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A. Franklin Shull,
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FUNCTIONAL ANATOMY
OF THE MAMMAL
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I
M£Graw-Hill Pubof which Edmund
in the Agricultui'q.l
Consultin~ Editor.
FUNCTIONAL ANAT~
OF THE MAMM~
A Guide to the Dissection
of the Cat and an Introduction to
the Structural and Functional Relationship
Between the Cat and Man
by W. James Leach .
ASSISTANT PROFESSOR OF BIOLOGY
TEMPLE UNIVERSITY
First Edition
McGRAW-HILL BOOK COMPANY, INC.
New York and London
1946
!'his 18 trom.
'Cotbari Book OeDot. 8.MBAY. 12
FUNCTIONAL ANATOMY OF THE MAMMAL
Copyright, 1946, by the
McGraw-Hill Book Company, Inc.
PRINTED IN THE UNITED STATES OF AMERICA
All rights reserved. This book, or
parts thereof, may not be reproduced
in any form without permission of
the publishers.
The quality of the materials used in the
manufacture of this book is governed by
continued postwar shortages.
PREFACE
THIS BOOK is intended for students who are beginning work in anatomy
and has been planned to meet the requirements of various curriculums.
Special attention has been given to th€ needs of students of anatomy in
educational field's, particularly in nursing, health, and physical education,
where opportunity to do human dissection may be la;cking or limited .
. Such considerations are also of value in liberal arts courses of a premedical
character. Therefore, the material has been s~lected to substantially
supplement courses in human anatomy (and phy"iology); to serve as the
mammalian portion of courses in comparative vertebrate anatomy; or to
be used in courses principally concerned with g~neral mammalian features.
The presentation is designed to integrate a rtJ- ther specific laboratory
study of the cat with text material of a more gerleral character with emphasis on man. As far as possible, descriptive avatomy has been treated
with special reference to the functional organization of the parts and their
interrelationships. In this, connection, functional anatomy gives emphasis
to the manner in which the parts work together rather than with how
each of the parts is constructed as a separate unit. However, a comprehensive view of anatomy must be based upon the observable details, and
considerable preliminary description seems necessary in presenting an
understandable treatment of functional relationships.
Text material in anatomy is really intelligible only when studied in
.connection \vith actual dissection, or after much laboratory experience
has been acquired. For this reason, the practice of substituting a quadruped mammal for man is a common laboratory ptoc~dure in many courses
which do not include human dissection. There can be but little doubt
that the practice is very helpful, but it also presents many difficulties to
the average student. One of the principal aims of this book is to consider
the relationships between quadruped mammals jl.nd man and to discuss
them in some detail. The modifications of structure, which have accompanied the assumption of the erect posture in man, would appear to deserve
much more consideration than has been given to them in usual comparative anatomy courses.
Certain specific conditions in the cat, however, have been especially
emphasized because of its common use in experiI1lental physiology, pharmacology, and as a subject for veterinary practice. Many medical school
students who have had work in mammalian anatomy appear poorly prepared for experimental studies on mammals bec:,J.use their attention had
not been directed early to the application of JIlammalian anatomy to
physiologic investi)l!;ations. Other considerations have been drawn to the
attention of the student to stimulate his interest in the cat as an animal
from which much other practical information can be obtained.
v
PREFACE
VI
Some tabulated material included in the text has been modified from
unpublished outlines prepared by Professor J. Percy Moore of the University of Pennsylvania. The author is also indebted to' Professor Moore
for many suggestions on the functional treatment of anatomy. The author
greatly appreciates the helpful advice and criticism of present and former
colleagues and students. Particular mention is made of the help of Profs.
M. L. Leitch, M. F. Keen, and O. G. Rybachok, who hav.e used an earlier
form of the book in their classes and have called the author's attention
to many matters-requiring correction. Other helpful advice has been contributed by Prof. A. A. Schaeffer, chairman of the Biology Department in
Temple University.
The' author is particularly indebted to W. B. Strickland who has copied
and relettered the original figures and assisted with the modification of
figures from l\livart. Publishers and authors have been most generous
in granting permission for use of other figures and the author wishes to
express his thanks here to W .. B. Saunders Company, Charles Scribner's
Sons, The C. V. Mosby Company, Medical Publishers, and Lea & Febiger.
Acknowledgment is also due S. H. Camp and Company for permission
to use four figures by Tom Jones, which are reproduced from his "Anatomical Studies, for Physicians and Surgeons." Many of my students have
contributed much to figures in the present work. Special mention is made
of assistance given by Earl Kvam on the drawings of the muscular system.
For terminology and pronunciation, the author has relied principally
on Dorland's "Medical Dictionary." For reference to the descriptive anatomy of the cat, Reighard and Jennings, "Anatomy of the Cat," has been
most helpful.
W. JAMES LEACH.
PHILADELPHIA, PA.,
. October, 1946.
CONTENTS'
PREFACE
v
Chapter I
.
GENERAL CONSIDERATIONS
1
Terms and definitions. The principle of homology. Divi~ions of structural
organization. Anatomical position and posture. Characteristics and classification of mammals. Anomalous and vestigial structures.
Chapter II
THE SKELETAL SYSTEM . . . . . .
23
Functions and divisions of the skeleton. Terms used in describing bones.
The mammalian skull. Skeleton of the cat. Articulations and lever systems.
Chapter III
SUPERFICIAL DISSECTION OF THE CAT
59
Superficial characters and landmarks. Dissection of the skin. Fascia, cutaneous nerves, and blood vessels.
Chapter IV
A STUDY OF THE VOLUNTARY MUSCLES.
67
Structural and functional features of a skeletal muscle. Anatomical position and muscle actions. A practical study of muscle actions in man.
:Method of muscle dissection. Functional anatomy of the principal muscles
of the cat. Special modification of muscles in man. Study list of muscular
activities.
Chapter V
A SURVEY OF INTERNAL ANATOMY
111
Sectional aspects of the head and pharynx. Body cavities, membranes,
and general visceral arrangements. Innervation of the viscera. Practical
problems on internal anatomy.
Chapter VI
THE ALIMENTARY SYSTEM . . . .
130
The alimentary canal. Glandular derivatives of the canal.
Chapter VII
)
141
THE RESPIRATORY SYSTEM
The course of respiratory air. General features of the lungs.
vii
Vlll
CONTENTS
Chapter VII I
147
THE VASCULAR SYSTEM . . . . . . .
The heart and main vessels. Systemic veinf'i. Systemic arteries. Anomalies
of the vascular system. Circulation before birth. Lymph vessels and nodes.
General discussion and problems.
'.
Chapter IX
l69
THE UROGENI,TAL SYSTEM . . . .
The reproductive system. Nephric system.
Chapter X
180
THE NERVOUS SYSTEM
General features 01 the brain and cranial nerves. The brain 01 the cat. The
cranial nerves. Spinal cord and nerves. The brachial nerve plexus. Sacral
and lumbal' plexi. Autonomic division. General discussion.
Chapter XI
207
SPECIAL SENSORY APPARATUS . .
Unique character of special sense organs. The functional anatomy of the
eye. The hearing apparatus.
j
Chapter XII
:"
THE ENDOCRINE ORGANS . . . . . .
215
A summary and discussion.
Appendix
LABORATORY PREPARATION AND PRES,ERVATION OF
DISSECTION MATERIALS . . . . .
221
Skeletal material preparation. Staining fetal animals for a study of bone
formation.
INDEX . . . . . . . . .
225
Chapter I
GENERAL CONSIDERATIONS
CONSIDERABLE part of the material in the following chapters
deals with the structure of the common domestic cat. Many students
properly ask why the cat is so commonly studied in mammalian anatomy
courses rather than some other type of mammal. Some of the reasons for
the use of the cat as laboratory material are easily explained. The cat is
of convenient size for laboratory work: it is large enough to allow for clear
observation in dissection. Strays and unwanted specimens are fairly
numerous and easily obtained. In large cities, thousands of cats are collected each year by city pounds and humane societies. From these sources,
biological supply companies obtain the bodies in considerable numbers and
at reasonable prices. But these advantages are really not so important
from the biological standpoint as is the position of the cat with reference
to mammals in general.
In a classification of all mammals, organized on a basis of structural
specialization, the cat occupies a position near the middle of the list. This
means that the cat may be used as a fairly representative type of the class
as a whole. From the purely structural standpoint, man is not far removed
from the position of the cat in the mammalian scale. This does not mean,
however, that the cat is most nearly like man of all mammals. Apes and
monkeys are obviously more similar, but they are not so readily available
for laboratory study. Rabbits, rats, and fetal pigs are other mammals
that are often used in general mammalian studies. But these forms are
commonly regarded as being more highly specialized structurally than
either man or the cat.
Terminology and methods learned in the dissection of the cat are readily
applicable to the human body. For most students, the principal value of
mammalian dissection is in making anatomical terms really intelligible.
Textbook anatomy has little real meaning unless the student can visualize
structures as they actually occur in the body. Proper visualization of
structure is learned only by laboratory observations. Therefore, it is of
utmost importance for the student to learn anatomical terms with direct
application and reference to the body, not merely as words in a textbook.
Throughout the dissection of the cat, the student should attempt to understand the relationship of structures observed with those of his own body.
A
1
2
FUNCTIONAL ANATOMY OF THE MAMMAL
TERMS AND DEFINITIONS
Anatomy is concerned with the structural features of an organism. The
parts of a body are named and described as separate units and in relation
to the whole. Descriptive anatomy of anyone type of animal serves as a
basis for making comparisons with animals of other types. Degrees of
relationships among various groups of animals are established from a study
of similarities and differences in structure, organization, and form. The
term morpr.ology is frequently used to include
studies of an anatomical
character.
A body (or a part) is described with reference to aspects, axes, and
sectional planes. Aspects are surfaces offered to space and are named with
reference to the direction from "rhich a body is viewed. The aspects or
views are (1) cranial (head), (2) caudal (tail), (3) dorsal (back), (4) ventral (belly), and (5) right and (6) left lateral (sides). On appendages, the
aspects are cranial (front), caudal (back), medial (inner), and lateral
(outer surfaces). The adverbial form of these terms ends in -ad; e.g., the
arm is craniad to the leg; the vertebrae are dorsad to the alimentary canal.
In human anatomy, the terms posterior and anterior are frequently used
as synonyms for dorsal and ventral and superior ·and inferior for cranial
and caudal. This is due to postural differences between man and quadrupeds.
Also, in comparative anatomy, the terms "anterior" and
"posterior" are used as synonyms for cranial and caudal.
An axis is an imaginary line passing through two aspects. The axes are
(1) craniocaudal (longitudinal), (2) dorsoventral, and (3) bilateral. These
are lines around which the body could be rotated like a wheel on an axle.
A sectional plane is an imaginary plane passing through four aspects of
the body like the blade of a knife. A transverse section cuts through the
dorsal, ventral, and bilateral aspects. A sagittal section passes through
the cranial, caudal, dorsal, and ventral aspects. The sagittal section, in
the mid-line, divides the body in relatively symmetrical halves. The new
aspects produced by making this section are right and left medial aspects
of the body. A frontal section passes through the cranial, caudal, and two
lateral aspects.
Unpaired structures tend to be median in position. The paired struc~ures are not identical, but mirror images of each other, as can be seen by
placing a hand before a mirror. Only in the same sense are homozygous
twins "identical."
A point farther away from the mid-line than some other point is distad
to it, while a nearer point is proximad. Thus the elbow is distad to the
shoulder but proximad to the wrist. Points on or near the surface of the
body or parts are superficial or peripheral in position, while underlying
structures are deep or centrally located. Thus, the skill is superficial, and
the bones tend to be deep in position; the covering of a bone is peripheral,
all
GENERAL CONSIDERATIONS
3
its marrow is centrally located. The cavity of a tubular structure is frequently referred to as its lumen (pI. lumina).
Any constant and conspicuous point on a body serves as an anatomical
landmark. Less prominent landmarks may be located by descriptions of
direction and position from conspicuous points. Body regions are described from locations of landmarks, as are the lines of incision in dissection.
or surgery. B,my landmarks that may be seen superficially or felt
(palpated) are important in describing less conspicuous or discernible
areas.
~
Dissection refers to intentional systematic separation or division (not
necessarily cutting) of the parts of an organism to expose new aspects and
relationships to view. This involves precise techniques and close observation since the anatomy is learned during the process of dissection as well
as after the dissection is completed. Structures under dissection should
be considered as integrated parts of a living body, not as isolated elements
of a dead one.
Gross anatomy is concerned with the more obvious aspects of form,
structure, and organization as exposed and studied without the microscope.
Histology refers to microscopic anatomy and requires the use of specially
prepared sections of tissues or the use of microdissection technique on
living tissue. Cytology deals wit~ the details of cellular anatomy and
merges closely with cellular physiology, genetics, and embryology. Embryology deals with the development of the individual structurally and physiologically.
Specialized branches of descriptive anatomy are usually treated as follows: osteology, the anatomy of the bony framework; neurology, the
nervous system; myology, the muscular system; cardiology, the heart and
blood vessels; splanchnology, the alimentary canal.
Anatomical terms and the specific names given to anatomical parts are
mostly Latin and, when properly translated, are usually descriptive of the
parts. The human body was described by early anatomists before most
other forms had been described in as much detail. Similar parts of other
organisms were later given the names first applied to man. This system
of establishing a terminology for similar parts, in different animals, has
been carried through to the lower vertebrates upon the assumption of
structural relationships and common ancestry. Fundamental similarities
in structural features and organization exist from fish to man.
Physiology is related to anatomy in that it is based upon the chemistry
and physics of living protoplasm, while anatomy is limited to the visible
structural organization through which physiological activity is expressed.
A study of the mechani~al arrangement of the bones, the attachments of
muscles, the nerve connections, and the blood supply and drainage of various organs are all ,parts of anatomy. The mechanical actions of the arm
as a functional unit could be readily ascertained by a study of its structural organization in a dead body. But the chemistry and physics of
6
FUNCTIONAL ANATOMY OF THE MAMMAL
thorax possess attachments for ribs ; etc. Thus, if one knows the structure
of anyone such segment, this knowledge serves as a basis for an understanding of similar segments. Ribs and spinal nerves are also serially
arranged. But the adults of mammals do not exhibit the original
FIG. 1.3.-8exual homologies in the external genitalia of man. A, external genitalia of
an embryo of 16.8 mm., showing the genital tuber cle from below; B, external genitalia of a
male embryo of 45 mm.; C, external genitalia of female embryo of 49 mm. (After Spaulding.)
A, anus; A.P., anal pit, at the bottom of which lies the a nal portion of the cloacal membrane;
A.T., a na l tubercle; E.T., epithelial tag, which later disappears; G, glans of penis and clitoris ; G.P., gluteal fold; L.S.S., la bioscrotal swellings; R, raphe; S , s haft of penis and clio
toris; T, tail ; U.F., urethral fold; U.G. , urethral groove; U.O., urogenital opening. (From
.
W eiman, "Vertebrate Embryology.")
segmental arrangement of parts superficially. Developmental stages in all
Vertebrata are conspicuously segmented. The remarkable serial homology
between the fore and hind limb of animals is obscured by the modifications
of use, but the similarities even here are striking as to fundamental structural organization and arrangement of the parts.
Sexual homologies. In both the male and female of any species the
embryonic development of sexual parts is begun on a similar architectural
GENERAL CONSIDERATIONS
7
pattern. For some time, no clear structural difference between sexes is
obvious. Following this indifferent period, however, a striking differentiation occurs which leads to a specialized condition of maleness in some
and to the less specialized femaleness in others. Abnormal development
sometimes occurs so that some sexual structures (genitalia) in an individual assume a male character while other sex structures, in the same
individual, assume femaleness. This unusual or anomalous condition is
called pseudohermaphroditism. It is not analogous or functionally
similar to true hermaphroditism. Complete bisexuality does not occur in
mammals. Some incomplete duplication of sexual parts, however, has
been reported for man as rare anomalies. In these, partial development of
both ovaries and testes in the same individual have been reported to occur.
External genitalia are most commonly affected.
A fourth type of homology occurs within the serially homologous appendages. This may be described as a radial distribution of similar parts.
Radial homology is best illustrated by an examination of the hand. For
example, the fingers tend to radiate from the wrist, and each possesses
serially distributed phalanges. The bones of the wrist and hand tend to
radiate from the two bones of the lower arm, and these two bones .are
extensions from the single bone of the upper arm. The bones of one digit
are not only similar to each other, but also to the bones of any other digit.
Five digits represent the generalized condition, and deviations from this
number are considered as specializations. The single digit of the horse
therefore represents a highly spe~lized condition.
DIVISIONS OF STRUCTURAL ORGANIZATION
The cell is considered the basic unit of structure.aince it is the smallest
division of a body having an apparent organization with respect to the
general functions. These general or basic biologic functions concern
growth~ reproduction, metabolism, sensitivity, and motility.
With the
differentiation of cells, from a generalized embryonic condition, various
types of cells are formed. The numerous cells of a common type become
associated in the performance of a special duty within the larger organization.
A tissue consists of a number of similar cells and their intercellular
elements associated together to perform a rather specific function. In
general, any cell within any type of tissue can perform all the basic biologic functions, except, perhaps, division or reproduction in some types.
The closely associated similar cells forming a tissue become highly specialized in one direction only, however. For example, muscular tissue or
the cells forming the bulk of a skeletal muscle are especially adapted for
contraction, "whereas the protoplasm of other types of cells is only slightly
contractile. Nervotis tissue is particularly sensitive and especially adapted
to detect various stimuli and transmit impulses; yet all cells are somewlJ.at
8
FUNCTIONAL ANATOMY OF THE MAMMAL
•
sensitive in their physiologic character to their environment and the changes
therein. It is said that no new nerve or 1~~ cle cells are formed in man
after birth; growth in these tissues is dependent on an increase in size of
existing cells rather than in reproduction of new o~es .
Types of tissues
Various classifications of the body tissues have been proposed. For our
purposes, we may regard the tissues as comprising five fundamental types.
These are epitheHal, connective, muscular, nervous, and vascular. Numerous subtypes of the fundamental kinds occur.
Epithelial tissues are first recognized by their position in covering free
surfaces and as lining cavities. In genera, the lining of cavities that open
to the outside possess numerous mucous cells and
are known as mucous membranes or mucous epithelium. The thin rnembranous lining of the body
cavity and the covering of viscera secretes a thin
watery l:1uid resem'oYmg 'o\ood seruIn, and these
membranes are known as serous epithelium. The
retina of the eye and specialized parts of other
A
sense organs form nervous epithelium; the surface
of the ovary and the lining of the tubules of the
testes form germinal epithelium. Glands that
possess ducts are IJlade up largely of glandular
epithelium. The epidermal layer of the skin is, of
course, epithelium and possesses several layers, or
strata.
Connective tissues are most readily characterized
B
by their intercellular elements, which are formed
FIG. l.4.-The secreby the cells and which usually separate them widely.
tory function in epitheThese products of connective-tissue cells perform the
lial cells. A, cells of
such a gland as the sali- functions of support, connection, and protection.
vary glands or pancreas,
Examples of subtypes are: bone, cartilage, tendons,
showing zymogen granules accumulated in the ligaments, fascia, and fat. The living protoplasm
part of the cell adjacent
of connective tissues is usually very scant compared
to the lumen, or cavity,
of the gland. B, two
with the abundance of the nonliving intercellular
goblet cells from the inmaterials or matrix, and the cells are relatively intestine of a vertebrate,
showing the accumulaactive in the actual performance of connective-tissue
tion of mucus and its exfunctions.
trusion into the lumen
of the intestine. (From
Muscular tissue is composed of elongated cells
Wolcott, "Animal Bithat are structurally and functionally adapted for
olooy.")
contraction. Three types occur: skeletal, cardiac,
and smooth: Skeletal muscle is under conscious control (voluntary)
and makes up the bulk of the body. Cardiac muscle is found only
in the heart. It has some histologic resemblance to )skeletal muscle but
differs fundamentally in that the cells are interconnected and not activated
GENERAL CONSIDERATIONS
A
s
9
c
FIG. 1.5.-Different typcs of muscle cells. A, portion ·of .a striated muscle fiber, showing
a section in which the contractile fibrils are divided into groups by semifluid sarcoplasm.
Two nuclei are shown, surrounded by undifferentiated cytoplasm, and the whole fiber is surrounded with a delicate sheath, or sarco lemma. B, three nonstriated muscle fibers, or cells.
C, several cardiac muscle cells. All highly magnified. (From Wolcott, "Animal Biology.")
Hoverskrncanal
FIG. 1.6.-Different t~es of connective tissues; sOlbewhat diagrammatic. A, bone, showing the Haversian canJIs, which transmit the blood vessels and nerves, and the lacunae,
which lodge the bone cells, or bone corpuscles. B, Portion of subcutaneous areolar connective tissue, shoy.ing several tissue elements. C, fat. D, tendon in longitudinal ' section,
showing longitudinal fiba bundles and rows of cells crowded int.o the space between them .
E, section of cartilage with the cells lodged in spaces in the chondrin. All highly magnified.
(From WolcoU, "Animal Biology.")
10
• FUNCTIONAL ANATOMY OF THE MAMMAL
by voluntary conscious control. The smooth musculature of the body is
distributed among many organs. Like cardiac muscle, it is involuntary,
but the fibers tend to be separate units and are spindle-shaped. The name
is derived from the absence of transverse striations, wh~h appear in the
fibers of skeletal and cardiac muscle when examined microscopically.
Smooth muscle is abundant, particularly along the alimentary canal and
urogenital tract. The cells also are numerous in small arteries, where they
serve to constrict these vessels and cause changes in the distribution of the
blood to the various parts of the body. This constricting action is seen in
paleness; whereas extreme dilation produces a flushed appearance.
Nervous tissue is highly specialized for the reception, transmission, and
coordination of stimuli. The morphology of the cell types is indicative of
their particular function: sensory, motor, or associative. In the central
nervous system, the nerve tissue is supported by a specialized connective
tissue consisting of neuroglia. Processes of nerve cells may be extremely
long. A nerve consists of these elongated processes of cell bodies.
Vascular tissue consists of the elements of blood and lymph, both liquid
parts and formed bodies (corpuscles and platelets). Included in this type
by some authors are lymph nodes, the. spleen, and the blood-forming
tissues such as red bone marrow. Some authorities consider the vascular
tissues as one of the connective-tissue types. In the blood and lymph,
the cells are separated by an abundant liquid intercellular part, the plasma.
Organs
The organized association of various types of tissues in the performance of a broader function than that of a single tissue constitutes an organ.
In many instances, an organ possesses one or more types of each of the
five fundamental kinds of tissues, one of which is dominant, the others
being supplementary. Thus, the tissues necessary to make the stomach a
functional organ in the alimentation of food may be cited as follows:
(1) epithelial of two general types (serous and mucous), (2) muscular of
the smooth type, (3) connective, binding the other types together. In a
more minute analysis we would also find (4) vascular tissue and (5) nervous
tissue which, respectively, nourish and help regulate the organ. The essential digestive function is performed by the dominant secretory mucosa, but
obviously the other types are necessary and contribute to the digestive
and alimentary function of the organ as a whole.
Systems
A series of associated organs, usually, but not necessarily, anatomically
connected with each other make up a system. The alimentary system
may be used as an example of a system of anatomically associated organs
that function in the alimentation of food. Each or!;,'an along the canal
has a rather specialized function in the general function of the system.
GENERAL CONSIDERATIONS
11
Thus an organ is less specialized than a tissue but more specialized than
a system to which it belongs.
The ductless glands are organs that make up a physiological system.
Parts of this system are anatomically associated with other systems, and
most of the several glands are anatomically isolated from each other and
show no structural continuity with each other to indicate functional associations. Even tcye skeletal muscular system lacks obvious continuity of
its parts, and in considering the various joints over which muscles work,
they are better understood as making up coordinated s:tries of similarly
acting systems.
Thus, we must say that a system is an association of organs of a close
structural or functional relationship. These are arbitrarily classified on
the basis of the similarity of the parts in contributing to a common function. The close interassociation of the systems constitutes the organism.
The unity of the organism, as a whole, is fundamental. An understanding
of how the systems work together is the aim of determining their separate
structures.
A classification of the systems
The systems are classified in various ways. The following will serve
our purpose in analyzing these with relation to function. The order given
is applicable in an orderly study of systematic functional anatomy, and this
order will be followed except where sectional considerations are interposed.
Integumental. The skin with its derivatives forms the integument. It
is the most generalized of the systems from the functional standpoint
because of its varied and overlapping functions, which include protection,
temperature regulation, and milk production in the female.
Skeletal. Connective and supporting tissues make up the skeletal
system. In a broad sense, it comprises both the gross and microscopic
framework of the body. The bony skeleton is only a part of this system.
Muscular. This system is made up of the skeletal musculature of the
body which has to do with the motive power in motion and locomotion.
It is unique in being controlled by volition, or will.
Alimentary. The term "alimentary" is used here rather than "digestive"
since the system is not only concerned with the digestion of food, but also
with the elimination of the wastes of digestion.
Vascular. The vascular system includes the muscular heart and the
blood and lymph channels. In a more detailed sense, it includes the structure of the fluids. Structures that give rise to blood cells may also be considered in this category.
Respiratory. In this system are considered the parts over which air
passes. These parts are concerned with exahange of gases from the blood
to the outside air. Although this system is anatomically associated with
the food canal, it is functionally more closely related to the blood stream.
12
FUNCTIONAL ANATOMY OF THE MAMMAL
Genitourinary. The genital and urinary systems are ltlually treated
together since the wastes of kidney excretion pass through outlets common
to the genital apparatus. In embryology and comparative anatomy, they
are closely associated in origin and gross function.
Nervous. The comparatively rapid regulation and coordination of
body activities are achieved through the mechanism of this system. Its
function is to detect, transmit, and coordinate various stimuli.
Endocrine. The ductless glands are functionally connected by means
of the blood stre1,m. They secrete hormones, which are chemical regula~
tors of body activities and which induce activity of a more persistent
character than is generally common to the nervous system. Many of these
glands seem closely interdependent upon each other functionally.
It is obvious that any attempt to treat anatomy entirely through the
study of the systems presents a great many difficulties. Recognition of
physiologic systems tends to emphasize these difficulties. Yet the complexities belong to the organism, and no simple method is yet available for
an understanding of living things.
THE ANATOMICAL POSITION AND POSTURE
. In describing movements of the appendages or shifts in position of parts
of the body, it is necessary to assume a definite starting point. Muscle
action, for example, is described for the human with the body standing
erect, the arms hanging at the sides, and the palms facing forward. The
terminology used in describing muscle action for the cat has been adapted
from the descriptions given for man. This has resulted in considerable
confusion, since the anatomical position for describing man would be impossible for the cat to assume under natural conditions.
The appendages of the Vertebrata primitively arose as lateral extensions, i.e., paired fins of fish, which act as stabilizers while the body is supported by water. The primitive tetrapods (aquatic salamanders) use the
appendages for limited support and creeping locomotion.
In most quadruped mammals, the body is carried comparatively high
from the ground. To achieve the advanced quadruped position, a rotation of 90 degrees in each limb has occurred, which brings the limbs ventrally to their present position under the body. The forelimb has rotated
caudally to bring the original dorsal surface of the appendage to face backward and to allow the elbow to be directed dorsocaudad. To prevent the
digits from pointing backward, an additional torsion of the appendage
occurs to bring them around to the front. In accomplishing this, the ulna
and radius of the forearm become crossed and the forearm assumes a prone
position. In most mammals, the forelimb is fairly well fixed in this position. In man, the crossing of the two bones can be felt in the forearm in
moving the hand from a "palm-up" to a "palm-down" condition. A forward rotation from the primitive condition has occurred in the hind limb,
QENERAL CONSIDERATIONS
13
which results in the toes pointing forward, the original dorsal surface
facing forward, and the knee being directed craniad. Thus the arm is
adapted to pull, and the leg is adapted to push. As previously mentioned,
a remarkably similar arrangement and number of bones occur in the arm
and leg.
Types of gait. The application of the foot to the ground, in walking,
differs among m~mmals, and three general types occur as to position.
Man walks on the entire sole of the foot, using the heel on the ground as
well as the digits. This type is known as plantigrad~ and,appears the least
specialized. Some carnivores such as the raccoon and bear possess plantigrade feet, but the cat and related carnivores walk up on their digits, the
claws being retracted. The gait as in cats is known as digitigrade. Horses,
cattle, pigs, etc., walk on structures homologous to nails or claws, which
are modified into hoofs. These are unguligrade. Thus the cat is not so
specialized in this respect as the horse but more so than man, bear, or
raccoon. The leverage principle is important in this connection. The
sprinter "gets up on his toes" when he runs, thus adding leverage and
efficiency in rapid locomotion.
• J>i
HORSE '.•~...
Ifoe
unguli.
grade
A
B
,;;i""
-.,:!
c
1.7.-Mammalian feet (left hind limb). A, human, generalized with five toes, w"lks
on entire foot (plantigrade) . B, dog, with four toes. "heel" raised. walks on fleshy pads
under toes (digitigrade) . C, horse. with only one toe (third). "heel" raised. walks on cornified hoof over tip of toe (unguligrade). Observe that phylogenetic homologies and specializations in the structure of mammalian feet are also shown. (From Storer. "General Zoology." )
FIG.
Ancestral conditions. Fossil remains and other evidences indicate that
remote ancestors of man were quadrupeds with a body position or posture
similar to that of the cat. The viscera were supported from above, along
the craniocaudal axis, like a pipe line suspended under a bridge. The
vertebral column was then efficiently arched to support the internal organs
suspended in thi'3 position. It is thought that the erect posture of man had
14
FUNCTIONAL ANATOMY OF THE MAMMAL
its beginning during a tree-inhabiting period. Both hands and fee~ppar­
ently became grasping organs during this arboreal period. But the hands
became so highly specialized as graspers that their further use in walking
was largely lost. The return to the ground of man's ancestors also occurred
with the feet poorly designed to support the entire weight of the body.
Many other changes also have occurred in the structural character of
man, apparently during his arboreal era: the body flattened dorsoventrally,
instead of bilaterally; the collar bone (clavicle) becam~ strengthened to
serve as a cross~brace between the breast bone (sternum) and shoulder
(scapula); the arms became more free of the trunk to move in wider ranges;
and the eyes moved to a more forward position, permitting better bifocal
vision.
The erect posture, however, resulted in a sagging of the viscera and a
change in the original curvature of the spinal column. Rupture (hernia)
and back sprain are common to man. The upper part of the body rests
heavily on the sacral vertebrae, which form a triangular wedge between
the hip bones. Because of the faulty architectural design of the union of
the sacrum and pelvic girdle, falls and jars often result in sacro-iliac
difficulties. Among other defects that may be attributed to our arboreal
ancestry are the poorly designed supporting arches of the feet and the
partly degenerate little toe. Shoulder injuries are also common to man
because much of the original strength of the joint has been sacrificed in
gaining freer movement for it.
Modifications of structure appear to follow modifications of their functional circumstances, and vice versa. While the posture of the cat in relation to the ground is more primitive than the erect posture of man, relatively more muscles are required to maintain it and to function in locomotion. Since both cat and man use the hind legs for locomotion, there is
less difference in the pelvic limbs of these forms than in the front appendages. In spite of the fundamental difference in posture, surprising similarities in occurrence and organization of structures exist in the two types
of bodies.
CHARACTERISTICS OF THE MAMMALS IN GENERAL
The Class Mammalia constitutes the "highest" of the classes of the
Vertebrata. The term "highest" implies more specialized perfection of
structure and function in meeting environmental influences. This indicates that the class exhibits a large number of characters and considerable
complexity. However, greater complexity is not found in all structures.
For instance, the mammalian skull compared with the skull of the bony
fish is relatively simple, through a reduction in the number of bones making
it up. In the mammal, the lower jaw is composed only of two bones fused
in the mid-line. Yet, as a biting structure, it is more e1E.cient than the jaw
of a fish which is composed of several bones. However, the increased effi-
GENERAL CONSIDERATIONS
15
ciency of the mammalian skull is due chiefly to a more precise and effective
articulation, rather than to the reduction of bony members.
We should recall here that the mammals possess the basic characteristics
common to all Vertebrata, but they exhibit certain additional and distinctive characters that place them in a special class. These special characters of the class are described below.
1. The presenct) of mammary glands is diagnostic and is the characteristic from which the class derives its name. All types of mammals possess
mammary-gland tissue which actively secretes milk. 'fhese structures,
although typically present in both sexes, are entirely rudimentary in the
male. Mammary glands are derived from the skin and are usually re':
moved in skinning. Since the young of mammals are nourished from these
glands, they are thereby forced W associate with the mother for a considerable period. This may be significant in the advancement of the group.
2. Hair is present, which is also a derivative of the skin. In some species
of truly aquatic mammals, it is limited in distribution to a few bristles on
the lip. Hair follicles usually assume a dilStinct pattern in each species.
The term "hair" should not be confused with similar appearing structures
such as cilia or chitinous material found amOng other animal groups. Hair
is as characteristic of the mammals as are f(lathers of the bird. The functional importance of hair or fur lies in helping maintain temperature and
in protection.
3. A muscular and tendinous diaphragm is always present. This forms
a complete partition across the body cavity (celom), dividing it into a
superior thoracic cavity and an inferior abdominal cavity. The diaphragm
is of great functional importance in perfecting the respiratory mechanism.
It is also of importance in parturition, the process of giving birth. This.
structure in the mammal should not be confused with the so-called "false
diaphragm" of the sharks since the latter serves only to separate the heart
cavity from the rest of the body cavity.
4. A single aorta from the heart occurs which bends sharply to the left
in an arch. Since the aortic arches arise as paired structures, it is evident
that only the left of the systemic pair persists in mammals. The circumstance that the left arch is present makes this character distinguishing.
In the birds there is also a single aortic arch, but it is the right arch that
persists.
5. The lower jaw bone, or mandible, consists of a single bilateral pair
of bones, the dentaries, which become firmly fused in front. The dentaries
articulate behind with the squamosal portion of the temporal bone. Thus,
we may further say that the temporals bear an articular surface for the
mandible. These are diagnostic characters of the mammals.
6. Seven cervical, or neck, vertebrae are characteristically present.
The skull articulate~ upon the first of these (the atlas) by means of a pair
of rounded processes (condyles) of the occipital bone. In whales and
dolphins, the cervical vertebrae may be fused together to act as a stem
I'
16
FUNCTIONAL ANATOMY OF THE MAMMAL
for the skull. In sloths, there may be as few as six cervicals in some species
or as many as nine in others. All variations from seven, however, occur in
the more obscure groups of mammals.
7. The ribs (except in the whales and some of the lower mammals)
possess two articular processes at the articulating point with the vertebral
column. The location of the rib tends to be between vertebrae (intervertebral) rather than in direct line with the rib vertebr~e. Thus, each of
the two heads articulate with a separate vertebra. This characteristic
may be stated at:': "vertebral articulation of ribs is by means of two processes, an anterior capitulum and a posterior tuberculum." Some of the
ribs, however, in any particular animal may not possess two heads, and a
single rib could not be used conclusively in identification unless these
characters were present. This conditiop. infers greater efficiency in the
use of the ribs as levers of respiration.
8. The middle ear contains a complex of three highly specialized bones:
the stapes, malleus, and incus. These small bones have helped perfect
the more efficient hearing apparatus of the mammal. The stapes is be-'
lieved to be homologous to the columella of lower vertebrates; the malleus
is considered as homologous with the articulare bone, which bears the
articular surface of the lower jaw of reptiles; and it is believed that the
incus is a modified remnant that is homologous to the quadrate or upper
articular jaw bone of the reptiles. Observations on the systematic reduction of the bones from the lower forms to mammals and studies of embryonic development support these beliefs.
9. A scapula, or shoulder blade, is present which characteristically
bears an anterior process, the coracoid. In other vertebrates (and in the
. lowest mammals), the coracoid is present as a separate bone. In the mammal, the coracoid is indistinguishably fused with the scapula.
10. The two cerebral hemispheres of the brain are connected by a distinctive band of nerve fibers, the corpus callosum. The corpus callosum
varies proportionally in mammals "lith the degree of brain development
of the different grouPl? It is very rudimentary in the most primitive
mammals, small in opossums and other marsupials, and reaches its most
conspicuous development in the primates. It is of functional significance
. in nervous coordination between the two hemispheres of the brain.
Many other distinctive characteristics occur in the mammals, a few of
which deserve mention in passing. The mature red blood cells are denucleated; the skin possesses sweat and oil glands; a larynx, or voice box,
is formed at the upper end of the windpipe, or trachea, a movable epiglottis
reflexly covers the glottis. With but few exceptions, two sets of teeth
occur, which are differentiated into types (heterodont). The openings of
the intestine and genital systems are separate (a few exceptions), and the
young before birth are nourished through a placenta (two orders excepted).
The large number of structural characters consiste';;tly present in such
a divergent group as the mammals seems remarkable. , In size, the mam-
GENERAL CONSIDERATIONS
17
mals range from a tiny field mouse no more than an inch long to the whale
of 50 feet or over. Thus, the largest of the mammals may be 600 times
longer than the smallest and millions of times heavier (600 3 = 216,000,000),
yet retain striking similarity in fundamental parts. Divergence is also
extreme in the habitats of the various orders and in the modes of locomotion from absolute swimming to terrestrial and aerial. Only the insects
excel or parallel the mammals in these respects.
As is generally known, sexual differences, or dimorphism, are common
to mammals. The primary sex characters are evident -in the presence of
reproductive organs which give rise to the sex cells. The secondary characters are those associated with the character of the primary. The type
of secondary characters is dependent upon the germinal gland, i.e., the
ovary or testis. Hormones formed by these organs determine structural
variations between the two sexes. Except in the young of some mammals,
particularly rodents, sex can be easily determined by the external genitalia.
In man, the more prominent of the secondary characters are found in,
the distribution and character of the hair, the relative size of the larynx,
and the conformation of the pelvis, together with its breadth in relation
to that of the shoulders. The development of the mammary glands of the
female at puberty belongs also to this group of characters. In most mammals, a conspicuous difference occurs in size, the male being usually larger
and more muscular.
Principal orders of mammals (present-day groups)
The following is a brief classification of the principal orders arranged on
the basis of the degree and number of structural specializations exhibited
by typical representatives of the groups. For detailed explanations and
further characteristics, the student is referred to Osborn, "The Age of
Mammals"; Gregory, "Orders of }\Ifammals" and "Studies on the Evolution of Primates"; and Beddard in the volume on "Mammalia" of the
Cambridge Natural History series. The arrangement followed here is
mostly from Romer's publications.
1. Monotremata. The monotremes are the egg-laying mammals, consisting of a few species native only to Australia and near-by islands. The
typical representatives are the Australian anteater, Echidna (spiny), and
the duckbill, Ornithorhynchus (bird-like nose). The more striking characters are as follows: the pectoral girdle has separate coracoid, precoracoid,
and interclavicular elements; no teats are present, the nourishing fluid
being secreted through simple ventrolateral openings; the young are
hatched from the eggs while outside the body and are presumed to lap up
the milk as it 'is secreted. The genital tract and alimentary canal open
together into a shallow common passage, the cloaca; the oviducts open
separately. The older is so distinct from others that it is given also a subclass rating, Prototheria, meaning first animal.
18
FUNCTIONAL ANATOMY OF THE MAMMAL
2. Marsupialia. Marsupials are those carrying the larva-like young in
an abdominal pouch that encloses a series of nipples and is supported by a
pair of epipubic bones; the vagina is double; the brain is primitive and·
smooth. The common examples are the opossums and kangaroos. Most
representatives of marsupial mammals are native to Australia, and these
are rather numerous in species superficially resembling moles, cats, anteaters, rabbits, wolves, etc. Huxley considered the grQUp as being different enough from other orders to warrant a subclass distinction, which
he called Metathcl'ia. In neither the monotremes nor the marsupials are
the developing young characteristically nourished by means of a placenta
similar to that of the higher forms. Most marsupials develop embryonically in a sort of "uterine milk." The opossum, Didelphys virginiana, is
the only species of the order native to North America. Some authorities
believe that the marsupials should be considered within the same subclass
as higher mammals, the Eutheria, or later mammals. It is evident that
marsupials are not so distinctive a group as the monotremes.
3. Insectivora. This is the lowest order of the so-called "clawed"
mammals. They are very primitive animals and mostly small. The order
includes the moles, hedgehogs, and shrew. The shrew is a small animal
superficially resembling the rat. The snout is generally long; the teeth
are primitive, generally 44 in number and more or less generalized; the
auditory region of the skull is poorly ossified; the brain is small and smooth;
the feet are plantigrade.
4. Chiroptera. The bats are markedly specialized only in that the
digits of the forelimbs are elongated and supplied with thin folds of skin
enabling them to fly. Otherwise the bat resembles the insectivores in
many respects.
5. Dermaptera. According to some authorities, this rather obscure
group represents an intermediate position between insectivores and true
bats. The flying lemur is the best known of the group. A fold of skin is
formed between the appendages which is used as a glider, somewhat as in
flying squirrels. The fingers are not elongated as in true bats.
6. Primates. These mammals have five digits on both the fore and
hind limb; the forelimb is adapted for grasping, and the heel is applied to
the ground in locomotion, or is plantigrade in position. A well-developed
clavicle is present. The orbital space of the skull is separate from the
temporal depression and faces predominately forward rather than laterad.
Teats are usually axillary or thoracic in position. A cecum, or blind pouch
of the large intestine, is always present and mayor may not continue as a
vermiform appendix. Some of these characters are not entirely diagnostic
but together are sufficient to characterize the order that include~ the
lemurs, monkeys, apes, and man.
7. Carnivora (Flesh-eating animals). The mamfi\als of this order
have sharp cutting teeth; the canines are large and usually curved. The
incisors are small, from four to six in number. The digits are never less
than four, usually with sharp strong claws. The clavicles are incomplete
GENERAL CONSIDERATIONS
19
or absent. There are two suborders: one aquatic, including the walrus,
sea lion, and seal; and the other terrestrial, including the dog, bear, raccoon, lion, cat, etc. The second suborder may be further defined as having
nearly always six poorly developed incisors and limbs that are not modified
as swimming appendages and that are usually digitigrade.
8. Ungulata. This is an extremely large group of highly specialized
terrestrial mammals. Two divisions are commonly giv'en: the odd-digitated
(Perissodactyla)' and the even-digitated (Artiodactyla) forms. These
may also be considered as separate orders. In the first ~roup is the zebra,
tapir, African rhinoceros, horse, etc.; in the even-digitated group are such
common species as goats, sheep, cattle, deer, and swine. The latter group
includes forms known as "cud chewers," or ruminants: cattle, giraffes,
goats, camels, etc. They characteristically swallow their coarse food
rapidly and later bring it back up for further mastication. This process
involves a highly specialized stomach.
9. Proboscidea. The elephant has many similarities with the ungulate
division and in many ways is one of the most highly specialized forms.
The elongated nose and lips, particularly the upper; the extreme size; the
tusks and the arrangement of the leg bones are striking features.
10. Cetacea. Whales, dolphins, and porpoises comprise this group.
Many profound specializations occur in this order, although several features ~ be considered of a degenerate character. This is seen in the
loss of .ir and claws and in the extreme modifications of the limbs when
present. An unusually thick layer of fat occurs under the skin to serve
as insulation; the forelimb has developed aceessory digits in addition to
the usual five; the stomach is extremely specialized; no external neck is
present; the skull is built like a wedging block, and the neck vertebrae
serve as a rigid stem for this block. Some representatives are extremely
large. Because of the great specialization, the group occupies a high
phylogenetic position, even though high brain development is not one of
its pJ.:incipal characters.
11. Rodentia. The rodents are mostly small and numerous as to species.
This order includes the rats, mice, squirrels, rabbits, prairie dogs, beavers,
guinea pigs, and many others. The incisor teeth are extremely well developed and assume a chisel-like form. No canines are present. Their
intelligence is usually low. Rodents are omnivorous as to diet. Usually
the testes do not descend into a scrotal sac.
12. Xenarthra. This is a rather diverse group previously known as
Edentata, which was not a good term since some representatives bear
some teeth that appear degenerately specialized. The group includes the
sloths, armadillos, and ant bears. They are highly specialized in some
respects but may have reached a more advanced racial development at an
earlier period than is now evident, and most of the extreme specializations
do not appear to lead to a successful advancement.
For our purposes, the above incomplete classification will suffice to illustrate the various types of existing mammals. It should serve to show the
20
FUNCTIONAL ANATOMY OF THE MAMMAL
general position of man in relation to other mammalian forms. From this
review of the orders of mammals, and by supplemental reading, the student should grasp the significant point of adaptive specialization in animals in relation to their functional activities.
Further classification of cat and man
According to the present arrangement of the orders, the carnivores are
regarded as the next higher above the primates. This m~rely means that
the typical repref-entatives of the order to which cats belong are considered to possess more or greater specializations than do the representatives of the primates. Here it should be noted that taxonomy, or orderly
classification of animals, rests principally upon morphologic features. Such
features as intelligence and relative size or quality of the brain are not of
so great taxonomic value as are differences in the number of digits or
types and numbers of teeth.
CAT
MAN
Family Felidae. Carnivores with
five digits in the front limb and four
in the hind limb. There are six
incisor teeth, two canines, two or
four premolars, and two molars in
both the upper and lower jaw.
There is a bulb or bulla enclosing
the ear bones from below. Cats,
lions, leopards, etc.
Family Hominidae. Primates collectively known as modern and
fossil man belong to this family.
They are distinguished from other
primates (Simiidae, the anthropoid
apes) more by the degree of the development of the characters present.
The anatomical points of difference
are due chiefly to the more erect
position. The brain case is relatively large, the incisors are better
developed with the canine usually
suppressed; and there is no gap
(diastema) between canine and incisors. In both ape and man the
same number of types of teeth occur,
however. Most apes use the forelimbs to some extent in walking,
whereas in man they swing freely.
In man the tendency is toward less
hair, more ineffective teeth, a rather
rudimentary little toe, emphasis of
brain, etc.
Genus Felis. The claws are more
completely retractile and typically
sheathed.
Legs are relatively
shorter than those of other genera.
The molar is usually suppressed
and not in line ,vith other teeth.
Coloration is varied, as spots in
the leopards, stripes in the tiger,
the more solid coloration of lions,
and the mottled appearance of the
jaguar. Most cats are rather closely
related structurally. The differences most obvious are in size and
coloration, although some differences occur in the skull bones of
various species.
Species F. domestica. The common house or alley cat is thought
I
Genus Homo. The modern a~d
prehistoric type::! of man are ordinarily placed in this single genus,
although most authorities consider
GENERAL CONSIDERATIONS
to have descended from a wild cat
of Asia which, after domestication
and introduction into England several centuries ago, possibly interbred with wild cats native to that
country. Man has undoubtedly
had much to do with the present
character of cats and by making
selective crosses has produced the
several varieties. The varieties of
cats, however, are neither so numerous nor so distinct as are those of
the domestic dogs.
21
certain prehistoric forms in other
genera, as, for example, the Java
ape man (Pithecanthropus ereetus).
Species H. sapiens. All modern
and some prehistoric forms of man
are included in this species by most
authorities. The characters that
distinguish the races are proportionate differences in structures common to all races rather than in the
possession of new or different structures. The characters include skin
color, hair form, facial features,
stature, and ratios of proportions of
body regions. When intercrossed,
all races of man are able to produce
fertile offspring. This is a test for
determining species.
ANOMALOUS AND VESTIGIAL STRUCTURES
Structures of individuals within a species frequently differ greatly from
the usual or average condition for the species. An extreme variation that
occurs rarely is known as an "anomaly." Before establishing a structure
or condition as anomalous, it is necessary to check on several individuals
to determine whether the variation is common or unusual to the species.
Extreme variations may occur in any of the systems. Often there is no
apparent effect upon the animal possessing anomalous conditions, and
many humans possess anomalies of which they are unaware.
The mammals are particularly susceptible to anomalies because they
must pass through so many embryonic changes in reaching the adult condition. These changes are partly correlated with the phylogenetic evolution of man or racial history, and there is an occasional tendency to reestablish some of the so-called "ancestral characteristics." An extra pair of
ribs in man or several additional tail vertebrae are not especially rare
anomalies. Supernumerary or additional nipples occur as anomalies in
man, indicating an earlier linear distribution of mammary glands. Occasionally, certain muscles may be entirely absent or remain as mere vestiges
as compared w-ith the average. Another circumstance commonly met is
the misplacement of the visceral elements with respect to the surface landmarks or associated structures. Perhaps the most common anomalies are
present in the vascular system. These will be discussed in connection
with that system.
The vestigial structures are remnants of structures that appear to have
once had functional importance. A classical example of a vestigial struc-
22
FUNCTIONAL ANATOMY OF THE MAMMAL
ture in man is the vermiform appendix of the large intestine. In some
mammals, especially rodents, an extension of a similar character is structurally and functionally prominent. In man, the appendix apparently
represents a degenerate remnant of an important part of the digestive
tract of our ancestors. Fortunately, few of our remnants of the past cause
so much trouble.
Ear
SC(cro-
Tail
coccygeal
ligame17ts
0
FIG. 1.8.-Vestigial structures in man. A, muscles of the ear, msplayed by removal of
the superficial tissues. B , appendix, seen from behind. C, embryo, showing the tail. D ,
abnormal persistence of tail muscles in adult, seen from behind. (A compiled from works on
human anaJ.omy; B, C, and D from Romanes, " Darwin and after Darwin," P art 1, The Open
Court Publishing Company. From Wolcott "Animal Biology.")
Man still retains vestigial muscles that are thought to once have ml1de
ear movements possible in ancestral forms. Only a few gifted individual;:;
now have any conscious control of these muscles. The tail vertebrae of
man degenerate and become fused into a single element called the coccyx.
Evidences from embryology and comparative anatomy indicate it to be a
vestige. Many other structures appe'a r to belong in this category.
Frequently, it is difficult to determine whether a part is degenerate or
merely in a primitive beginning stage. The term "rudimentary" has unfortunately been applied to both conditions. For example, the little toe
of adult mali apparently is not so well developed, compared with the other
toes, as it is in a baby. It is sometimes said to be rudimentary. Compare.d
with other anthropoids, the little toe of man is degenerate and apparently
destined to become a vestigial toe. Functional considerations should
always be correlated with morphological determinations of this character. -
Chapter II
THE SKELETAL SYSTEM
•
STUDY of a prepared skeleton, even with the bones fastened together (articulated) in their proper positions, is little more than suggestive of its true functional character in the living body. Obviously such
a skeleton, dried and cleaned, represents only the nonliving elements, or
intercellular materials, that persist in the process of preparing bones for
study. Bones, therefore, make up a sort of framework of the true skeleton
of the body as it exists functionally. Despite these circumstances, an articulated skeleton introduces, as well as any other system, the complexities
of the organism and the interdependence of the various systems in the
economy of the body as a whole. Most of the details of the skeleton have
little or no significance of themselves and are best studied in connection
with the muscular system, with which the skeleton functions most closely,
and with the nerve outlets of the skull. Muscle dissection should be done
concurrently with a detailed examination of skeletal parts.
In the living body, the bony skeleton is intimately associated with other
skeletal tissues such as cartilages and ligaments. Each bone is covered
with a tough membranous sheath, the periosteum, except for surfaces
that move on other bones. The periosteum contains both bone-building
cells, osteoblasts, and bone-destroying cells, osteoclasts. During growth,
both types of cells are normally active. When a bone is injured, the sheath
is also damaged and the irritation stimulates the bone-forming cells to
great activity. Consequently, the periosteal sheath is necessary in bone
repair.
