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ROSWELL P. FLOWER
FOR THE USE OF

THEN. Y. STATE VETERINARY COLLEGE
1897

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1897
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CORNELL UNIVERSITY. Fy. fe:
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Roswell P. Flower Library
THE GIFT OF

8394-1

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ELEMENTS

OF THE

COMPARATIVE ANATOMY

OF

VERTEBRATES

0.123

ELEMENTS

OF THE

COMPARATIVE ANATOMY

OF

VERTEBRATES

ADAPTED FROM THE GERMAN OF

DR. ROBERT WIEDERSHEIM

PROFESSOR OF ANATOMY, AND DIRECTOR OF THE INSTITUTE OF HUMAN AND COMPARATIVE ANATOMY
IN THE UNIVERSITY OF FREIBURG-IN-BADEN

BY
W. N. PARKER, Px.D.

PROFESSOR OF BIOLOGY AT THE UNIVERSITY COLLEGE OF SOUTH WALES AND MONMOUTHSHIRE
IN THE UNIVERSITY OF WALES

SECOND EDITION

(FOUNDED ON THE THIRD GERMAN EDITION)

WITH THREE HUNDRED AND THIRTY-THREE WOODCUTS
AND A BIBLIOGRAPHY.

Londvon
MACMILLAN AND CO., Liurep

NEW YORK: THE MACMILLAN COMPANY

1897

All rights reserved

on a

& OS Ricuarp Cuxy ann Soxs>

“LONDON AND BUNGAY.

WeoFe Nys [a3
16977

4IMITED

PREFACE TO THE FIRST EDITION

PROFESSOR WIEDERSHEIM’S Grundriss der vergleichenden
Anatomie der Wirbelthiere, published at Jena in 1884, was written
to supply a need which had been felt forsome time past for a short
text-book on Vertebrate Anatomy embodying some of the more
recent views on the subject. The present book is a modified
translation of the Grundriss, and it is hoped that it will serve to
render Professor Wiedersheim’s work more widely known amongst
English students.

The plan of the original has been retained throughout, though
numerous additions and modifications have been made to the work ;
for many of these I have to thank Professor Wiedersheim,—for
others I am myself responsible. I must also express my
indebtedness to Professor Wiedersheim for revising the whole
translation with me last summer, and for much help while the
work was in progress.

Within the limits of a short text-book like the present, much
of the matter is of necessity greatly condensed: more detailed
accounts of the various parts and organs will be found in the new
edition of Professor Wiedersheim’s Lehrbuch der vergl. Anatomie
der Wirbelthiere, which is to appear shortly, and on the first edition

of which the Grundriss was founded.

vi PREFACE

The brevity of the descriptions is, however, to some extent
made up for by the number of woodcuts. Most of these are taken
from the German edition, but several new figures have been
added.

The arrangement of the book according to organs, and not
according to groups of animals, is likely to render it more difficult
for a beginner, and a general knowledge of Zoology will be of
great assistance. The pages on which the different groups are
described are, however, collected together in the index, so that the
sections relating to any one group can be easily referred to. The
present arrangement seems to be the only possible one if the book
is to be founded on a scientific basis, for it is most important that
the student should grasp the fact that there has been an evolution
of organs, as well as of animals.

The more theoretical and detailed matter is printed in small
type, and in the form of notes: the student should in most cases
pass this over when reading the book for the first time. A black
and a spaced type have been used to render prominent important
words or sentences.

A bibliography is appended at the end of each chapter. This
in no case presumes to be anything like a complete list of the
literature of the subject: our object has been more particularly
to mention the recent and the more important works, though many
of these have doubtless been omitted. References to other re-
searches can be found by consulting the works mentioned.

At Professor Wiedersheim’s suggestion, I have not inserted a
translation of the preface to the original, as it seemed unnecessary
so todo. I may, however, mention that the book was written for
students of Medicine, as well as for those of Comparative Anatomy :

the intimate connection of the two subjects renders it most

PREFACE vii

important that medical students should have a general scientific
basis for their special anatomical knowledge,

My sincerest thanks are due to my friends Professors F. Jeffrey
Bell and G. B. Howes, who have kindly read through the proof-
sheets. To them J am indebted for numerous valuable suggestions,
as well as for correcting many faults of style and expression which
had escaped my notice. I must also express my thanks to my
father, Professor W. K. Parker, and to Dr. Gadow, for many special
details in connection with the skeleton, as well as to Mr. E.
Radford for help in making the index.

W. N. PARKER,

UNIVERSITY COLLEGE, CARDIFF,
May, 1886.

PREFACE TO THE SECOND EDITION

SINCE the publication of the first edition of the Grandriss, on
which the first English edition was founded, two further German
editions have appeared, one in 1888 and another in 1893, the
latter containing 695 pages as compared with 272 pages in the
first edition. The book has, in fact, grown beyond the limits of
a “Grundriss,” and has replaced the original Lehrbuch, no new edition
of which has appeared since 1886.

As it seemed desirable that the second English edition
should be brought up to date without greatly exceeding the
limits of the first, it has been necessary to use a free hand
in abridging and recasting the text. I have therefore, with
the author's permission, attempted to prepare a short text-
book which, while retaining the original descriptions and
arrangement as far as possible, should deal with the more
essential and well-ascertained facts of Comparative Anatomy,
presenting an approximate equality of treatment as regards its
different sections without entering too fully upon doubtful
theories or special details in Embryology and Physiology.

The book has thus been almost entirely rewritten, with the
approval of Professor Wiedersheim, who, besides revising the

work, has furnished me with much new material. A number

PREFACE ix

of the old figures have been replaced and several additional
ones inserted.

The bibliography appended to the book, which has been
considerably added to by Professor Wiedersheim since the third
German edition was published, is rather extensive for a work
of the kind, but I have not ventured to make selections from it
and have merely modified the arrangement in some respects and
made a few additions which seemed to me important for English
readers. It will, I trust, be found useful by more advanced students.

I must acknowledge my obligations to my brother, Professor
T. Jeffery Parker, F.R.S., for numerous suggestions, and also
to Professor G. B. Howes, F.R.S., Mr. Frank J. Cole, and Mr.
Martin F. Woodward for valuable information on several special

points.
W. N. PARKER.

UNIVERSITY COLLEGE, CARDIFF,
April, 1897.

CONTENTS

Preface to the First Edition . v
Preface to the Second Edition ne viii
INTRODUCTION ; ets ee |
I. On the Meaning and Scope of Comparative Anatomy . 1

II. Development and Structural Plan of the Vertebrate Body . ; 2
JII. Classified List of the Principal Vertebrate Groups. . . 13

IV. Table showing the Gradual Development of the Vertebrata in Time . 15

SPECIAL PART.

A. INTEGUMENT am ah Sica dings Eee & a. vetercpie 1G
of Amphioxus, Fishes, and Dipnoans . ORG 16

of Amphibians es. tye a & 18

of Reptiles. .... 2... s 3 4 - 20

of Birds . Paar ee 20

of Mammals t 2% is 23
Mammary Glands. . : ag , 2

B. SKELETON . . . . ..... enlg = . 30

1. EXOSKELETON .. .. . ‘ « «a5 30

2. ENDOSKELETON .. ...... : er . Bt

I, VERTEBRAL COLUMN. . 2 ae 4 lids 34

of Fishes and Dipnoans ... ‘ F : 36

of Amphibians . rr ee ee o 8 BR go ote fees

of Reptiles. . -_ 45

of Birds . a : ; ; ‘ 47

of Mammals ac 2 ra 49

Il RIBS . . 2 52
of Fishes and Digudane ; ot
of Amphibians ‘ ‘ 55
of Reptiles . 5 y. 8 56
of Birds 56

of Mammals

v

Xil CONTENTS

PAGE

Ill. STERNUM 38
IV. EPISTERNUM 62
Vv. SKULL 64
Introduction ' - z - 64

u. Brain-case (cranium)... ... 2... e 7

u. Visceral Skeleton 5. 69

c. Bones of the Skull . . 2... 70
Anatomy of the Skull (special part) 12

A. The Skull of Fishes 72

B. é6 of Dipnoans P 81

c. ss of Amphibians 82

D. 5 of Reptiles . 838

E. a6 of Birds . . 93

F. Ae of Mammals : 96

VI. LIMBS. . 3 102
a. Unpaired Bie: 102

», Paired Fins or Limbs. . 103
Pectoral Arch ap tls : 106

of Fishes and Dipnoans 106

of Amphibians ‘ aN 107

of Reptiles -. los

of Birds ols bea ; » » 109

of Mammals 2 Z 109

Pelvic Arch . . . 109

of Fishes . 109

of Dipnoans : : lll

of Amphibians F . ill

of Reptiles ey . ll4

of Birds are soa ES

of Mammals er ae . 120

Free Limbs .. ; 122,

of Fishes and Dipnoans é 7 a a b2224

Phylogeny of the Ichthyopterygium i: 124
General Considerations on the Limbs of the higher sp ciesbiaks 125

Free Limbs of Amphibians... . ‘ 127

of Reptiles . fe eens a ee ee 17

of Birds : So oe 3 ‘ « 129

of Mammals i Boe a : s 2 «iw ves 180

C. MUSCULAR SYSTEM . gn Sg heres igat Rhu. oJ . 135
INTEGUMENTARY MUSCULATURE . 2... ‘ ; . . . 136
MUSULES OF THE TRUNK... i x “ ae
of Amphioxus, Fishes, and Dionoues Ss 137

of Amphibians... 00... 0 1. . 137

of Reptiles... ¢ 244 gee w © 4 ao soa ABS

CONTENTS

MUSCLES OF THE TRUNK (continued)—

of Birds

of Mammals
MUSCLES OF THE DIAPHRAGM
MUSCLES OF THE APPENDAGES
EYE-MUSCLES

VISCERAL MUSCLES

of Fishes .

of Amphibia

of Amniota .

D. ELECTRIC ORGANS .

E, NERVOUS SYSTEM AND SENSORY ORGANS

I. CENTRAL NERVOUS SYSTEM

MEMBRANES OF THE BRAIN AND SPINAL CORD

1, SPINAL CORD

2, BRAIN (general description saa development)

of Cyclostomi

of Elasmobranchii and Holocephali

of Ganoidei
of Teleostei
of Dipnoi
of Amphibia .
of Reptiles .
of Birds .
of Mammals
II. PERIPHERAL NERVOUS SYSTEM
l. SPINAL NERVES
2, CEREBRAL NERVES
Sympathetic

III. SENSORY ORGANS (general dtdsredi nites swt dnveloprenity’

SENSE-ORGANS OF THE INTEGUMENT .
a. Nerve-Eminences
b. End-Buds . ‘
. Tactile Cells and ivonsdbe
d. Club-shaped Corpuscles . .

OLFACTORY ORGAN (general description and development) . . . .

of Cyclostomes

of Fishes .

of Dipnoans

of Amphibians

of Reptiles

of Birds

of Mammals
Jacobson’s Organ

Xiil
PAGE

140
140
141
142
142
142
142
143
144

xiv CONTENTS

EYE (general description and development)
of Cyclostomes . «
of Fishes and Dipnoans
of Amphibians
of Reptiles and Birds
of Mammals
Retina . 3 i
Accessory Organs in Connentton with the ae
a. Eye-Muscles
b. pee aes :
. Glands :
AUDITORY ORUAN (general descr ‘tion silt development)
of Cyclostomes
of Fishes and Dipnoans
of Amphibians : re ee ae
of Reptiles and Birds
of Mammals
F. ORGANS OF NUTRITION
ALIMENTARY CANAL AND ITS APPENDAGES een descrip-
tion)
I. MOUTH
Teeth (general description)
of Fishes, Dipnoans, and Amphibians .
of Reptiles and Birds
of Mammals
Glands of the Mouth
of Amphibians
of Reptiles .

of Birds
of Mammals . 4 pe ee
Tongue
THYROID
THYMUS

IL (ESOPHAGUS, STOMACH, AND INTESTINE
of Ichthyopsida .
of Reptiles
of Birds
of Mammals .
Histology of the Mucous Membrane of the Alimentary Canal
LIVER .
PANCREAS

G. ORGANS OF RESPIRATION
I. GILLS
of Amphioxus
of Cyclostomes

wok
~I

St Uo os

wow Ww Ww
rar re res |

CONTENTS

GILLS (continued)—
of Fishes
of Dipnoans
of Amphibians ‘
II. AIR-BLADDER AND LUNGS
1. AIR-BLADDER
2. LUNs
Air Tubes and iat
of Dipnoans
of Amphibians
of Reptiles .
of Birds
of Mammals
Lungs proper
of Dipnoans
of Amphibians
of Reptiles
of Birds
of Mammals
ABDOMINAL PORES

H. ORGANS OF CIRCULATION
General Description and Development
Heart, together with Origin of Main Vessels
of Fishes . ;
of Dipnoans
of Amphibians
of Reptiles .
of Birds and Mammals
Arterial System
Venous System
of Fishes .
of Dipnoans
of Amphibians
of Amniota
Retia Mirabilia .
Lymphatic System
MODIFICATIONS FOR THE INTER- UTERINE NUTRITION oF
THE EMBRYO: F@ITAL MEMBRANES
1. Anamnia
2. Amniota

I, URINOGENITAL ORGANS
General Description and Development
Male and Female Generative Ducts .
Gonads

xvi CONTENTS

PAGE

URINARY ORGANS 349
of Amphioxus Pak ‘ - 349

of Cyclostomes, Fishes and Dipnoans . e 2% 350

of Amphibians 352

of Reptiles and Birds 356

358

of Mammals jatencs : : 2.3 ‘
GENERATIVE ORGANS ate F st, 8 . 359
of Amphioxus 2g . 359

of Cyclostomes 359

of Fishes and Dipnoans . . . 360

of Amphibians 7 365

of Reptilesand Birds .... .. dis 8) . 368

of Mammals 370
COPULATORY ORGANS . .... s eH 377
SUPRARENAL BODIES ae : 385
APPENDIX (Bibliography). . .. . ‘ : 389

TIN DEX 3030 Wace a ac a ae GS : 481

COMPARATIVE ANATOMY

INTRODUCTION.
I. ON THE MEANING AND SCOPE OF COMPARATIVE ANATOMY.

A KNOWLEDGE of the natural relationships and ancestral history
of animals can only be gained by a comparative study of their
parts (Comparative Anatomy) and of their mode of develop-
ment (Embryology or Ontogeny). In addition to existing
animals, fossil forms must also be taken into consideration ( Pa-
leontology), and by combining the results obtained under these
three heads, it is possible to make an attempt to trace out the
development of the various races or groups in time (Phylogeny).
As the different phases of development of the race may be repeated
to a greater or less extent in those of the individual, the depart-
ments of Ontogeny and Phylogeny help to complete one another.

It must, however, be borne in mind that in many cases the
phases of development are not repeated accurately in the individual
—that is, are not palingenetic,—but that “ falsifications” of the re-
cord, acquired by adaptation, very commonly occur along with
them, resulting in cenogenetic modifications in which the original
relations are either no longer to be recognised at all, or are more
or less obscured. In this connection, two important factors must
be taken into consideration, viz., heredity and the capability of
variation. The former is conservative, and tends to the retention
of ancestral characters, while the latter, under the influence of
change in external conditions, results in modifications of structure
which are not fixed and unalterable, but are in a state of constant
change. The resulting “ adaptations,” so far as they are useful to
the organism concerned, are transmitted to future generations,
and thus in the course of time gradually lead to still further
modifications. Thus heredity and adaptation are parallel factors,
and a conception of the full meaning of this fact helps us not only
to gain an insight into the blood-relationships of animals in gene-

ral, but also to understand the meaning of numerous degenerated
B

Z COMPARATIVE ANATOMY

and rudimentary or vestiyial organs and parts in the adult organism
which would otherwise remain totally inexplicable.

Histology is a subdivision of anatomy which concerns the
structural elements—the building-stones of the organism, and the
combination of these to form tissues. Various combinations of
the tissues giye rise to organs, and the organs, again, combine to
form systems of organs.

The structural elements consist primarily of cells and second-
arily of cells and fibres, and the different tissues may be divided
into four principal groups :—

1. Epithelium, and its derivative, glandular tissue.

2. Supporting-tissue (connective-tissue, cartilage, bone).

3. Muscular tissue.

4, Nervous tissue.

Tn accordance with the functions they perform, epithelium and support-
ing-tissue may be described as passive, and muscular and nervous tissue as
active.

By an organ we understand an apparatus constructed to
perform a definite function: as, for instance, the liver, which
secretes bile; the gills and lungs, in which an exchange of
gases is effected with the surrounding medium; and the heart,
which pumps blood through the body.

The organ-systems, which will be treated of in order in this
book, are as follows:—1. The outer covering of the body, or 7ite-
gument ; 2. The skeleton; 3. The muscles, together with electric
organs; +. The nervous system and sense-organs; 5. The organs
of nutrition, respiration, circulation, excretion, and reproduction.

The closely-allied branches of science defined above are united
together as Morphology, as opposed to Physiology which con-
cerns the functions of organs, apart from their morphological rela-
tions. The results obtained from these two fields of study help to
complete one another, and thus to throw light on the organisation
of animals in general—that is, on Zoology in its widest sense.

II. DEVELOPMENT AND STRUCTURAL PLAN OF THE
VERTEBRATE BODY,

The structural elements described in the preceding section as
the building-stones of the organism, i.. the cells, all arise from a
single primitive cell, the egg-cell or ovum. This forms the
starting-point for the entire animal-body, and a general account
of its structure and subsequent development must therefore be
given here.

The ovum consists cf a rounded vesicle (Fig. 1), in the interior
of which the following parts can be distinguished :—the vitellus,,

INTRODUCTION 3

the germinal vesicle, and one or more germinal spots. The outer
covering of the ovum is spoken of as the vitelline membrane.

Since the ovum in its primitive form as above described repre-
sents a single cell, we may speak of the vitellus! as the protoplasm
of the egg-cell, the germinal vesicle as its nucleus, and the germinal
spot as its nwcleolus. The cell-nucleus is enclosed by a delicate
nuclear membrane, and is made up of two constituents—the
spongioplasm or chromatin, and the hyaloplasm or achromatin.
One or two small particles, the centrosomes, are also present in
the cell-body, and take an important part in the process of cell-
division. An outer limiting membrane, corresponding to the
vitelline membrane, is not an integral
part of the cell, but may be ditferen-
tiated as a hardening of the peripheral
protoplasm.

In sexual reproduction, such as (oN KB
occurs in all Vertebrates, the fusion of D------
the sperm-cell, containing the genera-
tive substance of the male, with the
ovum, is an absolute necessity for the
development of the latter. Fie, 1,—DracrkaM OF THR

But before this can occur, certain UNIMPREGNATED OvuM.
changes take place inthe ovum, which p, vitellus; AB, germinal
are known as maturation. Thiscon- vesicle; A, germinal spot.
sists of a twice-repeated process of cell-
division (karyokinesis) similar to that which occurs in tissue-
cells, except that the resulting daughter-cells are of different
sizes, two small nucleated polar-cells (Fig. 2) being successively
thrown off from the larger ovum, the portion of the original
nucleus remaining in the ovum being known as the “femals
pronuctcus.” A sperm-cell (spermatozoon) then makes its way into
the ovum, and its nucleus (the male pronweleus) unites with the
female pronucleus to form the segmentation nucleus. This
process, which is known as impregnation or fertilisation, thus
consists in a material fusion of the generative substances of both sexes,
or more accurately of the sperm-nucleus and egg-nucleus. The essential
cause of inheritance can thus be traced to the molecular structure of
the nuclei of both male and female germinal cells. This structure
is the morphological expression of the characters of the species.

After fertilisation has taken place development begins. The
segmentation nucleus divides into two equal parts, each of which
forms a new centre for the division of the oosperm, as it must
now be called, into two halves or blastomeres. This division, the
beginning of the process of segmentation, takes place by the
formation of a furrow round the egg which becomes deeper and
deeper until the division is complete. (Fig. 2, a).

AF

1 The vitellus consists of two different substances—protoplasm and deutero-
plasm (yo/k)—in varying proportions in different animals,

an RY

4 COMPARATIVE ANATOMY

The first stage in the process of segmentation is thus com-
pleted; the second takes place in exactly the same way, and
results in a division of the oosperm into four parts, and by a similar
process are formed eight, then sixteen, then thirty-two blastomeres,
and so on, the cells becoming smaller and smaller, and each being pro-
vided with a nucleus (Fig. 2C—D). In short, out of the original
oosperm a mass of cells is formed which represents the building-
material of the animal body and which, from its likeness in appear-
ance to a mulberry, is spoken of as a morula.

In the interior of the morula a cavity (seymentation cavity or

Fig. 2.—DIAGRAMS OF THE SEGMENTATION OF THE OOSPERM.

A, first stage (two segments): RK, polar cells. B, second stage (four segments).
C, further stage. D, morula stage.

blastocele) filled with fluid is formed, and the morula is now spoken
of as the blastosphere or blastula (Fig. 3). The peripheral cells
enclosing this cavity form the germinal membrane or blasto-
derm. Consisting at first of a single layer of cells, the blastoderm
later on becomes two- and then three-layered. From the relative
positions of these, they are spoken of respectively as the outer,
middle, and inner germinal layers, or as epiblast, (ectoderm, )
mesoblast, (mesoderm,) and hypoblast (endoderm).

An increase in the amount of food-yolk (deuteroplasm, see note on
p. 3) present in the ovum results in certain modifications of the primi-
tive process of segmentation as described above. Yolk is an inert

INTRODUCTION 5

substance, and its presence tends to hinder or even entirely to
prevent segmentation in those parts of the ovum in which it is
abundant. When the whole ovum undergoes division, the
segmentation is known as entire or holoblastic; when division is
restricted to part of the ovum
only, the segmentation is said
to be partial or meroblastic}
(Fig. 4).

The question as to the origin
of the germinal layers, on ac-
count of its important significa-
tion, is one of the most burning
problems in Morphology, and
as yet we cannot arrive at any
full and satisfactory conclusion
on the subject. It may, how-
ever, he affirmed with certainty

that in all Vertebrates the Fic. 3.—BLAsTospHERE.
blastosphere passes—or did so BD, blastoderm; FH, segmentation
in earlier times—into a stage cavity.

called the gastrula. One
must imagine this form as being derived primitively from the
blastula by supposing that the walls of the latter (Fig. 3) became
pushed in or invaginated at one part, thus giving rise to a double-
walled sac (Fig. 5). The outer wall then
represents the epiblast, which functions
as an organ of protection and sensation,
while the inner, or hypoblast, encloses
a central space, the primitive intestinal
cavity (archenteron), and represents the
assimilating and digestive primary ali-
mentary canal. The opening of the
latter to the exterior, where the two
germinal layers are continuous, represents
Fic. 4.—DracramoraMer- the primitive mouth or blastopore

OBLASTIC OosrERM WITH (Fig. 5).

Discoin Sutras MnrOs. Out of the epiblast arise later the
Bla, blastoderm ; Do, yolk. epidermis and its derivatives, the entire
nervous system, the sensory cells, the
crystalline lens of the eye, and the oral and anal involutions
(stomodewm and proctodeum). In an early stage the hypoblast
gives rise to an axial rod, the notochord (see p. 9), and eventually
to the epithelium of the greater part of the alimentary canal

1 In holoblastic segmentation the resulting cells are approximately «qua/ in
the Lancelet and in Mammals (with the exception of Monotremes) ; and unequal
in the Cyclostomes, Sturgeon, Lepidosteus, Ceratodus, and nearly all Amphibians,
the segmentation sometimes approaching the meroblastic type. In Elasmo-
branchs, Teleosts, Reptiles, Birds, and Monotremes the segmentation is meroblastic
and discoid, t.e., restricted to the upper pole of the ovum (Fig. 4).

6 COMPARATIVE ANATOMY

(Fig. 6, A and B) with its glands, including the thyroid, thymus,
liver and pancreas, as well as to the epithelial parts of the gill-
sacs and lungs.

Though we may look upon the epiblast and hypoblast,—that
is, both the primary germinal layers—as arising in the manner
above described, the problem as to the origin of the mesoblast is as
yet by no means settled. All that can be said at present is briefly
as follows :—The mesoblast is a secondary formation, and is phylo-
genetically younger than the other two germinal layers; both
as regards the origin of its cells and_ histologically, it is of a com-
pound nature, and thus forms a marked contrast to the germinal
layers proper. Reminding one in many points of the “ mesenchyme”
of Invertebrates, it always arises at first from the point where

Fic. 5.—GASTRULA.

Lkt, epiblast ; Ent, hypoblast ; B/p, blastopore ; C, archenteron.

epiblast and hypoblast pass into one another, that is, from the
region of the blastopore, or, what comes to the same thing in the
higher Vertebrates, from the primitive streak. Originating from
between the other two layers, one of its first and most important
functions is the formation of d/oced-cells; later it gives rise to the
heart, vessels, supporting and connecting substances (connective-tissue,
adipose tissue, cartilage, and bone), serous membranes (peritoneum,
pleura, pericardium, arachnoid), muscles, and almost the entire
exerctory and reproductive apparatus.

A cleft appearing in the mesoblastic tissue divides it into a
parietal or somatic (ayer (Fig. 6, A and B), lying along the inner
side of the epiblast, and into a visceral or splanchnic layer, which
becomes attached to the outer side of the hypoblast. The former,
together with the epiblast to which it is united, constitutes the

INTRODUCTION 7

Fic. 6, A AND B.—DIAGRAMMATIC TRANSVERSE SECTIONS THROUGH A DEVELOPING
VERTEBRATE EMBRYO.

D, alimentary canal; Hut, hypoblast, showing in Fig. A the thickening (Ch) which
will form the notochord ; Ch! (Fig. B), the notochord now constricted off from
the hypoblast ; UH", mesoblastic somite ; UG, primary urinary duct (pro-
nephric duct); A, aorta; SP, splanchnic and Sop, somatic mesoblast ;
Co, Cal, celome; H, remains of the upper part of the ccelome in the
interior of the mesoblastic somites; Zit, epiblast; Med, central nervous
system (medullary cord) :—in Fig. A it is shown still connected with the
epiblast, from which it has become constricted off in Fig. B.

8 COMPARATIVE ANATOMY

somatopleure, and the latter, together with the hypoblast, the
splanchnopleure. The cavity separating these is the body cavity,
or celome (Fig. 7), and is lined by an epithelium. The dorsal
part of the mesoblast which lies on either side of the middle line
early becomes transversely segmented to form a series of nesoblastie
somites or protovertebree, which lose their cavities (Fig. 6, A and B)
and are concerned in the formation of the vertebral column, body
muscles, and urinogenital apparatus. ;

As a general rule a thickened disc-shaped region can be recog-
nised at a certain stage of development on the dorsal pole of the

Fie. 7.—DIAGRAMMATIC TRANSVERSE SECTION THROUGH THE Bopy oF AN ADULT
VERTEBRATE.

Med, spinal cord ; NR, neural tube ; KW’, body-wall ; Co, dermis ; Hy, endodermic

epithelium of alimentary canal (intestine); MR, visceral tube; 0, aorta ;

Ms, mesentery ; Per, parietal layer of the peritoneum ; Per', visceral layer of

the peritoneum ; J/sc, muscular coat of intestine ; Subm, connective-tissue coat

of intestine ; DH, lumen of intestine ; II’, vertebral centrum with dorsal arch.

oosperm: this is the so-called embryonte area, and on it the first
indications of the body are seen. This region gradually becomes
constricted off from the yolk by the formation of furrows at its
anterior and posterior ends as well as laterally, and consequently
the connection of the body-rudiment with the ventral yolk-sae (the

1 The ceelome may arise as a segmentally arranged series of pouches
(enteroceles) from the archenteron, in which case its lining epithelium is at first
continuous with the hypoblast, as is most plainly seen in Amphioxus ; or it may
be formed secondarily by a splitting (delamination) of the mesoblastic tissue
(schizocele). The first of these must be considered as the more primitive.

INTRODUCTION i]

vitello-intestinal duct) is reduced in size, and when the yolk is
eventually entirely absorbed, disappears altogether (Fig. 8, +). In
the higher Vertebrates (Reptiles, Birds, and Mammals) folds of the
somatopleure arise externally to these furrows, and are known
respectively as the head, tail, and lateral folds; these gradually
grow upwards and eventually unite with one another dorsally so
as to form a membranous, dome-like sac, the amnion (Fig. 8)
which encloses the embryo and contains a fluid (diguor amntzt).

Owing to the presence of this structure the above-named
Vertebrates are usually distinguished as Amniota from the
Anamnia (Fishes and Amphibians), in which no amnion is
developed (p. 13).

A network of blood-vessels becomes developed over the yolk-
sac, which may therefore serve as an organ of respiration as
well as of nutrition. But in the higher Mammals this func-
tion is only a very subsidiary one, as at a very early stage a
vascular sac-like outgrowth, the allantois (Fig. 8), arises from
the hinder part of the intestine (ic, from the splanchnopleure).
This serves not only for respiration, but also for the reception of
excretory matters derived from the primitive kidney. It is also
present in Amphibians, but in them remains small, and does not
extend beyond the body cavity of the embryo; while in the
Amniota it gradually increases in size and grows round the embryo
as a stalked vesicle, which in Reptiles, Birds, and Monotremes
comes to lie close beneath the egg-shell and acts as an efficient
respiratory organ during the rest of the embryonic period.
Towards the close of this period the allantois gradually undergoes
more or less complete reduction.

In the higher Mammalia, however, an important vascular con-
nection takes place between the mother and foetus by means of the
ulantois. The latter becomes attached to a definite region of
the uterine wall, and from it vascular processes or villi arise, so
that the foetal and maternal blood-vessels come into very close
relations with one another. Thus an allantoic placenta is
formed, which serves both for the respiration and nutrition of the
foetus (Fig. 9). As an allantoic placenta is not developed in
Monotremes and is only slightly indicated amongst Marsupials,
these forms are distinguished as Aplacentalia from the higher
Mammals, or Placentalia (p. 14).

The following important points must be noted as regards the
structure of the Vertebrate body. After the main organs have ap-
peared, a smaller dorsal neural tube and a larger ventral visceral
tube extend longitudinally through the body, and between the two
is a rod-like supporting structure, the notochord (p. 5), which
arises as an axial thickening of the primary hypoblast and forms the
primitive skeletal axis: it is usually replaced by a vertebral column
consisting of centra and arches, at a later stage of development
(Fig. 7). All these are median in position, and the body is thus

10 COMPARATIVE ANATOMY

P34

Via. 8, A, B, aypb C.—D1IaAGRAMS ILLUSTRATING THE FORMATION OF THE AMNION,
ALLANTOIS, AND YoOLK-Sac. A anv B, in LonciITtuDINAL Sxction ; C, IN
TRANSVERSE SECTION.

i, embryo; Dh, alimentary cavity ; Do, yolk-sac ; +, vitello-intestinal duct ; PP,
cuwloine; Ah, amniotic cavity ; AJ’, amniotic fold ; A, amnion ; AJ, allantois ;
«, somatopleure ; }, splanchnopleure ; AZ, medullary cord ; C, notochord.

INTRODUCTION 11

bilaterally symmetrical. The neural tube, or cerebro-spinal cavity
enclosed by the skull and vertebral arches, contains the central ner.
vous system (brain and spinal cord); the visceral tube (cwlome,
p- 8, Fig. 7) encloses the viscera (alimentary canal, urinogenital
organs, &c.), and its muscular walls may be strengthened by a series

Pu

LC)

Fic. 9.—DIAGRAMMATIC SECTION THROUGH THE HumAN Gravip Urrnts.

U, uterus ; 7b, Tb, Fallopian tubes ; UH, uterine cavity ; Dv, decidua vera, which
at Pu passes into the uterine portion of the placenta; Dr, decidua reflexa ;
Pf, fetal portion of the placenta (chorion frondosum, Chf); Chi, chorion
leve; A, A, the cavity of the amnion filled with fluid : in the interior of the
amnion is seen the embryo suspended by the twisted umbilical cord ; H,
neart ; A, aorta; cs, precaval, ci, postcaval, and », portal vein; A/, allantoic
(umbilical) arteries; +, the liver, perforated by the umbilical vein; D, the
remains of the yolk-sac (umbilical vesicle).

of ribs, articulating dorsally with the vertebral column. Certain
of the ribs may reach the mid-ventral line and come into connec-
tion with a breast-bone or sternum, and thus form complete rings
or hoops around the visceral tube.

The anterior ends of the central nervous system (brain) and ali-
mentary tract enter into close relations with the outer world, the

12 COMPARATIVE ANATOMY

former coming into connection with the higher sense-organs, while
from the latter are developed the mechanisms for the taking i in of
nutriment and for respiration.

The anterior portion of the body, or head, passes behind into
the trunk, either with or without the intermediation of a neck. The
coelome is practically restricted to the trunk, in the hinder part of
which the intestinal (anal) and urinogenital apertures are situated,
and posterior to which again is the tai/, Head, trunk, and tail
constitute the body-axis, as distinguished from the limds or
appendages, which arise from the trunk and of which there are

typically two pairs.

INTRODUCTION 13

SYSTEMATIC ZOOLOGY.

On the ground of their relationship to one another, animals
have been classified into certain divisions and subdivisions, which
are designated as Classes, Orders, Suborders, Familtes, Genera, and
Species,

A general classification of the principal existing Vertebrate
groups is given in the following table.

A. Acrania.
Amphioxus (Lancelet).

B. Craniata.

I. CYCLOSTOMATA (Suctorial Fishes).
1. Petromyzontide (Lamprey).
2. Myxinoidee (Myxine, Bdellostoma).

Il. GNATHOSTOMATA (Animals provided with jaws).

(a.) ANAMNIA (without amnion).
1. Pisces (True Fishes).
a. Elasmobranchii (Sharks and Rays).
8. Holocephali (Chimera and Callorhynchus).
y. Ganoidet.
1. Selachoidei (Cartilaginuns Ganoids—Aci-
penser, Scaphirhynchus, Polyodon).
2. Teleostoidei (Bony Ganoids—Polypterus,
Calamoichthys, Lepidosteus, Amia).
6. Teleostei.
1. Physostomi (with open pneumatic duct
between the air-bladder and pharynx,
3 e.g., Cyprinus, Salmo, Silurus, Mor-
Ichthyopsida. i ra
2. Physoclisti (air-bladder, when present,
with closed pneumatic duct, e.g., Perca,
Gadus, Lophius, Labrus, Plectognathi,
Lophobranchii).

2. Dipnot,
1. Monopneumones (Ceratodus).
2. Dipneumones (Protopterus, Lepidosiren).
3. AMPHIBIA.
a. Urodela.
1. Perennibranchiata (Proteus, Siren,
\ Necturus).
2. Caducibranchiata.
Derotremata (Amphiuma, Menopoma).
Myctodera (Salamandra, Triton, Am-
blystoma).
B. Gymnophiona (Footless Ceecilians).
y. Anwra (Frogs and Toads).

14

Sauropsida.

Mammalia.

2

COMPARATIVE ANATOMY

(b. AMNrotTa (Vertebrates which develop an amnion

during fcetal life).

. Reprint.
a. Crocodilia (Crocodiles and Alligators).
B. Lacertilia (Lizards, including Hatteria).
y. Chelonia (Turtles and Tortoises).
6. Ophidi« (Snakes).
2. AVES.
a. Ratitc (Cursorial Birds—Ostrich, Rhea, Emu, &c.).
B. Carinate (Birds of flight).

Aplacentalia or Achoric.
a. Prototheria or Ornithodelphia (Monotremata—Orni-

thorhynchus and Echidna).

8. Metatheriu or Didelphia (Marsupialia—Kangaroos,

Phalangers, Opossums, &c. ).

. Placentalia or Choriata.

Eutheria or Monodelphia,
Edentata. :
Sirenia.

Cetacea.
Ungulata.
Hyracoidea.
Proboscidea.
Rodentia.
Cheiroptera.
Insectivora.
Carnivora.
Lemuroidea
Primates.

15

INTRODUCTION

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SPECIAL PART.

A. INTEGUMENT.

THE skin consists of a superficial ectodermal and a deeper
mesodermal layer. The former is called the epidermis (scarf-
skin) and the latter the dermis (coriwm, cutis). The subcutaneous
connective tissue is usually not sharply marked off from the dermis,
but the one passes gradually into the other. The epidermis always
consists of cells only, while the dermis is made up principally of
connective tissue fibres, and may also enclose muscular fibres.
Bony structures may occur in the dermis, as well as vessels
and glands, which only rarely extend into the epidermis, from
which the glands are all derived and with which they usually
remain in connection by means of their ducts. Nerves, migratory
leucocytes (lymph- or white blood-corpuscles), connective-tisswe cells,
including pigment-cells (chromatophores) and free pigment, are found
in both layers of the integument.

Pigment is never formed in the epithelial or connective-tissue cells them-
selves, but always originates in the blood.

In the epidermis two layers may in general be distinguished :—
a superficial, composed of flattened and hardened cells (stratum
corneum, horny layer), and a deeper layer made up of soft proto-
plasmic cells (stratum Malpightt, mucous layer). The latter serves
as a matrix for the regeneration of the horny layer, the superficial
part of which is continually scaling off. From the epidermis the
cuticular organs and integumentary glands, and all other parts
spoken of as epidermic structures take their origin. Such are,
hairs, bristles, nails, claws, hoofs, &e. The peripheral sensory end-
organs of the skin as well as the crystalline lens of the eye also arise
by a differentiation of epidermic cells (p.5): the definite relation
which many of these organs have with the dermis must be looked
upon as a secondary acquirement.

Amphioxus, Fishes, and Dipnoans.—The surface of the
epidermis is covered with cilia in the larval Amphioxus (gastrula
stage), and this must undoubtedly be considered as inherited from
Invertebrate ancestors. The striated cuticular border of the outer

INTEGUMENT 17

epidermic layer in many fishes (eg. Cyclostomi, Teleostei, and
Dipnoi), and, as will be mentioned presently, in Amphibian larve,
indicates the former possession of cilia (Figs 10 and 11).

se» Goblet-cells (wnicellular glands) are very abundant in the many
layered epidermis of Cyclostomes (especially Myxincids) and
osseous Fishes, and are extremely numerous in Protopterus.

Protopterus buries itself in the mud during the dry season, and its integu-
ment, which, besides the numerous goblet-cells, also contains simple muauiti-

cellular glands like those of the Amphibia, gives rise to a varnish-like secretion
oe

as well as to a hardened capsule or ‘‘ coccoon,” by means of which the animal

Fig. 10.—DIAGRAMMATIC TRANSVERSE SECTION ILLUSTRATING THE STRUCTURE OF
THE SKIN IN FISHEs.

Ep, epidermis; Co, derma; J’, subcutaneous fat ; CS, cuticular margin; Ko,
goblet-cells; B, B, goblet-cells opening on the surface ; Ko, granular slime-
secreting cells present in Petromyzon and Malopterurus; (/, vessels which
pass upwards in the vertical connective-tissue bundles of the derma ; W, hori-
zontal connective-tissue bundles.

is protected during its torpid period. In all Fishes which possess slime-
secreting cells in the integument, it is probable that the secretion serves tu
protect the outer skin from the action of the water.

Multicellular glands are not commonly present in the integu-
c

18 COMPARATIVE ANATOMY

ment of Fishes, but apart from Protopterus (see above) there are a
number of exceptions to this rule.

In male Elasmobranchs there is a large glandula pterygopodii (gland
of the clasper) at the base of each pelvic fin : it arises as a tube-like invagin-
ation of the skin, and is in relation with the copulatory organs. Poison-glands
are found amongst the Teleostei. Thus in the Weever (Trachinus) there
is a series of poison-glands lying on either side of the bases of the spines of
the dorsal fin and operculum. In Thalassophryne the operculum is provided
with a hollow spine, at the base of which a poison-gland is situated, and in
Synanceia there is also a series of glands at the bases of the grooved dorsal
spines. Poison organs are also present in Scorpeena and others ; but in many
cases in which such organs have been described a more detailed histological
examination is desirable. The phosphoresceit and eye-like organs present in
the integument of some Fishes (Scopelidee, Chauliodus, &c.) are probably
to be looked upon as modified glands.

In Lepidosiren, apparently in the male only, the integument of the
pelvic fins is provided with numerous (? erectile) villi.

Pigment-cells, which are under the influence of the nervous
system and are able to cause a change of colour, are present some-
times in both layers of the integument, sometimes in the epidermis.
only. The colouration is sometimes protective (¢.g. Flat-fishes) and
sometimes sexual (e.g. Stickleback).

The bony scales of Fishes lie in connective-tissue pouches of
the dermis and are formed as ossifications of the latter. In
Teleosts and Dipnoans they are covered by the epidermis through-
out life; in Ganoids and Elasmobranchs this is only the case in the
larva. In Teleosts the parts of the epidermis covering the ex-
ternally visible portions of the scales becorne cornified. (For
further details compare p. 30).

Amphibia.—The epidermis of Amphibian larve is for a short
period ciliated. In the adult, it may be said in general that the-

Fic, 11.—Skry or Larva or SavaMANDER (Salumandra maculosa).

Ep, epidermis; Co, dermis ; a, stratum corneum; ), stratum Malpighii; ZZ,.
Leydig’s cells ; CS, striated border.

integument of Amphibians is intermediate in structure between
that of Fishes and Reptiles.

The epidermis of those larvee which live in the water consists.
of two sharply differentiated layers. The outer layer is usually
made up of flat cells with a striated cuticular border on their
free edge (Fig. 11), like that occurring amongst Fishes: the inner:

INTEGUMENT 19

layer is composed of more cylindrical or cubical cells. The former
corresponds to the stratum corneum, the latter to the stratum
Malpighii. The horny layer is shed periodically, either entire or
in pieces.

Later, with advancing development, the layers of the epidermis
become more numerous, and involutions towards the dermis take
place in all parts, giving rise to a great number of sac-like and
tube-shaped glands similar to those of Protopterus (p. 17); these
are particularly abundant in certain regions—more especially on
the head and flanks (Fig. 12). The individual glands are sur-

Min

Fic. 12.—SEcTioN THROUGH THE SKIN OF ADULT SALAMANDER (S. maculosa).

Ep, epidermis ; Co, dermis, in the richly pigmented (P7) connective-tissue stroma
of which the various sized integumentary glands (4, C, D, D, Z) lieembedded ;
4M, the muscular layer of the glands, lying within the basement membrane
(Pr); M, the same, seen from the surface; 7, epithelium of glands; S,
secretion of glands; J/m, subcutaneous layer of muscles, through which
vessels (G) extend towards the dermis.

rounded by muscle and connective-tissue fibres, pigment, blood-
vessels, and nerves. Their secretion serves to keep the skin moist,
but as experiments have shown, it also forms an important weapon
of defence on account of its poisonous properties.

This richness in glands is a characteristic of the skin cf Amphi-
bia and to it they owe their moist and slippery nature. Frequently,
as for instance in Toads, the skin is not smooth, but has a rough,
warty appearance, caused by local proliferations of the epidermis.

Epidermic claws, analogous to those of the Amniota, are present
only in Xenopus (Dactylethra) and Onychodactylus.

The pigment, accumulated principally in the dermis—partly
diffused, partly enclosed within the cells—is under the control of the
nervous system, and thus renders a change of colour possible; and
5)

Qs

20 COMPARATIVE ANATOMY

as the colour becomes modified according to the surroundings of
the anirnal, it may serve as a protection (¢.9. Hyla). Saki

Calcifications may occur 1 the dermis, or, as in Ceratop uae
dorsata, definite bones may be formed (see p. 33): the dermis also
encloses numerous smooth muscle-fibres.

Reptilia.—The characteristic peculiarity of the skin of Reptiles
is its capacity of producing scales (these are very simple in Geckos
and Chameleons), warts, prickles, shields (c.g. the “ tortoiseshell
of Chelonians), claws, rattles (Rattlesnake), and other epidermic
structures (Fig. 13). All these are due in the first instance to
the formation of dermal papillz, the markedly stratified epidermis
covering which becomes cornified secondarily. The horny layer of
the epidermis may be periodically cast off either entire (Snakes)

Uanwite GWM EU

Fie. 13.—DiacnamMatic Sections THroucH Various Kinps oF EPIDERMIC
ScaLes OF REPTILES. (From Boas’s Zoology.)

A, rounded scales ; B, shields ; C, imbricating scales ; D, overlapping scales with
bony seutes in the underlying dermis; h, horny layer; s, Malpighian layer of
the epidermis ; 7, dermis; 0, bony scutes.

or in shreds: it is renewed from the Malpighian layer. The
integument of Hatteria retains the most primitive characters
amongst Reptiles.

Pigment-cells occur in the integument, rendering a change of
colour possible in many cases (¢.g. Chameleon).

Ossifications in the dermis are very common in Reptiles, and
there is great variation in the degree of their development, from
the small bony scutes present in Geckos (Ascalabota) to the large
exoskeletal plates of Chelonians (see p. 33). Muscles are also
present in the dermis. In contrast to the skin of Amphibians,
that of Reptiles is entirely wanting in glands.

In Lizards, the so-called femoral glands occurring along the ventral side
of the thigh are said to be merely solid cones of epidermic cells, which form
a series of papillze or warts and serve as clasping organs during copulation.

Birds.—Birds possess a thinner dermis than any other Ver-
tebrates, and it is less plentifully supplied with blood-vessels.

INTEGUMENT 2,

In the deeper layers there is a strongly developed network of
muscle-fibres showing traces of transverse striation: these are
inserted into the feather-sacs, and serve to erect the feathers.

Apart from a gland present in the neighbourhood of the
auditory passage amongst Gallinacez, there is only a single gland
situated at the base of the rudimentary tail (uropygium): this
wropygial gland is present in nearly all Birds, and its secretion
serves to oil the feathers. Dermal bones are characteristically
absent, while epidermic structures, such as feathers, claus, spurs,
foot-scales, and beak-sheaths, are strongly developed.

One of the most marked characteristics of Birds is the pos-
session of feathers. In the majority of Birds they are of two
kinds—down-feathers and contour-feathers, and are usually
arranged in so-called feather-tracts (pterylw) separated by naked
regions (apteria). The base of each feather is embedded in
an epidermic sac or follicle. Their mode of development corre-
sponds essentially with that of the epidermic scales of Reptiles.

In the region where a feather is to be formed, the dermal tissue becomes
raised up towards the ectoderm (Fig. 14, A), and thus gives rise to a vas-
cular papilla. As this papilla grows out to form an elongated cone with a
pointed apex, the ferther-yerm (B), its base sinks gradually deeper and deeper
into the dermis, and thus becomes surrounded by a sort of poeket—the
feather-follicle. The horny, as well as the Malpighian layer of the epidermis
extends into the base of the follicle, and thence into the feather-germ, the
interior of which is throughout filled by cells of the dermis, which give rise to
the pip. As the feather-germ keeps on growing, the cells of the Malpighian
layer begin to proliferate rapidly, giving rise to a series of radial folds
arranged along a central axis, which extend inward towards the pulp, and
are immediately bounded by the horny layer (C). These folds, between
which the nutritive pulp extends, then become cornified and separated from
above downwards from the surrounding cells ; and, by a gradual drying of
the central pulp-substance, give rise to a tuft of horny rays, which are,
however, at first bound together by the enclosing stratum corneum. Most
Birds are hatched when the feathers are in this stage of develupment, and
they thus appear as if covered with hbrush-like hairs.

By the shedding of the surrounding horny layer the rays or barbs become
free (D), and if these are all similar to one another, an embryonic down-
feather is formed. The whole feather-germ, however, does not become
divided up into barbs in this manner : its lower portion, embedded in the
skin, retains a more uniform character and forms the qill (calcuits).

The embryonic down-feathers (E), on the individual barbs of which
smaller secondary rays or barbiles become developed, may retain their char-
acter as such throughout life or may be replaced by definitive feathers. In
this case a second, larger, follicle early arises from the base of the follicle of
the down-feather, the pulp of the two being in connection (D). The papilla
developing within the interior of this new follicle grows rapidly, gradually
pushes the base of the down-feather out of its follicle, and comes to the
surface.

Each contour feather (penne) at first closely resembles a down-
feather (pluma) in structure, and consists of a tuft of similar rays
or barbs provided with secondary rays or barbules. In the course
of further growth, however, one of the rays becomes rapidly

a COMPARATIVE ANATOMY

thickened, and forms a main axis or stem (scapus), to which the
barbs are attached on either side. The proximal or basal portion of
the scapus which bears no barbs is called the gull (calamus), and
the distal part, to which the barbs are attached, the shaft (rachis).
The barbs together constitute the vane (veaillum) (Fig. 14, F).

A.

Fra. 1£—Six Staces IN THE DEVELOPMENT OF THE FEATHER.
(Mainly after Th. Studer. )

Cu, dermis; Si, stratum Malpighii; Sr, stratum corneum ; §.1/!, Sc!, extensions
of these tissues into the feather-papilla, Pap; /K, feather-germ; F, F",
feather-follicle ; P, pulp; Fal (SJ/1), folds of the Malpighian layer extending
into the feather-germ, and enclosed externally by the horny layer, HS (Sc?) :
both layers are seen in the transverse section (C); /"Sp, quill of feather, which
breaks up above into a tuft of rays or barbs (Sf); sec, sec, secondary rays
(barbules) arising from the latter; R, rachis ; V, vexillum.

For further details as to the different stages A-F’, compare text.

The barbules are so arranged on each barb as to make the latter
resemble an entire feather in appearance. The barbs may become
very closely united together by means of minute hooks on the
barbules, so that an extremely strong and resistant though plant
structure is formed; this is especially the case in the large wing
and tail feathers (renviges and rectrices).

Tn many Birds each quill of the ordinary feathers of the body bears two
yexilla, the second being spoken of as the aftershaft (huporachis),

INTEGUMENT 23

A periodic casting of feathers, or moulting, takes place in
all Birds, and corresponds to the similar process of the casting of
the horny layer of the skin in Amphibians and Reptiles.

The feather-covering of Birds must have been acquired in very early
geological periods, for Archeeopteryx, found in the Jurassic strata of Bavaria,
possessed well-formed feathers with a very delicate shaft and vane. Palseonto-
‘logical researches have not brought to light any definite intermediate stages
between scales and feathers, but that they must once have existed is shown
by the development of these structures.

Mammals.—The integument of Mammals gives rise to hatrs,
“which are characteristic of and confined to this Class. They may be
almost uniformly developed all over the body and even on the soles
of the feet, or may become reduced in more or less extensive regions.
They are most scanty in the Cetacea, where only a few occur on
the lips, and even these may disappear in the adult. The
first to appear are certain tactile-hairs (vibrisse) on the head, along
the course of the trigeminal nerve; all the hairs, however, serve
as tactile organs as well as for keeping the body warm.

Nothing definite can be at present stated as regards the
phylogeny of hairs, but it seems at any rate probable that they
are not directly comparable to the scales of Reptiles and feathers
of Birds:! the arrangement of the hairs in alternating groups is
probably the last indication of the former possession of scales.

Each hair first arises as a proliferation of the epidermic cells
in the region of the Malpighian layer which comes to project
inwards towards the dermis (Fig. 15, A, B and C). In this
manner the hair-germ is formed. Thus the epidermic portion is the
primary one; a corresponding dermal papilla is formed secondarily,
and is the homologue of the papilla which forms the first trace of
the scale in a Reptile or the feather in a Bird,

The thickening of the epidermis then grows downwards in the form of a
papilla and becomes surrounded by the cells of the dermis, so that, as in the
case of the feather, it comes to lie within a kind of pocket, the hair-follicle
(Fig. 14, C). The originally uniform mass of cells of the hair-germ later
becomes differentiated into a peripheral and a central portion. The latter
consists of more elongated cells, and gives rise later to the hair-shaft with its
medulla or pith, and to the cortex, as well as to the cuticle of the shaft and
the so-called inner rovt-sheath; the former gives rise the onter svovt-sheath
(comp. Fig. 16 A, which represents the fully-formed hair). The base of the
hair-shaft which fills up the bottom of the follicle is broadened out to form
the hair-bulb (Fig. 15, D), which grows round the later formed and highly
vascular hair-papilla like a cap (C, D). At Dr, in D, the sebaceous glands
(p. 27) are seen arising by a proliferation of the Malpighian cells. The hair
usually breaks through the skin in an oblique direction ; the direction differ-
ing in different parts of the body.

The hair or hair-shafé embedded at its base in the hair-
follicle, is more or less cylindrical: it consists of three parts—

1 It has been suggested that the hairs correspond to modified integumentary
sense-organs such as occur in the lower Vertebrates (comp. Figs. 15 and 150).

2+ COMPARATIVE ANATOMY

medulla, cortex, and cuticle (Fig. 16 A), all of which are formed
from cells. The follicular tissue, which is richly provided with
blood-vessels, extends into the bulb-like base or root of the hair-

Fie. 15.—Dracrams oy Four Staces (A-D) tx THE DEVELOPMENT OF Hatrrs.
(After F. Maurer.)

Se, stratum corneum; S.J/, stratum Malpighii, which gives rise to an epithelial
knob at Zp ; this grows inwards into the dermis (C) ; #, rudiment of the hair-
follicle ; HP, hair-papilla; HK, hair-bulb ; Dr, rudiment of the sebaceous
gland. In D,/ indicates the stratum lucidum with eleidin-granules in the
cells.

shaft, and gives rise to the huir-papilla. From this region a new
hair-shaft_ may develop when the hair is shed, periodically or non-
periodically as the case may be, often by the formation of a new
papilla. The colour of the hair is due to three causes -—Firstly,

INTEGUMENT 25

to the greater or less accumulation of pigment in the cells of the
cortical layer; secondly, to the air contained in the intercellular

Fic. 16, A.—Lonerruprnan SecTIoN THROUGIE A Harr. (Diagrammatic. )

Sc, stratum corneum ; S./, stratum Malpighii ; Co, dermis ; .j, arrectores pili ;
Ft, adipose tissue ; /, outer longitudinal layer, and J", inner transverse layer
of dermic coat (both composed of connective-tissue) ; Sch, hair-shaft ; 1/,
medulla; PR, cortex ; O, cuticle of shaft; WS, W'S!, external and internal
root-sheath, —the latter reaches above only as far as the point of entrance of
the duets of the sebaceous glands (WBD); HP, hair-papilla, containing
‘vessels ; GH, hyaline layer, which lies between the inner and outer hair-
sheaths, ¢.c., between the root-sheath and the follicle (dermic coat).

spaces of the medulla; and lastly, to the nature of the surface of
the hair, i.e, whether it is rough or smooth. The hairs are usually
arranged in groups of finer and coarser elements, and, especially
in the case of the vibrissee, are well innervated.

26 COMPARATIVE ANATOMY

A richer hairy covering (lanwgo) is often met with in the embryonic
-condition—as, for instance, in the human foetus—than occurs later ; and this
fact, together with the occasional appearance of abnormally hairy individuals,
indicates that at one time Man was distinguished by a far more abundant
clothing of hair than at the present day.

Other epidermic structures, formed as thickenings of the horny
layer, also play a very important part in Mammals; such are—
claws, nails, bristles, and spines (Hedgehog, Porcupine); the so-
called whalebone (baleen) of the Mystaceti; the horn-sheaths in
Ruminants; the nasal horns of the Rhinoceros; the scales in Manis
and on the tail of the Beaver and other Mammals; the palatal
plites of Sirenia ; and the ischial callosities of certain Apes.

When pigment is present, as, for instance, on the snout in many
Mammals and on the external genitals (labia majora and scrotum)
and the teats in the human subject, it is always situated in cells
of the Malpighian layer.

The outer layer of the dermis, as may be seen by a glance at
Fig. 16, B, may be divided into an outer papillary and an inner
reticular portion. The pa-
pille of the former are ac-
curately adapted to the
over-lying epidermis: some
of them contain blood- and
lymph-capillaries, and others,
nerves with tactile cor-
puscles. The latter, on the
other hand, becomes lost
without any sharp boundary
line in the sub-dermal con-
nective-tissue and in the
more or less strongly-de-
veloped fatty layer (panni-
culus adiposus). The pads
(tort) on the soles of the feet
of most Mammals are due to
large dermal papilla.

Fie. 16, 3.—Sxerion tHRoveH tHe Human In addition to numer-
SKIN. ous elastic fibres, smooth

Se, a Noe eat a tee oe muscle elements are distri-
sensory pepe s CP. vastulerpenilh ae buted throughout the der-
and G, nerves and vessels of the dermis; 4215 ; they are particularly
eae Ee ar with their ducts abundant in the scrotum

Hits Sle , hair with sebaceous (dartos) and in the teats,

and are present in connec-

tion with the hair-sacs
(arrcctores pili): the power of erecting the hair possessed by many
Mammals is due to these (Fig. 16, A). A bony dermal skeleton
is found only in the Armadillo amongst existing Mammals
(comp. p. 34),

INTEGUMENT 27

The integumentary glands, which are well developed in all
Mammals except the Cetacea, are of two kinds, twhular and acinous.
The former include the sweat-glands and their various modifica-
tions ; while the latter are spoken of as sebaccous glands, and include
the already-mentioned glands of the hatr-sacs, which serve to oil the
hair (Figs. 15 D, and 16, A and B), the preputial glands, the inguinal
glands of certain Rodents, the Meibomean glands of the eyelids, and
many others. It must be borne in mind, however, that there is
not always a sharp distinction between these two kinds of glands.

The paired femoral gland of Ornithorhynchus opens by means of a long
duct on to the spur present on the hind foot. Its secretion is poisonous.

Another important modification of the integumentary glands
of the Mammalia is seen in the mammary glands, which secrete

Fic. 17, A.—A, VENTRAL View or A Broopine Femaue or Aehidnua hystrix.
B, Dissection oF THE VENTRAL INTEGUMENT FROM THE Doksau (INNER)
Sipe. (After W. Haacke.)

t,-T, the two tufts of hair in the lateral folds of the mammary pouch (b.m.) from

which the secretion flows. On either side of the pouch, which is surrounded
by.strong muscles, a group of mammary glands (y.m.) opens ; ¢/, cloaca,

milk for the nutrition of the young. In Monotremes these
apparently correspond to sweat glands, while in other Mammals
they represent sebaceous glands.

COMPARATIVE ANATOMY

to
(oa)

Monotremes possess no ¢eats, and the milk probably passes
along the hairs, which in this region are arranged in bunches, and
is then licked off by the young animal. The gland is compressed by
a strong sphincter muscle. In Echidna, a mammary or marsupial
pouch which is primarily paired and becomes unpaired secondarily, is
early formed for the reception of the young, and the gland-masses
open into two depressions of the ventral integument where the
bunches of hair are situated (Fig. 17). These depressions may be
called mammary pockets, and are of especial interest as they repre-
sent the first stage in the development of the various forms of teats
present in all other Mammalia, in many of which distinct indica-
tions of the Monotreme
condition are met with.
The marsupial pouch
of the Marsupialia is
probably homologus
with that of Echidna.

Thus a_ similar
mammary pocket is
formed in the embryos
of Marsupials and pla-
cental Mammals by
the epidermis extend-
ing inwards towards
the dermis, and cylin-
drical, more or less
branched processes a-
rising from the base
of the pocket thus
formed (Fig. 17, B,
1). These processes
only are the glands
proper, the mammary
pocket being simply a
Fre. 17, B.—DracramMatic REPRESENTATIONS OF rate of the Outer all

roe Earty DEVELOPMENT or tHE Leapixy face of the skin which
Types or MamMary Grianps. (Modified from has sunk inwards, and
soREE RAN thus it may give rise to.

A, first or undifferentiated (mammary pit) stage; hairs and other intecu-
Std 8 =] € stay rue 5
£, stage of the false teat; C, stave of the true mentary structures.

teat; ¢, ©, rim (or rampait) of the glandular a
area ; f, 4, glandular area ; y/, mammary glands ; The teats may be-
d¢, maminary canal. come developed In one

of two ways. Th
the first of these, the skin surrounding the pouch becomes
raised up to form a circular rampart, and thus gives rise to a teat
perforated by a canal, into the base of which the ducts of the
gland open (Fig. 17, B, B). In the second case, the gland sur-
face itself becomes elevated into a papilla, while the surrounding

INTEGUMENT 29

skin remains almost on a level with the rest of the integument
(C). In the latter case the teats may be described as trxe or
secondary (Marsupials, Rodents, Lemurs, Monkeys, and Man), and
in the former as psewdo- or primary teats (Carnivora, Pigs, Horses,
and Ruminants). The latter condition is already indicated in
certain Marsupials (¢.g. Phalangista vulpina).

The number of teats varies greatly: there may be as few as
one pair, or as many as eleven pairs (Centetes). They are often
situated in two nearly parallel rows along the ventral side of the
thorax and abdomen which slightly converge towards the inguinal
region: in other cases they may be restricted either to the inguinal
(Ungulates and Cetaceans) or to the thoracic region (Sloths,
Elephants, Sirenia, many Lemurs, Cheiroptera, and Primates) :
while in others, they may be axillary or abdominal, or they may
oceur in various combinations of all these regions.

In the male, the mammary apparatus becomes aborted, though usually at
birth and puberty milk is produced in the human subject. Male goats and
castrated sheep have also been known to give milk, and the same is probably
true of male Bats. The occasional existence in men of supernunierary teats,
and in women of supernumerary mamme and teats (polimastism and polj-
thelism) is very remarkable. They are usually situated in the thoracic region,
and must be considered as atavistic to a primitive form which possessed
numerous teats and which produced a number of young at atime. Such a
transition from polymastism to bimastism may be seen plainly at the present
day in the Lemurs: in them the inguinal and abdominal teats are seen in
various degrees of retrogressive metamorphosis, while a single pair of thoracic
teats remain well developed. This accords with the fact that most Lemurs
bear only a pair of young ones at a time, which they carry with them at the
breast. Moreover, in various Mammals a greater number of teats are present
in the embryo than in the adult.

The mammary glands, which are at first solid, become secondarily
hollowed out and further differentiated. The whole intermediate
tissue during lactation is filled with white blood-corpuscles
(leucocytes); and possibly the well-known structural elements of
milk, known as colostrums and milk-spheres, owe their origin to
these corpuscles, which have passed through the walls of the acini.

B. SKELETON.

1, EXOSKELETON.

THE hard exoskeleton, consisting of bone or other calcified tissues,
must be distinguished from the horny exoskeletal parts described
in the last chapter, in which, however, the former was also referred
to. Thus it will be remembered that the term “scale” is some-
times used for a horny epidermal structure, and sometimes for a
bony dermal one (pp. 18, 20).

The first and most primitive hard structures in Vertebrates are
met with amongst Elasmobranchs in the form of small, pointed

Fic. 18.—DermMan DesxticLes
oF Centrophorus — caleeus.
(Slightly magnified. )

(From Gegenbaur’s Comp. An-
atomy. )

denticles (placoid organs) in the skin;
these consist of enamel and dentine,
resting on a basal plate of done, thus
resembling in structure ordinary oral
teeth, which will be described later.
Primitively, as in many Rays, there is
a relatively small number of these
placoids, which do not touch one
another, while in most Sharks and Dog-
fishes they are much more nunerous
and close-set (Fig. 18). Their shape
is rhombic or more or less rounded,
each bearing a spine, and new ones
being continually formed. The enamel,
developed in connection with epidermic
cells, is the primary part of the den-
ticle (Fig. 19) ; the dentine is developed
secondarily—that is, later—from the
phyletically younger mesoderm, and
this is also true of the bony portion.
The enamel is therefore the first, and
originally the only hard substance of
the placoid organ.

The first bony tissue to be developed
is thus formed in connection with

EXOSKELETON 31

these denticles, the basal-plate representing an accessory portion
of the denticle, and serving to fix it within the skin. In the-
further course of evolution the denticle itself undergoes reduc-
tion, the basal-plate remaining as an independent structure
This is illustrated by a study of the exoskeleton in other
Vertebrates.

In the Holocephali dermal denticles are only present on
certain appendages (the claspers), and the first dorsal-fin is
strengthened by a large bony spine.

In most Ganoids thick plates, usually rhombic in form, are
present in the skin; in bony Ganoids these cover the entire
body, their margins being in apposition.! These ganoid-scales:
correspond to the main (deeper) part of the placoid basal-plates,.

aS
ne

Fic. 19.—VerticaL SECTION THROUGH THE SKIN oF AN Empryo SHARK.
(From Gegenbaur’s Comp. Anatomy.)

C, dermis ; ¢, c, c, d, layers of the dermis; p, papilla; £, epidermis ; ¢, its layer-
of columnar cells ; 0, enamel layer.

the spine having become rudimentary. Their surface is dense
and smooth (ganoin-layer), and was formerly erroneously supposed
to consist of enamel. In Lepidosteus they bear numerous small
denticles; but from what has been said above, this fact does
not indicate that each ganoid-scale corresponds to a multiple
of placoids. The exoskeleton was largely developed amongst fossil
Ganoids.

The scales of Teleosts, the first indication of which, as in
the case of placoid scales, is seen in the form of small papille of
the dermis extending into the epidermis, correspond to the super-
ficial portions of the basal-plates. In the further course of develop-
ment they are seen to consist of bony plates arranged in oblique
rows and lying directly beneath the ep:dermis, the individual scales
not touching one another, and their surfaces lying parallel to the

1 In Amia, the scales have a ‘‘cycloid” form. (See note on p. 32.)

32 COMPARATIVE ANATOMY

surface of the body. In this stage their arrangement resembles that
seen in Ganoids. Subsequently they usually come to lie within
definite pockets or sacs, and to overlap one another like tiles on a
roof (Fig. 20 A). The surface of the scales may be sculptured.

YY:
Mbt HULL
fra. 2U\.—DrackamMatic LoNne@rrupINAL SECTION THROUGH THE SKIN OF A

TELEOSTEAN, TO SHOW THE RELATION OF THE Bony Scaues. (Fron Boas’s
Zooloyy.)

7, dermis ; s, scale; v, epidermis.

Amongst the Siluride (Fig. 29, B), Plectognathi, and Lopho-
branchii, they may be of relatively large size and so arranged as to
form a strong bony cuirass.

Scales are wanting in Cyclostomes, and may be reduced or absent in repre-
sentatives of the three larger Orders described above (viz., in Electric Fishes

Spatularia, and some Eels).

In the Dipnoi the arrangement of the scales is similar to that
seentin the Teleostei. They consist of an external hard substance

Fic. 208.—DERMAL ARMATURE OF Callichthys.

L, barbules ; Br’, pectoral fin; BF, pelvic fin; RF, dorsal fin; DS and VS,
dorsal and ventral bony shields; +, lateral line.

arranged in a network and provided with numerous denticles, and
of an internal portion composed of firm connective-tissue and bone.

1 Different forms of the rounded or polygonal scales in Teleostei are dis-
tinguished as eycloid and ctenoid. The former, which are the more primitive,
have a smooth margin, while in the latter the posterior margin is toothed and
com)-like. Various intermediate stages exist between the two forms,

EXOSKELETON 33

These denticles are developed from connective-tissue cells, and are
not comparable to the placoid denticle; the resemblance, too, between
the scales of the Dipnoi and Teleostei is only a superficial one.
Thus the exoskeleton plays an important part in Fishes, and
im numerous fossil Amphibians it reached a still higher develop-
ment (Stegocephala), Amongst these, specially strong dermal
plates were formed in the region of the shoulder-girdle, and very
commonly most of the body was covered with scales. Fossil genera
of Amphibia have, however, bequeathed but slight traces of this
strong dermal armour to the existing forms of the group: as
examples may be mentioned the bony plates in the skin of the
back of certain Anura (Ceratophrys dorsata and Ephippifer auran-
tiacus), as well as the scales lying between the ring-like scutes of

Fie. 21.—A, Carapace, and B, Puastron or « Younc TEstupo Graca ; C,
PLASTRON oF CHELONE Mipas.

VN, neural plates; C, C, costal plates; M/A, marginal plates; Np, nuchal
plate ; Py, Py, pygal plates ; H, entoplastron ; Zp, epiplastron ; Hy, hyoplas-
tron; Hp, hypoplastron ; X7, xiphiplastron; R, FR, ribs. (J” indicates the
anterior, and # the posterior end.)

the footless Amphibia (Gymnophiona). The latter resemble in
many points the scales of Fishes and Dipnoans, and may be derived
from such a scaly covering as that of the Permian Salamander, Dis-
cosaurus.

The dermal skeleton was still more highly developed amongst
fossil Reptiles, ¢.7., many Ornithoscelida (Stegosaurus). In these,
enormous bony plates and spines, sometimes as much as sixty-three
centimetres long, were present in the dorsal region. Teleosaurus
also, as well as the Triassic Aétosaurus ferratus and the Cretaceous
Nodosaurus textilis, possessed a strong exoskeleton. Amongst
existing Reptiles (comp. p. 20), Crocodiles, many Lizards
(Anguis, Cyclodus, Scincus), and more especially Chelonians,
exhibit a well-developed dermal skeleton. In the latter Order

D

34 COMPARATIVE ANATOMY

there is a dorsal and a ventral shield (carapace and plastron) con-
sisting of numerous pieces and completely enclosing the body
(Fig. 21). Both arise independently of the endoskeleton, which
is preformed in cartilage: that is to say, they are true exo-
skeletal membrane bones (cp. note on p. 71). The exoskeleton,
however, comes into the closest relation with the endoskeleton,
and may supplant it here and there: thus, in Testudo, for
instance, the thoracic and lumbar vertebre and ribs become quite

rudimentary.

Birds, as already mentioned in the chapter on the integu-
ment, have no dermal skeleton, and this is true of all Mammals
except Armadillos (Dasypodide). In these it consists of a series
of movable transverse bony scutes covering the head and body
and of smaller plates on the tail and limbs. Sparse hairs.
occur between these plates. It is very doubtful whether this
exoskeleton has been derived from that of Reptiles: more
probably it, like the horny exoskeleton of Manis (p. 26), has
arisen secondarily, and in consequence of its development the
hairs have become reduced. In Glyptodon, a fossil member
of this group, the dermal plates were firmly united together to
form a large shield which covered the whole body.

2, ENDOSKELETON.
I. VERTEBRAL COLUMN,

An elastic rod, the notochord or chorda dorsalis, lying
in the longitudinal axis of the embryo between the neural and
visceral tubes (see p. 9), is the first part of the endoskeleton
to be formed, and is the fore-runner of the vertebral column. It
is developed as a ridge of the primitive hypoblast, from which it
becomes constricted off, and is therefore of epithelial origin. The
large parenchyma-like cells of which it is composed coosequently
do not give rise to any intercellular substance ; vacuoles, however,
soon appear within the cells, the protoplasm of which undergoes.
modification, and thus a retrogressive metamorphosis sets in
(Fig. 22). The fact that this occurs at such early stages of develop-
ment shows that the notochord must long ago have begun to lose
its primitive function, whatever that function may have been.

As these degenerative processes are gradually carried still
further, only the walls of the cells persist in the greater part of the
notochord ; these become flattened by mutual pressure, so that they
appear like a meshwork of pith-cells. At the periphery, however,
the cells retain their protoplasm, and become arranged like
an epithelium. Around the notochord two sheaths (Fig. 22 4, B)

VERTEBRAL COLUMN 35

irp

sk.l

Fia. 22.—DIAGRAMS ILLUSTRATING THE DEVELOPMENT OF THE NoOTOCHORDAL
SHEATHS AND VERTEBRAL COLUMN.

A,—Farly stage, showing notochordal cells (xc) and primary sheath (sh), as well
as the mesoblastic skeletogenous layer (sh./).

B.—Later stage, in which the central notochordal cells (x) have become
vacuolated and the peripheral cells have given rise to the ‘‘ notochordal epithe-
lium” (nc. ep.) from which the fibrillar secondary sheath (sh®) is derived :
paired dorsal and ventral cartilages (d.a, 1.a) have arisen in the skeletogenous
layer.

C.—Cartilage cells have passed through the primary sheath, and are invading
the secondary sheath (Cartilaginous Ganoids, Holocephali, Dipnoi, Elasmo-
branchii: in the last named chorda-centra are thus formed).

D.—The cartilages are growing round the notochord, outside its sheaths, which
gradually become reduced: thus arch-centra are formed (Bony Ganoids,
Teleostei, Amphibia, Amniota).

A—D represent the caudal region.

E.—A later stage in the development of a pre-caudal vertebra. The notochord
(xc) has become constricted, and the cartilages have united into a single mass
and have given rise to a centrum (c), neural arch (z.@), neural spine (v. sy),
transverse processes (¢/.j/) and articular processes (art):

D2

36 COMPARATIVE ANATOMY

are successively developed from its cells, and these differ both
chemically and physically from one another. The primary sheath
(so-called elasticw) is first secreted by the peripheral notochordal
cells: the secondary sheath, which has a similar origin from
the so-called “notochordal epithelium,” appears later, and occurs
in all the Craniata; it is said not to be present in Amphioxus,
the notochord of which, like that of the Tunicata, apparently
represents the oldest and most primitive form of this struc-
ture, such as is still repeated ontogenetically in Elasmobranchs.
The thick secondary sheath, which like the primary, is at first
homogeneous, gradually becomes fibrillar and replaces the primary
sheath fanctionally.

From the surrounding mesoblast a skeletogenous layer is de-
veloped: this not only surrounds the notochord, but extends
dorsally to it as well as ventrally (Fig. 22). Thus a continuous
tube of embryonic connective-tissue is formed enclosing the spinal
cord and only broken through at the points of exit of the spinal
nerves. This stage is known as the membranous stage, and in
it no indication is seen of the segmentation which occurs later in
the vertebral axis. The cause of this segmentation is to be traced
primarily to the muscular-system ; and it is evident, for mechanical
reasons, that the segmentation of the vertebral column must
alternate with that of the muscular segments or myotomes. Small
masses of cartilage arranged metamerically later appear in the
skeletogenous tissue close to the notochord, and these represent the
rudiments of the dorsal and ventral arches and bodies or centra of
the vertebra (Fig. 22, B, D, E). This is the beginning of the
second or cartilaginous stage of the vertebral column; the various
processes (spinous, transverse, articular, &c., Fig. 22, E) are then
formed, and now ossification may occur (bony stage). Those
parts of the fibrous tissue which do not become consolidated in this
manner give rise to the /igaments of the vertebral column.

During these differentiations of the skeletogenous tissue, the
notochord suffers a very different fate in the various Vertebrate
groups; it may increase in size and persist as a regular cylindrical
rod, or it may become constricted at definite intervals by the forma-
tion of vertebral bodies, or even entirely disappear.

All these ontogenetic stages find their exact parallel in the
phylogenetic development of Vertebrates, as the following pages
will show.

Amphioxus, as already mentioned, apparently possesses the
most embryonic type of notochord. It is surrounded by a connec-
tive-tissue layer and is entirely unsegmented.

In Cyclostomes a very similar primitive condition is retained ;
but a secondary sheath becomes developed, and cartilaginous ele-
ments appear in the caudal region: in the adult Petromyzon
these are present all along the notochord in the form of rudi-

VERTEBRAL COLUMN 37

mentary newral (dorsal) arches, which, however, do not meet above
the spinal cord. These cartilages, of which there are two pairs to
each muscular segment or myotome, correspond to the “intercalary
pieces” of Elasmobranchs (p. 38); they serve in the first instance
for the origin and insertion of the muscles, and at the same time
form a protection for the spinal cord. Neural spines also occur
in the middle of the axis, and in the caudal region hemal
(ventral) arches enclosing the caudal aorta and vein, as well as
hamal spines, are present, and fusion of the cartilaginous elements
occurs.

To the condition found in Cyclostomes, that seen in the
Cartilaginous Ganoids, Holocephali, and Dipnoi is directly
connected, inasmuch as the metameric character of the skeletal axis

Fre. 23.—PortioN oF THE VERTEBRAL COLUMN oF Syritudaria. (Side view.)

Fic. 24.—TRANSVERSE NECTION OF THE VERTEBRAL COLUMN OF Aeipenser
ruthenus (in the anterior part of the body).

Ps, spinous process ; WL, longitudinal elastic band ; SS, skeletogenous layer ; Oh,
upper arch ; J/, spinal cord ; P, pia mater; Ic, intercalary pieces; C, noto-
chord ; He, primary, and C's, secondary sheath of the notochord ; Uh, lower
arch ; do, aorta ; /o, median parts of the lower arches, which here enclose
the aorta ventrally ; 7, basal processes of the lower arches.

is essentially indicated by the neural arches. In the two groups last
mentioned, however, skeletogenous cells break through the primary
notochordal sheath (elastica) and so invade the thick secondary
sheath, which in consequence encloses cartilage cells amongst its
fibres. In Chimera calcified rings are also developed in the central
part of the sheath: these are more numerous than the arches.
The latter are developed as paired dorsal and ventral cartilages :
they remain cartilaginous in the Cartilaginous Ganoids (Figs. 25
and 24) and Holocephali, but become densely ossified in the Dipnoi
(Fig. 25). In the caudal region the hemal arches enclose the
eaudal aorta and vein; further forwards the cartilages do not meet
in the middle line below, and consequently the lower arches end

3 COMPARATIVE ANATOMY

pA)

on either side in a laterally-directed cartilaginous projection, or
basal process, ;
The relations of the arches in Elasmobranchs, Bony Ganoids
and Teleosts is similar to that above described. For the further
strengthening of the vertebral column so-called intercalary pieces
(Figs. 23, 24, 26, 28) appear between the upper and -lower arches
in Cartilaginous Ganoids and Elasmobranchs, and these in the

Sag
LF

ae G ua eB

ccs i a nell ene u

Fic. 25.—PortTIoN OF THE VERTELRAL CoLtuMyN oF Protopterus.
C, notochord ; DF, neural spine ; F'7, interspinous bone ; FS, fin-ray.

case of the dorsal arches are often spoken of as interneural plates.
In Elasmobranchs the neural arch may be made up of several
more or less distinct pieces—the neural processes arising from the
centrum, the neural and interneural plates, and the neural spines.
In the Elasmobranchii, the skeletogenous cells invade the
notochordal sheath, as in the Holocephali and Dipnoi; but the
sheath then becomes segmented to form a series of cartilaginous

06 Te

Fic. 26.—Portiox or THE VERTEBRAL CoLtMy oF Scymnus.

WK, centra; Ob, upper arches; Iv, intercalary pieces. The apertures for, the
spinal rerves are seen ip the arches and intercalary pieces.

vertebral bodies or centra, which from the mode of their formation
may be called chorda-centra. The fact is thus accounted for that
the number of arch-elements does not necessarily correspond with
that of the centra in these Fishes. Ossification may occur in the

concave ends of the centra and in longitudinal bars along each
centrum,

VERTEBRAL COLUMN 39

In Bony Ganoids and Teleosts paired dorsal and ventral carti-
lages likewise arise above and below the notochordal sheath, but

in the course of development so
extend at the base as to completely
surround it. From the dorsal carti-
lages the upper arches take their
origin, and from the ventral the
lower ; while the cartilage surround-
ing the notochord gives rise to the
vertebral centra, which may there-
fore be distinguished from those
described above as arch-centra.

In the development of the
centra of both kinds, the notochord
becomes constricted by the growth
of the cartilage at regular intervals,
while the latter undergoes segmen-
tation into centra. Lach point of

Fic, 27.—PortTIoN OF THE VERTE-
BRAL CotumN oF Polypterus.

WK, centra; BI, basal processes ;
Ob, wpper arches ; Ps, neural
spine.

constriction corresponds to the middle of a centrum, «.¢., it is intra-
vertebral in position, and the notochord may here disappear entirely ;

\
ENR

Fic. 28.—PortTIoy of THE VERTEBRAL CoLUMN oF Lepidosteus. (After Balfour
and Parker.)

vertebra’ from anterior surface ; B, two vertebrz from the side. cx, anterior
convex face, and en}, posterior concave face of centrum ; h.a, basal process ;
na, wpper arch ; 7.¢, intercalary cartilages ; /./, longitudinal ligament ; 7.5,

interspinons bone.

40 COMPARATIVE ANATOMY

intervertebrally it remains expanded and so persists as a kind of
connecting- or packing-substance between contiguous centra, which
are consequently of a deeply biccneave or amphicelous form (Figs.
294 and 298).

One of the Bony Ganoids, Lepidosteus, forms a marked excep-
tion to other Fishes as regards its vertebral column, inasmuch as
definite articulations are formed between the centra. A con-
cavity is formed at the hinder end of each centrum (Fig. 28), which
articulates with a convexity on the next vertebra behind
(opisthocelous form). The notochord (except in the caudal region)
entirely disappears in the adult; in the larva it is seen to be ex-
panded dntravertebrally, and constricted intervertebrally, a condition
of things which appears again in the higher types—as, for instance,

Fru. 294.—DIAGRAM SHOWING THE INTERVERTEBRAL REMAINS OF THE
NorocHorp.

C, C), expanded and constricted portions of notochord ; WA, centra; Li, inter-
vertebral ligaments.

Fic. 293.—PorTION OF THE VERTEBRAL CoLUMN oF A Yotxe DouFisi
(Scy/linm canicula), After Cartier.

notochord ; An, outer, and Aw, inner, zone of cartilage ; FA, the fibro-carti-
laginous mass lying between these zones, which is undergoing calcification ;
In, invertebral ligament.

in Reptiles. In a still earlier larval stage, however, the constric-
tions are intravertebral, as in other Fishes.

The vertebral column of Fishes is characterised by a very
uniform character of its elements, so that a distinction can only be
seen between the trunk and caudal vertebre. Its primitive
character is shown by the fact that the neural arches are usually
incomplete dorsally. As a rule, the closing in of the arch is
effected by special pieces of cartilage (comp. p. 38) and by an
elastic longitudinal band (Figs. 24, 28) which is always present:
this also applies to the heemal arches. Articular processes between
the arches (zygapophyses) are usually present in Fishes which
possess bony vertebra; in Rays and Chimeroids only amongst
Fishes are definite articulations formed between the skull and

VERTEBRAL COLUMN 41

vertebral column, and in these Fishes the anterior vertebre are
fused into a single mass.

In the caudal region of Amia the centra are mostly double, an archless
pleuro- or post-centrim alternating with an inter- or pre-centiiin. A some-
what similar condition is found in the Jurassic Eurycormus and other fossil
Ganoids.

As a rule Elasmobranchs and Ganoids possess a greater number of
vertebree (in Alopecias vulpes there are 365) than Teleosts, in which we
seldom meet with more than 70: the Eel, however, possesses more than

200.

The caudal region of the vertebral column deserves particular
attention in Fishes, and the condition of this region in Amphioxus,
Cyclostomi and Dipnoi, may be taken as a starting-point. In
these, the notochord extends straight backwards to the hinder end
of the body and is surrounded quite symmetrically by the tail-
fin, which is therefore spoken of as protocercal or diphycercal
(Fig. 30). This condition is also met with in many Fishes of the

Fic. 30.—Tam or Protopterus.

Devonian strata as well as in young stages of Teleostei. In the
latter, however, the ventral half of the tail-fin with its sup-
porting skeleton (hzmal arches and fin-rays) is, as a result of un-
equal growth, more strongly developed than the dorsal, and the end
of the vertebral column becomes bent upwards, thus giving rise to
a heterocercal tail. This form of tail may be recognised exteinaily,
as in many Elasmobranchs, Ganoids, and numerous fossil Fishes ; or,
may be masked by a more or less symmetrical tail-fin, as in Lepi-
dosteus (Fig. 31), Amia, and more particularly in most Teleosts?
(e.g. Salmo, Fig. 32), in which the heterocercal character is only
visible internally. The posterior end of the vertebral column
is then frequently represented by a rod-like wrostyle, and in
Teleosts one or more wedge-shaped hypural bones (enlarged hemal
arches) generally occur directly beneath it (Fig. 32).

1 The term homocercal is sometimes used to describe the masked heterocerca
condition of the tail in-Teleostei.

42 COMPARATIVE ANATOMY

Amphibia.—The vertebral column of Urodeles may be ditfer-_
entiated into cervical, thoraco-lumbar, sacral, and caudal regions,
and these regions can be recognised, except in certain modified
forms, in all the higher Vertebrates. On account of the absence
cof extremities in Czcilians, the vertebral column can only be

Fic. 31.—Tam. or Lepidosteus.

divided into three regions—cervical, thoracic, and a very short
caudal. In Anura, no special lumbar region can be recognised,
and the caudal portion is modified to form a urostyle (see pp. 41 and
44), The centra of the Amphibia, as well as those of the
Amniota, correspond to arch-centra (see p. 39).

Fie. 32.—CacvaL Exp oF VERTEBRAL COLUMN oF SaLmMon. (From Boas’s
Zoology.)

A, centrum ; h’, urostyle ; n, hemal arch; 2’ hypural bone; 0”, neural arch ; ¢,
neural spine.

The notochord of Urodele larva, like that of most Fishes,
undergoes intravertebral constrictions, while intervertebrally it
grows thicker, and accordingly appears expanded. Thus the
vertebra here also are amphicwious, Later, intervertebral masses
of cartilage become developed, which, together with the bone
which is formed at the same time. in the surrounding conuective-

VERTEBRAL COLUMN 43

‘tissue, extend inwards towards the centre, gradually constricting
the notochord so that it may eventually become entirely
obliterated. Finally a differentiation, as well as a resorption,
extending inwards from the periphery, occurs in these cartilaginous
parts: in the interior of each an articular cavity is formed, so that
in the vertebrae of the higher Urodeles an anterior convexity and

Fic. 33.—LONGITUDINAL SECTION THROUGH THE VERTEBRAL COLUMN OF VARIOUS
Unovetes. A, Ranodonsibericus ; B, Amblystoma tigrinum ; C, Gyrinophilus
porphyriticus (the three anterior vertebre, J, ZZ, [IZ); D, Sulameudring
perspicillata.

‘Ch, notochord ; Jrh, invertebral cartilage: CK, vertebral cartilage and fat-cells ;
XK, peripheral bony covering of centrum; &, ribs and transverse processes ; S,
vertebral constriction of notochord in Amblystomea fiyrinum, without cartilage
and fat-cells in this region ; **, intervertebral cartilaginous tracts; A/h, Mh,
narrow cavities; @p, Gk, articular socket and head; Lig?, intervertebral
ligaments.

a posterior concavity may be distinguished, both covered with
cartilage ; they are, therefore, opisthocelous. A glance at Fig. 33,
A to D, will make this clear.

In the development of the vertebral column of Urodeles we
can thus distinguish three stages:—(1) A connection of the indi-

44 COMPARATIVE ANATOMY

vidual vertebree by means of the intervertebrally expanded
notochord; (2) a connection by means of intervertebral masses
of cartilage; and finally (3) an articular connection. These
three different stages of development find a complete parallel
in the phylogeny of tailed Amphibians, inasmuch as many of
the Stegocephala of the Carboniferous
period, as well as the Perennibranchiata,
Derotremata, and many Salamanders,
possess simple biconcave vertebrae without
differentiation of definite articulations? ,
The bony parts of the vertebre of
Urodeles are not formed from the carti-
laginous sheath of the notochord, but in
the surrounding connective-tissue, there
being only an intervertebral cartilaginous
zone, extending into the ends of the centra.
In the Anura,on the other hand, as in
Elasmobranchs, Teleosts, bony Ganoids,
and the higher Vertebrata, the vertebre
are preformed in cartilage, and true arti-
culations always arise between the
vertebrae: as a rule the convexity is
posterior and the concavity anterior (pro-
celous form). A further difference is
seen in the relations of the notochord,
which persists intravertebrally longer
than intervertebrally, a condition which
leads towards the Reptiles.
The configuration of the caudal region
Fic. 34. —- Verterra, of the vertebral column must also be re-
Cotumy or Discoglossus marked upon, as it differs in tailed and
ee tailless Amphibians. The long caudal
Pa, articular processes; portion of the vertebral column in Frog
Renee aes 4; larve, which is very similar to that of
trunk vertebre; Pte, Urodeles, undergoes during metamor-
a eal eas of phosis a gradual retrogressive change,
some, OF vr ure; and the vertebre of its proximal end
vertebra; Ob, upper become fused together and ossified to form
arch of first vertebra; a, Jong unsegmented dagger-like bone, the
Sy, its condylar facets ; sed :
Po, its anterior pro- uh ostyle (Fig. 34). :
cess; R, ribs. Both neural and haemal arches arise
in direct continuity with the centra.
Heemal arches are, however, present in the caudal region of
Urodeles only.
The neural spines, as well as the transverse processes, which are
as a rule bifurcated at the base and are present from the second

' In certain of the Stegocephala incomplete hoops of bone, the énéer- and
pleuro-centre, twice as numerous as the arches, surrounded the persistent notochord.

VERTEBRAL COLUMN 45

vertebra onwards, show the greatest variety as regards shape and
size, differing in the several regions of the body. The transverse
processes of the single sacral vertebra, which give attachment
to the pelvis, are particularly strongly developed, ‘especially i in the
Anura (Fig. 34).

Articular processes (zygapophyses, comp. p. 40) are well de-
veloped in all Vertebrates from Urodeles onwards, and consist of
two pairs of projections arising from the anterior and posterior
edges respectively of the neural arch. Their surfaces are covered
with cartilage, and overlap one another from vertebra to vertebra
like tiles on a roof: not unfrequently, in Urodeles, the neural
spines also articulate with one another, and thus a well-articulated
and mobile chain-like vertebral column results.

The first vertebra (and this is the only cervical vertebra of
Amphibia), becomes differentiated from the others, and consists of
a simple ring which articulates with the two condyles of the skull,
and also with the base of the latter by means of a more or less
marked process often spoken of as the “odontoid” process (Fig.
34) ; thus a freer movement between the skull and vertebral column
is rendered possible. This vertebra, however, is not homologous
with the first vertebra (7.¢., the atlas) of the higher Vertebrates,
as is demonstrated by a study of its development, which shows
that the real atlas loses its individuality as a separate mass, and
becomes united with the occipital region of the skull1 The
first vertebra of Amphibians is therefore more nearly comparable
to one of the next following cervical vertebre of higher forms.
It possesses posterior zygapophyses only, and its condylar facets
correspond to modified transverse processes.

The number of vertebrze present in Urodeles is inconstant, and varies
greatly : it may reach to nearly 100 (Siren), and in Cecilians may be very
much greater (up to 275). In Anura, on the other hand, there are only
eight precaudal vertebrae and one sacral, in addition to the urostyle. It is
evident from this fact alone that the recent forms of Urodela and Anura are
widely separated from one another.

Reptilia.—In contrast to the numerous fossil forms, only a few
existing Reptiles, viz., Hatteria (Rhynchocephala) and the Geckos
(Ascalabota), retain throughout life the primitive biconcave char-
acter of their vertebre, with the notochord expanded interverte-
brally.

In the generalised Rhynchocephala the formation of the vertebre out of
several pieces, such as occurs amongst the Stegocephala (p. 44), is still indicated
by sutures, each vertebra consisting of two processes, a centrum proper
(pleurocentrum) and an intercentrum.

In all the others, the notochord remains expanded longer in the
intravertebral regions than intervertebrally, but in the adult it be-

1 A similar fusion of the anterior part of the vertebral column with the skull
occurs in some Fishes and in Dipnoi.

+6 COMPARATIVE ANATOMY

comes entirely aborted and replaced by bony tissue. This stronger
and more solid ossification of the whole skeleton forms a character-
istic difference between the Ichthyopsida on the one hand and
the Amniota on the other. As a rule the vertebre cf Reptiles
become definitely articulated with one another, and are of the
procelous type: the above-named forms, with intervertebral re-
mains of the notochord, form an exception to this rule. In Croco-.
diles fibro-cartilaginous intervertebral discs ov meniscr occur between
the centra (Fig. 35).

In Crocodiles the vertebre are mostly proccelous, an exception being seen
in the two sacrals and first caudal. Jn Chelonians there is great variation in
the form of the individual centra of the cervical vertebree—even in the same
individual proccelous, opisthoccelous, biconcave, and even biconvex centra,
with intervertebral dises, may occur ; while the thoracic and lumbar vertebree-
have flattened faces, and are firmly united together by cartilage.

In the Jurassic Ichthyosaurus and Eosaurus the centra were short and
deeply biconcave, like those of Fishes, and the arches were connected with
them by cartilage and connective tissue ; as a sacrum was absent, only a.
precaudal and a caudal region can be recognised. In Plesiosaurus, Plio-
saurus, Nothosaurus, Simosaurus, the Anomodontia and others, the centra.
were also biconcave or flattened.

What has been said as to the classification of the vertebrae into-
different regions in Urodeles, as well as to the presence of the
various processes, usually applies here also to a still greater extent..
Except in limbless form, there are always several cervical vertebrae
instead of a single one: there are also typically at least two sacral.
vertebra. The two first cervical vertebre become differentiated
to form an at/as—usually consisting of three pieces, and an avis.
—with an odontoid bone (Fig. 35, and comp. p. 45).1

The neural spines vary in size, and transverse processes arise
from the centra themselves or close to them. Lower arches,
attached intercentrally (chevron bones) are present in the tail in
Lizards, Crocodiles, and some Chelonians; and besides these,
median inferior processes of the centra themselves (? intercentra) are
seen in many of the vertebre of Lizards, Crocodiles, and Snakes,.
and in the latter paired processes partly enclose the caudal vessels.
The arches in Snakes, Lizards, and Chelonians become united
with the centra by synostosis, while in Crocodiles they remain,
separated from them by sutures (Fig. 35).

In consequence of the absence of a pectoral arch, the vertebral
column of Snakes and Amphisbenians, like that of Cecilians,.
consists of trunk and caudal vertebre only. The vertebral column
of Chelonians deserves particular notice as a large portion of it
becomes anchylosed with the dermal bones of the carapace (p. 33,
Fig. 21), and is thus rendered immovable.

? The odontoid bone corresponds, morphologically to a part of a centrum of the:
atlas. A_ so-called pro-atlas—the remains of a vertebra situated between the:
skull and atlas proper—is present in the Crocodilia (Fig. 35), Hatteria, and.
Chamielaeo, as well as in many fossil forms. >

VERTEBRAL COLUMN 47

In Snakes and some Lizards (Hatteria, Iguana) extra articular
processess (zygosphenes and zygantra) are developed on the neural
arches. In Hatteria and the Geckos, small separate ossifications
(intercentra, comp. p. 43, 44, 46) are present on the ventral side
of the vertebral column between many of the centra. In the caudal
region of Lizards an unossified septum remains in the middle of each
centrum, so that the tail easily breaks off at these points when this
happens the tail grows again, but proper vertebre are not formed.

In fossil Reptiles, which both as regards size and number of species
usually surpassed the existing representatives of the class, the sacrum often
consisted of as many as four or five vertebrae. The following facts will give
some idea of the monstrous proportions of these old genera of Reptiles :—
Atlantosaurus immanis, a North American Dinosaur, reached a length of

LS
5

772

pe #
Fia. 35.—ANTERIOR PorRTION OF THE VERTEBRAL CoLUMN oF 4 Younu
CROCODILE.

WK, centrum; Ob, neural arch ; Ps, neural spine; Js, intervertebral disc ; P¢,-
transverse process, arising from the base of the arch and articulating with
the rib (R, A}, R?) at ¢; A, atlas ; w, ventral element, and » arch of atlas; 0,
“pro-atlas” ; Hp, axis, articulating with the atlas at h; Po, odontoid
process.

about 80 feet, and the transverse diameter of the individual vertebrie
amounted to 16 inches, while Apatoscanris laticollis, found in the same strata,
possessed cervical vertebrae which reached a diameter of 34 feet.

A knowledge of fossil genera of Reptiles is of the greatest interest, as in
many groups important points of connection with Birds can be recognised.

Birds.—The vertebral column of Birds corresponds with that
of Reptiles not only in its phylogenetic relations, but also onto-
genetically. In both groups the notochord eventually disappears
entirely, and the whole skeleton becomes strongly ossified.
Archeopteryx, as well as Ichthyornis (from the American Cre-
taceous), possessed biconcave vertebre, but in existing Birds this
character never occurs except in the free caudal vertebre (p. +9).
Cervical, thoracic, lumbar, sacral, and caudal regions can be distin-
guished. The arches always become united into a single mass
with the corresponding centra, and are no longer separated from

48 COMPARATIVE ANATOMY

them throughout life by sutures, as is the case in certain Reptiles:
even the ligament which keeps the odontoid process of the axis
in its place may become ossified. Fibro-cartilaginous discs or
menisci are present between the centra. In the cervical region,
which is extremely flexible and often very long, the centra are
in nearly all cases connected by means of saddle-shaped synovial
articulations ; the upper part of the bifurcated transverse processes
arises from the arch, the lower from the centrum, and these may
unite with the corresponding forked rib, the vertebral artery and
vein extending through the foramen thus formed (Fig. 36).

In the thoracic and lumbar regions more or fewer of the
vertebree usually become immovably united together.

The sacral region in Bird-embryos, like that in existing adult
Reptiles, consists of two vertebre only, the transverse processes of

RE Pt Upst

Fic. 36, A.—ATLAS AND Axis (from the left side); and B, THrrp CERVICAL
VERTEBRA (ANTERIOR FACE) OF WOODPECKER (Picus viridis).

A. Ob, A, arch and centrum of atlas; +, condylar facet ; Po, odontoid process ;
WA, centrum of axis, and Sa, its saddle-shaped articular surface for the
third vertebra ; Ps, neural spine of axis; Pt, transverse process.

B. Sa, articular surface of centrum ; Ob, upper arch ; Pa, articular process ; Pf, Pt,
the two bars of the transverse process, shown on one side anchylosed with
the cervical rib (2); Ft, vertebrarterial foramen ; Psi, median inferior pro-
cess (hyparpophysis).

which ossify separately and correspond to fused ribs, as in
Amphibians and Reptiles. During further development, however,
a number of other (secondary sacral) vertebre (thoracic, lumbar,
and caudal), with their rudimentary ribs, become fused with the
two primary ones (Fig. 37), so that the entire number of vertebra
in the sacrum may be as many as twenty-three. In Archeopteryx
the sacrum was much shorter than in existing Birds, and fewer
vertebrae were united with it.

In existing Birds the caudal region always exhibits a more or
less rudimentary character, and in its posterior portion the ver-
tebra usually fuse together to form a flattened bone, the pygostyle,
which supports the tail quills (Fig. 111). An exception to this rule
is found only amongst the Ratite, in which all the caudal vertebrae

VERTEBRAL COLUMN 49

remain distinct. That the latter is the more original condition in
Birds is shown by a study of their development as well as by the
condition of the tail in Archzopteryx, in which it was supported by
numerous elongated free vertebre (Fig. 38). Moreover, in many
Birds (e.g. Psittacus undulatus) more vertebrae are formed in the
embryo than are seen in the adult. It must, however, be borne
in mind that the pygostyle may be made up of from six to ten
fused caudal vertebre, and in the sacrum
even a greater number may be included
(cp. p. 48): thus in the common Duck,
seven become united with the pelvis,
eight remain free, and the pygostyle is
composed of ten separately ossified and
fused segments, making in all twenty-
five vertebree originally present in the
caudal region of this Bird.
Mammalia.—The notochord here
persists longer intervertebrally than in-
travertebrally, but it disappears entirely
by the time the adult condition is reached.
A jelly-like pulpy mass, the nucleus
pulposus, persists, however, throughout
life in the centre of the fibro-cartilaginous
menisci which are developed between
the centra. The whole vertebral column
is preformed in cartilage, and the centra
develop in continuity with the arches
but become ossified from separate centres,

Fic. 37.—PELVIs oF OwL
(Stria bubo). Ventral

as do algo the various processes. These sie
ossifications, however, become fused to- W, position of the primary
gether in the adult. The presence of sacral vertebre: be-
bony discs or epiphyses on the ends of tween R and JI, and
the centra which unite with the latter Loic kd elueae em dens
€ oe pe secondary sacral verte-
comparatively late,is very characteristic bre, fused with the
of Mammals; they are however absent primary (1"); Z7, ilium ;

Is, ischium ; P, pubis ;

or only imperfectly developed in Mono- A atime tice
trematas and in existing Sirenia. ilium and pubis; R,
True articulations between the centra last two pairs of ribs.

are never formed, except on the atlas

and anterior face of the axis; but as in Amphibians, Reptiles,
and Birds, well-developed articular processes (zvgapophyses)
are present, arising from the neural arches! The cervical
region is usually the most moveable, and the centra may be so
much hollowed out in this region as to give them an opisthoccelous
character (e.g. Ungulata). In some cases, on the other hand, the

1 In certain Edentata (e.g. Myrmecophaga, Dasypus) extra articular processes
are present besides the ordinary zygapophyses on the posterior thoracic and
lumbar vertebree (Fig. 398.).

E

50 COMPARATIVE ANATOMY

cervical vertebrae may become firmly fused together (Cetacea),
The distal parts of the transverse processes, representing rudi-
mentary ribs, are perforated by the vertebrarterial canal (p. 48):
in Monotremes these remain distinct at any rate for a long time.

EN [P*
ys

y

¥Fia. 38.—Archwopteryx lithographica. From the Solenhofen slates (Jurassic. )
After Dames, from the specimen in the Berlin Museum.

N

The atlas and axis essentially resemble those of Birds, but the
differentiation of the vertebral column into regions characterised
by difference of form is much more sharply marked than in any
other Vertebrates. There are as a rule seven cervical vertebra ;
Bradypus, however, possesses eight to nine, and Tamandua bivit-
tata eight, while in Manatus and Cholcepus there are only six.

VERTEBRAL COLUMN 51

The transverse processes are simple in all but the cervical
region and arise from the base of the arch: in the thoracic region
they are tipped with cartilage on the ventral side of their distal
ends for articulation with the tubercle of the rib (p. 58). In the

lumbar and sacral regions
they arise from the centra,
and contain fused rib-ele-
ments.

In long-necked Ungulates
(e.g. Horse, Camel, Ox) the
neural spines of the anterior
thoracic vertebree are greatly
developed, and a correspond-
ingly strong cervical ligament
(ligamentum nuchze) is par-
ticularly well developed to
support the weight of the
head. This is also true of
antler-bearing animals and of
the Gorilla.

The number of thoraco-
lumbar vertebreve varies greatly
in different Mammals: there
may be as few as fourteen
(Armadillo) or as many as
thirty (Hyrax). In Ungulates
the number is constantly
nineteen. Inthe lumbar ver-
tebree the transverse pro-
cesses are especially long,
and other processes (anapo-
physes, metapophyses, hypa-
pophyses) are characteristi-
cally present in this region.

Thus, as 12 Amphib-
ians, Reptiles and Birds,
the pelvis is connected
with the sacrum by means
of rudimentary ribs. As
in the two last-mentioned
groups, there are not more
than two primary sacral
vertebrae, but except in
Ornithorhynchusand most
Marsupials a few caudal
become later included in
thesacrum and are usually
more or less closely united

Fic. 394.—DIAGRAM SHOWING MODE oF Osst-
FICATION OF Human Axis. (Ventral
surface.) From Flower’s Osteology of the
Mammalia.

o, odontoid process, or centrum of atlas ; c,
proper centrum of axis; na, neural arch ;
as, anterior articular surface ; ¢, ¢, ¢, ¢, epi-
physes, completing the ends of the centra,

Fic. 398.—Sip— View or THE TWELFTH
AND THIRTEENTH THORAIC VERTEBRA
oF Great ANTEATER (A/yrmecophaya
jubata), 3. From Flower’s Osteology of
the Mammatic.

m, metapophysis ; te, facet for articulation of
tubercle of rib; cr, ditto for capitulum
of rib; az, anterior zygapophysis; az',
additional anterior articular facet; p:.
posterior zygapophysis ; pz! and pz”, addi-
tional posterior articular facets.

with it by synostosis. The various processes of the sacral vertebree
are more or less reduced. In Anthropoids, as in Man, the first
sacral vertebra is plainly marked off from the last lumbar by the
formation of the so-called promontory. A sacrum is wanting in

KH 2

52 COMPARATIVE ANATOMY

the Cetacea and Sirenia, in correspondence with the absence of
hind-limbs.

The caudal vertebrae vary extremely in their development, and
excepting in most long-tailed Mammals—such as Kangaroos,
Sirenians, Cetaceans and certain Apes—no longer develop lower
arches. When present these “chevron bones” are intervertebral
in position.

The greatest number of caudal vertebree is found in Microgale longicauda

(forty-eight), Manis macrura (forty-six to forty-nine), Paradoxurus (about
thirty-six), and certain Monkeys (thirty-two to thirty-three).

The caudal region is most reduced in the higher Primates, in
which it gives rise to a stump-like coccyx consisting of at most five to
six rudimentary vertebre, all fused together, and these may even (in
the human subject, especially in the male) fuse with the sacrum.
Many facts as regards the development as well as the structure of
the whole tail-region in the adult show however that the ancestors
of Man must have been provided with a distinct and functional
tail,

II. Ries.

The ribs do not a8 a general rule (with the exceptions to be
noted presently) arise as outgrowths from the vertebra] column, but
become developed independently in the skeletogenous layer—that
is, in the tissue of the somites, and their connection with the
vertebral column is a secondary one. They stand in the closest
connection with the intermuscular septa or myocommata of the
great lateral muscles of the body (Fig. 40 A,) are arranged seg-
mentally, and onto- as well as phylogenetically, pass through a
membranous, a cartilaginous, and a bony stage: their ossification is
independent of that of the vertebral column. In their primitive
form, the ribs have simple, unbifurcated heads, the articulation of
which with the vertebral column first takes place in the region of
the “intercentra ” (p. 47), and from this condition all the later modi-
fications as regards their form and connection are to be derived.

The ribs present great variation in the various vertebrate
Classes : they may be short and stump-like and. almost horizontal
in position, or may grow ventralwards so as to encircle the body-
cavity. Primitively, ribs may be present all along the vertebral
column, but in the higher types they become reduced in certain
regions.

In order to arrive at sound conclusions as to the morphological
value of the ribs, their relations to the soft parts must be taken into
consideration. It is then seen that they are not completely homo-
logous throughout the vertebrate scrics, and that those of Ganoidei,
Teleostei and Dipnoi are not exactly comparable to those of Elasmo-
bianchii, Amphibia, and Amniota (Fig. 404A).

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54 COMPARATIVE ANATOMY

Ganoidei, Teleostei, and Dipnoi—In these forms the ribs,
almost without exception, are connected with the ventral parts of
the notochordal sheath (Dipnoans) or with the “basal processes ”
(Ganoids and Teleosts, see p.38).! This is one point of difference
between the ribs of these forms and those of other Vertebrates:
another is that they are always situated beneath (internal to)
the lateral muscles, between these and the peritoneum (Fig. 40a, A,
B, C). In Teleosts the ribs are at first continuous with the basal
processes and become secondarily segmented off from them: this
may be a ccenogenetic modification.

Towards the caudal region, the ribs gradually take on the form
of hzmal arches, which have precisely the relations of the ribs as

Fic. 408.—Anrrrion END oF THE VERTEBRAL COLUMN oF PoLyprerus. From
the ventral side.

WK, centra ; I—J’,, first five pairs of dorsal ribs; ++, ventral ribs.

described above. In Teleosts, however, the ribs gradually disappear
in passing backwards to the tail, and the hemal arches are formed
by the basal processes alone (Fig. 40a, B, c.). In spite of these differ-
ences, however, there can be no doubt that the ribs of Teleosts are
homologous with those of Dipnoans and Ganoids.

Large rib-like structures (‘‘ upper ribs”) are present in Polypterus (Fig.
408), which have a similar position to that of the ribs in the forms next to be
described ; and amongst the Teleostei (Clupeoidei, Salmonide) small cartilages
are present beneath the lateral line in a similar position to that of the distal

_ + The ribs are rudimentary in certain species of all the orders of Fishes, and
in some cases their place is taken by fibrous bands, arising from the skeletogenous

layer. They are wanting in Cyclostomes.

RIBS 5D

ends of the upper ribs of Polypterus, to which they probably correspond.
There can be lttle doubt, however, that the more delicate bars which le
ventrally to the larger structures in Polypterus correspond to the ribs of
Fishes (‘‘lower ribs”) as described above. It is therefore possible that
Polypterus and certain Teleostei possess the representatives of two sets of
ribs—the one corresponding to those of the majority of Fishes, and the
other to those of Elasmobranchs, Amphibians, and Amniota (Fig. 40a, E).

The intermuscular bones present in the myocommata of Teleosts
probably correspond simply to ossifications of the septa, and have
nothing to do with ribs,

Elasmobranchii.—The small, cartilaginous ribs of these
Fishes arise independently of the vertebral column in the connec-
tive tissue of the intermuscular septa, and extend outwards between
the dorso-lateral and the ventro-lateral muscles (see Fig. 40 A,
D). They are thus not genetically connected with the basal pro-
cesses, although they early become united to them by ligament,
and therefore do not correspond either to differentiations of
the hzemal arches or to transverse processes segmented off
from these.

Amphibia. —The ribs of Amphibians arise in a very similar
manner to those of Elasmobranchs, but differ from them in being
from the first connected with the neural (dorsal) and not with the
heemal (ventral) arches or basal processes. This is due to the
phylogenetic upward displacement of the longitudinal septum
separating the dorso-lateral from the ventro-lateral muscles. Like
those of Elasmobranchii and Amniota, the ribs are situated between
these two masses of muscle, but never extend very far laterally or
ventrally.

The ribs of Urodeles are forked at their proximal ends, and
articulate with bifurcated transverse processes of the vertebra
arising from the arch and centrum respectively: the dorsal part
of the transverse process, arising from the arch, is a new acquis-
ition, In many cases ribs are present only in the region of the
trunk, but occasionally they extend into the base of the tail,
where hemal arches, corresponding to the basal processes of
Elasmobranchs, are also present! Urodeles therefore possess
the representatives of two kinds of ribs, morphologically distinct.
from one another (comp. Polypterus and Teleostei, p. 54). All
the precaudal vertebre except the first usually bear ribs; in rare
cases (Spelerpes) there are a few ribless lumbar vertebre.

In the Anura the ribs are much shorter, and are doubtless
degenerated. Asa rule, they become fused with the broad trans-
verse processes, at the ends of which they are situated ; the anterior
ones may sometimes, however, remain distinct (Fig. 84). They are
never bifurcated, and no trace of hemal arches exists.

1 The elements of true ventral arches (basal processes) may also be present all
along the trunk in the larva of Salamandra maculosa, and are still more marked
in Necturus (Menobranchus).

56 COMPARATIVE ANATOMY

In the Urodele Necturus four cartilaginous ‘‘abdominal ribs” (see
below) may be present in the septa between the ventral parts. of the
myotomes on the level of the shoulder-girdle. Bony abdominal ribs also
occur in certain Stegocephala.

Reptiles. As already mentioned, the ribs of the Amniota are
comparable to those of the Amphibia, but they grow further
ventralwards and so encircle the body-cavity to a greater or less
extent. The dorsal (proximal) section of the rib may also become
segmented from the distal (ventral) portion ; and as a rule a certain
number of the ribs unite together ventrally to form a sternum
(Fig. 44): these are usually distinguished as “true” ribs from the
others, or “ false” ribs. ;

The ribs of Snakes show the least amount of differentiation ; for,
without giving rise to a sternum, they extend along the whole
trunk from the third cervical vertebra to the anus, and retain
throughout a similar form and size. In Lizards, where a dorsal,
unforked, bony and a ventral cartilaginous portion can be distin-
guished, three or four ribs reach the sternum, and are not always
completely segmented off from it.

In Chelonians the cervical ribs unite with the vertebrae more or
less completely, and in the region of the trunk the ribs become fused
with the costal plates of the carapace (p. 33). Their proximal
unbifurcated ends are attached between the centra, at the junction
of centrum and arch. There is no sternum.

The proximal ends of the cervical ribs in the Crocodilia are
bifurcated, in correspondence with the double transverse processes
in this region, and thus a vertebrarterial canal is formed. Further
back, the ribs increase in length, and become segmented into two
or three articulated portions. In passing from before backwards,
their point of origin becomes gradually shifted, so that while the
anterior thoracic ribs ave attached to the centra, the posterior ones
arise entirely from the transverse processes, which increase in size
correspondingly. Hight or nine ribs reach the sternum, and from
the eighteenth vertebra backwards the transverse processes no
longer bear ribs, but only short cartilaginous apophyses.

Uncinate processes (see below) are present in connection with
the ribs in the Crocodilia as well as in Hatteria.

‘* Abdomincl ribs,” arising as ossifications of the inscriptiones tendinex
of the ventral muscles, occur in Crocodiles and in Hatteria, as well as in
numerous fossil Reptiles.

Birds——The ribs of Birds exhibit a much more marked
segmentation into vertebral and sternal portions, both of which
become ossified, and this evidently stands in relation to their
more active respiration. Uncinate processes, moreover, arise from
the vertebral portions in nearly all Birds, and overlap the
ribs next behind them (Fig. 41). The whole costal apparatus

RIBS 57

is rendered still firmer by the frequent fusion of the vertebre
(p. 48), by the individual ribs often being very broad, as well as
by the form and arrangement of the sternum and pectoral arch,
which will be treated of later. The last three or four cervical
vertebrae may bear comparatively large and movable ribs. The

a

Un

z it
ay

Ny i

Fic. 41.—SKELETON OF THE TRUNK OF A FALCON.

S, scapula; G, glenoid cavity for humerus ; Ca, coracoid, which articulates with
the sternum (S#) at +; /u(CZ), furcula (clavicles); Cr, keel of sternum ;
V, vertebral, and Sp, sternal, portion of rib; Un, uncinate process.

number of ribs which articulate with the sternum varies between
two (Dinornis elephantopus) and nine (Cygnus).
(Concerning the sacral ribs, see p. 48.)

Archeeopteryx possessed 12-13 pairs of ‘‘ abdominal ribs ” (comp. p. 56).

Mammals.—The cervical ribs here unite completely with the
vertebrae, and a vertebrarterial canal is thus formed, as in Croco-
diles and Birds. There is considerable variation with regard to the

+

58 COMPARATIVE ANATOMY

number of ribs which reach the sternum, and in some cases the
sternal, as well as the vertebral ribs may become ossified. In both
“true” and “false” ribs (p. 56), acapitulwm, a neck, a tuberculum, and
a body may be distinguished (Fig. 42).
The capitulum of the former usually
articulates with its own centrum as well
as with that next in front, in the
region of the epiphysis; the tuber-
culum articulates with the cartilagin-
ous facets on the transverse process,
In the “false” ribs, these characters
are to a greater or less extent lost.
As already mentioned (p. 51), rudi-
ments of ribs are present in the
lumbar and sacral regions, and unite

fi, 42.—CostaL ARCH OF . :
cial Sue ‘. with the corresponding transverse

processes.

WK, centrum of vertebra ;
Pt, transverse process ;
Ps, neural spine; Cy,
body of rib; Ca, capitu-

This fact, as well as the rudimentary
character and variety in size of the eleventh

lam; Co, neck; 7'b, tuber. and twelfth ribs and the occasional presence
culum; An, cartilaginous of a thirteenth rib in Man, shows that a reduc-
sternal rib; St, sternum. tion in the number of these structures is here

taking place: a gradual shortening of the

thoracic portion of the vertebral column and
a corresponding lengthening of the cervical and lumbar regions. is also
taking place in Mammals generally, and thus it may be stated that the
reduction in the number of ribs is correlated with a higher stage in
development of the Vertebrate body.

Ill. STERNUM.

Never present in Fishes, the sternum appears for the first time
in Amphibians in the form of a small variously-shaped plate of
cartilage situated in the middle line of the chest (Fig. 43). It
arises as a paired cartilaginous plate! in the inscriptiones tendinez
of the rectus abdominis muscle, and therefore may be looked upon
as corresponding to a pair of “abdominal ribs.” Such cartilaginous
abdominal ribs must have been present in greater numbers in
the ancestors of existing Urodeles (comp. Necturus, p. 56). In
many tailless Batrachians (¢.y., Rana) the ventral portion of the
pectoral arch is continued forwards in the middle line, from where
the two clavicles meet, as a slender omosternum (Fig. 48, D):
this has a similar origin, and the proximal portion both of it
and of the sternum become ossified. Thus the sternum and
omosternum of Amphibians are not to be considered as correspond-

? It is unpaired from the first in Triton and Rana, but this is probably due to
an abbreviation of development.

Fic. 43.—Prcrorat Arcu or Various AMPHIBIANS. (From the ventral side). A—Urodele
(diagrammatic) ; B—Axolotl ; C—Bombinator igneus ; D—Rana esculenta.

SS, suprascapula; 8, scapula; CZ, procoracoid; C/! (Cl in D), clavicle ; C, coracoid; EC,
Co'", epicoracoid; +, Pf, G, glenoid cavity for the humerus; S/, Sf, sternum; Lp.
omosternum ; /e, fenestra between procoracoid and coracoid bars. * and t in B indicate
nerve-apertures.

60 COMPARATIVE ANATOMY

ing to differentiations of the pectoral arch,! but as consisting of
skeletal parts which primarily belong to the body-wall, and only
secondarily come into connection with the limb-skeleton. .

In most Urodeles and certain Anurans the edges of the cartilag-
inous sternum are inserted into the grooved median margins of the
two coracoids (Fig. 43, B, C), to which they are united by connective
tissue. In Rana, on the other hand (D), in which the two halves
of the pectoral arch are much more closely connected in the
middle line, by far the greater part of the sternum lies entirely
posterior to the coracoids. In the Perennibranchiata and Dero-
tremata the sternum is much simpler than in other Amphibians,
and in Proteus and Amphiuma it undergoes complete degeneration.

Fic. 44.—Prcrorat ARCH AND STERNUM OF A GECKO
(Hemidactylus verrucosus).

St, sternum; R, ribs; Si, cartilaginous cornua to which the last pair of ribs is
attached ; SS, suprascapula; S, scapula; Co, coracoid; Co’, cartilaginous
epicoracoid: Hp, episternum ; a, b, c, membranous fenestre in the coracoid ;
C1, clavicle ; G, glenoid cavity for the humerus.

Nothing is known with regard to the sternum of fossil Amphibians,
which was probably entirely cartilaginous.

In the Amniota, the sternum arises by a number of ribs on
either side of the middle line running together to form a continuous
cartilaginous tract. An unpaired cartilaginous sternal plate is
formed by the tract of either side becoming more or less completely
fused with its fellow, and from this plate the ribs become
secondarily segmented off by the formation of true articulations.

1 It has been recently shown that in the Elasmobranch Notidanus cartilages

are present in the median ventral line of the pectoral arch which are segmented
off from the coracoids.

STERNUM 61

Later it may become calcified (Reptiles), or converted into true
bone (Birds, Mammals). In Reptiles, Birds, and Monotremes the
coracoids, as in Amphibians, always come into direct connection
with the lateral edges of the sternum (comp. Figs. 41, 44, and 48).

The sternum is greatly developed in Birds, and consists of a
broad more or less fenestrated plate, provided in the vast majority
of Carinatee with a projecting keel, which forms an additional
surface for the origin of the wing-muscles (Fig. 41). In contrast
to these, the cursorial Ratitee are characterised by a broad, more
or less arched, shield-like sternum without a keel. In some
flightless Carinate, however, the keel is rudimentary or even ab-
sent, and a keel may occasionally appear, though not constantly,

Fic, 45.—A, Sternum or Fox; B, or Waurus; anp C, or Man.

Mb, manubrium ; C, body ; Pe, xiphoid process ; R, ribs.

in certain Ratite. The presence or absence of a keel is not, there-
fore, a constant character separating these two groups of Birds
from one another.

A greater number of ribs are as a rule concerned in the forma-
tion of the sternum of Mammals than is the case in Reptiles and
Birds. Consisting at first of a simple cartilaginous plate, the
sternum later becomes segmented into definite bony portions
(sternebrae) the number of which may correspond to the affixed
ribs (Fig. 45, A, B). But in other cases, as, for instance, amongst
Primates (C), the individual bony segments may run together to
form a long plate (corpus sterni). The anterior end of the sternum
becomes differentiated into the so-called manubriwm, and the
posterior end into the xiphoid or ensiform process. ‘The latter owes
its origin in the embryo to the ventral fusion of a true pair of ribs.

1 A keel was also present in the flying Reptile Plesiosaurus, and may be
developed wherever a larger surface for the origin of the pectoral muscles is
required (e.g., Cheiroptera).

62 COMPARATIVE ANATOMY

IV, EPISTERNUM.

