutaneous nerve.
* Also termed the anterior tibial nerve.

TIBIAL NERVE

827

veins which ahnost always accompany the artery here is usually very large, and the layer of muscle
which intervenes between it and the nerve is often exceedingly thin. In the distal part of the leg
the nerve is in direct contact with the vein, and on the front of the hock it Ues behind the vessels.
In very exceptional cases the nerve lies for a variable distance in the middle of the leg in the lateral
part of the tibiahs anterior.

Tibial Nerve

The tibial nerve (N. tibialis) ^ is the direct continuation of the great sciatic

nerve (Figs. 576, 580, 583, 584, 659). It passes down between the two heads of the

gastrocnemius, and accompanies the recurrent tibial vessels to the distal third of

the leg, where it divides into the two plantar nerves. In the proximal third of the

Long digital extensor

Anterior tibial vessels

Deep peroneal nerve
Superficial peroneal
nerve
Intermuscular septum
Fibrous band

Lateral extensor
Intermuscular septum

Deep head of deep

flexor (flex, hall,

longus)

Peroneus tertius

Tibialis posterior
N. cutaneus surce
Recurrent tarsal vein
and artery

Soleus

Tibialis anterior

Saphenous vein'
Saphenous artery

Posterior tibial vessels

Tendon of long digital

flexor

Recurrent tibial vein
Recurrent tibial artery
Tibial nerve

Tarsal tendon of biceps femoris

and semitendinosus

Superficial flexor tendon

Gastrocnemius tendon

Fig. 659. — Cross-section of Dist.*.l Third of Left Leg of Horse.

The deep fascia is shown by red line.

leg it lies along the medial side of the superficial flexor under cover of the medial
head of the gastrocnemius; lower down it is covered by the common deep fascia
and is situated in the space between the deep flexor and the medial border of the
tendo calcaneus (Achillis).

At the usual point of election for tibial neurectomy, i. e., about a handbreadth above the
level of the tuber calcis, the nerve hes in areolar tissue and fat in a fascial compartment formed by
the special fascia of the deep flexor in front and by the common fascia and the tarsal tendon of the
semitendinosus and biceps femoris behind and medially.

At its origin the tibial nerve gives off a muscular branch (Ramus muscularis
distalis), the divisions of which pass between the two heads of the gastrocnemius
1 Also termed the posterior tibial nerve.

828 NERVOUS SYSTEM OF THE HORSE

and radiate to supply that muscle, the popliteus, the soleus, and the flexors of the
digit. Small cutaneous twigs are also detached along the course of the nerve.

Plantar Nerves
The plantar nerves, medial and lateral (N. plantaris medialis, lateralis),
result from the bifurcation of the tibial nerve in the distal part of the leg (Figs.
583, 584). They continue at first in the same direction and relations as the parent
trunk, in direct apposition and enclosed in a common sheath. At the hock they
diverge at a very acute angle and descend in the tarsal canal behind the deep flexor
tendon in company with the plantar arteries. The medial plantar nerve supplies
cutaneous nerves to the medial aspect of the tarsus and metatarsus, descends along
the medial border of the flexor tendons behind the superficial plantar metatarsal
vessels, and is otherwise arranged like the corresponding volar nerve of the fore-
limb. The lateral plantar nerve deviates outward between the two flexor tendons
to reach their lateral border. It supplies a branch to the suspensory ligament, and
in its further course resembles the corresponding nerve of the fore limb.

In so-called "tibial" neurectomy the operator really cuts the two plantar nerves which have
not yet separated. The anastomotic branch between the two plantar nerves is smaller and more
distal than that which connects the corresponding nerves of the fore limb, and is absent in 30 per
cent, of the cases according to Rudert.

Sacral Nerves

Five pairs of sacral nerves (Nn. sacrales) are present in the horse.

The small dorsal branches emerge through the dorsal sacral foramina and the
space between the sacrum and the first coccygeal vertebra, and ramify in the
muscles and skin of the sacral region and the adjacent part of the tail (Fig. 657).
The fifth anastomoses with the dorsal branch of the first coccygeal nerve.

The ventral branches leave the vertebral canal through the ventral sacral
foramina and the interval between the sacrum and first coccygeal vertebra. They
are connected with the sympathetic by rami communicantes, and contribute
branches to the pelvic plexus. The first and second are the largest, and unite with
each other and with those of the last three lumbar nerves to form the lumbo-sacral
plexus. The third and fourth are connected with each other, and the majority of
their fibers go to form the pudic and posterior hsemorrhoidal nerves.

The pudic nerve (N. pudendus) (Figs. 576, 580, 658) passes downward and
backward partly embedded in the sacro-sciatic ligament, then accompanies the
internal pudic artery to the ischial arch, turns around the latter, parting company
with the artery, and pursues a flexuous course along the dorsum penis as the nervus
dorsalis penis and ramifies in the glans penis and the penile layer of the prepuce.
Within the pelvis it anastomoses with the posterior hsemorrhoidal nerve, and gives
branches to the bladder and urethra, the terminal part of the rectum, and the skin
and muscles of the anus (Fig. 577) . It also supplies the nerve to the ischio-caverno-
sus muscle and numerous branches to the corpus cavernosum of the penis and
urethra. In the female it terminates in the clitoris and vulva (Fig. 578).

The posterior haemorrhoidal nerve (N. hsemorrhoidalis caudalis) passes do^\^l-
ward and backward above the pudic nerve, with which it anastomoses. It gives
twigs to the terminal part of the rectum, the sphincter ani externus, and the sur-
rounding skin (Fig. 577). In the female it supplies twigs to the vulva also (Fig.
578).

The ventral branch of the fifth nerve is small. It gives twigs to the sacro-
coccygeus ventralis lateralis and the skin of the root of the tail and joins the first
coccygeal nerve.

THE SYMPATHETIC NERVOUS SYSTEM 829

Coccygeal Nerves
The coccygeal nerves (Nn. coccygei) commonly number five pairs. Their
dorsal and ventral branches anastomose to form respectively two trunks on either
side, which extend to the tip of the tail and supply its muscular and cutaneous
nerves. The dorsal trunk runs with the dorso-lateral artery between the sacro-
coccygeus dorsalis and intertransversales muscles (Fig. 579). The ventral trunk
accompanies the ventro-lateral artery below the intertransversales.

The Sympathetic Nervous System ^

The sympathetic nervous system (Systema nervorum sympathicum) is that
part of the nervous system which serves (1) to transmit stimuli to the heart muscle,
unstriped muscle, and glands; (2) to conduct impulses from the viscera to the cere-
brospinal system.

Many of the fibers are derived from the cerebrospinal system and are rearranged and dis-
tributed in the sympathetic system. Numerous sympathetic fibers are contributed to the cerebro-
spinal nerves, tlirough which they are distributed to the unstriped muscular tissue and glands,
as vasomotor, pilomotor, and secretory nerves. The sympathetic, like the cerebrospinal system,
consists of neurones, each of which comprises the cell-body, an axone, and numerous branched
dendrites. The cell-bodies are aggregated into ganglia, some of which are large and more or less
constant in position and form, while others are microscopic and are scattered in an irregular man-
ner through the peripheral part of the system. Simple visceral reflexes may be mediated by sym-
pathetic neurones alone.

In descriptive anatomy the sympathetic system is regarded as consisting of
(1) a chain of ganglia extending along each side of the vertebral column and con-
nected by association fibers to form the sympathetic trunk ; (2) central branches
to and from the cerebrospinal nerves; (3) peripheral branches, which form plexuses
(Plexus sympathici) with each other and the cerebrospinal nerves; (4) the peripheral
gangUa which are interposed in the plexuses (Ganglia plexuum sympathicorum).

The S3nnpathetic triink (Truncus sympathicus) extends on either side from
the base of the cranium to the tail. In it are interposed, at intervals of varying
regularity, the gangha of the sympathetic trunk (Ganglia trunci sympathici).
These are comiected Avith the cerebrospinal nerves by central branches, the rami
communicantes.

Two kinds of rami communicantes occm-. Of these, one type consists largely of medullated
fibers derived from the spinal nerves and ganglia; they have therefore a wliite appearance, and
are termed white rami. They contain both efferent and afferent fibers. The efferent splanch-
nic fibers are derived from the ventral roots of the spinal nerves and terminate in great part
about the cells of the nearest sympathetic ganglion; others end in more distant or in peripheral
gangUa. The afferent splanchnic fibers are chiefly peripheral processes of the cells of the spinal
gangUa, but some are sympathetic fibers which enter the spinal nerve-trunk and terminate about
ceUs of the spinal ganglion. The gray rami consist mainly of non-medullated fibers derived from
the sympathetic gangha directly or through the trunk, which proceed centrally to the spinal
nerves and are distributed along the somatic divisions of the latter to unstriped muscle and glands
as vasomotor, pilomotor, and secretory fibers. Some go to the membranes of the spinal cord,
and a few terminate about cells of the spinal gangha as sensory sympathetic fibers.

Similar but more complex and irregular communications which exist between
the sympathetic system and the cranial nerves — with the exception of the first
and second — have been referred to in the accounts of the nerves.

It is convenient for descriptive purposes to divide the sympathetic system into
cephalic, cervical, thoracic, abdominal, and pelvic parts.

1. The cephaUc part (Pars cephalica systematis sympathici) comprises the
otic, sphenopalatine, and cihary ganglia, which may be regarded as homologues of
the ganglia of the trunk of other regions. It also includes three plexuses formed by

1 The special statements of this description refer to the system of the horse. A few important
differential features will be mentioned in the account of the nervous system of the other animals.

830

NERVOUS SYSTEM OF THE HORSE

branches derived from the anterior cervical ganglion. The ganglion gives off two
or three filaments which subdivide to form the internal carotid plexus (Plexus
caroticus internus) around the artery of like name. The cavernous plexus (Plexus
cavernosus) surrounds the artery within the cavernous sinus and communicates
with that of the opposite side. The external carotid plexus (Plexus caroticus
externus) is formed around the homonymous artery, and filaments from it go to the
vessel and its branches and to the salivary glands.

2. The cervical part (Pars cervicalis s. sympathici) includes two ganglia and
the trunk which connects them.

The anterior or superior cervical ganglion (G. cervicale craniale) lies on the
guttural pouch below the occipito-atlantal articulation (Fig. 562). It is reddish-
gray in color, fusiform, and about an inch (ca. 2-3 cm.) in length. It is connected
by rami communicantes with the last four cranial and first cervical nerves, sends
branches to form the plexuses mentioned above, and contributes to the pharyngeal
plexus.

The cervical trunk of the sympathetic connects the anterior and posterior

Fig. 660. — Right Cervico-thoracic Ganglion and
Rel.^.ted Structures of Horse.
G, G', Ganglia; S, sympathetic trunk; V, vagus;
R, recurrent nerve; V.c, cardiac nerves, CA'III, T.I.,
rami communicantes from eighth cervical and first thor-
acic nerves; -V./r., nervus transversarius; r.b., brachio-
cephalic trunk; A.d.c, dorso-cervical artery; A.b.d.,
right brachial artery; A.c.c, common carotid artery.

N-C.

Fig. 661. — Left Cervico-thoracic G.u^glion and
Related Structures of Hokse.
G, 6", Ganglia; S, sympathetic trunk; V, vagus;
R, recurrent nerve; C.VII, C.VIII, T.I, rami com-
municantes from last two cervical and first thoracic
nerves; N.tr., nervus transversarius; N.c, cardiac
nerves.

cervical ganglia. On leaving the former it is associated in a common sheath with
the vagus along the dorsal face of the common carotid artery. At the root of the
neck it separates from the vagus and joins the posterior cervical ganglion.

The posterior or inferior cervical ganglion (G. cervicale caudale) is situated
imder cover of the first rib and the insertion of the scalenus (Figs. 660, 661). On
the right side it lies upon the longus colli and the trachea, on the left side upon the
same muscle and the oesophagus. It is flattened, very irregular and variable in
outline, and is blended more or less with the first thoracic ganglion,^ so that the two
may be considered together as the ganglion stellatum. This receives at its antero-
dorsal angle the nervus transversarius, which accompanies the vertebral artery
in the canalis transversarius; it is a trunk formed by the rami communicantes of
the cervical nerves except the first and last. Large rami connect with the last
cervical and first and second thoracic nerves. Filaments also connect with the
vagus. From the ventral part of the ganglion proceed the carchac nerves now to
be described.

1 In some cases there exists a more or less distinct middle cer\acal ganglion which receives
the filaments from the vagus and is connected with the posterior cervical ganghon by a trunk. It
occurs oftenest on the right side and gives off one or two cardiac nerves.

THE SYMPATHETIC NERVOUS SYSTEM 831

The cardiac nerves (Nn. cardiaci) are formed by branches from the posterior
cervical and first thoracic gangha, together with twigs from the sympathetic trunks
and the vagi. They form the cardiac plexus (P. cardiacus) on the ventral face of the
trachea with each other and with branches of the vagus and recurrent nerves.
They are subject to considerable variation, but their general arrangement may be
stated as follows:

(a) On the right side there are usually two cardiac nerves. Of these one
passes back with the vagus in the angle between the right brachial artery and the
bicarotid trunk, pierces the pericardium, crosses the aortic arch, and divides into
branches which are mingled with those of the left nerves. The second crosses
obliquely over the right face of the trachea and joins the vagus, where the latter
gives off the right recurrent nerve; a small plexus is formed here, from which two
or three cardiac branches are detached. These pass back beneath the trachea and
ramify on the atria and ventricles.

(6) On the left side there are commonly three cardiac nerves. One of these is
distributed to the great vessels in the anterior mediastinum. The largest passes
back at first with the vagus beneath the arch of the left brachial artery, inclines
downward, perforates the pericardium, and divides into two branches. One
branch passes beneath the bifurcation of the pulmonary artery and is distributed
to the left atrium. The larger branch dips in between the aorta and the pulmonary
artery, gives tAvigs to these vessels, and ramifies on the ventricles, especially along
the course of the right coronary artery. The third nerve crosses the deep face of
the left brachial artery, passes back below the trachea, and unites with filaments
of a right cardiac nerve. It passes around the aorta and ramifies chiefly along the
course of the left coronary artery on the left face of the ventricles.

3. The thoracic part (Pars thoracalis systematis sympathici) extends back-
ward ventral to the costo-vertebral joints from the posterior cervical ganglion to the
crura of the diaphragm, and passes between the latter and the psoas minor to be con-
tinued by the abdominal part.

The trunk is concealed in the first part of its course by the subcostal vessels
and the lateral border of the longus colli, but further back it is visible under the
pleura.

The ganglia are arranged segmentally at each intercostal space and partly on
the heads of the ribs. They are flattened and are small and fusiform, with the
exception of the first. This (G. thoracale primum) is extensive, irregularly quadri-
lateral in outline, and is united with the posterior cervical ganglion, as previously
mentioned. The ganglia are connected with the thoracic nerves by white and gray
rami communicantes. Distinct ganglia may be absent at two or three spaces
succeeding the first, and here the trunk is thickened and contains ganglion cells.

The visceral branches comprise aortic, cardiac, pulmonary, and oesophageal
branches, and the splanchnic nerves. The aortic branches ramify on the thoracic
aorta, forming around that vessel the thoracic aortic plexus (P. aorticus thoracalis).
The cardiac branches concur with those of the vagus in forming the cardiac plexus
(P. cardiacus). From this branches go to form the coronary plexuses (P. coronarii)
along the course of the vessels of like name. The pubnonary branches join with
corresponding branches of the vagus and filaments from the cardiac plexus in
forming the pulmonary plexus (P. pulmonalis) at the root of the lung. Branches
of the plexus, on which are minute ganglia, ramify with the bronchi in the substance
of the lung.^ The oesophageal branches join with those of the vagus in the forma-
tion of the oesophageal plexus (P. oesophageus).

The great splanchnic nerve (N. splanchnicus major) arises by a series of roots
derived from the sixth or seventh to the fourteenth or fifteenth thoracic ganglia

1 The right and left plexuses communicate with each other, so that both lungs receive fibers
from both vagi.

832 NERVOUS SYSTEM OF THE HORSE

inclusive. It extends along the bodies of the vertebrae medio-ventral to the thoracic
trunk, then crosses the latter ventrally, passes back between the crus of the dia-
phragm and the lateral border of the psoas minor, and joins the coeliaco-mesenteric
ganglion. It is small at its origin, but becomes considerably larger than the sym-
pathetic trunk. Near its termination it may present a small splanchnic ganglion,
from which and from the nerve filaments go to the aorta, the oesophagus, and the
vertebrae. The fibers of the nerve are derived chiefly from the spinal cord; hence
its white appearance as compared with the sympathetic trunk.

The small splanchnic nerve (N. splanchnicus minor) is formed by roots derived
from the last two or three thoracic ganglia. It runs back with the great splanchnic
nerve, but ends in the coeliac or in the renal and adrenal plexuses.

The splanchnic nerves are quite variable. The greater splanchnic is often blended more or
less with the sympathetic trunk and may be separate only in the posterior part of the thorax.
The lesser splanchnic may be included in the greater, and thus appear to be absent. Its roots
communicate by filaments with the great splanchnic.

4. The abdominal part of the sympathetic trunk (Pars abdominalis systematis
sympathici) lies along the medial border of the psoas minor, above the aorta on the
left side and the posterior vena cava on the right (Fig. 656) . The trunk is smaller
than the thoracic part, and presents usually six small fusiform lumbar ganglia (G.
lumbalia), which are connected by rami communicantes with the ventral divisions
of the lumbar nerves. Visceral branches go to the aortic and pelvic plexuses
and to the coeliaco-mesenteric ganglion.

5. The pelvic and caudal part of the sympathetic trunk (Pars pelvina et cau-
dalis systematis sympathici) begins at the last lumbar ganglion and extends along
the pelvic surface of the sacrum medial to the emergence of the veni^ral branches
of the sacral nerves (Fig. 576). At the third or fourth segment of the sacrum the
trunk divides into medial and lateral branches. The medial branch inclines to the
median plane and unites with the opposite branch. At the junction there is often
found the small coccygeal ganglion (G. impar), which lies on the coccygeal artery
at the joint between the first and second coccygeal vertebrae. A filament from the
ganglion accompanies the artery. The lateral branch communicates with the last
two sacral nerves and joins the ventral coccygeal nerves. Sacral ganglia (G.
sacralia) occur near each of the first three sacral foramina, and are connected by
gray rami communicantes with the ventral branches of the sacral nerves. The
visceral branches are distributed through the pelvic plexus. They supply motor
fibers to the longitudinal, and inhibitory fibers to the circular, muscular coat of the
rectum; motor fibers to the bladder and uterus; and the vaso-dilator fibers (Nn.
erigentes) to the penis.

According to von Schumacher, minute segmental coccygeal ganglia occur along the caudal
branches of the sympathetic trunk. The lateral branch is regarded by van der Broek as an
aggregate of rami communicantes.

THE ABDOMINAL AND PELVIC PLEXUSES
The chief plexuses which distribute nerves to the viscera and vessels of the
abdominal and pelvic cavities are two in number, the coeliac and the pelvic. From
them fibers proceed to form numerous subsidiary plexuses which are named accord-
ing to the organs which they supply or the vessels which they enlace.

The coeliac plexus (Fig. 575)^ is situated on the dorsal wall of the abdominal
cavity, in relation to the aorta and the origin of its chief visceral branches. It is
formed by the splanchnic nerves, branches of the vagi, and filaments from the
anterior lumbar ganglia of the sympathetic. It contains the coeliaco-mesenteric
ganglia. From the coeliac plexus and its ganglia subsidiary plexuses are continued
upon the branches of the aorta.

^ Also known as the solai* plexxis.

THE ABDOMINAL AND PELVIC PLEXUSES 833

The ccBliaco-mesenteric ganglia (G. coeliaco-mesenterica)i are two in number,
right and left. They are situated on each side of the aorta, in relation to the origin
of the coeliac and anterior mesenteric arteries. The right ganglion is concealed by
the posterior vena cava; it is irregularly quadrilateral and is about two inches (4-
6 cm.) in length. The left ganglion is largely covered by the left adrenal; it is
narrower than the right one and is three or four inches (ca. 8-10 cm.) long. The
two ganglia are united by irregular connecting branches in front of and behind the
anterior mesenteric artery.^ Each receives the great splanchnic nerve of its own
side and branches from the dorsal oesophageal continuation of the vagus nerves.
Branches from the ganglia and the cords which connect them pass back to the
posterior mesenteric ganglion which is situated at the origin of the posterior mesen-
teric artery.

The following unpaired plexuses proceed from the coeliac plexus and coeliaco-
mesenteric ganglia :

1. The abdominal aortic plexus (P. aorticus abdominalis) occurs along the
abdominal aorta. It is connected with the renal plexuses and behind with the
pelvic plexus. It receives filaments from some of the sympathetic lumbar ganglia.

2. The gastric plexus (P. gastricus) enlaces the gastric artery and divides like
the artery into two parts, forming the anterior and posterior gastric plexuses.
These receive branches of the vagus nerves.

3. The hepatic plexus (P. hepaticus) is formed by several nerves of consider-
able size which accompany the hepatic artery and the portal vein. It receives
fibers from the left vagus, ramifies in the liver, and gives off branches which
accompany the collateral branches of the hepatic artery and supply the areas in
which these vessels are distributed.

4. The splenic plexus (P. lienalis) resembles the preceding in its arrangement.
In addition to its terminal branches to the spleen it gives collateral twigs to the
pancreas and the left part of the greater curvature of the stomach.

5. The anterior mesenteric plexus (P. mesentericus cranialis) is formed
mainly by branches from the posterior part of the cceliaco-mesenteric ganglia; it
is continuous with the coeliac plexus in front and the posterior mesenteric behind.
It surrounds the anterior mesenteric trunk and its branches, and supplies the viscera
to which these vessels are distributed.

The posterior mesenteric ganglion (G. mesentericum caudale) is unpaired; it
is irregularly stellate, and is situated on the origin of the posterior mesenteric
artery. It is connected with the cceliaco-mesenteric ganglia by anastomosing
branches which concur in the formation of the aortic plexus. Two or more pairs
of nerves proceed from it posteriorly. One of these, the internal spermatic nerve
(N. spermaticus internus), accompanies the spermatic artery to the spermatic cord
and testicle in the male; in the female it goes to the ovary, uterine tubes, and
adjacent part of the uterine horn. These concur in the formation of the spermatic
and utero-ovarian plexuses. The other branches from the ganglion pass back to
the pelvis ventral to the great vessels and concur in the formation of the pelvic
plexuses.

The posterior mesenteric plexus (P. mesentericus caudalis) accompanies the
artery of like name in its distribution.

The secondary plexuses which accompany the branches of the mesenteric arteries give off
branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the
myenteric plexus (P. myentericus) , or plexTis of Auerbach, hes between the layers of the mus-
ciUar coat, and is provided wdth microscopic gangha. The other is in the submucous tissue, and
is therefore termed the submucous plexus (P. submucosus) or plexus of Meissner.

1 It has been customary to designate these in veterinary works as the semilunar or coeliac
ganglia, but in the horse they evidently include the anterior mesenteric gangUa as well.

2 A good preparation of the ganglia in the horse is often difficult to obtain on account of
aneurysm of the artery and the formation of a quantity of connective tissue about it.

834 THE NEKVOUS SYSTEM OF THE OX

The following paired plexuses are derived mainly from branches of the coeliac
and aortic plexuses:

1. The renal plexuses (P. renales) proceed largely from the coeliaco-mesenteric
ganglia, but receive fibers also from the small splanchnic nerves. They enlace the
renal arteries and supply the kidneys. Minute renal ganglia occur on the course
of the nerves along the renal vessels.

2. The adrenal plexuses (P. suprarenales) are formed by a relatively very
large number of fine fibers derived in great part directly from the coeliaco-mesen-
teric ganglia. Numerous minute ganglia occur in their meshes.

3a. The spermatic plexuses (P. spermatid) proceed from the aortic plexus
and branches from the posterior mesenteric ganglion. Each accompanies the
corresponding (internal) spermatic artery to the testicle.

36. The utero-ovarian plexuses (P. ovarici) are the homologues in the female
of the preceding. They accompany the utero-ovarian arteries to the ovary and the
cornua of the uterus.

The pelvic plexuses (P. hypogastrici) are the pelvic continuations of the aortic
and posterior mesenteric plexuses. Two or more nerves proceed from the posterior
mesenteric ganglion and enter the pelvic cavity ventral to the large vessels, anasto-
mose with, each other and ^yith. branches from the sacral nerves — especially the
third and fourth — and ramify on the pelvic viscera. The peripheral plexuses
derived therefrom are named according to the organs which they supply; the chief
of these are the haemorrhoidal, vesical, utero- vaginal, prostatic, cavernous (of the
penis or clitoris) (P. hsemorrhoidalis, vesicalis, uterovaginalis, cavernosus penis s.
clitoridis, etc.). Others enlace the arteries (P. iliacus, femoralis, etc.).

THE NERVOUS SYSTEM OF THE OX^

The spinal cord resembles that of the horse in conformation and structure.
In cattle of medium size its length is about 165 to 170 cm. (ca. 65-67 inches), and
its weight about 240 to 250 grams (ca. 8 ounces).

In a cow 140 cm. in height Dexler found the weight of the cord (including the intradural
nerve-roots) to be 260 gm. and the length 162 cm. The lengths of the regions were: cervical 41
cm., thoracic 72 cm., lumbar 32 cm., sacral 7 cm.

The brain has an average weight of about 500 grams (ca. 16-17 ounces).
Its differences in general form are correlated with those noted in the consideration
of the cranial cavity.

The medulla oblongata is short, wide, and thick. Its ventral face is strongly
convex. The pyramids are narrow, short, and close together in front. Near the
decussation there is a well-defined oval prominence on either side which indicates
the position of the posterior olive. The corpus trapezoideum is large; it has no
cer-tral part between the pyramids. The external arcuate fibers are distinct. The
restiform bodies are short and thick and diverge more strongly than in the horse.
The floor of the fourth ventricle is only about two-thirds as long as in the horse.
The area acustica is a well-marked oval prominence lateral to the middle part of
the limiting sulcus. The tuberculum acusticum at the origin of the acoustic nerve
is very large. The anterior fovea is distinct. The posterior recess of the fourth
ventricle communicates through a median aperture (Apertura mediana)- with the
subarachnoid space.

^Only the most salient differences as compared with the horse will be mentioned.
2 Also known as the foramen of Magendie.

THE NERVOUS SYSTEM OF THE OX

835

The pons is smaller, both transversely and longitudinally, than that of the
horse. It is strongly convex and has a distinct central depression.

The cerebellum is smaller and more angular in form than in the horse. The
vermis is large and has a distinct depression on its anterior face for the posterior
corpora quadrigemina. The hemispheres are relatively small and are not clearly
divided into tabulations. The anterior peduncles are very short,.

The cerebral peduncles are short. A small eminence in the interpeduncular

Longitudinal Olfactory

fissure bulb Frontal pole

Transverse fissure

Occipital pole
'^rjhcllum

Medulla oblongata

Fig. 662. — Brain of Ox; Dorsal View.
1, Lateral; 2, suprasylvian ; 3, coronal; 4, transverse; o, marginal;
Marginal or sagittal pole.

itomarginal ; 7, ectomarginal. 8,

is caused by the presence of the interpeduncular ganglion. The medial gen-
iculate body is prominent. The pineal body is long and fusiform, and is often
pigmented in spots. The third ventricle forms two considerable recesses in rela-
tion to the pineal body: one (R. pinealis) extends up into the body; the other
(R. suprapinealis) is a long tubular prolongation in front of it.

The optic tracts cross the cerebral peduncles almost at a right angle.

The hypophysis or pituitary body is situated in a deep fossa and is surrounded

836

THE NERVOUS SYSTEM OF THE OX

l)y a plexus of vessels. It is much narrower and thicker than that of the horse.
The infiindibulum is relatively long and slopes do\^^lward and backward.

The cerebral hemispheres are shorter, higher, and relatively wider than in the
horse. The frontal poles are small, the occipital, large. The length from pole to
pole is about the same as the greatest transverse diameter of the two hemispheres.

Longitudinal fissure

Fig. 663. — Base of Brain of Ox.
1, Olfactory bulb; 2, 2', olfactory strise; 3, trigonum olfactorium; 4, fossa lateralis; 5, piriform lobe; 6, optic
chiasma; 7, optic tract; 8, tuber cinereum; 9, cerebral peduncle; 10, pons; 11, corpus trapezoideum; 12, pyramid;
IS, cerebellum; 14, chorioid plexus of fourth ventricle; C.I., first cervical nerve roots. The stumps of the cranial nerves
are designated by Roman numerals. The hypophysis has been removed and its contour is indicated by dotted line.
The central black area is the infundibular recess of the third ventricle opened up when the infundibulum is torn off.

Viewed from the side, the dorsal surface is strongly convex. The highest point of
the dorso-medial border is a little in front of its middle and forms a marked promi-
nence termed the sagittal or marginal pole (Polus sagittalis s. prominentia mar-
ginalis dorsalis). Anterior to this the border drops abruptly, being cut into by the
deep transverse fissure. The arachnoid on the basal and anterior parts of the
hemispheres is usually pigmented. The corpus callosum extends through a little

THE NERVOUS SYSTEM OF THE OX

837

more than a third of the length of the hemisphere. The pattern of the fissures
and gyri of the palHum is somewhat simpler than in the horse.

.• n ^" ^^^ lateral fissure (of Sylvius) is very deep. Its middle branch extends almost ver-
ticaUy upward on the middle of the lateral surface of the hemisphere, and is separated by a gyrus
■ X^^^}^'^^^ width trom the suprasylvian fissure. The anterior branch runs forward about parallel
with the sulcus rhinahs anterior, from which it is separated by the short gyri of the insula The
ktter are covered to a small extent only by the overhanging gyri (operculum). The posterior
branch may run back a distance of only about 1.5 cm. and end in T-shaped manner, or it mav
join the sulcus rhinahs posterior.

2 The suprasylvian fissure is deep and very distinct. It extends in an undulating manner
trom the lateral surface of the occipital pole to the lateral side of the sagittal pole. Here it may

Marginal pole

hell II

Olfactory Olfactory
I nfundibulum tract bulb

Hypophysis or pituitary body

Corpus
Medulla trape-
oblongata zoideum

Fig. 664
Fissures: i, Lateral; iJ, ;2, suprasylvian; 3,

Pons

V OF Ox; Right View.
4, transverse; J, ectomarginal;

diagonal; 7, posterior ecto-

sylvian; 8, presylvian; 9, 9', rhinal (anterior and posterior); P.ch., chorioid plexus of fourth ventricle; P.c, cerebral
peduncle; L.p., piriform lobe; 7, insula. Stumps of cranial nerves are designated by Roman numerals.

be interrupted or may be continued by the coronal fissure, which descends to the frontal pole
and divides into two short branches.

3. The diagonal fissure (S. diagonahs) begins in front of the stem of the lateral fissure and
runs upward and forward. Its form is very variable.

4. The transverse fissure cuts obUquely into the dorsal border in front of the sagittal pole.
It is short and deep and commonly communicates with the suprasylvian and coronal fissures, but
may be separated from the former.

5. The marginal fissure is distinct. It extends from the sagittal pole to the occipital pole.
It is flexuous and deviates outward somewhat in its posterior two-thirds.

6. The entomarginal fissure hes medial and parallel to the posterior part of the preceding.

7. The ectomarginal fissure is lateral and parallel to the marginal fissure. It does not ex-
tend so far in either direction as the latter, and is often more or less broken up by annectant gyri.

8. The sulcus rhinalis is more open than in the horse, since it is not overlapped by the gyri
above it.

9. The calloso-marginal fissure is flexuous and not so regular as in the horse. It is often
interrupted at or near the level of the genu of the corpus callosum, in which case the genual fissure
continues it downward.

10. The cruciate fissure is faint and is confined to the medial surface. It lies about one centi-
meter in front of the transverse fissure, and commonly joins the caUoso-marginal fissure below.

838

THE NERVOUS SYSTEM OF THE OX

11. Short and variable fissures occur in front of and behind the middle branch of the lateral
fissure (F. ectosyhna anterior, posterior).

The olfactory bulb is much smaller than m the horse. The lateral olfactory
stria is large, the medial one small and not distinct.

The cranial nerves have in general the same superficial origin as in the horse.
The more important differences in other respects are as follows:

The oculomotor nerve is larger than in the horse. It emerges with the fourth,
sixth, ophthalmic and maxillary nerves through the foramen orbito-rotundum.

The trigeminal nerve presents the following differences in its distribution:

Cerebellum

Olfactory
bulb

I nfundibulum
Hypophysis

Pons Cerebral
peduncle

Fig. 665. — Sagittal Section op Brain of Ox.
P.c, choroid plexuses; V.m., anterior medullary velum; A.c, cerebral aqueduct; C.q.,

V.IV. Fourth ventricle

corpora quadrigemina; C.p., posterior commissure; C.pin., pineal body; V.c.i., great cerebral vein; T, thalamus;
y./7/., third ventricle (arrow points to interventricular foramen); C.^v. anterior commissure; L./., lamina terminalis;
Co., chiasma opticum. Fissures: 7, callosal; ^, calloso-marginal; S, splenial; 4. transverse; 5, entomarginal.

The internal branch of the lacrimal nerve supplies twigs to the mucous mem-
brane of the frontal sinus; the large outer branch runs backward and supplies the
corium of the horn. The frontal nerve emerges from the orbit below the supraor-
bital process. The naso-ciliary nerve is large and sends filaments to the ocular
muscles. The ciliary ganglion is somewhat larger than in the horse, and is con-
nected with the lower division of the oculomotor nerve by several short filaments.
In consequence of the absence of the canine and upper incisor teeth the correspond-
ing branch of the infraorl^ital nerve is naturally wanting. The mandibular nerve
emerges through the foramen ovale. The superficial temporal nerve gives off a
large branch which joins the superior buccal division of the facial on the masseter,
about half-way between the zygomatic arch and the angle of the jaw. The otic
ganglion is larger than in the horse. According to Moussu the buccinator nerve
furnishes exeito-secretory twigs to the parotid and inferior buccal glands.

THE NERVOUS SYSTEM OF THE OX 839

The facial nerve divides into its two terminal branches before reaching the
border of the jaw. The superior buccal nerve is the larger of the two; it crosses
the masseter much lower than in the horse. The relatively small inferior buccal
nerve runs beneath the parotid or in the gland substance parallel with the l^order
of the lower jaw, crosses under the insertion of the sterno-cephalicus, and runs for-
ward along the depressor labii inferioris. At the point where it crosses the facial

Fig. 666. — Superficial Nerves op Head of Ox.
Nerves: a, Facial; a', a", a'", superior buccal and primary branches; 6, deep auricular; c, posterior auricular;
rf, d', d", auriculo-palpebral and primary branches; c, parotid plexus; /, digastric; 3, ff', inferior buccal; s", anasto-
mosis between g and a'; h, superficial temporal; i, k, I, branches of infraorbital; m, buccinator; m', branch of m to
zygomaticus and malaris muscles; m", branch of m to parotid gland; n, branches of infra trochlear; o, frontal; p, p',
p", lacrimal; g, dorsal branch of accessory; r, auricular branch of second cervical; r', r", branches of r; s, cutaneous
branch of second cervical; s', anastomotic branch connecting s and t; t, t' , t", third cervical and branches; u, zygo-
matic. Muscles: 1, Frontalis (part removed) ; 2, levator nasolabialis (part removed); 3, origin of levator labii
superioris proprius; 4, malaris; 5, 5', stumps of zygomaticus; 6, buccinator; 7, masseter; 8, sterno-cephaUcus; 10,
cleido-mastoideus; 11, 11', cleido-occipitalis; 12, zygomatico-auricularis; 13, fronto-scutularis; 14, scuto-auricularia
superficialis superior; 13, scuto-auricularis superficialis accessorius; IS, cervico-scutularis; 17, 17', stumps of parot-
ido-auricularis. 18, 18', Remnants of parotid gland; 19, 19', mandibular gland; 9, jugular vein; 30, facial vein.
(.\fter Schaehtschabel.)

vein and parotid duct it gives off an anastomotic branch to the superior nerve.
The auriculo-palpebral nerve is large.

The vagus bears — in addition to the relatively large jugular ganglion — a
ganglion nodosum at the point of origin of the anterior laryngeal nerve. The
trunk is large. The phar)mgeal branch is large and anastomoses -with the anterior
and external laryngeal nerves. The latter commonly arises directly from the trunk.
The dorsal oesophageal trunk communicates with the splanchnic nerve, contri-
butes twigs to the hepatic plexus, and ramifies chiefly on the right surface of the

840

THE NERVOUS SYSTEM OF THE OX

rumen and the adjacent surface of the abomasum. The ventral oesophageal trunk
goes to the left surface of the rumen; it supplies branches to the hepatic plexus
and to all the divisions of the stomach.

The spinal accessory nerve presents two special features. The part which
joins the jugular ganglion bears a small ganglion. The ventral branch supplies
both parts of the sterno-cephalicus.

The hjrpoglossal nerve is large. It is connected with the ventral division of
the first cervical nerve by a branch of considerable size, and detaches a long branch
which runs backward along the carotid artery.

Median nerve -

nar nerve

Fig. 667. — Nerves of Distal Part of Right Fore-
limb OF Ox; Dorsal View (Schematic).
p, Dorsal digital nerves.

Fig. 668. — Nerves of Distal Part of Right Fore-
limb OF Ox; Volar View (Schematic).
;), Volar digital nerves.

The spinal nerves resemble those of the horse in origin and general arrange-
ment. The thoracic nerves number thirteen pairs. The more important differ-
ences in the limb-plexuses and their branches are as follows :

The brachial plexus is formed by the ventral branches of the last three cervical
and first thoracic nerves; the second thoracic nerve usually furnishes no root, but
the ventral branch of the sixth cervical goes almost entirely to the plexus after
giving off the nerve to the rhomboideus and the serratus cervicis.

The differences in the nerves above the elbow are not of sufficient moment
to receive notice in this brief account, but below this point there are naturally

THE NERVOUS SYSTEM OP THE OX 841

important special features correlated chiefly with the arrangement of the
digits.

The radial nerve is continued below the elbow by a large cutaneous branch.
(N. cutaneus antibrachii dorsalis) which emerges at the lower border of the lateral
head of the triceps and descends on the dorsal aspect of the limb. It commu-
nicates above the carpus with the lateral cutaneous branch of the median nerve and
terminates in three dorsal digital nerves; two of these descend along the axial
or interdigital side of the dorsal surface of the chief digits, and the third along the
medial (abaxial) side of the medial chief digit.

The ulnar nerve divides at a variable distance down the forearm into two
branches. The dorsal (or superficial) branch emerges between the tendons of the
ulnaris lateralis and flexor carpi ulnaris, and is continued as the lateral dorsal
digital nerve on the lateral chief digit. The volar (or deep) branch descends along
the superficial digital flexor, gives a branch to the suspensory ligament below the
carpus, and unites with the lateral branch of the median nerve to form the lateral
volar digital nerve (N. digitalis lateralis digiti IV).

The median nerve is much larger than the ulnar. It passes beneath the prona-
tor teres, descends the forearm as in the horse, and divides in the distal part of the
metacarpus into two branches. The medial branch gives twigs to the medial small
digit and is continued on the medial side of the volar surface of the medial chief digit
as the medial volar digital nerve (N. digitalis medialis digiti III) ; it also concurs
with the lateral branch in forming the two digital nerves which descend along the
interdigital aspect of the chief digits. The lateral branch is larger. It bifurcates,
and one division unites with the twig from the medial branch to form a common
digital trunk. From the latter two digital nerves proceed as mentioned above;
these are the lateral and medial volar digital nerves of the medial and lateral
chief digits respectively (N. digitalis volaris lateralis digiti III, medialis digiti IV).
The other division unites with the volar branch of the ulnar nerve to form the
lateral volar digital nerve of the lateral chief digit (N. digitalis lateralis digiti IV).

The lumbo-sacral plexus and its branches to the pelvis and thigh present no
very striking special features.

The superficial peroneal nerve is much larger than in the horse. After crossing
beneath the peroneus longus it passes down on the front of the tarsus and meta-
tarsus and divides into three branches. The medial and lateral branches descend
as the medial and lateral dorsal digital nerves on the chief digits. The larger
middle branch joins a branch of the deep peroneal nerve in the interdigital space,
and from this union proceed the dorsal digital nerves which descend on the opposed
surfaces of the chief digits.

The deep peroneal nerve descends in the leg as in the horse, and continues
down the dorsal groove of the metatarsus with the dorsal metatarsal artery. It
gives collateral branches to the anterior muscles of the leg and to the extensor
digitalis brevis. Its terminal branches concur with branches from the superficial
peroneal nerve in the formation of the two axial dorsal digital nerves (N. dig. dors,
lat. dig. Ill et dig. dors. med. dig. IV pedis), and with a branch of the medial
plantar nerve in the formation of corresponding plantar digital nerves.

The tibial nerve divides at the back of the hock into medial and lateral plantar
nerves. The medial plantar nerve descends between the superficial flexor tendon
and the suspensory ligament and divides into two branches; the medial branch
descends as the medial plantar digital nerve (N. dig. plant, med. dig. Ill) along the
medial side of the flexor tendons of the medial chief digit; the lateral branch turns
around the flexor tendons to reach the interdigital space, where it concurs ^vith a
branch of the deep peroneal nerve in the formation of two axial plantar digital
nerves (N. dig. plant, lat. dig. Ill et dig. plant, med. dig. IV), which descend on
the opposed surfaces of the chief digits. The lateral plantar nerve descends along

842

THE NERVOUS SYSTEM OF THE OX

the lateral border of the flexor tendons, gives a branch to the suspensory ligament
and to the lateral small digit, and continues along the lateral face of the lateral
digit as the lateral plantar digital nerve (N. dig. plant, lat. dig. IV).

The S5rmpathetic system closely resembles that of the horse in its general
arrangement, and only a few differential features will receive attention. The
anterior cervical ganglion is closer to the cranial base and is thicker than in the
horse; its ])ranehes to the carotid and cavernous plexuses are large, and no con-
nection is formed with the spinal accessory nerve. The cerv'cal trunk is smaller

Superficial

nerve .
Deep peroneal nerve .
Saphenous nerve

Tibial nerve

Branch of com-
mon peroneal
nerve

Lateral plantar
nerve

'~Deep branch

Fia. 669. — Nerves op Distal Part of Right Hind

Limb or Ox; Dorsal View (Schematic).

p, Dorsal digital nerves.