Cartilages that are functionally associated with the bony skeleton are of
several kinds. The vertebrae are separated by disks of fibrocartilage; the
cartilaginous extension of the nasal septum is a translucent gristle; the
ends of the long bones are covered by a smooth glassy-appearing articular
cartilage. The bones are held together at movable joints by special bands
of ligaments and membranous enclosures, which may be observed following
the dissection of muscles.
A
FUNCTIONS AND DIVISIONS
When viewed as .a whole, the skeletal system performs three distinctive
functions: (1) it for~s the internal foundational material and framework
for the direct and indirect support of all other tisslfes; (2) by means of
23 ,
24
FUNCTIONAL ANATOMY OF THE MAMMAL
M. :;; muscle
M. TrapeziuS"
{\-I
I
I
-Mandible
\
\.
I
I
\ I
\~
,
--
' .....
M. Trice.ps
..... M. Pectora lis
. . .Sternum
11th Rib ,
'- M. txt. oblique
M. Sartorius
-<:Pubis
-,_ ..... , 'Femur
---M. T. fascia (ata
- --_ Patella
__- - - - M. Biceps femoris
- - - - Tibia
- - - fibula
- - - - - M.Gastrocnem;us
, -:-------Torsals
'. - - - - - - -...:. _ 'Metatarsals
,
FIG. 2.1.-Skeleton of the cat in relation to superficial muscles. In the later dissection
of the muscl es, the underlying skeletal parts should be visualized. (Drawn by John F.
Trainor. )
joints between rigid parts, the skeleton serves a leverage function, allowing
for motion and locomotion through the contraction of attached muscles;
and (3) the bony elements are arranged to provide protection for the more
vital and sensitive organs. The protective function is illustrated particularly by the arrangement of the thoracic basket protecting the heart and
lungs and by the cranial bones and vertebral column housing the central
nervous system.
•
THE SKELETAL SYSTEM
25
The skeleton is ordinarily divided, for purposes of study, into (1)
the axial portion consisting of the skull, vertebral column, ribs, and sternum; and (2) the appendicular division, made up of the elements of the
thoracic and pelvic girdles together with the series of limb bones extending
distally from them. One should especially note that the girdles supporting
the limbs operate at right angles to the axial portion of the skeleton and
are, therefore, par,ts of the appendicular complex of bones.
FIG. 2.2.-Skeleton of the domestic cat. Note particularly the structural and functional
divisions of the skeleton. (From Storer, "General ZooloIJY.")
The skeleton of adult man is usually described as consisting of 206 separate bones. Many bones that are formed from a number of centers and
that retain conspicuous divisions in early childhood are considered as
"separate bones." Examples of such bones are the sternum, sacrum, hip
bone, and certain skull bones. Of the 206 bones, 172 are paired (86 pairs):
11 pairs in the skull (including ear bones), 12 pairs of ribs, 31 pairs in the
thoracic appendages, and 32 pairs in the pelvic appendage including the
patellae, or kneecaps. Unpaired bones are median in position, although
some are formed by a rather late fusion of bilateral halves. These comprise 6 in the skull, 1 hyoid, 1 sternum, and 26 vertebrae.
Several more bones occur in the cat than in man, but none are of a new
type. The cat possesses 7 instead of 5 lumbar vertebrae and a variable
number of tail vertebrae represented by a single coccyx in man. The cat
also possesses 13 pairs of ribs instead of 12, and the early elements of the
sternum never fuse into one separate element but remain as segmental
sternebrae. Except-in extremely old cats, different elements of separate
skull bones are usually more pronounced than their homologues in man.
26
FUNCTIONAL ANATOMY OF THE MAMMAL
Fewer bones occur in the hind limb of the cat, because only four digits
occur in the hind limb.
FIG. 2.3.-Skeleton of man.
(From Millard and Kin(J, "Human Anatomy and Physiology.")
ORIGIN AND TYPES OF BONE
Bone originates in fetal life by the laying down of mineral substances '
in a tissue of a softer character. The process of bone->formation is known
as ossification, and the points at which ossification begins are known as
ossification centers. A long bone, such as the humerus of the upper arm,
THE SKELETAL SYSTEM
27
is formed from three such centers, one at each end, the epiphyses, and one
in the middle, the diaphysis. The diaphysis is established relatively early
in development, but even at birth the heads of the long bones are not well
ossified, and in man they do not firmly join the body (diaphysis) of the
bone for several years. The separate elements of the skull arise from
separate centers of ossification. At birth, certain of these bones also have
,
FIG. 2.4.-A longitudinal section of the head of the femur . Note the structure of compact
and spongy bone. The periosteum is shown cut and partly pulled aside. (From Rogers,
Hubbel. Byers, "Man and the Biological World." Redrawn from Williams, " T extbook oj
Anatomy and Physiology." )
not yet joined, thus leaving soft areas between known as fontanels. Later
in life, some of the elements that arise separately may fuse so completely
as to be indistinguishable from each other. A series of fetal animals stained
and cleared to show bone formation is invaluable in a study of the separate
elements of the skeleton and their relationships (see Appendix).
Bone arises developmentally in three different types of earlier tissue:
(1) in cartilage, (2) fn a membrane-like sheath of dermal tissue, and (3) in
tendons. Bone arising in a development of preformed cartilage is known
as replacement bone, and most of the bones of the body are formed in this
28
FUNCTIONAL ANATOMY OF THE MAMMAL
)
way. The skull possesses both replacing bOIie and bone formed in a dermal membrane. The floor, side walls, front, and back of the brain case
are preformed in cartilage; whereas, the roof joins these parts first as a
membranous sheath, later ossifying as dermal, or investing, bones. Early
cartilaginous bars representing the jaws also become invested by dermal
tissue which ossifies into dermal bone. Bones formed in tendons are known
as sesamoids. The kneecap (patella) is the most conspicuous example of
sesamoid bone, but sesamoids also occur in the wrist. Occasionally, extra
sesamoids
develop in the tendons as a result of injury or from constant
irritation and may become very troublesome.
"'11
FIG. 2.S.-A diagram to indicate the character of bones and muscles as organs and the mode
of attachment of a muscle to a bone. (From Wolcott, "Animal Biology." )
Terms used in describing bones
angle-corner of a bone, found between two borders.
articulation (ar-tik-u-la'shun)-a joint or union between two bones.
border-the edge of a bone; usually applied to flat bones.
capitellum (kap-it-el'um)-a small head.
capitulum (kap-it'u-lum)-literally means same as above but is applied
differently.
caput (ka'put)-"head," a rounded enlargement at the end of a long
bone.
condyle (kon'dil)-a smooth rounded articular surface; in pairs.
corpus (kor'pus)-:-"body," the largest or principal part of a bone.
crest-an eminence; usually a ridge with a sharp edge.
diaphysis (di-af'is-is)-central portion of a long bone; ossification center.
epiphysis (ep-if'is-is)--enlarged end of a long bone.
.
facet (fas'et)-small articulation face; smooth limited area.
fissure-a narrow cleft in a bone.
THE SKELETAL SYSTEM
°
29
fontanel (fon-tan-el')-unossified (at birth) region between skull bones.
foramen (for-a'men)-literally a "window" or opening through aobone.
foramina-plural of foramen.
fossa (fos'ah)-a concavity or depression; literally a "ditch."
groove-an elongated concavity between parallel ridges.
lamina (lam'in-ah)-a sheet of bone; a flattened portion.
linea (lin'e-ah)-.--literallya "line"; narrow crest or ridge.
malleolus (mal-e'o-lus)-a hammer-headed protuberance.
manubrium (man-u'bre-um)-a flat handle-like projeclion.
neck-a constricted portion immediately below the "head."
notch-a deep or large indentation (usually for articulation).
pedicle (ped'ik-el)-a column or base supporting an arch.
process-an extension or projection of a bone.
ridge-a narrow roughened elevation on the surface.
shaft-that part of a long bone formed from the diaphysis.
sinus-a pocket or cavity; applied principally to cavities within the
skull.
spine-a more or less sharp projection or short ridge.
squama (skwa'mah)-theO flat portions of the cranial bones.
styloid (sti'loid)-literally "pencil shaped"; a pointed process.
sulcus (sul'kus)-a furrow or groove, intermediate between fissure and
fossa.
suture (su'tur)-the line or union between two immovable bones.
symphysis (sim'fis-is)-a union in which two bones are firmly connected
by cartilage.
trochlea (trok'le-ah)-an articular surface having a pulley shape.
tubercle (tu'ber-kl)-a small rough eminence; usually for muscle attachment.
tuberosity (tu-ber-os'it-e)-a large uneven tubercle or eminence.
General features of the mammalian skull
The skull presents many more complexities than other parts of the skeleton, and this preliminary discussion may be helpful. In general architecture, the skull is roughly analogous to a three-story house and thus exhibits
three functional levels. (1) The upper floor (neural level) supports and
protects the brain; (2) the middle floor serves as a passageway for respiration; (3) and the first floor (alimentary) serves in the intake and mastication of food. In this analogy, the roof of the mouth is the floor of the
respiratory passageway, and the floor of the brain case acts also as the
roof of the respiratory channel together with the nasal bones, which extend
in front of the cranium.
The bones that enclose and support the brain make up the cranium, or
brain case. The cranium also supports and 'protects the organs of special
• and auditory. Bones of the skull that are not consense: optic, olfactory,
cerned with the neural function are the facial bones, located roughly from
30
FUNCTIONAL ANATOMY OF THE MAMMAL
the level of the bridge of the nose to the lower jaw. In man, the face is
relatively suppressed, and the neural level is greatly emphasized and
dome-shaped (Fig. 2.7). It is interesting to follow the shift of emphasis
and comparative development of the levels of the skull from the lower
mammals such as opossums to the monkeys, higher apes, and man. The
skull of a lion with open jaws strikingly illustrates the extreme difference
between the carnivores and man as to the proportionate importance of
visceral and neural functions in the two forms.
C
R
A
N
1
U
M
F
A
C
E
FIG. 2.6.-Fullctional levels in the skull of the cat.
C
R
A
N
I
U
M
F
A
C
E
FIG. 2.7.-Functional levels in the skull of man.
Compare with Fig. 2.6.
In all mammals, the different bones of the skull occupy the same positional relationships with each other and are remarkably constant in their
occurrence. For this reason, it is advantageous to figure these relationships
in a generalized scheme or map. The skull of most primates (including
man) is more compact than that of other mammals, and the exits of the
cranial nerves do not occur in such a distinct serial pattern as in an elongate
skull. For detailed examination of separate elements, the skull of a young
animal is preferable since many of the sutures between bones tend to become indistinct in older specimens. Some of the features must be seen in a
sagittal section or in a disarticulated skull.
•
THE SKELETAL SYSTEM
31
a
~
apparatus
{
Hyo id
l.orynseal
cartilo,!es
J
00
I to XII Cranial nerve
exits
FlG. 2.8 .-Typical arrangement of bones in the Inamma lian skull. Cartilaginous bones a r e
stippled. The hyoid is also of cartilaginous origin.
FIG. 2.9.-Diagram of the skull of the newborn child . Cartilaginous bones are stippled ;
membrane bones unsha<ied; derivatives of the vi~ceral arch es are shaded vertically ; fonta nels are shaded diagona1'!y . a, alisphenOld ; t, frontal; h, hyoid; m, mandible ; m.e., Meckels
cartilage; mx, maxilla; 0, occipital; p, periotic; pa, parietal; sq, squamosa!; st, styloid process;
t, thyroid cartilage; ty, tympanic; z, zygomatic Or malar. (From Weiman, "Vertebrate Embryology.")
32
FUNCTIONAL ANATOMY OF THE MAMMAL
SKELETON OF THE CAT
Axial division
The skull. The following description of the cat skull is given
with the assumption that the student will have the actual material
before him; reference should also be made to figures. Conspicuous
landmarks should first be noted. Observe the sagittal suture occupying the middorsal line from the cranial to the caudal end of the
skull. Note the position of the orbital fossae (eye sockets) which
in the cat are continuous with depressions just caudad to them, the
temporal fossae. In man the orbital fossa is separated from the
temporal depression by a complete rim of bone at the back of the
orbit. The cheek bone, or zygomatic arch, forms the lower rim of
the orbital fossa and extends back over the temporal depression
almost to the ear opening, the external auditory meatus. Observe
that between the floor of the brain case and the hard palate are the
paired respiratory passageways, which begin in front as paired
external nares. The floor of the brain case ends caudally at the
large opening, foramen magnum, which arbitrarily marks the position of the junction of the brain and spinal cord. On either side of
the foramen magnum smooth rounded projections occur, the occipital condyles, which articulate with the first cervical vertebra, the
atlas.
Brain case. The brain case should be regarded as a box-like
structure possessing a floor, side walls, roof, front, and back. A
modified ring of bone surrounds the foramen magnum at the back,
or base, of the skull. This is the occiput, made up of a dorsal supraoccipital, a ventral basioccipital, and the paired exoccipitals which
bear the occipital condyles. The basioccipital fuses cranially with
the basisphenoid, which is characterized by possessing the deep
pituitary fossa seen from within or in sagittal section. Craniad to
the basisphenoid is the more narrow presphenoid which encloses
the sphenoidal sinuses also seen in sagittal section. These thre~
median bones form the floor of the brain case; bones further anterior
belong to the face.
Beginning at the back of the skull again, the side wall in front of
the exoccipitals consists of the temporal complex of bones and
lateral sphenoids. All the bone surrounding the ear opening is
temporal. The flat portion above the opening and which bears the
zygomatic process of the cheek arch is squamosal. Directly back
of the ear opening is a mastoid process, which in man is very prominent and possesses honeycomb-like cavities (mastoidal cells or
sinuses). Beneath the ear opening is the bulb-like tympanic bulla,
•
THE SKELETAL SYSTEM
33
which in man is represented by the pencil-like or styloid process.
A small opening occurs between the undersurface of the mastoid
process and tympanic bulla, the stylomastoid foramen through
which passes a branch of the facial nerve. Occasionally this nerve
is injured in mastoid operations in man, resultipg in paralysis of
facial muscles of expression.
The lateral sphenoids consist of two parts that are indistinguishable in old specimens and that also become fused 'iith the median
Foramina
I.
Incisor
Incisive
2. Infra-orbital
3.
4.
Palatine
Mental
s.lacrimol canal
6. optic
!. sph enoida I
fissure
B.Rotund~m
~n,: t-nr' h i ta
I process 9. Ova Ie
lo.Eustachian tube
and Facial
II.Jugula r
Il.stylomastoid
of juqal
Zyqomatic process
uamosal
'~
"Postorbital process
of frontal
. . .. . ... . ........... ........ .
ndibularfossa Anqular process
B_
Alisphenoid
Basisphenoid
panic bulla
asiocci pita I
Exoccipital
[>coccipitaf condyle
FIG. _2 .10.- Dor sal , ventral, and lateral views of the cat skull.
Dentary
D
(Modifi·e d from Mi~(1rt.)
3.t
FUNCTIONAL ANATOMY OF THE MAMMAL
sphenoids of the floor. These are the ali- and orbitosphenoids.
They are best described with reference to the exits of the cranial
nerves (foramina). Looking directly into the orbital fossa, four
openings are seen in a continuous row. The first of these is the
optic foramen through which passes the optic nerve. It is surrounded by orbitosphenoid bone. The next opening is the largest
of the series and occupies a position between the' ali- and orbitosphenoids. Th~s is the sphenoidal fissure (foramen lacerum). The
other two foramina are the rotundum and ovale, both surrounded
by the alisphenoid which extends dorsally in a wing-like expansion,
the wing of the sphenoid in man. The foramina of the skull will be
further described later in a tabulated form.
The roof of the skull, from back to front, consists of the supraoccipital, paired parietals (an interparietal also in the cat), and the
more posterior portions of the frontals. The brain does not extend
craniad as far as the nasals so that the frontals cover a part of the
brain and also contribute to the roof of the nasal passageway. The
true front of the brain case is closed off by a vertical transverse
partition of ethmoid bone which separates the case from the nasal
cavity. This partition may be seen by looking into the foramen
magnum with proper light. In the extreme cranial end of the case
will be seen paired depressions housing the olfactory lobes of the
brain. The forward enclosure of these lobes is the partition referred
to and is known as the cribriform plate of the ethmoid. It is characterized by numerous olfactory foramina through which olfactory
nerves reach the olfactory lobes of the brain from the sensory epithelium of the nasal cavity.
Facial bones. The most prominent of the facial bones are those
of the upper and lower jaws. The part of the upper jaw bearing the
incisor teeth is premaxillary. Other teeth of the upper jaw are imbedded in the maxillary bone. The lower jaw consists of the paired
dentaries making up the entire mandible. The dentaries articulate
by means of mandibular condyles which fit into mandibular fossae
on the undersurface of the zygomatic process of the squamosal.
In addition to the premaxillary and maxillary, the roof of the
mouth contains the palatine bone, which lies caudad and mediad
to them. Back of the hard palate are vertical extensions of the
palatine bone which support the soft palate and above which air
passes to the larynx. These extensions terminate in a pterygoid
bone as the hamular process and together with the floor of the
brain case form an inverted trough. The pterygoids are closely'
associated also with the lateral sphenoids.
THE SKELETAL SYSTEM
35
Immediately above the nasal openings are the nasal bones, which
join with the frontals further back. An extension from the maxillary bone forms the lower rim of the orbital fossa. This is the
malar bone, sometimes called the jugal bone in lower vertebrates.
Just within the orbital fossa near the front is the lacrimal bone,
which may be recognized by the lacrimal canal that penetrates it
and carries the tear duct to the nasal cavity. Postorbital processes
of the frontal and of the malar bones form the back.rim of the orbital fossa. These do not join except in the primates. In this order
(including man) the caudal rim of the orbital fossa is complete, thus
separating the' fossa from the temporal depression that lies back of
the orbit. At the junction of the maxillary and malar toward the
front and lower rim of the orbit is the prominent opening, the infraorbital foramen. Other features of the skull are shown in the figures
and following tables.
The foramina of the skull
These foramina may be classed as (1) primary exits for,the cranial
nerves as they leave the brain case and (2) passageways for structures (principally nerves) through the facial bones. They are tabulated below and on the following page:
CRANIAL NERVE EXITS (CAT SKULL)
Foramen
Bones involved
Cranial nerves involved
1. Olfactory ....... . Cribriform plate of the ethmoid (I) Olfactory from nasal epithelium
(II) Optic from retina of eye
2. Optic .......... . Orbitosphenoid
3. Sphenoidal fissure Alisphenoid and orbitosphenoid (III) Oculomotor, (IV) trochlcar, and (VI) abducens to
(orbital fissure)
(foramen lacethe extrinsic muscles of the
rum anterior)
eye; ophthalmic division of
\ .
(V) trigeminal
4. Rotllndum....... AliRphenoid
(V) Maxillary division of trigeminal
5. Ovale. . . . . . . . . .. Alisphenoid
(V) Mandibular division of trigeminal
6. Facial canal. . . . .. Petrous and tympanic bulla
Branches of (VII) facial nerve
(VII) Branch of facial
7. Stylomastoid..... Tympanic and mastoid
(VIII) Auditory nerve
8. Internal acoustic Petrous (inner view)
meatus
9. Jugular .......... Tympanic and basioccipital
(IX, X, XI) Glossopharyngeal,
vagus, and spinal accessory
nerves; intcrnal jugular vein
10. Hypoglossal canal Exoccipital (inner margin)
(XII) Hypoglossal nerve
..
36
FUNCTIONAL ANATOMY OF THE MAMMAL
F AcrAL OR
Foramen
N ONCRANIAL
Bone surrounding
FORAMINA
Structures passing through
1. Incisive .. ' ...... , Horizontal parts of maxillary Nasal artery and nasopalatine
branch tJf trigeminal nerve
and premaxillary
Infra-orbital branch of maxil2. Infra-orbital. . . .. Maxillary at malar region
lary
3. Lacrimal ..
Lacrimal bone just dorsal to Tear duct or lacrimal canal
infra-orbital foramen
4. Sphenopalatine .... Vertical palatine just posterior Sphenopalatine nerve
to infra-orbital foramen; proceeds to penetrate horizontal
palatine
5. Posterior palatine .. Vertical palatine just back of Palatine artery and nerve
sphenopaJatine
6. Eustachian ...... . Tympanic and basisphenoid Eustachian tube
to facial canal
7. Mental (superior Mandible; on lateral surface Branches of dental nerves and
may be varied)
beneath and slightly postevessels
rior to canine tooth
8. Inferior dental, .. , Mandible; on medial surface Leads to "dental canal" which
carries the dental nerves and
anterior to condyle
vessels
"
,
The vertebral column
The vertebral column consists of a series of homologous bony
segments that are structurally &ifferentiated into five groups:
cervical! thoracic, lumbar, sacral, and caudal (coccyx of man). The
\ vertebrae of each group are not abruptly different from an adjacent
'. group, but a gradual transition of one type to another occurs in
keeping with the functional relationships. Thus, the last of the
seven neck vertebrae Ccervicals) does not resemble the first cervical
as much as it resembles the first thoracic to which it is adjacent.
The last, or thirteenth, thoracic bears a close resemblance to its
adjacent first lumbar. The lumbars may be considered most gen•
emlized and primitive in their structural
character since they are
relatively free from any highly specinlized function other than support. From a description of a typical lumbar vertebra, suitable
comparisons may be made with the other types.
Lumbar. The most conspicuous and constant feature of a vertebra is the neural canal through which passes the spinal cord. The
cord terminates in the caudal vertebrae as aD nonnervous filum
terminale. The neural canal lies above the body of the vertebra,
THE SKELETAL SYSTEM
37
or centrum, from which side walls project dorsally. The b ases of
the side walls are pedic1es which support the arch formed by neural
lamina. A spinous process, or neural spine, forins the most dorsal
part of the vertebra. Transverse processes project from the sides
of the centrum, and a small accessory process also extends from
the pedicle at its caudal aspect.
.
Place two lumbar vertebrae together in their normal positions.
The facets, or articular surfaces, for the adjacent vertebrae serve
in distinguishing cranial from caudal aspects on an isolated vertebra.
Spinous process
Vertebral
Neural
for~aen
lamina
"
.
.
.
Trans.
- process
Ant. articular
facet
ATLAS
Ant. art.
facet
Art. surface
co p. of rib
Art sur. \
tuber:ofr.ib
THORACIC
Spinous process
Post.
articular
facet
process c..-.__"''''
~~it.J/I!.~~ Ma m milia ry
odontoId
process
~rocess
AXIS
Ant. articular
facet
LUMBAR
'Post
pinous process
Neural canal
a rticu 10
facet
Centrum
Ilium
"'..··_·-0 rticu lotion
Vertebral
foramen
'~1Ift:r
Spinous
process
Tra n s. proc.
5 th
CERVICAL
SACRUM
FIG. 2.11.-T y pes of vertebrae-cat.
Post art. proc.
(Modified from kJivart.)
The anterior articulating process (prezygophysis) projects its face
(articular facet) dorsally and medially, while the posterior articulating process (postzygophysis) projects its facet ventrally and
laterally. This is ~rue of all types of vertebrae and is perhaps the
only definite character in properly orientating a single vertebra.
38
FUNCTIONAL ANATOMY OF THE MAMMAL
An intervertebral notch is formed between two articulate vertebrae
for the passage of the spinal nerves. The facing notches of two
adjacent vertebrae form the intervertebral foramen for the passage
of a spinal nerve. In life, the centra of adjacent vertebrae are
separated by a fibrocartilaginous disk, and the vertebrae are closely
bound together by means of a complex of ligaments.
Cervical. All the cervical vertebrae except the'seventh may be
roughly charac~erized by the presence of a vertebral foramen penetrating the transverse process on either side. These foramina carry
the vertebral arteries to the head. The seventh has a longer spinous
process, and only the upper portion of the transverse process is
present. In other features, the seventh closely resembles the first
thoracic, which is immediately adjacent posteriorly.
The most greatly modified of the cervicals, from a generalized
condition, are the first two: the atlas and axis. These are most
intimately concerned with the support and movement of the head.
Structural differences in the cat and man should be determined in
relation to functional planes and gravity influences. The chief
features of the atlas is the suppression of the spinous process and
the loss of the centrum. The presence of large wing-like transverse
processes is also characteristic. The articulating facets for the
occipital condyles are large and deeply concave. The axis is adapted
to serve as a pivotal center for the atlas. Its characteristic feature
is the odontoid process, which is directed anteriorly. This process
is described as representing the centrum missing from the atlas
which ossifies separately and later fuses with the axis. The spinous
process of the axis forms a rather prominent neural crest.
Thoracic. The thoracic vertebrae all have a common function in
that they serve as articulating points for the vertebral portion of
the rib. The transverse processes are highly modified so that they
may typically bear small articular surfaces, or facets, for this union.
Since a rib tends to be intervertebral in position instead of intravertebral, each rib characteristically joins two vertebrae rather
than one. Determine which of the vertebrae possess two facets on
each of the transverse processes. All the facets are not easily made
out in the cat. The long spinous process is typical of this series and
is associated with the deceivingly deep spinal muscles. Compare
the functions of the thoracic vertebrae with the cervicals. The.
lumbar vertebrae follow the thoracic and have already been
described.
THE SKELETAL SYSTEM
39
Sacral. The sacral vertebrae are fllsed into what may be considered a single bone, the sacrum. Note the articulation of the
sacrum with the pelvis. The number of vertebrae forming the
sacrum varies and is determined by counting the spinous processes.
The foramina for spinal nerves 're seen on the ventral surface.
Determine the functional character of the sacrum as a support to
the hip bones, arnd observe its articulation with the ilium of the
pelvic girdle.
Caudal. Caudal vertebrae of the cat are represented in man by
the coccyx, a vestigial series of vertebrae that are of no particular
importance. Except in relatively few mammals, the tail is of no
functional value. Occasionally, a child is born with several additional coccygeal vertebrae. In the cat, they may vary from the
few ill short-tailed varities to as mall;r as 2fi or more ill other rl),ces
of cats. They are all very similar in structure but become smaller
caudally. Note the absence of the neural canal in these vertebrae.
The thoracic skeleton
This section of the skeleton is composed of the thoracic vertebrae,
already discussed, the ribs, and the sternum. These bones form a
complex primarily designed for the respiratory framework and for
the protection and support of the more susceptible structures of
the thoracic cavity. Although this section is ordinarily considered
with the axial skeleton, its dorsoventral projection of the serially
arranged ribs involves this axis as prorXlinently as the craniocaudal.
The primitive bilaterally flattened forIll of the thorax in the cat is
reflected in the more rounded chest of !), child at birth, which resembles the shape of the chest of a kitten. Adult cats possess a bilaterally compressed chest; whereas, in man the chest develops dorsoventrally compressed. One may speculate on the advantages of
form in the two types. Obviously, a cat can pass through narrow
vertical passageways or vegetation to better advantage with the
bilaterally compressed thorax.
The ribs. In the cat, 13 pairs of ribs are typi'cal. The ribs are
directed so that when elevated or pulled craniad an increase in the
volume of the thorax results. Inspiration of air is accomplished by
elevation of the ribs and flattening the diaphragm.
The fifth or sixth rib may be considered as generalized. Its
proximal end is slightly thickened into a capitUlum which projects
dorsa-anteriorly. Posterior to the capitulum is the neck, back of
which is a small p~ojection, the tuberculum, articulating with the
40
FUNCTIONAL ANATOMY OF THE MAMMAL
vertebra immediately posterior to that with which the capitulum
Jams. Most of the ribs are therefore intervertebral in position.
The curved portion extends obliquely downward, forming an angle
and ending in a cartilaginous extension, the costal cartilage, which
typically joins the sternum, or breast bone.
Hyoid bones
Sternebrae
Trachea I
rin9s
LARYNX AND HYOID
Tuberculum
RIB
RIBS AND STERN UM
FIG. 2.12.-Axial portions of the cat skeleton.
(Modified from Mivart.)
The nine anterior ribs are considered vertebrosternal ribs because
they join the sternum directly by means of their cartilages. The
costal cartilages of the next three connect together and with the
cartilage. of the ninth (vertebrochondral), while the last forms no
ventral connection and is called a vertebral, or floating, rib. In
man the last two are of this type. The angle formed by the connecting cartilages is termed the costal angle a,}d is an important
landmark in determining the position of the diaphragm.
THE SKELETAL SYSTEM
41
It is said that in over 600 human bodies dissected about 5 per cent
possessed an additional rib or pair of ribs. This thirteenth rib,
usually a cervical, is called a "gorilla" rib since that number is characteristic of gorillas and chimpanzees. For no apparent reason, this
anomaly occurs much more frequently in males than in females.
Anomalous ribs are not at all uncommon in the cat and are apparently associated 'With the anomalous development of an intercentrum of a vertebra. In the human embryo, as in other mammals,
rudimentary ribs are formed on all the vertebrae from the seventh
to the coccYx. These normally disappear except for the thoracic.
Sternum. This structure in the cat retains its primitive segmental character. A full-term human fetus shows an irregular
series of button-like elements of the sternum. The anterior segment
is prolonged forward and is known as the manubrium. Then follow
six similar segments, the sternebrae, which are much longer than
broad. The last segment is constricted and is known as the xiphoid
process, which bears an expande~ tip, the xiphoid cartilage. Compare the sternum of the cat with that of man. In man, the xiphoid
process is frequently irregular and knobby, indicating rickets.
H yoid apparatus and larynx. The hyoid consists of a paired
chain of small bones and cartilages extending from either side of
the thyroid cartilage (Adam's apple) of the larynx in the form of
horns which contact the tympanic bullae. In man one can feel
this apparatus by pressing firmly with the thumb and forefinger
just above the larynx, and by extending the tongue the connection
of the extrinsic muscles of the base of the tongue with the hyoid
can be demonstrated. The action is best noted in swallowing.
-
The appendicular skeleton
The bones of the appendages include the bones making up the
girdles of the body, as well as their long free extensions with the
attendant distal parts. B~cause of comparative applications, we
shall speak oupe anterior, or superior, limb as the thoracic appendage and the posterior, or inferior, limb as the pelvic appendage.
In a generalized mammal, considered from the developmental viewpoint, each appendage is furnished with a number and a general
arrangement of skeletal parts that are strikingly similar. These
similarities were discussed in the first chapter under serial homology.
However, the functional arrangement of the bones of the two regions
are typically opposite in that the forelimb is a "puller" and the hind
limb is a "pusher."· This condition apparently arose through rotations in opposite direction of original lateral extensions.
42
FUNCTIONAL ANATOMY OF T HE MAMMAL
The thoracic appendage
Thoracic girdle. The girdle consists typically of a scapula with
a coracoid process and a clavicle, or collar bone. The clavicle m ay
be entirely missing, as in the horse, or rudimentary, as in t he cat. "
It is best developed in arboreal forms, such as the opossum and
monkeys, and most poorly developed in cursorial, or running, types .
..'']
j
!
.' .~
___ _Humerus _ _ _
:j
./
I
.,.
L
FlO. 2.13.-Elements of the thoracic appendage of man and the cat.
(By John F. Trainor .)
It is typically a key bone (cliethrum) between the sternum and
scapula. The student should attempt to account for its appearance
from the standpoint of range of action necessary for each type of
mammal.
The scapula is less 'subject to extreme variations in the different
groups of mammals. I n the lower forms, the coracoid process is
represented as a separate bone, and it develops embryologically in
the mammal generally from a distinct ossification center.
In origin, the clavicle is unique among appendicular bones in that it
is said to be derived from an earlier membrane rather than cartilage.
THE SKELETAL SYSTEM .
43
The scapula. This is a greatly flattened triangular bone bearing
a conspicuous spine on its lateral aspect and a concavity, the subscapular fossa, on the medial aspect. The proximal head of the
humerus articulates in its glenoid fossa, which is surrounded by i;!.
rath~r heavy glenoid border. The t>?ln.e Q{ the t>ca?ula terminateB
distally in an acromion process. A flattened metacromion process
occurs on the sp1ne just above the acromion process. The inferior
racoid proc.
Vertebra
border
etacrom ion process
Axi lIa ry border
Infras~ina+us
fossa
Inferioran'lle
FIG. 2. 14.-Scapula of the cat.
(Modified from Mivart .)
angle of the scapula is rather acute, while the superior angle is
rounded. Between these two angles is the vertebral border. The
border from the inferior angle to the glenoid border is axillary ; the
superior border extends from the superior angle to the glenoid
border. The area in front of the spine is the supraspinatus fossa,
that back of the spine, the infraspinatus fossa.
The humerus. This is the bone of the upper arm, or brachium.
Its proximal rounded head articulates in the glenoid fossa, or cavity
of the scapula, which was typically a focal point for the three com"
ponents of the girdle. Observe the appearance of twisting in the
humerus, and determine the direction and degree of rotation. Note
the twisting effect on the ultimate position of the forearm. Ridges
on the proximal third are named with reference to the insertions of
the deltoid and pectoral muscles, to be described later. The larger
proximal head is marked by a greater and lesser tuberosity, between
which is the intertubercular, or bicipital, groove. Above and on
the inner margin ot the distal head is the supracondylar foramen,
which is more characteristic of the el.1rly reptilian forms than of
44
FUNCTIONAL ANATOMY OF THE MAMMAL
mammals. Through this foramen passes the median nerve of the
brachial nerve plexus. The processes, tuberosities, and ridges are I.
adapted for muscle attachments and should be studied in more
detail in the course of muscle dissection. The deep olecranon fossa
should be particularly observed in relation to the ulna.
Greater
tu beros ity
Lesser
tuberosity
Lesser
tuberosity
.Bicipita I
9roove
'Pectora I rid'le
Deltoid
ridge
Epic<?ndylar
r,dqe
picondylar
fossa
Olecranon
fossa
Medial
epicondyle
lateral epicond
epicon
A
B
F IG . 2.15.-Humerus of the cat (A l (caudal a nd (B) cranial aspects).
(Modiji.ed from Mivart .l
Radius and ulna. Articulating with the distal head of the humerus are the two bones of the antibrachium, or forearm: the radius
on the thumb side and the ulna on the little-finger side. The semilunar notch of the ulna articulates in the trochlea of the humerus,
while the prominent olecranon process, which extends as the bony
tip of the elbow, works into the olecranon fossa on the humerus to
prevent overextension of the arm at the elbow joint. The lower
rim of the semilunar notch bears a rounded projection, the coronary
process.
The margin of the disk-shaped proximal head of the radil1>s rotates
in the radial notch of the ulna, while the proximal concavity of the
radial head articulates with the capitellum of t he humerus. The
distal head of both radius and ulna bear a pointed, or styloid process,
THE SKELETAL SYSTEM
45
and each forms a rather complicated articulation with the small
carpal; or wrist, bopes.
Carpal bones. These extend roughly in two transverse rows and
have been variously named in man and other mammals. They are
difficult to study in the cat because of their small size and co:rp.plications with variable sesamoids. The row adjacent to the radius
and ulna consists·of three i_rregulariy shaped bones: the scapholunar,
01ecl"C1non
proces~
Coronoid
process
Radial notch
Bicipital
tubercle
Ulnar
surfa
A
B
. Styloid
FIG. 2.16.-Ulna CA) and radius CB) of the cat.
(Modifi·ed from Mivart.)
the largest and on the radial side; the cuneiform, median in posi-.
tion ; and the pisiform, a process of which projects prominently on
the· lateral margin of the wrist. The scapholunar joins the radius
above and projects into a depression formed by the arrangement of
the second row of four bones. The cuneiform is wedged into position at about the level of the fourth digit and articulates with the
ulna . A projecting process of the pisiform is typical. The pisiform
is supported almost entirely with the cuneiform above and at the
side and the unciform of the second row below.
The bones of tl:/_~ second row articulate below with the metacarpals. Next to the unciform on the ulnar side is the os magnum,
46
FUNCTIONAL ANATOMY OF THE MAMMAL
which is smoothly convex above and roughly outlined below to
articulate chiefly with the third metacarpal, although it meets the
one on either side also. The trapezoid is rather small and articulates with the second metacarpal only. It is best seen on the dorsal
surface of the hand. The most radial of the series is the trapezium,
which supports the thumb, or pollex. Its form is that of a saddle
with the concavity articulating with the convex surface of the first,
or pollex, met3;carpal.
Metacarpals. The metacarpals comprise the bones of the hand
from the separated digits to the wrist. There is one for each digit,
all similar in general form except for the thumb, or pollex metacarpal. The irregularities of the proximal ends fit the carpals, and
the more regular distal articulations join the phalangeal bones.
A phalangeal formula is derived by counting the number of bones
in each digit. The phalanges of the human and cat should be compared. Each phalanx ossifies from a single center at the proximal
end. The digits are named from thumb to little finger as follows:
pollex, index, medius, annulus, minimus, or simply 1, 2, 3, 4, 5. The
action of the thumb in opposition to the fingers is the chief key to
our success in the use of tools, and the development of the hand and
brain has progressed together.
Compare the hand with the foot as to functional differences in
both cat and human. Compare the functional relationships of the
digits in cat and human.
The pelvic appendage
Pelvic girdle. The girdle of the pelvis in the adult is formed by
tvm irregularly curved bones. These are the paired innominates,
which unite rather firmly with the sacrum dorsally, and with each
other ventrally, to form a ring through which pass the outlets of
the alimentary canal and genito-urinary system. The shape of the
pelvis is further adapted for numerous muscle attachments and especially in man serves as a partial supporting base for the abdominal
viscera.
Each innominate arises from three separate elements embryologically which extend to a focal point for the articulation of the
thigh bone, or femur. At this juncture is a deep concavity for
femoral articulation known as the acetabulum. The three elements
are (1) the ilium, which extends most cranially and dorsally, and
(2) the pubis, meeting the ilium from below and in front. These
two form the cranial rim, or margin, of the pel~is (3) the ischium,
which meets the other elements frqID behind and below.·
47
THE SKELETAL SYSTEM
In the cat the ischium and pubis on either side join in the midventral line to form a fibrocartilaginous connection, the ischiopubic
symphysis. Only the pubes in the human unite to form a symphysis.
The separateness of the elements of the innominate bone are still
evident in a kitten, but in an old adult they are so completely fused
as to be indistinguishable from each other. The pubis and ischium
surround a large· oval obturator foramen. The ilium bears on its
______ Femur_ __ - - - _ -
/
/
//
/
,
.... Articuldtion ot fibula
/
/
'
/'
FIG. 2.17.-Bones of the pelvic appendage, man and cat.
(By John F. Trainor.)
inner margin a rough articular surface where it joins the sacrum,
and the entire girdle is but slightly movable as c'o mpared with the
pectoral.
The human pelvis varies to a considerable extent in the two
sexes. Both diameters of the pelvic opening are relatively greater
in the female, particularly the dorsoventral diameter, making the
outline more circular. In the female, the pubic angle is also less
acute than in the male. This is to accommodate the birth canal. In
the cat, as well as in man, there is a tendency of less complete union
48
FUNCTIONAL ANATOMY OF THE MAMMAL
at the symphysis of the female. Compare the pelvis of the cat and
human as they would appear in a "sitting position," and determine
which is better adapted for this position.
The femur. This is the thigh bone and is rather freely movable.
It bears a conspicuous ball-shaped proximal head and a rather long
neck, which serves to set the bone well out from the body. The
Crest of iii u m
)
Obturator
foramen
Ischial
+uberosi
Ischiopub,ic
symphysIs
F IG. 2.18.-Pelvis of the cat.
(Modifi ed from Mivart.)
proximal end is further characterized by the greater trochanter as a
dorsolateral extension and a lesser trochanter below and caudally.
A rather conspicuous intertrochanteric ridge extends from one to
the other. A deep trochantic fossa is formed between this ridge
and the neck. An oblique, slightly elevated ridge forms a linea
aspera on the caudal margin of the shaft. A slight pit will be noted
on the medial surface of the head which acts as an attachment point
for the ligamentum teres, which helps hold the head in the acetabulum. The distal head of the femur bears .a pair of smooth articular
surfaces, the internal (medial) and external (lateral) condyles between which is the trochlea, or intercondylar fossa. At the upper
margin of each condyle is an epicondylar tubero!lity which the fossa.
extends around in front to allow for the kneecap, or patella,
articulation.
THE SKELETAL SYSTEM
49
The tibia. The large shank bone, or tibia, articulates with the
femur- by means of tibial condyles bearing the same name as those
of the femur. An intercondylar notch separates the condyles.
Because of their concave character, the term "fossa" seems more
applicable than "condyle" here. The cranial margin of the tibia
below the head bears the prominent tibial crest which is affected in
"bumping the silins." The caudal margin of the tibia is marked by
Great
trochanter
I ntertrochanh!ric fossa
Head
Pit
rntertrocha nteric
Crest
lined
as~era
Adductor (med)
tubercle
Patellar .fossa
Medial
condyle
lateral
condyle
lntercondylar fossa
FIG. 2.19.-Femur of the cat (cranial and caudal aspects) .
(Modified from Mivart.)
a deep groove separating two ridges. Tuberosities occur on the
external and internal surfaces as well as above the crest. The distal
head is prolonged into a medial, or internal, malleolus, the projection of which is called the pyramidal process. The distal end is
deeply grooved for articulation with the talus (astragalus) of the
tarsal series. The tibia is the longest bone of the cat skeleton.
The patella. The kneecap at its upper margin is embedded in the
tendon of the rectus femoris muscle. Its lower surface is combined
with a ligament joining the crest of the tibia at its proximal end.
As a sesamoid bo~e, the k~eecap is unique in size and importance.
Its upper end is the broader.
50
FUNCTIONAL ANATOMY OF THE MAMMAL
The fibula. In relative proportion, the fibula is the most slender
bone of the body. It is placed on the lateral surface of the tibia
from below the knee joint to the tarsus. The proximal head is
usually slightly more expanded than the distal head and is held to
the head of the tibia chiefly by the external lateral ligament. The
lower head bears a smooth articular surface on the inner side for
Medial
'Proximal
head of
fibula
Med.
tuberosity
Lateral
malleolus
ial
malleolus
Di sto I fa cet
FIG. 2.20.-Tibia (cra nial and caudal aspects) and fibula of the cat.
lateral
malleolus
(Modifi.ed from M ivart.)
articulation with the astragalus. The external malleolus projects
as a conspicuous knob or bony prominence on the lateral side of the
ankle.
Tarsal bones. Of the tarsal series, the calcaneum (or calcis) is
by far the largest. It is the bone of the heel, and although the
astragalus (talus) bears the weight from the tibia, the calcaneum
is of great importance as a leverage bone for this articulation. Its
free end receives the prominent tendon of Achilles from the large
muscles of the shank. The lower medial half is deeply grooved for
the articulation with the astragalus, while its lo~er end articulates
with the most lateral cuboides of the second-row series.
THE SKELETAL SYSTEM
51
The astragalus lies medial to the calcaneum, is only about half
its length, and possesses a characteristic trochlear surface for the
articulation with the tibia. Lateral to the trochlea, the bone is
grooved sharply where it joins the calcaneum for additional support. Its lower and inner surface articulates with the third bone
of the first row series, the scaphoid (naviculare) of the tarsal series.
es} ell n e i fo rm
nto
Hallux
(vestiqial)
Metatars
FIG. 2.21.-Bones of the hind foot of the cat.
(Modified from Mivart .)
The latter bone may be recognized by the deep concavity for this
articulation. It serves as a key bone for the other six tarsal bones.
The cuboid, previously mentioned, is the most lateral of the
series of four in the second row of tarsal bones. It bears a deep
even groove on its lower border through which passes the tendon
of the peroneus longus muscle. Three cuneiforms follow toward the
medial aspect. The external cuneiform bears a prominent hooklike process. The middle cuneiform, a wedge-shaped bone and
smallest of the group, separates the external from the internal
cuneiform, which '~s but slightly larger. From above, the internal
cuneiform joins the scaphoid, and below it articulates with the first
52
FUNCTIONAL ANATOMY OF THE MAMMAL
two metatarsals of which there are but four fully developed in the
cat. Sesamoid bones of a variable character develop in the regions
of both metacarpals and metatarsals.
Metatarsals. The first metatarsal is extremely rudimentary in
the cat, and there is no "big toe." The others are larger and
stronger. The broader proximal end is called 'the base from which,
extends a shaft ending in a rounded and somewhat constricted head.
These bones ar~ not to be considered in the same sense as long bones,
.' however, since each develops from a single ossification center. From
the primitive standpoint, mammals characteristically possess five
metatarsals as well as the same number of metacarpals.
Each metatarsal of the four developed in the cat bears three
,phalanges in the digits. Since the first metatarsal is vestigial, the
phalangeal bones for it are missing. A stout, but not especially
sharp, claw is borne on the distal phalangeal bones. Compare the
phalanges of the cat with man, and note that claws and digits in
the cat are more specialized than in man.
Polydactylism, the presence of extra digits, is fairly common in both
man and cats. It is a hereditary condition. An interesting example was
seen by the writer recently. A pregnant female cat possessed six welldefined digits on the forelimb and five on the hind limb. The five fetal
kittens taken from the uterus exhibited exactly the same condition of
polydactylism. This indicates the dominant character of the factor.
ARTICULATIONS
\
Special dissection of joints is usually not attempted in general courses.
\ If time permits, an examination of the typical articulations should follow
.the dissection of muscles. Howev,er, because of the relations with skeletal
study, a text descriptioI_l is given here.
Articulations. Connections, or unions, between bony elements are
known as "joints" or "articulations." These are classified on the basis of
the range of movement permitted and the type of material interposed
between adjacent bones. This material varies with the type or range of
action allowed at the joint.
Attachments and associations of muscles tend to aid greatly in holding
the bony framework together, but the bones are more intimately bound
together by the more direct and special ligaments. While it is the primary
function of a tendon to afford efficient muscle attachment, ligaments are
primarily important in holding the bones closely within the proper limits
of their functional range.
The use of the term "ligament" is not restricted to the structures at the
joints. Supporting attachments of certain of the viscera are known by the
THE SKELETAL SYSTEM
53
same general t erm. Cartilages of the voice box (larynx) are also equipped
With ligamentous structures that join them together. The vocal cords
also represent specialized modifications of a type of ligamentous t issue.
Ligaments, tendons, fascia, and aponeuroses are all related connectivetlli'i:\u e elements. Ligaments ~onta,in a, mme or les'i:\ a,bunda,nt 'i:\upply 01
elastic fibers which aUow a controlled degree of mobility at the movable
joints and thus differ from tendons, which are inelastic. The elasticity of
ligaments, no doubt, prevents more serious injury to the joint in case of
dislocations. Ligaments at a joint usually lie outside a lBpecial capsular
ligamentous sheath that encloses movable articulations. The more specific
structure of some typical articulations should be observed in a later dissection.
Bones of the cra.nium are joined by means of sutures, allow for no movement, and possess a cementing substance between them. Since the bones .
of the cranium are functionally concerned with protection, they vary in
size, shape, and thickness, depending upon their use at their particular
position. Many of these unions are strengthened by interdigitating edges.
Go
Lateral
and
Tibio-fibul
Lateral and
liqoments
Interosseous capsular li9aments
Fibula
1i9amen-t
In terosseou
Jiqament
A
B
FIG. 2.22.-The elbow (A ) and knee '(B ) joints of the cat.
(Modified from Mivart.)
The centra of the v~tebrae are contacted by means of fibrous cartilage
and are particularly concerned with carrying weight. The movement is
slight between any two vertebrae, yet the combined column may curve
considerably. The intervertebral disks of fibrocartilage also act 'to prevent jars along the axial skeleton. The articular processes of vertebrae
lend additional strength to the column, and these move rather freely upon
each other.
Where free moverr1ent is common as between the long bones, t he articular surfaces are smooth and consist 01 hyaline cartilage. The heads 01 the'
54
FUNCTIONAL ANATOMY OF THE MAMMAL
bones are expanded to afford strength at the joint and to allow for more
elaborate ligament attachments. The freely movable joints are each completely encased in a sheath of fibrous tissue known as the capsule· of the
joint. The inner lining of the capsule is made up of a glandular epithelium,
or synovial membrane, which secretes the lubricant synovia, a fluid about
the consistency of fresh egg albumen. Ligaments lie to the outside of the
capsule, although there are instances where tendons. pass through the
capsule.
Outpushings <if synovial membranes to form closed sacs are known as
bursae. These are common at joints between surfaces likely to be irritated by friction of moving parts, as skin over a bone or joint or muscles
over bone. Special sheaths of tendons also serve as accessory ligaments
passing over a joint. These are similar to bursae and facilitate the movement of the tendon past the joint or joints.
The 10rm 01 heads or epiphyses of the long bones usually determines the
degree of action permitted at their joints. Thus the olecranon process of
the ulna not only prevents its overextension at the elbow, but also prevents
its rotation in either direction when it occupies
the fossa of the humerus.
I
In other types of bones the articulating substance and ligaments are more
concerned with their freedom of action.
Classes of joints
Types of articulations are classified into three major groups, each of
which contains several subclasses. The principal classes are (1) freely
movable, . or diarthroidal; (2) slightly movable, or amphiarthrodial; and
(3) immovable, or synarthrodial, joints.
Diarthroses
The subclasses of diarthrodial joints are distinguished" by the type of
free movement permitted. The joint surfaces are covered with the articular
cartilage enclosed in the synovial membrane and connected by ligaments.
The union of the atlas and axis allows for limited rotation and is known
as a pivot joint. The articulation of the proximal head of the radius with
the ulna is also of that type, although the bony make-up is quite different.
The hip and shoulder joints not only allow for rotation, but also permit
a rather free movement in all directions. The spherical head of the long
bone articulates in a cup-like depression of the girdle bone. Such a joint
is known as a ball-and-socket, or enarthrodial, type.
Condyloid joints allow for abduction, adduction, flexion, and extension
but not rotation. The union between the metacarpals and phalanges is of
this type. In the thumb of man, however, there is a modification in the
carpometacarpal union in which the articulating surfaces are each saddleshaped and fit into a reciprocal reception.
Gliding joints allow for a limited gliding action of two flat surfaces, as
the articular surfaces of the processes of vertebrae (zygapophyses). These
.
THE SKELETAL SYSTEM
55
articulations are most free in the cervical region and least free in the
thoracic. The capsular ligaments are supplemented by ligaments connecting the lamina of the vertebrae. These are particularly well developed
in the neck region to form the ligamentum nuchae which contains abundant elastic fibers and extends to the head. These ligaments assist the
muscles in movements of the spinal column, and the neck ligament in
quadrupeds gives considerable support to the extended head.
The hinge joints, or ginglymus type, permit flexion and extension only.
The elbow and knee joints are typical. It is well to recaV, however, that
at the elbow particularly where three bones are involved there are two
types of action. The rotation of the radius with the ulna at the humerus
allows for pronation and supination, while the articulation of the ulna
with the humerus is purely a hinge joint, allowing only for flexion and
extension .
• Amphiarthroses
This class allows for only slight movement. The articular surfaces of
the bones are of cartilaginous material and are held in close proximity by
ligaments. Joints between the centra of vertebrae are typical. The
ischiopubic symphysis belongs to the general class, but in this case the
union is more firm. In old males the symphysis more closely resembles a
suture. The sacro-iliac joint also belongs to this general class.
Synarthroses
As previously mentioned, the sutures of the skull are immovable unions
and are typical of this type of articulation. In an immature long bone
the epiphyses are likewise joined to the diaphysis, later to become diaphysis by the replacement of intervening cartilage with bone.
Obviously, more muscles are involved at joints where free movement is
permitted. These muscles serve not only in movement of parts, but are
also functional in protecting the joint from injury by being in a "tonic
state." This muscular tenseness, or tone, serves as "muscle sense" in
preventing dislocations in case a sudden or unexpected force acts upon the
joint. In the dissection of muscles, it will also be noted that tendons are
attached in a manner to prevent slipping of the joints. For example, the
contraction of the biceps brachii not only produces action at the elbow
joint, but also tends to pun the head of the humerus into the glenoid fossa.