Episternal structures, which are wanting in Fishes, Dipnoans
and recent Urodeles, play an important part in fossil Amphibians

Fic. 46.—Prcroran ArcuH oF VARIous STEGOCEPHALA (from the ventral side).
After H. Credner.

A, Branchiosaurus, x 3; B, Pelosaurus x 2; C, Discosaurus, x 2; D, Hylono-

mus, x 2; E, Archegosaurus, x about 4. ps, episternum; Cl, clavicle ;

s, scapula; ¢, coracoid ; s, calcification in the sternum or in the cartilage
of the coracoid.

and primitive Reptiles (¢.g., Stegocephala and Paleohatteria), in
which, both as regards form and structure, they bear a great re-
semblance to the episternum of certain existing Reptiles.

EPISTERNUM

63

In the Stegocephala, the episternum (“ interclavicle”) consists
of a large bony plate, situated ventrally to the sternum, some of

the various forms of which,
as well as its relation to
the pectoral arch and more
particularly to the clavi-
cles, will be seen by refer-
ence to Fig. 46.

The episternum of
Palwohatteria and of re-
cent Lizards and Crocodiles
is essentially similar to
that of the Stegocephala
(Figs. 44, 46, and 47). In
Lacerta and Crocodilus it
arises, from before back-

wards,as a paired structure,.

which is not preformed in
cartilage. An episternum
is wanting in Chelonia and
Ophidia, as well as in
Chameeleo and Anguis.

Fic. 47.—Prctoran Arca oF PaL®OHAT-

TERIA (from the ventral side) After
Credner.
S, scapula ; C, coracoid; CV, clavicle; Eps,

episternun.

In Birds no ‘independent elements corresponding to this

structure can be recognised ;

the ligament extending between

the clavicles and the sternal keel, the periosteal covering of the

rome

Recencee' als | Sabaiais
Fic. 474.—EPpIsTERNUM OF AN

Empryo Moe. (After
A. Gitte).

St, sternum ; es!, central por-
tion and es”, lateral por-
tion of the episternum ;
cl, clavicle; 7.c, ribs. (The
figure was constructed
fro ‘om two consecutive hori-
zontal sections. )

keel which is continued backward
from this ligament, and the median
portion of the fused clavicles when
separately ossified (“interclavicle ”)
may possibly have something to do
with an episternum without being
exactly homologous with it.

The origin and meaning of the
mammalian episternum, which is pre-
formed in cartilage, is not known; it
has probably no direct connection
with the similarly-named structure in
Reptiles, but apparently agrees with
the latter at any rate as regards
position and relations in the embryo
Mole (Fig. 474).

In Monotremes (Fig. 48) and certain
Marsupials a median and two lateral
portions can be distinguished, the
latter being in connection with the
clavicles. In these Marsupials the
median portion unites with the ster-
num, and as in Monotremes, becomes

64 COMPARATIVE ANATOMY

ossified; while the lateral portions remain cartilaginous. In
other Marsupials various stages in the reduction of the episternum
are met with.

Amonest the Placentalia the episternum is retained in the most
independent condition in certain South American Cavies as well as
in the Porcupine and other Rodents in which it consists of a median
and two lateral parts, which are, however, quite independent of one
another, and are only connected by ligaments. The median,

st.
Fic.—48.—PrEcToraL ARcH oF Ornithorhynchus puradoxus.

m.s, manubrium sterni ; c!, c?, c3, first, second, and. third ribs 3 ot, sternebra : ey
scapula ; m.c, coracoid (metacoracoid) ; e.c, epicoracoid ; c/, clavicle; es! nd
es, episternum (‘‘ interclavicle”’). ‘

cartilaginous portion is closely applied to the sternum, while the
lateral portions are connected with the clavicles,

In the Sciuromorphze and Myomorphe the episternal apparatus is still
further modified, the median piece having disappeared (or more probably
having united with the sternum), while the small lateral pieces are attached
to the manubrium and in the Sciuromorphe articulate with the clavicles.
In the Lagomorphe fibro-cartilaginous lateral portions only are present,
extending as far as the clavicles.

Vv. THE SKULL.
Introduction.

The question as to the primary origin of the skull in the
Craniata has always taken a foremost place amongst the morpho-
logical problems relating to the structure of Vertebrates. Until
past the middle of the present century the theory which held the
field was the “ vertebral theory” of Goethe and Oken, according to

THE SKULL 65

which the skull consisted of a number of modified vertebrae

“cranial vertebre”). On this theory, therefore, the skull was
regarded as a special modification of the anterior part of the
vertebral column, and a large number of facts were brought
forward in support of it: even when morphological science had
made further considerable advances, there still seemed to be a
certain amount of justification for it.

The arguments in support of the vertebral theory of the skull
may be briefly stated as follows. As in the vertebral column, three
stages may be distinguished in the skull, ontogenetically as well as
phylogenetically: viz. a membranous, a cartilaginous, and a bony stage
(comp. p. 36). There is thus an important correspondence between
these two parts of the cranio-spinal axis, and this is further em-
phasized by the fact that the notochord always extends for a certain
distance inte the base of the skull, so that the latter is developed on
the same skeletogenous basis as, and in“direct continuation of,
the vertebral axis.

This theory depended on giving an exact account merely of the
sheletogenous elements taking part in the formation of the skull,
and for a long time it was not recognised that this could not
possibly lead to a true interpretation of the origin of the verte-
brate head. To attempt to do so was to “put the cart before the
horse,” by looking upon the last acquesition of the head—its skeleton
—as the leading point for future researches.

It was only very gradually ascertained that the skull has never
consisted of segmentally arranged cartilaginous portions, either in
the course of its ancestral history or in that of the development of
the individual. In the occipital region alone did it possibly at one
time possess distinct neural arches, owing to the assimilation of
more or fewer of the anterior segments of the taunk; and the
view gradually gained ground that this important problem could
not be solved merely by an anatomical and embryological analysis
of the skeleton, but that a number of other parts and organs
which arise much earlier must also be taken into account
and their origin traced :—such are, the sensory organs, brain and
cerebral nerves, cranial muscles, and the anterior part af the
alimentary canal together with the mouth and visceral clefés.

A considerable advance was thus made, and the problem was
vigorously attacked both from the anatomical and embryological
sides; and many of the researches which resulted have become
classical in the history of the subject. It is impossible here to
give more than the barest outlines of the results obtained, and
even now much remains to be elucidated in this complex question,
about many details of which numerous differences of opinion still
exist. Moreover, a knowledge of the development and distribu-
tion of the cerebral nerves is a necessary preliminary to the study
of cranial morphology: these are treated of in a subsequent
chapter, to which the reader is referred for explanation of parts of
the following paragraphs.

F

66 COMPARATIVE ANATOMY

The portion of the skull which is situated along the main
axis in continuation of the vertebral column and which encloses.
the brain is known as the brain-box or cranium, and is primarily
composed of cartilage. A series of cartilaginous arches arise in
serial order on the ventral side of the brain-case; these encircle
the anterior part of the alimentary tract like hoops, incomplete:
dorsally, and are distinguished from the cranial region as the
visceral skeleton. The latter stands in important relation to
branchial respiration, inasmuch as each consecutive pair of arches.
encleses a passage (gill-slit), communicating between the pharynx
and the exterior; this is lined by endoderm, and through it the
water passes in branchiate forms. The foremost visceral arch
bounds the aperture of the mouth, thus forming a firm support
for it, and giving rise to the skeleton of the jaws; the other arches
function primarily as gill-supports. Both cranial and visceral
portions may become ossified later.

Before the cartilaginous skeleton begins to be formed in the
embryo, the greater part of the head consists of a soft, mesoblastic
formative tissue, which gives rise to a membranous capsule around
the brain: the individual cerebral nerves can already be plainly
distinguished (membranous stage, comp. p. 36). The three organs
of the higher senses also appear at a very early stage ; and these, in
the course of further development, come to be situated in definite
bays or cavities within the head, and thus are of extreme im-
portance in modifying the configuration of the skeletal structures
which are formed around them later.

In the embryos of lower Vertebrates (¢.g., Elasmobranchs)
more or less of the mesoblastic tissue which surrounds, isolates,
and supports these organs becomes divided up metamerically into
segments, so that a segmentation into somites (protovertebrw) occurs
in the posterior part of the head as well as in the body (comp.
pp. 8 and 36). The mesoblastic segments of the head, some of
which enclose cavities arismg from the ccelome (or the pre-oral
gut), consist of a tissue from which later become differentiated
all the supporting structwres—including, of course, the skull, as
well as the muscles (myotomes). Without going into further
details as to the number and fate of these segments and their
relation to the cerebral nerves, concerning which there is con-
siderable diversity of opinion, it may be stated that the primary
segmentation of the part of the head posterior to the auditory
organ, in the region of the vagus and hypoglossal nerves, is at any
rate more pronounced than that of the more anterior part of the
head.

The relations of the visceral to the cranial skeleton, and those
of both to the primary segmentation of the head, must also be
taken into consideration. Both cranial and visceral regions must
have been originally segmented, and each myotome at one time
included a ventral portion (lateral plate of the mesoblast)
which enclosed a corresponding section of the cranial ccelome, or

THE SKULL 67

“head-cavity.” Later, however, the visceral region became re-
latively shifted toa greater or less degree, especially in the anterior
part of the head, so that its segments no longer corresponded to
those of the cranial region. Thus we find that the segmentation of
the nervous, muscular, and visceral parts of the head do not correspond
with one another. But although the segmentation of the visceral
portion of the skull has in the course of phylogeny reached a certain
degree of independence, and the cranial portion alone can be looked
upon as being made up of a series of somites, it must not be
forgotten that mesoblastic tissue extends from the head-somites
into the visceral arches, each of the two anterior of which still
contain a coelomic cavity at a certain period of development.

a. Brain-Case (Cranium).

The first cartilaginous rudiments appear in the primitively
membranous skull-tube in the form of a pair of rods, the trabecule
crantt. These lie along the base of the brain, their posterior
parts embracing the notochord; they are thus divisible into pro-
chordal (anterior) and parachordal
(posterior) regions (Fig. 49), which
may be continuous with one another.
The parachordals soon unite to form a
basilar plate, which grows round the
notochord dorsally and ventrally, and
thus early forms a solid support for
the hinder part of the brain. The
slender trabecule project forwards and
enclose a space, which may be spoken
of as the primitive pituitary space
(Fig. 49).

These structures may undergo
further development in many dif-
ferent ways in the various Vertebrate
groups: the trabeculae may become
completely united with one another
in the median line (Fig. 50, A), and ye, 49, First Cartitacrnovs
the connective-tissue of the oral Rupiments or rue SKULL.
mucous membrane may become ossi- ¢, notochord; PH, separate

fied to form a parasphenoid (B). In parachordal elements ; 7'r,
other cases, the trabeculee may become hier ead ees
: ary space; iV, A, e
compressed and partly aborted owing three sense-capsules (olfac-
to the great development of the eyes: tory, optic, and auditory).

this obtains, ¢.g., in certain Reptiles
and in all Birds, in which a fibro-cartilaginous interorbital septum
appears in their place (C).
In most cases a median cartilaginous bar (intertrabecula) is
formed between the trabecule in front, fusing with them, and
F 2

68 COMPARATIVE ANATOMY

forming the ethmo-nasal septum (Fig. 51). It occasionally projects
forwards to form a rostrum (Figs. 55, 56, and 58).

Fic. 50.—DraGRaMMATIC TRANSVERSE SECTIONS OF THE HEAD IN EmMBRYO—

(A) SturRGEoNs, ELASMOBRANCHS, ANURANS, AND MAMMALS ; (B) URODELES
AND SNAKES ; (C) CERTAIN TELEOSTEANS, LIzaARDS, CROCODILES, CHELONIANS,

AND Brrps.

Tr, trabecule cranii; G, brain; 4, eyes; Ps, parasphenoid; JS, interobital

septum ; F, frontal ; O/f, olfactory nerve.

We must now further follow the processes of growth, start-
ing from the primary condition described above, in which

Fic, 51.—Later STAGE IN THE

DEVELOPMENT OF THE PRIM-
ORDIAL SKULL.

C, notochord ; B, basilar plate ;
Tr, trabecula, which has
united with its fellow in
front of the pituitary space
to form the ethmo-nasal sep-
tum (S); Ct, cornu trabe-
cule, and A/F, antorbital
process, which support the
olfactory organ (NK) in
front and behind ; Ol, for-
amina for exit of the olfac-
tory nerves from the crani-
um ; P/’, postorbital pro-
cess of trabecula; A, eye ;
O, auditory organ.

the trabecule have united together in
the middle line. The cartilaginous
basal plate now comes into relations
with the olfactory, optic, and auditory
organs (Fig. 51), around which carti-
laginous capsules are formed. Thus an
olfactory, an orbital, and an auditory
region are early differentiated.

The olfactory and auditory capsules,
especially in higher types, then become
more and more drawn in to the skull
proper, and the lateral edges of the
basal plate begin to grow upwards
round the brain on both sides, eventu-
ally extending even to the dorsal region.
Thus a continuous cartilaginous capsule
is formed, such as persists throughout
life in Elasmobranchs for example.
But in by far the greater number of
Vertebrates, the cartilage does not play
so great a part, and is, as a rule, con-
fined to the base and lower parts of
the sides of the skull and to the sense-
capsules, except in the occipital region,
where it always extends over the brain.
The rest of the skull, more particularly
the roof, becomes directly converted
from membrane into bone. At the
same time, bones may become differ-
entiated in connection with the primary

THE SKULL 69

cartilaginous skull (chondrocraniwm) itself, which is thus more or
less completely replaced by an osteocranium. In general the
higher the systematic position of the animal, the less extensive
are the cartilaginous constituents and the more important the
bony.

b. The Visceral Skeleton.

The primarily cartilaginous visceral arches encircle the anterior
section of the alimentary canal, lying embedded in the inner part
of the walls of the throat (Figs. 52 and 53) and usually becoming
ossified latter. They are always present in a greater number (up
to aS many as nine) in forms which
possess gills than in higher types
(Amniota), in which they gradually be-
come reduced, and may undergo a
change of function, certain of them in
some cases taking on definite relations
to the auditory organ and larynx.

The most anterior arch, serving as
a support for the walls of the mouth
and receiving its nerve supply from the
trigeminal, arises first, and is distin-
guished from the other or post-oral
arches as the mandibular arch. The ye. 59 — Dracrammaric
post-oral arches only function as gill- = Transverse Suction oF A
bearers in the Anamnia: even the first STILL Later Srace IN THE

. re . DEVELOPMENT OF THE.
of these, the hyoid, which is supplied by — Patorpran SKurz.
the facial nerve, becomes modified from

C, notochord ; Tr, trabecule,

those lying behind it: the latter, or
branchial arches proper, are supplied by
the glossopharyngeal and vagus. All
the visceral arches must originally, how-
ever, have borne gills.

Primarily unsegmented, the indi-
vidual post-oral arches may become
broken up into as many as four pieces,
of which the uppermost becomes inserted
under the base of the skull, while the

which enclose the brain
(C) ventrally and later-
ally; O, auditory capsule ;
RH, the cavity of the
pharynx, enclosed by the
visceral skeleton ; 1 to 4,
the individual elements
composing each visceral
arch, which is united
with its fellow by a basal
piece (Cp).

lowermost is connected with its fellow by a median basal piece

(Fig. 52).

The mandibular arch also undergoes segmentation, and becomes

divided into a short proximal piece, the guadrate, and a long distal
mandibular or Meckel’s cartilage (Fig. 53). The quadrate grows
out anteriorly into a process, the palatoquadrate or palatopterygoid,
which usually becomes fixed to the base of the skull and forms
the aaa upper jaw, Meckel’s cartilage forming the lower jaw.

70 COMPARATIVE ANATOMY

The quadrate, which serves as a support (suspensoriwm) for the
jaws, either remains separated from the skull by an articulation—
that is, is only united to it by connective-tissue—or it forms one
mass with it. ;

The hyoid—-which has always close relations with the man-
dibular arch, and may also take part in its suspensorial apparatus *

Fic. 53.—DIsAGRAMMATIC FiGURE OF AN EMBRYONIC ELASMOBRANCH SKULL,
SHOWING THE RELATIONS OF THE VISCERAL ARCHES.

NV, nasal capsule; A, eye; O, auditory capsule; Zr, trabecula; Q and PQ,
quadrate and palatopterygoid, which are bound to the trabecula by ligaments
at t; Mf, Meckel’s cartilage; L, labial cartilages; H, hyomandibular ; K,
hyoid arch ; a to e, branchial arches, between which the gill-clefts (Ito V) are
seen ; S, spiracle ; C, notochord ; b, vertebre, br, brain ; sp.c, spinal cord.

—becomes divided, as do the true branchial arches, into a number
of segments, the upper of which in many Fishes is distinguished as
the hyomandibular (Fig. 53), from which a symplectic may be
differentiated distally. Inthe mid-ventral line there is a basi-hyal
connecting the arch of either side, and embedded in the tongue
(entoglossal or glossohyal).

ce. The Bones of the Skull.

It is usual and convenient to distinguish in the entire skeleton
between the bones which are formed in connection with cartilage,
and eventually replace it to a greater or less extent (cartilage

1 It appears to be probable that the hyomandibular and hyoid proper are
separate in origin: possibly also the spiracular cartilage (p. 75), often looked
upon as representing fused mandibular rays, represents the remains of an entire
arch ; and Dohrn maintains that Meckel’s cartilage and the palatoquadrate each
represents a distinct arch.

THE SKULL 71

bones), and those which arise in connective-tissue, entirely inde-
pendent of cartilage (membrane- or investing-bones). But it must
be borne in mind that there is no hard and fast line between
these, and that histologically they are indistinguishable from one
-another. Bone is always phylogenetically formed outside the
cartilage, and its first appearance within cartilage (as in the
Amniota more particularly) is to be looked upon as a secondary
condition Again, in other cases (¢.g., in parts of the skeleton of
Elasmobranchs), true bones are not formed at all, there being
only a calcareous incrustation of the cartilage (calcified cartilage).
The bones arising in the membranous regions of the skull
(including the perichondrium) primarily come under the category
of the dermal skeleton and, as already mentioned with regard to
the latter, are to be looked upon as originating phylogenetically
in connection with dermal denticles (p. 30). In this manner
the bones of the mouth-cavity of Fishes and Amphibians, for
instance, still arise: it must be. remembered that the epithelium
of the oral cavity is formed by invagination of the outer skin.
Such a mode of origin of the first skull-bones appears to be the
oldest and most primitive, and it is most apparent in the lower
Vertebrates (Fishes). This holds good also for those cases in which
bones are formed merely by deposition of calcareous matter directly
in the connective-tissue layer, without giving rise to tooth-struc-
tures (¢g., all investing bones)—probably owing to an abbrevia-
tion of development.
The following lists give a summary of the most important
bones according to their different relations to the skull.

I. Investing Bones of the Mouth-Cavity (partly lying
within it, partly bounding it on the outer side).

. Parasphenoid.

Vomer.

. Premaxilla.

Maxilla.

Jugal,

. Quadratojugal (in part).
. Dentary.

NID OB Oo WO

1 The different varieties of ossification may be conveniently classified as
follows :—

I. “Membrane Bones.” («) Dermostoses—ossifications of the dermis ; (b)
parostoses—ossifications of the looser subcutaneous tissue; (c) ectostoses—ossifi-
cations of the inner layer of the fibrous investment (perichondrium) of a tract of
cartilage: these may extend into the latter, replacing it, and thus give rise
secondarily to

Il. ‘Cartilage Bones,” (endostoses). : ;

It may, however, happen that in the course of generations an investing bone
may take the place of a cartilage bone, and the formation of cartilage be entirely
suppressed and not repeated again ontogenetically.

-T
Ww

COMPARATIVE ANATOMY

8. Splenial.

y. Angular.

10. Supra-angular.
11. Coronoid.

12. Palatine.

13. Pterygoid.

Il. Investing Bones of the Outer Surface (enumerated
from before backwards).

Nasal.

Lachrymal.

Frontal.

Prefrontal (of Reptiles).
Postfrontal or postorbital.
Supraorbital.

Parietal.

Temporal or squamosal.
Supraoccipital (in part).

SSO Toe ot ie oe ho

Ill. “ Cartilage Bones.”

Basioccipital : 3 : eae
. Basisphewoid | Present only in Amniota (forming the base

" Presphenoid J of the skull).

. Exoccipital (and supraoccipital, in part).
. Pro-, epi-, and opisthotic, also (in Teleostei) sphenotic and
pterotic (forming the bony auditory capsule).

, va \ sphenoid, developed in the trabecular region.

Ore OF NO bE

DID

. Ethmoid, together with the rest of the skeleton of the nose
(turbinals, &c.).

. Quadrate.

. Articular.

. Visceral skeleton (in part).

=
Hoo

ANATOMY OF THE SKULL.
SPECIAL Part.
A, Fishes.!

In the Cyclostomata, the skull is developed essentially in the
manner already described. Later, however, it shows many special
peculiarities, probably in consequence of the suctorial (Petromyzon)

1 In Amphioxus (Acrania) there is no cranial skeleton, and the elastic non-
cartilaginous rods which support the branchial apparatus are not comparable with
the visceral skeleton of the Craniata,

THE SKULL 73

or parasitic (Myxine) mode of life of these animals: the most
important of these is the absence of jaws such as are present in all
other Craniata; for this reason these forms are spoken of as
Cyclostomata to distinguish them from the other craniate Verte-
brates or Gnathostomata. Instead of the jaw-apparatus, which
has doubtless become degenerated, and indications of which as well
as of the hyoid can apparently still be seen (Fig. 54, sb.oc.a,
p. lat.c, sty.c, en.c), a number of cartilages are present supporting
the anterior part of the head. In the adult Lamprey, for instance,
the suctorial mouth is supported by various skeletal elements,
amongst which may be mentioned a ring-like cartilage around the
margin of the dome-shaped oral funnel, between the dorsal side

brbe brb.s

Fic. 54.—SkvLL with BrancuiaL Basket oF Petromyzon marinas.
(After W. K. Parker.)

The cartilaginous parts are dotted. a.d.c. anterior dorsal cartilage; a.lat.c.
anterior lateral cartilage; au.c. annular cartilage ; au.c. auditory capsule ;
br.b. 1—7, vertical bars of branchial basket ; br.c/. 1—7, external branchial
clefts ; cu.c. cornual cartilage; cr.r. cranial roof; /.c. 1—4, longitudinal
bars of branchial basket ; /y.c. lingual cartilage; m.r.c. median ventral
cartilage ; na.ap. nasal aperture; nch. notochord ; Nv. 2, foramen for optic
nerve ; o/f.c. olfactory capsule; pe.c. pericardial cartilage; p.d.c. posterior
dorsal cartilage; p./at.c. posterior lateral cartilage; sh.oc.a. sub-ocular
arch ; st.p. styloid process ; sty.c. styliform cartilage ; ¢. teeth.

t

of which and the brain-case are a couple of large overlapping
cartilages : the tongue is supported by a long, lingual cartilage.
On the mucous membrane covering the annular and lingual
cartilages inside the oral funnel are a number of horny tecth.
The fibro-cartilaginous olfactory sac is unpaired, and opens
on the dorsal surface of the head by a single nostril. The
visceral skeleton also shows many exceptional peculiarities: it
consists of a delicate cartilaginous basket-work (Fig. 54), and has
a very superficial position; we may -accordingly speak of the
unsegmented cartilages of which it is composed as “eatra-
branchials” to distinguish them from the true branchial arches of
the Gnathostomata.

74 COMPARATIVE ANATOMY

In Myxine, the extra-branchial basket-work is quite rudimentary and
amongst other peculiarities, the long nasal passage 1s surrounded by
cartilaginous rings, and communicates with the pharynx by a naso-palatine

duct. :
No fossil Cyclostomes are known, but Paleospondylus gunn from the Old

Red Sandstone of Caithness possibly shows affinities with this group.

In the Elasmobranchii and Holocephali the skull presents
the simplest conditions and most easily comprehensible relations,
so that it may be taken as the starting-point for the study of the
skull of ali other Vertebrates. It consists of a simple carti-
laginous and fibrous capsule either more or less immovably united
with the vertebral column (Squalide,) or connected with it by
articulations only (Raiidze and Holocephall).

Fic. 55.—SKULL or Docrisy (Scyllinm canicula). (From T. J. Parker’s
Biology, after W. K. Parker.)

Cr. cranium ; aud.cp. auditory capsule; or. orbit; o/ficp. olfactory capsule ; 7.
rostral cartilage ; hy.m. hyomandibular ; wp.j. palatoquadvate ; /.j. Meckel’s
cartilage ; hy.cn. ventral part of hyoid arch ; /g./g’. ligaments supporting the
jaws from the cranium ; /b. labial cartilage ; br.a. 1—5, branchial arches ;
br.r, br.r’, branchial rays arising from the hyoid and branchial arches; ex.
br. extva-branchial cartilages; Nv. 2, optic foramen; Nv. 5, foramen for
trigeminal and facial nerves. (The spiracular cartilage is not indicated. )

True bones are never developed, the cartilage being merely
calcified. In Elasmobranchs the palatoquadrate and Jower jaw
are provided with numerous teeth, arranged in rows; in the
Holocephali, the teeth have the form of strong and sharp-edged
plates.

The nasal region is often elongated to torm a long cut-water or
rostrum (intertrabecula), at the proximal end of which the olfactory
sacs are situated, their cavities being separated from the cranial
cavity by a fibrous membrane (“lamina cribrosa”). Behind them
are the deep orbital hollows, which are bounded posteriorly by the

THE SKULL 75

strongly projecting auditory regions. Labial cartilages are present
in connection with the lips, nostrils, and jaws (Figs. 55, 56, and 57).

The palatoquadrate is usually only united to the basis craniil by
ligaments, but in the Chimeroids (Fig. 57) it becomes immovably
fused with it, whence their name of Holocephali. In the Sharks
and Rays the palatoquadrate is not directly united to the skull, but
is suspended from it by the hyomandibular (p.70, Figs. 55 and 56).
In this case the skull may be described as hyostylic, to distinguish
it from autostylie skulls, in which the hyoid takes no part in
the suspensorium (Fig. 57). A cleft, the spiracie, is situated in
front of the hyomandibular, and leads into the cavity of the mouth ;
on its anterior wall may be found remnants of the embryonic
spiracular gill, beneath which is a spiracular cartilage (comp. p. 70,
and Fig. 56).

The branchial skeleton is always well developed, and owing
to secondary segmentation and fusion of its parts exhibits char-

ALBrt EBr.2

HBr.
Fic. 56.——SkuLL or Sate. (After W. K. Parker.)

Au, auditory capsule ; Na, olfactory capsule ; P..N, prenasal rostrum ; Pl. Pt, Qu,
palatoquadrate bar ; Afri, mandibular (Meckel’s) cartilage ; ./. Pt, spiracular
cartilage ; H.M, hyomandibular ; 7.h./, interhyal ligament ; #. Hy, epihyal ;
C. Hy, ceratohyal; H.Hy, hypohyal; A.Br, 1, 2, 5, hypobranchials ; above
them are seen the cerato-, epi-, and pharyngo-branchials ; IZ, optic foramen ;

V, foramen for trigeminal and facial nerves. (The branchial rays and extra-
branchials are not indicated. )

acteristic modifications. On the outer circumference of each
branchial arch, as well as on the hyomandibular and hyoid, radially-
arranged cartilaginous rays are situated, which serve as supports
for the gill-sacs (Fig. 55). Externally to these rays small rod-like
“extra-branchial” cartilages are present.

In nearly all Elasmobranchs the gill-slits open freely on to
the surface of the body, but in Chlamydoselache and the Holo-
cephali a fold of skin arising from the hinder border of the
hyomandibular overlies them. This is the first indication of a gill-
cover or operculum, such as is present in Teleosts and Ganoids.

Amongst the Ganoids, the lowest condition is met with in

76 COMPARATIVE ANATOMY

those formsin which the hyaline primordial skull, immovably fixed -
to the vertebral column, is still retained (Fig. 58). These forms
are spoken of as Cartilaginous Ganoids. As in Elasmobranchs,
the cranial cavity reaches forwards to the ethmoidal region, but is
separated from the latter by cartilage. The appearance of detinite
bones, however, divides them sharply off from the Elasmobranchs,
and proves their skull to be at a much higher stage of develop-
ment. These bones have the form of richly sculptured plates and
shields, and are developed partly from the mucous membrane
lining the mouth and covering the visceral skeleton, and partly
from the skin covering the roof of the skull. In the first-named

Jrel

Fic. 57.—Skuny or Chimera monstrosa, LATERAL ViEw. (From
Parker and Haswell’s Zoology, after Hubrecht.)

@.8.C. position of anterior semicircular canal; c.hy. ceratohyal; ep.hy. epi-
hyal 3; Jr.cl. frontal clasper ; h.s.c. position of horizontal semicircular canal ;
2.0.8. interorbital septum; (b. 1, lb. 2, Ib. J, labial cartilages ; Mch.C.
mandible; Vv. 2, optic foramen; Nv. 10, vagus foramen; olf.cp. olfactory
capsule ; op.r. opereular rays; pal.qu. palatoquadrate ; ph.hy. pharyngo-
nye pe ¢. position of posterior semicircular canal; qu. quadrate region ;

. rostrum.

region a narrow parasphenoid forms a roof to the oral cavity
and extends for some distance along the ventral side of the
vertebral column. Ali- and orbito-sphenoids are present in
the walls of the brain-case. The operculum is more pronounced
than in the Holocephali, and is also supported by bones. The
whole palato-mandibular apparatus, which is comparatively small
and in connection with which bones are formed, is connected very
loosely with the skull by means of a hyomandibular and sym-
plectic, as well as by ligaments (Fig. 58).

The dermal skeleton attains a much more considerable develop-

THE SKULL 77

ment in a second group of these Fishes—the Bony Ganoids—
and gives rise to a dense armour composed of numerous bones
lying on the roof and extending into all parts of the skull and
jaws (Fig. 59). The cartilage thus becomes reduced : it is, however,
largely retained in Amia. The opercular bones are more highly
developed than in cartilaginous Ganoids, and consist of an oper-
culum, a preoperculum, a suboperculum, and an interoperculum.

Tf all the membrane bones are removed and the cranium separated from
the vertebral elements which are fused with it, a surprising similarity will be
seen between the skull of Polypterus and that of Elasmobranchs—more par-
ticularly that of Chlamydoselache and Notidanus. On the other hand, the chon-
drocranium of Polypterus shows certain resemblances to that of the Amphibia.

Rel Sig
NA oa.

we, _
= SOT ne

wy
2 ys ace i < °
Ri
+4 : oe
Cop
Fic. 58.—CraniAL SKELETON OF STURGEON (Acipenser) AFTER REMOVAL OF THE
EXOSKELETAL Parts.

WS, vertebral column ; Sp, apertures for spinal nerves ; Psp, neural spines ;
Ob, neural arches ; C, notochord; GK, auditory capsule; PF’, AF, postor-
bital and antorbital processes ; Orb, orbit ; 7, optic foramen; x, vagus
foramen ; Na, nasal cavity ; R, rostrum; *, prominent ridge on the basis
cranii ; Ps, Ps}, Ps", parasphenoid ; PQ, palatoquadrate ; Vu, quadrate ; Afd,
mandible ; De, dentary ; Ar, articular ; Hm, hyomandibular ; Sy, symplectic ;
Ih, interhyal ; hy, hyoid ; J to V, first to fifth branchial arches, with their
segments—the double pharyngo-branchial (a), the epibranchial (b) the cerato-
branchial (c), and the hypobranchial (¢); Cop, basal elements of the visceral
skeleton ; R2, ribs.

The branchial skeleton in Ganoids consists of four or five more
or less strongly ossified gill-arches, decreasing in size antero-
posteriorly (Fig. 58); and in bony Ganoids the surface which looks
towards the throat is beset with teeth.

The Ganoidei are of special interest, as they, with the Elasmobranchii,
constitute the entire Fish-fauna through the Silurian, Devonian, and Carbo-
niferous periods, and as the Teleostei which appear later, are doubtless derived
from them. They also show connection with the Dipnoi and with the oldest
Amphibia from the Carboniferous and Trias (Ganocephulu, Stegocephala).

In the Teleostei, the skull presents a large amount of varia-
tion ; its ground-plan, however, may always be derived from that

78 COMPARATIVE ANATOMY

of the bony Ganoids, as is best seen by a comparison of the
Siluroids with Amia. On the other hand, no relations with the

t

Fra. 59.—SKULL oF Polypterus bichir FROM
THE DorsAL SIDE.

Pmzx, premaxilla ; Na, external nostril ; V,
nasal; Sb, Sb!, anterior and posterior
suborbital; Orb, orbit; MM, maxilla;
Sp, spiracular bones; PO, preopercu-
lum (?); SO, suboperculum ; Op, oper-
culum; F, frontal; P, parietal; a, b,
c, d, swpraoccipital shields. The two
arrows pointing downwards under the
spiracular shields show the position of
the openings of the spiracles on to the
outer surface of the skull.

Amphibia are observable,
and we must consider the
whole group of the bony
Fishes as a side branch of
the piscine phylum.

Much of the cartilagin-
ous primordial skull persists
in most Teleostei1; the
cranial cavity may either
reach between the eyes as
far as the ethmoidal region,
or it may become narrowed
and arrested in the orbital
region (Fig. 50, ©), in
which ali-, orbito-, and
basi-sphenoid _ ossifications
may occur (Fig. 61). The
olfactory organs, as in most
other Fishes, consist of two
sacs lying in the cartilage of
the ethmoidal region.

The palatoquadrate bar
becomes differentiated into
a row of bony plates—
the quadrate, meso- and
metapterygoid, pterygoid,
and palatine. The audi-
tory capsule ossifies from
five centres (see p. 72),
and in the occipital region,
as well as on the dor-
sal surface of the skull,
numerous bones are de-
veloped, for details of which
the reader is referred to
Figs. 60 and 61.

In many Teleosts a canal,
lying in the axis of the base of
the skull, encloses the eye-
muscles, and opens on either
side into the orbit.

All the bones bounding the oral cavity, viz., the vomer, the
parasphenoid, the premaxilla, and the maxilla, may bear teeth.
The maxilla, however, is usually edentulous, and both it and the

THE SKULL 79

premaxilla vary much as to their development : the latter may even
be absent.

Besides the above-mentioned bones in connection with the
palatoquadrate bar, the cranial capsule of Teleosts is sur-
rounded by other outworks consisting of bony plates and_ bars.
These arise as true dermal bones in the region of the eyes (orbital
ring), and in the gill-covers (opercular bones) : the latter are similar
in number and name to those of bony Ganoids. A large number of

sphot par See

i
t
i
t
\

= eprot
_ptler yom

= tnlop

symp

Sbrunchiost

dent avt

1
1
i
1
i
:

preop

Fic. 60.—CRANIAL SKELETON OF THE SaLMoyx. (From the left side. )

soo

Pmzx, premaxilla; eth, supraethmoid ; nas, nasal; ma, maxilla; juy, jugal;
pt, pterygoid ; mpt, mesopterygoid ; mtpt, metapterygoid ; Quad, quadrate ; .
hyom, hyomandibular ; pal, palatine; fr, frontal; v, 0, 0, 0, orbital
Ting; par, parietal; sphot, sphenotic ; epiot, epiotic; pter, pterotic ; socc,
supraoccipital ; op, operculum ; prwop, preoperculum ; intop, interoperculum ;
subop, suboperculum ; branchiost, branchiostegal rays; dent, dentary; art,
articular ; Zunge, tongue.

branchiostegal rays are developed in the ventral part of the oper-
cular fold, or branchiostegal membrane (Fig. 60).

Anteriorly, the opercular apparatus lies against a bony chain
consisting of three pieces—the hyomandibular, symplectic, and
quadrate—which serves as a suspensorial apparatus for the lower
Jaw (Fig. 60). The latter consists of Meckel’s cartilage and of
several bony elements, the largest of which is the dentary:

80 COMPARATIVE ANATOMY |

SOCC------

seal

on isth

q

basoce--~~

;
f
i h ‘
Psp ; ;

basph proot

Fia. 61.—A. CRANIAL SKELETON OF SALMON AFTER REMOVAL OF THE JAwWs,

AND ORBITAL AND OPERCULAR Bonzs. (From the right side.)
B. Longitudinal section of the same. The cartilaginous parts are dotted.

basoce

vo, vomer; psph, parasphenoid ; fr, frontal; ehteth, ectoethmoid ; socc, supra-
occipital ; exocc, exoccipital ; basocc, basioccipital ; Col.re77, point of connec-
tion of the skull with the vertebral column; basph, basisphenoid ; orbsph,
orbitosphenoid ; alsph, alisphenoid ; cjiot, epiotic; pfero, pterotic ; opisth,

opisthotic; proot, prootic; sphot, sphenotic; .V.o/f, canal for the olfactory
nerve,

the others are, the articular, angular, and coronoid. The last two,
however, may be wanting.

The hyoid arch is followed by four branchial arches and a
rudimentary fifth which forms the ‘inferior pharyngeal bone.”

THE SKULL , 81

The dorsal segments of these arches become fused together to
form the “superior pharyngeal bone,’ which, like the inferior
pharyngeal, usually bears teeth.

A curious asymmetry is seen in the head of adult Pleurunectide. When
hatched, these Fishes are quite symmetrical, but later on the eye of one side
becomes rotated, so that eventually both eyes are situated on the same side ;
in consequence of this, the skull also becomes asymmetrical.

The tactile barbules present on the head of many Fishes (¢.g., Siluroids)
are supported by skeletal parts.

B. Dipnoi.

The skull of the Dipnoi is in a sense intermediate between that
of the Holocephali, Ganoidei, and Teleostei, on the one hand, and

YooN
‘
iy
See

i
4
\
)
9
J
oa

Fic. 62,—CraniaL SKELETON, PEcTORAL ARCH, AND ANTERIOR EXTREMITY OF
Protopterus.

W, W?, the vertebrae which are fused with the skull, with their neural spines (Psp,
Psp) ; Occ, exoccipital, with the hypoglossal foramina ; Ob, auditorycapsule :
Tr, trabecular region, with the foramina for the trigeminal and facial nerves ;
FP, fronto-parietal ; Ht, membranous fontanelle, perforated by the optic
foramen (17); SK, supra-orbital; SH, supra-ethmoid; A, cartilaginous
nasal capsule; AF’, antorbital process (the labial cartilage, which has a similar
position and direction, is not indicated) ; PQ, palatopterygoid, which converges
towards its fellow of the other side at P@!; Sq, squamosal, covering the
quadrate; A, A}, articular, joined to the hyoid (Hy) by a fibrous band (ZB) ;
D, dentary; +t, Meckel’s cartilage, which is freely exposed, and grows
out into prominences; SL, u, 6, teeth ; Op, Op, rudimentary opercular
bones ; J to V, the five branchial arches; AR, cranial rib; LK, AK,
lateral and median bony lamelle which ensheathe the cartilage of the
pectoral arch (Kn, Kn); co, fibrous band which binds the upper end of the
pectoral arch with the skull; x, articular head of the pectoral arch, with
which the basal segment (b) of the free extremity articulates ; *,*, rndimen-
tary lateral rays of the extremity (biserial type) ; 1, 2, 3, the three next seg-
ments of the free extremity ; A, external gills.

G

82 COMPARATIVE ANATOMY

that of Amphibia on the other. In certain respects, however, it
presents special characters in which it differs from that of all
these forms.

The chondrocranium is retained either entirely (Ceratodus) or
at any rate to a large extent (Protopterus and Lepidosiren), and
the cartilage bones are much less numerous than in Ganoids,
exoccipitals only being present (Fig. 62). The cranial cavity
extends forwards between the orbits to the ethmoidal region, and
the lamina cribrosa is largely cartilaginous. The quadrate, which
is covered by a sgquamosal (which corresponds to the preopercu-
lum of Fishes), is fused with the cranium, and the connection
between the latter and the strongly ossified palatopterygoid, which
unites with its fellow anteriorly, is a very close one.

The lattice-like cartilaginous nasal capsules are situated right
and left of the apex of the snout, close under the skin. As in
all the higher Vertebrates, each nasal cavity communicates with
the mouth by internal nostrils (choane) as well as with the exterior
by the external nostrils, which are, however, covered by the upper
lip. The labial cartilages are directly connected with the inter-
nasal septum.

The occipital region is immovably connected with the
vertebral column, some of the anterior vertebre being firmly
united with the skull. The teeth, which are sharp and blade-
like, are covered with enamel, and are borne on the palatoptery-
goid and mandible; small “vomerine teeth” are also present,
though there is no vomer. The gill-covers and branchiostegal
rays are greatly reduced, and even the five cartilaginous gill-
arches are in a very rudimentary condition in Protopterus and
Lepidosiren.

The strong lower jaw is ossified by an articular, a dentary, an
angular, and a splenial, on the last mentioned of which the teeth
are borne; Meckel’s cartilage extends for a short distance an-
teriorly to the dentary.

The Dipnoi are an extremely ancient group ; they existed in the Trias and
Carboniferous periods, and possibly even extended into the Silurian. Several
facts as regards their skull cannot be satisfactorily elucidated until something is
known of its development. The morphology of the so-called ‘cranial rib”
(Fig. 62), for instance, is not at present understood.

c. Amphibia.

Urodela.—The comparatively simple skull of tailed Amphi-
bians is distinguished from that of bony Fishes in general
principally by negative characters—on the one hand by the
presence of less cartilage in the adult, and on the other by
a reduction in the number of bones. In the larval condition
(Fig. 63), the chondrocranium, with its nasal, orbital, and auditory

Fov-

THE SKULI 83

Pune Vo IN

Sgu

e oS
Cee Coce Osp
Fic. 63.—SKuLL or A Youne Fic. 64.—SkKuLL oF Salamandra atra
AXoLoTL. Ventral view. (Aputt). Dorsal view.

Bux CF
e

Cun

Fic. 65.—SKvuLu or Salamandra atra (ADULT). Ventral view.

Tr, trabecula; OB, auditory capsule ; Fov, fenestra ovalis, closed on one side by

the stapes (St); Lgt, ligament between the stapes and suspensorium ; Cocc,
occipital condyles ; Bp, cartilaginous basilar plate between the auditory cap-
sules; Osp, dorsal tract of the occipital cartilage ; IN, internasal plate,
which extends laterally to form processes (7’F'and AF) bounding the internal
nostrils (Ch); NK, nasal capsule; Can, nasal cavity ; Na, external nostrils ;
Fil, foramen for the olfactory nerve ; Z, tongue-like outgrowth (intertrabecula)
of the internasal- plate, which forms a roof for the internasal cavity ;
Qu, quadrate ; Ptc, cartilaginous pterygoid ; Pot, otic process, Ped, pedicle,
and Pa, ascending process, of the quadrate; Ps, parasphenoid; Pt, bony
pterygoid ; Vo, vomer; Pl, palatine; Pp, palatine process of maxilla ; Vop,
vomero-palatine ; Pma, premaxilla; M, maxilla; Os, sphenethmoid; As,
prootic; N, nasal; Pf, prefrontal, perforated at D for the lachrymal duct ;
F, frontal; P, parietal ; Squ, squamosal (‘‘ paraquadrate,” Gaupp) ; LT, optic,
V, trigeminal, and VUJ, facial foramina; Mt, point of entrance of the
ophthalmic branch of the fifth nerve into the nasal capsule.
G2

84 COMPARATIVE ANATOMY

regions, has very distinctly the relations described in the introduc-
tion to this chapter. The auditory capsules (Figs. 63 to 65)—which
are bound together by cartilaginous tracts in the basi- and supra-
occipital regions, and generally become strongly ossified later by
the exoccipitals and prootics—show a new and _ important
modification as compared with those of Fishes in the presence of
an aperture, the fenestra ovalis, on the outer and lower side
of each. This fenestra is closed by a cartilaginous plug, the
stapedial plate, probably corresponding to a part of the wall of
the auditory capsule; from it a rod-like cartilage or bone, the
columella auris, corresponding phylogenetically to the upper
element of the hyoid arch, extends outwards towards the quadrate
in most Urodeles and serves to conduct the sound to the inner
ear, the position of the semicircular canals of which is indicated
by corresponding cartilaginous ridges on the capsule.

In all Amphibians two condyles for articulation with the first
vertebra are developed on the ventral periphery of the foramen

I TG oo WV VV,

Fic. 66.—SkULL anD VISCERAL ARCHES OF Menopoma. (From the side.)

I, mandible ; II, hyoid ; ITI-VI, branchial arches; gu, yuadrate, above which
is the squamosal; ar, articular; mk, Meckel’s cartilage, enclosed by the
dentary bone.

magnum. The occipital region is ossified by two exoccipitals, a
bony supra- and basioccipital rarely being present in recent
forms (certain Anura).

The large nasal capsules, consisting throughout life of consider-
able cartilaginous portions, are connected with the auditory
capsules by means of the trabeculae, which give rise to the side
walls of the skull and become more or less entirely ossified as
the sphenethmoid and prootics. The cranial cavity is closed
dorsally by the frontals and parietals, and ventrally by the
parasphenoid, which is sometimes provided with teeth. In
front of it are the vomers, which bound the internal nostrils; in
adults each vomer becomes fused with the corresponding palatine,
which forms a delicate bar lying on the ventral surtace of the

THE SKULL 85

parasphenoid. These relations are secondary, for in the larval
condition a typical palatoquadrate or pterygopalatine bar is present
(Fig. 63). The lamina cribrosa (p.74) is either cartilaginous (¢.g.,
Salamandra) or membranous (¢.g., Triton); or the cranial cavity
may be closed in front by special modifications of the frontals.

On the outer side of the vomer lies the maxilla, and in front of
this is a premaxilla which usually encloses, or at least bounds, a
cavity. The latter bone extends on to the dorsal surface of the
skull and abuts against the nasai, behind which usually follows a
prefrontal.

‘The suspensorium is much more simple than that of Fishes
(Figs. 68—66). It consists of the quadrate only, which has
usually four typical processes connecting it with surrounding parts.
and which becomes fused secondarily with the skull. On the
outer surface of the quadrate an investing bone, the squamosal,1
becomes developed.

In Tylototriton verrucosus the quadrate sends forwards a process which
connects it with the maxilla: this is quite exceptional amongst Urodeles.

With the exception of the lower jaw, in connection with which
articular, splenial, and dentary bones are developed, the visceral
skeleton of Urodeles undergoes various modifications in the different
types. We may consider the ground-form, as exhibited in the larva,
to consist of five pairs of bars in addition to the mandibular arch
(Fig. 66). The anterior bar, or hyoid, consists of two segments (Fig.
67, A), as do also the two first branchial arches. The third and
fourth branchial arches are much smaller, and each is composed of
a single segment. All the above-named arches are connected
with their fellows of the other side by means of a single or double
basal piece. At the close of larval life, that is, when the gills are
lost, the two hinder pairs of arches disappear entirely, while the
two anterior pairs undergo changes as regards form and position,
and may become more or less densely ossified (Fig. 67, B—D).

In the genus Spelerpes, which possesses a sling-like tongue, the dorsal
segment of the first branchial arch grows out into a long cartilaginous fila-
ment, which extends far back under the dorsal integument (Fig. 67, D).

The skull of the @ymnophiona differs from that of Urodeles mainly in its
extremely solid and strong character, the ossifications being more extensive.

In the extinct tailed Amphibians (7.e., Stegocephala, Fig. 68) some of which
were comparatively gigantic, the cranial bones were very numerous and dense.
A parietal foramen was present, as well as a ring of orbital bones. These
forms possessed the same number of visceral arches as Urodeles, and it has
been shown that they (e.g., Branchioscurus) underwent a metamorphosis.
Existing Amphibia cannot have been derived directly from them.

Anura.—The skull of the tailless Batrachia is at first sight
very similar to that of Urodeles. It undergoes, however, an

According to Gaupp, a true squamosal is never present in existing Amphibia,
and the bone which is usually so designated he calls the paraquadrate.

86 COMPARATIVE ANATOMY

essentially different and much more complicated development,

and cannot in any way be directly derived from that of tailed:

Amphibians.

Epp br ED:
A

Boel BL

Kebrd
pe
Oth
B

Fie. 67.—HyopraNcHIAL APPARATUS OF URODELES. A, Axolotl (S/redon stage

of Amblystoma); B, Salamandra maculosa; C, Triton ecristatus; D, Spelerpes
fuscus.

Bbr, I, I, first and second basibranchial; AeH, ceratohyal ; ApH, hypohyal ;
Kebr I, II, first and second ceratobranchial ; Lpbr £ to LV, first to fourth
epibranchial; KH, A, small anterior and posterior pairs of cornua ;
O.th, part of skeleton of larynx ; G.th, thyroid gland.

A suctorial mouth, provided with labial cartilages and horny
jaws, is present in the larva. An advance on Urodeles is seen in
the formation of a tympanic cavity which is closed externally by a
tympanic membrane, while internally it opens into the mouth by an

hae

THE SKULL ST

Eustachian aperture. With the exception of certain small regions
(fenestree) on the dorsal side, the skull of Anura forms a com-

Fic, 68.—RESTORATION OF THE SKULL OF A STEGOCEPHALAN (from the
Carboniferous of Bohemia). (After Fritsch.)

Pmx, premaxilla ; /, maxilla ; V, nasal ; V7, nostril; frontal ; Pf, prefrontal ;
P, parietal; Fp, parietal foramen; Soce, supraoccipital ; Br, branchial
apparatus : Oc, sclerotic ring (orbital bones.) ;

plete cartilaginous box, the ethmoid region being at first entirely
cartilaginous, and later becoming ossified by a sphenethmoid, which

Fic. 69.—-SKULL oF Rana esculenta. Ventral view. (After Ecker.)
The investing bones are removed on the right side.

Cocc, occipital condyles : Olat, exoccipital ; A’, auditory capsule ; Qu, quadrate ;
iy, quadratojugal : Pro, prootic ; Ps. parasphenoid : As, alisphenoid region ;
Pi, bony pterygoid ; PP, palatopterygoid ; FP, frontoparietal ; Z, spheneth-
moid :virdle bone); Pa’, palatine ; Vo, vomer ; MV, maxilla ; Pma, premaxilla ;
XN. NY cartilages in connection with the nasal capsules ; W.A, prorhinal
cartilage ; I7, T, TZ, foramina for optic, trigeminal, and abducent nerves.

88 COMPARATIVE ANATOMY

encircles the whole skull in this region and is perforated by the
olfactory nerves.

Tn the adult the bones are not so numerous as in Urodeles, and
the frontal and parietal of either side as a rule fuse together, thus
giving rise to a fronto-parietal. The maxillary bar grows back-
wards much further than in Urodeles, and becomes connected with
the suspensorium by means of a small intermediate bone, the quad-
ratojugal (Fig. 69). The maxillary arch is therefore complete, as
in Tylototriton amongst
Urodeles (p. 85). The
palatoquadrate is united
anteriorly with the carti-
laginous nasal capsule.
(For the relations of
the bones bounding the
mouth-cavity compare
Fig.69.) The bones of the
lower jaw are a dentary
and an angular, the distal
end of Meckel’s cartil-
age ossifying as a small
“ mentomeckelian.”

There is a much
greater reduction of the
branchial skeleton at the
close of larval life than
in Urodeles. In the
larva representatives of
the hyoid and of four
branchial arches can be
recognised, but these are
all fused together and
form a continuous struc-

ture, reminding one of

Fic. 70.—HYOBRANCHIAL SKELETON OF LARVAL the branchial basket-
(A) anp Apvut (B) Froc. ie af the

(After Gaupp.) wor 0 e amprey.

bs, body of the hyoid; a.c, anterior cornua ; In the adult this be-

p.¢, posterior cornua. comes greatly reduced,

and the apparatus con-

sists of a broad cartilaginous plate in the floor of the mouth, with

long anterior and shorter posterior (thyro-hyal) cornua, the latter
of which become ossified.

D. Reptiles.

Although as regards the structure of the skull existing Reptiles
and Amphibians are widely separated from one another, certain
resemblances exist between their extinct representatives (¢.g.,
Paleohatteria and the Stegocephala).

THE SKULL 89

Excepting in the naso-ethmoidal region, the whole chondro-
cranium usually becomes almost obliterated by an extensive process

suproc

Jormag

c

supra. 1 Ge

Fic. 71.—SKULL or Lacerta ayilis (from Parker and Haswell’s Zooloyy,
after W. K. Parker).

A, from above ; B, from below ; C, from the side. ang, angular; art, articular ;
bas.oc, basioccipital; bas.ptg, basipterygoid processes; bas.sph, Dasi-
sphenoid ; co’, epipterygoid ; cor, coronary; dent, dentary ; eth, ethmoid ;
ex.or, exoccipital ; eat.nar, external nares; for.mag, foramen magnum ;
fr, frontal ; int.nar, internal nares ; ju, jugal ; cr, lachrymal ; maa, maxilla ;
nas, nasal; oe.cond, occipital condyle; o/f, olfactory capsule ; opi.of, opis-
thotic; opt.x, optic nerve; pal, palatine; par, parietal; para, para-
sphenoid ; pur.f, parietal foramen; p.mx, premaxille ; pr.fr, prefrontal ;
ptg, pterygoid ; pt.orb, postorbital ; qu, quadrate; s.any, supra-angular ;
s.orb, supraorbitals; sg, squamosal ; supra.t.4, supra.t.*, supratemporals
(“ paraquadrate,” Gaupp) ; trans, transverse bone ; swpra.oc, supraoccipital ;
rom, vomer. d

90 COMPARATIVE ANATOMY

of ossification, which gives the skull a very firm and solid appear-
ance; only amongst Lizards (Fig. 71), and especially in Hatteria
is the cartilage retained to any considerable extent, and owing to the
conformation of the bones in the posterior region, the skullin these
forms presents a number of distinct spaces or fossze in the dry state.

In Snakes and Amphisbeenians the cranial cavity extends
forwards between the orbits as far as the ethmoidal region, while
in the Lacertilia, Chelonia, and Crocodilia—in which a fibro-carti-
laginous interorbital septum perforated by the olfactory nerve is
present—its anterior boundary is much further back.

The parasphenoid, which plays so important a part as an
investing bone of the roof of the mouth in Fishes and Amphibians,

Lh Pe

Fic. 72.—SKuLn or Snake (Tropidonotus natrix), dorsal view.
Fic. 73.— _,, 56 oe a ventral view.

Cocc, occipital condyle ; Osp, supraoccipital ; Ol, exoccipital ; For, fenestra ovalis ;
Pe, periotic; P, parietal; /, frontal; #", postfrontal; Pf, prefrontal ;
Lith, ethmoid ; N, nasal; Pmz, premaxilla; Af, maxilla; By, basioccipital ;
Bs, basisphenoid ; Ch, posterior nostrils; Vo, vomer; Pl, palatine; Pt,
pterygoid; 7's, transverse bone; Qu, quadrate; Squ, squamosal ; Art,
articular ; Ay, angular ; SA, supra-angular ; Dt, dentary ; IJ, optic foramen.

begins to disappear; amongst Reptiles it only attains any im-
portant development in Snakes, where the anterior part remains
and forms the base of the interorbital region. Its place is taken
by two cartilage bones, the basioccipital and basisphenoid, situated
along the basis cranii. In contradistinction to the Amphibia, only
a single condyle connects the skull with the vertebral column:
this, on close examination, is seen to be formed of three parts,
derived from the basioccipital and exoccipitals respectively.

THE SKULL 91

The roofing bones of the skull are well-developed and in the
Lacertilia may become closely united with overlying dermal bones,
while the trabecular region (ali- and orbitosphenoids) becomes of
secondary importance in the adult, its place being partly taken by
processes growing downwards from the frontal and parictal :
this is especially the case in Snakes.

The parietals are paired in the Chelonia and in Hatteria; in
all other Reptiles they become fused together, as do also the
frontals in many Lizards and Crocodiles. A parietal foramen? is
present in many Lizards.

The topographical relations of the several bones to one another
are shown in Figs. 71 to 74. It will be seen in them that the
ground-plan of the Urodele skull is here fundamentally retained.
In addition, however, to a postorbital, an imperfect circumorbital
ring of bones is present in Lizards. In many Lizards, moreover,

Fro. 74.—Sxkubyi or Younc Water-Torroise (Lmys europa). Side view.

Osp, supracccipital, which gives rise to a crest ; Pf, prefrontal, which forms a
great part of the anterior boundary of the orbit; J, point of entrance of the
olfactory nerve into the nasal capsule ; Na, external nostril ; Si, interorbital
septum ; J7K, horny sheaths of jaws ; Jug, jugal ; Qig, quadratojugal (‘ para-
quadrate,” Gaupp); Mt, tympanic membrane; BP, cartilaginous interval
between basioccipital and hasisphenoid ; A/d, mandible. Other letters as in
Figs. 72 and 73.

a rod-like bone, the epipterygoid (also represented in Crocodiles),
connects the parietal with the pterygoid, and a transverse bone
extending from the maxilla to the pterygoid is typically present
in Reptiles, but is wanting in the Chelonia and Typhlopide.

The auditory capsules are ossified from three centres, the
prootic usually remaining free, and the epiotic uniting with the
supraoccipital and the opisthotic with the exoccipital. A fenestra
rotunda is present in its walls in addition to a fenestra ovalis, into
which latter the stapedial plate of the columella is inserted (see
p. 84), and the tympanic cavity in most Reptiles communicates
with the pharynx by means of an Eustachian tube.

1 In certain Chameleons its representative is in the frontal.

COMPARATIVE ANATOMY

The columella here also probably arises in connection with the upper end
of the hyoid arch (see p. 84), with which it is continuous in Hatteria.

The quadrate alone forms as the suspensorium for the lower
jaw:

it may be articulated with the skull (Ophidia,’ most
Lacertilia) or firmly fixed to it
(Hatteria, Chelonia, Crocodilia).

According to Gaupp, a squamosal is
wanting in narrow-mouthed Snakes and
Hatteria, and a paraquadrate, comparable
to that of the Amphibia (p. 85) is present
in almost all Lizards and Chelonians, a
quadratojugal being found only in Hatteria.

The pterygopalatine arch is well
developed in all Reptiles. In Snakes
and Lizards it is more or less movable
and free from the base of the skull,
while in Chelonians and Crocodiles it
meets with its fellow to a greater or
less extent in the middle line, and
shelf-like palatine processes of the
maxilla also come into connection
with the palatines :—thus a secondary
roof is formed to the mouth-cavity
distinct from the true (sphenoidal)
base of the skull. The cavity thus
formed closes in the posterior pro-

Fic. 75.—Skvu, or a Youre longation of the nasal chambers,

Crocopite. (Ventral view.) which consequently become sharply

Cocc, occipital condyles; Ob, differentiated from the mouth. In
basioccipital ; Ch, internal

Chelonians the pterygoid bones do

Saini Te DRE veoh telea part in the formation of this

orbit; P/, palatine; J,

palatine process of maxilla ;
Pmzx, premaxilla ; 7's, trans-
verse bone; Jy, jugal; Qj,
quadratojugal (‘* paraquad-
rate,” Gaupp) ; Qu, quadrate.

hard palate, which in Crocodiles is
much more markedly developed,
and is formed by the premaxillz,
maxille, palatines, and pterygoids,

: the posterior nostrils here opening
far back into the pharynx (Fig. 75).
A number of bones arise in connection with the lower jaw,

viz., a dentary, angular, supra-angular, splenial, coronoid, and
articular.

Teeth are well developed in all Reptiles except Chelonians,

1 In Snakes (Figs. 72 and 73) (except Tortrix), the quadrate is only indirectly
connected with the skull by means of the squamosal, which extends backwards,
and thus throws the articulation of the lower jaw far back, giving rise to a very
wide gape. In most Snakes, and particularly in the Viperine forms, the facial
bones are capable of movement upon one another, but in Typhlops they are im-
movably connected with the skull. The two rami of the mandible are connected
by a more or less elastic ligament. :

THE SKULL 93

in which they are replaced functionally by strong horny sheaths
on the edges of the jaws. The teeth may be borne on the
palatine and pterygoid, as well
as on the maxilla, premaxilla
(which is usually unpaired),
and dentary.

In the young Hatteria only
amongst existing Reptiles do the
vomers bear teeth (usually one on
each). In certain fossil forms brush-
like masses of sphenoidal teeth
were present.

The remarkable horned skull of
the gigantic Ceratopside (Dino-
sauria) which reached a length of
nearly seven feet, possessed horny
beaks in addition to teeth on the
maxilla and dentary. <A parietal
foramen was present.

In correspondence with
the absence of branchial re-
spiration during development,
the branchial apparatus plays
no great part in Reptiles, and
often only the slightest traces
of it are seen: thus in Snakes,

Fic. 76.—HyoprancHiaL APPARATUS
witH Larynx anD TRACHEA OF Hmys

for instance, only the hyoid
remains, and this not always.
In Chelonians a basal piece
(“basihyobranchial”) as well
as the first branchial arch per-
sist in addition (Fig. 76).

europea.

4H, basihyobranchial, which widens at

ZB and bears the cricoid (RA) and
arytenoid (AK) cartilages of the
larynx; KH, lesser hyoid cornua;
ZH, greater hyoid cornua ; [K, first
branchial arch ; 7’r, trachea.

E. Birds.

The skull of Birds is formed on a similar plan to that of
Reptiles—more particularly of Lizards, but it exhibits certain
special characteristics (Fig. 77).

The brain-case is proportionately very large, and all the cranial
bones show a tendency to run together by the obliteration of the
sutures originally present between them ; they are usually delicate
and spongy (“pneumatic ”), thus contrasting greatly with those of
Reptiles.

Only in the region of the nose does the cartilage persist
throughout life to uny extent, and even here not always.

1 Tt should, however, be mentioned that the development of air spaces

within the bones of the skull is hinted at in Crocodiles and certain fossil
Reptiles.

94 COMPARATIVE ANATOMY

The wnpaired occipital condyle no longer lies at the posterior
boundary of the skull, but becomes relatively shifted forward along
its base, so that the axis of the latter lies at an angle with that of
the vertebral column. ;

The basis craniiis formed by a basioccipital and a basisphenoid,
from which latter a bony rostrum, the remains of the anterior part
of the parasphenoid, extends forwards. The posterior part of the
parasphenoid persists as a large plate, the basttemporal, which
underlies the basisphenoid and part of the basioccipital. Above
the rostrum a small presphenoid is present in the embryo, and
orbitosphenoids and alisphenoids are better developed than in
Lizards. The auditory capsules ossify by three centres, and the
relations of the tympanic cavity, auditory fenestrae, and columella
are very similar to those of Reptiles. The two Eustachian tubes
open together in the middle line.

The quadrate is movable upon the skull, as is also the whole
raaxillopalatine apparatus; the palatopterygoid bar is separated
from its fellow in the middle line and slides on the rostrum of the
basisphenoid, thus allowing the beak to be raised or lowered to a
greater or less extent: a complete bony palate comparable to that
of Crocodiles is consequently never present. This mobility of the
upper jaw is most marked in Parrots, in which the frontonasal joint
forms a regular hinge.

The vomers, which may be absent, usually unite with one
another, and with the palatines in a greater or less degree.1 The
posterior nostrils are always situated between the vomers and
palatines. The maxilla and quadrate are connected by a jugal
and a quadratojugal, and a squamosal is present ; small bones may
also occur in the neighbourhood of the lachrymal. (For other
details, compare Fig. 77.)

Teeth were present in Jurassic and Cretaceous Birds (Archeo-
pteryx, Hesperornis, Ichthyornis), but are no longer developed in
existing forms, their place being taken functionally by horny
sheaths covering the bones of the jaws, which thus form a beak,
much as in Chelonians.

Several bones are developed in connection with the lower jaw,
the relations of which are essentially similar to those seen in
Reptiles: they, however, become fused together in the adult, and
the two rami of the mandible unite distally by synostosis.

The visceral skeleton is greatly reduced, though the basihyal
and basibranchial—which are embedded in the tongue, as well as
the first branchial arch persist, and the latter may, as in the
Woodpecker, grow out into a pair of very long jointed rods
extending far over the skull.

1 The differences in details as regards the arrangement of the bones of the
palate are important for purposes of classification.

THE SKULL 95

Fie, 77.—SKULL oF A Winp Duck (Anas boschas). A, from above; B, from
below ; C, from the side. (From a preparation by W. K. Parker).

«1s, alisphenoid ; ag, angular ; ar, articular ; a.p.f, anterior palatine foramen ;
b.t, basitemporal ; b.o, basioccipital ; b.py, basipterygoid ; 6.s, basisphenoid ;
d, dentary; e.n, external nostrils; eth, ethmoid; e¢.0, exoccipital; ¢.,
Eustachian aperture ; fr, frontal; fim, foramen magnum ; 7.c, foramen for
internal carotid artery; j, jugal; dc, lachrymal; mz.p, maxillopalatine
process ; mz, maxilla; n, nasal ; n.pa, nasal process of the premaxilla ; pa,
premaxilla ; », parietal ; ps, presphenoid ; pg, pterygoid ; p/, palatine ; p.n,
internal nostrils; qg, quadrate; g.j, quadratojugal ; *g, squamosal; s.0,
supraoccipital ; ty, tympanic cavity ; v, vomer ; IJ, foramen for optic nerve ;
V, for trigeminal; IX, X, for glossopharyngeal and vagus; XJJ, for
hypoglossal.

96 COMPARATIVE ANATOMY

F. Mammals.

In Mammals there is a much closer connection between the
cranial and visceral regions of the skull than is the case in the
Vertebrates already described. In the fully-developed skull
both maxillary and palatopterygoid regions are united to

Fic. 78 a.—LoneirupInaL VerticaL SECTIONS THROUGH THE SKULLS or—A,
Salamandra maculosa, B, Testudo greca, AND C, Corvus corone, TO SHOW THE
RELATIONS BETWEEN THE CRANIAL AND VISCERAL PorTioNs.

the cranium, though a facial and a cranial region can still be
distinguished. The higher we pass in the Mammalian series,
the more does the former come to lie below instead of in front of
the latter. In Man the facial skeleton is proportionately small

THE SKULL 97

when contrasted with the large cranial portion of the skull,
and the reduction of the angle between the basi-cranial and

Fic. 78 3.—LoNnuITuDINAL VERTICAL SECTIONS THROUGH THE SKULLS OF A, DEER,
B, Basoon, Np C, Man, TO SHOW THE RELATIONS BETWEEN THE CRANIAL
AND VISCERAL PORTIONS.

vertebral axes is carried still further than in Birds (comp. Figs.
78 A and B).
The base of the skull is mainly preformed in cartilage, as in
Reptiles and Birds. The parasphenoid has practically disappeared,
H

COMPARATIVE ANATOMY

THE SKULL 99

Fic. 79.—_SKULL OF GREYHOUND. A, from above; B, from the side; C, from
below ; and D, in longitudinal section.

Jm, premaxilla ; V, nasal ; 12, maxilla, with the infraorbital foramen (Linf) ; Jy,
jugal; Sq, squamosal ; Pjt, zygomatic process of the squamosal ; L, lachry-
mal, surrounding the lachrymal canal; P, parietal; Sq.occ, supraoccipital ;
C.oce, occipital condyles, on the exoccipitals ; B.occ, Occ.bas, basioccipital ;
Pal(P in C), palatine ; Pt, pterygoid ; Sph, alisphenoid ; Sph’, basisphenoid ;
Sph", presphenoid ; Maud, external auditory meatus ; 7, tympanic ; For.m,
foramen magnum ; Pet, petrous portion of periotic ; Cho, posterior narial
passage; Vo, vomer; th, lamina perpendicularis of the ethmoid; Hth’,
cribriform plate ; Cav.gl, glenoid cavity for the lower jaw.

the anterior part of the basis cranii being formed by the ossification
of the cartilage : this either gives rise to a distinct presphenoid
(Marsupials, Rodents, and some Insectivores), or may be due
to a union of the basal parts of the two orbitosphenoids. Ali-
sphenoids, as well as a basisphenoid, a basioccipital, a supraoccipital,
and exoccipitals are always present, the paired condyles being
furnished by the exoccipitals (Fig. 79). The cranial cavity is
closed in anteriorly by the bony lamina cribrosa or cribriform
plate of the ethmoid, which has numerous perforations for the
olfactory nerves in all Mammals but Ornithorhynchus.

The auditory capsules are ossified from prootic, epiotic,
and opisthotic centres, which early fuse together to form the
pertotic or petromastoid bone. The denser internal (petrous)
portion of this encloses the essential part of the organ of hearing,
and a fenestra ovalis and fenestra rotunda are present on its outer
surface : the more spongy mastoid portion reaches the surface of
the skull between the exoccipital and the tympunic bone.1 The
latter overlies the petrous portion of the periotic, and gives
attachment to the tympanic membrane: in the Placentalia it
forms the tubular external auditory passage or meatus, below
which it usually expands into a bulla tympani, which encloses
the tympanic cavity and communicates with the pharynx
by means of the Eustachian tube. The “temporal bone” of
human anatomy represents the fused periotic, tympanic, and
squamosal.

The cranial cavity is roofed in by frontals, parietals, an inter-
parietal, and a supraoccipital : these, like many of the other cranial
bones, are united by sutures which usually persist, at any rate for
a long time. Many of the bones are more or less spongy internally,
and may contain definite air-sinuses.

Most of the true Ruminants are provided with horns projecting from the
frontal bones ; these are of three kinds :—

In the Cavicornia (Bovinee, Antelopinee, Caprinze, Ovinze) hollow bony pro-
cesses are developed from the frontals, which become enveloped by horn formed
from the epidermis. In the Cervidie, a solid membrane bone becomes developed
in the dermis round each process of the frontal, with which it fuses. This
grows out tv form the antler, and after attaining its full development, the
skin covering it dries up owing to the development of the ‘‘ burr” at its base ;

1 According to Gaupp, the tympanic corresponds to the ‘* paraquadrate ” of
Amphibia and Reptilia (pp. 85 and 92). ‘
H 2

100 COMPARATIVE ANATOMY

this constricts the vessels, and the antler, being deprived of nutriment, falls
off periodically at the close of the breeding season. In the young animal,
the antlers are simple, but year by year they become more complicated and
branched. Giraffes possess persistent antlers covered by hair and without any
process from the frontal : they do not become anchylosed to the latter bone.
The differentiation into horned and antlered forms first began in the
Miocene epoch.

In the nasal cavity, scroll-like turbinals} are present: these are
preformed in cartilage, and unite with the surrounding bones. The
two nasal chambers are separated from one another by a cartilaginous
septum nasi, the posterior part of which becomes ossified by a
vertical plate (mesethmoid) in connection with the lamina cribrosa,
The vomer, which is unpaired in the adult, is situated immediately
below the nasalseptum. Cartilage is retained only in the latter
region and around the external nostrils (“aliseptal” and “ alinasal
cartilages”). The nasal cavities communicate anteriorly with the
mouth by means of the incisive or naso-palatine canals as well as
posteriorly by the internal nostrils.

As regards the structure of the hard palate, Mammals
agree essentially with Crocodiles, but the small pterygoids (except,
c.g., in Anteaters and some Cetaceans) do not take part in its
formation. The palate is very long in Echidna and in certain
Edentata and Cetacea, and often (¢g., Marsupialia) presents
unossified vacuities.

The premaxilla takes an important part in enclosing the
nasal cavity : it also contributes to the hard palate, and surrounds
the nasopalatine canal. In the lateral parts of the face of most
Mammals, the jugal or malar connects the maxilla with a process
of the squamosal (instead of with the quadrate, as in Amphibia
and Sauropsida): thus a zygomatic arch is formed from these three
bones (Fig. 79). In most cases (¢.g., Ungulata and Primates) the
Jugal is also connected with a process of the frontal, and thus the
orbit becomes more or less completely separated from the temporal
fossa.

The tympanic membrane is connected with the membrane of
the fenestra ovalis by an articulated chain of small auditory
ossicles, extending across the tympanic cavity and consisting of the
malleus, ineus (with its orbicular apophysis), and stapes—instead of
by a single columella as in Amphibians and Reptiles. The two
former of these bones arise in the embryo from the proximal
end of the mandibular arch, one portion of which becomes
constricted off to form the incus and another the malleus,
both portions afterwards becoming ossified. The part of the arch
in the lower jaw, distal to the malleus, corresponds to Meckel’s
cartilage, and in Fig. 80 the two are seen still in continuity.
The stapes, which is stirrup-shaped in all Mammals but Mono-
tremes and certain Marsupials and Edentates, plugs the fenestra

* For details of the turbinals in Mammals and other Vertebrates, compare the
section on the olfactory organ.

THE SKULL 101

ovalis on the one hand and articulates with the incus on the
other, while the malleus articulates with the incus, and its
manubrial process is attached to the tympanic membrane. The
above facts indicate that the malleus corresponds to the articular
element of the mandible of lower Vertebrates, and the incus to
the quadrate,

The morphology of the stapes is not by any means clear ; phylogenetically
it certainly corresponds to the upper end of the hyoid arch (pharyngo-hyal or
hyomandibular of Fishes), but its homology with this element has not been
proved ontogenetically. Its basal plate, however, doubtless corresponds to
the stapedial plate of Amphibia and Sauropsida (comp. pp. 84 and 92).

Fi. 80.—Skvuis or Empryo or ARMADILLO (Tatusia hybrida). (Modified froma
drawing by W. K. Parker.)

a.ty, tympanic annulus ; av, auditory capsule ; b.hy, basihyal ; c.hy, ceratohyal ;
cr, cricoid ; d, dentary ; ¢.hy, epihyal ; ¢.n, external nostril ; co, exoccipital ;
J, frontal; h.hy, hypohyal; 7%, jugal; in, incus ; lc, lachrymal ; mk, Meckel’s
cartilage ; mi, malleus; ma, maxilla; 2, nasal; oc.c, occipital condyle ; p,
parietal ; pa, palatine ; pa, premaxilla ; so, supraoccipital; sf, stapes; »./.
superior turbinal ; sf.m, stapedius muscle; sq, squamosal; th, thyroid; ¢r,
trachea; J”, 7, foramina through which the first and second divisions of
the trigeminal pass out from the orbit ; ZZ, optic foramen.

Thus the parts of the mandibular arch which form the hinge of
the jaw in lower Vertebrates are in Mammals utilised to conduct
sound-vibrations to the internal ear. Around Meckel’s cartilage
a membrane-bone is developed corresponding essentially to the
dentary ; this forms the entire lower jaw of the adult and develops
a new articulation with the sqguamosal: this arrangement is
characteristic of and confined to the Mammalia (Figs. 79 and 80).
The two rami of the mandible usually unite distally.

Teeth, which are only exceptionally wanting (¢g., Echidna,

102 COMPARATIVE ANATOMY

certain Edentates), are confined to the premaxilla, maxilla, and
mandible.

The hyoid arch (Fig. 80) is connected proximally with the
auditory capsule and distally with the base of the third visceral
(that is, the first true branchial) arch. It becomes more or
less ossified, but the greater part is usually reduced to a fibrous
band, and may be quite rudimentary; its proximal end forms
the styloid process of the periotic, and its distal the lesser
(anterior) cornua of the so-called hyoid bone of the adult. The
body of this bone represents the basal parts of the hyoid and
first branchial arch, the greater (posterior) cornua belonging to
the latter.

VI. LIMBS

The problem of the origin and morphological meaning of the
fins and limbs of Vertebrates is one which, in point of interest and
importance, is comparable to that relating to the head. During
the last thirty years it.has been attacked vigorously both from the
embryological and the paleontological sides, and has given rise to
so many speculations—often of a very contradictory nature—that
only the barest outline of some of the more important results
obtained can be given in the course of the present chapter.

The fins or limbs, which are distinguished from the azial organs
(head, neck, and body), as appendicular organs, serve mainly for
locomotion, and may be divided into two groups, the wnpaired
and the paired (pectoral and pelvic). .

A. Unpaired Fins.

The unpaired, or median fins, which are mainly characteristic
of Fishes, arise in the embryo as aridge of the integument (epiblast
and mesoblast) extending along the median dorsal line from the
anterior part of the trunk backwards to the tail, around the apex
of which it is continued forwards for some distance along the
ventral side: thus a dorsal, caudal, and ventral portion can be
distinguished. In. the course of further development, these
portions either remain continuous, or else certain parts undergo
reduction, so that the ridge only persists in certain regions,
where it forms independent dorsal, cuudal, and ventral or anal Jims
(Fig. 81, A, B): in these regions muscles and skeletal parts be-
come developed.!

These skeletal parts consist of supporting rays of two kinds.
In the base of the fin cartilaginous radia, usually segmented, are

' The curious suctorial disc on the dorsal side of the head of the Teleostean
Remora (Echeneis), by means of which it attaches itself to foreign objects, arises
in the embryo from the anterior portion of the dorsal unpaired tin, and this is

indicated throughout life by the arrangement of the blood-vessels, nerves, and
skeletal parts.

LIMBS 103

formed in all the Fishes proper and in Dipnoans; these, which
may conveniently be distinguished as “ pterygiophores,” may unite
to form a basipterygiwm, and in bony Fishes they become ex-
tensively ossified: they frequently come into secondary con-
nection with the vertebral column (¢.g., by means of the so-called
“interspinous bones” of Teleostei). The peripheral part of the
fin is supported by dermal rays, which may consist of numerous
delicate horny fibres (e.g., Marsipobranchs, Elasmobranchs, Cartilag-
inous Ganoids, Dipnoans), or of bony rods, entire or jointed, often
cleft at the base, and not preformed in cartilage (Teleosts, Bony
Ganoids).

Median fins are also present in the Amphibia, in which they
may persist throughout life (¢.g., Perennibranchiata), or may only

BF

BF } n AF

Fie. 81.—Dr1aGRAM sHOWING (A) THE UNDIFFERENTIATED CONDITION OF THE
ParRED AND Uyrarrep Fixs ty THE Embryo, anp (B) THE MANNER IN
WHICH THE PERMANENT Frxs ARK FORMED FROM THE Continuous Forps.

D, dorsal fin-fold ; S, §, lateral folds, which unite together at S! to form the
ventral fold; RF’, FF, dorsal fins ; SF, tail-fin; A/’, anal fin; Bri’, pectoral
fin; BF, pelvic fin; An, anus.

occur in the larval stage and occasionally also during the breeding
season (e.g. Newt). They have the form of a continuous in-
tegumentary fold extending round the tail and along the back
for a greater or less distance, but enclose 20 skeletal elements.

Amongst Reptiles, median fins were present in Ichthyosaurus,
and these are comparable to the dorsal fins occurring in the
Cetacea amongst Mammals: in both cases they must be looked
upon as structures acquired secondarily in connection with ap
aquatic existence.

B. Paired Fins or Limbs.

Embryological researches have shown that lateral fin-folds must
have existed in the ancestors of Vertebrates in addition to the

104 COMPARATIVE ANATOMY

median fins, and these can still be recognised in young embryos
of Elasmobranchs (Fig. 81, A) and to a less extent in those of
Sturgeons, Teleosts, and Amphibians. They extended backwards
along the sides of the body from just behind the head, gradually
converging towards the anal region, where they became continuous
with the ventral part of the median fin-fold (Fig. 81, A), and thus
resemble the lateral or metapleural folds present in the adult
Amphioxus. As is usually the case in the median fins (p. 102),
certain parts of these lateral folds have undergone reduction,
only the anterior and posterior portions remaining to form two
paired (pectoral and pelvic) fins or limbs, which must therefore be

Fic. 81, A.—TRANSVERSE SECTION THROUGH THE EMBRYO OF A SHARK (Pristiurus
melanostomus), 9 MM. LONG, SHOWING THE MopE oF ORIGIN OF THE PEC-
TORAL Lima-Bups (ap.).

ch, notochord ; co, celome; m, myomeres, seen to be growing ventrally ; my,
spinal cord.

looked upon as the localised remains of a continuous lateral fin-fold
on either side of the body, and as being homodynamous (i.c., serially
homologous) structures.

Into these paired fins the myotomes extend, and cartilaginous
supports (pterygiophores) are formed from the mesoblast, as in the
case of the median fins. These radii appear first of all at the base
of the fin, gradually extending centrifugally into the latter, and
also, becoming fused, centripetally into the body-wall. An articula-
tion is then secondarily formed between the fused basal part of the
skeleton situated in the free portion of the limb (basipterygium) and
that which extends into the lateral body-wall and serves as a support
for the limb proper: this latter portion constitutes the Jimb-arch
or girdle. The arch may remain comparatively small and not extend

LIMBS 105

far dorsally; but when the limb is destined to perform more im-
portant movements in locomotion, or to give a more definite support
to the body, the arch may extend upwards so as to come into
connection with the axial skeleton as well as meeting with
its fellow ventrally, thus forming an almost complete girdle
around the body. The limb skeleton may become ossified later.

Fic. $2.—A, B, C. Dracram or THREE SuccEssivé STAGES IN THE DEVELOP-
MENT OF THE PELVIC FIN oF A SHARK.

rd, primitive radii, which in A are beginning to fuse into a basal plate (bs). In B
this fusion has taken place on both sides, and at * the proximal ends of the
two basals are approximating to form the arch. In C the process is com-
pleted, and at t an articulation has been formed between the arch and the
free portion of the fin. On the left sidein C the radii are becoming second-
arily segmented. fo, obturator foramen ; c/, cloacal aperture.

In the case of Fishes, the pelvic fin ag a rule remains at a simpler
and more embryonic stage than the pectoral.

The paired limbs are not connected with any particular body-
segments, but vary greatly in their relative positions and in the
number of nerves which supply them.

The essential part of this conception as to the origin of the paired limbs
is due to Thacher, Mivart, Balfour, Haswell, and Dohrn.! Gegenbaur had

1 A somewhat similar idea was put forward by Goodsir as early as 1856.

106 COMPARATIVE ANATOMY

previously put forward the view that the arches and fins correspond to meta-
morphosed gill-arches and rays: he supposed that one ray came to exceed
the others in size, and that the others then gradually became attached to it
instead of to the arch, the result being a bisevial form of fin (‘‘ crchiptery-,
gin”) which is most nearly retained in Ceratodus (Fig. 101 and p. 124).

Pectoral Arch.

Fishes and Dipnoans.—Paired fins and arches are wanting
in the Cyclostomi. In the Elasmobranchii and Holocephali the
pectoral arch consists of a comparatively simple cartilaginous bar

Fic. 83.—PrectorsL ARCH AND FIN or Heptanchus.

SB, SB, pectoral arch, with a nerve aperture at NZ; Pr, Ms, Mt, the three
basal elements of the fin—pro-, meso-, and metapterygium ; Ra, cartilaginous
fin-rays; a, b, the main fin-ray, lying in the axis of the metapterygium ;
+, single ray on the other side of the axis (indication of a biserial type) ; FS,
horny rays, cut through.

the two halves of which are united ventrally by cartilage or fibrous
tissue (Fig. 83), and in embryos of Ganoids and Teleosts it has
at first a similar structure.

Later, however, in both the last-named groups, a row of bony
structures arises in the perichondrivm in this region; so that a
secondary or bony pectoral arch may be distinguished from a
primary or cartilaginous one, the latter becoming less marked in
proportion to the development of the former (Fig. 84).

The free extremity, or fin, is always connected with the hinder

PECTORAL ARCH 107
and outer circumference of the (primary) arch, convex articulations
being formed on the arch which fit into concave facets on the fin,
the point of attachment of
which may be taken as
separating the arch into an
upper dorsal and a lower
ventral section. ‘The former,
which may exceptionally be
connected with the vertebral
column (viz., Ratidee), cor-
responds to a scapula, and
the latter to a coracoid plus
procoracoid of the higher
Vertebrata.

In Teleosts and Bony
Ganoids the bony (secondary)
arch forms the principal
support of the fin in the oo
adult, the main element :
being a large clavicle. The
primitive relations are thus

coco “*u"

Fie, 84.—Lerr Pecroran Arcu anp FIN or

much altered. The arch THE Trout. (From the outer side.)
becomes : secondarily con- D, D', D*, chain of secondary bones of the
nected with the skull. (For pectoral arch (clavicle and supra-clavicle),
further details, compare which is connected with the skull by means
Fic, 84 ) of the post-temporal (Cm); S and Co(Cl),
or ee bony scapula and coracoid, which have be-
come developed in the cartilage (Kn); L
Amphibia. In this ae i oe ; ae iene oe i 3
é . a, Ra, the second and third, and 4, the
Class the pectoral arch fourth basal element of the fin; Ra’, the

shows no direct connection
with that of Fishes, but is
similar in plan to that of
all the higher Vertebrates.

second cartilaginous row of radii; HS,
bony ray on the border of the fin which
is connected with the fourth basal element ;
FS, bony fin-rays, shown cut away from
their attachments.

It always consists on either side of a
cartilaginous or bony dorsal plate (scapula),
which curves round the side of the body
and becomes continuous ventrally with
two processes—an anterior (procoracoid)
and a posterior (coracoid) (Figs. 854 and B).
The ventral part of the arch becomes con-
nected with the sternal apparatus (com-
pare Fig. 43). The humerus articulates
with a concave glenoid facet at the junc-
tion of the scapula and coracoid. The
two coracoid plates either overlap one
another in the mid-ventral line (Uro-
1 The pectoral arch of Dipnoans is intermediate in character between that of

Elasmobranchs and Ganoids. It shows so many special peculiarities as regards
form and position that it cannot be fully described here.

Fig. 854.—DIAGRAM OF THE
Grouxp TYPE oF PEc-
TORAL ARCH MET WITH
IN ALL VERTEBRATA FROM
AMPHIBIA UP TO MaAmM-
MALIA.

S, scapula; Co, coracoid ;
Cl, procoracoid ; A, hu-
merus,

108 COMPARATIVE ANATOMY

deles and certain Anura—e.y., Bombinator, Fig. 43, C), or else
their free edges come into apposition and fuse together (other
Anura, ¢.g., Rana, see Fig. 43, D). In Anurans the procoracoids
have a more transverse position than in Urodeles, and come into

Fic. 85p.—PrcroraL Arch oF THE RIGHT SIDE oF Salamandra maculosa,
considerably magnified, and flattened out.

SS, supra-scapula; S, scapula (ossified); Co, coracoid ; Cl, procoracoid ; a, h,
bony processes extending into the procoracoid and cotacoid respectively ; (.
glenoid cavity, surrounded by a rim of cartilage (Z).

connection with the coracoid in the mid-ventral line, thus giving
rise to a fenestra between the two. The whole arch is, moreover,
‘more strongly ossified, the procoracoid being covered by an invest-
ing bone—the clavicle.

Reptilia.—In Reptiles the ossification is still more marked.
The simplest condition of the shoulder-girdle is seen in Chelonians
(Fig. 86), in which its similarity to
that of Amphibians as well as to that
of Hatteria is at once seen: no clavicle
is developed.

In other Reptiles the same general
plan is retained with modifications.
Thus in Lizards (Fig. 44) the well-
developed clavicle is more indepen-
Fic. 86.—Pucrora, Ancu or a dent of the rest of the arch and

Cusrontay. (Ventral view.) becomes ossified directly, forming a
S,scapula; Co,coracoid; Col,epi- delicate secondary bony lamella ex-

coracoid ; Cl, procoracoid; B, tending from th -
fibrous band between these two 8 p eepale ths ae

elements ; Fe, fenestrabetween Of the episternal apparatus. But it
them; @, glenoid cavity. must be remembered that the un-
differentiated cells of which it at

first consists are in direct continuity with those which form
the scapula. Unossified spaces are left in the coracoid, giving

PELVIC ARCH : 109

rise to fenestree closed over by fibrous membrane. In Crocodiles
and Chameleons the clavicles are either wanting or rudimentary.

The presence of a pectoral arch in numerous footless Reptiles (certain
Skinks, Amphisbeenians) indicates that they formerly possessed extremities ;
rudiments of the latter may even be seen in the embryo though they

disappear entirely later on (Angiuis frayilis). (For the peculiar pectoral
arch of the Stegocephala, see Fig. 46.)

Birds.—In Birds, the scapula consists of a thin and narrow
plate of bone often extending far backwards, the strong coracoid
being bent at a sharp angle with it in all Carinate Birds
(Fig. 41). The lower end of the latter is firmly articulated
in a groove on the anterior edge of the sternum.

In almost all Flying Birds the clavicle is well developed, and
becomes united with its fellow to form a furcula (comp. p. 63 and
Fig. 41). It is formed as a membrane bone investing a band of
cartilage present in the embryo in this region.

Amongst the Cursorial Birds, the Emeu and Cassowary possess
rudimentary clavicles: in the others they are wanting. They have

also undergone reduction in some Carinate Birds (eg., certain
Parrots).

Mammals.—In Monotremes only amongst Mammals does the
coracoid extend ventrally to reach the sternum (Fig. 48) ; in all
other members of this Class it characteristically becomes reduced,
and simply forms a prominent process on the scapula (coracord
process), which becomes ossified from a separate centre.t

Thus the scapula alone serves to support the extremity; it
becomes at the same time greatly broadened out, and gives rise on
its outer side—in connection with the highly differentiated muscles
of the limb—to a strong ridge (spina scapula), which extends
downwards to form the so-called acromion. The distal end of the
clavicle usually becomes connected with the acromion, its proximal
end articulating with the anterior edge of the sternum.

In those Mammals in which the fore-limbs are capable of very
varied and free movements, the clavicles are strongly developed.
In others, such as the Carnivora and Ungulata, they may be en-
tirely wanting or only rudimentary, and in the latter case their
relations to the scapula become altered.

Pelvic Arch.

Fishes.—The first rudimentary indications of a pelvis are seen
in Cartilaginous Ganoids, amongst which, however, they present
considerable variations—-even in individuals of the same species.
They consist of two calcified or even ossified pelvic plates, which

1 According to Howes the coracoid process represents an epicoracoid (comp.
Fig. 48), the coracoid itself being only occasionally indicated by a small centre of
ossification on the glenoid margin of the scapula.

110 COMPARATIVE ANATOMY

become segmented off from the basal cartilage (basi- or metaptery-
gium) of the free fin. In some cases even this segmentation does
not take place, and thus the pelvis remains undifferentiated. This
simple condition is also met with in the ancient forms Pleura-
canthus and Xenacanthus, and is essentially retained in Lepi-
dosteus, Amia, and the Teleostei (Fig. 87).

In Polypterus, which most nearly resembles the Devonian
Crossopterygii, the pelvis shows some advance on that of
Sturgeons. Owing, doubtless, to the necessity of a firmer connec-
tion of the fin with the body-wall, the two pelvic plates become

Bas! Bas’ is Bas!

Fic, 87.—DIaGRAMS ILLUSTRATING THE PHYLOGENY OF THE PELVI».

A, Pleuwracanthus—the pelvis is here undifferentiated tt ; B, Scaphirhyuchus
cataphractus; C, Polypterus bichir ; D, Necturus (Menobranchus). Bas},
basipterygium ; Ap, its cartilaginous apophysis; P, pelvis; Rad, radii ;
Fo, obturator foramen.

united together in the mid-ventral line (Fig. 87,C): but even here
the basipterygium may remain in continuity with the pelvic plate
on one or both sides. In spite, however, of the rudimentary
character of the pelvis of Polypterus, the essential form of that of
the Dipnoi and Amphibia is already sketched out.

The pelvis of the Elasmobranchii and Holocephali indicates that
they early branched off from the ancestral stock. Instead of
a small and narrow pelvic plate more or less elongated antero-
posteriorly, the pelvis forms a transverse bar of considerable
extent, developed in connection with the basipterygium (Fig. 82)

?

PELVIC ARCH

111

it is perforated by nerves, and gives rise on either side to an iliac
process (most marked in Holocephali) extending into the lateral

walls of the body (Fig. 88).

In all the above
cases we may look
upon the pelvic plate
as essentially corres-
ponding, more or less
completely, with the
ischio-pubis of higher
forms.

Dipnoi. — The
small cartilaginous
pelvic plate (Fig. 89)
is provided with a
long and delicate an-
terior median, a short
posterior median, and
two pairs of lateral
processes. Of the
latter the anterior

Fig. 88.—DIAGRAM OF THE ELASMOBRANCH PELVIS.

(From the ventral side. )

BP, Pelvie plate (ischio-pubis) ; 7, iliac process ;
PP, prepubic process; Cep, epipubic process ,
Sy, region of the ischiopubic symphysis; /’o!.
obturator foramen; Bas, Pro, Rad, basiptery-
gium, propterygium, and radii of the fin.

(prepubic processes) vary much in form and length, beg much
longer in Protopterus than in Ceratodus, and each is embedded

Fic. 89.—PELvis or Protopterus. (From
the ventral side. )

a, prepubic process, which may become
forked at its distal end ; b, process
to which the hinder extremity
(HE) is attached ; Gr, sharp ridge,
for attachment of muscles ; ¢, epi-
bubic process ; J/, A, myotomes ;
M, M’, intermuscular septa.

in an intermuscular septum ;
with the posterior the skeleton
of the free fin is articulated by
means of an intermediate piece.
The anterior unpaired process
must be looked upon as an
epipubic process, corresponding
with that of Amphibians, Rep-
tiles, and Mammals (pp. 113,
115, 121).

Amphibia. — Urodela. — It
will be seen by a glance at
Fig. 87, D, that the ventral
portion of the pelvic arch of
Necturus is formed on the same
plan as the pelvic plate of the
Dipnoi and Crossopterygii, but,
as in all Urodela and Amniota,
it is perforated by the obturator
nerve: this indicates a further
lateral extension. Like the
pelvis of all Vertebrates, it has
a paired origin, and in Proteus
and Amphiuma this is indi-
cated by the fact that its

iF ee

anna

Fic. 90.—Prnvis or (A) Protens ; (B) Amphiuma ; (C) Cryptobranchus ; ’xv (D)
Salamandra macifosa, (From the ventral side. )

JP, JP), IP, ventral pelvic plate (ischio-pubis); ** (in .1), ossified region of the
ischium; PP, prepubis; tt (Cep), Lp, epipubis ; ** (in C and D) secondary
bifureation of the epipubis ; =, outgrowth from this bifurcation ; t+ (in C), hypoi-
schiatic process, present in the Derotremata and Necturus ; Sy, symphysis, in
which region a strong tendinous area (SH) exists in Amphiuma, the pubic
regions only coming together in the middle line at * ; Fo, Fo!, obturator fora-
men ; Ac, acetabulum ; J, J!, /, /', ilium ; La/b, linea alba ; AZy, intermuscular
septa ; ('r, (Sy), muscular ridge on the ventral side of the ischio-pubis.

PELVIC ARCH 113

3

yan
On

i
4

ate

NS

Fic. 91.—PExvis or Various AMPHIBIA. A, Nenopus (Dactylethra), from below ;
B, the same from the front ; C, Rana esculenta, from the right side; D and
E, Salamandra atra; F and G, Salamandra maculosa ; H, Branchiosaurus ;
I, Disvosaurus, D-I, from the ventral side. (Figs. H and I after Credner. )

J, ilium ; Js, ischium ; P, pubis (P!in Rana, pubic end of ilium) ; JP, fused ischio-
pubic ossification; PP, prepubis; Cep, epipubic cartilage; Fo!, obturator
foramen ; J! (in Xenopus), the proximal end of the ilium, which is separated
from its fellow and from the pubis by a +-shaped zone of cartilage,}, *; Ac,
acetabulum.

I

lilt COMPARATIVE ANATOMY

anterior epipubic process is paired throughout life (Fig. 90, A, B),
In the Derotremata and Myctodera, on the other. hand, the
epipubis is unpaired from the first, owing probably to an abbrevia-
tion of development, its anterior end becoming bifurcated
secondarily (Fig. 90, C, D).

As in Fishes and Dipnoans, the two halves of the ischio-pubic
region tend to fuse together in the middle line to form an un-
paired pelvic plate, but all kinds of modifications
occur in this respect in adaptation to the move-
ments of the hind-limb in different forms ; and,
as in all cases the median zone of the plate
represents the line of least resistance, the lateral
halves may eventually become more or less dis-
tinct from one another. The effect of the action
of the muscles becomes, however, greater when
the pubic region is more distinctly marked off
from the ischium, and ossification takes place
‘in it (eg. Salamandra atra and, more rarely, 8.
maculata). Thus the typical triradiate arrange-
ment of the pelvis (iliwm, ischiwm, and pubis),
such as is further-ditferentiated in certain Stego-
cephala (Discosaurus) and in Reptiles, as well
as in Xenopus, is already sketched out (Fig. 91).

An important difference between the pelvis
of Ganoids and Dipnoans and that of Amphibians
is seen in the marked development of the zac

92. — Pevic

region in the latter group. The ilium, like the Fic.

scapula, extends upwards in the lateral walls of
the body (compare the iliac process of Elasmo-
branchs, Fig. 88), and in Proteus and Amphiuma,
owing to the reduction of the limbs in these
forms, does not reach the vertebral column (Fig.
90, A,B). In all other Amphibia, as in the
Amniota, it comes into connection with the
sacrum (p. 45), owing to the necessity for the
hind-limb to act asa support for the body in
terrestrial animals, and not merely as an organ
of propulsion, as in Fishes.

Anura.—The pelvis of the Anura differs from
that of Urodela in the following characteristics.

ARCH OF FrRoc
(Rana esculenta).
From below.

J, J}, ilium; Ix, is-

chium ; P, carti-
laginous _ pubic
region ; Cr, the
median ventral
ischio-pubic
crest ; (7, aceta-
bulum ; Oc, uro-
style; P?, trans-
verse process of
sacral vertebra.

Tn correspondence

with their mode of progression, the ilium of each side becomes
extended so as to form a long rod (Figs. 91 C, 92); and the flat
pelvic plate, which in Urodeles lies in the plane of the abdominal
walls, becomes closely pressed together in the middle line and gives
rise to a well-marked ventral keel: it is not perforated by the
obturator nerve. The pubic region, moreover, though often calcified,
is independently ossified only in the case of Xenopus (Fig. 91, A,B).

Reptiles.—The chief characteristics of the Reptilian pelvis as

PELVIC ARCH 115

Fic. 93.—Pretvic Arcu or Various Reprites. (From the ventral side). A,
Paleohatteria, after Credner ; A!-C, Plesiosaurus : Al, from a restoration in
the College of Surgeons; B, from Huxley’s Anatomy of Vertebrated
Animals; C, after D’Arcy Thompson; D, Labyrinthodon riitimeyert ; E,
Hatteria.

P, pubis ; PP, prepubis; Cep, epipubic cartilage ; Fo', obturator foramen ; Is,
ischiun ; J, ilium ; +,+, ischio-pubic foramina ; *, hypoischiatic process, which
becomes segmented off from the pelvis in other Reptiles.

I ”

=

116 COMPARATIVE ANATOMY

B C

LY ce

Cora

Is

Fic. 94.—Prnvic AncH or VARIous CHELONIANS. (From the ventral side.) A,
Macrochelys (after G. Baur); B, median pelvic cartilage of Chelys fimbriata ;

C, the same of Hmydura ; D, Sphargis coriacea (after Hoffmann) ; E, Vestudo ;
F, Chelone. °

Cep, epipubic cartilage ; HpIs, hypoischiatic process ; P, pubis ; PP, prepubis ;
Js, ischium ; Fopi, ischio-pubic foramen.

compared with that of Amphibians consist in :—(1) a much more
marked differentiation of the pubis, which is more distinctly
separated from the ischium by an ischio-pubic foramen; (2) the

PELVIC ARCH 117

greater development of the ilium, which is sometimes broadened
out atits vertebral end ; and (3) the more intense and solid ossifica-
tion of the arch as a whole.

Points of connection with the pelvis of Amphibians are seen in
Paleohatteria, the Plesiosauria, Hatteria, Telerpeton, and the
Chelonia (comp. Figs. 93 and 94), while the pelvis of the Ichthyo-
sauria approaches that of the Lacertilia. In the latter, and still
more in the Crocodilia and Dinosauria, the pelvic arch is much

Fic. 95.—A, LoneiruprnaL HorizontaL Section THROUGH THE VENTRAL Part
oF THE PELVIS oF AN Empryo or Lacerta agilis, 32mm. 1N Lenctu. B,
Penvis or Lacerta vivipara. (From the ventral side. )

Ep, epidermis ; P, pubis; PP, prepubis ; Zs, ischium, forming a symphysis at
SIs; HpIs, hypoischium, which becomes segmented off from the hinder ends
of the ischia in the embryo as a paired structure ; +, dense mass of embryonic
tissue ; J, ilium, with its small preacetabular process +t, which is much
more strongly developed in Crocodiles, Dinosaurians and Birds; Ac, aceta-
bulum, in which the three pelvic bones unite together so that the sutures
between them become obliterated ; Fol, obturator foramen ; Cep, epipubis,
composed of calcified cartilage ; Lg, fibrous ligament.

more highly differentiated ; while in Snakes, on the other hand, it,
like the pectoral arch, is entirely wanting.

In Hatteria (Fig. 93 E) there is a marked epipubis and a hypo-
ischiatic process continuous with the epipubic cartilage, and the
prepubic processes are strongly developed. The obturator and
ischiopubic foramina are distinct from one another, and not united
into one, as in Chelonia. (For the various modifications seen in
the pelvis of the latter Order, more particularly as regards the
relative development of the epipubic and prepubic processes and
the relations of the ischium and pubis, compare Fig. 94.)

118 COMPARATIVE ANATOMY

The pelvis of the typical Lacertilia (Fig. 95 B) is characterised by
a lightness of build. The rod-like pubis and ischium are separated
from one another by large ischiopubic foramina, and between them
in the middle line is a longitudinal fibro-cartilaginous ligament,
continuous anteriorly with the plug-like epipubic cartilage and
posteriorly with the hypoischium. This tract represents the

Fic. 96.—PeEnvis or A Youne Alligator lucius. (A, ventral, and B, side view.)

Ji, ilium ; Js, ischium; P, pubis; Sy, symphysis of ischium; F, ischio-pubic
foramen ; B, fibrous band between the symphyses pubis and ischii ; +, pars
acetabularis, which is interposed between the process a of the ilium and the
pubis ; b, foramen in the acetabulum, bounded posteriorly by the two pro-
cesses, @ and 0b, of the ilium and ischium respectively ; *, indication of a
forward growth of the ilium, such as is met with in Dinosaurians and Birds ;
G, acetabulum ; J, JJ, first and second sacral vertebre; Jf, fibrous mem-
brane extending between the ant rior.margin of the pubis and the last pair
of ‘abdominal ribs” (BR.)

remnant of the median ends of the pubis and ischium which.
are present in the embryo (Fig. 95 A); and thus in this, as in
certain other respects, the pelvis of the Lacertilia may be said to
pass through a Hatteria-like stage in the course of development.
The epipubis and hypoischium arise as paired rudiments. The
ilium in some cases is almost vertical in position : in others it is

PELVIC ARCH 119

more. oblique, sloping upwards and backwards from the aceta-
bulum. ;

The pelvis of Crocodiles exhibits special characteristics and is
of particular interest, as in some points it resembles that of
certain extinct forms. The pubes, which have at first a trans-
verse position, become later directed forwards much more
markedly than in Chelonians and Lizards, and thus the ischio-
pubic foramina (in which the obturator foramina are included) are
very wide, and are separated from one another by a fibrous cord
(Fig. 96). A symphysis, both of the pubis and ischium, is formed,
but the former is not present in the adult. The acetabulum is
perforated, and the pubis is separated from it by a cartilaginous
pars acetabularis, not represented in lower Vertebrates, formed
from the acetabular process of the ilium. The epipubis is.
possibly represented by a cartilaginous apophysis at the anterior
(distal) end of the pubis, but it never becomes ‘separately
differentiated.

The ilium becomes greatly broadened out in the antero-
posterior direction dorsally, where it is attached to the sacrum ; and
this is of special interest as a similar extension of the ilium
occurs still more markedly in Dinosaurians and Birds (Fig. 97).

Birds.—The pelvis-of Birds is chiefly characterised by the
relatively large development of the iliac region and by the position
of the delicate pubis, which in the course of development becomes

Fic. 97.—PExvis oF Aptery« australis. Lateral view. (After Marsh.)

il, ilium ; is, ischium ; p, spinous process from the pars acetabularis ; py’, pubis ;
a, acetabuluin.

directed backwards, parallel to the ischium and post-acetabular
process of the ilium, and is. often united with the ischium

120 COMPARATIVE ANATOMY

(Carinatee). The preacetabular portion of the ilium extends for-
ward for a considerable distance, and a number of vertebra
belonging to other than the true sacral region become secondarily
connected with the ilium (sce p. 48). The acetabulum is per-
forated, and the pars acetabularis (p. 119) forms a spinous process,
The elements of the pelvis usually become anchylosed together.
The pubis meets its fellow in the middle line only in Struthio,
and the ischium only in Rhea.

Mammals.—The elements of the pelvis here remain separated
for a long time by cartilage, but later they become fused together.
The pubis always takes less part in the formation of the aceta-
bulum than do the other two bones, and may be more or less
entirely shut out from it by an ossification of the pars acetabularis,
which subsequently unites with either the ilium, ischium, or
pubis (Figs. 98 and 99). This acetabular bone is especially well
developed in the Mole, in which it shuts the ilium, as well as the
pubis, out of the acetabulum: the latter is perforated in Mono-
tremes. The angle between the axes of the ilium and sacrum is
large in Ornithorhynchus, and more acute in other Mammals.

The original type with both pubic and ischiatic symphyses is
seen in Monotremes, Marsupials (Fig. 100), many Rodents, In-
sectivores and Ungulates. In many other Insectivores, in Carnivores,
and more particularly in the Primates, the ischia no longer meet
below. The greatest amount of variety in the form of the pelvis

Fic. 98.—ExtTERNAL Virw OF THE Fic. 99.—DiacRaM SHOWING THE
Ricut HALF OF THE Human RELATIONS OF THE Pars ACETA-
Petvis. (From the outer side.) BULARIS (in Ttverra civetta).

The three bones—ilium (J/), ischium J, ilium; Js, ischium; P, pubis ;
(Is), and pubis (P)—are shown dis- A, acetabular bone ; Ac, aceta-
tinct from one another in the balum.

acetabulum. Jo, obturator for-
amen.

im any one order. is seen in Insectivores, in some of which (6.9,
Mole), as well as in most Bats, there is no symphysis pubis. The
obturator foramen is always surrounded by bone.

PELVIC ARCH 121

In Whales, in which hind-limbs are wanting, paired rudiments of the
ischio-pubic region of the pelvis are present. They are unconnected with
one another and with the vertebral column.

In Monotremes and Marsupials of both sexes, two strong so-
called “marsupial bones” (Fig. 100) arise from the anterior
border of the pubes, right and left of the middle line, and extend
forward in a straight or oblique direction embedded in the

Vb

Fic. 100.—Pretvis or A, Echidna hystrix (ApcuLT), anp B, Didelphys azare
(Fetvs, 5°5 cm 1x Lenctu). (From the ventral side.)

Ep, epipubis (‘‘ marsupial bone”) ; P, pubis; Sy, ischiopubic symphysis ; Js,
ischium ; J, ilium ; Fobt, obturator foramen ; Tub.il.p, ilio-pectineal tubercle ;
Lg and Lgt, ligament between the pubis and epipubis; **, cartilaginous
apophysis at the anterior end of the epipubis.

In Fig. A, t*, +, tt, ilio- and ischio-pubic sutures; Z, process on the anterior
border of the pubis ; GH, articulation between the pubis and epipubis ; 7,
cartilaginous tuber ischii.

In Fig. B, 6, 61, cartilaginous base of the epipubis, continuous with the inter-
pubic cartilage at t; *, *t, ischio-pubic and ischio-iliac suture.

body-walls. They form an integral pari of the pelvis, and in the
embryo are seen to be in direct connection with its cartilaginous
symphysis ; but later on articulations are formed between them
and the pubes. There can be no doubt that these structures are
the homologues of the epipubis of lower Vertebrates, which has
been retained in non-placental Mammals in order to serve as a sup-
port for the abdominal walls in connection with the marsupial
pouch (p. 28).

122 COMPARATIVE ANATOMY

Free LiMes.
Fishes and Dipnoans.

In the following description the pelvic fin will be cousidered
before the pectoral, as it usually retains a simpler and more
primitive form.

2 Elasmobranchti and Holocephali.—The cartilaginous skeleton of
the fins is the most richly segmented in these Fishes. There
are usually two main elements (basalia)
in the pelvic fin which articulate with
the arch and with which a variable
number of segmented rays (radii) are
connected, the latter passing towards
the periphery of the fin (Fig. 88). Both
the larger, posterior main element (dasi-
or metapterygium), and the smaller,
inconstant propterygium must, as al-
ready stated (p. 105), be looked upon
as originating —phylogenetically, at any
rate—by a fusion of the proximal ends
of the primary cartilaginous rays of the
fin; and thé form and relations of
these main elements vary according to
the degree in which such a fusion
has taken place This is also true
as regards the pectoral fin, in which an
additional basal piece, or mcsoptery-
gium, is usually present between the
pro- and metapterygia, and, like these,
articulates with a special convexity on
the pectoral arch (Fig. 83): there may
even be four basalia. These compli-
cations arise in connection with tke
Fic. 101 Pecroral. Tix oF greater importance of the pectoral than
eratodus fostert. aes 5
the pelvic tin as an organ of locomotion.

a, b, the two first segments of The distal portions of both fins are
the main axial ray; t, t,

teil gavee Re bi supported by horny fibres (p. 108).
rays, ae only ‘on vone With the exception of one (Fig. 83, t)—
side. or at most of very few—all the rays are

situated on the same side of the basalia

(uniserial type).

Dipnoi—tThe cartilaginous pectoral and pelvic fins are here
also essentially similar to one another, the latter being
rather the simpler of the two. From a segmented main-ray or

1Jn male Elasmobranchii and Holocephali a number of pieces of cartilage are

connected with the distal end of the metapterygium of the pelvic fin as a support
for the copulatory organs or claspers : these may become more or less calcified.

LIMBS _ 123

axis a number of segmented secondary rays arise on either side in
Ceratodus : these are not, however, strictly symmetrical (Fig. 101).
Beyond them horny rays are present, as in Elasmobranchs. A
proximal (basal) segment of the axis, which bears no rays, articu-
lates with the arch. In Protopterus and Lepidosiren the fins, with
their skeleton, have undergone a marked reduction, so that little
more than the segmented axis remains.

Thus the fins of Dipnoans differ from those of Elasmobranchs
(as well as of Ganoids and Teleosts) in being formed on a bdiserial

type.
Ganoidet.—The skeleton of the fn is much simpler and the

Uae

cI
T
a

“Soa SFT (1
ey diye

Fic. 102,—Lerr Pecroran Fin or A, Polyodon (Spatularia), and B, Amia.

I-IV, cartilaginous radii connected with the arch (S); a-g, radii which do not
reach the arch and are connected with the most posterior ray (IV in A, III
in B); AS, bony rays.

primary rays much fewer in number in Ganoids than in Elasmo-
branchs.

In the pelvic fin of cartilaginous Ganoids more or fewer of the
radii unite together proximally to form a basale, which is perforated
by nerves, and from which a very primitive pelvic plate becomes
differentiated (p. 109, Fig. 87, B). It is important to bear in mind
that the distinction between an axis and secondary rays cannot
here, therefore, be strictly recognised, and the fin is thus more
primitive than in Elasmobranchs.

The primitive relations have to a certain extent disappeared in
the pectoral fin of cartilaginous Ganoids, which, however, consists
of a varied number of rays. Of these, four reach the arch in
Polyodon (Fig. 102, A) and five in Acipenser.

In the pectoral fin of Amia (Fig. 102, B) two large converging
marginal rays articulate with the shoulder-girdle, and only one

124 COMPARATIVE ANATOMY

intermediate ray reaches the arch : this condition may be compared
with that seen in the highly-developed pectoral fin of Polypterus
(comp. Fig. i103).

The form of the pelvic fin in bony Ganoids may be easily
derived from that seen in the cartilaginous representatives of this °
Order, but the number of radii is greatly reduced (Fig. 87). The
rays supporting the distal part of
both pairs of fins are bony (comp.
p. 103).

Teleostet.—A still further reduc-
tion has taken place in the primitive
skeleton of the paired fins in Tele-
osts, there being at most only a few
radials articulating with the arch
(Fig. 84), and even these (especially
in the case of the pelvic fin) may be
wanting. The main part of each fin
is supported by bony rays, as in
osseous Ganoids. The skeleton of
the fins of Siluroids, Cyprinoids,
and Gymnotide comes nearest to
that of Ganoids.

Phylogeny of the Ichthyopterygium.

Two essentially different views

Fic. 103.—Prcroran Fin or exist as to the primitive form of

Polypterus. fin-skeleton in Fishes. As already

Pr, Ms, Mt, pro-, meso-, and meta- mentioned on p. 106, Gegenbaur

Mapas lagers aes es ee ot postulates a biserzal fin as the primi-
mentionect meeting at J, so tha ce » igi =

the amesaptengiin dose. not tive type (archipterygium), which

reach the arch; OSS, centre is most clearly retained in Cera-

of ossification in MS ;* part of todus. He supposes that the

resin ana dce aele aaa ae uniserial form has been derived

the propterygium and the first from this by a reduction of the rays
ee a ice ae on one side and a further develop-
a, Fal eas PS, Dae dew, ment of those on the other. The
mal rays. axial ray of the biserial fin would
thus correspond to the basi- or
metapterygium, while the pro- and
mesopterygia of the uniserial fin would answer to special develop-
ments of the proximal ends of certain of the rays on one side of it.
The other view, which seems a far more probable one, is that
the wniserial type is the more primitive, and that this type is most
nearly retained in Elasmobranchs, which are as ancient a group as
the Dipnoans and which have not passed through a Dipnoan stage
in the course of their phylogenetic development.
Fig. 82 represents the mode of origin of the Elasmobranch fin

LIMBS 125

in accordance with this view, which is further supported by many
of the facts stated above and by numerous others relating to the
structure and development of the fins in Fishes, as well as by a
study of such fossil forms as the Paleozoic Cladoselache.

GENERAL CONSIDERATIONS ON THE LIMBS OF THE
HIGHER VERTEBRATA,

It thus appears possible to derive the skeleton of the fin of all
the orders of Fishes from a single ground-type, but to trace the con-
uection of the latter with the extremities of Amphibia and Amniota
is a far more difficult task. Between these two types of limb there
seems to be a wide gap, in consequence of the different conditions
of life existing between aquatic and terrestrial Vertebrates: we do
not know how the limb of an air-
breathing Vertebrate (chetroptery-
gium), adapted for progression upon
land, has been derived from the fin
(ichthyopterygiwnr), only fitted for use
in the water.

Paleontology furnishes no answer
to this question; we know of no
fossil intermediate forms of limb,
and the various hypotheses which
have been put forward on the sub-
ject cannot be discussed here. We

Fic, 104.—D1aGRAMMATIC FIGURES

may suppose th at when the primitive TO SHOW THE RELATIONS OF THE
Amphibian first began to take on a Ayterior Free Exrremiry ro
terrestrial mode of life, its fin, which THE TRUNK IN FisuEs (A), AND

i ; ae THE HicuER VERTEBRATES (B).
is practically a single-jointed lever,

amply sufficient for the movement of %; aa a te fa ia
the body in a fluid medium, became ae ee ‘ior malin
gradually transformed into a many- Ul and Rd is the humerus.
jointed system of levers.

In other words, as the function of the limb was no longer
simply to propel the body, but also to lift it up from the
ground, the firmly-connected elements of the skeleton of the
fin gradually became loosened from, and placed at an angle
to, one another (knee, elbow), definite articulations being
formed between them in a proximo-distal direction. Moreover,
the extremity must have changed its position with regard to the
body, so that, instead of projecting horizontally outwards, it became
bent downwards, and thus the angle between it and the median
plane of the trunk was gradually reduced, until in Mammals even-
tually, the longitudinal axis of the limb, when at rest, came to lie
parallel with the median plane of the body. In the higher types
this is more particularly the case as regards the posterior ex-

126 COMPARATIVE ANATOMY

tremities, the anterior undergoing the most varied adaptative
modifications, and giving rise to tactile, prehensile, or flying organs
—or, as in aquatic Mammals, becoming once more converted into
rowing organs. The limbs of all
the higher Vertebrata may, how-
ever, also be reduced to a single
ground-type.

The fore- and hind-limbs showa
great similarity as regards the form
and position of their various parts.
A division into four principal sec-
tions can always be recognised:
in the case of the fore-limb these
are spoken of as upper arm (brach-
qui), fore-arm (antibrachium), wrist
(carpus), and hand (manus); and
in the hind-limb as thigh (femur),
shank (crus), ankle (tarsus), and
foot (pes) (Figs. 105, 106). The
bone of the upper arm (Awmerus)
and of the thigh (femur) is always
unpaired, but two bones are present
in the fore-arm and shank. The
former are called radius and ulna,
and the latter ¢zbia and jibula. The
hand and foot are also respec-
tively divisible into two sections, a
proximal metacarpus and metatarsus,
Fic. 105.—Skeneron or run Riau and a distal series of phalanges,

Forr-arm, Carpus, anp Hany Which form the skeleton of the

oF Salamandra maculosa. (From fingers and toes (digits).

above.) Botl l d

oth manus and pes are made

R, radius; U, ulna; r, radiale; i, up of several series of cylindrical
ee ear ek ay Ree bones. There are never more than
carpalia (according to Emery, five complete series, which—except

Coed to the carpal of as regards number—present essen-

aa fie ee oan? he tially similar primary relations

II); Mc, Mv, metacarpals, throughout the higher Vertebrates.

Ph, phalanges; I to IV, first The skeleton of the carpus and

fo fount ep gett tarsus, each of which always consists

of a series of small cartilages or
bones, shows much variation; but the following may be taken
as a ground-type (Figs. 105 and 106). Round a centrale, which
may be double, is arranged a series of other elements, of
which three are proximal, and a varying number (four to six)
distal. The proximal, in correspondence with their relations
to the bones of the fore-arm and shank respectively, are spoken of
as radiale or tibiale, ulnare or fibulare, and intermedium ; while the

LIMBS 127

distal are called carpalia or tarsalia (in the narrower sense). They
are counted beginning from the pre-axial (radial or tibial) side of
the limb.

Amphibia.—The anterior and posterior extremities of Urodela
are formed essentially on the ground-plan described above. There
are usually five digits in the hind-limb,-and always four in the
fore-limb. In the Anura the radius and ulna become fused together,
and a separate intermedium is wanting; the proximal row of the
tarsus, moreover, consists of only two cylindrical bones, one of which
(astragalus) corresponds to a tibiale, and the other (caleanewm)
to a fibulare.t

In the distal row of the carpus four separate elements are
formed, but this number may become reduced owing to secondary
fusions ; in rare cases a fifth carpal may

also be present. Very different views iii iv
exist as regards the homologies of the : N 4
individual carpals of Anurans. In the » rs
distal row of the tarsus, tarsalia JZ and 4 \ r j f

but even these may undergo fusion; Gj
tarsalia JV and V are generally repre- \ Ih I L
sented by a ligament; and tarsale 7 %

ually d t long remain distinct. GS
usually does no remain distinc NOW

ITI are the most constant elements, \’

In Anura the metatarsals and
phalanges, between which the web of eS eis-#
the foot is stretched, are very long and
slender. The femur, as well as the
bones of the shank, which are fused
together, are also exceedingly long, in
correspondence with the mode of pro- Fic. 106.—SkeLeron or #THE
gression of these animals. The skeleton Sank, Tarsts, anpiFoor
of the extremities is more strongly Ci see ae
ossified in Anurans than in Urodeles, 1%, tibia; /b, fibula; ¢, tibiale ;
in which many of the elements remain aes ie neo aa
cartilaginous. tarsalia ; i-r, digits.

Traces of an extra toe (prehalluw:)
occur on the tibial side of the tarsus, and in both Urodeles and
Anurans indications of an additional pre-axial digit in the manus
are occasionally met with. The number of phalanges on the
individual digits varies in different Amphibians.

Rudiments of the extremities can be recognised externally in embryos of
the limbless Gymnophiona.

Reptiles.—Chelonians and Lizards (and more especially Hat-

1 It is possible that the tibiale and fibulare also include the representatives of
other elements.

128 COMPARATIVE ANATOMY

teria)! closely resemble Urodeles in the structure of the carpus,
although the exact homologies of all the different elements can-
not yet be stated with certainty. Five digits are always present
in both manus and pes, and in Chelonians traces also of the former
possession of an extra finger both on the radial and ulnar side
(*pisiform ”) are to be seen (Figs. 107, 108, and 109). he tibia
and fibula always remain separate.