Fig. 670. — Nerves op Distal Part of Right Hind

Limb of Ox; Plantar View (Schematic).

p, Plantar digital nerves.

than in the horse, and arises by two or three bundles from the anterior cervical
ganglion behind its middle. The posterior cervical ganglion is distinctly separable
from the first thoracic; the latter is large. There are thirteen pairs of thoracic
ganglia. The great splanchnic nerve begins at the fifth or sixth thoracic ganglion
and receives branches from the succeeding ones; it is commonly difficult to dis-
tinguish clearly from the thoracic trunk. The small splanchnic nerve is repre-
sented apparently by filaments which go from the first lumbar ganglion to the
adrenal plexus and the coeliac ganglion. The coeliac gangUon is rounded and lies
on the coeliac artery. The anterior mesenteric gangUon is longer and is closely

THE NERVOUS SYSTEM OF THE PIG

843

related to the anterior mesenteric artery. The two are connected by gangliated
cords, and are similarly connected with the ganglia of the opposite side, so that the
arrangement is plexiform. The coeliac plexus is more complex than that of the
horse in correlation with the compound character of the stomach. The posterior
mesenteric ganglion is small and is situated behind the artery of like name. It
receives fibers from the last three or four lumbar ganglia and two fasciculi from the
anterior mesenteric ganglia. The pelvic viscera receive branches from the posterior
mesenteric ganglion and from the

sacral ganglia; the latter number
five pairs, and the right and left
trunks are connected here by trans-
verse anastomoses. The coccygeal
trunks unite at a single fourth coc-
cygeal ganglion, then separate, and
reunite at the sixth coccygeal gan-
glion.

Longitudinal fissure Frontal pole

THE NERVOUS SYSTEM OF
THE PIG

The spinal cord weighs about
one and a half ounces (ca. 42 gm.).
It is almost circular in cross-section,
except at the enlargements, where
it is somewhat flattened dorso-ven-
trally. The conus medullaris ex-
tends to the anterior part of the
third sacral segment. The epidural
space is occupied by a large quan-
tity of fat.

The brain in adults of medium
size weighs about four to four and
a half ounces (ca. 125 gm.). When
viewed from above, the cerebrum
has an elongated oval form. The
hemispheres are widest at the pos-
terior third. The occipital pole is
larger than the frontal pole. The
medulla oblongata is relatively
broad. The cuneate tubercle is very
large and is limited laterally by a

groove. The corpus trapezoideum is very wide laterally. The pons is less promi-
nent than in the ox. The cerebellum is very wide and short. Its anterior face is
flattened and presents a depression for the corpora quadrigemina. The vermis is
large. The hemispheres consist of a large medial part and a small lateral part.
The cerebral peduncles are very short. The posterior corpora quadrigemina are
wide apart, rounded, and relatively large. The medial geniculate body is promi-
nent. The cerebral hemispheres are somewhat bean-shaped in lateral profile, the
convex border being dorsal. The arrangement of the gyri and sulci is simpler than
in the horse or ox.

The principal fissures are as follows:

1. The lateral fissure (of Sylvius) begins at the sulcus rhinalis and runs upward and
somewhat backward on the depressed part of the lateral surface of the hemisphere; it appears

Cerebellum

Medulla oblongata

Fig. C71. — Brain of Pig; Dorsal View.
Fissures: /, Lateral, S, suprasylvian, with anterior (2')
and dorsal {2") branches; 3, diagonal; 4, coronal; 5, presyl-
vian; 6, marginal; 7, ectomarginal; 8, entomarginal ; 9, cruciate.
Two different arrangements of the coronal and cruciate fissures
are seen on the two sides.

844

THE NERVOUS SYSTEM OF THE PIG

unbranched on superficial examination, but when the gyrus which almost completely conceals the
insula is raised, an anterior branch is exposed which forms the dorsal boimdary of the msula.

2. The suprasylvian fissure pursues a curved course approximately parallel with the
dorso-medial border of the hemisphere. Its posterior end is separated by a short interval from
the sulcus rhinalis posterior. From its highest point a branch proceeds obUquely upward and
forward, crosses the dorso-medial border, and joins the cruciate fissure.

3. The diagonal fisstire crosses the anterior part of the lateral surface. It is directed
obliquely downward and backward.

4. The coronal fissure is constant and deep. It is directed upward and medially over
the frontal pole, continues backward near the dorso-medial border, and often ends by passing
obliquely over the border to the medial surface of the hemisphere. It is usually continuous in
front with the presylvian fissure.

5. The presylvian fissure begins — apparently as a branch of the sulcus rhinalis anterior —
about 2 cm. in front of the lateral fissure, and curves over the lateral aspect of the frontal pole.

6. The marginal fissure begins behind the cruciate fissure close to the dorso-medial
border and extends in a gentle curve backward to the occipital pole.

Transverse fissure

Cerebellum

Olfactory hulh

Hrjpophysis Pons

Spinal cord

Medulla oblongata
Fig. 672. — Br.\in of Pig; Left View.
Fissures: 7, /', sulcus rhinalis (anterior et posterior) ; ;2, lateral; S, suprasylvian; ^, ectomarginal; 5, coronal,
of cranial nerves indicated by Roman numerals.

Stumps

7. The ectomarginal fissure lies above and nearly parallel to the posterior part of the
suprasylvian fissure.

8. The entomarginal fissure lies along the posterior part of the dorso-medial border.

9. The calloso-marginal fissure consists of two separate parts. The more extensive pos-
terior part is termed the splenial fissure. It extends from the tentorial aspect of the hemi-
sphere in a direction parallel with the corpus callosum nearly to the middle of the medial
surface; it is continued by the cruciate fissure and may be also connected with the coronal fissure
by a branch which passes obliquely upward and forward. The anterior part, the genual fissure,
lies about midway between the anterior part of the corpus callosum and the dorso-medial border.

10. The cruciate fissure runs obliquely upward and forward from the anterior end of the
splenial fissure on the inner surface of the hemisphere, cuts obliquely into the dorso-medial margin
about its middle, and usually joins the dorsal branch of the suprasylvian fissure.

11. The sulcus rhinalis extends in an undulating manner along the entire lower part
of the lateral surface of the hemisphere and forms the upper limit of the rhinencephalon.

The olfactory bulbs are \evy large and the tracts extremely broad and short.

The trigonum olfactorium is so prominent as to suggest the designation tuberculum

olfactorium.

The cranial nerves present the following special features :

The third, fourth, sixth, and the ophthalmic and maxillary divisions of the

fifth nerve emerge together as in the ox.

THE NERVOUS SYSTEM OF THE PIG

845

The lacrimal nerve resembles that of the horse, the frontal that of the ox.
The naso-ciliary nerve is relatively large and sends numerous filaments to the ocular
muscles. The maxillary nerve has a very short course in the pterygo-palatine
fossa. The infraorbital nerve is large in correlation with the development of the
snout, which receives numerous branches. The mandibular nerve emerges through
the foramen lacerum anterius. The superficial temporal nerve is small; according
to Moussu it furnishes the excito-secretory fibers to the upper part of the parotid
gland, while those going to the lower part are derived from the mylo-hyoid nerve.

The inferior buccal nerve passes downward and forward under cover of the
parotid gland and accompanies the parotid duct, with which it turns around the
lower border of the jaw in front of the masseter.

The vagus bears a jugular ganglion and a ganglion nodosum ; the latter occurs

Ulnar
{dorsal branch) — '

Anastomotic _
branch

"f ' Ulnar nerve
'" Dorsal branch

^^Deep branch

Fig. 673. — Nerves op Distal Part of Right Fore-
limb OP Pig; Dorsal View (Schematic).
•c, Dorsal common digital nerves; p, dorsal proper
digital nerves.

Fig. 674. — Nerves op Distal Part op Right Fore-
limb OF Pig; Volar View (Schematic).
p. Volar proper digital nerves.

at the point of origin of the anterior laryngeal nerve, and may be as large as a small
pea. Proximal to this the vagus is easily divided into two strands, one of which is
the accessory component. The oesophageal trunks form a posterior oesophageal
plexus, as in man, from which two nerves issue. The ventral nerve is small and
ramifies on the parietal surface of the stomach. The dorsal nerve is much larger;
it gives branches to the stomach, crosses the lesser curvature of that organ, and
joins the coeliac plexus.

The hypoglossal nerve may present a small dorsal root, on which there is a
minute hypoglossal ganglion.

The spinal nerves number on each side eight in the cervical region, fourteen
(commonly) in the thoracic, seven in the lumbar, and four in the sacral. Some
of the special features of the nerves of the limbs are as follows:

846

THE NERVOUS SYSTEM OF THE PIG

The brachial plexus is derived from the same nerves as in the ox, but the root
furnished by the sixth cervical is relatively smaller. The plexus consists of two
parts, the upper of which emerges above the scalenus, the lower between the two
parts of that muscle. The more important differences in the nerves emanating
from the plexus from the arrangement in the ox occur in the distal part of the limb.
The cutaneous branch of the radial nerve divides at the carpus into branches which
concur with the dorsal branch of the ulnar nerve in supplying the dorsal digital
nerves, two for each digit. The volar digital nerves, also two for each digit, are
formed by the terminal branches of the median nerve and the volar or deep branch
of the ulnar nerve. The formation and arrangement of the digital nerves are
indicated in the annexed schematic figures.

The lumbo-sacral plexus is derived from the ventral branches of the last three

Deep 'peroneal
nerve

Superficial
peroneal nerve

Tibial nerve

Medial plantar __
nerve

Fig. 675. — Nerves of Distal Part op Right Hind

Li.MB OF Pig; Dorsal View (.Schematic).

p, Dorsal proper digital nerves.

Fig. 676. — Nerves of Distal Part of Right Hind

Limb of Pig; Pl.vntar View (Schematic).

p, Plantar proper digital nerves.

lumbar and first sacral nerves. The distribution of the branches of the plexus
differs chiefly in the distal part of the limb. The superficial peroneal nerve is
large and terminates by forming the greater part of the dorsal digital nerves.
The latter, two for each digit, are also in part formed by the terminal branches of
the deep peroneal nerve.

The tibial nerve divides at the tarsus into medial and lateral plantar nerves.
The latter divide to form the plantar digital nerves, two for each digit. In addi-
tion, the lateral plantar nerve supplies a branch to the dorsal aspect of the lateral
(fifth) digit. The arrangement of the digital nerves is indicated by the annexed
schematic figures.

The sympathetic system of the pig has received very little attention from
anatomists. The anterior cervical ganglion is long and fusiform. It gives off

THE NERVOUS SYSTEM OF THE DOG 847

filaments which join the vagus near the ganglion nodosum. The cervical trunk is
short and relatively larger than in the ox; it is enclosed in a common sheath with
the vagus in the neck and separates from that nerve to join the middle cervical
ganglion at the thoracic inlet.

THE NERVOUS SYSTEM OF THE DOG

The spinal cord is almost circular in cross-section except at the well-marked
cervical and lumbar enlargements, where it is compressed dorso-ventrally. The
conus medullaris lies over the junction of the sixth and seventh lumbar vertebrae.
The length of the cord of a rather large dog was found to be about fifteen inches
(ca. 38 cm.) ; of this, the cervical part was about four and a half inches (ca. 11 cm.),
the thoracic a little less than seven inches (17.4 cm.), the lumbar a little less than
three inches (ca. 7 cm.), and the sacro-coccygeal about an inch (ca. 2.6 cm.)
(Flatau-Jacobson) .

The brain weighs about two to two and a half ounces (ca. 60-70 gm.) in dogs
of medium size, but there is, of course, a wide range of weight in the different breeds.
Thus in small terriers the weight is about an ounce (ca. 30 gm.) or even less, while
in very large dogs it may exceed five ounces (ca. 150 gm.). It corresponds much
more closely with the external form of the cranium in size and general form than in
the animals previously described ; this is specially true of the small breeds, in which
the bony crests and frontal sinuses are little developed.

The medulla oblongata is broad and thick. Its ventral surface is strongly
convex from side to side. The pyramids are large and prominent and are limited
by a distinct median fissure and lateral grooves. The median fissure ends at a
small depression, the foramen caecimi, just behind the pons. The olivary eminence
is a well-defined oval elevation situated between the pyramid and the superficial
origin of the hypoglossal nerve. The external arcuate fibers form a wide band
which crosses the lateral surface obliquely upward and forward, and obscures
the facial tubercle and the groove which limits the restiform body laterally. The
cuneate tubercle is distinct. The rhomboid fossa is deep and narrow. The
fourth ventricle communicates with the subarachnoid space on each side through
a lateral aperture.

The pons is relatively small, and in correlation with this fact the corpus trape-
zoideum is very wide; it is divided by the pyramids into two lateral parts. The
cerebellum is very broad, but is low and also compressed from before backward.
Rather more than half of it is overlapped by the cerebral hemispheres. The an-
terior surface is accurately adapted to the concave tentorial surfaces of the hemi-
spheres and to the posterior corpora quadrigemina and their commissure. The
posterior surface is almost vertical and is convex centrally and flattened laterally.
The vermis is prominent and in general well defined, although it is connected in its
middle part with the hemispheres. The latter are three-sided and consist of four
lobules. The small lobule lateral to the origins of the facial and acoustic nerves
is the flocculus. Lateral to this, and separated from it by a deep fissure, is the
paraflocculus; this is divided into dorsal and ventral parts by a sagittal fissure.
The anterior peduncles are very short.

The posterior corpora quadrigemina are large, very wide apart, and prominent,
and are connected by a curved commissure. The medial geniculate body is large
and distinct. In the deep interpeduncular fossa are two small bands which indi-
cate the course of the fasciculi retroflexi, tracts which connect the habenular and
interpeduncular ganglia. The mammillary body is double. The tuber cinereum
is relatively large. The hypophysis or pituitary body is circular and rather small.

S48

THE NERVOUS SYSTEM OF THE DOQ

Fig. 677. — Base of Brain op Dog.

Longitudinal fissure

Optic nerve

Optic chiasm

Optic tract

Hypophysis

Cerebral peduncU

Pom

Chorioid plexus of fourth
ventricle

Olfactory bulb

Olfactory tract
Sulcus rhinalis

Fossa lateralis
Piriform lobe
Oculo77iotor nerve

Trochlear nerve

Trigeminal nerve
Abducent nerve
Corpus trapezoideum
Glosso-pharyngeal nerve
Vagus nerve

Accessory nerve

Spinal cord Median fissure Pyramid

FiQ. 678.— Key to Fig. 677.

THE NERVOUS SYSTEM OF THE DOG

849

The cerebral hemispheres are very broad behind and diminish in width an-
teriorly; there is a sudden narrowing at the frontal poles, which are flattened
laterally. The tentorial surfaces are concave and form a deep cavity which re-
ceives the anterior part of the cerebellum. The arrangement of the fissures and
gyri is simpler than in the animals previously examined.

The chief fissures are as follows:

1. The lateral fissure extends upward and backward from the sulcus rhinalis a little behind
the middle of the lateral sm-face of the hemisphere.

2. The ectosylvian fissure has approximately the shape of an inverted U, and curves over
the lateral fissure. It is regarded as consisting

of three parts — anterior, middle, and posterior
(F. ectosylvia anterior, media, posterior).

3. The suprasylvian fissure hes above and
approximately concentric with the preceding. It
also consists of three parts — anterior, middle,
and posterior.

4. The ectomarginal or collateral fissure
runs forward on the dorsal aspect of the hemi-
sphere ahTiost parallel with the dorso-medial bor-
der. A Uttle in front of the middle of the surface
it gives off a short ansate fissure (F. ansata)
which runs obliquely medially and forward. It
is usually continued anteriorly by the coronal
fissure, and may be in continuity posteriorly
with the medilateral (or post-lateral) fissure.

Longitudinal fissure

Olfdclory bulb
Fruulal pole

Fig. 679. — Brain Stem of Dog; Dorsal View.

a, Spinal cord; 6, dorsal median groove; c, c', funicu-
lus gracilis; c", clava; d, d', funiculus cuneatus; d", tuber-
culum cuneatum; f, funiculus lateralis: e', tuberculum cin-
ereum; /, medulla oblongata; 7, II, III, fovese of floor of
fourth ventricle (fossa rhomboidea) ; g, limiting groove; h,
median fissure; i, eminentia inedialis; k, ala cinera; 1, I',
pons; m, posterior peduncle, and n, middle peduncle, of cere-
bellum (cut); o, anterior peduncle of cerebellum; p, p', cor-
pora quadrigemina, anterior and posterior; q, q', peduncles
(brachia) of corpora quadrigemina; r, thalamus; s, massa
intermedia; t, stria meduUaris; u, anterior tubercle of
thalamus; v, pulvinar; w, corpus geniculatum laterale; x,
corpus geniculatum mediale. (After Ellenberger, in Leiser-
ing's Atlas.)

Cerebellum

Medulla
oblongata

Fig. 680. — Brain of Dog; Dorsal View.
Fissures: 1, Lateral; 2, ectosylvian; 5, suprasyl-
vian; 4t ectomarginal (or collateral); 4'> ansate; S,
coronal; 6, ectolateral; 7, entomarginal; 8, presylvian
(or orbital); 9, cruciate; 10, medilateral (separated
from entomarginal on right side, but connected with it
on left hemisphere) ; 11, i. proreae.

5. The coronal fissure is usually the
continuation of the ectomarginal. It runs
forward and downward, curving around the
cruciate fissure, and ends behind the middle
of the presylvian fi.ssure.

6. The ectolateral fissure lies between
the posterior part of the ectomarginal fissure
and the suprasylvian fissure.

7. The entomarginal fissure lies between the anterior part of the ectomarginal fissure and
the dorso-medial border. It is often indistinct and not rarely absent.

8. The presylvian fissure — sometimes termed the orbital — begins at the sulcus rhinalis,
a little in front of its middle, and curves over the anterior third of the lateral surface of the hemi-
sphere in front of the coronal fissure.

350 THE NERVOUS SYSTEM OF THE DOG

9. The cruciate fissure is the deepest and most characteristic. It cuts deeply into the an-
terior third of the dorso-medial border and runs ahnost straight outward. It is continuous on the
medial surface of the hemisphere with the calloso-marginal or splenial fissure.

10. The sulcus rhinalis is continued on the tentorial
surface of the hemisphere by the occipito-temporal fissure.

7i.___:^ -.^,^^ Anteriorly it is prolonged as the olfactory fissure, which

^.-'•''''"^ (. — '"**v!^/^ is concealed by the oKactory bulb and tract. .

^jf^^^ii^n *«ni iiii *\,Jl^k' 11. The calloso-marginal fissure usually consists of

fy^^_. f„— -— ^ T'^-'-f t'^o parts, splenial and genual. The splenial fissure is

/( ^1^ /^ 'i'^^-^?^ f Ji ^ parallel with the splenium and middle part of the corpus

V*- ^*~ ' \ / )/ callosum on the medial surface of the hemisphere. It is

^'^^^^Tainmiiiii'i iilfi^^mr ir""*^'*^" continuous in front with the cruciate fissure and runs for-

^^^^^^NIH^^^^^^ ward and outward across the tentorial surface to join the

^^^^^"""^ occipito-temporal or calcarine fissure. It gives off from

„ ^_, _ „ M„.„=»=..o^ its highest part the short accessory cruciate fissure. The

Fig. 681. — Right Cerebral Hemisphere t ^ ■ • i i n i -xi xi. e

DM L View genual fissure is approximately parallel wath the genu of

OG, . edia . ^^^ corpus callosum.

i,Corpu.s callosum; i , genu; / , splen- ^2. The suprasplenial fissure runs almost parallel

ium of corpus callosum; a, genual fissure; ^^^i the posterior part of the calloso-marginal fissure on

6, splenial fissure; c, suprasplemal fissure; ^^^ -^^^^^ ^^^ tentorial surfaces of the hemisphere.
d, hippocampal fissure; e, sulcus corporis ^3 rpj^^ occipito-temporal or calcarine fissure is the

callosi; /, postsplemal fissure; g, lesser continuation on the tentorial surface of the hemisphere of

cruciate fissure; h, cruciate fissure. (After ^-^e splenial fissure.

Ellenberger, in Leisering's Atlas.) j4 ^j^p hippocampal fissure forms the medial

boundary of the piriform lobe.

The olfactory bulb is large and is compressed laterally; its anterior end pro-
jects beyond the frontal pole of the hemisphere. The tract is short and is also
flattened laterally. Both contain a narrow cavity which communicates with the
lateral ventricle. The piriform lobe is large and rounded.

The cranial nerves present the follo^\^ng special features which are worthy of
notice :

The ophthalmic nerve gives off frontal, long ciliary, ethmoidal, and infratro-
chlear branches. The lacrimal nerve arises from the ophthalmic at its origin;^ its
recurrent branch emerges at the orbital ligament and concurs with the zygomatic
and frontal nerves in the formation of the anterior auricular plexus. The frontal
nerve emerges from the orbit in front of the upper end of the orbital ligament,
ramifies in the upper lid and the adjacent skin of the forehead, and sends branches
backward to the anterior auricular plexus. The long ciUary nerve accompanies
the optic nerve and divides into several branches which pierce the posterior part of
the sclera. The ethmoidal nerve gives off internal nasal branches and ends in the
muzzle. The infratrochlear nerve runs forward between the medial straight and
the superior oblique muscles of the eye and ramifies on the face in the vicinity of
the medial canthus.

The maxillary nerve emerges through the foramen rotundum and gives off
five branches. The lacrimal nerve emerges from the orbit lateral to the frontal;
its branches concur with the frontal and auriculo-palpebral nerves in the formation
of the anterior auricular plexus. The zygomatic nerve emerges through an opening
in the upper part of the orbital ligament and ramifies in the lower lid and on the
adjacent surface of the face. The infraorbital nerves, two in number, divide within
the infraorbital canal and after their emergence upon the face, thus forming seven
or eight external nasal and superior labial branches. The sphenopalatine nerve
gives off lesser and greater palatine and posterior nasal nerves.

The mandibular nerve passes out through the foramen ovale. The superficial
temporal nerve divides into auricular, temporal, and malar branches; the last-
named crosses the masseter and ramifies with the buccal nerves. The mylo-hyoid
nerve is given off from the mandibular nerve almost immediately after the latter
emerges from the cranium; it innervates the mylo-hyoideus and occipito-mandib-
ularis and gives off a l^ranch which turns around the lower jaw, joins the inferior

1 The origin of the lacrimal nerve is such that Ellenberger-Baum and Martin describe it
as a branch o( the maxillary nerve.

THE NERVOUS SYSTEM OF THE DOG

851

buccal nerve, and ramifies on the lateral surface of the face. The inferior alveolar
nerve arises by a common trunk with the mylo-hyoid; it gives off dental branches
and terminates in mental and inferior labial branches. The lingual nerve supplies
vaso-dilator and excito-secretory filaments to the mandibular and sublingual
salivary glands; these fibers are derived from the chorda tympani.

The facial nerve divides near the posterior border of the jaw into four branches.
The upper branch is the auriculo-palpebral nerve, which divides after a very short
course into anterior auricular and zygomatic branches. The latter curves upward
and forward across the zygomatic arch toward the eye, and divides into branches
which supply the eyelids and nasal region and concur with the frontal and lacrimal
nerves in forming the anterior auricular plexus. The superior buccal nerve ac-
companies the parotid duct across the masseter. The inferior buccal nerve runs
forward along the lower border of the masseter and the mandible. The two nerves

Fig. 682. — Deep Dissection of Head of Dog, Showing Especially Trigeminal and Hypoglossal Nerves.
a, Hypoglossal nerve; 6, cervical branch of a; c, mandibular division of trigeminus; d, lingual nerve; e, nerve to
mandibular gland; /, deep temporal nerve; g, pterygoid nerve; h, buccinator nerve (cut); i, inferior alveolar nerve;
k, staphyline branch of lingual nerve; I, chorda tympani; m, mylo-hyoid nerve; n, sphenopalatine nerve; o, lesser
palatine nerve; p, great palatine nerve; g, infraorbital nerves; r, n. subcutaneus mate; s, branch of oculomotor nerve
to inferior oblique muscle; <, lacrimal nerve; m, frontal nerve; i;, trochlear nerve ; li), abducens nerve; i, carotid artery;
^.lingual artery; 5, internal maxillary artery; 4, m. thyro-pharyngeus; 5, m. hyo-pharyngeus; S, m. thyro-hyoideus;
7, m sterno-hyoideus; 5, m. hyo-glossus; 5, m. genio-hyoideus; ^0, m. genio-glossus; i^, m. stylo-glossus; 12, m.
pterygoideusmedialis; i 3, outline of mandibular gland (dotted) ; i4> atlas; ;.5, bulla ossea; iff, zygomatic arch (dotted;;
17, m. rectus ocuU inferior; 18, m. obhquus oculi inferior. (EUenberger-Baum, Anat. d. Hundes.)

ramify on the cheek and anastomose with each other and the infraorbital nerves
to form a plexus from which branches go to the muscles of the lips and nostrils.
The cervical branch runs downward and backward over the mandibular gland
and ramifies in the cervical cutaneus muscle; it communicates with the inferior
buccal nerve and sends twigs to the parotido-auricularis muscle and the mandibular
space.

The vagus bears a jugular ganglion and a ganglion nodosum. The former is
situated on the nerve just before the emergence of the latter from the cranium. The
latter is situated near the anterior cervical ganglion on the rectus capitis ventralis
major and dorsal to the internal carotid artery; it is fusiform and may be about half
an inch (ca. 1-1.5 cm.) long in a large dog. In its course in the neck the nerve is
inclosed with the sympathetic trunk in a common sheath and is related ventrally

852

THE NERVOUS SYSTEM OF THE DOG

to the common carotid artery. The two nerves separate after entering the thorax
(Figs. 613, 614). The right vagus crosses obliquely over the right face of the
trachea and divides a short distance behind the bifurcation of the latter into dorsal
and ventral branches. The left vagus crosses the lateral surface of the aortic arch
and divides similarly. By the union of the dorsal and ventral divisions of the two
nerves there are formed dorsal and ventral oesophageal trunks. The dorsal trunk
concurs with branches of the coeliac plexus in forming the posterior gastric plexus
on the visceral surface of the stomach. The ventral trunk ramifies on the parietal
surface of the stomach, forming the anterior gastric plexus, from which a consider-
able branch passes along the lesser curvature to the pylorus. Some special features
of the collateral branches are : Two pharyngeal branches are present. The anterior
pharyngeal branch arises from the vagus above the ganglion nodosum. It passes
under the deep face of the carotid artery and descends on the lateral surface of the
pharynx to end in the crico-thyroid muscle. It furnishes a root of the inferior pharyn-
geal branch, and communicates with the pharyngeal branch of the ninth and with the

Fig. 683. — Nerves of Face of Dog. Parotid Gland is Removed.
Nerves: a, Facial; b, posterior auricular; c, internal auricular; d, digastric; e, inferior buccal; /, cervical branch
of facial; 3, auriculo-palpebral; A, superior buccal; i, temporal branch; A;, i', A", zygomatic branch; Z, auriculo-tem-
poral; m, malar branch of I; n, buccinator; o, mylo-hyoid branch; p, subcutaneus malse; q, lacrimal; r, frontal; s,
infratrochlear; t, infraorbital. 1, Paramastoid process; 2, occipito-mandibularis; 3, base of concha; 4. masseter;
5, zygomaticus; 6, scutularis; 7, zygomatic arch; S, maxilla. (EUenberger-Baum, Anat. d. Hundes.)

anterior laryngeal and hypoglossal nerves. The posterior pharjmgeal branch is
formed by the union of roots derived from the anterior pharyngeal nerve and the
ganglion nodosum, together with filaments from the anterior cervical ganglion.
It crosses the side of the pharynx behind the anterior pharyngeal and ramifies on
the posterior constrictor of the pharynx and the origin of the oesophagus. It
contributes filaments to the pharyngeal plexus, communicates with the recurrent
nerve, and supplies twigs to the thyroid gland. The pharyngeal plexus is formed
on the lateral surface of the pharynx by branches of the pharyngeal nerves and the
communications above described; branches from it iimervate the muscles and
mucous membrane of the pharynx. The anterior lar3mgeal nerve arises from the
ganglion nodosum and descends over the side of the pharynx, crossing beneath the
carotid artery and the anterior laryngeal nerve. It passes through the thyroid
notch and ramifies in the mucous membrane of the larynx. It communicates with
the anterior cervical ganglion and the anterior pharyngeal branch of the vagus, and
gives twigs to the hyo-pharyngeus muscle. Immediately after its entrance into the
larynx it gives off a large branch which, instead of uniting with the recurrent as in the

THE NERVOUS SYSTEM OF THE DOG 853

other animals, has a pecuHar arrangement. It runs back near the dorsal border of the
thyroid cartilage, gives a branch to the crico-arytenoideus dorsalis as it passes over
that muscle, and continues along the trachea medial to the recurrent nerve. At the
thoracic inlet it communicates with the posterior cervical ganglion and continues
backward to unite with the vagus at or near the point of origin of the recurrent
nerve. Its collateral filaments supply the trachea and concur with the posterior
pharyngeal branch in forming a plexus on the cervical part of the oesophagus which
innervates that tube.^ The recurrent nerves present no remarkable special features.
The depressor nerve is a very delicate filament which arises usually from the an-
terior laryngeal nerve and is incorporated in the vago-sympathetic trunk to the
thorax. Here the nerve separates from the ventral border of the vago-sympathetic
trunk. The right nerve passes backward between the anterior vena cava and the
trachea, inclines to the left, and reaches the medial surface of the aortic arch. The
left nerve passes backward ventral to the vagus and across the lateral (left) face
of the aortic arch. Both nerves give filaments to the cardiac nerves and to the
aorta and pulmonary artery. Their terminal branches pass between these vessels
and enter the wall of the heart. The pulmonary and posterior oesophageal plexuses
are highly developed.

The hypoglossal nerve gives off a long branch (R. descendens) which runs
downward and backward across the pharynx and larynx, communicates with the
ventral branch of the first cervical nerve, and supplies the thyro-hyoid, sterno-
hyoid, and sterno-thyroid muscles.

The spinal nerves numl^er thirty-six or thirty-seven on either side, and com-
prise eight cervical, thirteen thoracic, seven lumbar, and five or six coccygeal.

The brachial plexus (Fig. 616) is derived from the ventral branches of the last
four cervical and first thoracic nerves; the root supplied by the fifth cervical nerve
is ver}^ small. The roots unite at the ventral border of the scalenus. The more
important special features in the arrangement of the nerves which emanate from
the plexus are as follows:

The musculo-cutaneous nerve passes between the coraco-brachialis and the
brachial artery and descends in the arm in front of the artery. At the shoulder
joint it gives off branches to the biceps and coraco-brachialis, and in the distal third
of the arm is coiuiected with the median nerve by an oblique branch. It terminates
near the elbow by dividing into a branch for the brachialis and a small cutaneous
nerve which passes down over the medial face of the elbow and, inclining a little
forward, descends over the deep fascia of the forearm to the carpus.

The radial nerve descends behind the ulnar nerve, gives branches to the
extensors of the elbow, dips in between the medial head of the triceps and the
accessory head of the anconeus, winds around the arm, and divides between the
brachialis and the lateral head of the triceps into two branches. The deep branch
(R. profundus) supplies the extensor and supinator muscles on the forearm. The
superficial branch (R. superficialis) emerges upon the flexor surface of the elbow
and divides into two branches which terminate by supplying two dorsal digital
nerves to each digit, except the fifth, which receives its lateral dorsal nerve from the
ulnar. The medial branch descends along the medial side of the cephalic vein to the
carpus, where it divides into dorsal nerves for the first digit and the medial side of
the second. The lateral branch is much larger. It descends on the middle of the
front of the forearm and supplies the remaining dorsal digital nerves except that to
the lateral side of the fifth digit.

The ulnar nerve is as large as or larger than the median, with which it is united
for some distance. At the distal third of the arm it separates from the median
and passes over the medial epicondyle of the humerus. At the proximal part of

1 Lesbre terms this the tracheo-oesophageal branch, and considers that it must be regarded
as an accessory or internal recurrent nerve.

854

THE NERVOUS SYSTEM OF THE DOG

the forearm it gives off the dorsal branch (R. dorsalis), which supplies cutaneous
twdgs to the dorso-lateral surface of the distal part of the forearm and carpus and
terminates as the lateral dorsal digital nerve of the fifth digit. Descending under
cover of the flexor carpi ulnaris, the ulnar inclines medially under 'he tendon of
insertion of that muscle and divides into superficial and deep branches. The
superficial branch (R. superficialis) descends along the lateral border of the flexor
tendons, gives off the lateral volar digital nerve of the fifth digit (N. dig. vol. lat. dig.
V), and a branch (N. met. vol. IV) which descends in the space between the fourth
and fifth metacarpal bones and unites with the deep branch. The deep branch
(R. profundus) descends in the carpal canal and divides under the deep flexor

Branches o^
radial nerve

Median nerve -—

Fig. 684. — Nerves of Distal Part of Right Fore-
limb OF Dog; Dorsal View (Schematic).
p, Dorsal proper digital nerves.

Fig. 685. — Nerves of Distal Part of Right Fore-
limb OF Dog; Vol.\r View (Schematic).
p, Volar proper digital nerves.

tendon into its terminal branches. The smaller of these supply the volar meta-
carpal muscles. The larger terminals are the three volar common digital nerves
(Nn. dig. col. comm. II, III, IV), which descend along the second, third, and fourth
intermetacarpal spaces, subdivide, and concur with the volar metacarpal branches
of the median nerve in forming the volar proper digital nerves (Nn. dig. vol. proprii).
The median nerve descends behind the brachial artery, passes over the medial
epicondjde of the humerus, then under the pronator teres, and continues in the
forearm under cover of the flexor carpi radialis. It gives branches below the elbow
to the flexor and pronator muscles, and lower down a volar branch to the skin on
the medial and volar aspect of the carpus, and terminates between the superficial
and deep flexor tendons by dividing into three volar metacarpal nerves (N. met. vol.

THE NERVOUS SYSTEM OF THE DOG

855

I, II, III). These descend in the first, second, and third intermetacarpal spaces
and unite with the volar common digital nerves in forming volar proper digital
nerves. The arrangement of the digital nerves is indicated in the annexed sche-
matic figures.

The lumbo-sacral plexus is formed from the ventral branches of the last five
lumbar and first sacral nerves. The more important special facts in regard to the
nerves of the pelvic limb are as follows :

The saphenous nerve (Fig. 621) is relatively large, and, in fact, might be
considered as the continuation of the femoral nerve. It descends at first in front
of the femoral artery, then passes over the lower part of the medial surface of the
thigh with the saphenous artery, continues down the leg with the dorsal branch of

Superficial -
peroneal nerve

Dorsal common
digital nerves

Medial plantar
nerve

Plantar
common
digital
nerves

Fig. 686. — Nekves op Distal Part op Right Hind

Limb op Dog, Dorsal View (Schematic).

p, Dorsal proper digital nerves.

Fig. 687. — Nerves op Distal Part op Right Hind

Limb of Dog, Plaj^tar View (Schematic).

p, Plantar proper digital nerves.

that vessel, and anastomoses with branches of the superficial peroneal nerve. It
supplies cutaneous twigs from the stifle to the metatarsus.

The common peroneal nerve separates from the tibial above the origin of the
gastrocnemius, runs downward and forward across the lateral head of that muscle,
passes between the deep flexor of the digit and the peroneus longus, and divides into
superficial and deep branches. The superficial peroneal nerve descends the leg
along the peroneus tertius and longus, gives off a dorsal branch to the first digit (N.
cutaneus dorsalis medialis), and divides at the proximal part of the metatarsus into
three dorsal common digital nerves (Nn. dig. pedis dors. comm. II, III, IV). These
descend with the superficial dorsal metatarsal arteries and concur with branches
of the deep peroneal nerve in forming dorsal proper digital nerves (Nn. dig. ped.
prop, dorsales). The deep peroneal nerve passes down the leg with the anterior

856 THE NERVOUS SYSTEM OF THE DOG

tibial vessels. It gives t^^'igs to the hock joint and the extensor brevis muscle, and
divides into three dorsal metatarsal nerves (Nn. met. dors. II, III, IV); these
descend ^\ath the corresponding arteries along the intermetatarsal spaces and unite
with the dorsal common digital nerves in supplying the dorsal proper digital nerves.

The tibial nerve divides at the tarsus into two plantar branches. The medial
plantar nerve descends along the medial border of the superficial flexor tendon and
divides near the middle of the metatarsus into two branches. Of these, the medial
branch constitutes the first plantar common digital nerve (N. dig. comm. plant. I).
The lateral branch descends on the superficial flexor tendon and divides into three
plantar metatarsal nerves (Nn. met. plant. II, III, IV), which unite with the
plantar common digital nerves. The lateral plantar nerve passes down between
the flexor tendons, sends twigs to the muscles on the plantar surface of the metatar-
sus, and divides into three plantar common digital nerves (Nn. dig. comm. plant. II,
III, IV). These descend mth the deep plantar metatarsal arteries in the second,
third, and fourth intermetatarsal spaces, receive the plantar metatarsal nerves,
and divide into plantar proper digital nerves, which pass down the opposed surfaces
of the second to the fifth digits.

The S3mipathetic system presents few special features worthy of mention.
The anterior cervical ganglion is situated behind the bulla ossea in close relation
to the internal carotid artery and the ganglion nodosum of the vagus. It is fusi-
form and is a little less than half an inch (ca. 1 cm.) long in a dog of medium size.
It forms connections directly or through the carotid plexus with the last seven
cranial and first cervical nerves. The cervical trtmk unites with the vagus so in-
timately as to form a vago-sympathetic trunk. The posterior cervical ganglion
is situated at the point where the sympathetic trunk separates from the vagus
(Figs. 613, 614). It is usually distinct from the first thoracic ganglion, which is
stellate and lies on the longus colli opposite the first space. The two are connected
by filaments which cross each side of the brachial artery, forming the ansa sub-
clavia. Two or three cardiac nerves proceed from these ganglia on the left side;
they pass to the lateral surface of the aortic arch, where they ramify and concur
with the nerves of the right side in the formation of the cardiac plexus. On the
right side one or two cardiac nerves appear to come from the vagus and one from
the first thoracic ganglion. They ramify on the right side of the trachea and with
those of the right side form the cardiac plexus at the base of the heart. From the
plexus branches go to the heart, pericardium, and pulmonary artery. The greater
splanchnic nerve separates from the posterior part of the thoracic trunk, most often
from the twelfth ganglion. It passes into the abdomen between the diaphragm
and the psoas minor and joins a small adrenal ganglion close to the coeliac ganglion.
The lesser splanchnic nerve arises from the last thoracic and first lumbar ganglia.
It may be divided into two or three strands which go to the adrenal plexus.

The cceliac and anterior mesenteric ganglia are separate. The former is
elongated and lies along the posterior face of the origin of the coeliac artery. The
latter is smaller and rounded and is in contact with the origin of the anterior mesen-
teric artery. On the left side the two ganglia are connected by a trunk which is
ganglionic in character. The coeUac, anterior mesenteric, and subsidiary plexuses
enlace the corresponding arteries. There is a small elongated posterior mesenteric
ganglion in relation to the origin of the posterior mesenteric artery. The posterior
mesenteric plexus includes left colic, anterior hsemorrhoidal, and spermatic plexuses.
The lumbar trunk is deeply placed at the medial side of the psoas minor. It has
seven ganglia, which are very small, with the exception of the last. There is a well-
developed aortic plexus. The sacral trimks are close to the middle sacral artery
and have each three ganglia when this part is fully developed. The caudal trunks
lie on each side of the coccygeal artery; the number and arrangement of the visible
ganglia are variable. The pelvic plexus is well developed and contains minute
ganglia.

>ESTHESIOLOGY
THE SENSE ORGANS AND COMMON INTEGUMENT

The organs of the senses (Organa sensiium) receive external stimuli and con-
duct impulses to the brain which result in sensations of sight, hearing, taste, smell,
and touch. They consist essentially of specially differentiated cells (neuro-epithe-
lium) and a conduction path which is simple in the more generalized sense organs,
elaborate in those which are highly specialized — the eye and the ear.

THE SENSE ORGANS AND SKIN OF THE HORSE
The Eye

The eye or organ of vision (Organon visus) in the broader sense of the term
comprises the eyeball or globe of the eye, the optic nerve, and certain accessory
organs associated therewith. The accessory organs (Organa oculi accessoria) are the
orbital fascise and muscles, the

eyelids and conjunctiva, and Upper eyelid

the lacrimal apparatus. These Third eyelid \

structures will be considered in Caruncula. ■ ■

the order in which they may be lacrinmlis -^^ ^ _ ^5,

most conveniently examined, SLv ^^ '3^

taking the horse as a type. The ^v. \ -^

bony walls of the orbit have
been described in connection
with the skull; the periorbita,
a fibrous membrane which en-
closes the eyeball together with
its muscles, vessels, and nerves,
may be appropriately included
in the account of the fasciae.

THE EYELIDS AND CONJUNC-
TIVA

Lower eyelid
Fig. 688. — Left Eye of Horse.
9, Zygomatic arch; 10, supraorbital depression; 12, supraorbital proc-
ess; 37, facial crest. (After Ellenberger-Baum, Anat. fiir Kiinstlcr.)

The eyelids, upper and
lower (Palpebra superior et in-
ferior), are movable folds of
integument situated in front
of the eyeball. When closed
anterior surface of the eyeball. The upper lid
more movable than the lower one, and its free
interval between the lids is termed the palpebral fissure (Rima palpebrarum).
When the eye is closed, it is an oblique slit about two inches (ca. 5 cm.)
in length; when open, it is biconvex in outline. The ends of the fissure are
the angles or canthi, and are distinguished as medial or nasal, and lateral or

857

they cover the entrance to the orbit and the
is much more extensive and
edge is more concave. The

858

THE SENSE ORGANS AND SKIN OF THE HORSE

temporal (Angiilus oculi medialis, lateralis). The lateral angle is rounded when the
eye is open, but the medial angle is narrowed and produced to form a 3-shaped
ba}^ or recess, termed the lacrimal lake (Lacus lacrimalis) . In this there is a rounded
pigmented prominence kno\\Ti as the lacrimal carimcle (Caruncula lacrimalis) ; it
is about the size of a small pea, and is covered A\dth modified skin, connected with
that of the medial commissure, from which project a number of hairs provided with
sebaceous glands. The lids unite on either side and form the commissures, medial

and lateral (Commissura palpebrarum
medialis, lateralis). The anterior sur-
face of the lids (Facies anterior palpe-
brarum) is convex and is covered with
very short hair. A considerable num-
ber of tactile hairs are scattered over
the lower part of the lower lid, but on
the upper lid they are very scanty.
The infrapalpebral depression (Sulcus
infrapalpebralis) indicates somewhat
indistinctly the limit of the lower lid.
The upper lid is marked by two fur-
rows when raised. The posterior sur-
face (Facies posterior palpebrarum) is
adapted to the free surface of the eye-
ball and is covered by the palpebral
conjunctiva. The free border of the
lid is smooth and usually black. It
has a well-defined posterior margin
(Limbus palpebralis posterior), along
which the ducts of the tarsal glands
open. The anterior margin (Limbus
palpebralis anterior) bears stiff hairs
termed the cilia (eyelashes). On the
upper lid the cilia are long and num-
erous except at its medial third, where
they are very small or absent. On
the lower lid the cilia are often scarcely
distinguishable from the ordinary hairs;
in other cases they may be clearly seen
except near the lateral canthus, and
are much finer and shorter than those
of the upper lid. The edge of each lid
is pierced near the medial angle by a
minute, slit-like opening, the pimctum
lacrimale, which is the entrance to
the lacrimal duct.
The skin of the eyelids is thin and freely movable, except near the free edge,
where it is more firmly attached. The underlying subcutaneous tissue is destitute
of fat. The muscular layer consists chiefly of the elliptical bundles of the orbicu-
laris oculi, with which are associated fibers of the corrugator supercilii in the upper
lid and the malaris in the lower lid. At the medial side there is a fibrous band, the
palpebral ligament, which is attached to the lacrimal tubercle and furnishes origin
to some fibers of the orbicularis. At the medial commissure a bundle detached
from the orbicularis passes inward behind the lacrimal sac, and is known as the pars
lacrimalis (or Horner's muscle). At the lateral side an indistinct palpebral raphe
occurs where fibers of the orbicularis decussate. The fibrous layer is thicker and

'7 3

Fig. 689. — Vertical Section of Anterior Part of Eye
OF Horse, with Lids Half Closed.
1, Tarsal gland of upper lid; 2, palpebral conjunctiva;
3, fornix conjunctivEe; 4, levator palpebrse superioris; S,
orbicularis oculi; 6, cornea; 7, anterior chamber; S, iris;
9, 0', granula iridis; 10, posterior chamber; 11, ciliary proc-
ess; 12, ciliary muscle; 13, ciliary zone or suspensory
Ug. of lens; H, chorioid; 15, sclera; 16, lens; 17, root of
tactile hair. (After Bayer, Augenheilkunde.)