At its point of insertion on the radius, it aids in holding the capitellum of
the humerus and the radius together.
LEVER SYSTEMS
The significant feature of joints of the movable type rests in the arrangement of the bones tIJ serve as levers. Although the mechanical principles
are obvious, certain of the arrangements are extremely complex and diffi-
56
FUNCTIONAL ANATOMY OF THE MAMMAL
FIG. 2.23.-Ways in which the foot may be used, involving the leverage principle. In
class I the foot is lifted and the toe is used to mOve a r esisting force W backward. II shows
the u se of the foot in lifting the body on tip-toe. If the true fulcrum is at F, and the weight
Wand power P are as mdicated, this illustrates I, class II lever. However, the weight appears to be shifted to the toes to cause the ankle to also act as a fulcrum as in class I. In
the class III lever, the power is applied between tbe weight and the fulcrum.
Distance
throu9 h
Humerus
which
wei9ht
is lift"ed
Distance of pull
at the
wrist
FIG. 2.24.-An example of a leverage system lidapted for the production of speed rather
than strength. The lever arm here is relatively short (from F to P which greatly reduces
to power advantage, but by operating through Ii short distance P-P the resisting force W
is moved relatively far W-W. This class III prirlCiple is most common in the body.
THE SKELETAL SYSTEM
57
cult to describe in terms of mechanics. A lever, in simple form, is a rigid
bar that can be employed to gain mechanical advantage against a resisting
force or weight. For example, in moving an object that is too heavy to
lift directly, we apply a lever. Also a lever may be employed to increase
velocity; for example, a ball in the hand passing in an arc in a throwing
motion is traveling at much greater speed than one attached to the upper
arm during the mot~on.
B
Prono..tion.
C
SupinC'l.tion
FIG. 2.25.-Pronation and supination of the hand and the location of the muscles performing these apposing actions. Note the leverage principle in the rotating radius. (From Millard and Kino, "Human Anatomy and Physiology." )
The essentials of a leverage system are (1) a fixed point for the lever to
act against, the fulcrum, (2) a power to move the lever around the fixed
point, (3) a resisting force or weight to be moved. In the body the fulcrums are located at the joints, power is supplied by muscles that attach
to bones by tendinous connection : the resistance may be merely moving a
part against gravity.
Three classes of levers are described with reference to the relative positions of these features of the system. Authorities differ as to whether all
three classes operate in the body. The foot illustrates the mechanical principles, as shown in Fig. 2.23.
58
FUNCTIONAL ANATOMY OF THE MAMMAL
Simple leverage is not common in the mechanics of the body. For example, the proximal tendon of the biceps brachii passes through the shoulder
joint somewhat like a rope is passed through a nonrotating pulley, thus
involving the joint there. The muscle forms a belly near the middle of the
humerus, then continues as an inserting tendon across the elbow joint to
attach at some distance below the joint on the radius. This attachment
is rotated with the radius when the hand is pronated or supinated, causing
the tendon to wrap itself partly around the radius in pronation. Although
the elbow joint. is chiefly affected by the power of contraction, the effect
is not simply one producing flexion, but the force also is applied to produce
rotatory movement.
Difficulties are likewise encountered in interpreting the character of the
lever in standing on tiptoe, usually described as a class II lever. Here the
body weight is shifted from the ankle to rest upon the toes, which may also
be considered the fulcrum. In this interpretation the resistance is the
surface to which the foot is applied, and the lever is essentially similar t~
A or class I. Most of the levers of the body are of class III type, which
are more effective in developing speed than efficient in lifting weight.
Chapter III
SUPERFICIAL DISSECTION OF THE CAT
ENERAL dissection is usually done on specially prepa~ed material.
Most laboratories use animals that have been embalmed with a
solution of glycerin, phenol, formalin, and water injected into the femoral
artery. Following the embalming fluid, a colored mass (preferably latex)
is injected into the same artery which fills all the systemic arteries, the left
side of the heart, and the pulmonary veins. A mass of blue colored material is usually injected into the veins so that the vessels may be easily distinguished and traced. The venous injection is usually not so complete
as the arterial because the lining of veins possesses valves that tend to prevent flow away from the heart. These preparatory procedures cause considerable change in the texture. color, and general appearance of the tissues
from the living condition.
G
Superficial characters and landmarks
A male can be distinguished from a female most readily by the
possession of a scrotal sac containing the testes. The scrotum lies
just ventrad to the anus as a prominent bilobed projection. The
penis is rather deeply retracted between the testes and is directed
ventrocaudad. The absence of testes does not always denote a
female specimen since castrated males are not particularly uncommon in laboratories. Other superficial characters should be noted,
but these are commonly so well known as to warrant an omission
of detailed description here.
Since preservatives harden the tissues and alter the general pliability of the body, some of the bony landmarks are best determined
on a live animal or on one freshly killed. Such features as the
spinous processes of the vertebrae, crest of the ilium, the spine and
acromion process of the scapula, angle of the ribs (costal angle),
etc., should be located by forceful pressure of the fingers. Also hold
the specimen in an upright position, and orient landmarks in relation to their position in your own body. Note particularly the
position of the heel, wrist, elbow, etc. Observe the general shape
of the body and the relative proportions of head, neck, trunk, and
tail ..
59
60
FUNCTIONAL ANATOMY OF THE MAMMAL
Dissection of the skin
Perhaps the best method of a laboratory dissection of the skin of
the cat begins with a longitudinal incision in the middorsal line over
the sacrolumbar region. A shallow incision 2 or 3 inches long
should first be made. This should be carefully deepened until the
skin has been penetrated. This can be determined by probing the
edges of the incision. The skin can now be loosened from the underlying tissues by inserting the fingers into the incision. Care should
be taken to cut no deeper than through the skin, particularly between the shoulders. By loosening the skin in front of the incision
with the fingers, it can be pulled free well over the front of the head
and back to the first three or four caudal vertebrae.
Underlying the original incision is a broad expanse of tough white
connective tissue, the dorsolumbar aponeurosis. A smaller expanse
of similar tissue lies between the vertebral borders of the scapulae,
the trapezius aponeurosis. These tissues should not be damaged
since they serve as muscle attachments. As the cut edges of the
skin are pulled laterad, white threads, the cutaneous nerves, will
be seen to extend from the body to the skin. These are obscured
by superficial fascia, or loose connective tissue, which aids in binding the skin to the underlying parts. Note that the cutaneous
nerves occur at regular intervals, indicating the position of the
spinal nerves of which they are branches. The distribution of the
cutaneous nerves indicates the original segmentation of the embryo,
and functionally the skin is segmentally divided into rather distinct bands of sensory areas corresponding with the nerves. These
are the most superficial of serial homologues in the mammal. Following the course of nerves will be seen the larger cutaneous arteries
supplying the skin. These vessels appear as red threads in an injected animal. Ordinarily, the cutaneous veins are difficult to see
because the blue injection mass does not reach them.
The skin should be pulled down along the sides of the body and
kept intact as far as possible. Transverse incisions about midway
may now be made through the skin, and by careful use of the scalpel
it may be further removed. First follow the cranial portion. In
the breast region, particularly, will be seen a thin layer of muscle
fibers that remain with the skin. These are cutaneous muscles
inserting to the skin and are used mostly in flicking movements
perhaps seen best in horses when annoyed by flies. Where cutaneous muscles appear to be continuous with deeper muscles, they
should be cut so as to leave them with the body rather than with
SUPERFICIAL DISSECTION OF THE CAT
61
the skin. These cutaneous muscles continue over the neck and
bear much resemblance to the facial muscles of expression.
The skin over the appendages, when free at their attachments to
the body, will usually pull down as far as the digits, where it may
be broken off. Around the neck and head the skin is extremely
thick and tough, particularly in old males. This condition appears
to be a protective' adaptation in combat.
The caudal portion of the skin can be separated completely
around the tail and the tail clipped off back of the third or fourth
caudal vertebra. Carry the incision around the anus and external
genitalia so as to leave these protected. Where such a portion is
left in dissection, it is said to have been "spared." In the case of
the tail and other skin removed, it is said to have been "sacrificed."
These terms will be useful later. The skin of the hind appendages
should be removed as in the forelimbs.
With the removal of the skin, drying of the body is prevented by
keeping the specimen wrapped in a damp cloth (unbleached muslin)
frequently moistened with a solution of phenol, glycerin, and water.
The student should assume the responsibility for keeping his specimen in good condition when proper materials are provided.
THE INTEGUMENT AND
ITs
DERIVATIVES
The in.tegument consists of the skin and the special structures
that are derived from it. The superficial layer is a stratified epidermis, details of which must be studied microscopically. The
underlying dermis is many times thicker than epidermis and is the
part of the skin from which leather is made. As the skin is removed
from an animal, some loose connective tissue comes free with it;
this is hypodermis, or superficial fascia. Usually no attempt is
made to dissect the separate sheets of fascia in mammalian dissection as in human dissection.
In the cat, both skin and fascia are thickest over the neck and
head regions. Note also that the skin at the distal parts of the
appendages is also relatively thick. At these regions, it also adheres
more closely to the underlying tissues or deep fascia, which helps
form the covering of muscles.
Although the hair follicles are imbedded in the dermis, hair is of
epidermal origin owing to inpushings of this layer. Cutaneous
nerves terminate j'lst at the point of reaching the epidermal layer,
and the cutaneous blood capillaries also reach this level but do not
penetrate the epidermis. The larger nerves and vessels (cutaneous
62
FUNCTIONAL ANATOMY OF THE MAMMAL
arteries) will readily be seen where they have been broken off when
the skin is removed, but their distribution must be studied microscopically.
Portions of the skin that are devoid of hair are notably the "soles"
of the feet and "palms" of the hands. At these points, where forceful contacts are made, the skin develops friction ridges. Note these
on the pads of the cat's feet. These ridges represent thickened
epidermis. It, is well known that a callus tends to form at any
hOlr sho ff
-----------.--.----.---11
epidermis
m alplghlon
sebaceous (oil) gland
dermis
sweaf
follide
nerve
F IG. 3. 1.-A diagrammatic cross section of the human skin. The blood vessels have been
omitted. (Rooers, H ubbel, B yers, "}lIan arui tM B ioiooicai World." R edrawn from Clendennino. )
point on the skin where continued and forceful friction occurs. This
serves as added protection for the live underlying cells and represents an adaptable character. In many mammals, sweat glands
are few or absent, and the nose tip is free of hair. This is supposed
to aid in eliminating heat.
Certain of the skin derivatives are of an extremely hardened
character. The enamel layer of the teeth is similar in origin to skin
derivatives and is the hardest of all parts of the body. Hoofs, nails,
and claws are also examples of hardened derivatives. Claws of the
cat are homologous with the nails of man. Examine these closely
and determine which you would consider more specialized. The
claws should then be clipped to prevent accidental scratches.
SUPERFICIAL DISSECTION OF THE CAT
63
The glandular derivatives of the skin that cannot be seen by gross observation are the sweat glands and the sebaceous, or oil, glands. There are
many modified glands among the different mammals which are similar in
origin but differ greatly in function.
The mammary glands are of a compound character, possessing numerous
branches terminating at a single nipple. In the cat, eight nipples are present, four on either side, distributed from the thorax to the pelvic region.
This type of distribution is known as universal. Compare with other
mammals.
Mammary glands become greatly enlarged during functional activity.
In the cat, those in the abdominal region are especially functional. The
number of glands that remain functionally active corresponds to the number of suckling young, usually four or five. Peculiarly enough, the mammary glands are more closely related to the sweat glands in similarity of
origin than to the oil glands. Oil glands are typically associated with hair
follicles. The secretory portions are derivatives of the epidermal layer.
The hair of mammals assumes definite hair patterns that vary among
different groups. These patterns are not so obvious on the cat because of
the dense nature of the fur. They are, perhaps, best demonstrated on pigskin gloves, where by close observation, without lens, one may make out
the characteristic pattern, which is repetitious. The coarse bristles of the
pig project well down into the thick dermis.
On the cat, note the heavy bristles projecting well out from the lips.
These are known as the vibrissae and are supposed to function as tactile
structures enabling the cat to determine immediately whether the size of
an opening will permit the passage of the body.
In considering the skin and its derivatives as a whole, from the functional standpoint, the integument is most diverse. Such apparent unrelated functions as providing nourishment to the young, aiding in the maintenance of constant body temperature, and the provision of structures of
use in defense and offense illustrate this point. Certain of the structures
of offense are peculiar, as, for instance, the scent glands of skunks.
Superficial dissection-fascia, cutaneous nerves, and vessels
The connective tissue (fascia) may be first removed over the
thoracic and neck regions. Fascia on the cat should be removed by
blunt dissection, and no attempt is made to remove fascia intact.
Except in extremely tough specimens, it is usually best removed by
the fingers alone.
The superficial skeletal muscles' are exposed by removing the
fascia. Each muscle should be cleared of fascia sufficiently to make
its exact limits readily apparent. Avoid picking at the muscle fibers,
and do not attem~t to remove more fascia than is necessary to
expose the separate muscles. It should be observed, by close exami-
64
FUNCTIONAL ANATOMY OF THE MAMMAL
,-/
--
Trapezius
(
I
I
·mox;mus&med·
.
I'
. I
I
CCludo- I
fe mor:o I is
I
T fascia
1"+(1
- -ope~ed to show
---Vostus laterali,
-- - Biceps feJTloris
insczrtion cut to show
-:-.:::-"" Gostrocn~mius
_-
-,--"j
FIG. 3.2.-Superficial muscles of the cat after the fascia has been removed .
F. Trai nor. )
(Drawn by John
nation of its fibers, that fascia tends to present a net-like appearancp.. Observe again the fascia-like binding between the shoulde.rs
and over the lumbar region. This binding should not be removed.
In these regions it will be noted that the muscle fibers thin out,
leaving broad flat tendons as attachments. Such tendons are known
as an "aponeuroses." These are superficially similar to ordinary
fascia, but the aponeurotic fibers tend to run parallel to each other
in layers. The dorsolumbar aponeurosis serve.J as a part of the
fixed attachment of the broadest muscle of the back, the latissimus
SUPERFICIAL DISSECTION OF THE CAT
65
dorsi, which extends to the humerus. The trapezius aponeurosis
serves to attach the right and left acromiotrapezius muscles with
each other in such a way as to provide a free area between the
shoulder blades (vertebral borders) which allows for their rotation.
Observe a large superficial vein on either side of the ventrolateral
surface of the neck, the external jugular. Carefully observe and
remove .the connective tissue that partly obscures the vein, and
note its passage posteriorly between two muscles; the one median
to the vein over which it passes is the sternomastoideus, the one
lateral and deeper is the c1eidomastoideus. Clear away the connective tissue . of these muscles up to the mastoid region of the skull.
Facial
Parotid
gland
uC'Co 1qland
Inferior facia vel n
Lymph nodes
Submaxillary q land
Ext jU9ular vein
FIG. 3.3.-Superficial dissection of the head of the cat.
(Modified from Mivdrt.)
Anteriorly and under the chin region, the two external jugulars
form a union (anastomosis) from side to side by means of a transverse jugular. Trace the external jugular craniad to observe its
formation by the union of facial veins.
Note a rounded mass of tissue back of the angle of the jaw and
under the sup eriCk facial vein, the submaxillary salivary gland.
Also no~e a more irregular mass of the same sort of tissue at the
66
FUNCTIONAL ANATOMY OF THE MAMMAL
base of the ear which is the parotid salivary gland. At about the
point where these two glands come in contact at their forward
margins may be seen the duct of the parotid (Stenson's duct), which
passes forward directly over the largest jaw muscle, the masseter.
The small lymph nodes which superficially resemble salivary glands
may be seen at the lower border of the masseter, one on either side
of the inferior facial vein and in contact with the submaxillary
gland.
Chapter IV
A STUDY OF THE VOLUNTARY MUSCLES
~HE
special function of skeletal muscle is to supply the power for volun-\ tary motion and locomotion. Activity of these muscles produces heat
as ~vell as movement, and most of the heat of the body is generated in the
muscles to be distributed by the general circulation. Furthermore, muscular activity sets up a series of physiological events affecting the degree of
activity of other body functions, notably respitation and circulation. Even
at rest, the muscles are in a state of readilll~ss or tonus, and joints are
usually held in a slightly flexed position. No other ti'3sues are under similar
control through the conscious centers of the brain.
Except in extraordinary situations, only a small fraction of the maximal
muscular power is needed. The muscular system really consists of a series
of functional groups of muscles which may act independently, concurrently, or in sequence in performing a comple:x: coordinated exercise. The
great amount of muscular tissue present and its capacity for doing work
is of particular advantage during short critical periods. This fact is important in circumstances of combat or in escaping from enemies or in other
situations that demand temporary bursts of m!}'ximal energy. No mammal
can maintain its maximal output of muscular energy for more than a few
minutes. The limiting factors of exertion are principally found in the
inability of the respiratory and circulatory sY13tems to supply oxygen and
remove wastes rapidly enough to prevent mu.scular fatigue and complete
exhaustion.
In mammals generally, skeletal muscles make up about half the total
weight and bulk of the body. Between 450 and 500 different muscles may
be recognized in man, and approximately thfl same number occur in the
cat. Almost all these are duplicated in coni'ormation with the bilateral
symmetry of the body. Some are repetitiou~ to conform with the serial
arrangement of the vertebrae and ribs. In the hand and foot, most of the
different muscles are also somewhat duplicatEld on the various digits in a
radial manner.
The muscles that are concerned with movements of the appendages are
known as appendicular muscles. Those which have no attachments to
either of the appendages make up the intrin;ic axial musculature of the
head, neck, thorax, and abdomen.
67
68
FUNCTIONAL ANATOMY OF THE MAMMAL
The cutaneous, or skin, muscles
These thin sheets of muscular tissue that attach to the skin were
mentioned in connection with superficial dissection. The cutaneous
muscles will not be considered here in any detail. After a specimen
has been skinned, the remaining portions of integumentary muscle
fibers must be cleared away with the fat and fascia.
On the skinned specimen, usually a thin flap of skin muscle
adheres to the 'underlying musculature over the back of the neck.
This is a fragment of the platysma, most of which was removed with
the skin. Another such remnant may be found just behind and
above the axilla, or armpit. This, the panniculus camosus, also
merges closely with the deeper muscles from which it arises. The
platysma is sometimes considered as an anterior extension of the
panniculus. The muscles of facial expression are similar to integumentary muscles. They should be observed when the skin is removed from the head.
Structural features of a skeletal muscle
From a purely morphological standpoint, each living muscle is an organ
consisting of representatives of each of the five fundamental types of tissues.
The dominant and most abundant tissue consists of striated muscJe fibers
arranged in bundles (fasciculi) and surrounded by sheaths of connective
tissue. On the surface of most muscles, the connective tissue forms a thin
enveloping cover known as epimysium. Internal extensions of the epimysium divide the muscle into bundles of fibers. The superficial muscles are
also largely interconnected along their margins with deep fascia, which is
a dense tough extension of the loose superficial fascia that binds the skin
\ to underlying parts. Another type of connective tissue, consisting principally of strong inelastic fibers, is present at each end of the muscle. This
white fibrous tissue may converge into a compact tendon; it may form
broad tendinous sheaths previously described as aponeuroses; or the fibers
may appear to attach directly to the periosteum of the bone without forming concentrated tendinous connections. All tendons are attached to the
periosteal sheaths of the bony framework; the periosteum is joined firmly
to the bone by minute fibers (fibers of Sharpey).
In addition to muscular and connective tissues, close examination of a
muscle reveals a distribution of nerves to each muscle. Microscopic examination reveals that each muscle fiber receives a neurofibril of a motor nerve,
and sensory fibrils are richly distributed near the tendinous attachments.
Each muscle receives a blood supply and drainage, thus possessing vascular
tissue. The blood vessels are lined with a special type of epithelium (endothelium). Therefore, an isolated muscle may be de~cribed as a more or
less independent organ. However, under actual working conditions, each
A STUDY OF THE VOLUNTARY MUSCLES
69
muscle must be considered merely as a unit of a functional group in understanding its true character. The central nervous system recognizes and
controls movement rather than individual muscles, and we should attempt
to study muscles from this standpoint.
Functional features of skeletal muscles
Certain other features are common to each of the skeletal muscles, regardless of their particular location, size, or general form. These features must
be kept in mind, and constant reference must be mad~ to the skeletal
system while muscles are being studied. (1) Each muscle does its work
only by contraction or shortening of its fibers. Its maximum contraction
terminates its usefulness in doing further work until the fibers have again
elongated by opposite force of an antagonistic muscle. (2) The fibers must
be attached by inelastic connections (tendons) to two different parts of
the bony framework with a movable joint or joints between the attachments. (3) The type of action at a joint depends primarily on the exact
positions of the attachments on the framework, the functional axis being
between the attachments and along the direction of the fibers. (4) The
bony framework on either side of the joint is affected differently by the
pull of the muscle; the framework on one side of the j oint remains relatively stationary, while the skeletal part on the other side is drawn or moved
toward the stationary part. Thus, the movable bone or part is pulled like
a lever with the joint acting as a fixed point of the lever (fulcrum) around
which the lever bone moves. The relatively stationary attachment of a
muscle is known as its origin, the movable point, the insertion.
Because of these features, muscles work in antagonistic groups. For
example, while the muscles of one set are undergoing contraction, producing
a bending action (flexion) at a joint, they are considered as protagonists,
and their antagonists (the extensors) are being stretched preparatory to
performing the opposite action. Other muscles are used to guide a principal action within the desired planes and to limit the activity. These are
known as synergists. Thus, one understands the actions of muscles not
only by studying the line of action between the two attachments (origin
and insertion), but by studying opposite lines of actions and the modifying
influences of synergic groups. Although muscles are commonly described
as isolated units, they do not act as such, and the simplest activity as picking up a pencil not only involves a large number of muscles but a complicated sequence of coordinated actions.
Anatomical position and muscle actions
Types of actions possible at joints were originally described for man as
beginning from the anatomical position of standing erect with the arms at
the sides and the palms of the hands facing forward (supine). This position
would not only be unhatural for the cat, but would be impossible to imitate
closely without distorting and dislocating the normal arrangement of the
70
FUNCTIONAL ANATOMY OF THE MAMMAL
bones of the thoracic appendage. Therefore, an attempt to describe the
muscle actions of the cat by exact terminology applied to human dissection leads to much confusion.
Most of the difficulties encountered in comparing conditions in the cat
and man are not in homologizing the parts (seeing the structural similarities), but in attempting to make functional analogies. These difficulties
are traceable to (1) the use of the forelimb of the cat in support of the body
and in locomotion, (2) the bilateral compression of the body and consequent position of the scapula, and (3) the reduction of the clavicle so that
the brace effect of the bone in man is lost in the cat. The clavicle is entirely
absent in the hoofed mammals, a condition that contributes to greater
mechanical efficiency in the extended stride and reach of the forelimb.
In walking on all fours, man is not only handicapped by interference of
the clavicle in the forelimb stride, but he also has difficulty in keeping the
arm directly under the body. Since the forelimb of the quadrupeds supports a considerable portion of the body weight, the supporting bones of
these animals must be kept more directly under them to relieve strain at
the joints. This position has not been well achieved in amphibians or even
in the reptiles whose elbmys are directed laterad as well as backward.
Since man is free from the necessity of using the arms for body support,
he possesses a considerably greater range of action of the thoracic appendage than does the cat. To achieve the greater range of action in the arm
of man, the breast muscles passing from the sternum to the humerus attach
relatively high, whereas in the cat these breast muscles hold the humerus
close to the body by inserting on more than half the length of the bone.
This fact leaves only a small part of the upper arm free of the body. Little
more than the elbow of the horse is visible externally, since the breast
muscles are even further developed here than in the cat.
One of the problems of comparative mammalian anatomy that appears
\, to have received inadequate attention concerns the evolution of the position of muscle attachments, and consequent effect on their actions, from
the quadruped condition to the biped condition in man. A study of the
muscular system of the cat should be made from a comparative functional
standpoint. For example, in paralysis of man, due to nerve injury, each
muscle or group of muscles affected IS considered from the standpoint of
efficient functional connections and favorable anatomical positions in doing
work. Nerve injury in man may immobilize the arm only so far as extension is concerned, with the arm hanging at the side in normal anatomical
position for man. Yet, if the arm of such a patient is placed in a primitive
position, i.e., partly extended, the paralysis may be overcome and further
extension may be effected voluntarily from the more favorable position.
Thus, reeducation of muscles that are partly paralyzed from nerve injury
is largely based on a knowledge of efficient anatomical positions from which
only small amounts of muscular energy are required to produce an action.
In many instances, the position in which a muscle may work most effectively in man corresponds with the normal anatomical position, not of man,
A STUDY OF THE VOLUNTARY MUSCLES
71
but of the quadruped mammals. Therefore, a knowledge of more primitive mammalian conditions is valuable in this connection.
A PRACTICAL STUDY OF MUSCLE ACTIONS IN MAN
A systematic survey of the mechanics of the skeletal system should precede a study of the particular or specific muscles concerned with the various
.,
Peroneus lon~us
£Xt..di~ito('um lon~us
.,
FIG. 4.1.-Superficial muscles of man. Anterior (ventral) view.
Anatomy and Physiology.")
(Millard and Kino • .. Huma'",
72
FUNCTIONAL ANATOMY OF THE MAMMAL
Extens or
dis3,itorurn
commUniS
G:tissimus dorsi
Gastroc nenUus
FIG. 4.2.-Superficial muscles of man. Posterior (dorsal) view.
Anatomy and PhYsiology." )
(Millard and King, "Human
actions. This study involves a review of the functional character of each
of the joints or parts affected by muscular pull. Many of the mechanical
aspects of muscular actions can be learned by the use of mounted skeletal
material and artificial models, but the student should perform the actions
himself on his own body. This procedure is not only valuable in clarifying
. definitions, but is essential in obtaining a more correct view of actual conditions and functional limitations of muscles which cannot be adequately .
or properly learned from nonliving material. Note, when possible, the
A STUDY OF THE VOLUNTARY MUSCLES
73
location of muscles that appear to contract in performing the various
actions.
The type of action produced by a single muscle is frequently complicated
and may be compound. These complications occur because (1) a muscle
may pass over and tend to affect the position of the bones at more than one
joint; (2) it may be divided into different parts, each of which may have a
somewhat different type of action on the joint; (3) the line of action may
be modified by the tendon passing around a bony process or through
restricting ligaments; (4) or the muscle may work effectively only when
other parts are in certain anatomical positions. For instance, flex your
forearm strongly ,,,ith the hand supine, and observe your biceps. Now,
in the same flexed position, turn the 'hand to the prone position and observe
that the biceps becomes stretched rather than contracted. With the hand
prone and the elbow flexed, the biceps acts only as a supinator of the hand;
whereas with the hand supinated and the elbow joint extended, the biceps
is essentially a flexor.
The actions of the thoracic appendage are more complex than those of
the pelvic appendage because the thoracic girdle is movable with respect
to the axial parts of the skeleton, whereas the pelvic girdle is closely fused
with the sacral vertebrae (sacro-iliac joint). Furthermore, the greater
freedom of action in the wrist and hand requires more complex muscular
equipment than is found for the ankle and foot. The most proximal movable articulation of the pelvic appendage is at the hip joint. In man, the
clavicle of the thoracic girdle articulates directly with the scapula and
sternum and serves as a strong cross brace between these bones. Hence
the thoracic girdle articulates directly with the sternum but not with the
vertebral column. The scapulae are held close to the vertebral column
entirely by muscles, and the thoracic girdle therefore has a considerable
range of movement conforming with the muscular attachments.
Actions at the thoracic girdle
The muscles that effect changes of position of the girdle are quite exten-,
.'live; they possess broad origins on the axial skeleton and insert to the
scapula, clavicle, and humerus. As suggested above, these muscles are
concerned with two distinctive functions: (1) they serve to hold the thoracic
girdle within a limited range of movement with reference to the axial parts
(skull, vertebral column, ribs, and sternum), and (2) they tend to move'
the appendage more or less as a whole, rather than moving some division
of it as a unit. The muscles producing these movements are said to be
extrinsic appendicular muscles, since one attachment is not on the appendage. Six primary actions are performed by the group. Each of the actions
described below should be performed by the student on his own body.
1. Pull the scapul!1e toward the head (elevation of shoulders in man).
2. Pull the scapulae caudad (depression), a relatively passive action in
man. These two actions occur in shrugging the shoulders.
74
FUNCTIONAL ANATOMY OF THE MAMMAL
3. Draw the shoulders backward (abduction), which pulls the arms
apart or away from the midventralline and pulls the vertebral borders of
the two scapulae together.
4. The opposite action is adduction, drawing the shoulders together in
front as in clasping arms.
5. Rotate the scapulae backward, which results in a forward upsweep of
the arm. In man, the arm is carried to a front horizontal position before
the scapula begins to rotate backward; in the cat, the normal standing
position is alm9st equivalent to the horizontal position of the humerus in
man.
6. Forward rotation of the scapula results in swinging the arm backward or in pulling the body forward in crawling.
A partial combination of these actions produces a more complex circumduction of the shoulder, which involves moving the entire shoulder in a
circular manner around an imaginary fixed axis. This is sometimes erroneously referred to as rotating the shoulder. Note that an upward thrust
of the arm produces a general lowering of the shoulder and a backward
thrust causes an elevation of the shoulder. This change in the height of
the shoulder is partly due to the triangular shape of the scapula and the
shift of position of the angles during rotation. However, some true elevation and depression of the scapula does occur with rotation, and actions
are frequently of a multiple character.
Intrinsic actions of the thoracic appendage
The intrinsic muscles of an appendage have both attachments on parts
of the appendicular skeleton and are, therefore, integral parts of the appendage. Four general groups occur when classified on the basis of the principal
position of their action: (1) those moving the humerus at the glenoid fossa
of the scapula; (2) those affecting the position of the radius and ulna with
respect to the humerus at the elbow joint; (3) those moving the wrist
, (carpal and metacarpal joints); and (4) those working on the digits (phalanges).
Movement of the humerus. The articulation of the humerus with the
scapula is of the ball-and-socket type, permitting a wide range and combinations of actions. The primary actions are (1) lateral rotation, (2) medial
rotation, (3) extension, (4) flexion, (5) abduction, and (6) adduction.
'Lateral rotation of the humerus occurs to a considerable degree upon turning the palm up (supination), and medial rotation occurs in turning the
palm down (pronation) with the elbow joint extended. Extension and
flexion of the humerus refers to swinging the humerus directly craniad and
caudad in a striding motion. These motions bring the humerus in line with
the long axis of the scapula (extended) and bent upon the scapula (flexed),
respectively. Abduction refers to drawing the humerus to a side horizontal
position; adduction is the opposite action. Thus, the normal anatomical
position of the cat is with the humerus mostly extended and in man with
A STUDY OF THE VOLUNTARY MUSCLES
15
the humerus hanging flexed upon the scapula. In the quadrupeds, as
previously indicated, the humerus is closely bound to the body by heavy
breast muscles which tend to strengthen the humeroscapular joint but
which considerably limit the extent of the actions compared with the col1d.\t\Ol\'i', \l\ ffi'(\,l\·, i.e., tb.~ ~'(\,t ~\)'u\.d. l\O\' 'il,~,,'(\,\'~b. \'b.~ b'(\,~k 0\ \\,'il, l\~~k.
Movement at the elbow joint. With the humerus relativel1 fixed in
position, the radius and ulna are made to move at the elbow. However,
in activities such as chinning a bar, the humerus is flexed upon the forearrn.
The actions of the ulna are those of a hinge producing exten$ion and flexion
of the forearm (ttntibrachium) on the humerus. The olecranon process
fitting into the fossa of the humerus prevents hyperextension or backward
bending of the elbow. The radius, however, acts also in a rotatory manner,
articulating at the side of its articular head with the ulna at the radial
notch and at its upper surface with the capitulum of the humerus. The
rotation of the radius produces most of the supination and pronation of
the hand. These positions of the hands may occur independently of the
rotations of the humerus, as can be determined by grasping the upper arm
firmly and working the elbow to produce pronation and supination. Lateral rotation of the humerus as well as of the radius, however, contributes
much to complete supination of the hand. This is a condition of distortion in quadrupeds.
.
Actions at the wrist. The actions at the wrist are of four types: (1) flexion, (2) extensioIl, (3) abduction, and (4) adduction. In standing on tne
hands, the wrists are overextended, or dorsiflexed. Abduction at the wrist
ln man reters to beno.mg the hano. outwaro. at the wTIst with the ha·[Iu
supine, and adduction means bending the hand in toward the body. Since
in the cat a completely supine position of the hand is abnormal anatomically, the same sort of action would be impossible to reproduce or imitate
as described for man.
Actions of the digits. The most powerful muscles acting on the digits
are located on the forearm and possess long tendinous extensions over tne
carpals and metttcarpais to reach the phalangeal bones. Other muscles
working on the phalanges are located entirely within the hand. The later
group will not be described. Their principal actions are abduction and
adduction of the digits, with some others assisting the more powerful
flexors in perforrning delicate graded movements. These are located on
the inner surface of the forearm. The tendons of the extensors of IDe
digits are located on the back of the hand. In the cat, the claws are retracted by special musculotendinous connections.
Other actions. Most of the actions described above apply also to movements in other parts of the body and need not be redefined further when
used in connection with them. Two additional terms are used for actions
of the foot: inversion for "toeing in," and eversion for "toeing out." Frequently actions can ge better described in general terms such as "pulling
the scapula dorsocraniad" or "bringing the arm to a side horizontal posi-
76
FUNCTIONAL ANATOMY OF THE MAMMAL
tion." In these cases, it is better to use a simple descriptive sentence than
to use some term, the meaning of which may be obscure. Further emphasis
should be placed on the circumstance that any simple activity requires the
use of numerous muscles and a series of coordinated actions. Changes in
posture produce differences in gravity effects, and compensating move- .
ments are instinctively made in balance and equilibrium. Thus, walking
involves a constant use of muscles other than those principally engaged in \
propelling the body forward.
,
The naming of muscles
Originally, muscles were described in long Latin sentences. For convenience, these descriptions were later cut down to a few words that were
most applicable to the muscle concerned. Muscles are named chiefly in
relation to (1) size, (2) position, (3) general shape, (4) points of attachments, (5) action, and (6) number of heads, or from a combination of
these factors. Since comparative anatomy had its background in human
anatomy, many structures described for man differ considerably in the cat,
and many of the terms are not quite so applicable in quadrupeds generally,
although the homology may be clear.
The biceps brachii is so named in man because it attaches to the scapula
by means of two heads and passes over the brachium, or upper arm. In
the cat, its homologue is readily apparent; yet here it attaches to the
scapula by a single head. Likewise, the muscle homologous to the rhomboideus major of man is easily determined in the cat, but it is the smaller
of the two divisions of the rhomboideus in the cat. But because of the
origin of the name it is retained in relation to the minor. An example of a
muscle that is constant for the cat and anomalous for man is the rhomboideus capitus (occipitoscapulfl1is), which extends from the occipital bone
of the skull to the scapula. This is not a good name for the muscle because
in the human, where it rarely occurs, it is considered as a slip of the rhomboideus group and is known as the rhomboideus capitus. A translation of
names is particularly helpful in recognizing and remembering muscles.
Thus, when the extensor carpi ulnaris brevis is translated into the short
extensor of the wrist on the ulnar side, it is more easily identified and under- .
stood than if it were given a name of no particular significance.
Comparatively few muscles occur in the cat which are not represented
by homologues in man. In general, a remarkable uniformity of position
and form occurs. With all the differences in locomotion and functional
levels, the circumstances of so much similarity seem more impressive than
that certain distinct differences do occur.
Method of muscle dissection
The general method of dissection presented here is designed to
allow for but one specimen to serve for a study of all the systems.
Since the connective tissues function in binding all other structures
A STUDY OF THE VOLUN'l'ARY MUSCLES
77
together, the major work in dissection is the removal or separation
of connective tissues. This should not be done as a mechanical
routine, but by careful analysis of functional connections. Few
rules in muscle dissection are to be observed, but those rules are
important. The deep muscles must be exposed by transecting the
more superficial. ones and reflecting the cut edges. A transection
should be made only after careful study of the superficial characters
of the muscles under consideration. Th~ dissection should be made
so that but one muscle is cut at one time. Therefo~e, the boundaries must be accurately known. The transection should be made
about midway between origin and insertion in most cases. By following this procedure neither the origin nor insertion is cut into, and
it is possible to replace the cut edges fOr later observations of the
trsmsected muscle .in .its or.ig.imJ pa.,«.itjD.1;l. 'The middle portion of a
muscle is usually relatively free from large nerves and blood vessels
so that danger in cutting these is pra,ctically eliminated. Each
muscle is to be reflected to its points of [tttachments, but not necessarily immediately after transecting. Frequently, the attachments
are obscured until further transections of other muscles are made.
It is assumed that the student may further work out a method of
approach to underlying parts with little additional preliminary
instruction.
In reaching the termination of tendohS it is sometimes difficult,
or impossible, to preserve the innervatioh and blood supply without
distracting too much from the muscle study. One side of the body
may be used primarily for muscle dissection, in case precise origin
and insertion are to be determined, while the other side may be
used for a study of the details of nerve and vascular relations to the
known muscles.
Close observations should be made of the association of muscle,
tendon, periosteum, and bone. The periosteal covering of the bone
should be observed in fresh material, if possible.
A "pulled tendon" infers that its connection with periosteum and bone
has been disrupted, An unusually forceful (~ontraction may result in this,
or injury may affect the muscle fibers to cal.{se "muscle strain."
FUNCTIONAL ANATOMY OF THE MUSCLES OF THE CAT
The muscles to be described have been organized into groups according
to functional associavons and positional rela,tionships. For the most part,
the organization closely follows the sequenre of dissection, Each group
makes up a sort of functional system, and the student will avoid confusion
78
FUNCTIONAL ANATOMY OF THE MAMMAL
in limiting himself, as far as possible, to the study of the muscles of one
group at a time. Later, he should associate the functions of related groups
and attempt to analyze the sequence of actions in performing a simple
activity.
A check list of the muscles in each functional group is given first to
acquaint the student with the number of muscles and general character of
each group. This is followed by a description of specific functional and
structural features of the muscles comprising the group. The student may
find it helpful to construct a table of muscles giving name, origin, insertion, action, and relationships as though the muscles acted separately,
, which they do not do, however. Construction of such a table should be
made from personal observations. For a more complete descriptive account
of the muscles, Reighard and Jennings, "Anatomy of the Cat," should be
consulted.
The check list for each group includes the English application of the
name; pronunciation is also given where thought to be helpful. In case
no counterpart or homology for a muscle is present in man, the name
appears in italics. The check list is numbered continuously through successive groups.
THE EXTRINSIC MUSCLES OF THE THORACIC ApPENDAGE
This system of muscles originates on the axial portions of the
skeleton and inserts to the appendage in such a way as to hold the
shoulder girdle in place and produce movement in the appendage
mostly as a complete unit. Some, however, produce their principal
action on the shoulder joint as will be seen from the insertions.
Check list
1. Clavotrapezius (trap-e'ze-us). Clavicular portion of the
trapezoid muscle in man.
2. Acromiotrapezius (ak-ro'me-o). Middle division of trape\
zoid muscle inserting to the meta-acromion.
,3. Spinotrapezius. Posterior portion of trapezoid muscle inserting to spine of scapula.
4. Latissimus dorsi (lat-is'im-us). Broadest muscle of the back.
5. Rhomboideus major (rom-boid'e-us). Rhomboid shaped
between vertebral borders of scapulae.
6. Rhomboideus minor. Small rhomboid in man (largest of
group in the cat).
7. Rhomboideus capitus. Rhomboid extending to head (same
as occipitoscapularis).
8. Pecto-antibrachialis (pek-to-an-ti-bra-kea'lis). From breast
to antibrachium.
A STUDY OF THE VOLUNTARY MUSCLES
79
9. Pectoralis major (pek-to-ra'lis). Large breast muscle.
10. Pectoralis minor. Minor breast muscle.
11. Xiphihumeralis (ziph'e-hu-mer-a'lis). Xiphoid process to
humerus.
12. Serratus anterior (serra'tus) . Serrated muscle on the front.
13. Levator scapulae (le-va'tor scap'u-Iae). Elevator of scapulae.
14. Levator scapulae ventralis (le-va'tor ven-tra'lis). Elevates
scapulae from below.
15. Cleidomastoideus (kli'do-mas-toi'de-us) . Clavicle to mastoid____'combined with a sternal division in man. as the sterno
cleidomastoideus.
Observations and dissection (see Fig. 4.5)
Two groups of muscles are particularly concerned with holding
the scapulae close to the vertebral column and pulling them together
at the back to abduct the arms. These are the trapezius and rhom-
FIG. 4.3.-Comparison of superficial muscles in man and cat.
boideus groups, and each has three divisions.
The origin of the
divisions of the trapezius extends from the supra-occipital bone of
the skull back to ab'but the middle of the thorax. The c1avotrapezius
passes over the side of the neck to insert to the rudimentary clavicle,
which can be located by freeing the margins of the muscle. Since
80
FUNCTIONAL ANATOMY OF THE MAMMAL
the clavicle is rudimentary in the cat, it is partly imbedded ill the
muscle, and the clavotrapezius appears to continue over the front
of the brachium. But this continuation of musculature from the
clavicle to the forearm is the clavicular portion of the deltoideus,
an intrinsic muscle 01 the appendage.
The acromiotrapezius is readily identified by its dorsal aponeurosis
over the vertebral borders of the scapula, and the spinotrapezius is
a triangular division passing from the spinous processes of thoracic
vertebrae to the spine'of the scapula . Each of the trapezius should
be transected separately halfway between their origins and inser-
Splenius
Levator scapu loe
Supraspi natus
~-""''=''-
rlCeps
eres major
erratus anterior
Serratus posterior inferio
FIG. 4.4.-Second layer of t horacic muscles in man a nd cat. (Superfi cial muscles removed .)
Note that t h e simil arities in this layer arc greater bet ween the two forms than in the superficial layer .
tions. Note especially the line of dissection in the spinotrapezius
in which the dorsal fibers are very short and lie under the edge of
the acromiotrapezius. Also take care in separating these two
muscles. When the cut ends are pulled toward their attachments
(reflected), the rhomboideus musculature is exposed, all of which
inserts to the vertebral border of the scapula. Immediately behind
and below the spinotrapezius is the large latissimus dorsi, which
should be identified and transected.
As previously mentioned, the rhomboideus major in the cat is
relatively small and can be identified as the portion that overlaps
the inferior angle of the scapula. The rhombpideus minor is quite
extensive, and the more cranial fibers run diagonally from the
spinous processes of the vertebrae back to the vertebral border of
the scapula. The rhomboideus capitus (occipltoscapularis) is a
thin ;:;trap-like ;:;lip extending over the neck to tb.e occipital bone.
A STUDY OF THE VOLUNTARY MUSCLES
81
In addition to abduction, the main mass of rhomboideus also draws
the scapula craniad in a rotary manner.
Opposing actions to the trapezius and rhomboideus are mostly
performed by the breast muscles, the pectoralis group (Fig. 46).
Here again the origin is extensive, from the manubrium to the
xiphoid process of the sternum in the cat. The insertion to the
humerus is designed not only for adduction, but also to keep the
forearm held closely to the trunk by medial rotatipn. The most
Gluteus mo ximus
Coud o-
Spino- }
Acromio- deltoideus
Clo vo-
FIG. 4.5.-The order of dissection, 1- 5.
Double lines indicate where tran:;ections are to be
made.
superficial of the pectoralis group is the pecto-antibrachialis, which
partly covers the pectoralis major. Muscle fibers of the pectoantibrachialis and pectoralis major tend to run transversely across
the breast, whereas the pectoralis minor, which merges with the
major caudally, passes obliquely from more caudal sternebrae. The
xiphihumeralis is the most caudal of the group, and its fibers extend
even more obliquely to the humerus. It appears as a narrow strip
from the xiphoid process and must be separated from the large
latissimus dorsi and pectoralis minor in an arbitrary manner. The
latissimus dorsi may now be transected and reflected if this has not
already been done.
The pecto-antibrachialis should be separated from the clavodeltoideus (continuation of clavotrapezius) at its cranial margin
and both transected and reflected. This procedure exposes the
broad insertion of the pectoralis major to the craniolateral margin
of the humerus. The oblique fibers of the pectoralis minor should
now be separated from the more transverse major fibers. Transection of the pectoralis major should be done carefully to avoid injury
to underlying nerves to expose the. more limited insertion of the
82
FUNCTIONAL ANATOMY OF THE MAMMAL
minor and xiphihumeralis. Attempt to follow the insertion of the
latissimus dorsi to each side of the humerus, and note its relation to
the insertion of the pectoralis muscles. Transect the medial insertion of the latissimus to expose the muscles on the front of the
brachium.
Transverse
jU9uJar vein
E",ternaf
jU9ular - - veIn
.Latissimus
dorsi
Rectus obdominis
(beneath aponeu rosis)
FIG. 4.6.-Superficial muscles on the ventral aspect of the cat.
A study of the attachments of the latissimus dorsi, from the dorsolumbar aponeurosis to the humerus, shows it to function in drawing
the arm backward and dorsad. A thin extensioJl of the latissimus
dorsi covers the medial aspect of the upper arm, as the epitrochlearis
muscle. Since the pectoralis (except the pecto-antibrachialis)
A STUDY OF THE VOLUNTARY MUSCLES
83
insert to the craniolateral border of the humerus, they not only
adduct the appendage, but also tend to rotate the humerus medially,
which aids in pronating the hand. Observe the difficulty in your
own body in drawing the arm in and supinating the hand simultaneously.
The rhomboideus minor and major should be transected to free
the vertebral border of the scapula from the vertebral column.
This transection exposes a broad fan-shaped mass of muscles originating from the last nine or ten ribs and continuing its origin
craniad to the lower borders of the last four cervical vertebrae.
Actually, two muscles make up this sheet of musculature: the serratus anterior .arises from the ribs and the levator scapulre from
cervical vertebrae; but no clear distinction can be made out between
them where the fibers merge. The fibers of the serratus anterior
pass to the more caudal part of the vertebral border of the scapula,
whereas the levator scapula inserts mostly to the superior angle of
the scapula. Observe that the body is suspended by these muscles
with the appendages acting as supports for the suspension. Contraction of the levator scapula rotates the scapula forward and
elevates it, which draws the arm backward. The serratus anterior
acts in the opposite manner by depressing the scapula and rotating
it backward to produce an upward thrust of the arm. If the two
muscles on both sides contract simultaneously with the body suspended low between the vertebral borders, a springing action is
performed, throwing the body upward with the appendages extended (see Figs. 4.10 and 4.11).
Two other extrinsic muscles of the thoracic appendage are yet to
be considered: the cleidomastoideus and levator scapulre ventralis.
The latter is a strap-like muscle that merges with the acromiotrapezius on the scapula and passes obliquely across the neck under
the clavotrapezius to the occipital bone of the skull. With the head
in a fixed position, the muscle acts to draw the scapula dorsocraniad.
The cleidomastoideus is closely associated at its insertion on the
mastoid process with an intrinsic muscle of the axial skeleton, the
sternomastoideus. The two form a triangular space where they
diverge on the side of the neck, with the sternomastoideus passing
to the sternum, the other to the clavicle. Note the external jugular
vein passing between these two muscles and over the cleidomastoideus. The action of these muscles depends upon which attachment
is to be stationary; usually the muscles function in turning the head
and depressing it.
84
FUNCTIONAL ANATOMY OF THE MAMMAL
Transections of the extrinsic muscles not yet cut may now be
made after noting especially that nerves are not involved in the
section. This leaves the appendage attached to the body by large
nerve trunks and blood vessels. The nerves and vessels should be
cleared of fascia to expose them and spare them from injury in
further dissection.
INTRINSIC MUSCLES OF THE THORACIC ApPENDAGE
These muscles have both origin and insertion on appendicular
bones and move parts of the appendage in relation to some other
parts of the appendage.
Muscles working principally over the shoulder joint
With the exception of one (clavodeltoideus), these muscles all
arise on the scapula and insert on the humerus and, therefore, function in moving the humerus at its articulation in the glenoid cavity
of the scapula.
Check list
16. Clavodeltoideus (del-toide'us). Portion of deltoid from clavicle.
17. Supraspinatus (spi-na'tus). Above the spine of the scapula.
18. Acromiodeltoideus (ak-ro'me-o). Portion of deltoid from
acromion process.
19. Spinodeltoideus. Portion of deltoid from spine of scapula.
20. Infraspinatus. Within the infraspinatus fossa.
21. Teres major (te'res). Large round muscle.
22. Teres minor. Small round muscle.
23. Subscapularis (skap-u-la'ris). Beneath the scapula.
24. Coracobrachialis (kor'ak-o-bra-ke-a'lis). From coracoid process to brachium .
. Observations and dissection
As previously mentioned, the clavodeltoideus appears as an
extension of the clavotrapezius; it arises from the insertion of the
latter muscle and inserts to the antibrachial fascia in front of the
elbow, on the ulnar side. The clavodeltoideus acts as an extensor
of the humerus and flexor of the forearm in a forward stride of the
appendage. Extension of the humerus is also effected by the supraspinatus, which lies under the acromiotrapezius and occupies the
supraspinatus fossa. This muscle narrows to a tendinous sheath
A STUDY OF THE VOLUNTARY MUSCLES
85
passing over the front of the head of the humerus to the great
tuberosity where it inserts.
Two other divisions of the deltoids, the acromio- and spinodeltoideus, are named also from their points of origin, which roughly
correspond with the insertions of the other trapezius divisions.
These pass across to the deltoid ridge of the humerus to act as lateral
rotators and abductors of the upper arm. Back of the spine of the
scapula, and occupying the infraspinatus fossa, is the. infraspinatus
muscle. The large teres major lies immediately adjacent, extending
along the entire axillary border of the scapula. The infraspinatus
passes to the lateral aspect of the head of the humerus, whereas the
teres major runs to the medial aspect to insert to the lesser tuberosity
. of the humerus. Although both may act as flexors of the humerus,
the insertion of the teres major indicates it to be also a medial rotator of the humerus, and the infraspinatus a lateral rotator. Simultane!Jus action of the two would appear to draw the humerus directly
backward.
The teres minor is a small round muscle which is exposed by
transecting and reflecting the spino- and acromio-deltoideus, under
which it lies. The teres minor arises from the distal third of the
axillary border of the scapula, and its insertion can be easily separated from that of the infraspinatus on the greater tuberosity. It
apparently aids in flexion and lateral rotation of the humerus.
This group includes two other muscles, which occupy the medial
aspect of the appendage: the subscapularis and coracobrachialis.
The subscapularis occupies the subscapular fossa of the scapula
between the supraspinatus in front and the teres major behind. Its
fibers converge into a tendon that crosses the shoulder joint to insert
to the lesser tuberosity. The muscle aids in holding the joint in
place and in drawing the humerus mediad. The coracobrachialis
is a tiny muscle running from the coracoid process to the humerus
and is variable as to its exact point of insertion. It appears to serve
more as a ligament in keeping the joint tensed in adduction.
Muscles of the upper arm
These muscles act principally over the elbow joint, mostly to produce extension and flexion of the forearm. But the actions of some
are complicated, as will be seen in tracing their origins and insertions.
Check list
Muscles of the btachium (flexors and extensor of elbow joint).
25. Epitrochlearis (ep-e-trok'le-a-ris). From above the trochlea;
occasionally a part is anomalous in man.