In Crocodiles, which, like Anurans, possgss no trace of -an
intermedium, the proximal row of the carpus consists of two hour-
glass-shaped bones—a larger radiale, and a smaller ulnare (Fig.
110). Arudiment of a sixth ray is present on the outer side of

Fic. 107.—Carpvus or A, Hatteria (Sphenodon) punctata, axp B, Emydura
krefftti. (After Baur. )

RF, radius; U, ulna; 7, radiale; wu, ulnare; 7, intermedium ; c!, radial centrale ;
ce’, ulnar centrale; 1-5, carpalia; py, ulnar sesamoid (pisiform); J-V, the
metacarpals.

the latter. The centrale, as in Anura, comes to be situated in the
distal row, which is much less developed than the proximal.

In all Reptiles the tarsus undergoes a marked reduction,
especially in its proximal portion, and gradually leads to the
type seen in Birds. Thus in Chelonians and Lizards the proximal
tarsals all run together intoa single mass which corresponds to the
tibiale, intermedium, fibulare, and centrale, and the last mentioned
element can no longer be recognised in Lizards, even in the embryo.
Traces of an extra radial ray are present.

In the distal row three or four (five in Palzeohatteria) separate
tarsals are developed, but these may unite partly with one another

'Tn Hatteria and Chelydra serpentina amongst existing Reptiles, a double
centrale is present in the carpus, and traces of a double condition of this element
are seen in certain other Chelonians.

LIMBS 129

(Chelonians), and partly with the corresponding metatarsals
(Lizards); thus there is an increasing tendency for the move-
ment of the foot to take place by means of an intertarsal articula-
tion, as in Birds.

Tn Crocodiles there are two bones in the proximal row of the
tarsus, one of which corresponds to a tibiale, intermedium, and
centrale, the other to a fibulare. The former is spoken of as the
astragalus, the latter as the calcaneum, and on it a definite heel
(caleaneal process) is seen for the first time in the animal series.

I ee ,
“. BENE, CB
WE" EN) \)
Fic. 108.—Ricut Carpus or Emys Fic. 109.—Lerr Carpus oF
europea. (From above.) pice agilis, (From
above.
RF, Radius ; UV, ulna; r.c, fused radiale )
and centrale (or centrale 1 and 2, R, radius; U, ulna; wu, ul-
Baur) ; 2, intermedium ; a, ulnare; nare ; 7, intermedium ; 7,
1-5, the carpalia, of which 4 and radiale, formed by the
5 have become fused together ; t fusion of two elements,
(radiale, Baur) and *, elements one of which corresponds
on the radial and ulnar side res- to a prepollex ; ¢, cent-
pectively, indications of additional rale; 1-5; carpalia; f,
radial and ulnar (pisiform) rays ; ulna sesamoid (pisiform);
I-V, the metacarpals. I-V, the metacarpals.

The distal row consists originally of four small cartilages, but these
later undergo a partial fusion.

The number of phalanges on the fourth and fifth digits in the manus is
greater in the embryos of Crocodiles than in the adult. This indicates that
the Crocodilia have been derived from forms possessing a fin-like fore-limb.

In Ichthyosaurus and Plesiosaurus the limbs are modified to form paddles,
the digits consisting of numerous phalanges, and additional rays being present
in the former genus. In Pterodactylus and Rhamphorhynchus the fourth finger
was produced intoa long jointed rod, which supported a wing-like expansion
of the integument.

Amongst the Lacertilia, various degrees of reduction of the extremities
may occur, and in certain Snakes (e.g., Python) traces of the hind-limbs exist.

Birds.—The fore-limb of Birds is considerably modified by
adaptation for flight. The manus loses its primitive character and
undergoes reduction, while the brachium and antibrachium, as

K

130 COMPARATIVE ANATOMY

well as the entire pectoral arch and ‘sternum, are extraordinarily
developed. In the Ratitz, however, the wing has undergone
regressive changes in connection with the habits of these Birds.

Of the six or seven carpals which may be present in the embryo,
the three distal become fused with the corresponding metacarpals,
thus forming a carpometacarpus (Figs. 111, 112 A), and in the
adult only the two proximal remain separate as a radiale and an
ulnare. The three metacarpals themselves
become united together proximally, and the
second and third distally: they only bear a
very limited number of phalanges at their
free ends.

Claws were present on the terminal phalanges
of all three digits in Archeopteryx. In certain
recent Birds the first digit bears a claw, and more
rarely the second and even the third also. -

The tarsus is sti!l more reduced in Birds
than in Reptiles, and consists in the embryo
of three elements, two small proximal and a
broader distal. The former (tibiale and
fibulare) unite later with the distal end of
the tibia, thus forming a ¢zbiotarsus, while
the latter, which corresponds to tarsalia I to
V, becomes included in the base of the

Fic. 110.—Ricur Car-
PUS OF A YOUNG
Alligator — lucius.
(From above.)

metatarsus,

R, radius ;

U, ulna; r,
radiale (including,
according to Hm-
ery, a carpal of the
prepollex); wu, ul-
nare ; C, centrale ;
1 to 5, the five car-
palia, as yet unossi-
fied, of which 1 and
2, as well as 3, 4,
and 5, have become
fused together ; +,
pisiform; J to V,
the metacarpals.

Thus the foot of adult Birds
uo longer possesses any distinct tarsal ele-
ments, though, as in Clelonians and Lizards,
the foot really moves by an intertarsal articu-
lation. Of the original five metatarsals, the
fifth soon disappears, while the second, third,
and fourth become united with one another

and with the distal element of the tarsus *

to form a single bone, the tarsometatarsus
(Figs. 111, 112 B). The first metatarsal
remains to a greater or less extent inde-

pendent.

The number of toes varies between two (Struthio) and four;
that of the phalanges is normally 2, 3, 4, 5, reckoning from the
first to the fourth digit. The tibia, even from the first, greatly
exceeds the fibula in size, and the two bones become fused to-
gether distally.

In both limbs the bones are usually pneumatic. (See under
Air-sacs.)

Mammals.—In Mammals the anterior extremity either re-
mains in the condition of a simple organ of locomotion, serving for
progression on land; or it may become modified in adaption to an

WAY.
ee J

LIMBS 131

aérial (Bats) or aquatic (Pinnipedia, Cetacea, Sirenia) mode of life ;

or, again, it may give rise to a prehensile organ. In the latter case
(Primates) the radius and ulna, instead of being firmly connected
together, articulate with one ‘another, the former being capable

y aa F
EE, a J

Fic. 111.—Sketrton or tHe Limps axyp Tart or a Cartnate Birp. (The
skeleton of the body is indicated by dotted lines. )

Sch, scapula; R, coracoid ; St, sternum, with its keel (Cr); OA, ns kd,
ulna ; Ul, radius ; H W, carpus ; MA, carpometacarpus; /, digits; OS,
femur ; T, tibiotarsus; J%, fibula; I/F, tarsometatarsus ; Zz, Z, digits ;
Py, pygostyle.

of rotation round the latter: thus the manus can be brought into
a position of pronation or of supination.

The tibia is the most important bone of the shank, and the
fibula often becomes fused with it to a greater or less extent ; the
ulna also may unite with the radius. Except in the Cetacea,

K 2

132 COMPARATIVE ANATOMY

Sirenia, Cheiroptera, and certain Marsupialia, a sesamoid bone is
developed in the distal tendons of the great extensor muscles of
the shank, and is known as the knee-cap or patella. This is
already present in certain Lizards and in Birds. ;

The carpus and tarsus most nearly correspond with those of
Urodeles and Chelonians, and, as in them, certain of the elements

=

LIL NOTED.
(onan ye

[73780

Fic. 112.—A. Forz-arm anpD Manus or Empryo Prncuin (Ludyptes chryso-
come). (Fourteenth day of incubation.) (After Th. Studer.) (SB is a sesa-
moid developed in the tendon of the triceps in this Bird.) B. Swank AnD
Foot or Empryo Preneuiy. (At the same stage.)

may become fused together. Thus the intermedium and tibiale
asa rule unite to form an astragalus, while the fourth and fifth
carpals become fused to form the so-called wneiform bone, and the
corresponding tarsals give rise to the cuboid. A centrale, varying
much in form and size, is usually present at an early stage in all
five-fingered Mammals, but as a rule it becomes fused later with
one, or with two, of the neighbouring carpals—generally the

LIMBS 133

radiale (eg., the Gorilla, the Chimpanzee, and Man, though
it may persist in the human subject throughout life or may
fuse with carpale 2 or 8). In the tarsus the centrale (navicular)
remains distinct, and usually lies on the inner border of the foot.

So much difference of opinion exists with regard to the homologies of the
bones of, the carpus and tarsus in Mammals, that it is not possible at present
to give a satisfactory account of them, or of the additional elements which are
often present in the embryo and disappear during-development. Thus the
pisiform may be a true sesamoid, or may represent an additional ulnar ray,
and the caleaneum may or may not be the complete serial homologue of the
pisiform. Elements occur occasionally in the carpus and tarsus which are
supposed to represent additional radial and tibial rays respectively—the
so-called prepollex and prehallux (Fig. 113).

There are typically five complete digits on each foot, but this
number may be reduced to four, three, or even one (Figs. 114 and

Fic. 113. —A, Carpus, AND B, SKELETON OF THE Foot or May. (The rudiments
of the so-called prepollex and prehallux ({ty7) are represented diagram-
matically.

U, ulna; R, radius; 7, radiale ; 2, intermedium; wu, ulnare; P, pisiform ; ce,
centrale, fused with the radiale ; ce?, second centrale, forming the head
of tarsale 3; 1-5, the carpalia and tarsalia, 4 and 5 being united to form
the unciform and cuboid respectively ; Cu I-III, the first to third tarsalia ;
c, centrale tarsi (navicular); it, intermedio-tibiale = astragalus (As) ;
f+, calcaneum (= fibulare and pisiform tarsi’); J-V, the metacarpals
and metatarsals.

115), the disappearance taking place in the following order—
1, 5, 2, 4: thus in the horse the third is the only complete digit
remaining (Fig. 115). The number of phalanges is similar in both
hand and foot: in the first digit there are only two, while in the
others there are three. An exception to this rule is seen in
Cetacea, in which the phalanges are numerous, as in Ichthyosaurus
and Plesiosaurus amongst Reptiles,

It is interesting to trace the reduction which has taken place in the feet
of Ungulates in the course of time. Fig. 115 represents successive stages in the

134 COMPARATIVE ANATOMY

phylogenetic development of the fore-foot of the Horse, showing how it
has been gradually derived from a tetra- or pentadactyle form; and it has

recently been ascertained that all
B C these stages are passed through in the

course of ontogeny. In this case the
third digit becomes greatly enlarged
relatively (perissodactyle form), and
eventually is the only one remaining,
while in cloven-footed Ungulates the
third and fourth digits are both
functional and equally strongly de-
veloped (artiodactyle form) and may
be united together to form a “ can-
non-bone,” the others becoming
gradually reduced. A similar re-
duction takes place in the hind-
foot, and is here as a rule more
rapid.

Ungulates diverged into Artio-
dactyles and Perissodactyles as far
back as the Eocene period, but a
large series of Tertiary forms shows
that they must all have been derived
from a common pentadactyle ances-
tral form.

Some of the many other adaptive
modifications of the limbs in Mam-
mals must also be briefly mentioned.
In Bats, the phalanges are greatly
elongated to support the wing-
membrane ; the hallux as well as
the pollex may be opposable amongst
the Primates; the fore-limbs are

Fic. 114.—Skenrron or tHe Lerr modified for digging in certain
Fors-Lims or A, Pic; B, Hyomos- Mammals (e.g. Mole); and in the
cuus; C, Tracutus; D, Rorpuck; Cetacea (see p. 133) and Sirenia the
E, Swezp; F, Camer. (From Bell, digits are not free, and serve as
after Garrod.) supports for the fin-like paddles.

nt sue Nails are present on the digits of
Sirenia, but have disappeared in the Cetacea, though they can still be
recognised in the embryo of toothed Whales. Hind-limbs are absent

1 3 4 5 6
win

v

Woe vo

Fig, 115.—Fore-Foot or ANCESTRAL Forms oF THE Horse. 1. OROHIPPUS
(Eocene). 2. Mxsoniprus (Upper Eocene). 3. Muiourrrus (Miocene).

4. Protoutrrus (Upper Pliocene). 5. PLionippus (Uppermost Pliocene).
6. Equus.

wX yp wig wo

in the two last mentioned Orders, but indications of them can be seen even
externally in very young embryos of the Porpoise, and rudiments of the thigh
and even shank bones occur in the adult in certain Whales (comp. p. 121).

Cc. MUSCULAR SYSTEM.

THE muscles, commonly spoken of as flesh, may be divided into
two groups, according to the histological character of their
elements, which consist of cells elongated to form contractile
fibres: namely, into those with sm:oth and those with transversely-
striated fibres. The former are phylogenetically the older, and are
to be looked upon as the precursors of the latter. The action of
both in causing movements is dependent on the nervous system.

The smooth or involuntary muscle-fibres preponderate in the
vascular system, viscera, and dermis, aud are not under the control
of the will; almost all the striated or volwitary muscles occur in
the body-walls and organs of locomotion, and are under the
control of the will! The following general statements refer
exclusively to the latter kind of muscles, which may, according
to their mode of development, be arranged in the following
groups :—

a. Aluseles of the trunk, including the
coracohyoid (sterno-hyoid) of

Fishes and its representatives in

I. Parietal muscles, de- higher Vertebrates: these repre-
rived from the meso- sent the oldest and most primitive
blastic somites. ; part of the muscular system.

b, duseles of the diaphragm.
c. Muscles of the extremities.
d. Eye-museles.

II. Visceral muscles, de- ( Cranial nuscles, with the exception of
rived from the lateral those included under a and d
plates of the mesoblast. \ above.

In its simplest form, an origin, a belly, and an ansertion, may be
distinguished in each muscle. The muscles of the trunk are as a

1 Exceptions are seen in the muscles of the heart, and of the alimentary
canal in the Tench. More or less of the anterior and posterior parts of the
digestive canal may contain striated fibres in other animals.

136 COMPARATIVE ANATOMY

rule flat, while those of the extremities have usually an elongated,
cylindrical, or prismatic form. In some cases, however, they
assume the most various shapes: for instance, there may be more
than one origin (bicipital, tricipital, or quadricipital forms), the
belly may be double (biventral or digastric form), or the muscle
may be saw-shaped, or have its fibres arranged in a single or
double series like a feather.

All the muscles are surrounded by fibrous sheaths, or fascia,
by means of which they are more or less firmly connected with
one another and with the integument and skeleton. Wherever a
marked friction occurs, ossifications (sesamotds) may become de-
veloped in the course of a muscle or tendon.

The differentiation of independent muscles may take place—(1) by the
separation of the originally single muscle into proximal and distal parts by
the formation of an intermediate tendon ; (2) by the splitting of a muscular
mass into layers ; (3) by a longitudinal splitting ; or (4) by a fusion of distinct
muscles. A muscle may undergo very considerable modification both in form
and position by a change of origin and insertion ; and when the action of a
muscle becomes unnecessary, it either disappears partly or entirely, or what
remains of it contributes to the strengthening of a neighbouring muscle.

The following important factors must be taken into consider-
ation in connection with the muscular system: (1) the homologies
of the parts of the skeleton; (2) the relative positions of the
neighbouring soft parts; and (3) the nerve-supply.

Most of the muscles bear a close relation to the skeleton from
which they take their origin and into which they are inserted.
The integumentary musculature, on the other hand, lies en-
tirely in the subcutaneous connective tissue, but in Mammals its
origin can be traced to the deeper, skeletal muscles: this is
most plainly seen in Monotremes. Only slightly developed in the
Anamnia, it becomes of great importance in Reptiles and Birds on
account of its relations to the scutes, scales, and feathers. It is
most highly developed amongst Mammals, where it may extend
over the back, head, neck, and flanks as the panniculus carnosus
(Echidna, Dasypus, Pinnipedia, Erinaceus, &c.). In Man, only a
rudiment of this muscle is found in the shape of the platysma
myotdes, which extends over the neck and part of the breast and
face.

The action of the integumentary muscles is very different in
different Vertebrates. It may (1) serve to roll the body up into a
ball (¢.g., Hedgehog, Armadillo); (2) be connected with a tail
adapted for swimming (¢e.g., Ornithorhynchus) ; (3) serve to erect
the integumentary spines (e.g., Echidna); or (4) cause local move-
ments (“twitching”) of the skin (many Mammals).

The facial muscles, though present in rudiment in the Anamnia,
form a marked feature for the first time in Mammals, arising mainly
in connection with the platysma myoides, and gradually extending

MUSCULAR SYSTEM 137

over the face so as to become grouped around the eyes, nose,
mouth, and ears. They are supplied by the facial nerve, and attain
their greatest development in the Primates, in which certain
other facial muscles are derived from the deeper-lying sphincter
colt,

Parietal Muscles.
A. Muscles of the Trunk.

In Amphioxus (Fig. 219) the body muscles are made up of a
series (60 or more) of lateral muscular segments or myotumesseparated
by > shaped connective-tissue septa or myocommata, between
which the fibres run longitudinally. The myotomes have an
alternating arrangement on the two sides. On the ventral region
of the anterior two-thirds of the body there is a thin transverse
sheet of fibres.

In Fishes and Dipnoans the myotomes and myocommata are
arranged in pairs and consist, on either side of the body, of two
portions, a dorsal and a ventral, separated from one another by a
connective-tissue septum extending from the axial skeleton to the
integument (comp. Fig. 116)! The myotomes meet together in
the mid-dorsal and mid-ventral lines.

This primitive metameric arrangement of the lateral muscles of
the trunk forms a characteristic feature in Vertebrates, and stands
in close relation with the segmentation of the axial skeleton and
spinal nerves, the number of vertebra and pairs of nerves corre-
sponding primitively to that of the myotomes.

The lateral muscles largely retain their primitive relations in
Fishes and Dipnoans, but on the ventral side of the trunk,
where they enclose the body-cavity (comp. Amphioxus), certain
differentiations occur which indicate the formation of the recti and
obliqui abdominis of higher types. The dorsal portions of these
parietal muscles, as well as the ventral portions in the caudal
region, retain the more primitive relations.

Amphibia. —In Urodeles (Figs. 116 and 117) primary and
secondary ventral trunk-muscles can be distinguished, and both of
these groups, like the dorsal muscles, are segmented. The former
group consists of internal and external obliqut and recti. The
secondary muscles arise by delamination from the primary, and
give rise to a superficial external oblique, a superficial rectus, a
transversalis, and a subvertebralis. These, however, only attain
importance in caducibranchiate forms, in which they become
marked during metamorphosis, and the primary musculature then

1 This septum is not present in Myxinoids, and is absent in Petromyzon and
Lepidosteus posteriorly to the gills.

138 COMPARATIVE ANATOMY

undergoes more or less reduction. Thus various conditions of the
ventral musculature are found amongst Urodeles. _

In the Anura, on the other hand, both primary and secondary
muscles present a marked uniformity and relative simplicity ; in
the adult they give rise to a segmented rectus, an obliquus
externus, and a transversalis, as well as to a cutancus abdominis
derived from the external oblique. No trace of an internal oblique
can be seen in the adult.

Reptiles.—In Reptiles, the lateral muscles of the trunk attain
a much higher grade of development. This is to be accounted

Ie

LAL

a at i De
/ Ret UNC 2,

Fic. 116.—Tue Muscunaturs oF Siredon pisciformis. (From the side.)

LI, lateral line ; D, dorsal, and V, ventral portion of caudal muscles ; R.V, dorsal
portion of lateral muscles of the trunk ; O, O, outer layer of the external
oblique muscle, arising from the lateral line, and extending to the fascia, F ;
at * a piece of this layer is removed, exposing the inner layer of the muscle
(Ob); at Re the oblique fibres of the latter pass into longitudinal fibres,

indicating the beginning of the differentiation of a rectus abdominis ; at Re’

the rectus-system is seen passing to the visceral skeleton ; Mc, fibrous parti-

tions between the myotomes of the dorsal portion of the lateral muscles; 7,

temporal ; Ma, masseter ; Dg, digastric ; 1/h}, mylohyoid (posterior portion) ;

Ce, external ceratohyoid muscle; Lv, levator arcuum branchialium ; ttt,

levator branchiarum ; Cph, cervical origin of the constrictor of the pharynx ;

Th, thymus; Lt, latissimus dorsi; Ds, dorsalis scapule ; Cu, cucullaris;

SS, suprascapula ; Ph, procoraco-humeralis.

for by the more perfect condition of the skcleton, more especially of
the ribs and pectoral arch. The ribs and intercostal muscles now
play an important part in respiration, and changes, necessitated by
the more important development of the lungs, are thus brought
about.

The distinction between thoracic and abdominal regions becomes
gradually more plainly marked, and distinct external and internal
intercostal muscles are now differentiated. In the lumbar region
the ribs become gradually withdrawn from the muscles lying

MUSCULAR SYSTEM 139

between them; the{muscles thus lose their intercostal character,
and form connected sheets, extending between the last pair of ribs

Fic. 117,.—Tae Muscunature or Stiredon pisciformis. (Ventral view.)

O, outer layer of the external oblique, passing into the fascia, which is shown
cut through at #; Ob, inner layer of the same muscle ; Re, rectus abdominis,
passing into the visceral musculature (sternohyoid) at Re!, and into the pector-
alis major at P ; Mh, Mh, anterior and posterior portions of the mylohyoid,
which is cut through in the middle line, and removed on the left side, so as
to show the proper visceral musculature ; Ce, Ci, Ci, external and internal
ceratohyoid : the former is inserted on to the hyoid (Hy); Add, adductor
arcuum branchialium ; C, constrictor arcuum branchialium ; Ch, portion of
the constrictor of the pharynx, arising from the posterior branchial arch ;
Dp, depressores branchiarum; (Gh, genio-hyoid ; Ph, procoraco-humeralis ;
Spc, supracoracoideus ; Cbb, coraco-branchialis brevis; Clo, cloaca; La,

linea alba.
and the pelvic arch (¢.g., the quadratus lwmborum, which lies close
against the vertebral column).

140 COMPARATIVE ANATOMY

The rectus abdominis, which is always well developed, but does
not extend anteriorly to the sternum, becomes divided into three
portions,—a ventral, an internal, and a lateral.

While no important differentiation is noticeable in the dorsal por-
tion of the lateral body-muscles in Urodeles, a marked subdivision
of these muscles is seen in Reptiles. In them may be distinguished
a longissimus, an wecostalis, interspinales, semispinales, multifidi,
splenit, and levatores costarum, together with the scalenz, certain
of which belong to the last-mentioned group, and others to the
intercostal muscles,

The muscles of the main part of the tail retain primitive rela-
tions similar to those seen in Fishes: at the root of the tail and in
the cloacal region, however, new muscles become differentiated.

Birds.—In Birds the primitive character of the trunk-muscles
has disappeared far more than in Reptiles. This is mainly to be
accounted for by the excessive development of the muscles
of the anterior extremity—the pectoralis major more particu-
larly,—and the corresponding backward extension of the breast-
bone.

External and internal oblique muscles are present, but only
slightly developed: this is more particularly true of the internal,
which appears to be undergoing degeneration. No trace of a
transversalis can be distinguished ; but, on the other hand, a paired,
unsegmented rectus is present.

External and internal intercostals are well developed, and a
triangularis sternt appears for the first time on the inner surface
of the sternal ends of the ribs.

The dorsal portion of the trunk musculature is only slightly
developed in the region of the trunk, though very strongly marked
in the neck.

All these modifications in Birds seem to be accounted for by
the specialisation of the mechanisms for flight and respiration, to
assist which the greatest possible number of muscles are brought
into play and thereby influence the whole organism: an essential
difference is thus brought about between Birds and Reptiles.

Mammals.—Three lateral abdominal muscles are always
present in Mammals, an external and internal oblique and a trans-
versalis. In many cases, more particularly in Tupaia and in Lemurs,
the external oblique possesses tedinous intersections, thus indicat-
ing its primitive segmental character; but in general all these
muscles consist of broad uniform sheets. Towards the middle line
they pass into strong’ aponeuroses, which ensheath the rectus
abdominis. The latter consists of a single band on each side and
possesses a varying number of myocommata; it is no longer con-
‘nected with the axial muscles of the neck belonging to the same
system (sternohyoid, sternothyroid, &c.) as is the case in Urodeles,

MUSCULAR SYSTEM 141

for the sternum is always interposed between them, as it is in
the Sauropsida.

In Monotremes and Marsupials, a strong pyramidalis muscle
lies on the ventral side of the rectus abdominis. It arises from
the inner border of the “ marsupial bones” (epipubes, p. 121) and
may extend forwards as far as the sternum. In the higher
Mammals, where the epipubes are absent, the pyramidalis usually
becomes greatly reduced or entirely lost. Traces of it are, however,
commonly to be met with even in the Primates, and always arise
from the anterior border of the pubis, right and left of the middle
line.

The external and internal oblique muscles are represented in
the thoracic region in Mammals, as in the Sauropsida, in the form
of external and internal intercostals.

What has been said above as to the differentiation of the dorsal
portion of the trunk-muscles in Reptiles applies also essentially
to Mammals.

The greater number of the muscles in connection with the
external genital organs become differentiated from the primitive
sphineter cloace : the origin of the others is not known.

B. Muscles of the Diaphragm.

A complete diaphragm dividing the ccelome into thoracic and
abdominal cavities occurs only in the Mammalia. It is dome-
shaped and muscular, its muscles arising from the vertebral column,
ribs, and sternum. The diaphragm is of great importance in
respiration, as it allows of a lengthening of the thoracic cavity in
a longitudinal direction. It is supplied by a phrenic nerve, arising
from one or more (8rd to 6th) of the cervical nerves; and usually
consists of a central tendon, perforated by the cesophagus and post-
caval vein, and of muscular fibres radiating from this to the
periphery and forming dorsally two strong “pillars of the dia-
phragm.” In some cases (¢.g., Echidna, Phocena) the diaphragm
is entirely muscular.

Amongst the Sauropsida, a partition is present between the
pleural and peritoneal cavities in Chelonians, and is still more
marked in Crocodiles and Birds!: this is connected with the
ribs by muscular fibres. It, however, does not enclose the peri-
cardium, which, as in the Anamnia, lies in the general peritoneal
cavity.

The evolution of the mammalian diaphragm is not yet tho-
roughly understood.

1JIn Birds, two entirely different structures have been described as a
diaphragm. (See under .477-sacs.)

142 COMPARATIVE ANATOMY

c. Muscles of the Appendages.

The most primitive condition of the muscles of the extremities
is met with in Fishes and Dipnoans, in which the musculature of
each surface of the fin forms a more or less uniform mass which
may become differentiated into layers. Everything goes to prove
that all the muscles of the appendages are to be looked upon
primarily as derivatives of the lateral muscles of the trunk, ie,
of the myotomes; and although in the Amniota they have
apparently an independent origin, this is probably only due to an
abbreviation of development.

Two principal groups of appendicular muscles may always be
distinguished : one lying in the region of the pectoral and pelvic
arches, dorsally and ventrally, the other in the free extremity. In
Fishes and Dipnoans the latter consist essentially of elevators,
adductors, and depressors of the fins; while from the Amphibia
onwards, in correspondence with the more highly-differentiated
organs of locomotion, considerable complication is seen, and
there is a much more marked separation into individual muscles
corresponding with the different sections of the extremity. Thus
elevators, depressors, rotators, flewors, extensors, and adductors are
present in connection with the upper arm and thigh, fore-arm and
shank, and hand and foot, and the digits are also moved by a
highly-differentiated musculature. The number of muscles gradu-
ally increases in passing from the Urodela through the Sauropsida
to the Mammalia.

When, as in the Primates, the anterior extremity is con-
verted into a prehensile organ, new groups of muscles appear
known as pronators and supinators, The former are derived from
flexors, the latter from extensors.

dD. The Hye-Museles.

(These will be treated of in connection with the organ of
vision.)

Visceral Muscles.

Fishes.—Cousiderable differences exist in the visceral mus-
culature of Fishes In Elasmobranchs, Fiirbringer classifies these
muscles as follows :—

A. Cranial muscles (consisting originally of transverse or
circular fibres) supplied by the V‘, VII, IX*, and X™
cerebral nerves.

1 In Cyclostomes there is a remarkable transformation of the cranio-visceral

musculature in correspondence with their peculiar cranial skeleton (suctorial
apparatus) and branchial basket.

MUSCULAR SYSTEM 143

1. Constrictor arcuum visceralium, incl. constrictor superficialis
dorsalis and ventralis.
Innervation.

Levator labii superioris
a maxille ,, Vv.
» palpebree nictitantis +
ss rostri
5 hyomandibularis VII
Depressor rostri 2
ae mandibularis and hyomandibularis
Interbranchiales . : <a . IX, X.
Trapezius X.
2. Arcuales dorsales . : LX, X.
8. Adductores, incl. adductor mandibules V.
and adductores arcuum branchialium. IX, X.

B. Spinal muscles (originally longitudinal), divided, like the
trunk-muscles, into myotomes. Supplied by the spino-
occipital (=the ‘‘ventral roots” of X) and spinal
nerves.

(a) Epibranchial spinal muscles, dorsal to visceral skeleton.

Lnnervation.
4, Subspinalis . ‘ ’ Spino-occipital nerves.
Spino-occipital nerves,
5. Interbasales. > ob : as well as the first

spinal nerve.
(b) Hypobranchial spinal muscles, ventral to visceral skeleton.
Spinal nerves, and
atl the last one or
more of the spino-
occipital nerves.

6. Coraco-arcuales, incl. coraco-bran-
chiales, coraco-hyoideus, and
coraco- <aiand; sulans ; |

The structure of the cranio-visceral musculature of Ganoids and Teleosts
differs considerably from that roughly sketched out above, so that the
different groups of muscles must be arranged in an entirely different manner.
Thus in Teleostei the following divisions may be distinguished :—(1) Muscles
of the jaw, (2) muscles of the dorsal, and (3) muscles of the ventral ends of
the visceral arches. ach of these groups may again be sub-divided, but
further details about their arrangement, which is often very complicated,
cannot be given here. The visceral muscles of Polypterus are of especial
interest, as they show an intermediate condition between those of Hlasmo-
branchs and Urodeles.

Amphibia.—It is to be expected, @ priori, that the muscula-
ture of the visceral skeleton should be more highly developed in
branchiate than in air-breathing Amphibians; we thus find
that in the former more primitive relations are met with, connect-

1 This muscle has therefore nothing to do with the cther eye-muscles.

144 COMPARATIVE ANATOMY

ing them with lower forms, while in the latter a greater modification,
or rather reduction, of these muscles takes place.

Between the two rami of the lower jaw is situated a muscle with
transverse fibres (the mylohyoid), supplied by the third division of
the trigeminal and the facial nerve ; this represents the last rem-
nants of the constrictor muscle of Fishes. As the elevator of the
floor of the mouth, it stands in important relation to respiration and
deglutition, and is retained throughout the rest of the Vertebrata
up to Man (Figs. 116, 117).

A continuation of the trunk-musculature (the omo-, sterno-, and
genio-hyoid) provided with tendinous intersections, lies above the
mylohyoid (Fig. 117). These muscles, which serve to pull the
visceral skeleton forwards and backwards, are supplied by the first
and second spinal nerves.

In contrast to Fishes, there isin Amphibians a definite differen-
tiation into muscles of the tongue, that is, into a hyoglossus and a
gentoglossus ; but these also must be considered as having been
derived from the anterior end of the ventral muscles of the trunk;
they are present in all Vertebrates, from the Amphibia onwards,
and are supplied by the hypoglossal (=the first spinal nerve of
Amphibians).

In the Perennibranchiata and in Salamander larve the muscles
of the hyoid and of the visceral arches may, asin Fishes, be
divided into a ventral and a dorsal group; the latter disappears in
adult Salamanders and Anurans, only the ventral persisting. Their
function is to raise and depress the branchial arches, as well as to
draw them forwards and backwards. To these may be added
constrictors of the pharynx, as well as (in branchiate forms)
levators, depressors, and adductors of the external gill filaments
(Figs. 116 and 117). They are innervated by the vagus and
glossopharyngeal.

The jaw-muscles include a depressor (digastric, or biventer
mandibule, Fig. 116), supplied by the facial nerve, and
elevators of the lower jaw (imasscter, temporal, and pterygoid
muscles), supplied by the third division of the trigeminal. All
these muscles, which may be derived from the adductor of the
mandible of Elasmobranchs and Ganoids, arise from the auditory
region of the skull.

Amniota.—With the simplification of the visceral skeleton in
Amniota there is a considerable reduction of the musculature
belonging to it. All muscles connected with branchial respiration
are of course wanting, and the ventral trunk-muscles, as mentioned
above, are always interrupted in their forward extension by the
sternum and pectoral arch. At the same time, the muscles along
the neck and on the floor of the mouth met with in Amphibia are
present here also; they are, a mylo-, sterno-, omo-, and genio-
hyoid, as well as a hyoglossus and genioglossus. To these may

MUSCULAR SYSTEM 145

be also added a sterno-thyroid, from which a thyro-hyoid is con-
tinued forwards.

The stylo-hyoid, stylo-glossus, and stylo-pharyngeus of Mam-
mals, arising from the styloid process and stylo-hyoid ligament and
undergoing numerous variations, are peculiar to Mammals, They
are supplied partly by the facial nerve, partly by the glossopharyn-
geal, and act as retractors of the tongue and levators of the pharynx
and hyoid.

The muscles of the jaws resemble those of Amphibia, although,
especially in the case of the pterygoids,| they are much more
sharply differentiated, and are throughout more strongly developed.

1 For the tensor tympani and stapedius muscules, see under Auditory Organ,

D. ELECTRIC ORGANS.

ELECTRIC organs are present in certain Fishes, being most.
strongly developed in certain Rays (Torpedinide, eg., Lorpedo,
Hypnos) found in the Atlantic Ocean and various southern seas,
in‘a South American Eel (Gymnotus electricus) and in an African
Siluroid (Malopterurus electricus). Gymnotus possesses by far
the strongest electric power, next to it comes Malopterurus,
and then Torpedo. The electric batteries of these three Fishes
are situated in different parts of
the body: in the Torpedinide they
have the form of a broad mass,
extending throughout the substance
of the part of the body lying be-
tween the gill-sacs and the pro-
pterygium on either side of the
head (Fig. 118); in Gymnotus they
lie in the ventral region of the
enormously long tail (Fig. 119),
that is, in the position usually
occupied by the ventral portions of
the great lateral muscles; and
finally, in Malopterurus, the electric:
organ extends between the skin and
muscles round almost the entire
circumference of the body, thus
enclosing the Fish like a mantle:
it is especially strongly developed
along the sides.

The electric power of those:
Fig. 118.— Torpedo marmorata, Fishes which were formerly known

wirn tHe Exrcrric Orcans (Z) ag “ pseudo-electric” has now been:
ee fully demonstrated, though it is.
S, skull; Sp, spiracle; AK, gills; much feebler than in the forms
adh eye. described above. To this category

belong all the Rays, excluding the

Torpedinide, the various species of Mormyrus, and Gymnarchus:
(both the latter genera belonging to the Teleostei). In all these,
the electric organs lie on either side of the end of the tailand have
a metameric arrangement like that of the caudal muscles; in the-

ELECTRIC ORGANS 147

Mormyride, for example, there is on each side an upper and lower
row of electric organs.

The electric apparatus in all the above-named Fishes is to be
regarded from the same point of view both as concerns its mode
of development and its
anatomical relations :
all electric organs are
to be looked upon as
consisting of metamor-
phosed muscular fibres
and the nerve-endings
belonging to them as
homologues of the motor
end-plates which «are
ordinarily found on
muscles,

As regards the
structure of the elec-
tric organs, the same
essential arrange-
ments are met with
in all: the details of |
their histology and
physiology cannot be
entered into here. The
framework is tormed
of fibrous tissue en-
closing numerouscells,
which, running partly
longitudinally, partly

transversely through Fic. 119, A and B.—Tue Execrric Orcan or

ihe organ, gives vise inj (B, from a preparation by

P| ROA LEC 7 arta oe ae uel eta OP
» Skin; ie, Tn ; Z, , dorsal portions o ©

gonal or more or less great lateral muscles, seen partly in transverse,
rounded chambers or partly in longitudinal, section; ViA/, VIP,
compartments. These ventral portions of ditto; #, the electric organ,
. ; : seen in transverse section at H (B), and from

latter are arranged In the side at £1; WS, vertebral column from
rows, either along the the side, and the spinal nerves, and WS',
longitudinal axis of in transverse section; LH, posterior end of

a body cavity ; Sep, median longitudinal fibrous
the body (Gymnotus, septum between the left and right electric
Malopterurus) orina organ and lateral trunk-muscles ; A, anus.

dorso-ventral direction

(Torpedo), forming definite prismatic columns (Fig. 120).
Numerous vessels and nerves ramify in the connective-tissue

lying betweeu these compartments, the nerves being enclosed in

thick sheaths, and having a different origin in the different

forms. In Torpedo, in which the clectric organs probably arise

in connection with the great adductor muscle of the mandible

Ted

148 COMPARATIVE ANATOMY

and the constrictor of the gill-arches, the nerves arise from
the “electric lobe” of the medulla oblongata, a single branch
coming also from the trigeminal nerve; in all pseudo-
electric Fishes, as well as in Gymnotus, in which over two
hundred nerves pass to the electric organ, they arise from the
spinal cord, and are probably in close relation
with the ventral cornua of the latter, which
are particularly well developed in the last-named
Fish. It is remarkable that the electric nerves
of Malopterurus arise on each side from a single
enormous lens-shaped nerve-cell, which, lying in
the neighbourhood of the second spinal nerve, is
continued into a very large primitive-fibre which
passes towards the end of the tail, dividing as

Hl

BGM QL

X|_E_E_E_ Ss;

7<SE\S =
Fic. 120.—EeEc-

TRIC PRISMS OF
Torpedo mar-
morata. (Semi-
diagrammatic. )

it goes. This fibre is invested by a thick sheath.

Experiments have shown that all Electric Fishes are
proof against the electric current, with the limitation that
muscles and nerves—even the electric nerves themselves—

separated out from the body are capable of being excited
by the current. ‘‘The last and most important question with regard to the
Electric Fishes is naturally concerning the mechanism whereby the electric
plates become temporarily charged with electricity. The reply to this ques-
tion, although probably not so difficult a one as that relating to the mechanism
of muscular contraction, is still far from being answered ” (Du Bois-Reymond).
The only thing that can be stated with certainty is, that the electromotive
force is under the influence of the will.

E. NERVOUS SYSTEM.

THE uervous system, as already mentioned in the Introduction
(p. 5), arises from the epiblast, and the first parts to become
differentiated histologically are the nerve-cells (ganglion-cells),
from which nerve-fibres arise later and serve as conductors of
nervous impulses. The most important constituent of the nerve-
fibre is a central a2is-cylinder or axts-fibre, and in those nerve-fibres
which are spoken of as medullated this is surrounded by a highly
refractile, fat-like substance (myelin), which forms the medullary
sheath. In certain (non-medullated) nerve-fibres this sheath is
wanting, but the two kinds of fibres are not sharply marked off
from one another, either locally or genetically: a fibre may be
medullated in one part of its course, and non-medullated in another.
Externally each nerve-fibre is enclosed by a delicate sheath, the
neurilemma.

Part of the epiblastic tissue which forms the nervous system of
the embryo does not become transformed into nervous tissue, but
gives rise to a supporting and connecting framework—the newroglia;
and externally, investing membranes as well as blood and lymph-
vessels, are formed from the mesoblast.

The nervous system consists of central and peripheral portions
(Fig. 121). The central part (brain and spinal cord) is the first
to arise, and is formed as a direct product of the epiblast; the
peripheral portion (cerebral, spinal, and sympathetic nerves) becomes
established later.

1. THE CENTRAL NERVOUS SYSTEM.

The first indication of the central nervous system is a longi-
tudinal furrow (medullary groove, Fig. 6, A) which appears on the
dorsal side of the embryo and gradually becomes converted into
a tube by the meeting of its edges; this tube, consisting ori-
ginally of epithelial cells like the epiblast from which it arises,
then becomes separated from the epiblast and gives rise to the
hollow medullary cord} (Fig. 6, B), in which nerve-cells and fibres
soon become differentiated; it comprises a more expanded an-
terior and a longer and more slender posterior section. From the
former arises the brain, from the latter the spinal cord.

1The cord is at first solid in Cyclostomes, Teleosts, and bony Ganoids,
cavity being formed secondarily.

150 COMPARATIVE ANATOMY

Fic. 121.—Tur Entire Nervous System or THE Frog. (After A. Ecker.)
From the ventral side.

He, cerebral hemispheres (prosencephalon) ; Lop, optic lobes (mesencephalon),
MM, spinal cord ; M1 to M10, spinal nerves, which are connected at S.W by
branches (rami communicantes) with the ganglia (SZ to S70) of the sympathetic
(S); No, femoral nerve; Ni, sciatic nerve; J to N, first to tenth cranial
nerves ; 4, ganglia of the vagus; Vg, Gasserian ganglion; 0, eye; N, nasal
sac; Vato Ve, the different branches of the trigeminal; /’, facial nerve;
Vs, connection of the sympathetic with the Gasserian ganglion; NZ to X4,
the different branches of the vagus. Some of the fibres of the sympathetic
should be shown accompanying the vagus peripherally.

MEMBRANES OF BRAIN AND SPINAL CORD 151

In an early stage of development the lumen of the medullary
cord is primitively continuous posteriorly with that of the primary
intestine (neurenteric canal). This. connection, however, soon dis-
appears, and the cord then consists of a cylindrical or more or less
flattened hollow cord with thick walls, the cavity of which is lined
by ciliated epithelium and expands in front to form the ventricles of
the brain. This cavity becomes greatly reduced later, and in the
spinal cord is spoken of as the central canal.

Membranes of the Brain and Spinal Cord.

The enveloping membranes of the brain and spinal cord arise
by the differentiation of a connective-tissue layer lying between the
central organs of the nervous system and the surrounding skeletal
parts. In Fishes, only two membranes are distinguishable :—one,

———
aa ae

Fic. 122.—Bratxn Mrpmpranes oF Man. (After Schwalbe.)

DM, dura mater ; SR, sub-dural (arachnoid) space ; 4, sub-arachnoid space ; P./,
pia mater ; @R, gray cortical substance of the brain.

the dura mater, lining the inner surface of the cerebro-spinal
canal, and the other, or pia mater, investing the brain and spinal
cord. The latter represents also the arachnoid of higher Verte-
brates, which is not here differentiated as a separate membrane.
The dura mater conveys vessels to the walls of the cerebro-spinal
canal—that is, to the perichondrium or periosteum, while the pia
mater, which is much richer in blood-vessels, has to do with the
nutrition of the nervous axis. The dura mater consists of two
lamella, which, however, only remain distinct along the whole
central nervous system in the lower Vertebrata. In higher Verte-
brates, its double nature persists only in the region of the vertebral
column, the two layers becoming fused in the cranial portion. As
in most Fishes the brain by no means fills the cranial cavity, a large
lymph-space lies between the dura and pia mater; this cor-
responds to the so-called sub-dural space of terrestrial Vertebrates.

152 COMPARATIVE ANATOMY

A differentiation of the primary vascular membrane of the
brain and spinal cord into pia mater and arachnoid takes place
from the Amphibia onwards, and these two layers become
separated in those places where there are deep depressions be-
tween the individual parts of the brain; the deeper of these (pia)
adheres closely to the brain, and also penetrates into the ventricles
in the form of tele choroidee and plexus chorotdei, while the
superficial one (arachnoid) simply bridges
over the depressions (Fig. 122). A lympb-
sinus (sub-arachnoid space) is thus de-
veloped between the two in the Saurop-
sida and Mammalia, but this never reaches
such an independent differentiation as
does the sub-dural (arachnoid) space.

1. The Spinal Cord.

The spinal cord is at first of a uniform
diameter throughout, but as a richer
nerve-supply becomes needed for the
extremities, it exhibits in these regions
definite swellings—the brachial and
lumbo-sacral enlargements (Fig. 123).
The cord originally extends along the
whole length of the neural canal, but
its growth is usually less rapid than that
of the vertebral axis, so that eventually
it is considerably shorter than the latter.
In such cases (¢.g. Primates, Cheirop-
tera, Insectivora, Anura, Fiys. 121 and
123) it passes at its posterior end
into a brush-like mass of lumbo-sacral
nerves, the so-called cauda equina, lying
within the neural canal. A prolongation
of the spinal cord nevertheless extends

Ph

{}

“OTTER TREE TTTTTTTT TT 777

Fig. 123. —D1aGRAMS OF THE
SpinaL CorD AND ITS
Nerves. In A the cord
passes to the end of the
tail, and at B it ends more
anteriorly and passes be-
hind into a filum termin-
ale (/.t).

M.o, medulla oblongata; Pec,

cervical nerves ; Pb, bra-
chial nerves ; P.th, thor-
acic nerves; Pl, lumbo-
sacral nerves ; Ce, cauda
equina.

far back amongst these as a thin thread-
like appendage, the filwm terminale.

The bilaterally-symmetrical form of
the spinal cord is pronounced by the

presence of longitudinal fisswres running

along it dorsally and ventrally ;! and if one imagines the points of

exit of the dorsal and ventral nerve-roots to be respectively con-

nected together by a longitudinal line, each half of the spinal

cord would thus be divided into three columns,—a, dorsal, lateral,
and ventral.

1 The ventral fissure is not always present, and the so-called dorsal fissure,

which is formed by obliteration of the greater part of the primitive central canal,
is better described as the dorsal septum.

THE BRAIN 153

As regards its minute structure, two parts can be distinguished
in the spinal cord,—a white substance, consisting of nerve-fibres only,
and a gray substance, composed of nerve-cells as well as fibres. Their
relative positions vary in the different animal groups, as well as in
the different regions of the cord ; the white substance, however,
has typically a more peripheral, the gray a more central position,
the latter surrounding the central canal and usually presenting a
pair of dorsal and ventral cornwa in transverse section.

2. The Brain.

Before the medullary groove becomes closed, the anterior ex-
panded part of the medullary tube presents three swellings, which
are spoken of as the primary fore-, mid-, and hind-brain, or anterior,
middle, and postertor cerebral-vesicles (Fig. 124); the cavities of
the vesicles (ventricles) are in direct connection with the central
canal of the spinal cord. Both the primary fore-brain and hind-
brain then become differentiated, each into two parts, and thus five

Ce a

eae 4

a a ey ee

Fic. 124.—D1aGRam oF THE EMBRYONIC CONDITION OF THE CENTRAL NERVOUS
SysTEM.

G, brain, with its three primary vesicles, J, 7, III; R, spinal cord.

divisions of the brain may be distinguished. Counted from before
backwards these are :—prosencephalon (secondary fore-brain), thala-
mencephalon (primary fore-brain), mesencephalon (mid-brain), meten-
cephaton (secondary hind-brain), and myelencephalon (primary
hind-brain). The prosencephalon usually gives rise to a pair of
lobes, the cerebral hemispheres, and in the mid-brain a pair of
optic lobes or corpora bigemina become differentiated dorsally, and
two longitudinal bands, the crura cerebri, ventrally. The meten-
cephalon is usually spoken of as the cerebellum, and the myelen-
cephalon as the medulla oblongata.

From the base of the prosencephalon cr hemispheres paired
olfactory lobes (rhinencephala) are given off anteriorly, and the floor
or central part of each hemisphere becomes thickened to form a
large “basal ganglion,” the corpus striatwm, while its peripheral
part is distinguished as the “mantle” or palliwm (Fig. 125).

The relative development and differentiation of the pallium

‘stands in close relation to the mental development of the animal, and

reaches its greatest perfection in Mammals, especially in Man. In
certain Fishes the pallium remains partially or entirely non-
nervous, retaining its primitive epithelial character, and a layer

154 COMPARATIVE ANATOMY

of cortical gray matter is only distinctly differentiated from Rep-
tiles onwards. No regular series of gradations can, however, be
traced in this respect in the various groups.

Connecting the two lateral halves of the fore-brain are certain
transverse bands of nerve-fibres or commissures. An anterior
commissure is present in the posterior region of the secondary fore-
brain, a middle in the primary fore-brain, and a posterior in
the anterior part of the mid-brain. In addition to these, others
may be developed between the hemispheres, but only attain im-
portance in Mammals: they are known as the corpus callosum and
the fornix.

The outer surface of the hemispheres in all Vertebrates below
the Mammalia is more or less smooth: in the latter Class, convolu-
tions (gyrt) separated by fissures (sulci) may be present. The

OY TH 22 Ma Sp A WO

Zoi , en
| & “sigs a0
Avia y, a
| “z ARLE ARA Te : orn
ty X& Ch
| a Ch Le

Opt

Fig. 125.—D1aAGRAMMATIC LONGITUDINAL SECTION THROUGH THE SKULL AND
Brary or AN (IDEAL) VERTEBRATE Embryo. (In part after Huxley.)

Be, basis cranii ; Ch, notochord ; SD, roof of skull; #1, nasal cavity; VH,
secondary fore-brain (prosencephalon), showing the corpus striatum (Cs) at the
base, and the olfactory lobe (O/f) anteriorly ; ZH, thalamencephalon (primary
fore-brain), which has given rise dorsally to the pineal body (epiphysis, 4),
and ventrally to the infundibulum (J), to which the pituitary body (hypo-
physis, H) is attached ;: anterior to this is seen the optic nerve (Opt), arising
from the optic thalamus (Tho); HC, posterior commissure; JfH, mid-brain
(mesencephalon) ; HH, cerebellum (metencephalon, secondary hind-brain) ;
NG, primary hind-brain (myelencephalon) ; Cc, central canal of spinal cord.

convolutions consist of folds of the gray cortical substance, which
cause a greater or less increase of the superficial area.

From the thalamencepha/lon, the ventricle of which is walled-in
anteriorly by the lamina terminalis, the following structures arise
(Fig. 125) :—the optic thalamt, formed as thickenings of its lateral
walls ; the primary optic vesicles, arising as paired ventro-lateral
outgrowths from which the optic nerves and retina are derived
later; the pincal apparatus, developed as tube-like outgrowths of
the roof; and finally, the infundibulum, formed as a funnel-like
extension of the floor, together with a part of the pituitary body
(hypophysis). The other portion of the pituitary body arises. by a
gradual pinching off of the epithelium of the primary oral involu-
tion (stomodeum, p. 5, and Fig. 126), which gives rise to a
gland-like structure, and other parts (sacews vasculosus, &c.) arise
in close connection with it.

THE BRAIN 155

The pineal apparatus consists of the epiphysis or pineal organ
proper, which persists in a more or less rudimentary condition in
all Vertebrates, and of a more anterior outgrowth which may be
called the parietal organ, arising from the epiphysis or indepen-
dently from the root of the thalamencephalon ; the latter organ
becomes atrophied in the majority of Vertebrates. Each of these
structures represents a vestigial sensory organ, and in certain cases
may retain to a greater or less extent the character of a median eye—
possibly in some degree comparable to that of Tunicates.!

Certain facts seem to indicate that both organs arose primitively in a
paired manner. Accessory vesicles occur occasionally in young Slow-
worms (Angus), in which as many as two or even three rudimentary vesicles
may be present behind the pineal organ.

Fic. 126.—Meprian LonciruptInaL Section THROUGH THE Hrap or A Newty-
HATCHED Larva oF Petromyzon planeri. (Mainly after Kupfer.)

J.b, fore-brain ; m.b, mid-brain ; h.b, hind-brain ; ep, epiphysis ; Ap, hypophysis ;
st, stomodeum ; al, endodermic alimentary cavity ; ch, notochord.

The hypophysis apparently represents a glandular organ, the
secretion of which formerly passed into the ventricles, and various
hypotheses have been put forward as to its first origin.

One of the more recent of these theories assumes that it corresponds to the
primitive mouth (paleostom) of the Proto-Vertebrata, which is to a greater
or less extent represented by the combined unpaired nasal and pituitary
passage of Cyclostomes (see under Olfactory Organ): the mouth of existing
Vertebrates must then be distinguished as a neostoma.

Both the primary and the secondary fore-brain are situated in
the pre-chordal region of the skull, all the other divisions of the
brain lying in its chordal portion (comp. p. 67).

The mid-brain and medulla oblongata undergo fewer modifi-
cations than the fore-brain ; only the anterior part of the thin

-«- «1 Still more anteriorly a third outgrowth or paraphysis, arising from the
secondary fore-brain, has been observed in the embryos of various Vertebrates.

156

COMPARATIVE ANATOMY

roof of the latter (valve of Vieussens) is nervous, and its Hoor

becomes greatly thickened.

The greater number of the cerebral

nerves arise from the medulla oblongata, so that its physiological

Fic.

127.—DIAGRAM OF
THE VENTRICLES OF THE
VERTEBRATE BRAIN.

V'H, cerebral hemispheres
containing the lateral
(1st and 2nd) ventricles
(SV); ZH, thalamen-
cephalon,with the third
ventricle (III) ;a thick-
ened vascular part of
the pia mater (choroid
plexus) roofs over the
third and fourth ven-
tricles; each lateral
ventricle communicates
with the third ventricle
by a small aperture, the
foramen of Monro(F'M);
MH, mid-brain, which
encloses the aqueduct
of Sylvius (4q), com-
municating between the
third and fourth vent-
ricles; HH, cerebel-
lum ; NH, medulla ob-
longata, enclosing the
fourth ventricle (IV) ;
Cc, central canal of the
spinal chord (2).

importance is very great. The cerebellum
may become more or less distinctly sub-
divided into lobes.

In the course of the development of the
brain the walls of the cerebral vesicles be-
come more and more thickened, so that
their cavities undergo a gradual constriction.

A series of unpaired ventricles (prosocele,
thalamocele, mesocele, metaccle, myelocele,
see p. 153), lying in the longitudinal axis of
the brain, as well as paired outgrowths from
certain of them, can always be distinguished
(Fig. 127). When cerebral hemispheres are
developed (as is generally the case), the
prosoccele gives rise to paired cavities, ex-
tending into them, and knownas the lateral
ventricles (ventriculus 1 and 2); each of these
communicates with. the thalamoccele or
third ventricle by means of an opening, the
foramen of Monro, and may be continued
into the corresponding olfactory lobe as a
rhinocele or olfactory ventricle. Each optic
lobe also usually contains an optic ventricle,
or optocele, communicating with the meso-
ceele or aqueduct of Sylvius. There may bea
distinct metaccele in the cerebellum opening
into the myeloccele or fowrth ventricle.

A so-called fifth ventricle, situated between the
corpus callosum and fornix, is found in Mammals,
but morphologically it has nothing to do with the
ventricles proper, and simply represents a space
between the thin internal walls (septa lucida) of
the two hemispheres.

All five cerebral vesicles lie at first in
the same horizontal plane, but in the course
of developmenta cerebral flexure takes place,
the axis of the vesicles becoming bent down-
wards, so that at a certain stage the mesen-
cephalon forms the apparent apex of the
brain. In Mammals, the parts of the brain

become still further folded on one another, so that a parietal, a
Varolian, and a cervical bend may be distinguished (Fig. 128):
this process is connected with the further development of the skull
and the rapid longitudinal growth of the brain.

THE BRAIN 157

In Fishes and Amphibians the cerebral flexure later becomes
practically obliterated, but it persists more or less markedly in the
higher types, more particularly in Mammals. In the latter Class,
moreover, the original relation of the parts becomes still further
complicated by the large development of the cerebral hemispheres,
which grow backwards, and thus gradually come to overlie all the
other parts of the brain, This condition of things attains its
greatest perfection in Man. Thus instead of
the various sections of the brain being situated yy 97, SP
one behind another, they come to lic eventually, 5 i
more wpon one another, the thalamencephalon,
mid-brain, cerebellum, and medulla oblongata
becomming covered over by the hemispheres.

Amphioxus.—The conical and enlarged anterior
end of the spinal cord of the Lancelet contains a
widened portion of the central canal which must be

looked upon asa ventricle. In the larva, this opens, )98 —CerEPRAL

freely on to the exterior dorsally by a nenropore,
which probably represents the last indication of the
primitive connection of the central nervous system
with the outer skin. It is possible that the anterior
enlargement of the cord corresponds to the fore-
brain—-and perhaps also the imid-brain—of the
Craniata.

Cyclostomi.—The brain of these forms
remains in many respects in an embryonic con-
dition : this is particularly the case in the larval
Petromyzonor Ammoceete (Fig. 129). Intheadult
the individual vesicles lie in an almost horizontal
direction one behind the other, and the prosen-
cephalon consists of a median part and of small
paired hemispheres continuous anteriorly with
the larger, rounded olfactory lobes. The median
portion of the prosoccele is continued trans-
versely outwards into each hemisphere, in which
it gives rise to a lateral ventricle: this is con-
tinued forwards for a short distance into the
base of the olfactory lobe, as well as backwards
into the hemisphere. The roof (pallium) of
the median portion of the ventricle is non-

FLEXURE OF A
MamMaL..

1H, prosencephalon;

ZH, thalamence-
phalon, with the
pituitary body
(H) at its base ;
MH, mesenceph-
alon, which at SB
forms the most
projecting por-
tion of the brain,
representing the
so-called ‘‘ parie-
tal bend”; HH,
metencephalon ;
NH, myelence-
phalon, forming
the “ cervical
bend” (VB): the
“Warolian bend”
(BB) arises on
the ventral cir-
cumference, at
the junction be-
tween HH and
NH; R, spinal
cord.

nervous, and consists of a single layer of epithelial cells, which,
together with the pia mater, has been removed in the prepa-
ration represented in Fig. 129, a. The mid-brain and medulla
oblongata are relatively broad, and the cerebellum is represented
by a mere narrow ledge overhanging the fourth ventricle ante-
riorly. The roof of the mesocele is formed mainly by a layer of
epithelial cells, and, like that of the third and fourth ventricles, is

158 COMPARATIVE ANATOMY

covered by a thickened and vascular portion of the pia mater. or
choroid pleaus.

Fic. 129. —Bratn or Larvat Lamprey. (A, from above; B, from below ;
C, from the side.) ;

VH (Bas.@), cerebral hemispheres, between which, in A, the median portion of the
prosencephalon is seen, with the membranous roof removed ; L.o/, olfactory
lobe; ZH, thalamencephalon ; G.p, pincal body; Hyp, hypophysis; Sr,
saccus vasculosus ; JH, mid-brain ; H/7, cerebellum ; NH, medulla oblon-
gata ; Med, spinal cord ; I-X, cranial nerves; XL, first spinal nerve (hypo-

glossal).

The brain of Myxine shows many special peculiarities: its
subdivisions are broader and more closely approximated than in

THE BRAIN 159

the lamprey, and the thalamencephalon cannot be seen from the
dorsal side owjng to the larger size of the solid prosencephalon.
The mesoccele ends blindly in front, the third ventricle being
almost completely obliterated. The cerebellum is relatively larger
than in Petromyzon, and no pallium has been recognised in the
prosencephalon of the adult.

In Petromyzon the pineal apparatus is represented by two
vesicles, each connected with the dorsal surface of the thalamen-
cephalon (ganglion habenule) and lying one above the other just
beneath the roof of the skull; the integument immediately above
these vesicles is pigmentless. The cells on the ventral side of the
dorsal vesicle (epiphysis) are arranged radially and contain pig-
ment, furming a kind of retina, but they show signs of degenera-
tion; the lower vesicle (parietal organ, p. 155) is without pigment.
In Myxine there is only a single pigmentiless vesicle.

A. saccus vasculosus (comp. pp. 154, 160, et seg.) is present in
connection with the infundibulum, to which a small pituitary
body is attached.

Elasmobranchii and Holocephali.—The brain of these
Fishes, like that of Cyclostomes, is in many respects of a specialised
form, characteristic of, and contined to, the group, though the par-
ticular regions are much more highly developed than in the
Cyclostomi. According to its external form two main types can
be distinguished. One of these, seen in Spinax, Scymnus, Noti-
danus and the Holocephali, is, characterised by its very narrow and
elongated form, while in the rest of the Elasmobranchii the indi-
vidual parts are more closely compressed and approximated together
(Fig. 130). In almost all Sharks the prosencephalon is relatively
much larger than any of the other regions. The olfactory lobes
arise from the anterior or antero-lateral ends of the prosencephalon,
and in some Elasmobranchs remain in close connection with the
latter ; in others in which the olfactory capsules are situated further
forwards, they become drawn out into long olfactory tracts each
continuous anteriorly with an olfactory bulb from which the olfac-
tory nerves arise. ies

A division of the prosencephalon into paired halves is hardly
indicated at all in Rays, and only slightly so in the commoner Dog-
fishes (e.g., Scyllium, Acanthias), in which, however, lateral and
olfactory ventricles are present. Only in Scymnus, and to seme
extent in the Notidanide, is there a distinct separation of the
pallium into two hemispheres. In Rays there is only a small
single prosoccele, the prosencephalon consisting of a practically
solid mass; and the olfactory lobes are also solid.

The thalamencephalon is roofed over by a choroid plexus, and
the tube-like epiphysis may reach sucha length as to extend beyond
the anterior end of the brain for a considerable distance, and pass
distally into the roof of the skull: no indication can be seen of a
parietal organ. <A pair of. small lobes—the lobe inferiores—are

160 COMPARATIVE ANATOMY

Fic. 130.—Bratn oF Scyllium canicula. (A, dorsal; B, ventral; and C,
lateral view. )j

7.b, prosencephalon ; 0.0, olfactory bulb; t.o, olfactory tract (very short in
Scyllium) ; th, thalamencephalon ; ep, base of pineal body ; 7f, lobi inferiores ;
h.p, hypophysis ; sc, saccus vasculosus ; m.b, mid-brain (optic lobes) ; A.0,
cerebellum ; m.d, medulla oblongata; jr, fourth ventricle; i-a, cranial
nerves (the ventral vagus roots are omitted from Fig. B. The epithelial and
vascular roof of the third and fourth ventricles has been removed.

present on the infundibulum, and an “‘infundibuiar gland” or saccus
vasculosus is present on the. sides and floor of the infundibulum,
which is connected posteriorly with the pituitary body.

THE BRAIN 161

The cerebellum is always very large, overlapping the optic lobes
and the medulla oblongata tu a greater or less extent: itis divided
up into several folds lying one behind the other, and usually con-
tains a metaccele opening into the fourth ventricle (Figs, 130 and
131). In Sharks the medulla oblongata is an elongated cylindrical
body, while in Rays it is more compressed and triangular; at its

Fic. 131.— Brain oF Cheilo-
scyllium. (From Parker and
Haswell’s Zoology. )

Viewed from the dorsal side,
the roof of the various ven-
tricles removed so as to show

the relations of the cavities Fic. 132.—Brarn or
(semi-diagrammatic). Lepidosteus. (Dorsal

cer, dilatation from which the view.) (After Balfour
metaccele is given off; dia, and Parker.)

. thalamocceele—the reference

line points to the opening cbl, cerebellum ; ¢.h, pro-
leading into the infundibu- sencephalon ; di, thal-
lum ; zer, aqueduct of Sylvius amencephalon; m.o,
(mesoceele), into which the medulla oblongata ;
optoceeles (opt) open; meta, olf.1, olfactory lobes ;
myeloceele ; para, lateral ven- opt./, optic lobes ; prs,
tricle ; pros, median part of lobes of prosencepha-
prosoceele ; rh, rhinoccele. lon.

anterior end are two lateral lobes, the corpora restiformia. In
electric Rays (p. 146) a pair of obi electrici arise from the
gray matter of the floor of the fourth ventricle, and these en-
close a mass of giant nerve-cells.
Ganoidei.—The pallium covering the median prosoccele
consists mainly or entirely of epithelial and connective tissue
M

162 COMPARATIVE ANATOMY

elements, much as in Cyclostomes, The olfactory lobes are
closely applied to the prosencephalon, which gives rise
anteriorly to cerebral hemispheres containing lateral ventricles
(Fig. 132).

The well-developed thalamencephalon has a marked ventral
flexure and from its roof arises a strong pineal peduncle, the distal
end of which extends into a hollow in the cranial roof, but
undergoes atrophy, in Amia becoming completely separated off
from the brain! Well-developed lobi inferiores are present,
and the hypophysis? and saccus vasculosus are voluminous:
the latter consists largely of glandular tubules which open
into the infundibulum, as is also the case in Elasmobranchs

. 160).

. The large cerebellum gives rise to a valvula cerebelli (comp.
Fig. 134) extending forwards into the ventricle of the mid-brain ;
the optic lobes are also large.

The brain of Amia on the whole most nearly approaches that
of the Teleostei in structure.

Teleostei—As is the case in many other Fishes, the brain in
most Teleosts by no means fills the cranial cavity, and it is separated
from the roof of the skull by a greater or less amount of a fatty
and lymph-like fluid. It never attains to so large a relative size
as does that of Elasmobranchs. Its form varies greatly, more by
far than in any other Vertebrate group, and only the following
essential points can be mentioned here.

The pallaum is entirely epithelial in structure (Figs. 183-135),
and, moreover, it presents no median involution dividing the
anterior part of the prosencephalon into two lateral hemispheres:
there is a median prosoceele. The lower part of the prosen-
cephalon is made up of large paired basal ganglia (corpora
striata) connected together by an anterior commissure. The
olfactory lobes are either closely applied to the prosencephalon
and contain a small rhinoccele, or they become differentiated into
olfactory tract and bulb, as in Elasmobranchs (p. 159).

The thalamencephalon is very small. The epiphysis (Figs.
133, 134) is plainly distinguishable, but it does not pass into
the roof of the skull; an outgrowth arising from the roof of the
brain in front of the epiphysis represents the parietal organ,
but this becomes constricted off from the brain and disappears
during development. Marked lobi inferiores, as well as a

"In Polypterus the pineal body gives rise to a peculiar and extremely large
epithelial vesicle. In Devonian Ganoids there was a parietal foramen (comp.
p. 171).

2In Polypterus and Calamoichthys the hypophysis communicates with the
mouth-cavity by a hollow duct, even in the adult (comp. p. 155).

* A parietal foramen is, however, often present in the embryo, and persists
throughout life in Callicthys.

THE BRAIN 163

‘hypophysis and glandular saccus vasculosus are present, but these
vary much in the degree of their development. The saccus

Fic, 133.—Brain or Satmon, (A, dorsal; B, ventral; and C, lateral view.)

Vit, prosencephalon ; Pal/, pallium (in part removed), and BG and Bas.G, basal
ganglia (corpora striata) of the prosencephalon ; L.o/, olfactory lobe; G.p,
pineal body ; Jnf, infundibulum ; Hyp, hypophysis; Sv, saccus vasculosus ;
OL, \obi inferiores ; V'r.opt, optic tract; Ch, chiasma; J/H, mid-brain ;
HH, cerebellum; NA, medulla oblongata; Jfed, spinal cord ; J-X, cranial
nerves; 1 and 2, first and second spinal nerves (the first represents the
hypoglossal, JJ).

vasculosus opens by several apertures into the infundibulum, and
is surrounded by a blood-sinus.
M 2

164 COMPARATIVE ANATOMY

The mid-brain (Fig. 133) is extremely large relatively, while
the thalamencephalon is depressed between it and the prosen-

cephalon.
The extremely well-developed cerebellum is bent upon itself,

Ylfay

Fic. 134.—LonGItuDINAL VERTICAL SECTION THROUGH THE ANTERIOR PART OF
THE TELEOSTEAN Braryx. (Founded on a figure of the Trout’s brain by Rabl-
Riickhard. )

To, roof of the optic lobes; 7’, torus longitudinalis ; Cy, posterior commissure ;
Gp, pineal body, with a cavity ((p) in its interior; Ep, Ep, the epithelium
(ependyme), lining the walls of the ventricles ; +, point at which the epithelial
roof of the secondary fore-brain (pallium, Pa) becomes continuous with the
lining of the anterior wall of the pineal tube ; at f is seen an outgrowth which
represents a rudimentary parietal organ ; J’.em, common ventricle (prosoccele)
of the secondary fore-brain ; V.t, third ventricle ; B.ol, N.ol, olfactory lobe
and nerve; C.st, corpus striatum, which lies on either side of the middle:
line; Ch.n.opt, optic chiasma ; Ct, inferior commissure ; Ch, horizontal com-
missure; J, infundibulum; H, #1, hypophysis; Sr, saccus vasculosus ;
Li, lobi inferiores; Aq, aqueduct of Sylvius (mesoccele) ; 7, pathetic nerve ;
Val, valvula cerebelli.

overlies the medulla oblongata behind, and is prolonged in front
into the ventricle of the mid-brain as a valvula cerebelli (Fig. 134),
as is the case in Ganoids.

The Teleostean brain is of a specialised type. It has no direct

THE BRAIN 165

connection with that of Cyclostomes or Elasmobranchs, but has
certainly passed through Ganoid-like stages.

Fic. 135. —TRANSVERSE SECTION THROUGH THE FoRE Part OF THE TELEOSTEAN
BRAIN.

fr, frontal bone, underneath which the pineal tube, Gp, is visible in transverse sec-
tion, and below this the pia mater, Pm; Pa, the pallium, or roof of the sec-
ondary fore-brain, formed of a simple epithelial layer ; V.em, prosoccele ; Lp,
ependyme; 7, 7, olfactory tracts at the base of the corpora striata (C.st.).

Dipnoi.—Both. as regards external and internal structure,
certain points of resemblance may be
seen between the brain of Dipnoans
and that of Elasmobranchs on the
one hand and Amphibians on the other.
This fact probably indicates that
though the Elasmobranchii and Dipnoi
have arisen from a common ancestral
type, they have become differentiated
along different lines.

The prosencephalon is well de-
veloped (Fig. 136): the thin pallium
is mainly nervous, and is involuted
along the median longitudinal line so
as to completely separate the two
hemispheres from one another in
Protopterus: in Ceratodus they are
united together posteriorly by a narrow
commissure. Olfactory lobes aise
from the prosencephalon anteriorly,
and contain ventricles.

Fic. 136.—Brain oF Ceratodus The thalamencephalon of Pro-
fosteri. Dorsal view. (From topterus presents certain very charac-
Parkerand Haswell’s Zoology.). teristic features, especially as regards
aud, auditory nerve ; «b/, cere- its roof. The pineal body has a long
ae facial nerve ;9/, stalk, and its distal vesicle perforates
ossopharyngeal ; med, me- ra ee

datiaauloddata;dis meceuce: the cartilaginous roof of the skull:
phalon ; oc,oculomotor nerve; in the embryo Ceratodus it even
opt, optic nerve ; pros, cere- yeaches as far as the integument.
bral hemispheres ; rh, olfac- i i o
tory lobes; ry, vagus nerve. The choroid plexus gives rise to a
vesicular organ, and as regards its

166 COMPARATIVE ANATOMY

network of blood-vessels more nearly resembles that of Elas-
mobranchs than that of Amphibians. Lobi inferiores are present.
Nervous and glandular portions can here also be recognised in the
hypophysis.

The well-marked mid-brain is indistinctly paired in Ceratodus,
but is unpaired in Protopterus.

The cerebellum is relatively much smaller than in Elasmo-
branchs. and Teleosts, though better developed than in Urodeles:
it gives rise to a valvula cerebelli.

Amphibia.—The prosencephalon of Amphibians is distin-
guished from that of Dipnoans by a higher development of the
pallium, which, however, even in the latter group, is differ-
entiated into an external layer of nerve fibres and an internal
cellular layer. The basal ganglia (corpora striata) are less
marked, and merely form a more or less prominent thickening
of the wall of each hemisphere projecting into the lateral
ventricle.

The Amphibian brain does not, however, lead towards that
of Reptiles. Although the prosencephalon is more highly differ-
entiated than in lower forms, the thalamencephalon and mesen-
cephalon are simpler than in Fishes; and, on the whole, the
brain of Amphibians is less complicated than that of any other
Vertebrates.

In Urodeles the individual parts are more elongated and
separated from one another than in Anurans, and the thala-
mencephalon is therefore more freely exposed. The hemispheres
are almost cylindrical and are separated from one another by the
pallial fold as far back as the anterior commissure, as in Pro-
topterus ; while in the Anura (Figs. 137 and 138, A) they are fused
together for a short distance anteriorly, where they are continuous
with the olfactory lobes. The thalamencephalon and optic lobes
are much broader in Anurans than in Urodeles. The cerebellum
consists simply of a small transverse fold, and is especially rudi-
mentary in Urodeles.

The infundibulum and hypophysis are well developed, but a
saccus vasculosus is no louger so distinct as in Fishes, though traces
of it can still be recognised. The epiphysis does not extend
beyond the skull in Urodeles, but in Anuran larve it reaches the
integument, undergoing reduction later, when the bony skull-roof
is formed ; indications, of its extracranial portion can, however,
sometimes be recognised even in the adult (the “brow-spot” in
¢g., Rana temporaria): thus its intracranial portion does not
represent the entire epiphysis. A parietal organ appears to be
entirely wanting in all Amphibians with the exception of some
few Anura in which traces of it have been described?

In the Gymnophiona the olfactory lobes and hemispheres are

1 The dorsal part of the anterior commissure has been said to represent a
rudimentary corpus cal/osum (comp. note on p. 174, and Fig. 138, a).

2 A parietal foramen was, however, present in the Paleozoic Stegocephalu
and other extinct Amphibians.

THE BRAIN 167

relatively larger than in other Amphibians, and the hemispheres
overlap the posterior parts of the brain to a larger extent.

Tropt— 2,
a5

WwW ZH MH W HA NIT Mea
Vita) x ed
rai

Wr

HU Lropt IE Hyp

Fic. 137.—Brain or Rana esculenta. (A, dorsal; B, ventral; and C,
lateral view.)

VH, cerebral hemispheres; ZH, thalamencephalon ; 1/H, mid-brain ; HH, cere-
bellum ; NH, medulla oblongata ; Med, spinal cord; -X, cranial nerves ;
Ta, lateral root of olfactory nerve ; XJZJ (1), ventral root of first spinal nerve
(hypoglossal), and 1, its dorsal root ; L.o/, olfactory lobe ; +, space between
the two hemispheres; Jr.opt, optic tract; Jn/, infundibulum; Hyp,

hypopbysis.

Reptiles —The brain of Reptiles reaches a considerably higher
stage of development than that of the forms already described, and
the individual parts overlie one another to a greater extent, especially
in the Agame and Ascalabote.

168 COMPARATIVE ANATOMY

The hemispheres are more highly developed, and the cortex is
definitely differentiated and contains the characteristic pyramidal
cells. In many cases also a distinct hippocampal lobe (Figs. 139, 140)

A

Fic. 138.—LoneituDINAL SECTION THROUGH THE Brain oF A, Rana, AND B,
Hatteria, (A after H. F. Osborn.)

VH, MH, HH, NH, prosen-, mesen-, meten-, and myelencephalon ; H in (B),
hemisphere, which possesses a furrow on its median face, where it is perforated
by numerous vascular foramina (S): this furrow forms the boundary between
the hemisphere and olfactory tract, the main root of which is seen at + ; Lol;
olfactory lobe; J, IZ, IV, origins of the olfactory, optic, and pathetic
nerves ; Hp, **, base of epiphysis, which is not shown; Ch.opt and Ch, optic
chiasma ; Lt, lamina terminalis (the reference line should point to the cut
edge below Ba and*), Co.a,* anterior commissure ; Cu, Ba, corpus callosum ;
Ff. Mo, Mo, foramen of Monro, above which, in A, is seen the folded choroid
plexus ; Cos, superior commissure ; Co.p, posterior commissure ; T!// and V!",
third and fourth ventricles ; 7h. opt and M, optic thalamas ; Lo (in B), aper-
ture, and Fu, furrow in the wall of the third ventricle ; 1g, dg.Syl, aqueduct
of Sylvius; Jnf, infundibulum ; Hyp, hypophysis.

is present (Hatteria, Chelonia, Crocodilia), and the commissural
system between the hemispheres known as the forniz as well asa
so-called “ corpus callosum” (comp. p. 174) are present in rudiment.

THE BRAIN 169

* ala
#
|

Gp MH HH
YR lh

BSS i

LT Inf Hyp

Fic. 139.—Braiy or Hatteria punctata. (A, dorsal; B, ventral; and (,
lateral view. )

VH, MH, HH, NH, as in Fig. 138; Jed, spinal cord; I-XJJ, cranial nerves ;
Ip, process of the hemisphere representing a hippocampal lobe; Vopr,
optic nerve ; Ch, optic chiasma; 7’r, optic tract; Jif, infundibulum ; Hyp,
hypophysis ; G.p, pineal body, shown in C continuous with the parietal eye
(Pa), and only indicated diagrammatically in A; #1, curved ridge at the
base of the optic lobe ; A, small elevation in front of the cerebellum.

170 COMPARATIVE ANATOMY

omit NH-

Sf

AN a ap ‘

see

Fic. 140.—Bratn or ALicator. (A, dorsal; B, ventral; and C, lateral view.)

VH, cerebral hemispheres, each of which gives rise postero-laterally to a hippo-
campal lobe partially overlying the corresponding optic tract, V'r.opt ; ZH,
thalamencephalon ; A/H, optic lobes; AHH, cerebellum; NH, medulla
oblongata ; I-X JJ, cranial nerves ; 1, 2, first and second spinal nerves ; B.ol,
olfactory bulb; 7'ro, olfactory tract ; G.p, pineal body ; Jnf, infundibulum ;
Hyp, hypophysis ; Med, spinal cord.

THE BRAIN 171

The olfactory lobes may be well marked or entirely invisible
externally, In such forms as Anguis, Amphisbzena and Typhlops
they are closely applied to the hemispheres, while in others (ey,
Hatteria, Lacerta, Crocodilus) each consists of a well-marked olfac-
tory tract, passing anteriorly into an olfactory bulb from which the
nerves of smeli arise. Olfactory ventricles are usually present.

The thalamencephalon is always depressed, and is hardly, or
not at all, visible from the dorsal side. A distinct hypophysis and

Fic. 141.—LoxeirupInaAL SECTION THROUGH THE PARIETAL Eyre anp irs Con-
NECTIVE-TISSUE CaPsuLE OF Hatteria punctata. (After Baldwin Spencer.)

cp, connective-tissue capsule ; 7, ‘‘lens;” cv, cavily of the eye, filled with fluid ;
rv, retinal portion of the vesicle ; vs, blood-vessels ; ¢.7, cells in the nerve
stalk (s.2.).

infundibulum as well as an epiphysis are present, and in Lizards
the parietal organ retains more or less distinctly, even in the adult,
its primitive structure as a median eye.

This parietal eye (Fig. 141) is situated in the parietal foramen
of the skull, and is in close connection with the epiphysis, though
in the embryo the nerve which supplies it is seen to arise in-
dependently from the brain, in front of the pineal outgrowth. The
eye has the form of a vesicle, the dorsal wall of which may become
thickened to form a transparent lens-like body, while the rest of

172 COMPARATIVE ANATOMY

the wall consists of several layers and forms a pigmented retina,
with which the more or less rudimentary nerve is continuous. -The
vesicle is surrounded externally by a connective-tissue capsule, and
in many cases the integument and connective-tissue immediately
overlying the vesicle is pigmentiless and transparent, forming a
kind of cornea. ‘Traces of a vitreous body have also been observed.
Various degrees of reduction of the different parts as they occur
c.g. in Hatteria (Fig. 141), are seen amongst Lizards. (See also p.
155). Traces of a parietal eye, with lens and pigment, have also
been observed in the embryo of the Viper (Pelias berus).

In the mid-brain the two well-marked optic lobes may show
indications of a further subdivision into four; from them the optic
tracts pass downwards and forwards to the chiasma. The cerebellum
is relatively small, except in the Crocodilia (Fig. 140), in which it
consists of a thicker median, and two lateral portions, while in
other Reptiles, and more particularly in Lizards, it is not much
more highly developed than in Amphibians. The medulla ob-
longata has a marked veniral flexure.

Birds.—The basal ganglia (corpora striata) of the hemispheres
reach a relatively larger size in Birds than in any other Vertebrates,
while the differentiation of the cortex and commissures does not
show any marked advance on that seen in Reptiles.

The different parts of the brain overlie one another much
more markedly than in any Reptile, and the hemispheres are
much larger relatively, covering over the thalamencephalon and part
of the mid-brain (Fig. 142). The olfactory lobes are short and
conical. The distal, enlarged end of the pineal body extends as
far as the dura mater, and the structure of the internal part of the
organ resembles that of a tubular gland, penetrated by fibrous tissue
and blood-vessels. There is no trace of a parietal organ.

The cerebellum consists of a well-developed and folded median
lobe, and of two lateral portions (flocculi), which vary much both in
form and size. Posteriorly it completely covers the fourth ventricle.
The two optic lobes are separated from one another and pressed
downwards, so as te lie on the sides of the brain in the angle between
the hemispheres, cerebellum, and medulla oblongata, and they are
connected by a broad commissure. The ventral side of the hind-
brain shows a marked flexure, bending upwards to the spinal cord.

Mammals.—The brain in embryo Mammalia is very similar
to that of the Sauropsida, but its later differentiation—more
particularly that of the pallium—gives it a very special character.
The cortex becomes much more highly differentiated, and in
many Mammals is more or less highly convoluted (Figs. 144, 146),
giving rise to gyri and sulci (p. 154). In others, again, the surface
of the hemispheres remains smooth (Fig. 143), but a subdivision
into lobes (frontal, parietal, temporal, &c.) can always be recog-
nised to a greater or less extent, and the hemispheres are
relatively so large as to cover over the more posterior parts of the
brain; in some of the lower forms, the mid-brain can still be seen

THE BRAIN 173

ae eer
A | Hyp
Tropt Inf
Fic. 142.—Brarin or Piaeon. (A, dorsal; B, ventral; and C, lateral view.)

VH, cerebral hemispheres; 1/H, optic lobes; HU/, cerebellum; VH, medulla
oblongata; Afed, spinal cord ; J-X IJ, cranial nerves ; ], 2, first and second
spinal nerves ; Lol, olfactory lobes; Tr.opt, optic tract ; Jif, infundibulum ;

Hyp, hypophysis.

a0 5

from above (Fig. 143) while in the higher types (Primates) even
part of the cerebellum is hidden (Figs. 145, 146).

The commissures between the hemispheres (corpus calloswm
and fornix, Fig, 145) are also much more highly developed than
in the Sauropsida. The corpus callosum or pallial commissure,
though small in the lower Mammalia (¢.g., Monotremes and

174 COMPARATIVE ANATOMY

Marsupials),! is usually a large and important structure; its
relative size is in inverse proportion to that of the anterior
commissure. In addition to the anterior and posterior commis-
sures, a niddle commissure is definitely differentiated from the

B

ol
ye abl

"

i ii pee. vi vii ix xii
Fic. 143.—Brain oF Raunsir. (A, dorsal; B, ventral; and C, lateral view.)

J.b., cerebral hemispheres; m.b., optic lobes; h.b., cerebellum ; ¢.b’., superior

vermis, and ¢.b"., lateral lobe of cerebellum; md., medulla oblongata ; ep.,

pineal body ; h.p., hypophysis ; pv., pons Varolii; cr., crura cerebri; /,p.,

pallial fissure ; 6.0., olfactory bulb ; 7-a:7/, cerebral nerves.
base of the brain as a distinct structure connecting the two optic
thalami.

In correspondence with the division of the hemispheres into
lobes, there is a marked differentiation of the lateral ventricles,

1 Recent researches indicate that a true corpus callosum is present only in
the Placentalia, and that the commissure which is usually supposed to represent
it in lower types may be more correctly described as the hippocampal commissure.

‘Se

: THE BRAIN 175

40 that an anterior, a posterior, and an inferior cornu can be dis-
dinguished in each ; the inferior cornu extends into what corresponds
‘to the hippocampal lobe of Reptiles (p. 168), and an eminence on
its floor, known as the hippocampus major, is much more marked
than in lower forms. The olfactory lobes, in which an olfactory

Fic. 144.—Brarn or Doc (Pointer). (A, dorsal; B, ventral; and C,
lateral view.)

VH, cerebral hemispheres; MH, optic lobes; HH, cerebellum, Iu, superior
vermis ; HH}, lateral lobe of cerebellum ; NH, medulla oblongata ; Acc,
spinal cord ; Hyp, hypophysis; Po, pons Varolii: Cr.ce, crura cerebri ;
Li.p, pallial fissure ; B.ol, olfactory bulb ; J-X JJ, cranial nerves.

tract and bulb can be distinguished, usually extend forwards freely
from the base of the prosencephalon and each may (¢.g., Horse)
contain a prolongation of the lateral ventricle ; but in some cases
(e.g., numerous aquatic forms and Primates) they are completely
covered by the frontal lobes.

176 COMPARATIVE ANATOMY

The pineal body is displaced downwards by the hemispheres.
and lies against the anterior part of the mid-brain, not reaching.
to the roof of the skull. Its bifurcated peduncle connects it
Sp BET z

'
1
'
,
'
1
i

'
Hidde gy 2
[amet
i
i

vanemany HULA pu

'
'
'
n
i
'
1
'
L

Fie. 145.—Human Brain. (Median longitudinal vertical section. )
(Mainly after Reichert. )

VA, cerebrum ; Jo, optic thalamus (thalamencephalon), with the middle commis-
sure (Cm); Z, pineal body; 7’, infundibulum; H, pituitary body ; JfH,
corpora bigemina, with the aqueduct of Sylvius (4q), anterior to which is
seen the posterior commissure (Cp); HH, cerebellum ; NH, medulla oblongata,
with the pons Varolii (P); R, spinal cord; B, corpus callosum ; G, fornix,
which extends antero-ventrally to the lamina terminalis (Col), in the upper
part of which is seen the anterior commissure (Ca), and between the latter
and the optic thalami (Zo) the foramen of Monro (FM) ; Th, tela choroidea ;
I, olfactory nerve ; IJ, optic nerve.

Fic. 146.—Coxvo.utions oF THE Human Brain. (After A. Ecker.)

Lf, frontal lobe ; Ly, parietal lobe ; Lo, occipital lobe ; 7’, temporal lobe ; a, b, c,
superior, middle, and inferior frontal gyri; \, 8, anterior and_ posterior
central convolutions, separated from one another by the fissure of Rolando
(2) ; cm, the calloso-marginal sulcus on the dorsal surface ; P, P!, superior and
inferior parietal gyri separated from one another by the interparietal fissure
(1); Po, parietal-occipital fissure ; FS, Sylvian fissure; 1 to 3, superior,
middle, and inferior temporal convolutions ; HH, cerebellum; NH, medulla
oblongata ; 2, spinal cord.

with the roof of the thalamencephalon and contains nervous
substance ; its distal end has the form of a rounded or oval sac,
consisting of compact epithelial tissue and containing concre-
tions. No indication of a parietal organ can be recognised.

PERIPHERAL NERVOUS SYSTEM 1li7

Traces of the saccus vasculosus and lobi inferiores still occur, even in Man,
in connection with the infundibulum.

The mid-brain is of smaller relative size than in other
Vertebrates. A transverse furrow across the solid optic lobes sub-
divides them into an anterior larger and a posterior smaller pair of
lobes (comp. p. 172).

The division of the cerebellum into a median and two lateral
portions, already indicated in Reptiles, but much more plainly
marked in Birds,.is carried to a still further extent in Mammals.
The median portion gives rise to the so-called superior vermis
while the lateral parts form the lateral lobes and floceuld (Figs. 143,
144). The two lateral lobes are connected by a large commissure,
the pons Varolii (Figs. 143-145) : this extends round the medulla
oblongata ventrally, and is more largely developed the higher
we pass in the Mammalian series. Other bands of nerve-fibres
connecting the cerebellum with other parts of the brain are
spoken of as anterior, middle, and posterior peduncles of the
cerebellum.

The brain in Cretaceous Birds (e.y., Hesperornis) and in Tertiary
Mammals (e.g., Dinoceras, Triceratops) was much less highly developed,
and the hemispheres relatively much smaller, than in existing forms.

IJ. PERIPHERAL NERVOUS SYSTEM.

Two principal groups of peripheral nerves may be distinguished,
viz., spinal and cerebral, that is, those which arise from the
spinal cord and brain respectively : by their means a physiological
connection is established between the periphery of the body and
the central nervous system both in centripetal and centrifugal
directions. The spinal nerves retain the more primitive and
simple relations, and all show a similar arrangement along both
dorsal and ventral regions of the spinal cord, so that each segment
of the trunk possesses a dorsal and a ventral pair. The former
consists of sensory, the latter of motor fibres (Fig. 147).

Each dorsal or sensory nerve has a ganglion in connection
with it, while in the ventral nerves a ganglion is wanting, at any
rate in the adult. The ventral nerves arise as direct outgrowths
from the spinal cord, while the dorsal nerves first appear as
outgrowths from their ganglia, coming into connection with the
cord secondarily. The ganglia themselves are developed from a
neural ridge of epiblast cells lying close to the junction of the
medullary cord (p. 149) and outer epiblast. On the distal side
of each ganglion, both nerve-roots almost always become bound
up ina common sheath, though many facts seem to indicate that
in the ancestors of existing Vertebrates the dorsal and ventral

N

178 COMPARATIVE ANATOMY

Fic. 147.—DIAGRAM ILLUSTRATING THE ORIGIN, CoURSE, AND TERMINATION OF
THE Motor AND SENSORY FIBRES OF THE SPINAL NERVES, AS WELL AS THE
RELATIONS OF THE SENSORY COLLATERAL FIBRES TO THE POINTS OF ORIGIN
OF THE VENTRAL Roots. (After M. V. Lenhossék. )

The; spinal cord is shown as if transparent. The fibres of the ventral roots
‘arise from the cells of the motor ventral cornua of the gray matter (a) and
end in fine branches on the striated muscle fibres (c). The spinal ganglion
(d) is shown relatively much larger than in reality, and in it only a single
unipolar nerve-cell is represented: the centripetal fibre of the latter is seen
entering the dorsal root, and at ¢ bifurcates in the spinal cord into ananterior
Vf yand a posterior (gy) branch, each of which ends freely in the gray substance,

rst giving off numerous collateral fibres (2). The centrifugal fibre of the cell
in the spinal ganglion forms a peripheral sensory fibre extending to the skin,
where part of it is shown ending in fine branches in the epidermis (7), another
part forming a coil in connection with a tactile corpuscle (4).

roots remained distinct, as, in fact, is still the case in Amphioxus
and Petromyzon.
The common nerve-trunk formed by the junction of the two

SPINAL NERVES 179

roots divides up again into a dorsal, a ventral, and a visceral
branch. The first of these goes to the muscles and skin of the
back, the second supplies the lateral and ventral portions of the
body-wall, while the intestinal branch comes into connection with
the sympathetic (p. 188).

1. SPINAL NERVES.

As a general rule, each corresponding pair of dorsal and ventral
roots lies in the same transverse plane: an exception to this is
seen, however, in Amphioxus,! Cyclostomes, Elasmobranchs, and
Dipnoans, in which the mesoblastic somites of the right and left
side are arranged alternately, and thus the poimts of exit of the
nerve-roots also alternate right and left, or each ventral pair
alternates with a dorsal pair. In Ganoids also, lateral displace-
ments of the nerve-roots are met with.

In Fishes the greatest variations are seen as regards the mode
of exit of the nerves (which pass through the intercalary pieces
of the vertebral column, through the arches, or between them);
but from the Amphibia onwards the nerves always make their
exit on each side between the arches, through the intervertebral
foramina.

In their primitive undifferentiated condition the spinal nerves
have a strictly metameric arrangement, and are equally developed
in all regions of the body. As already pointed out in the section on
the spinal cord, this condition becomes modified by the development
of the appendages, so that a number of spinal nerves unite together
to form plexuses, which, according to their position, are spoken of
as cervical, brachial, lwmbar, and sucral (Fig. 121). The number
of nerves composing these corresponds to the number of body-
segments taking part in the formation of the appendages, and
their relative size is usually directly proportional to the develop-
ment of the latter.

In contrast to Fishes, the great variation in the plexuses of
which renders it impossible to reduce them to a common plan, we
find from the Amphibia onwards a typical grouping of the branches
of the brachial plexus, from which numerous nerves arise supplying
the shoulder and fore-limb dorsally and ventrally (e.g., thorucic,
subscapular, axillary, radial, musculo-cutancous, and ulner}. The
lwmbo-sacral plezus shows in general, and more particularly in
Mammals, much greater variations than does the brachial plexus.
The nerves arising from it are also arranged in a dorsal and a
ventral series, the larger ones being spoken of as the obturator,

1In Amphioxus both the dorsal and ventral nerves innervate muscles, and
it appears that in many of the Craniata also the dorsal roots are not purely
sensory.
N 2

180 COMPARATIVE ANATOMY

crural, sciatic, and pudendic. The sciatic divides up in the hind-
limb into a ¢ibial and a fibular nerve.?

2. CEREBRAL NERVES.

The following twelve pairs of cerebral nerves can be distin-
guished, and of these the eleventh pair are plainly differentiated
only in the Amniota, and the twelfth are represented by the first.
spinal nerves in certain Fishes and in all Amphibians :—

I. Olfactory.
II. Optie.
III. Oculomotor.
IV. Pathetic or trochlear.
V. Trigeminal.
VI. Abducent.
VII. Facial.
VIII. Auditory.
IX. Glossopharyngeal.
X. Vagus or pneumogastric.
XI. Spinal accessory.
XII. Hypoglossal.

In their mode of early development the cerebral nerves resemble:
the spinal nerves in many respects (p.177), and a gradual tran--
sition between the two groups 1s indicated in the lower Vetebrata.
Certain of them, like the motor spinal nerves, arise as direct
ventral outgrowths from the embryonic brain (III, VI, XII, and.
probably IV). Others, again (V and VII in part, VIII, IX,
and X), arise dorsally, primarily in connection with their indi-.
vidual ganglia and becoming actually connected with the brain:
secondarily : these must therefore, so far as they consist of sensory,.
centripetal elements, be looked upon as homodynamous with the
dorsal roots of the spinal nerves. But it must be borne in mind’
that all these nerves, with the exception of the olfactory, optic,
and auditory, are of a mixed character, containing motor as well
as sensory fibres; and a’ further difference between them and the
dorsal roots of the spinal nerves (comp. note on p. 179) is seen in
the shifting of their origin to the ventral side of the brain during
development.

A study of development shows that portions of the epiblast lying
peripherally to the brain take part in the formation of the ganglia of the
trigeminal, facial, auditory, and vagus nerves, and that each definitive

*In animals in which the extremities have disappeared, all traces of the
corresponding plexuses have also usually vanished: Snakes, however, still retain
remnants of them.

2 The fourth nerve is peculiar in appearing from the dorsal surface of the
brain, but this is probably a secondary condition p. 184).

CEREBRAL NERVES 181

ganglion consists of a primary “‘ spin«l’’ ganglion and of a more peripheral
lateral ganglion in connection with the nerve, from which latter an epi-
branchial ganglion arises from the epiblast dorsally to the region of the gill-
clefts, and takes part in the formation of the terminal branches of the nerve.
The presence of an epibranchial ganglion on the trigeminal may indicate
the former presence of a gill-cleft in this region.

It must be remembered that the head is primitively composed
ofa series of metameres (p. 66), and it is therefore important to
ascertain, as far as is possible in the present state of our knowledge,
to which individual metameres the different cranial nerves belong.
The olfactory and optic nerves present certain peculiarities which
bring them under another category, and they will be treated of
later in connection with the corresponding sensory organs.

The following general summary gives a scheme of the prob-
able primitive relations of the head-segments and cerebral
nerves, founded mainly on the conditions existing in Elasmo-
branch embryos.

TALLE SHOWING THE SEGMENTAL ARRANGEMENT OF THE CEREBRAL NERVES,
WITH THEIR RELATION TO THE METAMERES OF THE HEAD.

=<

fi

Ventral branch. | Dorsal branch.

|
Oculomotor (JJ). Ramus ophthalmicus pro- ,
fundus of the trigeminal ;
(V), together with the ,
ciliary ganglion. i

lst Metamere (superior, in-
ferior, and anterior rec-
tus, and inferior oblique
inuscle).!

2k Metamere (superior | Trochlear (JV). | Trigeminal (with its gang-

oblique).+ | lion, minus the ramus

ophthalmicus _ profun-
dus).

3rd Metamere (posterior Abducent R 1?) aa

rectus). \ | Facial (TTI), and audi-

’ tory (VIIZ), with their

4th Metamere (muscles . Wanting. ganglia.
which are early aborted).

5th Metamere (muscles Wanting. Glossopharyngeal (IX),
which are early aborted). . . with its ganglion.

6th and 7th Metameres (part | Appears to be Vagus (X), with its gang-
of the most anterior | wanting. ha.
region of the large trunk-
muscles). | |

Ventral roots of the Vestigial dorsal roots of
hypoglossal. the hypoglossal (JJ),
usually only present in

| the embryo.

8th and 9th Aletameres (an-
terior part of trunk-
muscles).

Figures 148 and 149 illustrate the distribution of the cerebral
nerves in adult aquatic and terrestrial Vertebrates respectively (comp.

‘It is possible, however, that these eye-muscles belong, not to the somites,
as stated on pp. 133 and 143, but to the visceral muscles.

COMPARATIVE ANATOMY

182

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183

CEREBRAL NERVES

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184 COMPARATIVE ANATOMY

also Fig. 121). The ganglia belonging to the cerebro-spinal system
are shown in both figures, those belonging to the sympathetic in
Fig. 149 only.

Nerves of the Eye-muscles.—The oculomotor (III)
trochlear or pathetic (IV) and abducent (VI) nerves (Figs,
148 and 149) supply the muscles which move the bulb of the eye
as shown in the table on p. 181. The oculomotor arises from
the base of the mid-brain, and comes into secondary connection with
an oculomotor or ciliary ganglion which primarily belongs to the
sympathetic system.

The trochlear nerve, although actually arising in the interior
of the ventral part of the mid-brain, appears externally on the
dorsal side of the anterior margin of the hind-brain (valve of
Vieussens p. 156). Primitively it contains sensory as well as motor
fibres, and these in Fishes and Amphibians supply the connective-
tissue of the eye and the endocranium.

The abducent nerye, which arises far back on the floor of
the medulla oblongata, also probably contains mixed fibres in the
Anamnia. In the Anura it becomes closely connected within the
skull with the Gasserian ganglion of the trigeminal.

Trigeminal Nerve.—This is one of the largest of the cerebral
nerves. It arises from the ventro-lateral region of the anterior
part of the medulla oblongata by a large lateral sensory and a
small ventral motor root, has a large intra- or extra-cranial
Gasserian ganglion at the origin of the former and then, in
Fishes (Fig. 148), divides into two main branches, an ophthalmic
(including a superjictal and a deep or profundus portion), and a max-
allo-mandibular : in most terrestrial forms (Fig. 149) the maxillary
and mandibular nerves arise separately. From the presence of these
three characteristic branches, often known as the first, second, and
third divisions of the trigeminal, its name is derived. It passes
out from the skull sometimes through a single aperture, and some-
times by two or even three distinct ones.

The superficial branch of the first division is usually distinct in
Fishes and Dipnoans and probably also in Urodeles, and passes
dorsally over the eye-ball, the deep branch passing below the supe-
rior and anterior recti and superior oblique muscles. In other
Fishes and in higher forms the two branches appear to be united.
It supplies the integument of the forehead and snout as well as
the eye-ball, eye-lids and conjunctiva, branches apparently going to
the lachrymal glands when present: it is entirely sensory. A con-
oe of the profundus with the ciliary ganglion arises second-
arily.

The second division of the trigeminal, which is also a sensory
nerve and with which a sphenopalatine ganglion derived from the
sympathetic is connected, extends first along the floor of the

CEREBRAL NERVES 185

orbit, supplying the lachrymal and Harderian glands, when present,
as well as the roof of the mouth; it then passes to the upper jaw,
supplying the teeth; and finally, as the infraorbital branch, per-
forates the skull to reach the integument in the region of the
upper jaw, snout, and upper lip.

The third division of the trigeminal is of a mixed nature; it
supplies on the one hand the masticatory muscles and several
muscles on the floor of the mouth, and also gives rise, from
Amphibians onwards, to the great sensory nerve of the tongue
(lingual or gustatory nerve); while another branch, passing
through the inferior dental canal, supplies the teeth of the lower
jaw, and then gives off one or more branches to the integument of
the latter and of the lower lip. Two ganglia, the swbmamillary and
the otic (Fig. 149), derived from the sympathetic, are connected
with its mandibular division (sensory portion).

Facial nerve.—This, which is also a mixed nerve, originally
possesses two distinct ganglia in connection with its sensory and
mixed portion (Fig. 148): these can be recognised up to Urodeles,
but in the course of development one of them gradually comes into
connection with the ganglion of the trigeminal, and in Anura is
indistinguishable from it. The other—known as the geniculate
ganglion—is retained in all Vertebrates, in connection with its
mixed root (Fig. 149).

The facial nerve consists primarily (in aquatic Vertebrates) of
the following inain branches (Fig. 148) :—

I. A system of sensory branches for the supply of the integu-
mentary sense-organs of the head (p. 190),! as follows :—(a) a super-
ficial ophthalmic, running parallel to and usually accompanying the
corresponding branch of the trigeminal; (0) a buccal, which gives
off an otic branch; and (c) an external mandibular (=part of the
hyomandibular, see below).

II. A sensory (a) palatine, anastomosing with the maxillary
branch of the trigeminal, and (0) internal mandibular or chordu
tympant.

III. A main trunk, largely motor (=hyomandibular less the
elements which give rise to the sensory external mandibular),
which passes behind the spiracle, all the other branches passing
in front of it.

In adult terrestrial Vertebrates (Caducibranchiate Urodeles,
Anura, and Amniota) the integumentary sense-organs become re-
duced, and the corresponding branches of the facial nerve undergo
corresponding reduction (Fig. 149); the parts of this nerve which per-
sist are the pharyngeal section (palatine and chorda tympani) and

1 These branches, together with the lateral line branches of the glosso-
pharyngeal and vagus (p. 187) appear to form an independent and distinct
system of lateral line nerves, having a common internal origin in the brain, for the
innervation of the special sensory organs of the integument in Fishes, Dipnoans
and Amphibians. The auditory nerve arises from the same centre.

186 COMPARATIVE ANATOMY

the main trunk (hyomandibular /ess its lateral line elements). The
latter is connected with the glossopharyngeal by the anastomosis
of Jacobson, and is distributed, as its name implies, to the region
of the first and second visceral arches: thus in Fishes it goes
to the parts around the spiracle and to the muscles of the oper-
culum and branchiostegal membrane. A small remnant of this
branch in the higher Vertebrates supplies the stylohyoid muscle and
the posterior belly of the digastric and the stapedius.

In Mammals the facial is mainly a motor nerve. It is chiefly
important in supplying the facial muscles, as well as the platysma
myoldes, which has the closest relation to them (p. 136). The
more highly the facial muscles are differentiated (¢.g. Primates,
especially Homo), the more complicated are the networks formed
by the facial nerve.

Auditory Nerve.—This large nerve arises in close connection
with the facial, and corresponds to a sensory portion of the latter
nerve ; ' it possesses a ganglion (Figs. 148 and 149). Soon after its
origin from the brain it divides into a cochlear and a vestibular
branch. The former passes to the lagena or cochlea, while the
latter supplies the rest of the auditory labyrinth.

Vagus group.—This group includes the glossopharyngeal,
vagus, and spinal accessory, which stand in the closest relation
to one another, and are more nearly comparable to the spinal
nerves than are the cerebral nerves already described. It consists of
both sensory and motor fibres, the former being connected with
ganglia (the jugular and petrosal). The distribution of these
nerves differs from that of the other cerebral nerves in not being
limited to the head.

Thus the vagus supplies not only the pharynx, tongue, and
respiratory organs, but also sends branches to the heart, larynx,
and a considerable portion of the digestive tract, as well as to
integumentary sense-organs of the trunk in Fishes.

The spinal accessory nerve appears for the first time in the
Amniota, and will be dealt with after the vagus and glossopharyn-
geal have been described (p. 187).

The origin of both glossopharyngeal and vagus by numerous
roots in Fishes (Fig. 148) indicates that these nerves correspond to
a number of spinal nerves, and this comparison is further justified
by the fact that they give off branches in the region of the pharynx
and visceral arches, in which a metameric arrangement can be
recognised.

In many Fishes and in Dipnoans two or three nerves make their exit from
the skull ventrally to the root of the vagus (Fig. 148): these ‘‘spino-occipital

1On the supposition that the auditory organ corresponds to a modified
integumentary sense-organ, the auditory nerve would belong to the lateral line
system of nerves (sce note on p. 185).

CEREBRAL NERVES 187

or intracranial spinal nerves, which have been described as ‘ventral roots ”’
of the vagus (see p. 143), have nothing to do with this nerve, and perhaps
correspond to a part of the hypoglossal of higher Vertebrates.

In Fishes and perennibranchiate Amphibians the glosso-
pharyngeal leaves the skull through a special foramen, and not along
with the vagus, a lateral line branch! of which arises separately
from and anteriorly to the rest of nerve, dorsally to the glosso-
pharyngeal and near the origin of the sensory part of the facial
(Fig. 148). This lateral nerve, which may divide into two or even
three branches, extends along the side of the body to the tail,
either directly beneath the skin, or close to the vertebral column
(e.g. Elasmobranchii, Dipnoi), and supplies integumentary sense
organs.

In Protopterus the vagus also gives off superficial branches which extend
along the dorsal, lateral and ventral regions of the body close to the skin.
In certain Teleosts (Anacanthini) dorsal and ventral superficial nerves are
also present, which have sometimes been described as cutaneous branches of
the trigeminal. These require further investigation : they appear to belong
mainly to the facial, and from their origin and distribution correspond pre-
cisely to the ‘‘ ramus dorsalis recurrens”’ of Siluroids. The vagus invariably
takes part in their formation, and sometimes also the glossopharyngeal and
even the first spinal nerves.

In tracing the development of the lateral nerves, the nervous elements
are seen to be so closely united with the thickened epidermis in the region
of the lateral line that it is impossible to say whether the nerve arises in siti
or not; and this is also the case as regards all nerves (VII., [X., X.) supply-
ing integumentary sense organs in the Anamnia.

In branchiate Vertebrates, the glossopharyngeal gives off a
pharyngeal branch and forks over the first branchial cleft, while the
vagus gives rise to branchial branches which are similarly related to
the following clefts (Fig. 148): these branchial nerves suppiy the
muscles and mucous membrane of the branchial apparatus. In
Chimera each of the three branchial nerves arises independently
from the brain. It will be remembered that the facial nerve has
similar relations to the spiracuiar cleft (p. 185). Both glossopharyn-
geal and vagus contain mixed fibres, and become connected in various
ways with the trigeminal and facial. In correspondence with the
reduction of the gills in higher forms, the branchial branches of the
vagus can no longer be recognised, and the glossopharyngeal passes
into the tongue as the nerve of taste, giving off also a pharyngeal
branch (Fig. 149). This condition is first indicated in Dipnoi and
Amphibia.

The spinal accessory nerve first appears distinctly in Reptiles.
It arises some distance back along the cervical portion of the
spinal cord, in the region from which the fourth to fifth cervical
nerves come off; from this point it passes forwards as a collector,
taking up fibres from the cervical nerves as it goes. It extends
along the side of the medulla oblongata into the cranial cavity, and

1 The glossopharyngeal also possesses a lateral line branch in many Fishes.

188 COMPARATIVE ANATOMY

leaves the skull through the same foramen as the vagus, to which
it gives off motor elements. It supplies certain of the muscles
related to the pectoral arch, e.g. the sternocleidomastoid and the
trapezius.

Hypoglossal.—The hypoglossal corresponds to one or several
of the anterior spinal nerves, and its transformation into a cerebral
nerve can be traced in passing through the Vertebrate series.
In some Fishes and all Amphibia it does not pass through the
cranial wall and isa true spinal nerve ; and in most Fishes and in the
Dipnoi, its inclusion within the skull can be seen to be due to a
gradual assimilation of the anterior part of the vertebral column with
the skull (comp. p. 45). Inaddition to its numerous ventral-roots
one or more dorsal, ganglionated roots have been observed in the
embryos of various Vertebrates (Figs. 148 and 149). Two dorsal
roots, each with a ganglion, persist in Protopterus, and the same is
apparently true as regards Polypterus and certain Elasmobranchs:
even amongst Mammals, these roots can exceptionally be recog-
nised subsequently to the embryonic period

In Fishes (Fig. 148) the hypoglossal, like the next following
spinal nerves, sends branches to the muscles of the body, the:
floor of the mouth, and skin of the back, as well as being connected
with the brachial plexus. In higher Vertebrates (Fig. 149) it
supplies the intrinsic and extrinsic muscles of the tongue.
These lingual branches are most marked in Mammals, in which
the tongue reaches its highest development. Elements of the
cervical spinal nerves also run along with the hypoglossal, and
give rise to the so-called ramus descendens with which further
cervical nerves are associated; and from the “ansa hypoglossi”
thus formed, branches pass to the sterno-hyoid, sternothyroid,
omohyoid, and thyrohyoid muscles.

Sympathetic.

The sympathetic system arises in close connection with the
spinal system, with which it remains throughout life in close
connection by means of rami communicantes. It is distributed
mainly to the intestinal tract (in the widest sensc), the vascular
system, and the glandular organs of the body. The sympathetic
ganglia, like those of the spinal nerves, show originally a segmental
arrangement. They usually become united together later by
longitudinal commissures and thus give rise to a chain-like
paired sympathetic cord lying on either side of the vertebral
column, From its ganglia nerves pass off to the above-mentioned

1 The dorsal root of the first spinal nerve may he reduced or wanting in

Mammals —even in Man, so that here the modification of the primary
character of the nerves is not limited to those within the skull.

SENSORY ORGANS 189

systems of organs, forming numerous plexuses. Peripheral ganglia
are also present in the viscera.

The sympathetic extends not only along the vertebral column,
but passes anteriorly into the skull, where it comes into relations
with a series of the cerebral nerves (comp. pp. 184, 185 and Fig.
149) similar to those which it forms further back with the spinal
nerves.

The original segmental character frequently disappears later on
and this is especially the case in those regions where marked
modifications of the earlier metameric arrangement of the body
have taken place—viz., in the neck and certain regions of the
trunk, especially towards the tail: thus there are never more than
three cervical ganglia in Mammals.

A sympathetic is not known to exist in Amphioxus, and in
Petromyzon it appears to be rudimentary. In Fishes proper, it is
more highly differentiated, especially in the head region, while in
Dipnoans it has not been observed. In Amphibians the
sympathetic is well developed, especially in the higher forms
(Fig. 121). In the Myctodera it extends anteriorly to the vagus
ganglion and posteriorly through the trunk and hemal canal
almost to the apex of the tail, as is the case also in Teleostei.

In the Sauropsida the cervical portion of the sympathetic is
usually double, one part running within the vertebrarterial canal
alongside the vertebral artery. In all other Vertebrates the whole
cord lies along the ventral and lateral region of the vertebral
column : it is generally situated close to the latter, and overlies
the vertebral ends of the ribs.

III. SENSORY ORGANS.

The specific elements of the sensory organs originate, like the
nervous system in general, from the epiblast ; the peripheral ter-
minations of the sensory nerves are thus always to be found in
relation with cells of ectodermic origin, which become secondarily
connected by means of nerve-fibres with the central nervous
system. ae es

The sensory apparatus was primarily situated on a level with
the epidermis and served to receive sensory impressions of but
slightly specialised kinds ; but in the course of phylogeny parts of it
passed inwards beneath the epidermis, and certain of these became
differentiated into organs of a higher physiological order, viz.,
those connected with smell, sight, hearing, and taste. These are
situated in the head, and except the last mentioned, become
enclosed in definite sense-capsules (p. 68); they must be dis-
tinguished from the simpler tuteguimentary sense-organs, which are
concerned with the senses of touch, temperature, &e.

In many, and more especially in the higher sensory organs,

190 COMPARATIVE ANATOMY

supporting or isolating cells can be recognised in addition to the
sensory cells proper ; both kinds, however, being ectodermic. The
mesoderm may also take part in the formation of the sensory
organs, giving rise to protective coverings and canals as well as to
contractile and nutritive elements (muscles, blood- and lymph-
channels).

In the sensory organs of the integument of Fishes as weil as in
all the higher sensory organs the medium surrounding the end-organ
is always moist. In both cases, we meet with rod-, club-, or peur-
shaped sensory cells, but in the former the nerves coming from them
do not pass through nerve-cells, as they do in the organs of
higher sense. This indicates a lower stage of development, there
being no differentiation into sensory cell and nerve cell.

In those animals which in the course of development give up an
aquatic life and come on Jand (Amphibia) the external layers of the
epidermis dry up, and the integumentary sense-organs pass further
inwards from the surface, undergoing at the same time changes of
form. Thus from Reptiles onwards the rod-shaped end-cell no
longer occurs, and two kinds of nerve-endings are seen in the skin
—terminal cells, and fine intercellular nerve-networks known as
free nerve-cndings.

SENSE-ORGANS OF THE INTEGUMENT.
a. Nerve-eminences.

In Aimphioxus certain rod-shaped or pear-shaped cells can
be recognised in the epidermis, especially in the anterior part
of the animal ; each of these is provided distally with a hair-like
process and proximally is in contact with a nerve. The cells
are distributed irregularly, but in the neighbourhood of the mouth
and cirri they tend to form groups.

It is doubtful whether these structures in Amphioxus are
directly comparable to the integumentary sense-organs of Fishes
and Amphibians, but it is important to note that each of the latter
always arises in the first instance from a single cell which forms a
group by division. These organs always consist of central cells,
arranged in the form of a rounded and depressed pyramid, and
of a peripheral mass grouped around the former like a mantle.
The central cells are surrounded by a network of nerve-fibres ;
each of them bears at its free end a stiff cuticular hair, and they
are to be Jooked upon as the sensory cells proper. The others
function only as a supporting and slime-secreting mass (Figs 150
and 151).

In Dipnoi, aquatic Amphibia and all amphibian larve these
organs retain throughout life their peripheral free position, on

SENSE-ORGANS OF THE INTEGUMENT 191

a level with the epidermis,’ but in Fishes they may in post-em-
bryonic time become enclosed in depressions or complete canals,”
which are formed either by the epider-
mis only, or, as is more usually the case,
by the scales and bones of the head, and
which open externally. The organs are
thus protected.

These sensory organs are situated
characteristically along certain tracts,
the position of which is very constant:
in the head, supra-orbital, infra-orbital,
and hyomandbular tracts can be recog-
nised, and a lateral line (or several— “qon 6 a FREELY Pro.
Proteus and all Amphibian larvae) ex- — sucrine SeamENtaL SENSE-
tends along the sides of the body to the = OR@As.
caudal fin (Figs. 152 and 153). They The cuticular tube and the
are thus often spoken of as segmental vl ge epidermic cells

represented, CZ,
sensory organs or organs of the lateral central (sensory) cells; IZ,
line® The portions lying in the region —_—_1£2’, peripheral cells.
of the head are innervated by the lateral
line branches of the facial, glossopharyngeal, and vagus (see note
on p. 185).

Freely projecting nerve-eminences are not present in Rays and
Ganoids, and are only of minor importance in Sharks. In all
these Fishes the integumentary sense-organs are more or less deeply
situated, being enclosed in complete or incomplete canals arising
as proliferations of the epidermis extending into the dermis, and
becoming greatly branched.

The so-called Savi’s vesicles of Torpedo, the “nerve sacs” of
Ganoids, and the «mpullw of Elasmobranchs, correspond to modified
nerve-eminences. They are all limited in their distribution to the
head and anterior portion of the trunk, being most numerous on the
snout:.they arise from thickenings of the epidermis which later
become invaginated and in which a sensory epithelium is differ-
entiated. In Ganoids these organs retain a simple sac-like form,
and in Torpedo they become completely separated off from the
epidermis, while in other Elasmobranchs they are tubular, each
tube giving rise to one or more swellings or ampullz, separated

Fic. 150.—TRansverse SEc-

1 At the time when an Amphibian undergoes metamorphosis and gives up its
aquatic habits, these sensory organs sink downwards into the deeper layer of the
skin, and, as the epidermis grows together over them, they become shut off from
the exterior and reduced, and may finally disappear. (Anura and certain Caduci-
branchiata.) In other Urodeles they may, in some cases, he retained throughout
life, and are said to come to the surface when the animal returns to tne water
during the breeding season; but, more usually, new organs then become
developed.

2 This is also the case on the head in Dipnoans.

3 In the Dipnoi they are not limited to the lateral line, and in Marsipobranchii
they have no regular arrangement and are not numerous, although a lateral
branch of the vagus is present.

192 COMPARATIVE ANATOMY

Fic. 151.—Nerve ELevation oF a URopELE. (Semidiagrammatic.)

a, w, cells of the epidermis, through which the neuro-epithelium, b, 6, can be
seen ; ¢, the terminal hairs of the latter (the peripheral cells are not repre-
sented) ; R, hyaline tube, formed as a secretion ; NV, the nerve-fibres passing
to and surrounding the sensory cells.

Fic. 152.—Srexsory CANALS or Chimera monstrosa. (After F. J. Cole.) The
innervation is indicated by the different kinds of shading.

(1.) Supra-orbital canal (innervated by superficial ophthalmic of facial—cross-
hatched—the black segment is the portion innervated by the, profundus) =
cranial (C) + rostral (#) + sub-rostral (SR).

(2.) Infra-orbital canal (buccal + otic of facial—dotted) = orbital (Or) + sub-
orbital (SO) + portion of angular (A) + nasal (..)

(3.) Hyomandibular or operculo-mandibular canal (external mandibular of facial
—black)= remainder of angular (A) + oral (O) + jugular (J.)

(4.) Lateral canal (lateral line branch of vagus—-oblique shading) = lateral (Z) +
occipital (Oc) + aural (Aw) + post-aural (PAu.)

_SENSE-ORGANS OF THE INTEGUMENT 193

off from the rest of the tube by radial folds of connective tissue,
and containing the nerve- endings. The tubes are filled with a
gelatinous aiostanie:

The function of the nerve eminences is doubtful, but it appears
that they are concerned with the perception of mechanical stimuli

Fie. 1 153. Sipps oF THE LATERAL SENSE-ORGANS IN A SALAMANDER
Larva.

from the surrounding water, and thus are important as regards the
appreciation of the direction of these stimuli,

The horny wart-like structures arising periodically during the breeding
season in Cyprinoids and known as ‘‘ pearl organs,” are due to a modification
of the reduced nerve-eminences. Similar structures oceur in Anura.

b. End-buds,

The nerve eminences pass through a stage in development in
which they clearly resemble end-buds, and the latter may be
looked upon as the phyletically older organs, which do not become
so highly differentiated as the former. No sharp line of demarca-
tion can, however, be drawn between the two, as all kinds of inter-
mediate forms are met with: they are here described separately
merely for the sake of clearness.

In contrast to the nerve-eminences, which tend to sink below
the surface, the end-buds usually form a dome-like elevation pro-
jecting above the general level of the epidermis. A central
sensory epithelium, provided with sensory hairs, and peripheral
supporting cells can be recognised, but the former are as long as
the latter.

In Lampreys and most Elasmobranchs they remain at a primi-
tive stage of development, but become of great importance in
Ganoids and Teleosts, in which they are scattered irregularly over
the whole body and are particularly numerous in the fins, lip-
folds, barbules, and mouth. From the Dipnoi onwards they become
limited to the oral and nasal cavities. In Dipnoi and Amphibia
they occur on the papilla of the oral and pharyngeal mucous
membrane and tongue. In Reptiles their distribution is somewhat
more limited, and this is still further the case in Mammals, in
which, however, they are still found on the soft palate, on the walls
of the pharynx, and even extend into the larynx; but here they
are most numerous on the tongue, where they occur, situated more
deeply, on the circumvallate and fungiform papille as well as on
the papilla foliata, and function as organs of taste.

0

194 COMPARATIVE ANATOMY

Fic. 1544.—A TactiLe
SpoT FROM THE SKIN
oF THE FrRoa. Semi-
diagrammatic. | (Modi-
fied from Merkel. )

N, nerve, which loses its
medullary sheath at N? ;
a, @, neuro-epithelium ;
b, epidermis.

