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THE ELASMOBRANCH FISHES

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ELASMOBRANCH FISHES

Bigs. 1-9, 1. Cephaloseyllium, the California swell shar
acanthias, 6, Torpedo (Tetronarce), the electric ra
Storer; and 7 and 9, original.)

2. Alopias, the thresher. 3. Rhinodon typicus, the whale shark, 4. Cetorhinus (Selache) maximus, the basking shark. 5. Squalus
Rhinobatis productus. 8. Myliobatis californicus, 9, Urolophus halleri. (From Garman, except figs. 3, from Bean; 2 and 4, from

fare meASMOBRANCH
Fist hs

LORAIN DAWN LE

Professor of Zoology in the University of California

ENV RS LEY OF (CALLER O RIN TA PRESS
prkieh LE oCALTREORNITA
1934

First Eprrion ISSUED JUNE, 1922
SECOND EpiITIon ISSUED APRIL, 1928
THIRD, REVISED, Epirion IssuED Marcu, 1934

CoPyYRIGHT, 1922 AND 1928
BY
J. FRANK DANIEL

SALES REPRESENTATIVES

UNIVERSITY OF CALIFORNIA PRESS

BERKELEY, CALIFORNIA

CAMBRIDGE UNIVERSITY PRESS
LONDON, ENGLAND

For orders originating in Great Britain only

PRINTED IN THE UNITED STATES OF AMERICA

PREFACE TO FIRST EDITION

Tue ELASMOBRANCH FisHeEs are, I believe, unsurpassed as material on which
to study the fundamental plan of the vertebrate body. The ease with which a
large, cartilaginous form may be dissected makes a study of its systems of
organs a relatively simple matter, and the comparative simplicity of most of
the systems shows that at least some of the present-day Elasmobranchs closely
approximate the early vertebrates.

The importance of the shark as a type for classroom study has, I think, not
been generally appreciated in this country. This has been due in part to the
difficulty of obtaining specimens in centers removed from the seaboard; in
part, it has been due to the paucity of available literature. This I say in face
of the fact that an abundant literature in practically all languages exists. I
have attempted to remedy this latter difficulty by adding to each chapter a
working bibliography.

In my studies of the Elasmobranchs I have been fortunate in having at hand
perhaps the most generalized of these fishes, Heptanchus maculatus. In addi-
tion to a study of the systems of organs in this and in other forms, I have at-
tempted to collect and unify the work done by many workers on the various
types. These combined studies I present with the hope that they will serve as
a guide for undergraduate students of college grade, and at the same time be
sufficiently inclusive to be used as a book of reference on the entire subject.

I am indebted to the Scripps Institution for Biological Research for liberal
support during five summers at La Jolla, and to the Research Board of the
University of California for a grant in the final finishing of the plates. I am
further indebted to many students who have helped me. Among them I single
out Dunean Dunning, who, as a sophomore and junior student, made many of
the most important drawings in the book.

J. FRANK DANIEL
BERKELEY, CALIFORNIA,
January 16, 1922.

PREFACE TO SECOND EDITION

IN THE SECOND EDITION of the Elasmobranch Fishes I have followed the same
plan as in the first, but I have added subject-matter and illustration which
should make this edition somewhat more complete. Especially is this true for
the chapter on the blood system to which has been added the work of Keys on
the hypobranchial arteries of Hexanchus. The findings on Hexanchus supple-
ment and add to my work on Heptanchus and make it more certain that the
blood supply to the pectoral area in primitive vertebrates was from the hypo-
branchial system, rather than from the dorsal aorta (the subclavians) as is
true for higher vertebrates. | have also included in this edition Professor
Van Wijhe’s discovery that the thymus gland in the embryo of Heptanchus
cinereus is not ductless, and I have added experimental evidence to show that
the cutaneous vessels in Elasmobranchs are true blood-vessels.

BERKELEY, CALIFORNIA, J. FRANK DANIEL
February 24, 1928.

PREFACE TO THIRD EDITION

AMONG THE CONTRIBUTIONS ADDED to the third edition of Elasmobranch Fishes
is the work of Marine on the transformation of the endostyle of Ammocoetes
into the thyroid gland of the adult Cyclostome. Other contributions made
since the publication of the second edition are on the lymphatic system by
Hoyer, on the external carotid artery by O’Donoghue, and on the ampullae of
Lorenzini by Dotterweich.

O’Donoghue has shown that the external carotid in Elasmobranchs, as in
higher types, belongs to the lower jaw, and that the artery in the orbit pre-
viously designated as the external carotid or posterior carotid is, in fact, com-
parable to the stapedial artery of mammals. Through this work we now have
a complete history of the externa! carotid artery from sharks to man.

Dotterweich has shown that the wall of an ampulla of Lorenzini is made up
of two types of cells. One of these, a large goblet or gland cell, pours its secre-
tion into the ampulla; the other type is pyramidal and has an inside hex-
agonal face which is sensory in nature. An efferent nerve supplies the gland
cell, and an afferent nerve leaves each of the sensory cells.

BERKELEY, CALIFORNIA, J. FRANK DANIEL
January 4, 1934.

[vi]

CONTENTS

Introduction .

I. EXTERNAL FORM

External Form of Heptanchus maculatus .
External Form of Elasmobranchs in General .
Transitional series
External form in its deeclopmene:
Form and position of adult fins .
External form of fin and its bearing on Ginetion
Form of fin in its beginning .
Bibliography

Il. INTEGUMENT

Integument of Heptanchus maculatus .
Modified scales :
Integument of leew obranehen in (Conerale
Gland cells
Glands of claspers E
Poison glands of sting ray .
Light organs
Placoid scales
Finer anatomy of scale
Modification of scales
Fin spine
Saw tooth .
Stine. 2 2
Gill rakers . ;
Stomodeal denticles .
Teeth as modified scales
Bibliography

III. ENDOSKELETON

Endoskeleton of Heptanchus maculatus
Axial skeleton
Skull .
Visceral skeleton
Spinal column . ;
Appendicular skeleton
Skeleton of paired fins
Skeleton of unpaired fins
Dorsal fin
Caudal fin
Anal fin. :
Endoskeleton of Hlaemobranchal in cell
Axial skeleton
Skull .
Cranium . ;
Visceral skeleton
Extravisceral arches .
Spinal column .

[vii]

26052

PAGE

26
28
28

Endoskeleton of Elasmobranchs in General—Continued PAGE

Appendicular skeleton . . . PERO, Ne re co EUS
Skeleton of paired fins and of ap Pordien Age ee s, S ag a ae aera ae cane I)
Rectoralstingskelevomey Gin. 2 eeteesh oe bey eikke) “kets cu Ce en
ectoral @irdlevee ©" sf fs ke as = eo at ek ee
Pelweranuskeleton 6) 2 02 2 <-- & ‘geek “2 cs Gy ee ee
Pelvic girdle beh lo, \bes. RG RS eee ae ee Te ee
Skeleton of unpaired fins: ws 4. <4 (ee a) fet vate gt): Je ee
Biphorraphy |="... +... USE cTRASSE AS Ge cs cto eos ee get

IV. MUSCULATURE

Musculature of Heptanchus maculatus ae oe Ee a a eel Toho)
Muscles of theeye . . 5 ae en alee ee ede Dyes 3. GY)
Buccal and pharyngeal TATO GS eR, AS Pa go ee OU
Dorsaliconstrictorse= 2. = fo ay eR ee ee oe ee
Ventraliconstrictorss # af. co eowe OR Ae, OnE
IMteTATCUALCSH. “Sue Gros ee oS ke oS: ek Gh wie toes oebl ate, a nee
Adductors . . a or eee ees EE
Ventral longitudinal meen a eee PY MeN ee ble a a Ge er
Muscles of the fins . . . eM ER oF ate Apes a an CE
Musculature of Elasmobranchs in General ja fet 2s wile, of. o- SSR SO
IMusclesvofatheteye. 49 © 2 & 202 6 ‘ew tee sul seine) eee eee
INuscles ofmvasceralvarches@ec s)he eae eee
Superficial constrictors of pharynx- . . . . .°. . . » «= . % = —etOr
Dorsal constrictors oo ee oe we Pe Ue ee vee SA cp mci OO
Ventral constrictors. . « «9. .-« « « 5 « «© % © cee uueeMenne
Deeper muscles of pharynx << : 2 «= = + 3 «+.» > oSiine Beate
Imnterarcusles. a) a0.) 242) sO le as <b "ae 3 Ox Abyeck “ete ciate ee
Adductoresareus’ ='" . 0). 6 2 © 9% «© % “lent Gh Reclame ened
Hypobranchial musculature. . . . .- » |. «© ». « .>: = % ages
Musclessoh thesncm i 50 a. eek ok el ke oe a ee eo)
Muscles:of the claspers’ < 4.) (42 gx c=. <2 gi) SOO a
Electnc/Organin Hlasmobrapchs . . . + = 5 =» +5 = + « «oj eeeeeebe
Electric organ of rays . . fod al gw ew Se eh
Finer anatomy of electric oe a Peer Ce ere acts 8 cm, TIA!

Bibliooraphy 2 2 2 8. Ss ne me ee el

V. DIGESTIVE TRACT

Digestive Tract of Heptanchus maculatus . . - 9. & % 2). =2 552) eei2d
Mesenterialistructures &°. ~. 2 9.95 (3 (0. 2 Se ep ey oe
Buccal cavity. . . a8 he US dpe Lies RR Se, De
Pharynx and associated Pomicnunes seartieny at OO ae eitien ot ap <1 3G) oe ee
Oesophacusij te & gc yw fer Su Oe ae hoes 2 pd. 2 Re es
Stomach: 6 505, 2. % “Soe. s oe Go, bao’ ae ogy ce ce eee ees

Spleen... te Pe Oe eS a) lee
Duodenum or TArddle ateetine! Se Re Eee RS a er
Walvularintestine: os alse ats 4». Hie te Su Sl SRS 2 et
@olon .and:rectums, .. »95 in 6. ee ade be ae oe ee es

Rectaleland: soo: 0. (iMedia ee Se ee ee Ge |

Cloaca . . #2508), Us eee Gaia 4. Seo

Abdominal pores (Pani Bodonsinalesye. VO ee Ae UR AS Oo ae ee 2G

Digestive Tract of Elasmobranchsin General . . . . . . . . . . . . ‘7
WMesentenes; =. vo. os es Shas oe ca eee ees Gis cen te ET
Buccalicavity: Glen v8 oe 2) ee Ge Sos “Seo ee ky Eh ae ees

Teeth . . Nice spn che ce Oe ee “Se

Replacement of aenih tae Ae Oe we Ge & 1s. Oe st

[viii]

Digestive Tract of Elasmobranchs in General—Continued
Pharynx
Oesophagus
Stomach .
Duodenum or sabes inpeetines
Liver
Pancreas
Spleen
Valvular calestinel
Colon and rectum
Cloaca
Abdominal pores
Bibliography

VI. RESPIRATORY TRACT

Respiratory Tract of Heptanchus maculatus .
Gill pouch or pocket
Spiracle :
Gill or holobranch
Gill supports
Gill filaments .
Respiratory Tract of Bileria beaniehian in H@eneral

Gill pouch or pocket ae oe a Le ae a:

Production of respiratory eareent ;

Direction of respiratory current

Circulation of blood in filaments

Respiration or the exchange of gases .
Bibliography

VII. CIRCULATORY SYSTEM

Circulatory System of Heptanchus maculatus

Arteries

Ventral aorta .
Afferent arteries of fhe aaale
Efferent-collectors

Branches of the efferent- pollectors
Hypobranchial arteries
Efferent arteries

Dorsal aorta :
Arterial supply to Aieeetice Peet
Coeliac axis and its branches a:
Superior (anterior) mesenteric and its ranches
Inferior (posterior) mesenteric artery
Arterial supply to extremities
Arterial supply to deeper structures

Caudal aorta

Circulatory System of ema branehan in General

Heart

Arteries :

Ventral or pecodding norte
Afferent arteries of adult

Capillaries :
Efferent-collectors .

Branches of efferent-collectors .
Hypobranchial arteries
Arterial supply to head
Efferent arteries

[ix]

Circulatory System of Elasmobranchs in General—Continued
Arterial supply to trunk
Dorsal aorta
Unpaired arteries . :
Coeliac axis and its pennehen!
Superior mesenteric artery
Inferior mesenteric artery
Paired branches of aorta
Subclavians and iliaes .
Segmentals
Caudal segmentals .
Bibliography

VIII. CIRCULATORY SYSTEM (Continued)

Circulatory System of Heptanchus maculatus
Veins
Veins of head
Veins of tail :
Veins from kidney or mesonephros
Veins from digestive tract
Veins of body wall
Veins of skin :
Circulatory System of lasmrbr enc Halt in General
Veins
Anterior cardinal sy vatenn.
Renal portal system
Posterior cardinal veins .
Hepatic portal system
Development of hepatic portals sy en
Lateral abdominal system of veins
Veins of heart
Cutaneous system of veins 3
Nature of cutaneous system of “akalls
Lymphatic vessels
Bibliography

IX. NERVOUS SYSTEM

Nervous System of Heptanchus maculatus
Central nervous system
Brain .
Spinal cord :
Peripheral nervous system .
Cranial nerves .
Occipitospinal nerves .
Spinal nerves
Nervous System of Blaamapeancht in General
Development of central nervous system
Gross form of brain
Internal view of brain
Spinal cord . : :
Peripheral nervous system: .
Cranial nerves .
Spinal nerves :
Sympathetic or paearoaue nervous sy efor :
Bibliography

[x]

PAGE

. 186
. 186
. 186
. 186
. 188
. 190
AOL
. “181
. 192
. 198
. 195

. 198
198
. 198
. 199
. 200
. 200
. 202
. 202
. 204
. 204
. 204
. 208
. 209
. 210
4
. 213
. 215
. 216
. 217
. 218
= 2D

. 221
. 221
. 221
. 222
. 222
. 223
. 227
_ 227
. 229
. 230
. 230
. 235
. 237
. 238
. 238
. 246
. 247
. 249

X. SPECIAL SENSES

Special Senses of Heptanchus maculatus
Olfactory organ
Eye .
Ear ;

Innervation
Sensory canal system .

Special Senses of Bilge opranched in General :
Olfactory organ ;

Development of plnrctory, organ

Gustatory or taste organs .
Elasmobranch eye.
Structure of adult eye

Finer structure of retina .
Development of eye .

Accommodation apparatus
Auditory organ

Innervation of ear .

Development of ear :
Sensory canal system and patil pnd nie organs .
Sensory canal system

Function of sensory canal sy er :
Ampullary organs
Pit organs

Bibliography

XI. UROGENITAL SYSTEM

Urogenital System of Heptanchus maculatus
Urinary system
Genital system
Urogenital System of Dlesaweandiet in nG@encrals
Urinary system
Kidney (Mesonephr MS
Ducts of kidney
Finer anatomy of kidney
Nephrostome and segmental duct .
Semen of nephrostome and segmental aus
Bowman’s capsules
Genital system
Genital organs of male
Testes
Finer anatomy of He
Vasa efferentia . :
Genital organs of Females
Ovaries
Oviducts
Shell glands
Types of egg shells
Uterus
Relation of meron ae Smee
Secondary sexual characters
Bibliography
Index

[xi]

PAGE

. 258
. 258
. 258

258

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. 264
. 264
. 265
. 265
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. 267
. 268
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. 279
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280
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. 309
poll
. 319

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INTRODUCTION

HERE LIVES today a vast group of fishes, some of which are littoral, keep-
ing close to shore; others are the nomads of the ocean, roaming vast ex-
panses of its waters; others there are which are pelagic, living near its
surface; and still others that are the inhabitants of the profound depths into
which sunlight never penetrates—these are the sharks, to the man with nets the
most worthless, to the naturalist among the most interesting of living things.

But the vast numbers of today are few in comparison with the hordes which
have lived and passed in succession before them. They, the rulers of the waters
in bygone ages, have gone down like primitive man, leaving little to tell of
their presence. This little, however, is of singular interest. Some of these fishes
are known to us only by a spine. Others are represented by bits of armament
which show that many of the ancient sharks were clad in a protective covering
far more complex than that possessed by any of the living forms. But most of
these fishes are known to us by their teeth; of these, the heterodont sharks are
most instructive.

Before me are the teeth of a form which swam the primitive seas before the
formation of our western mountains. Beside them I place the teeth of another
which was taken with hook and line in the Pacific but yesterday. The vast
stretch of years separating the life of the one from the life of the other is be-
yond the comprehension of man, yet the close similarity of plan binding the
one form to the other clearly indicates that this of the present is that of the
past projected through the ages.

Not upon fragments alone does our information concerning these ancient
fishes rest. Within the past few decades our knowledge has been greatly en-
riched by the discovery of specimens, many parts of which were in an almost
perfect state of preservation. This preservation is the more wonderful when it
is recalled that even the harder cartilaginous parts are subject to rapid decay.
That some of these specimens have escaped the ravages of time makes us hope-
ful that others of still more archaic forms will yet be unearthed, to complete
our records of the ancient history of this group.

Of the extinct types discovered in an excellent state of preservation, Clado-
selachus (fig. 10), described by Dean, is one of the oldest and in many ways
one of the most generalized and interesting of fishes. From it we have learned
much; for even to detail, soft parts like muscle fibers and, in some specimens,
visceral organs have been obtained in a remarkable state of preservation. Two
other forms, Acanthodes and Pleuracanthus, are of special interest. In an
acanthodian type like Climatius(?) (fig. 11) spines have been developed to an
unusual degree so that even in the paired fins the fin is composed essentially
of web and anterior supporting spine. In this type the spine is essentially a
dermal structure encasing the exposed margin of the fins. In other regions of
the body the scales show the same tendency toward hypertrophy. Thus around
the eye and along the lateral line they are of unusual size. In Plewracanthus,

L1]

2 THE ELASMOBRANCH FISHES

there are many of the present-day characteristics peculiar to the sharks. In
addition, by the structure of its limbs and tail, it suggests relationship to the
interesting group of Dipnoans or lungfishes.

Equally as interesting as the extinct forms preserved to us in the rocks are
others, less ancient though they be, which have come down to us in flesh and
blood. Of these living representatives of the past some are among the most

; Wy
Le Ky
ty)
Ne a \\
Uw \ \
NN

Fig. 10. Cladoselachus. (From Dean.)

interesting and instructive of forms, interesting as antiquities are interesting,
instructive as all generalizations are instructive. Among these forms known to
us on the California coast are Heterodontus francisci (fig. 17), whose genus is
the sole survivor of a group, twenty-five genera of which are buried in the
rocks; and Hexanchus corinus and Heptanchus maculatus (fig. 13), the latter

Fig. 11. Climatius(?). (From Dean.)

with generalization of bodily plan surpassing that of any other present-day
Elasmobranch.

In addition to the ancient types there are many modern forms. Some of
them, like Acanthias (fig. 5, Squalus acanthias), have system upon system so
generalized as to approximate a ground plan on which nature has built up its
masterpieces of vertebrate life. Other forms, although simple in part, are
noted for extreme specialization in certain respects. Among these may be men-
tioned Cephaloscyllium, the California swell shark (fig. 1), Zygaena, the
hammer-head common to many seas, and Alopias, the thresher, a single genus
of world-wide distribution (fig. 2).

Still others of the recent sharks, although exceeding Zygaena and Alopias
but slightly in size, are singled out as large sharks. Of this group the forms
known to occur on the Pacifie Coast are Carcharias (Prionace), the “man-

THE ELASMOBRANCH FISHES 3

eater,” or great blue shark (fig. 16), and Cetorhinus, the basking shark (fig. 4),
which not infrequently exceeds twenty-five feet in length. Finally, as an occa-
sional visitor up this coast may be added the giant of all fishes, Rhinodon
typicus (fig. 3), specimens of which have been known to reach fifty feet in
length.

To the above recent Elasmobranchs may be added the flattened sharks or
rays. Some of the most singular of these are Pristis the sawfish (fig. 19) with
nose prolonged into a two-edged saw, and Myliobatis the batfish (fig. 8) ;
Torpedo the electric ray (fig. 6) provided with a powerful battery by means
of which shocks of electricity may be administered to food or enemy alike; and
lastly, Cephaloptera, the giant of the ray tribe, growing in tropical seas to
more than a thousand pounds in weight and sometimes having a measurement
from tip to tip of pectorals exceeding twenty feet.

Of the whole group of Elasmobranchs possibly none is of more interest than
the remaining notidanid sharks (Heptanchus and Hexanchus). Because of the
generalization found in these forms I propose in the following discussion of
the Elasmobranch fishes to use Heptanchus maculatus* (fig. 13) asa type with
which to compare in general other Elasmobranchs.

* This shark is variously known as Notorhynchus maculatus Ayres (1855), Heptanchus
maculatus Girard (1858), or Heptranchias maculatus Gill (1861). After making a detailed
study of this form and noting the marked differences between it and Heptanchus cinereus I
am almost persuaded that it merits the generic position ascribed to it by Ayers. Because of

the simple meaning of the word Heptanchus, however, and regardless of whether the etymol-
ogy of the word is or is not correct, I have retained the name given by Girard.

4 THE ELASMOBRANCH FISHES

Fig. 12

Fig. 14

Fig. 12. Heptanchus cinereus. (From Fitzinger.)
Fig. 13. Heptanchus maculatus. (C. G. Potter, del.)

Fig. 14. Heptanchus indicus. (From Macdonald and Barron.)

EXTERNAL FORM
EXTERNAL FORM OF HEPTANCHUS MACULATUS

Heptanchus maculatus (fig. 13), in general shape, lacks the grace character-
istic of many of the more active and predacious sharks. This is due in part to
a relatively heavy head; in part it results from the unusual dimensions of the
tail. In these features all heptanchid sharks (figs. 12 to 14) are similar. In
Hezxanchus, a close relative of Heptanchus, the body is still more ungainly.
This is readily apparent when a specimen is brought to shore, for on land the
body and head are so heavy that they flatten out and become distorted. Not-
withstanding this lack of grace in the heptanchid sharks, I agree with Dean
(1895) that “Heptanchus, of all living sharks, inherits possibly to the greatest
extent the features of its remote ancestors.”

The most superficial feature by which Heptanchus may be recognized is
the number of its gill clefts (cl., fig. 15). In fact it was from this characteristic
that Heptanchus received its name.' Anteriorly the clefts are of large size, but
posteriorly they decrease so that the last, which lies just in front of the pec-
toral fin, is about half the height of the first. Anterior to the first cleft and
somewhat dorsally is the modified cleft or spiracle (sp., fig. 15) which in the
adult is relatively diminutive in size.

Other superficial characteristics helpful in distinguishing Heptanchus from
most other sharks are the position of the nasal apertures and the shape of the
mouth. The nasal apertures are more nearly terminal than is usual in the
Elasmobranchs. They appear on the broad snout as relatively small crescents,
each of which is separated into a dorsal and a ventral part by an overlapping
median flap. This flap in fact forms of the nasal cup a tube which provides a
passageway for the water current over the olfactory organ. The mouth is of
unusual size (figs. 15 and 119). In side view it appears as a deep horizontal slit
extending back as far as the segment of the spiracle, and hence cleaving the
anterior region almost into dorsal and ventral halves. From this type of cleav-
age there results an exceptionally heavy lower jaw which gives to this form
much of its grotesque appearance.

At the side of the head is the eye, which has an orbit of relatively long hori-
zontal axis. The eye is shielded by an upper and a lower membranous lid, but it
is unprovided with the so-called nictitating membrane or third eyelid charac-
teristic of some of the Elasmobranchs.

This shark also possesses, in common with other Elasmobranchs, the small
apertures of the endolymphatic ducts which lead to the ear (see p. 42, fig. 45,
e.d.). These apertures are near the middorsal line and slightly in front of a
plane taken through the spiracles.

lérra, seven; dyxw, with reference to compressed gill clefts.

[5]

6 THE ELASMOBRANCH FISHES

The paired fins of Heptanchus partake shghtly of the enlargement charac-
teristic of the forward part of the body; the pectorals (pt., fig. 15) are large,
but the pelvies (ventrals, pl.) are much smaller. When considered in relation
to other parts of the body the pectoral and pelvic fins appear close together
but the distance between the two is considerable, the pelvie girdle being in the
region of the fortieth spinal segment. The inner margin of each pelvie fin of
the male is modified into a clasper, which extends backward (fig. 14). The
claspers, however, in the immature Heptanchus maculatus (see p. 288, fig.
2518, cls.) are small and inconspicuous. Between the inner margins of the
pelvic fins and back of their bases is the cloacal opening through which prod-
ucts of excretion as well as the sex cells leave the body.

Fig. 15. Lateral view, Heptanchus maculatus.

al., anal fin; cc., supracranial canal; cl., branchial clefts; dl., dorsal fin; hme., hyomandib-
ular canal; ioc., infraorbital canal; /l., lateral line; pl., pelvic fin; pt., pectoral fin; soc.,
supraorbital canal; sp., spiracle; v.l., ventral lobe of caudal fin.

One of the most marked characteristics of Heptanchus is a single, unpaired
dorsal fin (dl., fig. 15). It is from this shapely fin that we get the term noti-
danus (vérov, the back; isavés, comely ). The notidanids include both the heptan-
chid and hexanchid sharks. So far as this character is concerned it applies
equally as well to Chlamydoselachus.

In Heptanchus this dorsal fin lies above and slightly back of the pelvies,
having a position as far posterior as that occupied by the second dorsal of
many Elasmobranchs. The immense size of the caudal fin is due to the unusual
extent of its lobes and to the width of the ventral lobe (v.l., fig. 15). In the
ventral lobe the anterior dermal fin rays are especially well developed. These
fin rays are followed by a shorter series back to a notch near the terminus of
the lobe, behind which the dermal rays are again longer and extend in an
almost horizontal direction to the tip of the tail. Between the ventral lobe and
the cloacal opening is the smaller anal fin (al.).

The ground plan of coloration in Heptanchus maculatus (fig. 13) is an al-
most uniform drab above and light below. Scattered over the drab background
is a motley pattern of spots from which comes the specific name, maculatus,
spotted. These spots extend over the dorsal side of the paired fins and to the
unpaired fins, and vary in size from minute dots to clumps of pigment larger
than the pupil of the eye. Over the dorsal region of the body, where the pig-
ment is most dense, they are less conspicuous; as growth proceeds many of
them become hidden in the general color pattern.

THE ELASMOBRANCH FISHES

Overlying the coat of drab and the pattern of dots there is, in an adult, an
armament of denticles, the so-called placoid seales, myriads of which go to
make up the protective shagreen exoskeleton (see p. 24, fig.27). This armament
in the adult Heptanchus is made up of a vast number of closely set scales,
many of which are more or less spade-shaped. In the more exposed parts of
the body, however, which are subject to great wear, the scales often become
modified and plate-like.

Another characteristic made out in external view is the lateral line (Jl.,
fig. 15). In Heptanchus, this line is an open groove extending from the end of
the tail along the side of the body to the pharyngeal region. This groove is con-
nected with certain canals of the head, which, as closed tubes, are located
deeper in the integument. Branching from the canals are small chimney-like
tubes which retain connection with the surface by pores.

In the walls of this system of grooves and canals are groups of sense organs
which we shall consider more fully in Chapter X.

In addition to these lines of pores there are other aggregates of pores (for
example, p. 260, fig. 2274, soa.) in the region of the head, and pits which are
located along the dorsal and anterior parts of the trunk. Each of these pores
is the entrance to a tube which leads to an enlargement or ampulla of Loren-
zini. The tubes are filled with a jelly-like mucus which, if pressure be put on
the skin, may be made to exude from the pores. It is from this content that the
pores of the ampullae of Lorenzini and those of the canal system are known
as mucous pores.

8 THE ELASMOBRANCH FISHES

EXTERNAL FORM OF ELASMOBRANCHS IN GENERAL

A comparison of the adult in two types like Acanthvas, the spiny dogfish, and
Urolophus, the small sting ray (figs. 5 and 9), shows the two extremes of body
form to which the Elasmobranch fishes have diverged. In Acanthias, which is
beautifully adapted for cleaving the water in the running down and eapture

Fig. 16. Carcharias glaucus. (From Garman. )

of prey, the head is pointed, and the rounded body tapers gracefully into
a powerful organ of locomotion, the caudal fin; while in Urolophus, which
spends much of its time on the bottom, the head and body are depressed, carry-
ing the branchial clefts to a ventral position, and the pectoral fins, extending

Fig. 17. Heterodontus franciset.

from the pelvic fins behind to the tip of the nose in front, have become the
organs of effective locomotion.

It is by differences like these that the Elasmobranch fishes have been sepa-
rated into two general groups (suborders). One of these, the Selachi, contains

Fig. 18. Squatina californica.

the sharks; the other, the Batoidei, includes the rays. While this distinction
between the Selachii and the Batoidei is of special service in separating forms
like Acanthias from those like Urolophus, yet between the two extremes there
are types which link by link bridge the intervening gap. So effectively is this

THE ELASMOBRANCH FISHES 9

accomplished that on the border line between the two the characteristies of
the one often resemble those of the other so closely that it is difficult to say
this is a shark, that a ray. This will be made the more evident upon a consid-
eration of a series of these forms.

TRANSITIONAL SERIES

In such a series, Carcharias, the “man-eater” (fig.16),may be taken as a highly
specialized type. The fusiform body, even more than that of Acanthias, is
fashioned for cleaving the water; the caudal and pectoral fins are powerful;
and the sharp pointed teeth are adapted for seizing and holding prey. In fact
every line of its structure is an index of predacious perfection. To a less extent
the same is true of Galeus. In Mustelus, although the body is highly special-
ized in this respect, the teeth, varying from the type, have generally become
broad and flattened for crushing.

Heavier of body and clearly less graceful in form is the lamnoid type,
Lamna cornubica, in which, although the teeth are long and fang-like, the
body is relatively cumbersome and the pectorals are placed farther back. The
lamnoids, however, retain their restless nature and are classed among the
more predacious of the pelagic fishes.

In Heterodontus (fig. 17) we see a still less graceful type. In it the pectorals
are expanded, suggestive of a less active nature, more given to foraging over
the ocean floor in search of a shellfish diet. Furthermore, in Heterodontus the
posterior teeth are of the crushing type adapted to such food (see p. 130,
fig. 128). Yet it is worthy of notice that the most anterior of the teeth are pre-
hensile showing that the grasping of food is possible.

Next in the series is Squatina, the angel fish (fig. 18), in which the body is
greatly flattened. Furthermore, the pectorals extend forward and the dorsal
fins have shifted to a posterior position. In all these respects Squatina is
ray-like. But the gill clefts, although covered with a flap, open laterally, and
other significant internal structures of fin and skull cling tenaciously to the
shark type.

In Pristis, the sawfish (fig. 19), the anterior part of the body is still more
flattened; but the caudal region is like that of a shark. The gill clefts of Pristis,
however, are entirely ventral in position; and more important still its pee-
torals have fused to the sides of the head so that in essential respects it has
passed over the batoid line and is clearly among the rays.

Shehtly more ray-like is Rhinobatis productus, the guitar fish (fig. 7). But
even here, although the head and body are depressed, the pectorals are rela-
tively small and the tail is still the organ of active propulsion. From this‘shark-
hike ray to others singularly flattened in form are rays in great variety.

' In the skate, Raia erinacea (fig. 20), the pectorals extend forward to the

' region of the nose, and the pelvies are large. Correlated with the greater devel-

opment of the paired fins the caudal region, including the dorsal fins, is poorly
developed, the dorsal fins having migrated still farther back on the tail. In this

——

10 THE ELASMOBRANCH FISHES

fish we see sufficient modification of form to insure a new mode of locomotion.
Here the pectorals become the effective organs in propulsion, and the tail
remains at a stage of development insufficient to propel the body. The skate is
also an organism not only singularly adapted to its method of getting food,
but equally effective in crouching on the ocean floor so as to evade its enemies.

Last in the series we may place the sting ray, Disceus thayeri (fig. 21),
which even more than Urolophus undergoes profound depression of body. In

Fig. 19

Fig. 20

Fig. 19. Pristis cuspidatum. (From Garman. )
Fig. 20. Raia erinacea. (From Garman. )

Fig. 21. Disceus thayeri. (From Garman.)

it the pectoral fins mect in front and behind so that the body is essentially
dise-shaped. Like other rays of this type its tail is provided with a serrate
sting, but unlike Urolophus the tail is whip-like and has but slight indication
of fins or folds.

EXTERNAL ForM IN Its DEVELOPMENT

The transition in external form which we have just considered in the series of
sharks and rays may be similarly followed in a series of stages in the life-
history of an individual ray. In other words, while a ray and a shark are very
dissimilar in the adult, they are much alike in their earlier development. As
growth proceeds, the ray gradually diverges from the shark-plan so that
finally a fixed gulf separates the two. To illustrate this divergence we may
again compare Acanthias and Urolophus.

THE ELASMOBRANCH FISHES alg

At an early stage there appears above the germinal dise a horseshoe-shaped
mass of tissue, the closed end of which represents the head end, and the open
end, the tail end. This mass of tissue then becomes spatulate (see p. 230,
fig. 209). In a further stage, in which the body takes on definitive form, the
two types are characteristically similar. In both, the optic vesicles stand out
as prominent structures and the gill clefts, in breaking through, occupy about
the same lateral position.

We may figure two stages (fig. 224—p) which represent the parting of the
ways. The first (A) and third (c) of these are of Acanthias; the second (B)
and fourth (p) are of Urolophus. While in Urolophus (fig. 228) the clefts still

A B C D
Fig. 22. Development of body form in Acanthias and Urolophus.

A. Stage in development of Squalus acanthias. (Length 20.6 mm.) (From Scammon.)
B. Stage in development of Urolophus halleri. (Length 22 mm.) (C. G. Potter, del.)

C. Older stage in development of Squalus acanthias. (Length 28 mm.) (From Seammon. )
D. Older stage in development of Urolophus halleri. (Length 38 mm.) (C. G. Potter, del.)

open on the sides, other changes are taking place which immediately charac-
terize it as a ray. The most notable of these changes is the extension of the
pectoral fin.

In the figures of Acanthias (c) and of Urolophus (dD) both assume essen-
tially the features of the adult. While Acanthias retains its slender form,
Urolophus becomes greatly flattened, the disc-shape being the result largely
of the growth of the pectoral fins. Each pectoral now takes the shape of a
battle-axe, the blade of which extends outward. The posterior point of the
blade projects toward the pelvic fin, while the anterior point extends over the
branchial region. As the fin broadens, its anterior tip meets the growing antor-

12 THE ELASMOBRANCH FISHES

bital process and both anterior and posterior projections of the pectoral come
in contact with, and fuse to the sides of the head and body. The fusion of the
forward part thus profoundly modifies the branchial area, and the clefts take
up a ventral position. As growth continues, the forward extensions of right
and left pectorals meet in front, completing the dise of the adult body.

ForRM AND PosITION OF ADULT FINS

It was observed above that a determining factor in the external shape as a
whole is the form and position of the fins. The pectorals are of first importance
in such a determination. In fact sharks and rays could be separated with cer-
tainty by the character of the pectoral fin alone. In general the pectorals of
the sharks are relatively small, while those in the rays are large. But a point
of greater importance is the secondary fusion which, as we have just seen, the
pectorals of the rays make with the head during developmental stages. Border
types, like Squatina and Rhinobatis, which could not be separated by relative
size of fins alone, could be distinguished with certainty by the presence or lack
of such fusion.

The caudal fin, although of less value than the pectoral, may also be a deter-
mining factor in external form. The axis of the caudal in the sharks, although
compressed, is more or less fleshy and the lobes of the fin both dorsally and
ventrally are well developed. In adult and specialized rays, on the contrary,
the entire tail may be in a more or less complete state of atrophy. In the skate
(fig. 20), as an example, it is a long fleshy rod; in Myliobatis, although it may
reach an extreme length, it is slender and whip-like (fig. 8); and in Ptero-
platea it never develops beyond the rudimentary stage. In transitional types
of rays, however, especially among the Pristidae and Rhinobatidae, the axis of
the tail is muscular, and the lobes of the caudal fin are pronounced structures,
although they are less well developed than are those, say, of Squatina (fig. 18).

Among the other fins the dorsals, which are usually? correlated with the size
of the tail, are more poorly developed in the rays than in the sharks. Further-
more, these fins in the rays, if present, generally take up a position relatively
far posterior to the anal segment. Myliobatis as a type is exceptional in that
the single dorsal fin takes a position just anterior to the sting. In the skates the
dorsals are far out toward the tip of the tail. In fact, in some of the rays they
may not inaptly be said to have migrated practically off of the end of the tail.
An anal fin is always lacking in the rays; hence this would be of definitive
value were it not wanting in a few of the sharks such as the Spinacidae and
the Rhinidae.

EXTERNAL ForRM OF FIN AND ITS BEARING ON FUNCTION

If the pectoral fin be of sufficient extent it may perform the function of pro-
pulsion. But in the sharks propulsion is brought about largely by the caudal
fin. Two general types of locomotion may be described for the Elasmobranchs.

2 Excepting in the second dorsal of Lamna, Alopias, ete.

THE ELASMOBRANCH FISHES 13

In one, forward movement is produced principally by the pectorals; in the
other this function is performed chiefly by the caudal fin or tail. One of these
types of locomotion we may therefore designate as pectoral, the other as

caudal. Pectoral locomotion among the Elasmo-

a branchs is confined to the rays while the caudal
type, so far as I know, is universal among the
a sharks. It is, however, by no means peculiar to
them, since, as we have indicated, some trans1-

LR a tional rays retain this method of swimming.

To illustrate pectoral locomotion Urolophus

Qo may first be considered. In Urolophus progres-

sion is brought about by a synchronous wave

= movement in both pectorals. This wave begins

at the anterior margin of the fin and passes

<fAs = backward, terminating at the posterior margin;

thereupon another wave sets in and repeats this

0 action. In the skate pectoral locomotion may be
seen to excellent advantage. In it (fig. 234), as
ul — — in Urolophus, there is a wave motion which in-

volves not only the margin, but also the greater

5 width of the fin, throwing the pectoral into an
i inverted U with the sharper convexity directed

: ; ; forward. As this wave passes backward (1-9) it
Fig. 234. Diagram to illustrate eee : :
the different phases (1-9) of gains In size and evident momentum, serving as
pectoral locomotion in the skate. an effective pushing surface against the water.
(From Marey. ) : :
From this type of wave movement a beautiful
gliding motion results. A further modification of the type is present in Cephal-
optera, in which the stroke of right and left pectorals takes place alternately.
Transitional rays are instructive 1
in that they have not yet attained
the method of pectoral locomotion
although the pectorals are well de-
veloped. In Rhinobatis these fins
may be put to considerable use other
than in directing the course, as may
9

be seen EBON grasping the tail and Fig. 238. Diagram to illustrate the different
attempting to pull the fish out of the phases (1-9) of caudal locomotion in the

water. shark, Seyllium. (From Marey. )

In the sharks, in which caudal locomotion is employed, the body itself is
thrown into undulations which also provide concave surfaces with which to
push against the water (fig. 238). The wave here begins in the body just back
of the pectoral fins (1) and passes posteriorly and off at the tip of the tail (9),
and another undulation thereupon begins and repeats the course. At the same
time and with the greatest effect the dorsal and ventral lobes of the caudal fin
are directed by the strong muscles as a potent sculling organ.

14 THE ELASMOBRANCH FISHES

We have thus far spoken only of the fins which are propelling. In a type like
Myliobatis (fig. 8), direction of the course is effected through the paired fins.
In Urolophus (fig. 9) the horizontal course is also directed by the pectorals,
but the vertical direction is controlled in large part by the caudal which is
used effectively as a rudder.

In the sharks other fins are of service in directing the course. The use of the
directive fins may made out by a series of experiments. If a rubber band is
put over the pectorals of a young shark with the caudal fin free, there results
a downward swimming of the fish, the pectorals functioning as organs for
directing the horizontal course in the water. In function the pelvies are acces-

Fig. 24. Embryo of Scyllium canicula showing early epidermal fin-folds. (From Mayer.)

al., anal fin; df., dorsal fin-fold; dl., second dorsal fin; pl., pelvie fin; pt., pectoral fin;
v.l., ventral fin-fold.

sory to the pectorals. Both the dorsals and the anal may be bound down with-
out interfering seriously with propulsion. These fins are of service, however,
in keeping the fish in a vertical plane.

FORM OF FIN IN ITS BEGINNING

It is evident that the form of the fin in present-day Elasmobranchs differs
from that of the ancestral type. And the question arises, What was the form of
the ancestral fin? To this inquiry many answers have been given, few of which
have gained a hearing. We may mention briefly two of the best known theories
for the origin of the paired fins. One is the lateral fin-fold theory of Balfour
and Thacher; the other is the gill-arch theory of Gegenbaur.

According to the fin-fold theory the ancestors of the present-day fishes are
supposed to have possessed a median dorsal fold (df., fig. 24) which was con-
tinued over the tail as the dorsal lobe of the caudal fin and then forward to the
anal region as the ventral lobe. (v.l.) ; anterior to the anal region the ventral
lobe separated into right and left lateral folds not greatly unlike the meta-
pleural folds of Amphiorus. In certain regions of the dorsal and the lateral
folds greater development ensued than at the interspaces. These parts of the
fin-fold hence increased in size and became the present unpaired and paired
fins, while the intermediate parts finally dropped out.

The gill-arch theory of Gegenbaur holds that the framework of the girdles
for the paired fins and of the fins themselves have been derived from the gill
arches (g.a., fig. 25) and their attached branchial rays (b.r.). The arch itself
represents the girdle and the formation of the skeleton of the fin proper was

THE ELASMOBRANCH FISHES 15

understood to have resulted from a fusion of the branchial rays at their bases
into a main axis which by extension drew out the adjoining rays so that they
arose from this main axis (A-C).

When we consider that the pectoral girdle in form and position is much like
a gill arch (see p. 49, fig. 54), and that the fin rays may be arranged both pre-
and postaxially, Gegenbaur’s theory appeals to us with much foree. The appli-
cation of the theory to the pelvie fin is more difficult, however, for the fin is
assumed to have reached its present position by migrating from the branchial
region. This assumption strikes one as far-fetched. Indeed, Dean (19026) has
studied the problem of migration of the fins and concluded for Heterodontus,
at least, that there is no evidence of migration.

= “Willige Za
SS WASSSSS EEN

WZ ee mK WM in,

A B C D

Fig. 25. Diagram A—D illustrating the gill-arch theory of Gegenbaur for the origin of paired
fins. b.r., branchial ray; g.a., gill arch.

Further objections have been offered against the gill-arch theory. If the
skeleton of the pectoral fin arose from the branchial rays of a single arch
doubtless it at first occupied a dorsoventral position, a position disadvanta-
geous to the fin as a directing organ. Moreover, if the pectoral arose as a modi-
fied gill arch, why are there so many segments involved in the fin? Again,
paired fins both in their development and in their structure resemble in a
remarkable degree unpaired fins. But unpaired fins certainly have not arisen
as modified branchial arches. Still another objection which has been urged
against the theory is that the branchial arches lie in the walls of the digestive
tract (pharynx) and hence within the aortic arches of the blood system. The
pectoral girdle, on the contrary, is superficial to both the arteries and nerves
as is Shown by the fact that it is perforated by these as they pass out to the fin
(p. 78, fig. 844). It is therefore difficult to see how the pectoral girdle could
have reached its present position outside of blood vessels and nerves.

Evidence supporting the lateral fin-fold theory has been obtained from sev-
eral sources, It has been shown by Dean (1909), for example, that in Cladose-
lachus (see p. 2, fig. 10), one of the most ancient sharks yet discovered, the
paired fins are essentially lateral folds unconstricted at the base and with
radial supports nearly parallel. From development also comes evidence for
the lateral fin-fold theory. In a type like Scyllium (fig. 24) or Pristiurus or
Torpedo there may be in the embryo an epiblastic fold along the back and
over the tail, and in Torpedo embryonic lateral folds may extend from the
pelvic region behind to the pectoral region in front. Furthermore, Dohrn has
shown that the skeleton of the fin in Pristiurus arises as a series of parallel
radials and that the girdle at the same time arises from a fusion of the bases

16 THE ELASMOBRANCH FISHES

of the anterior radials. Similarly Balfour has demonstrated for Scyllwwm that
the pectoral girdle arises secondarily. It may also be added that the blood sys-
tem of the paired fins in a generalized type like Heptanchus and Hexanchus
can most readily be interpreted in terms of a lateral fin-fold theory (see Bib-
liography, p. 195, Daniel, 1926). Other characters of musculature and nerve
may be said to bear on this subject. To them we shall direct further attention
when we consider these systems.

THE ELASMOBRANCH FISHES 17

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, ; wi{ LIBRARY),
‘HAPTER
Zz eeam /»
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THE ELASMOBRANCH FISHES

EXTERNAL FORM

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THE ELASMOBRANCH FISHES 19

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THE ELASMOBRANCH FISHES

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DETAILED STUDY OF TYPES

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ite

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THE ELASMOBRANCH FISHES 21

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FINS AND THEIR ORIGIN
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THE ELASMOBRANCH FISHES

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THACHER (see p. 87).

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INTEGUMENT
INTEGUMENT OF HEPTANCHUS MACULATUS

One of the most characteristic structures observed in a study of the external
form is the integument, in which is located the pigment pattern and from
which project the shagreen denticles. The two layers-of the integument of a
young Heptanchus are shown in figure 26. The epidermis (e.) is relatively
thin and the dermis or corium (cr.) is considerably thicker.

The epidermis when examined in detail shows superimposed strata of cells,
the innermost layer of which, the basal or ger-
minative layer (gr.), is of a columnar nature;
while the outlying strata in which the cells are
horizontal may be designated as the superficial
layers of the epidermis. Between these two ex-
tremes are numerous intermediate cells which
are irregularly stratified. These cells arise in
development from the basal layer and pass out-
ward toward the surface, becoming more flat-
tened as they move outward.

At practically any level of the epidermis
from the deep basal layer outward to the sur-
face may be found large beaker or goblet cells
(g.c.) of a glandular nature. Each of these cells
arises as a modified cell divided off from a basal
layer cell and comes to be essentially a large sac
with the nucleus located near its base. Fig. 26. Section through the

The dermis or corium (cr.) is composed of Se or eee? Hepianchts
two more or less well defined layers in Heptan- Pet aealeerombeanc eer
chus. The first or more superficial of these is — corium or dermis; e¢., epidermis;
made up of a dense mass of irregularly ar- ners fea gM
ranged cells; the second or deeper layer is com-
posed of sparser cells which have protruding from them longer or shorter
processes, which interlace into a network of supporting tissue.

In the upper layer of the corium and between it and the epidermis are lo-
cated the pigment masses which are the causes of the color pattern. In the
adult the pigment cells are black or greyish and are distributed more or less
evenly over the back and sides, giving to the upper areas their drab hue. Over
the drab background are scattered the irregular blotches of black which are
produced by more deeply lying pigment. In the patches the cells are packed
so closely together that it is impossible to pick them out individually. Pig-
ment is absent from the integument on the ventral side, which is of a whitish,
metallie color.

[23]

24 THE ELASMOBRANCH FISHES

The scales present in the integument of a shark like Heptanchus provide a
relatively compact exoskeleton which, in a general way, serves to protect the
organism against external injury. In form the scales vary considerably de-

Fig. 27. Seale patterns, Hep-
tanchus maculatus. A. From
side of body. B. Modified
scales from margin of fin.
C. Stomodeal denticles from
roof of mouth.

pending upon their position. The first of these,
represented by figure 274, were taken from the
side of the body just above the lateral line. They
are therefore from a region which is not unduly
exposed and which may be characterized as
typical. By looking from the lower left- to the
upper right-hand corner it will be observed
that the scales are arranged more or less in
oblique rows. The same is true, although less
evident, if they be observed from the lower
right- to the upper left-hand corner of the
figure. If a larger piece of the integument be
drawn and lines be ruled through the rows of
scales, the lines will form a series of rhomboids,
producing the diamond-shaped pattern. In such
a pattern each scale normally points backward
and is attached anteriorly and centrally.

The details of a single scale have been figured
by Steinhard (1903) for Heptanchus cinereus
(fig. 28). Here an anterior arm (a.a.) is well
imbedded in the integument and a posterior
spine (sp.') projects more or less sharply up-
ward and backward. Two lateral arms appear
(l.a.) which, as a rule, curve more or less up-
ward and terminate in lateral spines (sp.°).
Passing along the middorsal line from the an-
terior arm to the tip of the posterior spine is the
primary or axial crest (cr.'). Located on the
lateral arms and branching from the primary
crests are the lateral crests (cr.*). Other terti-
ary crests (cr.*) connect primary and secondary
crests, and a fourth (cr.*) arises from the sec-
ondary crests to pass laterally around the sides
of the scale. Lying deeply buried in the integu-
ment is the enlarged supporting base (ba.)
which, in general, is rhomboidal in shape and is
attached by a narrow neck or pedicel to the
main body of the scale. Into the lower substance
of the base enter strong fibers of connective
tissue which anchor the seale to the integument.

Where the base may be broad, as in the seales over any of the exposed areas,
many such supporting fibers may be present.

THE ELASMOBRANCH FISHES 20

MopIFIED SCALES

Seales located in a region that is more exposed may differ greatly from the
typical ones which we have just described. The several areas in which the
scales may become modified in Heptanchus are along the dorsal margin of the

back and especially in front of the dorsal fin,
around and in front of the eye, over the tip of the
nose and the tip of the lower jaw; in fact, over
any of the surfaces which are particularly ex-
posed as the fish swims forward. An extreme ex-
ample of modification is shown in figure 27B, the
pattern of which was taken from the anterior mar-
gin of the pectoral fin. The crests and even the
spines of the seales previously studied have here
disappeared. In fact the entire form has become
so greatly modified as to be hardly recognizable.
Instead of having the regular spade-shape they
have become enlarged nodules, the anterior and
posterior parts of which can be distinguished only
with difficulty. Not infrequently such a scale in
this exposed area reaches a size many times that
of a protected seale.

A third type may be deseribed briefly. Covering
the lining of the buceal cavity and the pharyngeal
box, excepting the posterior part of the roof, there
are numerous modified scales which are designated
as stomodeal denticles (fig. 27c). These denticles

Fig. 28. Detail of placoid
scale, Heptanchus cinereus.
(From Steinhard.)

a.a., anterior arm; ba., base
of seale; cr.’, primary crest;
cr.”, lateral crest; cr.’, tertiary
crest; cr.*, fourth crest; l.a.,
lateral arm; sp.’, posterior
spine; sp.’, lateral spine.

resemble much more closely the normal scales previously deseribed than they
do those secondarily modified. Indeed, the stomodeal denticles, occupying a
position which in the young is more protected than the normal type of seale,
are sharply differentiated into parts. This is especially noticeable in their
prominent lateral spines; in some even a second pair of laterals is present,
making five spines in all. It will be observed that the stomodeal denticles
closely resemble the lower teeth (see p. 122, fig. 121).

26 THE ELASMOBRANCH FISHES

INTEGUMENT OF ELASMOBRANCHS IN GENERAL

The description given for the layers of the integument in Heptanchus may
serve to portray conditions which are more or less general. There is, however,
in the different Elasmobranchs considerable variation in the thickness of the
integument, affecting one or both of the layers. In a type like Scymnus, for
example, the upper or epidermal layer is thinner than that of Heptanchus,
yet the corium of Heptanchus is relatively thin, so that its integument as a
whole is of medium thickness. The

EE eS thickening of the skin may be due

a aes to the addition of many cells to the

ene : °
a Waa corium as, for example, in Het-
ase i

erodontus, or it may be brought
about asin Triakis (fig.29), where
the dermal cells, particularly in
the superficial layer, are much
less compact.

Color in the Elasmobranchs
while varying considerably usu-
ally assumes a quiet hue, the bril-
hant reds or blues characteristic
of the bony fishes rarely being
present. The color may be a light
drab as in Mustelus californicus,

Fig. 29. Section of the integument of the a deep blue as in the lamnoids,
Leopard shark, Triakis semifasciatus. brown as in Torpedo (Tetronarce
b.m., basal membrane; d.p., dermal papilla; - . 3
e.0., enamel organ; g.c., goblet or gland cell; californicus), or black as in Tor-
gr., basal or germinative layer of epidermis; pedo occidentalis. It may be seat-
ll.c., lateral line canal; n., ramulus of vagus
nerve; pg., pigment; s.c., sensory column. tered over dorsum and venter
alike as in the deep-sea forms,
Spina of the Mediterranean and Ltmopterus of Formosan waters; or it may
be confined largely to the dorsum as in Galeus, Acanthias, and a host of other
types; again, it may be collected in a remarkable pattern over a drab back-
ground as is characteristic of Cheiloscyllium and the Leopard shark, of Tigri-
num and Rhinodon typicus. Whether the color be light or dark or variegated
it is produced by chromatophores, several types of which are present.

The melanophore containing black or brown melanin is usually considered
to be a connective tissue type of cell’ rhizopod in shape, and sometimes capable
of amoeboid movement. Some of these cells in Heterodontus (pg., fig. 30)
though typically rhizopod are capable of but slight change of form. Other
melanophores, smaller in size, may have numerous processes which in extreme

1 There is evidence for the belief, however, that this cell is derived from a smooth
muscle cell.

THE ELASMOBRANCH FISHES 27

occurrences exceed in length many times the diameter of the body of the cell.
From the possession of great numbers of these processes expanded into a com-
plex web, the extreme black of a form like Torpedo occidentalis results.

The golden cells or lipophores (lp., fig. 30) (Xanthophores) containing the
fatty pigment, lipochrome, are beautifully shown in the young of Heterodon-
tus. Here, with the brown melanophores, they give patches of a warm glossy
yellow of remarkable beauty. In Cephaloscyllium (fig. 1) also, multitudes of
lipophores produce the sulphur spots so characteristic of this form. In Rhino-
don (fig. 3) the lipophores associated with reddish brown melanophores form
the great orange spots or color patches.

In most of the Elasmobranchs, ex-
cepting the deep-sea types, pigment
cells are absent from the venter. The
metallic white here results from the
presence of guanin, a waste product of
metabolism, which impregnates the
cells (leucophores) ventrally as do the
pigment granules dorsally. The guanin
granules although present are not visi-
ble dorsally, for in this location they
are obscured by the melanin granules.
Ventrally they are very numerous, and
have much to do with the production ip HaULOhiem at BHC Tess oun Gere.
of the light color. Contributing also to — dontus francisci.
the formation of a light-colored venter Ip., golden cells containing granules;
is a certain concentration of tissues ? Coa ah Pap ue ADS Bs
known as argentium. In this concentra-
tion the underlying tissues, through the deposition of calcic prisms, become
so compact as to form a highly reflecting surface to which the silvery sheen
characteristic of a fresh specimen is partly due.

The function of pigment has often been thought to be the protection of the
more delicate underlying tissues against the rays of the sun. While this per-
haps holds in general, such protection from the rays of the sun would not be
necessary for those forms like Spinax or Etmopterus which inhabit the pro-
found depths into which the light of the sun never penetrates. And it is the
more singular that in such deep-sea Elasmobranchs pigmentation is not con-
fined to the dorsum but is distributed over the ventral part of the body as well.
It has been suggested that at depths at which the rays of the sun are unknown
it may still be that pigmentation is in some way correlated with light; for per-
vading even the greatest depths there is present phosphorescent light, the
source of which being diffuse would not result in pigment on the back alone
but on the sides and venter as well. But the cause of pigmentation in deep-sea
sharks is as yet not understood. It seems not improbable that the pigmentation
is correlated not so much with light as with the lower temperature.

28 THE ELASMOBRANCH FISHES

GLAND CELLS

The integumentary beaker, or gland cell, as such (g.c., fig. 29) is produced
entirely from the epidermis. In sections taken through the body of the em-
bryo at different levels it is observed that these cells are distributed over the
entire surface, with but few exceptions, like the cornea of the eye. They may
likewise be found in the integument lining the buceal cavity (g.c., fig. 26) and
the cloaca, these cavities being formed as invaginations from the surface. The
first indication of the origin of such a gland cell is seen in the enlargement of
a cell derivative of the basal layer.
This cell migrates through the inter-
mediate layers to the surface as do
the superficial cells, but instead of
becoming flattened, as do the super-
ficial cells, it becomes vesicular and
reaches an enormous size. When it
gains the surface a lumen forms,
through which the gland pours out
its product of excretion.

te GLANDS OF CLASPERS
oS Ses Ses
re ee % eve
a h gee In addition to the gland cells of
eae DF ES 4 ; ;
sae? the type just described there are in
Fig. 31. Transverse section through siphon males of the Elasmobranchs numer-
sac (s.s.), Raia circularis, to show clasper 4 ;
gland. (From Leigh-Sharpe.) ous gland cells which are derived
Og; Sy ean oe Ss area from the epidermis and which sink
lm., longitudinal muscle; p., papilla from.
gland; s.w., siphon wall. in at the base of the claspers. Such a
gland inSquatina if examined under
the microscope is seen to be essentially a series of enlarged goblet cells. In
other forms as has been shown by Leigh-Sharpe (1920-21) the gland may fill
up the siphon (Lamna) or it may be in only a part of its wall. In Rava circu-
laris (fig. 31) the gland has been compared to a date stone, bilobed in appear-
ance with a longitudinal groove running its entire length. Into the groove the
papillae open to drain the different components of the gland.

Porson GLANDS OF STING Ray

Goblet or mucous cells which in the sting ray, Urolophus, are present in great
numbers at the root of and just under the sting, form what some believe to be
a poison gland (p.gl., fig. 32). It is evident that these would secrete an abun-
dant supply of mucus which might pass along the ventral groove into the
wound made by the sting. It is doubtful, however, that this mucus is more
toxic than is the acrid mucus of other glands.

THE ELASMOBRANCH FISHES 29

LIGHT ORGANS

In deep-sea fishes, in general, gland cells have contributed to a most remark-
able specialization: that is, they have become converted into light organs or
photophores. Such organs have been found in various Selachians, principal
among which are Spinax niger, Laemargus, and Etmopterus. In Etmopterus,
Oshima (1911) has made out two types of light organs: (1) punctate, cup-
shaped organs which in the living specimen have a pearly luster; and (2)
linear, semicylindrical organs which apparently result from a fusion of two
or more punctate organs. In Ht-
mopterus these light organs are
located in definite patterns, prin-
cipally along the sides and ven-
trally, but they are present also
on the dorsum.

Johann (1899) gives a section
through a luminous organ of
Spinax (fig. 334) which shows
that it is formed as a modification

of cells in the germinative or Fig. 32. Transverse section of sting, Urolophus
basal layer of the epidermis (gr.). fallert. (A. M. Paden, orig.)

These cells enlarge and, as a cup, {7 ¢pamel of sting; ca; enamel organs dy den
sink slightly into the corium. Two

types of cells are present, one, the lens cell (l.c.), the other, the light or photo-
genic cell (It.c.).

The lens cells are few in number and are located toward the surface where
they appear as enlarged mucous cells. In their beginning they arise from the
basal layer and migrate outward, becoming large and granular. Upon coming
in contact with the surface they pour out some or all of their contents and
become the lens cells of the adult type. The light or photogenic cells (t.c.) con-
sist of a few cells (Spinax) or a number of them (Htmopterus) which occupy
an irregular position at the base of the cup.

Under the basal membrane which supports the cup are blood sinuses (b.s.).
Usually indenting the walls of these sinuses are masses of enclosing pigment.
Figure 338 of Etmopterus shows the arrangement of pigment not given in
figure 33a. This heavy band of pigment lines the bowl of the cup and exten-
sions pass inward and practically cover the cup as the so-called iris (ir.).

There is doubt as to how the organ thus described functions. It is possible,
however, as in some of the bony fishes, that these basal cells, which are essen-
tially mucous cells, form a luminous secretion, the oxidation of which produces
the light. That the organ is effective in the production of light has been ob-
served through the study of living specimens. Thus in Spinar, Dr. Theodor
Beer has observed a strong phosphorescent light given off along the side and
ventral region. The light was of variable intensity, glowing for a time and then

30 THE ELASMOBRANCH FISHES

decreasing in brillianey. Oshima has also studied the luminosity, and has
noted that in Etmopterus the light was never produced spontaneously but was
emitted regularly upon the application of mechanical stimulation. Whether or
not the pigmented iris through contraction and expansion regulates the light
thus produced has not been sufficiently studied.

PLACOID SCALES

In figure 29, showing the layers of epidermis and corium, is also shown a devel-
oping placoid scale. The first indication of such a scale is the collection of a
group of cells in the upper layer of the corium to form a dermal papilla (d.p.).

Fig. 33. A. Section through a light organ or photophore, Spinaz niger. (From Johann.)
B. Pigmentation of a photophore, Etmopterus. (From Oshima.)

b.s., blood sinus; gr., basal or germinative layer of epidermis; ir., iris; l.c., lens cell;
It.c., light cell.

As the papilla grows upward it raises the basal layer of the epidermis, making
of it a cap, the enamel organ (e.0.). By continuous growth the cells of the
enamel organ assume the high cubical type with their nuclei located toward
the outer margin.

The cells of the enamel organ form a layer of enamel over the tip of the
papilla; while the odontoblasts of the dermal papilla which lie most superfi-
cially are the first to lay down dentine. The first layer covers the tip and sides
of the papilla lying immediately under the thin layer of enamel. Then the
odontoblasts which are located deeper send out processes around which den-
tine is deposited. The canals thus formed for the processes themselves are the
beginning of the dentinal canals and into them the protoplasmic processes of
those odontoblasts lying still deeper will later enter as the formation of the
dentine continues. Thus it is that the dentine produced from without inward
becomes thickened, finally crowding the core of the papilla into narrow
compass.

When a sceale like the one described above reaches the surface the epidermal
layers are rubbed off from the tip, and the body of the scale then erupts. In a
more mature embryo than the one here described many such seales erupt at
about the same time and come to take up a definite arrangement in patterns in

THE ELASMOBRANCH FISHES 31

Fig. 34. Scale patterns of Elasmobranchs. A. Mustelus californicus. (H. M. Gilkey, del.)
B. Squaliolus. (From Smith.) C. Anchor seale. D. Stomodeal denticles. E. Flattened transi-
tional scales. F. Nodules from fin margin. (C-F, Heterodontus francisci. Dunean Dunning,
del.)

32 THE ELASMOBRANCH FISHES

general like that of Heptanchus. In some, however, a pattern exists only over
limited areas. In others the scales may be confined to rows along the back, or,
in addition to this arrangement, they may be scattered more or less pro-
miscuously over the body, as they are in some of the rays. In other rays integu-
mentary scales may be entirely lacking (Myliobatis, Trygon).

The individual placoid scale may bear but a single spine as in Mustelus
californicus (fig. 344), Carcharias, Pristiophorus. Or it may be tricuspate,
multitudes of scales covering the surface as in Heptanchus (fig. 274), Scyl-
lium, Zygaena, Pristiurus, and Pentanchus. The scales may be found in geo-
metrical exactness and beauty as in Squaliolus (fig. 348), or they may present
various designs from a simple spade-shape to the anchor seale (fig. 34c) or to
the complex Greek cross of Heterodontus. The gross anatomy of the type
described for Heptanchus may be taken as an example of more or less gen-
eralization.

FINER ANATOMY OF SCALE

A section through a placoid scale of Scymnus (fig. 35) illustrates the finer
structure characteristic of the Elasmobranch scale. In such a section the crest
surmounting the main body continues backward to the spine. The base is rela-
atively large and a pedicel or
neck connecting it with the
body of the seale is practically
lacking. The base is fixed to the
corium by connective tissue
and is perforated by a central
canal (c.c.) which leads into a
large median pulp cavity
(p.c.) An anterior and a pos-
terior canal lead off from the
Fig. 35. Sagittal section showing finer anatomy of pulp cavity; and from the an-
placoid scale, Scymnus lehia: (From O. Hertwig.) terior and posterior canals, as

e.c., central canal; d.c., dentinal canals; e.,enamel; :
p.c., pulp cavity. well as from the pulp cavity

itself, smaller dentinal canals
(d.c.) extend into the dentine. The enamel (e.) surrounding the exposed part
and sinking slightly into the integument is much better developed anteriorly
than it is posteriorly.

Considerable doubt has been raised as to whether or not the so-called enamel
of the placoid seale and of the tooth of the Elasmobranchs is in fact compara-
ble to the enamel of the teeth of higher forms. The studies thus far made show
that the enamel formed in the Elasmobranch fishes presents a variety of types.
In the rays it appears to be in all essential respects true enamel; in some of the
sharks the evidence is not so clear. That the dentinal tubules in a type like
Galeus may be traced far into the outer layer shows that there is here no clear
demarcation between dentine and enamel. For the present, then, we may
think of the harder outer layer of the scale in some of the Elasmobranchs as
composed of a substance just beginning to differentiate into true enamel.

we
“

THE ELASMOBRANCH FISHES

MODIFICATION OF SCALES

By a peculiar hypertrophy modifications may arise which, although essen-
tially like the primitive shagreen denticles in structure, greatly differ from
them in form. Such hypertrophy may result in the production of a fin spine
like that in Heterodontus (fig. 88) and the Spinacidae; a tooth lke that in the
sawfishes, Pristis (fig. 38) and Pristiophorus; a sting like that in the sting rays
(fig. 42) ; or it may result in other variously modified structures, such for ex-
ample as the branchial rakers in Cetorhinus (fig. 44) and
Rhinodon.
Fin SPINE

In some of the types in which fin spines are present they
are so rudimentary as to be but little larger than enlarged
scales, as exemplified in Centroscymnus. In others, as in
Heterodontus (fig.88) and Acanthias,they are pronounced
structures. In general, they are located just anterior to the
dorsal fins, the posterior one (fig. 36) being longer than the
anterior. For almost half its length the spine is buried in
the integument. The buried part is designated as the root
or base and the exposed portion the crown or spine proper.

If such a structure be removed and more closely studied,
its deeply imbedded base is seen to be triangular in shape.
The spine contains a large central cavity which when in
place fits over a cartilage of the fin skeleton. The walls of
the spine are made of dentine which in the crown consists
of a double layer. The more superficial layer is bounded pig. 36. Second fin
anteriorly and laterally by a layer of enamel, but enamel spine, Squalus
does not extend over the posterior groove which fits close We
up against the basal cartilage of the fin skeleton. A more or less compact layer
of pigment (pg., fig. 40) separates the enamel (e.) in front from the layer of
dentiné (d.).

The development of such a fin spine is of considerable interest. Figure 37A
represents a sagittal section of an early stage of Acanthias in which a mass of
the epidermis (ep.) has sunk into the dermis, just in front of the dorsal fin.
The bounding layer of this section becomes the enamel organ (¢.0.). The for-
mation of the enamel of the spine, and of a part of the dentine, is singularly
modified by the peculiar position of this organ. It will be observed that the
enamel organ here covers only the anterior upper part and sides of the de-
veloping spine, instead of forming a cap over the entire structure as it does in
a placoid seale. As a result enamel is present only on the front and sides of the
crown, little being produced posteriorly (e., fig. 40). The odontoblasts (od.,
fig. 374) just under the enamel organ lay down dentine so that these two layers
so far as they go are like the enamel and dentine of a common placoid scale,
but the greater mass of dentine is formed back of this dentine.

34 THE ELASMOBRANCH FISHES

Markert (1896) says that in the formation of this secondary dentine certain
long fibers (fs., fig. 374) grow down in a sheath posterior to the core of carti-
lage (ct.). These fibers penetrate deeply and near the base spread out, curve
forward, and fuse anteriorly into a closed ring. Now this posterior sheath of
fibers runs through the odontoblasts in such a way as to leave some of them in

A. Young stage

B. Older stage

Fig. 37. Development of fin spine, Acanthias. (From Markert.)

ct., core of cartilage; d., primary dentine; d.’, secondary dentine; e., enamel; ¢.0.,
enamel organ; ep., epidermis; fs., connective tissue fibers; od., odontoblast; pg., pigment.

front of it and others behind it. Both of these sets of odontoblasts lay down
dentine so that the fibers (fs.) come to lie between two layers of dentine.
Finally the fibers themselves also give place to dentine. Hence a transverse
section of this secondary dentine, taken at the base of the spine where the
sheath of fibers is closed into a ring, shows a heavy circle of secondary dentine
like the broad band around the core of cartilage (d', fig. 40) ; a similar trans-
verse section taken toward the tip would indicate the layer of dentine as a
crescent just back of the central core.

THE ELASMOBRANCH FISHES 3d

Saw TootH

A secondary form of hypertrophy is seen in the saw tooth of the sawfishes.
Here the teeth are arranged along both edges of the saw (rostrum) as greatly
modified scales. In the specimen from which figure 38 was taken the teeth
were asymmetrical, 26 teeth being present on the left edge of the saw and 27
on the right. In the larger saws, some of which may reach a foot in width and
six feet in length, the crown of the tooth may reach four inches in length and
the teeth become most formidable organs of offense.

A sagittal section through an adult saw tooth according to
Engel (1910) shows that the core of the tooth, unlike that of the
spine, becomes converted into long columns of vasodentine, and
a transverse section through this dentine near the tip also dem-
onstrates numerous canals around which the dentine is formed
and through which blood vessels pass (see section through tooth,
p. 181, fig. 129). |

A saw tooth erupting from the side of the rostrum (fig. 41) Wha tl
presents something of the appearance of a developing fin spine ii" wpa
of Acanthias, but with one difference. The saw tooth arises di- hay
rectly through the mass of invaginated epidermis (ep.) and a een |
hence the posterior part is more completely surrounded by an | fee
enamel organ (¢.0.). It follows that there is a layer of enamel | |
over that part of the saw tooth just as there is over the placoid
seale.

A transverse section through the saw tooth near its tip (fig.

V3 : H ge
39) shows that, like the fin spine of Acanthias, it is more or less
flattened posteriorly. The central part of the immature tooth is Fig. 38.
occupied by the enlarged pulp cavity containing blood vessels rae
10) TUSTUS

and numerous odontoblasts. Just outside of the pulp cavity 18 antiquorum.
the layer of dentine (d.’), superficial to which is the thinner

band of enamel or vitrodentine (e.). The tissues outside of the enamel organ
(e.0., fig. 41) do not take part in the production of the saw tooth. They are to
be looked upon as the intermediate and superficial layers of the epidermis.

STING

A third form of hypertrophy occurs as the variously formed defensive organs
of the sting rays (fig. 42). Here a spine arising from the dorsal part of the tail
grows backward, varying greatly in size and in complexity. In the small sting
ray Urolophus this spine is but two inches in length; while in the larger types.
as in Myliobatis, it may reach a length of four or five inches. Usually the sting
or spine is simple, but it may be compound, numerous spines arising one be-
hind the other. Simple or compound, each spine is provided with a sharp
point, and its sides have smaller and recurved hooks arising from them.

re) ey
a
oD
sm
ap
=
er
ics
Dd,
OG,
SSeS
P;
i
t
t
+
T
—¥
<¥
=
on
ee

o f

ing

through develop

10n

unsverse secti

ve
c

tooth, P)

ection through developing saw tooth, Pristis. (From Engel.) Fig. 40. T

Transverse

Big, 39.

ngel.)

nl
4

. (From E

"Ls

3a W

1 developing

‘
c

through

10n

ttal seet

‘kert.) Fig. 41. Sz

«
c

. (From M

, Acanthias

spine

ment.

oO
to]

we Os>) 01

ity

avl

; p.c., pulp ¢

‘mis

ider

amel organ; ep., epic

‘
c

€.0., en

)

ine

; e., enamel (or vitrodent

d.’, secondary dentine

’

d., dentine

THE ELASMOBRANCH FISHES 37

A transverse section through the sting of Urolophus (p. 29, fig. 32) shows
that it is convex dorsally. The ventral side consists of right and left plane
surfaces separated by a median ventral ridge. Both the plane surface and the
convex dorsal sides are covered with a thin layer of enamel (e.) under which

COR ANG _ SE
ROD MH TS Deri Stipe:

WOODS

—
Pen)

= on Re Pee as

<SD ASSIS TEE LD DN
——
BRELIBEE

ees

Fig. 42.
Sting of
sting ray.

is the thick dentine (d.). But the dentine here is arranged differ-
ently from that of the placoid scale.

Figure 43 is drawn from the dorsal side of a sting and represents
it as a transparent object. In it may be observed numerous longi-
tudinal and anastomosing canals (c.) surrounded by heavy dentine
(d.). This arrangement of canals is much like that which we have
observed in the saw tooth of Prvstis.

The sting is clearly a protective structure. In those rays in which
it is attached nearer the body, as in Myliobatis, it is more effective
than in types like Dasyatis, in which it is located farther out on the
tail. In either type, the sting is brought into action by thrusting the
tail upward and forward over the back. In the thrust the weapon is
driven forward with precision and force, and is removed with great
difficulty from the wound, the recurved hooks (sp.) forming a
most painful tearing surface unless the sting can be pushed en-
tirely through.

GILL RAKERS

In some forms, structures located on the pharyngeal walls of the
internal branchial arches have undergone modification into gill
rakers, such, for ex- |

ample, as are seen in [ \
Squalus sucklii (p. 154, / |

fig. 147, gr.). These gill p
rakers evidently serve

as strainers to prevent food from
passing out with the respiratory
current. Structures somewhat like
these in function but very unlike
them in form have become remark-
ably specialized in Cetorhinus maxt-
mus (fig.44) and in Rhinodon typi-
cus, in which they form a highly
complex straining apparatus. Each
raker in Cetorhinus arises from a
semilunar base and extends as a
long slender filament across the in-
ternal branchial aperture (figs. 44
and 148).

} | ! |
Sei
q Y

GIN
1 aN
it | walt

Fig. 43. Segment of sting, Urolophus halleri,
seen as transparent object. Dorsal view. (A.
M. Paden, orig.)

c., canals of sting; d., dentine; sp., recurved
spine on sting.

It has long been known that one of these filaments with its adjoined base is
structurally like a placoid seale. In a section through the base numerous den-

THE ELASMOBRANCH FISHES

tinal canals appear which are essentially like those of the seale. Superficially
the filament is surrounded by a more compact layer, but structurally it is
similar to the base. The central canal of the filament is surrounded by a “‘non-

-Fig. 44.
Gill raker of
Cetorhinus
Maximus.
(From
Hendricks. )

vascular dentine” in which there is a network of dentinal canals.

STOMODEAL DENTICLES

The stomodeal denticles are also modified scales, although it may
be more correct to speak of them as atrophied rather than hyper-
trophied. These denticles may be abundant over the larger part
of the buceal and pharyngeal walls as well as over the branchial
arches (Heterodontus, fig. 34d), or they may be present in the
bueeal cavity and restricted to the hyoid and first branchial
arches (Squatina), or they may be confined to the pharyngeal
margins of the branchial arches (Alopias vulpes). In certain
types they are rudimentary (Squalus suckli1) and in others they
have ceased to be developed altogether (Scyllium canicula).

It has been suggested that the denticles may serve to hold and
to a slight extent to grind food, but it seems more probable that
they are structures which, because of their location and origin,
are without pronounced function, and hence are usually ves-
tigial (see Chapter V). This is indicated by the fact, as Imms
(1905) has suggested, that whether the food be hard or soft they
develop equally well (as in Galeus, and Mustelus). Further-
more, like vestigial structures they often appear much later
than do the seales of the body (Carcharias).

TEETH AS MopIFIED SCALES

The most important structures, however, with which placoid
scales are associated are the teeth. In a type like Acanthias, in
which these are sharp pointed, superficial resemblance between
the two is more or less pronounced. In a continuous section cut-
ting through both the scales and the teeth it has been observed
that the scales outside of the bueeal region have their spines pro-
jecting backward, while those within the mouth may have their
spines in a reverse direction, and still be pointing backward.
Some of the transitionals between the two regions, however,
possess both an anterior and a posterior spine, and hence are so
generalized that the retention of the latter projection would re-
sult in a seale, its loss would result in the formation of a tooth.
In other Elasmobranchs, little outward similarity between
tooth and scale is seen. Such is in part true of the immense tooth
of Carcharodon (see p. 129, fig. 127); especially is it true of

many of the plate-like crushing or pavement teeth lke those of Wyliobatis
(p. 128, fig. 1268). Invariably, however, the two are essentially identical in
nature. For a further consideration of the teeth, see Chapter V.

1915.

1904.

1907.

1868.

1850.

1873.

1908.

1874.

1905.

THE ELASMOBRANCH FISHES 39

BIBLIOGRAPHY

CHAPTER II

. AGAssIZ, L., Three Different Modes of Teething among Selachians. Amer. Nat., Vol. 8,

pp. 129-135.
BALKWILL, F. H., Teeth of Sharks. Zoologist, Ser. 2, Vol. 10, pp. 48-45.

BENDA, CarRL, Die Dentinbildung in den Hautziihnen der Selachier. Arch. mikr. Anat.,
Bd. 20, pp. 246-270, Taf. 16.

. BRACKEL, GREGORIUS A., De cutis organo quorundam animalium ordinis Plagiostomo-

rum disquisitiones microscopicae. Inaug. Diss., Dorpat, 1858, pp. 1-54, pl. 1.

BrouL, ENGELBERT, Die sogenannten Hornfaden und die Flossenstrahlen der Fische.
Jena. Zeitschr. Naturwiss., Bd. 45 (N. F. 38), pp. 345-380, Taf. 28-29, 5 text figs.
Also: Inaug. Diss. Jena, pp. 1-36, 5 text figs.

. BURCKHARDT, Rup., On the Luminous Organs of Selachian Fishes. Ann. Mag. Nat.

Hist., Ser. 7, Vol. 6, pp. 558-568, 8 text figs.

BurckKHArD?T, Rup., Die Entwickelungsgeschichte der Verknécherungen des Integu-
ments und der Mundhohle der Wirbeltiere. Hertwig’s Handb. vergl. u. expt. Entwick.
d. Wirb., Bd. 2, Teil 1, pp. 349-462, text figs. 208-263.

Cocco, Luier, Studi sui denti dei Plagiostomi con Note palaeontologische. Atti Acad.
Sci., Acireale (n. s.), Vol. 7, Classe Scienze, pp. 3-25.

DANIEL, J. FRANK, The Anatomy of Heterodontus francisci. I. The Exoskeleton.
Univ. Calif, Publ. Zool., Vol. 13, No. 6, pp. 147-166, pls. 8-9, 4 text figs.

ENGEL, HeErnricu, Die Zihne am Rostrum der Pristiden. Zool. Jalrb., Bd. 29 (Abt.
Anat. u. Ontog.), pp. 51-100, pls. 3-6, 2 text figs. 1909, Diss. Giessen, pp. 1-47, 2
text figs.

FAHRENHOLZ, Curt, Uber die Verbreitung von Zahnbildung und Sinnesorganen im
Vorderdarm der Selachier und ihre phylogenectische Beurteilung. Jena. Zeitsechr.
Naturwiss., Bd. 53, pp. 389-444, Taf. 6-7, 7 text figs.

GoopricH, E.8., On the Dermal Fin-Rays of Fishes—Living and Extinct. Quart. Jour.
Mier. Sci., Vol. 47, pp. 465-522, pls. 35-41, 6 text figs.

GoopricH, E.S., On the Seales of Fishes, Living and Extinct, and their Importance in
Classification. Proce. Zool. Soc. Lond., 1907 (2), pp. 751-774, pls. 438-46, text figs.
196-204.

HANNovER, A., Recherches sur la structure et le développement des écailles et des
épines chez les poissons cartilagineux. Ann. Sci. Nat. Zool., Sér. 5, T. 9, pp. 373-378.
Hannover, A., Om Bygningen og Udviklingen af Skjael og Pigge hos Bruskfisk.
Dansk. Vid. Selsk. Skr., Ser. 5, Vol. 7, pp. 483-529, tav. 1-4, 3 text figs.

Haruess, E., Ueber den Zahnbau von Myliobatis und dem verwandten Rochen
Trikeras. Abh. math.-phys. KI]. Bayer Akad. Wiss., Bd. 5, Abt. 3, pp. 841-876.
HeIncke, F., Untersuchungen tiber die Zahne niederer Wirbelthiere. Zeitschr. wiss.
Zool., Bd. 23, pp. 495-591.

HeEnpricks, K., Zur Kenntnis des gréberen und feineren Baues des Rausenapparates
an den Kiemenbégen von Selache Maxima. Inaug.-Diss., Minster, pp. 3-89, pls. 18—
19, 5 text figs.

Hertwie, Oscar, Ueber Bau und Entwickelung der Placoidschuppen und der Zahne
der Selachier. Jena. Zeitschr. Naturwiss., Bd. 8 (N. F. 1), pp. 331-404, Taf. 12-13.

Imms, A. D., On the Oral and Pharyngeal Denticles of Elasmobranch Fishes, Proe.
Zool. Soe. Lond., Vol. 1905 (1), pp. 41-49, pl. IIT.

40 THE ELASMOBRANCH FISHES

1897. JENTSCH, B., Beitrag zur Entwicklung und Struktur der Selachierzahne. Diss. Leip-
zig, 38 pp., 2 Taf.

1899. JoHANN, L., Uber eigenthiimliche epitheliale Gebilde (Leuchtorgane) bei Spinax ni-
ger. Zeitser. wiss. Zool., Bd. 66, pp. 136-160, Taf. 10-11.

1890. Kuaarscu, H., Zur Morphologie der Fischschuppen und zur Geschichte der Hartsub-
stanzgewebe. Morph. Jahrb., Bd. 16, pp. 97-202, Taf. 6-8, 209-258.

1894. KuaatscuH, H., Uber die Herkunft der Scleroblasten. Ein Beitrag zur Lehre von der
Osteogenese. Morph. Jahrb., Bd. 21, pp. 153-240, pls. 5-9, 6 text figs.

1901. Koppen, HERMANN, Ueber Epithelien mit netzformig angeordneten Zellen und tiber
die Flossenstacheln von Spinax niger. Zool. Jahrb. (Abt. Anat. u. Ontog.), Bd. 14,
pp. 477-522, pls. 38—40, 1 text fig.

1905. KWIETNIEWSEI, C., Ricerche interno alla struttura istologica dell’ integumento dei
Selachi. Padova, 156 pp., 6 tav.

1900. LAASER, Paut, Die Entwickelung der Zahnleiste bei den Selachiern. Anat. Anz., Bd.
17, pp. 479-489, 8 text figs.

1903. LAASER, PAu, Die Zahnleiste und die ersten Zahnanlagen der Selachier. Jena.
Zeitschr. Naturwiss., Bd. 37, pp. 551-578, Taf. 28, 13 text figs.