86
FUNCTIONAL ANATOMY OF THE MAMMAL
26. Triceps brachii. Three-headed muscle of brachium; additional parts in the cat.
27. Anconeus (an-ko'ne-us). Pertaining to the elbow.
28. Brachialis anticus (bra-kea'lis an-ti'kus). Against the brachium.
29. Biceps brachii (bra'chii). Two-headed muscle of brachium;
one head in cat.
~
Observations and dissection
In the cat, a thin wide extension from the latissimus dorsi covers·
the medial aspect of the brachium. This is the epitrochlearis,
which serves to help hold the humerus adducted. It should be
transected and reflected. The extensors of the forearm are mostly
located on the back of the humerus, and all insert to the olecranon
process of the ulna. The action is produced by the triceps brachii
and anconeus. In quadrupeds, these are especially well developed
since a considerable portion of the body weight is supported by the
extended forearm. Instead of three divisions of triceps as in man,
additional slips of this muscle occur in the cat. Superficially on the
back of the arm the long head of the triceps extends from the glenoid
margin of the scapula to the olecranon, thus passing over both the
shoulder and elbow joints. The broad lateral head of the triceps
lies immediately in front of the long head on the lateral aspect of
the arm. These two heads should be well separated, transected,
and reflected to expose the endotriceps, which consists of three slips
in the cat. Note that the lateral and endotriceps originate on the
\ humerus. The anconeus extends from. the external epicondyle of
.the humerus to the olecranon process of the ulna, forming a triangular area of rather short muscle fibers.
Flexion of the elbow is produced by two muscles: the biceps brachii
and the brachialis anticus. The biceps brachii is mostly covered in
quadrupeds by the overlying pectoralis musculature. It occupies
the cranial aspect of the humerus and extends from the glenoid
border of the scapula to the bicipital tubercle of the radius. The
tendon of origin is rather unique in that it passes through the capsular ligament of the shoulder joint and aids in holding the head of
the humerus into the glenoid fossa of the scapula.
The brachialis anticus superficially appears to be an extension of
the acromiodeltoideus, but is a different muscle entirely. It originates at the deltoid ridge and lateral aspect of. the humerus and
inserts on the coronoid process of the ulna immediately below the
elbow joint. Note that the two flexors are entirely distinct in
A STUDY OF. THE VOLUNTARY MUSCLES
87
origins and insertions. The biceps brachii is not a powerful flexor
with the hand pronated. It is a supinator of the pronated hand
when the arm is flexed and the hand pronated. Observe particularly
the state of contraction in your own biceps brachii in performing
Extensor carpi
radialis lon9us and brevis'
Extensor diqitorul11
co m m u n is
~-1IIM'__--
Extensor carpi
ulnaris
'flexor carpi
~-+--++---Ixtensor
diqitorum
latera I is
ulna ris
FIG. 4.7.-La teral muscl es of the thoracic appendage of the cat.
triceps has been r eflected.)
(The lateral head of the
flexion with the hand in the different positions of flexion and pronation. Note the shift in position of the bicipital tubercle of the radius
under these circUIllStances on an articulated skeleton. Only the
short head of the biceps brachii of man is represented in ~he cat.
88
FUNCTIONAL ANATOMY OF THE MAMMAL
MUSCLES OF THE FOREARM
Most of the muscles of the forearm are concerned with movement
at the wrist and within the hand, but some rotate the radius in producing pronation and supination. Extensors of the wrist and digits
occupy the back of the forearm and are associated with supinators,
whereas the flexors are located on the opp·osite side (palmar surface)
and are associated with pronators. Observe the relative difficulty
in flexing the digits simultaneously with supinating the hand and
how extension and supination of the hand are easily performed
simultaneously. Only by carefully following the tendons of insertion in these muscles is it possible to determine whether the action
is on the carpal bones (wrist) or on the phalanges (digits).
A careful dissection of this group of muscles is necessary to a
proper understanding of coordinated movements and activities of
the hand. In most instances the names of the muscles are descriptive of their position and particular action, and they should be
identified mostly from the names.
Extensors and supinators
Check list
30. Brachioradialis (bra'ke-o radia'lis). Brachium to radial side.
31. Extensor carpi radialis longus (car'pe). Long extensor of
wrist from radial side.
32. Extensor carpi radialis brevis (bre'vis). Short extensor of
wrist from radial side.
33. Extensor digitorum communis (kom-u'nis). Common extensor of digits.
34. Extensor digitorum lateralis (lat-er-al'is). Extensor of digits
on midlateral aspect (extensor digiti quinti proprius in man).
35. Extensor carpi ulnaris (ul-na'ris). Extends the wrist from
ulnar side.
36. Extensor pollicis brevis (pol'lic-is). Short extensor of thumb.
37. Supinator (su-pin-a'tor). Supinates hand.
38. Extensor indicis. Extends index finger.
Begin the dissection by carefully removing the tough sheath of
aponeurotic fascia that binds the muscles together and tends to
enclose them. On the cranial border and radial aspect of the forearm, this fascia is closely bound to an extreIPely slender muscle
accompanied by a rather conspicuous nerve, both of which terminate superficially at the hand. The muscle is the brachioradialis,
A STUDY OF THE VOLUNTARY MUSCLES
89
which originates on the humerus and spirals over the brachialis
anticus to reach the craniomedial aspect of the lower arm and hand.
The nerve is the radial branch of the musculospiral nerve, which
lies under the lateral head of the triceps brachii muscle. A void
injury to both.
Using the brachioradialis, a supinator, as a landmark, five superficial extensors are seen from the radial to the ulnar side. These
are, in order, extensor carpi radialis longus and brevis, extensor
digitorum communis, extensor digitorum lateralis, and extensor
carpi ulnaris. These all arise from the lateral supracondylar region
of the humerus and insert either to the metacarpals or carpals
(carpi) or to the phalanges (digiti), as the names indicate. The
tendons of the muscles that reach the fingers pass through transverse ligamentous tissue at the wrist, some of which should be left
intact to hold the tendons in their proper positions, while the tendons on the back of the hand are exposed. To demonstrate the
actions of the digital muscles, all the extensors should be transected
at slightly different levels, and by pulling on the insertion tendons,
the muscles to which they belong may be identified. Usually the
extensor digitorum lateralis inserts to the middle, fourth, and fifth
digits, and its tendons lie beneath those of the communis. Flex
the digits sharply, then pull on the insertion end of these muscles
to demonstrate their actions.
By following down the course of the extensor carpi radialis and
brevis to their insertions to the second and third metacarpal bones,
their tendons are seen to pass under a diagonal mass of musole that
tapers to a narrow tendon inserting to the thumb and index finger.
This overlying muscle is the extensor pollicis brevis, which has a
broad origin on the shaft of the ulna and must be transected to follow·the insertion tendons of the extensor carpi radialis.
A special extensor of the index finger, extensor indicis, lies under
the transected extensor carpi ulnaris. I ts tendon runs from the
origin on the ulna diagonally across the forearm as a narrow strip
to insert to the base of the second phalanx of the index finger. At
the wrist, it is held in place by the transverse ligaments over the
carpal bones. It is interesting to note that the extensors pollicis
and indices have their origins on the relatively fixed ulna and must
cross the radius in reaching their points of insertion on the thumb
side of the hand. This prevents the muscles being stretched, as
they would be, if they arose from the radius, when the radius rotated
in supinating the hand.
90
FUNCTIONAL ANATOMY OF THE MAMMAL
The supinator lies directly above the origin of the pollicis brevis
and may appear continuous with it overlying the radius. It arises
from tendinous connections from the elbow joint and ulna to wrap
itself partly around the radius so as to rotate it laterally in producing supination of the hand.
In man, the supinator and brachioradialis are the special supinators of the hand, and their homologues in the cat are obvious, but
not so well developed. The extensor digitorum lateralis is represented by the extensor digiti quinti proprius in man, and the extensor pollicis brevis of the cat is represented in man as two muscles,
extensor pollicis longus and brevis. Abductors and adductors of
the thumb are highly developed in man also and mostly missing in
the cat. Obviously, the hand of man is more complex than that of
the cat, particularly with reference to the use of the digits and the
thumb in opposition to the other fingers.
Flexors and pronators
As previously mentioned, the ventral or palmar aspect of the
forearm is occupied by flexors of the wrist, flexors of the digits, and
special pronators of the hand. The wrist is capable of being overextended with the hand bent upward, a condition that has been
called dorsiflexion, but that should not be confused with flexion as
described here.
Observe on yourself the difficulty in flexing the digits while the
wrist is also sharply flexed. Pull the skin tightly across the wrist,
and observe the appearance of a broad band running transversely
across the area above the wrist on its palmar surface. This band
is produced by the presence of transverse ligamentous tissue that
\serves to hold the cord-like tendons in their proper places. Flex
the digits strongly, and attempt to locate the position of the muscles
on the forearm which are producing the actions. Determine which
digits tend to operate most independently, and observe that the
tendon to the index finger crosses from the ulnar to the radial side.
In man, two conspicuous tendons will usually be seen above the
wrist: one lies in the middle of the area, and the other lies to the
radial, or thumb, side. The middle tendon belongs to the palmaris
longus muscle and the other to the flexor carpi radialis. An interesting circumstance occurs in man with respect to the palmaris
longus. In about 10 per cent of cases, the muscle is entirely lacking.
In one exceptional circumstance, three students in a class of 15
showed no evidence of possessing a palmaris longus. This is such a
common condition that it is considered as a variation and not as an
A STUDY OF THE VOLUNTARY MUSCLES
91
anomaly. It has not been reported as being missing in the cat even
as an anomaly.
Triceps 6rachii
_
___;~-Epitrochlearis
process
Clavodelt-oideus
Pectoantibrachalis ____.:~~~
Biceps 6rachii ---"'Brach iarad ia I is - - _
Pronator teres
Flexorcarpi ulnoris
humera I head
and
11I 1111I1I1111I.m_-u Ina r head
Il... ~\t--
Extensor carpi radio lis
\oll9
uS
_ _-1\"1'
and
brevis ----+H·11I1I11I1
~--'#4,II-- .3 rd h ea d of
Flexor' profundus
diqitorum
and
r/~flfl-tH--- 5th he a d
FIG. 4.8.-Muscles on t he med ia l asp ect o f t lw ant ibrachium.
Check list
39. Palmaris longus (pal-ma'ris). Long muscle on palmar surface.
40. Flexor digitorum sublimis (sub-li'mis) . Delicate flexor of
the digits.
41. Flexor digitorum profundus. D eep flexor of digits.
42. Flexor carpi ulnaris (car'pi). Flexor of wrist from ulnar side.
43. Flexor carpi radialis. Flexor of carpi from radial side.
44. Pronator teres (te'rez). A round pronator; term not descriptive for cat.,
45. Pronator quadratus (kwad-ra'tus). Quadrate-shaped pronator.
92
FUNCTIONAL ANATOMY OF THE MAMMAL
Three muscles of this group are flexors of the digits and hand:
palmaris longus, flexor digitorum sublimis, and flexor digitorum
profundus. The palmaris longus serves as a landmark. It is the
broadest superficial muscle on the ventral surface and arises from
the medial epicondyle of the humerus. Its insertion is complicated.
After transecting it, follow the insertion end toward the wrist
through the transverse ligament and note that two divisions are
formed. A fleshy ulnar division extends from the outer border of
the tendon to become a portion of the flexor digitorum sublimis.
The flat tendinous division diverges into the palmar fascia as four
or five tendons. Most of the tendons send a branch to the heavy
trilobed pad in the palm. The main tendons insert to the first
phalangeal bones to flex the hand.
Carefully dissect across the next deeper layer of ligamentous
tissue, and probe deeply within the wrist region to expose the extremely heavy tendon of the flexor digitorum profundus. A second
portion of th~ flexor digitorum sublimis arises from this muscle
and is located as a small mass on the superficial aspect of the profundus tendon and can be separated easily from it. Now trace the
delicate tendons of the parts of the flexor digitorum sublimis to
their attachments; note how they are perforated to allow tendons of
the profundus to pass through. If time permits, locate fibrous ,
pulley rings at the bases of the first phalanx of the digits, which keep.
the tendons in place.
The flexor digitorum profundus possesses five heads which converge to the common tendon, which, in turn, redivides into five
\ tendinous parts, one for each of the digits. The insertions are to
\the terminal phalanges. Before attempting to identify the heads
of the flexor profundus, the flexors of the wrist should first be studied
and transected. On the ulnar side, the two conspicuous heads of
the flexor carpi ulnaris should be observed. An ulnar head of this
flexor arises from the surface of the olecranon process of the ulna;
the other head is from the medial epicondyle of the humerus in
connection with the flexor profundus (second head). The ulnar
nerve passes between the two heads of the flexor carpi ulnaris.
The two heads join into a common tendon to insert to the pisiform
bone of the wrist.
On the radial side, only one muscle inserts to the wrist region,
the flexor carpi radialis. This slender muscle originates from the
medial epicondyle of the humerus and inserts :m the base of the
. second and third metacarpals.
A STUDY OF THE VOLUNTARY MUSCLES
93
The flexors of the wrist should now be transected and the separate
heads of the flexor digitorum profundus traced from the common
tendon to their positions of origin. The first head is from the ulna
on its radial border; the second, third, and fourth heads are from
the medial epicondyle of the humerus; the fifth head is from the
interosseous membrane between the radius and ulna and from the
periosteum of these bones.
Epitrochrearis
"Pectora lis
M, Biceps brachi i
N, Musculo-cutaneOu5
FIG. 4.9.-Muscles on the medial aspect ot the r'i ght thoracic appendage with reference to
the brachial nerve plexus. The short a nd long anterior thoracic n erves to the pectoralis
musculature are not shown. The extrinsic muscles have all been transec t ed and the a ppend age
turned away from the body. Return appendage to normal posit ion to determine relationships.
The two pronators are now left to be identified. The pronator
teres is a relatively short muscle extending diagonally from the
medial epicondylar area of the humerus to the medial aspect of the
proximal half of the radius. The action is medial rotation of the
radius to produce pronation. The pronator quadratus lies deep
beneath the tendon of the profundus as a mass of short muscle fibers
that run obliquely from the ulna to the radius to function like the
pronator teres (see Fig. 2.25).
~
94
FUNCTIONAL ANATOMY OF THE MAMMAL
The innervation of the muscles thus far studied can now be determined. This is described on page 197, and illustrated in Fig. 4.9.
PRINCIPAL IVluSCLES OF RESPIRATION
The intrinsic muscles of the thorax are those which have both
origin and insertion on the thoracic skeleton and are mostly concerned with respiration. By respiration, in this connection, we
refer to respiratory movements, or breathing which keeps the lungs
ventilated. The thorax acts as a bellows: when it is increased in
size, air rushes in; when it is decreased, the air is forced out. Muscles
of respiration furnish the power that operates the bellows; the ribs
are the levers. The thoracic vertebrae and sternum are the more
fixed parts of the thorax and of the respiratory bellows. The floor
of the thorax is formed by one of the principal respiratory muscles,
the diaphragm, which will be studied later when the body cavity is
opened. Note that on inspiration the ribs are elevated; on expiration, they are depressed.
Check list
46. Diaphragm. (To be observed later.)
47. Serratus posterior superior. Serrate muscle on back toward
head; named with reference to human posture.
48. Serratus posterior inferior. Serrate muscle on back a~d
posterior.
49. External intercostals. Between ribs on outside.
50. Internal intercostals. Between ribs but deeper.
51. Scalenus (ska-Ie'nus). Unequally three-sided.
52. Levatores costarum (le-va-tor'ez). Elevators of ribs.
Dissection and observations
First observe that some of the musculature of the thoracic wall
passes only from one rib to an adjacent rib and that other musculature passes over ribs when traced from one attachment to the other.
Two serrated muscles lie on the dorsolateral aspect of the thorax,
the serratus posterior superior and inferior. The first originates in
a thin aponeurosis extending from the cervical region to about the
tenth rib. The muscular serrations extend ventrocaudad to insert
to the ribs. The serratus posterior inferior lies just caudad to the
superior and may be distinguished from it by the serrations, which
here are directed ventrally to the last four or fiv~ ribs. The action
A STUDY OF THE VOLUNTARY MUSCLES
95
of both is in pulling the ribs craniad in inspiratory movements.
These may be transected to determine their relationships.
By locating an area where the bony portions of the ribs are clearly
shown, muscle fibers will be seen to occupy the intercostal spaces.
The external intercostals are superficial, and the fibers are directed
ventrocaudad, connecting adjacent ribs only. By carefully transecting these fibers, a second layer will be seen to underlie them.
This layer consists of the internal intercostals, which are directed
opposite to the externals. Contraction of external intercostals produces inspiration, whereas the internals act in expiration. The thin
membrane lining the internal intercostal muscles is the parietal
pleura.
The main trunks of the nerves of the brachial plexus pass between
divisions of scalenus musculature on the thorax and neck. Three
prominent divisions of the muscle occur together with variable
slips. A dorsal division extends back to the third rib, a medial
division to the seventh or eighth ribs; these join with a cervical porti8n to attach on the transverse processes of cervical vertebrae .
.. Scapula
FIG. 4.10.-Diagrammatic representation of muscles that hold the thoracic appendage to the
axial skeleton.
'
The scalenus acts to draw the ribs craniad when the neck is fixed
or to bend the neck when the ribs serve as the origin.
Immediately below the scalenus is a thin muscle passing from the
first rib to the sternum. This is the transverse costarum, which
functions to pull the sternum craniad. The levatores costarum are
continuous with external intercostals dorsally but lie deep under a
heavy muscle of tbe thoracic vertebrae (longis:;imus dorsi). The
96
FUNCTIONAL ANATOMY OF THE MAMMAL
levatores are small muscles running from transverse processes of
thoracic vertebrae to the angle of the rib below. They function
with the external intercostals in inspiratory movements. It will be
noted that inspiration requires considerable active energy and that
expiration is relatively passive.
Thoracic
region of
- --contracted
,,
trun~
......
_------,..,/
,,
/
/
appendicular bones
extended beneath
body
. FIG. 4.11.-Diagram to show how the serra tus anterior helps support the body of a quadruped. Broken lines indicate its possible action in springing the body upward.
AXIAL MUSCLES OF THE NECK
These muscles have both their origins and insertions on axial
parts of the skeleton and except for the sternomastoideus lie beneath the extrinsic muscles of the thoracic appendages. They produce movement of the head and neck.
Check list
53. Splet;tius (sple'ne-us). A compactly bound muscle.
54. Longissimus dorsi. Longest muscle on dorsal aspect.
55. Sternomastoideus. From mastoid to sternum.
56. Sternohyoid. From sternum to hyoid.
57. Sternothyroid. From sternum to thyroid ~artilage.
58. Thyrohyoid. From thyroid cartilage to hyoid bones.
A STUDY OF THE VOLUN1'ARY MUSCLES
97
Identification and dissection
The splenius is a large thick sheet of rrlUscle (one on either side of
the neck) lying beneath the trapeziu~ group and rhomboideus
capitus. It originates from the nuch~ (neck) ligament, which
occupies the middorsal line of the neck, and from deep fascia; the
insertion is to the lambdoidal ridge of the skull. The two together
raise the head. When they act separately, the neck is bent latetally
right or left. Caudally, the splenius is closely associated with the
thick longissimus dorsi musculature, which fills the area between
the spinous processes of the last two or three cervical vertebrae and
extends caudally along all thoracic and lumbar vertebrae.
On the ventral aspect of the neck, the stemomastoideus passes
from the lambdoidal ridge and mastoid process to the manubrium.
'Ibis bas been aescribea in connection' wlt'h the c'ieloomasto"Hleus
with which it functions in turning the head. The inner surface of
the sternomastoideus is in contact with a slender muscle, the sternohyoideus, occupying the mid-ventral lioe of the neck and named
also from its origin and insertion. It acts' to draw the hyoid bone
caudad. The sternothyroid is directly beneath the sternohyoid
but extends only from the first costal ca:(tilage to the thyroid cartilage of the larynx, which it draws back.
These muscles should be divided in the midline of the neck by
blunt dissection, to expose the trachea, :;LS far as the manubrium of
the sternum.
CHIEF MUSCLES OF MA-STICATION
These muscles lie under the thin superficial muscles of facial
expression, which will not be described here. Of the six principal
muscles of mastication, five are elevatore of the lower jaw and but
. one, the last on the check list, is a depre;3sor.
Check list
59. Masseter (mas-e'ter). A chewer.
60. Temporal. Pertaining to position in temporal fossa.
61. Pterygoideus externus (ter-ig-oid'e-us). Wing-shaped on
outside.
62. Pterygoideus internus. Wing-shaped on inner side.
63. Digastric. Two-bellied muscle.
Identification and dissection
J
The location of two of the most powe:fful muscles of mastication·
should first be determined on yourself by pressing firmly on the
98
FUNCTIONAL ANATOMY OF THE MAMMAL
side of the jaw and closing the jaws strongly. The prominent muscle
felt to contract is the masseter, which in the cat arises in three
layers from the malar bone and zygoma to insert to the coronoid
process and lateral fossa of the mandible. Now press the fingers to
the temporal fossa, just back of the posterior rim of the orbit, and
close the jaws firmly to feel the contraction of the temporal muscle.
The. temporal arises in the temporal fossa and passes to both surfaces of the coronoid process of the mandible. These are powerful
muscles used in biting.
Other muscles of mastication should not be dissected until the
salivary glands are studied. The pterygoideus externus lies on the
medial aspect of the mandible just below the lower portion of the
temporal. It arises from the pterygoid process and vertical sheet
of palatine bone which projects caudad from the horizontal portion
of palatine. The pterygoideus internus is connected to the externus
caudally. It arises in the fossa of the pterygoid process and inserts
with the externus and its tendon to the medial surface of the angle
of the mandible. The pterygoideus externus and internus also
assist in closing the jaw.
As is commonly known, the mouth drops open upon relaxation
of the elevators of the jaw. The most active muscle in forcefully
opening the mouth (depressing the jaw) is the digastric. This
muscle lies mediad to the angle of the jaw where it is inserted. Its
origin is from the outer surface of the skull near the jugular and
mastoid processes. In the cat, its two parts are not so prominent
as in man, one part being thick and fleshy from the jugular process,
the other a thin tendon from the mastoid process which then broadens out to the insertion. The insertion is to the lower border of the
mandible at the level of the molar tooth. The lever arm is fairly
long but not especially efficient, and it is much easier to hold an .
animal's jaws together than to pull them apart.
:MUSCLES OF THE ABDOMINAL WALL
These muscles cover the dorsolateral and ventral aspects of the
abdomen. Some of them extend craniad over a considerable area
of the thorax. Because of the thoracic connections, the group is
sometimes considered together with the muscles of respiration as
the thoracoabdominal muscles. The active function of the abdominal muscles is in producing constriction and cpmpression of the
abdomen. Normal tonus in the musculature aids in supporting
the viscera in the proper position. Constriction of the abdomen
A STUDY OF THE VOLUNTARY MUSCLES
99
forces the viscera principally upward and causes the diaphragm
to elevate in forceful expirations. This expiratory action is also
aided by a downward pull on the sternum and ribs. Note a tightening of the abdominal musculature in coughing. Active constriction of the abdominal muscles occurs in defecation and in the process
of giving birth (parturition).
Three of the group of four muscles occur as thin layers, or sheets,
closely applied together on the lateral aspect, and the fourth extends along the longitudinal axis of the front of the abdomen.
Check list
64. External oblique. Passing obliquely on the outside.
65. Internal oblique. Passing obliquely but deeper.
66. Transversus abdominis. Fibers run transversely over abdomen.
67. Rectus abdominis. Straight muscle of abdomen.
Identification and dissection
The external oblique is by far the most extensive of the group.
It attaches cranially at the digitations of the serratus anterior and
extends caudally to the junction of the body wall with the leg.
Dorsally, the external oblique arises from the dorsolumbar aponeurosis. The insertion of the two sides is at the mid-ventral line
(linea alba) by means of wide aponeurotic sheaths. These longitudinal sheaths enclose the rectus abdominis. In man, the junction of the external oblique with the leg is characterized by the
presence of a thickened connective-tissue attachment, the inguinal
ligament. This specialization is not obvious in the cat. Observe
that the lower part of the inguinal region is not covered by muscle
fibers of the external oblique, but only by a thin aponeurotic extension of it.
Locate the most cranial portion of the external oblique, and
observe that the fibers here are relatively short but are directed
caudoventrad as they are further caudad. Mark out a line of
incision to transect the muscle craniad to caudad. Make a shallow
cut, and reflect the fibers to determine their depth. A second
layer, the internal oblique, will be recognized by the fibers here
running in an opposite direction.
Transect and reflect the entire external oblique to expose the
extent of the int~rnal oblique and the rectus abdominis. The
rectus is attached cranially to the sternum and first and second
costal cartilages. I t passes to the ischiopubic. symphysis; the
100
FUNCTIONAL ANATOMY OF THE MAMMAL
abdominal portion of the rectus is rather completely surrounded
by aponeurotic sheaths of the obliques. Note interruptions by
transverse tendinous inscriptions along the rectus abdominis. In
man, these interruptions produce a corrugated appearance of the
mid-ventral aspect of the abdomen when it is strongly compressed.
The internal oblique is neither so extensive nor so thick as the
external. Transection of its fibers reveals the fibers of the transversus, which is also relatively thin and limited in extent. It can
be identified by the more transverse direction of its fibers and also
by the parietal peritoneum lining the abdominal wall, which is
applied to its inner surface.
Reexamine the character of the abdominal wall in the inguinal
region. Here the wall is particularly weak, and in man the intestine may be forced through to enter the inguinal canal in the male, ,
or to push under the skin at the outer lip of the vagina in the female.
This condition of rupture is known as inguinal hernia and is much
more common in the male as the most usual type of rupture. Inguinal hernia in girl babies sometimes occurs as a result of extreme
compression on the abdomen while they are being delivered through
the birth canal of the mother. The anatomy of these potential
conditions will be better observed when the abdominal cavity has
been opened .
.MUSCLES OF THE PELVIC ApPENDAGE
The muscles that originate on the pelvis are of two rather distinct types: (1) those which have an immediate insertion on the
. femur and (2) those which pass over both the hip and knee joints
to insert on the shank at the tibia or fibula. In addition to these
types is a third group that affects the hip joint, consisting of powerfulloin muscles. These originate mostly along the lumbar vertebrae
and insert to the femur and girdle. This latter group functions
especially in bending the back down on the legs when the legs are
fixed, as in stooping, and some act in flexing the femur when the
back is fixed, as in sitting erect and drawing the thighs toward the
abdomen. Because of their position, the loin muscles are best
studied in connection with internal anatomy and are described with
reference to the sacral and lumbar nerve plexi (page 200). Actions
of the pelvic appendages are described as though the legs were not
supporting the body weight and were free to move in all possible
directions.
Actions at the hip joint are similar in type to those at the shoulder,
but are more restricted in range. For example, the femur cannot
A STUDY OF THE VOLUNTARY MUSCLES
101
be rotated as freely as the humerus, nor can it be abducted or extended in so great a degree.
The bony landmarks of the appendage should be reviewed. Note
particularly the position of the crest of the ilium, the great trochanter of the femur, the ischial tuberosity, the crest of the tibia, the
external malleolus of the fibula, and the calcaneum.
Oriqin
~-~JUI--Aponeurosis
of
Tensor foscia 10+0
over Gluteus medius
<Ii-.lfll--.JI...-Muscu la r porhon
<;>t T. {~"'I:.'c. \t>1tl
and its
._;:~i~\\'tIi:Lr'rlrLN'i'~f~Lf"frrr'rmJ
~-:J.IW,.~J-Insertion
aponeurosis
over Quadriceps femoris
Course of Sci
nerve beneoth 1l1lr-t-.....;_-.!
the
Biceps femoris ~,._..
FIG. 4.1 2.-The distribution of aponeuroses on the lateral aspect of the pelvic appendage
and the order of the muscle transections, 1-5.
Preliminary dissection and identification
Observe first a tough aponeurotic sheath on the craniolateral
aspect of the thigh. This is the tendinous insertion of the tensor
fascia lata muscle, ,md it should not be broken into. Immediately
in front of the fascia lata is the sartorius muscle which covers the
102
FUNCTIONAL ANATOMY OF THE MAMMAL
cranial aspect of the thigh and extends medially as far as the femoral
artery and vein. Directly back of the fascia lata is the thick and
broad biceps femoris, while the gracilis superficially covers the
Gluteus l1'laximus
~.....+-Rectu.s femoris
~\!I.I~~':---":':""""':'I--
Sem.itendi.nOSlJ s
Tenuiss imu s (cut)
Adductor femoris -+--'ftAdductor lon9us -T-:-'\t';--~!Q1
Semimembranosus -T-+~
Insertion of
B ice ps femoris
Go strocnem ius
llotero I h eo d)
"+I:::.:n"---txtensor lonqus di'litorum
ftl/Iff'7'f;-~--Peroneus tertius
FIG. 4.13.-Muscles seen on the lateral aspect of the Ilelvic appendage with superficial muscles
transected. Aponeurotic Jascia has been mostly removed hom the gluteus medius.
caudomedial aspect of the thigh not cc)vered by the sartorius. The
exact limits of these muscles should be determined and transections
made of the sartorius and gracilis. Obtserve a he'c1vy mass of musculature passing from the ischiopubic symphysis diagonally down
A STUDY OF THE VOLUNTARY MUSCLES
103
to insert directly to the femur. This is mostly adductor femoris,
which is divisible in the cat as slips rather than as distinct and
separate adductors. The adductor portions should be distinguished
from "hamstring" muscles passing across the back of the joint to
the tibia.
Returning now to the tensor fascia lata, observe that it originates
from a fleshy extension occupying the area on the undersurface of
the ilium and from tough aponeurotic tissue over the upper rump
region. Its muscle fibers make up only a short irregular part of the
muscle as a whole. The tough aponeurotic tissue over the musculature of the rump must be largely sacrificed in identification of the
muscles.
The largest of the buttock muscles of the cat is the gluteus medius,
which originates on the lateral aspect and crest of the ilium and
inserts to the great trochanter. The gluteus minimus lies directly
beneath and medial to its lateral margin. Back of the medius is the
gluteus maximus, a small triangular muscle in the cat, the cranial
portion of which merges closely with tensor fascia lata fibers. The
minimus and medius are principally extensors and rotators of the
femur, while the maximus of the cat appears to be mostly an abductor.
The caudofemoralis can now be identified directly behind the
gluteus maximus and between it and the biceps femoris with which
it inserts. These should be separated and transected. Care should
be taken to avoid cutting the large sciatic nerve, which lies directly
beneath the biceps femoris.
Check list
Principal muscles working only over the hip joint (muscles 73 to
77 to be dissected later).
68. Gluteus medius (glu-te'us). Middle buttocks muscle.
69. Gluteus maximus. Largest buttock muscle (small in cat).
70. Gluteus minimus. Smallest buttocks.
71. Caudofemoralis. From tail to femur.
72. Adductor femoris (See also adductor longus and brevis, Fig.
4.14). Adductors of femur.
73. Psoas major (so'as). Major loin muscle (see page 200).
74. Psoas minor. Minor loin muscle (see page 200).
75. Iliopsoas. Loin to ilium (see page 200).
76. Pyriformis (pir-if-or'mis). A pear-shaped muscle.
77. Gamelli (jem-el'e). Pertaining to twins (superior and
inferior).
104
FUNCTIONAL ANATOMY OF THE MAMMAL
The muscles that pass over both hip and knee joints have been
described by some as producing actions at both joints. But we may
consider their principal function as acting on the knee joint rather
than at the hip, because these actions can occur regardless of the
position of the femur.
Check list
78. Sartorius. Tailor muscle (from cross-legged position).
79. Tensor fascia lata. A tensor of lateral fascia.
80. Biceps femoris. Two-headed muscle of femur.
81. Gracilis (gras/ii-is). From slender condition in man.
82. 'Semitendinosus. Name not applicable for cat.
83. Semimembranosus. Name not applicable for cat.
Quadriceps femoris. Four-headed muscle of the thigh [only
the rectus femoris (86) passes over the hip joint]. The four
parts of the quadriceps femoris are:
84. Vastus lateralis. Large muscle on lateral aspect.
85. Vastus medialis. Large muscle on medial aspect.
86. Rectus femoris. Straight along the femur.
87. Vastus intermedius. Large intermedial muscle.
Further identification. The extensors of the knee joint pass
principally to the patella and occupy the front of the thigh and are
enclosed by the sheath of the tensor ,fascia lata, which is bound to
their insertion tendons. The muscles are collectively known as the
quadriceps femoris. Carefully and completely transect the muscular part of the tensor fascia lata and peel the distal insertion half
down to the knee. It is seen to envelop a large muscle on the craniolateral aspect, the vastus lateralis, and an extensive muscle on the
medial aspect, the vastus medialis. The margins of these muscles
meet at the cranial aspect of the thigh a~d when separated reveal
a strong round muscle invested between them. This is the rectus
femoris, which should be transected and reflected to expose its
positions of origin and insertion. Under the rectus femoris and
originating directly on the front of the femur is the fourth part of
the quadriceps, the vastus internus.
Of the four quadriceps, only the rectus femoris originates on the
pelvis. This muscle originates on the ventral border of the ileum
so that it could conceivably serve to flex the femur and extend the
tibia when these actions occur simultaneously as in kicking a football. The other quadriceps originate along the femur, and all make
final attachments from the patellar area to the' front of the tibia just
below the knee. The patella serves not only in protecting the knee
A STUDY OF THE VOLUNT ARY MUSCLE S
105
joint from injury, but is highly specialized to afford more efficient
leverage in extending the t ibia.
Wit h your knee joint fully extended and the leg muscles fully relaxed,
observe that the patella moves freely from side to side when pushed with
the fingers. But when the extensor muscles are tightened (contracted),
~:~\'\\;~,..-Vostus
laterolis
brevis
.~~T-Rectus femoris
~~~~-Adductor
Adductor femoris
Sem imembranosus
Adductor lon9us -"""t\'~"""~~
Semitendinosus
Gastronem ius
(medial head)-~-'
Insertion of Sartorius
Insertion of
Gracilis
Popl iteu s --t------:fI::9:~
"flexor longus
d i 9i to ru m --+'''r---'--:?-A~
flexor lon<Jus hallicus·t.f"--nfO''I',
Sol e u s ---+i~"11/
Tendon of pia
Fro. 4. 14.-M uscles on the medial aspect of the P'llvic appendage, Portions of the gracilis
and semitendinosus haVe been removed.
t he patella may be felt to be pulled and becomes immobilized as to movements in side directions. This fixation Qf the patella occurs regardless of
the posit ion of the femur (extended or flexed). The patella is formed in
the tendon of the rec ~us femoris as a sesamoid type of bone.
Flexion at the knee is accomplished by three principal muscles : the
biceps femoris, previously observed, th(~ semitendinosus, and the semi-
106
FUNCTIONAL ANATOMY OF THE MAMMAL
membranosus. The tendons of these muscles are commonly known as
the hamstrings. By pressing with the fingers on the medial aspect of the
back of the knee in man, two tendons can be felt distinctly and one on the
lateral aspect. The concavity between is the popliteal space. The lateral
tendon is that of the biceps femoris; the heavy more medial of the other
two is the semimembranosus; the more superficial is the semitendinosus.
_,
In the cat, the biceps femoris arises as a narrow portion from the
ischial tuberosity. Its insertion has been noted as a broad aponeurotic sheath over the lateral aspect of the shank. Both semitendinosus and semimembranosus arise on the lower portion of the
ischium. The semimembranosus is the more fleshy of the two and
inserts immediately below the adductor femoris and may appear
to be continuous with it. The insertion tendon of the semitendinosus is slender and the point of attachment on the tibia considerably lower than that of the semimembranosus. Some authorities
consider the semimembranosus to consist of two parts, the upper
part, which inserts to the femur and acts as an extensor and adductor
of the femur, and a lower division inserting below the knee joint.
In the present interpretation, the so-called upper portion has been
regarded as being more nearly related to the adductor femoris than
to the hamstring muscles and is called the adductor longus. The
adductor brevis lies above the adductor femoris. The medial hamstrings pass to the medial aspect of the tibia to reach the crest,
while the biceps pulls from the lateral aspect. This condition of
insertion helps prevent a rotating strain on the hinge-type knee
joint.
.
MUSCLES OF THE SHANK
These muscles are similar in general character to the muscles of
the forearm, but are neither so numerous nor so complex as arm
muscles, since actions at the ankle and foot are more restricted than
those of the wrist and hand.
Care should be taken in tracing the tendons of the muscles reaching the more distal tarsals, metatarsals, and phalanges. These
tendons are held in place at the ankle by crura1ligaments that must
be broken through in following insertions. The muscles should be
carefully separated and traced well to origins and insertions.
Check list
88. Gastrocnemius (gas-trok-ne'me-us). Belly-like leg muscle.
89. Soleus (so'le-:us). Pertaining to sole (named from insertion
to undersurface of heel).
A STUDY OF THE VOLUNTARY MUSCLES
107
90. Plantaris (plan-ta'ris). Similar to above.
91. Popliteus (po-plit'e-us). Pertaining to space behind the
knee.
92. Tibialis anterior. On anterior aspect of tibia.
93. Extensor digitorum longus. Long extensor of digits.
94. Peroneus longus (per-o-ne'us). Pertaining to long muscle
over fibula.
95. Peroneus brevis. Short muscle on fibula.
96. Peroneus tertius (ter-she'us). Third of fibular group.
97. Flexor digitorum longus. Long flexor of digits.
98. Flexor hallicus longus (hal'ik-us). Long flexor of large toe.
99. Tibialis posterior. Posterior to tibia.
Dissection and identification
The dissection may well begin by a study of the calf muscles,
which insert to the heel bone as the tendon of Achilles. These are
the powerful extensors of the foot and make up the gastrocnemius
complex. The gastrocnemius proper consists of a lateral and medial
head, which meet behind in an indistinct line. These heads are
more widely separated above and should be peeled apart to reveal
a strong round muscle enveloped between them, the plantaris.
Another muscle, the soleus, also contributes to the formation of the
tendon of Achilles. The soleus arises from the lateral surface of the
head of the fibula and passes back under the lower part of the lateral head of the gastrocnemius. The insertion tendons of the soleus
and gastrocnemius form a sheath enclosing the cord-like tendon of
the plantaris, which passes through a groove at the back of the
calcaneus and becomes complicated with a small flexor of the
digits. In man it inserts with the other extensors of the foot to the
calcaneum.
The popliteus is a triangular sheet of muscle passing from the
lateral epicondyle of the humerus to the undersurface of the tibia
on the medial side. Its outer surface lies next to the semitendinosus
and gastrocnemius. The action appears principally to be inversion
of the foot by medial rotation of the femur.
Flexion of the foot is effected principally by the tibialis anterior
and peroneus longus. The former occupies the lateral side of the
tibia, where it overlaps the extensor digitorum longus from which
it should be separated. The tibialis anterior arises from the upper
lateral aspect of the tibia and inserts to the lateral aspect of the
•
first metatarsal. Peronei
muscles occupy the fibular aspect of the
shank. The peroneus longus is a slender tapering muscle extending
108
FUNCTIONAL ANATOMY OF THE MAMMAL
from the lateral aspect of the proximal head of the fibula. It inserts
by a small tendon passing through a groove on the lateral aspect of
the external malleolus at the ankle. The tendon then turns mediad
to reach the bases of the metatarsals on their upper surfaces.
Extension of the digits is produced by the extensor digitorum
longus and peroneus tertius. The extensor longus arises on the
lateral epicondyle of the femur and passes under the tibialis anterior
to reach the ankle, where it bends through a fibrous loop of ligamentous tissue and passes over the upper surface of the foot. The
tendon diverges into four parts, eventually to reach the phalangeal
bones. The peroneus tertius lies directly under the peroneus longus
and extends over about two-thirds the length of the fibula. It inserts
into an extensor tendon of the fifth digit.
The peroneus brevis may now be identified as a short muscle
beneath the other peronei. Its tendon passes around the back of
the external malleolus to reach a groove on its ventral aspect. It is
an accessory extensor of the foot, as is the tibialis posterior. This
latter is a slender muscle lying beneath the flexor longus digitorum
and between it &lid the flexor longus hallicus. The tibialis posterior
arises from the medial surface of the head of the fibula and adjacent
aponeurotic fascia and inserts to the scaphoid and middle cuneiform
tarsals.
Flexion of the digits is performed by the flexor digitorum longus,
which in the cat is combined with the flexor hallicus longus. The
two muscles lie immediately against the ventral surface of the tibia
and fibula and are partly covered by the soleus and popliteus. The
heads of the two flexors are recognized as distinct parts that combine into a single insertion tendon. The common tendon diverges
to the digits. The combining of these two muscles is associated
with the vestigial condition of the hallux in the cat. The tibialis
posterior lies along the medial border of the combined flexors.
PRINCIPAL MODIFICATIONS OF MUSCLES IN MAN
The increase in size of the gluteus major in man and its backward shift
in position are associated with lifting the body from a sitting or squatting
position and in holding the femur well extended in maintaining an efficient
center of balance. Eversion and inversion of the foot in man appear to
be functions originally associated with the ancestral arboreal habitat and
the use of the foot in climbing. The peroneus group of muscles in man are
considerably modified to aid in these functions and &lso act in supporting
the arch of the foot. Similar requirements are not present in digitigrade
types of feet.
A STUDY OF THE VOLUNTARY MUSCLES
109
Principal muscles of the. thoracic appendage which are highly modified
in man are the deltoids, pectorals, and trapezius. The deltoids have
shifted forward in man to pass mostly over the front of the humerus at
the shoulder to act more as extensors and abductors than as adductors
and rotators. The pectoralis muscles of man have become greatly reduced
structurally, and the insertion is to both the proximal portion of the humerus and the coracoid process of the scapula. The higher insertion of
the pectoralis group became necessary to allow greater range in abduction
and extension of the humerus, which stretches these muscles. The trapezius of man, like the deltoids, converge to a smaller area of insertion and
appear as slips of a rather continuous sheet of muscle.
Development and innervation
Muscles are strikingly adaptable and responsive to the kind and amount
of work they are called upon to perform. They diminish in size (atrophy)
when not used and overdevelop (hypertrophy) under conditions of heavy
continuous work. The change in size of the muscle as a whole is due to
decrease or increase in the size of the separate muscle fibers, not in the loss'
or gain of new ones. When the innervation of a muscle is nonfunction
because of mechanical injury, nervous lesions, or in infantile paralysis,
the muscle rapidly atrophies and may practically disappear in the course
of time.
Muscles receive their innervation early embryonically. When an embryonic premuscle mass possesses a single nerve and subsequently divides
into separate parts (as in the case of the deltoids innervated by the axillary),
each of the divisions carries a branch of the nerve with it. This allows us
to identify relationships that are not obvious. Because of this integrity
of innervation, we are reasonably certain that the clavodeltoideus of the
cat is closely related to the other deltoids because it is innervated by a
branch of the same nerve (axillary). From its position it appears to be
related to the trapezius rather than to other deltoids. Anomalous muscles
and unusual slips may usually be identified as to their formation and relationships from a study of their innervation.
STUDY LIST OF MUSCULAR ACTIVITIES
From the study of the cat and from references on human anatomy, determine
the muscles that are essentially involved in the following activities. Apply to your
own body by imitating the actions. Attempt to determine the sequence of activity
where more than one group is involved.
1. Abduction of the arm (raising the arm to the side-horizont~l position).
2. Horizontal circumduction of arm (carrying the arm to a forward-horizontal
position from a side-horizontal position).
3. Medial and later'll rotation of the upper arm at the shoulder~oint.
4. Flexion of the elbow joint as in chinning a bar and as in lifting a weight.
5. Supination of the forearm as in tossing a horseshoe.
110
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
FUNCTIONAL ANATOMY OF THE MAMMAL
Adduction of the scapulae as in drawing the shoulders back.
Pronation of forearm as in smoothing a paper.
Arm movements as in serving a tennis ball.
Movements of arm and shoulder as in throwing a ball.
Movements of arm and shoulder as in rowing a boat.
Extension of the hip and knee joints as in rising from a chair.
Elevation of the mandible as in biting.
Depression of mandible as in opening mouth.
Flexion of the femur as in kicking a football.
Extension of the knee joint as in kicking a football.
Muscles used in "take off" in standing broad jump.
Inhalation, i.e., taking a deep breath.
Exhalation, i.e., expelling the air from the lungs.
OTHER PROBLEMS
It is suggested that a study of the brachial nerve plexus follow the muscle study.
Wnen a study oi tne bracnial plexus Zor otner nerve piexi) nas been maae, ae'termine the activities that would be affected by injury or division of the different
nerves, e.(J., axillary, suprascapular, radial, median. Complete division of a nerve
results in complete paralysis of the muscles that the nerve supplies. Axillary
paralysis refers to complete inability of deltoid action; musculocutaneous paralysis
prevents flexion at the elbow joint; etc.
Chapter V
A SURVEY OF INTERNAL ANATOMY
MID-SAGITTAL section of the head and pharyngeal region serves
very well as a beginning to the study of internal anatomy. This section is most instructive in exposing the anatomical and functional relationships of the mouth, pharynx, esophagus, and larynx. These are the
principal parts concerned with the control of food with respect to respiration. Other important structural features are exposed in this section, and
the student should make the study mostly from the standpoint of regional
anatomy. In the further survey of internal organs, attention should be
directed principally to the interassociations of the systems. The dissection here should be limited to exposing the relationships of the various
parts without disturbing the interrelations. This survey is preliminary to
a more detailed examination of the systems and is intended to help prevent accidental destruction of important features of the anatomy when
the systems are considered as separate divisions.
A
SECTIONAL ASPECTS OF THE HEAD AND PHARYNX
Mark out a line of incision in the exact mid-line of the head, and
carry the line back to the first few cervical vertebrae. By means
of a bone saw (a machinist's hack saw is effective), cut directly
through the cranial portion of the skull to split it between the upper
incisors anteriorly and in line with the spinous processes of the
vertebrae. The tongue and lower jaw should be included in the
section, which should be carried back to the third or fourth cervical
vertebra. Spread the two sides apart, and wash thoroughly under
a tap.
The exact mid-sagittal section in the nasal region strikes the
mes-ethmoid bone; in the brain case, the section passes through the
deep depression between the cerebral hemispheres into which the
tough covering membrane (dura mater) of the brain extends; in the
spinal cord, the mid-point is occupied by the central canal. Orient
your section with respect to these landmarks to determine how far
off center the sectiun may be.
111
112
FUNCTIONAL ANATOMY OF THE MAMMAL
The skull bones involved in the section should first be reviewed.
Locate the frontal and sphenoidal sinuses, the former enclosed by
the frontal bone and the latter by the presphenoid on the floor of
the brain case. Observations should be made of the pituitary fossa
(sella turcica) in the basisphenoid bone; the mes- and lateral ethmoids, cribriform plate, tentorium cerebelli between the cerebrum
and cerebellum; and the palatine bone which forms most of the hard
Frontal
Pituitary
9 1and
Sphe.noidal
sinus
Lateral
ethmoid ~~~$
Mandibular
Har d
.
symp hYSls
palate
Palatine
tonsil
FrG. 5.1.-Sagittal section of the head of t he ca t. Note p articula rly the r ela tion of the alim entary and respiratory tracts .
. palate in the roof of the mouth. Note the extension of the soft
palate and its posterior curtain-like fold, or velum. Observe the
difficulty involved in reaching the pituitary gland surgically through
the roof of the mouth and floor of the brain case.
The mouth region is divided for convenience of description into
the oral cavity and the buccal cavity. The oral cavity is bounded
laterally and in front by the teeth and extends back to the velum
of the soft palate. The buccal cavity occupies the space between
the teeth and the cheeks and lips. It is capable of considerable distension. In some rodents it serves as a pouch in which food is transported to a hiding place. These cavities are the first divisions of
the digestive tube. In addition to housing the tongue and teeth,
they receive the ducts from the salivary glands.
A SURVEY OF INTERNAL ANATOMY
113
Types and numbers of teeth are represented by formulas. In the
case of most mammals, two sets appear: deciduous, or milk, teeth,
and the later or permanent set. The permanent teeth of the cat are
3-1-3-1
30 in number. The dental formula 3-1-2-1 represent.s a lateral
half, upper and lower, and indicates the number of incisors, canines,
premolars, and molars, respectively. Incisors of the cat are poorly
developed. They are best developed in the rodents. The canine,
which is separated from the last incisor by a considerable gap (diastema), is a flesh-tearing tooth of considerable importance to Carnivora. The premolars and molars are grinding teeth, and their
degree of development indicates their relative unimportance in the
carnivores. The eminences or sharp points are sometimes referred
to as the fangs. All the teeth serve in the mechanical or physical
preparation of the food for efficient chemical action of the digestive
juices, as well as in preparing it for swallowing (deglutition).
The deciduous teeth of the kitten appear 2 or 3 weeks after birth. Permanent teeth begin to replace these at about 7 months. These really are
developed very early beneath the deciduous dentition and gradually forge
to the surface. Although the teeth are tjet in deep cups (alveoli) of the jaw
bones, they arise similarly to the exoskeletal structures, i.e., nails or claws,
and show close homology with the placoid scales of sharks.
The tongue is anchored at its base to the bony hyoid apparatus
previously described. The free extension of the tongue occupies
the oral cavity. It is supplied with extrinsic and intrinsic musculature, which affords its movement both as a whole and in bending
itself. The hyoid apparatus may be felt in your owp. body by forcefully pressing the fingers above the voice box (larynx). When
swallowing movements are made, the hyoid is drawn craniad and
is adapted to allow for considerable free movement to the tongue.
When the tongue is protracted, the hyoid is carried forward and
upward.
A mucous membrane envelops the musculature of the tongue and
forms a fold of attachment on its ventral surface, the frenulum
. linguae. The mucous membrane continues as the soft floor of the
mouth to insert at the gums. The tongue is bounded behind and
above by a catilaginous flap, the epiglottis, which guards the
respiratory openiHg, or glottis. The opening appears as a narrow
slit between elevated lips and leads into the larynx, or voice box,
which continues into the trachea. The undersurface of the tongue
114
FUNCTIONAL ANATOMY OF THE MAMMAL
is relatively smooth, but its upper surface bears numerous elevations, or papillae, which give it a rough appearance.
The papillae have been described as being of four general kinds:
(1) vallate, (2) fungiform, (3) conical, (4) lenticular. The flattened
lenticular papillae occupy the most caudal position near the root
of the tongue and are large soft projections. Anterior to these are
those of the vallate type which are roughly arranged in a V-shaped
pattern with the apex pointing backward. As the name indicates,
each of these papilla is set in a depression. The fungiform papillae
are small and numerous and occur most abundantly along the
sides and near the tip of the tongue. Each papilla has a small enlargement near its tip. Conical papillae are extremely numerous.
Some are rather small, but many are large, sharply pointed, and
somewhat cornified or horny in texture. These latter serve as rasping structures. Most of the taste buds are located in the vallate
papillae and in the fungiform type along the sides of the tongue.
Submaxillary and parotid salivary glands have previously been
described as to position with reference to the superficial muscles.
The lower border of the parotid (which surrounds the base of the
ear) is extended down to the margin of the masseter muscle on the
side of the cheek. This lower extension gives rise to its duct (Stenson's), which passes forward across the masseter to the angle of the
• mouth. At the angle of the mouth it penetrates additional salivary
tissue, the small buccal glands, and opens into the buccal cavity
opposite the third premolar. The buccal glands open by numerous
small ducts near the same region.