THE CONJUNCTIVA 859

denser along the free edge of the Hd, forming here the tarsus. The tarsus furnishes
insertion to a layer of unstriped muscle known as the tarsal muscle. The tarsal
glands (Glandulse tarsales)i are partly embedded in the deep face of the tarsus, and
are visible when the lid is everted if the conjunctiva is not too strongly pigmented.
They are arranged in a linear series, close together, and with their long axes per-
pendicular to the free edge of each lid. In the upper lid they number forty-five to
fifty; in the lower, thirty to thirty-five. Each consists of a tubular duct beset
with numerous alveoli, in which a fatty substance, the palpebral sebum, is secreted.
The palpebral conjunctiva lines the internal surface of the eyelids.

The conjunctiva is the mucous membrane which lines the lids as palpebral
conjunctiva (C. palpebrarum), and is reflected upon the anterior part of the eyeball
as bulbar conjunctiva (C. bulbi); the line of reflection is termed the fornix con-
junctivaB. The palpebral part is closely adherent to the tarsus, but is loosely at-
tached further back. It is papillated and is covered with stratified cylindrical
epithelium in which many goblet-cells are present. In the fornix and its vicinity
there are tubular glands. Near the medial angle there are numerous lymph nodules.
The conjunctiva of the lateral part of the upper lid is pierced near the fornix by the
orifices of the excretory ducts of the lacrimal gland — twelve to sixteen in number.

Fig. 690. — Piece op Upper Eyelid; Inner Surface. Fig. 691. — Cartilage of Third Eyelid of Horse;

1, Cilia; S, limbus palp, posterior; 3, tarsal glands. Convex Surface.

(After EUenberger, in Leisering's Atlas.) /, Gland; 2, fat surrounding deep part of cartilage.

(After EUenberger, in Leisering's Atlas.)

The bulbar conjunctiva is loosely attached to the anterior part of the sclera and is
pigmented in the vicinity of the corneo-scleral junction. On the cornea it is repre-
sented by a stratified epithelium.

When the lids are in apposition, the conjunctiva (including the epithelium of the cornea)
encloses a capillary space between the lids and the eyeball, and constitutes what is known as the
conjunctival sac.

The third eyelid (Palpebra tertia) is situated at the medial angle of the eye.
It consists of a semilunar fold of the conjunctiva, known as the membrana nictitans,
which covers and partly encloses a curved plate of hyaline cartilage. Its marginal
part is thin and usually more or less pigmented. The cartilage has an elongated
quadrilateral outline. The part of it which lies in the membrana is wide and thin.
The deep part is narrower and thicker and is embedded in fat at the inner side of the
eyeball. Numerous minute lymph nodules occur in the membrana nictitans, and
the deep part of the cartilage is surrounded by a gland which resembles the lacrimal
gland in structure (Glandula superficialis palpebrse tertise).

Ordinarily the third eyelid extends very little over the medial end of the
cornea, but when the eyeball is strongly retracted, the membrana is protruded over
it so as to measure about an inch (ca. 2-3 cm.) in its middle. This effect results
from the pressure of the eyeball and its muscles on the fat which surrounds the deep
part of the cartilage.

Vessels and Nerves. — The arteries which chiefly supply the eyelids and con-
1 Also known as the Meibomian glands.

860 THE SENSE ORGANS AND SKIN OF THE HORSE

junctiva are branches of the ophthalmic and facial arteries, and the blood is drained
away by corresponding veins. The sensory nerves are branches of the ophthalmic
and maxillary divisions of the trigeminus. The motor nerves to the orbicularis
oculi, corrugator supercilii, and malaris come from the facial nerve; the levator
palpebrse superioris is innervated by the oculomotor nerve and the unstriped
muscle of the lids by the sympathetic.

THE LACRIMAL APPARATUS

The lacrimal apparatus (Apparatus lacrimalis) comprises: (1) the lacrimal
gland, which secretes the clear lacrimal fluid; (2) the excretory ducts of the gland;
(3) the two lacrimal ducts or canaliculi, lacrimal sac, and naso-lacrimal duct, which
receive the fluid and convey it to the nostril.

The lacrimal gland (Glandula lacrimalis) is situated between the supraorbital
process and the dorso-lateral surface of the eyeball (Fig. 563). It is flattened, oval
in outline, and measures about two inches (ca. 5 cm.) transversely and an inch or
more (2.5-3 cm.) in the sagittal direction. Its superficial face is convex and is
related to the concave lower surface of the supraorbital process. The deep face is
concave in adaptation to the eyeball, from which it is separated by the periorbita.
The excretory ducts (Ductuli excretorii) are very small and are twelve to sixteen
in number; they open into the lateral part of the conjunctival sac along a line a
little in front of the fornix conjunctivse superior. In appearance and structure the
gland resembles the parotid. It receives its blood-supply chiefly from the lacrimal
artery. The sensory nerve is the lacrimal, and the secretory fibers are derived
from the s>anpathetic.

The pimcta lacrimalia are the entrances to the two lacrimal ducts. Each is a
fine, slit-like opening (about 2 mm. long), situated close behind the free edge of the
lid and about a third of an inch (ca. 8 mm.) from the medial canthus. The lacri-
mal ducts (Ductus lacrimales), upper and lower, begin at the puncta and converge
at the medial commissure to open into the lacrimal sac. The latter (Saccus lacri-
malis) may be regarded as the dilated origin of the naso-lacrimal duct. It occupies
the funnel-like origin of the bony lacrimal canal, which is termed the fossa of the
lacrimal sac, and leads to the naso-lacrimal duct (Ductus nasolacrimalis), which
passes forward and a little downward along the outer wall of the frontal sinus and
the nasal cavity and opens near the lower commissure of the nostril. Its length
is about ten to twelve inches (ca. 25-30 cm.). In the first part of its course it is
enclosed in the osseous lacrimal canal ; further forward it lies in the lacrimal groove
of the maxilla, covered at first by a plate of cartilage and then by the mucous mem-
brane of the middle meatus (Fig. 59). The terminal part (Fig. 452) lies in the
ventral turbinate fold and opens on the skin of the floor of the nostril near the tran-
sition to mucous membrane. Accessory openings may occur a little further back.

The first part of the duct, about 6 to 7 mm. in diameter, extends in a gentle curve, convex
dorsally, from the medial commissure toward a point just above the level of the infraorbital fora-
men. The second part (isthmus) is narrower (ca. 3-4 mm.); it extends forward and a httle
ventrally about to a transverse plane through the first cheek tooth and lies in the groove above
the ventral turbinate crest. Beyond this the duct incUnes upward and widens very consider-
ably, crosses the nasal process of the premaxilla obUquely, and contracts at its termination. The
mucous membrane may present valvular folds, the most distinct of which is situated at the
origin.

THE PERIORBITA

The periorbita^ is a conical fibrous membrane which encloses the eyeball with

its muscles, vessels, nerves, etc. Its apex is attached around the optic and orbital

foramina, and its base is in part attached to the bony rim of the orbit, in part con-

1 Also known as the ocular sheath.

THE ORBITAL FASCIA AND OCULAR MUSCLES 861

tinuous with the fibrous laj^er of the Uds. Its medial part, which is in contact with
the orbital wall, is thin; incorporated with it beneath the root of the supraorbital
process is the bar of cartilage around which the superior oblique muscle is reflected.
The lateral part is thicker, and is strengthened by an elastic band which is attached
to the pterygoid crest and furnishes origin to the thin, unstriped orbital muscle. A
quantity of fat (Corpus adiposum extraorbitale) lies about the periorbita, and within
it is the intraorbital adipose tissue (Corpus adiposum intraorbitale) which fills the
interstices between the eyeball, muscles, etc.

THE ORBITAL FASCLE AND OCULAR MUSCLES (Figs. 563, 564, 692)
The straight muscles of the ej^eball and the oblique muscles in part are enclosed
in fibrous sheaths (Fasciae musculares), formed by superficial and deep layers of
fascia, which are united by intermuscular septa in the interstices between the
muscles. The superficial fascia is thin; it blends in front with the fibrous layer of
the eyelids saul is attached l^ehind around the optic foramen. The deep fascia
consists anteriorly of two layers, one of which is continuous with the fibrous tissue
of the lids, while the other is attached at the corneo-scleral junction.

The posterior part of the eyeball is covered by the fascia bulbi, so that between
them a lymph space (Spatium interfasciale) is enclosed which communicates with
the subdural space along the course of the optic nerve.

The levator palpebrae superioris muscle^ is a thin band about half an inch in
width which lies above the rectus dorsaUs. It is narrow at its origin above and
behind the ethmoidal foramen and ends by an expanded tendon in the upper lid.
Its action is to raise the upper lid.

The muscles of the eyeball (Mm. oculi) are seven in numl^er — four straight,
two oblique, and a retractor.

The straight muscles (Mm. recti) are designated according to their positions as
j-ectus dorsalis s. superior, rectus ventralis s. inferior, rectus medialis, and rectus
lateralis. They are all band-like, arise close together around the optic foramen,
and diverge as they pass forward to the eyeball. On reaching the latter they end
in thin tendons which are inserted into the sclera in front of the equator of the eye-
ball.

The retractor oculi surrounds the optic nerve, and is incompletely divided into
four parts which alternate with the recti. They arise around the optic nerve and
are inserted into the sclera behind the recti.

The obliquus dorsalis s. superior is the longest and narrowest of the ocular mus-
cles. It arises near the ethmoidal foramen and passes forward medial to the rectus
medialis. Under the root of the supraorbital process it is reflected almost at a
right angle around a cartilaginous pulley (trochlea), which is attached to the
anterior part of the inner wall of the orbit, a bursa being interposed here. The
muscle is then directed outward and somewhat forward, and ends in a thin tendon
which passes between the rectus dorsalis and the eyeball, and is inserted into the
sclera between the dorsal and lateral recti, about half an inch behind the margin
of the cornea.

The obliquus ventralis s. inferior is wide and much shorter than the rectL
It arises from the medial wall of the orbit in the small depression (Fossa muscularis)
behind the lacrimal fossa. It curves around the rectus ventralis and is inserted
into the sclera near and partly beneath the rectus lateralis.

Actions.— The dorsal and ventral recti rotate the eyeball about a transverse
axis, moving the vertex of the cornea upward and downward respectively.^ Snni-

1 This belongs to the upper eyelid, but is mentioned here on account of its position and the
fact that in dissection it must be dealt with before the muscles of the eyeball.

2 These terms are used vnth reference to the axis of the eyebaU, not that of the head.

862

THE SENSE ORGANS AND SKIN OF THE HORSE

larly the medial and lateral recti rotate the eyeball about a vertical axis, turning
the vertex of the cornea inward and outward respectively. The oblique muscles
rotate the eyeball about a longitudinal axis; the dorsal oblique raises the lateral
end of the pupil, while the ventral oblique lowers it. The retractor as a whole
draws the eyeball backward, and its parts may separately reinforce the correspond-
ing recti. Also the four recti acting together will retract the eyeball.

The actual movements of the eyeball are by no means so simple as might be inferred from
the foregoing general statements. Practically all movements are produced by the coordinated
actions of several muscles, involving combinations which are quite complex and difficult to analyze
accurately. Further complication is caused by the fact that the recti are not inserted at equal

Fig. 692. — Vertical Axial Section of Orbit of Horse.
a, Eyelids; b, fascia bulbi; c, c', retractor oculi; d, rectus ventralis; e, obliquus ventralis (in cross-section); /,
rectus donsalis; g, levator palpebrse superioris; h, obliquus dorsalis (in cross-section); i, lacrimal gland; k, k', peri-
orbita; /, superficial fascia; m, deep fascia; n, skin; o, retrobulbar fat; p, extraorbital fat; q, temporalis muscle; r,
supraorbital process; s, cranial wall; 1, cornea; 2, sclera; 3, chorioidea; 4, ciliary muscle; 5, iris; 6, granula iridis;
7, retina; 7', optic papilla; 5, optic nerve; S, crystalline lens; JO, capsule of lens; ii, ciliary zone; i^, posterior cham-
ber; /3, anterior chamber; 74, conjunctiva bulbi; 7.5, vitreous body. (After EUenberger, in Leisering's Atlas.)

distances from the equator and the axes of rotation of the oblique muscles do not correspond to
the longitudinal axis of the eyeball.

Nerve-supply. — The oculomotor nerve supplies the foregoing muscles, with
the exception of the rectus lateralis and obliquus dorsalis, which are innervated by
the abducens and trochlearis respectively.

THE EYEBALL

The eyeball (Bulbus oculi) is situated in the anterior part of the orbital cavity.
It is protected in front by the eyelids and conjunctiva, and in its middle by the
complete orbital ring, and is related behind to the fascia bulbi, fat, and ocular
muscles.

It has the form approximately of an oblate spheroid, but is composed of the
segments of two spheres of different sizes. The anterior transparent segment,
which is formed by the cornea, has a radius of curvature of about 17 mm., and the

THE FIBROUS TUNIC

863

posterior opaque, scleral segment one of about 25 mm. The anterior segment
therefore projects more strongly, and the junction of the two segments is marked
externally by a broad, shallow groove, the sulcus sclerae. The central points of
the anterior and posterior curvatures of the eyeball are termed respectively the
anterior and posterior poles (Polus anterior, posterior), and the line connecting the
poles is the external optic axis (Axis oculi externa).^ The angle of divergence of the
optic axes is about 137 degrees. The equator (^Equator) is an imaginary line drawn
around the eyeball midway between its poles, and meridians (Meridiani) are lines
drawn around it through the poles.

The average transverse diameter of the eyeball is about 5 cm., the vertical about 4.5 cm.,
and the axial about 4.25 cm. The distance from the anterior pole to the point of entrance of the
optic nerve is about 3 cm.

The eyeball consists of three concentric tunics or coats, within which three
refractive media are enclosed.

The Fibrous Tunic
The fibrous timic (Tunica fibrosa oculi) is the external coat and is composed
of a posterior opaque part, the sclera, and a transparent anterior part, the cornea.
1 . The sclera- is a dense fibrous

Lens seen through cornea

Corneoscleral \
junction \

Third
eyelid

Sclera

~ - Cornea

Pupil

membrane which forms about four-
fifths of the fibrous tunic. Thickest
in the vicinity of the posterior pole
(ca. 2 mm.), it thins at the equator
(ca. 0.4 mm.), and increases in thick-
ness toward the junction with the
cornea (ca. 1.3 mm.). It is in gen-
eral white, ])ut may have a bluish
tinge in its thinnest parts. Its ex-
ternal surface furnishes insertion to
the ocular muscles and is covered by
the conjunctiva sclerse in its anterior
part. The episcleral tissue, which is
richly supplied with vessels and
nerves, attaches the conjunctiva
to the sclera; it is abundant and
loosely meshed except at the junc-
tion with the cornea. The inner
surface is attached to the chorioid
coat by a layer of delicate, pig-
mented connective tissue, the
lamina fusca. The anterior bor-
der, which is oval, the long axis

being transverse, is continuous with the cornea. The transition from the opaque
scleral tissue to the transparent corneal substance occurs in such manner that the
sclera appears to form a groove (Rima cornealis), into which the cornea fits some-
what as a watch-glass in the case. Near the corneo-scleral junction there is a
circular venous plexus, the plexus s. sinus venosus scleras.^ The optic nerve
passes through the posterior part of the sclera a little below and lateral to the
posterior pole. The opening for the nerve is crossed by interlacing fibrous strands,
forming the lamina cribrosa sclerae. The sclera consists of interlacing bundles of
white fibrous tissue, associated with which there are a few elastic fibers. The

1 The term internal optic axis (Axis ocuU externa) is applied to a coincident line from the
posterior surface of the cornea to the anterior surface of the retina.

2 Also termed the sclerotic coat, and popularly known as the "white of the eye."

3 Formerly term.^-^ the canal of Schlemm.

Fig. 693. — Left Eyeball of Horse, in situ. After Removal.
OF Upper and Lower Lids.
9, Zygomatic arch; IS, supraorbital process; 19, orbital
fat; 27, facial crest. (After EUenberger-Baum, Anat. fur
Kiinstler.)

864

THE SENSE ORGANS AND SKIN OF THE HORSE

bundles are arranged chiefly in meridional and equatorial layers. The very limited
blood-supph^ is derived from the ciliary arteries, and the veins open into the vense
vorticosa? and ciliary veins. The lymphatics are represented by intercommunicat-
ing cell spaces. The nerves are derived from the ciliary nerves.

2. The cornea forms the anterior fifth of the fibrous tunic. It is transparent,
colorless, and non-vascular. Viewed from in front it is oval in outline, the long
axis being transverse and the broad end medial; it appears more nearly circular
when viewed from behind. Its anterior surface (Facies anterior) is convex and is
more strongly curved than the sclera; its central part is termed the vertex comeae.
The posterior surface (Facies posterior) is concave; it forms the anterior lioundary
of the anterior chamber, and is in contact with the aqueous humor. The margin
(Limbus corneae) joins the sclera; the latter overlaps the cornea more in front than
behind, and more above and below than at the sides, thus explaining the apparent

Sclera

Optic nerve ■

Optic papilla
Retrobulbar fat

Rectus oculi inferior

Reflection of conjunctiva

Granula iridis

Cornea

Lens
Anterior chamber

Ciliary processes

Chorioid

Fig. 694. — Vertical Section of Etebaix of Horse, abottt S.
The contour of the crystalline lens is dotted.

difference in outline of the two surfaces. The cornea is thinnest at the vertex.
The cornea consists, from before backward, of the following layers fl) The epi-
thelium corneae is continuous with that of the conjunctiva sclera?, and is of the
stratified squamous type. (2) The lamina limitans anterior is merely a condensa-
tion of the next layer. (3) The substantia propria forms the bulk of the cornea
and is composed of interlacing bundles of connective tissue, arranged in part in
lamellae disposed parallel with the surface. In the amorphous cement substance
between the lamellse are flattened connective-tissue cells, the corneal corpuscles.
These have branching processes which unite with those of other cells, thus form-
ing a protoplasmic network.^ (4) The lamina elastica posterior- is a thin and

1 According to Piersol, the system of spaces and canaliculi in the substantia propria is com-
pletely filled by the cells and their processes, upon which the nutrition of the cornea largely de-
pends. Tlie lamina elastica anterior (Bowman's membrane), formerly described as a distinct
layer between the corneal epithelium and the substantia propria, does not exist as such, but there
Is a condensation of the superficial part of the latter, which Rollett termed the anterior limiting
layer; it is not elastic.

2 Also known as the membrane of Descemet or Demours

THE VASCULAR TUNIC 865

practically homogeneous membrane which is less intimately attached to the sub-
stantia propria than the anterior lamina. It is clear, glistening, and elastic. At
the periphery the lamina divides into three sets of fibers. The anterior fibers join
the sclera, the middle give attachment to the ciliary muscle, while the posterior
pass into the iris and form the ligamentum pectinatum iridis. (5) The endothelium
of the anterior chamber (Endothelium camerae anterioris) consists of a layer of
flattened polygonal cells, and is reflected on to the anterior surface of the iris. The
cornea is non-vascular except at its periphery, where the terminal twigs of the vessels
of the sclera and conjunctiva form loops. The nerves are derived from the ciliary
nerves. They form a plexus around the periphery (Plexus annularis), from which
fibers pass into the substantia propria, become non-medullated, and form the funda-
mental or stroma plexus. From this perforating branches go through the anterior
limiting layer and form a subepithelial plexus, from which filaments pass between
the epithelial cells. Other branches from the plexuses in the substantia propria
end as fibrils which are in close relation with the corneal corpuscles.

The Vascular Tunic
The vascular tunic (Tunica vasculosa oculi) lies internal to the fibrous coat;
it comprises three parts — the chorioid, the ciliary body, and the iris.

1. The chorioid (Chorioidea) is a thin membrane which lies between the sclera
and retina. It is in general rather loosely attached to

the sclera by the lamina fusca, but is intimately adherent
at the point of entrance of the optic nerve and less closely
in places where the ciliary vessels and nerves pass through.
The inner surface is in contact with the layer of pigmented
cells of the retina, which adhere so closely to the chorioid
that they were formerly regarded as a part of the latter.
The general color of the chorioid is dark brown, but an
extensive semilunar area a little above the level of the
optic papilla has a remarkable metallic luster, and is
termed the tapetum of the chorioid (Tapetum chorioidese).
The appearance here varies in different individuals, but pj,, 695.— Tapetttm of Horse.
the prevailing colors in most cases are iridescent blue a, Optic papilla; &, lower bor-

and green in various nuances shading into yellow. Pos- ^er of tapetum. (After EUen-
teriorly the chorioid is perforated by the optic nerve, ^^^^^' *° ^'^^"°e ^
and anteriorly it is continuous with the ciliary body.

The chorioid consists of four layers, which from without inward are as follows:
(1) The lamina suprachorioidea consists of interlacing fine lamellae of fibrous tissue,
each containing a network of elastic tissue. Among these are large, branched, pig-
mented, connective-tissue cells. The spaces between the lamellae are lined with
endothelium, and form a system of lymph-clefts which together form the pericho-
rioid space (Spatium perichorioideale). (2) The lamina vasculosa is the outer part
of th« proper tissue of the chorioid. It contains the larger blood-vessels, which
are supported by areolar tissue. (3) The lamina choriocapillaris consists of an
extremely rich network of capillaries embedded in an almost homogeneous matrix.
Between it and the lamina vasculosa is a layer of fibro-elastic tissue, the tapetum
fibrosum, which causes the metallic luster mentioned above. (4) The lamina
basaUs is very thin and transparent. It is composed of an inner homogeneous part
and an outer elastic part.

2. The ciliary body (Corpus ciliare), the middle part of the vascular coat, con-
nects the chorioid with the periphery of the iris. In meridional section it has the
form of a narrow triangle, the base of Avhich is next to the iris. On its inner side
are the ciliary processes and on its outer side is the ciliary muscle. It consists of
three parts— the ciliary ring, ciliary processes, and ciliary muscle. The ciUary

866

THE SENSE ORGANS AND SKIN OF THE HORSE

ring (Orbiculus ciliaris) is the posterior zone, which is distinguished from the cho-
rioid mainly by its greater thickness and the absence of the chorio-capillaris. Its
inner face presents numerous fine meridional ridges, by the union of which the
ciliary processes are formed. The ciliary processes (Processus ciliares), more than
a hundred in number, form a circle of radial folds which surround the lens and fur-
nish attachment to the zonula ciliaris (or suspensory ligament of the lens). They
are small at their origin on the ciliary ring and become much thicker and higher
toward their central ends. The width of the circle formed by them is narrower
at the medial side than elsewhere. Their bases extend forward to the peri-
phery of the iris, and their central
ends are close to the margin of
the lens. They bear numerous
secondary folds (Plicae ciliares).
Their inner surface is covered by a
continuation of the lamina basalis
of the chorioid, on which there are
two layers of epithelial cells which
constitute the pars ciliaris retinae.
They consist of a rich network of
tortuous vessels supported in pig-
mented connective tissue. The cil-
iary muscle (M. ciliaris) (Figs. 689,
692, 696) constitutes the outer part
of the ciliary body, and lies between
the sclera and the ciliary processes.
It forms a circular band of unstriped
muscle, the fibers of which are for
the most part directed meridionally.
They arise from the inner surface of
the sclera and from the ligamen-
tum pectinatum iridis close to the
corneo-scleral junction, and run
l^ackward along the sclera to be
inserted into the ciliary processes
and ring. When the muscle con-
tracts, it pulls the processes and
ring forward, thus slackening the
ciliary zone of the lens, and allowing the latter to become more convex. This is
the mechanism of accommodation for near objects.

In man the muscle has the form of a prismatic ring which is triangular in meridional section,
the base being directed toward the periphery of the iris. It consists chiefly of meridional fibers,
but a ring of circular fibers forms the inner angle of its base. In the h()rs(> the muscle is much
less developed, and has the form of a flat band; it does not contain distinctly circular fibers, l)ut
the arrangement is rendered more or less plexiform by the existence of obhcjue and ecjuatorial fibers.

3. The iris (Figs. 689, 694, 696) is a muscular diaphragm placed in front of the
lens, and is visible through the cornea. It is pierced centrally by an elliptical
opening, the pupil (Pupilla), which varies in size during life and determines the
amount of light admitted to act on the retina. In strong light the vertical diameter
of the pupil is very short, but the opening is almost circular when the pupil is fully
dilated. The ciliary border (Margo ciliaris) is continuous with the ciliary body
and is connected with the corneo-scleral junction by strands of connective tissue
which constitute the ligamentum pectinatum iridis. The bundles of the ligament
interlace and enclose spaces (Spatia anguli iridis) which are lined with endothelium
and communicate with the anterior chamber. The pupillary border (INIargo

Horse; Front

Fig. 696. — Vascular Tunic of Kyeb.
View.
The cornea is removed and the sclera is reflected in flaps.
/, Sclera; 1', lamina fusca; 2, chorioidea; 2', ciliary veins; 3,
ciliary muscle; 4. iris; 5, 5', granula iridis; 6, pupil, through
which the lens is visible. (After Ellenberger, in Leisering's
Atlas.)

THE VASCULAR TUNIC 867

pupillaris) surrounds the pupil. Its upper part bears in its middle several black
masses of variable size, termed the granula iridisi; similar, but much smaller,
projections may be seen on the lower margin of the pupil. The anterior surface
(Facies anterior) is usually dark brown in color; it presents fine folds (Plic» iridis),
some of which are concentric with the pupil, others radial ; they fade out near the
pupil. 2 The smooth, narrow, central part is termed the annulus iridis minor, while
the much broader plicated part is the annulus iridis major. The posterior surface
(Facies posterior) is usually black; the color is caused by a layer of pigmented
cells which is regarded as part of the retina. It presents numerous fine radial lines
except at the pupillary margin. Its central part is in contact with the anterior
surface of the lens, but peripherally the two are separated by a narrow space
termed the posterior chamber. The iris consists chiefly of the stroma iridis, a
delicate framework of connective tissue which supports numerous blood-vessels,
and contains branched pigmented cells. The muscular tissue is unstriped and
consists of a sphincter and a dilator of the pupil. The sphincter pupillae lies in
the posterior part around the pupil, with which the fibers are largely concentric.
The dilatator pupillae consists of fibers which radiate from the sphincter to the
ciliary border. The anterior surface of the iris is covered by a continuation of the
endothelium of the cornea. Beneath this is a condensation of the stroma, in which
the cells are close together and are full of pigmented granules.^ There appear to
be minute clefts here by which the lymph-spaces of the stroma communicate with
the anterior chamber.

The arteries of the vascular tunic come from the ciliary branches of the oph-
thalmic artery. The arteries of the chorioidea are derived chiefly from the short
posterior ciliary arteries. These (four to six in numljer) perforate the sclera around
the posterior pole, run forward in the lamina vasculosa, ami form the rich capillary
network of the choriocapillaris. The two long (aliary arteries perforate the ^■clera
obliquely near the optic nerve; they run forward in the lamina suprachorioidea in
the horizontal meridian, one on the medial, the other on the lateral side of the
eyeball. On reaching the ciliary body each divides into two diverging branches;
the subdivisions of these unite with each other and with twigs of the anterior ciliary
arteries, thus forming near the periphery of the iris the circulus arteriosus major.
From this branches go to the ciliary muscle and processes and to the iris. The
branches in the iris run toward the pupillary margin, and by anastomotic branches
form an incomplete circulus arteriosus minor. The two anterior ciliary arteries,
dorsal and ventral, form an episcleral plexus around the corneo-scleral junction,
and give off branches which perforate the sclera. These supply twigs to the ciliary
muscle and recurrent branches to the chorioid, and assist in forming the circulus
arteriosus major. The l^lood is carried away from the vascular tunic chiefly by four
or five venous trunks, the venae vorticosae, which are formed by the convergence in
whorls of numerous veins from the chorioid, the ciliary body, and the iris. The
vense vorticosae perforate the sclera about at the equator and join the veins of the
ocular muscles.

The nerves come from the long and short ciliary nerves. They form a plexus
in the lamina suprachorioidea, which contains ganglion cells, and sends numerous
non-medullated fibers chiefly to the ])lood-vessels of the chorioid. At the ciliary
muscle a second plexus (P. gangliosus ciliaris) is formed, which supplies the muscle
and sends fibers to the iris. The sphincter pupillae is supplied by fibers derived
from the oculomotor nerve, while the dilatator pupillae is innervated by the sym-
pathetic.

1 Also known as corpora nigra.

2 Some of these folds are permanent, while others are temporary, i. e., produced by contrac-
tion of the iris.

3 In albinos the pigment is absent here, as elsewhere, and the iris is pink in color.

THE SENSE ORGANS AND SKIN OF THE HORSE

THE RETINA
The retina or nervous tunic of the eyeball is a delicate membrane which extends
from the entrance of the optic nerve to the margin of the pupil. It consists of
three parts. The large posterior part, which alone contains the nervous elements,
including the special neuro-epithelium and the optic nerve-fibers, is termed the
pars optica retinae. It extends forward to the ciliary body, where it terminates at
an almost regular circular line called the era ciliaris retinae.^ Here the retina
rapidly loses its nervous elements, becomes much thinner, and is continued over the
ciliary body and the posterior surface of the iris by two layers of epithelial cells as
the pars ciliaris retinae ; the inner stratum is non-pigmented, while the outer layer
is a direct continuation of the stratum pigmenti of the pars optica. The pars
iridica retinae is a layer of pigmented cells which covers the posterior surface of the
iris. In the dead subject the pars optica is an opaque, gray, soft membrane which

I 5.

Fig. 697. — Ixner Surface of Anterior Part of
Eyeball of Horse (Equ.^torial Section).
1, Sclera; 2, chorioidea; 3, retina (drawn away
from chorioidea); 4, ciliary processes; o, crystalline
lens, through which the pupil (ff) is seen. (After
Ellenberger, in Leisering's Atlas.)

Fig. 698. — Fundus Oculi, Seen on Equatorial Sec-
tion of Eyeball of Horse.
1, Sclera; 3, chorioidea; 3, retina (loosened);
4, tapetum; o, optic papilla; 6, optic nerve. (After
Ellenberger, in Leisering's Atlas.)

can be stripped off the chorioid, leaving most of its outer pigmented layer on the
latter. During life it is transparent, except as to its pigmented epithelium, and the
reddish appearance of the fundus as viewed by the ophthalmoscope is caused by
the blood in the network of the choriocapillaris. The entrance of the optic nerve
forms a sharply defined, oval, light area, the optic papilla (Papilla nervi optici),
situated about 15 mm. ventral to the horizontal meridian and 3 to 4 mm. lateral
to the vertical meridian. The central part of the papilla is slightly depressed
(Excavatio papillae n. optici).

The transverse diameter of the papilla is about 6 to 7 mm., and the vertical about 4 to .5 mm.
It is commonly situated a little below the margin of the tapetum, but the latter may extend down
somewhat on either side of the papilla. The lower margin is often indented a little. In inspec-
tion of the fundus with the ophthalmoscope numerous fine branches of the arteria centralis retinae
are seen radiating from the periphery of the papilla.

The optic nerve fibers converge from all parts of the pars optica to the papilla,
where they collect into bundles which traverse the lamina cribrosa of the chorioidea
and sclera, and constitute the optic nerve. The area centralis retinae is a round
spot, 2 to 3 mm. in diameter, situated dorso-lateral to the optic papilla; it corre-

1 In man the line is finely serrated and is termed the ora serrata.

REFRACTIVE MEDIA OF THE EYEBALL 869

sponds to the macula lutea of man, which is histologically more highly differen-
tiated than the rest of the retina and is the area of most acute vision.

The structure of the retina is very complex. It consists of nervous elements
which are supported in a peculiar sustentacular tissue, and are covered externally
by a layer of pigmented epithelium (Stratum pigmenti retinae). The nervous ele-
ments comprise a highly specialized neuro-epithelium, the rods and cones; ganglion-
cells, the axones of which form the optic nerve; and intermediate neurones. Ten
layers may be recognized in sections microscopically.^

The arteries of the retina are derived from the arteria centralis retinae and
anastomotic branches from the short ciliary arteries. The arteria centralis enters
the optic nerve a short distance behind the eyeball and runs in the axis of the nerve.
It divides two or three millimeters before reaching the papilla, and gives off thirty to
forty branches which radiate in the posterior part of the retina and divide dichoto-
mously into end-arteries in the layer of nerve fibers. The veins accompany the
arteries except in the capillary plexuses; their walls consist merely of a layer of
endothelial cells, around which are a lymph-channel and sheath. ^

CHAMBERS OF THE EYE AND AQUEOUS HUMOR
The anterior chamber of the eye (Camera oculi anterior) is enclosed in front by
the cornea and behind by the iris and lens (Figs. 689, 692, 694). It communicates
through the pupil with the posterior chamber of the eye (Camera oculi posterior) ;
this is a small annular space, triangular in cross-section, which is bounded in front
by the iris, behind by the peripheral part of the lens and its ligaments, and externally
by the ciliary processes. The chambers are filled by the aqueous humor (Humor
aqueus), a clear fluid which consists of about 98 per cent, of water, with a little
sodium chlorid and traces of albumin and extractives. It is carried off chiefly
through the spaces in the zonula ciliaris (or suspensory ligament of the lens) into
the plexus venosus sclerae.

REFRACTIVE MEDIA OF THE EYEBALL

The vitreous body (Corpus vitreum) is a semifluid, transparent substance
situated between the crystalline lens and the retina. In front it presents a deep
cavity, the fossa hyaloidea, which fits the posterior surface of the lens. It
consists of a framework of delicate fibrils, the vitreous stroma (Stroma vitreum),
the meshes of which are filled by the fluid vitreous hirnior (Humor vitreus). The
surface is covered by a condensation of the stroma known as the hyaloid membrane
(Membrana hyaloidea) .

The crystalline lens (Lens crystallina) is a biconvex, transparent body which
is situated in front of the vitreous body and in partial contact with the posterior
surface of the iris. Its periphery, the equator of the lens (^Equator lentis), is
almost circular and is closely surrounded by the ciliary processes. The anterior
surface (Facies anterior) is convex; it is bathed by the aqueous humor and is in
contact with the iris to an extent which varies with the state of the pupil. The
posterior surface (Facies posterior) is much more strongly curved than the anterior.
It rests in the fossa of the vitreous body (Fossa hyaloidea). The central points of
the surfaces are the anterior and posterior poles (Polus anterior et posterior lentis),
and the line which connects them is the axis of the lens (Axis lentis).

The transverse diameter of the lens is about 2 cm., the vertical diameter is slightly smaller,
and the axis measures about 13 mm. The radius of curvature of the anterior surface is 13.5 mm.,

1 For the minute structure of the retina reference must be made to histological works.

2 Martin states that in the horse a capillary plexus does not exist, but that the arteries com-
municate with the veins by closely wound loops.

870 THE SENSE ORGANS AND SKIN OF THE HORSE

and of the posterior surface, 9.5 to 10 mm. But the curvatures of its surfaces — especially that of
the anterior — varj' during Ufe according as the eye is accommodated for near or far vision.

The zonula ciliaris or suspensory ligament of the lens (Fig. 689) consists of
delicate fibers (Fibrae zonulares) which pass in a meridional direction from the
ciliary processes to the capsule of the equator of the lens. Many fibers cross each
other, and the spaces between the fibers (Spatia zonularia) are filled with aqueous
humor; they communicate with each other and with the posterior chamber.

The substance of the lens (Substantia lentis) is enclosed by a structureless,
highly elastic memlDrane, the capsule of the lens (Capsula lentis), and consists of a
softer cortical substance (Substantia corticalis), and a dense central part, the
nucleus of the lens (Nucleus lentis). The capsule is thickest on the anterior surface,
and here it is lined by a layer of flat polygonal cells, the epithelium of the lens
(Epithelium lentis). The lens substance, when hardened, is seen to consist of con-
centric laminae arranged somewhat like the layers of an onion, and united by an
amorphous cement substance. The laminae consists of lens fibers (Fibrae lentis),
hexagonal in section, and of very different lengths. Faint lines radiate from the
poles and indicate the edges of layers of cement substance which unite the groups
of lens fibers. These lines, the radii lentis, are three in number in the foetus and
new-born, and form with each other angles of 120 degrees. On the anterior surface
one is directed upward from the pole and the other two diverge downward ; on the
posterior surface one is directed doAvnward and the others diverge upward. The
developed lens has neither vessels nor nerves.

In the foetus the lens is nearly globular, and is soft and pink in color. During part of foetal
life it is surrounded by a vascular network, the tunica vasculosa lentis. This is derived chiefly
from a temporary vessel, the Iwaloid artery, which is a continuation forward of the arteria cen-
trahs retina} through the hyaloid canal that traverses the vitreous bodj'. In old age the lens tends
to lose its elasticity and transparency; it also becomes flatter and the nucleus especially grows
denser.

The Ear

The ear or organ of hearing (Organon auditus) consists of three natural divi-
sions— external, middle, and internal.

THE EXTERNAL EAR

The external ear (Auris externa) comprises — (1) the auricula, a funnel-like
organ which collects the sound waves, together with its muscles; and (2) the
external acoustic meatus, which conveys these waves to the tympanic membrane,
the partition which separates the canal from the cavity of the middle ear.

The auricula or pinna is attached by its base around the external acoustic
process in such a manner as to be freelj^ movable. In the following description it
will be assumed that the opening is directed outward and that the long axis is
practically vertical. It has two surfaces, two borders, a base, and an apex. The
convex surface or dorsum (Dorsum auriculae) faces medially and is widest in its
middle part; its lower part is almost circular in curvature, while above it narrows
and flattens. The concave surface (Scapha) is the reverse of the dorsum; it
presents several ridges which subside toward the apex. The anterior border is
sinuous; it is largely convex, but becomes concave near the apex. It divides below
into two diverging parts (Crura helicis). The posterior border is convex. The
apex is flattened, pointed, and curved a little forward. The base is stronglj'- convex.
It is attached to the external acoustic process of the petrous temporal bone, and
around this there is a quantity of fat. The parotid gland overlaps it below and
laterally. The structure of the external ear comprises a framework of cartilages

THE EXTERNAL EAR

871

(which are chiefly elastic), the integument, and a compHcated arrangement of
muscles.

The conchal or auricular cartilage (Cartilago auricula;) determines the shape
of the ear; its form can be made out in a general way without dissection, except
below, where it is concealed by the muscles and the parotid gland. The basal part
is coiled so as to form a tube, which encloses the cavity of the concha (Cavum con-
chse). This part is funnel-shaped and curves outward and a little Imckward. Its
medial surface is strongly convex, forming a prominence termed the eminentia
conchae. The lowest part of the medial margin bears a narrow, pointed prolongation,
the styloid process. This process is about an inch long and projects downward
over the annular cartilage; the guttural pouch is attached to its free end. Behind
its base there is a foramen through which the auricular branch of the vagus passes.

The basal part of the posterior border is cut into by a notch, which separates two irregular
quadrilateral plates. The upper plate (Tragus) is overlapped by the anterior border, and is sep-
arated from the adjacent part of the posterior border (Antitragus) by a notch (Incisura inter-
tragica). The lower plate is curved to form a half ring and partly overlaps the anterior border and
the annular cartilage. Behind the notch there is a foramen, which transmits the internal auricular
artery and internal auricular branch of the facial nerve.

The annular cartilage (Cartilago annularis) is a quadrilateral plate, curved to
form about three-fourths of a ring; its
ends are a little less than half an inch (ca.
1 cm.) apart medially and are united by
elastic tissue. It embraces the external
acoustic process and forms with the lower
part of the conchal cartilage the carti-
laginous part of the external acoustic
meatus.

The scutiform cartilage (Cartilago
scutiformis s. Scutulum) is an irregular
quadrilateral plate which lies on the tem-
poral muscle in front of the base of the
conchal cartilage. Its superficial face is
slightly convex from side to side and
its deep face is correspondingly concave.
The anterior end is thin and rounded ; the
posterior part or base is wider and thicker,
and its medial angle is prolonged by a
pointed process half an inch or more in
length. The cartilage moves very freely
over the underlying parts.

The external acoustic meatus leads
from the cavum conchse to the tympanic
membrane. It does not continue the
general direction of the cavity of the
concha, but extends medially, downward,

and slightly forward. It consists of a cartilaginous part (Meatus acusticus ex-
ternus cartilagineus) which is formed by the lower part of the conchal cartilage
and the annular cartilage, and an osseous part formed by the external acoustic
process of the temporal bone. These are united by elastic membranes to form a
complete tube. Its caliber diminishes medially, so that the lumen of the inner end
is about half of that of the outer end.

The skin on the convex surface of the concha presents no special features; it
is attached to the cartilage by a considerable amount of subcutaneous tissue except
at the apex. The integument which lines the concave surface is intimately ad-

FiG. 699. — Conchal and Annular Cartilages of
Ear of Horse, External View.
/, Base of concha; 2, posterior border, 3, anterior
border of concha; 4< intertragic notch; 5, eminentia
conchse; 6, styloid process; 7, annular cartilage; 9,
zygomatic arch. (After EUenberger-Baum, Anat. fiir
Kiinstler.)

872 THE SENSE ORGANS AND SKIN OF THE HORSE

herent to the cartilage and is relativelj^ dark in color. There are three or four
cutaneous ridges which run about parallel with the borders of the conchal cartilage,
but do not extend to the apex or the cavum conchse. The upper and marginal
parts and the ridges are covered ■v\'ith long hairs, but the skin between the ridges
and below is thin, covered sparsely with very fine hairs, and supplied ^^^th numerous
sebaceous glands. In the external acoustic meatus the skin becomes thinner; in
the cartilaginous part it is supplied with numerous large, coiled, ceruminous glands
(Glandulse ceruminosse) , and is sparsely covered ^\^th very fine hairs; in the osseous
part the glands are small and few or absent and there are no hairs.