Fie. 1548.—-DermMaL PAPILLA
FROM THE HtMan FINGER
ENCLOSING A TACTILE CorR-
puscLr. (After Lawdowski.)

u, fibrous and cellular invest-
ment; 6, tactile corpuscle,
with its cells; 7, nerve-fibre ;
n’, the further course of the
nerve-fibre, showing its
curves and bends ; 2”, termi-
nal twigs of the nerve-fibres
with club-shaped endings.

Fie. 154c.—A Tacrite Corpuscie (END-Butp)
FROM THE MARGIN OF THE CONJUNCTIVA oF
Man. (After Dogiel.)

x, medullated nerve fibre, the axis-fibre of
which passes into a closely coiled terminal
skein; 5, nucleated fibrous investment.

Fig. 154D.—TRANSVERSE SECTION
THROUGH A TACTILE CoRPUSCLE
FROM THE Brak OF A Dvck.
(After Carriére. )

n, nerve, entering the capsule A,
its sheath (8) becoming con-
tinuous with the latter. The
nerve passes between the two
covering-cells, DZ, DZ, widen-
ing out to form a tactile plate
at ni.

CLUB-SSHAPED CORPUSCLES 195

ce. Tactile-cells and corpuscles,
(Terminal ganglion cells.)

In these structures there is no longer any direct connection
with the surface of the epidermis, and supporting cells are want-
ing.
“ Tactile spots,” consisting of groups of touch cells, are met with
for the first time in tailless Amphibians, in which they are situated
mainly on small elevations, and are distributed over the skin of the
whole body (Fig. 1544). In Reptiles they are found chiefly in
the region of the head, on the lips and sides of the face, and on
the snout, but in some cases (as in Blindworms and Geckos), they
extend over the whole body close to the scales. In Snakes and
Birds the tactile cells are confined to the mouth-cavity (tongue)
and to the beak (cere), and lie much more closely together, forming
definite masses, or tactile corpuscles (Fig. 154D), Each of these is
surrounded by a nucleated connective-tissue investment, from which
septa extend into the interior, partially separating the individual
tactile cells from one another. In Mammals the tactile cells are
either isolated—as, for instance, on the hairless portions of the body,
or they give rise to oval corpuscles, each consisting of a many-
layered and nucleated investment, into which a nerve passes, be-
comes twisted up, and comes into relation with one or more ter-
minal cells (Fig. 154 B,c). These are most numerous and highly
developed on the volar and plantar surfaces of the hand and foot
respectively, and on the conjunctiva and snout.

d. Club-shaped corpuscles.
(Pacinian corpuscles.)

From the Reptilia (Lizards, Snakes) onwards, club-shaped
corpuscles are present in addition to the above-described tactile-
organs. In these Reptiles they occur chiefly in the region of the
lips and teeth ; they have an elongated, oval form, and their structure
is simple.

In the interior of each corpuscle is seen the continuation of
the axis-fibre of the nerve which becomes swollen distally, and
externally to this is a double column of cells which enclose the
club-shaped axis (Fig. 155). It is probable that a fine branch
is given off from the axis-fibre to each cell. The column of cells
is enclosed externally by an investment consisting of numerous
nucleated lamella in which longitudinal and circular layers can
be distinguished.

Organs of this kind are universally present, deeply situated,

0 2

196 COMPARATIVE ANATOMY

in the skin of Birds and Mammals, and in the former they are
particularly abundant on the beak and at the bases of the con-
tour-feathers of the wings and tail,
and are also found on the tongue.
They occur, moreover, in various
other regions, both in Birds and
Mammals (e.g. the various organs
of the abdominal cavity, the con-
junctiva, the fasciz, tendons, liga-
ments, vas deferens, periosteum, peri-
cardium, pleura, corpus cavernosum
and spongiosum, the wing-membrane
of Bats, &.).

The tactile cells and tactile and
club-shaped corpuscles are all con-
cerned with the sense of touch. It
is impossible to say definitely what
nerve-endings have to do with the
perception of temperature ; it is not

improbable that the touch cells, as

Fic. 155.—A Paciyzan Cor- well as the nerve-fibres often pro-
PUSCLE. vided with varicose swellings which

A, axis fibre; A}, tuftedorknob- end freely in the epidermis, are con-
like end of the same; NS,nuc- cerned in this process. Such /ree
See Pou Beer nerve-endings occur in the skin of
tudinal series oflamelle, 2;Q, all Vertebrates, and consist of an
internal, circular layer of the intercellular network, no direct con-
external part of the club ; JK; — nection between nerve and epithelial

internal part of the club formed :
of the cell-pillars. cell having been observed.

OLFACTORY ORGAN,

The olfactory lobe as already mentioned (p. 153) represents a pro-
longation of the secondary fore-brain, the ventricle of which is tem-
porarily or permanently continued intoit. In some cases it becomes
differentiated into olfactory bulb, tract, and tubercle (pp. 159-175).

The olfactory nerves proper are connected with the bulb, and are
usually arranged in a single bundle on either side, with more or less
distinct indications of a subdivision into two bundles: they ap-
parently arise in continuity with the epithelium of the nasal
involution (comp. pp. 177, 187) and then grow centripetally,
uniting with the olfactory lobe or bulb secondarily.

In all Mammals but Ornithorbynchus, as well as in Menopoma,
Apteryx, and the extinct Dinornis, the olfactory nerves pass into
this nasal cavity separately, through a cribriform plate of the
ethmoid (p. 99).

OLFACTORY ORGAN 197

The primary origin of the olfactory organs is by no means understood :
possibly it may have arisen by a modification of primitive integumentary
sense-organs. It is doubtful whether the organ can be said to have a true
olfactory function in Fishes and perennibranchiate Amphibians.

In its simplest form, the olfactory organ consists of a ventral,
paired, pit-like depression of the integument of the snout opening
on to the surface by an external nostril. Itis lined by an epithelium
which is connected with the brain by the olfactory nerves. The
olfactory mucous membrane contains sensory cells, or olfactory cells
proper—usually provided with sensory
hairs, separated by isolating or supporting
cells, both kinds having a smilar origin
(Fig. 156).

These olfactory cells are said to constitute the
only true newro-epithelinm in Vertebrates, as the
nerve arises in connection with the cell itself,
with which it remains continuous, as in many
Invertebrates (primary sensory cell, Retzius). The
cell is therefore not merely surrounded by a
nerve-network as in other secondary nerve-cells,
and the olfactory organ thus probably represents
a very ancient structure phylogenetically. It is
possible, however, that the central cells of the in-
tegumentary sense-organs of Anamnia (e.g. end-
buds) may be directly continuous with their
nerves, although surrounded by a nerve-network.

From the Amphibia onwards glandular 5 56 — Berrupnium
elements are present, the secretion of which Aik GEES MOLRICTORS
serves to keep the nasal cavity moist. Mucovs Mrmsraye.

The olfactory organs of all the true A, of Pacromyaon plan

: mee : é eri; B, of Salamandra
Fishes exhibit the above-described simple tia,
sac-like form, but from the Dipnoi onwards :
th t aati ith th it R, olfactory cells; 2,
they come to communicate W1 ie CaN LLY: interstitial epithelial
of the mouth as well as with the exterior. cells.
In consequence of this, anterior or external, ;
and posterior or internal nostrils (choane) can be distinguished,
and as a free passage is thus formed through which air can pass,
the olfactory organ takes on an important relation to the respira-
tory apparatus.

In Amphioxus, the ciliated pit situated above the anterior end of the
central nervous system probably represents an unpaired olfactory organ.
Traces of a structure possibly homologous with this are said to occur in the
embryos of the Lamprey and Sturgeon.

Cyclostomes.—In these forms (Fig. 54) the olfactory organ
consists of a sac, containing numerous radial folds of the mucous
membrane, and wnpaired externally. It lies close in front of the
cranial cavity, and opens on the dorsal surface of the anterior
part of the head by a longer or shorter chimney-like tube. In

198 COMPARATIVE ANATOMY

Myxine this tube is long, and is supported by rings of cartilage. In
the larval lamprey the organ is at first ventral and unpaired (Fig,
125), but subsequently becomes sunk in a common pit with the
pituitary invagination and takes on a dorsal position ; it is almost
completely divided into two lateral halves internally by the torma-
tion of a fold of the mucous membrane. The pituitary sac thus
extends backwards from the ventral side of the organ above the
mucous membrane of the mouth: in Petromyzon it ends blindly,
but in Myxine it opens into the oral cavity, perforating the skull
floor from above instead.of from below as in other Vertebrates,

Fishes.—The position of the olfactory organ in Elasmobranchs
(Fig. 157, A) differs from that seen in Cyclostomes in lying on the

i
iy Pa %

Fic. 157.—A, Ventrat View or tun Hnap or a Doarisu (Seylliiom cranicula).
iY, external nostril ; 1/, mouth; SO, integumentary sense-organs.

B, LATERAL View oF THE Heap or a Pike (soa lucius). a and b, the anterior
and posterior openings of the external nostrils; +, fold of skin separating «
and b; Ag, eye.

under instead of the upper surface of the snout, and thus retains
the more primitive position. From these Fishes onwards the
organ is always paired, each sac being more or less completely
enclosed by a cartilaginous or bony investment forming an outwork
of the skull.

From the Ganoids onwards it always has a similar position with
regard to the skull, being situated between the eye and the end of -
the snout, either laterally or more or less dorsally: originally,
however, it is ventral. In the course of development each external
nostril of Ganoids and Teleosts becomes completely divided into

OLFACTORY ORGAN 199

two portions, an anterior and a posterior (Figs. 157, B, and 158), by
a fold of skin. The nostvil often lies at the summit of a longer or
shorter tube, lined with ciliated cells, and the distance between
the anterior and the posterior aperture varies greatly, according to
the width of the fold of skin which separates them.

The mucous membrane of the nasal organ of Fishes is always
raised up into a more or less complicated system of folds, which
may have a transverse, radial, rosette-like, or longitudinal arrange-

Fie. 158.—LaAteraAL View oF THE HEAD oF JMurwne helena.

VR and HR, anterior and posterior tubes of the external nostrils; 4, eye:
HSO, integumentary sense-organs.

ment, and which are supplied by the branches of the olfactory
nerve.

The olfactory organ of Polypterus is more highly developed and compli-
cated than that of any other Fish. In certain representatives of the Plecto-
gnathi and Gymnodontes amongst the Teleostei, on the other hand, the organ
shows various stages of degeneration.

Dipnoi.—A nasal skeleton well differentiated from the skull
proper is met with for the first time in Dipnoans. In Protopterus
it consists of a cartilaginous trellis-work enclosing each olfactory
sac and united with its fellow in the median line by a solid septum :
the floor is formed mainly by the pterygopalatine and by con-
nective tissue. The mucous membrane is raised into numerous
transverse folds connected with a longitudinal fold, and the olfac-
tory organ in general most nearly resembles that of Elasmobranchs,

200 COMPARATIVE ANATOMY

except that, as already mentioned, postertor (internal) as well as
anterior (external) nostrils are present. The latter open beneath
the upper lip, and so cannot be seen when the mouth is closed;
the former open into the oral cavity rather further back.

The peculiar position of the anterior nares has a physiological significance,
at any rate in Protopterus, in connection with its habits (see p. 17) ; during
its summer sleep the animal breathes through a tube, passing between the
lips, formed from the capsule or cocoon which encloses it. The necessary
moisture for the olfactory mucous membrane during this time is provided
by the numerous goblet cells which line the walls of both nostrils.

Amphibia.—The olfactory organ of the Perennibranchiata re-
sembles in many respects that of the Dipnoi: it is always enclosed
within a complete or perforated
cartilaginous capsule situated
laterally to the snout close be-
neath the skin, and is not pro-
tected by the bones of the skull
(Fig. 159). Its floor is largely
fibrous, and the mucous mem-
brane is raised into radial folds
like those of Cyclostomes and
Polypterus. In all the other
Ampbibia it becomes included
within the cranial skeleton, and
lies directly in the longitudinal
axis of the skull in front of the
cranial cavity.

The structure of the olfac-
tory organ now becomes modified
in correspondence withthe change

Fic. ORGAN OF

(From the

159. -OLFACTORY
Necturus maculatus,
dorsal side. )

WV, olfactory sac; O/, olfactory nerve ;

Pm, premaxilla; JF, frontal; P,
process of the parietal ; PP, palato-
pterygoid ; A/’, antorbital process.

in the mode of respiration; the
nasal chamber becomes difler-
entiated into an olfactory and a

respiratory portion, and an ex-
tension of the olfactory surface takes place by the formation.
of one or more prominences on the floor and_ side-walls of
the nasal cavity. These prominences, which may be compared
to the turbinals of higher forms, are present in certain Mycto-
dera (Fig. 160), and attain a very considerable development in
Anura and Gymnophiona, especially in the latter, in which the
nasal chamber is converted into a complicated system of spaces
and cavities. A sain chamber and a more laterally situated
accessory cavity can in all cases be distinguished, even in the
Derotremata and Myctodera; the accessory cavity lies in the
maxillary bone (Fig. 160 and 165 A—E).

In certain Gymnophiona the accessory chamber becomes entirely shut off
from the main cavity and receives a special branch of the olfactory nerve,.
so that in these cases two separate nasal cavities can be distinguished.

OLFACTORY ORGAN 201

Glands, situated under the olfactory mucous membrane, are now
also met with; these are either diffused, or united to form definite
masses. They ejther open directly into the nasal cavity, their
secretion serving for the necessary moistening of the mucous mem-
brane (effected in Fishes by the external medium), or they pour
their secretion into the pharynx or posterior nostrils. The latter
always lie tolerably far forwards on the palate, and are for the most
part enclosed by the vomer, as well as the palatine.

Finally, the naso-lachrymal duct must be mentioned : it passes
out from the anterior angle of the orbit, through the lateral wall

Vop

Fic. 160.—TRANSVERSE SECTION THROUGH THE OLFACTORY CAVITIES OF
Plethedon glutinosus (Myctodera).

8, 8, olfactory mucous membrane ; .V, main nasal cavity; A, maxillary cavity ;
C, cartilaginous, and S', fibrous portion of the turbinal, which causes the
olfactory epithelium (Z) to project far into the nasal cavity; ID, inter-
maxillary gland, shut off from the cavity of the mouth by the oral mucous
membrane (8); /, frontal; Pf, prefrontal; 17, maxilla; Vop, vomero-
palatine; Sp, nasal septum.

of the nose, and opens into the nasal cavity on the side of the
upper jaw. It conducts the lachrymal secretion from the conjunc-
tival sac of the eye into the nasal cavity, and arises in all Verte-
brates, from the Myctodera onwards, as an epithelial cord which is
separated off from the epidermis, and, growing down into the
dermis, becomes hollow secondarily.

Reptilia.—Owing to the growth of the brain and facial region
and to the formation of a secondary palate (p. 92), the olfactory
organs, from Reptiles onwards, gradually come to be situated more
ventrally, beneath the cranium.

The Lacertilia, Ophidia, and many Chelonia possess the sim-
plest olfactory organs amongst Reptiles. The nasal cavity of
Lizards is divided into two portions, a smaller outer (anterior), and
a larger inner (posterior)—or olfactory chamber proper. The latter
only is provided with sensory cells, the former being lined by
ordinary stratified epithelium continuous with the epidermis and
containing no glands. A large turbinal, slightly rolled on itself,
arises from the outer wall of the inner nasal chamber, and extends
far into its lumen; this is also well developed in Ophidia, in
which a distinct outer nasal chamber is wanting; it may be
derived from that of the Amphibia.

202 COMPARATIVE ANATOMY

A large gland which. opens at the boundary between the inner
and outer nasal cavities lies within the turbinal. Below the latter
is the aperture of the lachrymal duct: this duct in some Reptiles
opens on the roof of the pharynx (Ascalabota), and in others into
the internal nostrils (Ophidia).

The structure of the nose in Chelonians is very complicated and varied.
In marine Chelonians it is divided into two passages, one above the other,
and connected by means of a perforation of the
septum. The comparative paucity of glands in
the olfactory organ of Lizards and Snakes forms
a marked contrast to the condition seen in
Chelonians, the nasal organ of which is charac-
terised by a great abundance of them.

The extension downwards and back-
Ch wards of the olfactory organ 1s most marked
ie, A eee ene 2 Semoace, correspondence with the
Ouracrory Orcax or a growth forwards of the facial region and
Lizarv. (Longitudinal the formation of the palate ; its posterior
penineal erections part thus comes to lie below the brain
AN, IN, outer and inner and base of theskull. Hach nasal chamber
nasal chambers; +, tube- jg divided posteriorly into two superim-
like connection between ar 1 f which
them; Ch, internal nos- Posed cavities, the upper of which repre-
trils; P, papilla of Jacob- sents the proper olfactory chamber, and is
son’s organ; Ca, aperture ined by sensory epithelium, while the
of communication of the lower i 4 eomaatneh a
latter with the mouth; lower functions as a respiratory portion
MS, oral mucous mem- only. Certain accessory air-chambers are
rang. connected with 'the nasal cavity. <A large
gland is present between the olfactory
chamber and its investing bones, and opens into the nasal cavity.
As in other Reptiles, there is only a single true turbinal, but ex-
ternally to it lies a second prominence, which may be spoken of as
a pscudo-turbinal.

Ca ms

Birds.—In all Birds, as in Lizards, there is an outer chamber,
lined by stratified epithelium, and a proper olfactory chamber,
situated above the former. Birds also possess only a single true
turbinal—if by this term is understood a free independent projection
into the nasal cavity supported by skeletal parts. Two other pro-
minences (pseudo-turbinals) are, however, present ; one of which lies,
like the true turbinal, in the proper olfactory chamber, while the
other, like the pseudo-turbinal of the Crocodile, is situated in the
outer portion: these are simply incurved portions of the whole
nasal wall (Fig. 162).

The form of the true turbinal, which is usually supported by
cartilage—more rarely by bone, varies greatly. It is either repre-
sented by a moderate-sized prominence, or else it becomes more
or less rolled on itself. The lachrymal duct opens below and an-

OLFACTORY ORGAN

203

teriorly to it. This turbinal is comparable to that of Urodeles and

Reptiles.

The so-called external nasal gland of Birds is situated on the
frontal or nasal bones, along the upper margin of the orbit. It

is supplied by the first and second branches
of the trigeminal, and corresponds to the
lateral nasal gland of Lizards.

Mammals.—Corresponding to the much
more marked development of the facial por-
tion of the skull, the uasal cavity of Mammals
is proportionately much larger than in the
forms yet described, and consequently there
is much more room for the extension of the
turbinals: these give rise to a spongy laby-
rinth, the cell-like compartments of which
are lined by mucous membrane ; and thus
variously shaped projections, supported partly
by cartilage and partly by bone, are seen ex-
tending into the nasal cavity (Fig. 163, a—c).

The normal number of these true olfactory
ridges or scrolls varies considerably.1 They
may be arranged in one row (Ornithorhyn-
chus, Cetacea, Pinnipedia, Primates), or in

Fic. 162,—TRANSVERSE
SECTION THROUGH THE
Ricut Nasau Caviry
OF A SHRIKE (Lantus
minor. )

OM, AMA, — superior
(pseudo) and middle
(true) turbinal; a,
upper, and 6, lower
nasal passage; LR,
air-chamber, which
extends into a hollow
of the superior tur-

several rows (other Mammals),in which latter ‘inal.

case the olfactory lobes are largely developed.

According to the degree of development of the olfactory appa-
ratus, taking specially into account its cerebral portion (olfactory
lobes), we may distinguish between Mammals which are macros-
matic (the majority of the mammalian orders), microsmatic (Seals,
Whalebone Whales, Monkeys, Man), und anosmatic (most Toothed
Whales).

The above-mentioned olfactory scrolls belong to the true olfac-
tory region, and are generally described as “ ethmoid turbinals,”
as in all but the first of the series their skeletal supports usually
become united with the ethmoid bone, the first coming into rela-
tion with the nasal, and being therefore usually spoken of as the
“nasal turbinal.” It must, however, be borne in mind that these
do not correspond to the turbinals of lower Vertebrates. The latter
are represented by the so-called “ maxillary turbinal,” situated in
the anterior (luwer) portion of each nasal chamber, which com-
municates with the pharynx by the internal nostrils, its skeletal
portion becoming united with the maxillary bone (Fig. 163, c).
This maxillary turbinal no longer possesses an olfactory epithelium

1 In most of the Mammalian orders, five olfactory scrolls are typically present. ;
in Echidna there are six or more; in Ungulates there may he as many as
eight ; amongst Edentates, Orycteropus possesses eleven; while in adult

Primates there are only from one to three, a greater number being present in the
embryo (Fig. 163).

204 COMPARATIVE ANATOMY

after the embryonic period,’ and has plainly undergone a change of
function in connection with the perception of the warmth and

Fie. 163, a.—LATERAL VIEW OF THE
Nasau CHAMBER oF A Human Em-

BRYO.

I, I, II, the three olfactory ridges; +,
supernumerary ridge which occurs in
the embryo; x, tip of the nose; pi,
hard palate; «vr, base of skull; os,

Eustachian aperture.

nasal apparatus, but may
lose their primary func-
tion, often persisting merely
as air-sinuses.

The nasal glands may
be divided into two sets,
—numerous small, diffuse
Bowman's glands, and a
large gland of Stenson.
The latter appears early in
the embryo, and often be-
comes greatly reduced later
on in development ; it is
situated in the lateral or
basal walls of the nasal
cavity, and may extend
into the maxillary sinus
when the latter is well
developed.

The appearance of an
eaternal nose is very charac-
teristic of the olfactory or-
gan of Mammals: this must
be regarded as a derivative
of the outer chamber of the
nose of Reptiles and Birds.

moisture of the inspired air.
When well developed, 1t forms
a single or double coil, and
may even be more or less
branched (Fig. 164). Branches
of the trigeminal extend over
it, and supply its mucous mem-
brane. An olfactory and a
respiratory region can there-
fore also be distinguished in the
nasal chamber of Mammals.
The nasal chamber usually
communicates with neighbour-
ing cavities, such as the maxil-
lary, frontal, and sphenoidal
sinuses (Fig. 163, B, c): the
two last-mentioned cavities
arise in connection with the

Fro. 163, 8. —SacGirraL SEcTION THROUGH THE.
Nasa AND BvecvaL CAVITIES OF THE
Human Heap.

I, II, II, the three olfactory ridges ; sn’,
frontal sinus; sv”, sphenoidal sinus; os,
aperture of Eustachian tube; be, entrance
to the mouth ; /y, tongue; v.?, atlas verte-
bra; ¢.i/, axis vertebra.

1 This is also true of the anterior (lower) ethmoid turbinal in microsmatic

Mammals.

OLFACTORY ORGAN 205

It is supported by an outward extension of the nasal bones and by the

cartilaginous septum nasi
which arises from the eth-
moid, as well as by other
secondarily independent car-
tilages (ale-nasals) which
were primarily continu-
ous with the general carti-
laginous wall, but become
differentiated from the
latter in various ways in
accordance with the varied
functional adaptations which
the outer nose undergoes.
Thus it may be provided
with a special valvular ap-
paratus for closing the nos-
trils (aquatic Mammals) ; or
may grow out to forma
longer or shorter trunk
provided with a complicated
musculature (Mole, Shrew,
Pig, Tapir, Elephant), and,
by means of its abundant
nerve-supply, serve as a
delicate organ of touch and
even as a prehensile appar-
atus.

A B

Fic. 163, c.—TRANSVERSE VERTICAL SECTION

THROUGH THE Nasau Cavity oF MAN.

I, I, III, inferior (maxillary), middle, and

superior turbinal ; a, b,c, inferior, middle,
and superior nasal passage; S, septum
nasi; J, J, position of rudimentary Jacob-
son’s organs, which are situated nearer the
floor of the cavity than is indicated in the
figure ; *, point at which the naso-lachrymal
duct opens ; t+, entrance into the maxillary
sinus (C.m); SZ, ethmoidal labyrinth ;
HG, hard palate; C.cr, cranial cavity ;
af, maxilla ; Or, wall of orbit.

\ i che
Ot rae

PTA

Fic. 164.—Various Forms OF THE MAXILLO-TURBINAL OF MAMMALS.

A, double coil; B, transition from latter to single coil, 2, F'; C, transition from

double coil to the dendritic form D.

(After Zuckerkandl. )

JACOBSON’S ORGAN,
By the term “ Jacobson’s organ” is understood a paired accessory

nasal cavity which in an early embryonic stage becomes differen-
tiated from the nasal chamber, and which is supplied by the
olfactory and trigeminal nerves; it communicates with the mouth
by a special aperture.

Fra. 165.—TRANSVERSE SECTIONS OF THE NOSE IN VARIOUS VERTEBRATES.

A—D, Illustrating the various ontogenetic and phylogenetic stages of the Jacob-
son’s organ of Urodeles. In A its position is median, and in D lateral.

E, Gymnophiona, in which the organ becomes separated from the main nasal cavity.

F, Lacerta agilis.

G, Placental Mammal; I, the same, in longitudinal vertical section.

H, Ornithorhynchus. (After Symington. )

N, main nasal cavity; jc, Jacobson’s organ; ¢.j, Jacobson’s cartilage ; g.m,
intermaxillary gland; g.n, nasal gland ; x.0, olfactory nerve ; 2.¢, trigeminal
nerve ; /., naso-lachrymal duct ; av, maxilla ; 0.¢@, dumb-bell shaped bone.

EYE 207

A Jacobson’s organ is first met with in Amphibians. In young
Triton larvee a small gutter-like medio-ventral outgrowth of each
nasal cavity arises, with which the ventral branch of the olfactory
nerve comes into relation. This outgrowth later undergoes a re-
lative change of position, and comes to be situated laterally towards
the upper jaw (Fig. 165 a—p). At its blind end a gland is developed.
In Siren the primary median position is retained, and in the Axolotl
it does not extend so far laterally asin the adult Triton. The acces-
sory nasal chamber of Ceecilians!(p. 2C0) is developed in a similar
manner (£), and a large gland is in connection with it. There can
also be little doubt that this cavity is represented in Anura,
although its relative position is somewhat different to that seen in
Urodeles.

The Jacobson’s organ of the Amniota is also developed in the
medio-ventral part of the nasal chamber, close to the septum nasi.
It loses its primary connection with the former, but retains its
median position, lying between the floor of the nasal cavity and
the roof of the mouth. It is lined by an olfactory epithelium and
communicates in front with the mouth through the corresponding
naso-palatine canal (p. 100). In Lacertilia and Ophidia a papilla
extends into its cavity from the floor (Figs. 161 and 165, F).

These organs are not present in Crocodiles, Chelonians, and
Birds, but rudiments have been observed in embryos of Crocodilus
biporcatus, and certain cartilages on the nasal floor in Birds
appear to correspond with the Jacobson’s cartilages of other forms.

Amongst Mammals, Jacobson’s organ is most marked in
Monotremes (Fig. 165, 4), in which it is much more highly developed
than in Lizards. It contains a well-marked, turbinal-like ridge,
supported by cartilage continuous with that enveloping the organ
and covered with ciliated epithelium, and numerous glands are
present in the mucous membrane, In other Mammals (G, 1) it
becomes more or less reduced, though often well-marked, consisting
of two tubes lying at the base of the septum nasi, usually enclosed
by separate cartilages (Marsupials, Edentates, Insectivores, Rodents,
Carnivores, Ungulates). A branch of the olfactory nerve enters the
tube posteriorly, and anteriorly the cavity of the organ communi-
cates with the mouth through the incisive or naso-palatine canals.
Rudiments of the organ exist even in Man (Fig. 163, c).

The function of Jacobson’s organ may consist in bringing the
food taken into the mouth under the direct control of the olfactory
nerve.

EYE.

As already mentioned (p. 154, Fig. 167, a and B), the optic
nerve is developed from the stalk of an outgrowth of the primary
1 A curious apparatus exists in Cecilians in connection with the nasal cavity

and orbit. It consists of « fibrous capsule with muscles and a large gland,
opening near the snout. Its function is not certainly known.

208 COMPARATIVE ANATOMY
fore-brain known as the primary optic vesicle. It, therefore, like the
olfactory lobe, represents a part of the brain.

In the adult brain, the optic nerve is seen to arise from the
thalamencephalon, and three more or less sharply-differentiated
portions of it may in most cases be distinguished; these are

Fic. 166.—CuIAsMA OF
THE Optic NERVES.
(Semidiagrammatic.)
A, chiasma charac-
-teristic of the greater
number of Teleostei ;
B, Herring; C, Lacer-
ta agilis; D, an Ag-
ama; E, a higher
Mammal.

Chi, chiasma of the
bundle of nerves ly-
ing centrally; Ce,
Cel, S, S?, lateral
fibres; Co, commis-
sure.

the epiblast,

the latter becomes thickened

spoken of, from the proximal to the distal end
respectively, as the optic tract, chiasma, and
NETUC.

The chiasma, that is, the crossing of the
two optic nerves, is always present, though
not always freely exposed, for it may retain
a primitive position deeply embedded in the
base of the brain, (¢.g., Cyclostomi, Dipnoi).

In most Teleosts the optic nerves simply
overlie one another (Fig. 166, 4), but in some
of these Fishes (Clupea, Engraulis Fig.
166, B), one nerve passes through a slit in the
other, and this condition of things is gradu-
ally carried still further in Reptiles, until
finally the fibres of the two nerves intercross
in a very complicated manner (Fig. 166, ¢, D),
giving rise to a sort of basket-work ; this is
finest and most delicate in Mammals, where
its structure can only be analysed by compar-
ing a series of sections. A more or less
complete crcssing of the fibres of each optic
nerve may also take place more peripherally
before they spread out in the retina.

In contrast to the eyes of Invertebrates,
which arise by a differentiation of the cells
of the superficial epiblast, the sensitive elc-
ments of the Vertebrate eye correspond to a
peripheral portion of the brain (Figs. 167, 4
and B).

As the primary optic vesicle grows out-
wards towards the outer skin of the embryo,
the portion which connects it with the brain
becomes constricted and by degrees loses its
cavity, giving rise to a solid cord, from which
the optic nerve is formed.

At the point where the vesicle touches
and the outer

wall of the vesicle invaginated to form a double-walled cur,
the secondary optic vesicle (Fig. 167, B). The inner and
outer walls of the cup then become fused together, the
former giving rise to the sensory epithelium of the retina, and
the latter to the pigment cpithelium. The fibres of the optic
nerve are first differentiated in its retinal portion, and grow

EYE 209

centripetally towards the brain; centrifugal fibres also arise
later.

In the course of further development, the epiblastic thickening
mentioned above, which is often at first hollow, becomes separated
from the epiblast, sinks more and more into the interior of the
optic vesicle, and is differentiated to form the crystalline lens
(Fig 167, 8). The remaining space withia the optic vesicle becomes
filled by mesoblastic tissue, which grows in from the ventral side
of the secondary optic vesicle through the so-called choroid fissure

Fic. 167, A.—Dracram Suow1se THE Move or FoRMATION oF THE PRIMARY
Optic Vesictes (A Bi.)

VH, fore-brain ; V, V, ventricular cavity of the brain, which communicates freely
with the cavities of the primary optic vesicles at tt.

B.—SEMIDIAGRAMMATIC FIGURE OF THE SECONDARY Optic VESICLE, AND OF
THE LENS BECOMING SEPARATED OFF FROM THE EPIBLAST.

TB, inner layer of the secondary optic vesicle, from which the retina arises ;
+, point at which the latter is continuous with the outer layer (AB), from
which the pigment epithelium is formed; H, remains of the cavity of the
primary optic vesicle ; L, lens, which arises as a cup-shaped involution of the
epiblast (Z); *, point of involution of epiblast to form the lens ; J/.17, meso-
blastic tissue, which at 17, AZ’, grows in between the outer epiblast and the
lens as the latter becomes separated off, and which gives rise to the corneaas
well as to the iris; C, vitreous chamber of the eye, between the lens and
retina, which later becomes filled by the vitreous humour.

and gives rise to the vitreous humour (Fig. 167, B), the bulk
of which, as compared with the lens, gradually increases. Blood-
vessels (vasa centralia nervi optici, arteria hyaloidea, tunica vasculosa
lentis) also extend into the vesicle in the same manner.

The secondary optic vesicle is thus plentifully supplied with
blood-vessels in its interior, and others arise at its periphery, where
a definite vascular and pigmented membrane, the choroid, is formed
from the surrounding mesoblast (Fig. 168).

Internally to the lens, the choroid gives rise to the ciliary
folds, while more externally it passes in front of the lens to form

Pp

210 COMPARATIVE ANATOMY

the iris (Fig. 168), which retains in the centre a circular or slit-like
aperture, the pupil, through which the rays of light pass. The
amount of light admitted is regulated by the dilator and con-
strictor (sphincter) muscles of the iris, which are able to increase
or lessen the size of the pupil; the iris thus serves as a screen to

regulate the amount of light which enters the eye.
Not only is the size of the pupil inconstant, but the lens is also
capable of undergoing considerable change in form, becoming more

flattened or more convex, as the case may be.

Te

Ch

Fic. 168.—DIAGRAM OF A HORIZONTAL
SECTION THROUGH THE LEFT
Human Eryx. (Seen from above.)

Op, optic nerve ; OS, sheath of optic
nerve; A/F, blind-spot ; Fo, yellow
spot (fovea centralis); Rt, retina ;
PE, pigment epithelium of the
retina ; Ch, choroid, with its lamina
fusca (Lf) and vascular layer (GS) ;
Sc, sclerotic; Co, cornea; Cj, con-
junctiva ; J/D, membrane of Desce-
met; CS, canal of Schlemm (the
dotted line should extend further
through the sclerotic to the small
oval aperture) ; Iv, iris; Lc, ciliary
ligament; C, ciliary process; T’K,
ATK, anterior and posterior chamber
of the eye; L, lens; H, hyaloid
membrane; Z, Zone of Zinn, CP,
canal of Petit ; Cv, vitreous humour.

The former con-
dition occurs when distant, the:
latter when near objects are
looked at. This delicate accom-
modating apparatus is regulated
by a ciliary muscle (tensor choro-
idew) supplied by the oculomotor
nerve, which arises in a circle all
round the eye from the point of
junction of the iris and sclerotic
and is inserted along the peri-
pheral border of the iris (Fig.
168).

Externally to the vascular
layer of the choroid is a lymph-
sinus with pigmented walls
(lamina fusca) ; and externally to
this, again, is a firm fibrous, partly
cartilaginous, or even ossified
layer, the sclerotic. The latter
passes internally into the sheath
of the optic nerve, which is con-
tinuous with the dura mater, and
externally into the cornea, the
outer surface of which is covered
over by an epithelial layer con-
tinuous with the epidermis—the
conjunctiva. The sclerotic and
cornea together form a firm outer
support for the eye, and thus, to-
gether with the gelatinous mass
of the vitreous humour, guarantee

the rigidity necessary for the physiological activity of the nerve

end-apparatus.

Between the cornea and iris there is a large lymph-

space, the anterior chamber of the eye (Fig. 168), its contained

fluid being called the aqueous humowr.

Other lymph-spaces are

also present, ¢.g., between the choroid and sclerotic.

The deep orbit, formed by the skull, serves as a further pro-
tection for the eye, as do also certain accessory structures, which
may be divided into three categories, viz. :—

EYE 211

1. Hyelids (palpebre).

2. Glandular organs.

3. Muscles, serving to move the eye-ball.

The eye-ball is thus formed of a series of concentric layers
which are called from within outwards retina, choroid and tris
(vascular layer), and sclerotic and cornea (skeletal layer). The first
corresponds with the nervous substance of the brain, the second with
the pia mater, and the third with the dura mater. The interior of
the eye contains refractive media, the lens and vitreous humour.
‘To these, certain accessory structures are added (pp. 216—220).

The relative development of the eye varies considerably amongst Verte-
brates. It may reach a very high degree of perfection ; or may, on the other
hand, undergo more or less degeneration in those animals which live in caves
or burrows (e.g., Fishes—Amblyopsis spleleus, Typhlogobius ; Amphibians
—Proteus, Gymnophiona; Snakes—Typhlops: Manmuls—Talpa, &c.).
In Ammocostes and Myxine the eye is hidden. beneath the integument (see
below), and in the Cetacean Platanista gangetica the eyes are extremely
minute.

The retina will be dealt with after a description of the eyes
of the various classes of Vertebrates has been given (p. 214).

In Amphioxus a simple pigment spot is present in the front’ wall of the
“cerebral ventricle” (p. 157, and Fig. 219).

Cyclostomes.—The eye of Cyclostomes remains at a very low
stage of development, not only as regards the structure of the retina,
but also—in Myxinoids, in the absence of a lens and iris and of a
differentiated sclerotic and cornea as well as of eye-muscles, and
in the persistence of the choroid fissure. Moreover, the eye in
Myxinoids and in the larval Ammoccete lies beneath the skin and
subdermal connective tissue. In Petromyzon the skin covering the
eye becomes thinned out at metamorphosis, and thus the animal,
which was blind, or nearly blind, in the larval state, can see on
reaching the adult condition: at the same time the eye becomes
more highly organised, though the primary lumen in the lens
(Fig. 167, B) does not entirely disappear.

Fishes and Dipnoans.—The eyes of all the true Fishes are,
with few exceptions, of considerable relative size, and are formed
on essentially the same plan as that described in the intro-
ductory portion of this chapter.

The lens of Fishes, like that of all aquatic animals, is globular,
and possesses therefore a high refractive index. It touches the
cornea and fills up the greater part of the eyeball, so that only a
small space is left for the vitreous humour. It differs from that of
other Vertebrates in the fact that,in the condition of rest, it is
accommodated for seeing near objects. In Teleosts accommodation
apparently takes place by means of a process of the choroid, the
processus falciformis. This extends into the vitreous humour
towards the Jens, around which it expands to form the so-called

, Be

212 COMPARATIVE ANATOMY

campanula Halleri (Fig. 169). In the interior of this structure
are nerves, vessels, and smooth muscle-fibres, and the latter possibly
exert an influence on the lens, draw-
ing it towards the retina. The pro-
cessus falciformis is never large in
Ganoids and is absent in Cyclo-
stomes, Elasmobranchs, and Dip-
noans: the question of accommoda-
tion in these Fishes is not under-
stood.

Externally to the choroid proper,
that is, between it and the lamina
fusca, lies a silvery or greenish-gold
iridescent membrane, the argentea.
It extends either over the whole
interior of the eye (Teleosts), or is
Fic. 169.—Eyz or A Tretxosrean. limited to the iris (Elasmobranchs).
Op, optic nerve; OS, sheath of optic A second layer with a metallic

nerve; Rt, retina; PH, pigment lustre, the tapetum lucidum, is
epithelium; 7p, tapetum; Lr, present internally to the iridescent
pring vaselosa: t argertes + portion, and within this again i the
sclerotic, enclosing cartilage or chorio-capillaris of the choroid. No
bone (+); Co, cornea ; Jr, Iris; tapetum appears to be present in

VK, anterior chamber ; Z, Lens ; :
CY, vitreous humour ; Pr, pro- Teleostei or Petromyzon.

cessus falciformis ; Cp, campanula The so-called choroid gland, pre-
Halleri. sent only in Teleostei and Amia,
consists of a network of blood-
vessels (rete mirabile) which has the form of a cushion, lying near
the entrance of the optic nerve, between the argentea and pigment
epithelium of the retina : it thus has nothing to do with a “ gland.”
The sclerotic is usually extensively chondrified, and not unfre-
quently becomes calcified or ossified towards its junction with the
cornea.

The eyeball is almost always surrounded by a gelatinous tissue, penetrated
by connective-tissue fibres, and in Elasmobranchs it is usually articulated on its
inner circumference with a rod of cartilage connected distally with the

lateral wall of the skull.

Amphibia.—The eyes of Amphibians are proportionately
smaller, and their form rounder than those of Fishes, but there are
many points of close correspondence between them. This is true,
for instance, as regards the more or less distinctly chondrified
sclerotic, the slightly convex cornea, and the globularlens, In other
important respects, however, the Amphibian eye is simpler than
that of Fishes; thus it is wanting in an argentea,a tapetum, a
choroid gland, and a processus falciformis and campanula Halleri.
The iris contains smooth muscle-fibres, and a true ciliary muscle
is present in the whole series of animals from this point onwards,
though not strongly developed in Amphibians. The pupil is usually
round, but may be angular. :

EYE 213

The eyes of Proteus and of the Gymnophiona, as already mentioned,
always lie more or less deeply beneath the skin ; they are very small, and
are much degenerated. In Proteus the crystalline lens and iris are both
wanting, and the vitreous humour is only slightly developed.

Reptiles and Birds.——In these also, the sclerotic is in great
part cartilaginous, and in Lizards and Chelonians it is provided
with a ring of delicate bony sclerotic plates around
the external portion (Fig. 170). Many fossil Rep-
tiles and Amphibians possessed similar plates, as
do also existing Birds (Fig. 171) ; in Birds horse-
shoe- or ring-shaped bony structures are also
usually present close to the entrance of the optic
nerve,

The eyeball of Reptiles has a globular form
(Fig. 170}, while that of Birds, more especially
nocturnal Birds of prey (Owls), is more elongated
and tubular, an external larger segment being
sharply marked off from an internal smaller
one: moreover the whole eye is relatively larger.
(Fig. 171). The
outer portion is bounded ex-
ternally by the very convex
cornea and encloses a large
anterior chamber as well as a
complicated ciliary muscle com -
posed of striated fibres. This
muscle is also transversely stri-
ated in Reptiles, in which—
especially in Chelonians, it is
always well developed, though
-not to such an extreme degree
as in Birds.

In Reptiles (Lizards, for in-
stance) a tapetum may be
developed, but an argentea and
choroid gland are never presert
all these parts are wanting in
Birds. A structure which is
homologous with the processus
falciformis of Fishes is, how-
ever, present in most Reptiles

Fie. 170. — Eryx
oF Lacerta mu-
ralis, SHOWING
THE RING OF
Bony SCLERO-
Tic PLATES.

Fic. 171.—Ever oF an OWL.

Rt, retina; Ch, Choroid; Se, sclerotic,

with its bony ring at t; CAV, ciliary
muscle; Co, cornea; V.V, point of
junction between sclerotic and cornea ;
Ir, iris; VK, anterior chamber; J,
lens ; Cr, vitreous humour ; P, pecten ;
Op, OS, optic nerve and sheath. The
dotted line passing across the broadest
portion of the circumference of the eye
divides the latter into an inner and
an outer segment.

and in Birds. Absent in
Hatteria and the Chelonia,
this so-called pecten is largely
developed in Birds! (Fig. 171),
and may extend from the poimt
of entrance of the optic nerve
to the capsule of the lens, but

'In Apteryx the pecten disappears during development.

214 COMPARATIVE ANATOMY

as a rule does not reach so far. In Birds it is always more or
less folded, and consists mainly of a closely-felted network of
capillaries. In both Reptiles and Birds, the pecten appears to
be important in the nutrition of the contents of the eyeball
and of the retina: it has nothing to do with accommodation.

The iris, which is regulated by striated muscle, by means of which it is
able to respond very quickly to visual impressions, is often brightly coloured,
and this colour is due to the presence, not only of pigment, but also of
coloured fat globules.

The pupil is as a rule round, but in many Reptiles and in Owls has the
form of a vertical slit.

Mammals.—In Mammals the eyeball is always more com-
pletely enclosed within the bony orbit than is the case in most
other Vertebrates, and this may partially account for the fact that,
except in Monotremes, the sclerotic no longer shows traces of
cartilage or bone, but is entirely of a fibrous character (Fig. 168).

With the exception of aquatic Mammals, in which it is some-
what flattened, the cornea is moderately convex, and the whole
eyeball is of a more or less rounded form.

A tapetum lucidum, consisting either of cells or fibres, exists in the choroid
of numerous Mammals, and gives rise by interference to a glistening appear-
ance when seen in the dark (Carnivores, Ruminants, Perissodactyles, &c.).

Certain structures homologous with the processus falciformis and pecten
are present in Mammals in the embryo only.

The ciliary muscle consists of smooth elements.

The external surface of the lens is less convex than the internal, which
latter lies in the so-called fossa patellaris of the vitreous humour.

The pupil is not always round, but may be transversely oval (Ungulates,
Kangaroos, Cetaceans), or slit-like and vertical (e.g., Cat).

Retina.

The fibres of the optic nerve, which pass into the eyeball at a
right or acute angle, cross one another at the point of entrance,
and are then distributed to the sensitive elements of the retina.
The latter is thus thickest at the point of entrance of the nerve,
which is known as the “blind spot” (Fig. 168), and gradually de-
creases in thickness towards the ciliary processes, until, at the point
of origin of the iris, it consists of a single layer of cells.

The retina is bounded externally by a structureless hyaline
membrane (Jimdtans externa),! while on its inner side it is covered
by the hyaloid membrane, which, strictly speaking, belongs
to the vitreous humour. The retina is quite transparent in the
fresh condition, and consists of two portions which are_histo-
logically and physiologically quite distinct: they are, a supporting

? The membrana limitans encloses the entire retina externally in the embryo,
but later the rods and cones come to project through it (see Fig. 172).

RETINA 215
part and a nervous part. The former is stretched as on a frame
between the limitans externa and hyaloid membrane.

The nervous elements are arranged in the following concentric
layers :—

I. Developed from the internal layer of the secondary optic vesicle.
A. Cerebral layer.

1. Layer of nerve-fibres (of optic nerve).

2. Layer of ganglion-cells.

3. Inner reticular layer.

4, Granular layer (inner).

5. Outer reticular or subepithelial layer.
B. Epithelial layer.

6. Layer of visual ceils (outer granular layer with the
rods and cones).

I]. Developed from the external layer of the secondary optic vesicle.
7. Pigment epithelium (retinal epithelium).

It seems probable that the various nerve-cells of the retina are not directly
connected with one another, but are only contiguous.

Rods and cones. |
Fibrous =—"——- i

a F _ Membrana
basket-work. = “—"~ limitans.

Outer granular
layer.

Concentric _ Outer recticular
supporting-cells.

ae ; SS layer.
(nucleated). = iz Ze Sub-epithelial —_
. = ganglion-cell.
Concentric = ——
supporting-cells

(non-nucleated), Star-shaped _.

ganglion-cell.

Radial fibres,

Bipolar
ganglion-cell.
Multipolar
ganglion-cell.
-—-Inner recticular
layer.

Centrifugal
nerve fibres.

Radial fibres. 7 7" 7

Multipolar
ganglion-cell.

Layer of
nerve fibres.

Fie. 172.—DIAGRAM OF THE ELEMENTS OF THE RETINA.

(Supporting elements
on the left, and nervous elements on the right.) After Ph. Stohr.

These layers are so arranged that the nerve-fibres lie next to
the vitreous humour, that is, internally, while the rods and cones

216 COMPARATIVE ANATOMY

are situated towards the choroid, or are external. Thus the
terminal elements of the neuro-epithelium are turned away
from the rays of light falling upon the retina, and the rays must
therefore pass through all the other layers before they reach the
rods and cones.

Fishes possess the longest, Amphibians the thickest rods, so that in the
latter there are only about 30,000 to a square millimetre, while in Man there
are from 250,000 to 1,000,000.

In Fishes the rods far exceed the cones in number, while in Reptiles and
Birds the reverse is the case. The cones of many Reptiles and all Birds are
distinguished by the presence of brightly coloured oil-globules, which are
also present in those of Marsupials.

In the centre of the retina of higher Vertebrates there is a specially
modified region of most acute vision, called the yellow-spot (fovea
centralis or macula lutea). It is due to the thinning-out of all the
layers except that of the rods and cones, and even the rods disappear, only
the cones persisting (Fig. 168).

Accessory Organs in Connection with the Eye.
(a) EYE-MUSCLES.

The movement of the eyeball is always (except in Myxinoids,
comp. p. 211) effected by six muscles, four of which are known
as the rectt (superior, inferior, anterior or internal, and posterior or
external), and two as the obligui (superior and inferior). The
former, which arise from the inner portion of the orbit, usually
from the dural sheath of the optic nerve, together circumscribe a
pyramidal cavity, the apex of which lies against the inner portion
of the orbit, while the base surrounds the equator of the eyeball,
where the muscles are inserted into the sclerotic.

Both the oblique muscles usually arise from the anterior or
nasal side of the orbit, and as they respectively pass from this region
dorsally and ventrally in an equatorial direction round the eyeball,
they constitute a sort of incomplete muscular ring.

A deviation from this arrangement is seen in Mammals, in which the
superior oblique has gradually come to arise from the inner part of the
orbit, and then passes forwards towards its anterior (internal) angle, where
it becomes tendinous, and passes through a fibro-cartilaginous pulley (trochlea)
attached to the upper border of the orbit, on the frontal bone. Hence it is
sometimes called the trochlear muscle. From this point it changes its direc-

tion, and becomes reflected obliquely outwards and backwards tv the globe of
the eye.

Besides these six muscles, others are usually present which
are known as the retractor Lulbi (best developed in Ungu-
lates), the guadratus (bursalis), and the pyramidalis, The last
two are connected with the nictitating membrane (see p. 217),
and are present in Reptiles and Birds. All three are supplied by
the abducent nerve (comp. p. 184).

GLANDS 2h bie

(b) EYELIDS (PALPEBR4).

In Fishes and other lower aquatic forms the upper and lower
eyelids are usually very rudimentary, having at most (¢.g., Elasmo-
branchs) the form of stiff folds of the skin; and in all Verte-
brates below the Mammalia they never reach a very high stage of
development. They are lined on the surface looking towards the
eyeball by a continuation of the epidermis, the conjunctiva (p. 210),
and in the Ichthyopsida and Sauropsida are usually not sharply
marked off: from the rest of the skin, being capable of no, or only
of very slight, movement.!

In Mammals, the eyelids, more particularly the upper one, are
extremely movable, and are provided with hairs (eyelashes) on
their free margin. In their interior a hard body, the so-called
“lid-cartilage” is developed, and they are closed by a circular
muscle which surrounds the whole slit between the lids; a levator
is also present in the upper eyelid. In Sauropsida and many
Mammalia (¢.g., Ungulates) there is a depressor of the lower lid.

The want, or comparatively slight development of upper and
lower eyelids in Vertebrates below the Mammalia is compen-
sated for in certain forms, at any rate to a certain extent, by the
presence of a nictitating membrane. This “third eyelid” differs
from the others in having nothing to do with the outer skin proper,
consisting simply of a reduplicature of the conjunctiva, and being
regulated by special muscles (see p. 216).

The nictitating membrane, which is represented in certain
Elasmobranchs (c.g., Carcharias, Galeus, Zygaena, Mustelus, comp.
p. 148) and which often encloses a cartilage, is situated within
the lower eyelid, or it may lie more towards the anterior angle
of the eye. The former condition is seen, ¢g., in Anurans, and
the latter in Birds, in which a third eyelid is so largely developed
as to be capable of covering the whole freely exposed portion of
the eyeball. In Reptiles and Mammals it always lies in the
anterior angle of the eye; in Primates it becomes reduced to a
small, half-moon-shaped fold (plica semilunaris), but in Monkeys
and certain races of Mankind traces of the cartilage are present.

(¢) GLANDS.

The glands in connection with the eyé are: (1) the /wehrymu/,
(2) the Harderian, or gland of the nictitating membrane, and (3)
the Meibomian glands.

The secretions of all these serve to keep the free surface of the
eyeball moist, and to wash away foreign bodies. In Fishes and

1In many Reptiles and Birds the upper eyelid, is supported by a membrane-
bone or fibro-cartilage. In Geckos, Amphibenians and Snakes the two eyelids
grow together to form a transparent membrane overlying the eye, and this comes
away with the rest of the outer part of the skin when the latter is shed.

218

COMPARATIVE ANATOMY

Dipnoans,! the outer medium appears to suffice for this purpose,
but the first attempt of a Vertebrate to exchange an aquatic for an

Fie. 173. — HarpERIAN
Guanpd (H, H?) anp
LAacHRYMAL GLAND (7h)
oF Anyuis fragilis.

M, muscle of jaw; B, eye-
ball.

aérial existence necessitated the develop-
ment of a secretory apparatus in connection
with the eye.

Thus in Urodeles a glandular organ is
developed from the conjunctival epithelium
along the whole length of the lower eye-
lid; in Reptiles this becomes mote
developed in the region of the anterior
and posterior angles of the eye, and the
original connecting bridge gradually dis-
appears: thus two glands are developed
from the primitively single one, each of
which becomes further ditferentiated both
histologically and physiologically. From

one is formed the Harderian gland, which always lies at the

anterior angle of the eye, sur-
rounding to a greater or less ex-
tent the antero-ventral portion of
the eyeball, while the other gives
rise to the lachrymal gland?
(Figs. 173 and 175). The latter
retains throughout life its primi-
tive position at the posterior
angle of the eye, and even
in Birds lies in the region of
the lower eyelid; it is supplied
by the second division of the
trigeminal. In Mammals it be-
comes gradually further sub-
divided, and extends into the
region of the upper eyelid, so
that its ducts open above the
eye into the upper conjunctival
sac (Fig. 175, A & B). Never-
theless, even in the , Primates,
more or fewer ducts are present
which open into the lower con-
junctival sac, and thus the primi-
tive position of the lachrymal
gland is indicated.

A well-differentiated Har-
derian gland is present from the

1) |
=

Fre, 174. —D1aGRAMMATIC TRANSVERSE
VERTICAL SECTION THROUGH THE
Eye or A MAMMAL.

Op, optic nerve ; B, eyeball; Fo, Fo,
upper and lower conjunctival sac ;
LH, LH, outer skin of the eyelids,
which at the free edges of the latter
at + becomes continuous with the
conjunctiva ; 7', the so-called tarsal
fibro-cartilages, in which the Meibo-
mian glands (A/D) lie embedded,
the latter opening at *; H, H, eye-
lashes.

tailless Amphibia to the Mammalia, but is very rudimentary in

the Primates.

1 Comp. p. 17.

° A lachrymal gland is absent in Crocodiles and Snakes,

GLANDS 219

The Merbomian glands, belonging to the group of sebaceous
glands, are confined to the Mammalia, and lie embedded in the

Fic. 1754.—DIAGRAM TO ILLUSTRATE THE SHIFTING OF THE LACHRYMAL GLAND
WHICH HAS TAKEN PLACE IN THE COURSE OF PHYLOGENY.

The gland shifts in the direction of the arrows; a, its position in the Amphibia ;
b, in Reptiles and Birds, and occasionally in Man, in which case it may be
regarded as atavistic ; c, normal position in Man.

substance of the eyelids in the form of branched tree-like tubes
or clustered masses. They open on the free edge of the lid, and
produce a fatty secretion. Certain modified sweat-glands known as

TD.
Tie COCR ;

Fig. 1758.—D1aGkRAM oF THE LACHRYMAL APPARATUS OF MAN.

TD, lachrymal gland, divided up into several portions ;**, ducts of the lachrymal
gland; tt, puncta lachrymalia ; 7’R, 7'R!, upper and lower lachrymal canals;
S, lachrymal sac ; D, naso-lachrymal duct.

the glands of Moll are also present immediately within the eyelids
of Mammals.

The naso-lachrymal duct, which conducts the lachrymal
secretion into the nose, has already been referred to (p. 201).

220 COMPARATIVE ANATOMY

In the Cetacea, the lachrymal and Meibomian glands, as well as the naso-
lachrymal duct, are wanting, and alachrymal duct is absent in the Otter, Seal,
and Hippopotamus. In the two last-mentioned animals the lachrymal gland
is much reduced : in Manis javanica there are no Meibomian glands, and in
the Mole the entire lachrymal apparatus has undergone reduction. +

AUDITORY ORGAN.

It is very probable that the auditory organ, like the organs
of smell and taste, has been derived primitively from a modified
integumentary sense-organ. It is developed from an invagination

Fic. 177.—SEMIDIAGRAMMATIC FIGURE OF
THE MEMBRANOUS LABYRINTH OF VERTE-

Fic. 176.—Heap axnp ANTERIOR BRATES. (Seen from the outer side.)
Portion or Bopy or A CuIck. ; : ons f
(In part after Moldenhauer. ) uw, utrjculus ; rec, recessus utriculi ; sp, sinus
i posterior utriculi; s, sacculus ; /, recessus

RG, olfactory pit; A, eye; I to sacculi (lagena); cus, utriculo-saccular
IV, first to fourth visceral canal ; de, se, ductus and saccus endolym-
arches ; +, point at which the phaticus, the former arising from the
external auditory passage begins sacculus at +; ss, sinus utriculi superior ;
to be formed; LB, primitive ass, apex of the same ; ca, ce, cp, anterior,
auditory vesicle seen through external, and posterior semicircular canals;
the wall of the head. aa, ae, ap, the corresponding ampulle.

of the ectoderm on either side of the primary hind-brain: this be-
comes separated off to form a vesicle (Fig. 176), and its epithelium
is differentiated into elongated cells of sensory epithelium pro-
vided with hair-like processes (Figs. 178 A and B) separated by
supporting cells. The sensory cells are surrounded by a nerve-
network, and are not continuous with the nerves as in the case of
the olfactory cells (p. 197).

Like the other higher sense-organs, the paired auditory organ

AUDITORY ORGAN 221

of Vertebrates is situated in the region of the head, between the
origins of the trigeminal and vagus nerves. After the vesicle of
each side has become separated off from the epiblast and connected
with the brain by means of the auditory nerve (which arises in
connection with a peripheral ectodermic ganglion and then grows
centripetally to the brain), it sinks deeper and deeper into the
mesoblastic tissue of the skull: it then loses its original pyriform
ér rounded shape, and becomes divided into two parts, called re-
spectively the wtriculus and sacculus (Fig. 177). From the former

Fic. 1784.—IsoLaTED ELEMENTS oF THE MEMBRANOUS LABYRINTH OF VARIOUS
VERTEBRATES. (After G. Retzius. )

A, from the macula acustica communis of Myzxine glutinosa ; B, from the macula
acustica neglecta of Raia clavata ; C, from the crista acustica of an ampulla
of Linedon (Amblystoma) meaicanus ; D, from the crista acustica of the
anterior ampulla of Roma esculanta.

hz, hair-cells with auditory hairs (h) ; fz, thread-like cells; n,n, dividing nerve.
On the left side of D the auditory hair has become broken up into its con-
stituent fibres.

the semicircular canals become developed, while from the latter
the tube-like ductus endolymphaticus and the lagena (cochlea) are
formed,

The whole of this complicated apparatus constitutes the internal
ear or membranous labyrinth. It becomes surrounded secondarily
by mesoblastic tissue, with which it is at first in close contact.
A process of absorption then takes place in the innermost layers
of the mesoblast, and thus a space is developed which closely

222 COMPARATIVE ANATOMY

repeats the form of the membranous labyrinth, as does also the
mesoblast which encloses this space and which later becomes
chondrified, and often also ossified. A membranous and a bony laby-
rinth can thus be distinguished, and between them is a cavity
(cavum perilymphaticum) filled with a lymph-lke fluid (perilymph),
The cavity within the membranous labyrinth, which also contains a
fluid (endolynph), is spoken of as the cavum endolymphaticum.
Except in Cyclostomes, three semicircular canals are always
present, and these lie in planes at right angles to one another,
They are distinguished as the anterior vertical, the posterior
vertical, and the horizontal (external) canals (Fig. 177). The first
and last-named arise from the portion of the utriculus known as
the recessus utriculi, and each has a vesicle-like swelling or ampulla

Fic. 1788.—-LonGITUDINAL SECTION oF AN AMPULLA OF Gonits. (The exact form
of the epithelium of the crista is not indicated.) After Hensen.

n, the nerve passing into the connective-tissue of the crista; a, base of semi-
circular canal ; b, ie of opening of the ampulla into the utriculus; ¢, the
epithelium on the free wall of the ampulla ; d, the auditory hairs.

at its origin. The posterior canal also arises with an ampulla from
a prolongation of the utriculus (sinus posterior). The other end of
the horizontal canal opens by a funnel-shaped enlargement into the
utriculus, while that of the anterior and of the posterior canal
fuse together to form a common tube, the so-called canal commissure
(sinus superior), which also opens into the utriculus.

Concretions composed mainly of carbonate of lime are present
in the regions of the various nerve end-plates of the auditory
organ in all Vertebrates. These otoliths present the greatest
variety both in form and size. The largest and most massive ones
are seen in Teleosts. They either consist of a single mass, or are
arranged in groups in different regions of the labyrinth.

AUDITORY ORGAN 223

The sensory epithelium, to which the branches of the auditory
nerve are distributed, is situated in the following parts of the
membranous labyrinth: (1) the three ampulle of the canals, in
each of which the auditory cells are situated on a ridge (crista
acustica) projecting into the lumen (Fig. 1788) ; (2) a large macula
acustica in the utriculus : this is continued into the recessus utriculi

Fic, 179.—D1AGRAM OF THE ENTIRE AUDITORY ORGAN OF MAN,

External Har.—M, M, pinna; Aue, external auditory meatus ; O, wall of latter;
Mt, tympanic membrane.

Middle Har.—Ct, Ct, typmanic cavity ; O01, wall of same ; SAp, sound-conducting
apparatus, indicated by a rod, representing the auditory ossicles, the end of
the rod marked + corresponds to the stapes, which closes up the fenestra
ovalis ; M, fenestra rotunda ; 7'b, Eustachian tube ; 71, its opening into the
pharynx ; O”, its wall.

Internal Lar, with the greater part of the bony labyrinth (KL, AL) removed. —
S, sacculus; a, b, the two vertical canals, one of which (b) is shown cut
through ; c, Co, commissure of the canals of the membranous and bony laby-
rinths respectively ; S.e, D.¢, saccus and ductus endolymphaticus ; the latter
bifurcates at-2; Cp, cavum perilymphaticum; Cr, canalis reuniens; Con,
membranous cochlea, which gives rise toa blind sac at -+ ; Cou', bony cochlea ;
Sv and St, scala vestibuli and scala tympani, which at * pass into one another
at the cupula terminalis (Ct); D.py, ductus perilymphaticus, which arises
from the scala tympani at d, and opens at D.p'. The horizontal canal is
seen between 2 and 8.

as well as into the sacculus and lagena, or rudiment of the cochlea,
which arises from the sacculus; (3) the rudimentary macula
acustica. neglecta, which in Fishes, Birds, and Reptiles is situated on
the floor of the utriculus close to the sacculo-utricular canal. In
Amphibians it lies on the inner side of the sacculus, and in
Mammals undergoes a gradual reduction and may even become

224 COMPARATIVE ANATOMY

obliterated. The several portions of the sensory plate or macula
acustica, which are originally continuous, become later disconnected
from one another, and except in Cyclostomes are seen as separate
macule acustice.

The higher we pass in the Vertebrate series, the greater share
loes the mesoblast take in the formation of the auditory organ,
At first—that is,in Fishes—the membranous labyrinth or internal
ear lies close under the roof of the skull, and is thus easily
accessible to the waves of sound, which are conducted partly
through the operculum (when present), and partly through the
gill-slits or spiracle. As we pass to the higher animals, however,
the auditory organ gradually sinks further and further inwards from
the surface, so that a new method for conducting the sound-waves
becomes necessary, and certain accessory structures are developed
(Fig. 179). A canal, the external auditory passage or meatus, passes
inwards from the surface; this opens into a spacious chamber, the
tympanic cavity, in which are situated the auditory ossicles, and
which is connected by the Hustachian tube with the pharynx. The
whole of this canal, which is divided into outer and inner portions
(external and middle ear) at the junction of the external auditory
passage and tympanic cavity by a vibratory membrane, the tympanic
membrane, lies in the position of the first embryonic visceral
(hyoid or spiracular) cleft. From Reptiles and Birds onwards the
first indications of a pinna (that is, the part of the external ear
which projects from the head) are seen, but this only reaches a
full development in Mammals.

Cyclostomes.—In Petromyzon there are only two (the vertical’
semicircular canals, and in Myxine only one canal is present, which,

as it possesses two ampulle, probably represents the two fused
together (Fig. 1804).

Fishes and Dipnoans.—The auditory organ of all the true
Fishes (Fig. 1804'c) follows the general plan given above, and the
same may be said for all higher Vertebrates. Almost without
exception we meet with a division into a pars supertor—represented
by the wiriculus and semicircular canals, which remains essentially
much in the condition already described, and a pars inferior—
constituted by the sacculus and lagena, which gradually becomes
more differentiated, and attains to a higher and higher degree of
development and functional perfection. In Fishes the lagena
consists simply of a small knob-like appendage of the sacculus,
which opens freely into the main cavity of the latter by means
of the sacculo-cochlear canal: it is absent in Chimera. The
utriculus and sacculus also communicate with one another by
the sacculo-utricular canal. In Elasmobranchs the ductus endo-
lymphaticus opens dorrally on the posterior part of the head, and is
thus in free communication with the sea-water,

Fie. 1830—Mermpranovus LABYRINTH OF VARIOUS

Pp spe
yl, I; ms | Cus

tN de \ Ta
Vd \ rue \ Tae

ac ocr
Trg

Fisues (after G. Retzius).
A, Myxine glutinosa, from the inner side.

se, saccus communis ; aa, ap, anterior and posterior ampulla; ¢r, canalis com-

munis ; de, ductus endolymphaticus ; se, saccus endolymphaticus ; me, macula
acustica communis ; cr, crista acustica of the anterior, and erp, of the
posterior ampulla ; ra, rp, anterior and posterior branches of the auditory

nerve.

Al, Acinenser sturio, outer side; B, Chimwra monstrosa, inner side; C, Perra

JSlurviatilis, inner side.

a, utriculus ; ss, sp, sinus utriculi superior and posterior ; ass, apex of the sinus

superior ; 7c, recessus utriculi; aa, ae, ap, anterior, external, and posterior
ampulla ; ca, ep, ce, anterior, posterior, and horizontal (external) semicircular
canals ; s, sacculus ; cus, utriculo-saccular canal ; de, ductus endolymphati-
cus, which in B opens externally through the skin ha at ade; se, saccus
endolymphaticus ; 7, lagena ; mu, macula acustica of the recessus utriculi ;
er, crista acustica of the ampulle ; ms, macula acustica of the sacculus ; mz,
macula acustica neglecta ; p/, papilla acustica of the lagena; ar, auditory
nerve; raa, rac, rap, ru, rs, rl, rn, the various branches of the same ; 0
(in C), otoliths (in the recessus utriculi, sacculus, and lagena. )
Q

226 COMPARATIVE ANATOMY

In Chimeroids, Ganoids, Teleosts and Dipnoans, the auditory
capsules are not completely surrounded by cartilage or bone, the
perilymphatic and cranial cavities only being separated by a fibrous
partition.

In certain Teleosts (Siluroidei, Gymnotidze, Characinidee, Gymnarchide,
Cyprinoide) the auditory organ comes into relation with the air-bladder by
means of a chain of bones (‘‘ Weberian ossicles”) derived from certain parts
of the four anterior vertebre and corresponding pairs of ribs, and by this
means the relative fulness of the air-bladder can be appreciated by the Fish.
Connections between processes of the air-bladder and the internal ear are
also met with in several other Teleosts.

The auditory organ of the Dipnoi most nearly resembles that
of Elasmobranchii, and more particularly that of Chimera,

Amphibia.—The membranous labyrinth of Amphibians re-
sembles that of Fishes and Dipnoans in many respects, but impor-
tant differences are seen, more particularly as regards the lagena,
which, especially in the Anura, becomes further constricted off
from the sacculus and reaches a higher stage of development.
Traces of a papilla acustica lagen lying within the lagena are met
with in the Myctodera, and even in Menopoma and Siredon. In
the Anura (Fig. 181) a higher condition is seen in the presence of
a small ridge-like outgrowth in the interior of the thickened lagena
on which a definite region, supported by cartilage, corresponds to
the basilar membrane of higher types; this bears another patch of
nerve endings—the papilla acustica basilaris.

The ductus endolymphaticus, as in certain Teleosts, may give
rise to large sac-like enlargements containing calcareous matter
and lie close to its fellow, either on the dorsal surface only, or
on both dorsal and ventral sides of the brain. The latter is the
case in Anura, for instance, in which the sac extends as an unpaired
structure along the whole vertebral canal dorsally to the spinal cord,
giving rise to paired outgrowths extending through the inter-
vertebral foramina and forming the characteristic calcareous bodies
situated close to the spinal ganglia. These are lined by pavement
epithelium and are plentifully supplied with capillaries: they are
not glandular, as was formerly supposed.

A further advance in structure as compared with Fishes is seen
in the gradual differentiation of a middle ear. In the outer wall
of the auditory capsule is a membranous space, the fenestra ovalis,
which is plugged by a cartilaginous stapedial plate; and from the
latter a rod-like cartilage or bone, the columella, usuaily extends
outwards towards the quadrate (p. 84). A tympanie cavity, with
a tympanic membrane supported by a ring of cartilage lying on
the level of the skin, and a Hustachian tube opening into the
pharynx and corresponding phylogenetically to the hyoid cleft
of Fishes, are met with in most Anura, in which also the colu-
mella is more perfect, consisting of a bony and cartilaginous rod

AUDITORY ORGAN 227

expanded distally to fit against the tympanic membrane. The
columella is wanting in certain Urodeles (e.g. Triton), A mem-
branous fenestra rotunda in the outer wall of the auditory capsule
is present in most Amphibians and in all higher Vertebrates in
addition to the fenestra ovalis.

The ear of the Gymnophiona resembles that of the Urodela, but the
membranous labyrinth shows further complications.

Fic. 181.—Ricur MempBranxous LAbyrintu or Rana esculenta, from the inner
side. (After G. Retzius.)

au, aperture of utriculus ; 7, lagena cochlee ; pb, pars basilaris cochlex ; cus,
utriculo-saccular canal; mi, mis, mn, macula acustica recessus utriculi,
sacculi, and neglecta ; p/, ppb, papilla acustica lagene and basilaris ; rua, rap,
rs, rn, rl, rb, branches of auditory nerve to the anterior and posterior ampulle,
sacculus, macula neglecta, lagena, and pars basilaris. (Other letters as in
Fig. 180, A1—C.)

Reptiles and Birds.—In Chelonians, the auditory organ
shows many points of resemblance to that of Urodeles; and in all
Reptiles and Birds the chief modifications are confined to the
lagena or cochlea, which gradually shows a higher condition of
development in passing from Chelonians and Snakes to Lizards
and Crocodiles. In Chelonians, the cochlea grows out in the form
of a short canal; in Crocodiles and Birds this canal is considerably
longer, and at the same time it becomes slightly coiled (Figs. 182
and 183). A more marked differentiation also gradually takes
place in the membrana basilaris and the papilla acustica basilaris.
Both become more and more elongated; and, at the same time,
distinct indications of seal tympant and restidult are seen. (Com-
pare the description of these parts on p. 232.)

In the Lacertilia the most varied types of auditory organ are met with ;
in many (Phrynosoma, Pseudopus, Anguis), the membrana basilaris is hardly
more highly developed than in Ophidia. In Iguana, an advance towards
Lacerta and the other higher Lizards is to be noticed. the membrana
hbasilaris is longer, though the lagena with its papilla is not so prominent.
In Acantias and Platydactylus this state of things is carried still further, and
finally the more highly developed auditory organ of Plestiodon and Egerina

Q 2

228 COMPARATIVE ANATOMY

leads up to that of Crocodilia. Thus there isa continuous and an unbroken
series from the lower forms to the higher. ;

The structure of the auditory organ of Hatteria shows many striking
peculiarities : it thus, like that of Chamzeleo, occupies an isolated position,

While the cochlea gradually becomes more independent of the
sacculus, the latter shows the greatest variety both as to form and
size in the different types. Thus, for instance, it is usually very
small in Birds, while in Lizards (¢.g., Lacerta) it is of considerable size

Fra. 182.—Ricut Membranous Lasyrintu or A, Lacerta viridis, AND B,
Alligator mississipiensis, from the outer side. (After G. Retzius.)

ade, aperture of the ductus endolymphaticus ; esc, sacculo-cochlear canal; /rt,
foramen recessus scale tympani; tv, tegmentum vasculosum; sc, septum
cruciatum ; mb, membrana basilaris. (Other letters as in Figs. 180 and 181.)

The aperture of communication between the utriculus and sac-
culus persists, though it gradually becomes narrowed, as does also
that between the sacculus and cochlea. The connection between
these latter may be drawn out to form a canal (canalis rewniens), and
this is particularly the case in Birds; in Crocodiles an_ inter-
mediate condition between Birds and Lizards is seen. The mem-
branous labyrinth of Birds, however, is always specially characterised
by the peculiar arrangement of the anterior and_ posterior
canals, which are greatly arched, and the position of their openings
into the sinus superior (canal commissure) is reversed.

In lower types (Swimming Birds) this peculiarity is less marked than in
the higher forms, and it would be interesting to ascertain the condition
of these parts in the Struthionide, as one would expect to find in them
important points of connection with Reptiles.

AUDITORY ORGAN 229

In many Reptiles the free end of the ductus endolymphaticus is
situated close under the roof of the skull beneath the parieto-
occipital suture, and in the Ascalabota the duct even leaves the
cranial capsule, passes back between the muscles of the neck, and
in the region of the pectoral arch becomes swollen to form a large
folded sac, from which finger-shaped processes extend to the
ventral surface of the vertebral column and to the sub-mucous
tissue of the pharynx. These processes may also branch out in a
labyrinthic manner into the
orbit, and they are always
filled with a white semi-
solid mass of calcareous
substance, as in Anura:
calcareous matter is present
in the ductus endolym-
phaticus of all Vertebrates,
at any rate in the embryo.
In Birds, the duct does not
pass out of the cranial
cavity.

A tympanic membrane

is present in Birds and all ire, 485 sin ;

: . . 1G. .—Ricut MemMBraNous LaByRINTH
Reptiles except Hatteria, oF Turdus musicus, from the inner side.
Snakes, and Amphisbze- (After G. Retzius.) Letters as before.

mians; and in the two last-

mentioned groups the tympanic cavity and Eustachian tube are also
wanting. In Crocodiles the tympanic cavity is very complicated,
and in them as well as in Birds, the two Eustachian canals open by
a single median aperture into the pharynx. The osseo-cartilaginous
columella is well developed in the Sauropsida, and is not distinct
from the stapedial plate ; in Hatteria it is continuous distally with
the hyoid (p. 92).

In certain Lizards (¢.g., Ascalabota, Monitor), an indication of
the development of an external auditory passage is seen, the
tympanic membrane being partially covered posteriorly by a small
fold of skin, usually enclosing the anterior border of the digastric
muscle ; and in Crocodiles there is a definite integumentary valve
moved by muscles. In certain Birds also (¢., Owls), there is
a moveable valve.

Mammals.—The auditory organ of Mammals reaches a much
higher stage of development (Fig. 184), but in Monotremes it
shows many points of resemblance to that of Reptiles and Birds.

The cochlea now reaches its highest development, and grows
into along tube which becomes spirally coiled on itself. In this

1Jn Man it forms nearly three coils, and in other Mammals from one and a
half (Cetacea) up to as many as four or more. Thus in the Rabbit there are two
and a half, in the Ox three and a half, in the Pig almost four, and in the Cat
three coils. The cochlea, as well as the sacculus and all parts of the pars superior
of the membranous labyrinth, vary considerably both in form and arrangement in
the various types.

230 COMPARATIVE ANATOMY

respect, as well as in the more highly-specialised histological struc-
ture of the cochlea, lies the characteristic peculiarity of the auditory
organ of Mammals. The auditory nerve forms the axis of the spiral,

In consequence of this development of the cochlea, the papilla

Fic. 184.—Ricut MemBranous LasyrintH or Rappir (Lepus eunicuus.)
A, from the inner, and B from the outer side. (After G. Retzius.)

sus, sinus utricularis sacculi ; ese, canalis reuniens Henseni ; 7), basilar branch of
the auditory nerve (ac); f, facial nerve ; mb, basilar membrane; /’s, spiral
ligament. (Other letters as Figs. 180-183.)

acustica, or, as it is called in Mammals, the organ of Corti, is drawn
out to a considerable length, and the part of the wall of the cochlea
on which it lies is called the basilar membrane, while the opposite
wall is spoken of as the membrane of Reissner (Fig. 186): this is
already represented in Crocodiles and Birds.

AUDITORY ORGAN 23)

The aperture of communication between the pars superior and
pars inferior of the membranous labyrinth—that is, between the
sacculus and utriculus, is entirely obliterated in Mammals, the two
parts being only indirectly connected with one another by means
of the ductus endolymphaticus. This bifurcates at its point of in-
sertion into the membranous labyrinth, one limb being connected
with the utriculus and the other with the sacculus (Fig. 179) ; while
its upper end perforates the inner wall of the cartilaginous or bony
auditory capsule, passes into the cranial cavity, and terminates by
an expanded extremity (saccus endolymphaticus) in the dura mater.
Osmosis can thus occur between the lymph contained in the en-
dolymphatic and epicerebral lymph-spaces respectively.

The tympanic membrane is secondarily situated deep down in the
external auditory meatus, and thus an important difference is seen
between the Amphibia and Sauropsida on the one hand, and the
Mammalia on the other. The tympanic cavity and Eustachian tube
are well developed, and in place of the single bony columella of the
Sauropsida there is a chain of three auditory ossicles, articulating with
one another and extending between the tympanic membrane and
the fenestra ovalis. These are—the malleus, the incus with its
orbicular apophysis, and the stapes.

The stupedins musele arises from the wall of the tympanic cavity, and is
inserted into the stapes, serving to keep the membrane of the fenestra
ovalis stretched. It is supplied by the facial nerve and corresponds tu a
specialised portion of the hinder belly of the biventer, and can be traced back
as faras Fishes. <A tensvr tympani supplied by the mandibular division of the
trigeminal and derived from the internal pterygoid muscle (primarily from
the masticatory muscles of Fishes) also arises from the wall of the tympanic
cavity, and is inserted into the manubrium of the malleus, serving to keep
the tympanic membrane stretched. Both these muscles are composed of
striated fibres.

As already mentioned, the form of the membranous labyrinth
is repeated by its enclosing cartilaginous or bony capsule, which
forms, so to speak, a sort of cast around its individual parts. Thus
it is usual to speak of a cartilaginous or bony labyrinth as distin-
guished from the membranous labyrinth enclosed within it, the
two being separated by the perilymphatic cavity. In Mammals
the skeletal labyrinth becomes ossified before any other part of the
skull, and is incompletely divided into two parts enclosing the
utriculus and sacculus respectively. With the latter part is
connected the bony cochlea, the axis of which lessens in size from
base to apex (Fig. 185), and round it a bony lamella (lamina
spiralis ossea) winds in a spiral manner; this extends into the
cavity of the coils of the cochlea without quite reaching the
opposite wall (Figs. 185 and 186), being continued outwards by
two laterally-diverging lamella, mentioned above as the basilar

1Cp. p. 100 and Figs. 80 and 233, in which the mode of development of these
parts is shown. There is often also a bony (interhyal) rudiment in the tendon
of the stapedius muscle.

232 COMPARATIVE ANATOMY

membrane and membrane of Reissner ; these lie at an angle to one
another and correspond to the inner walls of the membranous
cochlea or scala media, which is approximately triangular in
transverse section. The outer wall abuts against a portion of the
peripheral part of the bony cochlea (the region between Js and
the peripheral end of R in Fig. 186). It is apparent therefore that

It

!
i,
1

a1, axis; Lso, Lso!, lamina spiralis ossea, the free edge of which, perforated by the
fibres of the auditory nerve, is visible at +; H, hamulus.

Fie. 186.—DiackRAMMATIC TRANSVERSE SECTION OF THE COCHLEA OF A
MAMMAL.

KS, bony cochlea; Lo, Lo!, the two layers of the lamina spiralis ossea, between
which at NV the auditory nerve (together with the ganglion, left of L) is seen ; L,
limbus lamine spiralis ; 8, membrana basilaris, on which the neuro-epithe-
lium lies; #&, Reissner’s membrane ; Sv, scala vestibula ; St, scala tympani;
Sm, scala media (membranous cochlea); C, membrane of Corti; Ls, liga-
mentum spirale. :

the scala media does not by any means fill up the lumen of the bony
cochlea, but that a cavity is left on either side of it, corresponding
to those we have already met with in the auditory organ of Birds
and known as the scala vestibult and scala tympant (Figs. 179 and
186).

Both of these are continuous with the perilymphatic cavity,
and, following the direction of the scala media, open into one
another at the blind end of the latter (Fig. 179). The scala
vestibuli is shut off from the tympanic cavity by the membrane
of the fenestra ovalis, to which the stapes is applied externally ;
the scala tympani is closed by the membrane of the fenestra
rotunda.

On the floor of the bony cochlea, not far from the fenestra
rotunda, is an opening leading into a narrow canal, the ductus
perilymphaticus, which serves as a communication between the

perilymphatic cavity and the peripheral lymphatic trunks of the
head (Fig. 179).

The fibres of the auditory nerve running along the axis of the bony
cochlea extend in their course laterally outwards, between the two plates

1 A ductus perilymphaticus can be plainly made out from Reptiles onwards.

AUDITORY ORGAN 233

of the lamina spiralis ossea (Figs. 186, 187). On the free border of the
latter they pass out, and break up into terminal fibrille on the inner surface
of the basilar membrane.

The fibrillee extend to the sensory or auditory cells, and these are stretched
as in a frame between the firm supporting and isolating cells or bacilli.
From the surface of the bacilli a resistant net-like membrane (membrana
reticularis) extends laterally, and through the meshes of the latter the hairs
of the auditory cells project. The number of the outer hair-cells may be
estimated at about 12,000. The auditory cells are covered by a thick and

Fic. 187.—Tne ORGAN oF Corti. (After Lavdowsky.)

Lo, Lo', the two plates of the lamina spiralis ossea ; .V, auditory nerve with
ganglion ; .V!, V2, the nerve branching up into fibrille and passing to the
auditory cells (G, G); Ba, Ba, bacilli, or supporting cells; J/-, membrana
reticularis ; C, membrane of Corti; Ls, ligamentum spirale, passing into the
basilar membrane ; Sm, scala media; 2’, membrane of Reissner ; B, B, basilar
membrane.

firm membrane—the membrana tectoria ». Corti—which perhaps acts as a
damper, and which arises from the labiwm vestibulare of the lamina spiralis
ossea. The whole extent of the basilar membrane consists of clear thread-
like and very elastic fibres, of which about 16,000 to 20,000 can be made out
in Man.

A true pinna or auricula (Fig. 188), attached to the border of
the external auditory meatus and projecting freely from the head,
occurs in Mammals only (comp. p. 229). It is supported by
cartilage, and the intrinsic and extrinsic muscles in connection
with it are supplied by the facial nerve.

The pinna arises from a series of rounded eminences on the first
and second visceral arches, around the hyoid (spiracular) cleft, the lower
part of which closes up, while the upper part gives rise to the external

234 COMPARATIVE ANATOMY

auditory meatus. These auricular eminences unite to form a nearly con-
tinuous ring, on which are later formed the characteristic protuberances
known as the helir, anutihelir, tragus, and antitragqus. The variations in the
form of the pinna which are seen in various Mammals concern essentially the
later formed portion which projects upwards and backwards from the head
(Fig. 188).

Fic. “88.—THe Pinna or Various PRIMATES.

In A, the shaded portion (b) represents the zone of the auditory eminences of the-
embryo, the unshaded that of the later formed auditory fold. B, Man,
Baboon and Ox, drawn to the same scale and superposed : »’, s,s, spina or
tip of theear. C, Macacus rhesus, with upwardly directed tip ; and D, Cerco-
pithecus, with backwardly directed tip. EK, Man: the muscles are indicated
as follows—m.a, attolens auricule ; m.a’, antitragicus ; m.t, tragicus ;
md’, inconstant muscle, extending from the tragicus to the margin of the:
helix ; m.h’, helicis major; m.h” helicis minor ; s, tip of the ear rolled over.

A-D, after Schwalbe ; Ei after Henle.

F. ORGANS OF NUTRITION.

ALIMENTARY CANAL AND ITS APPENDAGES.

The alimentary canal consists of a tube which begins at the
aperture of the mouth, passes through the body cavity (ccelome),
and ends at the vent or anus Its walls consist of several layers
(Fig 214,), of which the mucous membrane, lining the cavity of
the tube, and the muscular layer external to this, extend throughout
the canal. The mucous membrane consists of a superficial
epithelium and a deeper connective-tissue layer, the outer part
of which, or swb-mucosa, forms a loose network extending to the
muscular layer. The epithelium is derived from the hypoblast,
with the exception of that lining the mouth and anus (stomodewm
and proctodeum?) which is epiblastic in origin (p. 5). The con-
nective tissue and muscular layers arise from the splanchnic layer
of mesoblast of the embryo; and the muscular coat, consisting
almost entirely of unstriated fibres, supplied with nerves from the
sympathetic system, is, as a rule, divided into two layers, the inner
being constituted by circular, and the outer by longitudinal fibres.
These serve for the contraction or peristalsis of the wall of the gut,
and thus fulfil the double function of bringing the nutritive con-
tents of the latter into the closest possible relation with the whole
epithelial surface, and at the same time of removing from the body
the substances which have not been absorbed. Striated (voluntary)
muscular fibres, supplied by cerebral or spinal nerves, occur only at
the anterior and posterior ends of the canal.

An outer accessory serous coat, the perifonewm, encloses the
eut externally in the region of the celome. This is covered on its

‘In embryos of many Vertebrates (¢.g., Elasmobranchii, Amphibia), a pig-
mented ridge of cells is formed on the dorsal side of the gut in the head and trunk,
and gives rise to a rod lying close beneath the notochord. In certain cases it
remains for a time in connection with the gut by a series of segmental canals

which later disappear. The meaning and subsequent fate of this sub-notochordal

rod or hypochorda are not known. ;
* Phylogenetically the proctodeum is older than the stomodeum, and in many

Vertebrates it is derived directly from the blastopore.

236 COMPARATIVE ANATOMY

free surface by pavement epithelium, and, dorsally to the alimentary
canal, is reflected round the entire body-cavity, converting the
latter into a large lymph-sinus. A parietal layer, lining the body-
cavity, and a viscerl layer, reflected over the viscera, can thus be
distinguished in the peritoneum (Fig. 7). The part where one
passes into the other, which is thus primitively double, is called
the mesentery,' and this serves not only to support the alimentary
canal from the dorsal body-wall, but also to conduct the vessels
and nerves passing from the region of the vertebral column to the
viscera. With the lengthening of the alimentary canal during
‘development, the mesentery may give rise to a more or less com-
plicated system of folds in which the viscera are enveloped.

The most anterior section of the primitive alimentary tract
of the Ichthyopsida functions as a respiratory cavity as well as a
jfood-passage. A row of sac-like outgrowths, lying one behind the
other, are developed from the mucous membrane and eventually
anite with the ectoderm, apertures being formed to the exterior
(Fig. 189, A). Between the channels thus: formed, the visceral
arches (p. 69) are situated, and along the latter certain vessels
are formed by means of which a continual interchange of gases can
take place between the blood and the air contained in the water
passing through the sacs. In this manner the gills or branchie
(p. 273) arise. Even in the Amniota, although gills are not
developed, the larger portion of the cavities of the mouth and
pharynx lying behind the internal nostrils serves as a common air-
and food-passage until a proper palate (pp. 92, 202) is formed (Fig.
189, C).

With the formation of a definite palate (most Amniota), the
primitive mouth-cavity becomes divided into an upper respiratory,
and a lower nutritive portion—that is, into a nasal and a sccondury
or definitive mouth-cavity. The separation, however, is not a com-
plete one, the passage being common to both cavities for a certain
region (Fig. 189, D). This region, in all Vertebrates, is called
the pharyna, and in Mammals it is partially separated from the
mouth by a fibrous and muscular fold, the velwm palati, or free
edge of the soft palate?

The alimentary canal of Vertebrates is typically divisible into
the following principal sections (Fig. 190):—Jouth or oral
cavity, pharyna, gullet or wsophagus, stomach, small intestine, and
large intestine. The large intestine may communicate with a
cloaea, into which the urinary and genital ducts also open, or it
may open directly to the exterior. The small intestine may be
further differentiated into duodenum, jejeunum and ilewm, and the
large intestine into colon and rectum. A blind-gut or cacum is

1 In Murienoids, Dipnoans, and Lepidosteus, a rentral mesentery is also present,

but in Lepidosteus it only extends for a short distance along the hinder part of
the gut.

* A membranous velum palati exists in Crocodiles.

ALIMENTARY CANAL AND ITS APPENDAGES

lo
ww
-T

Ka
Vi

\3
-\G—-o

CA

Fic. 189.—DracRams oF THE ORAL Cavity sND PHARYNX OF A Fisit (A),

AMPHIBIAN (B), REPTILE OR Birp (C), anD Maw (D).

NV, external nostril; Ch, internal nostril; D, alimentary canal; A, gill-slits ;

L, lung; 7, trachea; O, cesophagus: the arrow marked A indicates the
respiratory passage, that marked B the nutritive passage ; |, the point where
the two passages cross one another.

238 COMPARATIVE ANATOMY

often present at the junction of the large and small intestine,
Between the stomach and duodenum as well as between the ileum

Fria, 190,—DIAGRAM OF THE ALIMENTARY CANAL oF May.

Gils, salivary glands ; Ph, pharynx ; Gl.ih, thyroid; G/.thy, thymus; Lg, lung;
Oe, esophagus ; Z, diaphragm ; J/g, stomach; Lb, liver; Pa, pancreas ;
Dad, small intestine ; Vir, ileo-colic valve ; Pr, vermiform appendix (caecum) ;
Ca, Ct, Cd, ascending, transverse, and descending portions of the colon; R,
rectum ; .4, anus.

and large intestine there is, as a rule, a marked elevation of the
muscular coat serving as a sphincter (pyloric and ilco-colte valves).
There is also a sphincter muscle at the anus.

TEETH 239

The small intestine is in most cases the longest section of the
alimentary tract: the bile and pancreatic ducts open into its
-anterior portion.

In almost all cases the alimentary canal becomes more or less
coiled, and thus presents a greater surface for absorption. Asa
general rule, it is relatively longer in herbivorous than in carni-
vorous animals. A considerable increase of surface also commonly
‘results from the elevation of the mucous membrane to form folds,
villi, and papille (p. 269).

Certain appendages are present in connection with the ali-
mentary canal. These are all developed primarily from the
hypoblast and are thus of epithelial origin: mesoblastic elements
are added to them secondarily. Whether they function as
glands throughout life or not, they are all formed on the same
type as glands.

Beginning from the mouth the following appendicular organs
may be distinguished (Fig. 190) :—

(1) Mucous and salivary glands.
(2) The thyroid.

(3) The thymas.

(4) The lungs or atr-bladder.
(5) The liver.

(6) The pancreas.

In addition to these, gastric and intestinal glands are embedded
in the wall of the gut.

Movurtu.

In Amphioxus the entrance to the mouth (oral hood) is pro-
vided with cirrhi, and in Petromyzon! it is surrounded by a ring of
cartilage (Fig. 54): all other Vertebrates are provided with jaws.

Definite lips provided with muscles first appear in Mammals,
but are wanting in Monotremes. The space between them and the
jaws is spoken of as the vestibulum oris; this may become
extended on either side to form cheeh-pouches, which serve as fooa
reservoirs (many Monkeys and Rodents). ty

The chief organs of the oral cavity are the teeth, the glands,
and the tongue.

Teeth.

The teeth are developed quite independently of the endo-
skeleton, and both epiblast and mesoblast take part in their forma-
tion (comp. p. 30). The first traces of the teeth are seen primarily

1 The mouth of the Lamprey serves as a suctorial organ for attaching the
animal to foreign objects. The larva: of Lepidosteus and Anura are temporarily
provided with suctorial organs

240 COMPARATIVE ANATOMY

in the form of superficial papille of the mucous membrane; but
secondarily, owing to want of space, the epithelium of the mouth
grows inwards so as to give rise to a dental lamina which becomes.
enlarged distally at certain points to form the so-called enamel-organs,.
These as they grow deeper into the mesoblast become bell-shaped, and
enclose moditied masses of connective-tissue, the dental papille ;
the upper cells of the papille, ze. those next to the enamel-organ
are known as odontoblasts (Fig. 191, A). The epithelial and con-
nective tissue germs come into the closest relation with one another

Fic. 191A.—DIAGRAM OF THE DEVELOPMENT OF a TOooTH.

EM, epithelium of mouth; SK, dental lamina; 7K, dental papilla; Ma, mem-
brana adamantina of enamel-organ ; O, odontoblasts; DS, dentine ; Bg, Bg,
connective tissue follicle or sac surrounding the tooth.

Fic. 191n.—SemiprackAMMatTic Ficurn or aA LONGITUDINAL SECTION THROUGH
A Tooru.

ZS, enamel; ZB, dentine; ZC, cement; PA1, aperture of the pulp-cavity (PH).

and give rise respectively to the calcified enamel and dentine (ivory),
of which the teeth are composed. The enamel is the harder and
contains little organic matter, and the dentine is permeated by a
system of fine canals in which are delicate processes of the odonto-
blasts. A third, bone-like substance, the cement, is also formed
round the bases of the teeth, and between the folds of enamel
when these are present; it may unite with the bones of the jaw.
The root of the tooth, embedded in the gums, is provided at its

TEETH 241

lower end with an opening leading into the central pulp-cavity
(Fig. 191, B), into which blood-vessels and nerves extend.

In most Vertebrates below Mammals all the teeth are essentially
similar in form (hemodont dentition): m Mammals, on the other
hand, they become differentiated into distinct groups (heterodont
dentition), known as incisors, canines, and check-teeth or grinders
(premolars and molars).

A succession of teeth takes place throughout life in almost all
Vertebrates except Mammals, in which there are very exceptionally
more than two functional sets, the so-called milh- or deciduous tecth
and the suecesstonal teeth. This difference is expressed by the
terms polyphyodont and diphyodont. (Comp. p. 245).

Fishes, Dipnoans, and Amphibians.—The homology and
similarity of the teeth with the dermal denticles of Elasmobranchs
has already been treated of (p. 30). The most primitive form of the
tooth is that of a simple cone, but even amongst Elasmobranchs,
in which the teeth are arranged in
numerous parallel rows upon the car-
tilaginous jaws, this form has already
become modified in various ways for
seizing or crushing the food.

Of those Anamnia which possess
a bony skull, four groups of tooth-
bearing bones may in general be dis-
tinguished, viz., (1) the mavxillary arch
(premaville and maxilla); (2) the
palatal arch (comer, palatine, ptery-
goid); (3) the (unpaired) puvrusphe-
noid: and (4) the mandibular arch
(dentary and splenial)t

True teeth are wanting in Cyclo-
stomes, and amongst cartilaginous
Ganoids they are absent in the ep oeiiee a reas Maes
adult Sturgeon, though rudiments (ye Ne in : conn en
are present in the embryo. Amongst _ parasphenoid.)

Teleostei they are wanting in the
adult Lophobranchii and in Coregonus. In the Cyclostomes they
are represented functionally by a number of conical horny teeth.?

In bony Ganoids and Teleosts, teeth may be present on all the
bones bounding the oral eavity, as well as on the hyoid and the
branchial arches (“pharyngeal bones”). In the latter position,
as well as on the parasphenoid, they often form brush-like
groups. In form the teeth may be cylindrical, conical, or
hooked; or they may be chisel-shaped (Scarus, Sargine),

1 The teeth of Elasmobranchs may be compared to (2) and (4) of these.

2 Structures bearing a superficial resemblance to vestigial true teeth are
recognisable beneath the horny teeth, but they possess no odontoblasts or
enamel epithelium.

R

242 COMPARATIVE ANATOMY

Fic. 193, A.—Tootn or Froc, axp 193, B, Salamandra atra.

ZK, crown; ZS, base; RF, circular furrow; S, apex, covered with enamel ;
PH, pwlp-cavity ; J, maxilla.

Fic. 193, C.—TRANSVERSE SECTION THROUGH PoRTION oF A TootH oF a Lasy-
RINTHODONT (Mastodousaurus). (After J. Storrie.)

C.c, central pulp-cavity ; 1, inflections of the enamel, surrounded by dentine,
which reach the centre (¢.c); 2, half-length inflections between 1; 3, short
inflections between 1 and 2.

resembling the incisors of Mammals, and working together like
scissors; in some Fishes they give rise to a definite pavement,
are rounded in form, and serve to crush the food. They may,

TEETH 243

again, be delicate and bristle-like (Cheetodon), or sabre-shaped
(Chauliodus).

In the Dipnoi (Fig. 62) the teeth are compound and exceedingly
massive, presenting sharp edges and points.

In the Amphibia there is in general a considerable diminution
in the number of teeth as compared with Fishes; and at the same
time a much more uniform character is noticeable in their form
throughout (Fig. 193, A, B). They are enlarged conically below, and
rest on a definite base, while above they become narrower and
slightly curved, ending either in a double (Myctodera, Anura), or
a single apex (Perennibranchiata, Derotremata, Gymnophiona); the
latter is the more primitive condition. The teeth lie deeply em-
bedded in the mucous membrane, and are present, as a rule, on the
premaxilla, maxilla, and mandible (except in Anura), as well as on
the vomer and palatine, but rarely on the parasphenoid (certain
Urodeles, Fig. 192) ; in the larvee of Salamanders and in Proteus the
splenial of the lower jaw is also toothed. Horny teeth and horny
jwws, developed entirely from the epidermis, are present in larval
Anura, and similar structures occur in Siren lacertina.

Teeth are altogether absent in the Bufonide and in Pipa.

The teeth of certain of the Stegocephala (Labyrinthodonta)
were extremely complicated, the enamel appearipg as numerous

corrugated folds extending from the periphery towards the centre
(Fig. 198, C).

Reptiles and Birds.—Corresponding with the greater firm-
ness of the skull in Reptiles, the dentition is usually strongly
developed, and occasionally at the same time it is more highly
differentiated than in Amphibians. The teeth are either situated
upon a ledge on the inner side of the lower jaw, with which they
become fused basally (pleurodont dentition—most Lacertilia); or
they lie on the free upper border of the jaw (acrodont dentition-—
Chameleon); or finally ,as in Crocodiles and numerous fossil Reptiles,
they are lodged in alveoli (thecodont dentition) (Fig. 194, A, a, }, ¢).
Both upper and lower jaws, and occasionally the palatine and
pterygoid also, are toothed (Lizards and Snakes) ; and in Hatteria,
vomerine teeth may also be present. The teeth are usually conical
and more or less pointed, but in Lizards the apex is double, and in
many Reptiles (¢.g., Paleohatteria, Hatteria, Uromastix spinipes,
Agamz, and numerous fossil forms, especially the Theriodontia of
the Trias of South Africa), a heterodont dentition is already indi-
cated. Almost all Reptiles are polyphyodont.

In poisonous Snakes a varying number of maxillary teeth are
differentiated to form poison-fangs. Thus in the common Viper
(Pelias berus) there are on each side ten poison-fangs arranged
in transverse rows ; the stronger ones project freely, while the lesser,
reserve teeth lie within the gum (Fig. 195, A); only one of these
teeth, however, is firmly fixed to the maxilla at a time. Each fang

R 2

244 COMPARATIVE ANATOMY

is perforated by a poison-canal, which is incompletely surrounded
by the pulp-cavity, the latter having the form of a half-ring in

Fic. 194.—A, Dracrams or TRANSVERSE SECTION THROUGH THE JAWS oF
REPTILES, SHOWING PLEURODONT (a), ACRoDONT (+), AND THECODONT (c)

Dentitions. B, a, Lowrr Jaw or Zootoca vivipara; b, or Anguis fragilis,.
(After Leydig. )

transverse section (Fig. 195, B, C,): the duct of the poison-gland
passes into an aperture at the base of the tooth which leads into.

Fic. 195.—FicurEs oF THE PoIsoN-FANGS OF A VIPERINE SNAKE.

A, skull of Rattlesnake ; B, transverse section through about the middle of the:
poison-fang of Viper ammodytes ; C, transverse section through the poison-
fang of Vipera ammodytes near its distal end. (B and C after Leydig.)

Gz, poison-fang ; Rz, reserve fangs ; GC, poison-canal ; PH, pulp-cavity.

the poison-canal, and the latter opens at a short distance from the-
apex of the tooth (see the course of the arrow in Fig. 195, A).

' TEETH 245

Between the ordinary teeth of Snakes and the poison-fangs with closed
canals, there are numerous intermediate forms in which certain of the teeth
are simply grooved along their anterior side. A similar condition is also
seen in the teeth of the lower jaw of a poisonous Mexicam Lizard (Heloderma).
(Comp. p. 252.)

A peculiar tooth is present in the embryos of Lizards and some Snakes.
It projects considerably beyond its neighbours, and lies in the median line of
the lower jaw, extending vertically towards the snout and serving the young
asa means of breaking through the parchment-like egg-shell. This must
not be confounded with the horny ‘‘neb” in Crocodiles, Chelonians, Birds,
and Monotremes amongst Mammals, which is of a purely epithelial nature.

Chelonians, like existing Birds, are provided with horny sheaths
to the jaws instead of teeth. The presence of teeth in the embryo
of Trionyx, as well as of a rudimentary dental lamina in embryos of
Chelone and Sterna, for example, proves, however, that this is only
a secondary condition.

In the cretaceous Birds of N. America (Odontornithes) teeth were
present, and were either situated in a definite alveoli (Ichthyornis),
or simply in grooves (Hesperornis). The premaxille were tooth-
less, and seem to have possessed a horny beak. The single-pointed,
smooth teeth of Archaeopteryx were probably situated in alveoli.
It is possible that some of the Eocene Birds (c.g. Argillornis,
Gastornis) possessed teeth.

Mammals.—-The heterodont dentition characteristic of the
Mammalia as a Class must have arisen by a modification of a
simple homodont condition, in which the teeth were all conical
and of similar size and shape. Side by side with this modifi-
cation, a shortening of the jaws has usually taken place, and
the teeth serve not only to seize and bite the food, but also to
masticate it and to test its qualities. The frequent presence of
rudimentary, functionless teeth, renders it probable that in the
course of phylogenetic development the teeth have undergone a
decrease in number. An increase in number, such as is met with
in toothed Whales, is due to the separation, during ontogeny, of
the component cusps of complex teeth, and is therefore not a
primitive, but a highly specialised condition.

As already mentioned, the succession is nearly always reduced
to two functional sets, the so-called mlk or decidwous tecth and the
successional or permanent teeth, and in some cases (see p. 249) even
one of these may be rudimentary. Traces, however, of an earlier
set occur in certain Mammals: this may be spoken of as a “ pre-
milk dentition.” Occasionally also (e.g., in Man) one or more
teeth appear which replace the corresponding “ permanent” teeth
and thus indications of four—and possibly even of five—sets can
in all be recognised.

In each of the two functional sets, tcisors, canines, and cheek-

1 The last molar of Man, or so-called ‘‘ wisdom-tooth,” seems to be gradually

disappearing ; it appears last and is lost first, and often does not reach the
grinding surface. In many cases also the outer upper incisors are wanting.

246 COMPARATIVE ANATOMY

teeth, or grinders, can as a general rule be distinguished. The
teeth which replace the milk-grinders are distinguished as premolars
from the molars, which are situated further back in the jaw and
have no predecessors.'

All the teeth are imbedded in well-developed alveoli of the
jaw-bones, the upper incisors being situated in the premaxille, the
upper canines and cheek-teeth in the maxill, and the lower teeth
in the mandible (dentary). The canine, which corresponds to a
specially differentiated premolar, and is most characteristically
developed in Carnivora, lies in a more or less continuous series
with the incisors. The premolars follow behind the canine, the
space usually present between them being called the diastema, and
then come the molars. The primary arrangement of the teeth is
such that there is an alternation between those of the upper and
lower jaw: thus the teeth in one jaw do not usually correspond in
position with those of the other, but with the interspaces between
them.

In some cases the enamel-organ persists in all the teeth,
which then continue to grow throughout life (@¢g., Lepus); in
others this is true of the incisors only (eg., numerous Rodents,
Elephant); but more usually growth ceases after a certain time,
and the teeth then form definite fangs or roots, each perforated by a
small canal communicating with the reduced pulp-cavity.

The incisors are usually chisel-shaped, while the canines, in
those cases where they are most characteristically developed
(Carnivora), possess a pointed, conical form, and are more or
less curved. The cheek-teeth either possess sharp, cutting crowns
(e.g., Carnivora), or the crowns are broad and more or less flat and
tuberculated, and adapted for grinding the food. In the latter
case the relations of the enamel, dentine, and cement are such as
to produce an uneven surface with wear, showing a characteristic
pattern in the different groups (Figs. 196—200).

The relations and number of the tubercles—which may be conical (e.g., Pig)
or crescentic (e.g., Horse, Ruminants, Fig. 199), as well as the form of the
teeth in general, is of great importance in elucidating the ancestral history
of the Mammalia, and attempts have been made to trace the evolution of
the various forms of molar met with in the Class. According to one view
the tuberculated molar has arisen by the gradual modification of a single
conical tooth, which has produced lateral outgrowths or buds. Thus taking the
simple conical form such as exists in toothed Whales as the most primitive
form of mammalian tooth, we find that certain extinct Mammals (¢.g., Trico-
nodon) possessed teeth with a main cone and two lateral cusps. It has been
supposed that the more complicated forms have been derived from this
triconodont tooth—firstly by a rotation of the lateral cusps outwards in the
upper, and inwards in the lower tooth, thus forming a trituberculur tooth,
with three cusps arranged in a triangle ; and secondly by the addition of other
cusps, the first to appear being the posterior heel or talon.

Another hypothesis is that the mammalian cheek-teeth were primarily

‘Tt must, however, be remembered that in some cases the so-called pre-
molars have no predecessors (see p. 249).

TEETH 247

Fic, 197.—DEntirion or THE HepGEnoe (Erinaceus ewropwus).
(The teeth of both jaws from the side, and those of the upper jaw from below.)

2, incisors ; v, canines ; pm, premolars ; m, molars.

multitubercular, having originated by the fusion of a number of simple coni-
cal teeth ; and certain facts in their development and the presence of multi-
tuberculate Mammals in the Triassic rocks, as well as a comparison with
the massive teeth met with in various Fishes for example, seem to sup-
port this view. The resulting decrease in number is compensated for by the
greater perfection of the individual teeth,

248 COMPARATIVE ANATOMY

Fic. 198.—DENTITION OF THE PORCUPINE (Hystrix hirsutirostris).

Fic. 199.—DeEnTITION oF SHEEP (Oris aries).

(References as before, but in Fig. 199 the teeth of the lower instead of the
upper jaw are figured from the surface. )

TEETH 249

The limitation of the succession to two or even one functional
set is probably due to the concentration of several successive
generations of teeth in correspondence with the higher develop-
ment of the individual tooth. This concentration is most marked
in Marsupials,in which only a single tooth, usually described as the
fourth premolar, has a predecessor. Differences of opinion exist as
to whether this tooth is to be regarded as the last remains of the
first or of the second set, or whether it belongs to the same series
as the others and is only retarded in development. The fact that

Fic. 200.—Drntition or A CATARRHINE Monkey (Nasalis larvatus).

References as before.

in toothed Whales the milk-teeth persist and the second set is
only represented in rudiment, seems to indicate that the teeth cf
Marsupials, except the fourth “ premolar” belong to the first set,
and that the milk dentition of Mammals is not a secondary acqui-
sition. In other words, the primitive Mammalia were at least
diphyodont, and the apparent monophyodont condition seen (¢.., in
toothed Whales) is a secondary condition. In the placental Mammals
the second dentition becomes of greater importance than the first.’

1In many instances, however, the first premolar appears to belong to the
milk dentition, and this may possibly be the case as regards the molars also.

250 COMPARATIVE ANATOMY

In describing the teeth of a Mammal it is convenient to make use of a
dental formiala in which their number and arrangement .can be seen ata
glance, the teeth of one side only being represented. Thus the adult dental
formula of those animals, the teeth of which are represented in Figs. 196 to
200, would be—

Fig. 196. Dog, i = 42
,, 197. Hedgehog, gh = 36
», 198. Porcupine, a = 20
,, 199. Sheep, ee = 32

O° 1s s 3
;, 200. Catarrhine Monkey, 575 er 32

The most complete pseu is seen amongst Marsupials, the dental formula
*1°3°5o0r6
of Myrmecobius lad = 5575S one 50-52. The more typical arrange-

. Bala 3 Pr
ment 18 5-7 -9-3 = ‘

Sexual differences in dentition exist in a number of Mammals. Thus in
the male Wild Boar, Narwhal (Monodon), Dugong (Halicore), and Musk-deer
a modification of certain of the teeth (the canines or the incisors) to form
tusks occurs, and these serve as fighting weapons. In the Elephant and
Walrus tusks are present in both sexes: in the former they correspond to
incisors, and in the latter to canines.

In Ornithorhynchus the teeth become replaced functionally after
atime by the development of horny masticatory plates, and in
Echidna they are wanting altogether. Adult Whalebone Whales and
certain Edentates (Myrmecophaga, Manis) are toothless, but rudi-
ments of teeth exist in the embryo. In other Edentates the teeth
are wanting in enamel. Canines are absent in certain Mammals
(eg., Rodents) and the incisors may also be wanting. In the
typical Ruminants incisors and canines are present in the lower
jaw only,

Glands of the Mouth.

The glands of the mouth, like those of the orbit and integu-
ment, appear first in terrestrial Vertebrates, that is, from Amphi-
bians onwards, They have the function of keeping moist the mucous
membrane which comes into contact with the outer air. From
being at first almost entirely unspecialised, and giving rise simply
to a slimy fluid, they become differentiated later into structures the
secretions of which take on a very important function in relation to
digestion ; they may also, as in the case of poisonous Snakes and
Lizards, constitute dangerous weapons of offence.

With their gradually increasing physiological importance a

' Horny crushing plates are also present in the Sirenia, the existing forms of
which possess numerous teeth, while the extinct Rhytina was toothless.

GLANDS OF THE MOUTH 251

greater morphological complication both as regards number and
arrangement takes place. Their histological character also
becomes changed in such a manner that the most varied forms
of glands may he recognised.

Amphibians.—With the exception of the Perennibranchiata
Derotremata, and Gymnophiona, a tubular gland becomes developed
in all Amphibia from the anterior portion of the roof of the mouth
(comp. Fig. 160), the main mass of which in Urodeles lies in the
cavity of the nasal septum or premaxilla (intermawillary or inter-
nasal gland). In Anura its position is more anterior than in
the Urodela, and it is more largely developed; but in both cases
the ducts open on to the anterior part of the palate.

In Anura there is a second gland (pharyngeal gland) present in
the region of the internal nostrils, the secretion of which passes
partly into the latter and partly into the pharynx.

Numerous gland-tubes are also present in the tongue of
Amphibians, and in the Gymnophiona oral glands are abundant.

Fria, 201.—Tur Porson-APPARATUS OF THE RATTLESNAKE.

S, the fibrous poison-sac, which is surrounded by the constrictor-muscle, Mec .'at
Mc! an extension of the latter towards the lower jaw can be seen; Gc, the
duct arising from the poison-gland, which passes into the poison-fang at +;
the latter is embedded in a large sac of the mucous membrane, 7; Am,
masticatory muscles, some of which are seen cut through at * ; posterior to
this the cut edge of the scaly integument is seen ; .V, external nostril; 4,
eye displaced towards the antero-dorsal aspect ; z, tongue ; z«, aperture of the
poison-fang.

Reptiles.—The mouth-glands in Reptilia show an advance on
those of Amphibia inasmuch as they are separated into groups.
Thus not only is there a palatine gland, homologous with the
intermaxillary gland, but lingual and sublingual, as well as upper
and lower labial glands are present. Chameleons and Snakes
are distinguished by a remarkable richness in glands, which
become most specialised into definite groups in the latter. In
poisonous Snakes the poison-gland becomes differentiated from
a portion of the upper labial gland. It is enclosed in a strong

252 COMPARATIVE ANATOMY

fibrous sheath, and is acted upon by powerful muscles, so that: its
secretion can be poured with great force into the duct (Fig. 201),
and thence into the poison-fang (p. 243).

The sublingual gland of a Mexican Lizard, Heloderma, has a similar
poisonous nature. ‘The secretion passes out through four ducts, which
perforate the bones of the lower jaw in front of the grooved teeth (p. 245).

In marine Chelonians and Crocodiles there are no large glands united
into groups connected with the mouth.

Birds.—In Birds, and more especially in climbing Birds
(Scansores), a well-developed lingual gland is present opening on
the floor of the mouth, as weil as a gland at the angle of the
latter. There is no doubt that the lingual glands are homologous
with those of Lizards, but it is not known whether the gland at the
angle of the mouth corresponds with the posterior upper labial
gland of Reptiles—that is to the poison-gland of Snakes. The
palatine glands of Birds are not homologous with those of Reptiles
and labial glands are wanting.

Mammals.—Three sets of salivary glands may be distin-
guished in connection with the mouth in Mammals, which are
called, according to their position, (1) parotid, (2) submaxillary,
and (8) sublingual. Each of the two former of these opens into
the mouth by a well-detined duct, that of the sublingual having
several independent ducts. A special retrolingual portion usually
becomes differentiated from the sublingual gland and commu-
nicates with the submaxillary duct.

The parotid is usually situated at the base of the external
ear: its origin is not known. The submaxillary is a compound
gland, consisting of glandular elements which differ from one
another histologically : it lies beneath the mylohyoid muscle, close
to which the retrolingual gland is also situated; the latter is
wanting in only a few Mammals (c.g., Rabbit, Horse). The sub-
lingual gland extends between the tongue and the alveoli of the
teeth, and is rarely absent (¢.g., Mouse, Mole).

With the exception of the parotid, all these glands, together
with certain smaller and less important ones, are homologous with
the oral glands of lower Vertebrates.

Salivary glands are wanting in the Cetacea.

Tongue.

Fishes.—The tongue is, as a rule, rudimentary in Fishes, and
is simply represented by a fold of mucous membrane covering the
basi-hyoid, which in all the higher Vertebrates serves as a point of
origin for many of the lingual muscles. Except in Cyclostomes,
where it has to do with the suctorial apparatus, the tongue of

TONGUE 253

Fishes is not capable of movement apart from the visceral
skeleton, and is wanting in a proper musculature. It is provided
with papille and serves only as a tactile organ, or, when provided
with teeth (¢y., certain Teleostei, Fig. 60), as a prehensile organ
also.

In Dipnoans the tongue is not more highly differentiated
than in many Fishes.

Amphibians.---In the Perennibranchiata (¢.g., Proteus) there
is a little advance on the condition seen in Fishes, but in all other
Amphibia except the Aglossa (Pipa and Xenopus), in which it has
become degenerated, the tongue reaches a higher stage, owing to
the development of definite muscles which render an independent
movement of the organ possible,
as wellas of glands. The tongue,
moreover, is relatively larger,
and the numerous papille render
the surface velvet-like. Its
mobility varies greatly in the
different forms. It is usually
attached only by the anterior
end or by a portion of its ventral

surface (Fig. 202): in other cases fe nea pea
it is free all round, and in IG. 2U2.— HF IGURE SHOWING THE LONGUE

; OF THE FRoG IN THREE DIfFERENT
Spelerpes (Fig. 208) is capable — Posrrioys.

of being extended far out of the
mouth by means of a complicated mechanism, similar to that
which occurs in the Chameleon amongst Reptiles.

Fic. 203.—Hrap or Spelerpes fuscus, Witt THE ToNGuE EXTENDED.

Reptiles.—In most Reptiles the tongue is usually freely
moveable, but its form and relative size varies greatly! (Fig.
204, A to E). It is provided with numerous sensory organs,
but no glands are present in the tongue itself. It is least mobile
in Chelonians and Crocodiles: in Snakes and many Lizards it is
forked at the apex, and in the Chameleon it is protrusible, as in
Spelerpes.

Birds.—The tongue of Birds is usually poorly provided with
muscles. It possesses a horny covering, usually provided with
papille and pointed, recurved processes; it may, as in many

1 Thus in Lizards the tongue is used for classificatory purposes ( Vermilinguia,
Crassilinguia, Brevilinguia, Fissilingura). :

COMPARATIVE ANATOMY

to
or
rae

Fie, 204,—A, Toxavr, Hyoip Aprparatvs, AND BRoNcHI oF A GEcKo (Phylo-
dactylus europeus) + B, Toncve or Lacerta; C, oF Monitor indicus; D, OF
Emys europea; KE, oF AN ALLIGATOR.

Z, tongue; ZK, body of hyeid; TH and HZ, anterior and posterior cornua of
hyoid; A, larynx; 7h, thyroid; 7, trachea; B, bronchi; Lg, lung: WV,
mandible ; L, glottis; ZS, sheath of tongue.

THYROID 255

Reptiles, be split up at its distal end, being either bifurcated
(Trochilidze) or having a brush-like form. In Woodpeckers (the
extraordinarily developed epibranchials of which have already been
mentioned in the chapter on the skull), the tongue may be thrown
far out from the mouth by means of a complicated system of
muscles, and it thus serves as a prehensile organ.

The tongue is largest in predatory Birds (Rapaces) and Parrots, but its
size is here not due so much to the special development of muscles as to the
presence of fat, vessels, and glands.

Mammals.—The tongue reaches its most complete morpho-
logical and physiological development in Mammals, and, as else-
where, undergoes the most various modifications in form. It is
as a rule flat, band-like, rounded anteriorly, and extensile. In-
trinsic as well as extrinsic muscles are well developed. A fold,
the so-called sublingua (plica fimbriata), is present on the lower
surface of the tongue, and is especially well marked in
Lemurs; in the Slender Loris (Stenops) it is supported by carti-
lage. This probably corresponds to the last vestige of the tongue
of lower Vertebrates which has been replaced by the more highly-
developed organ characteristic of Mammals. ‘The latter has pro-
bably arisen from the posterior part of the degenerated sublingua.

THYROID.

The thyroid arises primarily as a median ventral diverticulum

of the pharynx in the region of the first four or five visceral clefts,
and in the course of development may become subdivided into two
lobes. In addition to this unpaired diverticulum, paired portions,
situated more posteriorly, are developed in Mammals.
- Inthe Ammoccete the single diverticulum, which is lined by a
ciliated epithelium, opens into the pharynx between the third and
fourth clefts (Fig. 221), but in the adult Petromyzon the organ,
as in all Vertebrates, loses its connection with the pharynx, under-
goes a modification, and gives rise to numerous closed glandular
vesicles enclosing an albuminous substance. ‘

In Elasmobranchs the thyroid is unpaired and lies beneath the
mandibular symphysis; in adult Teleosts it is paired, and is
situated in the region of the first branchial arch. In Dipnoans it
lies anteriorly to the muscles of the visceral skeleton and shows an
indication of a division into right and left lobes.

In the Urodela and Anura the thyroid gives rise to numerous
vesicles situated close to the anterior end of the pericardium,
posteriorly to the second ceratobranchials in the former and on the
ventral side of the posterior cornua of the hyoid in the latter.

In Lizards it is usually situated close to the trachea (Fig.
204, a), and in Chelonians and Crocodiles it often possesses right

256 COMPARATIVE ANATOMY

and left lobes lying on the great vessels just after they leave the
heart. In Birds (Fig. 205) the organ is paired, and lies close to
the origin of the carotid arteries.

The thyroid of Mammals consists of two lobes often connected

Fic. 205.—Tuymus anp THynkorb
or A Younu SToRK.

7’, trachea ; B, bronchi; Oe, ceso-
phagus; 7, heart; 7'm, thymus;
Tr, thyroid.

by a median isthmus, situated on
the ventral side of the larynx and
trachea (Fig. 190).

It appears probable that the
thyroid represents a very ancient
glandular organ, the secretory func-
tion of which in relation to the
alimentary canal was of great im-
portance in the ancestors of Verte-
brates. In existing forms it has
undergone a change of function, and
thus instead of disappearing, remains
as an important organ in the adult:
in Mammals especially it is charac-
terised by a great richness in blood-
vessels. What this function is, is not
thoroughly understood, but it has
been shown that its albuminous
secretion contains iodine, and is
passed into the blood- and lymph-

_ vessels; and that extirpation of the

organ is followed by various distur-
bances of the mental and organic
functions.

The structure known as the ‘‘ carotid
gland” in Mammals, which is situated at
the bifurcation of the common carotid into
external and internal carotids, has not, as
was formerly supposed, anything to do with
the thyroid or thymus. It is abundantly
provided with nerve-cells.