1852. Leypic, FRANZ, Beitrige zur mikroskopischen Anatomie und Entwicklungsgeschichte
der Rochen und Haie (Leipzig), pp. 1-127, pls. 1-4.

1903. Leypic, F., Bemerkung zu den Leuchtorganen der Selachier. Anat. Anz., Bd. 22, pp.
297-301.

1885. List, J. H., Uber einzellige Driisen (Becherzellen) in Cloakenepithel der Rochen.
Zool. Anz., Bd. 8, pp. 50-51.

1885. List, J. H., Uber einzellige Driisen (Becherzellen) in der Oberhaut von Torpedo mar-
morata. Zool. Anz., Vol. 8, pp. 388-389.

1874. LuUTKEN, Cur., Sur les différences dans la dentition que présentent, selon le sexe, les
Raies (Raja) qui habitent les cotes du Danemark. Jour. Zool. (Gervais), T. 3, pp. 318—
321. Revue: Arch. d. Zool. exper. et gén., Sér. 1, T. 3, pp. xxi—xxiii.

1896. MarkKeErT, F., Die Flossenstacheln von Acanthias. Ein Beitrag zur Kenntnis der
Hartsubstanzgebilde der Elasmobranchier. Zool. Jahrb. (Abt. Anat. u. Ontog.), Bd. 9,
pp. 665-722, pls. 46-49, 10 text figs.

1895. Maurer, F., Die Epidermis und ihre Abkémmlinge. Leipzig. 355 pp., pls. 1-9, 28
text figs. W. Engelmann.

1839. OWEN, R., Researches concerning the Structure and Formation of the Teeth of the
Squali, with a New Theory of the Development of the Teeth. London. 4°. Transl. in
C. R. Acad. Sci. Paris, T. 9, pp. 784-788; Ann. Sci. Nat. Zool., Sér. 2, pp. 209-229.

1840-45. Owen, R., Odontography. Vol. 1. London.

1911. OsHiMA, H., Some Observations on the Luminous Organs of Fishes. Jour. Coll. Sei.
Tokyo, Vol. 27, Art. 15, pp. 1-25, pl. 1, 4 text figs.

1896. Ripewoop, W. G., The Teeth of Fishes. Nat. Sci., Vol. 8, pp. 380-391, 22 text figs.

1900. Rirrer, P., Beitrage zur Kenntnis der Stacheln von Trygon und Acanthias. Diss.
Rostock. Inaug. Diss., Berlin. I-VI, pp. 1-56, pls. 1-6.

1894. Rosx, C., Ueber die Zahnentwicklung der Fische. Anat. Anz., Bd. 9, pp. 653-662, 8
text figs.

1894. Rosx, C., Ueber die Zahnentwicklung von Chlamydoselachus anguineus Garm. Morph.
Arb., Bd. 4, pp. 193-206.

1898. ROsE, C., Ueber die verschiedenen Abanderungen der Hartgewebe bei neideren Wir-
beltieren. Anat. Anz., Bd. 14, pp. 33-69, text figs. 4-28.

1908. RYNBERK, G. VAN, Sur une disposition particuliére dans le squelette cutané de quel-
ques Sélaciens. Arch. Ital. Biol., T. 49, pp. 203-212, 12 text figs.

1908.

1906.

1851.

1892.

1893.

THE ELASMOBRANCH FISHES 4]

RYNBERK, G. VAN, Di una disposizione particolare nello scheletro cutaneo di aleuni
Selacei. Rend. Accad. Lincei Roma, Ser. 5, Vol. 17, pp. 137-146, 12 text figs.

SPENGEL, J. W., In Beziehung auf Mund- und Schlundzihne der Elasmobranchier.
Zool. Anz., Bd. 29, pp. 332-333.

. STEENSTRUP, M., Sur la différence entre les poissons osseux et les poissons cartilagi-

neux au point de vue de la formation des écailles. Ann. Sci. Nat. Zool., Sér. 4, T. 15,
p. 368.

. STEINHARD, Orro, Uber Placoidschuppen in der Mund- und Rachen-Hohle der Plagios-

tomen. Arch. f. Natur., Jahr 69, Bd. 1, pp. 1-46. Also: Inaug. Diss. Bern, 1902, pp.
I-50, Taf. 1-2.

5. SrupnitKa, F. K., Ueber kollagene Bindegewebsfibrillen in der Grundsubstanz des

Hyalinknorpels, im Dentin und im Knochengewebe. Anat. Anz., Bd. 29, pp. 334-344,
10 text figs.

. SrupnitxKa, F. K., Zur Losung der Dentinfrage. Anat. Anz., Bd. 34, pp. 481-502, 2

text figs.

. Tomgs, C. S., On the Development of the Teeth of Fishes. (Elasmobranchii and

Teleostei.) Phil. Trans. Roy. Soc. Lond., Vol. 166 (1), pp. 257-267, pl. 31.

. Tomes, C. 8., Upon the Structure and Development of the Enamel of Elasmobranch

Fishes. Phil. Trans. Roy. Soc. Lond., Vol. 190B, pp. 448-464, pls. 17-18.

. TomEs, C. 8., Upon Rose’s Proposed Classification of the Forms of Dentine. Anat.

Anz., Bd. 14, pp. 343-348.

. TREUENFELS, PAuL, Die Zahne von Myliobatis aquila. Inaug. Diss., Univ. Basel, pp.

1-34, pls. 1-2.

. WILLIAMSON, W. C., On the Microscopie Structure of the Scales and Dermal Teeth of

Some Ganoid and Placoid Fish. Phil. Trans. Roy. Soc. Lond., 1849, Pt. 1, pp. 435-
475, pls. 40-43.

WILLIAMSON, W. C., Investigations into the Structure and Development of the Seales
and Bones of Fishes. Phil. Trans. Roy. Soc. Lond., 1851, Pt. II, pp. 643-702, pls.
28-31.

Woopwagp, A. S., The Evolution of Sharks’ Teeth. Nat. Sci., Vol. 1, pp. 671-675, 12
text figs.

WoopwarD, A. 8., On the Dentition of a Gigantic Extinct Species of Myliobatis from
the Lower Tertiary Formation of Egypt. Proce. Geol. Soc. Lond., pp. 558-559, pl. 48.

THE ELASMOBRANCH FISHES

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pejyotred “fd ‘4se10 [eyidrod90 “wo'o faAdou snotmyeyyydo [eryaiodns 107 uowresros “py ‘o's foAdou snpungoad snorwmyeyyydo
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Ill

ENDOSKELETON
ENDOSKELETON OF HEPTANCHUS MACULATUS

The endoskeleton in Heptanchus maculatus consists of a framework of rela-
tively simple cartilage which serves as a protection for the various internal
organs and at the same time acts as a support for the attachment of the mus-
culature of the body. The cartilage of the axial part, the skull and the spinal
column, is essentially like that of the appendages in that it has but little eal-
cium deposited in it.

AXIAL SKELETON

SKULL

The skull of Heptanchus maculatus is composed of (1) a relatively thin-walled
cranium or brain case to which in the adult are fused the nasal and auditory
capsules, and (2) a series of cartilaginous visceral arches which support the
mouth and the pharyngeal region.

The cranium in dorsal view (fig. 45) is like a violin box, broadly pointed in
front and almost square at the posterior margin. At the sides it is constricted,
and back of these constrictions are the heavy postorbital processes (po.p.). In
the middorsal line at the posterior margin of the cranium is a ridge, the occipi-
tal crest (0.cr.) which lies posterior to a pit, the parietal fossa (p.f.) ; from
the bottom of the fossa the foramina for the endolymphatic duets (ed.) and
the fenestrae (fn.) lead to the ear. Inclosing the parietal fossa and pointed
backward is faintly indicated a V produced by the two anterior oblique semi-
circular canals. This V, together with a similar V produced by the posterior
oblique semicircular canals (see p.o.s.) and inclosing the occipital crest poste-
riorly, roughly forms an hourglass. In front of the parietal fossa the roof is
shghtly convex and extends to a large dorsally placed opening, the anterior
fontanelle (F.).

On each side of the anterior fontanelle is a small foramen for the ophthal-
micus profundus nerve (f.0.p.'), and at the sides of the posterior part of the
fontanelle are two (or one) large openings (f.o.VIJ') for the ophthalmic
branch of the seventh cranial nerve. Running on a line posterior from this
large opening and parallel to the margins of the indenture is a row of smaller
foramina on each side, through which twigs of the same nerve pass.

It will be observed that the cranium of Chlamydoselachus in dorsal view
(fig. 46) is much like that of Heptanchus.

In side view (figs. 47 and 48) projecting forward there are the elongated
cartilaginous supports for the rostrum, at the sides of which is the olfactory
capsule (ol.c) for the nasal apparatus. The cartilages of the capsules are

[43 ]

+4 THE ELASMOBRANCH FISHES

exceedingly thin-walled and open to the exterior by the nasal apertures. Sur-
rounding the aperture is the arch-like nasal cartilage (n.c.). The optic capsule
does not fuse with the cranium.

On each side at the posterior third of the cranium is the auditory capsule
(a.c., fig. 47) in which the semicircular canals and the organs of hearing are
located. Between the auditory and the nasal capsule is the large orbit for the
eye. Overhanging this is the supraorbital crest (s.0., fig. 48), the anterior pro-
jection of which is the preorbital (pr.o.), and the posterior one the postorbital
process (po.o.). Ventral to the posterior part of the orbit the cranium bends
sharply downward forming the basal angle (b.a., fig. 47). On the anterior face
of the basal angle is a flattened articular surface against which the orbital
process of the upper jaw plays. Anterior to the basal angle and extending
from the margin of the cranium is an antorbital process (a.pr., fig. 47). This
process is called by Allis (1923) and by others the ectethmoidal process.

Numerous foramina through which nerves and blood vessels course perfo-
rate the walls of the cranium. The first of these between the orbit and the nasal
capsule is the anterior opening of the orbitonasal canal (0-n.), its posterior
opening (0-n.1) lying in the anterior angle of the orbit. Above this opening is
a smaller foramen for the anterior cerebral vein (f.a.c.). Ventrally and at the
middle of the orbit is the large optic foramen (f.J7) through which the second
cranial nerve reaches the brain. Directly above it is the ophthalmic fora-
men through which the superficial ophthalmic branch of the seventh nerve
(f.o.VIT) leaves the orbit. A short distance ventral and anterior to this is a
small opening through which the deep branch of the fifth nerve leaves the
orbit. Posterior to the ophthalmie is the small trochlear foramen (f.JV) for
the fourth cranial nerve which passes to the superior oblique muscle of the
eye. Behind the optie and below and slightly back of the tip of the postorbital
process is the large orbital fissure (o.f.) ; through this the fifth, and a part of
the seventh cranial nerves pass. The sixth nerve enters the orbit through its
own foramen in the anteroventral margin of the orbital fissure. Below and
slightly posterior to the orbital fissure is the facial foramen (f.VIJ*) for the
hyomandibular branch of the seventh nerve. On a line between the facial and
the optic foramina are two perforations, the larger and posterior of which is
for the interorbital canal (7.0.) by means of which the blood sinuses of the two
orbits communicate. The other of these perforations (f.7.a.) is for the entrance
of the ramus anastomoticus artery. Above this is the small opening (f.J77) for
the exit of the third cranial nerve to muscles of the eye.

VISCERAL SKELETON

The visceral skeleton is composed of a series of cartilaginous arches which
more or less completely surround the buccal cavity and the pharynx. The num-
ber of these in Heptanchus (nine) exceeds that of any other present-day Elas-
mobranch. The arches may be divided into two groups. The first group com-
prises the mandibular and the hyoid arches, each of which is made up of two
segments. The second group consists of seven branchial arches which support

Fig. 47. Lateral view of cranium. Heptanchus maculatus.

Fig. 48. Lateral view of skull, with branchial arches removed, Heptanchus maculatus.
(Duncan Dunning, del.)

a.c., auditory capsule; a.pr., antorbital process; b.a., basal angle; b.r., branchial rays;
ea.h., extrahyoid cartilage; f.JI, optic foramen; f.JII, foramen for oculomotor nerve; f.1V,
trochlear foramen; f.VIJ°, foramen for hyomandibular branch of facial nerve; f.1.X, fora-
men of glossopharyngeal nerve; f.a.c., foramen of anterior cerebral vein; f.o.V II, foramen
for ophthalmicus superficialis nerve (leaving orbit) ; f.r.a., foramen for ramus anastomoti-
cus artery; i.0., interorbital canal; l., labial cartilage; md., mandible; n.c., nasal cartilage;
o.f., orbital fissure; o-n., anterior opening of the orbitonasal canal; o-n.1, posterior opening
of the orbitonasal canal; ol.c., olfactory capsule; p-q., palatoquadrate cartilage; po.o.,

postorbital process; pr.o., preorbital process; qd.p., quadrate process; s.o., supraorbital
erest.

BLASMOB! Ww FISHE
Hed and o he exterior by the nasal aj “a, Sur-
erture is th xe nasal cartilage (m«.). The op msule
with the crasim
CUT Tam * .
eRe) I side vf ‘ ‘ rr —— = = @_seiié ory aes a

semicire p a Hinars avd PR organsyt
esiitory or ty fasfl capsuleds le ffs} [S: e by,
Sis is the supradéy ni teak hrest fro 48 }, \ SY
Bs he precrbieahiers $y and ec A 2 one Nee poeforbital
process | ). Ventral to+ Thafe fart A\bbyrieriniam bends
shar) iy downward forming the basa vig 47.0 pe in the anterior face
of the basal angle is a flattened artientgr surfa eeeainst which the orbital
proeas of the upper jaw plays. Aw terior to the Saaal angle and extending
from ‘the ro atwtplypbss} gas dosmytqa hh insdaraxthowbitabapinit Wh gE iy. 47). This
greeess is called by Allis (1923) and by others the ec ‘tethmoidal process,
Numerous foramina through which nerves and blood vessels course perfo-
te the walls of the cranium, The first of these between the orbit and the nasal
vesnle is he anterior opening of the orbitonasal canal (0-n.), its posterior

pening (< he anterior angle of the abi: Above this openinit ts
wnaller foray ar the auterier coren en AA geri and at the
: ile of rhe Grey 36 ty re : i ' : “a ¥v ee} h see “ond

Raswe ; at > z i {i the seventh nerve

nfal nerve whigh passes to the super
optie and below and slightly

( 0.f. ) >

the orbit through its
ore. Gelow and

f for the
. the facial and

ith the blood sinuses of the two -
rbits comm re oth sé perforations (f..a.) is for the entrance
é che ramus anastomoticus artery. Above this is the small opening (f.IIZ) for
‘he exit of the third cranial nerve to muscles of the eye.

‘agains asilompiqoH bovomoer eodois Isidoasid dtiw [lode to woiv Istotal .8h .giF

VISCERAL SKELETON (eb gatoun@ mesaut®)
ASHE Bitonsed ; 0 ;olgns Isesd ..0.d wag [stidtotas ..1q.9 ;9lueqss Yrotibus ..o.0

Ane :OVT9M toto: 99 Tot moor. ." Pa + oitqo
-810 oor en ee RENT ich i 464 we VR ER io ich
inidoneo. t9ipohas to in mre Dan\ povIen

oo, Soe ae ae

Balasqo, Hogi 8-9 glance feesndtidro odd to gnimoqovrorratmas|yn-0! potsealt or

intact ico WSR RE OS ABUL ii sab Veen taste org ees fyi nO td

segmen is, The second group consists of seven branchial 4 4 hat stage Ort

Fig. 48

"|
a
7 =
_
af
C
a
~4
= vy amy
a SS o

=
es
Va
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‘@
0
4
a

THE ELASMOBRANCH FISHES 45

the walls of the pharynx. In plan the branchial arches are essentially similar
to the first two, but in the branchial arches there are typically four segments
to every arch; these segments differ among themselves in minor details.

The mandibular or first arch upon which the teeth are borne has become
the most highly specialized of all the visceral arches. The massive upper pala-
toquadrate (pterygoquadrate) segment (p-q., fig. 48) of this arch is as large
as the lower mandibular segment or Meckel’s cartilage (md.). This arch in
Heptanchus, unlike that in most sharks, is closely bound to the cranium in two
places, giving the amphistylic
type of attachment (amphi,
both; stilar, pillar). Anteriorly
this union with the cranium is
effected by the orbital process
of the quadrate coming in con-
tact with the sides of the basal
angle (b.a.,fig.47). Posteriorly
the union is produced by a
strong quadrate process (qd.p.,
fig. 48) joining the postorbital
process of the cranium (o.o.).
The upper and lower segments
of the left side are connected in
front with similar segments of
the right side, but this articu-
lation in Heptanchus is loosely

made. Posteriorly the upper Fig. 49. First branchial arch, Heptanchus maculatus.

and lower segments are joined b.r., cartilaginous branchial ray; cb., ceratobran-
to each other byasimple double chial ; eb., epibranchial segment; ex.b., extrabranch-
joint, and made fast medially Reais cie Sr ce ake
by pronounced ligaments.

The hyoid or second visceral arch is, as we have said, composed of two seg-
ments. In Heptanchus these segments are slender and are entirely hidden in
side view by the mandibular arch. The upper segment, unlike that in more
highly specialized Elasmobranchs, is not a suspensorium for the mandibular
arch; the lower segment is long and slender. Connecting the two ceratohyoids
of opposite sides in the midventral line is an additional unpaired piece, the
basihyal cartilage (bh., fig. 50a).

Both segments of the hyoid are provided with numerous cartilaginous rays
(b.r., fig. 48) which support the main respiratory structures. These rays on
the hyoid are considerably more complex than are similar cartilaginous rays
found on the branchial arches.

The first branchial arch (fig. 49) may be taken as a type. Its segments, from
the dorsal to the ventral side, are: (1) the pharyngobranchial (pb.), (2) the
epibranchial (eb.), (3) the ceratobranchial (cb.), and (4) the small hypo-
branchial (hb.), respectively. These segments slant obliquely forward and

46 THE ELASMOBRANCH FISHES

downward, the pharyngobranchial and ceratobranchial lying almost parallel
to each other. All the branchial arches, except the last, are similar to the first.
They differ from it, however, in that their hypobranchial segments are better
developed. In the last arch a functional hypobranchial is lacking and the
pharyngobranchial has fused dorsally with that of the sixth arch.

bh.

Fig. 50a. The median branchial cartilages, Heptanchus maculatus, dorsal view. (H. M.
Gilkey, del.)

Fig. 50s. Area of rudimentary arches, Heptanchus maculatus, ventral view.

ar.*, ninth arch; bb.*, second basibranchial; bh., basihyoid; cb., ceratobranchial; ch.,
ceratohyoid; hb., hypobranchial; mp., median piece; 7., rudimentary rays; 2., part of
eighth arch.

In the midventral line of the branchial basket is a series of unpaired pieces
which unite the arches of opposite sides. The first of these is the basihyoid pre-
viously mentioned (bh., fig. 504). A first basibranchial piece is lacking,
but basibranchials are present on the second to the fourth arches following
(bb? *). A large median piece posteriorly (mp.) serves for the attachment of
the fifth and sixth hypobranchials and the seventh ceratobranchial (cb.").

All these arches, except the last, have cartilaginous branchial rays on their
epl- and ceratobranchial segments. These branchial rays, though simpler than
those on the hyoid arch (b.r., figs. 48 and 49), serve the same function of sup-
porting the gill septa.

The visceral arches are further provided with superficially placed pieces,
the extravisceral cartilages. Those accompanying the first or mandibular areh

THE ELASMOBRANCH FISHES 47

are the so-called labial cartilages (see fig. 48, /.), a single one of which is found
in Heptanchus maculatus. This is an irregular cartilage, interesting particu-
larly because of its unusual development in this species. An extravisceral is
present dorsally on the hyoid arch (ex.h., fig. 48), but none is present ven-
trally. Similar cartilages are found both dorsally and ventrally on all bran-
chial arches except the last. The extrabranchial cartilages (ezx.b., fig. 49)
curve around the tips of the branchial rays as a protection and a support for
the outer margins of the gill septa.

In addition to the arches above described there are, especially in some of the
young specimens of Heptanchus, supernumerary rudiments of still other

TMT MTT
Py eye WHT} i

MA
atti} NUL MR Pa
SUES

Fig. 51 Fig. 52
Fig. 51. Fifth to eighth segments of the spinal column, Heptanchus maculatus.

Fig. 52. Sagittal section through sixth to eighth segments of the column. (H. M. Gilkey, del.)

bd., dorsal basal (basidorsal) plate; bv., ventral basal (basiventral) plate; c., central
column; chd., unconstricted part of notochord; f.d., foramen for dorsal root nerve;
f.v., foramen for ventral root nerve; h.a., haemal arch; id., dorsal interealary (interdorsal)
plate; iv., ventral intercalary piece; iz., layer immediately around the gelatinous notochord ;
m.z., middle layer in sheath of notochord; n.c., neural canal; oz., cartilage; r., rib; s., sep-
tum constricting notochord; s.bd., so-called neural spine.

branchial arches. An eighth appears directly back of the last functional areh
(cb.*, fig. 504) and even a ninth arch may be indicated nearer the middle line
(ar.®, fig. 50B), (Daniel, 1916).

SPINAL COLUMN

The spinal column in Heptanchus, because of its simplicity, is especially inter-
esting. Unlike that of the higher Elasmobranchs, it consists of a long central
eolumn (c., fig. 51) which is essentially the enlarged sheath of the notochord.
Anteriorly the column is more or less continuous with the occipital region of
the cranium (see fig. 47) and posteriorly it extends to the tip of the tail. Above
this central column there is a series of neural arches formed for the protection
of the spinal cord; below it, in the region of the tail, is a similar series of
haemal arches (h.a., fig. 53) for the protection of the caudal artery and vein.

A segment of the column in the so-called neck region shows the central part
well developed. Above this central part are the neural plates making up the
neural arch. Each arch is composed of a dorsal plate (bd., fig. 51) and a dorsal

48 THE ELASMOBRANCH FISHES

intercalary piece (id.). Both of these cartilages are more or less triangular in
shape, the former having its base on the centrum, the latter with apex pointing
toward the centrum. Above the dorsal plate there may be pieces segmented off
(s.bd.) to form the so-called neural spines, and in the most anterior part of
the column two such pieces may be present one above the other (fig. 47). Each
dorsal plate in the anterior region is further perforated by a ventral root
(f.v.) of the spinal nerve, and each dorsal interealary by the dorsal root (f.d.)
of the same nerve.

In this region and ventral to the central column are also ventral plates
(bv., fig. 51). On the third and succeeding vertebrae back to the forty-fifth,
ribs (r.) are present. The eighth to twenty-fourth ribs in Heptanchus, like
some of those in Laemargus (Helbing, 1904, cited on p. 72), are divided into

44 fy.f.d.

PPI W mee, \? SON ave
ISLAKANELEGKARASR ie

Fig. 53. Lateral view of spinal column in transitional area. Drawn as transparent object.
(Katharine Rogers, orig.) (For explanation see fig. 52.)

an anterior and a posterior part, the former of which is a curious plate-like
process projecting forward and downward. Between two ventral plates there
is interpolated a small ventral intercalary piece (7v.).

A sagittal section through this region (fig. 52) shows the central column
composed of three concentric layers in the notochordal sheath. These layers
surround the notochord (chd.) and constrict it at intervals into a bead-like
chain. The outermost of these layers is relatively thin and consists of carti-
lage; within this cartilage is a second and lighter broad area (m.z., fig. 52)
which appears to be made up of transverse fibers. Within this second layer
and bounding the notochord is a third layer (7iz.) of a white tissue. At regular
intervals the third layer forms septa (s.) which produce the regular constrie-
tions in the central part of the notochord. It will be observed that the septa are
more pronounced ventrally than dorsally and that they pass intracentrally.

In the midbody the central column assumes its simplest form. Here it con-
sists essentially of a heavy and but slightly constricted sheath which if it be
allowed to dry slightly gives greater evidence of constrictions. At about the
fiftieth segment of this region (fig. 53) some of the dorsal plates extend en-
tirely to the top of the arch so that no neural spines are present. Following
these plates, and beginning at about the fifty-sixth segment two types of dorsal
plates obtain, one of which is high, the other much lower. The higher is per-
forated by the ventral root of the nerve; the lower is imperforate. The higher
plate is followed by a dorsal interealary plate, perforated by the foramen for
the dorsal root nerve. In the region beyond the fifty-fifth segment it will be

THE ELASMOBRANCH FISHES 49

observed that to each segment two neural arches are present, and that a similar
condition obtains in the haemal arches (h.a.) even farther forward. Such a
condition is incomplete diplospondyly.

APPENDICULAR SKELETON

The appendicular skeleton is the framework for the fins and the girdles to
which these, if paired, are attached.

The pectoral girdle (fig. 54) in Heptanchus is a slender arch open dorsally,
to which the framework of the pectoral fin is attached. It is composed of right

Fig. 54. Lateral view of the skeleton of the pectoral fin and girdle, Heptanchus maculatus.
(Dunean Dunning, del.)

a.pl., process for articulation of pectoral fin; co., coracoid; f.pt., foramen for nerves and
blood vessel; ms.p., mesopterygium; mt.p., metapterygium; pr.p., propterygium; ra., ra-
dials; sc., scapula.

and left cartilaginous halves which are united in the middle line below by
means of an unpaired median piece. The part of the girdle extending the more
dorsalward is the seapula (sc.), tipped by the suprascapula; that part which,
by means of the median piece, joins a similar part from the opposite side
below is the coracoid portion (co.). At the middle and posterolateral part of
each half of the girdle there is an irregular surface for articulation with the
pectoral fin (a.pl.). In front of and below this projection is a broad surface
for the attachment of the ventral muscles of the fin. Perforating the girdles in
this surface is a large foramen (f.pt.) through which the brachial artery and
nerves pass to supply the fin.

50 THE ELASMOBRANCH FISHES

SKELETON OF PAIRED FINS

The skeleton of the pectoral fin (fig. 54) is fan-shaped; the proximal part con-
sists of three basal cartilages, propterygium, mesopterygium, and metaptery-
gium; from the last two, numerous rows of radials radiate.

The propterygium (pr.p.) in Heptanchus maculatus is a small nodule of
cartilage located upon the mesopterygium. It is followed by four or five large

A. Female B. Male

Fig. 55. The skeleton of the pelvic fin and girdle, Heptanchus maculatus. (Ruth Jeanette
Powell, del.)

B, beta cartilage; b.*°, first and second connecting segments; ba., basal or axial cartilage ;
ba.p., basipterygium; pl., pelvic girdle; ra., radials.

radials, the first of which may fuse with the mesopterygium. The mesoptery-
gium (ms.p.) is a stout cartilage, from the enlarged distal end of which
extend ten or twelve rows of radials (ra.), depending upon the amount of
fusion which has taken place proximally. The most anterior row is composed
of large and irregular plates, but the remaining rows are broken up into small
segments. The metapterygium (mt.p.) isa large triangular cartilage, the base
of which points ventrally. It is segmented both proximally and distally and is
then continued into the most distal radial. From the metapterygium diverge
numerous rows of preaxial radials, in addition to which there are clearly
marked postaxial radials.

THE ELASMOBRANCH FISHES 51

The pelvic girdle (pl., fig. 55) is a flattened band of cartilage, slightly con-
eave dorsally and enlarged at the ends. Perforating the terminal parts of the
girdle are from one to three foramina (see p. 99, fig. 96) through which nerves
pass to the pelvic fin. At the termini of the girdle are the articular processes,
each consisting of two protuberances which fit into depressions (fossae) of the
pelvic fin skeleton. These are not well shown in figure 55.

Fig. 56 Fig. 57

Fig. 56. Dorsal fin, Heptanchus cinereus. (From Mivart.)

Fig. 57. Anal fin, Heptanchus cinereus. (From Mivart.)
be., basal cartilage; ra., radial.

The framework of the pelvie fin proper consists of a long posteriorly pro-
jecting basal cartilage, the basipterygium (ba.p.) which bears one or two
small terminal segments. From this cartilage in the female proceed 21 or 22
radials (ra., fig. 554), all of which, except the last five, are segmented. Ante-
riorly, a much enlarged plate meets the basal piece, forming an obtuse angle.
From this run three rows of radials. At the proximal ends of this enlarged
plate and the basal piece, are the two fossae with which the protuberances on
the pelvic girdle above described articulate.

In the male the long basipterygium (ba.p.) is continued by the basal or axial
cartilage of the claspers (ba.). Where the two join there are two segments
(b..-*), and dorsal to them is the so-called beta cartilage (8).

SKELETON OF UNPAIRED FINS
DORSAL FIN

Extending over the forty-ninth to the fifty-fifth segment of the vertebral col-
umn is the thin basal cartilage of the dorsal fin (see Heptanchus cinereus,
fig. 56, be.). From this plate in Heptanchus maculatus arise seventeen or
eighteen radial cartilages (ra.),one of which, the anterior, is unsegmented and
a few of the posterior radials may or may not be fused into a single piece.

CAUDAL FIN

The segments of the tail show a characteristic diplospondyly in the arches
both above and below the central column, although the pseudosegments of the
central column itself are not doubly constricted. The ventral rays of the caudal

52 THE ELASMOBRANCH FISHES

fin (see fig. 53) are an integral part of the axial skeleton, being the prolonga-
tions of haemal spines under the haemal arches (h.a.). These consist of a series
of rays, two of which correspond to a segment. The dorsal lobe of the fin is also
supported by rays which begin back of the segment shown in figure 53. These
dorsal rays are more than twice as numerous as the segments present.

ANAL FIN

The base of the anal fin (bc., fig. 57) ends anteriorly at about the fifty-third
centrum of the spinal column. The basal piece, barring the fact that it is seg-
mented in front, is remarkably similar to that of the dorsal. From it, however,
the radials (ra.) proceed in a less definite fashion.

THE ELASMOBRANCH FISHES 53

ENDOSKELETON OF ELASMOBRANCHS IN GENERAL

The endoskeleton in the Elasmobranchs in general varies a great deal in its
composition. While in all it is formed of cartilage and never of bone, yet this
cartilage differs greatly as to its rigidity. In a shark like Heptanchus macu-
latus the cartilage is usually of a clear hyalin type and relatively soft. In H.
cereus, on the contrary, it is strengthened by a deposit of calcium. In some of
the more specialized forms calcification is so abundant and so arranged that
the cartilage is almost as strong as bone.

Cartilage as such in Elasmobranchs is
composed of cartilage cells and ground
substance. The ground substance consists
of a mucin-like substance in which are co-
logen fibers. In certain forms elastic fibers
may also be included in the cartilage, and
calcification is present in many Elasmo-
branchs (see Roth, 1911).

AXIAL SKELETON
SKULL

The skull in the Elasmobranchs varies
considerably in shape. In the rays it is
depressed dorsoventrally, while in the
sharks in general it is similar in plan to
the skull as deseribed for Heptanchus. In
all Elasmobranchs the skull ineludes the
cranium, the capsules for the organs of
special sense, and the visceral arches.

Fig.58. Development of cranium,
Acanthias (Modified from Sewert-
zoff.)

a.c., auditory capsule; asp., alisphe-
noidal cartilage; pr., parachordal
plate; tr., trabecular cartilage.

CRANIUM

The cartilaginous cranium or brain case
in the Elasmobranchs is unlike the bony
eranium of higher forms in that its sides, roof, and floor are welded into a
single piece of cartilage. Joined to it also are the auditory and olfactory cap-
sules for organs of special sense. The cranium is perforated by nerves and
blood vessels which enter or leave the brain. Below the orbit the cranium may
project outward as an infraorbital plate (most sharks) or such a plate may
be absent (rays).

The rudiments for the brain ease are laid down in the embryo of Acanthias
according to Sewertzoff (1897) as three pairs of cartilages (see figs. 58 and
70). These are (1) the parachordal plates (pr.) which le at the sides of the
notochord and posterior to the internal carotid foramina; (2) a pair of ali-
sphenoidal cartilages (asp.); and (3) a pair of trabecular cartilages (tr.)
anterior to the internal carotid foramina. The parachordal and trabecular

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THE ELASMOBRANCH FISHES DD

rudiments by growth extend medially, forming the floor of the cranium; the
trabeculae bend to form the basal angle, and then project forward in the re-
gion of the rostrum, giving rise to the rostral plate. The alisphenoidals pro-
duce a large part of the sides of the cranium and extend dorsally, to form the
roof of the cranium. To these three pairs of cartilages the sense capsules fuse.
The nasal capsule joins the trabecula (rostral) ; the otic or auditory capsule
joins the parachordal; while the optic capsules, when present, remain free.

In the adult sharks and rays, as we shall see, the extent to which the plates
increase in size and the modifications to which they are subject vary greatly.
Indeed, in various species of the same group these differences often produce
entirely unlike crania. An example of this variation may be seen in Zygaena,
the hammerhead (fig. 65), in which the cranium in the region of the eye is so
modified as to be unlike that of the nearly related Galeus. The modification, or,
better, the progressive development of the cranium is best understood by con-
sidering first the simpler and more generalized, and then the more highly
specialized Elasmobranchs.

In dorsal view the adult Elasmobranch cranium may be said to take the
shape of an hourglass (figs. 59, 61, 62). In this hourglass the basal segment is
formed by the enlarged otie or auditory capsules; the middle part of the in-
dentation contains the orbits for the eyes; and the top segment is produced by
the olfactory capsules. Upon this as an apex may arise longer or shorter rostral
cartilages (7s.).

In more generalized forms, as, for example, Heptanchus or Chlamydosel-
achus, the positions of the semicircular canals of the ear are evident as super-
ficial ridges on the surface of the auditory capsule.

The ridge for the posterior canal runs from the parietal fossa or pit outward
and backward to the foramen for the ninth cranial nerve, while the ridge for
the anterior canal rises at the parietal fossa and runs forward at right angles
to the posterior canal. In more highly specialized types, where the parietal
fossa is shallower, external evidence of the canals is less distinet (fig. 62).

From the bottom of the parietal fossa certain apertures lead to the ear. Two
of these are for the endolymphatic ducts (e.d., fig. 59) and two other accessory
apertures are the fenestrae (fn.), for the perilymphatic spaces. In some forms
the parietal pit may be deep and the endolymphatic foramina may be sepa-
rated only by a short space, as in Heptanchus. Again it may be shallow, where-
upon these foramina are farther apart (Scylliwm). In still other forms, the
pit is only a slight depression and the endolymphatic foramina are more
widely removed from each other (Rhinobatis, fig. 62; Raja clavata; Trygon;
Myliobatis). The fenestrae are apertures of much larger size than are the
foramina for the endolymphatic ducts, and have at times been confused with
them. In a type like Heterodontus (fig. 61) the parietal pit is deep and hence
the fenestrae are difficult to see. They are evident, however, in Pseudotriacis
(fn., fig. 59) and in Rhinobatis (fig. 62). In a specimen of Galeorhinus, six
feet in length, and in a large Myliobatis californicus, they were relatively of
immense size.

THE ELASMOBRANCH FISHES

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THE ELASMOBRANCH FISHES o7

The middle region varies greatly in dorsal view. While it is typically con-
stricted, secondarily this constriction may be obscured by the expansion of the
supraorbital crests (Heterodontus, fig. 61), or the constriction present in the
young may be entirely lost in the adult, as in Carcharodon rondeletu (T. J.
Parker, 1887). In the rays a supracranial fontanelle is usually present in the
middorsal line. This fontanelle is small in Trygonorhina, but large in Rhino-
batis (F.?, fig. 62) and Raja clavata.

The olfactory capsules (ol.c., fig. 60) which represent the uppermost seg-
ment of the hourglass are in most Elasmobranchs more or less well developed.
In some of the sharks they may be relatively of immense size, as for example
in Zygaena where they are drawn far out with the preorbital processes of the
cranium (fig. 65). But the capsules are normally smaller as in Pseudotriacis
(fig. 59). In Rhinobatis (fig. 64) and many other rays they are large wing-like
expansions to which heavy antorbital pieces are attached. In the middorsal
line of this median segment there is present in all sharks and rays the anterior
fontanelle (#’.), which in some is confluent with the supracranial fontanelle
(Myliobatis) .

The rostral pieces which may form an apex to the hourglass may be flat and
divergent, as in Heterodontus (fig. 61) and Crossorhinus, or blunt and con-
vergent as in Scymnus and Laemargus; or there may be two long dorsolateral
bars which unite forward with a ventral bar as in Pseudotriacis microdon (rs.,
fig. 59), Mustelus, Galeus, and many others. In Acanthias the ventral cartilage
is broad and spoon-shaped and the dorsolateral bar is rudimentary, each bar
being joined to the nasal capsule by a double cord of connective tissue (Wells,
1917). In some of the rays (Myliobatis) a rostrum is lacking, but this is the
exception. In the majority of this group it is a long single piece (Rhinobatis,
fig. 62), and in some it is of great length, as for example in Pristis the saw ray.

In a ventral view of the cranium (figs. 60, 63, and 64) a similar hourglass
shape is apparent. The auditory region at the base is a broad expansion of the
parachordal cartilage of the embryo to which the auditory capsules have
fused. In the most posterior region of the midventral line is the notch separat-
ing the two occipital condyles (ocd., fig. 60); by means of the condyles the
spinal column articulates with the cranium. In primitive sharks like Hep-
tanchus the column is more or less completely fused with the cranium so that
no true articulation exists. In the rays the condyles are well developed, but
here a secondary fusion takes place which affects the occipitovertebral articu-
lation and the anterior part of the column (see p. 70, fig. 768). Posteriorly and
between the two condyles is the foramen magnum (f.m., fig. 61) through
which the spinal cord joins the brain.

The middle segment in ventral view is characteristically different in the
sharks and rays. In the adult of most of the sharks right and left infraorbital
plates broaden out into wing-like processes which form a floor for the orbits,
and consequently obscure the constriction. In the rays the form of the hour-
glass is very evident, for in them, as in Heptanchus, an extension of these
plates is characteristically absent.

58 THE ELASMOBRANCH FISHES

In the olfactory region the capsules are seen in their relation to the elliptical
nasal cartilages (n.c., figs. 60, 63, and 64) surrounding the nasal aperture.
Projections from the anterior and posterior margins of the ellipse meet and
cross, usually forming of it a figure 8. A second anterior accessory process may
be added as in Heterodontus (n.c.*, fig. 60), or may be more completely de-
veloped as in Scylliwm. In the rays the ellipse may be broken into segments. In
Rhinobatis (fig. 64) the anterior and posterior projections forming the bridge
are relatively slender cartilages. In Myliobatis numerous accessory projec-
tions are present.

Fig. 65. Dorsal view of cranium, Zygaena, left side. (Modified from Gegenbaur. )
or., orbit; po.o., postorbital process; pr.o., preorbital process.

In aside view (figs. 66 and 68) the auditory, optic, and olfactory regions of
the eranium are seen to advantage. With the exception of Chlamydoselachus
and the notidanids the auditory region is greatly modified superficially for
the attachment of the hyoid arch. In most of the recent sharks the articulation
is made by means of a deep pit (as is present in Heterodontus, fig. 66). In some
of the rays a special part from the hyoid arch makes an extended articulation
with this part of the cranium.

Anterior to the auditory region is the enlarged orbit in which the eyeball
rests. Its roof is usually formed by a supraorbital crest, modified posteriorly
into a postorbital process (po.o.), and anteriorly into a preorbital process
(pr.0.)..

In the sharks the postorbital process is rarely extended. Exception must be
made, however, of Zygaena, the hammerhead (po.o., fig. 65) and its near ally,
the bonnet shark, where it may be prolonged outward to meet the posterior
part of the preorbital process. Exception should be made also of Chlamydosel-
achus and the notidanids in which the postorbital process serves in suspend-
ing the upper jaw. In the rays, except those bearing stings, this process is
characteristically small or absent.

The preorbital process in Zygaena (pr.o., fig. 65) arises far out on the era-
nium and is divided into anterior and posterior parts. The anterior part

THE ELASMOBRANCH FISHES 59

Fig. 67. Skull of Heterodontus francisci (articulate). (Duncan Dunning, del.)

a.c., auditory capsule; ch., ceratohyoid; l., labial cartilage; f.op., foramen for profundus
nerve; f.r-a., foramen for ramus anastomoticus artery; f.J/, optic foramen; f.IV, troch-
learis foramen; f.V 1/7, foramen for hyomandibularis branch of facial nerve; f.X., foramen
for tenth nerve; im., hyomandibula; md., mandible; o.f., orbital fissure; 0.p., optie pedicel ;
po.o., postorbital process; p-q., palatoquadrate cartilage; pr.o., preorbital process; sp.c.,
spiracular cartilage.

60 THE ELASMOBRANCH FISHES

joins the nasal capsule and the posterior part extends back to the postorbital
process (po.o.). Between anterior and posterior parts is located the secondary
orbit (or.).

In the notidanid sharks, in Chlamydoselachus, and in the rays there is a
posterior projection from the preorbital region, the antorbital process (figs.
69 and 47, a.pr.). In the notidanids and Acanthias this serves for the attach-
ment of one of the superior labial muscles. In the rays it unites the pectoral fin

skeleton to the cranium.
The eyeball is held out from the cranial wall by a rod, the optic pedicel

(Heterodontus, fig. 67, o.p.) ; this pedicel in some of the sharks has a terminal
expansion into which the eyeball fits. In Chlamydoselachus (fig. 46) it further
serves as a place of origin for the rectus muscles. In the rays the pedicel is
plate-like and may be fixed to the eyeball (Torpedo).

The apertures which perforate the orbital region for the cranial nerves and
blood vessels vary considerably in size and position from those given for Hep-
tanchus. Ordinarily the optic foramen (f.IJ, fig. 66) is relatively large and
occupies a central position in the orbit, but in types hke Rhinobatis (fig. 68)
it is well forward. In the embryo (Acanthias) this foramen separates the
alisphenoid from the trabecular cartilage. The oculomotor and the troch-
learis foramina take positions respectively behind and above the optic; but the
trochlearis is variable. In the rays (Rhinobatis, fig. 68, f IV; Myliobatis) it is
above but posterior to the aperture for the optic nerve. The orbital fissure
(o.f.) usually gives exit to the fifth and a considerable part of the seventh
cranial nerves, and in a type like Rhinobatis is of unusual size. In this type it
is not unhke the large fissure which early forms a separation of the alisphen-
oids from the parachordal cartilages in the embryo of Acanthias. In Mustelus
henlei, where there are special foramina for the superficial division of the
seventh nerve and the profundus division of the fifth nerve, the fissure is re-
duced in size. The foramen for the sixth nerve usually opens separately at
the base of the orbital fissure. The facial foramen for the hyomandibular
branch of the seventh nerve may be located posterior to the orbit, as in Hep-
tanchus (f.VII°, fig. 47), in Scymnus, and in other forms; or it may be in the
posteroventral angle of the orbit (Heterodontus, fig. 66, f.VIIZ; and others).
In the upper anterior angle of the orbit is the ophthalmic foramen (or fora-
mina) which gives exit to the ophthalmicus superficialis of the seventh nerve.
In Heterodontus, as is general for the Elasmobranchs, the profundus nerve
(f.op.) leaves the orbit by an extra foramen ventral to that for the ophthal-
micus superficialis.

Anterior to the orbit is the ethmoidal region in which is situated the nasal
or olfactory capsule. The capsules in the simpler forms are more or less ter-
minal in position, while in the highly specialized rays, as for example Mylio-
batis, the region is bent sharply downward so that the apertures are entirely
ventral in position. The olfactory cups are usually more or less surrounded by
cartilage, leaving their apertures as relatively small openings. These openings
are visible in side view in the sharks only. The nasal cartilages surrounding
the openings have been described.

THE ELASMOBRANCH FISHES 61

Fig. 68. Cranium of Rhinobatis productus, lateral view. (Chester Stock, orig.)

Fig. 69. Skull of Raja clavata (articulate). (Modified from W. K. Parker. )

a.pr., antorbital process; f.JI, optic foramen; f.JV, trochlear foramen; f.V IZ, foramen
for hyomandibular branch of facial nerve; h.md., hyomandibula; md., mandible; o.f., orbi-
tal fissure; po.o., postorbital process; p-q., palatoquadrate; pr.o., preorbital process; s.0.,
supraorbital crest; sp.c., spiracular cartilage.

62 THE ELASMOBRANCH FISHES

VISCERAL SKELETON

The cartilaginous visceral skeleton in the Elasmobranchs usually consists of
seven visceral arches: the mandibular, the hyoid, and five branchial arches. In
Chlamydoselachus and the notidanids, however, there are additional branchial
arches making a total of eight visceral arches in Hexanchus and Chlamydosel-
achus and, as we have seen, nine in Heptanchus.

Fig. 70. Development of embryonic visceral arches in Acanthias. (From Sewertzoff.)
md.a., mandibular or first arch; or.p., orbital process.

The visceral arches of the adult are more easily understood if we first study
their early arrangement in the embryo. In a reconstruction made by Sewert-
zott of the embryo of Acanthias (fig. 70), all the arches appear as bent ecarti-
laginous bars which as yet have not divided into segments. The first or mandi-
bular arch (md.a.) takes the form of an inverted U. On the upper (anterior )
limb of the arch is a process which abuts against the trabecular cartilage, and,
in the adult, forms the orbital process (or.p.) for articulation with the cra-
nium, The second or hyoid arch at this stage is sigmoid in shape, and even here
joins the cranium in the region of the auditory capsule. The remaining five
branchial arches, third to seventh viscerals, are crescentic in shape and like
the preceding arches show no signs of segmentation at this stage.

The mandibular arch in all adult Elasmobranchs, as in Heptanchus, is di-
vided into (1) an upper palatoquadrate (pterygoquadrate) segment (p-q.)
and (2) the mandibular segment or Meckel’s cartilage (id., figs. 67 and 69).
In simple types like the notidanids the palatoquadrate may have two fairly
well defined regions, an anterior palatine (pterygoid) and a posterior quad-
rate. In more specialized forms, however, it is impossible to distinguish these
segments other than by position. On the anterior part of the quadrate segment
may be present an orbital (palatobasal) process which articulates with the me-
dian wall of the orbit (Chlamydoselachus, Scymnus, Acanthias) ; or it may be
wanting, as for example in Heterodontus (fig. 67) and Raja (fig. 69) where the
mandibular arch is shoved forward. The palatoquadrate cartilage unites in
front with a similar segment from the opposite side, as does also the mandible.

THE ELASMOBRANCH FISHES 63

The union of the right and left cartilages may be loosely made (notidanids ) or
it may be firmer as in most forms; that of the mandibular cartilage, while firm
in the rays, is loose in most sharks except Squatina and Heterodontus.

The articulation of the upper and lower jaws may be by a joint in all re-
spects similar to that of Heptanchus; such is the articulation in Chlamydosel-
achus and Heterodontus. Or the joint may be slightly more specialized as
in Scyllium. A highly specialized type found in the Elasmobranchs is that in
Raja (fig. 69), where a single ball and socket joint prevails. The joint may be
bound simply by short ligaments, or it may be firmly held by a most complex
ligamentous arrangement, as in Heterodontus francisci (figs. 67 and 128).

Following the mandibular arch, and above the quadrate segment, is the
spiracular cartilage (sp.c., figs. 67 and 69) whieh supports the filaments in the
anterior wall of the spiracle, where such exist. This cartilage may be composed
of several segments (three in Centrophorus, two in Acanthias), or it may con-
sist simply of a single piece. In other sharks where the spiracle is minute the
cartilaginous support may be absent (Lamna). In the rays (Torpedo, fig. 63;
Raja, fig. 69; Myliobatis) it is well developed, and serves as a framework for
the support of the spiracular valve. It follows a true prespiracular ligament.

The hyoid or second visceral arch, which is simple in primitive sharks, is
subject to great modification when the Elasmobranchs in general are con-
sidered. This arch in its generalized condition (Heptanchus) is composed of
a dorsal segment which suspends a ventral segment. Under such conditions
the hyoid does not function, or functions but slightly, in suspending the first
or mandibular arch. The proximal end of the dorsal segment consequently is
attached loosely by ligaments and hence indents the auditory capsule but
slightly as in Heptanchus cinereus. In other types it may indent the capsule
by only a part of its surface (Heranchus, Chlamydoselachus). When this oe-
curs the distal end of this segment suspends the ventral segment of the hyoid
and the latter is bound by ligaments to the mandible.

In general, an attachment of the second arch to the mandibular may be
made by a ligament at the joint and elsewhere. In Chlamydoselachus the form
of attachment is very simple. While the lower segment depends slightly upon
the mandible, the latter begins also to depend upon the upper segment for
support. In other words, the dorsal segment is on its way to become a hyoman-
dibula or suspensorium. Where it is a true hyomandibula, as in most sharks,
this upper segment of the hyoid arch is of service primarily to the first arch. As
a suspensorium it becomes stronger and its articulation with the cranium be-
comes deeper; furthermore, its ligamentous attachment to the mandibular
arch may be most complex (Heterodontus francisci, fig. 67; see Daniel, 1915).

When the upper segment of the hyoid has assumed the secondary function
of suspending the mandibular arch, that is, where it becomes hyomandibular,
it may still continue to suspend the lower part of its own arch also. This is
indeed characteristic of the sharks. But the lower segment may lose connec-
tion more and more with the upper (hyomandibular) segment. Instead of
being suspended from the distal end of the hyomandibula, it may be jomed

64 THE ELASMOBRANCH FISHES

posteriorly to the middle portion of the hyomandibula (Torpedo, fig. 63).
Such a union results from the method of growth of the hyomandibula. A proc-
ess extends from the anterior angle of the upper segment which, in the adult
Torpedo, forms the suspensorium or hyomandibula. This part suspends the
mandibular arch while the lower segment is attached to the posterior part of
the hyomandibula (fig. 69). In some of the other rays the lower segment may
not be attached at all to the hyomandibula, but may be united with the poste-

@ pb:

1Biven 7/1

Fig. 71. First branchial arch, Heterodontus francisci. (Duncan Dunning, del.)
Fig. 72. Fourth and fifth branchial arches, Heterodontus francisci. (Duncan Dunning, del.)

b.r., branchial ray; cb., ceratobranchial; eb., epibranchial; ex.b., extrabranchial carti-
lage; pb., pharyngobranchial.

rior part of the cranium (Urolophus). Ina still more specialized form it may
have no union either with the hyomandibula or with the cranium, but may be
bound to the tip of the first branchial (third visceral) arch, as in Rhinobatis
and Myliobatis. In some such occurrences the lower arch may be further
segmented.

The branchial arches in general are typically made up of four segments (fig.
71, Heterodontus) which from dorsal to ventral, as was given for Heptanchus,
are: (1) the pharyngobranchial (pb.), (2) the epibranchial (e.b.), (3) the
ceratobranchial (cb.), and (4) the hypobranchial (hb., fig. 73) segments.

The pharyngobranchials are usually flattened cartilages which he dorsal to
the pharynx. In sharks they are usually attached by strong connective tissues
(ligaments) to the roof of the pharynx or to the sides of the spinal column
but not to the pharyngobranchials of the opposite side, as is the first in Hep-
tanchus and Scyllium. In the rays, the pharyngobranchial segment of the first
branchial arch, as we have said, may join the cranium (Rhinobatis, Trygon).

THE ELASMOBRANCH FISHES 65

The most posterior pharyngobranchial, as a usual thing, in both sharks and
rays is fused with the one preceding, hence it may lose much of its character-
istic shape (Heterodontus, fig. 72).

The epi- and ceratobranchials are the ray-bearing segments of the arches.
In all, except the most posterior arches, these segments are similar. In the last
arch, both of these segments are more or less modified. Generally this modifica-
tion takes the form of a thickening of the ceratobranchial (sharks) and an
atrophy of the epibranchial because of its fusion with its pharyngobranchial
cartilage.

The hypobranchials, although perhaps more regular in a type like Chlamy-
doselachus (fig. 734) than in Heptanchus, are generally more variable than
are any of the other segments. In the sharks the first, if present, is usually
small and is located between the distal end of the first ceratobranchial and the
hyoid eartilage (Heterodontus, fig. 738, hb.'; Laemargus). The second may
fuse with a similar one from the opposite side across the midventral line
(Scymnus, Laemargus) ; or the two may join a median unpaired cartilage,
the second basibranchial, as in Acanthias, Trygon, Heterodontus (bb., fig.
73B) ; or they may arch backward to join the enlarged median piece (mp.) as
in Torpedo (fig. 63) and Rhinobatis. Generally the third and fourth hypo-
branchials of pentanchid forms, except in some of the rays, are well developed
and are attached to the large median unpaired piece. In general, except Hep-
tanchus (fig. 50), hypobranchials on the most posterior arch are lacking or are
fused with the unpaired median piece to which the third and fourth hypo-
branchials are attached. In the rays these segments may be present as plate-
like cartilages attached to the unpaired median piece (Raia erinacea, fig. 748).

In the midventral line unpaired basal elements join the arches of the right
and left sides. The element connecting the two halves of the hyoid arch is
the basihyoid (bh., fig. 73) and those connecting the branchials are the basi-
branchial cartilages (bb.). The basihyal cartilage may be a broad plate, per-
forated by the thyroid foramen (Chlamydoselachus, fig. 734, bh.) ; or it may
bear an anterior glossal projection as a support for the tongue (Heterodontus,
fig. 738, g.p.; Scyllium). Again it may be a narrow band as in Acanthias or as
in Raa erinacea (fig. 748) ; or it may be incomplete as in Torpedo (fig. 63).
Basibranchials are present as distinct irregular pieces of cartilage anteriorly,
but posteriorly they may fuse into a single mass. Generalized forms are char-
acterized by numerous basal elements. The first of these may be a peg-like
structure attached to the basihyoid (Chlamydoselachus), or it may lie free be-
hind the basihyoid (Laemargus). The second basibranchial is usually free and
the third, when present, is often attached to the larger posterior median piece
which may or may not be segmented. In the rays only the posterior median
piece is present (Rhinobatis, and Torpedo, fig. 63).

In the embryo of some forms well marked rudiments of still other branchial
arches persist, as we have seen in Heptanchus. Such rudiments are also pres-
ent in Chlamydoselachus, where a seventh arch has been deseribed, and in
Heterodontus and in some of the rays, where a sixth arch may occasionally be

66 THE ELASMOBRANCH FISHES

found. The rudimentary arch in the embryo of Heterodontus consists of at
least two segments, which in the adult may still be seen, welded more or less
closely to the fifth branchial arch (fig. 72). Rudiments of such structures are
of interest in forms like Heptanchus and Chlamydoselachus in which an un-
usual number of arches becomes functional in the adult. That still other rudi-
ments are present in the embryo indicates that ancestral forms possessed a
number of arches exceeding that of present-day types.

A B

Fig. 73. Median ventral basibranchial cartilages. A. Chlamydoselachus. (From Goodey.)
B. Heterodontus francisci.

bb., basibranchial; bh., basihyoid; cb., ceratobranchial; g.p., glossal process; hb., hypo-
branchial; mp., median piece.

Figure 50B represents the area of rudimentary arches in Heptanchus macu-
latus. It will be observed that a slight asymmetry is shown which gives a some-
what greater development of the midventral region on the right than on the
left side. Through this asymmetry the rudimentary arch and adjoining area
on the right side are more highly developed than on the left.

Upon examination of the ventral side of the rudimentary arch on the right
side I found certain round and pointed rays (r., fig. 50B) arising from the

THE ELASMOBRANCH FISHES 67

seventh ceratobranchial practically at right angles to its long axis. These rays
extend posteriorly between the plate « and the median piece as clear pieces of
hyalin cartilage. Whether they represent rudimentary branchial rays on the
seventh arch like those described by Gegenbaur (1872, pl. 12, fig. 5) on the
anterior margin of the fifth areh for Scyllium, or have to do with the rudi-
mentary arch following, is not certain.

On the middle piece a similar arrangement is found. Here there are three
pieces which are successively longer toward the middle line. They are essen-
tially identical in appearance with the rays above described on the seventh
ceratobranchial segment, but they are attached along their whole dorsal
length as flattened lamellae. Terminally the median two look very much like
the rays above described and they are much like them also in that they are of
clear hyalin cartilage. Farther toward the median line on the middle piece
there is clear evidence of still another similar group, except that it is nomena

iffer-
ing distinctly from the median piece, which, in the specimen, is of a dark

rated into rays or lamellae. This group is also of clear hyalin cartilage ‘d

color. I have interpreted this group as a remnant of a ninth areh (ar.°), al-
though I am not certain what part it represents.

The condition found in this specimen is suggestive as to the method of for-
mation of the enlarged median piece so characteristic of the Elasmobranchs. It
would appear that in this region the rudimentary arches are forced more and
more to take a longitudinal direction nearer the middle line, and that the
median piece represents in its most posterior part the fusion of these arch@s
from side to side.

Extending from all the visceral arches, except the first (mandibular) and
the last, is a series of cartilaginous branchial rays for the support of gills.
These supporting rays are confined to the epi- and cerato-segments. The bran-
chial rays may be complex and branched, the termini fusing into arches on
the hyoid (sharks), or they may be comparatively simple and straight (rays).
In Torpedo a curious modification of the branchial rays occurs in the form of
terminal dises (b.r., fig. 63), each of which is almost circular in shape. These
cartilaginous rays, although fewer the more posterior the arch, may be ex-
ceedingly numerous anteriorly as in Lamna, or relatively sparse as in Lae-
margus. The central ray, the one between the epi- and the ceratobranchial,
may exceed all others in length. This ray may be postulated as the main axis
of the fin skeleton according to the gill-arch theory for the origin of paired fins.

EXTRAVISCERAL ARCHES

Outside of the deep internal visceral arches are the extravisceral cartilages.
These may be divided into the labials' of the mandibular arch, the extrahyals
of the hyoid, and the extrabranchials of the branchial arches. Normally each

1 The labial segments are often interpreted as representing arches formerly present be-
tween the mandibular and hyoid arches.

68 THE ELASMOBRANCH FISHES

of these arches is made up of two segments, one dorsal, the other ventral in
position.

Three labial cartilages are usually present on a side in sharks, two dorsal,
the so-called premaxillary and the maxillary cartilages on the palatoquadrate,
and one ventral on the mandible. Of the dorsal segments the anterior is the
shorter. When well developed the labials serve to reduce the gape of the mouth.

Fig. 74. Extrabranchial cartilages of Raia erinacea. (From Foote.) A. Dorsal view.
B. Ventral view.

ex.b., extrabranchial cartilage; ex.h., extrahyoid cartilage; md., mandible; mp., median
piece; p-q., palatoquadrate (pterygoquadrate) cartilage.

An interesting series may be followed in the specialization of these carti-
lages from the simple condition of a single cartilage to the tripartite condition
just mentioned. Heptanchus cinereus has a single labial located dorsally,
which because of its small size long escaped observation (Fiirbringer, 1903).
In Heptanchus maculatus (1., fig. 48) there is a single cartilage, shaped like a
tuning fork, which extends across the gape of the mouth and ends dorsally in
two horns. It gives no evidence, however, of segmentation. In Hexranchus, the
labial extends across the gape of the mouth and according to Gegenbaur
(1872) is more or less divided into an anterior and a posterior division. In
the notidanids, then, we have practically a complete transition from the single
rudiment to the condition found in more specialized forms.

It may be said of transitional rays that the labial cartilages are poorly
developed (Rhinobatis).

THE ELASMOBRANCH FISHES 69

Since the extrahyoids and extrabranchials both serve the same purpose the
two types may be described together. These structures support the free mar-
gins of the gill septa and hence run parallel with the deeper visceral arches to
which the septa are attached. They may be present on the hyoid and on all the
branchial arches except the last, as in Acanthias and in Raia erinacea (ezx.b.,
fig. 74). In others, while the extrahyoid is lost dorsally it may persist ven-
trally, making five inferior and only four superior cartilages (Heterodontus
francisci). In still others, both segments of the extrahyoid arch may be absent,
and yet a full complement of extrabranchial arches on the first four branchials
may be present (Trygon). Ina reduction of the number of extrabranchials the
posterior cartilages are the
first to be absent. A fourth ex-
trabranchial may be lacking
ventrally, leaving three below
and four above (Scyllium).

While the extrahyal seg-
ments present are normally
small, the extrabranchials over
the branchial arches may be Fig. 75. Sagittal section through a developing verte-
well developed. Occasionally bra, Scyllium canicula. (From Schauinsland. )
the tips of the dorsal and ven- chd., notochord ; e.€., elastica externa ; é.t., elastica

; interna; ep., chordal epithelium ; 7z., inner zone; mz.,
tral segments of the anterior iadle zone; 02., outer zone.
arches overlap as in Hetero-
dontus (fig. 71). In most forms, however, the dorsal and ventral segments fail
to touch (Acanthias), and in many they are relatively insignificant structures
(Raia erinacea, fig. 74).

We have said above that the extravisceral arch is normally composed of a
superior and an inferior segment. In a number of species an interesting con-
dition is found in which lateral pieces, extraseptalia, are also added. These
may be present as flattened bands of cartilage between the external clefts
(Torpedo; Raja clavata) or they may be flattened plates lying underneath the
forward projection of the propterygial segment of the fin skeleton as this
passes over the region of the gills (Myliobatis). In Cephaloptera, the devil
ray, they are relatively large plates bound under the propterygium.

SPINAL COLUMN

The spinal column in Elasmobranch fishes shows great variation, from a
simple cartilaginous tube around the notochord, as in Heptanchus maculatus,
to the highly segmented and calcified column common to many forms. In gen-
eral, it consists of a central axis made up of centra upon which is a series of
neural arches, which extend throughout the body. In the region of the tail,
haemal arches, under the centra, furnish protection for the haemal or blood
vessels. A vertebra includes a centrum and its neural and haemal arches.
The vertebrae vary greatly in numbers. In a type like Heterodontus there are
only a few more than a hundred in the whole column, while in Alopzas there
are more than twice that number in the tail alone.

70 THE ELASMOBRANCH FISHES

In Elasmobranchs the column is particularly instructive because of its rela-
tion to the still more primitive notochord found in the prechordata and in the
embryo of all vertebrates. This new cartilaginous column arises around and in
the sheath of the notochord as a secondary and more effective support. Its
mode of development may be noticed briefly. :

In the embryo, cells proliferate from the sclerotome or inner part of the
somite (see p. 96, fig. 97, scl.) and migrate inward to a position around, above,
and below the notochord. Those which collect at the upper and lower levels
form four cogs with the notochordal sheath as the center. These cells lay down
cartilage for the neural and haemal arches and around the notochord.

Many of the cells around the notochord, however, may perforate its external

fd yc tan cues wall (elastica externa) and deposit car-
LOS é tilage within the notochordal sheath.
A sagittal section through a vertebra of
Scyllium canicula is shown in figure 75,
The sheath between the outer (e.e.) and
inner (e@.t.) layers in which cartilage is
deposited may be divided into outer
, (oz.), median (mz.), and inner (72.)
ees zones. The median zone is the one in

AEM AOC SOS TUG Ua Tok which calcium is usually deposited.

The central column, in
a simple type like Hep-
tanchus maculatus, is es-
sentially a thin tube of
cartilage (oz., fig. 52)
deposited in the sheath of
the notochord. The mid-
dle zone here is composed

B. Rhinobatis productus. (Chester Stock, orig.)

Fig. 76. Cervical vertebrae. -

bd., dorsal basal plate (basidorsal) ; bv., ventral basal of transverse fibers in the

plate; c., centrum; f.d., foramen for dorsal nerve; id., sheath, which in some re-

dorsal interealary (interdorsal plate) ; 7., rib; sbd., neural
spine.

spects appear to be like
the “chordafaserscheide”
deseribed for Amphiozus by Von Ebner (1895). As to the layer which is desig-
nated “72.” in figure 52 I am not sure whether this represents the inner zone of
more specialized Klasmobranchs or is a part of the elastica interna.

In types only a little more specialized than Heptanchus maculatus (Chlam-
ydoselachus and Heptanchus cinereus), a slightly greater amount of calei-
fication may be present in the column; and in still more specialized forms,
where the column becomes a stronger support than that just described, ealei-
fication is a pronounced feature. But different regions vary greatly in the
amount of calcification. For convenience of description the column may be
divided into three regions. The first of these, the anterior section, joins the
head; the second is in the area of the trunk; and the third we may designate
simply as the caudal segment of the column.

THE ELASMOBRANCH FISHES (al

The anterior section of the column differs in the various Elasmobranehs in
its relation to the cranium. In the notidanids, as we have seen, the two are
more or less continuous. This continuity is further emphasized in all general-
ized forms by the fact that this fused region is perforated by a number of
occipitospinal nerves which arise between the vagus and the first spinal nerve.
In a type lke Acanthias in which there are a dorsal and two lateral ridges
continuing directly from the column to the cranium, the relation of the two

r
A. Rhinobatis productus. (Chester Stock, orig.)

sbhd fv. £0

B. Heterodontus francisci. (Dunean Dunning, del.)

Fig. 77. Transitional vertebrae.
bd., dorsal basal (basidorsal) plate; bv., ventral basal plate; f.d., foramen for dorsal root

nerve; f.v., foramen for ventral root nerve; iv., ventral interealary; n.s. (and) sbd., neural
spine; r., rib.

regions is not so clear; while in still more specialized forms the column is more
or less clearly separated from the cranium, attachment of the two being made
by processes of the cranium and the column (rays).

This segment of the column (fig. 764, Heterodontus), unlike that of Hep-
tanchus, is usually clearly divided into centra (c.). In practically all forms the
relation of the dorsal and ventral arches to the centra is equally clear. In a
type like Pseudotriacis, however, the segmentation is irregular, both in the
centra and in the neural arches of the column. This irregularity is especially
marked in the most anterior vertebra which has fused into a solid ring. In the
rays (Rhinobatis, fig. 768) the larger part of this anterior region has second-
arily fused into a solid vertebral plate, the segmentation of which is made out
only through a study of the foramina and certain lateral processes.

72 THE ELASMOBRANCH FISHES

The trunk vertebrae lie between the pectoral and pelvie regions and their
dorsal and ventral plates are usually distinct and regular. In some types,
however, as for example Laemargus borealis, the dorsal interealary plates
represent the maximum of change in that each plate is subdivided into two or
more parts. A similar segmentation in the ventral intercalary plates may be
present in this area.

The anterior vertebrae of this region are rib-bearing but there is great
variation in the number of ribs present. In Laemargus borealis ribs are present
on only a few vertebrae, while in other forms ribs may extend almost to the

Fig. 78. Caudal vertebrae.

A. Heterodontus francisci. (Duncan Dunning, del.)
B. Rhinobatis productus. (Chester Stock, orig.)
h.s., haemal spine; id., dorsal intercalary plate.

posterior limits of the trunk area. The posterior part of the trunk segment
offers great variation in the different elements of the column and is of particu-
lar interest because of diplospondyly or doubling of the segments, which is
present here.

Diplospondyly may begin immediately after the last rib-bearing centrum ,
(Heterodontus, fig. 778), or a series of vertebrae may intervene before the
diplospondylous vertebrae are reached. In Scyllium, according to Ridewood
(1899), a brief area of transition follows the rib-bearing segments in which
the stages from monospondyly to diplospondyly may be traced. The first indi-
eation of the change is seen in the slight shifting backward of the dorsal
interealary plate of the first vertebra behind the last one bearing a rib, so that
one of the neurals rests directly upon the dorsal basal plate. In the vertebra
following, this condition is further accentuated and results in diplospondyly,
which is also seen in succeeding vertebrae. In a type like Rhinobatis (fig. 774)
the rib-bearing segments (7.) extend far posteriorly and are separated from
the true diplospondylous segments by only a few vertebrae. In this type, also,
the spines are of large size and rest between two or more of the irregular
interealary pieces.

THE ELASMOBRANCH FISHES

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74 THE ELASMOBRANCH FISHES

The doubling probably is to be interpreted as meaning that there is need
for greater freedom of movement in the active area preceding the caudal fin.
In this area where the most severe strain is imposed upon the column it is
important, as Ridewood has suggested, that greater strength and at the same
time greater freedom of movement be obtained. Strength is given by the in-
creased calcification, and freedom of movement is brought about by increasing
the number or decreasing the size of the segments; that is, by diplospondyly.
Diplospondyly may extend practically to the tip of the tail (Acanthias) or
the terminal segments may be irregularly segmented (heterospondyliec).

As a usual thing the vertebrae in the caudal segment of the column present
marked regularity in their centra and arches. In Heterodontus (fig. 784) the
radials are more numerous than are the vertebrae. In Lamna the dorsal
radials are inconspicuous, while those having a ventral position are usually
large. In this type we see the extreme of heterocerey, in which the axis of the

body turns sharply upward into the dorsal lobe of
the caudal fin. In Rhinobatis (fig. 78B) the caudal
segment is unlike that of the sharks especially in
that the vertebral column is here practically straight,
and dorsal and ventral radials of the caudal fin skele-
ton are of practically equal length. Such a type is

more nearly diphycereal than heterocereal.

©) a Helbing (1904) has shown for Laemargus that
chd- o3 there is a tongue of cartilaginous segments in the
area between the ventral lobe of the caudal fin and
Fig. 80. Cyclospondylous the pelvie fin. This tongue is attached to the haemal
vertebra, Squalus sucklii. process of one of the vertebrae posteriorly and ex-
ca., calcification; chd., tends anteriorly. While the basal plates of the

notochord; n.c., neural ‘ : : :
Ganel: neural arches are uniform in size, the intercalary
pieces are variable. In the anterior part of this area
(fig. 78B) they may segment irregularly, while more posteriorly they are con-
tinuous with the dorsal radials. At the most posterior tip the intercalaries and

radials represent an irregular mass.

In various regions of the column the ealcification takes up different lo-
calities, forming diverse and curious designs. Probably the simplest design
is that in which a single ring of calcium is produced in the middle zone of the
notochord sheath (fig. 75). A cross-section through a centrum thus calcified
shows the ring, of large or small diameter depending upon whether it is cut
near the end or at the middle of the centrum. A sagittal section would show it
as a broad V above and as an inverted broad V below within the centrum,
the two V’s being separated at their apices by the notochord. Such a type of
vertebra has been designated by Hasse as cyclospondylous (fig. 80, Squalus
suckli). ;

Another design formed by the ealcification is a further addition to the
eyclospondylous type. In this, two or more concentric rings of calcium are
formed in the sheath of the notochord. The inner ring is thick like that of the

THE ELASMOBRANCH FISHES 75

eyclospondylous type, but the outer cirele is usually a thin sheet. Such a type
of calcification is known as tectospondyly. A modification of the tectospondyl-
ous type may add still other outer circles, as, for example, in Squatina. A
sagittal section through this type would show the heavy inner circles as V’s
above and below, which are concentrically surrounded by sections of other
circles, appearing as more or less straight lines.

A most interesting and varied type of calcification is arranged around the
inner zone of the notochordal sheath as a central hub from which spokes or
rays diverge in a star-like fashion through the outer zone (asterospondyly).

Fig. 81. A and B. Stages in development of the pectoral fin of Seyllium canicula. (From
Balfour.)

Ms.p., mesopterygium; mt.p., metapterygium; pr.p., propterygium; ra., radial.

Few calcified rays may be present as in Galeus, or they may be more numerous
as in Heterodontus (fig. 794) and Rhinobatis (fig. 798). In Alopias more than
twenty rays are present.

So characteristic are the above types of calcification that Hasse has used
them as a basis for classification. Under such a classification exceptions must
be made, however, for many variations are to be found.

APPENDICULAR SKELETON
SKELETON OF PAIRED FINS AND OF FIN GIRDLES

PECTORAL FIN SKELETON

The skeleton of the pectoral fin, as noted in Heptanchus, consists of a more or’
less horizontal framework of cartilage attached to a vertical girdle. The car-
tilages making up the framework of the pectoral fin itself are: (1) a set of
basal cartilages from which projects (2) a series of median cartilaginous

THE ELASMOBRANCH FISHES

Fig. 82. The adult pectoral fin, Heterodontus francisci. (Duncan Dunning, del.)
ms.p., Mesopterygium; mt.p., metapterygium; pr.p., propterygium; ra., radials.

THE ELASMOBRANCH FISHES 77

radials (ra., fig. 82). In some forms there may also be found (3) a series of
distal plate-like radials (Heterodontus) between upper and lower dermal rays.
A knowledge of the development of such a skeleton is helpful to an under-

standing of the adult frame-
work. In Scylliwnm canicula
(fig. 81) Balfour (1881) has
shown that the pectoral skele-
ton arises as a horizontal bar or
plate of cartilage from which
radials (ra., fig. 81) extend.
These radials by fusion at their
outer tips form a rim from
which plate-like distal radials
pass well out into the fin. As
erowth progresses the original
bar of cartilage becomes the
main axis of the fin skeleton,
the metapterygium (mt.p., fig.
814) to which numerous ra-
dials are attached. Anterior to
the metapterygium, the so-
called median piece or mesop-
terygium (ms.p.) arises sec-
ondarily; fewer radials pro-
ject from it. There is next seg-
mented off from the anterior
part of the mesopterygium a
piece, the propterygium (pr.p.,
fig. 818), which bears a single
plate-like radial. As for the
pectoral girdle, it is formed
secondarily from the anterior
tip of the horizontal bar.

In the adult shark the sim-
pheity of plan characteristic
of this embryonie fin is rarely
retained (Chlamydoselachus),
vet the fundamental plan here
laid down is the same, even in
the most specialized of pec-
torals. Propterygium, meso-,
and metapterygium are usu-
ally present. The propteryg-
inm may be fused with the
mesopterygium. as in the adult

tal

Fig. 83. The adult pectoral fin, Rhinobatis produc-
tus. (Mildred Bennett, del.)

ms.p., mesopterygium; mt.p., metapterygium;
ne.p., neopterygium; pr.p., propterygium.

78 THE ELASMOBRANCH FISHES

Heterodontus philippi, although this does not occur in Heterodontus francisci
(fig. 82). The mesopterygium is usually an independent piece, but it may be
masked by fusion as in Pristiophorus japonicus. A considerable change from
the embryonic plan of the basals is found in Scymnus lichia, in which only a
single basal cartilage is present. It is supposed that the missing basal earti-
lages have secondarily fused in the adult.

The form of the fin in the rays differs greatly from that of a shark like Hep-
tanchus in that the basal cartilages are modified in keeping with the dorso-
ventral depression and the great extent, anteroposteriorly, to which the fins
are expanded. The pectoral of Squatina, although shark-like in its articulation,

Fig. 84. Pectoral girdles. A. Heterodontus francisci. B. Torpedo. (Modified from Gegen-
baur.)

co., coracoid; f.pt., aperture for nerve and blood vessels to pectoral fin; sc., seapula.

is like that of the rays in extent; it has, however, a much heavier mesopter-
ygium than have the rays. Usually the propterygium of the rays is divided
into anumber of segments which extend forward to join the antorbital process
(Rhinobatis, fig. 83, pr.p.; Raja, Myliobatis), or even to the tip of the ethmoid
region where the two from the opposite sides unite (Urolophus). The mesop-
terygia of the rays are very variable. In some forms a mesopterygium is absent
whereupon the radials extend to the girdle. In other types there is a consider-
able mesopterygial plate, as in Rhinobatis (ms.p., fig. 83). In others still, a
second plate back of the mesopterygium may be formed, as in Pteroplatia. The
metapterygium of the rays, like the propterygium, is greatly developed, pass-
ing backward to the region of the pelvie fin.

The propterygial radials of the sharks are usually few in number. They may
form a single line of segments which may be of more or less regular plates, as
in Heptanchus or Heterodontus francisci (fig. 82). In others the rows may be
more numerous. In the rays there are many rows of such propterygial radials,
some of which are made up of great numbers of segments (Rhinobatis, fig. 83).

The radials attached to the mesopterygium in the sharks are more numerous

THE ELASMOBRANCH FISHES 13)

than those of the propterygium. In the rays these are of unusual interest. In
addition to those extending from the mesopterygial cartilage there are certain
other radials posterior to this cartilage, as we have said, which extend to the
girdle. Five such oceur in Raja clavata, two or three in Squatina, a shark, and
a larger number in some other forms. The most interesting thing about these
extraradials is that in some of the rays they produce, as Howes (1890) has
shown, a fourth basal, the neopterygium (ne.p., fig. 83), indicated in Rhino-
batis and well formed in Pteroplatea.

In the rays the metapterygial radials are similar to those of the propteryg-

PAD

Vege

LLL pgs

LL,

SKA

ba.p.4_

Fig. 85. Pelvie fin and girdle, Chlamydoselachus (A 3, B 2). (From Goodey.)
For explanation see fig. 86.

ium. In the sharks these normally are found in the adult on the anterior side
of the main metapterygial axis. Not infrequently, however, postaxial radials
are well developed in the embryo (Acanthias, Carcharias, and many others).
The significance of postaxial radials has been pointed out by investigators
seeking a solution of the early form of the paired limb. Those who hold that
the early type of limb was like that of the present-day lungfish, Ceratodus,
with a central axis and anterior and posterior rays, think that the postaxial
rays of sharks are remnants of a past condition.

PECTORAL GIRDLE

The right and left limbs of the girdle are incomplete dorsally except in the
rays, in which the upper tips may be firmly joined to the spinal column or to
each other. Each half of the girdle is composed of two pieces, one dorsal, the
scapula (sc., fig. 84), another ventral, the coracoid (co.). The scapula varies

80 THE ELASMOBRANCH FISHES

a great deal in the direction which it takes. In Heptanchus it slopes very
obliquely backward, while in Heterodontus and especially in the rays it stands
more nearly vertical. In general it is capped by a suprascapular cartilage.

Fig. 86. Pelvic fin and girdle of male. A. Heterodontus francisci. B. Rhinobatis productus.
(Chester Stock, orig.)

B, beta cartilage; b.1~, intermediate segments; ba., basal or axial cartilage; ba.p., basip-
terygium; d.mg. and mg. (fig. 85), dorsal marginal; d.tr.*°, first and second dorsal termi-
nal cartilages; pl., pelvic cartilage; ra. (fig. 85), radials; spn., spine; tr.*, accessory termi-
nal; v.tr., ventral terminal.

Near the union of the coracoid and seapular pieces, but on the coracoid, is
the articular process. This area of articulation in the sharks is directed verti-
cally or obliquely and consequently is usually composed of two convex sur-
faces (Squatina). The surface in the rays differs from that in the sharks in
that it is longitudinal in position and much greater in extent. Torpedo (fig.
848) has a type of articulation intermediate between sharks and rays.

THE ELASMOBRANCH FISHES 81

There is a foramen entering the median side of the girdle for the brachial
artery and for nerves going to the pectoral fin. The canal leading through the
girdle from this foramen separates into a dorsal and a ventral part so that
laterally there are two foramina leaving the girdle.

The coracoids from the opposite sides may be separated by a special un-
paired sternal piece (Heptanchus maculatus). Usually, however, they are
joined ventrally in the sharks; in Heterodontus and Squatina they are firmly
welded together. In the rays this region is firm excepting in Torpedo.

PELVIC FIN SKELETON

The skeleton of the pelvic (ventral) fin is made up of' at least two basal car-
tilages, the basipterygium (ba.p., figs. 85-86) and the anterior basal. From

pl.
——— oe eee —ewt —= ;
Ss =3 = =" eS SD =
———aems ___es, _—_— — as
—— oS a — — a —_
——_ae == ae — —
ay — —— ba.p.... <r
—— —en — —— a —

SSS —= —— — —_ eS —.
——e eo — = ra.— a
— ee ee _ ae —_ mad
—— —= ——s GF Ra _ ==
——a —= = — ae x ~

ZZ = 7
“yf ic

Fig. 87. Diagram to illustrate the probable origin of the pelvie girdle. (From Mivart
after Thacher.)

ba.p., basipterygium; pl., pelvie girdle; ra., radial.

these two basal pieces the radials proceed. The basals are supported by a girdle
which in the Elasmobranchs is not in contact with the axial skeleton. The
structure of the adult pelvie fin is much simpler than that of the pectoral, but
in the embryo the two are built on the same fundamental plan. The basipteryg-
ium (ba.p.) is comparable to the metapterygium of the pectoral. This is
normally a single piece, but posteriorly it may be broken into three or four
segments (Centrophorus, Heterodontus, fig. 864; Rhinobatis, fig. 868). The
anterior basal is somewhat like the propterygium. It apparently represents a
fusion of the basal parts of the anterior radials, from the distal part of which
the radials extend freely. In Heptanchus (fig. 55) a segment may join the
girdle between the anterior basal and the basipterygium which in position is
like the mesopterygium. The radials belonging to the basipterygium proper
are more or less segmented anteriorly, but posteriorly, in both male and
female, they are usually unsegmented.

The skeleton of the clasper of the male is a continuation in the median axis
of the basipterygium of the fin, the two being connected by short segments
(b.' and b.’, fig. 864) asin Heptanchus. The terminal part of the basal or axial
cartilage assumes different degrees of complexity in the various Elasmo-
branchs. In some, the basal or axial cartilage (ba.) is provided with a single
accessory cartilage. In others there are present distally an outer marginal
and a ventral and a dorsal terminal accessory cartilage (Chlamydoselachus,

82 THE ELASMOBRANCH FISHES

fig. 85a.) A still more complex type (fig. 864) has one or two dorsal terminals
(d.tr.-?) and a ventral terminal (v.tr.), and along the furrow leading to the
terminal groove there is an accessory terminal (t7.*), and a dorsal marginal
(mg. and d.mg.) (Heterodontus, Mustelus, Scyllium, Carcharias, Raja).

PELVIC GIRDLE

The pelvic girdle is probably built on a generalized plan in Chlamydoselachus
(fig. 85). Here it is an unusually wide cartilage which is perforated by no
fewer than six to eight nerves. In most other types the adult girdle is a narrow
band which points backward in the middle line.

Fig. 88. Dorsal fins of Heterodontus francisci, showing fin spines. (Duncan Dunning, del.)
A. Second dorsal. B. First dorsal.

b.c., basal cartilage; ra., radial.

Figure 87 is a diagram showing the origin of the pelvie girdle as postulated
by Thacher (1877). This indicates that the anterior fin radials fuse and the
fusion joins a similar fusion from the opposite side to form a bar which be-
comes the girdle (pl.); the fusion of the tips of the rays back of this becomes
the basipterygium (ba.p.).

SKELETON OF UNPAIRED FINS

The first indication of the unpaired fins in the embryo of Pristiurus, Dohrn
(1884) found to be the development of a median longitudinal ridge in which
cartilage is laid down as a series of parallel rods. In adult Elasmobranchs
these cartilaginous rods are usually more or less completely segmented into:
(1) basal (b.c., fig. 89), (2) median (b.c.1), and (3) distal segments (0.c.”).
The first are proximal or nearest the body axis, and the third often run a con-
siderable distance into the fins between the two rows of dermal fin rays.