The submaxillary gland (behind the angle of the jaw) overlies
the sublingual salivary gland. Both are rather smooth and nodular
in appearance.. The duct of the submaxillary (Wharton's duct)
lies rather deep. This duct runs parallel with that of the sublingual
and somewhat dorsad to the anterior facial vein. Both pass to a
point somewhat below the angle of the mouth, where they penetrate
to open at small papillae on either side of the frenulum linguae
below the tongue. They may enter the mouth together. The rather
prominent, superficial lymph nodes that lie along the anterior facial
vein (usually one above and one below the vein) should not be mistaken for salivary tissue. Microscopically they resemble the salivary glands, but the histological differences are marked.
.
In addition to the four pairs of salivary glands now described,
salivary tissue is also present just inside the cra:r.;tial portion of the
zygomatic arch, between it and the eye. This fifth pair is known
as the orbital, or zygomatic, gland. It is rather difficult to reach,
A SURVEY OF INTERNAL ANATOMY
115
and its duct opens just behind the upper molar. The salivary
glands actively secrete salivr, containing the initial digestive enzyme
(ptyalin) which starts the conversion of starches into simple sugars.
The mucous membrane investing the palate of the cat is thrown
into ridges that curve transversely across. From the soft palate
extending from the sides of the palatine bone to the base of the
tongue are two folds of membrane that diverge from above to reach
the floor of the mouth. These folds are known as the anterior and
posterior pillars of the fauces. In between these pillars on either
side, the palatine tonsil is partly imbedded. The pillars form the
, lateral margins of the aperture of the oral cavity into the pharynx.
The pharynx
The oral cavity leads directly into the oropharynx through the
isthmus of the fauces. The pharyngeal extension above the palate
is the nasopharynx. This converges with the passageway from the
mouth (oropharynx) back to the region of the glottis and esophagus,
which is described as the laryngopharynx.
The paired respiratory passageways extend over the scroll-like
ethmoids through the nasal region and open caudally by internal
nares into a common channel, the choana. This channel is directly
continuous with the nasopharynx. The Eustachian tube openings
from the middle ear also open into the nasopharynx and should be
observed on the dorsolateral walls.
From these studies, the pharynx is seen to be a complex anatomical
region with communications of varied functional connections. In all,
seven communications occur: viz., the isthmus of the fauces, two internal
nares, two Eustachian tube openings, the glottis, and the esophagus.
In man particularly, variable amounts of tonsilar tissue occupy the
pharyngeal region. A mass of such tissue is located near the Eustachian
tube opening. This mass is commonly known as the adenoid tonsil. One
of the functions of the tonsilar tissue is to prevent the invasion of harmful
organisms by way of the pharynx. These tissues typically possess deep
crypts into which bacteria may be swept, but they are frequently infected
by the organisms intended for destruction. Tonsils are chiefly composed
of lymphoidal tissue which gives rise to certain of the white blood cells
(lymphocytes), and they also act as filtering systems for traversing lymph.
From the standpoints of embryology and comparative anatomy, the
pharynx passes through the most amazing changes. The numerous changes
that conform with the shift from an aquatic to a terrestrial existence form
a considerable part Q,f comparative anatomy. The gill region of a fish represents the primitive condition of the pharynx, and the modifications having
to do with respiration, food passage, gill support (arches), and the vascular
118
FUNCTIONAL ANATOMY OF THE MAMMAL
sion of the nervous system (see pages 184 to 1.89). Each half of the
brain should be removed carefully with as much of the roots of the
cranial nerves as possible. It should be hardened in 5 per cent
formalin solution for later study of details.
BODY CAVITIES, MEMBRANES, AND VIi:;CERAL ARRANGEMENT
A general survey of the body cavities serves as a further introduction to the internal systems, and observations of structures should
,· .. Heart
Ant.sup
w · ___
.s~)"Jne
FIG. 5.2.-Position of the viscera in r~lation to the skeleton in the human female.
Jones, courtesy o/S. H. Camp and Company.)
(By Tom
first be made with a minimum of dissection. Careful study should
be made of the normal positions and relationships of the organs and
also of their supporting membranes or mesenteries. These membranes should not be destroyed or detached until -iheir relationships
have been carefully noted, and then only if their presence interferes with necessary observations.
· A SURVEY OF INTERNAL ANATOMY
119
Dissection of body wall
The peritoneal space (abdominal cavity) may have been penetrated in the muscle study or by the preparator. In any event,
the upper limits of the abdominal cavity may be determined superficially at the area of the costal angle (angle of the ribs). From this
region, the thoracic cavity extends to a point slightly anterior to the
first rib.
A line of incision may be carried from the lower abdominal region
slightly to one side of the linea alba (ventral mid-line) to the costal
angle. The incision is best made with scissors to prevent cutting
deeper than the body wall. The wall, when opened, can be held up
with the fingers while the incision is being carried along.
The thorax may be opened by continuing the abdominal incision
craniad. First, determine the ex&Ct position of the sternum. Carry
the thoracic incision forward to miss the sternum about a centimeter from the mid-line and in line with the abdominal cut. This
incision will carry through the heavy musculature of the ventral
thoracic wall and the costal cartilages. These are rather easily cut
with heavy scissors. When the incision reaches the first rib, care
must be taken to avoid damage to a large artery (subclavian) that
crosses directly craniad to it. Carry the incision closely around the
first sternabrae (manubrium) through the pectoralis musculature,
and turn sharply to the mid-line on the ventral aspect of the neck.
Expose the trachea and larynx by means of blunt dissection, separating the muscles in the ventral mid-line of the neck.
Clear the fascia on either side of the trachea to expose the sheath
of the carotid artery along which also passes the vagosympathetic
nerve. Closely applied to the trachea and extending from the
larynx are the paired lobes of the thyroid gland, each about 2 cm .
.long. Usually the parathyroids, which appear on the doromedial
aspect of the thyroid, may be observed only partly imbedded in
the thyroid tissue. Parathyroid bodies appear as small light-colored
nodules. The lobes of the thyroid gland sometimes lie considerably
dorsad and ~sually appear completely separate from each other.
The two lob~s in man are connected across the front of the larynx
by an isthmus of the thyroid tissue.
The sex of the specimen should be determined before sectioning
the body wall very far caudally, if this has not previously been done.
In case the animal is a male, a prominent scrotal sac containing the
testes may be located below the anus. The absence of a scrotum is
not entirely conclusive that a specimen is a female because castrated males are rather common in laboratories.
120
FUNCTIONAL ANATOMY OF THE MAMMAL
If the specimen possesses testes, the spermatic cords should be
located. These cords extend from the testes and carry the sperm
duct (ductus deferens), spermatic blood vessels, and spermatic
nerve. They pass over the lower inguinal region just beneath the
skin and lie rather close together at the region of the ischiopubic
Su p. Vena cava
Arch of oorta
Rouricle of heart
Lobes of r. lu"'1
R vlZntridt - -
Diaphroqm (cut)
,--_
lobct--, __
C\.jstic
of livu
Gall bladder----
R. Kidne'1
Smail intestine
Urinar~
~.,..;;;;C~
---~-._
Inqu~nal conal
. ... remora I canal
bladder - ;_ ___r?'O""'--"_'
Urdhra -_
-_
.---Femora! artery
" .... "
P~ostate '1'and-------=·,........
.
j,'"
/
S'1mph'1sis pubis"
(cut)
/
and vein
;,. __ Spermotic cOl"d
.._____Testis
- . ~- M. Sartoris
I
--M. Gracilis
/ Peni.s
I
.
CowI'er$ 91and
FIG. 5.3.-0pen body cavity of the cat.
(By John F. Trainor.)
A SURVEY OF INTERNAL ANATOMY
121
symphysis. They should be freed from the skin and fascia and
traced to the inguinal canal of the abdominal wall through which
they pass to reach, the abdominal cavity. Carefully separate the
cords and clear them of fascia to avoid cutting them accidentally
in later dissection.
Again locate the position of the ischiopubic symphysis, and carry
an incision through the thick musculature covering it. If the symphysis is met exactly in the mid-line, it is usually not difficult to
separate the union with a heavy-bladed scalpel. The union in the
female is less ossified than in the male and, therefore, much easier
to separate. Care should be taken to cut no deeper than through
the bone. The outlets of the alimentary canal and genito-urinary
systems lie close to the symphysis to pass through the internal ring
of the pelvis.
The original incision of the body wall may now be brought back
to meet the posterior incision. Note that the abdominal wall at
the posterior brim of the abdominal cavity is slightly strengthened
by an extension of fascia joining the thigh. The fascia extends from
the symphysis toward the forward margin of the ventral surface of
the ilium. In man the thickened fascia assumes greater importance
and is called the inguinal, or Poupart's, ligament. The erect posture of man causes the abdominal viscera to sag into the floor of the
pelvis. The inguinal ligament aids the abdominal musculature in
supporting the viscera. In inguinal hernia (rupture) a portion of
the intestine enters the inguinal canal and may push into the scrotal
sac.
Pleura and peritoneum
By slightly separating the cut edges of the thoracic wall, observe
the median longitudinal partition of pleura which separates the
two lung cavities from each other. This is the mediastinal pleura
and consists of a double fold; the folds diverge to pass around each
side of the pericardial cavity. The folds then unite again dorsally
to enclose the pericardial region.
The body wall can be further pulled laterad by cutting the diaphragm, which separates the thoracic organs from the abdominal
viscera, Pull the side of the thoracic wall not bearing the sternum
laterad, and push the viscera away to observe the inner surfaces of
the ribs. Nick the ribs with a sharp scalpel in a straight line near
their dorsa: curv~ture. They usually break easily when nicked,
and allow the side to swing down like a door on a hinge. After a
122
FUNCTIONAL ANATOMY OF THE MAMMAL
study of the median or mediastinal pleura, the other wall may be
treated likewise. Transverse incisions through the body wall back
of the diaphragm should also be made.
Esophaqus
~_--i\- L pleura I cavity
L~~:j:.~_..l\__1i-Dorsal mediastinal
pleura
,,*-__;It-_-;"\-Viscera I pleura
J!\~~~~~~f!I----t--tt- In f ven a
co va
;llP~~~~--t--i1- Co rd i a c lobe
riqht lun 9
·~+--H--Lo6e of L I un 9
~~~~~~--1f---H-- Mediastina I pleu
ra
(over pericardium)
~H<.......+-t--f+--E pi co rd i u m
n doca rd i u m
.~--+ll-+o=.I''t--t---H- I
~~4i-+sT+--t""_---h1--- Per i card i a I c a vi ty
#---,/-f--Pa r i e to I pie u ra
'~H'----t--i+- Myocardium
:n.,.~.",
Ventra I mediastina I
'.+----",L----:fH'----
pie u ra
"--r~:__--jt;L--S tern
<---::>"'7"----
um
Peeto ra lis muse Ie
FIG. 5.4.-Tran sverse section through the heart region of the cat to show the distribution
of serous membranes.
The outer covering of the visceral elements, i.e., lungs, stomach,
liver, etc., is really a reflection of the same material that forms the
lining of the body wall. This serous membrane is essentially similar
in structure in both thorax and abdomen, but is named to conform
with its position. In the thorax it is known as pleura; in the abdome·n it is known as peritoneum. Where the membrane is reflected
to form the surface of the abdominal viscera, it is known as visceral
peritoneum; in the thorax, the lungs are covered with visceral pleura.
The walls are lined with the parietal portions of the same membrane,
which also forms the dorsal mesentery supporting the alimentary
A SURVEY OF INTERNAL ANATOMY
123
canal. On the surface of the alimentary canal, the peritoneum
forms the serosa, which is united closely to the underlying tissues.
Serous fluid, secreted by these membranes, serves to prevent the visceral
and parietal portions of the membrane from coming in direct contact with
each other. In this way it acts as a lubric::tnt bed to prevent pleural or
peritoneal adhesions and also facilitates visc~ral movements. A common
irritation of the pleural membranes is known as "pleurisy." Peritonitis is
an infection of the peritoneum.
VISCERAL ARRANGEMENTS IJ'l" THE THORAX
The right and left lungs are separated from each other by the
mediastinal pleura, and each lung lies in its own pleural cavity .
.s.i}:;O£'8 1.b8 .M.JaJ"t. Jj88 wj1.bit;1 .Ja d!:L"8D ~£' Df. its own, the pericardium,
the diverging mediastinal pleura is applied close to the pericardial
tissue over which it passes. Along this mediastinal pleura, close
between the root of the lung and the heart, on either side, are the
phrenic nerves passing to the diaphra~ which they innervate.
The nerves follow extensions of pleura that cover the diaphragm
as diaphragmatic pleura. On the right side, the nerve is closely
applied to the sheath of the large inferior vena cava. In this region
a peculiar condition occurs in the cat where a reflection of pleura
appears to curtain off the small posteri()r, or cardiac, lobe of the
right lung. This sheet of pleura is carri~d back during the formation of the inferior vena cava, which comes to lie in a dorsal position.
The mediastinal pleura may now be detached from the sternum
together with the pair of internal mammary arteries and the internal
mammary vein which pass to the sternal surface of the body wall.
Expose the heart by slitting the pericarctium. Note that the pericardium is attached only at the forward margin (base) of the heart
and around its large vessels. The thymQ.s gland lies in the mediastinal area or space anterior to the heart ftnd under the sternum. It
consists of rather soft and scattered gla1idular tissue, but may not
be evident in the older specimens. The heart and the large vessels
of the heart also lie in the mediastinal SPace between the reflections
of pleura forming the mediastinal portions. It is seen that the
thorax really contains three potential cavities or spaces, the two
pleural and the pericardia!.
Fascia and fat may be cleared away fOr closer observation of the
large vessels and nerves. Care must be taken to avoid damage to
the numerous nerV'es and vessels within 1jhe thoracic area, and they
should be cleared sufficiently to be easily recognized later. Much
124
FUNCTIONAL ANATOMY OF THE MAMMAL
of this work is best done with the fingers. The thymus tissue may
also be removed with the fat and fascia. The vagosympathetic
trunk, at least on the left side, should be carefully followed toward
the thorax and its divisions sufficiently exposed to prevent injury
to them during later dissection. It is most easily located along the
carotid artery in the neck region close beside the trachea.
SURVEY OF STRUCTURES OF THE ABDOMEN
The reflections of the peritoneum are much more complicated
than those of the pleura, for the structures of the abdomen are more
numerous and eccentric in position. Most conspicuous of the
modified mesenteries is the large fat-laden apron that covers the
abdominal viscera. This is the great omentum. The dorsal mesentery is the primary support for the viscera.
The liver, the largest glandular structure of the body, and the
stomach occupy the position directly beneath the diaphragm and
are partly protected by the thora9ic basket. The lobes of the liver
are divided into two unequal areas by a broad or falciform ligament
which passes ventrally from its origin on the dorso-anterior margin
of the diaphragm. It is formed by two folds of peritoneum which
act in a suspensory capacity. Other attachments of the liver will
be noted later.
Unless the stomach is abnormally distended, it is mostly obscured
by the liver where the lobes form a posterior concavity. Note
carefully the attachment of the great omentum from the outer, or
greater, curvature of the stomach, and find the elongate darkcolored spleen supported in the omentum. The great omentum is
a double fold or sac but really consists of four surfaces of peritoneum, since a serous membrane covers each surface of the two folds.
It is formed from the dorsal mesentery during the elongation and
rotation of the stomach. In fact, at all points regardless of how
folded the peritoneum faces a similar layer where a space intervenes.
In life, the spaces and cavities created by dissection contain only serous
fluid. The cavities are properly defined as the areas between visceral and
parietal pleura or peritoneum. Therefore, the viscera do not actually
occupy the cavities, which are merely potential spaces. In this interpretation, the cavities contain a small amount of serous fluid. Incisions through
the body wall create the condition of cavities seen in dissection.
The extension of omentum supporting the spleen is sometimes
referred to as the gastrosplenic omentum, and it attaches to the
A SURVEY OF INTERNAL ANATOMY
125
spleen at its hilus, or concave margin. From the posterior concavity of the liver to the point where the stomach continues into
the intestine is a third division of mesentery known as the lesser
omentum. The bile duct, the hepatic artery, and the hepatic-portal
vein lie between folds of the lesser omentum. The lesser omentum
also connects the duodenum (first division of the intestine) and the
liver, All the omenta are reflections of the original dorsal mesentery. which remains most unmodified where it supports the large
intestine.
The great omentum will be seen to protect and insulate the
numerous folds or loops of the small intestine. Here the supporting
dorsal mesentery is thrown into folds to accommodate the intestine,
which is much longer than the body wall in which it is suspended.
By tracing the small intestine toward the stomach, a portion of the
pancreas will be found invested in the peritoneum in the concave
margin of the first portion of the intestine, the duodenum. Another
portion of the pancreas lies caudad to the lower border of the stomach enclosed between two layers of the great omentum. The ducts
of the pancreas are imbedded in pancreatic tissue and are most
easily located where it is applied to the intestine. They will be
described later.
The small intestine opens caudally into the large intestine at
right angles to it. A blind extension of the large intestine is known
as the cecum. In the cat it does not bear a vermiform appendix as
in man and some other mammals. The large intestine (colon)
circles from the right of the mid-line, across, and down the cavity.
It is roughly divisble into ascending, transverse, and descending
parts. These divisions of the colon are much more pronounced in
man. Carnivores typically possess a very short large intestine,
since the diet tends to be highly concentrated.
The kidneys lie closely applied to the dorsal body wall and are
covered over ventrally by the parietal peritoneum but are not surrounded by peritoneum as are other visceral elementso They are
usually somewhat obscured by fat accumulations, particularly at
their cranial margins. In the fat of this region on either side and
. somewhat above and mediad to the kidneys are the adrenal glands.
Each adrenal body is about the size of a grain of corn and presents
a more dense, nodular appearance than the surrounding fat. Because of their position, the kidneys and adrenal glands are said to
be retroperitoneal., They may be removed surgically through the
dorsal body wall without entering the peritoneal space.
126
FUNCTIONAL ANATOMY OF THE MAMMAL
The urinary bladder is a pear-shaped organ at the extreme posterior region. It is suspended from the ventral body wall from the
position of the umbilicus (navel) by a broad sheet of membrane,
the umbilica1ligament. The neck of the bladder is usually heavily
padded by a large mass of fat on each side. Caudally, the neck
of the bladder extends to a constricted tube, the urethra, which
passes through the pelvis. By drawing the bladder sharply caudad,
the ureters are seen to enter the bladder near its neck (see Fig. 9.1).
If the specimen is a male, the spermatic cord will be seen to pass
from the internal inguinal ring of the body wall to form a loop across
the ureter on either side to enter the urethra at a point some distance below the neck of the bladder. Other structures of the spermatic cord continue craniad in the body cavity. If the specimen is
a female, the two horns of the uterus, together with the body, form
a Y-shaped structure. A horn of the uterus lies on either side of
the lower part of the large intestine. The urethra lies ventral to
the body of the uterus. The body of the uterus continues to the
vagina. At the upper extremity of each horn, just caudad to the
kidney, an ovary occurs, partly enveloped in a hood-like funnel,
the ostium tuba. The oviduct, also known as the Fallopian tube,
continues into the horn below. The system is supported by an
ovarian ligament and a broad and round ligament of the uterus. It
will be seen that in the female there is a communication from the
peritoneal space to the outside by way of the ostium tubae, uterus,
and vagina(see Fig. 9.2).
Larger vessels of the body cavity
Watch closely for nerves, and do not destroy them. Carefully
remove the pericardium surrounding the heart to observe its superficial characters. Note the large communicating vessels at the
base of the heart. In the cranial mediastinal area, and somewhat
to the right of the mid-line, is the superior vena cava. This vessel
is formed by the union of the two innominate veins. The superior
vena cava may be followed to the heart which it enters at the small
ear-like right auricle. The inferior vena cava comes up to the right
auricle from below, where it may be traced throu'gh the right thoracic area from the position where it penetrates the diaphragm.
The small right phrenic nerve to the diaphragm will be seen in close
approximation with the latter vein and should be separated from it.
By pulling the lungs sharply to the right and viewing the left
dorsal body wall, the thoracic aorta will be observed. It should be
distinguished from the esophagus, which appears as a flattened
A SURVEY OF INTERNAL ANATOMY
127
tube. Trace the aorta around its arch, which lies dorsad to the
vena cava. If the arteries are not injected with the red injection
mass, they may be distinguished from veins by their thicker walls
and empty appearance. Along the aorta a small beaded-like vessel
containing a clear amber fluid is usually observable, but is sometimes rather deeply imbedded. This is the thoracic lymph duct,
which should be carefully traced craniad. It enters the large external jugular vein just craniad to the first rib.
The aortic arch gives rise to the innominate artery, which lies in
the anterior mediastinal space. Near the origin of the innominate
and further down is also given off the left subclavian, which continues to the left arm. The innominate gives rise to the paired
common carotids, which follow along the trachea, one on either
side, and also to the right subclavian. Each subclavian artery
leaves the thorax just craniad to the first rib and continues through
the body wall as the axillary artery.
Between the left and right auricular appendages of the heart, the
right ventricle forms a tapering extension, the conus arteriosus,
which is the origin of the pulmonary artery leading to the lungs.
By pulling the lung somewhat away from the left auricular appendage, the short pulmonary veins are seen, but they are mostly imbedded in the lung tissue. Most of the pulmonary arteries are also
similarly imbedded in the lungs. The aorta below the diaphragm
is known as the abdominal aorta and lies parallel with the vena cava.
At about the upper level of the kidneys, the aorta comes to lie
dorsad to the inferior vena cava.
Innervation of the viscera (see Figs. 10.10 and 10.11)
A preliminary examination of the sympathetic division of the
autonomic nervous system should be made in connection with the
general survey of the arteries that serve as landmarks to the system.
It is necessary to clear fascia from the larger vessels of the body
cavity in connection with dissection of the nerves if the parts are
to be spared from injury or destruction in later dissection. The
sympathetic cord is easily found closely applied along the carotid
. artery on either side of the trachea. Here the sympathetic cord
is indistinguishably bound with the vagus nerve as the vagosympathetic trunk.
Although the sympathetic system is made up of paired parts, it
is not strictly symmetrical. For convenience in locating the parts
to be observed in the preliminary survey, the left side may be followed. First locate the vagosympathetic nerve trunk, which
128
FUNCTIONAL ANATOMY OF THE MAMMAL
passes close along the trachea beside the common carotid artery.
The sympathetic association with the vagus really begins just posterior to the tympanic bulla; but, for the present study, begin the
observations about halfway down the trachea.
The left vagosympathetic should be carefully traced caudad.
Just in front of the thoracic cavity a small branch passes to the left
and dorsally as the sympathetic cord, while the vagus portion of
the trunk proceeds directly toward the heart and lungs to which it
sends branches. The vagus continues to the abdominal viscera,
thus passing through the diaphragm.
The sympathetic portion of the vagosympathetic trunk, with
which we are now concerned, usually forms a rather inconspicuous
enlargement just in front of the large left subclavian artery in front
of the first rib. From this enlargement, a twig passes on either side
of the large subclavian artery; these twigs unite in a more conspicuous
enlargement just within the thorax between the bases of the first
and second ribs. This is the inferior cervical ganglion, whereas the
enlargement immediately above the subclavian is the middle cervical. Delica te branches extend from the ganglia; the larger of these
branches should be traced to the heart where it forms a network, or
plexus. The ganglia represent accumulations of nerve cell bodies,
and the thread-like extensions from the ganglia are bundles of the
long processes or axons. In the thorax, the sympathetic trunk
continues caudad from the inferior cervical ganglion and lies just
beneath the pleura along the aorta.
In some classes, detailed dissection on the autonomic division of •
the nervous system may not be done. However, if time permits a
thorough treatment of this important mechanism, most of the dissection should be done before other systems are studied in detail.
The description for the dissection is given in the chapter on the
nervous system (see pages 202 to 205).
SUGGESTED PROBLEMS
1. In recording respiration and direct blood pressure with physiological apparatus, a respiratory tube (cannula) is usually inserted into the trachea and another
cannula is placed in the carotid artery to connect with a mercury manometer.'
Work out a method whereby the trachea might be opened (tracheotomy performed)
most easily. Describe the operation in terms of anatomical position and structures involved.
2. In a study of the effect of electrical stimulation of the vagosympathetic nerve
on a cat under anesthesia, work out a suitable method to follow in reaching the
nerve, Which muscles would be involved in blunt dissection' in reaching the nerve,
and what landmarks could be followed?
A SURVEY OF INTERNAL ANATOMY
129
3. Suppose you wished to study the effect of tying off (ligating) the bile duct:
describe how it could best be reached, and name the parts involved in the operation.
4. Describe the location of the incision necessary to reach the cecum at its closest
point to the body wall. Review the character of the wall musculature at that
point, and demonstrate how the wall could be penetrated without cutting transversely through muscle fibers.
.
5. Since the kidneys and adrenal glands are retroperitoneal, and may be removed
dorsally, work out the position of an incision whereby they might be reached to
best advantage.
6. Name, in order, the epithelial tissues that would be penetrated by a bullet
passing through the skin between the fifth and sixth rib and lodging in the musculature of the heart.
7. Make a semidiagrammatic drawing to show the relative positions of the structures that pass through the diaphragm.
Chapter VI
THE ALIMENTARY SYSTEM
HE alimentary canal is a highly specialized tube the lining of 'which is
T
directly continuous with the surface of the body. Skin gradually
merges with the mucous lining of the canal at the mouth and anus. When
considering the elongated alimentary canal and its derivatives as enclosed
within the relatively short body wall, the fundamental "tube within a
tube" plan of organization is considerably obscured. This plan in a simplified form is best seen in embryonic stages. The principal function of the
canal is to prepare the elements needed by the body from food materials,
which progressively move along, and to allow for their selective absorption
into the blood stream. Materials that have been rejected by the blood
have really never entered into the body composition but have merely
passed through the canal. These are eliminated as part of the feces.
Digestion refers to the preparation of food so that it may be utilized by
the body cells. Absorption concerns the transfer of the prepared food from
the canal into the blood stream. Assimilation is the process whereby food
passes from the circulation through the cell membranes and intercellular
spaces into the body cells where it is to be used. Although each living cell
of the body must be supplied by circulation and assimilation, digestion is
the primary physiological process necessary for most food utilization. The
alimentary canal is structurally adapted to effect this fundamental process
by its physical make-up and by the formation of chemical agents, the
digestive enzymes, which change the molecular character of the food substances.
In a strict sense, food may be defined as any substance required or capable of being used by the body cells for the production of energy or for the
construction or reconstruction of cells and which aids in maintaining
intercellular activities. All substances that pass through the canal without being absorbed by the blood, together with excess digestive juices, are
known as the wastes of digestion. Certain ones, such as cellulose, however, should not be considered strictly as wastes since they facilitate the
alimentation process. Faulty elimination of the wastes of digestion,
which accumulate in the large intestine, may result in the formation of
toxic substances through the action of fermentative and putrefactive
organisms. The entire alimentary channel acts as a linear series of communicating organs to effect proper digestion, absorption, and elimination.
130
THE ALIMENTARY SYSTEM
131
THE ALIMENTARY (::;ANAL
. The lining of the alimentary canal is mucC>US membrane, or the mucosa. l
This lining in a modified form is carried into the innermost branches of the
secretory areas of the pancreas and liver, which are formed embryonically
as outpushings from the primitive canal. 1'he positions of the outpocketings of the liver and pancreas are marked by' their constricted ducts, which
continue to communicate with the principa} channel and empty the glandular secretions into it. Next to the lining; of the canal is a connectivetissue layer, the submucosa, which binds the muscularis (a layer of muscle)
to the mucosa. Outside the muscular area is the reflected peritoneum, or
serous membrane. Thus, the serosa formr the outer coat of the canal.
These four layers, mucosa, submucosa, muscularis, and serosa, are typically
found in the canal from the lower part of th~ esophagus to the rectum but
with many variations in relative importance ana with special modificatiom
of the lining. The mucosa, or inner layer I1djacent to the food material,
forms various small and numerous glands that are characteristically different in the various regions of the channel. Other modifications of the
lining occur which serve to increase the sur-face area for absorption or tc
accommodate the changes in tension created by the food passage. ThE
muscularis is of the smooth involuntary type of muscle.
The salivary glands are not derived embryonically from the endoderm
that forms the lining of the canal, liver, arJ. d pancreas, but they are alsc
glands of digestion. These glands are all of a compound character; i.e.,
they possess numerous branches and commtmicate with collecting tubuleE
to a common duct. Ducts of all digestive glands may be regarded aE
tributaries of the canal proper.
The more tubular structures concerned with the digestion and alimentation of food are as follows: (1) mouth (bucoal and oral cavities), pharynxl
esophagus, stomach, small intestine, large intestine (colon), rectum, and
anus. The mechanical preparation of food by means of the teeth and its
partial liquefaction by means of saliva, of course, precedes swallowing or
deglutition.
The mouth region and pharynx have been sufficiently described
with respect to the sagittal section of the head (see pages 111 to
115). The following description begins with the esophagus.
Esophagus
The esophagus extends from the pharynx to the more dilated
(cardiac) end of the stomach. It is a sttaight , undifferentiated tube
1 Soon after death, the lining of the alimentary canal begins to become digested by
the action of its own en~ymes. If the true character of the lining is to be observed, the
canal should be promptly removed, washed out, a~cl filled with a fixative.
132
. FUNCTIONAL ANATOMY Of THE MAMMAL
lying immediately dorsad and somewha,t to the left of the trachea.
In the thorax it lies in the mediastinal space (between the mediastinal pleurae). Only a short part of the esophagus extends into the
abdomen, since the stomach is directly beneath and closely adjacent
to the diaphragm. A loose layer of connective tissue, the tunica
adventitia, unites the esophagus with the surrounding parts. At
its lower end where it traverses the diaphragm, somewhat to the
left of the mid-line, it is expanded slightly to meet the cranial, or
cardiac, portion of the stomach. The opening of the esophagus to
the stomach is at this expansion and is lcnown as the cardiac orifice.
This orifice is said to be surrounded by 11 specialized arrangement of
elastic connective-tissue fibers with which the muscularis here forms
a cardiac valve. However, this is not all actively controlled sphincter as are other valves along the canal.
Functionally, the esophagus serves to convey food rapidly to the stOIpach.
The four layers typical of the canal, in general, are present except for an
incomplete serosa. At the upper pharyugeal end, striated voluntary
muscle is present in the muscular layer which only gradually gives way
to the smooth involuntary type usual to tlle canal. The muscular coats
perform a series of contractions that propel the food'along. These contractions occur at regular intervals, and the phenomenon is known as peristalsis. In ruminants (cud-chewing mammals) a reverse peristalsis is normal
from the first and second divisions of the stomach .(rumen and reticulum) .
Later the hastily swallowed food material is returned to the mouth 'where
it is chewed at the animals' leisure. The food then passes to another
division of the stomach and continues along the canal. Peristaltic action
is typical all along the alimentary canal.
The mucous layer of the esophagus in many mammals bears numerous
glands, chiefly of the mucous type. However, these are not present in the
cat and are also said to be absent in the horse and all rodents. In these
animals, the lining of the esophagus is kept moist and lubricated by the
mucus and saliva from the mouth. In maJ11mals feeding on dry or coarse
vegetable materials the lining of the esophagus becomes considerably
hardened, or cornified. When empty, the esophagus in the neck region
does not retain its cylindrical form as does the trachea but becomes dorsoventrally flattened. The lining assumes a folded appearance due to the
greater bulk of the distensible submucosa.
Stomach
Unlike the esophagus, which is concerned with rapid transportation, the stomach is constructed as 11 storage receptacle, which
permits small quantities of partly digested food to pass through at
controlled intervals. The stomach receives the food at the ex-
THE ALIMENTARY SYSTEM
133
panded cardiac end and expels it into the intestine at the pyloric
valve, a sphincter marked by a constriction between the stomach
and intestine. To the left of the cardiac orifice is a prominent
bulge, the fundus, which may protrude upward. The greater part
of the stomach as observed in a dead animal lies somewhat to the
left of the mid-line. The caudal part is tapering and folds partly
back upon the wider portion. This recurving part is the pyloris.
In the living body the stomach possesses considerable muscle tone,
and its shape is somewhat different as determined by X ray. Its
shape is also sensitive to changes-in blood flow. When the circulation stops entirely, a partial collapse of the stomach occurs to result
in the curved bag-like structure with a relatively large cavity.
The outer rim of the stomach is known as the greater curvature,
while the lesser curvature is the concavity formed above. The
pyloric region in some mammals is partly separated from the cardiac
region by a deep constriction. These regions are histologically different owing to the variations in the distribution of glands. In
addition to the circular and longitudinal muscle fibers common to
the tract, oblique bands of muscle tissue are present in the stomach,
and it is capable of a more complex peristaltic action than the other
regions of the canal. These actions aid in the digestion of food by
keeping it more or less agitated and mixed.
'When the stomach is empty, the lining collapses into folds, or
rugae. With the aid of a hand lens the openings of the numerous
gastric pits may be seen. These pits in microscopic sections appear
as invaginations (inpushings) of the mucosa. The character of the
glands and their distribution vary in the cardiac, fundus, and pyloric
regIOns.
Although the stomach of ruminants consists of a series of four divisions,
only the last of the series, the abomasum, possesses gastric glands. The
others are more esophageal in the character of their linings. Gastric juice
contains hydrochloric acid and the digestive enzymes pepsin and rennin.
These serve to further the process of digestion, which is finally completed
in the small intestine. Pepsin and rennin are prepared commercially from
the lining of animals' stomachs obtained from meat packers. Rennin is a
milk coagulent; pepsin helps in protein digestion.
The pyloric valve is formed by a concentration of the circular muscle
fibers that abruptly thin out in the first division of the intestine. Concentration of muscularis forms a true sphincter, which in this case is reflexly
affected by the acic) concentration within the stomach. Together with
other factors, an increase in the acidity causes the sphincter to relax,
134
FUNCTIONAL ANATOMY OF THE MAMMAL
which allows the passage of food into the duodenum. As the term pyloris
indicates, the valve here is the gatekeeper of the stomach.
Small intestine
Although no marked surface differentiation occurs along the
small intestine, it is described as comprising three regions: duodenum, jejunum, and ileum. It should be traced caudad from the
pyloric valve. Even by means of histological sections no sharp
line of demarcation is found between the divisions, which gradually
merge with each other. The div;sion is based chiefly on the histologic character of the lining and the occurrence and distribution
of the associated intestinal glands. The lining throughout has a
velvety appearance due to the finger-like projections known as
villi. These numerous projections serve to add considerable surface
area to the regions where the digested food is absorbed into the
capillaries, which are at most only a few cells removed from the
digested food.
At the bases of the villi, extended pits occur which are lined with the mucosa covering the villi. These are the intestinal glands, or crypts of LieberkUhn seen in histologic sections. Even when the intestine is distended, the
pits and villi retain their form to a considerable degree. The villi are said to
project and retract individually. The rate of absorption appears to be
directly proportionate to the rate of movement of the villi and number of
them involved at any particular time. In the duodenum, an additional
type of gland occurs known as duodenal, or Brunner's, glands. Instead of
resembling a simple pit, these are branched and possess numerous mucous
cells.
The common bile duct (ductus choledochus) and the chief duct
of the pancreas pour the secretions of the liver and pancreas into
the duodenum just caudad to the pyloric sphincter. This position
is marked internally by a small papilla. The submucosa and mucosa
are interrupted here, while in their stead is the common outlet for
the two ducts at an expansion, the ampulla of Vater. The posterior
limit of the duodenum is poorly defined. The term was originally
used to designate the first "twelve finger widths" of the intestine in
the human.
The jejunum is so named because it is often found empty in a
dead body. Roughly, it extends as the middle third of the intestine and together with the duodenum serves as the
, chief absorptiye
region for food leaving the tube to be taken into the circulation...
Here the action of the additional secretions received, bile, pan-:' - .
THE ALIMENTARY SYSTEM
135
creatic juice, and the intestinal juices_, have completed their work
so that by the time food reaches the ileum most absorption has
taken place. The ileum is the continuation of the intestine which
terminates at the large intestine by means of the ileocecal valve.
This valve allows the wastes to pass from the small to the large
intestine.
Gastroepiploico-+~-H-__"'.
Superior mesenreric
-t-"'I--+W.
vein
FIG. 6.1.-Upper abdominal viscera and hepatic portal vein.
The cecum is the blind pouch extending at right angles to the
channel of the ileum. In most rodents a relatively large and long
vermiform process is present as an extension of the cecum, and this
process together with the cecum may occupy as much space as the
entire small intestine. The appendix of man is a relatively small
vestigial remnant M such an extension; no appendix is present in
the cat.
136
FUNCTIONAL ANATOMY OF THE MAMMAL
The numerous vessels supported by the dorsal mesentery should
be noted'. It is evident that the region of the duodenum and ileum
is highly vascular, i.e., contains numerous blood capillaries. All
the blood draining from the area is collected into the hepatic portal
vein, which carries the absorbed sugars and broken-down proteins
(amino acids) to the liver. The fats have been transformed by
digestion to glycerin and fatty acids, which make them soluble in
water and otherwise absorbable.
These fat products are taken into
Ftrffy a:Cic/s}<ForfsI
Glycenn
l
small lymphatic vessels, which
are particularly abundant in the
walls of the small intestine and
which forIll channels traversing
the supporting mesentery. A
minute central lymph vessel lies
within each villus. Because of
the milky appearance of the larger
lymph channels after a heavy
meal of fat, the lymphatics here
become known as lacteals. The
lac teals are not seen in preserved
FIG. 6.2.-Diagra m of a villus to show specimens. These unite to form
ho w t he absorption of foods occurs. The
lymph ' vessels are in solid black, blood ves- the main portion of the left
sels, stippled. (From Wolcott, "Animal
thoracic duct. A large mass of
Biology." )
lymphatic tissue will be found in
the mesentery which is known as Aselli's pancreas because of an
early erroneous identification that considered it as pancreatic tissue.
Another conspicuous lymph node characteristically lies near the
junction of the large and small intestine. By spreading and stretching the mesentery at 'this point and holding it before a light, small
oval opaque-appearing ~pots will be seen. These are end organs
of sensory nerves and are known as Pacini's corpuscles. This
region is evidently very sensitive since an anim),! under deep
anesthesia responds reflexly ·to sharp pulls on the viscera here.
Large intestine
The cecum, mentioned in connection with the ileum, is really a
part of the large intestine with its terminal portion bent rather
sharply back toward the ileum. Like the cecum of man it lies on
the right side in the cat rather low in the abdo)llen but sOlllewhat
nearer to the mid-line than that of the human.
THE ALIMENTARY SYSTEM
137
The large intestine of the cat does not exhibit the ascending,
transverse, and descending portions to a marked degree since it is
relatively shorter than in man. At about half of the length of the
descending colon it bears to the mid-line, a region in the human
known as the sigmoid flexure. The extreme caudal straight portion, known as the rectum, opens to the outside at the anus where
the anal sphincter is formed by a thickened area of the circular
musculature of the canal. Except in the monotreme mammals the
anus is separated from the urogenital openings by a partition, the
perineum, a mammalian character.
Functionally, the large intestine serves as a concentrating and storage
area for the so-called "was~es" of digestion. The concentrated diet of the
carnivores may be responsible for its relative shortness in these forms and
for the absence of the appendix, which ,,,hen functional is associated with
a rather coarse diet. Little if any absorption of food takes place from the
large intestine. The four typical layers are present, but there are no villi.
These discontinue shortly before the ileocecal valve is reached in the small
intestine. The mucosa contains the crypts of Lieberktihn and small patches
of glandular tissue, Peyer's patches, which are also found in the small
intestine. The entire intestine of the cat is completely invested in peritoneum which forms the serous coat. The alimentary canal of the cat is a
little over 4 feet and in man approximately 20 feet long. This length provides opportunity for the complete process of digestion to occur. It also
allows for the essential absorption of required materials and the temporary
storage of wastes.
GLANDULAR DERIVATIVES OF THE CANAL
The liver
Although the liver performs several diverse functions, it is mOit closely
associated, anatomically, with the alimentary canal. But the function of
the liver in producing bile for the digestive process is of minor importance
",-hen compared with its duties in carbohydrate storage and release, in the
fornation of urea, and as a regulator of protein and sugar concentration
of the blood. The liver possesses certain phagocytic cells that are dest~uC'­
tive to harmful substances, produces heparin, an anticoagulant, and in
early embryonic stages forms red blood cells. In the liver of fish, the carbohydrates are stored chiefly as fats, rather than as animal starch (glycogen).
The liver makes its appearance early in the embryonic differentiation of
the gut as a hepatic diverticulum. This outpushing occurs just caudad to
the developing stomach and becomes complicated as a many-lobed gland.
These lobes in the cat are difficult to homologize exactly with those of man.
138
FUNCTIONAL ANATOMY OF THE MAMMAL
To the right of the broad falciform ligament, which suspends the
liver from the diaphragm, lies the cystic lobe. This lobe bears the
gall bladder, or storage receptable for the bile. The lobe is somewhat variable but tends to be divided where the gall bladder is
applied. Dorsad to the cystic lobe and somewhat to the right are
two rather distinct but also variable lobes that may appear as a"
single right lateral lobe deeply divided. Its caudal lobe (Fig. 6.1)
extends to the ventral margin of the right kidney. The left lateral
lobe extends posteriorly to approximate the left kidney. In the
cleft between these lobes lies the pyloris and the first few centimeters of the duodenum, which bends sharply back. Viewed further anteriorly, in the concavity, the lobes are separated by the
portal fissure, along which pass the bile duct, the hepatic portal
vein, and the hepatic artery. This is at the right limits of the lesser
omentum. A deep transverse fissure crosses over here so that the
neck of the gall bladder lies near the middle of the cross. Directly
to the left of the falciform ligament is the left central lobe, which
lies between the left lateral lobe and the ligament under the diaphragm. To the left of the portal fissure and obscured by a fold of
the lesser omentum lies a small, rather sharply pointed caudate
lobe, sometimes called the spigelian lobe. The apex of the latter
lobe is directed somewhat to the left and dorsad to the pyloric
valve. On its dorsal surface the liver is partly supported by a round
ligament that continues along the portal fissure. Much of this ligament represents the remnant of the umbilical vein from the fetal
stage where mother and young were connected.
To expose the gall bladder and the hepatic ducts they must be
carefully dissected from the liver tissue. The hepatic ducts carry
bile from the various lobes of the liver to the lower constriction and
extension of the gall bladder, the cystic duct. The common bile
duct, which opens into the duodenum, is the continuation of the
cystic duct below the entrance of the hepatic ducts. These ducts
are best demonstrated on a fresh specimen, where the greenish-colored bile may be forced along the ducts by the fingers. The hepatic
ducts should be cleared so that the essential connections may be
made out. By a special control, bile either passes directly from the
hepatic ducts and down the common bile duct or may be taken up
the cystic duct to be stored in the gall bladder for later use. Bile
is strongly alkalin~, saponifies fats, and serves to help neutralize
the acid condition of the food just entering the daodenum from the
stomach. Its pigments (colors) are mostly wastes from processes
THE AbIMENT ARY SYSTEM
f
139
not directly concerned with bile formation. Some mammals never
possess a gall bladder; it is sometimes removed surgically in man.
The surface of the liver is visceral peritoneum, similar in character to the serosa of the intestine. The deeper portion is pulpy, and
small areas (lobules) may be seen making a compact pattern. The
liver is extremely vascular since it not only is supplied by a hepatic
artery, but also possesses the rich capillary network of the hepatic
portal vein. Injuries to the liver are particularly dangerous because
of the difficulties in stopping hemorrhage.
The pancreas
Along the duodenum the pancreas appears rather thin, and in
places the tissue even appears scattered. It consists of two divisions, one of which is bent back upon the other to form a V-shaped
Oesophagus··cardiac porfion of sfomach ----
opening of -_.
commonducf
pancre.a f/c duel
small infesfine
6.3.-The relationship of the pancreas and its duct, and the ducts from the liver and
gall bladder to the small in testine. (From RO(Jers, H ubbel, Byers, "Man and the Biolo(Jical
World.")
FIG.
structure. The duodenal portion is closely applied to the duodenum,
whereas the gastrosplenic portion lies obscured by the great omentum, a posterior fold of which encloses it. Like the liver it is a
derivative of the embryonic canal.
The pancreas serves two important functions. The more obvious
is production of pancreatic juice, an exocrine function concerned
with the digestion of all three food classes: proteins, carbohydrates,
140
FUNCTIONAL ANATOMY OP THE MAMMAL
and fats. A more obscure function is that of an endocrine organ.
Small areas, islands of Langerhans, are demonstrated histologically.
The cells of these areas produce insulin, which is taken up directly
by the blood capillaries passing through the pancreatic tissue.
Diabetes mellitus is due to a deficiency in the endocrine function
of the pancreas.
The chief duct of the pancreas (Wirsung's duct), although imbedded within the pancreatic tissue, is easily demonstrated by
gross dissection. It empties with the bile duct into the duodenum
and may be found near the bile duct at the point where it penetrates the duodenal portion of the pancreas. By carefully picking
away the substance of the pancreas around this area, the main
trunk of the pancreatic duct is exposed. It receives numerous
branches throughout the substance of the pancreas. The smaller
duct (Santorini's duct) is difficult to locate. By injecting a color
mass into Wirsu~g's duct away from the intestine, the branches of
the two ducts are found to anastomose (form unions) but open independently into the duodenum.
Chapter VII
THE RESPIRATORY SYSTEM
HE respiratory system, in a broad sense, is a ventilating mechanism
T and
is designed to provide for an efficient interchange of oxygen and
carbon dioxide between the air and the vascular system. In this functional
interpretation, the system consists not only of the structures acting as
passageways for air, but also includes the thoracic musculature operating
the ribs, the ribs acting as levers, and the lining membranes into which
the lungs are reflected. This constitutes a bellows system by means of
which the lungs are inflated and deflated in effecting ventilation of their
deepest recesses. Thus, the respiratory system is the breathing mechanism.
Respiration proper is defined as a physiological process involving an
exchange of gases. The exchange of oxygen and carbon dioxide between
the pulmonary circulation and respiratory air in the lungs is called external
respiration. The blood gives up carbon dioxide to the air in the lungs and
renews its oxygen supply. The oxygen is delivered to the tissues through
the capillaries, which take up the carbon dioxide to be expelled. The interchange of gases between the tissues and the blood stream is called internal
respiration.
As was seen in the general survey of thoracic structures, the mediastinum
effectively separates the two lungs. This arrangement permits one lung
to function if the other becomes collapsed as a result of puncture of the
thoracic wall. If the wall is punctured, air rushes in to increase the intrathoracic pressure to that of the atmosphere. In treating pulmonary tuberculosis, air is intentionally injected through the thoracic wall into the
potential space between it and the lung, thus causing the lung to collapse.
This operation is called a pneumothorax. The inactivated lung usually
recovers more promptly during this rest period than it would if left in a
functional state. The introduced air is slowly resorbed by the body, and
the collapsed lung gradually reassumes its original character and function.
During fetal life, the lungs are inactive and partly collapsed since atmospheric air cannot enter them. But after the first breath is taken, the pleura
covering the lungs lies in direct contact with that forming the lining of the
thoracic wall. A small amount of serous fluid intervenes between the two
pleurae. Since air can enter the thorax only through the trachea, this
relative position is n1aintained by the pleurae regardless of thoracic changes
in respiration. The intrathoracic suction is produced by increasing the
141
142
FUNCTIONAL ANATOMY OF THE MAMMAL
__ pulmonary
arlery
·T'ilh'''.t-'r~- lefl auricle
~~:,e1":f!r"1,",4 _ pulmonary
veins
inferior vena cava
FIG. 7.1.-The h eart and lungs from a ventral view. (Rogers, Hubbel, Byers, "Man and
the Biological World." Modified from T urtox Classroom Charts, courtesy of General Biological
Supply Home.)
Visceral pleura
Potential
pleural space
l-t-t---=.;..,-----l--+_ Me d ia sti n a 1
pleura
't-----+-I--Pericardial
space
Diaphrogm
Diaphragmatic pleura
FIG. 7.2.-Diagram of the lungs and pleura to show their relationships.
THE RESPIRATORY SYSTEM
143
size of the thorax. This can be easily demonstrated by holding the breath
while performing inspiratory movements.
In severe inflammation of the pleura, the serous fluid increases and may
be drained out to prevent it exerting too great a pressure on the heart and
lungs. Such pressure interferes with the venous return of blood and causes
difficult respiration.
In children the lungs are clear pink in color, but in older individuals
they become dark and mottled owing to the imbedding of dust p.articles
in the tissues. Adhesions of the pleura covering the lung and that lining
the thorax frequently occur in man, usually near the apex. The lungs of
coal miners particularly are greatly discolored and frequently are almost.
black. These extreme colorations are seldom seen in animals, but in those
used for food, the lungs are examined by meat inspectors to determine
possible tubercular conditions.
COURSE OF RESPIRATORY
AIR
The respiratory system proper consists only of the structures
that serve as channels over which air passes. Thus, it includes the
nasal passageways, pharynx, larynx, trachea, and lungs into which
the trachea enters, forming a tree-like series of bronchial branches
that terminate in clusters of small air sacs, the alveoli. The alveoli
are designed to provide an extensive surface of moist membrane
through which the exehange of' gases takes place. Water is also
constantly being expelled by the lungs in the form of vapor. In
man, the maximum respiratory capacity may be more than ten
times the minimum requirement at rest, and more than 100 square
yards of thin membrane may constitute the combined area of
alveoli.
The sagittal section of the head should be reviewed with special
reference to the respiratory passages. Beginning with the paired
nasal passageways, .the respiratory system is lined with mucous
membrane, which in life is kept further moistened by water vapor.
Air enters the nasopharynx by way of the paired internal nares
from which it passes through the nasopharynx to reach the opening
of the larynx called the glottis. The larynx is the specialized upper
end of the trachea, or windpipe, and is commonly referred to as the
voice box.
Laryngeal structures
The conspicuous feature of the larynx is the presence of specialized
supporting cartilages in its walls. The most prominent of these is
seen on the ventral surface, the thyroid cartilage, or Adam's apple.
The circular cartilage adjacent to the first tracheal ring is known as
144
FUNCTIONAL ANATOMY OF THE MAMMAL
the cricoid cartilage. It is thickest on its dorsal surface and, unlike
the other cartilages of the larynx, forms a complete ring.
The epiglottis is the cartilaginous flap of the larynx guarding the
opening, or glottis. Paired cartilages, the arytenoids, form the
lateral walls of the opening and protfude slightly forward. The
thyroid cartilage is incomplete dorsally, and the arytenoids lying
beneath it are paired with internal ligamentous attachments of
which the vocal cords are most important. The larynx_articulates
with the hyoid apparatus and possesses ligamentous and muscular
connections with it.
In the cat, between the arytenoid cartilages and the base of the
epiglottis are two folds of membrane extending on either side. The
thicker outer ridges are the false vocal cords~ while the inner ~ more
membranous folds are the true vocal cords. These are difficult to
demonstrate with the larynx split and stretched out. The folds are
modified by changes in the shape of the glottis so that the edges are
vibrated in varying intensity by the action of respiratory air.
Articulated sounds in man are made only during expiration.
Thus, the function of voice and respiration are closely allied. It is
said that "purring" in the cat is produced by the streaming of air
over the false vocal cords.
Trachea, bronchi, bronchioles, alveoli
Cartilaginous rings of the trachea are incomplete on their dorsal
surface where the trachea is adjacent to the esophagus. This is
apparently an accommodation to the distensible character of the
esophagus in swallowing. The rings are sufficiently elastic to bring
the two ends together and sufficiently rigid to hold the air tube
constantly open. At the lungs the trachea bifurcates to form the
primary bronchi. Each bronchus further branches into the lobes as
a secondary bronchi. Gross dissection does not show further details
of the tubes very clearly. However, these in turn form numerous
smaller branches usually referred to as "bronchioles." At the extremities of these smaller tubes, which do not possess the cartilaginous rings carried into the bronchi, are the alveoli, which occur
as clusters of small air sacs.