THE AURICULAR MUSCLES

The auricular muscles may be subdivided into two sets, viz., (a) extrinsic
muscles, which arise on the head and adjacent part of the neck, and move the ex-
ternal ear as a whole, and (b) intrinsic muscles, which are confined to the auricula.
In this connection the scutiform cartilage may be regarded as a sesamoid cartilage
intercalated in the course of some of the muscles.

The extrinsic muscles are as follows:

1. The scutularis is a thin muscular sheet situated subcutaneously over the
temporalis muscle. Its fibers arise from the zygomatic arch and the frontal and
parietal crests, and converge to the scutiform cartilage. It consists of three parts:

(a) The fronto-scutularis comprises temporal and frontal parts, which arise
from the zj'gomatic arch and the frontal crest, and are inserted into the lateral and
anterior borders of the scutiform cartilage respectively.

(h) The interscutularis arises from the parietal crest, over which it is in part
continuous "svith the muscle of the opposite side. Its fibers converge to the medial
border of the scutiform cartilage.

(c) The cervico-scutularis is not well defined from the preceding muscle. It
arises from the nuchal crest and is inserted into the medial border of the scutiform
cartilage.

2. The anterior auricular muscles (Mm. auriculares orales) are four in number:
(a) The zygomatico-axiricularis arises from the zygomatic arch and the parotid

fascia, and is inserted into the outer face of the base of the conchal cartilage partly
under, partly above, the insertion of the parotido-auricularis.

(h) The scutulo-auricularis supedicialis inferior arises on the lateral part of
the superficial face of the scutiform cartilage and ends on the base of the conchal
cartilage with the preceding muscle.

(c) The scutulo-auricularis superficialis medius arises from the posterior part
of the deep surface of the scutiform cartilage and is inserted into the dorsum of the
conchal cartilage, close to the lower part of its anterior border, and above and behind
the preceding muscle. It receives a slip from the cervico-scutularis.

(d) The scutulo-auricularis superficialis superior is a thin slip which is de-
tached from the interscutularis over the medial border of the scutiform cartilage.
It ends on the anterior aspect of the lower part of the dorsum of the conchal car-
tilage.

3. The dorsal auricular muscles (]\Im. auriculares dorsales) are two in
number.

(a) The scutulo-auricularis superficialis accessorius is a narrow band which is
largely covered by the preceding muscle. It arises from the posterior prolongation
and the adjacent part of the superficial face of the scutiform cartilage, and is
inserted into the convex surface of the conchal cartilage medial to the preceding
muscle, the two crossing each other at an acute angle.

(6) The parieto-auricularis is flat and triangular; it arises from the parietal
crest under cover of the cervico-scutularis, runs outward and a little backward,

THE AURICULAR MUSCLES 873

and is inserted by a flat tendon into the lower part of the convex surface of the
concha under cover of the cervico-auricularis superficialis.

4. The posterior auricular muscles (Mm. auriculares aljorales) are three in
number :

(a) The cervico-auricularis superficialis is a thin triangular sheet. It is wide
at its origin from the nuchal crest and the adjacent part of the ligamentum nuchse,
and becomes narrower as it passes outward to be inserted into the medial side of
the convex surface of the concha.

(b) The cervico-auricularis profundus major arises from the ligamentum
nuchse, partly beneath and partly liehind the preceding muscle. It is directed
outward and is inserted into the postero-Iateral aspect of the base of the ear, partly
under cover of the parotido-auricularis.

Fig. 700. — External Ear of Horse and its Muscles; Lateral View.
The cervico-auricularis superficialis has been removed. 2, Posterior border; 3, anterior border of auricula; 8,
scutiform cartilage; 9, zygomatic arch; n, parotido-auricularis; o, zygomatico-auricularis; o', scutulo-auricularis
superficialis inferior; o", scutulo-auricularis superficialis medius et superior; p, interscutularis; p', fronto-scutularis
(pars temporalis) ; g, cervico-auricularis profundus major; s, anterior oblique muscle of head; «, splenius; y, tendon of
brachiocephalicus; x, wing of atlas. (After Ellenberger-Baum, Anat. fiir Kiinstler.)

muscle and passes downward and outward to be inserted into the lowest part of
the convex surface of the concha, partly under cover of the parotid gland.

5. The parotido-auricularis (s. M. auricularis inferior) is a ribbon-like muscle
which lies on the parotid gland. It is thin and wide at its origin from the fascia on
the lower part of the parotid gland, and becomes somewhat narrower and thicker
as it ascends. It is inserted into the conchal cartilage just below the angle of junc-
tion of its borders.

6. The deep auricular or rotator muscles (M. auricularis profundi s. rotatores
auriculae), two in number, are situated under the scutiform cartilage and the base
of the concha and cross each other.

(a) The scutulo-aiuicularis profimdus major is the strongest of the auricular
muscles. It is flat and is about an inch wide. It arises from the deep face of the

874

THE SENSE ORGANS AND SKIN OF THE HORSE

scutiform cartilage and passes backward to end on and below the most prominent
part of the base of the concha (eminentia conchae).

(6) The scutulo-auricularis profundus minor lies between the base of the con-
cha and the preceding muscle, and is best seen when the latter is cut and reflected.
It is flat and about an inch in length. It arises from the posterior part of the deep
face of the scutiform cartilage and from the cervico-scutularis, and passes down-
ward, backward, and outward to be inserted into the base of the concha under
cover of the preceding muscle.

7. The tragicus (or mastoido-auricularis) is a very small muscle which arises
from the temporal bone just behind the external acoustic process and from the an-

FiG. 701. — Muscles of External Ear of Horse; Dorsal View.
On the right side parts of the superficial muscles have been removed and the scutiform cartilage turned back to
•display the deeper muscles, n. Frontal part; a', temporal part of f ronto-scutularis ; b, interscutularis; c, cervico-
scutularis; (I, e, scutulo-auricularis superficialis superior and medius; /, zygomatico-auricularis; g, scutulo-auricularis
superficialis accessorius; o, cervico-auricularis superficiahs; q, scutulo-auricularis superficialis inferior; t, scutiform
cartilage; u, parieto-auricularis ; v, cervico-auricularis profundus major; w, cervico-auricularis prof, minor; x, x\
scutulo-auricularis prof, major et minor; y, temporalis. (EUenberger-Baum, Anat. d. Haustiere.)

nular cartilage; it passes upward to be inserted into the lower part of the anterior
border of the conchal cartilage.

The intrinsic muscles are very small and of little importance. The}^ are as
follows :

1. The antitragicus consists of a few bundles which are attached to the conchal
cartilage behind the junction of its two borders, and are partially blended with the
insertion of the parotido-auricularis.

2. The helicis is a small muscle attached in a position opposite to the preceding
on the anterior border of the conchal cartilage ; it extends also into the depression
between the two divisions of the border. It is in part continuous with the insertion
of the parotido-auricularis.

THE MIDDLE EAR 875

3. The verticalis auriculae^ is a thin stratum of muscular and tendinous fibers
which extends upward on the convex surface of the concha from the eminentia
conchse.

Actions. — The base of the concha is rounded and rests in a pad of fat (Corpus
adiposum auriculae), so that the movements of the external ear resemble those of
a ball-and-socket joint. It is noticeable that movements about the longitudinal
and transverse axes are accompanied by rotation. When the ear is vertical or
drawn forward ("pricked up"), the opening is usually directed forward ; conversely,
when the ears are "laid back," the opening faces backward. These movements
evidently result from the coordinated actions of several muscles which are very
complex and cannot be discussed in detail here. The scutularis acting as a whole
fixes the scutiform cartilage, so that the muscles which arise on the latter act
efficiently on the concha. The anterior auricular muscles in general erect the ear
and turn the opening forward. The interscutularis concurs in this action, causing
adduction and a symmetrical position of the ears; it also acts directly on the
conchal cartilage, since the scutulo-auricularis superficialis superior is in reality a
conchal insertion of the interscutularis. The scutulo-auricularis superficialis
accessorius draws the concha forward and turns the opening outward. The parieto-
auricularis adducts the concha and inclines it forward. The cervico-auricularis
superficialis is chiefly an adductor of the conchal cartilage, and directs the opening
outward. The cervico-auricularis profundus major turns the opening outward and,
acting with the parotido-auricularis, inclines the ear toward the poll. The cervico-
auricularis profundus minor tends to direct the opening downward and outward.
The parotido-auricularis draws the ear downward and backward, and acts with the
cervico-auricularis profundus major in "laying back the ears." The scutulo-
auricularis profundus major chiefly rotates the concha so that the opening is turned
backward. The scutulo-auricularis profundus minor assists in rotating the ear
so that the opening is directed forward. The tragicus shortens the external acoustic
meatus. The actions of the intrinsic muscles are inappreciable.

Vessels and Nerves. — The arteries of the external ear are derived from the
anterior auricular branch of the superficial temporal, the posterior or great auricular
branch of the internal maxillary, and the anterior branch of the occipital artery.
The veins go chiefly to the jugular and superficial temporal veins. The nerves
to the muscles come from the auricular and auriculo-palpebral branches of the
facial nerve and from the first and second cervical nerves. The sensory nerves are
supplied by the superficial temporal branch of the mandibular nerve and the
auricular branch of the vagus.

THE MIDDLE EAR

The middle ear (Auris media) comprises the tympanic cavity and its contents,
the auditive or Eustachian tubes, and two remarkable diverticula of the latter,
which are termed the guttural pouches.

The t3mipanic cavity (Cavum tympani) is a space in the tympanic and petrous
parts of the temporal bone situated between the membrana tympani and the in-
ternal ear. It is an air-cavity, which is lined by mucous membrane, and communi-
cates with the pharynx and the guttural pouches by the auditive or Eustachian
tubes. It contains a chain of auditory ossicles by which the vibrations of the
membrana tympani are transmitted to the internal ear.

The cavity consists of: (1) A main part or atrium, which lies immediately to
the medial side of the membrana tympani; (2) the recessus epitympanicus, situated
above the level of the membrane and containing the upper part of the malleus

1 Ellenberger and Baum regard this aa the homologue of the transversus and obliquus
auriculae of man.

876

THE SENSE ORGANS AND SKIN OF THE HORSE

and the greater part of the incus; (3) a relatively large ventral recess in the bulla

The lateral, membranous wall (Paries membranacea) is formed largely by the
thin membrana tympani, which closes the medial end of the external acoustic
meatus, and thus forms the septum between the external and middle parts of the ear.
The membrane is an oval disc, which slopes ventro-medially at an angle of about
30 degrees A\ath the lower wall of the external acoustic meatus. The circumference
is attached in a groove (Sulcus tympanicus) in the thin ring of bone (Annulus
tjTnpanicus) which almost completely surrounds it. The handle of the malleus
(the outermost of the auditory ossicles) is attached to the inner surface of the
membrane and draws the central part inward, producing a slight concavity of the
outer surface. The periphery is thickened, forming the annulus fibrosus. The
membrana tympani consists of three layers. The external cutaneous layer (Stratinn
cutaneum) is a prolongation of the lining of the external acoustic meatus. The

Fig. 702. — Right Petrous Temporal Bone of Horse;
Antero-medial View.
1, External acoustic meatus; 2, annulus tym-
panicus; S, laminse radiating from $; 4, membrana
tympani; 5, malleus; 6, incus; 7, stapes; S, fenestra
cochlese (s. rotundum); 9, facial canal; 11, 11", semi-
circular canals; 11', vestibule; 12, cochlea. (After
Ellenberger, in Leisering's Atlas.)

Fig. 703. — Right Auditory Ossicles and Mem-
brana Tympani, Enlarged a.vd Viewed from
Inner Side and Below.

1, Malleus; 2, incus; 2', 2" , short and long proc-
esses of 2; 3, stapes; 4, tensor tympani; 3, ligament
attaching long process of malleus; 6, stapedius muscle;
7, fenestra cochleae (s. rotundum). (After Ellenberger,.
in Leisering's .\tlas.)

middle fibrous layer or membrana propria includes two chief sets of fibers; the
external layer (Stratum radiatum) consists of fibers which radiate from the handle
of the malleus, while the internal layer (Stratum circulare) is composed of circular
fibers which are best developed peripherally. There are also branched or dendritic
fibers in part of the membrane. The internal mucous layer (Stratum mucosum)
is a part of the general mucous membrane wdiich lines the tympanic cavity.

The medial, labyrinthine wall of the tympanic cavity (Paries labyrinthica)
separates it from the internal ear; it presents a numl^er of special features. The
promontory (Promontorium) is a distinct eminence near the center which corre-
sponds to the first coil of the cochlea, and is marked by a faint groove for the super-
ficial petrosal nerve. Above this is the fenestra vestibuli, a reniform opening which
is closed by the foot-plate of the stapes and its annular ligament. The fenestra
cochleae is situated below and behind the preceding; it is an irregularly oval
opening and is closed by a thin membrane (Membrana tympani secundaria),
which separates the tympanic cavity from the scala tympani of the cochlea.

The anterior, tubal wall (Paries tubaria) is narrow, and is pierf'ed by the slit-

THE MIDDLE EAR

877

like tympanic opening of the auditive tube. Above this and incompletely separated
from it by a thin plate of bone is the semicanal for the tensor tympani muscle.

The tegmental wall or roof (Paries tegmentalis) is crossed in its medial part by
the facial nerve; here the facial canal is more or less deficient ventrally, and the
nerve is covered by the mucous membrane of the tympanum.

The posterior, mastoid wall (Paries mastoidea) presents nothing of importance;
a tympanic antrum and mastoid cells, such as are found behind the tympanic
cavity proper in man and many animals, are not present in the horse.

The t3mipanic wall or floor (Paries tympanica) is concave and thin. It is
crossed by delicate curved ridges, which radiate from the greater part of the annulus
tympanicus.

The auditory ossicles (Ossicula auditus) form a chain which extends from the
outer to the inner wall of the cavity. They are named, from without inward, the
malleus, the incus, the os lenticulare, and the stapes. The first is attached to the
inner surface of the tympanic membrane and the last is fixed in the fenestra ves-
tibuli.

The malleus or hammer, the largest of the ossicles, consists of a head, neck,
handle, and two processes. The bead (Capitulum mallei) is situated in the epi-

Fio. 704. — Auditory Ossicles and Membrana
Tympani; Medial View, Enlarged.
1, Annulus tympanicus; S, membrana tym-
pani; J, malleus; 4, incus; 5, stapes. (After
Ellenberger, in Leisering's Atlas.)

Fig. 70o. — Right Auditory Ossicles, Enlarged as In-
dicated BY Lines Giving their Actual Length.
a. Malleus: 1, head; 3, neck; S, handle; 4. long proc-
ess; o, muscular process, b. Incus: 1, body; S, short
branch; 3, long branch; c, os lenticulare. c. Stapes; 1,
head; 2, crus; ,3, base; .{, attachment of stapedius. (After
Ellenberger, in Leisering's Atlas.)

tympanic recess. It is smooth and convex above and in front, and presents on
its postero-medial aspect a concave facet for articulation with the body of the
incus. The neck (Collum mallei) is the constricted part below the head; its medial
surface is crossed by the chorda tympani nerve. The handle (Manubrium mallei)
is directed downward, inward, and a little forward from the neck, and is attached
along its entire length to the membrana tympani. On its medial surface, near the
upper end, there is a slight projection to which the tendon of the tensor tympani
muscle is attached. The long process (Processus longus) is a pointed spicule which
projects forward from the neck toward the petro-tympanic fissure. The short
process (Processus brevis) is a slight projection of the lateral side of the neck, and
is attached to the upper part of the membrana tympani.

The incus or anvil is situated chiefly in the epitympanic recess. It may be
said to resemble in miniature a human bicuspid tooth with two divergent roots, and
consists of a body and two processes. The body (Corpus incudis) articulates with
the head of the hammer. The long process (Crus longum) projects downward
from the body and then curves inward; its extremity has attached to it a small
nodule of bone, the os lenticulare, which articulates with the head of the stapes.
The short process (Crus breve) projects chiefly backward, and is attached to the
wall of the recess by a small ligament.

878 THE SENSE ORGANS AND SKIN OF THE HORSE

The stapes or stirrup consists of a head, two crura, and a base. The head
(Capitulum stapedis) is directed outward and articulates with the os lenticulare.
The crura, anterior and posterior (Crus anterius, posterius), are directed inward
from the head, and join the ends of the base. The base or foot-plate (Basis stapedis)
occupies the fenestra vestibuli, to which it is attached. The space between the
crura and the base is closed by a membrane.

The articulations and ligaments of the auditory ossicles comprise: (1) A
diarthrodial joint between the head of the malleus and the body of the incus (Articu-
latio incudomalleolaris), enclosed by a capsule. (2) An enarthrosis between the os
lenticulare and the head of the stapes (Articulatio incudostapedia), also surrounded
by a capsule. (3) The base of the stapes is attached to the margin of the fenestra
vestibuli by a ring of elastic fibers (Lig. annulare baseos stapedis). (4) Small
ligaments attach the head of the malleus and the short crus of the incus to the roof
of the epitympanic recess. (5) The axial ligament (of Helmholtz) attaches the
neck of the malleus to a small projection (Spina tympanica anterior) above and in
front of the annulus tympanicus.

The muscles of the auditory ossicles are two in number, viz., the tensor tj^m-
pani and the stapedius. The tensor tympani arises from the upper wall of the
osseous Eustachian tube, and ends in a delicate tendon which bends outward and
is inserted into the handle of the malleus near its upper end. When it contracts,
it draws the handle of the malleus inward and tenses the membrana tympani; it
probably also rotates the malleus around its long axis. It is innervated by the
motor part of the trigeminus through the otic ganglion. The stapedius arises from
a small prominence (Eminentia pyramidalis) of the posterior wall of the tympanum,
runs forward on the facial nerve, and is inserted into the neck of the stapes. Its
action is to draw the head of the stapes backward and rotate the anterior end of the
base outward, thus tensing the aimular ligament. It is innervated by the facial
nerve.

The tjnnpanic mucous membrane (Tunica mucosa tympanica) is continuous
with that of the pharynx and the guttural pouch through the auditive or Eustachian
tube. It is thin, closely united with the underlying periosteum, and is reflected
over the ossicles, ligaments, and muscles, the chorda tympani, and the facial nerve
in the open part of the facial canal. It contains minute lymph nodules and small
mucous glands (Glandulse tympanicae). The epithelium is in general columnar
ciliated, but over the meml^rana tympani, ossicles, and promontory it is flattened.

The artery of the tympanum is the stylo-mastoid, a small vessel which arises
from the posterior auricular branch of the internal maxillary artery. It enters the
tympanum through the stylo-mastoid foramen, and forms a circle around the tym-
panic membrane. The nerves of the mucous membrane come from the tympanic
plexus.

The Auditive or Eustachian Tube
The auditive or Eustachian tube (Tul)a auditiva) extends from the tympanic
cavity to the pharynx; it transmits air to the former and equalizes the pressure
on the two surfaces of the membrana tympani. It is directed forward, downward,
and slightly inward, and is four to five inches (ca. 10 to 12 cm.) in length. Its
posterior extremity lies at the medial side of the root of the muscular process of
the petrous temporal, and communicates with the anterior part of the tympanic
cavity by the small, slit-like tympanic opening (Ostium tympanicum tubae auditiva?).
For a distance of about a quarter of an inch (ca. 6-7 mm.) in front of this opening
it is a complete tube, with a curved lumen which is little more than a capillary space.
Further forward it has the form of a plate which widens anteriorly and is curved to
enclose a narrow groove that opens ventrally into an extensive diverticulum termed
the guttural pouch. The pharyngeal opening (Ostium pharyngeum tuba? audit-

THE GUTTURAL POUCHES 879

tivse) is situated on the postero-superior part of the lateral wall of the pharynx, just
below the level of the posterior nares (Fig. 349). It is a slit, about two inches
(ca. 5 cm.) in length, which slopes downward and backward. It is bounded medi-
ally by the thin free edge of the tube, from the lower part of which a fold of mucous
membrane (Plica salpingo-pharyngea) extends in the same direction on the lateral
wall of the pharynx for a distance of a little more than an inch usually. The outer
boundary of the opening is the lateral wall of the pharynx. The basis of the tube
is a plate of fibro-cartilage (Cartilago tubse auditivae) which is firmly attached
dorsally to the fibrous tissue which closes the foramen lacerum, the temporal wing
of the sphenoid, and the pterygoid bone.^ On cross-section the cartilage is seen
to consist — except at its ends — of two laminse which are continuous with each
other above (Fig. 348). The medial lamina (Lamina medialis) gradually widens
toward the pharyngeal end, where it forms a broad valvular flap; this is convex
medially, and its thin anterior edge forms the basis of the inner margin of the pharyn-
geal opening. Behind this the lamina has a thick free edge which projects ventrally
from the roof of the guttural pouch. The lateral lamina (Lamina lateralis) is
narrow and thin, and is related laterally to the levator and tensor palati muscles,
which are in part attached to it; it does not extend to the pharyngeal end of the
tube. The mucous membrane of the tube is continuous behind with that of the
tympanum and in front with that of the pharynx. On either side it is reflected to
form a large diverticulum, the guttural pouch. It is covered with ciliated epi-
thelium, and contains mucous glands and lymph nodules.

The pharyngeal opening appears to be closed ordinarily. Vermeulen states that it opens
during deglutition, and that tliis action is apparently produced by the part of the palato-pharyn-
geus muscle which is attached to the flap-hke expanded part of the tube.

The Guttural Pouches
The guttural pouches, right and left (Figs. 349, 706), are large mucous sacs,
each cf which is a ventral diverticulum of the Eustachian tube (Diverticulum
tubse auditivse) ; they are not present in the domesticated animals other than the
equidse. They are situated between the base of the cranium and the atlas dorsally
and the pharynx ventrally. Medially they are in apposition in part, but are to
some extent separated by the intervening ventral straight muscles of the head.
The anterior end is a small cul-de-sac which lies below the body of the presphenoid,
between the Eustachian tube and the median recess of the pharynx. The posterior
end lies near or below the atlantal attachment of the longus colli. The pouch
is related dorsally to the base of the cranium, the atlanto-occipital joint capsule,
and the ventral straight muscles. Ventrally it lies on the pharynx and the origin
of the oesophagus. Laterally the relations are numerous and complex. They
comprise the pterygoid, levator palati, tensor palati, stylo-hyoideus, occipito-
hyoideus, occipito-mandibularis, and digastricus muscles; the parotid and mandib-
ular salivary glands; the external carotid, internal maxillary, and external maxil-
lary arteries; the internal maxillary and jugular veins; the pharyngeal lymph
glands; the glosso-pharyngeal, hypoglossal, and anterior laryngeal nerves. The
vagus, accessory, and sympathetic nerves, the anterior cervical ganglion, the in-
ternal carotid artery, and the ventral cerebral vein are situated in a fold of the
dorsal part of the pouch. The pouch is reflected around the dorsal border of the
great cornu of the hyoid bone so as to clothe both surfaces of the dorsal part of the
latter. It thus forms an outer compartment, which extends backward lateral to
the great cornu and the occipito-hyoideus muscle; this compartment is related
laterally to the parotid gland, the articulation of the jaw, the ascending part of the
internal maxillary artery, the superficial temporal artery, and the facial nerve; dor-

1 There is, strictly speaking, no osseous part of the tube 3uch as occurs in man. In the horse
the cartilage extends to the tympanic orifice.

880

THE SENSE ORGANS AND SKIN OF THE HORSE

sally it covers the mandibular nerve and its chief branches, and is attached to the
styloid process of the conchal cartilage.

Each pouch communicates with the pharynx through the pharyngeal orifice
of the Eustachian tube, and is in direct continuity with the mucous membrane of
the latter.

The average capacity of each pouch is about ten fluidounces (ca. 300 c.c); of
this, the lateral compartment is about one-third.

Temporal muscle

Scutiform cartilage,
posterior process

Conchal cartilage

Brachiocephalicus
tendon

Nerves IX, X, XI

^ 'entral cerebral vein
Internal carotid artery
(luttural pouch
Occipito-hyoideus
muscle

Jugular vein

Int. maxillary artery
Ext. maxillary artery

Parapharyngeal lymph
glands

Occipito-mandibularis
muscle

Sterno-cephalicus tendon
Mandibular gland
Thyroid cartilage
Ext. maxillary vein

Omo-hyoidei + sterno-hyoidei
Fig. 706. — Cross-section of Head of Horse.
The section passes through the base of the external ear and just behind the posterior border of the mandible. 1,
Rectus capitis ventrahs minor; 2, rectus capitis ventralis major; 3, medial walls of guttural pouches in apposition;
4, 4. arytenoid cartilage, upper piece being apex; 5, posterior pillar of soft palate; 6, false vocal cord; 7, lateral ventricle
of larynx; S, true vocal cord; S, vocal muscle; 70, thyro-hyoideus muscle. The cavity in which the number .5 is placed
is the pharynx, which was left unmarked by an oversight.

The pouch is a delicate mucous membrane which is in general rather loosely
attached to the surrounding structures. It is lined with ciliated epithelium and is
supplied with glands which are chiefly mucous in type.

It_ is worthy of note that the pharyngeal orifice of the Eustachian tube is at such a level as
to provide (in the ordinary position of the head) only an overflow outlet for the escape of fluid
which may accumulate in the pouch. The expanded part of the tube forms with the wall of the
pharynx a sort of vestibule, at the posterior part of which is the opening of the guttural pouch.

THE INTERNAL EAR THE OSSEOUS LABYRINTH 881

This opening is only about an inch (ca. 2.5 cm.) long. The two pouches are often unequal in size,
and variations in regard to the distance which they extend backward are not uncommon. In one
case, for instance, a small aged horse, the right pouch extended along the oesophagus about five
inches (ca. 12 cm.) behind the ventral tubercle of the atlas, and the left one a little more than two
inches (ca. 6 cm.) . No pathological changes were apparent, and the condition was not recognizable
externally. Cases of extreme size — so-called tympanites — of the pouches occur, and are apparently
congenital defects. In a case in a yearling cok, the head of which was 24 inches long, the left
pouch extended about 12 inches (ca. 30 cm.) behind the tubercle of the atlas, and had a capacity
of six quarts. The anterior end formed a cul-de-sac about two inches (ca. 5 cm.) long between the
Eustachian tube and levator palati medially and the lateral pterygoid muscle laterally.

THE INTERNAL EAR
The internal ear or labyrinth (Auris interna s. Labyrinthus) consists of two
parts, viz.: (1) A complex membranous sac, which supports the auditory cells and
the peripheral ramifications of the auditory nerve; (2) a series of cavities in the
petrous temporal bone, which encloses the membranous part. The first is called
the membranous labyrinth, and contains a fluid, the endolymph. The second is
the osseous labyrinth. The two are separated by the perilymphatic space, which is
occupied by a fluid termed the perilymph.

The Osseous Labyrinth
The osseous labyrinth (Labyrinthus osseus) (Fig. 702) is excavated in the
petrous temporal bone medial to the tympanic cavity. It consists of three divisions':
(1) a middle part, the vestibule; (2) an anterior one, the cochlea ; and (3) a pos-
terior one, the semicircular canals.

1. The vestibule (Vestibulum) is the central part of the osseous labyrinth,
and communicates in front with the cochlea, behind with the semicircular canals.
It is a small, irregularly ovoid cavity, which is about 5 to 6 mm. in length. Its
lateral wall separates it from the tympanic cavity, and in it is the fenestra vestibuli,
which is occupied by the base of the stapes. The medial wall corresponds to the
fundus of the internal acoustic meatus. It is crossed by an oblique ridge, the
crista vestibuli, which separates two recesses. The anterior and smaller of these is
the recessus sphdericus, which lodges the saccule of the membranous labyrinth.
In its lower part there are about a dozen minute foramina which transmit filaments
of the vestibular nerve to the saccule. The posterior and larger depression is the
recessus ellipticus, which lodges the utricle of the membranous labyrinth. The
crista vestibuh divides below into two divergent branches, which include between
them the small recessus cochlearis ; this is perforated by small foramina, through
which nerve-bundles reach the ductus cochlearis. Similar foramina in the recessus
elhpticus and the crista vestibuli transmit nerve filaments to the utricle and the
ampullae of the dorsal and lateral semicircular ducts. The anterior wall is pierced
by an opening which leads into the scala vestibuli of the cochlea. The posterior part
of the vestibule presents the four openings of the semicircular canals. The inner
opening of the aquaeductus vestibuh is a small slit behind the lower part of the
crista vestibuli. The aquaeductus passes backward in the petrous temporal bone,
and opens on the medial surface of the latter near the middle of its posterior border;
it contains the ductus endolymphaticus.

2. The osseous semicircular canals (Canales semicirculares ossei), three in
number, are situated behind and above the vestibule. They are at right angles to
each other, and are designated according to their positions as dorsal, posterior,
and lateral. They communicate with the vestibule by four openings only, since
the inner end of the dorsal and the upper end of the posterior canal unite to form a
common canal (Crus commune), and the ampuUate ends of the dorsal and lateral
canals have a common orifice. Each canal forms about two-thirds of a circle,
one end of which is enlarged and termed the ampulla. The dorsal canal (Canalis
semicircularis dorsalis) is nearly vertical and is placed obliquely with regard to a

gS2 THE SENSE ORGANS AND SKIN OF THE HORSE

sagittal plane, so that its outer liml) is further forward then than the inner one. The
antero-lateral end is the ampulla and opens into the vestibule with that of the lateral
canal. The opposite non-dilated end joins the adjacent end of the posterior canal
to form the crus commune, which opens into the dorso-medial part of the vestibule.
The posterior canal (Canalis semicircularis posterior) is also nearly' vertical. Its
ampulla is ventral, and opens into the vestibule directly, while the non-dilated
end joins that of the dorsal canal. The lateral canal (Canalis semicircularis lateralis)
is nearly horizontal. Its ampulla is external and opens into the vestibule with that
of the dorsal canal.

3. The cochlea is the anterior part of the bony labyrinth. It has the form of a
short blunt cone, the base of which (Basis cochleae) corresponds to the anterior
part of the fundus of the internal acoustic meatus, while the apex or cupola (Cupola)
is directed outward, forward, and downward. It measures about 7 mm. across the
base and about 4 mm. from base to apex. It consists of a spiral canal (Canalis
spiralis cochleae) , which forms two and a half turns around a central column termed
the modiolus. The modiolus diminishes rapidly in diameter from base to apex.
Its base (Basis modioli) corresponds to the area cochleae of the fundus of the internal
acoustic meatus, and its apex extends nearly to the cupola. Projecting from the
modiolus like the thread of a screw is a thin plate of bone, the lamina spiralis ossea.
This begins between the two fenestras and ends near the cupola as a hook-like
process (Hamulus laminae spiralis). The lamina extends about half-way to the
periphery of the cochlea and partly divides the cavity into two passages; of these,
the upper one is termed the scala vestibuli, and the lower the scala tympani. The
membrana basilaris extends from the free margin of the lamina to the lateral wall
of the cochlea and completes the septum between the two scalae, but they com-
municate through the opening at the cupola (Helicotrema). The modiolus is
traversed by an axial canal which transmits the nerves to the apical coil, and by a
spiral canal (Canalis spiralis modioli), which follows the attached border of the
lamina spiralis, and contains the spiral ganglion and vein. Close to the beginning
of the scala tympani is the inner orifice of the aquaeductus cochleae, a small canal
which opens behind the internal acoustic meatus, and establishes a communication
between the scala tympani and the subarachnoid space.

The internal acoustic meatus has been described in part {vide Osteology).
The fundus of the meatus is divided by a ridge (Crista transversa) into upper and
lower parts. The anterior part of the upper depression (Area n. facialis) presents
the internal opening of the facial canal; and the posterior part (Area vestibularis
superior) is perforated by foramina for the passage of nerves to the utricle and
the ampullae of the dorsal and lateral semicircular ducts. The anterior part of
the inferior depression (Area cochleae) presents a central foramen and a spiral tract
of minute foramina (Tractus spiralis foraminosus) for the passage of nerves to the
cochlea. Behind these is an area of small openings which transmit nerves to the
saccule (Area vestibularis inferior), and the foramen singulare for the passage of a
nerve to the ampulla of the posterior semicircular duct.

The Membranous Labyrinth

The membranous labyrinth (Labyrinthus membranaceus) lies within, but
does not fill, the osseous labyrinth. It is attached to the latter by delicate tra-
beculae which traverse the perilymphatic space. It conforms more or less closely
to the bony labyrinth, but consists of four divisions, since the vestibule contains
two membranous sacs — the utricle and saccule.

1. The utricle (Utriculus), the larger of the two sacs, lies in the postero-
superior part of the vestibule, largely in the recessus ellipticus. It receives the
openings of the semicircular ducts, and the small ductus utriculo-saccularis leads
from its lower part to the ductus endolymphaticus.

THE MEMBRANOUS LABYRINTH

883

2. The saccule (Sacculus) is situated in the recessus sphaericus of the vestibule.
From its lower part the ductus reuniens proceeds to open into the ductus cochlearis,
a little in front of the blind end of the latter. A second narrow tube, the ductus
endolymphaticus, passes from the posterior part of the saccule, and is joined by the
ductus utriculo-saccularis; it then traverses the aquaeductus vestibuli, and ter-
minates under the dura mater on the posterior part of the medial surface of the
petrous temporal bone in a dilated blind end, the saccus endolymphaticus.

3. The semicircular ducts (Ductus semicirculares)^ correspond in general to
the osseous canals already described, but it may be noted that while the ampullae of
the ducts nearly fill those of the osseous canals, the other parts of the ducts only
occupy about one-fourth of the bony cavities.

4. The cochlear duct (Ductus cochlearis) is a spiral tube situated within the
cochlea. It begins by a blind end (Caecum vestibulare) in the cochlear recess of
the vestibule, and ends by a second blind end (Caecum cupulare) , which is attached
to the cupola of the cochlea. The vestibular part is connected with the saccule
by the ductus reuniens. The duct is triangular in cross-section, and it is usual to
regard it as having three walls. The vestibular wall or roof, which separates the
cochlear duct from the scala vestibuli, is formed by the very delicate membrana
vestibularis (of Reissner), which extends obliquely from the lamina spiralis ossea

Fig. 707. — Left Membranous Labyrinth (En-
larged).
i. Cochlea; ;2, fenestra vestibuli; 3, fenestra coch-
leae; 4. ductus endolymphaticus; 5, dorsal, 6, lateral, 7,
ventral, duct. (After EUenberger, in Leisering's At-
las.)

Fig. 708.— Schematic Sectional View of Labyrinth
(Enlarged).
1, 2, 3, Dorsal, lateral, and ventral ducts; 4.
utricle; 5, saccule; 6, cochlea; 7, acoustic nerve.
(After EUenberger, in Leisering's Atlas.)

to the outer wall of the cochlea. The tympanic wall or floor intervenes between
the cochlear duct and the scala tympani; it is formed by the periosteum of the mar-
ginal part of the lamina spiralis and the membrana basilaris, which stretches be-
tween the free edge of the lamina and the outer wall of the cochlea. The outer
wall consists of the fibrous lining of the cochlea, which is greatly thickened to formi
the ligamentum spirale cochleae.

Structure.^ — The membranous labyrinth consists in general of an outer thin
fibrous layer, a middle transparent tunic, and an internal epithelium, composed of
flattened cells. But in certain situations special and remarkable structures occur,
among which are the following: (1) The maculae acousticae appear as small whitish
thickenings of the inner walls of the saccule and utricle. The epithelium here
consists of two kinds of cells, viz., supporting cells and hair cells. The latter are
flask-shaped and are surrounded by the fusiform supporting cells. The free end
of each hair cell bears a stiff, hair-like process composed of a bundle of cilia. Fibers
of the saccular and utricular branches of the vestibular nerve form arborizations
about the basal parts of the hair cells. Adherent to the surface of the maculae

1 Also termed the membranous semicircular canals.

2 For the finer structure reference is to be made to the histological Uterature.

884 THE SENSE ORGANS AND SKIN OF THE HORSE

are fine crystals of lime salts, embedded in a mucoid substance, and termed otoconia.
(2) The cristae acusticae are linear thickenings of the wall of each ampulla of the
semicircular ducts. Their structure is similar to that of the maculae. (3) The
spiral organ of Corti (Organon spirale) is an epithelial elevation which is situated
upon the inner part of the membrana basilaris, and extends the entire length of the
ductus cochlearis. It is very complicated in structure, but consists essentially of
remarkable supporting cells and hair cells. Fibers of the cochlear nerve ramify
about the basal parts of the hair cells.

Vessels and Nerves. — The artery of the internal ear is the internal auditory
artery, a very small vessel which usually arises from the posterior cerebellar artery,
and enters the internal acoustic meatus. The veins go to the ventral petrosal
sinus. The vestibular nerve is distributed to the utricle, saccule, and semi-
circular ducts, and mediates equilibration. The cochlear nerve gives a branch
to the saccule and enters the central canal of the modiolus. Along its course it
gives off fibers which radiate outward between the two plates of the lamina spiralis
ossea, and ramify about the hair cells of the organ of Corti. The ganglion spirale
is situated in the spiral canal of the modiolus near the fixed border of the lamina
spiralis. The cochlear nerve mediates the sense of hearing.

The Common Integument

The common integument (Integumentum commune) is the protective covering
of the body, and is continuous at the natural openings with the mucous membranes
of the digestive, respiratory, and urogenital tracts. It consists of the skin (Cutis),
together with certain appendages or modifications thereof, as hair, horn, feathers, etc.
It contains peripheral ramifications of the sensory nerves, and is thus an important
sense organ. It is the principal factor in the regulation of the temperature of the
body, and by means of its glands it plays an important part in secretion and ex-
cretion. Some of its special horny modifications or appendages are used as organs
of prehension or as weapons.

The thickness of the skin varies in the different species, on different parts of
the body of the same animal, and also with the breed, sex, and age. The color
also varies greatly, but this is masked in most places by the covering of hair or wool.
The skin is in general highly elastic and resistant.

Permanent folds of the skin (Plicse cutis) occur in certain situations, and in
some places there are cutaneous pouches or diverticula (Sinus cutis) .

The skin is attached to the underlying parts by the subcutaneous tissue or
subcutis (Tela subcutanea). This consists of connective tissue containing elastic
fibers and fat. When the fat forms a layer of considerable thickness, it is termed
the panniculus adiposus. Over a considerable part of the body the subcutis con-
tains striped muscle, the m. cutaneus or panniculus camosus ; in some regions the
fibers of the muscle are inserted into the skin, and their contraction tAvitches the
skin or produces temporary folds.^ The amount of subcutaneous tissue varies
widely; in some places it is abundant, so that the skin can be raised considerably;
in other situations it is practically absent and the skin is closely adherent to the
subjacent structures. Subcutaneous bursas often develop over prominent parts
of the skeleton where there is much pressure or friction, e. g., at the olecranon,
tuber coxae, tuber calcis.

Structure. — The skin consists of two distinct strata, viz., a superficial epithelial
layer, the epidermis, and a deep connective-tissue layer, the coritmi. The epi-
dermis is a non-vascular, stratified epithelium of varying thickness. It presents

^ This muscle has been described in the Myology.

THE COMMON INTEGUMENT 885

the openings of the cutaneous glands and the hair-folhcles, and its deep surface is
adapted to the corium.^ It is divisible into a superficial, harder, drier part, the
stratum comeum, and a deeper, softer, moister part, the stratum germinativum.
The cells of the latter contain pigment, and by their proliferation compensate the
loss by desquamation of the superficial part of the stratmn corneum. In many
places further subdivision into strata is evident on properly prepared cross-sections.
The cerium consists essentially of a feltwork of white and elastic fibers. It is well
supplied with vessels and nerves, and contain the cutaneous glands, the hair-fol-
licles, and unstriped muscle. The deeper part of the corium, the tunica propria,
consists of a relatively loose network of coarse bundles of fibers, and in most places
there is no clear line of demarcation between it and the subcutis. The superficial
part, the corpus papillare, is of finer texture and is free from fat. Its superficial
face is thickly beset with blunt conical prominences, the papillae, which are received
into corresponding depressions of the epidermis. They contain vascular loops and
nerves, or, in certain situations, special nerve-endings.^

The glands of the skin (Glandulse cutis) are chiefly of two kinds, sudoriferous
and sebaceous. The sudoriferous or sweat glands (Glandulae sudoriferse) consist
of a tube, the lower, secretory part of which is coiled in the deep part of the corium
or in the subcutis to form a round or oval ball (Corpus glandulae sutloriferse). The
excretory duct (Ductus sudoriferus) passes almost straight up through the corium,
but pursues a more or less flexuous course through the epidermis, and opens into a
hair-follicle or by a funnel-shaped pore (Porus sudoriferus) on the surface of the
skin. The sebaceous glands (Glandulae sebaceae) are in great part associated with
the hairs, into the follicles of which they open. Their size varies widely, and is
in general in inverse ratio to that of the hair. The larger ones are easily seen with
the naked eye, and appear as small, pale yellow or brownish bodies. In certain
situations (e. g., the labia, vulvae, anus, prepuce) they are independent of the hairs
and are well developed. In form they may be branched alveolar, simple alveolar,
or even tubular in type. They secrete a fatty substance, the sebum cutaneum,
which serves as a protective against moisture, and may also (by its aromatic con-
stituents) play an important part in the sexual life of animals.

The two kinds of glands described above are those which are most widely distributed, but
many special types occur. Some of these are to be regarded as modified sweat glands, e. g., the
naso-labial glands of the ox, the glands of the snout of the pig, and the glands of the digital
cusliion of the horse. Others, e. g., the tarsal glands of the eyelids, are modified sebaceous. Still
others are not yet classified satisfactorily. Some of these special types have been referred to in
previous chapters, and others will receive attention in the special descriptions which follow. The
mammary glands are highly modified cutaneous glands, which are intimately associated in func-
tion with the genital organs, and have been described with the latter.

Vessels and Nerves. — The arteries of the skin enter from the subcutis, where
they communicate freely. In the deeper part of the corium they form a plexus,
and another network is formed under the papillae. Small vessels from the deep
plexus go to the fat and sweat glands, and the subpapillary plexus sends fine
branches to the papillae, hair-follicles, and sebaceous glands. The veins form two
plexuses, one beneath the papillae, and another at the junction of the corium and
subcutis. The lymph vessels form subpapillary and subcutaneous plexuses.

The nerves vary widely in number in different parts of the skin. The terminal
fibers either end free in the epidermis and in certain parts of the corium, or form
special microscopic corpuscles of several kinds.

1 To prevent a possible misapprehension, it may be stated that the epidermis primarily
molds the corium, and that the glands and hair-follicles are invaginations of the epidermis.

2 The papiUiE are best developed where the epidermis is thick and hairs are small or absent.
On tliickly haired regions they are small or even absent. On certain parts of the body (anus,
vulva, prepuce, scrotum, eyelids, etc.) the corium contains pigment in its connective-tissue cells.

886 THE SENSE ORGANS AND SKIN OF THE HORSE

THE APPENDAGES OF THE SKIN

The appendages of the skin are modifications of the epidermis, and comprise
the hairs, hoofs, claws, horns, etc.