In the dorsal fins all these types may be present as single segments of the
radials (Mustelus antarcticus, fig. 89a, or Zygaena). In some forms the distals

THE ELASMOBRANCH FISHES 83

may be further segmented (Ginglymostoma) or they may be absent (Squatina,
fig. 898) ; or, finally, all the basal segments may fuse into a single basal plate
(Heptanchus, Heterodontus, fig. 88). In certain forms the basals may come in
contact with the column. Such a condition occurs in Squatina (fig. 898),
Rhinobatis, and Pristis, in which numerous segments in front of the fin may
be present joining the neural spines.

Fig. 89. Dorsal fin skeleton of Elasmobranchs. (From Mivart.) A. Mustelus antarcticus.
B. Squatina. C. Raja.

b.c., basal cartilages; b.c.', median segments; b.c.*, distal segments.

The skeleton of the anal fin, like that of the other unpaired fins, is made up
of two or three different types of segments, which, in general, show modifica-
tions similar to those in the dorsals.

1901.

1906.

1886.

THE ELASMOBRANCH FISHES

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1899.

1884.

1886.

lige

1902.

1903.

1906.

1897.

1899.

Os ELe

1877.

Ie aly

1892.

1896.

THE ELASMOBRANCH FISHES 87

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88 THE ELASMOBRANCH FISHES

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pl. 20.

MUSCULATURE

MUSCULATURE OF HEPTANCHUS MACULATUS

The muscles in Heptanchus may be divided into two groups. In one the fibers
are short, reaching from one connective tissue septum (myoseptum) to an-

other; in the other they are more
or less extended and are not con-
fined within myosepta. The mus-
cles of the body are of the short
type; while those of the eyeball,
of the hypobranchial region, and
of the claspers in the male are of
the long type.

In aside view the muscles of the
body of Heptanchus maculatus
are divided at the lateral line (J1.,
fig. 90) into dorsal bundles (d.b.)
which attach to the cranium, and
ventrolateral bundles which at-
tach to the pectoral girdle. Both
the dorsal and the ventrolateral
muscles extend to the tip of the
tail. In these bundles the myo-
septa (ms.) are bent into zigzag
shape. Above the lateral line one
of the columns has the apices of
its myosepta directed forward,
the other backward. Below the
line there appears to be a single
column with apex pointed pos-
teriorly. Some of the anterior

Fig. 90. Lateral view of body musculature in
pectoral region, Heptanchus maculatus. (Evelyn
Forsythe, orig.)

el., gill cleft; d.b., dorsal bundle; d.f., dermal
fin-rays; d.r.m., dorsal radial muscles of pectoral
fin; /.b., lateral bundle; ll., lateral line; ms., myo-
septum; ¢7., trapezius muscle; v.b., ventral me-
dian muscle.

fibers of the ventral bundle are specialized as the pectoral muscles of the
pectoral fin. Of the long muscles we may consider those of the eyeball first.

MuscuEs OF THE EYE

Two groups of muscles are present in the orbit. The first group is placed an-
teriorly and consists of the superior oblique (s.0., fig. 91) and inferior oblique
(i.0.) muscles. These muscles extend from the anterior part of the orbit out-
ward and backward to be inserted on the eyeball. The second group consists

[89]

90 THE ELASMOBRANCH FISHES

of the four rectus muscles, all of which arise from the posterior surface of the
orbit around the base of the optic pedicel (0.p.). The most dorsal of the rectus
muscles is the superior rectus (s.r.), the most ventral the inferior rectus (7.r.),
the most posterior the external or posterior rectus (p.7.), and the most ante-
rior the internal or anterior rectus (a.r.). They pass outward and forward,
also to be inserted on the eyeball.

BuccaL AND PHARYNGEAL MuSCLES

The muscles in the region of the mouth and pharynx may be separated into
four groups. The first group includes the superficial constrictor muscles; the
second comprises the interarcuales; the third
the adductors; and the fourth the hypobran-
chial muscles.

The superficial constrictor muscles are vis-
ible upon removal of the skin from the re-
gion around the gill clefts. The levator maxil-
lae (l.mz., fig. 92) apparently is the forward
continuation of these muscles. It lies just
back of the eye and has its origin on the era-
nium under the postorbital process (po.o.) ;
it extends from its origin downward and for-
ward to the palatoquadrate cartilage (p-q.).
The constrictors appear as eight dorsoven-
tral bands (csd.1*) separating the gill clefts
and functioning in their closure. Each con-

Fig. 91. Muscles of the eye, Hep-
tanchus maculatus, dorsal view. strictor, except the first, may be considered

a.r., anterior or internal rectus; to be made up of dorsal and ventral com-
i.o., inferior oblique muscle; 7.r., in- fe alt ahi thei wie sti hentai F
ferior rectus; n.II, optic nerve; o.p., Ponents, although the two in Heptanchus are
optic pedicel; p.r., external oe pos- more or less continuous. The constrictors
terior rectus; s.o., superior oblique ; ;

s.r. superior rectus. bound the clefts so that the first and second
are separated by the spiracular cleft (sp.)
above, and the 2-3, 3-4, ete., are separated by the cleft following. The last of

these superficial muscles lies in front of the last cleft.
DORSAL CONSTRICTORS

The first dorsal constrictor (csd.’) arises from the occipital part of the era-
nium and from heavy connective tissue (fascia) surrounding the dorsal longi-
tudinal bundles. As a thin slip of muscle it passes downward and slightly
backward around the anterior border of the spiracle to be inserted on the in-
ner and upper margin of the palatoquadrate cartilage (p-q.). Dorsally and
anteriorly the first dorsal constrictor is difficult to separate from the levator
maxillae muscle; furthermore the two have a common line of origin and of
insertion.

THE ELASMOBRANCH FISHES 91

The second dorsal constrictor (csd.*) is a very broad band lying between the
spiracle and the first branchial cleft. It arises also along the fascia of the
dorsal bundle, its anterior margin in Heptanchus maculatus being continu-
ous with the first dorsal constrictor. In Heptanchus cinereus it is overlapped
by the first constrictor. From its place of origin it extends downward and its
anterior and more superficial fibers are inserted on the quadrate; the fibers
lying underneath the superficial fibers join the upper segment of the hyoid;
while those fibers lying back of them pass over to join the fibers of the ventral
constrictor. In Heptanchus maculatus, where the dorsal constrictor meets the
ventral there is superficially a heavy connective tissue septum.

csd.! ——— 2

( i glgwOx S

KGa Mt me 3

> fans <All nr
ie =

a.m

I.mx.

csy.? csv.

Fig. 92. Lateral view of the constrictor muscles, Heptanchus maculatus. (From Davidson. )

a.md., adductor mandibulae; a.pr., antorbital process; csd.-“*, first to eighth dorsal con-
strictors; csv.?*, second to eighth ventral constrictors; lls., medial levator labialis; I/s.1,
lateral levator labialis; /.ma., levator maxillae; md., mandible; po.o., postorbital process;
p-q., palatoquadrate (pterygoquadrate) ; sc., scapular cartilage; sp., spiracular cleft; tr.,
trapezius muscle.

The third to the eighth (csd.*) dorsal constrictors are more slender and have
their origin largely from the dorsal fascia and by tendons through the tra-
pezius muscle (tr.). The superficial fibers pass over into those of the ventral
constrictors, while deeper fibers, acting as interbranchial muscles (see p. 149,
fig. 143, 7b.d.), lie just anterior to the cartilaginous branchial rays. In a section
cutting through the dorsal constrictor between two gill clefts, the dorsal con-
strictors (csd.) are the thicker bundles lying over the margin of the septum;
and the deeper fibers (7b.d.), comparable to the interbranchial muscle of the
more specialized Elasmobranchs, extend inward as thinner bands.

VENTRAL CONSTRICTORS

The ventral constrictors of Heptanchus cinereus are seen in figure 93. They
have their origin from a seam of connective tissue in the midventral line. The
superficial, posterior fibers pass over into the dorsal constrictors, but the
deeper ones are inserted on the ceratobranchial segments of the visceral arches.

92 THE ELASMOBRANCH FISHES

In Heptanchus maculatus a first ventral constrictor is closely united with
the second, which as an immense sheath passes from the midventral line to be
inserted on the mandibular and hyoid arches. By removing a V-shaped seg-
ment from the anterior third of the mandible and hyoid, it will be seen that
this bundle is separated into superficial fibers to the
mandible and deeper fibers to the hyoid cartilage.

The third to the eighth ventral constrictors arise simi-
larly from the midventral, triangular seam. Their su-
perficial fibers are continuous with those of the third to
the eighth dorsal constrictors (fig. 92). The deeper slips
or interbranchial parts of these muscles pass through
the coracobranchial muscles and are inserted on the
neck of the ceratobranchial cartilages (7bw., fig. 95).

The trapezius muscle (tr., fig. 92) arises from the side
of the dorsal longitudinal bundle and passes backward
and downward between this bundle and the dorsal con-
strictors. A gall slip of it is attached to the upper part
of the last arch, but most of its fibers are inserted on the
scapula which it draws forward.

INTERARCUALES

The interarcuales (fig. 94) are deep muscles which bind
the branchial arches together. Two systems of these are
present, one of which is dorsal (ia.d.+-°) and the other
lateral (za.l.--°) in position. The dorsal interarcuales
consist of bands which bind the pharyngobranchial car-

tilages together. In Heptanchus maculatus the first or

Fig. 93. The ventral
constrictors, Heptan- : .
chus cinereus. (From to the second pharyngobranchial cartilage. The follow-

anterior interarcualis is large and extends from the first
Vetter.) ing dorsal interarcuales decrease in size and bridge sue-
csv." first, second, ceeding pharyngobranchials.
peepee tt vit There is present in Heptanchus the so-called sub-
spinalis (s.sp., fig. 94) which, unlike the dorsal inter-
arcuales, takes its origin from the posterior part of the cranium, from the
spinal column, and from the ventral fascia of the longitudinal bundle. Like
the dorsal interarcuales it is inserted on pharyngobranchial cartilages, but,
unlike them, it is inserted by a double tendon on the tips of the first and second
pharyngobranchials.

The lateral interarcuales (7a.l., fig. 94), exeept the sixth (ia.l.°), are double
bands, the anterior of which in each pair bridges the angle between pharyngo-
branchial and epibranchial cartilage of the single arch; while the posterior one
extends from the following pharyngobranchial to a common insertion with
the anterior muscle on the upper and posterior surface of the epibranchial.

THE ELASMOBRANCH FISHES 93

There are in Heptanchus maculatus two levator labiales muscles. One of
these (lls.1, fig. 92) arises from the median side of the antorbital process,
passes backward over the angle of the jaw, and as a fibrous band divides the
adductor mandibulae into dorsal and ventral parts. The other labialis (Us. )
arises from the cranium in front of the antorbital process and nearer the mid-
ventral line as a wide and loose band of connective tissue; it passes under the
orbit, and over the adductor mandibulae to be inserted at the angle of the jaw.

ADDUCTORS

The adductor mandibulae (a.md., fig. 92) is an immense and complex muscle
which closes the jaws. Superficially it is divided into a dorsal and a ventral
part by the insertion of the first labialis muscle. The fibers of the adductor
mandibulae arise from the
quadrate and are inserted in
two groups: first, a smaller
deep posterior group is in-
serted directly on the man-
dible;second, a major group
joins the tendon of the la-
bialis, and fibers are then
continued from the labialis
tendon ventrally to insert on

the mandible. The insertion

in general is somewhat ob- Fig: 94. Interarcuales muscles, Heptanchus maculatus.
ca (From Davidson.)

S.Sp

scured by a fibrous capsule eb.1, first to seventh epibranchial cartilages; ia.d.*°,
over the ventral part of the _ first to fifth dorsal interarcuales; ia./.*°, first to sixth
lateral interarcuales; pb.*°, first to sixth pharyngo-

muscle. branchial cartilages; s.sp., subspinalis muscle.

An adductor is absent
from the hyoid, but adductors similar to the deep posterior part of the addue-
tor mandibulae are present on all the branchial arches. These muscles have
their origin in a groove on the inner side of the epibranchial (see p. 149, fig.
143, ad.) and join the ceratobranchial cartilage. They act in closing the bran-
chial arch and hence in spreading the cartilaginous branchial rays to enlarge
the gill pocket.
VENTRAL LONGITUDINAL MUSCLES

The last group of muscles to be considered in the region of the pharynx is com-
posed of the hypobranchial or ventral longitudinal muscles. These are forward
continuations of the ventral body musculature, the segmental nature of which
is seen in a series of myosepta in the coracoarcuales (c.ar., fig. 95). The
arcuales communes take origin from the coracoid cartilage and are inserted
on the heavy connective tissue which forms the floor of the pericardial cavity.

The coracomandibularis (c.md.) arises from fascia above and between the
anterior projection of the arcuales and passes forward as a large band to be

94 THE ELASMOBRANCH FISHES

inserted at the symphysis of the mandible. The paired coracohyoideus muscles
(c.hy.) continue forward from the coracoarcuales as a layer just dorsal to the
sides of the coracomandibularis. They are relatively broad muscles in Hep-
tanchus and are inserted on the basi- and ceratohyoid cartilages (ch., fig. 50a),
only a few of the fibers reaching the base of the ceratohyoid cartilage. Dorsal
to the region of the coraco-
hyoideus muscle is the third
group, the coracobranchi-
ales muscles (c.br.1-7). The
first six of these arise from
the heavy connective tissue
dorsal to the coracoarcuales
and pass forward, upward,
and outward as narrow slips
to be inserted on the hypo-
branchial cartilages. The
last or seventh (c.br.") arises
in two parts; one part is
continuous with the sixth,
and the other originates di-
rectly from the coracoid
cartilage. This muscle in-
serts as a wide band along
the whole length of the last
eceratobranchial cartilage
and a part of the median
piece. Shps of the ventral
constrictor (interbranchial,
ibu*, fig. 95) muscles pass
through the ceratobranchial
muscles.

Fig. 95. Ventral longitudinal or hypobranchial muscles,
Heptanchus maculatus. (From Davidson.) MUSCLES OF THE FINS

bh., basihyal cartilage; c.ar., coracoareualis muscle ;
eb, first ceratobranchial cartilage; c.br.“, first to
seventh coracobranchial muscles; ch., ceratohyal earti- The muscles on the dorsal
lage; c.hy., coracohyoideus; c.md., coracomandibularis gide of the pectoral fin
muscle; co., coracoid cartilage; ibv.*, first to sixth in- ; iE ee
terbranchial slips; md., mandibular cartilage. (d.r.m., fig. 90) take origin
from the posterolateral

margin of the scapula, and from the basal and, in part, from the radial ear-
tilages of the fin skeleton. The radial muscles are distinet in the central part of
the fin, but on the posterior margin the separation into definite bundles is not
so evident. The muscles run toward and are attached to the heavy sheet of
connective tissue continuous with the dermal fin-rays (d.f.). The radials
while appearing to be long are, according to Davidson, made up of short fibers.
The ventral radial muscles arise from the posterior side of the coracoid and

THE ELASMOBRANCH FISHES 95

from the basal and radial cartilages, and extend outward to be attached to the

connective sheath of the ventral side of the fin.

The muscles governing the claspers of the fins in the male are in bundles

specialized from dorsal and ventral radial mus-
cles. We may first examine them on the dorsal side
of the pelvic of the male (fig. 96). Here they are
continued from the myomeres to the fin, parallel
with the radials, and are firmly attached to the pe-
ripheral part of the fin skeleton. The first of these
muscles is the adductor (ad.), which arises from
the posterior border of the pelvie girdle and is
inserted on the distal end of the basipterygium
(see p. 50, fig. 558, ba.p.). The external flexor
muscle (f.e., fig. 96), which has its origin along
the inner margin of the basipterygium (ba.p.), 1s
inserted on the “beta” cartilage (8, fig. 558). In
Heptanchus the internal flexor (f.7.) arises in
common with, but deeper than the external flexor
on the basipterygium and on the “beta” cartilage
and is inserted on the segment b* (fig. 55) and on
the proximal part of the basal cartilage (ba.). On
the dorsal side are also to be seen the dilator (dl. )
and the compressor (cp.) muscles. The dilator
arises on the proximal end of the basal cartilage
(ba.) and is inserted distally with the connective
tissue covering the tip of the basal cartilage. The
compressor muscle (cp.) has its origin from the
“beta” cartilage (, fig. 558) , and passes backward
and outward to be inserted on the last radial car-
tilage. One of the muscles associated with the
clasper, which is not seen in dorsal view, is the
constrictor of the sac. Its fibers arise from the seg-
ments b.'~-*, and from the proximal end of the basal

Fig. 96. Muscles of the pelvie
fin of male, Heptanchus mac-
ulatus, dorsal view. (From
Davidson.)

ad., adductor muscle of
clasper; cp., compressor of
the sac; dl., dilator muscle;
f.e., external flexor muscle;
f.i., internal flexor; pl., pelvie
girdle; ra., radial muscles;
s.m., muscle of sac.

cartilage. Its dorsal fibers are inserted on the curved radial and its ventral

fibers form the wall of the pterygopodial sae.

96 THE ELASMOBRANCH FISHES

MUSCULATURE OF ELASMOBRANCHS IN GENERAL

In a consideration of the musculature of Elasmobranchs in general we may
first notice the primitive segments or somites which in the embryo are ar-
ranged in series from the region back of the ear to the tip of the tail. A trans-
verse section through the trunk (fig. 97) shows the somite to be made up of
an outer and an inner layer between which is a
central cavity or myocoele (mc.). The outer layer
produces the dermatome or cuticle plate (dt.) and
the inner layer is divided into an upper myotome
(my.) and a lower sclerotome (scl.). These two
layers extend ventrally as the lateral plate and
inclose between them the body cavity or coelom
(c.). For a time in the Elasmobranchs these two
cavities are continuous, but later they are sepa-
rated by the fusion of the two layers giving a
somite dorsally independent of the lateral plate
(see p. 298, fig. 257).

The sclerotome of the somite, as we have seen in
Chapter III, produces the elements of the verte-
bral column, while the dermatome gives rise to

Fig. 97. Transverse section

through developing somite,
Pristiurus. (From Rabl.)

c., coelom; chd., notochord;
dt., dermatome; heh., hypo-
chorda; mc., myocoele; my.,
myotome or muscle plate;
n.t., neural tube; scl., sclero-
tome; so., somatic layer mes-
oderm; spl., splanchnic layer
mesoderm.

those connective tissue fibers characteristic of the
corium and sometimes may also give rise to a
part of the muscle tissue. The myotome, however,
produces the mass of skeletal muscle. The lateral
plates which enclose the coelom are divided into
an inner splanchnic layer (spl.) which produces
the muscular layer of the digestive tract; and a

somatic layer (so.) which thins out ventrally,
forms the peritoneal lining of the body cavity, and gives rise to connective
tissue cells.

The cells of the myotome, the myoblasts, elongate and attach themselves
both anteriorly and posteriorly to the connective tissue septa (myosepta) sep-
arating somites (fig. 98). Such a muscle cell or fiber furthermore becomes
differentiated into longitudinal fibrils and is crossed by a series of transverse
stripes or bands. In the body of the adult Elasmobranch the fibers generally
retain the simple plan of attachment to myosepta. But the myosepta in the
adult have secondarily changed their course, always, or at least generally, so
as to take a zigzag direction.

The myotome next extends its boundaries dorsally to the middorsal line, and
ventrally it grows toward the midventral line. The fibers formed dorsally
between the dorsal septum and the lateral line septum compose the dorsal
longitudinal bundles (d.b., figs. 100 and 112) which extend from the occipital

THE ELASMOBRANCH FISHES OF

region of the skull to the tip of the tail. These fibers universally take a horizon-
tal direction. Those fibers between the lateral line septum and the midventral
line are divided into a lateral (1.b.) and a ventral (v.b.) region. The lateral
muscle (1.b.) is readily recognized by the fact that it lies just ventral to the
lateral line and is of a dark color. Between pelvic and pectoral regions this
bundle is folded in in such a way (figs. 99 and 100) as to be overlapped by the
ventral bundle (v.b.). Anterior to the pelvis the fibers in the lateral bundle
may take an almost horizontal direction (1.b., fig. 112) but they usually take
an oblique direction of anterior and
upward (fig. 100); while posterior to
the pelvic area the fibers of this bundle
run more or less horizontally.

The ventral bundle (v.0., figs. 100 and
112) is highly specialized and its fibers
take a characteristic anteroventral di-
rection. In some of the Elasmobranchs,
as in Zygaena, the ventral bundle is
further specialized into a rectus ab-
dominis at the midventral line (7.c.,
fig. 100).

Figure 99 is a model for Squalus
sucklu of all muscle fibers between two
myosepta in the region of the first dor- Fig. 98. Showing the finer anatomy of de-

: ; veloping muscle. (Modified from Erik
sal fin. Dorsally it will be seen that the — \ijler. )
septa run posteriorly close together
and almost parallel with the middorsal line. They then turn anteriorly and
run forward. Next they bend on an acute angle and curve backward; and then
they turn forward and downward to the lateral line, where they fold inward
and are carried forward. When the septa emerge from the fold they are dis-
placed backward so that as they pass through the lateral bundle they are fully
a half-segment posterior to the same myosepta above the lateral line. In the
lateral bundles the septa curve downward and backward and then turn for-
ward where they fold inward and backward to emerge in the ventral bundle
(v.b.).In the ventral bundle they run sharply downward and slightly forward.
They then turn backward, and finally run forward to the midventral line.

In a transverse section of the tail of Zamna the various muscle cones appear
in their relation to one another (fig. 101). The rows here are so arranged that
a dorsomedian (dm.), a dorsolateral (dl.), and a lateral row (1.b.) lie above
the lateral septum which extends from the spinal column to the skin in the
region of the lateral line (not drawn in the figure). The ventrolateral (vl.)
and ventromedian (vm.) rows are below the septum. The bundles are made up
of concentric lamellae, the concentricity of which is due to the projection of
the apex of one cone into the angle of the V’s in front of or back of it. The
dorsolateral and ventrolateral bundles are small, the dorsomedian and ventro-
median bundles are large, and the lateral bundle, composed of nine concentric

98 THE ELASMOBRANCH FISHES

oe et |
LES

Fig. 99. Model of muscle fibers between two myosepta, Squalus sucklii. (From Coles.)

en., extension of myosepta forming cone; d.a., dorsal aorta; d.vm., dorsal vertebromuseu-
lar artery; i., intercostal artery; 7.b., intercostal branches to preceding segments; L., lateral
bundle; /l., lateral line fold; ll.’, fold between lateral and ventral musculature; ms., myo-
septa; rn., renal artery; V’,, V2, V;, bends in myosepta.

THE ELASMOBRANCH FISHES 99

lamellae, is of immense size. In side view the V’s would appear very long and
acute, many of them being cut in transverse section.

We may next consider the specialized or long muscles of the adult which
are present in the head and in the pharyngeal region.

MUSCLES OF THE EYE

The muscles of the eye originate from head somites (fig. 102) which in a way
are like the body segments or somites previously described. The first or pre-
mandibular somite, the second or mandibular, and the third or hyoidean
somite, all take part in the formation of these muscles. It will be observed

it
WT»

NAN

Uy, "ZS
ODE
QO

=;
=.

Fig. 101

Fig. 100. Trunk musculature, Zygaena side view. (From Maurer.)
Fig. 101. Transverse section, muscle bundles of tail, Lamna. (From Ewart.)

d.b., dorsal bundles; dl., dorsolateral bundle; dm., dorsomedian bundles; /.b., lateral
bundle; Jl., lateral line; r.a., rectus abdominis; v.b., ventral bundle; vl., ventrolateral
bundle; vm., ventromedian bundle; x, part of ventral bundle removed to show overlapping
of lateral bundle.

from the figure that somites four, five, and six, which are in the region near
the enlarging ear capsules, degenerate and consequently take no part in the
formation of eye muscles.

The most anterior of these head somites, the premandibular,! gives rise to
four of the six muscles of the eye. The first muscle to bud off from this somite,
arising ventrally as shown by the ruled lines in figure 103 (Lamb, 1902) is
the inferior oblique (7.0.). Following this the inferior rectus (7.7.) arises also
from the ventral part of the somite. From the dorsal side the internal or an-
terior rectus (a.r.) and the superior rectus (s.r.) are budded off. The second
or mandibular somite divides into two parts, a small upper part and a larger
lower part. From the upper part the superior oblique muscle (s.0.) arises.
The cells which form this muscle first take a longitudinal direction; later, as
they become muscle fibers, they lie more in a dorsoventral direction. From the
ventral part of the second somite a part of the rectus externus arises (Neal).

1In front of the premandibular has been described (Platt, 1891) still another somite
(Acanthias).

100 THE ELASMOBRANCH FISHES

The third or hyoidean somite is simpler than the rest, and from its lower part
the remainder of the external or posterior rectus muscle (p.r.) arises. The
relations of the muscles to the somites and nerve supply are tabulated by Neal
as follows:

Myotome Muscle Innervated by
+ Ree § Rectus superior Oculomotor nerve III
ea Rectus internus Oculomotor nerve IIT
ge eee Rectus inferior Oculomotor nerve III
iT eae a | Obliquus inferior Oculomotor nerve III
20:8 ee Obliquus superior Trochlearis nerve IV
DN ccseecees eee eae Rectus externus

Pe at etune externus | Abducens nerve VI

The position occupied by the inferior oblique muscle of the adult varies
somewhat in different forms. In Heptanchus the inferior oblique is attached to
the orbit practically against the superior oblique, while in Acanthias the two
may be slightly apart. In the saw shark, Pristiophorus, an interesting condi-

Vi.

passossacse DOT
8!

Qy X

Fig. 102. Diagram showing the head somites in relation to the body somites in Squalus
acanthias. (From Neal.) The eye muscles are derived from the first three somites.

hyp., hypobranchial (hypoglossus) musculature; m., mouth; of., otic capsule; IJJ and VJ,
third and sixth head somites.

tion obtains in which a second strip of the inferior oblique is attached along
the infraorbital plate. This is evidently a forerunner of the condition present
in the rays, in which the whole of the muscle has its attachment as a broad
band ventral to the orbit (Rhinobatis, Raja). In this respect, then, Pristio-
phorus is a transitional form between the sharks and the rays.

MuSscLES OF VISCERAL ARCHES

The levator labu superioris muscle in a type lke Acanthias (lls., fig. 104)
consists of a single muscle on each side, which has its origin on the interorbital
space ventral to the cranium. The muscle passes backward and outward along
the upper jaw and over the dorsal labial cartilages. At the angles of the mouth
it becomes tendinous and is inserted on the mandible. In all probability, this
muscle is comparable to l/s. of Heptanchus. In Torpedo (fig. 1054) (see
Tiesing, 1896), the muscle is divided into two parts, a median (Ills.1) and a

THE ELASMOBRANCH FISHES 101

lateral levator (//s.*). The lateral levator labii has its origin behind the angle
of the ethmoidal region and is inserted on the process of the quadrate. The
median head arises as a broader muscle near the preorbital process and passes
as a tendon around the angle of the mouth to join the mandibular muscle as in
Acanthias.

A more complex condition is reached in Rhinobatis and in Raja. In the
former there are four (or even five) parts to the muscle, and in the latter five
parts are characteristically present. In Raja (fig. 107) the first division of
the muscle Ils.1 represents the me-
dian division of the muscle in Tor-
pedo. There is a second muscle (fig.
1078, lls.2) which is large in Raja
and which holds a peculiar position
in Rhinobatis, being surrounded at
its base by the mandibular muscle
soon to be described. A third slip
(lls.*) is isolated, and a fourth and
a fifth(?) join the mandibular
muscle.

The levator maxillae superioris
muscle in Acanthias (l.mz., fig. 104)
has its origin from the postorbital
processes and supraotic crest, and

Fig. 103. Development of the muscles to the
eye, Acanthias, right, median view. (From

passes downward in common with
the first dorsal constrictor, the fibers
of the latter lying directly against
the spiracle and the fibers of the

Lamb.)

a.r., anterior rectus; cl.g., ciliary ganglion
of fifth nerve; g.g., gasserian ganglion; i.0.,
inferior oblique; i.r., inferior rectus; 0.p.,
optie pedicel; op.V, ophthalmicus profundus;

p.r., external or posterior rectus; s.0., supe-
rior oblique; os.V and VII, ophthalmicus su-
perficialis branches of the fifth and seventh
nerves; s.7., superior rectus; JJJ and VI, ocu-
lomotor and abducens nerves respectively.

former (levator maxillae) being
those of the anterior group. The
levator maxillae is inserted on the
palatoquadrate. In Carcharias, how-
ever, in addition to its postorbital relations, it extends its origin anteriorly
along almost the whole of the supraorbital crest. In the rays, this muscle and
the first dorsal constrictor are distinct and separate. In Torpedo (l.mz.. fig.
1054) the levator maxillae is well defined and runs far forward to be inserted
on the median palatal part of the palatoquadrate. In Rhinobatis it is much
broader than in Torpedo and is inserted still farther forward. In Raja (l.inz.,
fig. 1058) it arises by two heads, a superior and an inferior; the fibers of the
two unite anteriorly, whereupon insertion is made on the palatine part of the
palatoquadrate cartilage.

SUPERFICIAL CONSTRICTORS OF PHARYNX

The superficial constrictor muscles vary considerably from those studied in
Heptanchus. These muscles in pentanchid Elasmobranchs are six in number.

102 THE ELASMOBRANCH FISHES

In the rays, the fibers of the dorsal constrictors are not continuous with those
of the ventral constrictors, the two sets being separated by a horizontal tendon.

DORSAL CONSTRICTORS

The first dorsal constrictor in Acanthias (fig. 104), as has been said, is sepa-
rated from the levator maxillae only at the ventral part of the spiracle where
its fibers curve posteriorly around the base of the spiracle to be attached to

l
Ny

ANY

Fig. 104. Lateral pharyngeal muscles, Acanthias. (From Vetter.)

a.md., adductor mandibulae; esd.*, second dorsal constrictor; cesv., ventral constrictor ;
lis., levator labii superioris; l.mz., levator maxillae; tr., trapezius.

the quadrate. In a boiled specimen of Mustelus californicus the first dorsal
constrictor can readily be distinguished from the levator maxillae by a differ-
ence in its color. Furthermore its anterior ventral margin folds in under the
levator maxillae. In the rays (fig. 105) the first dorsal constrictor is a clearly
marked band which forms a crescent in front of the spiracle.

In Elasmobranchs which have a nictitating membrane the muscles con-
trolling that membrane are derivatives of the first dorsal constrictor. The nic-
titator in Mustelus californicus may here be described with the other accom-
panying muscular slips. It has its origin posterior to that of the first dorsal
constrictor and under the second dorsal constrictor. From its origin it passes
anteriorly and downward in front of the spiracle (nt., fig. 106) to be inserted
on the nictitating membrane (n.). Crossing the nictitator almost at right
angles is a deeper muscle, the depressor (dp.) of the upper eyelid, which takes
origin somewhat posterior and dorsal to the spiracle and over the second con-
strictor. This passes forward and upward to be inserted at the tail of the eye
on the upper eyelid. Arising in the common mass with the depressor of the
upper lid but superficially, is a rudimentary retractor palpebrae superioris
(r.p.) which ends anteriorly against the nictitator so that the nictitator oper-
ates between it and the depressor. Arising from the anterodorsal margin of

THE ELASMOBRANCH FISHES 103

the spiracle is the dilator (dl.) of the spiracle, which passes anteriorly and up-
ward between the retractor and depressor finally to join the nictitator. Sur-
rounding the spiracle (sp.) superficially is the constrictor spiraculae (c.s.).

The second dorsal constrictor (csd.”, fig. 104) in the sharks extends from the
supraotie crest of the cranium back to and even perforating the anterior end
of the trapezius (tr.) ; other fibers arise from the seam dorsal to the cleft. The

\
\

WIAA RRO
IWKSOSSNNS

SIL
bois
iii, \ \

Fig. 105. Dorsal pharyngeal muscles. (From Tiesing.) A. Torpedo. B. Raja.

a.md., adductor mandibulae; csd., dorsal constrictor muscle; l.hm., levator hyoman-
dibularis; Uls.'°, first to fifth slips of levator labiales; l.ma., levator maxillae; lr., levator
rostri.

insertion of this muscle in Acanthias is interesting. Part of its fibers touch the
hyomandibula and a number of other fibers impinge on the ceratohyoid; while
still a third set joins a horizontal tendinous bridge, separating dorsal and
ventral constrictors. Back of this tendon other fibers are continuous with the
ventral constrictors.

Those fibers inserted on the hyoid in Heterodontus and Squatina are sepa-
rated into a kind of levator hyomandibularis. In the rays the levator hyo-
mandibularis (l.im., fig. 105) is a muscle of great importance. It may be in-
serted on the hyomandibula at the angle (Torpedo, fig. 105, l.hm.; Raja (fig.
1058), or on the lower part as in Rhinobatis. In the rays those fibers back of the
levator hyomandibularis and in front of the first cleft form the second dorsal
constrictor proper. These fibers run practically in a horizontal direction.

The remaining dorsal constrictors are similar to the second. A point or two,
however, may be added. From the third to the fifth constrictors in the sharks

104 THE ELASMOBRANCH FISHES

(Acanthias), the fibers dorsally arise largely from the seam above the cleft
and from the extrabranchial cartilages. These fibers pass downward and
those more anterior are inserted on the seam in front and on its underlying
extrabranchial cartilage (fig. 104). The posterior fibers pass on and are con-
tinuous with the ventral constrictors. The sixth dorsal constrictor in addition
has some of its fibers arising from the scapular part of the pectoral girdle.

In the rays there is present a levator rostri (L.r., fig. 105). This muscle has
its origin dorsally in the fascia of the longitudinal muscle, near the posterior
seam at the sides of the dorsal con-
strictor, and extends to the margin of
the rostrum (Rhinobatis) where it is
inserted on heavy tissue.

The trapezius, which is not a part of
the constrictor system, may here be
considered. In sharks it arises from the
fascia of the dorsal bundles, and from
the cranium above and at the sides of
the ninth foramen (Acanthias), its

; ona. origin extending almost from the era-

Fig. 106. Muscles to the nictitating mem- : é
brane and associated parts, lateral view, ium to the region of the scapula. In
ETEUA SEED ETS: Acanthias (tr., fig. 104) it is perforated
syireeaiaes ap weer a Be cae by slips of the dorsal constrictors and
l., upper eyelid; 7., nictitating membrane; has its insertion largely on the scapula.
bay ae Er Sane ee nee In the rays several slips of muscle are
found in the location of the trapezius,

but it is not certain that these are comparable with the trapezius of the sharks.

VENTRAL CONSTRICTORS

In Acanthias, according to Marion (1905) there may be two parts to the first
ventral constrictor, the more anterior of which is the smaller and bridges the
anterior symphysis of the lower jaw. The more posterior part is much wider
and is like that in Heptanchus. These parts take origin from a midventral
seam and are inserted on the posterior margin of the mandible. In the rays the
second part acts as a depressor mandibulae (d.md., fig. 107B).

The second ventral constrictor in the sharks is similar to that in Heptanchus.
This also arises from the midventral seam and is inserted on the border of the
hyoid cartilage. In the rays the second ventral constrictor is divided into an
anterior and a posterior part. The anterior part acts as a depressor hyomandib-
ularis (d.hm., fig. 1078), a muscle antagonistic to the levator hyomandibularis
previously mentioned as derived from the second dorsal constrictor. The more
posterior and narrower ventral part is the second ventral constrictor.

Each of the remaining ventral constrictors in the rays (fig.1078) consists
of two parts, a large outer and a small inner portion.

THE ELASMOBRANCH FISHES 105

Superficial to this ventral region in the rays, arising from the fascia of the
ventral longitudinal muscle (the coracomandibularis), is a depressor rostrt
(d.r., fig. 107). This is inserted far forward between the end of the propter-
ygium and the tip of the rostrum (Raja). It has a balancing effect on the
levator rostri (see fig. 105, l.r.) previously deseribed.

DEEPER MuscLES OF PHARYNX

The interbranchials of more specialized Elasmobranchs are usually more
completely separated from the constrictors into distinct bundles than are

Fig. 107. Ventral pharyngeal muscles. (From Tiesing.) A. Torpedo. B. Raja.

a.md., adductor mandibulae; cl., first gill cleft; c.br., coracobranchial muscle; ¢.hy., cora-
cohyoideus; c.md., coracomandibularis; esv., ventral constrictor muscle; d.hm., depressor
hyomandibularis; d.md., depressor mandibulae; d.r., depressor rostri; lls.t, median levator
labii; J/s.2, lateral levator labii; lls.4°, fourth and fifth slips of levator labii; n.a., nasal
aperture.

those of Heptanchus. In Acanthias (fig. 1084), as is true in general, they lie
between the demibranchs, in front of and against the branchial rays of all the
whole gills. The dorsal fibers arise from the seams, separating the dorsal con-
strictors above the cleft, and from the dorsal extrabranchial cartilages. The
shorter, inner fibers are attached to the outer margin of the epibranchial seg-
ment of the branchial arch, while the outer fibers pass over to ventral inter-
branchial fibers (sharks). The ventral fibers of the interbranchials arise from
the fascia around the coracomandibularis muscle and from the ventral extra-

106 THE ELASMOBRANCH FISHES

branchial cartilages. The shorter or inner fibers join the ceratobranchial earti-
lage, and the outer fibers in the sharks pass into the dorsal interbranchial
fibers.

In the rays the interbranchials are somewhat like those of the sharks. Here,
however, the dorsal and ventral fibers do not form a continuous muscle even
at the outer margin. The fibers both dorsally and ventrally arise as in the
sharks. The inner dorsal fibers are inserted also on the epibranchial (eb., fig.

eb.
NW,

b d--= Am Im Be:
(0 > -—axe

| mi! I fi I}
Oe

Fig. 108. Interbranchial musculature. (From Marion.) A. Acanthias. B. Raia erinacea.

ad., adductor muscle; br., branchial ray; cb., ceratobranchial cartilage; eb., epibranchial
cartilage; ex.b., extrabranchial cartilage; td., longitudinal tendon.

1088) and the inner ventral fibers on the ceratobranchial cartilages (cb.). The
outer fibers are attached to the cartilaginous branchial ray which proceeds
outward at the angle between the epibranchial and ceratobranchial segments.
Some of the most median fibers ventrally take origin from the fascia of the
coracomandibularis muscle.

INTERARCUALES

The interarcuales, as in Heptanchus, are divided into two systems, a dorsal
(medial of Marion) and a lateral system. The subspinalis, which is considered
by some as the first of the dorsal systems, arises from the base of the cranium,
the ventral side of the vertebrae, and the fascia ventral to the longitudinal
bundle, and tapers back to be inserted near the tip and laterally usually on the
first pharyngobranchial cartilage. In Scyllium, as in Heptanchus, the sub-
spinalis is divided into two bands; in Squatina it is very slender; and in Scym-
nus and in the rays it is generally absent.

The true dorsal interarcuales (ia.d., fig. 109) unite sueceeding pharyngo-
branchial segments. The dorsal interarcuales vary in number; five in Hep-
tanchus, four in Hexanchus, three in Acanthias and Heterodontus, and two
in Raja. In Scymnus the tips of the pharyngobranchial segments are bound by
strong ligaments to a sheet of connective tissue ventral to the spinal column.

In Acanthias (fig. 1094), as in Heptanchus and many other sharks, the
lateral interarcuales system (ia.l.) consists of V-shaped muscles, one limb of

THE ELASMOBRANCH FISHES 107

the V arising on the posterior side of the base of the first pharyngobranchial,
and the other limb, on the anterior side of the base of the following pharyngo-
branchial. The fibers of the two limbs of the V pass ventrally and anteriorly
and unite before they are attached on the posterior side of the epibranchial
cartilage. The first to the third interarcuales of the lateral system in pentachid
sharks are alike, but the fourth is undivided in its origin.

Fig. 109. Interarcuales muscles. A. Acanthias. (From Vetter.) B. Heterodontus francisci.
(Lucile Graham, orig.)

eb., epibranchial cartilage; ia.d., dorsal interarcuales muscles; ia.l., lateral interarcuales;
pb., pharyngobranchial cartilage.

In Heptanchus maculatus (p. 93, fig. 94) the second or posterior branch of
the first lateral interarcualis is seen to be closely related to the dorsal system;
while in the second to the fifth, the lateral interarcuales come to be more and
more widely separated from the dorsal system. In Heterodontus (fig. 1098)
the dorsal system consists of very broad bands, and the lateral system is also
composed of wide bands, the inserting heads of which are not divided.

ADDUCTORES ARCUS

Under this head are included the adductor mandibulae and the branchial ad-
ductors. The adductor mandibulae in a type like Acanthias (a.md., fig. 104)
may be described as a mass of muscle at the outer angle of the jaw, which arises
from the quadrate and passes over to the whole of the side of the posterior
part of the mandible. According to Vetter a small slip of the adductor mandi-
bulae in Acanthias may also pass downward and join the ventral constrictor
already deseribed. In a form like Heterodontus the adductor is of unusual
size. In Torpedo (a.md., fig. 1074) it is divided into a large median and a
smaller lateral part; and in Raja (fig. 107B) and Rhinobatis the median part
is small and the outer part is subdivided into a large inner and an immense
outer division.

Adductors are present on all the gill-bearing arches, except the hyoid. They
arise from grooves on the inside of the epibranchials, and are inserted on simi-
lar grooves inside of the ceratobranchials (fig. 108B, ad.). In the branchial

108 THE ELASMOBRANCH FISHES

region of Chlamydoselachus the adductors diminish in size from behind for-
ward, so that, in addition to the absence of one from the hyoidean arch, there
is but slight evidence of a first branchial adductor.

HYPOBRANCHIAL MuSCULATURE

The hypobranchial or ventral longitudinal muscles extend from the coracoid
cartilage forward under the branchial basket, and consist of the arcus com-
munes which continue forward from the pectoral girdle, the coracomandt-

A B

Fig. 110. Hypobranchial muscles. (From Max Fiirbringer.) A. Scymnus. B. Heterodontus
philippi.

c.ar., coracoarcualis muscle; ¢.br., coracobranchialis; c.hy., coracohyoideus muscle; ¢.md.,
coracomandibularis.

bularis, lying in the middle line, the coracohyoideus at the sides of the cora-
comandibularis, and the deeper coracobranchiales extending to all the bran-
chial arches. All these muscles except the coracobranchials arise from the
first five trunk myotomes (fig. 102) as buds which migrate forward, and me-
diad and take up their position under the branchial and bueeal areas. The
coracobranchiales in Scyllium, according to Edgeworth (1903), are developed
from head myotomes. In the sharks the hypobranchials usually come to be
heavy round muscles, while in the rays they are more or less flattened.

The arcus communes (see coracoarcualis, c.ar., fig. 110) are separated by
myosepta (seriptores tendiniae), much like other ventral bundles, into a vary-
ing number of segments in different forms. In Heterodontus philippi (fig.
110s), for example, a single segment is produced, in Raja two, and in Scymnus
(fig. 1104) anda number of other types, five are present anterior to the girdle.

THE ELASMOBRANCH FISHES 109

The coracomandibularis (c.md.) in the shark is seen upon removing the
skin and the first and second ventral constrictors. In the rays it lies directly
under the skin. In Scymnus (c.md., fig. 1104) it is an unpaired muscle which
originates directly from the coracoid cartilage and is inserted near the man-
dibular symphysis. That the muscle is of a paired nature, however, is shown
by its being innervated by paired nerves. In Raja its paired condition is indi-
eated anteriorly, and in Aetobatis the two muscles are entirely separate.

The coracohyoideus muscle (c.hy., fig. 110) is seen lying at the sides of the
coracomandibularis (Heterodontus, fig.110B). It arises from the fascia around
the arcus communes and is inserted on the
hasihyoid and lower part of the hyoid
arch. In Scymnus (fig. 1104) it passes
more directly forward from the most an-
terior arcual segment than it does in Hep-
tanchus. In Raja (see fig. 1078) the coraco-
hyoideus is small and lies more or less over
the coracomandibularis. It is inserted on
the ventral part of the basihyal segment.

The coracobranchiales (c.br.) are the
deepest of the hypobranchial muscles and
support the floor of the pericardial cavity.
They consist of five separate parts in pen-
tanchid sharks, six in Hexanchus, and
seven in Heptanchus. In the rays they
arise in a common mass. The first coraco-
branchialis (c.br.) is large in Scymnus;
and the remaining muscles, except the last
which is the largest, are smaller. They are
normally inserted on the ceratobranchial
segment of the branchial arches.

MuSscLES OF THE FINS Fig. 111. Development of the muscles
ue to the peetoral fin, Acanthias. (From

Erik Miller.)
In Elasmobranchs the muscles of the 1-23, muscle buds; I-XII, nerves.

paired fins arise in the embryo as buds

from the ventral downgrowth of the myotome. Varying numbers of these buds
take part in the formation of the fins in different species of Elasmobranchs.
After the dorsal somite is separated off from the lateral plates its myotome
erows rapidly both dorsally and ventrally. As the ventral downgrowth
passes the fin area it gives off the muscle buds as lateral growths. The muscle
bud separates into an anterior and a posterior primary bud, each of which in
turn divides into an upper and a lower secondary bud so that from one myo-
tome four buds arise. The two of these buds which are dorsal in position go to
make up dorsal fin muscles, while the two ventral in position compose the
ventral musculature of the fin (fig. 111).

110 THE ELASMOBRANCH FISHES

It is evident that the number of segments that take part in the formation
of buds for the pectoral fin is fewer in the sharks than in the rays. This fact is
clear when we consider two types like Mustelus and Torpedo, in the former of
which the fin is relatively narrow and in the latter is of great extent. Accord-
ing to Maurer (1912), in the embryo of Mustelus only ten segments contribute
to the formation of the musculature of the pectoral fin; while in Torpedo there
are twenty-six such segments.

The further course of the development of these buds in two forms like the
above has been studied in great
detail because of the bearing which
such development has on the lateral
fin-fold theory. That in a type like
Mustelus segments (myotomes) an-
terior to the pectoral fin and between
the pectoral and pelvie fins form
buds which atrophy without enter-
ing the fin is taken by those who
accept the lateral fin-fold theory to
mean that the fin previously had a
much greater anteroposterior extent
than at present; and it is hence in
agreement with what would be ex-
pected from that theory.

Muscles of the unpaired fins are
formed in essential respects like
: » those of paired fins. As the myotome
Fig. 112. Adult pectoral muscles, Squalus grows dorsally to the middorsal line
Suchiat, EivelyosS Onsyuac One) it gives off buds in the regions of the

cl., gill cleft; d.b., dorsal bundle; d.r.m.,
dorsal radial muscle of pectoral fin; 1.b., lat- dorsal fins and the dorsal lobe of the
eral bundle; /l., lateral line; ms., myoseptum; egudal fin. Each bud for the un-
tr., trapezius muscle; v.b., ventral median ; aa ‘ ‘
sees a paired fins divides into an anterior

and a posterior bud but no further
division takes place since the buds from opposite sides unite to form the muscu-
lature of the unpaired fins. Ventral buds arise from the tip of the tail forward
to the anal region. The more posterior of these supply the ventral lobe of the
caudal fin, while those in the region of the anal fin, in forms in which an anal
fin develops, provide musculature for that fin.

MUSCLES OF THE CLASPERS

The muscles which control the claspers are usually more complex than those
described for Heptanchus. In Chlamydoselachus, however, few points of modi-
fication are shown. The principal change is noted in the area of the adductors.
While the adductor in the notidanids is a long muscle, in Chlamydoselachus
(ad., fig. 113) it is relatively broad and fan-shaped. Here, too, the external

THE ELASMOBRANCH FISHES 111

\
SN

\ \
C4
Ti Z

— Zz

\
Lf

LES
AT LT FY OF BF

dl--

Fig. 113. Muscles of the claspers, Chlamydoselachus. A and B, ventral and dorsal views.
(From Goodey.) ad., adductor; cp., compressor; dl., dilator; f.e., external flexor; f.i., in-

ternal flexor.

Fig. 114. Muscles of the claspers, Raja. (From Bachman.) A and B, ventral and dorsal
views. ad., adductor; cp., compressor; dl., dilator; f.e., external flexor.

112 THE ELASMOBRANCH FISHES

flexor (f.e.) differs in that its point of origin is far removed from that of the
internal flexor (f.7.).

In the rays, where the skeleton of the fin is much more complex, the muscles
have undergone a relatively high degree of specialization. In figure 1144 of
Raja clavata the adductors (ad.) are shown on the ventral side as diverging
fibers passing toward the sac. Surrounding the sac is the large compressor, a
part of which also appears in dorsal view (cp., fig. 1148). The large dilator
(dl.) in the same view is divided into a ventral and a dorsal part, the latter
being very heavy. Continuing from this muscle on the dorsal side is the large
external flexor (f.e.) and at its sides is the margin of the adductor seen also in
ventral view.

ELECTRIC ORGAN IN ELASMOBRANCHS

One of the most highly specialized organs found in the animal kingdom is
present in the rays. This is the electric organ by means of which electric shocks
can be generated. While this organ is found in its perfected form in Torpedo,

ane C8 068 a
todas Smet veeads.
DOO0ODERE a Bp soo8

LS
—

Fig. 115. The relation of the electric organ to the muscles, Raia batis. (From Ewart.)
ds., electric dises; mf., muscle fibers.

it is also present in the genus Raja. In Torpedo it consists of vertically placed
dises located on the dorsal part of the pectoral fin. In the rays, on the other
hand, it is made up of a series of cones located in the tail.

ELECTRIC ORGAN OF Rays

The electric organ of the ray is spindle-like and extends throughout the greater
length of the tail. It is spindle-shaped, however, only in part. While it tapers
gradually at both ends, in the middle region it is not always cylindrical, since
it is subject to pressure from the surrounding ligaments, muscles, and the
vertebral column, resulting often in deep grooves in the organ. (Ewart. )
Figure 115 shows the relation of the electric organ of the ray to the sur-
rounding muscular tissue. From this it is seen that the organ is continuous
with the lateral row of muscle cones. In fact it is clear that the organ itself is
formed as a series of cones altogether similar to those of the muscle, with the
single exception that the direction of the muscle fibers (mf.) in the muscle is
more oblique to the myosepta than are the dises (ds.) of the electric organ.

THE ELASMOBRANCH FISHES 113

SN?

STE

fy IM

Sik

A B

Fig. 116. Development of electric organ of Raia batis. Stages A-C. (From Ewart.)

ds., electric disc; el.c., electric club; mf., muscle fiber; ms., myoseptum; n., nerve.

114 THE ELASMOBRANCH FISHES

The electric dises (ds.), although directed more at right angles to their con-
nective tissue septa, have otherwise the same general relations as the fibers of
the muscle. Like them they are smaller and less regular at the tip and base of
the cone. They are, however, much larger
than the muscle fibers. As individual units
they are more or less quadrangular in
shape, their walls being formed of connee-
tive tissue. A glance will show that there
are a great number in a single organ. It has
been estimated that as many as 20,000 dises
are present in an adult Rava batis.

One of the most interesting things about
the electric organ is the fact that, whether
it be in Raja or in Torpedo, it is formed as
a series of metamorphosed muscle fibers.
The organ as described by Ewart in Raia
batis first appears when the embryo is
about an inch long. Here it is confined to
the tail and only those muscle fibers are af-
feeted which belong to the lateral bundles,
as described for Lamna (fig. 101). These
fibers undergo complete change of form
and assume an entirely secondary fune-
tional role.

A group of such fibers (fig. 1164) shows
the beginning stages in this metamorphosis.
Fig. 117. Finer structure of electric = The anterior fibers, near their attachment
Gise- af Brome wart? to the myoseptum, are beginning to enlarge
into elub-shaped structures (el.c.), while
the posterior fiber (mf.) is still of the mus-
cle type. By further growth and differentiation each incipient electric club
comes to assume the form of a cone, in the enlarged end of which in time a con-
cavity forms. A nerve entering this concavity breaks up into many branches
(n., fig. 1168). At this stage, striation characteristic of the muscle fiber has
decreased on the cups, but striations are still present on the body of the cone.
In a later stage (fig. 116c) the organ has acquired essentially the adult char-
acteristics. In this stage it is seen that the dise (ds.) has greatly enlarged and
that the terminal part of the cone has lost something of its muscle-like appear-
ance. From a somewhat more mature organ we may study the detail of its
finer structure.

av., alveolar layer; 0.e., outer elec-
tric layer; str., striate layers.

FINER ANATOMY OF ELECTRIC ORGAN

The dise may be divided into three well defined layers (fig. 117), an outer
electric layer (0.e.), a middle striated layer (str.), an inner alveolar layer
(av.). The outer layer is in fact composed of two layers, the more superficial
of which is made up of a net of nerves, and the next layer is characterized by

THE ELASMOBRANCH FISHES 115

the presence of cells with enormous nuclei. The middle striated layer consists
of fibers probably of connective tissue which take a transverse and wave-like
course. In this, nuclei are rarely seen. The inner or alveolar layer is at first
composed of granular tissue which later gives rise to long, backward directed
projections. At the base of these three layers is a thick cushion of gelatinous
tissue which is contained in the connective tissue walls of the cone.

Fig. 118. Electrie organ, Torpedo. (After Schimkevitsech from Krupski’s atlas. )
el.c., electric columns.

In the adult organ of Torpedo, the dises, as previously noted, are located in
the body in the region of the pectoral fins. Removal of the skin from this area
(el.c., fig. 118) shows the organ to be made up of multitudes of hexagonal
columns resembling the cells in honeycomb. Each column further consists of a
series of dises piled one upon another, ten to twelve of these being present in
each column. Each dise may be considered as having two surfaces, one ventral,
the other dorsal. The ventral surface bears a negative charge of electricity
while the dorsal is positively charged.

The innervation of the electric organ will be considered in Chapter LX.

; ne » >

5 i ear vk
a” :

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Os a ar = al : - WA 7
ry) 7 : 4 2 ee
Mes : 3 Ane ARNOT HAY i i 6 a
~~ ity ; a ig a
‘Wien rriiey :
i pc Sade cae Go
in ait 8 ihe sileeet SO eer ae
n ‘ ay - if - mer® * ve aA "7 8 it

<: ive : : 4 Pte (hap fon’ Ww ei LD

Pee yee be
“Tiiva es 4 7) a eset ' r) v1 rey TP ee qt] 7

1899.

1901.

1899.

1910.

1902.

1904.

1909.

THE ELASMOBRANCH FISHES

BIBLIOGRAPHY

CHAPTER IV

MUSCULATURE

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Bd. 16, pp. 605-607, 1 text fig.

ALLIS, E. P., Jr., The Lateral Sensory Canals, the Eye-Muscles and the Peripheral
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Braus, H., Beitrage zur Entwicklung der Muskulatur und des peripheren Nervensys-
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CorNING, H. K., Ueber die Entwickelung der Zungenmuskulatur bei Reptilien. Anat.
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CorNnING, H. K., Uber die vergleichende Anatomie der Augenmuskulatur. Morph.
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DAVIDSON, Piriz, The Musculature of Heptanchus maculatus. Univ. Calif. Publ. Zool.,
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DEAN, BASHFORD, The Preservation of Muscle-Fibers in Sharks of the Cleveland Shale.
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Dourn, A., Studien zur Urgeschichte des Wirbelthierkérpers. Mitt. Zool. Stat. Nea-
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. HARMAN, N. B., The Palpebral and Oculomotor Apparatus in Fishes. Jour. Anat. and

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. HowE Lt, A. Brazier, The Architecture of the Pectoral Appendage of the Dogfish.

Jour. Morph., Vol. 54, pp. 399-413, 4 text figs.

Hurecut, A. A. W., and SAGEMEHL, M., Muskulatur Bronn’s Klassen und Ordnungen
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2, HUMPHREY, Professor, The Muscles of the Smooth Dogfish (Mustelus levis). Jour.

Anat. and Physiol., Vol. 6, pp. 271-278, pl. 138.

KAESTNER, S., Ueber die allegemeine Entwickelung der Rumpf und Schwanzmuscu-
latur bei Wirbelthieren. Mit besonderer Beriicksichtigung der Selachier. Arch. f. Anat.
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Knauer, Karu, Die Bauchmuskulatur der Fische. Abt. Zool. Inst. Wien, T. 18, Heft.
3, pp. 207-226, Taf. 1-3, 6 text figs. (Selachians, fig. 1, pp. 5-8.)

Lamp, A. B., The Development of the Eye Muscles in Acanthias. Amer. Jour. Anat.,
Vol. 1, pp. 185-202, 9 text figs. Also: Tufts College Studies, No. 7, Vol. 1, pp. 275-292,
9 text figs.

LANGELAAN, J. W., On the Form of the Trunk-Myotome. (Proc.) Sci. Akad. Amster-
dam, Vol. 7, Pt. 1, pp. 34-40, 7 text figs.

LutHer, ALEX., Untersuchungen iiber die von n. trigeminus innervierte Muskulature
der Selachier (Haie und Rochen) unter Beriicksichtigung ihrer Beziehungen zu be-
nachbarten Organen. Acta Soe. Sci. fenn., T. 36, No. 3, pp. 1-176, Taf. 1-5, 23
text figs.

118

1909.

1905.

1892.

1906.

1912.

OEE

1874.

1882.

1876.

1893.

1897.

1873.

THE ELASMOBRANCH FISHES

LurHeEr, ALEX, Beitrige zur Kenntnis von Muskulatur und Skelet des Kopfes des
Haies Stegostoma tigrinum Gm., und der Holocephalen mit einem Anhang iiber die
Nasenrinne. Acta Soe. Sci. fenn., T. 37, No. 6, pp. 1-60, 36 text figs.

Marion, G. E., Mandibular and Pharyngeal Muscles of Acanthias and Raia. Amer.
Nat., Vol. 39, pp. 891-924, 15 text figs.

Maurer, 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. 18, pp. 76-179, pls. 4-6, 6 text figs.

Maurer, F., Die Entwickelung des Muskelsystems und der elektrischen Organe. Hert-
wig’s Handb. vergl. u. expt. Entwick. d. Wirb., Bd. 3, Teil I, pp. 1-80, 41 text figs.
Maurer, F. Die ventrale Rumpfmuskulatur der Fische (Selachier, Ganoiden, Teleos-
tier, Crossopterygier, Dipnoer). Jena. Zeitschr. Naturwiss., Bd. 49, pp. 1-118, Taf.
j—2, 6 text figs. (on Elasmobranchs).

MUuLuer, Erik, Untersuchungen tuber die Muskeln und Nerven der Brustflosse und der
Korperwand bei Acanthias vulgaris. Anat. Hefte, Bd. 43, pp. 1-147, pls. 1-26, 11
text figs.

. MUuueER, J., Vergleichende Anatomie der Myxinoiden. Abh. Akad., Berlin.
. NEAL, H. V., The Development of the Hypoglossus Musculature in Petromyzon and

Squalus. Anat. Anz., Bd. 13, pp. 441-463, 2 text figs.

. NEAL, H. V., The History of the Eye Muscles. Jour. Morph., Vol. 30, pp. 433-453, 20

text figs.

. PLattT, JuLIA B. (See Bibliography, Chap. I.)
. RipEwoop, W. G., On the Eyelid-Muscles of the Carchariidae and Seyllium. A contri-

bution to the Morphology of the Nictitating Membrane of Sharks. Jour. Anat. and
Physiol., Vol. 33, pp. 228-242, 7 text figs.

. RuGE, G., Ueber das peripherische Gebiet des nervus facialis bei Wirbelthieren.

Festschr. f. Gegenbaur, Vol. 3, pp. 195-348, 76 text figs.

. TIESING, BERTHOLD, Ein Beitrag zur Kenntnis der Augen-Kiefer und Kiemenmuske-

latur der Haie und Rochen. Jena. Zeitschr. Naturwiss., Bd. 50 (N. F. 23), pp. 75-126,
pls. 5-7.

VeErTeER, B., Untersuchungen zur vergleichenden Anatomie der Kiemen- und Kiefer-
musculatur der Fische. Jena. Zeitschr. Naturwiss., Bd. 8 (N. F. 1), pp. 405-458,
pls. 14-15.

WIJHE, J. W. VAN, Ueber die Mesodermsegmente und die Entwickelung der Nerven
des Selachierkopfes. Verh. d. k. Akad., Amsterdam, Deel 22, pp. 1-41, Taf. 1-5.

ELECTRIC ORGAN

BABUCHIN, A., Uebersicht der neuen Untersuchungen tiber Entwickelung, Bau und
physiologische Verhiltnisse der elektrischen und pseudoélektrischen Organe. Arch. f.
Anat. u. Physiol., Bd. 1876, pp. 501-542, Taf. 11-12, 2 text figs.

BauLowiTz, Emit, Ueber den Bau des elektrischen Organes von Torpedo mit beson-
derer Beriicksichtigung der Nervenendigungen in Demselben. Arch. mikr. Anat., Bd.
42, pp. 459-568, Taf. 29-31.

. BatitowiTz, E., Ueber die Uebereinstimmung des feineren Baues der elektrischen Or-

gane bei den starkelektrischen und schwachelektrischen Fischen. Anat. Anz., Bd. 13,
pp. 124-126.

BatLowiTz, E., Uber den feineren Bau des elektrischen Organs des gewohnlichen
Rochen (Raja clavata L.). Anat. Hefte, Bd. 7, pp. 283-375, Taf. 19-29.

Bout, F., Beitrige zur Physiologie von Torpedo. Arch. f. Anat. u. Physiol., Bd. 1873,
pp. 76-102.

THE ELASMOBRANCH FISHES 119

1874. Bout, F., Die Structur der elektrischen Platten von Torpedo. Arch. mikr. Anat., Bd.
10, pp. 101-121, Taf. 8.

1876. Botu, F., Neue Untersuchungen iiber die Structur der elektrischen Platten von Tor-
pedo. Arch. f. Anat. u. Physiol., Bd. 1876, pp. 462-479, Taf. 8.

1898. CREVATIN, F., Ueber das sogenannte Stabchennetz im elektrischen Organ der Zitter-
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1849. Ecker, A., Einige Beobachtungen iiber die Entwicklung der Nerven des electrischen
Organs von Torpedo galvanii. Zeitschr. wiss. Zool., Bd. 1, pp. 38-47.

1888. Ewart, J. C., The Electric Organ of the Skate. On the Development of the Electric
Organ of Raia batis. Phil. Trans. Roy. Soe. Lond., Vol. 179B, pp. 399-409, pl. 68.

1888. Ewart, J. C., The Electric Organ of the Skate. On the Structure of the Electric Organ
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1888. Ewart, J. C., The Electric Organ of the Skate. The Electric Organ of Raia radiata.
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1892. Ewart, J. C., The Electrie Organ of the Skate—Observations on the Structure, Rela-
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| Trans. Roy. Soe. Lond., Vol. 183B, pp. 389-420, pls. 26-30.
| 1883. FritscH, G., Bericht iiber die Fortsetzung der Untersuchungen an elektrischen
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| 1883. FritscH, G., Die elektrischen Fische in Lichte der Descendenzlehre. Samm. gemein.
Wissen. Vortr., Bd. 18, Ser. 1, pp. 835-898, 7 text figs. (Virchow Holtzendorff Vor-
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1801. Grorrroy, E., Mémoire sur ’anatomie comparée des organes électriques de la Raie
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1845. Goopsir, J., Observations on Electric Organs (Ray). Ann. Mag. Nat. Hist., Ser. 1,
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887. GoTCcH, FRANCIS, The Electromotive Properties of the Electrical Organ of Torpedo
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88. (orcH, F., Further Observations on the Electromotive Properties of the Electrical
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ils. 51-52, 3 text figs.

1861. IARTMANN, Ropr., Bemerkungen tiber die elektrischen Organe der Fische. Arch. f.
Anat. u. Physiol., Bd. 1861, pp. 646-670, Taf. 16.

1911. LaGuEssE, E., Un Exemple bien net d’architecture lamellaire du tissu conjonetif lache.
C. R. Soe. Biol. Paris, T. 71, pp. 328-329.

1861. M’DONNELL, R., On an Organ of the Skate which appears to be a Homologue of the
Electrical Organ of the Torpedo. Nat. Hist. Review, pp. 57-60.

1906. PorTiIER, P., Les Poissons électriques. Bull. Mus. Ocean. Monaco, No. 76, 1906, pp.
1-23, 18 text figs.

1873. REICHENHEIM, MAX, Beitrage zur Kenntnis des elektrischen Centralorgans von Tor-
pedo. Arch. f. Anat. u. Physiol., Bd. 1873, pp. 751-759, Taf. 15-16.

1856, RrmMAk, R., Ueber die Enden der Nerven im elektrischen Organ der Zitterrochen. Arch.
f. Anat. u. Physiol., Bd. 1856, pp. 467-472.

1898. Rerzius, G., Ueber die Endigung der Nerven im elektrischen Organ von Raja clavata
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1846. Rosin, Cu., Recherches sur un organe particulier qui se trouve sur les poissons du
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THE ELASMOBRANCH FISHES

Rosin, Cu., Mémoire sur la démonstration expérimentale de la production d’électricité
par un appareil propre aux poissons du genre des Raies. Jour. de |’Anat. et Physiol.,
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SANDERSON, J. B., and Gorcu, Francis, On the Electrical Organ of the Skate. Jour.
Physiol., Vol. 9, pp. 137-166, 5 text figs.

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Jour. Physiol., Vol. 10, pp. 259-278, pl. 22, 1 text fig.

ScHULTzZE, Max, Zur Kenntnis des den electrischen Organen verwandten Schwanz-
organes von Raja clavata. Arch. f. Anat. u. Physiol., Bd. 1858, pp. 193-214, Taf. 9.
ScHuLzE, O., Zur Frage von dem feineren Bau der elektrischen Organe der Fische.
Biol. Centralbl., Bd. 26, pp. 640-656. Festschr. f. J. Rosenthall, Leipzig, pp. 101-118.
SrarRK, Dr., On the Existence of an Electrical Apparatus in the Flapper Skate and
Other Rays. Ann. Mag. Nat. Hist., Vol. 15, p. 121.

Fig. 119. Body cavity opened to show viscera, Heptanchus maculatus. (C. G. Potter, orig.)

el., cloaca; co., colon; ¢.s., cardiac stomach; /v., liver; pn.t*, dorsal and ventral lobes of
pancreas; p.s., pyloric stomach; re., rectum; re.g., rectal gland; sp.i., valvular intestine.

Fig. 120. Digestive tract and its mesenteries, Heptanchus maculatus.
(Ruth Jeanette Powell, del.)
co., colon; ¢.s., cardiae stomach ; d.ch., bile duct; du.,duodenum; h.p., hepatic portal vein;
m.p., median fold of mesentery (omentum) ; mr., mesorectal mesentery; 0¢., oesophagus;

pn.**, dorsal and ventral lobes of pancreas; p.s., pylorie stomach; r.f., right fold of mesen-
tery; re., rectum; re.g., rectal gland; sp.i., spiral intestine; spl., spleen; spl.', anterior exten-

sion of spleen.

V
DIGESTIVE TRACT
DIGESTIVE TRACT 0F HEPTANCHUS MACULATUS

MESENTERIAL STRUCTURES

The digestive tract of Heptanchus (figs. 119 and 120) is suspended from the
dorsal body wall by mesenteries, which are present in two general areas, an
anterior and a posterior (fig. 120). The anterior mesenteries are somewhat
complex; while those which suspend the posterior part of the tract are simpler.
For convenience of description the mesentery in the anterior region may be
considered as made of a right, a median, and a left fold. The right fold of the
mesentery (7.f., fig. 120) passes from the middorsal line and from the right
suspensory ligament to the hepatic portal vein (/.p.) and to the spiral intes-
tine (sp.v), the extent of its origin, in other words, being along the middorsal
line from the liver in front, back to the region of the superior mesenterie ar-
tery. Since the anterior part of the right mesentery is attached along the
hepatic portal vein and back to the suspensory ligament of the spiral intestine,
it is largely hidden in figure 120.

The second or median division extends from the right suspensory ligament
of the liver and the higament along the hepatic portal vein, across to the
oesophagus and down the lesser curvature of the stomach to the proximal tip
of the duodenum. The larger part of this is shown in figure 120 (m.p.) witha
portion removed to show underlying organs. The left mesentery extends from
the middorsal line to the dorsal side of the oesophagus and the stomach. Along
its line of origin the left fold lies against the right and the two are firmly
fused together. Remnants of this part of the mesentery appear on the outer
angle of the stomach separating the stomach from the spleen (spl.) and from
the pancreas (pn.?).

These three parts of the mesentery may be considered as loosely enveloping
the digestive tract and extending from the middorsal line on the right side to
the suspensory ligament and hepatic portal vein. From here the middle seg-
ment (omentum) stretches across to the lesser curvature of the stomach; the
left segment continuing around is attached to the middorsal line on the left.

The posterior mesentery or mesorectum (m7.) extends from the middorsal
line to the rectal region; it suspends the rectal or digitiform gland, and reaches
forward to the posterior mesenteric artery.

Buccau Cavity

The mouth or entrance to the buccal cavity is ventral in Heptanchus. If seen
from below (fig. 119) it presents the appearance of a large crescentie slit with
regular margins, except near the angles where there are enlarged folds. The

[121]

122 THE ELASMOBRANCH FISHES

mouth and nasal pits in Heptanchus are not connected by oronasal grooves
characteristic of some of the Elasmobranchs. The buceal cavity proper is
large and spacious. Its floor is lifted up by the basihyal cartilage, forming a
skeleton for the so-called tongue. The mucous membrane lining the mouth is
provided both dorsally and ventrally with numerous stomodeal denticles (see
p. 24, fig. 27c) which, as we have seen in a study of the integument, are modi-
fications of placoid seales. In the region just within the crescent of teeth
the lining of the mouth is thrown into heavy folds, which lie over the concen-
tric rows of tooth buds.

The teeth of Heptanchus (see fig. 48, facing p. 44) consist of a heavier lower
series and a cuspidate upper series. The first tooth in the lower row of Hep-
tanchus maculatus, like that
for H. indicus (fig. 121), is
unpaired and without a me-
dian cusp. On either side of
it are seven teeth, the most
posterior of which is cusp-
less and is followed by sev-

ee ee
uw » “ts eral rows of smaller flat

“oot nodules not shown in figure
Fig. 121. Teeth of Heptanchus indicus. (From Mae-
donald and Barron.) 48. The first of the large

teeth is provided with a se-
ries of three conules on the median margin and usually six larger conules on
the lateral margin. Other lower teeth including the sixth, though differing in
size, are essentially like the first paired tooth. Unlike Heptanchus indicus (fig.
121) there is usually no unpaired upper tooth in Heptanchus maculatus. The
first paired tooth above bears a long fang which is directed downward; at its
sides are small basal denticles like those in Heptanchus indicus. The second
tooth and the ones following, although larger, differ from the first only in that
they possess median conules and outer cusps, several of which are present on
each tooth.

PHARYNX AND ASSOCIATED STRUCTURES

The pharyngeal part of the tract is wide from side to side and depressed or
flattened dorsoventrally. Through its ventrolateral walls are perforations, the
internal branchial openings by means of which the respiratory current reaches
the gill pockets (see fig. 142, facing p. 148). These openings are of interest
in a consideration of the respiratory system. The lining of the pharynx, like
that of the buccal cavity, is provided with denticles, but these on the roof in
the posterior part are confined to a narrow strip just above the internal bran-
chial clefts. The pharynx narrows toward the region of the oesophagus, which
is closed except during the passage of food. By this closure of the oesophagus
the bueeal cavity and pharynx form a relatively large room.

In connection with the pharynx are the thymus and thyroid glands. The
thymus in Heptanchus, figure 122, lies dorsal to the first six gill clefts and
takes the form of bunches of grapes. Van Wijhe has made the remarkable dis-

THE ELASMOBRANCH FISHES 123

covery that in the young embryo of H. cinereus the thymus is not a ductless
gland. In this type ducts lead from the first six lobes of the thymus into the
pharynx. The thyroid gland is located at the symphysis of the lower jaws
between the coracomandibularis and coracohyoideus muscles (see p. 200, fig.
184, th.). It is a mass of semitransparent glandular tissue slightly crescentice
in shape and surrounded by a capsule of connective tissue.

OESOPHAGUS

The digestive tract is continued posteriorly from the pharynx by a short,
thick-walled portion, the oesophagus (oe., fig. 120). The lining of the oesopha-
gus is thrown into whitish longitudinal
folds, some of which may be continuous
with those of the stomach. The oesopha-
gus is distinguished from the stomach,
however, by the character of its folds,
the folds of the latter being much more
pronounced. The epithelium of the
oesophagus differs from that of the
pharynx in that it does not contain
stomodeal denticles.

STOMACH

The stomach of Heptanchus is U-

shaped, the larger left limb being the Ti8;1%2, Section through ymus, gland
eardiae end (c.s., fig. 120), and the (From Van Wijhe.)

smaller right limb, the pyloric division d., duct of thymus; e., epithelial body;
(ps). Superfcially the eardiae por- lms. hyomandibnlor cartilages, of. at
tion of the stomach appears as a more thymus nodules; JJ, second gill cleft.

or less distended bag, while the pyloric

division is thick-walled. Within the cardiac stomach is usually found a consid-
erable amount of undigested food material in the form of pieces of fishes, the
shell and claws of crabs, and the like.

Internally the pronounced folds of the cardiac stomach continue in a more
or less longitudinal direction from its union with the oesophagus throughout
two-thirds of its length where they become more or less tortuous. At the distal
end of this part of the stomach there is present a blind sae in which some of
the folds terminate. Some of the small folds abut against a circular fold which
in a way separates the cardiac from the pyloric division. The pyloric lumen
of the stomach is long and narrow, and its folds are not especially marked at
the proximal end. As the terminus of the pylorus is reached, however, they
become much higher. Three-fourths of an inch from the termination of the
pyloric limb there is a slightly enlarged portion which opens into the duod-
enum through the pyloric valve.

124 THE ELASMOBRANCH FISHES

SPLEEN

The spleen (spl.) although unconnected with the digestive tract may be con-
sidered here. In Heptanchus this organ, when its relation to that in other
forms is studied, is very instructive. It consists of a long, more or less lobate
band extending from the ventral lobe of the pancreas over the greater (outer)
angle of the stomach. It then crosses over the stomach dorsally and is con-
tinued in the lesser curvature, one of its branches extending as far forward as
the tip of the cardiae portion (spl.', fig. 120).

DUODENUM oR MIDDLE INTESTINE

The part of the digestive tract immediately following the pylorus, the duo-
denum or middle intestine, is well defined in Heptanchus. In figure 120, this
segment (du.) is covered in part by the ventral lobe of the pancreas (pn.?).
As in several other forms, the valve of the spiral intestine extends forward
throughout the length of the middle intestine and touches the pylorie valve.
Into this segment of the intestine the ducts of the liver and the pancreas empty.

The liver (lv., fig. 119) consists of a right and a left lobe between which is a
small eaudate lobe, not shown in the figure. In the caudate lobe is located the
gall bladder which is emptied by a long duct (d.ch., fig. 120) into the duod-
enum.

The entrance of the duct into the duodenum is of interest. It reaches and
enters the wall on the dorsal side only a short distance from the pyloric ter-
minus of the stomach. It then runs in the wall backward and outward on a line
almost at right angles to the attachment of the first whorl of the spiral valve.
After having encircled about one-fourth of the duodenal circumference it
empties into the duodenum a short distance from the first loop of the valvular
intestine.

The pancreas is composed of two compact and connected lobes. The smaller
of these is dorsally placed (pyn.*, fig. 120), while the more compact lobe lies
ventrally on the angle between the pyloric division of the stomach and the
duodenum (p2.*). The two lobes empty by a common duct which leaves the ven-
tral lobe and, passing through the duodenal wall, runs almost parallel with the
first annular artery. As it passes backward and outward it approaches the first
fold of the valvular intestine and finally empties into the duodenum only a
short distance to the left of (dorsally to) a line drawn from the entrance of
the bile duct at right angles to the first fold of the valvular intestine.

VALVULAR INTESTINE

The most interesting part of the intestine (figs. 120, sp.7., and 123) is the spiral
valve contained within its cavity. The attachment of the valve to the intestine
may be seen from the outside as a series of annular folds traversed by blood
~ vessels, seventeen or eighteen turns of which are present in Heptanchus macu-
latus. By making a window in the valvular intestine (fig. 123) it may be

THE ELASMOBRANCH FISHES 125

Fig. 123. Valvular intestine, with middle segment omitted, Heptanchus maculatus. (Dun-
can Dunning, del.)
pv., pyloric valve.

126 THE ELASMOBRANCH FISHES

observed that the folds are far apart anteriorly and very much closer together
posteriorly. The valve is formed as an ingrowth into the intestine and extends
from the duodenum throughout the large intestine to the region where the
opening of the rectal gland enters the intestine posteriorly. This fold is con-
siderably broader than the diameter of the intestine and is thrown into a series
of cones having their apices pointing anteriorly. The surface of the valve, if
seen under the microscope, shows numerous finger-like villi which serve for the
absorption of digested food.

CoLoN AND REcTUM

The part of the large intestine immediately following the valve is known as the
colon (co., fig. 120). It is a muscular segment and superficially appears as
slightly bulbous. Its lining, together with that of the part succeeding it, the
rectum (7rc.), is thrown into longitudinal folds. In the most posterior part,
however, the walls of the rectum are smoother. The line of demareation be-
tween the colon and the rectum is formed by a
lumen from the rectal or digitiform gland.

RECTAL GLAND

The rectal or digitiform gland (re.g., fig. 120 and
fig. 124) in Heptanchus is a finger-like structure
which is composed of multitudes of gland cells
and which empties by a central lumen into the in-
testine. It is so arranged, however, that the lumen
does not enter immediately at the point at which
it reaches the intestine, but passes sharply for-
ward and downward emptying on a level with the

Fig. 124. Sagittal section terminus of the spiral valve.

through rectal gland, Hep-
tanchus. (From Howes.) CLOACA

co., colon; fd., fold of spi-
ral intestine; lu., lumen of The rectum empties into an enlarged room, the

Sada feanteclnmn cloaca, which is lined with a smooth mucous mem-
brane (see fig. 252, facing p. 290). Into the anterior part of the cloaca empty
the products from the digestive, the urinary, and the genital systems, and in its
posterior part are two finger-like processes, the cloacal papillae (p.).

ABDOMINAL PORES (PORI ABDOMINALES)

As a usual thing the cloacal papillae in Heptanchus are imperforate. Ocea-
sionally, however, as on the left side in figure 252, they are perforate, forming
the so-called pori abdominales. These pores connect the abdominal cavity or
coelom with the exterior.

THE ELASMOBRANCH FISHES 127

DIGESTIVE TRACT OF ELASMOBRANCHS IN GENERAL

The digestive tract constitutes a tube in which food is digested and through
the walls of which it is absorbed into the circulatory system. In the adult, as
we have seen in Heptanchus, the tract is folded upon itself so that when seen in
ventral view it takes the form of an |. A median line parallel to the body axis
may bisect the oesophagus and cloaca leaving the stomach to the left and the
spiral intestine to the right.

MESENTERIES

The mesenteries of Heptanchus are generalized when the Elasmobranchs as a
group are considered, but they are more specialized than are those described

2006
GG OFC e0%
2, 206 of
°F 4
UOT

Fig. 125. Development of teeth in lower jaw of Spinax niger. (From Laaser. )

d.r., dental ridge; e., enamel; e.o., enamel organ; md., mandibular cartilage; o.f., outer
furrow; p., tooth papilla.

by Howes (1890) for Hypnos subnigrum, the Australian torpedo. In Hypnos,
which has the most generalized type of any adult Elasmobraneh with which I
am acquainted, the mesentery extends as an almost unbroken sheet along the
entire digestive tract. Only in the region of the spleen and of the rectal gland
are there any indications of a break in the folds. In the adult of most other
Elasmobranchs, however, there is a more pronounced tendency than in Hep-
tanchus toward a loss of parts of the folds. In Acanthias, for example, rela-
tively small parts of the folds which we have described as right and left remain.

In its development the digestive tract of the Elasmobranch fishes is a more
or less simple tube. It consists of a median segment which is put into com-
munication with the outside: (1) by an anterior invagination which finally,
as the stomodeum, breaks through to join the middle segment, and (2) by a
posterior pit which also reaches the middle segment as the proctodeum. There
is thus formed a tube including three parts: (1) the anterior stomodeum,
lined with the outside ectoderm, which in the adult becomes the buecal and

128

THE ELASMOBRANCH FISHES

pharyngeal(?) regions; (2) along middle portion lined with entoderm which
includes in the adult the segments from the oesophagus to the end of the
rectum, and finally (3) a posterior proctodeum or cloacal area also lined with

Fig. 126. Tooth pat-
terns. A. Chlamy-
doselachus. (From
Rose.) B. Mylio-
batis. (From Gar-
man. )

ectoderm. From these simple beginnings the complex tract
results. As growth proceeds a series of dilations and con-
strictions divides the tract into parts characteristic of the
adult. These we shall next consider in order.

Buccau Cavity

The mouth in Elasmobranchs is a large crescent which is
usually ventral, although in certain types it is terminal, in
position. It is bounded by membranous folds or lips and
leads into a voluminous buceal cavity.

The floor of the buccal cavity is raised up into a heavy
fold, the “tongue,” which in some forms (Lamna) is well
developed; in others it is less pronounced. The buceal cav-
ity is lined with a smooth or papillated mucous membrane
(Mustelus, Scyllium, Chlamydoselachus), the cells of
which secrete mucin; but it is devoid of all glands which
are characteristically present in higher forms. Perforating
the lining of the cavity are two structures which, although
differing in form, are essentially identical: the stomodeal
denticles and the teeth. The former we have considered in
Chapter II, page 38. The latter may be discussed here more
in detail.

TEETH

The teeth’ characteristic of the Elasmobranchs are of two
types: sharp or prehensile teeth and pavement or crushing
teeth. Between these extremes multitudes of patterns, more
or less complex, occur. In the early stages the two types
are essentially alike, but as development proceeds each
takes on its specific character. The general mode of devel-
opment we may examine before considering the types
further.

A sagittal section made through the lower jaw of Spinax

niger by Laaser (fig. 125) shows the ectoderm sinking in to form a dental ridge
(d.r.). In this ridge several tooth germs are developing, and cells are collect-
ing at the papilla (p.) to form still another tooth. In the tooth germs which are
more mature than those just mentioned the papillae have grown outward
carrying caps of epidermis, the enamel organ (e.0.), over them. In their for-
mation the teeth are much like the saw tooth already studied (p. 35).