The internal arrangement of mucouS epithelium lining the respiratory passages ensures the area against desiccation, or drying
out. The lining of the trachea and bronchi is further provided with
cilia, or hair-like processes of protoplasm, which ,drive foreign substances and accumulated mucus to the pharynx. The mucous
material is carried upward by the strong and rapid upbeats of these
THE RESPIRATORY SYSTEM
145
abundant cilia which alternate with relatively slow and weak downbeats.
General features of the lungs
It has been seen that the greater part of lung substance is composed of air tubes and minute alveoli; these are held together by
connective tissue. The outer covering is, of course, the reflected or
visceral pleura, which closely adheres to the underlying connective
Body cells
G
8
Right heart
·
·
·
Pulmonary
circuit
·
02.
Lymph
spaces
Left heart
FIG. 7.3.-The functional relationship between circulation and respiration-external and
internal.
tissue. By inserting a tube in the trachea and blowing into it, the
lung may be inflated and the somewhat elastic and resilient character' of the tissues demonstrated.
A cast of the tubes and sacs may be made by forcing melted paraffin
down the trachea with the lungs held in water heated almost to the melting
point of the wax. The surrounding tissue can then be destroyed by the
use of an acid which leaves the wax as a tree-like affair with the dilated
terminal ending of the twigs.
The left lung of the cat possesses three deeply divided lobes,
which are known as the cephalic, intermediate, and caudal, from
forward back. The right lung, in addition to these three, possesses
the small cardiac, or azygos, lobe which projects posteriorly into
the curtain of pleura posterior and dorsal to the heart. This curtain of pleura on its dorsal surface is involved with the formation
of the inferior vena cava.
It is advantageous to supplement a study of embalmed material
with fresh lungs, which may be secured by special request from a
slaughterhouse. Those of the pig or sheep are most satisfactory
and should be obt~ined with the heart and the complete trachea,
including the laryngeal cartilages. The fresh material may be
146
FUNCTIONAL ANATOMY OF THE MAMMAL
compared with conditions of the cat and with the human, as described in human anatomy texts. Usually a study of the lungs is
combined with a study of the anatomy of the heart.
W1th hesh mateY1a\ one 1'lhou.\d l)aYt1~u.hY\:y note the ~h~;ra{)tey 01
the pleura, the mucosa lining of the trachea, and the extellt of
bronchioles which are supported by cartilaginous rings. The character of the cartilage (hyaline) should also be observed by making
thin sections through the rings.
From the functional standpoint, the close relationship of the
pulmonary arteries and veins with respect to the lung tissue should
be observed in considerable detail.
Chapter VIII
THE VASCULAR SYSTEM
T
HE vascular system involves two distinct, but intimately related, types
of systems and circulating fluids: (1) blood and (2) lymph. By gross
examination, the blood circulatory system is more readily observed and
understood. Structures of this system, seen in gross dissection, are the
heart, arteries, and veins. Only by a microscopic examination can the
essential capillary network between the arteries and veins be structurally
demonstrated.
The circulating fluid of this system is the blood, consisting of formed
elements, the corpuscles, and the liquid plasma. Blood corpuscles normally do not leave their restricting channels. The system is therefore
called a closed system. However, lymph is formed as a filtrate of plasma
which passes through the capillary walls into intercellular spaces and thus
makes up the immediate environment of the cells.
The more obscure lymph circulation originates in the intercellular spaces
and is essentially a drainage system for materials that are not absorbed
back into the capillaries. Areas are drained by a convergence of these
spaces into lymph channels and definite vessels. Unlike the blood system,
lymph vessels possess no pumping mechanism and depend on other pressures to keep drainage active. Lymph vessels are essentially constructed
as a series of closely connected valves that form a specialized tube. Lymph
drains toward the large veins near the upper portion of the thorax and
passes through filter beds in lymph nodes before being emptied into the
veins and mixing with the blood. Only the larger lymph vessels and lymph
nodes may be seen in gross dissection. Since lymph is formed by filtration
of the liquid part of the blood, excess filtration due to high capillary pressure or defective capillary walls produces swollen areas (edemas) by
accumulating in the intercellular spaces.
When blood is withdrawn from circulation, certain elements entangle
the corpuscles and form a clot which separates from a clear fluid, the serum.
In normal circulation the liquid portion of the blood or plasma is similar
to serum, except that the serum is deprived of essential coagulating elements that have been utilized in clot formation. Serous fluids of the body
cavities and the cerebrospinal fluid resemble lymph in many respects.
The circulatory sy,stem serves to maintain the balance of change in the
environment of all body cells. It is the transport and distributing system
absorbing essential elements as oxygen, food, hormones, and water from
147
148
FUNCTIONAL ANATOMY OF THE MAMMAL
specialized parts of the body for distribution to all living cells. It carries
away for disposal the wastes of cellular activity and acts as a distributor of
heat. Reactions of blood produce protection against invading organisms,
and because of its multiple duties the circulatory system profoundly affects
the well-being of the organism as a whole.
THE HEART
It has been previously noted that the heart lies in a tough membranous sac, the pericardium, the inner surface of which is a. serous
Fro . S.1.-The positio n of heart in the thoracic skeJeton. (From Eycleschymer and Jones,
"Ha,ndbook of Clinical Anatomy." )
membrane that faces the outer surface, or epicardium, of the heart.
The pericardia! space between these facing membranes contains a
serous pericardia! fluid in life. In removing the pericardium it will
be observed that it attaches only around the base.Jof the heart where
the large vessels emerge. The cavities of the heart are lined with
THE VASCULAR SYSTEM
14!:l
endocardium, which is the same type of tissue lining all the blood
vessels as endothelium. Between the epicardium and endocardium
is the bulk of heart tissue, the myocardium or heart musculature.
_lntjugul", V"m
'-.om.ceTot1d 3.1't •
An:hof aorta
;,t:.::;....•- _.=:.__....;:;. .•...5perrnatic art
endyein
~--~ ...-
. . Com. ilia c
•.,.4-4-+~· - · ·veinand art.
~vpoqa~tr~C" _:-:- 4_. __
', ·",mand el't. i
FIG. 8.2.-Heart and principal blood vessels in the human female. Thy., thyroid gland;
Umb., position of ~mbilfcu:;; Ul., uterus. (By Tom Jones, courtesy of S . H. Camp and Company.)
Note that the apex of the he .1rt is directed to the left and lies
close to the thoracic wall but that the heart does not occupy much,
if any, more space to the left side than to the right.
Since all mammalian heart'; are essentially similar, a general
description of one' type servef our purposes here. As previously
suggested, in connection with the respiratory system, a fresh heart
150
FUNCTIONAL ANATOMY OF THE MAMMAL
with the lungs intact is far superior to preserved material in this
study. The cat heart is not only small but in prepared specimens
is usually stained and distorted by the colored injection mass. The
superficial characters of the heart and large vessels have been described in relation to a survey of internal anatomy (see page 123
and Figs. 5.3 and 8.3).
Dissection of the heart
General topography. (Heart of a pig or sheep.) The heart of
the pig or sheep is approximately the size of the human heart.
Proper orientation can be determined from the cat dissection.
Place the heart with the ventral or sternal surface up and with the
apex pointed away from you.
Right and left sides of the heart can be determined in two ways:
(1) the apex i§ entirely a part of the left ventricle, and the right and
left divisions are indicated superficially by a diagonal furrow followed
by coronary vessels; (2) by palpating the ventricular musculature,
the left side appears firm and muscular, whereas the right ventricle
feels soft and flabby. The auricles appear as ear-like projections
at the base of the heart. The cavity within each auricle is more
properly referred to as an atrium, or reception chamber for incoming
blood.
The right auricle. Make a long incision through the auricle in
line with the superior vena cava. Lift the edges of the flaps and
observe the wide mouths of the great veins (superior and inferior
vena cava) as they enter the atrium. With scissors, carry the incision downward toward the ventricle and determine the relationships
between the two cavities. Note the irregular bands of muscle lining
the interior of the auricular wall, the pectinate muscles. Find the
coronary sinus, which receives venous blood directly from the heart
musculature and which enters the auricle as a wide cavity. Locate
the thinnest portion of the interauricular septum (wall between the
two auricles). This area is the fossa ovalis, an oval depression
marking the position in fetal circulation at which blood was carried
directly to the left heart and thus by-passed the pulmonary circuit.
The coronary sinus lies just above the fossa (see Fig. 8.4).
The right ventricle. Carry the incision from the auricle in a
straight line through the lateral wall of the ventricle. Note the
three rounded flaps of membranous tissue suspended into the ventricle and held in place by tendinous cords. These flaps are the
tricuspid valve. Study in detail its position, structural character,
and attachments. If necessary, wash out both cavities. Note that
•
THE VASCULAR SYSTEM
•
151
pointed columns of ventricular muscle (papillary muscles) are continuous with the wall of the ventricle and with the strong fibrous
cords (cordae tendhteae) that extend to the edges of the cusps or
segments of the valve. What function would you ascribe to these
structures with reference to the valve'? Observe the heavy muscu-
~ ~~l;~laVi~r. <;~~,/:Jv
Inn~ or't l' ~ - -~--
//
R~nn or(\inut.~_ ve:'n- - ~-- - -----1< coronary a l"t
'.
FIG. 8 .3.-Superficial aspect of the heart and la rge v essels in man. N ot e particul arly the
coronary vessels of t he heart which supply a nd drain its muscula ture. (By Tom JO'lU)S ,
courtesy of S . H . Camp and Compan/l.)
lar ridges within the ventricle, the columnae carneae. Find the
exit of blood from the right ventricle, considering the tricuspid
valve as closed between auricle and ventricle. Carry an incision
upward through the wall of this exit (pulmonary artery), and note
that the mouth of the artery is surrounded by three membranous
pockets (the pulmf}nary semilunar valve ). Determine how this
structure prevents a backflow of blood into the ventricle when the
ventricle relaxes.
152
FUNCTIONAL ANATOMY OF THE MAMMAL
The left auricle. Open tills auricle in a similar manner as on the
right side. Before cutting on down through the ventricle, push the
finger from the auricle into the ventricle and distend the auriculoventricular opening. Determine the number of veins draining into
the auricle from the lungs. These openings are the mouths of
pulmonary veins. In what ways does the left auricular differ from
or
vena cava
Wall of
Corona rLf - __.
SInus
. Tricuspid valve
Wallof __
r. ventricle
Chordae .-"
tendineae
",..
F IG.
S.4.-The cavities of the right auricle and ventr icle of t he ox.
Trainor.)
(Drawn ~)!I John F.
the right? Note that the partition separating the auricles is membranous rather than muscular.
The left ventricle. Make an incision to expose the cavity. Study
the details of the mitral, or bicuspid (two-parted), valve between
tills auricle and ventricle. Explore the septum between the two
ventricles as to its tillckness and kind of tissue. With your finger,
find the outlet of the ventricle into the aorta. In what respect is
tills outlet similar to the pulmonary artery? Open the aorta to
expose its semilunar valve. Find the openings of the two coronary
arteries just above the valve, i .e., within the pockets. Trace these
to the walls of the heart. ' Observe the .tough ligamentous connection between the pulmonary artery and aorta which usually is
THE VASCULAR SYSTEM
co~ered with
153
conspicuous pad of fat. This is the ligamenttnn
arteriosus, a remnant of a vessel connecting the pulmonary artery
8.
I,..,
FIG. 8.5.-Semilunar valves and coronary artery fro m the aorta of the ox.
Trainor.)
Sup.
Vena cava
R.Coronary__-+~~~~u~~
artery
AZY.9° S
vein
(Drawn by J ohn F.
Left subclovia n
artery
Pulmonary
artery
..._ _.,I..,.........~....Pu 1m ona ry
veins
AorTa
FIG. 8.6.-Semidiagrammatic view of the mammalian heart to show course of cir culation.
and aorta embryonically, the ductus arteriosus. If the vessel remains persistently ~pen (patent), a mixing of oxygenated and unoxygenated bl(}od occurs.
154
FUNCTIONAL ANATOMY OF THE MAMMAL
Observe from your dissection where the following type of heart
leakage would occur: (1) auricular-ventricular, (2) semilunar,
(3) interauricular, and (4) interarterial.
Only the more essential features of the heart have been described
here. For more detailed information, students should consult
special texts on human anatomy.
In studying the dissected heart, emphasis should be placed on the structural arrangement of the parts and their functional continuity. The
mammalian heart is essentially a double pump equipped with specially
designed valves. It serves as the propelling force for two circuits of blood
that do not mix in the heart. The circuit from the heart to the lungs and
back is (1) the pulmonary circuit, and the circuit from the heart to all the
body tissues and back is (2) the systemic circuit. These circuits act concurrently and interdependently since no more blood can be sent through
the pulmonary circuit than is delivered to it by the systemic.
Left carotid artery
Vaqa-sympathetic trunk
L. Sympathetic trun R
Middle cervical 'l0n'jlion
/~Lefta~r:r~CYiOn
. ·"··""'-.Position of 1st rib
'Inferior cervical
"\.
'lon'lJion
Cardiac
accelerator
nerves
\{j~;rhorOCiC ~e'lmenta I
-'S
.
"
iI[J:_~
Va'lus inhib,t,on
of heart
-\
qanq"o
' t run""
'ympat h
etlc
Arch of aorta
"
'
V0'lus nerye +0 abdomlnol
or9 ons
FIG. 8.7.-Parts of the autonomic division of the nervous system concerned with innervation
of the heart. (Only the left nerve trunks are shown.) See also Fig. lD.lD.
SYSTEMIC VEINS
Because of their more ventral position, it is more convenient to describe
the systemic veins before considering the arteries in much detail. However,
both types of vessels may well be exposed together, since each-'Vein generally has a corresponding artery. Veins are defined as vessels that carry
blood toward the heart. They, therefore, make up a drainage system and
should be traced from that standpoint. In the study of the heart it should
have been observed that veins possess relatively thin walls compared with
the arteries. Another important feature of veins is that there are numerous
I
155
THE VASCULAR SYSTEM
•
valves
distributed internally to prevent flow away from the heart. These
act throughout the larger tubes particularly to ensure a prompt venous
return of blood to the heart. Veins are typically formed from converging
Ext-ern 0 I jU'lular
Inf. Vena cava
.,,.,,
,
I
.......'
I
Adreno-Iumbar:
lew. S.S.-Principal syst:mic veins of the cat (somewhat diagrammatic).
the thoracic lymph duct. See also Fig. 6.1.
Note position of
156
FUNCTIONAL ANATOMY UF THE MAMMAL
TABLE OF PRINCIPAL SYSTEMIC VEINS (CAT)
Termination
Name of vein
Superior vena cava ..... Right atrium
Azygos (unpaired), ~, , "
Innominate
(b~chio-
cephalic)
External jugular,
/
,I, , . . .
I~ternal jup.tlar........
\
\
Subclavian (distal to
first rib, known as
axillary)
Inferior vena cava ..... ,
Principal drainage, position,
and tributaries
Drains head, neck, forelimbs, anterior abdominal region. Is formed
by union of innominates; lies on
right side of vertebral column;
receives small mediastinal vein
usually
Superior vena cava
Seen as a large vessel on dorsal body
wall to the right of the mid-line;
drains the W8))S DJ cnl15i'8nd anterior abdomen by means of intercostals; drains bronchi and esophagus by vessels named from
drainage
Superior vena 'cava (op_ Paired; eaen formed by union of
posite firstint.ereostl1J
subclavian and exterior jugular
space)
and passes caudad; drains head
and neck by jugulars and forelimbs by the subclavians; receives
vertebral and costocervical which
may unite and enter as one from
upper rib and cervical regions
Innominate
Formed by union of facial veins,
transverse jugular anastomoses;
crosses sternomastoid obliquely;
receives cervical vessels, interior
jugular, cephalic vein along front
of forelimb
Exterior jugular (oPPC)- Passes caudad at side of trachea
site first rib)
vagus, common carotid artery,
and sympathetic cord; drains
brain, back of head, and dorsum
of neck; frequently obscure on one
or both sides in embalmed material
lrmomin.afu·
Deeper drainage of forelimb; receives vertebral usually; axillary
portion chief branches are radial,
ulnar, and median from subcutaneous networks, occupying
position as named
Right atrium
Begins at junction of iliacs of hind
limbs dorsad to aortic forks;
spirals to right to lie ventrad to
aorta; passes craniad at right of
middorsal line through liver and
diaphra~j drains diaphragm,
THE VASCULAR SYSTEM
TABLE OF PRINCIPAL SYSTEMIC VEINS
Name of vein
Termination
Common iliac (variable Inferior venl!> cava
as to position of union)
External iliac .......... Common iliac
Hepatic portal. ....... , Liver
..
, '
Hepatic .............. , Inferior vena cava
157
(CAT)-(Continued)
Principal drainage, position,
and tributaries
liver, genital and urinary organs,
parities of abdominal region.
Vessel tends to be variable at kidneys; renals also variable
Posterior extremity by large external iliac; smaller hypogastric
branch joins medially, draining
lower pelvic organs, etc.
Appendage by superficial femoral
and deep femoral with saphena
tributaries
Formed near pyloric end of stomach.
by union of superior mesenteric
and gastrosplenic; receives other
veins named from structures
drained, alimentary tract, spleen,
and pancreas; reaches liver in
company with common bile duct
and hepatic artery through omental foramen
In substance of liver anteriorly;
drains liver
capillaries, and being far removed from the rhythmjc propelling beat of
the heart they do not exhibit a pulse.
In the mammals, there is but one system of veins that does not return
blood directly back to the heart, the hepatic portal system. A portal vein
differs from an ordinary vein in that it is formed from a set of converging
capillaries, but the main stream before entering the heart is distributed by
diverging vessels through an organ. The hepatic portal vein collecting
the blood from the stomach, intestine, etc., redistributes the blood through
a second set of capillaries in the liver. These capillaries then reunite to
form the hepatic vein, which drains into the inferior vena cava.
Systemic veins are properly identified only by determining the
particular areas that they drain. They should be traced from the
areas from which they are seen to emerge as small tributaries and
should be regarded as branches of a principal stream draining eventually into the right atrium. The principal veins are tabulated and
figured as they usb.ally occur; but variations are common and rare
anomalies may also be encountered.
158
FUNCTIONAL ANATOMY OF THE MAMMAL
The hepatic portal circuit
This system deserves special comment also from a functional standpoint.
The hepatic portal capillaries of the intestinal region absorb the amino
acids and sugars that have been digested. The concentration of these
substances in the blood of the hepatic portal vein at any particular time
depends upon the amount of these substances present in the intestine.
Since these factors are variable, it is a function of this system to stabilize
the amount of sugars and amino acids that are permitted to go into the
general circulation. To effect this, the blood draining the viscera is distributed first to the liver where excesses are stored or transformed into
inactive compounds until occasion demands their release and utilization.
Therefore blood leaving the liver through the hepatic veins carries a rather
constant percentage of sugar and amino acids which is increased or decreased as conditions in general bodily activity require.
To demonstrate the presence of hepatic veins it is necessary to
dissect away the substance of the liver near the diaphragm and
close to the inferior vena cava, which passes through it. If the
veins have been injected through a systemic branch only, no injection mass enters the hepatic portal. Capillaries of the hepatic
veins block the injection mass from reaching the hepatic portal
vein. Therefore, unless specially injected, the hepatic portal system
contains only variable amounts of partly dried blood.
SYSTEMIC ARTERIES
An artery is defined as any tube that carries blood away from the
heart. As previously indicated, the systemic arteries carry blood
from the left ventricle to all parts of the body. They are to be
.. regarded as supplying areas and should be followed and identified
from that standpoint. The return is by way of the venae cavae.
This makes up the systemic circuit. The pulmonary circuit begins
at the right ventricle; the blood is carried to the lungs by the pulmonary artery and returned to the left auricle by pulmonary veins.
Observe in this connection that the pulmonary artery carries unoxygenated blood and that the pulmonary vein carries oxygenated
blood. Under usual injection methods the color mass follows the
type of blood carried; i.e., the pulmonary veins are injected red
and the pulmonary arteries, blue.
SiI).ce the heart pumps rhythmically, the propelling force is reflected in
the arteries as a pulse. Smaller arteries (arterioles) reflect the pulse in a
diminished form so that when the branching of the tubes reaches its ulti-
THE VASCULAR SYSTEM
159
mate goal, the capillaries, a pulse may not be discernible.
bed here is several hundred times wider than at the aorta.
The stream
L.common carotid
Thyrocervica I
Vertebra I
1. Brach ia I
Intercostals
Pancreaticoduodenal
~'L/"""'l---Superior
mesenteric
Adrenolumbar
'--::-Adrenal qland
Midd Ie colic
. Su p. hemorrhoida I
Internal iliac
femoral
•
FIG. 8.9.-Principal systemic arteries of the cat (somewhat diagra mmatic) .
and 10.11 for course of nerves in relation to arteries.
See Figs. 10.10
)
160
FUNCTIONAL ANATOMY OF THE MAMMAL
The area where capillaries may be seen to converge from a capillary
network, rather than to further diverge, is arbitrarily taken as distinguishing arterial capillaries from venous capillaries, although the capillary bed
is continuous. The smaller veins formed by converging capillaries are
considered as venules in the same sense that s!llaller arteries are arterioles.
Capillaries do not come to an end, but act as the connecting tubes between
arteries and veins.
Principal arteries are tabulated according to their usual occurrence. Here, again, anomalous conditions may be present. These
are discussed later.
TABLE OF SYSTEMIC ARTERIES (CAT)
Name of artery
Usual origin
Chief distribution and position
Aorta ............... " Left ventricle
Ascending arch, descending to all
parts of the body
Coronary(s) ..... .
Aortic sinus (at .semi- To heart walls, right and left. (The
lunar valve)
shortest circuit from the heart
and back to the heart by way of
the coronary sinus.)
Innominate .......... '.. Arch of aorta
To common carotids; right subclavian
Mediastinal. . . . . . . . . .. Innominate
To mediastinum
Common carotids (right Innominate.
Pass craniad on either side of the
and left)
trachea to supply structures in
laryngeal and head regions and
brain by internal division
Right subclavian. . . . . .. Innominate
Passes to right arm, gives rise to
vertebral, internal mammary,
costoccrvical, and thyroid axis
before leaving thorax as axillary
Left subclavian. . . . . . .. Arch of aorta
Passes to left arm (same as right
except as to origin)
Vertebral. ............ Left subclavian
Passes dorsad to vertebral part,
(branches similar
enters vertebro-arterial canal,
right and left)
supplies some muscles of neck,
spinal cord, brain to (circle of
Willis) anastomoses
Internal~amm8,ry (ster- Subclavian
Arises opposite vertebral on the
naIl
sternal surface; numerous divisions to intercostals, sternum,
mediastinum, pericardium, diaphragm, rectus abdominis
Costocervical axis (supe- Subclavian
To dorsal intercostals and cervical
rior intercostal)
region (IIPd,y leave subclavian as
c()Stat and cervical branches)
\
/
THE VASCULAR SYSTEM
TABLE OF SYSTEMIC ARTERIEiS
N arne of artery
Usual origin
Thyroid axis ........... Subclavian
161
(CAT)-(Continued)
Chief distribution and position
Arises just anterior and on the same
side as vertebral, arches forward
and upward over scapula, sends
branch to thyroid gland
Axillary ............... Continuation of the sul:>- First portion of subclavian outside
clavian
thoracic cavity; passes over first
rib into the limb where it continues as the brachial
Sternal portions of pectoral musculaAnterior thoracic ..... " Axillary
ture
Lateral portions of pectorals and
Long thoracic. . . . . . . .. Axillary
to the latissimus dorsi
Numerous branches: tere~ major,
Circumflex (subscapula- Axillary forks
latissimus dorsi; deltoids and
ris)
triceps; supra- and infraspinatus;
subscapular; and trapezius
Brachial. . . . . . . . . . . . .. Continuation of axillary Numerous branches to arm; at elbow
forms two principal branches,
at forks
radial, and ulnar which follow
radius and ulna, respectively, to
muscles of antibrachium and hand
Proximal end of biceps brachii
Anterior circumflex .... ' Brachial
Arise in paired series, to deep
Intercostal(s) .......... Descending aorta
muscles of back, intercostals, and
meninges
Bronchial(s) (two) ..... Descending aorta (at Accompany bronchi to lungs
fourth
intercostll.t'
space)
To esophagus (anastomose)
Esophageal(s) .....
Descending aorta
Pass between lumbar vertebra to
Lumbar (first two).
Descending aorta
body wall (as intercostal)
Arises just below fliaphragro, chief
Celiac axis. . . . . . . . . . .. Abdominal aorta
branches are hepatic, left gastric,
and splenic
Just caudad to celiac; to plJ,ncreas,
Superior mesenteric ..... Abdominal aorta
small intestine, ascending and
transverse colon
Inferior phrenic. . . . . . .. Celiac or adrenolumb~r To caudal surfitee of diaphragm
Passes laterad to abdominal wall
Adrenolumbru-. . . . . . . .. Abdominal aorta
To kidneys; often to adrenals
Renal(s). . . . . . . . . . . . .. Abdominal aorta
In male caudad through inguinal
Genital(s). . . . . . . . . . . .. Abdominal aorta
canal; in female caudad to ovaries
and uterus. May be first observed at gonad and traced back
Divides into left colica to descending
Inferior mesenteric. . . .. Abdominal aorta
colon and into superior hemorrhoidal to descending colon and
rectum (anastomose)
162
FUNCTIONAL ANATOMY OF THE MAMMAL
TABLE OF SYSTEMIC ARTERIES
Usual origin
Name of artery
(CAT).-(Continued)
Chief distribution and position
Iliolumbar. . . . . . . . . . . .. Abdominal aorta
Lower dorsal abdominal muscles
and sartorius muscle
External iliac .......... Abdominal aorta (forks) Passes beneath inguinal ligament
to thigh; gives off profunda femora to muscle on medial side of
thigh, genitalia; inferior epigastric to ventral abdominal wall;
continues as the femoral
Internal iliac .....•.... Abdominal aorta (forks) To pelvic wall and viscera by following branches: (1) umbilical
passing ventrad to bladder; (2)
superior gluteal to gluteal muscles,
rectus femoris, etc.; (3) middle
hemorrhoidal which passes ventrocaudad to rectum, urethra, prostate, and penis in male; in female
a branch forms uterine artery to
uterus, bladder, and vagina. Continues as (4) inferior gluteal.
Note the caudal artery which is
a continuation of the aorta to
supply thc tail
ANOMALIES OF THE VASCULAR SYSTEM
Variations are particularly numerous in the vascular system. Some of
these are extreme in character and occur only in exceptionally rare cases.
The extreme and rare variations are considered as anomalies and may
\
FIG. S.lO.-An anomalous condition of origin of carotid and subclavian arteries in the cat.
(Seen but once by the author in approximately 1,000 student dissections.)
occur only in one case out of several thousand. Obviously, most of the
anomalies of the vascular system, when found in he:1'lthy adults, cause no
disturbance, and many of us possess anomalies of which we are entirely
unaware.
,
\,
\
THE VASCULAR SYSTEM
163
vein
Transverse vessel
failed to develop
Retained as an
anomalous
.~ vein
FIG. 8.11.-Failure of an embryonic transverse vessel to develop resulted in this cat having
no true superior vena cava. The innominates empty separately into the right auricle. (Soon
by the author but on~e in approximately 1,000 disseotions.)
Two ri'lht renal veins
(one anomalous)
Ri9ht geni~al
vein
~
(1
Anomalous
terminus
of left
C\e~itcd 'Jein
FIG, S.12.-A fairlY common anomalous condition in possessing'a "renal collar."
of left genital vein over the renal vein appears less common.
The loop
1M
FUNCTIONAL ANATOMY OF THE MAMMAL
Although most variations in the blood vessels of adults cause no obvious
a
difficulty to the individual, some result in considerable disability.
condition known as a patent ductus arteriosus, the embryonic communication between the aorta and pulmonary artery fails to close, which permits
unoxygenated blood to mix with the oxygenated. Some individuals so
affected have difficulty performing the slightest muscular tasks, their lips
appear blue, and ordinarily they do not live beyond twenty years. A delicate operation has been performed in some instances in which the ductus is
tied off (ligated), which prevents the mixing of blood and allows for the
assumption of normal physical activities. A review of the structure of the
thorax and the mediastinal area will indicate the precision with which the
operation must be made.
Many anomalies occur during embryonic development wnich critically
interfere with normal activities following birth in babies, and these usually
cause death within a few hours or days after birtl}.. In general, any extreme anomaly in any vital system results either in prenatal death and
. abortion or in stillbirths.
When we follow through the complex changes that occur in the blood
system during embryonic development, it is surprising that so many individuals are so similar in the final pattern rather than that anomalies do
occur. Mammals pass through an embryonic history (ontogeny) in many
ways parallel to the racial history or phylogeny of the Vertebrata. Since
the changes that occur in reaching the adult mammalian condition are
comparatively numerous and complex, mammals possess many more
variations and anomalies than are common to lower vertebrates, such as
fish, amphibians, or reptiles.
In
\
CIRCULATION BEFORE BIRTH
/
During embryonic and fetal life, the young of mammals secure food and
oxygen and give off waste products through a highly vascular structure,
the placenta. This is an extra-embryonic organ that develops on the lining
of the mother's uterus and is designed to permit a large capillary area of
the mother's vascular system to be in close proximity with a similar capillary bed that belongs to the fetus. Thus the fetus possesses a special circuit that passes through the placenta. Outside the body of the young the
vessels of this circuit consist of a single umbilical vein and a pair of umbilical arteries, which make up the essential part of the umbilical cord.
The arrangement of the capillaries within the placenta allows for exchange of dissolved substances between the blood of the mother and young,
but does not permit formed bodies such as corpuscles and bacteria to pass
from one circulation to the other. Each new individual not only forms its
own vascular mechanism, but also develops its own blood from nutrients
absorbed from the mother's blood. In this way tlle fetus is protected
against infection and does not necessarily form the type of blood that the
mother posseSReR.
.
THE VASCULAR SYST..I!;M
165
•Respiratory
and digestive functions are inactive during intra-uterine
life; circulation before birth conforms to these conditions. The umbilical
vein conveys relatively well-oxygenated blood to the fetus which enters
the body at the abdomen (the navel represents the proximal end of the
umbilical cord). The vein widens in the liver as a ductus venosus and
becomes associated with the portal circulation. From the ductus the
blood passes directly into the inferior vena cava but a short distance from
the right auricle. Here the blood apparently mixes with the more venous
blood entering the auricle from above (superior vena cava). Pulmonary
LV.C.
FIG. 8.13.-Diagram of the fetal heart and large ve~sels. showing the ductus arteriosus and
foramen ovalis.
circulation is mostly by-passed by a short circuit through the open foramen
ovale in the inter auricular wall. Therefore, the blood is directed immediately into systemic circulation. Further mixing of blood occurs through
the ductus arteriosus, a fetal aortic arch that connects the left pulmonary
artery with the aorta. We must assume that the oxygen requirement of
the fetus is relatively low in view of the mingling of oxygenated and unoxygenated blood. However, circulation in the fetus appears to be relatively
rapid; this is associated with the high rate of heart beat.
Closure of the foramen ovale is effected by means of curtain-like foldH
that are developed before birth, and their fusion results in the formation
of the fossa ovale of the heart. The ductus arteriosus degenerates into a
fibrous ligamentum arteriosus. These openings apparently are functionally closed, or nearly so, soon after birth. Respiratory activity is
thought to be largely responsible for the functional opening up of the
pulmonary circuit and partly responsible for the functional closure of the
foramen ovale and dlJctus arteriosus. Complete structural closure of the
openings seems to occur relatively late and occasionally not at all, as in
the anomalous cases previously discussed.
166
FUNCTIONAL ANATOMY OF THE MAMMAL
It is of interest to observe that pulsation of the umbilical arteries normally ceases soon after the lungs are filled on the first inspiration. In
domestic animals, generally, the umbilical cord is usually broken at birth
by the activity of the young when thrust into its new environment. In
man, the cord is tied and severed an inch or so from the body after the
pulse in the cord is no longer felt. The cord and placenta are delivered as
parts of the afterbirth.
LYMPH VESSELS AN}) NODES
The largest lymph vessel is the left thoracic duct, which empties
near the juncture of the left internal and external jugular veins.
A main portion of the duct may be traced as draining from the intestjnal region, but. it. is best. seen where it Jies near the aorta in thE
thorax. The vessel here is identified by its distinct beaded appearance. Often a small lymph vessel draining from above may be seen
to enter the duct near the point where it empties into the venous
system. In experimental work on lymph flow, the left thoracic
duct is located by following the course of the left external jugular
vem.
A right thoracic duct, which drains only the right appendage and
right side of the head, is present but is usually collapsed and difficult
or impossible to demonstrate in the usual preserved material.
Since the flow of lymph is chiefly dependent upon pressure
changes, massage is frequently employed to increase the flow of
lymph and waste products from the intercellular areas into the
larger lymph channels. After VigorOllS and continuous exercise,
massage is beneficial in aiding the elimination of fatigue products
to prevent soreness and stiffness. Open a lymph vessel, and observe
the character of the valves.
The more prominent lymph nodes are (1) Aselli's pancreas, a
large mass of lymphoidal tissue lying ill the mesentery of the small
intestine; (2) armpit, or axillary, nodeE;; (3) and groin, or inguinal,
nodes. Scattered but rather prominent nodes are common in the
neck region just below the ears, the cel"Vical nodes.
A remarkable histologic resemblance OCCmrs between lymph nodes and
such structures as the tonsils, spleen, and thymus glands. Lymph picks
up intercellular materials that are not resorbed back into the blood capillaries. Infectious bacteria are also carried in the lymphatics and in reaching lymph nodes may produce an infection in them. Swollen lymph nodes
indicate an infection in areas distad to them. For eXll:Plple, swollen cervical
lymph nodes may occur as a result of infection of the teeth.
THE VASCULAR SYSTEM
167
the digested fats are absorbed from the intestine into lymph channels
(lacteals) that converge to form the main trunk of the thoracic duct.
These may be traced by feeding an animal such as a cat with butter and a
fat stain, i.e., Sudan III. The cat must first be starved for some time,
and since fat is slow to be digested and absorbed, a period of 5 hours or
more must elapse before the red-stained fat traverses the lymph channels.
The animal is opened up at this time, and the lacteals and thoracic duct
usually show up to great advantage. Injection techniques are also employed to bring out those channels more clearly.
General discussion
In order to understand the functional character of the circulatory system, certain physical principles governing the flow of liquids should be
reviewed. In a functional analysis, all the tubular mechanisms of the
system, including the heart, exist only to serve the capillary beds. The
essential exchange of materials between the body cells and blood stream
occurs only in the capillary areas of the system. This circumstance is
strikingly demonstrated in the study of the heart. Despite the volume of
blood constantly being pumped by this organ, its musculature depends
entirely upon the coronary circulation for food and oxygen, and the coronary arteries are the first branches of the aorta. Occlusion, or blockage,
of the coronary circulation promptly results in death, and even partial
occlusion is an extremely serious condition. Coronary thrombosis and
embolism are related types of occlusion that cause many deaths. Thus,
the capillary areas of the circulatory system are the areas of great physiologic importance and are extremely sensitive to deficiencies.
Blood must be delivered to all the capillary beds under sufficient pressum to maintain a constant supply of blood to the tissues. This pressure
is also essential to their eventual drainage. Pressure and velocity of blood
are greatest in the large arteries emerging from the aorta. As the stream
bed widens out because of the branching of the vessels, the velocity and
pres~ure diminish to their lowest points in the capillary areas.
Pressure in the arteries is determined by several factors of a physical or
mechanical character; i.e., the principles may be demonstrated on physical
material. "The principal factors that determine the pressure in the
arteries are (1) the total amount of blood in circulation, (2) the rate and
amplitude of the heart beat, (3) the elastic character of the arterial wall,
and (4) the resistance of the lining of the vessel to the flow.
The blood is distributed to various parts of the body in varying amounts
according to the special needs of the parts. For example, after a heavy
meal the viscera become richly supplied by blood that has left other parts
of the body where it is not especially needed for the time being. This sort
of regulation is effectejl through the autonomic nervous system, principally
by constricting arterioles at certain areas and dilating those in areas need-
168
FUNCTIONAL ANATOMY OF THE MAMMAL
mg the blood. The action is known as vasoconstriction and vasodilation
and is produced by smooth muscle fibers in the walls of the vessels. A
general vasoconstriction causes a pronounced rise in blood pressure,
whereas the opposite effect occurs in general vasodilation.
In experimental animals, blood pressure is determined directly by inserting a small tube (cannula) into an artery such as the carotid. The cannula
is connected to a U tube of mercury with an intervening solution of citrate
between the blood and mercury column of one arm of the tube. The pressure exerted by the blood forces the mercury up into the other arm of the
tube, and the difference in the levels is recorded in millimeters.
In man, blood pressure is determined by indirect means and is conventionally taken at the brachial artery at the level of the heart. Circulation
is cut off temporarily by inflating a rubber bag around the arm which is
connected to a mercury column that indicates the pressure of the air in the
bag. In releasing the air from the bag, one can hear (with a stethoscope)
the blood rushing through the constricted vessel at the apex of the heart
beat. By observing the height of the mercury at the precise moment the
blood first breaks through its restrictions, one determines the systolic
pressure. The lowest ebb of the pulse is more difficult to determine accurately. This low ebb of the beat is the diastole. The difference between
systole and diastole is the pulse that is lost in the capillaries.
In tracing either the comparative anatomy or the embryonic development of animal forms, we deal largely with problems of how an organism
can increase in size and yet keep its living protoplasm in close contact
with a suitable environment. Embryonically, the systems to be precociously formed are those which bring to all cells the essentials of their
existence: nutrition, vascularity, and nervous coordination. These specializations ensure that the immediate environment of each cell is suitable to
the protoplasmic needs in maintaining life. Regardless of how far the
living protoplasm may be removed from the raw materials of its requirements, systems must develop to supply its immediate needs. There is no
other function of a system than that of serving the vital activity of protoplasm generally. This principle is well illustrated by the vascular system.
SUGGESTED PROBLEMS
To test your knowledge of the vascular system as a whole, trace the course of a
corpuscle from one specific organ to some other organ. What is the shortest course
a corpuscle could take in leaving the left ventricle and returning to the right auricle?
Why could not a drop of blood be traced in the same sense one traces the course
of a corpuscle?
Chapter IX
THE UROGENITAL SYSTEM
repr~duction a~e
~ri­
HE. organs of
unique in that their function is
T
manly concerned wIth the mamtenance of the race, rather than wIth
contributing to the essential maintenance of the individual. This means
that the reproductive organs could be removed from an individual surgically without producing more than secondary modifications in its particular
existence. Individuals are the conveyers of generative structures and
processes that reappear in the formation of new individuals from generation to generation as a continuous cyclic phenomena.
Individuallife begins with the fusion of a male and female germ cell.
But the germ cells that give rise to new individuals were originally living
parts of the parent's body, and thus we may trace the individual to a
living preindividual existence. The germ cells are formed in the gonads
(testes and ovaries). However, the primordial germ cells (those first seen
there in the development of the gonad) appear to arise elsewhere and
secondarily migrate to the early gonad. The chromosomal character of
the early germ cells determines whether the new individual is male or
female. It appears to be entirely a matter of chance as to which sex the
individual will be. In the same way, chance and probability determine
the particular hereditary characters that will be exhibited, and each new
individual is a unique being.
Sexual homologues between the male and female external genitalia
have been discussed in the first chapter. Many internal parts are also
regarded as homologous. Thus, the testis of the male is represented by
the ovary (in part). These are the primary sex organs and are responsible
for secondary and accessory sex differentiation. Secondary sex characters
such as distribution of the hair, muscular and skeletal conformation, and
the differences in the development of the larynx in the two sexes are referable to the endocrine function of gonads and the difference in the hormones produced by each type. Thus, castration (removing the testes)
of the male before puberty prevents the expression of maleness in both
structural and physiopsychic ways.
Castration is a common practice on domestic livestock not kept for
breeding purposes (cattle, sheep, hogs, horses). The operation on animals
raised for slaughter is>usually done while 'the individual is relatively young
so they will fatten more readily and produce finer quality meat. Castra169
170
FUNCTIONAL ANATOMY \)F THE MAMMAL
tion is usually delayed in horses until the stronger shoulder and muscular
development of the stallion has begun to take place.
Removal of the ovaries (oophorectomy) is performed most frequently
on house pets, dogs and cats, and is commonly known as "spaying." This
not only eliminates the possibility of the Itnimal having young, but terminates the occurrence of "heat periods" which are induced by ovarian
activity. In approximately 600 female cats obtained from an animal
refuge (in Philadelphia) only 3 had been Spayed, while in about 400 males,
at least 10 had been castrated. This does not give a true picture of actual
conditions, however, since most pet animltls never reach humane societies
as do the unwanted "strays."
REPJWJ)IJCTIVE SYSTEM
Male organs
This system has been partly desCl'ibed in the introduction to
internal anatomy (page 111) and SUIlerficial dissection (page 59).
The scrotal sac should be opened by a careful incision over each
testis, and the incision should be det~p enough to cut through a
tough membranous sheath beneath tlle skin, the tunica vaginalis.
The testis can now be delivered thrOUgh the incision.
Observe that the tunica vaginalis ehcloses the testis and is continuous with the spermatic cord, which passes craniad to the inguinal region. The spermatic cord t:Jonsists of the membranous
sheath enclosing the ductus deferell.S (sperm duct), spermatic
artery, vein, and nerve. The latter tW() parts are difficult to demonstrate in a preserved specimen.
The ductus deferens is readily iderltified by following the spermatic cord through the body wall whE~re the ductus is seen to loop
over the ureters (from the kidneys) and pass dorsad of the urethra,
which drains the bladder. In followirlg the ductus deferens t'o the
testis, it is seen to emerge from an etongated mass of convoluted
tube, the epididymus, lying on the sluface of the testis and connected to it. The sperm are formed in the microscopically small
seminiferous tubules of the testes and pass through collecting vasa
efferentia to reach the epididymis bef(\re entering the vas deferens.
The character of the tunica vagina1ts and spermatic cord is best
understood in following the migration of the testis from the abdominal cavity into the scrotal sac. Testes arise, embryonically, mediad
to the kidneys, and a little below this r~gion they receive their blood
supply and drainage (review genital arteries and veins). They then
descend, carrying with them the ductus deferens. Because of their
171
THE UROGENITAL SYSTEM
•
early position in relation to the ureters, the ductus deferens crosses
them in reaching the lower pelvic region.
Further descent of the testes pushes them into the peritoneal
lining of the abdominal cavity which envelops them as' an invagi-
"..::;.~'*-Medull('J
~~':";":"';'.:L....Pelvis
Epididymis
Ductus
deferens
~A''.JF+- r.fferen t
ductules
Sem'miferous
tubules
Section of Testis
(semi dio9rammatic)
Spermatic vessels
Spermatic cord
:E~ididymis
Testi s
Tunica va9inalis
"'<lll~~ Skin of scrotum
+-\',Hi!--
Glans penis
FIG. 9 .1.-Urogenital system of the male cat .
nating tunic. But the musculature of the wall is not carried along;
it separates to form the inguinal canal, which extends from the
internal inguinal nag (seen on the inside) and the external inguinal
ring on the outer surface of the body wall. By splitting the inguinal
172
FUNCTIONAL ANATOMY 'OF THE MAMMAL
canal and drawing the testes up to their developmental position
mediad to the kidney, these relationships will be better understood.
In case the testes fail to pass through the inguinal canal, the condition is known as cryptorchidism and results in sterility in man and
other mammals in which the testes normally leave the body cavity.
If the condition is corrected surgically, fertile sperm may be produced. In the scrotal sac, the two testes are separated by a partition, the mediastinum testes.
Observe that the spermatic cords are superficial and may be
reached surgically by a simple skin incision. Sterilization of the
male may be accomplished by a simple operation known as vasectomy. This consists of splitting the sheath of each spermatic cord,
removing a section of the ductus deferens between two ligatures
without disturbing the vascular and nervous connections to the
testis. The operation does not interfere with hormone activity.
The ductus deferens should now be followed to the urethra which
it enters at a glandular enlargement, the prostate gland. The
prostate nearly encircles the urethra and discharges prostatic fluid
into it through a duct common with the ductus defere'ns which conveys the sperm. The cat does not possess a seminal vesicle as is
present in man. In following the urethra (and course of sperm)
further cauctad, a pair of rounded Cowper's (bulbo-urethral) glands
are found rather deep and near the ischiopubic symphysis to which
the penis is attached. These also open into the urethra by means
of ducts.
The penis is retracted into a fold of skin between the testes on the
wall of the abdomen. The distal end bears an enlarged cone-shaped
glans around the base of which the skin is attached as a prepuce,
or foreskin. In the cat, the glans penis bears numerous horny
spines on its surface which may be observed easily with a hand lens.
A transverse section of the penis shows it to consist largely of three
distinct columns bound together with dense connective tissue.
Ventrally, a single column encloses the urethra as the corpus cavernosa urethra, while above are a pair of corpora cavernosa penis.
These possess blood cavities (caverns), and erection is due to the
blood becoming trapped in these vascular areas. The character of
the attachment of the penis to the symphysis and abdominal wall
causes it to become directed craniad during erection.
Obviously, the penis is primarily an organ of reproduction rather than a
urinary structure. The function of urination (micturition) could occur
effectively with the urethra opening in some other manner. Thus, the
173
THE UROGENITAL SYSTEM
penis is primarily designed to convey sperm to the vagina of the female,
where they may proceed directly to effect fertilization. The urethra
serves both genital and urinary functions only from the point at which the
ductus deferens enter.
The female system
The genital system of the female does not become so highly
specialized as the male. The gonads (ovaries ~ remain rather close
Oviduct
(uterine tube).
Ovary
Horn of uterus
Broad I i90 ment
Cervix of Uterus
FIG. 9.2.-Urogenital system of the female cat.
to their position of origin and lie somewhat below and mediad to
the kidneys on the dorsal body wall. Ettch ovary is partly invested
by peritoneum and partly hidden by a fringed funnel-like expansion
of the uterine tube,~the ostium tuba. The ovaries are elongate ovoid
bodies about 1 cm. long with most of their surface exposed to the
174
FUNCTIONAL ANATOMY OF THE MAMMAL
body cavity. The ostium tuba is the part of the oviduct that
receives the mature ovum that is cast from the surface of the ovary
at ovulation. The oviducts (Fallopian tubes or uterine tubes) pass
somewhat craniad in a convoluted manner and then descend to
become continuous with the larger comuae (horns) of the uterus,
which join below into a single corpus (body). This type of uterus
is known as bipartite. The body of the uterus is continuous with a
thinner walled vagina which terminates at vaginal vestibule. The
vestibule receives the urethra from the.bladder on its ventral aspect.
The ovaries are attached to the dorsal body wall by a .specialized
mesentery, the ovarian ligaments. These continue craniad and
caudad as broad uterine ligaments supporting the horns of the
uterus. An extension of each broad ligament extends laterocaudad
as the round ligament, which attaches in a position comparable with
the ir~.ternal inguinal ring of the male.
FIG. 9.3.-Section of ovary of the cat. 1 free and 1', attached border; 2, connective tissue
5, early germ cells: 6, 7, 8, and 9, developing follicles. An ovum is seen in 8 and 9; 10, corpus
luteum. (From Zoethout, "Text-book 0/ PhysioloOY," C. V. Mosby Company.)
The horns of the nonpregnant cat are very slender and in pregnancy become surprisingly distended. The number of young in a
pregnant uterus can be readily ascertained by the series of enlargements along the horns. Careful inspection of the ovaries of a pregnant cat ' shows them to possess conspicuous elevated bumps that
are located at the sites of the ovulations preceding the pregnancy.
These bump-like areas are corpora lutea of pregnancy and persist
in an endocrine function to maintain the pregnancy. If they are
destroyed early in the pregnancy, the young are aborted. Apparently, these conditions hold for mammals generally. A corpus
luteum of ovulation is formed for each egg shed by the ovary, but
these do not persist if no pregnancy ensues. In young females the
THE UROGENITAL SYSTEM
175
ovary appears smooth on its surface, but in older individuals the
ovary shows scars of previous ovulations (corpora albicantia) at the
positions where the eggs were. shed through rupture at the surface.
FIG. 9.4.-Pregnant uterus of cat (A) and membranes of fetal kitten (B).
"General Zoology.")
(From Storer,
The uterus is highly vascular. When a fertilized egg is implanted, its
lining (endometrium)' contributes' to the formation of a placenta through
'which the young obtains nourishment from the maternal capillaries. No
direct circulation between the mother and young occurs. The capillaries
of the placenta of the embryo come in close proximity to maternal capillaries, and exchange of materials takes place between them. In the human
and in other mammals, an ovum may become fertilized before entering the
Tube
Ovary
Round
ligament
Ovary
Fundus
Vagina
U retel
cavity
FIG. 9.5.-Uterus and as,;'ociated organs in the human.
Uterine
U terine
tube
Ovarian
artery
Uterine
a rtery
(From Pitzman, "Fundamentals of
Human Ar>atomy," C. V. Mosby Company.)
176
FUNCTIONAL ANATOMY OF THE MAMMAL
"
oviduct and implant itself outside the reproductive tract, along mesenteries
or intestine. These abdominal, or extra-uterine, pregnancies ordinarily
do not advance far since the blood supply is inadequate to maintain the
development of the embryo in the position in which implantation has
occurred.
Intra-uterine life
As is commonly known, the period of intra-uterine development varies
greatly among the mammals. In some species, a peculiar delay in the
implantation of the fertilized egg occurs; in others a different sort of delayed development is found, A table of gestation periods for some representative mammals is given below.
Ammal
Gestation
period
Opossum, , , , , , . . . . . . . . . . . . .. 13
Rat ........................ 21
Rabbit. . . . . . . . . . . . . . . . . . . . .. 30
Dog ........................ 63
Cat ......................... 63
Pig ....................... "
4
Sheep ............... , . . . . . . . 5
Monkey (Macacus rhesus)..... \)
Man .... , , . . . . . . . . . . . . . . . . . . 9
Cattle. , . , . . . . . . . . . . . . . . .
9
Horse, . . . . . . . . . . . . . . . . . . . . .. 11
Elephant. , , .... , . , , .... , .. " 20
days
days
days
days
days
months
months
months
months
months
months
months
Usual number
of young
7 to 12
6 to 7
4 to 6
5 to 7
4 to 7
6 to 15
2
1
1
1
1
1
NEPHRIC SYSTEM
The kidney of the mammal tends to be a compact bean-shaped
organ. However, in some forms (as in tb.e bear and in cattle) the
kidney exhibits external lobation and elongation which resemble
the more primitive condition. The ureters connect with the kidney
at its hilus near the connections of the renal artery and vein.
Ureters carry urine to the urinary bladder, which is drained through
the urethra to the outside. As has been observed in the study of
the genital system, the urine at some point along the tract follows
an outlet that also serves the reproductive system. In the female
the common outlet is the vestibule of the vagina, but in the male
the common outlet extends from the position ;of entrance of the
ductus deferens and its associated parts at this point. The urethra
,
THE UROGENITAL SYSTEM
177
of the male is, therefore, more specialized and extensive than in the
female.