The hairs (Pih) cover almost the entire surface of the bod}^ in the domesticated
mammals, and some parts which appear at first sight to be bare are found on close
inspection to be provided with sparse and very fine hair. The hairs are constantly
being shed and replaced, but at certain periods in the horse, for example, they fall
out in great numbers, constituting the shedding of the coat. It is customary to
distinguish the ordinary hairs (the coat), which determine the color of the animal,
from the special varieties found in certain places. Among the latter are the long

i^\v.

l^\

-Lateral View of Horse to Show Hair-streams and Vortices.
Kiinstler.)

(After KIIenberger-B;nim, Anat. fiir

tactile hairs about the lips, nostrils, and eyes; the eyelashes or cilia; the tragi of
the external ear; and the vibrissae of the nostrils. Other special features will be
noted in the discussion of the skin of the various species. The hairs are directed
in such a way as to form more or less definite hair-streams (Flumina pilorum),
and at certain points these converge to form vortices (Vortices pilorum).

The part of the hair above the surface of the skin is the shaft (Scapus pili),
while the root (Radix pili) is embedded in a depression termed the hair-follicle
(Folliculus pili). A vascular papilla (Papilla pili) projects up in the fundus of the
follicle and is capped by the expanded end of the root, the bulb of the hair (Bulbus
pili). The hair-follicles extend obliquely into the corium to a varying depth; in
the case of the long tactile hairs they reach to the underlying muscle. Most of the
follicles have attached to them small unstriped muscles known as the arrectores
pilorum; these are attached at an acute angle to the under side of the deep part

THE SKIN OF THE HORSE THE HOOF 887

of the follicle, and their contraction causes erection of the hair and compression of
the sebaceous glands, one or more of which open into the follicle.

The hairs are composed of epidermal cells, and consist from without inward of
three parts. The cuticle is composed of horny, scale-like cells which overlap like
slates on a roof. The cortex consists of horny fusiform cells which are packed close
together and contain pigment. The medulla is the central core of softer, cubical
or polyhedral cells; it contains some pigment and air-spaces.

The hair-follicles, being invaginations of the skin, are composed of a central
epidermal part and a peripheral layer which corresponds in structure to the corium.
The follicles of the tactile hairs have remarkably thick walls which contain blood-
sinuses between their outer and inner layers; in ungulates the sinuses are crossed
by trabecules and assume the character of cavernous or erectile tissue.

The hoofs, claws, horns, and other horny structures consist of closely packed
epidermal cells which have undergone cornification. In structure they might be
compared to hairs matted together by intervening epidermal cells. They cover a
specialized corium from which the stratum germinativum derives its nutrition.

THE SKIN OF THE HORSE

The thickness of the skin of the horse varies from one to five millimeters in
different regions, and is greatest at the attachment of the mane and on the tail.

The glands are numerous and are larger than those of the other domesticated
animals. The sebaceous glands are specially developed on the lips, the prepuce,
mammary glands, perineum, and labia of the vulva. The sweat glands are yellow
or brown in color. They occur in almost all parts of the skin, but are largest and
most numerous in that of the lateral wing of the nostril, the flank, mammary glands,
and free part of the penis.

In addition to the ordinary and tactile hairs certain regions present coarse
hairs of great length. The mane (Juba) springs from the dorsal border of the neck
and the adjacent part of the withers; its anterior part, which covers the forehead
to a variable extent, is termed the foretop (Cirrus capitis). The tail, with the
exception of its ventral surface, bears very large and long hairs (Cirrus caudse).
The tuft of long hairs on the flexion surface of the fetlock (Cirrus pedis) gave rise to
the popular name of this region.

The development of these special hairs varies widely, and is in general much greater in the
draft breeds than in others. In Shire and Clydesdale horses, for instance, the hair on the poste-
rior aspect of the metacarpus and metatarsus and fetlock is often so long and abundant as to ac-
count for the term "feather, " which is commonly appUed to it by horsemen.

Subcutaneous bursas (Bursse subcutaneae) may be present at various prominent
points, e. g., the olecranon, the tuber coxae, the tuber calcis, the withers, etc. They
are not present in the young subject and appear to be the result of traumatism.

THE HOOF
The hoof (Ungula) is the horny covering of the distal end of the digit. It is
. convenient to divide it for description into three parts, termed the wall, sole, and
frog.

1. The wall (Paries ungulse) is defined as the part of the hoof which is visible
vvhen the foot is placed on the ground.^ It covers the front and sides of the foot,
and is reflected posteriorly at an acute angle to form the bars. The latter (Pars
inflexa medialis, lateralis) ^ appear on the ground surface of the hoof as convergent

1 The term foot is used here in the popular sense, i. e., to designate the hoof and the structures
enclosed witliin it.

2 The term "pila ungulae" has been suggested by Schmaltz for the part popularly known as
the "bar."

THE SENSE ORGANS AND SKIN OF THE HORSE

ridges, which subside in front and are fused with the sole; they are united with each
other by the frog. For topographic purposes the wall may be divided into an an-
terior part or " toe " (Paries unguis? dorsahs), medial and lateral parts or " quar-
ters " (Paries ungulse medialis, lateralis), and the angles or " heels " (Anguli parie-
tales). It presents two surfaces and two borders. The external surface is con-
vex from side to side and slopes obliquely from edge to edge. In front the angle of
inclination on the ground plane is about 50° for the f orelimb, 55° for the hind limb ;
on the sides the angle gradually increases and is about 100° at the heels. The curve
of the wall is wider on the lateral than on the medial side, and the slope of the medial
quarter is steeper than that of the lateral one.^ The surface is smooth and is crossed
by more or less distinct ridges, which are parallel with the coronary border and
indicate variations in the activity of the growth of the hoof. It is also marked by

fine parallel strise, which extend from border to
border in an almost rectilinear manner and in-
dicate the direction of the horn tubes.

The internal surface is concave from side to
side, and bears about six hundred thin primary
laminae, which extend from the coronar^^ groove
to the basal border of the wall. Each bears a
hundred or more secondary laminae on its sur-
faces, so that the arrangement is pennate on
cross-section. These horny laminae are continued
on the inner surface of the bars, and dovetail with
corresponding laminae of the the corium. The cor-
onary border (Margo coronarius) is thin. Its outer
aspect is covered by a layer of soft horn known
as the periople (Limbus corneus) ; this appears as
a ring-like prominence above and gradually fades
out below; at the angle it forms a wide cap or
bulb and blends centrally with the frog. The
inner aspect of the border is excavated to form
the coronary groove (Sulcus coronarius ungulae),
which contains the thick coronary corium. The
groove is deepest in front, narrows on the sides,
and is wide and shallow at the heels.- It is per-
forated by innumerable small, funnel-like openings
which are occupied by the papillae of the coronary
corium in the natural state. Between the border
of the wall proper and the periople there is a small
groove which contains the corium of the periople.
At the heel this groove is merged with the coronary
groove. The basal or ground border (Margo l)asi-
laris) of the unshod hoof comes in contact with the ground. Its thickness is greatest
in front and decreases considerably from before backward on the sides, l)ut there is
a slight increase at the angles. Its inner face is united with the periphery of the

Fig. 710. — Digit of Horse, Showing
Surface Relations of Bones and
Joints. The Cartilage is Largely
Exposed.

o, First phalanx; b, second phalanx;
c, third phalanx; d, cartilage; e, distal sesa-
moid or navicular bone; /, pastern joint;
g, cofSn joint; h', cut edge of wall of hoof
(h) ; i, laminar corium. (After Ellenberger,
in Leisering's Atlas.)

1 The slope of the wall varies considerably in apparently normal hoofs. Lungwitz found
by careful measurements of 56 fore and 36 hind feet the following average angles:

Fore Foot Hind Foot

Toe 47.26° 54.1°

Medial angle 101.57° 96.5°

Lateral angle 101.37° 96.1°

The wall of the fore foot may even be more upright than that of the hind, and may have an
angle of 60°. The length of the wall at the toe, quarters, and heels is in the ratio of about 3:2:1
m the fore foot and about 2 : 1 J^ : 1 in the hind hoof.

2 The wide groove at the heels, however, contains chiefly the corium of the periople.

THE HOOF

889

sole by horn of lighter color and softer texture, which appears on the ground surface
of the hoof as the so-called white line (Zona lamellata) .

Wall
Lamince of wall

Laminar corium
Third phalanx
Digital cushm:

Bar

Frog

Space between
bar and frog

Angle of wall
Periople of heel

Fig. 711. — Cross-section of Foot of Horse, Cut Parallel with the Coronary Border.
The wall appears much thicker at the angles than it actually i.s, because it is cut very obliquely.

In the case of unshod horses at liberty the wall is usually worn off to the level of the adjacent
sole, but if the ground is too soft the wall is likely to become unduly long and spht or break or
undergo deformation. On very hard or rough ground, on the other hand, the wear may be in ex-

Periople

Coronary

groove

Laminoe

Periople of heel

White line

Ridge formed
by bar and frog

Half of Hoof of Horse; Internal Surface.

cess of the growth. In the case of shod horses it is necessary to remove the excess of growth of the
wall at each shoeing. The thickness of the wall at the toe, quarters, and heels is about in the
ratio of 4 : 3 : 2 for the fore foot and about 3 : 23^ : 2 for the hind foot.

2. The sole (Basis s. solea unguis) forms the greater part of the ground sur-

890

THE SENSE ORGANS AND SKIN OF THE HORSE

^^ace of the hoof. It is somewhat crescentic in outhne, and presents two surfaces
and two borders. The internal surface is convex, and slopes vnth a varying
degree of obhquity doA\Tiward to the convex border. It presents numerous small
funnel-like openings Avhich contain the papillae of the sole corium in the natural
state. The external or ground surface is the converse of the preceding. It is nor-
mally arched— and more strongly in the hind than in the fore foot— but the curvature
is subject to wide variation; in heavy draft horses the sole is commonly less curved
than in the lighter breeds and may even be flat. The surface is usually rough, since
the horn exfoliates here in irregular flakes. The convex border is joined to the wall by
relatively soft horn, previously referred to as forming the white line on the ground
surface of the hoof. The angle of junction is rounded internally and presents a

Fig. 713. — Right Fore Hoof of Horse; Ground Sttrface.
1, Basal or ground border of wall; 2, laminae of wall; 3, angle of wall; 4, bar; 5, sole; 5', angle of sole; 6, white
line (junction of wall and sole); 7, apex of frog; 8, central sulcus of frog; 9, 9, collateral sulci between frog and bars;
10, 10, bulbs of hoof.

number of low ridges and specially large openings for the papillte of the corium.
There is frequently a ridge of larger size at the toe. The concave border has the
form of a deep angle which is occupied by the bars and frog. It concurs in part
with these in forming two pronounced ridges in the interior of the foot. The parts
of the sole between the wall and bars are termed its angles (Anguli solese).

3. The frog (Cuneus ungulae) is a wedge-shaped mass which occupies the angle
bounded l)y the bars and sole, and extends considerably below these on the ground
surface of the foot. It may be described as having four surfaces, a base, and an
apex. The internal surface bears a central ridge, the spine or "frog-stay" (Spina
cunei ungulse), which is high posteriorly and subsides abruptly in front. On either
side of this there is a deep depression, which is bounded outwardly by the rounded

THE HOOF

891

ridge formed by the junction of the frog with the bar and sole. This surface
presents fine striae and openings for the papillae of the corium. The external or
ground surface presents a central
sulcus (Sulcus cunei), which is
bounded by two ridges or crura
(Crura cunei). The medial and lat-
eral surfaces (Facies medialis et lat-
eralis) are united at the upper part
with the bars and sole, but are free
below and form the central wall of
the deep collateral sulci (Sulci para-
cuneati), which are bounded out-
wardly by the bars. The base (Basis
cunei) is depressed centrally and
prominent at the sides, where it
unites with the angles of the wall;
the junction here is covered by the
expanded periople and constitutes
the bulb of the hoof (Pulvinus digi-
talis). The apex (Apex cunei) oc-
cupies the central angle of the con-
cave border of the sole, and forms a
blunt, round prominence a little in
front of the middle of the ground sur-
face of the hoof.

Structure of the Hoof. — The hoof
is composed of epithelial cells which
are more or less completely keratin-
ized except in its deepest part, the
stratum germinativum ; here the cells
have not undergone cornification, and

by their proliferation maintain the growth of the hoof. The cells are in part
arranged to form tubes (Cylindri cornei) which are united by intertubular epi-
thelium, and enclose medullary
cells and air-spaces. The wall
may be regarded as consisting of
three layers. The external layer
consists of the periople and the
stratum tectorium. The periople
is composed of soft, non-pig-
mented, tubular horn, and be-
comes white w^hen the hoof is
soaked in water. It is contin-
uous with the epidermis of the
skin above, and extends down-
ward a variable distance. Usually
it forms a distinct band somewhat
less than an inch wide, except at
the heels, where it is much wider,
and caps the angle of inflection of
the wall. The stratum tectorium
is a thin layer of horny scales
which gives the outer surface of the wall below the periople its smooth, glossy ap-
pearance. The middle layer (Stratum medium) forms the bulk of the wall, and

Fig. 714. — SErriON of Hoof of Horse.
The section is cut just above the ridges of the frog and
bars and parallel with the ground surface. 1, Wall; 2, sole;
S, spine of frog or "frog-stay"; .4, ridge formed by junction
of frog and bar; 5, central furrow over apex of frog; 6,
huninEe of wall; 7, laminae of bar.

Fig. 715. — Frontal Section of Hoof of Horse, Posterior

Part Viewed from in Front.

;, Wall; 2, sole; 3, bar; 4, frog; 5, central ridge of frog; 6,

lateral ridge formed by junction of frog and bar; 7, laminae of

bar; S, laminae of wall; 9, coronary groove; 10, periople of heel.

892 THE SENSE ORGANS AND SKIN OF THE HORSE

is the densest part of the hoof. Its horn tubes run in a straight direction from the
coronary to the basal border. In dark hoofs it is pigmented except in its deep part.
The laminar layer (Stratum lamellatum) is internal; it consists of the homy
laminae (Lamellae cornese), and is non-pigmented. The primary laminae are narrow
and thin at their origin at the lower margin of the coronary groove, but become %\'ider
and thicker distally. At the junction of the wall and sole they are united by inter-
laminar horn to form the white line. Only the central part of the laminae becomes
fully keratinized. They are composed of non-tubular horn in the normal state.

The sole consists of tubular and intertubular horn. The tubes run parallel
with those of the wall and vary much in size.

The frog is composed of relatively soft horn, which is much more elastic than
that of the wall or sole, and is not fully keratinized. The horn tubes in it are slightly
flexuous.

The hoof is non-vascular and receives its nutrition from the corium. It is
also destitute of nerves.

THE CORIUM OF THE HOOF

The corium of the hoof or pododerm (Corium ungulae) is the specially modified
and highly vascular part of the corium of the common integument which furnishes
nutrition to the hoof. It is convenient to divide it into five parts which nourish
corresponding parts of the hoof.^

1. The perioplic corium or ring (Corium limitans) is a band 5 to 6 mm. in
width which lies in a groove between the periople and the coronary border of
the wall. It is continuous above with the corium of the skin, and is marked off by
a groove from the coronary corium. At the heels it widens and blends with the
corium of the frog. It bears very fine, short papillae which curve downward and
are received in depressions of the periople, to which it supplies nutrition.

2. The coronary corium (Corium coronarium) is the thick part of the corium
which occupies the coronary groove, and furnishes nutrition to the bulk of the wall.
It diminishes in width and thickness posteriorly, and along the upper border of the
bar it is not clearly defined from the corium of the frog. The convex superficial
surface is thickly covered with filiform papillae 4 to 6 mm. in length, which are re-
ceived into the funnel-like openings of the coronary groove. At the heels and along
the bars the papillae are arranged in rows, separated by fine furrows. The deep
surface is attached to the extensor tendon and the cartilages of the third phalanx
by an abundant subcutis which contains many elastic fibers and a rich venous
plexus.

3. The laminar corium (Corium lamellatum) bears primary and secondary
laminae which are interleaved with the horny laminae of the wall and bars in the
natural state.^ It is attached to the dorsal surface of the third phalanx by a modi-
fied periosteum (Stratum periosteale) which contains a close-meshed network of
vessels, and to the lower part of the cartilages by a subcutis which contains a rich
venous plexus. The laminae are small at their origin above, become wider below,
and end in several papillae 4 to 5 mm. in length. They supply nutrition to the horny
laminae and to the interlaminar horn of the white line.

4. The coriimi of the sole (Corium soleare) — also termed the sensitive sole —
corresponds to the horny sole, to which it supplies nutrition. It is often more or
less pigmented and bears long papillae, which are specially large along the convex

1 In some veterinary works the statement is made that the various parts of the corium "se-
crete" corresponding parts of the hoof. The statement is, of course, hidicrous, as the relationship
here, both anatomically and physiologically, is the same as in the case of the corium and epidermis
of the skin. Hence the terms " keratogenous membrane" and "matrix" should be dropped.

'^The laminae of the corium are commonly termed "sensitive" laminae to distinguish them
from the "horny" laminae, which are, of course, insensitive.

THE CORIUM OF THE HOOF

893

border and at the angles. Centrally it is continuous with the corium of the frog
and bars. The deep surface is attached to the sole surface of the third phalanx
by a modified and highly vascular periosteum.

Cut edge of skin
Corium of periople
Coronary corium
Laminar corium ■'

Cartilage of third
phalanx
Position of
navicular bursa
Position of
navicular bone

*■ — ' Outline of hoof

Fig. 716. — Later.^l View of Foot of Horse After Removal of Hoof and Part of Skin. (After Schmaltz, Atlas

d. Anat. d. Pferdes.)
Dotted lines in front of navicular bone indicate position of coffin joint.

5. The corium of the frog (Corium cuneatum) — also called the sensitive frog —
is moulded on the deep surface of the frog and bears small papilljE. Its deep face is

Periople of heel or bulb

Angle of wall
Angle of sole

Perioplic corium
Coronary corium

Laminar corium

Corium of frog
Position of navicular bone

Corium of sole

Position of insertion of
deep flexor tendon

White line

Basal border of wall

Fig. 717. — Ground Surface of Foot of Horse After Removal of Half of Hoof to Show Corium. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)

blended with the digital cushion. The germinal cells of the frog derive their
nutrition from this part of the corium.

894

THE SENSE ORGANS AND SKIN OF THE HORSE

The digital cushion (Torus digitahs) is a wedge-shaped mass whicn overlies the
frog. It presents for description four surfaces, a base, and an apex.^ Its deep
surface faces upward and forward and is connected with the distal fibrous sheath of
the deep flexor tendon. The superficial surface, covered by the corium of the frog,
is moulded on the upper face of the frog. The sides are related chiefly to the
cartilages of the third phalanx; distally the cushion is closely attached to the
cartilages, but higher up a rich venous plexus intervenes. The base, situated
posteriorly, is partly subcutaneous, and is divided by a central depression into two
rounded prominences termed the bulbs of the cushion. The apex lies below and
is adherent to the terminal part of the deep flexor tendon. The cushion is poorly
supplied with vessels. It consists of a feltwork of fibrous trabeculse and elastic
fibers, in the meshes of which are masses of fat. The bulbs are soft and loose in

Coronary
Wall corium

Extensor tendon

Collateral ligament

Fig. 718. — Section op Digit of Horse at Coronary Border op Hoof.
1, Extenso? process of third phalanx; 2, distal end of second phalanx; 3, distal sesamoid or navicular bone; 4,
deep flexor tendon; 5, digital cushion; 6, cartilage ©f third phalanx; 7, 7, cavity of coffin joint; 8, podotrochlear or
navicular bursa; 9, digital vessels; 10, digital nerve.

texture and contain a relatively large amount of fat, but toward the apex the cushion
becomes denser and more purely white fibrous in structure. Branched coil glands
occur chiefly in the part of the cushion which overlies the central ridge of the frog.
Their ducts pursue a slightly flexuous course through the corium and pass in a spiral
manner through the frog. Their secretion contains fat.

Vessels and Nerves.^ — The corium is richly supplied with blood by the digital
arteries. The veins are valveless, and form remarkable plexuses which communi-
cate freely with each other and are drained by the digital veins. The lymph vessels
form subpapillary plexuses in the corium of the sole and frog, and a wider-meshed
plexus at the base of the digital cushion. A lymph vessel lies in the attached edge
of each of the laminae. The nerves are branches of the digital nerves; some fibers
end in lamellar corpuscles and end-bulbs.

* Ths cushion is to be regarded as a special modification of the subcutaneous tissue, bearing
on its superficial face the corium of the frog. It is an important factor in diminishing concussion.

THE ERGOT AND CHESTNUT THE ORGAN OF TASTE 895

The Ergot and Chestnut

The ergot is a small mass of horn which is situated in the tuft of hair at the
flexion surface of the fetlock. It is commonly regarded as the vestige of the second
and fourth digits of extinct equidse, since it is absent in cases in which these
digits are developed. A small fibrous band, 3 to 5 mm. in width, extends downward
and slightly forward from the fibrous basis of the ergot on each side, crosses over the
digital vessels and nerves very obliquely, and blends below with the digital fascia
and the digital cushion. It is known as the ligament or tendon of the ergot (Fig.
572).

The term chestnut is applied to the masses of horn which occur on the medial
surface of the forearm, about a handbreadth above the carpus, and on the distal
part of the medial face of the tarsus. They have an elongated oval form and are
flattened. They are regarded usually as vestiges of the first digit. That of the
hind limb is absent in the donkey and very small in the mule.

These horny excrescences are quite variable in form and size and are correlated with the fine-
ness or coarseness of the integument in general. The supracarpal chestnut is about l}<2 to 2}^
inches long, oval in outline, the proximal end being pointed; it overlies the flexor carpi radialis at
a quite variable distance above the carpus, and hence should not be used as a surgical landmark.
The tarsal chestnut lies at a point behind the lower part of the medial Ugament of the hock. When
well developed it is about 2 to 2}^ inches long, broad below and produced above to form a long
pointed end, with a short blunt anterior process. They are composed of horn somewhat like that
of the frog.

Organ of Smell

The peripheral part of the olfactory apparatus or organ of smell (Organon
olfactus) is that part of the nasal mucous membrane which was referred to in the
description of the nasal cavity as the olfactory region; this (Regio olfactoria) is
limited to the ethmoturbinates and the adjacent part of the dorsal turbinate and
the septum nasi, in which the fibers of the olfactory nerve ramify. It is distin-
guished by its yellow-brown color, thickness, and softness. It contains character-
istic tubular olfactory glands, which are lined by a single layer of pigmented cells,
and a neuro-epithelium, the olfactory cells, the central processes of which extend
as non-meduUated fibers to the olfactory bulb.

The epithelium is non-ciliated and is covered by a structureless hmiting layer. It consists
essentially of three kinds of cells, supporting, basal, and olfactory. The supporting cells are of
long columnar form above and contain pigment granules; below they taper and often branch,
and their central processes unite with those of adjacent cells to form a protoplasmic network.
The basal cells are branched and lie on a basement membrane. The olfactory cells are situated
between the supporting cells; they have the form of long narrow rods, with an enlarged lower
part which is occupied by the nucleus. The peripheral end pierces the limiting membrane and
bears a tuft of fine, hair-Uke ciUa (olfactory hairs). A central process extends from the nucleated
pole of the cell to the olfactory bulb as a non-medullated oKactory nerve-fiber.

The vomero-nasal organ (Fig. 452) lies along each side of the anterior part
of the lower border of the septum nasi. It communicates with the nasal cavity
through the naso-palatine canal. It consists of a tube of hyaline cartilage lined
with mucous membrane; a small part of the latter along the medial side is olfactory
in character.

The Organ of Taste

The peripheral part of the gustatory apparatus (Organon gustus) is formed by
the microscopic taste buds (Calyculi gustatorii), which occur especially in the foliate,
fungiform, and vallate papillae, in the free edge and anterior pillars of the soft
palate, and the oral surface of the epiglottis. The taste buds are ovoid masses.

896 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX

which occupy corresponding recesses in the ordinary epithehum; each presents a
minute opening, the gustatory pore. The buds consist of fusiform supporting cells
grouped around central gustatory cells. The latter are long and narrow; the
peripheral end of each bears a small filament, the gustatory hair, which projects at
the gustatory pore; the central end is produced to form a fine process which is often
branched. The taste buds are innervated by fibers of the glosso-pharyngeal nerve
and the lingual branch of the trigeminus.

Upper eyelid

THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX

THE EYE
The eyelids are thick, prominent, and less pliable than those of the horse.

The lower lid bears a considerable number of cilia, which are, however, finer than

those of the upper lid. The tarsal
glands are more deeply embedded
./ -;«.#ipiv. and therefore not so evident. The

conjunctiva of the lower lid presents
folds or ridges, and one or two promi-
nences which contain numerous leuko-
cytes; the conjunctival epithelium is
transitional in type. The superficial
part of the cartilage of the third eye-
lid is leaf or shovel-shaped and thicker
than in the horse; the edge bears a
narrower process, on which there is a
transverse bar, giving the arrange-
ment some resemblance to an anchor.
The gland of the third eyelid is very
large — an inch or more in length —
and may be divided into two parts.
The deep part is pink and consists of
loose lobules, but the much larger
superficial part is more compact.
There are two large and several

smaller excretory ducts. The subconjunctival tissue of the third eyelid contains

lymph nodules, which are specially

numerous on the bulbar side.

The lacrimal gland is thick and

distinctly lobulated. It is more or less

clearly divided into a thick upper and

a thinner lower part (Glandula lacri-

malis dorsalis, ventralis). There are

six to eight larger excretory ducts and

several smaller ones. The naso-lacri-

mal duct is shorter than in the horse,

and is almost straight. Its terminal

part is enclosed between two plates

of cartilage, and it opens near the

nostril on the lateral wall of the vesti-
bule of the nasal cavity; the orifice is

placed on the medial side of the alar fold of the ventral turbinate, and is therefore

not easily found.

Fig. 719.— Eye of Ox.

Lower eyelid

(After Ellenberger-Baum, Anat. fiir
Kiinstler.)

Conjunctiva

biilbi

Sclera

Third eyelid

r^"/

Caruncula \^

^«"^\

lacrimalis

\»J'

^K^^^wBk_\

^no

Cornea

^^^

Pupil

Fig. 720.-

■Left

Eyeball of Ox

in situ.

19, Orbital fat.

(After

Ellenberger-Baum, Anat. fur

Kunstler.)

THE EAR 897

The eyeball resembles that of the horse in shape, but is considerably smaller.^
The sclera is often more or less pigmented; where non-pigmented, it may have
a bluish tinge. The point of entrance of the optic nerve is about 2 mm. lateral
to the vertical meridian, and about 7 mm. below the horizontal meridian.^ The
cornea is thicker than that of the horse. The tapetum of the chorioid is extensive
at the outer side, but is a narrow strip medially. It has a metallic luster, shading
from a brilliant green to a deep blue; centrally it has a reddish sheen. The iris is
usually very dark colored. The granula form a continuous series of small nodules
along the upper margin of the pupil and are most prominent centrally; they are
very small on the lower margin. The optic papilla is much smaller and is not so
sharply defined on ophthalmoscopic examination as that of the horse. Several
relatively large retinal arteries radiate from the center of the papilla to the periphery
of the retina. They may be seen to wind spirally around the veins, which are very
large. The vitreous body is less fluid than that of the horse.

The arteria centralis retinae arises from a posterior ciliary artery and divides close to the
optic papilla into three branches usually; the upper one is larger than the two lateral branches.
The retina is more vascular than that of the horse; it has a round area centraUs at the medial side,
which is continued outward by a narrow strip of a similar histological structure.

THE EAR
The external ear is inclined outward. The middle part is much wider and less
curved than in the horse. The apex is also wide and does not curve forward.
The lower part of the anterior border is bent backward and bears long hairs. The
posterior border is thin and is regularly convex, except below, where it is indented.
The opening is wide and the concave surface presents four ridges; the convex
surface presents corresponding depressions. The styloid process of the conchal
cartilage is short and blunt. The edges of the annular cartilage are in contact at
the medial side and the upper border is notched laterally. The scutiform cartilage
is a very irregular quadrilateral plate; it is situated on the lateral aspect of the
cranium, with its concave surface in contact with the fat and temporalis muscle.
The osseous external acoustic meatus is directed practically straight inward; it is
about twice as long as that of the horse, and tapers very gradually from without
inward. The chief special characters of the auricular muscles are as follows:
(1) The scutularis blends with the frontalis muscle. The interscutularis arises
from the base of the processus cornus (or the corresponding area in polled cattle)
and from the frontal crest. (2) The cervico-scutularis arises from the posterior
surface of the cranium below the frontal eminence, and receives slips from the
parieto-auricularis and cervico-auricularis superficialis. (3) The zygomatico-
auricularis and scutulo-auricularis superficialis ventralis are fused. (4) The scutulo-
auricularis superficialis dorsalis is distinct from the interscutularis; it arises from
the superficial face of the scutiform cartilage. (5) The cervico-auricularis super-
ficialis arises from the ligamentum nuchas and ends on the convex surface of the
conchal cartilage. (6) The parieto-auricularis arises from the nuchal surface of
the frontal bone, the adjacent part of the parietal bone, and the ligamentum nuchse;
it is inserted below the preceding muscle. (7) The scutulo-auricularis superficialis
accessorius arises from the superficial face of the scutiform cartilage and is inserted
by a round tendon into the anterior part of the convex surface of the conchal car-
tilage. (8) The cervico-auricularis profundus minor consists of two fasciculi: the
medial, narrow part is deep red in color, and arises from the fascia of the cervical
muscles lateral to the occipital attachment of the ligament nuchse; the lateral

1 The average transverse diameter is about 42 mm., the vertical diameter, 41 mm., and the
axis, 36 mm. The angle between the optic axes is about 119°.

2 The thickness of the sclera is about 2 mm. at the Dosterior pole, 1 mm. at the equator, and
1.2 to 1.5 mm. near the cornea.

898

THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX

wider part is pale, and arises beneath the cervico-auricularis superficiahs indirectly
from the scutiform cartilage. The two unite and are inserted into the lower aspect
of the base of the conchal cartilage. (9) The scutulo-auricularis profundus minor
arises from the temporal crest above the external acoustic meatus and is inserted
into the anterior part of the deep face of the scutiform cartilage.

The cavum t3anpani is small; it communicates ventrally with the air-cells of
the bulla ossea. The tympanic membrane is nearly circular and is not so oblique
as in the horse. The auditory ossicles are smaller than those of the horse; the
malleus is more curved, the body of the incus is longer, and there is a small promi-
nence on the front of the head of the stapes for the attachment of the stapedius
muscle.

The auditive or Eustachian tube is small and is only about two inches long.

The pharyngeal opening is small and is situated on the side of the fornix of the

pharynx close to the base of the cranium. There is no flap-like expansion of the

cartilage, but the medial border of the orifice is formed l^y

a fold of mucous membrane (Fig. 476).

The internal ear has essentially the same arrangement
as in the horse.

COMMON INTEGUMENT

The thickness of the skin of the ox is greater than
that of any of the other domesticated animals; in general
it is about three or four millimeters, but at the root of
the tail and the point of the hock it is about five milli-
meters and on the brisket six or seven millimeters. The
variably developed prominence at the anterior part of the
pectoral region known as the brisket consists of a fold of
skin (Plica colli ventralis longitudinalis), which contains
posteriorly a mass composed of coarse fibrous trabeculse
and fat.

The cutaneous glands are fewer and less developed
than in the horse. Except about the natural openings, at
the point of the hock, and the flexion surface of the fet-
lock, the sweat glands do not form a coil, but are enlarged
at the deep end and are variably flexuous. The sebaceous
glands are best developed about the natural openings and on the udder, l)ut there
are none on the teats. The naso-labial glands form a thick layer under the bare
skin of the muzzle. They are compound tubular glands and are lined with cubical
epithelium. The openings of their excretory ducts are easily seen.

The hairs are extremely variable in color and size in the different breeds and
in different individuals. The hair of the frontal region is often curly, especially
in the bull. There is no mane, and the long hairs of the tail occur only at the end,
where they form the ''brush" (Cirrus caudse).

The claws, four in number on each limb, cover the ends of the digits. Those
of the chief digits conform in a general way to the shape of the third phalanges,
and each may be regarded as having three surfaces. The abaxial surface is convex
from side to side, and is marked l^y ridges parallel with the coronary border. Its
anterior part is concave from edge to edge, and the angle which it forms with the
ground is about 30°. The interdigital surface is concave and grooved; it touches
the opposite claw only at its ends. The basal or ground surface consists of two
parts, viz., a slightly concave sole, which is pointed in front and widens behind, and
a prominent bulb of soft thin horn, which is continuous al)ove with the skin. The
claw may be regarded as consisting of three parts — periople, wall, and sole. The

Fig. 721. — Claws (
Volar Aspect.
Ellenberger-Baum
fiir Kiinstler.)

• Ox;

(After
Anat.

COMMON INTEGUMENT

899

periople surrounds the coronary border in the form of a flat band, which is about
half an inch wide, except at the heels, where it widens to cover the entire surface.
The wall forms most of the abaxial part of the claw and is reflected in front upon the
interdigital surface. It thins out toward the bulb or heel, which appears, as stated
above, to consist of the thin expansion of the periople. The sole occupies the angle
of inflection of the wall; it is continuous Avithout demarcation with the periople of
the bulb. The perioplic corium bears relatively long papillae. The coronary corium
is much less developed than in the horse and its papilla; are short. The laminae are
much narrower and are more numerous than in the horse; secondary laminae are
not present. The corium of the sole is not marked off behind from that of the
periople; its papillae are very small and close together. The corium of the bulbs

Lateral extensor tendon
Metacarpal bone

Metacar po-phalangeal articulation
First phalanx
Lateral extensor tendon
Common extensor tendon
Proximal inter phalangeal joint
Second phalanx _
Periople

Coronary corium

Third phalanx

Wall of hoof

Upper pouch
of metacarpo-
phalangeal
joint capsule
Superficial
[flexor tendon
Sitspinsory
liijinnent
peep flexor
tendon
Superficial
flexor tendon
Annular
ligament
Proximal
Sesamoid
Cruciate
ligament
Small claw
Annular ligament
Digital cushion
Upper pouch of capsule
of distal inter phalangeal
joint
Distal sesamoid bone

Bursa

Fig. 722. — Sagittal Sectiox of Distal Part of Forelimb of Ox.

is separated from the flexor tendon by a mass of elastic, fatty tissue, which is
analogous with the digital cushion of the horse. The papillae here are long and
often compound.

The accessory digits bear short conical horn capsules which resemble in a
general way those of the chief digits, and have a similar corium, which covers one
or two nodular vestigial phalanges. From these a fibrous band descends obliquely
on the volar aspect of each chief digit and is attached below to the distal phalanx
and sesamoid bones, sending fibers also to the elastic pad of the heel.

The horns (Cornua) enclose the horn processes of the frontal bones (except in
the polled breeds). They vary very greatly in size, form, and curvature. The root
or base of the horn (Radix cornus) has a thin edge which is continuous with the

900 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG

ordinary epidermis. It is covered bj^ a thin layer of soft horn similar to the periople
of the hoof of the horse. Near the root the horn is encircled by variable rings.
Toward the apex (Apex cornus) the thickness of the horn increases till it becomes
practically a solid mass. The horn consists mainly of tubes which are very close
together, except at the rings, where there is more intertubular horn. The corium
of the horn (Corium cornus) is united to the horn process by periosteum which is
traversed by numerous blood-vessels. The corium at the root of the horn is thick
and bears long, slender papillae; in the body of the horn it becomes thin and the
papillae are smaller, but increase in size apically. Rudimentary papillated laminae
also occur.

The skin of the sheep varies in thickness from 0.5 to 3 mm., but differs greatly
in fineness and in other respects in various breeds. In Merinos large folds
occur on the neck. Cutaneous pouches (Sinus cutis) are constantly present
in certain situations. The infraorbital or lacrimal pouch (Sinus cutaneus infra-
orbitalis) is an invagination about half an inch in depth, which is situated in front
of the medial angle of the eye. It bears scattered fine hairs, into the follicles of
which large compound sebaceous glands open; coil glands are also present. The
secretion of the glands is fatty and forms a yellow, sticky covering on the skin when
dry. The inguinal (or mammary) pouch (Sinus cutaneus inguinalis) is much more
extensive, and is situated in the inguinal region in both sexes. The skin of the
pouch bears scattered fine hairs and contains well-developed sebaceous glands and
exceedingly large coil glands. The interdigital pouch (Sinus cutaneus interdigi-
talis) is a peculiar tubular invagination of the integument which opens at the
anterior part of the interdigital cleft. On sagittal section it appears as a bent tube,
an inch or more (ca. 2.5-3 cm.) in length, and about a fourth of an inch (ca. 6-
7 mm.) in diameter. The pouch extends downward and backward, and then
curves sharply upward between the distal ends of the first phalanges. Its
deep blind end is somewhat ampullate. The subcutis forms a capsule around it.
The skin of the pouch is thin and pale; it bears fine colorless hairs, the follicles of
which receive the secretion of several sebaceous glands. The coil glands here are
compound and very large; they open into the hair-follicles or directly into the pouch.
The secretion of the glands is a colorless fatty substance. The skin is covered in
great part by wool, which is similar in structure to hair, but is finer, curly, and
usually contains no medullary cells. The follicles of the wool are curved, and are
arranged more or less distinctly in groups of ten or a dozen, several of which open
in common on the surface. A considerable part of the face and the limbs is covered
with short, stiff hair, and long hairs occur more or less interspersed among the wool.
The claws resemble those of the ox. The horns, when present, are more or less
prismatic, distinctly ringed, and vary in length and curvature in different breeds.
Their structure is similar to those of the ox.

The olfactory and gustatory organs resemble in general those of the horse.

THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG

THE EYE

The posterior part of the orbital margin is formed chiefly by the orbital liga-
ment, which extends from the extremely short supraorbital process to the small
eminence at the junction of the malar and the zygomatic process of the temporal.

Cilia occur only on the upper eyelid. The medial canthus is prolonged by a
groove on the infraorbital region. The tarsal glands are very short and curved.
The conjunctival epithelium is of the transitional type, with many goblet cells.

THE EAR THE SKIN AND APPENDAGES 901

The deep part of the cartilage of the third eyelid is broad and spoon-like, the
superficial part somewhat anchor-shaped. In addition to the gland which sur-
rounds the deep part of the cartilage, there is a deeper one, often termed the gland
of Harder (Glandula palpebrae tertise profunda), which is surrounded by a distinct
capsule and a blood-sinus. This gland is brownish or yellowish-gray in color,
elliptical in outline, and about an inch (2-3 cm.) in length. It is situated deeply
below the attachment of the ventral oblique muscle.

The caruncula lacrimalis has the form of a ridge; it divides into two branches
which join the skin at the medial commissure. It is red in color and contains
numerous large coil glands.

The lacrimal gland is mucous in type. There is no lacrimal sac, and the two
lacrimal ducts pass through separate openings at the infraorbital margin. The
naso-lacrimal duct is usually short and opens into the ventral nasal meatus at the
posterior end of the ventral turbinate.^ The eyeball appears small, partly on
account of the narrowness of the palpebral opening; it closely approaches the spheri-
cal form. The cornea, although in reality almost circular, appears oval when viewed
from the front, the medial end being much the broader. The chorioid has no
tapetum. The iris is usually dark grayish-brown or yellowish-brown, but sometimes
has a blue tinge. The pupil is a transverse oval in ordinary light, l)ut almost
circular when dilated; granula are not present. The optic papilla is nearer the
posterior pole than in the horse and ox, and has a distinct central artery and vein.

THE EAR
The external ear differs considerably in size, thickness, and position. It may
be carried vertically, inclined inward, or hang downward. It is relatively wide and
is little curved except at the base. The concave surface presents several cutaneous
ridges which correspond approximately with the long axis of the ear. The anterior
border of the concha is strongly recurved in its lower part, and divides into two
branches, one of which passes almost horizontally backward in the cavum conchse,
while the other continues the general direction of the border. The posterior border
is slightly concave above, strongly convex below, forming a prominence somewhat
analogous to the lobule of the human ear. The osseous external acoustic meatus
is very long and is directed ventro-medially. The tympanic membrane is almost
circular. The tympanic cavity proper is small, but it is continuous with the numer-
ous cells of the large bulla ossea. The auditive or Eustachian tube is short; its
pharyngeal opening is situated in the upper part of the wall of the pharynx, imme-
diately behind the posterior nares. It is somewhat infundibular, and is bounded
medially by a thick fold of mucous membrane (Torus tubarius).

THE SKIN AND APPENDAGES

The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually accu-
mulates in the subcutis and forms a distinct and often extremely thick panniculus
adiposus over the greater part of the body. The sebaceous glands are in general
small and much fewer than in the other animals. The sweat glands, on the other
hand, are large, yellow or brownish in color, and are in many places visible to the
naked eye. At the medial side of the carpus there are small cutaneous diverticula,
the so-called carpal glands, into which numerous compound coil glands open. Large
glands also occur in the skin of the digits and interdigital space. Compound
tubular glands are present in the skin of the snout. Large sebaceous and sweat

1 The lower punctum lacrimale is frequently absent and the corresponding duct therefore
blind. There is often a duct or its remnant which opens below the ventral turbinate fold, but is
not connected behind with the functional duct.

902 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG

glands are found at the entrance to the preputial diverticulum. The hairs are
sparsely scattered in improved breeds — indeed, in some cases the skin is almost
bare. The long hairs or bristles are arranged usually in groups of three. They
are most developed on the neck and back. The bristles about the snout and the
chin are sinus hairs.

The claws and their corium resemble those of the ox, but the bulbs are more
prominent and form a greater part of the ground surface; they are also better
defined from the sole, which is small. The claws of the accessory digits are more
developed and their parts better differentiated than those of the ox.

The olfactory region is extensive in correlation with the large size of the
olfactory bulbs; the mucous membrane here is brown in color.

THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG

THE EYE

The posterior margin of the orbit is formed by the orbital ligament, as in the
pig. The orbital axes if produced backward would include an angle of about 79",
the optic axes an angle of about 92.5° (Koschel). The lower eyelid has no distinct
cilia. The medial angle is wide, the lacus lacrimalis shallow, and the caruncula
lacrimalis small and yellowish-brown. The conjunctival epithelium is cylindrical,
with many goblet cells. The gland which surrounds the deep end of the cartilage
of the third eyelid is large and pink; it is a mixed gland.

The lacrimal gland is flat and lies chiefly under the orbital ligament. It is
pink in color and mixed in structure. The naso-lacrimal duct is variable in arrange-
ment and may differ on the two sides. It may open into the ventral meatus im-
mediately after its emergence from the osseous lacrimal canal; thence it continues
forward and opens on the lateral wall of the nostril below the ventral turbinate fold.