Teeth thus formed in other Elasmobranchs may be long and fang-like,

1 For bibliography on the teeth, see Chap. IT.

129

THE ELASMOBRANCH FISHES

Fig. 127. Tooth of extinet Carcharodon. (Photograph natural size.)

130 THE ELASMOBRANCH FISHES

resulting from a single narrow papilla, of which several may fuse at the base
into a simple triconodont tooth as in Chlamydoselachus (fig. 126A) ; or in the
rays a most complex arrangement of large median and smaller lateral hexag-
onal plates as in Myliobatis (fig. 1268) may result in pavement or crushing
teeth; or the plates may reach from side to side in an unbroken line as in
Aetobatis. The teeth of Heterdontus (fig. 128) are particularly interesting in
that they represent both anterior prehensile and posterior crushing teeth.
Furthermore, in the area between these two, transitional teeth are present

Fig. 128. Median view of teeth in jaws, Heterodontus francisci.
(Duncan Dunning, del.)

which have characteristics of both. The teeth in the sixth row from the front
are flattened out and are provided with cusps essentially like the pavement
teeth of Mustelus henlet.

The finer structure of a tooth (fig. 129) is somewhat similar to that of a
seale. In both there is an outside harder cap usually of structureless enamel
(e.) over a heavier inside layer of dentine. The enamel in some teeth is of a
coarse grain, closely resembling dentine and by some held to be identical with
it. The dentine (d.) is of the tubular type formed by the odontoblasts of the
dentinal papilla. In the connective tissue cells at the base of the tooth vaso-
dentine (vd.) is formed, which is somewhat softer than dentine proper. In the
adult Myliobatis the whole core of the tooth becomes filled with dentine as
does the core in the tooth of the saw (Pristis), leaving only central canals from
which run numerous dentinal canals (d.c.).

It is generally held that enamel results from the basal layer of the epidermis,
with the exception that in Carcharias, according to Tomes (1898) it arises
from a special amelioblastic layer formed by the corium. All agree that den-
tine is produced in and by the corium. Here the odontoblasts send out pro-
cesses along which are deposited the lime salts which harden as dentine. The
processes become surrounded and are retained within dentinal canals (d.c.,
fig. 129) which ramify throughout the dentine. In some forms the dentinal

THE ELASMOBRANCH FISHES 131

tubes end in enlarged islands continuous with the enamel (Galeus). In others
the tubules penetrate far outward into the enamel and either divide into
branches (Carcharias) or are lost as fine single tubules (Lamna).

REPLACEMENT OF TEETH

Teeth which have been injured or lost are replaced by new ones. To gain a
notion of the provision made for repairing injury or loss it is only necessary
to examine the mouth of a form like Carcharias, or Heterdontus (fig. 128). In

Pays
Stil

esac MOU

Fig. 129. Finer structure of a tooth, Myliobatis. (From Rose.) A. Sagittal section of whole
tooth. B. Transverse section cutting a few canals; highly magnified.

c.c., central canals; d., dentine; d.c., dentinal canals; e., enamel layer; vd., vasodentine.

these forms the teeth are arranged horizontally in crescentic rows, several of
the outer rows functioning at the same time; upon injury or loss the outermost
teeth are replaced by others which migrate outward over the jaw to take their
places. It may thus happen that the teeth in several rows may be lost in en-
counter or in capture of food. In such an event, provision has been made for
their replacement, for at the base of the innermost row are other deeply buried
and less mature teeth ranging in development down to flabby tooth-buds.

PHARYNX

The pharynx is that part of the tract which leads from the buccal cavity and
which is characterized by branchial perforations or clefts opening through
its walls. In addition to the spiracle seven such apertures perforate the
pharynx in Heptanchus, six in Hexanchus and Chlamydoselachus, and five in
pentanchid Elasmobranchs. In the adult the spiracle opens into the hyoidean
pocket and is of small size. The remaining perforations are large but de-

132 THE ELASMOBRANCH FISHES

crease in size posteriorly. The lining of the pharynx is a continuation of that
of the buccal cavity, being made up of a deeper layer of connective tissue and
a superficial epithelium; in the latter are located the mucous cells. Special
interest attaches to the pharyngeal region because of two structures associated
with it, the thymus and the thyroid glands.

The thymus gland is an embryonic structure appearing as a series of nodules
connected into a chain above the gill pockets. We have seen that six such

Fig. 130. Developing thymus gland, Spinaz. (From Fritsche.) A. Transverse section.
B. Seetion of gland magnified.

a.c.s., anterior cardinal sinus; chd., notochord; cl.*“*, third and fourth ¢lefts; ht., heart;
my., myotome; n.t., neutral tube; ph., pharynx; th., thymus gland.

nodules may be present in Heptanchus. In Spinax, Acanthias, Mustelus, and
Scyllium four of these, corresponding to the first four branchial clefts, are
present, and, in the embryo of Spinaz, transitional thymus buds have also
been found over the spiracular and the fifth clefts. In the rays thus far studied
a similar number is present lying back of the spiracle and between the gill
pockets and the lateral line. Figure 22p gives a dorsal view of the embryo of
Urolophus in which the nodules of the thymus are seen between the gill
pockets and the lateral line canal.

In development the thymus arises as an anterodorsal thickening of the
epithelium of the gill pouches (th., fig. 1304). These thickenings as we have
said may represent the spiracular and the five branchial pockets in pentanchid
Elasmobranchs, but the first and the last never pass the rudimentary stage.

Figure 122 of Heptanchus cinereus shows that each thymus nodule has the
form of a bunch of grapes.

A highly magnified section through the thymus of Spinazx (fig. 130B) shows
two types of cells, one outer and larger, and the other a more deeply located,
small, round cell. Among them are to be found occasional lymphocytes, and it
has been questioned whether the smaller cells of the thymus are not trans-

THE ELASMOBRANCH FISHES 133

formed directly into lymphocytes. It is generally believed, however, that the
function of the thymus, whatever it may be, is not that of a lymphoid organ
(Fritsche, 1910).

That the thymus possesses a duct in Heptanchus, as has been demonstrated

A B

Fig. 131. Thyroid follicles making up the gland. (From Ferguson.) A. Carcharias littorulis.
B. Raia erinacea.

by Van Wijhe, is an unusually interesting fact, although the significance of
the duct has not yet been made out.

The thyroid? gland in the Elasmobranch fishes is a gelatinous mass of tissue
surrounded by a connective tissue capsule. In the sharks it is located in the
region behind or below the basihyal cartilage,
between the coracomandibular and the coraco-
hyoideus muscles. It may be crescentie in shane
or it may be more or less irregular (Acanthias).
Where the basihyal cartilage is broad it occupies
its ventral side, resting in a depression ( Acanthias,
Mustelus) or in a deep groove (Carcharias litto-
ralis). It occupies the space between the basihyoid
and the bifurcation of the ventral aorta. Where
the cartilage is narrow as in Rava erinacea the
thyroid may lie farther posterior on the terminal
bifureation of the ventral aorta.

Upon removal of the connective tissue capsule
from the thyroid it is seen to be made up of groups

of follicles of various forms. They may be small Fig. 132. Sagittal section
(Carcharias, fig. 1314; Mustelus; Squatina) or through the thyroid gland of
seth 2 : Chlamydoselachus anguineus.
are oy eealis a , Ue,
large (fava, fig. 1318). A section through an in- (From Goodey.)
dividual follicle shows an outer wall of epithelium 4, follicle; s.d., remnant of
enclosing a mass of colloidal substance (Fergu- Stomodeal denticle ; t.d., thy-
= es roid duct.

sone L912

The history of the thyroid in forms lower than the Elasmobranchs is of in-
terest. In Amphioxus, the Ascidians, and Ammocoetes, there is present in the

floor of the pharynx a median groove, the ciliated endostyle, the walls of which

2 Thyreoid.

134 THE ELASMOBRANCH FISHES

possess groups of cuneiform secreting cells. By the beating of the cilia, food
caught in the mucous secretion is directed into the intestine.

Marine (1913) has shown for Ammocoetes of the brook lamprey that the
groups of cuneiform secreting cells degenerate at the time of metamorphosis,
and that the follicles of the thyroid gland arise from certain areas in the walls
surrounding these columns.

In the embryo of the Elasmobranchs the thyroid arises similarly as an
evagination of the pharyngeal floor, or as a solid block of cells in which a lumen
may form (Acanthias). Either way, in development, it sinks deeper. While it
may retain its connection with the pharynx practically until the period of
birth, later than this all relation with the pharynx is usually lost and the
thyroid becomes a “‘ductless gland.”

Especially significant in this regard is the discovery by Goodey (1910) that
in Chlamydoselachus the duct (t.d., fig. 182) retains its connection with the
pharynx. In this form the aperture of the duct enters the pharynx, through
a perforation in the basihyal cartilage, and is lined with the pharyngeal epi-
thelium as is the endostyle of Amphioxus. Within this invaginated lining of
Chlamydoselachus numerous scale-like structures are present, the remnants
of stomodeal denticles (s.d.).

OESOPHAGUS

In most of the Elasmobranchs the segment of the digestive tract known as the
oesophagus (oe., figs. 173 and 175) is short. In some forms it is easily distin-
cil. guished from the stomach by its smaller

Ne ee ee Ge eA wy — Size, Dut in others it is wide and passes al-
| most imperceptibly over into the stomach.
q Ay Denticles which may be present on the
*{_(n- pharyngeal lining cease more or less ab-

“ ruptly at the beginning of the oesophagus.

a/®) VONAGE ) The mucous membrane lining the oesoph-
2 o> SS A agus may be covered with long, finger-
like papillae as in Acanthias, but usually

Hagel Aeceton thronch the Ene it is thrown into numerous folds. Ante-

ing of the oesophagus of Squatina riorly these folds are low and regular;
(ont Eekersen) posteriorly they may run transversely

cil., long ciliated cell; m.c., mu- f . .

Cann call marking a boundary between the oesopha-

gus and the stomach. Anteriorly, too, the

mucous membrane is similar to that of the pharynx, but posteriorly it consists
mainly of ciliated and goblet cells.

A section of the membrane lining the oesophagus of Squatina, by Petersen
(1908), shows the two main types of cells (fig. 183). One of these is of long
ciliated cells (cil.), among which are scattered the mucous cells (mc.). The
mucous cells are extremely large and vacuolated, and each has its nucleus well
toward the basal end of the cell.

THE ELASMOBRANCH FISHES 135

STOMACH

The stomach of Elasmobranchs when seen in ventral view is a U- or J-shaped
tube (for types see figs. 173 to 175, c.s. and p.s.), the left arm of which, as in
Heptanchus, is the cardiae and the right arm the pyloric division. The great
variety in shape of the stomach found among the Elasmobranchs is due largely
to variation in the relative length of the pyloric arm. In some, although the
pyloric division is small in diameter, in length it
is practically equal to the cardiac (leopard shark,
fig. 1734; Raja); in others this arm is less than
one-half the length of the cardiac, so that the
shape of the stomach in these is better described
asaJ (Acanthias). In still others the pyloric limb
is only a small projection from the eardiae divi-
sion of the stomach (Scymnus lichia, fig. 135B;
Laemargus rostratus, fig. 13868). In the latter
there is a so-called “blind sae” (sc.?) at the angle.

The mucous lining of the adult stomach is
thrown into folds which, as we have said, may be
continuous with those of the oesophagus. The folds
on the walls of the eardiae division are high and
may extend in part as the finer folds into the py-
lorie Limb, but those of the two regions are usually
distinct.

A section through the mucosa of the stomach of
Squalus acanthias according to Ringoen (1919;
fig. 134) shows a gland as long and flask-shaped.
The superficial epithelial cells (ep.) are somewhat
hike those found in the oesophagus, that is, they
are columnar or pyramidal cells, the upper part

: : Fig. 134. Section through lin-
of which contains a plug of mucus (pl.). The cells die orethenacomach USauctns
lining the median part of the erypt are large and —acanthias. (From Ringoen.)

their nuclei are vertical in position. In the deeper _, &P-, epithelial cell; pe., pep-
tic cells; pl., mucous plug.

crypts are the gastric cells that are peculiar to the
cardiac stomach. They lie at the base of the erypts and are large and granular
and of a polygonal shape with their nuclei taking a more or less horizontal
position. These are the true peptic cells (pc.), which secrete the digestive
substances.

The function of gastric juice, which contains hydrochloric acid and a fer-
ment, pepsin, is the digestion of protein matter. Such digestion takes place at
a much lower temperature in the stomach of the shark than in the stomach of a
higher animal. While, in the latter, digestion is carried on at body temperature
(37° C), in the former it takes place at 10° to 15° C, although the pepsin may
also be active at as high as 40° C.

156 THE ELASMOBRANCH FISHES

At the terminus of the pyloric division of the stomach is a circular band of
muscle fiber, the pyloric valve, separating the pyloric stomach from the duo-
denum or middle intestine. This valve varies considerably in extent in differ-
ent forms. In some types it shows only slight signs of constriction, as for ex-
ample in Heterodontus, where it may allow food of considerable size to pass
into the spiral intestine. In Heptanchus we have seen that it projects as a well
defined circular band into the duodenum; and in Laemargus the valve is
greatly extended.

In some of these forms an interesting condition obtains in which a room, the
bursa entiana, may be formed and into which the pylorus may empty. This

Fig. 135. Relation of the terminal part of the pylorus to the next segment, the duodenum.
A. Galeus. (From Redeke.) B. Scymnus. (From Helbing.) C. Hypnos. (Australian tor-
pedo.) (From Howes.)

b.e., bursa entiana; d.ch., bile duct; prt., intraintestinal partition; p.v., pyloric valve;
py., pylorus; spl., spleen; sp.v., spiral valve; y.s., yolk stalk.

oceurs in Galeus (b.e., fig. 1354) and in Cetorhinus. In Scymnus (fig. 1358)
such an enlargement is formed in a different way. Here the pylorus enters a
special room the upper part of which is the bursa entiana, and the lower is
continued into the intestine as a valve-free portion. In the Australian torpedo
Hypnos (fig. 135c) there is an interesting modification of this plan. The en-
larged room is separated into an anterior and a posterior chamber by an intra-
intestinal partition (prt.). Into the former the pylorus (py.) empties and into
the latter the ductus choledochus (d.ch.) enters.

DUODENUM oR MiIppue INTESTINE

The duodenum may be encroached upon by the spiral valve through its entire
course, as in Heptanchus, or it may be free as in a few of the sharks and rays.
In a type like Spinax niger (fig. 1364) the valve-free portion is long. This
segment is present in Rhinobatis, but, of all the rays, it is best developed in
Trygon. In the great majority of types, however, the valve has so encroached
upon the pylorus that no free portion exists (Galeus, fig. 1854, Carcharias,
Lamnidae, Notidanidae, Seyllidae, Rhinidae, and some of the Rajidae).

The proximal part of the duodenum shows different stages of complexity.
This may be illustrated by Spinax niger, where the pyloric tip is small and

THE ELASMOBRANCH FISHES 1}

enters the duodenum in such a way as to form two miniature blind saes (se.*~*).
In Laemargus rostratus (fig. 1368) the blind sac is divided so that the proxi-
mal part of the intestine appears as a bilobed structure. Into one of the lobes
the pylorus enters.

The ducts from the liver (d.ch., fig. 1378) and pancreas (p.d.) enter this
middle or duodenal part of the intestine as in Heptanchus, and their entrance

l-d.ch.

Fig. 136. The duodenum. A. Spinax niger. (From Redeke.) B. Laemargus rostratus. (From
Helbing. )

d.ch., bile duct; p.v., pylorie valve; py., pyloric stomach; sc.‘-*, first and second blind
sacs; spl., spleen.

marks the region from which the liver and the pancreas arose in the embryo,
the length of the ducts in the adult showing how far the two organs have be-
come separated from their place of origin.

LIVER

The liver in the adult consists of a right and a left lobe, connected solidly an-
teriorly as in Heptanchus (see fig. 119). From the posterior part of the union
of the two lobes a caudate lobe may arise. In this or in either of the other lobes
the gall bladder may be located. The main lobes of the liver are character-
istically large in the sharks and may extend the entire length of the coelom.
In some of the larger sharks (Cetorhinus) as much as five barrels of oil are
reported to have been obtained from the liver of a single specimen. In the
rays the lobes are less well developed, but here, too, they are often large.
Bile secreted by the liver is collected by a series of tubules some of which
empty into the gall bladder. The gall bladder is drained by a duet which,
joined with other ducts from the liver, is the ductus choledochus. This duct
in Squalus sucklit (d.ch., fig. 1378) reaches the intestine at its proximal part

138 THE ELASMOBRANCH FISHES

and on the dorsal side, but unlike that of Heptanchus it passes backward
within the intestinal wall, making a half-loop before it empties into the ventral
side of the duodenum. In its course it becomes thrown into a series of ridges
much like the ridges in the seminal vesicles of some Elasmobranchs.

PANCREAS

The pancreas (fig. 187) in the adult consists of two lobes. One of them, the
dorsal lobe (pn.*), runs parallel with and over the terminal part of the cardiac
stomach and near its middle part sends a bridge over the pylorus to join the
ventral lobe (pn.?) which is closely bound to the ventral surface of the proxi-

Fig. 137. The pancreas and associated structures. A. Acanthias, dorsal view. (From Kan-
torowiez.) B. Squalus sucklii, dorsal view. (Chester Stock, orig.)

d.ch., bile duet or ductus choledochus from the liver; ia., intraintestinal artery; iv., intra-
intestinal vein; pn.', dorsal lobe of pancreas; pn.’, ventral lobe of pancreas; p.d., pan-
creatic duct; spl., spleen.

mal part of the middle intestine. In all specimens which I have examined the
pancreatic duct (p.d., fig. 137B) empties into the duodenum much as was de-
scribed for Heptanchus (p. 124).

SPLEEN

The spleen, although not connected by ducts leading to the digestive tract,
is located in the mesentery and may be regarded as an organ made up of cells
specialized from the connective tissue of the mesentery. In sharks it is often
triangular in shape and its characteristic position (spl., fig. 1374) is on the
ereater curvature of the stomach, that is, on the outer angle between the
cardiac and pylorie divisions. In the rays (see p. 187, fig. 175, spl.) it is a lobu-
lar or round structure located in the angle of the lesser curvature of the
stomach. In Heptanchus we have observed that the spleen takes a generalized
form in which it extends along the outer angle of the stomach and across the

THE ELASMOBRANCH FISHES 189
mesentery into the lesser angle. In other words, in addition to the type of
spleen on the outer angle characteristic of sharks, Heptanchus also has splenic
tissue on the inner angle of the stomach like that of the rays.

VALVULAR INTESTINE

The valvular intestine receives its name from the fact that it contains within
its lumen a membranous fold or valve. This fold as a general thing in the

A B C

Fig. 138. Valvular intestine. (From T. J. Parker.) A. Attachment in Zygaena. B. Valve in
Scyllium. C. Valve in Zygaena.

Elasmobranchs is spiral in nature, and produces a spiral valve. In a few forms,
however (Zygaena), it is of the seroll type, with the line of attachment along
the wall of the intestine only slightly curved (fig. 1384). This valve in Zy-
gaena (fig. 138c) is rolled up within the intestine and has a width two-thirds
of its length.

Seen from the outside the spiral valve presents the aspect of a screw over
the threads of which has been wrapped some thin substance through which the
threads are evident superficially. But such a likeness would be correct only if
the threads grew from and were a part of the outer covering.

140 THE ELASMOBRANCH FISHES

In development the valve first appears as a ridge or fold of the intestinal
mucosa along the intestinal wall. Whether the increase in the width of the
valve is due to the growth of the mucosa pulling the tissue within the folds as
in Ammocoetes (Daniel, 1931), or to the growth of connective tissue which
forces the mucosa downward as a cap, is not clear. The likelihood is that
both of these processes take place. This fold in a young Zygaena hangs down
as a simple longitudinal plate which, upon reaching the opposite side of the
lumen, rolls up into a seroll valve as would a sheet
of paper similarly dropped down. In the spiral

) valve, however, another factor enters. Here a tor-

f é. sion occurs in the lining of the intestine which
\ | ee throws the scroll into a spiral. Figure 139 from
Riickert (1896) represents the mucosa of the in-

testine in the formation of the spiral. The turns in .
figure 1398 are more numerous in the posterior re-
gion, and the intestine in the older stage is seen to
be relatively shorter.

The number of turns of the valve in the adult
varies greatly among the Elasmobranchs. In fact,
slight variation in the number within a single spe-
cies is common. In some the number is as low as
four (Prionace), or eight (Raja), or ten (Muste-
lus). In others it is increased but slightly (twelve
in Heterodontus). In some, however, great num-
bers are present, twenty in Lamna and forty-five
in Alopias.

In width the valve in the adult may approach or
extend beyond the middle of the lumen (Hep-
tanchus). When it is less than one-half the width
S of the intestine there appears in end view a canal
- which would represent the core of the screw. If it
Fie sor xe.stapes AB to exceeds one-half the diameter of the intestine the
show the development of the free edge representing the core of the screw rolls
eat e, Pristiurus.(From 1 so as to appear from side view as a series of con-

centric cones pointing anteriorly or posteriorly
(Scyllium, fig. 1388). In some forms the valve anteriorly may thus be thrown
into cones, while posteriorly the free edge does not reach the middle line.
Hence an end view from the posterior would present a central lumen (Raja,
fig. 140).

The lining of the valvular intestine from the duodenum to the end of the
spiral valve consists of cylindrical and goblet cells (Carcharias, Mustelus)
and is thrown into multitudes of tiny points or villi (fig. 140). From the type
of lining it is apparent that the function of the spiral valve, in addition to pre-
venting the too rapid passage of food, is the absorption of digested substances.

THE ELASMOBRANCH FISHES 141

CoLOoN AND RECTUM

The segments of the intestine succeeding the valvular intestine, the colon and
the rectum, usually differ in their lining from the valvular intestine in the ab-
sence of villi. Separating these two areas and emptying into the dorsal side of
the digestive tract is the rectal gland.

The rectal or digitiform gland varies in size from a tiny structure one-half
an inch long, as in some of the rays, to one three or four inches long in some of
the larger sharks. It is a compound, tubular
structure, the secreting cells of which are
surrounded by a strong, fibremuscular layer.
These cells empty their secretion through
tubules into a median lumen which, as we
have seen in Heptanchus, enters the intes-
tine between the colon and the rectum. In
some of the rays the lumen is large, that part
at which it enters the intestine being espe-
cially expanded (Raja, fig. 1418). In most of
the sharks, however, the gland is constricted
at its base, and its lumen is small. As a gen-
eral thing the lumen is prolonged forward
so that the entrance to the intestine is ante-
rior to the position of the gland (Zygaena,
fig. 1414). Although the rectal gland has
been studied in a great number of forms, its
function has not yet been made out.

CLOACA

The cloaca is the common receptacle into
which the digestive tract and the urinary
and genital systems empty. It is generally an
enlarged room, the walls of which are more =
or less loosely folded. In some types, trans- % iF
verse crescentic folds from the dorsal wall of ae oor cre
the cloaca separate it into an anterior and a |
posterior division on each side. In the ante- Fig. 140. Valvular intestine of Raja.
rior division two types of structure may be (From Paul Mayer.)

found. One of these is a pair of finger-like

papillae (see fig. 252, p., facing p. 290) ; the other is a pair of cloacal pits. The
papillae, when present, usually contain prolongations of the lining of the body
cavity. The cloacal pits are often located lateral and posterior to the papillae.
In some forms both the pits and the papillae are present. In connection with
the pits or with the papillae may occur apertures, the abdominal pores, which
put the abdominal cavity into connection with the outside.

142 THE ELASMOBRANCH FISHES

ABDOMINAL PORES

The abdominal pores in the Elasmobranchs may perforate the tips of the
papillae or, as was just said, they may pass through the cloacal pits. Some of
the types having perforated papillae are Triakis semtfasciatus, Carcharias
glaucus, Zygaena, Mustelus. In some the papillae are imperforate (Squatina).
The slit-like type of abdominal pores is in connection, not with the papillae,
but with the cloacal pits. This type is especially common among the rays.

A B
Fig. 141. Sections through rectal gland. (From Howes.) A. Zygaena. B. Raja.

The abdominal pores vary so greatly in different species and in fact in
different individuals of the same species as to suggest that they are vestigial
structures. In the Cyclostome fishes they function as apertures through which
the sex cells leave the body; but in the Elasmobranchs, if the pores have ever
been thus used, this function has been lost upon the appropriation of special
channels formed for the passage of the sex cells. It hence becomes a question
whether or not in the Elasmobranchs the openings subserve any particular
function at the present time.

TOO.

1892.

1888.

1900.
1900.

1902.

1878.

1882.

1897.

1898.

HOOT.

1896.

1879.

1887.

1903.

1899.

1931.

1886.

1905.

1906.

THE ELASMOBRANCH FISHES 143

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“

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THE ELASMOBRANCH FISHES 145

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matiéres albuminoides chez les poissons cartilagineux. C. R. Soc. Biol. Paris, T. 54,
pp. 1405-1407.

Sutykg, D. D. VAN, and WHITE, G. F., Digestion of Protein in the Stomach and Intes-
tine of the Dogfish. Jour. Biol. Chem., Vol. 9, pp. 209-217.

SULLIVAN, M. X., The Physiology of the Digestive Tract of Elasmobranchs. Bull. Bur.
Fish., Vol. 27, pp. 1-27. Also: Brown Univ. Contrib., Vol. 6, No. 87, pp. 1-27, pl. 1.
TURNER, Professor WM., A Contribution to the Visceral Anatomy of the Greenland
Shark (Laemargus borealis). Jour. Anat. and Physiol., Vol. 7, pp. 233-250, 3 text
figs.

TURNER, WM., On the Pori Abdominales in Some Sharks. Jour. Anat. and Physiol.,
Vol. 14, pp. 101-102.

VINCENT, S., and THOMPSON, FLORENCE D., The Islets of Langerhans in the Elasmo-
branch Fishes (Prelim. Comm.), Jour. Physiol. London, Vol. 35, pp. xlv-xlvi.
WEINLAND, ERNST, Zur Magenverdauung der Haifische. Zeitschr. f. Biol., Bd. 41
(N. F., Bd. 23), Hft. 1, pp. 35-68, Taf. 1, Hft. 2, pp. 275-294.

YUNG, EMILE, Sur les phénoménes de la digestion chez les Squales. Arch. des Sci.
phys. et nat., T. 34, pp. 464-468.

YUNG, EMILE, De la digestion gastrique chez les Squales. C. R. Acad. Sci. Paris, T. 126,
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YUNG, EMILE, Sur les fonctions du pancréas chez les Squales. C. R. Acad. Sci. Paris,
T. 127, pp. 77-78.

YUNG, EMILE, Recherches sur la digestion des poissons. (Histologie et physiologie de
Vintestin.) Arch. de Zool. expér. et gén., Sér. 3, T. 7, pp. 121-201, pl. 9.

RESPIRATORY TRACT
RESPIRATORY TRACT OF HEPTANCHUS MACULATUS

Heptanchus is characterized by having the greatest number of gill clefts or
external branchial apertures of any known Elasmobranch. In fact it is from
the number of clefts, as we have said, that it has received its name. These per-
forations in Heptanchus are lateral in position and lie between the cranium
and the pectoral fin. The first branchial cleft, not the spiracle, is the largest of
the series, while the one farthest from the cranium is the smallest. By opening
one of the clefts both dorsally and ventrally we may study the structures of
the gill pouch or pocket.

GitL Poucu or PocKET

If the second gill pocket of Heptanchus (fig. 142, facing p. 148) be opened
as suggested above, the cavity is seen to be shaped somewhat like a funnel
flattened from side to side, with the apex pointing inward and opening into
the pharynx as the internal branchial aperture. The internal branchial aper-
ture of the second pocket is supported by the first branchial arch anteriorly
and by the second branchial arch posteriorly. On the margin of the first arch,
and pointing backward, are one or two low projections which resemble in-
cipient gill rakers. On the anterior branchial arch are also numerous eleva-
tions, the bases of the cartilaginous branchial rays (b.r.), which support the
gill septum. The tips of these cartilages are visible on the posterior surfaces.
The walls of the pocket, both anteriorly and posteriorly, are covered with nu-
merous radiating gill filaments or folds (fl.), the effective organs of respiration.

The remaining pockets, excepting the seventh, are essentially similar to the
first. The seventh external branchial cleft has the same funnel-shaped arrange-
ment with its smaller apex connecting with the pharynx. On its anterior wall
filaments similarly appear although these are fewer in number than in the
preceding pockets. The posterior wall, however, is perfectly smooth, all sem-
blanee of gill filaments being entirely wanting.

SPIRACLE

The spiracular pocket upon being opened is found to be similar to the last
pocket, that is, it bears filaments only on the anterior wall. But it differs from
the others in the reduction in size of both its external and internal apertures
and in the reduction in the number of its filaments.

The spiracle in Heptanchus is not a straight tube, but as Ridewood (1896)
says, it bears diverticula on its walls. The most important of these diverticula

[147]

148 THE ELASMOBRANCH FISHES

is located dorsally and extends inward until it meets and joins the cartilage of
the auditory capsule. A second smaller diverticulum also extends dorsally
from the spiracular walls near their union with the pharynx.

GILL oR HOLOBRANCH

A holobranch consists of the tissue between two gill pockets; for example, the
tissue between the second and third pockets constitutes the second gill or holo-
branch. This second holobranch hence includes all filaments on the posterior
wall of the second pocket, and those on the anterior wall of the third gill
pocket, as well as the supporting structures between the two. The filaments on
the anterior and posterior sides of a whole gill are also designated as the an-
terior and posterior demibranchs. Thus the filaments on the posterior side of
the second pocket form the anterior demibranch of the second gill, and the fila-
ments on the anterior side of the third pocket constitute the posterior demi-
branch of the second gill.

With this understanding of a gill there are thus present in Heptanchus six
whole gills, located between pockets 1-2, 2-3, 3-4, 4-5, 5-6, 6-7. In addition
there is present on the anterior wall of the first pocket a half-gill, the hyoidean
demibranch. It is often more convenient to consider the number of demi-
branchs rather than the number of holobranchs. Thus there are present in ad-
dition to the first unpaired hyoidean demibranch, a second and third, a fourth
and fifth, a sixth and seventh, an eighth and ninth, a tenth and eleventh, and a
twelfth and thirteenth branchial demibranch, these pairs representing the
first, second, third, fourth, fifth, and sixth gills or holobranchs, respectively.

The gill filaments of the adult differ from certain external filaments present
in the embryo. The external filaments of the embryo arise from the tissue on
the posterior part of the hyoidean and branchial arches, and in Heptanchus
are of particular interest because of their great numbers, a mark of a general-
ized condition. Those filaments arising on the hyoid in Heptanchus cinereus,
according to Braus (1906), consist of 14 filaments; those from the first bran-
chial opening, 39; from the second to the fifth, 29 each; from the sixth, 26, and
from the last, 18. o

GILL SUPPORTS

The arches supporting the gills of the adult (see fig. 48, facing p. 44, and
fig. 49, p. 45) are the hyoidean and all the branchial arches except the last.
From epi- and ceratobranchial segments of all the visceral arches, except the
mandibular and the last branchial, cartilaginous branchial rays (b.r.) extend
outward toward the integument. The branchial rays on the hyoidean arch
(fig.48) are often branched and complex, but on the other visceral (branchial)
arches they are simple unbranched rods. In the latter they are separated from
the gill filaments anteriorly by the interbranchial musculature and extend as
supports beyond the ends of the filaments.

The septum of each holobranch, or wall between two sets of filaments, ex-

Ady
TIME

Wy,
/

WT)
if

- br.

Fig. 142. Second gill pocket opened, Heptanchus maculatus. (Duncan Dunning, del.
s ie ] I . . . . 8)
b.r., branchial rays; ex.b., extrabranchial cartilage; ff., gill filaments.

THE ELASMOBRANCH FISHES 149

tends from the visceral skeleton outward and is attached to the integument;
it is further secured in its outer margin by the dorsal and ventral extra-
branchial cartilages, where such exist. These extrabranchials (see p. 45, fig. 49,
ex.b.) extend around the margin of the septum roughly at right angles to the
branchial rays. At their dorsal and most ventral angles the extrabranchials
pass posteriorly across the pockets so that

in the opened pocket their transected ends
show on both sides of the incision (e..b., fig.
142).

GILL FILAMENTS

Fig. 143. Section
cutting parallel
to branchial fil-
aments through
second holo-

P|csd. branch, Heptan-

The respiratory membrane is formed of LETTS ECHOES

) :
5 ae : H. M. Gilkey,
the series of folds or filaments (/l.) attached 3 ae CT ) i
to the anterior and posterior sides of the sep- i a
ad., adductor

tum of each whole gill. Anteriorly these folds
compose the respiratory surface of the an-

muscle; af.,third
afferent artery ;

terior demibranch; posteriorly, that of the a b.r., branchial
: IG ie
posterior demibranch. The filaments of the — 54/28 Lance enor:
esd., fourth dor-

sal constrictor
muscle; eb., epi-
branchial seg-
ment of internal
branchial arch;
CfiGar) LOWnrt hl
and fifth effer-
ent-colleetor ar-
ef teries; ex.b., ex-
BI - trabranchial car-
: tilage; fl.a., an-
terior filament;
fi.p., posterior
filament; ib.d.,
dorsal inter-
branchial mus-
cle; ”., posterior
division of the
branchial nerve.

posterior demibranch in Heptanchus macu-
latus extend considerably farther distally on
the septum than do those of the anterior set,
but they also arise farther out from the base.
In both they consist of a series of plates flat-
tened from side to side. The longest of these
plates is located medially and from this point
they get shorter and shorter until at both the
dorsal and ventral angles of the pocket they
are relatively minute. Above and below the
epi- and ceratobranchial segments filaments

ESE

UOC

Ei]

Fe DEE
2 sd = )
=\@59 Sere

are absent.

A section taken at right angles to the in-
ternal branchial arch and eutting through
the epibranchial segment, parallel with an
anterior and a posterior filament, is seen in figure 143. In this, the fourth dor-
sal constrictor muscle (esd.) is thickened toward the margin of the septum,
where it is supported by the extrabranchial cartilage (er.b.). It is continued
toward the internal branchial aperture as an interbranchial muscle (7b.d.)
directly in front of the cartilaginous branchial ray (b.7.), the upper part of
which in figure 143 has been cut off. Anterior to the branchial ray is the third
afferent artery (af.) which is surrounded by the nutrient vein (sinus) of the
arch, and anterior to the union of the branchial ray with the internal branchial
arch is the large anterior efferent-collector artery (efc.*); just posterior to
this efferent-collector is the pretrematic division of the branchial nerve (ecross-
hatched), and below the posterior filament is the small posterior efferent-
collector artery (efc.°).

150 THE ELASMOBRANCH FISHES

RESPIRATORY TRACT OF ELASMOBRANCHS IN GENERAL

The respiratory tract or passageway through which the water current passes
in bathing the gills of Elasmobranchs, unlike the tract in higher forms in
which the respiratory current may enter external nares, begins with the
mouth and terminates with the external branchial clefts. The following parts
are included in the respiratory tract : the buccal cavity, the enlarged pharynx,
and, in the wall of the pharynx, the gill pockets. The gill pockets, as in Heptan-
chus, are reached from the pharynx by the internal branchial apertures and
open to the exterior through the external branchial apertures or clefts. We
shall describe first the external branchial apertures.

Many of the Elasmobranchs are of the pentanchid type, that is, those
possessing five gill clefts; only Chlamydoselachus and those sharks belonging
to the notidanids exceeding this number. Record is also made of a greater
number occasionally occurring in other forms. In Chlamydoselachus and in
Hexanchus six clefts are present and in Heptanchus, as we have seen, there
are seven, the greatest number known for any gnathostome or jaw-possessing
vertebrate.

The position of the external branchial apertures or clefts has long been used
in separating the sharks from the rays. Characteristic of the former the clefts
are lateral in position, while in the latter they are ventrally located. In the
rays, however, there enters the element of time, for while a ventral position of
the clefts is characteristic of the adult, the position for a considerable period
of time in the embryo is lateral (see p. 11).

The external branchial apertures in the sharks vary greatly in relative size.
In a type like Acanthias (fig. 5) they extend as slits practically one-half the
height of the body. In Heterodontus (fig. 17) the first cleft is large, but the
last is so small as to be of slight functional value. Many other forms are like
Heterodontus in this regard. In some of the other sharks the clefts are of
immense size. This condition is found especially in the lamnoids and in Ceto-
rhinus and Rhinodon (fig. 3), in all of which the apertures are practically
the height of the pharyngeal diameter. In the rays the clefts are relatively of
a much smaller size.

The first cleft to open and one of the most important in the embryo is the
spiracle. As growth proceeds, however, the spiracle fails to keep pace with the
other clefts, so that at its maximum development in types like Acanthias (see
p. 11, fig. 22) and Squatina it is relatively small. In others, as for example
Lamna and Carcharias, the spiracle of the adult is often minute; and in still
others all superficial trace of it may be lost. In the rays, on the contrary, it
has assumed a secondary function and hence has become enlarged.

GiuL PoucH or PocKET

In shape the gill pockets of the sharks are generally like those of Heptanchus.
In types like Lamna, Cetorhinus, or Rhinodon, however, the external clefts
are so large that the normal form of the closed pocket is more like that of the

THE ELASMOBRANCH FISHES 151

opened pocket in Heptanchus. In the rays the pocket is somewhat like an in-
verted U, in which the internal and external branchial apertures are repre-
sented by the tips of the U close together.

The first indication of a pocket in the embryo appears as an evagination or
outpocketing of the pharyngeal wall toward the exterior (qp., fig. 144). As
this approaches the surface it meets a slight pitting in from the outside, and
the wall between the two breaks through to form the external branchial cleft
or aperture.

In pentanchid types six of these pouches, ineluding the spiracular, are
formed; but accessory pockets are often indicated.
Thus in Acanthias a small pouch on the left side
(or a pair of pouches) is produced as an evagina-
tion from the floor of the pharynx just back and
mediad of the sixth pouch. This pouch does not
reach the outside layer but comes in contact with
the roof of the pericardial cavity. Here it forms
numerous tubules and becomes the so-called post-
branchial or suprapericardial body. These bodies
have also been described for Scyllium, Galeus,
Pristiurus, and Raja.

In figure 144 the anterior clefts have thus broken
through. Between the pockets are columns, from
which all the tissues of the holobranchs are later
produced including their supporting cartilages
and musculature. On the posterior wall of the
hyoidean cleft will appear a little later the begin-
nings of the embryonie or external gill filaments.

ae
soy

ri)
see
of 0 Ms
0 .
H
oP
wap 870), orld
co fps Awa oeg
C. oboe Le Voce
ors eyeret! Arey
, i
Payee? 04
gfe ar'so
S VAT Ey,
3
A
A

The whole column from the internal branchial
arch toward the exterior lengthens out and the Rae iden Hors zontalnsection
central core becomes a plate, the septum or dia- through pharynx to show for-
phragm of the gill. This plate supports the fila- Fae ae ee ee
ments or respiratory membrane, and is peculiar in — shall Williamson, del.)
the Elasmobranchs in that it extends outward Pee Naa Mae whe eke
beyond the filaments which are attached to it. It is
from the peculiar attachment of the filaments to the septa that the Elasmo-
branchs have received their name (’EXacuos: blade- or strap-like; Bpayxia:
gilled). The septum may be said to attach internally on the internal visceral
arches, and to extend outward to the lower layer of the integument. Hach
septum is limited anteriorly and posteriorly by a heavy layer of tissue which
is continuous with the mucous membrane of the pharynx. Terminally the an-
terior and posterior plates of this tissue run parallel and are separated only
by the interbranchial musculature, connective tissue, and cartilaginous bran-
chial rays (Heptanchus) which support the septum.

The interbranchial muscles (ib.m., fig. 145) are located on the anterior sur-

152 THE ELASMOBRANCH FISHES

face of, and run at right angles to, the cartilaginous branchial rays of each
whole gill. These muscles form thin sheaths dorsally and ventrally by which
attachment is made to the fascia and to the extrabranchial cartilages; medially
a part of the interbranchial joins the epi- and ceratobranchial segments of the
internal branchial arches. Some of the outer fibers in their course are attached
to cartilaginous branchial rays, but in the sharks most of them are continuous
above and below. In the rays these muscles are regularly attached to the bran-
chial rays (see p. 106, fig. 1088). They are thus able by contraction to decrease
the size of the pocket.

The filaments of the adult gill are to be distinguished from those of the early
embryo which we may first consider. Upon the breaking through of the ex-
ternal clefts in the embryo of all Elasmobranchs a series of nodules arises from
the posterior margins of the hyoidean and the branchial arches. These grow
outward as long external gill filaments which sometimes exceed the entire
body in length (Urolophus, fig. 22p); in others they are shorter (Acanthias,
fig. 22c). Such filaments are characteristically more numerous in the more
generalized types. In Heptanchus we have seen the greatest number known in
Elasmobranchs. In Acanthias they are more numerous than in Scylliwm, and
in Scyllium they exceed in number those of most rays.

These filaments in the living embryo are particularly noticeable from the
fact that they are kept constantly in motion and are filled with blood, giving to
them their striking color. Under the microscope the circulation of blood ean
here be seen to remarkable advantage. Each embryonic filament is a more or
less flattened plate with a blood vessel encircling it near its outer border. The
whole tissue of the filament acts as the respiratory membrane.

External branchial filaments thus developed in the embryo are early ab-
sorbed, giving place to permanent or internal filaments. In some forms the
filaments of the adult may be of great length reaching practically to the outer
margin of the septum (Lamna). In many others, however, they are of medium
length (Scylliwm); while in a few they are relatively short (Squatina).
Usually in the Elasmobranchs the filaments of the posterior demibranch are
longer than those of the anterior; and those of the middle of the septum are
the longest of the series.

Sections through the septum parallel to the filaments give a clear notion of
the structure of a gill. Dréscher (1882) gave such a section through a holo-
branch of Torpedo (fig. 145) which shows that here the filament of the pos-
terior demibranch, like that in Heptanchus, is longer than that of the anterior,
and that both extend only two-thirds the length of the septum. Running
transversely through the central part of the septum, from the internal bran-
chial arch toward the exterior is the interbranchial muscle; back of this is the
cartilaginous branchial ray. It is observed further that the filaments, instead
of being round as in face view, are flattened from side to side. A section of the
filaments of Torpedo, so far as considered, is essentially like the one studied
of Heptanchus. It differs from it somewhat in the position of its blood and in
its nerve supply.

THE ELASMOBRANCH FISHES 153

The finer structure of the gill of Torpedo shows that the relation of the blood
system to the gill is much like that of Mustelus and Heptanchus. Passing
through the base of the septum, and anterior to the cartilaginous branchial
ray (b.r.), is an afferent branchial artery (af.). From this an arteriole (a.b.")
passes to the anterior filament and another (a.b.”) to the posterior filament.
These arterioles give off smaller branches which break up into a net of capil-
laries which, in turn, form a complex web over
the larger part of the surface of the filament.
The eapillaries are continued to efferent bran-
chials (e.b.1 and e.b.*) as efferent arterioles
which carry the oxygenated blood down the
filament into the efferent-collectors (efc.), an
anterior and a posterior of which are present
at the base.

In the spiracular pocket as in branchial
pockets the anterior wall is usually also pro-
vided with filaments. These are numerous in the
rays but few in number in the sharks, as in Het-
erodontus. In a type like Carcharias, in which
the spiracle is minute or wanting, they are en-
tirely absent.

From the anteromedial wall of the spiracular
pocket and dorsally located there is an evagina-
tion which may reach the auditory capsule and LRG | yy
be attached to it above the postorbital groove | he W/ oY, O
(de., Scyllium, fig. 146, Mustelus, Gaelus, | ow fy , GIA
Squatina, Rhinobatis, Zygaena). At its begin- Z
ning the diverticulum may be practically closed
(Galeus), but as it approaches the auditory
capsule it becomes enlarged. In Squalus acan-

Wan ee,

Fig. 145. Section of branchial
filaments, parallel to branchial
ray, Torpedo. (From Droscher. )

a.b.*, afferent branchial ar-

thias, Norris and Hughes (1920) have recently
shown that this evagination may be divided
into two or three diverticula each of which is
supplied with a branch of the ramus oticus
VII nerve. The organ is considered to be a

terioles from afferent artery;
ad., adduetor muscle; af., affer-
ent artery; b.r., branchial ray;
e.b.”*, efferent branchial arte-
rioles to efferent-collectors; efc.,
efferent-colleetor; ib.m., inter-
branchial muscle.

modified ampulla of Lorenzini. A second diver-

ticulum on the anteromedial wall of the spiracular pocket is located ventrally
near the union of the pocket with the pharynx. This in Scylliwm is shallow,
but in some of the other Selachians it is connected to the spiracular pocket by
a neck. In the spiracle of rays there is a well developed valve on the anterior
side of the cleft. It is composed of a stiff crescentic fold of connective tissue
which is constantly opened and closed in respiration. Serving as a support for
the fold is the strong crescentie spiracular cartilage which at each end is fixed
by ligament. The closure of the spiracle is due to the contraction of the first

154 THE ELASMOBRANCH FISHES

dorsal constrictor muscle. A similar valve, although less well developed,
occurs in some of the sharks, as for example in Acanthias and Mustelus.

The internal branchial apertures of the branchial pockets may be simple
slits or the aperture may be modified by the presence of certain gill rakers.
The gill rakers in Squalus sucklu (gr., fig. 147) form a series of processes from
the pharyngeal arches across the internal branchial apertures. On the first
two branchial arches they project
only from the anterior surface of
the arch, while on the third and
fourth they extend from both the
anterior and the posterior sur-
faces. These projections are cov-
ered with caps of the mucous lin-

ED See
ww Vi“ ing, on which stomodeal denticles
<a are present, and are supported

Fig. 146. Transverse section through spiracles, internally by cartilages, the ante-
Sey tinaney (i nomnidewecd>) rior ones of which practically
de., dorsal caecum. : ;

touch the internal branchial arch

and the posterior ones are directed outward from the adductor muscle (ad.).
In Cetorhinus a straining apparatus is differently formed. As we have
remarked (p. 37) the gill rakers in Cetorhinus and Rhinodon are modifica-
tions of placoid seales which arise from semilunar bases and are continued as
long filaments across the internal branchial aperture. Upon opening a gill
pocket in Cetorhinus (fig. 1484) myriads of these rakers or filaments (g.7r.)
are seen to be attached to the internal branchial arches and to extend inward
so that those from the arch in front of the pocket overlap those from the arch
behind it (fig. 1488). There is thus formed of these rakers a V-shaped strain-

Fig. 147. Horizontal section cutting through the gill pockets to show gill rakers, Squalus
sucklii. (H. M. Gilkey, del.)

ad., adductor muscle; af., afferent artery; b.r., branchial ray; efc.', anterior efferent-
collector; gr., gill rakers; ia., internal branchial aperture; ib.m., interbranchial muscle.

ing apparatus which points into the pharynx and completely covers the inter-
nal branchial aperture. By means of this strainer small organisms, prevented
from passing out with the respiratory current, are collected in great numbers
and passed down the digestive tract as food.

THE ELASMOBRANCH FISHES 155

PRODUCTION OF RESPIRATORY CURRENT

For the sharks and rays in general the respiratory current is produced by
the interaction of the complieated series of buccal and pharyngeal muscles
which insure that when the current enters the mouth the external clefts close
and when the clefts open, the mouth closes. In general the action is as follows:
By the contraction of the ventral, longitudinal, or hypobranchial musculature

A B

Fig. 148. A. Part of a gill pocket of Cetorhinus. (From Pavesi.) B. Diagram of a section
parallel to the gill rakers.

b.r., branchial ray; fl., filaments; g.r., gill rakers; g.p., gill pocket; ia., internal branchial
aperture.

the floor of the mouth and pharynx is lowered, thus enlarging the buccal and
pharyngeal rooms, at the same time that the mouth is opened. Into this cavity
the water rushes. The adductors then act, closing the mouth and at the same
time flexing the epi- and ceratobranchial segments of the arches, thereby
spreading apart the cartilaginous branchial rays and causing the pockets to
enlarge. The water now enters the pockets and is then forced out through
the external clefts by the contraction of the constrictor and interbranchial
muscles. By this action of the muscles a rhythm is produced which under
conditions of rest is about thirty-five respirations a minute (Heterodontus
francisct).

156 THE ELASMOBRANCH FISHES

DIRECTION OF RESPIRATORY CURRENT

In the free-swimming sharks the current enters the mouth, from which it
passes through the pharynx and into the gill pockets, the external clefts, in-
cluding the spiracle, at the same time remaining closed. The mouth then closes,
the external clefts open, and the water is forced out.

In the rays, which spend most of their time on the bottom and hence often
in mud or sand, there is an interesting change in the direction of the current.
In these the greater part of the current enters through the spiracle and but
little through the mouth. The valve of the spiracle then closes and the water
is forced out ventrally through the external branchial clefts. At the expulsion
of the water the mouth does not entirely close, but only a little of the current
is able to gain exit through it because
of valves which are located on its
roof and floor (w., fig. 149).

In rays there often occurs a rever-
sal of the current, by which the water
is spouted outward through the spir-
acle. Rand (1907) has shown that
this may be brought about experi-
Fig. 149. Sagittal section through buccal cay. mentally in several ways. In the first

ity of Raia erinacea to show valves (v.).(From place spouting may be produced by
Rand.)

putting the ray into water over-
charged with carbon dioxide, or it may be the result of fatigue as is shown by
compelling the ray to keep in rapid motion for a period of time. Again, spout-
ing may be produced by putting a soft substance, as for example sea moss, into
the spiracle. To any of these experiments the ray responds by ejecting a col-
umn of water through both spiracles. Rand has shown further that by striking
the margin of the spiracle or of the eye on a single side, spouting may be pro-
duced by a single spiracle on the side thus irritated.

While spouting is characteristic of the rays it is not confined to them. In
Squatina, a form which spends much time on the bottom, I have also found
spouting to occur. But in this type it is not so much an indication of a reversal
of the current. Here as in other sharks water enters the mouth and passes
out through the clefts. To study the spouting behavior and to note the diree-
tion of the current, I have observed Squatina (a shark) and Rhinobatis (a ray)
in the same large aquarium. Under such conditions both are seen to spout
occasionally. With exercise the spouting occurs more frequently. If now the
water in the aquarium is let off so as to expose the spiracular clefts, Rhino-
batis becomes greatly agitated while Squatina is little disturbed. These
observations show that the spiracle in Squatina is not, as it is in the rays, the
principal intake. Darbishire (1907) says for Squatina, however, that carmine
liberated in the region of the spiracle enters, and furthermore, that it enters
not rhythmically but in a constant stream. This regularity of the current is
produced by a rhythmic action of the free margins of the gill septa. In the

THE ELASMOBRANCH FISHES 157

experiments on Squatina, above mentioned, I have also observed the phenome-
non of the outgoing current, but that the spiracle is not of great importance
as an aperture for the intake of the current is shown by my experiment.

Something of the same rhythmic current occurs in the rays, although it may
be produced differently. In specimens of the small sting-ray, Urolophus, which
are buried in the sand with only the spiracular clefts and the outline of the
body discernible, the spiracular clefts open and close regularly. The only evi-
dence of the outgoing current, however, is seen in a regular geyser of sand
grains arising to an inch or two in height at the anterior margin of the pec-
toral fin.

CIRCULATION OF BLOOD IN FILAMENTS

Ina later study of the blood system (Chapter VII, p. 161) it will be found that
the afferent arteries bear non-oxygenated blood from the heart to all the
demibranchs and give off to them smaller branches which run outward toward
the tips of the filaments; the branches in turn give off thin-walled arterioles
which in their course break up into capillaries. It is in these capillaries that
the exchange of oxygen and carbon dioxide takes place. From the capillaries
efferent branchial arterioles convey the oxygenated blood toward the base of
the filaments into either an anterior or a posterior efferent-collector (efc.). By
means of these collectors oxygenated blood is removed from the region of the
gills. In other words, while a single afferent artery supplies both anterior and
posterior series of filaments with non-oxygenated blood, two efferent-col-

lectors, one at the base of each demibranch, carry away the blood which has
been oxygenated.

RESPIRATION OR THE EXCHANGE OF GASES

The respiratory current thus brought into the gill pockets is separated from
the blood contained in the capillaries of the filaments only by the thin eapil-
lary wall. The free oxygen of the water passes by osmosis through this wall
into the blood to be distributed to the body, and the carbon dioxide brought to
the capillaries from the body tissues passes outward into the water to be
eliminated by the respiratory current. The exchange of gases takes place with
extreme rapidity as 1s evident from the fact that the blood makes its complete
transit of the capillaries in a very short time.

158

1840.

1886.

1818.

1906.

OUT.

1857.

1870.

1907.

1886.

1882.

1890.

1909.

1836.

1880.

1894.

1920.

1874.

OIE

1904.

THE ELASMOBRANCH FISHES

BIBLIOGRAPHY

CHAPTER VI

ALESAANDRINI, ANTONI, Observationes super intima branchiarum structura piscium
cartilagineorum. Novi Comment. Acad. Bonon., Vol. 4, pp. 329-344.

BEMMELEN, J. F. vAN, Uber vermuthliche rudimentire Kiemspalten bei Elasmo-
branchiern. Mitt. Zool. Stat. Neapel, Bd. 6, pp. 165-184, pls. 11-12.

BLAINVILLE, H. D., Uber den Bau der Kiemen bei den Foetus der Haifische. Arch. f.
Physiol., Bd. 4, pp. 275-296.

Braus, H., Ueber den embryonalen Kienienapparat von Heptanchus. Anat. Anz., Bd.
29, pp. 545-560, 2 text figs.

Camp, W.E., The Development of the Suprapericardial (Post-branchial, Ultimo-
branchial) Body in Squalus acanthias. Jour. Morph., Vol. 28, pp. 369-415, pls. 1-2,
29 text figs.

CoRNALIA, EMILIO, Sulle branchie transitorie dei feti Plagiostomi. Gior. dell’ I. R.
Istit. Lombardo (n. s.), T. 9, pp. 256-258.

CorRNISH, THOMAS, On a Shark Captured in Mount’s Bay on June 11, 1870, Supposed
to be Identical with the Basking Shark of Pennant and the Broadheaded Gazer of
Couch. Zoologist, August, 1870, pp. 2253-2260.

DARBISHIRE, A. D., On the Direction of the Aqueous Current in the Spiracle of the
Dogfish: together with some observations on the Respiratory Mechanism in other
Elasmobranch Fishes. Jour. Linn. Soe. Lond., Vol. 30, pp. 86-94, 3 text figs.
Douren, A., Studien zur Urgeschichte des Wirbelthierkorpers. XI. Spritzlochkieme
der Selachier, Kiemendeckelkieme der Ganoiden, Pseudobranchie der Teleostier. Mitt.
Zool. Stat. Neapel, Bd. 7, pp. 128-176, Taf. 2-5.

DROSCHER, WILHELM, Beitrige zur Kenntnis der histologischen Struktur der Kie-
men der Plagiostomen. Diss. Leipzig, 1881, pp. 12-176, pls. 9-12.

Ewart, J.C., On the Spiracles of the Porbeagle Shark (Lamna cornubica). Jour.
Anat. and Physiol., Vol. 24 (n.s., Vol. 4), pp. 227-229.

Hypk, Ipa H., A Study of the Respiratory and Cardiac Activities and Blood Pressure
in the Skate following Intravenous Injections of Salt Solutions. Kansas Univ. Sci.
Bull., Vol. 5, No. 4, pp. 29-63, pl. 10, 49 text figs.

LeucKkartT, F. 8., Untersuchungen iiber den fusseren Kiemen der Embryonen von
Rochen und Haien. Ein Beitrag zur Entwicklungsgeschichte der Abtheilung der
Knorpelfische angehérenden Plagiostomen. Stuttgart, pp. 1-44, pls. 1-5.
M’Kenprick, J. G., On the Respiratory Movements of Fishes. Jour. Anat. and
Physiol., Vol. 14, pp. 461-466, pl. 28.

Mayer, P., ther die vermeintliche Schwimmblase der Selachier. Mitt. Zool. Stat.
Neapel, Bd. 11, pp. 475-478, 1 text fig.

Norris, H. W., and Hugues, Satty P., The Spiracular Sense-Organ in Elasmo-
branchs, Ganoids and Dipnoans. Anat. Rec., Vol. 18, pp. 205-209, 1 text fig.

Pavesi, P., Contribuzione alle storia naturale del genere Selache. Ann. Mus. Civ.
Storia nat., Genova, Vol. 6, pp. 5-72, pls. 1-3.

PoLIMANTI, Osw., Uber den Beginn der Atmung bei den Embryonen von Scyllium
(Catulus Cuv., Canicula L.). Zeitschr. Biol., Bd. 57, pp. 237-272, 2 text figs.

QuINTON, RENE, Communication osmotique chez le poisson Sélacien marin, entre le
milieu vital et le milieu extérieur. C. R. Acad. Sei. Paris, T. 139, pp. 995-997.

1898.

1876.

THE ELASMOBRANCH FISHES 159

Ranp, H. W., The Functions of the Spiracle of the Skate. Amer. Nat., Vol. 41, pp.
287-302, 3 text figs.

. RipEwoop, W. G., On the Spiracle and Associated Structures in Elasmobranech Fishes.

Anat. Anz., Bd. 11, pp. 425-433, 2 text figs.

. SCHENK, 8. L., Die Kiemenfiiden der Knorpelfische wihrend der Entwickelung. Sitz-

ber. Akad. Wien, math.-naturwiss. Klasse, Vol. 71, pp. 227-238, Taf. 1.

5. TURNER, WM., On the Presence of Spiracles in the Porbeagle Shark (Lamna cor-

nubica). Jour. Anat. and Physiol., Vol. 9, pp. 301-302.

. TURNER, Wa., The Structure of the Comb-like Branchial Appendages and of the Teeth

of the Basking Shark (Selache maxima). Jour. Anat. and Physiol., Vol. 14, pp. 273-
286, pl. 12.

VircHow, H., Ueber Oberflaichenbilder von Selachierkiemen und Mesodermursprungs-
zone. Anat. Anz. (Verh.), Bd. 14, pp. 43-49, 4 text figs.

Wricut, EK. P., The Basking Shark. Nature, Vol. 14, pp. 315-314, 2 text figs.

VII

CIRCULATORY SYSTEM
CIRCULATORY SYSTEM OF HEPTANCHUS MACULATUS

The heart in Heptanchus (fig. 150) is located over, and in front of, the sternal
symphysis of the pectoral arch in the region between the gills, and is retained
within a relatively large pericardial cavity. It is made up of two rooms
proper, an auricle (atrium) (au.) and a ventricle (vn.), into the former of

hy.af..
br.af* ¢

NOU

Fig. 150. A heart of Heptanchus maculatus. (Marie Weldt, orig.) B. Valves of conus, ven-
tral view. (From Garman.)

ap., aperture of last afferent artery; au., auricle (atrium) ; br.af.~*, first and sixth bran-
chial afferent arteries; ¢c.a., conus arteriosus; cr.l., left coronary artery; hy.af., hyoidean
afferent artery; p.c., pericardial; v.a., ventral aorta; v.c., valves of conus; vn., ventricle.

which the blood enters from the sinus venosus (see p. 203, fig. 188, s.v.), and
from the latter of which it is expelled through the conus arteriosus (c.a.,
fig. 150).

The auricle, or atrium, is a greatly enlarged, thin-walled sae which lies dor-
sally over the ventricle. Connecting it with the sinus venosus is the sinu-
auricular opening. At the sides of this opening are the two sinu-auricular
valves (sa., fig. 188), which prevent the backward flow of the blood into the
sinus venosus upon the contraction of the auricle. Connecting the auricle with
the ventricle is an auriculoventricular opening guarded by valves of the same
name attached to the ventricular walls.

The more or less triangular ventricle forces the blood by way of the conus
arteriosus through the gill capillaries and as a consequence of the strain

[160]

THE ELASMOBRANCH FISHES 161

imposed upon it, its walls have become greatly thickened. Inside, the lining
has become thrown into numerous irregularities and is richly provided with
supporting chordae tendineae stretched from the walls of the ventricle to the
auriculoventricular valves. These tendinous cords prevent the valves from
being forced into the auricle upon the contraction of the ventricle.

The conus arteriosus connects the ventricle and the ventral (ascending )
aorta (v.a.). Its walls are muscular so that it serves to keep the blood sent out
from the ventricle at a more constant pressure. A longitudinal section through
the conus of Heptanchus shows its thickened walls and, on the sides of the
lumen, a series of pocket-like valves (v.c., fig. 1508), which prevent blood
from reéntering the ventricle. These are arranged in three longitudinal rows,
one dorsal and two ventrolateral in position. The anterior and much larger
valves in each row are located just back of the exit of the most posterior
afferent branches of the ventral aorta. Following these are other small valves,
behind which are three valves of medium size, in each row.

ARTERIES
VENTRAL AORTA

The ventral aorta (v.a., fig. 1504) continues forward from the conus and, in
the region back of the mandibular symphysis, divides into right and left
halves. Along its course it gives off paired branches, the afferent arteries
(hy.af., and br.af..~°, fig. 1504) which distribute blood to the gills.

AFFERENT ARTERIES OF ADULT

In Heptanchus these branches are seven in number. An anterior pair, con-
sisting of the hyoidean afferent (hy.af.) and the first branchial afferent
(br.af2), arises from a common trunk formed by the bifurcation of the an-
terior end of the ventral aorta. The first or hyoidean supphes the hyoidean
demibranch, entering in front of the first gill pocket. The second enters the
first whole gill between the first and second pockets, supplying both of its
demibranchs. Following these on each side are given off the second to the sixth
branchial afferents, the last two of which arise close together from the ventral
aorta (fig. 1508, ap.). The second to the sixth branchial afferents enter and
supply the fourth-fifth, sixth-seventh, eighth-ninth, tenth-eleventh, and
twelfth-thirteenth demibranchs. Branches from the afferents break up into
smaller and smaller arterioles and finally as capillaries supply the filaments

of all the gills.
EFFERENT-COLLECTORS

From the capillaries the blood passes down the filaments into efferent-col-
lectors. If the most anterior gill pocket of an injected specimen be opened, as
is the second pocket in figure 142, an efferent-collector artery would be seen to
drain the demibranch in front of the cleft, the hyoidean demibranch (see also

162 THE ELASMOBRANCH FISHES

fig. 151), and another, the one behind the cleft. These two arteries, the first and
second efferent-collectors, unite both ventrally and dorsally, forming a loop
around the cleft (fig. 151). The third and fourth efferent-collectors encircle
the second pocket as the first and second encircle the first pocket, but the one
forming the anterior part of the loop, which is the posterior efferent-collector
of the first holobranch, is small and has an irregular course. As it passes ven-

Fig. 151. Efferent-collector arteries, Heptanchus maculatus. (R. T. Trotter, orig.)

br.ef.-*, first and sixth branchial efferent arteries; cm.**, second and sixth commissural
arteries; c.tr., eross-trunk; d.a., dorsal aorta; e.c., external carotid; efc.’, first and thir-
teenth efferent-collector arteries; hy.ef., hyoidean efferent; ps., pseudobranchial artery;
th., posterior thyroid artery.

trally it may increase somewhat in size and is connected with the efferent-
collector in front of it by numerous eross-trunks. Ventrally it joins the larger
efferent-collector behind the cleft, the anterior efferent-collector of the second
holobranch, and dorsally it loops back also making connection with the same
vessel. Similar efferent-collectors encircle the remaining pockets, except the
last, where a complete loop is not formed due to the lack of gill filaments on
the posterior wall of the pocket. The blood from the last (thirteenth) efferent-
collector is drained by means of cross-trunks (c.t7.) into the twelfth efferent-
collector through the greater part of the holobranch; and ventrally the last
efferent-collector joins the one in front of it directly.

BRANCHES OF EFFERENT-COLLECTORS

HYPOBRANCHIAL ARTERIES

From the ventral angles of the second to the fifth (or sixth) efferent-collector
loops in Heptanchus, large commissural arteries (cm.*°, figs. 151 and 153)
pass inward toward the middle line. Near their origin they are usually con-
nected by small vessels which, joined together, may be called the lateral hypo-

THE ELASMOBRANCH FISHES 163

branchial artery (l.Ab., fig. 153); or the lateral hypobranchial vessels may
arise from the ventral parts of the efferent-collector loops; or again a lateral
hypobranchial segment may be incomplete between certain of the commis-
surals. Just before reaching the midventral line the commissurals of each side
form a larger longitudinal vessel, the median hypobranchial (m.hb.), the right
and left median hypobranchials being connected by several small connectives
(cn.) which may or may not unite right and left pairs of commissurals. The
two median hypobranchial trunks are continued posteriorly above the peri-

Fig. 152. Arterial branches of first efferent-collector, Heptanchus maculatus. (Marie Weldt,
orig. )

a.c., anterior cerebral; a.sp., arteria spinalis; br.ef.', first branchial efferent; d.a.t, paired
dorsal aorta; d.a., dorsal aorta; hy.ef., hyoidean efferent; i.c., internal carotid ; m.c., median
cerebral; ns., nasal artery; o.m., ophthalmica magna; or., orbital artery; p.c., posterior
cerebral; ps., pseudobranchial artery; r.a., ramus anastomoticus; rs., rostral artery; sg.,
segmental artery.

cardial roof as the two large pericardial arteries (pc.). The pericardials may
be of essentially the same size or the right one may be the better developed
(see fig. 154, ».pc.). The epigastric artery (epg., fig. 154), which supplies
branches to the oesophagus and the stomach, is a branch off of the pericardial
or is the direct continuation of the right one.

A large vessel is given off from the median hypobranchial between commis-
sures two and three, or three and four, which passes to the midventral line and
joins a similar artery from the opposite side. This united trunk extends poste-
riorly, and at the sixth commissural divides into the right and left coracoid
arteries (co.a.), which join the subelavian arteries. Similarly, near the sixth
commissural, an artery arises from the median hypobranchial on each side to
pass posteriorly and toward the midventral line. This artery, however, does
not reach or fuse with its fellow from the opposite side, but continues as the
coronary artery (cr.l., figs. 153 and 150) to the heart.

In Heptanchus maculatus the left coronary (cr.l., fig. 1504) runs along the
dorsal and left side of the conus arteriosus, supplying it and the dorsal side of

164 THE ELASMOBRANCH FISHES

the ventricle. About midway of the conus it sends a branch to the ventral side
of the ventricle. The right coronary passes around to the ventral side of the
conus, supplying branches to the tissues on the right side and to the ventral
and dorsal parts of the ventricle and to the auricle. A posterior coronary

Fig. 153

Fig. 153. Hypobranchial arteries, Heptanchus maculatus, dorsal view. (Marie Weldt, orig.)

a.dl., anterior dorsolateral artery; a.l., anterior lateral artery; br.a., brachial artery ;
ce., coeliac axis; em.?°, second and sixth commissural arteries; en., connective; co.d., cora-
coid artery; cr.l., left coronary artery; er.p., posterior coronary artery; e.c., external ca-
rotid; U.hb., lateral hypobranchial; m.hb.,median hypobranchial; mt.,metapterygial artery ;
pe., pericardial artery; p.dl., posterior dorsolateral artery; p.s., posterior scapular; s.cl.,
subclavian artery; th.°, anterior and posterior thyroid arteries; I-VI, first and sixth bran-
chial clefts.

Fig. 154. Epigastric artery (epg.), Heptanchus maculatus, ventral view. (Cecil Rowe, orig. )
m.hb., median hypobranchial; r.pe., right pericardial; VI-V II, sixth and seventh bran-
chial clefts.

(cr.p., fig. 153), arising from each coracoid artery, passes inward to supply
the sinus venosus.

From the ventral angle of the first efferent-collector loop a posterior thyroid
(th.?, fig. 153) is given off which in general position takes the place of a first
commissural. From about the same position or a little more anterior than the
posterior thyroid the large external carotid artery (e.c., figs. 151 and 153)
passes forward and the stem then divides, one part passing inward to the sym-

THE ELASMOBRANCH FISHES 165

physis of the lower jaw and giving branches to the coracomandibularis mus-
ele; and the other upward between the hyoid and mandibular cartilages to
supply the structures around the mandibular and hyoid regions. The external
carotid or one of its branches gives off a small branch (¢th.’, fig. 153) which
supplies the anterior part of the thyroid gland.

From the upper third of the first efferent-collector another large artery, the
pseudobranchial (ps., figs. 151 and 152), runs forward to break up into a num-
ber of strong branches in the spiracle. From the spiracle this artery is con-
tinued inward and forward as the ramus anastomotiecus (7.a., fig. 152), which
passes through a foramen in the orbit (see fig. 47, f.r.a., facing p. 44) to join
the internal carotid artery inside the cranial wall. Before entering the orbit,
however, this ramus gives off the ophthalmica magna (0.m., fig. 152) to the
eye region.

EFFERENT ARTERIES

The first efferent artery, the hyoidean efferent (hy.ef., fig. 152), extends as a
continuation of the first efferent-collector from the anterodorsal angle of the
first efferent-collector loop forward and mediad to the paired dorsal aorta
(d.a.1). The remaining efferents, branchial efferents (br.ef.'®, fig. 151) simi-
larly arise from the dorsal angles of efferent-collector loops, but they, as con-
tinuations of the anterior efferent-collector, extend backward and inward to
join the unpaired dorsal aorta. In Heptanchus five of these efferents, above
the first to the fifth holobranchs, reach the unpaired dorsal aorta and a sixth
joins the fifth.

Near the union of the hyoidean efferent and the paired dorsal aorta an or-
bital (stapedial) artery (or., fig. 152) is given off laterally and extends for-
ward through the orbit. The paired dorsal aorta is continued forward as the
internal carotid (7.c., fig. 152) which enters the cranium from the midventral
line to supply the brain. After perforating the cartilage the right internal
carotid joins the left and the two run for a short distance as a common trunk.
They then separate and pass forward and slightly outward where they are
joined by the right and the left ramus anastomoticus, respectively (7.a., fig.
152). Given off after the union of the ramus anastomoticus and internal caro-
tid are the three cerebral arteries to the brain. The anterior cerebral (a.c.,
fig. 152) passes anteriorly between the hemispheres of the brain and is usually
joined to its fellow from the opposite side by an intercommunicating artery.
The median cerebral (m.c.) passes forward to supply the olfactory tract and
bulb. The posterior cerebral (p.c.) passes backward, and its two branches join
to form the arteria spinalis (a.sp., fig. 152) which extends down and ventral
to the spinal cord. There is thus formed by the union of the anterior and the
posterior cerebrals a complete circle around the ventral part of the brain.

DorsaL AORTA

The dorsal aorta (fig. 152) is composed of a short anterior paired part (d.a.")
and a long posterior unpaired part (d.a.). The paired part receives the hy-
oidean efferent, and the unpaired part receives the first four pairs of efferents

166 THE ELASMOBRANCH FISHES

and the united trunk of the fifth and sixth efferents. The unpaired dorsal aorta
then passes backward ventral to the spinal column, becoming in the tail region
the caudal aorta. In its course through the body it gives off arteries to the di-
gestive tract and its appendages, to the extremities, and to the body museula-
ure and deeper structures.

ARTERIAL SUPPLY TO DIGESTIVE TRACT

The arteries given off from the dorsal aorta to the digestive tract consist of
three large trunks, the coeliac axis, the anterior mesenteric, and the posterior
mesenteric arteries.

COELIAC AXIS AND ITS BRANCHES

In Heptanchus maculatus the coeliac axis (ce., fig. 155) arises as a single trunk
from the ventral side of the dorsal aorta, only a short distance posterior to the
union of the last efferents. It passes downward and backward as a relatively
long artery and at the place where it strikes the portal vein it divides into:
(1) a very short gastrohepatic which bifurcates into a small hepatic branch
(h., fig. 155) to the liver and a large gastric branch to the stomach, and (2) a
large anterior intestinal artery (a.7.a.) which is continued along the valvular
intestine as the ventral intestinal artery.

The gastric artery separates into two main divisions, the anterior gastric
(a.g.) and ventral gastric (v.g.) arteries. The anterior gastric sends a branch
to the ventral union of oesophagus and stomach and also supplies a branch to
the dorsal side of the anterior part of the cardiac stomach. The ventral gastric
artery (v.g.), which is the posterior of the gastric divisions, passes down the
ventral side of the cardiac stomach and at the angle between the cardiae and
the pyloric arms of the stomach breaks up into numerous branches some of
which pass along the pylorus and anastomose with a posterior gastrosplenic
artery.

The hepatic artery (h.) passes toward the liver, and after giving branches
to the anterior segment of the spleen, bifurcates, giving off a smaller artery to
the left lobe of the liver and a larger branch to the right lobe. These two he-
patie divisions follow the course of the larger hepatic veins almost to the tip of
the liver, giving off numerous branches as they go.

The anterior intestinal division of the coeliac axis (a.7.a., figs. 155 and 156)
runs posteriorly and strikes the anterior part of the duodenum. Before enter-
ing the duodenum as the intraintestinal artery (see fig. 156, 7.4.) it gives off:
(1) a posterior gastro-pancreaticosplenie artery (p.gps.), (2) the ventral in-
testinal artery (v.i.a.), and (3) the gastroduodenal artery (gd.). The poste-
rior gastro-pancreaticosplenic supplies a short branch to the distal part of the
pylorus (py.a.) and along branch which after supplying branches to the pan-
creas (pn.) and spleen passes along the pyloric arm as the posterior gastro-
splenic (p.gs., fig. 155). This branch finally reaches the posterior side of the
pylorus where it gives off splenic branches and receives certain anastomosing

Fig. 155. Vascular supply to the digestive tract, Heptanchus maculatus. (Duncan Dunning,
del.) (Dorsal and ventral intestinal arteries and veins drawn relative ly close together in
ae that they may be seen.)

a.g., anterior gastric artery; a.gps., anterior gastro-pancreaticosplenic artery; a.gps.v.,
anterior gastro-pancreaticosplenic vein; d.7.d., anterior intestinal artery; a.i.v., anterior
intestinal vein; ce., coeliac axis; d.i.a. and d.i.v., dorsal intestinal artery and vein; /i., he-
patie artery; h.p., hepatic portal vein; i.m., inferior mesenteric; p.gs., posterior gastro-
splenic artery ; ; D-98.U., eas gastrosplenic vein; p.i.a., posterior intestinal artery ; p.i.v.
posterior intestinal vein; r., rectal artery; v.g., ventral ¢ paetne artery 3 v.g.v., ve ntral gastric
vein; V.i.d., and v.i.v., ae al intestinal artery and vein.

THE ELASMOBRANCH FISHES 167

branches from the ventral gastric artery. It then extends to the cardiac
stomach where it anastomoses with the anterior gastrosplenic artery which
supphes a more anterior segment of the stomach.

The ventral intestinal artery (v.i.a.) passes over the distal end of the py-
lorus and the ventral lobe of the pancreas, to appear on the ventral side of the
valvular intestine. On the intestine it supplies the distal part of the duodenum
and furnishes the ventral side of the valvu-
lar intestine with numerous paired annular
branches which run on the attached edge of
the spiral valve more or less nearly encir-
cling the intestine (see fig. 155).

The gastroduodenal artery (qgd., fig. 156)
in addition to supplying the proximal part
of the duodenum sends a short branch to the
tip of the pylorus.

SUPERIOR (ANTERIOR) MESENTERIC AND
ITS BRANCHES

The superior mesenteric artery (s.m., fig.
157) as such is usually absent in Heptanchus
maculatus and when present it is never more
than a short stem given off from the dorsal

: : : 3 Fig. 156. Arterial supply to the du-
aorta a little more than one-half the way Gdenum! Toreal vicaalientanchts
back in the body eavity. (In figure 155 the maculatus. (Marie Weldt, orig.)
superior mesenteric branches [a.gps. and a.i.a., anterior intestinal artery ;

‘ i : 3 du., duodenum; gd., gastroduodenal
p.v.a.] have been displaced forward.) It im- artery; i.a., intraintestinal artery;
mediately divides into: (1) an anterior gas- p”., pancreatic branch; pn.'*, dor-

*neleas A fe SAR sal and ventral lobes of pancreas;
tro-pancreaticosplenic (a.gps., fig. 155) and p-gps., posterior gastro-pancreatico-
(2) a posterior intestinal (/.2.a.). splenic artery; py.a., pyloric artery ;

. . : v.i.da., ventral intestinal artery.

The anterior gastro-pancreaticospleni¢
(a.gps.) sends branches to the dorsal and distal parts of the cardiac stomach,
to the dorsal lobes of the pancreas, and to the spleen in and on the angle of the
stomach.

The posterior intestinal artery runs back over the mesentery to the valvular
intestine which it joins at about the middle of its length. Then, as the dorsal
intestinal (d.7.a.), the artery continues backward to supply the dorsal poste-
rior half of the spiral valve with annular branches. Some of these branches
anastomose with similar annular branches from the ventral intestinal artery.
Finally the dorsal intestinal artery traverses the region of the colon and ter-
minates in the rectal gland where it joins branches of the inferior mesenteric.

INFERIOR (POSTERIOR) MESENTERIC ARTERY

The inferior mesenteric artery (7.m., figs. 157 and 155) arises as a single trunk
a few segments behind the superior mesenteric region. It runs along the an-
terior margin of the mesorectal mesentery to the anterior part of the rectal

168

THE ELASMOBRANCH FISHES

gland where it divides, the anterior branch joining the dorsal intestinal artery
to which reference has been made. The posterior part supplies numerous

WISTS ESE

Dewees

seen ey nL 4

ic. )
Ne }
a
by
J?
Loss
SS am |
ean. \ p.l.
lie
i
\
\\
\™ Ue

Fig. 157. The dorsal aorta and its
branches, Heptanchus maculatus.
(Marie Weldt, orig.)

a.dl., anterior dorsolateral artery;
a.l., anterior part of lateral artery;
br.a., brachial artery; ce.. coeliac axis;
c0.d., coracoid artery; ic., intercostal
artery; il., iliac artery; 7.m., inferior
mesenteric; od.a.,oviducalartery ; p.dl.,
posterior dorsolateral artery; p.l., pos-
terior part of lateral artery; 7., asym-
metrical rectal artery; s.cl., subclavian
artery; sg., segmental artery; s.m., su-
perior mesenteric artery.

branches to the rectal gland and reetum.
ARTERIAL SUPPLY TO EXTREMITIES

The arterial supply to the extremities in-
cludes a pair of subclavian arteries (s.cl.,
fig. 157) carrying blood to the pectoral
fins, and a pair of iliac arteries (7.) lead-
ing toward the pelvie fins.

The subclavian arteries in Heptanchus
maculatus are unusual in that they often
are no better developed than are the com-
mon intercostals (ic.). They pass from the
dorsal aorta near the union of the last ef-
ferents and out toward the pectoral re-
gion. A short distance out each subelavian
gives off a dorsolateral artery, one rela-
tively large division of which passes for-
ward (a.dl., fig. 157) and one backward
(p.dl.). From about this point a smaller
artery passes dorsally supplying the area
posterior to the scapula. The brachial ar-
tery (br.a.) leaves the subelavian and con-
tinues through a foramen in the pectoral
girdle to the pectoral fin. From the
brachial foramen the subclavian is con-
tinued forward by a larger brachioseapu-
lar vessel (see also bsc., fig. 169) to join
the coracoid artery (co.a., fig. 153) at a
place where it meets the lateral (abdomi-
nal) artery (a.l.). The coracoid in turn
joins the median ventral unpaired artery
(see fig. 153), described with the hypo-
branchial system.

Arising from the brachioscapular ves-
sel isa branch (mt., fig. 153), which passes
along the metapterygium of the pectoral
fin. The lateral artery (a.l., figs. 153 and
157) is a continuation of the coracoid; it
passes backward, hidden by the lateral
abdominal vein, to join the iliac artery
(il.) from the posterior region. Also leay-

ing the coracoids, but farther anterior than the origin of the lateral, is the pos-
terior coronary artery (cr.p., fig. 153), which has been previously described.

THE ELASMOBRANCH FISHES 169

The iliae artery arising from the dorsal aorta in the pelvic region is larger
than the subelavian. The first branch of the iliae on the left side, the rectal, is
asymmetrical and passes forward to supply the wall of the rectum (see r., figs.
155 and 157). Before the iliac, as the femoral, passes through a foramen in the
pelvie girdle to supply the pelvie fin, it joins the posterior part of the lateral
artery (pl.).

ARTERIAL SUPPLY TO DEEPER STRUCTURES

The third set of paired arteries arising from the dorsal aorta consists of seg-
mental arteries (sg., fig. 157). The first of these segmentals may arise from the
paired dorsal aorta (sg., fig. 152) throughout the pharyngeal region and per-
forate the deeper musculature around the spinal column.

In the region between the subclavians and iliaes about thirty pairs of regu-
larly arranged segmental arteries leave the aorta. Each segmental sends a
branch dorsally around the spinal column supplying a median branch to the
spinal cord and lateral branches to the musculature, and is continued by a
superficial intercostal branch (7c.) which runs along the peritoneum bound-
ing the body cavity. These intercostals extend outward to supply the inter-
septal musculature and are often of great length. Occasionally, however, some
of these are lacking, and the interseptal spaces, especially in the region of the
mesonephros or kidney, may be supplied by neighboring arteries.

The renals are the most ventral branches of the segmentals. They are more
irregular along the anterior prolongation of the kidney, but in the posterior
region where the kidney is enlarged they are regular in position and of large
size.

The ovidueal arteries in Heptanchus (od.a., fig. 157) arise from the third
pair of segmentals back of the subelavians. These arteries run posteriorly, and
at about the eighth segment behind the subelavians become tortuous in their
course ending in segment nine or ten.

CAUDAL AORTA

The dorsal aorta, as the caudal artery, traverses the haemal canal to the tip of
the tail giving off segmentals similar in general to those of the trunk. These
pass from the caudal aorta laterally through interhaemal spaces and branch
into ventral and dorsal divisions; the ventral branches go to the ventral mus-
cles and the dorsal branches pass upward and around the body of the centrum.
From the dorsal part, spinal arteries are given off which enter the neural canal
to supply the spinal cord.