Kidneys are formed on the dorsal body wall . of the developing
young and do not push ventrad sufficiently to become enveloped by
the peritoneum. The position in the body is said to be retroperitoneal, since they may be removed surgically without entering the
peritoneal cavity. The operation is a nephrectomy, so called from
the term "nephric system" commonly used to designate urinary
parts of the urogenital tract.
A fibrous sheath encloses the kidneys which makes rather weak
attachments to the body wall and peritoneum. A kidney may
become dislodged from these attachments to produce a condition
known as a "floating kidney. " Considerable variation occurs in
the size of kidneys in specimens of similar size. The right kidney
usually lies somewhat craniad to the left, and both are usually
somewhat hidden by fat deposits in a capsular mass.
renal vejn-/- - ·
main col/eding duels in
pelVIS of kidney
.!::_ •.
,-,'
FIG. .9.6.-A longitudinal section through the kidney of man. (Rogers . Hubbel. Byers
"Man and the Biological World." Redrawn/rom Maximow. "Textbook 0/ Histology. ")
Internal structure of the kidney
The functional unit of the kidney cannot be demonstrated without
using the microscope on special preparations. In a longitudinal
section, which splits the kidney into symmetrical halves, certain
178
FUNCTIONAL ANATOMY OF THE MAMMAL
"
internal fea tures may be observed by gross inspection. A superficial cortical area is distinguished from a more central medullary
area. The cortical portion has a somewhat stippled appearance,
whereas the medulla is characteristically made up of renal pyramids,
which in the cat appear to have fused into a single pyramid. In
man, the pyramids taper from a broad base at the cortex to rounded
apices, or papillae. The apices of the pyramids project into separate channels, or calyces, which c,onverge into a common cavity,
the pelvis of the kidney. The renal pelvis is continuous with the
opening of the ureter.
loop offht>
uriniferous fu/Ju/e·····
FIG, 9.7.-Diagrammatic figure of a renal corpuscle and uriniferou s t ubule. (Rogers ,
H ubbel, Byers, "111an and the Biological World ." R edrawn fro m Amberson and Smith, "Outline
of Physiology. ")
The cortex is reddish brown and contains numerous renal corpuscles (approximately a million in man). A renal corpuscle consists of a tuft of capillaries, a glomerulus, projected into an enclosing
renal capsule (Bowman's capsule) which continues as a renal tubule.
These parts make up the functional unit, or nephron, of the kidney.
Urine is formed as a filtrate of the blood through the capsule, but
its purely physic~l character is modified by activity of the cells of
the tubule in connection with the blood stream. Renal tubules
form convolu.tions in the cortical area and eventually open into
larger collecting tubules and excretory tubules that converge to the
pelvis and produce the striated and radiating appearance of the
medullary area.
)
THE UROGENITAL SYSTEM
179
I
Course of urine and structure of channels. The urine from the
pelvis of the kidney follows a channel lined with mucous membrane.
The ureters possess an outer fibrous coat and middle layer of smooth
muscle. The bladder has a serous layer on the outside, layers of
smooth muscle, and a submucosa of connective tissue joining the
mucous lining. At the neck of the bladder, the circular muscular
layers form a sphincter to control micturition (emptying the bladder). From the bladder the muscular coat continues into the
. urethra as its outer covering (except for a fascia-like sheath), and a
thin layer of spongy connective tissue lies between the muscularis
and mucous lining. The female urethra is relatively short and
undifferentiated.
In the male the urethra from the sphincter of the bladder to the
prostate gland is designated as the cystic urethra; from the prostate
gland to Cowper's gland, as the prostatic urethra; and the portion
enclosed in the penis, as the urethra penis.
Chapter X
THE NERVOUS SYSTEM
nervous mechanism is both structurally and functionally complex.
T HEramifies
to all parts of the body to serve as the dominating and coordi-
It
nating system of the organism as a whole. For convenience of study, the
system is considered as being divided into three parts: (1) central,
(2) peripheral, and (3) autonomic. However, these divisions are closely
interdependent, and they should never be regarded as separate units of
the system as a whole. Nerve tissue is 'described as the master tissue of
the body, but it too is dependent for its existence upon the other tissues
that it dominates.
Central division
The central nervous division consists of the brain and spinal cord. This
part of the system is protected by the skull and vertebral column and is
supplied with a special set of protective membranes, the meninges (cranial
and spinal). Further protection to the central nerve tissue is afforded by
a water bed of cerebrospinal fluid surrounding the brain and cord. These
carefully protected central parts communicate with the environment by
means of nerve fibers of the brain and spinal cord. The body is acquainted
with outside conditions especially through the sense organs: olfactory,
optic, and auditory, Other sensory end organs and nerves not only connect the central nervous system with external environmental conditions,
but also carry impulses from internal parts so that adjustments through
outgoing impulses can be made for conditions generally. Centers of the
central division act in reception, transmission, initiation, or termination
of impulses.
Peripheral division
This division consists of the cranial and spinal nerves and sensory
epithelium of the organs of special sense. Sensory elements make up the
receptor part of the peripheral division. Motor impulses leaving the central division pass through the effector fibers of the peripheral division to
muscles and glands.
The voluntary muscles are innervated by peripheral motor fibers that
pass directly to them, but involuntary muscular tissue ~cardiac and smooth)
and the various glands possess a double motor innervation and receive
their impulses through an autonomic mechanism.
180
181
THE NERVOUS SYSTEM
Telencepha Ion
(olfactory bu I bs
cerebra I
hem ispheres)
Latera I ventricles
(l st and 2nd)
Aqueduct of Monro
Diencephalon
(thalamus etc.)
Mesencepha I on
corpora q_uadriqemina etc.
Metencepho Ion
(cerebellum and
pons)
M yelencepho I on
(medu 110)
Myelen
(cord)
FIG. lO.l.-General plan of mammalian brain. The stippled central area represents the
caviti es (ventricles) of the brain; heavily drawn inside lines show the linear series of divi sion;
par ts in broken lines are covered dorsally by the s uperficial portions shown by t he outside
\i,,~. 1 \.\'> XII c!'3.""a\ mwve \)o~ition. \~ul>e!ncia\ connection) in relation to divisions or hr ain.
Sp inal nerve
Ventra \ bra n ch
Se9mentol9an'11 ion
Sympathetic
trunl<~!>l--",",
FIG. 10.2.-Cross-sectional plan of the nervous system. The structural connections of central, peripheral, and autonomic divisions shown ~emidjagrammatically.
182
FUNCTIONAL ANATOMY OF THE MAMMAL
Autonomic division
The autonomics include special nerve fibers and tracts of the cranial
and sacral nerves (peripheral division) that reach the involuntary organs
directly from the central nervous system as parasympathetics and, through
another special arrangement of nervous tissue, as sympathetics. Impulses from the sympathetics may originate in the central division but
pass through special centers outside the central division, the sympathetic
ganglia, before reaching the parts to be affected. Thus, the involuntary
organs possess two distinct sets of nerve fibers, one from either cranial or
sacral parasympathetics, and one from the postganglionic sympathetic
fibers. Control of the involuntary actions by the autonomics involves a
constant shift of balance between two antagonistic forces; where one set
of fibers act as an inhibitor of an action, the other accelerates; if one acts
to constrict vessels, the other dilates them. Autonomic fibers are essentially motor or effector in character to control the secretion of glands and
the activity of cardiac and smooth muscle.
Endocrine organs (ductless glands) share with the nervous system the
function of governing and controlling the involuntary activities of the
body. Thus, we recognize chemical regulation by hormones secreted by
the ductless glands and nervous regulation that is essentially dependent
upon impulses coming from the central nervous system. Hormones reach
all the tissues of the body by way of the blood stream, and nerves likewise
ramify to all other tissues. Thus all parts of the body are under both
chemical and nervous control. Investigations have shown that hormonelike substances may be formed directly from some of the nervous tissues.
Therefore, the actual physiologic character of the control of the two systems may be much closer than is commonly thought. In general, however,
a reaction to a nervous stimulus is extremely prompt and transitory,
whereas the hormones are slower in action and more persistent in their
regulatory effects.
The neuron
A neuron is the structural unit of the nervous system. I t is a highly
specialized cell consisting of a rather conspicuous cell body from which
protoplasmic processes are extended. In man, some of these processes
may be more than 3 feet long; e.g., cell bodies located in the spinal cord
bear processes reaching the tips of the toes. Cell bodies are located either
within the central nervous system, or in compact associations outside the
brain and cord, the ganglia. Bundles of elongate processes make up the
nerves as such and, when associated in tracts, also appear as the white
matter of the brain and cord. The gray matter is largely made up of cell
bodies that are located peripherally in the brain and centrally in the cord.
A process of a cell body that carries the impulse away from the cell body
is known as its axon. Other processes conducting impulses to a cell body
are called dendrites. Impulses pass from one neuron to another byapprox-
THE NERVOUS SYSTEM
,
183
imating, or synaptic, junctions of the processes and follow a law of forward
progression.
Three general types of neurons are generally described: (1) receptors,
(2) effectors, and (3) connectors, or associative neurons. The receptors
are also known as sensory or afferent cell types since the impulse originates
outside the central division of the nervous system and is conducted to it.
Effectors are also called motor, or efferent. In the latter, the impulse
'.;:)IJ>mHW
pr'oce,$$ - ' .... ~ _. _
Li S. flavuffi __ ____
- - I'"-Si1_~'_
Int",r _s pinal lig. --- -- ----~---I
Spin,,) cord ---- --
PMterior long_lig _ -- --:--
FIG. 1O.3.-Detail of spinal nerve in man. Upper figure, transverse section of dorsal
thoracic wall; lower figure, sagittal section in same region. (Drawn by Tom Jones, courtesy
S. H. Cam p and Company.)
leaves the central nervous system or sympathetic ganglia and is conducted
by an axon to the parts to be effected. Associative neurons are located in
the brain and cord and make connections with the afferent and efferent
types.
The segmental character of the spinal cord and the arrangement of
nerves make it possible for impulses to enter the central division and be
transferred at any level, depending upon the circumstances. In the brain,
.
.
184
FUNCTIONAL ANATOMY OF THE MAMMAL
•
the serial levels are not so clear cut, and many complex centers are involved
which may more strongly modify an impulse. Here an original impulse
may be intensified, inhibited, delayed, or tenninated. The central system
is essentially a complex of nerve tracts and centers that influences, and is
"Fronta I lobe
Lon']ifudinal fissure
of cerebrum
empora I lobe
R. hemis~here of
cerebellu m
l-:xn
A
Source of
Cranial nerves
o Ifa dory tract
Mammillary body.
Pituita rJ
Glan
Crura cerebri-~'-4!I,"""
Pons
Trapezium
Pyramidal
tract
B
FIG. lO.4.-Dorsal (A) and ventral (E) aspects of the <Jat's brain.
(Modified from lYIivart.)
influencoo by, all the conditions of the body through its ample connections
with peripheral and sympathetic parts.
General features of the brain and cranial nerves
The brain and cord arise tog~ther from a longitudinal thickening of
ectoderm along the middorsal axis of developing embryo. This thickened
THE· NERVOUS SYSTEM
. 185
ar~a soon becomes deeply grooved, and finally a complete cylinder is
formed which becomes pinched off from the overlying skin as the neural
tube. Through different~ation and growth the neural tube forms the spinal
cord and brain. The brain of the mammal, particularly in the primates,
becomes complex because of extreme differences in the development of the
fundamental parts. Because of this differentiation of parts and attendant
flexures to make for compactness, the original plan or linear arrangement
of the divisions is greatly obscured.
For clearer understanding of the plan of the mammalian brain, the
student should first ·study or review the brain of a more primitive form
such as the shark, where differentiation of parts is not so extreme. The
spinal cord is never greatly modified throughout the vertebrates generally,
not only with respect to its structure, but also in connection with the
arrangement of the spinal nerves.
Pdrieta.1 lobe
FIG. lO.5.-Lateral view of the human brain. (From Francis, "Fundamentals of Anatomy,"
C. V . Mosby Company.)
Early in development, the brain differentiates into three thickened
vesicles. The three primary vesicles from posterior to anterior are known,
respectively, as the prosencephalon, mesencephalon, and rhombencephalon.
The brain from its early inception to the adult condition is referred to as
the encephalon. The prosencephalon (forebrain) divides into two regions,
the telencephalon and the diencephalon. The mesencephalon (midbrain)
does not further divide, but the rhombencephalon (hindbrain) differentiates into the metencephalon and myelencephalon. These differentiations, therefore, result in the formation of a longitudinal series <?f five
divisions that grow and develop at very unequal rates in the mammal to
obscure the primitive linear arrangement. In the shark all these fundamental divisions may be seen superficially on the dorsal aspect, since the
parts are more nearly of equal size and none is completely covered as the
result of flexure or e.ixtreme specialization.
The telencephalon forms the cerebral hemispheres, the olfactory tracts,
and lobes; the diencephalon forms complex transfer paths between the
186
FUNCTIONAL ANATOMY OF THE MAMMAL
cerebral cortex and posterior divisions, the thalami, the optic nerves, retitla,
and chiasma, the infundibulum of the pituitary gland and the pineal body;
the mesencephalon gives rise to the corpora quadrigemini, which are homologous with corpora bigemini or optic lobes of the lower vertebrates. In
the mammal, the midbrain appears wedged between the cerebellum and
cerebrum, although it is actually adjacent to the thalamus of the diencephalon. The metencephalon includes the cerebellum (little brain) and
the pons, a transverse thickening on the ventral aspect. The myelencephalon becomes the medulla oblongata, which is directly continuous with
the spinal cord. If this fundamental plan is well understood, few difficulties are encountered in a further study of details.
Twelve pairs of cranial nerves are present in the mammal. These have
been referred to briefly in connection with t he foramina of the cranium.
The first has its sup~rficial origin (point of contact) with the telencephalon
Decusso.tion Of
corticospinal trocts
(pyro.mids)
FIG. lO.B.-Ventral view of the brain stem of man to show attachments of cranial nerves.
(From Francis, "Fundamentals of Anatomy, C. V . Mosby Company")
as an anterior extension. The second originates from the diencephalon,
the third and fourth are from the mesencephalon, and all the rest are from
the medulla.
.
The original cavities of the early vesicles differentiate into four ventricles. The first two are the lateral ventricles of the cerebral hemispheres
which communicate with each other centrally. From t he central com-
THE NERVOUS SYSTEM
187
m~mication extends the foramen of Monro to connect the lateral ventricles
with the third ventricle, which occupies the diencephalon. The third ventricle narrows posteriorly to form a channel, the iter (aqueduct cerebri),
which broadens in the medulla as the fourth ventricle. This is covered
only by memhranous tissue and appears as a deep groove in the medulla
when the membrane is removed. Tufts of capillaries extend into the fourth
ventricle as a choroid plexus. A similar condition occurs in the roof of
the third ventricle, b\lt here the corpus callosum between the cerebral
hemispheres covers the true membranous roof of the diencephalon and its
choroid plexus.
Cerebrospinal fluid occupies the ventricles of the brain, the central
canal of the cord, and the area between the meninges and neural parts.
The choroid plexi are considered as serving the cerebrospinal fluid in maintaining its volume and proper constituents.
THE BRAIN OF THE CAT
Removal of the brain intact requires considerable time and
patience, particularly if any attempt is made to spare the roots of
the cranial nerve sufficiently well for their proper identifications.
If the brain is to be removed intact, a circular drill-like saw
(trephine) is useful in entering the cranial cavity: If the directions
were followed in the survey of internal anatomy (page 111), the
brain may be removed as separate halves from a sectioned head.
Care sh;uld be taken to sever the roots of the cranial nerves while
the brain is being gently lifted away. As much of the nerve roots
should be kept with the brain as possible. The two sections may
be placed together with only the pituitary and pineal bodies materially damaged if the section has followed the mid-line.
Dorsal surface. Note the prominent cerebral hemispheres that
make up the bulk of the brain. The paired anterior extensions are
the olfactory lobes. By separating the hemispheres, the position
of the corpus callosum will be seen as the thickened white band
connecting the hemispheres. The roof (pallium) of the cerebrum
consists of a thick layer of cells that form ,the cerebral cortex. The
cortex is marked superficially by fissure's (sulci) which separate
convolutions (gyri). More complete fissures tend to divide each
hemisphere into more or less distinct lobes. These are named with
respect to the positions occupied in the cranium, i.e., (1) frontal,
(2) parietal, (3) temporal, and (4) occipital. The last three lobes
are rather poorly outlined in the cat. The development of gyri and
sulci indicate adv41ncement since, in general, their occurrence and
emphasis coincide with advanced mental powers. The obvious
188
FUNCTIONAL ANATOMY OF THE MAMMAL
explanation of this condition is that the area of cerebral cortex"is
~ncreased by the corrugations.
The cerebellum is deeply folded, which also increases the area of
gray matter. It is made up of a median lobe, the vermes, and a
pair of lateral lobes. By gently separating the cerebrum and cerebellum, the corpora quadrigemina are exposed. These are seen as
bodtt
ra 9,uadri'lem rna ,
I '!I'
~I
,
Hypophysis
' Pons:
(anterior and posterior)
tobes
,/
'/ "t.
4th Ventricle,/ , ....
,). /
Choroid plexus'/ , ,..,
Medu 110 . . . ..-<
,... -1-:'"
,,', "
Fro. 10.7.-Mid-sagittal section tluough brain of man (eerebml hemispheres are not shown).
(B y John P. Trainor.)
two pairs of elevations. The posterior pair is the more prominent.
The single pineal body lies in the median line directly anterior to
the anterior air of corpora quadrigemina.
Under the cerebellum and caudad to it lies the medulla oblongata.
The membranous roof of the medulla is often removed with the
bony covering, or it may be collapsed to expose the fourth ventricle
of the brain.
Ventral surface. A conspicuous landmark on the ventral surface
of the diencephalon is the optic chiasma produced by the entrance
of the optic nerves. Each optic nerve sends part of its fibers to the
side of the brain opposite that of its retinal connections. The optic
chiasma is the "crossing over" bridge for these ,fibers. The continuation of the nerve from the chiasma into the brain is known as
THE NERVOUS SYSTEM
189
\
the optic tract. Directly anterior to the chiasma is the anterior
perforated space, lateral to which are the olfactory tracts of the
qerebrum. These spread as they pass posteriorly from the olfactory
lobes. The tracts may be distinguished by slight differences in
coloration and indentation. They extend to the medial rounded
edge of the cerebrum at a region known as the hippocampus.
Within the posterior curvature formed by the optic chiasma and
tracts is the pituitary body . . This is attached to a slight rounded
elevation, the tuber cinereum. When the stalk of the pituitary is
Pineal bod~ .
Corpora'1.uadriCjemind
Moss~
//;"
intermedib -
Ventricle
/ . /
I
/
Arlterior ;_
commisure
,I
. Connecfi6n
+0 Hypophysis
FIG. lO.8. -Mid-sagittal section through brain of the cat (cerebral hemispheres not shown).
(By John F. Trainor .)
detached from the brain, a slit-like opening appears in the cincreum
which is continuous with the third ventricle. Directly caudad to
the tuber cinereum is a pair of small rounded mammillary bodies.
On either side may be seen processes that tend to unite the cerebellum and cerebrum. These are the anterior extensions of the crura
cerebri, which become hidden posteriorly by the pons varolii.
The pons appears as a wide band crossing the brain near the
forward limits of ·the cerebellum. It carries fibers that connect the
cerebrum and cerebellum with the medulla. The anterior pyramids
are caudal extensions of the crura cerebri and appear just posterior
to the pons, immediately adjacent to the mid-line. Here occurs a
decussation, or c1lOssing over, of fibers that pass from the brain to
the cord. Lateral to the pyramids anteriorly, the rounded margins
190
FUNCTIONAL ANATOMY OF THE MAMMAL
of the brain form the trapezoid bodies, which consist of transver~e
fibers interrupted by the pyramids in the mid-line area.
Caudad to the trapezoid bodies and lateral to the pyramids are
the olivary bodies, which are oval-shaped elevations somewhat
obscure in the cat. Partly surrounding the olivary bodies are the
. rather inconspicuous restiform bodies, or posterior crura. They
are caudolateral connections between the medulla and cerebellum
and appear as continuations of the ventral and lateral columns of
the spinal cord. The restiform bodies, crura cerebri, and a third
paired process, the middle crura, formed by the lateral margins of
the pons, make up the three more superficial connecting clements
of the longitudinal series of brain divisions.
The internal features of the brain. In the median sagittal section of the cerebral hemispheres, cut edges of the corpus callosum
are seen as forming the roof of the median communication of the
lateral (first and second) ventricles. This large commissure connecting the two cerebral hemispheres spreads internally as corpora
radiata in the thick roof of the lateral ventricles. Since such connections consist chiefly of nerve processes, they appear white and
more dense in contrast to the gray matter. Below the anterior
curve (genu) of the callosum is a ventral fork, the fornix, which is
the sharply reflected posterior wall of the median portion of the
cerebrum.
A prominent rounded massa intermedia appears below and posterior to the fornix, occupying the depressed area that represents
a lateral half of the third ventricle. This rounded portion of the
diencephalon appears as a dense grayish-white mass crossing the
mid-line. Since the fornix above represents the posterior limit of
the cerebrum, the massa intermedia represents the medial part of
the thalami. N ear the more ventral extension of the fornix is a
much smaller transverse bundle of tissue, the anterior commissure,
directly in front of the conspicuous massa intermedia of the thalamus. The cut edges of the optic chiasma will be seen at the floor
of the region.
The principal mass of the diencephalon is seen by gently lifting
the cerebral hemisphere where it overlies the other portions of the
brain, Each hemisphere covers a rounded elevation of thalamus,
which is connected centrally by the more narrow massa intermedia.
The thalamus is thus shaped somewhat like a dumbbell with the
mass a intermedia as the central handle. The conspicuous enlarge~
ments are lateral thalami, lying immediately craniad and laterad to
the corpora quadrigemini.
THE NERVOUS SYSTEM
191
}
The cerebellum does not contain a cavity and in the sagittal
section presents a branching effect of the white matter known as the
lp'bol\ vitae. The communications of the ventricles may also be
observed in this section if care is taken to locate the exact mid-line.
Transverse and frontal sections of the brain expose many more
details. The interrelations of the various nerve tracts may be determined by such sections. However, without carrying such a study
far beyond the sc~pe of this text, these details are more or less
meaningless.
Some functions of the brain. In general, the brain is analogous to a
complicated s\vitchboard possessing numerous connections with various
relay centers and lines of communication. The cerebral cortex has to do
with consciousness and the so-called higher faculties which involve initiativeness. The thalami contain important exchange centers connecting the
cerebrum with lower divisions of the central nervous system.
Anterior corpora quadrigemina form a part of the deep origin of the optic
nerves. It is said that the relative size of the anterior corpora are proportionate to the developed use of the eyes, the anterior pair in the mole being
rudimentary. The posterior pair is associated with hearing and has developed in connection with the more efficient hearing mechanism of the
mammal.
The exchange centers of the thalami and corpora quadrigemina also
involve nerve tracts of complex character. The midbrain is also associated
with "muscle sense," or the activities of skeletal muscles that do not require
strict conscious effort through cerebral centers.
The cerebellum is especially concerned with equilibrium and muscle
coordination in maintaining balance. The control is largely of a reflex
character. Because of its equilibrium function, it is also in close communication with the semicircular canals of the internal ear.
The medulla contains many of the so-called "lower centers" that are
persistently active in the nervous control of essential involuntary activities.
Here are the centers that affect respiration, heart beat, and the control of
blood flow to areas where it is most needed. These centers are of fundamental importance in merely maintaining life. A cat may live hours or
even days without the cerebrum, but any severe injury to the medulla is
of serious consequence. For this reason a blow on the back of the head is
likely to be much more dangerous than one on the frontal region. These
centers in the medulla, however, are greatly influenced through conscious
connections. The heart may be seriously affected by a shock of consciousness. Although one may be able to hold one's breath long enough to lose
consciousness, respitations begin immediately when the influence of conscious effort is terminated.
192
FUNCTIONAL ANATOMY OF THE MAMMAL
THE CRANIAL NERVES
This portion of the peripheral nervous system is concerned with the
nerves that have their superficial origin on the brain and their exits through
the cranial foramina . . In the mammal 12 pairs of such nerves are found.
Because of the morphological and physiological complexity, early anatomists (and physiologists) were content with numbering them in accordance
with their position. Some attempts have been made to indicate the probable relation of cranial nerves to nerves of the cord, but evidences of embryology, as well as of comparative anatomy, tend to complicate any
Sl.Iperior rectus muscle
tera 1 rectu s
'or rectus
Rdentary
(medial aspect)
FIG. 1O.9.-Distrihution of principal cranial nerves of the cat.
The orbit is cut open; the
zygomatic arch and part of thc .craniat wall is removed. and the mandible rellected downward
to expose its inner surface. Numbers refer to numbers assigned cranial lIerve,. (Modified
(rom Mivart.)
simple homologous features. However, the more posterior cranial nerves
do bear certain morphological and physiological resemblances to the
adjacent spinal series as the medulla merges into the cord.
The principal points of difference presented by the cranial series as compared with the spinal nerves are (1) spatial regularity is not so well exhibited; (2) they arise from a single root; (3) the purely sensory nerves from
special sense organs bear no ganglia; (4) they are not all of similar embryonic origin; (5) some are strictly motor, some strictly sensory, and
others are mixed with ganglia present for sensory portions of the mixed
nerves; (6) the superficial origins are extensive in some cases; (7) only the
more caudal of cranial nerves connect to the sympathetic division of the
autonomic system.
THE NBRVOUS SYSTEM
I
~§
..,
....o
i:'
o
en
§
W.
2o
. S
<' 0
:c;~
0."
00
193
194
FUNCTIONAL ANATOMY OF THE MAMMAL
THE NERVOUS SYSTEM
195
'1'0 dissect the cranial nerves of a mammal in any detail, several
specimens may be needed, and it is not usually attempted in general
anatomy courses. For special study, the skull can be partly opened
a~d placed in 10 per cent formalin to harden the nerve tissue. After
a few days, the bones may be decalcified by leaving the head and
neck in about 5 per cent nitric acid for several days and then washing
for several hours in running water. This procedure allows one to
follow the nerves more easily to their origin, but it is still difficult
to study the innervation with accuracy and completeness. A
descriptive table precedes for use as a general reference. It should
be noted that the superficial origin or attachment of a nerve on the
brain does not indicate the position where the cell bodies of the
nerves may be located internally.
GENERAL FEATURES OF THE SPINAL CORD AND NERVES
The cord is an extension of the medulla and has to do with conduction, modification, transfer, and association of nervous impulses
as well as the control of certain reflexes. In the extreme caudal
region, the cord terminates as a nonnervous filum terminalis. The
small central canal extends throughout the cord as a continuation
from the fourth ventricle of the brain (see Figs. 10.2 and 10.3).
When free of the meninges, \he cord exhibits a deep dorsal and a
more shallow ventral fissure, the two incompletely separating it
into halves. On either half are two lateral fissures, or furrows, that
roughly divide each half into three columns. The dorsal lateral
furrow is indistinct but may be seen at the point where the dorsal
roots of the spinal nerves join the cord. The more distinct ventral
lateral furrow lies at the position of the origin of the ventral roots.
Between these furrows is the lateral column of the cord, while above
and below are the dorsal and ventral columns, respectively. Some
of these points are best seen in a histologic section.
In cross section, the centrally located gray matter resembles the
form of a short-bodied butterfly with wings extended. The upper
lateral extensions are known as the dorsal (posterior) horns, while
the lower extensions are the ventral (anterior) horns. These contrast sharply with the surrounding white matter. The superficial
origins of the spinal nerves approximate the horns with which they
communicate.
......
Each spinal nerve arises by the two roots, previously mentioned;
which may be demonstrated by removing the lamina of the
vertebrae. Near the superficial origin of each dorsal root is a gan-
196
FUNCTIONAL ANATOMY OF THE MAMMAL
glion in which cell bodies relay sensory impulses to the cord- by
relatively short axon processes. The ventral roots carry motor
fibers away from the cord, and the cell bodies of these neurons lie
within the ventral horn of the cord. The motor cell bodies are relatively large and numerous, and smear preparations are easily made
for histological study from the ventral root. The spinal cord of the
cow, if secured rather fresh from a slaughterhouse, is good material
for these preparations. The dorsal root ganglion lies just inside
the intervertebral foramen and is protected by the meninges. The
two roots immediately unite to form the common spinal nerve.
Since the spinal nerves carry both motor and sensory fibers distad
to the union, they are mixed nerves (see Fig. 1.2).
THE SPINAL NERVES OF THE CAT
About 40 pairs of spinal nerves t:ypically occur in the cat, many
of which are involved in plexi. The nerves are named in relation
to the vertebrae with which they are associated. Since the first
cervical nerve finds an exit above the atlas, 8 pairs of cervicals are
present (Cl to C8), 13 thoracic (Tl to T13), 7 pairs of lumbar (Ll to
L 7), 3 sacral (Sl to S3), while the caudal may be somewhat variable
in number in accordance with the number of tail vertebrae.
Just distad to the union of the dorsal and ventral roots of each
nerve, a small dorsal branch extends to the dorsal musculature and
skin. From the ventral surface of the nerve, small twigs are also
given off to the sympathetic ganglia. These are known as rami
communicantes. The main trunk of the nerve passes ventrally to
become more or less widely distributed. Rather distinct plexi are
formed by unions of the spinal nerves in the cervical, brachial,
lumbar, and sacral regions. Each plexus invqlves the intermingling of
nerves to form complications of flbers rather close to their origin from
the cord. The extensions from the plexus are much longer than
the nerve trunks from the cord to the plexus. The cervical plexus
is formed by an interlac~ment of the first four or five cervical nerves.
The trunks of these nerves pass from below the anterior portion of
the scaleni muscles and below the sternomastoid. The phrenic
nerve in the cat is characteristically formed from branches of the
fifth and sixth cervicals to pass back to the diaphragm through the
thoracic cavity. The brachial plexus observed in the muscle dissection is formed from the sixth, seventh, and eighth cervical, and
•
the first thoracic, to supply the thoracic appendages. The last four
THE NERVOUS SYSTEM
·197
lumbars form the lumbar plexus, which is closely associated with
the sacral plexus since the last two lumbars also communicate with
the three sacrals to form the sacral division. The lumbar and
sacral are sometimes considered together as the lumbosacral plexus.
The nerves that are not involved in plexi (most thoracic and the
first few lumbar) are more primitive in character and retain their
segmental distribution. The segmental arrangement may be seen
by their terminations on the trunk when the skin was removed.
Plexi are developed in conformation with the highly developed
appendages that call for more than mere segmental innervation.
The neck and thorax are ihnervated by less complex nerve associations.
The brachial plexus (see Fig. 4.9)
If the suggested method of muscle dissection was followed, the
brachial plexus became exposed with the transection of the rhomboideus, serratus magnus, and levator scapulae muscles. In the
muscles dissection it was suggested that a preliminary examination·
of nerves be made with the view to studying muscle innervation.
If necessary, the muscles of the region. should be reviewed, since
the nerves are described chiefly in relation to the muscles innervated.
The nerves making up the plexus should be carefully cleared of
connective tissue back to their emergence from between the divisions of the scaleni musculature. To observe the dorsal and ventral
roots, it is necessary to chip away the neural arches and lamina of
the vertebrae. A suitable instrument for this is a small pair of
electrician's nippers. The dorsal branches are small and difficult
to locate as are the twigs to the sympathetic ganglia which pass
ventrally from the spinal nerves. These latter may be picked up
later from inside the body cavity and traced back to the spinal
nerves. The large ventral divisions of the nerves that contribute to
the plexus form a complex of interconnecting branches which is
difficult to follow. However, it is possible to determine rather
accurately the unions from which the longer extensions arise. These
unions which participate in the formation of an extension are somewhat variable, but there is remarkable uniformity in the ultimate
nerves that continue from the plexus to innervate both extrinsic
and intrinsic musculature of the appendage. Some also send
branches to the skin of the region.
If we consider t\le phrenic nerve as being outside the brachial
plexus, 13 nerves (and their branches) arise from the plexus. Eight
198
FUNCTIONAL ANATOMY OF THE MAMMAL
nerves of the plexus innervate the shoulder region, and five ext~nd
into the forelimb. The following description will be found typical,
and variations that may occur may be easily recognized. The
nerves are named mostly from their positions.
To shoulder region
1. Suprascapular. Most craniad of plexus; chiefly from C6 to
penetrate the supraspinatus near the cranial border of the scapula
where it divides, one branch going deeply under the acromion
process to the infraspinatus muscle. May also give a branch to
clavodel toideus.
2. Anterior subscapular. From C6 and C7; or may have no
main trunk but arise as two or three extensions to digitate to the
subscapularis muscle which occupies the subscapular fossa.
3. Middle subscapular. From C7 to anterior border of teres
major somewhat below the middle; may send branch to teres minor.
4. Posterior subscapular. Arises from C7 and C8; passes directly to the anterior border of the latissimus dorsi where it breaks
up into numerous branches.
5. Short anterior thora~ic. Arises from C7 and passes sharply
ventrocraniad to middle region of pectoralis major. May be located
most easily on the muscle and traced to the plexus.
6. Long anterior thoracic. From C8 and Tl; passes back to
pectoralis minor; a short branch usually extends across to the latissimus dorsi.
7. Axillary. Arises chiefly from C7; passes between teres major
near its proximal end and the subscapularis, going through the
angle formed by the head of the humerus and glenoid portion of
scapula (at axilla); gives branches to acromio- and spino-deltoids;
and extends a branch to the clavodeltoideus somewhat below the
clavicle.
8. Posterior thoracic. Arises from C7 to pass posteriorly and
dorsally beneath scaleni to the serratus anterior, near the origin of
the third digitation. The nerve is usually flattened and obscured
by the fascia where it emerges beneath the scalini to reach the
serratus musculature.
To arm region
9. Ulnar. The ulnar nerve arises chiefly from TI, passes down
the upper arm, following the course of the brachial artery to enter
the antibrachium around the elbow at the media:l epicondyle (crazybone nerve). Divides into two branches, one going to flexor carpi
THE NERVOUS SYSTEM
199
uln1tris and continuing down over wrist ventrally, the other takes a
dorsal course.
10. Musculospiral (radial). Arises from C7 and C8 and occasionally Tl. As one of the longest trunks, it winds obliquely around
the lateral musculature of the humerus under the lateral head of
the triceps. Above the humerus it divides into two branches. The
radial branch follows along the superficial fascia of the brachioradialis muscle to continue to the digits. The other branch passes
deeper as the posterior interosseus nerve, innervates the brachioradialis, extensor communis digitorum, extensor carpi radialis
longus and brevis, and other extensor15 and supinators of the antibrachium.
11. Median. Arises from C7 and C8 and occasionally Tl.
Passes along humerus and through the supracondoloid foramen,
where it may readily be identified. Divides into two branches:
one supplying pronator teres, flexor profundus digitorum, and
palmaris longus; the other continues down to supply other parts of
the flexor profundus digitorum and extends past the wrist where it
supplies th~ digits.
12. Musculocutaneous. From C6 and C7 to shoulder joint
where it gives a branch to coracobrachialis; thence along biceps
brachii which it innervates by small twigs near the proximal head.
Distally it gives a branch to the brachialis anticus and proceeds to
the integument of the antibrachium.
13. Internal cutaneous. This is the most caudad of the plexus;
it arises posteriorly from TI, passes in between the epitrochlearis
muscle and pecto-antibrachalis muscle, and comes to the medial
surface of the arm right at the margin of their separation. It then
follows along directly under the skin just proximal to the elbow to
emerge to the skin on the medial side of the wrist.
Other features of spinal nerves
The smaller dorsal branches of the spinal nerves pass dorsad and laterad
directly to the skin and muscles above the nerve trunk. One of the larger
of the dorsal branches is the rhomboideus nerve, which arises from the
sixth thoracic to innervate the rhomboideus muscles. It may also send
fibers to the levator scapulae. Other muscles to receive the dorsal branches
are the spinatus, which connect the spinous processes of vertebrae. The
nerves then proceed to the skin where the segmentally arranged ends may
be observed when the skin is removed.
The rami communicantes fibers ,yhich pass to the sympathetic cord may
best be studied in coIfnection with that system. Posterior to the brachial
plexus, the spinal nerves of the thoracic region are independent of each
200
FUNCTIONAL ANATOMY OF THE MAMMAL
other structurally, i.e., do not form plexi. The ventral branches are fela, tively smaller, and the bulk of each nerve extends along a rib just inside
the thorax as an intercostal nerve. These may be observed by tearing away
the pleura next to the internal intercostal muscles. They innervate the
internal and external intercostals, and each nerve possesses fibers to both
inspiratory and expiratory muscles. These act in an alternating rhythmic
manner through a control center in the medulla. The respiratory center
in the medulla communicates with cell bodies of the cerebral cortex so that
conscious change in respiratory rate and amplitude can be made. Since
each muscle fiber between the ribs is relatively short, the intercostals are
favorite histological material in studying nerve terminations.
The lumbar plexus
The last four pairs of the seven lumbars are concerned in this
plexus. The three lumbar nerves craniad to the plexus pass independently to the skin and muscles of the ventral and lateral abdominal wall. One reason for considering the lumbar plexus separately
from the sacral series seems apparent in locating the nerves. Essential features of the plexus are most easily exposed by removing the
abdominal viscera and approaching the nerves from the internal
aspect of the body ,vall. The entire alimentary canal may be freed
from the dorsal mesentery and carried forward past the kidneys.
The genito-urinary apparatus may be removed, leaving only the
vena cava and aorta below the kidneys as landmarks. This dissection exposes the dorsal body wall and brings into view the prominent
psoas, or loin, muscles, which lie under the peritoneum of the dorsal
body wall. The more prominent in the cat are the iliopsoas and the
psoas minor.
The iliopsoas is the larger of the two, and its lateral margin lies
next to the transversus abdominis.
The psoas minor somewhat
overlies it and must be separated posteriorly where it tapers considerably as a tendinous structure. Before removing the muscles
to locate the plexus proper, the nerves of the plexus should be
located and traced in both directions. These nerves will be described in general, the details may be worked out more completely
if desired.
Lumbar division
1. Genitocrural. Two branches of this nerve may be seen rather
easily. A small medial branch may be observed just laterad to the
external iliac artery near the bifurcation of the aorta. It follows
the iliac artery to the ventral pelvic region. A luteral branch passes
along the psoas minor muscle where posteriorly it crosses the ilio-
THE NERVOUS SYSTEM
201
psoas. It then passes obliquely through the abdominal wall to the
medio-anterior surface of the thigh. The genitocrural arises as an
extension of L4.
2. External cutaneous femoris. This nerve is somewhat larger
than the genitocrural. It passes between the iliopsoas and psoas
minor where it crosses transversely at the level of the iliolumbar
artery, which it follows to penetrate the abdominal wall. It is
distributed along the anterior margin of the thigh and extends along
the integument almost to the knee. It arises from a connecting
strand between L4 and L5.
3. Anterior crural. This is the largest of the group. It may be
seen under the posterior limits of the iliopsoas in the wall dorsocraniad to the bifurcation of the common iliac veins. At this point
branches arise, one of which follows superficially along the femoral
artery and vein on the medial surface of the leg as the saphenus
nerve. Its cutaneous branches extend to the digits. Other branches
innervate the sartorius, vastus medialis, vastus intermedius, and
rectus femoris. It arises from L5 and L6.
4. Obturator. This nerve lies just mediad to the anterior crural
of which it superficially appears as a branch. It may be readily
verified since it passes through the obturator foramen. It innervates the obturator externus, adductor femoris, gracilis, and others
and arises from a connection between L6 and L7.
The sacral plexus
The chief extensions from the sacral plexus are located more
dorsally than those of the lumbar. The plexus proper may be
uncovered by picking away the musculature over the sacral region
and then carefully removing the heavy transverse processes of the
adjacent lumbar vertebrae. The dissection of the lumbosacral
plexus as a whole requires considerable time and patience. For our
purposes the chief nerves of the sacral division will be described so
that they may be traced either to the plexus or to their points of
distribution, or both.
1. Great sciatic. The great sciatic nerve is by far the largest
nerve of the division; in fact, it is the largest of all peripheral nerves.
It is exposed with the transection and reflection of the biceps femoris
muscle to which it is rather closely applied on its inner surface.
The nerve arises chiefly from the seventh lumbar nerve but also
receives branches from L6 and 81; in the plexus region it lies ~dorsad
and mediad to the -lbturator nerve of the lumbar division. From its
origin it passes around the great sciatic notch of the pelvis down the
202
FUNCTIONAL ANATOMY OF THE MAMMAL
leg, where back of the knee (popliteal space) it divides into an
internal and external popliteal nerve. The external branch, also
known as the peroneal nerve, further divides into the musculocutaneous, to the peronei musculature and to the dorsal surface of
the foot, and the anterior tibial nerve, which supplies the skin;
tibialis anterior, etc. The internal popliteal nerve passes posterior
to the tibia to form the plantar nerves which reach the digits. There
are other minor branches anterior to the popliteal.
2. Lesser sciatic. The lesser sciatic nerve is distributed to the
lateral surface of the biceps femoris muscle and in the region of the
anus sends branches around the perineum and to the fat around the
base of the taiL The longest extension is along the lateral surface
of the biceps femoris and reaches almost to the popliteal space. It
arises from 81 and 82 and usually receives a conspicuous branch
from the great sciatic.
3. Posterior hemorrhoidal. This nerve passes along the lateral
aspect of the rectum, which it crosses to the urethra and bladder.
It arises from 82 and 83.
4. Superior gluteal. This nerve extends over the dorsal border
of the ilium between the pyriformis and gluteus medius and is distributed to the gluteus medius, gamellus superior, and gluteus
minimus. It arises chiefly from the first sacral.
5. Inferior gluteal. This nerve lies along the dorsal surface of
the great sciatic nerve in the pelvic region, which it also leaves at ('
the great sciatic notch. It sends branches to the caudofemoralis,
gluteus maximus, and pyriformis. It arises from the lumbosacral
cord or union in the region of the first sacraL
Other smaller branches are the pudic nerve, which supplies the
genital parts, and certain nerves to the smaller muscles around the
anus and root of the tail.
The nerves of the tail, or caudal nerves, are similar to the other
generalized spinal nerves. They innervate the musculature and
skin of the region. With these there are no direct communications
to the sympathetic cords.
THE AUTONOMIC DIVISION
Much of this division has been described in connection with the survey
of internal anatomy and in the description of the peripheral division of the
nervous system. We may now further amplify previous descriptions and
summarize the essential features of involuntary inner~ation.
THE NERVOUS SYSTEM
203
'the- cranial portion of the parasympathetics consists of parts of the
oculomotor, facial, glossopharyngeal, and vagus nerves. The sacral portion consists of fibers of the sacral spinal nerves. The other set of nerves
nqlion nodosum of voqus
Voqo-sympathetic trunl.
:::r--Carotid artery
renlc nerve
Lobe of lun9 (cut)
R. ventricle
1.:.
A~'lt-fl:;"_- 'Pulmonary veins
:D._-Sympathetic trunk
phrenic-i..---'y:::....-__.~I
n er\ie
Splanchnic nerve
II-___,,-Abdominol sympathetic
trun k
FIG.
lO.lO.-Cervical and thoracic nerves of the cat in relation to conspicuous landmarks
(left side only is shown).
of the autonomic division is the sympathetic, which arises from ganglia
receiving impulses from the central nervous system by way of the rami
communicantes. Plistganglionic fibers extend from the ganglia to innervate the same structures that are innervated by the parasympathetics.
204
FUNCTIONAL ANATOMY OF THE MAMMAL
The most craniad of the sympathetic ganglia is the superior
cervical, near the jugular foramen. This ganglion sends branches
further craniad to effect dilation of the pupil of the eye, increase
secretion of the salivary glands, and dilate arterioles of the nose
and throat. The small nerves from this ganglia tend to follow the
branches of the external carotid artery in reaching the structures
innervated and are difficult to follow in gross dissection. The
superior cervical ganglion lies just mediad and adjacent to the
ganglion nodosum of the vagus nerve. Slightly below the two
ganglia, the sympathetic trunk and vagus nerve join into the vagosympathetic trunk. Somewhat above the level of the first rib, the
sympathetic portion of the trunk leaves the vagus to pass laterocaudad toward the base of the first rib. Before reaching this point,
a small ganglion is usually present immediately in front of the
subclavian artery. This is the middle cervical, which sends cardiac
fibers to the heart and extensions (ansa subc1avia) around the subclavian artery to join at the inferior cervical ganglion just back of
the artery on the dorsal body wall. Other cardiac nerves frop! this
larger ganglion extend to the heart and form a cardiac plexus. The
sympathetic innervation to the heart produces acceleration when
stimulated.
To return to the parasympathetics, which are difficult to demonstrate, the
oculomotor sends parasympathetic fibers to constrict the pupil; the chor~a
tympani branch of the facial constricts the blood supply to the submaxil\ lary gland, reducing the salivary flow; the glossopharyngeal acts similarly
upon the parotid and sublingual glands; and the vagus reaches the heart
to serve as an inhibitor. The actions of cranial parasympathetics are
antagonistic to the sympathetics. If the vagus nerve to the heart is cut,
the heart usually increases in rate of beat, which shows that the heart is
- normally under inhibitory vagus tone. When stimulated, the vagus produces inhibition or reduction in rate, and in the turtle, the heart may be
completely stopped for a half-hour or longer.
The vagus nerve also gives off branches to the trachea, lungs, and esophagus; it passes through the diaphragm to innervate the stomach, other
upper abdominal viscera, and most of the intestines. From the sacral por- ,
tion, parasympathetic fibers pass craniad to reach the urinogenital tract
and the lower portion of the alimentary canal. Thus the sacral portion
extends craniad to innervate the structures that are not reached by the
descending vagus.
In tracing the sympathetic trunk further caudad from the inferior
cervical ganglion, segmental thoracic ganglia "will be observed.
This arrangement illustrates the primitive condition of the sympa-
205
THE NERVOUS SYSTEM
thetic division, and the large cervical ganglia represent fusions of
the original segmental type. Before reaching the diaphragm, one
or two conspicuous splanchnic branches are seen to diverge from
the trunk and pass through the diaphragm to a pair of ganglia that
lie on the celiac and superior mesenteric arteries. These are named
Splanchnic nerve
Diaphragm
Seqmental9on'llia
of
Superior mesenteric
artery
Adrena I 91and
La r~ e -----\"".
Intestine
Abdomina I sym.pathetic
tru nk.
Kidney
+--tl--Abdominal aorta
~":::..I-_LGenitol
artery
Inf mesenteric
artery
Inf. mesenteric
qanqlion
:FIll. lO.ll.-Lower thoracic and abdominal oY llIpathetic nerves of the cat.
with reference to the arteries but appear superficially as a single
semilunar ganglion. From this ganglion, numerous fibers form a
plexus (solar plexus) that innervates the viscera of the region.
The sympathetic trunk continues caudad to the caudal region,
but only one conspicuous ganglion lies further along its course. This
is the inferior mesenteric, which lies on the artery of the same name.
Here again a network of fibers extends to the viscera of the lower
pelvic region. In general, these fibers innervate the parts supplied
by the sacral parasympathetics. Particular functions of these
• learned from standard texts on physiology.
autonomics may be
'206
FUNCTIONAL ANATOMY OF THE MAMMAL
1
Discussion. In man and some other mammals, the sympathetic cord
and vagus nerve do not combine into a common trunk. Furthermore,
the connections of the ganglia with peripheral nerves appear to be somewhat variable. However, the superior cervical ganglion, in mammals
generally, communicates with the last three cranial nerves and the first
three cervicals. The last five cervical nerves and first three thoracic, in
mammals generally, send rami communicantes to the inferior cervical ganglion. The first segmental thoracic sympathetic ganglion, therefore, is
found at the level of the fourth thoracic nerve. Confusion in terminology
appears in this connection since in the cat, for example, the inferior cervical
ganglion is clearly within the thoracic area rather than in the neck. The
fusion of thoracic ganglia with lower cervical segmental ganglia has led
to the use of the term "stellate ganglion" (star-shaped) to be applied to
the ganglion under these conditions. But its application does not appear
to be consistent in the literature. In the dog, the stellate ganglion lies
somewhat craniad, compared with its position in the cat. The cardiac
accelerators in the dog can therefore be reached more easily without so
much danger of entering the pleural cavity and causing collapse of the
lung in experimental work. This feature is important in experimental
physiology, which involves surgical technique on anesthetized animals.
One of the most interesting circumstances of the autonomic division is
its close functional (physiologic) similarity with certain endocrine organs.
Recent investigations have shown that the superior cervical ganglion of
the cat, when stimulated through its nervous connections, produces a
substance that is similar, if not identical, to adrenalin. For some time,
it has also been known that stimulation of the vagus nerve produces a
chemical substance (acetylcholine) that causes cardiac inhibition when
administered to the heart musculature as a drug and that is antagonized
by adrenalin. Thus, we see that nervous stimulation in these cases produces hormone-like substances from sympathetic ganglia and at parasympathetic terminations. Here the basic processes of nervous and chemical regulation appear not to be different or distinct phenomepa.
Chapter XI
SPECIAL SENSORY APPARATUS
ACH of the various kinds of sensory end organs is strikingly specific
in its sensitivity to stimuli. Thus the retina of the eye is responsive
to light; sensory epithelium of the inner ear is responsive to vibrations in
the air; nasal epithelium and taste buds are responsive to chemicals; and
sensory end organs of the skin and internal areas are each responsive to
their particular kind of stimulus. End organs show striking structural
specialization in conformation with their type of function.
E
D
~':~;:"!!::\ 0\r:
FIG. l1.l-The mechanism for taste in man. A, dorsal surface of tongue; B, two types of
taste papillae in section and enlarged; C, relative sensitivity on the tongue for the four tastes; '
D, section of a taste bud enlarged and diagrammatic. (Partly after Parker. From Storer,
"General ZoolOGY.")
Impulses are transmitted from the terminal receptors to more or less
localized conscious centers of the brain. But we do not recognize or perceive these sensations as being within the brain.
In the case of the visual sense we have no feeling that an object is photographed in the eye, nor that visual impulses are transmitted to conscious
areas. The sensation is projected as at a judged distance from the body.
Likewise the sensation or perception of sound is projected at a distance,
and we form judgments as to the direction and distance from which the
sound waves arose.
The olfactory sense is projected to the tongue, smell to nasal epithelium,
and touch to the ski,n. We also possess a sense of balance and position
that enables us to know the situation and position of the body or of hands
207
208
FUNCTIONAL ANATOMY OF THE MAMMAL
and feet, and we can make well-directed movements such as feeding ourselves while blindfolded. This curious projection of sensations is well
illustrated in cases where feet have been amputated and the subject will •
olfactory
FIG. 11.2.-Anatomy of the olfactory sense in man. A , location of the olfactory epithelium
in lateral wall of nasal cavity; B, transverse section of cavity; C, enlarged section of olfactory
epithelium. (Adapted from Parker. From Storer, "General Zoolo(JY. " )
pressure waves in endolymph
stimulate hair cells
HI !H iii ill HI II I
HI II: III Ii[ Ii ! II I III in III U!
cochlea (as ifuncoilcdl
FIG. 11.3.-The mechanism of hearing and equilibrium in mall. A, general structure of
the ear; B , c ro~~ section of a par t of the cochlear area; C, enlarged section through the spira l
organ of Corti showing sensory hair cells; D, diagram of sound transmi~sion from outside
air to impulse in auditory n erve. (From Storer, " General Zoology.")
experience itching or painful sensations at specific areas of the toes long
after the feet have been amputated.