The eyeball is almost spherical and is relatively large, especially in the small
breeds. The sclera is thick in the ciliary region, where it contains a well-developed
venous plexus; in the vicinity of the equator it is thin, and the chorioid shows
through it. The cornea is almost circular. The chorioid is richly pigmented,
and presents a well-defined tapetum cellulosum; this is somewhat triangular in
outline and has a metallic luster. Its color is often golden green, shading to blue
peripherally, but the blue tone may predominate, and in other cases it is mainly
golden yellow or reddish-yellow. The appearance is due to several layers of peculiar
flattened polygonal cells. The ciliary muscle is more developed than in the other
species. The iris is commonly light or yellow brown, but not rarely has a blue
tinge; the color often differs in the two eyes. The pupil is round; its edge is
either smooth or bears minute round prominences. The retina presents a round
area centralis lateral to the optic papilla. The latter is variable in outline; com-
monly it has the form of a triangle with the angles rounded off, but is often round
or oval. Branches of the central vessels of the retina radiate from the middle of
the papilla. The surfaces of the lens are not so strongly curved as in the other
domestic animals, and there is little difference in the radius of curvature of the two
surfaces.

THE EAR

The external ear differs greatly in size and form in the various breeds; in most
it is relatively wide and thin and the greater part of it hangs down over the opening.

THE SKIN AND APPENDAGES 903

The anterior border has a prominence (Spina helicis) at its lower part, and below
this it divides into two branches (Crura helicis). One of these continues down to a
blunt point, while the other turns into the cavity of the concha. The posterior
border forms a pouch below its middle, and is thick and rounded in its basal pan.
Here the conchal cartilage bears a pointed process (Processus uncinatus), which pro-
jects upward and backward. The outer wall of the cavum conchae is supported
by a quadrilateral plate (Tragus) above and a semi-annular cartilage below. The
concave surface presents several cutaneous folds, and in the cavum conchae there
are ridges and irregular prominences. There are long hairs on the borders, apex,
and the folds of the concave surface, but the skin of the cavum conchae is bare.
The annular cartilage is a complete ring. The osseous external acoustic meatus
is wide and extremely short.

The auricular muscles are thin. The scutularis is extensive and is divisible
into interscutularis and fronto-scutularis. It partly covers the occipitalis muscle,
which is oval and unpaired and ends in the fascia of the frontal region. The
scutulo-auriculares superficiales, ventralis et accessorius, and the cervico-scutularis
are not differentiated as separate muscles. The cervico-auricularis superficialis
and the parieto-auricularis both bifurcate and are inserted into the base of the
concha and the scutiform cartilage. The parotido-auricularis is narrow and almost
long enough to meet the opposite muscle. The tragicus consists of two parts; of
these, the lateral one is long and arises fron the border of the mandible above the
angular process. The helicis and the verticalis auriculae are well developed.

The tympanic cavity is very roomy, extending ventrally into the large but
simple cavity of the bulla ossea. The tympanic membrane is extensive and oval.
The promontory is very pronounced. The auditory ossicles are large. The
auditive or Eustachian tube is short, and has a fibrous lateral lamina. Its pharyngeal
opening is an oblique slit situated on the lateral wall of the naso-pharyngeal meatus,
and is margined medially by a thick mucous fold. The cochlea has three and a
half turns and is more sharply pointed than in the ungulates.

THE SKIN AND APPENDAGES

The skin varies greatly in thickness in different breeds. It is remarkably
loose on the dorsal aspect of the neck and trunk, where it can be raised in extensive
folds. The coat is also subject to extreme variation in length, thickness, color, etc.
The hairs are arranged in groups of three to a large extent. The sebaceous glands
are best developed in the short and rough haired breeds. They are largest and
most numerous at the lips, anus, dorsal surface of the trunk, and sternal region.
The sweat glands are relatively better developed in the long and fine haired breeds.
The largest are found in the digital pads. Coil glands occur in the skin of the
perineum and the paranal pouches. In the muzzle glands are absent or very
scanty.^

On the flexion surface of the carpus and digit there are hairless, cushion-like
pads. The carpal pad (Torus carpalis) is situated medial and distal to the accessory
carpal bone. The metacarpal and metatarsal pads (Torus metacarpalis, meta-
tarsalis) are the largest and are situated behind the distal ends of the metacarpal
or metatarsal bones and the greater part of the first phalanges. They are somewhat
heart-shaped, with two unequal lateral lobes, and the apex distal. The metapodio-
phalangeal joints rest on them when the paw supports the weight. The digital
pads (Toruli digitales) are oval and are much smaller; they similarly support the
second digital joints. That of the first digit is small on the forelimb, and usually
absent from the hind limb. Each receives two suspensory bands from the tubercles

' Trautmann has shown that the secretion which appears on the muzzle comes from the
lateral nasal gland, which is well developed.

904

THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG

at the distal end of the corresponding second phalanx. The pads have a basis of
fibro-elastic tissue and fat, which is intimately adherent to the skin and is connected
by trabeculae with the bones and tendons. The epidermis is thick and largely
keratinized, and is studded with numerous rounded papillae which are readily seen

Fig. 723. — Pads of Right Fore Paw of Dog. Fig. 724. — Pads of Right Hind Paw of Dog.

1-5, Digital pads; 6, 6, metacarpal and metatarsal pads; 7, carpal pad.

with the naked eye. The corium has large papillae, and contains sweat glands and
lamellar corpuscles.

The claws (Ungues) correspond in form to the ungual part of the distal pha-
langes, which they enclose. The horn of the claw consists of a body or wall and a
sole. The former is strongly curved in both directions, and is compressed laterally.

Fig. 725. — Half op Claw of Dog; Inner Surface.
Coronary part; 6, volar part of wall; c, sole; d, section of c; e, section of wall; i, coronary border;
3, dorsal surface. (From Leisering's Atlas.)

Its coronary border fits into the depression under the bony collar or ungual crest
of the third phalanx and is covered by skin. The lateral borders converge and
enclose the sole anteriorly. The corium presents a coronary part which bears
papillae only near the coronary border. On the dorsal surface it is thickened to
form a ridge, and the corresponding part of the horny covering is thick and main-

OLFACTORY AND GUSTATORY ORGANS 905

tains the pointed character of the claw. The coriiim of the sides of the wall bears
small laminae which converge to the corium of the sole. The latter is papillated.
When the flexor muscles are inactive, the distal phalanges and the claws are main-
tained in dorsal flexion by two elastic ligaments. These arise from the tubercles
at the proximal end of the second phalanx and converge to the dorsal aspect of the
ungual crest of the third phalanx.

OLFACTORY AND GUSTATORY ORGANS

The olfactory region lies above the lamina transversa, which separates it from
the naso-pharyngeal meatus. The mucous membrane is distinguished by its
thickness and yellow color, and is very extensive. It covers about half of the large
ethmoturbinates, and one-third to one-half of the septum nasi. The ethmotur-
binate which projects into the frontal sinus and the adjacent inner wall of the sinus
are olfactory in character. Olfactory nerve-fibers ramify in the vomero-nasal
organ.

The gustatory apparatus presents no special features of importance.

INDEX

Abdomen, lymph vessels of,

701
Abdominal aortic plexus, 833

cavity, 410, 452

inguinal ring, 290, 292

part of sympathetic system,
832

plexuses, 832

tunic, 288, 361
Abomasum, 453, 456, 474
Accessory organs, 385

pancreatic duct, 434

parotid glands, 482

spleens, 441

thyroids, 536, 553
Acetabular angle, 106, 109

fossa, 109
Acoustic meatus, external,
61, 870, 871
internal, 62, 882

process, external, 61, 74
Aditus laryngis, 406, 407, 521

oesophagi, 407
Adrenal bodies, 563, 566, 567,
569, 570

plexuses, 834
Adventitia of ductus deferens,
575

of Fallopian tubes, 599

of seminal vesicles, 578
^sthesiology, 857
Aggregated nodules of large
intestine, 431
of small intestine, 442,
487, 501
Ahd nasi, 508
Alar canal, 54, 75, 78

cartilages, 509, 537

fold, 509

notch, 184
Alimentary canal, 385
Alveolar border of premaxillaj,
65

ducts of lungs, 534

periosteum of teeth, 395

tuberosity, 64, 78
Alveoli, 71

dental, 64

of mammary glands, 605

of thyroid gland, 536
Alveus, 787

Amphiarthroses, 210, 211
Ampulla ductus deferentis,
575

of semicircular canals, 881

of uterus, 613

recti, 429
Amygdaloid nucleus, 792
Anal sacs, 502
Anastomosis of arteries, 614
Anatomy, 17

comparative, 17

Anatomy, gross, 17

macroscopic, 17

microscopic, 17

philosophical, 17

special, 17

systematic, 17, 18

topographic, 17, 18

veterinary, 17
Angiology, 614
Angle, acetabular, 106, 109

duodenal, 433

of mandible, 70, 71

of rib, 27

splenic, 433
Angular process of mandible,

195
Annular cartilage of ear, 871
Ansate fissure, 849
Antrum pyloricum, 416
Anus, 432

Aortic plexus, abdominal, 833
thoracic, 831

orifice of heart, 626

valve, 626
Aperture, posterior, of pelvis,

111
Apex of hoof, 891
Apical lobe of lung, 540, 547,

548, 551, 553
Aponeurosis, 253

of obliquus abdominis ex-
temus muscle, 288

of transversus abdominis
muscle, 291

pharyngeal, 407
Appendages of skin, 886, 901,

903
Appendix epididymidis, 573

testis, 571

ventriculi laryngis, 522
Aquaeductus cochleae, 882

vestibuli, 881
Aqueduct of cerebrum, 780
Aqueous humor, 869
Arachnoid granulations, 763
Arachnoidea, 762

cerebral, 762

spinal, 763
Arbor meduUaris, 777
Arch, distal volar, 657

hemal, 188

lumbo-costal, 287

of aorta, 629

of cricoid cartilage, 515

plantar, deep, 697, 721
distal, 678, 697, 719
proximal, 678, 679, 719

subcarpal, 657

venous, 692

zygomatic, 60, 73
Arcuate fibers, external, 773,

774

907

Arcuate fibers, internal, 774

of cerebellum, 777
Area acustica, 779
centralis retinae, 868
cribrosa, 558
parolfactoria, 788
Arteria profunda penis, 673
Arteries or artery, 614, 629,

706, 736, 744
abdominal, anterior, 635

posterior, 675, 752

subcutaneous, 675
adrenal, 563, 666
adventitia of, 615
alveolar, inferior, 647, 737,

747
anastomosis of, 614
angular, 709

of eye, 644, 710
antibrachial, volar, 749
aorta, 629, 736, 744

abdominal, 630, 661, 713,
750

ascending, 629

brachiocephalic, trunk,
631

thoracic, 630, 660, 713, 750
asternal, 635

auricular, anterior, 646, 709,
747

great, 747

posterior, 644, 709, 736
basilar, 640
bicipital, 749

brachial, 650, 707, 710, 736,
738, 744, 747

deep, 651, 710, 749

left, 632

right, 631
brachiocephalic, 631, 736,

744
bronchial, 534, 535, 660, 713,

737
broncho-cesophageal, 535,

660, 750
buccinator, 649, 710, 737
cajcal, 737, 751

lateral, 665

medial, 665
carotid, common, 635, 707,
736, 744, 746
left, 637
right, 636

external, 641, 709, 736,
747

internal, 640, 736, 747
central, of retina, 649
cerebral, anterior, 641, 747

deep, 641

middle, 641

posterior, 640
cerebrospinal, 640, 747

908

INDEX

Arteries, cervical, deep, 633,
707, 736, 745
dorsal, 745

inferior, 635, 707, 736, 746
chorioid, anterior, 641
ciliary, 649

circulus arteriosus, 641
major, 867
minor, 867
circumflex, anterior, 748,
749
of humerus, 651
external, 718
lateral, 752

of thigh, 673
of coronary cushion, 660
of scapula, 651
posterior, 710, 749
of humerus, 651
clitoridis, 717
coats of, 615

coccygeal, lateral, 672, 717
middle, 672, 717
superficial lateral, 754
ccEhac, 662, 713, 737, 750
colic, 751
dorsal, 666

middle, 666, 715, 737, 751
right, 737, 751
ventral, 665
commimicating, posterior,

640
condyloid, 639, 708, 747
coronary, 628, 630, 631, 707,

744
costo-cervical. 632
cremasteric, 674
digital, 659, 681, 739, 740,
894
common, 659, 739, 749
dorsal, 712, 719
plantar, 719
volar, 712
lateral, 719
volar, 712
medial, 719
volar, 712
plantar, 754
proper, 739, 749
volar, 712
dorsal, 632, 707, 736, 745
dorsalis penis, 717
end, 614
ethmoidal, 649
external coat, 615
facial, 642

transverse, 646, 673, 674,
709, 747
femoral, 717, 740, 752
anterior, 675, 718, 752
deep, 675, 718, 739, 752
posterior, 676, 754
first, of small colon, 666
frontal, 710
gastric, 535, 662, 750
gastro-duodenal, 662, 750
gastro-epiploic, 750, 751
left, 663
right, 662
gastro-hepatic, 737
gastro-splenic, 751
gluteal, anterior, 672, 717,
754
posterior, 672, 717

Arteries, haemorrhoidal, ante-
rior, 666

middle, 670, 754
hepatic, 438, 662, 713, 750
hypogastric, 669
ileal, 665, 737, 751
ileo-ca^co-colic, 716, 737
iliac, circumflex, 673, 752

external, 673, 717, 752

internal, 669, 717^754
iliaco-femoral, 673, 717
ilio-lumbar, 672, 717, 739,

754
incisor, 647
infraorbital, 649, 710, 737,

747
intercarotid, 640
intercostal, ■ 660, 713, 737,
750

aortic, 660
internal coat, 615
interosseous, common, 654,
711, 749

dorsal, 656, 711

recurrent, 656, 711

volar, 655, 749
intima of, 615
labial, inferior, 643, 709

superior, 643, 709
lacrimal, 649
laryngeal, 637, 707, 746
lingual, 642, 708, 736, 747
lumbar, 668, 669, 717, 738,

750
malar, 650, 710
mammary, 675, 718
masseteric, 641, 709
maxillary, external, 642, 708,
736, 747

mtemal, 646, 710, 736, 747
median, 654, 711, 738, 748
medullary, 22
meningeal, anterior, 641

middle, 648, 710, 737, 747

posterior, 639, 709, 747
mental, 647

mesenteric, anterior, 665,
715, 737, 751

posterior, 666, 716, 737,
752
metacarpal, 711, 712, 739,
749

dorsal, 657, 712

lateral volar, 657

medial volar, 657
metatarsal, 678, 719, 740,
753, 754

dorsal, 680

great, 681

plantar, deep, 753
superficial, 753
middle coat, 615
musculo-phrenic, 635
nasal, 709

dorsal, 644, 710

lateral, 643, 710
nutrient, of femur, 676

of humerus, 654

of tibia, 676
obturator, 673, 717, 718
occipital, 660, 662, 713, 737,

750
oesophageal, 660, 662, 713,

737, 750

Arteries of bladder, 562
of bone, 22
of brain, 792
of bulb, 670, 754
of clitoris, 670
of corpus callosum, 641
of digital cushion, 659
of ductus deferens, 575
of external ear, 875
of eye, 859

of Fallopian tubes, 599
of first phalanx, 65,9
of internal ear, 884
of pelvic limb, 673, 717
of penis, 582, 754 .

anterior dorsal, 675

deep, 754

dorsal, 754
of rete carpi volare, 657
of retma, 869

central, 649
of second phalanx, 659, 660
of skin, 885
of small intestine, 665
of third phalanx, 660
of thoracic limb, 650, 710
of tympanum, 878
of uterus, 601
of vagina, 602
of vascular tunic of eye, 867
omaso-abomasal, 713
ophthalmic, 710

external, 649, 747

internal, 747
ovarian, 598, 668
palatine, 737

greater, 650, 710

lesser, 650
pancreatic, 662
pancreatico-duodenal, 662,

750
parotid, 637, 736

inferior, 707

superior, 709
pericardiaco-phrenic, 635
perineal, 670, 754
periosteal, 22
peroneal, 678
pharyngeal, 642, 708, 709,

746
phrenic, 661, 713
phrenico-abdominal, 737,

751
plantar, 678, 753

lateral, 719

medial, 719
popliteal, 673, 676, 717, 740^

754
prepubic, 675
profunda penis, 717
pterygoid, 647
pudic, external, 575, 675,
717, 740, 752

internal, 669, 717, 754
pulmonary, 534, 614, 629,

736
pyloric, 662
radial, 712, 738, 749

anterior, 654

collateral, 710

distal collateral, 749

posterior, 654

proximal collateral, 749
ramus collateralis, 716

INDEX

909

Arteries, renal, 560, 666, 717,
737, 751
ruminal, 713
sacral, lateral, 670, 717
middle, 629, 717, 750
saphenous, 675, 718, 740,

753
spermatic, 573, 575, 717,
737, 751
external, 674
internal, 666
spinal, ventral, 640
splenic, 662, 715, 737, 751
structure of, 615
stylomastoid, 645
subcostal, 633, 707, 736, 745
sublingual, 642, 709
submental, 642
subscapular, 651, 710, 748
supraorbital, 649
suprascapular, 651
systemic, 614, 629
tarsal, lateral, 677, 718, 753
medial, 678, 718
perforating, 678, 719, 740
recurrent, 677
temporal, deep, 747
anterior, 648, 710
posterior, 648
superficial, 646, 709, 737,
747
terminal, 614

thoracic, external, 635, 707,
736, 746
internal, 634, 707, 736,
746
thoracico-dorsal, 651, 710
thoraco-acromial, 746
thymic, 635
thyroid, 707

anterior, 637, 746
posterior, 638, 736, 746
thyro-laryngeal, 637
tibial, anterior, 678, 719,
740, 754
posterior, 676, 719, 740,

754
recurrent, 678
tracheal, 746
tympanic, 648
ulnar, 654, 712, 738, 749
proximal collateral, 710,
749
umbilical, 670, 704, 717,

754
uterine, 754
anterior, 668
middle, 674, 717
posterior, 670, 717
utero-ovarian, 668, 717, 751
vena cava, anterior, 755
vertebral, 634, 707, 736,

745
vesical, 670
vesico-prostatic, 670
Arthrodia, 210
Arthrology, 207

comparative, 244
Articular cartilages, 208
Articulations, 207. See also

Joints.
Arvtenoid cartilages of larynx,

517, 538, 546, 550
Atlantal bursa, 213

Atlanto-occipital membrane,
dorsal, 215
ventral, 215
Atrio-ventricular bundle, 628
orifice, left, 625, 626
right, 621, 623
Atrium of heart, left, 625
right, 620

openings in, 620
ventriculi, 453, 458
Auditive tube, 878, 898
Auditory ossicles, 877

tube, osseous, 63
Auricle, 620, 870
Auricular cartilage, 871
plexus, anterior, 803
Axis of lens, 869
of orbit, 74
of pelvis. 111
optic, external, 863

Bands, longitudinal, of caecum,
424
of great colon, 428
of small colon, 429
moderator, of right ventri-
cle, 625
recto-coccygeus, 431
Bars of hoof, 887
Basal border of hoof, 888
Basilar plexus, 689

tubercles of occipital bone,
51
Basis pedunculi, 780
Bicipital groove of humerus, 89
Bicuspid valve, 626
Bifurcation of trachea, 525
Bile duct, 463, 468, 487, 490,
501
common, 476
Bladder, 415, 554, 561, 566,
569, 570
fixation of, 561
lateral ligament of, 414
middle ligament of, 414
structure of, 562
Blind sacs of rumen, 454
Blood-vascular system, 614,

617, 705
Blood-vessels, 614
Body, ciliary, 865

geniculate, medial, 781, 835,

847
mammillary, 769, 782, 847
pineal, 781, 835
pituitary, 769, 780, 782, 835,

847
restiform, 773
vitreous, 869, 897
Bone or bones, acetabulum,
109, 152, 181, 202
acromion, 146, 197
arteries, 22
atlas, 35, 162, 184
auditory, 877
axis, 36, 163, 184
basihyoid, 72
breast-, 28

carpal, 29, 93, 98, 148, 160,
179, 200
accessory, 94
first, 95

Bone, carpal, fourth, 96

intermediate, 94

radial, 94

second, 95

third, 96

ulnar, 94
carpus, 29
cartilage, 23

chemical composition, 24
chevron, 188
clavicle, 29, 197
collar-, 29

compact substance, 21
condyle, of mandible, 71
coracoid, 29

cranial, 28, 49, 131, 166, 188
descriptive terms, 25
development and growth, 23
digital, 29, 30, 31, 161
digits, 29, 30, 31, 149, 180,

201
diploe, 21
endosteum, 22
endoturbinates, 56
epihyoids, 73
ethmoid, 54, 134, 157, 170,

191
ethmo-turbinates, 55
facial, 28, 63, 170, 191
femur, 31, 112, 152, 160

182, 203
fibula,31, 117, 154, 160, 183,

204
fibular tarsal, 120, 155
flat, 20
frontal, 59, 135, 157, 168,

189
gelatinous marrow, 22
hip, 31
hock, 118
humerus, 29, 88, 146, 176,

198
hyoid. 72, 140, 173, 195
ilium, 31, 105,151, 160,180,

200
incus, 877
innominate, 30, 105, 160,

180
interparietal, 56, 134, 167,

189
irregular, 20
ischium, 31, 107, 151, 160,

181, 202
keratohyoid, 72
knee, 29
knee-cap, 31
lacrimal, 68, 139, 159, 172,

194
lenticulare, 877
long, 20

lymph-vessels, 22
malar, 68, 139, 194, 159, 172
malleus, 877
mandible, 70, 139, 159, 172,

194
marrow, 21, 22

spaces, 21
maxilla, 63, 137, 158, 170,
191

inferior, 70
maxillo-turbinal, 69
medullary arteries, 22

cavity, 20, 21
membrane, 23

910

INDEX

Bone, mesosternum, 28

Bone, ribs, floating, 27

Bone, vertebrae, joints of, 244

metacarpal, 29, 30, 98,

149,

head, 27

hgaments of, 211, 244

180, 200

intercostal spaces, 27

lumbar, 25, 39, 128, 156,

large, 98, 160

lateral surface, 27

164, 187

small, 99, 160

medial surface, 27

mammillary processes, 26

third, 98

neck, 27

movable, 25

metasternum, 28

posterior borders, 27

notches, 26

metatarsal, 31, 123,

161,

shaft, 27

ossification of, 26

184, 205

sternal, 27, 45

sacral, 25, 41, 156

fom-th, 124

extremity, 27

spinous process, 26

large, 123, 155

tubercle, 27

thoracic, 25. 37-39, 127,

lateral, 124

vertebral extremity, 27

156, 163, 186

medial, 124

sacrum, 41, 129, 156, 164,

transverse processes, 26

second, 124

187

true, 25

small, 124, 155

scapula, 29, 86, 145, 176,

ventral spine, 26

third, 123

160, 197

vessels, 21, 22

nasal, 67, 139, 171, 194

sesamoid, 30, 104, 125, 151,

vomer, 70, 139, 159, 172,

naso-turbinal, 69

156, 160, 180, 201, 203,

194

navicular, 105

204

yellow marrow, 22

nerves, 21, 22

distal, 30

zygomatic, 68

number, 20

proximal, 30

Brachial plexus, 814, 840, 846,

occipital, 49, 131, 157,

166,

short, 20

853

188

shoulder-blade, 29

Brachycephalic skull, 195

condyle, 50, 78, 79
development, 52

sinuses, 21

Brain, 768, 834, 843, 847

sphenoid, 52, 132, 157, 170,

blood-vessels of, 792

of arm, 29

190

Bronchi, 525, 534, 540, 546,

of cranium, 131

spongy substance, 21

550

of forearm, 29, 63, 137

158

stapes, 877, 878

interlobular, 534

of leg, 31

sternum, 28, 48, 131, 157,

structure of, 534

of manus, 29

166, 188

Bronchial branches of lungs,

of pelvic limb, 30, 105,

151,

structure, 21

534

160, 180, 202

stylohyoids, 73

Bronchioles, lobular, 534

of skull, 28, 49, 73, 173,

188,

tarsal,31, 118, 155, 161,183,

respiratory, 534

195

205

Buds, taste, 895

of thoracic limb, 29, 86,

145,

central, 121, 155

Bulb of hair, 886

160, 176, 197

fibular, 120, 155

of urethra, 581, 585, 593,

of thorax, 28, 49

first, 122, 155

595

ossa cordis, 705

fourth, 123, 155

olfactory, 769, 771, 787, 838,

palatine, 66, 138, 159,

171,

second, 122, 155

844, 850

193

third, 122, 155

Bulbar conjunctiva, 859

parietal, 57, 134, 157,

167,

tibial, 120, 155

Bulbus aorta?, 629

189

temporal, 60, 137, 158, 169,

glandis of penis, 594

patella, 31, 118, 155,

161,

189

vestibuli, 603

183, 204

condyle of, 60

Bulla, lacrimal, 139

pelvis, 110

thigh, 31

ossea, 63

periosteal arteries, 22

thorax, 49, 131, 166, 188

Bundle, atrio-ventricular, 628

periosteum, 21

thyrohyoids, 72

Bursa, atlantal, 213

phalanges, 30, 100, 125,

149,

tibia, 31, 114, 153, 160, 182,

bicipital, 302

150, 156, 160, 180,

184,

203

intertuberal, of biceps bra-

200

condyles of, 116

chii, 302

first, 100

tibial tarsal, 120, 155

navicular, of deep digital

second, 30, 102

tissue, 21

flexor, 316

third, 30, 102

turbinate, 68, 139, 159, 172,

of biceps femoris, 323

physical properties, 24

545

. of common digital extensor,

pneumatic, 21

dorsal, 194

307

premaxilla, 65, 138,

159,

ventral, 194

of gastrocnemius, 338

170, 193

ulna, 29, 92, 148, 177, 199

of lateral digital extensor,

prenasal, 172

veias of, 22

309

presternum, 28

vertebra?, 25, 33, 125, 156,

of obturator internus, 329

pterygoid, 67, 139, 159,

171,

161, 184

of rectus femoris, 329

193

accessory processes, 26

of semimembranosus muscle,

pubic, 31, 109, 151, 160,

181,

anticlinal, 44

325

202

arch, 26

of semitendmosus muscle,

radius, 29, 90, 147, 160,

177,

articular processes, 26

323

198

body, 26

of tibialis anterior, 337

red marrow, 22

cervical, 25, 34, 156, 161,

of triceps brachii muscle,

ribs, 27, 45, 130, 156,

165,

184 '

303

188

coccygeal, 25, 43, 129, 156,

ovarica, 599

angle, 27

164, 187

ovarii, 612

anterior borders, 27

diaphragmatic, 44

podotrochlearis, 316

asternal, 27, 45

false, 25

subcutaneous, 254, 884, 887

costal groove, 27

fixed, 25

of superficial digital flexor,

development, 27

foramen, 26

339

extremities, 27

hsemal arch of, 26

subfascial, 254

INDEX

911

Bursa, supraspinous, 213
synovial, 253

of infraspinatus muscle,

299
of superficial digital flexor,

339
of teres minor muscle, 299
trochanteric, 322

C^CAL impression of liver, 435
Ca;co-colic fold, 424, 428

orifice, 424
Caecum, 422, 465, 475, 487, 502
Calcarine fissure, 850
Caliber of great colon, 427
Callosal sulcus, 786
Calloso-marginal fissure, 785,

837, 844, 850
Calyces ma j ores, 565

minores, 565
Canal, alar, 54, 75, 78

alimentary, 385

carotid, 190

carpal, 306

central, of spinal cord, 766

cervical, 607

condyloid, 131

dental, superior, 65

facial, 62

femoral, 326

infraorbital, 65

inguinal, 292

lacrimal, 82
osseous, 68

mandibular, 71

of Gartner, 607

of tarsus, 123

palatine, 64

parieto-temporal, 63

petro-basilar, 190

pterygoid, 54, 67

sacral, 43

semicircular, osseous, 881

semilunar, of third phalanx,
103

spiral, of cochlea, 882

subsphenoidal, 54

supraorbital, 137

temporal, 63, 81

vertebral, 44

vidian, 54
Canine teeth, 394, 398, 448,
479, 493
deciduous, 403
Canthi of eye, 857
Capillaries, 614
Capsula adiposa, 557
Capsule, external, 792

fibrous, of adrenal bodies,
563
of kidney, 558
of liver, 438

internal, 781, 792

of kidney, 559

of lens, 870

of lymph nodule, 616

of prostate, 579

of spleen, 441
Cardia of rumen, 458

of stomach, 472, 498
Cardiac impression of lung,

531

Cardiac lobe of lung, 540, 547,
548, 551, 553

notch of lung, 533

opening of stomach, 416

plexus, 831

sphincter, 417
Cariniform cartilage, 48
Carnassial teeth, 494
Carotid canal, 190

foramen, 190

notch, 54

plexus, 804
external, 830
internal, 830
Carpal articular surface, 92

canal, 306

sheath of deep digital flexor,
315
of superficial digital flexor,
313
Carpo-metacarpal sac, 222
Cartilage, alar, 509, 537, 538

annular, of ear, 871

articular, 208

arytenoid, of larynx, 517,
538, 546, 550

auricular, 871

bones, 23

cariniform, 48

conchal, 871

costal, 27, 47

cricoid, 515, 550
of larynx, 538, 546

cuneiform, of larynx, 550

epiglottic, 516

epiphyseal, 24

interarytenoid, of larynx,
546, 550

marginal, 209

of larynx, 515

of septum nasi, 510

of third phalanx, 104

parietal, of nasal cavity,
510, 537

scutiform, 871

thyroid, 515, 538, 546, 550

xiphoid, 28, 49
Caruncle, lacrimal, 858
Caruncula sublingualis, 390,

405
Cauda equina, 764
Caudal part of sympathetic

system, 832, 856
Caudate lobe of liver, 434, 468,
488, 503

nucleus, 792

process of liver, 434
Cavernous plexus, 830, 834

sinuses, 688
Cavity, abdominal, 410, 452

articular, 209

costal, of sternum, 48

cranial, 81, 142, 159, 175,
197

glenoid, 60, 73, 78, 87

nasal, 82, 143, 159, 175, 197,
508, 537, 545, 548

of larynx, 521

of mouth, 385, 444

of rumen, 456

of tunica vaginalis, 576

of uterus, 601

omental, 442

pelvic, 152, 412, 453

Cavity, peritoneal, 411

pleural, 526

pulp, of teeth, 395

thoracic, 525, 540

tympanic, 875
Cavum tympani, 898
Cecum, 422, 465, 475, 487, 502
Cell, nerve-, 760

ethmoid, 55

gustatory, 896

olfactory, 895
Cement of teeth, 395
Center, tendinous, of dia-
phragm, 287
Central canal of spinal cord,

766
Cephalic part of sympathetic

system, 829
Cerebellar peduncles, 777
anterior, 776
middle, 776

tract, direct, 777
Cerebello-olivary fasciculus,

774
Cerebellospinal fasciculus, 775,
777
descending, 777
Cerebellum, 771, 776, 835, 843,

847
Cerebral arachnoidea, 762

dura mater, 761

hemispheres, 771, 783, 836,
843, 849

peduncles, 769, 780, 835, 843

pia mater, 763
Cerebrospinal fasciculus, 776
Cerebrum, 843
Cervical canal, 607

enlargement, 764

ganglion, anterior, 830, 842,
846, 856
middle, 847
posterior, 830, 842

part of sympathetic system,
830, 842, 847, 858

plexus, dorsal, 812

ventral, 812
Cervix uteri, 601, 606
Chambers of eye, 869
Cheek teeth, 394, 399, 400,

401, 448, 471, 480, 494
Cheeks, 444, 471, 477, 492
Chemical composition of bone,

24
Chestnut, 895
Chiasm, optic, 769, 783
Choans, 78, 512

posterior, 406
Chordae tendineae, 624
Chorioid, 865

plexuses, 763, 780, 783, 787,
792
of fourth ventricle, 773
Chyle, 615

vessels, 615
Cilia, 858, 886
Ciliary body, 865

border of iris, 866

ganglia, 829

ganglion, 796, 838

processes, 866

ring, 866
Circle, coronary, 660
Circulation, foetal, 704

912

INDEX

Circulation, pulmonary, 704
Circulatory system, 734, 742
Circulus arteriosus, 641
Cistema chyli, 697, 722, 756
Cisterns, subarachnoid, 762
Claustrum, 792
Claws, 902, 904
Cleft, \'ulvar, 603
Clinoid processes, anterior,
190
posterior, 170, 190
Clitoris, 604, 608, 610, 611, 613

prepuce of, 604
Coccygeal ganglia, 832

ganglion, 832
Cochlea, 881, 882
Cochlear duct, 883
Cceliac ganglia, 856

ganglion, 842

plexus, 832, 843, 856
CcEhaco-mesenteric ganglia,

833
Colic impression of liver, 435

mesentery, 412, 429

plexus, 856
Collateral fissure, 849

sulci of hoof, 891

vessel, 614
CoUiculus facialis, 779

seminalis, 585, 590
Collum glandis of penis, 581
Colon, 465. 475, 488, 502

great, 425

small, 429
Color of skin, 884
Columns, gray, of spinal cord,
767

of fornix, 790

renal, 558

white, of spinal cord, 767,
768
Commissure, anterior, of cere-
brum, 783

gray, of spinal cord, 766

hippocampal, 787

of nostrils, 508

of vulva, 603

optic, 769

posterior, of cerebrum, 782,
783

white, of spinal cord, 766
Compact substance of bone,

21
Comparative anatomy, 17
Concave border of hoof, 890
Conchal cartilage, 871
Condyloid canal, 131

crest, 90

fossa, 50, 78
Conical papillae of mouth, 444

of tongue, 447
Conjugate diameter of pelvis,

110, 112, 152
Conjunctiva, 859, 896

bulbar, 859

palpebral, 859
Conjunctival sac, 859
Conus arteriosus, 623

medullaris, 764, 765
Convex border of hoof, 890
Coracoid process, 88
Core, horn, 136
Corium, 884, 885

coronary, 892

Corium, laminar, 892

of hoof, 892

of sole, 892

perioplic, 892
Cornea, 864, 897
Comu, anterior, of thyroid
cartilage, 515

of nostrils, 509

posterior, of thyroid carti-
lage, 516
Comua, great, of horse, 73

middle, 73

of uterus, 600, 606

small, 72

thyroid, 72
Corona glandis of penis, 580

radiata, 792
Coronal fissure, 837, 844, 849
Coronary border of hoof, 888

circle, 660

corium, 892

groove of heart, 619
of hoof, 888

pillars of rumen, 457

plexus, 692, 831

sinus, 681, 754
opening of, 621
Coronoid fossa of humerus, 90

process of mandible, 71
Corpora quadrigemina, 780,

847
Corpus albicans s. fibrosum,
598

callosum, 784, 785, 789, 836

cavemosum, 615
of penis, 581
urethrse, 581

clitoridis, 604

luteum, 598

papillare, 885

rubrum, 598

striatum, 792

trapezoideum, 773, 847
Corpuscle, renal, 558, 559
Cortex of thymus gland, 536
Cortical substance, 777

of lymph nodule, 616
Corticopontile fibers, 776
Costal arch, 28

cartilages, 27, 47

cavities of sternum, 48

facets of thoracic vertebrae,
37, 38

groove, 27

pleura, 526
Cotyledons, uterine, 607
Cranial cavity, 81, 142, 159,
175, 197

region, 73, 78

sutures, 217
Crest, condyloid, 90

facial, 64, 68, 77

frontal, 73
external, 59

intervenous, 622

nasal, 65, 66, 82

nuchal, 51, 79

occipital, 51

parietal, 135

external, 51, 57, 73
internal, 58, 81

petrosal, 62, 81

pterygoid, 54

renal, 558, 559

Crest, sacral, lateral, 129
median, 129
semilunar, of third phalanx,

103
spheno-occipital, 53
supracondj'loid, lateral, of
femur, 112
medial, of femur, 112
temporal, 137
tibial, 116
turbinate, dorsal, 67

ventral, 64
urethral, 585
Cribriform plate of ethmoid,

54
Cricoid cartilage, 515, 550

of larynx, 538, 546
Crico-thyroid membrane, 518
Crico-tracheal membrane, 518
Crista acustica, 884
gaUi, 55, 56, 82
terminahs, 622
vestibuh, 881
Crown of tooth, 395
Cruciate fissure, 837, 844, 850
Crura fomicis, 790

of chtoris, 604
Crus laterale dextrum, 287
sinistrum, 287
mediale dextrum, 287

sinistrum, 287
of fornix, 792
penis, 581
Cryptorchism, 577
Crystalline lens, 869
Cuneiform cartilages of larynx,
550
processes, 517
Cupola, 882
Cushion, digital, 894
Cuticle, 887
Cystic duct, 468

Dartos of scrotum, 574
Deciduous teeth, 394, 403
Decussation of anterior pe-
duncles, 778

of fillet, 774

pyramidal, 773, 774
Deferential fold of testicles,

577
Deltoid tuberosity, 88
Dental alveoli, 64

canal, superior, 65

plexus, maxillary, 798
Dentine, 395
Descent of testicles, 577
Descriptive terms, 18
Diagonal fissure, 837, 844
Diameter, conjugate, of pel-
vis, 110, 112, 152

transverse, of pelvis, 110,
112, 152
Diaphragma sellae, 762
Diaphragmatic flexure, 425

line of pleural reflection, 530

lobe of lung, 540, 547, 551,
553

pleura, 526
Diarthroses, 208
Diencephalon, 781
Digestive system 385, 444,

470, 477, 491

INDEX

913

Digital cushion, 894

synovial sheath of deep
digital flexor, 316
of superficial digital
flexor, 314
Dilatator pupillse, 867
Diploe, 21

Diverticulum, cutaneous, 884
duodeni, 421
nasi, 508
pharyngeum, 482
preputial, 593
suburethral, 607
ventriculi of stomach, 483
Dolichocephalic skull, 195
Dorsum linguae, 390
Duct or ducts, alveolar, of
lungs, 534
bile, 463, 468, 487, 490, 501

common, 476
cochlear, 883
cystic, 468
excretory, 383, 578

of bulijo-urethral glands,
580
hepatic, 438
lacrimal, 860
lactiferous, 605, 609
lymphatic, 725
right, 615, 698
tracheal, 725, 756
mandibular, 405, 496
naso-lacrimal, 509, 860, 896
of bulbo-urethral glands,

585 _
of epididymis, 573
of mammary glands, 605
of testicles, 573
pancreatic, 434, 463, 487,
491, 501, 506
accessory, 434
parotid, 404, 477, 482, 492,

495
prostatic, 579, 585, 589
semicircular, membranous,

883
sublingual, 405, 496
submaxillary, 405
thoracic, 615, 697, 722, 740,

756
tracheal, 700
Ductuli aberrantes, 573
Ductus arteriosus, 629, 704
deferens, 575, 587
deferentes, 571
endolymphaticus, 883
incisivus, 387, 445, 514
reuniens, 883
sublinguales minores, 482
sublingualis major, 482
utriculo-saccularis, 882
venosus, 468, 704
Duodenal angle, 433

impression of liver, 435
Duodeno-colic fold, 429
Duodenum, 4^9, 463, 486, 500
Dura mater, 761
cerebral, 761
sinuses of, 687
spinal, 762

Ear, 870, 901, 902
external, 870, 897

Ear, internal, 881, 898

middle, 875
Ectolateral fissure, 849
Ectomarginal fissure, 785, 837,

844, 849
Ectosylvian fissure, 849
Ejaculatory orifice, 575
Elastic membrane of trachea,

525
Embryology, 17
Eminence, frontal, 136

ilio-pectineal, 109

intercondyloid, of tibia, 116
Eminentia conchae, 871

medialis, 779
Enamel of teeth, 395
Enarthrosis, 210
Encephalon, 768
End-brain, 783
Endocardium, 621, 628
Endolymph, 881
Endoskeleton, 20
Endosteum, 22
Endothelium of eye, 865
Entomarginal fissure, 785, 837,

844, 849
Epicardium, 617, 627
Epicondvle, lateral, of femur,
114
of humerus, 90

medial, of femur, 114
of humerus, 90
Epidermis, 884
Epididymis, 571, 573, 586

structure of, 572
Epidural space, 762
Epigastric zone, 411
Epiglottic cartilage, 516
Epiglottis, 538, 546, 550
Epiphyseal cartilage, 24
Epiphysis cerebri, 781
Epiploic foramen, 442, 461
Epithelium, 383

corneae, 864

of lens, 870
Equator of eye, 863

of lens, 869
Erectile tissue of urethra,

585
Ergot, 895

tendon of, 306
Eruption of teeth, 403, 450,

471, 481, 495
Esophagus, 409, 451, 472, 483,

497
Ethmoid cell, 55
Ethmoidal foramen, 53, 55, 75,
82

fossa, 55, 82

meatuses, 55, 512

sinus, 86
Eustachian tube, 878, 898
osseous, 63

pharyngeal orifices of,
406
Excretory duct, 383, 578

of bulbo-urethral glands,
580
Extensor fossa of femur, 114
Eve, 857, 896. 900, 902
Eyeball, 862, 897
Eyelashes. 886
Eyelids, 857, 896

'third, 859, 896

Facet, anterior, of larynx, 515
costal, of thoracic vertebrae,

37, 38
of tibia, 116
posterior, of larynx, 515
Facial canal. 62
crest, 64, 68, 77
nucleus, 801
tuberosity, 137
Fallopian tubes, 596, 599, 606,

609, 610, 612
False nostril, 260, 508

vocal cords, 522, 550
Falx cerebri, 761
Fascia, 254

abdominal, 287
buccal, 255
bulbi, 861
carpal, 305
coccygeal, 279
common, of leg, 318
cruris, 318
deep, 254

of abdomen, 288

of forearm, 305

of head, 255

of neck, 266

of shoulder and arm, 298

of metacarpus and digit,
306

of thigh, 317
digital, 318
endothoracic, 530
femoral, medial, 318
gluteal, 317
iliac, 317
lata, 318

lumbo-dorsal, 276
metatarsal, 318
of back, 276
of forearm, 305
of head, 255
of loins, 276

of mammary glands, 604
of manus, 305
of neck, 266
of pelvic limb, 317
of tail, 279
orbital, 861
pectoral, 295
pelvic, 317, 413
perineal. 413
pharJ^lgeal, 255
propria of neck, 266
scrotal, 574
superficial, 254

of abdomen. 287

of forearm. 305

of gluteal region, 317

of head, 255

of metacarpus and digit,
306

of neck, 266

of shoulder and arm, 298

of thigh, 317
tarsal, 318
temporal, 255
transversalis of transversus

abdominis muscle, 291
Fasciculus, cerebello-olivary,

774
cerebellospinal. 775, 777

descending, 777
cerebrospinal, 776

914

Fasciculus cuneatus, 768
dorsal longitudinal, 776
nucleo-cerebellar, 777
pyramidal, 776
Femoral canal, 326

lamina of external oblique

abdominal muscle, 290
Fenestra cochleae, 876

vestibuli, 876, 881
Fibers, corticopontile, 776
of heart, 628
of stomach, 417
Fibro-cartilap;es, interverte-
bral, 211
of patella, 118
Fibrous capsule of adrenal
bodies, 563

of kidney, 558

of liver, 438
coat of kidney, 559

of ureters, 561

of viscera. 384
layer of pericardium, 617
membranes, 384
rings of heart, 628

of intervertebral fibro-
cartilage, 211
sheath of tendon, 254
tunic of eye, 863
Filiform papilla of tongue, 391
Fillet, 774
lateral, 776
medial, 776
Filum terminate, 764, 765
Fimbria of brain, 787, 791, 792
of Fallopian tubes, 599
of ovary, 599
Fissure, 837
ansate, 849
calcarine, 850
calloso-marginal, 785, 837,