170 THE ELASMOBRANCH FISHES

CIRCULATORY SYSTEM OF ELASMOBRANCHS IN GENERAL

The circulatory apparatus in the Elasmobranchs in general consists of four
structures, all formed first as simple tubes. These structures are (1) a rela-
tively simple two-roomed heart, the walls of a part of which have become thick-
ened for pumping; (2) arteries, which bear blood from the heart and from the
gills; (3) aseries of terminal thin-walled capillaries which connect the arteries
with (4) the veins. The veins in
Elasmobranchs are relatively large
and return the blood to the heart.

As is true for vertebrates in gen-
eral, the arteries and veins are dis-
tinguished by two or three well de-
fined characteristics. Both are made
up of layers from the inside out as
follows: a thin lining, the intima,
around which is the muscularis or
muscular layer. Surrounding the
muscular layer is the serosa. But in
the artery the muscular layer is
much thicker than it is in the vein. It
is this layer in the artery which
keeps the blood under more constant
pressure and forces it through the
capillaries and veins back to the heart. A second distinction between the two
is that the veins possess valves. These valves are numerous and are especially
large at the ends where the vessels empty. They are so arranged that blood
can pass freely towards the heart, but its passage in the opposite direction
is precluded.

The blood stream in the Elasmobranchs, as in other vertebrates, is made up
of arelatively large amount of plasma in which is contained a small amount of
serum. The erythrocytes or red corpuscles (fig. 158) contain only a small
amount of haemoglobin or red coloring matter and are nucleated cells much
greater in diameter than are the red corpuscles of man. The white corpuscles
are also nucleated and may be filled with granules.

Fig. 158. Red blood corpuscles of Squalus
sucklii. (M. C. Williamson, orig.)

HEART

The heart in the Elasmobranchs, as was seen in Heptanchus, does not undergo
the differentiation characteristic of the more complex heart of higher animals.
Asausual thing, it is composed of a thin-walled auricle (atrium) (aw., fig. 159)
and a thick-walled ventricle (wn.). The auricle receives the non-oxygenated
blood from the sinus venosus (s.v.) and the the ventricle sends it forward
through the conus (truncus) arteriosus (c.d.).

THE ELASMOBRANCH FISHES Ayal

The sinus venosus may in general be described as a delta-shaped collecting
sac, the apex of which leads to the auricle and the base of which is posterior in
position (see p. 203, fig. 188). Dorsally the sinus venosus is fused to the pos-
terior part of the roof of the pericardial cavity; laterally each angle of the
delta extends to the right or left as the duct of Cuvier. The principal change in
the form of the sinus venosus from that just described is found in some of the
rays (see p. 209, fig. 1948) in which the lateral angles are drawn out into the
elongated ducts of Cuvier.

Connecting the sinus venosus with the auricle is the sinu-auricular aperture
which, as in Heptanchus, is guarded by the sinu-auricular valves. These valves
are nothing more than double folds of the endothelial lining of the auricle

A B Cc

Fig. 159. The heart opened to show valves. (From Garman.) A. Isurus. B. Cephaloscyllium.
C. Mobula.

au., auricle (atrium) ; ¢.a., conus arteriosus; s.v., sinus venosus; vn., ventricle.

projecting into the sinus venosus. They are so arranged as to permit the free
passage of blood into the auricle, but a flow in the opposite direction is pre-
vented by their closure.

The auricle (atrium) in the Elasmobranchs in general is thin-walled and
lies over the ventricle. The walls of the sac, however, may be folded and may
even give the appearance of possessing two rooms. Internally the auricle in
practically all Elasmobranchs is smooth, that is, it rarely possesses tendinous
supporting cords which pass across the cavity from one wall to the other. The
auriculoventricular opening may be shifted sharply to the left, so that the
communication between the auricle and ventricle is visible in ventral view.
The auriculoventricular valve consists of two pocket-like flaps, the concavities
of which are directed toward the ventricle.

The ventricle is relatively small in all the Elasmobranchs, although in the
rays it may be relatively thick. It may be described as a pyramid with the base
posterior, two faces directed ventrally and outward, and the other dorsally in
position. A section through the ventricle shows its greatly thickened walls
(un., fig. 159). The lining, unlike that of the auricle, is often exceedingly rough
and irregular. The tendinous cords (chordae tendineae) present in the ven-
tricle of the Elasmobranchs are muscular at one end and drawn out into
longer or shorter tendons at the other. The ends are attached to opposite walls
and prevent the vessel from spreading beyond its capacity.

172 THE ELASMOBRANCH FISHES

The apex of the ventricle is continued anteriorly by the conus arteriosus
(c.a.), ashort and narrow tube, the lumen of which is triangular and the walls
muscular. Internally the conus of the Elasmobranchs is universally provided
with three longitudinal rows of semilunar valves, corresponding to the faces
of the triangle, one row dorsal and the other two ventrolateral in position.
Figure 159 shows several types of valves. As a rule, in the sharks the number
of tiers in each longitudinal row decreases in the more highly specialized
forms. A somewhat generalized condition was seen in Heptanchus (fig. 1508)
in which four or five tiers oceur, and a fairly general condition is that of
Tsurus (fig. 1594). Much greater specialization is present in Cephaloscyllium
(fig. 1598), in which only two tiers of valves are present. A decrease in the
number of tiers does not necessarily indicate specialization in the rays, as is
shown by the fact that several tiers are present in Mobula (fig. 159c), which
is a highly specialized form. In most sharks the valves of the anterior row
are best developed and often cover practically the entire lining of this section
of the conus. The valves in the succeeding tiers usually decrease in size the
farther they are located posteriorly. Not infrequently the lips of the valves
are held in position by chordae tendineae and chordae may also extend from
the fold of a valve posteriorly (fig. 1594). Among the regular valves, further-
more, are often found smaller or accessory valves (see fig. 159c).

ARTERIES
VENTRAL OR ASCENDING AORTA

The ventral aorta (v.a., fig. 167) in the adult passes forward as a continuation
of the short conus arteriosus. In all the Elasmobranchs this, also, is a relatively
short trunk and divides anteriorly into right and left halves. The ventral
aorta is smaller in caliber than the conus and its walls are thinner. As in
Heptanchus, it gives off afferent arteries which carry the blood to the gill
region to be oxygenated.

AFFERENT ARTERIES OF ADULT

In all Elasmobranchs the hyoidean afferent (hy.af., fig. 1668) and the first
branchial afferent on each side (br.af.t) arise from a common trunk, this
being a bifureation of the ventral aorta above mentioned. In many sharks
(Squalus, fig. 161; Mustelus antarcticus, fig. 1664) the last two afferents also
arise from a common trunk, but when this occurs the trunk is short. In some
forms the last two arise separately, as in Heptanchus (ap., fig. 150B) and
Chlamydoselachus (fig. 160). The second branchial afferent arises as a single
outgrowth from the ventral aorta between the common trunk of the hyoidean
and first branchial afferents and that of the last two afferents in pentanchid
Elasmobranchs (Mustelus, fig. 166). This is also the condition in at least one
of the rays, Dasyatis dipterura (fig. 167). In rays in general, however, the

Fig. 161. Dorsal view of afferent and efferent arteries, Squalus sueklii. (Elizabeth Chris-
tiansen, orig.)

br.af.', first branchial afferent artery; br.ef., branchial efferent artery ; ¢.tr., cross trunk ;
ce., coeliac axis; da.’, paired dorsal aorta; d.a., unpaired dorsal aorta; e.c., external carotid
artery; hy.af., hyoidean afferent; ps., pseudobranchial artery.

THE ELASMOBRANCH FISHES 173

second branchial afferent joins the common trunk of the last two so that, in
them, only two stems leave the ventral aorta.

Each afferent continues around the base of the cartilaginous gill arch in
front of the branchial rays, giving off smaller afferent arterioles both to the
anterior and to the posterior filaments of a gill (Squalus sucklu, fig. 161,
br.af.). In their course upward the afferents grow smaller and smaller and
terminate in the dorsal part of the branchial region. An interesting arrange-
ment is reported by Allis (1911) for Chlamydoselachus (fig. 160) in which the
afferent arteries, except the hyoidean and last branchial, instead of ending
dorsally, bifureate, one branch (af.*) passing over the cleft anteriorly to join

CFF!
Jou hy. af; sf A

Fig. 160. Branchial arteries of Chlamydoselachus. (From Allis.)

af.“, anterior division of afferent; af.%, posterior division of afferent; br.af’, fifth bran-
chial afferent; efc., efferent-collector; hy.af., hyoidean afferent artery; or., orbital artery.

the afferent in front, the other (af.”) passing dorsally and back over the suc-
ceeding cleft to join the following afferent. In this arrangement, which is not
greatly unlike that of Squalus, the afferents are connected into a series of
closed loops around all the clefts.

CAPILLARIES

The capillaries in the gill filaments or folds connect the arterioles of the
afferents (see fig. 145, a.b.) with a similar series of efferent arterioles (e.b.)
leaving the gills. They form a net so complex that it is impossible to trace an
individual capillary. The wall of each capillary is made up of a single layer of
cells, forming the effective membrane through which the exchange of gases is
made. If a longitudinal section could be made through the entire length of a
single capillary it would begin where the thicker walled afferent arteriole ends
and end with another thicker walled arteriole, the beginning of the efferent-
collector type of vessel.

EFFERENT-COLLECTORS

Blood brought to the gills by the afferents passes into the capillaries of the
gill filaments. Here it is oxygenated and is then sent down the gill filaments
(e.b.°, fig. 145) into efferent-collectors (efc.) lying at their bases. The efferent-

174 THE ELASMOBRANCH FISHES

collector which forms the anterior part of the loop, however, is a posterior
efferent-collector, for it drains the posterior demibranch of a whole gill; and
the efferent-collector posterior to the cleft is the anterior efferent-collector of
the following gill. To make this clear, if the area between two pockets, for
example between the first and second pockets, be considered (fig. 161), its
anterior efferent-collector (the second) drains the demibranch just behind

-S.M.

Fig. 162. Dorsal view of afferent and efferent arteries, Dasyatis dipterura. (Blanche Lilli-
bridge, orig.)

ac., accessory branchial arteries; br.ef., branchial efferent arteries; c.tr., cross-trunk; ce.,
coeliac axis; efc., efferent-collector; e.c., external carotid; hy.ef., hyoidean efferent; p.c.,’
posterior cerebral artery; ps., pseudobranchial artery; s.cl., subclavian artery; s.m., su-
perior mesenteric; J, first gill cleft.

THE ELASMOBRANCH FISHES 175

the first pocket, and the posterior efferent-collector (the third) drains the
area in front of the second pocket. The anterior efferent-collector, by its con-
nection through ecross-trunks (c.tr., fig. 161) with the posterior collector back
of it and by its ventral continuation with the collector in front of it, receives a
considerable amount of blood and is a much larger vessel than is the posterior
efferent-collector of the same gill. It is the anterior efferent-collector which is
continued directly outward to the dorsal aorta as the branchial efferent proper
(see fig. 161, br.ef.). All the efferent-collector loops posterior to the one just
described are similarly made up of posterior and anterior efferent-collectors,
and all are emptied into the unpaired dorsal aorta similarly through branchial
efferents (br.ef.) which are the direct continuation of the anterior efferent-
collectors.

Fig. 163. The developing branchial arteries, Squalus acanthias. (From Scammon.)

a.a.’~, first and sixth embryonic aortic arches; af., first afferent artery; cl., gill cleft;
d.a, paired dorsal aorta; d.a., dorsal aorta; ef., efferent artery; efc.”, anterior efferent-
collector; efc.%, posterior efferent-collector; ps., pseudobranchial artery; sp. spiracle; v.a.,
ventral aorta; x., where break in primary arch will take place.

We may briefly consider the formation of the afferent and efferent systems
in the embryo of Squalus as described by Scammon (1911). The arterial
system here consists of (1) a ventral aorta (v.a., fig. 163) running forward
from the heart under the gill region, (2) a dorsal aorta (d.a.) extending
backward above this and dorsal in position, and (3) six aortic arches (a.a.*°)
connecting dorsal and ventral aortae in the pharyngeal or branchial region.
Upon the formation of the gill filaments a new branch (efc.*) is budded off
which collects the blood from the newly formed gill tissues. The origin of this
collector from the embryonic aortic arch marks the place where the embryonic
arch later separates (see last arch at x) into two parts, the upper becoming
the efferent (ef.) which joins the dorsal aorta, and the lower the afferent
(a.f.), which joins the ventral aorta. The collector (efe.*) (efferent-collector )
next sends cross-trunks backward to the posterior demibranch and a posterior
efferent-collector (efc.”) is formed. In the last arch it will be observed that the
posterior efferent-collector has not as yet formed. In a general way it may be
said that for every embryonic aortic arch, except the first and second, two ef-
ferent-collectors thus arise. One of them is formed for the anterior demibranch
(efc.*), the other for the posterior (efc.”). The two collectors then continue to
grow downward and the tip of the posterior efferent-collector now joins the

176 THE ELASMOBRANCH FISHES

collector behind it. Soon the gill cleft is surrounded ventrally by these vessels,
but dorsally the loop is not yet completed around the cleft. A second important
change then takes place. A branch from the posterior efferent-collector passes
backward above the cleft and connects with the anterior efferent-collector
following. There is thus completed an efferent-collector loop around the entire
cleft characteristic of the adult.

In certain forms, even in the adult, the posterior efferent-collector may re-

Fig. 164

Fig. 164. Arteries derivative of the first efferent-collector, Squalus sucklii. (LL. H. Bennett,
orig.)

br.ef., first branchial efferent; e.c., external carotid; ef.c."*, first and second efferent-
collector arteries; hy.ef., hyoidean efferent; ps., pseudobranchial artery.

Fig. 165. Cross-trunks from eighth to ninth efferent-collectors, Squalus sucklii. (LL. H. Ben-
nett, orig.)
ct., cross-trunk; ef.c.°°, eighth and ninth efferent-collectors.

tain a dorsal commissural connection with the anterior efferent-collector of the
same gill. This interesting condition obtains in the adult Chlamydoselachus
(fig. 160). In this form the posterior efferent-collector sends a branch to join
the efferent-collector back of it, but it also retains an embryonic attachment
with the anterior efferent of its own holobranch. Usually, however, the branch
connecting it to the sueceeding efferent-collector becomes so important that
the original connection of the posterior efferent-collector to its own efferent
anteriorly is entirely lost in the adult. In any event there results in the adult
a complete efferent circuit around the gill cleft, each circle being composed of
the posterior efferent-collector of one gill and the anterior efferent-collector
of the gill following. Around all the clefts (except the last) and the spiracle,
complete loops are formed as thus described. ;

Since there are no demibranchs posterior to the last cleft no efferent-col-
lector lies back of this cleft and hence a circuit is incomplete around it. The
last posterior efferent-collector, that one in front of the last cleft, is usually

THE ELASMOBRANCH FISHES iy

separated from the anterior efferent-collector dorsally, and its blood reaches
the anterior efferent-collector in front of it only by means of cross-trunks
(c.tr., figs. 162 and 165). It is by means of such ecross-trunks that the last
efferent-collector is relieved of its blood. In facet, the posterior collector of

A B

Fig. 166. Hypobranchial arteries. A. Mustelus antarcticus. (From T. J. Parker.) B. Mus-
telus canis. (From Ferguson.)

a.l., anterior lateral (lateral abdominal) artery; br.a., brachial artery; br.af.*, first and
fourth branchial afferent arteries; co.a., coracoid artery; cm., commissural artery; cr.l., left
coronary artery; cr.p., posterior coronary; é.c., external carotid; hy.af., hyoidean afferent ;
L.hb., lateral hypobranchial; m.a., mandibular artery; m.hb., median hypobranchial; n.a.,
nutrient artery; pc., pericardial; s.cl., subclavian; v.a., ventral aorta; ZI, position of
third gill cleft.

each gill empties a considerable amount of its blood into the anterior effer-
ent-collector of its own gill by similar cross-trunks. These trunks may be
numerous as in Heptanchus maculatus, few as in Squalus, or they may be
single as in Dasyatis (c.tr., fig. 162).

The circuits made by the efferent-collectors, as we have said, are drained
into the dorsal aorta by means of the efferent arteries. These arteries we shall
consider after discussing certain branches given off by the efferent-collectors.

178 THE ELASMOBRANCH FISHES

BRANCHES OF EFFERENT-COLLECTORS
HYPOBRANCHIAL ARTERIES

The hypobranchial arteries in Elasmobranchs form a most complex system of
vessels in the ventral walls and floor of the pharyngeal area. In general the
ventral ends of the different efferent-collector loops may be more or less com-
pletely connected by a longitudinal vessel which, following Parker and Davis,
Ihave termed in Heptanchus the lateral hypobranchial artery (U.Ab., fig. 153).
This vessel sometimes formsa con-
tinuous ventral chain on each side
from the first to the fourth effer-
ent-colleector loop (Mustelus, fig.
166). In Raia erinacea, and some-
times in Carcharias littoralis,
according to Parker and Davis
(1899), the lateral hypobranchial
may even include the fifth loop,
but there is considerable irregu-
larity about this. Whatever con-
nections the loops may make with
the lateral hypobranchials, how-
ever, the tendency is to make
them in the region of the second
and third branchial arches rather
than from the first or last loops.
£0.4- Tn other forms the lateral hypo-
scl. branchial line isincomplete (Raja

Fig. 167. Hypobranchial arteries, Dasyatis dip- clavata), and in still others a
terura. (Blanche Lillibridge, orig.) (For expla-
nation see fig. 166.)

lateral hypobranchial is absent
(Dasyatis dipterura, fig. 167).
Commissural arteries (cm.) may arise from the hypobranchial, at or pos-
terior to the angles of the efferent-collector loops, and pass toward the mid-
ventral line anterior to the third and fourth afferent arteries (Mustelus
antarcticus, fig. 166A); or only a single one may be present as is usual for
Squalus sucklii. The commissurals passing from the lateral hypobranchials
medially may meet paired median hypobranchials as in Heptanchus macula-
tus (fig.153 and Hexanchus corinus, fig. 169). Some evidence of paired median
vessels is also seen in Mustelus (m.hb., fig. 166). In certain forms the commis-
sural may join an unpaired median hypobranchial as in Carcharias littoralis.
The commissures may be of a dorsal or a ventral type. In the former type
the artery passes to the median line above the ventral aorta, while in the latter
it passes below the ventral aorta. In Mustelus canis (fig. 1668) both com-
missures are of the ventral type; in Scylliwm catulus both are of the dorsal

Fig. 168. Hypobranchial arteries, Heranchus corinus, ventral view. (From Keys.)

a.co., median coracoid artery; af.", third afferent artery; co.a., coracoid artery; La.,
lateral (abdominal) artery; l.a.v., lateral abdominal vein; p.cr., posterior coronary artery ;
v.a., ventral aorta.

47 * :

fi Ps 7 : » * > re a

THE ELASMOBRANCH FISHES Ai)

type. In Carcharias littoralis one is dorsal and the other ventral. In Zygaena
two are ventral and a third is dorsal.

In Hexranchus corinus the median stem of the coracoid artery (co., fig.
169) arises from the left median hypobranchial and is continued posteriorly
by the coracoid artery (co.’). The coracoid is continued as the lateral (ab-
dominal) artery which follows the course of the lateral abdominal vein. From
the lateral (abdominal) artery
the brachioscapular artery (bsc.,
fig. 169) carries a large supply of
blood to the pectoral area and
joms the subclavian at a point
where the brachial artery (br.) is
given off to the fin.

From the median hyprobran-
chials, or from the last commis-
sural, the pericardial (pc., fig.
1668) and the coronary arteries
(cr.l.) may arise, and near the
origin of perieardials and coro-
naries in the rays, the coracoid
artery (co.a.) joins the last com-
missural (Dasyatis, fig. 167). In
Carcharias littoralis a branch,
designated by Parker and Davis
ue CIs aetnlG; arises from ulate Fig. 169. Relations of coracoid to lateral (ab-
median unpaired hypobranchial. dominal) artery, Hexanchus corinus, ventral

The pericardial, as in Heptan- view. (From Keys.)

co., median stem of coracoid artery; co.’, cora-
chus, goes to supply the dorsal coid artery; br., brachial artery; Bselinrachio:
pericardial wall, and to furnish scapular artery; er.p., posterior coronary ar-
branches to the oesophagus and SE nee Rak diane eee Eee
one or more epigastri¢ arteries to

the dorsal side of the stomach. An interesting condition obtains in Lamna cor-

nubica (Burne, 1923) in which the pericardials, after having traversed the
“supra-hepatic retia,” supply practically the whole of the blood to the
digestive tract.

The coronary arteries (cr.l., figs. 1668 and 167) in the Elasmobranchs are
unusually well developed. They may consist of a median ventral artery aris-
ing from the ventral type of commissure and a single dorsal arising from the
dorsal type as in Carcharias littoralis. Or they may consist of a pair of vessels,
the left one of which may go to the ventral side of the conus and ventricle, and
the right to the dorsal side. In Heterodontus two pairs of coronaries are pres-
ent, one of which is dorsal, the other ventral. In the rays, as in Heptanchus, a
posterior pair of coronaries (cr.p., fig. 169) arises from the coracoid arteries
and runs forward to the sinus venosus and ventricle. These coronaries are
especially interesting in Dasyatis. While the right posterior artery extends

180 THE ELASMOBRANCH FISHES

only to the sinus venosus, the larger left one passes across the ventricle to unite
with the right (dorsal) coronary forming a strong continuous vessel, A branch
arising from this trunk on the ventricle passes across the conus to the left
ventral coronary.

It will be observed that at the ventral angles of the efferent-collector loops
are certain smaller nutrient vessels (n.a., fig. 1664) which supply arterial

B
Fig. 170. The carotids and associated arteries. (From Hyrtl.)
A. Acanthias. B. Zygaena. C. Raja.

a.dl., anterior dorsal artery; cé., coeliac axis; d.a., unpaired dorsal aorta; d.a.*, paired
dorsal aorta “vertebral artery”; hy.ef., hyoidean efferent; 7.c., internal carotid; ml., mye-
lonal artery to cord; or., orbital (stapedial) artery; ps., pseudobranchial artery ; 7.a., ramus
anastomoticus; s.cl., subelavian; s.m., superior mesenteric.

blood to the gills and surrounding tissue. In Dasyatis arteries are well devel-
oped both at the ventral and the dorsal angles of the loops. Here they are ac-
cessory efferent-collectors (ac., fig. 162) from accessory gills.

ARTERIAL SUPPLY TO HEAD

In the Elasmobranchs in general the two branches from the first efferent-
collector to the head are essentially like those noted in Heptanchus. They often
differ, however, in extent of distribution. The first, the external carotid artery
(e.c., figs. 164 and 166), arises from the ventral angle of the hyoidean efferent-
collector and its branches are similarly distributed, as in Heptanchus. The
mandibular artery (m.a., fig. 167) extends toward the symphysis of the lower
jaw and supplies structures in this area. The hyoid artery runs upward be-
tween the hyoid and the mandibular arch, giving off twigs along its course.
The second branch, the pseudobranchial, arising from the middle of the first
efferent-collector, differs greatly in the sharks and rays (ps., fig. 164). Only in

THE ELASMOBRANCH FISHES 181

the sharks may it be spoken of as a true anastomoticus. In a type like Seylliuim
it courses by the spiracular region almost uninterruptedly and passes through
a foramen in the orbit to join the internal carotid. In some of the other forms
(Acanthias, Zygaena, fig. 170) instead of being straight it may pursue a most
tortuous course. In these, and in many other forms it is interrupted at the
spiracle. In Cetorhinus (fig. 1718), for example, it forms the so-called ‘“‘won-

Fig. 171. Arteries associated with the spiracle.
A. Raja. (From Hyrtl.) B. Cetorhinus. (From Carazzi.)

i.c., internal carotid artery; op., optic artery; ps., pseudobranchial artery; r.a., ramus
anastomoticus.

der net,” the wonder net being composed of a coil of arteries connecting the
part going to the spiracle with the part leaving it.

A different condition is found in this artery in the rays. In these the spiracle
is usually large and the blood supply to the filaments is better developed than
in the sharks. The artery here takes its origin similarly from the first efferent-
collector and as a large vessel (ps., fig. 1714) passes toward the pseudobranch.
Before reaching the latter, however, it gives off a large branch to the adductor
mandibularis muscle. At the pseudobranch it separates into numerous fila-
mentous arteries, and then continues as a smaller artery (7.a.) to join the
internal carotid artery (7.c.), as in the sharks. On its way it gives off the
ophthalmica magna to the eye.

Much attention has been given to the function of the ramus anastomoticus.
In some of the sharks in which the spiracle is closed and in which the artery
passes almost directly from the collector to the internal carotid, it is a true
ramus anastomoticus. But in the rays it is composed of an afferent and an
efferent part. It has been urged by Hyrtl (1858) that in the rays the branch
connecting the internal carotid and the spiracular gill is the afferent branch

182 THE ELASMOBRANCH FISHES

to the spiracular pseudobranch and that it carries, at least in part, non-oxy-
genated blood from the eye; and further that the branch extending from the
pseudobranch to the first efferent-collector is the true efferent pseudobranchial.

In the embryo of Squalus acanthias the pseudobranchial (ps., fig. 163) is
seen in relation to the remnant of the first embryonic arch, which at this stage
has broken, and the segment from the ventral aorta is only a nodule (a.a.").
The pseudobranchial itself is somewhat like a cross-trunk in that it is attached
to the posterior efferent-collector, but it crosses a relatively long span through
the posterior demibranch of the hyoidean gill and through what would be the
anterior demibranch of the hyoidean gill and the posterior demibranch of the
spiracular gill were such demibranchs present.

EFFERENT ARTERIES

We may now continue the description of the efferent arteries (see figs. 161—
162). In the large majority of forms five efferent arteries are present (pentan-
chid sharks). These represent the dorsal parts of the second to the sixth
embryonic aortic arches and consist of the hyoidean and four branchial effer-
ents. The hyoidean efferent artery passes forward and inward to join the
paired dorsal aorta when such persists, or is continued into the head by the
orbital (stapedial) artery (Heptanchus, fig. 152). In the embryo of Squalus
acanthias (fig. 163) this vessel is relatively large where it joins the paired
dorsal aorta. The four branchial efferents may reach the aorta as four arteries
on each side (Selachians) ; or the first may fuse with the second so as to give
only three pairs of branches (most rays, fig. 170c). In Hexranchus and in
Chlamydoselachus (fig. 160) the fifth branchial efferent joins the fourth
before entering the aorta just as, in Heptanchus, the sixth branchial joins
the fifth.

The orbital (stapedial) artery may arise at the union of the hyoidean effer-
ent and paired dorsal aorta (or., fig. 152) or it may arise near or anterior to
this union (fig. 1704). When the latter condition obtains there is formed a
common stem from which the orbital and the internal carotid spring. In the
adult rays where the paired dorsal aortae may be absent the hyoidean efferent
may continue directly into the common stem.

The orbital (stapedial) artery may reach the orbit without perforating the
basis cranil as in Heptanchus, or it may enter by a foramen in the margin of
the foramen through which the hyomandibular nerve enters (Heterodontus,
p. 59, fig. 66). The orbital gives off one or two branches (Chlamydoselachus,
fig. 160) which supply the muscles of the eye, and a second important branch
which passes backward to the hyoid area where it may anastomose with the ex-
ternal carotid system. The main stem then passes forward under the eyeball
and leaves the orbit through the orbitonasal canal. This stem gives off a buccal
artery which turns downward and backward to supply the adductor mandi-
bulae muscle and finally the stem divides into the nasal and rostral arteries.

The internal carotid (7.c., left side, p. 163, fig. 152), which may be consid-
ered as the direct continuation of the paired dorsal aorta, enters the cranium

THE ELASMOBRANCH FISHES 183

through a foramen or pair of foramina in or near the middle line. Within the
cranium it may be joined to the corresponding internal carotid of the opposite
side by a cross-connective, as in Squatina; or the two may run for a short dis-
tance as a fused common trunk. The internal carotid then passes forward, and
after receiving the ramus anastomoticus, gives off the optic artery (op., fig.

Fig. 172. Cerebral arteries. A. Squalus sucklii. (E. H. Barbera, orig.) B. Cetorhinus.
(From Carazzi.) C. Raja clavata. (From Hyrtl.)

a.c., anterior cerebral artery ; a.sp., spinalis artery; bs., basal artery; i.c., internal carotid
artery; m.c., median cerebral; ml., myelonal artery; p.c., posterior cerebral; tn., terminal
nerve.

1714), which runs with the optic nerve to the eye. Each internal carotid then
turns upward, as in Heptanchus, and divides into the three cerebral arteries
which vary considerably in the different Elasmobranchs.

The cerebral arteries, consisting of an anterior, a median, and a posterior
pair of arteries are, as we have seen in Heptanchus, derivatives of the right
and left internal carotids. The anterior cerebral arteries (a.c., fig. 1724) pass
forward ventrally around the lobi inferiores of the brain and over the optie
chiasma; in front of this, right and left arteries may be put into communica-
tion by a cross-trunk. From here forward great variation ensues. In some
types these arteries pass as single strands between the right and left divisions
of the telencephalon. In others they extend forward as numerous branches
(Heterodontus, rays). The median cerebrals (m.c.) extend under the telen-
cephalon and along the olfactory tracts as fairly simple vessels (Squalus

154 THE ELASMOBRANCH FISHES

sucklii, fig. 1724). In certain forms they may extend forward in a number of
strands (Cetorhinus, fig. 1728). The posterior cerebrals in Squalus (p.c., fig.
172a) loop around the inferior lobes of the brain and fuse into a single strand.
By the union of right and left posterior cerebrals behind and the anterior cere-
bral in front a circle of Willis is formed somewhat like that in man. Further-

2 |
!

Ay
:

Fig. 173. Vascular supply to the digestive tract. A. Triakis semifasciatus, ventral view.
(Elizabeth Christiansen, orig.) B. Mustelus antarcticus, dorsal view. (From T. J. Parker.)

a.g., anterior gastric artery; a.g.v., anterior gastric vein; a.gps., anterior gastro-pancre-
aticosplenic artery; a.gs., anterior gastrosplenic artery; a.i.a., anterior intestinal artery ;
a.i.v., anterior intestinal vein; ce., coeliac axis; co., colon; c.s., cardiac stomach; d.g., dorsal
gastric artery; d.i.a., dorsal intestinal artery; d.i.v., dorsal intestinal vein; gh., gastro-
hepatic artery; h., hepatic artery; h.p., hepatic portal vein; i.a., intraintestinal artery; é.v.,
intraintestinal vein; i.m., inferior mesenteric artery; lv., cut end of liver; oe., oesophagus ;
p.gs., posterior gastrosplenie artery; p.gs.v., posterior gastrosplenic vein; p.i.a., posterior
intestinal artery; pn., pancreatic artery; pn.**, dorsal and ventral lobes of pancreas; rc.,
rectum; spl., spleen; v.g., ventral gastric artery; v.g.v., ventral gastric vein.

THE ELASMOBRANCH FISHES 185

A ANE Naive

C
aN as

Fig. 174. Vascular supply to the digestive tract, Heterodontus francisci. (Duncan Dunning,
del.)

a.g., anterior gastrie artery; a.g.v., anterior gastric vein; a.gs., anterior gastrosplenie
artery; d.gs.v., anterior gastrosplenic vein; a.i.a., anterior intestinal artery; an., annular
artery; ce., coeliac axis; co., colon; c¢.s., cardiac stomach; dch., ductus choledochus; d.i.a.,
dorsal intestinal artery; d.i.v., dorsal intestinal vein; du., duodenum; ep., epigonal artery ;
gh., gastrohepatic; h., hepatic artery; h.p., hepatie portal vein; i.m., inferior mesenteric ;
oe., oesophagus; p.gs., posterior gastrosplenic artery; p.gs.v., posterior gastrosplenic vein;
p.i.a., posterior intestinal artery; p.i.v., posterior intestinal vein; pn., pancreatic artery ;
p.s., pyloric stomach; re., rectum; s.m., superior mesenteric artery; v.g., ventral gastric
artery; v.g.v., ventral gastric vein; v.i.a., ventral intestinal artery.

186 THE ELASMOBRANCH FISHES

more, upon the posterior fusion of right and left cerebrals a midventral artery,
the basilaris (bs.), is produced, which supphes the medulla of the brain and as
the spinalis (a.sp., fig. 1724) continues ventrally down the spinal cord. The
spinalis will again be considered in our description of the arteries of the spinal
cord. In Raja (fig. 172c) the posterior cerebrals form broad arches on the
brain stem before uniting. Here the spinalis is made up of several strands.
According to Hyrtl it receives the myelonal vessel (ml.) from the united first
and second efferents, as was seen in figure 170c.

ARTERIAL SUPPLY TO TRUNK
DORSAL AORTA

The dorsal aorta in all the Elasmobranchs is supplied with blood from the
branchial efferent arteries; it extends through the body and is continued into
the tail as the caudal aorta. It arises in the embryo as a pair of arteries. Evi-
dence of this condition may be absent in the adult, but in forms like Acanthias
and Zygaena the anterior part of the aorta, “the vertebral,” to which the
second embryonie aortie arch is attached, indicates the paired condition. In
Acanthias the paired aortae (da.', fig. 170), as widely separated arteries, pass
forward and are joined by the hyoidean efferents; while in Zygaena (fig.
1708) the two are fused far forward. In the adult ray, on the contrary (fig.
170c), all indication of the paired aortae is lacking. In the region of the trunk
the paired embryonic aortae early fuse into a single median dorsal aorta,
which is the source from which many vessels arise. These arteries, as In Hep-
tanchus, spring from the aorta either as paired or as unpaired vessels.

UNPAIRED ARTERIES

The unpaired arteries in anteroposterior direction are the coeliac axis (ce.,
figs. 173-175), the superior mesenterie¢ (s.m.), and the so-called inferior mes-
enteric (7.m.) arteries. When a fourth is present, as is usual in the sharks, it
is due to a failure to form a superior mesenteric, the two branches of which
arise separately from the dorsal aorta.

COELIAC AXIS AND ITS BRANCHES

The coeliac axis (ce., figs. 173-175) arises posterior to the union of the fourth
branchial efferents and behind the paired subclavians. In some forms this is
a relatively short trunk (Mustelus), while in others it is long (Acanthias).
Normally as in Heterodontus (ce., fig. 174) it supplies the gonad and then
divides into two parts, one of which, the gastrohepatie (gh.), supplies the
stomach and the liver; the other, the anterior intestinal. (a.v.a.), passes back-
ward to the region of the intestine.

The gastrohepatic may be a fairly well developed segment as in Triakis (fig.
1734). It is, however, usually a short trunk as in Acanthias; or it may be en-

THE ELASMOBRANCH FISHES 187

tirely absent (Dasyatis, fig. 175). The gastrie arteries follow much the same
plan in the Elasmobranchs generally as has been described for Heptanchus.
In certain forms, however, a dorsal gastric may be well developed.

The hepatic artery may arise as a single trunk, Heptanchus, or a hepatic
branch may be given off from the anterior intestinal artery, as in Mustelus ant-
arcticus (fig. 173B). Occasionally a second hepatic branch may be given off
from the ventral gastric in Triakis. The hepatic artery (or arteries) supply
twigs to the ductus choledochus, to the gall bladder, and to the liver.

Fig. 175

Fig. 175. Arteries to the digestive tract, Dasyatis dipterura, ventral view. (Blanche Lilli-
bridge, orig.)

Fig. 176. Duodenal supply, Dasyatis dipterura, dorsal view. (Blanche Lillibridge, orig.)

a.g., anterior gastric artery; a.g.v., anterior gastric vein; a.gps., anterior gastro-pancrea-
ticosplenic artery; a.gs., anterior gastrosplenie artery; a.i.a., anterior intestinal artery;
ce., coeliac axis; ¢.s., cardiac stomach; d.i.a., dorsal intestinal artery; d.ch., ductus choled-
ochus; d.i.v., dorsal intestinal vein; du., duodenum; gd., gastroduodenal artery; h., hepatic
artery; h.p., hepatic portal vein; 7.a., intraintestinal artery; 0e., oesophagus; p.gps., pos-
terior gastro-pancreaticosplenic artery; p.gs., posterior gastrosplenic artery; p.gs.v., pos-
terior gastrosplenic vein; p.i.v., posterior intestinal vein; pn., pancreatic branch; pn.?,
dorsal and ventral lobes of pancreas; py., pylorus; s.m., superior mesenteric artery; sp.i.,
valvular intestine; v.g., ventral gastric artery; v.g.v., ventral gastric vein.

188 THE ELASMOBRANCH FISHES

The anterior intestinal artery (a.1.a., figs. 173 and 174) is a relatively large
vessel in the sharks, while in the rays it is usually less important. In both it is
continued as the intraintestinal (7.a.) along the free edge of the spiral valve.
In sharks before it enters the intestine as the intraintestinal it gives off the
ventral intestinal artery which runs along the ventral side of the valvular in-
testine to which it gives numerous annular branches. In the rays a ventral
intestinal artery is characteristically absent.

In Dasyatis the anterior intestinal gives off an anterior gastro-pancreatico-
splenic artery (a.gps., fig. 175), which in sharks is given off from the dorsal
aorta. In Rhinobatis and Raja this artery is a branch from the superior mesen-
teric artery. This artery sends a strong branch to the dorsal lobe of the pan-
ereas (fig. 175), and then, as the anterior gastrosplenic (a.gs., fig. 1738)
divides, supplying the spleen and the dorsal side of the cardiac stomach. Just
before the anterior intestinal disappears as the intraintestinal it gives off a
posterior gastro-pancreaticosplenie (p.gps., fig. 176), which artery after sup-
plying pancreatic branches to the ventral lobe of the pancreas passes in the
gastrosplenic omentum around the outer margin of the pyloric stomach as the
posterior gastrosplenic artery (p.gs., fig. 175). In the rays, where there is no
spleen on the angle of the stomach, all the branches of this artery go to the
stomach. A second branch, the gastroduodenal artery (gd.), is given off at
about the same place or farther posteriorly (Raja) from the anterior intes-
tinal artery. This supplies the duodenum and may also supply the dorsal side
of the pyloric arm of the stomach as did a similar artery in Heptanchus.

There is usually considerable anastomosing of the branches on the pyloric
angle of the stomach. Branches of the anterior gastrosplenic join with those
from the posterior gastrosplenic as also do branches from the ventral gastric
artery.

SUPERIOR MESENTERIC ARTERY

The superior or anterior mesenteric artery is variable as to its place of origin.
It may arise in the midbody far removed from the coeliae axis, as in Hetero-
dontus (s.m., fig. 174), or it may more nearly approach the coeliac as in Scyl-
lium, Galeus, Triakis (fig. 1734). In the rays the superior mesenteric and the
eoeliae are often in close proximity (Raja clavata; Dasyatis, fig. 1778). The
office of the superior mesenteric in the sharks is to supply blood to two general
areas. The main artery to one of these areas is the anterior gastro-pancreatico-
splenic (fig. 173B), which supplies the distal part of the eardiae stomach
(a.gs.), the panereas, and the spleen. The other is the posterior intestinal
(p..a.), Which is continued along the dorsal wall of the valvular intestine as
the dorsal intestinal artery (d.7.a.).

A superior mesenteric, as just described, is present in Heterodontus (sm.,
fig. 174) and may occasionally be found also as a short trunk in Acanthias (out
of 500 specimens examined in Squalus sucklii seven had short superior mesen-
teric trunks). In this form, then, while a short trunk is occasionally present, in
the majority of occurrences the branches of the superior mesenteric arise sepa-

THE ELASMOBRANCH FISHES 189

rately from the dorsal aorta. In such, the posterior intestinal arises anterior
to and crosses over the anterior gastro-pancreaticosplenic. This condition is
characteristic of many types of which it should be said that no true superior
mesenteric artery exists.

Fig. 177. Dorsal aorta and its segmentals. A. Scyllium. (From Carazzi.)
B. Dasyatis. (Blanche Lillibridge, orig.)
br.a., brachial artery; ce., coeliac axis; cl., cloacal branch; cla., branch to clasper; d.a.,
dorsal aorta; d.l., dorsolateral artery; f.m., iliac artery; mt.a., metapterygial artery; o.d.,
oviduct; od.a., oviducal artery; p.i.a., posterior intestinal artery; p.l., posterior lateral
artery; pr.a., propterygial artery; r., rectum; s.cl., subclavian artery; s.m., superior mesen-
teric; u.v., urinary vesicle.

The anterior gastro-pancreaticosplenic (a.gps.) is contrasted with the pos-
terior gastro-pancreaticosplenic (p.gps.), previously described, by its supply-
ing a more anterior (proximal) segment of the digestive tract. While, as we
have seen, the posterior artery of this name is in relation to the pyloric part

190 THE ELASMOBRANCH FISHES

of the stomach, the anterior gastro-pancreaticosplenic supplies the cardiac
stomach. Its gastric part divides into two branches which supply the dorsal
and distal halves of the cardiae stomach. The branch supplying the dorsal
half may anastomose with twigs from the dorsal gastrie artery which in Mus-
telus may be a derivative of the
anterior gastric (a.g., fig. 173B).
Thesplenic branch of the anterior
gastro-pancreaticosplenic leaves
, the gastrosplenic stem near the
ip AAW ayy ele union of cardiac and pyloric limbs

Bn St Hf and passes to the spleen on the

> 4) angle of the stomach.
a

The posterior intestinal divi-
sion of the superior mesenteric
uniformly in the sharks is con-
tinued as the dorsal intestinal ar-
tery along the dorsal side of the
intestine. In the rays a posterior
intestinal artery as such is absent,
for in them the superior mesen-
teric is a long stem which reaches
entirely to the valvular intestine
(see s.m., figs. 175 and 176). As
in the sharks, its continuance
along the dorsal side of the intes-
tine may be designated as the
dorsal intestinal artery.

In higher vertebrates the coe-
liac and superior mesenteric ar-
teries combine into a coeliacomes-
enteric. This, however, does not
Fig. 178. Arteries of the pectoral fin, Acanthias, occur in Elasmobranchs. In a ray

dorsal view. (From Erik Miiller.) like Dasyatis (fig. 175) part of
br., brachial artery; l.p., lateral pterygial ar- ihe t a f the supedioenmae
tery; m.p., median pterygial. 1e function of the superior mes-

enteric may be performed by the
coeliae, that is, the anterior gastro-pancreaticosplenic which in sharks, as a
branch of the superior mesenteric, arises from the anterior intestinal artery,
which is a derivative of the coeliae axis.

INFERIOR MESENTERIC ARTERY

The inferior or posterior mesenteric artery (i.m., figs. 173 and 174) usually
arises as a Single vessel, except occasionally as in Acanthias (see fig. 179), and
is more or less removed from the anterior mesenteric. It supplies branches to
the epigonal organ or non-functional part of the sex gland in forms in which
such exists (Heterodontus, fig. 174, ep.; Triakis, and Mustelus antarcticus),

THE ELASMOBRANCH FISHES 1191

and then runs to the rectal gland and the surrounding parts of the digestive
tract, where it breaks up into a network of vessels. Unlike Heptanchus, how-
ever, it does not usually anastomose with the dorsal intestinal artery.
Oceasionally median vessels arise from the dorsal aorta posterior to the
origin of the inferior mesenteric. They are characterized by passing directly
downward to the region of the rectum and, occasionally, to the oviducts. Such
vessels may be present in Acanthias and one or several of them may be present
in Raja. These vessels have been held by
Howes (1891) to represent the true inferior
mesenteric comparable to that in mammals.

PatrRED BRANCHES OF, AORTA

SUBCLAVIANS AND ILIACS

The subelavians of the more specialized Se-
lachii are similar in position to the same ar-
teries in Heptanchus (s.cl., fig. 157) and
Hexanchus (fig. 169). Considerable varia-
tion in the origin of the subclavians may oc-
eur. As a rule they are given off from the
dorsal aorta at the region between the third
: : Fig. 179. Relations of rectal artery,
and fourth pairs of efferent arteries, but ggjaius sucklii. (C. E. Bird, orig.)
they may arise farther back at the base of d.a., dorsal aorta; fm., femoral
the fourth pair of efferents (Dasyatis, fig. artery; w., iliac artery; t.m., inferior
¥ . Sa mesenteric; r., rectal artery; 1r.g.,
162, s.cl.). While their origin is usually sym- — yeetal gland.
metrical, sometimes right and left arteries,
as Monroe (1785) long ago claimed for the ray, arise asymmetrically. Such a
condition is found in Dasyatis (fig. 177B).

The subelavians (fig. 1664) are usually much stronger vessels than are those
of Heptanchus where they take little blood from the dorsal aorta. In some
specimens of Heptanchus twigs given off from the subelavians indicate that
the blood is flowing toward the dorsal aorta. In other types, as the subclavians
pass outward along the pectoral girdle they give off important branches which
differ considerably in the sharks and the rays. Usually in both, after the dorso-
lateral (a.dl., fig. 170c) is given off it divides into a relatively large branch
which passes forward across the scapula, and another which passes backward
between the bundles of muscles. The brachial leaves the subclavian and enters
the foramen of the pectoral girdle. As it passes through the girdle it fol-
lows the ventral canal and consequently enters the fin on the ventral side
(Squalus).

In the fin of Acanthias the brachial artery separates into a median pterygial
(m.p., fig. 178) and a lateral pterygial artery (/.p.). In the rays the brachial
separates into a strong branch to the propterygium and another to the meta-
pterygium. From these branches numerous smaller arteries run to the radial
muscles of the fin.

192 THE ELASMOBRANCH FISHES

The subclavian is continued ventrally along the coracoid segment of the
girdle by the coracoid artery (co.a., fig. 1664), which at the ventral part of
the girdle gives off posteriorly the anterior lateral artery (a.l.) which is the
anterior part of the lateral (abdominal) artery. This artery, as in Heptanchus,
runs under the walls of the lateral abdominal vein and continues posteriorly
past the iliae artery. As the coracoid is followed forward and inward it is seen
to meet its fellow from the opposite side in the midventral line and to give off
the posterior coronary (cr.p., figs. 153 and 169) to the heart. By the union of
right and left coracoids a median stem is formed. This stem joins the commis-
surals from the ventral efferent-collector loops.

The iliaes have the same form and take the same direction as the renal ar-
teries but their terminal parts extend into the pelvic fins as the femoral ar-
teries. The iliac artery arises from the posterior part of the lateral (abdomi-
nal) artery (p.l., figs. 157 and f.m., 177B). In the rays Parker has figured renal
arteries arising from the iliacs. These renal arteries apparently are not com-
parable to the rectal artery in Heptanchus. A rectal (hypogastric) artery in
Squalus suckli (r., fig. 179) may arise from the femoral or from the iliac. As
in Heptanchus maculatus it runs to the digestive tract and anastomoses with
the posterior intestinal. The iliac is continued to the pelvic fin as the femoral
which distributes smaller arteries both to the dorsal and the ventral sides of
the fin.

SEGMENTALS

For convenience the segmentals may be divided into three groups. One group
consists of the musculospinal arteries (fig. 1704), anterior to the subclavian
arteries; the second group is situated between the subclavians and the iliaes;
and the third set is posterior to the iliaes in the region of the tail.

The musculospinal arteries are usually paired, but sometimes they are more
or less irregularly arranged. The first pair of these in Heterodontus passes
upward and around the spinal column and through small canals in the poste-
rior walls of the cranium (see p. 54, fig. 61). The intercostal branches of these
segmentals may divide just over the pharynx as in Zygaena (fig. 170B), or
they may be regular as in Acanthias (fig. 1704). In Raja the myelonal artery
(ml., fig. 170c) supplies the spinal cord.

A trunk segmental sends a large vertebromuscular branch dorsally around
the vertebra and up the dorsal septum to the middorsal line. As seen in a trans-
verse section of Squalus sucklii (d.vm., fig. 180) this artery gives rise to a
number of branches, the most dorsal of which (dms.) passes upward along the
myoseptum to supply the musculature of the dorsomedian bundle. In the re-
gion of the dorsal fins large branches of this artery extend into the fins. The
next branch given off, the vertebrospinal artery, passes mediad through the
neural arch to supply the spinal cord. Inside of the neural canal this artery
divides into a dorsal branch, the ramus dorsalis (Acanthias, fig. 181, d.r.), and
a ventral branch, the ramus ventralis (v.r.). The smaller ramus dorsalis forms
the tractus arteriosus lateralis (tr.l.), which passes both backward and for-

THE ELASMOBRANCH FISHES 193

ward on the cord. The ramus ventralis passes to the midventral line where it
enters the arteria spinalis (a.sp.). Branches, especially from the tractus la-
teralis, enter the substance of the cord and terminate in large part around the
grey matter (Sterzi, 1904). Other branches given off laterally from this dorsal
branch of the segmental pass outward in a spiral direction along the myosep-
tum dorsally and laterally to the muscle bundles.

The segmental, as the intercostal (7., fig. 180),
is continued laterally to supply the musculature
encircling the peritoneum. The intercostals in all
recent Elasmobranchs are reduced in number (fig.
177). While in Heptanchus there are about thirty
pairs, in the rays they may be reduced to only a
few pairs, and those remaining may present great
irregularities in size and position. This irregu-
larity is especially noticeable in the trunk region
where there is a considerable crowding of the vis-
cera.

The most ventral branch of the segmental, the
renal artery (rn.), turns ventrally and enters the
tissue of the kidney. In the posterior region where
the kidney is enlarged the vessels come to be strong
trunks which pass downward, then sharply back-
ward, to break up into numerous branches.

The renal divisions of the segmental artery may
be modified as the ovidueal arteries. In Scyllium
several pairs of the segmentals just posterior to
the subelavians (od.a., fig. 1774) pass to the ovi-
duet and shell glands. The fourth to the sixth are

Fig. 180. Transverse section
through trunk region, Squalus
sucklii, showing branches of
a segmental artery. (From
Coles.)

C., central muscle bundle;
c., artery to central bundle;
d.a., dorsal aorta; DMS., dor-

the main ones, which pass to the oviduct and along
the greater part of its length. In Heterodontus
francisci two sets of these arteries are present. An
anterior set arises from the eleventh and twelfth
segmentals, and a posterior set from the nine-
teenth and twentieth segmentals. The ovidueals
anastomose on the oviduct and in viviparous types
send arteries to the inner lining of the uterus to
supply the villi. In those forms in which the young

somedial septal bundle of
muscles; dms., dorsomedial
septal artery ; DS., dorsal sep-
tal bundle; ds., dorsal septal
artery; d.vm., dorsal verte-
bromuscular artery; 7., inter-
costal artery; JL., lateral
bundle; /a.v., lateral abdomi-
nal vein; ll., lateral line; N.,
neural musele bundle; v., ar-
tery to neural bundle; rv.,
renal artery; vs.a., vertebro-
spinal artery.

are carried for a considerable time the ovidueal
arteries may be remarkably developed (Acanthias, see p. 306, fig. 267;
Rhinobatis).

CAUDAL SEGMENTALS

The segmentals in the region of the tail differ somewhat from those of the body
just described. The principal change is the result of the haemal arch. The
segmental, in addition to sending a vertebromuscular branch upward, sends

194 THE ELASMOBRANCH FISHES

a similar vertebromuscular branch downward to supply the segment at the
sides of the haemal arch. Branches from this ventral artery supply the ventral
muscles in the caudal region. From the ventral branch of the vertebromuscu-
laris, the anal fin, where such is present, and the ventral lobe of the caudal fin

Fig. 181. Arteries and veins of the spinal cord, Acanthias. (From Sterzi.)

a.sp., arteria spinalis; d.r., ramus dorsalis artery; d.r.v., dorsal ramus vein; tr.l., tractus
lateralis; v.l., vena limitans; v.r., ramus ventralis artery; v.r.v., ventral ramus vein; Vs.a.,
vertebrospinal artery; vs.v., vertebrospinal vein.

are supplied with arterial blood. The ventral branches in the region of the fins
are better developed than are those of the dorsal series. In a type like Squatina
where a dorsal fin is located on the tail the dorsal branches similarly supply
this fin as well as the dorsal lobe of the caudal fin.

1908.

1911.

1912.

1889.

1909.

1923.

1904.

1905.

HOMER

THE ELASMOBRANCH FISHES 195

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VAT

CIRCULATORY SYSTEM (Continued)

CIRCULATORY SYSTEM OF HEPTANCHUS MACULATUS

Fig. 182. Anterior cardinal sinus, Hep-
tanchus maculatus. (Mast Wolfsohn,
orig.)

a.c.s., anterior cardinal sinus; d.s.,
Danielian sinus; nu., nutrient vessel;
0.8., orbital sinus.

VEINS

Blood distributed by the arteries is re-
turned to the heart by several important
systems of veins. We shall consider these
vessels for Heptanchus maculatus in the
particular regions which they occupy.

VEINS OF HEAD

The anterior cardinal sinus (a.c.s., figs.
182 and 183) drains the blood from the
region around the eye, and as a large ves-
sel passes backward dorsal to the gills. At
the pectoral girdle it drops downward and
enters the duct of Cuvier. The vessel may
be thought of as arising from two terminal
vessels, the anterior cerebral and the an-
terior facial veins.

The anterior cerebral vein (see fig. 182)
collects blood from the forward part of
the brain by two main branches; the ante-
rior branch runs over the telencephalon
recelving numerous venules; the posterior
division drains the dorsal part of the dien-
cephalon and receives a few branches from
the optic lobes. The anterior facial or or-
bitonasal vein returns the blood from the
nasal region (see fig. 190, a.f.v.). Both the
anterior cerebral and the anterior facial
vessels empty into the large orbital sinus
(o.s.) back of the eyeball. Connecting the
two orbital sinuses is the interorbital vein
which passes through the cranium by way
of the interorbital canal (see fig. 47, 7.0.,
facing p. 44).

From the orbital sinus the anterior ear-

dinal passes backward through the postorbital groove and, in the region of
the hyoidean arch, broadens out as the anterior cardinal sinus proper (4.c.s.,
fig. 183). In the pharyngeal region it receives certain nutrient veins (nu., figs.

[198]

THE ELASMOBRANCH FISHES 199

182-184) from the hyoidean demibranch and from all the holobranchs. Pos-
teriorly, the anterior cardinal sinus drops suddenly downward into the duct
of Cuvier (d.c., fig. 183).

A second vessel, dorsal to the branchial region but nearer the middle line, is
the Danielian sinus (d.s., figs. 182 and 183) discovered by Mast Wolfsohn.
Anteriorly this sinus extends almost to the vagus foramen and posteriorly it
reaches practically to the end of the anterior cardinal sinus. The anterior ex-
tremity ends in a blind sae (bs.) and similarly the posterior extremity may
end blindly. The Danielian sinus is connected with the anterior cardinal by
numerous openings (ap., fig. 183) the most anterior of which is near the en-

Fig. 183. Danielian sinus, Heptanchus maculatus. (Ruth Conrad, orig.)
ap., apertures connecting anterior cardinal (a.c.s.) and Danielian sinuses (d.s.); Ds..
blind sacs leading from Danielian sinus; d.c., entrance to duct of Cuvier; nu., nutrient
vessels; po.o., postorbital process.

trance of the hyoidean vein. Other openings (ap.) between the anterior cardi-
nal and Danielian sinuses, posterior to this point, are arranged more or less
segmentally as may be seen by lifting up the vagus nerve.

The inferior jugular vein (7./., fig. 184) drains the ventral area of the phar-
ynx and extends as an enlarged vein or sinus back to the heart. Anteriorly it
receives a tributary from the symphysis of the lower jaw (smt.) and another
from the thyroid region (th.v.). It next receives the hyoidean vein or sinus
(h.s.) and, at regular intervals back of this, ventral nutrients (nw.) which are
continuous with the dorsal nutrients of the anterior cardinal. Notwithstand-
ing the fact that it receives veins from all the holobranchs, the inferior jugu-
lar decreases in caliber in its course backward. Near its termination it curves
laterally and then passes backward to enter the duct of Cuvier just mediad of
the entrance of the subclavian vein (fig. 188).

VEINS OF TAIL

The caudal vein (cd.v., fig. 185) passes forward in the haemal canal of the
tail, and back of the cloaca divides into the renal portal veins (7.p.). It receives
branches from the dorsal and posterior ventral cutaneous veins (fig. 189) and
numerous segmental veins from the tail; other segmentals join the renal
portals as they pass along the dorsolateral margins of the kidney. The ventral
rami of the segmental veins receive the blood from the musculature of the
ventral lobe of the caudal fin, and each dorsal ramus collects venous blood
from dorsal musculature and from the spina! cord. The renals finally break up
into a net in the tissues of the kidney.

200 THE ELASMOBRANCH FISHES

VEINS FROM KIDNEY OR MESONEPHROS

Blood is returned from the kidneys and the back by the two large posteardinal
veins (p.c., fig. 185) which run along the sides of the spinal column just under
the lining of the body cavity. The right one of these veins may be traced as
a Single vessel from the posterior tip of the kidney forward to the region of
the inferior mesenteric artery, where it
is Joined by the left posteardinal. Just
behind the origin of the posterior in-
testinal artery the two posteardinals in
Heptanchus are joined by two or more
eross-trunks (c.tr.).

The posteardinals receive numerous
revehentes (rv., fig. 1868) from the kid-
ney, which have collected the blood dis-
tributed by the advehentes (aw., fig.
1864) of the renal portal veins. As the
two posteardinals pass forward they
receive segmental veins from the body
wall and before reaching the heart in-
crease in size to form the enlarged post-
cardinal sinuses (p.c.s., fig. 185). The
walls of right and left sinuses freely
intercommunicate posteriorly and an-
teriorly and are held in place by multi-

tudes of tendinous cords. The posterior
cardinals enter the duct of Cuvier (d.c.,
fig. 185) posterior and mediad of the

aperture for the anterior cardinal sinus.

Fig. 184. Diagram of inferior jugular
vein, Heptanchus maculatus. (Mast Wolf-

sohn, orig.) ; VEINS FROM DIGESTIVE TRACT
co., coracoid eartilage; h.s., hyoidean

vein or sinus; hy.af., hyoidean afferent : :
artery; 4.j. inferior jugular vein; nu., Venous blood is returned from the di-

nutrient vein; smt., submental vein; th., gestive tract to the heart by the hepatic
en cae a portal system of veins (see fig. 155,
h.p.,facing p. 166).The principal veins

making up this system in Heptanchus are : the posterior intestinal, the intrain-
testinal, the anterior intestinal, the gastries, the portal, and the hepatie veins.
The posterior intestinal vein, as the dorsal intestinal (d.7.v., fig. 155), drains
the rectal gland and passes forward along the colon and valvular intestine.
At about the place where the posterior intestinal artery (p.7.a.) reaches the
valvular intestine the vein, as the posterior intestinal proper, leaves the in-
testine and passes over the bridge of the pancreas. Before joining the anterior
intestinal vein it receives the large anterior gastro-pancreaticosplenie vein
formed by a gastric branch from the dorsal side of the eardiae stomach, splenic

THE ELASMOBRANCH FISHES 201

branches from the spleen on and in the angle of the stomach, and smaller pan-
creatie veins. As it passes the anterior segment of the spleen it receives one or

more additional strong branches.

The anterior intestinal vein is a forward continuation of the intraintestinal

vein and, as such, drains the free margin of the valve within the valvular intes-
tine. Near the place where it leaves the intestine the anterior intestinal vein re-

ceives several branches. The first of these
branches is the ventral intestinal vein
(v.2.v., fig. 155) which arises on the rectum
and passes over the colon and along the
ventral side of the valvular intestine par-
allel with and not far from the dorsal in-
testinal vein. At the distal part of the val-
vular intestine the ventral intestinal vein
is usually connected by a transverse ves-
sel with the dorsal intestinal vein (d.7.v.),
and along the valvular intestine it re-
ceives annular branches. The ventral in-
testinal in continuing over the ventral lobe
of the pancreas receives certain branches
from the pancreas. It next receives a
long gastrosplenie branch (p.gs.v.) which
drains the posterior side of the pyloric
stomach along which it travels from the
cardiae division where it receives splenic
branches. The anterior intestinal may
next be joined by the large anterior branch
of the gastric which drains the most ante-
rior part of the cardiae stomach and, in
part, the main division of the anterior seg-
ment of the spleen; or the anterior gastric
vein may join the ventral gastric and
empty with it into the portal.

After the union of the anterior and the
posterior intestinal veins the large ventral
gastric (v.g.v.) joins the stem of the he-
patic portal system (h.p.). The hepatic
portal vein extends a short distance for-
ward and divides into right and left
halves to the lobes of the liver. The blood
thus distributed to the liver is finally col-
lected by right and left hepatic trunks
which enter the sinus venosus of the heart
a short distance from the middle line
(h.v., fig. 188).

Fig. 185. General view of veins in Hep-
tanchus maculatus. (C. G. Potter, orig.)

a.c., anterior cardinal; br.v., brachial
vein; ¢.tr., eross-trunk; cd.v., caudal
vein; cl.v., cloacal vein; co.v., coracoid
vein; f.v., femoral vein; i.j., inferior
jugular vein; l.a.v., lateral abdominal
vein; p.c., posteardinal vein; p.c.s.,
posteardinal sinus; r.p., renal portal;
s.cl.v., Subelavian vein; s.sc.v., subscap-
ular vein; s.v., sinus venosus.

202 THE ELASMOBRANCH FISHES

VEINS OF BODY WALL

The veins of the body wall empty into the lateral abdominal system, the chief
vessels of which are the lateral abdominal veins (l.a.v., fig. 185) which run
along the sides of the body just under the lining of the body cavity. In the re-
gion of the cloaea, right and left lateral abdominal veins are continuous across

~da

Fig. 186. Finer vessels in kidney, Heptanchus maculatus. (C. G. Potter, orig.) A. Segment
of kidney showing renal vein and advehentes. B. Section of the kidney showing revehentes
entering the posteardinal.

av., advehentes; da., dorsal aorta; p.c., posteardinal vein; rn., renal vein; rv., revehentes;
ur., ureter; vd., vas deferens.
the midventral line. Each lateral abdominal receives a cloacal vein (cl.v.)
from the rectal region and a femoral vein (f.v.) from the pelvic fin. Between
the pelvic and the pectoral regions the lateral abdominals receive numerous
tributaries from the thinner musculature of the body wall, which are not
shown in figure 185. In the pectoral region it receives the brachial vein (br.v.,
fig. 187) from the pectoral fin, the subscapular (s.sc.v.), including the lateral
cutaneous vein (l.c.v., fig. 187),
and the coracoid vein (co.v.)
from the ventral part of the
girdle; the last-named vessel re-
ceives the ventral cutaneous vein
from the skin. As the subclavian
vein, the lateral abdominal turns
sharply upward and enters the
duct of Cuvier (s.cl.v., fig. 187).

VEINS OF SKIN

The dorsal cutaneous vein in Hep-
tanchus maculatus (p.d.c., fig.
Fig. 187. The subclavian vein and its relations, 189) runs in the connective tis-

Heptanchus maculatus, lateral view. : :
. A = A o , -
br.v., brachial vein; co.v., coracoid vein; d.c., sue of the skin along the mid

duct of Cuvier; l.a.v., lateral abdominal vein; dorsal line. For convenience of
l.c.v., lateral cutaneous vein; p.c.s., posteardinal description it may be divided
sinus; S.cl.v., subclavian vein; s.sc.v., subscapular ; ; é
vein. into a posterior and an anterior

THE ELASMOBRANCH FISHES 203

part. The posterior part is first found about halfway between the pectoral and
pelvie segments and continues from this point posteriorly almost to the tip of
the tail. In the region of the dorsal lobe of the caudal fin the dorsal cutaneous
vein is double, and around the dorsal fin right and left dorsal cutaneous veins
form a loop from which a strong intercommunicating branch passes to join the
lateral cutaneous vein. From the unpaired vein just back of the loop a medium

Fig. 188. Sinus venosus opened, Heptanchus maculatus. (Ruth Jeanette Powell, del.)

a.c., anterior cardinal; au., auricle; h.v., hepatic vein; 7.j., inferior jugular vein; p.c.s.,
postcardinal sinus; sa., sinu-auricular valve; s.cl., subclavian vein; s.v., sinus venosus; V.,
valves of anterior cardinal sinus.

deep vein (m.v.) passes to the right of the spinal column to join the caudal
vein (cd.v.). The anterior part of the dorsal cutaneous vein ends anteriorly
in a V-shaped sinus over the brain ease.

The lateral cutaneous vein (l.c.v., fig. 189) runs directly under the skin,
parallel with and ventral to the lateral line groove. It extends from the middle
region of the caudal fin forward, and joins the subscapular sinus near its tip
(fig. 187). In its course forward it receives numerous segmentally arranged
cutaneous branches, and in the region of the dorsal fin it has strong intercom-
municating branches which join the cloacal vein (cl.v.) of the lateral ab-
dominal system.

WO | Wek isn

Lent ry BN ve

a os RR seh
an |

Fig. 189. Cutaneous veins, Heptanchus maculatus. (Helen Hopkins, orig.)

ed.v., caudal vein; cl.v., cloacal vein; l.c.v., lateral cutaneous vein; m.v., median unpaired
vein; p.d.c., posterior dorsal cutaneous vein; p.v.c., posterior ventral cutaneous; s.sc.v., sub-
scapular vein.

The ventral cutaneous vein lies in the subcutaneous tissue in the midventral
line. In the region of the anal fin it forms a loop and like a V its right and left
branches run backward on the caudal fin. The posterior part of the vessel
empties into the cloacal vein (cl.v.) and the anterior segment of this vein joins
the coracoid vein (co.v., fig. 187).

204 THE ELASMOBRANCH FISHES

CIRCULATORY SYSTEM OF ELASMOBRANCHS IN GENERAL

Blood which has been distributed by the arteries to the capillaries of the
tissues is collected and returned to the heart by the veins. The veins, as we
have said, differ as a rule from the arteries in possessing thinner walls. In see-
tion this is seen to be due especially to a lack in the muscular layer. A back-
ward flow of blood, which in the arteries is prevented by the muscular elas-
ticity of the larger proximal arteries and by the rhythmic action of the heart,
is prevented in the veins by valves. These valves are present at irregular in-
tervals throughout the course of some of the veins and are especially marked
at the junction of principal trunks, as for example at the entrance of the an-
terior cardinal to the duct of Cuvier (v., fig. 188). The valves are formed by
the lining of the veins as loose erescentie folds, the coneavity of which is
directed toward the heart. These permit a free course of the blood toward the
heart but prevent its backward flow by filling with blood and thus blocking
the lumen.

The Elasmobranch veins frequently become greatly enlarged sinuses. An
incision through the posteardinal sinus shows that its walls, though similar in
other respects to those of the veins, differ from them especially in two ways.
In the first place if they possess any musculature it is exceedingly thin, and
secondly they have, passing from wall to wall, numerous tendinous supporting
cords. Many such enlarged sinuses are present in the Elasmobranchs espe-
cially in the region of the head and in the proximal part of the veins near
the heart.

VEINS

For convenience of deseription the veins of the Elasmobranchs in general may
be grouped into seven systems as follows: (1) those which return blood from
the head, the anterior cardinal system; (2) veins which bring blood from the
caudal region to the kidney, the renal portal system; (3) the vessels draining
the kidneys along the dorsal body wall, the posterior cardinals; (4) the veins
which carry the blood from the digestive tract and its appendages to the liver,
the hepatie portal system; (5) those veins which return blood from the ex-
tremities and sides, the lateral abdominal system; (6) a system of veins drain-
ing the walls of the heart; and (7) the cutaneous veins or veins of the skin.

ANTERIOR CARDINAL SYSTEM

The anterior cardinal system consists of the anterior cardinal or jugular veins
and the inferior jugulars together with their tributaries. The anterior cardinal
vein (a.c.s., fig. 190), like that of Heptanchus, passes from the orbital sinus
(0.s.) back over the branchial basket. The orbital sinus receives the anterior
facial (a.f.v.) or orbitonasal and the anterior cerebral veins (a.c.v., fig. 191),
together with certain cutaneous veins of the head. Right and left orbital sinuses

THE ELASMOBRANCH FISHES 205

are connected by the interorbital vein which traverses the interorbital canal
(see fig. 47, facing p. 44). The blood thus collected in the orbital sinus passes
through the postorbital groove and then backward in the enlarged anterior
eardinal sinus over the pharyngeal region. The sinus receives nutrients from
the gills. At the level of the most posterior gill arch the anterior cardinal drops
down and enters the duct of Cuvier or the posteardinal sinus (Scylliwm, fig.
190p, a.c.s.). The branches to the anterior cardinal may be considered further.

p.c.s.

= a s.clv
2a XS brv.
D
Lav
B
Fig. 190. Anterior cardinal system. .
A. Mustelus. (From T. J. Parker.) B. Scylliwm. (From O’Donoghue.)

a.c.s., anterior cardinal sinus; a.c.v., anterior cardinal vein; a.f.v., anterior facial vein;
br.v., brachial vein; h.s., hyoidean sinus; h.v., hyoidean vein; i.j., inferior jugular; l.a.v.,
lateral abdominal vein; l.c.v., lateral cutaneous; 7.s., nasal sinus; 0.s., orbital sinus; p.C.s.,
postcardinal sinus; p.c.v., posterior cerebral vein; s.cl.v., subclavian vein; s.sc.v., subseapu-
lar vein.

A supraorbital vein (so.v., fig. 1924) collects blood from the skin and the
jelly-like tissue overlying the cranium, and passes forward from the segment
of the parietal fossa (p.f.) over the dorsal surface of the nasal capsule. At the
place where the superficial ophthalmicus nerve (fo.V IJ, fig. 1924) perforates
the cartilage the left supraorbital receives a small dorsomedian rostral vein
(dm.v.).

206 THE ELASMOBRANCH FISHES

The supraorbital then extends forward, receiving a dorsolateral branch
(dl.v.), and then passes through the foramen in the roof of the olfactory
capsule and continues as the nasomaxillary (nm.v.). As this vein curves down-
ward within the capsule and along its posterolateral aspect it receives a fairly
large branch (n.v., fig. 192B), which is the result of a remarkable leash of ves-
sels coming from the folds of the olfactory organ. Just after the nasomaxillary

Fig. 191. Cerebral veins. (From Rex.) A. Scyllium catulus. B. Raja asterias.

d.c.v., anterior cerebral vein; my., myelonal vein; p.c.v., posterior cerebral vein.

enters the cartilage in the posteroventral region of the capsule it is joined by
the orbitonasal (on.v.) or anterior facial vein (a.f.v., fig. 190), which serves to
connect the veins under discussion with the orbital sinus (0.s., fig. 190). The
nasomaxillary vein next emerges from the nasal cartilage just laterad of the
point where the maxillary nerve first passes under the basal fenestra (fn.,
fig. 2, Wells, 1917). Here it receives twigs from the skin and tissue outside of
the capsule, and a subrostral vessel (s7.v.) from the tip of the snout. In the
posterior part of its course the nasomaxillary vein swings mediad in front of
the superior labialis muscle (lls.) to jom its mate from the opposite side to
form a dorsal sinus (s.). From the sinus (s.) the buecopharyngeal veins (bp.v.,
fig. 1928) lead backward, and at the basal angle of the cranium, right and left
vessels swing outward following the margin of the orbits. At the postorbital
process each buccopharyngeal receives one or two lateral tributaries from the
sides of the upper jaw, and then right and left vessels take an almost parallel
course posteriorly finally to empty into the anterior cardinal sinus.

The anterior cerebral vein (a.c.v., fig. 1914), which, as we said above, enters
the orbit as the principal vein from the anterior part of the brain, may vary

THE ELASMOBRANCH FISHES 207

considerably from the condition seen in Heptanchus. It is formed by an
anterior vessel on the olfactory bulb which receives a branch from the olfac-
tory lobe, a median branch from the ventral olfactory and diencephalic areas,
and a posterior vein which in the middorsal line joins a similar vein from the
opposite side as the mesencephalic vein. In other words, the first branch of

Fig. 1924. Veins dorsal to roof of Fig. 1928. Veins in roof of buccal
cranium, Squalus sucklii. cavity, Squalus sucklit.

bp.v., buecopharyngeal vein; dl.v., dorsolateral rostral vein; dm.v., dorsomedian rostral
vein; fn., basal fenestra; fo. VII, exit of superficial ophthalmic nerve; Ils., attachment,
superior levator labialis muscle; n.a., nasal aperture; n.c., nasal capsule; nm.v., nasomaxil-
lary vein; n.v., nasal vein; on.v., orbitonasal (facial) vein; p.f., parietal fossa; po.p., post-
orbital process; s., sinus; so.v., supraorbital vein; sr.v., subrostral vein.

the anterior cerebral drains the olfactory lobe and tract, the second the whole
of the ventral area back to the optie chiasma, and the third the whole of the
remaining dorsal region anterior to the cerebellum. It is through the last-
named vessel that the roof of the third ventricle is drained.

The anterior cardinal sinus (fig. 190) receives the hyoidean vein and the
nutrients (not shown) from all the holobranchs. These nutrients, as in Hep-
tanchus, are continuous with ventral nutrients.

The posterior cerebrals (p.c.v., fig. 191) from the brain enter the anterior
cardinal sinus. In a type like Scyllium (fig. 1914) they collect the blood from
the cerebellum and medulla and pass it posteriorly in large right and left
dorsal veins through the foramina with the vagus nerves. In Raja asterias
(fig. 1918) the posterior cerebral is usually a single vessel. Continuing pos-

208 THE ELASMOBRANCH FISHES

terior from this vessel in both Scylliwm and Raja is the dorsal myelonal vein
(my.). This vein is absent, however, in Acanthias (fig. 181). A ventral
myelonal vein, arising posterior to the optic chiasma, drains the vascular saes
and passes on down the cord.

The hyoidean vein in Mustelus enlarges ventrally into the hyoid sinus. Each
sinus (h.s., figs. 190 and 193) is triangular and of large size, the base of the
triangle extending from the tip of the
lower jaw in front to back of the first
afferent artery. In Acanthias the fore-
most of the communicating vessels be-
tween right and left hyoidean veins
forms the hyoidean sinus. In Car-
charias and Raja a thyroidean sinus of
considerable size is formed in the mid-
line ventral to the thyroid gland (Fer-
guson, 1911).

From the posteroventral angle of the
hyoidean sinus, the inferior jugular
vein passes backward to enter the duet
of Cuvier (figs. 190 and 193). On its
way it receives the ventral nutrient
veins (nuw.) which are connected with
the dorsal nutrients of the anterior car-
dinal sinus.

RENAL PORTAL SYSTEM

In the embryonic condition a subintes-
tinal vein extends from the tail to the
heart. It later separates into an ante-
rior and a posterior part, the anterior
Fig. 193. Veins ventral to pharynx, Mus- part becoming the line of the hepatic
telus antarticus. (From T. J. Parker.) .

‘ i portal system and the posterior part

a.¢c.s., anterior cardinal sinus; br.v., 2
brachial vein; h.s., hyoid sinus; h.v., hyoi- that of the renal portal system now
dean vein; Ujey inferior jugular ; L.a.v., under consideration.
. pee ea ee Pere ee The caudal vein, as the basis of the
renal portal system of the adult, ex-

tends from the tip of the caudal fin through the haemal canal to the cloaca.
It represents the stem of a Y, the arms of which pass to the sides of the cloaca
as the renal portal veins (r.p., fig. 1944). Each renal portal continues forward
and upward dorsal to and along the lateral margin of the kidneys, giving to
each numerous advehentes.

In its course as a single median vessel, the caudal receives dorsal and ven-
tral segmental veins on each side, which are of large size at the place where the
dorsal and ventral lobes of the fin are deepest. The two renal portals also re-
ceive segmental veins from the body wall in the region of the kidneys and from

THE ELASMOBRANCH FISHES 209

the oviduct of the female. In certain forms, as we shall see later, the tips of
the ovidueal veins are in communication with other veins in the cloacal region.

POSTERIOR CARDINAL VEINS

The posterior cardinal veins in the Elasmobranchs in general are two enlarged
vessels located at the sides of, and ventral to, the spinal column and ventro-
lateral to the dorsal aorta. In some types right and left posteardinals may

)

NS ios

Fig. 194. General view of veins of body.

A. Mustelus antarcticus. (From T. J. Parker.) —B. Raia erinacea. (From Rand.)

a.c.s., anterior cardinal sinus; br.v., brachial vein; ed.v., caudal vein; cl.v., cloacal vein;
f.v., femoral vein; i.7., inferior jugular vein; il.v., iliac vein; /.a.v., lateral abdominal vein;
p.c., posteardinal vein; p.c.s., posteardinal sinus; 7.p., renal portal vein; s.sc.v., subscapular
vein; s.cl.v., subclavian vein.

form a fused vessel posteriorly (Scylliwm and Raja). In others the posteardi-
nals extend as separate vessels from the posterior tip of the kidney behind to
the sinus venosus in front. As a usual thing, however, only the right one ex-
tends backward the whole length of the kidney, while the left is attached to
the right (Mustelus, fig. 194A, p.c.).

In the sharks the anterior third of the posterior cardinals forms the enlarged

210 THE ELASMOBRANCH FISHES

posteardinal sinuses, the two usually being freely intereommuniecating. At the
middle of the posteardinals in the rays (fig. 1948) a spacious sinus (p.c.s.) is
formed which is prolonged backward by a narrower outpocket toward the
rectal gland. In most forms the thin walls of the sinuses are strengthened by
the unusual development of the trabeculae.

The posteardinals may enter the posterior inner angle of the duct of Cuvier
a considerable distance from the entrance of the hepatic veins, as in Hep-
tanchus, or they may empty as in Mustelus (fig. 1904).

The first and most posterior branches received by the posterior cardinals
are the revehentes draining the kidneys; while the tributaries from the an-
terior region are usually the large genital sinus draining the gonads, and the
subscapular vessel coming from under the scapula. Between these two areas
and throughout the greater part of their course forward they receive seg-
mental veins from the body walls. The ventral branches of the segmentals
drain the blood from the interseptal spaces, and the dorsal branches the blood
from the deep musculature of the back. Into the dorsal rami the veins (vs.v.,
fig. 181) from the spinal cord enter.

In a type like Acanthias the vertebrospinal veins leave the neural canal
through the foramina of the dorsal nerve roots. Within the canal each vein
divides into a dorsal ramus (d.7.v.) which drains the dorsal part of the cord
and a ventral ramus (v.7.v.) draining the ventral part. The ventral ramus is
also connected with a vena limitans which extends longitudinally along the
ventral side of the cord. In Scylliwm the dorsal rami of each side of the cord
form plexuses of veins each of which is more or less united into a longitudinal
dorsolateral tract. In the rays, longitudinal tracts form a dorsal spinal vein
of large size which as we have seen joins the posterior cerebrals anteriorly.

HEPATIC PORTAL SYSTEM

Blood which has been distributed to the digestive tract by the coeliac axis and
the mesenteric arteries is returned from the tract by branches of the hepatic
portal system. Two such branches in both the sharks and the rays are of
special interest. These are the intraintestinal, including the anterior intestinal
vein, and the posterior intestinal or mesenteri¢ veins. To these branches should
be added the gastric veins mentioned for Heptanchus.

The intraintestinal vein (see fig. 1738, 7.v.) represents a part of the anterior
segment of the subintestinal vein of the embryo. It was discovered first on the
free margin of the seroll valve of Zygaena where it is of so large a size that
Duvernoy (1833) described it as a “venous heart.” Such, however, is not its
nature. As it emerges from the anterior end of the valvular intestine it is
continued as the anterior intestinal vein.

The anterior intestinal vein (see p. 184, fig. 1738, a.7.v., and figs. 174 and
175) is usually well developed in the sharks, but is small or relatively insig-
nificant in the rays. As it continues forward from the intraintestinal vein it
is Joined by the ventral intestinal which arises on the ventral side of the
valvular intestine, and receives annular branches from the attached side of

THE ELASMOBRANCH FISHES 211

the valve. At the anterior end of the valvular intestine it receives branches
from the lobes of the pancreas and the posterior gastro-pancreaticosplenic
vein (p.gs.v., fig. 173B).

The posterior gastro-pancreaticosplenie is continued in the mesentery
(omentum) between the spleen and the stomach as the gastrosplenic vein
(p.gs.v., figs. 173-175). While in Heptanchus it is relatively small, although
a long vessel, in most of the other sharks it is well developed, and in the ray
(Dasyatis, fig. 175) is of relatively immense size. Here, in the absence of a
spleen on the greater curvature of the stomach, it drains only the stomach
and pancreas.

The anterior intestinal then passes forward to join the posterior intestinal.
The segment of the anterior intestinal vein as it passes forward to join the pos-
terior intestinal varies greatly in length. In Scylliwm it is exceedingly short,
but in Acanthias and Mustelus (fig. 1738) it isa relatively long segment.

The posterior intestinal vein is the direct continuation of the dorsal intes-
tinal vein (d.2.v., fig. 173) which arises within the tissue of the rectal gland,
from the tip of the gland (leopard shark, fig. 1734), or from a sinus which runs
longitudinally along the lumen of the gland to its base (Acanthias, Mustelus,
fig. 1738). The dorsal intestinal passes along the dorsal side of the valvular
intestine, receiving annular branches. In some forms the posterior intestinal
vein leaves the intestine at the place where the posterior intestinal artery
strikes it, that is, at about the middle of the intestine (Acanthias, Dasyatis,
fig. 175), or it may leave it farther forward (Heterodontus, fig. 174; Triakis,
fig. 173). It extends forward by the spleen, from which it receives the anterior
gastrosplenic vein (Squalus sucklii; Heterodontus, fig. 174, a.gs.v.). The pos-
terior intestinal vein then proceeds forward to join the anterior intestinal
vein to form the portal.

The anterior gastro-pancreaticosplenie vein, which is an important vessel
in Heptanchus, is much simpler in Mustelus (fig. 1738) and in Scylliwm. In
all types it is divided into gastric and splenic parts, and as in Triakis (fig.
1734) it usually receives a branch from the dorsal lobe of the pancreas.

The portal or hepatic portal is formed by the union of the posterior intes-
tinal vein, anterior intestinal trunk, and one or more gastrics. It passes to the
liver usually as a vessel of large size, receiving on its way the large ventral
gastric (v.g.v., figs. 174 and 175), two or more branches of which drain the
ventral surfaces of the cardiae and pylorie stomach. Upon reaching the liver
the portal divides into two branches, one to each of the lobes. These branches
extend to the tips of the lobes, giving off in their course numerous other
branches which break up into a net.