THYMUS.

The thymus has always a paired
origin, and in the adult consists of
lymphoid tissue. In Elasmobranchs
it arises on either side from the epi-
thelium lining the upper part of
the first five gill-clefts, close to the
ganglia of the ninth and tenth cere-

ral nerves, as well as in the neigh-
bourhood of the spiracle. The func-
tion of this organ, though doubtless
averylmportant one, is not understood.

(ESOPHAGUS, STOMACH, AND INTESTINE 257

In Fishes and Dipnoans the thymus is more or less subdivided,
and is situated dorsally to the gill-arches. In Amphibians it
lies behind and above the articulation of the lower jaw, and in
Reptiles in the neighbourhood of the carotid artery, either close in
front of the heart (¢.g., Snakes) or more anteriorly. In Birds, as
in young Crocodiles, it is elongated and more or less lobed,
extending all along the neck (Fig. 205). In Mammals the greater
part of the thymus is situated in the thorax, between the sternum
and heart, only a small portion extending into the neck. It is
largest in young animals, and usually becomes more or less
completely degenerated subsequently.

(ESOPHAGUS, STOMACH, AND INTESTINE.

Ichthyopsida.—The cesophagus is short, and usually not
distinctly marked off from the stomach, though exceptions to this
rule often occur (¢.g., many Teleostei, Siren lacertina Fig. 210, A).

The stomach is often defined as a widened section of the
enteric canal situated between the posterior end of the gullet
and the entrance of the bile duct. Such a dilatation cannot
accurately be spoken of as a stomach unless its epithelium
possesses specific characteristics and gives rise to gastric glands
(p. 267); in this sense a stomach is wanting in Amphioxus, Cyclo-
stomi, Holocephali, certain Teleostei (¢g., Cyprinids, certain
Labride, Gobiide, Bleniide, Syngnathus acus, Cobitis fossilis),
and Dipnoi (Fig. 209). Whether this is a primitive character in.
these forms or is due to degeneration is uncertain.

In other Fishes (Elasmobranchs, Ganoids, numerous Teleosts),
as well as in all Amphibians, a true stomach is present, and is
usually externally recognisable as a more or less dilated sac; it
may be curved on itself, so as to form a U-shaped loop, the two
(cardiac and pyloric) limbs of which lie parallel to one another (Fig.
206). In general, its form is adapted to that of the body: thus
Rays and Anurans possess a far wider stomach than do most
other Fishes and Amphibians (comp. Figs. 206—210), and this rule
holds good also for Reptiles. The stomach of Teleosts varies con-
siderably in form.

The intestine may be straight or nearly straight, or may be
more or less coiled, and in the former case a spiral fold or valve
may be developed in Fishes, to increase the absorptive surface.

In the Lamprey a longitudinal fold or ¢yphlosole, taking a slightly
spiral course, extends into the lumen of the intestine. In Elasmo-

1JIn numerous Teleosts (e.g., Tinca vulgaris, Cobitis fossilis) outer longi-
tudinal and inner circular striated fibres are present in both stomach and intestine
externally to the unstriated muscular coat. They grow_ backwards from the

wsophagus.
iS)

COMPARATIVE ANATOMY

2

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(ESOPHAGUS, STOMACH, AND INTESTINE 259

branchs, Ganoids, and Dipnoans, the fold is more highly developed

and forms a well-marked spiral valve, the
turns of which may lie so close together
as to almost fill the cavity of the intestine
(Figs. 206, 207, 209). In the Ganoids it
begins to undergo degeneration; thus in
Lepidosteus (Fig. 207) it is only present
in the hinder part of the intestine.
Traces of a spiral valve can even be re-
cognised amongst the Teleostei (Cheiro-
centrus and possibly certain Salmonidee),

Pyloric ceca are met with in Ganoids
and numerous Teleosts, and consist of
longer or shorter finger-shaped processes
of the small intestine, situated posteriorly
to the pylorus in the region of the bile-
duet (Figs. 207 and 208). Their number
varies from 1 (Polypterus and Ammo-
dytes) to 191 (Scomber scomber). The
pyloric ceeca and spiral valve seem to have
a similar function, and, as a general rule,
to be developed in inverse proportion to
one another.

In the narrow-bodied Gymnophiona
the intestine is only slightly coiled, while
in Anura it becomes considerably folded
on itself: its form in Salamanders is about
mid-way between these two extremes.

In the Cyclostomi, Holocephali,
Ganoidei, and most Teleostei, there is
a separate anus; in all other Fishes as
well as in the Dipnoi and Amphibia the
large intestine opens into a cloaca common
to it and tothe urinogenital ducts. The
large intestine (rectum) is comparatively
short and takes a straight course; in
Amphibians, as well as to some extent
in certain Ganoids and Teleosts, it is
plainly marked off from the small
intestine, and between the two there is
often a circular valve. In some cases
the rectum is considerably swollen and
may even exceed the stomach in cap-
acity (Fig. 210, B). An outgrowth of
the ventral wall of the cloaca in Am-
phibia gives rise to the wrinary bladder,
and represents the allantois (p. 9) of
higher forms.

Fic. 207. —ALIMENTARY Vis-
CERA AND AIR-BLADDER OF
Lepidosteus, in situ. (After
Balfour and Parker. )

uw, anus; a@.b, air-bladder ;
a.b', its aperture into the
throat ; b.d!, aperture of
bile-duct into intestine ; ,
pyloric ceca; 9.b, gall-
bladder; hp.d, hepatic
duct ; 7r, liver ; py, pyloric
valve; s, spleen ; sp., spiral

valve ; st, stomach.

8 2

Fre. 208. Fie. 209.
Fic. 208.—ALIMENTARY CANAL OF PERCH.

Oc, esophagus ; J/, stomach ; t, cecal process of latter ; P—P, short pyloric
region ; Ap, pyloric ceca ; MD, small intestine ; HD, rectum ; A, anus.

Fic. 209.—ALIMENTARY CANAL AND APPENDAGES OF Protopferus annectens.
(After W. N. Parker.)

ws, cesophagus; st, “stomach”; py.r, pyloric valve; b.ent, bursa entiana
(anterior portion of intestine) ; sp.r, spiral valve ; re, rectum ; ¢/, cloaca ;
cl.c, cloacal cecum ; 7, vent ; a.p, abdominal pore; ood, base of oviduct ;
kd, base of kidney duct; /r, liver; g.b, gall-bladder ; h.d, hepatic ducts ;
cy.d, cystic duct ; 6.d, common bile duct, and b.d!, its aperture into the
intestine ; ¢.m.a, cceliaco-mesenteric artery ; m.a°, m.a’, mesenteric arteries ;
h.p.r, hepatic portal vein; sy, spleen. The pancreas is not seen, as it is
embedded in the walls of the “stomach” and anterior part of the intestine
on the dorsal and right side.

(ESOPHAGUS, STOMACH, AND INTESTINE 261

Fig. 2104. Fia. 210z.

Ftc. 210A, —ALIMENTARY CANAL oF Stren lacertina.

Oe, esophagus, marked off from the stomach (2/) by a constriction, + ; P, pyloric
region ; A/D, small intestine; LD, large intestine.

Fic. 210n.—ALIMENTARY CANAL OF Rana esculenta.

Oe, cesophagus ; VW, stomach; Py, pyloric region ; Du, duodenum; D, ileum; +,
boundary between the latter and the large intestine (2); A, opening of the
rectum into the cloaca (Cl); Hd, urinary bladder ; J/:, spleen.

In Elasmobranchs a finger-shaped rectal gland (processus digiti-
forms) opens into the anterior part of the rectum, and this perhaps
corresponds to the caecum of higher forms (see pp. 262, 266). Traces

262 COMPARATIVE ANATOMY

of a cecum are seen in certain Teleosts. In the Dipnoi a cloacat
czecum is present (Fig. 209).

In all Fishes in which a cloaca is absent (p. 259) the anus is
anterior to the urinogenital aperture.

Reptiles —In correspondence with the more definitely differen-
tiated neck, the cesophagus of Reptiles is relatively longer than in
the animals as yet considered; it is always plainly marked off
from the much wider stomach, which is usually sac-like, or bent
upon itself, in which latter case it lies transversely (Chelonians)+
As regards external form, the stomach of Crocodiles is more
specialised than that of other Reptiles, approaching that of Birds.

Snakes, Snake-like Lizards, and Amphisbeenians possess a
narrow, spindle-shaped stomach, which lies in the long axis of the
body; in correspondence with the large size of the masses of food,
which are swallowed whole, it is capable of great distension. In
these the intestine is only slightly coiled: in Lizards the coils
are more marked, and in the other forms, with broad bodies, the
folding is carried still further.

The large intestine has a straight course, is often considerably
swollen, and opens into a cloaca. It may (¢g., certain Chelonians)
be as long as the small intestine and be bent onitself. An account
of the urinary (allantoic) bladder present in many Reptiles will be
found in a subsequent chapter.

From the Reptilia onwards a blind-gut or cwewm is usually
formed at the anterior portion of the large intestine: it is
generally asymmetrical.

Birds.—In correspondence with the kind of nutriment, the
mode of life, and the absence of teeth, certain modifications of the
cesophagus and stomach occur in Birds. In graminivorous Birds and
Birds of Prey either the whole gullet forms a dilated sac or else it
gives rise to a ventral outgrowth; in both cases the enlargement
is known as the crop (inglwvies) (Fig. 211). This serves as a food
reservoir, and in some cases its walls are glandular.

The stomach, instead of remaining simple, generally becomes
divided externally into two portions, an anterior and a posterior
(Fig. 211). The former, which on account of its richness in glands
is called the glandular stomach (proventriculus), alone takes part
in dissolving the food; while the latter, which is lined by a horny
layer consisting of a hardened glandular secretion, has simply a
mechanical function, in correlation with which a peculiar and very
thick muscular wall provided with two tedinous discs is developed.
The degree of development of this muscular stomach, or gizzard,
stands in direct proportion to the consistency of the food. In

' The cesophagus of marine Chelonians, ‘like that of many Birds, is lined by
horny papillw.

CGSOPHAGUS, STOMACH, AND INTESTINE 263

graminivorous Birds we find the strongest muscular layer and the
thickest horny lining, while in the series of insectivorous Birds, up
to the Birds of Prey, this condition becomes gradually less marked,
and the division of Jabour is less noticeable.

Thus in the series of existing Birds we can

trace the course of the phylogenetic differ- ae
entiation of the organ.

The small intestine is usually of consider- |
able length and becomes folded on itself to
a greater or less degree; it varies, however, |
both in form, length, and diameter. As? |

The straight large intestine opens into a a4
cloaca, and varies as to its relative diameter. |
The cwcum is usually paired, and may reach i
a relatively enormous length (Lamellirostres,
Rasores, Ratitw). All kinds of imtermediate ee eee aa
stages between this and an entire absence |
of a cecum are to be met with. When 4, i
the eecum is largely developed, it has » -——S ~
an important relation to digestion, as an ee \ Wy
increase of surface of the mucous membrane \ oh
is thus effceeted; this increase may even be :
curied further by each caecum being provided — Fie. 211.-Dracram or

with a spiral fold consisting of numerous ae (Esornaces
. . AND TOMAC 2
turns, as in the Ostrich. Pa ne

The so-called bursa Fabricii is a structure

i : % 2 Od rer
peculiar to Birds, and arises as a small, Ge, (c', eezophagus s

Ig, crop; D&A, glan-

solid, epithelial outgrowth from the ectoder- dular stomach; ILM,
mal portion of the cloaca, later becoming muscular stomach ;

excavated to form a vesicle. It is situated AED, duodenum.

in the pelvic cavity between the vertebral

column and the posterior portion of the intestine, and extends to
the outer section of the cloaca, into which it opens posteriorly to
the urinogenital ducts. It is probably present in all Birds, but
becomes atrophied more or less completely in the adult; its physio-
logical function is quite unknown.

Mammals.—The cesophagus, like that of Birds, is sharply
marked off from the stomach, and its muscles consist to a greater
or less extent of striated fibres: in Ruminants the latter extend as
far as the stomach.

The stomach undergoes much more numerous modifications
than are met with in any other Vertebrate Class. As a rule it
takes a more or less transverse position and has a sac-like form,
the cardiac portion, into which the cesophagus opens. being usually
more swollen and having thinner walls than the pyloric portion
which communicates with the duodenum.

According to the definition given on p. 257, a true stomach is

264 COMPARATIVE ANATOMY

Fre. 212.—Dr1aGkams oF THE StoMAcH IN Various MAMMALS SHOWING THE
DirFERENT Recions. (After Oppel.)

A, ORNITHORHYNCHUS ANATINUS 3 B, Kancaroo (Dorcopsis /uctuosa) + C, TOOTHED
WHALE (Ziphius); D, Porpoise; EK, Horse; F, Pra; G, Hare; H, Han-
STER (Cricetus frumentarius).

(The «esophageal region (lined by stratified epithelium) is indicated by transverse
lines ; the region of the cardiac glands by oblique lines ; that of the fundus
glands by dots, and that of the pyloric glands by crosses. )

Ovs, wsophagus ; P, pylorus ; ), duodenum ; J—IV (in D), the four chambers of
the stomach ; / (in B), lymphoid tissue ; a...2 (in B), boundary line between
the «wsophageal and cardiac regions ; f(in H), fold bounding the wsophageal
region.

CSOPHAGUS, STOMACH, AND INTESTINE 265

wanting in Monotremes (Fig. 212, a): although the organ is
represented by a wide sac, it is entirely wanting in glands, and is
lined throughout by a stratified epithelium. This remarkable
condition is doubtless due to degeneration. Amongst Edentates,
a similar peculiarity is seen in Manis javanica—in which, however,
the glands are retained in a sac-like outgrowth from the greater
curvature, and in Sloths—in which the glands are more numerous.
In herbivorous Mammals the stomach is, as a rule, relatively
larger and more complicated than in carnivorous Mammals

Fic. 213.—Stomacu or SHEEP. (From Oppel. After Carus and Mito.)

a, ocsophagus ; 6. ¢, d, the three subdivisions of the paunch, marked off from one
another by the folds e and f; g, reticulum; h, cesophageal groove ; 7, psalte-
rium ; k, aperture leading from the psalterium into the abomasuin (/, mi) ; 1,
pyloric valve ; 0, duodenum.

(Figs. 212 and 213), and it may become divided into two or more
chambers. In some Rodents and in the Horse distinct cardiac and
pyloric chambers can be recognised, and in Ungulates numerous
intermediate forms between a simple and an exceedingly complex
stomach, such as occurs in the typical Ruminants, are to be met
with. In the latter (Fig. 213) the stomach is divided into four
chambers, which are called respectively rwmen (paunch), reticulin,
psalterium, and abomasum. The two first, which may be looked

266 COMPARATIVE ANATOMY

upon as parts of one and the same chamber, simply serve as storage
cavities, the food returning from them into the mouth, once more
to undergo mastication. It then passes into the psalterium, and
finally into the abomasum, the latter alone being provided with
gastric (rennet) glands, and serving as the true digestive stomach.
The psalterium is the latest to be differentiated both phylo- and
ontogenetically, and is rudimentary in the Tragulide. In Camels
the rumen gives rise to two masses of gland-containing outgrowths,
known as “ water-cells.” In the Cetacea (Fig. 212, c and D), Hippo-
potamus, and Bradypus, the stomach is divided into several chambers,
and various other modifications in form and structure are met with
amongst Mammals. Thus in the Kangaroo, for instance (Fig. 212,
B), the walls of the stomach are curiously folded.

The small intestine is usually long, and varies more as to rela-
tive length and diameter in domesticated than in wild forms,

The large intestine, which is made up of a varying number
of coils, usually reaches a great length, and its diameter is
much greater than that of the small intestine: these two por-
tions are thus sharply marked off from one another, and the
distinction between them is rendered still more marked by the
sacculations of the anterior part of the large intestine. Only the
posterior portion of the latter, or rectwm, which passes into the
pelvic cavity, corresponds to the large intestine of lower Verte-
brates ; the remaining and far larger part occurs only in Mammals,
and is called the colon.

The caecum, which is almost always present, undergoes various
modifications both as to form and size. Thus in Edentates (Manis,
Bradypus), Carnivora, Odontoceti, Insectivora, and Cheiroptera,
it is very small or even entirely wanting, while in Herbivora
it may exceed the whole body in length. An inverse development
in size is usually noticeable between it and the rest of the large
intestine. In many cases (many Rodents, Monkeys, and Man) an
arrest of a portion of the caecum takes place in the course of
individual development, so that little more than the distal end
(processus vermiformis) remains (Fig. 190). In Lepus the enor-
mous cecum is provided with a spiral valve; and in Hyrax, besides
a large sacculated caecum at the junction of the small and large
intestines, there is a pair of large, simple, conical ceca further back.

Monotremes only amongst Mammals possess a distinct cloaca,
though in Marsupials and some Rodents the anal and urinogenital
apertures are surrounded by a common sphincter. In other
ors these apertures become completely separated from one
another.

bo

6

oy

HISTOLOGY OF THE MUCOUS MEMBRANE

HISTOLOGY OF TRE MUCOUS MEMBRANE OF THE ALIMENTARY
CANAL.

The epithelium lining the alimentary canal of Vertebrates—with
the exception of that of the mouth and cloaca, which is usually
stratified—consists primitively, that is, phylogenetically, of amceboid
or cilated cells. In some cases this is also true ontogenetically, and
in Amphioxus and Protopterus, for instance, the ciliated epithelium
persists throughout life, and in the Ammoceete until metamorphosis.
In the adult Petromyzon, as well as in many Fishes and even Amphi-
bians, ciliated epithelium occurs constantly only in certain parts of
the gut, and in the higher Vertebrates cilia are only seen excep-
tionally after the embryonic period, so that, as a rule, only ordinary
columnar epithelium is present. A striated margin is observable
along the free border of the columnar cells (Fig. 214, a, B, @) ; this
is probably to be looked upon as the expression of the earlier
ciliated covering, and in some lower Vertebrates (¢.g., Proteus and
Salamander larvee) it is capable of an active amoeboid movement
(B, 0). In this active participation of the cells in the process of
absorption, we recognise an old inheritance from primitive Inver-
tebrates (intracellular digestion); but, at the same time, eatra-
cellular or chemical digestion is the more, important and occurs
exclusively in the higher types.

Numerous lymph-cells or lewcocyies (p. 299) are present in great
numbers in the connective-tissue layer of the mucous membrane,
and often form definite masses or follicles (¢.g., “ Peyer's patches ”).
Jn some cases (¢.g., Protopterus), the development of this lymphatic
tissue along the gut is relatively enormous (comp. p. 334). The
ameeboid leucocytes may even force their way into the lumen of
the intestine: a similar migration of these cells occurs in all
mucous membranes and in the walls of many vessels.

In Amphioxus, Cyclostomi, and Dipnoi, the whole of the
alimentary epithelium must be considered as secretory, each
individual cell acting as an independent gland. In Fishes,
Amphibians, and Reptiles, a higher stage is reached, masmuch
as groups of cells in the stomach gives rise to tubular glands of a
simple nature (Fig. 214)! A further differentation of the cells
leads to the condition seen in the gastric glands of Mammals, in
which the cells become differentiated into chief cells and parvetal cells.

According to their position, three kinds of glands can be dis-
tinguished in the stomach of Mammals, viz., cardiac, fundus-, and
pyloric glands. The fundus glands have the greatest physiological
importance (comp. Fig. 212).

In the higher Vertebrates, more especially in Buds and
Mammals, the epithelium of the intestine also gives rise to tubular

1 Even in Ganoids and Teleosts the cells of the neck and fundus of each gland
are said to be different in character, pepsin being formed in the latter.

268 COMPARATIVE ANATOMY

structures known as the crypts or glands of Licberktihn, as well ag
to acinous mucous glands. Mucous-secreting goblet cells are

By

H
i 1
! i
4 1

‘
4
'
1
1

Fru, 214.—A, SEMIDIAGRAMMATIC TRANSVERSE SECTION OF A PORTION OF THE
WALL or THE INTESTINE. (Combined from the condition seen in both lower
and higher Vertebrates.) B, Epithelial cells of the intestine.

P, peritoneal investment of the gut; J/, longitudinal muscular layer ; M?, circular
muscular layer ; Z, connective-tissue layer ; S, mucous membrane, which is
raised to form villi at Zo. (The connective-tissue layer and epithelium are
designedly drawn much too large relatively as compared with the outer
coats.) G', G, vessels, the larger trunks running between the peritoneum
and the muscular layer ; the finer vessels branch out into the intermediate
layer ; these surround the masses of lymph-cells, LL, as well as the glands,
and send fine loops into the villi (at G!); DD, apertures of the glands;
Ij, H, epithelial cells of the mucous membrane, with their striated border,
from which at Z! amceboid processes are extruded: in Fig. B, a, b, these
cells are drawn to a much larger scale (Sa, striated border); Ly, scat-
tered lymph-cells in the intermediate layer ; Z1, LZ, lymph-cells in the act of
passing through the mucous membrane; at L*, several have already passed
into the alimentary cavity ; ZL, masses of lymph-cells (solitary follicles) ;
Lym, lymph-vessels in the villi.

common throughout the alimentary epithelium of Vertebrates.
In Monotremes, as already mentioned (p. 265), gastric glands are
ubsent, but the intestinal glands are highly developed.

LIVER 269

In order to effect an increase of the absorptive surface, longi-
tudinal folds of the mucous membrane are formed, and a special
development of such a fold, taking a spiral course, may result in
the formation of a spiral valve (see p. 257). A further advance is
seen in the development of transverse folds between the longi-
tudinal ones—these are already seen in Elasmobranchs and many
other Fishes; and by still further modifications, crypts of varied

Fru. 215.—SEMIDIAGRAMMATIC FIGURES oF THE Mtcots MEMBRANE OF THE
INTESTINE OF FISHES, SHOWING INTERMEDIATE FORMS BETWEEN LOoNGITU-
DINAL FoLtps axp Rotnp Crypts.

A, Petromyzon, showing the distinct spiral fold; B, an Elsmobranch C to E,
various Teleosts.

form and depth are produced, into which open the microscopic
glands, when present (comp. Fig. 215).

Finger-shaped outgrowths or vi//i of the mucous membrane of
the intestine are first plainly distinguishable in Amphibians (espe-
cially Anura) and are especially well developed in Mammals.
In addition to these, folds of varied forms, on the surface of which
the villi may be situated, occur from the Amphibia onwards: as

examples may be mentioned the valvuli conniventes of Mammals
and Birds.

LIVER.

The liver, the form of which is always closely adapted to that
of the surrounding parts, underlies to a greater or less extent the
ventral side of the intestinal tract, and is present in all the Craniata.
It arises as an outgrowth from the endodermic epithelium of the
intestine close to the junction of the latter with the stomach.

In Amphioxus a simple sac-like cecum is present in this

0%
theet

Fic. 2164.—Liver or Rana esculenta. (From the ventral side.)

L, L}, L*, the different obes of the liver; J/, stomach ; Du, duodenum ;
HT, heart.

Fic. 2163.—Pancrpas AND Liver or Frog, To sHOW THE ARRANGEMENT OF
THEIR Ducts.

L, I’, L3, the lobes of the liver turned forwards; G, gall-bladder ; Dey, cystic
ducts, which, together with the hepatic ducts (Dh), form a network from
which three collecting ducts arise, and these unite to form the common bile-
duct (De): the latter passes through the substance of the pancreas (P),
receiving further hepatic ducts (Dh!), and the pancreatic ducts (P}); at
De! it becomes free from the pancreas, and passes back to open into the
duodenum (Du) at De?; Lhp, duodeno-hepatic omentum ; Mf, stomach ; Py,
pylorus.

LIVER 271

region which possibly represents the rudiment of the liver (Fig. 219).
In Craniates the outgrowth develops into a large vascular and
glandular organ, which gives rise to bile, and remains in communi-
cation with the intestine by means of one or more Dile-ducts}

Oe

Fig. 217.—Viscera or Lacerta agilis. (From the ventral side.)

Oe, esophagus; JA, stomach; J/D, small intestine; ED, large intestine; L,
liver; GB, gall-bladder; Pn, pancreas; B/, urinary bladder; Ly, Ly’,
the two lungs, with their network of vessels; H, heart; C'’, postcaval, 7'r,
trachea,

(Figs. 206, 209, and 216-218). Itis united to the body-wall by a fold
of the peritoneum, and varies considerably in the number of its
lobes: in Mammals there may be as many as six or seven (¢.9., Dog,
Weasel). We may nevertheless fix upon a ground-form consisting

1 The single-lobed liver of the Lamprey undergoes a histological retrogression

(fatty metamorphosis) after transformation. The tubuli disappear, the cells
become filled with fat, and the gall-bladder and bile-duct become atrophied.

2H2 COMPARATIVE ANATOMY

of two lobes as the primary one in all Vertebrates. The liver of
the Anamnia is usually relatively larger than that of the Amniota,

Carnivorous (fat-eating) animals generally possess a larger liver than
Herbivores.

A gall-bladder is very commonly present partially imbedded in
the right primary lobe. It is connected with the system of hepatic

Fic. 218.-— A, B, C, Various MopiricaTIONS IN THE ARRANGEMENT OF THE
BILE-DUCTS.

PD, duodenum; Vf, gall-bladder; ¢ and _s, cystic duct; h, hepatic duct; ch,
common bile-duct ; Ac, hepato-cystic duct ; he, hepato-enteric duct.

ducts by means of a cystic duct, thus forming a common bile-duct
which opens into the anterior part of the intestine (duodenum).
Some of the chief variations in the relative arrangement of these
ducts are shown in Fig. 218.

PANCREAS.

The pancreas arises from the proximal portion of the small in-
testine, near the liver, in the form of several (usually two dorsal
and one ventral) independent endodermic outgrowths: these may
become fused later, or certain of them may undergo degeneration.
Thus in the adult there may be a single duct, or several inde-
pendent ducts opening into the intestine (¢g., Birds, Crocodiles,
Emydee, and some Mammals) or in some cases into the bile-duct
(Fig. 216, 8), Varying much in form and size, the pancreas early
gives rise to a band-shaped or more or less lobulated organ, usually
lying in the fold of the duodenum. In some cases it remains em-
bedded within the wall of the gut (¢.g., Protopterus,! Fig. 209), and
amongst Teleosts (in which Order the pancreas was formerly sup-
posed to be absent in the adult) it may be surrounded by the liver
or have the form of scattered lobules extending throughout the
mesentery.

1In Myxinoids a lobular gland is present in a similar relative position to the
pancreas of Protopterus in the neighbourhood of the bile-duct, into which it
opens : this probably corresponds to a pancreas. A dorsal pancreas is also de-
veloped in the embryo of Petromyzon, and a pancreas-like organ can be recognised
in the adult. The pancreas is not represented in Amphioxus.

G. ORGANS OF RESPIRATION.

THE respiratory organs of Vertebrates are closely connected with
the alimentary canal both as regards position and development, and
are of two kinds, gills and lungs.! The former are phylogenetically
the older organs, and are adapted for aquatic respiration: they are
connected with the pharynx in the region of the visceral arches. The
latter always arise as sac-like outgrowths of the pharynx, which
grow backwards so as to lie within the body-cavity.

Both gills and lungs may be developed in the same individual,
but are usually not functional at the same time. They are sup-
plied with venous blood, which becomes purified while passing
through their capillaries.

The wir-bladder or swim-bladder present in many Fishes, and
acting as a hydrostatic organ (p. 280), arises in a similar manner to
the lungs—that is, as an outgrowth from the fore-part of the ali-
mentary tract: it receives arterial blood from the aorta, and
venous blood passes from it; but in some cases (¢.g., Bony Ganoids
and a few Teleosts) it may act as an accessory respiratory organ.

I. GILLS.

The gills arise in connection with a series of laterally-arranged
outyrowths of the pharynx lying one behind the other, which be-
come open to the exterior. Passages or clefts are thus formed for
the water entering by the mouth, and in order that oxygen may
become absorbed, leaf-like or thread-like vascular processes, the
gills or branchice, become developed in the region of each cleft.
These are internal or external, according to their position.”

Fishes possess gills throughout ‘life; amongst Amphibians this

1 The integument (e.g., in Periophthalmus and Amphibia) and the intestine
(e.g., in Callichthys, Hypostomos, and Doras) may also take part in respiration.
2 External gills persist after hatching as functional respiratory organs only in

Polypterus, Calamoichthys, Protopterus, and the Amphibia, and in the Anura
they are soon replaced by internal branchiz (comp. pp. 278—280).

T

COMPARATIVE ANATOMY

4

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GILLS 275

is only the case in the Perennibranchiata: all the others simply
pass through a gilled stage, and later breathe by means of
lungs. Thus the study of this one Order furnishes us with an
excellent representation of the course of phylogenetic development
through which all the higher Vertebrates must have passed, and
which is still indicated in them by the appearance in the embryo
of gill-clefts and gill-arches with a corresponding arrangement of
the blood-vessels. These occur throughout the entire series of
the Amniota up to Man—that is, in forms in which they are no
longer concerned in respiration.

Thus rudiments of five clefts are seen in the embryos of most Reptiles
and Birds, and of four in Mammals; in many cases, however, they do not
become open to the exterior. Their order of disappearance is from behind
forwards, and the most anterior (hyoid) cleft persists in a modified condition
even in the adult, undergoing a change of function in connection with the
auditory organ (p. 224). Certain of the anterior arches persist in a modified
form (p. 69).

Amphioxus.—The numerous (80—100, or more) gill-clefts of
Amphioxus, which are arranged in pairs and are supported by elastic
rods, extend backwards nearly to the middle of the body. At first
they open freely to the exterior, but at a later period of develop-
ment they become enclosed in an atrial or peribranchial chamber,
which opens by a single pore situated somewhat behind the middle
of the body (for details compare Fig. 219).

The relative extent of the branchial apparatus is considerably
limited even in the lowest Craniata.

Cyclostomes.—In the larval Ammoccete the cesophagus is
continued directly backwards from the pharynx (Fig. 220, A), and
at the anterior end of the latter there is a muscular fold, the velwm,.
covered by the mucous membrane (Fig. 221).

The seven gill-sacs provided with leaf-like folds of mucous mem-
brane which are present in the Ammoceete, persist in Petromyzon ;
but, with the formation of a suctorial mouth, the portion of the
cesophagus into which they open becomes closed posteriorly, and
the cesophagus apparently grows forwards above the latter, and
joins the mouth-cavity at the velum. Thus two canals pass back-
wards from the mouth, a ventral branchial or respiratory tube, and
dorsal cesophagus (Fig. 220, B).

In Petromyzon and Bdellostoma! the individual branchial sacs,
which communicate directly with the pharynx, open freely to the
exterior : in Myxine this original condition becomes modified by the
outer parts of the gill-passages growing out into long tubes, which

1 In Bdellostoma there are usually six or seven pairs of branchial sacs, and
behind these, on the left side, an wsophageo-cutaneous duct opens directly into the
pharynx, as is also the case in Myxine. Bdellostoma polytrema possesses thirteen
or fourteen pairs of gill-pouches. ‘

T

276 COMPARATIVE ANATOMY :

unite to form a common duct on either side; this opens far behind
the branchial apparatus on the ventral side of the body.

SN

SN

Fic. 220.—Driacram oF 4 LoNnGIruDINAL SECTION THROUGH THE HEAD oF
THE LaRVAL (A) AND ADULT (B) Pelromyzon.

Ep Jaf Ht

H
1 i}
‘ ki ,
rio
1 1
a eo,

Fig, 221.—LonciruDINaL SECTION THROUGH THE HEAD oF AN Ammocete.

V, velum ; P, papille of mucous membrane; K, K, K, three anterior gills ; Th,
thyroid (hypobranchial furrow); .V, nasal sac; *, communication be-
tween the ventricle of the olfactory lobe and that of the prosencephalon ;
Ep, epiphysis; Jnf, infundibulum; HH, metencephalon; J//, medulla
oblongata ; b, c, ventricles of the mid- and hind-brain; 0, subdural cavity ;
Ch, notochord ; R, spinal cord.

Fishes.—From the Elasmobranchii onwards, the gills are in
close relation with the visceral skeleton, and in these Fishes they
consist of closely-approximated transverse lamine (Figs. 222 A, 228),
which are firmly attached to both sides of the septa which separate
the individual gill-sacs from one another, so that each septum bears a
half-gill, or hemibranch, on both its anterior and posterior surface.
A gill, or holobranch, thus consists of the branchial arch plus the
posterior hemibranch of the sac in front of it and the anterior
hemibranch of the following sac. The gill-sacs, of which there are
commonly five, open separately to the exterior, and a rudimentary

1 There are six in Hexanchus and Chlamydoselache and seven in Heptanchus.

GILLS 207

gill-cleft known as the spiracle (p. 75), is as a rule present more
anteriorly, between the mandibular and hyoid arches. In the Holo-
cephali, however, the spiracle becomes reduced, there are only three
holobranchs in addition to hemibranchs on the hyoid and fourth

iri

A. B

Fic, 222.—Dissection of the head from the ventral side of A, an Elasmobranch
(Zygena malleus), and B, a Teleost (Gadus aeglefinus), to show the branchial
apparatus. In both figures the branchial arches on the left side are shown
cut through horizontally. (From R. Hertwig’s Zoology.)

Pq, palatoquadrate, and wu, its connection with the cranium anteriorly; wh,
lower jaw; m, oral cavity; prm, premaxilla; ma, maxilla; pa, palatine ;
hm, hyomandibular ; zs, internal branchial apertures ; as, external branchial
apertures ; ops, opercular aperture ; h, branchial septum; b/!, anterior, and b/?,
posterior hemibranch of a gill-pouch ; op, operculum; s, pectoral arch; =,
tongue ; phi, inferior pharyngeal bone ; 0, cesophagus.

branchial arch, and an opercular membrane is present, covering the
external branchial apertures and opening by a slit posteriorly ;
traces of a similar structure are seen in Chlamydoselache.

In Ganoids and Teleosts there are no longer chambered gill-
sacs. The septa on which the gill-lamine are borne become
greatly reduced, so that the apices of the latter extend freely out-
wards ; the whole branchial region is, moreover, covered over by the
operculum and branchiostegal membrane (comp. pp. 75 and 79),

278 COMPARATIVE ANATOMY

and thus, as in the Holocephali, the gill-slits open into a common
branchial chamber, which communicates with the exterior by a
single slit-like aperture on either side (Figs. 222 B and 223), A
spirazle is present in Acipenser, Polyodon,
and Polypterus amongst Ganoids.

As a rule Teleosts possess only four holo-
branchs,! and this holds good for all Ganoids.

A rudimentary gill or psendobranch is present
on the anterior wall of the spiracle of many
Elasmobranchs and of cartilaginous Ganoids
(mandibular pseudobranch) ; and the posterior
hyoid hemibranch, which is functional in Aci-
penser and Lepidosteus, becomes more or less
reduced in Ganoids and Teleosts, forming
the so-called opercular pseudobranch. Traces of
a cleft, lying behind the functional branchial
clefts, are found in the embryos of certain
Elasmobranchs. All these facts indicate that
Fishes formerly possessed a more extensive
branchial apparatus than at present.

Fic. 223. — TRANSVERSE
SECTION THROUGH A
HoLoprancu or Zyyena
(ON THE RIGHT) AND
Gadus (ON THE LEFT).
SticHtLy ENLARGED.
(From R. Hertwig’s
Zoology).

b, branchial arch; z, gill-

rakers; a, afferent,
and v, efferent branchial
vessels; 0/', anterior,
and b/?, posterior hemi-
branch of the gill; r,

In the Lophobranchii the gills are replaced
by tufted processes, and in many Teleostei
certain accessory structures are developed in
the region of. the branchial chamber by a modi-
fication of the branchial arches or cavities.
These serve to retain the water, and thus the
Fish is able to live for some time out of the
water (Anabas, Saccobranchus, Heterobranchus,
Clarias).

External gills are met with in young stages
of Elasmobranchii and Holocephali as well as
in Polypterus and Calamoichthys ; in Elasmo-
branchii and Holocephali, at any rate, they are
endodermal and not ectodermal in origin.

cartilaginous gill-ray; h,
septum. Fishes breathe by taking in water
through the mouth, and, by the con-
traction of the latter, forcing it out again through the gill-
slits.2 In this process the gill-arches rise and fall, separating
from one another during inspiration, and approximating during
expiration.

Dipnoi.—These, as their name implies, possess both gills and
lungs, only the latter organs being functional in Protopterus during
its summer sleep (see p. 17). Besides the internal gills, which
are covered by a small operculum, Protopterus possesses three pairs
of external gills situated just above the operculum and supplied by
vessels from the arterial arches. In Ceratodus, in which, as in
Lepidosiren, no external gills are present, there are four complete
gills on the first four branchial arches, as well as a pseudobranch

1 They may be reduced to three, or two, and even these may become more or

less rudimentary.

_. *In the Lamprey inspiration as well as expiration takes place through the
gill apertures when the animal is attached by means of its suctorial mouth.

GILLS 279
on the hyoid. In Protopterus and Lepidosiren a reduction of these
organs has taken place, gills being absent in the former genus on
the first and second branchial arches ; there is, however, in addition,
an anterior hemibranch on the fifth branchial arch.

Amphibia.—In the embryos of Urodeles, five gill-clefts can
usually be recognised, but the most anterior and posterior of these
do not become open to the exterior. In the larvae, as well as in adult
Perennibranchiates, there are three external gill-tufts in connection
with the three anterior branchial arches, lying one over the other ;

Fie, 224, A and B.—Larva or Lpicrium glutinosum, w1TH EXTERNAL GILLS.
(After Sarasin. )

these extend backwards, projecting freely to the exterior, and are
composed of connective-tissue, unsupported by cartilage. They
either have the form of tufts, or may be delicately branched,
showing the most varied arrangements for increasing the respira-
tory surface (comp. Fig. 224). These external gills are ectodermal
in origin, and must not be confused with the internal gills, which
are wanting in all Urodeles. They are acted on by a complicated
system of muscles, and are covered by ciliated epithelium, which
serves to keep up a continual current in the surrounding medium.
In the Axolotl and in larval Salamanders there are four, and in
Necturus (Menobranchus) and Proteus only two gill-clefts perfora-

280 COMPARATIVE ANATOMY

ting the pharynx. The former thus show a more primitive con-
dition, while in the latter these structures have become reduced.
There is always only a single external opening covered over by an
opercular-like fold of skin.

The usually feather-like external gills present at first in Anura
soon disappear, and their place is taken by internal gills, the epi-
thelium covering which is also said to be ectodermal in origin. By
the growth of the opercular folds, which contain no skeletal parts,
the external respiratory aperture of either side becomes gradually
reduced in size, and the two branchial chambers usually open
eventually by a single aperture, which is situated either in the
median ventral line, or laterally.

The larvee of the Gymnophiona also possess external gills, which
vary much in form in the different genera (Fig. 224).

In certain Batrachia in which there is no free larval stage it appears
that respiration may take place before hatching in the broad and vascular
tail (Hylodes martinicensis), in folds of the ventral body wall (Rana
opisthodon), or in peculiarly modified external gills (Nototrema.).

Except in the Perennibranchiata, the gills disappear at meta-
morphosis and the respiratory apertures close up. In the Derotre-
mata, however, the gill cleft between the third and fourth branchial
arches persists.

IJ. AIR-BLADDER AND LUNGS.
1. THE AIR-RLADDER.

As already mentioned (p. 273), the lungs and swim-bladder are
developed in a similar manner, and only differ from one another in
the fact that the lungs always arise from the ventral side of the
pharynx, while this is only exceptionally the case as regards the
air-bladder (¢.g., Polypterus, Calamoichthys), which usually arises
on the dorsal side. The exact point of origin of the air-
bladder from the alimentary canal varies, and its duct (ductus
preumaticus) may either remain open throughout life, as in all
Ganoids and some Teleosts (Physostomt), or it may later become
reduced to a solid fibrous cord or even entirely obliterated, as in
other Teleosts (Physoclisti). In the latter case there is no com-
munication between the swim-bladder and the external air, and it is
probable that the contained gas is given off from the walls of the
swim-bladder itself. A vascular organ (the so-called “rete mirabile”),
consisting of numerous glands and capillaries, is present in the walls
of the swim-bladder in the Physoclisti, and in certain Physostomi a

1 In Erythrinus it arises laterally, and in some Physostomi (e.g., Herring) it
opens further back into the stomach.

THE AIR-BLADDER AND LUNGS 281

somewhat similar organ (“red-body”) is present, but consists of
capillaries only.

The air-bladder lies above the peritoneum on the dorsal side of
the body-cavity, between the vertebral column, aorta, and kidneys
on the one hand, and the alimentary canal on the other: it is
invested by the peritoneum on the ventral side only, It is more
or less sac-like in form, and is
only exceptionally paired (Poly-
pterus); it usually extends along
the whole length of the body-
cavity, and its walls are composed
of connective, elastic,and muscular
tissue. In some Teleostei it is
transversely constricted so as to
form several successive divisions ;
in other cases it may give rise to
a more or less numerous series
of cwcal processes.! Its internal
surface may be either smooth or Fic. 225.—Inverna SURFACE OF THE
spongy (Fig. 225) owing to the AMADDER op | Luriposecs,
formation of a meshwork of
trabecule, the structure of which 4%, fibrous longitudinal band.
resembles that of the lungs of
Dipnoi and Amphibia, and as already stated, it has a respiratory
function in some cases.

An air-bladder is wanting in Cyclostomes and Elasmobranchs.

Attention has already been directed to the relations which often
exist between the air-bladder and the auditory organ (see p. 226).

2. THE Lunas.

The lungs arise at the hinder border of the branchial region of
the pharynx, which here becomes divided by a longitudinal hori-
zontal fold into a dorsal and a ventral portion, the latter of which
gives rise to a blind sac, opening anteriorly by a wide aperture into
the former and composed of endoderm surrounded by mesoderm (Fig.
226). A longitudinal vertical furrow is then formed, dividing this
primitive lung-sac into right and left halves: the narrower proximal
portions of these represent the primitive bronchi, which communicate
with the pharynx by a single tube, the primitive windpipe or
trachea. The proximal end of the latter usually becomes differen-
tiated to form a larynx, or organ of voice, which opens into
the pharynx on its ventral side by means of a slit-like aperture, the
glottis. The lungs are therefore phylogenetically older organs than

"In the Gymnodonts (e.g., Diodon, Tetrodon), the whole esophagus is capable
of great distension.

282 COMPARATIVE ANATOMY

the bronchi, trachea, and larynx, and this statement is supported by
a study of their comparative anatomy.

ges ~

Fic. 226.—A, B, C, Dracrams sHowING THE MopE or DEVELOPMENT OF THE
Lunes.

PD, primitive alimentary tube ; S, S$, the lung-sacs, which are at first unpaired ;
t, trachea ; b, bronchus.

S eoge

Fic. 227.—Diacram ILLustrRaTING THE PHYLOGENETIC DEVELOPMENT OF THE

Lunes; A GrapvsL INcREASE OF THE RESPIRATORY SURFACE IS SEEN IN
PASSING FROM A To D,

.. abe

Hollow outgrowths and buds arise from the endoderm of the
lungs and extend into the surrounding vascular mesoderm, which

Fic. 228.—Diacram oF THE Empryonic Human Lunu. (After W. His.)

Ap, pulmonary artery ; /r, air-passage; sp, cesophagus; /b, pulmonary vesicle
undergoing division; O, right upper (anterior) lobe of the lung with its
eparterial bronchus ; J/, V, middle and lower (posterior) lobes ; O!, left upper
lobe with its hyparterial bronchus ; V1, left lower lobe.

gives rise to muscular fibres and connective-tissue, and thus a
branched system of cavities communicating with the bronchi is

AIR-TUBES AND LARYNX 283

gradually formed (secondary and tertiary bronchi). The ends of
these branches are swollen, forming vesicles known as infundibula,
which are made up of a number of alveoli, and are surrounded by
blood capillaries, through the thin walls of which the interchange
of respiratory gases takes place (Figs. 227 and 228).

In the following account the air-tubes will be dealt with
separately from the lungs proper.

Air-Tubes and Larynx.

The walls of the air-tubes may consist, in addition to their
lining of ciliated epithelium, of connective-tissue and elastic and
muscular fibres only, but usually cartilaginous elements are also
formed, and these serve to keep the tubes permanently open. The
most anterior of these cartilages, which support the larynx, become
differentiated to form a frame on which the structures by means of
which the voice is produced—the vocal cords,—are stretched : these
cartilages are acted upon by muscles. The relative length of the
windpipe, as a rule, corresponds with that of the neck.

Dipnoi.—In these the glottis is supported by a fibro-cartilage,
and leads into a muscular vestibule communicating with the lung.
A larynx and trachea are not differentiated.

Amphibia.—The vestibule, or laryngo-tracheal chamber, com-
municates with the pharynx on the one hand and with the lungs on
the other, and is supported by cartilages: it is provided with
intrinsic (dilator and constrictor) and extrinsic muscles, the former
derived from pharyngeal muscles and the latter from trunk muscles.
A definite trachea is differentiated in Siren, Amphiuma, and the
Gymnophiona only; it reaches a length of 4 to 5 or more centi-
metres, and its wall is strengthened by a series of small irregular
cartilages, which usually tend to unite into bands (Fig. 229):
only in the Gymnophiona, however, do these bands begin to take
on the form of half-rings, and to surround the trachea more or less
completely.

The phyletically oldest skeletal parts are a pair of arytenoid
cartilages, situated in the walls of the vestibule (Fig. 229): these
are to have arisen by a modification of part of the fifth bran-
chial arch (comp. Fig. 233). Distally to them there is, in the
Anura, another cartilage corresponding to the criccid of higher
forms, and traces of this also occur amongst Urodeles (¢.g., Siren).

In Anura a highly differentiated larynx is present. This is
regulated by a well-developed series of muscles, and is provided
with vocal cords, the sound produced by which is often intensified
by the presence of vocal sacs developed from the floor of the mouth.
The laryngo-tracheal chamber lies between the posterior cornua of
the hyoid (thyro-hyals) and is supported by a thin arytenoid cartilage

284 COMPARATIVE ANATOMY

on either side of the glottis as well as by a ring-shaped cricoid
cartilage, from which delicate processes pass backwards to the

Ag=

ior? Bomeacoty ee

VAAL AC ung acog

on

Fic. 229.—LaryNGEAL AND TRACHEAL SKELETON OF URopeELEs. A, Vecturus
(Menobranchus) ; B, Siren lacertina ; C, Amphiuma ; D, Salamandra maculosa.

u, the cartilages (arytenoids) on either side of the glottis; a’, ridge for muscles ;
*, the representative of the cricoid cartilage; tt, cartilages of the trachea
in Siren ; Kb, the more definite tracheal cartilaginous tracts in Amphiuma
and Salamandra ; K!Y, fourth branchial arch, from which the dilator (d) of
the trachea and larynx arises ; co, constrictor of the larynx ; L, L’, lungs.

roots of the lungs (Fig. 230). Vocal cords are developed in the
Anura only, each being attached to the imner concave surface
of the corresponding arytenoid.

.

Frc. 230.—CarTILAGINOUS SKELETON OF THE LARYNGO-TRACHEAL CHAMBER OF
Rana esculenta. (A, from above ; B, from the side.)

Ca, Ca, arytenoid cartilage ; C./! to C.l4, cricoid cartilage ; Sp, process of the
latter ; P, plate-like broadening out of the ventral part of the cricoid; SR,
glottis; ***, three tooth-like prominences of the arytenoids.

Reptiles.—The larynx of Reptiles is supported by cartilaginous
elements comparable to those of Anura, there being two sets of

AIR-TUBES AND LARYNX 285

iz)

cartilages—a paired arytenoid, and a ring-shaped cricoid (Figs. 76
and 231). No considerable advance in structure is seen ; there is
even a reduction noticeable as regards the musculature as compared
with the Anura.

One point, however, must be specially noticed, viz., the close
connection which obtains between the larynx and the hyoidean

Fic. 231.—Laryyx or Phyllodactylus europeus. (A, skeleton, and B,
musculature of larynx.)

-ir, arytenoids ; Ce, cricoid ; S, anterior median process of cricoid ; S!, sphincter ;
D, dilator ; 7, trachea; Qe, basi-hyal.

apparatus—more particularly the dorsal surface of the basi-hyal.
In Crocodiles and Chelonians, for instance, the larynx is firmly em-
bedded in a shallow depression of the latter (Fig. 76).

A well-developed trachea, supported by cartilages, is present in
all Reptiles; but the cartilages are not in all cases fused together
to form complete rings. The walls of the bronchi are also usually
provided with cartilaginous supports.

Birds.—In Birds there are two larynges, an upper and a lower.
The former lies in the usual position behind the tongue on the floor
of the pharynx, and is plainly homologous with that of other
Vertebrates, though it has become rudimentary and is incapable of
producing sound.

The lower larynx, or syrin.,is of much greater importance; it is
usually situated at the junction of the trachea and bronchi, or more
seldom at the lower end of the trachea alone or on the bronchi
alone. It functions as the organ of voice, and appears first in, and
is restricted to, Birds. In the most usual form (broncho-tracheal
syrinz), there is a movable connection between the most anterior
bronchial rings, with which a complicated system of muscles is con-
nected ; these, by their contraction, cause a stretching or relaxing of

286 COMPARATIVE ANATOMY

certain vibratory membranes. <A bar of cartilage or bone, the
pessulus, extends from the junction of the bronchi into the more or
less swollen “ tympanum” at the base of the trachea: this supports
a slight fold of the mucous membrane called the membrana
semtlunaris, while the membranous inner wall of each bronchus js
known as the membrana tympaniformis interna: the external wall
may also give rise to a membrana tympaniformis externa. The

Fic, 232.—Larynx or Mate Duck. (A, external, and B, internal view.)

Tr, trachea; Br, bronchus; 7, the ‘‘tympanum”; S, pessulus, from which
a lateral outgrowth (S between b and b) extends into the tympanum,
thus dividing its aperture into the trachea into two portions (b, b); the
aperture is further diminished by the circular fold of mucous membrane, SF ;
+, thin region in 8S.

tympanum attains a relatively enormous development in some
Water-Birds (¢.g., the male Duck), where it gives rise to a bony
vesicle which serves as a resonance cavity (Fig. 232).

The length of the trachea in Birds varies greatly, and its complete cartila-
ginous rings usually become ossified. In some cases (e.g., the Swan and Crane)
it extends into the hollow keel of the sternum, where it becomes more or less
coiled, and then again passes out close to its point of entrance and enters the
body-cavity. In certain representatives of the Sturnide it extends between
the skin and the muscles of the thorax, and there gives rise to numerous
spiral coils.

Mammals.—The larynx of Mammals is distinguished from
that of all other Vertebrates by the marked differentiation of the
muscles—the constrictors always exceeding the dilators in number
—and by the constant presence of an epiglottis and a thyroid
cartilage.

The thyroid cartilage is derived from part of the fourth and
fifth branchial arches (comp. Fig. 233), and in Monotremes, in which
it is paired, it is still closely connected with the hyoid apparatus

AIR-TUBES AND LARYNX 287

(comp. p. 285). In all other Mammals the thyroid is unpaired, though
still showing traces of its primary paired nature, and it becomes

Ca. A

Pw oe
: ae ANY | =

Fic. 233.—Diacram to ILLUSTRATE THE METAMORPHOSIS DURING DEvVELOpP-
MENT OF THE First To FirrH ViscERAL SKELETAL ARCHES (I—V) IN
Man.

From the proximal end of the first arch (Meckel’s cartilage) two of the auditory
ossicles, the malleus and incus (mb and in) are represented as arising. p, pinna; *
pr, mastoid process of skull.

From the second arch (hyoid) arise proximally the styloid process (p.s), distally
the anterior (lesser) cornu of the hyoid (c.a) and a portion of the basi-hyoid (b.s).
By far the greater portion of this arch becomes the stylo-hyoid ligament (/.9).
(Concerning the stapes (st) comp., p 101).

The third (first branchial) arch gives rise to the greater part of the body (b.s)
and the posterior or greater cornu of the hyoid (c.p.).

The fourth (second branchial) arch gives rise to the upper segment (th’) of the
thyroid cartilage, and the fifth (third branchial) to the lower one (th"). The
arytenoid cartilage (ar) is probably a derivative of the fifth arch. ¢r, cartilago
triticea ; cv, cricoid cartilage ; t7, trachea.

separated from the hyoid: it is shield-shaped, and surrounds the
lateral and ventral regions of the larynx, overlapping the cricoid

288 COMPARATIVE ANATOMY

above, and serving as a point of origin and insertion for important
intrinsic and extrinsic muscles,

The vocal cords extend between the thyroid and the arytenoids,
and the mucous membrane above them becomes involuted to form
the laryngeal pouches. In Anthropoids and certain other Monkeys
(e.g., Mycetes) these may reach such a large size that they serve
as resonance cavities, and lie partially within the body of the
hyoid, which is swollen to form a large bony chamber (Fig. 234).
The folds of mucous membrane bounding the laryngeal pouches
anteriorly are spoken of as false vocal cords; these are not present
in all Mammals.

The epiglottis, which consists of elastic fibro-cartilage, stands in
close relation to the soft palate, extending upwards from the anterior
border of the larynx, in front of the glottis : it is often, when at rest,
embraced more or Jess firmly by the soft palate in such a way
that its distal end lies in the passage of the posterior nostrils (naso-
pharyngeal chamber), so that respiration and feeding can go on
independently of one another.?

An interesting adaptation for the method of lactation is seen in the
larynx of Marsupial embryos, in which it, together with the epiglottis,
becomes greatly elongated and is firmly embraced by the soft palate, so that
it cannot be moved from this position. Thus respiration can go on freely
while the milk passes down the oesophagus on either side of the larynx.
In Cetecea (e.g., Phoceena), a similar arrangement occurs, and is here
adapted for the aquatic life of the animal. Probably in all Mammals a
similar position of the larynx is seen in the embryo.

The Lungs proper.

Dipnoi.—In Ceratodus the lung is a wide unpaired sac, without
any trace of a dividing septum: in other Dipnoans it is dis-
tinctly paired throughout the greater part of its length, the anterior
unpaired portion being largely filled up by spongy trabecule.

The lung extends through the whole length of the body-cavity,
and is covered by peritoneum on the ventral surface only; the
lining mucous membrane forms bands and networks similar to those
seen in the air-bladder of many Fishes (e.g., Lepidosteus, Fig. 225).

Amphibia.—The lungs of Proteus and Necturus (Fig 285),
though paired throughout, remain at a lower stage than those
of the Dipnoi, inasmuch as their internal surface is perfectly smooth,
and has, therefore, a much smaller superficial extent. They

1 The cricoid may be complete or incomplete ventrally, and its dorsal portion
usually becomes raised to form a broad plate with which the arytenoids are articu-
lated (Figs. 233 and 234).

° The epiglottis was probably originally a paired structure, consisting of
hyaline cartilage, and it is possible that the small cartilages of Wrisberg and
Santorini present in the larynx in addition to the more important cartilages de-
scribed above may be specialisations of part of the same structure.

LUNGS 289

A, larynx of Deer, seen from the left side; B, longitudinal section through the

a

larynx of the Fox ; C, larynx of the Howling Monkey (M/ycetes ursinus), from
mes left side ; D, Larynx of Chipanzee (Simza troglodytes), from the ventral
side.

trachea ; Ctr, cartilaginous rings of the trachea ; S, mucous membrane of the
trachea and tongue ; Cr, ventral, and Cr, dorsal plate of the cricoid; C%,
Ct, thyroid cartilage ; oh, wh, anterior and posterior cornua of the latter ;
Ca, arytenoid cartilage ; pm, processus muscularis of the latter; Zp, epi-
glottis ; H. body of hyoid; h, lesser, h!, greater cornua of the hyoid; Lt,
crico-thyroid ligament ; Mth, thyro-hyoid ligament ; ./, laryngeal pouch,
which shows an enlargement at +; 7, 2, 3, the three resonance cavities of
Simia troglodytes ; mu, submucous tissue with muscles; Ifge, genioglossus

muscle ; Z, tongue.
U

290 COMPARATIVE ANATOMY

consist of two delicate elongated sacs of unequal length, and con-
stricted in the middle; in Proteus they extend much further
backwards than in Necturus. A difference in length between
the two lungs is seen also in other Am-
phibia, such as Amphiuma and Siren, in
which the two cylindrical lungs lie near
together, close to the aorta. Their in-
ternal surface is raised into a network,
corresponding with the distribution of
the blood-vessels, the meshes being
much finer in Amphiuma, and still more
so in Menopoma, than in Siren.

In many Salamanders (¢g., Salaman-
drine, Amblystomatine, Desmognathina,
Plethodontinz) the lungs undergo a more
or less complete degeneration, even though
all traces of the gills disappear. The fact
that the floor of the mouth is continually
raised and lowered as in other Amphibians
which possess lungs, and that in some
cases, at any rate, the animal dies if these

\ respiratory movements are prevented, in-

j dicates that a bucco-pharyngeal respiration

; takes place, and that cutaneous respiration

Frc, 235.—Lunes or Pro. (Which occurs in most Amphibians) alone

revs (A) AND Necturus is insufficient. In other Salamanders the

(B). The communication |yngs are as arule equal in size, and have

Ag eas =e the form of cylindrical tubes extending

anteriorly. backwards as far as the end of the stomach;

their internal surface is more or less

smooth. The lungs of the Gymnophiona are similar to those of

Salamanders, but the right alone is fully developed, and this

shows in its interior a complicated trabecular network: the left
is only a few millimetres long.

The sac-like lungs of Anura are quite symmetrical. Their
internal surface, which is lined partly by ciliated epithelium,
is raised up into a rich respiratory network of trabecul, and
numerous smooth muscular fibres are present in their walls.

y

Reptiles.—In Reptiles, as in all other air-breathing Verte-
brates, the form of the lungs is to a great extent regulated by
that of the body. In the higher types, such as the Chelonia and
Crocodilia, their structure is much more complicated than in
Amphibia ; this complication finds expression in a very considerable
increase of the respiratory surface. With the exception of the
thin-walled lungs of Lizards, which retain a very primitive con-
dition, we no longer meet with a large central cavity, but the
organ becomes penetrated by a branched system of bronchi, which

LUNGS

give rise to a tubular and sponge-

like meshwork (comp. Fig. 236).

The lung of Snakes exhibits an in-
termediate form, for in spite of the
finely-meshed tissue arising from the
periphery, it still retains a narrow central
cavity. The right lung only is as a rule
fully developed in Snakes and Amphis-
beenians, owing to the elongated form of
the body, while the left remains in a
rudimentary condition, or even disap-
pears entirely.

In the Chameleon (Fig. 236) the an-
terior portion of the lungs is much more
compact and spongy than the posterior,
which grows out into numerous sac-like
processes, some of which reach as far
back as the pelvic region ; their form
is very variable, being spindle-shaped,
club-shaped, or lobulated, and their
walls are very thin; they extend in
amongst the viscera wherever there is
room. If these processes have any res-
piratory function, it is at most only a
very slight one. An indication of a
similar arrangement is seen in the lungs
of Testudo, in which a single thin-walled
process extends backwards to the pelvic
region. These processes seem to fore-
shadow a condition which reaches its
highest development in Birds.

A uniform ground-plan is to be
observed in the arrangement of the
intra-pulmonary bronchial system
through the whole series of the
Amniota, from Crocodiles onwards.
A continuation of the bronchus,
which is almost straight, always
passes through the lung to its pos-
terior end. This may be called the
main bronchus ; from it a series of
lateral broncht arise.

Birds.—The respiratory appar-
atus of Birds presents so many
remarkable peculiarities, both as
regards the structure of the lungs

Fig. 236.—Lunes or Chameleo
monachus.

T—trachea.

and in the presence of azr-sacs, that it must be considered in some

detail.

The comparatively small but highly vascular lungs (Figs. 237
and 238) are closely applied to the thoracic vertebre and heads of

uo 2

292 COMPARATIVE ANATOMY

the ribs, and are capable of very little distension. They are pene-
trated by a system of bronchi which will be described presently.
The lower surface of each lung is closely invested by a thin fibrous
membrane, the pulmonary aponeurosis,’ into which are inserted a
variable number of muscular bands (costo-pulmonary muscles) :
these arise from the vertebral ribs, and are supplied by the inter-
costal nerves (Fig. 288).

When the ventral body-wall of a Bird is removed, the heart,
stomach, liver, and intestine are seen pressed towards the mid-line,
and on either side of them a tightly-stretched fascia, the oblique
septum, is observable, which shuts them off from a paired lateral
sub-pulmonary chamber (Fig. 237). Other chambers are situated
in the anterior thoracic region, ventral tothe lungs, Others, again,
are seen in the region of the heart and in the posterior part of the
abdominal cavity. These chambers are occupied by the atr-sues
with which certain of the bronchi communicate.

The most posterior chamber on either side encloses an abdominal
(posterior) air-sac (Fig. 237). In Apteryx, this is completely closed in by
the oblique septum, but in other Birds it gives rise to a large, distensible
diverticulum which extends backwards ventrally to the kidney, amongst the
viscera.

In front of this there are two air-sacs lying above and externally to the
oblique septum, and constituting the main part of the sub-pulmonary
chamber ; these may be called the anterior and posterior intermediate sacs.
A transverse dividing-wall separates these, at the level of the celiac
artery, and a second septum shuts off the anterior intermediate sac from the
one lying in front of it, to be described presently. The posterior inter-
mediate air-sac presents the simplest and most constant relations, and never
communicates with any of the neighbouring chambers, as is often the case
with the anterior intermediate.

A pair of prebronchial air-sacs lies on either side of the cesophagus above
each bronchus, anterior to the hilum of the lung, and below this a sub-bronchial
sac is situated, which is separated behind from the anterior intermediate sac
by aseptum. This is usually unpaired, the sac of either side fusing with its
fellow to form an interclavicular chamber, bounded by the furcula?; it com-
municates with neighbouring air-cavities which lie between the pericardium
and sternum and in the axilla, outside the body-cavity (aaillary sac).

The main bronchus (mesobronchium) runs close to the ventral surface of
the lung surrounded by the lung-parenchyma, and extends to its posterior
end, where, as a rule, it opens directly into the abdominal air-sac (Fig. 238).
From it a large lateral bronchus is given off, which opens into the posterior
intermediate sac by one or two (e.g., in Passeres) apertures. Besides this
there are from four to six other lateral bronchi, all of which become
broadened out in a fan-like manner on the ventral surface of the lung.
These may be called entobronchia (bronchi divergentes) : they all arise from
the anterior portion of the mesobronchium. The first of these radiates out

1 The pulmonary aponeurosis, as well as the oblique septum, is often spoken of
as a ‘‘ diaphragm” (comp. is 141). The chamber (pleural cavity) in which the
lungs are situated is shut off from the rest of the abdominal cavity in Chelonians
and Crocodiles also.

* In some Birds (e.g., Rhea, Vulture, Adjutant) a median septum is present
separating the two sub-bronchial sacs.

Fic, 237.—ABDOMINAL VISCERA AND AIR-Sacs OF A Duck AFTER THE Re-
MOVAL OF THE VENTRAL Bopy-WaLL. (From a drawing by H. Strasser.)

T, trachea; H, heart, enclosed within the pericardium ; rL,/L, right and left
lobes of liver ; 7sh, suspensory (falciform) ligament, and /cd, les, right and
left coronary ligament of the liver; D, intestine; P, pectoralis major ; pa,
pv, pectoral artery and vein; S, subclavius muscle ; Cd, coracoid ; /, furcula ;
(fed, coraco-furcular ligament; Ly, Lg}, lung; r.abd.S, Labd.S, right and
left abdominal (posterior) air-sac; D.th.a, oblique septum; +t, posterior
intermediate air sac; +, anterior intermediate air-sac; s!, s!, partition-walls
between these sacs; s, s, partition walls between the anterior intermediate
air-sacs and the unpaired sub-bronchial sac, lying in the anterior part of the
body-cavity; v, portion of anterior wall of latter; p, axillary sac lying
between the coracoid, scapula, and the anterior ribs, and communicating with
the sub-bronchial air-sac; C, C, prebronchial sacs; *, point of entrance of
the bronchi into the lung; Ap, pulmonary artery ; Aa, Va, innominate artery
and vein with their branches.

294 COMPARATIVE ANATOMY

pape, UA

,
}

Fig. 238.—Lert Lune oF THE Duck, in situ. (From a drawing by H. Strasser.
The main bronchus is cut open; internally to it lies the pulmonary vein, and
externally the pulmonary artery.

Oe, esophagus ; m./.c, muse. longus colli; Br. Ws, thoracic vertebre ; v, ”, ends
of free vertebral ribs ; stv, stv, sections of ribs which are connected with the
sternum ; NV, kidney; 7'r, trachea, J, first entobronchium, and c, its ostium
communicating with the prebronchial air-sac ; 7, a, ¢, its internal, anterior,
and external branches ; I/i, JZe, internal and external branch of the second
entobronchium: the end of Je opens into the sub-bronchial sac at d; IIJ,
third entobronchium, with the aperture for the anterior intermediate air-sac ;
IV, fourth entobronchium; au, opening of the main bronchus into the
abdominal sac ; b, opening of the outer lateral branch of the mesobronchium
into the posterior intermediate air-sac ; b', second ostium of the latter, more
towards the middle line (present in Passeres). The boundary of the pul-
monary aponeurosis is seen along the outer edge of the lung, and the costo-
pulmonary muscles are shown extending from it to the ribs.

anteriorly to the hilum of the lung, and gives off internal, external and
anterior branches, one of which opens into the prebronchial sac. The other
entobronchia give rise to two series of branches, one of which extends
inwards and backwards between the factors of the pulmonary vein, and the
other outwards between the arterial branches. Almost without exception
a large aperture or ostium is present on the wall on the third entobronchium,

.

LUNGS 295

communicating with the anterior intermediate air-sac. A branch of the
second entobronchium opens externally to the hilum of the lung into the
sub-bronchial sac. :

The lateral bronchi considered as yet have to do with the ventral surface
of the lung only ; but besides these there are a variable number of ecto-
bronchia arising from the dorsal side of the main bronchus posteriorly to the
entobronchia. These come off in alongitudinal row, those of the outer row
being larger than those of the inner. They pass dorsally to the costal face
of the lung. Both ecto- and entobronchia give off numerous bronchi of a
third order, or parabronchia : the walls of these are raised into numerous
transverse net-like folds, into which the pulmonary capillaries extend.

The air-sacs arise from the embryonic pulmonary vesicles as
delicate-walled hollow processes, lined by pavement epithelium: these
grow rapidly, and soon exceed the lung proper in size, extending
amongst the viscera. Their form and extent depend largely upon
their surroundings : they consist simply of interstitial cavities lined
by the membrane of the air-sacs. Moreover, they are not confined
to the body-cavity, but in numerous places extend beyond it, pass-
ing in between the muscles, beneath the skin, and even into most
of the bones. The latter are thus rendered pnewmatic, and con-
sequently the specific gravity of the body is lessened, and the power
of flight increased. The pneumaticity of the bones is not, however,
an essential peculiarity connected with flight, for in many Birds
which are extremely good fliers (¢.g., Larus, Sterna) the bones are
not pneumatic.! In these cases, however, a compensation is
effected by a more marked development of the muscles, and the
abdominal (posterior) air-sac, which in no Birds appears to be
entirely wanting, is here well developed. In the cursorial Ratitz,
on the other hand, the bones are markedly pneumatic.

The air-sacs must be looked upon as integral parts of the
respiratory apparatus : a greater amount of air can, by their means,
pass in and out during inspiration and expiration, especially through
the larger bronchi, and consequently there is less necessity for the
expansion of the lung-parenchyma. The function of the prolonga-
tions of the air-sacs lying towards the outer surface of the body
consists in the giving off of watery vapour and in regulating the
heat of the body. Those which extend in between the muscles,
and supplant the connective and fatty tissue in these regions, have
a further importance in causing less power to be lost in friction.

But by far the greatest importance of the air-sacs situated towards
the periphery consists in the enlargement of the anterior thoracic
region, principally that surrounded by the pectoral arch. A larger
development of the skeleton can thus take place, giving an increase

1 The pneumaticity of the bones is not a special peculiarity of Birds : amongs
Mammals, frontal, maxillary, and sphenoidal sinuses are present in Anthropoids
Elephants, and Marsupials for instance ; the skull of Crocouliles is also strongly
pneumatic. All these sinuses communicate with one another, and also with the

. tympanic cavity. They are in many cases developed in order to give a greater
surface for the attachment of muscles, and also to effect a saving of material and
atlightening of the skull.

296 COMPARATIVE ANATOMY

of surface for muscular attachment without any considerable in-
crease in weight. Everything, in fact, combines to establish an
organ of flight with a large wing-surface and an increased strength
of the muscles.

Mammals.—As in Reptiles, the blood-vessels are of funda-
mental importance in determining the structure of the bronchial
system. The pulmonary artery crosses the main bronchus formed
by the bifurcation of the trachea at
its anterior end, and this point may
be taken as dividing the lateral
bronchi into two systems—an an-
terior eparterial and a posterior hy-
partertal.

The hyparterial series is always
well developed, and consists of a
double row of lateral bronchi, be-
tween the roots of which the pul-
monary artery passes backwards
dorsally, while the corresponding vein
runs along the median side of the
main bronchus (Fig. 239). The epar-
terial system, on the other hand,
gradually becomes of much less im-
portance and in certain cases is re-
presented only by a single external
lateral bronchus on either side (Fig.
239); and, as a rule, even the left of
these disappears, only the right re-
maining, and even this is not always
retained. The eparterial bronchus,

whether developed on one or on both
ee Reet sides, may ee from the trachea
ty Mammats. (From the ven- instead of from the main bronchus.
tral side.) In by far the greater number of
w, a, eparterial bronchus of either Mammals, then, the left cparterial
sles J grin of'vental od bronchus has disappeared, while the
A, pulmanere artery; V; pule right is retained; and as, therefore,
monary vein. the anterior lobe of the right lung
belongs to the eparterial and that of
the left lung to the first hyparterial bronchus, these lobes are
evidently not homologous, the middle right lobe corresponding
much more nearly to the anterior lobe of the left side. There is
thus a want of symmetry between the right and left sides, the
right lung usually retaining one more element than the left
(Fig. 2404). The so-called accessory fourth lobe does not correspond
to a true lobe, but represents the main axis of the lung enclosing
the main bronchus.

LUNGS 297

The cartilages of the bronchi become more and more sparse and
finally disappear as the latter divide up into finer and finer
branches.

The thoracic cavity is lined by a serous membrane, the pleura,
in which, as in the case of the peritoneum (p. 235), a parietal and

Fic. 240a.—Lune or Man. (From the ventral side.)

1, 2, 3, lobes of the right, and 2c, 3a, of the left lung ; 7, base of lung ; T, incisura
cordis ; S, sulcus for the subclavian artery ; 7'’r, trachea.

Wn

Fic. 240n and c.—D1aGRAM OF THE PLEURAL AND PERICARDIAL CAVITIES OF
MAMMALS, FOUNDED ON THE RELATIONS oF THESE Parts IN Man. (B,
horizontal section ; C, transverse section. )

Tr, trachea; Br, bronchi; L, L, lungs; H, heart; W, vertebral column; P,
parietal, and P}, visceral layer of the pleura; ++, points at which these pass
into one another at the hilum pulmonalis (Hz) ; m, mediastinum; Pc, Ps!,
parietal and visceral layers of the pericardium; FR, ribs (wall of thorax); S,
sternum.

visceral layer may be distinguished (Fig. 240, B, C): the latter is
spoken of as the pulmonary pleura, the former as the costal pleura.

298 COMPARATIVE ANATOMY

Towards the middle line, the pulmonary pleura of either side is
reflected so as to form a septum between the right and left thoracic
cavities. This septum is called the medzastinum, and the space
between its two layers the mediastinal space: through this, the
aorta, cesophagus, and postcaval vein run, and in the region of
the heart the mediastinum is reflected over the parietal layer of
the pericardium.

There is a lymphatic fluid between the two layers of the pleura
which renders the movements of the lungs smooth and easy.

ABDOMINAL PORES.

By the term abdominal pore is understood a perforation—usually
paired—of the posterior end of the wall of the peritoneal cavity
which puts the celome into direct communication with the
exterior.t

In Cyclostomes a pair of pores opens into the urinogenital sinus,
serving to conduct the generative products to the exterior: they
probably do not correspond to the abdominal pores of other forms,
which never have this function, and are better described as genttal

ores.

In the Holocephali and Elasmobranchii the abdominal pores are
usually paired and are situated posteriorly to the cloaca (Figs. 206,
289, 290),and may be enclosed within its lips. They are wanting in
the Notidanide, Cestracionide, and Rhinide, and are not con-
stantly present in the Scylliide, even in individuals of the same
species. In Ganoids, they open between the urinogenital aperture
and anus, but are apparently wanting in Amia. Amongst Teleosts,
they are said to be present only in the Salmonidz and Mormyride,
right and left of the anus; but even in these, the pore of one or
of both sides may be absent. In the Murenide,‘there is a single
genital pore, which is apparently more nearly comparable to the
similarly named structure in other Teleosts (see under Generative
Organs) and to the genital pores of Cyclostomes. In Ceratodus the
abdominal pores are paired, and open behind the cloaca, while in
Protopterus a single, apparently blind, canal is present on the same
side of the ventral fin as the vent (Fig. 209), sometimes to the
right and sometimes to the left of the middle line, either within or
without the sphincter of the cloaca.

Abdominal pores are not known to occur in the Amphibia and
Mammalia, but amongst Reptiles they are perhaps represented by the
peritoneal canals of the Chelonia and Crocodilia, which in the

former are in close relation with the penis or clitoris, and usually
end blindly.

1 The abdominal pores may possibly correspond to the remains of segmental
ducts. Other connections of the ccelome with the exterior (by means of the
nephrostomes of Anamnia and the ostia of the oviducts in the majority of
Vertebrata) will be mentioned in a subsequent chapter.

H. ORGANS OF CIRCULATION.

(VASCULAR SYSTEM.)

THE organs of circulation, which arise from the mesoblast,!
consist, in the Craniata, of a hollow central muscular organ, the
heart, which is connected with a series of completely closed tubes,
the blood-vessels. The heart and blood-vessels contain a coloured
fluid, the blood, and their cavities probably represent the remains
of the blastoccele (p. 4). Another system of vessels containing a
colourless fluid, the lymph, must be distinguished from the blood
vessels: lymph, however, is present in various spaces or sinuses
in the body as well as in the lymph-vessels (p. 333) : the lymphatic
system is, therefore, not completely closed, the vessels communicat-
ing with the sinuses on the one hand, and with the blood-vessels on
the other.

Both blood and lymph consist of a colourless fluid, the plasma,
in which float numerous cells or corpuscles. The blood-corpuseles are
of two kinds—colourless, nucleated, amceboid cells, known as white
or colourless corpuscles or leucocytes, and far more numerous red
blood-corpuscles or erythrocytes.2 The lymph contains colourless
corpuscles only, and these are precisely similar to those of the
blood. Both blood and lymph are kept in constant circulation
through the vessels by the contraction of the heart, which acts
both as a force-pump and a suction-pump, and they serve to carry
the absorbed food and oxygen to, and the waste products from, all
parts of the body.

All the blood vessels which bring back the blood to the heart
are known as veins, while those which carry it from the heart
are called arteries: the latter usually contain oxygenated, the
former impure blood, but this is by no means always the case.
Many of the veins are provided with valves, which are adapted to
prevent the reflux of the blood: they have the form of semilunar
folds of the internal coat, and each is usually made up of two folds,

1 According to some embryologists the hypoblast also takes part in the forma-

tion of the vascular system. :
? In Amphioxus the blood contains white corpuscles only; there is no heart,

and the vessels are only partially comparable to those of the Craniata.

300 COMPARATIVE ANATOMY

placed opposite to one another. The arteries (and also certain of
the veins) divide up into smaller and smaller branches, eventually
giving rise to microscopic tubes called capillaries, the walls
of which consist merely of a single layer of epithelial cells,
and these again unite to form the factors of the veins. The walls
both of veins and arteries consist, in addition to the epithelium, of
connective and elastic tissue and of unstriated muscular fibres, and are
much thicker in the case of the arteries than in that of the veins,
in which the muscular elements may be altogether wanting.

The nucleus of the red corpuscles persist, and the whole cell is biconvex,
in all Vertebrates below Mammals ; and, even in these, nucleated red cells
may be seen in the marrow of the bones, in the blood of the spleen, and
often in that of the portal vein. In all other parts of the body of Mammals
they lose their nuclei and become biconcave. In all Mammals, except the
Camelidze, the red corpuscles have the form of circular discs ; in the last-
mentioned group and in all other Vertebrates except Cyclostomes they are
oval. They are largest in certain Urodeles, being in Amphiuma as much
as 75y in their longest diameter; then come, in order, those of other
Urodeles and of Dipnoans, Reptiles, Anurans, Fishes, Birds, and Mammals,
in which latter order they are the smallest, varying in different families from
2°5y (Tragulide) to 10y.

The heart is enclosed within a serous membrane, the pericar-
dium (Fig. 240c), which consists of parietal and visceral layers ;
the former is invested by the mediastinum (p. 298), and the latter
is closely applied to the heart. Between the two layers is a space
filled with lymph, representing part of the ccelome; this is usually
completely shut off from the abdominal cavity, but in Elasmo-
branchs the two communicate by means of pericardio-peritoneal
canals.

The heart arises either as a single (Elasmobranchii, Amphibia)
or as a paired (Teleostei, Sauropsida, Mammalia) tubular cavity
in the splanchnic layer of the mesoblast (comp. note on p. 299)
along the ventral region of the throat, close behind the gill-clefts.
Its wall becomes differentiated into three layers, an outer serous
(pericardial), a middle muscular, and an inner epithelial. In this
respect it essentially corresponds with the larger vessels, in the walls
of which, as already mentioned, three layers can also be distinguished;
but in the heart the muscular fibres are striated. By a study of its
development we thus see that the heart corresponds essentially to
a strongly developed blood-vessel, which at first lies more or less in
the longitudinal axis of the body ; later, however, it becomes much
more complicated by the formation of various folds and swellings.
Thus the embryonic tubular heart becomes folded on itself and
divided into two chambers, an atrium or auricle and a ventricle
(Fig. 241). Between these, valvular structures arise, which only
allow the blood to flow in a definite direction on the contraction of
the walls of the heart, viz., from the atrium to the ventricle; any
backward flow is thus prevented. The valves are formed by

VASCULAR SYSTEM 301

a differentiation of the muscular trabecule of the walls of
the heart. The atrium, into which the blood enters, represents
primitively the venous portion of the heart; the ventricle, from
which the blood flows out, corresponding to the arterial portion.
The venous end further becomes differ-
entiated to form another chamber, the
sinus venosus, and the arterial end gives
rise distally to a truncus arteriosus; the
proximal end of this (conus arteriosus) is
provided with more or less numerous
valves, and its distal end (budbus arteriosus)
is continued forwards into the arterial
vessel (ventral aorta).

The ventral aorta gives off right and
left a series of symmetrical afferent bran-
chial arteries (Figs. 242, 243), each of
which runs between two consecutive gill-

Fic. 241.—D1ackam sHow-

clefts, branches out into capillaries in the
gills, when present, and then becomes con-
tinuous with a corresponding efferent
branchial artery. After the first pair of
these has given off branches to the head
(carotids), they all unite above the clefts
to form a longitudinal trunk on either
side, and there form the right and left roots
of the dorsal aorta; this extends back-

ING THE PRimiTive ReE-
LATIONS OF THE DIFFER-
ENT CHAMBERS OF THE
HEskr.

Sv, sinus venosus, into

which the veins from the
body open; 1, atrium ;
V, ventricle; Ca, conus
arteriosus; Ba, bulbus
arteriosus, from which the
main artery arises.

wards along the ventral side of the ver-

tebral axis into the tail as a large unpaired trunk, which gives off
numerous branches—-including paired vitelline or omphalo-mesenteric
arteries to the yolk-sac, and (except in Fishes and Dipnoans)
allantoic arteries to the embryonic urmary bladder or allantois
(pp. 9 and 3387, and Figs. 8, 9, 242, 24+).

Primarily, the blood becomes purified in the vessels which
branch out over the yolk-sac, from whence it is returned by the
vitelline or omphalo-mesenteric veins (Fig. 244). These join with
the allantoic veins and veins of the alimentary canal to form what
eventually becomes the hepatic portal vein, which divides up into
capillaries in the liver. These capillaries then unite to form the
hepatic veins, which open into the sinus venosus.

Into the sinus venosus there also opens on either side a pre-
caval vein or antertor vena cava, which receives an anterior cardinal
or jugular vein from the head, and a posterior cardinal vein from
the body generally (not including the alimentary canal). The
caudal vein which lies directly below the caudal aorta, is con-
nected with the posterior cardinals, usually indirectly, through the
renal portal veins (comp. Fig. 264). The further development of
the embryonic vessels may take place in one of three ways.

The embryo may either leave the egg, and take on an aquatic

302 COMPARATIVE ANATOMY

existence (Anamnia), making use of its branchial vessels for pur-
poses of respiration, the entire allantois, in the case of the Am-

Fic. 242.—D1aGRAM OF THE EMBRYONIC VASCULAR SYSTEM.
(The portal systems are not shown. )

A, A, dorsal aorta; RA, RA, right and left roots of the aorta, which arise from
the branchial vessels, Ab, by means of the collecting trunks, S, 81; ¢, ¢,
the carotids; Sb, subclavian artery ; KZ, gill-clefts; $i, sinus venosus ; A,
atrium; V, ventricle; B, truncus arteriosus; J’m, vitelline veins; Am,
vitelline arteries ; Jc, [c, common iliac arteries ; H, H, external iliac arteries ;
Ail, allantoic (hypogastric) arteries ; cd, caudal artery; VC, HC, anterior.
and posterior cardinal veins ; Sb!, subclavian vein ; D, precaval veins (ductus
Cuvierii), into which the anterior and posterior cardinals open.

phibia, giving rise to the bladder. In the Amniota, which from
the first breathe by means of lungs, a modification and reduction of

VASCULAR SYSTEM 303

D

Fic. 243.—D1aGRAM OF THE ARTERIAL ARCHES OF VARIOUS VERTEBRATES.
(After Boas.)

A, embryonic condition; B, Fish; C, Urodele; D, Reptile (Lizard); Z, Bird;
F, Mammal. The parts which disappear are dotted.

k and h, the two first embryonic arches, which almost always disappear ; 1—4,
the four more posterior arches ; 1! and 3}, first and third afferent branchial
arteries; 1” and 3”, the corresponding efferent branchial arteries ; 2 in D and
fF, second arch of the left side ; 2! in D, # and F, second arch of the right
side ; u, b, c, the vessels into which the ventral arterial trunk is divided in
Reptiles, Birds, and Mammals ; ao, dorsal aorta ; ca, carotid ; 7, pulmonary
artery ; s (in /), left subclavian artery; st, and s (in B), ventral aorta.

304 COMPARATIVE ANATOMY

the branchial vessels and allantois takes place, and the latter ma:

even disappear entirely (see under Urinary organs). In the third
case, the embryo undergoes a longer intra-uterine existence, the
allantois coming into close connection with the walls of the uterus
by means of the chorionic villi: the allantoic vessels extend into the
wall of the uterus and come into more or less close relations with

Fic, 244.—D1aAGRAM OF THE CIRCULATION OF THE YOLK-SAC AT THE END OF
THE THIRD Day or INCUBATION IN THE CHiIck. (After Balfour.)

H, heart ; AA, the second, third, and fourth aortic arches: the first has become
obliterated in its median portion, but is continued at its proximal end as the
external carotid, and at its distal end as the internal carotid; Ao, dorsal
aorta; L.Of.A, left vitelline artery; R.OfA, right vitelline artery; 8.7,
sinus terminalis; D.Of, left vitelline vein; R.Of, right vitelline vein; S8.V,
sinus venosus ; D.C, ductus Cuvieri; S.Ca.V, anterior cardinal or jugular
vein; V.Ca, posterior cardinal vein. The veins are marked in outline, and
the arteries are made black. The whole blastoderm has been removed from
the egg, and is supposed to be viewed from below. Hence the left is seen on
the right, and vice versa.

the maternal vessels, thus serving for the respiration and nutrition
of the foetus. In this way a placenta and a placental circulation
arise (comp. Fig. 9, and pp. 9 and 337).

On the appearance of pulmonary respiration, important changes
take place in the branchial vessels and heart. The formation
of a septum in both the atrium and ventricle leads to the presence

VASCULAR SYSTEM 305

of two atria or auricles, and two ventricles, and the conus arteriosus
and sinus venosus become eventually more or less incorporated in
the ventricles and right auricle respectively. Thus a right (venous)
and a left (arterial) half can be distinguished; and a new vessel,
the pulmonary artery, arising from the last arterial arch, becomes
connected with the right ventricle : this conveys venous blood to the
lungs, while special vessels (pulmonary veins) return the oxygenated
blood from the lungs to the left auricle, from which it passes into the
left ventricle and so into the general circulation of the body.

The branchial vessels never become functional as such, in any
period of development either in Sauropsida or Mammalia ; but those
which persist give rise, as already mentioned, to important vascular
trunks of the head, neck (carotids), anterior extremities (sub-
clavians), and lungs (pulmonary arteries), and also to the roots of
the aorta, one or both of which may remain (comp. Fig. 243).

The primitive number of arterial arches is six, the first two of
which (belonging to the mandibular and hyoid arches respectively)
almost always disappear early: in caducibranchiate Amphibia
(including Anura) and in Amniota, the fifth arch also disappears.
The third gives rise to the carotid arch; the fourth of both sides
(Amphibia, Reptilia), or of one side (Aves, Mammalia), to the aortic
or systemic arch, and the sixth to the pulmonary arch (Fig. 243).

From the Dipnoi onwards, the posterior cardinals become more
or less completely replaced functionally by a large unpaired vein,
the postcaval or postervor vena cava, which opens independently into
the right auricle.

THE HEART, TOGETHER WITH THE ORIGINS OF THE MAIN
VESSELS.

Fishes (including Cyclostomes).—The heart in Fishes is
situated in the anterior part of the body-cavity, close behind the
head. It is formed on the same general plan as that described on
p. 300, consisting of a ventricle with a truncus arteriosus or
merely a bulbus (Cyclostomi, Teleostei), and an atrium or
auricle, the latter receiving its blood from a sinus venosus, and
being laterally expanded to form the appendices awricula (Figs. 245
and 246),

In correspondence with the work which each portion has to
perform, the walls of the atrium are thin, while those of the ventricle
are much stronger, its muscles giving rise in the interior to a network
and usually to aseries of large trabecule : this holds good through-
out the Craniata.

Between the sinus venosus and atrium, and also between
ventricle and atrium, membranous valves are present ; there are
primarily two atrioventricular valves, but they may be further sub-

divided. Numerous valves, arranged in rows, are present in the
53

306 COMPARATIVE ANATOMY

muscular conus arteriosus (Fig. 246, A): these are’most numerous
in Elasmobranchs and Ganoids. There is a tendency, however, for
the posterior valves, or those which lie nearest the ventricle,

? ‘ \
Fic. 245.—Heart or A, Zyyena malleus, FROM THE VENTRAL SIDE; B, or Acan-

thias rulyaris, FROM THE DORSAL SIDE, WITH THE ATRIUM CUT OPEN (after
Rose); C, or A TELEosT (Stlurus glances).

A, A, atria; a, a, auricular appendages ; V, ventricle ; ¢r (in B) and Ba (in C),
bulbus arteriosus ; ¢7 (in A) and co (in B), conus arteriosus, f (in C), ventral
aorta.

D.C.d and D.C.s, right and left precavals; Ta.d. and V.a.s, right and left
valve of the sinus venosus; O.a.v, atrio-ventricular aperture; 1,a—4,a,
atferent branchial arteries.

gradually to undergo reduction (B). The most anterior row always
persists, and corresponds to the single row of valves between the
ventricle and bulbus in Teleosts (c) and Cyclostomes. Together
with the reduction of these valves, the conus arteriosus also be-
comes reduced in the last-mentioned forms, so that the non-

VASCULAR SYSTEM 307

contractile bulbus arteriosus usually lies close against the ventricle
(Fig. 246, c).
The heart of Fishes contains venous blood only, which it forces

Th

IT
Na

A

esate

A B Cc

Fic, 246.—DiacramMatic LoncitupiINnaL SECTION THROUGH THE HEARTS of
Various Fisues. (From Boas’s Zoology.) A, Fish with well developed
conus anteriosus (¢.g., Elasmobranch); B, Amia; C, a Teleost. In Band C
the sinus venosus and atrium are not indicated.

a, atrium ; b, bulbus arteriosus ; «, conus arteriosus ; /, valves ; x, sinus venosus -
t, ventral aorta; v, ventricle.

through the afferent branchial arteries (Figs. 248, B, 245, c, and 264)
into the capillaries of the gills, where it becomes oxygenated, to
pass thence into the efferent branchial arteries, and so into the
aortic roots.

Dipnoi.—In the Dipnoi, as in Fishes proper, the heart lies
far forwards, near the head. In correspondence with the double
mode of respiration, by lungs as well as by gills, it reaches a
stage of development mid-way between that seen in Elasmo-
branchs and in Amphibians (Figs. 247 and 248). The atrium
becomes divided into a left and a right chamber by a septum, as
does also the ventricle to some extent, owing to the presence of
a cushion composed of muscular fibres and connective-tissue (Fig.
247) situated between the atrium and ventricle, and extending
into both of these chambers: this acts as a valve, ordinary atrio-
ventricular valves being absent. The sinus venosus, from the
Dipnoi onwards, opens into the right atrium.

The conus arteriosus is twisted spirally on itself (Fig. 248): in
Ceratodus it is provided with eight transverse rows of valves, and

x2

308 COMPARATIVE ANATOMY

rpost.car Lpostcar Lantcar

roru~>

7 8CU—
ade
| peel.vein
+-Lpostcard
AG
Fic. 248.

Fic. 247.—HeEart or Protopterus annectens. From the left side, part of the
wall of the left atrium being removed. (After Rose.)

W, fibrous cushion extending into the ventricle; S?.r, sinus venosus, within
which the pulmonary vein (Lv) extends to open into the left auricle by a
valvular aperture; Z.7h and R.Vh, left and right atria; S.a, septum
atriorum ; Co, conus arteriosus.

Fic. 248.—Ceratodus forsteri. DIAGRAMMATIC VIEW OF THE HEART AND MAIN
Buioop VESSELS AS SEEN FROM THE VENTRAL SuRFACE. (From Parker and
Haswell’s Zoology, after Baldwin Spencer. )

aff. 1, 2, 3, 4, afferent branchial arteries; 1 br, 2 br, 3 br, 4 br, position of gills ;
c,d, conus arteriosus; d.a, dorsal aorta; d.c, ductus Cuvieri ; epi.1, epi.2,
epi.3, epi.4, efferent branchial arteries ; hy.art, hyoidean artery ; ¢. r.¢, post-
caval vein ; /.anf.car, left anterior carotid artery ; /.aur, left auricle ; /.br.v,
left brachial vein; /.juy., left jugular vein ; /.post.car, left posterior caro-
tid artery ; /.post.card, left posterior cardinal vein ; U.pul.art, left pulmonary
artery ; /.se.v, left sub-scapular vein ; r.an/.car, right anterior carotid artery ;
r.aur, vight auricle ; r.br.v, right brachial vein ; ».jug.7, right jugular vein ;
r.post.cur, vight posterior carotid ; ».pul.art, right pulmonary artery ; 7.s¢.v,
right sub-scapular vein ; vert, ventricle.

begins to be divided into two chambers. In Protopterus this divi-
sion is complete, so that two currents of blood, mainly arterial and

VASCULAR SYSTEM 309

mainly venous respectively, pass out from the heart side by side.
The former comes from the pulmonary vein, from which it passes
into the left atrium, thence into the left side of the ventricle, and
so to the two anterior branchial arteries. The venous current,
on the other hand, passes from the right side of the ventricle into
the third and fourth afferent branchial arteries and thence to the
corresponding gills, where it becomes purified ; it reaches the aortic
roots by means of the efferent branchial arteries. The paired pui-
monary artery arises from the fourth efferent branchial in Ceratodus
(Fig. 248), and from the aortic root in Protopterus and Lepidosiren,
that of the right side bifurcating to supply the dorsal surface of the
lung or lungs (p. 288), while that of the left side supplies the
ventral surface. The two pulmonary veins unite to form a median
trunk which becomes closely connected with the sinus venosus, so
as to appear sunk within its walls (Fig. 247). Thus the blood
becomes once more purified before it passes into the left ventricle.
A postcaval vein, present from the Dipnoi onwards, opens into the
sinus venosus posteriorly to the precavals, and with it the hepatic
veins communicate (Figs. 248 and 267).

Amphibia.— With the exception of the Gymnophiona, in which
it is situated some distance back, the heart in all Amphibians lies far
forwards, below the anterior vertebre. A septum atriorum is well
developed, but in Urodela and Gymnophiona it is more or less fenes-

A

Pic. 249.--DIAGRAM SHOWING THE CovRsk oF THE BLoop TITROUGIE TUE HEART
1s Urodela (A) AND Anurea (B).

A, right atrium; A’, left atrium ; I’, ventricle ; fr, conus arteriosus, divided:sin
Anura (B) into two portions, 7, fr! : through fr venous blood passes into the
pulmonary arteries, Ap!, Ap', while through tr’ mixed blood goes to the
carotids, ci—ce, and to the roots of the aorta, RA ; /r, (rv, pulmonary veins 3.
v, ¢, pre- and post-cavals (only one precaval is indicated),

trated (Fig. 250). There are always two fibrous, pocket-like atrio-
ventricular valves, which are connected with the walls of the
ventricle by cords, The two pulmonary veins unite before opening
into the left atrium.

310 COMPARATIVE ANATOMY

The cavity of the ventricle is unpaired, and neither in Urodela
nor Anura shows any trace of a septum, so that the blood passing
out from it must have a mixed character (Fig. 249). The ven-
tricle is usually short and compressed, but is more elongated in
Amphiuma, Proteus, and the Gymnophiona. It is continued an-
teriorly into a conus arteriosus, as in Elasmobranchs, Ganoids, and
Dipnoans; this has usually a slight spiral twist, and possesses a
transverse row of valves at either end, as well as a spiral fold ex-
tending into its lumen. This holds good for the Axolotl, Amblystoma,

Fre. 250.—Huarer or Cryptobranchis japonicus, From the ventral side. (After
Rése.) Tura left atrium is cut open.

S.a, septum atriorum, perforated by numerous small apertures ; L.v, L.2, the
two pulmonary veins, opening by a single aperture into the left atrium ; O.ar,
atrio-ventricular aperture ; 1%, 4%, the four arterial arches ; P.d. and P.s, left
and right pulmonary arteries ; ‘7, truncus arteriosus; L. lh, R.Vh, left and
right atria; V.s.d and V.s.s, subclavian veins ; J.j.d and V.j.s, jugular veins ;
V.c.d, V.c.s, posterior cardinal veins ; J’.c.7, postcaval vein.

Salamandra, Amphiuma, and Siren. In others (eg., Necturus,
Proteus, Gymnophiona), retrogression is seen in a lengthening of
the conus, the disappearance of the spiral fold, and the presence of
only a siugle row of valves.

In Anura, the fold lying within the conus extends so far back
that no undivided portion of the cavity is left. The consequence
of this is that the blood passing into the hindermost pair of the
arterial arches—that from which the pulmonary arteries arise—is
mainly venous, while the others contain more or less mixed blood
(Fig. 249, B) ; for, owing to the spongy nature of the ventricle, there

1 This spiral fold corresponds to a series of fused valves.

VASCULAR SYSTEM 311

is no time for its contained blood to get thoroughly mixed before it
is forced into the conus. :

_ As in the Dipnoi, four afferent branchial arteries (Fig. 250)
arise on either side from the short conus in the Amphibia, which
—taking as a type the larva of Salamandra—have the ‘follow-
ing relations (comp. Fig. 243, ¢).

_ The three anterior arteries pass to numerous external gill-tufts
in which they break up into capillaries (Fig. 251). From the latter
three efferent vessels arise, which pass to the dorsal side, and there
unite on either side to form the aortic root. The fourth afferent

Fie, 251.—THe ARTERIAL ARCHES oF THE Larva or a SALAMANDER. (Slightly
diagrammatic.) (After J. E. V. Boas.)

tr, truncus arteriosus ; 1 to 3, the three afferent branchial arteries ; J to IZI, the
corresponding efferent arteries ; 4, the fourth arterial arch, which becomes
connected with the pulmonary artery (Ap); a, w, direct anastomoses between
the second and third afferent and efferent branchial arteries; ce, external
carotid ; «7, internal carotid ; +, net-like anastomoses between the external
carotid and the first afferent branchial artery, which give rise later to the
“carotid gland”; RA, aortic roots ; .40, dorsal aorta. The arrows show the

course which the blood takes.

branchial artery, which is smaller than the others, does not pass to
a gill, but to the pulmonary artery, which arises from the third
efferent branchial. The pulmonary artery, therefore, contains far
more arterial than venous blood, and thus the lungs of the Sala-
mander larva, like the air-bladder of Fishes, can only be of
secondary importance in respiration.

The internal carotid arises from the first afferent branchial
artery, towards the middle line, the external carotid coming off
further outwards (Fig. 251). The latter, as it passes forwards,
becomes connected with the first afferent branchial by net-like anas-
tomoses, and these give rise later to the so-called “ carotid gland” }

1The ‘carotid gland” loses its character as a refe mirabile (comp. p. 333),
and in the adult consists simply of a muscular vesicle with septa in its interior.

312 COMPARATIVE ANATOMY

of the adult, which probably functions as an accessory heart. Direct
connections exist between the second and third afferent and
efferent arteries.

Towards the end of the larval period, the second efferent bran-
chial artery increases considerably in relative size, and the fourth
arterial arch also becomes larger. By a reduction of the anasto-
mosis with the third arch, the fourth carries most of the blood for
the pulmonary artery, and the latter thus now contains more venous
than arterial blood. When branchial respiration ceases, the anasto-
moses between the afferent and etferent branchial arteries no longer
consist of capillaries, but a direct connection between them be-
comes established (Fig. 252). Finally, the connection between the

Fic. 252.—ARTERIAL ARCHES oF aN ADULT Salamandra maculosa, SHOWN
SPREAD ouT. (After J. E. V. Boas.)

co, tr, truncus arteriosus; 1 to 4, the four arterial arches; ce, external carotid ;
cd, “ carotid gland” ; ¢/, internal carotid. The fourth arterial arch, which gives
rise to the pulmonary artery (4), has increased considerably in size relatively,
and is only connected by a delicate ductus Botalli (t) with the second and
third arches ; RA, root of the aorta; «, cesophageal vessels.

first and second branchial arches disappears, the former giving
rise to the carotid and the latter forming the large aortic root;
an anastomosis remains throughout life, however, between the
fourth arch, which forms the pulmonary artery, and the second and
third arches. This is usually spoken of as the ductus Botalli.

The third arch varies greatly in its development; it may be
present on one side only, or may even be entirely wanting.

In the larve of Anura there are also four afferent branchial
arteries present on either side, but these are connected with the
corresponding efferent vessels by capillaries only, there being no
direct anastomoses (compare Fig. 251). The consequence of this
is that all the blood becomes oxygenated.

In the adult Frog the third arterial arch becomes entirely

.

VASCULAR SYSTEM 313

obliterated, and there is no ductus Botalli: the other vessels re-
semble those of the Salamander. In lungless forms (p. 290) a
correlative reduction of the pulmonary vessels occurs.

Reptiles.— As in all Amniota, the heart of Reptiles arises far
forwards in the neighbourhood of the gill-clefts, but on the forma-
tion of a neck it comes to lie much further back than is the case in

Fic. 253.—Heart or A, Lacerta muralis, AND B,
oF A Larce Varquius, SHOWN CUT OPEN ; C,
DiaGRAM OF THE REPTILIAN Heart.

V, V}, ventricles ; A, A’, atria ; fr, 7rca, innomi-
nate trunk; 1, 2, frst and second arterial
arches; Ap, Ap', pulmonary arteries; Vp,
pulmonary vein; + and *, right and left

aortic arches ; RA, root of aorta; Ao, dorsal aorta ; Ca, Ca}, carotids ; Asc, As,
subclavian arteries. J, jugular vein; J's, subclavian vein ; Ci, postcaval : these
three veins open into the sinus venosus, which lies on the dorsal side of the
heart, above the point indicated by the letter 8. In the diagram C the pre- and
postcavals are indicated by Ve, Ve, only one precaval being represented.

the Anamnia.! The carotid arteries and jugular veins are thus
correspondingly elongated.

The principal advance in structure as compared with the Am-
phibian heart is seen in the appearance of a muscular ventricular

1 It is situated furthest forwards in the majority of Lizards and in Chelonians :
in Amphisbenians, Snakes and Crocodiles it lies much further back.

314 COMPARATIVE ANATOMY

septum, which may be incomplete, as in Lizards (Fig. 253, 3),
Snakes, and Chelonians, or complete, as in Crocodiles.

The conus arteriosus now becomes practically absorbed into
the ventricular portion of the heart, and each aortic root may be
made up at its origin of two arches, anastomosing with one another
(Lacerta, Fig. 243, 4), or of one only (certain Lizards, Snakes,.-
Chelonians, and Crocodiles, Figs. 253, B, 255), from which the
carotid artery arises directly. The left and right aortic arches cross
at their base, so that the left arises on the right side, and vice
versa.! The most posterior arterial arch gives rise to the pul-
monary artery (comp. Fig. 243, D).

The blood from the right ventricle passes into the pulmonary
artery as well as into the left aortic arch, and, according as the septum

Lteaabd.

Fie. 254.—Heart or Cyclodus bodduertei. From the dorsal side. (After Rise).
The sinus venosus is almost entirely absorbed into the right atrium.

D.C.s, D.C.d, precaval veins; V.c., postcaval vein; I7j.d, jugular, V.s.d, sub-
clavian, and V.C.d. posterior cardinal vein of the right side. L.v, pulmonary
vein; P.s, P.d, pulmonary arteries ; An.s, An, innominate arteries ; ,o.abd,
dorsal aorta ; Sp.i, spatinm intersepto-valvulare (comp. Fig. 257).

ventriculorum is complete or incomplete, is either entirely venous
(Crocodiles) or mixed (other Reptiles, Fig. 253, c).

The valves of the heart have undergone a considerable reduction
in Reptiles: at the origin both of the aorta and of the pulmonary
artery there is only a single row; this is also the case in all other
Amniota. In Crocodiles the right atrio-ventricular aperture is
guarded by a large muscular valve on the right (outer) side of the
aperture,

The sinus venosus, which even in the Amphibia—especially
Anura—shows indications of becoming sunk into the right atrium,
is now usually no longer recognisable as a distinct chamber ex-

? A small aperture of communication between the two aortic roots, the foramen
Poanizzw, exists in Crocodiles.

VASCULAR SYSTEM 315

ternally (Figs. 254256). It becomes partially divided into two
portions by a septum ; and the left precaval, opening on the left of

Pe
i Si.

Amn“ \\

Fic. 255. Fig. 256.

Fic. 255.—Hzart or a Youna Crocodilus niloticus. From the dorsal side.
(After Rise).

Tr.ce, common carotid ; 8.x, S.d, subclavian arteries ; 4.s and A.d, left and right
aortic arches ; A.m, mesenteric artery ; L.V.h, R.V.h, left and right atria ;
V.c.c, coronary vein. Other letters as in Fig. 244.

Fic. 256.—HeEart or Crocodilis niloticus. From the right side. (After Rése).
Part of the wall of the right atrium is removed.

0.a.v, atrio-ventricular aperture ; Va.d and Va.s, the two sinu-auricular valves,
the white line between which is the margin of the sinu-atrial septum. Other
letters as in Figs. 244 and 245.

this septum, may appear to enter the right atrium independently
(e.g., Snakes.) The pulmonary veins unite into a single trunk
before entering the left atrium.

Birds and Mammals.—lIn these Classes, the atrial and ventri-
cular septa are always complete, and there is no longer any mixture

316 COMPARATIVE ANATOMY

of the arterial and venous blood. The muscular walls of the ventricle
are strongly developed and very compact. This is particularly the
case in the left ventricle, on the inner wall of which the papillary
nuuseles are well developed : the left ventricle is partially surrounded
by the right, the cavity of the latter having a semilunar transverse
section, and its walls being much thinner than those of the former
(Fig. 258).

In both Birds and Mammals the blood from the head and body
passes by means of the precavals and postcaval into the right

Fic. 257.—HEARt or Goosk (Anser vulgaris), DISSECTED FROM THE RIGHT SIDE.
(After Rise. )

The right atrium and ventricle are cut open, and their walls reflected. S.a,
septum atriorum ; ZL. Vi, limbus Vienssenii—a ridge arising from the ventral
wall of the right atrium ; the space between this and the septum atriorum is
known as the spatium intersepto-valvulare (comp. Figs. 254 and 255). Via.s,
V.a.d, the two sinu-auricular valves, situated at the entrance of the postcaval ;
MLK, MK’, muscular right atrio-ventricular valve; Ao, aorta; V.c.s.d, right
precaval ; J’.c.c, aperture of coronary vein.

atrium, as docs also that from the walls of the heart through the
coronary vein? (Figs. 257, 259, 260, B), and the sinus venosus—
especially in Mammals—is scarcely recognisable (Figs. 257, 250) :
the right atrium is separated from the right ventricle by means of
a well-developed valve. In Birds (Fig. 257) this valve resembles
that of Crocodiles, and is very large and entirely muscular, while in
most Mammals it consists of three membranous lappets (tricuspid

1 Coronary reins ave present in most of the lower Vertebrates also (comp. ¢.9.,
Fig. 255), and the heart is supplied with arterial blood by coronary arteries, usually

arising in Fishes from a hypobranchial artery connected with the efferent branchials
or subclavians, and in higher forms from the base of the aorta.

VASCULAR SYSTEM 317

valve) to which are attached tendinous cords,! arising from the
papillary muscles.

In Birds the left atrio-ventricular aperture is provided with a
valve consisting of three membranous folds : in Mammals there are
only two folds, and the valve is therefore known as the déeuspid or
mitral ; three semilunar pocket-like valves are also present at the
origins of the pulmonary artery and aorta in both Birds and
Mammals.

As regards the origin of the great vessels, Birds are distinguished
_ from Mammals by the fact that in them the right, while in Mammals

Fie. 258.

Fic. 258.—TRANSVERSE SECTION THROUGH THE VENTRICLES OF (rus cinerce.
Td, right, and Vg, left ventricle ; $8, septum ventriculorum.
Fic. 259.—HeEart oF Ornithorhynchus paradoxus. From the dorsal side.
(After Rése. )
Vies.s, Wes.d, precaval veins; 17¢.7, posteaval ; Vie.r, coronary vein; Tve.s.s,
coronary sinus; 1.7, pulmonary veins; 10, aorta; P.x, P.d, pulmonary
arteries; R.V.L, right atrium ; S.p./, Spatium intersepto-valvulare.

the left aortic arch persists (Fig. 243, E,F); the corresponding arch
of the other side in both cases gives rise to part of the subclavian
artery. Thus in both Birds and Maminals there is only a single
aortic arch. As in Amphibians, the posterior arterial arch gives
rise to the pulmonary artery. The pulmonary veins, two from
each lung, open close together into the left atrium (Fig. 254).
Amongst the more important points in the development of the
heart may be mentioned the fact that in the embryo the two atria
communicate with one another secondarily by means of the foramen
ovale, through which the blood from the postcaval passes into the
left ventricle (Fig. 260). This foramen closes up when the lungs

1 There are no chord tendinex in Monotremes, the heart of which in many
respects resembles that of the Sauropsida.

318 COMPARATIVE ANATOMY

come into use, but its position can still be recognised as a thin area
(fossa ovalis) in the atrial septum, surrounded by a fold (annulus
ovalis). Extending from this to the base of the postcaval and right
precaval respectively are two folds, known as the Eustachian and

Fic. 260.—Hearr or Human Forrus (8tH Montn). A, From the right, and B,
from the left side. (After Rése.) The walls of the atrium and ventricle are
partly removed in each figure.

Va.s, left. sinu-auricular valve, fused with the septum atriorum (S.a,V.a,f);
Va.Th, Thebesian valve, in direct connection with the Eustachian valve
(Va.L); L.V, left atrium ; /’.0.v, foramen ovale; V.c.s, left precaval ; I’.c.1,
postcaval ; .1.0, aorta; P, P.d, P.s, pulmonary artery; DB, ductus Botalli
(ductus arteriosus); L.v. pulmonary vein; V.c.c, coronary vein.

Thebesian valves (Fig. 260, 4); these represent the remains of the
right sinu-auricular valve, and serve in the embryo to conduct the
blood from the right atrium into the left.

Great variations are seen in the mode of origin of the carotids
and subclavians from the arch of the aorta in Mammals. Thus

“Ao

Fig. 261.—Five Dirrerent Moprs or ORIGIN OF THE GREAT VESSELS FROM
THE ARCH OF THE AORTA IN MAMMATS.

Ao, aortic arch , 1h, tbe, brachiocephalic trunk ; c, carotids ; s, subclavians.
there may be a brachiocephalic or innominate trunk on either side

(Fig. 261, A); or an unpaired common brachiocephalic, from which
the carotid and subclavian of one or both sides arise (B, C, E) ; or,

ARTERIAL SYSTEM 319

finally, a common trunk of origin for the carotids, the subclavians
arising independently on either side of it (D).

ARTERIAL SYSTEM,

The essential relations of the carotid arteries, dorsal aorta, and
pulmonary arteries, as well as the embryonic vitelline arteries, have
already been dealt with (pp.301-305, Figs. 242, 264, &c.), An external
carotid and an internal carotid arise on either side independently from
the anterior efferent branchial arteries in Fishes and Dipnoans, but
from the Amphibia onwards these vessels are formed by the bifurca-
tion of each common carotid. In these higher types, the internal
carotid passes entirely into the cranial cavity, and supplies the brain
with blood, while the external carotid goes to the external parts of
the head (face, tongue, and muscles of mastication).

The origin of the subclavian artery, which supplies the anterior
extremity, is very inconstant, being sometimes symmetrical, some-
times asynimetrical. It arises either in connection with the
posterior efferent branchial vessels, or from the roots or main trunk of
the aorta (Figs. 262-264, &.). Extending outwards towards the free
extremity, the subclavian passes into the brachial artery, from
which a dorsal and aventral branch arise, and these subdivide again in
the limb.

From the dorsal aorta, in which a thoracic and an abdominal
portion can be distinguished in Mammals in addition to the caudal
portion, arise parietal (intercostal, lumbar), and culiac, mesenteric,
and wrinogenital arteries, supplying the body-walls and viscera re-
spectively. ‘These all vary greatly both in number and relative
size ; thus, for instance, there is sometimes a single caliaco-mesen-
teric artery (Fig. 262), sometimes a separate coeliac, and one or more
mesenteric arteries (Fig. 264);! the venal and genital arteries also
vary in number and arrangement. All the branches of the dorsal
aorta, however, present primarily an approximately metameric
character, their number becoming more or less reduced owing to a
concentration of the vessels, which is more marked in short-bodied
than in long-bodied Vertebrates.

The aorta is continued posteriorly into the caudal artery, which
usually lies within a coelomic canal enclosed by the ventral arches of
the vertebree (Figs. 262-264); the degree of its development is
naturally in correspondence with the size of the tail. In cases
where the latter is rudimentary, as in Anthropoids and Man for
instance, the caudal aorta is spoken of as the median sacral artery,
and the aorta here appears to be directly continued, not by it, but

1 The caliac typically supplies the stomach, liver, and spleen ; one or more

anterior mescnterics the whole intestine with the exception of the rectum, as well
as the pancreas ; and a posterior mesenteric the rectun,

520 COMPARATIVE ANATOMY

BEuAs
Gj "| oy ;

XS ‘
NS CZ

Fie. 262.—Tun ARTERIAL System oF Salameandra maculosn.

LA, roots of the aorta ; Ao, Ao, dorsal aorta; Sc, subclavian artery, from which
the cutaneous artery (Cu) arises ; the latter anastomoses posteriorly with the
epigastric artery 4; Ov, ovarian arteries; Com, cceliaco-mesenteric ; A,
hepatic artery ; J, J, Z, anterior mesenteric arteries passing to the small
intestine ; M/, .1/, posterior mesenteric arteries; R, &, renal arteries; I/r,
common iliac; Cr, crural artery; Hy, hypogastric artery; 4, A, vesical
(allantoic) arteries; Joc, caudal aorta; P, pharynx and cesophagus; m,
stomach ; 7, pancreas ; /, liver ; ¢, 2, small intestine ; e¢, rectum ; B/, urinary
bladder ; C7, cloaca.

ARTERIAL SYSTEM 321

Fic. 263.—Tur ARTERIAL System or Hmys ewropwa.

Tr, trachea; Br, Br, the two bronchi; m, stomach; d, d, small intestine ; ¢,
large intestine ; Ap, pulmonary artery ; Cac, common carotids, with
tracheal and cesophageal branches (77, Oe); Sc, subclavian artery; Ver,vertebral

artery ; RA, roots of the aorta; Ao, dorsal aorta ; Co, Co!, and Me, eceliaco-

mesenteric artery, which here arises as a bundle of separate vessels; UG,
urinogenital arteries; Cr, crural artery ; H, epigastric artery; Js, sciatic
artery ; J[B, posterior mesenteric arteries ; C, caudal aorta.

Y

322 COMPARATIVE ANATOMY

by the common iliac arteries, which pass outwards into the pelvic
region.

Each common iliac artery becomes divided into an ‘internal
iliac, or hypogastric, supplying the viscera of the pelvis, and
derived from the proximal portion of the embryonic allantoic
artery, and an external iliac, which is continued into the erural or
femoral and supplies the hinder extremity (Fig. 262). In some
cases the internal and external iliacs come off separately from the
aorta (Fig. 263). The function of the femoral may be largely taken
by a sciatic artery arising separately from the aorta (Birds). The
main vessels again branch out in the limb.

VENOUS SYSTEM,

Fishes.—Taking the Elasmobranchii more particularly into
consideration, a few of the more important facts as regards the
development of the veins must first be considered (comp. p. 301).

The first veins to appear in the embryo are the paired omphalo-
mesenteric veins, which bring back the blood from the surface of
the yolk and from the walls of the gut (Fig. 265, 1, II). The vessels
from the former region are known as vitelline veins, while those
from the latter give rise to swbintestinal veins (III—VII),
running beneath the embryonic intestine, which primarily extends
into the caudal region as the post-anal gut. On the disappearance
of the latter, the posterior part of the subintestinal vessels gives
rise to the caudal vein, which now lies directly beneath the caudal
aorta and loses its direct connection with the anterior part (VIIJ—
XII). As the liver is gradually developed, the main trunk of the
left omphalo-mesenteric vein breaks up into capillaries within this
organ, and these again unite anteriorly, opening into the proximal
ends of both omphalo-mesenteric veins. The latter thus give rise
to the hepatic veins, which open into the sinus venosus (or precaval,
e.g., in Cyclostomes), New vessels from the various parts of
the alimentary canal (gastric, splenic, and mesenteric veins) are
gradually developed, the pre-caudal portion of the subintestinal
vein becoming of minor importance; all these vessels unite to
form what is now known as the hepatic portal vein, and thus
pour their blood through the capillaries of the liver (Figs. 270,
264—268).

Anteriorly to the heart, a paired precaval vein (ductus Cuvieri)
is developed (Figs. 264—268),and opens into the sinus venosus. This
is formed, on either side, by the confluence of ananteriorand a posterior
cardinal vein, the former bringing back the blood from the head
(external and internal jugular veins), and the latter from the body,

1 A single or paired inferior jugular from the ventral part of the head may
also be present (Fig. 266).

323

VENOUS SYSTEM

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A subclavian vein from the pectoral fin also opens into

kidneys.

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idl hs ill

324 COMPARATIVE ANATOMY

Fia. 265.—Di1aGRAmM oF STAGES IN THE DEVELOPMENT OF THE VEINS IN Exasmo-
BRANCHS. (I—XJ after Rabl, XII after F. Hochstetter.)

Ca, Cp, anterior and posterior cardinal veins; Cd, caudal vein; D,D, vitelline
veins; DC, precaval vein or sinus; Cl, region of the cloaca; H, sinus
venosus of heart ; J, subintestinal vein; J7.V, interrenal vein; Lb, hepatic
veins ; **, hepatic sinus ; Np/, renal portal system ; VP, hepatic portal vein ;
Vpo, capillaries of the hepatic portal system; +, cardinal sinus; Sbc, sub-
clavian vein ; Os, Od, left and right omphalo-mesenteric veins.

the precaval sinus or proximal end of the posterior cardinal
vein.

The caudal vein usually bifurcates posteriorly to the cloaca, each
branch passing along the outer side of the corresponding kidney,

VENOUS SYSTEM 325

Card. ant.\ Jug)

Duct. Cuv.

a

Fic. 266.—For description see next page.

326 COMPARATIVE ANATOMY

Fie. 266.—D1AGkamM or THE VEINS OF AN ELASMOBRANCH.

H, heart; Duct.Cur, precaval sinus ; Card.ant (Jug), anterior cardinal (jugular) ;
the inferior juyular is seen nearer the middle line ; Subcl, subclavian ; Seit,
V, lateral vein, which arises from « venous network in the region of the
cloaca (Ven.Cl.B), from one or more cutaneous veins of the tail (Cut./),
from the veins of the body-walls, and from those of the pelvic fing
(HEV) ; Caud.v, caudal vein, which divides into two renal portals, A, A},
at the posterior end of the kidneys (N): from these arise the adve-
hent veins of the renal portal system (V.adv); V-rev, revehent renal
veins, from which the posterior cardinals (CV) arise; Card.V.S, cardinal
sinus, communicating with its fellow in the middle line; V.port, hepatic
portal vein, receiving its blood from the intestine (ZD), stomach (My), and
wsophagus (Oes.V), and anastomosing with the lateral vein posteriorly, and
with the cardinal sinus anteriorly ; Gen.V, genital veins; L.V.S, hepatic
sinus ; Leb, liver.

and giving off advehent vessels into the latter (Figs. 264, 265, IX
—XIIT, 266-268). These divide up into capillaries, forming a renal
portal system, the capillaries again uniting to form revehent veins
which open into the posterior cardinals, ‘lhus the typical condition
of the veins seen in adult Fishes is reached, and only a few of the
more important modifications can be mentioned here.

In Cyclostomes and Elasmobranchs, the anterior part of the
subintestinal vein still persists as a small vessel running within
the spiral valve of the intestine. In the latter Order, many of the
veins (e.g., precavals, anteriorand posterior cardinals, inferior jugulars,
hepatic and genital veins) enlarge to form capacious sinuses, and
a large lateral vein (Figs. 264, 266), running in the body-walls either
close to the skin or just external to the peritoneum, opens into each
precaval or posterior cardinal. This probably corresponds to the
vein of the primary lateral-fin folds (p. 104).

A renal portal system is said to be absent in Cyclostomes, and
is inconstant and very variable amongst Ganoids and Teleosts: in
many instances the caudal vein communicates directly with one or
with both posterior cardinals, and in the former case the other
cardinal shows a tendency to become reduced in size: a similar
reduction occurs in many of the forms to be described next.

Dipnoi.—The chief point of interest as regards the veins of
Dipnoans (Fig. 267) is the presence of a large unpaired postcaval
vein, derived in part from the posterior cardinal, and comparable to
that of the Amphibia and Amniota. A renal portal system is
present, and the blood from the kidneys is collected into two veins
having the relations of posterior cardinals. Only the left of these
however, opens anteriorly into the corresponding precaval, the
right, which is much the larger of the two, passing along the
dorsal border of the liver to open independently into the sinus
venosus in the middle line. The renal portion of this vein is
evidently homologous with the corresponding part of the posterior
cardinal, the anterior portion of which can no longer be recognised.