844, 850
collateral, 849
coronal, 837, 844, 849
cruciate, 837, 844, 850
diagonal, 837, 844
ectolateral, 849
ectomarginal, 785, 837, 844,

849
ectosylvian, 849
entomarginal, 785, 837, 844,

849
genual, 837, 844, 850
hippocampal, 850
interlobar, of lung, 540
lateral, 785, 837, 843, 849

of cerebrum, 478
longitudinal, of brain, 769,
771

of cerebrum, 784
marginal, 785, 837, 844
medilateral, 849
naso-maxillary, 85
occipito-tempora], 850
palatine, 66, 78, 82
palpebral, 857
petrotympanic, 63
portal^ 434, 468
presylvian, 785, 844, 849
splenial, 844, 850
sublimbic, 786
suprasplenial, 850
suprasylvian, 785, 837, 844,

849

Fissure, transverse, 786. 837

of brain, 771

of cerebrum, 784
umbilical, 435
ventral median, 765, 766
Flexure, diaphragmatic, 425
sigmoid, 589
sternal, 425
Floccular fossa, 190
Floor of mouth, 390
Fa'tal circulation, 704

lung. 531
Fold, alar, 509

CcTco-colic, 424, 428

deferential, of testicles, 577

duodeno-colic, 429

gastro-pancreatic, 417

genital, 414

glosso-epiglottic, 391

ileo-csecal, 421

of mucous membrane, 383

of skin, 884

of vena cava, 526

rumino-reticular, 457

serous, 384

spiral, of abomasum, 460

sublingual, 390

turbinate, dorsal, 513

ventral, 513
umbilical, lateral, 414

median, 414
valvular, of ca?cum, 424
Foliate papilla of tongue, 391
Follicle, hair-, 886
lingual, 392
lymph, 616
of thyroid gland, 536
Folliculi oophori, 598
Foramen alare parvum, 54, 75
caecum, 847
carotid, 190
epiploic, 442, 461
ethmoidal, 53, 55, 75, 82
hypoglossal, 50, 78^, 82
incisivum, 65, 73, 78
infraorbital, 64, 77
intervertebral, 26, 125, 128,

703, 791
lacerum, 51, 63, 78, 82
lacrimal, 172
magnum, 50, 78, 79
mandibular, 71
mastoid, 62
maxillary, 65, 76
mental, 70
nutrient, 22

of femur, 112

of humerus, 88

of ilium, 106

of metacarpus, 99

of tibia, 116
obturator, 109, 112, 152, 202
optic, 53, 75, 82
orbital, 53, 75
orbito-rotundum, 134
ovale, 134, 622, 704
palatine, 76

anterior, 66

posterior, 65
postglenoid, 60
pterygoid, 54
rotunclum, 53, 75
sacral, 41

ventral, 129

Foramen, sciatic, greater, 231
lesser, 231

spheno-palatine, 65, 67, 76,
82

stylo-mast oid, 62

supraorbital, 59, 73

supratrochlear, 198

temporal, 54

trochlear, 54, 75

vense cavae, 287

vertebral, 26

volar, of third phalanx, 103
Fore-fo9t, 29
Formatio reticularis, 767
Fornix, 785, 790

conjunctiva*, 859

vaginae, 602
Fossa, acetabular, 109

anterior, of skull, 82

cUtoridis, 603

condyloid, .50, 78

coronoid, of humerus, 90

ethmoidal, 55, 82

extensor, of femur, 114

floccular, 190

glandis of penis, 581

hyaloidea, 869

hypophyseal, 53

infratemporal, 78

intercondvloid, of femur,.
114 '
of tibia, 116

interpeduncular, 769, 780

lacrimal, external, 159

lateral, 769

of cerebrum, 784

masseteric, 19.5

middle, of skull, 82

olecranon, 90

ovalis, 622, 704

ovulation, 597

pituitarj^, 53

posterior, of skull, 82

pterygoid, 170

pterygo-palatine, 67, 76

rhomboidea, 778

supracondyloid, of femur,
112

synovial, 208

temporal, 73

trochanteric, of femur, 113
Fourth ventricle, 778
Fovea, anterior, of fourth ven-
tricle, 779

capitis of femur, 113

dentis, 36
Fraenula labii, 387
Frenum hnguae, 390, 391

preputial, 583
Frog of hoof, 890, 892
Frog-stay, 890
Frontal crest, 73
external, 59

eminence, 136

process, 191

region of skull, 73

sinus, 59, 85, 143, 175, 197

suture, 60
Fronto-lacrimal sutures, 60
Fronto-maxillary opening, 85

suture, 60
Fronto-palatine suture, 60
Front o-turbinate sinus, 85
Fundus reticuh, 456

INDEX

915

Fundus uteri, 601
Fungiform papilla of tongue,
391

Gall-bladder, 468, 490, 505
Ganglia, 760, 829

ciliary, 829

coccygeal, 832

coeliac, 856

coeliaco-mesenteric, 833

lumbar, 832

mesenteric, anterior, 856

of sympathetic trunk, 829

otic, 829

peripheral, 829

sacral, 832

sphenopalatine, 797, 829

thoracic, 831, 842
Ganglion, cervical, anterior,
830, 842, 846, 856
middle, 847
posterior, 830, 842, 856

ciUary, 796, 838

coccygeal, 832

coeliac, 842

geniculate, 801

intercaroticum, 804

jugular, 805, 839, 845, 851

mesenteric, anterior, 842
posterior, 833

nodosum, 805, 839, 845, 851

otic, 799, 838

petrous, 804

semilunar, 795

spinal, 811

spirale, 884

splanchnic, 832

stellatum, 830

vestibular, 803
Gartner, canals. of, 607
Gastric impression of hver, 434

plexus, 833
anterior, 852
posterior, 852
Gastro-pancreatic fold, 417
Gastro-splenic omentum, 412,

417, 441
Gelatinous marrow of bone, 22
Geniculate body, medial, 781,
835, 847

ganglion, 801
Genital fold, 414

organs, 554

female, 596, 605, 609, 610,

612
male, 571, 586, 591, 593
Genu of corpus callosum, 789
Genual fissm-e, 837, 844, 850
Ginglymus, 210
Girdle, pelvic, 30, 105

shoulder, 29
Glands or gland, 382

adrenal, 563, 566, 567, 569,
570

alveolar, 383

alveolo-tubular, 383

anal, 502

buccal, 387, 445, 477

bulbo-urethral, 571, 579,
589, 592, 594
ducts of, 585

cardiac, of stomach, 419

ceruminous, 872

Glands, circumanal, 502
coil, of digital cushion, 894
compound, 383
cutaneous, 898
duct of, 383
ductless, 439
duodenal, 501
fundus, 383

of stomach, 419
gastric, 418
haemolymph, 616
labial, 387, 444
lacrimal, 860, 896
laryngeal, 523
lingual, 392
liver, 434, 465, 475, 488, 503

structure of, 438
lobules of, 385
lymph, 616, 722, 733
abomasal, 731
anal, 703, 742
atlantal, 724, 733
atrial, 730

axillarv, 703, 728, 741, 757
broncliial, 700, 727, 741,

757
CcTcal, 702, 731, 742
cervical, anterior, 699,
724, 756
middle, 699, 724, 741,

756
posterior, 699, 724, 725,

741, 756
superficial, 699, 756
coeliac, 728

coHc, 702, 731, 742, 759
costo-cervical, 725
coxal, 733
cubital, 703, 757
duodenal, 731
epigastric, 729
gastric, 702, 730, 742
hepatic, 702, 732, 742
hyoid, 724
iliac, external, 701, 729,

742, 758
infraspinatus, 728
inguinal deep, 703
iliac, internal, 701, 728,

742, 758
inguinal, superficial, 701,

729, 734, 742, 759
intercostal, 700, 725, 757
ischiatic, 701, 730, 742
jejuno-ileal, 731
lumbar, 701, 728, 742, 758
mammarv, 701, 734
mandibular, 698, 722,733,

740, 756
mediastinal, 741, 757
anterior, 700, 726
diaphragmatic, 726
dorsal, 726
posterior, 700, 726
ventral, 726
mesenteric, 702, 731, 733,

742, 759
of abdomen, 701
of head, 698
of pelvic limb, 703
of pelvis, 701
of thoracic limb, 703
of thorax, 700
of neck, 698

Glands, Ijonph, omasal, 731

pancreatic, 702

pancreatico-intestinal, 732

paralumbar, 729

parapharyngeal, 699, 724

parietal, 701

parotid, 723, 733, 740, 756

pericardiac, 727

pharyngeal, 699

popliteal, 703, 733, 742,
759

portal, 758

prefemoral, 703, 732, 733,
742

prepectoral, 699, 741

prescapular, 699, 725, 741,
756

pterygoid, 724

pulmonary, 727, 757

rectal, 702, 732

renal, 701, 728, 759

reticular, 731

rhomboid, 728

ruminal, 730, 731

sacral, 701, 730, 758
external, 730
internal, 730

splenic, 702, 742

sternal, 727, 733, 741, 757
anterior, 727

subiliac, 703, 732

submaxillary, 698

supramammary, 729, 759

supraphar\Tigeal,699, 722,
733, 740, 756

tarsal, 742

thoracic, 741

visceral, 701, 702
mammary, 596, 604, 609,

610, 611, 613
mandibular, 404, 451, 482,

496
mucous, of pharynx, 408
nasal, 514
naso-labial, 444, 898

of duodenum, 421
of kidneys, 559
of large intestine, 431
of skin, 885, 887
of small intestine, 421
of third eyelid, 896
olfactory, 514, 895
palatine, 389
pancreas, 432, 468, 470, 476,

491, 505
parathyroids, 536, 544, 553
parotid, 404, 451, 482, 495

accessory, 482
preputial, 583
prostate, 571, 578, 589, 592,

593
pyloric, of stomach, 419
renal, 742

salivary, 404, 451, 471, 495
sebaceous, 885, 898
simple, 383

spleen, 439, 476, 491, 506
sublingual. 405, 451, 482, 496
submaxillary, 404, 482
sudoriferous, 885
sweat, 885, 898
tarsal. 859
thvroid, 535, 536, 544, 548,

553

916

INDEX

Glands, th>Toid, accessory,
536, 544, 553
tracheal, 525
tubular, 383

tubulo-alveolar, 383

urethral, 585
lateral, 585

uterine, 607

zygomatic, 496
Gland ulaj vestibulares ma-
jores, 603, 608
minores, 603, 608
Glans clitoridis, 603, 604

penis, 580, 589, 594
Glenoid cavity, 60, 73, 78, 87

notch, 87
Glomerulus of kidney, 559
Glosso-epiglottic fold, 391
Glottis, 522
Gluteal Ime, 105
Gomphosis. 208
Granula iridis, 867
Granulations, arachnoid, 763
Gray columns of spinal cord,
'767

commissure of spinal cord,
766

matter of nervous system,
760
of spinal cord, 766

rami, 829
Great colon, 425
Greater omentum, 442, 461,

499
Groove, bicipital, of humerus,
89

coronary, of heart, 619
of hoof, 888

dorsal intermediate, 766
median, 765

dorso-lateral, 765

intertuberal, of humerus, 89

lacrimal, 64

longitudinal, of heart, 619

musculo-spiral, 88

oesophageal, 458, 473

of rumen, 454, 455

of tibia, 116

optic, 53

rumino-reticular, 454

supraorbital, 137

palatine, 65, 78

pubic, 109
Gross anatomy, 17
Ground border of hoof, 888
Gubernaculum testis, 577
Gums, 387
Gustatory cells, 896

organs, 905
Guttural pouches, 879

region, 78
Gyri, 837

cerebellar, 777

cerebri, 771, 785
Gyrus dentatus, 786

subcallosal, 788

HEMORRHOIDAL plexus, 834

anterior, 856
Hair-follicle, 886
Hairs, 886, 887, 898

tactile, 886
Hair-streams, 886

Hamulus pterygoideus, 67
Hard palate, 78, 387, 445, 470,

477, 492
Head, lymph vessels of, 698
Heart, 614, 617, 705, 734, 735,
742, 743

structure of, 627
Hemal arches, 188
Hemispheres, cerebral, 771,
783, 836, 843,^849

of cerebellum, 771, 776

of lu-ethra, 595
Hepatic duct, 438

plexus, 439, 833
Hiatus aorticus, 287

ocsophageus. 287
Hilus of lung, 531

of ovary, 597

of spleen, 440, 470, 477

renal, 555
Hippocampal commissure, 787

fissure, 850
Hippocampus, 786, 792
Histology, 17
Hock, 31
Hoof, 887
Horns, 899

core, 136

of female uterus, 610

of lateral ventricle, 791

of spinal cord, 767

of uterus, 600
Horny lamina of hoof, 892
Humeral articular surface, 92
Humor, aqueous, 869

vitreous, 869
Hyaloid membrane, 869
Hydatides terminales, 599
Hymen, 602
Hyoid process, 62
Hypogastric zone, 411
Hypoglossal foramen, 50, 78,

82
Hypophyseal fossa, 53
Hypophysis, 769, 780, 782,

835, 847
Hypothalamic nucleus, 781

tegmental region, 781

Ileo-cecal fold, 421

orifice, 424

valve, 421
Ileo-colic orifice, 501

valve, 501
Ileum, 420

Iliac lamina of external ob-
lique abdominal muscle, 290
Ilio-pectineal eminence, 109

line, 105
Impression, caecal, of liver, 435

cardiac, of lung, 531

colic, of liver, 435

duodenal, of liver, 435

gastric, of liver, 434
Incisive foramen, 65, 73, 78
Incisor teeth, 394, 397, 448,
471, 479, 493
deciduous, 403, 448
Infraorbital canal, 65

foramen, 64, 77

pouch, 900
Infratemporal fossa, 78
Infundibular recess, 783

Infundibulum, 769, 780, 782,
836
of incisor teeth, 397
tubse uterina^, 599
Inguinal canal, 292
pouch, 900

ring, abdominal, 290, 292
external, 288, 292
internal, 290, 292
subcutaneous, 288, 292
Inlet of orbital cavity, 76
of thoracic cavity, 525
pelvic, 152, 160, 181, 202
Inscriptiones tendineae of rec-
tus abdominis muscle, 291
Interalveolar septa, 64
space, 64, 65, 71, 78
Interarytenoid cartilage of

larjTix, 546, 550
Inter-brain, 781
Intercarpal sac, 222
Intercavernous sinus, 688
Intercondjdoid eminence of
tibia, 116
fossa of femur, 1 14

of tibia, 116
spaces, 27
Interdental space, 64
Interdigital pouch, 900
Interlobar fissures of lung, 540
Interlobular bronchi, 534

tissue, 383
Intermediate zone of kidney,

550
Intermuscular septa, 254
of forearm, 305
of gluteal region, 317, 318
of leg, 318
of shoulder, 298
Interosseous membrane of
til)io-fibular articulation,
239
space of leg, 31, 116

of radius, 91
tendon, 225
Interpeduncular fossa, 769,

780
Intertarsal sac, 240
Intertuberal groo\'e of hum-
erus, 89
Interventricular foramen, 783,
791
septum, 627
Intervertebral fibro-car t ilages,
211

foramen, 26, 125, 128
Intestine, 463, 475, 486, 500
large, 422, 465, 487, 502

structure of, 430
small, 419, 463, 475, 486,
500
Intraosseous plexus, 692
Iris, 866, 897
Ischiatic spine, 106, 107
Isthmus faucium, 390, 406, 446
oesophagi, 497
of male urethra, 585
of prostate, 579
of thyroid gland, 535, 553
pharyngeal, 408

Je.iuno-ilbum, 420, 486
Joints, 207, 211

INDEX

917

Joints, abduction of, 210
adduction of, 210
angular movements, 209
antibrachio-carpal, 221
arteries of, 209
atlanto-axial, 214
atlanto-occipital, 214
basi-comual, 218
capsule of, 208
carpal, 221, 246
carpo-metacarpal, 221
cartilages of, 208
cavity, 209
chondro-sternal, 216
circumduction of, 210
coccygeal, 213
coffin, 228
costo-central, 215
costo-chondral, 216
costo-trans verse, 216
cost o- vertebral, 215
crico-arytenoid, 517
crico-thyroid, 517
discs of, 209
elbow, 219, 246
extension of, 209
femoro-patellar, 232
femoro-tibial, 235
fetlock, 224
fibrous layer, 208
flexion of, 209, 210
folds of, 20S
gliding movements, 209
hip, 231, 250
hock, 239, 251
hyoidean, 218
intercarpal, 221
intercentral, 211
intercomual, 218
intermetacarpal, 223, 247
intemeural, 212
interphalangeal, 248

distal, 228

proximal, 228
interstemal, 245
intertransverse. 213
knee, 221

lymph-vessels of, 209
mandibular, 217
metacarpo-phalangeal, 224,

247
movements of, 209
nerves of, 209
of auditory ossicles, 878
of larynx, 517
of pelvic limb, 229, 250
of skull, 217

of thoracic limb, 218, 245
of thorax, 215, 245
of vertebrae, 244
pastern, 228
radio-carpal, 221
radio-ulnar, 221, 246
rotation of, 210
sacral, 213
sacro-iliac, 229, 250
shoulder, 218, 245
sternal, 217
stifle, 232, 250
surfaces of, 208
synovial layer, 208
temporo-hyoid, 218
temporo-mandibular, 245
thyro-hyoid, 518

Joints, tibio-fibular, 239, 251

tibio-tarsal, 239

veins of, 209

villi of, 208
Jugular ganglion, 805, 839,

845, 851

Kidneys, 554, 564, 566, 567,
569
capsule of, 559
cortical substance of, 558
fibrous capsule of, 558

coat of, 559
fixation of, 557
glomerulus of, 559
intermediate zone of, 558
left, 555, 565, 569
lobules of, 559
lymph-vessels of, 560
medullary substance, 558
mucous coat of, 559
muscular coat of. 559
right, 554. 564, 569
stroma of, 559
structure of, 558
vessels and nerves, 560
weight and size of, 557

Ivnee, 29

Labia vulvae, 603
Labyrinth, membranous, 881,
882

of ethmoid bone, 55

osseous, 881
Labyrinthine wall, 876
Lacrimal apparatus, 860

bulla, 139

canal, 82
osseous, 68

caruncle, 858

ducts, 860 ^

foramen, 172

fossa, external, 159

groove, 64

lake, 858

pouch, 900

process, 194

sac, 860

tubercle, 68
I^acteals, 615
Lactiferous ducts, 605, 609

sinus, 605, 609
Lake, lacrimal, 858
Lamina basalis, 865

choriocapillaris, 865

cribrosa sclerse, 863

elastica posterior, 864

externa, 21

fusca, 863

homy, of hoof, 892

interna, 21

lateralis of ethmoid bone,
55

layer of hoof, 892

limitans anterior, 864

medullary, 777

of cricoid cartilage, 515

of hoof, 888

of nostrils, 509

of thyroid cartilage, 515

omasi, 460

propria, 383

Lamina spiralis ossea, 882
suprachorioidea, 865
terminalis, 783
transversalis of ethmoid
bone, 170, 191

of palatine bone, 171
vasculosa, 865
Laminar corium, 892
Laryngeal saccule, 522, 550
Larynx, 514, 538, 546, 550
arytenoid cartilages, 517,

538, 546, 550
cartilages of, 515
cavity of, 521
cricoid cartilage of, 515, 538,

546, 550
cuneiform cartilages, 550
facets, 515
interarytenoid cartilage of,

546, 550
lateral ventricle, 522, 539,

550
membranes of, 517
middle ventricle, 522
mucous membrane, 523
posterior compartment, 523
vessels and nerves, 523
vestilnile of, 522
Layer, fibrous, of pericardium,

617
laminar, of hoof, 892
parietal, 384, 412
serous, of pericardium, 617
visceral, 384, 412

of pericardium, 617
Lemniscus, 774
Lens, crystalline, 869

fibers, 870
Lenticular nucleus, 792

papillae of tongue, 447
Ligament or ligaments, 209
accessory, of hip joint, 232

of prepubic tendon, 292
alar, 244
annular, 254

digital, distal, 306
proximal, 306

dorsal, of carpus, 305

of leg, 318

of radius, 246

volar, of carpus, 306
of fetlock, 306
arytenoid, transverse, 518
atiantal, lateral, 215
atlanto-axial, dorsal, 214

ventral, 214
l)road, of uterus, 415, 601,

607, 612
carpal, dorsal, 222

volar. 222
caudate, of liver, 437
check, 240

inferior, 222, 315

of deep digital flexor, 341

subcarpal, 315

superior, 313
collateral, 209

of coffin joint, 228

of fetlock joint, 224

of meiacarpo-phalangeal
joints, 247

of pastern joint, 228
conjugal, 215
coronary, 437, 488

918

INDEX

Ligament, costo-sternal, radi-
ate, 216
costo-transverse, dorsal, 216
cruciate, of stifle joint, 238
dorsal, of hock joint, 241

of interphalangeal joints,
250
dorso-scapular, 276
falciform, 437, 488
lemoro-patellar, 233
gastro-phrenic, 416
hepato-renal, 437
ilio-lumbar, 231
inferior check, 315
inguinal, 288
interchondral, 216
interdigital, 248

cruciate, 249

distal, 249
interosseous, 209

of forearm, 221

of tibial and fibular tar-
sal bones, 242
intersesamoidean, 224
interspinous, 214
intra-articular, 209
lateral, left, of liver, 437

of bladder, 414, 562

of carpal joints, 222

of elbow joint, 221

of hock joint, 240

of stifle joint, 238

right, of liver, 437
longitudinal, dorsal, 211

ventral, 211
medial, of carpal joints, 222

of ell)ow joint, 221

of hock joint, 241

of stifle joint, 237
metacarpal, interosseous,

223
middle, of bladder, 414, 562
navicular, distal, 229

suspensory, 229
odontoid, 214
of auditory ossicles, 878
of cartilages of third pha-
lanx, 229
of coffin joint, 228
of dens, 214
of ergot, 306

of fibular tarsal bone, 242
of hock joint, 240, 242
of larynx, 517
of liver, 437, 488
of neck, 215
of ovary, 597, 612
of pelvic girdle, 230
of peritoneum, 412
of stifle joint, 233, 237
of tibial tarsal bone, 242
of vertebrae, 211, 244
palpebral, 858
patellar, 233, 234
periarticular, 209
pericardiaco-phrenic, 742
phalango-sesamoidean, 229
plantar, of hock joint, 241
pulmonary, 526
radial, 313
radiate, 215

costo-sternal, 216
round, of bladder, 414, 562

of hip joint, 231

Ligament, round, of liver, 437,
490

of uterus, 601, 607, 612
sacro-iliac, dorsal, 230

lateral, 230

ventral, 230
sacro-sciatic, 230
scrotal, 574
serous, 384
sesamoidean, 224

collateral, 224, 229

cruciate, 227

deep, 227

distal, 226

middle, 226

short, 227

straight, 226

superficial, 226

suspensory, 317
sternal, internal, 217
sterno-pericardiac, 705
subcarpal, 222

check, 315
subtarsal, 240
superior check, 313
supraspinous, 212
suspensory, 225

navicular, 229
■ of anus, 432

of penis, 580

of spleen, 441

sesamoidean, 317
thyro-epiglottic, 518
tracheal annular, 525
transverse, of atlas, 245

of carpus, 306

of radio-ulnar articula-
tion, 221
vaginal, 254
ventricular, 518
vocal, 518

volar, of pastern joint, 228
Ligamenta flava, 212
Ligamentum arteriosum, 629,

704
denticulatum, 764
nuchee, 213

pectinatum iridis, 865, 866
spirale cochleae, 883
Line, diaphragmatic, of pleu-
ral reflection, 530
gluteal, 105
ilio-pectineal, 105
mylo-hyoid, 70
of pleural reflection, 530
popliteal, of tibia, 115
sternal, of pleural reflection,

530
terminal, 110, 410
vertebral, of pleural reflec-
tion, 530
white, of hoof, 889
Linea alba, 288
Lingual follicles, 392

process, 72
Lingula, 776

Lips, 385, 444, 470, 477, 491
Liquor folliculi, 598
pericardii, 617
pleurae, 530
Lobe or lobes, apical, of lung,

540, 547, 548, 551, 553
cardiac, of lung, 540, 547,

548, 551, 553

Lobe, caudate, of liver, 434,

468, 488, 503
cerebellar, 777
diaphragmatic, of lung, 540,

547, 551, 553
intermediate, of lung, 540,

534, 547, 551
of liver, 438, 488, 490, 503
of lung, 540, 547, 551
of mammary glands, 605
of prostate, 579
of thymus gland, 536
of thyroid gland, 535, 536,

553
of urethra, 595
piriform, 784, 788, 850

of brain, 769
Lobular bronchioles, 534
Lobulation of lungs, 534, 544
Lobules of kidney, 559
of liver, 438
pulmonary, 534
Lumbar enlargement, 765
ganglia, 832
part of sympathetic system,

856
Lum))o-costal arch, 287
Lumbo-sacral plexus, 824, 841,

846, 855
Lung, 530, 540, 544, 547,

551
alveolar ducts of, 534
apex of, 533, 534
apical lobe of, 540, 547, 548,

551, 553
basal border of, 533
base of, 533
body of, 534

bronchial branches of, 534
cardiac impression of, 531

lobe of, 540, 547, 548, 551,
553

notch of, 533
color of, 531
costal surface of, 531
diaphragmatic lobe of, 540,

547, 551, 553
dorsal border of, 532
foetal, 531
form of, 531
hilus of, 531

interlobar fissures of, 540
intermediate lobe of, 534,

540, 547, 551
lobes of, 540, 547, 551
lobulation of, 534, 544
lymph-vessels of, 534, 535
mediastinal surface of, 531
root of, 534
ventral border of, 533
vessels and nerves of, 534
Lymph, 616

ducts, tracheal, 725, 756
follicles, 616
nodes, 616
nodules, 616
sinus, central, 616

peripheral, 616
spaces, 616
vessels, 615

of abdomen, 701

of adrenal bodies, 564

of bladder, 562

of bone, 22

INDEX

919

Lymph vessels of corium of
hoof, 894

of Fallopian tubes, 599

of head and neck, 698

of heart, 828

of kidneys, 560

of lung, 534, 535

of ovary, 599

of pelvic limb, 703

of pelvis, 701

of penis, 582

of skin, 885

of spermatic cord, 576

of testicles, 574

of thoracic limb, 703

of thorax, 700

of uterus, 602

of vagina, 602
Lymphatic duct, 725

right, 615, 698
system, 615, 697, 722, 740,

756
Lymphocytes, 616
Lyssa, 493

Macroscopic anatomy, 17
Maculae acusticae, 883
Malleolus, lateral, of tibia, 117
medial, of tibia, 117
of tibia, 117
Mammillary body, 769, 782,
847
processes, 26, 45, 163
Mandibular canal, 71
duct, 405, 496
foramen, 71
notch, 71
space, 70
teeth, 401
Manubrium stemi, 28, 48
Marginal cartilage, 209
fissure, 785, 837, 844
pole, 836
Margo plicatus, 418
Marrow of bone, 21, 22

spaces, 21
Masseteric fossa of mandible,

195
Mastoid border of occipital
bone, 52
foramen, 62
process, 61, 74
Maxillary dental plexus, 798
foramen, 65, 76
process, 194
region, 76

sinus, 84, 144, 175, 197
inferior, 84
superior, 85
teeth, 400
tuberosity, 65
Meatus, acoustic, external, 61,
870, 871
internal, 62, 882
common, of nose, 69
dorsal, of nasal cavity, 545

of nose, 69, 83
ethmoidal, 55, 512
middle, of nasal cavity, 545,

550
nasal, common, 511
dorsal, 511
middle, 69, 83, 511

Meatus, nasal, ventral, 69, 83,
511
ventral, of nasal cavity, 546,
550
Medial epicondyle of femur,
114
malleohis of tibia, 117
supracondyloid crest of fe-
mur, 112
Mediastinal pleura, 526
Mediastinum thoracis, 525
Medilateral fissure, 849
Medulla oblongata, 769, 771,
773, 834, 843, 847
of thymus gland, 536
cavity, 20, 21
Medullary cords, 616
lamina, 777
substance, 777

of adrenal bodies, 563
velum, 776
anterior, 779
posterior, 779
Membrana basilaris, 883
nictitans, 859
propria of middle ear, 876
tympani, 876
vestibularis, 883
Membrane, atlanto-occipital,
dorsal, 215
atlanto-occipital, ventral,

215
crico-thyroid, 518
crico-tracheal, 518
elastic, of trachea, 525
fibrous, 384
hyaloid, 869
interosseous, of tibio-fibular

articulation, 239
obturator, 231
of larynx, 517
serous, 384

s\Tiovial, of carpal joints,
222
of elbow joint, 219
of hip joint, 232
thyro-hyoid, 518
Membranous labvrinth, 881,

882
Meninges, 761
Meniscus, 209, 235
Mental foramen, 70
Meridians of eye, 863
Mesaticephalic skull, 195
Mesencephalon, 780
Mesenteric ganglion, anterior,
842, 856
posterior, 833, 843
plexus, anterior, 833, 856
posterior, 833, 856
Mesentery, 412
colic, 412, 429
great, 412, 420
Mesocolon, 502
Mesoduodenum, 419, 500
Mesogastric zone, 411
Mesorchium, 576, 577
Mesorectum, 413, 429
Mesosalpinx, 599, 612
Mesotendon, 253
Mesothelium, 384
Mesovarium, 597
Microscopic anatomy, 17
Mid-brain, 780

Moderator bands of right

ventricle, 625
Modiolus, 882
Molar teeth, 394, 399
Morphology, 17
Motor fibers, 808
nucleus, dorsal, 808
of fifth nerve, 776
ventral, 808
root of fifth nerve, 776
Mouth, 385, 444, 477, 491
cavity of, 385, 444
floor of, 390

mucous membrane of, 385
Mucous coat of bladder, 562
of Fallopian tubes, 599
of kidney, 559
of small intestine, 421
of stomach, 418
of vagina, 602
membranes, 383
of abomasum, 462
of ductus deferens, 575
of large intestine, 431
of larynx, 523
of mouth, 385
of nose, 512
of oesophagus, 410
of omasum, 462
of pharjmx, 407
of reticulum of stomach,

462
of rumen, 458
of seminal vesicles, 578
of small intestine, 421
of tongue, 390
of trachea, 525
of ureters, 561
of urethra, 585, 604
of uterus, 601, 607
of vulva, 603
tympanic, 878
Mucus, 383

Muscle or muscles, 252, 264
abdominal, 287, 349, 361,

377
abductor cruris posterior,
378
digiti quinti, 381
hallucis, 382

pollicis brevis et opponene
pollicis, 375
longus, 373
accessory structures, 253
action of, 253
adductor, 326, 356, 365
digiti quinti, 375

secundi, 375
femoris, 380
hallucis, 382
of second and fifth digits,

381
pollicis, 375
anconeus, 304, 363
antitragicus, 874
arrectores pilorum, 886
articularis genu, 355
ar\'tenoideus transversus,

520
attachments of, 252
auricular, 872, 897
anterior, 872
deep, 873
dorsal, 872

920

INDEX

Muscle, auricular, posterior,
873
belly of, 253
biceps, 351

brachii, 302, 363, 372
femoris, 322, 355, 365, 378
bipennate, 253
biventcr cervicis, 376
blood supply of, 253
brachialis, 302, 363, 373 _
brachiocephalicus, 294, 351,

360, 362, 371
brachioradialis, 308, 373
buccinator, 258, 345, 368
bulbo-cavemosus, 586, 589,

595
capsularis, 301, 333, 351,

355, 363, 365, 380
cervical cutaneous, 347, 376
cervicalis ascendens, 269
cervico-auricularis profun-
dus major, 873
minor, 873
superficialis, 873
cervico-scutularis, 872
chondro-pharyngeus, 407
ciliary, 866
cleido-cervicalis, 371
cleido-mastoideus, 351, 362,

371
cleido-occipitalis, 351, 362
coccygeus, 279, 377
complexus, 273, 361, 376

major, 376
constrictor vestibuli, 603

vulvae, 603
coraco-brachialis, 300, 351,

363, 371
corrugator supercilii, 260
cremaster, external, 291,

381, 576, 587, 591
crico-arytenoideus dorsalis,
519
lateralis, 519
crico-pharyngeus, 407
crico-thyroideus, 519
cutaneous, 252, 254, 343,
350, 368, 884
colli, 254
faciei, 254
labiorum, 254
omo-brachialis, 254
trunci, 254
deltoid, 351, 362, 371

deltoideus, 298

depressor labii inferioris,
258, 344, 359, 368
superioris, 344
rostri, 359
diaphragm, 285, 349, 361
digastric, 253
digastricus, 264, 346, 359,

370
digital extensor, common,
307, 352. 363, 373
lateral, 308, 335, 352,
356, 363, 367, 373,
380
, long, 333, 356, 366, 380
medial, 352, 356
of second digit, 363
short, 356
flexor, deep, 315, 339, 354,
364, 367, 374, 381

Muscle, digital flexor, long, 340
superficial, 313, 339,
353, 364, 367, 374, 381
dilatator naris apicalis, 345
lateralis, 258, 345, 359
extensor carpi obliquus, 310,
352, 363, 373
radialis, 306, 352, 363,
373
brevis, 373
longus, 373
ulnaris, 374
digitalis brevis, 343, 367,

380
hallucis longus, 367, 380
of fifth digit, 374
of first and second digits,

373
of third and fourth digits,
373
facial cutaneous, 359
flexor carpi radialis, 310,
364, 374
ubiaris, 310, 364, 374
deep, 359

digitahs longus, 368
pedis longus, 381
hallucis, 341, 368
brevis, 382
longus, 381
polhcis brevis, 375
superficial, 359
front aUs, 343
fronto-scutularis, 872
gastrocnemius, 338, 359,

367, 381

gemeUus, 329, 356, 365, 378
genio-glossus, 394
genio-hyoideus, 265, 347
gluteus accessorius, 322

medius, 321, 355, 365, 378

profundus, 322, 355, 365,
378

superficialis, 321, 365, 378
graciUs, 325, 356, 365, 380
head of, 253
heUcis, 874
hyo-epiglotticus, 519
hyo-glossus, 392
hyoid, 264, 347, 359, 370
hyoideus transversus, 265,

347, 359
hyo-pharyngeus, 407
iUacus, 320, 354, 378
ilio-psoas, 319, 378
incisivus inferior, 257, 344

superior, 257
infraspinatus, 299, 351, 362,

371
insertion of, 252
intercostal, external, 283,
349, 361, 376

internal, 283, 349, 361
interosseous, 317, 343, 365,

368, 375, 381
interosseus medius, 354
interscutularis, 872
interspinals, 349, 362, 376,

377
intertransversales, 347, 349,
361, 362, 376, 377
caudse, 281
coUi, 270
lumborum, 279

Muscle, ischio-cavernosus, 582,
589, 604
ischio-urethral, 586, 595
kerato-hyoideus, 265, 347,

359
kerato-pharyngeus, 407
lateralis nasi, 259
dorsal part, 345
ventral part, 345
latissimus dorsi, 295, 351,

362
levator labii superioris pro-
prius, 256, 344, 359, 368
nasolabialis, 255, 258,

343, 359, 368
palati, 389
palpebrse superioris, 260,

861
rostri, 359
levatores costarum, 281,

349, 361, 376
Ungual, 392

longissimus atlantis, o76
capitis, 376

et atlantis, 271, 361,
376
costarum, 277, 349, 362,

377
dorsi, 278, 349, 371, 377
longus colU, 270, 347, 360,

376
lumbricales, 317, 343, 354,

365, 368, 375, 381
malaris, 260, 345
mandibular, 260, 346, 359,

370
masseter, 261, 346, 359, 370
mentahs, 258
multifidus, 362
cer\acis, 273
dorsi, 279
multipennate, 253
mylo-hvoideus, 264, 347,

359, 370
nasal, 368

nerve supply of, 253
non-striated, 252
obliquus abdominis exter-
nus, 288, 349, 361,
377
internus, 290, 350, 361,
377
capitis anterior, 275
posterior, 273, 361
dorsalis s. superior, 861
ventraUs s. inferior, 861
obturator, 378

externus, 328, 356, 365

internus, 328, 356, 365

occipito-hyoideus, 265, 347,

359
occipito-mandibularis, 262,

346, 370
ocular, 861
of abdomen, 287, 349, 361,

377
of anus, 432
of arm, 302, 351, 363
of auditory ossicles, 878
of back, 349, 361, 376, 377
of cheeks, 255
of digit, 343
of eveball, 861
of eyelids, 260

INDEX

921

Muscle of face, 343, 359, 368
of foot, 333, 356
of forearm, 305, 352, 363
of head, 255

ventral, 360
of hip, 365

lateral, 320, 355
of larynx, 518

extrinsic, 518

intrinsic, 519
of leg, 333, 356, 366
of lips, 255

of loins, 276, 349, 361, 377
of manus, 305, 352, 363
of metatarsus, 343
of neck, 266, 347, 360, 376

lateral, 271

ventral, 266
of nostrils, 258
of pelvic limb, 319, 354, 365,

378
of penis, 582
of pharynx, 407
of shoulder, 298, 351, 362

girdle, 293, 350, 362
of soft palate, 389
of tail, 279, 349, 362, 377
of thigh, 365

anterior, 329, 355

lateral, 320, 355, 356

medial, 325
of thoracic limb, 293, 350,

362, 370
of thorax, 281, 349, 361, 376
of tongue, 392
omo-hyoideus, 268, 347, 359,

360
omo-transversarius, 360,351,

362, 370
orbicularis oculi, 260, 345

oris, 255, 343, 359, 368
origin of, 252
palatinus, 389
palato-pharyngeus, 407
palmaris brevis, 375

longus, 374
palpebral, 368
panniculus carnosus, 254,

884
parieto-auricularis, 872
parotido-auricularis, 873
pectineus, 326, 356, 365, 380
pectoral, 295

deep, 296, 351, 371
anterior, 296, 362
posterior. 296, 362

superficial, 295, 351, 371
anterior, 295, 362
posterior, 296, 362
peroneus brevis, 380

longus, 356, 366, 380

tertius, 335, 356, 366, 386
piriformis, 378
popUteus, 343, 367, 381
preputial, anterior, 590

posterior, 590
pronator quadratus, 375

teres, 354, 364, 374
protractors, 590
psoas major, 319, 354, 365,
378

minor, 319, 354, 365, 378
pterygoideus lateralis, 262,

346, 359, 370

Muscle, pterygoideus medi-
alis, 261, 346, 359
pterygo-pharyngeus, 407
quadratus femoris, 328, 356,
365, 378
lumborum, 320, 354, 365,

378
plantiP, 381
quadriceps femoris, 329, 355,

365, 379
recti capitis dorsales, 361
rectus abdominis, 290, 350,
361, 379
capitis dorsalis major, 275
minor, 276
lateralis, 270, 347, 376
ventralis major, 269,
347, 376
minor, 269, 347, 376
dorsalis s. superior, 861
femoris, 329, 379
lateralis, 861
medialis, 861
thoracis, 283, 361
ventrahs s. inferior, 861
relations, 253
retractor, 590
ani, 432, 502
costfp, 283, 361
oculi, 861
penis, 582, 589
rhomboideus, 293, 351, 371,
362
cervicalis, 293, 371
thoracalis, 293, 371
rotator, 873

sacro-coccygeus, 362, 377
accessory, 377
dorsalis, 280
lateralis, 280
ventralis, 281
sartorius, 325, 356, 365, 380
scalenus, 268

dorsalis, 347, 360, 376
ventralis, 347, 360, 376
scutularis, 872
scutulo-auricidaris pro-
fundus major, 873
minor, 874
superficialis accessorius,
872
inferior, 872
medius, 872
superior, 872
semimembranosus, 324, 365,

355, 379
semitendinosus, 323, 355,

365, 379
serratus cervicis, 297

dorsalis anterior, 277, 349,
361, 377
posterior, 277, 349, 361,
377
thoracis, 297

ventrahs, 297, 351, 362,
371
shape of, 252
skeletal, 252
soleus, 359, 339, 367
sphincter, 252
ani exiernus, 432

internus, 432
vesicae, 562
spinalis, 273

Muscle, spinalis et semispi-

nalis, 362
splenius, 271, 347, 361, 376
stapedius, 878
sterno-cephalicus, 266, 347,

360, 376
sterno-hyoideus, 359, 370
sterno-mandibularis, 347
sterno-mastoideus, 347
sterno-thyro-hyoideus, 268,

347, 360, 370
sterno-thyi'oideus, 370
striated, 252
structure of, 253
stylo-glossus, 392
stylo-hyoideus, 265, 347,

370
stylo-pharyngeus, 407
sublumbar, 319, 354, 365
submultifidus, 376
subscapularis, 300, 351, 363,

371
supinator, 364, 374
supraspinatus, 298, 351, 362,

371
synovial membranes of, 253
temporahs, 261, 346, 370
tendinous inscriptions, 253

intersections, 253
tensor fascial antibrachii,
303, 352, 363, 373
latff, 320, 355, 365, 378

palati, 390

tympani, 878
teres major, 300, 351, 363,
371

minor, 299, 351, 362, 371
thyro-arytenoideus exter-

nus, 521
th>TO-hyoideus, 518
thyr()-i)iuu>ngeus, 407
tibialis ant(>rior, 336, 357,
366, 380

posterior, 340, 367, 381
trachealis, 525
tragicus, 874

transversus abdominis, 291,
350, 361, 378

nasi, 259, 359

thoracis, 285, 361
trapezius, 293, 350, 362, 370

cervicalis, 293

thoracaUs, 293
triceps, 352, 363, 373

brachii, 303, 304
ulnaris laterahs, 313, 364,

374
unipennate, 253
urethral, 586, 590, 593, 595,

604
vastus intermedins, 333, 379

lateralis, 330, 379

medialis, 331, 379
ventricularis, 520
verticalis auricula^, 875
visceral, 252
vocalis, 520

zygomatico-auricularis, 872
zygomaticus, 257, 344, 359,

368
Muscular coat of abomasum,
462

of bladder, 562

of ductus deferens, 575

922

INDEX

Muscular coat of Fallopian
tubes, 599

of kidney, 559

of large intestine, 430

of a'sophagus, 409

of omasum, 462

of reticulum of stomach,
462

of rumen, 461

of seminal vesicles, 578

of small intestine, 421

of stomach, 417

of ureters, 561

of m-ethra, 604

of uterus, 601, 607

of vagina, 602

of viscera, 384
process of temporal bone,

63
tissue, 384
Muscularis mucosa?, 383

of small intestine, 421
IVIusculi papillares of left ven-
tricle, 627

of right ventricle, 624, 625
pectinati of right atrium,

621
Musculo-spiral groove, 88
Myenteric plexus, 833
Mylo-hyoid hne, 70
Myocardium, 628
Myology, 252

Nares, posterior, 78, 406, 512
Nasal cavity, 82, 143, 159, 175,
197, 508, 537, 538, 545,
548
common meatus, 511
dorsal meatus, 511, 545
ethmoidal meatuses, 512
meatuses, 511
middle meatus, 511, 545,