The blood thus distributed to the liver by the hepatie portal vein and by the
hepatic arteries is re-collected by the hepatic veins and taken to the heart. The
hepatie veins may empty near the median line by a right and left vein, as in
Acanthias; or these veins may break up into a more or less complex net before
entering the sinus venosus (Lamna). In other forms the two hepatic vessels
join and enlarge in the anterior part of the liver, forming immense hepatic

212 THE ELASMOBRANCH FISHES

sinuses. Where the two vessels fuse together the walls between the two sides
are more or less broken down and the remaining walls are supported by
trabeculae. These hepatic sinuses may empty by relatively small apertures
near the middle line into the sinus venosus (Scylliwm). In certain types the
hepatic veins enter the outer tips of the duct of Cuvier (Torpedo, Raja).

DEVELOPMENT OF HEPATIC PORTAL SYSTEM

In the embryo, the vitelline veins from the yolk sae (v.v., fig. 195) are among
the first vessels to appear. These are followed by the subintestinal vein (s.2.),
previously mentioned, which unites with the vitelline to form an omphalo-

om.

V.V.

Si.

A B C D

Fig. 195. Diagram of development of hepatic portal system in Elasmobranchs, ventral view.
(From Rabl, modified. )

a.c.v., anterior cardinal vein; cd.v., caudal vein; h.v., hepatie vein; lv., liver capillaries;
om., omphalomesenteric vein; p.c., posteardinal; p.i.v., posterior intestinal vein; r.p., renal
portal vein; s.7., subintestinal (intraintestinal) vein; s.v., sinus venosus; v.v., vitelline vein.

mesenteric. The right vein remains rudimentary, but the left omphalomes-
enteric becomes an important vessel (om.). When the developing liver comes
in contact with the omphalomesenteric the latter vessel sends branches into
the tissue of the liver and divides into two parts, each of which forms a series
of capillaries in the liver (lv. fig. 195c). After the absorption of yolk, and the
consequent loss of the vitelline veins, the main stem of the hepatic portal sys-
tem is along the subintestinal line. This vein in the adult is carried in with the
developing valve into the valvular intestine, as the intraintestinal, to drain the
free margin of the valve. There is next formed the posterior intestinal or
mesenteric vein (p.i.v., fig. 195B-c). Blood now empties by the united sub-
intestinal and posterior intestinal into the hepatic portal and this empties into
the liver. From the liver the blood is collected and passes to the sinus venosus

THE ELASMOBRANCH FISHES 213

(s.v., fig. 195c) by the hepatic veins (h.v.), which were previously the anterior
ends of the vitelline veins. In figure 195c and p the cardinal and renal systems
are also well developed.

LATERAL ABDOMINAL SYSTEM OF VEINS

The lateral abdominal veins (l.a.v., fig. 194) extend from the pelvic to the
pectoral segments of the body just under the peritoneum in the sides of the
body wall. Posteriorly each vein may arise from a net of fine veinlets on the
side of the rectal and cloacal walls
(Raja, fig. 1948) ; or right and left
veins may be continuous across
the pelvie cartilage (Mustelus
antarcticus, fig. 1944; Scylliwm
canicula). Posteriorly a rectal
branch joins the lateral abdomi-
nal of Scyllium near the midven-
tral line. The first important trib-
utary (or tributaries) to the lat-
eral abdominal system of veins is
the iliac, resulting from a fusion
of the cloacal and femoral veins
from the cloacal and pelvic areas,
respectively (Mustelus, fig. 1944).
In certain forms the cloacal and
femoral veins join the lateral
abdominal independently, as in
Heptanchus. In Raja an acces-
sory femoral vein also empties
into the lateral abdominal (fig.
1948). The femoral veins (f.v.)
are formed in the pelvie fin from
numerous veinlets, while the cloa-
eal veins (cl.v.) drain the sides of Fig. 196. Veins of pectoral fin, Acanthias. (From
the cloacal region. ee Phe oie

Blood collected from the deeper Ree ene pterygial vein; m.p.v., medial
structures in the posterior region,
then, whether from the cloaca or the pelvic fin, is carried forward by the
lateral abdominal vessel. As this vessel passes anteriorly many veins from
the body wall enter it.

At the pectoral girdle the lateral abdominal vein receives important tribu-
taries. The first of these is the brachial vein. In the sharks the brachial arises
from the union of a dorsal, a median pterygial (m.p.v., fig. 196), and a lateral
pterygial vein (l.p.v.) of the fin. In rays where the pectoral fin is large in
extent, a much larger median pterygial branch is present and is joined by
the smaller lateral, ventral vein. In addition a large anterior branch from the

214 THE ELASMOBRANCH FISHES

propterygium joins the lateral abdominal vein independent of the brachial
(Raia erinacea, fig. 1948). In Raja nasuta two independent brachial branches
join the lateral vein.

In Heptanchus it was seen that the subscapular vein (s.sc.v., fig. 187) is an
important tributary of the lateral abdominal, emptying, in common with the
brachial as a brachioscapular vessel, blood from the pectoral girdle and from
the lateral cutaneous vessel. In Mustelus henlei a short subscapular trunk
joins the brachial but all blood from the lateral cutaneous reaches the heart
through the posteardinal. Squalus
sucklu is of interest as a type
which actually bridges these two
extremes. In it the lateral abdom-
inal (l.a.v., fig. 197), just before
entering the duct of Cuvier, re-
celves the brachioscapular trunk
which ineludes the subscapular
vein (s.sc.v.). Now the subseapu-
lar vein dorsally comes in contact
with, and has an opening into,

Fig. 197. Di ae : Paes the posteardinal sinus (p.c.s.).
ig. 197. Diagram of relations of postcardina ; ;
to lateral abdominal system, Squalus sucklit. The lateral cutaneous vein (1.c.v.)

br.v., brachial vein; b.s.c., brachioscapular; empties into the subscapular near
eats, goraeold vein; Ze, duet of Cuvier; Lat the union of the subseapular with
vein; p.c.s., posteardinal sinus; s.cl.v., subclavian the posteardinal sinus, so that the
vein; $.s¢.v., subscapular. blood from the lateral cutaneous
vein after entering the subscapular may pass dorsally into the postecardinal
sinus or ventrally into the lateral abdominal vein. In other words, if the sub-
scapular vein of Squalus sucklii had no connection with the posteardinal sinus,
Squalus would be in all essentials of the type of Heptanchus. If, however, that
segment of the subscapular between the entrance of the lateral cutaneous
(l.c.v., fig. 197) and the brachial vein (br.v.) were dropped out, then the
lateral cutaneous would be independent of the lateral abdominal system and
the type would be like that of Mustelus or Scyllium.

After receiving the brachioscapular trunk (brachial and subscapular), the
lateral abdominal vein as the subelavian (s.cl.v.) turns sharply upward in the
pericardio-peritoneal wall and across the scapular cartilage to empty into the
duct of Cuvier (d.c.) asin Heptanchus.

The history of the lateral abdominal system is of interest. In origin it is one
of the earliest of the systems to appear. Furthermore it occupies a position
which would have been of particular value had a lateral fin-fold been present,
for such a vessel would have drained this fold directly as it does those parts
of the fold which remain, that is, the paired fins.

The lateral abdominal vein has often been considered in relation to the
ventral abdominal vein of the amphibians which in its anterior and posterior
sections drains the paired appendages, but in the middle region is a single

THE ELASMOBRANCH FISHES 215

ventral vessel. Anteriorly, in the embryonic amphibian, it enters the duct of
Cuvier, but later, by secondary twigs, it comes to empty directly into the liver.
From these characteristics it appears likely that the ventral abdominal in
Amphibia is homologous with the lateral abdominal of Elasmobranchs.

VEINS OF HEART

Three sets of vessels return blood, distributed by the coronary arteries, from
the heart itself. These are a small right coronary, a median cardiac vein, and a
larger left coronary vein. These veins enter the sinus venosus, near the sinu-
auricular opening, usually by two or more apertures. The right and left
systems in Acanthias, however, join and empty into the sinus venosus by a
single large aperture.

Fig. 198. Cutaneous system of veins, Squalus sucklii. (Helen Hopkins, orig. )

ed.v., caudal vein; l.c.v. and /.¢.v.1, superior and inferior lateral cutaneous veins; ‘m.v.,
median vein; p.c., postcardinal vein; p.d.c., posterior dorsal cutaneous vein; p.v.c., posterior
ventral cutaneous; s.sc.v., subscapular vein.

The right coronary may drain the right side of the ventricle and the dorsal
side of the conus (Carcharias littoralis), emptying into the sinus venosus by
its own aperture at the right side of the sinu-auricular opening; or the right
may arise as two vessels on the dorsal and ventral sides of the conus and on the
ventral side of the ventricle. These two continue separately and open inde-
pendently (Rava erinacea). The left coronary in Raia erinacea is of consider-
able size and drains the ventral and lateral parts of the ventricle. In other
forms it is a vessel of importance (Carcharias littoralis, Cetorhinus, Scyl-
lium), draining the ventral and lateral parts of the ventricle.

The cardiac veins drain the dorsal part of the ventricular wall. They may
form as a double vessel and unite to enter the sinus venosus with the left
coronary (Carcharias littoralis), or they may empty independently into the
sinus venosus by a half-dozen smaller mouths (Raja rubens). In Raia erinacea
numerous vessels receive blood from the large triangular area lying parallel
to the posterior margin of the sinus venosus and empty it directly into the
sinus venosus.

The vessels of Thebesius in the Elasmobranchs, according to Parker and
Davis (1899), are deep in the walls of the heart and are connected with the
coronary veins. They may be detected by immersing the heart in water and

216 THE ELASMOBRANCH FISHES

then inflating the left coronary vein with a blow pipe, whereupon bubbles of
air emerge from the left atrial wall into the atrium (Acanthias). No bubbles,
however, appear upon the inflation of the right coronary vein. The same may

Fig. 1994. Veins of, and in the region of, first dorsal fin, Squalus sucklii. (LL. H. Bennett,
orig.)

c., vein connecting dorsal and lateral cutaneous systems; c¢.v., vena circularis; d.c., dorsal
cutaneous vein; dfv., vein draining dorsal fin.

be demonstrated in the coronary arteries but with more difficulty. In Rava
erinacea by inflating either right or left vein a similar bubbling occurs from
the inner surface of the atrium, although none occurs from the ventricle. In
the Elasmobranchs, then, the superfi-
cial veins of the heart empty into the
sinus venosus and the deeper Thebesian
vessels enter the atrium direct.

CUTANEOUS SYSTEM OF VEINS

The cutaneous veins consist of the dor-
sal, ventral, and lateral vessels of the
skin.

The dorsal cutaneous vein collects
blood from the skin on the back
(Squalus suckli, fig. 198, p.d.c.). It ex-
tends along the middorsal line from the
caudal fin to the endolymphatic duets,
and surrounds both dorsal fins in closed
loops (c.v., fig. 1994). Posterior to the
loop surrounding the first dorsal in
Mustelus antarcticus according to T. J.
Fig. 1998. Cutaneous veins in region of Parker (1886) a median vein passes
cloaca, Squalus sucklii. (Edith Stoker, i
orig.) downward to the left of the column to

l.a.v., lateral abdominal vein; p.c., post- join the left renal portal. This is essen-
cloacal segment of ventral cutaneous; pl. tially the condition found. in Squalus

pelvie vein from ventral cutaneous to : ;
sinus (s.). except that this deep vessel arises as a

THE ELASMOBRANCH FISHES 217

double vein the parts of which later unite to form the vena profunda of Mayer.
Further, in Squalus the vena profunda joins the posteardinal vein. In Mus-
telus henlei if the deep vessel passes to the right of the column it breaks up
in a leash of vessels and may join the renal portal vein. In Heptanchus macu-
latus a similar vessel in the region of the single dorsal fin, which is comparable
to the second dorsal fin of Squalus, passes to the right of the column and joins
the caudal vein. The vena profunda of the second dorsal loop in Squalus and
in Mustelus henlet joins the caudal vein.

The lateral cutaneous veins (l.c.v., fig. 198) accompany the lateral line sys-
tem, the main trunk of the lateral cutaneous passing just mediad of and ven-
tral to the lateral line. They collect blood from dorsal and ventral branches
to the corium and underlying connective tissue and empty anteriorly into the
subscapular sinus (s.sc.v.), which in turn enters the posteardinal sinus except
in types hke Heptanchus. A system of cross-trunks in the regions of the dorsal
fins puts the lateral cutaneous in connection with the dorsal cutaneous vein
(c., fig. 1994). In a number of Elasmobranchs (Squalus sucklu, fig. 198) an
accessory lateral cutaneous vein (l.c.v.') extends from the pelvic to the pec-
toral segments, parallel with the lateral cutaneous proper. This vessel has
segmental connections with the lateral cutaneous above it and the ventral
cutaneous below it.

The ventral cutaneous vein is divided into pre- and posteloacal parts
(p.v.c.). The precloacal part, not shown in figure 199B, extends as an unpaired
median vein between the pelvic and pectoral regions. In the region of the
pectoral it bifureates, sending a right and a left branch to the lateral abdomi-
nal vein. These branches seem to be the same as those which I deseribed for
Heptanchus maculatus as the coracoid veins (Daniel, 1918). Posteriorly in the
pelvic area, the vessel also divides (pl., fig. 1998). Here its right and left
branches in Squalus sucklii empty into a sinus (s.), from which the blood
enters the lateral abdominal vein (l.a.v.).

The posteloaeal division of the ventral cutaneous extends from the tail to
the cloacal area. It arises as a pair of vessels on the right and left sides of the
caudal fin, which do not meet around the tip of the ventral lobe of the fin. These
vessels communicate with the caudal vein. If an anal fin be present (Scylliwm)
the ventral cutaneous forms a loop around the anal fin and then extends to
the cloaca (p.c., fig. 1998), bifureating into right and left branches. The blood
collected by this vein also passes into the sinus (s.) and thence into the lateral
abdominal system.

NATURE OF CUTANEOUS SYSTEM OF VESSELS

It was early observed that the cutaneous vessels in Elasmobranchs are not
accompanied by arterial trunks. From this fact it was argued that they are
not blood vessels but are lymphatic in nature. Work done by Miss Coles (1928)
in this laboratory, however, showed that while no longitudinal arterial trunks
accompany these vessels in Squalus sucklu, yet they are provided with a rich
arterial supply which is given off by branches from the segmental arteries.

218 THE ELASMOBRANCH FISHES

Moreover, Burne (1923) has shown for Lamna that well marked cutaneous
arteries do accompany some of these veins. Parker (1886) called attention to
the presence of blood in these vessels and Mayer (1888) proved that they are
provided with valves. Furthermore, the cutaneous vessels are put into direct
connection with the deeper veins, for example, the caudal vein. Also, Mayer
reported the circulation of blood in these vessels in a semitransparent embryo.

All the above points made it likely that these vessels are true blood-vessels.
The actual proof that they are haemal and not lymphatic in nature was made
by Edith Stoker (see Daniel and Stoker, 1927) in the following way. The
shark was first anaesthetized and a glass canula was inserted into a cut
through the lateral cutaneous vessel. In this experiment the blood will cireu-
late through the canula, demonstrating that the vessels are for the circulation
of blood.

LyMPHATIC VESSELS

Lymphatic vessels have been difficult to demonstrate in Elasmobranchs.
Within recent years, however, Hoyer (1928) has succeeded in injecting these
vessels, and reports that they have the following arrangement. Right and left
trunks (thoracic ducts) accompany the dorsal aorta from the tip of the tail
to the head. These trunks collect lymph from the muscles of the tail and trunk
through tiny branches which run with the intersegmental arteries. They re-
ceive lymph from other vessels which run with the arteries and veins along
the myosepta and the longitudinal septa separating dorsal and ventral
bundles. A net of these vessels is present under the peritoneum and over the
kidney. Lymphatics from the intestine unite in a plexus at the base of the
mesentery and these plexuses are put into connection with the thoracic ducts
through cross-trunks. In addition to these right and left ducts in the tail and
trunk, there are two jugular trunks in the area of the head and pharynx,
which accompany and finally enter the cardinal sinuses. Further, acecompany-
ing the subclavian arteries there are two branches which also enter the eardi-
nal sinuses.

1878

1923.
1918.

1927.

1931.

1833.

1887.

1893.

1906.

1893.

1901.

1859.

1910.

1785.
1900.

1914.

1928.

1881.

1899.
1892.

1905.

THE ELASMOBRANCH FISHES 219

BIBLIOGRAPHY

Cuapter VIII

. Batrour, F. M., A Monograph on the Development of Elasmobranch Fishes. London,
pp. 1-295, 9 pls., 9 text figs.

Burnge, R. H. (see p. 195).

DANIEL, J. FRANK, The Subclavian Vein and Its Relations in Elasmobranch Fishes.
Univ. Calif. Publ. Zool., Vol. 18, pp. 479-484, 2 text figs.

DANIEL, J. FRANK, and SToKER, Epiru, The Relations and Nature of the Cutaneous
Vessels in Selachian Fishes. Univ. Calif. Publ. Zool., Vol. 31, pp. 1-6, 4 text figs.
DANIEL, J. FRANK, and BENNETT, L. H., Veins in the Roof of the Buccopharyngeal
Cavity of Squalus sucklii. Univ. Calif. Publ. Zool., Vol. 31, pp. 35—40, 3 text figs.
Duvernoy, G. L., Sur quelques particularités du systéme sanguin abdominal et du
canal alimentaire de piusieurs poissons cartilagineux. Ann. Sci. Nat. Zool., Vol. III
(1835), Sér. 2, pp. 274-281, pls. 10-11.

HocuHSsTEtTtTeER, F., Beitrige zur vergleichenden Anatomie und Entwicklungsgeschichte
des Venensystems der Amphibien und Fische. Morph. Jahrb., Bd. 13, pp. 119-172,
pls. 2-4, 7 text figs.

Hocustetter, F., Entwicklung des Venensystems der Wirbeltiere. Ergebn. d. Anat.
u. Entwick., Bd. 3, pp. 460-489, 24 text figs.

Hocustettrer, F., Die Entwicklung des Blutgefassystems. Hertwig’s Handb. vergl.
u. expt. Entwick., Bd. 3, Teil 2, p. 116.

HorrMan, C. K., Zur Entwicklungsgeschichte des Venensystems bei den Selachiern.
Morph. Jahrb., Bd. 20, pp. 289-304, pl. 12.

HorMaNN, Max, Zur vergleichenden Anatomie der Gehirn- und Riickenmarksvenen
der Vertebraten. Zeitschr. Morph. u. Anthropol., Bd. 3, pp. 239-299, pls. 16-20, 6
text figs.

JOURDAIN, S., Recherches sur la veine port rénale. Ann. Sci. Nat., T. 12 (Sér. 4), pp.
134-188, 321-369, 5 pls.

LaFiTE-Dupont, Sur le développement de la paroi des sinus veineux des poissons car-
tilagineux. (Réun. biol. Bordeaux.) C.R. Soe. Biol. Paris, T. 68, p. 694.

Mowrok, A., The Structure and Physiology of Fishes. Edinburgh, 128 pp., 44 pls.
NeEuviLuE, H., Note préliminaire sur l’endothelium des veines intestinales chez les
Sélaciens. Bull. Mus. Hist. Nat., No. 6, pp. 71-72.

O’DonocHuE, C. H., Notes on the Circulatory System of Elasmobranchs. I. The Ve-
nous System of the Dogfish (Seyllium canicula). Proce. Zool. Soe. Lond., 1914, pp.
435-455, pls. 1-2, text figs, 1-4.

O’DonoGHuE, C. H., and ABBOTT, EILEEN (see p. 197).

ParkeER, T. J., On the Venous System of the Skate (Raja nasuta). Trans. N. Z. Inst.,
Vol. 13, pp. 413-418, pl. 15.

PaRKER, G. H., and Davis, F. K. (see p. 197).

Ras, C., Ueber die Entwicklung des Venensystems der Selachier. Festschr. z. 70.
Geburtstag R. Leuckarts, pp. 228-235, 3 text figs.

Ranp, H. W., The Skate as a Subject for Classes in Comparative Anatomy; Injec-
tion Methods. Amer. Nat., Vol. 39, pp. 365-379, 1 text fig.

Ranp, H. W., and Unricn, J. L., Posterior Connections of the Lateral Vein of the
Skate. Am. Nat., Vol. 39, pp. 349-364, 5 text figs.

220

1891.

1845.

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ig alas

1902.

1908.

1906.

1928.

THE ELASMOBRANCH FISHES

Rex, H. Beitrige zur Morphologie der Hirnvenen der Elasmobranchier. Morph. Jahrb.,
Bd. 17, pp. 417-466, Taf. 25-27.

Rosin, Cu., Le Systéme veineux des poissons cartilagineux. C.R. Acad. Sci. Paris, T.
21, pp. 12-82.

Rosin, CH., Note sur le systeme lymphatique des Raies et des Squales. L’ Institut Paris,
T. 13, pp. 144-145, 232-233.

Rosin, Cu., Mémoire sur les dispositions anatomiques des lymphatiques des Torpilles,
comparées a celle qu’ils présentent chez les autres Plagiostomes. C.R. Acad. Sci. Paris,
T. 64, pp. 20-24.

ScamMon, R., Normal Plates of the Development of Squalus acanthias. Normenta-
feln z. Entw. d. Wirbel., Heft 12, pp. 1-123, 4 pls., 25 text figs.

VIALLETON, L., Les Lymphatiques du tube digestif de la Torpille (Torpedo marmo-
rata, Risso). Arch. d’Anat. micr., T. 5, pp. 378-456, pls. 13-14.

WiIpDAKowIcH, V., Wie gelangt das Hi der Plagiostomen in den Hileiter? Ein Beitrag
zur Kenntnis des Venensystems von Scyllium canicula. Zeitschr. wiss. Zool., Bd. 91,
pp. 640-662, Taf. 29, 2 text figs.

WooDLAND, W., A Suggestion concerning the Origin and Significance of the Renal-

portal System, with an Appendix relating to the Production of the Subabdom-
inal Veins. Proce. Zool. Soe. London, 1906 (2), pp. 886-901, 1 text fig.

LYMPHATICS

Hoyer, Henry, On the Lymphatic Vessels of Scyllium canicula. Anat. Record, Vol. 40,
pp. 143-145.

Hoyer, Henry, Recherches sur les vaisseaux lymphatiques des Sélaciens. Bull.
Internat. Acad. Polon. Sci. et Lett. el. Sci. (Math.-Natur. B), pp. 79-104, pls. 7-10.

Fig. 200A. The brain and associated sense organs, Heptanchus maculatus, dorsal view.
(Dunean Dunning, del.)

bu.VII, buccal branch of facial nerve; cb., cerebellum; cl., ciliary nerve; e.r., restiform
body; di., diencephalon; hmd., hyomandibular division of the facial nerve; i./., inferior
lobe; md.V’, mandibular division of the fifth nerve; m.n., median olfactory nucleus; med.,
medulla; ms., mesencephalon ; ma.V, maxillary division of trigeminal nerve; ol.b., olfactory
bulb; ol.l., olfactory lobe; ol.t., olfactory tract; op.l., optic lobe; op.V, ophthalmicus pro-
fundus division of the trigeminal nerve; os.V and VII, ophthalmicus superficialis of tri-
geminal and facial nerves; ¢/., telencephalon; tn., terminal nerve; v.s., vascular sac; w-z,
occipitospinal nerves; I, olfactory nerve; IJ, optic nerve; JIJ, oculomotor or third nerve;
IV, trochlearis or fourth cranial nerve; lJ, abducens or sixth cranial nerve; VIII, auditory
or eighth cranial nerve; 1X, glossopharyngeal nerve; XY, vagus nerve.

NERVOUS SYSTEM
NERVOUS SYSTEM OF HEPTANCHUS MACULATUS
CENTRAL NERVOUS SYSTEM

BRAIN

The brain of Heptanchus maculatus may be described as made up of five
divisions, as is common for the Elasmobranchs. These divisions, beginning
anteriorly are: the telencephalon, the diencephalon, the mesencephalon, the
metencephalon, and the myelencephalon.

The telencephalon (t1., fig. 2004) ,if seen »
from the dorsal side, appears as a bilobed lar 4
mass which is continued forward by long
olfactory tracts (ol.t.). Between the tracts
and projecting slightly anteriorly is the
median olfactory nucleus (m.n.), better
seen in ventral view (fig. 200B). Dorsally
the telencephaion is raised up into the so-
called pallial eminences. At the angle be-
tween the median olfactory nucleus and
the pallial eminence is the recessus neuro-
poricus, at the sides of which arises the
terminal nerve (tn.). The telencephalon
is continued posteriorly by the diencepha-
lon (di., fig. 200s).

The diencephalon is provided with a
thin roof through which the pineal stalk
passes as a Slender thread upward and
forward to the cartilaginous roof. This
segment of the brain continues posteriorly
as a gradually narrowing mass back to the
place where the optic nerves (JZ) form
the optic chiasma. From the posterior and
ventral part of this division arises the in- Fee DOORS Bee Mieandl- chante ieneeree:
fundibulum, at the sides of which are the Heptanchus maculatus, ventral view.
inferior lobes (i.J.) and the vascular sacs F'" ¢xplanation see fig. 200a.

(v.s.) of the brain. In the middle line and ventral to the vaseular sacs are the
lobes of the pituitary (see fig. 215).

The mesencephalon is well developed (ms., fig. 200B). Dorsally it consists of
two hollow optic lobes (op.l., fig. 2004) or corpora bigemina. These in their
posterior part are overlapped by the cerebellum (cb.) and ventrally by the
infundibulum and its associated structures. Through the posterior roof of

[221]

222 THE ELASMOBRANCH FISHES

the mesencephalon and near the cerebellum the fourth cranial or trochlear
nerve arises (IV). Ventrally the mesensephalon is composed of large fiber
tracts through which the third cranial or oculomotor nerve (J77) emerges and
passes forward to muscles of the eye.

The metencephalon consists, in large part, of the cerebellum (cb.), a large
shield-shaped mass, separated dorsally into right and left halves by a median
groove. The cerebellum extends anteriorly over the posterior half of the optic
lobes, and posteriorly it overlies the fol-
lowing division of the brain. Ventrally
and under the cerebellum are heavy fiber
tracts which also belong to the segment
of the metencephalon.

The myelencephalon is the last seg-
ment of the brain. It comprises the me-
dulla oblongata (med.) which from above
extends upward on each side almost to
Bee sure Goreccivon ler cord aaen: the tip of the cerebellum as the resti-
tanchus cinereus. (From Sterzi.) (Grey form bodies (corpora restiforme, c.r.).
Dee) Back of the restiform bodies the medulla

d.h., dorsal horn; v.h., ventral horn. : :

grows smaller and smaller in diameter
until it joins the cord. Within the myelencephalon and the metencephalon is
the fourth ventricle which is covered over by a thin roof. The myelencephalon
gives rise to all the cranial nerves back of the fourth.

SPINAL CORD

The spinal cord extends from the medulla practically to the tip of the tail.
Externally, as is seen in figure 201, it presents no evidence of a dorsal or a
ventral groove which in some Elasmobranchs (see fig. 2178) may mark the
boundaries of the cord into right and left halves. Superficially the cord con-
sists of numerous fiber tracts surrounding masses of nerve cells.

In the section (fig. 201) the central, more solid part of the cord constitutes
the grey matter (cells) roughly in the form of an X, the upper arms of which
are the dorsal horns (d.h.) and the lower arms, the ventral horns (v.h.) of the
cord. The less conspicuous dorsal horns lie near the middorsal line, while the
ventral horns extend outward and downward as an expanded mass on each
side. Furthermore there is a median ventral mass extending toward the mid-
ventral line from the union of the ventral horns. Where the crossing of the X
takes place there is a considerable thickening, in which is located the neuro-
coele or cavity of the spinal cord. It will be observed that the neurocoele is
practically at the middle of the section and is circular in outline.

PERIPHERAL NERVOUS SYSTEM

The cranial and spinal nerves arising from the central nervous system per-
forate the cranium and spinal column respectively. Also perforating the era-
nium but back of the last cranial nerve are certain accessory nerves.

THE ELASMOBRANCH FISHES 223

CRANIAL NERVES

The first cranial or olfactory nerve has its end organs in the mucous membrane
of the olfactory organ. The nerve passes backward in two short bundles, one
median and the other lateral in position (J, fig. 2004) to the olfactory bulbs
(ol.b.) The bulbs are joined to the olfactory lobes (ol.l.) of the brain by means
of long olfactory tracts (ol.t.).

Running parallel with this tract is the terminal nerve (fn.), which in Hep-
tanchus arises near the recessus neuroporicus and passes along the tract as a
slender strand. Near the olfactory bulb it runs laterad and enters the fissure
dorsally between the lateral and median divisions of the olfactory nerve. To
the median nerve it gives an exceedingly slender strand and continues with
the lateral division of the nerve, finally reaching the mucous membrane of
the cup.

The second or optic nerve (JJ, figs. 2004 and 2008) has its origin from the
retina of the eye. Asa thick stem it passes inward, crosses in the optic chiasma,
and enters the diencephalon.

The third cranial nerve or oculomotor (J//) springs from the ventral side
of the midbrain and passes to muscles of the eye. In the orbit it divides so as to
supply branches to the inferior, the superior, and the anterior rectus, and
to the inferior oblique muscles of the eye.

The trochlearis or fourth nerve (JV) also arises from the mesencephalon,
but the fibers perforate the roof of the brain instead of the floor. The fibers
then as a small band pass under the overhanging cerebellum and down over the
mesencephalon forward and outward to the superior oblique muscle of the eye.

The trigeminal or fifth cranial nerve in Heptanchus maculatus arises from
the brain in common with, but slightly anterior and ventral to, the seventh
nerve. A short distance from its origin it separates into its main branches.
The first of these nerves, the ophthalmicus profundus (op. V, fig. 2004), runs
to the median side of the eyeball. Before reaching the latter, however, it
gives off the ciliary branch (cl.) to the eye; it then perforates the cartilagi-
nous capsule surrounding the eyeball and continues forward under the supe-
rior rectus, next emerging from the cartilage to pass forward under the ante-
rior rectus muscles and between the superior and inferior obliques. It leaves
the orbit by a separate foramen, and finally breaks up in the skin over the
nasal capsule. The ophthalmicus superficialis of the fifth (os.V) is a small
branch or branches running with the ophthalmicus superficialis of the seventh
nerve. The maxillary branch (mz.V, fig. 2004) of the trigeminal breaks up
into three or four main divisions which go to supply the region of the upper
jaw; while the mandibular division of the fifth (md.V) passes backward and
downward around the angle of the mouth to the mandibular region.

The abducens or sixth nerve (VJ, fig. 2008), after leaving the midventral
line of the myelencephalon back of the fifth-seventh complex, passes under the

224 THE ELASMOBRANCH FISHES

main stems of this complex and out from the cranium through its own fora-
men. It enters the base of the external rectus muscle.

The facial or seventh cranial nerve like the fifth is composed of four im-
portant branches. These are first the superficial ophthalmic nerve (os.VIJ,
figs. 2004 and 2008) which runs above all the eye muscles through the orbit,
gives branches dorsally to the supraorbital sensory canal, and then leaves the
orbit by the large anterodorsal ophthalmic foramen (f.0.VII, fig. 47). Out-
side of the orbit it supplies branches to the supraorbital canal and to certain
groups of the ampullae of Lorenzini. The second or bueeal division of the

Fig. 202. Branches of the facial nerve, Heptanchus maculatus. (W. R. Dennes, orig.)

bu.VII, bucealis of facial; ¢.t., chorda tympani; hmd., hyomandibular (postspiracular)
division of seventh nerve; md.e., superior and inferior branches of external mandibularis of
seventh; md.i., internal division of mandibularis of seventh; os.VII, ophthalmicus super-
ficialis of seventh nerve; pl.V II, palatinus; po.s., postspiracular twigs; pr.s., prespiracular
nerve; sp., spiracle.

facial nerve (bu.VIT) passes from the brain stem just dorsal to the maxillary
division of the fifth (maz.V). In the orbit it divides much like the maxillary
division of the fifth. It goes to supply the infraorbital canal and the ophthal-
mie and bueeal groups of ampullae. The palatine division of the seventh
(pl. VIT, fig. 202) leaves the main stem of the hyomandibular nerve and passes
ventralward, dividing into an anterior and a posterior branch, to the palate
of the mouth. The most posterior division of the facial, the hyomandibular
(hmd., figs. 2004 and 202), after giving off the palatine branch, passes
sharply backward around the spiracle, downward around the angle of the
jaw and forward along the mandible. It first gives a prespiracular branch
(pr.s., fig. 202) to the anterior wall of the spiracle; other twigs (po.s.) are
next given off to the posterior wall of the spiracle. Back of the angle of the
jaw a superficial branch runs forward toward the angle of the Jaw, and two
branches (md.e.) pass along the external side of the mandible to the hyoman-
dibular canal and mandibular groove (hme. and mg., fig. 228). A deep branch
(md.i., fig. 202) given off at the angle runs along the body of the hyoid, and
another branch, the chorda tympani (c.t.), passes forward between the hyoid
and the mandible.

The auditory or eighth nerve in Heptanchus (VIII, figs. 2004 and 200s) is
more or less clearly separated from the seventh. It has a large ganglion from

THE ELASMOBRANCH FISHES 223

which run two main branches; the anterior branch passes outward and divides
into two divisions; the other passes backward and separates into numerous
twigs. This nerve supplies the ampullae of the semicircular canals and sends
divisions to other parts of the ear.

The glossopharyngeal or ninth nerve (LX, figs. 200a and 203) arises back
of the sixth and farther from the middle line and passes posteriorly under
the floor of the auditory capsule. Before reaching the surface it gives off a
branch (st.LX, fig. 203) from which supratemporal branches are sent off pre-
sumably to the anterior segment of the lateral line canal. Another branch
(dr.IX) passes upward and backward from the supratemporal but its desti-
nation has not been determined. After leaving the cranium the glossopharyn-
geal bears a ganglion (gn.) dorsal to the first branchial cleft, from which pro-
ceeds the main pretrematicus nerve (prt.) ; this nerve runs down the hyoidean
demibranch in front of the first gill pocket. A pharyngeal branch (ph.LY)
arises from the ganglion over the dorsal angle of the first cleft and passes for-
ward to supply the dorsal pharyngeal wall. From the pharyngeal in Hep-
tanchus maculatus there is given off an internal pretrematic (prt.i.). The
third division of the nerve is the post-trematicus (po.t.) which passes back
of the first cleft, in the anterior demibranch of the first whole gill. In Hep-
tanchus maculatus the post-trematicus is divided into two distinct bundles,
of which the anterior is sensory and the posterior is mixed. The posterior
branch of the post-trematicus continues to the ventral pharyngeal region,
supplying motor branches to muscles and sensory fibers to the mucous mem-
brane. One of its sensory branches curves forward and runs dorsally past the
end of the anterior sensory root.

The vagus or tenth cranial nerve (X, figs. 2004 and 2008) leaves the brain
stem by a number of roots. Some of these roots arise ventrally close to the
origin of the ninth. Others arise in a ecrescentic line from this almost to the
middorsal line. The nerve leaves the cranium through a large foramen and
outside appears in three main divisions. One of these, the lateralis nerve (l1.X,
fig. 203), supplies the lateral line and extends practically to the tip of the
tail. The branchial divisions (br.X'~°) ,consisting of six nerves, pass backward
and then ventrally to supply the gill area not supplied by the glossopharyn-
geal; while the third division, the visceral (bi.X ), passes on to the viscera.

The lateralis nerve (lJ. ) is the most anterior bundle of the vagus arising
from the brain (figs. 2004 and 200B). It continues backward more or less
separate and distinct even in the canal where it gives off two branches, one of
which (st.X, fig. 203) passes to the supratemporal and lateral sensory canals,
the other (dr.X ) being distributed to the area of the pit organs along the back.
The lateralis then runs along the wall of the anterior cardinal sinus and
finally passes posteriorly between the dorsal and lateral bundles giving off
branches to the lateral line.

The branchial nerves to the gills (b7.X*°) lie in the floor of the anterior
cardinal sinus. Distal to their ganglia each of these nerves comprises the same
number of parts as the ninth, pretrematicus, post-trematicus, and pharyngeal

THE ELASMOBRANCH FISHES

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THE ELASMOBRANCH FISHES 227

branches. The pharyngeal is unlike that of the ninth only in that it first passes
posteriorly and then curves forward. The nerves posterior to the seventh cleft
have undergone considerable change. The third division of the vagus, the
ramus intestinalis (b7.Y), breaks up into a number of important divisions,
some of which go to the heart, others to the oesophagus, and still others to the
stomach and associated parts.

OCCIPITOSPINAL NERVES

Arising posterior to the vagus are certain small nerves known as the oceipi-
tospinales (w-z, figs. 200a. 200B, and 204). These nerves are unusually numer-
ous in Heptanchus and con-

sist of both ventral and eA \ \l pe
dorsal branches. The first \ vt pdr.
pair to arise ventrally (w, = y. SR

fig. 200B) is near the mid- A ;

ventral line and not unlike

the sixth or abducens nerve
in origin. Posterior to this

are three others (2, y, 2), br.p
making in all four ventral ee
pairs. Dorsally in Heptan- Fig. 204. Cervical and brachial plexus, Heptanchus

cinereus. (From Max Fiirbringer.)
chus maculatus (fig. 200A ) br.p., brachial plexus; cr.p., cervical plexus; d.r., dor-
there are two pairs, the first sal or sensory nerve; g.,dorsal root ganglion; sp.,spinal
(mixed) nerve; v.r., ventral or motor nerve; w, 2, Y, 2,
occipitospinal nerves.

-Sp.

of which joins the “y” divi-
sion ot the ventral nerve.
These nerves supply the subspinalis and dorsal interarcuales muscles (fig.
204) and are like the spinal nerves with which x, y, and z form a plexus.

SPINAL NERVES

A spinal nerve arising from the spinal cord in Heptanchus cinereus (M.
Fiirbringer, 1897) is composed of a single ventral (motor) and a dorsal
(sensory) root. The ventral root comes from cells in the ventral horn of the
coré (v.h., fig. 201) and passes outward to be joined by the dorsal root (fig.
204); while the dorsal root extends to the dorsal horn of the cord (d.h., fig.
201) through the dorsal root ganglion (4., fig. 204). After the union of dorsal
and ventral divisions the mixed nerves thus formed, in the region of the neck
and the pectoral and pelvic fins, are pressed together.

The cervical (cr.p., fig. 204) and pectoral plexuses (br.p.) may be consid-
ered together since they form a continuous bundle. In Heptanchus cinereus
these plexuses (fig. 204) are made up of the first seven spinal nerves together
with occipitospinales which were above mentioned. At the region of the scapula
the nerve trunk separates, the cervical nerves (c7r.p.) going to the hypobran-
chial or ventral longitudinal muscles, and the pectoral plexus (b7.p.) to the
pectoral fin.

228 THE ELASMOBRANCH FISHES

Beginning with the twenty-fifth spinal nerve (sp. 25, fig. 205), the terminal
divisions of some of the spinal nerves are connected at the region of the lateral
abdominal vein (/.a.v.) into a nervous collector. This in Heptanchus cinereus
as described by Braus (1898) forms a collector of unusual length, which
continues to the thirty-eighth spinal nerve (sp. 38), but does not perforate
the cartilage of the pelvie girdle.

Posterior to the pelvic girdle a pelvic plexus of nerves (pl.p., fig. 205) is also
found in Heptanchus. This plexus in the adult Heptanchus cinereus usually
involves only the forty-eighth and forty-ninth nerves, and the plexus thus
formed is considerably back of the pelvie girdle.

Fig. 205. Nervous collector, Heptanchus cinereus. (From Braus.)

l.a., lateral artery; l.a.v., lateral abdominal vein; pl.p., pelvic plexus; sp. 25, 38, twenty-
fifth and thirty-eighth spinal nerves.

Fig. 206. A multipolar motor cell. (From Houser. )

a.x., axone; dt., dendrite; 7., nucleus; nu., nucleolus.

THE ELASMOBRANCH FISHES 229

NERVOUS SYSTEM OF ELASMOBRANCHS IN GENERAL

The central nervous system, comprising the brain and the spinal cord, is com-
posed of neurones. A neurone consists of a nerve cell from which proceed the
axone and dendrites. The nerve cells themselves are of three general types.
One of these is a multipolar cell (fig. 206) with numerous dendritic processes

Fig. 207 Fig. 208
Fig. 207. Bipolar cells of cord, Pristiurus. (Modified from Von Lenhossék. )

a-c., stages in development of a bipolar cell; ax., axone or fiber; c., adult type of cell;
d.r., dorsal root; g., dorsal root ganglion.

Fig. 208. Supporting elements, Mustelus canis. (From Houser.) A. Neurogleal cell. B.
Ependymal cell.

(dt.) an axone (axz.), and a large nucleus (n.); another is the bipolar type
with two processes to the cell body. Figure 207 shows the development of
some bipolar cells in the dorsal root ganglion of Pristiurus. An early stage (a)
shows the two processes, one of which, the axone proper, passes in toward the
cord; the other process extends toward the periphery. Stage (c) shows the
union of the two processes to form the stem of a T. In this stage the cell appears
to be unipolar or with a single process extending from it.

In addition to the cells and fibers found in the central nervous system, cer-
tain supporting elements are also present. The first of these are the ependymal

230 THE ELASMOBRANCH FISHES

eells (fig. 2088) which are modifications of the cells bounding the central canal
or neurocoele. The processes from these cells often reach entirely across to
the external margin of the cord. The second type of supporting cell is the
neurogleal cell which may take the form shown in figure 208a, or its processes
may be long.

DEVELOPMENT OF CENTRAL NERVOUS SYSTEM

In its origin the nervous system is laid down as a flattened, horseshoe-shaped
plate of cells, of ectodermal origin, which later becomes spatulate (fig. 209).
The broad end of the spatula, which will later form the brain, differs consider-
ably from the narrower handle which is the
rudiment of the spinal cord. The margins of the
plate (n.f., fig. 209) fold up and the whole
plate then sinks down along the middorsal line.
In the region of the brain, where the plate
widens, the lips of the plate close slowly; but in
the region of the cord the closure goes on with
more rapidity. Even before the closure of the
plate, however, outpocketings to form the primi-
tive optic vesicles (op.v.) appear. The plate
then closes into a tube, the point at which
closure last takes place remaining as the neuro-
pore (np., fig. 212).
The tube thus formed is divided into the
- primitive forebrain, the midbrain, and the
Fig. 209. Development of medul- hindbrain. By further development the fore-
lary plate, Acanthias. (From : nae : i
Loey.) brain and the hindbrain are separated into four
n.f., neural fold; op.v., optic of the permanent segments of the adult brain,
vesicle. : ey.
while the mesencephalon does not divide
further. The prosencephalon or forebrain becomes the telencephalon and
diencephalon and the hindbrain or rhombencephalon becomes the metenceph-
alon and myelencephalon. Thus the five divisions of the adult brain which we
have described for Heptanchus are formed.

GROSS FORM OF BRAIN

Superficially, different Elasmobranch brains present very different appear-
ances. This difference is due largely to the condition of the olfactory tracts and
their appended olfactory bulbs. The bulbs, arising as outgrowths from the
prosencephalon, may still be practically in contact with it in the adult. In
Scymnus (fig. 2134) they may extend but a short distance out from the pros-
encephalon. In other types, however, as in Heptanchus, they may be drawn
far forward so as to be remotely removed from their place of origin (Squatina,
Laemargus borealis, and especially Hexranchus). In addition the olfactory
tracts may be widely divergent as in Raja (fig. 2118) and Zygaena, or they

THE ELASMOBRANCH FISHES 231

may take a course more or less nearly parallel as in Carcharias and Myliobatis
(fig. 212).

In the greater number of Elasmobranehs the brain is elongated so that in a
dorsal view at least parts of all the five segments are visible. In a few, how-
ever, the brain may appear as a more or less compact mass. As a normal thing

“cig tN repel RE RA A Waa

A B

Fig. 210. Brain of Heterodontus francisci. (Mildred Bennett, del.) A. Dorsal view. B.
Ventral view.

cb., cerebellum; c.r., restiform body ; di., diencephalon or thalamencephalon; i./., inferior
lobe; m.n., median olfactory nucleus; med., medulla; ms., mesencephalon; ol.b., olfactory
bulb; ol.l., olfactory lobe; ol.t., olfactory tract; op.l., optic lobe; p.e., pallial eminence; t1.,
telencephalon; v.s., vascular sac; J, olfactory nerve; IJ, optic nerve; IV, trochlearis or
fourth nerve; J, abducens or sixth cranial nerve; LY, glossopharyngeal nerve; X, vagus
nerve.

the compactness is the result of the enlargement of the cerebellum (cb., fig.
212) whereby it overlies the mesencephalon or, occasionally, even a part of the
diencephalon (Scoliodon, or Myliobatis). /
We may now consider in more detail the different segments of the brain. In
form the telencephalon (tl.) depends largely upon the proximity of the right
and left halves. In Heterodontus francisci (fig. 210) these are clearly sepa-
rated by a median anterior suleus so that the lobes have undergone but slight
fusion in the middle line. In Heptanchus we have noted a similar condition

232 THE ELASMOBRANCH FISHES

although in it fusion is greater. From Heterodontus to Scoliodon (fig. 2114)
a series of forms may be obtained, showing a progressive specialization to a
condition in which practically no sign of right and left lobes remains.

In the component parts of the telencephalon there is also great diversity.
The median olfactory nucleus (m.n.) produces very different effects depend-
ing on the degree of its own development and also on the degree of fusion of
the right and left telencephalic lobes. In Scymnus these nuclei constitute a

A B
Fig. 211. Dorsal view of brain. (From Locy.) A. Scoliodon. B. Raja.

cb., cerebellum; c¢.r., restiform body; di., diencephalon; m.n., median olfactory nucleus;
med., medulla; np., neuropore; ol.b., olfactory bulb; ol./., olfactory lobe; ol.t., olfactory
traet; op.l., optie lobe; tl., telencephalon; tn., terminal nerve; J, olfactory nerve; I/, optic
nerve; JV, trochlearis or fourth nerve; X, vagus nerve.

pair of rounded masses located terminally between the olfactory tracts (m.n.,
fig. 213) and extending ventrally. Much the same condition obtains in Squalus
sucklit (see p. 183, fig. 1724), but in this form the median nucleus is not pro-
jected forward into so sharp a mass. In a type like Heterodontus it stands out
in a particularly striking way. In many other forms, on the contrary, the
median olfactory nucleus is poorly developed.

The pallial eminencees also are very differently developed in different Elas-
mobranehs. In Scymnus again they are sharply defined as prominent dorsal
mounds built up of masses of cells (p.e., fig. 2134). In other forms these lobes
are less well developed (Acanthias); while in still others they are scarcely
discernible.

The diencephalon (di.) in general may be said to be narrow from side to side
and show no marked swellings. In some forms it is well seen from above, as in
Heterodontus (fig.210) and Raja (fig.2118). In all such occurrences the brain
stem is well drawn out in this region. In those Elasmobranchs in which a

THE ELASMOBRANCH FISHES 233

ereater compactness of brain obtains, or in those where the cerebellum is
especially well developed, the diencephalon may be more or less completely
hidden (Scoliodon, fig. 2114; Myliobatis, fig. 212).

Both dorsally and ventrally the diencephalon is characterized by out-
erowths which are of interest. From the roof arises the chimney-like epiphysis
(pineal stalk) (ep., fig. 2134) which passes upward and forward to the roof of
the cranium. In general the stalk terminates at
the roof immediately posterior to the anterior
fontanelle and is usually spread out terminally
into the dise-like pineal body.

In development the pineal region in the early
embryo of Acanthias (Minot, 1901) shows a
series of arches in the roof of the brain which
are separated by a series of projections. The
long anterior projection (v., fig. 214) is the
velum, an important landmark separating
telencephalon from diencephalon. The velum in
figure 2148 separates the paraphysial arch
(pa.) from the small postvelar arch (p.v.).
Back of the postvelar arch is a projection in
which the superior commissure (s.c.) runs. An
early stage of the epiphysis (ep., fig. 2144) is
shown behind this projection, and in the projec-
tion is the posterior commissure (p.c.). Figure
2148 is a later stage in the development of the
pineal stalk in which the surrounding strue-
tures have reached a definitive form. The pineal
stalk (ep.) has almost reached the surface; the
paraphysis (pa.) is enlarged; and the velum
and commissures are well marked.

From the floor of the diencephalon an evagi-
nation, the infundibulum (in., fig. 2138), drops Fig. 212. Dorsal view of brain,

: 4 Myliobatis californicus. (For ex-
downward and backward, and at its sides are _ planation see fig. 211.)
the inferior lobes (lobi inferiores, 7.1., fig. 2154)
and the vascular saes (saecei vasculosi, v.s.). The infundibulum meets and
fuses with the hypophysis, an outgrowth from the buccal cavity, to form the
pituitary. The hypophysis may present a complex appearance, or it may be
comparatively simple. In Scymnus, as in Heptanchus, it is composed of three
well defined divisions, an anterior terminal, a median, and a paired posterior
division, the posterior division being considerably removed from the body of
the infundibulum and connected with it only by a narrow strand.

Figure 215 is a detailed drawing in side view of the pituitary and surround-
ing structures, in the adult of Squalus suckli. In this area, in addition to the
inferior lobes (7.1.b.) and vascular sacs (v.s.) of the brain, there are three
unpaired parts of the hypophysis lying in the midventral line. These are the

234 THE ELASMOBRANCH FISHES

anterior (a.l.), intermediate (7./.), and inferior lobes (7.l.h.). To these parts
are to be added the paired superior lobes (s.l.) which he at the sides of and
above the intermediate lobes.

The mesencephalon (fig. 213, op.l.) is a conservative segment and yet it
varies considerably in different forms. In many it is relatively inconspicuous
because of the extreme development of the cerebellum, while in others it comes

Fig. 213. Brain of Scymnus. (From Burckhardt.) A. Side view. B. Median sagittal view.

eb., cerebellum; ¢.r., restiform body; ep., pineal stalk; flm., median longitudinal bundles ;
in., infundibulum; i./., anterior lobe; l.v., lobe of the vagus; m.n., median olfactory nucleus ;
op.l., optic lobe; p.e., pallial eminence; p.l., posterior or inferior lobe of hypophysis; v.s.,
vascular sacs; IJ, optic nerve.

to be unusually large. In all forms the roof of the mesencephalon is composed
of aright and a left optie lobe (op.L., figs. 210 and 213) which are hollow out-
pockets from the dorsal side of the mesencephalic segment. It is largely among
the cells of these lobes that the fibers of the optic nerve terminate. The ventro-
lateral part of this segment of the brain (see fig. 2138) is enlarged by longi-
tudinal swellings, the lateral fiber tracts of the mesencephalon. Through the
ventral walls the third cranial or oculomotor nerve passes, and from the roof
the fourth nerve leaves the brain stem (JV, figs. 210 and 212).

The metencephalon as a segment is usually well developed in the Elasmo-
branchs. Dorsally it consists of the cerebellum (cb.) and ventrally it is swollen
by large fiber tracts (Scymnus, fig. 2138). The cerebellum is usually rhomboid
in shape and divided dorsally by a median longitudinal furrow into right and
left halves (fig. 2104). These may be further separated into anterior and
posterior parts by a second furrow at right angles to the first. In some forms,
as has been said, the cerebellum comes to be very complex and of immense size.

THE ELASMOBRANCH FISHES 235

It is so in Lamna, Scoliodon (fig. 2114), Galeus, Trygon, and Myliobatis (fig.
212). In all these the surface is thrown into numerous irregular folds or
convolutions.

The myelencephalon (medulla) (med., figs. 211-213) when seen in dorsal
view is shaped like the letter Y, the anterior limits of the Y being made by the
restiform bodies, corpora restiforme (c.7°.). These in many of the simpler types
of sharks, such for example as Scymnus, appear as prominent structures. In
others the corpora restiforme are entirely hidden by the enlarged cerebellum
(Myliobatis, fig. 212). Both in dorsal and in ventral view the medulla is conical

—

Fig. 214. Stages A and B in the development of the pineal region of Acanthias. (From
Minot. )

ep., epiphysis; pa., paraphysis; p.c., posterior commissure; p.v., postvelar arch; s.c.,
superior commissure; v., velum.

in shape and tapers gradually back to the spinal cord. It is from this segment
that most of the cranial nerves arise; all in fact except the first four take
their origin here.

INTERNAL VIEW OF BRAIN

A sagittal section through the brain of Scymnus (fig. 2158) shows within the
medulla the large cavity of the fourth ventricle. The floor and sides compose
the fossa rhomboidealis. Along each side of the middle line of this fossa are
two median longitudinal bundles, fasiculi longitudinales mediales (flm.).
Running parallel to these in the posterior part of the fossa are the ventro-
lateral bundles, fasiculi lateroventrales. Above these bundles and in the side
wall are the lobes of the vagus (l.v.) which vary in number of segments from
types in which only a few are present to those in which there are several
nodules (Heptanchus and Hexanchus). Above the lobes is a dorsolateral
bundle which continues forward as the bundle to the tubereulum acusticum.
Above this are other bundles which continue into the ridge of the restiform
bodies or corpora restiforme.

In the region of the mesencephalon the cavity is so large that it is an aque-
duct of Sylvius only in name. It connects the cavity of the metencephalon and

236 THE ELASMOBRANCH FISHES

myelencephalon, the fourth ventricle above mentioned, with the cavity of
the diencephalon, the third ventricle. In the wall of the diencephalon is the
optic thalamus, and, in its roof, the habenular ganglion from which the pineal

Fig. 215. The pituitary, Squalus sucklii, side view. (Marie Carlson, orig.)

a.l., anterior lobe; i./., intermediate lobe; i.1.b., inferior lobe of brain; i.1.h., inferior lobe
of pituitary; inf., infundibulum; s.l., superior lobe; v.s., vascular sae of brain; IJ, III,
second and third nerves.

stalk arises. In the floor of the diencephalon is the infundibulum (in.). The
cavities in the right and left lobes of the telencephalon are the lateral
ventricles.

Figure 216 (Houser, 1901) is of a transverse section through the medulla of
Mustelus to show something of its finer structure. In its median ventral mass
hes the abducens nucleus, the fibers of which form the abducens or sixth
cranial nerve. Around the nucleus of the sixth nerve the tract cells are seat-
tered. These cells are of interest in that they are exceeded in size only by the
cells in the roof nucleus of the mesencephalon (see fig. 206). The lobes of the
vagus (l.v.) are made up of masses of cells which receive visceral sensory
fibers from the seventh, ninth, and tenth cranial nerves. Some of the axones
from the cells of these lobes pass down-
ward a short distance to the viscero-
motor nucleus (vm.n.). The cells in this
large nucleus give rise to the motor
fibers of the fifth, seventh, ninth, and
tenth nerves.

Houser states that the general cuta-
neous nucleus (g.c.n.) is the terminus
for the somatic sensory fibers of the
fifth, ninth, and tenth nerves, but ac-
cording to Norris and Hughes (1920)
the ninth and tenth nerves contain no
somatic sensory elements.

The tuberculum acustiecum (t.a., fig.
Fig. 216. Transverse section through the 216) forms a swelling on the lateral
SS TTE EAU URC SU) wall of the fourth ventricle (v.4) and

fim., median longitudinal bundles; f.r.,
formatio-reticularis; l.v., lobes of vagus; iS principally a center for fibers from
g.cn., general cutaneous nucleus; t.a., the lateral line organs and from the

tuberculum acusticum; vm.n.,visceromotor |
nucleus; v.*, fourth ventricle. internal ear.

THE ELASMOBRANCH FISHES

bs
4

SPINAL CORD

The spinal cord extends from the brain practically to the tip of the tail. Unlike
that in the higher forms it does not possess marked pectoral and pelvic swell-
ings produced by the passage of the nerve bundles to the limbs. In its external
aspect and in its internal structure the cord may be spoken of as a simplifi-
cation of the medulla. The place occupied in the medulla by the nucleus of the

Fig. 217. Transverse sections of the spinal cord. (From Sterzi.) A. Acanthias vulgaris. B.
Raja clavata.

ca., calcification ; d.h., dorsal horn; d.r., dorsal root; e7., endorachis; ne., neurocoele; pm.,
paracentral mass; ps., perimeningeal space; v.h., ventral horn.

sixth nerve and the grey matter of the formatio-reticularis (f.r., fig. 216) is
occupied in the cord by the ventral horn (w.h., fig. 217); while the general
cutaneous nucleus of the medulla (g.c.n.) gives place to the dorsal horn of the
cord (d.h., fig. 217); and the lobes of the vagus and the visceromotor nuclei
are supplanted by the paracentral mass (pm.). Furthermore, the enlarged
fourth ventricle of the medulla becomes the small neurocoele of the cord (ne.).

A transverse section shows the spinal cord lying within the neural canal
from which it is separated by a considerable perimeningeal space, especially
in the rays (fig. 217B). The endorachis (e7.) lines the neural canal and is
further surrounded by ealcification (ca.). Directly surrounding the cord is
the meningeal lining, through which ventrally the spinal blood-vessels pass.
The cord itself (Acanthias, fig. 2174) is much lke that of Heptanchus (fig.
201) in that the dorsal horns (d.h.) are close together and the ventral horns
(v.h.) are almost at right angles to the central mass. Above the ventral horns
are the outgrowing paracentral masses (pm.). In the rays, however, the cen-
tral grey matter of the cord is more diffuse.

The relation of the grey and white matter, cells and fibers, in the Elas-
mobranchs is essentially like that in higher forms, although the proportion

238 THE ELASMOBRANCH FISHES

of one to the other is greatly altered. Burckhardt (1911) has estimated that
in Scymnus the grey to the white is as 1 to 17, while in man it is as 5 to 12.

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system in general, like that in Heptanchus, is made up
of cranial and spinal elements. Both the cranial and the spinal nerves origi-
nate from cells in or derived from the central nervous system. We may briefly
review their development in a type like Acanthias.

At the time when the neural tube closes, the cells which make up its walls
form a single layer (fig. 218). These cells later become pear-shaped and collect

in groups in the region of the ventral horns.
eee | | FG In the adult the motor fibers extend from
these cells.

The question has often arisen as to the
formation of the nerve fiber or axone. Is it
formed in place from preéxisting proto-
m. plasmic strands, or is the axone an out-
erowth from the cell body ? An examination
of a section by Neal (1914) taken from the
posterior region of the cord (fig. 218) shows
that the fiber or axone (ax.) here has just
reached the myotome (m.) and that its end,
Fig. 218. Transverse section through which is the actively growing part of the
developing cord, notochord (chd.), ; : :
and myotome (m.), Squalus acan- fiber, is rhizopod in appearance. As the
thias. (From Neal.) muscle bud grows outward toward the

ax., motor axone growing out to fin, the fiber becomes attached to it and is
sc oem ie) enous cen ue Pew drawn out with it, forming a so-called end

ral tube.
plate. Such a growing fiber is protected by

a thin covering, the neurilemma, and sometimes a medullary sheath is formed
between the neurilemma and the axis cylinder of the fiber. The axis cylinder
itself becomes differentiated into numerous fibrillae.

In the sensory (dorsal) nerves an overgrowth, the neural crest, is pro-
duced on each side along the neural tube at the place of closure. From each
crest, dorsal root ganglia result (g., fig. 207) which migrate shghtly farther
down the sides of the tubes. Composing these ganglia are multitudes of bipolar
cells, the fibers from which pass from both ends or poles of the cell. Several of
these cells (fig. 207, a to c) are here seen in different stages of development;
(c) represents the mature cell in which the two poles have fused at the base
into the stem of a T. One of the fibers thus formed by the arms of the T enters
the central system while the other extends outward and receives sensation.

CRANIAL NERVES

The first cranial or olfactory nerve extends from the epithelium of the olfae-
tory capsule as a double nerve backward to the olfactory bulb. In extent it

THE ELASMOBRANCH FISHES 239

varies greatly. In some forms the nerve is so short as hardly to be observed
from the outside. This is observable in types like Heptanchus (fig. 2004),
Galeus, and Scymnus. In Scoliodon (fig. 2114) the olfactory bulbs are farther
separated from the nasal epithelium so that the two divisions of the nerve (J)
are distinct. In Echinorhinus the nerves are of an extreme length, rarely met
with in any other Elasmobranch.

A sagittal section through the anterior part of the olfactory bulb would
show how the fibers come to masses of cells (glomeruli) in the bulb from the
olfactory membrane. These are arranged in two
bundles. One of these is median and ventral in posi-
tion; the other is lateral. The fibers from the cells in
the glomeruli of the olfactory bulb are continued to
the olfactory lobe of the brain by the olfactory tracts
(ol.t.). These tracts similarly vary in extent through
extremes shown in Echinorhinus and Hexanchus. In
the former the bulb and the lobe are practically con-
tinuous; in the latter the tracts are greatly drawn out.

Accompanying the olfactory nerve is the terminal s.vi!!
nerve (tn., fig. 211) studied in detail by Loey (1905).
This nerve in Acanthias as a type (t.n., fig. 1724)
ends in the thickened lamina terminalis. The right

bu.VIT

Fig. 219. Ganglia of tri-
geminal (V) and facial
(VII) nerve, median view,
Chlamydoselachus. (From
Mrs. Hawkes. )

and left nerves at the entrance of the brain would
thus be separated by the median fissure. Through

growth of the brain and fusion of the median olfac-

bu.VIT, bueeal division
of seventh nerve; g., gas-
serian ganglion; md.JV,
mandibular nerve; mz./,

tory nuclei it so happens that the terminal nerve
instead of passing directly forward may arise dor-

sally or ventrally. Those forms in which the nerve
has a connection with the brain dorsal to the neuro-
pore are: Raja, Trygon, Myliobatis. In others the
connection is more nearly dorsal than ventral (Acan-
thias, Squatina, Hexanchus). In still others the con-

maxilliary branch of fifth
nerve; op.V, ophthalmicus
profundus nerve; os.V,
ophthalmicus superficialis
of fifth; os.VII, ophthal-
micus superficialis of
seventh.

nection is ventral,as in Galeus, Scoliodon (fig. 2114),

Scyllium, Pristiurus, and Carcharias littoralis. In all the above forms the
nerve passes forward as a double or triple strand on which is a ganglion (or
a series of gangha). The nerves join the olfactory fila as in Heptanchus and
go to the mucous lining of the olfactory cup.

The optic or second nerve (JJ, figs. 210 and 213a) is sufficiently similar in
the different forms to need but little description. It arises from cells in the
retina and its fibers cross to form the optie chiasma. They then extend to, and
terminate in, the diencephalon and mesencephalon.

The oculomotor nerve (J/TJ, figs. 200A and 2008) arises in a nucleus under
the aqueduct of Sylvius and leaves the brain stem near the middle line of the
mesencephalon. It enters the orbit and gives off a dorsal branch to the superior
rectus and the anterior rectus and a ventral branch which divides into an an-

240 THE ELASMOBRANCH FISHES

terior and a posterior division. These divisions supply the inferior oblique and
the inferior rectus muscles as in Heptanchus.

The relation of the nerve to the ciliary ganglion in some forms is interesting.
Sometimes this ganglion (or ganglia) is on the oculomotor nerve and is called
the ganglion oculomotoris. Or, again, it may be on a branch joining the gan-
elion of the ophthalmicus profundus with the oculomotor nerve.

The trochlearis nerve, as we have said, has its nucleus in the mesencephalon.
Its fibers cross and pass out through the roof between the mesencephalon and
the cerebellum and go to innervate the superior oblique muscle of the eye.

The trigeminal or fifth cranial nerve is composed of an anterior portio
minor and a posterior portio major. While both of these roots contain motor

Fig. 220. Cranial nerves, Squalus acanthias. (From Norris and Hughes.)

br.p., brachial plexus; bu.VII, buccalis of seventh; d.X, ramus dorsalis of tenth nerve;
gn., first spinal ganglion; hb., hypobranchial bundle; hmd., hyomandibularis; lI.X, lateral
line nerve; md.e.V II, mandibularis externus of seventh; md.i.V II, mandibularis internus of
seventh; md.V, mandibularis of fifth; ma.V, maxillaris of fifth; op.V, ophthalmicus pro-
fundus; os.V, and os.VII, ophthalmicus superficialis of fifth and seventh; ph.[X, pharyn-
geal branch of ninth; pl.VIJ, palatinus of seventh; po.t., post-trematicus of ninth; pr.t.,
pretrematicus of ninth; sp., spiracle; st.JX, supratemporalis of ninth; st.X, supratem-
poralis of tenth nerve; vi.X, visceral nerve; y and ¢z, occipitospinal nerves; IJ, optic; III,
oculomotor; IJV, trochlearis; VJ, abducens; VII, auditory nerve.

and sensory portions, motor fibers predominate in the anterior part and
sensory in the posterior root. The motor fibers arise from the visceromotor
nucleus in the medulla (vm.n., fig. 216) and are distributed principally to the
muscles of the jaws. The sensory fibers arise from various ganglia, such as the
ganglion of the ophthalmicus profundus, the ophthalmicus superficialis (Mus-
telus californicus), and the gasserian ganglion. Sensation brought from the
region around the nose passes by the ganglion cells and on to the brain.

In the Elasmobranchs the ganglia of the trigeminal and the buceal division
of the facial nerves are so intimately associated as often to be inseparable;
usually the former are more or less covered up by the latter. In Chlamydosel-
achus, however (fig. 219), the two are distinct medially (Hawkes, 1906). From
the gasserian ganglion (g.) the large maxillaris and the mandibularis divisions
of the fifth nerve arise and from the small ganglion on the inner side of the
gasserian, the two smaller nerves, the ramus profundus (op.V) and the ramus
superficialis (os.V) of the fifth, take their origin.

THE ELASMOBRANCH FISHES 241

The ophthalmicus profundus (op.V, fig. 220), after leaving its ganglion
passes forward deep in the orbit, between superior and inferior rectus muscles
and out anteriorly under the anterior rectus and between the obliques. On its
way past the eyeball it gives off the ciliary nerves to the eye and then passes
to the dorsal and lateral parts of the snout (Squalus), or also to the ventral
part (Mustelus).

The ophthalmicus superficialis of the fifth (os.V, fig. 220) may have an ex-
tracranial ganglion as in Mustelus californicus or it may be connected directly
with the gasserian ganglion as in Squalus acanthias. In either form the nerve
is closely associated with the superficial ophthalmic of the seventh on its way
through the orbit. In Squalus acanthias according to Norris and Hughes
(1920) there are three or four branches of this nerve which apparently ter-
minate in the skin over the supraorbital crest. In Mustelus californicus the
nerve is larger and continues farther anteriorly.

Both the ophthalmicus profundus and the ophthalmicus superficialis of the
fifth nerve are sensory.

The maxillaris of the fifth (mz.V, fig. 220) originates in the gasserian gan-
elion and passes to the jaw and on to the skin ventral to the snout. In its course
over the floor of the orbit it is accompanied by the bucealis of the seventh.
Near its ganglion it is often mediad of the buccalis but farther distally it may
lie dorsal to it. As a usual thing the maxillaris branches into two or three main
divisions, the most anterior of which passes forward almost to the tip of the
snout.

The mandibularis may accompany the maxillaris over the floor of the orbit
and separate from it late to turn sharply back around the angle of the jaw as
in Laemargus. Or, if the angle of the jaw is relatively far posterior, the
mandibularis may leave the maxillaris early and pass over the posterior wall
of the orbit to reach the angle of the mouth (Chlamydoselachus, Acanthias).
In either form certain sensory bundles from the intracranial part of the gas-
serian ganglion, after passing the angle of the jaw, turn forward and supply
the skin of the lower jaw to the symphysis of the mandible. Motor fibers, dorsal
to the sensory fibers, supply the levator maxillae, the first dorsal constrictor,
the adductor mandibulae, and a considerable part of the first ventral con-
strictor muscle (Norris and Hughes).

The abducens or sixth cranial nerve is a motor nerve. It arises, as we have
seen, from a nucleus in the medulla and passes forward and outward to the
posterior rectus muscle, entering it at its base.

The seventh or facial nerve like the fifth is composed both of motor and of
sensory components. Its motor fibers arise in the visceromotor nucleus (vm.n.,
fig. 216) just posterior to that of the fifth nerve and extend to the lower jaw
and the facial region. Its sensory fibers are connected with large ganglia and
are distributed essentially as in Heptanchus. In Acanthias, the nerve may join
the brain in common with the branches of the eighth, and it is usually united
above with the fifth. In Mustelus canis, however, it may be more or less clearly
separate from the fifth (fig, 221).

242 THE ELASMOBRANCH FISHES

For convenience of description we may consider the facial nerve as made up
of two groups of fibers. One of these supples the sensory canal system; the
other belongs to the facial proper. Three great nerves are in the service of the
sensory canal system. These are: the ophthalmicus superficialis (os.V IJ, figs.
220 and 221) which goes to the supraorbital canal and associated ampullae of
Lorenzini; the buecalis, to the infraorbital canal and associated ampullae of
Lorenzini; and the external mandibular, a branch of the hyomandibular
nerve. This supphes the hyomandibular and the mandibular canals (figs. 220
and 245), and ampullae
of Lorenzini.

The ophthalmicus su-
perficialis of the facial
(os.VIT) is a somewhat
large nerve which arises
from a large ganglion
(figs. 220 and 221) and
runs forward into the or-
bit. Generally it enters
the orbit through the or-
bital fissure in common

with the trigeminal, but
Fig. 221. Roots of fifth and sev nth nerves, Mustelus canis. jn certain types (Mus-
(From Green.) *

bu.VII, bucealis of seventh; ct., chorda tympani; g., telus henlev) it may enter
geniculate ganglion; hmd.,hyomandibular nerve ; ma.md.J’, through its own foramen
sunsias gad maadibnlarieat Ath, YUL auditor aeti.: ehovs-andei ae ae aa
ficialis of fifth; os.V II, ophthalmicus superficialis of the the orbital fissure. As it
peer ge palatinus of seventh; prt., pretrematicus ; passes through the orbit

superficially, it gives off
numerous branches dorsally to the supraorbital canal and associated ampul-
lae and leaves the orbit by a large anterodorsal foramen. It extends forward
giving off a large branch which passes downward in front of the eye to supply
the lower part of the supraorbital canal and numerous small branches which
pass toward the tip of nose.

The bueealis may arise from a large ganglion which is continuous wien that
of the ophthalmicus superficialis VII (Acanthias, fig. 220, bu.VII). In Mus-
telus californicus these two ganglia are distinct but the ganglion of the bue-
ealis is in close relation to the ganglion of the external mandibular nerve. The
bucealis, as was previously mentioned, runs across the floor of the orbit closely
associated with the maxillaris of the fifth. In the anteroventral angle of the
orbit it divides into two or three main divisions, the twigs of which go to sup-
ply the infraorbital canal and associated ampullae of Lorenzini. From the
ganglion the bucealis sends off branches which supply the part of the infra-
orbital canal posterior to the eye (see p. 279, fig. 245), and from the dorsalmost
part of the ganglion it gives the important ramus oticus VII to a short seg-
ment of the most anterior part of the lateral line canal.

THE ELASMOBRANCH FISHES 243

The external mandibularis is in relation to a ganglion by the same name. It
leaves the cranium through the facial foramen (see fig. 47, f.VII*, facing
p. 44), and passes upward around the spiracle as a part of the ramus hyo-
mandibularis. In Squalus acanthias the external mandibularis (md.e. VII, fig.
220) divides into an anterior and a posterior division. The anterior division
goes to the hyomandibular and mandibular canals. The posterior division
supphes the hyoidean ampullae and pit organs.

The first divisions of the facial which are not connected with lateral line or
ampullary organs are certain branches of the hyomandibularis.

The hyomandibular trunk after leaving the brain stem passes backward,
the main stem arching posteriorly around the spiracle as was described above
for its external branch. Before reaching the spiracle, however, the palatine
nerve separates from the hyomandibular trunk. It arises in the geniculate
ganglion (g., fig. 221) and passes as a sensory nerve to the roof of the mouth
where, as in Heptanchus, some of its fibers pass forward and others extend
over the posterior part of the roof to supply “taste buds.” After having given
off the palatine, the hyomandibularis supplies a small pretrematicus to the
anterior side of the spiracle.

At about the place where the external mandibular VII, previously de-
scribed, is given off from the ramus hyomandibularis the internal mandibular
(md.i.VII) separates from the main trunk. This, like the palatine nerve, is
sensory and goes to the mucous membrane along the inner side of the man-
dibular arch.

The ramus hyoidius VII (fig. 220) is a motor branch which in Squalus acan-
thias divides into an anterior and a posterior division. The anterior branch
supplies the second, and the posterior, a part of the first ventral constrictor
muscles.

The chorda tympani is variously interpreted for the Elasmobranchs. In
Acanthias (ct., fig. 221) it is apparently a continuation from the palatine
branch (pl.VIZ) and is therefore in front of the spiracle. In Hexanchus it has
been considered by Ruge (1897) to be a direct continuation of the hyoman-
dibularis and as such is therefore a post-trematicus. In both it is a sensory
nerve and supplies the mucous lining in the floor of the mouth just mediad
of the teeth.

The hyomandibularis, in Torpedo, gives rise to a first electric nerve which
goes to the anterior and inner part of the electric organ.

The auditory nerve (VIJIJJ, fig. 220) has a large ganglion just back of the
ganglia of the seventh nerve. From this fibers extend to the ear in two general
groups, an anterior vestibular and a posterior saccular group. Root fibers join
the ganglion to the medulla just back of the seventh nerve and terminate
around cells in the tuberculum acusticum of the medulla. The distribution of
the fibers to the ear will be discussed further in a study of the ear.

The glossopharyngeal, as described for Heptanchus, may be taken as a typ-
ical “mixed” nerve. It is made up of both motor and sensory fibers, the former
arising in its visceromotor nucleus of the medulla and the latter springing

244 THE ELASMOBRANCH FISHES

from a ganglion located on the nerve in or just outside the glossopharyngeal
canal (see fig. 220). The main divisions of the nerve are a branch (st.LX, fig.
220) to the anterior segment of the lateral line canal, and nerves in relation
to the first and second demibranchs.

The supratemporalis (st.LX ) in Squalus acanthias, according to Norris and
Hughes, supphes three neuromasts of the lateral line canal located between
the neuromasts supphed by the supratemporalis of the vagus and the ramus
oticus VII, but it is not provided with other branches to pit organs. In Chlamy-
doselachus, Hawkes (1906) mentioned, in addition to the twigs to the neuro-

br.p., brachial plexus; er.p., cervical plexus; d.r., dorsal root; 2., occipitospinal nerve.

masts of the lateral line canal, other twigs to the skin. These she suggested
were cutaneous. They possibly supply pit organs. In Raja radiata according to
Norris and Hughes there are no lateral line elements in the ninth nerve.

Above the first branchial pocket, as in Heptanchus, the main part of the
ninth nerve, as the first branchial nerve, separates into three divisions, a pre-
trematicus (pr.t.), a post-trematicus (po.t.), and from the pretrematicus a
pharyngeal division (ph.LX), the last-named branch being sensory and com-
parable to the palatine division of the facial nerve. The pretrematicus is also
sensory; it extends down the hyoidean demibranch back of the branchial earti-
lages, supplying the mucous membrane and gill filaments. Unlike Heptanchus
the majority of Elasmobranchs seem to lack the internal pretrematicus. The
post-trematicus or larger division, unlike that of Heptanchus, is not always so
clearly separated into its components. The post-trematicus supphes the mu-
cous lining along the anterior part of the first holobranch and other sensory
fibers continue forward under the gill cleft and are distributed to the mucous
membrane of the pharynx and buceal cavity. The motor branches supply
muscles associated with the first holobranch.

Accompanying the glossopharyngeal and a part of it, in Torpedo, is the
second electric nerve.

The vagus is the most widely distributed of any of the nerves. It is much
like the ninth in its supply of the gills, but in addition it gives off a dis-
tinct lateral line nerve, and its branchial divisions are bound with intestinal

THE ELASMOBRANCH FISHES 245

branches into a branchio-intestinal bundle. The lateral line nerve can be traced
from the brain as a distinct stem. As it emerges from the cranium it swells out
into a large ganglion from which this branch proceeds posteriorly practically
to the end of the tail. From the lateral line ganglion there is given off a dorsal
root, the supratemporalis (fig. 245) which passes upward and forward to
supply the supratemporal canal, pit organs in the region of the supratemporal
canal, and the anterior part of the lateral line canal immediately behind the
segment supplied by the supratemporal branch of the ninth nerve. Posterior
to this branch there is given off a second branch, the dorsalis (d_X, fig. 220)

Fig. 223. Brachial and pelvie plexuses, Raja vomer. (From Braus.)

which runs posteriorly almost to the first dorsal fin. This nerve supplies sense
organs of the anterior part of the lateral canal and also pit organs above the
line and anterior to the dorsal fin. Many branches are given off from the lateral
line nerve as it passes backward in the body to the sense organs along the
lateral line canal.

The branchial stem in the vagus is a strong bundle which divides into four
(pentanchids), five (hexanchids), or six (heptanchids) branchial nerves. The
first two or three of these branchial nerves, except in Torpedo, where the first
and second branchials give off the third and fourth electric nerves, are essen-
tially like the branchial division of the glossopharyngeal. Each branchial con-
sists of pharyngeal and pre- and post-trematic nerves. The post-trematicus of
the vagus is composed of two strong branches, one of which is motor, the
other sensory. The motor division innervates the interarcual, interbranchial,
adductor, and ventral constrictor muscles. The last branchial nerve is com-
posed only of visceral sensory fibers (Norris and Hughes, 1920).

The ramus intestinalis or visceralis (v7. ) proceeds posteriorly after sepa-
rating from the branchial stem. Its motor fibers are distributed to the
trapezius muscle and to the digestive tract. Its sensory fibers go largely to the
digestive tract.

The occipitospinales (y, 2, fig. 220), back of the vagus, like spinal nerves
consist of dorsal and ventral roots, but dorsal roots to the ones most anterior
are frequently absent. In lowly forms, as we have seen in Heptanchus, several
pairs may be present. As many as five of the ventral occipitospinales have been

246 THE ELASMOBRANCH FISHES

located on each side of the young of Hexanchus and Chlamydoselachus. In
Acanthias there are only two or three of the ventral nerves present and two
dorsal rami. These nerves united with the first and second spinals are marked
hb. in figure 220. In Torpedo a single ventral occipitospinal nerve as such is
present.

The more posterior of these nerves unite with the first group of spinal
nerves to form the cervical plexus which in turn joins the pectoral plexus, the
fused trunks of which may run for a short distance, with, although it is no
part of, branches of the vagus. The whole group forming the two plexuses may

Fig. 224. Nervous collector, Chlamydoselachus. (From Braus.)

l.a.v., lateral abdominal vein; pl.p., pelvic plexus; sp.”-*, twenty-fifth and thirty-eighth
spinal nerves.

be composed of relatively few nerves (five in Spinax) or it may include many
(twenty in Torpedo). The nerves of the cervical plexus (cr.p., fig. 222) sepa-
rate from the pectoral plexus and pass in front of the girdle to supply the
hypobranchial muscle as in Scylliwm and Squatina, while those of the pee-
toral plexus (br.p.) pass through the girdle and are distributed to the pee-

toral fin.
SPINAL NERVES

In the region of the cord proper a sensory root and motor root (solid line, fig.
220) unite to form a mixed spinal nerve, much as in Heptanchus. Each of
these roots after leaving the cord passes backward within the neural canal,
then perforates the basal or dorsal interecalary cartilages as single roots.
Shortly before perforating the basal plate the motor branch may bifureate
(fig. 220) and send a branch dorsally to join a branch from the ganglion (gn.)
of the dorsal root; or this motor root may pass by the ganglion without receiv-
ing from it sensory fibers. This branch passes dorsally to the dorsal longi-
tudinal bundles. When no sensory fibers join this root a sensory bundle runs
dorsally from the ganglion. The other branch of the bifurcated ventral root
joins a sensory root from the ganglion, the two united passing as a mixed
nerve ventrally.

Posterior to the pectoral fin and in the region of the lateral abdominal vein
the ventral rami of the various spinal nerves often form a connected strand,

THE ELASMOBRANCH FISHES 247

the nervous collector (fig. 224) as in Heptanchus. This has been studied in a
number of forms by Braus (1898). Extremes of variation obtain in the num-
ber of nerves taking part in this collector. In primitive forms, as in Hep-
tanchus, the number may vary greatly and the collector may consist of multi-
tudes of strands which may or may not fuse together. A good example is
Chlamydoselachus (fig. 224), in which the twenty-fifth to the thirty-eighth
nerves take part. In other forms few nerves take part in its formation
(Spinax) or no collector as such is found (Squatina, Raja, fig. 223).

Fig. 225. Sympathetic nervous system, Scyllium canicula. (From Botazzi.)
d.a., dorsal aorta; s.f., sympathetic fibers to stomach (st.); s.g., sympathetic ganglia.

The collector has been studied in great detail as to the relation which it
bears to the origin of paired fins. By those who hold to the gill-arch theory
of origin of the fins the collector is an argument for the posterior migration of
the pelvic fins, while those who accept the lateral fin-fold theory believe that
the collector shows principally that the paired fins formerly had a wider ex-
tent than they have at the present time. A greater extent is indicated further
by the fact that there may be a plexus posterior to the pelvic fin (fig. 224).

In Chlamydoselachus the posterior collector (fig. 224) comprises a num-
ber of segments. In the embryo of Acanthias a posterior collector is present,
although it is absent in the adult. The pelvie plexus in Raja vomer is shown in
figure 223.

SYMPATHETIC OR AUTONOMIC NERVOUS SYSTEM

Although the sympathetic nervous system has been studied by many workers
but little is known concerning its form in the different Elasmobranchs. It ex-
tends from the region of the head to the posterior part of the kidney or meso-
nephros.

The ciliary ganglhon in the region of the oculomotor nerve represents the
sympathetic system in the head. In various Selachians one or more small gan-
glia are related to the third nerve. These in Acanthias are located near the
branching of the oculomotor nerve into its dorsal and ventral rami. The gan-
glion (or ganglia) gives rise to non-medullated fibers which make up the short

248 THE ELASMOBRANCH FISHES

ciliary nerve. Norris and Hughes say that in Squalus acanthias these ganglia
are connected by fibers with the oculomotoris, the ophthalmicus profundus V,
and the palatinus VII nerves.