VENOUS SYSTEM 327

Fic. 267.—D1acram oF THE VENOUS System or Proftopferus annectens.
(After W. N. Parker.)

v, ventricle ; at, atrium ; p, pericardium; ca, conus arteriosus ; Jz, Je, internal
and external jugular; Vsbc, subclavian ; DC, DC’, precaval veins ; Cp, post-
caval; Vh, Vh, hepatic veins; ZL, liver; G@.B, gall-bladder ; (.G, bile-duct ;
M, “stomach”; Da, intestine; L.(/, lymphoid organ in the walls of the
stomach, the blood from which passes into the hepatic portal veins (Vpo,
Vpo'); par.v, parietal veins, from the body-walls; Ov.v, ovarian veins ;
N, N, kidneys; BV, pelvic vein; V.eawl, caudal vein; V.ren.port, renal
portal vein ; ws, cesophageal vein; V.card, left posterior cardinal vein, which
is connected by anastomoses (ans) with the postcaval (Cp) in the region of
the kidneys,

s28. COMPARATIVE ANATOMY

Thus the postcaval is made up of a posterior or renal portion, and
of an independently developed anterior or hepatic portion.

In Ceratodus, the posterior cardinal and postcaval are directly
continuous with the caudal vein, and the renal portal, receiving
branches from the posterior end of the body, arises from the iliac vein,
which also gives off a pelvic branch. The latter unites with its
fellow in the middle line to form a median abdominal vein, com-
parable to that of the Amphibia, and opening into the sinus
venosus.

The two pulmonary veins unite into a single trunk before
opening into the left atrium (p. 309).

Amphibia.—A large postcaval vein arises in essentially the
same manner as in the Dipnoi, its renal section being formed by
the fusion of the two posterior cardinals in this region. The
hepatic portion apparently arises in part from the right omphalo-
mesenteric vein, and in part independently, while the hepatic
portal vein is developed from the left omphalo-mesenteric. The
postcaval receives blood from the kidneys and generative organs,
as well as indirectly from the posterior extremities, body-walls, and
tail (when present), The anterior part of both posterior cardinals
persists in Urodeles and in Bombinator as the paired azygos vein,
and this may exceptionally be present on one or both sides in other
Anurans. It communicates with the corresponding precaval
(Fig. 268).

A renal portal system is present, and is formed, as in Fishes,
by the bifurcation of the caudal vein, which is wanting in adult
Anura; into the renal portal open the veins from the hind-limb,
and vessels from the body-wall often also communicate with it.
The blood from the kidneys passes into the postcaval. Connecting
the right and left renal portals (or femorals) is a transverse pelvic
vein, from which, in the medio-ventral line of the body, an abdominal
or epigastric vein arises,as in Ceratodus: this is primitively paired, and
corresponds genetically with the lateral veins of Elasmobranchs ;
it extends forwards in the ventral body-wall into the liver, in
which it breaks up into capillaries, becoming secondarily connected
by anastomoses with the hepatic portal vein (Fig. 268), The ab-
dominal vein receives blood from the cloaca, bladder, and body-
walls. In Urodeles remains of the subintestinal vein also open
into the hepatic portal system,

The arrangement of the anterior cardinals (external and inter-

nal jugulars) is essentially similar to that seen in Fishes and
Dipnoans.

Amniota.—The section of the right posterior cardinal vein in
the region of the embryonic kidney (mesonephros, p. 341) gives
rise, as in the Dipnoi, to the hinder part of the postcaval: the
hepatic section of the latter arises as in Amphibia. In the Saur-
opsida, the anterior portions of both posterior cardinals disappear,

Duct Cuv. ---- Card. ant. (Jug)

Card.post.
( Azygas.)

V Cava anf:

pars anter.

V. Cava inf.
ars post.
Ee.

Fic. 268.—D1acram of THE VENOUS SysTEM OF Salamandra maculosa.

Caud.V, caudal vein, which bifurcates at the posterior end of the kidneys (NV, NV)
to form the renal portal system (Nier.Pft.Kr); V.adv, V.rer, advehent and
revehent renal veins; V,z/iaca, femoral vein, which divides into an anterior
(tt) and a posterior ({) branch: the latter opens into the renal portal, and
the former (pelvic vein) unites with its fellow to form the abdominal vein
(Abd. V), and also receives vessels (*) from the cloaca, bladder, and posterior
part of the intestine. V’.Cava inf. pars anter, and V.Cara inf. pars poster,
anterior and posterior sections of the postcaval ; Card.ant (Jug), and Card.
post (Azyg), anterior and posterior cardinal veins (/.¢., the jugular
and azygos). Subel, subclavian vein ; Duct.Cur, precaval ; H, heart ; D, D,
alimentary canal, from which the hepatic portal vein (J’. port) arises ; Ly,
longitudinal vein of the intestine; Lypft.Ar, hepatic portal system; L.V,
hepatic vein.

’

330 COMPARATIVE ANATOMY

and are replaced by vertebral veins, while in Mammals. they persist
as the azygos veins. An anastomosis is formed between these, and
eventually the anterior part of the left disappears, the blood from
both sides passing into the right azygos (hemiazygos), which opens
into the right precaval (Figs. 269 and 270).

The anterior cardinals give rise, as in lower Vertebrates, to the
jugulars, which, as well as the subclavians and vertebrals or azygos,

ES:

SAS

Sea

MS

ti

ti

ial

peter
ty

Fig. 269.—D1acRAM SHOWING THE RELATIONS OF THE PosTERIOR CARDINAL
and PostcavaL VEINS IN A, THE Rapsit, AND B, May. (After Hoch-
stetter).

V.r.d, V.r.s, renal veins; V. cl. 8.e, common iliac vein; J.J, lumbar vein ¢ Pigi
postcaval; V.c.p. d, V.c.p.s, right and left posterior cardinals ; 7”. il.int.comm,
common internal iliac vein.

open into the precavals. In Reptiles, Birds, Monotremes, and
Marsupials, as well as in many Rodents, Insectivores, Bats, and
Ungulates, both precavals persist throughout life; but in other
Mammals the main part of the left disappears, all the blood from
the head and anterior extremities passing into the right. The
coronary veins open into the base of the left precaval (coronary
sinus, Fig. 259).

VENOUS SYSTEM 331

A renal portal system occurs in connection with the embryonic
kidney in all Sauropsida, and traces of it can also be recognised
in embryos of Echidna. In adult Reptiles, renal portal veins give
off branches into the permanent kidney (metanephros, p. 346): in

Fie. 270.—Dr1aGRAM ILLUSTRATING THREE STAGES IN THE DEVELOPMENT OF
THE Hepatic Portat System. (See next page for c.)

Hf, heart ; Sv, sinus venosus ; DC, DC, precavals ; Ci, postcaval; L, liver; Om,
Om, Om, the three sections of the omphalo-mesenteric vein (the first still
shows its originally paired nature at tt: in stage B, the second section of this
vein, which passes through the liver, disappears, so that Om and Om? are
only connected by capillaries: in stage C, the first section (Om) has quite
disappeared, and the umbilical vein (Umb) has become developed); DA,
ductus venosus ; *, connection of the umbilical vein with the capillaries of
the liver; Vr, revehent veins; Vad, advehent veins; Mes., mesenteric
vein, which later gives rise to the hepatic portal (V.port), receiving
blood from the alimentary canal (D); Az., azygos; Jl, iliac vein; N,
kidney.

Birds only a slight indication of such a renal portal system exists,
and in Mammals it is entirely wanting.

As in Fishes, the first veins to appear in the embryo are the
omphalo-mesenteric veins (Fig. 270, A), bringing back the blood from

332 COMPARATIVE ANATOMY

the yolk-sac, and uniting into a single trunk before opening mito
the heart. As the liver becomes developed, a portal circulation
arises, and the main trunk of the vein, where it passes through the
liver, disappears. In the meantime, the cceliac and mesenteric
veins have become developed, and all the blood from them, as well
as from the vitelline veins, now passes through a common trunk,
the hepatic portal vein, into the capillaries of the liver, whence it

I
_ Me

Fic, 270, c.—Reference to lettering on previous page.

reaches the sinus venosus through the hepatic veins. The vitelline
veins gradually disappear as the yolk-sac becomes reduced.

In addition to these vessels, the umbilical vein must also be
mentioned. This vessel is originally paired, and corresponds
genetically to the lateral veins of Elasmobranchs and to the
abdominal or epigastric vein of Ceratodus and Amphibians. It
is situated originally in the body-walls, and comes into rela-
tion with the allantois (pp. 9 and 337), opening eventually into the

LYMPHATIC SYSTEM 333

postcaval: as the allantois increases in size, it brings back the
oxygenated blood from this organ (i.e., from the placenta in the
higher Mammalia). The right umbilical vein, however, early be-
comes obliterated, and the left comes into connection with the
capillaries of the liver, its main stem in this region disappearing
(Fig. 270, B). Thus the blood from the allantois has to pass through
the capillaries of the liver before reaching the heart. In the course
of development, however, a direct communication is formed be-
tween the left umbilical vein and the remains of the fused vitelline
veins, and this trunk is known as the ductus venosus (Fig. 270, Cc).
On the cessation of the allantoic (or placental) circulation, the
ductus venosus becomes degenerated into a fibrous cord, so that
all the portal blood has to pass through the capillaries of the liver.

The intra-abdominal portion of the umbilical vein persists
throughout life as the epigastric vein in Reptiles and in Echidna,
but disappears in Birds and in other Mammals.

The mode of development of the veins of the extremities is essentially
similar in all the Amniota, and at first resembles that occurring in
Amphibia, though later on considerable differences are seen in these two
groups, more especially as regards the veins of the digits.

Retia Mirabilia.

By this term is understood the sudden breaking-up of an arte-
rial or venous vessel into a cluster of fine branches, which, by
anastomosing with one another, give rise to a capillary network ;
the elements of this network may again unite to form a single
vessel. The former condition may be described as a wnipolar, the
latter as a bipolar rete mirabile. If it is made up of arteries or of
veins only, it is called a rete mirabile simplex; if of a combination
of both kinds of vessels, it is known as a rete mirabile duplex.

The retia mirabilia serve to retard the flow of blood, and thus
cause a change in the conditions of diffusion. They are extremely
numerous throughout the Vertebrate series, and are found in the
most varied regions of the body, as, for instance, in the kidneys

glomeruli, p. 345)—where their above-mentioned function is most

clearly seen; on the ophthalmic branches of the internal carotid ;
on the vessels of the air-bladder in Fishes (p. 280); along the
intercostal arteries of Cetacea; on the portal vein; and along the
caudal portion of the vertebral column in Lizards.

LYMPHATIC SYSTEM.

In Fishes, Amphibians, and Reptiles, but more particularly in
the first-named Class, lymph vessels (p. 299) are often not
plainly differentiated, and occur mainly along the great blood-

334 COMPARATIVE ANATOMY

vessels, as. well as on the bulbus arteriosus and ventricle, lying
in the connective-tissue surrounding these structures. Numerous
independent lymphatic vessels may, however, also be present,
arising from a capillary network under the skin, and extending into
the intermuscular septa ; the intestinal tract and the viscera are also
generally provided with definite lymph-vessels in the Amphibia
and Amniota.

Contractile lymph-hearts may be present in connection with the
vessels. They occur in Fishes, but are much better known in
Amphibians, Reptiles, and Bird-embryos. Thus, in Urodeles, nume-
rous lymph-hearts are present under the skin along the sides of
the body and tail, at the junction of the dorsal and ventral body-
muscles; in other Amphibians they are either confined to the poste-
rior end of the body (pelvic region), or, as in the Frog, are present
also between the transverse processes of the third and fourth
vertebre. In Reptiles posterior lymph-hearts only are present,
and are situated at the boundary of the trunk and tail regions,
close to the transverse processes or ribs, Similar structures are not
known to be present in Mammals.

Large lacunar lymph-sinuses are present under the skin of tail-
less Amphibia, and the skin is thus only loosely attached to the un-
derlying muscles. These subcutaneous lymph-sinuses are connected
with those of the peritoneal cavity. Amongst the latter, the sub-
vertebral lymph-sinus is of great importance in Fishes, Dipnoans,
and Amphibians; it surrounds the aorta and is connected with the
(mesenteric) sinus lying amongst the viscera, into which the
lymphatic vessels of the intestine open. In Fishes and Dipnoans
there is also a large longitudinal lymphatic trunk lying within the
spinal canal.

As already mentioned, the higher we pass in the animal series
the more commonly are lymphatic trunks with independent walls to
be met with. From Birds onwards a large longitudinal subverte-
bral trunk (the thoracic duct) is always present. In Mammals this
arises in the lumbar region, where it is usually dilated to form the
cisterna or receptaculum chyli; it receives the lymph from the
posterior extremities, the pelvis, and the urinogenital organs, as
well as the dacteals, or lymphatics of the intestine. In Mammals it
communicates anteriorly with the left, and in Sauropsida with both
left and right precaval veins. The lymphatics of the head, neck,
and anterior extremities open into the same veins.

The lymphatic vessels of Birds and Mammals are, like certain
of the veins, provided with valves, the arrangement of which allows
the lymph stream to pass in one direction only, <.¢., towards the
veins,

The lymph, as already mentioned (p. 299), consists of two
elements, a fluid (plasma) and cells (lymph-corpuscles, leucocytes) ;
and similar cells are present in the lymphoid or adenoid tissue which
occurs beneath the mucous membrane in various parts of the body °

LYMPHATIC SYSTEM 335

(eg., alimentary canal, bronchi, conjunctiva, urinogenital organs)
and is particularly abundant in Fishes, Dipnoans, and Am-
phibians (pp. 267, 352, 363).

The migration of the amceboid leucocytes to the surface (p. 267) is due
to various causes. It may simply result in getting rid of superfluous
material, or may be of considerable importance in removing broken-down
substances and harmful bodies (e.g., inflammatory products, Bacteria), the
particles being ingested by leucocytes (hence often called phagocytes)
before the latter are got rid of.

The mass of lymphoid tissue on the heart of the Sturgeon, and possibly
also the so-called fat-bodies (corpora adiposa) of Amphibia and Reptilia
(pp. 368, 370), and the ‘“‘hibernating gland” of certain Rodents, may be
placed in this category ; they consist of lymphoid and fatty tissue, and serve
as stores of nutriment.

The agglomeration of a number of lymphoid follicles gives rise
to those structures which are spoken of as “lymphatic glands”
or adenoids. ‘These are always interposed along the course of
a lymphatic trunk so that afferent and efferent vessels to each
can be distinguished. They probably appear first in Birds, and
are most numerous in Mammals, where they are present in
abundance in various regions of the body; they differ greatly in
size,

The spleen which is present in almost all Vertebrates, is
closely related to these structures. It corresponds to a specially
differentiated portion of a tract of lymphoid tissue primarily
extending all along the alimentary canal, and in Protopterus
it still remains enclosed within the walls of the stomach
(Fig. 209). In other Vertebrates it is situated outside the
walls of the canal, but even then may extend along the greater
part of the latter (¢.g., Siren). Usually, however, either the
proximal or the distal portion of it undergoes reduction, and the
organ is generally situated near the stomach, though it is occa-
sionally met with in other regions of the intestinal tract, as, for
instance, at the commencement of the rectum (Anura, Chelonia).
In some cases (¢g., Sharks) it is broken up into a number of
smaller constituents.

The tonsils are also adenoid structures. They are most
highly developed in Mammals, where they give rise to a paired
organ lying on either side of the fauces—that is, in the region
where the mouth passes into the pharynx, and usually also to a
mass situated more posteriorly on the walls of the pharynx
itself (pharyngeal tonsils); the latter are phylogenetically the
older organs and are present in Reptiles, Birds, and most Mam-
mals! The tonsils consist of a retiform (adenoid) connective-
tissue ground-substance enclosing a number of lymph-corpuscles,
which are arranged in so-called follicles, and are capable of mi-
grating to the surface.

1 Tonsil-like organs are also present in Amphibians.

336 COMPARATIVE ANATOMY

New leucocytes are continually formed in the marrow of the
bones, as well as in the lymphatic glands and spleen; the spleen
is apparently also of importance in absorbing the broken-down
remains of the red blood-corpuscles,

MODIFICATIONS FOR THE INTER-UTERINE NUTRI-
TION OF THE EMBRYO: FQ@TAL MEMBRANES.

J. ANAMNIA.

In several Blasmobranchs the oviduct gives rise to glandular
villi which secrete a nutritive fluid, and in an Indian Ray (Ptero-
platea micrura) there are specially long glandular villiform pro-
cesses which extend in branches through the spiracles into the
pharynx of the embryos, of which there may be as many as three
in each oviduct. The gill-clefts of the embryos are in close appo-
sition, and there are no gill filaments (see p. 278).

In certain viviparous Sharks (viz., Mustelus levis and Carcha-
rias) the walls of the vascular yolk-sac become raised into folds or
villi, which fit into corresponding depressions in the walls of the
oviduct, the latter becoming very vascular. A kind of wmbilical
placenta is thus formed, by means of which an interchange of nutri-
tive, respiratory, and excretory matters can take place between the
maternal and foetal blood-vessels.

Amongst viviparous Teleosts (comp. p. 360) various arrange-
ments for the nutrition of the embryo occur. In Zoarces
viviparus (and probably also in the Embiotocideg), the embryos
are retained in the hollow ovary, the empty follicles (corpora lutea)
of which give rise to extremely vascular villi, from which a serous
fluid containing blood- and lymph-cells is extruded into the cavity
of the ovary and thus surrounds the masses of embryos. These
swallow the fluid and digest the contained cells. In other forms
(¢.g., Viviparous Blennies, and Cyprinodonts), the embryos undergo
development within the vascular follicles, and are probably nour-
ished by diffusion ; while in Anableps, villi are developed from the
yolk-sac, and these doubtless absorb the nutritive fluid from the
walls. of the ovary.

In certain Amphibians which have no prelarval existence, in-
teresting modifications occur for nourishing the young until the
larval stage is passed. Thus in the Alpine Salamander (Salaman-
dra atra), a large number of ova (40—60) pass into each oviduct,
just as in the allied 8. maculosa, in which the young are born as
gilled larve. Were this the case in S. atra, the young would be
carried away in the mountain streams and destroyed, and acurious
adaptive modification has therefore arisen in this form, in

>

FQTAL MEMBRANES 337

which only one embryo (that nearest the cloaca) in each oviduct
undergoes complete development, remaining within the body of
the parent until the gills are lost and metamorphosis has taken
place. The other eggs break down and form a food-mass for
the survivors after their own yolk has become used up. Degene-
rative changes, moreover, take place in the epithelium of the ovi-
duct, and masses of red blood-corpuscles pass into the lumen of the
latter, undergo degeneration, and become mixed with the broken-
down yolk-masses, the resulting broth being swallowed by the
surviving young. After the birth of the latter, the uterine epithe-
lium becomes regenerated; and thus a process occurs which some-
what resembles that of the formation of a decidua in placental
Mammals (p. 340).

II, AMNIOTA.

In all the Amniota, as already mentioned (pp. 9 and 302), foetal
membranes, known as the amnion and allantois are developed,
the latter, or primary urinary bladder, represented only in rudi-
ment in the Amphibia (p. 259), being of great importance in con-
nection with respiration, secretion, and (in the higher Mammals)
nutrition of the embryo.

A glance at Fig. 8 will show that, owing to its mode of develop-
ment, the amnion! consists primarily of two layers; an inner, the
amnion proper, and an outer or false amnion. The latter les close
to the vitelline membrane, and forms the so-called serosa, or serous
membrane. As the allantois grows it extends into the space con-
tinuous with the celome between the true and false amnion, and
may entirely surround the embryo.

Amongst Reptiles, the eggs of the viviparous Lizard, Seps chal-
cides, are relatively poor in yolk, and this is compensated for by
the yolk-sac and allantois coming into close relation with the
walls of the oviduct, thus forming an wmbilical and an allantoic
placenta, one at either pole of the embryo; the latter of these is
the more important. Both foetal and maternal parts of the pla-
cente become extremely vascular, and thus the necessary inter-
change of materials can take place between the blood of the em-
bryo and mother. In Trachydosaurus and Cyclodus, as well as in
the Chelonia, a kind of umbilical placenta is apparently also
formed.

The fact that a vascular yolk-sac (often known as the wmbilical
vesicle) is present in placental Mammals, indicates that they are
descended from forms in which, like the Sauropsida, the eggs were
rich in yolk, and which were viviparous. This condition is

1 As the head enlarges and sinks downwards, it is at first surrounded by a
modification of the head fold (p. 9) consisting entirely of epiblast and called the

pro-amnion: this is afterwards replaced by the amnion.
Z

338 COMPARATIVE ANATOMY

moreover retained in the Monotremes, and even in Marsupials
the ova are relatively large as compared with those of the higher
Mammalia. ;

As the amount of yolk gradually became reduced in the course
of phylogenetic development, close relations were set up between
the foetal (allantoic) and maternal blood-vessels, the allantois
becoming closely applied to the serosa to form a chorion (Fig.
271); but that this condition was only very slowly evolved is
shown by the fact that, even at the present day, Mammals exist in
which it has not been reached. These (viz., Monotremes and most
Marsupials) are therefore known as Aplacentalia or Achoria, in
contradistinction to the higher Placcutalir or Choriata. Moreover,
in the Rodentia, Insectivora, Cheir-
optera, Carnivora, and Ungulata
more or less distinct indications
of an wmbilical placenta, formed
in connection with the yolk-sac,
can still be observed, and ata still
earlier stage the ova are nourished
by uterine lymph (compare p. 336).

In Monotremes and Marsu-
pials, both the yolk-sac and allan-
tois take part in respiration; in
the former the two are of equal
importance, while amongst the
latter the yolk-sac is solely or
ae 271.—DIAGRaM OF beaten mainly (Phalcolarctos) important

Aiawicen, (tout Boas's Sevens in this respect. In Perameles
Posiouics en eeeina Gi cain obesula a further approach towards
< a (umbilical vesicle) ; the citer the format ion of a true allantow
most line represents the serous placenta 18 seen, the allantois
membrane. The outer wall of giving rise to small vascular villi.

the allantois has united with the In most Marsupials the allantois
serous membrane to form the P

chorion from which branchial villi Serves merely as a urinary reser-

arise. voir, and in none of them does

it possess any important function

as an organ of nutrition, the young being born ut a relatively early

stage, when they become attached to the teats of the mother, and
are then nourished by means of milk (see p. 288).

In the higher Mammals, the umbilical placenta has usually
only a very temporary importance, though in some cases (eg.,
Rodents) it probably takes some part in respiration and nutrition
during the whole uterine life. The allantois extends out from the
body of the embryo and becomes attached to the serous membrane
to form the chorion, from which numerous villi extend into the
uterine wall (Fig. 271). As both the latter and the allantois become
extremely vascular, the uterine and allantoic capillaries and
sinuses coming into close contact with one another, a complicated

FETAL MEMBRANES 339

allantoic placenta arises, consisting of maternal and fcetal parts
(Fig. 9). Thus the embryo is supplied with the necessities for
existence during its comparatively long intra-uterine life.

Various forms of placenta are met with amongst the Placentalia.
The most primitive type is apparently that in which the allantois
becomes attached around the whole serosa, so that the resulting
chorion, from which the comparatively simple villi arise, are equally
distributed over the whole surface (Fig. 271). This form is known
as a diffused placenta, and is met with in Manis, the Suide, Hippo-
potamus, Tylopoda, Tragulidz, Perissodactyla, and Cetacea.

The next stage is characterised by the chorionic villi becoming
more richly branched, so as to present a greater superficial extent,
and at the same time being concentrated into definite and

Choriongelacsse

Mii tert. Wey: oe my :
Decidia a i aaa pate

Zotton das Cherion.

Prondosum.

Mea Herd. Blatyeorsss

Fru. 272.-—-DraGRAM TO ILLUSTRATE THE RELATIONS OF IHE F@TAL AND
MATERNAL VESSELS IN THE HumMAN PLACENTA, SHOWING CHORIONIC AND
MaterRNAL VESSELS AND CAPILLARIES, VILLI (Zotten), AND DuEcrpvA.
(After Keibel.)

more or less numerous patches or cotyledons. Thus a polycoty-
ledonary placenta arises, such as is met with in most Ruminants,
some of which, such as Cervus mexicanus and the Giraffe, show an
interesting intermediate form of placenta between the diffuse and
the cotyledonary.

The chorionic villi in these two types of placenta, even though
more or less branched, separate from the uterine mucous membrane
at birth, the latter not becoming torn away: these placente are
therefore spoken of as non- decidwate.

A further complication is seen in the forms of placenta known as
the zonary, the dome- or bell-shaped, and the discoidal, in which the
connection between fcetal and maternal parts becomes much more
close, the villi giving rise to a complicated system of branches
within the uterine mucous membrane (Fig. 272). Thus the latter

Z2

340 COMPARATIVE ANATOMY

becomes to a greater or less extent torn away at birth (decidua),
the placenta being therefore spoken of as deciduate. In these
cases, the placental part of the chorion does not extend all round
the embryo. In the zonary placenta only the two opposite poles
of the chorion are more or less free from vascular villi, and this
girdle-like form occurs in the Carnivora, as well as in the Elephant
Hyrax, and Orycteropus. In Lemurs and Sloths, the placenta is
dome- or bell-shaped, while in Myrmecophaga, Dasypodide (Arma-
dilloes), and Primates (Hig. 9) it forms a discoidal mass on the
dorsal side of the embryo (metadiscoidal form). The discoidal
placenta of Rodentia, Insectivora, and Cheiroptera has probably
not arisen, like that just mentioned, from a diffused type, but was
originally restricted to a discoidal area, owing to the umbilical
vesicle occupying a large surface of the chorion.

From the above description it is evident that the differences
in the form of the placenta are mainly those of degree, and that
the latter gives little indication of the systematic position of the
animal in question.

The histological structure of the placenta and the various modifications
seen in the maternal mucous membrane cannot be described here ; it is,
however, important to note that there is no direct communication between the
maternal and feetal blood, and that the maternal capillaries usually enlarge
to form sinuses, the walls of which become invaginated by the villi:
thus the latter are covered by an epithelium furnished by the maternal
tissues (Fig. 272).

In the course of development the embryo becomes more and
more folded off from the yolk-sac (Fig. 8), the stalk of which latter
and that of the allantois, enveloped by the base of the amnion,
together form the wmbilical cord. At birth, the fcetal membranes
are shed, the intra-abdominal portion of the allantois persisting as
the urachus (comp. p. 358).

I. URINOGENITAL ORGANS.

a. GENERAL PART.

The first traces of the urinary and generative organs of Verte-
brates arise on the dorsal side of the ceelome, right and left of the
aorta, and are more or less closely connected with one another,
both morphologically and physiologically.

The part of the urinogenital system first to arise is the paired
pronephros and its duct, the pronephric duct. This is the
most ancient and primitive excretory organ of Vertebrates; it is
usually restricted to a few of the anterior body segments, close
behind the head, whence it is often known as the “head-kidney.”
It originates primarily as a series of segmentally arranged
invaginations of the somatic mesoblast in the region of the ventral
section of the mesoblastic somites, these invaginations giving rise
to excretory tubules or nephridia (Figs. 273 and 274) ; secondarily,
however, in consequence of alterations in the relative rate of
growth of the parts, the tubules come to arise in connection with
the unsegmented body-cavity. Each tubule opens into the coelome
by a ciliated funnel or nephrostome, and comes into relation with a
segmental blood-vessel which primarily connects the aorta with the
subintestinal vein. These vessels become coiled to form a rete
mirabile known as the glomus (Fig. 274). Primarily, as in Cheto-
pods, the tubules must have opened at the other end on to the
surface independently, through the ectoderm (Fig. 277, A, and comp.
Amphioxus, p. 348 and Figs. 219 and 277, A), but this condition is
no longer observable in the Craniata, in which they all communi-
cate with a longitudinal pronephric duct. The number of nephro-
stomes is in most cases not more than two or three.

The pronephric duct is apparently a later acquisition than the
pronephros itself. It first appears in the somatic mesoblast,!
arising by the fusion of the peripheral ends of the pronephric
tubules to form a longitudinal collecting tube (Figs. 274, 277, B),
which extends backwards to open into the cloaca, thus establishing
a communication between the ccelome and the exterior.

1 In Elasmobranchs its origin can be traced to the epiblast.

---d.pn.

2 hy.s. ewe a
das BS Ca

G4
a

Fic.

URINOGENITAL ORGANS 343

273.—A Serres of DiaGramMatic FIGURES ILLUSTRATING THE ACCOUNT OF
THE COMPARATIVE MorrHoLoGy oF THE URINOGENITAL ORGANS OF THE
VERTEBRATA GIVEN IN THE FoLLOwING PaGEs.

A, the pronephros stage of the Anamnia; B, a later stage of the same; C, the

p)

=

urinogenita] apparatus of the male Amphibian; D, the same of the female ;
E, pronephros stage of the Amniota, the mesonephros as yet rudimentary ;
F, urinogenital apparatus of the Amniota at a stage at which the sexes are
not differentiated ; G, urinogenital apparatus of male Amniota; H, the same
of female Amniota.

.» pronephros ; d.pn., duct of the pronephros; ms., the developing me-

sonephros ; ms.s, part of the mesonephros, becoming converted into the
epididymis and parovarium ; #is.r, vestiges of the mesonephros, the para-
didymis and the paroophoron; +, rete and vasa efferentia testis; tt, a
network homologous with these structures at the hilum of the ovary; hy.s,
stalked hydatid ; ms.z, portion of the mesonephros which in Amphibians and
Elasmobranchs becomes the so-called pelvic kidney; d.ms, duct of the
mesonephros, which in male Amphibians and Elasmobranchs becomes
(Fig. C) the urinogenital, and in females (Fig. D) the urinary duct. In the
male Amniota it gives rise to the seminal duct (Fig. G), and in the female to
Girtner’s duct (Fig. H); 7.s, the seminal vesicle, an outgrowth of the duct
of the mesonephros; d.m., Miillerian duct, which in Mammals becomes
differentiated (fig. H) into the Fallopian tube (fl), the uterus (vf), and the
vagina (vy); vs, its abdominal aperture; hy, and w.m (Fig. G), unstalked
hydatids and uterus masculinus (vestiges, in the male, of the Miillerian duct,
d.m.); m.t., the definitive kidney or metanephros of the Amniota, said to
arise from the ureter (17), itself an outgrowth of the mesonephric duct ; ai,
allantois or urinary bladder ; sv, urinogenital sinus ; p.g, genital prominence,
y.g, gonads, undifferentiated stage; ov, ovary; ¢s., testis; c/, cloaca; «/,
rectum ; p.a, abdominal pore ; g.c, Cowper’s glands.

TABULATED RESUME OF THE Facts PicroRIALLy ILLUSTRATED ON THE OPPOSITE

Pronephros.

Pace.

Ananimnia. Amniota.

|
ea
|

Develops in all Anamnia, but | Still develops in the Amniota,
| = y | rarely persists as a permanent | but as an excretory organ under-
’ SS | excretory organ. goes entire degeneration in the
|. = embryo: it may take part in the
[ Ss ion formation of the suprarenal

body (7)

In Elasmobranchii, appears to Probably persists as the meso-

7]

° o

= ‘a give origin by subdivision to | nephric (Wolffian) duct, and con-

2 | 3 | both mesonephric (Wolffian) tributes in some to the forma-

8] |and Miillerian ducts. In Am- | tion of the Miillerian duct.

& \ = | phibia, becomes converted into |

«; | © | the mesonephric duct. Its fate in |

5 s other Anamnia is not yet fully

3/s investigated.

a let Li

af Functions in all Anamnia asa, Loses its renal function in all

S| & jurinary gland. In Elasmo-, Amniota (as a rule in the em-

| 2 | branchs, Amphibians, and one bryo), and becomes vestigial,

Q(z | or two higher Fishes, its anterior except so far as it becomes an

S| 3 | portion becomes related to the accessory portion of the repro-

S| © |male genital apparatus, the ductive apparatus in the male

“| = | posterior portion persisting as a and enters into the formation of
= | permanent kidney. the suprarenal body (7)

COMPARATIVE ANATOMY

TABULATED REsumE—(Continaed).

Anamnia. Amniota.
The proximal portion becomes The proximal end becomes the
3 in most cases (except in Cyclo. rete and vasa efferentia testis,
‘2 | stomes and Teleosts) related to the caput epididymis, and per-
_ | | the testis and functional in the . haps also the stalked hydatid
S transmission of the semen, the | of Morgagni: the distal end be-
ze distal functioning as a kidney. | comes the paradidymis (Giraldé’s.
> ' organ).
q 1
g
3 CMM Sr at apne AT soe aa eae
Al Persists as the kidney. | The greater part of the proxi-
el /mal portion becomes the par-
om | ovarium, the distal the paroo-
\ ‘ ' phoron.
/ Functions in most higher | The proximal portion becomes
| 3 | Fishes merely as the urinary | the corpus and cauda epidymis
S| duct. | and the distal the seminal duct
gl In Elasmobranchs, Amphi- | (vas deferens).
a | bians, and some Ganoids, serves
eB as the urinogenital duct.
§ Jae = Sao et 4
Oo.
=i Functions exclusively as the |The greater part, as a rule,
rie duct of the mesonephros, 7.e., degenerates ; the proximal por-
5 the urinary duct. | tion may be retained in a vestigial
Se ‘form in the region of the par-
A's /ovarium. In certain cases it
i 8 ‘may persist, as a whole, as
& | Gartner’s canal. The distal end
‘becomes the organ of Weber.
i In Elasmobranchs it degene- The proximal portion becomes
_% ;rates in post-embryonic life, | the unstalked hydatid of Mor-
/.& | vestiges of its proximal portion | gagni, the distal, in some Mam-
3 cae being retained. Its existence! mals, the so-called ‘uterus
Sl in most other Fishes is doubt- | masculinus.” In exceptional
A. ful. In Dipnoi and Amphibia it | cases the whole is retained as
E. is retained, at any rate for some | Rathke’s duct. In Sauropsida
ap time, for its whole length, in aj; the distal part usually dis-
a | functionless and often but little | appears.
‘2 | 3 | degenerate condition.
alo |
a Se Sess es ane
= | When present, becomes the Becomes the whole genital
| whole genital duct. duct.
S 121. pe . i'8
5 g | Probablyunrepresented(comp . Appears to arise in part (ure-
ie 5 ip. 352). ter) from the distal end of the
E Bar tl At a mesonephric duct, and in part
Bo) sz ‘(secreting elements) as a caudal
ap s extension of the mesonephros.
ni vo
o rad
a a

|

URINOGENITAL ORGANS

345

The pronephros itself has only a transitory function as an
excretory organ. Its duct, however, always persists, and usually
undergoes important modifications, which are closely connected
with the appearance of a second and more extensive series of

indung

tomhohtle tr Verb
mit dem Color.

Myo

~—4ussere Haut

os
de

l
th

, resp: Von Acer Urnicre

adbgeschrairt: Myotonv.
Derivat des Cocloms

tame Coe

(ina

SU

Nopthrostorm-
derVornicre (bervimprt)

(Perttoncum)

DIAGRAMMATIC TRANSVERSE SECTION ILLUSTRATING THE PRIMARY RELATIONS OF THE PRONEPTTROS

Tone Glomus dcr Vornicre

vorgcbauchte Coclomrvand’

ay

crise Neberrtcre

Al

sn

Kt

(bevurgrcrt)

Nathrostom
der Urnicre’

Partetal.

Peritore

Urnierengang

274.

Fie,

(ON THE Rreir) AND MESONEPHROS (ON THE LEFT) wir THEIR Ducts.

eovoro
aaSon
Pin ee
Boe, Tt
Or°OsgE
ob. 2
ep yo
nen =
ae ee
Asge
oe s
FEoxv
od 2
Br oe
Sea
7 oy
= =
ia)

in}

On the left

lome, and a mesonephric tubule (CUrriere) and its duct

iated nephrostome of the m

the spinal cord, notochord, aorta, and intestine.

ome are seen to be continuous

), and the glomus are shown.

Between the

n capsule are shown.
intestine are seen the rudiments of the gonad

right the cavities of the myotome and the cel
myotome has become shut off from the ere

(Vornierc), the pronephric duct (Vorniergand

In the middle line are seen, from above downwards,
as a Malpie

(Vebenniere).

(Aeémdriise) and suprarenal

excretory segmental tubules, which appear later, mainly posteriorly
to the pronephros, and constitute the mesonephros or mid-
kidney; the pronephric duct now serves as a mesonephric duct.

The mesonephros, often known as the MWoljian body (Figs.
273, 274, 277, B), is sometimes regarded as corresponding simply to

346 COMPARATIVE ANATOMY
a “later generation” of pronephric tubules. It appears more
probable, however, that this organ originates independently from
a part of the mesoblastic somites situated more dorsally than that
which gives rise to the pronephric tubules. Primitively, the
mesonephros is strictly metameric, owing to the fact that each of
its tubules corresponds to the primary channel connecting the
cavity of a somite with the unsegmented ccelome (Fig. 274). The
loss of connection between these two sections of the primary
ccelome results in a series of segmental nephridia, each of which
opens into the body-cavity by a nephros-
tome, while at its other, or blind end, it
comes into connection with the prone-
phric duct—or mesonephric duct as it
must now be called (Fig. 275). The
glomus of the pronephros is continued
backwards, and in the region of the
mesonephros breaks up into portions, or
glomeruli, each of which is situated in a
small cavity constricted off from the
colome and opening into a mesonepbric
tubule, forming what is known as a
Malpighian capsule (Figs. 274, 275).
Each mesonephric tubule, then, in
its primitive form, is made up of the
following portions (Fig. 275):—(1) a

Fic.

275.—DIAGRAM OF THE

MESONEPHRIC TUBULES,

SHOWING THEIR (SECOND-
ARY) CONNECTION WITH THE
Mesonepuric Duct (SG).

The two anterior tubules are
already connected with the
duct, while the two posterior
have not yet reached so far.

S7, nephrostome; IM, Mal-
pighian capsule with glome-
rulus ; DS, coiled glandular
tubule ; HS, terminal por-
tion of latter.

funnel-shaped ciliated aperture, commu-
nicating with the body-cavity (nephro-
stome, or peritoneal funnel); (2) a
rounded mass of capillaries (glomerulus),
which is situated within a cavity (Mal-
pighian capsule) derived from the
celome; and (8) a coiled glandular
tubule, opening into a collecting (me-
sonepbric) duct. Thus the mesonephros,
as well as the pronephros, besides its

main function of excreting waste pro-
ducts by means of the epithelial cells
lining the tubules, serves also to conduct water derived from the
blood in the glomeruli, and peritoneal fluid, from the body.

The mesonephros is of greatest importance in the Anamnia: in
many Fishes it serves exclusively as a urinary organ, but in
Elasmobranchs and higher forms it also takes on certain relations
to the generative apparatus, giving rise to the refe and vasa
efferentia of the testis, as well as to the parorchis or epididymis (p.
350), and, in Amniota, to other more or less rudimentary organs
of secondary importance (compare Fig. 273). Nevertheless, it may
still serve as the permanent urinary organ (Klasmobranchs, Am-
phibians), or may more or less entirely disappear as such (Amniota) ;
in the latter case, a third series of tubules is formed, giving rise

URINOGENITAL ORGANS 347

to a metanephros, or hind-kidney, with which is connected a
metanephric duct or ureter.

The metanephros corresponds to a later developed posterior
section of the mesonephros. Each metanephric duct apparently
arises as a hollow outgrowth from the posterior end of the meso-
nephric duct, where the latter opens into the cloaca. It gradually
extends forwards, and comes into connection with a series of
tubules developed as buds from the hinder end of the mesone-
phros and provided with ccelomic Malpighian capsules and with
glomeruli, but not with nephrostomes. The posterior end of the
ureter soon loses its connection with the mesonephric duct, and
opens independently either into the cloaca or into a urinary bladder
(Figs. 294—297).

THE MALE AND FEMALE GENERATIVE Ducts.

In the Elasmobranchii, Amphibia, and Amniota, ¢wo canals are
formed in connection with the primary excretory apparatus : one
of these is known as the secondary mesonephric or Wolffian duct—
which in male Elasmobranchii and Amniota functions as a seminal
duct or vas deferens and in male Amphibia as a urinogenital duct, and
the other as the Miillerian duct—which opens anteriorly into the
cceelome and serves in the female as an oviduct (Figs. 278, 279).
The Wolffian duct becomes rudimentary in the female—except in
Amphibians, in which it still serves as a urinary duct (Fig. 279)—
and the Miillerian duct remains in a more or less rudimentary
condition in the male. These two ducts in some cases (Elasmo-
branchs) arise by a splitting of the primary mesonephric duct
into two (Fig. 278), but more usually the Miillerian duct arises
independently from the ceelomic epithelium. All the urinogenital
ducts are lined by a mucous membrane, external to which are
muscular and connective tissue layers. (For the relations of the
urinary and generative ducts in other Fishes and in Dipnoans
see pp. 3860-363.)

THE GonaDs (“GENERATIVE GLANDS ”).

The sexual cells, which give rise to the ova and spermatozoa
originate from the germinal epithelium, which corresponds to
a differentiation of part of the celomic or peritoneal epithelium on
the dorsal side of the body-cavity on either side of the mesentery,
and into which the adjacent mesoblastic stroma penetrates; thus
a pair of gonads or “sexual glands” is formed (Fig. 274).

Primitively the gonads were arranged segmentally, and extended through-
out a greater number of body segments (compare Amphioxus, p. 359).

The primitive germinal cells ave at first entirely undifferen-
tiated, but in the course of development a differentiation takes
place, resulting in the formation of a male or a female gonad, we.,
a testis or an ovary.

348 COMPARATIVE ANATOMY.

The mode of development of the ova and spermatozoa is briefly as
follows :—

Ova.—The cells of the germinal epithelium grow inwards amongst the
stroma of the ovary in the form of clustered masses : some of these increase
in size more than the others, and give rise to the ova, while the smaller cells
form an investment of follicle round them, and serve as nutritive material.
The investing cells multiply, and in Mammals a cavity containing a fluid
is formed in the middle of each follicle (Fig. 276): the main mass of the
follicular cells which enclose the ovum project, as the discus proligerus, into
the cavity of the follicle. When ripe, the ovum, surrounded by a vitelline
membrane, comes to the surface of the ovary and breaks through into
the abdominal cavity; it then passes into the coelomic aperture of the
oviduct. A certain amount of blood is poured out through the broken ends
of the vessels in the stroma of the ovary into the cavity of the follicle in
which the ovum lay : this ‘‘ wound” then closes up, and its contents undergo
fatty degeneration, giving rise to a body of yellow colour, known as the
corpus butewmn, ;

Spermeatozoa.—As in the case of the female, primitive germinal cells can
be at first distinguished in the development of the male generative elements,
These give rise to a series of seminal tubules (Fig. 300), containing larger and
smaller cells; the former undergo division to form the sperm-cells or

PS Ke Ps

2

ray
RO: iS

(i

'o,

if
a
Q

Fic. 276.—Srcrion THROUGH A PoRTION OF THE OVARY OF A MAMMAL, SHOWING
tHE Mop oF DEVELOPMENT OF THE GRAAFIAN FOLLICLES.

KE, germinal epithelium, ingrowths from which extend into the stroma of the
ovary to form the ovarian tubes (PS): the stroma is penetrated by vessels
(g.g)3; U, U, primitive ova; S, cavity between the follicular epithelium
(tunica granulosa, Vy) and the primitive ova; Lf, liquor folliculi; D, discus
proligerus ; Mi, ripe ovum, with its germinal vesicle (A) and germinal spot ;
Mp, zona pellucida, showing racliated structure ; Z'f, theca folliculi.

spermatozoa, The nucleus gives rise to the so-called ‘‘ head” of the sperma-
tozoon, while the surrounding protoplasm becomes differentiated to form the
motile ‘tail,’ which serves as an organ of propulsion, the ‘*neck”
(Mittolstiick) arising from the centrosome of the cell (p. 3).

URINOGENITAL ORGANS 349

). SPECIAL PART.

URINARY ORGANS.

In Amphioxus a series (90 or more) of independent segmental
tubules are present on either side in the reduced section of the
ceelome situated on the dorsal side of the pharynx (“dorsal

y\
[we x
>

MTN

Qi
es

<esum

Fig, 277.—DrackamMatic TRANSVERSE SECTIONS THROUGH A, AMPHIOXUS, LN
THE BRANCHIAL REGION, AND B, AN ELASMOBRANCH EMBRYO, BASED ON
Boveri’s Ficurgs.

In A, the section passes through a branchial cleft on the right side, and shows a
transverse section of the anterior limb of a nephridium (X); on the left, a
nephridium (X) is indicated showing its communication with the ccelome (B)
and with the atrial chamber (C). 4, genital section of ccelome (an ovary is
indicated on the right side); D, section of the ccelome which extends down
the branchial bars ; /, ventral aorta.

In B, the section represents the pronephric region on the left, and the meso-
nephric region on the right. A, rudiment of a mesonephric tubule, the
blind end of which subsequently comes to open into the pro- (or meso-)
nephric duct (C) as indicated by the dotted lines on the right. 8, nephro-
stome ; D, celome: /’, subintestinal vein.

In both figures, E, lumen of gut; @, aorta; H, portion of commissural vessel
which comes into relation with the excretory system.

ceelomic canals”). Each of these tubules comes into close relation
with a branchial blood-vessel, possesses a varied number of lateral
branches, and opens on the one hand into the ccelome by several
ciliated funnels or nephrostomes, and on the other by a single
aperture into the atrial or peribranchial chamber (p. 275), which

350 COMPARATIVE ANATOMY

thus also serves as an excretory duct (Figs. 219 and 272, a).
The segmental arrangement of the tubules in the adult corre-
sponds to that of the branchial apparatus, and not to that of the
myotomes. No nephridia are present posteriorly to the pharynx,
and it is possible that the excretory system of Amphioxus may be
to a certain extent comparable to an early stage of the pronephros
of the Craniata.

In Cyclostomes the pronephros persists beyond the larval
period, and for some time at any rate, functions as the sole excre-
tory organ: it possesses three or four nephrostomes. In Petro-
myzon it is soon replaced by a mesonephros, and the pronephros
then becomes rudimentary : between the two a fat-body is situated.
In Myxine it is uncertain whether the whole kidney, or only its
anterior part, represents the pronephros. The kidney does not
come into relation with the generative organs, and its duct, which
opens on either side into the urinogenital sinus, probably represents
the unaltered pronephric duct.

In the Teleostei the pronephros has, in the majority of cases,
only a temporary significance, and the mesonephros constitutes
the excretory organ of the adult: it consists of a narrow
band varying in size and diameter in different regions, situated
on the dorsal side of the body-cavity, between the vertebral
column and the air-bladder. Secondary fusions between . the
organ of either side often occur. The urinary duct in both groups
probably represents the pronephric duct, and may lie more or less
freely, or be embedded in the substance of the kidney. Posteriorly
the two ducts usually fuse together and become expanded to form
a kind of urinary bladder (compare Figs. 286 and 287) which has
nothing to do with the allantoic bladder of Amphibia and Am-
niota. The bladder usually opens behind the anus—either inde-
pendently or together with the genital ducts—by a simple pore, or
on the summit of a urinogenital papilla.

Thus a differentiation of the pronephrie (or primary mesonephric)
duct into a Wolffian and a Miillerian duct is not known to occur in
Teleostei, nor does the mesonephros come into connection with
the gonads; in Elasmobranchii, in which the pronephros is
more rudimentary, this differentiation takes place (p. 346), and
at the same time a distinction between an anterior and a
posterior section of the mesonephros may be observed (compare
Figs. 278, 289, and 290). In the male, the former (parorehis or
epididymis) comes into connection with the testis by means
of small ducts, the vasw efferentia, and its tubules open directly
into the Wolffian duct, which thus functions as a vas deferens
only; while the latter, which persists as the permanent kidney,
empties its secretion by means of separate urinary ducts into
the base of the Wolffian duct. In the female the Wolffian

It is said to persist in Pieraxfer, Lophius, Dactylopterus, Orthagoriseus mola,
Mora mediterranea, and the Macruride.

URINOGENITAL ORGANS 351

Fic. 2784.—D1acRam oF THE PRIMITIVE CONDITION OF THE KIDNEY IN AN
ELasmMoprancn Embryo. (After Balfour.)

pd, pronephric duct : it opens at o into the body-cavity, and its other extremity
communicates with the cloaca; 2, line along which the division appears which
separates the pronephric duct into the Wolffian duct above, and the Miillerian
duct below ; s.¢, nephridial tubes: they open at one end in the bhody-cavity,
and at, the other into the Wolffian duct.

Fic. 278p.—DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS IN
AN Aputt Femate Evasmoprancu. (After Balfour.)

m.d, Miillerian duct ; w.d, Wolffian duct ; d, urinary duct ; s.¢, nephridial tubes :

five of them are represented with openings into the body-cavity : the posterior
nephridial tubes form the functional kidney ; ov, ovary.

6 & “h

Fru. 278c.—DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS IN
AN ApuLT Mate ExLasmoprancn. (After Balfour.)

m.d, rudiments of Miillerian duct ; w.d, Wolffian duct, marked vd in front, and
serving as vas deferens ; s.f, nephridial tubes : two of them are represented
with openings into the body-cavity: the anterior tubules give rise to the
parorchis or epididymis and the posterior ones to the functional kidney ; @,
urinary duct; ¢, testis; nt, canal at the base of the testis; VZ, vasa
efferentia ; /c, longitudinal canal of the Wolffian body.

352 COMPARATIVE ANATOMY

duct is rudimentary, and the ova pass to the exterior by means of
the Miillerian duct.

This special differentiation of the hinder part of the meso-
nephros, and the formation of special ducts in connection with it,
seems to foreshadow the condition which occurs in the Amniota
(pp. 346 and 356).

The anterior (sexual) part of the kidney is usually broader than the
posterior (renal) part. The outer border is usually notched, and this,
together with the arrangement of the nephrostomes in the embryo, points
to the original segmental arrangement of the organ. The segmental char-
acter, however, disappears later on; in the adult the nephrostomes are
much less numerous than the vertebree of this region, but their number
and size vary much in different genera and even in individuals, and they
apparently do not persist in all.

The morphology of the kidneys and renal ducts in Ganoids (Figs.
286 and 287) requires further investigation. They seem on the
whole to resemble those of Teleosts, though in the Sturgeon they
apparently show points of similarity to those of Elasmobranchs.
As in the Teleostei, a well-developed pronephros is present in
the larva, and the kidney duct probably represents the pronephric
duct.

In many Fishes the kidneys extend far back into the root of
the tail.

A close examination of the organ, which appears to the naked eye as the
kidney in Teleosts and Ganoids, shows that a larger or smaller portion of it
Ree particularly the anterior part—consists of an adenoid or lymphoid
Substance.

In the Dipnoi the kidneys also undoubtedly correspond to
the mesonephros. They are relatively longer in Protopterus
(Fig. 288) than in Ceratodus, extending through a considerable
portion of the body-cavity: as in Elasmobranchs, a narrower
anterior can be distinguished from a broader posterior part, and
the whole is largely invested by lymphoid and adipose tissue.
Nephrostomes are wanting. Until their development is known,
it is uncertain to what extent the renal ducts correspond to the
primary mesonephric ducts: each opens into the cloaca inde-
pendently, behind the genital aperture. The cloacal czecum (p. 262)
probably functions as a urinary bladder.

Amphibia.—The pronephros is well developed in the larva,
and is particularly large in the Gymnophiona, in which as many as
12 or 18 nephrostomes may be present.

In adults, the most primitive condition is met with in the
Gymnophiona, in which the kidney (mesonephros) consists of long,
narrow, varicose bands, usually extending from the heart to the
anterior part of the cloaca, which latter - is often much elongated.
In the embryo they consist of definite masses, which are arranged
metamerically, and in each of them a elomerulus, a nephrostome,
and an excretory duct can be distinguished (Fig. 291). This con-
dition sometimes persists in the anterior portion of the kidney,

URINOGENITAL ORGANS 353

but, owing to secondary processes of growth, as many as twenty
nephrostomes are later on met with ina single body-segment. The
number of nephrostomes in the entire kidney may amount to a
thousand or more.

As regards the urinary duct and the relations of the entire

B

Fic. 279.—DiacRam oF THE URINOGENITAL SysTEM oF (A) A MALE AND (B) A
FemaLE URoDELE ; FOUNDED ON A PREPARATION oF J'riton teniatis.
(After J. W. Spengel.) °

Ho, testis; Ve, le, vasa efferentia of testis, which open into the longitudinal canal
of the mesonephros, + ; a, collecting tubes of the mesonephros, which open into
the Wolffian (urinogenital) duct (/g, 7g); in the female the latter serves
simply as the urinary duct (Ur), and the system of the vasa efferentia (testicu-
lar network) is rudimentary ; mg, mg! (Od), Miillerian duct ; Of, ccelomic
aperture of latter in the female ; Ov, ovary; G.N, anterior sexual portion of
kidney (parorchis of the male); .V, posterior non-sexual portion of kidney.

renal apparatus to the generative organs, the Gymmnophiona in
all essential points resemble other Amphibia.

The kidneys of Urodela and Anura are situated in the usual
position on the dorsal side of the body-cavity ; in the former they are
band-like and more extended longitudinally than in the latter,

AA

354 COMPARATIVE ANATOMY

in which they are shorter and more compact, and are confined
to the middle portion of the ccelome.

In Urodeles they always consist of a narrow anterior, and a
broader and more compact posterior portion. The latter, as in
Elasmobranchs, gives rise to the functional kidney (Fig. 279),
while the former becomes connected in the male with the
generative organs. Delicate vasa efferentia, developed from the
mesonephros, pass out from the testis (Figs. 279, 280,
292) into the substance of the kidney, and there open into the
renal tubules; they may either enter the kidney direct, or
else open first into a longitudinal
collecting duct, from which fine
canals pass to the tubules. Thus
the seminal fluid passes through
the nephridia as well as through
the Wolffian duct, which serves as
a urinogenital duct.

In Urodela and Anura of both
sexes the Wolffian duct nearly
always opens separately on either
side into the cloaca, receiving first,
in Urodeles, a number of ducts
from the posterior part of the
kidney (compare Elasmobranchs,
p. 350). In Anura the Wolffian
ducts pass some distance indepen-
dently along the body-cavity, in
correspondence with the position
of the kidneys, and a_ seminal
vesicle opens into each (Fig. 281).

The wrinary (allantoic) bladder
(see p. 259) opens into the cloaca
ventrally, opposite to the urino-
genital apertures. In its simplest

form it is finger-shaped (e.g., Siren,

Ur, Ur, Urinogenital (Wolffian) Proteus), but it usually becomes

ducts, which appear on the lateral c = 5

surface of the kidneys at +; 8, SWollen distally and is often Di-

S’, their apertures into the cloaca lobed: in Alytes and Bombinator
(Cl); Ho, Ho, testes; FK, FK, it forms a double sac.

corpora acdiposa; Cv, postcaval : ye p
vein; Jo, aorta; Ir, revehent Slight indications of a seg-

renal veins. mental arrangement are found only

in the anterior sexual portion of

the kidney of Urodeles; in the posterior part, and in the entire

kidney of Anura, all traces of segmentation have disappeared. In

both cases, however, the nephrostomes remain throughout life

in great numbers on the ventral surface of the kidney, which
is covered over by the peritoneum (Fig. 281).

The nephrostomes are connected with the urinary tubules in larval Anura,
but later on they become separated from them, and open into the renal

Fiu. 280.—MaLe URINoGENITAL
OrGans oF Rana esculenta.

URINOGENITAL ORGANS 355

Sa \
Fic. 281.—-Kipney oF Discoylossus pictus. From the ventral surface, showing
the nephrostomes ($7). (After J. W. Spengel).
Ur, urinogenital duct, enlarging at Ur! to form a seminal vesicle.

veins. In consequence of this change of function, for such it must be
considered, the body-cavity of adult Anura forms a closed lymph-sinus, as in
the Amniota ; the peritoneal fluid, which in the larva was carried to the
exterior and lost, is in the adult poured into the general circulation, like the
rest of the lymph.

AA 2

356 COMPARATIVE ANATOMY

Reptiles and Birds.—In the Sauropsida, as in the Mammalia,
the mesonephros, so far as it is retained in the adult, is entirely
separate from the functional excretory apparatus; this consists
of a metanephros, entirely wanting in nephrostomes (compare
p. 846 and Fig. 273).

The metanephros never extends so far along the body-cavity
as does the mesonephros; as a rule it has the form of a small
compact or lobulated organ, usually situated in the posterior
half of the body-cavity, or even entirely confined to the pelvic
region: it has the latter position, for instance, in most Reptiles

Fic. 282.—EXxcrETORY APPARATUS oF JVonitor indicus.

The right kidney is shown in its natural position, while the left is turned on its
longitudinal axis, so that the ureter and the collecting tubes are visible. The
urinary bladder is not represented.

NV, N, kidneys ; SG, collecting tubes which open into the ureter (U7, (72); Ur',

aperture of ureter into the cloaca.

(Figs. 282, 294 and 295) and all Birds (Fig. 283). The posterior
end of the kidney, which is generally narrower than the rest,
may even extend under the root of the tail, as in Lacerta, in
which region there is a fusion of the organ of either side.

Thus, according to the position of the kidneys, the ureters
(metanephric ducts) cither do not extend freely along the.
body-cavity, or they may have a longer or shorter free course.
The latter is the case, for instance, in Crocodiles, and more
especially in Birds (Fig. 283): in the latter the kidneys
are closely embedded within the pelvis, and their ventral
flattened surface, which is usually divided into three lobes, is

URINOGENITAL ORGANS 357

often penetrated by deep furrows and clefts in which the veins
le embedded; posteriorly they may fuse together in the middle
line, as in Lizards.

There is not always a perfect symmetry between the organ
of either side, and this is most marked in Snakes, in which the

Fic. 283.-—MALE URINOGENITAL APPARATUS OF HERON (Aiiled cincrec).

NV, kidneys ; Ur, ureter, opening into the cloaca (Cr) at Sr; Ho, testis; Hp, epi-
didymis ; Vd, vas deferens, which opens at V«/! on a papilla in the cloaca :
V, V, furrows on the ventral surface of the kidney in which veins lie em-
bedded; Ao, aorta; BF, bursa Fabricii, which opens into the cloaca at BF".

greatly lobulated kidneys, like those of limbless Lizards, are
elongated, narrow, and band-like, in correspondence with the
form of the body.

A urinary (allantoic) bludder arising from the ventral wall of
the cloaca, is present in Lizards and Chelonians ; it is more or less
bilobed. A bladder is wanting in Snakes, Crocodiles, and Birds.

358 COMPARATIVE ANATOMY

Mammals.—The definitive kidneys (metanephros) of Mammals
are proportionately small, and lie on the quadratus lumborum
muscle and ribs. They usually possess a convex outer, and a
concave inner border; the latter is called the hilum, and at this
point the ureters arise and the blood-vessels enter. The expanded
proximal portion of the ureter is divided up to form one
or more calyces (Fig. 284), into which small papilliform processes
of the pyramids (see below) project ;
on the summits of these the urmary
tubules open in varying number.
The calyces are continuous with a
large cavity in the widened portion
of the ureter called the elvis, and
from this the ureter (metanephric
duct) passes freely backwards for
some distance to open into the
bladder (except in Monotremes, Fig.
296) on its dorsal side, sometimes
Hie Ht —aceaarre Tose. Neete the apex, sometimes towards

TODINAL SECTION THROUGH tum the fundus. The bladder communi-

Kipyey of 4 Mawnan. cates with the wrinogenital canal or
R, R, cortical substance; AZ, JZ, urethra. y :
medullary substance arranged in The kidney 1S greatly lobulated

pyramids (Pr); between the in the embryo; this condition may
latter the cortical substance ex-

tends in the form of the columns remain throughout life, or the lobes
of Bertini (B, B); Ca, calyces; may become more or less completely
Pe, pelvis ; Ur, ureter. united (Fig. 285). In the latter case
the original division into lobes may
still be recognised more or less plainly internally. A section of
the kidney shows an inner layer, the medullary substance, arranged
in the form of wedges—the urinary pyramids,—and an outer layer,
or cortical substance, extending as the columns of Bertini between
the pyramids (Fig. 284). The pyramids correspond roughly to the
embryonic lobes of the kidney, though several lobes may fuse
together in one pyramid.

The glomeruli as well as the coiled portions of the tubules, sur-
rounded by a network of blood-capillaries, lie in the cortical
substance, while the straight portions of the tubules extend through
the pyramids, where they gradually anastomose to form larger
collecting tubes.

The greater part of the wrinary bladder does not corre-
spond with the proximal end of the allantois, but to a special
differentiation of the cloaca, which becomes divided into a
dorsal and a ventral portion by the formation of a horizontal
septum. The ventral portion gives rise to the bladder, which
is continuous distally with the stalk of the allantois (urachus,
see p. 340), from which the median ligament of the bladder
is formed. In Monotremes and nearly all Marsupials (see

URINOGENITAL ORGANS 359

p. 338) the whole allantois takes part in the formation of the
bladder.

Fic. 285.—A, Ricut Kipyey or a Deer; B, Kipyeys (VY) axp SUPRARENAL
Bopres (N.N) oF THE Humax Empryo. (Both from the ventral side.)
Ur, ureters.

GENERATIVE ORGANS.

In Amphioxus the gonads are developed in a part of the
reduced ccelome situated on either side of the pharynx and
intestine (Fig. 277, A) between the outer body-wall and the atrial
cavity. They have a marked segmental arrangement, and each
portion sheds its products independently into the atrial cavity,
whence they pass out through the atrial pore (compare p. 275 and
Fig. 219).

In Cyclostomes also, generative ducts are wanting ; the sper-
matozoa or ova are shed directly into the body-cavity, and pass
through the genital pores (p. 298) into the urogenital sinus, and
so to the exterior. The gonad is a long unpaired organ suspended,
as in other Vertebrates, to the dorsal wall of the body-cavity by
a fold of peritoneum, the mesorchium or mesoarium, as the case
may be.

In Fishes the gonads are only exceptionally unpaired, and
even then, this is only a secondary condition, due to the fusion
of the two organs or to the reduction of that of one side; as in all

360 COMPARATIVE ANATOMY

other Vertebrates, they are originally paired. There is usually a
want of symmetry observable between the organ of the right and
left. sides.

The testes and ovaries of Teleostei closely correspond with one
another as regards position and the arrangement of their ducts.
Dorsal and ventral folds of the peritoneum are developed in con-
nection with the elongated ovary, and these in most cases meet
along its outer side, so as to enclose a portion of the ccelome and
thus convert the ovary into a hollow sac, blind anteriorly,
on the inner folded walls of which the ova arise; this sac is
continued backwards to form the oviduct (compare Fig. 286). The
latter, which is generally short, as a rule fuses with its fellow to
form an unpaired canal; this opens either by a genital pore
(p. 298) between the rectum and the urinary aperture on a level
with the integument, or on a papilla, which may become elongated
to form a tube or “ovipositor”; or the ducts may communicate
with a urinogenital sinus.

The testis of Teleosts is elongated, and often lobulated in form.
Its duct has similar relations to those seen in the female.

Thus the ducts, both of the ovary and testis, correspond to folds
of the peritoneum enclosing a ceelomic cavity continuous with that
of the gonads, and originate quite independently of the nephridial
system. The oviducts must therefore be distinguished from true
Miillerian ducts.

In some Teleosts the ovary is solid, and the ova are shed into
the body-cavity. In the Smelt (Osmerus) and in Mallotus the
oviducts (“peritoneal funnels ”) have cpen ccelomic apertures close
to the ovaries into which the ova pass (compare Fig. 286, B); while
in other Salmonide and in the Murenide and Cobitis, for
instance, these peritoneal funnels are shorter, and may even be
absent, the ova then being shed into the urinogenital sinus
through a paired or single genital pore. It is uncertain whether
the latter is the primitive arrangement amongst Teleostei, or
whether the peritoneal funnels represent reduced oviducts.

Most Teleostei are oviparous, but viviparous forms occur (p. 336). The
male Stickeback builds a nest for the protection of the young formed of a
hardened secretion (mucin) of the kidney, which undergoes a change of
function at the breeding-season ; in Syngnathus and Hippocampus the young
are protected within a pouch on the abdomen of the male, and in the female
Solenostoma on a pouch between the ventral fins. Amongst Siluroids they
are carried within the pharynx in the male Arius, and the eggs are attached
to the soft ventral integument in the female Aspredo.

Amongst Ganoidei the female organs of Lepidosteus are formed
on the same type as those of the Teleostei. In Amia (Fig.
286, B) and Acipenser each oviduct opens by a funnel into the
ccelome, but in all Ganoids the oviduct is probably comparable to
that of Teleosts, and not to a Miillerian duct. In the male
Lepidosteus a series of vasa efferentia pass out from the testis and

URINOGENITAL ORGANS 361

open into a longitudinal canal from which ducts pass into the
kidney, the duct of which therefore serves as a urinogenital duct
(Fig. 287). The latter dilates before uniting with its fellow to
open into the urinogenital sinus. A somewhat similar arrange-
‘ment appears to occur in the male Sturgeon, in which representatives
of the oviducts of the female are present in the form of short ccelomic
funnels opening into the kidney-ducts. It is probable that the other
male Ganoids also resemble Lepidosteus in the structure of their
urinogenital organs, which, however, require further investigation.

In the Dipnoi (Fig. 288) the elongated gonads are invested

Lg-AP
Fiu. 286. Fic. 287.
Fic. 286.—FemaLe Urtnocenrran Oruans or A, LeprposTEus, AND B, AMIA.
(A, after Balfour and Parker ; B, after Huxley.)

a, degenerate anterior portion of kidney ; 6/, bladder ; kd, kidney ; ord, oviduct 3
oud’, aperture of oviduct into bladder ; ord", peritoneal aperture ; ory, ovary ;
p, peritoneum ; wy. ap, urinogenital aperture ; wr, kidney duct.
Fic. 287.—Mave URINOGENITAL ORGANS OF LEPIDOSTEUS. (After Balfour and
Parker.)

bl, bladder ; /.r, longitudinal canal ; ¢s, testis ; w.g, ep, urinogenital aperture ; ur,
kidney duct ; v.¢f, vasa efferentia.

Fic. 288.—URinoGEnITaL Orcans or Protopterus annecters. A, FEMALE; B,
Youne Mate. From the'ventral side. (After W. N. Parker.) The peritoneum
is removed on the right side in A, and on the left in B.

In both figures: N,N, kidneys ; Ost, ccelomic aperture of Miillerian duct ; /y, lg,
lymphatic tissue in connection with the kidneys ; VG’, kidney ducts: ANG,
apertures of kidney ducts into the cloaca (Cl) ; Pap, genital papilla in the
cloaca formed by the fusion of the base of the Miillerian ducts; RD, cloacab
cecum; Fe, rectum ; Poab, abdominal pore ; Cp, postcaval vein, connected
by transverse anastomoses (as) with the left posterior cardinal vein ( J”. card).
The veins from the gonads are also indicated.

In A. OV, Ov!, ovaries ; ord, ord’, oviducts.

In B: Hod, testes, with their investment of lymphoid and adipose tissue (LG) ;
Hod.(, free portion of sperm-duct,uniting with the Miillerian duct (J7G)
at *. Per, peritoneum.

URINOGENITAL ORGANS 363.

with lymphoid and adipose tissue, and are closely attached to the
outer border of the kidneys; when ripe, they become greatly
enlarged, so as to embrace the gut ventrally. The oviducts, which
doubtless correspond to Miillerian ducts, are long and coiled, re-
sembling those of the Amphibia: posteriorly they unite before
opening into the cloaca, and each communicates anteriorly with the
body-cavity by a funnel-shaped aperture. The wall of the ovi-
duct secretes albumen round the eggs as they pass along it.

The manner in which the sperm is conducted to the exterior in
Ceratodus is not understood. In Protopterus (Fig. 288, B) the
seminal tubules of the testis open into a duct, embedded between
the lobes of the testis ventrally. Behind the testis the duct ex-
tends freely for a short distance, and then unites with the base of
the Miillerian duct, which, as in the female, joins with its fellow
to open into the cloaca on the summit of a papilla. The rest of
the Miillerian ducts, with their ostia, can still be recognised in
immature individuals. The sperm-duct of Protopterus is ap-
parently a structure sui generis ; like that of Teleosts, it is probably
developed quite independently of the nephridial system.

In the greater number of Elasmobranchs the ovaries are
paired, and the oviducts, like those of Dipnoans, are separate
from the ovaries, and correspond to Miillerian ducts. Their
anterior portion has a common opening into the body-cavity,
and further back each is provided with an oviducal or shell-gland.
The anterior part of the oviduct is always narrower and more
delicate than the posterior, which dilates to form a kind of uterus,
in which (when the Shark is viviparous) the embryo undergoes de-
velopment. -Posteriorly, the oviducts open into the cloaca some-
what behind the aperture of the ureters—either separately, or by
a common canal (Figs. 278, B, 289).

The oviducal gland secretes the horny material for the egg-case or
“purse,” which is usually elongated and produced at its four angles into
longer or shorter tendril-like threads ; in Cestracion it has a spiral ridge.
The majority of Sharks are viviparous, and in these the egg-shell becomes
more or less reduced. In Mustelus antarcticus the uterus becomes divided
into several compartments, each containing an embryo surrounded by a
membrane apparently representing the horny egg-shell of other forms.

The testis of Elasmobranchs is paired and symmetrical, but the
two organs may become partially fused with one another. Vasa
efferentia connect each testis with the anterior end of the corre-
sponding mesonephros (parorchis), the Wolffian duct serving as a
vas deferens (p. 346), and giving rise to a dilated portion or
vesicula seminalis, as well as to a cecal sperm-sac where it com-
municates with the urinogenital sinus: the latter opens into the
cloaca on the apex of a papilla (Figs. 206, 278,c, 290). Vestiges of
the anterior end of the Miillerian ducts can be recognised even in
the adult as a short transverse tube with a central aperture,
situated below the cesophagus anteriorly to the liver.

364 COMPARATIVE ANATOMY

Fertilisation is internal in all Elasmobranchs except Leemargus, in which
generative ducts are said to be wanting.

Fie, 289. Fig. 290.

Fras. 289 and 290.—FEMALE AND MALE URINOGENITAL ORGANS OF Raja batis. x 4.
(From T. J. Parker’s Zootomy.)

a.p, abdominal pore; ¢/, cloaca; epd, left epididymis (the right is removed) ;
fi.t, anterior portion of oviducts (Miillerian duct); fl.t’, common opening
of the two oviducts into the celome; 7.7, internal body; A, kidney ;
mu.d, mesonephric (Wolffian) duct; od.g, oviducal gland ; cs, cesophagus ;
ov, right ovary (the left is removed); pn.d, remains of anterior part of
Miillerian duct; ».s, sperm sac; 8.9’, its opening into the urinogenital
inus; ¢, left testis (the right is removed); w.b, dilated end of mesonephric
duct ; «g.p, urinogenital papilla; wg.s., urinoyenital sinus; w.p, urinary
papilla; wr, kidney ducts; ur’, opening of kidney duct into the urino-
genital sinus; w/, uterine portion of left oviduct (that on the right side
is removed); wf, its opening into the cloaca; r.d, vas deferens; vs,
vesicula seminalis; ¢.s’, its opening into the sperm-sac.

In female Holocephali the generative organs are essentially
similar to those of Elasmobranchs, but in the male they present
certain peculiarities. The unripe sperms pass into the immense
epididymis, in which they become ripe and invested by spermato-

URINOGENITAL ORGANS 365

phores, which pass into a large vesicula seminalis at the base of
the vas deferens; the Miillerian ducts are complete in the male,
though small.

Hermaphroditism occurs amongst Fishes. In Myxine the posterior part of
the gonad usually first gives rise to spermatozoa, and subsequently the anterior
part to ova, so that self-fertilisation is prevented. Serranus and Chryso-
phrys, again, are hermaphrodite, and hermaphroditism has been occasionally
observed in various other Fishes (e.9., Gadus morrhua, Scomber scomber,
Clupea, Harengus). .

Amphibia.—The paired and symmetrical gonads of Amphibians
are situated in about the middle of the celome; their
form is usually modified by the shape of the body. Thus in the
Gymnophiona the ovary has the form of a long and narrow band,
while the testis is made up of a long chain of small bodies united
together by a collecting duct (Fig. 291). Each individual portion

Fig, 29].—DracraM oF A PortioN oF THE MaLe GENERATIVE APPARATUS OF
THE GYMNOPHIONA.

Ho, Ho, testis; Sg, collecting duct of testis ; Poa. testicular capsules ; Q, 0
transverse canals connecting the collecting duct with the longitudiual canal
(L, L); @, @!, second series of transverse canals; WV, M, Malpighian
capsules ; .V, .V, kidney ; ‘7’, nephrostome ; 5, convoluted portion of urinary
tubule; A/S, urinogenital duct.

of the testis of Cezecilians is made up of a double row of rounded
capsules in which the sperm is formed, and from which it is passed
into a collecting duct, which perforates each portion of the organ.
A transverse canal is given off from the free portion of the collect-
ing duct lying between every pair of testis lobes; this passes to-

366 COMPARATIVE ANATOMY

wards the kidneys, and opens into a longitudinal canal. From the
latter the sperm passes through a second system of transverse canals
to the Malpighian capsules, and thence through the urinary tubules
into the urinogenital duct. :

The male generative apparatus of all Urodela and certain
Anura (comp. p. 854) corresponds in the main with that seen in
-Cecilians, except as regards the form of the gonads: thus the testis
is either pointed at one or both ends (Fig. 279), or more or less
round or oval (Figs. 280, 292).

In Rana, Bombinator, and Alytes the vasa efferentia of the testis become
gradually separated from the kidney: that is, they either open directly into
the urinogenital duct, without becoming connected with the urinary tubules

Fic, 292.—Txstis axp AnrTEeRIon Exp or Kipney or Rana esculenta.
(Semidiagrammatic. )

-Ho, testis ; q, q, transverse canals of the testicular network, which give rise to
blind processes at +t +; Z, longitudinal canal of the testicular network, from
which the interrenal network (C, C) arises ; NV, kidney ; Ur, urinogenital
duct.

(Rana, Fig. 292), or the greater number of the posterior canals end
blindly, while only the anterior ones are directly connected with the
urinogenital duct (Bombinator), In Alytes the relations of the generative
ducts require further investigation.

Millerian ducts are always present, but they always remain in a more or
less rudimentary condition in the male, and lie along the outer border of the
kidneys in a similar position to those of the female. They may or may not
be provided with a lumen and apertures of communication with the body-

cavity and cloaca.

Hermuphroditism occasionally occurs amongst the Anura : only one case
(Triton teniatus) is known amongst Urodeles. A body attached to the
anterior end of the testis in various species of Toads (‘* Bidder’s organ ”) is
apparently capable of giving rise to ova and spermatozoa. In the males of
Rana temporaria ova are at times developed, embedded within the sub-

URINOGENITAL ORGANS 367

stance of the testis (hermaphrodite gland or ovotestis), and one testis may
even be replaced by a rudimentary ovary. In these cases, the Miillerian
duct may be as well developed as in the female.

The ovaries of Urodela are always formed on a common plan:
each consists of an elongated closed tube, with a continuous lumen.
In Anura, on the contrary, the ovarian sac (Fig. 293) is divided up

Fic, 293.—URINOGENITAL ORGANS OF A FEMALE Rana esculenta,

Ov, left ovary (that of the right side is removed); Od, oviduct; Ot, abdominal
aperture of oviduct; Ut, the dilated posterior end of the oviduet 5 P,
opening of latter into the cloaca; .V, kidneys; S, S', apertures of urinary
ducts into the cloaca, surrounded by longitudinal folds (*), which are
separated by a deep depression (t).

into a longitudinal row of numerous (3 to 20) separate pockets or
chambers. The oviducts open far forwards into the body-cavity by
funnel-shaped apertures; they take a tolerably straight course
along the outer borders of the kidneys to the cloaca in young
animals, but become greatly convoluted later. A short distance
from its termination each oviduct in Anurans becomes dilated to
form a thin-walled sac, and, after becoming again narrowed, usually

368 COMPARATIVE ANATOMY

opens separately on a papilla on the dorsal wall of the cloaca.
Only in the genera Bufo and Alytes do the two oviducts fuse
together into a posterior unpaired canal.

In female Urodeles a number of tubes serving as a receptaculum seminis
may be present in connection with the cloaca, and the male is provided with
a cloacal gland which secretes spermatophores.

After receiving a gelatinous coating from the glands in the wall of the
middle part of the oviduct, the eggs of Anurans pass into the dilated portion
of the duct, and become united together into irregular masses (Frog) or chains

Toad).

: 1 apioxium glutinosum (Gymnophiona) the eggs are very similar to those
of Sauropsida: they are exceptionally large (9 mm. long), of an oval shape,
and possess a large yolk. They become coated after fertilisation with a
tough albumen in the oviduct, and this becomes drawn out at the poles into
chalazz, by means of which the eggs are connected together like the beads of
a necklace. The segmentation is meroblastic, and takes place in the oviduct ;
and the eggs are laid in the earth, the mother coiling herself round them.

Fat-podies (conpora adiposa) are present in all Amphibia in
connection with the gonads: they are formed of adenoid substance,
fat, and leucocytes, and contain numerous blood-vessels.

The corpora adiposa probably have an important physiological (nutritive)
relation to the gonads : Amphibians, after remaining for months without food,
throughout their winter sleep, are able as soon as spring arrives to give rise
to thousands of offspring.

Reptiles and Birds.—The essential differences between the
urinogenital organs of the Anamnia and Amniota have already
been described (pp. 346, 356, and Fig. 273). =

In the Sauropsida, as in other Vertebrates, the forin of the
gonads is influenced by that of the body: thus in Chelonians they
are broad, while in Snakes and snake-like Lizards they are more
elongated. In the latter cases, as well as in other Lizards, they
are asymmetrical, so that the organ of one side is situated more
or less in front of that of the other. More room is thus obtained
for the development of the ovaries; and, in cases where the eggs
are very large, the organ of one side tends to disappear, as in
certain Elasmobranchs (e¢.g., Scyllium): in Birds, for instance, the
left ovary only is completely developed and functional.

In Reptiles the ovaries are penetrated by a highly vascular
network of trabecule, and in the lymph-cavities thus formed the
formation of ovarian follicles takes place. —

The oviducts (Fig. 294) possess wide funnel-shaped abdominal
apertures, and are usually much folded transversely ; the right is
often longer than the left. Their walls are provided with numerous
muscular elements and glands for the formation of the albumen
and _egg-shell, and they increase in size in the breeding-season.
In Birds the right oviduct, as well as the right ovary, becomes
ek or less completely degenerated ; the left oviduct is considerably
coiled.

URINOGENITAL ORGANS 369

Only slight remnants of the mesonephros and Wolffian duct persist
in female Reptiles, and these undergo fatty degeneration. They are asym-
metrical, and are arranged in a single row on either side, between the oviduct

Fic. 294.—FEMALE URINOGENITAL APPARATUS OF Lacerta muratis.

i r i ; i lder ;
N, - Ur, apertures of the ureters into the cloaca (C7) 5 B, urinary blac ;
a Pet ee of she lather (cut open); &, rectum ; f!, opening of rectum into the

cloaca ; Ov, ovaries ; f, remains of mesonephros ; Od, oviducts, which open
into the cloaca at Od!; Ot, abdominal openings of oviducts.

i Hi duct are more
and vertebral column, The remams of : the Wolffian e
ano in female Snakes, Chelonians, and in Geckos than in the majority of

izards.
Lizards ae

370 COMPARATIVE ANATOMY

The testes of Sauropsida correspond in position with the ovaries,
and, like them, increase in size in the breeding-season. They have
an oval, round, or pyriform shape (Figs. 283 and 295), and are made

Fic. 295.—MaLr URINOGENITAL
Orcans or Anguis fragilis.
(After F. Leydig.)

Ho, testis; t, the so-called ‘‘yellow
body ” (suprarenal) ; #), paror-
chis ; Vd, vas deferens; p, p,
common aperture of the ureter
(Ur, Ur!) and vas deferens on a
papilla on the dorsal wall of the
cloaca (C7); B, urinary bladder ;
r, rectum ; .V, kidney ; mg, rudi-
ment of the Miillerian duct.

up of greatly convoluted seminal
tubules, held together by fibrous
tissue. In Reptiles (¢.g. Lacerta,
Anguis), “ yellow bodies,” which cor-
respond to suprarenals (p. 385), lie
along the outer border of the testis,
and at this point transverse canals
pass out from the testis to the par-
orchis.

The latter consists of greatly con-
voluted canals, and from it arises
the vas deferens (Wolffian duct),
which either takes a straight course,
or is more or less coiled. In Birds
it opens by an independent aperture
into the cloaca, while in Lizards it
fuses with the ureter shortly before
entering the latter.

Remains of the Miillerian ducts are
present in the male, corresponding in
position with those of the female. Their
lumen is not continuous throughout, but
the abdominal aperture may remain open
(Emys europea), and exceptionally (¢.q.
Lacerta viridis) they may be as well de-
veloped as in the female.

Lymphoid organs are present in many
Reptiles, and probably have a physiological
relation to the generative organs (compare
p. 368). In many Lizards they are large
and variously coloured, and lie within the
pelvic region; in Snakes they extend
along almost the entire body-cavity.

Hermaphroditism has been observed
very exceptionally in the Chaftinch. Occa-
sionally the ovary of some Birds undergoes
structural changes, and no longer produces
ova, the female then taking on certain
secondary sexual characters of the male.

Mammals.—In Mammals the generative apparatus no longer
extends along the entire body-cavity, as in the lower Vertebrates,
but is confined to the lumbar and pelvic regions. Moreover,
in correspondence with the close relations which usually take
place between mother and embryo (p. 338), there is a much greater
differentiation of the generative organs than occurs in lower types.
The transition is not, however, a sudden one, for in the lowest
Mammals, viz., the Montremes and Marsupials (Figs. 296 and 297),

URINOGENITAL ORGANS 371

these organs show many points of resemblance with those of Reptiles
and Birds.

Fic, 296.—A, Mane Urinocenrran ORGANS oF Ornithorhynchus paradoxus ; B,
FremaLe URInoGenitaL Orcans or Echidna hystriz.

NY, kidneys; Ur, ureter; B, urinary bladder; Sug, urinogenital canal; Ho,
testis ; Ve, vas efferens; Hp, epididymis; I’, vas deferens ; Od, oviduct ;
r, rectum ; C7, cloaca, opening to the exterior at C7}; m to m*, muscles of the
cloaca and penis (or clitoris); (yp, glans penis, enclosed within its fibrous
tube; Pp, prepuce ; Chi, clitoris ; *, aperture through which the copulatory
organ extends into the cloaca.

Thus in the oviparous Monotremes the left ovary is more strongly
developed than the right, and each has the appearance of a bunch
of grapes; the cloaca persists, and the oviducts (Miillerian ducts),

BB 2

Fic. 297.—FemaLtn GENERATIVE APPARATUS OF CERTAIN Marsvuprrats. <A,
Didelphys dorsiyera (jue.) ; B, Phalungista vulpina ; C, Phascolomys wombnt.
(After A. Brass.)

NN, kidneys; Ur, ureters; Ov, ovary; Ot (Fim), abdominal opening of
Fallopian tube ; Od, oviduct ; Ut, uterus; Ut!, openings of uteri into the
vaginal evecum, VgB; t+, bend between uterus and vagina, Vy; Vy, apertures
of yagine into the urinogenital canal (Sw); B, urinary bladder ; 7, rectum,
which opens to the exteriur (CZ) at r'; g, clitoris; *, +, rectal glands.

URINOGENITAL ORGANS 373

which in other Mammals become more or less fused with one
another proximally, remain distinct throughout, and open into the
urinogenital canal anteriorly to the ureters and bladder.

In the higher Mammals the oviducts become distinctly differ-
entiated into three portions,—a Fallopian tube, a uterus, aod a
vagina. The vagina opens to the exterior (Figs. 278, 297, 298),
while the Fallopian tube communicates with the abdominal cavity
by a ciliated funnel-shaped aperture.

In Marsupials the fusion of the two oviducts is much less
marked than in the higher Mammals, and in order to trace
the gradual differentiation of these parts, their condition in Opos-
sums (Didelphidee) must now be described in greater detail.

A dilated portion of each oviduct (Fig. 297, A), giving rise to a
uterus, is plainly distinguishable from the rest, and its narrowed
posterior end comes into close contact with its fellow in the middle
line. At this point (+) each uterus communicates with the vagina
by a distinct os wtert. The vagina curves sharply outwards, and,
then backwards, opening close to its fellow into the elongated urino-
genital canal. The ureters, as in all other Marsupials in which the
vagine have a similar arrangement, pass between the curved
portions of the vagine to the bladder.

From the condition of the female generative organs in Didel-
phys, that seen in other Marsupials can be easily explained. In
Phalangista vulpina and Phascolomys wombat (Fig. 297, B and c)
the anterior ends of the knee-shaped bends of the vagine lie
closer together, and begin to extend backwards towards the urino-
genital canal, the septum between them disappearing at the
same time. <A vaginal cecum is thus formed: this may
become more elongated, and finally extend backwards so as to
meet the anterior wall of the urinogenital canal, into which it
may open by the formation of a so-called third vagina. The
anus and urinogenital apertures are surrounded by a common
sphincter.

In the placental Mammals the posterior portions of the Miiller-
ian ducts become fused together to form an unpaired vagina, and a
definite cloaca exists only in the embryo, although even in the
adult in certain cases (¢.g., amongst Rodents), the anus and urino-
genital aperture may be enclosed by a common fold of the integu-
ment as in Marsupials, and a median septum may be present in
the vagina distally, indicating its primary double nature. The
uterine portions of the oviducts may also fuse with one another to
a greater or less extent, and thus the most various forms of uteri
result (uterus duplea, bicornis, bipartitus, and simple’), as shown in
Fig. 298, ato D. The Primates possess a single uterus, and in this
case the primitively paired condition of the Miillerian ducts is seen
only in the Fallopian tubes. The latter vary much in form, and
their abdominal apertures are usually provided with fringe-like
appendages (fimbrize). The ureters, unlike those of Marsupials,

374 COMPARATIVE ANATOMY

/ Pe

Sa) SS
BENS

B D
E F

Fic. 298.—Various Forms or Uterr. A, B,C, D, diagrams showing the
different stages in the fusion of the Miillerian ducts: A, uterus duplex; B,
uterus bicornis ; C, uterus bipartitus ; D, uterus simplex; E, female urino-
genital apparatus of J/usfe/ina, containing embryos (*, *) in the uterus; F,
ditto of Hedgehog (Hrinaceus).

Od, Fallopian tube; Ut, uterus; Jy, vagina; Ce, cervix uteri; Ot, abdominal
aperture of Fallopian tube; +, t, accessory glands; 7, rectum; Sug, urino-
genital canal; A, kidney; Nn, adrenal; Ur, ureter; B, urinary bladder.

always pass to the outer sides of the genital passage, the vagina
being single.

The urinogenital canal may, as in Marsupials, be of a consider-
able length (¢.g. amongst Rodents), and a fold of the mucous

URINOGENITAL ORGANS 375

membrane (hymen) is often present where the vagina opens into
it. On the ventral (anterior) wall of the urinogenital canal, the
clitoris (Pp. 380-384) is situated. In both male and female the
space between the urinogenital aperture and the anus is known as
the perineum.

The ovaries are usually small, and rounded or oval in
shape, their surface being either smooth, irregular, or furrowed.
The point at which the nerves and vessels enter is not covered
by peritonerm, and is called the hilum.

Remains of the mesonephros, known as the parovarinm, are present in
the neighbourhood of the ovary, oviduct, and uterus. These usually consist
of small czecal tubes, forming a network, which are connected together by
a collecting duct. In cases where the Wolffian duct persists in the female,
it passes from the parovarium to the urinogenital sinus and is spoken of as
Gartnei’s duct (Fig. 273, 8).

A fold of the skin of the abdomen forming a pouch or mar-
supium is present in Echidna and to a greater or less extent
in Marsupials (p. 28): this serves to protect the egg (Echidna)
and young, which in the latter are born in a very unripe con-
dition, thus rendering possible a longer connection between the
mother and embryo during lactation. The aperture of the marsu-
pial pouch opens anteriorly or posteriorly, according to the mode of
life of the animal, and is provided with a muscle capable of clos-
ing it. In Marsupial embryos the margins of the lips become
partially fused secondarily and temporarily to form a suctorial
mouth, by means of which the young, many of the organs of which
are still in a “larval” condition, become attached to the teats
(compare p. 288).

In male Mammals, the testes arise in the same relative position
as the ovaries of the female. The ovary, however, never moves in
the course of development further backwards than the pelvis; but
the testis may pass out of the abdomen through an tnguinal
canal into a purse-like outgrowth of the integument in the inguinal
region called the scrotal sac, which is lined by a continuation of the
peritoneum, the tunica vaginalis. The two scrotal sacs (which are
represented amongst female Primates by the so-called labia majora
of the vulva) may remain separate, or unite to form a scrotwm: in
Marsupials this is situated in front of, and in placental Mammals
behind the penis (p. 382). If the inguinal canals remain widely
open, they may be withdrawn periodically into the abdomen (as «.g
in Rodentia and Insectivora, in which they only descend at sexual
maturity); this is effected by means of the cremaster muscle, a con-
tinuation of the fibres of the internal oblique and transversalis, or of
the latter only, and corresponding to the “compressor mammre” of
Marsupials. When the inguinal canals become reduced, the testes
remain throughout life in the scrotum. In many Mammals, how-

1 A similar fold, closing the apertures of the oviducts in the immature condi-
tion, is present in Elasmobranchs.

376 COMPARATIVE ANATOMY

ever (¢.g., Monotremes, most Edentates, Elephant), the testes remain

permanently within the abdomen. ;
The testes are smooth, and somewhat oval in form, and their
relative size varies in different Mammals; they are covered by a

i

Fic. 299.—Ma Le URINOGENITAL APPARATUS OF THE HEDGEHOG (Evrinaceits).

N, kidney; Ur, ureters; B, urinary bladder; Pm, membranous portion of
urinogenital tube ; Cpe, corpus cavernosum ; Pp, prepuce; Gp, glans penis ;
PD, preputial glands ; C7, Cowper’s glands; Pr, Pr!, the different lobes of
the prostate ; Sh, vesicula seminalis ; Ho, testis; Zp, epididymis; Iv, Vad,
vas cleferens.

fibrous investment (Fig. 300), from which processes (trabecule)
usually extend inwards. Thus the seminal tubules become
separated into definite lobed masses, and a sort of lattice-work is
also formed (corpus Highmori), through which the elements of
the vasa efferentia pass to the epididymis. In the latter the

COPULATORY ORGANS 377

seminal tubules become rounded off to form the so-called coni
vasculosi, and these are connected together by a collecting duct,
the vas epididymitis. The vas deferens arises from the last
conus vasculosus, and gives rise towards its distal end, shortly
before it opens into the urinogenital sinus close to an elevation—the
colliculus seminalis, to glandular outgrowths (vesicule seminales),
which may attain a relatively enormous size in Rodents and In-
sectivores (Fig. 299). From this point to its termination at the

Fic. 300.—DiacrRamMMatic SECTION OF THE TESTIS OF A MAMMAL.

Ho, testis; NH, epididymis; Vd, vas deferens; A, albuginea of the testis, which
gives rise to the trabeculz (¢, t) and the corpus Highmori (+); L, LZ, coils of
the seminal tubules; Ve, vasa efferentia (rete Halleri) ; Cv, coni vasculosi,
which are connected together by the collecting duct, Jp; Va, vas aberrans.

apex of the penis, the seminal canal is spoken of as the ductus
ejaculatorius.

In many Mammals rudiments of the Miillerian ducts are pre-
sent in the male, and open into the urinogenital sinus. In Man,
only the most posterior end of the ducts remain in the form of an
unpaired vesicle (wlerus masculinus), which lies embedded within
an accessory genital gland, the prostate (Fig. 299). This gland, which
more or less completely surrounds the urinogenital sinus, consists
of glandular tubules connected together by means of fibrous and
muscular tissue: its secretion is poured into the urinogenital sinus,
and is apparently of great importance in connection with the
activity of the spermatozoa.

Copulatory Organs.

Various forms of copulatory organs, morphologically distinct
from one another, occur amongst Vertebrates. In male Blasmo-
branchs a specially modified portion of each pelvic fin (clasper or
pterygopodium, p. 122) serves this purpose. It consists of a series

378 COMPARATIVE ANATOMY

of more or less calcified cartilages, covered by skin and muscles,
which are movable upon one another and are derivatives of the
fin-rays, and it is provided with a channel along the inner side.
These claspers are inserted, in a closed condition, into the cloaca:
of the female, and thence into the oviducts; they are then opened
out by means of special muscles, and the seminal fluid flows along
their channels into the distended oviducts. In connection with
this apparatus there is a gland (p. 18) surrounded by muscular
fibres, which is formed as an involution of the integument; in
its histological character this calls to mind the uropygial gland of
Birds (p. 21).

Tn addition to pterygopodia, similar to those of Elasmobranchs
the Holocephali possess a pair of curious anterior claspers
(Fig. 301), which are protruded from a shallow pouch situated

YW

123

Fic. 301.—Petyic ARCH AND NKELETON oF PrLvic Fin And CLASPER OF A
MALE Chimera monstrose. (After Davidoff.) Ventral view.

Pri, B, dorsal part of pelvic arch (iliac process) ; §.B, anterior clasper ; a—y,
1—3, the various segments of the posterior clasper ; If, basipterygium ;
Ra, Re, radii of fin.

in front of the pelvic fins; each of these consists of a plate

covered with dermal denticles, and in Callorhynchus a grooved

structure is present in addition. There is also a knob-like organ,
usually known as the frontal clasper, on the upper surface of the

head. (Fig. 57).

} These may correspond to portions of the primitive lateral fin-folds (p. 103)
which are not represented in other Craniata.

COPULATORY ORGANS 379

Amongst the Teleostei, the terminal portion of the anal fin in
the male Girardinus is modified to form an apparatus for holding
the female, and in many Cyprinoids certain modifications occurring
in the anal fin may have a similar function.

Amongst the Amphibia, a marked swelling of the lips of the
cloaca may occur in Urodeles during the breeding season and inter-
nal impregnation may take place, but only in the male Gymno-
phiona is a definite copulatory organ present; this simply consists
of the eversible cloaca, which is regulated by a well-developed
musculature (Fig. 302).

Fic. 302.—Tur Posrerion Part oF THE URINOGENITAL APPARATUS OF A,
Epicrium glutinosum anv B, Cucilia lumbricoides.

Cl, CM, Cl, the different sections of the cloaca, and Bs, its cxcal processes : the
cloaca is shown retracted in A and everted in B; c/s, cloacal sheath ; m.r.e/,
retractor muscle of the cloaca; B, B', the two horns of the urinary bladder ;
AN, kidneys; /y, Wolffian duct ; my, Miillerian duct ; 7, rectum ; J/dy, cloacal
aperture ; HS, scales in the integument.

Two kinds of copulatory organs are found in Reptiles, the one
being seen in Lizards and Snakes, and the other in Chelonians and
Crocodiles.

In the former there are two copulatory sacs or penes lying outside
the cloaca, under the skin at the root of the tail, and these can be
everted and protruded through the vent and again withdrawn by
means of a muscle inserted into the blind end of the sac (Fig. 303).
In its everted condition, a spiral furrow extends along each sac down

380 COMPARATIVE ANATOMY

which the seminal fluid passes. These organs are also represented
in the female, in which they are, however, much smaller.

In Chelonians and Crocodiles the penis is single, and corre-
sponds to a thickened portion of the ventral wall of the cloaca

Frc. 303.—Coputatory OrGans or Lacerta agilis. (After F. Leydig.) In A they
are shown everted, and in B their position in the retracted condition is indicated
by dotted lines extending backwards from the vent (Ce).

R, Penes; +, spinal furrow ; SD, the so-called ‘‘ femoral glands” (see p. 20).

(Figs. 304, 305, 4). It consists of fibrous and cavernous (erectile),
tissue, and is protrusible, being regulated by muscles. In the
female it is represented by a smaller clztoris. The penis bifurcates

Tic. 304.—TRANSVERSE SECTION OF THE CLOACA oF A CHELONTAN. (Slightly
diagrammatic.) After Boas.

f, fibrous body ; 7, seminal furrow, bounded by cavernous tissue; «, wall of
cloaca.

proximally, and its distal tongue-shaped portion ends freely; a
longitudinal groove extends along the upper surface, at the proxi-
mal end of which the vasa deferentia open. In Crocodiles the
free portion is relatively longer and the groove deeper than in
Chelonians.

In many Birds a copulatory organ is present, formed on a
similar plan to that of Chelonians and Crocodiles. It is well
developed amongst the Ratitz and Lamellirostres, and in many
other Birds can be recognised in a rudimentary condition. In
Struthio it resembles that of tle Crocodile, and is supported by a

Fie, 305.—DracramMatic LoncirupiyaL SEcTIONS OF THE PosTERIOR Part oF
THE RECTUM, THE CLOACA, AND THE COPULATORY ORGANS OF Vakriors
VERTEBRATES. (After Boas.) The position of the ureter and vas deferens
are indicated, although not situated in the median line.

A, Crocodile; B, hypothetical form between A and C; C, Monotreme (penis
extruded) ; D, Monotreme (penis retracted).

bi, connective-tissue ; b/, urinary bladder; ¢/, cloaca; 7, rectum; /, fibrous body
(corpora cavernosa of human anatomy); 7s, sheath of penis ; ps!, aperture of
the sheath ; 7, seminal furrow or tube (penial urethra) ; s, vas deferens ; 1
urinogenital canal. :

382 COMPARATIVE ANATOMY

fibrous body, bifurcated at the base. In Dromzus and Rhea there
is an aperture at the apex of the penis leading into an elongated
and curved blind sac, in which is a furrow, lined by cavernous
tissue, continuous with the groove on the dorsal side of the
organ. In the Duck and Swan the spiral penis is essentially
similar to that of Dromzus and Rhea. ‘The absence of the blind
sac in the Ostrich, however, is probably a secondary modification.
A clitoris is present in the female of the above-mentioned Birds.

The penis of Monotremes may be best understood by imagin-
ing a hypothetical form intermediate between it and that of Croco-
diles and Chelonians (Fig. 305, B). We must suppose that
a sac-like outgrowth into which the ureter and vasa defe-
rentia open has become developed from the ventral cloacal wall at
the base (anterior end) of the penis, the groove in which has
become converted into a canal. The Monotreme condition is
reached by the sac elongating to form a urinogenital canal, into
the distal end of which the urinary and genital ducts and the
bladder open (c, D). The penis consists of an unpaired fibrous
body enclosing the canal, and is only loosely surrounded by the
mucous membrane of the cloaca, so that it can be protruded from
and retracted into a sheath in which the apex or glans lies.

In Echidna, cavernous tissue is present in the glans; and in Ornitho-
rhynchus the latter is bifurcated and covered with soft spines, the seminal
canal opening in a groove on each fork by numerous fine canals situated on
papille.

A clitoris is present in the female of all Mammals. .

In Marsupials (Fig. 306, a), the penis-sheath opens directly
on to the surface of the body; the opening of the urinogenital
canal into the cloaca has become closed, and is continuous with
the seminal tube or urethra of the penis. The fibrous body
is paired, and both it and the walls of the penial urethra are com-
posed of cavernous tissue.

Amongst Placental Mammals the penis of Rodents (Fig.
306, B) and Insectivores comes nearest to that of Marsupials. The
paired fibrous body (corpus cavernosum) bifurcates proximally
to form two crura, which are nearly always attached to the
ischia. The opening of the penis-sheath gradually becomes further
separated from the anus, and is situated more on the ventral side of
the body (compare B and ¢), the penis itself lying horizontally
along the abdomen. In Primates the organ becomes more or less
free from the body-wall, and either its distal end (Apes, C), or the
whole of it (Man, D) hangs freely, and the sheath forms a double
tube-like investment, the foreskin or prepuce, over the glans.

In the course of development, the penis of Marsupials and
Placental Mammals passes through stages which resemble succes-
sively those which are permanent in Crocodiles and Chelonians
andin Monotremes. It arises from a “ genital prominence” on the

Fic. 306.—Continuation of Fig. 305. For description see next page.

384 COMPARATIVE ANATOMY

Fic. 306.—(The special thickening of the corpus spongiosum and the glans penis
present in some Mammals is not indicated).

A, Marsupial (very diagrammatic, for comparison with Fig. 305 C ; the obliterated

opening of the urinogenital canal into the cloaca is indicated by dotted lines);

B, Rodent (Celogenys paca) ; C, Ape (Cercopithecus): in most placental Mam-

mals the apex of the penis does not hang down; D, Man; E, Human fetus.

Additional letterings: a, anus ; b, pelvic symphysis ; », genital prominence, which
gives rise to the penis or clitoris ; a/, stalk of allantois.

ventral wall of the cloaca. A channel passes along the side facing
the cloaca to the opening of the urinogenital sinus: this condition
is usually retained throughout life in the case of the clitoris of the
female, while in the male (and occasionally in the female also) the
groove becomes closed to form a canal continuous with the
urinogenital canal or urethra, which thus becomes considerably
lengthened. In addition to the paired erectile corpora cavernosa
there is a median corpus spongiosum or corpus cavernosum urethre
in connection with the penis (Fig. 307): corpora cavernosa are also

Cou B rd
A

Fic. 307.—A, SEMIDIAGRAMMATIC FIGURE OF THE Human Peis. (In transverse
section and from the side.) B, Cirroris or 4 Monkey (Cebus capucinus).

A, albuginea penis ; A’, albuginea urethra ; Sp, septum between the two corpora ,
cavernosa ; S, sulcus dorsalis penis ; Ccp, corpus cavernosum ; Ceu, corpus
spongiosum, which gives rise to the glans penis at Gp, and forms an oval
enlargement (bulbus) at B; rd, rd!, crura of the corpora cavernosa; Cli,
clitoris, with its ventral furrow (2), glans (Gc), and prepuce (Py).

present in the clitoris, and the corpus spongiosum, which retains
its paired character, is represented by the so-called bulbi vestibuli
at the vulva or entrance to the vagina.

In many Mammals a bone (0s penis) becomes developed in
the septum between the corpora cavernosa (¢.g., many Marsupials,
Rodents, Bats, Carnivores, Whales, Lemurs, and Apes). In some
(¢.g., Seal) there is an os clitoridis in the female also. The glans is
provided with a special kind of tactile corpuscles, and in the male
may bear horny papilla and even calcified plates and spines (e.g ,
-certain Rodents).

SUPRARENAL BODIES 385

In addition to the glandular vesicule seminales and the
prostate (Fig. 377), paired Cowper's glands (Fig. 299), open in the
male into the urinogenital canal, and representatives of these
(glands of Bartholini) usually occur in the female. Preputial
glands axe also present between the prepuce and glans penis and
in a corresponding position in the female.

SUPRARENAL Boptes.

The suprarenals or adrenals are bodies of a glandular structure
situated in the ccelome right and left of the vertebral column,
generally in close proximity to the kidueys.

Nothing is known of these bodies in Amphioxus or in the
Dipnoi. In Cyclostomes they are said to be present and to arise in
connection with the anterior part of the pronephros. In
Elasmobranchii and Holocephali they are represented by two
distinct sets of structures—paired or unpaired interrenals of a
yellow colour, close to the kidneys (Fig. 290), and a segmentally
arranged row of suprarenal bodies, situated close to the inter-
costal arteries in the neighbourhood of the kidneys. The former
apparently represent the cortical (mesoblastic) and the former the
medullary (epiblastic) portions of the adrenals of higher forms.
In Teleostei the adrenals are usually paired and are in close
relation with the kidneys—they correspond to the interrenals
of Elasmobranchs. Amongst Ganoids the Sturgeon possesses
numerous yellow bodies of the same nature. In Amphibia these
organs form yellow streaks or dots on the ventral surface or inner
border of the kidneys, receiving blood from the renal portal veins
as well as from the renal arteries.

In the higher Vertebrates the adrenals consist of “cortical”
and “medullary” portions, the latter derived from the sympathetic
nervous system, and therefore epiblastic, and the former from the
pronephros or mesonephros, or from the germinal epithelium
(mesoblastic): the mode of development of the cortical substance,
however, requires further investigation. They are abundantly
supplied with blood-vessels and must have an important function,
but their physiology is not understood. In Reptiles and Birds they
are elongated and lobulated, and are situated close to the gonads.
Both medulla and cortex are apparently represented in all these
forms, but the relative relations of the two parts vary greatly.
In Mammals each adrenal forms a definite and uniform rounded
or oval mass lying near the corresponding kidney (Fig. 285 B), the
medullary substance being central, and the cortical substance
peripheral. In many Mammals these organs contain pigment cells
as well as numerous lymphatic follicles and vessels.

APPENDIX

APPENDIX.

BIBLIOGRAPHY.

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(The abbreviations used in the following pages are given in brackets.)

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390 APPENDIX

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APPENDIX 391

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Transactions of the Royal Irish Academy, Dublin. (Vr. Irish Ac.)

Transactions of the Linnean Society of London: Zoology. (Tr. Linn. Soc.)

Transactions and Proceedings of the New Zealand Institute. Wellington. (Tr.
N.Z. Inst.)

Transactions of the Royal Society of Edinburgh. (Zr. R. Soc. Edin.)

Transactions of the Zoological Society of London. (Zr. Zool. Soc.)

Verhandlungen der Anatomischen Gesellschaft. (Verh. Anat. Ges., see Anat.
Anz.)

Verhandlungen der naturforschenden Gesellschaft in Basel. (Verh. Ges. Basel.)

Verhandlungen der k.k. zoologisch-botanischen Gesellschaft in Wien. (Verh.
Ges. Wien.)

Verhandlungen der k. Akademie der Wissenschaften zu Amsterdam (Verh. Ak.
Amsterdam. )

Verhandlungen der physikalisch-medicinischen Gesellschaft zu Wiirzburg (Verh.
Ges. Wiirzburg.)

Zeitschrift fiir wissenschaftliche Zoologie. Leipzig. (Zeitschr. f. wiss. Zool.)

Zoologischer Anzeiger, zugleich Organ der deutschen zoologischen Gesellschaft.
Leipzig. (Zool. Anz.)

Zoologische Jahrbiicher, Abtheilung fiir Anatomie und Ontogenie der Thiere.
Jena. (Zool. Jahrb.)

Zoologischer Jahresbericht, herausgegeben von der zoologischen Station zu Neapel.
Berlin. (Zool. Jahresber.) ‘

Zoological Record. London.

GENERAL EMBRYOLOGY.

Ban, K. E. von. Ueber die Entwicklungsgeschichte der Thiere. Kunigsberg,
1828-37.
Ba.rour, F. M. Comparative Embryology. 2vols. London, 1880-81.
A Monograph on the Development of Elasmobranch Fishés. London, 1878.
The Works of (Memorial Edition). 4 vols. London, 1885,

392 APPENDIX

Beard, JoHN. On certain Problems of Vertebrate Embryology. Jena, 1896.

Biscnorr, TH. Entwicklungsgeschichte der Saugethiere und des Menschen.
Leipzig, 1842.

Bonnet, R. Grundriss der Entwicklungsgeschichte der Haussiiugethiere. Berlin,
1891.

Dourn, A. Der Ursprung der Wirbelthiere und das Princip des Functionwech-
sels. Leipzig, 1875.

Studien zur Urgeschichte des Wirbelthierkérpers. Mittheil. Zool. Stat.

Neapel, from 1892.

DuvaLt, M. Atlas Vembryologie. Paris, 1888.

Foster, M. and Batrour, F. Elements of Embryology, revised by A. Sedg-
wick and W. Heape. London, 1883.

FrAIssp, P. Die Regeneration von Geweben und Organen bei den Wirbelthieren,
besonders Amphibien und Reptilien. Cassel und Berlin, 1885.

Havpon, A. C. An Introduction to the Study of Embryology. London, 1887.

Harcket, E. Natiirliche Schépfungsgeschichte. Leipzig, 1889. (Eng. trans.
London, 1870.)

Studien zur Gastraeatheorie. Jena, 1887, and Jen. Zeitschr. VIII and IX,
1874 and 1875.

Anthropogenie. Leipzig, 1891.

Hertwic, O. Die Coelomtheorie. Jena, 1881.

Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbelthieve.
Jena, 1893. (Eng. trans. of 3rd ed. by E. L. Mark. London and New
York, 1892).

His, W. Unsere Kirperform. Leipzig, 1878.

Anatomie menschlicher Embryonen (with Atlas). Leipzig, 1S80—1sS85.

Die Lehre vom Bindesubstanzkeim (Parablast). Riickblick nebst kritischer
Besprechung einiger neuerer entwicklungsgesch. Arbeiten. Arch. f. Anat.
u. Physiol. 1882.

KGLLIKER, A. Entw.-Geschichte des Menschen und der hoheren Thiere. 2nd
ed. Leipzig, 1879.
Grundriss der Entw.-Geschichte des Menschen und der hiheren Thiere.
Leipzig, 1880. Compare O. Schultze.
MARSHALL, A. Mrtygs. Vertebrate Embryology. London, 1893.
Prenaxt, A. Eléments d’Embryologie de Homme et des Vertébrés. Paris, 1595.
Quatn’s Elements of Anatomy. Vol. i., part 1. Embryology, by E. A. Schiifer.
London, 1892.
Mixot, Cu. Sep@wick. Human Embryology. New York, 1892.

A Bibliography of Vertebrate Embryology. Boston, 1892.

Rabu, C. Theorie des Mesoderms. Morph. Jahrb. Bd. NV & NIX. Lsso—
1892

RatHKe, H. Entw.-Geschichte der Wirbelthiere. Leipzig, 1861.
Remak, R. Untersuch. tiber die Entwicklung der Wirbelthiere. Berlin, 1850—
1859.
Romrt1, G. Lezioni di embriogenia umana e comparata dei Vertebrati. Siena,
1881, 1882, 1888. :
Roux, W. Ueber die Zeit der Bestimmung der Hauptrichtungen des Frosch-
embryo. Leipzig, 1883.
“Ueber die Bedeutung der Kerntheilungsfiguren. Leipzig, 1883.
Beitr. z. Entwicklungsmechanik des Embryo. No. 4. “Arch. f. mikr. Anat.
Bd. XXIX.
Die Entwicklungsmechanik der Organismen, eine anatomische Wissenschaft
der Zukunft. 189.
Ueber das entwicklungsmechanische Vermigen jeder der beiden ersten.
Furchungszellen des Kies. Verh. Anat. Ges. 1892.
Scucvitze, O. Grundriss der Entwicklingsgeschichte des Menschen und dev
Siugetiere. Bearbeitet unter zu Grundlegung der 2te Auflage des Grund-
risses der Entwicklungsgeschichte von A. Kélliker. Leipzig, 1897.
Sebenka, E. Studien itber die Entwicklungsgeschichte der Thiere. Heft V.
2. Hilfte: Affen Ostindiens, Schluss ; Keimbildung des Kalong
(Pteropus edulis) ; Dottersack und Placenta des Kalong, von R. Gohre.
Wiesbaden, 1892.
Heft I: Keimblitter und Primitivorgane der Maus. 1883. — Heft
IL: Die Keimblitter der Echinodermen. 1883. — Heft III: Die Blitter-

APPENDIX 393

umkehrung im Ei der Nagethiere. 1884. — Heft IV: Das Opossum
(Didelphys virginiana). 1887. — Band V. 1. Hiilfte: Beutelfuchs
und Kangaruhratte (Phalangista u. Hypsiprimnus); zur Entstehungs-
geschichte des Amnion; des Kantjil (Tragulus javanicus); Affen Ost-
indiens. 1891. :

Watpsrer, W. Archiblast u. Parablast. Arch. f. mikr. Anat. Bd. XXII.

ZIEGLER, H. Ernst. Der Ursprung der mesenchymatischen Gewebe bei den
Selachiern. Arch. f. mikr. Anat. Bd. XXXII. 1888.

GENERAL COMPARATIVE ANATOMY, &c.

Beit, F. Jerrrey. Comparative Anatomy and Physiology. London, 1885.

BiuMENBACH. Handbuch der vergl. Anatomie. 1824.

Boas, J. E. V. Ueber Neotenie. Festschrift fiir Carl Gegenbaur. Leipzig, 1S9U.

Lehrbuch d. Zoologie. Jena, 1894. (Eng. trans. by Kirkaldy and Pollard.
London, 1896).

Bronn’s Classen und Ordnungen des Thiereiches. Pisces, by Hubrecht and Sage-
mehl ; Amphibia and Reptilia, by C. K. Hoffmann; Aves, by Selenka and
Gadow ; Mammalia by Giebel and Leche.

Brtanr, C. B. Zootomie aller Thierklassen. 1876-86.

Carus, C. G. Lehrbuch der vergl. Zootomie. II Bde. Leipzig, 1834.

Carus, C. G. and Orro. Erliuterungstafeln zur vergl. Anatomie. VIII Hette.
Leipzig, 1826-52.

Ciaus, C. Grundziige der Zoologie. Marburg and Leipzig (4th ed.), 1880-2,

Lehrbuch der Zoologie. Marburg and Leipzig, 1883. (Eng. trans. by Scdg-
wick and Heathcote, 2nd vol., 1885.)

Corr, E. D. The Vertebrata of the Tertiary Formations ofthe West. Book I.
(Report of the United States Geolog. Survey of the Territories. Vol. IIL.)
Washington, 1884.

The Origin of the Fittest. New York, 1887.

Cuvier, G. Leecons d’Anatomie comparée, V. vol. Paris, 1799-1805. In
German, with notes by H. Froriep and J. F. Meckel. — Leipzig, 1809-10.
2nd French ed. Paris, 1835-46.

Ecxrr, A. Icones physiologice. Leipzig, 1855-9.

Fores, W. A. The collected scientific papers of, edited by F. E. Bedldard.
London, 1885.

GaRrop, A. H. The collected scientific papers of, edited by W. A. Forbes.
London, 1881.

(;aupRY, J. Les enchainements du monde animal dans les temps géologiyues.
1878, &e.

GEGENBAUR, C. Grundziige der vergl. Anatomie. Leipzig, 1870.

Grundriss der vergl. Anatomie. Leipzig, 1878. (Eng. trans. by I’. Jeltre)
Bell. London, 1878.)
(Gorre, A. Ueber den Ursprung de Wirbelthiere. Verh. deutsch. Zool. Ges. V. Bd.
Haxrcken, E. Generelle Morphologie d. Organismen. 2 Bde. Berlin, 1866.
Systematische Phylogenie der Wirbelthiere. Berlin, 1895.

Hatscuex, B. and Cort, C. T. Elementarcurs der Zootomie in fiinfzehn Vorles-
ungen. Jena, 1896.

Hentz, J. Handbuch der systemat. Anatomie. 2 Aufl. 1875.

Hertwic, R. Lehrbuch d. Zoologie, 3rd ed. Jena, 1895. (Eng. trans. by G.
W. Field. New York.)

Hertwic, O. The Cell : Outlines of General Anatomy and Physiology. (Eng. trans.
by Campbell. London, 1895.)

Howss, G. B. An Atlas of Practical Elementary Biology. London, 1885.

Huxzey, T. H. Lectures on the Elements of Comparative Anatomy. London,
1864.

Anatomy of Vertebrated Animals. London, 1871.

Houxiey and Martiy. A Course of Elementary Instruction in Practical Biology.
Revised ed. by Howes and Scott. London, 1888.

Koéuirker, A. Handbuch der Gewebélehre, 6te Aufl. Leipzig, 1889 and 186
(not yet completed).

LanKEsTER, E. R. Article, Vertebrata in the Encyclopedia Britannica, 9th ed.
London, 1891.

394 APPENDIX

Leypic, F. Vom Bau des thierischen Kirpers. I. Bd. 1. Halfte. Tiibingen,

1864. (With Atlas.)

Untersuchungen z. Anatomie u. Histologie d. Thiere. Bonn, 1883.

Zelle und Gewebe. Neue Beitriige zur Histologie des Thierkérpers. Bonn,
1885.

Lehrbuch der Histologie des Menschen und der Thiere. Frankfurt, 1857.

Macauister, A. Introduction to Animal Morphology. 2nd vol. (Vertebrates).
London, 1878.

Mecken, J. F. System der vergl. Anatomie. VI Bde. Halle, 1821-33.

Mitne-Epwarps, H. Legons sur la Physiologie et Anatomie comparée de
V'Homme et des Animaux. XIV Bde. Paris, 1857-80.

MarsHaut, A. Minnus, and Hurst, C. H. A Junior Course of Practical Zoology.
4th ed. London, 1896.

Mivarrt, St. G. Lessons in Elementary Anatomy. London.

Nicuorson, H. A., and Lypexxer, R. Manual of Paleontology. 2 Vols. 1889.

Nuun, A. Lehrb. d. vergl. Anatomie. 1878.

Oweyx, R. Anatomy of Vertebrates. London (4th ed.), 1871.

Parker, T. J. A Course of Instruction in Zootomy (Vertebrates). London, 1884.

Lessons in Elementary Biology. 3rd ed. London, 1896. (German trans. by
Von Hanstein, Braunschweig. )

Parker, T. J., and Hasweit, W. A. Text-book of Zoology. (2nd vol.) London,
1897.

Poucuet, G., and BEAUREGARD, H. Traité d’Ostéologie comparée. Paris, 1889.

Ranvier. Legons d’Anatomie générale. Paris, 1880.

Reports of the Scientific Results of the Voyage of H.M.S. Challenger.

Roxiieston, G. Forms of Animal Life. 2nd ed. by W. Hatchett Jackson.
Oxford, 1888.

Scumipt, O. Handbuch der vergl. Anatomie. VIII Aufl. Jena, 1882.

Handatlas der vergl. Anatomie. Jena, 1852.

ScHNEIDER, A. Beitrage zur vergl. Anat. u. Entwickelungsgesch. der Wirbel-
thiere. Berlin, 1879.

SIEROLD, v., and Stannius. Handbuch der Zootomie. Berlin, 1854. (Handbuch:
der Anatomie der Wirbelthiere Bd. I. Heft 1—2, containing the
Anatomy of Fishes, Amphibians and Reptiles. )

Stricker, 8. Handbuch der Lehre von den Geweben, etc. Leipzig, 1871.

THomson, J. ArntHUR. Outlines of Zoology. Edin. and Lond., 1895.

Voet, Cart, and Yune, Emin. Lehrbuch d. pract. vergleichenden Anatomie.
Braunschweig, 1883-94. (Also a French edition.)

Wacwer, R. Lehrbuch der Zootomie. II Bde. Leipzig, 1843-8.

Icones zootomicae. Handatlas zur vergl. Anatomie. Leipzig, 1841.

WiepersHEIM, R. Lehrbuch der vergl. Anatomie der Wirbelthiere. 2nd. ed.
Jena, 1886. Grundriss der vergl. Anat. der Wirbelthiere. 3rd ed. Jena,.
1893.

ZittEL, K. v. Handbuch der Paliontologie. Miinchen u. Leipzig. (Eng. trans.
by Rastman. )

PAPERS, MONOGRAPHS, &c., DEALING WITH INDIVIDUAL TYPES
AND GROUPS OF ANIMALS.

AMPHIOXUS.

ee B. Studien iiber Entwicklung des Amphioxus. Arb. Inst. Wien,

1882.

Lancernans, P. Zur Anatomie des Amphioxus lanceolatus. Arch. f. mikr.
Anat. Bd. XII.

LANKESTER, E. Ray. Contributions to the knowledge of Amphioxus lanceolatus,
Q. Journ. Micr. Sci. (new Series). No. 124. Vol. 31. 1890.

Lankersrer and Wintzy. The development of the atrial chamber of Amphioxus :
Q. Journ. Micr, Sci. (new Series). No. 124. Vol. 31. 1890.

Mvuier, J. Ueber:den Bau und die Lebenserscheinungen des Branchiostoma
ae Ab. Ak. Berlin. 1844.

Ronieu, W. ntersuchungen iiber den Bau des Amphioxus lane ¥
Jahrb. Ba. IL. 1876. : pe ips ee

Wisk, J. W. vax. Ueber Amphioxus. Anat. Anz. VIII. Jahrg. 1893.

APPENDIX 395

cr The Later Larval Development of Amphioxus. Q. Journ. Mier. Sci.
eon and the Ancestry of the Vertebrates. New York and London,

Pisces anp DIpnot.