Another striking feature of the special sensory mechanism is in the specific character of the sensation regardless of the type of the initiating
stimulus. A sharp blow on the head may mechantcally stimulate the
retina by jarring it, and we "see stars." A strong flash of light is seen
SPECIAL SENSORY APPARATUS
209
when the optic nerve is cut in surgically removing the eye. Pressure
stimuli or foreign bodies in the ear may make the "head roar." An even
more specific response is exhibited by the end organs of touch. An end
Organ specific for cold will produce a sensation of cold even when stimulated by a warm rod.
THE FUNCTIONAL ANATOMY OF THE EYE
The eye is usually described as being constructed like a camera. Eyes
of vertebrate animals in general are fundamentally similar, not only in
design but as to the number, character, and innervation of the muscles
that move it within the orbital fossa. The fundamental features of the eye
and closely associated parts together with nerve and brain connections are
more readily dissected in a cartilaginous fish than in the mammal. In
forms such as the shark, the nerves can be followed through the brain case
by dissecting through the relatively soft cartilage.
Eyes of sheep or pigs, which may be obtained fresh from slaughterhouses or as special preparations from supply companies, are generally more suitable for study than eyes from embalmed bodies.
Therefore, the descriptions given for the study of the organ as a
separate part of anatomy is generalized rather than specifically
referable to the cat.
Mirror examination of own eye
A study of the eye and closely associated structures may well
begin with an examination of the superficial characters of your own
eye as seen in a mirror. Observe that the upper eyelid extends to
the lower margin of the eyebrow and that the lower lid more gradually merges with the skin at the lower rim of the orbital fossa. The
lower lid is relatively stationary. With the eye wide open and
looking directly ahead, the free margins of upper lid and lower lid
are separated from each other by an elliptical gap. The gap is
called the palpebral fissur_e. The exposed surface of the eye is kept
uniformly moist by frequent blinking.
The outer margins of the two lids are joined at inner and outer
angles. The inner angle is rounded, and the eyelids here do not
press so firmly against the surface of the eyeball. These conditions
leave a little lake in which tears collect. In the inner margin of this
area (lacus lacrimalis) is a fleshy elevation, the caruncle, best seen
when the eye is rotated laterally. A red-colored fold is attached to
the outer margin Of the caruncle. The outer fold is the plica semilunaris, which is a vestige of the third eyelid of the cat, most other
210
FUNCTIONAL ANATOMY OF THE MAMMAL
mammals, and other terrestrial vertebrates. The third eyelid
spreads horizontally across the eye and is usually referred to as the
nictitating membrane. The caruncle usually appears somewhat\
yellow in color; it possesses modified sebaceous glands associated
with extremely fine hairs.
When the eyes are wide open and looking straight ahead, the
upper and lower lids expose the upper and lower limits of the central
pupil and the surrounding pigmented iris. The pupil appears black
because it is an aperture into the dark interior of the eyeball and is
covered by transparent tissue.
The outer tunic or covering of the entire eyeball is called the
tunica fibrosa. The portion of the tunic passing over the iris and
pupil becomes highly modified as the transparent cornea. It joins
the rest of the eyeball at a circular furrow and curves more prominently than does the posterior part of the globe.
The junction of the cornea with the rest of the fibrous tunic of
the eye consists of a gradual transition of corneal cells into an
epithelial covering, the conjunctiva. This consists of several layers
of cells that continue over the eyeball, as the scleral conjunctiva,
to its attachment with the inner surface of the eyelids, and also
continue in a modified condition to form the entire inner surface of
the lids. The inner lining of the lid is called the palpebral conjunctiva and is a type of mucous epithelium.
The white tissue back of the cornea is the scleral portion of the
tunica fibrosa. This is a tough firm connective tissue that gives
support and protection to the delicate internal mechanism. The
sclera back of the attachments of the inner lining of the lids, of
course, does not possess the scleral conjunctiva. When a study is
made of the excised eye, these attachments should be located.
The free rims of the eyelids are thin at the lateral angle and
broaden as the inner, or medial, angle is approached. By pulling
the lower lid down and the upper lid upward we can distinguish an
outer and inner margin, the lashes occurring on the outer. At the
level of the plica semilunaris the rim of each lid possesses a fine
opening, the punctum lacrimalis, situated on an elevation, the
papilla lacrimale, which appears pale in color. The opening is
perhaps most easily seen in the lower lid by drawing the lid down
so as to protrude it away from the globe. These openings (upper
and lower) lead into lacrimal canals, which eventually drain tears
into the nasal region.
Tears are formed by lacrimal glands that lie In the upper and
lateral portion of the orbital region. The secretion is carried down-
SPECIAL SENSORY APPARATUS
211
• by numerous ducts into the space between the lining of the
ward
lids and surface of the eyeball and spreads to the inner angle of the
lids. Some accumulates in the lacus lacrimalis to be drained through
the punctum lacrimalis. The tears serve to prevent the exposed
portions of the eye from drying. Overflow of tears at the rims is
largely prevented by oily secretions from a series of small sebaceous
glands. The openings of these can usually be seen in a row on the
inner surface of the rim.
Extrinsic muscles of the eye (see Fig. 10.9)
These muscles move the eyeball in the orbit and in man and most
vertebrates consist only of two oblique and four recti muscles. In
the cat, sheep, and some other mammalian forms an additional
muscle occurs which is known as the retractor. When present, the
retractor mostly surrounds the optic nerve as a series of slips and
functions in keeping the eyeball close within the orbit when the
head is bent down. All recti muscles and the superior oblique arise
near the optic foramen. The inferior oblique arises from the anterior floor of the orbit. The recti muscles are the medial, lateral,
superior, and inferior. They arise close together near the optic
foramen and diverge to their insertions on the eyeball to positions
from which the names are derived.
All the recti group are innervated by the oculomotor nerve,
except the lateral rectus which is supplied by the abducens. The
oculomotor also supplies the inferior oblique. Only the superior
oblique is innervated by the trochlear nerve. The muscle is unique
in that its tendon passes through a pulley-like attachment.
Internal features of the eye
If a section of the sidewall of the eyeball is removed, the wall is
seen to consist of three coats: (1) the superficial tunica fibrosa
previously described; (2) a middle vascular coat, which forms the
black pigmented choroid layer and the iris as a modification; and
(3) the lining epithelium, or retina. In the cat, and some other
mammals, the choroid coat contains peculiar crystal-bearing cells
forming the tapetum, which appears iridescent green in color and
produces the peculiar glow of the eye in the dark.
The retina in preserved material appears opaque and may be
somewhat shrunken away from its choroid base. It extends forward
only a little more othan half of the globe and is an expansion of the
optic nerve. Near the center of the nerve as it appears to leave the
212
FUNCTIONAL ANATOMY OF THE MAMMAL
retina is the blind spot, which does not possess retinal cells but'" is
quite vascular.
The forward margins of the retina attach to a ciliary body, whic,9
in turn is attached to the crystalline lens. In front of the lens is the ·
anterior chamber containing a lymph~like aqueous humor. Back
of the lens is the much larger posterior chamber which contains a
gelatinous mass, the vitreous body. Thus light entering the cornea
passes through four different transparent elements that may affect
for
gear
~l'"
,_for
distant
objects
l~
o
FIG. 11.4.-Mechanism of sight in man. A, median vertical section of the eye; B, enlarged
diagram of the structure of the retina; C, changes in shape of the lens (accommodation) to
focus on near and far objects; D, manner in which lellS serves to form an image on the retina.
(A, modified from Dakin.) (From Storer, "General. Zoology.")
the course of the rays: the cornea, aqueous humor, crystalline lens,
and vitreous body.
The lens functions chiefly in accommodation for distance; the cililil'Y
apparatus controls its curvature. Working with the lens in accommodation is the pupil, the size of which responds to light intensity and proper
focus.
To demonstrate the effect of reducing the size of the pupil, one can look
at a pinhead so close to the eye that it appears blurred. If viewed from
the same distance through a small pinhole, much better focus is obtained.
The retina acts as a sensitive plate to the light rays that produce chemical changes setting up a flow of impulses through the optic nerve. Not
all these impulses reach the conscious centers, and .. unless attention is
directed to things they may make no impression on consciousness. The
retina is afforded complete rest only in darkness.
SPECIAL SENSORY APPARATUS
213
THE HEARING ApPARATUS
Dissection of the essential internal parts of the auditory structures
much time, patience, and skill, even when done on large mammals.
Detailed examination of the mechanism is usually not attempted in general courses. The following is mostly a generalized description from which
observations may be made.
r~quires
The ear is considered as consisting of three divisions: (1) external,
(2) middle, and (3) internal. External parts are the expanded portion, or pinna, apparently designed to facilitate picking up sound
waves as a megaphone in reverse, and the external auditory meatus,
or ear opening. The pinna is of various forms among the different
mammals and is generally supported by a well-defined auricular
cartilage. Rather specialized hair surrounds and extends partly
over the meatus, apparently serving to keep out dust particles and
insects. In man, a prominent, firm projection, the tragus, extends
partly over the meatus, and a lobule forms the lower portion of the
pinna which is devoid of cartilage.
When the meatus is explored with a suitable light, it is seen to
terminate at a partition, the tympanic membrane. The middle ear
extends from this membrane to the petrous bone of the temporal
complex. The cavity of the middle ear contains three auditory
ossicles that form a bridge from the tympanic membrane to the
margin of a lateral opening of the petrous bone, the vestibular
fenestra. In a dried skull, two such openings are seen on the lateral
aspect of the petrous: the upper vestibular and a lower cochlear
fenestra, which in life is covered by a thin membrane.
Adjacent to the tympanic membrane is the malleus, next is the
incus, and then the stirrup-shaped stapes which joins the petrous.
The function of the auditory ossicles is to transmit the vibrations of
the diaphragm-like tympanic membrane to the internal ear within
the petrous bone. Another feature of the middle ear is the opening
of the Eustachian tube which leads to the pharynx and serves to
permit the air pressure within the cavity to conform with atmospheric conditions.
Dissection of the internal ear is especially difficult since it is entirely
enclosed by the dense petrous bone. The parts cannot be well identified
without using special methods and reconstructions. The essential part is
the membranous labyrinth consisting of semicircular ducts, a cochlea,
sacculus, and utriculus. These are housed in a bony labyrinth. The space
between the cavitie;~ in the bone and membranous labyrinth is occupied
by perilymph. A similar fluid, endolymph, circulates within the membranous walls.
214
FUNCTIONAL ANATOMY OF THE MAMMAL
The semicircular canals are essentially concerned with equilibrium rather
than with hearing. The sensory auditory membrane of the cochlea only
is said to function in an auditory capacity. The sacculus and utriculus are
associated with the stationary position of the head. As in the dissection Jf
cranial nerves and extrinsic muscles of the eye, the fundamental character
of the internal ear is best demonstrated in the elasmobranch fish.
Qhapter XII
THE ENDOCRINE ORGANS
ALTHOUGH all the specialized endocrine organs have oeen partly described in the preceding chapters, it seems desirable to consider then1
in a more systematic and detailed manner. Since the different organs of
the system are arranged with neither any obvious structural continuity
nor any evident functional interrelations, they may be listed merely as they
occur spatially from a cranial to caudal position in the body. Classified
in this way the system includes (1) pituitary (hypophysis), (2) thyroid,
(3) parathyroids, (4) thymus, (5) islands of Langerhans in the pancreas,
(6) adrenals, and (7) portions of gonad tissue (ovaries and testes). In
addition to these, several other tissues produce substances with effects
similar to the secretions of the more conspicuous endocrine organs. All
tissues appear to have a share in the general regulation of the body as an
integrated whole.
The essential functional feature of endocrine organs is in chemical regulation of body activities. Their secretions are effective in remarkably
minute concentration and are conspicuously concerned with such fundamentally important functions as growth, differentiation, metabolism, and
the differential regulation of the various organs and systems. The active
properties of the secretions are known as hormones. Some act as accelerators of activity, while others serve as inhibitors. The secretions are
absorbed by the blood, since the endocrines are ductless glands, and the
hormones are carried to all parts of the body by general circulation. Many
of the hormones are rather specific in action, whereas others produce a
widespread response in tissues generally.
The pituitary. The gland lies in the pituitary fossa of the basisphenoid
bone and is made up mostly of two distinctive parts, anterior and posterior.
These are derived differently embryonically and are also histologically
different. The anterior pituitary produces a number of distinct hormones,
or principles. The more striking of these affect (1) growth, (2) reproduction, and (3) metabolism. The latter action is principally through activation of the thyroid gland.
I
An excess of the growth hormone appears to be a direct stimulus to general growth and is responsible for gigantism in man. Lack of the hormone
results in a type of dwarfishness. The reproductive hormone may have
multiple properties,. but the most striking effect on the gonads is to produce
ripening of the germ cells. When extremely immature mammals are
n
215
216
FUNCTIONAL ANATOMY OF THE MAMMAL
treated with this principle, precocious ripening (maturation) of the ge"m
cells is initiated. The metabolic principle acts in an indirect manner. This
thyrotrophic hormone stimulates both development and active secretion
of the thyroid gland which, in turn, produces an increase in the metabolfc
rate, as well as inducing other changes traceable to thyroid activity.
Pituiiary o r hypophysis •
(at base of bram)
Thyroid - - - _
(over trachea)
Jo-o'....'--4-IsIets of Iangerhans
(in pancreas)
,
Ovaries
--..£
(in female)
FIG. 12. 1.-E ndocrine organs of man shown semidiagrammatically. Although no speci fi c
hormones a re known from the thymus, it is included becau se of suspected relationships.
(From Storer, General Zoolo(JY." )
The posterior pituitary, separated from the anterior, also produces a
of effects when an extract is injected into normal animals. But
removal of the posterior lobe does not seem to induce any particular ill
effects in man. Possibly, other endocrines may be substituted fOr it in
deficiency, but excesses produce changes not compensated for. The crude
extract is known as pituitrin. It is particularly effective in intensifying
contraction of the uterine muscularis even when given in minute concentration and also induces a sustained constriction of arterioles generally,
causing a marked increase in blood pressure.
The thyroid gland. The thyroid , in mammals generally, is a bilobect'
structure adjacent to the upper portion of the trachel!. Its hormone in a
purified form is known as thyroxin, which contains a large proportion of
num~r
THE ENDOCRINE OR(}ANS
217
imJine. Extracts of the whole gland affect Qevelopment, growth, and
metabolism. It is not known ,,,hether these are all separate properties, but
investigations on lower vertebrates indicate that distinct fractions may be
wesent. Thyroid tissue when fed to small tadpoles causes them to transform into small frogs in 10 to 14 days. RemovljJ of thyroid prevents tadpoles from becoming frogs. Because of the thyroid relation to the anterior
pituitary, similar effects are produced when the pituitary is removed.
The most noticeable effect of excess thyroid ()n mammals is the greatly
increased metabolic rate. Deficiency of thyroili during infancy produces
a peculiar dwarfishness known as cretinism. Various types of goiter are
associated with abnormal conditions of the thyroid gland. Goiters are
frequently produced by iodine deficiencies in the diet and are not limited
to man.
The parathyroids. Small masses of tissue, <lifferent from the thyroid
but usually partly imbedded in it, are known. as parathyroids. These
\JIIit'rr"CLI'iry- m"CLY- o-e b'BBlT 1f~ NglTG p'd:tC'ITt§ \fIT tlTe medial aspect of the thyroid
lobes as a pair on each lobe. In the rat, the barathyroids are generally
entirely free from the thyroid tissue, and much experimental work on
parathyroids has consequently been done on thi:, animal.
Complete removal of the parathyroids causei'; an extreme irritability of
the nervous mechanism, which results in mUSCUlar twitching within a few
days. This is followed by muscular spasms resulting soon in rigidity.
Death occurs when respirations are cut off by spaBms of respiratory muscles.
The peculiar contracted state of muscles is knmm as parathyroid tetany.
When only a portion of the parathyroids is rernoyed, general metabolism
is upset, the animal becomes more susceptible to disease, blood calcium is
reduced, bone development may cease, and the itnimal is extremely hypersensitive. Most of the symptoms are traceable to an upset in the calcium
regulation and consequent disturbance of bloc)d balance. Special care
must be taken, in removal of parts of the thyrc)id in goiter operations, to
leave adequate parathyroid tissue to ensure proper calcium balance.
No specific hormone has been identified from. the thymus gland, but it
is suspected by some to secrete substances of an endocrine character affecting growth. The thymus lies in the mediastinal space immediately above
the heart and is extremely variable in form and size. In general, the gland
is large at birth and tends to diminish as the iI1dividual advances in age.
In man, it has mostly disappeared at the age of twenty-five. However,
some remnants of thymus tissue can usually be found in old cats. Qualitative changes in the thymus tissue may possibly occur also with age.
A theory has been proposed that the thymui'; is largely concerned with
muscular development. Among the marsupial%, at least, the presence of
the thymus appears to be correlated with the character of muscle development. It is said to be absent even in the youn~ wombat, which is a powerfully developed animal when adult. On the c)ther hand, in the weakest
developed types, such as the Tasmanian devil, &. well-developed thymus is
218
FUNCTIONAL ANATOl\lY OF THE MAMMAL
retained throughout life. In man, the thymus gland is best develo~ed
while the muscular system is weakest. At about five years, when the
muscles assume considerable strength, the thymus commences to disappear. These conditions may suggest that the thymus is more speciall,y
concerned with muscular development than with general growth.
Islands of Langerhans. These consist of minute isolated areas of special
cells scattered throughout the pancreas. The hormone produced is insulin.
Insulin is essential for sugar assimilation. When insulin is deficient, sugar
cannot be taken up by the cells in proper amounts, and that not assimilated
is removed from the blood by the kidneys. This condition is referred to as
diabetes mellitus. An overdose of insulin causes the sugar to be removed
too rapidly from the blood and produces a condition knmvn as "insulin
shock." The treatment for insulin shock is in providing sugar immediately.
The adrenal glands. Because of their position somewhat above and
adjacent to the kidneys, the adrenal glands are also known as suprarenals
and epinephric bodies. Each gland consists of an outer cortical area and
an inner core, or medullary portion. These parts are derived very differently embryonically and produce entirely unrelated hormones.
The medullary portion secretes a hormone most commonly known as
adrenalin. Unlike other endocrine secretions, adrenalin is secreted and
released intermittently under direct influence of nervous conditions. Its
action appears more transitory than that of other hormones; and because
of its activity during periods of stress, adrenalin has been called an emergency hormone.
Adrenalin affects smooth and cardiac musculature and the secretion of
various glands. Thus it functions in a manner suggestive of the autonomic
nervous system. Adrenalin causes constriction of arterioles, but relaxation
in the musculature of the stomach, intestine, uterus, and bronchioles.
Remarkably small amounts result in accelerating and strengthening the
heart beat and cause the liver rapidly to discharge glycogen into the blood.
It also causes increased salivary secretion and brings about a genera11ncrease in the metabolic rate.
Removal of both adrenal bodies have been shown to result in the death
of cats or dogs within 10 or 12 days, even ,vhen adrenalin was supplied
artificially. In these experimental cases, death was due to absence of the
adrenal cortex. The most apparent effects of removing the adrenals
intact is in an upset of water balance and blood volume. Cortical extracts
have been prepared which, when injected, prevent much of the dis~urb­
ances. The hormone is known as cortin, or interrenalin. Extracts containing this hormone appear to be partly effective in treating a disease in '
man known as Addison's disease. Symptoms of the disease are similar to
those of cortical deficiency. There is also considerable evidence to show
that the adrenal cortex has a role in the development of the sex organs and
the formation of secondary sex characters.
THE ENDOCRINE ORGANS
219
• Gonads as endocrine organs. Although the primary function of the
gonads is the production of germ cells, both ovaries and testes produce
chemical regulators. In general, these hormones have to do with proper
development of the reproductive organs and associated secondary characters of sex and reproduction. These hormones may function in connection
with the adrenal cortex.
In the male, the testis produces the interstitial hormone named from
the tissue from which it is secr.eted. This hormone controls the other
tissue of the testis which is sperm-producing (spermatogenic). Absence
of interstitial tissue or castration before puberty results in the failure of
the individual to develop structural and psychic characters assumed by
normal males.
The ovary produces a number of hormones. One functions to bring
about development of female secondary characters, the others with female
cyclic phenomena, including lactation. Some apparently operate closely
with other endocrines. Ovulation sets up a condition that may lead to the
formation of a complex series of hormones. The rupture of the ovary fills
in with a body called the corpus luteum of ovulation. If a pregnancy
ensues, the corpus luteum is persistent and is known as the corpus luteum
of pregnancy. These corpora are quite easily seen on the surface of the
ovary. If they are destroyed, the pregnancy is not maintained. When
pregnancy is maintained, other hormones are formed by the placenta,
some of which resemble ovarian hormones.
Ovulation is correlated with the menstrual cycle in man and apes and
with the somewhat analogous estrus cycle (heat period) in most mammals.
In endocrine studies on reproductive hormones, rabbits have been used
extensively because they do not exhibit these periods. In these forms,
ovulation occurs at mating and the experimenter can predict rather closely
the conditions of the ovary and the stages of pregnancy.
Discussion. Endocrine organs are characteristically present in all
vertebrate animals, from cyclostomes to mammals. None of the invertebrate animals possess endocrine structures that appear homologous with
conditions in the vertebrates. Somewhat analogous conditions, however,
are reported. This feature appears to have been overlooked in the taxonomist's listings of vertebrate characters. The comparative anatomy of the
endocrine organs throughout the vertebrate series is fairly well known,
but systematic studies of the comparative physiology have not progressed
far. Yet it appears that the endocrines have played a major role in evolution. Without adequate thyroid tissue, for example, a tadpole remains a
fish-like form and never acquires the structures that would enable it to
live as a terrestrial animal. Likewise, if man is deprived of thyroid secretion in infancy, the differentiation and development is incomplete and the
victim remains dwarfish and possesses a low mentality and a deficient
metabolic rate.
220
FUNCTIONAL ANATOMY OF THE MAMMAL
Throughout this text, we have been dealing largely with structural evidences of animal relationships, but physiologic evidences of relationships
may appear even more striking. The fact that hormones, drugs, and other
agents behave in a similar manner in so many different types of animal,",
seems remarkable.
The endocrine system illustrates the importance of integration and balance within a body as a whole. Most of what we know about the function
of the system is by disturbing its normal physiologic balance. The norm~l
function of each organ must be assumed from experimental studies on the
influence of excesses and deficiencies of the secretion. These studies are
correlated with clinical cases involving diseased conditions of the endocrine organs.
SUGGESTED PROBLEMS
1. An adrenalectomy refers to the removal (extirpation) of an adrenal gland.
Both glands are removed in a bilateral operation. Determine the poo;ition of an
incision (unilateral) through which the gland could be removed without entering
the body cavity. What vessel would have to be ligated before removing the gland?
2. Male mammals may be sterilized either by removal of the testes or by ligating
the paired vas deferens. In sterilizing the criminally insane, a small section of the
vas deferens is removed (vasectomy). This requires only a skin incision. Determine the position of incision for performing a vasectomy on the cat. How would
early castration affect the individual? Would effects, other than sterilization, be
produced by vasectomy?
3. Describe how a thyroidectomy could be performed. Could all the gland be
removed without also removing the parathyroids? What effects would removal
of both glands produce?
4. Why would ligation of the pancreatic duct produce only digestive disturbances, while removal of the pancreas produce death within a few days?
,Appendix
,
LABORATORY PREPARATION AND PRESERVATION
OF MATERIALS
In some laboratories the specimens may be prepared by the instructor or assistants. The writer has found the method given below to be very satisfactory, and
for muscles and the nervous system particularly, it seems superior to the embalming
methods of commercial supply companies. However, this method requires that
the animal be skinned soon after the injections are made.
Equipment
1. Veterinary injection syringe; metal, 60 to 100 cc. capacity with attachment
for Luer interlocking injection needles.
2. Interlocking needles; (two) size 16, and (two) size 18.
3. Artery clamps; bulldog type, at least three or four.
4. Sharply pointed scissors.
5. Heavy bladed scissors.
6. Bluntly pointed forceps.
7. Carpet thread, or thread of a similar size and strength.
Materials: 95 per cent alcohol; phenol (saturated solution), glycerin (U.S.P.),
formalin (commercial strength), cornstarch in I-pound packages, carmine dye and
Berlin blue dye; thymol crystals.
Formulas for Injection Materials
Embalming Fluid. This is quite concentrated-25 parts phenol, 50 parts glycerin, 10 parts formalin, 15 parts 95 per cent alcohol. About 60 to 100 cc. is necessary for each cat. It should be injected warm but not hot.
Color Mass. Mix 150 cc. glycerin, 150 cc. commercial strength formalin, and
300 cc. water. Add 1 pound of cornstarch slowly, and stir thoroughly. Divide
into two lots: to one, add carmine until well colored; to the other, add Berlin blue.
For double injection, each cat requires about 30 to 40 cc. of the red for arteries
and 40 to 50 cc. of the blue for veins. The starch mass should not be heated and
should be strained through three or four layers of cheesecloth just before using.
Latex is much superior to starch and should be used when available. Animals
should not be skinned for a day or so following latex injection, or until the latex
"sets."
Procedure of Injection
The animal may be killed by any of the usual methods. If the bodies are kept
fairly warm, they are suitable for injection 2 or 3 hours after death. In general,
however, the injection should be done as promptly as possible, and certainly before
rigor mortis has set in.
.
Place the animal on its back, spread the hind legs and tie them down. Split the
skin along the media~ aspect of the thigh with scissors, and carry the incision from
a point slightly above the knee to the body wall. Loosen the skin from the body
waH with the fingers, and carry the incision further toward the back so as fully to
221
222
FUNCTIONAL AKATOMY OF THE MAMMAL
expose the region where the leg joins the body. The skin may be held back fro~
the area by clamping it in position.
With blunt forceps, used as a probe, carefully clear away the connective tissue
to expose the parallel femoral artery and vein as far as side branches will permit...
Pass a thread (4 or 5 inches) under each separately, leaving at least an inch or more
of each vessel between the thread and the body wall. These threads should be tied
tightly to serve in lifting the vessels. The artery lies laterad to the vein and usually
appears empty.
Lift the artery by means of its ligature, and with sharply pointed scissors directed
toward the body make a small incision in it. A few drops of blood serve as a guide
to the point of incision. A 16-gauge needle is next inserted into the artery toward
the body for about 72 inch and is tieq, in place with a single looped knot. Fill the
syringe with warm (not hot) embalming fluid, and with a slow constant pressure
force the fluid into the artery.
A small cat requires no more than 60 cc., but large ones should be given more.
Before detaching the syringe from the needle, place an artery clamp on the artery
above the point of the needle. Make sure the clamp does not strike the point of
the needle. The syringe may now be refilled (either with more embalming fluid
or with color mass as required). After the syringe is refitted to the needle, the
artery clamp is removed and the injection continued. The syringe should 'be
flushed with water after color mass is injected. About 30 to 40 cc. of the red mass
fills the arteries, depending upon the size of the specimen. It is important to maintain a constant and slow flow of the injection mass until considerable back pressure
is developed. After some experience one judges the amount of material to be used
by the resistance or back pressure, but it is better to under-inject than to rupture
vessels by too great a pressure. When the arterial injection is complete, the artery
is again clamped, the needle ,,,ithdrawn from the artery, and the thread pulled into
a tight ligature above the needle incision.
The femoral vein usually stands out clearly following the arterial injection, and
the same procedure follows here except that no embalming fluid is injected into the
vein and blue starch mass is used. Veins cannot withstand so much pressure as
arteries, and care must be taken to inject very slowly. Furthermore, veins possess
valves that frequently prevent injection material from entering them except when
directed toward the heart. Therefore injections only through the femoral vein
usually are incomplete. The blood and color mass together serve to make most of
them recognizable, but if more satisfactory venous injections are required, it is
advisable to bleed the animal and inject also toward the heart through other veins
such as the external jugular.
For an injection of the hepatic portal system it is necessary to open the body
cavity and inject through tributaries leading to the liver.
Further Treatment and Preservation
The skin is now removed (see superficial dissection). When the specimen is
skinned, make an incision about 3 inches long through the abdominal wall about _
I inch from the mid-ventral line and parallel with it. If the urinary bladder is distended, it may be punctured and emptied.
Specimens should be placed in a 5 per cent solution of commercial strength formalin allowing 2 or 3 gallons of solution per specimen. Leave the specimens in
formalin for approximately a week, and then transfer them to a solution consisting
of 15 parts glycerin, 1 part phenol, 10 parts alcohol, with 74 parts water. They
may be packed tightly in this solution. If left a few weeks in the phenol-glycerin
solution, the material needs little further care. They should be wrapped with damp
cloths of the same solution and kept in fairly tight containers'. If dissection work
is begun soon after the formalin treatment, the specimens should be returned to
the glycerin-phenol solution occasionally to prevent drying.
PREPARATION AND PRESERVATION OF MATERIALS
223
PREPARATION OF SKELETAL MATERIAL
A mounted skeleton of the cat should be available to the student to illustrate
tIft) functional relationships of the parts, but for detailed study of separate elements, it is more satisfactory to use the disarticulated bones. These may be prepared from a fresh specimen or from preserved material previously studied. If a
well-bleached white skeleton is desired, the use of a fresh animal usually gives best
results.
The specimen should be skinned, and most of the flesh should be removed by
simply cutting it away. All the internal organs should also be removed without
clipping the osseous portions of the ribs. Since the clavicle of the cat is small and
rudimentary, it should be located and removed separately to avoid losing it. The
forelimbs, not being firmly attached to the vertebral column, should be taken off.
To keep the bones of each appendage together, it is well to place each appendage
in a separate cloth bag.
Cook the material at almost boiling point in a weak soap solution (100 grams
powdered soap to 5 quarts of water) for 2 or 3 hours, or until the flesh can be easily
brushed off in a pan of clean water. A good method is to rub the bones together
in a cloth bag, thereby freeing most of the flesh. The remaining flesh can then be
"panned" from the bones in a large sieve under a tap. A stiff wire brush is most
effective in removing closely adhering tissues. The brain should be broken up with
a bent wire and washed out through the foramen magnum, and care should be
taken to cJean out the foramina of the skull under a tap. The bones may be dried
in the sun, and if not perfectly white and free from grease they should be immersed
for a couple of hours in a solution of hydrogen peroxide to bleach.
With preserved material a stronger soap solution should be used, and the material must be boiled for several hours. The bones are quite satisfactory, however,
with the exception of the ribs which may be clipped. It is desirable to have a skull
sawed in a median sagittal plane and one sectioned in a frontal plane. These sections are best made before removing the flesh from the animal; dissected specimens
not used for complete skeletons serve very well for sectioned skulls.
In case it is desirable to preserve the ligaments, with the view of preparing a
mounted skeleton, high temperatures should be avoided. Young but mature specimens should be selected. First string the vertebral column on a stiff wire, remove
the head at the atlas, remove the forelimbs, and clean off all the flesh that is practical. Heat the parts in a weak soap solution for about 1 hour at a temperature of
75 or 80° C. The flesh of most specimens should brush off without separating the
bones. The length of time in heating depends largely on the age of the specimen.
Another method of preparing skeletal material is to place the bones in an earthen
jar of plain water (with a lid) and allow the adhering flesh to decay. This method
gives good results, and the flesh can usually be removed after 2 weeks by thoroughly
flushing the skeleton with a hose and brushing clean in water. The chief objection to this method is the odor. Obviously, in mounting a specimen certain of the
bones must be wired in place. Detailed instructions on methods for preparing
anatomical material are published as "Turtox Leaflets" by the General Biological
Supply House, Chicago, Ill. They are distributed free to instructors.
PREPARATION OF FETAL MATERiAL FOR STUDY OF BONE FORMATION
A series of stained and cleared fetal kittens (or other mammals) is especially
valuable in the study of the skeletal system. The series should consist of advancing
stages which strikingl1 show the sequences in the ossification of the parts. There
is little ossification in a fetal kitten under 5 cm. long. A satisfactory series may
consist of sets of fetuses of three sizes: about 5,7, and 9 cm. in length. Litter mates
224
FUNCTIONAL ANATOMY OF THE MAMMAL
~
may be divided into two groups, one for bone stain and the other for cartilage.
Avoid using specimens after the hair begins its appearance. The preparation
process requires little work, but considerable time. Two or three months may be
required for larger specimens.
~
The method to be described is Schultze's modification of the Spalteholtz method
and is applicable to small vertebrate animals in general. Fetal specimens taken
directly from a fresh uterus give best results, particularly in bone staining.
Bone Staining
1. Place in 95 per cent alcohol; if formalin-preserved material is used, strongly
color the alcohol with iodine. Leave 3 to 5 days, depending on the size of the
material.
2. Transfer to 1 to 3 per cent aqueous solution of potassium hydroxide; the concentration depending on the size of specimen, and clear until ribs or other superficial skeletal parts become visible. This may require a month or more for large
material, which should be turned occasionally to ensure uniform penetration. This
hydroxide treatment is an important part of the method. Usually best results are
obtained by using weak concentrations of hydroxide over longer periods of time.
The hydroxide disintegrates the tissues of a soft character more rapidly than the·
connective tissues. Consequently, the action is to be stopped when other tissues
are dissolved but while sufficient connective tissue is yet present to hold the specimen in its original morphological form. The specimens may now be stained (3),
but if the appendages appear to be getting too soft, transfer immediately. to Mall's
solution (20 parts glycerin, 79 parts water, and 1 part potassium hydroxide) to slow
the action and harden the appendages.
3. When clearing conditions appear favorable, transfer directly to a stain made
up of a ~d,turated solution of alizarin sodium sulfonate in 95 per cent alcohol, to
which enough 1 per cent potassium hydroxide has been added to produce a clear
burgundy color.
4. Transfer to Mall's solution. For larger specimens, use less glycerin for quicker
results, but if appendages appear in danger of fragmenting use more glycerin. Turn
occasionally to ensure uniformity of action, and keep in strong sunlight to bleach
out any pigmentation that may be present. Allow to remain until destaining is
complete. It may be necessary to change the solution. To prevent mold developing, a small crystal of thymol may be added.
5. Gradually carry the material through stronger concentrations of glycerin until
.in pure glycerin. This may take 2 or 3 weeks.
Cartilage Staining
1. The material may be either in formalin or alcohol. Leave 2 or 3 days in a
solution of 70 per cent alcohol to which a few drops of ammonia has been added.
2. Transfer to a solution made up of 400 cc. 70 per cent alcohol, 2 cc. hydrochloric acid, and 1 gram toluidin blue. This solution should stand for several hours
and be thoroughly mixed and then filtered.
/
3. Stain the specimens for several days at room temperature---J(rgher teinperatures hasten the process if time is limited.
4. Leave in 70 per cent alcohol overnight, and transfer to 95 per cent alcohol to
harden and destain.
5. Clear as for bones, but use weaker concentrations of hydroxide.
6. Transfer to Mall's solution of about one-half concentration.
7. Carry through gradually into pure glycerin.
Litter mates, which have been stained differently, can be ,compared. Cartilage
stains almost black, and the ossified parts in those stained with alizarin are bright
red.
INDEX
A
Abduction, 74
Acetabulum, 46, 48
Adduction, 74
Alveoli, 143
Anomaly, 21
examples of, 162, 163
Aorta, abdominal, 127, 161, 205
arch, 15, 160
thoracic, 126, 159, 203
Aponeurosis, 64, 68
dorsolumbar, 60, 64
external oblique, 82, 99
tensor fascia lata, 101, 104
Aqueduct cerebri, 187
Aqueduct Monro, 181, 187
Arachnoidea (membrane), 117
Arteries, 158-162
Artery, adrenolumbar, 159, 161
axillary, 127, 161
brachial, 159, 161
carotid, 119, 127, 159, 160, 203
caudal, 159, 162
celiac (axis), 159, 161, 205
circumflex (anterior), 161
coronary, 151, 153, 160, 167
costocervical, 159, 160
femoral (deep), 159, 161
gastric, 159, 161
genital (uterine), 159, 161
hemorrhoidal (superior), 159, 161
hepatic, 159, 161
iliac, 159, 162
iliolumbar, 159
intercostal, 159
mammary (internal), 159, 160
mesenteric, 161
inferior, 161, 205
superior, 159, 161, 205
phrenic, 159
pulmonary, 127, 151, 152
renal, 159, 161
spermatic, 170
(See also Artery, genital)
subclavian, 127, 159, 203
Artery, subscapular, 159
thyrocervical, 159
thyroid axis, 159
umbilical, 164
vertebral, 159, 160
Articulations, 52
types of, 54, 55
Artiodactyla, 19
Atrium, 150
Atrophy, 109
B
Bladder, gall, 118, 120, 135, 138, 139, 171,
173
urinary, 126, 176, 179
Blood, 10, 141
Bone, alisphenoid, 31, 34
astragalus, 50, 51
atlas, 37, 38
basioccipital, 31-33
calcaneum, 50, 51
carpal,44
clavical, 42
coccyx, 39
corocoid (process), 42, 43
costal (ribs), 40
cribriform plate, 31, 34, 112
cuboides, 50, 51
cuneiform, 51
dentary, 31, 33, 34
ethmoid, 31, 34, 112
exoccipital, 31
femur, 47-49
fibula, 47, 50
formation, 26-28
frontal, 31, 33, 34
sinus of, 112
general structure, 27
humerus, 43, 44
hyoid, 31, 40, 113
ilium, 46-48
incus, 16
interparietal, 31, 34
ischium, 46-48
lacrimal, 31, 35
225
226
FUNCTIONAL ANATOMY OF THE MAMMAL
Bone, malar (jugal), 31, 33, 35
malleus, 16
maxillary, 31, 33, 34
metacarpal, 45, 46
metatarsal, 51, 52
nasal, 31, 33, 34
occipital, 31
orbitosphenoid, 31, 34
palatine, 31, 33, 34
parietal, 31, 33, 34
patella, 49, 53
petros, 31
phaitlllgeal, 46, 52
pisiform, 45
premaxillary, 31, 33, 34
presphenoid, 31-33
pterygoid, 31-33
pubis, 47, 48
radius, 44, 45
sacrum, 37, 39
scapula, 42, 43
sesamoid, 28, 45, 49
sphenoid, 31
squamosal,31-33
staining technique, 223, 224
stapes, 16
sternum, 25, 40, 41
supr:wccipital, 31-33
tarsal, 50, 51
temporal complex, 31, 32
terms describing, 28, 29
tibia, 49, 50
tympanic, 31-33
ulna, 44, 45
vomer, 31
zygomatic, 31, 33, 34
Brachium, 43
Bronchus, 142, 144
Bulla, tymnanic, 32, 33
C
Canal, alimentary, 130, 131
central, 181, 195
facial, 33
inguinal, 120, 121
lacrimal, 33, 35
neural, 36, 37
Capillaries, 147
Carnivora, 18, 20
Cartilage, arytenoid, 144
costal, 40
cricoid, 40, 144
epiglottic, 113, 144
Cartilage', thyroid, 40, 143
Cavity, buccal, 112
oral, 112
pericardial, 122, 123, 148
peritoneal (abdominal), 119, 121
pleural, 121, 122
thoracic, 119
Cell,7
Cells, of mastoid, 32
Center, cardiac, 191
respiratory, 191
Cerebellum, 188, 191
Cerebrum, 184, 185, 187
Cetacea, 19
Chiasma, optic, 189, 188
Chiroptera, 18
Choana, 112
Clitoris, 6
Cloaca, 17
Cochlea, 208, 213
Colon, 125
Column, vertebral, 36
Commissure, 188, 189
Condyle, lateral, 48, 49
mandibular, 33, 34
medial, 48, 49
occipital, 32, 33
Cord, spermatic, 170, 171
spinal, 181, 194
Corpora cavernosa, 172
Corpora lutea, 174
Corpora quadrigemina, 186, 188, 189
Corpus callosum, 187-1g0
Cortex, cerebral, 187
Cranium (brain case) 29, 32
Crura, penis, 171
D
Dermaptera, 18
Dermis, 61, 62
Diaphragm, 15
Diencephalon, 181, 185
Digestion, 130
Dimorphism, 17
Divergence, 5
Duct, bile, 117, 134, 138
cystic, 135, 138
hepatic, 138
pancreatic, 13g, HO
parotid, 65, 66
sublingual, 114
submaxillary, 114
thoracic, lymph, 127, 156, 166
Ductus arteriosus, 165
INDEX
Ductus choledochus, 134
Ductus deferens, 170, 171
Ductus efferentia, 170, 171
D~denum, 134, 135
Dma mater, 1 n
E
Ear, 208, 213
Endocrine, 12
Epicardium, 148
Epidermis, 61, 62
Epididymis, 170, 171
Epiglottis, 1i3, 116, 144
Epimysium, 68
Epiphysis, 27
Epithelium, 8
Esophagus, 126, 131
Evolution, 5
Extension, 74
Eye, 209, 212
muscles of, 211
Eyelids, 209
F
Fascia, 61
Fauces, pillars of, 116
Felidae, 20
Fenestra, 213
"Flexion, 7 -\, 75
Follicle, hair, 62
ovarian, 174
Foot, 13
Foramen, :facial (carotid), 33, 35
hypoglossal, 35
incisive, 33, 36
infraorbital, 33, 36
jugular, 33, 35
lacrimal (canal), 33, 36
magnum, 32
mental, 33, 36
obturator, 47, 48
optic, 33-35
ovale, 33-35
rotundum, 33, 34, 35
sphenoidal (fissure), 33-35
sphenopalatine (palatine), 33, 36
stylomastoid, 33
supracondylar (epicondylar), of humerus,43
Fornix, 188, 190
Fossa, glenoid, 43
infraspinatus, 43
intercondylar, 48, ~~ ~
intertrochanteric, 48, 49
221
Fossa, m::mdibular, 33, 34
orbital, 32, 35
patellar, 49
pituitary, 32, 112
'i>\lb",~'U,))\.\\."",'i, <!.~
supraspinatus, 43
temporal, 32
G
Ganglia, of dorsal root, 181, 195, 196
of sympathetic trunk, 154, 204
Ganglion, celiac (semilunar), 205
cervical, 154, 203, 204
mesenteric, inferior, 205
superior, 205
nodosum, 203
stellate, 206
thoracic, 154, 204
Girdle, pelvic, 46, 73
thoracic, 42, 73
Gland, adrenal, 125, 155, 159, 218
buccal, 65
Cowper's, 171, 172
lacrimal, 210
lymph (nodes), 65, 66, 136
mammary, 15,63
orbital, 114
parathyroid, 119, 216
parotid, 65, 66
pineal, 188, 189
pituitary (hypophysis), 112, 184, 18S,
215
prostate, 171, 172
sebaceous, 62, 63
sublingual, 65
submaxillary, 65
sweat, 62, 63
thymus, 123, 217
thyroid, 119, 216
Glans, clitoris, 6
penis, 6, 172
Glottis, 116
H
Hair, 15,63
Hallux, 51
Heart, 122, 123, 148
Hermaphroditism, 7
Hippocampus, 189
Hominidae, 20
Homology, phylogenetic, 4
ranial, 'I
serial, 5
228
FUNCTIONAL ANATO:\1Y OF THE MAMMAL
Homology, sexual, 6
Hyoid, 31, 40, 41
Hypertrophy, 109
Hypophysis (see Gland, pituitary)
I
Ileum, 134, 135
Infundibulum, 186
Inguinal canal, 120, 121, 171
Insectivora, 18
Integument, 10, 61
Intestine, large, 125, 136
small, 125, 134
Isles of Langerhans, 218
Iter (see Aqueduct cerebri)
J
Jejunum, 134
Joint, ankle, 56
elbow, 53, 75
hip, 54, 73
knee, 53
shoulder, 54, 73, 94
types of, 53-58,
wrist, 75
K
Kidney, 125, 176, 177
L
Larynx, 113, 143
Ligament, broad, 173, 174
capsular, 53, 54
crural, 106
falciform, 138
inguinal, 99
interosseus, 53
nuchal,97
ovarian, 126
round, of uterus, 126, 173
umbilical, 126
Linea alba, 99
Liver, 124, 135, 137
Lung, 122, 123, 142, 143
Lymph,147
:'IIalleolus, lateral, 50
medial,50
:\Iammalia, 14
:\Iandible, 15
t.farsupials, 18
:'IIassa intermedia, 188-190
:\Iastoid cells, 32
:'IIastoid process, 32, 33
:'IIeatus, external, 32
:'IIediastinum, 123
:'IIedulla oblongata, 181, 184, 186, 191
:\Iembrane, arachnoid, 117
mucous, 8, 130
olfactory, 112
pericardial, 148
serous, 8, 122, 123, 130
synovial, 54
tympanic, 213
:\Ieninges, 102, 180
:\Iesencephalon, 181, 185
:\Iesentery, dorsal, 122, 124
:'IIetacromion, 43
!\Ionotremata, 17
:'IIucosa, 130, 131
:!'IIuscle, adductor brevis, 102, 103
longus, 102, 103
femoris, 102, 103, 105
anconeus, 86, 87
biceps, brachii, 86, 91, 93
femoris, 101, 102, 104, 105
brachialis, 86, 87
cleidomastoideus, 65, 82, 83
coracobrachialis, 84, 85
cutaneous, 60, 68
deltoideus, 71, 79, 109
acromio-, 81, 84, 85
clavo-, 81, 84
spino-, 81, 84, 85
digastric, 97, 98
e,;tensor carpi radialis brevis, 88, 89, 91
longus, 88, 89, 91
carpi lateralis, 88, 89
ulnaris, 88, 89
digiti quinti, 88
digitorum communis, 88, 89
lateralis, 88, 89
longus, 105, 107, 108
indices, 88, 89
pollicus brevis, 88
external oblique, 79, 99
facial, 61
flexor carpi radialis, 91, 92
ulnaris, 87, 91, 92
digitorum longus, 107, 108
profundus, 87, 91, 92
sublimis, 91, 92
longus hallicuO>, 105, 107, 108
pollicus brevis, 87, 88, 89
INDEX
MUjcle, gamellus inferior, 103
superior, 103
gastrocnemius, 101, 105-107
gluteus maximus, 101-103
, medius, 101-103
minimus, 103
gracilis, 102, 104, 105
histologic types, 8-10
iliopsoas, 103, 200
infraspinatus, 80, 85
intercostal, 94, 95
internal oblique, 99
latissimus dorsi, 78-80
levator costarum, 94, 95
scapula, 79, 80, 83
levator scapulae ventralis, 79, 81, 83
longissimus dorsi, 96, 97
masseter, 65, 66, 97, 98
pectoantibrachialis, 78, 81, 82
pectoralis major, 79, 81, 82
minor, 79, 81, 82
peroneus, brevis, 102, 107, 108
longus, 102, 107, 108
tertius, 102, 107, 108
plantaris, 105, 107
platysma, 68
popliteus, 105, 107
pronator quadratus, 57, 91, 93
teres, 57, 91, 93
psoas minor, 103, 200
pterygoid, 97, 98
quadriceps femoris, 101, 104
rectus abdominis, 82, 99, 100
femoris, 101, 104, 105
rhomboideus major, 78, 79, 83
minor, 78, 79, 83
capitus, 78, 79
sartorius, 79, 104, 105
scalenus, 93-95
semimembranosus, 101, 104, 105
semitendinosus, 101, 104, 105
serratus anterior, 79, 80, 83, 96
posterior inferior, 80, 94
superior, 94
skeletal, as organs, 68, 69
soleus, 102, 103, 106, 107
splenius, 80, 97
sternohyoideus, 82, 96, 97
sternomastoideus, 65, 82, 83
sternothyroideus, 96, 97
subscapularis, 84, 85, 93
superficial (of man), 71, 72
supinator, 88, 90
supraspinatus, 80, 81
Muscle, temporalis, 97, 98
tensor fascia lata, 101, 102, 104
_teres major, 80, 84, 85
minor, 84, 85
thyrohyoideus, 96
tibialis anterior, 101, 102, 107, 108
posterior, 105, 107
transverse abdominal, 99, 101
costarum, 95
trapezius, of man, 72, 78
acromio-, 78, 80, 81
clavo-, 78, 80, 81
spino-, 78, 80, 81
triceps brachii, 86, 87
vastus intermedius, 104
lateralis, 102, 104
medialis, 104, 105
xiphihumeralis, 79, 81, 82
Muscle action, types of, 73-76
Nerve, abducens, 186, 194
anterior crural, 201
auditory (acoustic), 186, 194
axillary, 93, 198
cardiac, 154, 203, 204
chorda tympana, 192
cranial, 192
cutaneous, 60
facial, 65, 186, 194
genitocrural, 201
glossopharyngeal, 186, 194
gluteal, 202
hypoglossal, 186, 194
internal cutaneous, 93, 198
mandibular, 193
maxillary, 193
median, 93
musculocutaneous, 93, 198
musculospiral, 93, 198
obturator, 201
oculomotor, 186, 193
olfactory, 193
ophthalmic, 193
optic, 186, 193
peroneal, 202
phrenic, 123, 203
plexus, brachial, 93, 197
lumbar, 200
sacral, 201
posterior hemorrhoidal, 202
radial,93
sciatic, 201, 202
229
230
FUNCTIONAL ANATOMY OF THE MAMMAL
Nerve, spermatic, 120
spinal, accessory, 186, 194
of cat, 196
splanchnic, 205
subscapUlar, anterior, 93, 198
middle, 93, 198
posterior, 93, 198
suprascapular, 93, 198
sympathetic, 127
thoracic, anterior, 198
posterior, 198
trigeminal, 193
trochlear, 186, 193
ulnar, 93, 198
vagus, 127, 194
Nervous system, autonomic, 182,
central, 182
peripheral, 182
Nipples, 21, 63
o
Olecranon, 44
Olives (olivary bodies), 190
Omentum, greater, 124, 125
lesser, 124, 125
Ontogeny, 164
Ossicles, auditory, 213
Osteoblasts, 23
Osteoclasts, 23
Ostium tubae, 173
Ovary, 173-175
Oviduct, 173, 174
P
Palate, 112
Pancreas, 125, 135, 139
Pelvis, bony, 46, 48
renal, 171, 177, 178
Penis, 6
Pericardium, 122,148
Perineum, 137
Periostium, 23, 27
Perissodactyla, 19
Peritoneum, 121, 122
Peyer, lymph nodules of, 137
Pharynx, 115
Phylogeny, 164
Placenta, 175
Pleura, 121, 122, 142
Plexus, brachial, 197
cardiac, 204
choroid, 187, 188
20~
Plexus, lumbar, 200
sacral, 201
solar (celiac, mesenteric), 205
Pollex, 46
Polydactylism, 52
Pons, 188, 189
Portal system, 135, 156, 158
Prepuce, 172
Primates, 18, 20
Proboscidia, 19
Process, accessor, 37
acromion, 43
articular, 37
of dentary, 33
of ulna, 45
coracoid, 43
coronoid, 44, 45
mastoid, 32, 33
odontoid, 38
postorbital, of frontal, 33, 35
of malar, 33, 35
spinous, 37
styloid, 45 ..
transverse, 37
xiphoid, 40, 41
zygomatic, 33, 34
Pronation, 57
Prosencephalon, 185
Pyloris, 133, 134
Pyramid, of brain, 184, 186
renal, 177, 178
R
Rectum, 137
Reproduction, 169
Respiration, 141
Retina, 211, 212
Rhombencephalon, 185
Ridge, deltoid, 43, 44
pectoral, 43, 44
Rib, 16, 39, 40
Rodentia, 19
Sac, scrotal, 59
Sacculus, 213
Sacrum, 37, 39
Sclera, 210
Scrotum, 59, 120, 170
Sinus, ethmoid, 116, 117
frontal, 112, 116
maxillary, 116, 117
sphenoidal, 112: 116