In sharks the sympathetic system in the trunk is divided into two parts. The
anterior part only is associated with the suprarenal bodies. The first trunk
ganglion (s.g., fig. 225) of this system is the result of a fusion of several
ganglia and further it is fused more or less intimately with the first supra-
renal body. It receives many fibers from the anterior spinal nerves and gives
off splanchnic fibers to the viscera. The ganglia in the posterior region are
small and are separated from the suprarenal (interrenal) bodies. Further-
more, these ganglia of the sympathetic system seldom have connecting strands
putting the various ganglia of a side in longitudinal communication, as occurs
in the higher animals. The posterior ganglia are never thus connected into a
longitudinal chain. From the posterior ganglia fine branches go to the kidneys
and the genital ducts as well as to the posterior viscera.

THE ELASMOBRANCH FISHES 249

BIBLIOGRAPHY

CHAPTER IX

CENTRAL NERVOUS SYSTEM

1915. BAUMGARTNER, E. A., The Development of the Hypophysis in Squalus acanthias.
Jour. Morph., Vol. 26, pp. 391-446, 43 text figs.
1903. BorcHert, M., Zur Kenntnis des Zentralnervensystems von Torpedo. I. Mitt. Neurobiol.

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1901

1897.

NO OTs

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THE ELASMOBRANCH FISHES 259

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text figs.

FURBRINGER, Max, Ueber die spino-occipitalen Nerven der Selachier und Holoce-
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Gegenbaur. Bd. III, Leipzig, pp. 349-788, pls. 1-8, 1 text fig.

02. FURBRINGER, Max, Morphologische Streitfragen. 1. Nervus trochlearis. Rabl’s Me-

thode und Behandlung der Extremitatenfrage. Morph. Jahrb., Bd. 30, pp. 85-274.

. Gast, R., Die Entwickelungen des Oculomotorius und seiner Ganglien bei Selachier-
embryonen. Mitt. Zool. Stat. Neapel, Bd. 19, pp. 269-444, Taf. 12-16.

. GEGENBAUR, C., Ueber die Kopfnerven von Hexanchus und ihr Verhaltnis zur “Wir-

beltheorie” des Schadels. Jena. Zeitschr. Naturwiss., Bd. 6, pp. 497-559, pl. 13.
. GoopricH, EH. 8., On the Segmental Structure of the Motor Nerve-Plexus. Anat. Anz.,
Bd. 36, pp. 109-112, 1 text fig.
. GREEN, H. A., On the Homologies of the Chorda Tympani in Selachians. Jour. Comp.
Neurol., Vol. 10, pp. 411-421, 3 text figs.
GUTHKE, Ernst, Embryologische Studien tber die Ganglien und Nerven des Kopfes
von Torpedo ocellata. Jena. Zeitschr. Naturwiss., Bd. 42, pp. 1-60, Taf. 1-38, 7
text figs.
Hawkegs, O. A. M., The Cranial and Spinal Nerves of Chlamydoselachus anguineus
Garman. Proc. Zool. Soc. Lond., 1906 (2), pp. 959-991, pls. 68-69, 2 text figs.
HorrMann, C. K., Beitrage zur Entwicklungsgeschichte der Selachii. Morph. Jahrb.,
Bd. 25, pp. 250-304, Taf. 13-14.
HoFrrMann, C. K., Beitrage zur Entwicklungsgeschichte der Selachii. (Fortsetzung.)
Morph. Jahrb., Bd. 27, pp. 325-414, Taf. 14-18, 5 text figs.
HorrMann, C. K., Zur Entwicklungsgeschichte des Sympathicus. (I. Bei den Acan-
thias vulgaris.) Verh. K. Akad. Wet., Amsterdam, Bd. 7, pp. 1-80, 3 Taf.
His, W., Die morphologische Betrachtung der Kopfnerven. Arch. Anat. u. Entwick.,
1887, pp. 379-453, 8 text figs.
HoumeGreEN, E., Kurze vorlaufige Mitteilungen iiber die Spinalganglien der Selachier
und Teleostier. Anat. Anz., Bd. 15, pp. 117-125, 11 text figs.
. Houser, G. L., The Neurones and Supporting Elements of the Brain of a Selachian.
Jour. Comp. Neurol., Vol. 2, pp. 65-175, pls. 6-13.
JoHNSTON, J. B., The Radix Mesencephalica Trigemini. The Ganglion Isthmi. Anat.
Anz., Bd. 27, pp. 364-379, 8 text figs.
Kappers, C. V. A., Der Gesechmack, perifer und central, zugleich eine Skizze der
phylogenetischen Verinderungen in den sensibilen VII, 1 X,und X Wurzeln. Psychiatr.
en neur. Bloden, Bd. 1 u. 2.

. KuINKHARDT, W., Beitrige zur Entwicklungsgeschichte der Kopfganglien und Sinnes-

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KOLLIKER, A., Ueber die Ausbreitung der Nerven in der Geruchsschleimhaut von
Plagiostomen. Verh. d. Phys.-med. Ges. Wiirzburg, Bd. 8, pp. 31-37.

Kuntz, A., The Development of the Sympathetic Nervous System in Certain Fishes.
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Kuprrer, C. von, Die Entwickelung der Kopfnerven der Vertebraten. Verh. d. Anat.
Ges. 1891. Trans. by Strong, Jour. Comp. Neurol., Vol. 1, pp. 246-264, 315-332,
pl. XXII.

Lanpacre, F. L., The Cerebral Ganglion and Early Nerves of Squalus acanthias.
Jour. Comp. Neurol., Vol. 27.

THE ELASMOBRANCH FISHES

LENHOSSEK, M. von, Beobachtungen an den Spinalganglien und dem Riickenmark
von Pristiurusembryonen. Anat. Anz., Bd. 7, pp. 519-539, 19 text figs.

Locy, Wm. A., New Facts Regarding the Development of the Olfactory Nerve. Anat.
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Locy, Wm. A., On a Newly Recognized Nerve Connected with the Fore-Brain of Se-
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McKissen, Pau, Ganglion Cells of the Nervus Terminalis in the Dogfish (Mustelus
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MarsHAtu, A. M., and SPENCER, W. B., Observations on the Cranial Nerves of Seyl-
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. Merritt, O. A., The Theory of Nerve Components. Jour. Anat. and Physiol., Vol. 39,

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NEAL, H. V. See Central Nervous System.

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NeraL, H. V., The Morphology of the Eye Muscle Nerves. Proce. 7th Internat. Zool.
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1911.

1888.

1889.

1894.

1908.

1904.

1895.

1885.

1882.

1897.

THE ELASMOBRANCH FISHES 257

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494, 4 text figs.

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Vol. 29, pp. 1-15.

VINCENZI, L., Sull’ origine reale del nervo ipoglosso. Atti R. Acad. Sci., Torino, Vol.
20, pp. 798-806, tav. 7.

WIJHE, J. W. VAN, Ueber die Mesodermsegmente und die Entwickelung der Nerven
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(Also Groningen, 1915.)

Wikstr6M, D. A., Ueber die Innervation und den Bau der Myomeren der Rumpfmus-
kulatur einiger Fische. Anat. Anz., Bd. 13, pp. 401-408.

SPECIAL SENSES

SPECIAL SENSES OF HEPTANCHUS MACULATUS

Under the organs of special sense in Heptanchus we may consider the olfac-
tory organ, the eye, the ear, and the lateral line and associated organs. For the
relation of the first three of these to the brain see figure 200a.

OLFACTORY ORGAN

The olfactory organ in Heptanchus is an almost terminal encapsulated strue-
ture, with a convoluted mucous lining. From the outside this organ is reached
by the nasal aperture which is separated by an overlapping median flap into
an upper and a lower opening through which the water current circulates.
Upon dissecting away the narial flaps the cup appears elliptical in outline and
the lamellae are arranged in a series of folds which radiate outward from a
central hub, like the spokes in a wheel.

Located in the convoluted lining of the olfactory membrane are the primary
olfactory cells (receptors). These cells send fine projections, hair cells, into
the cup and they also send fibers posteriorly to the olfactory bulb in two
bundles. These bundles compose the olfactory nerve, one part of which passes
to the olfactory organ externally and the other internally (J, fig. 2004). Olfae-
tory sensations are carried backward by the olfactory tracts or peduncles
(ol.t.) to the olfactory lobes (ol.l.) of the brain.

EYE

The eye in Heptanchus is provided with dorsal and ventral membranous and
non-funetional lids, but it is unprovided with a third eyelid or nictitating
membrane. It appears to fit the orbit but poorly, especially in the young in
which the orbit is unusually large.

If the eyeball be dissected free from the orbit (figs. 91 and 2004) it is seen
to be shightly pear-shaped and to be held in position by the optic pedicel (0.p.,
fig. 91) and the eye muscles which were described in a study of the muscular
system (pp. 89-90). The coat which appears externally covering the eye is the
heavy sclera. In Heptanchus the sclera is chondrified and surrounds the ball,
except laterally over the clear elliptical cornea; in the center of the cornea is
the pupil surrounded by a dark colored curtain, the iris.

Ear

The ear proper (figs. 2004 and 226) is located in the otic capsule. It is composed
of the semicircular canals with their ampullae and the utricular and saccular
regions. The anterior oblique and the horizontal canals have their anterior

[258]

THE ELASMOBRANCH FISHES 259

ends enlarged into ampullae (a.a. and a.h. respectively ) which are placed close
together. These two canals join the utriculus (w.) above. The ampulla of the
posterior canal (a.p.) is located ventrally and that part of the canal lying
near the sacculus is by some considered to be a second or posterior utriculus.

Fig. 226. Ear of Heptanchus maculatus. (Dunean Dunning, del.) A. Left ear, lateral view.
B. Left ear, median view.

a.a., ampulla of anterior oblique semicircular canal; a.h., ampulla of horizontal canal;
aos., anterior oblique semicircular canal; a.p., ampulla of posterior canal; cn., connection
between utriculus and sacculus; d.c., connection between sacculus and posterior oblique
semicircular canal; e.d., endolymphatic duct; lr., horizontal canal; /., lagena; pos., pos-
terior oblique semicircular canal; s., sacculus; w., utriculus.

At its base the utriculus is connected with the sacculus (s.) by a recessus
utrieuli (at cn.). The sacculus is pear-shaped and continues upward in the
chimney-like endolymphatic duct, the outer opening of which we saw in a
study of the skull (ed., p. 42, fig. 45). From the posterior part of the floor
of the sacculus a tongue-like sac, the lagena (l.), projects backward and
downward.

260 THE ELASMOBRANCH FISHES

A: B

Fig. 227. Cephalic canals and ampullae of Lorenzini, Heptanchus maculatus. (G. L. Hanner,
orig.) A. Dorsal view. B. Ventral view.

c¢c., supratemporal canal; e.d., endolymphatie duet; hmc., hyomandibular canal; iba.,
inner buccal ampullae; ioc., infraorbital canal; isa., infraspiracular ampullae; ll., lateral
line; mg., mandibular groove; mpo., pit organs in gular line (gl.); n.ap., nasal aperture;
oba.*~, outer buceal and posterior outer buccal ampullae; soa., supraophthalmic ampullae;
soc., supraorbital canal; sp., spiracle.

THE ELASMOBRANCH FISHES 261

INNERVATION

The ear receives its innervation from the auditory or eighth nerve. This nerve
as it leaves the brain stem separates into two main divisions, each of which
further subdivides. Principal among the branches are the rami to the ampullae
of the anterior oblique, the horizontal, and the posterior oblique semicircular
canals; and those rami to the utriculus, the sacculus, and to the lagena.

SENSORY CANAL SYSTEM
The sensory canal system in Heptanchus consists of cranial canals in the head

connected with a canal over the pharynx and a lateral open groove in the
body region (see figs. 15, 227, and 228). The lateral canal in Heptanchus is

Fig. 228. Cephalic canals and ampullae of Lorenzini, Heptanchus maculatus, side
view. (G. L. Hanner, orig.) (For explanation see fig. 227.)

especially simple for even in large specimens the canal as such is closed poste-
riorly only to about the fifth cleft, back of which it remains an open groove
toward the tip of the tail.

Anterior to the spiracle and just posterior to the endolymphatic ducts a
small transverse or supratemporal canal (cc., figs. 15 and 227A) passes oft
from the lateral canal toward the median line. This, however, does not meet
and fuse with the similar canal from the opposite side. In Heptanchus macu-
latus there may be two supratemporal canals on a side, one posterior to the en-
dolymphatie duct as just described, the other anterior to it. From the supra-
temporal canal the lateral line canal passes slightly outward and forward to
join the cranial canals. The cranial canal passing above the eye is the supra-
orbital canal (figs. 227 and 228, soc.). In front of the eye the supraorbital
‘swerves outward and then sharply inward; it then turns backward and down-
ward above the nasal aperture. The infraorbital canal (7oc.) back of the eye
drops downward, sends the hyomandibular canal (imc.) backward, and then
continues forward under the eye. Before reaching the nasal aperture this
canal is joined by the supraorbital canal (fig. 228). The main infraorbital
next bends sharply toward the middle line, without joining the canal of the

262 THE ELASMOBRANCH FISHES

opposite side, and then passes outward and forward to the tip of the rostrum,
where it efids blindly (fig. 2278). A mandibular groove (mg., fig. 2278) runs
along the lower jaw parallel with the membranous lower lip.

In the groove on the body and in the canals on the head are located sense
organs, the neuromasts, of the sensory canal system. In Heptanchus, as in
other Elasmobranchs, the sense cells joining these organs are specializations
of the cells in the wall of the canal or groove. The sense organs along the
lateral line are supplied largely by branches of the vagus nerve. The glosso-
pharyngeal and the otie division of the facial supply a few of the anterior
neuromasts of the lateral line canal. The canals of the head are innervated

Fig. 229. Pit organs, Heptanchus maculatus. (Madeline Marlowe, orig.)
A., anterior; /l., lateral line; p.o., pit organs; P., posterior.

wholly by the facial nerve. The superficial ophthalmic division supplies the
supraorbital; the buccal branch, the infraorbital; and branches of the hyoman-
dibular nerve supply the hyomandibular canal and the mandibular groove.

In addition to the sense organs characteristic of the sensory canal system in
the head are other integumentary sense organs of a tubular nature. The first
of these tubular organs are the ampullae of Lorenzini, which take the same
relative position as do the canals of the head, and like them are similarly
named. The ampullae, however, are grouped together, five or six such groups -
in Heptanchus maculatus being shown in figures 227 and 228. These are the
supraophthalmie (soa.) ampullae above the supraorbital canal and in front
of the eye; outer buceal (oba.'), posterior outer bueeal (oba?), and inner
bueeal (2ba.) groups located respectively above and below the infraorbital
canal and a part of the hyomandibular canal. A small bundle of ampullae hes
ventral to the spiracle (isa., fig. 228). Each sense organ of an ampulla of
Lorenzini sinks into the integument and is put into connection with the out-
side by means of a longer or shorter canal (or canals) opening by a mucous
pore (see p. 280, fig. 246). Connecting with the base of such an organ is a
nerve twig, the twigs being furnished by the branches of the facial nerves
which also supply the canals of the head region.

A second kind of sense organ is the pit organ (figs. 227B, mpo., and espe-
cially 229). These pit organs are particularly interesting in Heptanchus macu-
latus in that they have a wide distribution and are distinctly segmental in

THE ELASMOBRANCH FISHES 263

their arrangement. Most of these pits lie between the segment of the spiracle
and the dorsal fin although four of them lie near the middorsal line in front
of the apertures for the endolymphatic ducts. Further, a line extends down
the arch back of the spiracle, as the so-called gular line (gl., fig. 228) described
by Garman (1888) for Chlamydoselachus. This passes downward and for-
ward in front of the first branchial cleft and ends ventrally before reaching
the mandibular symphysis (fig. 2273).

264 THE ELASMOBRANCH FISHES

SPECIAL SENSES OF ELASMOBRANCHS IN GENERAL

The organs of special sense, olfactory, gustatory, optic, auditory, and sensory
canal organs, although very different in the adult are, with the exception of
the taste buds and the eye, similar in the beginning. In general, with the ex-
ceptions made, these organs arise as thickened plates or placodes of ectoderm.
An anterior placode gives rise to the nasal pit and a posterior placode sepa-
rates into three parts (Mitrophanow, 1893). The
first or anterior of these gives origin to a branchial
sense organ over the first gill; the second gives rise
to the ear, and the third or posterior part produces
the lateral line organ which, in the sharks, later
extends to the tip of the tail.

OLFACTORY ORGAN

The olfactory organ in the adult is a blind sae,

which in simpler forms like the notidanids and

Chlamydoselachus is more or less terminal in posi-

tion. In many other Elasmobranchs, however, its

position is more ventral. The olfactory sae or pit

\ itself varies greatly as to its shape, the nature of

its lining, and the number and depth of the folds

produced in it. In general it may be said to be ellip-

i tical in form, the long axis pointing anteromedially.

/ / The sae may be single or it may be double. In either

we case the lining is thrown into two series of ridges,

the Schneiderian folds (fig. 231), which greatly in-

Fig. 230. Types of olfactory crease the extent of its surface. The so-called see-
sensory cells, Mustelus lae- ‘ ;

vis. (From Asai.) ondary folds are usually anterior and dorsal in po-

sition while the primary folds are posterior and

ventral. In certain forms the folds become exceedingly numerous, more than

eighty primary folds being present.

The sensory cells (fig. 230) have a group of hair-like processes which extend
into the olfactory cup, and fibers which run back as the olfactory nerves to
the glomeruli of the olfactory bulb. From the bulb, fibers extend posteriorly
in the olfactory tract to the olfactory lobe of the brain, as we have described
for Heptanchus.

When seen from the outside the aperture to the olfactory organ is usually
separated by flaps across its middle part into two divisions. One of these
apertures is incurrent, the other is excurrent. In Heterodontus the excurrent
aperture leads backward so that the water current, instead of passing out,
passes backward and into the mouth. In some Elasmobranchs two flaps, instead
of one, may pass over the nasal pit. When this occurs, the one passes inward
from the ventral margin, while the other hangs down and slightly overlaps it

THE ELASMOBRANCH FISHES 265

from the dorsal side. In certain forms more than a single dorsal flap obtains.
In Scylliwm a-double dorsal, and in Myliobatis numerous dorsals are present.
In some of the rays (also in Squatina) these dorsal flaps extend downward as
loose extensions of skin and are of slight value in forming a tube of the cup.
By the meeting of dorsal and ventral flaps the normally elliptical aperture is
changed into a figure 8, thus producing an anteromedial and a posterolateral
opening to the olfactory organ.

As the fish moves forward a current
is produced mechanieally through the
olfactory cup and over the olfactory
membrane. The importance of such a
current in forms which have no direct
connection from the nose to the mouth,
that is, in which the olfactory organ is
solely an organ of sense taking no part
secondarily in respiration, is clearly
seen. That the sense of smell is well
developed in Elasmobranchs has been
demonstrated by the experiments of Fig. 231. Sagittal section of developing
Sheldon (1911). If for example the ae eae alate)
nostrils of the shark be plugged with
cotton so as to prevent a circulation of the water over the olfactory membrane,
the shark will swim over food without detecting it by sight; but if the nostrils
now be unplugged, or even a single nostril, food will be found although it has
been concealed. In fact, of all the special senses the sense of smell is probably
of the most service.

DEVELOPMENT OF OLFACTORY ORGAN

We may now notice briefly the development of the olfactory organ in the
Elasmobranchs. As is common for vertebrates in general this organ first ap-
pears as a thickened epidermal placode or plate which early pits in from the
outside toward the brain so as to form a shallow vesicle. By further growth
this vesicle sinks deeper and forms a blind sae (fig. 231) in which arise the
Schneiderian folds (s.f.) of the primary and secondary types. Furthermore
these folds have produced from their sides numerous accessory folds in which
are found the olfactory sense-cells above mentioned (fig. 230). The two divi-
sions of the olfactory nerve put these two areas of folds into communication
with the olfactory bulb, but each division of the nerve may be connected with
both of the areas of the folds.

GUSTATORY OR TASTE ORGANS

Taste buds are present in the Elasmobranchs often in considerable numbers.
These are located in the buceal cavity and pharynx and are distributed over
the floor and tongue, along the sides, and over the roof of both cavities. An in-

266 THE ELASMOBRANCH FISHES

dividual organ is well illustrated in Heterodontus, in figure 34D, where it is
seen as a papilla arising from the floor of the mouth. These organs often are
surrounded by a more or less circular group of stomodeal denticles.

A section through such a taste bud shows it to be placed over a cup-shaped
base which looks something like the base of a placoid scale. The organ itself is
made up of cells elongated in a vertical direction. These cells are of two sorts.
One is a supporting cell and the other is a sense cell.

ELASMOBRANCH EYE

Extremes to which the Elasmobranch eye may be developed may be exempli-
fied in two types like Isistiws and Squatina. In the former, which is a deep sea
shark, the eye reaches a size which makes it a conspicuous structure standing
out from the sides of the head. In the latter, which is slow moving and noc-

A B C D

Fig. 232. Types of Elasmobranch eyes. (From Garman.) A. Parmaturus pilosus. B. Triakis
henlei. C. Scoliodon. D. Carcharias milberti.

n., nictitating membrane.

turnal, there is but little exact vision and the eye is therefore more or less
rudimentary. Between the two extremes are multitudes of types.

In external view (fig. 232) the eye varies greatly in the type of its pupil
and the nature of its lids. The pupil may be large, denoting a type of eye un-
used to a great deal of light. Figure 233c of Spinax, a deep sea form, shows
such a condition. In Triakis henlei the pupil is smaller and assumes a hori-
zontal position, while in Scoliodon and Carcharias (fig. 232c and p) the pupil
is vertical.

The eyelids, especially the third or nictitating membrane (n., fig. 232), are
also marked characters in external view. In fact on this character alone the
Elasmobranchs were separated by J. Miiller into two groups: (1) those hav-
ing a nictitating membrane and (2) those devoid of it. To the former group
belong Galeus, Mustelus, ete., and to the latter Heptanchus, Acanthias, ete.
The nictitating membrane varies greatly in the degree of its development. In
a type like Carcharias (fig. 232p) it reaches an optimum development where it
can be drawn entirely over the eye.

There has been considerable interest over the relation of the nictitating
membrane to the lower membranous lid. The question is: Is the nictitating
membrane the made-over lower lid with the present lower lid formed anew, or
does it arise from the lower lid? In Mustelus, at least, it has been shown by
Harman (1899) to arise as a ridge on the inner (ocular) side of the lower lid.

THE ELASMOBRANCH FISHES 267

From an external view the eye is seen to be further protected by the orbit
and in a way by upper and lower membranous lids. In Chlamydoselachus the
lower lid is a deep fold which is interesting because a part of its inner surface
is covered with placoid scales. The same is true of Mustelus. In fact it was from
the possession of scales that the lower lid was formerly incorrectly supposed
to be a newly formed structure.

\ WA

U) yy

Fig. 233. Sagittal section of eye. (From Franz.) A. Acanthias. B. Cetorhinus. C. Spinax.
D. Raja batis.

ah., space for aqueous humor; ¢., ciliary body; ch., choroid coat; en., cornea; ir., iris;
l., lens; l.m., lens muscle; o.p., optie pedicel; r., retina; sc., sclerotic coat; sl., dorsal suspen-
sory ligament; sch., suprachoroidea; II, optic nerve.

The eyelids are movable in only a few Elasmobranchs. In Scyllium, while
they are so sluggish as rarely to close, yet the eye has been observed to bat. In
many other forms the lids are more or less completely devoid of musculature
and are therefore immovable. In others musculature may be fairly well de-
veloped (see p. 104, fig. 106). In the rays the eyes are firmly fixed so that
movement is impossible.

STRUCTURE OF ADULT EYE

The structure of the adult eye in a number of Elasmobranchs has been studied
in detail by Franz (1905). In a median sagittal section through the eye of
Acanthias striking the optic pedicel (fig. 2334) the various structures making
up the eye appear. In the anterior part is the clear cornea (cn.) and extending
almost against it is the spherical crystalline lens (l.). The clear space between
the two (ah.) is filled with aqueous humor. The dark layer (ir., fig. 233¢) is
the pigmented iris, a circular curtain which contains the color of the eye; the

268 THE ELASMOBRANCH FISHES

aperture within the iris is the pupil. At (c.) is the ciliary body. The large
cavity back of the lens is filled with the vitreous body. The lining of this cavity
is the retina (7.) under which is the pigmented choroid layer (ch.). Between
the choroid and the sclerotic layers there is a suprachoroidea (sch.) of con-
nective tissue. As an outer protective eapsule, and continuing in front to the
cornea, is the strong sclerotic layer (sc.) through which the optic nerve passes.

If the eye of Acanthias be compared with that of the closely allied Spinax
niger (figs. 2334 and c), which is an inhabitant of the deep sea, several im-
portant differences will be noted. In the first place the eyeball in Spinaz bulges
out in front, and the enlarged lens extends far into the pupil. As a result, in
Spinax the pupil is of immense size and is thus correlated with the environ-
ment in which little light is present. The
sclerotic layer in Spinaz is thin and the
optic pedicel is absent.

Two other types, Cetorhinus maximus,
the basking shark (fig. 2338), and Raja
batis (fig. 233p), may be briefly noted. In
Cetorhinus the eye is of large size and is
marked by several distinguishing fea-
tures. The pupil is small as is also the lens
located well back in the cavity in the vit-
reous body. Back of the choroid, the supra-
choroid coat (sch.) extends dorsally and
ventrally as a strongly vascular area. The
sclera forms an unusually heavy earti-
Fig. 234. Section through the retina laginous capsule from which the optic
aay HATES IEE IS) 1) pedicel (0.p.) is removed by a wide mass

co., cone; ep., epithelial lining; of connective tissue.

i.h., inner wide layer; i.p., inner In Raja (fig. 233p) the eye is of peculiar
Sen baz Oot Outer Reaver shape. The cornea bulges forward at the

. ventral margin, and the lens sinks deep
within the eye. The pupil here is of minute size and the layers of the anterior
part of the eye are exceedingly thin. On the posterior boundary of the eye,
however, the sclera is heavy and is separated from the choroid by a highly
vascular suprachoroidea. The optie pedicel (0.p.) is wide and is joined to the
sclera by connective tissue.

FINER STRUCTURE OF RETINA

A section through the retina of the eye of Wustelus (fig. 234) (Sehaper, 1899)
shows that this important coat of the eye is made up of numerous strata of
cells and fibers. These may be briefly described from the inner to the outer side
of the retina as an inner ganglionic layer containing fibers and cells, then an
inner plexus layer (7.p.). Following this is an inner wide layer (7.4.) and an
outer narrow heavy layer (0.h.). There then follows the important area of

THE ELASMOBRANCH FISHES 269

cones (co.) and rods (rd.) which are intimately associated with vision. These
occupy the layer farthest removed from the lens and next to the epithelial
lining (ep.). The rods and cones together with the cells from the first or gan-
glionic layer may be described more fully.

The rods (rd.) and cones (co.) are characterized by the extreme length of
the cell body. The nuclei of the rods extend almost to the heavy outer layer,
and the slender cells reach the epithelial lining. The cones are heavier but are
fewer in number with their nuclei staining as dark bodies also in the heavy
outer layer. The cone cells extend toward the outer epithelium, but unlike the
rods they do not reach the outer layer.

t is the axones from cells of the retina that pass to the brain as the optic
nerves.

DEVELOPMENT OF EYE

For convenience the development of the eye may be considered in two parts:
(1) the development of the retina and its associated parts; and (2) the de-
velopment of the lens.

The first indication of the eye makes its appearance as a slight down-pitting
of the cephalic plate even before the plate closes (see fig. 209, op.v.). Upon its
closure these pits are directed
outward toward the ectoderm,
as the optic vesicles. The optie
vesicles are therefore direct
outgrowths from the forebrain.
As each vesicle nears the ecto-
derm it sinks in at its outer
margin forming a two-layered
cup, the stem of which as the Fig. 235. Sagittal section through fenestra to ear,
optie stalk binds the bowl of Raja. om Howes.) A. Median sagittal. B. Para-

: ittal.
eg eae MO MERE Lees ENE ake endolymphatic duct; ff., fluid; fn., fenestral
layer of the bowl does not de- tube ; mb., tympanic membrane; ty., tympanic cavity.
velop as nerve tissue but be-
comes pigmented. The choroid coat develops back of this. The inside (invagi-
nated) layer thickens to form the retina, the fibers from which pass along the
old optic stalk to the brain as the optic nerve.

The first indication of the lens is seen as a thickening of the Bean at the
place where the optic vesicle touches it and before the vesicle invaginates to
form the optic cup. The lens then becomes spherical, pinches off from the ecto-
derm, and sinks into the cup.

ACCOMMODATION APPARATUS

In almost all the Elasmobranchs, excepting types like Squatina, the eyes
are so far separated that it would be impossible for both eyes to focus on a
given point at the same time. In all these, binocular vision is impossible and
monocular vision is the rule. Little adjustment of the lens is here possible. It

270 THE ELASMOBRANCH FISHES

will be observed that in a type like Acanthias (fig. 2334) the lens is suspended
by a dorsal suspensory ligament (s/.) and is joined ventrally and laterally by
a muscle (/.m.) from the iris. This might be regulatory in that it would draw
the lens slightly forward but the lens cannot be focused with precision as it
can in man and other higher animals.

Fig. 236. Ear of Elasmobranchs. (Olive Swezy, orig.)
Squalus sucklii: A. Outer view of left ear. B. Inner view of right ear.
Heterodontus francisci: C. Outer view of left ear. D. Inner view of right ear.

a.a., ampulla of anterior oblique semicireular canal; a.h., ampulla of horizontal canal;
aos., anterior oblique semicircular canal; a.p., ampulla of posterior canal; d.c., connection
from posterior canal to sacculus; e.d., endolymphatic duct; e.s., endolymphatic sac;
hr., horizontal canal; l., lagena; pos., posterior oblique semicircular canal; ra.a., ramus
of eighth nerve to ampulla of anterior oblique canal; ra.h., ramus to horizontal ampulla;
ra.n., ramus to macula neglecta; ra.p., ramus to posterior ampulla; ra.s., ramus to sacculus;
ra.u., ramus to utriculus; 7.u., recessus utriculi; s., sacculus; w., utriculus.

THE ELASMOBRANCH FISHES 271

AUDITORY ORGAN

Superficially the ear is protected by the cartilaginous auditory capsule which,
in the embryo, joins the parachordal cartilages of the cranium (see p. 53, fig.
58). In certain types the capsule is so thin as to give indications of the semi-

Fig. 237. Ear of Elasmobranchs. (From Retzius.)
Squatina: A. Outer view of left ear. B. Inner view of right ear.
Raja: C. Outer view of left ear. D. Inner view of right ear.
(For explanation see fig. 236.)

circular canals superficially. Two pairs of apertures may enter the capsule
from the parietal fossa in the middorsal line. The first and smaller of these is
for the endolymphatic ducts (e.d., figs. 59 and 62), while the second and larger
pair of apertures are the fenestrae (fn.). These apertures may be considered
more in detail.

I have previously mentioned fenestrae for a number of sharks and for some
of the rays (p. 55). If we refer to figures of the dorsal view of the skull (figs.
59 and 62) we observe that these openings are well marked and take up their

272 THE ELASMOBRANCH FISHES

position posterior to the apertures for the endolymphatic ducts. A sagittal
section through the cranium of the skate as given by Howes (1883) shows that
each fenestra enters a well defined cavity or tympanum (ty., fig. 2358) within
the ear capsule, and further (fig. 235) that the aperture is closed dorsally by
amembrane (mb.). Over the membrane is a semifluid layer (fl.), above which
is the integument. In a type in which the head is flattened (ray) this mem-
brane fits closely over the fenestrae, and may serve to transmit sound waves
to the cavity below it and thus to act some-
thing after the fashion of the tympanic
membrane of the middle ear of higher
forms.

The endolymphatic duet (e.d., figs. 236
and 237) is normally small proximally
and then enlarges into a more or less tor-
tuous endolymphatie sae (e.s.). In Squa-
tina, on the contrary, and to a certain
extent in Acanthias, the mouth of the
duct is enlarged and although bent at its
upper part it is little changed in caliber
throughout its course. At its base the duet
broadens out into the saceulus (s.). In
some forms this is relatively small (Alo-
Fig. 238. Finer anatomy of an otic pias; Heterodontus, fig. 236c), but it may
ieee eee. Bee. be of large size (Squalus sucklii, fig. 236a,
tail of cells. s.). It is within this cavity as well as in the

cr., crista acustica; cu., cupula ter- utriculus that the otoliths or so-called ear
ee ob deat well Gens stones are lodged. These in Squalus con-
sist of a mass of caleareous material con-
tained within the endolymph. In some of the other forms they are small, and
in the embryo of Squatina they are apparently absent. In the adult Squatina
a most interesting condition is reported. Here it is said that the place of the
concretions of other forms is taken by sand grains which enter the wide endo-
lymphatie duet.

From the inferior and posterior angle of the sacculus (figs. 236 and 237) the
lagena (l.) arises. This is usually a tongue-like projection as in Heptanchus,
but it may assume a form greatly enlarged at the end, as in Lamna. The lagena
is that part of the ear in the Elasmobranchs which is probably the forerunner
of the complex cochlea of higher forms.

At its inferior and anterior angle the sacculus is connected with the utricu-
lus (w.) by the recessus utriculi. In figure 2364, the aperture from the utricu-
lus to the recessus utriculi is shown as a solid ellipse. The utriculus itself is
sometimes considered as made up of an anterior and a posterior component,
the anterior of which is entered by the recessus utriculi, and if seen in side
view may represent a T, the right and left arms of which are the horizontal

THE ELASMOBRANCH FISHES 273

(hr.) and anterior oblique semicircular (aos.) canals. The posterior utriculus
is the posterior connective of the posterior oblique semicircular canal. This
frequently, as in Heterodontus francisci (pos., fig. 236D), may be well devel-
oped, the two parts of the utriculus being widely separated by the sacculus and
endolymphatic duet. The posterior part of the utriculus has its connection
with the sacculus by an elliptical aperture (d.c.) in Squalus, but this connec-
tion is much longer in a type like Heterodontus. In Laemargus borealis the
posterior part of the utriculus is connected with
the sacculus by a long tube as it is also in Raja
clavata (d.c., fig. 237D).

The semicircular canals, although assuming dif-
ferent degrees of compression, as is shown by a
comparison of the compact ear of Heptanchus
with the elongate ear of Squalus, are similarly ar-
ranged in three planes. One of these planes is an-
terior and oblique, another posterior and oblique,
and the third horizontal in position. The anterior
and horizontal canals join the utriculus proper,
pass forward and backward respectively and then
downward to their ampullae, which are in close F18- 289. Development of

os ‘ bor Pe aa the ear of Scyllium. (From
proximity. The posterior canal is similarly a con- Krause.)
tinuation of the posterior part of the utriculus up- aos., anterior oblique semi-
ward and backward and downward to its ampulla @"¢ular canal; e.d., endo-
lymphatie duct; hr., horizon-
(figs. 236 and 2378 and D). tal canal; s., sacculus.

The ampullae (a.a., a.p., and a.h., figs. 236 and
237) are interesting from their terminal relations as end organs of the nerve.
A section through such an otic ampulla (fig. 2384) by Retzius (1881) shows
the erista acustica (cr.) which is the terminal mass of sense cells capped by
the cupula terminalis (cw.). A more detailed view cutting through the am-
pulla demonstrates two kinds of cells in the crista. One of these is the support-
ing or thread cell (t.c., fig. 2388) and the other is the sense or hair cell (/.c.).
The latter of these projects into the endolymph of the ampullary cavity and is
capable of receiving sensations. Multitudes of cells of this sort are located in
all the ampullae and also in the saeculus, lagena, and macula neglecta.

INNERVATION OF EAR

The innervation of the ear is, as we have said for Heptanchus, through the
eighth or auditory nerve. Just before reaching the ear the nerve separates
into two main divisions (figs. 236 and 237). The anterior division, the vestib-
ular nerve, separates into an anterior ramus (ra.a.) to the anterior ampulla
and a second ramus to the ampulla of the horizontal canal (ra.h.). Other
branches from the stem supply the area of the recessus utriculi. The posterior
of these, the saccular nerve, finally reaches the ampulla (a.p.) of the posterior
canal. On its way it gives off a dorsal branch, the ramus neglectus (ra.n.) to
the macula neglecta of the sacculus, and ventral branches to the lagena and to
the saceulus (ra.s.).

274

THE ELASMOBRANCH FISHES

DEVELOPMENT OF EAR

The ear (Scyllium, fig. 239), like the nose, forms as a pit. In the development
of the ear, however, the vesicle thus formed sinks in and, as the sacculus (s.),
becomes far removed from the exterior. It does not, however, lose entire con-
nection with the outside for as it sinks inward it becomes flask-shaped, the

cc. : :

Fig. 240. Dorsal view of cephalic canals in
Laemargus. (From Ewart.) (Drawn as
transparent object.)

ec., commissural or supratemporal canal;
hme., hyomandibular eanal; ioc., infraorbi-
tal canal; ll., lateral canal; soc., supraorbital
canal.

long neck being the endolymphatie
duct (e.d.). At this stage the outer
wall of the vesicle becomes thin and
the anterior oblique and horizontal
semicircular canals (aos. and hr.) de-
velop from them.

SENSORY CANAL SYSTEM AND
AMPULLARY AND PIT
ORGANS

The sensory canal system as we have
seen in Heptanchus consists of exten-
Sive sensory canals over the head and
along the side of the body. The am-
pullary organs associated with cer-
tain of the canals and innervated by
the same nerves are confined to the
region of the head. Certain modifica-
tions of the latter, the vesicles of Savi,
may also be present. The pit organs
are mainly in the anterodorsal trunk
region but some of them are in the
segment of the head.

SENSORY CANAL SYSTEM

The sensory canals take a general
course parallel to the long axis of the
body. In the region of the trunk and
tail they compose the lateral line ob-
served in our study of external form,
and in the region of the head they
form the cephalic canals, three or four
main divisions of which are present in
the sharks. One of these, the supra-

orbital canal (soc., figs. 240-242), runs above the eye; another, the infraorbital
(voc.), passes back of and forward below the eye; the third or hyomandibular

THE ELASMOBRANCH FISHES 275

canal (hmc.) passes backward from the infraorbital to the region of the hyoid
arch; and a fourth, the mandibular (mc.), traverses the lower jaw. Various
modifications of these and their accessory parts will be noted later.

The formation of the lateral and cephalic canals may first be briefly de-
scribed. The earliest rudiment of the lateral line appears as a flattened plate

A B

Fig. 241. Sensory canals and ampullae of Lorenzini, Squalus sucklii. (Olive Swezy, orig.)
A. Dorsal view. B. Ventral view.

cc., commissural or supratemporal canal; e.d., endolymphatic duct; hme., hyomandibular
eanal; iba., inner buceal ampullae; ioc., infraorbital canal; isa., infraspiracular (hyoid)
ampullae; ll., lateral line; mc., mandibular canal; mpo., mandibular ampullae; n.ap., nasal
aperture; oba., outer buccal ampullae; soa., supraophthalmie ampullae; soc., supraorbital
canal; sp., spiracle.

of ectoderm continuous with, and like that of, the placode for the ear, but this
extends both forward and backward. Forward it gives rise to the long canals
of the head region. Backward it becomes the lateral line organ. Hither way,
in order to become a canal rather than an open groove the sensory cord or
plate of ectoderm, usually as a pocket, pushes deep into the underlying corium.
It may be mentioned here that at regular intervals throughout its course the
sensory cord differentiates into patches of ectoderm, the end organs or neuro-
masts characteristic of these canals.

In the adult Elasmobranch the lateral line canals (figs. 240-242) are simi-
lar in distribution. They extend in or under the skin from the tip of the tail
to the segment of the ear. The lateral line canal in Chlamydoselachus is an

276 THE ELASMOBRANCH FISHES

open groove practically to the supratemporal canal, and in the notidanids it is
open as far forward as the anterior region of the pectoral fin. In Acanthias on
the contrary the canal is closed excepting in the region toward the tip of the
tail. In all higher Elasmobranchs it is usually closed throughout the entire
length. In some of these the canals run to a considerable depth, but in all such
they still remain in communication with the exterior by tubules. The tubules
putting the canal in com-
munication with the out-
side may be as numerous
as are the branches of
nerves (ramuli) reach-
ing them (fig. 244). In
certain forms, however,
they are fewer innumber,

In its anterior segment
the lateral line of each
side is Joined to its fellow,
posterior to the endolym-
phatie ducts, by the su-
pratemporal canal (cc.).
This canal, however, is in-
complete in Heptanchus.
Furthermore, on each
side it may branch so as
to send a part anterior to
the endolymphatic ducts
in addition to the regular
branch posterior to the
ducts. In Chlamydose-
lachus the supratemporal
connection passes ante-
rior to the endolympha-
tic ducts. It seems reason-

able to suppose that this
Fig. 242. The cephalic canals, Raia batis, dorsal view. ranch is comparable to
(From Ewart and Mitchell, modified.) 1 é ; pt

c¢c., commissural or supratemporal canal; hmc., hyoman- the occasional anterlor
dibular canal; ioc., infraorbital canal; Il., lateral line; branch of Heptanchus.
me., mandibular canal; soc., supraorbital canal; se.-’, first The lateral lanelenntl

and second scapular canals; sp., spiracle. :
usually passes directly

into the cephalic canals, but in Heterodontus francisci at its anterior end it
swerves sharply toward the middorsal line and joins the supratemporal canal;
it then joins the supraorbital canal by making a sharp bend laterally.

The cephalic canals are usually, as we have said, a direct continuation of
the lateral line canal. In Laemargus (fig. 240) these canals are made up of the
divisions above named. The supraorbital (soc.) passes forward above the eye

THE ELASMOBRANCH FISHES 277

and at the tip of the nose passes through to the ventral side. It then continues
backward to meet the infraorbital (ioc.). This condition is unlike that in Hep-
tanchus (fig. 228) in which the terminal part going to the infraorbital is
usually broken in its course. The infraorbital drops back of the eye to a ventral
position and then forward under the eye; after passing the ventral terminus
of the supraorbital, it turns inward toward the middle line, where it approxi-
mates or meets (Lae-
margus) the infraor-
bital of the opposite
side. It then continues
forward and slightly
outward to the tip of
the nose. The hyoman-
dibular canal (hime.)
in the sharks branches
off posteriorly from
the infraorbital at the
place where the latter
reaches a ventral posi-
tion back of the eye.
Essentially the same
plan obtains in Squa-
lus sucklii (fig. 241) as
that here described
for Laemargus.

This plan is consid-
erably modified in the
rays. In these, the su-
praorbital canal (soc.,
fig. 242) in its ventral
course is characterized
by a peculiar loop for-
ward and outward. It
then meets the infra- Fig. 243. Cephalie canals in Dicerobatis, dorsal view. (From

orbital ventrally as in Garman.)

sharks. The hyoman- CC. commissural or supratemporal canal; hme., hyoman-
dibular (hmc.,fig.242) dibular canal; ioc., infraorbital canal; ll., lateral line; soc.,
/ fas SH —

supraorbital canal.

in the rays is greatly

modified. It passes from the infraorbital backward, outward, and then for-
ward on the ventral side of the pectoral fin, making a large ventral loop (in-
complete in Torpedo). It then perforates the fin at the side of the olfactory
capsule, and continues its course on the dorsal side of the fin, first inward and
backward; then it swerves far outward and backward and then inward to join
an anterior scapular branch (sc.') from the lateral canal, forming with the
scapular branch dorsally on the pectoral fin a characteristic loop.

eek ae
S—~ a

=
wen:

PN
ess

SSne
SSR So 5

SSS

278 THE ELASMOBRANCH FISHES

In addition to what we have said of this system in a typical ray, it may be
added that in a sluggish type like Torpedo certain of the cephalic canals may
be lacking ventrally while in an active form like Dicerobates (Cephalopoda)
tubules may branch off of the canal, unlike the simple tubules of Raja clavata,
and form a complex net (fig. 243).

The internal structure of the canals may be studied in a transverse section
through the lateral sensory canal of the leopard shark, Triakis semifasciatus
(see p. 26, fig. 29, Il.c.). In such a figure it will be seen that the walls of the
canal are unequal in thickness. Both in the lateral line and the dorsal cephalic

YE:

ie aM irua ee APTI Naik MEIN MHA > aren atric nil cD
He) S Aaa petal ieee HES, 4 ‘(6 et Ra GUS AO | fF he Ha i 5 Ot i jak i ait ‘,
escleeain ceioneueemsiN corsa ean deem ruenecescaos os
——
Nas A
. Wr Clm. Sn.Ch
= ~ Amok

Fig. 244. Longitudinal section of lateral sensory canal, Mustelus canis. (From 8. E.
Johnson.)

Grp., neuromasts; Clm., nerve; Lat.Cn., lateral sensory canal; Rml., ramus of lateral
nerve; Sn.Cl., primary hair cell; Spn., supporting cells; Tub., tubule to exterior.

canals the lumen is flattened; but in the ventral canals it is rounded. On the
median wall of the canal the section passes through a sense organ or neuro-
mast, composed of cells derived from the basal layer of epidermis (s.c.). These
are of two types, one a crescentic supporting cell and the other an elongated
elub-shaped sense cell. A longitudinal section through the lateral sensory
canal of Mustelus canis (fig. 244) by Johnson (1917) shows that the neuro-
masts are much more numerous than are the tubes (7'ub.) which open to the
surface. Each of these groups (Grp.) is composed of primary hair cells
(Sn.Cl.), secondary sense cells at the sides of the primary cells, and under-
lying these the supporting cells.

Innervation of the lateral line in the body is by means of the lateral division
of the vagus or tenth cranial nerve. It will be observed from figure 244 that the
ramuli (#ml.) reach the canal at about the position of the tubules, but that
they break up into numerous fibers, which supply a multitude of neuromasts
(Grp.). In the most anterior part of the lateral line canal, however, a few
twigs are received from the ramus dorsalis X (dr.X, fig. 245) and the supra-
temporalis X. Other twigs of the supratemporalis X supply the supratemporal
canal. The segment of the lateral canal immediately anterior to the supratem-

THE ELASMOBRANCH FISHES 279

poral canal is supplied by a few twigs of the supratemporalis IX (Chlamydo-
selachus, Laemargus, Squalus acanthias, fig. 245, st. 1X) and the most anterior
part of this segment is supplied by a few fibers from the ramus oticus VII.

The supraorbital canal is supplied by branches from the ophthalmicus
superficialis of the facial nerve, and the infraorbital by the bucealis nerve,
while the neuromasts of the hyomandibular and mandibular canals are sup-
plied by the external mandibular division of the seventh nerve.

FUNCTION OF SENSORY CANAL SYSTEM

The function of the sensory canal system has been made the subject of many
studies. It was observed by early workers that the pores contained mucus. The

WEE. AN eee

re 380 CATTLE

\) | ae

Fig. 245. Innervation of the sensory canal system and certain of the pit organs, Squalus
acanthias. (From Norris and Hughes.)

bu.VII, bucealis nerve; cc., supratemporal canal; dr.X, ramus dorsalis of tenth nerve;
hme., hyomandibular canal; ioc., infraorbital canal; /l., lateral line canal; 1/.X, lateral line
nerve; me., mandibular canal; mde.VIJ, external mandibular nerve; os.V II, ophthalmicus
superficialis of seventh nerve; po., pit organs; soc., supraorbital canal; st.1X, supratem-
poralis of ninth nerve; st.X, supratemporalis of tenth nerve.

system was therefore taken to function in the production and distribution of
mucus and the pores were therefore called mucous pores. Later study also
demonstrated the relation of these organs to the nervous system.

It has been shown by G. H. Parker (1904) that a shark which has been de-
prived of hearing and sight responds to wave movement, like that produced by
throwing a stone into the water, so long as the nerves to the lateral line are
intact. When these nerves are cut, however, no further response is given.

AMPULLARY ORGANS

The ampullary sense organs, as in Heptanchus, are confined to the head and
are generally arranged in four or five groups. These are, in Squalus sucklii
(fig. 241), the supraophthalmic (soa.), the inner (iba.) and outer buccal
(oba.) groups; and the mandibular just behind the mandible; and the hyoid

280 THE ELASMOBRANCH FISHES

groups (isa. and mpo.). In addition to these there is a modified ampulla in
the spiracular wall. In active forms the pores to these organs may be very
numerous as in Mustelus canis in which practically 1600 have been counted.
In a sluggish type like Torpedo there are as few as 162 (Norris, 1929).

Each ampullary organ (fig. 246) consists of three parts: (1) a pore or
opening to the exterior (ap.); (2) acanal or tubule (tb.) ; and (3) the ampulla
proper (a.), located in the in-
tegument. The ampulla varies
as to pattern in the different
Elasmobranchs. In some it is
not divided up into ampullary
pockets. In others it may have
from eight to twelve pockets.
These pockets are usually con-
nected by a single canal with
the outside pore. In Hexan- A
ae chus, however, Dotterweich

(1932) has recently shown that
each ampullary pocket in a
eroup has its own canal and
that a group of canals empties
by a common pore. A trans-
verse section through the am-
pulla (fig. 2474) shows how
they and the partitions sepa-

raOe
8 eae

ap. rating them are cut. Accord- SEX
Fig.246. Ampullary ing to Peabody (1897) each
organ of Lorenzini. agmpullary pocket (pk.) has B

2 } ye ee . ] Vf 7, 1
(From Peabody.) a double lining, the inner layer Fig. 247. A. Transverse section.

‘ Dae : B. Sagittal section of an am-
a., ampulla; ap, of which is of cells of large size. pula, Galeus. (From Peabody.)
aperture to outside ; ’

76 tabule: The pockets are surrounded by — en., centrum; pk., ampullary
connective tissue and may Pocket

themselves surround a central part, the ampullary centrum (cn.). Figure 24738

is a sagittal section through the centrum. The section is through a pocket on

the left and a partition between two pockets on the right. In figure 248 it is

seen that the nerve to the ampulla enters through the centrum and spreads out

over the ampullary pockets.

It was formerly supposed that the cap over the centrum was the sensory
area in which the nerve terminated, but in figure 248 it appears that, while
the nerves lose their medullary sheaths and only the axis cylinders run toward
the central cap, the fibers turn outward as the fibrils surround the ampullary
saes. Dotterweich (1932) has recently shown that the wall of an ampulla of
Lorenzini is made of a single layer but that this layer consists of two impor-
tant types of cells. One of these is a flask-like cell (g., fig. 249) which forms
mucus. The other is a pyramidal or sensory cell (s.). These pyramidal re-

THE ELASMOBRANCH FISHES 281

ceptor cells, as hexagonal plates, line the ampulla. They are apparently not
provided with hair-like processes which extend into the ampullary cavity but
each pyramidal cell has a sensory nerve (af.) leaving from the apex of the cell.

A motor axone (ef.) extends to
Vf
W,

each of the secreting or flask-like egy AVION Von
cells. iN Sy NG WD
In their development the am- iS yy MG Sy Px
APA WE IS (Z

j L
pullary organs, like the long ca- Ze LWA
nals, form as pits of the epider- SE IES \\
mis. These pits sink deeply into —% ee
the integument and often extend if \ SEAS Swe
MAA Ya \ NSS Ret REN
far forward or backward forming h Yah Re EK
(UY RASS
more or less elongate tubules. At \ ) IN RWS
the end of the deepest part the U\\/AVIEP \ ae ROXAS
tubule swells out, forming an am- | ANS OSS
pulla of Lorenzini. | /
The vesicles of Savi found in \ NK
Torpedo consist of from one hun- _. ve: . :
Fig. 248. Section showing ending of nerves (n.)
dred to two hundred hollow saes in ampulla. (From Retzius. )

in the region of the nasal pit and

ventrally between the cartilage of the pectoral fin and the electric organ.
Each vesicle is a transformed canal organ which, unlike an ampulla of Loren-
zini, is unconnected with the exterior. Such a vesicle is composed of three dises,
one of which is large and occupies a median position while at the sides of this
are two lateral and smaller ones.

Pit ORGANS

In addition to the above-mentioned organs, pit organs found in sharks and
rays may here be described. These organs were early seen in the rays along the
back just mediad of the lateral line and from the suprascapular line to the

Fig. 249. Receptor cells and gland

cells in an ampulla of Lorenzini, ees

(From Dotterweich. ) Fig. 250. Pit organ, Raia batis. (From
af., afferent nerve; ef., efferent Ewart and Mitchell. )

nerve; g.,glandcells; s., sensory cell.

first dorsal fin. Others occur along the hyomandibular and the infraorbital
canals in the head.

Ewart and Mitchell (1891) have given a section through a pit organ of the
ray (fig. 250) which shows it to be not unlike a taste bud. The narrow neck
leads to a group of sense cells which form a ball. Each of the sense cells is long

282 THE ELASMOBRANCH FISHES

and has passing from it dorsally a sensory process. A sensory nerve leaves the
base of the organ and passes along with the lateral line nerve.

Attention has been directed by several workers to the pit organs in sharks.
These have been studied recently for Squalus acanthias by Norris and Hughes
(1920). Pit organs are here distributed between the lateral lines and anterior
to the first dorsal fin, and are supplied by the dorsal ramus (dr.X) of the
tenth nerve. In Heptanchus maculatus (fig. 229) this system of organs is
especially worthy of note since its organs have a segmental arrangement. In
places the lines of organs from one side to another are in almost unbroken
continuity, while other lines are limited to one side.

1904.

1903.

1894.

1883.

1896.

1899.

1886.

1905.

1891.

THE ELASMOBRANCH FISHES 283

BIBLIOGRAPHY

CHAPTER X

ORGANS OF SMELL

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ORGANS OF SIGHT

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284 THE ELASMOBRANCH FISHES

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1880. MATTHIESSEN, L., Untersuchungen uber den Aplanatismus und die Periscopie der
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pp. 83-111, 25 text figs.

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Movements of the Dogfish Mustelus canis (Mitchell). Bull. Bur. Fish., Vol. 29, pp.
43-57.

1899. ScHAPER, A., Die nervésen Elemente der Selachier-retina in Methylenblaupripara-
ten. Nebst einigen Bemerkungen iiber das “Pigmentepithel” und die konzentrischen
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1905. SCHNAUDIGEL, O. A. F., Neurofibrillen in den Retinalganglienzellen der Selachier.
(Ber. Ophthalm. Ges. Heidelberg) Bd. 32, pp. 329-331.

1898, SHEARER, CRESWELL, On the Nerve Terminations in the Selachian Cornea. Jour. Comp.
Neurol., Vol. 8, pp. 209-217, 4 text figs.

ORGANS OF HEARING

1892. Ayers, H., Vertebrate Cephalogenesis. II. A Contribution to the Morphology of the
Vertebrate Ear, with a Reconsideration of Its Functions. Jour. Morph., Vol. VI, pp.
1-360, pls. 1-12, 26 text figs.

1884. BEARD, J., On the Segmental Sense Organs of the Lateral Line, and on the Morphol-
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1899. BrETHE, A., Die Locomotion des Haifisches (Seyllium) und ihre Beziehungen zu dem
einzelnen Gehirntheilen und zum Labyrinth. Arch. f. d. ges. Physiol., Bd. 76, pp. 470-

493, 2 text figs.

1896. EvErETT, W. H., Anatomy of the Ear of the Dogfish (Galeus canis). (Prelim.) Trans.
N. Y. Acad. Scei., Vol. 15, pp. 176-182, pls. 12-13.

1902. Gacuio, G., Expériences sur l’anesthésie du labyrinthe du Voreille chez les chiens de
mer (Seyllium eatulus). Arch. Ital. Biol., T. 38, pp. 383-392.

1883. Howes, G. B., On the Presence of a Tympanum in the Genus Raia. Jour. Anat. and
Physiol., Vol. 17, pp. 188-190, pl. 8.

1901. Krause, R., Die Entwickelung des Aquaeductus vestibuli s. Ductus endolymphaticus.
Anat. Anz., Bd. 19, pp. 49-59, 21 text figs.

1907. Larire-Dupont, Recherches sur Vaudition des poissons. C.R. Soc. Biol. Paris, T. 63,
pp. 710—711.

1899. LAUDENBACH, J., Zur Otolithen-Frage. Arch. f. d. Ges. Physiol., Bd. 77, pp. 311-320,
1 text fig.

1893-94. Ler, F. S., A Study of the Sense of Equilibrium in Fishes. Part I. Jour. Physiol.,
Vol. 15, pp. 311-348, 1893. Part IL. Ibid., Vol. 17, pp. 192-210, 1894.

1898. Lez, F. S., The Functions of the Ear and the Lateral Line in Fishes. Amer. Jour.
Physiol., Vol. 1, pp. 128-144.

1900. Lyon, E. P., Compensatory Motions in Fishes. Amer. Jour. Physiol., Vol. 4, pp. 77-82.

1910. MaxweELL, S. S., Experiments on the Functions of the Internal Ear. Univ. Calif.
Publ. Physiol., Vol. 4 (1910-1915), p. 1.

1911. MAxwELL, S. S., On the Exciting Cause of Compensatory Movements. Amer. Jour.
Physiol., Vol. 29, p. 367.

1919.

1897.

1903.
1909.
1903.

1881.

1883.

1906.

1901.

1884.

1868.

1875.

1898.

1900.
1908.

1891.

1902.

1905.

1896.

1878.

THE ELASMOBRANCH FISHES 285

MAXxweELL, S. S., Labyrinth and Equilibrium. I. A Comparison of the Effects of Re-
moval of the Otolith Organs and of the Semicircular Canals. Jour. Gen. Physiol.,
Vol. 2, pp. 123-132.

. MaAxwe tt, 8. S., II. The Mechanism of the Dynamic Functions of the Labyrinth.

Ibid., pp. 349-355, 1 text fig.
MAXWELL, S. S., III. The Mechanism of the Static Functions of the Labyrinth. /bid.,
Vol. 3, pp. 157-162.

21. MAxweELL, S. S., The Equilibrium Functions of the Internal Ear. Science (n.s.), Vol.

53, pp. 423-429.

Morritt, A. D., Innervation of the Auditory Epithelium of Mustelus canis De Kay.
Jour. Morph., Vol. 14, pp. 61-82, pls. 7-8.

ParKER, G. H., The Sense of Hearing in Fishes. Amer. Nat., Vol. 37, pp. 185-204.
ParkeER, G. H., The Sense of Hearing in the Dogfish. Science (n.s.), Vol. 29, p. 428.
Quix, F. H., Experimenten over de Functie van het Labyrinth bij Haaien. Tijdschr.
Nederland Dierk. Ver. (Ser. 2), Deel. 8, pp. 35-61, 1 text fig.

Rerzius, G., Das Gehérorgan der Wirbeltiere. Morph.-hist. Stud., Bd. 1, Pt. I, pp.
1-217, Taf. 1-35. Stockholm.

SEWALL, H., Experiments upon the Ears of Fishes with reference to the Function of
Equilibrium. Jour. Physiol., Vol. 4, pp. 339-349.

STEWART, CH., On the Membranous Labyrinths of Certain Sharks. Jour. Linn. Soe.
Zool., Vol. 29, pp. 407-409, pl. 40.

LATERAL LINE AND ASSOCIATED ORGANS

Auuis, E. P., The Lateral Sensory Canals, the Eye-Muscles, and the Peripheral Dis-
tribution of Certain of the Cranial Nerves of Mustelus laevis. Quart. Jour. Mier. Sci.,
Vol. 45, pp. 87-236, pls. 10-12.

BEARD, J., On the Segmental Sense Organs of the Lateral Line, and the Morphology
of the Vertebrate Auditory Organ. Zool. Anz., Vol. 7, pp. 123-126, 140-143.

Bou, Franz, Die Lorenzini’schen Ampullen der Selachier. Arch. mikr. Anat., Bd. 4,
pp. 375-390, pl. 23.

Bou, FRANZ, Die Savi’schen Bliischen von Torpedo. Arch. f. Anat. u. Physiol., Jahrg.
1875, pp. 456-468, Taf. 11.

BRANDES, G., Die Lorenzini’schen Ampullen. Verh. deutsch. zool. Ges. 8. Vers. Heidel-
berg, pp. 179-181. (Histologie. )

BRANDES, G., Die Lorenzini’schen Ampullen. Zool. Centralbl., 7. Jahrg., p. 567.
BrouMeER, P., Die Sinneskaniile und die Lorenzini’schen Ampullen bei Spinax-Embry-
onen. Anat. Anz., Bd. 32, pp. 25-40, 8 text figs.

Coaet, A., Le visicole di Savie gli organi della linea laterale nelle Torpedini. Atti Ace.
Lincei Roma (4), Vol. 7, pp. 197-205, 7 text figs. Arch. Ital. Biol., Vol. 16, pp. 216—
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286
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1891.

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1899.
1888.

1895.

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1892.

LOA

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THE ELASMOBRANCH FISHES

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(Abt. Zool.), Bd. 50, pp. 347-418, 43 text figs.

Ewart, J. C., The Lateral Sense Organs of Elasmobranchs. I. The Sensory Canals of
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ForsELL, G., Beitrage zur Kenntnis der Anatomie der Lorenzini’schen Ampullen bei
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Fritscu, G., Ueber Bau und Bedeutung der Kanalsysteme unter der Haut der Se-
lachier. Sitzber. wiss. Akad. Berlin, 1888, pp. 273-306, 4 text figs.

Fucus, S., Ueber die Function der Organe der Seitenlinie bei den Selachiern. Centralbl.
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Taf. 6.

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Vol. 28, pp. 1-74, 83 text figs.

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Dogfish Squalus acanthias. Some Comparisons with Other Plagiostomes and Correc-
tions of Prevalent Errors. Jour. Comp. Neurol., Vol. 47, pp. 449-465.

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Vol. 24, pp. 185-207.

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ORGANS OF TASTE AND TOUCH

FAHRNEHOLZ, Curt, Uber die Verbreitung von Zahnbildungen und Sinnesorganen im
Vorderdarm der Selachier und ihre phylogenetische Beurteilung. Jena. Zeitschr.
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Vol. 30 (n.s.), pp. 515-518, pl. 33 (figs. 1-4).

XI
UROGENITAL SYSTEM
UROGENITAL SYSTEM OF HEPTANCHUS MACULATUS

URINARY SYSTEM

The mesonephrotic kidneys in Heptanchus (kd., fig. 251) appear as right and
left longitudinal bands lying along the entire roof of the body cavity and at
the sides of the spinal column. Each kidney extends as a narrow ribbon of
tissue from the pericardio-peritoneal septum posteriorly one-half the length
of the body cavity; back of this it broadens out and becomes much thicker so
that the main mass of the tissue les posterior to the region of the superior
mesenteric artery.

In general it may be said that the kidney is made up of multitudes of small
lobules which in ventral view give little evidence of segmentation. A close
study, however, reveals the fact that a division into segments is present. This
may be further verified by the segmental arrangement of the collecting tubules
which extend from the kidney tissue to the Wolffian duct (w.d.), or in the
posterior part to the ureter (w.).

From the upper part of the kidney the collecting tubules enter the Wolffian
duct and in the lower part they join the enlarged ureter. In an immature fe-
male ten of these collecting tubules may be seen to join the Wolffian duct on its
median side and twelve to join the ureter laterally, twenty-two in all being
present. A similar condition is present for the upper part of the kidney of the
adult female as is seen in figure 252 (facing p. 290). But in that figure the ure-
ter has not been thrown to the side and so not all the ducts entering it appear.

In the immature female (fig. 2514, 70.3 em. in length) the Wolffian duct
passes the entire length of the kidney apparently as a straight tube, increas-
ing from 0.5 to 1 mm. in size. In its anterior segment it lies just ventral to the
kidney, and in the posterior division it passes along the ventral and median
margin of the ureter. In the lower part of its course it does not receive col-
lecting tubules.

The Wolffian duct of the adult female (fig. 252) presents a most interesting
condition in its upper segment where it is singularly coiled like that of the
male. This distinct torsion, however, extends only a little over one-half of the
anterior segment or to the posterior part of the sex gland (ov.). The remain-
ing part of this segment is straight and the posterior segment, like that in the
immature female, passes ventral to the enlarged ureter.

The ureter in Heptanchus is a thin walled, elongated blind sae which in the
immature specimen above described reaches a diameter of 7 mm. Anteriorly,
and essentially at the segment where the kidney begins to increase in size, the

[287]

288 THE ELASMOBRANCH FISHES

A B

Fig. 251. Urogenital system of immature Heptanchus maculatus. (Frances Torrey, orig.)
A. Female. B. Male.

c.c., central canal of testis; cl., cloaca; cls., clasper; ct., collecting tube; fl., funnel;
kd., kidney ; od., oviduct; ov., ovary; s.g., shell gland; t., testis; w., ureter; wg., urogenital

sinus; w.p., urinary papilla; w.s., urinary sinus; v.d., vas deferens; v.e., vas efferens;
w.d., Wolffian duet.

THE ELASMOBRANCH FISHES 289

ureter ends blindly. In its median segment it increases somewhat in diameter
and then tapers gradually to its posterior part where as a usual thing it joins
the Wolffian duct. The collecting tubules which enter the ureter are arranged
with regularity throughout the greater part of its course, but the anterior two
or three join as a common duct and enter a kind of pocket in the median side
of the ureter (see fig. 252). In the short common segment formed by the union
of ureter and Wolffian duct, near the cloaca, considerable variation prevails.
In one immature female the left combined Wolffian duct and ureter entered
slightly posterior to the right and in another these relations were reversed.
In figure 252 it will be observed that the Wolffian duct and the ureter enter
the urinary sinus (w.s.) separately and that in this specimen a singular condi-
tion obtains in which there are two urinary sinuses, one on the right, the other
on the left side.

The urinary sinus terminates in a urinary papilla (two papillae in fig. 252)
which is perforated at its end. Nitrogenous waste matter collected from the
kidney is ejected through this into the cloaca (cl.) and thence to the exterior.

It would appear from general proportions that the posterior part of the
kidney is by far the more effective part of the organ in the removal of nitrog-
enous waste matter. If this is so the greater part of the waste passes through
the ureter.

The urinary organs in the male have much the same appearance in general
as those in the female. In the male, however, some of the tissue and ducts have
undergone great change correlated with the fact that in the adult they entered
secondarily into the service of the genital system.

The kidney of an immature male of 75 em. in length is shown in figure 251s.
It is 18.8 em. long and has 12 segments in the anterior part and 14 in the poste-
rior. In general it extends farther forward and is somewhat better developed
anteriorly than is that of the female. But this is due, as we shall see presently,
to its relation to the genital organs.

The collecting tubules (ct., fig. 2514) entering the Wolffian duct are ex-
ceedingly small and could be made out with care in the most anterior part of
the kidney. Posterior to this region they are distinctly arranged segmentally,
each tubule leaving the segment at about its middle part. At the proximal end
of the kidney there are certain other tubules (v.e., fig. 2518) which are a part
of another system which will be described presently.

The Wolffian duct, in the upper part of its course, is thrown into numerous
coils like those of the adult female, but here they are more pronounced and
continue to the beginning of the enlarged part of the kidney. From this place
posteriorly the tube increases in diameter and passes ventral to the enlarged
ureter as it does in the female.

The ureter (w., fig. 2518) is much like that of the female and receives prac-
tically the same number of collecting tubules. After it unites with the vas def-
erens (modified Wolffian duct) the two empty into the urogenital sinus (1g.).

bo
No)
So

THE ELASMOBRANCH FISHES

GENITAL SYSTEM

The genital system in Heptanchus is of an interesting type. Each ovary (ov.,
fig. 252) of the adult female is large and is located in the anterior part of the
body cavity where it is suspended by a mesentery, the mesovarium. It con-
tains numerous ova which can be seen through the thin wall. From the main
mass of the ovary there is a posterior continuation of tissue which is devoid
of ova. This is possibly the rudiment of an epigonal organ (epg.) found in
some of the other Elasmobranchs.

A singular condition is found in Heptanchus, similar to that described by
Semper (1875) for Hexanchus, in which a rudimentary testis is associated
with the ovary. In Heptanchus maculatus this testis (t., fig. 252) lies in the
mesovarium at the base of the ovary and runs parallel with it. It consists of an
anterior larger part and a marked ridge or swelling which extends posteriorly
practically the entire length of the ovary. It will be noted that the posterior
extent of this rudimentary testis is about the same as that of the coil in the
Wolffian duct previously described.

Unconnected with the ovaries are the tubes or oviducts (od.) through which
the ova reach the exterior. Right and left oviducts are reached from the body
cavity by a common opening or wide funnel (f1., figs. 2514 and 252) located
~ just ventral to the base of the liver. The oviduects pass outward from the fun-
nel and then inward to the anterior margin of the mesovarium where they en-
large to form the shell gland (s.g.). Posterior.to the shell gland the oviduct
passes ventral to the Wolffian duct as a tube of considerable size, but it is not
so greatly enlarged in Heptanchus as in many other Elasmobranchs in which
it forms the conspicuous uterus (see fig. 253a, Squalus sucklii). At their
termini the two oviducts enter the cloaca separately and not in common with
ureters or Wolffian ducts, that is, not through the urinary papilla.

The genital glands of the male are the paired testes which like the ovaries of
the female occupy an anterior position in the body eavity. In figure 2518 of
the immature specimen the testis (¢.) appears as a long mass of tissue. Only
the anterior part of this, however, is functional. The posterior part represents
the rudimentary epigonal organ like that in the female. The testis is swung
from the body wall by a mesentery, the mesorchium, which is comparable to
the mesovarium suspending the ovary.

Running along the median and anterior part of the testis is the central canal
(c.c.), which is put into communication with the vas deferens (Wolffian duct)
by vasa efferentia (v.e.), six of which are present in Heptanchus. The vasa
efferentia are derived from funnels, present on the mesorchium. We shall de-
scribe this system more completely in the general part, but here attention may
be directed to it briefly. The general plan of these tubes may be made out in
figure 2544 (nph.) where several of them open on the mesorectum which sus-
pends the rectal gland. These openings are the nephrostomes, the tubes of
which pass out toward the kidney tissue. In the region of the testis the mouths

THE ELASMOBRANCH FISHES 291

of the most anterior of these are united with the central canal of the testis,
and the tubes pass down over the mesorchium and join the upper part of the
coiled vas deferens.

The vas deferens in Heptanchus is very simple in that it is a single con-
voluted tube which inereases only slightly in size back to the anterior tip of
the ureter. From here it passes backward in the immature specimen more or
less as a straight tube. After having received the ureter, as we have seen, it
enters the urinary sinus. Since in the adult this urinary sinus also receives sex
cells from the vas deferens it becomes a urogenital sinus in the male. The
spermatozoa and the fluid collected in the urogenital sinus are forced through
the papilla and out through the cloaca. As they leave the cloaca they are di-
rected through a groove on the clasper and may be transferred to the cloaca
of the female.

In a number of immature males examined, right and left rudimentary ovi-
duets were present. These were united at the midventral line and had a com-
mon funnel as in the female. In all the specimens examined, however, they
were of short extent, all of them ending blindly posterior and being attached
to the body wall anterior to the segment of the shell gland.

292 THE ELASMOBRANCH FISHES

UROGENITAL SYSTEM OF ELASMOBRANCHS IN GENERAL

The two systems, urinary and genital, included under this head, although
differing in function, are so closely associated anatomically that they are usu-
ally considered together. First, however, we shall consider them separately
and then discuss their secondary relationship.

URINARY SYSTEM
KIDNEY (MESONEPHROS)

Upon opening the body cavity by a ventral incision and removing the viscera,
the urinary organs of an Elasmobranch appear as dorsally placed structures
on each side of the spinal column. In the sharks they may extend as ribbon-
like bands, narrow at the base of the liver anteriorly, and only slightly wider
at the cloacal region posteriorly. In the rays they are characteristically en-
larged posteriorly where most of the tissue is confined. These statements are
true only in general, for great variation is present in different species of
sharks and rays; differences are further to be noted in the different sexes of
the different species.

The long ribbon-like type of mesonephros or kidney characteristic of Squa-
lus (fig. 2534) and Galeus loses something of this shape in Scyllium where its
anterior part is narrower and, in the female, ends short of the base of the liver.
Again, the type of kidney characteristic of the shark although extending far
anteriorly may be at the same time like the kidneys of the rays, broader poste-
riorly (Squatina, fig. 2544). In the rays, excepting Torpedo, the kidney rarely
extends far forward, but sometimes a large part of it is located back of the
cloaca (Raja clavata, fig. 2548, Trygon).

Sexual differences which are marked in the kidney of the Elasmobranchs
are produced by two factors: one is the reduction of the anterior part of the
kidney in the female; the other is the hypertrophy of this part in the male.
This hypertrophy results from the fact that the anterior part in the male
comes into the service of the genital system and takes on a secondary function.
In Torpedo sexual differences are slight, for a ray. In the female a band of
tissue is continuous forward, and this is only slightly less developed than
in the male. Sexual differences are evident in a type hike Squatina in which
the kidney of the adult female does not extend anteriorly to the liver. In
Scyllium, where the difference in the two sexes is marked, the anterior part of
the kidney of the female falls short of the base of the liver; and in R. clavata
the kidney is limited to the posterior segment, while the anterior part in the
male (fig. 2548) represents a great mass of tissue.

Furthermore, the kidney varies greatly in its degree of complexity in the
different Elasmobranchs. In some of the sharks it retains in part a simple
metameric arrangement by which in dorsal view it agrees with the segmenta-
tion of the body, characteristie of the embryo (Squatina, fig. 2544). In most
other sharks, however, this simple arrangement is lost at least in the posterior

THE ELASMOBRANCH FISHES 293

A B

Fig. 253. Urogenital system, Squalus sucklii. (Duncan Dunning, orig.) A. Female. B. Male.

cl., cloaca; cls., clasper; d.a., dorsal aorta; kd., kidney; od., oviduct; ov., ovary; sc., in
male, sperm sac; s.g., shell gland; t., testis; u., ureter; up., urinary papilla; u.s., urinary
sinus; ut., uterus; ug., urogenital sinus; v.s., vesicula seminalis; v.d., vas deferens; w.d.,
Wolffian duct.

294 THE ELASMOBRANCH FISHES

part and the only way that the number of segments can be determined is by
the number of collecting tubules leaving the kidney. In the rays the kidneys
may be divided into numerous asymmetrical lobules, which show little tend-
ency toward orderly arrangement; or the kidneys of the two sides may be en-
tirely dissimilar. This is seen sometimes in Raja clavata where the left kidney,

Fig. 254. Urogenital system of male. A. Squatina. B. Raja. (From Boreea. )

c.c., central canal of testis; ct., collecting tube; kd., kidney; m.v., median vesicle; nph.,
nephrostome; sc., sperm sac; s.d., segmental duct; s.v., vesicula seminalis; ¢., testis; w.,
ureter; ug., urogenital sinus; v.d., vas deferens; v.e., vas efferens.

probably because of pressure from the digestive organs, becomes divided into
widely separated parts.

DUCTS OF KIDNEY

In atype like Squatina (see male, fig. 2544) the collecting tubules (ct.) which
drain the anterior part of the kidney empty directly into the Wolffian duct,
and those of the posterior part join a ureter (w.). This is essentially the con-
dition in Heptanchus, except that in Heptanchus the ureter is of immense
size. In Scyllium (see p. 189, fig. 1774) the Wolffian duct is terminated by an
enlarged portion, the urinary vesicle (w.v.), and the collecting tubules in the
posterior part of the kidney are dispersed at their termini, several of them
joining to form a diminutive ureter only at the place where they empty into
the urinary sinus. A modification of this plan is met with in the rays in

THE ELASMOBRANCH FISHES 295

which the part of the kidney lying posterior to the urinary sinus is drained by
collecting tubules (fig. 2548) some of which unite anteriorly into one or two
groups (ureters), while others of them enter enlarged horns of the urinary
sinus (female of FR. clavata). In the female of the sting ray, Trygon, all the

PPE

a Zi; j
ihe

ey
Hi
uHolow ow,

7
le

f
i

Lu
i)
i

}

f
bs

sy
iy

Mb A

if
ru: i,

RE,

Fig. 255. Renal corpuscles, Acanthias. (From Borcea.) A. Active. B. Atrophied and in the
service of the male sex system.

cil., ciliated cells; cp., Bowman’s capsule; c.t., collecting tube; gl., glomerulus; r.t., renal
tubule; w.d., Wolffian duct.

collecting tubules enter the large horns of the urinary sinus independently,
excepting the single anterior one which is a direct continuation of the small
Wolffian duct.

The lower part of the Wolffian duct in a type in which this does not receive
tubules may be enlarged as the so-called urinary vesicle. In Squatina the duet
is swollen and in Scyllium it is of large size (p. 189, fig. 177A, w.v.).

From this it is seen that the Wolffian duct decreases in importance in the
female as we approach the rays. Ina type like Squalus sucklii, however, a plan
is given in which the Wolffian duct assumes a more important role. Here in
the female (fig. 2534) the ducts receive the collecting tubules from practically
the whole of the kidney, so that a ureter may be said to be absent, or if present.
to receive only a few tubules.

The urinary sinus (w.s., fig. 253) into which the Wolffian ducts empty varies
greatly in size and shape. In the sharks it is simpler in its external form than
in the rays and may be described as a delta-shaped sac which empties posteri-

296 THE ELASMOBRANCH FISHES

orly by a conieal urinary papilla. Its complexity in the rays results, from the
anterior extension of the horns of the sinus, which take the shape of the
arms of a tuning fork, the narrower urinary sinus being the base (Trygon).

An incision through the papilla (Squalus, fig. 2534) gives a view of the
inner walls of the urinary sinus. Emptying into it on each side of the female
is the Wolffian duct (w.d.), and as evaginations of its walls are certain wide
pockets (sc.) comparable to the sperm sacs of the male.

The relation of the ureter to the Wolffian duct (vas deferens) in the male is
markedly different from that of the female. Only the ureter will be described
at this place since a description of the Wolffian duct will be given in a study
of the genital system. The ureter in the male is confined to the posterior part
of the kidney where it receives collecting tubules from ten to fourteen seg-
ments. These may enter regularly as short tubules along its course (Squalus
and Squatina) or they may join it in two groups, one at its anterior end and
the other near its entrance to the urinary sinus (Scyllium, Raja). In Scyllium
the ureter of the male is an enlarged sinus, as in Heptanchus.

FINER ANATOMY OF KIDNEY

In a section through the Elasmobranch kidney multitudes of structures are
met which are the effective organs for the removal of nitrogenous waste; these
are the renal corpuscles. A renal corpuscle, in simple terms (fig. 2554), is like
a hollow rubber ball (Bowman’s capsule ), one side of which has been pushed in
to form a double wall and the opposite side pulled out over a small area into
a long neck (renal tubule, 7.t.). Into the cavity of this invagination a blood
vessel enters, coiling up as the glomerulus (gl.) or knot of vessels. Nitrog-
enous waste matter collected by the blood is brought by the glomerulus into
the capsule through the walls of which it passes into the renal tubule. The
renal tubule (7.t.) carries it into the collecting tuble (c.t.) which joins the
Wolffian duct (w.d.) (or the ureter). Thus it passes through the urinary
papilla and out at the cloaca.

NEPHROSTOME AND SEGMENTAL DUCT

In order to understand the origin of a Bowman’s capsule a second series of
correlated structures may first be considered. Each one of these when com-
plete, consists of a nephrostome (mph.) or funnel (fig. 258) opening from the
body cavity, a terminal part, the median vesicle (m.v.), and between the two a
segmental duct (s.d., fig. 258B).

The nephrostome may best be studied in the Elasmobranchs by treating
them first with Flemming’s fluid. To get the best results the digestive tract
should be removed from a fresh specimen and a little of the fluid allowed to
remain for a short time in the dorsal part of the body cavity. Under such a
procedure the nephrostomes are colored as dark patches of the dorsal peri-
toneal lining of the body cavity near the middle line and on the mesentery.
These are the funnels which may be relatively large as in Squatina (nph.,

THE ELASMOBRANCH FISHES 297

fig. 2544), where some of them are two to three and a half millimeters in
diameter; or they may be small as in Scyllium. Frequently when funnels are
present in the embryo they become rudimentary or wholly absent in the adult
(Raja). When the nephrostomes are present they may be traced along the
mesorectal mesentery and the mesenteries proper, the most anterior of which
reach the mesenteries of the sex glands. The number of nephrostomes varies
according to the species, the individual, the sex, and the age. In a type like
Squatina (fig. 2544) there are usually nineteen or twenty pairs present, but
these may be reduced in number. In the female the number is always smaller
than in the male. Twenty-three or twenty-four pairs are present in the adult
Acanthias; while in the embryo there may be as many as thirty-five pairs.

The segmental ducts lead from the funnels (nephrostomes) outward toward
the kidney tissue. These may be clearly marked as in Squatina or they may

fl.

Fig. 256. Diagram of development of segmental ducts and their relation to the Wolffian
and Miillerian ducts in the embryo of Scyllium. (From Balfour. )

fi., funnel; nph., nephrostome; o.d., Miillerian duct (oviduct); s.d., segmental duct;
w.d., Wolffian duct.

partly degenerate so that the nephrostome is sessile (Scyllium). In some
other types no trace either of the ducts or of the funnels remains in the adult.
In those types in which they are developed, the ducts may run more or less
directly outward in the midbody region (Squatina), or they may be V-shaped
with the apex pointing forward (Squalus suckli). In the region of the rectal
gland they may be more difficult to see by reason of the thickness of the meso-
rectum. Here in general they extend obliquely backward and may be long
drawn out (Squatina) or short as in Scyllium. As the segmental ducts pass
outward they pass above the Wolffian duets (Acanthias).

It was formerly supposed that the segmental ducts were directly continued
into collecting tubules of the urinary system. If this were so it would be
possible for waste substances to be collected from the body cavity and passed
out through the Wolffian duct or ureter to the exterior (see fig. 256, Scyllium).
Such a connection between the two systems, however, probably does not exist
for the adult of any forms since in the adult the segmental duct ends blindly as
the median vesicle ventral to the kidney tissue (see Squatina, fig. 254A, m.v.).

Proof that no connection exists between segmental duct and collecting
tubule has been beautifully shown by the experiments of Schneider (1897)
who injected india ink mixed with carmine into the body cavity of the living
Squatina. If a connection exist between the nephrostomes of the body cavity
and the kidney tissue the ink should be eliminated to the exterior through the
Wolffian duct or through the ureters. Upon killing the fish a few days after
the experiment Schneider found that the ink and grains of carmine had col-

298 THE ELASMOBRANCH FISHES

lected in the median vesicles at the end of the segmental duct (see fig. 254a,
m.v.) and there appeared as large colored patches. In no specimen did the ink
or carmine which entered the nephrostome gain access to the tissue of the

kidney.
DEVELOPMENT OF NEPHROSTOME AND

SEGMENTAL DUCT

A section through the body cavity of an embryo of Heterodontus francisct
(fig. 257) cuts through the nephrostome or funnel (nph.). If traced farther
back, it would be found that this funnel
by means of the segmental duct joins the
pronephrotic duct (pr.d.). At first the
most anterior of such funnels may pro-
vide a passageway from the body cavity
to the pronephrotie duct, but later the
most anterior of these fuse into a single
enlarged funnel. Those segmental funnels
arising back of this have segmental ducts
(s.d., fig. 258) which join the pronephrotie
duet only secondarily.