550
parietal cartilage, 510
ventral meatus, 511, 546,

550
vessels and nerves, 510
crest, 65, 66, 82
process, 65
region, 73
septum, 82, 84
spine, posterior, 193
Naso-frontal suture, 60, 67
Naso-lacrimal duct, 509, 860,
896
groove for, 82
orifice, 508
suture, 67
Naso-maxillary fissure, 85
notch, 67
opening, 511
suture, 67
Neck, lymph vessels of, 698

of tooth, 395
Nerve or nerves, 760
abducent, 770, 801
acoustic, 770, 803
alveolar, inferior, 851
mandibular, 800
maxillarv, 798
middle, 798
posterior, 798
articular, 761

Nerve, am-icular, 805

anterior, 803

internal, 802

posterior, 802, 812
auriculo-palpebral, 802, 839,

851
axillary, 815, 816
broncliial, 80S
buccal, 803, 839, 845, 851
buccinator, 799
cardiac, 808, 831, 856
cerebral, 793
cervical, 803, 812, 851

eighth, 813

fifth, 813

first, 812

fourth, 813

second, 812

seventh, 813

six-th, 813

third, 813
chorda tympani, 801, 802
ciliary, long, 850

short, 796
coccj'geal, 829
cochlear, 803, 884
cranial, 793, 838, 844, 850
cutaneous, lateral, of leg,
826

of neck, 813

of thigh, 823

posterior, of leg, 826
of thigh, 825
dental, 798
depressor, 807, 853
digastric, 802

digital, 819, 841, 846, 853,
854, 855, 856

lateral volar, of fifth digit,
854
dorsalis penis, 828
eighth, 770
eleventh, 771
ethmoidal, 796, 850
facial, 770, 801, 839, 850
femoral, 824
fifth, 770
fourth, 770

frontal, 796, 838, 845, 850
glosso-pharyngeal, 771, 773,

804
gluteal, anterior, 824

posterior, 824
hsemorrhoidal, posterior,

828
hypoglossal, 771, 773, 810,

840, 845, 853
ilio-hypogastric, 822
lio-inguinal, 822
infraorbital, 798, 845, 850
nfratrochlear, 796, 850
ntercostal, 820
nterosseous, 819
abial, 850

superior, 798
acrimal, 795, 838, 845, 850
aryngeal, 852

anterior, 807
Ungual, 800, 805, 851
lumbar, 822

fifth, 823

first, 822

fourth, 823

second, 822

Nerve, lumbar, sixth, 823

third, 823
mandibular, 798, 800, 838,

845, 850
masseteric, 799
maxillary, 796, 845, 850

incisor, 798
median, 814, 818, 841, 846,

854
metacarpal, 819

volar, 854
metatarsal, dorsal, 856
musculo-cutaneous, 814,815,

819, 853
mylo-hyoid, 800, 850
nasal, anterior, 798

external, 798, 850

posterior, 797, 850
naso-ciliary, 796, 838, 845
ninth, 771
obturator, 824
oculomotor, 769, 773, 780,

794, 806, 808, 838
ttsophageal, dorsal, 839

ventral, 840
of adrenal bodies, 564
of corium of hoof, 894
of cornea, 865
of ductus deferens, 575
of external ear, 875
of eye, 859, 860
of Fallopian tubes, 599
of heart, 629
of kidneys, 560
of penis, 582
of pterygoid canal, 798
of skin, 885
of spermatic cord, 576
of testicles, 574
of uterus, 602
of vagina, 602
of vascular tunic of eye, 867
of veins, 615
olfactory, 793
ophthalmic, 795, 850
optic, 769, 793
palatine, 850

anterior, 798

greater, 798

posterior, 798
pectoral, 814, 815
peroneal, 826

common, 855

deep, 826, 841, 846, 855

superficial, 826, 841, 846,
855
petrosal, 802
pharyngeal, 804, 807, 839,

852
phrenic, 813
plantar, 828, 846

digital, 841

lateral, 841, 856

medial, 841, 856

metatarsal, 856
pterygoid, 799
pudic, 828
pulmonary, 534, 535
radial, 815, 816, 841, 846,

853
recurrent, 807, 853
sacral, 828
saphenous, 824, 855

INDEX

923

Nerve, sciatic, great, 825
second, 769
seventh, 770
sixth, 770
spermatic, external, 823

internal, 833
sphenopalatine, 797, 850
spinal, 810, 840, 845, 853
accessory, 771. 808, 840
splanchnic, great, 831, 842
gi-eater, 856
lesser, 856
smaU, 832, 842
stapedial, 802
subscapular, 814
suprascapular, 814, 815
sympathetic, 629
temporal, 803
deep, 799

superficial, 800, 838, 845,
850
tenth, 771
third, 769
thoracic, 820
anterior, 814
external, 815
long, 815
posterior, 815
thoraco-dorsal, 815
tibial, 827, 841, 846, 856
tracheal, 808
fefigeminal, 770, 795, 838
trochlear, 777, 780, 794
twelfth, 771
tympanic, 804
uhiar, 814, 817, 841, 846,

853
vagus, 629, 771, 773, 805,
839, 845, 851
left, 806
right, 805
vestibular, 803, 884
volar, 819, 841
lateral, 819
medial, 819
zygomatic, 796, 850
Nerve-cell, 760
Nerve-fibers, olfactory, 769
Nerve-plexus, 761
Nervous system, 760, 764, 834,
843, 847
sympathetic, 829, 842,
846, 856
Nervus dorsalis penis, 828

transversarius, 830
Neuroglia, 760
Neurology, 760
Neurone, 760, 829
Nippers, 395
Nodes, lymph, 616
Nodules, aggregated, of large
intestine, 43
of small intestine, 422,
487, 501
lymph, 616
of thyroid tissue, 536
soUtary, of large intestine,
431
of small intestine, 422,
487
splenic, 441
Nodulus, 776

Nostrils, 508, 537, 545, 548
false, 260, 508

Nostrils, true, 508
Notch, alar, 184

cardiac, of lung, 533
carotid, 54
mandibular, 71
naso-maxillary, 67
oesophageal, 435
oval, 54

popliteal, of tibia, 116
sciatic, greater, 106

lesser, 108
semilunar, of ulna, 93
sphenoidal, 60
spinous, 54
Nuchal crest, 79

of skull, 51
Nucleo-cerebellar fasciculus,

777
Nucleus ambiguus, 808
amygdaloid, 792
caudate, 792
cuneatus, 774
dorsaUs, 767
facial, 801
gracilis, 774
hypothalamic, 781
lenticular, 792
motor, dorsal, 808

of fifth nerve, 776

ventral, 808
of lens, 870

of origin of nerves, 760, 774
of soUtary tract, 808
olivary, anterior, 776

posterior, 774
pulpy, of intervertebral

fibro-cartilage, 211
red, 781

sensory, dorsal, 808
terminal, of nerves, 760, 774
Nutrient foramen, 22

of femur, 112

of humerus, 88

of iUum, 106

of metacarpus, 99

of tibia. 116

Obex, 779

Obturator foramen, 109, 112,
152, 202

membrane, 231
Occipital condyles, 50

crest, 51

protuberance, external, 51,
79
internal, 57

sinuses, 688
Occipito-mastoid suture, 52
Occipito-temporal fissure, 850
Esophageal groove, 458, 473

notch, 435

plexus, 808, 831, 853
(Esophagus, 409, 451, 472, 483,

497
Olecranon fossa, 90
Olfactory bulb, 769, 771, 787,
838, 844, 850

cells, 895

nerve-fibers, 769

organs, 905

stria-, 769, 788

tract, 769, 788, 844

Olivary nucleus, anterior, 776

posterior, 774
Olivo-cerebellar fibers, 777
Omaso-abomasal orifice, 460
Omasum, 453, 456, 474
Omental cavity, 442
Omentum, 412

gastro-splenic, 412, 417, 441

greater, 412, 417, 442, 461,
499

lesser, 412, 417, 456, 460,
499
Ontogeny, 17
Optic axis, external, 863

chiasm, 769, 783

commissure, 769

foramen, 53, 75, 82

groove, 53

papilla, 868

recess, 783

tract, 769, 780, 783, 835
Ora ciliaris retinae, 868
Orbit, 74

Orbital foramen, 53, 75
internal, 53

region, 74

wings, 53
Organ, spiral, of Corti, 884

vomero-nasal, 514, 895
Organs of senses, 857, 896, 900,

902
Orifice, aortic, of horse, 626

atrio-ventricular, left, 625,
626
right, 621, 623

ca?co-cohc, 424

ejaculatory, 575

ileo-caecal, 424

ileo-coHc, 501

naso-lacrimal, 508

omaso-abomasal, 460

preputial, 583

pulmonary, of right ventri-
cle, 624

reticulo-omasal, 459

rumino-reticular, 458

ureteral, 562
internal, 562

urethral, external, female,
603, 607
male, 585, 589
internal, male, 585
Orificium externum uteri, 601

internum uteri, 601
Os acetabuli, 110

penis, 594

rostri, 545
Osseous labyrinth, 881
Ossicles, auditory, 877
Ossification, 23

center of, 23

endochondral, 23

intramembranous, 23
Osteoblasts, 23
Osteoclasts, 23
Osteogenesis, 23
Osteology, 20
Ostium abdominale tubae, 599

uterinum tubs, 599
Otic ganglia, 829

ganglion, 799, 838

papilla, 897
Outlet of pelvis. 111, 112, 413
Ova, 598

924

INDEX

Oval notch, 54

Ovaries, 596, 605, 609, 610,

612
Ovisacs, 598
Ovulation, 598

fossa, 597

Palate, hard, 78, 387, 445,
470, 477, 492

soft, 388, 446, 477, 492
Palatine canal, 64

fissure, 66, 78, 82

foramen, anterior, 66
posterior, 65, 76

groove, 65, 78

process of maxilla, 64, 65
of premaxilla, 66

region, 78

sinus, 137, 145

suture, median, 78
transverse, 79
Pallium, 785
Palpebral conjunctiva, 859

fissure, 857

sebum, 859
Pampiniform plexus, 693

of testicles, 574
Pancreatic duct, 434, 463, 487,
491, 501, 506
accessory, 434
Panniculus adiposus, 884
Papilla, 383

filiform, of tongue, 391

foliate, of tongue, 391

fungiform, of tongue, 391

hair, 886

incisiva, 387

of hard palate, 445

of cheeks, 445

of hps, 444

of mammary gland, 604

of skin, 885

of tongue, 391, 447

optic, 868

otic, 897

renal, 565

vallate, of tongue, 391
Paradidymis, 573
Paramastoid process, 50, 78,

79
Paranasal sinuses, 84
Parenchyma of adrenal bodies,
563

of Uver, 438

of mammary glands, 604

testis, 572
Pai'letal border of occipital
bono, 52

cartilage of nasal cavity,
510, 537

crest, 135

external, 51, 57, 73
internal, 58, 81

layer, 384, 412

pleura, 526

radicles, 693

region of skull, 73

suture, 57
Parieto-frontal suture, 57, 60
Parieto-occipital suture, 52, 57
Parieto-temporal canal, 63
Paroophoron, 599

Parotid duct, 404, 477, 482,
492, 495

plexus, 803
Pars ciliaris retinse, 868

disseminata, 589, 592

iridica retinte, 868

longa glandis, 594

optica retina?, 868
Patches, Peyer's, 422, 487, 501
Pecten ossis pubis, 109
Peduncles, anterior, decussa-
tion of, 778

cerebellar, 777
anterior, 776
middle, 776

cerebral, 769, 780, 835, 843

middle cerebellar, 776
Pelvic cavity, 152, 412, 453

girdle, 30, 105

inlet, 152, 160, 181, 202

limb, lymph vessels of, 703

outlet, 413

part of sympathetic system,
832

peritoneum, 413

plexus, 832, 834, 856
Pelvis, lymph vessels of, 701

renal, 559

symphysis, 231
Penis, 580, 589, 592, 594

collum glandis of, 581

corona glandis, 580

corpus cavernosum, 581

fossa glandis of, 581

glans, 580, 589, 594

structure of, 581

suspensory ligaments, 580

trabecular of, 581

tunica albuginea, 581

vessels and nerves of, 582
Pericardiac pleura, 526
Pericardium, 617, 705, 734,

742
Perilymph, 881
Perilymphatic space, 881
Perimysium, 252
Periople, 888, 891
Periophc corium, 892
Periorbita, 860
Periosteum, 21

alveolar, of teeth, 395
Peripheral gangha, 829
Peritoneal cavity, 411
Peritoneum, 411, 441

pelvic, 413
Permanent teeth, 394, 396
Petro-basilar canal, 190
Petrosal crest, 62, 81

sinuses, dorsal, 688
ventral, 688
Petrotympanic fissure, 63
Petrous ganghon, 804
Peyer's patches, 422, 487, 501
Pharyngeal aponeurosis, 407

isthmus, 408

opening of Eustachian tube,
878

orifices of Eustachian tubes,
406

plexus, 807, 852

recess, 407
Pharynx, 405, 451, 472, 482,

497
Philosophical anatomy, 17

Phrenico-costal sinus, 530
Phylogeny, 17
Pia mater, 763
cerebral, 763
spinal, 763
Pillar, posterior, of soft palate,

408
Pillars of rumen, 457
Pilomotor fibers, 829
Pinchers, 395
Pineal body, 781, 835

recess, 783
Piriform lobe, 784, 788, 850
of brain, 769
recess, 408
Pituitary body, 769, 780, 782,
835, 847
fossa, 53
Plantar arch, deep, 697, 721
distal, 678, 697, 719
proximal, 678, 679, 719
Plate, cribriform, of ethmoid,

54
Pleura, 526, 540, 547
costal, 526
diaphragmatic, 526
mediastinal, 526
parietal, 526
pericardiac, 526
pulmonary, 526
visceral, 526
Pleural cavity, 526

reflection, diaphragmatic
line of, 530
lines of, 530

sternal reflection of, 530
vertebral fine of, 530
Plexus, abdominal, 832
adrenal, 834
aortic, abdominal, 833

thoracic, 831
auricular, anterior, 803
basilar, 689

brachial, 814, 840, 846, 853
cardiac, 831
carotid, 804
external, 830
internal, 830
cavernous, 830, 834
cervical, dorsal, 812

ventral, 812
chorioid, 763, 780, 783, 787,
792
of fourth ventricle, 773
ca>Uac, 832, 843, 856
colic, 856
coronary, 692, 831
dental, maxillary, 798
dorsal, 692
gastric, 833
anterior, 852
posterior, 852
ha^morrhoidal, 834

anterior, 856
hepatic, 439, 833
intraosseous, 692
lumbosacral, 824, S41, 846,

855
mesenteric, anterior, 833,
856
posterior, 833, 856
myenteric, 833
nerve-, 761
oesophageal, 808, 831, 853

INDEX

925

Plexus, pampiniform, 693
of testicles, 574

parotid, 803

pelvic, 832, 834, 856

pharyngeal, 807, 852

prostatic, 834

pulmonary, 808, 831, 853

renal, 834

s. sinus venosus sclerse, 863

spermatic, 574, 834, 856

splenic, 833

submucous, 833

subsidiary, 856

tracheal, 808

tympanic, 804

utero-ovarian, 834

utero-vaginal, 834

vascular, 614

venous, 614

vesical, 834

volar, 692
Plica pterygomandibularis,

390
Pododerm, 892
Pons, 769, 775, 835, 843, 847
Pophteal line of tibia, 115

notch of tibia, 116
Portal fissure, 434, 468

ring, 433

system, 614
Post glenoid foramen, 60

process, 60, 73
Pouch, cutaneous, 884

guttural, 879

infraorbital, 900

inguinal, 900

interdigital, 900

lacrimal, 900

recto-genital, 415

recto-vesical, 414

vesi co-genital, 415
Premaxillary region, 73
Premolar teeth, 394, 399

deciduous, 403
Preorbital region of horse, 76
Prepubic tendon, 292
Prepuce, 582, 590, 593, 595

of clitoris, 604
Preputial di v^erticulum, 593

frenum, 583

orifice, 583

ring, 583
Presylvian fissure, 785, 844,

849
Process, acoustic, external, 61,
74

angular, of mandible, 195

caudate, of Uver, 434

cihary, 866

clinoid, anterior, 190
posterior, 170, 190

coronoid, of mandible, 71

cuneiform, 517

frontal, 191

hyoid, 62

lacrimal, 194

hngual, 72

mammillary, 45, 163

mastoid, 61, 74

maxillary, 194

muscular, of temporal bone,
63

nasal, 65

palatine, of maxillae, 64, 65

Process, palatine, of pre-
maxillae, 66
paramastoid, 50, 78, 79
postglenoid, 60, 73
pterygoid, 54, 171
spinous, of lumbar vertebrae,
129
of thoracic vertebrae, 128
of vertebrae, 44
styloid, 63, 871
of radius, 199
of ulna, 148
supraorbital, 59, 73
urethral, 581
vocal, 517

zygomatic, of frontal bone,
59
of malar bone, 68
of maxillary bone, 65
of temporal bone, 60
Processus anconaeus, 93
cornus, 136
urethrae, 585
vaginalis, 577
Projection fibers, 792
Promontory, 876
Prostatic ducts, 579, 585, 589

plexus, 834
Protuberance, occipital, ex-
ternal, 51, 79
internal, 57
Proventriculi of stomach, 453
Psoas tubercle, 106
Pterygoid canal, 54, 67
crest, 54
foramen, 54
fossa, 170
process, 54, 171
Pterygo-palatine fossa, 67, 76
Pubic groove, 109
Pulmonary circulation, 704
lobule, 534

orifice of right ventricle, 624
pleura, 526
plexuses, 808, 831, 853
valve, 625
Pulp cavity of teeth, 395
of tooth, 395
spleen, 441
Pulpy nucleus of interverte-
bral fibro-cartilage, 211
Puncta lacrimaha, 860
Punctum lacrimale, 858
Pupil, 866

Pupillary border of iris, 866
Pyloric opening of stomach,
416

sphincter, 417
valve of stomach, 419
Pyramid of medulla oblongata,
773
renal, 558, 565
Pyramidal decussation, 773,
774
fasciculus, 776
tracts of oblongata, 774

Radiation of corpus callosum,

790
Radicles, parietal, 693

visceral, 693
Radii lentis, 870
Radio-carpal sac, 222

Rami communicantes, 829

of lower jaw, 70
Ramus communicans, 811

gray, 829
Raphe of oblongata, 774

pharyngis, 407

praeputii, 583

scroti, 574
Recess, infundibular, 783

optic, 783

pharyngeal, 407

pineal, 783

piriform, 408
Recessus cochlearis, 881

elUpticus, 881

sphaericus, 881
Recto-coccygeus band, 431
Recto-genital pouch, 415
Recto-vesical pouch, 414
Rectum, 429, 488, 465, 502
Red nucleus, 781
Refractive media of eyeball,

869
Region, cranial, 73, 78

frontal, of skull, 73

guttural, 78

maxillary, of horse, 76

nasal, 73

orbital, 74

palatine, 78

parietal, of skull, 73

premaxillary, 73

preorbital, 76
Renal columns, 558

corpuscles, 558, 559

crest, 558, 559

hilus, 555

papilla, 565

pelvis, 559

plexuses, 834

pyramids, 558, 565

sinus, 555

tubules, 559
Respiratory bronchioles, 534

system, 508, 537, 545, 548
Restiform bodies, 773
Rete carpi dorsale, 657

mirabile, 614, 707
cerebrale, 710

testis, 586
Retia vasculosa, 614
Reticulo-omasal orifice, 459
Reticulum of lymph nodule,
616

of stomach, 453, 455, 473
Retina, 868
Retractor ani, 432
Rhombencephalon, 773, 785,

787
Rhomboideus capitis, 371
Ridgp, trochanteric, of femur,

113
Rima glottidis, 522, 539, 546

oris, 477, 491
Ring, cihary, 866

fibrous, of heart, 628

of intervertebral fibro-
cartilage, 211

inguinal, abdominal, 290,
292
external, 288, 292
internal, 290, 292
subcutaneous, 288, 292

portal, 433

926

INDEX

Ring, preputial, 583

of trachea, 525

vaginal, 290, 576, 587
Root of hair, 886

of tongue, 390

of tooth, 395
Rostrum of corpus callosum,
789

suis, 545
Rubro-spinal tract, 778
Rumen, 453, 472

blind sacs of, 454

cardia of, 458

ca\aty of, 456

dorsal curvature of, 454

grooves of, 454, 455

longitudinal grooves of, 454

mucous membrane of, 458

muscular coat of, 461

pillars of, 457

serous coat of, 460

ventral curvature of, 454
Rumino-reticular fold, 457

groove, 454

orifice, 458

Sac, anal, 502

blind, of rumen, 454

carpo-metacarpal, 222

conjunctival, 859

intercarpal, 222

intertarsal, 240

lacrimal, 860

radio-carpal, 222

synovial, of hock-joint, 240

tarso-metatarsal, 240

tibio-tarsal, 240
Sacculations of caecum, 424
Saccule, 883

laryngeal, 522, 550
Saccus csecus, 416
Sacral canal, 43

crest, lateral, 129
median, 129

foramen, 41
ventral, 129

ganglia, 832

part of sympathetic system,
856
Sagittal pole, 836

sinus, 687, 688
Scala tympani, 882

yestibuli, 882
Sciatic foramen, greater, 231
lesser, 231

notch, greater, 106
lesser, 108
Sclera, 863, 897
Scrotum, 574, 586, 591, 593
Scutiform cartilage, 871
Sebum outaneum, 885

palpebral, 859
Secretory fibers, 829
Sectorial teeth, 494
Semicircular canals, osseous,
881

ducts, membranous, 883
Semilunar canal of third pha-
lanx, 103

crest of third phalanx, 103

ganglion, 795

notch of uhia, 93

Seminal vesicles, 571, 578, 587,

591, 593
Seminiferous tubules of testi-
cles, 572
Sense organs, 857, 896, 900,

902
Sensory fibers, 808
nucleus, dorsal, 808
root of fifth nerve, 776
Septum, dorsal, median, 766
interalveolar, 64
intermuscular, 254
of forearm, 305
of gluteal region, 317, 318
of leg, 318
of shoulder, 298
interventricular, 627
nasi, 82, 84, 510

cartilage of, 510
pellucidum, 791
penis, 589, 594
scroti, 574
Serous coat of bladder, 562
of Fallopian tubes, 599
of large intestine, 430, 465
of liver, 438
of rumen, 460
of small intestine, 421
of spleen, 441
of stomach, 417, 499
of uterus, 601
folds, 384

layer of pericardium, 617
membranes, 384
Shaft of hair, 886
Sheath, carpal, of deep digital
flexor, 315
of superficial digital
flexor, 313
fibrous, of tendon, 254
synovial, 253

digital, of deep digital
flexor, 316
of superficial digital
flexor, 314
of common digital ex-
tensor, 307
of coraco-brachialis mus-
cle, 300
of extensor carpi ob-
liquus, 310
radialis, 306
of flexor carpi radialis, 310
of lateral digital extensor,

309, 335
of long digital extensor,
335
flexor, 340
of tibialis anterior, 337
of ulnaris lateralis, 313
tarsal, of deep digital flexor,
342
Shoulder girdle, 29
Sidebone, 104
Sigmoid flexure, 589
Sinus, cavernous, 688
communicans, 688
coronary, 681, 754
opening of, 621
ethmoidal, 86

frontal, 59, 85, 143, 175, 197
fronto-turbinate, 85
intercavernous, 688
lactiferous, 605, 609

Sinus, longitudinal, dorsal, 687
ventral, 688

lymph, central, 616
peripheral, 616

maxillary, 84, 144, 175, 197
inferior, 84
superior, 85

occipital, 688

of aorta, 630

of bone, 21

of dura mater, 687

of lymph nodule, 616

of pulmonary artery, 629

palatine, 137, 145

paranasal, 84

petrosal, dorsal, 688
ventral, 688

phrenico-costal, 530

renal, 555

sagittal, 687, 688

sphenoidal, 53, 145, 175

sphenopalatine, 53, 67, 86

straight, 688

tarsi, 120

tonsillar, 446

transverse, 688

of pericardium, 617

urethral, 581

urogenital, 603

venarum of right atrium of
heart, 620

venous, 615

vertebral, longitudinal, 689
Skeleton, 20, 32, 125, 156, 161,
184

appendicular, 20

axial, 20

flat bones, 20

irregular bones, 20

long bones, 20

medullary cavity, 20

number of bones, 20

short bones, 20

splanchnic, 20

visceral, 20
Skin, 884, 887, 898, 900, 901,
903

appendages of, 886, 901, 903

of concha, 871

of eyelids, 858

of mammary glands, 604

of nostrils, 509
Skull, brachycephalic, 195

dolichocephalic, 195

mesaticephalic, 195

synarthroses of, 217

synchondroses of, 218
Smegma prsputii, 583
Smell, organ of, 895
Snout, 545

Soft palate, 387, 446, 477, 492
Sole, 889, 892

Sohtary nodules of large in-
testine, 431
of small intestine, 422,
487
Space, epidural, 762

interalveolar, 64, 65, 71, 78

interdental, 64

interosseous, of leg, 116
of radius, 91

mandibular, 70

perilymphatic, 881

subarachnoid, 762

INDEX

927

Space, subdural, 762

submaxillai-y, 70
Special anatomy, 17
Spermatic cord, 575, 586, 591,
593

plexus, 574, 834, 856
Spheno-frontal suture, 60
Sphenoidal notch, 60

sinus, 53, 145, 175
Spheno-occipital crest, 53
Sphenopalatine foramen, 65,
67, 76, 82

gangUa, 797, 829

sinus, 53, 67, 86
Spheno-squamous suture, 61
Sphincter ani externus, 432
internus, 432

cardiac, 417

ilei, 424

of mammary gland, 605

pupillse, 867

pyloric, 416, 417

vesica;, 562
Spinal arachnoidea, 763

cord, 764, 834, 843, 847

dura mater, 762

gangUon, 811

pia mater, 763

root of fifth nerve, 775
Spine, ischiatic, 106, 107

nasal, posterior, 193

of hoof, 890

of tibia, 116

ventral, 26

of cervical vertebrse, 125
Spinous notch, 54

process of cervical vertebrse,
125
of lumbar vertebrae, 129
of thoracic vertebrse, 128
of vertebrse, 44
Spiral canal of cochlea, 882

folds of abomasum, 460

organ of Corti, 884
Splanchnic fibers, afferent, 829
efferent, 829

ganglion, 832
Splenial fissure, 844, 850
Splenic angle, 433

nodules, 441

plexus, 833
Splenium, 789

Spongy substance of bone, 21
Squamous suture, 58, 60, 61

temporal bone, 60
Sternal flexure, 425

line of pleural reflection, 530
Stomach, 415, 453, 472, 483,
497

cardiac opening of, 416, 472,
498

fibers of, 417

greater curvature of, 416

lesser curvature of, 416

mucous coat of, 418

pyloric extremity, 416
opening, 416

serous coat of, 417, 499

structure of, 417
Stop of face, 196
Straight sinus, 688
Stratum corneum, 885

germinativum, 885
of hoof, 891

Stratum granulosum, 598

tectorium of hoof, 891
Stria, lateral, 769, 788

medial, 769, 788

medullaris, 781

olfactory, 769, 788
^ terminahs, 781, 792
Stroma iridis, 867

of kidney, 559

of ovary, 598

of thyroid gland, 536

vitreous, 869
Styloid process, 63, 871
of radius, 19tf
of uhia, 148
Stylo-mastoid foramen, 62
Subarachnoid cisterns, 762

space, 762
Subcallosal gyrus, 788
Subcarpal arch, 65.7
Subcutaneous inguinal ring,
288, 292

tissue, 884
Subcutis, 884
Subdural space, 762
Sublimbic fissure, 786
Sublingual duct, 405, 496

fold, 390
Submaxillary duct, 405

space, 70
Submucous plexus, 833

tissue, 383
Subserous tissue, 384
Subsidiary plexus, 856
Subsphenoidal canal, 54
Substantia gelatinosa of spinal
cord, 767

perforata posterior, 769, 780

nigra, 780

propria, 864
Suburethral diverticulum, 607
Succus entericus, 421
Sulcus, callosal, 786

central, of hoof, 891

cerebellar, 777

collateral, of hoof, 891

intertubercularis, 89

limiting, of fourth ventricle,
779

median, of fourth ventricle,
779

muscularis of tibia, 117

of brain, 771

omasi, 460

rhinahs, 785, 837, 844, 850

sclerae, 863
Supracondyloid crest, lateral,
of femur, 112
medial, of femur, 112

fossa of femur, 112
Supraoccipital part of skull, 51
Supraorbital canal, 137

foramen, 59, 73

groove, 137

process, 59, 73
Supraspinous bursa, 213
Suprasplenial fissure, 850
Suprasylvian fissure, 785, 837,

844, 849
Supratrochlear foramen, 198
Suspensory ligaments of penis,

580
Sustentaculum tali of fibular

tarsal bone, 121

Sutura harmonia, 207
serrata, 207
squamosa, 207
Suture, 207
cranial, 217
frontal, 60
fronto-lacrimal, 60
fronto-maxillary, 60
fronto-palatine, 60
naso-frontal, 60, 67
naso-lacrimal, 67
naso-maxillary, 67
occipito- mastoid, 52
palatine, median, 78

transverse, 79
parietal, 57
parieto-frontal, 57, 60
parieto-occipital, 52, 57
spheno-frontal, 60
spheno-squamous, 61
squamous, 58, 60, 61
Sympathetic nervous system,
829, 842, 846, 856
trunk, 829
Symphysis, 207

mandibulsp, 72, 218
pelvis, 231
Synarthroses, 207

of skull, 217
Synchondrosis, 207

'of skull, 218
Syndesmosis, 207
Synovial bursa, 253
' fossa?, 208

membrane of carpal joints,
222
of elbow joint, 219
of hip joint, 232
sacs of hock joint, 240
sheath, 253

310
of lateral digital extensor,

309, 335
of long digital extensor,
335
flexor, 340
of tibialis anterior, 337
of ulnaris lateralis, 313
Systematic anatomy, 17, 18

Tabttla vitrea, 21
Tactile hairs, 886
Taenia thalami, 783
Tapetum, 897

cellulosum, 902

fibrosum, 865

of chorioid, 865
Tarsal sheath of deep digital

flexor, 342
Tarso-metatarsal sac, 240

928

INDEX

Tarsus of eye, 859
Taste buds, 895

organ of, 895
Teat of mammary glands, 604,

609, 613
Teeth, 394, 396, 448, 471, 478,
479, 493

alveolar periosteum of, 395

canine, 394, 398, 448, 479,
493
deciduous, 403
, carnassial, 494

cement of, 395

cheek, 394, 399, 448, 471,
480, 494
lower, 401
upper, 400

crown of, 395

deciduous, 394, 403

enamel of, 395

eruption of, 403, 450, 471,
481, 495

incisor, 394, 397, 448, 471,
479, 493
deciduous, 403, 448

mandibular, 401

maxillary, 400

molar, 394, 399

neck of, 395

nippers, 395

permanent, 394, 396

pinchers, 395

premolar, 394, 399
deciduous, 403

pulp of, 395
cavity of, 395

root of, 395

sectorial, 494

structure of, 395

temporary, 394

wolf, 64, 71, 395, 400
Tegmentum, 780
Tela chorioidea, 763, 773, 779,

783, 787
Telencephalon, 783
Temporal canal, 63, 81

crest, 137

foramen, 54

fossa, 73

wings of horse, 53
Temporary teeth, 394
Tendinous center of dia-
phragm, 287
Tendo AchiUis, 338

calcaneus, 338
Tendon, 252

interosseous, 225

of ergot, 306

prepubic, 292
Tentorium cerebelli, 762

osscum, 81
Teres tuberosity, 88
Terminal line, 110, 410

nuclei of nerves, 760, 775
Testicles, 571, 586, 591, 593

deferential fold of, 577

descent of, 577

ducts of, 573

lymph-vessels of, 574

pampiniform plexus of, 574

parenchyma of, 572

seminiferous tubules, 572

structure of, 572

tunica albuginea of, 572

Testicles, tunica vaginalis
propria of, 572

vessels of, 573
Thalamo-cortical fibers, 778
Thalamus, 781
Theca folliculi, 598
Thickness of skin, 887
Third eyeUd, 859, 896

ventricle, 783
Thoracic aortic plexus, 831

cavity, 28, 525, 540

duct, 615, 697, 722, 740, 756

ganglia, 831, 842

limb, lymph vessels of, 703

part of sympathetic system,
831
Thorax, 547

lymph vessels of, 700
Thyro-hyoid membrane, 518
Thyroid cartilage, 538, 546,
515, 550

cornua, 72
Tibial crest, 116
Tibio-tarsal sac, 240
Tissue, interlobular, 383

muscular, 384

subserous, 384
Tongue, 390, 447, 471, 478,

493
Tonsil, 388, 471, 478, 493
Tonsillar sinus, 446
Topographic anatomy, 17, 18
Torus pyloricus, 485
Trabecular carnese of right
ventricle, 625

of lymph nodule, 616

of penis, 581

splenic, 441
Trachea, 523, 540, 546, 550
Tracheal ducts, 700

lymph ducts, 725, 756

plexus, 808
Tract, oKactory, 769, 78S, 844

optic, 780, 783, 835

pyramidal, 774

rubro-spinal, 778
Tractus centralis of thymus

gland, 536
Tragus, 886
Tricuspid valve, 624
Trigonum olfactorium, 769,
784, 788

vesicae, 562
Trochanter major of femur,
113

minor of femur, 112

tertius, 112
Trochanteric fossa of femur,
113

ridge of femur, 113
Trochlea of femur, 113

of tibial tarsal bone, 120
Trochlear foramen, 54, 75
Trochoid, 210
True nostril, 508

vocal cords, 522, 550
Truncus bicaroticus, 635

intestinaUs, 737

of corpus callosum, 789
Tuber calcis of fibular tarsal
bone, 121

cinereum, 769, 782, 847

coxse, 106

ischii, 108

Tuber sacrale, 106
scapulae, 87
spina?, 86
Tubercle, anterior, of tha-
lamus, 781
lacrimal, 68
psoas, 106
Tuberculum cinereum, 773
faciale, 773
olfactorium, 844
pubicum, 109
Tuberosity, alveolar, 64, 78
deltoid, 88
facial, 137
maxillary, 65
of tibia, 116
Tubules of mammary glands,
605
renal, 559
seminiferous, of testicles,

572
uriniferous, 559
Tunic, abdominal, 288, 361
fibrous, of eye, 863
vascular, of eye, 865
Tunica albuginea, 572, 589
of penis, 581
propria of skin, 885
vaginaUs, 576, 586, 593
communis, 576
parietal layer of, 574, 576
propria, 572
visceral layer of, 576
Turbinate crest, dorsal, 67
ventral, 64
fold, dorsal, 513
ventral, 513
Tusks, 479

Tympanic cavity, 875
mucous membrane, 878
opening of Eustachian tube,

878
plexus, 804

Umbilical fissure, 435
fold, lateral, 414
median, 414
Ureteral orifice, 562

internal, 562
Ureters, 554, 561, 566, 569, 570
Urethra, 554
bulb of, 581
female, 604, 609, 611
male, 571, 584, 590, 593, 595
Urethral crest, 585

orifice, external, female, 603,
607
male, 585, 589
internal, male, 585
process, 581
sinus, 581
Urinary bladder. See Bladder

organs, 554, 564, 567, 569
Uriniferous tubules, 559
Urogenital sinus, 603

system, 554
Uterine cotyledons, 607

tubes, 596, 599, 606, 609,
610, 612
Utero-ovarian plexuses, 834
Utero-vaginal plexus, 834
Uterus, broad ligament of, 415

INDEX

929

Uterus, female. 596, 599, 606,

609, 610, 612
masculinus, 579, 589, 592,

593, 594
Utricle, 882
Uvula, 478

Vagina, 596, 602, 607, 610,

613
Vaginal ring, 290, 576, 587
Vallate papilla of tongue, 391
Valve, aortic, 626
bicuspid, 626
ileo-csecal, 421
ileo-colic, 501
pulmonary, 625
pyloric, of stomach, 419
tricuspid, 624
Valvular fold of caecum, 424
Vas deferens, 575, 576, 591
Vasa vasorum, 615
Vascular plexus, 614

tunic of eye, 865
Vasomotor fibers, 829
Vein or veins, 614, 681, 719,

740, 754
abdominal, posterior, 696

subcutaneous, 696, 721
adrenal, 563, 693
alveolar, inferior, 684
auricular, great, 685
brachiocephalic, 755
bronchial, 683, 690, 755
buccinator, 686, 740
cardiac, 681

great, 681, 755

lesser, 755

middle, 681

small, 682
central, of adrenal bodies,

563
cephalic, 687, 690, 755

accessory, 690, 720, 755
cerebellar, dorsal, 689

ventral, 689
cerebral, 687, 689

ascending, 689

basal, 689

deep, 689

descending, 689

dorsal, 685

great, 689

internal, 689

ventral, 685, 720
cervical, deep, 682

inferior, 687
circumflex, lateral, 695
coats of, 615
condyloid, 685
coronary, 628

left, 681

right, 681
dental, 684
digital, 692, 721, 756

common, 692

dorsal, 720, 755

lateral, 720

medial, 720

volar, 720, 755
common, 720
diploic, 687, 689
dorsal, 682
59

Vein or veins, emissarium, 615
emissary, 687

facial, anterior auricular,
684

transverse, 685, 686
femoral, 695, 756

anterior, 696

deep, 695

posterior, 696
frontal, 720
gastric, anterior, 695

posterior, 695
gastro-duodenal, 695
gastro-epiploic, right, 695
hepatic, 439, 693
hypogastric, 695
iliac, circumflex, 695

common, 695

external, 695, 756

internal, 695, 756
iliaco-femoral, 695
ilio-lumbai', 695
infraorbital, 686
intercostal, dorsal, 683

ventral, 682
internal coat, 615
interosseous, common, 692
jugular, 683, 719, 755

external, 720, 755

internal, 719, 755
labial, 685

common, 685

superior, 720
lingual, 686

dorsal, 683
lumbar, 693, 695
masseteric, 685
maxillary, external, 685, 740

internal, 683, 755
median, 691
meningeal, 687, 689

middle, 684
mesenteric, 693

anterior, 694

posterior, 694
metacarpal, 692,J20, 755
metatarsal, 697, 721, 756
middle coat, 615
nasal, dorsal, 720, 740
obturator, 695
occipital, 685
oesophageal, 683, 687
of bladder, 562
of bone, 22
of brain, 793
of corium of hoof, 894
of cranium, 689
of ductus deferens, 575
of external ear, 875
of Fallopian tubes, 599
of head, 683
of internal ear, 884
of mammary glands, 721
of neck, 683
of ovary, 598
of pehnc limb, 695
of penis, 582
of retina, 869
of skin, 885

of thoracic limb, 690, 720
of uterus, 602
of vaginn, 602
of vascular tumc of eye, 867
ophthalmic, 686

Vein or veins, orbital, 720
palatine, gi'eat, 686
pancreatic, 695 '
pancreatico-duodenal, 695
parotid, 687
perineal, 721
phrenic, 693
plantar, 697
popliteal, 696, 756
portal, 438, 693, 722, 755
pterygoid, 684
pudic, external, 696, 721

internal, 575
puhnonary, 534, 535, 614,

625, 681
radial, 755

anterior, 692
renal, 560, 693
sacral, middle, 721
saphenous. 696, 721, 756
satellite, 614
spermatic, 574, 576

internal, 693
sphenopalatine, 686
spinal, 689
splenic, 693, 694
structure of, 615
sublingual, 687, 720
submental, 685
tarsal, perforating, 697, 721

recurrent, 696, 721, 756
temporal, posterior, deep,
684

superficial, 684
thoracic, external, 690

internal, 682
thoraco-dorsal, 690
thyroid, 687
tibial, anterior, 696, 756

posterior, 697, 756

recmrent, 696
tracheal, 687
ulnar, 692, 755
umbilical, 704
utero-ovarian, 693
valves of, 615
vena azygos, 621, 682, 755

cava, 614
anterior, 682

opening of, 620
posterior, 692, 720, 755
opening of, 620

hemiazygos, 683, 719, 755

reflexa, 686, 720, 740

rhinalis posterior, 689
vertebral, 682, 689
Velum, medullary, 776

anterior, 779

posterior, 779
Vena comitans, 614
Venae vorticosje, 867
Venous arch, 692
plexuses, 614
sinuses, 615
Ventricle, fourth, 778
lateral, 785, 791

of larynx, 522, 539, 550
middle, of larvnx. 522
of heart, left, 625

right, 623
of olfactory bulb, 787
third, 783
Vermis cerebelli, 771, 776
Vertebral canal, 26, 44

930

INDEX

Vertebral column, 25, 125,
156, 161, 184

curves, 129, 165

foramen, 26

formula, 25

line of pleural reflection, 530

notches, 26

sinuses, longitudinal, 689
Vertex corneje, 864
Verticalis auriculae, 875
Vesical plexus, 834
Vesicles, seminal, 571, 578,

587, 591, 593
Vesico-genital pouch, 415
Vesicular seminales, 571, 578,

587, 591, 593
Vestibular ganglion, 803
Vestibule of ear, 881

of larynx, 522

of omental cavity, 442
Veterinary anatomy, 17
Vibrissae, 886

Vidian canal of horse, 54
Visceral layer, 384, 412
of pericardium, 617

pleura, 526

radicles, 693
Vitreous body, 869, 897

humor, 869

stroma, 869
Vocal cords. 521, 539, 546, 550
false, 522, 550
true, 522

process, 517
Vomero-nasal organ, 514, 895
Vortex cordis, 628
Vulva, 596, 603, 607, 610, 611,

613
Vulvar cleft, 603

Wall of hoof, 887, 891
White columns of spinal cord,

767, 768

White commissure of spinal
cord, 766
line of hoof, 889
matter of nervous system,
760
of spinal cord, 767
Wolf tooth, 64, 71, 395, 400

Xiphoid cartilage, 28, 49

ZoisTE, epigastric, 411
hypogastric, 411
intermediate, of kidney, 558
mesogastric, 411
Zonula ciliaris, 870
Zygomatic arch, 60, 73
process of frontal bone, 59
of malar bones, 68
of maxillary bone, 65
of temporal bone, 60

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