Acassiz, A. The Development of Lepidosteus. P. Amer. Ac. Vol. XIII.

On the Young Stages of some Osseous Fishes. Loc. cit., Vol. XIII., 1877,
Vol. XIV., 1878, and Vol. XX., 1884.

Agassiz, A., and Wuirman, C. O. The Development of Osseous Fishes I. The
Pelagic Stages of Young Fishes. Mem. Mus. Harvard. Vol. XIV. No. I.
part l. 1885.

Acassiz, L. Recherches sur les poissons fossiles. V. vol. avec atlas, 1833-43.

Ayers, H. Beitr. zur Anatomie und Physiologie der Dipnoér. Jen. Zeitschr.
Bd. XVII. N. F. XI. Bd. 1884.

Barrour, F. M. (See p. 391.)

Batrour, F. M. and W. N. Parker. On the Structure and Development of
Lepidosteus. Phil. Trans. 1882. 7

Biscuorr, Ta. Lepidosiren paradoxa. Leipzig, 1840.

Busor, P. Contribution 4 Pétude de la Métamorphose de l Ammocoetes branchi-
alis en Petromyzon planeri. Thése présentde a la Faculté des Sciences de
PUniversité de Genéve, etc. Rev. Biol. Nord France, T. III. 1891.

Cuvier and VALENCIENNES. Hist. nat. des Poissons. XXII. vol., 1828-48.

Dean, Basurorp. Fishes, Living and Fossil. Columbia University Biol. Ser. ITI.
New York, 1895.

Emery, C. Fierasfer. Studi intorno alla Sistematica, ’ Anatomia e la Biologia
delle specie mediterranee di questo genere. Atti Acc. Lincei, 1879-80.

Fritscu, A. Fauna der Gaskohle und der Kalksteine der Performation Boh-
mens. Bd.II. Heft 3. Die Lurchfische, Dipnoi. Nebst Bemerkungen
tiber Silurische und Devonische Lurchfische. Prag, 1888. Bd. III. Se-
lachii (Traquairia, Protacanthodes, Acanthodes), Actinopterygii (Megalich-
thys, Trissolepis). Prag, 1893. Palaeoniscidae. Prag, 1894.

GarmaN, 8. Chlamydoselachus anguineus, Garm. aliving species of cladodont
shark. Bull. Mus. Harvard. Vol. XII., No. 1.

Gorrr, A. Entwicklungsgeschichte des Flussneunauges (Petromyzon fluy.). I.
Theil. Leipzig, 1890.

sUNTHER, A. Description of Ceratodus. Phil. Trans., 1871.
Introduction to the Study of Fishes. Edin., 1880. (German trans. by G. von
Hayek. Handbuch der Ichthyologie. Wien, 1886. )

GuiTEL, I’. Rech. sur les Lepadogasters. Arch. Zool. Exp. 2c Série. Vol. VI.

Hasse, C. Das natiirliche System der Elasmobranchier auf Grundlage des Baues
und der Entwicklung ihrer Wirbelsiule. Jena, 1879. Besonderer Theil,
I. and II. Lieferung. Jena, 1882. Ergiinzungsheft, 1885.

Beitrag zur allgemeinen Stammesgeschichte der Wirbelthiere. Jena, 1883.
Howes, G. B. On the Affinities, Inter-Relationships, and Systematic Position of
the Marsipobranchii. Trans. Biol. Soc., Liverpool. Vol. VI., 1892.
Huxtey, T. H. On Ceratodus fosteri, with observations on the classification of

Fishes. P. Zool. Soc., 1876.

Hyrti, J. Lepidosiren paradoxa. Abh. béhm. Ges., 1845.

Juin, Cu. Rech. sur Anatomie de PAmmocoetes. Extr. du Bull. scientif. du
Departement du Nord. 7, Ser. X. Année. 1887. (Dealing with cerebral
and lateral nerves and thyroid.)

Kuprrer, C. Die Entwicklung des Herings im Ei. Jahresbericht der Com-
mission zur wissenschaftlichen Untersuchung der deutschen Meere in Kiel
fiir die Jahre, 1874-6. Berlin, 1878.

Die Entwicklung von Petromyzon planeri. Arch. f. mikr. Anat. Bd. XXYV.
1890.

Laneeruans, P. Untersuchungen iiber Petromyzon planeri. Verh. Naturforsch.
Ges. Freiburg, 1875.

Leyvic, Fr. Beitriige zur mikrosk. Anatomie und Entw.-Geschichte der Rochen
und Haie. Leipzig, 1852.

Anatomisch-histologische Untersuchungen iiber Fische und Reptilien. Berlin,
1853.

396 APPENDIX

Leypic, Fr. Zur Anatomie und Histologie der Chimaera monstrosa. Arch. f.
Anat. und Physiol., 1851. '

Munter, J. Ueber den Bau und die Grenzen der Ganoiden. Berlin, 1846.

Vergl. Anatomie der Myxinoiden. 1833-438. :

Neve, J. P. Quelques phases du développement du Petromyzon planeri. Arch.
Biol. Vol. I. 1881.

Owen, R. Description of Lepidosiren annectens. Tr. Linn. Soc. XVII.

Owssannikow, Pu. Zur. Entwickl. d. Flussneunauges. Vorliuf. Mittheilg.
Bull. Ac. St. Petersb. Tome XIII. 1889.

Parker, T. J. Studies in New Zealand Ichthyology. I. On the Skeleton of
Regalecus argenteus. Tr. Zool. Soc. Vol. XII. part 1. 1886.

Notes on Carcharodon rondeletii. P. Zool. Soc., 1887.

ParkKER, W. N. On the Anatomy and Physiology of Protopterus annectens. Tr.
Irish Ac. Vol. XXX. p. 3. 1892. (Abstract in P. R. Soc. Vol. 49.
1891.)

PoLiarp, H. B. On the Anatomy and Phylogenetic Position of Polypterus.
Zool. Jahrb. Bd. V. 1892.

ReIcHarD, I. Development of the Wall-Eyed Pike. Bull. Michigan Fish Com-
mission, 1890.

Ryper, J. A. A contribution to the Embryography of osseous fishes with special
reference to the development of the Cod (Gadus morrhua). Extracted
from the Annual Report of the Commissioner of Fish aud Fisheries for 1882.
Washington, 1884.

SALENSKY, W. Entwicklung des Sterlets (Acipenser ruthenus). II. Th.
Verhdlg. der naturf. Gesellsch. zu Kasan, 1878-79. French trans. in Arch.
Biol. T. II, fasc. 2, 1881.

Scanerper, A. Beitrige zur vergl. Anatomie und Entw.-Geschichte der Wir-
belthiere. Berlin, 1879.

Scorr, W. B. Beitriige zur Entw.-Geschichte der Petromyzonten. Morph.
Jahrb. Bd. VII.

Development of Petromyzon. Journ. Morphol. Vol. I. 1887.

Semon, R. Zoolog. Forschungsreisen in Australien und dem malayischen
Archipel. I. Die dussere Entwickelung des Ceratodus Forsteri. Jena, 1893.

Semper, C. Die Stammesverwandtschaft der Wirbelthiere und Wirbellosen.
Arb. Inst. Wiirzburg. Bd. II. 1875.

SurpLtey, A. E. On some points in the Development of Petromyzon fluviatilis.
Q. Journ. Mier. Sci. Vol. XXVIT. 1887.

Tragvam, R. H. Papers on Paleospondylus Gunni, see Ann. Nat. Hist. (6),
Vol. VI., 1890, and Proc. Roy. Phys. Soc. Edin. Vol. NXII., 1893.

Voat, C. Embryologie des Salmones. Neuchétel, 1842.

WrepersuEiIm, R. Zur Biologie von Protopterus. Anat. Anz., 1887.

Wricut, R.; McMurnricu, J.; Macantum, A.; Mackenzie T. Contrib. to
the Anatomy of Amiurus. Proceed. Canad. Inst. Toronto. N.&. Vol.
II. No. 3. Toronto, 1884.

AMPHIBIA.

AssHETON, R. Studies in the Development of the Rabbit and the Frog. Q.
Journ. Mier. Sci., 1894.

Bayer, F. Ueber das Skelet der Pelobatiden. Ein Beitrag zur vergl. Osteologie
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Corr, E. D. The Batrachia of North America. Bull. of the United States Nat.
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Crepver, H. Die -Stegocephalen und Saurier aus dem Rothliegenden des
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Die Urvierfiissler [Eotetrapoda] des Sachsischen Rothliegenden. Naturw.
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Ducks, A. Recherches sur lostéologie et la myologie des Batraciens a leurs
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Kekrr, A., and WrepersHermm R. Die Anatomie des Frosches. Braunschweig,
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APPENDIX 397

Favio, V. Faune des Vertébrés de la Suisse. Vol. III. Hist. nat. des Reptiles
et des Batraciens. Genéve et Bale, 1872.

Fiscuer, J. G. Anatomische Abhandlungen iiber die Perennibranchiaten und
Derotremen. Hamburg, 1864.

Fritscw, A. (See p. 395.)

Gaupry, A. L’Actinodon Arch. Mus. Paris, 1887.

Gétrr, A. Entwicklungsgeschichte der Unke. Leipzig, 1875.

GRonBERG, G. Zur Anatomie der Pipa americana. Zool. Jahrb. WII. Bd. 1894.

es Se Cryptobranchus japonicus. Schediasma anatomicum. Vindobone,

i inet ye A.v. Zur Anatomie der Pipa americana. Zool. Jahrb. VII.
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Leypie, F. Die Anuren Batrachier der deutschen Fauna. Bonn, 1877.
Die Molche der wiirttembergischen Fauna. Berlin, 1867, and Arch. f.
Naturg. Bd. XXIII.
MarsHaLL, A. Mites. The Frog. An introduction to Anatomy, Histology,
and Embryology. 6th ed. London, 1896.
Rusvont, M. Histoire naturelle, développement et métamorphose de la Sala-
mandre terrestres. Pavie, 1854.
Rusconi, M., and Conriciiacui. Del Proteo anguineo di Laurenti monografia.
Pavia, 1818.
SARASIN, P. and F. Ergebnisse naturwissenschaftl. Forschungen auf Ceylon in
den Jahren 1884-6. II. Bd. I. u. II Heft.
Zur Entwicklungsgeschichte und Anatomie der ceylonesischen Blindwiihle,
Ichthyophis glutinosus. Wiesbaden, 1887-90.
WIrEDERSHEIM, R. Bemerkungen zur Anatomie des Euproctus Rusconii. Annal.
del Museo civico di Stor. nat. di Genova. Vol. VII., 1875.
Labyrinthodon Riitimeyeri. Abh. Schweiz. Pal. Ges. Vol. V. 1878.
Die Anatomie der Gymnophionen. Jena, 1879.
Salamandrina perspicillata und Geotriton fuscus. Versuch einer vergl.
Anatomie der Salamandrinen. Genua, 1875.
Zur Anatomie des Amblystoma Weismanni. Zeitschr. f. wiss. Zool. Bd.
XXXII.
Beitrige zur Entwicklungsgeschichte von Proteus anguineus. Arch. f. mikr.
Anat. Bd. XXXV. 1890.
Winver, Harris H. A Contribution tothe Anatomy of Siren lacertina. Zool.
Jahrb. IV. Bd. 1891.

REPTILiIA.

BemMEeLeN, J. F. van. Beitrage zur Kenntnis der Halsgegend bei Reptilien.
I. Anatomischer Theil. Amsterdam, 1888.

Bosanus. Anatome testudinis europaeae. Vilnae, 1819-21.

Crepxrk, H. (See p. 396.)

DumériL and Brnron. Erpétologie générale. Paris, 1834-54.

Gtnruer, A. Contrib. to the Anatomy of Hatteria (Rhynchocephalus). Phil.
Trans., 1867.

Leypi, F. Die in Deutschland lebenden Arten der Saurier. Tiibingen, 1872.
Ueber die einheimischen Schlangen. Zool. und anatom. Bemerkungen.
Abh. Senckenb. Ges. Bd. XIII. 1883.

Marsu, O. C. The Dinosaurs of North America. Sixteenth Annual Report of
the U. S. Geol. Survey. Washington, 1896.

Maurer, F. Die ventrale Rumpfmuskulatur einigen Reptilien. Festschrift fiir

* Carl Gegenbaur. Leipzig, 1896. :

Meunert, E. Gastrulation und Keimblatterbildung der Emys lutaria taurica.
I. Theil einer Entwicklungsgeschichte der Emys lutaria taurica. Morph.
Arb. I. Bd. 3 Heft. 1891.

Mrrsvkuri, K. On the Process of Gastrulation in Chelonia. Journ. Coll.
Sci., Japan. Vol. VI., p. iv. 1893. ais

On the fate of the blastopore, the relations of the primitive streak and the

formation of the posterior end of the embryo in Chelonia, together
with remarks on the nature of meroblastic ova in Vertebrates. Journ.
Coll. Sci., Japan. Vol. X., Pt. 1. 1896.

398 APPENDIX

ORLANDI, 8. Note anatom. sul Macroscincus Coctei (Barb du Boc). Mus. di
Zool, Anat. comp. della Universita di Genova, No. 22, 1894. Atti Soc.
Sigust. Vol. V.

Owen, R. Description and Illust. Catalogue of the Fossil Reptilia of South
Africa.

RatHks, H. Entwickl.-Geschichte (1) der Natter, (2) der Schildkréten, (3) der
Crocodile. (Kénigsberg, 1837; Braunschweig, 1848 and 1866.)

Srepenrock, F. Das Skelet von Brookesia superciliaris, Kuhl. Sitz. Ber. Ak.
Wien. Bd. CIL. Abth. I., 1893.

Das Skelet der Lacerta Simonyi, Steind. und der Lacertidenfamilie tiber-
haupt. Sitz. ber. Ak. Wien. Bd. CIIL, 1 Abth. 1894.

Das Skelet der Agamide. Loc. cit, Bd. CIV., 1 Abth. 1895.

Various papers on Reptiles in the Annal. d. k. k. Naturhistor. Hof-
museums in Wein from 1892 onwards.

SMALIAN, C. Beitriige zur Anatomie der Amphisbiniden. Zeitschr. f. wiss.
Zool. Band XLII. 1885.

WIEDERSHEIM, R, Zur Anat. und Phys. des Phyllodactylus europaeus, &c.
Morph. Jahrb. I. 1876.

ZitreL, K. Ueber Flugsaurier aus dem lithogr. Schiefer Bayerns. Palaeon-
tographica N. F. IX. 2. (XXIX.)

AVES.

Baur, G. W. K. Parker’s Bemerkungen iiber Archaeopteryx 1864. (Geol.
Mag.) Zool. Anz. 1886.

Dames, W. Ueber Archaeopteryx. Paliontol. Abhdlg., herausgeg. von W.
Dames und E. Kayser. Bd. IJ. Heft 3. Berlin, 1884.

Firprincer, M. Untersuchungen zur Morphologie und Systematik der Vogel,
zugleich ein Beitrag zur Anatomie der Stiitz- und Bewegungsorgane.
I. Specieller Theil: Brust, Schulter und proximale Fliigelregion der
Vogel. II. Allgemeiner Theil: Resultate und Reflexionen auf morphol.
Gebiete, systematische Ergebnisse und Folgerungen. Amsterdam, 1888.
See also abstract in Bivl. Centralbl. Bd. IX—XVII., 1897. (To be
continued. )

See literature in II. Internat. Ornithol. Congress. I. Section. Anat. d.

Vogel.

Heapiey, F. W. Structure and Life of Birds. London, 1896.

Hurst, C. H. The Structure and Habits of Archaeopteryx. Stud. Owens
Coll. Vol. III. Manchester, 1895.

Marsu, O. C. Odontornithes, a Monograph on the extinct toothed birds of
North America. Washington, 1880.

Jurassic Birds and their Allies. Amer. Journ. of Science and Arts.

Vol. XXII.

MarsHatt, W. Der Bau der Végel (Weber’s Naturwissensch. Bibliothek).
Leipzig, 1895.

MiuneE-Epwarps, A. Recherches sur la faune ornithologique éteinte des fles
Mascareignes et de Madagascar. 1866-79.

‘Owrn, R. Aves, in Todd’s Cyclopaedia I. On the anatomy of the southern
Apteryx. Tr. Zool. Soc. Vol. IL, II. Archaeopteryx lithographica.
Phil. Trans., 1863.

Parker, W. K. Numerous papers on the Osteology of Birds in P. Zool. Soc.
1860-5, 1889, 1890; Tr. Zool Soc. 1862, 1866, 1869, 1891; P. Roy.
Soc. 1887-8; Ann. Nat. Hist. 1864, 1865; Ibis, 1888-9; Tr. Irish. Ac.
1890 ; Encycl. Brit. 9th ed. (Article ‘“ Birds.’’)

Parker, T. JEFFERY. Observations on the Anatomy and Development of
Apteryx. Phil. Trans. Vol. 182. 1891. Additional Observations, &c.
Loe. cit. Vol. 183, 1892. See also p. 413.

(QJUATREFAGES, A. DE. Les Moas et les chasseurs de Moas. Ann. Sci. Nat.
XVI. Nos. 4, 5, 6. Paris, 1883.

TIEDEMANN, F. Anatomie und Naturgeschichte der Végel. Heidelberg, 1810-
14.

nig 3 and Nitscu. In Naumann’s ‘‘ Naturgeschichte der Vigel Deutch-
ands,

APPENDIX 399

MammMatia.

ASsHETON, R. (See p. 396.)

BENEDEN, Van, and GERvaIs. Ostéographie des Cetacées. Paris, 1868-80.

BLAINVILLE, H. Ostéographie ou description iconographique comp. des
Mammiféres rec. et fossiles. 4 Bde. Text and Atlas with 323 Plates.
Paris, 1839-64.

Branpr. Untersuchungen iiber die fossilen und subfossilen Cetaceen Europas.
Mém. Acad. St. Petersb. 1873.

Burmeister. Annales del Museo publico de Buenos-Aires, 1874-89.

CaLDWELL, W. H. The Embryology of Monotremata and Marsupialia. Part I.
Phil. Trans. Vol. 178. 1887.

CamERANO, L. Ricerche intorno all’ anatomia di un feto di Otaria jubata
(Forster). Mem. Acc. Torino. Ser. II. Tom. XXXV. 1882.

CorE, EK. D. Report upon the U. 8. Geogr. Surveys west of 100th Meridian.
Vol. IV. Paleontology, 1877. (See also P. Ac. Philad. and Amer. Nat.)

Cuvier, G. Rech. sur les ossements fossiles. 4 ed. 1834-6.

Deiace, Y. Histoire du Balaenoptera musculus. Arch. Zool. exp. 2 sér. t.
III. 1885 ed. 1887.

ELLENBERGER, W., and Baum, H. Systemat. und topogr. Anatomie des
Hundes. Berlin, 1891.

Escuricut. Zoologisch-anatomisch-physiologische Untersuchungen iiber die
nordischen Walthiere. Leipzig, 1849.

Fick, R. Vergl. anatom. Studien an einem erwachsenen Orang-Utang. Arch.
f. Anat. 1895. :

Finyoi. Recherches sur les Phosphorites du Quercy. Etudes sur les fossiles
qu’on yv rencontre et spécialement les mammiféres. Annal. des sci.
géolog. VII., VIII. Mammiféres fossiles de St.-Gérard le Puy. Loe.
eit. X. Mammiféres de Ronzon, NII. See also XNIV., XXI.

FLEISCHMANN, A. Embryol. Untersuchungen. A. Die Stammesgeschichte der
Nagethiere. B. Die Umkehr der Keimblitter. Wiesbaden, 1891.

Fietcuer, J. J. Catalogue of papers and works relating to the mammalian
orders, Marsupialia and Monotremata. Extracted from Vol. IX. part 3,
of the P. Linn. Soc. N.8.W.

Fiower, W. H. Introduction to the Osteology of the Mammalia. 3rd ed.
revised with Gadow. London, 1885.

Frower and LypExKER. Mammals, living and extinct. London, 1891.

Frank, L. Anatomie der Hausthiere. Stuttgart, 1871.

Gaupry, A. Animaux fossiles et Géologie de lAttique. Paris, 1862-7.

Die Vorfahren der Saéugethiere in Europa. Trans. by W. Marshall. Leip-
zig, 1891.

Cracemn C. Annotazioni sulla Anatomia del Negro. Fiinf Abtheilungen.
Torino, 1878-92.

GigBEL, C. G. Die Saugethiere in zoologischer, anatomischer, und paliontolo-
gischer Beziehung. 1855.

GwLpBerc, G., and Nansen, F. On the development and structure of the
Whale. Part I. On the development of the Dolphin. Bergens Mus.
Skrifter, V. 1894.

Guret. Anatomische Abbildungen der Haussiugethiere.

Gurit. Handbuch der vergl. Anatomie der Haussiiugethiere. Berlin, 1860.

Keser, F. Studien zur Entwicklungsgeschichte des Schweines. Morph. Arb.
1 Teil III. 1893. 2 Teil V. 1895.

Kowatewsky, W. Sur lAnchitherium Aurelianense, Cuv. Mem. Ac. St.-
Petersb., 1873. Osteology of the Hyopotamidae. Phil. Trans.
1873. — Versuch einer natiirl. Classification der fossilen Hufthiere.
Monographia der Gattung Anthracotherium. Palaeontographica, 1876.

Krauss, W. Anatomie der Kaninchens. Leipzig, 1884.

KtckenrHaL, W. Vergl. anatomische und entwicklungsgeschichtliche Unter-
suchungen an Walthieren. I. Theil (Haut, Hand, und Centralnerven-
system der Cetaceen). Jena, 1889. II. Theil (Die Entwicklung der dusseren
Kérperform, Bau und Entwicklung ausserer Organe, die Bezahnung).

Ueber die Entstehung und Entwicklung des Saugethierstammes. Biol.
Centralbl. XII. Bd. No. 13. 1892.

LEISERING and Miityer. Handbuch der vergl. Anatomie der Haussiugethiere.

1855.

400 APPENDIX

Levu. Handbuch der Anatomie der Hausthiere. 1850.
Lucur, W. Zur Anatomie der Beckenregion bei Insectivora, &c. K. Schwed.
Acad. d. Wissensch. Bd. XX. 1882.

Uchber die Siugethiergattung Galeopithecus. Loc. cit. Bd. XXI. No.

11. 1885.
Lrtpy, L. The ancient Fauna of Nebraska. 1853. 2 ;
Contrib. to the extinct Vertebrate Fauna of the Western Territories.
United States Geological Survey. I. Washington, 1873.

Marsu, O. C. Dinocerata, an extinct order of gigantic Mammals. Washington,

1884.
Numerous papers in Amer. J. Sci., 1874-92.
Mecxe, J. F. Ornithorhynchi paradoxi descriptio anatomica. Leipzig, 1826.
Mivarr, St. G. The Cat. An Introd. to the Study of Backboned Animals,
especially Mammals. London, 1881.

Osvory, H. F. Present Problems in Evolution and Heredity. The Cartwright.

Lectures for 1892. Reprint. from the Medical Record. February 20th,
March 5th, April 23rd, and May 14th, 1892.
Owen, R. Extinct Mammals of Australia. London, 1877. With 131 Plates.
Monogr. of the fossil Mammalia of the Mesozoic formation. Palaentol-.
Society, 1871.

Parker, T. J., and Scott, J. H. On a specimen of Ziphius recently obtained
near Dunedin. Tr. Zool. Soc. Vol. XII.

Parker, W. K. Mammalian Descent. London, 1884.

Quatn’s Elements of Anatomy. Edited by E. A. Schiffer and G. D. Thane. (3
vols.) London, 1891-2.

Ravr. (1) Anatom. Untersuchungen tiber die Edentaten. (2) Die Cetaceen.
Stuttgart and Tiibingen, 1837.

Rosrnson, A. Observations upon the Development of the Segmentation Cavity,
the Archenteron, the Germinal Layers, and the Amnion in Mammals. Q.
Journ. Mier. Sci., Vol. XN NIIL, N.S.

Rivimeyen, L. Die Fauna der Pfahlbauten der Schweiz. Basel, 1861.

Beitr. zur Kenntnis der fossil. Pferde. Basel, 1863.

Ueber clie Herkunft unserer Siiugethiere. Basel, 1867.

Versuch einer natiirl. Geschichte des Rindes. Abh. Schweiz. pal. Ges.
Bd. XXII. 1877 fg.

Die natiirl. Geschichte der Hirsche. Loc. cit., 1880.

Die eociine Siiugethierwelt von Egerkingen. Joc. cit., 1891.

Scumipt, QO. Die Saugethiere in ihrem Verhaltniss zur Vorwelt. (Internationale
wissenschaftl, Bibliothek. 45 Band). Leipzig, 1884.

Sermon, R. Zoolog. Forschungsreise in Australien, etc. JI. Band. i. Lieferg.
Monotremen u. Marsupialier.

(a) Beobachtungen iiber d. Lebensweise u. Fortpflanzg. der Monotremen
nebst notizen tiber ihre Kérpertemperatur.

(b) Die Embryonalhiillen der Monotremen u. Marsupialier.

(c) Zur Entwicklungsgeschichte der Monotremen.

Sewertzorr, A. Beitrag z. Ent. Gesch. d. Wirbelthierschiidels. Anat. Anz. Bd.
NII, 1897.

Weber, M. Studien tiber Siugthiere. Ein Beitrag zur Frage nach dem Ursprung
der Cetaceen. Jena, 1886.

Anatomisches tiber Cetaceen. Morph. Jahrb. Bd. XIII., 1888.
Zoolog. Ergebnisse einer Reise in Niederliind. Ost-Indien. Bd. II. Beitr.
z Anat. und Entwickl. des Genus Manis. Leiden, 1891.
Wirprrsuemm, R. Der Bau des Menschen als Zeugnis fiir seine Vergangenheit.
Il. Aufl. Freiburg i. B. 1893. (Eng. trans. by Bernard, ‘‘ The Structure
of Man.” London, 1896.)

Winper, B. G., and Gace, §.H. Animal Technology, as applied to the Domestic
Cat. New York and Chicago, 1882. ,

Witson, J.T. Description (with figs.) of a young Ornithorhynchus anatinus.
P. Linn. Soc., N.8.W., Vol. IX., part 4 (2nd Ser. ).

APPENDIX 401

WORKS DEALING WITH INDIVIDUAL SYSTEMS OF
ORGANS.

A. INTEGUMENT.?
(a) Pisces AND DIPNOI.
Borrarp, A. Les Poissons venimeux, Contribution 4 Hygiene navale. Paris,

Fritscu, G. Die iiussere Haut und die Seitenorgane des Zitterwelses (Malop-
terurus electricus). Sitz-Ber. Ak. Berlin. XXII. 1886.
Die elektrischen Fische. Leipzig, 1887 and 1850.
Lanceruans, P. Unters. iiber den Bau des Amphioxus lanceolatus. Morph.
Jahrb. Bad. II., 1876.
Lankester, E. R. On the Lepidosiren of Paraguay, and on certain external
characters of Lepidosiren and Protopterus. ‘Tr. Zool. Soc., Vol. XIV.,
part 1, 1896.
wag R. v. Die Leuchtorgane der Fische. Biol. Centralbl. Bd. VII.,
1887.
Leypie, F. Die augeniihnlichen Organe der Fische. Bonn, 1881.
Neue Beitr. zur anatomischen Kenntnis der Hautdecke und Sinnesorgane
der Fische. Halle, 1879.
Integument briinstiger Fische und Amphibien. Biol. Centralbl. Bd. XII.
1892. 3
List, J. Ueber Wanderzellen im Epithel. Zool. Anz. No. 198. VIII. Jahrg.,
1885. Seealso Arch. f. mikr. Anat. Bd. XXV.
Parker, W. N. On the poison-organs of Trachinus. P. Zool. Soc., 1868. Anat.
Anz. III. Jahrg. 1888.
Saccur, Maria. Sulla struttura del tegumento negli embrioni ed avannotti del
Salmo lacustris. Rend. del R. Istituto Lombardo. Vol. XX. fase. XV—
XVI. Milano, 1887.
Sulla struttura degli organi del veleno della Scorpena. Boll. Mus. Genova.
Nos. 30 and 36, 1895. Publ. i. d. Atti Soc., Ligust. Vol. VI.
Scuuuze, F. E. Epithel- und Driisenzellen. Arch. f. mikr. Anat. Bd. III.
Ueber cuticulare Bildungen und Verhornungen von Epithelzellen bei Wirbel-
thieren. Arch. f. mikr. Anat. Bd. V.
Scuuttze, M. Die kolbenférmigen Gebilde in der Haut von Petromyzon und ihr
Verhalten im polaris. Licht. Arch. f. Anat. u. Phys. 1861.
Sotcrr, B. Zur Kenntnis der Verbreitung von Leuchtorganen bei Fischen.
Arch. f. mikr. Anat. Bd. XIX. ;
Ueber pigmentirte Zellen und deren Centralmasse. Mittheil. d. naturw.
Vereines von Neuvorpommern und Riigen. 22 Jahrg. 1890.
‘WoLrr, G. Die Cuticula der Wirbelthierepidermis. Jen. Zeitschr. Bd. XXIII.
N.F. XVI. 1889.

(6b) AmMpuHIBIA.

‘CALMELS. Etude histologique des glandes 4 venin du crapaud et recherches sur
les modifications apportées dans leur évolution normale par Pexcitation ¢lec-
trique de animal. Arch. Physiol. Bd. XV. 1853.

-CARRIERE, J. Die postembryonale Entwicklung der Epidermis des Siredon pisci-
formis. Arch. f. mikr. Anat. Bd. XXIV. 1884.

Drascu. Beob. an lebenden Driisen mit und ohne Reizung der Nerven derselben.
Arch. Physiol. 1889.

Ueber die Giftdriisen des Salamanders. Verh. Anat. Ges. 1892.

Untersuchungen % norm. u. path. Anat. d. Froschhaut. Leipzig,
1869.

Ficauui, E. Ricerche sulla struttura minuta della Pelle degli Anfibi (Hy-
lide). Attidella R. Accad. Peloritana in Messina, Anno XI., 1896-7.

Hatuer, B. Ueber das blaue Hochzeitskleid des Grasfrosches. Zool. Anz. No.

207. 1885.
1 Compare also under sensory organs.

402 APPENDIX

HeEIDENHAIN, M. Ueber das Vorkommen von Intercellularbriicken zwischen
glatten Muskelzellen und Epithelzellen des a4usseren Keimblattes und deren.
theoretische Bedeutung. Anat. Anz. VIII. Jahrg., 1893. ‘

Die Hautdriisen der Amphibien. Sitz. Ber. Ges., Wiirzburg, 1893.

Huser, O. Ueber Brunstwarzen bei Rana temporaria. Zeitschr. f. wiss. Zool.
Bd. XLV. 1887.

Junivs, P. Uber die Hautdriisen des Frosches. Arch. Anat. Bd. XLVII.
1896.

LANGERHANS, P. Ueber die Haut der Larve von Salamandra maculosa. Arch.
f. mikr. Anat. Bd. IX.

Lrypic, F. Die Hautdecke und Hautsinnesorgane der Urocdelen. Morph.
Jahrb. Bd. II. 1876.

Ueber die allgemeinen Bedeckungen der Amphibien. Arch. f. mikr. Anat.
Bd. XII. 1876.

Zum Integument niederer Wirbelthiere abermals. Biol. Centralbl. Bd. XII.
Nos. 14 and 15. 1892. (See also Bd. XIII. 1893.)

Maurer, F. Glatte Muskelzellen in der Cutis der Anuren und ihre Beziehung
zur Epidermis. Morph. Jahrb. Bd. XXI. 1894.

Die Epidermis u. ihre Abkémmlinge. Leipzig, 1895.
Nicociu, Pa. Ueber die Hautdriisen der Amphibien. Zeitschr. f. wiss. Ziol.

Bd. LVI. 1893.
Pavuuicki. Ueber die Haut des Axolotls.. Arch. fiir mikr. Anat. Bd. XXIV.
1884,

Pritzner, W. Die Epidermis der Amphibien. Morph. Jahrb. Bd. VI. 1880.
Die Leydig’schen Schleimzellen in der Epidermis der Larve von Salamandra
maculosa. Inaug.-Diss. Kiel, 1879.

Scuuserc, A. Ueber den Bau und die Function der Haftapparate des Laub-
frosches. Arb. Inst., Wiirzburg. Bd. X. 1891.

Beitrag zur Kenntnis der Amphibienhaut. Zool. Jahrb. Bd. VI.

Scivuuz, P. Ueber die Giftdriisen der Kréten und Salamander. Arch. f. mikr.
Anat. Bd. XXXIV. 1889.

WiepErsHEIM, R. Die Kopfdriisen der geschwinzten Amphibien und die
Glandula intermaxillaris der Anuren. Zeitschr. f. wiss. Zoologie. Bd.
XXVIII.

ZALESKY. Ueber das Samandrin. Medic. chem. Untersuchungen, herausgegeben
von Hoppe Seyler. Berlin, 1866.

(c) REPTILIA.

Bate, A. Beitriige zur Kenntnis des Baues der Reptilienhaut. Arch. f.
mikr. Anat. Bd. XVII.

BuiancarpD, H. Recherches sur la structure de la peau des lézards. Bull. Soc.
zool. France, 1880.

Braun, M. Zur Bedeutung der Cuticularborsten auf den Haftlappen der
Geckotiden. Arch. zool.-zoot. Wiirzburg. Bd. IV.

Cartier, O. Studien tiber den feineren Bau der Haut bei den Reptilien.
Verhandl. phys.-med. Wiirzburg. N. F. III, V.

Frcausi, E. Ricerche istologiche sul Tegumento dei Serpenti. Atti. d. Soc.
Toscana d. Scienze nat. Vol. IX. 1888. (A French abstract in Arch.
Ital. Biol. Vol. X. Turin, 1888.) :

Osserv. sulla Istologia della Pelle dei Rettili Cheloniani. Atti. d. R.

Accadem. dei Fisiocritici. Ser. IV. Vol. I. Siena, 1889.

Gorrert, KE. Zur Phylogenese der Wirbelthierkralle. Morph. Jahrb. Bd.
XXV. 1896. (Deals also with the Amphibia.)

KeERBERT, C. Ueber die Haut der Reptilien und anderer Wirbelthiere. Arch.
f. mikr. Anat. Bd. XIII.

Lvorr. Beitr. zur Histologie der Haut der Reptilien. Bull. Soc., Moscou, 1885.

OprenHEIMER, E. Ueber eigentiiml. Organe in d. Haut. einiger Reptilien. Ein
Beitrag zur Phylogenie der Haare. Morph. Arb. Bd. V. 3H. 1896.

Osawa, GAKUTARO. Beitriige zur feineren Structur des Integuments der Hatteria
punctata. Arch. f. mikr. Anat. Bd. XLVII. 1896.

APPENDIX 403

(d) AVEs.

Davius, H.R. Zur Entwicklung der Feder und ihre Beziehungen zu anderen
Integumentalgebilden. Morph. Jahrb. Bd. XV. 1889.

Ficarsr, E. Sulla architettura istologica di aleuni peli degli uccelli con con-
siderazioni sulla Filogenia dei peli e delle penne. Atti Soc. Toscana.
Vol. XI. 1890.

GARDINER, E. Beitr. zur Kenntnis des Epitrichiums und der Bildung des
Vogelschnabels. Inaug. Dissert. Leipzig, 1884.

Hacker, V. Ueber die Farben der Vogelfedern. Arch. f. mikr. Anat. Bd.
XXXV. 1890.

Mewere, T. C. H. de Ueber die Federn der Vigel, insbesondere uber ihre
Anordnung. Morph. Jahrb. Bd. XXIII.

SrupErR, Th. Die Entwicklung der Federn. Inaug.-Diss. Bern, 1873.

Taree zur Entwicklungsgeschichte der Feder. Zeitschr. f. wiss. Zool. Bd.

(e) MAMMALIA.

ALsSHEIMER, A. Ueber die Ohrenschmalzdriisen. Inaug.-Dissert. Wiirzburg,
1888.

BaRvELEBEN, K. vy. Ueber 600 neue Falle von Hyperthelie bei Mannern. Verh.
d. Anat. Ges. 1892.

BuLAascHarp, R. Sur un cas de polymastie et sur la signification des mamelles.
surnumeéraires. Bull. de la Société d’ Anthropologie, Séance du 19 Mars,
1885.

BrascuKo, A. Beitriige zur Anatomie der Oberhaut. Arch. f. mikr. Anat.
Bd. XXX.

Boas, J. E. V. Ein Beitrag zur Morphologie der Nigel, Krallen, Hufe und
Klauen der Siiugethiere. Morph. Jahrb. Bd. XI. 1884.

Zur Morphol. d. Wirbelthierkralle. Morph. Jahrb. Bd. XXI. Heft. TIT.
1894

Bonnet, R. Haarspiralen und Haarspindeln. Morph. Jahrb. Bd. XI.

Ueber Eingeweidemelanose. Verhdl. Phys.-Med. Wiirzburg. N. F. XXIV.
Bad. 1890.

Ueber Hypotrichosis congenita universalis. Anat. Hefte. Heft. III. 1892.

Die Mammarorgane im Lichte der Ontogenie und Phylogenie. Anat.
Ergebnisse. Bd. II. 1892.

Bowen, J. T. The epitrichial Layer of the human Epidermis. Anat. Anz.
IV. Jahrg. 1889.

Creiuuton, C. On the Development of the Mamma, etc. Journ. Anat. and
Physiol. Vol. XI.

DomsBrowskI, R. v. Geweihe und Gehérne. Naturwissenschaftl. Studie. Wien
1885. With 40 Coloured Plates.

Ecxer, A. Ueber abnorme Behaarung des Menschen, etc. Gratul.-Schrift fiir
y. Siebold, 1878. Reprinted in ‘‘ Globus” 1878.

Der Steisshaarwirbel (Vertex coccygeus), die Steissbeinglatze (Glabella
coccygea) und das Steissbeingriibchen (Foveola coccygea) etc. Arch. f.
Anthropologie. Bd. XII.

Emrry, C. Ueber das Verhialtnis der Sdugethierhaare zu schuppenartigen
Hautgebilden. Anat. Anz. VIII. Jahrg. 1893.
Escuricut. Ueber die Richtung der Haare am menschlichen Kérper. Arch. f.
Anat. und Physiol. 1837.
Exner, A. Die Function der Menschlichen Haare. Biol. Centralbl. Bad.
XVI. 1896.
Ferertac, F. Ueber die Bildung der Haare. Inaug.-Diss. Dorpat, 1875.
Fyetstrup, A. Ueber den Bau der Haut bei Globiocephalus melas. Zool. Anz.
XI. Jahrg. 1888.
Fuemmine, W. Ein Drillingshaar mit gemeinsamer_innerer Wurzelscheide.
Monatshefte fiir prakt. Dermatologie. II. Bd. No. 6. 1883.
GrcEnBaur, C. Zur genaueren Kenntnis der Zitzen der Sdugethiere. Morph.
Jahrb. Bd. I. 1876. :
Zur Morphologie des Nagels. Morph. Jahrb. Bd. X. 1885.
Zur Kenntnis der Mammarorgane der Monotremen. Leipzig, 1886.

DD 2

404 APPENDIX

Grarr, K. Vergl.-anatom. Unters. iiber den Bau der Hautdriisen der Haus-
siiugethiere und des Menschen. Inaug.-Diss. Leipzig, 1879. :
Grore, G. Ueber die Glandulae anales des Kaninchens. Inaug.-Dissert.

Kénigsberg, 1891.
Haackxr, W. Kierlegende Siugethiere. Humboldt. VI. Jahrg. Stuttgart,
1887.

On the Marsupial ovum, mammary pouch and the male milk glands of
Echidna hystrix. Proc. R. Soc. 1885.

Hessuine, Th. v. Ueber die Brunftfeige der Gemse. Zeitschr. f. wiss. Zool.
Ba. VI.
Huss, M. Beitriige zur Entw. der Milchdriisen, etc. Jen. Zeitschr. Bd. VII.
Jaxopis. Pathogenese der Pigmentirungen und Entfirbungen der Haut.
Centralblatt f. allg. Pathol. u. pathol. Anat. I. Bd. No. 20. 1890.
Kauurvus, E. Ein Fall von Milchleiste bei einem menschl. embryo. Anat.
Heft, I. Abth. Heft 24 (Bd. VIII., Heft 1), 1897.

KerseL, F. Zur Ontogenie u. Phylogenie von Haar u. Feder. Anat. Hefte,
II. Abth., 1895.

Kuaatscu, H. Zur Morphologie der Saugethierzitzen. Morph. Jahrb. Bd. IX
1883.

Zur Morphologie der Tastballen der Siugethiere. Morph. Jahrb. Bd. XIV.
1888.

Ueber die Beziehungen zwischen Mammartasche und Marsupium. Morph.
Jahrb. Bd. XVII. 1892. (See also Bd. XX. 1893.)

Ueber Marsupialrudimente bei Placentaliern. Morph. Jahrb. Bd. XX.
1893.

Studien zur Geschichte der Mamarorgane. Teil I. Die Taschen- und
Beutelbildungen am Driisenfeld der Monotremen. Jena (Semon’s Zoolog.
Forschungsreise. 1895).

Koéiiiker, A. v. Ueber die Entwicklung der Nigel. Sitz.-Ber. Ges. Wiirzburg,
1888.
aera Oberhautpigment der Siugethiere. Arch. f. mikr. Anat. XLII.
. 1893.
KtxentoaL, W. Ueber die Anpassung von Siiugethieren an das Leben im
Wasser. Zool. Jahrbiicher, V. Bd.

Ueber Reste eines Hautpanzers bei Zahnwalen. Anat. Anz. V. Jahrg.
1890.

Lesouca, H. Rech. sur la Morphologie de la main chez les Mammiféres marins,
etc. Arch. de Biol. T. IX. 1889.

LEICHTENSTERN. Ueber tiberzihlige Briiste. Arch. f. path. Anat. 1878.

Leypic, F. Ueber die ausseren Bedeckungen der Siugethiere. Arch. f. Anat.
und Physiol. 1859.

List, J. - a die Herkunft des Pigmentes in der Oberhaut. Biol. Centralbl.

Martin, C. T. and TrpsweLi, Frank. Observ. on the femoral Gland of Orni-
thorhynchus, ete. Proc. Linn. Soc. N. 8. W. Vol. IX.

Maurer, F. Haut-Sinnesorgane, Feder- und Haaranlagen, und deren gegenseitige
Beziehungen : ein Beitrag zur Phylogenese der Siiugethiere. Morph. Jahrb.
XVIII. u. XX. Bd. 1892.

Meiere, T. C. H. de. Ueber die Haare der Siugethiere, besonders iiber ihre
Anordnung. Morph. Jahrb. Bd. XXI. 1894.

Norver, C. Ueber den feineren Bau des Pferdehufes. Arch. f. mikr. Anat.
Bd. XXVIII. 1886.

Poutton, E. B. The structure of the Bill and Hairs of Ornithorhynchus

aradoxus ; with a discussion of the Homologies and Origin of mammalian
air. . Journ. Micr. Sci. Vol. 36, No. 5. 1894.

Rauber, A. Ueber den Ursprung der Milch und die Ernihrung der Frucht im
Allgemeinen. Leipzig, 1879.

Reu. Die Schuppen der Siugetiere. Jen. Zeitschr. Bd. XXIX. 1894.

Rein, G. Unters. iiber d. embr. Entw.-Geschichte der Milchdriise. Arch. f.
mikr. Anat. Bd. XX. und XXI. 1882.

Rua, G. (See p. 424.)

Scumiptr, H. Ueber normale Hyperthelie mensch. Embryonen u. iiber die erste
Anlage der mensch. Milchdriisen tiberhaupt. Morph. Arb. Bd. VII.
Heft 1, 1897.

APPENDIX 405:

ScuuLrze, O. Ueber die erste Anlage des Milchdriisenapparates Anat. Anz:
VII. Jahrg. 1892.

Milchdriisenentwicklung und Polymastie. Sitz.-ber. Ges. Wiirzburg. VIII.
1892. See also Verh. Ges. Wiirzburg. N. F. XXVI. Bd. 1893.

Scuwaupe, G. Ueber den Farbenwechsel winterweisser Thiere. Ein Beitrag
zur Lehre vom Haarwechsel und zur Frage nach der Heukunft des Haut-
pigments. Morph. Arb. II. Band, 3 Heft.

SeuL, K. Ueber Hyperthelie, Hypermastie und Gyndkomastie. Inaug.-Dissert.
Freiburg, 1894. (See also Ber. Ges. Freiburg Bd. IX.)

Sunvio Torri, G. Sul Significato di un’appendice epiteliale dei follicoli piliferi
ae Ricersche. Lab. Anat. Roma é altri Lab. Biolog. Vol. V.

SitrepA, L. Ueber den Haarwechsel. Biol. Centralb. WII. Bd. 1887. ‘

Unna, P. Beitr. zur Histologie und Entw.-Geschichte der menschlichen Oberhaut
und ihrer Anhangsgebilde. Arch. f. mikr. Anat. Bd. XII. 1876.

Waupeyrer, W. Atlas der menschl. u. thierischen Haare sowie der ahnlichen
Fasergebilde. Herausg. v. J. Grimm in Offenburg. Lahr 1884.

WeseER, M. Ueber neue Hautsecrete bei Siugethieren. Arch. f. mikr. Anat.
Bd. XNXI. 1888.

Bemerk. iiber den Ursprung der Haare und iiber die Schuppen bei Sauge-
thieren. Anat. Anz. VIII. Jahrg. 1893.

Witson, J.T. and Martin, C. J. Further observations upon the Anatomy of
the Integumentary Structures in the Muzzle of Ornithorhynchus. P.
Linn. Soc. N. 8. W. Vol. IX. Series 2nd. 1894.

ZANDER, R. Die friihesten Stadien der Nagelentwicklung und ihre Beziehungen
zu den Digitalnerven. Arch. Anat. Jahrg. 1884.

Untersuch. itber den Verhornungsprozess. II. Mittheil. Der Bau der menschl.
Epidermis. Loc. cit. Jahrg. 1888.

B. EXOSKELETON.

Brenz, A. Dermatemys Mavii, Gray, eine osteol. Studie mit Beitr. z. Kenntnis
vom Bau der Schildkréten. Revue Suisse de Zool. ITI. Bd. 1895.
Cotuixcs, W. E. On the presence of Scales in the integument of Polyodon
folium. Journ. Anat. and Physiol. Vol. XXIX.
GoLp1, E. Kopfskelet und Schultergiirtel von Loricaria cataphracta, Balistes
capriscus und Acipenser ruthenus. Jen. Zeitschr. Bd. XVII. N. F.
X. Bd. 1884.
Haycrart, J. B. The Development of the Carapace of the Chelonia. Trans.
Roy. Soc. Edin. Vol. XXXVI. part 2. 1891.
Hertwic, O. Ueber den Bau und Entwicklung der Placoidschuppen und der
Zihne der Selachier. Jen. Zeitschr. Bd. VIII. N. F. I.
Ueber das Hautskelet der Fische. Morph. Jahrb. Bd. II. 1876. Bd. V.
1879. Bd. VII. 1881.
Horsr, B. Ueber den Bau und die Entwicklung der Cycloid- und Ctenoid-
schuppen. Sitz.-Ber. Morphol. und Physiol. Miinchen. 1889.
Kraatscu, H. Zur Morphologie der Fischschuppen und zur Geschichte der
Hartsubstanzgewebe. Morph. Jahrb. Bd. XVI. 1890.
Ueber die Herkunft der Scleroblasten, Morph. Jahrb. Bd. XXI. 1894.
Ueber die Bedeutung der Hautsinnesorgane fiir die Ausschaltung der
Scleroblasten aus dem Ektoderm. Verh. Anat. Ges., 1895.
Latastge, F. (See p. 414.)
WirpeErsHEIm, R. Die Anatomie der Gymnophionen. Jena 1879.
Zur Histologie der Dipnoérschuppen. Arch. f. mikr. Anat. Bd. XVIII.
1880.

406 APPENDIX

THE FOLLOWING DEAL WITH THE EXOSKELETON OF FossiL FISHES, AMPHIBIANS
AND REPTILES.

Crepner, H. (See p. 396.)
Dorto. Numerous papers on Fossil Reptiles in the Bulletin du Musée royal
VHistoire naturelle de Belgique from 1882 onwards (e.g. ‘‘ Troisiéme note
sur les Dinosauriens de Bernissart,” tome II. 1883).
Fraas, O. Aétosaurus ferratus, Fr. Die gepanzerte Vogelechse aus dem Stuben-
sandstein bei Stuttgart. Stuttgart, 1877.
Fritscu, A. Die Reptilien und Fische der béhmischen Kreideformation. Prag,
1878.
Fauna der Gaskohle und der Kalksteine der Permformation Bihmens. Prag,
1879—85.
Marsu, O. C. Numerous papers in the American Journal of Sciences and Arts.
Meyer, H. v. Numerous papers in Palaeontographica, ¢.y. Bd. VI. Archego-
saurus.
Romer, F. Ueber den Bau und die Entwicklung des Panzers der Giirtelthiere.
Jen. Zeitschr. Bd. 2F.
Zur Frage nach dem Urspr. der Schuppen der Saugethiere. Anat. Anz. VIII
Jahrg. 1893.
Ritimeyer, L. Ueber den Bau von Schale und Schidel bei lebenden und foss.
Schildkréten. Verh. Ges. Basel, VI, 1.

C. ENDOSKELETON.
1. VERTEBRAL COLUMN.
(a) AmpuHioxus, Pisces, aND DIPNot.

Agassiz, A. (See p. 395.)
CALBERLA, E. Ueber die Entw. d. Medullarrohres und der Chorda dorsalis der
Teleostier und Petromyzonten. Morph. Jahrb. Bd III. 1887.

Cartier, O. Beitr. 2. Entw-Geschichte der Wirbelsdule. Zeitschr. f. wiss. Zool.
Bd. XXV. Suppl. 1875. :
Cuaus, C. Ueber die Herkunft der die Chordascheide der Haie begrenzenden

ausseren Elastica. Sitz.-ber. Ak. Wien. 1894. (Akad. Anz. Nr. XII.)
Epsner, V. v. Ueber den feineren Bau der Chorda dorsalis der Cyclostomen.
Sitz.-ber. Ak. Wien. Bd. C. IV. Abth. 1II. 1895.
Ueber den feineren Bau der Chorda dorsalis von Myxine nebst weiteren
Bemerkungen iiber die Chorda von Ammoceetes. Sitz.-ber. Ak. Wien.
Bd. C. IV. (Abth. III.) 1895.
1. Ueber den feiner. Bau der Chorda dorsalis y. Acipenser. Loc. cit.
2. Ueber den ,, <3 <5 ae 38 »5 bei Amphioxus lanceolatus.
‘ Ueb. die Wirbel der Knockenfische und die Chorda dorsalis der Fische u.
Amphibien, Sitz.-ber. Ak. Wien. Bd. CV. Abth. III. 1896.
ee C. Ueber das Skeletgewebe der Cyclostomen. Jen. Zeitschr.
Ueber die Entw. der Wirbelsitule des Lepidosteus mit vergl. anat.
Bemerkungen. Loc. cit. Bad. III.
Corre, A. Beitriige zur vergl. Morphologie des Skeletsystems der Wirbelthiere.
Arch. f. mikr. Anat. Bd. XV. 1878.
Grassi, B. Beitr. z. naheren Kenntnis der Entwickling der Wirbelsiiule der
Teleostier. Morph. Jahrb. Bd. VIII. 1882.
Lo Sviluppo della Colonna vertebrale ne’ Pesci ossei. Atti Acc. Lincei.
1882—83.
(,apow Hans and Apsort, E. C. On the Evolution of the Vertebral Column in
Fishes. Phil. Trans. Vol. 186. 1895.
Hasse, C. Die fossilen Wirbel. Morph. Jahrb. II. (1876), III. (1877), 1V.
(1878).
Die Entwicklung der Wirbelsiule der Elasmobranchier. Zeitschr. f. wiss.
Zool. Bd. LY. 1892.
Die Entwicklung und der Bau der Wirbelsiiule der Ganoiden. Loe. eit.
Bd. LVII. 1893. Der Cyclostomen. Loc. cit. Bad. LVII. 1893.

APPENDIX 407

aaa A aaa der Wirbelsiiule der Dipnoi. Zeitschr. f. wiss. Zool.
cd. 4.
-JosEPH, H. Ueber das Achsenskelet des Amphioxus. Zeitsch. f. wiss. Zool.
Bd. LIX. 3. 1895.
Kuaatscu, H. Beitr. zur vergl. Anatomie der Wirbelsiule. Morph. Jahrb.
Bd. XIX, XX, XXII, XXIII.
K6LLikgr, A. Ueber die Beziehung der Chorda zur Bildung der Wirbel der
Selachier und einiger anderer Fische. Verh. Ges. Wiirzburg. Bd. X.
Weitere Beobachtungen tiber die Wirbel der Selachier. Abh. Senckenb.
Ges. Bd. V.
Ueber das Ende der Wirbelsiule der lebenden Teleostier und einiger Ganoiden.
Gratul.-Schrift f. d. Univ. Basel 1860.
Lvorr, B. Vergl-anatom. Studien tiber die Chorda und die Chordascheide.
Bull. Soc. Moscou. 1887.
Ueber Bau u. Entw. d. Chorda von Amphioxus. Mitth. Zool. Stat. Neapel.
Bd. IX. 1890.
Die Bildung der primaren Keimblatter und die Entstehung der Chorda und
des Mesoderms bei d. Wirbelthieren. Bull. de Moscou, 1894.
Mayer, P. (See p. 420).
Mutter, Auc. Beobacht. z. vergl. Anat. der Wirbelsiule. Arch. f. Anat. und
Physiol. 1853.
Mtiier, W. Ueber den Bau der Chorda dorsalis. Jen. Zeitschr. 1871.
Retzius G. Uber das hintere Ende des Riickenmarks bei Amphioxus, Myxine
u. Petromyzon. Biol. Untersuch. N.F. VII. 1895.
ScHEEL, C. Beitr. z. Entw. Gesch. der Teleostierwirbelsiiule. Morph. Jahrb.
Bd. XX. 1893.
Scumipt, V. Das Schwanzende der Chorda dorsalis bei den Wirbelthieren.
Anat. Hefte, I Abthiel, VI/VII Heft (II Bd. Heft III/IV).
Scumipr,"L. Untersuch. z. Kenntnis des Wirbelbaues von Amia calva. Inaug.
Dissert. Strassburg i/E. 1892.
WIEDERSHEIM, R. Das Skelet und Nervensystem von Lepidosiren annectens
(Protopterus). Morphol. Studien. Heft. I. Jena 1880.

(b) AMPHIBIA, REPTILIA, AND AVES.

ALBRECHT, P. Ueber einen Processus odontoides des Atlas bei den urodelen
Amphibien. Centralbl. f. die medic. Wissenschaft. 1878.

Ueber den Proatlas, einen zwischen dem Occipitale und dem Atlas der amnioten
Wirbelthiere gelegenen Wirbel, und den Nervus spinalis Is. proatlanticus.
Zool. Anz. Bd. III. 1880.

Note sur la présence d’un rudiment de Proatlas sur un exemplaire de Hatteria
punctata. Extr. Bull. Mus. roy Vhist. nat. de Belgique. Tome II. 1883.

Notes sur une hémivertébre gauche surnuméraire de Python sebe. loc. cit.
Tome IT. 1883.

Note sur le basi-occipital des batraciens anoures. loc. cit. Tome II. 1883.

Baur, G. Ueber den Proatlas emer Schildkréte (Platypeltis spinifer Les.). Anat.
Anz. X. Bd. 1895.

Osteolog. Notizen tiber Reptilien. Zool. Anz. IX und X. Jahrg. 1886,
1887.

Ueber die Morphogenie der Wirbelsiule der Amnioten. Biol. Centralbl.
VI. Bd. 1886.

Busssic, E. Eine morphol. Untersuchung iiber die Halswirbelsiule der
Lacerta vivipara. Inaug.-Dissert. Dorpat 1885. ;

‘CLaus, C. Beitr. z. vergl. Osteologie der Vertebraten. Sitz.-ber. Ak. Wien.
I. Abthl. Bd. LXXIV. 1876.

‘Corr, E. D. Extinct Batrachia from the Perm. Form. of Texas. Pal. Bullet
Nr. 29; Proc. Amer. Philos. Soc. 1878, 1880, 1886. Pal. Bull. Nr. 32;
Amer. Nat. 1880, 1882, 1884, 1885, 1886.

Dotto, L. Sur la Morphologie de la Colonne vertébrale. Travaux du Laboratoire
de Wimereux. 1892.

Enver, V. v. (See p. 406.)

Fraissz, P. Beitr. zur Anatomie des Pleurodeles Waltlii. Arb. Inst. Wiirzburg.
Bad. V,

408 APPENDIX

Fraisse, P. Eigenthiimliche Structurverhiltnisse im Schwanz erwachsener
Urodelen. Zool. Anz. ITI. Jahrg. 188. Pes
Fietp, H. H. Bemerk. iiber die Entwicklg. d. Wirbelsiiule der Amphibien ete.

Morph. Jahrb. Bd. XXII. 1895. re 7

Gavow, H. On the Evolution of the vertebral column of Amphibia and Amniota.
Phil. Trans. Vol. 187. (1896) B.

Ueber die Zusammensetzung der Wirbel bei den Reptilien. Zool. Anz. No.
458. 1894.
GEGENBAUR, C. Unters. z. vergl. Anatomie der Wirbelsiiule der Amphibien u.
Reptilien. Leipzig 1862. ;
x0TTE, A. Ueber die Zusammensetzung der Wirbelsiiule bei den Reptilien.
Zool. Anz. 1894.
Ueber den Wirbelbau bei den Reptilien und einigen andern Wirbelthieren.
Zeitschr. f. wiss. Zool. Bd. LXII. 1896.

HassE, C. Anatomische und paliontologische Ergebnisse. Leipzig 1878.

Die Entwicklung der Wirbelsiule von Triton teniatus. Zeitschr. f. wiss.
Zool. L. 1UL. Bd. Suppl. 1892.
Die Entwicklung der Wirbelsiule der ungeschwiinzten Amphibien. Loc. cit.

Hasse C. und Scuwarcx. Stud. zu vergl. Anat. d. Wirbelsdule etc. in ‘ Hasse,
Anatomische Studien, H. I.”

Horrmann, C. K._ Beitr. z. vergl. Anatomie d. Wirbelthiere. Niederl. Arch. f.
Zool. Bd. IV., V.

Marsu, 0. C. Various articles on fossil Reptiles and Birds. Amer. Journ. of
Science and Arts. Vols. XV.—XXIII.

MU.uer, E. Uber die Abstossung u. Regeneration des Eidechsensthwanzes. Jahr.
Ber. d. Vereins fiir vaterlind. Naturkunde Wiirtemburg. 52 Jahrgang
Stuttgart. 1896.

Parker, W. K. On the Morphology of Birds. P. Roy. Soc. Vol 42. 1887.

Prrrr, K. Die Wirbelsiule der Gymnophionen. Ber. Ges. Freiburg. Bd. IX.
1894.

Ueber die Bedeutung des Atlas der Amphibien. Anat. Anz. Bd. X. 1895.

RipEwoop, W. G. On the development of the vertebral column in Pipa and
Xenopus. Anat. Anz. Bd. XIII. 1887.

ScHwink, F. Ueber die Entwicklung des mittleren Keimblattes und der Chorda
dorsalis der Amphibien. Miinchen, 1889.

Srepenrock, F. Zur Kenntnis des Rumpfskeletes der Scincoiden, Anguiden und
Gerrhosauriden. Annal. d. K.K. Naturhistor. Hofmuseums. Bd. X. H. 1.
1895.

VAILLANT, Lion. Mém. sur la disposition des vertébres cervicales des Chcloniens.
Ann. sci. nat. zool. art. No. VII.

WIeDEsHEIM, R. (See pp. 397 and 413.)

ZrrreL, K. Ueber Flugsaurier aus dem lithograph. Schiefer Bayerns. Palaeonto-
graphica. Bd. XXIX.

MamMattia.

ALBRECHT, P, Die Epiphysen und die Amphiomphalie der Siugethierwirbelkirper.
Zool. Anz. 1879.

Note sur un sixiéme costoide cervical chez un jeune Hippopotamus amphibius.
Extr. du Bull. Mus. roy. Whist. nat. de Belgique. Tome I. 1882.

Ueber die Wirbelkérpergelenke zwischen dem Epistropheus, Atlas und
Occipitale der Siiugethiere. Comptes rendus des internat. medic. Congresses.
Kopenhagen 1884.

Ueber die Chorda dorsalis und sieben knicherne Wirbelcentren im knorpeligen
i tae Jaa eines erwachsenen Rindes: Biol. Centralbl. Bd. V. No.
5 u. 6.

Coryer, J. Note sur le prétendu Pro-Atlas des Mammiféres et de Hatteri
punctata. Bull. Ac. Belgique. 3me série. t. XV. 1888.

Cunninenam, D.J. The Lumbar Curve in Man and the Apes, with an account of
the topogr. Anatomy of the Chimpanzee, Orang-Utang, and Gibbon. Tr.
Trish Ac., Cuningham Memoirs, No. II. 1886.

Evyer, V. v. Urwirbel und Umgliederung der Wirbelsiiule. Nitz.-ber, Ak.
Wien. Bd. NCVIL Abth. TT. 188s.

Ueher die Beziehungen der Wirbel zu den Urwirbeln. Loe. eit. Ba. C. 1.
Abth. III. 1892.

APPENDIX 409

Ecker, A. Der Steisshaarwirbel, die Steissbeinglatze und das Steissbeingriibchen,
etc. Arch. f. Anthropologie. Bd. XII.

For, H. Sur la queue de ?embryon humain. Comptes rendus. 1885.

Frorier, A. Zur Entwickl.-Geschichte der Wirbelsiiule, insbesondere des Atlas
ene Epistropheus und der Occipital-Region. Arch. f. Anat. u. Physiol.

Grrzacu, L. Ein Fall von Schwanzbildung beieinem menschl. Embryo. Morph:
Jahrb. Bd. VI.

Hasse, C. und Scowarck. Studien zur vergl. Anatomie der Wirbelsiule etc.
Hasse, Anat. Studien. Heft I.

Kereen, F. Ueber die Entwicklungsgeschichte der Chorda bei Siiugern (Meer-
schweinchen und Kaninchen). Arch. f. Anat. 1889.

Ueber den Schwanz des menschlichen Embryos. Arch. Anat. 1891. (See

also Anat. Anz. VI. Jahrg. 1891.)

Ko.iiker, A. Ueber die Chordahéhle und die Bildung der Chorda beim
Kaninchen. Sitz. ber. Ges. Wiirzburg. 1883.

Lrzoucg, H. Recherches s. 1. mode de Disparition de la corde dorsale chez les
Vertébrés supérieurs. Arch. Biol. Vol. I. 1880.

RosENBERG, C. Ueber die Entwicklung der Wirbelsiule und das Centrale Carpi
des Menschen. Morph. Jahrb. Bd. I. 1876.

Rosenverc, E. Ueber die Wirbelsiule der Myrmecophaga jubata. Festschrift
fiir Carl Gegenbaur. Leipzig, 1896.

Srurnpacu, E. Die Zahl der Caudalwirbel beim Menschen. Inaug.-Dissert.
Berlin. 1889.

Wa.peyrer, W. Die Caudalanhinge des Menschen. Sitz.-ber. Ak. Berlin.

2. RIBS AND STERNUM.

ALBRECHT, P. Ueber die im Lauf der phylogenetischen Entwicklung entstandene,
angeborene Spalte des Brustbeinhandgriffes des Briillaffen. Sitz.-ber. Ak.
Berlin. XX. 1885.

BarpELEBEN, K. Ueber das Episternum des Menschen. Sitz.-ber. Jenaisch
Gesellsch. f. Medic. u. Naturwiss. 1879.

Baur, G. On the Morphology of Ribs. Amer. Nat. 1887.

On the Morphology of Ribs, etc. Journ. Morphol. Vol. III. 1889.
Ueber Rippen und rippeniihnliche Gebilde und deren Nomenclatur. Anat.
Anz. IX. Bd., 1893.

BLancHARD, R. La septiéme céte cervicale de Phomme. Revue scientif. 1885.
(3e série.) No, 23.

Cuaus, C. Beitriige zur vergl. Osteologie der Vertebraten. Sitz.-ber. Ak. Wien.
Bd. LXXIV. 1876.

Dotto, L. Sur la Morphologie des Cétes. Bull. sci. France-Belgique. Tome
XXIV. 1892.

Euers, E. Zoolog. Miscellen. I. Der Processus Xiphoideus und seine Muscu-
latur von Manis macrura, Erxl, und Manis tricuspis, Sundev. Abh. Ges.
Gottingen. Bd. 39. 1894.

Fick, A. E. Zur Entw.-Geschichte der Rippen und Querfortsiitze. Arch. f.
Anat. und Physiol. 1879.

GEGENBAUR, C. Ueber die epistern. Skelettheile und ihr Vorkommen bei den
Saugethieren und beim Menschen. Jen. Zeitschr. Bd. I.

Gorrert, E. Zur Kenntnis der Amphibienrippen. Zool. Jahrb. XXII. Ba.
1895.

Untersuchungen zur Morpholog. d. Fischrippen. Loc. cit. Bd. XXIII.
Die Morphologie der Amphibienrippen. Festschrift ftir Carl Gegenbaur.
Leipzig, 1896. : : .

Gorrr, A. Beitrige zur vergl. Morphologie des Skeletsystems der Wirbelthiere.

Arch. f. mikr. Anat. Bd. XV., pag. 143—147. (See also p. 397.)
Beitriige zur vergl. Morphologie des Skeletsystems der Wirbelthiere.
Brusthein und Schultergiirtel. Arch. f. mik. Anat. Bd. XIV.

Hasse, C., und Bors, G. Bemerkungen tiber die Morphologie der Rippen. Zool.
Anz. 1879.

Haswetn, W. A. Studies on the Elasmobranch Skeleton. P. Linn. Soc. N.S.W
Vol. IX. 1884.

410 APPENDIX

Harscuex. Die Rippen der Wirbelthiere. Verh. Anat. Ges. 1889. Jena, 1889.

HorrMann, C. K. (See p. 408.)

Howss, G. B. The Morphology of the Sternum. Reprinted, with a Correction,
from ‘‘ Nature.” Vol. 43. p. 269.

Lezouce, H. Rech. sur les variations anatomiques de la premiére céte, chez
VYhomme. Mémoires couronnés et Mém. des savants étrangers, publi¢s par
lAcad. royale des Sciences de Belgiques. I. LV. 1896.

Linpsay, B. On the avian Sternum. P. Zool. Soc. 1885.

Mtuer, A. Beitr. z. vergl. Anat. der Wirbelsdule. Mliiller’s Archiv. 1853.

ParkKER, W. K. A monograph on the structure and development of the shoulder-
girdle and sternum. Ray Soc. 1867.

Parker, T. J. On the Origin of the Sternum. Tr. N.Z. Inst. Vol. XXIII.
1890.

On the Presence of a Sternum in Notidanus indicus. ‘‘ Nature,” Vol. 43,.
1890—91. pp. 142 and 516.

Pruuinc, E. Ueber die Halsrippen des Menschen. Inaug. Dissert. Rostock. 1894.

Rast, C. Theorie des Mesodermes (Fortsetzung). Morph. Jahrb. Bd. XIX.
1892.

Ratuke, H. Ueber den Bau und die Entwicklung des Brustbeins der Saurier.
Kénigsberg 1853.

Ruer, G. Untersuchungen iiber Entwicklungsvorginge am Brustbeine und an
der Sternoclavicularverbindung des Menschen. Morph. Jahrb. Bd. VL
1880.

SIEBENROCK, F. (See p. 408.)

Wuirr, P. J. A Sternum in Hexanchus griseus. Anat. Anz. XI. Bd. No. F.
1895.

WIEDERSHEIM, R. (See p. 415 and 416.)

3. SKULL.

(a) Pisces.
AHLBORN, F. Ueber die Segmentation des Wirbelthierkirpers. Zeitschr. f. wiss.
Zool. 1884.
Baur, G. On the Morphology and Origin of the Ichthyopterygia. Amer. Nat.
- 1887.

BripcE, T. W. On certain features of the skull of Osteoglossum formosum. P.
Zool. Soc. 1895.

Donry, A. Studien zur Urgeschichte des Wirbelthierkérpers. Mittheil. Zool.
Stat. Neapel. Bd. III, H.1,2. Bd. V.,H.1. Bd. VI, H. 1.

Studien zur Urgeschichte des Wirbelthierkirpers. XV. Neue Grundlagen
zur Beurtheilung der Metamerie des Kopfes. Mittheil. Zool. Stat. Neapel.
IX. Bd. 3. Heft. 1890.

Bemerk. iiber den neuesten Versuch einer Lisung des Wirbelthierkopf-
Problems. Anat. Anz. V. Jahrg. 1890.

Dotto, L. Nouvelle Note sur le Champsosaure, Rhynchocéphalien adapté a la vie
fluviatile. Bull. de la Société Belge de Géologie etc. T. V., 1891. (See
also numerous papers in previous vols., and in Bull. Mus Roy. Hist. Nat.
Belg. und Bull. scient. Giard.)

Foot, Ethelwyn. The extra-branchial cartilages of the Elasmobranchs, Anat.
Anz, XIII. Bd. 1897.

(sapow, H. On the Modifications of the first and second visceral arches with
especial reference to the homologies of the auditory ossicles. Phil. Tran.
Vol. 179, 1888.

(+EGENBAUR, C. Unters. z. vergl. Anat. d. Wirbelthiere. III. H. Das Kopskelet
der Selachier. Leipzig, 1872.

Ueber das Kopfskelet von Alecocephalus rostratus, Risso. Festgabe des
Morph.-Jahrb. Leipzig, 1878.

Ueber die Occipitalregion und die ihr benachbarten Wirbel der Fische. Fest-
schrift zu A. v. Kéllikers 70. Geburtstag. Leipzig, 1887.

Die Metamerie des Kopfes und die Wirbeltheorie des Kcpfskeletes. Morph.
Jahrb. Ba. XII. 188s.

Hasweni, W. A. (See p. 409.)

APPENDIX 411

biaulaaer rs Metamerie des Amphioxus und des Ammocoetes, Verh. Anat.

es, 2,

Horrmayy, C. K. Zur Entwickl. Gesch. des Selachierkopfes. Anat. Anz.
IX. Bd. 1894. ‘

Houxiey, T. H. The nature of the craniofacial apparatus of Petromyzon. Journ.
Anat, and Physiol. Vol. X.

JAEKEL, O. Uber die Organisation der Pleuracanthiden. Sitz.-ber. Naturf.
Berlin, Jahrg. 9. 1895.

Kiuuran, G. Zur Metamerie des Selachierkopfes. Verh. Anat. Ges. 1891.

Kur, v. Beitr. zur Bildung des Schidels der Knochenfische. Jahresh, des
Vereins fiir vaterlind. Naturkunde in Wiirttemberg. 1884—1886.

Kuprrer, C. Studien z. vergl. Entw.-Gesch. d. Kranioten. I. Heft. Die Ent-
wicklung des Kopfes von Acipenser sturio an Medianschnitten untersucht.
Miinchen u. Leipzig, 1893. II. Heft. Die Entwicklung des Kopfes von
Petromyzon planeri, 1894. III. Heft. Die Entwicklung des Kopfnerven
von Petromyzon planeri.

Entwicklungsgeschichte des Kopfes. Anat. Hefte Ergebn. 1895.

Locy, W. A. Contrib. to the Structure and Development of the vertebrate Head.
Journ. Morphol. Vol. XI, No. 3. 1895.

Marsa, A. Mityes. The segmental value of the cranial nerves. Journ. Anat.
and Physiol. Vol. XVI.

On the Head Cavities and Associated Nerves in Elasmobranchs. Q. Journ.
Micr. Science. Vol. XXI.
Parker, W. K. On the Structure and Development of the Skull in Sharks and
Skates. Tr. Zool. Soc. Vol. X., Pt. IV.
On the Skeleton of the Marsipobranch Fishes. Part I., The Myxinoids
(Myxine and Bdellostoma). Part II., Petromyzon. Phil. Trans. 1883.
On the Structure and Development of the Skull in the Sturgeons. Phil.
Trans. 1882.

On the Development of the Skull in Lepidosteus osseus. Phil. Trans.
1882.

On the Structure and Development of the Skull in the Salmon. Phil. Trans.
Vol. CLXITI., 1873. t

Parker, W. K., und Berrany, G. T. The Morphology of the Skull. London,
1877. (German Trans. by B. Vetter. Stuttgart, 1879.)

Puatt, J. A Contribution to the Morphology of the Vertebrate Heal. Journ.
Morphol. Vol. V., 1891.

Further Contributions to the Morphology of the Vertebrate Héad. Anat.
Anz. VI. Jahrg., 1891.

PotiarD, H. B. The Suspension of the Jaws in Fish. Anat. Anz. X. Bd. No. ],
1894.

The Oral Cirri of Siluroids and the Origin of the Head in Vertebrates. Zool.
Jahrb. Bd. VIII., 1895.

Poucuretr, D. Du développement du squelette des poissons osseux. Journ. de
Panat. et physiol. 1878.

Ras. Ueber die Metamerie des Wirbelthierkopfes. Verh. Anat. Ges., 1892.

Ripewoop, W. G. On the Spiracle and Associated Structures in Elasmobranch
Fishes. Anat. Anz. Bd. XI., 1896.

RosENBERG, E. Unters iiber die Occipitalregion des Cranium und den proximalen
Theil der Wirbelsiule einiger Selachier. Eine Festscrift. Dorpat, 1884.

Ueber das Kopfskelet einiger Selachier. Sitz. ber. der Dorpater Natur-
forsch. Gesellsch. Jahrg. 1886.

‘SacemMrEnL, M. Beitriige zur vergl. Anat. der Fische. Morph. Jahrb. Bd. IN.

and X., 1884, 1885. : ree
Beitrige zur vergl. Anatomie der Fische. IV. Das Cranium der Cyprinoi-
den. Morph. Jahrb. XVII. Bd., 1891. :

Sewerrzorr, A. Die Entwicklung der Occipitalregion der niederen Vertebraten
im Zusammenhang mit der Frage iiber die Metamerie des Kopfes. Bull.
Soc. Moscou, 1895. No. 2.

Srour, Pu. Zur Entw.-Geschichte des Kopfskelets der Teleostier. Aus der
Festschrift zur Feier des 300 jihr. Bestehens der Universitiit Wiirzburg.
Leipzig, 1882. é

Vrouik, J. A. Studien itber die Verkniécherung und die Knochen des Schiidels
der Teleostier. Niederl. Arch. f. Zool. Vol. I.

412 APPENDIX

Warner, J. Die Entwicklung der Deckknochen m Kopfskelet des Hechtes.
Jen. Zeitschr. XVI. N. F. IX.

Wurre, P. J. The Existence of Skeletal Elements between the Mandibular and
Hyoid Arches in Hexanchus and Lemargus. Anat. Anz. Bd. XI. No. 2,
1895.

Wusur, J. W. vax. Ueber das Visceralskelet und die Nerven des Kopfes der
Ganoiden und von Ceratodus. Niederl. Arch. f. Zoologie. Bd. V. Heft
3, 1882.

Ueber die Mesodermsegmente und die Entwickelung der Nerven des
Selachierkopfes. Veriffentl. durch. die K. Acad. der Wissensch. zu
Amsterdam, 1882.

Die Kopfregion der Cranioten beim Amphioxus, nebst Bemerkungen tiber die
Wirbeltheorie des Schiidels. Anat. Anaz. IV. Jahrg., 1889.

Wricut, Ramsay R. On the Skull and Auditory Organ of the Siluroid
Hypophthalmus. Trans. Roy. Soc. Canada. Section IV., 1895.

(b) Drpnot.
(See pages 395 and 407.)

(c) AMPHIBIA.

Born, G. Ueber die Nasenhihlen und den Thrinennasengang der Amphibien.
Bresl. Habil.-Schrift. Leipzig, 1877, and Morphol. Jahrb. Bad. IL,

1876.
Corr, E. D. On the Structure and Affinities of the Amphiumide. Amer. Philos.
Soc., 1886.

On the Relation of the Hyoid and Otic Elements of the Skeleton in the
Batrachia. Journ. Morphol. Vol. IL, 1888.

Duats, A. Recherches sur l’ostéologie et la myologie des Batraciens. Paris,
1835.

Fritscu, A. Fauna der Gaskohle, etc. Prag, 1879-1881.

Gaupp, E. Grundziige der Bildung und Umbildung des Primordialcraniums
von Rana fusca. Verh. Anat. Ges., 1892.

Beitr. z. Morphologie des Schidels. 1. Primordialcranium und Kieferregion
von Rana fusca. II. Das Hyo-branchial-skelet der Anuren und seine
Umwandlung. Morph. Arb. II. Bd. 2. Heft. III. Bd. 3. Heft.

Beitr. zu. Morphol. d. Schidels. III. Zur vergl. Anatomie der Schlifengegend
ete. Morph. Arb. IV. Bd. 1. H., 1894.

Hay, O. P. The Skeletal Anatomy of Amphiuma during its Earlier Stages.
Journ. Morphol. Vol. IV. No. 1, 1890.

Hertwic, O. Ueber das Zahnsystem der Amphibien und seine Bedeutung fiir
die Genese des Skelets der Mundhihle. Arch. f. mikr. Anat. Vol. XI.
Suppl.-H., 1874.

Houxtey, T. H. On the Structure of the Skull and of the Heart of Menobranchus.
lateralis. P. Zool. Soc., 1874, pt. II.

Kinestuy, J. 8. The Head of an Embryo Amphiuma. Amer. Nat., 1892.

Parker, W.K. On the Structure and Development of the Skull in the Urodelous
Amphibia, pt. I. Phil. Trans. London, 1877.

On the Morphology of the Skull in the Amphibia Urodela. Tr. Linn. Soc.
(Ser. 2) Zool. ol. II.

ee Structure and Development of the Skull in the Urodeles. Tr. Zool.

oc., 1882.

On the Structure and Development of the Skull of the common Frog. Phil.
Trans. London, 1871.

On the Structure and Development of the Skull in the Batrachia, pt. II.
Phil. Trans. 1881. ;

On the Structure and Development of the Skull in the Batvachia, pt. III.
Phil. Trans., 1881.

Rerukrr, C. Bo Verel. Entw.-Geschichte des Kopfes der nackten Amphibien.
Konigsherg, 1838.

ae _ oy z Anatomie des Tylototriton verrucosus. Zool. Jahrb.

ad. VL, TSOT.

APPENDIX 413

Scnuize, F. E. Ueber die inneren Kiemen der Batrachierlarven ete. I. IL.
__aAbth. Ab. Ak. Berlin, 1888 und 1892.
Sréur, Po. Zur Entw.-Geschichte des Urodelenschadels. Wiirzburger Habil.-
Schrift, 1879, and Zeitschr. f. wiss. Zool. Bd. XXXII.
Zur Entw.-Geschichte des Anurenschidels. Zeitschr. f. wiss. Zool. Bad.
XXXVI.
Watter, F. Das Visceralskelet und seine Muskulatur bei den einheimischen
Amphibien und Reptilien (gekr. Preisschrift). Jen. Zeitschr. Bd. XXI.

N. F. XVI.
Ve R. Das Kopfskelet der Urodelen. Morph. Jahrb. Bd. IIL.
Das Skelet von Pleurodeles Waltlii. Morph. Studien. Heft 1. (See also
page 397.)

(@) Repritra.

Baur, G. Osteolog. Notizen tiber Reptilien. Zool. Anz. Jahrg. IX. 1886. (See
also other papers in Anat. Anz.)
BemMeEten, J.F. von. Bemerk. zur Phylogenie der Schildkréten. Compte-rendu
d. séances du troisiéme Congrés internat. de Zool. Leyde, 1896.
Bemerkungen iiber den Schidelbau von Dermochelys coriacea. Festschrift
fiir Carl Gegenbaur. Leipzig, 1896.
Gaurr, E. Beitr zur Morphol. d. Schidels. III. Fiir vergl. Anat. der Schlifen-
gegend, &e. Morph. Arb. IV. Bd. J. H., 1894.
OppEL, A. Ueber Vorderkopfsomiten und die Kopfhéhle von Anguis fragilis.
Arch. f. mikr. Anat. Bd. XXXVI. 1890.
Parker, W. Kk. On the structure and development of the skull in the common
Snake. Phil. Trans. 1878.
On the structure and development of the skull in the Lacertilia. Phil. Trans.
1879.
The development of the Green Turtle. The Zoology of the Voyage of H.M.S.
Challenger. Vol. I., pt. V.
On the structure and development of the skull in the Crocodilia. Tr. Zool.
Soc. Vol. XIX. pt. IX. 1883.
On the structure of the skull in the Chameleons. Tr. Zool. Soc., 1881.
SIEBENROCK, F. Zur Kenntnis des Kopfskeletes der Scincoiden, Anguiden und
Gerrhosauriden. Annal. d. K. K. Naturhistor. Hofmuseums. Bd. VII.
Heft 3. Wien, 1892. (See also p. 408.)

(ce) AVEs.

Parker, W. K. On the structure and development of the skull of (a) the Ostrich
tribe ; Phil. Trans., 1866; (b) the common Fowl. Phil. Trans., 1869.
On Cgithognathous birds. Parts I. and II. Tr. Zool. Soc. Vols. IX. and X.
On the morphology of the skull in the Woodpeckers and Wrynecks. Tr.
Linn. Soc. (ser. 2) Zool., vol. I., 1875.
On the structure and development of the Bird’s Skull, part IT., /oc. cit. (see
also various papers in Monthly Micros. Journ., 1871-1873).
Parker, T. J. On the skeleton of Notornis mantelli. Trans. N. Y. Inst.
Vol. XIV. 1881. (See also Vol. XVIII. 1885.)
On the classification and mutual arrangement of the Dinornithide. Loc. cit.
Vol. XXV. 1892.
On the cranial osteology, classification and phylogeny of the Dinornithide.
Zool. Soc. Vol. XIII. 1895.
Waker, M. L. On the form of the quadrate bone in Birds. Stud. Mus. of
Zool. in University College, Dundee. 1888.
(Comp. also p. 398.)

(f) MamMszia.

Avsrecut, P. Sur la fente maxillaire double sousmuqueuse et les 4 os inter-
maxillaires de ?Ornithorhynche adulte normal. Bruxelles, 1883.
Mémoire sur le basiotique, un nouvel os de la base du crane, situé entre
Yoccipital et le sphénoide, présenté a la Société Pathologique de Bruxelles.
Bruxelles, 1883.

414 APPENDIX

Axprecut, P. Sur les 4 os intermaxillaires, le bec-de-liévre et la valeur morpho-
logique des dents incisives supérieures de ’homme. Bruxelles, 1883.

Sur la valeur morphologique de Varticulation mandibulaire, du cartilage de
Meckel et des osselets cle louie avec essai de prouver que l’écaille du tem-
poral des mammiféres est composée primitivement d’un squamosal et d’un
quadratum. Bruxelles, 1883.

ALLEN, Harrison. Ona revision of the ethmoid bone in the Mammalia. Bull.
Mus. Harvard. Vol. X. No. 3.

Baur, G. Ueber das Quadratum der Siugethiere. Biol. Centralbl. Bd. VI. 1887,
und Gesellsch. fiir Morphol. und Physiol. zu Miinchen. 1886.

Cottixce, W. E. The skull of the Dog. A manual for students. London and
Birmingham, 1896.

Corr, E. D. The phylogeny of the Camelidae. Amer. Nat. Extra, July, 1886.

Drcexer, F. Ueber den Primordialschidel einiger Siugethiere. Zeitschr. f. wiss.
Zool. Bd. NXXXVIII. 1884. 2

Dusots, Eve. Pithecanthropus erectus, eine menschenihnl. Ubergangsform.
Batavia, 1894. (See also Anat. Anz., Bd. XII.)

Dursy, E. Entw.-Geschichte des Kopfes des Menschen und der héheren
Wirbelthiere. Tiibingen, 1869.

Fieanvi, E. Sulla ossiticazione delle Capsule periotiche nell’uomo e negli altri
Mammiferi. Atti d. R. Accadem. Medica di Roma. Vol. III. Ser. II.
1886-87.

Frorirp, A. Bemerkungen zur Frage nach der Wirbeltheorie des Kopfskeletes.
Anat. Anz. II. Jahrg. 1887.

Hatimann. Die vergl. Anatomie des Schlifenbeins. 1837.

Hartiavs, C. Beitrige zur Kenntnis der Manatus-Arten. Zool. Jahrb. Bad. I.
1886.

Howes, G. B. On the mammalian hyoid. Report Brit. Assoc. Adv. Sci., 1895.

Jacopy, M. Ein Beitrag zur Kenntnis des menschlichen Primordialeraniums.
Arch. f. mikr. Anat. Bd. 44. 1894.

Josepu, G. Morphol. Studien am Kopfskelet des Menschen und der Wirbelthiere.
Breslau, 1873.

Lataste, F. Les Cornes des Mammiféres. Dans leur axe osseux aussi bien que
dans leur revétement corné sont des productions cutanées. Act. Soc. Scient.
du Chili, IV. année. T.1V. 5 livr. 1894.

Lvear, J. Die Sutura transversa squamae occipitis. Abh. Senkenb. Ges.

Minanxovics, V. vox. (See under Olfactory Organ.)

Natutsivus, H. vy. Vorstudien fiir Geschichte und Zucht der Hausthiere zunichst
am Schweineschidel. Mit einem Atlas. 1864.

Nevner, R. Ueber angebliche Chordareste in der Nasencheidewand des Rindes.
Inaug.-Dissert. Miinchen, 1886.

Osborn, H. F. See numerous papers on Bulletin of the American Museum of
Natural Ilistory. (Comp. also Wortman, (oc. cit.)

Parker, W. K. On the structure and development of the skull in the Pig. Phil.
Trans. 1874.

On the structure and development of the skull in the Mammalia. Part IT.
Edentata, Phil. Trans. No. 232, 1884; and part III, Insectivora, (oc. cit.
No. 235. 1885.

RuvimEYER, L. Versuch einer naturlichen Geschichte des Rindes, &c. Neue
Denkschr. d. Allg. schweiz. Gesellsch. f. d. ges. Naturw. 22 Bd. 1866.

Die Rinder der Tertidirepoche, etc. Abh. Schweiz. paleont. Gesellsch. Bd.
IV. 1877.

Ueber das zvuhme Schwein und das Hausrind. Verh. Ges. Basel. VII. 1. 1882.

Beitriige z Gesch. d. Hirschfamilie. I. Schidelbau. Verh. Ges. Basel-
VI. 3. 1877. .

SALENSKY, W. Beitr. z. Entw.-Geschichte der knorpeligen Gehérkniéchelchen
bei Siiugethieren. Morph. Jahrb., Bd. VI.

Scuwink, F. Ueber den Zwischenkiefer und seine Nachbarorgane bei Siuge-
thieren. Miinchen, 1888.

Svéxpit, H. Ueber den Primordialschidel der Siiugethiere und des Menschen.
Inaug.-Dissert. Zurich, 1846.

Srumbin, H. G. Fur Kenntnis der postembryonalen Schidelmetamorphosen bei
Wiederkiiuern. Basel, 1893.

APPENDIX 415

4, PECTORAL ARCH.

Doren, A. Studien zur Urgeschichte des Wirbelthierkirpers. VI. Die paarigen
und unpaaren Flossen der Selachier. Mittheil. Zool. Stat. Neapel. V.
Band, 1 Heft. 1886.

Duuks. Recherches sur lostéologie et la myologie des Batraciens A leurs différens
ages. Mémoires présentés par divers savants 4 l’académie royale des
sciences de Vinstitut de France. Sciences mathématiques et physiques.
Tom VI. Paris, 1835.

Emury, C. et Srmonr, L. Recherches sur la ceinture scapulaire des Cyprinoides.
Arch, ital Biol. T. VIL, Fasc. 3. 1886.

Ueber die Beziehungen des Cheiropterygium zum Ichthyopterygium. Zool.
Anz., X. Jahrg. 1887.

GarMAN, 8. Chlamydoselachus anguineus, Garm.—A living species of cladodont
Shark. Bull. Mus. Harvard. ;

GEGENBAUR, C. Unters. zur vergl. Anatomie der Wirbelthiere: Schultergiirtel der
Wirbelthiere. Carpus und Tarsus und Brustflosse der Fische. Leipzig,
1864-65.

Clavicula und Cleithrum. Morph. Jahrb. Bd. XXIII. 1895.

GoxpI, E. A. Kopfskelet und Schultergiirtel von Loricaria cataphracta, Balistes
capriscus und Acipenser ruthenus. Vergl. anatomisch-entwicklungs-
geschichtl. Studien zur Deckknochenfrage. Jena, 1884.

HorrMann, C. K. Beitriige zur vergl. Anatomie der Wirbelthiere. Niederlind.
Archiv f. Zool. Vol. V. 1879.

Zur Morphologie des Schultergiirtels und des Brustbeines bei Reptilien,
Vogeln, Saiugethieren und dem Menschen. Loc. cit.

Howss, G. B. Observations on the pectoral fin skeleton of the living Batoid
fishes and of the extinct genus Squaloraja, &¢. P. Zool. Soc. 1890.

The Morphology of the Mammalian Coracoid. Journ. Anat. and Physiol.
Vol. XXT. (N.S. Vol. I.) 1887.
On the Coracoid of the Terrestrial Vertebrata. P. Zool. Soc. June 20, 1893.

Hyrti, J. (See p. 397.)

Parker, W. K. Amonograph on the structure and development of the Shoulder
Girdle and Sternum in the Vertebrata. Ray Society. 1868.

SABATIER, A. Comparaison des ceintures et des membres antérieurs et postérieurs
dans la Série des Vertébrés. Montpellier, 1880.

Swirski1, G. Unters. tiber die Entwicklung des Schultergiirtels und des Skelets
der Brustflosse des Hechtes. Inaug.-Dissert. Dorpat, 1880.

Wrepersuemm, R. Morphologische Studien. Heft I. Jena, 1880.

Das Gliedmassenskelet der Wirbelthiere mit besonderer Beriicksichtigung
des Schulter-und Beckengiirtels bei Fischen, Amphibien und Reptilien.
Jena, 1892. (See also pp. 397 and 407.)

5. PELVIC ARCH.

AuBRecHT, P. Note sur le pelvisternum des Edentés. Bruxelles, 1883.

Baur, G. The Pelvis of the Testudinata; with notes on the evolution of the
Pelvis in general. Journ. Morphol. Bd. IV. Boston, 1891.

Box, L. Beziehungen zwischen Skelet, Musculatur und Nerven der Extremi-
tiiten, dargelegt am Beckengiirtel, an dessen Musculatur und am Plexus
lumbo-sacralis. Morph. Jahrb., Bd. XXI. 1894.

Buner, A. Unters. zur Entwicklung des Beckengiirtels der Amphibien,
Reptilien und Vogel. Inaug.-Dissert. Dorpat, 1880.

Donry, A. (See above.)

GrcEenpaur, C. Ueber den Ausschluss des Schambeines von der Pfanne des
Hiiftgelenkes. Morph. Jahrb., Bd. IT. 1876.

Beitr. z. Kenntnis des Beckens der Vigel. Jen. Zeitschr., Bd. VI. 1871.
Gorski. Ueber das Becken der Saurier. Inaug.-Dissert. Dorpat, 1852.
Hincenporr, R. Das Ileo-Sacral-Gelenk der zungenlosen Frésche (Pipa, Dacty-

lethra). Sitz. ber. Naturf. Berlin, 1884.

Horrmann, 0. K. Beitr. z. Kenntnis des Beckens der Amphibien und Reptilien..

Niederl. Arch. f. Zool., Bd. IT.

116 APPENDIX

Howes, G. B. On the Mammalian Pelvis with especial Reference to the young
of Ornithorhynchus anatinus. Journ. Anat. and Physiol. Vol. XXVII.

Huxtry, T. H. On the characters of the pelvis in the Mammalia, &c. P. Roy.
Soc., Vol. XXVIII. 1879.

Jounson, Anicr. On the Development of the pelvic Girdle and Skeleton of the
Hind Limb in the Chick. Stud. Morph. Lab. Camb. Vol. IT., part I. 1884.

Lecur, W. Das Vorkommen und die morphol. Bedeutung des Pfannenknochens
(Os acetabuli). Internationale Monatsschrift fiir Anatomie und Histologie.
Bd. I. 1884.

Zur Morphologie der Beutelknochen. Verhdlg. d. Biolog. Vereins zu
Stockholm. III. Bd. 1891. No. 7. Comp. numerous articles on Fossil
Reptiles in Amer. Journ. of Sc. (and see p. 400).

Meunert, E. Untersuch. tiber die Entwicklung deg Os pelvis der Vogel.
Morph. Jahrb., Bd. XTII. 1888.

Untersuch. iiber die Entwicklung des Beckengiirtels bei einigen Saugethieren.
Loc. cit. Ba. XV. 1889.

Untersuch. tiber die Entwicklung des Beckengiirtels der Emys Ilutaria
taurica. Loc. cit, Bd. XVI. 1790.

Untersuch. iiber die Entwicklung des Os hypoischium (Os cloacae), Os
epipubis und Ligamentum medianum pelvis bei den Kidechsen. Loe. cit,
Bd. XVII. 1891.

SABATIER, M. A. Compar. d. ceintures thoraciques et pelv. dans la Série des
Vertébrés. Acad. Sci. et Lettr. de Montpellier. Tom. IX. 1880.

WiepERsHEIM. R. Ueber das Becken der Fische. Morph. Jahrb., Bd. VII.
1881.

Zur Urgeschichte des Beckens. Ber. Ges. Freiburg, VI. 1888.

Ueber die Entwicklung des Schulter- und Beckengiirtels. Anat. Anz. V.
Jahrg. 1894. No. 1.

Weitere Mittheilhungen iiber die Entwicklungsgeschichte des Schulter- und
Beckengiirtels. Anat. Anz, V. Jahrg. 1890 No 1.

Die Phylogenie der Beutelknochen. Eine entwicklungsgeschichtlich-
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Woopwarp, A. Suiru. Palaeontological Contributions to Selachian Morphology.
P. Zool. Soc. 1888.

6. FINS AND LIMBS (free portion).

AupRecut, P. Beitrag zur Torsionstheorie des Humerus und zur morph.
Stellung der Patella in der Reihe der Wirbelthiere. Inaug. Dissert.
Kiel, 1875.

Das Us intermedium tarsi der Siugethiere. Zool. Anz., VI. Jahrg. No.
145. 1883.

1) Os trigone du pied chez Phomme, 2) Epihallux chez "homme. 3) Epiphyses
entre Doccipital et le sphénoide chez homme. Bulletin de la Société
@anthropologie de Bruxelles. Tome ITI., 3e fascicule. 1885.

Batrour, F. M. On the development of the skeleton of the paired fins of
Elasmobranchs, &c. P. Zool. Soc. 1881. (Comp. also p. 391.)

BARDELEBEN, K. Das Os intermedium tarsi der Siiugethiere. Zool. Anz., VI.
Jahrg. 1883. No. 139.

Beitr. z Morphologie des Hand- und Fusskeletes. Sitz.-ber. d. Jen.
Gesellsch. Medic. u. Naturwissensch. 1885.

Ueber neue Bestandtheile der Hand- und Fusswurzel der Siiugethiere,
sowie das Vorkommen von Rudimenten “‘iiberziihliger” Finger und
Zehen beim Menschen. Jen. Zeitschr., Bd. XIX. N. F. NII. Suppl.
Heft IIT. 1886.

On the Bones and Muscles of the Mammalian Hand and Foot. P. Zool. Soc.
1894.

Hand und Fuss, Referat Verh. Anat. Ges., Jahrg. 8. 1894.

Bacr, G. Der Tarsus der Végel und Dinosaurier. Morph. Jahrb., Bd. VIII.
TS83.

Ueber das Archipterygium und die Entwicklung des Cheiropterygium. Zool.
Anz, No. 209, VIII. Jahrg. 1885.

APPENDIX 417

Baur, G. Zur Morphologie des Carpus und Tarsus der Reptilien. Loc. cit. No.
208. VIII. Jahrg. 1885.

Bemerkungen tiber den Astragalus und das Intermedium tarsi der Siuge-
thiere. Morph. Jahrb., Bd. XI. 1885.

Zur Morphologie des Carpus und Tarsus der Wirbelthiere. Zool. Anz., VIII.
Jahrg. 1885.

Der alteste Tarsus (Archegosaurus). Loc. cit. Jahrg. IX. 1886.

Die zwei Centralia im Carpus von Sphenodon (Hatteria) und die Wirbel von
Sphenodon und Gecko verticillatus Laur. (G. verns Gray.) Zool. Anz.
Jahrg. IX. 1886.

Ueber die Kaniile im Humerus der Amnioten. Morph. Jahrb. Bd. XII. 1887.

beitrige zur Morphologie des Carpus und Tarsus der Vertebraten. I. Theil .
Batrachia. Jena, 1888.

ee ae z. Morphol. des Carpus der Siugethiere. Anat. Anz. Jahrg.

BEMMELEN, VAN. Ueber die Herkunft der Extremititen- und Zungenmuskulatu:
bei den Eidechsen. Anat. Anz. Jarg. IV. 1889.

Boas, J. E. V. a) Ueber den Metatarsus der Wiederkiuer. b) Ein Fall von
vollstindiger Ausbildung des 2 und 5 Metacarpale beim Rind. Morph.
Jahrb. Bd. XVI. 1890.

Born, G. Die sechste Zehe der Anuren. Morph. Jahrb. Bd. I. 1876.

Eine frei hervorragende Anlage der vorderen Extremitiit bei Embryonen von
Anguis fragilis. Zool. Anz. 1883, No. 150.

Ueber das Skelet des Fersenhickers von Rana fusca, &c. Sitz. d. Schles.
Gesellsch. f. vaterlind. Kultur vom 2 Juli 1879.

Zum Carpus und Tarsus der Saurier. Morph. Jahrb. Bd. 11. 1876.

Nachtrage zuin Carpus und Tarsus. Morph. Jahrb. Bd. VI. 1880.

Boyer, E. R. The mesoderm in Teleosts, especially its share in the formation
of the pectoral fin. Bull. Mus. Harvard. Vol. XXIII. No. 2. 1892.

Branpt, E. Vergl. anatom. Untersuchungen iiber die Griffelbeine (Ossa calami-
formia) der Wiederkiiuer. Zool. Anz. XI. 1888. ‘

Briper, T. W. The mesial fins of Ganoids and Teleosts. Journ. Linn. Soc.
Zool. Vol. XXYV. 1896.

Buncz, A. Ueber die Nachweisbarkeit eines biserialen Archipterygiums bei
Selachiern und Dipnoérn. Jen. Zeitschr. Bd. VIII.

‘Carusson, A. Von den weichen Theilen des sogen. Praepollex und Praehallux.
Biolog. Féreningens Firhandlingar (Verh. d. biolog. Vereins) in Stockholm.
Stockholm, 1890.

Untersuch. tiber die weichen Theile der sog. iiberziligen Strahlen an Hand
und Fuss. K. Svenska. Vet.-Akad. Handlinger. Bd. XVI. Afd. 4.
Stockholm, 1891.

Corg, E. D. New and little known Paleozoic and Mezozoic Fishes. Journ. Acad.
Nat. Sci. Philad. 2nd Ser. Vol. IX.

Cutnop, A. L’articulation du coude. Int. Monatschr. Anat. 1888. Bd. V.

Davivorr, M. v. Beitr. z. vergl. Anatomie der hinteren Gliedmassen der Fische.
Morph. Jahrb. Bd. V., VI, IX.

Dean, BAsuForD. The Fin-fold origin of the paired limbs in the light of the
Ptychopterygia of Paleozoic Sharks. Anat. Anz. Bd. XI. 1896. (See
also Nat. Sci. Vol. VIII. 1896.)

Dépertern, L. Das Skelet von Pleuracanthus. Zool. Anz. Jahrg. XII. 1889.

Doury, A. Studien zur Urgeschichte des Wirbelthierkirpers. VI. Die paarigen
und unpaarigen Flossen der Selachier. Mittheil. Zool. Stat. Neapel. Bd.
V. Heft 1, 1886. :

Dotto, L. Sur Vorigine de la nageoire caudale des Ichthyosaures. Bull. Soc.
Belge Géol. T. VI. 1892. : ;
Ducrert, E. Contrib. 4 ’étude du développement des membres pairs et impairs
des poissons téléostéens, type Trutta lacustris. Inaug. Dissert. Lausanne,

1894.

Fister, P. Die Homologie der Extremitiiten. Abh. Ges. Halle. Bd. NIX. 1895.

Emery, C. Ueber die Beziehungen des Cheiropterygiums zum Ichthyoptery-
gium. Zool. Anz. Jahrg. X._ 1887.

Zur Morphologie des Hand- und Fussskelets. Anat. Anz. Jahrg. V. 1890.

Ulteriori studi sullo scheletro della mano degli Antibi Anuri. Atti. Acc.
(Rend.) Lincei. VolI, 1. Serie 5a. 1892.

EE

418 APPENDIX

Emery, C. Studi sulla Morfologia dei Membri dei Mammiferi. Mem. R. Accad.
d. Scienze dell’ Istituto di Bologna. T. II, 1892. . : :
Studi sulla Morfologia dei Membri degli Anfibi sulla Filogenia del Chiropteri-
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1894. j
Sulla Morfologia del Tarso dei Mammiferi. Atti. (Rend.) Ace. Lincei. Vol.
IV. 20sem., Sér. 5a, fase. 1lo, 1895. :
Beitr. «. Ent. Gesch. u. Morphol. des Hand. u. Fuss.-Skelets der Marsupi-
alier. Semon’s Forschungsreisen, &c. Bd II 1897.

Ewart, J.C. The Development of the Skeleton of the Limbs of the Horse.
Journ. of Comp. Pathology and Therapeutics. 1894. (Comp. also Journ.
Anat. and Physiol. Vol. XXVIII. 1894.)

Fraas, E. Ueber einen neuen Fund von Ichthyosaurus in Wiirttemberg. Neues
Jahrb. f. Mineralogie, &c. Bd. Il. 1892.

Fritscu, A. Ueber die Brustflosse von Xenacanthus Decheni, Goldf. Zool. Anz..
Bd. XI. 1888.

Fauna der Gaskohle und der Kalksteine der Permformation Biéhmens. Prag,
1879—-1890. Bd. III. Heft 1. Selachii (Pleuracanthus, Xenacanthus),
Prag, 1890.
Ftrprincer, M. Die Knochen und Muskeln der Extremitiiten bei den
schlangeniihnlichen Sauriern. Leipzig, 1870. ; :
Untersuchungen zur Morphologie und Systematik der Vigel, zugleich ein
Beitrag zur Anatomie der Stiitz- und Bewegungsorgane. II. Theile.
Amsterdam, 1888.
Ueber die Nervencaniile im Humerus der Amnioten. Morph. Jahrb. Bd.
XI. 1886.

Gaurp, E. Mittheilungen zur Anatomie des Frosches. I. Carpus und Tarsus.
Anat. Anz. Bd. XI. 1895.

GrcEnpaur, C. Ueber das Skelet der Gliedmassen der Wirbelthiere im Allge-
meinen und der Hintergliedmassen der Selachier insbesondere. Jen.
Zeitschr. Bd. V. 1870.

Ueber die Modificationen des Skelets der Hintergliedmassen bei den Minn-
chen der Selachier und der Chimiren. Loc. cit,

Ueber die Drehung des Humerus. Jen. Zeitschr. Bd. IV.

Untersuch. zur vergl. Anatomie der Wirbelthiere. Leipzig, 1864-5. Heft 1:
Carpus und Tarsus. Heft 2: Brustflosse der Fische.

Ueber das Archipterygium. Jen. Zeitschr. Bd. VII. 1872.

Zur Morphologie der Gliedmassen der Wirbelthiere. Morph. Jahrb. Bd.

II. 1876.

Kritische Bemerkungen iiber Polydactylie als Atavismus. Morph. Jahrb.
Bd. IV. 1880.

Ueber das Gliedmassenskelet der Enaliosaurier. Jen. Zeitschr. Bd. V..
Heft 3. 1870.

Ueber Polydactylie. Morph. Jahrb. Bd. XIV. 1888.
Das Flossenskelet der Crossopterygier und das Archipterygium der Fische.
Loc. cit. Bd. XXII. 1894.

Gervais, P. Théorie du squelette humain fondée sur la comparaison ostéologique
de ’homme et des animaux vertébrés. Paris, Montpellier, 1856.

Goopstr. On the Morphological Constitution of Limbs. The Edinburgh New
Philosoph. Journ. Vol. V. New series, 1857.

Gérrz, A. Ueber Entwicklung und Regeneration des Gliedmassenskelets der
Molche. Leipzig, 1879.

GuitEL, F. Rech. sur le développement des Nageoires paires der Cyclopterus
lumpus. Arch. Zool. exp. 3° Sér. Vol. IV.

Harrison, R. G. Ueber die Entwicklung der nicht knorpelig vorgebildesen
Skelettheile in den Flossen der Teleostier. Arch. f. mikr. Anat. Bd.
XLIT. 1893.

The Development of the Fins of Teleosts. Johns Hopkins University
Cireulars. No. 111. May, 1894.
Die Entwicklung der unpaaren u. paarigen Flossen der Teleostier. Arch. f..
Mikr. Anat. Bd. 46, 1895.
Haswenyt, W. A. (See p. 409.)
aS B. Die paarigen Extremitiiten der Wirbelthiere. Verh, Anat.
res, 1889.

APPENDIX 419

Henke, W. und Reyuer, C. Studien tiber die Entwicklung der Extremititen des
Menschen, &c. Sitz.-ber. der K. Acad. d Wiss. Abthlg. III. 1878.

Horrmanyn, C. K. (See p. 415.) Niederl. Arch. f. Zool. Bd. IX.

Hout, M. Ueber die Entwicklung der Stellung der Gliedmassen des Menschen.
Sitz.-ber. Ak. Wien. Bd. é. Abth. 3. Febr. 1891.

Howrs, G. B. On the Skeleton and Affinities of the Paired Fins of Ceratodus,
with Observations upon those of the Elasmobranchii. P. Zool. Soc. 1887.

On. the pedal skeleton of the Dorking Fowl, with remarks on hexadacty-
ae and phalangeal variation. Journ. Anat. and Physiol. Vol. XXVI

Notes on variation and development of the vertebral and limb skeleton of the
Amphibia. P. Zool. Soc. 1893 (and see p. 415).

Howes, G. B. and Davies, A. M. Observations upon the Morphology and
Genesis of Supernumerary Phalanges, with especial reference to those of
the Amphibia. P. Zool. Soc. 1888.

Howes, G. B. and RipEewoop, R. On the Carpus and Tarsus of the Anura. P.

; Zool. Soc. 1888.

Humerury, G. M. Observations on the limbs of vertebrate animals; the plan of
their construction ; their homology and the comparison of the fore and
hind limbs. 1860.

Huxuey, T. H. On Ceratodus. (See p. 395.)

JorpaN, P. Die Entwicklung der vorderen Extremitit der Anuren Batrachier.
Inaug.-Dissert. Leipzig, 1888.

JuNGERSEN, Hecror F. E. Remarks on the structure of the Hand in Pipa
and Xenopus. Ann. Nat. Hist. 1891.

Kenrer, G. Beitr. zur Kenntnis des Carpus und Tarsus der Amphibien,
Reptilien und Siuger. Ber. Ges. Freiburg. Bd. I. 1886.

Kuiaatsen, H. Die Brustflosse der Crossopterygier. Ein Beitrag zur .Anwen-
dung der Archipterygium-theorie auf die Gliedmassen der Landthiere.
Festschrift fiir Carl Gegenbaur. Leipzig, 1896.

Koiimann, J. Handskelet und Hyperdactylie. Verh. Anat. Ges. 1888.

KUKentuanL, W. Ueber die Hand der Cetaceen. Anat. Anz. III. Jahrg. 1888.
(Comp. also Anat. Anz. Jahrg. IV., V., and X., and also “‘ Vergl.-anat. und
entwickl.-geschichtl. Untersuch. an Walthieren.” Jena, 1889, und 1893.

Ueber die Anpassung von Saiugethieren an-das Leben im Wasser. Zool. Jahrb.

Bd. V. 1890.
Mittheilungen iiber den Carpus des Weisswals. Morph. Jahrb. Bd. XIX.
1892.

Zur Entwicklung des Handskeletes des Krokodils. Loe. cit.
Lazarus, 8. P. Zur Morphol. des Fusskelets. Morph. Jahr. Bd. XXIV. 1896.
Lrgoucy, H. Le dévelopement du prémier métatarsien et de son articulation
tarsienne chez VPhomme. Extr. d’annal. de la société de Médecine de Gand.
1882.
Resumé d’un mémoire sur la morphologie du carpe chez les mammiféres.
Bull. de Acad. r. de médecine de Belgique : 3. sér. t. XVIII. No. 1.
Rech. sur la morphologie du carpe chez les mammiféres. Arch. de Biol.
Tome V. 1884.
Sur la morphologie du carpe et dutarse. Anat, Anz., I. Jahrg. No. I.
Jena. 1886. *
De los central du carpe chez les mammiféres, Bull. Ac. Belgique. 3. sér. tom.
IV. 1882.
La nageoire pectorale des cétacés au point de vue phylogénique. Anat. Anz.
II. Jahrg. 1887.
L’Apophyse styloide du 3e Metacarpien chez ’homme. Annal. de la Soc.
_ de Médecine de Gand. 1887.
Rech. sur la Morphologie de la main chez les Pinnipédes. Studies from the
Museum of Zool. in the Univ. Coll. Dundee. 1888. (Comp. also Anat. Anz.
1888.
Rech. a la Morphologie de la main chez les Mammiféres marins (Pinnipédes,
Siréniens, Cetacés). Arch. de Biol. T. IX. 1889.
Lerauron, V. L. The development of the wing of Sterna Wilsonii. Amer.
_ Nat., Vol. XXVIII. 1894.
Leutuarpt, F. Ueber die Reduction der Fingerzahl bei Ungulaten. Inaug.
Dissert. Jena, 1890.

EE 2

420 APPENDIX

Leypia, F. Ueber den Bau der Zehen bei Batrachiern und die Bedeutung des
Fersenhickers. Morph. Jahrb. Bd. II. 1876. ;

Marxert, F. Die Flossenstrahlen von Acanthias. Ein Beitrag zur Kenntnis
der Hartsubstanzgebilde der Elasmobranchier. Zool. Jahrb. Bd. IX.
1896.

Mars, 0. C. Various papers on Fossil Reptiles in Amer. Journ. of Science and
Arts, Vol. XVI.—XXIII. The following are of special interest :-—

1) The. limbs of Sauranodon (Vol. XIX.).

2) The wings of Pterodactyles (Vol. XXIIL.).

3) Polydactyle horses, recent and extinet (Vol. XVII).

4) On the Affinities and Classification of the Dinosaurian Reptiles (Vol. L.).
5) Restoration of some European Dinosaurs (/oc. cit.) ;

Recent polydactyle horses. Amer. Journ. of Science. Vol. XLIII. April,
1892.

Martins, Co. Nouvelle comparaison des membres pelviens et thoraciques chez
Vhomme et chez les mammiféres, déduite de la torsion de l’humerus.
Extr. de mém. del’Acad. d. Montpellier. T. IIL, VIII. 1857.

Ost. comp. des articulations du coude et du genou. Mémoires de l’Acad. de
Montpellier. T. III. 1862.

Mayer, P. Die unpaaren Flossen der Selachier. Mittheil. Zool. Stat. Neapel.
Bd. VI. 1885.

Mrvart, G. Notes on the fins of Elasmobranchs, &c. Tr. Zool. Soc. Vol. X. pt.
10. 1879.

Mounier, 8. Zur Entwickelung der paarigen Flossen des Stirs. Anat. Anz.
Bd. XII. 1896.

Die paarigen Extremitaten der Wirbelthiere. I. Das Ichthyopterygium. II.
Das Cheiropterygium. III. Die Entwicklung der paarigen Flossen des
Stirs. Anat. Hefte, I Abtheil. VIII Heft (Bd. III. Heft 1) 1893, 1
Abtheil. and XVI. Heft. (Bd. V. Heft 3). XXIV. Heft (Bd. VII. Heft 1).

Ueber die Entwickelung der fiinfzehigen Extremitiit. Sitz. ber. Morph.
Physiol. Miinchen, 1894. Heft 1.

Niemizc, J. Rech. Morphol. sur les ventouses dans le régne animal. Dissert.
Genf, 1885.

Norsa, Exisa. Alcune Ricerche sulla Morfologia dei Membri anteriori degli
uccelli. Ricerche Lab. Anat. Romae altri Lab. Biologici. Vol. IV. Fasc. I.

PaRKER, W. K. On the Morphology of Birds. P. Roy. Soc. Vol. 42. 1887.

On the Structure and Development of the Wing in the Common Fowl. Phil.
Trans. Vol. 179. 1888. (See also p. 398).

Paterson, A. MELVILLE The position of the mammalian limb, regarded in the
light of its innervation and development. Stud. in Anat. from the Anat.
Dept. of Owens College. Vol. I. 1891.

On the Fate of the Muscle Plate, and the Development of the Spinal
Nerves and Limb Plexuses in Birds and Mammals. Q. Journ. Micr.
Sci. Vol. XXVIII. N. Ser. 1888.

Perrin, A. Constitution du Carpe des Anoures. Bull. scientifique de la France
et de la Belgique. ‘‘ Recherches sur les affinités zoologiques de lHatteria
punctata.” Ann. Sci. Nat. (7) XX. F. XXVII. 1896.

PrirzNner, W. Die kleine Zehe. Eine anatomische Studie. Arch. f. Anat. u.
Physiol. 1890. s

Bemerk z. Aufbau des menschl. Carpus. Verh. Anat. Ges. 1893.

Ein Fall von beiderseitiger Doppelbildung der fiinften Zehe, nebst Bemer-
kungen iiber die angeblichen Riickbildungserscheinungen an der ‘‘ kleinen”
Zehe des Menschen. Morph. Arb. Bd. I. 2. H. 1895.

Pycrart, W. P. The Wing of Archeopteryx. Nat. Science, Vol. VIII. No. 50.
1896.

Rabi, C. Theorie des Mesoderms (Fortsetzung). Morph. Jahrb. Bd. XIX. 1892.

RavutTENFELD, E. V. Morphol. Untersuchungen tiber das Skelet der hinteren
Gliedmassen von Ganoiden und Teleostiern. Inaug.-Dissert. Dorpat,
1882.

RosenBerc, E. Ueber die Entwicklung des Extremitiitenskelets bei einigen
durch Reduction ihrer Gliedmassen characterisirten Wirbelthieren. Zeitschr.
f. wiss. Zool. Bd. XXIII.

Ueber die Entwicklung der Wirbelsiiule und das Centrale Carpi des Menschen.
Morph. Jahrb, Bd. I. 1876.

APPENDIX 42]

RosENBERG, E. Ueber einige Entwicklungsstadien des Handskelets der Emys
lutaria, Marsili. Morph. Jahrb. Bd. XVII. 1891.

Roux, W. Beitr. zur Morphologie der functionellen Anpassung. Structur eines
hoch-differenzirten bindegeweb. Organs (Schwanzflosse des Delphins).
Arch. fiir Anat. und Physiol. 1883.

Ryper, J. A. On the genesis of the extra terminal phalanges in the Cetacea.
Amer. Nat. 1885. Vol. XIX. p. 1013.

ScuiossER, M. Ueber die Modificationen des Extremititen-Skeletes bei den
einzelnen Saiugethierstimmen. Biol. Centralbl. Bd. IX.

SCHNEIDER, A. Ueber die Dipnoi und besonders die Flossen derselben. Zoolog.
Beitrige. Bd. II. Breslau, 1887.

Strepa, L. Der Talus und das Os trigonum Bardeleben’s beim Menschen. Anat.
Anz. Jahrg. IV. 1889.

Ueber die Homologie der Gliedmassen der Siiugethiere und des Menschen.
Biol. Centralbl. Bd. XIII. 1893.

Srorms, R. The Adhesive Disk of Echeneis. Ann. Nat. Hist. 1888.

Srrasser, H. Zur Entwicklung der Extremititenknorpel bei Salamandern und
Tritonen. Morph. Jahrb. Bd. V. 1879.

StuckENs, M. Note sur la ventouse abdominale du Liparis barbatus. Bull. Ac.
Belgique. 3me série, t. VIII. No. 7. 1884.

StupeEr, Tu. Die Forschungsreise 8. M.S. ‘‘ Gazelle” in den Jahren 1874 bis 1876.
Herausgegeben von dem hydrograph. Amt der Admiralitit. III. Theil :
Zool. und Geol. (Extremitiiten-Entwicklung des Pinguin). Berlin, 1889.

TracnEr, J. K. Median and Paired Fins, a Contribution to the History of
Vertebrate Limbs. Trans. Connecticut Academy. Vol. III. 1878.

Ventral Fins of Ganoids. Trans. Connecticut Academy. Vol. IV. 1878.

TurLentus, G. Untersuchungen iiber die morpholog. Bedeutung accessor.
Elemente am menschl. Carpus u. Tarsus. Morphol. Arb. Bd. V. 3 Heft
1896.

Die “iiherziihligen”” Carpuselemente menschlicher Embryonen. Anat. Anz.
Bd. IX. 1894.

Fur Entwicklungsgeschichte der Sesambeine der menschl. Hand. Morph.
Arb. Bd. V. 2. H. 1895.

Das Os intermedium antebrachii des Menschen. Loc. cit. 1 H.

Tuino, O. Die Umbildungen an den Gliedmassen der Fische. Morph. Jahrb.
Bd. XXIV. 1876.

THompsox, D'Arcy W. On the Hind Limb of Ichthyosaurus, and on the
Morphology of Vertebrate Appendages. Report Brit. Assoc. Adv. Soc.
1885. pp. 1065-1066.

On the Hind-Limb of Ichthyosaurus and on the Morphology of Vertebrate
Limbs. Journ. Anat. u. Physiol. Vol. XX. 1886.

TornrieR, G. Ueber den Siugethier-Praehallux, &c. Arch. f. Naturgeschichte,
1891.

Das Enistehen der Gelenkformen. Arch. f. Entw. Mechanik Bd. I. H.
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Tscuau, A. Rech. sur ’Extremité antérieure des Oiseaux et des Reptiles.
Inaug. Dissert. Genéve, 1889.

Voert, Cu. Ueber die Verknicherung des Hohlhandbandes und andere Sesam-
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WIkEDERSHEIM, R. Die iltesten Formen des Carpus und Tarsus der heutigen
Amphibien. Morphol. Jahrb. Bd. II. 1876. Nachtriigl. Bemerkungen
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Ueber die Vermehrung des Os centrale im Carpus und Tarsus des Axolotl.
Morphol. Jahrb. Bau. VI.

ZAnvER, R. Ist die Polydactylie als theromorphe Varietit oder als Missbildung
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Zwunter, L. Beitrige zur Entwicklung von Cypselus melba. Inaug.-Dissert.
Bern, 1890.

D. MUSCLES.
Arsrecut, P. Beitrag zur Morphologie des M. omo-hyoideus und der ventralen,

inmneren Interbranchial-Muskulatur. Inaug.-Dissert. Kiel, 1876.
BanvELEBEN, C. Muskel und Fascie. Jen. Zeitschr. Bd. XI. N. F. VIII.

422 APPENDIX

BARDELEBEN, C. Ueber die Hand- und Fussmuskeln der Saugethiere, besonders
die des Praepollex (Praehallux) und Postminimus. Anat. Anz. VY. Jahrg.
1890. (Comp. also p. 416.) : ‘

BERTELLI, D. Ricerche sulla Morfologia del Muscolo Diaframma nei Mammi-
feri. Arch. per le Scienze mediche, Vol. XIX., No. 19. 1895. (Comp.
also Atti. Soc. Toscana. (Memor.), Vol. XV.)

Biscuorr, Tu. Beitr. zur Anat. des Hylobates leuciscus. Miinchen, 1870.