In the segments farther back, however,
=e Seie each segmental duct of Acanthias grows
ts, awe a from its funnel laterally, enlarging into a
ew ee median vesicle (m.v., fig. 2584). From this
it may even continue inward to join an
outgrowth from the pronephrotie duet
(pr.d.). The following structures are
Fig. 257. Development of nephrostome, found in order from the funnel or nephro-
Heterodontus francisci. (H.M.William- stome to the pronephrotic duct: (1) the
Bon 0r8:) : nephrostome (nph.); (2) its segmental

nph.,nephrostome ; od., oviduct; pr.d., : : :
pronephrotie duct. duct (s.d.); (3) a median vesicle (m.v.)

which supplies the tissue for Bowman’s
capsules; (4) the tube leaving the capsule which becomes the renal tubule
(v.t.); and (5) the primitive collecting tubule (c.t.) which according to
Borcea (1906) buds off from the pronephrotie duct and later lengthens out
into the collecting tubule of the adult.

At this point in its development, connection is made from the nephrostome
to the pronephrotie duct (Scyllium, fig. 256), and it is not impossible that
while this temporary connection lasts nitrogenous waste may pass from the
body eavity through the pronephrotiec (now the Wolffian) duct and out
through the cloaca. But this connection is early lost even in Scyllium. Such
connection between the coelom and the kidney tissue is never actually present
in Acanthias, for in it the tube early fragments at the median vesicle before
its terminal part, the renal tubule, has reached the pronephrotic (Wolffian)
duet. It is from the fragmenting tissue of the median mass that Bowman’s
capsules are formed.

Sor

Says
oe,

gaeo Uo
sc

THE ELASMOBRANCH FISHES 299

BOWMAN’S CAPSULES

According to Boreea (1906) a Bowman’s capsule is produced from a part of
the median vesicle in the following manner (Acanthias). The median vesicle
(fig. 258n—c) divides into two parts, a median part connected with the seg-
mental duct (s.d.) and an outer (deeper) part continued by the renal tubule
(r.t.). The outer part is the first to give rise to a Bowman’s capsule (fig. 258c)
and this is accomplished by the loose cells from the lining forming over the
aperture caused by the separation of the median vesicle. Into this the knot of

A B Cc

Fig. 258. Diagrams A to E to show stages in the development of Bowman’s capsules,
Acanthias. (From Borcea.)

c.t., collecting tubule; m.v., median vesicle; nph., nephrostome; pr.d., pronephrotic duct ;
r.t., renal tubule; s.d., segmental duet; I, IZ, and II, primary, secondary, and tertiary renal
corpuscles.

blood vessels (the glomerulus) pushes. The body segment is thus provided at
first with asingle primary (J) renal corpuscle on each side, and a true metam-
erism obtains in the kidney tissue. As development progresses, however,
secondary and tertiary Bowman’s capsules are formed. Some of these pass
over into the adjacent segments and soon destroy the primitive metamerism.

The formation of the secondary Bowman’s capsules and their connection
with the pronephrotie duct takes place as follows: from that part of the
median vesicle of the segmental canal which remains after the formation of a
primary, that is, from the superior and inferior vesicles, other Bowman’s
capsules (secondary and tertiary) arise. The secondary capsules are formed
from the median part of each superior and inferior vesicle and then extend in
the shape of a gourd toward the collecting tubule (see fig. 258p, Z7). It will be
further noted that enlargements arise on each collecting tubule (c.¢.) and
that these send out processes which meet and fuse with the tips of the gourd-
like structure, the superior processes fusing with the terminus of the sec-
ondary Bowman’s capsule derived from the inferior vesicle. Upon the fusion
of this terminus of the gourd with the process of the collecting tubule and the
breaking through of the connection between them, a secondary urinary tubule
results (IJ, fig. 2588).

300 THE ELASMOBRANCH FISHES

Tertiary Bowman’s capsules result from the further fragmentation of the
remains of the inferior and superior parts of the median vesicle. These, like
the secondary capsules, are gourd-like and their termini unite with tertiary
processes. The tertiary collecting tubules (///, fig. 258£) result in part as
processes which spring from the sides of the origin of the secondary process.
These pass to meet and fuse with the tertiary Bowman’s capsules.

At this stage, Acanthias, 8 em., each body segment has one primary (J), two
secondary (//), and four tertiary Bowman’s capsules (J7Z). Four of these,
one primary, one secondary, and two tertiary, belong to the median vesicle
from which the primary was derived; the remainder arise from the following
vesicle. By the time the adult stage is
reached numerous renal corpuscles and
renal tubules are present in each seg-
ment. In fact it is these, together with
connective tissue, which make up the
mass of the kidney.

GENITAL SYSTEM

Fig. 259. Early sex cells, Acanthias.
(From Woods.)
p.0., primitive ova.

The genital system consists of the sex
olands and their tubes. The adult glands
arise as a collection of germ cells (p.o., fig. 259), which, before passing into the
alands are scattered more or less widely in the tissues. These cells appear very
early and are well shown before a genital ridge is formed. They later, through
migration, take up their position in the sex gland. At this early “indifferent”
stage it is impossible to tell what the sex of the individual will be. The cells
then begin to specialize and to take on the characters of the sex cell of the male
or the female, whereupon the glands become the testes or the ovaries, respec-
tively. We shall describe these organs in the male first.

GENITAL ORGANS OF MALE

TESTES

The paired testes of the male vary considerably in size. In some of the Elasmo-
branchs they are relatively small (Torpedo) ; while in many others, especially
during the breeding season, they are of large size (Heterodontus; Raja clavata,
fig. 2548). It often happens at this time that the testes are irregular in outline,
being made up of numerous lobes (t., fig. 2538, Squalus suckli). In certain
forms the testes may be connected posteriorly with the rectal gland by a heavy
mass of tissue, the epigonal organ (Heterodontus, Scyllium), a vestige of
which we saw in Heptanchus. An epigonal organ, however, is only slightly
developed or entirely wanting in many types (Acanthias, fig. 253; Squatina,
fig. 2544; and Torpedo).

THE ELASMOBRANCH FISHES 301

FINER ANATOMY OF TESTIS

The testis is divided into columns, each of which consists of connective tissue
and follicular cells. The sex cells appear in various stages of development
which may be followed from the indifferent stage, previously mentioned, to
the mature sperm cell or spermatozoon. Through division, the primitive ova

Fig. 260 ig. 261

Fig. 260. Horizontal section cutting testis and anterior part of kidney of Squatina.
(From Borcea.)
c.c., central canal of testis; /.c., longitudinal canal of epididymus; v.e., vas efferens.

Fig. 261. Section through ovary of Spinax to show corpus luteum (X), which fills the
place occupied by the ovum. (From Wallace. )

of the male form multitudes of spermatogonia, which after a period of rest
form spermatids. The spermatids next undergo an interesting series of
changes in shape and form, becoming the adult spermatozoa.

VASA aaa

The sex cells in the male instead of passing into the body cavity and out at the
abdominal pores, as they do in the Cyclostome fishes, pass out through the
Wolffian duct, now called the vas deferens, which they reach through the vasa
efferentia. The vasa efferentia arise as metamorphosed tubules of the anterior
segmental ducts. Those ducts in the region of the sex glands of the male have
some of their funnels opening into the tissues of the testis or into the central
canal at its base and afford a passageway for the sex cells.

A horizontal section through the testis and anterior part of the kidney of a
young Squatina (fig. 260) shows that the segmental ducts themselves thus
become the efferent ducts or vasa efferentia within the tissues of the testis;
the parts of the nephrostomes representing the funnels fuse to form a central
canal (c.c.) while the median vesicles of the segmental ducts similarly join the
kidney to form the longitudinal canals (l.c.) of the epididymus, From this
canal a connection is effected, through collecting tubules, with the Wolffian

302 THE ELASMOBRANCH FISHES

ducts. Several of the anterior segmental ducts may now become vasa efferentia,
* but others which are on the mesorchium may fail to reach the tissue of the
testis. Those actually penetrating each testis in Squatina (v.e., fig. 2544) are
six in number. In Squalus four such enter, while four others end on the mes-
orchium. In Scylliwm two or three vasa efferentia are present and in the rays
(fig. 2548) a single vas efferens is present. In this form the vas efferens joins
the vas deferens directly without the intermediation of a longitudinal canal.

The passageway for the sex cells of the adult male, then, is from the testes
through the vasa efferentia.into the greatly coiled Wolffian ducts each of which
is now a vas deferens. We may next notice in detail the changes which the
Wolffian duct and its associated parts undergo in its metamorphosis into the
vas deferens. We shall first consider the changes undergone in the anterior
segment of the kidney.

The anterior part of the kidney, which in the young male is in the service
of the urinary system, undergoes profound modification in the adult male,
characteristically coming to be of large size (Borcea, 1906). If a transverse
section is taken of this area in the adult it will be found to be devoid of the
Bowman’s capsules which were previously present in it (see fig. 2558, Acan-
thias). In their places will be found numerous enlarged sacs the walls of which ©
have become greatly thickened. The two types of cells which compose the walls
are: (1) cilated cells (cil., fig. 2558), which border on the lumen, and (2) non-
ciliated cells with basal nuclei. These cells secrete a viscous whitish substance
which acts as a seminal fluid. The upper end of the kidney, therefore, which at
first functioned in the young male in the removal of the nitrogenous waste,
has thus entirely changed its function in the adult so that it now acts as a
gland for the secreting of a kind of spermatic fluid.

Upon the transformation of the anterior part of the kidney, the vas deferens
becomes a coiled tube (Squalus, fig. 2538; Raja, fig. 2548; Torpedo) which as
it passes posteriorly receives collecting tubules. In the region of the posterior
kidney it becomes the enlarged vesicula seminalis into which no collecting
tubules empty. The a ae in many of the sharks (Squalus, fig.
2538, v.s.) is a long tube but in the rays (fig. 2548) it is much shorter.

When opened longitudinally the vesicula seminalis in Squalus shows a
series of transverse semipartitions which give to the inner wall a corrugated
appearance. Along this wall in the breeding season are found myriads of
sperm cells or spermatozoa.

The seminal vesicles of the right and left side empty into the enlarged
urogenital sinus (1.s., fig. 253B) usually ventral to and laterad of the entrance
of the ureter (w.). Passing forward on each side of the urinary sinus is the
blind sperm sae (sc.) which appears to be an evagination of the urinary sinus
but which is formed from the posterior remnants of an oviduct like that of the
female. The sperm sae of Squalus or of Raja is of small size and in the rays it
has been spoken of as a urinary bladder. In Squatina (fig. 2544) and Scyllium
(see p. 189, fig. 1774) the saes reach a much greater length. Since the sinus
receives both the nitrogenous waste and spermatozoa it is properly designated

THE ELASMOBRANCH FISHES 303

urogenital. The urogenital sinus, as in Heplanchus, then empties by means
of a urogenital papilla into the cloaca.

Leigh-Sharpe (1920-21) has deseribed fully the siphons of a number of
Elasmobranchs. These are composed of longer or shorter closed sacs which
end posteriorly by siphon tubes. In a type like Acanthias the sae lies under the
skin ventral to the base of the pelvic fin, and its tube empties into the proximal
part of the clasper tube. In a large specimen of Galiorhinus this siphon sae
extended almost to the pectoral girdle. The walls of the sac are muscular and
its function appears to be the forcing
of the sperm cells through the clasper
groove. Glands may line the whole sae
as in Lamna or the dorsal side of its
wall only (see p.28, fig. 31). The fune-
tion of the clasper gland in the latter
condition is not definitely known.

GENITAL ORGANS OF FEMALE
OVARIES

The ovaries of the adult female usu-
ally arise as paired structures, and Fig. 262. Section through shell gland, Scyl-

; lium. (From Boreea.)
are bound to the anterodorsal wall of t.gl., secretory cells.
the body cavity by a mesentery, the
mesovarium (Squalus, fig. 2534). Not infrequently, however, the left ovary
atrophies in the adult (Scyllium, Pristiophorus, Carcharias, Galeus, Mustelus,
and Zygaena). They occupy the anterior part of a mass of tissue which, as the
epigonal organ, may extend along the dorsal wall of the body cavity pos-
teriorly where it joins the rectal gland. In numerous forms, however, the
epigonal organ is wanting as, for example, in Acanthias. The ovary varies
greatly, depending upon the stage of maturity of the ova contained. It appears
as a sac through the walls of which the ova may be seen varying in size from
relatively minute spots to mature ova often from 3 to 5 em. in diameter (see

v., fig. 252).

In development an indifferent sex cell divides several times forming
oogonia. Each odgonium then undergoes a period of growth to become a pri-
mary oocyte. By the first maturation division, this primary odcyte gives rise
to the secondary odcyte and first polar cell. The former soon undergoes the
second maturation division, thereby forming the odtid and second polar cell.
The o6tid without further division increases in yolk content to become the
ovum. The ovum then breaks through the wall of the ovary. At this stage it
contains only one-half the number of chromosomes characteristic of the body
cells. If it be fertilized by a spermatozoan, which also bears only one-half the
normal number of chromosomes, the number of chromosomes characteristic
for the species is restored.

The place where the egg was located in the ovary now becomes filled up by
a corpus luteum (z, fig. 261).

304 THE ELASMOBRANCH FISHES

OVIDUCTS

The oviduets in an immature female consist of a pair of slender tubes extend-
ing the entire length of the body cavity and emptying into the cloaca. They
take their origin by splitting off from the Wolffian duct (see fig. 257, od.) and
therefore retain the primitive funnel (fi., fig. 256) by means of which they
open anteriorly into the body cavity. Occasionally one of the oviduets is
rudimentary in the adult (Trygon). This in all probability is due to the

Fig. 263. The egg shell of Heterodontus. A. H. francisci (orig.). B. H. galeatus. (From
Waite.)

crowding of the unusually large valvular intestine. In the adult the oviduet
is divided into several functional sections which may now be discussed.

The ovidueal funnel or the opening into the body cavity is formed as a
common aperture for the two oviduets (fl., fig. 2514). This is slit-like and is
lined with ciliated cells, the cilia of which may have something to do with
directing the eggs into the oviduct after they have reached the body cavity
from the ovary. Just below the funnel, in the part comparable to the fallopian
tube of higher forms, fertilization of the mature egg takes place. The egg then
passes downward to the area of the shell gland, where such exists, to receive
its shell.

SHELL GLANDS

The shell glands (s.g., fig. 2534) vary greatly in the different Elasmobranchs.
In Torpedo there are present in this region of the oviduct only a few strands
of granular tissue, which are incapable of producing a shell. In a type like

Fig. 264. Egg shell, Cephaloseylliam.

THE ELASMOBRANCH FISHES 305

Squalus the gland is considerably increased in size and in Raja, Scyllium, and
Heterodontus francisci it becomes relatively of immense dimensions. If the
eland in Scyllium be taken as a type for study we find that it is divided into
a dorsal and a ventral half. A section through it shows that these halves are
divided into anterior and posterior areas; the former secretes albumen, the
latter the shell proper. The glands which are actively engaged in secreting the
shell are seen to advantage in figure 262. Here the folds are very high and the
secretory cells (¢.gl.) at their bases are large. As the horny substance is formed
for the shell it passes into the cavity of the
shell gland which acts as a mold for the shell.

TYPES OF EGG SHELLS

Two types of shells are formed: the per-
manent and the temporary shells. In the per-
manent shell the young undergoes its de-
velopment to the form of the adult, after
which it emerges (Scyllium, Raja, Hetero-
dontus).In both Scyllium and Raja the shell
is a rectangle, from the angles of which pro-
jections extend. These projections function
either as tendrils (Scylliwm) which coil
around solid objects and anchor the egg, or
they serve as spikes to fix the developing egg
in mud or sand flats (rays). Figure 264
shows the shell of the California swell shark,
Cephaloscyllium, which in all essential re-
spects is like that of the other Seyllidae eXx- Tis SbS oN enC ee NENe PETC
cept that in the figure its tendrils appear — geyitiwm. (After Kopsch.)
shorter. These tendrils are, however, long

and are produced both from the upper and the lower angles. In color the ma-
ture shell is clear amber of equal shade throughout. Such shells of Cephalo-
scyllium, however, which are in the process of formation are whitish when first
removed from the oviducts; but these color with age.

In Heterodontus the shell is shaped like a screw with a characteristic double
flange extending from its apex to the large perforate end. The flange in Heter-
odontus francisci (fig. 2634) or H. philippi is broad and is thrown into four
or five coils. In Heterodontus galeatus (fig. 263B) the flanges are narrower,
and tendrils are present which may reach the extreme length of more than
seven feet (Waite, 1896).

The attachment of the egg in egg-laying has been studied in Scylliwm by
Kopsch (1897). It is found that as the egg passes through the cloaca its
tendrils, upon coming in contact with a solid, coil firmly around it, thus fixing
the egg in place (fig. 265). Two eggs are usually deposited at about the same
time and many are laid during the season.

306 THE ELASMOBRANCH FISHES

The young, thus protected by the-shell and supplied with an abundance of
food yolk, undergo a period of development outside of the body. This period
varies greatly depending largely upon the temperature of the surrounding
water. Under favorable conditions the
egos may hatch in sixorsevenmonths,
but the period is more likely to ap-
proximate nine months. At the end of
this time hatching is accomplished by
the perforation of the upper end
(Scyllium), or the lower end (Raja)
of the shell. In Heterodontus the two

Fig. 266. Oviducal valve, Squalus sucklii. layers at the large or perforate end
Oa, MRE ok uterus; vl., valve. separate making a large aperture
through which the young emerges.

In many of the Elasmobranchs a temporary shell is formed which serves
the young fish only through its early development. From this temporary shell
the embryos emerge and undergo more or i
less of their development in the oviduct of
the mother (Acanthias, Mustelus, Rhino-
batis).

A temporary shell is very often a strue-
ture of exquisite beauty. In Squalus
suckli it consists of a long thin-walled
tube of a clear amber color, each shell con-
taining from four to six eggs. The eggs
undergo their early development incased
and protected until the time when the ex-
ternal gills begin to be absorbed. The shell
then ruptures and the young embryos
take up their development in the uterus
of the mother. In Rhinobatis a similar
shell is found and after it has been dis-
earded by the embryos it may be found
rolled up in the uterus.

Fig. 267. A. Section of uterine lining
to show villi and blood supply, Squalus.
B. Transverse section through a single
villus, Acanthias. (From Brinkmann.)

We have said that the uterusismuch more —_¢P-, capillaries; t.a., terminal artery ;
- c vi., villus.

highly developed in those sharks which

ceive birth to living young; for in these it serves as a place in which a consider-
able part of the development is undergone. Such a uterus is that of Squalus
sucklii (ut., fig. 253) in which it may be a greatly enlarged sac with well de-
fined boundaries. Anteriorly the uterus of Squalus is separated from the for-
ward part of the oviduct by a well defined oviducal valve (fig. 266) which is a
wavy constriction with a very narrow lumen effectively closing the uterus to
the upper part of the oviduct.

UTERUS

THE KELASMOBRANCH FISHES 307

The lining of the uterus differs greatly in oviparous and viviparous types.
In the former it may be practically smooth or it may be thrown into low folds
as in Scyllium. In viviparous types it may be singularly modified as maturity
is reached. In an immature specimen of Squalus the lining is smoother than
that of the oviparous Scyllium, but in a specimen of Squalus which is pregnant
the whole surface of the lining is thrown into oblique rows of flaps or villi
(vi., fig. 2674), each of which is a leaf-like strueture with exceedingly thin
walls. In a type like Torpedo or the butterfly ray, Pteroplatea micrura, the
uterine wall may be thickly covered with long papillae some of which in the
latter may reach 10 to 20 mm. in length. The terminal part of such a papilla
is shown in figure 2698, in which it is seen that the wall is like a sponge.

Fig. 268. Section through the uterus of Mustelus antarcticus. (From T. J. Parker.)
m., muscular layer; mu., mucous lining; p., peritoneal layer.

Viviparous females injected during pregnancy show that the blood supply
to the uterus is exceedingly profuse. The arterial supply, in Acanthias, for
example, consists in part from anterior and in part from posterior ovidueal
arteries which break up into branches to the oblique rows of villi. Each ter-
minal artery courses along the free border or fold of the row of villi (t.a., fig.
267A) supplying each individual villus with blood. If a cross-section be taken
through a single villus of Acanthias (fig. 267B) the finer vessels of the villus
may be made out. The large openings are for the terminal artery (t.a.) and
the central and smaller apertures are for the central veins which drain the
villus into a main uterine vein. Around the surface of the villus is the capillary
net (cp.) connecting the two systems. The same arterial arrangement is pres-
ent in Scymnus, although here a single villus is not so wide.

RELATION OF UTERUS TO EMBRYO

The relation of the villi to the embryo is seen to advantage upon opening the
uterus of Acanthias. Here the villi come in close contact with the embryo and
multitudes of them are found clinging to the yolk sae on which the embryonic
blood system is profusely spread out. By the close relation of the embryo to
the maternal tissue an exchange between the two is insured.

In Mustelus laevis the blood system of the yolk sae comes into still closer
relation with the walls of the uterus than in Acanthias. For here, branched

308 THE ELASMOBRANCH FISHES

processes from the yolk sac of the embryo form close attachment to the uterine
wall. Through this attachment nutriment may be secured by the embryo.

The relation of the uterine wall to the embryo in Mustelus antarcticus (fig.
268) shows still another widely different relationship. In this form, according
to T. J. Parker (1882), the uterus, by the ingrowth of its lining, becomes

Fig. 269. Development of the butterfly ray, Pteroplatea micrura. (From Alcock.)
A. The embryo in the uterus. B. A tip of a single villus highly magnified.

divided up into as many rooms as there are embryos within the uterus. The
uterine wall is composed of an outer peritoneal lining (p.), a second or thin
muscular layer (m.), and a third or inner mucous lining (mu.). It is the last-
named layer that grows out to form the partitions separating the uterus into
rooms. These rooms are filled with fluid in which the embryos lie and by which
they are protected. In this type of Elasmobranch we see a device for protecting
the developing young which, in a way, is like that in higher animals. In this
form, however, the protective sae is produced by the maternal tissue, while
in higher forms it is formed by the embryo.

In Pteroplatea micrura the villi or papillae on the uterine wall of the mother
may be numerous and those which are over the spiracle of the embryo become
long and strap-shaped (fig. 2694). In an embryo that is far advanced the yolk

THE ELASMOBRANCH FISHES 309

sae is small and its blood supply is lacking. There is therefore no passage of
nutriment from the villi of the female through the blood system on the yolk
sac. But the long strap-like villi (fig. 269B) enter the spiracle and supply
nutriment direct to the digestive tract, as can be demonstrated by opening up
the digestive tract of the embryo (Alcock, 1892).

At their posterior terminus the two uteri in an immature female may be
separated from the cloaca by a membrane or hymen across the oviduct. The
relation of the hymen (in Torpedo) may be seen from figure 270 by Wida-
kowich (1908). The median union of the right and left uteri is prolonged back-
ward toward the cloaca by the uterine septum (s.) and a fold on each side
separates the oviduct from the cloaca. During
pregnancy the uterus is filled with a fluid and the d)
apertures remain closed. \

In Elasmobranehs in which the shape of the
claspers of the male is flat, the openings into the
uteri are slit-shaped, and in those forms in which
the claspers of the male are provided with sharp
hooks the lining of the terminal part of the uterus
is thickened.

SECONDARY SEXUAL CHARACTERS

Fig. 270. Diagram to show

Barring the fact that the female may be slightly the hymen between oviduct

larger than the male, the most important second- 274 cloaca. (From Widako-
ary character separating the sexes in the Elasmo- wicks

> : : cl.,cloaca; hy., hymen; o.d.,
branchs is the presence of claspers in the male. gyiauet; s., uterine septum.
These, as we have seen, are formed as modifica-
tions of the inner lobe of the pelvic fin. In types like Heptanchus maculatus
the claspers in immature specimens are relatively insignificant so that it is
often difficult upon casual examination to distinguish male from female. In
most other types, however, the claspers are well developed and in the rays
they may be of enormous size.

In one immature specimen of Heptanchus supposed to be a male, in addition
to the rudimentary oviduct only one of the pelvic fins bore a clasper. The con-
dition of gynandromorphism, in which one side of the body is male, the other
female, has been found in insects and birds, and its occurrence in the Elasmo-
branchs has also been previously noted (Vayssiére and Quintaret, 1915).

The mucous covering of the claspers is usually devoid of placoid scales and
is provided with a lubricant. Distally, as we have seen in a study of the skele-
ton, the claspers are provided with one or more terminal pieces. These by
muscular action may be erected at right angles to the main axis of the clasper.

The claspers have long been known to function in uniting the male and
female in copulation. This process among the Selachians was early studied
by Agassiz (1871) who discovered that one (or both) of the claspers is inserted

310 THE ELASMOBRANCH FISHES

into the cloacal opening of the female and fixed in position by the erection of
terminal pieces. The sperm cells reach the groove or tube in the claspers and
are forced thence into the oviduct of the female by a current produced by the
siphon (Acanthias). The cells traverse the oviduct to the region of the fal-
lopian tube where they remain until the mature eggs enter the oviduct and
fertilization takes place.

1858.

1871.

THE ELASMOBRANCH FISHES 311

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THE ELASMOBRANCH FISHES

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1893.

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1909.

1831.

1840.

1842.

1903.

1899.

1882.

1889.

1896.

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THE ELASMOBRANCH FISHES 315

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THE ELASMOBRANCH FISHES

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INDEX*

Abdominal pores, 126, 142; function of,
in Cyclostomes, 142

Abducens nerve, 223-224, 236, 241; fora-
men of, 44, 60; muscle supplied by,
100, 223-224, 241; nucleus of, 236

Abyssal habitat, 1

Acanthias, 2, fig. 5; ef. Urolophus, 8, 10,
1b

Acanthodes, 1

Accessory efferent-collector arteries, 180

Accessory lateral cutaneous vein, 217

Accessory valves of conus, 172

Accommodation of eye, 269-270

Adductor mandibulae, 93, 107; artery to,
182; function of, 93; nerves of, 241

Adductor museles, 93, 107; absent from
hyoid, 98, 107; of Chlamydoselachus,
107-108; of claspers, 95, 110-112; of
visceral arches, 90, 103, 107

Adductores areus, 107

Advehentes, 200, 208

Afferent arteries, 149, 161, 172-173;
branchial, 161, 172, 173; formation of,
178; hyoidean, 161, 172, 173; in holo-
branch, 149, 153, 157, 173

Alisphenoidal cartilage, 53, 55

Alopias, 2, fig. 2

Amphistylic, 45

Ampullae of Lorenzini, 7, 262, 274, 279-
280; development of, 281; distribution
of, 262, 279-280; modified in spiracle,
153, 280; nerves to, 224, 242, 243, 262,
280

Ampullae of semicircular canals, 258-259,
273; nerves to, 224-225; 261, 273; struc-
ture of, 273

Ampullary centrum, 280

Ampullary organs. See Ampullae of Lor-
enzini

Ampullary pockets, 280

Anal fin, 6, 12, 52; absence of, 12; ar-
teries to, 194; skeleton of, 52, 83; vein
from, 217

Ancient sharks, 1, 2

Angel fish. See Squatina

Annular arteries, 167, 188

Annular veins, 201, 210, 211

Anterior cardinal sinus, 198, 205, 206, 207

Anterior cardinal system, 204-208

*For coordination of entries see Contents.

[319]

Anterior cardinal vein, 198, 204

Anterior cerebral artery, 165, 183

Anterior cerebral vein, 204, 206-207; fo-
ramen for, 44; tributaries of, 206-207

Anterior dorsolateral artery, 168, 191

Anterior facial vein, 204

Anterior fontanelle, 43, 57

Anterior gastric artery, 166, 190

Anterior gastric vein, 201

Anterior gastro-pancreaticosplenic artery,
167, 189-190; in Dasyatis, 188

Anterior gastro-pancreaticosplenic vein,
200, 211

Anterior gastrosplenic artery, 188

Anterior intestinal artery, 166, 188;
branches of, 166

Anterior intestinal vein, 201, 210-211; in
rays, 210; tributaries of, 201, 210-211

Anterior lateral artery, 192. See also Lat-
eral abdominal artery

Anterior lobe of hypophysis, 234

Anterior mesenteric artery. See Superior
mesenteric artery

Anterior oblique semicireular canal, 258,
261, 273

Anterior rectus muscle. See Internal rec-
tus muscle

Antorbital process, 44, 60; function of, 60;
muscle from, 93

Aortie arches. See Embryonic aortic arches

Appendicular skeleton, 49-52, 75-83; div-
isions of, 49

Aqueduct of Sylvius, 235-236

Aqueous humor, 267

Arcuales communes museles, 93

Arcus communes, 108, 109

Argentium, 27

Armament, 1

Arteria spinalis, 165, 193

Arteries, 161, 170, 172; ef. veins, 170; in
Elasmobranchs in general, 172-194; in
Heptanchus, 161-169; to deeper struc-
tures, 169, 192-193; to digestive tract,
166-168, 186-191; to extremities, 168,
169, 191-192; to head, 165, 180-186; to
heart, 163-164, 179-180; to hypobran-
chial area, 162-165, 178-180; to trunk,
186; to tail, 169, 186, 193-194

Ascending aorta. See Ventral aorta

320 THE ELASMOBRANCH FISHES

Asterospondyly, 75

Atrium. See Auricle

Auditory (otic) capsule, 43, 55, 258, 271;
in embryo, 55

Auditory nerve, 224-225, 248, 261, 273;
ganglion of, 224-225, 243

Auditory organ (ear), 258-259, 264, 271-
273

Auricle, 160, 170-171

Auriculoventricular valves, 161, 171

Autonomic nervous system. See Sympa-
thetic system

Axial cartilage. See Basal cartilage

Axial skeleton, 43-49, 53-75

Axis cylinder, 238

Axone, 229, 238; origin of, 238

Basal angle, 44, 55; origin of, 53-55; re-
lation of, to orbital process, 44

Basal (axial) cartilage, 50, 51, 81

Basal (germinative) layer of epidermis,
23, 26

Base of scale, 24, 32

Basibranchial cartilage, 46, 65, 66

Basilar artery, 186

Basipterygium, 50, 51, 81, 82

Batoidei, 8

Beaker cell. See Gland cell

“Beta” cartilage, 50, 51, 80, 95

Bile, 137

Bile duct, 124, 137

Bipolar nerve cell, 229, 238; development
of, 229, 238

Blood, 204

Blood stream, 170

Body cavity. See Coelom

Body shape. See External form

Bowman’s capsule, 296, 298, 299-300, 302;
origin of, 299-300; transformation of,
in male, 302

Brachial artery, 168, 191; in ray, 191

Brachial vein, 202, 213, 214

Brachioscapular artery, 168, 179

Brachiosecapular vein, 214

Brain, 221-222; 229-236; arteries to, 165,
183-186; development of, 230; form of,
230-235; finer structure of, 236; veins
of, 198, 205, 206-207

Branchial adductors, 93, 107

Branchial afferent arteries, 161, 172-173;
in Chlamydoselachus, 173

Branchial arches, 45-46, 64-66; muscles
of, 93, 105-108; relation of, to gill
pouch, 147-148; segments of, 45-46,

64-66; supernumerary rudimentary, 47,
65-67

Branchial basket, 46, 204

Branchial clefts, external, see Gill clefts;
internal, see Internal branchial aper-
tures

Branchial efferent arteries, 165, 182

Branchial nerves: of glossopharyngeal,
244; of vagus, 149, 225-226, 245

Branchial rakers. See Gill rakers

Branchial rays, 45, 46, 67; in Torpedo, 67;
on hyoid arch, 45, 67; relation of, to
gill septum, 91, 152; relation of, to
muscles, 93, 105-106, 152

Buccal ampullae, 262, 279; divisions of,
262, 279; nerve to, 224, 242

Buceal artery, 182

Buceal cavity, 121-122, 128; lining of,
128; stomodeal denticles in, 31, 38, 128;
teeth in, 38, 128-131

Bucealis nerve, 224, 242; function of, 262,
279; ganglion of, 242

Bursa entiana, 136

Caleification, 53, 74-75

Canals of head, 261-262, 274, 276-277;
development of, 275; divisions of, 274—
275; in rays, 277-278; nerves to, 262,
278-279

Capillaries, 153, 157, 161, 170, 173, 212

Carcharias, 2, 9, fig. 16

Cardiae stomach, 123, 135

Cartilage, 53

Cartilaginous branchial rays. See Bran-
chial rays

Caudal (aorta) artery, 166, 169, 186

Caudal fin, 6, 12, 14; skeleton of, 51-52,
74

Caudal vein, 199, 208

Caudal vertebrae, 72, 74

Caudate lobe of liver, 124, 137

Central canal of testis, 290, 301

Central nervous system, 221-222, 229-
238; development of, 230

Centrum, 48, 69, 71; calcification of, 70;
development of, 70

Cephalic canals. See Canals of head

Cephaloptera, 3; locomotion in, 13

Cephaloscyllium, 2, fig. 1; color in, 27

Ceratobranchial cartilages, 45, 46, 64, 65,
67; muscles to, 92, 152

Ceratohyoid cartilage, 45

Cerebellum, 222, 234

INDEX

Cerebral arteries, 165, 183-186; divisions
of, 165, 183

Cervical plexus, 227, 246

Cetorhinus (Selache) maximus, 3, fig. 4;
gill rakers of, 37, 38, 154, 155

Cheiloscyllium, color of, 26

Chlamydoselachus anguineus, adductor
muscles of, 108; afferent arteries of, 172—
173; cranium of, fig. 46; dorsal fin of,
6; duct to thyroid, 134; nervous col-
lector of, 247; plan of fin skeleton, 77;
teeth of, 128-130

Chorda. See Notochord

Chorda tympani, 224, 243

Chordae tendineae, 161, 171

Choroid coat of eye, 269

Chromatophores, 26

Circular constrictor muscles. See Super-
ficial constrictors

Ciliary body, 267, 268

Ciliary ganglion, 240; relation to sympa-
thetic, 247

Ciliary nerve, 223, 241

Cirele of Willis, 184

Cireulation of blood, in gill filament, 157

Circulatory system, 160, 170, 198, 204;
divisions of, 170; of Elasmobranchs in
general, 170-194, 204-218; of Heptan-
chus maculatus, 160-169, 198-203

Cladoselachus, 1, fig. 10; muscle fibers of,
1; paired fins of, 15

Clasper, 6; as secondary sexual character-
istic, 309; function of, 291, 309; mus-
cles of, 95, 110-112; relation of, to
apertures of uterus, 309-310; relation
of, to siphon, 310; skeleton of, 51, 81-
82

Climatius (?), 1, fig. 11

Cloaca, 126, 141; ducts to, 126, 141, 291,
298; lining of, 126, 141

Cloacal papillae, 126, 141

Cloacal pits, 141

Cloaeal vein, 203, 213

Coeliae axis, 166, 186; branches of, 166,
167, 186-188

Coeliacomesenteric artery, 190

Coelom, 96

Collecting tubules, 287, 289, 294, 295, 297,
298, 299; development of, 299-300

Colon, 126, 141

Color, 6, 26-27

Commissural arteries, 162, 178-179

Compressor muscle, 95, 111-112

Cones of retina, 269

Le ee

Constrictor spiraculae,“103

Conus arteriosus, 160-161, 170, 172; valves
of, 161, 172

Coracoarcuales muscles, 93, 94, 108

Coracobranchial muscles, 94, 109

Coracohyoideus muscles, 94, 109

Coracoid artery, 163, 168, 179, 192

Coracoid cartilage, 49, 79, 80, 81

Coracoid vein, 202,°203, 217

Coracomandibularis muscles, 93-94, 109

Corium, 23, 26; origin of, 96

Cornea, 258, 267

Coronary artery, 164, 179-180; posterior,
164,168 _

Coronary vein, 215

Corpora bigemina. See Optic lobes

Corpora restiforme, 222, 235

Corpus luteum, 301, 303

Cranial canals. See Canals of head

Cranial nerves, 223-227, 238-246; abdu-
cens, 223-224, 241; auditory, 224-225,
243; facial, 224, 241-243;- glosso-
pharyngeal, 225, 243-244; oculomotor,
223, 239-240; olfactory, 223, 238-239;
optic, 223, 239; trigeminal, 223, 240-
241; trochlearis, 223, 240; vagus, 225-—
227, 244-245

Cranium, 42-44, 53-61; development of,
538-55; of Chlamydoselachus, 43; of
Zygaena, 58-60

Cross-trunks, 162, 174, 175, 176-177

Crystalline lens. See Lens

Cupula terminalis, 272, 273

Cutaneous veins, 204, 216-217; nature of,
217-218

Cuticular plate. See Dermatome

Cyclospondyly, 74

Constrictor of sae, 95

Danielian sinus, 198, 199

Dasyatis dipterura, anterior gastro-pan-
creaticosplenic artery of, 190; sting of,
37

Demibranch, 148; absent behind last
cleft, 176; kinds of, 148

Dendrite, 229

Dental ridge, 128

Dentinal canals, 32, 35, 37, 130-131

Dentinal papillae, 128

Dentine, 32, 33, 131; of fin spine, 33-34;
of saw tooth, 35; of sting, 37; types of,
33-35

Depressor hyomandibularis, 104, 105

Depressor of lid, 102

322 THE ELASMOBRANCH FISHES

Depressor mandibulae, 105

Depressor rostri, 105

Dermal fin-rays, 89, 94

Dermal papilla, 30

Dermatome, 96

Dermis. See Corium

Digestive tract, 121-126; 127-142; ar-
teries to, 166-168, 186-191; develop-
ment of, 127-128; mesenteries of, 121,
127; veins of, 200-201, 210-212

Diencephalon, 221, 230-233; cavity of,
236; outgrowths from, 233

Digitiform gland. See Rectal gland

Dilator muscle of sae, 95, 111, 112

Dilator spiraculae, 102-103

Diphycereal, 74

Diplospondyly, 51, 72, 74; function of,
74; incomplete, 49

Disceus thayeri, 10, fig. 21

Diverticula of spiracle, 148, 153; nerve to,
153

Dorsal aorta, 165-166, 186; development
of, 186; paired, 165, 186; tributaries
of, 166, 186; unpaired, 165, 186

Dorsal bundles, 89, 96, 99

Dorsal constrictor muscles, 90-91, 102-—
104

Dorsal cutaneous vein, 202, 203, 216-217

Dorsal fin, 6, 12, 14; in notidanids, 6;
position of, 12; skeleton of, 51, 82-83

Dorsal gastric artery, 187

Dorsal horn of cord, 222, 237

Dorsal interealary plate, 47, 48, 70, 71

Dorsal intestinal artery, 167, 190

Dorsal intestinal vein, 200-201, 211;
tributaries of, 211

Dorsal marginal cartilage, 82

Dorsal myelonal vein, 208

Dorsal plate, 47, 48, 72; foramen of, 48;
incomplete diplospondyly, 49

Dorsal pterygial vein, 213

Dorsal root ganglion, 227, 246

Dorsal root nerve, 227, 246; foramen of,
48, 210, 246

Dorsal spinal vein of ray, 210

Dorsal suspensory ligament of eye, 270

Dorsolateral artery, 168, 191

Dorsolateral bundle, 97

Dorsomedian bundle, 97

Duet of Cuvier, 171; tributaries to, 198—
199, 200, 202, 205, 210, 212, 214

Ductless glands, 134

Ducts of kidney, 294-296

Ductus choledochus, 124, 137-138

Duodenum, 124, 136-137; arteries to, 166-
167; blind saes of, 137; derivatives of,
136-137; ducts to, 124, 137, 138; mesen-
tery of, 121

Ear, 258-261, 264, 270-274; capsule of,
258, 271; development of, 274; nerve
of, 261, 273; parts of, 258-259

Ear stones. See Otoliths

Ecetethmoidal process. See Antorbital pro-
cess

Efferent arteries, 165, 182; branchial,
165, 175, 182; development of, 175;
hyoidean, 165, 182

Efferent branchial arterioles, 157

Efferent-colleetor arteries, 161-162, 173-
177; branches of, 163-165, 178-180; de-
velopment of, 175-177; in holobranchs,
149, 153, 157, 162

Egg (ovum), 303; development of, 303;
hatching of, 305-306

Egg shell, 305-306; attachment of, 305;
flanges on, 305; perforation of, 306;
production of, 305; tendrils of, 305;
types of, 305-306

Elasmobranch fishes, divisions of, 8; se-
ries of, 9-10

Elastica externa, 69, 70

Elastica interna, 69, 70

Electric cone, 114

Electric dises, 112, 113, 114; layers of,
114

Electric nerve, 115, 243, 244

Electric organ, 112; anatomy of, 114-115;
in Torpedo, 115; nerves of, 115, 243,
244; origin of, in rays, 114

Electric ray (Torpedo), 3

Embryonie aortie arches, 175; derivatives
of, 178

Enamel, 30, 32; derived from, 132-133;
in rays, 32; nature of, 32; of fin spine,
33; of saw tooth, 35; of sting, 37; of
teeth, 128, 130; in Carcharias, 132-133

Enamel organ, 30, 33, 35, 128

Endolymphatie ducts, 5, 43, 55, 259, 271,
272, 273

Endorachis, 237

Endoskeleton. See Skeleton

Ependymal cells, 229-230

Epiblastie fold, 15

Epibranchial cartilages, 45, 64, 65, 93, 107

Epidermis, 23, 28, 30; derivatives of, 28-
38; layers of, 23, 26, 30

Epididymus, 301

INDEX o20

Epigastrie artery, 163, 179

Epigonal organ, 190, 300, 303; artery to,
190; relation of, to rectal gland and
testes, 300

Epiphysis, 233; development of, 233

Erythrocytes, 170

Etmopterus, light organs of, 29-30

External branchial apertures. See Gill
clefts

External carotid artery, 164, 180

External filaments of embryo, 148, 151,
152

External flexor muscle, 95, 110-112

External form, 5-7, 8-16; in development,
10-12

External mandibular (VII) nerve, 243;
divisions of, 243; ganglion of, 243

External (posterior) rectus muscle, 90,
100; nerve to, 100, 223-224, 241; origin
of, 99

Extrabranchial cartilages, 47, 67, 69; re-
lation to gill septum, 69, 149

Extrahyal cartilage, 67, 69

Extraseptalia, 69

Extravisceral cartilages, 47, 67, 69

Kye, 5, 258, 266-270; development of,
269; muscles of, 89-90, 99-100; orbit
of, 58; pupil of, 258; structure of, 267—
269

Eyeball, 60, 258; muscles to, 89-90, 99,
101

Eyelid, 5, 258, 267; muscles to, 102; mov-
able, in Seyllium, 267

Eye muscles, 89-90, 99-100, 258; develop-
ment of, 99-100; nerves to, 221, 223,
240, 241, 242

Facial nerve, 224, 241-242; divisions, 224,
241-242; nucleus of, 241; sensory fibers
of, 241

Fallopian tube, 304, 310

Fasiculi lateroventrales, 235

Fasiculi longitudinales mediales, 235

Femoral artery, 169, 192

Femoral vein, 202, 213

Fenestrae, 43, 55, 271

Fibrillae of nerve, 238

Filaments. See Gill filaments

Fins, 1; anal, Heptanchus, 6, 12; ancestral
type of, 14-16; caudal, Heptanchus, 6,
12; dorsal, Heptanchus, 6, 12, 13; form
and position of, 12-16; function of, 12-
14

Fin-fold theory, 14-15, 247

Fin spine, 33; development of, 33-34;
parts of, 33

Foramen of (foramina): abducens nerve,
44; 60; anterior cerebral vein, 44; dor-
sal plate, 48; dorsal root nerve, 48,
246; facial, 44, 60; interealary plate,
48; internal carotid artery, 53; inter-
orbital canal, 44; magnum, 57; oculo-
motor nerve, 44, 60; ophthalmicus pro-
fundus nerve, 43, 60; ophthalmicus su-
perficialis (VII) nerve, 44, 60; orbito-
nasal canal, 44; optic, 44, 60; pectoral
girdle, 49, 81; pelvie girdle, 51; ramus
anastomoticus artery, 44; trochlear, 44,
60; ventral root nerve, 48, 246

Forebrain, 230

Formatio-reticularis, 237

Fossa rhomboidalis, 235

Fourth ventricle, 222, 235, 236

Funnel (nephrostome), 296

Funnel of oviduct, 290

Galeus, color of, 26

Gall bladder, 124, 137

Ganglion: gasserian, 240, 241; geniculate,
242, 243; habenular, 236; oculomotor,
240; ophthalmicus profundus, 240;
ophthalmicus superficialis (V), 240;
sympathetic, 247-248

Gastric artery, 166-167, 187

Gastric juice, 135

Gastric veins, 200, 201

Gastroduodenal artery, 166, 167, 188

Gastrohepatic artery, 166, 186

Gastro-pancreaticosplenie artery, 188

Gastrosplenic vein, 201

General cutaneous nucleus, 236

Genital glands, 290

Genital organs: of female, 290, 291, 303-
309; of male, 290, 291, 300-303

Genital ridge, 300

Genital system, 290-291, 300-309; rela-
tion of, to urinary system, 292

Germ cells, 300

Germinative layer of epidermis, 23

Gill. See Holobranch

Gill-arch theory of Gegenbaur, 14-15

Gill clefts, 5,11, 132, 147, 148, 150; in Hep-
tanchus, 147; in rays, 150; in Squatina,9

Gill filaments, 147, 148, 149, 151, 152, 154,
173, attachment of, 149, 151; blood to,
153, 157, 175; cireulation in, 157; em-
bryonic, 148, 152; on spiracular pocket,
153

324 THE ELASMOBRANCH FISHES

Gill pocket, 147, 150; accessory, 151;
apertures of, 147, 151; development of,
151; filaments on, 147; in Heptanchus,
147

Gill rakers, 37, 147, 154; of Cetorhinus,
37, 154; of Squalus sucklii, 37, 154

Gill septum, 147, 148-149; attachment of,
149

Gill supports, 148

Gland cell, 23, 28; in buccal cavity, 28;
in cloaca, 28; lumen of, 28; modified, in
light organs, 29; of claspers, 28; of
sting, 28; origin of, 28

Glomeruli of olfactory bulb, 239, 264

Glomerulus, 296, 299

Glossal projection, 65

Glossopharyngeal nerve, 225, 243-244;
branches of, 225, 244; ganglion of, 225,
244; nucleus of, 243

Goblet cells. See Gland cells

Golden cells, 27

Grey matter of cord, 237

Guanin, 27

Gular line, 263

Gustatory organs, 264, 265-266

Gynandromorphism, 309

Habenular ganglion, 236

Haemal arch, 47

Haemoglobin, 170

Hair cell, 273, 278; of ampulla, 273; of
neuromast, 278

Hammerhead shark (Zygaena), 2.

Head somite, 99

Heart, 160, 170-172; arteries to, 163-164,
178-180; nerves to, 227; position of,
160; rooms of, 160, 170; veins of, 215-
216

Hepatic artery, 166, 187

Hepatic portal system, 200, 204, 210-212;
development of, 212; parts of, 200-
201, 210-212; relation of, to subintes-
tinal, 208, 212

Hepatic portal vein, 201, 211; tributaries
of, 211

Hepatic vein, 200, 201, 211, 213

Heptanchus, figs. 12, 13, 14, 15

Heptanchus maculatus, 2, 3; antorbital
process of, 44; arteries of, 161-169;
digestive tract of, 121-126; endoskele-
ton of, 43-52; external form of, 5-7;
genital system of, 290-291; integument
of, 23-25; musculature of, 89-95; ner-
vous system of, 221-228; respiratory

tract of, 147-149; special senses of,
258-263; veins of, 198-203

Heptranchias, 3 note

Heterocerey, 74

Heterodontus francisci, 2, fig. 17; egg ease
of, 305; melanophores of, 27; teeth of,
130

Hexanchus, 2, 3; hypobranchial arteries
of, fig. 169

Hindbrain, 230

Holobranch, 148

Horizontal semicircular canal, 258, 273;
development of, 274

Horns of cord, 222, 237; dorsal, 222, 237;
ventral, 222, 237

Hymen, 309

Hyoid arch, 45, 63; attachment of, 45,
58, 63; muscles of, 92

Hyoidean afferent artery, 161, 172

Hyoidean ampullae, 279-280

Hyoidean efferent artery, 165, 182

Hyoidean nerve. See Ramus hyoideus
(VII)

Hyoidean sinus, 208

Hyoidean somite, 99

Hyoidean vein, 208

Hyomandibula, 63-64

Hyomandibular canal, 261, 274, 277;
modification of, in rays, 277; nerves to,
224, 242, 243, 279

Hyomandibular nerve, 224, 242, 243;
branches of, 224; foramen of, 44

Hypobranchial arteries, 162-165, 178-
180; lateral, 163, 178; median, 163, 179

Hypobranchial cartilages, 45-46, 64, 65;
attachment of, 46; muscles to, 94

Hypobranchial muscles, 90, 93, 108-109;
nerves to, 227, 246; origin of, 108

Hypophysis, 233; divisions of, 233

Tliae artery, 169, 192

Tliae vein, 213

“Indifferent stage” of sex, 300

Inferior jugular vein, 199, 204; tributaries
of, 199

Inferior lobes of brain, 221, 233

Inferior lobes of hypophysis, 234

Inferior mesenteric artery, 167-168, 186,
190-191

Inferior oblique muscle, 89, 100; in Pris-
tiophorus, 100; origin of, 99; nerve to,
100, 223, 239-240

Inferior rectus muscle, 90, 99; origin of,
99; nerve to, 100, 223, 239-240

Infraorbital canal, 242, 261, 274, 277;
nerve to, 224, 242, 279

Infraorbital plate, 53, 57; absence of, 5

Infundibulum, 221, 233, 236

Inner bueceal ampullae, 262, 279

Inner zone, 70

Integument, 23, 26; in Elasmobranchs in
general, 26-38; in Heptanchus, 23-25

Interarcuales muscles, 90, 92, 106; dorsal,
92, 106; lateral, 92, 106-107

Interbranchial muscles, 91, 105-106, 149,
151

Interealary plate, 48, 72

Intercostal arteries, 169, 193

Intermediate lobe of hypophysis, 234

Internal branchial aperture, 37, 147, 154;
relation to gill rakers, 154

Internal carotid artery, 165, 182-183; fo-
ramen of, 53; relation to ramus anas-
tomotieus, 165, 183

Internal flexor muscle, 95, 112

Internal mandibular nerve, 243

Internal pretrematicus (IX), 225

Internal (anterior) rectus muscles, 90,99;
nerve to, 100, 239; origin of, 99

Interorbital canal, 44, 205

Interorbital vein, 198, 205

Intima, 170

Intraintestinal artery, 166, 188

Intraintestinal vein, 200, 210, 212; in
Zygaena, 210; relation of, to subintes-
tinal vein, 210, 212

Tris, 258, 267; of light organ, 29

Kidney, 287, 289, 292; arteries to, 169,
193; ducts of, 294-296; finer anatomy
of, 296; in Elasmobranchs in general,
292-294; in Heptanchus, 287; in rays,
292; metamerism of, 292, 299; metamor-
phosis in male, 292, 302; sexual differ-
ences in, 289, 292; veins of, 200, 208,
209, 210

Labial cartilage, 67, 68; in Heptanchus,
68; in Hexanchus, 68

Laemargus, photophores of, 29

Lagena, 261, 272; nerve to, 273

Lamina terminalis, 239

Lamna cornubica, 9; muscles in tail of, 97

Lateral (abdominal) artery, 168, 179

Lateral abdominal system, 202, 204, 214,
217; history of, 214-215

Lateral abdominal vein, 202, 213; tribu-
taries to, 202, 213-214

Xx 320

Lateral bundles, 97

Lateral cutaneous veins, 203, 214, 217;
relations of, 203, 217

Lateral fin-fold, 14, 15, 214

Lateral fin-fold theory, 14; evidence for,
15

Lateral hypobranchial artery, 162-163,
178

Lateral line, 264, 274, 275, 276; in Acan-
thias, 276; development of, 264, 275—
276, 278; function of, 279; in Heptan-
chus, 7, 89, 261; nerves to, 225, 242, 243,
278; section through, 278

Lateral plate, 96, 109

Lateral pterygial artery, 191

Lateral pterygial vein, 213

Lateral septum, 97

Lateral ventricles, 236

Lateralis nerve, 225, 245, 278

Lens cell of light organ, 29

Lens of eye, 267; development of, 269

Leopard shark (Triakis), color of, 26

Levator hyomandibularis, 103

Levator labialis muscles, 93, 100-101

Levator maxillae, 90, 101, 102; nerves of,
241; relation of, to first dorsal constric-
tor, 90

Levator rostri, 104

Lipochrome, 27

Lipophores, 27; in Heterodontus, 27

Littoral, 1

Liver, 124, 137; artery to, 166, 187; ducts
of, 124, 137; lobes of, 124, 137; oil of,
137; veins of, 211-212

Lobes of vagus, 236, 237

Lobi inferiores, 233

Locomotion: caudal, 13; pectoral, 12, 13

Longitudinal canal of epididymus, 301

Lymphatie vessels, 218

Lymphocytes, 133

Lymphoid organ, 133

Macula neglecta of ear, 273; hair cells of,
273; nerve to, 273

Mandible, 63, 92, 279; muscles to, 92, 93—
94

Mandibular ampullae, 279

Mandibular arch, 44, 45, 62, 63; articu-
lation of, 45, 63; attachment of, in
Heptanchus, 45; in embryo, 62; parts
of, 45, 62

Mandibular branch (V), 223, 240, 241;
ganglion of, 240; motor fibers of, 240;
sensory fibers of, 240

326 THE ELASMOBRANCH FISHES

Mandibular canal, 275; nerves to, 243
Mandibular groove, 262; nerve to, 224

Mandibular somite, 99; muscle derivatives

of, 99

Marginal cartilage of clasper, 81-82

Maxillaris branch (V), 223, 240, 241;
ganglion of, 240, 241; origin of, 241

Meckel’s cartilage. See Mandible

Median anterior sulcus, 231

Median cardiae vein, 215

Median cerebral artery, 165, 183

Median hypobranchial artery, 163, 178,
179

Median hypobranchial piece, 46, 65, 67

Median longitudinal bundles of medulla,
235

Median olfactory nucleus, 221, 232, 239

Median pterygial artery, 191

Median pterygial vein, 213

Median vesicle, 296, 298; derivation of,
298, 300; relation of, to segmental duct,
296, 298; relation of, to collecting tu-
bules, 297

Medulla, 222, 235, 236; finer structure of,
236; section through, 236

Melanophore, 26; in Heterodontus, 26

Meningeal lining, 237

Mesencephalon, 221, 222, 230, 234; fibers
terminating in, 239; in Heptanchus,
221-222

Mesenteri¢ arteries: inferior, 167-168,
190-191; superior, 167, 188-190

Mesenteries, 121, 127-128; in Heptanchus,
121; in Hypnos, 127

Mesopterygium, 50, 77, 78

Mesorchium, 290; vasa efferentia on, 302

Mesorectum, 121, 297; nephrostomes on,
290

Mesovarium, 290, 303

Metapterygium, 50, 77; development of,
a—19

Metencephalon, 221, 222, 230, 234; cavity
of, 235-236; in Heptanchus, 221-222

Midbrain. See Mesencephalon

Mixed nerve, 2438, 246

Motor fibers, 236; origin of, 236

Motor (ventral) root, 246

Mouth, 5, 121, 128

Mucous pores, 7, 262

Multipolar nerve cell, 229

Muscle buds, 109, 110; growth of, 238;
of fin, 109, 110; bearing of, on origin
of fin, 110

Muscles of eye. See Museulature

Muscle fibers, 96-97; in Cladoselachus, 1;
metamorphosis of, to electric dises, 114—
115

Muscularis, 170

Musculature: buccal and pharyngeal, 99—
93, 101-108; dorsal bundles, 89; of
claspers, 95, 110-112; of Elasmobranchs
in general, 96-112; of electric organ
(developing), 112-114; of eye, 89-90,
99-100; of eyelid, 102-103; of fin, 89,
95, 109-110; of Heptanchus, 89-95; of
hvpobranchial region, 93, 108-109; to
lens, 269-270; ventral bundles, 89, 97

Musculospinal artery, 192

Mustelus californicus, 9; color of, 26; nie-
titating membrane of, 102

Myelencephalon, 221, 222, 235; eavity of,
235-236; in Heptanchus, 221; nerves
from, 235

Myelonal artery, 186, 192

Myelonal veins, 208

Myliobatis californicus, 3, fig. 8

Myoblast, 96

Myocoele, 96

Myosepta, 89, 96, 97; direction of, 89, 96,
97; in electric organ, 112

Myotome, 96, 109; derivative of, 109

Nasal apertures, 5; in Elasmobranchs in
general, 264-265; in Heptanchus, 5, 44,
258

Nasal capsule. See Olfactory capsule

Nasal cartilage, 43-44, 58

Nasal pit or cup, 5; relation of, to oro-
nasal groove, 122

Neopterygium, 79

Nephrostome, 296, 297, 298, 301; develop-
ment of, 298

Nerve eéells, 229

Nerve fiber. See Axone

Nerves: cranial, 223-227, 238-246; occip-
itospinales, 227, 245-246; spinal, 227—
228, 246-247; sympathetic, 247-248

Nervous collector, 228, 247; relation of,
to origin of paired fins, 247

Nervous system: central, 221-228, 229-
248; development of, 230; in Elasmo-
branchs in general, 229-248; in Hep-
tanchus, 221-228; peripheral, 222, 238

Neural arches, 47, 69; composition of, 47—
48

Neural canal, lining of, 237

Neural crest, 238

Neural fold, 230

INDEX 327

Neural tube, 230, 238; cells of, 229-230,
238

Neurilemma, 238

Neurocoele, 230

Neurogleal cell, 230

Neuromast, 262, 275, 278

Neurone, 229

Neuropore, 230, 239

Nictitating membrane, 5, 102, 266; ab-
sent in Heptanchus, 5; development of,
266; muscles of, 102-103

Nictitator muscle, 102, 103

Nitrogenous waste matter, removal of, 289,
296, 298

Notidanids, 8, 6, 71, 264; auditory re-
gion of, 58

Notochord, 47, 70; constructions, 47-48;
relation of, to spinal column, 47, 70;
section through, 48, 70; sheath of, 47,
70

Notochordal sheath, 48, 70, 75; zones of,
48, 70

Notorhynchus (Heptanchus), 3 note

Nutrient arteries, 180

Nutrient vein, 205, 207

Occipital condyle, 57; in rays, 57

Occipital crest, 43

Occipitospinales nerves, 71, 227, 245-246

Oculomotor nerve, 222, 223, 234, 239;
division to eye muscles, 239-240; fora-
men of, 44; ganglion of, 240; muscles
supplied by, 100; origin of, 239

Odontoblasts, 30, 33, 34, 130

Oesophagus, 123, 134; cells of, 134; folds
of, 123; lining of, 123, 134

Olfactory bulbs, 223, 239, 258, 264

Olfactory bundle. See Olfactory nerve

Olfactory capsule, 43, 53, 57, 238; in em-
bryo, 58-55; in Zygaena, 55

Olfactory cells, 264

Olfactory fila, 239

Olfactory lobe of brain, 2238, 239, 258, 264

Olfactory membrane, 239, 258, 265

Olfactory nerve, 223, 238-239, 258, 264,
265

Olfactory organ, 258, 264-265; circulation
in, 265; divisions of, 264-265; fune-
tion of, 265; nerves of, 264

Olfactory receptors, 258

Olfactory sac, 264

Olfactory tract, 221, 223, 239, 258, 264

Omentum, 121

Omphalomesenteri¢ vein, 212

Odcyte, 303; primary, 303; secondary,
303

Odgonium, 303

Ootid, 303

Ophthalmica magna artery, 165, 181

Ophthalmicus profundus (V), 223, 241;
ganglion of, 240-241; origin of, 240;
sensory fibers, 240

Ophthalmicus superficialis (V), 223, 240,
241; ganglion of, 240, 241; origin of,
240; sensory fibers, 240

Ophthalmicus superficialis (VIT), 224,
242

Optic artery, 183

Optic chiasma, 221, 223, 239

Optic cup, 269

Optic lobes, 221

Optic nerve, 221, 234; origin of, 239, 269;
relation of, to sclera, 268; termination
of, 234, 239

Optic organ. See Eye

Optic pedicel, 60, 90, 268; function of,
258

Optic stalk, 269

Optic thalamus, 236

Optic vesicles, 230, 269

Orbit, 53, 55, 60, 89; in Heptanchus, 5, 44;
muscle attachment to, 89

Orbital artery, 182

Orbital fissure, 44, 60; in embryo, 60; re-
duced, in Mustelus, 60

Orbital process, 44, 62; in embryo, 62

Orbital sinus, veins to, 198, 204, 205

Orbitonasal canal, 44

Organ of special sense, 258, 264

Oronasal groove, 122

Otolith, 272

Outer buccal ampullae, 262, 279

Outer (heavy) layer of retina, 268

Ova, 290, 303

Ovary, 290, 303; development of, 303

Ovidueal artery, 169, 193; anterior, 193;
posterior, 193

Ovidueal funnel, 290, 304

Ovidueal valve, 306

Ovidueal vein, 209

Oviduct, 290, 304; arteries to, 169, 191,
193; development of, from Wolffian
duct, 304; divisions of, 304; rudimen-
tary, in male Heptanchus, 291, 309

Oviparous, 307

Paired fins, muscles of, 94, 109; origin of,
14-16; skeleton of, 50

328 THE ELASMOBRANCH FISHES

Palatine nerve, 224, 243

Palatoquadrate cartilage, 45, 62; muscles
to, 90

Pallial eminence, 221, 232

Panereas, 124, 138; arteries to, 166; duct
of, 124, 138; lobes of, 124, 138

Pancreatic duct, 124, 138

Papillae of oesophagus, 134

Paracentral mass, 237

Parachordal plates, 53

Paraphysial arch, 233

Paraphysis, 233

Parietal fossa, 43, 55, 271

Pectoral fin, 6, 12; arteries to, 168, 191;
function of, 12, 13, 14; fusion of, to
sides in rays, 12; muscles of, 89, 94;
nerves of, 227, 246-247; veins of, 202,
213

Pectoral girdle, 49, 79-81; development
of, 77; muscles to, 89; parts of, 49, 79-
81

Pectoral muscles, 89, 94; development of,
110

Pectoral plexus, 227, 246

Pelagic, 1

Pelvie fin, 6, 14; claspers of male on, 6

Pelvie girdle, 6, 51, 82, 228; origin of, 82

Pelvic plexus, 228, 247

Pentanchid types, 150

Pepsin, 135

Peptic cells, 135

Pericardial artery, 163, 179

Pericardial cavity, 151, 171

Pericardio-peritoneal septum, 287

Perimeningeal space, 237

Peripheral nervous system, 223-228, 238—
248; development of, 238

Pharyngeal nerve (IX), 225, 244; (X),
225-227, 245

Pharyngobranchial cartilages, 46, 64; fu-
sion of, in last arch, 65; muscles of,
92, 106-107

Pharynx, 122, 131-134; lining of, 132;
muscles of, 90-93, 101-108; perfora-
tions of, 122, 131; stomodeal denticles
in, 122

Photogenic cell, 29

Photophore, 29

Pigment, 23, 27, 29, 33; function of, 27

Pineal stalk, 221, 233, 236; development
of, 233

Pit organs, 262, 274, 281-282; nerves to,
225, 244, 282

Pituitary, 221, 233

Placodes, 264

Placoid scales, 7, 30-32; absence of, 32,
309; base of, 24, 32; canals of, 30, 32;
development of, 30; finer anatomy of,
32; modified, 24-25, 33, 154; spines of,
32, 33

Plasma, 170

Pleuracanthus, 1

Poison gland of ray, 28

Pori abdominales. See Abdominal pores

Portal vein. See Hepatic portal

Portio major (V), 240

Portio minor (V), 240

Postbranchial body, 151

Posteardinal sinus, 200, 204, 210; in rays,
210; relation of, to subscapular vein,
214

Posteardinal vein, 200, 204, 210; tribu-
taries of, 200, 210

Posterior cerebral artery, 165, 184

Posterior cerebral vein, 207

Posterior commissure, 233

Posterior coronary artery, 168, 179, 192

Posterior dorsolateral artery, 168

Posterior efferent-collector artery, 176

Posterior gastro-pancreaticosplenie artery,
166, 188

Posterior gastro-pancreaticosplenie vein,
211

Posterior gastrosplenic artery, 166, 188

Posterior intestinal artery, 167, 188, 190;
in rays, 190

Posterior intestinal vein, 200, 211; tribu-
taries of, 200

Posterior mesenteric artery. See Inferior
mesenteric

Posterior oblique semicircular canal, 259,
261, 273

Posterior (outer) buccal ampullae, 262,
279

Posterior rectus muscle. See External ree-
tus

Posterior thyroid artery, 164

Postorbital groove, 205

Postorbital process, 43, 44, 45, 58, 60; in
Chlamydoselachus, 58; in notidanids,
58; in rays, 58

Post-trematicus nerve (IX), 225, 244;
(X), 225, 245

Postvelar areh, 233

Premandibular somite, 99

Preorbital process, 44, 58; in Zygaena, 58

Prespiracular ligament, 63

Prespiracular nerves, 224, 243

INDEX 329

Pretrematicus nerve (VII), 243; (1X),
225, 244; (X), 149, 225, 245

Primary renal corpuscle, 299

Primitive ova, 301

Pristis, 3, 9, fig. 19; tooth of, figs. 39, 41

Pristiurus, development of fin skeleton of,
15-16

Proctodeum, 128

Pronephrotie duct, 298, 299

Propterygium, 50, 77; development of, 77

Prosenceplahon, 230; derivatives of, 230

Pseudobranchial artery, 165, 182; in em-
bryo, 182; in rays, 180

Pterygial arteries, 191

Pulp eavity, 32, 35

Pupil of eye, 268

Pylorie stomach, 123, 135

Pylorie valve, 123, 136

Quadrate, 45, 62

Radial cartilages, 50, 51, 77, 78, 79; de-
velopment of, 77-78; of pectorals, 75—
76; of pelvic, 81; postaxial radials, 50,
79; preaxial radials, 50

Radial muscle, 94-95

Raia erinacea, 9, fig. 20

Ramuli to lateral line canal, 278

Ramus anastomoticus artery, 165, 183;
foramen of, 44; function of, 181

Ramus dorsalis artery, 192

Ramus dorsalis nerve (IX), 225; (X),
225, 245, 278

Ramus hyoideus (VII), 243

Ramus oticus (VII), 242, 279; relation of,
to spiracle, 153

Ramus palatinus, 224, 243

Ramus ventralis artery, 192

Ramus visceralis (or intestinalis) (X),
227, 245

Rays: batfish, 3; Cephaloptera, 3; elee-
tric, 3; guitar fish, 9; sawfish, 3, 9;
small sting, 8; spiracle of, 150

Recessus neuroporicus, 221

Recessus utriculi, 259, 272; nerve to, 273

Rectal gland, 121, 126, 141; artery of, 167,
191; function of, unknown, 141; rela-
tion of, to epigonal organ, 300; strue-
ture of, 141; veins of, 200, 211

Rectal artery, 169, 192

Rectum, 126, 141; artery to, 169, 192; in
Heptanchus, 126; mesentery to, 121;
veins of, 213

Rectus abdominalis, 97

Red blood cells. See Erythrocytes

Renal artery, 169, 192, 193

Renal corpuscle, 296, 299, 300; develop-
ment of, 299-300; function of, 296;
primary, 299; secondary, 299

Renal portal system, 204, 208-209; rela-
tion of, to subintestinal vein, 208

Renal portal vein, 208

Renal tubule, 297, 298, 299, 300

Respiration, 157

Respiratory current, 155; course of, 156;
direction of, 156; reversal of, in rays,
156; in Urolophus, 157

Respiratory membrane, 149

Respiratory tract, 147, 150; of Elasmo-
branchs in general, 150-157; of Hep-
tanchus, 147-149

Restiform bodies. See Corpora restiforme

Retina, 268; cells of, 268-269; develop-
ment of, 269; nerve from, 269; struc-
ture of, 268-269

Retractor palpebrae superioris, 102

Revehentes, 210

Rhinobatis productus, 9, fig. 7.

Rhinodon (Rhineodon) typicus, 3; color
of, 26, 27

Rhombencephalon, 230

Ribs, 48, 72

Rods of retina, 269

Rostrum, 43, 55, 57; in Acanthias, 57

Saeci vasculosi, 233

Saceular nerve, 273

Sacculus, 259, 272

Sawfish (Pristis), 9

Saw tooth, 35; development of, 35; strue-
ture of, 35

Seales. See Placoid seales

Scapula, 49, 79; muscles to, 94, 104

Scapular canal, 277

Schneiderian folds, 264; development of,
265; primary, 265; secondary, 265

Sclera, 258, 268; in Cetorhinus, 268

Sclerotome, 70, 96

Scroll valve, 139

Scyllium, development of pectoral girdle
of, 15

Scymnus, epidermis of, 26

Secondary dentine, 34; origin of, 34

Segmental artery, 169; branches of, 169,
192-193; caudal, 169, 193

Segmental duct, 296, 297, 298; develop-
ment of, 298

Selachii, 8

330 THE ELASMOBRANCH FISHES

Semicireular canal, 55, 258, 271, 273; am-
pullae of, 259, 273; anterior oblique,
43, 258, 273; development of, 275;
nerves to, 261, 273; posterior oblique,
43, 259, 273

Seminal vesicle, 302

Sense of smell, 265

Sensory canal system, 261-263; canals of,
261-262; function of, 279; nerves to,
262; neuromasts of, 262, 278; of Elas-
mobranchs in general, 274-279; of
Heptanchus, 261-263; structure of, 278

Sensory fibers, 238; origin, 238

Sensory (dorsal) root nerve, 246

Septum, constricting notochord, 48; of
gill, 147, 148, 149

Serosa, 170

Serum, 170

Sex cells, 301, 302, 303; passage of, to
cloaca of female, 310; passage of, to
clasper of male, 303; sex gland, 300

Sex characters (secondary), 309; claspers,
309

Shagreen denticles, 7, 23

Sharks: angel fish (Squatina), 9, fig. 18;
ancient, 1; basking,3; blue,3; flattened,
3; generalized, 2; hammerhead, 2; hep-
tanchid, 5-7, figs. 12, 13, 14; heterodont,
1, fig. 17; lamnoid, 9; man-eater, 2, 9,
fig. 16; modern or recent, 2, 3; preda-
cious, 9; specialized, 2; swell, 2, fig. 1;
thresher, 2, fig. 2

Shell gland, 290, 304-305; secretory cells
of, 305

Sinu-auricular aperture, 171

Sinu-auricular valve, 160, 171

Sinus, 204

Sinus of photophore, 29

Sinus venosus, 160, 170, 171; tributaries
to, 201, 211, 215

Siphon, 28, 303; function of, 303; relation
of, to clasper tube, 303

Skeleton, 43-52, 53-83; development of,
77-79; nature of, 53; in anal fin, 52, 83;
of caudal fin, 51; of clasper, 51, 81-82;
of dorsal fin, 51, 82-83; of pectoral fin,
49, 75-79; of pelvic fin, 51, 81-82; of
paired fins, 50-51, 75-82; of unpaired
fins, 51, 82-83

Skin. See Integument

Skull, 48-47, 53-69; components of, 43,
53

Somatic layer, 96

Somatie sensory fibers; terminus of, 236

Somite, 70, 96; degeneration of, 97; of
head, 99-100; parts of, 96

Special senses, of Elasmobranchs in gen-
eral, 264-282; of Heptanchus, 258-263.
See also Organs of special sense

Sperm sac, 302

Spermatagonia, 301

Spermatie fluid, 302

Spermatid, 301

Spermatozoa, 291, 301, 302; course of, to
female, 309

Spinal artery, 186

Spinal column, 47, 69; calcification in, 74—
75; in Elasmobranchs in general, 69—
75; in Heptanchus, 47-48; relation of,
to notochord, 70

Spinal cord, 222, 237-238; arteries to,
169, 192, 193; development of, 230, 237;
in Elasmobranchs in general, 237-238;
in Heptanchus, 222

Spinal nerves, 227, 246; in Elasmobranchs
in general, 246-247; roots of, 227, 237,
246

Spinalis artery, 186

Spina, color in, 27; photophores of, 29

Spiracle, absence of, 150; blood supply
to, 181-182; diverticula of, 147-148,
153; filaments of, 147, 153; in rays,
150; relation of, to gill clefts, 150

Spiracular ampulla, 280

Spiracular cartilage, 63, 153

Spiracular diverticulum. See Diverticula
of spiracle

Spiracular valve, 153; muscles of, 153-
154; support of, 153

Spiral intestine, 139-140; mesentery to,
121

Spiral valve, 124, 126, 139; arteries to,
167; development of, 140; extent of,
126, 139-140; funetion of, 140; lining
of, 126, 140; turns of, 124, 140; veins of,
210-211

Splanchinic layer, 96

Spleen, arteries to, 166, 167, 188; in Hep-
tanchus, 124, 138; position of, 138-139

Spouting, 156-157; course of, 156-157; in
Squatina, 156-157

Squalus sucklii, gill rakers of, 37; relations
of subscapular vein of, 214

Squatina, 9, fig. 18; clasper gland of, 28;
spouting in, 156-157

Stapedeal artery. See Orbital artery

Sting, 35, 37; function of, 37; glands of,
28; structure of, 37

INDEX

Stomach, 1238, 185-136; arteries to, 166,
167, 186, 188, 189-190; erypts of, 135;
glands of, 135; limbs of, 123; lining of,
123, 135; mesentery to, 121; nerves to,
227, 245; secretion of, 135; veins of,
200-201, 211

Stomodeal denticles, 25, 38, 122, 266;
function of, 38; in thyroid, Chlamydosel-
achus, 134; location of, 38, 122; of Hep-
tanchus, 25, fig. 27; rudimentary, 38

Stomodeum, 127

Subelavian artery, 168, 191; in Heptan-
chus, 168, 191-192

Subelavian vein, 202, 214

Subintestinal vein, 208, 212; derivatives
of, 208, 210

Subseapular sinus, 203; tributary to, 2038

Subseapular vein, 202, 214; in Squalus,
214

Subspinalis muscle, 92, 106; nerve to, 227

Superficial constrictors, 90, 101; function
of, 90

Superficial intercostal artery, 169

Supraophthalmie ampullae, 262, 279

Superior commissure, 233

Superior lobes of hypophysis, 233-234

Superior mesenteric artery, 167, 188-190;
in rays, 190; its branches, 167, 188-190

Superior oblique muscle, 89, 99; nerves to
44, 100, 223, 240; origin of, 99

Superior rectus muscle, 90, 99; nerve to,
100, 223, 241; origin of, 99

Supernumerary branchial arches, 47

Supporting cells in ampulla, 273

Suprachoroidea, 268

Supracranial fontanelle, 57; in rays, 57

Supraorbital canal, 261, 274, 276-277; in-
nervation of, 224, 242, 274

Supraorbital crest, 44, 57, 58, 241

Suprapericardial body, 151

Suprarenal body, 248

Suprascapula, 49

Supratemporal canal, 261, 276, 278; in
Elasmobranchs in general, 278; in Hep-
tanchus, 261; nerves to, 225, 245, 278

Supratemporal nerve (IX), 244, 279; (X),
245, 278

Suspensory ligament of liver, 121

Sympathetic nervous system, 247-248

Tail (caudal fin); electric organ in, 112;
of Heptanchus, 6; of Pristis, 9; of
Rhinobatis, 9

ey
Co
—

Taste buds, 265, 266; nerve to, 243

Taste organ, 265-266

Tectospondyly, 75

Teeth, 1, 38, 122, 128; development of,
128; finer structure of, 130; of Car-
charodon, 38; of Heptanchus, 122; of
Heterodontus, 130; of Lamna, 9; of
Mustelus, 9; of Myliobatis, 38; pave-
ment, 130; replacement of, 131

Telencephalon, 221, 230

Tendineae. See Chordae tendineae

Terminal cartilage, of clasper, 81-82

Terminal nerve of Locy, 221, 223, 239; in
Heptanchus, 221, 223

Tertiary renal corpuscles, 300

Testes, 290-291, 300, 301; central canal of,
290-291, 301; development of, 300; rela-
tion of, to epigonal organ, 300; rudi-
mentary, in female Heptanchus, 290;
structure of, 300, 301

Third ventricle, 236

Thread cell of ear, 273

Thymus gland, 122—123, 132-133; develop-
ment of, 132; with duct in Heptanchus,
122-123; function of, 133

Thyroid artery, 164-165

Thyroid gland, 122, 123, 133-134; arteries
to, 164-165; capsule of, 133; denticles
of, in Chlamydoselachus, 134; develop-
ment of, 134; duct of, in Chlamydose-
lachus, 134; follicles of, 133, 134; his-
tory of, 133-134

Thyroidean sinus, 208

Tongue, 122, 128

Tooth germs, 128

Torpedo, 3, fig. 6; color of, 26, 27; electric
organ of, 112, 115

Trabecular cartilage, 53

Tract cells, 236

Tractus arteriosus lateralis, 192

Trapezius muscle, 92, 104

Triakis semifasciatus, integument of, 26

Trigeminal nerve, 223, 240-241; divisions
of, 223, 240-241; ganglion of, 240-241;
nucleus of, 240

Trochlear nerve, 223, 240; foramen of,
44; muscle supplied by, 100; origin of,
234

Trunk myotome. See Myotome

Tuberculum acusticum, 236

Tympanic membrane, 272

Tympanum, of Heptanchus, 272; of rays,

272

€
=

332 THE ELASMOBRANCH FISHES

Unpaired arteries, 186

Ureter, 287, 289, 291, 295; relation of, to
collecting tubules, 294, 295; relation
of, to male Wolffian duct, 296

Urinary papilla, 289, 290, 291, 296, 303

Urinary sinus, 289, 291, 294, 295; ducts
to, 294-295; horns of, 295, 296; walls
of, 296

Urinary system, in Elasmobranchs in gen-
eral, 292-300; in Heptanchus, 287-289

Urinary vesicle, 294

Urogenital sinus of male, 291; relation
of, to seminal vesicle, 302; relation of,
to vas deferens, 302

Urogenital system, in Elasmobranchs in
general, 292-310; in Heptanchus, 287—-
291

Urolophus halleri, fig. 9; ef. Acanthias, 8,
10-12; poison gland of, 28

Uterine septum, 309

Uterus, 290, 306-309 ; blood supply to, 193,
307; lining of, 307, 308; partitions of,
308; relation of, to embryo, 307-309

Utriculus of ear, 259, 272, 273

Vagus nerve, 225-227, 244-245; divisions
of, 225-227, 244-245; lobes of, 236;
nucleus of, 236; vistors sensory fibers
of, 236

Valves, ovidueal, 306; of heart, 160-161,
171, 172; of spiral intestine, 124, 126,
139, 140; of uterus, 306; of veins, 204

Valvular intestine, 124, 126, 139-140; ar-
teries to, 166, 167, 188, 190; veins of,
201, 210-211

Vas deferens, 290, 291; relation of, to
Wolffian duct, 290, 296

Vasa efferentia, 290, 301-302 ; origin of, 301

Vascular saes, 208, 221, 233

Vasodentine, 35, 130

Veins, 170, 198, 204; ef. arteries, 170, 204;
of body wall, 202, 204; from digestive
tract, 200-201, 204, 210-213; from
head, Heptanchus, 198, 204; of heart,
215-216; of kidney, 208, 210; of skin,
202-203, 204, 216-217; of tail, Hep-
tanchus, 199; walls of, 170, 204

Velum, 233

Vena limitans, 210

Vena profunda, 217

Venous system, in Elasmobranchs in gen-
eral, 204-218; in Heptanchus, 198-203

Ventral aorta, 161, 172, 175

Ventral bundles, 89, 97

Ventral constrictor muscles, 91, 104-105;
nerves to first ventral constrictor, 243

Ventral cutaneous veins, 203, 217; rela-
tion of, to cloacal vein, 217

Ventral gastric artery, 166, 187

Ventral gastrie vein, 201, 211

Ventral horn of cord, 222, 237, 238; cells
of, 238

Ventral intercalary piece, 48

Ventral intestinal artery, 167, 188; ab-
sent in rays, 188

Ventral intestinal vein, 201, 210; tribu-
taries of, 201, 210-211

Ventral lobe of pancreas, 124, 138

Ventral longitudinal muscles. See Hypo-
branchials

Ventral myelonal vein, 208

Ventral root nerve, 227; foramen of, 48

Ventricle, 160,161,170, 171, 179; arteries to,
163-164, 172; walls of, 160-161,170, 171

Ventrolateral bundles in medulla, 235

Ventrolateral muscle bundles, 89, 97

Ventromedian muscle bundles, 97

Vertebrae, 69, 70, 71, 72; in Alopias, 69

Vertebral plate, in rays, 71

Vertebromuscularis artery, 192, 193-194

Vertebrospinalis artery, 192

Vertebrospinal vein, 210

Vesicula seminalis, 302

Vesicles of Savi, 274, 281

Vessels of Thebesius, 215-216

Vestibular nerve, 273

Villus, arteries of, 307; of intestine, 140;
nutriment from, 307-308; of uterus,
307-309; veins of, 307

Visceral arches, 44-47, 62-67; in embryo,
62; muscles to, 100-108

Visceral nerve (X), 225

Visceral sensory fibers, 236

Visceral skeleton, of Elasmobranchs in
general, 62-69; of Heptanchus, 44-47

Visceromotor nucleus, 236, 240

Vitelline vein, 212, 213

Vitreous body (humor), 268

Vitrodentine, 35

Viviparous, 307

White blood cells, 170

White matter of cord, 237

Wolffian duct, 287, 289, 294, 295, 296, 297;
modified as vas deferens, 290, 296, 301;
relation of, to collecting tubules, 294;
relation of, to vas deferens, 302

“Wonder net,” 181

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