Buum, F. Die Schwazmusculatur des Menschen. Anat. Hefte. 1. Abth.
Heft XIII. (Bd. IV. H. 3). 1894.

Bracuer, A. Rech. sur le développ. du Diaphragme et du Foie chez le lapin.
Journ. de lAnat. et Physiol., XXXI. Année 1895. No. 6.

Brooks, H. On the Morphology of the Extensor Muscles. Studies from the
Museum of Zool. in Univ. Coll., Dundee. Dundee, 1889.

Bruner, H. L. Ein neuer Muskelapparat zum Schliessen und Oeffnen der
Nasenlocher bei den Salamandriden. Anat. Anz. Bd. XII. 1896. (Comp.
also Arch. Anat. 1896.)

Caprat, M. Du développement de la partie cephalothoracique de l’embryon, de
la formation du diaphragma, des pleures, du péricarde, du pharynx et de
Yoesophage. Journ. de Anat. et Physiol. Vol. XIV. 1878.

Carson, A. Untersuch. iiber Gliedmassenreste bei Schlangen. Kinigl. Schwed.
Acad. Bd. XI. No. 11.

Cuappurs. Die morphol. Stellung der kleinen, hintern Kopfmuskeln. Inaug.-
Dissert. Bern, 1876.

Ducks, A. Rech. sur Postéologie et la myologie des batraciens 4 leurs différents
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Davivorr, M. v._ (See p. 417.)

Ecertinc, H. Zur Morphologie der Dammuskulatur. Morph. Jahrb. Bad.
XXIV. 1896.

Fiscuen, A. Zur Entwicklung der ventralen Rumpf- und der Extremitiiten-
muskulatur d. Vogel und Siugetiere. Morph. Jahrb. Bd. NNT. 1895.

Fiscuer, J. G. Anat. Abhdlg. tiber die Perenibranchiaten u. Derotremen.
Hamburg, 1864.

Firprincer, M. Die Knochen und Muskeln der Extremitiiten bei den schlan-
geniihnlichen Sauriern. Leipzig, 1870. ;

Zur vergl. Anat. der Schultermuskeln. 1 und 2 Theil. Jen. Zeitschr. Bd.

VIL und VIII. 3. Theil. Morph. Jahrb. Bd. I. 1876.

Uber die mit dem Visceralskelett verbundenen spinalen Muskeln bei Sela-
chiern. Jen. Zeitschr. Bd. XXX. N. F. XXUIT

FURBRINGER, P. Unters. z. vergl. Anat. der Muskulatur des Kopfskelets der
Cyclostomen. Jen. Zeitschr. Bd. IX. N. F. IL.

Ueber Deutung und Nomenklatur der Muskulatur des Vogelfliigels. Morph.
Jahrb. Bd. VI. 1885.

Gapow, H. Unters. tiber die Bauchmuskeln der Krokodile, Eidechsen und Schild-
kroten. Morph. Jahrb. Bd. VII. 1881.

Zur vergl. Anat. der Muskeln des Beckens und der hinteren Gliedmassen der
Ratiten. Jena, 1880.

Beitr. z. Myologie d. hinteren Extremitit der Reptilien. Morph. Jahrb.
Bd. VII. 1881.

GAupp, E. 1. Mittheil. zur Anatomie des Frosches. 2. Hand- und Fussmuskeln
des Frosches. Anat. Anz. Bd. XI. 1895. 3. Die Bauchmuskeln des
Frosches, loc. cit. 4. Uber d. angebl. Nasenmuskeln des Frosches nebst
penrmeen iiber die Hautmuskulatur der Anuren tiberhaupt. Loc. cit.

Che .

GEGENBAUR, C. Ueber der M. omo-hyoideus und seine Schliisselbeinverhindung.
Morph. Jahrb. Bd. I. 1876.

Giciio-Tos, E. Sul? Omologia tra il Diaframma degli Anfibi aruri e quello dei
Mammiferi. Atti. Acc. Torino, Vol. NNIX. 1894.

GorskI, v. Ueber das Becken der Saurier. Inaug.-Diss. Dorpat, 1852.

GRENACHER. Muskulatur der Cyclostomen und Leptocardier. Zeitschr. f. wiss.
Zool. Bd. XVII.

Hair, ae _ the muscular Fibres of the Alligator. Journ. Anat. and Physiol.

ol. .

Harrison, R. G. The Metamerism of the Dorsal and the Ventral Longitudinal
Muscles of the Teleosts. Johns Hopkins University Circulars, No, 111,
May, 1894.

APPENDIX 423

Havecuton, M. Gn the muscular Anatomy of the Crocodile. P. Irish Ac.,
Vol. IX., and Ann. Nat. Hist. ILL Ser. vol. XVI.

On a muscular Anatomy of the Alligator. Ann. Nat. Hist. IV. Ser.
vol. I.

Herzury, D. The Comparative Anatomy of the Muscles and Nerves of the
Superior and Inferior Extremities of the Anthropoid.Apes. Journ. Anat.
and Physiol. Vol. XXVI. 1892.

His, W. Mittheil. zur Embryologie der Siugethiere und des Menschen. Arch.
f. Anat. und Physiol. Anat. Abth. 1881

Hout, M. Zur Homologie und Phylogenese der Muskeln des Beckenausganges
des Menschen. Anat. Anz. Bd. XII. 1896.

Homeury, G. M. The muscles of the smooth Dog-Fish (Mustelus levis). Journ.

Anat. and Physiol. Vol. VI.

The muscles of Ceradotus. Loc. cit.

The muscles and nerves of the Cryptobranchus japonicus. Loc. cit.

The muscles of Lepidosiren annectens with the cranial nerves. Loe. cit.

The muscles of the Glass-Snake (Pseudopus Pallasii). Loc. cit.

On the disposition of muscles in vertebrate animals. Loc. cit.

On the disposition and homologies of the extensor and flexor muscles of the
leg and fore-arm. Journ. Anat. and Physiol. Vol. III.

Kazstner, 8. Ueber die allgemeine Entwicklung der Rumpf- und Schwanz-
muskulatur bei Wirbelthieren. Mit besonderer Berticksichtigung der
Selachier. Arch. f. Anat. und Physiol. 1892.

Die Entwicklung der Extremitiiten-und Bauchmuskulatur bei den anuren
Amphibien. Arch. Anat. 1893.

KILLIAN, G. Zur vergl. Anatomie und Entwicklungsgeschichte der Ohrmuskeln.
Anat. Anz. V. Jahrg. 1890.

Koutsriicer, J. H. F. Versuch einer Anatomie des Genus Hylobates (Muskeln
und Nerven). Zool. Ergebnisse einer Reise in Niederl. Ost-Indien. Heft
2. Leiden, 1890.

LARTSCHNEIDER, T. Die Steissbeinmuskeln des Menschen. Denk. Ak. Wien.
Bd. LXI. 1895.

Zur vergl. Anat. des Diaphragmapelvis. Sitz. ber. Ak. Wien. Bd. CIV.
1895.

Lecuz, W. Zur Morphologie der Beckenregion der Insectivora. (Vorl. Mitthlg.)
Morph. Jahrb. Bd. VI. 1880.

Zur Anat. der Beckenregion bei Insectivora, &. K. Schwed. Acad. der
Wissensch. Bd. XX. No. 4. 1882.

Macauister, A. On the homologies of the flexor muscles of the vertebrate
limbs. Journ. Anat. and Physiol. Vol. IT.

Man, Dz. Verglijkende myologische en neurologische Studien over Amphibien
en Vogels. Leiden, 1873.

Mavrer, F. Der Aufbau und die Entwicklung der ventralen Rumpfmuskulatur bei
den urodelen Amphibien und deren Beziehung zu den gleichen Muskeln der
Selachier und Teleostier. Morph. Jahrb.. Bd. XVIII. 1892.

Die Elemente der Rumpfmuskulatur bei Cyclostomen und héheren Wirbel-
thieren. Morph. Jahrb. Bd. XXI. 1894.

Mrivart, St. G. On the myology of Menopoma allegh., Menobranchus lat., and
Chamaeleon Parsonii. P. Zool. Soc. 1869 und 1870.

Perrin, A. Contrib. 4 étude de la myologie comparée: Membre postérieur
chez un certain nombre de Batraciens et des Sauriens. Bull. Sci. France,
Belgique. T. XXIV. 1893.

Porpowsky, T. Zur Entwicklungsgeschichte des N. facialis beim Menschen.
Morph. Jahrb. Bd. XXIII. 1895.

Ravn, E. Unters. iiber die Entwicklung des Diaphragmas und der benachb. Organe
bei den Wirbelthieren. Arch. f. Anat. und Physiol. 1889 und Suppl.
1889. Comp. also Biolog. Centralblatt. Bd. VII.

Rerzius, G. Biol. Untersuchungen. N. F. I. No. 2. Muskelfibrille und
Sarkoplasma. Stockholm, 1890.

Rex, H. Ein Beitrag zur Kenntnis der Muskulatur der Mundspalte der Affen.
Morph. Jahrb. Bd. XII. 1887.

Rucz, G. Entwickl.-Vorgiinge an der Muskulatur des menschl. Fusses. Morph.
Jahrb. Bd. IV. Suppl.-H. 1878.

Zur vergl. Anat. der tieferen Muskeln in der Fussohle. Loc. cit.

424 APPENDIX

Rucs, G. Untersuchungen tiber die Extensorengruppe am Unterschenkel und Fuss.
des Menschen und der Siiugethiere. Loc. cit.

Ueber die Gesichtsmuskulatur der Halbaffen. Morph. Jahrb. Bd. XI. 1885.

Untersuchungen tiber die Gesichtsmuskulatur der Primaten. Leipzig, 1887.

Die vom Facialis innervirten Muskeln des Halses, Nackens und des Schiidels
eines jungen Gorilla (‘‘Gesichtsmuskeln”). Morph. Jahrb. Bd. XII.
1887.

Anatomisches tiber den Rumpf der Hylobatiden (Skelet., Musculatur, Ab-
schnitte des Gefiss- und Nervensystems, serése Héhlen). Ein Beitrag zur
Bestimmung der Stellung dieses Genus im Systeme. Zool. Ergebnisse
einer Reise in Niederl. Ost-Indien. Heft 2. Leiden, 1890.

Zeugnisse fiir die metamere Verkiirzung des Rumpfes bei Siiugethieren. Der
M. rectus thoraco-abdominalis der Primaten. Morph. Jahrb. Bd. XIX.
1892.

Die ventrale Rumpfmuskulatur der anuren Amphibien. Morph. Jahrb.
Bd. XXII. 1894.

Die Hautmuskulatur der Monotremen und ihre Beziehungen zu dem Marsu-
pial- u. Mammarapparate. Semon’s Zoolog. Forschungsreisen in Au-
stralien und dem Malayischen Archipel. Bd. II. Jenaische Denkschrift V.

Rtpvincer, N. Die Muskeln der vordern Extremitat der Vogel und Reptilien.
Mit besonderer Riicksicht auf die analogen und homologen Muskeln bei
Sdugethieren und Menschen. Hamburg, 1868.

ScHNEIDER, A. Beitr. zur vergl. Anatomie und Entwicklungsgeschichte der
Wirbelthiere. Berlin, 1879. With appendix. (‘* Grundziige einer My-
ologie der Wirbelthiere.”’)

SEYDEL, O. Ueber die Zwischensehnen und den metameren Aufbau des M.
obliquus thoraco-abdominalis (abdominis) externus der Siiugethiere. Morph.
Jahrb. Bd. XVIII. 1892.

Suureipt, L. W. The myology of the Raven. London, 1890.

Srox1. Vergl. Untersuch. tiber die Bauch- und Zwischenrippenmuskulatur der
Wirbelthiere. Inaug.-Dissert. Halle, 1875.

Trstut, L. Les anomalies musculaires chez ’homme expliquées par l’anatomie
comparée leur importance en Anthropologie. Paris, 1884.

Tresinc, B. Kin Beitrag z. Kenntn. der Augen-Kiefer-und Kiemenmuskulatur
der Haie u. Rochen. Jen. Zeitschr. Bd. XXX. N.F. XXIII.

Usxow, N. Ueber die Entwicklung des Zwerchfells, des Pericardiums und des
Coeloms, Arch. f. mikr. Anat. Bd. XXII. 1883.

Vetter, B. Untersuchungen zur vergl. Anatomie der Kiemen- und Kiefermus-
kulatur der Fische. Jen. Zeitschr. Bd. VIII. und XII. N. F. I. Bd.

Westriine, Ch. Anat. Unters. tiber Echidna. Svenska Vet. Akad. Handl.
Bd. XV. Afd. IV. 1889.

WisHE, J. W. van. Ueber die Mesodermsegmente und die Entwicklung der
Nerven des Selachierkopfes. Werh. Ak. Amsterdam, 1883.

Witson, J. T. On the Myology of Notoryctes typhlops, with comparative
Notes. Trans. Roy. Soc. of §. Australia. 1894.

Winvig, B. C. A. The flexors of the digits of the hand. I. The Muscles of
the Fore-Arm. Journ. Anat. and Physiol. Vol. XXIV. 1889.

The pectoral Group of Muscles. Tr. Irish Ac. Vol. NXIN., part XII. 1889.

E. ELECTRIC ORGANS,

Bazucntn. Ueber die Bedeutung und Entwicklung der pseudoelektrischen
Organe. Medic. Centr.-Blatt No. 35, pp. 545-548.

Entwicklung der elektrischen Organe und Bedeutung der mot. Endplatten,
Medic. Centr.-Blatt. 1870. No. 16 und 17.

Uebersicht der neueren Untersuchungen iiber Entwicklung, Bau, und physiol.
Verhiltnisse der elektrischen und pseudo-elektrischen Organe. Arch. f.
Anat. u. Physiol. 1876.

Beobachtungen und Versuche am Zitterwelse und Mormyrus des Niles. Arch.
f. Anat. und Physiol. 1877.

Batiowitz, E, Ueber den Bau des elektrischen Organes von Torpedo mit
besonderer Beriicksichtiguny der Neryvenendigungen in demselben, Arch.
f. miki, Anat. 42 Bd. 1898.

APPENDIX 425:

Batiowi1z, E. Ueber den feineren Bau des elektrischen Organs des gewéhn-
lichen Rochen (Raja clavata, L.). Anat. Hefte, 1. Abth. Heft XXIII.
(Bd. VII., H. 3).

Bott, i Beitrage z. Physiologie von Torpedo. Arch. f. Anat. und Physiol.

(1) die Structur der elektrischen Platten von Torpedo. (2) Die Structur der
elektrischen Platten von Malopterurus. Arch. f. mikr. Anat. Bd. X. 1874.

Neue Untersuchungen zur Anat. und Physiol. von Torpedo. Monatsbericht
der Berliner Akad. 1875.

Neue Untersuchungen tiber die elektrischen Platten von Torpedo. Arch. f.
Anat. und Physiol. 1876.

Craccto, G. V. Intorno all’ intima tessitura dell’ organo elletrico della torpedine
(Torpedo Narke). Acad. delle scienze dell’ istituto di Bologna. 21.
Maggio, oC and in German-—Moleschott’s Untersuchungen. Bd. XI., 4.

Du Bots-Reymonp, E. Gesammelte Abhandlungen zur allgemeinen Muskel- und
Nerven-physik. Bd. IT.

Vorl. Bericht iiber die von Professor G. Fritsch in Aegypten angestellten
neuen Untersuchungen an elektrischen Fischen. Monatsschrift d. Berl.
Akad. Dec., 1881.

Ecxrr, A. Einige Beobachtungen iiber die Entwicklung der Nerven des elek-
trischen Organs von Torpedo Galvanii. Zeitschr. f. wiss. Zool. Bd. I. 1848.

Unters. zur Ichthyologie. Freiburg, 1857.

Ewart, J.C. The Electric Organ of the Skate. Phil. Trans. Vol. 179. 1888,
and Vol. 183. 1892.

Fritscu, G. Bericht iiber die Fortsetzung der Untersuchungen an elektrischen
Fischen, Beitr. zur Embryol. von Torpedo. Sitz. ber. Ak. Berlin, 1883.

Die electr. Fische. Nach neuen Untersuchungen anatomisch-zoologisch
dargestellt. Abth. I, Malopterurus electricus. Leipzig, 1887. Abth. I.
Die Torpedineen. Leipzig, 1890. (See also other papers in Sitz.-ber. Ak.
Berlin ¢.g., Ueber Discopyge tschudii, 1895.)

Zur Organisation des Gymnarchus niloticus. Sitz.-ber. Ak. Berlin.

GorcH, F. The Electromotive Properties of the Electrical Organ of Torpedo
marmorata. Phil. Trans. Vols. 178 (1887) and 179 (1888).

Hartmann, R. Bemerk. iiber die elektrischen Organe der Fische. Arch, f. Anat.
und Physiol. 1861.

Iwanzorr, N. Der mikrosk. Bau des elektrischen Organs von Torpedo. Bull.
Soc. Moscou, 1894.

Das Schwanzorgan von Raja. Loe. cit. 1895.

Sacus, C. Beobachtungen und Versuche am_siidamerikanischen Zitteraale
(Gymnotus electricus). Arch. f. Anat. u. Physiol. 1877.

Sanctis, L. pz. Embryogénie des Organs électriques de la torpille et des organs
pseudo-électriques de la raie. Journ. de Zool. p. Gervais I., p. 336—342.

Sanperson, J. Burpon, and Gorcn, Francis On the Electrical Organ of the
Skate. Journ. Physiol. Vol. X. 1889.

ScuuttzE, M. Zur Kenntnis der elektr. Organe der Fische. Abh, Ges.
Halle, IV. und V. Bd. 1858 and 1859.

F. NERVOUS SYSTEM.
(«) CENTRAL NERVOUS SYSTEM.
1, PIsces.

AuLuorn, F. Zur Neurologie der Petromyzonten. (Vorl. Mitth.) Nachr. Ges,

Gottingen, No. 20. 1882.
Untersuchungen tiber das Gehirn der Petromyzonten. Zeitsch. f. wiss. Zool.

Bd. XXAXIX. 1883.

Aversacu, L. Die Lobi optici der Teleostier und die Vierhiigel der hiéher
organisirten Gehirne. Morph. Jahrb. Bd. XIV. 1888.

Brarp, T. The History of a Transient Nervous Apparatus in certain Ichthyopsida.
Zool. Jahrb, Bd. IX. 1896.

426 APPENDIX

Bettonci, J. Ueber den Ursprung des Nervus opticus und den feineren Bau des
Tectum opticum der Knochenfische. Zeitschr. f. wiss. Zool. Bd. XXXV.
1880.
Ueber die centrale Endigung des Nervus opticus bei den Vertebraten.
Zeitschr. f. wiss. Zool. Bd. XLVII. 1888.
Burcxuarpt, R. Zur vergl. Anat. des Vorderhirns bei Fischen. Anat. Anz.
IX. Bd. 1894,
Der Bauplan des Wirbelthiergehirns. Morph. Arb. IV. Bd. 2 Heft. 1894,
Buscu, W. De Selachiorum et Ganoideorum encephalo. Berlin, 1848.
CaLBERLA, E, Zur Entwicklung des Medullarrohrs und der Chorda dorsalis der
Teleostier und Petromyzonten. Morph. Jahrb. Bd. NI. 1877.

Carus, C. G. Versuch einer Darstellung des Nervensystems und besonders des
Gehirns. Leipzig, 1814.

Dourn, A. Stud. zur Urgesch des Wirbelthierkirpers. Mitth. Zool. Stat. Neapel.
Ill. Bd., 1881, Heft. 2 und IV., Bd., 1882, Heft. 1. Also Bd. VI. Heft. 3,
1884, and Bd. VIII., 1888, Bd. IX., 1890, Bd. X., 1891.

Ecxrer, A. Anat. Beschreib. des Gehirns vom karpfenartigen Nilhecht. 1854.

Epincer, L. Untersuchungen iiber die vergl. Anatomie des Gehirns. 1. Das
Vorderhirn. 2. Das Zwischenhirn (Selachier, Amphibien). Abh. Senkenb.
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Vorlesungen iib. den Bau den nervisen Centralorgane des Menschen u. der

Thiere, 5th Aufl. Leipzig, 1896.

Fritscu, G. Unters. iiber den feineren Bau des Fischgehirns. Berlin, 1878.

Ueber einige bemerkenswerthe Elemente des Centralnervensystems von

Lophius picatorius. Arch. f. mikr. Bd. XXVII. 1886.

Fousari, R. Untersuchungen tiber die feinere Anatomie des Gehirns der Telostier.
Internat. Monatsschr. Anat. Bd. IV., 1887.

Gort, A. Beitr. z. Entw.-Geschichte der Wirbelthiere. III. Ueber die Entwick-
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Ueber die Entstehung und die Homologieen d. Hirnanhangs. Zool. Anz.

VI. Jahrg. 1883. No. 142.

(soronowrtscH, N. Das Gehirn und die Cranialnerven von Acipenser ruthenus.
Ein Beitrag zur Morphologie des Wirbelthierkopfes. Morph. Jahrb. Bd.
XIII. 1888.

GorrscHE, M. Vergl. Anatomie des Gehirns der Gritenfische. Arch. Anat.
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Haier, B. Ueber das Centralnervensystem, insbesondere iiber das Riickenmark
von Orthagoriscus mola. Morph. Jahrb. Bd. XVII. 1891.

Untersuch. tiber das Riickenmark der Telostier. oc. cit. Bd. NNIII.

1895.

Untersuchungen tiber der Hypophyse und die Infundibularorgane. Lor.

cit, Bd. XXV. 1897.
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HorrmMann, C.K. Zur Ontogenie der Knochenfische. Verh. Ak. Amsterdam.
Bd. XXIII. 1882, und Arch. fiir mikr. Anat. Bd. NNITI., 1883.
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fiir. mikr. Anat. Bd. IV. 1868.
Die Deutung des Hirmmanhanges. Sitz. ber. Morph. und Physiol. Miinchen.
1894.

Mittheil. z. Entwicklungsgeschicte des Kopfes bei Acipenser sturio. Sitz.-
ber. Morphol. u. Physiol. Miinchen. 1891.
Studien z. vergl. Entw.-Gesch. der Cranioten. 1. Heft. Die Entwicklung
des Kopfes von Acipenser Sturio an Medianschnitten untersucht.
2. Heft. Die Entwicklung des Kopfes von Ammocoetes Planeri. Miinchen
und Leipzig. 1893. ;
LennosstK, M. v. Beobachtungen an den Spinalganglien und dem Riickenmark
von Pristiurusembryonen. Anat. Anz. VIL Jahrg. 1892. (Comp.
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Locy, W. A. Metameric Segmentation in the Medullary Folds and Embryonic
Rim. Anat. Anz. Bd. IX. 1894.
Luxpsore, H. Die Entwicklung der Hypophysis und des Saccus vasculosus bei
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APPENDIX 427

Mayser, P. Vergl. anat. Studien tiber das Gehirn der Knochenfische. Zeitsehr.
f. wiss. Zool. Bd. XXXVI. 1881.

Migiucuo-Mactal, v._ Beitr. z. vergl. Neurologie der Wirbelthiere. Das Gehirn
der Selachier. Leipzig, 1870.

Mi ter, J., and HENLE, J. Syst. Beschreibung der Plagiostomen. Berlin, 1841.

MUiier, W. Ueber Entwicklung und Bau der Hypophysis und des Processus
infundibuli cerebri. Jen. Zeitschr., Bd. VI., 1871.

NansEN, F. The Structure and Combination of the Histological Elements of the
Central Nervous System. Bergen, 1887.

Neat, H. V. A Summary of Studies on the Segmentation of the Nervous
System in Squalus acanthias. Anat. Anz., Bd. XII. 1876.

Neumayer, L. Histol. Unters. iiber den feineren Bau des Centralnervensystems
von Esox lucius. Arch. f. mikr. Anat. Bd. 44. 1895.

OrtuacuER, J. Beitr. zur Entwicklung der Knochenfische nach Beobachtunven
am Bachforelleneie. Zeitschr. f. wiss. Zool., Bd. XXIII.

Ossorn, H. F. The Origin of the Corpus callosum, &c. Parts I. and II. Morph.
Jahrb. Bd. XII. 1888.

Parker, T. JEFFERY. Notes from the Otago University Museum. On the
Nomenclature of the Brain and its Cavities. Nature, Vol. NXXV., No.
896. 1886.

Notes on Carcharodon rondelettii. P. Zool. Soc. 1887.

Puart, J. A Contribution to the Morphology of the Vertebrate Head. Journ.
Morph. Vol. V. No.1. 1891.

Rasi-Rickuarp, H. Die gegenseitigen Verhiltnisse der Chorda, Hypophysis,
etc., bei Haifischembryonen, nebst Bemerkungen tiber die Deutung der
einzelnen Theile des Fischgehirns. Morph. Jahrb. Bd. VI. 1880.

Zur Deutung und Entwicklung des Gehirns der Knochenfische. Arch. f.
Anat. u. Physiol. 1882.

Entwicklung des Knochenfischgehirns (Entw. der Zirbel). Sitz.-ber. Naturf.
Berlin. 1882.

Weiteres zur Deutung des Gehirns der Knochenfische. Biol. Centralbl.
Bd. III. 1883. No. 1.

Das Grosshirn der Knochenfische und seine Anhangsgebilde. Arch. f. Anat.
u. Physiol. 1883.

Das Gehirn der Knochenfische. Vortrag, gehalten in der Gesellschaft fiir
Heilkunde zu Berlin am 20 Juni, 1884. Deutsch. medic. Wochenscrift,
No. 33 ff. 1884. Berlin.

Zur onto- und phylogenetischen Entwicklung des Torus longitudinalis im
Mittelhirn der Knochenfische. Anat. Anz. IT. Jahrg. 1887.

Der Lobus olfactorius impar der Selachier. Anat. Anz. VIII. Jahrg.
1893.

Das Vorderhirn der Cranioten. Eine Antwort an Herrn F. K. Studnicka.
Anat. Anz. Bd. IX. 1894.

RaruKe, H. -Ueber die Entstehung der Glandula pituitaria. Arch. f. Anat.
und Physiol. 1838.

REICHENHEIM, M. Beitr. zur Kenntnis des elektrischen Centralorganes von
Torpedo. Arch. f. Anat. u. Physiol. 1873.

ReissNer, E. Beitr. zur Kenntnis vom Bau des Riickenmarkes von Petromyzon
fluviatilis. Arch. f. Anat. u. Physiol. 1860.

Rerzius, G. Biol. Untersuchungen. Neue Folge. IL, IIL, 1V., V., VL, VIL.
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Die morphol. und histol. Entwicklung des Kleinhirns der Teleostier. Morph.
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Sepewick, A. On the Inadequacy of the Cell Theory and on the Early Develop-
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Serres. Anatomie comparée du cerveau dans les quatres classes des animaux
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428 APPENDIX

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3. AMPHIBIA.

Buxckuarpt, R. Untersuchungen am Hirn und Geruschorgan von Triton und
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Epinerr, L. (See p. 426.)

Fisu, P. A. The Central Nervous System of Desmognathus fuscus. Journ.
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Fiscugr, J. G. Amphibiorum nudorum neurologie specimen primum. Berlin,
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Gace, 8. Puetrs. The Brain of Diemyctylus viridescens from Larval to Adult
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Kévpen, M Zur Anatomie cles Froschgehirns. Arch. Anat.

Kurreur, C Ueber primiire Metamerie des Neuralrohres der Vertebraten. Abh.
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McCriune. The Segmentation of the Primitive Vertebrate Brain. Journ.
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APPENDIX 429

‘OszorN, H. F. Preliminary Notes upon the Brain of Menopoma. P. Ac. Philad.
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A Contribution to the internal Structure of the Amphibian Brain. Journ.
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4, REPTILIA.

Braun, M. Die Entwicklung des Wellenpapageies, etc. Wiirzburg. 1881, and

Ver. Ges. Wiirzburg. Bd. XV., IV.
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‘Gaupp, E. Ueber die Anlage der Hypophyse bei Sauriern. Arch. f. mikr.
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5. AVES.

Branpvis, F. Untersuchungen iiber das Gehirn der Vigel. Arch. f. mikr. Anat.
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Bua, A. Das Grosshirn der Vogel. Zeitschr. f. wiss. Zool., Bd. XNXVIIIL.,
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430 APPENDIX

6. MAMMALIA.

Bepparp, F. KE. On the Brain in the Lemurs. P. Zool. Soc., 1895. (Comp.
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Bexuam, W. Boaxtanp. A Description of the Cerebral Convolutions of the
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Berre.ii, D. II solco intermediario anteriore de! midollo spinale umano. Atti
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Anatomie comparée des circonvolutions cérébrales. Loc. cit., 1878.

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Dexter, F. A Contribution to the Morphology of the Medulla Oblongata of the
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Dursy, E. Zur Entw.-Geschichte des Kopfes des Menschen und der héheren
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Die Himmwindungen des Menschen. Braunschweig, 1869. II. Aufl., 1885.
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Frurcusic, P. Die Leitungsbalnen im Gehirn und Riickenmark des Menschen.
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GANSER, 8. Vergl. anat. Studien iiber das Gehirn des Maulwurfs. Morph.
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Die Neuroblasten und deren Enstehung im embryonalen Mark. Loe. cit.,
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Zur Geschichte des Gehirns sowie der centralen und peripheren Nerven-
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Die Entwicklung des menschlichen Rautenhirns, etc. Loc. cit., Bad. XVII.
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Histogenese und Zusammenhang der Nervenelemente. Referat i. d. anatom.
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APPENDIX 431

His, us a das frontale Ende des Gehirnrohres. Arch. f. Anat. und Physiol.

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432 APPENDIX

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.

FF

434 APPENDIX

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CHEVREL, O. Sur /’Anatomie du Systéme nerveux grand sympathique des Elas-
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APPENDIX 435

GASKELL, H.W. On the Relation between the Structure, Function and Distribution
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FF 2

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Ueber die Retina der Neunaugen. .Sitz.-ber. der niederrhein. Gesellsch. f.
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Ueber die Netzhaut des Stéres. Loe. eit. 1872. (Comp. also Arch. f. mikr.
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Scuuntze, O. Zur Entwicklungsgeschichte des Gefisssystems im Siugethier-
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ScuwaLBeE, G. Mikrosk. Anatomie des Sehnerven, der Netzhaut und des Glas-
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Untersuchungen iiber die Lymphbahnen des Auges. Arch. f. mikr. Anat.
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StreinacH, KE. Untersuch. zur vergleich. Physiologie der Iris. Arch. f. d. ges.
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Ueber die Form der Falten des Corpus ciliare bei Siiugethieren. Morph.
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Die physikal. Natur des Glaskirpergewebes, die morphol. Natur desselben,
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Mittheil. z. vergl. Anat. der Wirbelthieraugen. Ber. d. Versammlung deut-
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Ueber die Augen der Selachier und die Verbindung derselben mit den Kopf-
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Anatomie microscopique (Traité complet @’ophthalmologie par L. de Wecker
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+446 APPENDIX

AUDITORY ORGAN.

Anbrecut, P. Sur la valeur morphologique de Varticulation mandibulaire du
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Dreyrtss, R. Beitrige zur Entwicklungsgeschichte des Mittelohres und des
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Fraser, A. On the Development of the Ossicula Auditus in the higher Mam-
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Bemerkungen gegen die Cupula terminalis. Arch. f. Anat. u. Phys. 1878.
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APPENDIX 447

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Over de Ontwikkelingsgeschiedenis van het Gehoororgaan en de Morpholo-
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KastscHenko, N. Das Schicksal der embryonalen Schlundspalten bei Sauge-
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Kiuan, G. Zur vergl. Anatomie und Entwicklungsgeschichte der Ohrmuskeln.
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Die Ohrmuskeln des Krokodiles, nebst vorliuf. Bemerk. iiber die Homologie
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Krause, R. Entwicklungsgeschichte der hiutigen Bogengiinge. Arch. f. mikr.
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Endigungen des Nervus acusticus im Gehérorgan. Verh. Anat. Ges.

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Ueber das hiutige Labyrinth der Amphibien. Zoe. cit. Bd. XVII. 1880.
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445 APPENDIX

Ripinuer, 8. Ueber die Abflusskaniile der Endolymphe des inneren Ohres.
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Zur Anatomie und Entwicklung des inneren Ohres. Berlin, 1888. Verlag
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Sicemmnn, M. ° Beitrage zur vergl. Anat. der Fische, III. Morph. Jahrb. Bd.
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SALENsKY, W. Beitriige zur Entwickl.-Geschichte der knorpeligen Gehérkno-
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Das Darwin’sche Spitzohr beim menschlichen Embryo. Anat. Anz. IV.
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Inwiefern ist die menschl. Ohrmuschel ein rudimentiires Organ? Arch. f.
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Veber Auricularhicker bei Reptilien. Ein Beitrag zur Phylogenese des
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Zur Methodik statistischer Untersuchungen iib. d. Ohrformen von Geistes-
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STRIFENSAND. Das Gehérorgan der Wirbelthiere. Arch. f. Anat. u. Physiol.
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Tatrarorr, D, Ueber die Muskeln der Ohrmuschel und einige Besonderheiten
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Troutscu, v. Die Anatomie des dusseren u. mittleren Ohres, etc. Lehrbuch der
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APPENDIX 449

H. ALIMENTARY ORGANS.
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Azpy, Cu. Die Architectur unvollkommen getheilter Zahnwurzeln. Arch. f.
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AmeEcuHINo, F. L’evolution des dents des Mammiféres. Bull. Acad. de Ciencias
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Batiowitz, E. Das Schmelzorgan der Edentaten, seine Ausbildung im Embryo
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Bearp, J. The Teeth of Myxinoid Fishes. Anat. Anz. III. Jahrg. 1888.

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Bruny, A. v. Ueber die Ausdehnung des Schmelzorganes und seine Bedeutung
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Carison, U. Ueber die Zahnentwicklung bei einigen Knochenfischen. Zool.
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Ueber die Schmelzleiste bei Sterna hirundo. Anat. Anz. Bd. XII. 1896.
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Cuic1, A. Sulla dentaturer dell’ Hemicentetes semispinosus (Mivart). Monit.
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Corr, E. D. The mechanical Origin of the Sectorial Teeth of the Carnivora.
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On the Tritubercular Molar in Human Dentition. Journ. Morphol. Vol. II.
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Crepner, H. Zur Histologie der Faltenzihne paliiozoischer Stegocephalen. Bd.
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Cuvier, G. Recherches sur less ossements fossiles. Tome V. Abth. II.

Dewo.etzxy, R. Neuere Untersuchungen ueber das Gebiss d. Sauger. Jahres-
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Dorsry, G. A. A Peruvian Cranium with suppressed upper Lateral Incisors.
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Numerical variations in the Molar Teeth of fiftren New Guinea Crania.
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Esner, V. v. Histologie der Zihne mit Einschluss der Histogenese. Scheff,
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Heinecke. Unters. iiber die Zihne niederer Wirbelthiere. Zeitschr. f. wiss.
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Henset, R. Ueber Homologieen u. Varianten in den Zahnformeln einiger
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Hertwic, 0. Ueber das Zahnsystem der Amphibien und seine Bedeutung fiir
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Jacosy, M. Die Hornzihne der Cyclostomen, ete. Arch. f. mikr. Anat. Bd.
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KtKkenruat, W. Einige Bemerkungen iiber die Saugethierbezahnung. Anat.
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Zur Dentitionenfrage. Anat. Anz. X. and XI.
GG

450 APPENDIX

KtKentuaL, W. Zur Entwickelungsgeschichte des Gebisses von Manatus.
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1889

Studien iiber die Entwicklung des Zahnsystems bei den Sdugethieren. Morph.
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The Rise of the Mammalia in North America. Stud. from the Biol. Lab. of
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The history of the cusps of the human molar teeth. Internat. Dental Journ.
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Zur Phylogenese des Siiugethiergebisses. Biol. Centralbl. Bd. XII.
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APPENDIX 451

Rész, C. 1. Ueber d. Zahnbau und Zahnwechsel von Elephas indicus. Morph.
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Bd. IV. 1895. 4. Ueber die Zahnentwicklung von Chlamydoselachus
anguineus, Garm. Loc. eit.

RosEnBERG, E, Ueber Umformungen an den Incisivi der zweiten Zahngeneration
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Ryver, J. A. On the Evolution and Homologies of the Incisors of the Horse.
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The Mechanical Genesis of Tooth-Forms. P. Ac. Philad. p. 45. 1878.
Scuzrpr, P. Morphologie und Ontogenie des Gebisses der Hauskatze. Morph.
: Jahrb. Bd. XXII 1894.

Scutosser, M. Beitr. zur Kenntnis der Stammesgeschichte der Hufthiere und
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GG 2

452 APPENDIX

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APPENDIX 453

KUKENTHAL, W. (See p. 399.)

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Tuyrorw, Tuymus, AND CaRotip (LAND.

AFANASSIEW, B. Ueber Bau und Entwicklung der Thymus der Siugethiere.
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AnpErson, O. A. Zur Kenntnis der Morphologie der Schilddriise. Arch. f.
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Antipas, G. Ueber die Beziehungen der Thymus zu den sog. Kiemenspalten-
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Bearp, J. ‘The Development and probable Function of the Thymus. Anat.
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BemMerLen, J. F. vax. Die Visceraltaschen und Aortenbogen bei Reptilien und
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Ueber die Suprapericardialkirper. Anat. Anz. IV. Jahrg. 1889.

Buumreicn, L. and Jakosy, M. Experiment. Untersuchungen iiber die Bedeu-
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Donen, A. Studien zur Urgeschichte des Wirbelthierkirpers. Mittheil. Zool.
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Fiscueis, Pain. Beitrag zur Kenntnis der Glandula thyreoidea und Glandula
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Gurart, T. Etude sur la (lande Thyroide dans la série des Vertébrés et en
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Jakospy, M. Ueber die mediane Schilddriisenanlage bei Siugern (Schwein).

_Anat. Anz. Bd. X. 1894.

Uber die Entwicklung der Nebendriisen der Schilddriise und der Carotiden-
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Jutiex, Cu. Quelle est Ja valeur morphologique du corps thyreoide des
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Kastscuenko, N. Das Schicksal der embryonalen Schlundspalten bei Siuge-
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Koux, A. Studien iiber die Schilddriise. Arch. f. mikr. Anat. Bd. XLIV. 1895.

LANGENDORFF, O. Aeltere und neuere Ansichten iiber die NSchilddriise. Biol.
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Luscuka, H. Ueber die driisenartige Natur des sogenannten Ganglion inter-
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Maromanp. Beitr. z. Kenntnis der normalen und pathologischen Anatomie der
Glandula carotica und der Nebennieren. Internat. Beitrage z. wissens-
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Mavrer, F. Schilddriise und Thymus der Teleostier. Morph. Jahrb. Bd. XI.
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Nchilddriise, Thymus und Kiemenreste der Amphibien. Morph. Jahrb. Ba.
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454 APPENDIX

Mayer, 8. Zur Lehre von der Schilddriise und Thymus bei den Amphibien.
Anat. Anz. III. Jahrg. 1888.

Maevrox, P. pr. Recherches sur le développement du Thymus et de la glande
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ensein bei Amphioxus und den Cyclostomen. Jen. Zeitsch. Bd. VII.

Ueber die Entwicklung der Nchilddriise. Loc. cit, Bd. VI.

Die Hypobranchialrinne der Tunicaten. Loe. cit. Bd. VII.

Orro, M.° Beitr. z. vergl. Anat. d. Glandula thyreoidea u. thymus d. Siiuge-
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Puart, J. The Development of the Thyroid (and and of the Suprapericardial
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Reuak. Untersuch. iiber Entwicklung der Wirbelthiere. Berlin, 1855.

Scuaper, A. Beitr. z. Histologie der Glandula carotica. Arch. f. mikr. Anat.
Bd. XL. 1892.

Ueber die sog. Epithelkirper (Glandulae parathyreoideae) in der Nachbarschaft
der Schilddriise und der Umgebung der Art. carotis. der Siuger u. des
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ScuvitzE, M. Die Entwickl.-Geschichte von Petromyzon planeri. Natuur-
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SEEssEL, A. Zur Entwickl.-Gesch. des Vorderdarmes. Arch. f. Anat. und
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Smiox, J. A. Physiological essay on the Thymus. London, 1845.

Sriepa, L. Unters iiber die Entwicklung der Glandula thymus, thyreoidea und
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Watney, H. The minute anatomy of the Thymus. Phil. Trans. 1882.

Wourier, A. Ueber die Entwicklung der Schilddriise. Berlin, 1880.

ZIMMERMANN. Ueber die Carotisdriise von Rana esculenta. Inaug.-Dissert.
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ALIMENTARY CANAL.
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BriaxcHarD, R. Mittheil. ittberd. Bau und die Entwicklung der sogen. finger-
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Bracuet, A. Rech. sur le dévelop. du pancreas et du foie (Selaciens, Reptiles,
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Bravs, H. Untersuch zu vergl. Histologie der Leber der Wirbelthiere.

CATTANEO, G. Struttura e sviluppo dell’ intestino dei pesci. Bolletino scientifico.
No. I. 1886, Pavia.

Sulla formazione delle cripte intestinali negli embrioni del Salmo salar.
Rend. del. R. Istit. Lomb. serie II, Vol. XIX, Fase. IX. Milano, 1886.

Istologia e sviluppo del Tubo digerente dei pesci. Milano, 1886.

Sulla stomaco del Globiocephalus Svineval, Flow. e sulla digestione gastrica
nei delfinide. Atti Soc. Ligust. Vol. V. 1894.

NulP esistenza delle glandule gastriche nell’ Acipenser sturio e nella Tinca
vulgaris. Rend. Istit. Lomb. Vol. NIX. 1886.

(1) Ulteriori ricerche sulla struttura delle glandule peptiche dei selaci,
ganoidi e teleostei. (2) Sul significato fisiologico delle glandule da me
trovate nello stomaco dello Sturione e sul valore morfologico delle loro
cellule. Bollett. scientif. No. 3 und 4. Pavia, 1886.

FEprincer, L. Ueber die Schleimhant des Fischdarmes, &c. Arch. f. mikr. Anat.
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GoErPeRT, E. Die Entwicklung des Pankreas der Teleostier. Morph. Jahrh.
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Hoim, J. F. Ueb. ad. fein. Bau der Leber ber den niederen Wirbelthieren.
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Howes, G. B. On the Intestinal Canal of the Ichthyopsida, with especial
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APPENDIX 455

Howes, G. B. On the Visceral Anatomy of the Australian Torpedo (Hypnos
subnigrum), with especial reference to the Suspension of the Vertebrate

Z Alimentary Canal. P. Zool. Soc. 1890.

Krvkenserc. Versuche zur vergl. Physiologie d. Verdauung, &c. Unters. aus
d. physiol. Inst. der Univ. Heidelberg, Bd. I.

Kuprrer, C. v. Ueber die Entwicklung von Milz und Pankreas. Miinchener
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Ueb. das Pankreas bei Ammoceetes. —_Sitz.-ber. Morph. Physiol. Miinchen.
H. II.-ITL., 1893.

Lacvussse, E. Développement du pancréas chez les poissons osseux. Comptes

rendus hebdomaclaires de la Société de Biologie. Jahrg. 1889 und 1890.

Structure du pancréas et pancréas intrahépatique chez les poissons. Comptes
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Lecoyis. Rech. sur les tubes de Weber et sur le pancréas des poissons osseux.
Ann. sci. nat. Zool., T. XVII. u. XVIII. 1873.

List, J. Untersuch. tiber d. Cloakenepithel der Plagiostomen. Sitz.-her. Ak.
Wien. XC., XCII. 1884, 1885.

Lorent, H. Ueber den Mitteldarm von Cobitis fossilis Lin. Arch. f. mikr. Anat.
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Maas, O. Uber ein Pankreas-ihnl. Organ bei Myxine. Sitz. ber. Morph. und

Physiol. Miinchen, 1896.
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1896.

Mayr, J. Ueb. die Entwick. d. Pankreas bei Selachiern. Anat. Hefte. I
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Mazza, F. and Pervera, A. Sulla glandola digitiforme (Leydig) nella Chimaera
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Nest_eR, K. Beitr. z. Anat. u. Entw. Gesch. von Petromyzon planeri. Berlin,
Nicolai, 1890. Comp. also Arch. f. Naturgesch. 1890.

OppreL, A. Die Magendriisen der Wirbeltiere. Anat. Anz. Bd. XI. 1896.

Lehrbuch d. vergl. mikros. Anatomie der Wirbelthiere. Theil I., Magen.
Jena, 1896.

Parker, T. J. On the Intestinal Valve in the Genus Raia. Tr. Zool. Soc.
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RatuHkeE, H. Zur Anatomie der Fische. (1) Ueber den Darmeanal. (2) Ueber
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RtcKkert, J. Ueber die Entwicklung des Spiraldarmes bei Selachiern. Arch. f.
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WieprersHemm, R. Ueber die mechanische Aufnahme der Nahrungsmittel in der
Darmschleimhaut. Freiburger Festschrift zur 56. Versammlung deutscher
Naturforscher und Aerzte, 1883.

Yuna, E. De la physiologie comparée de la Digestion. Arch. d. Scienc. phys.
et nat. III. Période. T. XXXIV., 1895.

AMPHIBIA AND KEPTILIA.

BeMMELEN, J. F. van. Beitriige zur Kenntnis der Halsgegend bei Reptilien.
Anat. Theil. Amsterdam, 1888. (See also Zool. Anz. XI. Jahrg.,
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Over den oorsprong van de voorste ledematen en de tongspieren bij Rep-
tilien. K. Akademie van Wetenschappen te Amsterdam. Zitting van 30
Juni, 1888.
Exsrrtu. Untersuch. tiber die Leber der Wirbelthiere. Arch. f. mikr. Anat.
Bd. III. (Comp. also Virchow’s Arch. Bd. XXXIX.)
GéprErt, E. Die Entwicklung und das spiitere Verhalten des Pankreas bei
Amphibien. Morph. Jahrb, Bd. XVII. 1891.
Hirox-Royer et Cu. vaAN Bampecke. La vestibule de la bouche chez les
tétards des Batraciens anoures d’Europe, &c. Arch. de Biol., T. IX,
1889.
Hout, M. Zur Anatomie der Mundhihle von Lacerta agilis. Sitz.-ber. Ak.
Wien. Bd. XCVI. 1887.

456 APPENDIX

Kiscssery, B. T. The Histological Structure of the Enteron of Necturus macu-
latus. Proc. Amer. Microscop. Soc. 1894. ;

OpreL, A. Beitr. zur Anatomie des Proteus anguineus. Arch. f. mikr. Anat.
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Osawa, G. Beitr. z. Lehre von den Eingeweiden der Hatteria punctata. Arch.
f. mik. Anat. Bd. XLIX. 1897.

Saccut, Marta. Contrib. all’ Istologia ed Embriologia dell’Apparechio digerente
dei Batraci e dei Rettili. Atti della Societa Ital. di scienze nat. Vol.
XXIX. Milano, 1886.

Sulla morfologia delle Glandule intestinali dei Vertebrati. Bollet. Scientif.
No. 2. Pavia, 1887.

Scuvuze, F. E. Ueber die inneren Kiemen der Batrachierlarven. I. Mittheil-.
Ueber das Epithel der Lippen, der Mund-, Rachen- und Kiemenhéhle
erwachsener Larven von Pelobates fuscus. Abh. Ak. Berlin, 1888. II.
Mittheil. Skelet, Muskulatur, Blutgefisse, Filterapparat, Respiratorische
Anhange und Athmungsbewegungen erwachsener Larven von Pelobates
fuscus. Loc. cit. 1892.

Stéur, Pu. Ueber die Entwicklung der Hypochorda und des dorsalen
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AVES.

Cazix, M. Recherches sur la structure de l’estomac des oiseaux. Comptes rendus.
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CatTaNeEo, G. Istologia e sviluppo dell’ apparato gastrico degli uccelli. Milano,
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CuoetTta, M. Beitr. z. mikrosk. Anatomie des Vogeldarmes. Arch. f. mikr.
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Forses, W. A. On the Bursa Fabricii in Birds. P. Zool. Soc. 1887.

Gapow, H. Versuch einer vergl. Anatomie des Verdauungssystems der Vogel.
Jen. Zeitschr., Bd. NII. N. F. VI.

Gasser. Die Entstehung der Cloakeniffnung bei Hiihnerembryonen. Arch. f.
Anat. und Physiol. Anat. Abtheil. 1880.

Hescuke. De bursae Fabricii origine. 1838.

Letcxart. Zoolog. Bruchstiicke, II. 1841. Ueber eine zusammenges. Magen-
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Mors. Sugli stomachi degli uccelli. Denkschr. K. Acad. d. Wissensch. Bud.
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OppEL, A. (See p. 455.)

Postixa, G. Bydrage tot de Kennis van den Bouw van het Darmkanaal der
Vogels. Inaug.-Dissert. Leiden, 1887.

Strepa, L. Ueber den Bau und die Entw. der Bursa Fabricii. Zeitschr. f. wiss.
Zool. NNNIV.

TercHMann, M. Der Kropf der Taube. Arch. f. mikr. Anat. Bd. XXXIV.
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TIEDEMANN and GMELIN. Die Verdauung. Bd. II. Heildelberg, 1826.

WENCKEBACH, K. F. De Ontwikkeling en de Bouw der Bursa Fabricii. Inaug.-
Dissert. Utrecht, 1888.

WHIEDERSHEIM, R. Die feineren Structurverhiltnisse der Driisen im Muskel-
magen der Vigel. Inaug.-Dissert. Wiirzburg, 1872. See also Arch. f.
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MAMMALIA.

BrzzozEro, G. Ueber die Regeneration der Elemente der schlauchfirmigen
Driisen und des Magendarmeanals. Anat. Anz. Jahrg. IIT. 1888, und Arch.
f. mikr, Anat. Bd. XXIII. 1889.

Boas, J. E. V. Zur Morphologie des Magens der Cameliden und der Traguliden,
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Bracuer. (See pp. 422, 454.)

Evetmany, R. Vergl. anat. und physiol. Untersuchungen tiber eine besondere
Region der Magenschleimhaut (Cardialdriisenregion) bei den Siugethieren.
Inaug.-Dissert. Rostock, 1889.

APPENDIX 457

Eprncer, L. Zur Kenntnis der Driisenzellen des Magens, besonders beim Menschen.
Arch. f. mikr. Anat. Bd. XVII. 1879.

Ermer, Tu. Neue und alte Mittheilungen ueber Fettresorption im Diinndarm
und im Dickdarm. Biol. Centralbl. Bd. IV. No. 19. 1884.

Expres, H. Beitr. z. Entwicklungsgeschichte und Anatomie des Darmes, des
Darmgekrises und der Bauchspeicheldriise. Arch. f. mikr. Anat. Bad.

XL. 1892.
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462 APPENDIX

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Bovert, Tu. Ueber die Bildungsstiitte der Geschlechtsdriisen und die
Entstehung der Genitalkammern beim Amphioxus. Anat. Anz. VII.
Jahrg. 1892.

Brunn, A. v. Beitriige zur Kenntnis der Samenkirper und ihrer Entwicklung
bei Saiugethieren und Vigeln. Arch. f. mikr. Anat. Bd. XXIII. 1883.

Burnett, W. J. Researches on the Development and intimate Structure of the
Renal Organs of the four Classes of the Vertebrates. Amer. Journ. of
sciences and arts. II. Ser., Vol. NVII.

APPENDIX 469

ee ee ‘0 Der Harnleiter der Wirbelthiere. Anat. Hefte. I. Abth. (4

Exner, V. v. Unters. iiber den Bau der Samencanilchen und die Entwicklung
der Spermatozoiden bei den Saugethieren und beim Menschen. 1872.

OE po mnagenete der Saiugethiere. Arch. f. mikr. Anat. Bd. XXXI.

Eimer, Th. Unters. itber den Bau und die Bewegung der Samenfiden. Verh.
Ges. Wiirzburg. N. F. Bd. VI.

Fiemmine, W. Die ektoblastische Anlage des Urogenitalsystems beim Kanin-
chen. Arch. f. Anat. u. Physiol. 1886,

Weitere Beobachtungen iiber die Entwicklung der Spermatozoén bei Sala-
__mandra macul, Loe. cit. Bd. XXXI._ 1887.

FUrprincer, M. Zur vergl. Anatomie und Entw.-Geschichte der Excretions-
organe der Vertebraten. Morph. Jahrb., Vol. IV. 1878.

Haackz, W. Ueber die Entstehung des Siugethiers. Biol. Centralbl. Bd.
VIII. 1888,

Havvon, A. C. Suggestion respecting the epiblastic Origin of the Segmental
Duct. P. Dublin Soc. N.S. Vol. V. 1887.

HEIDENHAIN, R. Mikrosk. Beitr. zur Anat. u. Physiol. der Niere. Arch. f.
mikr. Anat. Bd. X. 1874.

HeEnsEN, V. Physiologie der Zeugung. Handbuch der Physiologie von L. Her-
mann. Bd. VI, 2. Th.

Hermann, F. Beitr. zur Histologie des Hodens (Salamandra and Maus). Arch,
f. mikr. Anat. Bd. XXXIV. 1889.

Hertwie, O. Vergleich von Ei- und Samenbildung bei Nematoden. Eine
Poe fiir cellulaire Streitfragen. Arch. f. mikr. Anat. Bd. XXXVI.

Horrmann, C. K. Zur Entwicklungsgeschichte der Urogenitalorgane hei den
Anamnia. Zeitschr. f. wiss. Zool. Bd. XLIV. 1886.

Hou, M. Ueber die Reifung der Eizelle bei den Saugethieren. Sitz.-ber, Ak.
Wien, Bd. CII. Abth. III. 1893.

Janosik, J. Bemerk. tiber der Entwickl. d. Genitalsystems Sitz.-ber.Ak., Wien.
1890. Bd. XCIX. Abth. III.

JENSEN, O. Die Structur der Samenfiden. Bergen, 1879.

Juuin, Cu. Structure et développement des glandes sexuelles ; ovogenése sper-
matogenése et fécondation chez Styelopsis grossularia. Bull. sci. France
Belgique T. XXV. 1893.

KLEINENBERG, N. Ueber die Entstehung der Eier bei Eudendrium. Zeitschr.
f. wiss. Zool. Bd. XXXV. 1881.

Koéuiiker, A. Zur Bedeutung der Zellenkerne fiir die Vorgiinge der Vererbung.
Zeitschr. f. wiss. Zool. Bd. XLII. 1885.

Koxtimann, J. Ueber Verbindungen zwischen Coelom und Nephridium. _Fest-
schrift zur Feier des 300jihr. Bestehens der Univers. Wiirzburg, 1882.

La Vauette St. George. Der Hoden. Abschnitt in dem Handbuch der Lehre
von den Geweben des Menschen und der Thiere. Herausgeg. von §.
Stricker. Leipzig, 1871. (Comp, also numerous papers in Arch. fiir mikr.
Anat.)

LeREBOULLET. Rech. sur l’anatomie des organes génitaux des animaux vertébrés.
Nov. act. Acad. Leop -Car., &c. 1851.

Lupwic, H. Ueber die Eibildung in Thierreiche. Arb. Inst. Wirzburg. Bd.
I. 1874.

Martin, E. Ueber die Anlage der Urniere beim Kaninchen. Arch, f. Anat. und
Physiol. 1888.

Martin-Sarnt-Ance, G. J. Etude de l'appareil réproducteur dans les cing
classes d’animaux vertébrés, &c. Paris, 1854.

Mecxet, H. Zur Morphologie der Harn- und Geschlechtswerkzeuge der Wirbel-
thiere, &c. Halle, 1884.

Mriuaxcovics, V. v. Entw. des Harn- und Geschlechtsapparates der Amnioten.
I. Der Excretionsapparat. II. Die Geschlechtsginge. III. Die Geschlechts.
driisen. Internat. Monatsschr. Anat. Bd. II. 1885.

Minot, CHARLES SepGwick. A sketch of comparative Embryology. The History
of the Gonoblasts and the theory of sex. Amer. Nat., 1880. Abstract in
Biol. Centralbl. No. 12, Bd. I.

470 APPENDIX

Mrrsuxuri, K. The ectoblastic Origin of the Wolffian Duct in Chelonia. Zool.
Anz. XI. Jahrg. 1888.

Muir, Jon. Bildungsgeschichte der Genitalien, &c. Diisseldorf, 1830.

Nacen, W. Das menschliche Ei. Arch. f. mikr. Anat. Bd, XXXII. 1888. :

Pertnyt, J. v. Entwicklung des Amnion, Wolff’schen Ganges und der Allantois
bei den Reptilien. Zool. Anz. XI. Jahrg. 1888.

Ratu, O. vom. Beitr. zur Kenntnis der Spermatogenese von Salamandra
maculosa. Zeitschr. f. wiss. Zool. Bd. LVII. 1893. ;

Ratuxe, H. Beobachtungen und Betrachtungen iiber die Entwicklung der
Geschlechtswerkzeuge bei den Wirbelthieren. Neue Schriften d. natur-
forsch. Gesellsch. in Danzig. Bd.I. 1825.

Rerzius, G. Zur Kenntnis der Spermatozoén. Biol. Untersuch. Stockholm.
1881.

Zur Kenntnis vom Bau des Eirstockeies und des Graaf’schen Follikels.
Hygiea. Festband No. 2. 1889. :

Rickert, J. Entwicklung der Excretionsorgane. Anat. Hefte, Ergbn. Wies-
baden, 1892.

Ruce, G. Vorginge am Eifollikel der Wirbelthiere. Morph. Jahrb. Bd. XV.
1889,

Scuutrze, O. Untersuchungen tiber die Reifung und Befruchtung des Amphibien-
Kies. I. Abhdlg. Zeitschr. f. wiss. Zool. Bd. XLV. 1887.
Semon, R. Die indifferente Anlage der Keimdriisen beim Hiihnchen und ihre
Differenzirung zum Hoden. Jen. Zeitschr. Bd. XXI. N. F. XIII.
1887.
Studien iiber den Bauplan des Urogenitalsystems der Wirbelthiere. Dargelegt
an der Entwicklung dieses Organsystems bei Ichthyophis glutinosus.
Jen. Zeitschr. Bd. XXVI. 1891.
Semper, C. Das Urogenitalsystem der Plagiostomen und seine Bedeutung fiir die
tibrigen Wirbelthiere. Arb. Inst. Wiirzburg. Bd. IT. 1875.
Die Stammesverwandtschaft der Wirbelthiere und Wirbellosen. Loc. cit.
Bd. II.
Sotcer, B. Beitr. z. Kenntnis der Niere und besonders der Nierenpigmente
niederer Wirbelthiere. Abh. Ges. Halle. Bd. XV. 1882.
Eierstock und Ei. Leipzig, 1870.
Spex, Graf F. Ueber directe Betheiligung des Ektoderms an der Bildung der
Urnierenanlage des Meerschweinchens. Arch. f. Anat. u. Phys. 1884.
Ueber weitere Befunde zur Entwicklung der Urniere. Mittheil. des Vereins
Schleswig Holstein. Aerzte. Heft 11,2. 1886.
Wa.peyer, W. Bau und Entwicklung der Samenfiden. (Referat.) Anat. Anz.
Il. Jahrg. 1887.
Ueber Karyokinese und ihre Beziehungen zu den Befruchtungsvorgingen.
Arch. f. mikr. Anat. Bd. XXXII. 1888.
Eierstock und Ei. Leipzig, 1870.
Wetsmann, A. Die Entstehung der Sexualzellen bei den Hydromedusen. Mit
Atlas. Jena, 1883. i
Numerous ‘‘ Essays upon Heredity and kindred Biological Problems.” English
translation by Poulton and Shipley. Vols I. and II. Oxford, 1889-91
and 1892.
The Germ-plasm, a theory of Heredity. Translated by Parker and
Rénnfeldt. London, 1893.
Germinal Selection. Jena, 1896. (English trans. in ‘‘ The Monist,” vol. VI.
No. 2.) Chicago, 1896. :
WuueE, J. W.van. Die Betheiligung des Ektoderms an der Entwicklung des
Vornierenganges. Zool. Anz. IX. Jahrg. 1886.
Ueber die Mesodermsegmente des Rumpfes und die Entwicklung des
sr abies dias bei Selachiern. Arch. f. mikr. Anat. Bd. XXXIII.

(a) AMPHIOXUS, CYCLOSTOMATA,

Boveri, Ta. Ueber die Niere des Amphioxus. Miinchener Medicin. Wochen-
schrift, 1890. No. 26.
Ueber die Bildungsstitte der Geschlechtsdriisen und die Entstehung der
Genitalkammern beim Amphioxus. Anat. Anz. VII. Jahrg. 1892,

APPENDIX 471

Boveri, Tu. Die Nierencaniilchen des Amphioxus. Ein Beitrag zur Phylogenie
des Urogenitalsystems der Wirbelthiere. Zool..Jahrb. Bd. V. 1892.

CaLBerLa, E, Der Befruchtungsvorgang beim Ei von Petromyzon planeri.
Zeitschr. f. wiss. Zool., Bd, XXX. 1877.

Cunnincuam, J.T. On the Structure and Development of the reproductive
a Myxine glutinosa, Q. Journ. Micr. Sci. Vol. XXVII. N.

er, i

Ewart, J.C. Note on the abdominal pores and urogenital sinus of the Lam-
prey. Journ. Anat. and Physiol. Vol. X. 1876.
Howes, G. B. On the Affinities, Inter-Relationships and Systematic Position of
the Marsipobranchii, Trans. Biol. Soc. Liverpool. Vol. VI. 1892.
JUNGERSEN, H. Beitr. zur Kenntnis der Entwicklung der Geschlechtsorgane
bei den Knochenfischen, Arb. Inst. Wiirzburg. Bd. IX. 1889.

Kuprrer, C. and Brewecks, Der Vorgang der Befruchtung am Eie der
Neunaugen. Festschr. zur Feier von Th. Schwann. Kinigsberg, 1878.

Lecros, R. Sur la Morphologie des glandes sexuelles de l’Amphioxus lanceo-
latus. Compte-Rendu des Séances du troisieme congrés internat. de
Zoologie, Leyde. 1895.

Meyer, Fr. Ueber die Nieren der Flussneunaugen (Petromyzon fluviatilis).
Centralbl. f. d. medic. Wissensch. 1876, No. 2.

Mitier, A. Ueber die Befruchtungserscheinungen im Ei der Neunaugen.
Verhdl. d. Kinigsb. physik.-dkonom, Gesellsch. 1864,

Mier, J. Unters. iiber die Kingeweide der Fische. Abh. Ak. Berlin, 1845.

Mitier, W. Ueber das Urogenitalsystem des Amphioxus und der Cyclostomen.
Jen. Zeitschr. Bd. IX. 1875.

Ueber die Persistenz der Urniere bei Myxine glutinosa. Loc. cit. Bd. VII.

1873.

Nansen, F. A Protandric Hermaphrodite (Myxine glutinosa, L.) amongst the
Vertebrates. Bergens Museums Aarsberetning for 1887. Bergen 1888.

RtcKkErtT. Ueber die Entstehung der Excretionsorgane bei Selachiern. Arch. f.
Anat. und Physiol. 1888.

ScuNEIDER, A. Beitr. zur vergl. Anatomie und Entwicklung der Wirbelthiere.
Berlin, 1879.

Scorr, W. B. Beitrage zur Entwicklung der Petromyzonten. Morph. Jahrb.
Bd. VII. 1881.

Semon, R. Das Exkretionsystem der Myxinoiden in seiner Bedeutung fiir die
Morphol. Auffassung des Urogenitalsystem der Wirbelthiere. Festschrift
fiir Carl Gegenbaur. Leipzig, 1896.

Sosorra, T. Die Befruchtung des Eies von Amphioxus lanceolatus, Anat. Anz.

Bd. XI. 1895.
SpenGEL, J. W. Die Excretionsorgane von Myxine. Anat. Anz. Bd. XIII.
1897.

(b) ELASMOBRANCHII.

Borau, H. Ueber die Paarung und Fortpflanzung der Scylliumarten. Zeitschr.
f. wiss. Zool. Bd. XXXV. 1882.
La VALETTE ST. GEORGE. Diss. de Spermatosomatum evolutione in Plagiostomis.
Festschr. Bonn, 1878.
Parker, T. J. On the gravid uterus of Mustelus antarcticus. Tr. N. Z. Inst.
Vol. XV. 1882.
Notes on the Anat. and Embryol. of Scymnus lichia. Zoe. cit, Vol. 15. 1882.
Prelim. Note on the Vesicule Seminales and the Spermatophores of Mustelus
antarcticus. Proc. Austr. Assoc. Adv. Sci. Vol. IV. 1892.
Notes from the Otago Museum, ‘‘ Nature.” On some embryos of Callorhyn-
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(Vol. XXXIV.) ; ;
Perri, K. Die Copulationsorgane der Plagiostomen. Zeitschr. f. wiss. Zool.
Bd. XXX.
Rasn, C. Ueb. die Entwick. d. Urogenitalsystems der Selachier. Morph.
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Rickert. Ueber die Entstehung der Excretionsorgane bei Selachiern. Arch. f.
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Scuutty, A. Zur Entwicklung des Selachiereies. Arch, f. mikr. Anat. Bd.

XI. 1875.

472 APPENDIX

Semper, C. (See p. 470.)

Turner, W. Addit. Observ. on the Anatomy of the Greenland Shark (Laemargus
borealis). Journ. Anat. and Physiol. Vol. VIII.

Wisue, J. W. vay. Ueber die Entwicklung des Excretionssystemes und anderer
Organe bei Selachiern. Anat. Anz. II. Jahrg. 1888. (And see p. 470.)

(c) GANOIDEI AND TELEOSTEI.

Batrour, F. M. On the nature of the organ in adult Teleosteans and Ganoids
which is usually regarded as the Head-Kidney or Pronephros. Q. Journ.
Micr. Sci. 1882 (See also p. 395.)

Brarp, T. The Pronephros of Lepidosteus osseus. Anat. Anz. Bd X. No. 6.
1894.

Brock. J. Beitr. zur Anat. und Histol. der Geschlechtsorgane der Knochen-
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Ueber Anhangsgebilde des Urogenitalapparates von Knochenfischen.
Zeitschr. f. wiss. Zool. Bd. XLV. 1887,

Durosst. De Vhermaphrodisme chez le Serran. Annal. de sc. nat. 1V. Ser.
tome V. Paris, 1856.

Emery, C. Zur Morphologie der Kopfniere der Teleostier. Biol. Centralb.
Bd. I. 1881 bis 82.

Studi intorno allo sviluppo ed alla morfologia del rene dei Teleostei. Mem.
Acc. Lincei. Anno. 279. Mem. Vol. XIII

Ferx. Ueber die Entwicklung des Excretionssystems der Forelle (Vorniere,
Urniere, Nachniere). Verh. Anat. Ges. 1895.

Futiarton, T. H. On the Development of the Plaice (Pleuronectes platessa)
Rep. Fishery Board of Scotland, 1895.

GroseLik, 8S. Zur Morphologie der Kopfniere der Fische. Zool. Anz. Jahrg.
VII, No. 207. 1885.

Zur Frage tiber die Persistenz der Kopfniere der Teleostier. Zool. Anz.
Jahrg. IX. 1886.

GuireL, F. Description des Orifices génito-urinaires de quelques Blennius.
Arch. Zool. exp. B. Sér. Vol. I. 1893.

Hermes, O. Ueber reife minnl. Geschlechtstheile des Seeals (Conger vulgaris)
und einige Notizen iiber den mannlichen Flussaal (Anguilla vulgaris).
Zool. Anz. Jahrg. IV. 1881.

Hout and Catperwoop. Survey of Fishing Grounds. Journ. Dublin Soc., Vol.
V. (Ser. II.), IX. 1895.

Howes, G. B. Onsome Hermaphrodite Genitalia of the Codfish (Gadus morrhua),
with Remarks upon the Morphology and Phylogeny of the Vertebrate
Reproductive System. Journ. Linn. Soc., Zool., Vol. XXIII. 1891.

On the Arrangement of Living Fishes, as based upon the Study of their
Reproductive System. Cardilf Meeting of the British Association. 1891.

Hyrti, J. Beitr. z. Morphol. der Urogenitalorgane der Fische. Denkschr. d.
Wien. Acad. d. Wiss. I. 1850.

Ueber den Zusammenhang der Geschlechts- und Harnwerkzeuge bei den
Ganoiden. Denkschr. d. Wien. Acad. d. Wiss., VIII. 1854.

Juerinc, H. v. Zur Kenntnis der Gattung Girardinus. Zeitschr. f. wiss.
Zool. Bd. XXXVIII. 1883.

Juncersen, H. Beitr. zur Kenntnis der Entwicklung der Geschlechtsorgane
bei den Knochenfischen. Arb. Inst. Wiirzburg. Bd. IX. 1889.

Die Embryonalniere des Stérs (Acipenser sturio). Zool. Anz., Nos. 4385 and
436. 1893. (Comp. also Saertryk af Vidensk. Meddel. fra den naturh.
Foren. i. Kbhn. 1893).

Die Embryonalniere von Amia calva. Zool. Anz., No. 451. 1894.

Korrrer, C. Beobachtung iiber die Entwicklung der Knochenfische. Arch. f.
mikr. Anat. Bd. IV. 1868.

MacLeop, J. Rech. sur l'appareil reproducteur des poissons osseux. Bull. Ac.
Belgique. 50 Ann., Ser. III., Tom. I

Rech. sur la structure et le développement de l'appareil reproducteur femelle
des Teléostiens. Arch. de Biol. IT.

Mosius, K. Ueber die Eigenschaften und den Urspruny der Schleimfiden des
Seestichlingnestes. Arch. f. mikr. Anat. Bd. XAV. 1885.

APPENDIX 473

ake Beitr. zur Entw. der Knochenfische. Zeitschr. f. wiss. Zool. Bd.

Owstanyikow, Pu. Studien iiber das Ei, hauptsiichlich bei den Knochenfischen.
Mém. Ac. St. Pétersb., Série VII. Tome XXNIII, No. 4. 1885.

RaTuKE, H. Ueber die Geschlechtstheile der Fische. Neueste Schrift. d. naturf.
Gesellsch. « Danzig. Bd.I. Heft. 3. Halle, 1824. (Also in Beitrage zur
Geschichte der Thierwelt. IT. Halle, 1824, p. 117).

Zur Anatomie der Fische. Arch. f. Anat. und Physiol. 1836.

a A. Unters. iiber die Entwicklung der Teleostierniere. Dorpat,

STUHLMANN, F. Zur Kenntnis des Ovariums der Aalmutter (Zoarces viviparus
Cuv.) ‘‘Abhandl. aus dem Gebiete der Naturwissenschaften.” Bd. X.
Festschrift zur Feier 50 jiihr. Bestehens des Naturwissensch. Vereins zu
Hamburg. Hamburg, 1887.

Syrsk1. Ueber die Reprod.-Organe des Aals. Sitz.-ber. Ak. Wien. Bd.
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Voer, C. Embryologie des Salmones. Neuchatel, 1842.

Voer and ParreNueim. Rech. sur l’anatomie comparée des organes dle la génér-
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Weser, M. Ueber Hermaphroditismus bei Fischen. Tijdschrift der Neder-
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Dipnot.
(See pages 395, 396.)

Bepparp, F. E. The Ovarian Ovum of Lepidosiren (Protopterus). Zool. Anz.
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Observations on the Ovarium Ovum of Lepidosiren (Protopterus). P. Zool.
Soc. 1896. ,

AMPHIBIA.

Bipper, F. G. Vergl. anat. und histol. Unters. iiber die minnl. Geschlechts-
und Harnwerkzeuge der nackten Amphibien. Dorpat, 1846.
Buaycuarp, R. Sur les glandes cloacales et pelviennes et sur la papille cloacale
des Batraciens Urodéles. Zool. Anz. Jahrg. IV. 1883.
CuarkE, 8. P. The early Development of the Wolffian Body in Amblystoma
punctatum. Stud. Biol. Lab., Johns Hopk. Univ., Vol. II., No. 1.
CoLe, - J. Acase of Hermaphroditism in Rana temporaria. Anat. Anz. Bd.
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Duvernoy, C. L. Fragments s. les Organes génito-urinaires des Reptiles, ete.
Mém. Acad. Sciences. Paris. Wol. XI. 1851.
Fretp, H. H. The Development of the Pronephros and Segmental Duct in
Amphibia. Bull. Mus., Harvard, Vol. XXI., No. 5. 1891.
Ueber streng metamere Anlage der Niere bei Amphibien (Vortrag).
Verhandl. d. Deutschen Zool. Gesellsch. 1892.
Die Vornierenkapsel, ventrale Muskulatur, und Extremitaten-Anlagen bei
den Amphibien. Anat. Anz. Bd. IX. 1894.
Ueber die Morphologie der Amphibien-Harnblase. Morph. Arb. Bd. IV.
1894. (Comp. also Anat. Anz. Bd. IX. 1894).
Firprincer, M. Zur Entw. der Amphibienniere. Heidelberg, 1877. Morph.
Jahrb. Bd. IV. 1878.
GieLio-Tos. E. Lui Corpi grassi degli Anfibi. Atti Acc. Torino. Vol. XXX.
1894-95.
Sull Origine dei Corpi grassi negli Anfibi. Loc. cit. Vol. XNXI. 1895-96.
GitEs, A. E. Development! of the Fat-bodies in the Frog: a Contribution to
the History of the Pronephros. @. Journ. Micr. Sci., 1888, and Stud.
Owens Coll., Vol. II. Manchester, 1890.
HEWweENHAIN, R. Mikr. Beitrige zur Anatomie und Physiologie der Nieren.
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Beitrag zur Kenntnis der Topographie und Histologie der Cloake und ihrer
driisigen Adnexa bei den einheimischen Tritonen. Arch. f. mikr. Anat.
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474 APPENDIX

Juncrrsen, H. Om Udviklingen af den Miillerske Gang (Aeggelederen) hos
Padderne. Vidensk. Meddel. fra den naturhist. Forening i. Kjobenhavn.
1892.

Kinespury, B. F. The Spermatheca and Methods of Fertilisation in some
American Newts and Salamanders. Proc. Amer. Mier. Soc., Vol. XIII.
1895.

Knapre, E. Das Bidder’sche Organ, ein Beitrag zur Kenntnis der Anatomie,
Histologie und Entw.-Gesch. der Geschlechtswerkzeuge einiger Amphibien,
besonders der einheimisclien Bufoniden. Morph. Jahrb. Bd. XI. 1886.

Leprun, H. Recherches sur lappareil génital femelle de quelques Batraciens
indigénes. ‘‘ La Cellule,” t. VIL, 2 fascicule. 1891.

Leypic, F. (See p. 395.) :

MacBripe. The Development of the Oviduct in the Frog. . Journ. Micr.
Sci., Vol. XXXITI. 1892.

MarsHAtL, A. Minnes. On certain Abnormal conditions of the Reproductive
Organs in the Frog. Journ. Anat. and Physiol. Bd. XVIII. 1885.
MarsHatu, M., and Buss, E. J. The Development of the Kidneys and Fat-

bodies in the Frog. Stud. Owens Coll., Vol. IJ. 1890. ; .

Meyer, F. Anat. des Urogenitalsystems der Selachier und Amphibien. Sitz.-
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Moxuier, §. Ueber die Entstehung des Vornierensystems bei Amphibien.
Arch. f. Anat. u. Physiol. Jahrg., 1890.

Muuuen, A. von zur. Unters. tiber den Urogenit. App. d. Urodelen. Inaug.
Dissert. Dorpat (Jurjew). 1894.

MUiier, J. Ueber d. Wolff. Kérper bei den Embryonen der Frische und
Kréten. Meckel’s Arch. f. Anat. u. Phys. 1829.

Nusspaum, M. Ueber die Endigung der Wimpertrichter in der Niere der
Anuren. Zool. Anz. Bd. III. 1880.

Ueber den Bau und die Thitigkeit der Driisen. Arch. f. mikr. Anat. Bd.
XXVII._ 1886.

RatuKke, H. Bemerk. iib. mehrere Kirpertheile der Coecilia annulata. Arch. f.
Anat. u. Physiol. 1853.

ScHNEIDER, A. Ueber die Miill. Gange der Urodelen und Anuren. Centralbl.
f. d. med. Wissensch. 1876.

SELENKA, E. Der embryonale Excretionsapparat des kiemenlosen Hylodes
Martinicensis. Sitz.-ber. Ak. Berlin, 1882.

Semon, R. Ueber die morphol. Bedeutung der Urniere in ihrem Verhiltnis zur
Vorniere und Nebenniere und iiber ihre Verbindung mit dem Genital-
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SPENGEL, J. W. Das Urogenitalsystem der Amphibien. Arb. Inst. Wiirzburg.

Bad. III. 1876.

La VauerTe St. Grorce v. Die Spermatogenese bei den Amphibien. Arch. f.
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Zwitterbildung beim kleinen Wassermolch (Triton taeniatus). Loc. cit. Bd.
XLV. 1895.

WIEDERSHEIM, R. (see p. 397.) ;

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The Development of the Miillerian Duct of Amphibians. Tr. R. Soc. Edin.
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APPENDIX 475

Eimer, Tu. Unters. iiber die Eier der Reptilien. I., II. Arch. f. mikr. Anat.
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AVES.

Batrotr, F. M., and Sepawick, A. On the Existence of a Head-kidney in the
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BENEDEN, E. vay. Contrib. a la connaissance de l‘ovaire des Mammiferes. Vol. I.
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Boas, J. E. V. Zur Morphologie der Begattungsorgane der amnioten Wirbel-
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Bruxy, A. v. Die Riickbildung nicht ausgestossener Eierstockseier bei den
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Burcer, H. De Ontwikkeling van de Miiller’ sche Gang bij de Eend en de
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Dansky, J., and Kostexirscu, J. Ueber die Entwicklung der Keimblatter und
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Feirx, W. Die erste Anlage des Excretionssystems des Hiihnchens. Festschrift
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476 APPENDIX

Gasser, E. Die Entstehung der Cloakenéffnung bei Hiihnerembryonen. Arch. f.
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Das obere Ende des Wolffschen Ganges. Sitz-ber. der Gesellsch. zur. Be-
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Kowatevski, R. Die Bildung der Urogenitalanlage bei Hiihnerembryonen.
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Miter, Jou. Erectile minnliche Geschlechtsorgane der straussenartigen Vogel,
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Arnpt, R. Beitr. z. Anat. und Entwickl.-Geschichte des Ruthenknochens.
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BuaNcHARD. Etudes sur la stéatopygie et le tablier des femmes Boschimanes.
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Carraneo, G. Sugli organi riproduttori femminili dell’ Halmaturus Benetti
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‘APPENDIX 477

Ecu, Tx. Beitr. z. Anatomie und Entwicklung der Geschlechts-Organe. I.
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On some points in the Anatomy of the Urogenital Organs in Females of
certain species of Kangaroos, Part I., P. Linn. Soc. N. 8. W. Vol. VII.
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GitpERT, Tu. Das Os priapi der Siuger. Morph. Jahrb. Bd. VIII. 1892.

Haacks, W. Meine Entdeckung des Eierlegens der Echidna hystrix. Zool.
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Hasse, C. Die Wanderung des menschl. Eies. Zeitschr. f. Geburtshilfe und
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Haycrart, J. B. The development of the Kidney in the Rabbit. Internat.
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Hensen, V. Beobacht. iiber die Befruchtung und Entwicklung des Meer-
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JariscH, A. Ueber die Schlagadern des menschlichen Hodens. Ber. d. naturw.
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Kaprr, H. Unters. iiber das Ovarium und dessen Beziehungen zum Peritoneum.
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Karz, O. Zur Kenntnis der Bauchdecke und der mit ihr verkniipften Organe
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KerseL, F. Zur Entwicklungsgeschichte der Harnblase. Anat. Anz. VI.
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Ueber die Harnblase und die Allantois des Meerschweinchens nebst einer
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Zur Entw. Geschichte des menschl. Urogenitalapparates. Arch. Anat. 1896.

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Kuaatscu, H. Ueber den Descensus testiculorum. Morph. Jahrb. Bd. XVI.
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Kocxs (und WaAsILIEFF). Ueber die Gartner’schen Caniile beim Weib. Arch. f.
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Koéurker, A. Ueber die Entwicklung d. Graaf’schen Follikel der Saiugethiere.
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LANDWEHR. Hermann’s Physiologie (Abschnitt: Die Zeugung. Bearbeitet von
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Laneuans, P. Ueber die accessorischen Driisen der Geschlechtsorgane. Virch.
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Lataste. Sur le bouchon vaginal des Rongeurs. Zool. Anz. Jahrg. VI. 1883.
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Dorpat, 1877.

Meyer, H. Die Entwicklung der Urnieren beim Menschen. Arch. f. mikr.
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Mitier, Gerrit §., sR. On the Introitus vaginae of certain Muridae. Proc.
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Moran, H. Des transformations épithéliales de la Muqueuse du vagin de
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Mixer, P. Das Porenfeld (Area cribrosa) oder Cribrum benedictum aut. der
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Nacet, W. Ueber die Entwicklung des Urogenitalsystems des Menschen.
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Ueber die Entwicklung des Uterus und der Vagina beim Menschen. Loc.
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Ueber die Entwicklung der Urethra und des Dammes beim Menschen.
Loc. cit. Bd. XL. 1892.

478 APPENDIX

PaLapDINxo, G. Ulteriori ricerche sulla distruzione e rinnovamento continuo del
parenchima ovarico nei mammiferi, etc. (Dal Laboratorio d’Istologia e
fisiolgia generale dell’ Universita di Napoli.) Napoli, 1887. Abstract in
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Priitcer, E. Die Eierstécke der Siugethiere und des Menschen. Leipzig, 1863.

PINNER, O. Ueber den Uebertritt des Eies aus dem Ovarium in die Tube beim
Saugethiere. Arch. f. Anat. und Phys. 1880.

Poutton, E. B. The structures in connection with the Ovarium Ovum of
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RertERER, M. Ep. Note sur le développement du pénis et du squelette du
gland chez certaines rongeurs. Comptes Rendus Hebdom. des Séances
et Mémoires de la Soc. du Biol. Tome IV. 1887.

Risse, H. Die feinsten Nervenfasern und ihre Eadigungen im Ovarium der
Saugethiere und des Menschen. Anat. Anz. VI. Jahrg. 1891.

Roginsox, A. On the Position and peritoneal Relations of the Mammalian
Ovary. Journ. Anat. and Physiol. 1887, and Stud. Owens Coll. Vol. II.
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Rotu, M. Ueber einige Urnierenreste beim Menschen. Festschrift zur Feier
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Scuvuury, H. Zur Morphologie des Ovariums. Arch. f. mikr. Anat. Bd. XIX.
1881.

SELENKA, E. Studien iiber Entwicklungsgeschichte der Thiere. 4. Heft, II.
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Srermvacu, E. Unters. z. vergl. Physiol. d. minnl Geschlechtsorgane. Arch f.
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Fatat MEMBRANES, PLACENTA, ETC.
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BearpD, Joun. The yolk-sac, yolk, and merocytes in Scyllium and Lepidosteus.
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BENEDEN, E. van and Junin, Cu. Recherches sur la formation des annexes
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Bumm, E. Ueber die Entwicklung des miitterlichen Kreislaufes in der mensch-
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Ueber die Entwiklung des miitterl. Blutkreislaufes in der menschl. Placenta.
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CaLpweLL, W. H. Onthe Arrangement of the Embryonic Membranes in Mar-
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The Embryology of Monotremata and Marsupalia. Phil. Trans. Vol. 178.
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Duvat, M. Le Placenta des Rongeurs. Paris, 1889-93.

Freiscumany, A. Der einheitliche Plan der Placentarbildung bei Nagethieren.
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Embryol. Untersuchungen ITI. Heft. Die Morphol. d. Placenta bei Nagern
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FromMet, R. Ueber die Entwicklung der Placenta von Myotus murinus.
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Giacomini, E. Nuovo Contributo alla migliore conoscenza degli annessi fetali nei
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GoprEt, R. Rech. sur la structure intime du Placenta du Lapin. Inaug-Diss.
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Hernrictus, G. Ueber die Entwicklung und Structur der Placenta beim Hunde.
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Hint, J. P. On the placenta of Perameles obesula. P. Linn. Soc., N.S.W. 1895.

Hint, J. P., and Martin, C. J. On a Platypus embryo from the intra-uterine
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APPENDIX 479

Hirota, 8. On the sero-amniotic connection in the chick. Journ. Coll. Sei.,
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Hormeier, M. Beitr. z. Anat. u. Entwick. d. menschl. Placenta. Zeitschr. f.
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Hverecut, A. A. W. Spolia Nemoris (includes Lemurs and Edentates). Q.
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The Placentation of the Shrew (Sorex vulgaris). Loc. cit. Vol. XXXV.
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Die Phylogenese des Amnions und die Bedeutung des Trophoblastes. Verh.
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1891.
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Japan, Vol. IV. 1890.

Osporn, H. F. The Feetal Membranes of the Marsupials. Journ. Morphol. Vol.
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Parker, T. J. Note on the fceetal membranes of Mustelus antarcticus. Tr.
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Pororr, D. Die Dottersask-Gefiisse des Huhnes. Wiesbaden, 1894.

Rogixsoy, A. The Nutritive Importance of the Yolk-Sac. Journ. Anat. and
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Ryper, J. A. The origin of the Amnion. Amer. Nat. Vol. XX. 1886. (And
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SELENKA, E. Zur Entstehung der Placenta des Menschen. Biol. Centralbl.
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Semoy, R. Entstehung u. Bedeutung der embryonalen Hiillen u. Anhangs-
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Zool. Forschungreisen in Australien u. dem Malayishen Archipel. Bd. I.
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STRAHL, H. See numerous papers on the Placenta in Arch. f. Anat. und Physiol.
and Marburger Nitzungsberichten fom Jahr, 1888, onwards.

Der Uterus post partum I. Anat. Hefte. I. Abth. Bd. TI. H. 3. 1894.
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Taraxt. Sulle condizioni uteroplacentari della vita fetale. Firenze, 1886.

TuRNER, W. Observations on the structure of the human placenta. Journ.
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Some general observations on the- placenta with special reference on the
theory of evolution. Loc. cit. Vol. XI. 1877.
Lectures on the anatomy of the placenta. Edinburgh, 1876.

Wapever, W. Bemerkungen iiber den Bau der Menschen- und Affenplacenta
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Ueber den Placentarkreislauf des Menschen. Sitz.-ber. Ak. Berlin. VI.
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Wirepersnem, R. Beitr. zur Entw.-Gesch. von Salamandra atra. Arch. f.
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Wirsoy, J. T. Description (with figures) of a_young specimen of Ornithorhyn-
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Woop-Masox, J. and Ancock, A. On the uterine villiform papille of Ptero-
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ZiruLteR, H. E. Die Entstehung des Periblastes bei der Knochenfischen. Anat.
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480 APPENDIX

-SUPRARENAL BoDIEs.

ALEXANDER, ©. Untersuchungen tiber die Nebenniere und ihre Beziehungen zum
Nervensystem. Ziegler’s Beitr. d. path. Anat. u. allg. Path. Bd. XI.
Heft 1. 1891. 8. 145-197.

Braun, M. Ueber den Bau und die Entwicklung der Nebennieren bei Reptilien.
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Bruny, A. v. Ein Beitrag zur Kenntnis des feineren Baues und der Entwick-
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Coittincr, W. E. On the so-called suprarenal bodies in Cyclostoma. Anat, Anz.
Bd. XII. 1896.

The suprarenal bodies of Fishes. Nat. Sci. Vol. X. 1897.

Dostorzwsky, A. Ein Beitrag zur mikroskop. Anatomie der Nebennieren bei
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GorrscHat, M. Ueber Nebennieren der Saugethiere, speciell iiber die des
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Ueber die Nebennieren der \Sdugethiere. Biol. Centralbl. Bd. III. 1883,
No. 18.

Structur und embryonale Entwicklung der Nebennieren bei Saiugethieren.
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JANosik. Bemerkungen tiber die Entwicklung der Nebenniere. Arch. f. mikr.
Anat. Bd. XXII. 1883.

Masamaro Inapa. Notes on the Development of the Suprarenal Bodies in the
Mouse. Journ. Coll. Sci. Japan. Vol. IV. 1891.

Mrwatcovics, v. (See p. 469.)

Mitsuxvuri. On the Development of the Suprarenal Bodies in Mammalia. Q.
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Perit, A. Recherches sur les capsules surrénales. Théses présentées a la
faculté des sciences de Paris, etc. Paris, 1896. (See also Bull. Soc. Zool.
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PraunpDLer, M. Zur Anatomie der Nebenniere. Sitz.-ber. Ak. Wien. Bd.
CI. Abth. III. 1892.

RAvger. Zur feineren Structur der Nebennieren. Inaug.-Diss. Berlin, 1881.

Srintinc, H. Zur Anatomie der Nebennieren. Virchow’s Arch. Bd. C. IX.
1887.

Vincent, SwALE. The suprarenal capsules in the lower Vertebrates. Proc.
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On the morphology and physiology of the suprarenal capsules in Fishes. Anat.
Anz, Bd. XIII. 1897.

Contribution to the Comparative Anatomy and Histology of the suprarenal
capsules. The suprarenal bodies in Fishes, and their relation to the
so-called head kidney. Tr. Zool. Soc. Vol. XIV. Part 3. 1897.

Wetpon, W. F.R. On the Head Kidney of Bdellostoma with a suggestion as to
the origin of the Suprarenal Bodies. Stud. Morph. Cam. Vol. IJ. Part 1.
1884.

On the suprarenal Bodies of Vertebrata. Q. Journ. Micr. Sci. 1885.

ZanvER, R. Ueber functionelle und genetische Beziehungen der Nebennieren
za andern Organen, speciell zum Grosshirn. Beitr. z. pathol. Anat. und
z. allgem. Pathol., herausgegeb. von Prof. E. Ziegler. Bd. VII. 1890.

INDEX

AMPHIOXUS :—segmentation of ovum, 5;
development of body-cavity, 8 ; inte-
gument, 16; notochord, 36; central
nervous system, 157 ; nerves, 178, 179,
189; sense-organs, 190, 197, 211;
lateral or metapleural folds, 104;
muscles, 137 ; mouth, 239 ; alimentary
canal, 257, 267; liver, 269; gills, 275 ;
blood-vessels and corpuscles, 299 ;
urinary organs, 348 ; generative organs,
359 (Compare Fig. 219)

CycLosToMES :—segmentation of ovum, 5;
integument, 16 ; vertebral column, 36 ;
skull, 72; median fins, 103; muscles,
137, 142; brain, 157; spinal nerves,
179, 189 ; sense-organs of the integu-
ment, 191, 193 ; olfactory organ, 197 ;
eye, 211 ; auditory organ, 224 ; mouth,
239; horny teeth, 241; tongue, 252 ;
thyroid, 255; alimentary canal, 257,
259, 267; liver, 271; pancreas, 272 ;
gills, 275; genital pores, 298 ; blood-
corpuscles, 300; heart, 305; veins,
322, 326 ; urinary organs, 349 ; genera-
tive organs, 359

FisuEs :—integument, 16; exoskeleton,
30; vertebral column, 37; ribs, 54;
skull, 74-81; unpaired fins, 103;
paired fins, 104; pectoral arch, 106 ;
pelvic arch, 109; free limbs, 122 ;
parietal muscles, 137 ; visceral muscles,
142; muscles of the appendages, 142;
electric organs, 146; spinal cord, 151;
brain, 159-165; spinal nerves, 179 ;
cerebral nerves, 180 ; sympathetic, 188;
sense-organs of the integument, 190-
193; olfactory organ, 198; eye, 211 ;
retina, 214; eye-muscles and eyelids,
216, 217; auditory organ, 224; rela-
tions of auditory organ with air-
bladder, 226 ; teeth, 241 ; tongue, 252 ;
thyroid, 255 ; thymus, 256 ; alimentary
canal, 257, 267; liver, 260; pancreas,

272; gills, 273, 276; air-bladder, 273,
280 ; abdominal and genital pores, 298 ;
heart and vessels, 300, 305 ; arteries,
319; veins, 302; retia mirahilia, 333 ;
lymphatic system, 333; spleen, 335 ;
nutrition of embryo, 336; urinary
organs, 300; generative organs, 360 ;
claspers, 377 ; suprarenal bodies, 385

Dipnoans :—integument, 16; exoskele-

ton, 31; vertebral column, 37; ribs,
54; skull, 81; unpaired fins, 103;
pectoral arch, 107; pelvic arch, 111 ;
free limbs, 122 ; parietal muscles, 137 ;
muscles of the appendages, 142 ; brain;
165; cerebral nerves, 180; sense-
organs of the integument, 190-193;
olfactory organ, 199; eye, 211; audi-
tory organ, 224; teeth, 243; tongue,
252; thyroid, 255; thymus, 257 ; ali-
mentary canal, 257, 267; pancreas,
272; gills, 278 ; lungs, 283, 288; ab-
dominal pore, 278 ; heart, 307 ; blood-
vessels, 319, 326 ; spleen, 335 ; urinary
organs, 352 ; generative organs, 361

AMPHIBIANS :—segmentation of ovum,

5; integument, 18; exoskeleton, 20, 33;
vertebral column,42 ; ribs,55 ; sternum,
58; episternum, 62; skull, 82, 88;
median fins, 183 ; pectoral arch, 107 ;
pelvic arch, 111; free limbs, 127 ;
parietal muscles, 137 ;_ visceral
muscles, 143; muscles of the appen-
dages, 142; spinal cord, 152; brain,
166; spinal nerves, 179; cerebral
nerves, 180); sympathetic, 189; sense-
organs of the integument, 190, 193 ;
tactile cells, 175 ; olfactory organ, 200 ;
Jacobson’s organ, 205; eye, 212;
retina, 214; eye-muscles and eyelids,
216, 217; glands of the eye, 218;
auditory organ, 226 ; teeth, 243 ; glands
of the mouth, 251 ; tongue, 253; thy-
roid, 255; thymus, 257; alimentary

II

482

canal, 257, 267 ; liver, 269; pancreas,
272; gills, 273, 279; air-tubes and
larynx, 283; lungs, 288; blood-cor-
puscles, 300 ; heart, 309 ; arteries, 319 ;
veins, 328; lymphatic system, 333;
spleen, 335; nutrition of embryo, 336 ;
urinary organs, 352 ; generative organs,
365 ; copulatory organs, 379 ; adrenals,
385

RepriLes :—segmentation of ovum, 5 ;

integument, 20; exoskeleton, 33;
vertebral column, 45; ribs, 56; ster-
num, 60; episternum, 63; skull, 88 ;
median fins, 103; pectoral arch, 108 ;
pelvic arch, 113; free limbs, 127;
parietal muscles, 138 ; visceral muscles,
144; muscles of the appendages, 142 ;
“diaphragm,” 141; spinal cord, 152 ;
brain, 167; spinal nerves, 179; cere-
bral nerves, 180; sympathetic, 189;
end-buds, 193 ; tactile cells, 195; Pa-
cinian corpuscles, 195 ; olfactory organ,
201 ; Jacobson’s organ, 207; retina,
214 ; eye-muscles and eyelids, 216, 217 ;
glands of eye, 218; auditory organ,
227; teeth, 243; glands of mouth, 251 ;
tongue, 253; thyroid, 255; thymus,
257 ; alimentary canal, 262, 267 ; liver,
269; pancreas, 272; air-tubes and
larynx, 284; lungs, 290; abdominal
pores, 298 ; heart, 313; arteries, 319 ;
veins, 328; lymphatic system, 333;
spleen, 335; urinary organs, 356;
generative organs, 368; copulatory
organs, 379 ; suprarenals, 370, 385

Birps :—segmentation of ovum, 5; inte-

gument, 20; vertebral column, 47 ;
ribs, 56 ; sternum, 60 ; episternum, 63 ;
skull, 93; pectoral arch, 109; pelvic
arch, 119; limbs, 129; parietal
muscles, 140; spinal cord, 152; brain,
172 ; cerebral nerves, 180 ; sympathetic,
189 ; tactile cells, 195; Pacinian cor-
puscles, 195; olfactory organ, 202 ;
eye, 213; retina, 214 ; eye-muscles and
eyelids, 216, 217; glands of the eye,
218; auditory organ, 227; teeth, 245 ;
glands of the mouth, 252 ; tongue, 253 ;
thyroid, 256; thymus, 257; alimen-
tary canal, 262, 267 ; liver, 269; pan-
creas, 272; air-tubes and larynx,
285; lungs and air-sacs, 291; circu-
lation in embryo, 364; heart, 315;
arteries, 319; veins, 328 ; lymphatic
system, 384; urinary organs, 356;
generative organs, 368; copulatory
organs, 380; suprarenals, 385

MAMMALS :—segmentation of ovum, 53

integument, 23 ; mammary glands, 27 ;
exoskeleton, 34 ; vertebral column, 49 ;
ribs, 57 ; sternum, 60; episternum, 63 ;

INDEX

skull, 96; median fins, 103; pectoral
arch, 109; pelvic arch, 120; limbs,
130; parietal muscles, 140; visceral
muscles, 144; muscles of appendages,
142 ; diaphragm, 141; spinal cord, 152 ;
brain, 172; spinal nerves, 179 ; cere-
bral nerves, 180; sympathetic, 189 ;
end-buds, 193; tactile cells, 195; Pa-
cinian corpuscles, 195 ; olfactory organ,
203 ; Jacobson’s organ, 207 ; eye, 214;
retina, 214; eye-muscles and eyelids,
216, 217; glands of eye, 218 ; auditory
organ, 229; histology of cochlea, 232 ;
lips, 239 ; teeth, 245 ; glands of mouth,
252 ; tongue, 255; thyroid, 256; thy-
mus, 257; alimentary canal, 263, 267 ;
liver, 269; pancreas, 272; air-tubes
and larynx, 286; lungs, 296 ; blood-
corpuscles, 300; heart, 315; arteries,
319; veins, 328; lymphatic system,
334; spleen, 335 ; tonsils, 335 ; urinary
organs, 358; generative organs, 370 ;
copulatory organs, 382; suprarenals,

385
ae

Abdominal pores, 298

Acetabular bone, 120

Acetabulum, 113-120

Achromatin, 3

Acrania, 13

Acrodont dentition, 243

Acromion, 109

Adrenals (see Suprarenals)

Air-bladder, 273, 280

Air-sacs of birds, 291

Air-tubes, 283

Alimentary canal, 235-269
appendages of, 269
mucous membrane of, 267

Allantois, 9, 259, 337

Amnion, 9, 337

Amniota, 9

Amphiccelous vertebra, 40

Anamunia, 9

Antibrachium, 126

Antlers, 100

Anus, 235

Aortic arches, 303

Aponeurosis, pulmonary, 292

Appendages, 12

Appendices auricula, 305

Apteria, 21

Avachnoid, 151

Archenteron, 5

Arches, neural and hemal, 36

Archipterygium, 196, 124

Arteries, 299—322

Artiodactyle foot, 134

Arytenoid cartilages, 283

Astragalus, 127—132

Atlas and axis of Reptiles, 46; of Birds,

48 ; of Mammals, 49, 50

INDEX

Atrial chamber of Amphioxus, 275

Auditory capsules, 68

Auditory organ, 220—234 :—development
of, 220; relations with air-bladder, 226

Auditory ossicles, 100, 231

Autostylic skulls, 75

B.

Baleen, 26

ee processes of vertebral column, 38,

Basilar plate, 67

Basipterygium, 103, 104, 110, 122—125

Bidder’s organ, 366

Bile-duct, 272

Biserial fin, 106, 123, 124

Blastoderm, 4

Blastopore, 5

Blastosphere, 4

Blastula, 4

Blood corpuscles, 299. 300

Blood vessels, 299

Bodies of vertebrie (see Centra)

Body-axis, 12

Body-cavity, 8

Bones, cartilage-, membrane-, and invest-
ing-, 70; dermal, 18, 20, 26

Bones of skull (see Skull)

Brachium, 126

Brain :—development, 149, 153; mem-
branes of, 151; general structure, 153 ;
convolutions, 154, 172; epiphysis, 154,
155; hypophysis, 154, 155; optic
vesicles, 154; pallium, 153; saccus
vasculosus, 154, 159, 160; ventricles,
156

Brain of Cyclostomi, 157; of Elasmo-
branchii and Holocephali, 159; of
Ganoidei, 162; of Teleostei, 162; of
Dipnoi, 165; of Amphibia, 166; of
Reptilia, 167; of Aves, 172; of Mam-
malia, 172

Brain-case, 67

Branchiz (see Gills)

Branchial arches, 69, 75—80, 85, 88, 93,
94, 102

Branchial basket of Cyclostomes, 73, 74

Branchial clefts, 69, 72, 236, 273

Branchiostegal membrane and rays. 79.
82

Bronchi, 281, 285, 296

Bursa Fabricii, 263

C.

Czecum, 236, 262, 266
Calcaneum, 126—133
Campanula Halleri, 212
Cannon-bone, 134
Capillaries, 300

483

Carapace, 34

Carpalia, 126—133
Carpometacarpus, 130
Carpus, 126—133
Cartilage-bones, 71
Cauda equina, 152
Cement of teeth, 240
Centra of vertebrie, 36
Central nervous system, 11, 149
Centrosome 3, 348
Cerebral flexure, 156
Cerebral nerves, 180
Cerebral vesicles, 153
Cerebro-spinal cavity, 11
Cheiropterygium, 125
Chevron bones, 46, 52
Chiasma, optic, 208
Choanez, 82
Chondrocranium, 69
Chorda dorsalis (see Notochord)
Chorion, 338

Choroid, 209

Choroid fissure, 209
Choroid ‘‘ gland,” 212
Choroid plexus, 158
Chromatin, 3

Cilia, 16

Ciliary folds, 209

Ciliary muscles, 210
Circulation (fcetal), 300
Claspers, 31, 377
Classification of Vertebrates, 13
Clavicle, 107—109

-Claws, 16, 19, 20, 21, 26, 130

Clitoris, 373, 380, 384

Cloaca, 236, 259, 262

Coccyx, 52

Cochlea, 221—232 : histology of, 233

Ceelome, 8

Colon, 236

Colostrums, 29

Columella auris, 84

Commissures of brain, 154

Conjunctiva, 210

Constriction of notochord, 39, 40, 42, 45,
47, 49.

Copulatory organs, 377

Coracoid, 107—109

Corium, 16

Cornea, 210

Corpora adiposa, 368, 370

Corpora cavernosa and corpus spongio-
sum, 382, 384

Corpus callosum, 173

Corpus luteum, 347

Corpuscles of blood, 268

Craniata, 13

Cranium, 66, 67

Cribriform plate, 99

Cricoid cartilage. 283

Crop, 262

Crus, 126

Cuboid, 132

Cutis, 16

484

D.

Decidua, 340
Dental formule, 250
Denticles, dermal, 30, 71
Dentine, 240
Dentition, milk, 245
Dermal skeleton, 30—34
Dermis, 16
Deuteroplasm, 3, 4
Development :—general, 3—12; feathers,
21; hairs, 23; teats, 28 ; dermal skele-
ton, 30; vertebral column, 34; tail of
Fishes, 41; ribs, 52; sternum, 58 ;
skull, 64—72; horns, 99; limbs,
102—106 ; muscles, 135, 142; electric
organs, 147; central nervous system,
149; brain, 153; nerves, 177, 180;
sympathetic, 188; sensory organs,
189 ; olfactory organ, 196; eye, 207;
glands of eye, 218; auditory organ,
220; alimentary canal, 235; teeth,
239; thyroid, 255; thymus, 256; ali-
mentary glands, 267—272 ; gills, 272;
air-bladder, 273 ; lungs, 281 ; air-sacs,
295; heart, 300; placenta, 337;
urinogenital organs, 341 ; suprarenals,
385
Diaphragm, 141
Digestion, intracellular, and extracellu-
lar, 267
Digits, 123—134.
Diphycercal tail, 41
Diphyodont, 241
Discoid segmentation, 5
Duct :—hepatic, 272; naso-lachrymal,
201 ; naso-palatine of Myxinoids, 198 ;
pancreatic, 272; pneumatic, 280; sali-
vary, 251, 252; urinogenital, 346.
Ductus Botalli, 312.
Cuvieri, 322
ejaculatorius, 377
endolymphaticus, 221
perilymphaticus, 232
venosus, 333
Duodenum, 236
Dura mater, 151

E.

Ear, 220—234

Echeneis, suctorial disk, 103
Ectoderm, 4

Egg-cell (see Ovum)
Electric lobes of brain, 161
Electric organs, 146, 150
Embryonic area, 8
Enamel organs, 240
End-buds, 193

Endoderm, 4

Endolymph, 222

Ensiform process. 61
Enterocceles, §

INDEX

Epiblast, 4

Epicoracoid, 109

Epidermis, 16

Epididymis, 346, 350

Epiglottis, 286

Epiphyses of vertebra, 4!)

Epiphysis cerebri, 155

Epipubis, 111. 114, 117, 118, 121

Episternum, 62—64

Eustachian aperture and tube, 87 91, 94

Exoskeleton, 30, 34

Extra-branchials, 73, 75

liye, 207—216:—glands in connection
with, 217; muscles cf, 216

Eyelids, 217

Eyes, rudimentary, 211 213

F,

Fallopian tube, 373

Fascix, 136

Fat-bodies, 368, 370

Feathers, 21

Femur, 126—131

Fenestra :—rotunda, 91, 227, 232; ovalis.
84, 226, 232

Fertilisation of ovum. 3

Fibula, 126, 131

Fibulare, 126, 133

Filum terminale, 152

Fin-rays, 103, 105, 122. 125

Fins (see Limbs)

Food-yolk, 3, 5

Foramen ovale (of heart), 317

Foramen Panizzx, 314

Fureula, 109

ts.

Gall-bladder, 272

Giartner’s duct, 375

Gastrula, 5

Generative cells, development of, 347

Generative ducts, 346

Generative organs, 359—385

Genital pores, 298

Germinal epithelium, 347

Germinal layers, 4

Germinal spot, 3

Germinal vesicle, 3

Gill-arches and clefts
arches and Clefts)

Gills, 236, 273

Gills, external, 273, 278, 279

Gills, spiracular, 278

Gizzard, 262

Glands :—Bowman’s, 204; of Bartholini
385; of claspers, 18, 378; Cowper’s,

(see Branchial

385; digestive, 267; femoral, 27:
gastric, 257, 267 ; Harderian, 217:

inguinal, 27; integumentary, 17—29 -
intermaxillary or internasal, 251:
a >

INDEX

labial, 251 ; lachrymal, 217 ; of Lieber-
kithn, 268; lingual, 251; mammary,
27; Meibomian, 219; Moll’s, 219;
nasal (external) of Birds, 203 ; of olfac-
tory mucous membrane, 201, 202 ; ovi-
ducal, 363; palatine, 251; parotid,
252; pharyngeal, 251 ; poison, 18, 251 :
preputial, 27, 385; prostate, 377;
rectal, 261; sebaceous, 27; Stenson’s,
204 ; sublingual, 252 ; sweat, 27; uni-
cellular, 217; uropygial, 21.

Glomerulus, 345

Glomus, 341

Glottis, 281

Glyptodon, exoskeleton of, 34

Gnathostomata, 73

Goblet-cells, 17

Gonads, 347

Gut, postanal, 322

Gyri, 154

Hairs, 16, 24
Head, 12
Heart, 299—319
Hemibranch, 276
Heredity, 1
Hermaphrodite structures, 365, 366, 370
Heterocercal tail, 41
Heterodont dentition, 241
Hibernating gland, 335
Holoblastic segmentation, 5
Holobranch, 276
Homocercal tail, 41
Homodont dentition, 241
Horns, 99
Humerus, 126—133
Humour, vitreous, 209
aqueous, 210
Hyaloplasm, 3
Hymen, 375
Hyoid arch, 69, 70, 75, 76, 80, 82, 85.
88, 93, 94, 102
Hyomandibular, 70, 75, 76
Hyostylic skulls, 75
Hypoblast, 4
Hypoischium, 117, 118
Hypophysis cerebri, 155
Hypural bones, 41

Ichthyopsida, 13

Ichthyopterygium, 125

Tleum, 236

Ilium, 114—120

Impregnation, 3

Incus, 100, 231

Inguinal canal, 375

Integument, 16—29; sense, organs, of, 190
Intercalary pieces of vertebra. 38

485

Intercentra, 41, 44, 45, 47, 52
Interclavicle, 63
Intermedium, 126—133
Intermuscular bones, 55
Interspinous bones, 103
Intertrabecula, 67, 74
Intervertebral discs, 46, 48, 49
Intestine, small and large, 236, 257, 262.
263
Tris, 210
Ischium, 114, 120

a

Jacobson, anastomosis of,. 186
Jacobson, organ of, 205
Jejunum, 236

K.

Karyokinesis, 3
Kidney, 340—359

L.

Labial cartilage, 73, 75
Labyrinth :—membranous, 221; bony,
222
Lachrymal glands, 217
Lacteals, 334
Lagena, 221
Lamina cribrosa, 74, 85
Lanugo, 26
Laryngeal pouches, 288
Laryngo-tracheal chamber, 283
Larynx, 281, 283
Lateral fin-folds, 103
Lateral line, sensory organs of, 191
Lens, crystalline, 209
Leucocytes, 334
Ligaments, intervertebral, 36
Limbs :—unpaired, 102; paired, 103—134
Lips, 239
Liver, 269
Lungs, 273, 281, 288
Lymph, 299, 334
Lymph-hearts, 334
sinuses, 334
vessels, 299, 333
Lymphatic glands, 267, 335
system, 333
Lymphoid substance in relation with
urinogenital organs :—of ‘Teleostei,
Ganoidei, and Dipnoi, 352, 363; of
Amphibia, 368 ; of Reptilia, 370

M.

Macula acustica, 228
Malleus, 100, 231 :
Malpighian capsule, 345
Mammalia, 14
Mammary glands, 27

486

Mammary pouch, 28

Mandibular arch, 69

Manubrium sterni, 61

Manus, 126—134

Marsupial bones, 121}

Marsupial pouch, 28, 375

Maturation, 3

Meatus, external auditory, 224

Meckel’s cartilage, 69

Mediastinum, 298

Medullary cord and groove, 149

Membrana tympani, 224

tympaniformis, 286

Membrane bones, 71

Membranous labyrinth, 221

Menisci of vertebra, 46, 48, 49

Meroblastic segmentation, 5

Mesentery, 236

Mesoblast, 4, 6

Mesoblastic somites, 8, 66

Mesoderm, 4

Mesonephric duct, 341, 346

Mesonephros, 341

Mesopterygium, 122—125

Metacarpus, 126—134

Metamerism of head and body, 33, 65, 181

Metanephric duct, 346

Metanephros, 246

Metapterygium, 110

Metatarsus, 126—134

Milk dentition, 245

Morula, 4

Mouth, 235, 239

Miillerian duct, 346

Muscular system, 135—145 :—voluntary
and involuntary, 135; integumentary
musculature, 136; facial muscles, 136 ;
muscles of the trunk, 137; of the dia-
phragm, 141; of the appendages, 142 ;
of the eyes, 181, 216; visceral muscles
—Fishes, 142; Amphibia, 143; Amni-
ota, 144; muscles of the feather sacs,
21; arrectores pili, 26; ciliary, 210,
213, 214; of iris, 210, 214; cremaster,
375; lateral, 137; papillary, 316 ;
platysma myoides, 136; stapedius, 231;
tensor tympani, 231

Myocommata, 137

Myotomes, 66, 137

N.

Nails, 26

Nares (see Nostrils),
Naso-lachrymal duct, 201
Naso-palatine duct of Cyclostomes, 74
Navicular, 133

Neck, 12

Neostoma, 155
Nephridia, 341, 346
Nephrostomes, 341, 345
Nerye-eminences, 19)
Nerve-plexuses, 179

INDEX

Nerve, lateral, 185, 187
phrenic, 14]

Nerves, cerebral, 180—188 ; olfactory,
196 ; optic, 207 ; oculomotor, trochlear,
and abducent, 184, trigeminal, 184 ;
facial, 185; auditory, 186 ; glossopharyn-
geal, 186 ; vagus, 186 ; spinal accessory,
187 ; hypoglossal, 188

Nerves, spinal, 177, 179

Nervous system, 149 ; central, 149—177 ;
peripheral, 177—189; sympathetic, 189

Neural ridge, 177

Neural tube, 9

Neurenteric canal, 151

Neuroglia, 149

Neuropore of Aiphioxus, 157

Nictitating-membrane, 217

Nose, external, 204

Nostrils, 73, 82, 197

Notochord, 5, 9, 34—49

Nucleolus, 3

Nucleus, 3

Nucleus pulposus, 49

O.

Obturator foramen, 111, 117, 119
Odontoid bone, 46
(Esophageo-cutaneous duct, 275
(Esophagus, 238, 257, 262, 263
Olfactory organ, 196—207
Olfactory scrolls, 203
Olfactory tract and bulb, 159
Omosternum, 58

Oosperm, 3

Opercular bones, 77,79
Operculum, 75

Orbital ring, 79, 91

Organ of Corti, 230

Os penis and clitoridis, 384
Ossification, 71

Osteocranium, 69

Otic bones, 78

Otoliths, 222

Ovarian follicle, 347

Ovary, 347, 359—375
Oviducal gland, 363

Oviduct, 346

Ovipositor, 360

Ovotestis, 367

Ovum, 2, 347

P.

Paeinian corpuscles, 195

Palate, 92, 94, 28s

Paleostoma, 155

Palatoquadrate, 69, 75, 76, 78

Pancreas, 272

Panniculus adiposus, 26

Parachordal and prechordal cartilages, 67
Paraphysis, 155

Parietal foramen, 85, 91, 162, 166, 171

Parietal organ, 155, 171
Parorchis, 346, 350
Parovarium, 375

Pars acetabularis, 119, 120
Patella, 132

Pecten, 213

Pectoral arch, 106

Pelvic arch, 109

Pelvic plate, 109, 111

Penis, 377, 379—384
Pericardium, 300

Perilymph, 222

Perinzeum, 375
Perissodactyle feet, 134
Peritoneal funnels, 235
Peritoneum, 235

Pes, 126—134

Phalanges, 126—134
Pharyngeal teeth of Teleosts, 81
Pharynx, 236, 273
Phosphorescent organs, 18
Physoclisti, 280

Physostomi, 280

Pia mater, 151

Pigment of skin, 18, 19, 20, 26
Pineal organ, 155, 159

Pinna of ear, 233

Pisiform bone, 128, 133
Pituitary body, 155
Pituitary space, 67

Placenta, allantoic, 9, 337--340
Placenta, umbilical, 336—338
Placoid organs, 30

Plastron, 34

Pleura, 297

Pleurocentra, 41, 44, 45
Pleurodont dentition, 243

Pleuronectide, asymmetry of head, 81

Plica semilunaris, 217
Pneumatic bones, 93, 99, 130, 295
Poison fangs, 243

Polar cells, 3

Polymastism and Polythelism, 29
Polyphyodont, 241 ;
Prehallux, 127, 128, 133
Prepollex, 128, 133

Prepubic process, 117
Prepuce, 382

Primitive steak, 6
Pro-amnion, 357

Pro-atlas, 46

Processus falciformis, 21]
Processus vermiformis, 266
Procoracoid, 107

Proctodeum, 5, 235
Promontory of sacrun, 51
Pronephric duct, 3 £1
Pronephros, 341

Pronucleus, male and female, 3
Propterygium, 122—125
Prostate, 377

Protocercal tail, 41
Protovertebre, 8, 66

INDEX

Proventriculus, 262
Pseudobranch, 278
Pterygiophores, 103, 105, 122—125
Pterygopodium, 378

Pteryl, 21

Pubis, 114—120

Pupil, 210

Pygostyle, 18

Pyloric cwca, 259

().

Quacdrate cartilage, 69

R.

Raciale, 126—133

Radii of fins, 102, 105, 122—125
Radius, 126—133
Receptaculum chyli, 334
Rectum, 236

Reproduction of tail in Lizards, 47
Respiratory organs, 273—298
Rete testis, 346

Retia mirabilia, 280, 333
Retina, 208, 214

Ribs, 11, 52—61

Ribs, abdominal, 56, 57, 58
Ribs, cranial, of Dipnoi, 82

Rudimentary limbs, 109, 121, 127,

S

Ruminant stomach, 265
S.

Sacculus, 221
Sauropsida, 14

487

129,

Scala vestibuli, tympani, and media, 232
> v Pp 2

Seales, 18, 20, 26, 30
Scapula, 107—109
Schizoccele, 8
Sclerotic, 210

plates, 213
Scrotal sacs, 375
Segmentation cavity, 4

nucleus, 3

of head, 66

of oosperm, 3, 5
semicircular canals, 221
Sense-capsules, 68

Sense organs of integument, 190—196

Sensory organs, 189—234
Septum, oblique, 202
Sesamoids, 136

Sheaths of notochord, 34

Skeletogenous layer of vertebral column,

Skin, 16
Skull, 64—102

bones of, 71, 76—102
Somatopleure, 8
Spermatozoa, 3, 348

488

Spinal cord, 149, 152

Spines, neural and heemal, 37

Spiracle, 75, 277

Spiracular cartilage, 75

Spiral valve of intestine, 257

Splanchnopleure, 8

Spleen, 335

Spongioplasm, 3

Spots, blind and yellow, of retina, 214,
216

Stapedial plate, 84

Stapes, 100, 231

Sternum, 11, 56, 58—61

Stomach, 236, 257, 262, 263

Stomodzeum, 5, 235

Stratum corneum and Malpighii, 16

Sublingua, 255 .

Sub-notochordal rod, 235

Suctorial mouth, 73, 86

Sulci, 154

Suprarenal bodies, 370, 385

Suspensorium, 70, 85, 92

Swim-bladder (see Air Bladder)

Sympathetic, 188

Symphysis pubis and ischii, 114--1v1

Symplectic, 70, 76

Syrinx, 258 -

T.

Tactile cells and corpuscles, 194
Tapetum, 212

Tarsalia, 126—133
Tarsometatarsus, 130

Tarsus, 126—133 °
Taste, organs of, 193
Teats, 28

Teeth, 74, 78, 82, 84, 92, 94, 239—250
horny, 73, 241, 248, 250
Testis, 347, 359—377
Thecodont dentition, 243
Thoracie duct, 344
Thymus, 256
Thyroid, 255
Thyroid cartilage, 286
Tibia, 126—131
Tibiale, 126—133
Tibiotarsus, 130
Tissues, 2
Tongue, 252
muscles of, 144
Tonsils, 335
Tori, 226
Trabeculw cranii, 67
Trachea, 281, 283
Triconodont tooth, 246
Tritubercular tooth, 246
Trunk, 12
Tubules of kidney, 341
Turbinals, 100, 200—203
Tusks, 250
Tympanic membrane and cavity, 86, 224
Typhlosole, 257

INDEX

U.

Ulna, 126—133
Ulnare, 126—133
Umbilical cord, 340

vesicle, 337
Uniserial fin, 122, 124
Unciform bone, 132
Uncinate processes, 56
Urachus, 340, 358
Ureter, 346
Urethra, 358
Urinary bladder, 259, 262, 354, 357, 358

of Fishes, 350

organs, 348 —359
Urinogenital organs, 340—385
Urostyle, 41, 44
Uterus, 363, 373

masculinus, 377
Utriculus, 221

Ne
Vagina, 373
Vas deferens, 346
Vasa efferentia, 346, 350
Vascular system, 299—336
Veins, 299—318, 322—333
Velum, 275
Vent, 235
Ventricles of brain, 156
Vertebral column, 9, 34-52
theory of skull, 64
Vertebrarterial canal, 50
Vesicula seminalis, 354, 363, 377
Villi of intestine, 269
of placenta, 338
Viscera, 11
Visceral arches, 66, 69, 75—85, 88, 93,
94, 102
Visceral tube, 9
Vitelline membrane, 3
Vitello-intestinal duct, 9
Vitellus, 2
Voeal cords, 283
Vocal sacs of Anura, 283

He

W.
Wolttian body, 341
duct, 346
Ns

Niphoid process, 61

Die
Yolk, 3, 4
Yolk-sac, 8

Z.
Zygantra and Zygosphenes, 47

Zygapophyses, 40, 45, 47, 48, 49
Zygomatic arch, 100

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